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, vaporizer, and superheater sections to transfer heat from said exhaust gas to said working fluid; means to convey said exhaust gas at a mass flow rate EG in a first direction through said superheater, vaporizer, and economizer sections of said boiler; means to convey said working fluid at a mass flow rate WF along said working fluid path, in a second direction counter to said first direction, through said economizer, vaporizer, and superheater sections of said boiler to thereby heat, vaporize, and superheat said working fluid in said respective sections; a heat engine to expand said vaporized and superheated working fluid to thereby 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; 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 EG of said exhaust gas being in the range from 0.50 to >1; the temperature differential between said exhaust gas and said working fluid being at its minimum where said working fluid enters said economizer section and said exhaust gas leaves said economizer section; said working fluid having unique thermophysical properties such that upon leaving said boiler it is theoretically capable, in an ideal, constant entropy expansion process, of yielding a total isentropic enthalpy drop of at least 70% of the available energy of said exhaust gas as determined by second-law analysis.

Claim 10

A method of producing shaft work in a heat engine operating in a Rankine cycle, including the following steps: transferring heat from a fluid heat source to a working fluid to vaporize and superheat said working fluid; admitting said working fluid to said engine at an inlet pressure between 650 psia and 900 psia, at an inlet temperature below 850° F., and in a sub-critical state; expanding said working fluid in said engine to convert thermal energy of said working fluid to mechanical energy; and exhausting said expanded working fluid from said engine to a recuperative feedheater to recover thermal energy from said exhausted working fluid; said working fluid having thermophysical properties such that, in a hypothetical ideal, frictionless, and adiabatic expansion through said engine, said fluid exhausting to pressure corresponding to saturation at dead state temperature is theoretically capable of total isentropic enthalpy drop of at least 70% of the available energy of said heat source as determined by second law analysis.

Claim 11

A method of producing shaft work in a heat engine operating in a Rankine cycle, including the following steps: transferring heat from a fluid heat source to a working fluid to vaporize and superheat said working fluid; admitting said working fluid to said engine at an inlet pressure between 650 psia and 900 psia, at an inlet temperature below 850° F., and in a sub-critical state; expanding said working fluid in said engine to convert thermal energy of said working fluid to mechanical energy; and exhausting said expanded working fluid from said engine to a recuperative feedheater to recover thermal energy from said exhausted working fluid; said working fluid having thermophysical properties such that, in a hypothetical ideal, frictionless, and adiabatic expansion through said engine, said fluid exhausting to pressure corresponding to saturation at dead state temperature is theoretically capable of total isentropic enthalpy drop of at least 70% of the available energy of said heat source as determined by second law analysis.