Application Center - Maplesoft

# Thermal Efficiency of the Combined (Binary) Cycle

You can switch back to the summary page by clicking here.

Thermal Efficiency of the combined (binary) cycle

Author: Valery Ochkov (http://twt.mpei.ac.ru/ochkov/v_ochkov.htm)

Introduction

The figure shows the scheme of a simplest ideal combined (binary) cycle, i.e. steam turbine (6-7) cycle with use of superheated water steam. At this plant the boiler (6-9) burner is replaced with gas turbine unit (Brayton cycle: 1-4) equipped with air compressor (1-2), combustion chamber (2-3), gas turbine (3-4) and one more electric generator.

 >

Calculations

Steam turbine cycle

Input data:

 >

Specific entropy of fresh (live) steam (the turbine inlet):

 >

Specific enthalpy of fresh (live) steam (the turbine inlet):

 >

Outlet steam specific entropy from the turbine (an ideal process of the steam extension)

 >

Dryness of steam in outlet of the turbine:

 >

Outlet wet steam temperature from the turbine

 >

Outlet wet steam specific enthalpy from of the  turbine:

 >

Specific work of steam in the turbine:

 >

Specific enthalpy of water at saturated line at temperature in the condenser

 >

Specific entropy of water at saturated line at temperature in the condenser

 >

Specific enthalpy of condensate

 >

Pressure of feed water

 >

Specific entropy of feed water (an ideal process in the pump):

 >

Temperature of feed water:

 >

Specific enthalpy of feed water:

 >

Specific useful work of the feed pump:

 >

Specific heat supplied to the boiler:

 >

Hence the thermal efficiency of the steam turbine cycle:

 >

Gas turbine cycle

Input data:

 >

Specific enthalpy of fresh air

 >

Specific entropy of fresh air

 >

Outlet air specific entropy, temperature and spacific enthalpy from the compessor

 >
 >

 >

Inlet gas pressure, specific entropy and specific enthalpy to  the gas turbine

 >
 >

 >

Outlet gas pressure, specific entropy, temperature and specific enthalpy from the gas turbine

 >
 >
 >

 >

Specific heat supplied to the combustion chamber:

 >

Specific work of the gas turbine

 >

Specific work of the air compressor

 >

Hence the thermal efficiency of the gas turbine cycle:

 >

Combined (binary) cycle

Outlet gas pressure and specific enthalpy from the steam boiler

 >
 >

Ratio of gas and steam mass flow

 >

Specific heat supplied to the combustion chamber:

 >

Specific work of the gas turbine cycle

 >

Specific work of the steam turbine cycle

 >

Hence the thermal efficiency of the Combined (binary) cycle is higher than separate steam or gas turbine cycles:

 >

 >