Analysis of Captive Cogeneration Power Plant Upset ... · PDF fileTechniques# Machinery###...

Analysis of Captive Cogeneration Power Plant Upset Scenarios using Dynamic Simulation

Software By : Arvind Kaushik – Chemical Engineer C Nageswara Rao – Mechanical Engineer Soumya Majumdar – Mechanical Engineer Ramesh Kumar G – Mechanical Engineer

Larsen & Toubro Limited – Hydrocarbon -‐ IC Research & Development -‐ Thermal Powai Works, Mumbai – 400076

India.

About Larsen & Toubro

•  Turnover : US $ 11.7 bn (FY 11

-‐12)

•  Employees: 50,000

•  Ownership: Majority with Public

& Financial InsNtuNons

•  Founded in 1938 by two Danish Engineers.

•  Technology, engineering, construcNon and manufacturing company

•  Ranks Among Top 5 Companies in India’s Private Sector.

•  Professionally Managed since IncepNon.

•  Successful Track Record in Oil & Gas, Refinery, Power, Petrochemicals, Cement & Infrastructure.

•  Network of Offices Worldwide.

•  State-‐of-‐the-‐art Manufacturing FaciliNes in India and Oman .

2

OCEAN ENGG.

Reforming & syngas related Processes

Hydrogen, Ammonia & Methanol

Gas Processing

SeparaUon Process

Well head & Process plaVorms

Water Treatment

DesalinaUon

-‐ RO -‐ Thermal

STP / ETP

Recycling

CHEMICAL ENGG.

WATER TECHNOLOGIES

Fired Heaters

Modular Systems

Super CriUcal Boilers

Power plant SimulaUon

CFD

THERMAL ENGG.

MECHANICAL ENGG.

MATL. SCI. & CORROSION

Stress Analysis

Structural Analysis

Piping Analysis

Experi-‐ mental Techniques

Machinery & System Design

Machinery / Structural DiagnosUcs

Rotor Dynamics & Tribology

ROTATING MACHINERY

Equip. Metallurgy

Cathodic ProtecUon

Residual Life Assessment

Composites Failure Analysis Corrosion Control)

Research & Development, Hydrocarbon IC

4

1. Study the effects of load disturbances on the system.

2. Study the effects of any one equipment trip or mulNple equipment trip . The trips could be isolated events or cascade.

3. To define, design and refine the operaNons / control philosophy, system and mechanism of a given power plant / system.

4. To test the plant operaNon under various modes of operaNon.

5. Tuning and adjustment of controller parameters.

6. Off-‐line training of plant operators.

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1. Modular approach to mathemaNcal modeling of power plants.

2. One or more modules represents one equipment (e.g. boiler, turbine, valve, pipe, pump, duct , fan, motor, transformer, generator, etc., )

3. The plant/system model is created by interconnecNng modules through ports.

4. An MMS model is processed through automated steps that produce a simulaNon executable.

5. Programming languages – ACSL, Fortran and Visual C++.

6. Library of various modules – Electrical, Mechanical, BoP and Controls.

Features of Modular Modeling System (MMS) Soiware

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1. Choice of integraNon algorithms such as Euler, Runge–kuja, Gear, Adam-‐Smith etc.,

2. AutomaNc sorNng and sequencing of differenNal equaNons for soluNon.

3. User needs to have understanding of ACSL, to build and execute models.

4. Knowledge of Visual C++ required if one needs to develop new modules.

5.In-‐built simplified property rouNnes for water, air, and fuels etc,

6. Vendor – nHance Technologies , US.

Features of MMS soiware – Contd.

7

1. Steady state heat balance diagram.

2. P&I diagram.

3. G.A. drawings.

4. Equipment specificaNon sheets (Pumps, Control valves, HX, etc).

5. Control system logic diagrams and descripNon.

6. OperaNon and control philosophy.

7. Start-‐up sequence.

8. Shut down sequence.

Dynamic Model PreparaNon – Data Required.

8

Modeling Sequence

Define the System

Boundaries and gather equipment

data

Generate model of

each equipment

and test

Link the equipment modules

Execution and

achieving the steady

state operation

Controller tunings

Generate upset

conditions Get results and analyze

Tie to a training

simulator, if desired

9

5 nos. Boilers – Thermax.

4 nos. Steam turbines; Triveni – 11.8 MWe base load; Condensing

4 nos. Generators – 11 kVA .

5 nos. deaerators.

5 no. boiler feed water pumps along with drive turbines

3 nos. power fluid pumps and 3 nos. injecNon water pumps

BOP (PRDS; De-‐aerators, Pipes, Pumps, Valves, condenser, FD fans, etc)

Transformers, Electrical network bus, Electrical motors, etc.

Major Equipment Modeled

LC

LC

PC

PC

PC PC

Boiler 1 Boiler 2 Boiler 3 Boiler 4 Boiler 5

STG 2 STG 4

PC

PC

PC

HP STEAM HEADER

MP STEAM HEADER

MP CONDENSATE HEADER

STG 1

ProducNon Heaters InjecNon

Heaters Offspec Oil / Skim Oil Heaters

Tank / Vessel Heaters

MP CONDENSATE FLASH DRUM

LP CONDENSATE FLASH DRUM

InjecUon Water Pump Turbines Power Fluid Pump Turbines Boiler Feed Water Pump Turbines

D D D D D D

S

ATM

ATM

ATM

Deaerators UNlity StaNons

600 psig & 700F 41.4 barg & 371°C

100 psig & 338F 6.9 barg & 180°C

7.2 psig & 234F 0.5 barg & 112°C

D D D D D PC D

S ATM

S ATM ATM

S ATM S S

ATM

STG 3

ATM

FC LC

To Deaerator To Deaerator To Deaerator To Deaerator

To BFW Pump To BFW Pump To BFW Pump To BFW Pump

To Boiler 2 To Boiler 3 To Boiler 4 To Boiler 5

BFW Makeup Tank Demineralised

Water Make-‐Up

N2 Blanket

LC Deaerator

ATM

43 psig & 304F 3 barg & 173°C

Thumbli Water Wells

Filter Package

DesalinaNon Package Condensate

Polishing Package

SCHEMATIC DIAGRAM: STEAM AND POWER GENERATION SYSTEM

AcNvated Carbon Filter Package Treated Condensate Storage

Tank

N2 Blanket

LP STEAM HEADER

LP CONDENSATE

ACC

ACC

LEGEND

STG Steam Turbine Generator

LP Low Pressure

MP Medium Pressure

HP High Pressure

ACC Air Cooled Condenser

ATM Atmospheric

PC Pressure Control

LC Level Control

FC Flow Control

D S

Desuperheater

Silencer

ACC

LC

LC

ACC ACC ACC

ATM ATM ATM

ATM LC LC LC

G1 G2 G3 G4

SB1 SB2 SB3 SB4 SB5 SB6

Well Pads Well Pads OperaNons Base

M1 M2

M3 M4

M5 M6

M7 M8

M9 M10

M11 M13 M12 M14

6.6 kV Motors

EM8 EM1

6.6 kV Emergency Motors/Loads

SB7 SB8 SB9 SB10 SB11 SB12 SB13 SB14

EM2 EM3

EM4 EM5

EM6 EM7 EM9

EM10 EM11

EM12 EM13

EM14 EM15

6.6 kV Bus

33 kV Bus

11 kV Bus B

6.6 kV Emergency Bus

11 /0.433 kV 11 /6.9 kV

SS SS

11 /6.9 kV

11 /6.9 kV 11 /6.9 kV

11 /35 kV 11 /35 kV

6.6 /0.433 kV

415 V Split Bus

415 V Split Bus

GENERATORS; 15 MVA,

12 MW, 11 kV, 3φ, 50 Hz 11 kV Bus A 11 kV Bus C

Plant Configuration (Electrical System)

TRANSFORMERS

EG1 EG2 EG3

EMERGENCY DIESEL GENERATORS

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Control Systems Implemented

•  UUlity Boilers

–  Three-‐element / single element drum level control based

on steam drum level, Steam flow rate and the Feed water

flow rate.

–  Firing rate control based on HP header pressure.

–  Air fuel raNo control by FD fans

–  Temperature control of steam by desuperheaNng

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Control Systems implemented (Contd.)

•  Steam Turbines

–  Turbine Governor Model (vendor’s Controller Block

Diagram and Transfer FuncNon Diagram)

– Mechanical Power output, MW.

•  Generators

–  AutomaNc Voltage Regulator (AVR) vendor’s Transfer

FuncNon Diagram

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Control System implemented (contd..)

•  De-‐aerator

•  Pressure & Level •  Steam turbine drives for pumps

•  BFW pump rpm is controlled based on steam flow

•  Discharge pressure of power fluid pump is maintained @

203.91 bar) by controlling steam flow to the PF pump drive

turbine.

•  InjecNon water pump discharge pressure is maintained at

121.02 barg •  Soh starter for start-‐up of the power fluid pump motor

Work Procedure Step 1 -‐ Data Gathering

•  Process flow diagrams, Heat Balance diagram and P&I diagram.

•  Equipment specificaNons, physical and Geometric Details data •  OperaNng parameters data, allowable metal temperatures.

•  Control Valves, controllers specificaNons, and •  Control system logic descripNon.

Step 2 -‐ Data Input to Modules and Individual Module TesUng •  Fuel System

•  Boilers complete with the Boiler feed pumps, economizer, superheater FD fans etc.,

•  Steam Turbines with Condensers

•  Generators •  Heavy Duty Pumps with motors, •  Heat Exchangers, InterconnecNng Pipes Valves etc.,

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Work Procedure (Contd.)

Step 3 – InterconnecUng the Modules and System TesUng •  Preliminary runs of the model to test the operaNon performance.

•  Achieving trouble-‐free steady state operaNon of the plant matching with heat balance diagram.

Step 4 – Modeling disturbances, study and analyze their effects. •  One Boiler trips. •  One steam turbine trips.

•  One steam turbine driven power fluid pump trips. •  One electric motor power fluid pump trips.

•  One boiler feed water pump trips.

•  Fuel change-‐over from Fuel gas to Diesel.

•  Plant Start-‐Up.

Step 5 – Suggest remedial acUon, if any. 16

Different Modes of Operation of Steam Turbines Modeled in the Project.

 MODE -‐ A : 1 ST in Isochronous Mode and 3 STs in Droop Mode with Remote AutomaNc Set Point Change.

 MODE -‐ B : 1 ST in Isochronous Mode and 3 STs in Droop Mode.

 MODE -‐ C : All four STs in Droop Mode.

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Note: This presentaUon gives results for all STs operaUng in MODE C

Features Considered for Modeling All Upset Conditions

 All five boilers operaNng with HP Steam Header Pressure control on fuel firing in steady state.

  All four steam turbines operaNng in DROOP Mode.

  Steam Turbine Governor Model implemented as given by the Vendor (Triveni).

 AutomaNc Voltage Regulator (AVR) implemented as given by Vendor (ABB).

 Soi Starter modeled for start-‐up of Power Fluid Pump Motor.

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Operating Parameter Trends When One Out Of Five Boilers Trips

Case of Steam Load Shedding To Maintain Plant Frequency

1 Boiler Trip Case Results 19

Upset Condition – One Boiler Trip

  Steam supply lost due to the boiler trip = 110 TPH.

  Steam deficiency will be met by remaining four Boilers

ramping up @ ~30 tph/min.

  Steam supply to one InjecNon Water Pump Turbine is

stopped .

 MP steam header pressure drops.

  Flow through the HP to MP steam PRDS will increase to

maintain MP steam header pressure. 20 1 Boiler Trip Case Results

List of Control Actions – One Boiler Trip

  IsolaNng Boiler steam line from HP steam Header.

  Switching off Fuel supply to the tripped Boiler.

  Closing the Boiler Feed water valve.

  ConNnue 1 BFW Pump of tripped boiler in a minimum recycle mode.

  FD Fan of the tripped boiler conNnues to operate at a reduced load.

  IsolaNng boiler blow-‐down valve.

  IsolaNng Boiler from BFW distribuNon Header.

  To maintain plant frequency, steam load shedding is done by stopping one InjecNon water pump turbine drive and corresponding pump within a duraNon of 2 seconds of trip of the boiler.

  Closing the XSVs on sucNon line to the turbine driven InjecNon Water pump .

  No Electrical load shedding is required to be considered in this case 21 1 Boiler Trip Case Results

Effect on other operating boilers parameters- Flow (-------) kg/s, Pressure (-------) Pa, Temperature (-------) oC.

1 Boiler Trip Case Results

 With drop in HP Steam Header pressure the remaining 4 Boilers Ramp by approx. 30 TPH/min

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Effect on MP steam header pressure & steam Plow through the PRDS.


 Flow through HP to MP PRDS increases to maintain the MP Steam Header Pressure.

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Effect on steam Plow (---) kg/s and Power (----) MW of one boiler trip.

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Effect on Plant Frequency, Hz

 Plant frequency is maintained within acceptable limits (> 49).

 The drop is due to the fall in HP Steam Pressure

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Observations – One Boiler Trip

 Due to a sudden shorvall of 110 tph steam the HP header pressure falls sharply from 43 barg to 33-‐34 barg.

  It takes around 10 minutes for the HP header pressure to stabilize at a new value of 34 barg.

 To stabilize the HP steam header pressure:   Remaining 4 boilers are ramped-‐up to their maximum capacity   InjecNon Water Turbine driven Pump is tripped aier 2 seconds.

 HP Steam header pressure stabilizes at 34 bar.

 Plant Frequency is maintained within acceptable limits so that there is no need for the load shedding.

26 1 Boiler Trip Case Results

1 Steam Turbine Trip Results

Operating Parameter Trends When One Out Of Four Steam Turbines Trips

Case of Electrical Load Shedding To Maintain Plant Frequency

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Upset Condition – One ST Trip

  Power Lost from Steam Turbine = 8.67 MW

  The remaining 3 operaNng STGs ramp up to compensate for the power loss due to 1 Steam turbine trip.

  To maintain plant frequency, electrical load shedding is done.

28 1 Steam Turbine Trip Results

List of Control Actions – One ST Trip

-‐  IsolaNng the tripped Steam Turbine from the HP steam Header.

-‐  IsolaNng the Generator connected to the tripped Turbine from the connected 11 kV Bus.

-‐  Total electrical load shedding of 5.171 MW is considered to keep frequency within a range of 48.5 to 51.5 Hz by tripping one motor driven IW pump and one export oil pump.


Effect on 11 kV Bus Voltage, kV


 11 kV Bus voltage dips to a minimum 8.98 kV.

 DuraNon of voltage dip below 9.9 kV is 0.8 s.

 Thereaier the 11 kV Bus Voltage stabilizes within 40 seconds.

30

Fig.1 Total Plant Power MW

Effect on Plant Frequency, Hz

 The plant stability is achieved by ramping remaining STs to 11.22 MW & shedding 5.17 MW load aier a Nme interval of 0.5 s.

 If the electrical load shedding of 3.8 MW is done by tripping only one Motor Driven IW Pump then the frequency drops to 48 Hz.

Min. Frequency is 48.54 Hz.



Effect on operating boilers parameters- Steam Flow (-------) kg/s, Pressure (-------) Pa, Temperature (-------)

oC.

32

Boiler 1 Drum level (----) m, Feedwater Plow (----) kg/s & Steam generation (-----) kg/s

1 Steam Turbine Trip Results 33


  Tripping of ST results in short-‐fall of 8.67 MW of power. The plant stability is achieved by ramping remaining STs to 11.22 MW & shedding 5.17 MW of electrical load within a Nme interval of 0.5 s.

  The maximum drop in frequency is up to 48.54 Hz.

  If Electrical Load Shedding of 3.8 MW is done by tripping only one Motor Driven InjecNon Water Pump then the maximum drop in frequency is upto 48 Hz.

  Immediately aier the trip due to sudden loss of power generaNon the 11 kV Bus voltage dips to a minimum value of 8.98 kV and the voltage dip is for a total duraNon of 0.8 s.

  Thereaier the 11 kV Bus Voltage recovers back to 11 kV and stabilizes within 40 seconds.

Observations – One ST Trip

34

Operating Parameter Trends When Steam Driven PF Pump Trips

Case of Additional of Electrical Load

1 Boiler Trip Case Results 35

Upset Conditions - Steam Driven PF Pump Trips

  Auto start of 1 Motor driven PF Pump aier the turbine driven pump trips.

  Power GeneraNon from the steam turbines ramp-‐up to make up for the addiNonal electrical load of 4.583 MW to the Plant.

  Soi Starter is modeled for the start up of motor driven PF Pumps having an iniNal voltage of 0.3 Nmes of the full voltage and a voltage ramp rate to achieve the full voltage within 20 seconds.


List of Control Actions - Steam Driven PF Pump Trips

-‐  Tripping one Power Fluid Pump Turbine Drive.

-‐  IsolaNng PF Pump Turbine Drive from HP Steam Header.

-‐  Closing XSV on sucNon line of PFP.

-‐  Opening XSV on sucNon line to motor driven PFP.

-‐  Switching on the motor for the PFP by closing the Breaker connecNng it to the 6.6 kV Bus.

-‐  No Electrical Load Shedding is considered in this case.


Fig.2 11 kV Bus Voltage, kV

Fig.1 Plant Frequency, Hz

Results for 1 PFP Changeover from Turbine Drive to Motor Drive

 11 kV Bus Voltage drops to a minimum of 10.24 kV, 11.7 s aier the changeover.

 At the instant the motor achieves its full speed, 11 kV Bus Voltage goes up to 15.7 kV.

 Voltage stabilizes within 90 s.

  The minimum Plant frequency is 48.38 Hz.

 The dip in plant frequency below 48.5 Hz is for 4 s.

 Plant Frequency stabilizes at a lower value of 49.79 Hz.

Fig.3 HP Steam Header Pressure, Pa

Fig.4 MP Steam Header Pressure & PRDS Flow


 Due to a sudden reducNon in HP steam consumpNon HP steam header pressure rises to 43.6 bar.

 Sudden Loss of 61 TPH of HP Steam results in MP Steam Header pressure drop.

 57.6 TPH of HP Steam is diverted through the HP to MP Header PRDS to maintain MP Steam Header Pressure.


Fig.6 Total Electrical Load, MW

 Corresponding to 11 kV bus voltage reaching a peak of 15.7 kV the total electrical load also reaches a peak of 55 MW resulNng in the plant frequency dipping to a minimum of 48.38 Hz.

 Increase in Electrical Load corresponding to the addiNon of PF Pump Motor of 4.583 MW.

 The motor achieves full speed within 28 seconds.

 At the same instant the motor torque and the motor current drops rapidly, hence, the voltage goes up to a maximum of 15.7 kV.

Fig.5 PFP Motor Parameters

  11 kV Bus Voltage drops to and reaches a minimum of 10.24 kV 11.7 s aier the changeover.

  At the instant the motor achieves its full speed, 11 kV Bus Voltage going up to a maximum of 15.7 kV.

  The 11 kV bus voltage exceeds 12.1 kV in a single peak for a total duraNon of 3.5 s. Thereaier the 11 kV bus voltage is stable.

  Total electrical load also reaches a peak of 55 MW resulNng in the plant frequency dipping to a minimum of 48.38 Hz.

  The dip in plant frequency below 48.5 Hz is for 4 seconds.

  HP steam header pressure peaks to a maximum of 43.6 bar and this results in immediate reducNon in steam output from the boilers to bring the HP header pressure back to 42.5 bar.

  Aier the PFP changeover is complete the plant frequency stabilizes at a lower value of 49.79.

  This phenomenon is as per reducNon in turbine speed with increase in load as per Droop curve.

Observations - Steam Driven PF Pump Trips


  It is significant to note that steam load shedding is required during one boiler trip, whereas electrical load shedding is necessitated by the Steam Turbine trip.

  MMS soiware from nHance Technologies Inc., is a robust, convenient and powerful tool available to the Power Plant equipment and control systems designers and analysts to predict performance of a given power plant to meet a given duty.

  The power plant thermal and electrical systems and the associated downstream plants can be designed for all conNngencies with the performance predicNons available by using the MMS Soiware.

Conclusions

42

  A complete thermal and electrical systems modeling was done using MMS Soiware from nHance Technologies Inc. for the 48 MWe thermal power plant.

  Significant insights were gained about the power plant operaNon in island mode and the effect of various disturbances (i.e. equipment trips)

  Although the study was carried out for a large number of cases such different operaNng loads during years 2, 4 and 6 of operaNon, start-‐up of the plant and the fuel change over etc. and with various turbine governor operaNng modes, this presentaNon is for two trips cases for year 6 (full load) operaNon.

Contd.

Conclusions

43

Author ProPiles

Mr. Arvind Kaushik is a post graduate (M.Tech) Chemical Engineer from Indian InsNtute of Technology (IIT) Kanpur, India, since 1990. He has wide experience of over 23 years in the design of thermal equipment, process opNmizaNon, energy conservaNon in process plants, dynamic simulaNon of process and power plants, commissioning and trouble-‐shooNng in India and overseas. At present, as Sr. Dy. General Manager (R&D) at Larsen & Toubro Limited, Mumbai, India, he is leading a team of Mechanical and Chemical Engineers in the Thermal Engineering Group of Research & Development for innovaNons in design of waste heat recovery equipment. His areas of interest include solar thermal energy, low temperature thermal desalinaNon, thermal energy storage systems, dynamic simulaNon of power plants, energy opNmizaNon of industrial processes and commissioning and trouble-‐shooNng of process equipment. E-‐mail: [email protected]

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Author ProPiles (Contd.)

Mr. C. Nageswara Rao completed his Masters in Design & ProducNon of Thermal Power Equipment from NaNonal InsNtute of Technology, Trichy in 2004 and has since been working with R&D-‐Hydrocarbon IC of Larsen & Toubro. His work experience is in the areas of thermal design of Fired Heaters, Shell & Tube, Air-‐Cooled exchangers, Waste Heat Recovery Coils. He has also used CFD tools for criNcal troubleshooNng acNviNes and has carried out Dynamic SimulaNon studies of two capNve power plants. His other interests include design of specialized heat recovery equipment and energy efficiency of power plants. E-‐mail: [email protected]

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Mr. Soumya Majumdar is Master of Technology in Mechanical Engineering (specializaNon in Fluid Mechanics & Thermal Science) from IIT Kanpur in 2004. At present he is working as a Manager in Thermal Engineering group of Research & Development -‐ Hydrocarbon Division at Larsen & Toubro Limited, Mumbai, India. Mr. Majumdar has worked in the areas related to the thermal design, analysis and troubleshooNng of heat transfer equipment such as Shell & Tube Heat Exchangers, Air Cooled Heat Exchangers, Waste Heat Recovery Coils and Waste Heat Recovery Boilers for various Hydrocarbon projects. He has also worked in the area of thermo-‐hydraulic design of regeneraNve type pebble-‐bed and cored-‐brick bed heaters. His varied work experience and field of interest also includes Dynamic SimulaNon of Power Plants and Process Gas Compression modules. E-‐mail: [email protected]

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Mr. Gajam Ramesh kumar earned his Masters in Thermal Engineering from NaNonal InsNtute of Technology, Warangal. He did his thesis work on “ReacNve Flow Field Analysis using CFD” at Defense Research & Development Laboratory (DRDL), Hyderabad. At present he is working at the Research and Development Department (PRDH) of Larsen & Toubro Limited, Mumbai (India). The areas of his experNse are dynamic simulaNon of power plants, thermal design / analysis / trouble shooNng of heat transfer equipment such as S&T, ACHE, PFHE, WHR coils etc and other special heat transfer and fluid flow studies. E-‐mail: [email protected]

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Analysis of Captive Cogeneration Power Plant Upset ... · PDF fileTechniques# Machinery###...

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