Rankine cycle and working fluid therefor

• US 6,233,938 B1
• Filed: 03/27/2000
• Issued: 05/22/2001
• Est. Priority Date: 07/14/1998
• Status: Expired due to Fees

• Current Assignee: Helios Energy Technologies, Inc.
• Original Assignee: Helios Energy Technologies, Inc.
• Inventors: Nicodemus, Mark
• Primary Examiner(s): NGUYEN, HOANG M
• Application Number:
  US09/536,494
• Time in Patent Office: 421 Days
• Field of Search: 606/51, 606/71, 606/57
• US Class Current: 60/651
• CPC Class Codes: F01K 25/08 using special vapours

Abstract

Thermal decomposition studies have been performed on methylene chloride at temperatures of 450, 480, 550, 650, 750, and 850° F. After the 550, 650, 750, and 850° F. studies, samples were taken and analyzed for acidic decomposition products of methylene chloride. Qualatative analyses were also done using a gas chromatograph. This report presents the results of the studies. A description of the apparatus and procedures used to obtain the measured data is also included in the report.

Claims

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.

2. A thermodynamic system as defined in claim 1, wherein said working fluid is esentially methylene chloride.

4. A Rankine cycle system as defined in claim 1, wherein said working fluid is esentially methylene chloride.

3. A Rankine cycle system for transferring thermal energy from a fluid heat medium to a working fluid and converting said thermal energy to mechanical energy, said system including a boiler, a turbine, a condenser, and a boiler feedpump, all operatively connected to form a series flowpath for said working fluid;

said boiler being a single-pressure heat recovery boiler with economizer, vaporizer, and superheater sections to transfer thermal energy from said fluid heat medium to said working fluid;

said fluid heat medium moving at a mass flow rate FHM in a first direction through said superheater, vaporizer and economizer sections of said boiler, said fluid heat medium entering said superheater section at a temperature not greater than 1250°

F.;

said working fluid moving at a mass flow rate WF 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, said working fluid being in a sub-critical state through said boiler, and at a pressure not less than 650 psia in said boiler;

the ratio of mass flow rates of said working fluid WF to said fluid heat medium FHM being in the range from 0.50 to >

1;

said boiler and the internal heat transfer surfaces thereof being so configured that the temperature differential between said fluid heat medium and said working fluid is at its minimum where said working fluid enters said economizer section and said fluid heat medium leaves said economizer section;

said working fluid capable of extracting heat from said fluid heat medium to cool said fluid heat medium from above 1000°

F. to below 200°

F.

5. A Rankine cycle system for transferring heat from a heat source to a working fluid, and producing shaft work by expansion of said working fluid in a heat engine, said working fluid being admitted 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;

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;

said system including a recuperative feedheater operatively connected to said engine to recover heat from said working fluid exhausted from said engine.

6. A Rankine cycle system as defined in claim 5, wherein said working fluid is esentially methylene chloride.

7. 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.

8. A method as defined in claim 7, wherein said working fluid is esentially methylene chloride.

9. A process for tansferring heat from the exhaust gas of a gas turbine topping cycle to a working fluid in a bottoming Rankine cycle, including the following steps:

directing said exhaust gas in a first direction successively through superheater, vaporizer, and economizer sections of a boiler at a mass flow rate EG;

directing said working fluid in a second direction, counter to said first direction, successively through said economizer, vaporizer, and superheater sections of said boiler at a mass flow rate WF;

the ratio of said mass flow rate WF of said working fluid to said 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 being theoretically capable, in an ideal isentropic expansion process, of yielding a total enthalpy drop of at least 70% of the available energy of said exhaust gas as determined by second-law analysis.

10. A process as defined in claim 9, wherein said working fluid is essentially methylene chloride.

11. A process as defined in claim 10, wherein:

said exhaust gas enters said superheater section at a temperature not greater than 1250°

F.;

said working fluid is in a sub-critical state through said boiler, and at a pressure not less than 650 psia in said boiler;

whereby said working fluid is effective to extract heat from exhaust gas to cool said exhaust gas from above 1000°

F. to below 200°

F.