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Thermodynamic Study of Multi Pressure HRSG in Gas/Steam Combined Cycle Power Plant

  • Meeta SharmaEmail author
  • Onkar Singh
Original Contribution

Abstract

Combined cycle power plants have a combination of gas based topping cycle and steam based bottoming cycle through the use of Heat Recovery Steam Generator (HRSG). These HRSG may be either of single pressure (SP) or dual pressure (DP) or multiple pressure type. Here in this study thermodynamic analysis is carried out for optimal performance of HRSG using different types of HRSG layout for combined cycle efficiency improvement. Performance of single pressure HRSG and dual pressure HRSG, utilized in gas/steam combined cycle is analyzed and presented here. In comparison to single pressure, dual pressure HRSG offers 10 to 15% higher reduction in stack temperature due to greater heat recovery and thus improved plant efficiency.

Keywords

Combined cycle Gas turbine HRSG Ambient temperature Pinch point Approach point 

Notations

CCPP

Combined cycle power plant

Cpa

Specific heat of flue air, kJ/kg K

Cpg

Specific heat of exhaust gases, kJ/kg K

DP

Duel pressure

hlf

Heat losses (percentage of total heat available at HRSG inlet)

HRSG

Heat recovery steam generator

ma

Mass flow rate of air used in combustion chamber, kg/s

mf

Mass flow rate fuel used in combustion chamber, kg/s

mg

Mass flow rate of exhaust gases, kg/s

mw

Mass flow rate of feed water in the HRSG, kg/s

NTPC

National Thermal Power Corporation, Limited (NTPC, Ltd)

p

Pressure for steam generation, bar

Qadd

Heat added to the combustion chamber in gas turbine cycle, kJ

Qav

Net heat available at HRSG inlet, kJ

Qcond

Heat rejected in condenser, kJ

rp

Gas turbine pressure ratio

SP

Single pressure

T1

Ambient air temperature at compressor entry, K

T1wHP

Temperature of water at economizer inlet (high pressure)

T1wLP

Temperature of water at economizer inlet (low pressure)

T2wHP

Temperature of water at economizer outlet (high pressure)

T2wLP

Temperature of water at economizer outlet (low pressure)

Tap

Approach point temperature at various point in HRSG

Tg

Gas temperature at various point in HRSG, K

TIT

Turbine inlet temperature, K

Tpp

Pinch point temperature at various point in HRSG, K

Wgt

Gas turbine power output, kW

Wp

Pump work in bottoming cycle, kW

Wst (net)

Net power output by bottoming cycle, kW

Wst

Power output of the steam turbine, kW

ηc

Polytropic efficiency of air compressor

ηcc

Efficiency of combined cycle

ηm

Mechanical efficiency of compressor

ηst

Efficiency of steam turbine

ηt

Polytropic efficiency of gas turbine

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Copyright information

© The Institution of Engineers (India) 2018

Authors and Affiliations

  1. 1.Mechanical Engineering DepartmentAmity UniversityNoidaIndia
  2. 2.Madan Mohan Malaviya University of TechnologyGorakhpurIndia

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