WO2013094905A1 - Heat engine based on transcritical rankine cycle with improved exergy efficiency and method thereof - Google Patents

Heat engine based on transcritical rankine cycle with improved exergy efficiency and method thereof Download PDF

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Publication number
WO2013094905A1
WO2013094905A1 PCT/KR2012/010664 KR2012010664W WO2013094905A1 WO 2013094905 A1 WO2013094905 A1 WO 2013094905A1 KR 2012010664 W KR2012010664 W KR 2012010664W WO 2013094905 A1 WO2013094905 A1 WO 2013094905A1
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Prior art keywords
working fluid
heat
turbine
recuperator
condenser
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PCT/KR2012/010664
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French (fr)
Inventor
Young-Min Kim
Chang Ki Kim
Dong Kil Shin
Sun Youp Lee
Daniel Favrat
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Korea Institute Of Machinery & Materials
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Publication of WO2013094905A1 publication Critical patent/WO2013094905A1/en

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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01K—STEAM ENGINE PLANTS; STEAM ACCUMULATORS; ENGINE PLANTS NOT OTHERWISE PROVIDED FOR; ENGINES USING SPECIAL WORKING FLUIDS OR CYCLES
    • F01K25/00—Plants or engines characterised by use of special working fluids, not otherwise provided for; Plants operating in closed cycles and not otherwise provided for
    • F01K25/08—Plants or engines characterised by use of special working fluids, not otherwise provided for; Plants operating in closed cycles and not otherwise provided for using special vapours
    • F01K25/10—Plants or engines characterised by use of special working fluids, not otherwise provided for; Plants operating in closed cycles and not otherwise provided for using special vapours the vapours being cold, e.g. ammonia, carbon dioxide, ether
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01K—STEAM ENGINE PLANTS; STEAM ACCUMULATORS; ENGINE PLANTS NOT OTHERWISE PROVIDED FOR; ENGINES USING SPECIAL WORKING FLUIDS OR CYCLES
    • F01K23/00—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids
    • F01K23/02—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids the engine cycles being thermally coupled
    • F01K23/06—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids the engine cycles being thermally coupled combustion heat from one cycle heating the fluid in another cycle
    • F01K23/10—Plants characterised by more than one engine delivering power external to the plant, the engines being driven by different fluids the engine cycles being thermally coupled combustion heat from one cycle heating the fluid in another cycle with exhaust fluid of one cycle heating the fluid in another cycle
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01K—STEAM ENGINE PLANTS; STEAM ACCUMULATORS; ENGINE PLANTS NOT OTHERWISE PROVIDED FOR; ENGINES USING SPECIAL WORKING FLUIDS OR CYCLES
    • F01K25/00—Plants or engines characterised by use of special working fluids, not otherwise provided for; Plants operating in closed cycles and not otherwise provided for
    • F01K25/08—Plants or engines characterised by use of special working fluids, not otherwise provided for; Plants operating in closed cycles and not otherwise provided for using special vapours
    • F01K25/10—Plants or engines characterised by use of special working fluids, not otherwise provided for; Plants operating in closed cycles and not otherwise provided for using special vapours the vapours being cold, e.g. ammonia, carbon dioxide, ether
    • F01K25/103—Carbon dioxide
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01K—STEAM ENGINE PLANTS; STEAM ACCUMULATORS; ENGINE PLANTS NOT OTHERWISE PROVIDED FOR; ENGINES USING SPECIAL WORKING FLUIDS OR CYCLES
    • F01K7/00—Steam engine plants characterised by the use of specific types of engine; Plants or engines characterised by their use of special steam systems, cycles or processes; Control means specially adapted for such systems, cycles or processes; Use of withdrawn or exhaust steam for feed-water heating
    • F01K7/34—Steam engine plants characterised by the use of specific types of engine; Plants or engines characterised by their use of special steam systems, cycles or processes; Control means specially adapted for such systems, cycles or processes; Use of withdrawn or exhaust steam for feed-water heating the engines being of extraction or non-condensing type; Use of steam for feed-water heating
    • F01K7/38—Steam engine plants characterised by the use of specific types of engine; Plants or engines characterised by their use of special steam systems, cycles or processes; Control means specially adapted for such systems, cycles or processes; Use of withdrawn or exhaust steam for feed-water heating the engines being of extraction or non-condensing type; Use of steam for feed-water heating the engines being of turbine type

Definitions

  • the present invention relates to a heat engine based on a transcritical Rankine cycle with improved exergy efficiency, and a method thereof.
  • a transcritical CO 2 cycle advantageously has high efficiency and compactness in comparison to an existing Rankine cycle using steam or a Brayton cycle using helium.
  • FIGS. 1, 2, and 5 are views illustrating the related art heat engine based on a Rankine cycle using CO 2 .
  • the related art heat engine based on the Rankine cycle using carbon dioxide includes a turbine working while adiabatically expanding carbon dioxide as a working fluid, a recuperator, a condenser condensing and cooling the working fluid, a pump compressing the working fluid, and a heater.
  • the recuperator heat-exchanges a working fluid discharged from the turbine with a working fluid discharged after being compressed by the pump, and the heater heat-exchanges the working fluid discharged after being heat-exchanged by the recuperator with a high heat source and discharges the same to the turbine.
  • the working fluid circulating in the Rankine cycle in FIG. 1 undergoes a change in temperature and pressure as shown in FIGS. 2 and 5. Meanwhile, for the convenience of understanding, temperatures of respective pipe channels 0. 1, 2, 3, 4, and 5 illustrated in FIG. 1 are shown in FIGS. 2 and 5.
  • the working fluid discharged from the turbine has a temperature of T 4 , and a quantity of heat of Q R (449.0 kJ/kg) of the working fluid while passing through the recuperator is transferred to the working fluid discharged by the pump. Thereafter, the working fluid discharged from the recuperator is condensed and cooled by the condenser to have a temperature of T 0 (20). In this process, heat (70.7 + 152.0 kJ/kg) as much as Q L +Q C is discarded.
  • the working fluid having the temperature of T 0 (20) is compressed by the pump to have a temperature of T 1 (39), and thereafter, the temperature is increased up to T 2 (298) upon receiving a quantity of heat Q R (449.0kJ/kg) from the recuperator.
  • the working fluid having a temperature increased up to T 2 (298) is further increased up to T 3 (600) upon receiving heat from an external heat source in the heater.
  • FIGS. 3, 4, and 6 are views illustrating a heat engine operating in a related art Brayton cycle mode.
  • the related art heat engine based on the Brayton cycle using carbon dioxide includes a turbine working while adiabatically expanding carbon dioxide as a working fluid, a recuperator, a cooler cooling the working fluid, a compressor compressing the working fluid, and a heater.
  • the recuperator heat-exchanges a working fluid discharged from the turbine with a working fluid discharged after being compressed by the compressor, and the heater heat-exchanges the working fluid discharged after being heat-exchanged by the recuperator with a high heat source and discharges the same to the turbine.
  • FIGS. 4 and 6 The working fluid circulating in the Brayton cycle in FIG. 3 undergoes a change in temperature and pressure as shown in FIGS. 4 and 6. Meanwhile, for the convenience of understanding, temperatures of respective pipe channels 0. 1, 2, 3, 4, and 5 illustrated in FIG. 3 are shown in FIGS. 4 and 6.
  • the working fluid discharged from the turbine has a temperature of T 4 , (449) and a quantity of heat of Q R (355.5kJ/kg) of the working fluid while passing through the recuperator is transferred to the working fluid discharged by the compressor. Thereafter, the working fluid discharged from the recuperator is cooled by the cooler to have a temperature of T 0 (20). In this process, heat (164.2kJ/kg) as much as Q L is discarded.
  • the working fluid having the temperature of T 0 (20) is compressed by the compressor to have a temperature of T 1 (115), and thereafter, the temperature is increased up to T 2 (370) upon receiving a quantity of heat Q R (355kJ/kg) from the recuperator.
  • the working fluid having a temperature increased up to T 2 (370) is further increased up to T 3 (600) upon receiving heat (283.6kJ/kg) from an external heat source in the heater.
  • the present invention has been made in an effort to provide a transcritical Rankine cycle with improved exergy efficiency.
  • the present invention has also been made in an effort to provide a heat engine based on a transcritical Rankine cycle with improved exergy efficiency.
  • the present invention has also been made in an effort to provide a method for increasing exergy efficiency of a heat engine.
  • the present invention has also been made in an effort to provide a method for operating a heat engine with improved exergy efficiency.
  • An exemplary embodiment of the present invention provides a Rankine cycle with improved exergy efficiency used in a heat engine, including: condensing and cooling a working fluid discharged from a turbine; compressing the condensed and cooled working fluid; a first heat exchange step of heat-exchanging the compressed operation fluid with a low grade heat source; a second heat-exchanging step of heat-exchanging the working fluid discharged from the turbine with the working fluid which has undergone the first heat exchange step before being condensed and cooled; wherein the working fluid which has undergone the first heat exchange step and the second heat exchange step is introduced into the turbine.
  • the working fluid may be dioxide carbon.
  • the Rankine cycle may further include: a third heat exchange step of heat-exchanging the working fluid which has undergone the second heat exchange step with the compressed working fluid before the working fluid which has undergone the second heat exchange step is condensed and cooled, wherein the working fluid which has undergone the first heat exchange step, the second heat exchange step, and the third heat exchange step may be introduced into the turbine.
  • a Rankine cycle-based heat engine including: a turbine discharging a working fluid; a condenser condensing and cooling the working fluid discharged from the turbine; a pump compressing the condensed and cooled working fluid; a first recuperator heat-exchanging the compressed working fluid with a low grade heat source; and a second recuperator heat-exchanging the working fluid, which has been discharged from the turbine but not introduced into the condenser yet, with the working fluid heat-exchanged by the first recuperator, wherein the working fluid, which has undergone heat-exchanging by the first recuperator and the second recuperator, is introduced into the turbine.
  • the first recuperator may heat-exchange the working fluid, which has been heat-exchanged by the second recuperator but not introduced into the condenser yet, with the working fluid compressed by the pump.
  • Yet another embodiment of the present invention provides a steam cycle-based heat engine including: a turbine working by a working fluid; a condenser condensing and cooling the working fluid discharged from the turbine; a pump compressing the condensed and cooled working fluid from the condenser; a first pipe channel providing a path allowing the working fluid discharged from the turbine to move to the condenser therethrough; a second pipe channel providing a path allowing the working fluid discharged from the pump to move to the turbine therethrough; a first recuperator heat-exchanging the working fluid moving through the second pipe channel with a low grade heat source; and a second recuperator disposed between the first recuperator and the turbine and heat-exchanging the working fluid flowing through the first pipe channel with the working fluid flowing through the second pipe channel.
  • Still another embodiment of the present invention provides a heat engine with improved exergy efficiency operating in a Brayton cycle mode and a Rankine cycle mode, including: a turbine working by a working fluid; a direction changing unit allowing the working fluid discharged from the turbine to any one of a condenser and a compressor; and a first recuperator heat-exchanging the working fluid before flowing to the condenser or the compressor, with a thermal storage fluid, wherein the working fluid discharged from the condenser or the compressor is introduced into the turbine.
  • the heat engine may further include: a thermal storage configured to store the thermal storage fluid.
  • the direction changing unit may change a direction of the working fluid discharged from the turbine such that the working fluid flows to the compressor.
  • the heat engine may further include: a cooler disposed between the direction changing unit and the compressor, wherein the cooler receives the working fluid from the direction changing unit, cools the received working fluid, and discharges the cooled working fluid to the compressor.
  • the direction changing unit may change a direction of the working fluid discharged from the turbine such that the working fluid flows to the condenser.
  • the heat engine may further include: a pump compressing the working fluid discharged from the condenser.
  • the first recuperator may heat-exchange the working fluid before flowing the condenser or the compressor, the thermal storage fluid stored in the thermal storage, and the working fluid discharged from the pump with each other.
  • the heat engine may further include: a second recuperator heat-exchanging the working fluid before being introduced into the first recuperator and the working fluid discharged from the condenser or the compressor.
  • Still another embodiment of the present invention provides a method for increasing exergy efficiency of a heat engine including a turbine, a compressor, and a condenser, including: changing a direction of a working flow discharged from the turbine such that the working flow flows to the compressor in a Brayton cycle mode and flows to the condenser in a Rankine cycle mode; heat-exchanging the working fluid before flowing to the compressor and a thermal storage fluid in the Brayton cycle mode; and introducing the working fluid discharged from the condenser or the compressor into the turbine.
  • the method may further include: storing the thermal storage fluid in the Brayton cycle mode.
  • the method may further include: cooling the working fluid before being introduced into the compressor, in the Brayton cycle mode.
  • the method may further include: compressing the working fluid discharged from the condenser by a pump in the Rankine cycle mode.
  • the method may further include: heat-exchanging the thermal storage fluid stored in the Brayton cycle mode with the working fluid discharged after being compressed by the pump, in the Rankine cycle mode.
  • the method may further include: heat-exchanging the working fluid before flowing to the condenser with the working fluid discharged after being compressed by the pump, in the Rankine cycle mode.
  • Still another embodiment of the present invention provides a method for operating a heat engine, including: operating a heat engine which works by circulating a working fluid, in a Brayton cycle mode or a Rankine cycle mode; heat-exchanging a thermal storage fluid with a working fluid before being cooled and storing the same, in a Brayton cycle mode in which a working fluid discharged from a turbine is cooled and subsequently compressed; and heat-exchanging the compressed working fluid with a thermal storage fluid stored in the Brayton cycle mode, in a Rankine cycle mode in which the working fluid discharged from the turbine is condensed, cooled, and subsequently compressed.
  • the heat engine according to one or more embodiments of the present invention can have improved exergy efficiency.
  • FIG. 1 is a view illustrating the related art heat engine operating in a Rankine cycle mode
  • FIGS. 2 and 5 are graphs for explaining the heat engine of FIG. 1;
  • FIG. 3 is a view illustrating the related art heat engine operating in a Brayton cycle mode
  • FIGS. 4 and 6 are graphs for explaining the heat engine of FIG. 3;
  • FIG. 7 is a view illustrating a heat engine according to an embodiment of the present invention.
  • FIG. 8 is a graph for explaining the heat engine of FIG. 7;
  • FIGS. 9 and 10 are views illustrating a heat engine according to another embodiment of the present invention.
  • FIGS. 11 and 12 are views for explaining an effect of the present invention.
  • FIG. 13 is a view illustrating a modification of the embodiment of FIG. 7.
  • FIGS. 14, 15, and 16 are views illustrating steam cycles that may be implemented in the heat engine according to an embodiment of the present invention.
  • steam cycle includes a transcritical Rankine cycle and a supercritical Brayton cycle.
  • FIG. 7 is a view illustrating a heat engine according to an embodiment of the present invention
  • FIG. 8 is a graph for explaining the heat engine of FIG. 7.
  • a heat engine may include a turbine 10, a first recuperator 30, a second recuperator 20, a condenser 40, a pump 50, and a high temperature heater 60. Meanwhile, in order to explain the concept of the present invention, an LT heat source and pipe channels.
  • the heat engine according to an embodiment of the present invention may operate in a Rankine cycle mode and improve exergy efficiency by appropriately utilizing the LT heat source.
  • the turbine 10 works while adiabatically expanding a working fluid, and discharges the working fluid to the second recuperator 20.
  • the second recuperator 20 heat-exchanges a working fluid discharged from the first recuperator 30 with the working fluid discharged from the turbine 10. Namely, the second recuperator 20 heat-exchanges the working fluid flowing through a fifth pipe channel 5 with the working fluid flowing through a second pipe channel 2.
  • the first recuperator 30 heat-exchanges a working fluid discharged from the second recuperator 20 with a working fluid discharged after being compressed by the pump 50. Namely, the first recuperator 30 heat-exchanges the working fluid flowing through a sixth pipe channel 6 and the working fluid flowing through a first pipe channel 1.
  • the first recuperator 30 may heat-exchange a working fluid discharged after being compressed by the pump 50 and the LT heat source. Namely, the first recuperator 30 heat-exchanges the working fluid flowing through the first pipe channel with the LT heat source.
  • the first recuperator 30 heat-exchanges the working fluid flowing through the first pipe channel 1 with the LT heat source and also heat-exchanges the working fluid flowing through the first pipe channel 1 with the working fluid flowing through the sixth pipe channel 6, but the configuration of using one recuperator is merely illustrative and any other configuration may also be implemented.
  • the recuperator may include a single recuperator and a single low temperature heater 1.
  • a low temperature heater 34 for heat-exchanging the working fluid flowing through the first pipe channel 1 with the LT heat source and a recuperator 32 for heat-exchanging the working fluid flowing through the first pipe channel 1 with the working fluid flowing through the sixth pipe channel 6 may be separately configured.
  • the condenser 40 receives the working fluid discharged from the first recuperator 30, condenses and cools the received working fluid, and subsequently discharges the condensed and cooled working fluid to the pump 50.
  • the pump 50 compresses the condensed and cooled working fluid received from the condenser 40, and discharges the compressed working fluid to the first recuperator 30.
  • the working fluid which has been compressed by and discharged from the pump 50 sequentially pass through the first recuperator 30 and the second recuperator 20, heat-exchanged with the HT heat source by the heater 60, and subsequently is introduced into the turbine 10.
  • the foregoing working fluid may be carbon dioxide, but this is merely illustrative and it should be appreciated by a skilled person in the art that the present invention is not limited to carbon dioxide.
  • the working fluid may undergo the steps illustrated in FIG. 8.
  • the working fluid which has been introduced into the turbine 10 works (169. 9kJ/kg), and is subsequently discharged with heat (T 5 ) to a fifth pipe channel 5.
  • the working fluid discharged to the fifth pipe channel is discharged to the sixth pipe channel 6 through the second recuperator 20.
  • a temperature of the working fluid in the fifth pipe channel 5 is T 5 (449°C), and a temperature of the working fluid after being heat-exchanged by the second recuperator 20 is 112°C.
  • heat Q R2 358.1kJ/kg
  • the working fluid which has been discharged to the sixth pipe channel 6 is heat-exchanged by the first recuperator 30, and flows to the condenser 40. Referring to FIG. 8, it can be seen that, during this process, heat Q R1 (91.0kJ/kg) has been transferred to the working fluid flowing through the first pipe channel 1.
  • the condenser 40 Upon receiving the working fluid discharged from the second recuperator 20, the condenser 40 performs condensing and cooling process thereon. Referring to FIG. 8, the section in which the condenser 40 performs condensing and cooling is denoted by reference numeral 7 ⁇ 0. In this section, heat (Q L + Q C ) may be discarded.
  • the pump 50 compresses (Wp) the working fluid received through a pipe channel 0, and discharges the compressed working fluid to the first recuperator 30. Namely, the working fluid compressed by the pump 50 is introduced into the first recuperator 30 through the first pipe channel 1.
  • the working fluid introduced into the first recuperator 30 is heat-exchanged with the working fluid flowing through the LT heat source and the sixth pipe channel 6. Namely, the working fluid introduced into the first recuperator 30 receives heat Q H1 from the LT heat source and receives heat Q R1 from the working fluid flowing through the sixth pipe channel 6.
  • the working fluid discharged from the first recuperator 30 is introduced into the second recuperator 20 again through the second pipe channel 2, performing heat-exchange operation. Namely, the working fluid introduced into the second recuperator 20 is heat-exchanged with the working fluid flowing through the fifth pipe channel 5. Referring to FIG. 8, the working fluid introduced into the second recuperator 20 receives heat Q R2 .
  • the working fluid discharged from the second recuperator 20 is heat-exchanged with the high heat source Q H in the high temperature heater 60 and subsequently supplied again to the turbine 10. Referring to FIG. 8, the working fluid receives heat Q H2 from the high heat source.
  • FIG. 9 is a view illustrating an operation of a heat engine in a Brayton cycle mode according to another embodiment of the present invention
  • FIG. 10 is a view illustrating an operation of a heat engine in a Rankine cycle mode according to another embodiment of the present invention.
  • the heat engine according to an embodiment of present invention illustrated in FIGS. 9 and 10 may alternately operate in the Brayton cycle mode and the Rankine cycle mode.
  • the heat engine illustrated in FIGS. 9 and 10 includes a turbine 110, a first recuperator 130, a second recuperator 120, a compressor 125, a thermal storage 135, a condenser 140, a cooler 145, a pump 150, direction changing units 155 and 165, and a high temperature heater 160.
  • the heat engine illustrated in FIGS. 9 and 10 operates in a Brayton cycle mode or a Rankine cycle mode, and when the heat engine operates in the Brayton cycle mode, the heat engine heat-exchanges a working fluid discharged from the turbine 110 with a working fluid after the compressor 125, and stores the residual heat of a working fluid in a fifth pipe channel 5 to a thermal storage 135. Also, when the heat engine operates in the Rankine cycle mode, the heat engine condenses and cools the working fluid discharged from the turbine 110, compresses the same, and heat-exchanges the compressed working fluid with the thermal storage 135 stored in the Brayton cycle mode.
  • the working fluid moves through the cooler 145 and the compressor 125.
  • the direction changing unit 155 performs a switching operation to allow the working fluid, which is discharged from the compressor 125 and flows through a seventh pipe channel 6, to flow toward the cooler 145, rather than toward the condenser 140.
  • the direction changing unit 165 performs a switching operation to allow the working fluid, which is discharged from the compressor 125, to flow toward the second recuperator 120.
  • the first recuperator 130 heat-exchanges a thermal storage fluid stored in the thermal storage 135 with a working fluid flowing through the sixth pipe channel 5 after passing through the second recuperator 120.
  • the thermal storage 135 includes a cool tank and a hot tank, and a thermal storage fluid (which may be, for example, water but the present invention is not limited thereto) stored in the cool tank may be pumped by the pump 175, passes through the first recuperator 130, and is subsequently stored in the hot tank.
  • the pump 175 may be a bi-directional pump, but it is merely illustrative and a person skilled in the art may configure the pump 175 as a uni-directional pump.
  • a controller may control a pumping direction of the pump 175, and control the heat storage fluid to move from the cool tank to the hot tank in the Brayton cycle mode and control the heat storage fluid in the opposite direction (i.e., from the hot tank to the cool tank) in the Rankine cycle mode. Also, as discussed above, the controller (not shown) may control the direction changing unit 155 to move the working fluid through the compressor 125 in the Brayton cycle mode.
  • the second recuperator 120 heat-exchanges the working fluid discharged through the compressor 125 with a working fluid flowing through a fourth pipe channel 4 discharged from the turbine 110. Thereafter, the high temperature heater 160 receives the working fluid flowing through a third pipe channel 2 after being discharged through the second recuperator 120, heat-exchanges the working fluid with a high pressure heat source, and discharges the same to the turbine 110.
  • the thermal storage fluid stored in the storage unit 135 may store heat corresponding to Q L in FIG. 4. In this manner, heat stored in the heat storage fluid is used in the Rankine cycle mode.
  • a working fluid moves through the condenser 140 and the pump 150.
  • the direction changing unit 155 performs a switching operation to allow the working fluid, which is discharged from the first recuperator 130, to flow toward the condenser 140, rather than toward the cooler 145.
  • the direction changing unit 165 performs a switching operation to allow a working fluid, which is discharged from the first recuperator 130, to flow toward the second recuperator 120.
  • the first recuperator 130 heat-exchanges the heat storage fluid stored in the hot tank of the thermal storage 135 with the working fluid pumped by the pump 150.
  • the pump 175 performs a pumping operation to allow the thermal storage fluid stored in the hot tank to move toward the cool tank under the control of the controller (not shown).
  • the first recuperator 130 heat-exchanges the working fluid flowing through the sixth pipe 6 after passing through the second recuperator 120 with the working fluid pumped by the pump 150. Thereafter, the high temperature heater 160 receives the working fluid flowing through the third pipe channel 3 after being discharged through the second recuperator 120, heat-exchanges it with the high temperature heat source, and discharges the same to the turbine 110.
  • the thermal storage fluid stored in the storage unit 135 may serve as a low temperature heat source.
  • FIG. 11 illustrates an effect of the heat engine according to an embodiment of the present invention illustrated in FIGS. 9 and 10.
  • a horizontal axis represents temperature and a vertical axis represents specific heat of a working fluid, in which the curve (1) indicates specific heat in a low pressure region, the curve (2) indicates specific heat in a high pressure region, and the curve (3) is obtained by doubling the curve (1).
  • an area indicated by the curve (1) may be heat stored by the thermal storage fluid in the Brayton cycle mode described above with reference to FIG. 9, and an area indicated by the curve (2) in FIG. 11 may indicate heat required for heating a working fluid in a state of being compressed in the Rankine cycle mode described above with reference to FIG. 10.
  • the thermal storage fluid (which may be, for example, water) stored in the hot tank have characteristics almost similar to the specific heat characteristics indicated by the curve (1) in FIG. 11, and the working fluid (which may be, for example, carbon dioxide) flowing through the sixth pipe channel 6 after passing through the second recuperator 120 may also have specific heat characteristics indicated by the curve (1) in FIG. 11.
  • the sum of them has the characteristics similar to those of the fluid having the specific heat of the curve (3) in FIG. 11.
  • the heat engine according to an embodiment of the present invention alternately operating in the Brayton cycle mode and the Rankine cycle mode shows that heat (the curve (3) in FIG. 11) obtained from the low pressure side is sufficient to heat the working fluid in the high pressure side.
  • FIG. 12 is a view for explaining an effect of the present invention.
  • FIG. 12 shows the comparison of exergy efficiency of the heat engine (R-CO2) operating in the conventional Rankine cycle mode, exergy efficiency of the heat engine (B-CO2) operating in the conventional Brayton cycle mode, and exergy efficiency of the heat engine operating in the Rankine cycle mode (LH T-CO2 LH R-CO2) in which both a low temperature heat source and a high temperature heat source are used according to an embodiment of the present invention.
  • the exergy efficiency of heat engine operating the Rankine cycle mode (LH R-CO2) in which both a low temperature heat source and a high temperature heat source are used according to an embodiment of the present invention is 0.723, and thus, it can be seen that the exergy efficiency is improved.
  • the outputs of the existing Rankin cycle (R-CO2) and the Rankine cycle (LH R-CO2) according to an embodiment of the present invention are the same 150.4 but the present invention is superior in the exergy efficiency.
  • the related art heat engines (R-CO2 and B-CO2) achieve the outputs (150.4 and 119.4, respectively) by using only high grade heat source 100%
  • the heat engine (LH R-CO2) according to an embodiment of the present invention achieves the output of 150.4 by using a low grade heat source 25% and a high grade heat source 75%, and in this aspect, it can be said that the heat engine according to an embodiment of the present invention has a superior effect to those of the related art heat engines.
  • heat efficiency of a low grade heat source does not exceed a maximum of 10%, but the heat engine according to an embodiment of the present invention increases heat efficiency of a low grade heat source up to about 25%, and this is supposedly because the low grade heat source was not used at any random timing but used in an appropriate section.
  • FIG. 13 is a view illustrating a modification of the embodiment of FIG. 7.
  • a heat engine illustrated in FIG. 13 may include the turbine 10, a first recuperator 32, a low temperature heater 34, the second recuperator 20, the condenser 40, the pump 50, and the high temperature heater 60.
  • the other remaining components excluding the first recuperator 32 and the low temperature heater 34, perform the same or similar operation as those of the components of FIG. 7 using the same reference numerals.
  • the low temperature heater 34 heat-exchanges a working fluid compressed by the pump 50 with a low grade heat source, and the first recuperator 32 heat-exchanges a working fluid discharged from the low temperature heater 34 with a working fluid flowing through the sixth pipe channel 60 after passing through the high temperature heater 20.
  • the working fluid compressed by the pump 50 is first heat-exchanged with the low grade heat source, but it may also be first heat-exchanged with the working fluid flowing through the sixth pipe channel 60.
  • the heat engine according to an embodiment of the present invention may have the Rankine cycle mode with improved exergy efficiency, and in a modification thereof, a low grade heat source may be secured in the Brayton cycle mode and used in the Rankine cycle mode.
  • FIGS. 14, 15, and 16 are views illustrating steam cycles that may be implemented in the heat engine according to an embodiment of the present invention.
  • the working fluid when an operation condition of a lower pressure side is higher than a transcritical pressure of a working fluid, the working fluid has the characteristics in that it does not go through an obvious phase-change process during a condensing process.
  • a liquid and gas are not conspicuously discriminated, making it vague to discriminate the Rankine cycle (which accompanies a phase change) and the Brayton cycle (gas cycle).
  • a completely cooled cycle as illustrated in FIG. 14 may be considered to be the Rankine cycle (FIG. 5) of the foregoing technique in the present invention
  • the partially cooled cycle as illustrated in FIG. 15 may be considered to be the Brayton cycle (FIG.
  • the concept of the present invention may be applied as is even to an operation region in which a conspicuous phase change is not made because the low pressure side has a pressure higher than the transcritical pressure of a working fluid, as well as in the operation condition in which the low pressure side undergoes a conspicuous phase change.
  • a Rankine cycle method with improved exergy efficiency used in a heat engine including condensing and cooling a working fluid discharged from a turbine, compressing the condensed and cooled working fluid, a first heat exchange step of heat-exchanging the compressed operation fluid with a low grade heat source, a second heat-exchanging step of heat-exchanging the working fluid discharged from the turbine with the working fluid which has undergone the first heat exchange step before being condensed and cooled.
  • the working fluid which has undergone the first heat exchange step and the second heat exchange step is introduced into the turbine.
  • the Rankine cycle method with improved exergy efficiency further includes: a third heat exchange step of heat-exchanging the working fluid which has undergone the second heat exchange step with the compressed working fluid before the working fluid which has undergone the second heat exchange step is condensed and cooled, wherein the working fluid which has undergone the first heat exchange step, the second heat exchange step, and the third heat exchange step may be introduced into the turbine.
  • a method for increasing exergy efficiency of a heat engine including a turbine, a compressor, and a condenser.
  • this method may be implemented to include changing a direction of a working flow discharged from the turbine such that the working flow flows to the compressor in a Brayton cycle mode and flows to the condenser in a Rankine cycle mode, heat-exchanging the working fluid before flowing to the compressor and a thermal storage fluid in the Brayton cycle mode, and introducing the working fluid discharged from the condenser or the compressor into the turbine.
  • a method for operating a heat engine including operating a heat engine which works by circulating a working fluid, in a Brayton cycle mode or a Rankine cycle mode, heat-exchanging a thermal storage fluid with a working fluid before being cooled and storing the same, in a Brayton cycle mode in which a working fluid discharged from a turbine is cooled and subsequently compressed, and heat-exchanging the compressed working fluid with a thermal storage fluid stored in the Brayton cycle mode, in a Rankine cycle mode in which the working fluid discharged from the turbine is condensed, cooled, and subsequently compressed.
  • compressor 135 thermal storage

Abstract

A Rankine cycle in which a working fluid discharged from a turbine is condensed and cooled, the condensed and cooled working fluid is compressed, and the compressed working fluid is heat-exchanged with a low grade heat source is provided. Accordingly, exergy efficiency is improved.

Description

HEAT ENGINE BASED ON TRANSCRITICAL RANKINE CYCLE WITH IMPROVED EXERGY EFFICIENCY AND METHOD THEREOF
The present invention relates to a heat engine based on a transcritical Rankine cycle with improved exergy efficiency, and a method thereof.
Recently, people are increasingly interested in a cycle of a heat engine utilizing every available heat source including a next-generation nuclear reactor, solar heat, fossil fuel, or biofuel. For example, a transcritical CO2 cycle advantageously has high efficiency and compactness in comparison to an existing Rankine cycle using steam or a Brayton cycle using helium.
FIGS. 1, 2, and 5 are views illustrating the related art heat engine based on a Rankine cycle using CO2.
Referring to the related art heat engine based on the Rankine cycle using CO2 (hereinafter, referred to as ‘carbon dioxide’), the related art heat engine based on the Rankine cycle using carbon dioxide includes a turbine working while adiabatically expanding carbon dioxide as a working fluid, a recuperator, a condenser condensing and cooling the working fluid, a pump compressing the working fluid, and a heater.
The recuperator heat-exchanges a working fluid discharged from the turbine with a working fluid discharged after being compressed by the pump, and the heater heat-exchanges the working fluid discharged after being heat-exchanged by the recuperator with a high heat source and discharges the same to the turbine.
The working fluid circulating in the Rankine cycle in FIG. 1 undergoes a change in temperature and pressure as shown in FIGS. 2 and 5. Meanwhile, for the convenience of understanding, temperatures of respective pipe channels 0. 1, 2, 3, 4, and 5 illustrated in FIG. 1 are shown in FIGS. 2 and 5.
Namely, the working fluid discharged from the turbine has a temperature of T4, and a quantity of heat of QR (449.0 kJ/kg) of the working fluid while passing through the recuperator is transferred to the working fluid discharged by the pump. Thereafter, the working fluid discharged from the recuperator is condensed and cooled by the condenser to have a temperature of T0 (20). In this process, heat (70.7 + 152.0 kJ/kg) as much as QL+QC is discarded.
The working fluid having the temperature of T0 (20) is compressed by the pump to have a temperature of T1 (39), and thereafter, the temperature is increased up to T2 (298) upon receiving a quantity of heat QR (449.0kJ/kg) from the recuperator. The working fluid having a temperature increased up to T2 (298) is further increased up to T3 (600) upon receiving heat from an external heat source in the heater.
As described above, in the related art heat engine based on the Rankine cycle using CO2, in order for the working fluid in the compressed state (T1) to have the temperature of the state (T3) in which it works, a relative great amount of heat (for example, QH = 373.1 kJ/kg) should be supplied thereto from the outside in comparison to a heat engine based on the Brayton cycle as described hereinafter.
FIGS. 3, 4, and 6 are views illustrating a heat engine operating in a related art Brayton cycle mode.
Referring to these drawings, the related art heat engine based on the Brayton cycle using carbon dioxide includes a turbine working while adiabatically expanding carbon dioxide as a working fluid, a recuperator, a cooler cooling the working fluid, a compressor compressing the working fluid, and a heater.
The recuperator heat-exchanges a working fluid discharged from the turbine with a working fluid discharged after being compressed by the compressor, and the heater heat-exchanges the working fluid discharged after being heat-exchanged by the recuperator with a high heat source and discharges the same to the turbine.
The working fluid circulating in the Brayton cycle in FIG. 3 undergoes a change in temperature and pressure as shown in FIGS. 4 and 6. Meanwhile, for the convenience of understanding, temperatures of respective pipe channels 0. 1, 2, 3, 4, and 5 illustrated in FIG. 3 are shown in FIGS. 4 and 6.
Namely, the working fluid discharged from the turbine has a temperature of T4, (449) and a quantity of heat of QR (355.5kJ/kg) of the working fluid while passing through the recuperator is transferred to the working fluid discharged by the compressor. Thereafter, the working fluid discharged from the recuperator is cooled by the cooler to have a temperature of T0 (20). In this process, heat (164.2kJ/kg) as much as QL is discarded.
The working fluid having the temperature of T0 (20) is compressed by the compressor to have a temperature of T1 (115), and thereafter, the temperature is increased up to T2 (370) upon receiving a quantity of heat QR (355kJ/kg) from the recuperator. The working fluid having a temperature increased up to T2 (370) is further increased up to T3 (600) upon receiving heat (283.6kJ/kg) from an external heat source in the heater.
As described above, in the related art heat engine based on the Brayton cycle using CO2, since the compression process is directly performed in the gaseous state, better energy efficiency can be obtained relative to the foregoing Rankine cycle heat engine, but further compression power is required, degrading an output.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.
The present invention has been made in an effort to provide a transcritical Rankine cycle with improved exergy efficiency.
The present invention has also been made in an effort to provide a heat engine based on a transcritical Rankine cycle with improved exergy efficiency.
The present invention has also been made in an effort to provide a method for increasing exergy efficiency of a heat engine.
The present invention has also been made in an effort to provide a method for operating a heat engine with improved exergy efficiency.
An exemplary embodiment of the present invention provides a Rankine cycle with improved exergy efficiency used in a heat engine, including: condensing and cooling a working fluid discharged from a turbine; compressing the condensed and cooled working fluid; a first heat exchange step of heat-exchanging the compressed operation fluid with a low grade heat source; a second heat-exchanging step of heat-exchanging the working fluid discharged from the turbine with the working fluid which has undergone the first heat exchange step before being condensed and cooled; wherein the working fluid which has undergone the first heat exchange step and the second heat exchange step is introduced into the turbine.
The working fluid may be dioxide carbon.
The Rankine cycle may further include: a third heat exchange step of heat-exchanging the working fluid which has undergone the second heat exchange step with the compressed working fluid before the working fluid which has undergone the second heat exchange step is condensed and cooled, wherein the working fluid which has undergone the first heat exchange step, the second heat exchange step, and the third heat exchange step may be introduced into the turbine.
Another embodiment of the present invention provides a Rankine cycle-based heat engine including: a turbine discharging a working fluid; a condenser condensing and cooling the working fluid discharged from the turbine; a pump compressing the condensed and cooled working fluid; a first recuperator heat-exchanging the compressed working fluid with a low grade heat source; and a second recuperator heat-exchanging the working fluid, which has been discharged from the turbine but not introduced into the condenser yet, with the working fluid heat-exchanged by the first recuperator, wherein the working fluid, which has undergone heat-exchanging by the first recuperator and the second recuperator, is introduced into the turbine.
The first recuperator may heat-exchange the working fluid, which has been heat-exchanged by the second recuperator but not introduced into the condenser yet, with the working fluid compressed by the pump.
Yet another embodiment of the present invention provides a steam cycle-based heat engine including: a turbine working by a working fluid; a condenser condensing and cooling the working fluid discharged from the turbine; a pump compressing the condensed and cooled working fluid from the condenser; a first pipe channel providing a path allowing the working fluid discharged from the turbine to move to the condenser therethrough; a second pipe channel providing a path allowing the working fluid discharged from the pump to move to the turbine therethrough; a first recuperator heat-exchanging the working fluid moving through the second pipe channel with a low grade heat source; and a second recuperator disposed between the first recuperator and the turbine and heat-exchanging the working fluid flowing through the first pipe channel with the working fluid flowing through the second pipe channel.
Still another embodiment of the present invention provides a heat engine with improved exergy efficiency operating in a Brayton cycle mode and a Rankine cycle mode, including: a turbine working by a working fluid; a direction changing unit allowing the working fluid discharged from the turbine to any one of a condenser and a compressor; and a first recuperator heat-exchanging the working fluid before flowing to the condenser or the compressor, with a thermal storage fluid, wherein the working fluid discharged from the condenser or the compressor is introduced into the turbine.
The heat engine may further include: a thermal storage configured to store the thermal storage fluid.
In the Brayton cycle mode, the direction changing unit may change a direction of the working fluid discharged from the turbine such that the working fluid flows to the compressor.
The heat engine may further include: a cooler disposed between the direction changing unit and the compressor, wherein the cooler receives the working fluid from the direction changing unit, cools the received working fluid, and discharges the cooled working fluid to the compressor.
In the Rankine cycle mode, the direction changing unit may change a direction of the working fluid discharged from the turbine such that the working fluid flows to the condenser.
The heat engine may further include: a pump compressing the working fluid discharged from the condenser.
In the Rankine cycle mode, the first recuperator may heat-exchange the working fluid before flowing the condenser or the compressor, the thermal storage fluid stored in the thermal storage, and the working fluid discharged from the pump with each other.
The heat engine may further include: a second recuperator heat-exchanging the working fluid before being introduced into the first recuperator and the working fluid discharged from the condenser or the compressor.
Still another embodiment of the present invention provides a method for increasing exergy efficiency of a heat engine including a turbine, a compressor, and a condenser, including: changing a direction of a working flow discharged from the turbine such that the working flow flows to the compressor in a Brayton cycle mode and flows to the condenser in a Rankine cycle mode; heat-exchanging the working fluid before flowing to the compressor and a thermal storage fluid in the Brayton cycle mode; and introducing the working fluid discharged from the condenser or the compressor into the turbine.
The method may further include: storing the thermal storage fluid in the Brayton cycle mode.
The method may further include: cooling the working fluid before being introduced into the compressor, in the Brayton cycle mode.
The method may further include: compressing the working fluid discharged from the condenser by a pump in the Rankine cycle mode.
The method may further include: heat-exchanging the thermal storage fluid stored in the Brayton cycle mode with the working fluid discharged after being compressed by the pump, in the Rankine cycle mode.
The method may further include: heat-exchanging the working fluid before flowing to the condenser with the working fluid discharged after being compressed by the pump, in the Rankine cycle mode.
Still another embodiment of the present invention provides a method for operating a heat engine, including: operating a heat engine which works by circulating a working fluid, in a Brayton cycle mode or a Rankine cycle mode; heat-exchanging a thermal storage fluid with a working fluid before being cooled and storing the same, in a Brayton cycle mode in which a working fluid discharged from a turbine is cooled and subsequently compressed; and heat-exchanging the compressed working fluid with a thermal storage fluid stored in the Brayton cycle mode, in a Rankine cycle mode in which the working fluid discharged from the turbine is condensed, cooled, and subsequently compressed.
The heat engine according to one or more embodiments of the present invention can have improved exergy efficiency.
FIG. 1 is a view illustrating the related art heat engine operating in a Rankine cycle mode;
FIGS. 2 and 5 are graphs for explaining the heat engine of FIG. 1;
FIG. 3 is a view illustrating the related art heat engine operating in a Brayton cycle mode;
FIGS. 4 and 6 are graphs for explaining the heat engine of FIG. 3;
FIG. 7 is a view illustrating a heat engine according to an embodiment of the present invention;
FIG. 8 is a graph for explaining the heat engine of FIG. 7;
FIGS. 9 and 10 are views illustrating a heat engine according to another embodiment of the present invention;
FIGS. 11 and 12 are views for explaining an effect of the present invention;
FIG. 13 is a view illustrating a modification of the embodiment of FIG. 7; and
FIGS. 14, 15, and 16 are views illustrating steam cycles that may be implemented in the heat engine according to an embodiment of the present invention.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
The terms used in the present application are merely used to describe particular embodiments, and are not intended to limit the present invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. Throughout the specification and claims, unless explicitly described to the contrary, the word "comprise" and variations such as "comprises" or "comprising", will be understood to imply the inclusion of stated elements but not the exclusion of any other elements.
The exemplary embodiments of the present invention will now be described with reference to the accompanying drawings
In describing particular embodiments below, various characteristics are described to specifically help understand the present invention. However, a person skilled in the art to understand the present invention may recognize that the present invention may be used even without such various characteristics. In describing the present invention, moreover, the detailed description will be omitted when a specific description for publicly known technologies to which the invention pertains is judged to obscure the gist of the present invention.
Definition of terms
In the present disclosure, ‘steam cycle’includes a transcritical Rankine cycle and a supercritical Brayton cycle.
FIG. 7 is a view illustrating a heat engine according to an embodiment of the present invention, and FIG. 8 is a graph for explaining the heat engine of FIG. 7.
With reference to FIGS. 7 and 8, a heat engine according to an embodiment of the present invention may include a turbine 10, a first recuperator 30, a second recuperator 20, a condenser 40, a pump 50, and a high temperature heater 60. Meanwhile, in order to explain the concept of the present invention, an LT heat source and pipe channels.
The heat engine according to an embodiment of the present invention may operate in a Rankine cycle mode and improve exergy efficiency by appropriately utilizing the LT heat source.
The turbine 10 works while adiabatically expanding a working fluid, and discharges the working fluid to the second recuperator 20.
The second recuperator 20 heat-exchanges a working fluid discharged from the first recuperator 30 with the working fluid discharged from the turbine 10. Namely, the second recuperator 20 heat-exchanges the working fluid flowing through a fifth pipe channel 5 with the working fluid flowing through a second pipe channel 2.
The first recuperator 30 heat-exchanges a working fluid discharged from the second recuperator 20 with a working fluid discharged after being compressed by the pump 50. Namely, the first recuperator 30 heat-exchanges the working fluid flowing through a sixth pipe channel 6 and the working fluid flowing through a first pipe channel 1.
Also, the first recuperator 30 may heat-exchange a working fluid discharged after being compressed by the pump 50 and the LT heat source. Namely, the first recuperator 30 heat-exchanges the working fluid flowing through the first pipe channel with the LT heat source.
In FIG. 7, it is illustrated that the first recuperator 30 heat-exchanges the working fluid flowing through the first pipe channel 1 with the LT heat source and also heat-exchanges the working fluid flowing through the first pipe channel 1 with the working fluid flowing through the sixth pipe channel 6, but the configuration of using one recuperator is merely illustrative and any other configuration may also be implemented.
For example, the recuperator may include a single recuperator and a single low temperature heater 1. Referring to FIG, 13 a low temperature heater 34 for heat-exchanging the working fluid flowing through the first pipe channel 1 with the LT heat source and a recuperator 32 for heat-exchanging the working fluid flowing through the first pipe channel 1 with the working fluid flowing through the sixth pipe channel 6 may be separately configured.
The condenser 40 receives the working fluid discharged from the first recuperator 30, condenses and cools the received working fluid, and subsequently discharges the condensed and cooled working fluid to the pump 50.
The pump 50 compresses the condensed and cooled working fluid received from the condenser 40, and discharges the compressed working fluid to the first recuperator 30.
The working fluid which has been compressed by and discharged from the pump 50 sequentially pass through the first recuperator 30 and the second recuperator 20, heat-exchanged with the HT heat source by the heater 60, and subsequently is introduced into the turbine 10.
According to an embodiment of the present invention, the foregoing working fluid may be carbon dioxide, but this is merely illustrative and it should be appreciated by a skilled person in the art that the present invention is not limited to carbon dioxide.
According to the embodiment illustrated in FIG. 7, the working fluid may undergo the steps illustrated in FIG. 8.
Referring to FIG. 8, the working fluid which has been introduced into the turbine 10 works (169. 9kJ/kg), and is subsequently discharged with heat (T5) to a fifth pipe channel 5. The working fluid discharged to the fifth pipe channel is discharged to the sixth pipe channel 6 through the second recuperator 20.
A temperature of the working fluid in the fifth pipe channel 5 is T5 (449℃), and a temperature of the working fluid after being heat-exchanged by the second recuperator 20 is 112℃. Referring to FIG. 8, it can be seen that heat QR2 (358.1kJ/kg) has been transferred to the working fluid flowing through the second pipe channel 2.
The working fluid which has been discharged to the sixth pipe channel 6 is heat-exchanged by the first recuperator 30, and flows to the condenser 40. Referring to FIG. 8, it can be seen that, during this process, heat QR1 (91.0kJ/kg) has been transferred to the working fluid flowing through the first pipe channel 1.
Upon receiving the working fluid discharged from the second recuperator 20, the condenser 40 performs condensing and cooling process thereon. Referring to FIG. 8, the section in which the condenser 40 performs condensing and cooling is denoted by reference numeral 7~0. In this section, heat (QL+ QC) may be discarded.
The pump 50 compresses (Wp) the working fluid received through a pipe channel 0, and discharges the compressed working fluid to the first recuperator 30. Namely, the working fluid compressed by the pump 50 is introduced into the first recuperator 30 through the first pipe channel 1.
The working fluid introduced into the first recuperator 30 is heat-exchanged with the working fluid flowing through the LT heat source and the sixth pipe channel 6. Namely, the working fluid introduced into the first recuperator 30 receives heat QH1 from the LT heat source and receives heat QR1 from the working fluid flowing through the sixth pipe channel 6.
The working fluid discharged from the first recuperator 30 is introduced into the second recuperator 20 again through the second pipe channel 2, performing heat-exchange operation. Namely, the working fluid introduced into the second recuperator 20 is heat-exchanged with the working fluid flowing through the fifth pipe channel 5. Referring to FIG. 8, the working fluid introduced into the second recuperator 20 receives heat QR2.
The working fluid discharged from the second recuperator 20 is heat-exchanged with the high heat source QH in the high temperature heater 60 and subsequently supplied again to the turbine 10. Referring to FIG. 8, the working fluid receives heat QH2 from the high heat source.
As described above, the numeral values described above with reference to FIG. 8 are merely illustrative and it should be appreciated by a skilled person in the art that the present invention is not limited thereto.
FIG. 9 is a view illustrating an operation of a heat engine in a Brayton cycle mode according to another embodiment of the present invention, and FIG. 10 is a view illustrating an operation of a heat engine in a Rankine cycle mode according to another embodiment of the present invention.
The heat engine according to an embodiment of present invention illustrated in FIGS. 9 and 10 may alternately operate in the Brayton cycle mode and the Rankine cycle mode.
The heat engine illustrated in FIGS. 9 and 10 includes a turbine 110, a first recuperator 130, a second recuperator 120, a compressor 125, a thermal storage 135, a condenser 140, a cooler 145, a pump 150, direction changing units 155 and 165, and a high temperature heater 160.
The heat engine illustrated in FIGS. 9 and 10 operates in a Brayton cycle mode or a Rankine cycle mode, and when the heat engine operates in the Brayton cycle mode, the heat engine heat-exchanges a working fluid discharged from the turbine 110 with a working fluid after the compressor 125, and stores the residual heat of a working fluid in a fifth pipe channel 5 to a thermal storage 135. Also, when the heat engine operates in the Rankine cycle mode, the heat engine condenses and cools the working fluid discharged from the turbine 110, compresses the same, and heat-exchanges the compressed working fluid with the thermal storage 135 stored in the Brayton cycle mode.
Hereinafter, the Brayton cycle mode will be described with reference to FIG. 9.
In the Brayton cycle mode, the working fluid moves through the cooler 145 and the compressor 125. Namely, the direction changing unit 155 performs a switching operation to allow the working fluid, which is discharged from the compressor 125 and flows through a seventh pipe channel 6, to flow toward the cooler 145, rather than toward the condenser 140. Also, the direction changing unit 165 performs a switching operation to allow the working fluid, which is discharged from the compressor 125, to flow toward the second recuperator 120.
Also, in the Brayton cycle mode, the first recuperator 130 heat-exchanges a thermal storage fluid stored in the thermal storage 135 with a working fluid flowing through the sixth pipe channel 5 after passing through the second recuperator 120.
For example, the thermal storage 135 includes a cool tank and a hot tank, and a thermal storage fluid (which may be, for example, water but the present invention is not limited thereto) stored in the cool tank may be pumped by the pump 175, passes through the first recuperator 130, and is subsequently stored in the hot tank. Here, the pump 175 may be a bi-directional pump, but it is merely illustrative and a person skilled in the art may configure the pump 175 as a uni-directional pump.
A controller (not shown) may control a pumping direction of the pump 175, and control the heat storage fluid to move from the cool tank to the hot tank in the Brayton cycle mode and control the heat storage fluid in the opposite direction (i.e., from the hot tank to the cool tank) in the Rankine cycle mode. Also, as discussed above, the controller (not shown) may control the direction changing unit 155 to move the working fluid through the compressor 125 in the Brayton cycle mode.
The second recuperator 120 heat-exchanges the working fluid discharged through the compressor 125 with a working fluid flowing through a fourth pipe channel 4 discharged from the turbine 110. Thereafter, the high temperature heater 160 receives the working fluid flowing through a third pipe channel 2 after being discharged through the second recuperator 120, heat-exchanges the working fluid with a high pressure heat source, and discharges the same to the turbine 110.
In the Brayton cycle mode, the thermal storage fluid stored in the storage unit 135 may store heat corresponding to QL in FIG. 4. In this manner, heat stored in the heat storage fluid is used in the Rankine cycle mode.
Hereinafter, the Rankine cycle mode will be described with reference to FIG. 10.
In the Rankine cycle mode, a working fluid moves through the condenser 140 and the pump 150. Namely, the direction changing unit 155 performs a switching operation to allow the working fluid, which is discharged from the first recuperator 130, to flow toward the condenser 140, rather than toward the cooler 145. Also, the direction changing unit 165 performs a switching operation to allow a working fluid, which is discharged from the first recuperator 130, to flow toward the second recuperator 120.
In the Rankine cycle mode, the first recuperator 130 heat-exchanges the heat storage fluid stored in the hot tank of the thermal storage 135 with the working fluid pumped by the pump 150.
In the Rankine cycle mode, the pump 175 performs a pumping operation to allow the thermal storage fluid stored in the hot tank to move toward the cool tank under the control of the controller (not shown).
In the Rankine cycle mode, the first recuperator 130 heat-exchanges the working fluid flowing through the sixth pipe 6 after passing through the second recuperator 120 with the working fluid pumped by the pump 150. Thereafter, the high temperature heater 160 receives the working fluid flowing through the third pipe channel 3 after being discharged through the second recuperator 120, heat-exchanges it with the high temperature heat source, and discharges the same to the turbine 110.
In this manner, in the Rankine cycle mode, the thermal storage fluid stored in the storage unit 135 may serve as a low temperature heat source.
FIG. 11 illustrates an effect of the heat engine according to an embodiment of the present invention illustrated in FIGS. 9 and 10.
Referring to FIG. 11, a horizontal axis represents temperature and a vertical axis represents specific heat of a working fluid, in which the curve (1) indicates specific heat in a low pressure region, the curve (2) indicates specific heat in a high pressure region, and the curve (3) is obtained by doubling the curve (1).
In FIG. 11, an area indicated by the curve (1) may be heat stored by the thermal storage fluid in the Brayton cycle mode described above with reference to FIG. 9, and an area indicated by the curve (2) in FIG. 11 may indicate heat required for heating a working fluid in a state of being compressed in the Rankine cycle mode described above with reference to FIG. 10.
As a result, when heat is stored while the heat engine operates in the Brayton cycle mode as illustrated in FIG. 9 and the stored heat is used in the Brayton cycle mode while the heat engine operates in the Rankine cycle mode as illustrated in FIG. 10, the heat-exchanging operation of the first recuperator 130 in the Rankine cycle mode exhibits the same effect as that of heat-exchanging between the fluid having the specific heat characteristics indicated by the curve (2) in FIG. 11 and the fluid having the specific heat characteristics indicated by the curve (3) in FIG. 11.
This is because, in the Rankine cycle mode of FIG. 10, the working fluid discharged through the pump 150 is heat-exchange with all of the heat storage fluid stored in the hot tank and the working fluid flowing through the sixth pipe channel 6.
Namely, the thermal storage fluid (which may be, for example, water) stored in the hot tank have characteristics almost similar to the specific heat characteristics indicated by the curve (1) in FIG. 11, and the working fluid (which may be, for example, carbon dioxide) flowing through the sixth pipe channel 6 after passing through the second recuperator 120 may also have specific heat characteristics indicated by the curve (1) in FIG. 11. Thus, the sum of them has the characteristics similar to those of the fluid having the specific heat of the curve (3) in FIG. 11.
Thus, as described above with reference to FIGS. 9 and 10, the heat engine according to an embodiment of the present invention alternately operating in the Brayton cycle mode and the Rankine cycle mode shows that heat (the curve (3) in FIG. 11) obtained from the low pressure side is sufficient to heat the working fluid in the high pressure side.
FIG. 12 is a view for explaining an effect of the present invention.
FIG. 12 shows the comparison of exergy efficiency of the heat engine (R-CO2) operating in the conventional Rankine cycle mode, exergy efficiency of the heat engine (B-CO2) operating in the conventional Brayton cycle mode, and exergy efficiency of the heat engine operating in the Rankine cycle mode (LH T-CO2 LH R-CO2) in which both a low temperature heat source and a high temperature heat source are used according to an embodiment of the present invention.
Namely, in comparison to the exergy efficiency of the heat engine (R-CO2) operating the conventional Rankine cycle mode as 0.614 and the exergy efficiency of the heat engine (B-CO2) operating the conventional Brayton cycle mode as 0.629, the exergy efficiency of heat engine operating the Rankine cycle mode (LH R-CO2) in which both a low temperature heat source and a high temperature heat source are used according to an embodiment of the present invention is 0.723, and thus, it can be seen that the exergy efficiency is improved.
It can be seen that, in the three types of heat engines, the outputs of the existing Rankin cycle (R-CO2) and the Rankine cycle (LH R-CO2) according to an embodiment of the present invention are the same 150.4 but the present invention is superior in the exergy efficiency. Namely, the related art heat engines (R-CO2 and B-CO2) achieve the outputs (150.4 and 119.4, respectively) by using only high grade heat source 100%, but the heat engine (LH R-CO2) according to an embodiment of the present invention achieves the output of 150.4 by using a low grade heat source 25% and a high grade heat source 75%, and in this aspect, it can be said that the heat engine according to an embodiment of the present invention has a superior effect to those of the related art heat engines.
In this case, in general, heat efficiency of a low grade heat source does not exceed a maximum of 10%, but the heat engine according to an embodiment of the present invention increases heat efficiency of a low grade heat source up to about 25%, and this is supposedly because the low grade heat source was not used at any random timing but used in an appropriate section.
FIG. 13 is a view illustrating a modification of the embodiment of FIG. 7.
A heat engine illustrated in FIG. 13 may include the turbine 10, a first recuperator 32, a low temperature heater 34, the second recuperator 20, the condenser 40, the pump 50, and the high temperature heater 60.
The other remaining components, excluding the first recuperator 32 and the low temperature heater 34, perform the same or similar operation as those of the components of FIG. 7 using the same reference numerals.
The low temperature heater 34 heat-exchanges a working fluid compressed by the pump 50 with a low grade heat source, and the first recuperator 32 heat-exchanges a working fluid discharged from the low temperature heater 34 with a working fluid flowing through the sixth pipe channel 60 after passing through the high temperature heater 20.
Meanwhile, in the embodiment of FIG. 13, the working fluid compressed by the pump 50 is first heat-exchanged with the low grade heat source, but it may also be first heat-exchanged with the working fluid flowing through the sixth pipe channel 60.
As described above, the heat engine according to an embodiment of the present invention may have the Rankine cycle mode with improved exergy efficiency, and in a modification thereof, a low grade heat source may be secured in the Brayton cycle mode and used in the Rankine cycle mode.
FIGS. 14, 15, and 16 are views illustrating steam cycles that may be implemented in the heat engine according to an embodiment of the present invention.
As illustrated in FIGS. 14, 15, and 16, when an operation condition of a lower pressure side is higher than a transcritical pressure of a working fluid, the working fluid has the characteristics in that it does not go through an obvious phase-change process during a condensing process. In the working fluid cooled in this case, a liquid and gas are not conspicuously discriminated, making it vague to discriminate the Rankine cycle (which accompanies a phase change) and the Brayton cycle (gas cycle). However, even in this case, a completely cooled cycle as illustrated in FIG. 14 may be considered to be the Rankine cycle (FIG. 5) of the foregoing technique in the present invention, the partially cooled cycle as illustrated in FIG. 15 may be considered to be the Brayton cycle (FIG. 6) of the foregoing technique in the present invention, and the cycle using both a low temperature heat source and a high temperature heat source in the completely cooled cycle as illustrated in FIG. 16 may be considered to be a Rankine cycle (FIG. 8) using both the low temperature heat source and the high temperature heat source of the foregoing technique in the present invention. In this manner, although the steam cycle is not conspicuously discriminated as the Rankine cycle or the Brayton cycle, the foregoing configuration according to an embodiment of the present invention can be applied and the same effect can be obtained. Namely, the concept of the present invention may be applied as is even to an operation region in which a conspicuous phase change is not made because the low pressure side has a pressure higher than the transcritical pressure of a working fluid, as well as in the operation condition in which the low pressure side undergoes a conspicuous phase change.
According to an aspect of the present invention, there may be provided a Rankine cycle method with improved exergy efficiency used in a heat engine, including condensing and cooling a working fluid discharged from a turbine, compressing the condensed and cooled working fluid, a first heat exchange step of heat-exchanging the compressed operation fluid with a low grade heat source, a second heat-exchanging step of heat-exchanging the working fluid discharged from the turbine with the working fluid which has undergone the first heat exchange step before being condensed and cooled. Here, the working fluid which has undergone the first heat exchange step and the second heat exchange step is introduced into the turbine.
The Rankine cycle method with improved exergy efficiency further includes: a third heat exchange step of heat-exchanging the working fluid which has undergone the second heat exchange step with the compressed working fluid before the working fluid which has undergone the second heat exchange step is condensed and cooled, wherein the working fluid which has undergone the first heat exchange step, the second heat exchange step, and the third heat exchange step may be introduced into the turbine.
According to another aspect of the present invention, there may be provided a method for increasing exergy efficiency of a heat engine including a turbine, a compressor, and a condenser. For example, this method may be implemented to include changing a direction of a working flow discharged from the turbine such that the working flow flows to the compressor in a Brayton cycle mode and flows to the condenser in a Rankine cycle mode, heat-exchanging the working fluid before flowing to the compressor and a thermal storage fluid in the Brayton cycle mode, and introducing the working fluid discharged from the condenser or the compressor into the turbine.
According to still another aspect of the present invention, there may be provided a method for operating a heat engine, including operating a heat engine which works by circulating a working fluid, in a Brayton cycle mode or a Rankine cycle mode, heat-exchanging a thermal storage fluid with a working fluid before being cooled and storing the same, in a Brayton cycle mode in which a working fluid discharged from a turbine is cooled and subsequently compressed, and heat-exchanging the compressed working fluid with a thermal storage fluid stored in the Brayton cycle mode, in a Rankine cycle mode in which the working fluid discharged from the turbine is condensed, cooled, and subsequently compressed.
While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
<Description of symbols>
10, 110: turbine 30, 130: first recuperator
20, 120: second recuperator 40, 140: condenser
50, 150: pump 60: high temperature heater
125: compressor 135: thermal storage
145: cooler 155, 165; direction changing unit
160: high temperature heater

Claims (24)

  1. A Rankine cycle with improved exergy efficiency used in a heat engine, the Rankine cycle comprising:
    condensing and cooling a working fluid discharged from a turbine;
    compressing the condensed and cooled working fluid;
    a first heat exchange operation of heat-exchanging the compressed operation fluid with a low grade heat source;
    a second heat-exchanging operation of heat-exchanging the working fluid discharged from the turbine with the working fluid which has undergone the first heat exchange operation before being condensed and cooled; and
    wherein the working fluid which has undergone the first heat exchange operation and the second heat exchange operation is introduced into the turbine.
  2. The Rankine cycle of claim 1, wherein the working fluid is dioxide carbon.
  3. The method of claim 1, further comprising:
    a third heat exchange operation of heat-exchanging the working fluid which has undergone the second heat exchange operation with the compressed working fluid before the working fluid which has undergone the second heat exchange operation is condensed and cooled,
    wherein the working fluid which has undergone the first heat exchange operation, the second heat exchange operation, and the third heat exchange operation is introduced into the turbine.
  4. A Rankine cycle-based heat engine comprising:
    a turbine discharging a working fluid;
    a condenser condensing and cooling the working fluid discharged from the turbine;
    a pump compressing the condensed and cooled working fluid;
    a first recuperator heat-exchanging the compressed working fluid with a low grade heat source; and
    a second recuperator heat-exchanging the working fluid, which has been discharged from the turbine but not introduced into the condenser yet, with the working fluid heat-exchanged by the first recuperator,
    wherein the working fluid, which has undergone heat-exchanging by the first recuperator and the second recuperator, is intordcued into the turbine.
  5. The Rankine cycle-based heat engine of claim 4, wherein the working fluid is carbon dioxide.
  6. The Rankine cycle-based heat engine of claim 4, wherein the first recuperator heat-exchanges the working fluid, which has been heat-exchanged by the second recuperator but not introduced into the condenser yet, with the working fluid compressed by the pump.
  7. A steam cycle-based heat engine comprising:
    a turbine working by a working fluid;
    a condenser condensing and cooling the working fluid discharged from the turbine;
    a pump compressing the condensed and cooled working fluid from the condenser;
    a first pipe channel providing a path allowing the working fluid discharged from the turbine to move to the condenser therethrough;
    a second pipe channel providing a path allowing the working fluid discharged from the pump to move to the turbine therethrough;
    a first recuperator heat-exchanging the working fluid moving through the second pipe channel with a low grade heat source; and
    a second recuperator disposed between the first recuperator and the turbine and heat-exchanging the working fluid flowing through the first pipe channel with the working fluid flowing through the second pipe channel.
  8. The steam cycle-based heat engine of claim 7, wherein the working fluid is carbon dioxide.
  9. The steam cycle-based heat engine of claim 7, wherein the first recuperator heat-exchanges the working fluid, which has been heat-exchanged by the second recuperator but not introduced into the condenser yet, with the working fluid compressed by the pump.
  10. A heat engine with improved exergy efficiency operating in a Brayton cycle mode and a Rankine cycle mode, the heat engine comprising:
    a turbine working by a working fluid;
    a direction changing unit allowing the working fluid discharged from the turbine to any one of a condenser and a compressor; and
    a first recuperator heat-exchanging the working fluid before flowing to the condenser or the compressor, with a thermal storage fluid,
    wherein the working fluid discharged from the condenser or the compressor is introduced into the turbine.
  11. The heat engine of claim 10, further comprising:
    a thermal storage configured to store the thermal storage fluid.
  12. The heat engine of claim 11, wherein in the Brayton cycle mode, the direction changing unit changes a direction of the working fluid discharged from the turbine such that it flows to the compressor.
  13. The heat engine of claim 12, further comprising:
    a cooler disposed between the direction changing unit and the compressor,
    wherein the cooler receives the working fluid from the direction changing unit, cools the received working fluid, and discharges the cooled working fluid to the compressor.
  14. The heat engine of claim 11, wherein in the Rankine cycle mode, the direction changing unit changes a direction of the working fluid discharged from the turbine such that the working fluid flows to the condenser.
  15. The heat engine of claim 14, further comprising:
    of claim 14, wherein:
    a pump compressing the working fluid discharged from the condenser.
  16. The heat engine of claim 14, wherein in the Rankine cycle mode, the first recuperator heat-exchanges the working fluid before flowing the condenser or the compressor, the thermal storage fluid stored in the thermal storage, and the working fluid discharged from the pump with each other.
  17. The heat engine of claim 10, further comprising:
    of claim 10, wherein:
    a second recuperator heat-exchanging the working fluid before being introduced into the first recuperator and the working fluid discharged from the condenser or the compressor.
  18. A method for increasing exergy efficiency of a heat engine including a turbine, a compressor, and a condenser, the method comprising:
    changing a direction of a working flow discharged from the turbine such that the working flow flows to the compressor in a Brayton cycle mode and flows to the condenser in a Rankine cycle mode;
    heat-exchanging the working fluid before flowing to the compressor and a thermal storage fluid in the Brayton cycle mode; and
    introducing the working fluid discharged from the condenser or the compressor into the turbine.
  19. The method of claim 18, further comprising:
    storing the thermal storage fluid in the Brayton cycle mode.
  20. The method of claim 18, further comprising:
    cooling the working fluid before being introduced into the compressor, in the Brayton cycle mode.
  21. The method of claim 19, further comprising:
    compressing the working fluid discharged from the condenser by a pump in the Rankine cycle mode.
  22. The method of claim 21, further comprising:
    : heat-exchanging the thermal storage fluid stored in the Brayton cycle mode with the working fluid discharged after being compressed by the pump, in the Rankine cycle mode.
  23. The method of claim 22, further comprising:
    heat-exchanging the working fluid before flowing to the condenser with the working fluid discharged after being compressed by the pump, in the Rankine cycle mode.
  24. A method for operating a heat engine, the method comprising:
    operating a heat engine which works by circulating a working fluid, in a Brayton cycle mode or a Rankine cycle mode;
    heat-exchanging a thermal storage fluid with a working fluid before being cooled and storing the same, in a Brayton cycle mode in which a working fluid discharged from a turbine is cooled and subsequently compressed; and
    heat-exchanging the compressed working fluid with a thermal storage fluid stored in the Brayton cycle mode, in a Rankine cycle mode in which the working fluid discharged from the turbine is condensed, cooled, and subsequently compressed.
PCT/KR2012/010664 2011-12-20 2012-12-07 Heat engine based on transcritical rankine cycle with improved exergy efficiency and method thereof WO2013094905A1 (en)

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