Calculation of thermal efficiency of combined- cycle plant Author: Valery Ochkov ([email protected]), Aung Thu Ya Tun ([email protected]), Moscow Power Engineering Institute (MPEI) Start > > > > Steam turbine cycle Input data: > (2.1) > (2.2) > (2.3) Specific entropy of live steam (the turbine inlet): > Specific enthalpy of 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: > (2.4) Outlet wet steam temperature from the turbine > (2.5) Outlet wet steam specific enthalpy from of the turbine: > (2.6) Specific work of steam in the turbine: > (2.7) Specific enthalpy of water at saturated line at temperature in the condenser > (2.8) Specific entropy of water at saturated line at temperature in the condenser > (2.9) Specific enthalpy of condensate > Pressure of feed water > Specific entropy of feed water (an ideal process in the pump): > Temperature of feed water: > (2.10) Specific enthalpy of feed water: > (2.11) > Specific useful work of the feed pump: > (2.12) Specific heat supplied to the boiler: > (2.13) Hence the thermal efficiency of the steam turbine cycle: > (2.14) Gas turbine cycle Input data: > > > > > Specific enthalpy of air entering the compressor: > (3.1) Specific entropy of air entering the compressor: > (3.2) Specific entropy of air at compressor outlet: > The air temperature at the outlet of the compressor: > (3.3) Specific enthalpy of air at compressor outlet: > (3.4) Inlet gas pressure, specific entropy and specific enthalpy to the gas turbine > Specific entropy of gas at the entrance to GTP: > > (3.5) Specific enthalpy of gas at the entrance to GTP: > (3.6) The gas pressure at the exit of the gas turbine: > Specific entropy of gas at the exit of the gas turbine: > The gas temperature at the exit of the gas turbine: > (3.7) Specific enthalpy of gas leaving the gas turbine: > (3.8) Specific heat supplied to the combustion chamber: > (3.9) Specific work of the gas turbine > (3.10) Specific work of the air compressor > (3.11) Thermal efficiency of cycle gas turbine: > (3.12) Combined (binary) cycle Outlet gas pressure and specific enthalpy from the steam boiler > Specific enthalpy of gas at the outlet of the recovery boiler: > (4.1) > > (3.5) (4.1) Ratio of gas and steam mass flow > (4.2) Specific heat supplied to the combustion chamber: > (4.3) Specific work of the gas turbine cycle > (4.4) Specific work of the steam turbine cycle > (4.5) Hence the thermal efficiency of the combined (binary) cycle is higher than separate steam or gas turbine cycles: > (4.6).