Exhaust heat recovery system

Abstract

To provide an exhaust heat recovery system capable of efficiently reducing thermal energy recovered from exhaust heat to power even when the exhaust heat from an internal combustion engine is small.SOLUTION: An exhaust heat recovery system includes: an exhaust heat recovery device having a high-temperature side exhaust heat recovery section for recovering thermal energy of exhaust gas discharged from an internal combustion engine and a low-temperature side exhaust heat recovery section for recovering thermal energy of exhaust gas that has passed through the high-temperature side exhaust heat recovery section; a water supply line including a first water supply line for guiding first supply water to the high-temperature side exhaust heat recovery section and a second water supply line for guiding second supply water to the low-temperature side exhaust heat recovery section; a steam heat exchanger for heating the second supply water by using the thermal energy of the first supply water vaporized in the high-temperature side exhaust heat recovery section; and a circulation cycle for circulating a low-boiling heating medium, the circulation cycle including an evaporator for vaporizing the low-boiling heating medium by using the thermal energy of the second supply water heated by the low-temperature side exhaust heat recovery section and the steam heat exchanger and a turbine driven by the low-boiling heating medium vaporized by the evaporator.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] There is known an exhaust heat recovery system that recovers the thermal energy of exhaust gas discharged from an internal combustion engine (e.g., a marine main engine) by an economizer or the like, and drives a steam turbine of a generator with steam generated by the recovered thermal energy of the exhaust gas to recover electric power.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, with the improvement of fuel efficiency of internal combustion engines (marine main engines), the thermal energy of exhaust gas discharged from internal combustion engines has been decreasing. If the thermal energy of the exhaust gas discharged from the internal combustion engine is small, it may be difficult to secure an amount of steam sufficient to drive a steam turbine to meet the power demand.

[0005] Patent Document 1 discloses an invention that drives an organic Rankine cycle (ORC) equipped with a turbine using exhaust gas discharged from a gas engine as a heat source. In the invention described in Patent Document 1, when transferring the thermal energy of exhaust gas capable of generating saturated steam to a heat medium circulating in the organic Rankine cycle, there is a risk that an intermediate heat medium that transfers thermal energy between the exhaust gas and the heat medium will vaporize. In order to suppress the vaporization of the intermediate heat medium, there is a risk of complicating the structure of the exhaust heat recovery system.

[0006] In view of the above circumstances, an object of at least one embodiment of the present disclosure is to provide a waste heat recovery system capable of efficiently reducing the heat energy recovered from waste heat into power even when the waste heat from the internal combustion engine is small.

Means for Solving the Problems

[0007] A waste heat recovery system according to an embodiment of the present disclosure is a waste heat recovery system configured to recover the heat energy of the exhaust gas discharged from the internal combustion engine, including a high-temperature side waste heat recovery unit configured to recover the heat energy of the exhaust gas discharged from the internal combustion engine, and a low-temperature side waste heat recovery unit configured to recover the heat energy of the exhaust gas that has passed through the high-temperature side waste heat recovery unit; a water supply line for guiding water to the waste heat recovery device, including a first water supply line for guiding the first water supply to the high-temperature side waste heat recovery unit, and a second water supply line branched from the first water supply line for guiding the second water supply to the low-temperature side waste heat recovery unit; a steam heat exchanger configured to transfer the heat energy of the first water supply vaporized in the high-temperature side waste heat recovery unit to the second water supply and heat the second water supply; and a circulation cycle for circulating a low-boiling heat medium having a boiling point lower than that of water, including an evaporator configured to vaporize the low-boiling heat medium by the heat energy recovered from the second water supply heated by each of the low-temperature side waste heat recovery unit and the steam heat exchanger, and a turbine configured to be driven by the low-boiling heat medium vaporized in the evaporator. A water supply line for guiding water to the waste heat recovery device, including a first water supply line for guiding the first water supply (which is the water supply) to the high-temperature side waste heat recovery unit, and a second water supply line branched from the first water supply line for guiding the second water supply (which is the water supply) to the low-temperature side waste heat recovery unit. A steam heat exchanger configured to transfer the heat energy of the first water supply vaporized in the high-temperature side waste heat recovery unit to the second water supply and heat the second water supply. A circulation cycle for circulating a low-boiling heat medium having a boiling point lower than that of water, including an evaporator configured to vaporize the low-boiling heat medium by the heat energy recovered from the second water supply heated by each of the low-temperature side waste heat recovery unit and the steam heat exchanger, and a turbine configured to be driven by the low-boiling heat medium vaporized in the evaporator.

Effects of the Invention

[0008] According to at least one embodiment of the present disclosure, a waste heat recovery system capable of efficiently reducing the heat energy recovered from waste heat into power even when the waste heat from the internal combustion engine is small is provided.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Mode for Carrying Out the Invention

[0010] Hereinafter, some embodiments of the present disclosure will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described as embodiments or shown in the drawings are not intended to limit the scope of the present disclosure, but are merely illustrative examples. For example, expressions representing relative or absolute arrangements such as "in a certain direction", "along a certain direction", "parallel", "orthogonal", "center", "concentric", or "coaxial" not only strictly represent such arrangements, but also represent a state of relative displacement with tolerances or at angles and distances that provide the same function. For example, expressions representing that things such as "identical", "equal", and "homogeneous" are in an equal state not only strictly represent an equal state, but also represent a state in which there are tolerances or differences that provide the same function. For example, expressions representing shapes such as a rectangular shape or a cylindrical shape not only represent shapes such as a rectangular shape or a cylindrical shape in a geometrically strict sense, but also represent shapes including concave and convex portions, chamfered portions, etc. within a range where the same effect can be obtained. On the other hand, the expressions "comprising", "including", or "having" a component are not exclusive expressions that exclude the existence of other components. Note that the same reference numerals may be given to the same configurations and the description may be omitted.

[0011] (Exhaust Heat Recovery System) FIG. 1 is a schematic configuration diagram schematically showing the configuration of a ship equipped with an exhaust heat recovery system according to an embodiment of the present disclosure. The exhaust heat recovery system 10 according to some embodiments is configured to recover the thermal energy of the exhaust gas discharged from the internal combustion engine 11. As shown in FIG. 1, the exhaust heat recovery system 10 includes an exhaust heat recovery device 20 configured to recover the thermal energy of the exhaust gas discharged from the internal combustion engine 11, a water supply line 30 for guiding water supply to the exhaust heat recovery device 20, a steam heat exchanger 40, and a circulation cycle 50.

[0012] In the illustrated embodiment, the internal combustion engine 11 includes a main engine 11A. The exhaust heat recovery system 10 is mounted on a ship 1 equipped with the main engine 11A. In other words, the ship 1 includes the exhaust heat recovery system 10 and the main engine 11A. The ship 1 is a structure that can float on water and is configured to be self-propelled by driving the main engine 11A. The main engine 11A is configured to generate a driving force (propulsive force) that drives a propeller (in the illustrated example, a propeller) 12 mechanically connected to the drive shaft of the main engine 11A by the energy of the supplied fuel (fuel gas or fuel oil). In other embodiments, the exhaust heat recovery system 10 may be mounted on a structure other than the ship 1, for example, a floating body or a structure provided on land. The floating body is a non-self-propelled structure that does not have a propeller for self-propulsion.

[0013] In the illustrated embodiment, the exhaust heat recovery system 10 further includes an exhaust gas line 13 for sending the exhaust gas discharged from the internal combustion engine 11, an exhaust gas turbine 14 provided in the exhaust gas line 13, and a supercharger 16 including a compressor 15 provided coaxially with the exhaust gas turbine 14.

[0014] (Exhaust heat recovery device, water supply line) The exhaust heat recovery device 20 includes a high-temperature side exhaust heat recovery unit 21 configured to recover the thermal energy of the exhaust gas discharged from the internal combustion engine 11, and a low-temperature side exhaust heat recovery unit 22 configured to recover the thermal energy of the exhaust gas that has passed through the high-temperature side exhaust heat recovery unit 21. The water supply line 30 includes a first water supply line 31 for guiding the first water supply, which is the water supply, to the high-temperature side exhaust heat recovery unit 21, and a second water supply line 32 for guiding the second water supply, which is the water supply, to the low-temperature side exhaust heat recovery unit 22.

[0015] The high-temperature side exhaust heat recovery unit 21 is configured to perform heat exchange between the exhaust gas discharged from the internal combustion engine 11 and guided to the high-temperature side exhaust heat recovery unit 21, and the first water supply guided to the high-temperature side exhaust heat recovery unit 21 by the first water supply line 31. The exhaust gas introduced into the high-temperature side exhaust heat recovery unit 21 is at a higher temperature than the first water supply introduced into the high-temperature side exhaust heat recovery unit 21. Through the heat exchange between the exhaust gas and the first water supply in the high-temperature side exhaust heat recovery unit 21, the thermal energy of the exhaust gas is transferred to the first water supply. As a result, in the high-temperature side exhaust heat recovery unit 21, the exhaust gas is cooled, and at the same time, the first water supply is heated and vaporized. Hereinafter, the first water supply in the gaseous state vaporized in the high-temperature side exhaust heat recovery unit 21 is referred to as the first vapor.

[0016] In the illustrated embodiment, the exhaust heat recovery system 10 includes a gas-liquid separator 17 provided in the first water supply line 31 and configured to separate the first water supply into a gas phase and a liquid phase, a first water supply delivery line 18 for guiding the first water supply that has recovered thermal energy from the exhaust gas in the high-temperature side exhaust heat recovery unit 21 to the gas-liquid separator 17, and a first water supply side pump 19 provided on the downstream side (the high-temperature side exhaust heat recovery unit 21 side) of the gas-liquid separator 17 in the first water supply line 31.

[0017] The first feed water in the liquid phase is led to the gas-liquid separator 17 through the first feed water line 31. By the first feed water side pump 19, the first feed water in the liquid phase extracted from the gas-liquid separator 17 is led to the high-temperature side exhaust heat recovery section 21. The first feed water that has recovered thermal energy from the exhaust gas in the high-temperature side exhaust heat recovery section 21 is sent to the gas-liquid separator 17 through the first feed water delivery line 18. The first feed water sent to the gas-liquid separator 17 through the first feed water delivery line 18 contains the first vapor vaporized in the high-temperature side exhaust heat recovery section 21. In the gas-liquid separator 17, the first vapor is separated from the first feed water in the liquid state.

[0018] In the illustrated embodiment, the above-described gas-liquid separator 17 consists of the steam drum of the boiler. In this case, since the existing steam drum of the boiler can be diverted as the gas-liquid separator 17, the manufacturing cost of the exhaust heat recovery system 10 can be reduced.

[0019] The low-temperature side exhaust heat recovery section 22 is configured to perform heat exchange between the exhaust gas led to the low-temperature side exhaust heat recovery section 22 after passing through the high-temperature side exhaust heat recovery section 21 and the second feed water led to the low-temperature side exhaust heat recovery section 22 through the second feed water line 32. The exhaust gas introduced into the low-temperature side exhaust heat recovery section 22 is at a higher temperature than the second feed water introduced into the low-temperature side exhaust heat recovery section 22. By the heat exchange between the exhaust gas and the second feed water in the low-temperature side exhaust heat recovery section 22, the thermal energy of the exhaust gas is transferred to the second feed water. As a result, in the low-temperature side exhaust heat recovery section 22, the exhaust gas is cooled and the second feed water is heated. The second feed water does not vaporize even after being heated in the low-temperature side exhaust heat recovery section 22 and maintains its liquid state.

[0020] (Steam heat exchanger) The steam heat exchanger 40 is configured to transfer the thermal energy of the first vapor (the first feed water vaporized in the high-temperature side exhaust heat recovery section 21) to the second feed water and heat the second feed water. As shown in FIG. 1, the exhaust heat recovery system 10 further includes a first steam introduction line 60 for leading the first vapor from the gas-liquid separator 17 to the steam heat exchanger 40. The first vapor is led from the gas-liquid separator 17 to the steam heat exchanger 40 through the first steam introduction line 60.

[0021] The first steam introduced into the steam heat exchanger 40 is at a higher temperature than the second feed water introduced into the steam heat exchanger 40. Through the heat exchange between the first steam and the second feed water in the steam heat exchanger 40, the thermal energy of the first steam is transferred to the second feed water. Thereby, in the steam heat exchanger 40, the second feed water is heated. The second feed water does not vaporize even after being heated in the steam heat exchanger 40 and maintains its liquid state.

[0022] In the illustrated embodiment, the low-temperature side exhaust heat recovery section 22 includes a first low-temperature side heat exchanger 23 configured to perform heat exchange between the exhaust gas that has passed through the high-temperature side exhaust heat recovery section 21 and the second feed water, and a second low-temperature side heat exchanger 24 configured to perform heat exchange between the exhaust gas that has passed through the first low-temperature side heat exchanger 23 and the second feed water. The high-temperature side exhaust heat recovery section 21 is provided on the downstream side in the flow direction of the exhaust gas from the exhaust gas turbine 14 in the exhaust gas line 13 and on the upstream side of the low-temperature side exhaust heat recovery section 22 (the first low-temperature side heat exchanger 23, the second low-temperature side heat exchanger 24). The first low-temperature side heat exchanger 23 is provided on the upstream side in the flow direction of the exhaust gas from the second low-temperature side heat exchanger 24 in the exhaust gas line 13.

[0023] In the illustrated embodiment, the exhaust heat recovery system 10 further includes a relay line 34 for guiding the second feed water that has passed through the second low-temperature side heat exchanger 24 to the first low-temperature side heat exchanger 23. The steam heat exchanger 40 is provided in the relay line 34.

[0024] (Circulation cycle) The circulation cycle 50 is configured to circulate a low-boiling heat medium having a boiling point lower than that of water. The circulation cycle 50 includes at least an evaporator 52 and a turbine 53. The evaporator 52 is configured to vaporize the low-boiling heat medium by the thermal energy recovered from the second feed water heated by the low-temperature side exhaust heat recovery section 22 and the steam heat exchanger 40 respectively. The turbine 53 is configured to be driven by the low-boiling heat medium vaporized in the evaporator 52.

[0025] The circulation cycle 50 is configured to circulate a low-boiling heat medium. As the low-boiling heat medium, low-molecular hydrocarbons such as isopentane, butane, and propane, or R134a, R245fa, etc. used as refrigerants can be used. The circulation cycle 50 further includes a circulation flow path 51 that is a flow path for circulating the low-boiling heat medium, a condenser 54 configured to liquefy the low-boiling heat medium, and a circulation pump 55 for sending the liquid-phase low-boiling heat medium. The circulation pump 55 is configured to compress the liquid-phase low-boiling heat medium.

[0026] Hereinafter, the upstream side in the flow direction of the low-boiling heat medium in the circulation cycle 50 is simply referred to as the upstream side, and the downstream side in the flow direction of the low-boiling heat medium in the circulation cycle 50 is simply referred to as the downstream side. The evaporator 52 is provided in the circulation cycle 50 on the downstream side of the circulation pump 55 and on the upstream side of the turbine 53. The condenser 54 is provided in the circulation cycle 50 on the downstream side of the turbine 53 and on the upstream side of the circulation pump 55.

[0027] The circulation pump 55 is configured to send the liquid-phase low-boiling heat medium to the downstream side of the circulation pump 55 in the circulation cycle 50. By driving the circulation pump 55, the low-boiling heat medium circulates through the circulation flow path 51 (circulation cycle 50). The liquid-phase low-boiling heat medium compressed by the circulation pump 55 is guided to the evaporator 52.

[0028] As shown in FIG. 1, the waste heat recovery system 10 further includes a second feed water introduction line 33 for guiding the second feed water heated by the low-temperature side waste heat recovery unit 22 and the steam heat exchanger 40 to the evaporator 52. The liquid-phase second feed water heated by the low-temperature side waste heat recovery unit 22 and the steam heat exchanger 40 is guided to the evaporator 52 through the second feed water introduction line 33.

[0029] The evaporator 52 is provided in a circulation flow path 51A that connects the outlet side of the circulation pump 55 and the inlet side of the turbine 53. The evaporator 52 is supplied with a liquid-phase low-boiling heat medium compressed by the circulation pump 55 through the circulation flow path 51A. The evaporator 52 is configured to perform heat exchange between the liquid-phase low-boiling heat medium compressed by the circulation pump 55 and introduced into the evaporator 52, and the liquid-phase second feed water introduced into the evaporator 52 through the second feed water introduction line 33. The second feed water introduced into the evaporator 52 is at a higher temperature than the low-boiling heat medium introduced into the evaporator 52. Through the heat exchange between the low-boiling heat medium and the second feed water in the evaporator 52, the heat energy of the second feed water is transferred to the low-boiling heat medium. As a result, in the evaporator 52, the low-boiling heat medium is heated and vaporized.

[0030] The low-boiling heat medium vaporized by the evaporator 52 is led to the turbine 53. The turbine 53 is configured to rotate by the energy of the low-boiling heat medium vaporized in the evaporator 52. The circulation cycle 50 is configured to recover the rotational force of the turbine 53 as power.

[0031] In the illustrated embodiment, the circulation cycle 50 further includes a generator 56. The generator 56 is mechanically connected to the drive shaft of the turbine 53 and is configured to convert the rotational force of the turbine 53 into electric power. In some other embodiments, instead of converting the rotational force of the turbine 53 into electric power, the circulation cycle 50 may recover the rotational force of the turbine 53 as power directly through a power transmission device (such as a coupling, belt, pulley, etc.).

[0032] The condenser 54 is provided in a circulation flow path 51B that connects the outlet side of the turbine 53 and the inlet side of the circulation pump 55. The condenser 54 is supplied with the low-boiling heat medium that has passed through the turbine 53 through the circulation flow path 51B. The condenser 54 is configured to perform heat exchange between the low-boiling heat medium that has passed through the turbine 53 and introduced into the condenser 54, and the external water introduced into the condenser 54 from outside the circulation cycle 50. The external water may be any water that can cool the low-boiling heat medium, which is the heat exchange target as a refrigerant in the condenser 54 (water at a lower temperature than the low-boiling heat medium).

[0033] Through heat exchange between the low-boiling heat medium and external water in the condenser 54, the thermal energy of the low-boiling heat medium is transferred to the external water. As a result, in the condenser 54, the gaseous low-boiling heat medium is cooled and condensed.

[0034] The waste heat recovery system 10 according to some embodiments includes a waste heat recovery device 20 including the above-described high-temperature side waste heat recovery unit 21 and low-temperature side waste heat recovery unit 22, a water supply line 30 including the above-described first water supply line 31 and second water supply line 32, the above-described steam heat exchanger 40, and a circulation cycle 50 including at least the above-described evaporator 52 and turbine 53.

[0035] According to the above configuration, the waste heat recovery system 10 can heat the low-boiling heat medium by using the second water heated by each of the low-temperature side waste heat recovery unit 22 and the steam heat exchanger 40 as a heat source in the evaporator 52. Even when the waste heat from the internal combustion engine 11 is small, the waste heat recovery system 10 can utilize the thermal energy recovered from the exhaust gas by the waste heat recovery device 20 as a heat medium in the evaporator 52 and convert it into power in the turbine 53.

[0036] In some embodiments, the above-described waste heat recovery system 10 is configured such that the second water heated by each of the low-temperature side waste heat recovery unit 22 and the steam heat exchanger 40 maintains a liquid state. In this case, the waste heat recovery system 10 can suppress the vaporization of the water supplied to the evaporator 52, and the water supplied to the evaporator 52 can recover the thermal energy of the exhaust gas while remaining in a liquid state. By suppressing the vaporization of the water supplied to the evaporator 52, it is not necessary to provide a steam turbine in the waste heat recovery system 10, so that the complexity of the waste heat recovery system 10 can be suppressed.

[0037] In conventional exhaust gas economizers and steam turbine generators, if the heat energy of the exhaust gas discharged from the main engine 11A (internal combustion engine 11) is small due to the improvement of fuel efficiency of the main engine 11A, there is a risk that the amount of steam that can cover the power demand cannot be generated. For this reason, in the exhaust heat recovery system 10, a turbine 53 and a generator 56 that can recover the heat energy of the exhaust gas even from a low-temperature heat source are used.

[0038] The exhaust gas discharged from the main engine 11A has heat energy sufficient to vaporize the feed water. For this reason, if the configuration is such that heat energy is transferred from the exhaust gas to the second feed water in the high-temperature side exhaust heat recovery section 21, the second feed water cannot maintain a liquid phase under conditions below a predetermined pressure (for example, the saturation pressure of the feed water temperature corresponding to below the pinch temperature with the exhaust gas temperature in the high-temperature side exhaust heat recovery section 21). Therefore, it is necessary to increase the feed water pressure to maintain the liquid phase state. On the other hand, in the exhaust heat recovery system 10, the second feed water heated in the steam heat exchanger 40 can maintain a liquid state under a normal feed water pressure lower than the above predetermined pressure.

[0039] If the configuration is such that the feed water vaporizes in the feed water system of the exhaust heat recovery system 10, it is necessary to make the above feed water system have piping and a structure that can withstand vaporization, which may lead to complication of the structure of the above feed water system. Further, as a measure for maintaining a liquid phase in the heat medium that has recovered the heat energy of the exhaust gas, it is conceivable to use high-pressure water or heat medium oil as the heat medium. However, compared with the case of using the feed water (second feed water) sent at a normal feed water pressure as the heat medium, there is a risk of complication of the structure of the above feed water system. When the structure of the above feed water system becomes complicated, there is a risk of causing enlargement of the equipment provided in the above feed water system and reduction of the safety of the exhaust heat recovery system 10.

[0040] According to the above configuration, water (warm water) that can be sent at normal water supply pressure can be used as the water supply (second water supply) guided to the evaporator 52. When using water (warm water) as the water supply (second water supply) guided to the evaporator 52, compared with the case of using high-pressure water, heat transfer medium oil, etc. as the heat transfer medium guided to the evaporator 52, simplification of the water supply system structure in the waste heat recovery system 10, miniaturization of the equipment provided in the water supply system, improvement of the safety of the waste heat recovery system 10, etc. can be achieved.

[0041] (Mixing chamber, water supply branch line) In some embodiments, as shown in FIG. 1, the waste heat recovery system 10 described above includes the second water supply introduction line 33 described above, a mixing chamber 70 provided in the second water supply introduction line 33, and a water supply branch line 35 that branches from the water supply line 30 to guide the water supply to the mixing chamber 70.

[0042] The mixing chamber 70 is configured to be able to store the water supply therein. The second water supply heated by the low-temperature side waste heat recovery unit 22 and the steam heat exchanger 40 respectively is introduced into the mixing chamber 70 through the second water supply introduction line 33. Further, the water supply branched from the water supply line 30 is introduced into the mixing chamber 70 through the water supply branch line 35.

[0043] In the illustrated embodiment, the water supply branch line 35 branches from the water supply line 30 at the branch portion P1 of the water supply line 30. The first water supply line 31 and the second water supply line 32 branch at the branch portion P1 of the water supply line 30. Note that the first water supply line 31 and the second water supply line 32 may branch upstream or downstream of the branch portion P1 of the water supply line 30, or the water supply branch line 35 may branch from either the first water supply line 31 or the second water supply line 32.

[0044] The heat recovery system 10 further includes a water supply side pump 36 provided upstream of the branch portion P1 of the water supply line 30, and a first water supply side flow rate adjustment valve 37 provided in the first water supply line 31. The water supply side pump 36 is configured to send the liquid-phase water supply downstream of the water supply side pump 36 in the water supply line 30. The water supply side pump 36 generates a water supply pressure in the water supply flowing downstream of the water supply side pump 36 in the water supply line 30. The first water supply side flow rate adjustment valve 37 is provided upstream of the gas-liquid separator 17 in the first water supply line 31 and is configured to be able to adjust the flow rate of the first water supply led to the gas-liquid separator 17.

[0045] The flow rate of the first water supply led to the gas-liquid separator 17 is adjusted by the first water supply side flow rate adjustment valve 37 according to the storage amount of the first water supply in the gas-liquid separator 17 described above. Specifically, the first water supply for supplementing the vaporized first water supply passes through the first water supply side flow rate adjustment valve 37 and is supplied to the gas-liquid separator 17. When the flow rate of the water supply led to the mixing chamber 70 through the water supply branch line 35 is increased, the flow rate of the second water supply led to the low-temperature side heat recovery section 22 through the second water supply line 32 decreases by that amount.

[0046] According to the above configuration, by branching the water supply line 30 into three, namely the first water supply line 31, the second water supply line 32, and the water supply branch line 35, compared with the conventional structure in which all the water supply is introduced into the low-temperature side exhaust heat recovery section 22, the water supply flow rate to be controlled is small, so the responsiveness of the water supply flow rate control is improved. In the above conventional structure, for example, when trying to reduce the flow rate of the water supply to suppress sulfuric acid corrosion, it is necessary to control the total amount of the water supply by the water supply side pump 36. In contrast, according to the above configuration, by increasing the flow rate of the water supply guided to the mixing chamber 70 through the water supply branch line 35, it is possible to adjust so as to reduce the flow rate of the second water supply guided to the low-temperature side exhaust heat recovery section 22. By adjusting the flow rate of the second water supply guided to the low-temperature side exhaust heat recovery section 22, since the amount of heat energy recovery (transfer amount) from the exhaust gas to the second water supply in the low-temperature side exhaust heat recovery section 22 can be adjusted, the temperature of the exhaust gas discharged from the low-temperature side exhaust heat recovery section 22 can be adjusted. By improving the responsiveness of the water supply flow rate control, the responsiveness of the exhaust gas temperature control is also improved.

[0047] Also, according to the above configuration, by branching the water supply line 30 into three, namely the first water supply line 31, the second water supply line 32, and the water supply branch line 35, the flow rate of the second water supply guided to the low-temperature side exhaust heat recovery section 22 can be reduced. By suppressing the flow rate of the second water supply, the resistance is also reduced, so the low-temperature side exhaust heat recovery section 22 and the steam heat exchanger 40 to which the second water supply is guided can be downsized. Also, according to the above configuration, in the mixing chamber 70, by mixing the second water supply heated by the low-temperature side exhaust heat recovery section 22 and the steam heat exchanger 40 respectively, and the water supply guided by the water supply branch line 35, the heated second water supply can be made to have a suitable uniform temperature for introduction into the circulation cycle 50.

[0048] In some embodiments, as shown in FIG. 1, the exhaust heat recovery system 10 described above further includes an exhaust gas temperature acquisition device 71 and a water supply amount adjustment device 72. The exhaust gas temperature acquisition device (a temperature sensor in the illustrated example) 71 is configured to be able to acquire the temperature of the exhaust gas that has passed through the low-temperature side exhaust heat recovery unit 22 described above. The water supply amount adjustment device 72 is configured to be able to adjust the flow rate of the water supply flowing through the second water supply line 32 so that the temperature of the exhaust gas acquired by the exhaust gas temperature acquisition device 71 approaches a predetermined temperature (the first predetermined temperature). The first predetermined temperature is a temperature with a margin from the temperature at which low-temperature sulfuric acid corrosion occurs (a temperature higher than the temperature at which low-temperature sulfuric acid corrosion occurs by the margin).

[0049] In the illustrated embodiment, the water supply amount adjustment device 72 includes a water supply amount adjustment valve 72A provided in the water supply branch line 35. The water supply amount adjustment valve 72A is configured to be able to adjust the flow rate of the fluid led to the mixing chamber 70 through the water supply branch line 35. By adjusting the flow rate of the water supply flowing through the water supply branch line 35 with the water supply amount adjustment valve 72A, the flow rate of the second water supply sent to the low-temperature side exhaust heat recovery unit 22 through the second water supply line 32 can be adjusted. Note that the water supply amount adjustment valve 72A may be provided upstream of the mixing chamber 70 of the second water supply line 32, the relay line 34, and the second water supply introduction line 33. The water supply amount adjustment device 72 may further include a control device (not shown) that instructs the opening degree of the water supply amount adjustment valve 72A. Further, the water supply amount adjustment device 72 only needs to be configured to be able to adjust the flow rate of the water supply flowing through the water supply branch line 35, and is not limited to the water supply amount adjustment valve 72A. By reducing the opening degree of the water supply amount adjustment valve 72A provided in the water supply branch line 35, the flow rate of the water supply flowing through the water supply branch line 35 decreases, and the flow rate of the second water supply flowing through the second water supply line 32 increases. By increasing the opening degree of the water supply amount adjustment valve 72A provided in the water supply branch line 35, the flow rate of the water supply flowing through the water supply branch line 35 increases, and the flow rate of the second water supply flowing through the second water supply line 32 decreases.

[0050] In the illustrated embodiment, the exhaust gas temperature acquisition device 71 is configured to be able to measure the temperature of the exhaust gas line 13A (13) located downstream of the low-temperature side exhaust heat recovery section 22. When the temperature of the exhaust gas acquired by the exhaust gas temperature acquisition device 71 exceeds a predetermined temperature (first predetermined temperature), by reducing the opening degree of the water supply amount adjustment valve 72A provided in the water supply branch line 35, further heat energy can be recovered from the exhaust gas flowing through the exhaust heat recovery device 20. Also, when the temperature of the exhaust gas acquired by the exhaust gas temperature acquisition device 71 is lower than the predetermined temperature (first predetermined temperature), by increasing the opening degree of the water supply amount adjustment valve 72A provided in the water supply branch line 35, the recovery of heat energy from the exhaust gas flowing through the exhaust heat recovery device 20 is suppressed so as not to approach the temperature at which low-temperature sulfuric acid corrosion occurs.

[0051] According to the above configuration, since the water supply amount adjustment device 72 can adjust the flow rate of the second water supply sent to the low-temperature side exhaust heat recovery section 22, while suppressing the vaporization of the second water supply, the amount of heat energy recovered (transferred amount) from the exhaust gas to the second water supply in the low-temperature side exhaust heat recovery section 22 can be adjusted. By adjusting the flow rate of the water supply flowing through the water supply branch line 35 by the water supply amount adjustment device 72 so that the temperature of the exhaust gas acquired by the exhaust gas temperature acquisition device 71 approaches a predetermined temperature (first predetermined temperature), in the low-temperature side exhaust heat recovery section 22, heat energy can be recovered from the exhaust gas to the second water supply as much as possible while suppressing low-temperature sulfuric acid corrosion. Therefore, according to the above configuration, the exhaust heat recovery system 10 can efficiently recover heat from the exhaust gas.

[0052] (First low-temperature side heat exchanger, second low-temperature side heat exchanger) In some embodiments, as shown in FIG. 1, the above-described low-temperature side exhaust heat recovery section 22 includes the above-described first low-temperature side heat exchanger 23 and the above-described second low-temperature side heat exchanger 24. The above-described exhaust heat recovery system 10 further includes the above-described relay line 34 for guiding the second water supply that has passed through the second low-temperature side heat exchanger 24 to the first low-temperature side heat exchanger 23.

[0053] One side of the second water supply line 32 is connected to the second low-temperature side heat exchanger 24. One side of the relay line 34 is connected to the second low-temperature side heat exchanger 24, and the other side of the relay line 34 is connected to the first low-temperature side heat exchanger 23. One side of the second water supply introduction line 33 is connected to the first low-temperature side heat exchanger 23, and the other side of the second water supply introduction line 33 is connected to the evaporator 52. The second water supply is led to the second low-temperature side heat exchanger 24 through the second water supply line 32. The second water supply that has passed through the second low-temperature side heat exchanger 24 is led to the first low-temperature side heat exchanger 23 through the relay line 34. The second water supply that has passed through the first low-temperature side heat exchanger 23 is led to the evaporator 52 through the second water supply introduction line 33.

[0054] The exhaust gas introduced into the first low-temperature side heat exchanger 23 is at a lower temperature than the exhaust gas introduced into the high-temperature side exhaust heat recovery section 21, and is at a higher temperature than the exhaust gas introduced into the second low-temperature side heat exchanger 24 and the second water supply introduced into the first low-temperature side heat exchanger 23. Also, the exhaust gas introduced into the second low-temperature side heat exchanger 24 is at a higher temperature than the second water supply introduced into the second low-temperature side heat exchanger 24.

[0055] Through the heat exchange between the exhaust gas and the second water supply in each of the first low-temperature side heat exchanger 23 and the second low-temperature side heat exchanger 24, the exhaust gas is cooled and the second water supply is heated. Specifically, in the second low-temperature side heat exchanger 24, the second water supply led to the second low-temperature side heat exchanger 24 is heated by the exhaust gas that has passed through the first low-temperature side heat exchanger 23. In the first low-temperature side heat exchanger 23, the second water supply pre-heated in the second low-temperature side heat exchanger 24 is heated by the exhaust gas that has passed through the high-temperature side exhaust heat recovery section 21.

[0056] According to the above configuration, in the second low-temperature side heat exchanger 24, the exhaust gas that has had its thermal energy recovered by the first low-temperature side heat exchanger 23 and has become low in temperature is introduced. In the first low-temperature side heat exchanger 23, the second feed water heated by the second low-temperature side heat exchanger 24 is introduced through the relay line 34. Therefore, each of the exhaust gas and the second feed water introduced into the second low-temperature side heat exchanger 24 is at a lower temperature than each of the exhaust gas and the second feed water introduced into the first low-temperature side heat exchanger 23. The first low-temperature side heat exchanger 23 and the second low-temperature side heat exchanger 24 can transfer thermal energy from the exhaust gas to the second feed water step by step. Thereby, the exhaust heat recovery system 10 can efficiently recover heat from the exhaust gas.

[0057] In the illustrated embodiment, the exhaust heat recovery device 20 includes an exhaust gas economizer in which the high-temperature side exhaust heat recovery section 21 and the first low-temperature side heat exchanger 23 are integrally provided, and a second low-temperature side heat exchanger 24 provided separately from each of the high-temperature side exhaust heat recovery section 21 and the first low-temperature side heat exchanger 23. The second low-temperature side heat exchanger 24 is configured to be separable from the exhaust gas economizer. Since the temperature of the exhaust gas flowing inside the second low-temperature side heat exchanger 24 is lower than that of the exhaust gas economizer, corrosion (low-temperature sulfuric acid corrosion) is likely to occur on the flow path wall surface (heat transfer surface) thereof. According to the above configuration, when corrosion occurs on the flow path wall surface of the second low-temperature side heat exchanger 24, only the second low-temperature side heat exchanger 24 needs to be replaced, and the exhaust gas economizer does not need to be replaced. Therefore, according to the above configuration, the replacement cost in the exhaust heat recovery system 10 can be reduced.

[0058] In some embodiments, as shown in FIG. 1, the steam heat exchanger 40 described above is provided in the relay line 34. The exhaust heat recovery system 10 described above includes the first steam introduction line 60 described above for guiding the first steam to the steam heat exchanger 40 provided in the relay line 34.

[0059] The steam heat exchanger 40 performs heat exchange between the second feed water introduced into the steam heat exchanger 40 through the relay line 34 and the first steam introduced into the steam heat exchanger 40 through the first steam introduction line 60, and the second feed water is heated. The second feed water heated in the steam heat exchanger 40 is led to the first low-temperature side heat exchanger 23.

[0060] According to the above configuration, in the steam heat exchanger 40 provided in the relay line 34, the second feed water can be heated by the thermal energy of the vaporized first feed water. By heating the second feed water with the steam heat exchanger 40, the temperature difference between the second feed water led to the first low-temperature side heat exchanger 23 and the exhaust gas can be reduced, and it is possible to suppress the exhaust gas temperature from becoming too low due to the heat exchange between the exhaust gas and the second feed water in the first low-temperature side heat exchanger 23. Thereby, low-temperature sulfuric acid corrosion in the first low-temperature side heat exchanger 23 can be effectively suppressed.

[0061] In the embodiment shown in FIG. 1, the above-described exhaust heat recovery system 10 further includes an auxiliary steam heat exchanger 41 provided in the second feed water line 32. The auxiliary steam heat exchanger 41 is configured to perform heat exchange between the second feed water introduced into the auxiliary steam heat exchanger 41 through the second feed water line 32 and the high-temperature drain after heat exchange in the steam heat exchanger 40. Heat exchange is performed between the second feed water introduced into the auxiliary steam heat exchanger 41 and the high-temperature drain, and the second feed water before being led to the second low-temperature side heat exchanger 24 is heated. According to the above configuration, the auxiliary steam heat exchanger 41 can recover the thermal energy remaining in the first steam and suppress low-temperature sulfuric acid corrosion in the second low-temperature side heat exchanger 24. When sulfuric acid corrosion occurs at the set exhaust gas temperature or feed water temperature for some reason, by raising the temperature of the second feed water using the auxiliary steam heat exchanger 41, the temperature of the exhaust gas discharged from the second low-temperature side heat exchanger 24 can also be raised. Thereby, active suppression control of low-temperature sulfuric acid corrosion becomes possible.

[0062] In some embodiments, as shown in FIG. 1, the waste heat recovery system 10 described above further includes a steam supply line 62 for guiding the first steam to the steam supply destination 61. The steam supply destination 61 may include at least one of the air conditioning system 61A of the ship 1 or the chimney 61B. The unnecessary first steam in the ship 1 may be discharged through the chimney 61B. In the illustrated embodiment, the first steam introduction line 60 and the steam supply line 62 form a shared line 62A from the gas-liquid separator 17 to the branch portion P2. The first steam introduction line 60 and the steam supply line 62 branch at the branch portion P2.

[0063] In some embodiments, as shown in FIG. 1, the waste heat recovery system 10 described above further includes a second feed water temperature acquisition device 73 and a first steam flow rate adjustment device 74. The second feed water temperature acquisition device (temperature sensor in the illustrated example) 73 is configured to be able to acquire the temperature of the second feed water heated by the low-temperature side waste heat recovery unit 22 and the steam heat exchanger 40. The first steam flow rate adjustment device 74 is configured to adjust the flow rate of the first steam (the first feed water vaporized in the high-temperature side waste heat recovery unit 21) flowing through the first steam introduction line 60 so that the temperature of the second feed water acquired by the second feed water temperature acquisition device 73 is equal to or lower than a predetermined temperature (the second predetermined temperature, the second feed water set temperature).

[0064] The first steam flow rate adjustment device 74 includes a first steam flow rate adjustment valve 74A provided on the downstream side (the steam heat exchanger 40 side) of the branch portion P2 of the first steam introduction line 60. The first steam flow rate adjustment valve 74A is configured to be able to adjust the flow rate of the first steam (fluid) guided to the steam heat exchanger 40 through the first steam introduction line 60. Note that the first steam flow rate adjustment device 74 may further include a control device (not shown) that instructs the opening degree of the first steam flow rate adjustment valve 74A. Further, the first steam flow rate adjustment device 74 only needs to be configured to be able to adjust the flow rate of the first steam guided to the steam heat exchanger 40, and is not limited to the first steam flow rate adjustment valve 74A.

[0065] In the illustrated embodiment, the second feed water temperature acquisition device 73 is configured to be able to measure the temperature on the upstream side (the side of the second low-temperature side heat exchanger 24) of the mixing chamber 70 in the second feed water introduction line 33. When the temperature of the second feed water acquired by the second feed water temperature acquisition device 73 exceeds a predetermined temperature (the second predetermined temperature, the second feed water set temperature), there is a possibility that the second feed water will vaporize.

[0066] According to the above configuration, by adjusting the flow rate (steam amount) of the first feed water sent to the steam heat exchanger 40 through the first steam introduction line 60 by the first steam flow rate adjustment device 74, the heating amount of the second feed water in the steam heat exchanger 40 can be adjusted. By adjusting the flow rate of the first feed water flowing through the first steam introduction line 60 so that the temperature of the second feed water acquired by the second feed water temperature acquisition device 73 becomes equal to or lower than a predetermined temperature (the second predetermined temperature, the second feed water set temperature) by the first steam flow rate adjustment device 74, the vaporization of the second feed water led to the evaporator 52 can be suppressed.

[0067] The fuel supplied to the main engine 11A (internal combustion engine 11) is liquefied natural gas (LNG), ammonia, hydrogen, methanol, etc. that do not contain sulfur in their components. However, there is a possibility that components such as the pilot fuel and lubricating oil of the main engine 11A contain sulfur. When the temperature of the exhaust gas flowing through the exhaust heat recovery device 20 becomes equal to or lower than the acid dew point, which is the temperature at which sulfuric acid in the exhaust gas begins to condense, the exhaust heat recovery device 20 may be corroded (low-temperature sulfuric acid corrosion) by the condensed sulfuric acid.

[0068] The exhaust heat recovery system 10 described above is configured such that the exhaust gas passing through the low-temperature side exhaust heat recovery unit 22 (particularly the second low-temperature side heat exchanger 24) described above becomes equal to or higher than the lower limit temperature at which preset low-temperature sulfuric acid corrosion does not occur. However, in actual operation, in order to keep the exhaust gas at the above lower limit temperature or higher, it may be necessary to raise the temperature of the feed water.

[0069] FIG. 2 is a schematic configuration diagram schematically showing the configuration of a ship equipped with an exhaust heat recovery system according to an embodiment of the present disclosure. In some embodiments, as shown in FIG. 2, the above-described exhaust heat recovery system 10 further includes a second feed water preheater 42 provided in the above-described second feed water line 32, and a second steam introduction line 63 for guiding the first steam (the first feed water vaporized in the high-temperature side exhaust heat recovery section 21) to the second feed water preheater 42. The second feed water preheater 42 is configured to transfer the thermal energy of the first steam (the first feed water vaporized in the high-temperature side exhaust heat recovery section 21) to the second feed water and heat the second feed water.

[0070] In the illustrated embodiment, the second steam introduction line 63 and the first steam introduction line 60 form a shared line 63A from the gas-liquid separator 17 to the branch portion P2. The second steam introduction line 63 and the steam supply line 62 form a shared line 63B from the gas-liquid separator 17 to the branch portion P3 located on the downstream side in the flow direction of the first steam from the branch portion P2. The second steam introduction line 63 and the steam supply line 62 branch at the branch portion P3.

[0071] In the embodiment shown in FIG. 2, the second feed water preheater 42 is configured to perform heat exchange between the second feed water guided to the second feed water preheater 42 through the second feed water line 32 and the first steam guided to the second feed water preheater 42 through the second steam introduction line 63. Heat exchange is performed between the second feed water and the first steam guided to the second feed water preheater 42, and the second feed water is heated. The second feed water heated in the second feed water preheater 42 is guided to the second low-temperature side heat exchanger 24.

[0072] According to the above configuration, the first steam can be introduced into the second feedwater preheater 42 through the second steam introduction line 63. In the second feedwater preheater 42, the second feedwater flowing through the second feedwater line 32 can be heated by the first steam. By heating the second feedwater guided to the second low-temperature side heat exchanger 24, it is possible to suppress the exhaust gas temperature from becoming too low due to the heat exchange between the exhaust gas and the second feedwater in the second low-temperature side heat exchanger 24. Therefore, low-temperature sulfuric acid corrosion in the second low-temperature side heat exchanger 24 can be effectively suppressed. When sulfuric acid corrosion occurs at the exhaust gas temperature and feedwater temperature set for some reason, by using the second feedwater preheater 42 to raise the temperature of the second feedwater, the temperature of the exhaust gas discharged from the second low-temperature side heat exchanger 24 can also be raised. Thereby, active suppression control of low-temperature sulfuric acid corrosion becomes possible.

[0073] In some embodiments, as shown in FIG. 2, the waste heat recovery system 10 described above includes the exhaust gas temperature acquisition device 71 described above and a second steam flow rate adjustment device 75. The second steam flow rate adjustment device 75 is configured to be able to adjust the flow rate of the first steam flowing through the second steam introduction line 63 so that the temperature of the exhaust gas acquired by the exhaust gas temperature acquisition device 71 is equal to or higher than a predetermined temperature (the third predetermined temperature). The third predetermined temperature is lower than the first predetermined temperature. The third predetermined temperature may be the same as the lower limit temperature at which the above-mentioned preset low-temperature sulfuric acid corrosion does not occur, or may be a temperature equal to or higher than the lower limit temperature with a margin provided for the lower limit temperature.

[0074] The second steam flow rate adjustment device 75 includes a second steam flow rate adjustment valve 75A provided on the downstream side (the side of the second feedwater preheater 42) of the branch portion P3 of the second steam introduction line 63. The second steam flow rate adjustment valve 75A is configured to be able to adjust the flow rate of the fluid introduced into the second feedwater preheater 42 through the second steam introduction line 63. The second steam flow rate adjustment device 75 may further include a control device (not shown) that instructs the opening degree of the second steam flow rate adjustment valve 75A. Further, the second steam flow rate adjustment device 75 only needs to be configured to be able to adjust the flow rate of the first steam introduced into the second feedwater preheater 42, and is not limited to the second steam flow rate adjustment valve 75A. When the temperature of the exhaust gas acquired by the exhaust gas temperature acquisition device 71 is less than the third predetermined temperature, low-temperature sulfuric acid corrosion may occur in the second low-temperature side heat exchanger 24.

[0075] According to the above configuration, by adjusting the flow rate of the first steam sent to the second feedwater preheater 42 through the second steam introduction line 63 by the second steam flow rate adjustment device 75, the heating amount of the second feedwater in the second feedwater preheater 42 can be adjusted. By adjusting the flow rate of the first steam flowing through the second steam introduction line 63 so that the temperature of the exhaust gas acquired by the exhaust gas temperature acquisition device 71 becomes equal to or higher than the third predetermined temperature by the second steam flow rate adjustment device 75, while suppressing low-temperature sulfuric acid corrosion in the second low-temperature side heat exchanger 24, the second feedwater can be heated as much as possible in the second low-temperature side heat exchanger 24.

[0076] FIG. 3 is an explanatory diagram for explaining the feedwater preheater in an embodiment of the present disclosure. In some embodiments, as shown in FIGS. 1 to 3, the exhaust heat recovery system 10 described above further includes a feedwater preheater 81 configured to heat the feedwater supplied to the feedwater line 30. In the illustrated embodiment, one side of the feedwater line 30 (the other side of each of the first feedwater line 31 and the second feedwater line 32) is connected to the feedwater preheater 81.

[0077] As shown in FIGS. 1 to 3, the exhaust heat recovery system 10 includes a feed water circulation line 80 for guiding feed water from the evaporator 52 to the feed water preheater 81, a feed water storage device (storage tank) 83 provided in the feed water circulation line 80, a feed water flow rate adjustment valve 84 provided upstream (on the evaporator 52 side) of the feed water storage device 83 in the feed water circulation line 80, and a feed water circulation pump 85 provided downstream (on the feed water preheater 81 side) of the feed water storage device 83 in the feed water circulation line 80.

[0078] By opening the feed water flow rate adjustment valve 84, feed water is guided from the evaporator 52 to the feed water storage device 83 through the feed water circulation line 80. The feed water storage device 83 is configured to be able to store feed water. By driving the feed water circulation pump 85, feed water is drawn out from the feed water storage device 83 into the feed water circulation line 80, and the drawn-out feed water is sent to the feed water preheater 81.

[0079] In the embodiments shown in FIGS. 1 and 2, the feed water preheater 81 (81A) is configured to transfer the thermal energy recovered from the cooling water (engine jacket water) that has cooled the above-described internal combustion engine 11 to the feed water supplied to the feed water line 30, thereby heating the feed water.

[0080] In the embodiments shown in FIGS. 1 and 2, the exhaust heat recovery system 10 further includes a storage unit 86A for storing engine jacket water, and a feed water line 87A for the preheater for guiding the engine jacket water from the storage unit 86A to the feed water preheater 81. The feed water preheater 81 (81A) is configured to perform heat exchange between the feed water supplied to the feed water line 30 (in the illustrated example, the feed water guided to the feed water preheater 81A through the feed water circulation line 80) and the engine jacket water guided to the feed water preheater 81A through the feed water line 87A for the preheater. The engine jacket water guided to the feed water preheater 81A has a higher temperature than the feed water guided to the feed water preheater 81A by recovering thermal energy from the internal combustion engine 11. Heat exchange is performed between the feed water and the engine jacket water guided to the feed water preheater 81A, and the feed water is heated. The feed water heated in the feed water preheater 81A is supplied to the feed water line 30.

[0081] In the embodiment shown in FIG. 3, the feed water preheater 81(81B) is configured to transfer the thermal energy recovered from the compressed gas (e.g., compressed air) by the cooling water (compressed gas cooling water) that has cooled the compressed gas compressed by the compressor 15 described above to the feed water supplied to the feed water line 30, thereby heating the feed water.

[0082] In the embodiment shown in FIG. 3, the exhaust heat recovery system 10 further includes a cooler 86B that cools the compressed gas, and a feed water line 87B for the preheater that guides the compressed gas cooling water from the cooler 86B to the feed water preheater 81. The feed water preheater 81(81B) is configured to perform heat exchange between the feed water supplied to the feed water line 30 (the feed water guided to the feed water preheater 81B through the feed water circulation line 80 in the illustrated example) and the compressed gas cooling water guided to the feed water preheater 81B through the feed water line 87B for the preheater. The compressed gas cooling water guided to the feed water preheater 81B has a higher temperature than the feed water guided to the feed water preheater 81B by recovering the thermal energy from the compressed gas. Heat exchange is performed between the feed water guided to the feed water preheater 81B and the compressed gas cooling water, and the feed water is heated. The feed water heated in the feed water preheater 81B is supplied to the feed water line 30. Note that the feed water preheater 81 may include a feed water preheater 81A and a feed water preheater 81B. That is, the feed water preheater 81 may be configured to perform heat exchange between each of the engine jacket water and the compressed gas cooling water and the feed water supplied to the feed water line 30. In this case, in the feed water preheater 81, each of the engine jacket water and the compressed gas cooling water can be used as a heating source to heat the feed water supplied to the feed water line 30.

[0083] According to the above configuration, the feed water preheater 81 preheats the feed water supplied to the feed water line 30 in advance, thereby reducing the amount of thermal energy required to raise the temperature of the feed water (first feed water or second feed water) guided by the feed water line 30 to a desired temperature. By reducing the amount of thermal energy required to raise the temperature of the feed water to the desired temperature in this way, the thermal energy of the exhaust gas discharged from the internal combustion engine 11 can be utilized for other purposes, so that the effective utilization of the thermal energy of the exhaust gas can be achieved.

[0084] Each of the plurality of flow rate adjustment valves (the first water supply side flow rate adjustment valve 37, the water supply amount adjustment valve 72A, the first steam flow rate adjustment valve 74A, and the second steam flow rate adjustment valve 75A) described above may be an on-off valve whose opening degree can be adjusted between fully closed and fully open, or may be an opening degree adjustment valve whose opening degree can be adjusted between fully closed, fully open, and at least one intermediate opening degree therebetween.

[0085] The present disclosure is not limited to the above-described embodiments, and includes forms obtained by modifying the above-described embodiments and forms obtained by appropriately combining these forms.

[0086] The content described in some of the above-described embodiments is understood as follows, for example.

[0087] 1) The exhaust heat recovery system (10) according to at least one embodiment of the present disclosure is an exhaust heat recovery system (10) configured to recover the thermal energy of the exhaust gas discharged from the internal combustion engine (11), an exhaust heat recovery device (20) including a high-temperature side exhaust heat recovery unit (21) configured to recover the thermal energy of the exhaust gas discharged from the internal combustion engine (11), and a low-temperature side exhaust heat recovery unit (22) configured to recover the thermal energy of the exhaust gas that has passed through the high-temperature side exhaust heat recovery unit (21), a water supply line (30) for guiding water to the exhaust heat recovery device (20), the water supply line (30) including a first water supply line (31) for guiding the first water supply to the high-temperature side exhaust heat recovery unit (21), and a second water supply line (32) branched from the first water supply line (31) for guiding the second water supply to the low-temperature side exhaust heat recovery unit (22), a steam heat exchanger (40) configured to transfer the thermal energy of the first water supply vaporized in the high-temperature side exhaust heat recovery unit (31) to the second water supply to heat the second water supply, A circulation cycle (50) that circulates a low-boiling heat medium having a boiling point lower than that of water, comprising an evaporator (52) configured to vaporize the low-boiling heat medium by the heat energy recovered from the second feed water heated by each of the low-temperature side exhaust heat recovery section (22) and the steam heat exchanger (40), and a turbine (53) configured to be driven by the low-boiling heat medium vaporized in the evaporator (52).

[0088] According to the configuration of 1) above, the exhaust heat recovery system (10) can heat the low-boiling heat medium using the second feed water heated by each of the low-temperature side exhaust heat recovery section (22) and the steam heat exchanger (40) as a heat source in the evaporator (52). Even when the exhaust heat from the internal combustion engine (11) is small, the exhaust heat recovery system (10) can utilize the heat energy recovered from the exhaust gas by the exhaust heat recovery device (20) as a heat medium in the evaporator (52) and convert it into power in the turbine (53).

[0089] 2) In some embodiments, it is the exhaust heat recovery system (10) described in 1) above, a second feed water introduction line (33) for guiding the second feed water heated by each of the low-temperature side exhaust heat recovery section (22) and the steam heat exchanger (40) to the evaporator (52), a mixing chamber (70) provided in the second feed water introduction line (33), and a feed water branch line (35) branched from the feed water line (30) for guiding the feed water to the mixing chamber (70).

[0090] According to the configuration of 2) above, by branching the water supply line (30) into three: the first water supply line (31), the second water supply line (32), and the water supply branch line (35), compared with the conventional structure that introduces all the water supply into the low-temperature side exhaust heat recovery section (22), since the water supply flow rate to be controlled is smaller, the responsiveness of the water supply flow rate control is improved. In the above conventional structure, for example, when trying to reduce the flow rate of the water supply to suppress sulfuric acid corrosion, it is necessary to control the total amount of the water supply by the water supply side pump (36). In contrast, according to the configuration of 2) above, by increasing the flow rate of the water supply led to the mixing chamber (70) through the water supply branch line (35), it is possible to adjust so as to reduce the flow rate of the second water supply led to the low-temperature side exhaust heat recovery section (22). By adjusting the flow rate of the second water supply led to the low-temperature side exhaust heat recovery section (22), since the amount of heat energy recovered (transferred amount) from the exhaust gas to the second water supply in the low-temperature side exhaust heat recovery section (22) can be adjusted, the temperature of the exhaust gas discharged from the low-temperature side exhaust heat recovery section (22) can be adjusted. By improving the responsiveness of the water supply flow rate control, the responsiveness of the exhaust gas temperature control is also improved.

[0091] Also, according to the configuration of 2) above, by branching the water supply line (30) into three: the first water supply line (31), the second water supply line (32), and the water supply branch line (35), the flow rate of the second water supply led to the low-temperature side exhaust heat recovery section (22) can be reduced. Since the resistance also decreases by suppressing the flow rate of the second water supply, the low-temperature side exhaust heat recovery section (22) and the steam heat exchanger (40) to which the second water supply is led can be downsized. Also, according to the configuration of 2) above, in the mixing chamber (70), by mixing the second water supply heated in the low-temperature side exhaust heat recovery section (22) and the steam heat exchanger (40) respectively, and the water supply led by the water supply branch line (35), it is possible to make the heated second water supply reach an appropriate uniform temperature to be introduced into the circulation cycle (50).

[0092] 3) In some embodiments, it is the exhaust heat recovery system (10) described in 2) above, an exhaust gas temperature acquisition device (71) configured to be able to acquire the temperature of the exhaust gas that has passed through the low-temperature side exhaust heat recovery section (22); A water supply amount adjusting device (72) is further provided, which is configured to be able to adjust the flow rate of the second water supply flowing through the second water supply line (32) so that the temperature of the exhaust gas acquired by the exhaust gas temperature acquisition device (71) approaches a first predetermined temperature.

[0093] According to the configuration of 3) above, since the water supply amount adjusting device (72) can adjust the flow rate of the second water supply sent to the low-temperature side exhaust heat recovery unit (22), while suppressing the vaporization of the second water supply, the amount of heat energy (transfer amount) recovered from the exhaust gas to the second water supply in the low-temperature side exhaust heat recovery unit (22) can be adjusted. By adjusting the flow rate of the water supply flowing through the water supply branch line (35) by the water supply amount adjusting device (72) so that the temperature of the exhaust gas acquired by the exhaust gas temperature acquisition device (71) approaches the first predetermined temperature, in the low-temperature side exhaust heat recovery unit (22), heat energy can be recovered from the exhaust gas to the second water supply as much as possible while suppressing low-temperature sulfuric acid corrosion. Therefore, according to the configuration of 3) above, the exhaust heat recovery system (10) can efficiently recover heat from the exhaust gas.

[0094] 4) In some embodiments, it is the exhaust heat recovery system (10) described in any one of 1) to 3) above, wherein the low-temperature side exhaust heat recovery unit (22) includes a first low-temperature side heat exchanger (23) configured to perform heat exchange between the exhaust gas and the second water supply, and a second low-temperature side heat exchanger (24) configured to perform heat exchange between the exhaust gas that has passed through the first low-temperature side heat exchanger (23) and the second water supply. The exhaust heat recovery system (10) further includes a relay line (34) for guiding the second water supply that has passed through the second low-temperature side heat exchanger (24) to the first low-temperature side heat exchanger (23).

[0095] According to the configuration of 4) above, in the second low-temperature side heat exchanger (24), the exhaust gas that has had its thermal energy recovered by the first low-temperature side heat exchanger (23) and has become low in temperature is introduced. In the first low-temperature side heat exchanger (23), the second feed water heated by the second low-temperature side heat exchanger (24) is introduced through the relay line (34). For this reason, each of the exhaust gas and the second feed water introduced into the second low-temperature side heat exchanger (24) is at a lower temperature than each of the exhaust gas and the second feed water introduced into the first low-temperature side heat exchanger (23). The first low-temperature side heat exchanger (23) and the second low-temperature side heat exchanger (24) can transfer thermal energy from the exhaust gas to the second feed water step by step. Thereby, the exhaust heat recovery system (10) can efficiently recover heat from the exhaust gas. Also, the second low-temperature side heat exchanger (24) can be configured to be separable from the exhaust gas economizer (the high-temperature side exhaust heat recovery section 21 and the first low-temperature side heat exchanger 23). Thereby, when corrosion occurs in the second low-temperature side heat exchanger (24), only the second low-temperature side heat exchanger (24) needs to be replaced, and the exhaust gas economizer does not need to be replaced. For this reason, according to the above configuration, the replacement cost in the exhaust heat recovery system (10) can be reduced.

[0096] 5) In some embodiments, there is provided the exhaust heat recovery system (10) described in 4) above, wherein the steam heat exchanger (40) is provided in the relay line (34), and the exhaust heat recovery system (10) further includes a first steam introduction line (60) for guiding the first feed water (first steam) vaporized in the high-temperature side exhaust heat recovery section (21) to the steam heat exchanger (40).

[0097] According to the configuration of 5) above, in the steam heat exchanger (40) provided in the relay line (34), the second feed water can be heated by the thermal energy of the vaporized first feed water. By heating the second feed water with the steam heat exchanger (40), the temperature difference between the second feed water and the exhaust gas introduced into the first low-temperature side heat exchanger (23) can be reduced, and it is possible to suppress the exhaust gas temperature from becoming too low due to the heat exchange between the exhaust gas and the second feed water in the first low-temperature side heat exchanger (23). Thereby, low-temperature sulfuric acid corrosion in the first low-temperature side heat exchanger (23) can be effectively suppressed.

[0098] 6) In some embodiments, there is the waste heat recovery system (10) described in 5) above, a second feed water temperature acquisition device (73) configured to be able to acquire the temperature of the second feed water heated by the low-temperature side waste heat recovery unit (22) and the steam heat exchanger (40); a first steam flow rate adjustment device (74) configured to be able to adjust the flow rate of the first feed water (first steam) flowing through the first steam introduction line (60) so that the temperature of the second feed water acquired by the second feed water temperature acquisition device (73) is equal to or lower than a second predetermined temperature.

[0099] According to the configuration of 6) above, by adjusting the flow rate (steam amount) of the first steam (first feed water) sent to the steam heat exchanger (40) through the first steam introduction line (60) by the first steam flow rate adjustment device (74), the heating amount of the second feed water in the first steam heat exchanger (41) can be adjusted. By adjusting the flow rate of the first steam (first feed water) flowing through the first steam introduction line (60) by the first steam flow rate adjustment device (74) so that the temperature of the second feed water acquired by the second feed water temperature acquisition device (73) is equal to or lower than a second predetermined temperature, vaporization of the second feed water led to the evaporator (52) can be suppressed.

[0100] 7) In some embodiments, there is the waste heat recovery system (10) described in 5) or 6) above, A second feed water preheater (42) provided in the second feed water line (32), configured to transfer the thermal energy of the first feed water (first steam) vaporized in the high-temperature side exhaust heat recovery section (21) to the second feed water and heat the second feed water. It further includes a second steam introduction line (63) for guiding the first feed water (first steam) vaporized in the high-temperature side exhaust heat recovery section (21) to the second feed water preheater (42).

[0101] According to the configuration of 7) above, the first steam (the first feed water vaporized in the high-temperature side exhaust heat recovery section 21) can be guided to the second feed water preheater (42) by the second steam introduction line (63). In the second feed water preheater (42), the first steam can heat the second feed water flowing through the second feed water line (32). By heating the second feed water guided to the second low-temperature side heat exchanger (24), it is possible to suppress the exhaust gas temperature from becoming too low due to the heat exchange between the exhaust gas and the second feed water in the second low-temperature side heat exchanger (24). Therefore, low-temperature sulfuric acid corrosion in the second low-temperature side heat exchanger (24) can be effectively suppressed. When sulfuric acid corrosion occurs at the set exhaust gas temperature or feed water temperature for some reason, by using the second feed water preheater (42) to raise the temperature of the second feed water, the temperature of the exhaust gas discharged from the second low-temperature side heat exchanger (24) can also be raised. This enables active suppression control of low-temperature sulfuric acid corrosion.

[0102] 8) In some embodiments, the exhaust heat recovery system (10) described in 7) above, An exhaust gas temperature acquisition device (71) configured to be able to acquire the temperature of the exhaust gas that has passed through the low-temperature side exhaust heat recovery section (22), A second steam flow rate adjustment device (75) configured to be able to adjust the flow rate of the first feed water (first steam) flowing through the second steam introduction line (63) so that the temperature of the exhaust gas acquired by the exhaust gas temperature acquisition device (71) is equal to or higher than a third predetermined temperature.

[0103] According to the configuration of 8) above, by adjusting the flow rate of the first steam sent to the second feed water preheater (42) through the second steam introduction line (63) by the second steam flow rate adjusting device (75), the heating amount of the second feed water in the second feed water preheater (42) can be adjusted. By adjusting the flow rate of the first feed water flowing through the second steam introduction line (63) by the second steam flow rate adjusting device (75) so that the temperature of the exhaust gas acquired by the exhaust gas temperature acquisition device (71) becomes equal to or higher than a third predetermined temperature, while suppressing low-temperature sulfuric acid corrosion in the second low-temperature side heat exchanger (24), the second feed water can be heated as much as possible in the second low-temperature side heat exchanger (24).

[0104] 9) In some embodiments, there is a waste heat recovery system (10) according to any one of 1) to 8) above, further comprising a feed water preheater (81) configured to transfer the thermal energy recovered from the cooling water that has cooled the internal combustion engine (11) to the feed water supplied to the feed water line (30) and heat the feed water.

[0105] According to the configuration of 9) above, by preliminarily raising the temperature of the feed water supplied to the feed water line (30) by the feed water preheater (81), the amount of thermal energy required to raise the temperature of the feed water (the first feed water or the second feed water) guided by the feed water line (30) to a desired temperature can be reduced. By reducing the amount of thermal energy required to raise the temperature of the feed water to the desired temperature in this way, the thermal energy of the exhaust gas discharged from the internal combustion engine (11) can be utilized for other purposes, so that the effective utilization of the thermal energy of the exhaust gas can be achieved.

Explanation of Reference Numerals

[0106] 1 Ship 10 Waste heat recovery system 11 Internal combustion engine 11A Main engine 13, 13A Exhaust gas line 14 Exhaust gas turbine 15 Compressor 16 Supercharger 17 Gas-liquid separator 18 First water supply line 19 First water supply side pump 20 Exhaust heat recovery device 21 High temperature side exhaust heat recovery section 22 Low temperature side exhaust heat recovery section 23 First low temperature side heat exchanger 24 Second low temperature side heat exchanger 30 Water supply line 31 First water supply line 32 Second water supply line 33 Second water supply introduction line 34 Relay line 35 Water supply branch line 36 Water supply side pump 37 First water supply side flow control valve 40 Steam heat exchanger 41 Auxiliary steam heat exchanger 42 Second water supply preheater 50 Circulation cycle 51, 51A, 51B Circulation flow path 52 Evaporator 53 Turbine 54 Condenser 55 Circulation pump 56 Generator 60 First steam introduction line 61 Steam supply destination 61A Air conditioning system 61B Chimney 62 Steam supply line 62A, 63A, 63B Shared line 63 Second steam introduction line 70 Mixing chamber 71 Exhaust gas temperature acquisition device 72 Water supply amount adjustment device 73 Second water supply temperature acquisition device 74 First steam flow control device 75 Second steam flow control device 80 Water supply circulation line 81, 81A, 81B Water supply preheater 83 Water supply storage device 84 Water supply flow control valve 85 Water supply circulation pump 86A Reservoir 86B Cooler 87A, 87B Feed water lines for preheater P1, P2, P3 Branching parts

Claims

1. An exhaust heat recovery system configured to recover the thermal energy of the exhaust gas discharged from an internal combustion engine, comprising: An exhaust heat recovery device including a high-temperature side exhaust heat recovery unit configured to recover the thermal energy of the exhaust gas discharged from the internal combustion engine, and a low-temperature side exhaust heat recovery unit configured to recover the thermal energy of the exhaust gas that has passed through the high-temperature side exhaust heat recovery unit; A water supply line for guiding water to the exhaust heat recovery device, including a first water supply line for guiding the first water supply, which is the water supply, to the high-temperature side exhaust heat recovery unit, and a second water supply line branched from the first water supply line for guiding the second water supply, which is the water supply, to the low-temperature side exhaust heat recovery unit; A steam heat exchanger configured to transfer the thermal energy of the first water supply vaporized in the high-temperature side exhaust heat recovery unit to the second water supply and heat the second water supply; A circulation cycle for circulating a low-boiling heat medium having a boiling point lower than that of water, including at least an evaporator configured to vaporize the low-boiling heat medium by the thermal energy recovered from the second water supply heated by each of the low-temperature side exhaust heat recovery unit and the steam heat exchanger, and a turbine configured to be driven by the low-boiling heat medium vaporized in the evaporator; An exhaust heat recovery system.

2. A second water supply introduction line for guiding the second water supply heated by each of the low-temperature side exhaust heat recovery unit and the steam heat exchanger to the evaporator; A mixing chamber provided in the second water supply introduction line; Further comprising a water supply branch line branched from the water supply line for guiding the water supply to the mixing chamber; The exhaust heat recovery system according to Claim 1.

3. An exhaust gas temperature acquisition device configured to be able to acquire the temperature of the exhaust gas that has passed through the low-temperature side exhaust heat recovery unit; Further comprising a water supply amount adjustment device configured to be able to adjust the flow rate of the second water supply flowing through the second water supply line so that the temperature of the exhaust gas acquired by the exhaust gas temperature acquisition device approaches a first predetermined temperature; The exhaust heat recovery system according to Claim 2.

4. The low-temperature side exhaust heat recovery unit includes: A first low-temperature side heat exchanger configured to perform heat exchange between the exhaust gas and the second water supply; A second low-temperature side heat exchanger configured to perform heat exchange between the exhaust gas that has passed through the first low-temperature side heat exchanger and the second water supply; The exhaust heat recovery system includes: It further includes a relay line for guiding the second feed water that has passed through the second low-temperature side heat exchanger to the first low-temperature side heat exchanger. The exhaust heat recovery system according to any one of claims 1 to 3.

5. The steam heat exchanger is provided in the relay line. The exhaust heat recovery system further includes a first steam introduction line for guiding the first feed water vaporized in the high-temperature side exhaust heat recovery section to the steam heat exchanger. The exhaust heat recovery system according to claim 4.

6. A second feed water temperature acquisition device configured to be able to acquire the temperature of the second feed water heated by the low-temperature side exhaust heat recovery section and the steam heat exchanger; A first steam flow rate adjustment device configured to be able to adjust the flow rate of the first feed water flowing through the first steam introduction line so that the temperature of the second feed water acquired by the second feed water temperature acquisition device is equal to or lower than a second predetermined temperature. The exhaust heat recovery system according to claim 5.

7. A second feed water preheater provided in the second feed water line, configured to transfer the thermal energy of the first feed water vaporized in the high-temperature side exhaust heat recovery section to the second feed water and heat the second feed water. It further includes a second steam introduction line for guiding the first feed water vaporized in the high-temperature side exhaust heat recovery section to the second feed water preheater. The exhaust heat recovery system according to claim 5 or 6.

8. An exhaust gas temperature acquisition device configured to be able to acquire the temperature of the exhaust gas that has passed through the low-temperature side exhaust heat recovery section; A second steam flow rate adjustment device configured to be able to adjust the flow rate of the first feed water flowing through the second steam introduction line so that the temperature of the exhaust gas acquired by the exhaust gas temperature acquisition device is equal to or higher than a third predetermined temperature. The exhaust heat recovery system according to claim 7.

9. It further includes a feed water preheater configured to transfer the thermal energy recovered from the cooling water that has cooled the internal combustion engine to the feed water supplied to the feed water line and heat the feed water. The exhaust heat recovery system according to claim 1.

Images