JP2018021485A - Multistage rankine cycle system, internal combustion engine and operation method of multistage rankine cycle system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multistage Rankine cycle system which comprises a relatively-high temperature heat source and a relatively-low temperature heat source and recovers heat from both of the heat sources, and can fully recovers the heat from the relatively-low temperature heat source by using the heat from the relatively-low temperature heat source for the evaporation of a working fluid, and which therefor can provide a higher heat utilization effect, and an internal combustion engine with the multistage Rankine cycle system.SOLUTION: The multistage Rankine cycle system is provided that comprises: a first Rankine cycle system which has a first working fluid pump, a first evaporator, a first expander and a first capacitor, makes a first working fluid circulate, and recovers heat from a first heat source; and a second Rankine cycle system which has a second working fluid pump, a second evaporator, a second expander and a second capacitor, makes a second working fluid circulate, and recovers heat from a second heat source. In the multistage Rankine cycle system, the first working fluid flowing from the first expander is introduced into the high-temperature side piping of the first capacitor, and the second working fluid flowing from the second evaporator is made to pass through a low-temperature side heat transfer pipe of the first evaporator, and after that, made to flow into the second expander.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a multistage Rankine cycle system, an internal combustion engine, and an operation method for a multistage Rankine cycle system that can recover heat from both a high temperature side heat source and a low temperature side heat source and can expect a higher fuel efficiency improvement effect.

  As a Rankine cycle system that uses exhaust heat from an internal combustion engine or the like mounted on a vehicle, the first working fluid is evaporated in a first organic Rankine cycle (ORC) using the heat of a high-temperature waste heat source of exhaust gas, and a jacket Cascade type organic Rankine cycle system using exhaust heat from an internal combustion engine that heats the second working fluid to a temperature lower than the evaporation temperature in the second organic Rankine cycle using the heat of the low-temperature waste heat source of the cooling water Is known (see, for example, Patent Document 1).

  In this Rankine cycle system, the condensation of the first organic working fluid and the evaporation of the second organic working fluid are performed with one heat exchanger. In other words, this heat exchanger serves as both the condenser of the first organic Rankine cycle and the evaporator of the second organic Rankine cycle.

Special table 2010-540837

  However, in this Rankine cycle system, a heat sink is provided upstream of the heat exchanger, and the second working fluid is maintained at a temperature lower than the evaporation temperature, that is, in a liquid state by the low-temperature waste heat source of the jacket cooling water. It is heated as it is. Therefore, the heat of the low-temperature waste heat source is only used for raising the temperature of the second working fluid in the liquid state, and is not used for the evaporation of the second working fluid. is there.

  The object of the present invention is to recover heat from both the high temperature side heat source and the low temperature side heat source, and to sufficiently recover heat by using the heat from the low temperature side heat source for the evaporation of the working fluid. An object of the present invention is to provide a multistage Rankine cycle system, an internal combustion engine, and an operation method of the multistage Rankine cycle system capable of obtaining a heat utilization effect.

  In order to achieve the above object, a multi-stage Rankine cycle system of the present invention is a multi-stage Rankine cycle system comprising a first Rankine cycle system and a second Rankine cycle system, wherein the first Rankine cycle system includes a first working fluid. The first working fluid circulates by connecting the first pump, the low temperature side heat transfer tube of the first evaporator, the first expander, the high temperature side heat transfer tube of the first condenser, and the first working fluid pump in this order. And the first heat source fluid as the first heat source is connected by piping so as to pass through the high temperature side heat transfer tube of the first evaporator. In the second Rankine cycle system, 2. The working fluid pump, the low temperature side heat transfer tube of the second evaporator, the low temperature side heat transfer tube of the first condenser, the second expander, the high temperature side heat transfer tube of the second condenser, and the second working fluid pump. It is connected by piping so that the second working fluid circulates, and the second heat source fluid as the second heat source is connected by piping so as to pass through the high temperature side heat transfer tube of the second evaporator. It is a system characterized by that.

  As used herein, “connected by piping” means that the working fluid can be circulated between the respective devices. Normally, the mutual devices are connected via the piping, but there is a piping between the mutual devices. Does not mean that it is essential, and a directly connected structure may be used.

  In order to achieve the above object, an internal combustion engine of the present invention is an internal combustion engine including the multi-stage Rankine cycle system described above.

  In order to achieve the above object, an operating method of a multi-stage Rankine cycle system of the present invention comprises a first working fluid pump, a first evaporator, a first expander, and a first condenser. A first Rankine cycle system that circulates one working fluid; a second working fluid pump; a second evaporator; a second expander; and a second condenser that circulates the second working fluid. In the operation method of the multi-stage Rankine cycle system including the two Rankine cycle system, in the first Rankine cycle system, the first working fluid is sent to the first evaporator by the first working fluid pump. The first working fluid is evaporated by using the heat of the first heat source in the evaporator, the first working fluid is driven by the first working fluid in the evaporated state, and the first working fluid is discharged from the first working device. Before liquefying with the first condenser The second working fluid is circulated to the first working fluid pump, and in the second Rankine cycle system, the second working fluid is sent to the second evaporator by the second working fluid pump, and the second evaporator provides a second heat source. The second working fluid is evaporated by using the heat of the second working fluid, the second working fluid in the evaporated state is sent to the first condenser, and the heat from the first working fluid is sent to the second working fluid by the first condenser. After moving to the fluid, the second expander is driven by the second working fluid in the evaporated state, and the second working fluid discharged from the second expander is liquefied by the second condenser, and the second condenser is liquefied. It is an operating method characterized by circulating in a working fluid pump.

  According to the multistage Rankine cycle system, the internal combustion engine, and the operation method of the multistage Rankine cycle system of the present invention, the heat from both the high temperature side heat source and the low temperature side heat source is recovered and the heat from the low temperature side heat source is operated. By using it for the evaporation of the fluid, sufficient heat recovery can be achieved, and a higher heat utilization effect can be obtained.

It is a figure showing typically composition of a multi stage Rankine cycle system of a 1st embodiment concerning the present invention. It is a figure which shows typically the structure of the multistage Rankine cycle system of 2nd Embodiment which concerns on this invention. It is a figure which shows typically the structure of the multistage Rankine cycle system in a comparative example. It is a PV diagram for description of a Rankine cycle system. It is a Ts diagram for description of a Rankine cycle system.

  Hereinafter, a multistage Rankine cycle system, an internal combustion engine, and an operation method of the multistage Rankine cycle system according to embodiments of the present invention will be described with reference to the drawings. Here, the multistage Rankine cycle system uses the exhaust gas of the diesel engine mounted on the vehicle as the first heat source fluid of the first heat source of the high temperature side heat source, and uses the engine coolant as the second heat source of the low temperature side heat source. An example in which the second heat source fluid is used will be described.

  However, the operation method of the multistage Rankine cycle system, the internal combustion engine, and the multistage Rankine cycle system of the present invention is not limited to this, and a heat source and a heat source fluid other than the diesel engine mounted on the vehicle may be used. . For example, it may be a stationary internal combustion engine, or a heat source and heat source fluid from other than the internal combustion engine.

  In addition, the following “connected by piping” means that the working fluid can be circulated between the respective devices. Normally, the mutual devices are connected via the piping, but there is a piping between the mutual devices. Does not mean that is essential, and may be a directly connected structure.

  As shown in FIG. 1, the multistage Rankine cycle system 1 according to the first embodiment of the present invention includes a first Rankine cycle system 10 and a second Rankine cycle system 20.

  In the first Rankine cycle system 10, the first working fluid pump 12, the low temperature side heat transfer tubes of the first evaporator 13, the first expander 14, the high temperature side heat transfer tubes of the first condenser 15, and the first working fluid use. The pump 12 is connected with a pipe in order, and the first working fluid Fw1 is circulated.

  At the same time, the first heat source fluid G, which is the first heat source, is connected by piping so as to pass through the high temperature side heat transfer tube of the first evaporator 13. Here, the first heat source fluid G is the exhaust gas G discharged from the engine body 2. That is, the exhaust gas G exhausted from the engine main body 2 and passed through the turbocharger turbine 3 and the aftertreatment device 4 that purifies the exhaust gas G is used as the first heat source. The exhaust gas G passes through the high temperature side heat transfer tube of the first evaporator 13 and gives the heat to the first working fluid Fw1 passing through the low temperature side heat transfer tube of the first evaporator 13, so that the first working fluid Evaporate Fw1.

  On the other hand, in the second Rankine cycle system 20, the second working fluid pump 22, the low temperature side heat transfer tube of the second evaporator 23, the low temperature side heat transfer tube of the first condenser 15, the second expander 24, and the second condenser. 25 high temperature side heat transfer tubes and the second working fluid pump 12 are connected in order by piping so that the second working fluid Fw2 circulates.

  At the same time, the second heat source fluid We, which is the second heat source, is connected by piping so as to pass through the low temperature side heat transfer tube of the second evaporator 23. Here, the second heat source fluid We is engine cooling water We that cools the engine body 2. That is, as the second heat source, the engine coolant water We that is supplied from the coolant pump 6 and passes through the engine main body 2 and the EGR cooler 5 and rises in temperature is joined. This engine cooling water We passes through the high temperature side heat transfer tube of the second evaporator 23, gives the heat to the second working fluid Fw2 passing through the low temperature side heat transfer tube of the second evaporator 23, and 2 The working fluid Fw2 is evaporated.

  For the first working fluid Fw1, an organic refrigerant suitable for recovering heat of a relatively high-temperature heat source such as the exhaust gas G of about 200 ° C. to 400 ° C. is used. As the organic refrigerant, a binary mixed medium such as water and ethanol, water and methanol, or water and ethylene glycol can be used, but only pure water or ethanol may be used. Further, an organic liquid having a low boiling point such as n-pentane or toluene may be used.

  In addition, as the second working fluid Fw2, a chlorofluorocarbon-based refrigerant suitable for recovering the heat of a relatively low-temperature heat source such as the engine cooling water We such as 80 ° C. to 100 ° C. is used. R123, R134a, R236fa, R245fa, or the like can be used as the fluorocarbon refrigerant.

  The first working fluid pump 12 is a device for circulating the first working fluid Fw <b> 1 in a liquid state through the first Rankine cycle system 10. The second working fluid pump 22 is a device that circulates the second working fluid Fw <b> 2 in a liquid state through the second Rankine cycle 20.

  The first evaporator 13 and the second evaporator 23 are also called evaporators, and are devices having a function of positively evaporating liquid by reducing the pressure, and are configured by a boiler or the like. As the first heat source on the high temperature side in the first evaporator 13, exhaust gas G of an in-vehicle diesel engine, in particular, exhaust gas G after passing through the aftertreatment device 4 is used as a heat source, but EGR gas, supercharging Intake air compressed by a container may be used as a heat source. Further, the low temperature side heat source in the second evaporator 23 is preferable because the engine cooling water We after heat absorption by the engine body 2 and the EGR cooler 5 becomes high temperature.

  The first expander 14 and the second expander 24 are also called expanders, and have a function of extracting mechanical energy such as rotational torque when a high-pressure steam is adiabatically expanded into a low-pressure steam. It is composed of a turbine or the like. Here, the first expander 14 and the second expander 24 are configured to rotate the same drive shaft (turbine shaft) 14a.

  The use of the energy extracted by the drive shaft 14a is not particularly shown, but when assisting the rotation of the engine, the crankshaft of the engine is connected to the drive shaft 14a and the generator is used for power generation. The generated electric power connected to the drive shaft 14a is charged in a battery and used for an electrical component of a vehicle on which the engine is mounted.

  The first condenser 15 and the second condenser 25 are devices called a condenser and a condenser, and have a function of cooling vapor (gas) into a liquid. Here, the first working fluid Fw1 of the first condenser 15 is cooled by the second working fluid Fw2 exiting the second evaporator 23. With this configuration, the first condenser 15 of the first Rankine cycle system 10 has a function as a superheater (super heater) that superheats the second working fluid Fw2 in the gaseous state of the second Rankine cycle system 20.

  On the other hand, the second working fluid Fw2 of the second condenser 25 is cooled by air (outside air, atmosphere) A. In the case of this air cooling, a cooling fan (not shown) is usually arranged. According to this configuration, the cooling unit for the first working fluid Fw1 of the first Rankine cycle system 10 on the high temperature side is the heat recovery unit for the second working fluid Fw2 of the second Rankine cycle system 20 on the low temperature side. Even in one Rankine cycle system 10, 20, only one second condenser 25 is required for the heat radiation part to the outside.

  The second condenser 25 that cools the second working fluid Fw2 is not necessarily limited to air cooling, and may be water cooled. For example, you may cool with the engine cooling water We which thermally radiated and fell with the radiator 7.

  Next, an operation method of the multistage Rankine cycle system according to the first embodiment of the present invention will be described. The operation method of the multi-stage Rankine cycle system in the multi-stage Rankine cycle system 1 of the first embodiment includes a first working fluid pump 12, a first evaporator 13, and a first expander as shown in FIG. 14 and the first condenser 15, the first Rankine cycle system 10, the second working fluid pump 22, the second evaporator 23, the second expander 24, and the second condenser 25. Is a method of operating the multi-stage Rankine cycle system 1 including the second Rankine cycle system 20 having

  In the operation method of this multi-stage Rankine cycle system, in the first Rankine cycle system 10, the first working fluid Fw1 is sent to the first evaporator 13 by the first working fluid pump 12, and the first evaporator 13 sends the first heat source. The first working fluid Fw1 is evaporated using the heat of the exhaust gas G. The first expander 14 is driven by the evaporated first working fluid Fw, and the first working fluid Fw1 discharged from the first expander 14 is liquefied by the first condenser 15, and the first working fluid pump 12 is used. To circulate.

  More specifically, in the first Rankine cycle system 10, as shown in FIGS. 4 and 5, the first working fluid Fw1 stored in the first working fluid container (not shown) is used for the first working fluid. Compressed and circulated in the liquid state (C1) by the pump 12 (Win), and sent to the first evaporator 13 in the compressed liquid state (C2). In the first evaporator 13, the exhaust gas G (Qin), the first working fluid Fw1 is vaporized into superheated steam. Then, the first working fluid Fw1 in the state of the high-pressure superheated vapor (C3) that is vaporized and heated at a constant pressure (C3) is adiabatically expanded by the first expander 14 to extract the driving force (Wout), and this pressure is reduced. The first working fluid Fw1 in the gas state (C4) is sent to the first condenser 15, and the first condenser 15 releases heat to the outside (Qout) to liquefy the first working fluid Fw. To the working fluid container and the first working fluid pump 12.

  On the other hand, in the second Rankine cycle system 20, the second working fluid Fw2 is sent to the second evaporator 23 by the second working fluid pump 22, and the heat of the engine cooling water We serving as the second heat source is sent by the second evaporator 23. To evaporate the second working fluid. The second working fluid Fw2 in the evaporated state is sent to the first condenser 15, and the first condenser 15 moves the heat from the first working fluid Fw1 to the second working fluid Fw2, and the second working fluid in the vapor state. Fw2 is overheated. After that, the second expander 14 is driven by the second working fluid Fw2 in the vapor state, and the second working fluid Fw2 output from the second expander 14 is liquefied by the second condenser 25 to be liquefied by the second working fluid. It is made to circulate to the pump 22.

  More specifically, in the second Rankine cycle system 20, similarly, as shown in FIGS. 4 and 5, the second working fluid Fw2 stored in the second working fluid container (not shown) is used as the second working fluid. It is compressed and circulated in the liquid state (C1) by the fluid pump 22 (Win), and sent to the second evaporator 23 in the compressed liquid state (C2). Upon receiving heat from the cooling water We (indicated by the exhaust gas G in FIGS. 2 and 4) (Qin), the second working fluid Fw2 is vaporized (evaporated) and superheated by the first condenser 15 to be superheated. And Then, the second working fluid Fw2 in the state of the high-pressure superheated vapor (C3) that has been vaporized and heated at a constant pressure (C3) is adiabatically expanded by the second expander 24 to extract the driving force (Wout). The second working fluid Fw2 in the gas state (C4) is sent to the second condenser 25, and the second condenser 25 releases heat to the outside (Qout) to liquefy the second working fluid Fw2. Is sent to the second working fluid container and the second working fluid pump 22.

  Looking at the heat transfer in the multistage Rankine cycle system 1, the heat of the exhaust gas G, which is the first heat source, is transferred from the exhaust gas G to the first working fluid Fw 1 by the first evaporator 13, and in the first expander 14. Converted to mechanical energy. Further, the heat of the engine cooling water We, which is the second heat source, moves from the engine cooling water We to the second working fluid Fw2 by the second evaporator 23, and is converted into mechanical energy by the second expander 24.

  Therefore, in the present invention, the first condenser 15 cools the first working fluid Fw1 with the second working fluid Fw2, in other words, the first working fluid Fw1 overheats the second working fluid Fw2, thereby The heat energy of the first working fluid Fw1 that has not been used up by the expander 14 is given to the second working fluid Fw2 and converted into mechanical energy by the second expander 24, so that the heat recovery efficiency can be improved.

  As shown in FIG. 2, the multistage Rankine cycle system 1A according to the second embodiment of the present invention further includes a recuperator 16 in the first Rankine cycle system 10A. The inlet side of the low temperature side heat transfer tube is connected to the first working fluid pump 12, and the outlet side of the low temperature side heat transfer tube of the recuperator 16 is connected to the low temperature side heat transfer tube of the first evaporator 13. At the same time, the inlet side of the high temperature side heat transfer tube of the recuperator 16 is connected to the first expander 14, and the outlet side of the high temperature side pipe of the recuperator 16 is connected to the high temperature side heat transfer tube of the first condenser 15. Has been. Other configurations are the same as those of the multistage Rankine cycle system 1 of the first embodiment.

  The recuperator 16 is also called a recuperator, and has a function of heating the low-temperature side liquid with the heat of the high-temperature side gas, and conversely, cooling the high-temperature side gas with the low-temperature side liquid. . Here, the first working fluid Fw1 in the liquid state on the low temperature side from the first working fluid pump 12 is heated and preheated with the first working fluid Fw1 in the gas state on the high temperature side from the first expander 14. On the other hand, the temperature of the first working fluid Fw1 in the gas state on the low temperature side entering the first condenser 15 is lowered to increase the temperature difference from the second working fluid Fw2 in the gas state on the high temperature side from the second evaporator. Thus, the efficiency of heat transfer from the second working fluid Fw2 that has recovered heat from the engine cooling water We to the first working fluid Fw1 is improved. Thereby, the thermal efficiency of the heat recovery from the engine cooling water We is increased.

  Next, an operation method of the multistage Rankine cycle system according to the second embodiment of the present invention will be described. The operation method of the multi-stage Rankine cycle system in the multi-stage Rankine cycle system 1A of the second embodiment includes a first working fluid pump 12, a first evaporator 13, and a first expander as shown in FIG. 14, a first Rankine cycle system 10A having a recuperator 16 in addition to the first condenser 15, a second working fluid pump 22, a second evaporator 23, and a second expander 24. The operation method of the multistage Rankine cycle system 1 </ b> A including the second Rankine cycle system 20 having the second condenser 25.

  In the operation method of this multi-stage Rankine cycle system, in the first Rankine cycle system 10, the first working fluid Fw1 is sent to the first evaporator 13 by the first working fluid pump 12, and the first evaporator 13 sends the first heat source. The first working fluid Fw1 is evaporated using the heat of the exhaust gas G. The first expander 14 is driven by the evaporated first working fluid Fw, and the first working fluid Fw1 output from the first expander 14 is allowed to pass through the recuperator 16 to be discharged from the first expander 14. The heat of the first working fluid Fw1 that has come out is transferred to the first working fluid Fw1 before flowing into the first evaporator 13 and heated, and then sent to the first condenser 15. The first working fluid Fw1 is liquefied by the first condenser 15 and circulated to the first working fluid pump 12.

  Looking at the heat transfer in the multistage Rankine cycle system 1A of the second embodiment, in addition to the heat transfer in the multistage Rankine cycle system 1 of the first embodiment, the pump for the first working fluid in the recuperator 16 The first working fluid Fw1 in the liquid state before exiting the first evaporator 13 and entering the first evaporator 13 is heated by the first working fluid Fw1 in the gaseous state before exiting the first expander 14 and entering the first condenser 15. Therefore, evaporation in the first evaporator 13 and liquefaction in the first condenser 15 can be promoted more efficiently. Thereby, heat recovery efficiency can be improved.

  The Rankine cycle system 1X of the comparative example, which is configured by only the one Rankine cycle shown in FIG. 3, includes the first working fluid pump 12 and the second stage Rankine cycle system 1, 1 A of the embodiment according to the present invention. 1 is a system that has an evaporator 13, a first expander 14, and a first condenser 15, and circulates the first working fluid Fw1 to recover heat from the exhaust gas G that is the first heat source. In the first condenser 1, the first working fluid Fw1 is cooled by the engine cooling water We and returned to the liquid. Therefore, not only the heat energy of the engine cooling water We cannot be used for heat recovery, but also the engine cooling water We rises in temperature, so that it is necessary to increase the heat radiation amount in the radiator 7 and the like.

  In contrast to this comparative example, the multi-stage Rankine cycle system 1, 1 </ b> A according to the embodiment of the present invention can recover heat from the engine cooling water We and can lower the temperature of the engine cooling water We. It is possible to reduce the amount of heat release.

  Therefore, according to the operation method of the multistage Rankine cycle system 10, 10A and the multistage Rankine cycle system according to the embodiment of the present invention, the heat sources of both the exhaust gas G of the high temperature side heat source and the engine cooling water We of the low temperature side heat source. In addition, the heat from the engine coolant water We of the low-temperature side heat source can be used for the evaporation of the first working fluid Fw1, so that the heat can be sufficiently recovered and a higher heat utilization effect can be obtained.

  As shown in FIGS. 1 and 2, the internal combustion engine (engine) according to the embodiment of the present invention includes the multi-stage Rankine cycle system 1, 1 </ b> A, and these multi-stage Rankine cycle system 1. The effect obtained from 1A can be obtained similarly, and the fuel efficiency improvement effect in the internal combustion engine can be improved.

  1 and 2, the exhaust gas G generated from the engine body 2 is used as the first heat source fluid, and the engine coolant water We is used to cool the EGR gas using the engine body 2 and the EGR cooler 5 as the second heat source fluid. However, the present invention is not necessarily limited to this, and another heat source may be used.

10, 10A 1st Rankine cycle system 10X Rankine cycle system 12 of comparative example 12 1st working fluid pump 13 1st evaporator 14 1st expander 15 1st condenser 16 Recuperator 20 2nd Rankine cycle system 22 2nd Working fluid pump 23 Second evaporator 24 Second expander 25 First condenser A Air (cooling source)
Fw1 first working fluid Fw2 second working fluid G exhaust gas (first heat source)
We engine coolant (second heat source)

Claims (6)

In a multi-stage Rankine cycle system including a first Rankine cycle system and a second Rankine cycle system,
In the first Rankine cycle system, the first working fluid pump, the low temperature side heat transfer tube of the first evaporator, the first expander, the high temperature side heat transfer tube of the first condenser, and the first working fluid pump are sequentially arranged. It is connected by piping so that the first working fluid circulates, and the first heat source fluid as the first heat source is connected by piping so as to pass through the high temperature side heat transfer tube of the first evaporator. And
In the second Rankine cycle system, the second working fluid pump, the low temperature side heat transfer tube of the second evaporator, the low temperature side heat transfer tube of the first condenser, the second expander, and the high temperature side heat transfer tube of the second condenser, The second working fluid pump is connected to the second working fluid in order so that the second working fluid circulates, and the second heat source fluid as the second heat source serves as the high temperature side heat transfer tube of the second evaporator. A multi-stage Rankine cycle system characterized by being connected by piping so as to pass through. A recuperator is provided in the first Rankine cycle system, and the inlet side of the low-temperature side heat transfer tube of the recuperator is connected to the first working fluid pump, and the outlet side is connected to the low-temperature side heat transfer tube of the first evaporator. Connected,
2. The multistage according to claim 1, wherein an inlet side of a high temperature side heat transfer tube of the recuperator is connected to the first expander and an outlet side is connected to a high temperature side heat transfer tube of the first condenser by piping. Rankine cycle system.   The multistage Rankine cycle system according to claim 1 or 2, wherein the first expander and the second expander are configured to drive the same drive shaft.   The multistage according to any one of claims 1 to 3, wherein the first heat source fluid is exhaust gas generated from an internal combustion engine, and the second heat source fluid is engine cooling water of the internal combustion engine. Rankine cycle system.   An internal combustion engine comprising the multistage Rankine cycle system according to claim 4. A first Rankine cycle system having a first working fluid pump, a first evaporator, a first expander, and a first condenser and circulating the first working fluid; and a second working fluid pump; In the operation method of the multi-stage Rankine cycle system comprising the second evaporator, the second expander, and the second Rankine cycle system having the second condenser and circulating the second working fluid,
In the first Rankine cycle system, the first working fluid is sent to the first evaporator by the first working fluid pump, and the first working fluid is utilized by the heat of the first heat source in the first evaporator. The first working fluid is vaporized, the first working fluid is driven by the first working fluid in the evaporated state, the first working fluid discharged from the first working device is liquefied by the first condenser, and the first working fluid pump And circulate to
In the second Rankine cycle system, the second working fluid is sent to the second evaporator by the second working fluid pump, and the second working fluid is utilized by the heat of the second heat source in the second evaporator. The evaporated second working fluid is sent to the first condenser, and after the heat from the first working fluid is transferred to the second working fluid by the first condenser, the second working fluid in the evaporated state is sent to the first working fluid. The second expander is driven by two working fluids, and the second working fluid discharged from the second expander is liquefied by the second condenser and circulated to the second working fluid pump. To operate a multistage Rankine cycle system.

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