A Lignite Fired Unit of 1000mw

A Lignite Fired Unit of 1000 MW

A LIGNITE FIRED UNIT OF 1000MW - RWE NIEDERAUSSEM, GERMANY

I had been in Germany from August’2003 to July’2004 to undergo a one-year advanced training on “Energy & Environment”. Fifteen engineers, who had thermal power plant O&M experience from all over India, were selected by INWENT, German Government’s economic cooperation wing to undergo the training. During my stay in Germany I had been exposed to many technological advancement in the area of power generation though my own area of interest was Automation & IT Application in Power Plant. To attract interest of a larger section of reader I choose this topic. The same technology can be applied for normal coal fired power plant but in Germany lignite is of specific interest as lignite mining is still economic in Germany whereas coal production is not and is imported from South Africa or Australia. RWE Energie AG is a major power utility of Germany. It’s Niederaussem power station is having a total capacity of 3830 MW with 2X150 MW, 4X300 MW, 2x600MW and recently commissioned 1X1000 MW BoA block. Germany’s experience with supercritical technology is reflected in RWE Energie AG's 1000-MW BoA (Brownkohlekraftwerke mit Optimierung Anlage-technik) block in Niederaussem plant near Cologne. Completed in 2002, it is one of the world's largest and most environment friendly lignite-fired power plants. Niederaussem BoA block is equipped with extraction condensing turbines, to deliver high-efficiency (43%) base-load electricity. The large tower type steam generator is designed and built by a consortium of Alstom Energy Systems, Babcock Kraftwerkstechnik and Steinmueller. Other major suppliers are Siemens (Steam Turbine and Instrumentation and Control), Blacke-Duerr (Cooling Tower) and Apparatebau Rothemuehle (Electro-Static Precipitator). Alstom Energie, Nuremburg, was responsible for conceptual design engineering based on RWEs specifications and has overall engineering responsibility, including system optimisation, layout and planning of civil work. In the new BoA block apart from the greatly improved efficiency (43 %), this will result in a 30% saving in lignite consumption and a 30% reduction in CO2 emission. Nearly 2 percentage points of the efficiency gain compared with recent lignite fired power plants come from the advanced steam turbine design. It will be the first application of Siemens 3DV blading and the biggest MHN-type supercritical turbine yet built. The 200 m high natural draft wet cooling tower with flue gas discharge (no separate stack) is the highest in the world.

Manoj Chakraborty, Asst. Manager, Bk.T.P.P, WBPDCL 1


The BoA Concept: The concept of the BoA unit comprises the idea of developing a modern lignite fired unit with high efficiency and high availability on the basis of the available operating experience, which presents an optimum solution in terms of technology and economic efficiency and environmental impact.

N ie d e r a u ß e m P o w e r P la n t U n i t L a y o u t



EFFICIENCY INCREASE Specific measures taken in BoA block to increase in the overall efficiency are as follows-

Optimisation of steam – water cycle 1.6 %

Main steam and RH parameter improvement 1.6% Increasing turbine efficiency 2.3%

Reducing the condenser pressure 1.4% Decrease in Auxiliary power consumption 1.5%

Use of Flue gas heat 1.3% IMPORTANT TECHNICAL DATA

Unit output MW 950 Year of commissioning 2002 Gross output MW 1012 Aux power consumption % 4.6 Net output MW 965 Net plant efficiency % 45.2 Steam Generator Data CV of design coal KJ/Kg 9200 Fuel heat input MJ/s 2165 SH steam mass flow TPH 2620 Final Feed water temperature Deg C 295 Live steam condition Bar / Deg C 274 / 580 HRH steam condition Bar / Deg C 60 / 600 SH / RH pressure loss Bar / Bar 34 / 2 FG temperature after boiler Deg C 100 Steam generator efficiency % 94.4 TURBINE HP TURBINE Single flow IP TURBINE Double flow LP TURBINE Six flow LP outlet area M2 6X12.5 Preheating stages No 10 Condenser pressure Mbar 28.9 / 34 Cooling water temperature Deg C 14.7/ 24.7 TURBINE EFFICIENCY % 92.6

WHAT IS SUPERCRITICAL? "Supercritical" is a thermodynamic expression describing the state of a substance where there is no clear distinction between the liquid and the gaseous phase. Supercritical condition occurs when the boiler pressure increases above the critical pressure of 221.2 Bar and temperature above 371.4 deg C. Above this point the two



phases of water and steam cease to exist and are replaced by a single supercritical fluid. Any supercritical conditions where the throttle and/or reheat steam temperatures exceed 566 Deg C are termed as “ ULTRA SUPERCRITICAL”. WHY SUPERCRITICAL? • Superior environmental performance – low specific emissions of CO2, SOx, NOx, Dust. • High unit efficiency & lower fuel cost - >43% in Lignite fired, >45% in Coal fired • Greater Operating flexibility. Capable of cycling and / or two-shift operation. The 900 MW Heyden power

plant is even operating in two-shift operation. • Ability to respond and adjust to changes in demand while maintaining tight control of steam temperatures.

Operate in the SLIDING PRESSURE mode, constant turbine temperature reduces the thermal stress on components as the unit is cycled. Less stress translates into less maintenance and higher availability.

• Plant availability comparable to subcritical plant. • Improved plant efficiency at lower loads due to higher HPT internal efficiency, RH Temp, less BFP power

consumption. • Boiler drum limits the load change rate to 3% per minute while once through boilers can step-up the load by

6% per minute due to low thermal inertia. • No critical drum level control, instead feed flow is controlled by a shift in heat transfer between the

evaporator and superheater. • Faster start-up time. First fire to turbine synchronization (in min) Hot start up, after 2 hr shutdown 30 Warm start-up, after 8 hr shutdown 45 Cold start up, after 36 hr shutdown 90 • Fuel flexibility and firing system (front, opposed, tangential, corner, four wall, arch firing with slag tap or

dry ash removal, fluidised bed) not compromised. • Better frequency response though greater pressure variation. Rapid response BFP required. • Much lower operating cost as increase in cycle efficiency reduces fuel and all other flow rates. • Reduction in size of various plant items due to the reduction in thermal duty and general flow rates like Fuel

and ash handling plant, Firing equipment and draft plant, Condenser, Cooling tower, Furnace size • For water chemistry combination of a condensate polishing plant with oxygenated treatment (OT) is used. • Investment cost is only 2% more. Difference: Feed flow based on shift in heat transfer between evaporator and superheater. No blow down and for water chemistry combination of a condensate polishing plant with oxygenated treatment (OT) is used. THE SUPERCRITICAL BOILER The steam generator is of TOWER type design i.e. all pressure parts except for the flue gas heat recovery system are suspended from the boiler-supporting grid. The grid itself is supported by the four main columns arranged in a square shape. The tower type design has been selected in view of the high steam parameters. The boiler has a floor surface of 86.5 X 90 M and a roof parapet height of 168 m.



At full load operation approximately 20000 ton of coal is fired every day and seven out of eight mills are needed for steam generator full load. The maximum coal throughput per mill is 142.5 Ton/Hr. The beater wheel mills with overhung shaft are arranged evenly around the steam generator in order to supply the burners of the tangentially firing system, which are, arranged each vertically above the pulveriser. A multiple circuit variable-

n to a minimum over the whole speed range. speed gear is installed for reducing the power consumptioTHE FIRING SYSTEM A developed tangential firing system with reburning

lue below 200 mg/Nm3 by

s air coefficient of 15 % to minimise exhaust gas loss.

ace centre by

04.

el particles lead to a

06. urning burners

07. ns and contact of incandescent ash particles with the furnace wall owing to the

08. r fire air levels at optimised distances to the burner zone.

he above optimisation and the design of the firing system and combustion chamber were safeguard by means

capacity up to 35%, is provided for the start

HE FLUE GAS SYSTEM WITH INTEGRATED HEAT RECOVERY

burners limits the NOx vain-furnace measures alone. The firing system is characterised with following features: 01. Combustion with a low total exces

02. Stable combustion by an exact adjustment of the fuel / air mixture in the burner area.

03. Nearly complete gasification of the fuel in a hot pyrolisis zone in the area of the furnthe high fuel concentration in the burner belt area. Separation of fine and coarse fuel particles for the main and reburning burners

05. Good reaction conditions and the extended burnout path for the coarse funearly complete combustion, thus considering reducing the tendency towards slagging in the upper furnace and platen heating surface area.

A good lateral mixing in the combustion zone and an improved firing rate control of the re-band the wall air nozzles. Avoidance of stratificatiogood firing rate control. Air staging over two ove

Tof highly sophisticated, three-dimensional computational models. A dry lignite firing system, which is designed for a steam generatorup. The start-up firing system consists of eight dry lignite circular type burners with a furnace heat output 100MJ/s each. These burners will be the first dry lignite burners in this capacity class. Use of dry lignite firing during start-up provides low heat flow densities, which has favourable impact on the temperature distribution in the welded walls and the NOx emission during the start-up procedure. T

fter having passed the convection heating surfaces arranged above the furnace the flue gas is conveyed in the downward open pass to the two parallel rotary air pre-heaters and to the air heater bypass economiser

A



(LUBECO), which is also arranged parallel to these two rotary air heaters then conveyed to the two electro static precipitators, the two Flue gas coolers and then to the Flue Gas Desulphurisation (FGD) system. The flue gas cooler reduces the temperature from 160 Deg C to 100 Deg C. The heat is transferred via a water circuit in a feed water/air heater to the cold combustion air in a first stage. As the quantity of heat to be absorbed by the combustion air in

ir the second preheating stage is now reduced, a part of the flue gas heat can be utilised for the preheating of d water and condensate. Owing to this arrangement, less extraction steam flow from turbine is required for

t feed water preheater at a temperature of 295 Deg c: In e upper part which is passed first, the working fluid is led in counter flow to the flue gas, and in the lower part

p of the enclosing walls of the steam generator. The evaporator consists of

0% load.

Furnace

RAH

LUBECO

ESP

WATER AIR HEATER

Plastic tube heat exchanger

FGD

AIR

FG

afeefeed water and condensate preheating and generator produces a larger output with the same steam mass flow. THE STEAM GENERATOR PRESSURE PARTS A.ECONOMISER: The feed water enters the two parthwhich passed after wards in parallel flow to the flue gas. This arrangement provides high terminal temperature difference between the working fluid and flue gas, while simultaneously minimising the HP pressure loss with a high stability of the economiser. B.EVAPORATOR: After leaving the economiser the water at the bottom part of the furnace hopper is led to the evaporator, which is made uhelical- pattern wall tubes in the furnace area, which are provided with a cross sectional expansion of the tubes in order to improve the distribution of working fluid to the parallel evaporator tubes at the upper part. C.SUPERHEATER: The fluid leaving the evaporator is then led to the separation system consisting of six separators and one level vessel, where water and steam are separated in part load operation below 4The filled level vessel is maintained hot in supercritical steam condition. From there, the steam flows through the super heaters in five stages. The 3rd Super heater stage integrated into the TRIFLUX heat exchanger does



not absorb any heat from the flue gas, but helps to maintain the RH temperature. The annular cross section of the triflux heat exchanger, which is made up of two concentric tubes, is passed by the reheat steam. Superheated steam flows through the internal tube in counter flow and dissipates heat to the reheater on account of the higher temperature level. The amount of heat absorption can be influenced on the SH side via the SH side triflux spray and the SH side bypass flow.

Cross Section of Boiler N STEAM GENERATOR CONSTRUCTION

The pr gth of SH and RH and also the advanced steam parameters require a particular rly for the following components-

The steam generator enclosure walls – The highest –alloy material available for these marginal conditions,

high

• n heating surfaces SH2, SH4,

rrosion and for stability reasons.

CrMoWVNb 9-1-1 ( E 911), which belongs to the group of

•

For on the 5 levels at the wall entre. The cleaning is made with a bundled water jet, which is computer-controlled and directed towards the

Apart from the transient operating conditions no efficiency reducing RH spray attemperation is thus necessary for control of the RH outlet temperature. Triflux Heat Exchanger

Main Steam

Flue Gas

RH Steam

NEW MATERIAL I

ocessing of large lenattention for the material. The material concept had redesigned particula•

i.e. 13 Cr Mo 44 is used. This material requires no post weld heat treatment. • The separators- material X10CrMoVNb 9-1 ( P 91) is used to resist strain-induced corrosion at

temperatures. The final super heater / reheater heating surface- Concerning the convectioSH5 and RH3 are manufactured from the Austenitic steel X3 CrNiMoN 17- 13 for resistance against high temperature co

• The SH outlet headers- in order to avoid any thick walled ferritic martens tic welded joint between SH or RH outlet and turbine, the SH and RH outlet headers are also made from a martens tic material. For the first time in a large steam generator, the material X11the tungsten alloy 9- 12 % chromium steels is used for this purpose. Compared to material P 91, this leads to reduction of the wall thickness from 100 mm to 75 mm for the HP outlet headers. For the other thick walled headers and connecting pipings the usually applied material X20 CrMoV 12-1 is completely replaced by P 91 which is less difficult to process. The flue gas cooler-In order to avoid any low temperature corrosion, due to condensate containing sulphuric acid, flue gas cooler tubes and wall coatings are made of PFA-a fluor polymer.

THE HEATING SURFACE CLEANING PLANT the on-line cleaning of the furnace walls, water – lance blowers are installed

c



opposite wall at a horizontal blowing angle of max 90 deg and a vertical blowing angle of 60 deg. On account

ines the condition of the fouling of the individual heating surfaces and arranges for the

mens KWU HMN series of supercritical machines with the advanced 3D urved turbine blades. The blades play an important role in helping to boost efficiency.

h energy as

bar was a specific design point (stepped

of these wide swivelling ranges of the blowing lance, large surfaces can be evenly cleaned with water by means of only a few lances. A special diagnostic system (DORA; FACOS) enables specific soot blowing which is oriented towards the relevant heating surface. This diagnostic system makes a thermal check of calculation at an interval of some minutes each, determspecific operation of the soot blowers. THE SUPERCRITICAL TURBINE The steam turbine is one of the new SiecTheir job is to ensure that as mucpossible goes toward driving the generator. Also they have to be able to withstand unimaginably high temperatures. The special blades are known as 3DS blades because of their distorted curved structure. The turbo set consists of a single flow high-pressure section, a twin flow medium pressure section, and three twin flow low-pressure sections. These drive a bipolar generator with exciter. Alongside standard medium and low-pressure tapping, high-pressure tapping to raise the feed water temperature is also envisaged. The low-pressure turbines have exhaust steam cross sections of 6X12.5m2. The condenser pressure of 28.5 / 34.8 m condenser). This condenser pressure is attained through a cold-water temperature of around 14.7 / 24.7 deg c.

Supercomputers simulate the flow of steam and gases through a turbine and the forces they exert on the blades. This computational fluid dynamics technique is used to design turbine. Tiny cooling channels and new coating materials or alloys offer protection against high temperatures

ype Two-pole THDF series Power factor 0.8

THE GENERATOR Supplier Siemens / KWU Cooling medium Hydrogen T



The bipolar generator is equipped with the direct water-cooled stator winding and a hydrogen-cooled inductor. IGES from

r ers pr ion of the he he

upplier Siemens / KWU

he C&I use free programmable controls with bus connection and a hierarchic control system. Operation is one om, monitoring with large projector screens aiming at unit control by one nly.

ue to increase in the electrical net efficiency from just 31% in earlier 150 MW UNITS to more than 43% in bout 30%(almost 3 million tonnes per year). One percent increase

Advanced diagnostic system (D T SIEMENS) for monitoring of Generator and Generator transfo m ovides reliable informat alth of the equipments. Argon gas is used in tGENERATOR for H2 purging and also in Primary water circuit for Generator stator water system. INSTRUMENTATION & CONTROL SSystem Teleperm – XP Tdone from central control rooperator o ENVIRONMENTAL PERFORMANCE Dthe BoA unit, CO2 emission is reduced by ain efficiency reduces by two percent specific emissions such as CO2, NOx, SO2 and particulates .A

long with high temperature steel is the next target. BoA plus technology will use dried lignite for the power moval from the Lignite will be done from the waste heat from flue gas.

m- 720 o C PR- 350 bar

today’s scenario of highly competitive market and strict environmental norms SUPERCRITICAL technology ffers a good choice for efficient, reliable and environmental friendly electrical power generation. Increased

four-stage ESP removes 99.9% of the dust. Unit has two precipitators arranged in parallel with inlet and outlet nozzles for even gas distribution. Advanced combustion techniques, including an air staging process, keep NOx emissions below a 200-mg/m3 limit, so post-combustion controls are not needed. The high sulphur content of the lignite places tough demands on the desulphurisation system. It reduces the SO2 content of the flue gas to below the level of 400 mg/m3 prescribed by the German Air Pollution Control Code. Virtually 100% of the gypsum produced by the flue-gas desulphurisation process is recycled. FUTURE PLANNING In order to achieve maximum possible efficiency all efforts are being taken in this direction. Use of BoA plus ageneration and moisture re

Lignite Preheating Live Steam-700 o C RH Stea

SUMMARY Ino



fuel costs, improved technology and an a heightened focus on reducing power plant emissions have combined

Minimization of the HP pressure loss to 36 bar and RH pressure loss to 2 bar. nd RH in order to avoid the

ure up to 100 deg C.

the exhaust gas volume and thus the exhaust has losses as low as possible. fans by

pow latest technological advancement in the area of thermal power eneration. Given the fact the cutthroat competition ahead among Indian power producers sooner they embrace

e field of thermal power generation WBPDCL should

d to thermal power generation. Funds are also available from German bank KFW.

e),

to revitalize power industry interest in coal fired plants utilizing ultra supercritical steam conditions. To achieve an economically optimised plant, the cycle conditions under which these plants operate need to be carefully evaluated, taking into account such parameters as the boiler tube design, number of reheats employed, inlet steam conditions and feed water heater arrangements and process control system. The BoA technology represents the highest standard at the moment and the steam generator described above contributes in a decisive manner to the increase of the unit efficiency with the following measures: • Realisation of the high steam parameters of 274 bar / 580 deg C/ 600 deg C. • Realisation of high feed water temperature of 295 deg C. •• The use of Triflux heat exchanger for the heat exchange between SH a

efficiency reducing RH spray. • The use of flue gas heat recovery system for the reduction of flue gas temperat• Minimization of excess air for the firing to 15% as well as the minimization of leakage air flows to the

steam generator in order to keep• Minimization of the auxiliary power requirement of the mills in the total speed range and of the

sensor controlled seals of the air preheaters.

Taking into account the proven technology and comparable investment cost there is no reason why Indian er producers are not taking the advantage of

glatest technology better positioned they are in the business. In fact it is even more important for optimal utilization of national fuel resource, less impact on environment & society, affordable and reliable power supply. Competition among power plant equipment manufacturers will promote the up gradation of technology, engineering and services provided by Indian companies. In 2002, 2x900 MW (279bar/542oC/562oC) coal fired plant was commissioned in Waigaoqiao, China with 43% efficiency. Recently NTPC and APGENCO have decided to leap forward with supercritical technology power plant of 660MW. Being the pioneer in eastern India in thlead the way by adopting latest technology. A policy is needed to go for best available technology and not for least initial investment cost- in the whole life span best available technology will pay off. Failure or non-optimal functioning of all load bearing equipments & automation system will affect the availability, reliability & profitability of the plant. Still German (Siemens) & other European Manufacturers like Alstom & ABB (having strong presence in Germany), Engg. Consultants like Vattenfall Europe Power Consultant holds topmost position in terms of technology & Engg. relateWe should take advantage of latest generation DCS (Distributed Control System) for maximum safety, availability & reliability and Integrated (with DCS) IT Applications required for efficient management of Power Plant which offer virtually everything like Engineering, Project Management (in construction phasDocumentation, Maintenance Management, Inventory Management, Real Time Data Acquisition, On Line Performance Calculation, Optimisation Packages, Production Management and Energy Trading. Siemens and ABB are world leaders in these systems.


A Lignite Fired Unit of 1000mw

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