Rankine cycle and working fluid therefor

Claim 1

A combined cycle thermodynamic system for transferring heat from the exhaust gas of a gas turbine topping cycle to a working fluid, and converting said heat to mechanical energy in a bottoming Rankine cycle, said system including, in a closed cycle forming a working fluid path: a boiler with economizer and vaporizer sections to transfer heat from said exhaust gas to said working fluid; means to convey said exhaust gas at a mass flow rate FHM in a first direction through said vaporizer and economizer sections of said boiler; means to convey said working fluid at a mass flow rate WF along said working fluid path, counter to said first direction, through said economizer and vaporizer sections of said boiler to heat said working fluid in said economizer section and vaporize said working fluid in said vaporizer section; a heat engine to expand said vaporized working fluid and convert thermal energy thereof to mechanical energy; a condenser to condense said working fluid; a condensate pump to recirculate said condensed working fluid back to said boiler; an open deaerating heater disposed to receive working fluid condensate from said condenser, a heat exchanger disposed to receive said working fluid from said deaerating heater and working fluid condensate from said condenser en route to said deaerating heater, and a boiler feed pump disposed to receive working fluid from said heat exchanger and return it to said boiler, whereby working fluid intake to said boiler feed pump is deaerated and subcooled liquid; a recuperative feed heater disposed between said engine and said condenser to receive working fluid exhaust vapor from said engine, and to receive liquid working fluid from said boiler feed pump en route to said boiler; the ratio of mass flow rate WF of said working fluid to mass flow rate FHM of said exhaust gas being in the range from 0.5 to >1, whereby the temperature differential between said exhaust gas and said working fluid is at minimum where said working fluid enters said economizer section and said exhaust gas leaves said economizer section; said working fluid possessing peculiar thermophysical properties such that upon leaving said boiler it is thermodynamically capable, in an ideal isentropic expansion process, of yielding a total isentropic enthalpy drop of 75% or more of the available energy of said fluid heat medium as determined by second-law analysis.