DK1936129T3

DK1936129T3 - Method and apparatus for converting heat into usable energy

Info

Publication number: DK1936129T3
Application number: DK07110803.9T
Authority: DK
Inventors: Alexander I Kalina; Richard I Pelletier; Lawrence B Rhodes
Original assignee: Kct Power Ltd
Priority date: 1999-07-23
Filing date: 1999-07-23
Publication date: 2019-03-04
Also published as: DE69938039T2; EP1936129A2; PT1070830E; ES2301229T3; EP1936129B1; SI1070830T1; DE69938039D1; EP1936129A3

Description

DESCRIPTION

Background of the Invention [0001] The invention relates to implementing a thermodynamic cycle to convert heat to useful form.

[0002] Thermal energy can be usefully converted into mechanical and then electrical form. Methods of converting the thermal energy of low temperature heat sources into electric power present an important area of energy generation. There is a need for increasing the efficiency of the conversion of such low temperature heat to electric power.

[0003] Thermal energy from a heat source can be transformed into mechanical and then electrical form using a working fluid that is expanded and regenerated in a closed system operating on a thermodynamic cycle. The working fluid can include components of different boiling temperatures, and the composition of the working fluid can be modified at different places within the system to improve the efficiency of operation. Systems that convert low temperature heat into electric power are described in Alexander I. Kalina's U.S. Pat. Nos. 4,346,561; 4,489,563; 4,982,568; and 5,029,444 . In addition, systems with multicomponent working fluids are described in Alexander I. Kalina's U.S. Pat. Nos. 4,548,043; 4,586,340, 4,604,867; 4,732,005; 4,763,480, 4,899,545; 5,095,708; 5,440,882; 5,572,871 and 5,649,426.

[0004] US-A-4,573,321 discloses a multi-step process for generating energy from a source heat flow, comprising passing a heated media having a mixture of a low volatility component and a high volatility component into a phase separator. The vaporous working fluid is withdrawn from the phase separator and passed into a work zone, such as a turbine, wherein the fluid is expanded. The expanded vaporous working fluid is withdrawn from the work zone and passed into a direct contact condenser or absorber. The separated weak solution is withdrawn from the phase separator and passed into counter-current heat exchange relationship in an interchanger with a portion of media from the direct contact condenser or absorber. The media from the direct contact condenser or absorber is withdrawn and passed into a fluid pressurizing zone. A portion of the media is then pumped into the interchanger where the media is heated and passed into counter-current heat exchange relationship in a trim heater with a portion of the source heat flow. The remaining portion of the media from the fluid pressurizing zone is pumped into counter-current heat exchange relationship in a regenerator with the remaining portion of the source heat flow. The heated media flows from the trim heater and the regenerator are combined to form the heated media and the cycle repeated.

[0005] EP-A-0,649,985 discloses a thermal power generator for generating electric power by utilizing a high heat source and a low heat source, comprising an evaporator, a vapor-liquid separator, and an absorber and a regenerator, to increase thermal efficiency of an evaporator and a condenser, and to reduce cost for building apparatuses [0006] US-A-4,756,162 discloses method for utilising sensible heat energy supplied by a high-temperature heating fluid, employing a multi-component working fluid thermodynamic cycle, wherein a solution rich in a lower boiling component is heated in a vapor generator in countercurrent heat exchange with the heating fluid to produce a vapor-fluid mixture which is separated in a rectifier into a lean solution and a vapor mixture. The enthalpy of the vapor mixture is optionally increased in a superheater by counter-current heat exchange with said heating fluid at its highest temperature; the vapor mixture is then expanded thereby to perform the function of the cycle; and the spent vapor mixture is dissolved in said lean solution in an absorber so as to regenerate the rich solution. The rich solution leaving the absorber is compressed and divided into a first and second parts. The first part is heated by countercurrent heat exchange with said lean solution drawn from the rectifier, whereafter said first part of the rich solution is recycled to the vapor generator, whereas the second part of the rich solution extracts additional heat from the heating fluid leaving the vapor generator, by countercurrent heat exchange, and is then fed into the rectifier for counter-current mass and heat exchange with the vapor-liquid mixture formed in the vapor generator.

Summary of the Invention [0007] In accordance with a first aspect of the invention, there is provided a method for implementing a thermodynamic cycle, having the features of claim 1.

[0008] In accordance with a second aspect of the invention, there is provided an apparatus for implementing a thermodynamic cycle, having the features of claim 9.

[0009] Embodiments of the invention may include one or more of the following advantages. Embodiments of the invention can achieve efficiency of conversion of low temperature heat to electric power that exceeds the efficiency of standard Rankine cycles.

[0010] Other advantages and features of the invention will be apparent from the following detailed description of particular embodiments and from the claims.

Brief description of the drawings [0011] The accompanying Figures 1 and 2 and the description thereof, illustrate the invention by way of example. In the drawings:-

Fig. 1 is a diagram of a thermodynamic system for converting heat from a low temperature source to useful form.

Fig. 2 is a diagram of another embodiment of the Fig. 1 system which permits an extracted stream and a completely spent stream to have compositions which are different from the high pressure charged stream.

Fig. 3 is a diagram of a simplified embodiment that does not form part of the invention in which there is no extracted stream.

Fig. 4 is a diagram of a further simplified embodiment that does not form part of the invention.

Detailed Description of the Invention [0012] Referring to Fig. 1, a system for implementing a thermodynamic cycle to obtain useful energy (e.g., mechanical and then electrical energy) from an external heat source is shown. In the described example, the external heat source is a stream of low temperature waste-heat water that flows in the path represented by points 25-26 through heat exchanger HE-5 and heats working stream 117-17 of the closed thermodynamic cycle. Table 1 presents the conditions at the numbered points indicated on Fig. 1. A typical output from the system is presented in Table 5.

[0013] The working stream of the Fig. 1 system is a multicomponent working stream that includes a low boiling component and a high boiling component. Such a preferred working stream may be an ammonia-water mixture, two or more hydrocarbons, two or more freons, mixtures of hydrocarbons and freons, or the like. In general, the working stream may be mixtures of any number of compounds with favorable thermodynamic characteristics and solubility. In a particularly preferred embodiment, a mixture of water and ammonia is used. In the system shown in Fig. 1, the working stream has the same composition from point 13 to point 19.

[0014] Beginning the discussion of the Fig. 1 system at the exit of turbine T, the stream at point 34 is referred to as the expanded, spent rich stream. This stream is considered "rich" in lower boiling point component. It is at a low pressure and will be mixed with a leaner, absorbing stream having parameters as at point 12 to produce the working stream of intermediate composition having parameters as at point 13. The stream at point 12 is considered "lean" in lower boiling point component.

[0015] At any given temperature, the working stream (of intermediate composition) at point 13 can be condensed at a lower pressure than the richer stream at point 34. This permits more power to be extracted from the turbine T, and increases the efficiency of the process.

[0016] The working stream at point 13 is partially condensed. This stream enters heat exchanger HE-2, where it is cooled and exits the heat exchanger HE-2 having parameters as at point 29. It is still partially, not completely, condensed. The stream now enters heat exchanger HE-1 where it is cooled by stream 23-24 of cooling water, and is thereby completely condensed, obtaining parameters as at point 14. The working stream having parameters as at point 14 is then pumped to a higher pressure obtaining parameters as at point 21. The working stream at point 21 then enters heat exchanger HE-2 where it is recuperatively heated by the working stream at points 13-29 (see above) to a point having parameters as at point 15. The working stream having parameters as at point 15 enters heat exchanger HE-3 where it is heated and obtains parameters as at point 16. In a typical design, point 16 may be precisely at the boiling point but it need not be. The working stream at point 16 is split into two substreams; first working substream 117 and second working substream 118. The first working substream having parameters as at point 117 is sent into heat exchanger HE-5, leaving with parameters as at point 17. It is heated by the external heat source, stream 25-26. The other substream, second working substream 118, enters heat exchanger HE-4 in which it is heated recuperatively, obtaining parameters as at point 18. The two working substreams, 17 and 18, which have exited heat exchangers HE-4 and HE-5, are combined to form a heated, gaseous working stream having parameters as at point 19. This stream is in a state of partial, or possibly complete, vaporization. In the preferred embodiment, point 19 is only partially vaporized. The working stream at point 19 has the same intermediate composition which was produced at point 13, completely condensed at point 14, pumped to a high pressure at point 21, and preheated to point 15 and to point 16. It enters the separator S. There, it is separated into a rich saturated vapor, termed the "heated gaseous rich stream" and having parameters as at point 30, and a lean saturated liquid, termed the "lean stream" and having parameters as at point 7. The lean stream (saturated liquid) at point 7 enters heat exchanger HE-4 where it is cooled while heating working stream 118-18 (see above) . The lean stream at point 9 exits heat exchanger HE-4 having parameters as at point 8. It is throttled to a suitably chosen pressure, obtaining parameters as at point 9.

[0017] Returning now to point 30, the heated gaseous rich stream (saturated vapor) exits separator S. This stream enters turbine T where it is expanded to lower pressures, providing useful mechanical energy to turbine T used to generate electricity. A partially expanded stream having parameters as at point 32 is extracted from the turbine T at an intermediate pressure (approximately the pressure as at point 9) and this extracted stream 32 (also referred to as a "second portion" of a partially expanded rich stream, the "first portion" being expanded further) is mixed with the lean stream at point 9 to produce a combined stream having parameters as at point 10. The lean stream having parameters as at point 9 serves as an absorbing stream for the extracted stream 32. The resulting stream (lean stream and second portion) having parameters as at point 10 enters heat exchanger HE-3 where it is cooled, while heating working stream 15-16, to a point having parameters as at point 11. The stream having parameters as at point 11 is then throttled to the pressure of point 34, obtaining parameters as at point 12.

[0018] Returning to turbine T, not all of the turbine inflow was extracted at point 32 in a partially expanded state. The remainder, referred to as the first portion, is expanded to a suitably chosen low pressure and exits the turbine T at point 34. The cycle is closed.

[0019] In the embodiment shown in Fig. 1, the extraction at point 32 has the same composition as the streams at points 30 and 34. In the embodiment shown in Fig. 2, the turbine is shown as first turbine stage T-1 and second turbine stage T-2, with the partially expanded rich stream leaving the higher pressure stage T-1 of the turbine at point 31. Conditions at the numbered points shown on Fig. 2 are presented in Table 2. A typical output from the Fig. 2 system is presented in Table 6.

[0020] Referring to Fig. 2, the partially expanded rich stream from first turbine stage T-1 is divided into a first portion at 33 that is expanded further at lower pressure turbine stage T-2, and a second portion at 32 that is combined with the lean stream at 9. The partially expanded rich stream enters separator S-2, where it is separated into a vapor portion and a liquid portion. The composition of the second portion at 32 may be chosen in order to optimize its effectiveness when it is mixed with the stream at point 9. Separator S-2 permits stream 32 to be as lean as the saturated liquid at the pressure and temperature obtained in the separator S-2; in that case, stream 33 would be a saturated vapor at the conditions obtained in the separator S-2. By choice of the amount of mixing at stream 133, the amount of saturated liquid and the saturated vapor in stream 32 can be varied.

[0021] Referring to Fig. 3, this embodiment does not form part of the invention and differs from the embodiment of Fig. 1, in that the heat exchanger HE-4 has been omitted, and there is no extraction of a partially expanded stream from the turbine stage. In the Fig. 3 embodiment, the hot stream exiting the separator S is admitted directly into heat exchanger HE-3. Conditions at the numbered points shown on Fig. 3 are presented in Table 3. A typical output from the system is presented in Table 7.

[0022] Referring to Fig. 4, this embodiment does not form part of the invention and differs from the Fig. 3 embodiment in omitting heat exchanger HE-2.

Conditions at the numbered points shown on Fig. 4 are presented in Table 4. Atypical output from the system is presented in Table 8. While omitting heat exchanger HE-2 reduces the efficiency of the process, it may be economically advisable in circumstances where the increased power given up will not pay for the cost of the heat exchanger.

[0023] In general, standard equipment may be utilized in carrying out the method of this invention. Thus, equipment such as heat exchangers, tanks, pumps, turbines, valves and fittings of the type used in a typical Rankine cycles, may be employed in carrying out the method of this invention.

[0024] In the described embodiments of the invention, the working fluid is expanded to drive a turbine of conventional type. However, the expansion of the working fluid from a charged high pressure level to a spent low pressure level to release energy may be effected by any suitable conventional means known to those skilled in the art. The energy so released may be stored or utilized in accordance with any of a number of conventional methods known to those skilled in the art.

[0025] The separators of the described embodiments can be conventionally used gravity separators, such as conventional flash tanks. Any conventional apparatus used to form two or more streams having different compositions from a single stream may be used to form the lean stream and the enriched stream from the fluid working stream.

[0026] The condenser may be any type of known heat rejection device. For example, the condenser may take the form of a heat exchanger, such as a water cooled system, or another type of condensing device.

[0027] Various types of heat sources may be used to drive the cycle of this invention.

Table 1

Table 2

REFERENCES CITED IN THE DESCRIPTION

This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

Patent documents cited in the description • US4346561A [0003] • US4489563A [00031 • US4982568A [00031 • US5029444A [00031 • US4548043A [0003] • US4586340A [0003] • US4604867A [00031 • US4732005A [00031 • US4763480A [00031 • US4899545A [0003] • US5095708A [0003] • US5440882A [00031 • US5572871A [00031 • US5649426A [00031 • US4573321A [0004] • EP0649985A [0005] • US4756162A [00001

Claims

A method of implementing a thermodynamic cycle comprising: separating a heated gaseous working stream by a first separator (S), including a low boiling point component and a higher boiling point component, to provide a heated gaseous bold stream with relatively more of the low boiling component and a lean stream with relatively less of the low boiling component, expanding the heated gaseous fatty stream to convert the energy of the stream into usable form and providing an expanded, used fat stream (34), combining it lean current and the expanded, used fat stream (34) to provide the workflow, in which the workflow, after combination and before separation, is condensed by transferring heat to a low temperature source at a first heat exchanger (HE-1) and then the workflow is pumped to a higher pressure, dividing the workflow into a first workflow (117) and a second workflow m (118) and heating the first working part stream (117) with an external heat source (HE-5) to provide a heated first working part stream (17), characterized in that the method comprises heating the second working part stream (118) with heat from the lean stream and thus produce a heated second working part stream (18) with the first set of thermodynamic properties, and combining the heated first working part stream (17) with the heated second working part stream (18) with the first set of thermodynamic properties to form the heated gas-containing workflow.

The method of claim 1, further comprising transferring, by another heat exchanger (HE-2), heat from the workflow, prior to condensing the workflow, to the workflow, after the workflow is pumped to the higher pressure and prior to heating with the external heat source.

The method of claim 2, further comprising transferring, by a third heat exchanger (HE-3), heat from the lean stream to the workflow, after the workflow has received heat at the second heat exchanger (HE-2) and prior to partitioning.

A method according to any one of the preceding claims, wherein the expansion takes place in a first expansion step and a second expansion step, wherein the heated gaseous fatty stream is partially expanded to provide a partially expanded fat stream in the first expansion stage, further comprising dividing the partially expanded fatty stream in a first portion and a second portion (34), wherein the first portion (33) is expanded to provide the expanded spent fat stream in the second stage of expansion, and further comprising the combination of the second portion (34). with the lean stream before the combination of the lean stream and the expanded, used fat stream.

The method of claim 4, wherein the division comprises separating the partially expanded fatty stream into a vapor portion and a liquid portion, wherein the first portion (33) contains at least some of the vapor portion and the second portion (34) contains the liquid portion.

The method of claim 4, further comprising combining some of the vapor portion with the liquid portion to provide the second portion (34).

The method of claim 6, further comprising transferring, by a heat exchanger (HE-3), of heat from the lean stream and the second portion (34) to the working stream, before the working stream has been divided into the first working subflow (117) and the second working part stream (118).

A method according to any one of the preceding claims, further comprising recovering a partially expanded stream from a turbine (T) and mixing the partially expanded stream with the lean stream to produce a mixed lean stream.

An apparatus for implementing a thermodynamic cycle comprising: a separator (S) for dividing a heated gaseous working stream, including a low boiling point component and a higher boiling point component, to provide a heated gaseous bold stream with relatively more of the low boiling component and a lean current with relatively less of the low boiling component, an expansion device connected to receive at least a portion of the heated gaseous work stream and convert the energy of the stream into usable form and send an expanded stream, a mixer combining the expanded fat stream and the lean stream (12), a first heat exchanger (HE-1) and a pump connected between the expansion device and the separator (S), the first heat exchanger (HE-1) condensing the expanded current by transferring heat to a low-temperature source and where the pump then pumps the expanded current to a higher pressure to form the work stream, a current divider (16) connected to divide the work stream after pumping to a first work part stream (117) and a second work part stream (118), a heat exchanger to heat the first work part stream with an external heat source (HE-5 ), a heat exchanger (HE-4) for heating the second part of the work stream with the lean stream from the separator (S), a second mixer combining the first heated work part stream with the second part of the work stream, and a second heat exchanger (HE 2) connected to transfer heat from the workflow (13) before the workflow is fully condensed, to the workflow (21), after the workflow has been pumped to the higher pressure at the pump and before the workflow is divided by the power divider, characterized know that the heated second work part stream has a first set of thermodynamic properties and that the combined heated first work part stream and heated second work part stream tea sets thermodynamic properties to form the gas-containing workflow.

The apparatus of claim 9, further comprising a third heat exchanger (HE-3) connected to transfer heat from the lean current to the workflow after the workflow has received heat at the second heat exchanger (HE-2), and before the workflow has been divided by the power divider.

The apparatus of claim 9, wherein the expansion device comprises a first expansion step and a second expansion step, wherein the first expansion step is connected to receive the heated gaseous fatty stream and transmit a partially expanded bold stream, further comprising a second separator (S-2 ) which is connected to receive the partially expanded fat stream and divide it into a first portion (33) and a second portion (32), the second stage being connected to receive the first portion and expanding the first portion to providing the expanded used fat stream (34), and further comprising a third stream mixer connected to combine the second portion (32) with the lean stream before combining the lean stream with the expanded spent fat stream at the first power mixer.

The apparatus of claim 11, wherein the second separator (S-2) is connected to receive the partially expanded fat stream and separate it into a vapor portion and a liquid portion, wherein the first portion (33) contains at least some of the vapor portion, and wherein the second portion (32) contains the liquid portion.

The apparatus of claim 11, wherein the second separator (S-2) contains a fourth flow mixer connected to combine some of the vapor portion of the second separator (S-2) with the liquid portion of the second separator (S-2). to provide the second portion (32).

The apparatus of claim 11, further comprising a heat exchanger (HE-3) connected to transmit heat from the lean current and the second portion (32) to the workflow before the workflow is divided by the power divider.