Thermal power cycle

Abstract

One embodiment of an improved thermal power cycle comprising a wet binary motive fluid, pump (21), evaporator (22), expander (23), and condenser (24). Using a binary motive fluid, it can operate efficiently over a lower range of heat source temperatures than the steam Rankine cycle. Using a wet binary motive fluid, it eliminates the need for superheating the fluid in evaporator (22), allows for complete expansion of the fluid in expander (23), and reduces back-pressure by the fluid on expander (23), thereby providing higher efficiency than the ORC (organic Rankine cycle), Eliminating the regenerator that is used by ORC systems results in a simpler, less costly system. Using direct-contact heat exchange in condenser (24) rather than the indirect-contact heat exchange used by ORC systems results in more efficient condensation of the fluid. Using a pump (21) rather than the power-hungry compressor used by ORC systems further reduces power losses and expenses. Accordingly, the improved cycle provides higher overall system efficiency at lower overall system cost. Other embodiments are described and shown.

Claims

1. A method for converting heat into mechanical power comprising: (a) compressing a motive fluid to form a subcooled liquid, the motive fluid being a non-aqueous wet fluid; (b) evaporating a first portion of the subcooled liquid with the heat at subcritical conditions to form a vapor; (c) expanding the vapor to produce mechanical power and a two-phase vapor and liquid mixture, the vapor being expanded approximately isentropically; (d) combining a second portion of the subcooled liquid with the two-phase vapor and liquid mixture to form a combined mixture; (e) condensing the combined mixture to form the motive fluid in step (a); repeating steps (a)-(e); and producing the mechanical power; wherein the motive fluid is an azeotrope.

2. The method of claim 1 wherein the boiling point of the motive fluid at standard atmospheric pressure is no more than 100° C.

3. The method of claim 1 wherein the motive fluid comprises methanol.

4. The method of claim 1 wherein the motive fluid includes a mixture of at least two substances.

5. The method of claim 1 wherein the first portion of the subcooled liquid is evaporated by a heat source having a temperature of no more than 200° C.

6. The method of claim 1 wherein the two-phase vapor and liquid mixture in step (c) is a first two-phase vapor and liquid mixture and wherein step (c) further comprises: reheating the first two-phase vapor and liquid mixture to produce a reheated fluid; and expanding the reheated fluid to produce a second two-phase vapor and liquid mixture; and wherein the two-phase vapor and liquid mixture in step (d) is the second two-phase vapor and liquid mixture.

7. The method of claim 1 wherein the vapor formed by evaporating the subcooled liquid is superheated vapor.

8. The method of claim 1 comprising expanding the vapor in a reaction turbine.

9. The method of claim 8 wherein the reaction turbine is an axial-flow, reaction turbine.

10. The method of claim 1 wherein the subcooled liquid is evaporated in an evaporator, the vapor is expanded in an expander, and the combined mixture is condensed in a condenser.

11. A method for converting heat into mechanical power comprising: (a) compressing a motive fluid to form a subcooled liquid, the motive fluid being a non-aqueous wet fluid; (b) evaporating a first portion of the subcooled liquid with the heat at subcritical conditions to forma saturated motive fluid, the saturated motive fluid being substantially saturated vapor with no superheat; (c) expanding the saturated motive fluid to produce mechanical power and a two-phase vapor and liquid mixture, the saturated motive fluid being expanded approximately isentropically; (d) combining a second portion of the subcooled liquid with the two-phase vapor and liquid mixture to form a combined mixture; (e) condensing the combined mixture to form the motive fluid in step (a); repeating steps (a)-(e); and producing the mechanical power; wherein the motive fluid is an azeotrope.

12. The method of claim 11 wherein the boiling point of the motive fluid at standard atmospheric pressure is no more than 100° C.

13. The method of claim 11 wherein the motive fluid comprises methanol.

14. The method of claim 11 wherein the motive fluid includes a mixture of at least two substances.

15. The method of claim 11 wherein the two-phase vapor and liquid mixture in step (c) is a first two-phase vapor and liquid mixture and wherein step (c) further comprises: reheating the first two-phase vapor and liquid mixture to produce a reheated fluid; and expanding the reheated fluid to produce a second two-phase vapor and liquid mixture; and wherein the two-phase vapor and liquid mixture in step (d) is the second two-phase vapor and liquid mixture.

16. The method of claim 11 comprising expanding the saturated motive fluid in a reaction turbine.

17. The method of claim 16 wherein the reaction turbine is an axial-flow, reaction turbine.

18. The method of claim 11 wherein the subcooled liquid is evaporated in an evaporator, the saturated motive fluid is expanded in an expander, and the combined mixture is condensed in a condenser.

19. The method of claim 18 wherein the motive fluid is compressed by a pump, and wherein the motive fluid moves from the condenser to the pump without passing through a fluid reservoir.

Description

DRAWINGS

(1) FIG. 1 is a schematic of a typical Timlin cycle.

(2) FIG. 2 is a T vs. s diagram of a typical Timlin cycle.

(3) FIG. 3A is a T vs. s diagram of a first embodiment.

(4) FIG. 3B is a version of FIG. 3A with a lower condenser temperature.

(5) FIG. 4A is a T vs. s diagram of a second embodiment.

(6) FIG. 4B is a version of FIG. 4A with a lower condenser temperature.

(7) FIG. 5A is a T vs. s diagram of a third embodiment.

(8) FIG. 5B is a version of FIG. 5A with a lower condenser temperature.

(9) FIG. 5C is a version of FIG. 5B with addition of superheat and reheat.

(10) FIG. 6—PRIOR ART is a T vs. s diagram of a steam Rankine cycle.

(11) FIG. 7—PRIOR ART is a T vs. s diagram of an isopentane organic Rankine cycle.

REFERENCE NUMERALS

(12) 11 Saturated liquid 12 Subcooled liquid 13 Saturated vapor 14 Two-phase vapor and liquid mixture 15 Superheated vapor 16 Supercritical fluid 21 Pump 22 Evaporator 23 Expander 24 Condenser 25 Reheat inlet 26 Direct-contact heat exchange inlet

DETAILED DESCRIPTION

FIGS. 1 and 2—First Embodiment

(13) FIG. 1 is a schematic of a typical Timlin cycle. The states that comprise the cycle are:

(14) 1 Saturated liquid 11

(15) 2 Subcooled liquid 12

(16) 3 Saturated vapor 13

(17) 4 Two-phase vapor and liquid mixture 14

(18) The Timlin cycle also includes the possibility of superheated vapor 15 in state 3.

(19) The processes that comprise the cycle are:

(20) 1 Isentropic compression by pump 21 of saturated liquid 11 to subcooled liquid 12

(21) 2 Isobaric heating by evaporator 22 of subcooled liquid 12 to saturated vapor 13

(22) 3 Isentropic expansion by expander 23 of saturated vapor 13 to two-phase vapor and liquid mixture 14

(23) 4 Isobaric cooling by condenser 24 of two-phase vapor and liquid mixture 14 to saturated liquid 11

(24) The Timlin cycle includes the possibility of process 2 being isobaric heating by evaporator 22 of subcooled liquid 12 to superheated vapor 15.

(25) The Timlin cycle also includes the possibility of process 3 being isentropic expansion by expander 23 of superheated vapor 15 to two-phase vapor and liquid mixture 14.

(26) The Timlin cycle further includes the possibility of process 3 being isentropic expansion by expander 23 of superheated vapor 15 to two-phase vapor and liquid mixture 14, reheating to a dryer condition, and then further isentropic expansion to a wetter and cooler condition at the exhaust of expander 23.

(27) The system components that perform each of the above processes are shown and labeled on FIG. 1. The states of the wet binary motive fluid between the system components and their associated processes are also shown and labeled on FIG. 1. This cycle does not require the costly, inefficient regenerator and compressor that are usually required by ORC systems.

(28) FIG. 2 is a T vs. s diagram of a typical Timlin cycle. As can also be seen from this diagram, the wet binary motive fluid expands isentropically from saturated vapor 13 at the hot source temperature all of the way to two-phase vapor and liquid mixture 14 at the cold sink temperature. This allows exploitation of the entire heat source—sink temperature difference. Since condensation begins in expander 23 and finishes in condenser 24 at low pressure, the wet binary motive fluid, its thermophysical properties, and the Timlin cycle eliminate the expensive, inefficient regenerator and compressor that are usually required by ORC systems.

(29) For this embodiment, I contemplate the wet binary motive fluid being methanol, but other substances will work.

(30) I contemplate pump 21 being a conventional radial-flow, centrifugal pump, as is commonly used in industry to pump liquids, but other types will work.

(31) I contemplate evaporator 22 being a conventional indirect-contact, shell-and-tube heat exchanger, but other types will work.

(32) I contemplate expander 23 being a conventional axial-flow, reaction turbine, with at least one reheat inlet 25 to receive saturated vapor 13 or superheated vapor 15 from evaporator 22, but other types will work. This is often referred to as a pass-in turbine.

(33) I contemplate condenser 24 being based on a conventional shell-and-tube heat exchanger, but other types will work. It will be enhanced on the outside with at least one direct-contact heat exchange inlet 26 to receive subcooled liquid 12 from pump 21. It will be enhanced on the inside with at least one conventional spray, shower, jet or their equivalents for efficient direct-contact heat exchange between the two-phase vapor and liquid mixture 14 from expander 23 and the subcooled liquid 12 from pump 21. An external cooling sink will be available, such as cooling water passing through the tubes, and the shell will contain saturated liquid 11. The cooling water removes heal from condenser 24 by indirect-contact heat exchange then and rejects it to the external cooling sink. In any case, wet binary motive fluid never makes contact with cooling water.

(34) I contemplate fabricating substantially all components, connectors, and pipes from austenitic steel, but other materials will work.

Operation

FIGS. 3A and 3B

(35) In operation in a normal manner the Timlin cycle of embodiment shown in FIG. 3A operates as follows. Pump 21 receives wet binary motive fluid as saturated liquid 11 from condenser 24, compresses saturated liquid 11 to subcooled liquid 12, and delivers subcooled liquid 12 to evaporator 22. Using heat that is externally supplied at 100° C. from the heat source, evaporator 22 heats subcooled liquid 12 to saturated vapor 13, and delivers saturated vapor 13 to expander 23. Expander 23 receives saturated vapor 13, expands saturated vapor 13 isentropically to two-phase vapor and liquid mixture 14, drives an output shaft to deliver mechanical power, and delivers two-phase vapor and liquid mixture 14 to condenser 24.

(36) Using coolant that is externally supplied at 50° C. from the heat sink, condenser 24 receives two-phase vapor and liquid mixture 14 from expander 23 and subcooled liquid 12 from pump 21, mixes them together, and produces a combined saturated liquid 11 condensate. Using coolant that is externally supplied at 50° C. from the heat sink, condenser 24 cools saturated liquid 11 by indirect-contact heat exchange and delivers saturated liquid 11 to pump 21, completing the cycle.

(37) Expander 23 typically delivers mechanical power via an output shaft to turn a generator for electric power production or directly provides mechanical power to a local load. Pump 21 consumes a small amount of the power that is produced by expander 23. In addition to supplying subcooled liquid 12 to evaporator 22, pump 21 returns a portion of subcooled liquid 12 to condenser 24 to provide direct-contact heat exchange within condenser 24.

(38) The embodiment shown in FIG. 3B operates in the same manner as the embodiment shown in FIG. 3A. In addition, the embodiment shown in FIG. 3B uses coolant that is externally supplied to condenser 24 at the lower temperature of 0° C. from the heat sink to produce significantly more power than the embodiment of FIG. 3A.

FIGS. 4A and 4B

Second Embodiment

(39) The embodiment shown in FIG. 4A operates in the same manner as the embodiment shown in FIG. 3A. In addition, the embodiment shown in FIG. 4A uses heat that is externally supplied to evaporator 22 at the higher temperature of 150° C. from the heat source to produce significantly more power than the embodiment of FIG. 3A.

(40) The embodiment shown in FIG. 4B operates in the same manner as the embodiment shown in FIG. 4A. In addition, the embodiment shown in FIG. 4B uses coolant that is externally supplied to condenser 24 at the lower temperature of 0° C. from the heat sink to produce significantly more power than the embodiment of FIG. 4A.

FIGS. 5A, 5B, and 5C

Third Embodiment

(41) The embodiment shown in FIG. 5A operates in the same manner as the embodiment shown in FIG. 4A. In addition, the embodiment shown in FIG. 5A uses heat that is externally supplied to evaporator 22 at the higher temperature of 200° C. from the heat source to produce significantly more power than the embodiment of FIG. 4A.

(42) The embodiment shown in FIG. 5B operates in the same manner as the embodiment shown in FIG. 5A. In addition, the embodiment shown in FIG. 5B uses coolant that is externally supplied to condenser 24 at the lower temperature of 0° C. from the heat sink to produce significantly more power than the embodiment of FIG. 5A.

(43) The embodiment shown in FIG. 5C operates in the same manner as the embodiment shown in FIG. 58. Also, it includes the addition of superheat by delivering superheated vapor 15 from evaporator 22 to expander 23. In addition, it includes the addition of reheat by delivering superheated vapor 15 to expander 23 at reheat inlet 25. The addition of superheat and reheat to this embodiment can be used to reduce and control the wetness of two-phase vapor and liquid mixture 14 within expander 23 and at its exhaust.

ADVANTAGES

(44) From the description above, a number of advantages of some embodiments of my thermal power cycle become apparent: (a) use of wet binary motive fluids allows for expansion from the heat source temperature to the heat sink temperature, maximizing power production and efficiency, (b) elimination of the need for superheating the motive fluid maximizes the average temperature at which heat is transferred to the motive fluid, maximizing power production and efficiency, (c) use of wet binary motive fluids with boiling points higher than the heat sink temperature, allowing the motive fluid to be condensed at or below standard atmospheric pressure, reducing back-pressure and further increasing power production and efficiency, (d) use of fewer components results in a simpler, less costly system, (e) use of an efficient liquid pump rather than the power-hungry compressor required by many ORC systems, further reducing power losses and expenses, (f) overall higher system efficiency, and (g) overall lower system cost.

CONCLUSIONS, RAMIFICATIONS, AND SCOPE

(45) Accordingly the reader will see that, according to one embodiment of the invention, I have provided a simpler, more efficient, and less costly thermal power cycle that can address a wide range of heat source—sink temperatures.

(46) While the above description contains many specificities, these should not be construed as limitations on the scope of any embodiment, but as exemplifications of various embodiments thereof. Many other ramifications and variations are possible within the teachings of the various embodiments. For example, the first embodiment can be adapted to exploit low-temperature and oil/gas co-produced geothermal resources. The second embodiment can be adapted to exploit separated produced water from flash geothermal powcr systems. The third embodiment can be adapted to exploit the entire energy flow of high-temperature geothermal systems. Alternative embodiments can exploit unused thermal power in waste heat recovery and other applications. In addition, motive fluids can be developed and selected for optimal performance in other heat source—sink temperature differences and ranges. These can include pure substances or mixtures or azeotropes of two or more pure substances, with water possibly being one of them.

(47) Thus, the scope should be determined by the appended claims and their legal equivalents, and not by the examples given.