Exhaust heat recovery system

Abstract

To prevent a structure of an exhaust heat recovery system from becoming complicated and provide an exhaust heat recovery system capable of stably recovering thermal energy from exhaust heat even when an amount of exhaust heat from an internal combustion engine is small.SOLUTION: An exhaust heat recovery system includes: a heat exchanger configured to recover thermal energy of exhaust gas flowing in an exhaust gas line from an internal combustion engine; a hot water circulation cycle for circulating hot water warmed in the heat exchanger; a heating medium circulation cycle for circulating a heating medium having a lower boiling point than that of water, the heating medium circulation cycle at least including an evaporator configured to vaporize the heating medium by using thermal energy recovered from the hot water flowing in the hot water circulation cycle and a turbine configured to be driven by the heating medium vaporized in the evaporator; a separator provided downstream of the heat exchanger and upstream of the evaporator in the hot water circulation cycle to separate hot water; and a pressure holding device.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an exhaust heat recovery system configured to recover thermal energy of exhaust gas emitted from an internal combustion engine. [Background technology]

[0002] A known exhaust heat recovery system is a power generation system that recovers thermal energy from exhaust gas emitted from an internal combustion engine (e.g., a marine main engine) using an economizer or the like, and uses the recovered thermal energy of the exhaust gas to generate steam, which drives a steam turbine of a generator to recover electric power. In recent years, with improvements in fuel efficiency of internal combustion engines (marine main engines), the temperature of exhaust gas emitted from the internal combustion engine has been decreasing. If the temperature of exhaust gas emitted from the internal combustion engine is low, it is difficult to secure a quantity of steam sufficient to drive the steam turbine and meet electric power demand, which may make it difficult to stably operate the power generation system. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5875253 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 discloses a power generation system that uses exhaust gas emitted from a gas engine as a heat source to drive an organic Rankine cycle (ORC) equipped with a turbine. In the invention described in Patent Document 1, when the thermal energy of exhaust gas capable of generating saturated steam is transferred to a heat medium circulating through the organic Rankine cycle, there is a risk that the intermediate heat medium that transfers the thermal energy between the exhaust gas and the heat medium may vaporize. To reduce greenhouse gas emissions, fuel efficiency improvement (reduced fuel consumption) is necessary, and a system that can recover heat from low-temperature heat sources is desired. Even when hot water is used as the intermediate heat medium, there is a risk that the hot water may vaporize (turn into steam), which could prevent the power generation system from generating electricity stably. Furthermore, suppressing the vaporization of the intermediate heat medium may result in a complex structure of the exhaust heat recovery system.

[0005] In view of the above circumstances, at least one embodiment of the present disclosure aims to provide an exhaust heat recovery system that can suppress the complexity of the structure of the exhaust heat recovery system and can stably recover thermal energy from exhaust heat even when the amount of exhaust heat from the internal combustion engine is small. [Means for solving the problem]

[0006] An exhaust heat recovery system according to at least one embodiment of the present disclosure includes: An exhaust heat recovery system configured to recover thermal energy of exhaust gas emitted from an internal combustion engine, an exhaust gas line for guiding exhaust gas emitted from the internal combustion engine; a heat exchanger configured to recover thermal energy of the exhaust gas flowing through the exhaust gas line; a hot water circulation cycle that circulates hot water heated in the heat exchanger; a heat medium circulation cycle that circulates a heat medium having a boiling point lower than that of water, the heat medium circulation cycle including at least an evaporator configured to vaporize the heat medium by thermal energy recovered from the hot water flowing through the hot water circulation cycle, and a turbine configured to be driven by the heat medium vaporized in the evaporator; a separator that separates the hot water into a gas phase and a liquid phase, the separator being disposed downstream of the heat exchanger and upstream of the evaporator in the hot water circulation cycle; and a pressure maintaining device configured to maintain the pressure inside the separator at or below a predetermined value at which the hot water flowing through the hot water circulation cycle is vaporized. [Effects of the Invention]

[0007] According to at least one embodiment of the present disclosure, an exhaust heat recovery system is provided that can suppress the complexity of the structure of the exhaust heat recovery system and can stably recover thermal energy from exhaust heat even when the amount of exhaust heat from an internal combustion engine is small. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic configuration diagram of a ship equipped with an exhaust heat recovery system according to an embodiment of the present disclosure. [Figure 2] 1 is a schematic configuration diagram of a ship equipped with an exhaust heat recovery system according to an embodiment of the present disclosure. [Figure 3] 1 is a schematic configuration diagram of a ship equipped with an exhaust heat recovery system according to an embodiment of the present disclosure. [Figure 4] 1 is a schematic configuration diagram of a ship equipped with an exhaust heat recovery system according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

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

[0010] (Waste heat recovery system) 1 to 4 are schematic configuration diagrams of a ship equipped with an exhaust heat recovery system 10 according to an embodiment of the present disclosure. The exhaust heat recovery system 10 according to some embodiments is configured to recover thermal energy of exhaust gas emitted from an internal combustion engine 11.

[0011] In the following embodiments, a case will be described in which the internal combustion engine 11 is a dual-fuel engine 11A that can be operated using at least one of oil fuel (liquid fuel) and gas fuel (gaseous fuel). Note that some embodiments of the present disclosure can also be applied to engines that can be operated using only either oil fuel or gas fuel as the used fuel.

[0012] As shown in FIGS. 1 to 4, the exhaust heat recovery system 10 may be mounted on a ship 1. The internal combustion engine 11 may be the main engine of the ship 1. The ship 1 is a structure that can float on water and is configured to be self-propelled by driving the main engine. The main engine is configured to generate driving force (propulsion force) that drives a propeller (a propeller in the illustrated example) 13 mechanically connected to the drive shaft of the main engine, using the energy of the fuel (oil fuel or gas fuel) supplied to the main engine. Note that in other embodiments, the exhaust heat recovery system 10 may be mounted on a structure other than the ship 1, such as a floating body or a structure provided on land. A floating body is a structure that is not self-propelled and does not have a propeller for self-propulsion.

[0013] 1 to 4, the exhaust heat recovery system 10 includes an exhaust gas line 12 for guiding exhaust gas emitted from an internal combustion engine 11, a heat exchanger 20 configured to recover thermal energy of the exhaust gas flowing through the exhaust gas line 12, a hot water circulation cycle 30 for circulating hot water (feed water) heated in the heat exchanger 20, and a heat medium circulation cycle 40 for circulating a heat medium having a boiling point lower than that of water. The heat medium circulation cycle 40 includes an evaporator 41 configured to vaporize the heat medium by thermal energy recovered from the hot water flowing through the hot water circulation cycle 30, and a turbine 42 configured to be driven by the heat medium vaporized in the evaporator 41.

[0014] In the illustrated embodiment, the exhaust heat recovery system 10 includes a turbocharger 14. The turbocharger 14 includes an exhaust gas turbine 15 provided upstream of the heat exchanger 20 in the exhaust gas line 12 in the flow direction of the exhaust gas, and a compressor 16 provided coaxially with the exhaust gas turbine 15. The exhaust gas turbine 15 is configured to recover energy of the exhaust gas flowing through the exhaust gas line 12. The compressor 16 is configured to compress a fluid (e.g., air used for combustion in the internal combustion engine 11) guided to the compressor 16 by being rotated by the energy recovered by the exhaust gas turbine 15.

[0015] (heat exchanger) The heat exchanger 20 is configured to exchange heat between the exhaust gas discharged from the internal combustion engine 11 and flowing through the exhaust gas line 12 and the circulating water flowing through the hot water circulation cycle 30. The exhaust gas guided to the heat exchanger 20 has a higher temperature than the circulating water guided to the heat exchanger 20. Through the heat exchange between the exhaust gas and the circulating water in the heat exchanger 20, the thermal energy of the exhaust gas is transferred to the circulating water. Through the heat exchange in the heat exchanger 20, the exhaust gas is cooled and the circulating water is heated.

[0016] (hot water circulation cycle) As shown in FIGS. 1 to 4 , the hot water circulation cycle 30 includes a first hot water line 31 that forms a flow path for guiding hot water (circulating water) from the heat exchanger 20 to the evaporator 41, a second hot water line 32 that forms a flow path for guiding hot water from the evaporator 41 to the heat exchanger 20, and a hot water-side pump 33 that sends the hot water flowing through the hot water circulation cycle 30. The hot water-side pump 33 is configured to increase the pressure of the hot water flowing through the hot water circulation cycle 30. In the illustrated embodiment, the hot water-side pump 33 is provided on the second hot water line 32. By driving the hot water-side pump 33, the hot water circulates through the first hot water line 31 and the second hot water line 32. Hereinafter, the upstream side of the hot water flow direction in the hot water circulation cycle 30 will be simply referred to as the upstream side, and the downstream side of the hot water flow direction in the hot water circulation cycle 30 will be simply referred to as the downstream side.

[0017] 1 to 4, the hot water circulation cycle 30 includes a bypass line 34 for guiding hot water from the first hot water line 31 to the second hot water line 32, bypassing the evaporator 41. One end of the bypass line 34 is connected to the first hot water line 31, and the other end of the bypass line 34 is connected upstream of the hot water pump 33 in the flow direction of the hot water in the second hot water line 32 (toward the evaporator 41).

[0018] (evaporator) The evaporator 41 is configured to exchange heat between the hot water flowing through the hot water circulation cycle 30 and the heat medium flowing through the heat medium circulation cycle 40. The hot water introduced to the evaporator 41 has a higher temperature than the heat medium introduced to the evaporator 41. Through heat exchange between the hot water and the heat medium in the evaporator 41, thermal energy of the hot water is transferred to the heat medium. Through heat exchange in the evaporator 41, the hot water is cooled and the heat medium is heated and vaporized. The hot water cooled in the evaporator 41 is introduced to the heat exchanger 20 through the second hot water line 32.

[0019] (heat medium circulation cycle) The heat medium circulating through the heat medium circulation cycle 40 can be low-molecular-weight hydrocarbons such as isopentane, butane, or propane, or refrigerants such as R134a, R245fa, or R1233zd. As shown in FIGS. 1 to 4 , the heat medium circulation cycle 40 includes a first heat medium line 43 that forms a flow path for guiding the heat medium from the evaporator 41 to the turbine 42, and a second heat medium line 44 that forms a flow path for guiding the heat medium from the turbine 42 to the evaporator 41. The heat medium vaporized in the evaporator 41 is guided to the turbine 42 through the first heat medium line 43.

[0020] The heat medium circulation cycle 40 includes a condenser 45 configured to liquefy a gas phase heat medium, and a heat medium circulation pump 46 for feeding the liquid phase heat medium. The heat medium circulation pump 46 is configured to compress the liquid phase heat medium. Hereinafter, the upstream side of the heat medium flow direction in the heat medium circulation cycle 40 will be simply referred to as the upstream side, and the downstream side of the heat medium flow direction in the heat medium circulation cycle 40 will be simply referred to as the downstream side. The condenser 45 is provided in the second heat medium line 44. The heat medium circulation pump 46 is provided in the second heat medium line 44 downstream of the condenser 45 (on the evaporator 41 side).

[0021] The heat medium circulation pump 46 is configured to send a liquid-phase heat medium to the second heat medium line 44 downstream of the heat medium circulation pump 46. By driving the heat medium circulation pump 46, the heat medium circulates through the second heat medium line 44 and the first heat medium line 43. The liquid-phase heat medium compressed by the heat medium circulation pump 46 is guided to the evaporator 41 through the second heat medium line 44. The heat medium vaporized by heat exchange in the evaporator 41 is guided to the turbine 42.

[0022] The turbine 42 is configured to be rotated by the energy of the heat medium vaporized in the evaporator 41. The heat medium circulation cycle 40 is configured to recover the rotational force of the turbine 42 as power. In the illustrated embodiment, the heat medium circulation cycle 40 includes a generator 47. The generator 47 is mechanically connected to a drive shaft of the turbine 42 and configured to convert the rotational force of the turbine 42 into electric power. Note that in some other embodiments, the heat medium circulation cycle 40 may recover the rotational force of the turbine 42 directly as power using a power transmission device (for example, a coupling, a belt, a pulley, etc.) instead of converting it into electric power.

[0023] The heat medium that has passed through the turbine 42 is guided to the condenser 45. The condenser 45 is configured to perform heat exchange between the heat medium guided to the condenser 45 and cooling water introduced into the condenser 45 from outside the heat medium circulation cycle 40. The cooling water may be water that can cool the heat medium, which is the heat exchange target as a refrigerant in the condenser 45 (water that is at a lower temperature than the heat medium). The heat exchange in the condenser 45 cools the heat medium and condenses it.

[0024] (boiler) The exhaust heat recovery system 10 may include a boiler 90 as shown in Figures 1 to 4. The boiler 90 includes a boiler body 91 that heats and vaporizes feedwater by burning fuel, a boiler-side heat exchanger 92, a first boiler feedwater line 93 that forms a flow path for guiding the boiler feedwater from the boiler body 91 to the boiler-side heat exchanger 92, a second boiler feedwater line 94 that forms a flow path for guiding the boiler feedwater from the boiler-side heat exchanger 92 to the boiler body 91, and a boiler-side pump 95 for sending the boiler feedwater.

[0025] In the illustrated embodiment, the boiler-side pump 95 is provided in the first boiler feedwater line 93. By driving the boiler-side pump 95, the boiler feedwater circulates through the boiler body 91, the boiler-side heat exchanger 92, the first boiler feedwater line 93, and the second boiler feedwater line 94.

[0026] The boiler-side heat exchanger 92 is configured to exchange heat between the exhaust gas flowing upstream (toward the internal combustion engine 11) of the heat exchanger 20 in the exhaust gas line 12 in the flow direction of the exhaust gas and the boiler feedwater introduced to the boiler-side heat exchanger 92. When the temperature of the exhaust gas in the boiler-side heat exchanger 92 is higher than that of the boiler feedwater, the thermal energy of the exhaust gas is recovered by the boiler feedwater.

[0027] The exhaust heat recovery system 10 may have a feedwater supply system that supplies feedwater to the boiler body 91. In the illustrated embodiment, the exhaust heat recovery system 10 includes a feedwater tank 96 configured to store feedwater, a feedwater supply line 97 that forms a flow path for guiding the feedwater from the feedwater tank 96 to the boiler body 91, a feedwater supply-side pump 98 provided on the feedwater supply line 97, and a flow rate adjustment valve 99 provided on the feedwater supply line 97 that can adjust the flow rate of the feedwater flowing through the feedwater supply line 97. By driving the feedwater supply-side pump 98, the feedwater stored in the feedwater tank 96 is guided to the boiler body 91 through the feedwater supply line 97. Drain water may be guided to the feedwater tank 96 from inside or outside the exhaust heat recovery system 10.

[0028] (Steam line) 1 to 4, the exhaust heat recovery system 10 may include a steam line 100 for guiding steam obtained by vaporizing feedwater in a boiler body 91. The upstream end of the steam line 100 is connected to the boiler body 91, and the downstream end of the steam line 100 is connected to equipment or the like that is a supply destination 101 of the steam.

[0029] (separator) An exhaust heat recovery system 10 according to some embodiments includes a separator 50 and a pressure retention device 60, as shown in FIGS. 1, 3, and 4. The separator 50 is provided downstream of the heat exchanger 20 and upstream of the evaporator 41 in the hot water circulation cycle 30. In the illustrated embodiment, the separator 50 is provided upstream of the connection portion of the first hot water line 31 with the one end of the bypass line 34, and is configured to be able to store hot water therein. The separator 50 has a stationary structure that separates hot water introduced into the separator 50 into a gas phase and a liquid phase. The hot water introduced into the separator 50 is separated into a gas phase and a liquid phase. By driving the hot water-side pump 33, the liquid-phase hot water is extracted from the separator 50 to the first hot water line 31 downstream of the separator 50.

[0030] The exhaust heat recovery system 10 may have a feedwater supply system that supplies feedwater to the separator 50. In the illustrated embodiment, the exhaust heat recovery system 10 includes a feedwater supply line 51 for guiding feedwater to the separator 50, and a flow rate adjustment valve 52 that is provided in the feedwater supply line 51 and is capable of adjusting the flow rate of the feedwater flowing through the feedwater supply line 51. In the embodiment shown in FIGS. 1 and 3 , the upstream end of the feedwater supply line 51 is connected to the feedwater supply line 97 downstream of the feedwater supply-side pump 98, and the downstream end of the feedwater supply line 51 is connected to the separator 50.

[0031] (Pressure retention device) The pressure maintaining device 60 is configured to maintain the pressure inside the separator 50 at or below a predetermined value at which the hot water flowing through the hot water circulation cycle 30 vaporizes. In the illustrated embodiment, the pressure maintaining device 60 includes a steam discharge line 61 that forms a flow path for discharging steam from inside the separator 50, and a steam flow rate adjusting device (steam flow rate adjusting valve) 62 that is configured to be able to adjust the flow rate of steam flowing through the steam discharge line 61. The upstream end of the steam discharge line 61 is connected to the separator 50, so that steam (hot water in a gas phase) is led from inside the separator 50 to the steam discharge line 61.

[0032] The pressure inside the separator 50 increases as the hot water is heated, and when this increased pressure reaches a predetermined value (for example, saturated steam pressure), it is determined that the hot water temperature has reached the saturated steam temperature. When the hot water temperature reaches the saturated steam temperature, vaporization occurs. When the pressure inside the separator 50 increases and reaches a predetermined value, the opening of the steam flow control device 62 provided in the steam discharge line 61 is increased, and steam is discharged from inside the separator 50 to the steam discharge line 61, thereby suppressing the increase in pressure inside the separator 50. When steam is discharged from inside the separator 50 to the steam discharge line 61, heat is also discharged. This suppresses the temperature increase of the hot water flowing through the hot water circulation cycle 30, and the hot water can be kept below the saturated steam temperature, preventing the hot water from vaporizing.

[0033] 1, 3, and 4, the pressure maintaining device 60 includes a pressure acquisition device (a pressure sensor in the illustrated example) 63 configured to acquire (measure) the pressure inside the separator 50, and an opening degree instructing device (a controller in the illustrated example) 64 that instructs the steam flow rate adjusting device 62 to an opening degree corresponding to the pressure inside the separator 50 acquired by the pressure acquisition device 63. Note that the steam flow rate adjusting device 62 may be a pressure adjustment valve configured to open the valve when the pressure exceeds the predetermined value or a set pressure lower than the predetermined value. In this case, the pressure maintaining device 60 does not need to include the pressure acquisition device 63 and the opening degree instructing device 64.

[0034] The pressure retention device 60 maintains the pressure inside the separator 50 at or below a predetermined value at which the hot water flowing through the hot water circulation cycle 30 vaporizes, thereby preventing an excessive rise in temperature of the hot water flowing through the hot water circulation cycle 30 and preventing the hot water flowing through the hot water circulation cycle 30 from vaporizing. By preventing the hot water flowing through the hot water circulation cycle 30 from vaporizing, it becomes possible to stably recover thermal energy from the exhaust heat even when the amount of exhaust heat from the internal combustion engine 11 is small. The simple configuration of the separator 50 and the pressure retention device 60 can prevent the hot water flowing through the hot water circulation cycle 30 from vaporizing, thereby preventing the exhaust heat recovery system 10 from becoming too complicated.

[0035] In the exhaust heat recovery system 10 according to some embodiments, as shown in FIGS. 1 and 3 , the downstream end of the steam discharge line 61 is connected to the steam line 100. The steam flow rate control device 62 is configured to increase the flow rate of steam guided from the separator 50 to the steam line 100 via the steam discharge line 61 when the pressure inside the separator 50 exceeds a threshold value that is lower than a predetermined value. The threshold value is set to a value that generates a pressure difference between the separator 50 and the steam line 100 and allows the steam to be discharged. The threshold value is set to a value higher than the steady-state pressure of the boiler body 91. In one embodiment, the threshold value is set to a value higher than the steady-state pressure of the boiler body 91 by 0.5 kg / cm or more.

[0036] When the pressure inside the separator 50 exceeds a threshold value that is lower than a predetermined value, the steam flow rate regulator 62 increases the flow rate of steam guided from the separator 50 to the steam line 100 via the steam discharge line 61, thereby suppressing the increase in pressure inside the separator 50 so that it does not exceed the predetermined value. By setting the threshold value to a value that generates a pressure difference between the separator 50 and the steam line 100 and allows steam to be discharged, the pressure difference between the separator 50 and the steam line 100 allows steam to be guided from the separator 50 to the steam line 100, eliminating the need for a device for sending steam, such as a blower. The steam guided from the separator 50 to the steam line 100 can be used at the steam supply destination 101 located downstream of the steam line 100, thereby suppressing a decrease in the efficiency of the exhaust heat recovery system 10.

[0037] In the exhaust heat recovery system 10 according to some embodiments, as shown in FIG. 4 , the downstream end of the steam discharge line 61 is connected to a steam discharge destination 101A that is different from the steam supply destination 101. The threshold value of the steam flow rate control device 62 is set to a value that generates a pressure difference between the separator 50 and the steam discharge destination 101A, allowing the steam to be discharged. The steam discharge destination 101A has a lower pressure than the steam line 100. The steam discharge destination 101A is a facility on the ship 1, and the steam sent to the steam discharge destination 101A may be used as miscellaneous steam within the ship 1.

[0038] As shown in Figures 1, 3, and 4, the exhaust heat recovery system 10 according to some embodiments includes a steam heat exchanger 110 configured to transfer thermal energy of steam discharged from the boiler 90 described above to hot water in the separator 50 and heat the hot water in the separator 50.

[0039] In the illustrated embodiment, the exhaust heat recovery system 10 includes a steam branch pipe 111 having one end connected to a steam line 100 and the other end connected to a steam heat exchanger 110, and a flow rate adjustment valve 112 provided in the steam branch pipe 111 and capable of adjusting the flow rate of steam flowing through the steam branch pipe 111. By opening the flow rate adjustment valve 112, steam is guided from the boiler 90 to the steam heat exchanger 110 through the steam branch pipe 111 and the steam line 100 upstream of the connection between the steam branch pipe 111 and the steam branch pipe 111. The steam heat exchanger 110 is preferably disposed in a storage section (liquid phase) in which hot water in the separator 50 is stored.

[0040] The steam heat exchanger 110 is configured to exchange heat between steam discharged from the boiler 90 and guided to the steam heat exchanger 110 and the hot water in the separator 50. The steam guided to the steam heat exchanger 110 has a higher temperature than the hot water in the separator 50. Heat energy of the steam is transferred to the hot water by heat exchange between the steam and the hot water in the steam heat exchanger 110. The hot water is heated by heat exchange in the steam heat exchanger 110.

[0041] The hot water in the separator 50 is heated by the thermal energy of the steam discharged from the boiler 90, thereby raising the temperature of the hot water flowing through the hot water circulation cycle 30. By raising the temperature of the hot water flowing through the hot water circulation cycle 30, a decrease in the efficiency of the exhaust heat recovery system 10 can be suppressed.

[0042] (Tanks, water level control devices) 2, the exhaust heat recovery system 10 according to some embodiments includes a tank 70 and a water surface height maintaining device 80. The tank 70 is connected to the hot water circulation cycle 30 so as to allow hot water to flow therethrough, and is configured to store hot water so as to have a water surface 71.

[0043] In the illustrated embodiment, the exhaust heat recovery system 10 includes a connection pipe 72 that connects the hot water circulation cycle 30 and the tank 70. In the embodiment shown in FIG. 2, one end (header) 73 of the connection pipe 72 is connected to the second hot water line 32 upstream of the hot water pump 33, and the other end is connected to the tank 70. The tank 70 is disposed above the one end 73 of the connection pipe 72. At least a portion of the hot water storage section of the tank 70 that stores hot water is disposed above the heat exchanger 20. A water surface 71 formed by the hot water stored in the tank 70 has a water surface height that corresponds to the pressure of the hot water flowing through the hot water circulation cycle 30, specifically, the connection section of the second hot water line 32 with the connection pipe 72. As the pressure of the hot water flowing through the hot water circulation cycle 30 decreases, the water surface height decreases.

[0044] (Water surface height maintenance device) The water surface height maintaining device 80 is configured to maintain the height of the water surface 71 at or above a predetermined value (predetermined height) at which the hot water flowing through the hot water circulation cycle 30 will vaporize. The water surface height maintaining device 80 has a pressurizing means (for example, a tank-side pump 82) for increasing the pressure inside the tank 70. When the pressure inside the tank 70 drops and the height of the water surface 71 drops and approaches the predetermined value, the water surface height maintaining device 80 pressurizes the inside of the tank 70, thereby suppressing a drop in the pressure of the hot water inside the tank 70 and the hot water flowing through the hot water circulation cycle 30.

[0045] The pressure inside the tank 70 is maintained above a certain pressure. When the pressure in the entire circulation system (hot water circulation cycle 30) through which the hot water circulates drops, the height of the water surface 71 drops, and the pressure inside the tank 70 drops. By supplying water into the tank 70 and maintaining the height of the water surface 71, the water head pressure can be maintained, and the pressure in the entire circulation system (hot water circulation cycle 30) through which the hot water circulates can be maintained above a predetermined pressure. By maintaining the pressure in the entire circulation system (hot water circulation cycle 30) through which the hot water circulates above a predetermined pressure, the hot water can be suppressed from vaporizing.

[0046] The water surface height maintaining device 80 maintains the height of the water surface 71 in the tank 70 at or above a predetermined value (predetermined height) that corresponds to the predetermined pressure at which the hot water flowing through the hot water circulation cycle 30 vaporizes, thereby suppressing the vaporization of the hot water flowing through the hot water circulation cycle 30. By suppressing the vaporization of the hot water flowing through the hot water circulation cycle 30, it becomes possible to stably recover thermal energy from the exhaust heat even when the amount of exhaust heat from the internal combustion engine 11 is small. The simple configuration of the tank 70 and the water surface height maintaining device 80 can suppress the vaporization of the hot water flowing through the hot water circulation cycle 30, thereby suppressing the complexity of the exhaust heat recovery system 10.

[0047] 2, the water level maintaining device 80 includes a tank-side water supply line 81 that forms a flow path for guiding tank-side water supply into the tank 70, a tank-side pump 82 that pressurizes the tank-side water supply flowing through the tank-side water supply line 81, and a liquid level control device (a controller in the illustrated example) 83 that is configured to turn the tank-side pump 82 on and off so as to maintain the height of the water surface 71 within a predetermined range. By driving the tank-side pump 82, the water pressurized by the tank-side pump 82 is introduced into the tank 70 from a water supply source through the tank-side water supply line 81.

[0048] In the illustrated embodiment, the exhaust heat recovery system 10 includes a water surface height acquisition device 84 configured to acquire the height (level) of the water surface 71 in the tank 70. The water surface height acquisition device 84 may be a liquid level sensor that measures the height of the water surface 71 in the tank 70, or may be a plurality of level sensors provided at a plurality of height positions in the tank 70. The liquid level control device 83 turns the tank-side pump 82 on and off in accordance with information about the height of the water surface 71 acquired by the water surface height acquisition device 84.

[0049] The lower limit of the predetermined range is set so that the height of the water surface 71 is higher than the predetermined value. In one embodiment, the liquid level control device 83 has a lower limit threshold and an upper limit threshold set within the predetermined range so that the height of the water surface 71 is set higher than the lower limit threshold, and drives the tank-side pump 82 when the height of the water surface 71 acquired by the water surface height acquisition device 84 falls below the lower limit threshold, and stops driving the tank-side pump 82 when the height of the water surface 71 acquired by the water surface height acquisition device 84 exceeds the upper limit threshold.

[0050] Tank-side supply water pressurized by a tank-side pump 82 can be supplied to the inside of the tank 70 via a tank-side water supply line 81. The height of the water surface 71 in the tank 70 can be adjusted by turning the tank-side pump 82 on and off using a liquid level control device 83. Note that in the above-described embodiment, the height of the water surface 71 in the tank 70 is adjusted by supplying a relatively high-pressure liquid into the tank 70, but in some other embodiments, the height of the water surface 71 in the tank 70 may be adjusted by supplying a relatively high-pressure gas (e.g., steam, air, nitrogen, etc.) into the tank 70.

[0051] As shown in FIG. 2, the exhaust heat recovery system 10 according to some embodiments includes a hot water side heat exchanger 102 configured to transfer the thermal energy of the steam discharged from the boiler 90 described above to the hot water flowing through the hot water circulation cycle 30 and heat the hot water flowing through the hot water circulation cycle 30.

[0052] In the illustrated embodiment, the exhaust heat recovery system 10 includes a steam branch pipe 103 having one end connected to a steam line 100 and the other end connected to a hot water side heat exchanger 102. Steam is guided from the boiler 90 to the hot water side heat exchanger 102 through the steam branch pipe 103 and a portion of the steam line 100 upstream of the connection between the steam branch pipe 103 and the steam branch pipe 103. A flow rate adjustment valve may be provided in the steam branch pipe 103. In the illustrated embodiment, the hot water side heat exchanger 102 is provided in the first hot water line 31 and is configured to heat the hot water guided to the evaporator 41.

[0053] The hot water side heat exchanger 102 is configured to exchange heat between steam discharged from the boiler 90 and guided to the hot water side heat exchanger 102, and hot water guided to the hot water side heat exchanger 102. The steam guided to the hot water side heat exchanger 102 has a higher temperature than the hot water guided to the hot water side heat exchanger 102. Heat energy of the steam is transferred to the hot water by heat exchange between the steam and the hot water in the hot water side heat exchanger 102. The hot water is heated by heat exchange in the hot water side heat exchanger 102.

[0054] Oil fuel may contain sulfur, and when the dual-fuel engine 11A described above is operated using oil fuel as the used fuel, the exhaust gas emitted from the dual-fuel engine 11A may contain sulfur. If the exhaust gas becomes colder than the acid dew point of the oil fuel due to heat exchange in the heat exchanger 20, there is a risk of low-temperature corrosion occurring in the heat exchanger 20. By heating the hot water through heat exchange in the hot-water-side heat exchanger 102, it is possible to prevent the exhaust gas from becoming colder than the acid dew point of the oil fuel due to heat exchange in the heat exchanger 20, and it is possible to prevent low-temperature corrosion from occurring in the heat exchanger 20.

[0055] 1 to 3, the exhaust heat recovery system 10 according to some embodiments further includes a hot water flow rate control device (controller in the illustrated example) 120. The hot water flow rate control device 120 is configured to reduce the flow rate of hot water guided to the evaporator 41 and increase the flow rate of hot water flowing through the bypass line 34 when the dual-fuel engine 11A (internal combustion engine 11) is operating using oil fuel as the used fuel, compared to when the dual-fuel engine 11A is operating using gas fuel as the used fuel.

[0056] The hot water flow rate control device 120 is configured to obtain information (signals) related to the fuel used by the dual-fuel engine 11A during operation from other devices or equipment (in the illustrated example, the dual-fuel engine 11A). In the illustrated embodiment, the exhaust heat recovery system 10 includes a flow rate control valve 121 that is provided in the bypass line 34 and configured to be able to adjust the flow rate of hot water flowing through the bypass line 34, and a flow rate control valve 122 that is provided downstream of the connection point of the first hot water line 31 with the bypass line 34 and configured to be able to adjust the flow rate of hot water guided to the evaporator 41.

[0057] When the dual-fuel engine 11A is operated using oil fuel as the used fuel, the hot water flow rate control device 120 instructs the flow rate control valves 121 and 122 to open larger and smaller degrees, respectively, compared to when the dual-fuel engine 11A is operated using gas fuel as the used fuel. When the dual-fuel engine 11A is operated using oil fuel as the used fuel, the proportion of hot water that passes through the bypass line 34 out of the hot water circulating through the hot water circulation cycle 30 is increased compared to when the dual-fuel engine 11A is operated using gas fuel as the used fuel.

[0058] Oil fuel may contain sulfur, and in order to prevent low-temperature corrosion in the exhaust gas line 12, it is necessary to manage the temperature of the hot water led to the heat exchanger 20 so that it is equal to or higher than the acid dew point temperature of the oil fuel. The hot water flow rate control device 120 reduces the flow rate of the hot water led to the evaporator 41 and increases the flow rate of the hot water flowing through the bypass line 34, thereby suppressing a drop in the temperature of the hot water due to heat exchange in the evaporator 41, and therefore the temperature of the hot water led to the heat exchanger 20 can be maintained at or higher than the acid dew point temperature of the oil fuel.

[0059] In some embodiments, the above-described exhaust heat recovery system 10 is configured to stop operation of the heat medium circulation cycle 40 when the dual-fuel engine 11A is operated using oil fuel. The above-described hot water flow rate control device 120 is configured to stop the supply of hot water to the evaporator 41 and cause the hot water flowing through the hot water circulation cycle 30 to pass through the bypass line 34 when the dual-fuel engine 11A is operated using oil fuel.

[0060] When the dual-fuel engine 11A is operating using oil fuel as the used fuel, the hot water flow rate control device 120 instructs the flow rate control valve 121 and the flow rate control valve 122 to open fully and fully close, respectively. Note that instead of the flow rate control valve 121 and the flow rate control valve 122, a three-way valve may be provided at the connection point of the first hot water line 31 with the bypass line 34, and the hot water flow rate control device 120 may adjust the proportion of hot water in the three-way valve that flows toward the bypass line 34.

[0061] By stopping the operation of the heat medium circulation cycle 40 and causing the hot water flowing through the hot water circulation cycle 30 to bypass the evaporator 41, heat exchange in the evaporator 41 no longer occurs, thereby reliably preventing a drop in the temperature of the hot water due to heat exchange in the evaporator 41.

[0062] The exhaust heat recovery system 10 is configured to increase the amount of hot water circulated in the hot water circulation cycle 30 when the dual-fuel engine 11A is operated using oil fuel compared to when the engine is operated using gas fuel as the fuel used.

[0063] 3, the second hot water line 32 described above branches into multiple lines at a branch point P1 and includes multiple (two in the illustrated example) branch pipes 321, 322 that merge at a junction P2 downstream of the branch point P1. The hot water pump 33 described above includes multiple hot water pumps 331, 332 that are respectively provided on the multiple branch pipes 321, 322. When the dual-fuel engine 11A is operated using oil fuel, the exhaust heat recovery system 10 increases the number of operating hot water pumps 331, 332 compared to when the dual-fuel engine 11A is operated using gas fuel. This increases the amount of hot water circulated in the hot water circulation cycle 30.

[0064] In another embodiment, the hot water pump 33 may be configured to have a variable rotation speed, and the exhaust heat recovery system 10 may increase the rotation speed of the hot water pump 33 when the dual-fuel engine 11A is operated on oil fuel compared to when the dual-fuel engine 11A is operated on gas fuel. This also increases the amount of hot water circulated in the hot water circulation cycle 30.

[0065] Since heat exchange in the evaporator 41 is no longer performed, the temperature of the hot water circulating through the heat medium circulation cycle 40 gradually increases due to heat exchange in the heat exchanger 20. If the temperature of the hot water flowing through the hot water circulation cycle 30 exceeds a specified temperature, there is a risk of damaging the equipment constituting the hot water circulation cycle 30. Increasing the amount of hot water circulating through the hot water circulation cycle 30 increases the amount of hot water heated in the heat exchanger 20 per unit time, and therefore more energy is required to heat the hot water. However, since the energy (heat) that can be recovered from the exhaust gas through heat exchange in the heat exchanger 20 is constant, the hot water temperature decreases. In this way, by increasing the amount of hot water circulating through the hot water circulation cycle 30, the influence of heat exchange in the heat exchanger 20 can be reduced, and the temperature of the hot water flowing through the hot water circulation cycle 30 can be kept below a specified temperature.

[0066] In some embodiments, the exhaust heat recovery system 10 may include a temperature acquisition device 140 as shown in FIGS. 1 to 3. The temperature acquisition device 140 is configured to acquire the temperature of hot water flowing downstream of the heat exchanger 20 and upstream of the evaporator 41 in the hot water circulation cycle 30. In the embodiments shown in FIGS. 1, 3, and 4, the temperature acquisition device 140 includes a temperature sensor that measures the temperature of hot water flowing upstream of the separator 50 in the first hot water line 31. The temperature acquisition device 140 makes it possible to determine the temperature of the hot water heated by heat exchange in the heat exchanger 20, and to confirm that the hot water flowing in the hot water circulation cycle 30 is at a temperature at which it will not vaporize. Note that the above-described embodiments can be implemented even if the exhaust heat recovery system 10 does not include the temperature acquisition device 140.

[0067] In this specification, expressions expressing relative or absolute arrangement such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial" not only express such an arrangement strictly, but also express a state in which there is a relative displacement with a tolerance or an angle or distance to the extent that the same function is obtained. For example, expressions such as "identical," "equal," and "homogeneous" that indicate that something is in an equal state not only indicate a state of strict equality, but also indicate a state in which there is a tolerance or a difference to the extent that the same function is obtained. Furthermore, in this specification, expressions representing shapes such as a rectangular shape or a cylindrical shape not only represent rectangular shapes or cylindrical shapes in the strict geometric sense, but also represent shapes including uneven portions, chamfered portions, etc., to the extent that the same effect can be obtained. Furthermore, in this specification, the expressions "comprise," "include," or "have" a component are not exclusive expressions that exclude the presence of other components.

[0068] The present disclosure is not limited to the above-described embodiments, but also includes modifications to the above-described embodiments and appropriate combinations of these modifications.

[0069] The contents of the above-described embodiments can be understood, for example, as follows.

[0070] 1) The exhaust heat recovery system (10) according to at least one embodiment of the present disclosure includes: An exhaust heat recovery system (10) configured to recover thermal energy of exhaust gas discharged from an internal combustion engine (11), an exhaust gas line (12) for guiding exhaust gas discharged from the internal combustion engine (11); a heat exchanger (20) configured to recover thermal energy of the exhaust gas flowing through the exhaust gas line (12); a hot water circulation cycle (30) for circulating the hot water heated in the heat exchanger (20); a heat medium circulation cycle (40) for circulating a heat medium having a boiling point lower than that of water, the heat medium circulation cycle (40) including at least an evaporator (41) configured to vaporize the heat medium by thermal energy recovered from the hot water flowing through the hot water circulation cycle (30), and a turbine (42) configured to be driven by the heat medium vaporized in the evaporator (41); a separator (50) that separates the hot water into a gas phase and a liquid phase, the separator (50) being provided downstream of the heat exchanger (20) and upstream of the evaporator (41) in the hot water circulation cycle (30); and a pressure maintaining device (60) configured to maintain the pressure inside the separator (50) at or below a predetermined value at which the hot water flowing through the hot water circulation cycle (30) is vaporized.

[0071] According to the configuration 1), the pressure maintaining device (60) maintains the pressure inside the separator (50) at or below a predetermined value at which the hot water flowing through the hot water circulation cycle (30) vaporizes, thereby preventing an excessive increase in temperature of the hot water flowing through the hot water circulation cycle (30) and preventing the hot water flowing through the hot water circulation cycle (30) from vaporizing. By preventing the hot water flowing through the hot water circulation cycle (30) from vaporizing, it becomes possible to stably recover thermal energy from the exhaust heat even when the amount of exhaust heat from the internal combustion engine (11) is small. The simple configuration of the separator (50) and the pressure maintaining device (60) can prevent the hot water flowing through the hot water circulation cycle (30) from vaporizing, thereby preventing the exhaust heat recovery system (10) from becoming complicated.

[0072] 2) The exhaust heat recovery system (10) according to at least one embodiment of the present disclosure includes: An exhaust heat recovery system (10) configured to recover thermal energy of exhaust gas discharged from an internal combustion engine (11), an exhaust gas line (12) for guiding exhaust gas discharged from the internal combustion engine (11); a heat exchanger (20) configured to recover thermal energy of the exhaust gas flowing through the exhaust gas line (12); a hot water circulation cycle (30) for circulating the hot water heated in the heat exchanger (20); a heat medium circulation cycle (40) for circulating a heat medium having a boiling point lower than that of water, the heat medium circulation cycle (40) including at least an evaporator (41) configured to vaporize the heat medium by thermal energy recovered from the hot water flowing through the hot water circulation cycle (30), and a turbine (42) configured to be driven by the heat medium vaporized in the evaporator (41); a tank (70) connected to the hot water circulation cycle (30) so as to be able to circulate the hot water and capable of storing the hot water so as to have a water surface (71); and a water surface height maintaining device (80) configured to maintain the height of the water surface (71) at or above a predetermined value at which the hot water flowing through the hot water circulation cycle (30) is vaporized.

[0073] According to the configuration 2), the height of the water surface (71) in the tank (70) fluctuates in response to fluctuations in the pressure of the hot water flowing through the hot water circulation cycle (30). The water surface height maintaining device (80) maintains the height of the water surface (71) in the tank (70) at or above a predetermined value at which the hot water flowing through the hot water circulation cycle (30) vaporizes, thereby suppressing the hot water flowing through the hot water circulation cycle (30) from vaporizing. By suppressing the hot water flowing through the hot water circulation cycle (30) from vaporizing, it becomes possible to stably recover thermal energy from the exhaust heat even when the amount of exhaust heat from the internal combustion engine (11) is small. The simple configuration of the tank (70) and the water surface height maintaining device (80) can suppress the hot water flowing through the hot water circulation cycle (30) from vaporizing, thereby suppressing the complexity of the exhaust heat recovery system (10).

[0074] 3) In some embodiments, the exhaust heat recovery system (10) described in 1) above, a boiler (90) configured to recover thermal energy from the exhaust gas flowing upstream of the heat exchanger (20) in the exhaust gas line (12) and generate steam; a steam line (100) for guiding the steam discharged from the boiler (90); The pressure maintaining device (60) a steam discharge line (61) for discharging steam from the separator (50) to the steam line (100); a steam flow rate control device (62) configured to increase the flow rate of the steam guided from the separator (50) to the steam line (100) through the steam discharge line (61) when the pressure inside the separator (50) exceeds a threshold value that is lower than the predetermined value; The threshold value is set to a value that allows a pressure difference to be generated between the separator (50) and the vapor line (100) so that the vapor can be discharged.

[0075] According to the configuration 3), when the pressure inside the separator (50) exceeds a threshold value that is lower than a predetermined value, the steam flow rate control device (62) increases the flow rate of steam guided from the separator (50) to the steam line (100) through the steam discharge line (61), thereby suppressing an increase in pressure inside the separator (50). By setting the threshold value to a value that generates a pressure difference between the separator (50) and the steam line (100) and allows steam to be discharged, the pressure difference between the separator (50) and the steam line (100) allows the steam to be guided from the separator (50) to the steam line (100), thereby eliminating the need for a blower for sending the steam. The steam guided from the separator (50) to the steam line (100) can be used at a steam supply destination located downstream of the steam line (100), thereby suppressing a decrease in the efficiency of the exhaust heat recovery system (10).

[0076] 4) In some embodiments, the exhaust heat recovery system (10) described in 1) or 3) above, a boiler (90) configured to recover thermal energy from the exhaust gas flowing upstream of the heat exchanger (20) in the exhaust gas line (12) and vaporize feedwater; and a steam heat exchanger (110) configured to transfer thermal energy of steam discharged from the boiler (90) to the hot water in the separator (50) to heat the hot water.

[0077] According to the above configuration 4), the hot water in the separator (50) is heated by the thermal energy of the steam discharged from the boiler (90), thereby increasing the temperature of the hot water flowing through the hot water circulation cycle (30). By increasing the temperature of the hot water flowing through the hot water circulation cycle (30), it is possible to suppress a decrease in the efficiency of the exhaust heat recovery system (10).

[0078] 5) In some embodiments, the exhaust heat recovery system (10) described in 2) above, The water surface height maintaining device (80) a tank-side water supply line (81) for introducing tank-side water supply into the tank (70); a tank-side pump (82) for increasing the pressure of the tank-side supply water flowing through the tank-side supply water line (81); and a liquid level control device (83) configured to turn on and off the tank-side pump (82) so as to maintain the height of the water surface (71) within a predetermined range.

[0079] According to the configuration 5), the tank-side supply water pressurized by the tank-side pump (82) can be supplied to the inside of the tank (70) through the tank-side water supply line (81). The liquid level control device (83) turns on and off the tank-side pump (82), thereby making it possible to adjust the height of the water surface (71) in the tank (70).

[0080] 6) In some embodiments, the exhaust heat recovery system (10) according to any one of 1) to 5) above, The hot water circulation cycle (30) a first hot water line (31) for guiding the hot water from the heat exchanger (20) to the evaporator (41); a second hot water line (32) for guiding the hot water from the evaporator (41) to the heat exchanger (20); a bypass line (34) for guiding the hot water from the first hot water line (31) to the second hot water line (32) bypassing the evaporator (41); The internal combustion engine (11) includes a dual-fuel engine (11A) that can be operated using at least one of oil fuel and gas fuel as a fuel, The exhaust heat recovery system (10) The internal combustion engine (11) further includes a hot water flow rate control device (120) configured to reduce the flow rate of the hot water introduced to the evaporator (41) and increase the flow rate of the hot water flowing through the bypass line (34) when the internal combustion engine (11) is operated using oil fuel as the fuel used, compared to when the internal combustion engine (11) is operated using gas fuel as the fuel used.

[0081] According to the above configuration 6), since the oil fuel may contain sulfur, it is necessary to control the temperature of the hot water introduced into the heat exchanger (20) to be equal to or higher than the acid dew point of the oil fuel in order to prevent low-temperature corrosion in the exhaust gas line (12). The hot water flow rate control device (120) reduces the flow rate of the hot water introduced into the evaporator (41) and increases the flow rate of the hot water flowing through the bypass line (34), thereby suppressing a decrease in the temperature of the hot water due to heat exchange in the evaporator (41). As a result, the temperature of the hot water introduced into the heat exchanger (20) can be maintained equal to or higher than the acid dew point of the oil fuel.

[0082] 7) In some embodiments, the exhaust heat recovery system (10) described in 6) above, When the internal combustion engine (11) is operated using oil fuel, the operation of the heat medium circulation cycle (40) is stopped, The hot water flow rate control device (120) When the internal combustion engine (11) is operated using oil fuel, the supply of the hot water to the evaporator (41) is stopped, and the hot water flowing through the hot water circulation cycle (30) is made to pass through the bypass line (34).

[0083] According to the above configuration 7), the operation of the heat medium circulation cycle (40) is stopped and the hot water flowing through the hot water circulation cycle (30) is caused to bypass the evaporator (41). This prevents heat exchange in the evaporator (41), thereby reliably preventing a decrease in the temperature of the hot water due to heat exchange in the evaporator (41).

[0084] 8) In some embodiments, the exhaust heat recovery system (10) described in 7) above, When the internal combustion engine (11) is operated using oil fuel, the amount of hot water circulated in the hot water circulation cycle (30) is increased compared to when the internal combustion engine (11) is operated using gas fuel as the fuel used.

[0085] According to the configuration of 8), heat exchange in the evaporator (41) is no longer performed, and the temperature of the hot water circulating in the heat medium circulation cycle (40) gradually increases due to heat exchange in the heat exchanger (20). If the temperature of the hot water flowing in the hot water circulation cycle (30) exceeds a specified temperature, there is a risk of damaging the components of the hot water circulation cycle (30). By increasing the amount of hot water circulating in the hot water circulation cycle (30), the influence of heat exchange in the heat exchanger (20) can be reduced, and the temperature of the hot water flowing in the hot water circulation cycle (30) can be kept below the specified temperature.

[0086] 9) In some embodiments, the exhaust heat recovery system (10) according to any one of 1) to 8) above, The hot water circulation system further includes a temperature acquisition device (140) configured to acquire the temperature of the hot water flowing downstream of the heat exchanger (20) and upstream of the evaporator (41) in the hot water circulation cycle (30).

[0087] According to the above configuration 9), the temperature acquisition device (140) can grasp the temperature of the hot water heated by heat exchange in the heat exchanger (20), and it can be confirmed that the hot water flowing through the hot water circulation cycle (30) has a temperature at which it will not vaporize. [Explanation of symbols]

[0088] 1 ship 10. Waste heat recovery system 11 Internal combustion engine 11A Dual Fuel Engine 12 Exhaust gas line 14 Supercharger 15 Exhaust gas turbine 16 Compressor 20 Heat exchanger 30 Hot water circulation cycle 31 First hot water line 32 Second hot water line 33 Hot water pump 34 Bypass Line 40 Heat Transfer Medium Circulation Cycle 41 Evaporator 42 Turbine 43 First heat transfer medium line 44 Second heat transfer medium line 45 Condenser 46 Heat medium circulation pump 47 Generator 50 Separator 60 Pressure Retention Device 70 Tank 80 Water surface height maintenance device

Claims

1. An exhaust heat recovery system configured to recover thermal energy of exhaust gas emitted from an internal combustion engine, an exhaust gas line for guiding exhaust gas emitted from the internal combustion engine; a heat exchanger configured to recover thermal energy of the exhaust gas flowing through the exhaust gas line; a hot water circulation cycle that circulates hot water heated in the heat exchanger; a heat medium circulation cycle that circulates a heat medium having a boiling point lower than that of water, the heat medium circulation cycle including at least an evaporator configured to vaporize the heat medium by thermal energy recovered from the hot water flowing through the hot water circulation cycle, and a turbine configured to be driven by the heat medium vaporized in the evaporator; a separator that separates the hot water into a gas phase and a liquid phase, the separator being provided downstream of the heat exchanger and upstream of the evaporator in the hot water circulation cycle; a pressure maintaining device configured to maintain the pressure inside the separator at or below a predetermined value at which the hot water flowing through the hot water circulation cycle is vaporized, Waste heat recovery system.

2. An exhaust heat recovery system configured to recover thermal energy of exhaust gas emitted from an internal combustion engine, an exhaust gas line for guiding exhaust gas emitted from the internal combustion engine; a heat exchanger configured to recover thermal energy of the exhaust gas flowing through the exhaust gas line; a hot water circulation cycle that circulates hot water heated in the heat exchanger; a heat medium circulation cycle that circulates a heat medium having a boiling point lower than that of water, the heat medium circulation cycle including at least an evaporator configured to vaporize the heat medium by thermal energy recovered from the hot water flowing through the hot water circulation cycle, and a turbine configured to be driven by the heat medium vaporized in the evaporator; a tank connected to the hot water circulation circuit so as to be able to circulate the hot water and capable of storing the hot water so as to have a water surface; a water surface height maintaining device configured to maintain the height of the water surface at or above a predetermined value at which the hot water flowing through the hot water circulation cycle is vaporized, Waste heat recovery system.

3. a boiler configured to recover thermal energy from the exhaust gas flowing upstream of the heat exchanger in the exhaust gas line and generate steam; a steam line for guiding the steam discharged from the boiler, The pressure maintaining device is a steam discharge line for discharging steam from the separator to the steam line; a steam flow rate control device configured to increase a flow rate of the steam guided from the separator to the steam line via the steam discharge line when the pressure inside the separator exceeds the predetermined value, the predetermined value is set to a value that can generate a pressure difference between the separator and the vapor line and discharge the vapor. The exhaust heat recovery system according to claim 1 .

4. a boiler configured to recover thermal energy from the exhaust gas flowing upstream of the heat exchanger in the exhaust gas line and vaporize feedwater; a steam heat exchanger configured to transfer thermal energy of steam discharged from the boiler to the hot water in the separator to heat the hot water, The exhaust heat recovery system according to claim 1 or 3.

5. The water surface height maintaining device is a tank-side water supply line for guiding tank-side water supply into the tank; a tank-side pump for pressurizing the tank-side supply water flowing through the tank-side supply water line; and a liquid level control device configured to turn on and off the tank-side pump so as to maintain the height of the water surface within a predetermined range. The exhaust heat recovery system according to claim 2 .

6. The hot water circulation cycle is a first hot water line for guiding the hot water from the heat exchanger to the evaporator; a second hot water line for guiding the hot water from the evaporator to the heat exchanger; a bypass line for guiding the hot water from the first hot water line to the second hot water line, bypassing the evaporator; The internal combustion engine includes a dual-fuel engine that can be operated using at least one of oil fuel and gas fuel as a used fuel; The exhaust heat recovery system includes: The hot water flow rate control device is further configured to reduce the flow rate of the hot water guided to the evaporator and increase the flow rate of the hot water flowing through the bypass line when the internal combustion engine is operated using oil fuel as the used fuel, compared to when the internal combustion engine is operated using gas fuel as the used fuel.

6. The exhaust heat recovery system according to claim 1, 2, 3, or 5.

7. When the internal combustion engine is operated using oil fuel, the operation of the heat medium circulation cycle is stopped, The hot water flow rate control device includes: When the internal combustion engine is operated using oil fuel, the supply of the hot water to the evaporator is stopped, and the hot water flowing through the hot water circulation cycle is caused to pass through the bypass line. The exhaust heat recovery system according to claim 6.

8. When the internal combustion engine is operated using oil fuel, the amount of hot water circulated in the hot water circulation cycle is increased compared to when the internal combustion engine is operated using gas fuel as the used fuel. The exhaust heat recovery system according to claim 6.

9. The hot water circulation system further includes a temperature acquisition device configured to acquire a temperature of the hot water flowing downstream of the heat exchanger and upstream of the evaporator in the hot water circulation cycle.

6. The exhaust heat recovery system according to claim 1, 2, 3, or 5.

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