Paper on Super Critical Technology and Analysis for Indian Environment

Analysis of Supercritical technology in Indian Environment and Utilizing Indian coal

Boben Anto CHead of Plant services

Evonik Energy Services India Ltd

Prof: M M HasanMechanical Engineering dept

Jamia Islamiya New Delhi

DESIGN, INSTALLATION & OPERATION OF SUPERCRITICAL POWER PLANTS

TABLE OF CONTENTS

SECTIONS PAGE

1.0 INTRODUCTION..........................................................................91.1 ASSIGNMENT AND OBJECTIVES.........................................................10

1.1.1 Assignment.......................................................................................101.1.2 Objectives.........................................................................................10

1.2 APPROACH AND METHODOLOGY......................................................111.2.1 Data Collection..................................................................................111.2.2 Choice of supercritical technology.....................................................111.2.3 Design Issues....................................................................................111.2.4 Implementation Issues......................................................................121.2.5 Operational Issues.............................................................................121.2.6 Environment Issues...........................................................................121.2.7 Development of Simulation Models...................................................13

2.0 EVOLUTION OF TECHNOLOGY................................................142.1 NEED FOR INCREASING EFFICIENCY.................................................152.2 DEVELOPMENT OF SUPERCRITICAL TECHNOLOGY............................17

2.2.1 Technology evolution in U.S.A...........................................................172.2.2 Technology evolution in Europe and Japan........................................192.2.3 Technology evolution in China..........................................................202.2.4 Development of supercritical technology in India..............................202.2.5 Development prospects....................................................................20

3.0 POPULATION OF SUPERCRITICAL PLANTS...........................233.1 PROPOSED AND UNDER CONSTRUCTION SUPERCRITICAL PLANTS IN

INDIA................................................................................................243.2 SUPERCRITICAL PLANTS IN OTHER COUNTRIES................................27

4.0 AVAILABILITY OF MANUFACTURES OF SUPERCRITICAL PLANTS......................................................................................35

5.0 SPECIAL MATERIALS FOR SUPERCRITICAL PLANTS...........385.1 BOILER..............................................................................................39

5.1.1 Materials for Boilers in Ultra Supercritical Power Plants.....................395.1.2 Boiler Materials Requirements...........................................................415.1.3 Historical Evolution of Steels.............................................................425.1.4 Evolution of Ferritic Steels.................................................................445.1.5 Evolution of Austenitic Steels............................................................485.1.6 Choice of Materials for Headers and Steam Pipes.............................515.1.7 Choice of Materials for Superheater/Reheater Tubes........................575.1.8 Creep Rupture Strength....................................................................575.1.9 Fire-side Corrosion............................................................................615.1.10 Steam-side oxidation.........................................................................635.1.11 Summary of SH/RH Tube-Material Status..........................................645.1.12 Choice of Materials for Waterwalls....................................................655.1.13 Waterwall Corrosion Concerns...........................................................655.1.14 Summary...........................................................................................66

5.2 TURBINE...........................................................................................695.2.1 Materials for Turbines in Ultra Supercritical Power Plants..................695.2.2 Materials for Casings and Shells........................................................695.2.3 Materials for Bolting..........................................................................715.2.4 Materials for Rotors/discs..................................................................725.2.5 Materials for Blading.........................................................................735.2.6 Summary...........................................................................................735.2.7 Role of owner of plant.......................................................................74

E040/ REPORTBoben Anto CPAGE 2 OF 161


6.0 OPERATIONAL FLEXIBILITY AND PERFORMANCE OF SUPERCRITICAL PLANTS.........................................................77

6.1 OPERATIONAL FLEXIBILITY OF SUPERCRITICAL PLANTS....................786.1.1 Start-up flexibility in supercritical boilers..........................................786.1.2 Shorter start-up times.......................................................................796.1.3 Flexibility for Load Changes..............................................................826.1.4 Fuel flexibility....................................................................................826.1.5 Water Chemistry...............................................................................826.1.6 Higher efficiency...............................................................................836.1.7 High availability.................................................................................836.1.8 Improved cost effectiveness..............................................................836.1.9 Reliability..........................................................................................84

6.2 OPERATIONAL PERFORMANCE OF SUPERCRITICAL PLANTS..............856.2.1 Assumptions for Plant Parameters.....................................................856.2.2 Coal Analysis.....................................................................................866.2.3 Ambient Conditions...........................................................................876.2.4 Performance Modelling Results.........................................................88

7.0 DESIGN ISSUES........................................................................917.1 LAYOUT AND CLEARANCES...............................................................92

7.1.1 Plant Layout......................................................................................927.1.2 Pipe Layout........................................................................................937.1.3 Typical Longitudinal Sectional View...................................................94

7.2 BOILER CONFIGURATION AND TECHNICAL FEATURES......................957.2.1 Two path/Tower type.........................................................................957.2.2 Constant Pressure / Sliding (Variable) Pressure Type........................957.2.3 Spiral Type........................................................................................98

7.3 TUBE LAYOUT...................................................................................997.4 BFP & HP BY PASS SYSTEM...............................................................997.5 IMPROVEMENT IN COMBUSTION SYSTEM........................................1027.6 OPERATION IN INDIAN CONDITIONS...............................................1037.7 ELECTRO-STATIC PRECIPITATOR (ESP)...........................................1057.8 MILLS..............................................................................................1067.9 DESIGN FEATURES OF TURBINES....................................................106

7.9.1 Materials for High Temperature.......................................................1067.9.2 Materials for High Temperature.......................................................1077.9.3 Continuous Cover Blade (CCB)........................................................1077.9.4 Tandem-Compound High Supercritical STG.....................................108

7.10 MATURITY OF SUPERCRITICAL TECHNOLOGY.................................110

8.0 IMPLEMENTATION ISSUES....................................................1118.1 INTRODUCTION...............................................................................1128.2 TECHNOLOGY ISSUES.....................................................................112

8.2.1 Waterwall Cracking.........................................................................1128.2.2 Negative Flow Characteristic...........................................................1138.2.3 Slagging..........................................................................................1138.2.4 Welding of Special Materials............................................................1148.2.5 Tube Spacing to Handle Indian Coal................................................1148.2.6 Height of Structure..........................................................................115

8.3 OTHER ISSUES ASSOCIATED WITH DEPLOYMENT OF SC TECHNOLOGY IN INDIA..........................................................................................115

8.3.1 Transportation of Major Equipment.................................................1158.3.2 Material Handling............................................................................1158.3.3 Grid Code........................................................................................1168.3.4 Skilled Manpower............................................................................1168.3.5 Coal Quality and Boiler Performance...............................................1168.3.6 Environmental Benefits...................................................................1178.3.7 Socio-economic Benefits.................................................................118



9.0 OPERATION AND MAINTENANCE ISSUES...........................1199.1 SUPER CRITICAL TECHNOLOGY IN INDIAN AMBIENT CONDITIONS and

INDIAN COALS................................................................................1209.2 OPERATION AND MAINTENANCE ISSUES FOR SUPER AND ULTRA

SUPER CRITICAL TECHNOLOGY IN INDIA.........................................1219.2.1 Design and manufacture of components for supercritical coal fired

plants in developing countries.........................................................1219.2.2 Availability of contractor for maintenance.......................................1229.2.3 Availability of Critical Spare, Tools and Tackles in India..................1229.2.4 Status of super and ultra super critical boiler manufacturers /

suppliers..........................................................................................122

10.0 ENVIRONMENT ISSUES..........................................................12410.1 INTRODUCTION...............................................................................12510.2 INDIAN STANDARDS.......................................................................125

10.2.1 Ambient Air Quality Standards........................................................12510.2.2 Flue Gas Emission Standards..........................................................12510.2.3 Wastewater Quality Standards........................................................12610.2.4 Noise Standards..............................................................................127

10.3 EMISSIONS RESULTS.......................................................................12710.3.1 CO2 Emissions Results.....................................................................12710.3.2 Other Emission Results....................................................................12810.3.3 Nitrogen oxides Emissions...............................................................12810.3.4 Sulphur oxides Emissions................................................................12910.3.5 Particulate Emissions......................................................................130

10.4 APPLICABILITY OF STANDARDS AND COMPLIANCE.........................13010.5 CDM ISSUES....................................................................................132

10.5.1 Methodology....................................................................................13210.5.2 Applicability Conditions...................................................................132

11.0 COST IMPLICATION OF TECHNOLOGY IN INDIA.................134

REFERENCE.......................................................................................139

LIST OF ABBREVIATION..................................................................140

LIST OF TABLESTable 2-1: Classification for Coal Fired Plants................................16Table 3-1: List of Ultra Mega Power Projects in India......................................24Table 3-2: List of Under Construction Supercritical Thermal Power Stations in

India.............................................................................................24Table 3-3: List of Proposed Supercritical Power Stations in India...................25Table 3-4: Supercritical Power Plants in the World.........................................28Table 3-5: Supercritical Power Plants of each Electric Power Co....................29Table 3-6: Steam Parameters of Supercritical Plants in Japan........................29Table 3-7: Advanced Supercritical Plants in Japan..........................................30Table 3-8: Steam Parameters of Supercritical Plants in USA..........................30Table 3-9: Steam Parameters of Supercritical Plants in Germany..................31Table 3-10: Advanced Supercritical Plants in Germany..................................31Table 3-11: Steam Parameters of Supercritical Plants in Russia.....................31Table 3-12: Steam Parameters of Supercritical Plants in China......................32Table 3-13: Availability Factor (%) 1982-1984................................................33Table 3-14: Availability Factor (%) 1988-1997................................................33Table 3-15: Availability Factor (%) in 1954.....................................................34Table 5-1: Steam conditions for coal-fired plants in EPRI program.................40Table 5-2: Evolution of Four Generations of Ferritic Steels............................43



Table 5-3: Nominal Chemical Compositions of Ferritic Steels for Boilers.......46Table 5-4: Nominal Chemical Compositions of Austenitic Steels for Boiler (wt

%)................................................................................................49Table 5-5: Candidate Materials for Advanced Supercritical Plants for Various

Steam Conditions.........................................................................50Table 5-6: Application of New Tungsten-Bearing Steels in European Power

Stations........................................................................................56Table 5-7: Chemical Compositions of Alloys considered for Steam Turbines (in

weight percent)............................................................................74Table 5-8: Materials Selection for the High-Pressure Steam Turbine..............75Table 5-9: Ranking and Development Effort Needed for Materials for Turbines

.....................................................................................................76Table 6-1: Availability of Supercritical Plants..................................................83Table 6-2: Cycle Conditions for the Coal Fired Plant Options..........................85Table 6-3: Proximate Analysis for Domestic Coal...........................................87Table 6-4: Typical Ultimate Analysis (as received basis) for Domestic Coal.. .87Table 6-5:Common Ambient Conditions.........................................................87Table 6-6: Turbine Performance Estimates (Domestic Coal, 100% MCR).......89Table 6-7: Plant Performance Estimates using Domestic Coal (LHV basis,

100% MCR)..................................................................................89Table 6-8: Plant Performance Estimates using domestic Coal (HHV basis,

100% MCR)..................................................................................89Table 6-9: Coal, Ash & Water Consumption/Production Estimates (relevant

unit size, 100% MCR)...................................................................90Table 7-1: Line-up of LSB with CSB Structure...............................................108Table 10-1: Ambient Air Quality Standards...................................................125Table 10-2: Flue Gas Emission Standards.....................................................125Table 10-3: Wastewater Standards...............................................................126Table 10-4: Noise Standards.........................................................................127Table 10-5: CO2 Emission Estimates (100% MCR)........................................127Table 10-6: CO2 Emission Reduction % Estimates Relative to Base Subcritical

Plant (100% MCR)......................................................................127Table 10-7: NOx Emission Limits for New Coal Fired Power Stations.............129Table 10-8: SOx Emission Limits for New Coal Fired Power Stations.............129Table 10-9: Particulate Emission Limits for New Coal Fired Power Stations..130Table 11-1: Plant Characteristics..................................................................135Table 11-2: Plant equipment capital costs per unit......................................136Table 11-3: Other Capital Costs....................................................................136Table 11-4: Capital and Specific Capital Cost for Each Unit Size..................136Table 11-5: Capital and Specific Capital Cost for two units..........................137Table 11-6: O&M Costs – Fixed and Variable for Each Unit Size...................137

LIST OF FIGURES Figure 2-1: Efficiency Performance in Germany TPS........................16Figure 2-2: Worldwide Introduce Supercritical Technology.............................22Figure 3-1: Capacity of SC & USC Power Plants Worldwide............................27Figure 5-1: Improvement in heat rate (efficiency) achieved by increasing

steam temperature and single and double cycles , compared to the base case of 535ºC/189 kg/cm2.............................................39

Figure 5-2: Historic evolation of materials in terms of increasing creep rupture strength.......................................................................................43

Figure 5-3: Evolution of ferritic steels for boiler..............................................45Figure 5-4: Evaluation of authentic steels for boiler.......................................50



Figure 5-5: Comparison of allowable stress of ferritic steels for boiler...........54Figure 5-6: Comparison of allowable stresses and sectional view of main

steam pipes designed at 570ºC and 600ºC..................................55Figure 5-7: Cost of P-22, P-91 and P-122 steels header materials as a function

of temperature at 316 kg/cm2 steam pressure............................55Figure 5-8: Comparison of allowable stresses 18Cr-18Ni and 15Cr steels......58Figure 5-9: Comparison of allowable stresses for austenitic alloys containing

more than 20% Cr........................................................................59Figure 5-10: Allowable metal temperatures at constant allowable stress of

500 kg/cm2 (7ksi) as a function of chromium content for various alloys............................................................................................60

Figure 5-11: Relationship between hot-corrosion weight loss and temperature for ferritic steels...........................................................................60

Figure 5-12: Relationship between hot-corrosion weight loss and chromium content for various alloys.............................................................61

Figure 5-13: Comparison of fire side corrosion resistance of various alloys.. .62Figure 5-14: Corrosion of steels containing 0.5-18% Cr under FeS containing

deposits in oxidizing flue gas.......................................................66Figure 5-15: Materials Development Stages and Related Steam Parameters

Limits...........................................................................................68Figure 5-16: Plot of Creep Rupture Stress Versus Larson-Miller Parameter....70Figure 6-1: Chart Presents Higher Efficiency..................................................83Figure 7-1: Standard two unit layout..............................................................92Figure 7-2: Three dimensional model of pipe layout.......................................93Figure 7-3: Turbine hall..................................................................................93Figure 7-4: Longitudinal Sectional view..........................................................94Figure 7-5: Plot allocation..............................................................................94Figure 7-6: Constant Pressure Program for C-E Type......................................96Figure 7-7: Constant Pressure Diagram of C-E Type.......................................96Figure 7-8: Sliding (Variable) Pressure Program for C-E Type.........................97Figure 7-9:Furnace Configuration...................................................................97Figure 7-10: Basic Principle of Spiral-wall Furnace.........................................98Figure 7-11: Tube layout................................................................................99Figure 7-12: HP bypass.................................................................................100Figure 7-13: Vertical and spiral type boilers.................................................100Figure 7-14: Tubing in Once through and Drum type boilers........................101Figure 7-15: Heat transfer and temperature range......................................101Figure 7-16: Heat transfer in vertical and spiral type boilers........................102Figure 7-17: Frame Structure of Hitachi NR2 Burners...................................103Figure 7-18: Materials of Boiler.....................................................................105Figure 7-19: Modified mill.............................................................................106Figure 7-20: The new technology of the High Supercritical Steam turbine (HP

& IP Sections).............................................................................107Figure 7-21: Continuous Cover Blade (CCB) Structure..................................108Figure 7-22: Correlation between Unit Output and Turbine Exhaust Annulus

Area...........................................................................................109Figure 7-23: Sectional Arrangement of TC4F-40 high supercritical Steam

Turbine for.................................................................................110Figure 7-24: Sectional Arrangement of TC4F-43 high supercritical Steam

Turbine for 50 Hz use.................................................................110

LIST OF ANNEXURES



3.1 300 MW or Over Coal Fired Supercritical Power Plants since 1985

Worldwide

3.2 300 MW or Over Supercritical Power Plants in Japan

3.3 300 MW or Over Supercritical Power Plants in Germany

3.4 300 MW or Over Supercritical Power Plants in Russia

3.5 300 MW or Over Supercritical Power Plants in China

3.6 300 MW or Over Supercritical Power Plants in Other Countries



1.0 INTRODUCTION



INTRODUCTION1.1 ASSIGNMENT AND OBJECTIVES1.1.1 Assignment

The primary purpose of the study is to assess whether supercritical thermal plant technology is a proven and mature commercial technology and whether modern supercritical power plants installed in India will have a robust availability and reliability.

1.1.2 ObjectivesThe objective of the study is to provide a comprehensive report regarding supercritical technology specifically in the context of setting up supercritical thermal power plants in India. The report shall include qualitative and quantitative analysis of the issues and risks involved which would assist the owner in taking an appropriate investment decision regarding setting up a supercritical power plant at a suitable location in India. The study will address the following issues.

1. Evaluation of the current state of supercritical technology with respect to typical range of steam pressure and temperature and efficiency of plant.

2. Design related issues that differentiate supercritical technology from sub-critical technology such as sliding pressure versus constant pressure, feed water quality, startup time and ramp-up rates.

3. Adaptability of technology to Indian conditions. Effect of use of Indian coal on cost and performance.

4. Operational issues, breakdowns, outages in Indian conditions, availability of spares.

5. Suggest range of parameters to be adopted for proposed plant. Provide assessment of design areas requiring focus during manufacture and installation of plant and execution of project.

6. Materials of construction; availability in India.

7. Availability of plants from Indian and foreign manufacturers

8. Ability of supercritical technology in meeting Indian environmental regulations and World Bank norms.

1.2 APPROACH AND METHODOLOGY1.2.1 Data CollectionThe experience of supercritical thermal power plants in India is limited. While work in various stages is in progress at a few supercritical plants, none of them has been commissioned as yet. Supercritical technology, however, has been an established technology in Germany, Russia and eastern block countries, Japan, China and U.S.A.

Data shall be collected for supercritical plants under construction in India. Information about proposed supercritical plants will be collected, also, to the



extent it is available. Information about plants in other countries will be obtained from conference papers, internet, published literature and from our parent company in Germany.

1.2.2 Choice of supercritical technology The evolution of supercritical technology worldwide and the driving forces contributing to its adoption will be described.

The reasons for developers in India now preferring supercritical technology for the establishment of large capacity power plants in preference to the currently prevalent sub-critical technology will be analysed.

1.2.3 Design IssuesThe current state of supercritical technology with respect to typical range of steam temperature, pressure and efficiency of the power block will be studied.

The impact of plant design data and operating parameters of the plant on design margin of various plant auxiliaries will be assessed.

Typical design related issues that differentiate supercritical technology from subcritical technology such as sliding pressure versus constant pressure, feed water quality, startup time and ramp-up rates will be studied specifically.

The progressive improvement in materials of construction of supercritical plants to bring greater stability and increase operational efficiency will be studied.

1.2.4 Implementation IssuesExperience of construction of supercritical power plants in India is limited and problems likely to arise during construction need to assessed beforehand. Some issues such as welding of special materials are likely to arise on account of special design of equipment. Transport of heavy equipment from manufacturer’s workshops to plant site requires proper route survey and handling facilities at points of transfer. Requirements of skilled manpower during construction period will be assessed to enable its availability in time.

1.2.5 Operational IssuesThe data collected and information gathered from different sources will be analysed for availability and reliability achieved and for breakdowns and outages suffered by supercritical plants during their operation. The causes of breakdowns and outages as also, causes of poor performance regarding availability will be sought from the data gathered and ways to mitigate them will be suggested.

Other problems faced in maintenance and operation such as lack of experienced personnel, problems of spares and availability of experienced contractors for maintaining large supercritical power stations will be studied.

1.2.6 Environment IssuesOne of the main driving forces for the development, acceptability and encouragement of supercritical technology has been its potential for



reduction of green house gases. Compatibility of supercritical technology with and its ability to conform to the Indian environmental regulations and the World Bank norms as applicable to thermal power plants will be studied.

The benefits of the proposed supercritical plants in terms of saving in coal consumption and reduction in carbon-di-oxide emissions will be evaluated.

The possibility of the project obtaining credits under the Clean Development Mechanism (CDM) will be explored in general terms.



1.2.7 Development of Simulation Models The actual operating data available for supercritical plants being limited, simulation models will be employed to obtain operating results under different operating parameters.



2.0 EVOLUTION OF TECHNOLOGY



EVOLUTION OF TECHNOLOGY2.1 NEED FOR INCREASING EFFICIENCYThe demand for energy is closely related to economic growth and standard of living. Currently, demand for all global energy is increasing at an average rate of approximately 2% per annum. The growth rate in India is higher and was about 4 percent during the previous plan period even with serious constraints of generation capacity. Electricity generated from coal currently accounts for about 40 per cent of the electricity generated worldwide and about 53% in India. As coal is a relatively more abundant fuel resource in India, it is likely to remain a dominant fuel for electricity generation in future also. The Integrated Energy Plan developed by Planning Commission also considers that coal is likely to be the primary energy source for the electricity sector in the foreseeable future.

The main argument advanced against coal fired thermal power generation is the large amount of carbon-di-oxide (CO2) emissions produced by them which contribute in a large measure to greenhouse effect and global warming. CO2

emissions can be lowered by improving the efficiency of coal fired power plants. Increasing the temperature and pressure in a steam turbine increases the efficiency of the Rankine steam cycle used in power generation, in other words it decreases the amount of fossil fuel consumed and the emissions generated. A one percent increase in efficiency leads to reduction of emission of CO2 by 2.5 per cent. For an 800 MW coal based unit, the 1% increase in efficiency would lead to a life time reduction in CO2 emission of approximately one million tones.

There has been a gradual evolution in the increase in steam parameters used in coal fired plants. Steam parameters have been raised from 80 kg/cm2 for 50 MW plants to 170 kg/cm2 for 500 MW units. Supercritical units use higher steam parameters of 240 kg/cm2.

"Supercritical" is a thermodynamic expression describing the state of a substance where there is no clear distinction between the liquid and the gaseous phase (i.e. it behaves as a homogenous fluid). Water reaches this state at a pressure above 221 bar.

The water-steam cycle is sub-critical up to an operating pressure of around 190 bar in the evaporator part of the boiler. This means, that there is a non-homogeneous mixture of water and steam in the evaporator part of the boiler. In this case a drum-type boiler is used because the steam needs to be separated from water in the drum before it is superheated and led into the turbine. Above an operating pressure of 221 bar, the cycle is supercritical. The cycle medium is a single phase fluid with homogeneous properties and there is no need to separate steam from water in a drum. Once-through boilers are therefore used in supercritical cycles.

The classification for the coal fired plants with increasing steam parameters is shown in the table below.

Table 2-1: Classification for Coal Fired Plants

Unit sizeMain Steam

PressureMain Steam Temperature

Reheat Steam Temperature

Sub-critical 500 MW 166 bar 538°C 538°C



Low supercritical 660 MW 247 bar 538°C 565°C

Ultra supercritical 800 MW 270 bar 565°C 593°C

Advanced supercritical

1000 MW 295 bar 600°C 600°C

Comparative efficiencies for typical steam parameters and temperatures are depicted in diagram below. While plant efficiencies of sub-critical plants in India are still around 32%, modern sub critical cycles have attained efficiencies close to 40% (LHV basis). Current supercritical coal fired power plants have efficiencies above 45% (LHV basis). It is thus, obvious that the supercritical (SC) and ultra-supercritical (USC) coal fired power plant technology is one of the major options for high-efficiency, low-emissions power generation

The gradual evolution of increasing efficiencies of coal fired thermal power plants in Germany is depicted in the diagram below.

Figure 2-1: Efficiency Performance in Germany TPS

Supercritical power plants using once through boilers can maintain higher efficiency at rather low loads as compared to sub-critical plants.. Conventional drum-type boilers in sub-critical plants have bigger material requirements because of the thick-wall drums, and also the water/steam inventory.

A Committee was set up by the Central Electricity Authority in 2003 to recommend the next higher unit size for coal fired thermal power stations. The Committee felt that with the progressive increase in installed capacity, higher share of thermal generation and large peak to off peak ratios, backing down, and cyclic operation of thermal units would become imminent. Super critical thermal units offer better operational profile in such an environment. The Committee recommended that the next higher units size adopted in the country should be from 800 to 1000 MW. The steam parameters of 246 - 250 kg/cm2, and higher steam temperatures of 568ºC to 593 ºC may be adopted depending upon site specific techno-economics for deriving maximum efficiency gains from higher size units.



2.2 DEVELOPMENT OF SUPERCRITICAL TECHNOLOGY 2.2.1 Technology evolution in U.S.A.The first supercritical units, 375MW Drakelow C and 125MW Philo plants. were put into commercial operation in UK and USA in the year 1957. In 1959, the famous Eddystone 1 plant owned and operated by the Philadelphia Electric Co. was commissioned in U.S.A. It was designed for 650º/565º/565ºC/351.8 kg/cm2 steam conditions but due to serious mechanical and metallurgical problems, it was later down-rated to 605º/565º/565ºC/330.38 kg/cm2. Most of the problems were due to the use of austenitic steels for thick section components operating at high temperatures. These steels have low thermal conductivity and high thermal expansion resulting in high thermal stresses and fatigue cracking.

These problems reduced the availability of the then operating supercritical plants leading to new investments in developed countries flowing back to sub-critical plants with live steam conditions of about 550°C/183.54 kg/cm2.

118 supercritical plants were built in U.S.A. during 1967 to 1976 with maximum unit capacity of 1300 MW. Further installation of SC plants was slowed due to their low availability. Environment concerns for green house emissions dominated in 1970s causing oil and gas combined cycle units to be substituted for coal fired units. Nuclear power stations were also, established but later nuclear generation went out of favour completely on account of some major accidents to nuclear plants such as that of Three Mile Island in 1979 and of Chernobyl in 1986. The energy crisis in the mid-1970s and consequent sharp rise in fuel prices, however, rekindled interest in the development of more efficient coal based power plants. Problems of materials suitable for high temperatures and pressures also, were solved gradually and availability of supercritical plants converged to and then became higher than that of comparable sub-critical ones. With improvements in pollution control equipment in 1990s, new supercritical plants have been constructed with capacities of 500 to 800 MW and more than 190 supercritical plants were in operation in U.S.A. by 2004.

The evolution of coal fired thermal power plant technology in U.S.A. over the years is shown below:

1924 First reheat generating unit – Philo Plant

1941 First very high pressure (2,300 psi) natural circulation

generating unit – Twin Branch Plant

1949 First high pressure high temperature combination (2,000

psi & 1050 F main steam & 1,000 F reheat) – Twin Branch

Plant

1950 First heat rate below 10,000 Btu/kWh – Philip Spom Plant

1957 First supercritical pressure steam (4,500 psi) and super-

high temperature steam (1,150 F) and double reheat – Philo

Plant

1960 First heat rate below 9,000 Btu/kWh – Church River Plant



1966 First control room simulator to train plant operating

personnel – Cardinal Plant

1961 First application of sliding pressure technique on

supercritical pressure generating units - Gen. James M

Gavin Plant

2000 to 2008 Installation of advanced steam path turbine components on

600 MW, 800 MW and 1,300 MW units

2011 Planned startup new 600 MW pulverized coal plant using

3,800 psi/1,100 F/1,125 F steam cycle with 8,900 Btu/kWh

heat rate (HHV)

The Department of Energy (DOE) of U.S.A. proposed three power generation initiatives namely Vision 21, Future-Gen and Clean Coal Power to promote increases in power generating plants efficiencies and decreases in emissions. The Vision 21 initiative has the goal of achieving 7,200 kJ/kWh heat rate for coal fired power plants. This is proposed to be achieved in two major steps, 675°C live steam temperature by year 2010 ( n*=45-50%) and 760°C by year 2020 (6,000-7,200 kJ/kWh n*=50-60%). The final live steam temperature and pressure goal is 760°C and 393 kg/cm2 by the year 2020 2.2.2 Technology evolution in Europe and JapanDevelopment of supercritical coal fired units in Europe started late mainly after 1990 and has been confined to Germany, Italy, Denmark and Holland. Early units were designed for 254.92 kg/cm2/540°C/540°C. Steam temperatures were raised to meet higher environment protection requirements. The sliding pressure design was incorporated into supercritical design in which pressure is reduced with load. This allows the maintenance of relatively constant first stage turbine temperature reducing stress on components in the unit and providing higher availability. A number of the units were operated in daily Start-Stop mode and had a good control capability for load change.

Originally, the supercritical technology of Japan was from USA, and in order to have the capability of partial load operation and Daily Start-Stop (DSS) operation, the technology of sliding pressure from Europe was incorporated into the power plant design. After many years of Research & Development studies and improvements, the thermal efficiency and availability of supercritical plants was improved to match those of sub-critical units. Japan is, now, a leading manufacturer of power generating equipment for unit capacities of 700 MW and 1000 MW as standard products. Coal-fired power generation in Japan is operated with a total efficiency rate of 40% or more, the highest rate in the world.

The historical development of increases in operating pressures and temperatures for supercritical plants in Germany, Denmark and Japan are shown in table below.

Country Year Pr (kg/cm2) Temp ºC



Germany 1995 290.60 545 /5601999 275.30 580 /600

Denmark 1991 254.92 540 /5401997 295.70 580 / 580 / 580

Japan 1991 230.85 538 / 5661995 230.85 566 / 5932000 230.85 593 / 593



2.2.3 Technology evolution in China About 70% of China's total energy consumption comes from coal and the country still has huge reserves. Burning it, however, has severely damaged the environment for Chinese people themselves and people in surrounding countries. In northern China, cities like Beijing and Shenyang have some of the highest readings for total suspended particulates and SO2 in the world, with coal burning being a major source of this pollution. In southern China, large areas have growing acid rain problems.

Coal based power generation in China started with small low efficiency units and more than 8,000 units of less than 200 MW are in operation The first 300 MW sub-critical unit was commissioned in 1982 and first 600 MW sub-critical unit in 1989. To reduce emission of pollutants, China started using supercritical and ultra supercritical technologies in its thermal power plants. China's first 1,000MW ultra-supercritical power plant is located at Yuhuan on the coast of East China's Zhejiang Province. Units 1 and 2 went on line in 2006, and units 3 and 4 in 2007. With all units working, the plant generates 22 billion kWh of electricity a year. The plant is operated by China Huaneng Group, China's largest power producer. It is claimed that Yuhuan Units 1 and 2 are the world's cleanest, most efficient and most advanced ultra-supercritical units

2.2.4 Development of supercritical technology in IndiaThe average efficiency of coal based power plants in India is very low being in the range of 27–34%. Increases in unit size have been done to increase efficiency and reduce green house gas emissions. Bharat Heavy Electricals Ltd, (BHEL), the Indian manufacturer of large power plants has commissioned about 135 plants of capacities 200–250 MW and about 25 units of 500 MW. The first supercritical plant of capacity 3X660 MW is under construction at Sipat with South Korean technology. Another SC plant (3X660) at Barh is under construction A number of supercritical and ultra-supercritical plants in the public sector, private sector and joint sector are in different phases of development. Details are given in Section 3 of this report.

2.2.5 Development prospectsWith coal regaining its dominant position for power generation and with increasing environment consciousness, emphasis worldwide is shifting to supercritical and ultra-supercritical power plants. More than 600 SC&USC power plants (status 2004), with total capacity above 300 GW, were operating or were under construction mainly in USA, Japan, China, Europe, Russia, Korea and other countries. The greatest concentration of SC power plants is in Russia and in the former Eastern bloc countries, where more than 240 are in service providing about 40% of all electricity needs those countries.

An important problem faced by power generation systems is the substantial difference between peak load and base load. Thermal stations have to adapt to frequent load changes and even shift operation. The steam boilers are required to have fast load-following capability, which includes two characteristics: 1) ability for fast startup from different conditions, and 2) ability to handle sharp changes in load. Supercritical once-through boilers, because of the absence of a drum and other thick-walled parts, require 15 to


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20 percent less time for cold startups than conventional boilers. Using full/partial flow separators, modern once-through SC boilers also are capable of very fast load changes, typically 3 to 4 percent per minute, and even 5 percent per minute when using an advanced control system.

Regarding availability and reliability, previous studies of the coal fired sub-critical and supercritical plants had revealed that conventional sub-critical boilers have had better reliability during their first 10 years of operation. After 10 years, the average outage time caused by the pressure parts of SC units had leveled off at less than 500 hours/year (representing about 94 percent availability) which is comparable to figures for sub-critical plants. Availability of older SC units, when used for base load duty, is as good as sub-critical units. The average annual availability factor for all 300 MW units in the former Soviet Union from 1990 to 1995 was 95 to 97 percent, which was somewhat higher than SC power plant availability in the United States and Germany, where the best units had availability factors of 94 to 97 percent. Present generation supercritical plants, however, have availability comparable to that of sub-critical plants.

The chart below indicates that more and more new plants worldwide are likely to introduce supercritical technology.

Figure 2-2: Worldwide Introduce Supercritical Technology

Development of alloys suitable for use in supercritical and ultra- supercritical boilers is a major challenge for supercritical technology.

Some materials for supercritical and ultra- supercritical boilers have been identified already. A remaining major challenge is the selection or development of candidate alloys suitable for use in the USC steam turbines.

Another important aspects is the role of pressure on steam-side oxidation. It is now known that most of the efficiency gains in higher capacity supercritical and ultra-supercritical plants result from increased temperature and not from increased pressure.



As a result, material requirements, in terms of high temperature strength and steam-side oxidation, could lead to the use of lower pressures to make the supercritical and ultra- supercritical turbines more economical, and yet be beneficial in terms of efficiency increases.

Manufacturers of high efficiency thermal power plants are undertaking intensive research work continuously for developing new materials for different components of the plants to withstand the increasing temperatures and pressures required for efficiency enhancement.

Development of materials for different components of supercritical plants is dealt with in detail in Section 5 of this report.



3.0 POPULATION OF SUPERCRITICAL PLANTS



POPULATION OF SUPERCRITICAL PLANTS3.1 PROPOSED AND UNDER CONSTRUCTION SUPERCRITICAL PLANTS

IN INDIA

The details of Ultra mega Power Plants (4000 MW each) other supercritical

plants under construction and those proposed are given in Table 3-1, 3-2 and

3-3 below:Table 3-2: List of Ultra Mega Power Projects in India

S.No.

Name/Location of Thermal Power Station

No. ofunits

Unit capacity(in MW)

Utility

1 UMPP, Mundra 5 800 M/s. Tata Power Limited

2 UMPP, Sasan 6 660 M/s. Reliance Power Limited

3 UMPP, Krishnapatnam 5 800 M/s. Reliance Power Limited

4 UMPP, Tilaiya 5 800 M/s. Reliance Power Limited

5 Orissa, UMPP 5 800 -6 Chhatisgarh, UMPP 5 800 -7 UMPP, Tamil Nadu 5 800 -

Table 3-3: List of Under Construction Supercritical Thermal Power Stations in India

S.No.


No. ofunits


Utility

1 Hissar 2 660 M/s. HPGCL2 Jhajjar 2 660 M/s. HPGCL3 Talwandi Sabo 2 660 M/s. PSEB4 Mundra, Kutch 2 660 M/s. Adani Power

Limited5 Meja IV, Uttar Pradesh 2 660 M/s. NTPC Joint

Venture6 Sipat-I, Bilaspur 3 660 M/s. NTPC Limited7 New Nabinagar, Bihar 3 660 M/s. NTPC Joint

venture 8 Krishnapatnam 3 800 M/s. APGENCO9 Sholapur Thermal Power

plant, Maharashtra 2 660 M/s. NTPC

10 Barh Super Thermal Power Station

3 660 M/s. NTPC Limited

11 Raghunathpur-II, West Bengal

2 660 M/s. DVC

12 Gidderbaha Station-I, Punjab

2 660 M/s. PSEB

13 Sahapur Thermal Power Company Limited

2 660 M/s. STPCL

14 Jewargi Power Company of Karnataka Limited

2 660 M/s. Power Company of Karnataka Company Limited



Table 3-4: List of Proposed Supercritical Power Stations in IndiaS.

No.Name/Location of

Thermal Power StationNo. ofunits


Utility

1 Dhenknal, Orissa 2 660 M/s. Lanco Infratech Limited

2 Pussurar Region, Raigarh, Chhatisgarh

3 660 M/s. Infrastructure Leasing & Financial Services Ltd.

3 Chutru region of Jharkhand

3 660 M/s. Infrastructure Leasing & financial Services Ltd.

4 Chandil region of Jharkhand

3 660 M/s. Infrastructure Leasing & financial Services Ltd.

5 Bade Dumarpali, Raigarh, Chhatisgarh

2 660 M/s. Athena Chattisgarh Power Private Limited

6 Gondia, Maharashtra 3 660 M/s. Adani Power Maharashtra Private Limited

7 East Godavari, Kakinda 2 660 M/s. Spectrum Power Generation Limited

8 Sinnar, Nasik, Maharashtra

2 660 M/s. Fama Power Company Limited

9 Nagapattinam, Tamil Nadu

2 660 M/s. PEL Power Limited

10 Nandgaon pet, Amravati, Maharashtra

4 660 M/s. Sophia Power Company Limited

11 Tamnar Raigarh, Chhatisgarh

2 660 M/s. Opelina Finance and Investment Limited

12 Tamnar Raigarh, Chhatisgarh

2 660 M/s. Jindal Power Limited

13 Lathur, Maharashtra 2 660 M/s. Amravati Thermal Power Limited

14 Machillipatnam, Andhra Pradesh

2 660 M/s. Thermal Powertech Corporation (I) Limited

15 Gopuvanipalem, Krishna, Andhra Pradesh

3 660 M/s. Nagarjuna Construction Company Limited

16 Simar Thermal Power Plant, Junagarh, Gujarat

2 800 M/s. JSW Energy Limited

17 Salaboni Thermal Power Plant, Paschim Midnapore.

2 800 M/s. JSW Energy Limited

18 Manappad, Tuticorin, Tamil Nadu

2 660 M/s. Ind-Bharat Power (Madras) Limited

19 Mudnra, Kutch, Gujarat 3 660 M/s. Adani Power Limited

20 Sompeta, Drikakulam, Andhra Pradesh

3 660 M/s. Nagarjuna Construction



S.No.


No. ofunits


Utility

Company Limited 21 Central India Power,

Phase-II, Maharashtra1 668 M/s. Central India

Power Company Private Limited

22 Tanda Expansion, Uttar Pradesh

2 660 M/s. NTPC Limited

23 Katwa, West Bengal 2 660 M/s. WBPDCL24 Bakreshwar, Extension

Project1 660 M/s. WBPDCL

25 Koradi Extension Project, Maharashtra

2 660 M/s. Mahagenco

26 East Coast, Andhra Pradesh

2 660 M/s. East Coast Energy

27 NSL Power, Tamil Nadu 2 660 M/s. NSL Power Private Limited

28 Marakanam, Tamil Nadu 4 800 M/s. NTPC Limited29 Darlipali, Orissa 4 800 M/s. NTPC Limited30 Lara, Chhatisgarh 5 800 M/s. NTPC Limited31 Kudgi, Karnataka 3 660 M/s. NTPC Limited JV

with M/s. PCKL

3.2 SUPERCRITICAL PLANTS IN OTHER COUNTRIES

More than 600 SC&USC power plants, with total capacity above 300 GW, were

operating or were under construction in 2004 mainly in Europe, South Africa,

USA, Japan, China and Russia. Around 170 units have been commissioned in

USA, about 100 in Japan, and more than 60 in Europe. The greatest

concentration of SC power plants is in Russia and in the former Eastern bloc

countries, where more than 240 are in service providing about 40% of all

electricity needs in those countries. (Figure 3-3).



Figure 3-3: Capacity of SC & USC Power Plants Worldwide

Advanced SC designs can now be found at several Asian power plants, which

are currently under construction in the People's Republic of China, South

Korea and Taiwan with the capacity in range of 25 GW. Emerging interest in

advanced SC coal fired power plants has fueled development of new, cutting-

edge technologies.

Power plants with record-breaking steam parameters approaching or

exceeding levels of 300kg/cm2 and 600ºC have been commissioned in the last

decade or are under construction in Denmark, Germany and Japan.

This is, however, not the case for the traditional developers of SC technology like Russia and the USA. In these two countries no further major growth of SC technology has been seen in the last decade. Most of the 170 US SC power plants with combined installed capacity above 107 GW came on-line prior to 1980.

Ultra-Supercritical TechnologyIncreasing the temperature and pressure in a steam turbine increases the efficiency of the Rankine steam cycle used in power generation; in other words it decreases the amount of fossil fuel consumed and the emissions generated per kW of electricity generated.

Status in the World Operation data of 573 units has been collected and tabulated as follows. The data relates to the year 2004.

Table 3-5: Supercritical Power Plants in the WorldCountry/Region Units MW

Japan 120 77,900USA 170 107,000

Germany 28 17,286Russia 67 29,730China 32 19,800

Other-Countries 156 58,722

The data cover most of principal power plants in the world with supercritical steam conditions with capacities of 300 MW or more as shown in Annexure-3.1.

Actual status for the adoption of Supercritical Power Technology in major countries is shown below:



(a) JapanThe first supercritical unit Anegaski Unit No. 1 of Tokyo Electric Power Co. had started operation in 1967. Since then, supercritical power plants with 120 units aggregating to 77,900 MW output have been constructed and were operating successfully till 2004.

The unit capacity increased to 350, 500, 600, 700, 1000 MW step by step and reached 1050 MW in the Tachibanawan unit no. 1&2 of Electric Power Development Co. Japan.

The installed capacity of each electric power company in Japan is as follows:

Table 3-6: Supercritical Power Plants of each Electric Power Co.Utility Total Units Total Capacity (MW)

Hokkaido Electric Power Co. 4 2,000Tohoku Electric Power Co. 8 5,600Tokyo Electric Power Co. 25 18,750Chubu Electric Power Co. 19 12,900Kansai Electric Power Co. 22 12,300Hokuriku Electric Power Co. 6 3,400Chugoku Electric Power Co. 7 4,400Shikoku Electric Power Co. 5 2,050Kyushu Electric Power Co, 12 6,900Electric Power Development Co. 8 6,400Joban Kyodo Power Co. 2 1,200Soma Kyodo Power Co. 2 2,000Total 120 77,900

Steam parameters and the numbers of installation of supercritical power plant in Japan are shown as follows:

Table 3-7: Steam Parameters of Supercritical Plants in Japan

Steam Parameters No. or Units

Year

MSP246 kg/cm2 MST533/RST538ºC 21 1968-1985




MSP246 kg/cm2 MST593-600 / RST 593-610ºC 13 1997-2004

Most advanced steam condition power plants, namely, Ultra Supercritical Pressure Power Plants exceeding steam temperature 593ºC have already been operated in Japan and their typical units are shown below;

Table 3-8: Advanced Supercritical Plants in JapanStation Year Unit Capacity (MW) Steam Parameters

Mtsuura 2 1997 1,000 246 kg/cm2 593/593ºCHaramachi 2 1998 1,000 250 kg/cm2 600/600ºCMisumi 1 1998 1,000 250 kg/cm2 600/600ºC



Tachibanawan 1&2 2000/2001 1,050/1,050 250 kg/cm2 600/610ºC

Supercritical thermal power plants in Japan are summarized in Annexure-3.2.

(b) USABoth subcritical (drum) type and supercritical (once-through) type units were in operation from 1960 to 1980. Subsequently there was a shift to subcritical units owing to lower availability and other problems with supercritical plants. Most of the 170 supercritical units of 300MW or over, were put into operation in 1970s or earlier, 4 units in 1980s and only 1 unit in 1990s.

Typical steam parameters in USA are as follows.

Table 3-9: Steam Parameters of Supercritical Plants in USA246 kg/cm2 538/538ºC 116 units

234 kg/cm2 538/538ºC 11 units

246 kg/cm2 538/566ºC 40 units

246 kg/cm2 566/566ºC 2 units

325 kg/cm2 649/566ºC 1 units

(c) GermanyGermany is an advanced country is supercritical technology and has a lot of supercritical thermal power plants.

Supercritical power plants with 28 units (17,286 MW) were constructed between 1969 and 2001.

The unit capacity increase to 300 MW in 1969 and achieved 1,000 MW in 2001.

Steam parameters of MSP280kg/cm2 and MST580ºC / RST600ºC were achieved in 2000 while they were MSP230kg/cm2 and MST532ºC /RST533ºC in 1969.

Steam parameters and the numbers of installation of supercritical power plants in Germany are shown in Table 3-9 below.

Table 3-10: Steam Parameters of Supercritical Plants in GermanySteam Parameters No. of Units YearMSP230-298 kg/cm2 MST 527-537/RST 533-543ºC 13 1969-1989MSP243-257 kg/cm2 MST 542/RST 566ºC 7 1993-1997MSP250-266 kg/cm2 MST 541-577/RST 580-588ºC 6 1992-2001MSP260-280 kg/cm2 MST 575-580/RST 600ºC 2 1999-2000

Advanced supercritical plants in Germany are listed in Table 3-10 below.

Table 3-11: Advanced Supercritical Plants in Germany

UtilityCapacity

(MW)Steam Parameter

Year in Operation



MST (kg/cm2) x MST (ºC) / RST (ºC)

Bexbach 2 750 260x575/600 1999Lippendorf R-S 2x930 265x550/582 1999-2000Niedderaussem K 980 280x580/600 2000Frimmcrdorf 1000 250x577/588 2001

Supercritical thermal power plants in Germany are summarized in Annexure 3.3

(d) RussiaSupercritical power plants with 67 units aggregating to 29,730MW were constructed between 1964 and 1996.

Steam parameters and the numbers of installation of supercritical power

plants in Russia are shown in Table 3-11.

Table 3-12: Steam Parameters of Supercritical Plants in RussiaSteam Parameters No. of Units YearMSP240 kg/cm2 MST540/RST54OºC 65 1969-1996MSP255 kg/cm2 MST545/RET545ºC 1 1996MSP255 kg/cm2 MST565/RST575ºC 1 1968

Supercritical thermal power plants in Russia are summarized in Annexure 3.4.

(e) ChinaChina has constructed supercritical power plants with progressive increase since 1995, and the total installed capacity had reached 32 units with thermal output of 19,800 MW in 2006.

Furthermore, power plants with 37 units and capacity 23,800 MW have been under construction after 2006. Steam parameters and number of units of supercritical plants in China are shown in Table 3-12 below.

Table 3-13: Steam Parameters of Supercritical Plants in ChinaSteam Parameters No. of Units YearMSP246 kg/cm2 MST540/RST 540ºC 5 1999-2006MSP246 kg/cm2 MST53S/RST 566ºC 13 1997-2006MSP246 kg/cm2 MST566/RST 566ºC 12 2004-2006MSP259 kg/cm2 MST600/RST 600ºC 2 2006

Supercritical thermal power plants in China are summarized in Annexure 3.5

(f) Other CountriesSupercritical thermal power plants with total 156 units aggregating to 58,720 MW capacity in 22 countries/ areas such as the Denmark, Netherlands, Britain, Italy, Ukraine, Uzbekistan, South Korea and Taiwan have been constructed and are operating successfully.

Supercritical thermal power plants in Other Countries are summarized in Annexure 3.6.



It is seen that, large number of supercritical plants with 552 units aggregating to 309,800 MW capacity have been constructed and put in operation in Europe, USA, Japan and China since 1960s. Supercritical technology is now established in almost all the countries in the world and the technology can be estimated as a proven technology in the power sector.



(2) Availability of Supercritical PlantsAvailability of supercritical plants is analyzed and evaluated by utilizing the public reports/data issued by EPRI(USA), VGB (Germany), JEPIC (Japan) and FEPC (Japan) as follows.

(a) EPRI ReportThe data below shows the comparison of supercritical and subcritical coal-fired unit performance on Availability Factor for several size ranges from 1982 to 1984.

Table 3-14: Availability Factor (%) 1982-1984Size Range (MW) 300-399 400-499 500-599 600-799 800+Subcritical 76.5 77.4 76.3 78.5 77.2Supercritical 64.4 74.6 73.8 74.2 75.6

In1982-1984, supercritical units had lower availability factor than subcritical units of the order of a few percentage points.

(b) VGB ReportThe data below shows the comparison of supercritical and subcritical performance regarding Availability Factor from 1988 to 1997.

Table 3-15: Availability Factor (%) 1988-1997Year 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 88-97Subcritical 84.2 82.5 84.1 84.9 84.5 82.0 83.8 83.7 86.6 88.5 84.4Supercritical 80.2 74.9 84.2 85.2 87.1 89.8 83.0 84.7 79.5 90.3 84.0

Availability of supercritical units was almost equal to that of subcritical units from 1988 to 1997. In 1997, availability factor of supercritical unit was superior to that of subcritical unit.

(c) JEPIC/FEPC DataJEPIC / FEPC collected the data on the availability factor of subcritical / supercritical coal-fired power plants of Japan in 1994. These are summarized in Table 3-15.

Table 3-16: Availability Factor (%) in 1954

Nos. of UnitRated Output

(MW)Availability Factor

(%) (Average)Subcritical 12 250-350 83.4Supercritical 20 600-1,000 88.1

According to these data, supercritical units had higher availability than subcritical units by 4.7 percentage points.

The detailed availability data for subcritical and supercritical plants in Japan, available in J-POWER was compiled and evaluated. In this survey, no significant difference in availability between subcritical and supercritical plants in recent years was noticed.



It is apparent from the availability data for supercritical units installed worldwide, that supercritical units cannot be differentiated from conventional subcritical units with respect to unit availability.



4.0 AVAILABILITY OF MANUFACTURES OF SUPERCRITICAL PLANTS



AVAILABILITY OF MANUFACTURERS SUPERCRITICAL PLANTS 4.1 SUPERCRITICAL PLANT MANUFACTURERS IN INDIA

At present, Bharat Heavy Electricals Ltd. (BHEL) is the only manufacturer of

supercritical thermal power plants in India. BHEL has Technical Collaboration

Agreement with Alstom, France for the manufacture of “once through boilers”

of both single pass and two pass designs used in supercritical plants. The

agreement provides for transfer know how from Alstom to BHEL.

BHEL, also, has Technical Collaboration Agreement with Siemens, Germany

for the complete range of Steam Turbines and Generators. BHEL will be able

to manufacture large unit rating machines of Siemens design under their

agreement.

BHEL is implementing capacity addition at its Hardwar plant for Steam turbine

and Generator and at Trichy plant for Boilers to augment its manufacturing

capacity for thermal units of existing range as also supercritical sets of 800

MW and 1,000 MW.

In addition to BHEL, Larsen & Toubro Ltd (L&T) has Cooperation Agreement

with Mitsubishi Heavy Industries Ltd. (MHI), Japan for transfer of technology

for supercritical boilers. Under the agreement, MHI will transfer design and

engineering know-how to L&T who will initially manufacture part of the boiler

in India and increase indigenous content in a phased manner.

In addition to the above two, few other companies are planning to setup

manufacturing plant in India. Their proposed commissioning capabilities are

shown in table below:


Capability


4.2 SUPERCRITICAL PLANT, MANUFACTURER OUTSIDE INDIA

There are a number of large manufacturers of supercritical plants in the

world.

The main manufacturers are:

Siemens AG, Germany

Alstom SA, France

Mitsubishi Heavy Industries Ltd., Japan

Technoprom Export, Russia

Doosan Heavy Industries, Korea

Babcock Hitachi, Japan

Ishikawajima Harima Heavy Industries (IHI), Japan

Toshiba Corporation, Japan

Hitachi Ltd, Japan

Harbin Power, China

Dong Fang Electric, China

Shanghai Electric Corporation, China

Hitachi Ltd, Japan

General Electric Power System, U.S.A,

Ansaldo Energia, Italy

4.3 DELIVERY PERIODS

Manufacturing capabilities for supercritical plants are available in India

presently with two manufacturers. Manufacturing capabilities for supercritical

and ultra- supercritical plants are available, however, with a large number of

manufacturers in other countries and some of them have some

manufacturing or commercial presence in India already. Choice of a

manufacturer suitable to meet specific requirements of any developer at an

economical price is available. The main problem, at present, is the

comparatively long delivery period on account of the order books of most of

the manufacturers being full already. Shorter delivery periods are likely to

invite higher prices and a balance has to be arrived at between the benefits

of early commissioning as against those of lesser initial capital cost.



5.0 SPECIAL MATERIALS FOR SUPERCRITICAL PLANTS



SPECIAL MATERIALS FOR SUPERCRITICAL PLANTS5.1 BOILER

Basic boiler design criteria guidance to be followed for the boiler as follows for

utilizing the Indian erosive high ash content coal as follows.

5.1.1 Materials for Boilers in Ultra Supercritical Power PlantsImproving the efficiency of pulverised coal (PC) power plants, by increasing the temperature and pressure of the working fluid (steam) has been pursued for many decades. Figure 5-1 illustrates the improvements in heat rate that can be achieved by increasing steam temperature and pressure by use of advanced steam conditions.

Figure 5-4: Improvement in heat rate (efficiency) achieved by increasing steam temperature and single and double cycles , compared to the base case of 535ºC/189 kg/cm2.

Eddystone 1 power plant in USA commissioned in 1959 was one of the first supercritical plant designed to operate under steam conditions of 346 kg/cm2



and 650/565/565°C (1200/1050/1050°F). The plant has been operational since 1959 but has operated under rated conditions of 330 kg/cm2 and 605°C for most of its service life, because of mechanical and metallurgical problems. Most of the problems were due to the use of austenitic steels for heavy section components operating at high temperatures. These steels have low thermal conductivity and high thermal expansion resulting in high thermal stresses and fatigue cracking. These problems and the general low availability of many supercritical plant due to "teething" problems temporarily dampened utility interest in building super or ultra supercritical plants and consequently most utilities reverted back to plants with sub-critical conditions of about 525°C and 173 kg/cm2.

EPRI initiated a study of the development of more economic coal-fired power plants in 1978. A number of research and development activities was initiated involving US, Japanese and European manufacturers. These activities focused on developing further the existing high-temperature-resistant ferritic-martensitic 9%Cr and 12%CrMoV steels for the production of rotors, casings and chests, pipes and headers capable of operating at inlet steam temperatures of up to 650°C. One of the early conclusions from this project was that the construction of a plant with a 593°C/ 316 kg/cm2steam condition would be feasible with only minor evolutionary improvements in materials technology. This has proved to be correct as evidenced by the spate of power plants built in Japan and Europe over the last decade. In Japan, nearly 16 plants, most of them with typical main steam temperature of about 593°C and pressure of 245 kg/cm2 are operational. In Europe, nearly a dozen plants are operational with main steam temperature/ pressure or 583°C (1080°F)/305.91 kg/cm2 (4200 psi).

An improvement in thermal efficiency of the plant not only reduces the operating costs but also reduces the release of SO2, NOx and CO2 emissions. The latter is very significant in view of die world-wide agreements to reduce CO2 emissions by 2010 and the fact that a 1% increase in efficiency of an 800 MW machine would lead to a life-lime reduction in CO2 approaching one million tones. These environmental factors have provided an added incentive to building SC & USC plants in recent years.

Intense R&D efforts have been carried out in Japan, USA and Europe to evolve materials suitable for temperatures of 593°C and beyond. In each case, a phased approach was adopted. In USA, the phases of development were defined as shown in Table 5-1, where the temperatures given are for the main steam and first and second reheats.

Table 5-17: Steam conditions for coal-fired plants in EPRI programEPRI Program Pressure Temperature

Phase kg/cm2 °C0 22.21 566/566/5661 22.21 593/593/593

1B 22.21 620/620/6202 24.39 649/649/649

The Phase 0 conditions were considered to be achievable with the state-of-the-art technology in 1978 while the Phase 1 conditions were considered to be achievable with only minor improvements. The technology needed for phase 2 was considered well beyond reach and hence, an intermediate goal



of 620-630°C 305 kg/cm2 was introduced. For convenience, this Phase may be referred to as phase IB. Although the material developments For Phase 2 have not been fully achieved, technology exists today that will enable building plants that can meet Phase IB conditions. This has been made possible by the development of highly creep resistant 9 to l2%Cr ferritic steels.

EPRI performed review of materials technology for ultra supercritical power plants. The results of the review show that high strength ferritic 9-12Cr steels for use in thick section components are now commercially available for temperatures up to 620°C. Initial data on two experimental 12Cr ferritic steels indicate that they may be capable of providing long term service up to 650°C. Advanced austenitic stainless steels for use in super- and reheater tubing are available for service temperatures up to 650°C and possibly 700°C. None of these steels have been approved by the ASME Boiler Code Group so far. Higher strength materials are needed for upper water walls of boilers with steam pressure above 245 kg/cm2. A high strength 2-1/2%Cr steel ASME code approved alloy T-23 is the preferred candidate material for this application.

5.1.2 Boiler Materials RequirementsThe key components whose performance is critical for supercritical and ultra supercritical plants are high-pressure steam piping and headers, superheater tubing and waterwall tubing. All of them have to meet creep strength requirements. In addition, pipes and headers, being heavy section components, are subject to fatigue induced by thermal stresses. Ferritic/martensitic steels arc preferred because of their lower coefficient of thermal expansion and higher thermal conductivity compared to austenitic steels. Many of the early problems in the SC & USC plants were traceable to the use of austenitic steels which were highly prone to thermal fatigue. Research during the last decade has, therefore, focused on developing cost-effective, high-strength ferritic steels that could be used in place of austenitic steels. This has resulted in development of ferritic steels capable of operating at metal temperatures up to 620°C, with good weldability and fracture toughness.

Superheater and reheater (SH/RH) tubing application calls for high creep strength, thermal fatigue strength, weldability, resistance lo fireside corrosion/erosion and resistance to steamside oxidation and spallation. Thermal fatigue resistance as well as cost considerations would dictate the use of ferritic/martensitic steels. Unfortunately, the strongest of these steels which can be used up to metal temperature of 620°C purely from a creep strength point of view are still limited by fireside corrosion to metal temperature of 593°C. This corresponds to a steam temperature of about 565°C since SH/RH metal temperature can exceed the steam temperature by as much as 28°C. Excessive corrosion of ferritic steels caused by liquid iron-alkali sulfates in the lube deposits is an acute concern, where high sulfur corrosive coals are used more frequently than elsewhere. Therefore high strength ferritic stainless steels such as T-91 are infrequently used. The standard practice is to use T-22 for the lower temperatures and SS304H or SS347 for the highest temperatures.

With respect to waterwall tubing, the concern is twofold. High supercritical pressures and the use of high heat release furnaces will increase the waterwall temperatures to the point that easily weldablc low alloy steels such



as T-113 (1.25Cr, 0.5Mo) have insufficient creep strength. Higher strength steels such as T-91 are available, but require postweld heat treatments. The second concern is corrosion. Recent results in on boilers retrofitted with low NOx burner systems indicate that the present low alloy steels can suffer from excessive corrosion, as high as 2 mm/yr. Weldable high strength alloys clad or overlaid with high Cr alloys have to be utilized to reduce or eliminate excessive corrosion.

5.1.3 Historical Evolution of Steels

Masuyama has presented an excellent historical perspective on the

development of steels for power plants as shown in Figure 5-2. The figure

shows 105h creep rupture strength at 600°C (1112°F) by year of

development. They classify the ferritic steel development in terms of four

generations as shown in Table 5-2.



Figure 5-5: Historic evolation of materials in terms of increasing creep rupture strength

Table 5-18: Evolution of Four Generations of Ferritic Steels

Generation Years Alloy Modifications

Strength 105 hr Creep Rupture Achieved kg/cm2

Example AlloysMaximum Metal Use Temp. °C

1 1960-70 Addition of Mo or Nb, V

to simple 12Cr and 9Cr

Mo steels

611.82 EM 12, HCM9M,

HT9, Tempaloy

F9.HT91

565

2 1970-85 Optimization of C, Nb.V 1019.71 HCMI2.T91,

HCM2S

593

3 1985-95 Partial substitution of

W Tor Mo

1427.60 P-92, P-122

(HCMI2A, NF616)

620

4 Emerging Increase of W and

addition of Co

1835.48 NFI2.SAVEI2 650

In the field of austenitic steels, efforts were made from the 1970s to the early

1980s to improve conventional l8Cr-8Ni series steels originally developed as

corrosion resistant materials for chemical use, mainly with respect to their

creep strength. Another goal pursued from the 1980s to the early 1990s was



to improve the creep strength of conventional 20-25Cr series steels having

superior oxidation and corrosion resistance.

5.1.4 Evolution of Ferritic Steels

Ferritic sled developments are mostly aimed at their use for thick section

pipes and headers. Table 5-3 shows the chemical compositions of ferritic

steels for power boilers. The systematic evolution of these steels has been

thoroughly reviewed by Masuyama, as shown in Figure 5-3. Among the 9%Cr

steels fully commercialized, the P91 steel has the highest allowable stress

and has been extensively used all over the world as a material for headers

and steam pipes in ultra supercritical plants operating at steam

temperatures up to 593°C. Alloy NF6I6 (P-92), developed by substituting part

of the Mo in P91 by W, has an even higher allowable stress and can be

operated up to steam temperatures of 620°C. E911 is a European alloy

similar in composition to NF6I6 with similar capabilities. Beyond 620°C, the

9%Cr steels become limited by oxidation resistance and 12%Cr steel and

austenitic steels have to be used.



105h Creep Rupture Strength at 600°CFirst Generation Second

GenerationThird

GenerationFourth

Generation357 kg/cm2 612kg/cm2 1020 kg/cm2 1428 kg/cm2 1835 kg/cm2

Figure 5-6: Evolution of ferritic steels for boiler


2.25Cr-1Mo 2.25Cr-1MoV 2.25Cr-1.6MVNb

ASME T22(STBA24)

9Cr-2Mo

HCM2S(ASME T23STBA24J1)

+V

+Mo

9Cr-1Mo 9Cr- 2MoVNb

+Mo+V+N

HCM9M(STBA 27

ASME T9(STBA26)

EM12(NFA 49213)+V

+Nb

9Cr- 1MoVNb 9Cr- 1MoVNb

Tempaloy F-9ASME T91(STBA28)

V.NbOptimize

d E 911

9Cr-0.5 Mo-1.8WVNb

NF616(ASME T92STBA29)

12Cr-0.5Mo-1.8WVNb

12Cr-WCo-NiVNb

TB12 NF12

+Mo+W

+W+Co

12Cr 12Cr-0.5Mo

AISI 410

+Mo

12Cr-1Mov 12Cr-1MoWV

+W

+Mo+v

12Cr-1Mo-1WVNb

12Cr-0.5Mo-2 WCuVNb

12Cr-WCoVNb

HT91 (DINX20C

r MoV121)

HT9 (DINX20C

r MoV121)

HCM12 (SUS410J

2TB)

HCM12A (ASME T122

SUS4410J3TB)

-C+W+Nb

-Mo+W+Cu +W

+Co


Table 5-19: Nominal Chemical Compositions of Ferritic Steels for BoilersSpecification Chemical Com

positionMass %) Manufacturers

Steels ASME J1S C Si Mn Cr Mo W Co V Nb B N Others1-1/4 Cr T11 T11 0.15 0.5 0.45 1.25 0.5 -- -- -- -- -- -- --

MFIH 0.12 -- -- 1.25 1.0 -- -- 0.20 0.07 -- -- -- Nippon Steel2Cr F22 T22 STBA24 0.12 0.3 0.45 2.25 1.0 -- -- -- -- -- -- --

SCM2S T23 STBA24J1 0.06 0.2 0.45 2.25 0.1 1.6 -- 0.25 0.05 0.003 -- -- SumitomoTempaloy F-2W

2.0 0.6 1.0 0.25 0.05 -- NKK

9Cr T9 T9 STBA26 0.12 0.6 0.45 9.0 1.0 -- -- -- -- -- -- Vallourec-MannesmanHCM9M — STBA27 0.07 0.3 0.45 3.0 2.0 -- -- -- -- -- -- -- SumitomoT91 T9I STBA28 0.10 0.4 0.45 3.0 1.0 0.20 0.08 0.05 0.8Ni Vallourec-Mannesman

SumitomoE911 0.12 0.2 0.51 3.0 0.94 0.9 -- 0.20 0.06 0.06 0.25Ni

12Cr HT91 (DINx20CrMoV121) 0.20 0.4 0.60 12.0 1.0 -- -- 0.25 -- -- -- 0.5Ni Vallourec MannesmanHT9 (DIN x 20 Cr MoWV

121)0.20 0.4 0.60 12.0 1.0 0,5 -- 0.25 -- -- -- 0.5Ni Vallourcc Mannesman

Tempaloy F12M

12.0 0.7 0.7 -- NKK

HCMI2 SUS410J2T B

0.10 0.3 0.55 12.0 1.0 1.0 -- 0.25 0.05 0.03 --

TB12 -- -- 0.08 0.05 0.50 12.0 0.50 1.8 - 0.20 0.05 0.30 0.05 0.1NiHCM12A T122 SUS410J3T

B0.11 0.1 0.60 12.0 0.4 2.0 -- 0,20 0.05 0.003 0.06 1.0Cu Sumitomo

NF12 -- -- 0.08 0.2 0.50 11.0 0.2 2.6 2.5 0.20 0.07 0.004 0.05 -- Nippon SteelSAVE 12 -- -- 0.10 0.3 0.20 11.0 -- 3.0 3.0 0.20 0.07 -- 0.04 0.07Ta,

0.04NdSumitomo

E040/ REPORT boben PAGE 44 OF 161

`DESIGN, INSTALLATION & OPERATION OF SUPERCRITICAL POWER PLANTS

Among the l2%Cr steels, HT91 has been widely used for tubing, headers and piping in Europe. Use of the steel in Japan and US has been limited due to its poor weldability. HCM12 is an improved version of HT91 with 1% W and 1% Mo, having a duplex structure of 5-ferrite and tempered martensite with improved weldability and creep strength. Further increases in creep strength by substituting more of the Mo with W and addition or Cu has resulted in alloy HCM12A (P-122), which can be used for header and piping up to 620°C - Two alloys NF12 and SAVE12 having an even higher creep strength than HCMI2A are in the developmental stage. NF12 contains 2.5%Co, 2.6%W and slightly higher B compared to HCM12A. SAVE12 contains 3% Co, 3% W, and minor amounts of Ta and Nb. These latter elements contribute to strengthening by producing fine and stable nitride precipitates. HCM2S (T-23), a low carbon 2-1/401.6W steel with V and Mb, is a cost-effective steel with higher creep strength than T22. Because of its excellent weldability without pre- or post-weld heat treatment it is a good candidate for waterwall tubing.

The role of alloying elements in development of the ferritic steels has been extensively investigated. W and Mo and Co are primarily solid solution strengthened. V and Nb contribute to precipitation strengthening by forming fine and coherent precipitation of M(C, N)X carbonitrides in the ferritc matrix. Vanadium also precipitates as VN during tempering or during creep. The two elements arc more effective in combination at levels of about 0.25%V and 0.05%Nb. Chromium contributes to solid solution strength as well as to oxidation and corrosion resistance. Nickel improves the toughness but at the expense of creep strength. Partial replacement of Ni by Cu helps stabilize the creep strength. Carbon is required to form fine carbide precipitates but the amount needs to be optimized for good weldability.

Atom probe results have shown that boron enters the structure of M23C6 and boron segregates to M23C6 - matrix interface. It has also been suggested that boron helps reduce coarsening of M23C6 and that boron also assists in nucleation of VN, the mechanism of “latent creep resistance.

Cobalt is an austenite stabilizer and developers of NFI2 suggest that is why they used cobalt additions. Cobalt is known to delay recovery on tempering of martensitic steels. Cobalt also promotes nucleation of finer secondary carbides on tempering. This is attributed both to its effect on recovery and its effect on the activity of carbon. Cobalt also slows coarsening of alloy carbides in secondary hardening steels. This was suggested to be the result of cobalt increasing the activity of carbon and cobalt not being soluble in alloy carbides. Results of Hidaka suggest that Co has a positive effect on creep rupture stress.

5.1.5 Evolution of Austenitic SteelsAustenitic steels are candidates primarily in the finishing stages of superheater/reheater tubing, where, oxidation resistance and fireside corrosion become important in addition to creep strength. From a creep strength point of view, T91 is limited to 565°C steam (metal 593°C) and NF616, HCM12A and E911 arc limited lo 593°C steam (metal 620°C). Even the strongest ferritic steel today is limited to 593°C (metal temperature) from an oxidation point of view. At temperatures above these, austenitic steels are required. Hence there has been considerable development with respect to austenitic stainless steels. In actual practice, in SS304M and SS347 are widely

E040/ REPORT/MARCH 2009 PAGE 45 OF 161

`DESIGN, INSTALLATION & OPERATION OF SUPERCRITICAL POWER PLANTS

used the U.S. instead of T-91 in superheater applications, mainly because they are easier to weld, while the cost difference is relatively small.



Table 5-4 lists the compositions of various stainless steels for SH/RH lube applications.

Table 5-20: Nominal Chemical Compositions of Austenitic Steels for Boiler (wt%)SpecificationsASME JIS C Si Mn Ni Cr Mo W V Nb Ti B Others

18Cr-8Ni TP304H SUS304HTB 0.08 0.6 1.6 8.0 18.0 -- -- -- -- -- -- -Super 304H SUS304JIHT B 0.10 0.2 0.8 9.0 18.0 -- -- -- 0.40 -- -- 3.0Cu, 0.10NTP321H SUS321HTB 0.08 0.6 1.6 10.0 18.0 -- -- -- -- 0.5 -- -Tempaloy A-1 SUS321JIHT B 0.12 0.6 1.6 10.0 18.0 -- -- -- 0.10 O.OS -- -TP316H SUS316HTB 0.08 0.6 1.6 12.0 16.0 2.5 -- -- - -- -- ..TP347H SUSTP347H TB 0.08 0.6 1.6 10.0 18.0 - - -- 0.8 - - -TP347 HFG 0.08 0.6 1.6 10.0 18.0 - - - 0.8 - -- -

15Cr-15Ni 17-l4CuMo 0.12 0.5 0.7 14.0 16.0 2.0 -- - 0.4 0.3 0.006 3-0CuEsshete 1250 0.12 0.5 6.0 10.0 15.0 1.0 0.2 1.0 - 0.06 --Tempaloy A-2 0.12 0.6 1.6 14.0 15.0 1.6 -- -- 0.24 0,10 --

20-2SCr TP310 SUS310TB 0.08 0.6 1.6 20.0 25.0 - -- - - - -TP310NbN SUS310J1TB 0.06 0.4 1.2 20.0 25.0 - -- - 0.45 - - 0.2NNF707* 0.08 0.8 1.0 35.0 21.0 1.5 -- - 0,2 0.1 - -Alloy 800H NCF800HTB 0.03 0.8 1.2 32.0 21.0 - - - - 0.5 - 0.4A1Tempaloy A-3* SUS309J4HT B 0.05 0.4 1.5 15.0 22.0 - - - 0,7 - 0.002 0.15NNF709* SUS310J2TB 0.15 0.5 1.0 25.0 20.0 1.5 -- - 0.2 0.1 -SAVE25* 0.10 0.1 1.0 18.0 23.0 - 1.5 - 0.45 - - 3.0Cu. 0.2N

HighCr-High Ni CR30A* 0.06 0.3 0.2 50.0 30.0 2.0 - -- -- 0.2 -- 0.03ZrHR6W* 0.08 0.4 1.2 43.0 23.0 - 6.0 - 0.18 0.18 0.003Inconel 617 0.40 0.4 54.0 22.0 8.5 - - -- - - 12.5Co. 1.2A1Inconel 671** 0.05 -- -- 51.5 43.0 -- -- -- -- -- -- --

* Not ASME code approved.** Low strength material for use in co-extruded tubing. For weld overlays. IN72 (44%Cr-bal Ni) is the matching weld wire


\DESIGN, INSTALLATION & OPERATION OF SUPERCRITICAL POWER PLANTS

The austenitic steels fall into four categories: l5Cr, 18Cr, 20-25Cr and higher

Cr stainless steels. The various stages in the evolution of these steels have

consisted of initially adding Ti and Nb to stabilize the steels from a corrosion

point of view, then reducing the Ti and Nb content (underslabilizing) lo

promote creep strength rather than corrosion, followed by Cu additions for

increased precipitation strengthening by fine precipitation of a Cu rich phase.

Further trends have included austenite stabilization using 0.2% nitrogen and

W addition for solid solution strengthening. This development sequence is

illustrated in Figure 5-4.

Figure 5-7: Evaluation of authentic steels for boiler

Table 5-21: Candidate Materials for Advanced Supercritical Plants for Various Steam Conditions

Component

Phase 0316 kg/cm2

565/565/565°C (1050/1050/1050°F)

Phase 1316 kg/cm2

593/593/593°C1050/1050/1050°F)

Phase IB 316 kg/cm2

620/620/620°C 1050/1050/1050°F)

Phase 2316 kg/cm2

650/650/65O°C1050/1050/1050°F)

Headers/steam pipes

P22, HCM2S (P23) P91, P92, P122

P9LP92.P122, E911 P92,PI22 E911, NFI2, SAVE 12

SAVE 12+ NF12+

Finishing SH non-corrosive

T91, 304H, 347 TP347 HFGSuper 304 H/P-l 22*

NF709 Super 304 H NF709 Inconel 617

Corrosive 310NbN(HR3C) 3IONbN(HR3C) SS347/IN72**

3I0NbN(HR3C)Super304H/IN72**

Cr30ANF 709/1N72**

Finishing RH Same as SH Same as SH Same as SH Same as SHWater wall Lower wall Upper wall

For low NOx Boilers + High S coal

C steelT11, T12, T22Clad with alloy containing >20% Cr or chromized

Tll,TI2, T22 T23 (HCM12)

Same as Phase 0

Same as Phase 1 Same as Phase 1

Same as Phase 0 Same as Phase 0

E040/ REPORT/Boben Anto C PAGE 48 OF 161


* High strength ferritic alloys with 9%Cr arc suitable for steam piping and

headers, but may suffer excessive fire side oxidation. l2Cr steels may be

suitable, but further testing is needed.

** IN72 (44Cr, bal Ni) weld overlay for corrosion protection

+ Developmental Alloy

5.1.6 Choice of Materials for Headers and Steam PipesFerritic steels for thick section applications at various temperatures are shown in Table 5-5. Material-property requirements for headers and steam pipes are likely to be similar, and hence they have been grouped together. Some minor differences exist which may affect material selection. The steam temperature is likely to be much more uniform in steam pipes, but subject to time-dependent and location-dependent fluctuations in headers. Hence, the thermal-fatigue-strength requirements are greater for headers than for steam pipes. Self-weight-induced stresses are less important for headers than for steam pipes, permitting heavier-wall construction and an attendant higher temperature/pressure capability for a given material when used in headers. An important difference is that headers have many welded attachments to inlet stub tubes from reheaters and superheaters and intersections of outlet nozzles connecting pipework. Depending on the selection of materials for the superheater/reheater tubes and the header piping, dissimilar-metal welded joints may be required. The integrity of such austenitic-to-ferritic welds, when 9 to l2%Cr steels form the ferritic components, needs to be more thoroughly investigated.

Headers and pipes have traditionally been made from low alloy steels such as P11 and P22. Even in conventional boilers, such headers can fail due to thermal fatigue cracking, caused by cycling. A common failure mode is the cracking of the ligaments between the tube boreholes. The use of higher temperatures and pressures can only increase the problem. Previous attempts lo use austenitic steels have not been successful due to high thermal expansion of these steels.

Several candidate ferritic steels have emerged succeeding the P11 and P22 steels, which are capable of operation up lo 593°C. These include HT9, HT91, HCM9M, HCM12 and P91. Alloys HT9 and HT91 are well-established steels with an extensive stress-rupture database which exceeds 105 h at temperatures in the range 500 to 600°C for all product forms. There is also extensive operating experience (>20 years) in Germany, Belgium, Holland, South Africa, and Scandinavia for steam temperatures up to 540°C (1000°F) and some limited experience on a few small units with steam temperatures from 560 to 580°C. This experience generally has been satisfactory. Difficulties have. however, been reported during fabrication and particularly during welding and post-weld heal treatment. This arises because the relatively high carbon content of the steel (0.2%) and the correspondingly low Ms temperature promote the possibility of austenite retention after welding, high residual stresses, and cracking prior to and during stress relief. It is reported that these problems have been overcome by careful control of preheat treatment and post weld heat treatment backed up by vigorous quality control. Difficulties have also been reported when the material has been given inadequate solution heal treatment. Due lo these concerns, these



alloys have not found much favor in the United Slates, the United Kingdom, or Japan. Alloys with improved weldability characteristics, such as HCM12M have been adequately characterized for tubing and large-diameter, thick-wall pipes.

With regard to the 9Cr-2Mo steel (HCM9M), the feasibility of fabrication of large-diameter, (hick-wall piping and application to in-plant header and main steam piping was first demonstrated in 1985. The practical use of this material has been easy because its simple composition lends fabricability and weldability comparable to those of low-alloy steels. The toughness of large-diameter pipes has been found to be over 102 kg/cm2 (460 ft-lb/in.2) at 0°C (32°F). Allowable stresses arc comparable to those for the HT9 alloy, but lower than those for P91. Service experience of nearly 25 years has accumulated since the alloy was developed with about 2000 tons having been produced specifically for SH/RH lubes and steam pipes.

The modified 9Cr alloy, P91, appears to be quite superior to HT9, HT-91 and lo HCM9M in terms of creep-rupture strength and is, thus, the most promising candidate for use in header and steam piping for temperatures up to 595°C (I100°F). One of the early applications was by the Chubu Electric Power Company (Kawagoe Power Station, Units 1 and 2) for 565°C (I050°F) steam conditions as headers and steam pipes. A majority of the recent European supercritical plants have utilized P91 as main steam and reheat piping. Numerous retrofit applications have also been carried out for headers/steam pipes. The alloy was approved by the ASME Boiler Code Committee for various uses between 1983 and 1986 as T, P, F-91. Since that time, the alloy has found applications worldwide and is available from many sources, since the composition is not proprietary. It is especially popular in Europe, where it proved superior in creep strength as well as weldability, compared lo the well-known HT9I steel, used in supercritical boilers.

The high creep strength of grade 91 steel is due to small additions of V, Nb and nitrogen, which lead to the precipitation of M23C6 carbides and (Nb, V) carbonitrides, in addition to solution strengthening by Mo. Very extensive studies were made world wide to evaluate the suitability of P-91 for heavy section components. These included manufacturing studies, welding trials, both similar and dissimilar, bending trials, both hot and cold, and various mechanical tests, on both virgin and aged samples. The net result of all these tests is that P-91 is now the preferred heavy section material for supercritical boilers worldwide. However, most designers feel the use of P-91 will probably be limited to steam conditions of about 593°C/254.92 kg/cm2. This is especially the case in Europe, where the allowable creep strength is 254.92 about 10% lower than in Japan and the U.S.

Recent development in Japan has indicated that the creep strength of 9-12Cr. Mo, V, Nb steels can be raised by about 30% through partial substitution of Mo by W. This has spawned another round of intensive alloy development and evaluation worldwide. Two of these steels, a 9Cr steel developed by Nippon Steel NF6I6 (P-92) and a 12Cr steel HCMI2A developed by Sumitomo metals (P-122) have been approved for use in boiler heavy section components by ASME. Another W containing steel E-911 is in an advanced stage of development in Europe. The allowable strength of the new steels at 600°C is about 25% higher than that of P-91. Thus these steels should allow steam temperatures up to 620°C and pressures up to 347 kg/cm2.



Figure 5-5 shows a plot of the allowable stress at various temperatures for ferritic steels. The figure clearly shows the enormous advances in the materials technology which have been made in the last 20 years. Especially at the higher temperatures, the most advanced steels show allowable stresses that arc nearly 2.5 to 3 times that of the workhorse steel in conventional plants, i.e., 2-1/4Cr-lMo steel (P22). The layering of the alloys into the different generations described earlier is also evident. HCM12A (P122), NF616 (P92) and E911 emerge as the three highest strength alloys suitable for ultra supercritical plants up to 620°C, followed by T91, HCM12, EMI2. HCM9M and HT91 suitable for intermediate temperatures up to 593°C followed by T22 for use up to 565°C. NF1'2 and SAVE12 are still developmental but are expected to meet the Phase 2 goals. This rationale has been incorporated in the materials selection shown in Table-5.6.

Figure 5-8: Comparison of allowable stress of ferritic steels for boiler

An interesting fact is that application of the new steels may actually result in a capital cost reduction. Figure 5-5 shows the allowable design stresses and a comparison of the relative wall thicknesses at various temperatures. At any given temperature, higher allowable stresses for a material permit design of thinner wall headers/pipes. This not only reduces thermal stresses, but also reduces cost. From Figure 5-6, section thicknesses and materials costs can be calculated as a function of temperature and pressure. Figure 5-7 shows the results for a pressure of 316 kg/cm2. The cost of using high strength steel becomes lower than that of P-22 steel at about 520°C. The cost of using the W containing steel is lower than that of P-91 above about 550°C. These relations do not change very much with decreasing pressure down to 203 kg/cm2. Actual fabricated and installed cost differences should be even larger



as the thinner pipes need less welding and arc easier to install. Fewer supports are needed thus reducing costs further.

Figure 5-9: Comparison of allowable stresses and sectional view of main steam pipes designed at 570ºC and 600ºC

European power stations using the most advanced steels NF616 (P92), HCM12A (PI22) and E911 are shown in Table 5-22.

Figure 5-10: Cost of P-22, P-91 and P-122 steels header materials as a function of temperature at 316 kg/cm2 steam pressure



Table 5-22: Application of New Tungsten-Bearing Steels in European Power Stations

Power Station Material Grade Size ComponentSteam

Conditions °C/ kg/cm2

Installation

Vestkraft Unit 3 P92(NF616) ID 240 x 39 Straight PipeMain Steam

560/254.92 1992

Nordjyllands-vacrkct P92 (NF616) P122 (HCM12A)

ID 160x45 Header 582/295.71 1996

Schkopau Unit B E91I ID 550 x 24 Induct. BendHot Reheat

560/71.38 1996

Staudinger Unit 1 E9II ID 201x22 Induct. BendMain Steam

540/217.19 1996

Skaerback Unit 3 E911 ID 230 x 60 Induct. BendMain Steam

582/295.71 1996

GK. Kiel P92 ID 480 x 28 Header 545/54 1997VEW E911 OD3J.8x4 Superheater 650 1998Westfalen E911 ID 159 x 27 Steam Loop 650/183.54 1998Westfalen P92 ID 159x27 Steam Loop 650/183.54 1998

There is considerable interest in using these alloys for outlet headers and main steam and reheat pipe work. Full-scale headers have been being installed in a 415MW supercritical plant under consideration by the Danish utility, ELSAM. Headers using P92 and P122 have been constructed and installed. Two of the headers will be tested under accelerated high-temperature conditions in a high-pressure cell operated by Mitsubishi Heavy Industries.

Some additional design considerations in applying the advanced steels are as follows:1. The high temperature strength of the advanced alloys, e.g. NF616,

HCM12A and E9II (P-92, P-122, E911) is essentially the same as that of austenitic alloys. But oxidation resistance is less than that of austenitic alloys. This parameter of advanced 9 to 12Cr alloys must be more fully evaluated prior to application to high temperature parts.

2. Post weld heal treatment (PWHT) is always required for welded joints of advanced 9 to 12 Cr alloys to ensure minimal stress and optimal ductility. Design must allow to reduce field heat treatment as much as possible to keep production and PWHT costs minimal.

3. In the weldment of dissimilar alloys, material selection must be based on consideration of PWHT temperature. For example, the 9Cr-lMo alloy and ICr-0.5Mo steel would not be acceptable material for the joints in a longitudinal direction; measures must be taken to consider the behavior of welded joint creep rupture strength.

4. It is the apparent susceptibility of ferritic steel welds to Type IV cracking, which occurs at the edges of line grained HAZ material adjacent to unaffected parent material. Susceptibility to this has been clearly demonstrated for l/2CrMoV, 2-l/4Cr-IMo and 9Cr-IMo (T91) steels. Safety margins of 10 to 20% are sometimes adopted to provide for this problem. Since the problem in girth welds is primarily associated with bending stresses, the problem can be overcome by proper plant design and maintenance. This issue has therefore been generally glossed over.

5.1.7 Choice of Materials for Superheater/Reheater Tubes



The superheater tubes in the boiler are likely lo undergo the most severe service conditions and must meet stringent requirements with respect to fire-side corrosion, streamside oxidation, creep rupture strength and fabric ability. In addition, they must be cost-effective. Based on these issues candidate materials for various steam conditioning have been summarised in Table 5-5. The rationale for these selections is discussed in the following sections.

5.1.8 Creep Rupture StrengthIn terms of creep rupture strength, application of ferritic steels for tubes follow the same logic as for the headers/pipes discussed earlier. Thus, tubes made of T22 should be limited to steam temperature of 538°C. Alloys T91, HCM12, EM12. HCM9M and HT91 are limited lo steam temperature of 565ºC, Alloys T-92, P-122 and E911 limited to steam temperature of 593°C. Under corrosive conditions however, even the best ferritic steel may be limited to 563°C temperature and austenitic steels arc needed. Although the creep resistance of 9Cr steels is adequate for use at 593°C, there is considerable doubt about their fireside oxidation resistance. Thus 12Cr steels, such as P122 are preferred.

In practice, the high Cr, high strength ferritics have found little use in the U.S. because of perceived welding problems. T-22, SS30411 and SS347 are the steels most commonly used in supercritical boilers (3500 psi) in the USA.

For convenience, austenitic steels can be classified as those containing less than 20% Cr and those containing more than 20% Cr. Alloy modifications based on the 18Cr-8Ni steels, such as TP304H, 316H, 34711 and Tempaloy A-l, and alloys with lower chromium and higher nickel contents, such as 17-14 CuMo steel, Esshete 1250, and Tempaloy A2, fall into the classification of steels with less than 20% Cr. The allowable tensile stresses for steels in this class are compared in Figure 5-8. Tempaloy A1, Esshete 1250, and 17-14 CuMo steel are found to offer major improvements over the 300 series stainless steels. It has been reported that grain-size modifications of AISI type 347H stainless steel can in some instances lead to rupture properties somewhat better than those of Tempaloy A-1.



Figure 5-11: Comparison of allowable stresses 18Cr-18Ni and 15Cr steels

Several high-crcep-strength alloys containing more than 20% Cr, such as NF707, NF709, and HR3C, have been developed, and offer low-cost alternatives to Incoloy 800 for use in the temperature range from 650 to 700°C (1200 to 1290°F). A comparison of the ASME Code allowable stresses for the high-chromium alloys is shown in Figure 5-9. Clearly, NF709 and HR3C are leading candidates for use in the highest-temperature applications. The latter steel was approved for use in boilers by ASME as SS310NbN. The highest creep strength is achieved in Inconel 617, which contains 22% Cr, but it is also likely to be the most expensive alloy to use, due to its high Ni content.



Figure 5-12: Comparison of allowable stresses for austenitic alloys containing more than 20% Cr.

A comparison of allowable temperatures at a constant allowable stress of 500 kg/cm2, as a function of chromium content, is shown in Figure 5-10. With increasing chromium, a discontinuity is seen in the allowable metal temperatures of austenitic steels, rising about 50°C (90CF) above those of ferritic steels. In terms of increasing temperature capability, stable austenitic alloys offer the highest capability, followed by melaslable austenitic steels, and then by ferritic steels. The fully enhanced, stable austenitic alloys are clearly capable of operating under phase 2 steam conditions (650°C, or 1200°F).



Figure 5-13: Allowable metal temperatures at constant allowable stress of 500 kg/cm2

(7ksi) as a function of chromium content for various alloys

Figure 5-14: Relationship between hot-corrosion weight loss and temperature for ferritic steels



5.1.9 Fire-side CorrosionFireside corrosion results from the presence of molten sodium-potassium-iron trisulfates. Because resistance to fireside corrosion increases with chromium content, the 9 to 12% Cr ferritic steels are more resistant than the 2-1/4Cr-lMo steels currently used. The 12% Cr in turn steel shows belter corrosion resistance than 2-1/4% Cr steel and 9% Cr steel, as shown in Figure 5-11. Stainless steels and other supcralloys containing up to 30% Cr represent a further improvement. Increasing the chromium content beyond 30% results in a saturation effect on the corrosion resistance at least in the laboratory, as shown in Figure 5-12. For practical purposes, when corrosive conditions are present, line distinctions between ferritic steels may be academic, and it is usually necessary to use austenitic steels containing chromium in excess of 20%.

Figure 5-15: Relationship between hot-corrosion weight loss and chromium content for various alloys

A ranking of the performance of various austenitic alloys in the presence of trisulfates has been provided by Ohtomo on the basis of short-term laboratory tests (see Figure 5-13). The plots or weight loss versus temperature exhibit a bell-shape curve. At temperatures below 600°C (1110°F). corrosion is believed to be low because the trisulfate exists in solid form. Above 750°C (I380°F), corrosion rates arc once again low, as the trisulfates vaporize. The worst corrosion problem is in the range 600 lo 750°C (1110 to I380°F). The data indicate that the high-chromium alloys such as type 310 stainless steel and Incoloy 800H arc superior to the other alloys tested and that Inconel 671 (Ni-50Cr) or its matching weld metal IN72 is virtually immune to attack. Lower-chromium stainless steels, such as type 316H, type 321H, and Esshete 1250, show considerable susceptibility to attack. The alloy most susceptible



to attack seems to be the 17-14 CuMo alloy used in the Eddystone 1 plant. Results of field probe studies confirm the following ranking of alloys in increasing order of corrosion resistance: T91, HCM12, type 347 stainless steel, Incoloy 800, and Inconel 671. In addition to alloy selection, other “fixes’’ to minimize fire-side corrosion, such as shielding of the tubes may also be applied, if economical.

Figure 5-16: Comparison of fire side corrosion resistance of various alloys

Test carried out in U.S.A indicate that substantial superheater corrosion can occur, especially in high strength austenitic alloys with a low chromium content. For most coals, high strength modified Alloy 800 type alloys such as NF709, will probably have sufficient corrosion resistance, while for more corrosive coals modified SS310 type alloys, e.g. HR3C, should given an extra margin of safety. It is of interest to note here that a T-91 sample exposed in the low sulfur coal fueled boiler had a corrosion loss similar to SS 347, which is considerably less than that of SS 304 and 17-l4CuMo. A probable reason is that scales and deposits usually adhere tight to ferritic/martensitic steels, but spall readily from all austenitic steels.

Based on the favorable results from the air-cooled probes in one of the plants, the SS304M reheater, which suffered from severe alkali sulfate corrosion was replaced by one made from SS310 NbN (HR3C). Test sections of other alloys were built into the reheater and carefully monitored. It was found thai 310NbN (HR3C) was a satisfactory material for 90% of the reheater, with less than 0.25 mm/yr (10 mils/yr) corrosion. However in one area, about 10 tubes wide and 10 ft (3m) high, corrosion rates ranged from 0.5 - 1.25 mm/yr (20-50 mils/yr). Here the corrosion resistance of SS310 was about the same as that of SS347 and alloy 800H. Only a Cr-Ni steel (Cr30A) with 30% Cr had significantly lower corrosion rate, ranging from 0.125 - 0.5 mm/yr (5 - 20 mils/yr). Il is concluded that increasing the Cr content of the alloy from 18-



20% to 23-25% will significantly increase corrosion resistance, when the corrosivity of the deposits is moderate, i.e. ≤ 0.5 mm/yr (20 mils/yr for 18-8 stainless steels). For more corrosive conditions, co-extruded tubes or weld overlay claddings containing at least 40% Cr are strongly recommended.

5.1.10 Steam-side oxidationSteam-side oxidation of tubes and exfoliation of the oxide scale and its solid-particle erosion damage to the turbine are well known. This problem is expected to be more severe in advanced steam plants, because the much higher steam temperatures employed are likely to cause more rapid formation of oxide scale.

Very limited data are available regarding the steam-side scale-growth characteristics of the fcrritic tubing alloys. In a study by Sumitomo Metal Industries, the oxide growth in steam for alloys T22 (2-14Cr-IMo), T9, HCM9M, and the modified 9Cr-lMo (T91) were compared based on 500 hr tests. Results showed the superiority of the T91 alloy over the other alloys.

Masuyama compared alloys HCMI2, HCM9M, 321H, and 347H in field tests in the temperature range 550 to 625°C(1020 to 1155"F) over a period of one year. Samples were inserted in the tertiary and secondary superheaters and re heaters. From the results, it was concluded that the resistance to steam oxidation of HCM12 is superior to those of 321H and HCM9M and comparable to that of fine-grained 347H for exposure to the high-temperature region of the reheater. Subsequent monitoring over a period of three years has borne out these conclusions. In addition to the inherent resistance of HCMI2M steel to steam-side oxidation, Masuyama suggests that the tendency toward exfoliation or oxide scale would also be less for this alloy than for austenitic steels. Additional improvements in 9 to 12% Cr steels may be possible by extending the chromizing and chromate conversion treatments(30) that currently arc applied to lower-alloy steels. Grain refinement during heat treatment has been shown to be clearly beneficial as well. Internal shot blasting is also known to improve the steam oxidation resistance of 300 series stainless steels by enhancing chromium diffusion. Il is therefore anticipated that these steels would be used in the fine-grain and shot-peened conditions.

5.1.11 Summary of SH/RH Tube-Material StatusBased on the discussion so far recommendations for materials selection have been made. For phase 0 steam conditions, alloys T91, HCM12M, and AISI type 304 stainless steel are viable candidates for superheater and reheater tubing, provided that fire-side corrosion is not a major problem. Under mildly corrosive conditions, 310NbN stainless steel may be the most cost-effective option. For severe corrosion cladding, SS304 with IN72 (44%Cr) is recommended.

For intermediate-temperature applications corresponding to phase I steam conditions (595°C, or 1100°F), Tempaloy A-l and type 347 fine-grained stainless steel are deemed to be adequate in the absence of corrosive conditions. Under mildly corrosive conditions, 310NbM stainless steel may offer the best combinations of creep strength and corrosion resistance. For severe corrosion, cladding with IN72 is recommended.



For phase 1B i.e. 620°C conditions Super 304H, Tempaloy AAI, Esshele 1250 and 17-14 CuMo may be acceptable under non-corrosive conditions. For mildly corrosive conditions alloys with 20-25% Cr such as HR3C. and NF709 will have the best combination of creep strength and corrosion resistance. For severe corrosion, cladding with IN 7 2 is again recommended.

For the highest-temperature application corresponding lo phase 2 steam conditions (650/650°C. or 1200/1200°F). the creep strength requirements are met by Inconel 617, 17-14 CuMo steel, Esshete 1250 and NF709. Among these alloys, 17-14 CuMo steel and Esshele 1250 have inadequate corrosion resistance and will have to be clad with corrosion-resistant claddings of Inconel 671 If corrosive conditions are present. NF709 and CR30A may be used without any corrosion protection for mildly corrosive conditions, but will require cladding with IN72 for severely corrosive conditions.



5.1.12 Choice of Materials for WaterwallsMetal Temperature ConcernsThis issue has been discussed recently by Blum. In boilers operating at 625°C/326 kg/cm2, maximum midwall temperatures can be as high as 500-525°C, depending on magnetite deposits at the inside of the tube. This means that the creep resistance of standard low alloy ferritic steels such as T-l 1 is not adequate. Originally T-91 steel was the only suitable substitute. Under the COST program it was demonstrated that this material can be fabricated into waterwalls. However a postweld heat treatment is required, which is difficult to do in the field. Two steels containing 2.5 and 12Cr% respectively developed by Sumitomo and Mill are more promising in that they do not require preheat or postweld heat treatment. Both steels have creep strength in the same range as T-91 and \ use similar precipitation strengthening mechanisms. Especially the 2.5%Cr steel appears promising for this application. It also has recently been approved by the ASME Boiler Code Committee as T-23. Test panels are now in service in various boilers.

5.1.13 Waterwall Corrosion ConcernsRecent reductions in NOx emissions, mandated by the Environmental Protection Agency in the USA have led to the introduction of deeply staged combustion systems, in which the air/fuel ratio is significantly less than 1, and additional combustion air is added above the burners via overfire air ports. Several boilers in the USA retrofitted with such systems have reported severe corrosion of low alloy steel waterwalls, with metal losses in the 1-3 mm/yr (40-120 mil/yr) range. Supercritical units are generally more severely affected than subcritical units and severe corrosion is generally limited to coals with more than 1%S. However above 1%S there is no strict correlation between S and corrosion rate. The highest corrosion losses are found in regions where H2S rich substiochiometric flue gas mixes with air from the overfire air ports. Laboratory studies indicate that the high corrosion rates cannot be explained by the presence of H2S and CO in the flue gas alone. Work by Kung has shown that corrosion rales in gas mixtures, actually found in boilers, containing 500-1500 pm H2S and 5-10% CO, are generally less than 0.5 mm/yr (20 mils/yr) at 450°C. More recently it was shown that the presence of FeS deposits can greatly increase the corrosion rate, but only under alternating oxidizing/reducing conditions or oxidizing conditions alone. Figure 5-17 shows corrosion losses of a low alloy steel, T-91 and SS-304 in the presence of FeS containing deposits and a gas mixture containing 1% oxygen. Although the corrosion rates arc probably artificially high, because of the short duration of the test, it is clearly demonstrated that low alloy steels will corrode quite rapidly in the presence of FeS deposits and an oxidizing gas. The tests further show that claddings or weld overlays containing at least 18 and preferably more than 20% Cr are needed to assure acceptably low corrosion rates.



Figure 5-17: Corrosion of steels containing 0.5-18% Cr under FeS containing deposits in oxidizing flue gas

5.1.14 SummaryThere has been extensive development in the strengthening of 9 to 12% ferritic steels resulting in temperature/pressure capabilities well over the conventional framework of 538°C 174 kg/cm2 for the steam. Nearly two dozen plants have been commissioned worldwide with main steam temperatures of 585 to 600°C and pressures of 245-305 kg/cm2. Specific materials developments with respect to key components are as follows:

For heavy section components such as pipes and headers. minimising thermal fatigue has been a major driver in addition to achieving high creep strength. For this reason, alloy development has focussed on ferritic steels containing 9-12% Cr. Optimisation of C, Nb, Mo and V and partial substitution of W for Nb in the 9-12% Cr fcrrtitic steels has resulted in three new alloys HCM12A, NF616 and E911 (P92, P122 and E911) capable of operating up to 620ºC at steam pressures up to 347 kg/cm2. Beyond 620ºC oxidation resistance may become an additional limiting factor, especially for the 9% containing steels. A newer class of 12% Cr alloys NF12 and SAVE 12, containing cobalt and additional W is being evaluated for possible 650ºC (I200ºF) application. It appears from preliminary results that austenitic steels or Nickel alloys would be needed for temperatures exceeding 650ºC.

For SH/RH tubes steam side oxidation resistance, and fireside corrosion resistance are major drivers in addition to creep resistance. Furthermore, tube metal temperatures often exceed the steam temperature by as much as



28°C It is unlikely that any of ferritic steels can be used in the finishing stages of SH/RH circuits at steam temperatures exceeding 565°C. Austenitic steels need to be used at these higher temperatures. Depending on the corrosivity of the coal used, higher Cr steels or clad steels may be required. For 620°C application. Super 304H, Tempalloy AA1, Esheat 1250 and 17 CW-MO are acceptable under non corrosive conditions while 20-25% Cr alloys such as HR3C, NF709 and cladding with 1N72 are recommended for more corrosive conditions. Several candidate alloys Inconcl 617, NF709 and Cr30A and alloys clad with Inconcl 671 (50% Cr) arc available for use at 650°C. For upper waterwall sections, two new steels containing 2.5 and 12% Cr known as HCM2(T23) and HCM 12 respectively are very promising in terms of creep strength and weldability. They are suitable for use in the range of 595-650°C steam conditions purely from a creep strength point of view. When fireside corrosion in low NOx boilers is an issue, these alloys will have to be clad or weld overlaid with alloys containing more than 18-20%Cr.

Several boiler materials with improved mechanical properties have been developed recently, and new materials still in the R&D stages will enable higher ultra-supercritical steam cycles than are today commercially available. Most materials development is being conducted under national or internationally coordinated programs including the AO 700 / CQMTES 700 program funded by the European Commission, and the US Ultra-Supercritical Materials Consortium sponsored by the US Department of Energy.



Materials Development Stages – and Related Steam Parameter Limits

Figure 5-18: Materials Development Stages and Related Steam Parameters Limits

E040/ REPORT/boben anto c PAGE 65 OF 161


5.2 TURBINE5.2.1 Materials for Turbines in Ultra Supercritical Power PlantsThe requirements for advanced steam turbine materials include commercial or near-commercial availability, sufficient strength, steam oxidation resistance and temperature capability at 650-750°C, appropriate physical properties (ie. thermal expansion and conductivity) for the part/component being considered, fabric ability, and acceptable cost. While there is some debate as to the actual upper temperature limit of commercial advanced 9-12Cr ferritic/martensitic steels, it does appear that for temperatures of 625-650°C or above, they do not have adequate strength or steam oxidation resistance, and must be replaced by alloys with more performance and reliability at higher temperatures.

5.2.2 Materials for Casings and ShellsSteam turbine casings are typically large structures, with complex shapes that must provide the pressure containment for the steam turbine. Because turbine casing components are massive, their cost has a strong impact on the overall cost of the turbine. The materials used currently for inner and outer casings are the 1-2CrMo steels, usually as castings. The temperature limit of these alloys in this application is approximately 566°C, mainly due to their resistance to steam oxidation. For higher temperatures, cast 9Cr-1MoVNb alloys are considered to be adequate in terms of strength capabilities to 593°C, while the 12Cr steels in either cast or forged form currently appear to be limited to 620°C, assuming acceptable steam oxidation resistance. Casings made of cast martensitic/ferritic steels must still be heat-treated and tempered to produce the best combination of high temperature strength and ductile-to-brittle transition temperature (DBTT) behavior at low temperature.

In terms of strength, the next step up in cast alloys for casings logically would be an austenitic stainless steel: cast 316 was used in Eddystone. However, problems experienced with that-cast stainless steel, such as thermal fatigue cracking, led the industry to discontinue use of such alloys in steam turbines. Recent modifications to cast 347H (CF8C) stainless steel have resulted in development of a new steel, CF8C-Plus developed by ORNL and Caterpillar, with creep strength better than NF709 and Super304H, and close to that of the Ni-based superalloy 617.The possibility of using an austenitic stainless steel in significantly thinner sections (due both to better castability and much better strength) has the potential for reducing thermal fatigue sensitivity compared to earlier cast stainless steels. This new properties data suggest this class of alloys should be reconsidered for steam turbines.



LMP (C=20)Figure 5-19: Plot of Creep Rupture Stress Versus Larson-Miller Parameter

Plot of creep rupture stress versus Larson-Miller Parameter (LMP) for cast CF8C-Plus steel, and various wrought alloys including TP347HFG and Super 304H stainless steels, NF709 stainless alloy, and superalloy 617. The upper axis reflects extrapolation to use temperature for rupture life of I00,000h.



The CF8C-P!us steel was developed based on a unique "engineered microstructure" method to be have a stable austenite matrix phase (free of delta ferrite) for resistance to the aging-induced sigma phase embrittlement that plagues standard CF8C steel. The high temperature creep strength of CF8C-Plus steel is based on stable nano-scale dispersions of NbC within the grains. CF8C-Plus steel also has much higher creep-rupture ductility (despite its higher strength) due to the lack of sigma or other embrittling precipitate phases. CF8C-Plus also has outstanding fatigue and thermal fatigue resistance. These properties are achieved in the as-cast condition without the need for any additional heat-treatments, which is a benefit for large castings. CF8C-Plus also has good castability, and in July 2004, MetalTek International used it to cast a large gas turbine end-cover component (6,700 lb) of this new steel. Steam oxidation behavior of CF8C-PIus steel is much better than 9-12Cr martensitic/ferritic steel 650CC and should be comparable to other austenitic stainless steels and alloys to about 700°C or slightly higher temperatures.

For the highest temperatures, Ni-based alloys will be required, and the question will be whether adequate strengthening can be developed in solid-solution strengthened cast alloys, or whether age-hardenable wrought alloys will be needed. The candidate alloys chosen for evaluation by the European AD700 program included both Fe-based superalloys and Ni-base alloys: 155, 230, 263, 617, 625, 706, 718, 901, and Waspaloy. There are strong incentives to minimize the temperature requirement for the outer shell components by design, and to improve the quality of large 12-Cr martensitic/ferritic and austenitic stainless steel castings. There is considerable experience in producing castings of Inconel 625 and, in the European programs, data were generated from trial castings of both Inconel alloys 617 and 625. A step-block casting geometry was used for the prototypical component, and a full-scale valve chest was cast in alloy 617. Considerable experience also exists for large forgings of alloys such as IN 706 and 718, and long-term creep data are available for the wrought forms of alloys such as 617, 625 and Haynes 230. Only a modified version of 617 (CCA617), and the new alloy, Inconel 740, appear to meet the strength and creep-rupture criteria for the 760°C goal of the U.S. USC steam boiler program.

The major materials needs are for Ni-based alloys for operation at 760°C with (i) adequate creep rupture strength; (ii) ability to cast them into the required size and shape, and to inspect for defects; and (iii) ability to perform initial fabrication welding (on cast or wrought forms, including dissimilar metal welds), and to make repair welds on aged material. Considerable experimental effort to generate data is required, and will involve the development of rupture, creep, and rupture ductility relationships for these materials. 5.2.3 Materials for BoltingThe major requirements for bolting materials are high resistance to stress relaxation (ageing characteristics) at temperatures that can range up to the maximum steam temperature experienced by the casing for the hot gas path; thermal expansion characteristics compatible with those of the structure to be bolted; and low notch sensitivity. There is a wide range of alloys available for this application, and the specific alloy selection depends for the most part on the criteria used by each manufacturer. In current usage, ferritic steels (variants of type 422 steel) are used up to approximately 566°C, and the Ni-base Nimonic alloys are typically used for higher temperatures. Based on world-wide experience, Nimonic 80A and a few proprietary alloys (such as Refractaloy 26) appear to be good candidates for temperatures up to



593°C. For the bolting needs to 720°C in the. European program, and to 760°C in the U.S. USC Steam Program, Ni-based alloys will be required.

Overall, for bolting, the choice of materials appears to be relatively straightforward. There do not appear to be significant manufacturing issues, since these alloys are available as bar stock

5.2.4 Materials for Rotors/discsThe HP rotor/discs will have to handle the highest steam conditions, so that a Ni-based alloy will be required for temperatures greater than 620°C; a mitigating factor is that this component may be relatively small (depending on the overall steam turbine design). The IP rotor handles steam at the maximum system temperature, but at reduced pressure. The strength requirement may be relaxed compared to the HP rotor, but the issue of oxidation in steam remains. Materials selection for this component may be a critical issue because of its size. For maximum overall efficiency, it would be desirable also to increase the temperature of the steam entering the low-pressure (LP) rotor. This component will require a NiCrMoV steel of the type in current use, but which is likely to be susceptible to temper embrittlement in this application (>316°C). Resort may be made to cooling of this rotor, or to alloy modification. Alternatively, metallurgical processing changes may be introduced to reduce the susceptibility to temperature embrittlement (by reducing the levels of P, Sn, Mn, Si).

The alloys most commonly used for steam turbine rotors and/or discs are the CrMoVWNbN steels, which can vary in chromium content from 1-13% depending on the preference of individual manufacturers. These alloys are widely used up to a temperature limit of about 566°C, and the higher-W, lower-Nb and -C versions are capable of 593°C. The issues for alloys for higher-temperature use are similar to those for materials for steam piping. Versions of these ferritic steels, based on the advanced 9-12% Cr compositions, are already in service at steam temperatures of 600°C, and it is expected that they will be usable to approximately 620°C (and possibly 650°C). Ni-based alloys will be required for the higher temperatures, and candidates include Inconel alloys 617, 625, and the new 740 and 718Plus alloys, and Haynes 230. Except for 740 and 718Plus, these alloys are approved by the ASME Boiler and Pressure Vessel Code (not required for rotors), so that a significant design database exists for them, but more complex mechanical data, such as creep-fatigue and thermal-fatigue, is needed.

The main issues for rotors/discs concern manufacturing, especially the capability to produce large castings and forgings. With modern secondary steel making practices, such as ladle furnaces, electroslag remelting to control freezing segregation, and control of the sulfur and phosphorus levels in the alloy, very large rotors now can be produced, but experience is related mostly to Cr-Mo-V alloys (used in current 541-566°C plants), and for 12 Cr alloys (needed for advanced steam cycles to 620°C). A further major issue, depending on the design approach used, is the need for developing the techniques required for making dissimilar metal welds when Ni-based alloys are used for the HP turbine and the lower alloy/ferritic steels used for the IP turbine.

5.2.5 Materials for BladingThe current supercritical steam plants in the U.S. typically use vanes and blades made from 12 Cr ferritic steels such as type 422, or proprietary alloys of similar composition.



For higher temperatures there is available a wide choice of wrought Ni-based alloys, for which a substantial design database exists from their application in gas turbines. The choice of blading material will depend on (i) the-temperature-of-the rotor, hence on the thermal expansion characteristics of the component material, and (ii) the size and shape of the blade, which will be designed using computational fluid dynamics modeling. Steam-compatibility data for these materials will be required. Recent research data on moisture effects on oxidation suggest that it will be important to have higher-Cr levels in these alloys to avoid preferential internal attack in steam. Consideration needs to be given to the problem of solid particle erosion from entrained particles of oxide scale that may exfoliate from the superheater and reheater tubing. While this problem may not be greater in USC turbines than problems encountered in current steam turbines, it will be prudent to ensure that erosion-mitigating coatings technology is available and compatible with new high-temperature blading materials.

5.2.6 SummaryChemical composition of alloys considered for steam turbines is given in Table 5-7. Summary of materials considered suitable for different components of high pressure steam turbines in given Table 5-8.

The issues regarding materials and manufacturing resulting from the need for turbines to operate under ultra-supercritical steam conditions are summarized in Table 5-9, which attempts to provide a simple ranking of the level of effort needed to provide materials choices for three target steam temperatures, 620, 700, and 760°C. In the Table, the level of effort required is given a numerical rating, from 1-5, where '5' suggests that considerable research and development will be needed, while a ranking of '1' indicates that most of the capability required is already available.

5.2.7 Role of owner of plantThe development of materials for fabrication and manufacture of different components of supercritical power plants described in this section indicates that material technology for these plants has matured and stabilised. The problems faced in the early years of development of SC technology were, mostly, material related and led to low availability of early SC plants established in USA as compared to sub-critical plants due to higher planned and unplanned outages of SC plants. With development of suitable materials to take care of higher pressures, higher temperature and higher requirement of creep strength, availabilities of both type of plants later converged and now availabilities of SC plants are better than those of sub-critical plants of similar capacity.

Different manufacturers, however, may use different materials for the same components depending upon their experience, availability of materials and economic considerations. The purchaser of the plant is not in a position to specify the materials to be used nor is he in a position to do so. The purchaser has to specify the ambient conditions, the quality of coals, requirements of sliding pressure and ramp-up rates grid code and conditions minimum acceptable efficiency and any other desired operating parameters. The purchaser has to depend, then, upon the manufacturer to design his plant accordingly for which he will offer performance guarantees.



Table 5-23: Chemical Compositions of Alloys considered for Steam Turbines (in weight percent)

Alloy Fe Ni C Co Cr Nb Mo W Ti A1T92 Bal 0.4 0.1 — 9 0.1 0.5 1.8 — —Type 422 Bal 0.7 0.22 — 12 — 1 1 — —T122 Bal 0.3 0.1 — 12 0.05 0.4 2 — —Nimonic 901 Bal 42.5 0.04 1 12.5 — 6 — 3 0.3A286 Bal 26 0.05 — 15 — 1 — — 2Type 316 Bal 11-14 0.06 — 16-18 — 2-3 — — —Type 347H Bal 10 0.08 — 18 0.8 — — —. —NF7091 Bal 25 0.1 — 21 0.3 1.5 — — —-Haynes1201 Bal 32 0.05 — 25 0.7 2 — — —Refraclaloy 26

Bal 36 0.03 19 18 — 3 — 2.6 —

CF8C Bal 10 0.08 — 19.5 0.85 — — — —CF8C-P1US2 Bal 12.5 0.1 — 19 0.8 0.3 — — —N155 Bal 20 0.15 20 21 — 3 2.5 — —Haynes 230 3 Bal 0.1 5 22 — 2 14 — 0.3Hastelloy X 18.5 Bal 0.1 1.5 22 — 9 0.6 — —CCA6I7 0.7 Bal 0.06 12 22 — 9 — 0.4 1.2Inconel 625 3 Bal 0.05 — 22 4 9 0.2 0.2 0.2Inconel 740 2 Bal 0.07 20 24 2 0.5 — 2 1IN706 40 Bal 0.03 0.5 16 — 0.5 — 2 0.2IN718 18 Bal 0.04 — 19 5 3 — 1 0.5Allvac 10 Bal 0.025 9 17.5 5.4 2.7 1 0.7 1.5718PlusIN939 — Bal 0.15 19 22 1 — 2 3.7 1.9Nimonic 80A 5 Bal 0.1 2 20 — — — 3 2Nimonic 105 1 Bal 0.2 20 15 — 5 — 2 4Nimonic 115 — Bal 0.2 15 15 —- 4 — 4 5Nimonic 263 1 Bal 0.06 20 20 — 6 — 2 0.5U700 1 Bal 0.15 18.5 15 — 5.2 — 3.5 4.25U710 — Bal 0.07 15 IS — 3 1.5 5 2.5U720 — Bal 0.01 14.7 16 — 3 1.25 5 2.5Waspaloy 2 Bal 0.07 14 20 — 4 — 3 1

1- contains >0.1 N2- contains additions of Mn and N

Table 5-24: Materials Selection for the High-Pressure Steam TurbineComponent 566°C 620°C 700°C 760°CCasings/Shells CrMoV (cast) 9-10%Cr(W) CF8C-Plus CCA617(valves; steam 10CrMoVNb 12CrW(Co) CCA617 Inconel 740

chests; nozzle box;

CrMoWVNbN Inconel 625 CF8C-Plus (?)

cylinders) IN 718 Nimonic 263

Bolting 422 9-12%CrMoV Nimonic 105 U7009-12%CrMoV A286 Nimonic 115 U710Nimonic 80A IN718 Waspaloy U720IN718 IN718

Allvac718PlusNimonic 105 Nimonic 115

Rotors/Discs 1CrMoV 9-12%CrWCo CCA617 CCA61712CrMoVNbN 12CrMoWVNbN Inconel 625 Inconel 74026NiCrMoV115 Haynes 230



Inconel 740Vanes/Blades 422 9-12%CrWCo Wrought Ni- Wrought Ni-

10CrMoVNbN base basePiping P22 P92 CCA617 Inconel 740



Table 5-25: Ranking and Development Effort Needed for Materials for Turbines

ComponentSteam

Temperature, °CMajor Issues

620 700 760Casing Materials 3 4 5 Design data; improved alloys

Manufacturing

3 5 5 Cost vs wrought; process control

Bolting Materials 1 3 3 Design data; design proceduresManufacturing

1 1 1

Rotors/Discs Materials 3 3 5 Design data; weldabilityManufacturing

4 4 4 Melting and fabrication

Vanes/Blades Materials 3 4 4 Improved austenitics; Ni-base alloys

Manufacturing

3 4 4 Forging process (modeling)



6.0 OPERATIONAL FLEXIBILITY AND PERFORMANCE OF SUPERCRITICAL PLANTS



OPERATIONAL FLEXIBILITY AND PERFORMANCE OF SUPERCRITICAL PLANTS6.1 OPERATIONAL FLEXIBILITY OF SUPERCRITICAL PLANTS6.1.1 Start-up flexibility in supercritical boilers

Power systems are subject to wide diurnal as well as seasonal variations in demand.

There is a substantial difference in the peak demand and the base load. The magnitude

of variations is such that they cannot be taken care of entirely by the hydroelectric or

gas fired power plants in the system and coal fired plants , also have to face frequent

shut downs. It is, therefore, important that coal fired plants have a low start up time

and the capability to build up to the designed load conditions in a short time i.e. a

short ramp up time. Once through boilers used in supercritical plants are better

equipped to cater to these frequent load changes in the system.

In the supercritical cycle, water converts to steam in the evaporator itself and thus

steam flow is always available in super heaters. This leads to assured steam flow,

better heat transfer and better control of super heater metal temperature. These

factors reduce the limitation of firing rate in boiler and thus reduce the time required

to reach the required parameters. Shorter start-up times lead to lower start-up losses.

Once through boilers used in supercritical plants can adjust to frequent load variations

which could go up to as much as 10% per minute as against about 3% per minute for

drum type boilers used in sub-critical plants. Some supercritical power plants are

required to operate in two shift operation depending upon demand in the system. With

higher steam parameters in supercritical boilers, steam extraction, also, is high giving

higher regenerative heater output and higher temperature of condensate leading to

improvement in efficiency.

The transition from the re-circulation mode to the pure once – through operation, if

required, is fully automatic for supercritical boilers.

The sliding pressure operating mode thus enables load gradients of 5% to 10% per

minute for the steam turbine over the load range from 30% to 100% as the

temperatures remain mostly constant over load changes in this range. Thermal

stresses are also prevented.



6.1.2 Shorter start-up times

Start-up is classified as cold, warm or hot depending upon the period for which the

boiler remains shut-down.

Hot start up - after to 2 hours shut-down

Warm start up - after 8 hours shutdown

Cold start up - after 36 hours shut down

The comparative start up times for supercritical and sub-critical boilers are given in

table below.

Type of start Supercritical Sub-critical

Hot start up 2 hours 2 hours

Warm start up 8 hours 12 hours

Cold start up 36 hours 52 hours

The system usually followed in start up is diagrammatically depicted below which lists

the important steps to be followed in the operation. The different operating cycle and

efficiency achieved were listed below



The advantages and area wise attention as follows

Standard riffled tubes- require high mass flux to safely pass through critical pressure, “OT” Characteristic Results



Comparison of pressure part weight between DRUM, Multi pass , spiral and vertical tube wall for the same capacity

Technological impact on Operation and Maintenance



Operating parameter comparison for the subcritical and supercritical plants and reduction in co2 emission due to the increase in efficiency.

The trend of efficiency improvement in Indian power sector as follows



One of the Start up systems followed in shown below



Typical start up curves for cold, warm and cold start ups for supercritical and sub-

critical plants in Germany as available with in India are given below. It will be seen for

all the three types of start ups, higher temperatures and pressures are attained within

the same period in supercritical boilers as compared to sub-critical ones indicating

better ramp up rates.



Start Up Curve for Cold Start

We normally due to cold start up when the shutdown period crosses the 48 hours and

all equipments in cold conditions In the graph below we have symmetrically explained

the mainsteam parameters that is mainsteam pressure, temperature and flow tobe

maintained during the rolling and ramp up period with time has shown. We have

described the warm start as well as hot start condition below

The time taken to build the pressure and temperature and ramp up already plotted as

per our supercritical plant at Parent company



Start Up Curve for Warm Start



Start Up Curve for Hot Start

Hot Start Up Curve

6.1.3 Flexibility for Load ChangesThe sliding pressure operating mode enables a better load gradient and the load can easily be raised from 30 % to 70 as temperature remains mostly constant. This flexibility can be seen from the start up curves which indicate faster change in the steam parameters faster. This enables convenient operation of the station in two shifts. One of the optional design allows a circulating pumps and the scheme as follows.In this case of low load the circulation can be achieved either by a circulating pump or by bypassing some part to the condensate flash tank and inturn send to condenser



6.1.4 Fuel flexibilitySupercritical boilers are able to operate efficiently with all types of furnaces like front, opposed, corner, four wall, arch firing with slag type or dry ash removal.

6.1.5 Water ChemistryWater chemistry had presented problems in early stages of supercritical development. These problems basically related to the use of the de –oxygenated all volatile(AVT) cycle chemistry. The solution to these problems was combination of a condensate polishing unit with oxygenated treatment which is, now, a well proven procedure. Further, once through boilers do not have a blow down which has a positive effect on water balance of the plant with less condensate needing to be fed into the water steam cycle and less waste water to be disposed off. 100% polishing unit is incorporated with high quality water used

6.1.6 Higher efficiencyVery high plant efficiencies upto 48% (based on HHV) are achievable as compared to lower unit capacity of sub-critical plants (35% - 37%). This is represented in the Figure 6-1.



Figure 6-20: Chart Presents Higher Efficiency

Note: The above efficiencies are based on UHV



6.1.7 PROBLEMS FACED BY SUPERCRITICAL PLANTS IN INDIA - IMPACT OF FIRING

INDIAN COAL ON AVAILABILITY OF SUPER AND ULTRA SUPER CRITICAL BOILERS

The state-wise distribution of coal resources in India is as follows:

State Coal Resources in Million TonnesProved Indicated Inferred Total

Andhra Pradesh 8403 6158 2584 17145Arunachal Pradesh 31 40 19 90Assam 315 27 34 376Bihar 0 0 160 160Chhattisgarh 9570 27433 4439 41442Jharkhand 36148 31411 6339 73898Madhya Pradesh 7565 9258 2935 19758Maharashtra 4653 2432 1992 9077Meghalaya 117 41 301 459Nagaland 4 1 15 20Orissa 16911 30793 14295 61999Uttar Pradesh 766 296 0 1062West Bengal 11383 11879 4553 27815Total 95866 119769 37666 253301

Non-coking Coal used available in India is classified into seven grades as follows.

Gr

a

de

Useful Heat Value

(UHV)

(Kcal/Kg)

Corresponding

Ash% + Moisture %

at (60% RH & 40O

C)

Gross Calorific Value GCV

(Kcal/ Kg) (at 5%

moisture level)

A Exceeding 6200 Not exceeding 19.5 Exceeding 6454

B Exceeding 5600 but

not exceeding

6200

19.6 to 23.8 Exceeding 6049 but not

exceeding 6454

C Exceeding 4940 but

not exceeding




5600 exceeding. 6049

D Exceeding 4200 but

not exceeding

4940


Exceeding 5597

E Exceeding 3360 but

not exceeding

4200


exceeding 5089

F Exceeding 2400 but

not exceeding

3360


exceeding. 4324

G Exceeding 1300 but

not exceeding

2400


exceeding 3865

Generally Grade ‘G’ coal is available for thermal power plants.

The quality of coal available from domestic sources compares very unfavourably with the quality of coals imported from other countries such as Australia, Indonesia or South Africa. Comparative analysis of coal available from Singrauli mines in India and Mount Arthur coal from Australia is given in Table brlow.

Typical Proximate Analyses for Singrauli and Mount Arthur Coals

Item UnitSingrauli

Coal1

Mount

Arthur

Coal2

Fixed carbon % 34.50 51.50

Volatile matter % 20.00 33.00



Moisture % 9.55 3.50

Ash% 40.00 12.00

Grindability index HGI 50.00 50.00

Higher heating value

(HHV)

kCal

/

k

g

3,667.09 6,320.00

Higher heating value

(HHV)

MJ/

k

g

15.35 26.46

Lower heating value

(LHV)

MJ/

k

g

14.52 25.32

Notes:1 Average data based on typical analysis of run of mine design coal from

Singrauli coal fields.2 Typical analysis of steam coal from Mount Arthur, Australia. Data sourced

from Chapter 7 of “McCloskey’s Big Coal Book 2002”.

Typical Ultimate Analyses (as received basis) for Singrauli and Mount Arthur Coals is

given in table below.

Typical Ultimate Analyses (as received basis)

for Singrauli and Mount Arthur Coals

ItemU Singrauli

Coal1Mount Arthur

Coal2

Carbon % 38.70 69.29

Oxygen% 8.67 8.20

Sulphur % 0.50 0.70

Hydrogen % 2.61 4.63

Nitrogen % 0.75 1.69

Water % 9.38 3.50

Ash % 39.39 11.99



ItemU Singrauli

Coal1Mount Arthur

Coal2

Sum of all

constituents% 100.00 100.00

Notes:1 Average data based on typical analysis of run of mine design coal from

Singrauli coal fields. 2 Typical ultimate analysis (dry basis) of steam coal from Mount Arthur,

Australia sourced from Chapter 7 of “McCloskey’s Big Coal Book 2002”. This data was manipulated to determine the typical ultimate analysis (as received basis).

As seen from data presented above, imported coal has higher GCV and contains low

ash with low silica in the ash. Therefore there is lower erosion of the boiler tubes

than with Indian coals, which have high ash and high silica. However, the ash

fusion temperature of imported coals is lower than Indian coals, and this can

lead to clinker formation in the SH/RH sections causing higher outages. The

estimation of outage in supercritical boilers for imported coal is given in the

table below.

Power plant outage factors have been derived from boiler/turbine manufacturers

planned outage figures and forced outage figures are based on estimates from

data of existing plants in India using imported coal.

Estimate of Power Plant Outage Factors with imported coal

Year

s

Planned outages

Forced Availabil

% % %

1 4.1 5.5 90.4

2 4.1 4.4 91.5

3 6.8 3.3 89.9

4 4.1 4.4 91.5

5 4.1 5.5 90.4

6 6.8 3.3 89.9

7 4.1 4.4 91.5

8 4.1 5.5 90.4

9 12.3 3.3 84.4

10 4.1 4.4 91.5



Year

s

Planned outages

Forced Availabil% % %

11 4.1 5.5 90.4

12 6.8 3.3 89.9

13 4.1 4.4 91.5

14 4.1 5.5 90.4

15 6.8 3.3 89.9

16 4.1 4.4 91.5

17 4.1 5.5 90.4

18 12.3 3.3 84.4

19 4.1 5.5 90.4

20 4.1 5.5 90.4

21 6.8 6.0 87.2

22 4.1 6.6 89.3

23 4.1 7.1 88.8

24 6.8 8.2 85.0

25 4.1 9.9 86.0

Problems associated with firing Indian coal are: Indian coal typically has higher moisture content. This can lead to lower

boiler efficiencies than with imported coal.

Low volatile matter in Indian coal leads to high-unburnt carbon loses.

Low boiler efficiency due to low CV and high ash content in Indian coals

High ash and coal handling costs and milling power lead to high auxiliary

power consumption

High ash and high silica in the coal leads to higher erosion. Though lower

flue gas velocities and provision of shielding plates can reduce erosion, it

leads to higher capital costs for the boiler

However, Indian coals have also some advantages. They are:

Low sulphur, therefore do not need Flue Gas Desulphurisation

High ash fusion temperature therefore cause less slagging and clinker

formation in the boiler

Indian ambient conditions



High ambient temperature leads to higher cooling water temperature

reducing the achievable condenser vacuum to a maximum of 0.13 bar. This

in turn leads to a higher steam consumption and a poorer turbine heat rate.

High relative humidity leads to more losses in cooling tower

Based on Indian coal characteristics, the outages are estimated as follows.

Estimate of Power Plant Outage Factors with Indian Coal

Year

s

Planned Force Availabilit

% % %

1 4.1 4.38 91.52

2 4.1 3.51 92.39

3 6.8 2.63 90.57

4 4.1 3.51 92.39

5 4.1 4.38 91.52

6 6.8 2.63 90.57

7 4.1 3.51 92.39

8 4.1 4.38 91.52

9 12.3 2.63 85.07

10 4.1 3.51 92.39

11 4.1 4.38 91.52

12 6.8 2.63 90.57

13 4.1 3.51 92.39

14 4.1 4.38 91.52

15 6.8 2.63 90.57

16 4.1 3.51 92.39

17 4.1 4.38 91.52

18 12.3 2.63 85.07

19 4.1 4.38 91.52

20 4.1 4.38 91.52

21 6.8 4.82 88.38

22 4.1 5.26 90.64

23 4.1 5.70 90.20

24 6.8 6.58 86.62

25 4.1 7.89 88.01- Other operational problems



The original supercritical units installed were designed for constant

pressure operation, i.e. the boiler operates at full load pressure from start-up

and across the entire load range. For start-up, constant pressure

operation boilers require a start-up bypass system, which is complex in

configuration and operation compared with the new sliding pressure Benson

boilers. As a result, the start-up time for constant pressure boilers is longer

and the plant minimum load must be kept higher than for the sliding

pressure units. In addition, the load ramp rate of constant pressure

operation is restricted because of the limit in temperature change rate in HP

(High Pressure) turbine during a load change.

The start-up valves on constant pressure boilers have to withstand

larger pressure differentials during bypass operation, which leads to

higher erosion damage and hence the requirement for more frequent valve

maintenance.

Severe slagging on the waterwalls as well as the coils has been one of the

major issues in older coal-fired boilers constructed during the 1960s and 1970s.

This was primarily because the furnaces of those plants were relatively

small in volume. Since then, the furnace size has been continuously reviewed

for better performance, and larger sizes have been used for recently

constructed units. Appropriate furnace dimensions including plan area, height

and volume must be provided to reduce slagging potential, regardless of

whether the boiler is to be designed as sub-critical, supercritical, NC or once-

through type.

These causes of common problems faced in earlier supercritical boilers and

counter measures employed in new supercritical boilers are given in table

below.

- 12 –



Table Causes and countermeasures of experienced problemsIssues experienced in older supercritical units

Causes Countermeasures(As applied in new supercritical units)Er osion of start-up

valvesHigh differential pressure due to

constant pressure operation and complicated start-up system

Sliding pressure operation, simplified start-up system, and low load recirculation system.

Long start-up times Complicated start-up system and operation (ramping operation required, difficulty establishing metal matching condition, etc.)

Sliding pressure operation, simplified start-up system, and low load recirculation system.

Low ramp rates Turbine thermal stresses caused temperature change in HP turbine during load changing (due to constant pressure operation)

Sliding pressure operation.

High minimum stable operating load

Bypass operation & pressure ramp-up operation required

Application of low load recirculation system

Slagging Undersized furnace and inadequate coverage by soot blower system

Design of adequate plane area heat release rate and furnace height, without division walls. Provision of adequate system of soot blowing devices and/or water blowers.

Circumferential cracking of water wall tubes

Metal temperature rise due to inner scale deposit and fire side wastage

Oxygenated water treatment(OWT).Protective surface in

combustion zone of furnace for high 97ulphur coal, e.g.

thermal spray or weld overlay.Frequent acid cleaning Inappropriate water chemistryApplication of OWTLower efficiency than

expectedHigh air leakage due to

pressurized furnace.RH spray injection required

due to complications of RH steam temperature control in the double reheat cycle configuration.

Tight seal construction. Single reheat system with high steam temperature and temperature control by parallel damper gas biasing.

Low availability All the above All the above

6.1.9 Improvements/upgradations made in plants to mitigate the problems

The Hitachi-Naka Thermal Power Station Unit No.1 (1,000 MW) of the Tokyo

Electric Power Company (TEPCO), has been taken as an example to

demonstrate the manner in which manufacturers have tried to mitigate the

problems faced by earlier supercritical plants. The Naka plant uses a “Benson”



type boiler which was designed and built by Babcock-

Hitachi K. K. (BHK is the latest supercritical coal-fired utility plant to commence

commercial operation in Japan. State-of-the-art technologies such as high pressure,

high temperature steam parameters of 3680 psig /(604ºC/602ºC)and Hitachi’s

advanced burner system for low NOx combustion were integrated into the new

design. Flexible sliding pressure operation, advanced steam temperature control

methods, and sophisticated computer control technologies make this unit an

ideal plant for load demand following applications. The sliding pressure

supercritical Benson boiler technology has been fully established and has

markedly surpassed drum type boilers in the areas of efficiency, flexibility in

operation and availability, as proven by over10 years operating experience in

Japan.

Since the start-up period, the Hitachi-Naka boiler has been operating with

stable and reliable performance parameters for both steady load and

dynamic load operation modes. The main features of the boiler are

summarized as follows.

Sliding pressure operationAs the nuclear power has become the primary source for base load generation in

Japan, coal-fired power plant equipment suppliers were challenged to design new supercritical coal-fired units with flexibility for frequent load cycling. By adopting the sliding pressure operation with lower boiler pressures at partial loads, the plant heat rate can be improved at partial loads due to 1) improvement of high pressure (HP) turbine efficiency, 2) reduced auxiliary power consumption by boiler feed pumps, and 3) higher steam temperature at the HP turbine outlet. In addition to the plant efficiency advantages, there are other benefits such as reduction in start-up time, increase in ramp rate and reduced erosion of bypass valves.

Spiral Waterwall

For sliding pressure boilers, maintaining uniform fluid conditions during low

load / low pressure operation becomes critical to reduce the potential of

tube damage caused by high metal temperatures. The lower part of the

Hitachi-Naka boiler furnace is arranged in a spiral configuration such that the

fluid path wraps around the boiler as it travels up the furnace. A comparison of

fluid temperature distribution between the conventional vertical wall and the

spiral waterwall is shown in Figure 5.

As a result of the uniform waterwall fluid temperature profile that is achieved

across the full range of boiler loads, the spiral waterwall system does not

require any flow adjusting devices to be installed at the furnace inlet.


FLOW FLOW

BURNERS BURNERS BURNERS BURNERS


Water WallOutletFluid Temp.

Heat Flux

FLOW FLOW

BURNERS BURNERS BURNERS BURNERS

FRONT SIDE REAR SIDE FRONT SIDE REAR SIDE

Vertical Type Water Wall Spiral Type Water Wall

Figure 5 Fluid Temperature profile comparison for Water Wall Type

- 7 -


Steam Separator

As the Hitachi-Naka boiler is a Benson type unit, a steam separator

and a separator drain tank were installed to separate the steam and the

water at the furnace outlet during a low-load recirculation operation. This

design is different from that of a conventional NC boiler, for which a steam

drum is installed to separate the water from the steam under all operating

loads. The steam drum is designed to have sufficient water storage

capacity, and usually contains complicated internal parts, such as steam

cyclones, scrubbers, internal feed pipes, and baffles. Because

of the complex internals, steam drums require a large amount of maintenance

work during outage periods. However, the steam separator design of a

Benson boiler is simple in configuration and has no internal, therefore

significantly less maintenance work is required.

Boiler start-up systems

The Hitachi-Naka Boiler includes fully automatic start-up systems such

as the turbine bypass system and the low load recirculation system. The

turbine bypass system was designed to minimize the start-up time by

controlling the main steam pressure and temperature before turbine rolling,

and enabling the steam to flow through the superheater sections at a

short time after light-off. The low-load recirculation system was designed

to recover residual heat during start-up by circulation of the un-evaporated

water from the furnace back to the economizer inlet, which also can assist in

reducing start-up time. As this system is automatically operated, the start-

up process is as simple as with a natural circulation (NC) boiler.

Table 2 shows a comparison of the start-up systems betweem a NC

boiler, a constant pressure once-through boiler and a sliding pressure

Benson type boiler

(the Hitachi-Naka boiler).

ER ER

REHEATER

ECONOMIZER

W ATER W ALL

S/H

S/H

H.P.HEATER

REHEATER

ECONOMIZER

ALL

L.P.HEATERH.P.HEATER

REHEATER

ECONOMIZER

W ATER W ALL

L.P.HEATER

Table 2 Comparison of Start-up Systems

NC Boiler Typical Constant Pressure

Operation Once Through Boiler

Benson Boiler

Flow diagramIP&LP

3'ry S/HTURBINE

HP TURBINE

2'ry S/H

REHEATE

1'ry S/H

CAGE

CONDENSER

DEAER ATOR

W ATERW ALL CP

ECONOMIZER

IP&LP TURBINE'ryS/H 210

HP TURBINE

200 201

REHEATER207205

'ryS/H

203 202

242 240

CONDENSER

CAGE FLASH TANK

CPATER W ALL

220 DEAER ATOR

ECONOMIZER

BFP

H.P.HEATER L.P.HEATER

IP&LPyS/H TURBINE

316HP TURBINE

yS/H

REHEATER

yS/H

307

SEPARATOR

DRAIN TANKCONDENSER

CAGE361

BCP START UP CPATER BLOWW ALL

360 DEAER ATOR

ECONOMIZER BFP

H.P.HEATER L.P.HEATER

Start-up bypass system

Not installed- Operation of

drain valves is necessary to establish turbine

Required for· Maintaining furnace

minimum flow· Heat recovery to HP

heater and deaerator through flash tank

· Ramping (shift fromrecirculation mode to once

through mode, temperature dip is inevitable)

- Continuous recirculation mode

operation is impossible

Installed for steamtemp and press control(TB bypass)

Low load recirculation system

Not required Required- Maintaining

furnace minimum flow

- Automatic smooth shift operation from recirculation mode to once through mode

- Direct heat recovery to economizer inlet

- Continuous recirculation Start-up pressure

at furnace during cold start

Atmosphere Full pressure(3500psig)

Atmosphere

Main and Reheat steam temperature controls

As the Hitachi-Naka boiler was to be designed to fire coals with a wide

range of combustion and slagging properties, the steam temperature

control system was designed to maintain rated temperature in varying heat

absorption profiles and load levels.

The primary parameter for the steam temperature control is the ratio of a

furnace water flow to a fuel input. This simple and effective temperature

control method cannot be used with an NC boiler as its water flow in the

furnace is driven by a natural circulation phenomenon. For

additional controllability, superheater attemperators were installed

between each superheater sectionsto maintain a rated main steam

temperature steadily when firing different types of coals with variant

combustion properties.

For the outlet reheater steam temperature (RST) control, a gas flow

biasing system with a parallel damper was adopted to maintain a rated steam

temperature over a wide load range without the help of water spray

attemperators, which were installed for emergency. For the Hitachi-Naka

boiler, a backpass heating surface arrangement has been optimized for

improved controllability of RST. In Figure 6, RST fluctuations during a load

ramp from 50% to 100% are shown for an older unit

(previous design) installed with a gas recirculation system and the Hitachi-

Naka boiler (no gas recirculation system). The results show that fluctuations

in RST for the Hitachi-Naka boiler were kept to a minimal level similar to the

older unit, and without use of the reheater spray attemperator. These

provisions for steam temperature control in the Hitachi-Naka boiler help the

power block to achieve a lower heat rate.

- 10 -

degree

er outlet emperature

Damper op

3%/min (Reheater s

50%

Re ste

heat am t

ening

No Reheater Spray

Reheater Evaporator Percent of Heating Surface

Superheater Economizer

Controlled by Damper

Parallel Gas Damper+ Gas Recirculation

Parallel Gas DamperOnly

650

3%/min

100%

Damper opening degree(Reheater side)

Load Demand

50%

550(oC)

Reheater outletsteam temperature

0 　 30min. 60min.

No Reheater Spray

Previous Design with Gas Recirculation

Hitachi-Naka No.1without Gas Recirculation

Figure 6 Reheater Outlet Steam Temperature Fluctuation during Load Change

Advanced control systems

The latest developments in plant distributed control systems have led to a

highly automated operation from boiler light-off to shutdown. Advanced

dynamic control from computerized calculation algorithms for the main control

functions (e.g. steam temperature control) have been developed such that

recently installed boilers can

be controlled with reduced operator action.

-


6.1.11 High availabilityAs stated earlier, the rapid introduction of very large plants in the USA in the early 1970s had created problems of their availability due to their forced outages. Feedback from other operators (in Japan, Europe and Russia) for plants installed later was, however, positive. With sustained improvements in plant design and materials of construction, the average availability of supercritical plants is, now, equal to or even higher than that of comparable sub-critical plants as shown in Table below,.

Table 6-26: Availability of Supercritical PlantsSubcritical % Super critical %

Availability time ratio 83.7 84.1Available capacity factor 82.6 82.9Planned outage period 5.6 6.2

Unplanned outage period 11.8 10.9

6.1.11 Improved cost effectivenessThe life cycle costs of supercritical coal fired power plants are lower than those of the sub critical power plants. Current designs of supercritical power plants have installation costs that are only 2% higher than those of subcritical plants. Fuel costs are considerably lower due to the increased efficiency and operating costs are at the same level as subcritical plants. Specific installation cost i.e. the cost per megawatt (MW) decreases with increased plant size. For countries like India and China, unit ratings from 500 MW to 900 MW are possible due to their large electrical grids.

The specific coal consumption of calorific value 25 MJ/kg can be reduced from 294.9 to 283.3 g/kWh by increasing steam parameter from 167 bar/538/538°C to 250 bar/566/ 566°C. This corresponds to an annual reduction in coal consumption of 116,000 tonnes in Unit capacity range of 600 to 700 MW.

The material expenditure in a 250 bar ONCE THROUGH boiler yields a cost advantage over the evaporator system of a 167-bar drum boiler. However, this advantage is offset in part by the higher manufacturing and erection and assembly cost and by additional cost of feed pump. However, with latest design of vertical-tube water walls and an adapted start-up system, the investment costs for a ONCE THROUGH boiler still comes out lower than those for a drum type boiler.

6.1.12 ReliabilityDue to high steam parameters, there was initially lower availability of the supercritical plants. However, with improvements in production technology for the components and welding procedures, this gap no longer exists and availabilities for subcritical and supercritical plants have converged.

Our analysis on the technical details at the Herne supercritical plant is that there have been hardly any boiler tube failures.

Availability details to show this convergence over time are given below:

E040/ REPORT Boben Anto C PAGE 108 OF 161


As can be seen from the above chart, the availability figures have converged for subcritical and supercritical plants by the 1990s.

6.2 OPERATIONAL PERFORMANCE OF SUPERCRITICAL PLANTS6.2.1 Assumptions for Plant ParametersThe steam cycle parameters and unit sizes used for performing the thermodynamic modelling for coal fired plant options under Indian conditions are given below.

Table 6-27: Cycle Conditions for the Coal Fired Plant Options

Plant Type Unit sizeMain Steam

PressureMain Steam Temperature

Reheat Steam Temperature

Subcritical 500 MW 166 bar 538°C 538°C

Low supercritical 660 MW 247 bar 538°C 565°C

High supercritical 800 MW 270 bar 565°C 593°C

These steam cycle conditions and unit sizes represent the typical conditions that are available to be deployed in the Indian market.

The following assumptions regarding the boiler, turbine, and common auxiliaries have been considered:

Boiler Radiation losses 0.24%Unburnt carbon losses 1.2 %Unaccounted losses – domestic coal 0.85%

Boiler efficiency is assumed constant across all technologies but different for each coal type. In actual practice, there would be a lower efficiency in



subcritical plants due to blow down. However as performance guarantee figures have been used in the model, blow down has been taken as zero.

Condensing Steam TurbineCondenser average vacuum 0.13 bar aGenerator efficiency 99.5%

In all cases 3 HP heaters and 4 LP heaters have been considered with a final temperature of 270 °C and motor-driven boiler feed pumps

It is assumed that there are no steam cycle make up losses since the performance guarantee conditions have been taken as the basis of comparison with the modelling results.

No degradation of the gross heat rate is assumed in the first year.

The auxiliary power considered as 7.5 to 8.0 % for plants burning indigenous coal.

An average cooling water temperature of 33°C has been considered.

Natural draft cooling towers and make up has been considered to replace losses due to blow down and leakage in the cooling water cycle.

The performance modelling results are shown in Tables 6-6 to 6-9.

6.2.2 Coal Analysis

Singrauli coal from India has been considered.

The typical proximate and ultimate analysis (as received basis) for the

Singrauli coal are given in Table 6-3 and Table 6-4 respectively.

Table 6-28: Proximate Analysis for Domestic Coal

Item Unit Singrauli Coal

Fixed carbon % 34.50

Volatile matter % 20.00

Moisture % 9.55

Ash % 40.00

Grindability index HGI 50.00

Higher heating value (HHV) kCal/kg 3667.09

Higher heating value (HHV) MJ/kg 15.35

Lower heating value (LHV) MJ/kg 14.52

Table 6-29: Typical Ultimate Analysis (as received basis) for Domestic Coal


Carbon % 38.70




Oxygen % 8.67

Sulphur % 0.50

Hydrogen % 2.61

Nitrogen % 0.75

Water % 9.38

Ash % 39.39

Total % 100.00

6.2.3 Ambient ConditionsThe selection of design ambient conditions was based upon the metrological conditions at site shown below.

Table 6-30:Common Ambient ConditionsItem Unit Site Conditions

Mean daily maximum temperature (January) °C 24.3

Mean daily minimum temperature (January) °C 8.1

Mean daily maximum temperature (May) °C 42.0

Mean daily minimum temperature (May) °C 25.8

Average RH during morning % 66%

Average RH during evening % 49%

Site elevation M 280

On the basis of the information presented above, the following common design site ambient conditions were selected for modelling the performance of the coal fired plant options:Ambient dry bulb temperature : 35.0°CAmbient relative humidity : 60.0%Ambient atmospheric pressure : 0.9802 bar.

6.2.4 Performance Modelling ResultsWith the above steam cycle parameters and for unit sizes chosen, modelling and simulation studies have been carried out.The simulation covered the following: Gross heat rate with lower Heating Value (LHV) of coal, and high Heating

Value (HHV) of coal Net heat rate with lower Heating Value (LHV) of coal, and high Heating

Value (HHV) of coal Gross efficiency with lower Heating Value (LHV) of coal, and high Heating

Value (HHV) of coal Net efficiency with lower Heating Value (LHV) of coal, and high Heating

Value (HHV) of coal Auxiliary power consumption Fuel consumption



Ash production Water consumption (circulating water makeup, auxiliary circulating water

makeup)

In addition, the results of Ebsilon models for the boiler were verified by manual calculations according to international codes (BS 2885) using the heat loss method. For the turbine, the gross heat rates were calculated and crosschecked with figures from existing sub critical, low supercritical and high supercritical plants in India. Manufacturers’ data were used to cross check the ultra-supercritical figures as also using manual calculations using ASME PTC 6)

For each of the power plant options, the results presented are on the basis of a single gross output unit operating at 100% MCR at the design ambient conditions.

Table-6-6 shows the turbine performance estimates for coal fired power plant and is applicable for domestic coals.

Table-6.7 and Table-6.8 show the plant performance of coal fired power plant options for domestic coal, and based on either Lower Heating Value (LHV) or Higher Heating Value (HHV).

Table-6.9 shows the coal, ash and water consumption or production estimates for the three coal fired power plant for domestic coal.

Table 6-31: Turbine Performance Estimates (Domestic Coal, 100% MCR)Item Unit Base

SubcriticalBase

SupercriticalHigh

Supercritical

Turbine gross output MW 500 660 800

Unit auxiliary power MW 40 52.8 60

Turbine net output MW 460 607.2 740

Turbine gross heat rate kcal/kWh 1920 1860 1820

Average turbine gross efficiency

% 44.79 46.24 47.25

Boiler steam duty GJ/h 4.10 3.92 3.79

Table 6-32: Plant Performance Estimates using Domestic Coal (LHV basis, 100% MCR)

Item Unit Base Subcritical

Base Supercritical

High Supercritical

Boiler efficiency, LHV % 92.5 92.50 92.50

Unit coal burn, LHV Kg/kwh 0.597 0.578 0.566

Unit gross heat rate, LHV kcal/kWh 2075.68 2010.81 1967.87

Unit gross efficiency, LHV % 41.43 42.71 43.71

Unit net heat rate, LHV kcal/kWh 2256.17 2185.66 2127.1

Unit net efficiency, LHV % 38.12 39.35 40.43

Table 6-33: Plant Performance Estimates using domestic Coal (HHV basis, 100% MCR)

Item UnitBase

SubcriticalBase

SupercriticalHigh

Supercritical

Boiler efficiency, HHV % 87.8 87.8 87.8

Unit coal burn, HHV Kg/kwh 0.597 0.578 0.566



Item UnitBase

SubcriticalBase

SupercriticalHigh

Supercritical

Unit gross heat rate, HHV kcal/kWh 2186.79 2118.45 2072.89

Unit gross efficiency, HHV % 39.33 40.6 41.49

Unit net heat rate, HHV kcal/kWh 2376.94 2302.66 2240.97

Unit net efficiency, HHV % 36.18 37.35 38.38

Table 6-34: Coal, Ash & Water Consumption/Production Estimates (relevant unit size, 100% MCR)

Item Unit Base Subcritical Base Supercritical High Supercritical

Unit coal consumption (Singrauli coal)

t/h 298.74 382.02 453.09

Unit ash production (Singrauli coal)

t/h 117.67 150.48 178.47

CW makeup t/h 1150 1396.57 1589.24

ACW makeup t/h 39.3 47.68 54.24

The impact of efficiency in Indian conditions and Indian coal conditions- we can expect a deduction of 9%



7.0 DESIGN ISSUES



DESIGN ISSUES7.1 LAYOUT AND CLEARANCES

7.1.1 Plant LayoutThe main considerations in deciding plant layout are:

There should be enough space for the placement of different components in configurations decided by technical considerations.

Enough space should be available for handling, placement and removal of heavy and large size equipments.

Convenient access for emergency services like fire-fighting should be provided.

Provision must be made for statutory requirements like green belt. In case of uneven land, the layout should conform to the topography

requiring minimum grading and levelling.

As the precise location of the proposed plant has not been decided as yet. The plant layout proposed below is based on typical size and configuration of main project components for a supercritical plant.

Sizing and area allocated for different sub systems is shown below, taking the standard design features. Standard two unit layout is shown in figure below.

Figure 7-21: Standard two unit layout



7.1.2 Pipe Layout

Pipe layout can be created utilizing a 3 dimensional model as shown below.

Figure 7-22: Three dimensional model of pipe layout

Engineering of turbine hall is shown below:

Figure 7-23: Turbine hall

7.1.3 Typical Longitudinal Sectional View



Typical longitudinal sectional view of lower supercritical plant is shown in

Figure 7-4 below:

Figure 7-24: Longitudinal Sectional view

Typical plot allocation for such a plant is shown below:

Figure 7-25: Plot allocation



7.2 BOILER CONFIGURATION AND TECHNICAL FEATURESThe choice of boiler type is governed by the operational requirements of generation which include substantial variations in load and quick start up times.

7.2.1 Two path/Tower typeFurnace configuration for the boiler is derived from each plant manufacturer's characteristics; two path types is favoured in Japan while tower type is favoured in Europe.

No significant difference is observed in the adaptability of the two types to different types of coal as the boiler design can be adjusted in accordance with coal characteristics such as the abrasiveness of ash.

7.2.2 Constant Pressure / Sliding (Variable) Pressure TypeSupercritical boilers can be classified in two basic design categories according to their operating pressure regimes. For units designed for constant pressure operation, supercritical pressures are maintained in both furnace walls and superheater over the normal operating range. This type is suitable for the base load mode thermal power plant.

On the other hand, for units designed for full sliding (variable) pressure, the furnace walls and superheater pressures may vary with load, including operation at subcritical pressure. This type is desirable for the middle load mode thermal power plant which operates under system load variations.

Pressure program and fluid diagram of both types of constant pressure and sliding (variable) are shown in Figure 7-6, 7-7 and Figure 7-8, 7-9 respectively.

Boiler manufacturers have developed their own fluid circulation systems, and C-E type system has been adopted for this report as a typical example.

Constant pressure circulation system consists of the recirculating pump, water separator and associated valves as shown in Figure 7-6 and 7-7. The fluid system is kept as high as the rated pressure from the initial stage to full load. The required minimum water flow is maintained by running of recirculating pump and low pressure steam from separator is led to steam turbine for warming. With subsequent rise of turbine load, recirculating pump is stopped and once through operation starts.

Sliding (variable) pressure type is equipped with recirculating pump, water separator, drains system and associated valves as shown in Figure 7-8.

For start up and low load operation below 30%, of maximum load the unit utilizes pump recirculation system to provide an adequate mass flow through the furnace wall tubes.

The once through design for supercritical boilers eliminates the boiler throttling valves and adopts a full sliding (variable) pressure approach (Figure 7-9). The furnace walls are allowed to enter the subcritical pressure range along with the superheater circuits by using the spiral structure of water wall



tube or rifled tube for vertical water wall. Supercritical pressure operation begins in the higher load range.

Figure 7-26: Constant Pressure Program for C-E Type

Figure 7-27: Constant Pressure Diagram of C-E Type



Figure 7-28: Sliding (Variable) Pressure Program for C-E Type

Figure 7-29:Furnace Configuration



Figure 7-30: Basic Principle of Spiral-wall Furnace

7.2.3 Spiral TypeSpiral (plain/bare tube) wall and vertical (rifled/ribbed tube) wall types are in use. Type both furnace configurations are shown in Figure 7-10.

The principal concern with a sliding (variable)-pressure supercritical pressure design is the requirement for once-through operation. The mass flow in the furnace-wall tubes must be sufficiently high to avoid overheating or departure from nucleate boiling (DNB) while generating steam at subcritical pressures, and to avoid excessive metal temperatures and uneven steam outlet temperatures when operating at supercritical pressure at higher boiler loads.

To accomplish these objectives, the spiral-wall design has evolved. The principle of the spiral- or helical-wail furnace is to increase the mass flow per tube by reducing the number of tubes needed to envelop the furnace without increasing the spacing between the tubes. This is done by arranging the tubes at an angle and spiraling them around the furnace. For instance, the number of tubes required to cover the furnace wall can be reduced to one half by putting the tubes at a 30 degree angle (Figure 7-11). The centerline spacing or pitch (P) is made the same as on a vertical wall to prevent fin overheating. Additionally, by spiraling around the furnace, every tube is part of all the walls, which means that each tube acts as a heat integrator around the four walls of the combustion chamber.

The spiral-wall concept thus addresses two major challenges of the full-sliding (variable) pressure supercritical pressure boiler:

Achieving the required mass flows to avoid overheating and excessive metal temperatures by reducing the number of tube circuits

Minimizing differences in tube-to-tube heat absorption by exposing each tube to all four furnace walls

Spiral-wall furnaces have been in operation in Europe and Japan for many years and have given satisfactory performance.

As an alternative to the spiral-wall design for larger-size steam generators, some manufacturers offer a tangentially fired unit with vertical walls consisting of rifled tubes for ease of fabrication, erection, and maintenance. A stable fireball is formed in the center of the furnace with tangential firing, with essentially equal distribution of the lateral heat absorption on all furnace



walls. With this design unbalances are minimized and lateral heat-absorption patterns are predictable over the entire load range.

7.3 TUBE LAYOUT

Typical tube layout is depicted below:

Figure 7-31: Tube layout

7.4 BFP & HP BY PASS SYSTEM

Special features to be incorporated in the design to improve the reliability

include – HP by pass with safety function, condensate preheating and 3 * 50

% BFP etc. shown below:



Figure 7-32: HP bypass

Figure 7-33: Vertical and spiral type boilers



Figure 7-34: Tubing in Once through and Drum type boilers

The heat transfer and temperature range of operation in different sections is

shown in the diagram below.

Figure 7-35: Heat transfer and temperature range



The heat transfer in vertical and spiral type boilers is depicted in Figure

below.

Figure 7-36: Heat transfer in vertical and spiral type boilers

7.5 IMPROVEMENT IN COMBUSTION SYSTEM

An important concern in combustion system is NOx reduction. An innovative

concept of in-flame NOx reduction, is the development of NR2 burner, having

strengthened the high temperature reducing flame to achieve extremely low

NOx emissions in addition to improved combustion efficiency. This enables a

small amount of excess air at the economizer outlet (15%) when firing various

kinds of imported coal. The NOx reduction principle is shown in Figure 7-17.

Another feature of the combustion system is the large capacity roller-type

pulverizers (MPS300) with rotating classifiers, which improve pulverized coal

finenesses. These combustion system technologies contribute substantially to

significantly higher boiler efficiency.



Figure 7-37: Frame Structure of Hitachi NR2 Burners

A third generation burner (NR3), which enhances the reaction of in-flame NOx

reduction, has been developed in response to needs for higher efficiency and

lower NOx combustion. The performance of the NR3 burner has been verified

at the Inkoo Thermal Power Station Unit No.3 of Imatran Voima Oy (IVO),

Finland. It was confirmed that the NR3 burner had approximately 25% lower

NOx level at the same UBC (unburned carbon) level, than the current NR2

burner. The NR3 burner equipped boiler is now in the construction stage and

will be in commercial operation in 2003.

The above descriptions relate to component design as available in published

documents. Different manufactures adopt designs which differ in detail. The

choice of different materials for different components has to satisfy the

design parameters and availability of materials, in turn, imposes limits on

units performance.

7.6 OPERATION IN INDIAN CONDITIONS

Increased operating pressure for SC boilers increases the medium

temperature and increased regenerative feed heating increases the inlet

temperature to economizer. This leads to high exit flue gas temperature from

economizer. Indian coal does not have much sulphur, so normally FGD for flue



gas cleaning is not required. Exit flue gas temp can be lower (125 deg) to

gain the boiler efficiency.

Indian coal has high ash content and low calorific value. In order to restrict

the flue gas velocity and attain required heat transfer, furnace area will be

larger. This will help in reducing the NOx and limit the operational furnace

temperature within limits of ash fusion temperature.

Due to high pressure operation, material thickness has to be more. Steam

piping material also changes due to the elevated operating temperature and

pressure.

Super heater and reheater tube metal temperature in final section increases

with the high operating parameters. This will lead to high temperature

corrosion and steam side oxidation which to be considered has in material

selection. High thickness requirement due to high pressure operation leads

higher to gradient across the walls.

New materials have been developed to achieve-greater long term rupture

strength and lower oxide film growth inside surface in high temperature zone.

Materials like T91/P91 have high creep strength compared to earlier ferritic

steels.

Lower thickness of tubes has resulted in design for higher strength to meet

transient temperature changes. Better materials like T 92/P92 having creep

rupture strength 20 to 30% higher at 600 deg C, will facilitate raising the

steam temperature. Even in sub critical boilers in India T91 is being used in

super heaters, restricting the metal temperature to 600 deg in place of earlier

570 deg in T22.

Use of T-92 increases the operation margin and reliability. T23 /T24 have

higher creep strength compared to T22- Some manufacturers have already

started using it for evaporator walls.

Materials used in Walsum power plant in Germany enable it to operate to

achieve high net efficiency. This is achieved as follows:

Steam temperature upto 620°C are possible with new materials

adopted at Walssum



Special alloys P91, P92 and VM12SHC have been extensively used to

ensure efficiency at high pressures and temperatures VM12SHC was

used for the first time in this plant

Creep behaviour of these new materials is superior

The materials used in Walsum boiler are shown in diagram below.

Figure 7-38: Materials of Boiler

7.7 ELECTRO-STATIC PRECIPITATOR (ESP)

ESP is an important auxiliary to the boiler.

Ash properties effect precipitator sizing as shown in table below:

7.8 MILLS

New modified mill with dynamic classifiers for better fineness control is shown

in figure below.



Figure 7-39: Modified mill

7.9 DESIGN FEATURES OF TURBINES

Turbine design features are developed to work for 300 bar pressure and 600

deg with size to accommodate the high pressure and temperature. The

design takes care of the metallurgical requirement of the selected material to

withstand high operating parameters to ensure flexibility in operation and

reduce overhauling frequency.

1.1.1 Materials for High Temperature

9Cr - 1Mo forged steel is applied to the valves and the leading steam pipes

which are exposed to 600ºC steam and 12Cr cast steel is applied to the

internal casing of IP No.1. Cr-Mo-V-B cast steel is used for the HP internal

casing. 12Cr rotor and blade material for the HP and the IP turbine are also

applied.

1.1.2 Materials for High Temperature

New design criteria are applied along with the high temperature materials

described below.



(a) Overlay welding for the bearings

The overlay method is applied to the main bearings instead of the

usual sleeve method.

(b) Steam cooling technology

The structural welding between 9Cr-1Mo forged leading pipes and the

Cr-Mo-V casted outer casing are cooled by low temperature steam. The

cooling affect is confirmed by analysis and actual operation.

(c) High efficiency nozzle

An Advanced Vortex Nozzle (AVN) is used to improve turbine efficiency

for all the stages except for the first stage.

The new technologies as applied for 600ºC class high temperature plant, are

shown in Figure 7-20.

Figure 7-40: The new technology of the High Supercritical Steam turbine (HP & IP Sections)

1.1.3 Continuous Cover Blade (CCB)

The last stage blade of a steam turbine is one of the most important

components to determine the overall turbine performance and reliability,

because it generates about 10 % of the entire output and is operated at

severe

centrifugal forces. The longer last stage blade yields higher velocity, larger

centrifugal force and a lower natural frequency, so a highly advanced design

technology is required to develop the last stage blade from the standpoint of

performance, strength and vibrational characteristics. Hitachi has been



developing long blades and adopting the CCB structure, having a high rigidity

and dampening effect at the specified rotational velocity, and incorporates

the latest aerodynamic blade profile based on three-dimensional stage flow

analysis. Figure 7-21 shows blade structure concept for CCB. Table 7-1 shows

the line-up of current last stage blades with the CCB structure, which

performed the rotational test.

Figure 7-41: Continuous Cover Blade (CCB) Structure

Table 7-35: Line-up of LSB with CSB Structure

Rotational Speed Last Stage Blade Length

3600 rpm 26 in., 33.5 in., 40 in., 46 in.

3000 rpm 26 in., 33.5 in., 43in.

1800 rpm 48 in.

1.1.4 Tandem-Compound High Supercritical STG

The correlation between unit output and turbine exhaust annulus area is

shown in Figure 7-22. The tandem-compound four-flow type with Ti-alloy 40-

inch or 46-inch last stage blades (TC4F-40 or TC4F-46) and improved high

strength 12Cr steel 43-inch last stage blade (TC4F-43) can be applied to 60Hz

and 50Hz operation respectively. The described machines are based on 3556

psig – 600ºC advanced steam condition design.

Figure 7-23 shows the sectional arrangement of TC4F-40, high supercritical

steam turbine for 60 Hz use.

Figure 7-24 shows the sectional arrangement of TC4F-43, high supercritical

steam turbine for 50 Hz use.

The tandem-compound high supercritical plant generator design has been

completed. The design of the large-diameter rotor was verified by performing



tests using an actual section sized model of the 60Hz machines, which

sustains

greater centrifugal forces compared to the 50Hz machines. The strength

against fatigue caused by the start-stop operation and extended running was

evaluated

to verify reliability. In addition, an improved ductility high-strength shaft

material was developed to further enhance the design.

Figure 7-42: Correlation between Unit Output and Turbine Exhaust Annulus Area



Figure 7-43: Sectional Arrangement of TC4F-40 high supercritical Steam Turbine for 60 Hz use

Figure 7-44: Sectional Arrangement of TC4F-43 high supercritical Steam Turbine for 50 Hz use

7.10 MATURITY OF SUPERCRITICAL TECHNOLOGYThe design features stated in this section indicate the development of equipment of supercritical power plant by manufactures to take care of the concerns of the owners. These concerns typically include high efficiency, economic operation, ability to adopt in a fast manner to changes in load and quick start up. Development of sliding pressure operation can take care of load changes from 100% to 30% and load changes upto 10% per months can be taken care of. Similarly high rank up rates involving short start up times are not a problem now. Another concern related to feed water chemistry which was related to the use of the de-oxygenerated all volatile (AVT) chemistry in early super critical boilers. The solution to these problems was a combination of the condensate polishing unit with oxy generated treatment.Different manufactures adopt designs, which are basically similar in concept but differ in details. These details could be due to availability of materials and technology as well as their own evolution of manufacturing practices. The owner / developer needs to state his requirements with precision and in detail and then depend upon manufacture’s performance

guarantees. IMPLEMENTATION ISSUES



IMPLEMENTATION ISSUES7.11 INTRODUCTION

Existing coal fired power plants in India are all based on subcritical technology

(pressure up to 168 kg/cm2 and temperature of 538°C). Supercritical

technology has been advanced in India only within this decade. Technology

and implementation issues relevant to the deployment of supercritical or

advanced supercritical PC power plants in India are discussed in this section.

7.12 TECHNOLOGY ISSUES

Supercritical boiler technology has matured to a point such that the technical

risks associated with supercritical boilers are now similar to those of

subcritical boilers. However, as supercritical boilers are designed for higher

steam temperatures and pressures than subcritical boilers and also operate

using a once-through evaporator, designers and owners have to be aware of

certain issues in order to reduce technical risks to an acceptable level. These

include:

• Waterwall cracking• Negative flow characteristic• Slagging.

There is no reason to believe that all of these risks will appear in every

project. However, there remain some risks that should be addressed during

design and operation of the plant

8.2.1 Waterwall Cracking

Thermal fatigue cracking of waterwall tubes is believed to be the leading

cause of tube failures in supercritical boilers. It is not clear why supercritical

boilers are more susceptible to this type of cracking than subcritical boilers,

however possible reasons include higher metal temperatures and the use of



low alloy steel. Thermal fatigue cracking is caused by the combined action of

elevated metal temperatures and thermal cycling. Elevated metal

temperatures may be caused by the growth of internal tube deposits, high

heat flux, deterioration of fluid-side cooling or external fireside coatings.

Slagging and shedding, Scot blowing, water cleaning or other factors may

cause thermal cycling. Fireside corrosion is also believed to be a contributing

factor to thermal fatigue cracking. The use of oxygenated water treatment

may reduce the risk of waterwall cracking.

This phenomenon is currently under investigation by various organizations

and supercritical plant owners and operators should be aware of this problem,

which represents a potential risk to plant availability.

8.2.2 Negative Flow Characteristic

Most modem supercritical boilers operate using sliding pressure. When the

boiler is operating at part-load the pressure is subcritical and the furnace acts

as a once through evaporator. This design requires a high mass flux through

the tubes to avoid departure from nucleate boiling (DNB) and subsequent

overheating of the tube metal. A high mass flux design has an undesirable

feature referred to as a negative flow characteristic. This feature causes tubes

that experience higher than average heating to draw lower than average fluid

flow. Subcritical boilers that operate using natural circulation have a positive

flow characteristic whereby tubes that experience higher than average

heating tend to draw higher than average fluid flow.

If the furnace heal flux distribution is non-uniform due to slagging or other

factors, the negative flow characteristic can lead to a non-uniform fluid

temperature profile and high fluid temperatures at the outlet of the

waterwalls. This can result in possible overheating of tubes in the upper

furnace, DNB at high heat flux areas and differential thermal expansion of the

waterwalls.

Some supercritical boiler suppliers are now offering low mass flux designs

with internally rifled tubing to overcome this problem.

8.2.3 Slagging

Supercritical boilers are typically designed with a spiral tube configuration in

the furnace to produce a high fluid mass flux in the tubes. The spiral

configuration requires the tubes to be installed at an inclined angle typically



between 10 to 15 degrees from the horizontal. The inclination of the tubes is

thought to increase the propensity of slag and clinker to form on the

waterwalls compared to vertical tubing, which is typically used in subcritical

boilers. The higher fireside metal temperatures of supercritical boilers may

also contribute to increased slagging.

The risk issues stated above are observed in some supercritical plants. There

are over 600 such plants operating around the world. In order to mitigate

these risks, the following aspects need to be considered in the design and

operation of the plant:

• use of oxygenated water chemistry• use of non-slagging coal in the boiler• selection of coal to avoid fire-side corrosion• consider rifled furnace tubes and possibly vertical tube furnaces with rifled

tubing.

8.2.4 Welding of Special Materials

The development of special steels and alloys to ensure technically sound and

safe operation of the plant has been dealt with in detail in Section 5. The

major components are manufactured at the works of the manufacturer who

have developed the materials either themselves or can procure them in the

market. However, substantial fabrication work is required to be done at the

site of the project and this involves welding of different pieces and

components.

Welding of dis-similar pieces i.e. two pieces fabricated out of different

materials is a difficult process, in itself. The difficulty increases when the

metals, out of which the pieces to be welded are fabricated, are newly

developed and not conventional. The best alternative, if available, will be to

avoid the necessity of welding pieces of dis-similar metals. This may,

however, not be possible and special welding techniques required for such

jobs will need to be learnt at the workshops of original equipment

manufacturers.

Special welding equipment will need to be procured by the EPC/ Non-EPC

contractor responsible for implementation.



8.2.5 Tube Spacing to Handle Indian Coal

It is known that Indian coal has high ash content and lower calorific value as

compared to coals available in other countries such as Australia and South

Africa. The designs of supercritical boilers developed by foreign

manufacturers are based on the superior type of coals and have to be

adopted to suit Indian coals.

The tubing has to ensure that steam parameters required for the supercritical

steam cycle are maintained. The materials used for fabrication of tubing will

affect their diameter and spacing. Ultimately, it is the responsibility of the

manufacturer to design and fabricate tubing for the most efficient operation

of the steam generator.

8.2.6 Height of Structure

It will be convenient and economical to restrict the height of the boiler

structure. The height of the boiler will be governed, however, by design

considerations.

The height of the smoke stack (Chimney) is governed by environmental

considerations.

7.13 OTHER ISSUES ASSOCIATED WITH DEPLOYMENT OF SC TECHNOLOGY IN INDIA

7.13.1 Transportation of Major Equipment

The transportation requirement will depend on the fact whether the major

equipment is imported or is indigenous. The imported equipment will require

facilities at a port close to project site and thereafter transport by rail or road.

Route survey including load bearing capacity of bridges involved (rail or road)

will need to be determined and carriers designed accordingly.

7.13.2 Material Handling

Material handling involves handling of equipment received from

manufacturers and suppliers for erection and commissioning and of

consumables including coal and fuel.

Material handling involves lifting and handling of heavy pieces including

assembly of boiler, steam turbine and generator. The heaviest single piece

for a 800 MW plant will be the generator weighing about 275 tonnes. In

addition to overhead cranes, use of modern erection techniques like jack and



winch system should be considered for lifting of water wall, tube bundles,

reheater and economizer panels.

The coal handling system should be designed for the coal available. The

milling system, conveyors etc should be designed accordingly. The ash

handling system should be designed for the ultimate objective of “no ash” to

be disposed of beyond the plant boundary. Storage of coal and fuel oil should

be provided for.7.13.3 Grid CodeThe plant should operate as a base load station in order to ensure efficient operation. This may not be possible at all times on account of fluctuations in power demand in the system of which the plant is a part. It might be necessary under low demand conditions in the region to back down the unit/units to partial load or even shut down the plant.

In view of these grid conditions, the boiler procured for the plant should be capable of fast adaptation to load changes from 100% to say 30%. It should be capable, also, of fast start ups and high ramp up rates. Provision of these capabilities could result in increase in the initial price of equipment but would be unavoidable under grid conditions likely to prevail over the near future.

7.13.4 Skilled ManpowerAs mentioned earlier, there is enough experience and skill available for the erection and commissioning of coal based power plants upto 500 MW capability. The erection and commissioning of a 660 MW/ 800 MW supercritical plant will not be different materially. However, it is advisable that some senior technical persons who will actually be incharge of erection and commissioning of the supercritical plant are trained at such plants already under construction in India as also in other countries.

7.13.5 Coal Quality and Boiler PerformanceCoal properties affect PC plant beat rates and boiler size. Indian coal is known as low grade with high ash content (as high as 45%). Therefore, the furnace and the pulverizes need to be designed to work satisfactorily for this high ash coal, Sub-bituminous fuels generally have alkaline ashes with low ash softening temperatures, which require large PC furnaces. This is primarily because the PC furnace heat transfer area must be increased in order to reduce furnace exit gas temperature as the ash softening temperature drops, and thereby prevent slagging of the convective pass. The gas velocity needs to be low in the convective pass of the boiler, which will require an increased area of the back pass of the boiler. The pulveriser throughput needs to be higher as the same boiler will handle a significantly larger quantity of coal for the same power output when compared with an imported high-grade coal. The boiler efficiency is expected to reduce due to the lower calorific value of the coal.

Indian coal would require increased soot blowers in the boiler and frequent soot blowing during operation.



The ash plant capacities should be appropriately designed to handle the large quantity of ash generated from the boiler.

The quartz content in Indian coals is high. The use of Indian coals shall require frequent maintenance of the pulverisers. A better option could be to blend these coals with an imported coal.

The advantage of using Indian coal is that the sulphur content is low which avoids the use of FGD plants. The choice of fabric filter or electrostatic precipitator will depend upon the type of coal to be used (i.e. Indian coal or imported coal or a blend of both), and the particulate emission limits for plant.

Fireside corrosion may not be an issue with the Indian coal as the sulphur content is very low (0.5%). Although corrosion can happen due to other chemicals in coal (eg chlorine), this may not be an issue for this type of coal.

7.13.6 Environmental BenefitsIndia has large coal deposits and the country has virtually no other option but to use this large coal resource for electricity generation. India classifies is a host country for CDM development but does not have a legally binding cap for its CO2 or equivalent emissions under the Kyoto Protocol. India is a member of the Asia-Pacific Partnership on Clean Development and Climate, popularly known as AP6, which is another international forum for climate change. Other countries in this forum are China, Japan, Republic of Korea, Australia and the United States. The vision statement of this forum says:

"The Partners have come together voluntarily to advance clean development and climate objectives, recognizing that development and poverty eradication are urgent and overriding goals internationally. By building on the foundation of existing bilateral and multilateral initiatives, the Partners will enhance cooperation to meet both our increased energy needs and associated challenges, including those related to air pollution, energy security, and greenhouse gas intensities, in accordance with national circumstances. The Partners recognize that national efforts will also be important in meeting the Partnerships shared vision."

India has therefore committed to working together with other countries to reduce greenhouse gas emissions. The deployment of supercritical technology may be seen as an essential step in reducing greenhouse gas emissions.7.13.7 Socio-economic BenefitsA large number of supercritical plants are being considered by many agencies as mentioned in Section 3. It is expected that new manufacturing plants will be built and plants of Indian manufacturers like BHEL and L&T expanded in near future to facilitate fabrication of these plants. This will obviously lead to new investment opportunities and job opportunities. New job opportunities will also be created during construction of these plants.

A new technology often means new job opportunities. The manufacturers of these plants in other countries are expected to make licensing arrangements with the existing Indian companies or engage Indian companies or consultants for design purposes. This will potentially increase new job opportunities for Indian technologists and engineers.



8.0 OPERATION AND MAINTENANCE ISSUES



OPERATION AND MAINTENANCE ISSUES8.1 SUPER CRITICAL TECHNOLOGY IN INDIAN AMBIENT CONDITIONS

and INDIAN COALSThere are a number of issues pertaining to Indian ambient conditions and Indian coals. Indian ambient conditions are different from those of other countries and the heat rates achieved there may not be achieved under Indian conditions. The Indian coals have higher moisture content, have low calorific value and have high ash content. The ash also has a high silica content giving it a higher abrasive character.

The ambient conditions are the same for sub critical or supercritical plants and therefore the differential improvement in heat rate between the two technologies shall remain the same in India as elsewhere. The techno-economic viability of supercritical and ultra supercritical technology is not altered under different ambient conditions in India and in other countries.

With respect to Indian coal, there is some drop in efficiency due to higher moisture content and due to a higher requirement of auxiliary consumption. There would also be a higher capital cost due to larger furnace size required and lower flue gas velocities. In addition there are technology risks associated with use of imported coal also. Imported coal generally has high sulphur content. Though the current regulations ask for only the provision of space for FGD in the plant layout, with increasing use of imported high sulphur coals, FGD may become a regulatory requirement. Secondly, the international coal costs are also likely to go up in the future if the oil prices go up. On the other hand if the Indian plants have captive coal mines the cost of coal would remain largely stable. Thus, the risks with imported coals are higher than with Indian coal.

The risks with Indian coal and possible remedial measures that can be taken are given below.

(i) Indian coal typically has higher moisture content, low CV and high ash content. This can lead to lower boiler efficiencies than with imported coal.Remedial Measures: High furnace volume, better boiler tube materials with more design

margins Smart soot blowing system and online performance optimization

software

(ii) Low volatile matter in Indian coal leads to high-unburnt carbon loses. Remedial Measure are: Higher capacity milling system to achieve better fineness and more

retention time in the boiler. Higher capacity of boiler in Indian condition to meet more steam

consumption due to low vacuum in Indian ambient condition

(iii) Higher erosion of the boiler tubes due to high ash content and quartz particles in the ash Remedial measures are:

Lower flue gas velocities to reduce erosions Better shielding of the tubes and other erosion prone areas High capacity 60% capacity for HP/LP by pass to deal with grid fluctuations



8.2 OPERATION AND MAINTENANCE ISSUES FOR SUPER AND ULTRA SUPER CRITICAL TECHNOLOGY IN INDIA

8.2.1 Design and manufacture of components for supercritical coal fired plants in developing countries

The issues regarding use of supercritical and ultra supercritical technology are as follows: The ability of the Indian electricity sector to absorb new supercritical and

ultra supercritical technology. The availability of skill set to set-up such plants. The ability of the plant personnel to operate and maintain such plants. The availability of spares etc., in the Indian market. The techno economic viability of such plants given that under Indian

ambient conditions, the heat rate and efficiency figures would be lower than those obtaining abroad.

The techno-economic viability of such plants in India taking into consideration higher capital costs and lower efficiencies if Indian coal is used.

The Indian electricity sector has matured over the years. The teething troubles and the stabilization period required are no longer as significant as they were earlier. The 660 MW unit sizes are expected to stabilize much quicker than the lower capacity units. The Indian manufacturers are also able to adapt the technology received from others to suit Indian conditions. Significant adaptations have been carried out in boiler designs and the milling systems to address the problems with Indian coal. Further, the Indian market today has much more depth in terms of manufacture of components and use of newer materials. Special steels are also being manufactured in India and therefore there is much more experience available in the country to absorb new technology than earlier.

The other reason to believe that supercritical and ultra supercritical technology can be absorbed reasonably quickly is that India has already chosen to introduce sufficient number of such plants. This means that there would be sufficiently large number of units to build up the requisite manufacturing and support infrastructure. Therefore, introduction of super critical units does not introduce any major technology risk.

8.2.2 Availability of contractor for maintenanceSupercritical and ultra supercritical technologies introduce only a small number of special components requiring specific skills for maintenance. By and large O&M operations for the supercritical and ultra supercritical plants are the same as for sub critical plants. Maintenance persons are familiar with new materials used in supercritical plants as they are already in use in Indian plants. The operational flexibility with super critical technology is more than for subcritical units and should pose no major problems. Therefore, the ability of the Indian electricity sector to absorb supercritical and ultra supercritical technology should pose no major hurdle for its introduction. However, as a necessary measure, it is important to provide extensive training to the plant personnel using similar facilities abroad and also using training simulators.

8.2.3 Availability of Critical Spare, Tools and Tackles in India



No major problems can be foreseen on this count. Given the number of such plants and projects to be set up, the availability of critical spares, tools and tackles are unlikely to be a constraint on the introduction of supercritical ultra supercritical technology in India.

8.2.4 Status of super and ultra super critical boiler manufacturers / suppliers

In terms of local manufacturing capability, BHEL and L&T in India are entering into supercritical technology. BHEL has obvious core strength in power plant manufacture and should be able to absorb new technology quite easily. Its collaboration with Siemens for the turbines can be easily scaled up to cover supercritical technology. It is also tying up with Alstom for the boiler technology. Similarly L&T, which has worked on the power plant cycle for some time including nuclear power plants, has an extensive experience of engineering, fabrication and installing of such equipment. With their collaboration with Mitsubishi Heavy Industries (MHI), L & T will provide a second manufacturer of supercritical and ultra supercritical plants.

Apart from this, major international companies such as ABB, Alstom, GE, TPE, Skoda and Doosan are also active in India. They are involved in supply of boilers and turbines to the Indian market. Chinese companies such as Harbin, Dongfeng and Shanghai Electric are also active in India. Therefore, apart from the two Indian companies, who have manufacturing presence in supercritical plants, there are also other manufacturers of supercritical plants who are active in India and also have some manufacturing presence.



9.0 ENVIRONMENT ISSUES



ENVIRONMENT ISSUES9.1 INTRODUCTION

The prescribed environmental standards and guidelines for pollution control

measures are described below.

9.2 INDIAN STANDARDS9.2.1 Ambient Air Quality Standards

Ministry of Environment & Forests (MoEF), Government of India, have, established

the National Ambient Air Quality Standards for the various categories, which

are followed by State Pollution Control Boards. These are given in the following

Table:

Table 10-36: Ambient Air Quality Standards

Pollutants

Time & weighted average

Industrial area (µg/m3)

Residential area & other areas (µg/m3)

Sensitive area (µg/m3)

Annual average

24 hours

Annual -average

24 hoursAnnual average

24 hours

S02 80 120 60 80 15 30NOx 80 120 60 80 15 30SPM 360 500 140 200 70 100

(Source: Air Prevention & Control of Pollution Act. I981 Dt. April 11. 1994)

Since Thermal Power Station falls in the category of industrial area, the

standards followed for industrial category will be applicable to the plant.

9.2.2 Flue Gas Emission Standards

The present emission standards prescribe Particulate Matter emission limits and

stack height criteria in coal-fired thermal power stations in India. Table 10-2

provides the prescribed standards for stack height and particulate matter

emission applicable to thermal power plants. However, no specific emission

values of S02 and NOx are prescribed.

Table 10-37: Flue Gas Emission StandardsParameter Standard

1. Sulphur dioxide (SO2) Stack Height limit in meter500 MW and above 275200 MW/2I0 MW and above to less than 500 MW

220

Less than 200 MW/210 MW H = 14 (Q)0.3

Where Q is emission rate of SO2

in kg/hr, and H is slack heightin meters.



Parameter Standard2. Particulate Matter (PM) mg/m3N (concentration not to

exceed)Generation capacity 210 MW or more

150

Generation capacity less than 210 MW 350

(Source: 1. EPA Notification [G.S.R. 742 (E), dated 30th August 1990]

2. EPA Notification [S.O.8(E), dated 3rd January 1989])

9.2.3 Wastewater Quality Standards

The wastewater discharge norms pertain to the use of the respective source(s)

of discharge. Table 10-3 provides the wastewater quality standards applicable to

thermal power plants.

Table 10-38: Wastewater Standards

Source ParameterConcentration not to

exceed, (mg/l)

Boiler blow down

Suspended Solids 100Oil & Grease 20Copper (total) 1.0Iron (total) 1.0

Cooling tower blow down

Free available Chlorine 0.5Zinc 1.0Chromium (total) 0.2Phosphate 5.0Other corrosion inhibiting material

Limit to be established on case by case basis

Ash Pond Effluent

pH 6.5-8.5Suspended Solid 100Oil & Grease 20

(Source: EPA Notification [S.O. 844 (E), dated 19th November 19861)



9.2.4 Noise Standards

Table 10-4 provides the noise level standards applicable to thermal power

plants. Since thermal power plant site falls in the category of industrial area, the

standards followed for industrial category will be applicable in the power plant

premises.Table 10-39: Noise Standards

Category Day Time (dB) Night Time (dB)

Industry 75 70

Commercial 65 55

Residence 55 45

Silence 50 40

(Source: EPA Notification [Gazette, dated 14th February 2000])

9.3 EMISSIONS RESULTS 9.3.1 CO2 Emissions ResultsThe CO2 emission estimates for the three coal fired power plant options for domestic coal are presented below. The figures given in the table are based on the conversion of all the carbon in the coal to CO2 during the combustion process.

Table 10-40: CO2 Emission Estimates (100% MCR)Item Unit Base

SubcriticalBaseSupercritical

High Supercritical

CO2 emission rate (Domestic coal)

t/h 425 406 390

Gross CO2 emission intensity (Domestic coal)

kg/MWh 850 812 779

Net CO2 emission intensity (Domestic coal)

kg/MWh 904 864 829

The CO2 emission reduction percentage estimates relative to the base subcritical plant as compared to the high efficiency coal fired plant options considered in this report are presented below.

Table 10-41: CO2 Emission Reduction % Estimates Relative to Base Subcritical Plant (100% MCR)

Coal Fired Plant OptionCO2 Emission Reduction Compared to the

Base Subcritical Plant (%)Base subcritical 0.0%Base supercritical 4.4%High supercritical 8.3%

9.3.2 Other Emission ResultsThe following emissions are discussed: NOx emissions SOx emissions Particulate emissions

For each of these types of emissions, the following information is discussed: production of the emission control technologies to reduce the emission licence limits for the emission



The emissions listed above are by-products of the fuel and gas cycle, which is largely independent of the steam cycle. As such, the emission performance of subcritical, supercritical and advanced supercritical power plants is comparable when measured as a function of fuel consumption. However, as subcritical plants are less efficient than supercritical and advanced supercritical power plants, the emissions generated per unit of electrical energy produced is greater in the case of the subcritical plant than that for the supercritical and advanced supercritical power plants.

9.3.3 Nitrogen oxides EmissionsOxides of nitrogen (NOx) are a by-product of the combustion of coal in air. The production of NOx is dependent on the type of burners installed, excess air conditions, and the furnace flame temperature. The following technologies can be used to minimize the production or emission of NOx emissions: low NOx burners (LNB) over-fire air (OFA) flue gas recirculation (FGR) selective catalytic reduction (SCR) selective non-catalytic reduction (SNCR)

The NOx emission limits set by Governments, or organizations around the world for new coal fired power stations vary. The NOx emission limits for new coal fired power stations are presented below. Typical control technologies that could be employed to comply with the stated emission limits are also included in table below.



Table 10-42: NOx Emission Limits for New Coal Fired Power StationsRegion or Organisation SOx Emission Limit Control Technology

World Bank 750 mg/m3 at 6% O2 dry basis LNB and OFA

India No limits at present LNBEuropean Union 200 – 500 mg/Nm3 at 6% O2 LNB, OFA and SCR

LNB : Low NOx BurnerOFA : Over Fire AirSCR : Selective Catalytic Reduction

9.3.4 Sulphur oxides EmissionsSOx is a by-product of the combustion of the sulphur in the coal. The quantity of SOx produced during combustion is directly proportional to the quantity of sulphur in the fuel entering the furnace. It is possible to minimize the emission of SOx emissions through pre-treatment of the coal or post-treatment of the flue gases. The following technologies can be used to minimize the production or emission of SOx emissions: selection of low sulphur coals flue gas desulphurization (FGD)

The sulphur content of the domestic coal considered in this study is 0.5%. The amount of SOx emissions produced by these coals without post-treatment of the flue gases is estimated as 1,880 mg/Nm3 at 6% O2 dry basis for domestic coal.

The SOx emission limits set by Governments, or organizations around the world for new coal fired power stations vary. The SOx emission for new coal fired power stations by region or organization are presented below. Typical control technologies that could be employed to comply with the stated emission limits are also included in table below.

Table 10-43: SOx Emission Limits for New Coal Fired Power StationsRegion or

OrganisationSOx Emission Limit Control Technology

World Bank 0.20 t/d/MW of capacity for the first 500 MW 0.10 t/d/MW of capacity for the each additional

megawatt of capacity above 500 MW. The concentration of SO2 in the flue gas should not

exceed 2,000 mg/m3 at 6% O2 dry basis. Maximum emission level of 500 t/d Construction of two or more separate plants in the

same airshed to circumvent the maximum emission level of 500 t/d is not acceptable.

Low sulphur coal and FGD (as required)

European Union

200 – 400 mg/Nm3 at 6% O2 Low sulphur coal and FGD

India No limits at present Low sulphur coal

9.3.5 Particulate EmissionsParticulates are non-combustible mineral particles that enter the furnace in the fuel stream and leave the furnace entrained in the flue gas (fly ash). The quantity of particulate emissions produced is related to the ash content of the coal. Particulate emissions have been proven to be successfully controlled by



the use of both electrostatic precipitators and fabric filters. Electrostatic precipitators can provide collection efficiencies up to 99.5% but are highly dependent on the electrical resistivity of the fly ash. Low sulphur coals and coals with high silica/ alumina compositions generally result in fly ash with a high electrical resistivity that reduces collection efficiency. Fabric filters are capable of achieving particle collection efficiencies of up to 99.95%.

The particulate emission limits set by governments or organizations around the world for new coal fired power stations vary. The particulate emission for new coal fired power stations are presented below. Typical control technologies that could be employed to comply with the stated emission limits are also included in table below.

Table 10-44: Particulate Emission Limits for New Coal Fired Power StationsRegion or Organisation Particulate Emission Limit Control Technology

World Bank 50 mg/Nm3 Fabric filterEuropean Union 30 mg/Nm3 at 6% O2 Fabric filter

India 150 mg/Nm3 Electrostatic precipitator, or fabric filter

9.4 APPLICABILITY OF STANDARDS AND COMPLIANCE

The proposed supercritical project will need to comply with prescribed

standards as described below:

The domestic coal fired thermal power plants are normally designed at

subcritical technology and operate at 33% thermal efficiency. As the

Supercritical Technology Project shall be provided with Supercritical boiler

with higher thermal efficiency (40.2%), the coal consumption and the

greenhouse gas emission per kW generation will be reduced.

As for as discharge of particulate matters (PM) is concerned, the project will

be required to meet the limit of 100 mg/m3N as per Charter on Corporate

Responsibility for Environmental Protection which is an agreement signed

between the related authorities including the Power and Environment

Ministries. The installation of an electrostatic precipitator (with dust collection

efficiency of 99.8 % or more), will be able to reduce the PM at the ESP outlet

to a maximum of 100 mg/m3N.

Regarding SO2 discharge, a 275m high stack per unit will be installed as per

statutory requirement. Besides, low sulfur coal will be mainly used in this

Project. The sulphur content is about 0.3% to 0.5%, representing SO2 emission

in this case of 400-700 ppm (average values), which is not high. There is no

proposal for the installation of Flue-gas Desulphurization (FGD) plant for SO2



removal; however, adequate space will be provided behind the stack for future

stricter control measures.

Regarding NOx discharge, coal usually contains 1% to 3% of N and results in

NOx emissions of 500-800 ppm (average values). The actual N content of the

major coal used in the Project is about 1%. Measures to improve combustion

process including Low NOx burners will be able to reduce the NOx emission to

around 400 ppm.

Wet bottom ash disposal to the exiting ash pond and dry fly ash collection/storage

will be adopted in ash handling system. The fly ash will be reused for making ash

bricks and aggregates, and also for cement manufacturing.

Plant effluent from Clarification plant & Demineralizing (DM) plant will be

treated in waste water treatment system and discharged after meeting the

stipulated norms. The treated waste water will be re-circulated and reused as

much as possible.

Coal Storage yard, Water Spray sprinkler system will be installed for

suppressing the coal-dust from the coal storage/handling areas.

9.5 CDM ISSUES 9.5.1 Methodology

This CDM project benefits envisage a coal plant that is more efficient and

thus emits less greenhouse gas emissions as compared to a conventional

plant. Coal plants come in various categories, such as subcritical, supercritical

and ultra supercritical. This project shall be a new (not-yet-built) coal plant

that would normally be constructed by the developer according to a less

efficient but chapter technology is accordance with the developer’s financial

capabilities. The incentive of CDM, shall enable the developer to build a more

efficient power plant instead. Clear and transparent documentation shall be

furnished to establish that in the absence of a CDM project, the less efficient

plant would be constructed.

The key measure to compare more and less efficient plants will be overall

efficiency. Typical coal plants range from 35-45% efficiency, as measured on

an energy (joule) basis. In other words, if a power plant is 37% efficient, only

37% of the joules contained in the coal fuel end up producing useful joules



worth of electricity. The rest of the joules are lost in the fuel combustion and

electricity generation process. This project would take a power plant that

would have been only 37% efficient and build a plant instead that is 40%

efficient with CDM benefit contribution.

While the efficiencies of older power plants in developing countries are still

around 35-36% lower heating value (LHV), modem subcritical cycles have

attained efficiencies close to 40% (LHV). Further improvement in efficiency

can be achieved by using supercritical steam conditions. These plants can

have efficiencies above 45% (LHV).

Coal-fired power stations using "supercritical" boilers produce hotter steam to

run the turbines: around 600°C compared to around 540°C in an older

technology plant. Supercritical plants make more efficient use of the energy

created by coal's combustion, so less carbon is emitted — around 5-15% less

than the average coal plant per unit of electricity generated.

9.5.2 Applicability Conditions

The methodology which will render a new coal fired plant eligible for

obtaining CDM benefits will need to establish that the new coal plant would

be built normally using a conventional technology, which is standard in the

country. With the incentive of CDM, a more efficient coal plant would be built

instead (eg: instead of a subcritical plant, a supercritical or ultra supercritical

plant will be constructed). If construction of a coal plant using standard

technology has not commenced, it shall be made clear that a new, standard-

efficiency coal plant would be built in that location. This can be confirmed

through clear and transparent documentation, such as utility

expansion/investment plans, feasibility studies, licenses and approvals

granted, power purchase agreements signed, financing/investment/loan

process underway, etc. These documents need to make clear that the power

plant that would be built has the standard efficiency level).

A baseline efficiency should be clearly established through comparisons with

other coal plants in the country.

The "standard efficiency" coal plant and the new, more efficient plant should

have the same capacity. If a more efficient plant is built, which has a larger

capacity, the overall emissions would be higher than if the plant were of the



same size as the standard coal plant but emission per KW of electricity

generated shall be lower.



10.0 COST IMPLICATION OF TECHNOLOGY IN INDIA



COST IMPLICATION OF TECHNOLOGY IN INDIA10.1 COST ESTIMATE OF SUPER CRITICAL PLANTS IN INDIAThe tables below gives the cost implications of super critical plants in India. They take into account the following: The capital costs for supercritical and high super critical plants using

Indian coals. The impact of higher auxiliary power consumption in Indian plants Slightly poorer heat rates due to higher ambient temperatures Some loss of efficiency in the boiler due to higher moisture content of

Indian coals

For the purpose of computing the costs of subcritical, supercritical and high super critical units, the costs for each unit size have been scaled up using scaling factors. We have carried out study for cost comparison for using super critical technology on domestic coal. The tables below summarise the calculations for the above.

It might be noted that the costs computed here are based on prices of projects already executed or under execution. The prices however are sensitive to steel prices, both of which have seen sharp variations in recent times.

There would be some increase in the capital cost of plants if Indian coals are used. The impact of Indian coals on the cost of the boiler is due to higher furnace size in order to burn lower calorific value fuel and also the need for lower flue gas velocities for preventing erosion. Though the manufacturers indicate that the price difference for using Indian coals is of the order of 2.5%, we have used a slightly higher figure. The other additional costs for Indian coals are in the coal handling, milling and ash handling systems. These have been addressed in the cost calculations based on our estimates.

Table 11-45: Plant Characteristics

Indian Coal / Pithead site

Steam cycle parameters

Units Base Sub-critical

Low super-critical High super-critical

Pressure bar 166 247 247

MST Deg C 538 538 565RST Deg C 538 565 593

Unit size MW 500 660 800Construction and

start up timemonths 36 48 52

Table 11-46: Plant equipment capital costs per unitIndian Coal / Pithead site

Units Base Sub-criticalLow super-

criticalHigh super-

critical

Boiler & auxiliaries Rs. million 8035 13850 20025Steam turbine generator & auxiliaries

Rs. million4287 6772 9900

Electrical Equipment Rs. million 1199 1782 2475Plant control system Rs. million 277 446 540 Balance of plant Rs. million 2470 3483 3960



Buildings & common structures

Rs. million1188 1620 1800

Site preparation, roads and general infrastructure

Rs. million

619 770 990Total Rs. million 18076 28723 39690

Table 11-47: Other Capital Costs



Low super-critical

High super-critical

Land costs Rs. million 270 360 383

EPC contractor engineering & management (10%)

Rs. million

1807 2553 3175

Spares, tools & training Rs. million 454 612 720

Site accommodation Rs. million 540 540 540 Insurance (1%) Rs. million 181 287 397Owner's engineer & approvals (2.5%)

Rs. million452 718 992

Owner's contingency (2%)

Rs. million362 575 794

Table 11-48: Capital and Specific Capital Cost for Each Unit Size



Low super-critical

High super-critical

Total Unit Cost Rs. million 22141 34368 46690.7Total unit capital specific cost

Rs. million /MW 44 52 58



Table 11-49: Capital and Specific Capital Cost for two unitsIndian Coal / Pithead site


Low super-critical

High super-critical

Total Capital Cost

Rs. million 41264 65113 89735

Specific capital cost

Rs.million/MW 41 49 56

Table 11-50: O&M Costs – Fixed and Variable for Each Unit Size


UnitsBase Sub-

criticalLow super-

criticalHigh super-

critical

Fixed O&M CostRs. million /yr 608.4 690.3 844.2

Variable O&M cost Rs./MWh 116 136 150.87

10.2 BASIS Supercritical technology based power plants are not very common in India. Only two plants are in advanced stages of construction namely Barh (3x660 MW) and Sipat stage – I (3x660 MW). The capital cost (as approved by CEA and also mentioned in Central Regulatory Commissions order of Oct25, 05) is given below and can be used as a benchmark for the proposed project.

Particulars Sipat STPS Stage – I Barh STPSCapacity 3 x 660 MW 3 x 660 MWHard costForeign component (US $ million) 827 (Rs. 3515 Crores) 905 (Rs. 4208 crores)Domestic component (Rs. Crore) 3780 3079Total Hard Cost excluding IDC and FC charges (Rs. Cr.)

7295 7287

Hard cost (Rs. Crore/ MW) 3.68 3.68IDC & FCForeign component (US$ million) 165 (Rs.701 crores) 166 (Rs. 770 crores)Domestic component (Rs. Crore) 1017 1036Total project costForeign component (US$ million) 992 (Rs. 4216 crores) 1070 (Rs. 4977 crores)Domestic component (Rs. Crore) 4797 4116Total capital cost (Rs. crore ) 9013 9093Total capital cost (Rs. Crore/MW ) 4.55 4.59

10.3 LIFE CYCLE COSTS OF SUPERCRITICAL COAL FIRED POWER PLANTSThe life cycle costs of supercritical coal fired power plants are lower than those of subcritical plants. Current designs of supercritical plants have installation costs that are only 2% higher than those of subcritical plants. Fuel costs are considerably lower due to the increased efficiency and operating costs are at the same level as subcritical plants. Specific installation cost i.e. the cost per megawatt (MW) decreases with increased plant size. For countries like India and China, unit ratings from 500MW up to 900MW are possible due to their large electrical grids. In countries with smaller grids, unit sizes of 300MW are more appropriate and the specific installation cost will be higher than that of larger plants.



REFERENCE

1 High-efficiency Supercritical Technology

Alstom

2 Advance Boiler design Alstom3 The supercritical difference Alstom4 Supercritical & Ultra supercritical

TechnologyPowerGen Asia 2004

5 Steam Generator for the next generation of power Plant

Siemens AG, Power Generation Group Kwu

6 Material for Boilers in Ultra Supercritical Power Plant

Proceeding of 2000 international Joint Power Generation Conference Miami Beach, Florida, July 23-26,2000

7 India’s Ultra Mega Power Projects exploring

The use of Carbon Financing, MottMacdonald

8 Analysis of Technological risks associated with using Super and Ultra critical technology in India

Evonik Energy Services, India

9 Feasibility study report, Anpara E, 2007

Electric Power Development Company Ltd.

10

Defining the materials issues and research for ultra-supercritical steam turbines

Natural Energy Technology Laboratory, Morgantown

11

Development of gCrW tube, pipe and forging for ultra supercritical power plant boilers

Nippon Steel, Technical Report



LIST OF ABBREVIATION

APH AIR PRE-HEATER

APGENCO ANDHRA PRADESH GENERATION CORPORATIONASME AMERICAN SOCIETY OF MECHANICAL ENGINEERSAVT ALL VOLATILE CYCLE CHEMISTRYAVN ADVANCED VORTED NOZZLE

BHEL BHARAT HEAVY ELECTRICALS LIMITEDBMCR BOILER MAXIMUM CONTINUOUS RATINGBMS BURNER MANAGEMENT SYSTEMBS BRITISH STANDARDS

BTU BRITISH THERMAL UNITC&I CONTROL AND INSTRUMENTATION

CDM CLEAN DEVELOPMENT MECHANISMCO2 CARBON DIOXIDECR CHROMIUMCV CALORIFIC VALUE

CU COPPERCEA CENTRAL ELECTRICITY AUTHORITYCERC CENTRAL ELECTRICITY REGULATORY COMMISSIONCRH COLD REHEAT LINEDM DE MINERAL

DNB DEPARTURE FROM NUCLEATE BOILING

DSS DAILY START STOP

EPRI ELECTRIC POWER RESEARCH INSTITUTE

EPC ENGINEERING, PROCUREMENT AND CONSTRUCTIONEPMS ELECTROSTATIC PRECIPITATOR MANAGEMENT SYSTEMESP ELECTRO STATIC PRECIPITATORFGD FUEL GAS DESULPHURISATION PLANT

GW GIGA WATTHHV HIGH HEATING VALUEHP HIGH PRESSUREHR HOURHRH HOT REHEAT LINEHV HIGH VOLTAGEHZ HERTZIBR INDIAN BOILER REGULATIONSID INDUCED DRAFTIP INTERMEDIATE PRESSUREIS INDIAN STANDARDSKG KILOGRAMKW KILOWATTKWH KILOWATT HOUR

LHV LOWER HEATING VALUELNB LOW NOX BURNERLP LOW PRESSURELV LOW VOLTAGEL&T LARSON & TOUBRO



MAHAGENCO

MAHARASHTRA GENERATION CORPORATION

MCR MAXIMUM CONTINOUS RATINGMG MILLIGRAMMHI MITSUBISHI HEAVY INDUSTRIES LIMITEDMOEF MINISTRY OF ENVIRONMENT AND FORESTS

MPA MEGA PASCALMSP MAIN STEAM PRESSURE

MST MAIN STEAM TEMPERATUREMT METRIC TONNEMV MEDIUM VOLTAGEMVA MEGA VOLT AMPERESMW MEGA WATTSNI NICKELNM3 NEWTON CUBIC METRENOX OXIDES OF NITROGEN

NTPC NATIONAL THERMAL POWER CORPORATION

O&M OPERATION AND MAINTENANCEPC PULVERISED COALPLF PLANT LOAD FACTOR

PM PARTICULATE MATTERPSEB PUNJAB STATE ELECTRICITY BOARD

PSI PRESSURE SQUARE INCH

PWHT POST WELD HEAL TREATMENTRH REHEATERRST REHEAT STEAM TEMPERATURESCAPH STEAM COIL AIR PRE-HEATERSEB STATE ELECTRICITY BOARDSERC STATE ELECTRICITY REGULATORY COMISSIONSH SUPERHEATERSO2 SULPHUR DIOXIDET TONNETMCR TURBINE MAXIMUM CONTINUOUS RATINGUMPP ULTRA MEGA POWER PROJECTVGB VERBAND DER GROBKESSEL BESITZER

VN VANADIUMWBPDCL WEST BENGAL POWER DEVELOPMENT CORP. LTD


Paper on Super Critical Technology and Analysis for Indian Environment

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