ORC cycle

Abstract

An ORC cycle is configured to circulate a heat medium using exhaust heat from an internal combustion engine as a heat source, and comprises: a turbine configured to be driven by the heat medium; an evaporator configured to evaporate the heat medium guided to the turbine by using thermal energy recovered from a first exhaust heat source of the internal combustion engine; a preheater configured to preheat the heat medium guided to the evaporator by using thermal energy recovered from a second exhaust heat source of the internal combustion engine; a second hot water supply line for guiding, to the preheater, second hot water obtained by recovering thermal energy from the second exhaust heat source; and a second hot water flow rate adjustment valve configured to be capable of adjusting the flow rate of the second hot water guided to the preheater via the second hot water supply line.

Description

ORC cycle

[0001] The present disclosure relates to an ORC cycle. The present application claims priority based on Japanese Patent Application No. 2025-029639 filed with the Japan Patent Office on February 27, 2025, the content of which is incorporated herein by reference.

[0002] Patent Document 1 discloses a power generation system that drives an ORC cycle (Organic Rankine Cycle) including a refrigerant turbine using exhaust gas discharged from a gas engine as a heat source. Patent Document 1 discloses recovering waste heat from different waste heat sources of a gas engine by using a heat exchanger configured to perform heat exchange between a working fluid guided to a refrigerant turbine and exhaust gas, and a refrigerant heater that heats the working fluid guided to the heat exchanger with heat of engine jacket water.

[0003] Japanese Patent No. 5875253

[0004] In the invention described in Patent Document 1, waste heat is recovered from different waste heat sources of a gas engine. However, such waste heat varies depending on the engine load, and the evaporation pressure and evaporation temperature of the working fluid in the heat exchanger and the refrigerant heater also change. If the input pressure and heat amount to the refrigerant heater is excessive, vaporization of the working fluid starts in the refrigerant heater. When the heat medium introduced into the heat exchanger is in a gas-liquid two-layer flow state, it becomes difficult to predict the performance of the heat exchanger, and there is a risk that the operation of the ORC cycle becomes unstable. For this reason, it is desired for the ORC cycle to recover waste heat to the maximum extent possible in accordance with the engine load while suppressing vaporization of the working fluid in the refrigerant heater, but this is difficult to achieve with the invention described in Patent Document 1.

[0005] In view of the foregoing circumstances, an object of at least one embodiment of the present disclosure is to provide an ORC cycle that can suppress an excessive amount of input heat to a preheater and enables waste heat recovery within a range where the heat medium is not evaporated in the preheater.

[0006] An ORC cycle according to at least one embodiment of the present disclosure is an ORC cycle configured to circulate a heat transfer medium that uses waste heat from an internal combustion engine as a heat source, comprising: a turbine configured to be driven by the heat transfer medium; an evaporator configured to evaporate the heat transfer medium led to the turbine by thermal energy recovered from a first waste heat source of the internal combustion engine; a preheater configured to preheat the heat transfer medium led to the evaporator by thermal energy recovered from a second waste heat source of the internal combustion engine; a second hot water supply line for leading a second hot water, which is hot water from which thermal energy has been recovered, to the preheater; and a second hot water flow control valve configured to adjust the flow rate of the second hot water introduced to the preheater via the second hot water supply line.

[0007] According to at least one embodiment of the present disclosure, an ORC cycle is provided that can suppress excessive heat input to the preheater and enable waste heat recovery in the preheater without evaporating the heat transfer medium.

[0008] This is a schematic diagram illustrating the configuration of a waste heat recovery system equipped with an ORC cycle according to one embodiment of this disclosure. This is a schematic diagram illustrating the ORC cycle according to the first embodiment of this disclosure. This is a schematic diagram illustrating the ORC cycle according to the second embodiment of this disclosure. This is a graph illustrating the relationship between heat quantity and temperature change in the preheater and evaporator of the ORC cycle. This is a graph illustrating the relationship between heat quantity and temperature change in the preheater and evaporator of the ORC cycle. This is a graph illustrating the relationship between heat quantity and temperature change in the preheater and evaporator of the ORC cycle. This is a graph illustrating the relationship between heat quantity and temperature change in the preheater and evaporator of the ORC cycle. This is a graph illustrating an example of control by a second flow control valve in an ORC cycle according to one embodiment of this disclosure. This is an explanatory diagram illustrating information showing the correspondence between the load of the internal combustion engine and the set temperature and opening degree of the second hot water flow control valve.

[0009] Hereinafter, several embodiments of this disclosure will be described with reference to the attached drawings. However, the dimensions, materials, shapes, relative arrangements, etc., of the components described or shown in the drawings as embodiments are not intended to limit the scope of this disclosure, but are merely illustrative examples.

[0010] (ORC Cycle) Figure 1 is a schematic diagram showing the configuration of a waste heat recovery system 1 equipped with an ORC cycle 2 according to one embodiment of the present disclosure. As shown in Figure 1, the ORC cycle (Organic Rankine Cycle) 2 is configured to circulate a heat transfer medium that uses the waste heat of an internal combustion engine 3 as a heat source. The ORC cycle 2 includes a heat transfer medium circulation line 4 that forms a flow path for circulating the heat transfer medium. The heat transfer medium circulation line 4 is composed of piping and the like.

[0011] The heat transfer medium circulating in the heat transfer medium circulation line 4 is a low-boiling-point heat transfer medium with a lower boiling point than water. As low-boiling-point heat transfer mediums, low molecular weight hydrocarbons such as isopentane, butane, and propane, or HFCs (hydrofluorocarbons) such as R-134a and R-245fa, which are used as refrigerants, and HFOs (hydrofluoroolefins) such as R-1233zd can be used.

[0012] Hereinafter, the upstream side in the flow direction of the heat transfer medium in ORC cycle 2 will be simply referred to as the upstream side, and the downstream side in the flow direction of the heat transfer medium in ORC cycle 2 will be simply referred to as the downstream side. As shown in Figure 1, ORC cycle 2 comprises a turbine 5 provided in the heat transfer medium circulation line 4, an evaporator 6 provided upstream of the turbine 5 in the heat transfer medium circulation line 4, and a preheater 7 provided upstream of the evaporator 6 in the heat transfer medium circulation line 4.

[0013] (Turbine) The turbine 5 is configured to be driven by a heat transfer medium. The evaporator 6 is configured to evaporate the heat transfer medium that is led to the turbine 5 using thermal energy recovered from the first waste heat source HS1 of the internal combustion engine 3. The preheater 7 is configured to preheat the heat transfer medium that is led to the evaporator 6 using thermal energy recovered from the second waste heat source HS2 of the internal combustion engine 3. The heat transfer medium that has been preheated in the preheater 7 and evaporated in the evaporator 6 is introduced into the turbine 5.

[0014] The turbine 5 is configured to rotate a rotating body 8, such as an impeller, using the energy of the heat transfer medium evaporated in the evaporator 6. The ORC cycle 2 is configured to recover the rotational force of the rotating body 8 as power.

[0015] In the illustrated embodiment, the ORC cycle 2 includes a generator 9 configured to generate electricity using power recovered by the turbine 5. The generator 9 is mechanically connected to the rotating body 8 of the turbine 5 and is configured to convert the rotational force (power) transmitted from the rotating body 8 into electricity. Alternatively, the ORC cycle 2 may recover the rotational force of the rotating body 8 directly as power using a power transmission device (e.g., a coupling, belt, pulley, etc.) instead of converting it into electricity.

[0016] (Condenser) The ORC cycle 2 includes a condenser 10 located downstream of the turbine 5 in the heat transfer medium circulation line 4, as shown in Figure 1. The condenser 10 is configured to receive the heat transfer medium that has passed through the turbine 5 and to liquefy the heat transfer medium.

[0017] The condenser 10 is configured to perform heat exchange between a heat transfer medium introduced into the condenser 10 and cooling water introduced into the condenser 10. Through heat exchange between the heat transfer medium and the cooling water in the condenser 10, the heat transfer medium is cooled and condenses. The cooling water can be any water at a lower temperature than the heat transfer medium that can cool it, but when the ORC cycle 2 is installed on a ship 100, it is preferable to use water (seawater, river water, lake water, etc.) that is readily available on the ship 100 and is within the ship's navigation area.

[0018] (Circulation Pump) As shown in Figure 1, the ORC cycle 2 includes a circulation pump 11 located downstream of the condenser 10 and upstream of the preheater 7 in the heat transfer medium circulation line 4. The circulation pump 11 is configured to receive the heat transfer medium liquefied in the condenser 10, compress the heat transfer medium, and send it downstream of the circulation pump 11 in the heat transfer medium circulation line 4.

[0019] In ORC cycle 2, the circulation pump 11 is driven by power supplied from a power source (not shown), causing the heat transfer medium to circulate through the heat transfer medium circulation line 4. The heat transfer medium liquefied in the condenser 10 is compressed by the circulation pump 11 and guided to the preheater 7.

[0020] (Waste Heat Recovery System, Ship) The waste heat recovery system 1, as shown in Figure 1, is configured to recover the thermal energy of waste heat discharged from the internal combustion engine 3. The waste heat recovery system 1, as shown in Figure 1, comprises the ORC cycle 2 described above, the water jacket 12 described above, and the waste heat recovery device 13. In the illustrated embodiment, the waste heat recovery system 1 and the internal combustion engine 3 are mounted on a ship 100, as shown in Figure 1.

[0021] (Main engine 3A) The internal combustion engine 3 is the main engine 3A of the ship 100. The ship 100 is a structure that can float on water and is configured to be self-propelled by driving the main engine 3A. The main engine 3A is configured to generate a driving force (thrust force) that drives a thruster (propeller in the illustrated example) 14 mechanically connected to the drive shaft of the main engine 3A using the energy of the supplied fuel (fuel gas or fuel oil). In other embodiments, the waste heat recovery system 1 may be mounted on a structure other than the ship 100, for example, a floating body or a structure located on land. A floating body is a structure that does not have a thruster for self-propulsion and is not self-propelled.

[0022] (Supercharger, intake air cooler) In the embodiment shown in Figure 1, the exhaust heat recovery system 1 includes an exhaust gas line 15 for sending exhaust gas discharged from the internal combustion engine 3, a supercharger 16, and an intake air cooler 17. The supercharger 16 includes an exhaust gas turbine 18 provided in the exhaust gas line 15 and a compressor 19 provided coaxially with the exhaust gas turbine 18.

[0023] The intake air cooler 17 is a water-cooled cooler for cooling the intake air that is compressed by the compressor 19 and led to the internal combustion engine 3. The intake air cooler 17 is configured to cool the intake air by exchanging heat between the intake air and water (cooler water) and recovering the thermal energy of the intake air into the cooler water.

[0024] (Waste Heat Recovery Device) The waste heat recovery device 13 includes a high-temperature side heat exchanger 20 configured to recover the thermal energy of exhaust gas discharged from the internal combustion engine 3, and a low-temperature side heat exchanger 21 configured to recover the thermal energy of exhaust gas that has passed through the high-temperature side heat exchanger 20. The low-temperature side heat exchanger 21 is located downstream of the high-temperature side heat exchanger 20 in the exhaust gas flow direction of the exhaust gas line 15. Exhaust gas cooled in the high-temperature side heat exchanger 20 is led to the low-temperature side heat exchanger 21.

[0025] The high-temperature side heat exchanger 20 is configured to perform heat exchange between the exhaust gas introduced to the high-temperature side heat exchanger 20 and water, recovering the thermal energy of the exhaust gas into the water. The low-temperature side heat exchanger 21 is configured to perform heat exchange between the exhaust gas introduced to the low-temperature side heat exchanger 21 and water, recovering the thermal energy of the exhaust gas into the water.

[0026] In the illustrated embodiment, the exhaust heat recovery device 13 is an exhaust gas economizer 13A. The exhaust gas economizer 13A has a casing 23 that forms a space 22 through which exhaust gas flows, provided in the exhaust gas line 15. The high-temperature side heat exchanger 20 has a pipe 20A through which water, which is the refrigerant for the high-temperature side heat exchanger 20, flows, located in the space 22. The low-temperature side heat exchanger 21 has a pipe 21A through which water, which is the refrigerant for the low-temperature side heat exchanger 21, flows, located downstream of the pipe 21A in the exhaust gas flow direction of the space 22.

[0027] In the illustrated embodiment, the internal combustion engine 3, as shown in Figure 1, includes an auxiliary boiler 24, a feedwater line 25 for supplying feedwater to the auxiliary boiler 24, a boiler-side circulation line 26 for circulating water between the auxiliary boiler 24 and the high-temperature side heat exchanger 20 (piping 20A), and a steam line 27 for supplying steam from the auxiliary boiler 24.

[0028] The auxiliary boiler 24 includes a boiler furnace 28 configured to heat water using thermal energy generated by combustion, and a gas-liquid separator 29 configured to separate water into a gas phase and a liquid phase. By driving the boiler-side pump 30 provided in the boiler-side circulation line 26, water circulates through the boiler-side circulation line 26, supplying water from the auxiliary boiler 24 to the high-temperature side heat exchanger 20, and the water heated by the thermal energy of the exhaust gas in the high-temperature side heat exchanger 20 is returned to the auxiliary boiler 24.

[0029] In the gas-liquid separator 29, steam heated and vaporized by the boiler furnace 28 or the high-temperature heat exchanger 20 is separated from water. The steam line 27 is connected to the gas phase of the gas-liquid separator 29. Steam is supplied via the steam line 27 to equipment and facilities that require steam.

[0030] (First Exhaust Heat Source, Second Exhaust Heat Source) In the illustrated embodiment, the first exhaust heat source HS1 described above is exhaust gas discharged from the internal combustion engine 3, and the second exhaust heat source HS2 described above is water (jacket water) flowing through the water jacket 12 of the internal combustion engine 3. The water jacket 12 forms a passage through which jacket water flows, provided around the cylinders of the internal combustion engine 3. The water jacket 12 is configured to cool the internal combustion engine 3 by recovering the thermal energy of the exhaust heat from the internal combustion engine 3 into the jacket water flowing through the water jacket 12. Note that the first exhaust heat source HS1 and the second exhaust heat source HS2 are not limited to the illustrated example. For example, the second exhaust heat source HS2 may be water (cooler water) flowing through the intake air cooler 17.

[0031] (First Hot Water Supply Line) As shown in Figure 1, the ORC cycle 2 includes a first hot water supply line 31 for guiding the first hot water, which is hot water recovered from the first waste heat source HS1, to the evaporator 6 described above. In the illustrated embodiment, the upstream end of the first hot water supply line 31 is connected to the low-temperature side heat exchanger 21 (piping 21A), and the downstream end is connected to the evaporator 6.

[0032] In the illustrated embodiment, the ORC cycle 2 includes a first hot water return line 32 for returning the first hot water that has passed through the evaporator 6 to a low-temperature side heat exchanger 21 (piping 21A), which is a heat exchanger for the first hot water to recover thermal energy from the first waste heat source HS1, and a first hot water side pump 33. The upstream end of the first hot water return line 32 is connected to the evaporator 6, and the downstream end is connected to the low-temperature side heat exchanger 21 (piping 21A). The first hot water side pump 33 is provided on either the first hot water supply line 31 or the first hot water return line 32 (illustrated example), and is configured to send the first hot water downstream of the first hot water side pump 33.

[0033] In the illustrated embodiment, the ORC cycle 2 includes a first hot water side bypass line 34 for guiding the first hot water from the first hot water supply line 31 to the first hot water return line 32, bypassing the evaporator 6. The first hot water side bypass line 34 has its upstream end connected to the first hot water supply line 31 and its downstream end connected to the first hot water return line 32.

[0034] (Second Hot Water Supply Line) As shown in Figure 1, the ORC cycle 2 includes a second hot water supply line 41 for guiding the second hot water, which is hot water recovered from the second waste heat source HS2, to the preheater 7 described above. In the illustrated embodiment, the upstream end of the second hot water supply line 41 is connected to the water jacket 12 and the downstream end is connected to the preheater 7.

[0035] In the illustrated embodiment, the ORC cycle 2 includes a second hot water return line 42 for returning the second hot water that has passed through the preheater 7 back to the water jacket 12, which is a heat exchanger for the second hot water to recover thermal energy from the second waste heat source HS2, and a second hot water pump 43. The upstream end of the second hot water return line 42 is connected to the preheater 7 and the downstream end is connected to the water jacket 12. The second hot water pump 43 is provided on either the second hot water supply line 41 or the second hot water return line 42 (illustrated example) and is configured to send the second hot water downstream of the second hot water pump 43.

[0036] In the illustrated embodiment, the ORC cycle 2 includes a second hot water side bypass line 44 for guiding the second hot water from the second hot water supply line 41 to the second hot water return line 42, bypassing the preheater 7. The upstream end of the second hot water side bypass line 44 is connected to the second hot water supply line 41, and the downstream end is connected to the second hot water return line 42.

[0037] (Cooler) In the illustrated embodiment, the ORC cycle 2 includes a cooler 51 for cooling the second hot water led from the water jacket 12 to the second hot water supply line 41, a temperature sensor 52 configured to measure the temperature of the second hot water led from the water jacket 12 to the second hot water supply line 41, a first temperature control valve 53 configured to adjust the flow rate of the second hot water led to the preheater 7 based on the second hot water temperature measurement from the temperature sensor 52, and a second temperature control valve 54 configured to adjust the flow rate of the second hot water led to the cooler 51 based on the second hot water temperature measurement from the temperature sensor 52. Note that the ORC cycle 2 may include either the first temperature control valve 53 or the second temperature control valve 54 (but not the other).

[0038] In the embodiment shown in Figure 1, the ORC cycle 2 includes a bypass line 55 whose upstream end is connected upstream of the connection point between the second hot water supply line 41 and the second hot water side bypass line 44, and which is connected downstream of the connection point between the second hot water return line 42 and the second hot water side bypass line 44.

[0039] (First temperature control valve) The first temperature control valve 53 adjusts the flow rate of the second hot water supplied to the preheater 7 by adjusting the flow rate of the second hot water flowing through the bypass line 55 based on the measured value of the second hot water temperature at the temperature sensor 52. In other words, the first temperature control valve 53 is configured to adjust the distribution ratio of the second hot water supplied to the bypass line 55 and the downstream side of the connection point between the bypass line 55 and the second hot water supply line 41, so that the flow rate of the second hot water according to the distribution ratio flows through these lines.

[0040] Specifically, the first temperature control valve 53 is configured to increase the flow rate (distribution ratio) of the second hot water flowing through the bypass line 55 when the measured value of the second hot water temperature at the temperature sensor 52 is lower than the lower threshold value of the first temperature control valve 53. Furthermore, the first temperature control valve 53 is configured to decrease the flow rate (distribution ratio) of the second hot water flowing through the bypass line 55 when the measured value of the second hot water temperature at the temperature sensor 52 is higher than the upper threshold value of the first temperature control valve 53.

[0041] In the illustrated example, the first temperature control valve 53 is located at the downstream end of the bypass line 55 (the connection point between the bypass line 55 and the second hot water return line 42), but in some other embodiments, it may be located at the upstream end or in the middle of the bypass line 55.

[0042] In the embodiment shown in Figure 1, the cooler 51 cools the second hot water by exchanging heat between the second hot water and the cooling water. Upstream of the cooler 51, the second hot water return line 42 branches into a cooler line 42A through which the cooler 51 is located and a cooler bypass line 42B that bypasses the cooler 51. Downstream of the cooler 51, the cooler line 42A and the cooler bypass line 42B merge.

[0043] (Second temperature control valve) The second temperature control valve 54 adjusts the flow rate of the second hot water that passes through the cooler 51 and is led to the water jacket 12 by adjusting at least one of the flow rate of the second hot water flowing through the cooler line 42A or the flow rate of the second hot water flowing through the cooler bypass line 42B. In other words, the second temperature control valve 54 is configured to adjust the distribution ratio of the second hot water distributed to the cooler line 42A and the cooler bypass line 42B, so that the flow rate of the second hot water according to the distribution ratio flows through these lines.

[0044] Specifically, when the measured value of the second hot water temperature obtained by the temperature sensor 52 is lower than the lower threshold of the second temperature adjustment valve 54, the second temperature adjustment valve 54 is configured to increase the flow rate (distribution ratio) of the second hot water flowing through the cooler bypass line 42B, and decrease the flow rate (distribution ratio) of the second hot water flowing through the cooler line 42A.

[0045] Further, when the measured value of the second hot water temperature obtained by the temperature sensor 52 is higher than the upper threshold of the second temperature adjustment valve 54, the second temperature adjustment valve 54 is configured to decrease the flow rate (distribution ratio) of the second hot water flowing through the cooler bypass line 42B, and increase the flow rate (distribution ratio) of the second hot water flowing through the cooler line 42A.

[0046] In the illustrated example, the second temperature adjustment valve 54 is provided at the confluence of the cooler line 42A and the cooler bypass line 42B; however, in some other embodiments, the second temperature adjustment valve 54 may be provided at the branch of the cooler line 42A and the cooler bypass line 42B, in the middle of the cooler line 42A, or in the middle of the cooler bypass line 42B.

[0047] Fig. 2 is a schematic configuration diagram schematically showing the ORC cycle 2 according to the first embodiment of the present disclosure. Fig. 3 is a schematic configuration diagram schematically showing the ORC cycle 2 according to the second embodiment of the present disclosure. As shown in Fig. 2 and Fig. 3, the ORC cycle 2 according to some embodiments comprises the aforementioned turbine 5, the aforementioned evaporator 6, the aforementioned preheater 7, the aforementioned second hot water supply line 41, and a second hot water flow rate adjustment valve 62 configured to be capable of adjusting the flow rate of the second hot water introduced into the preheater 7 via the second hot water supply line 41.

[0048] Hereinafter, the portion of the first hot water supply line 31 on the downstream side of the connection with the upstream end of the first hot water side bypass line 34 is referred to as a first hot water main flow line 31A, and the portion of the second hot water supply line 41 on the downstream side of the connection with the upstream end of the second hot water side bypass line 44 is referred to as a second hot water main flow line 41A.

[0049] As shown in Figures 2 and 3, the second hot water flow rate control valve 62 is configured to adjust the flow rate of the second hot water flowing through the second hot water main line 41A and the flow rate of the second hot water flowing through the second hot water side bypass line 44. In other words, the second hot water flow rate control valve 62 is configured to adjust the distribution ratio of the second hot water distributed to the second hot water main line 41A and the second hot water side bypass line 44, so that the flow rate of the second hot water according to the distribution ratio flows through these lines.

[0050] In the illustrated example, the second hot water flow control valve 62 is a three-way valve provided at the connection point between the second hot water main line 41A and the second hot water side bypass line 44. However, instead of the three-way valve, flow control valves may be provided in both the second hot water main line 41A and the second hot water side bypass line 44.

[0051] In the illustrated embodiment, the ORC cycle 2 includes a control device 60, which is an electronic control unit for controlling the valve opening of the second hot water flow control valve 62, as shown in Figures 2 and 3. The control device 60 (controller) may be configured as a microcomputer including an input device (input interface) 601, an output device (output interface) 602, a storage device (such as ROM or RAM memory, or an external storage device) 603, and an arithmetic unit (CPU) 604. The control device 60 is configured such that, for example, the CPU operates (for example, performs calculations on data) according to instructions of a program loaded into the main memory of the above-mentioned memory, thereby achieving control of the valve opening of the second hot water flow control valve 62.

[0052] Figures 4 and 5 are graphs illustrating the relationship between heat quantity and temperature change in the preheater 7 and evaporator 6 of the ORC cycle 2, respectively. Figures 4 to 7 show graphs in which the amount of heat H added to the heat transfer medium in the preheater 7 and evaporator 6 is on the horizontal axis, and the temperature T of the second hot water and heat transfer medium is on the vertical axis.

[0053] In Figures 4 to 7, the amount of heat added to the heat transfer medium in the preheater 7 is denoted as H1, and the amount of heat added to the heat transfer medium in the evaporator 6 is denoted as H2. Line L1 in Figures 4 to 7 schematically shows the temperature change of the second hot water in the preheater 7, with the inlet temperature of the preheater 7 being the highest temperature on line L1 and the outlet temperature of the preheater 7 being the lowest temperature on line L1. Line L2 in Figures 4 to 7 schematically shows the temperature change of the first hot water in the evaporator 6, with the inlet temperature of the evaporator 6 being the highest temperature on line L2 and the outlet temperature of the evaporator 6 being the lowest temperature on line L2. Line L3 in Figures 4 to 7 schematically shows the temperature change of the heat transfer medium in the preheater 7 and the evaporator 6.

[0054] As shown in region A of Figure 4, if the amount of heat H1 added to the heat transfer medium in the preheater 7 is excessive, the heat transfer medium may reach its saturation temperature before being introduced into the evaporator 6, and vaporization of the heat transfer medium may begin. When the heat transfer medium introduced into the evaporator 6 is in a gas-liquid two-layer flow state, it becomes difficult to predict the performance of the evaporator 6, and there is a risk that the operation of the ORC cycle 2 will become unstable, which is undesirable. As shown in Figure 5, it is preferable that the heat transfer medium reaches its saturation temperature after being introduced into the evaporator 6 and that vaporization of the heat transfer medium begins.

[0055] In this embodiment, the ORC cycle 2 adjusts the flow rate of the second hot water introduced into the preheater 7 via the second hot water supply line 41 using the second hot water flow rate adjustment valve 62. This suppresses excessive heat input to the preheater 7, enabling waste heat recovery in the preheater 7 within a range where the heat transfer medium does not evaporate (a range where region A in Figure 4 is not formed). While adjusting the flow rate of the heat transfer medium introduced into the preheater 7 is a possible means of adjusting the amount of heat input to the heat transfer medium in the preheater 7, this flow rate adjustment restricts the flow rate of the heat transfer medium introduced into the evaporator 6, making it difficult to control the amount of thermal energy recovered in the evaporator 6, which is undesirable.

[0056] In some embodiments of the ORC cycle 2, the first waste heat source HS1 described above is exhaust gas discharged from the internal combustion engine 3, and the second waste heat source HS2 described above is jacket water flowing through the water jacket 12 of the internal combustion engine 3. Even in such cases, the ORC cycle 2 can suppress excessive heat input to the preheater 7 by adjusting the flow rate of the second hot water introduced to the preheater 7 via the second hot water supply line 41 using the second hot water flow rate control valve 62, thereby enabling waste heat recovery in the preheater 7 within a range that does not evaporate the heat transfer medium.

[0057] (First Embodiment) As shown in Figure 2, an ORC cycle 2 according to several embodiments comprises the above-mentioned second hot water flow control valve 62, a heat transfer medium pressure sensor 63, a saturation temperature calculation unit 64, and a heat transfer medium temperature sensor 65.

[0058] The heat transfer medium pressure sensor 63 is configured to measure the pressure Pre of the heat transfer medium flowing downstream of the preheater 7 and upstream of the turbine 5 in the ORC cycle 2. Preferably, the heat transfer medium pressure sensor 63 measures the pressure of the heat transfer medium flowing downstream of the preheater 7 and upstream of the evaporator 6 in the ORC cycle 2, as shown in the illustrated example. In some other embodiments, the heat transfer medium pressure sensor 63 may measure the pressure of the heat transfer medium flowing downstream of the evaporator 6 and upstream of the turbine 5 in the ORC cycle 2. In this case, the saturation temperature Tr2 of the heat transfer medium can be calculated using the estimated pressure of the heat transfer medium flowing downstream of the evaporator 6 and upstream of the turbine 5, which is estimated based on the measurement value of the heat transfer medium pressure sensor 63 and the pressure loss in the evaporator 6.

[0059] The saturation temperature calculation unit 64 is configured to calculate the saturation temperature Tr2 of the heat medium based on the pressure Pre of the heat medium measured by the heat medium pressure sensor 63. The saturation temperature calculation unit 64 is configured to calculate the saturation temperature Tr2 corresponding to the pressure Pre of the heat medium from the pressure Pre of the heat medium measured by the heat medium pressure sensor 63, using information that shows the correspondence between the pressure Pre of the heat medium and the saturation temperature Tr2 of the heat medium, such as a conversion formula for converting the pressure Pre of the heat medium to the saturation temperature Tr2 of the heat medium.

[0060] The heat transfer medium temperature sensor 65 is configured to measure the temperature Tr1 of the heat transfer medium that is guided from the preheater 7 to the evaporator 6.

[0061] The second hot water flow rate control valve 62 described above is configured to reduce the flow rate of the second hot water introduced into the preheater 7 via the second hot water supply line 41 when the temperature difference Tr2-Tr1 between the temperature Tr1 (measured value) of the heat medium measured by the heat medium temperature sensor 65 and the saturation temperature Tr2 falls below a threshold. By reducing the flow rate of the second hot water introduced into the preheater 7, the amount of heat added to the heat medium in the preheater 7 can be reduced.

[0062] The threshold for the temperature difference Tr2 - Tr1 may be zero. That is, the second hot water flow rate control valve 62 may be configured to reduce the flow rate of the second hot water introduced to the preheater 7 via the second hot water supply line 41 when the temperature Tr1 (measured value) of the heat transfer medium exceeds the saturation temperature Tr2. In the illustrated embodiment, reducing the flow rate of the second hot water introduced to the preheater 7 via the second hot water supply line 41 is equivalent to reducing the distribution ratio of the second hot water main line 41A in the second hot water flow rate control valve 62.

[0063] In the illustrated embodiment, the saturation temperature calculation unit 64 is implemented by the control device 60, and the saturation temperature Tr2 is calculated by the calculation unit 604. The control device 60 acquires the pressure Pre (measured value) of the heat medium measured by the heat medium pressure sensor 63 and the temperature Tr1 (measured value) of the heat medium measured by the heat medium temperature sensor 65 via the input device 601, and stores them in the storage device 603. Information showing the correspondence between the pressure Pre of the heat medium and the saturation temperature Tr2 of the heat medium is stored in the storage device 603.

[0064] The arithmetic unit 604 uses the information stored in the memory device 603, which shows the correspondence between the pressure Pre of the heat medium and the saturation temperature Tr2 of the heat medium, the pressure Pre (measured value) of the heat medium, and the temperature Tr1 (measured value) of the heat medium, to perform processing in the control device 60, such as calculating the saturation temperature Tr2 and the temperature difference Tr2-Tr1. The control device 60 instructs the second hot water flow control valve 62 to open via the output device 602. The second hot water flow control valve 62 is configured to open to the valve degree in accordance with the instruction from the control device 60.

[0065] In this embodiment, the ORC cycle 2 is controlled by the control device 60 to reduce the flow rate of the second hot water introduced into the preheater 7 so that the heat transfer medium does not reach the saturation temperature Tr2. This suppresses excessive heat input to the preheater 7 and enables waste heat recovery in the preheater 7 without evaporating the heat transfer medium.

[0066] Figures 6 and 7 are graphs illustrating the relationship between heat quantity and temperature change in the preheater 7 and evaporator 6 of the ORC cycle 2, respectively. The point where the temperature of the first hot water, which is the preheating side in the evaporator 6, and the temperature of the heat transfer medium, which is the heat receiving side in the evaporator 6, are closest, as shown in region B of Figure 6, is called the pinch point. Figure 6 shows the state where the pinch point limit in the evaporator 6 has been reached. Figure 7 shows the state where the pinch point limit in the evaporator 6 has been reached, and the heat input to the preheater 7 has further increased. In Figures 6 and 7, the sum of the heat recovered in the preheater 7 H1 and the heat recovered in the evaporator 6 H2 is the same, but in Figure 7, the recovered heat H1 is ΔH larger than in Figure 6. In the case shown in Figure 6, the recovered heat H2 in the evaporator 6 is reduced by ΔH and the outlet temperature of the evaporator 6 is increased by ΔT compared to the case shown in Figure 7. When the amount of heat recovered H2 in the evaporator 6 decreases in this way, the thermal energy recovered from the first waste heat source HS1 may be wasted, or the heat balance between the first hot water and the heat transfer medium in the evaporator 6 may change and deviate from the optimal point.

[0067] As shown in Figure 2, some embodiments of the ORC cycle 2 include a first hot water temperature sensor 71 and a first hot water flow rate control valve 72.

[0068] The first hot water temperature sensor 71 is configured to measure the temperature Tw1 of the first hot water that has passed through the evaporator 6. In the illustrated embodiment, the first hot water temperature sensor 71 is configured to measure the temperature Tw1 of the first hot water flowing downstream of the connection point between the first hot water return line 32 and the first hot water side bypass line 34.

[0069] The first hot water flow rate control valve 72 is configured to adjust the flow rate of the first hot water introduced into the evaporator 6 via the first hot water supply line 31. The first hot water flow rate control valve 72 is configured to increase the flow rate of the first hot water introduced into the evaporator 6 when the temperature Tw1 of the first hot water, measured by the first hot water temperature sensor 71, exceeds a first threshold.

[0070] In the illustrated embodiment, the first hot water flow rate control valve 72 is configured to adjust the flow rate of the first hot water flowing through the first hot water main line 31A and the flow rate of the first hot water flowing through the first hot water side bypass line 34, as shown in Figures 2 and 3. In other words, the first hot water flow rate control valve 72 is configured to adjust the distribution ratio of the first hot water distributed to the first hot water main line 31A and the first hot water side bypass line 34, so that the first hot water flows through these lines at a flow rate corresponding to the distribution ratio.

[0071] The first hot water flow rate control valve 72 is configured to increase the flow rate (distribution ratio) of the first hot water introduced into the evaporator 6 when the temperature Tw1 (measured value) of the first hot water exceeds a first threshold. Alternatively, the first hot water flow rate control valve 72 may be configured to decrease (return to normal) the flow rate (distribution ratio) of the first hot water introduced into the evaporator 6 when the temperature Tw1 (measured value) of the first hot water falls below the first threshold or a third threshold that allows for a margin of safety on the lower side of the first threshold after exceeding the first threshold.

[0072] In the illustrated example, the first hot water flow control valve 72 is a three-way valve provided at the connection point between the first hot water main line 31A and the first hot water side bypass line 34. However, instead of the three-way valve, flow control valves may be provided in both the first hot water main line 31A and the first hot water side bypass line 34.

[0073] The second hot water flow rate control valve 62 described above is configured to reduce the flow rate of the second hot water supplied to the preheater 7 when the temperature Tw1 of the first hot water measured by the first hot water temperature sensor 71 exceeds a first threshold or a second threshold that has a margin of safety on the higher side of the first threshold.

[0074] The control device 60 acquires the temperature Tw1 (measured value) of the first hot water measured by the first hot water temperature sensor 71 via the input device 601 and stores it in the storage device 603. The first threshold or second threshold is stored in the storage device 603. The second hot water flow rate control valve 62 is configured to open to a degree corresponding to the instruction from the control device 60.

[0075] The second hot water flow rate control valve 62 is configured to supply a relatively high flow rate of second hot water to the preheater 7 when the temperature Tw1 of the first hot water measured by the first hot water temperature sensor 71 is lower than the first threshold or the second threshold which has a margin of safety on the higher side of the first threshold. In other words, when the temperature Tw1 (measured value) of the first hot water is lower than the first threshold or the second threshold, the amount of second hot water supplied to the preheater 7 is increased so that a relatively large amount of heat H1 is added to the heat transfer medium in the preheater 7. When the temperature Tw1 (measured value) of the first hot water exceeds the first threshold or the second threshold, it is highly likely that the pinch point limit in the evaporator 6 has been reached, so the amount of second hot water supplied to the preheater 7 is reduced so that a relatively small amount of heat H1 is added to the heat transfer medium in the preheater 7. The second hot water flow rate control valve 62 may be configured not to change its opening degree when the temperature Tw1 of the first hot water measured by the first hot water temperature sensor 71 is within a predetermined temperature range provided between the first threshold and the second threshold.

[0076] In the evaporator 6, if the heat transfer medium reaches its pinch point limit, the amount of thermal energy recovered in the evaporator 6 may decrease. Here, if the heat transfer medium in the evaporator 6 reaches its pinch point limit and the amount of heat input to the preheater 7 increases, the temperature Tw1 of the first hot water that has passed through the evaporator 6 may rise to a temperature exceeding the first threshold. In this embodiment, the ORC cycle 2 reduces the flow rate of the second hot water introduced into the preheater 7 by the second hot water flow rate control valve 62 when the temperature Tw1 of the first hot water that has passed through the evaporator 6 exceeds the first or second threshold, thereby suppressing the decrease in the amount of thermal energy recovered in the evaporator 6 due to excessive heat input to the preheater 7. Therefore, in this embodiment, the ORC cycle 2 can recover as much thermal energy as possible in the heat transfer medium in the preheater 7, within a range that does not adversely affect the evaporator 6.

[0077] (Second Embodiment) Figure 8 is a graph illustrating an example of control by the second hot water flow rate control valve 62 of the ORC cycle 2 according to one embodiment of the present disclosure. As shown in Figure 3, the ORC cycle 2 according to several embodiments includes the above-mentioned second hot water flow rate control valve 62, a second hot water temperature sensor 81, a first upper limit heat quantity acquisition unit 82, a first upper limit temperature acquisition unit 83, and a set temperature determination unit 80. The ORC cycle 2 according to this embodiment does not include the above-mentioned heat medium pressure sensor 63, the above-mentioned saturation temperature calculation unit 64, and the above-mentioned heat medium temperature sensor 65. The ORC cycle 2 according to this embodiment may include the above-mentioned first hot water temperature sensor 71 and the above-mentioned first hot water flow rate control valve 72, as shown in Figure 3.

[0078] The second hot water temperature sensor 81 is configured to measure the temperature Tw2 of the second hot water that has passed through the preheater 7. In the illustrated embodiment, the second hot water temperature sensor 81 is configured to measure the temperature Tw2 of the second hot water flowing downstream of the connection point between the second hot water return line 42 and the second hot water side bypass line 44.

[0079] The first upper limit heat quantity acquisition unit 82 is configured to acquire the first upper limit heat quantity UH1 for each load EL (first upper limit heat quantity curve L4 in Figure 8) from the relationship between the first upper limit heat quantity UH1, which is the amount of heat required for the heat transfer medium to begin evaporating in the preheater 7, and the load EL of the internal combustion engine 3. The first upper limit heat quantity acquisition unit 82 is configured to acquire the first upper limit heat quantity UH1 corresponding to the load EL from the load EL of the internal combustion engine 3 using information showing the correspondence between the first upper limit heat quantity UH1 and the load EL of the internal combustion engine 3. The line L4 shown in Figure 8 shows the correspondence between the first upper limit heat quantity UH1 and the load EL of the internal combustion engine 3.

[0080] Figure 9 is an explanatory diagram illustrating the correspondence between the load EL of the internal combustion engine 3 and the set temperature and opening degree of the second hot water flow control valve 62. Figure 9 shows a graph with the load EL of the internal combustion engine 3 on the horizontal axis and the temperature T of the second hot water on the horizontal axis. Line L7 in Figure 9 indicates the set temperature of the second hot water flow control valve 62. In the embodiment shown in Figure 9, the set temperature of the second hot water flow control valve 62 is the lowest temperature among the first upper limit temperature, second upper limit temperature, and third upper limit temperature for each load. The set temperature of the second hot water flow control valve 62 shown in Figure 9 includes the first upper limit temperature, second upper limit temperature, and third upper limit temperature. Line L8 in Figure 9 indicates the temperature of the second hot water discharged from the internal combustion engine 3. As shown in Figure 9, the temperature of the second hot water discharged from the internal combustion engine 3 is adjusted so that it does not change according to the load EL of the internal combustion engine 3. If the cooling of the internal combustion engine 3 is insufficient, the internal combustion engine 3 may overheat, potentially causing malfunction or damage. Conversely, if the cooling of the internal combustion engine 3 is excessive, it may result in wasted cooling (loss). The temperature difference between lines L7 and L8 at each load EL shown in Figure 9 corresponds to the maximum amount of heat that can be recovered by the second hot water in the preheater 7 at each load EL, and the opening degree of the second hot water flow control valve 62 is set according to the maximum amount of heat that can be recovered by the second hot water.

[0081] The first upper limit temperature acquisition unit 83 is configured to acquire the first upper limit temperature of the second hot water flow rate control valve 62, which is a set temperature corresponding to the first upper limit heat quantity UH1 acquired by the first upper limit heat quantity acquisition unit 82. The first upper limit temperature acquisition unit 83 is configured to acquire the first upper limit temperature corresponding to the first upper limit heat quantity UH1 from the first upper limit heat quantity UH1, using information indicating the correspondence between the first upper limit heat quantity UH1 and the first upper limit temperature, such as a conversion formula for converting the first upper limit heat quantity UH1 to the first upper limit temperature.

[0082] The set temperature determination unit 80 is configured to determine the set temperature of the second hot water flow control valve 62 to a temperature that does not exceed the first upper limit temperature. The set temperature determination unit 80 is configured to acquire the first upper limit temperature acquired by the first upper limit temperature acquisition unit 83. The set temperature determination unit 80 determines the set temperature of the second hot water flow control valve 62 based on at least the first upper limit temperature. The set temperature determination unit 80 may use the first upper limit temperature as the set temperature of the second hot water flow control valve 62, or it may calculate a temperature with a margin of safety on the lower side of the first upper limit temperature and use the calculated temperature as the set temperature of the second hot water flow control valve 62.

[0083] The second hot water flow rate control valve 62 is configured to adjust its opening so that the temperature Tw2 of the second hot water, measured by the second hot water temperature sensor 81, does not exceed the set temperature of the second hot water flow rate control valve 62, thereby reducing the flow rate of the second hot water introduced into the preheater 7 via the second hot water supply line 41. In the illustrated embodiment, reducing the flow rate of the second hot water introduced into the preheater 7 via the second hot water supply line 41 is equivalent to lowering the distribution ratio of the second hot water main line 41A in the second hot water flow rate control valve 62. Note that if the temperature Tw2 of the second hot water, measured by the second hot water temperature sensor 81, exceeds the set temperature of the second hot water flow rate control valve 62, the flow rate of the second hot water introduced into the preheater 7 via the second hot water supply line 41 may be reduced to zero.

[0084] The above-described set temperature determination unit 80 is configured to determine (change) the set temperature of the second hot water flow control valve 62 in accordance with the load EL of the internal combustion engine 3, so that the set temperature of the second hot water flow control valve 62 does not exceed the first upper limit temperature (so that it is below the first upper limit temperature). It is preferable that the set temperature of the second hot water flow control valve 62 be as close to the first upper limit temperature as possible. In one embodiment, the set temperature determination unit 80 is configured to determine (change) the set temperature of the second hot water flow control valve 62 so that the amount of heat recovered by the second hot water in the preheater 7 follows the first upper limit heat curve L4. By setting the set temperature of the second hot water flow control valve 62 to below the first upper limit temperature, it is possible to suppress the amount of heat H1 added to the heat transfer medium in the preheater 7 from exceeding the first upper limit heat amount UH1.

[0085] In the illustrated embodiment, the set temperature determination unit 80, the first upper limit heat quantity acquisition unit 82, and the first upper limit temperature acquisition unit 83 are implemented by the control device 60, while the determination of the set temperature of the second hot water flow control valve 62, the acquisition of the first upper limit heat quantity UH1, and the acquisition of the first upper limit temperature are performed by the calculation unit 604. The control device 60 is capable of acquiring information (signals) indicating the current load EL of the internal combustion engine 3. The control device 60 acquires the load EL of the internal combustion engine 3 via the input device 601 and stores it in the storage device 603. Information showing the correspondence between the first upper limit heat quantity UH1 and the load EL of the internal combustion engine 3 (first upper limit heat quantity curve L4), information showing the correspondence between the first upper limit heat quantity UH1 and the first upper limit temperature, and information showing the correspondence between the load EL of the internal combustion engine 3 and the set temperature and opening degree of the second hot water flow control valve 62 (see Figure 9) are stored in the storage device 603.

[0086] The arithmetic unit 604 uses information stored in the memory device 603, which indicates the correspondence between the first upper limit heat quantity UH1 and the load EL of the internal combustion engine 3, information indicating the correspondence between the first upper limit heat quantity UH1 and the first upper limit temperature, and information indicating the correspondence between the load EL of the internal combustion engine 3 (acquired value) and the load EL of the internal combustion engine 3 and the set temperature and opening degree of the second hot water flow control valve 62, to execute processing in the control device 60, such as acquiring the first upper limit heat quantity UH1 and acquiring the first upper limit temperature. The control device 60 instructs the second hot water flow control valve 62 via the output device 602 to set a temperature corresponding to the load EL of the internal combustion engine 3 (acquired value). The second hot water flow control valve 62 is configured to adjust its opening degree so that the temperature becomes the set temperature according to the instruction from the control device 60.

[0087] In this embodiment, the ORC cycle 2 is controlled by the control device 60 so as not to exceed the first upper limit temperature, depending on the load EL of the internal combustion engine 3, and the set temperature of the second hot water flow control valve 62 is determined by the control device 60. The ORC cycle 2 controls the opening of the second hot water flow control valve 62 so that the set temperature of the second hot water flow control valve 62 is set to a temperature that does not exceed the first upper limit temperature, thereby suppressing excessive heat input to the preheater 7 and enabling waste heat recovery in the preheater 7 within a range that does not evaporate the heat transfer medium.

[0088] As shown in Figure 3, some embodiments of the ORC cycle 2 include a second upper limit heat quantity acquisition unit 84 and a second upper limit temperature acquisition unit 85.

[0089] The second upper limit heat quantity acquisition unit 84 is configured to acquire the second upper limit heat quantity UH2 for each load EL (second upper limit heat quantity curve L5 in Figure 8) from the relationship between the second upper limit heat quantity UH2, which is the preheater heat quantity at which the heat transfer medium reaches the pinch point limit in the evaporator 6, and the load EL of the internal combustion engine 3. The second upper limit heat quantity acquisition unit 84 is configured to acquire the second upper limit heat quantity UH2 corresponding to the load EL from the load EL of the internal combustion engine 3 using information showing the correspondence between the second upper limit heat quantity UH2 and the load EL of the internal combustion engine 3. The line L5 shown in Figure 8 shows the correspondence between the second upper limit heat quantity UH2 and the load EL of the internal combustion engine 3.

[0090] The second upper limit temperature acquisition unit 85 is configured to acquire the second upper limit temperature of the second hot water flow rate control valve 62, which is a set temperature corresponding to the second upper limit heat quantity UH2 acquired by the second upper limit heat quantity acquisition unit 84. The second upper limit temperature acquisition unit 85 is configured to acquire the second upper limit temperature corresponding to the second upper limit heat quantity UH2 from the second upper limit heat quantity UH2, using information that shows the correspondence between the second upper limit heat quantity UH2 and the second upper limit temperature, such as a conversion formula for converting the second upper limit heat quantity UH2 to the second upper limit temperature.

[0091] The temperature setting unit 80 according to this embodiment is configured to determine the temperature of the second hot water flow control valve 62 to be a temperature that does not exceed the first upper limit temperature and the second upper limit temperature. The temperature setting unit 80 is configured to acquire the first upper limit temperature acquired by the first upper limit temperature acquisition unit 83 and the second upper limit temperature acquired by the second upper limit temperature acquisition unit 85. The temperature setting unit 80 determines the temperature of the second hot water flow control valve 62 based on the first upper limit temperature and the second upper limit temperature. The temperature setting unit 80 may use the lowest temperature among the first upper limit temperature and the second upper limit temperature (the lowest upper limit temperature) as the temperature of the second hot water flow control valve 62, or it may calculate a temperature with a margin on the lower side relative to the above temperature (the lowest upper limit temperature) and use the calculated temperature as the temperature of the second hot water flow control valve 62.

[0092] The above-described temperature setting unit 80 is configured to determine (change) the temperature of the second hot water flow control valve 62 so that the temperature of the second hot water flow control valve 62 does not exceed the first upper limit temperature and the second upper limit temperature (i.e., it is below the first upper limit temperature and below the second upper limit temperature), in accordance with the load EL of the internal combustion engine 3. It is preferable that the temperature of the second hot water flow control valve 62 be as close as possible to the lower of the first upper limit temperature or the second upper limit temperature. In one embodiment, the temperature setting unit 80 is configured to determine (change) the temperature of the second hot water flow control valve 62 so that the amount of heat recovered by the second hot water in the preheater 7 follows the lower heat curve of the first upper limit heat curve L4 or the second upper limit heat curve L5. By setting the temperature of the second hot water flow control valve 62 to below the second upper limit temperature, it is possible to suppress the amount of heat H1 added to the heat transfer medium in the preheater 7 from exceeding the second upper limit heat amount UH2.

[0093] In the illustrated embodiment, the second upper limit heat quantity acquisition unit 84 and the second upper limit temperature acquisition unit 85 are implemented by the control device 60, and the acquisition of the second upper limit heat quantity UH2 and the second upper limit temperature is performed by the calculation device 604. Information showing the correspondence between the second upper limit heat quantity UH2 and the load EL of the internal combustion engine 3 and information showing the correspondence between the second upper limit heat quantity UH2 and the second upper limit temperature are stored in the storage device 603.

[0094] The arithmetic unit 604 uses information stored in the memory device 603, which indicates the correspondence between the second upper limit heat quantity UH2 and the load EL of the internal combustion engine 3, information indicating the correspondence between the second upper limit heat quantity UH2 and the second upper limit temperature, the load EL of the internal combustion engine 3 (acquired value), and information indicating the correspondence between the load EL of the internal combustion engine 3 and the set temperature and opening degree of the second hot water flow control valve 62, to perform processing in the control device 60, such as acquiring the second upper limit heat quantity UH2 and calculating the second upper limit temperature.

[0095] In the evaporator 6, if the heat transfer medium reaches its pinch point limit, the amount of thermal energy recovered in the evaporator 6 may decrease. In the ORC cycle 2 according to this embodiment, the control device 60 determines the set temperature of the second hot water flow control valve 62 so that the set temperature of the second hot water flow control valve 62 does not exceed the second upper limit temperature, according to the load EL of the internal combustion engine 3. The ORC cycle 2 can suppress the decrease in the amount of thermal energy recovered in the evaporator 6 by adjusting the opening degree of the second hot water flow control valve 62 so that the set temperature of the second hot water flow control valve 62 is set to a temperature that does not exceed the second upper limit temperature. Therefore, in the ORC cycle 2 according to this embodiment, thermal energy can be recovered in the heat transfer medium as much as possible in the preheater 7, within a range that does not adversely affect the evaporator 6.

[0096] As shown in Figure 3, some embodiments of the ORC cycle 2 include a third upper limit heat quantity acquisition unit 86 and a third upper limit temperature acquisition unit 87.

[0097] The third upper limit heat quantity acquisition unit 86 is configured to acquire the third upper limit heat quantity UH3 for each load EL (second upper limit heat quantity curve L5 in Figure 8) from the relationship between the third upper limit heat quantity UH3, which is the upper limit heat quantity that can be recovered from the second hot water in the preheater 7, and the load EL of the internal combustion engine 3. The third upper limit heat quantity acquisition unit 86 is configured to acquire the third upper limit heat quantity UH3 corresponding to the load EL from the load EL of the internal combustion engine 3 using information showing the correspondence between the third upper limit heat quantity UH3 and the load EL of the internal combustion engine 3. The line L6 shown in Figure 8 shows the correspondence between the second upper limit heat quantity UH2 and the load EL of the internal combustion engine 3.

[0098] The third upper limit temperature acquisition unit 87 is configured to acquire the third upper limit temperature of the second hot water flow rate control valve 62, which is a set temperature corresponding to the third upper limit heat quantity UH3 acquired by the third upper limit heat quantity acquisition unit 86. The third upper limit temperature acquisition unit 87 is configured to acquire the third upper limit temperature corresponding to the third upper limit heat quantity UH3 from the third upper limit heat quantity UH3, using information that shows the correspondence between the third upper limit heat quantity UH3 and the third upper limit temperature, such as a conversion formula for converting the third upper limit heat quantity UH3 to the third upper limit temperature.

[0099] The temperature setting unit 80 according to this embodiment is configured to determine the temperature of the second hot water flow control valve 62 to be a temperature that does not exceed the first upper limit temperature, the second upper limit temperature, and the third upper limit temperature. The temperature setting unit 80 is configured to acquire the first upper limit temperature acquired by the first upper limit temperature acquisition unit 83, the second upper limit temperature acquired by the second upper limit temperature acquisition unit 85, and the third upper limit temperature acquired by the third upper limit temperature acquisition unit 87. The temperature setting unit 80 determines the temperature of the second hot water flow control valve 62 based on the first upper limit temperature, the second upper limit temperature, and the third upper limit temperature. The temperature setting unit 80 may set the lowest temperature among the first upper limit temperature, the second upper limit temperature, and the third upper limit temperature (the lowest upper limit temperature) as the temperature of the second hot water flow control valve 62, or it may calculate a temperature with a margin on the lower side relative to the above temperature (the lowest upper limit temperature) and set the calculated temperature as the temperature of the second hot water flow control valve 62.

[0100] The above-described set temperature determination unit 80 is configured to determine (change) the set temperature of the second hot water flow control valve 62 in accordance with the load EL of the internal combustion engine 3, so that the set temperature of the second hot water flow control valve 62 does not exceed the third upper limit temperature (so that it is below the first upper limit temperature, below the second upper limit temperature, and below the third upper limit temperature). It is preferable that the set temperature of the second hot water flow control valve 62 be as close as possible to the lower of the first upper limit temperature, the second upper limit temperature, or the third upper limit temperature. In one embodiment, the set temperature determination unit 80 is configured to determine (change) the set temperature of the second hot water flow control valve 62 so that the amount of heat recovered by the second hot water in the preheater 7 follows the lower heat curve among the first upper limit heat curve L4, the second upper limit heat curve L5, or the third upper limit heat curve L6. By setting the temperature of the second hot water flow rate control valve 62 to below the third upper limit temperature, it is possible to suppress the amount of heat H1 added to the heat transfer medium in the preheater 7 from exceeding the third upper limit heat amount UH3.

[0101] In the illustrated embodiment, the third upper limit heat quantity acquisition unit 86 and the third upper limit temperature acquisition unit 87 are implemented by the control device 60, and the acquisition of the third upper limit heat quantity UH3 and the third upper limit temperature is performed by the calculation device 604. Information showing the correspondence between the third upper limit heat quantity UH3 and the load EL of the internal combustion engine 3 and information showing the correspondence between the third upper limit heat quantity UH3 and the third upper limit temperature are stored in the storage device 603.

[0102] The arithmetic unit 604 uses information stored in the memory device 603, which indicates the correspondence between the third upper limit heat quantity UH3 and the load EL of the internal combustion engine 3, information indicating the correspondence between the third upper limit heat quantity UH3 and the third upper limit temperature, the load EL of the internal combustion engine 3 (acquired value), and information indicating the correspondence between the load EL of the internal combustion engine 3 and the set temperature and opening degree of the second hot water flow control valve 62, to execute processing in the control device 60, such as acquiring the third upper limit heat quantity UH3 and acquiring the third upper limit temperature.

[0103] The maximum amount of heat that can be recovered from the second hot water in the preheater 7 changes according to the load EL of the internal combustion engine 3. In this embodiment, the ORC cycle 2 is controlled by the control device 60 so as not to exceed the third upper limit temperature, according to the load EL of the internal combustion engine 3, by determining the set temperature of the second hot water flow control valve 62. The ORC cycle 2 adjusts the opening of the second hot water flow control valve 62 so that the set temperature of the second hot water flow control valve 62 is set to a temperature that does not exceed the third upper limit temperature, thereby allowing the preheater 7 to recover as much thermal energy as possible into the heat transfer medium, within a range that does not exceed the maximum amount of heat that can be recovered from the second hot water.

[0104] In addition, the temperature setting unit 80 according to some other embodiments may be configured to determine the set temperature of the second hot water flow control valve 62 to a temperature that does not exceed the first upper limit temperature and the third upper limit temperature. The temperature setting unit 80 may set the lowest temperature among the first upper limit temperature and the third upper limit temperature (the lowest upper limit temperature) as the set temperature of the second hot water flow control valve 62, or it may calculate a temperature with a margin on the lower side relative to the above temperature (the lowest upper limit temperature) and set the calculated temperature as the set temperature of the second hot water flow control valve 62.

[0105] In some embodiments of the ORC cycle 2, the third upper limit heat quantity acquisition unit 86 described above is configured to acquire the third upper limit heat quantity UH3 according to the load EL and the temperature of the second hot water flowing through the second hot water supply line 41, based on the relationship between the third upper limit heat quantity UH3, the load EL of the internal combustion engine 3, and the temperature of the second hot water flowing through the second hot water supply line 41. In this embodiment, it is preferable to use the temperature of the second hot water flowing through the second hot water supply line 41 (measured by the temperature sensor 52 described above) which is guided from the water jacket 12 to the second hot water supply line 41.

[0106] The third upper limit heat quantity acquisition unit 86 is configured to acquire the third upper limit heat quantity UH3 corresponding to the load EL and the temperature of the second hot water flowing through the second hot water supply line 41, based on information stored in the storage device 603 that shows the relationship between the third upper limit heat quantity UH3, the load EL of the internal combustion engine 3, and the temperature of the second hot water flowing through the second hot water supply line 41.

[0107] In the ORC cycle 2 according to this embodiment, the upper limit of heat that can be recovered from the second hot water in the preheater 7 changes not only depending on the load EL of the internal combustion engine 3, but also on the temperature of the second hot water flowing through the second hot water supply line 41. By setting the third upper limit temperature corresponding to the third upper limit heat amount UH3 to a temperature corresponding to the load EL of the internal combustion engine 3 and the temperature of the second hot water flowing through the second hot water supply line 41, the preheater 7 can recover as much thermal energy as possible into the heat transfer medium.

[0108] In this specification, expressions describing relative or absolute arrangements such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial" shall not only describe such arrangements strictly, but also describe states of relative displacement with tolerances or angles or distances sufficient to achieve the same function. For example, expressions describing things being in an equal state such as "identical," "equal," and "homogeneous" shall not only describe states of being strictly equal, but also describe states where tolerances or differences exist to the extent that the same function is achieved. Furthermore, in this specification, expressions describing shapes such as quadrilaterals or cylindrical shapes shall not only describe geometrically precise quadrilaterals or cylindrical shapes, but also describe shapes including concave and concave parts, chamfered parts, etc., to the extent that the same effect is achieved. In addition, in this specification, expressions such as "equipment," "includes," or "possesses" a component are not exclusive expressions that exclude the existence of other components.

[0109] This disclosure is not limited to the embodiments described above, but also includes modified forms of the embodiments described above, as well as forms that combine these forms as appropriate.

[0110] The contents described in some of the embodiments above can be understood, for example, as follows:

[0111] [1] An ORC cycle (2) according to at least one embodiment of the present disclosure is an ORC cycle (2) configured to circulate a heat transfer medium that uses waste heat from an internal combustion engine (3) as a heat source, comprising: a turbine (5) configured to be driven by the heat transfer medium; an evaporator (6) configured to evaporate the heat transfer medium led to the turbine (5) by thermal energy recovered from a first waste heat source of the internal combustion engine (3); a preheater (7) configured to preheat the heat transfer medium led to the evaporator (6) by thermal energy recovered from a second waste heat source of the internal combustion engine (3); a second hot water supply line (41) for leading a second hot water, which is hot water from which thermal energy has been recovered, to the preheater (7); and a second hot water flow control valve (62) configured to adjust the flow rate of the second hot water introduced to the preheater (7) via the second hot water supply line (41).

[0112] According to the configuration described in [1] above, the ORC cycle (2) can suppress excessive heat input to the preheater (7) by adjusting the flow rate of the second hot water introduced to the preheater (7) via the second hot water supply line (41) using the second hot water flow rate control valve (62), thereby enabling waste heat recovery in the preheater (7) within the range where the heat transfer medium does not evaporate. Although adjusting the flow rate of the heat transfer medium introduced to the preheater (7) can be considered as a means of adjusting the amount of heat input to the heat transfer medium in the preheater (7), this flow rate adjustment restricts the flow rate of the heat transfer medium introduced to the evaporator (6), making it difficult to control the amount of thermal energy recovered in the evaporator (6), which is undesirable.

[0113] [2] In some embodiments, the ORC cycle (2) described in [1] above further comprises: a heat transfer medium pressure sensor (63) configured to measure the pressure (Pre) of the heat transfer medium flowing downstream of the preheater (7) and upstream of the turbine (5) in the ORC cycle (2); a saturation temperature calculation unit (64) configured to calculate the saturation temperature (Tr2) of the heat transfer medium based on the pressure (Pre) measured by the heat transfer medium pressure sensor (63); and a heat transfer medium temperature sensor (65) configured to measure the temperature (Tr1) of the heat transfer medium led from the preheater (7) to the evaporator (6), wherein the second hot water flow rate control valve (62) is The system is configured to reduce the flow rate of the second hot water introduced into the preheater (7) via the second hot water supply line (41) when the temperature difference (Tr2-Tr1) of the heat medium temperature (Tr1) measured by the heat medium temperature sensor (63) with respect to the saturation temperature (Tr2) falls below a threshold.

[0114] According to the configuration described in [2] above, the ORC cycle (2) can suppress excessive heat input to the preheater (7) by reducing the flow rate of the second hot water introduced into the preheater (7) using the second hot water flow rate control valve (62) so that the heat transfer medium does not reach its saturation temperature, and enables waste heat recovery in the preheater (7) within the range where the heat transfer medium does not evaporate.

[0115] [3] In some embodiments, the ORC cycle (2) described in [2] above, wherein the evaporator (6) is configured to perform heat exchange between the first hot water, which is hot water from which thermal energy has been recovered from the first waste heat source, and the heat transfer medium, the ORC cycle (2) comprises: a first hot water supply line (31) for leading the first hot water to the evaporator (6); a first hot water temperature sensor (71) configured to measure the temperature of the first hot water that has passed through the evaporator (6); a first hot water flow rate control valve (72) configured to adjust the flow rate of the first hot water introduced into the evaporator (6) via the first hot water supply line (31), wherein the first hot water flow rate control valve (72) is configured to increase the flow rate of the first hot water introduced into the evaporator (6) when the temperature of the first hot water measured by the first hot water temperature sensor (71) exceeds a first threshold, and the second hot water flow rate control valve (62) is The system is configured to reduce the flow rate of the second hot water supplied to the preheater (7) when the temperature of the first hot water measured by the first hot water temperature sensor (71) exceeds the first threshold or a second threshold that has a margin of safety on the higher side of the first threshold.

[0116] When the heat transfer medium in the evaporator (6) reaches the pinch point limit, the amount of thermal energy recovered in the evaporator (6) may decrease. Here, when the heat transfer medium in the evaporator (6) reaches the pinch point limit, the temperature of the first hot water that has passed through the evaporator (6) may rise to a temperature exceeding the first threshold. According to the configuration of [3] above, the ORC cycle (2) can suppress the decrease in the amount of thermal energy recovered in the evaporator (6) by reducing the flow rate of the second hot water introduced into the preheater (7) when the temperature of the first hot water that has passed through the evaporator (6) exceeds the first threshold or the second threshold, using the second hot water flow rate control valve (62). Therefore, according to the configuration of [3] above, the ORC cycle (2) can recover as much thermal energy as possible in the heat transfer medium in the preheater (7) without adversely affecting the evaporator (6). The configuration of [3] above is preferably combined with the configuration of [2] above. The configuration in [2] above suppresses evaporation in the preheater (7), and the configuration in [3] above maximizes the amount of heat recovered in the preheater (7) without wasting the heat recovered in the evaporator (6). The configurations in [2] and [3] above allow for highly accurate control because the control is based on measured values ​​of the pressure and temperature of the heat transfer medium.

[0117] [4] In some embodiments, the ORC cycle (2) described in [1] above further comprises: a second hot water temperature sensor (81) configured to measure the temperature of the second hot water that has passed through the preheater (7); a first upper limit heat acquisition unit (82) configured to acquire the first upper limit heat for each load from the relationship between the first upper limit heat, which is the amount of heat that causes the heat medium to begin evaporating in the preheater (7), and the load of the internal combustion engine (3); a first upper limit temperature acquisition unit (83) configured to acquire a first upper limit temperature of the second hot water flow control valve (62), which is a set temperature corresponding to the first upper limit heat acquired by the first upper limit heat acquisition unit (82); and a set temperature determination unit (80) configured to determine the set temperature of the second hot water flow control valve (62) to a temperature that does not exceed the first upper limit temperature, wherein the second hot water flow control valve (62) is configured to adjust its opening degree so that it becomes the set temperature determined by the set temperature determination unit (80).

[0118] According to the configuration described in [4] above, the ORC cycle (2) can suppress excessive heat input to the preheater (7) by adjusting the opening of the second hot water flow control valve (62) so that the temperature does not exceed the first upper limit temperature, thereby enabling heat recovery in the preheater (7) within a range that does not cause evaporation of the heat transfer medium.

[0119] [5] In some embodiments, the ORC cycle (2) described in [4] above further comprises: a second upper limit heat acquisition unit (84) configured to acquire the second upper limit heat amount for each load from the relationship between the second upper limit heat amount, which is the preheater heat amount at which the heat transfer medium reaches the pinch point limit in the evaporator (6), and the load of the internal combustion engine (3); and a second upper limit temperature acquisition unit (85) configured to acquire a second upper limit temperature, which is a set temperature corresponding to the second upper limit heat amount acquired by the second upper limit heat acquisition unit (84), wherein the set temperature determination unit (80) is configured to determine the set temperature of the second hot water flow control valve (62) to a temperature that does not exceed the second upper limit temperature.

[0120] When the heat transfer medium in the evaporator (6) reaches its pinch point limit, there is a risk that the amount of thermal energy recovered in the evaporator (6) will decrease. According to the configuration of [5] above, the ORC cycle (2) can suppress the decrease in the amount of thermal energy recovered in the evaporator (6) by adjusting the opening of the second hot water flow control valve (62) so that the temperature of the second hot water flow control valve (62) is set to a temperature that does not exceed the second upper limit temperature. Therefore, according to the configuration of [5] above, the ORC cycle (2) can recover as much thermal energy as possible in the heat transfer medium in the preheater (7) without adversely affecting the evaporator (6).

[0121] [6] In some embodiments, the ORC cycle (2) described in [4] or [5] above further comprises: a third upper limit heat acquisition unit (86) configured to acquire the third upper limit heat amount for each load from the relationship between the third upper limit heat amount, which is the upper limit heat amount that can be recovered in the preheater (7), and the load of the internal combustion engine (3); and a third upper limit temperature acquisition unit (87) configured to acquire the third upper limit temperature, which is a set temperature corresponding to the third upper limit heat amount acquired by the third upper limit heat acquisition unit (86), wherein the set temperature determination unit (80) is configured to determine the set temperature of the second hot water flow control valve to a temperature that does not exceed the third upper limit temperature.

[0122] According to the configuration of [6] above, the upper limit of heat that can be recovered from the second hot water in the preheater changes according to the load of the internal combustion engine (3). The ORC cycle (2) adjusts the opening of the second hot water flow control valve (62) so that the temperature of the second hot water flow control valve (62) is set to a temperature that does not exceed the third upper limit temperature, thereby allowing as much thermal energy as possible to be recovered in the heat transfer medium in the preheater (7) within a range that does not exceed the upper limit of heat that can be recovered from the second hot water. The configuration of [6] above is preferably combined with the configurations of [4] and [5] above. The configurations of [4], [5] and [6] above suppress the occurrence of hunting and reduce costs (temperature sensors and pressure sensors are not required) because the only parameter actually referenced is the load of the internal combustion engine.

[0123] [7] In some embodiments, the ORC cycle (2) described in [6] above, wherein the third upper limit heat acquisition unit (86) is configured to acquire the third upper limit heat amount corresponding to the load and the temperature of the second hot water flowing through the second hot water supply line (41) from the relationship between the third upper limit heat amount, the load of the internal combustion engine (3), and the temperature of the second hot water flowing through the second hot water supply line (41).

[0124] According to the configuration described in [7] above, the maximum amount of heat that can be recovered from the second hot water in the preheater (7) changes not only with respect to the load of the internal combustion engine (3) but also with respect to the temperature of the second hot water flowing through the second hot water supply line (41). By setting the third upper limit temperature, which corresponds to the third upper limit heat amount, to a temperature that corresponds to the load of the internal combustion engine (3) and the temperature of the second hot water flowing through the second hot water supply line (41), the preheater (7) can recover as much thermal energy as possible into the heat transfer medium.

[0125] [8] In some embodiments, the ORC cycle (2) described in any of [1] to [7] above, wherein the first exhaust heat source is exhaust gas discharged from the internal combustion engine (3), and the second exhaust heat source is jacket water flowing through the water jacket (12) of the internal combustion engine (3).

[0126] According to the configuration described in [8] above, the first waste heat source is exhaust gas discharged from the internal combustion engine (3), and the second waste heat source is jacket water. Even in such a case, the ORC cycle (2) can suppress excessive heat input to the preheater (7) by adjusting the flow rate of the second hot water introduced to the preheater (7) via the second hot water supply line (41) using the second flow control valve (62), thereby enabling waste heat recovery in the preheater (7) within a range that does not cause the heat transfer medium to evaporate.

[0127] 1. Waste heat recovery system 2. ORC cycle 3. Internal combustion engine 3A. Main engine 4. Heat transfer fluid circulation line 5. Turbine 6. Evaporator 7. Preheater 8. Rotating body 9. Generator 10. Condenser 11. Circulation pump 12. Water jacket 13. Waste heat recovery device 13A. Exhaust gas economizer 14. Propulsion unit 15. Exhaust gas line 16. Supercharger 17. Intake air cooler 18. Exhaust gas turbine 19. Compressor 20. High-temperature side heat exchanger 21. Low-temperature side heat exchanger 22. Space 23. Casing 24. Auxiliary boiler 25. Feedwater line 26. Boiler side circulation line 27. Steam line 28. Boiler furnace 29. Gas-liquid separator 30. Boiler side pump 31. First hot water supply line 32. First hot water return line 33. First hot water side pump 34 First hot water bypass line 41 Second hot water supply line 42 Second hot water return line 42A Cooler line 42B Cooler bypass line 43 Second hot water pump 44 Second hot water bypass line 51 Cooler 52 Temperature sensor 53 First temperature control valve 54 Second temperature control valve 55 Bypass line 60 Control device 62 Second hot water flow rate control valve 63 Heat transfer medium pressure sensor 64 Saturation temperature calculation unit 65 Heat transfer medium temperature sensor 71 First hot water temperature sensor 72 First hot water flow rate control valve 80 Set temperature determination unit 81 Second hot water temperature sensor 82 First upper limit heat quantity acquisition unit 83 First upper limit temperature acquisition unit 84 Second upper limit heat quantity acquisition unit 85 Second upper limit temperature acquisition unit 86 Third upper limit heat quantity acquisition unit 87 Third upper limit temperature acquisition unit 100 Ship 601 Input device 602 Output device 603 Storage device 604 Arithmetic device HS1 First exhaust heat source HS2 Second exhaust heat source

Claims

1. An ORC cycle configured to circulate a heat transfer medium that uses waste heat from an internal combustion engine as a heat source, comprising: a turbine configured to be driven by the heat transfer medium; an evaporator configured to evaporate the heat transfer medium led to the turbine by thermal energy recovered from a first waste heat source of the internal combustion engine; a preheater configured to preheat the heat transfer medium led to the evaporator by thermal energy recovered from a second waste heat source of the internal combustion engine; a second hot water supply line for leading a second hot water, which is hot water from which thermal energy has been recovered, to the preheater; and a second hot water flow control valve configured to adjust the flow rate of the second hot water introduced to the preheater via the second hot water supply line.

2. The ORC cycle according to claim 1, further comprising: a heat medium pressure sensor configured to measure the pressure of the heat medium flowing downstream of the preheater and upstream of the turbine in the ORC cycle; a saturation temperature calculation unit configured to calculate the saturation temperature of the heat medium based on the pressure measured by the heat medium pressure sensor; and a heat medium temperature sensor configured to measure the temperature of the heat medium led from the preheater to the evaporator, wherein the second hot water flow rate control valve is configured to reduce the flow rate of the second hot water introduced to the preheater via the second hot water supply line when the temperature difference of the heat medium measured by the heat medium temperature sensor with respect to the saturation temperature falls below a threshold.

3. The ORC cycle according to claim 2, wherein the evaporator is configured to perform heat exchange between the first hot water, which is hot water from which thermal energy has been recovered from the first waste heat source, and the heat transfer medium, and the ORC cycle comprises: a first hot water supply line for guiding the first hot water to the evaporator; a first hot water temperature sensor configured to measure the temperature of the first hot water that has passed through the evaporator; and a first hot water flow control valve configured to adjust the flow rate of the first hot water introduced into the evaporator via the first hot water supply line, wherein the first hot water flow control valve is configured to increase the flow rate of the first hot water introduced into the evaporator when the temperature of the first hot water measured by the first hot water temperature sensor exceeds a first threshold, and the second hot water flow control valve is configured to reduce the flow rate of the second hot water introduced into the preheater when the temperature of the first hot water measured by the first hot water temperature sensor exceeds a first threshold or a second threshold with a margin of safety on the higher side of the first threshold.

4. The ORC cycle according to claim 1, further comprising: a first upper limit heat acquisition unit configured to acquire the first upper limit heat amount for each load based on the relationship between the first upper limit heat amount, which is the amount of heat at which the heat medium begins to evaporate in the preheater, and the load of the internal combustion engine; a first upper limit temperature acquisition unit configured to acquire a first upper limit temperature of the second hot water flow control valve, which is a set temperature corresponding to the first upper limit heat amount acquired by the first upper limit heat acquisition unit; and a set temperature determination unit configured to determine the set temperature of the second hot water flow control valve to a temperature that does not exceed the first upper limit temperature, wherein the second hot water flow control valve is configured to adjust its opening degree so that it reaches the set temperature determined by the set temperature determination unit.

5. ORC cycle according to claim 4, further comprising: a second upper limit heat acquisition unit configured to acquire the second upper limit heat amount for each load from the relationship between the second upper limit heat amount, which is the preheater heat amount at which the heat transfer medium reaches the pinch point limit in the evaporator, and the load of the internal combustion engine; and a second upper limit temperature acquisition unit configured to acquire the second upper limit temperature of the second hot water flow control valve, which is the set temperature corresponding to the second upper limit heat amount acquired by the second upper limit heat acquisition unit, wherein the set temperature determination unit is configured to determine the set temperature of the second hot water flow control valve to a temperature that does not exceed the second upper limit temperature.

6. The ORC cycle according to claim 4 or 5, further comprising: a third upper limit heat acquisition unit configured to acquire the third upper limit heat amount for each load based on the relationship between the third upper limit heat amount, which is the upper limit heat amount that can be recovered in the preheater, and the load of the internal combustion engine; and a third upper limit temperature acquisition unit configured to acquire the third upper limit temperature of the second hot water flow control valve, which is a set temperature corresponding to the third upper limit heat amount acquired by the third upper limit heat acquisition unit, wherein the set temperature determination unit is configured to determine the set temperature of the second hot water flow control valve to a temperature that does not exceed the third upper limit temperature.

7. The ORC cycle according to claim 6, wherein the third upper limit heat quantity acquisition unit is configured to acquire the third upper limit heat quantity corresponding to the load and the temperature of the second hot water flowing through the second hot water supply line, based on the relationship between the third upper limit heat quantity, the load of the internal combustion engine, and the temperature of the second hot water flowing through the second hot water supply line.

8. The ORC cycle according to any one of claims 1 to 5, wherein the first exhaust heat source is exhaust gas discharged from the internal combustion engine, and the second exhaust heat source is jacket water flowing through the water jacket of the internal combustion engine.

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