Exhaust gas waste heat recovery system for ship

Abstract

To provide a waste heat recovery system of exhaust gas for a ship for recovering energy usable in the ship from waste heat of exhaust gas exhausted from an engine.SOLUTION: A gas-liquid separator 200 configured to separate the working fluid heated by the vaporizer 100 into gas and liquid, a condensing heat-exchanger 400 configured to cool and condense the working fluid cooled by an expansion turbine 300 configured to generate shaft power by expanding the separated gaseous working fluid, a feed pump 600 configured to pressurize and feed the condensed working fluid to the vaporizer, and a first coolant feed line CL1 configured to feed a coolant for cooling the working fluid to the condensing heat-exchanger 400, liquefied gas of a low flash point is supplied to an engine as fuel, and three flows of working fluid cooled by expansion by an expansion turbine 300, working fluid pressurized by a supply pump 600, and cooling water are heat-exchanged.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a waste heat recovery system for exhaust gas for a ship, and more particularly to a waste heat recovery system for exhaust gas for a ship, which uses exhaust gas emitted from an engine that uses a low-flashpoint liquefied gas as fuel as a heat source to change the phase of a working fluid circulating in a closed-loop heat medium circulation line and generate shaft power. [Background technology]

[0002] Conventionally, ship propulsion engines are equipped with fuel supply systems that use relatively inexpensive heavy oil such as bunker C oil. When fuel is burned, such fuel supply systems that use heavy oil emit large amounts of exhaust gases containing greenhouse gases such as carbon dioxide, sulfur oxides, nitrogen oxides, and other substances whose emissions are regulated by the International Maritime Organization (IMO).

[0003] As global warming becomes more serious, efforts to reduce greenhouse gas emissions are underway worldwide. The Kyoto Protocol, adopted in 1997 and requiring developed countries to reduce their greenhouse gas emissions, expires in 2020. The Paris Climate Change Accord, adopted at the 21st Conference of the Parties to the United Nations Framework Convention on Climate Change (UNFCCC) held in Paris, France in December 2015, came into effect in November 2016. The 195 signatory countries to the Paris Climate Change Accord are implementing various initiatives to reduce greenhouse gas emissions. Coupled with these strengthening international environmental regulations, countries are increasingly concerned about greenhouse gas and air pollutant emissions, leading to active development of environmentally friendly fuel technologies for ships.

[0004] Liquefied gas is known as an environmentally friendly fuel because it emits fewer air pollutants than heavy fuel oil or marine diesel oil (MDO) due to the ability to remove or reduce air pollutants during the liquefaction process. Liquefied natural gas (LNG), a representative liquefied gas, is a colorless, transparent liquid obtained by liquefying natural gas, primarily composed of methane, at approximately -163°C. LNG occupies approximately 1 / 600th the volume of natural gas in its gaseous state, making it superior in terms of storage and transportation efficiency. For these reasons, liquefied gas has been actively developed and used as a marine fuel. Another representative liquefied gas, LPG (Liquefied Petroleum Gas), is liquefied petroleum gas (LPG), primarily composed of low-boiling hydrocarbons such as propane and butane found in crude oil. It is easier to store than LNG, which requires cryogenic liquefaction. Furthermore, LPG's specific energy and energy density are comparable to those of HFO (heavy fuel oil C), and it is superior to HFO in that it can reduce emissions of SOx, NOx, CO2, PM, etc. For these reasons, LPG is being actively developed and used as a marine fuel.

[0005] In recent years, research and development into using ammonia as a marine fuel has been actively conducted in order to achieve complete decarbonization. Ammonia (NH3) is a substance in which three hydrogen atoms are bonded to one nitrogen atom. Due to the strong hydrogen bonds formed between molecules, it is easily liquefied, with a boiling point of -33.34°C and a melting point of -77.73°C under standard pressure. In particular, ammonia is easy to store and transport, and can be easily mass-produced using the Haber-Bosch process, making it more economical than other carbon-neutral fuels (see Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Korean Patent Publication No. 10-2021-0115364 Summary of the Invention [Problem to be solved by the invention]

[0007] To supply fuel to an engine, liquefied gases such as fuel oil and LNG must be heated according to the engine's fuel supply requirements. Ships using HFO as fuel recover waste heat from the engine's exhaust gas to generate steam, which is then used to heat fuel oil and supply the heated fuel oil to the engine. Similarly, ships using LNG as fuel recover waste heat from the engine's exhaust gas to generate steam, which is then used to vaporize LNG, and the vaporized natural gas is then supplied to the engine. In this way, recovering waste heat from the exhaust gas and using it to heat fuel can improve the ship's thermal efficiency. However, fuel oil contains sulfur, and during exhaust heat recovery, sulfur dioxide (SO2) contained in the exhaust gas condenses on metal surfaces as sulfuric acid (H2SO4), potentially causing sulfuric acid dew point corrosion (SDC). For this reason, in systems where a heat exchanger is installed that utilizes the waste heat from exhaust gas, corrosion is likely to occur on the metal surface if the temperature of the device's metal surface falls below the dew point of sulfuric acid. To avoid this, waste heat is recovered only from exhaust gas with a temperature of 150°C or higher.

[0008] Among low flashpoint fuels, LPG and ammonia have relatively high boiling points, so they require very little heat to heat up to the supply temperature required by the engine when supplied, and there is almost no risk of icing of the fuel supply heater. For this reason, LPG and ammonia can be heated using engine coolant or the like without using waste heat from exhaust gas.

[0009] Furthermore, because these fuels do not contain sulfur components, low-temperature corrosion is unlikely to occur even when waste heat is recovered from exhaust gases at temperatures below 150°C.

[0010] The present invention focuses on these points and proposes a method for recovering energy that can be used on board a ship from the waste heat of exhaust gas emitted from the engine when liquefied gas, particularly liquefied gas with a low flash point such as LPG or ammonia, is supplied to the engine as fuel. [Means for solving the problem]

[0011] In order to solve the above problem, an embodiment of the present invention provides a waste heat recovery system for exhaust gas for a ship, comprising: a heat medium circulation line provided on a ship and through which a working fluid circulates; a vaporizer provided in the heat medium circulation line and vaporizing the working fluid by heat exchange with exhaust gas discharged from an engine of the ship; and an expansion turbine provided in the heat medium circulation line and expanding the working fluid to generate shaft power, wherein a low-flash point liquefied gas is supplied to the engine as fuel, and the working fluid circulates through the heat medium circulation line and undergoes a phase change from liquid to gas using the exhaust gas as a heat source.

[0012] Preferably, the heat medium circulation line is provided with a condenser that cools and condenses the working fluid cooled by expansion in the expansion turbine, and a supply pump that pressurizes the working fluid condensed in the condenser and sends it to the evaporator.

[0013] Preferably, the compressor further comprises a compressor that compresses air using shaft power generated by the expansion turbine, and an air supply line that supplies air to the compressor.

[0014] Preferably, the air compressed by the compressor is supplied to a consumer within the ship via the air supply line, and the consumer within the ship injects air onto the outside of the bottom of the ship while it is in operation, thereby reducing frictional resistance with seawater.

[0015] Preferably, the engine further includes a turbocharger that supercharges scavenging air to be supplied to the engine, a scavenging air supply line that cools the scavenging air compressed by the turbocharger and supplies the cooled scavenging air to the engine, a branch line that branches off from the scavenging air supply line and is connected to the air supply line downstream of the compressor, and a branch valve that is provided in the branch line.

[0016] Preferably, when the pressure of the scavenging air compressed by the turbocharger is higher than the discharge pressure of the compressor and therefore the pressure of the scavenging air needs to be reduced, the opening of the branch valve is adjusted to supply part of the scavenging air compressed by the turbocharger to a consumer within the ship.

[0017] Preferably, the working fluid is an organic refrigerant or an aqueous ammonia solution.

[0018] Preferably, the low flash point liquefied gas includes at least one of LPG and ammonia.

[0019] In order to solve the above problem, an embodiment of the present invention provides a waste heat recovery system for exhaust gas for a ship, comprising: a heat medium circulation line provided in a ship and through which a working fluid circulates; a vaporizer provided in the heat medium circulation line and configured to heat the working fluid by heat exchange with exhaust gas discharged from an engine of the ship; a gas-liquid separator provided in the heat medium circulation line and configured to separate the working fluid heated in the vaporizer into gas and liquid; an expansion turbine that expands the gaseous working fluid separated in the gas-liquid separator to generate shaft power; a condenser that cools and condenses the working fluid cooled by expansion in the expansion turbine; a supply pump provided in the heat medium circulation line and configured to pressurize the working fluid condensed in the condenser; and a liquid line that supplies the liquid working fluid separated in the gas-liquid separator to a portion of the heat medium circulation line downstream of the expansion turbine, wherein a liquefied gas having a low flash point is supplied as fuel to the engine.

[0020] Preferably, the system further includes a recuperator provided in the heat medium circulation line for heating the working fluid pressurized by the supply pump and supplying the working fluid to the evaporator, wherein the working fluid circulates through the heat medium circulation line and changes phase from liquid to gas using the exhaust gas as a heat source.

[0021] Preferably, the recuperator is provided downstream of a junction of the heat medium circulation line with the liquid line, and the recuperator heats the working fluid pressurized by the supply pump by heat exchange with the working fluid supplied to the condenser.

[0022] Preferably, the working fluid is a fluid having a boiling point lower than that of water.

[0023] Preferably, the recuperator heats the working fluid pressurized by the supply pump by heat exchange with the liquid working fluid separated by the gas-liquid separator and flowing through the liquid line.

[0024] Preferably, the working fluid is an aqueous ammonia solution.

[0025] Preferably, the engine is an engine that uses a low-flash point liquefied gas as fuel, and the low-flash point liquefied gas includes at least one of LPG and ammonia.

[0026] Preferably, air is compressed by a compressor using shaft power generated by the expansion turbine, and the air compressed by the compressor is supplied to a consumer within the ship, and the consumer within the ship is an air lubrication system that injects air onto the outside of the bottom of the ship while it is in operation to reduce frictional resistance with seawater.

[0027] In order to solve the above-mentioned problems, an embodiment of the present invention provides a heat medium circulation line provided in a ship and through which a working fluid circulates; a vaporizer provided in the heat medium circulation line and configured to heat the working fluid by heat exchange with exhaust gas discharged from an engine of the ship; a gas-liquid separator provided in the heat medium circulation line and configured to separate the working fluid heated by the vaporizer into gas and liquid; an expansion turbine configured to expand the gaseous working fluid separated by the gas-liquid separator to generate shaft power; and a condensation heat exchanger configured to cool and condense the working fluid cooled by expansion in the expansion turbine. The present invention provides a waste heat recovery system for exhaust gas for a ship, comprising: a supply pump provided in a heat medium circulation line for pressurizing the working fluid condensed in the condensing heat exchanger and sending it to the vaporizer; and a first cooling water supply line for supplying cooling water to the condensing heat exchanger for cooling the working fluid, wherein a low-flash point liquefied gas is supplied to the engine as fuel, and heat is exchanged in the condensing heat exchanger among three flows: the working fluid cooled by expansion in the expansion turbine, the working fluid pressurized by the supply pump, and the cooling water in the first cooling water supply line.

[0028] Preferably, the system further includes a suction pot that additionally cools the working fluid condensed in the condensation heat exchanger before supplying it to the supply pump, and a second cooling water supply line that supplies cooling water to the suction pot to cool the working fluid, and the working fluid additionally cooled in the suction pot can be supplied to the supply pump to prevent cavitation at the suction part of the supply pump.

[0029] Preferably, the system further includes a liquid line that supplies the liquid working fluid separated in the gas-liquid separator to the heat medium circulation line downstream of the expansion turbine, and the liquid working fluid separated in the gas-liquid separator is supplied to the condensing heat exchanger via the liquid line together with the working fluid discharged from the expansion turbine.

[0030] Preferably, the working fluid is a fluid that circulates through the heat medium circulation line, changes phase from liquid to gas using the exhaust gas as a heat source, and has a boiling point lower than that of water.

[0031] Preferably, the system further includes a recuperator provided in the heat medium circulation line, heating the working fluid that has been pressurized by the supply pump and then heat-exchanged in the condensing heat exchanger, and supplying the heated working fluid to the evaporator.

[0032] Preferably, in the recuperator, the working fluid that has been pressurized by the supply pump and then heat exchanged in the condensing heat exchanger is heated by heat exchange with the liquid working fluid that has been separated in the gas-liquid separator and flows through the liquid line.

[0033] Preferably, the working fluid is an aqueous ammonia solution.

[0034] Preferably, the low flash point liquefied gas includes at least one of LPG and ammonia.

[0035] Preferably, air is compressed by a compressor using shaft power generated by the expansion turbine, and the air compressed by the compressor is supplied to a consumer within the ship, and the consumer within the ship is an air lubrication system that injects air onto the outside of the bottom of the ship while it is in operation to reduce frictional resistance with seawater.

[0036] In order to solve the above-mentioned problems, an embodiment of the present invention includes a heat medium circulation line provided in a ship and through which a working fluid circulates; a vaporizer provided in the heat medium circulation line and configured to perform heat exchange between the working fluid and exhaust gas discharged from an engine of the ship that uses a low-flash point liquefied gas as fuel; an exhaust gas supply line that supplies the exhaust gas to be heat exchanged with the working fluid to the vaporizer; a gas-liquid separator provided in the heat medium circulation line and configured to separate the working fluid heated in the vaporizer into gas and liquid; an expansion turbine that expands the gaseous working fluid separated in the gas-liquid separator to generate shaft power; and a cooling unit that cools the working fluid cooled by expansion in the expansion turbine. a condensing heat exchanger for condensing working fluid condensed in the condensing heat exchanger, and a supply pump provided in the heat medium circulation line for pressurizing the working fluid condensed in the condensing heat exchanger and sending it to the vaporization unit, the vaporization unit including a vaporizer and a superheater provided in this order in a flow direction of the working fluid supplied from the supply pump, the exhaust gas supplied from the exhaust gas supply line being supplied to the superheater and then the vaporizer, the working fluid having exchanged heat with the exhaust gas in the vaporizer being separated into gas and liquid in the gas-liquid separator, the separated working fluid in a gas state being additionally heated in the superheater and supplied to the expansion turbine.

[0037] Preferably, the system further includes a cooling water supply line for supplying cooling water to the condensation heat exchanger for cooling the working fluid, and in the condensation heat exchanger, heat is exchanged between three flows: the working fluid cooled by expansion in the expansion turbine, the working fluid pressurized by the supply pump, and the cooling water in the cooling water supply line.

[0038] Preferably, the system further includes a liquid line that supplies the liquid working fluid separated in the gas-liquid separator to a portion of the heat medium circulation line downstream of the expansion turbine, and the liquid working fluid separated in the gas-liquid separator is supplied to the condensing heat exchanger via the liquid line together with the working fluid discharged from the expansion turbine.

[0039] Preferably, the working fluid is a fluid that circulates through the heat medium circulation line, changes phase from liquid to gas using exhaust gas discharged from the engine as a heat source, and has a boiling point lower than that of water.

[0040] Preferably, the system further includes a recuperator provided in the heat medium circulation line, which heats the working fluid pressurized by the supply pump and subjected to heat exchange in the condensing heat exchanger, and supplies the heated working fluid to the evaporator.

[0041] Preferably, in the recuperator, the working fluid that has been pressurized by the supply pump and then heat exchanged in the condensing heat exchanger is heated by heat exchange with the liquid working fluid that has been separated in the gas-liquid separator and flows through the liquid line.

[0042] Preferably, the vaporization unit further includes a waste heat heater that exchanges heat between the exhaust gas discharged from the vaporizer and the working fluid that has been pressurized by the supply pump and then heat exchanged in the condensing heat exchanger, and further includes a branch line that branches the working fluid that has been pressurized by the supply pump and then heat exchanged in the condensing heat exchanger and supplies it to the waste heat heater, and supplies the working fluid discharged from the waste heat heater to a side of the heat medium circulation line downstream of the recuperator.

[0043] Preferably, the working fluid is an aqueous ammonia solution.

[0044] Preferably, the low flash point liquefied gas includes at least one of LPG and ammonia.

[0045] Preferably, air is compressed by a compressor using shaft power generated by the expansion turbine, and the air compressed by the compressor is supplied to a consumer within the ship, and the consumer within the ship is an air lubrication system that injects air onto the outside of the bottom of the ship while it is in operation to reduce frictional resistance with seawater.

[0046] In order to solve the above-mentioned problems, an embodiment of the present invention includes a heat medium circulation line provided in a ship and through which a working fluid circulates; an evaporation unit provided in the heat medium circulation line and performing heat exchange between the working fluid and exhaust gas discharged from an engine of the ship that uses a low-flash point liquefied gas as fuel; a gas-liquid separator provided in the heat medium circulation line and separating the working fluid heated in the evaporation unit into gas and liquid; an expansion turbine that expands the gaseous working fluid separated in the gas-liquid separator to generate shaft power; a condenser that cools and condenses the working fluid cooled by expansion in the expansion turbine; and a cooling unit provided in the heat medium circulation line and configured to cool the working fluid condensed in the condenser. a supply pump for pressurizing a working fluid, a first recuperator for heating a portion of the working fluid pressurized by the supply pump and supplying the portion to the vaporization section; and a second recuperator arranged in parallel with the first recuperator for heating another portion of the working fluid pressurized by the supply pump and supplying the other portion to the vaporization section, wherein the first recuperator exchanges heat between the working fluid pressurized by the supply pump and the working fluid that is cooled by expansion in the expansion turbine and then supplied to the condenser, and the second recuperator heats the working fluid pressurized by the supply pump using waste heat supplied from a compression device or a cooling device on the ship.

[0047] Preferably, the vaporization unit includes a vaporizer and a superheater arranged in this order in the direction of flow of the working fluid supplied from the supply pump, and an exhaust gas supply line that supplies exhaust gas to the vaporizer and the superheater for heat exchange with the working fluid, and the exhaust gas is supplied from the exhaust gas supply line to the superheater and then to the vaporizer, the working fluid that has exchanged heat with the exhaust gas in the vaporizer is separated into gas and liquid in the gas-liquid separator, and the separated gaseous working fluid is further heated in the superheater and supplied to the expansion turbine.

[0048] Preferably, the system further includes a cooling water supply line that supplies cooling water to the condenser for cooling the working fluid, and a liquid line that supplies the liquid working fluid separated in the gas-liquid separator to a portion of the heat medium circulation line downstream of the expansion turbine, and the liquid working fluid separated in the gas-liquid separator is supplied to the first recuperator from the liquid line together with the working fluid discharged from the expansion turbine, and then supplied to the condenser.

[0049] Preferably, the ship further comprises a compressor that compresses air using shaft power generated by the expansion turbine, and an air supply line that supplies air to the compressor, and the air compressed by the compressor is supplied to the second recuperator through the air supply line, where it is heat exchanged with another part of the working fluid pressurized by the supply pump and then supplied to a consumer within the ship.

[0050] Preferably, the system further includes a third recuperator that is provided in the heat medium circulation line and that heats the working fluid that has been pressurized by the supply pump and then heat-exchanged in the first or second recuperator, and supplies the working fluid to the vaporizer.

[0051] Preferably, in the third recuperator, the working fluid that has been pressurized by the supply pump and then heat exchanged in the first or second recuperator is heated by heat exchange with the liquid working fluid that has been separated in the gas-liquid separator and flows through a liquid line.

[0052] Preferably, the vaporization unit further includes a waste heat heater that performs heat exchange between the exhaust gas discharged from the vaporizer and a working fluid that is pressurized by the supply pump, heat exchanged in the first recuperator, and then branched, and further includes a branch line that supplies the working fluid that has been heat exchanged in the waste heat heater to a side of the heat medium circulation line downstream of the third recuperator.

[0053] Preferably, the ship further includes a compressor that compresses air using shaft power generated by the expansion turbine, and an air supply line that supplies air to the compressor, and the air compressed by the compressor is supplied to the second recuperator through the air supply line, where it is heat exchanged with another part of the working fluid pressurized by the supply pump and then supplied to a consumer within the ship.

[0054] Preferably, the working fluid is an aqueous ammonia solution.

[0055] Preferably, the low flash point liquefied gas includes at least one of LPG and ammonia. [Effects of the Invention]

[0056] The exhaust gas waste heat recovery system of the present invention can improve the energy efficiency of ships by efficiently recovering the waste heat from exhaust gas emitted from engines that use low-flashpoint liquefied gas as fuel.

[0057] The exhaust gas waste heat recovery system of the present invention converts the waste heat of the exhaust gas into power to generate compressed air, which is then supplied to an onboard consumer such as an air lubrication system. In this case, the air lubrication system reduces frictional resistance with seawater during ship operation, thereby improving the ship's fuel efficiency.

[0058] The exhaust gas waste heat recovery system of the present invention utilizes an organic Rankine cycle (ORC) suitable for recovering waste heat from low-temperature exhaust gas, and includes a heat transfer medium circulation line equipped with three heat exchangers, a heat transfer medium circulation line equipped with a condensing heat exchanger that exchanges heat between three fluid flows, or a heat transfer medium circulation line equipped with multiple recuperators to improve thermal efficiency within the system, to recover waste heat from exhaust gas emitted from an engine that uses low-flashpoint fuel. The recovered waste heat is then converted into electricity to generate electricity and compressed air that can be consumed on board the ship, effectively utilizing the waste heat from the exhaust gas and improving the energy efficiency of the ship.

[0059] Furthermore, the exhaust gas waste heat recovery system of the present invention has a suction pot provided upstream of the supply pump to additionally cool the working fluid condensed in the condensing heat exchanger, thereby preventing cavitation at the suction part of the supply pump caused by steam flowing into the supply pump and improving the stability of the system.

[0060] In addition, the exhaust gas waste heat recovery system of the present invention is configured with an evaporation section divided into a superheater and a vaporizer according to the temperature of the exhaust gas, and the gaseous working fluid, which is evaporated in the vaporizer and then separated into gas and liquid, is further heated in the superheater by the high-temperature exhaust gas, and the superheated working fluid is supplied to the expansion turbine, thereby preventing the generation of liquid droplets and improving the waste heat recovery efficiency and system stability. [Brief explanation of the drawings]

[0061] [Figure 1] 1 is a schematic diagram illustrating a waste heat recovery system for exhaust gas for a ship according to a first embodiment of the present invention. [Figure 2] 5 is a schematic diagram showing a waste heat recovery system for an exhaust gas for a ship according to a second embodiment of the present invention. [Figure 3] 10 is a schematic diagram illustrating a waste heat recovery system for an exhaust gas for a ship according to a third embodiment of the present invention. [Figure 4] 10 is a schematic diagram illustrating a waste heat recovery system for an exhaust gas for a ship according to a fourth embodiment of the present invention. [Figure 5] 10 is a schematic diagram illustrating a waste heat recovery system for an exhaust gas for a ship according to a fifth embodiment of the present invention. [Figure 6] 10 is a schematic diagram illustrating a waste heat recovery system for exhaust gas for a ship according to a sixth embodiment of the present invention. [Figure 7] 10 is a schematic diagram illustrating a waste heat recovery system for exhaust gas for a ship according to a seventh embodiment of the present invention. [Figure 8] 10 is a schematic diagram illustrating an exhaust gas waste heat recovery system for a ship according to an eighth embodiment of the present invention. [Figure 9] 13 is a schematic diagram illustrating a waste heat recovery system for exhaust gas for a ship according to a ninth embodiment of the present invention. [Figure 10] 13 is a schematic diagram illustrating a waste heat recovery system for exhaust gas for a ship according to a tenth embodiment of the present invention. [Figure 11] 13 is a schematic diagram showing an exhaust gas waste heat recovery system for a ship according to an eleventh embodiment of the present invention. [Figure 12] 12 is a schematic diagram showing a waste heat recovery system for exhaust gas for a ship according to a twelfth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0062] The operating advantages of the present invention and the objects achieved by embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which: FIG.

[0063] Hereinafter, the configuration and operation of the embodiments of the present invention will be described with reference to the accompanying drawings. Note that the same components are designated by the same reference numerals in this specification and the accompanying drawings.

[0064] The ships of the embodiments of the present invention described below are any type of ship equipped with propulsion engines or power generation engines that can use liquefied gas as fuel. Examples of such ships include self-propelled ships such as LPG carriers, LNG carriers, liquid hydrogen carriers, and LNG regasification vessels (RVs), as well as floating offshore structures that do not have self-propelling capabilities, such as LNG floating production storage offloading (FPSOs) and LNG floating storage regasification units (FSRUs).

[0065] Furthermore, embodiments of the present invention can be applied to any type of liquefied gas that can be liquefied at low temperatures, transported, and supplied as engine fuel. Examples of such liquefied gases include liquefied petrochemical gases such as LNG (Liquefied Natural Gas), LEG (Liquefied Ethane Gas), LPG (Liquefied Petroleum Gas), liquefied ethylene gas, and liquefied propylene gas, as well as ammonia. In the embodiments described below, ammonia and LPG, which are liquefied gases with low flash points and relatively high boiling points, are used as engine fuel.

[0066] Fig. 1 schematically shows a waste heat recovery system for exhaust gas for a ship according to a first embodiment of the present invention, and Fig. 2 schematically shows a waste heat recovery system for exhaust gas for a ship according to a second embodiment of the present invention.

[0067] As shown in FIGS. 1 and 2 , the exhaust gas waste heat recovery systems of the first and second embodiments include a heat medium circulation line RCL that is provided on a ship and through which a working fluid circulates, a vaporizer 100 that is provided in the heat medium circulation line RCL and vaporizes the working fluid by heat exchange with exhaust gas discharged from an engine of the ship, and an expansion turbine 200 that is provided in the heat medium circulation line RCL and expands the working fluid to generate shaft power.

[0068] In the first and second embodiments, a liquefied gas with a low flash point is supplied as fuel to an engine (not shown). The working fluid circulates through a closed-loop heat medium circulation line RCL and changes phase from liquid to gas using exhaust gas emitted from the engine that uses the liquefied gas with a low flash point as fuel as a heat source.

[0069] Ammonia and LPG have relatively high boiling points among low-flash-point liquefied gases. LPG, which is primarily composed of propane, has a flash point of −105°C and a boiling point of −42°C under standard pressure. Furthermore, the boiling point of ammonia is −33°C under standard pressure, which is higher than that of methane (LNG), which has a boiling point of −161°C under standard pressure, and hydrogen, which has a boiling point of −253°C under standard pressure. Therefore, when ammonia or LPG is supplied to an engine as fuel, only a very small amount of heat is required to heat it to the required supply temperature. Therefore, ammonia or LPG can be heated using engine coolant or the like and then supplied to the engine as fuel, without using steam generated using high-temperature exhaust gas from the engine. Furthermore, since the fuel does not contain sulfur components, low-temperature corrosion is unlikely to occur, and waste heat can be recovered from exhaust gas with a temperature of 150°C or less. Therefore, in the first and second embodiments, an organic Rankine cycle, which is suitable for recovering low-temperature waste heat, is applied to the heat medium circulation line RCL to recover waste heat from the exhaust gas discharged from the engine.

[0070] The heat medium circulation line RCL is provided with: a vaporizer 100 that vaporizes the working fluid by heat exchange with exhaust gas; an expansion turbine 200 that expands the working fluid vaporized in the vaporizer 100 to generate shaft power; a condenser 300 that cools and condenses the working fluid cooled by expansion in the expansion turbine 200; and a supply pump 400 that pressurizes the working fluid condensed in the condenser 300 and supplies it to the vaporizer 100.

[0071] In the systems of the first and second embodiments, the working fluid circulating through the heat medium circulation line RCL may be, for example, an organic refrigerant or an aqueous ammonia solution. The working fluid is supplied in a liquid state to the supply pump 400, pressurized by the supply pump 400 to a pressure required to drive the expansion turbine 200, and then supplied to the vaporizer 100. In the vaporizer 100, the working fluid is heated by waste heat from the exhaust gas HM supplied through the exhaust gas supply line HRL, and the heated and vaporized gaseous working fluid is supplied to the expansion turbine 200. The gaseous working fluid expands in the expansion turbine 200 to drive the turbine and generate shaft power. The working fluid partially cooled by the expansion is supplied to the condenser 300. In the condenser 300, the working fluid before being supplied to the supply pump 400 is further cooled and condensed by cooling water CM supplied through the cooling water supply line CRL. The condensed liquid working fluid is then supplied to the supply pump 400. In this way, the working fluid undergoes a phase change while circulating through the closed-loop heat medium circulation line RCL, thereby recovering the waste heat of the exhaust gas and converting it into power.

[0072] The shaft power generated by the expansion turbine 200 by utilizing the waste heat of the exhaust gas can be used to drive a generator to generate electricity. Furthermore, in the first and second embodiments, a compressor 250 that compresses air using the shaft power generated by the expansion turbine 200 and an air supply line AL that supplies air to the compressor 250 are provided. The compressed air compressed by the compressor 250 is supplied to a consumer CS within the ship through the air supply line AL. Furthermore, the compressor 250 can be connected to the expansion turbine 200 via a shaft. The compression ratio of the compressor 250 can be determined depending on the consumer within the ship to which the compressed air is supplied.

[0073] Furthermore, a consumer CS within a ship to which compressed air is supplied may be, for example, an air lubrication system that injects air onto the outside bottom of the ship's hull. The air lubrication system injects air onto the outside bottom of the hull to form a continuous air layer between the hull and seawater, thereby reducing frictional resistance between the hull and seawater during operation and improving the ship's fuel efficiency.

[0074] The air lubrication system is configured with an air compressor (not shown) that compresses air to generate compressed air, piping for supplying compressed air, an air injection unit (not shown), an air layer (not shown) formed on the outer surface of the bottom of the hull, a control unit (not shown), and the like. Compressed air generated by a waste heat recovery system can also be supplied to the air lubrication system. In the systems of the first and second embodiments, air is compressed by the compressor 250 using shaft power generated by the expansion turbine 200, and the compressed air compressed by the compressor 250 is supplied to the air lubrication system. In this way, the compressor of the waste heat recovery system can be used instead of the air compressor of the air lubrication system, eliminating the need to provide a separate air compressor or the like in the air lubrication system. Even if an air compressor is provided in the air lubrication system, a smaller-capacity air compressor can be used because the compressed air generated by the waste heat recovery system can make up for any capacity shortfall in the air compressor. When compressed air is supplied to the air lubrication system, the compressor 250 is operated at a compression ratio of approximately 2. In this case, the compressor 250 can be configured as a single-stage centrifugal compressor.

[0075] As described above, the systems of the first and second embodiments recover waste heat from exhaust gas emitted from an engine that uses low-flashpoint fuel. The recovered waste heat is converted into electricity or compressed air, which is then supplied to the air lubrication system on the ship. This reduces frictional resistance with seawater during ship operation, improving the ship's fuel efficiency and energy efficiency.

[0076] 2 differs from the system of the first embodiment in that a portion of the configuration is added so that surplus compressed air from the turbocharger 500 can be supplied to a waste heat recovery system and then to consumers within the ship. Hereinafter, a description of the configuration that is the same as that of the first embodiment will be omitted, and the following description will focus on the configuration that is different from that of the first embodiment.

[0077] As shown in FIG. 2, the system of the second embodiment further includes a turbocharger 500 that supercharges scavenge air to be supplied to the engine, a scavenging air supply line SL that cools the scavenging air compressed by the turbocharger 500 and supplies the cooled scavenging air to the engine, a branch line BL that branches off from the scavenging air supply line SL and is connected to the air supply line AL downstream of the compressor 250, and a branch valve BV that is provided in the branch line BL.

[0078] In order to improve the efficiency of a ship engine, intake air (called scavenging air) compressed to high pressure by a turbocharger 500 is supplied to the engine. The compressed air, which has been compressed to high pressure by the turbocharger 500 and has reached a high temperature, is supplied to a scavenging air cooler SC to be cooled and then supplied to the engine. The scavenging air pressure supplied to the engine varies depending on the engine load, the outside air temperature, and the like. When the scavenging air pressure is high, it is necessary to discharge (vent) part of the scavenging air in order to adjust the scavenging air pressure. In this embodiment, when the scavenging air pressure is high and it is necessary to discharge part of the scavenging air in order to adjust the pressure, the excess compressed air is supplied via a branch line BL to the air supply line AL downstream of the compressor 250, and then supplied to a consumer CS within the ship, such as an air lubrication system, for use.

[0079] That is, when the pressure of the scavenging air compressed by the turbocharger 500 is higher than the outlet pressure of the compressor and it is necessary to reduce the scavenging air pressure supplied to the engine, the opening of the branch valve BV provided in the branch line BL is adjusted in accordance with the scavenging air pressure detected by the pressure transmitter PT provided in the scavenging air supply line SL, and part of the scavenging air compressed by the turbocharger 500 is supplied to the air supply line AL, and this is supplied to the consumer CS inside the ship.

[0080] As described above, in the system of the second embodiment, the scavenging air pressure supplied to the engine is adjusted in accordance with engine load fluctuations, and excess compressed air from the turbocharger 500 is supplied to a consumer within the ship.

[0081] Next, Fig. 3 shows a schematic diagram of a waste heat recovery system for exhaust gas for a ship according to a third embodiment of the present invention, and Fig. 4 shows a schematic diagram of a waste heat recovery system for exhaust gas for a ship according to a fourth embodiment of the present invention.

[0082] As shown in Figures 3 and 4, the exhaust gas waste heat recovery systems of the third and fourth embodiments include a heat medium circulation line RCL that is provided on a ship and through which a working fluid circulates, a vaporizer 100 that is provided in the heat medium circulation line RCL and heats and vaporizes the working fluid by heat exchange with exhaust gas discharged from an engine of the ship, a gas-liquid separator 200 that separates the working fluid heated (vaporized) in the vaporizer 100 into gas and liquid, and an expansion turbine 300 that is provided in the heat medium circulation line RCL and expands the working fluid to generate shaft power.

[0083] In the third and fourth embodiments, a liquefied gas with a low flash point is supplied as fuel to an engine (not shown). The working fluid circulates through a closed-loop heat medium circulation line RCL and changes phase from liquid to gas using exhaust gas emitted from the engine that uses the liquefied gas with a low flash point as fuel as a heat source.

[0084] Ammonia and LPG have relatively high boiling points among low-flash-point liquefied gases. LPG, which is primarily composed of propane, has a flash point of −105°C and a boiling point of −42°C under standard pressure. Furthermore, the boiling point of ammonia is −33°C under standard pressure, which is higher than that of methane (LNG), which has a boiling point of −161°C under standard pressure, and hydrogen, which has a boiling point of −253°C under standard pressure. Therefore, when ammonia or LPG is supplied to an engine as fuel, only a very small amount of heat is required to heat it to the required supply temperature. Therefore, it can be heated using engine coolant or the like and then supplied to the engine as fuel, without using steam generated using high-temperature exhaust gas from the engine. Furthermore, since the fuel does not contain sulfur components, low-temperature corrosion is unlikely to occur, and waste heat can be recovered from exhaust gas with a temperature of 150°C or less. Therefore, in the third and fourth embodiments, an organic Rankine cycle, which is suitable for recovering low-temperature waste heat, is applied to the heat medium circulation line RCL to recover waste heat from the exhaust gas discharged from the engine.

[0085] The heat medium circulation line RCL is provided with a vaporizer 100 that heats and vaporizes the working fluid by heat exchange with exhaust gas, a gas-liquid separator 200 that separates the working fluid heated (vaporized) in the vaporizer 100 into gas and liquid, an expansion turbine 300 that expands the gaseous working fluid separated in the gas-liquid separator 200 to generate shaft power, a condenser 500 that cools and condenses the working fluid cooled by expansion in the expansion turbine 300, a supply pump 600 that pressurizes and sends out the working fluid condensed in the condenser 500, and a recuperator 400a or 400b that heats the working fluid pressurized by the supply pump 600. The working fluid heated in the recuperator 400a or 400b is supplied to the vaporizer 100. In addition, the liquid working fluid separated in the gas-liquid separator 200 is supplied to the heat medium circulation line RCL downstream of the expansion turbine 300 via the liquid line LLa or LLb, and is supplied to the condenser 500 together with the working fluid discharged from the expansion turbine 300.

[0086] In the system of the third embodiment, a fluid having a boiling point lower than that of water can be used as the working fluid circulating through the heat medium circulation line RCL so that waste heat from low-temperature exhaust gas can also be recovered.

[0087] As shown in FIG. 3 , in the system of the third embodiment, the liquid working fluid condensed in the condenser 500 is pressurized by the supply pump 600 to a pressure required to drive the expansion turbine 300, and is then supplied to the recuperator 400a, and then to the vaporizer 100. In the recuperator 400a, downstream of the junction of the heat medium circulation line RCL with the liquid line LLa, the working fluid pressurized by the supply pump 600 is heated by heat exchange with the working fluid before being supplied to the condenser 500. That is, in the recuperator 400a, heat exchange occurs between the working fluid pressurized by the supply pump 600 and discharged from the supply pump 600 and the working fluid before being supplied to the condenser 500. The working fluid discharged from the recuperator 400a and supplied to the vaporizer 100 is heated and vaporized by waste heat of the exhaust gas HM supplied from the exhaust gas supply line HL, and the gaseous working fluid separated in the gas-liquid separator 200 is then supplied to the expansion turbine 300. The gaseous working fluid expands in the expansion turbine 300 to drive the turbine and generate shaft power. The working fluid that has been partially cooled by the expansion is supplied to the recuperator 400a for heat exchange and then supplied to the condenser 500. In the condenser 500, the working fluid before being supplied to the supply pump 600 is further cooled (additionally cooled) and condensed by cooling water CM supplied from the cooling water supply line CL. The condensed working fluid in a liquid state is then supplied to the supply pump 600. In this way, the working fluid circulates through the closed-loop heat medium circulation line RCL while undergoing a phase change, thereby recovering waste heat from the exhaust gas and converting it into power.

[0088] In addition, in this embodiment, the shaft power SP generated in the expansion turbine 300 by utilizing the waste heat of the exhaust gas can be used to drive a generator to generate electricity, and the shaft power SP may also be used in a compressor to generate compressed air to be supplied to consumers on the ship.

[0089] Also, a compressor (not shown) may be configured to be connected to the expansion turbine 300 via a shaft. The compression ratio of the compressor may be determined depending on the destination within the ship where the compressed air is to be supplied.

[0090] Furthermore, a consumer CS within a ship to which compressed air is supplied may be, for example, an air lubrication system that injects air onto the outside bottom of the ship's hull. The air lubrication system injects air onto the outside bottom of the hull to form a continuous air layer between the hull and seawater, thereby reducing frictional resistance between the hull and seawater during operation and improving the ship's fuel efficiency.

[0091] The air lubrication system is configured with an air compressor (not shown) that compresses air to generate compressed air, piping for supplying compressed air, an air injection unit (not shown), an air layer (not shown) formed on the outer surface of the bottom of the hull, a control unit (not shown), and the like. Compressed air generated by a waste heat recovery system can also be supplied to the air lubrication system. In this embodiment, the system compresses air using the shaft power SP generated by the expansion turbine 300, and the compressed air is supplied to the air lubrication system. In this way, the compressor of the waste heat recovery system can be used instead of the air compressor of the air lubrication system, eliminating the need for a separate air compressor or the like in the air lubrication system. Even if an air compressor is provided in the air lubrication system, a smaller-capacity air compressor can be used because the compressed air generated in the waste heat recovery system can make up for any capacity shortfall in the air compressor.

[0092] As described above, the system of the third embodiment recovers waste heat from exhaust gas emitted from an engine that uses a low-flashpoint fuel by using the heat medium circulation line RCL provided with three heat exchangers: the vaporizer 100, the condenser 500, and the recuperator 400a. The recovered waste heat is converted into electricity or compressed air is generated and supplied to consumers on the ship, thereby improving the energy efficiency of the ship.

[0093] 4 differs from the system of the third embodiment in the position where the recuperator 400b is provided. Hereinafter, a description of the same configuration as the system of the third embodiment will be omitted, and the configuration different from the third embodiment will be mainly described.

[0094] As shown in Figure 4, the system of the fourth embodiment is configured so that in the recuperator 400b, the working fluid pressurized by the supply pump 600 is heated by heat exchange with the liquid working fluid separated in the gas-liquid separator 200 and flowing through the liquid line LLb.

[0095] By arranging the recuperator 400b in this manner, thermal energy can be recovered from the working fluid that remains in a liquid state without being vaporized even when heated by the waste heat of the exhaust gas in the vaporizer 100, and the working fluid discharged from the condenser 500 and the supply pump 600 can be preheated before being supplied to the vaporizer 100.

[0096] In the system of the fourth embodiment, the working fluid circulating through the heat medium circulation line RCL may be, for example, an aqueous ammonia solution. When the aqueous ammonia solution is heated in the vaporizer 100 by heat exchange with low-temperature exhaust gas, the ammonia, which has a low boiling point, is vaporized into a gaseous state, but water may remain in a liquid state without being vaporized. The gaseous ammonia separated in the gas-liquid separator 200 is then supplied to the expansion turbine 300. Meanwhile, the water separated in the gas-liquid separator 200 is supplied to the recuperator 400b through the liquid line LLb, where thermal energy is recovered. Thereafter, the water is supplied to the heat medium circulation line RCL upstream of the condenser 500, and is then supplied to the condenser 500 together with the ammonia discharged from the expansion turbine 300 and condensed.

[0097] As described above, the system of the fourth embodiment improves the thermal efficiency of the ship by effectively recovering waste heat from the exhaust gas using the heat transfer medium circulation line RCL equipped with three heat exchangers. Furthermore, using an aqueous ammonia solution as the working fluid of the heat transfer medium circulation line RCL facilitates replenishment and management of the working fluid. In particular, when the system of this embodiment is applied to an ammonia-fueled ship or an ammonia carrier that uses ammonia as engine fuel, ammonia as fuel or cargo can be directly used as the working fluid of the heat transfer medium circulation line RCL, eliminating the need for a separate refrigerant management system and reducing the installation costs of related equipment such as refrigerant storage tanks.

[0098] Fig. 5 schematically shows a waste heat recovery system for exhaust gas for a ship according to a fifth embodiment of the present invention, and Fig. 6 schematically shows a waste heat recovery system for exhaust gas for a ship according to a sixth embodiment of the present invention.

[0099] As shown in Figures 5 and 6, the exhaust gas waste heat recovery systems of the fifth and sixth embodiments are provided with: a heat medium circulation line RCL that is provided on a ship and through which a working fluid circulates; a vaporizer 100 that is provided in the heat medium circulation line RCL and that heats and vaporizes the working fluid by heat exchange with exhaust gas discharged from an engine of the ship; a gas-liquid separator 200 that separates the working fluid heated (vaporized) in the vaporizer 100 into gas and liquid; and an expansion turbine 300 that is provided in the heat medium circulation line RCL and that expands the working fluid to generate shaft power.

[0100] In the fifth and sixth embodiments, a liquefied gas having a low flash point is supplied as fuel to an engine (not shown). The working fluid circulates through a closed-loop heat medium circulation line RCL and changes phase from liquid to gas using exhaust gas emitted from the engine that uses the liquefied gas having a low flash point as fuel as a heat source.

[0101] Ammonia and LPG have relatively high boiling points among low-flash-point liquefied gases. LPG, which is primarily composed of propane, has a flash point of −105°C and a boiling point of −42°C under standard pressure. Furthermore, ammonia has a boiling point of −33°C under standard pressure, which is higher than methane (LNG), which has a boiling point of −161°C under standard pressure, and hydrogen, which has a boiling point of −253°C under standard pressure. Therefore, when ammonia or LPG is supplied to an engine as fuel, only a very small amount of heat is required to heat the fuel to the required supply temperature. Therefore, the ammonia or LPG can be heated with engine coolant or the like and then supplied to the engine as fuel, without using steam generated from high-temperature exhaust gas emitted from the engine. Furthermore, since the fuel does not contain sulfur components, low-temperature corrosion is unlikely to occur, and waste heat can be recovered from exhaust gas with a temperature of 150°C or less. Therefore, in the fifth and sixth embodiments, an organic Rankine cycle, which is suitable for recovering low-temperature waste heat, is applied to the heat medium circulation line RCL to recover waste heat from the exhaust gas discharged from the engine.

[0102] The heat medium circulation line RCL is provided with a vaporizer 100 that heats and vaporizes the working fluid by heat exchange with exhaust gas, a gas-liquid separator 200 that separates the working fluid heated (vaporized) in the vaporizer 100 into gas and liquid, an expansion turbine 300 that expands the gaseous working fluid separated in the gas-liquid separator 200 to generate shaft power, a condensation heat exchanger 400 that cools and condenses the working fluid cooled by expansion in the expansion turbine 300, and a supply pump 600 that pressurizes the working fluid condensed in the condensation heat exchanger 400 and sends it to the vaporizer 100. The liquid working fluid separated in the gas-liquid separator 200 is supplied to the heat medium circulation line RCL downstream of the expansion turbine 300 via a liquid line LLa or LLb, and is supplied to the condensation heat exchanger 400 together with the working fluid discharged from the expansion turbine 300.

[0103] In the condensation heat exchanger 400, the working fluid partially cooled by expansion in the expansion turbine 300 and the working fluid supplied from the liquid line LLa or LLb are cooled and condensed. The condensed working fluid in a liquid state is then supplied to the supply pump 600. In the systems of the fifth and sixth embodiments, cooling water for cooling the working fluid is supplied to the condensation heat exchanger 400 from the first cooling water supply line CL1. The working fluid condensed in the condensation heat exchanger 400 and then pressurized by the supply pump 600 is supplied to the condensation heat exchanger 400 before being supplied to the vaporizer 100. In this way, the condensation heat exchanger 400 exchanges heat among three fluid flows: the flow of the working fluid in the heat medium circulation line RCL cooled by expansion in the expansion turbine 300, the flow of the working fluid in the heat medium circulation line RCL pressurized by the supply pump 600 and supplied to the vaporizer 100, and the flow of cooling water in the first cooling water supply line CL1.

[0104] By exchanging heat among the three fluid flows, in the condensing heat exchanger 400, the working fluid cooled by expansion in the expansion turbine 300 is supplied with cold energy from the other two flows, and the working fluid cooled by expansion in the expansion turbine 300 is effectively condensed. In addition, the working fluid pressurized by the supply pump 600 can be preheated before being supplied to the vaporizer 100. Therefore, the condensing heat exchanger 400 functions not only as a condenser that condenses the gaseous working fluid, but also as a recuperator that preheats the working fluid pressurized by the supply pump 600 before being supplied to the vaporizer 100. This reduces the number of devices and maximizes the thermal efficiency of the ship.

[0105] In the system of the fifth embodiment, a fluid having a boiling point lower than that of water can be used as the working fluid circulating through the heat medium circulation line RCL so that waste heat from low-temperature exhaust gas can also be recovered.

[0106] As shown in FIG. 5 , in the system of the fifth embodiment, the liquid working fluid condensed in the condensing heat exchanger 400 is pressurized by a supply pump 600 to a pressure required to drive the expansion turbine 300, and is then supplied to the condensing heat exchanger 400, and then to the vaporizer 100. The working fluid preheated in the condensing heat exchanger 400 and then supplied to the vaporizer 100 is heated and vaporized by waste heat from the exhaust gas HM supplied through the exhaust gas supply line HL, and the gaseous working fluid separated in the gas-liquid separator 200 is supplied to the expansion turbine 300. The gaseous working fluid expands in the expansion turbine 300 to drive the turbine and generate shaft power. The working fluid partially cooled by the expansion is then supplied to the condensing heat exchanger 400. In the condensation heat exchanger 400, the working fluid that has been partially cooled by expansion in the expansion turbine 300 is further cooled (added) and condensed by the flow of the cooling water CM supplied from the first cooling water supply line CL and the flow of the working fluid that has been sent out from the supply pump 600 and is not yet supplied to the evaporator 100. The condensed working fluid in a liquid state is then supplied to the supply pump 600 and pressurized to a pressure required to drive the expansion turbine 300.

[0107] In this embodiment, a suction pot 500 is provided downstream of the condensation heat exchanger 400 on the heat medium circulation line RCL to further cool (additionally cool) the working fluid condensed in the condensation heat exchanger 400 before supplying it to the supply pump 600. A second cooling water supply line CL2 that supplies cooling water is connected to the suction pot 500. The working fluid before being supplied to the supply pump 600 is further cooled (additionally cooled) by heat exchange with the cooling water supplied from the second cooling water supply line CL2. In this way, by supplying the working fluid cooled in the condensation heat exchanger 400 to the supply pump 600 after being additionally cooled by the suction pot 500, cavitation at the suction portion of the supply pump, which occurs when vapor flows into the supply pump, is prevented, and system stability is improved.

[0108] The working fluid in a liquid state is cooled and condensed in the condensation heat exchanger 400, and then further cooled in the suction pot 500. After being pressurized by the supply pump 600, the working fluid is supplied to the condensation heat exchanger 400, where it is preheated, and then supplied to the vaporizer 100. In this way, the working fluid circulates through the closed-loop heat medium circulation line RCL while undergoing a phase change, thereby recovering the waste heat of the exhaust gas and converting it into power.

[0109] In addition, in this embodiment, the shaft power SP generated in the expansion turbine 300 by utilizing the waste heat of the exhaust gas can be used to drive a generator to generate electricity, and the shaft power SP may also be used in a compressor to generate compressed air to be supplied to consumers on the ship.

[0110] Also, a compressor (not shown) may be configured to be connected to the expansion turbine 300 via a shaft. The compression ratio of the compressor may be determined depending on the destination within the ship where the compressed air is to be supplied.

[0111] Furthermore, a consumer CS within a ship to which compressed air is supplied may be, for example, an air lubrication system that injects air onto the outside bottom of the ship's hull. The air lubrication system injects air onto the outside bottom of the hull to form a continuous air layer between the hull and seawater, thereby reducing frictional resistance between the hull and seawater during operation and improving the ship's fuel efficiency.

[0112] The air lubrication system is configured with an air compressor (not shown) that compresses air to generate compressed air, piping for supplying compressed air, an air injection unit (not shown), an air layer (not shown) formed on the outer surface of the bottom of the hull, a control unit (not shown), and the like. Compressed air generated by a waste heat recovery system can also be supplied to the air lubrication system. In this embodiment, the system compresses air using the shaft power SP generated by the expansion turbine 300, and the compressed air is supplied to the air lubrication system. In this way, the compressor of the waste heat recovery system can be used instead of the air compressor of the air lubrication system, eliminating the need for a separate air compressor or the like in the air lubrication system. Even if an air compressor is provided in the air lubrication system, a smaller-capacity air compressor can be used because the compressed air generated in the waste heat recovery system can make up for any capacity shortfall in the air compressor.

[0113] As described above, the system of the fifth embodiment recovers waste heat from exhaust gas emitted from an engine that uses a low-flashpoint fuel by using the heat medium circulation line RCL, which is provided with the condensing heat exchanger 400 that exchanges heat among three fluid flows. The recovered waste heat can be converted into electricity or compressed air, which can be supplied to consumers on the ship, thereby improving the energy efficiency of the ship.

[0114] 6 differs from the system of the fifth embodiment in that a recuperator 450 is additionally provided to recover thermal energy from the liquid working fluid that is separated in the gas-liquid separator 200 and flows through the liquid line LLb. Below, a description of the configuration that is the same as the system of the fifth embodiment will be omitted, and the description will focus on the configuration that differs from the fifth embodiment.

[0115] 6, in the system of the sixth embodiment, a recuperator 450 is provided in the heat medium circulation line RCL to further heat (additionally heat) the working fluid that has been pressurized by the supply pump 500 and then heat exchanged in the condensing heat exchanger 400 before being supplied to the vaporizer 100. In the recuperator 450, the working fluid that has been pressurized and preheated by the supply pump 600 and the condensing heat exchanger 400 is heated by heat exchange with the working fluid in a liquid state that has been separated in the gas-liquid separator 200 and flows through the liquid line LLb.

[0116] By arranging the recuperator 450 in this manner, thermal energy can be recovered from the working fluid that remains in a liquid state without being vaporized even when heated by the waste heat of the exhaust gas in the vaporizer 100, and the working fluid discharged from the supply pump 500 and the condensation heat exchanger 400 can be preheated before being supplied to the vaporizer 100.

[0117] In the system of the sixth embodiment, the working fluid circulating through the heat medium circulation line RCL may be, for example, an aqueous ammonia solution. When the aqueous ammonia solution is heated in the vaporizer 100 by heat exchange with low-temperature exhaust gas, the ammonia, which has a low boiling point, is vaporized into a gaseous state, but water may remain in a liquid state without being vaporized. The gaseous ammonia separated in the gas-liquid separator 200 is then supplied to the expansion turbine 300. Meanwhile, the water separated in the gas-liquid separator 200 is supplied to the recuperator 450 via the liquid line LLb, where thermal energy is recovered. Thereafter, the water is supplied to the heat medium circulation line RCL upstream of the condensing heat exchanger 400, and is then supplied to the condensing heat exchanger 400 together with the ammonia discharged from the expansion turbine 300 and condensed.

[0118] As described above, the system of the sixth embodiment is provided with a condensing heat exchanger 400 that exchanges heat between three fluid flows, effectively recovering waste heat from the exhaust gas and improving the thermal efficiency of the ship. This simplifies the system configuration and maximizes the thermal efficiency of the ship. Furthermore, using an aqueous ammonia solution as the working fluid of the heat transfer medium circulation line RCL facilitates replenishment and management of the working fluid. In particular, when the system of this embodiment is applied to an ammonia-fueled ship or an ammonia carrier that uses ammonia as engine fuel, ammonia as fuel or cargo can be directly used as the working fluid of the heat transfer medium circulation line RCL. This eliminates the need for a separate refrigerant management system and reduces the installation costs of related equipment such as refrigerant storage tanks.

[0119] Fig. 7 schematically shows a waste heat recovery system for exhaust gas for a ship according to a seventh embodiment of the present invention. Fig. 8 schematically shows a waste heat recovery system for exhaust gas for a ship according to an eighth embodiment of the present invention.

[0120] As shown in Figures 7 and 8, the exhaust gas waste heat recovery systems of the seventh and eighth embodiments include a heat medium circulation line RCL that is provided on a ship and through which a working fluid circulates, an evaporation unit 100A or 100B that is provided in the heat medium circulation line RCL and heats and vaporizes the working fluid by heat exchange with exhaust gas discharged from an engine of the ship, a gas-liquid separator 200 that separates the working fluid heated (evaporated) in the evaporation unit 100A or 100B into gas and liquid, and an expansion turbine 300 that is provided in the heat medium circulation line RCL and expands the working fluid to generate shaft power.

[0121] In the seventh and eighth embodiments, a liquefied gas with a low flash point is supplied as fuel to an engine (not shown). The working fluid circulates through a closed-loop heat medium circulation line RCL and changes phase from liquid to gas using exhaust gas emitted from the engine that uses the liquefied gas with a low flash point as fuel as a heat source.

[0122] Ammonia and LPG have relatively high boiling points among low-flash-point liquefied gases. LPG, which is primarily composed of propane, has a flash point of −105°C and a boiling point of −42°C under standard pressure. Furthermore, the boiling point of ammonia is −33°C under standard pressure, which is higher than that of methane (LNG), which has a boiling point of −161°C under standard pressure, and hydrogen, which has a boiling point of −253°C under standard pressure. Therefore, when ammonia or LPG is supplied to an engine as fuel, only a very small amount of heat is required to heat the fuel to the required supply temperature. Therefore, the ammonia or LPG can be heated with engine coolant or the like and then supplied to the engine as fuel, without using steam generated from high-temperature exhaust gas emitted from the engine. Furthermore, since the fuel does not contain sulfur components, low-temperature corrosion is unlikely to occur, and waste heat can be recovered from exhaust gas with a temperature of 150°C or less. Therefore, in the seventh and eighth embodiments, an organic Rankine cycle, which is suitable for recovering low-temperature waste heat, is applied to the heat medium circulation line RCL to recover waste heat from the exhaust gas discharged from the engine.

[0123] The heat medium circulation line RCL is provided with an evaporation unit 100A or 100B that heats and vaporizes the working fluid by heat exchange with exhaust gas, a gas-liquid separator 200 that separates the working fluid heated (evaporated) in the evaporation unit 100A or 100B into gas and liquid, an expansion turbine 300 that expands the gaseous working fluid separated in the gas-liquid separator 200 to generate shaft power, a condensation heat exchanger 400 that cools and condenses the working fluid cooled by expansion in the expansion turbine 300, and a supply pump 500 that pressurizes the working fluid condensed in the condensation heat exchanger 400 and sends it to the evaporation unit 100A or 100B. The liquid working fluid separated in the gas-liquid separator 200 is supplied to the heat medium circulation line RCL downstream of the expansion turbine 300 via a liquid line LLa or LLb, and is supplied to the condensation heat exchanger 400 together with the working fluid discharged from the expansion turbine 300.

[0124] In the condensation heat exchanger 400, the working fluid partially cooled by expansion in the expansion turbine 300 and the working fluid supplied from the liquid line LLa or LLb are cooled and condensed. The condensed working fluid in a liquid state is then supplied to the supply pump 500. In the systems of the seventh and eighth embodiments, cooling water CM for cooling the working fluid is supplied to the condensation heat exchanger 400 from the cooling water supply line CL. The working fluid condensed in the condensation heat exchanger 400 and pressurized by the supply pump 500 is supplied to the condensation heat exchanger 400 before being supplied to the evaporation unit 100A or 100B. In this way, the condensation heat exchanger 400 exchanges heat among three fluid flows: the flow of the working fluid in the heat medium circulation line RCL cooled by expansion in the expansion turbine 300, the flow of the working fluid in the heat medium circulation line RCL pressurized by the supply pump 500 and supplied to the evaporation unit 100A or 100B, and the flow of the cooling water CM in the cooling water supply line CL.

[0125] By exchanging heat among the three fluid flows, in condensing heat exchanger 400, the working fluid cooled by expansion in expansion turbine 300 is supplied with cold energy from the other two flows, effectively condensing the working fluid cooled by expansion in expansion turbine 300. In addition, the working fluid pressurized by supply pump 600 can be preheated before being supplied to vaporization unit 100A or 100B. Therefore, condensing heat exchanger 400 functions as a condenser that condenses the gaseous working fluid into a liquid, and also functions as a recuperator that preheats the working fluid pressurized by supply pump 500 before being supplied to vaporization unit 100A or 100B. This reduces the number of devices and maximizes the thermal efficiency of the ship.

[0126] In the systems of the seventh and eighth embodiments, the vaporization unit 100A or 100B includes a vaporizer 110a or 110b and a superheater 120a or 120b, respectively, which are arranged in accordance with the flow direction of the working fluid delivered from the supply pump 500. The exhaust gas HM supplied from the exhaust gas supply line HL is supplied to the superheater 120a or 120b of the vaporization unit 100A or 100B, and then supplied to the vaporizer 110a or 110b of the vaporization unit 100A or 100B. The exhaust gas supplied to the superheater 120a or 120b has a higher temperature than the exhaust gas supplied to the vaporizer 110a or 110b.

[0127] As shown in FIG. 7 , in the system of the seventh embodiment, the working fluid pressurized by the supply pump 500 is preheated in the condensing heat exchanger 400, and then vaporized by heat exchange with relatively low-temperature exhaust gas in the vaporizer 110a of the vaporization unit 100A. The working fluid is then separated into gas and liquid in the gas-liquid separator 200. The gaseous working fluid separated in the gas-liquid separator 200 is supplied to the superheater 120a of the vaporization unit 100A, where it is further heated (additionally heated) by the relatively high-temperature exhaust gas, and then supplied to the expansion turbine 300. In this way, in the system of the seventh embodiment, the working fluid before being supplied to the expansion turbine 300 is additionally heated to a superheated state by the high-temperature exhaust gas in the superheater 120a, thereby preventing the generation of droplets. Furthermore, the system of this embodiment can improve waste heat recovery efficiency and system stability.

[0128] In the system of the seventh embodiment, a fluid having a boiling point lower than that of water can be used as the working fluid circulating through the heat medium circulation line RCL so that waste heat from low-temperature exhaust gas can also be recovered.

[0129] As shown in FIG. 7 , in the system of the seventh embodiment, the liquid working fluid condensed in the condensing heat exchanger 400 is pressurized to the required pressure by the supply pump 500 by driving the expansion turbine 300, and is then supplied to the condensing heat exchanger 400 for preheating before being supplied to the vaporizer 110a of the vaporization unit 100A. The working fluid preheated in the condensing heat exchanger 400 and supplied to the vaporizer 110a is heated and vaporized by the waste heat of the exhaust gas HM supplied through the exhaust gas supply line HL, and the gaseous working fluid separated in the gas-liquid separator 200 is supplied to the superheater 120a of the vaporization unit 100A. The working fluid supplied to the superheater 120a is heated to a superheated state by the high-temperature exhaust gas HM supplied through the exhaust gas supply line HL and is then supplied to the expansion turbine 300. The gaseous working fluid expands in the expansion turbine 300 to drive the turbine and generate shaft power. Furthermore, the working fluid that has been partially cooled by expansion is supplied to the condensation heat exchanger 400. In the condensation heat exchanger 400, the working fluid is further cooled (additionally cooled) and condensed by the flow of cooling water CM supplied from the cooling water supply line CL and the flow of the working fluid that has been sent out from the supply pump 500 and is not yet supplied to the evaporator 110a. The condensed working fluid in a liquid state is then supplied to the supply pump 500 and pressurized to a pressure required to drive the expansion turbine 300.

[0130] The working fluid pressurized by the supply pump 500 is supplied to the condensing heat exchanger 400, where it is preheated, and then supplied to the vaporizer 110a. In this way, the working fluid undergoes a phase change while circulating through the closed-loop heat medium circulation line RCL, thereby recovering waste heat from the exhaust gas and converting it into power.

[0131] In addition, in this embodiment, the shaft power SP generated in the expansion turbine 300 by utilizing the waste heat of the exhaust gas can be used to drive a generator to generate electricity, and the shaft power SP may also be used in a compressor to generate compressed air to be supplied to consumers on the ship.

[0132] Also, a compressor (not shown) may be configured to be connected to the expansion turbine 300 via a shaft. The compression ratio of the compressor may be determined depending on the destination within the ship where the compressed air is to be supplied.

[0133] Furthermore, a consumer CS within a ship to which compressed air is supplied may be, for example, an air lubrication system that injects air onto the outside bottom of the ship's hull. The air lubrication system injects air onto the outside bottom of the hull to form a continuous air layer between the hull and seawater, thereby reducing frictional resistance between the hull and seawater during operation and improving the ship's fuel efficiency.

[0134] The air lubrication system is configured with an air compressor (not shown) that generates compressed air to be injected onto the outside of the bottom of the hull, piping for supplying the compressed air, an air injection unit (not shown), an air layer (not shown) formed on the outside surface of the bottom of the hull, a control unit (not shown), and the like. Compressed air generated by a waste heat recovery system can also be supplied to the air lubrication system. In this embodiment, the system compresses air using the shaft power SP generated by the expansion turbine 300, and the compressed air is supplied to the air lubrication system. In this way, the compressor of the waste heat recovery system can be used instead of the air compressor of the air lubrication system, eliminating the need to provide a separate air compressor or the like in the air lubrication system. Even if an air compressor is provided in the air lubrication system, a smaller-capacity air compressor can be used because the compressed air generated in the waste heat recovery system can make up for any capacity shortfall in the air compressor.

[0135] As described above, the system of the seventh embodiment recovers waste heat from exhaust gas emitted from an engine that uses a low-flashpoint fuel by using the heat medium circulation line RCL, which is provided with the condensing heat exchanger 400 that exchanges heat among three fluid flows. The recovered waste heat can be converted into electricity or compressed air, which can be supplied to consumers on the ship, thereby improving the energy efficiency of the ship.

[0136] 8 differs from the system of the seventh embodiment in that it additionally includes a recuperator 450 that recovers thermal energy from the liquid working fluid that is separated in the gas-liquid separator 200 and flows through the liquid line LLb, and an exhaust heat heater 130b that recovers exhaust heat from the low-temperature exhaust gas. Hereinafter, a description of the same configuration as the system of the seventh embodiment will be omitted, and the following description will focus on the configuration that differs from the seventh embodiment.

[0137] 8, in the system of the eighth embodiment, a recuperator 450 is provided in the heat medium circulation line RCL to further heat (additionally heat) the working fluid that has been pressurized by the supply pump 500 and then heat exchanged in the condensing heat exchanger 400 before being supplied to the vaporizer 110b of the vaporization section 110B. In the recuperator 450, the working fluid that has been pressurized and preheated by the supply pump 500 and the condensing heat exchanger 400 is heated by heat exchange with the working fluid in a liquid state that has been separated in the gas-liquid separator 200 and flows through the liquid line LLb.

[0138] By arranging the recuperator 450 in this manner, thermal energy can be recovered from the working fluid that remains in a liquid state even when heated by the waste heat of the exhaust gas in the vaporizer 110b and does not vaporize, and the working fluid discharged from the supply pump 500 and the condensation heat exchanger 400 can be preheated before being supplied to the vaporizer 100.

[0139] In the system of the eighth embodiment, the working fluid circulating through the heat medium circulation line RCL may be, for example, an aqueous ammonia solution. When the aqueous ammonia solution is heated by heat exchange with low-temperature exhaust gas in the vaporizer 110b of the vaporization unit 110B, the ammonia, which has a low boiling point, is vaporized into a gaseous state, while water may remain in a liquid state without being vaporized. The gaseous ammonia separated in the gas-liquid separator 200 is heated to a superheated state in the superheater 120b and then supplied to the expansion turbine 300. Meanwhile, the water separated in the gas-liquid separator 200 is supplied to the recuperator 450 via the liquid line LLb, where thermal energy is recovered. The water is then supplied to the heat medium circulation line RCL upstream of the condensing heat exchanger 400, and is then supplied to the condensing heat exchanger 400 together with the ammonia discharged from the expansion turbine 300 and condensed.

[0140] In the eighth embodiment, the vaporization unit 100B further includes a waste heat heater 130b that exchanges heat between the working fluid and the low-temperature exhaust gas supplied to the superheater 120b and the vaporizer 110b via the exhaust gas supply line HL and discharged from the vaporizer 110b. A portion of the working fluid that has been pressurized by the supply pump 500 and then heat-exchanged in the condensation heat exchanger 400 is branched via a branch line RCLb, heated by the low-temperature exhaust gas in the waste heat heater 130b, and then supplied to the heat medium circulation line RCL downstream of the recuperator 450. That is, a portion of the working fluid that has been pressurized by the supply pump 500 and then preheated in the condensation heat exchanger 400 is heated in the recuperator 450 by the fluid flow in the liquid line LLb, and a portion of the branched working fluid is heated by the low-temperature exhaust gas flow in the waste heat heater 130b. These are then joined together on the heat medium circulation line RCL downstream of the recuperator 450 and supplied to the vaporizer 110b of the vaporization section 110B, thereby further improving the amount of waste heat recovered from the exhaust gas.

[0141] As described above, the system of the eighth embodiment is provided with a condensing heat exchanger 400 that exchanges heat between three fluid flows, effectively recovering waste heat from the exhaust gas and improving the thermal efficiency of the ship. This simplifies the system configuration and maximizes the thermal efficiency of the ship. Furthermore, using an aqueous ammonia solution as the working fluid of the heat transfer medium circulation line RCL facilitates replenishment and management of the working fluid. In particular, when the system of this embodiment is applied to an ammonia-fueled ship or an ammonia carrier that uses ammonia as engine fuel, ammonia as fuel or cargo can be directly used as the working fluid of the heat transfer medium circulation line RCL, eliminating the need for a separate refrigerant management system and reducing the installation costs of related equipment such as refrigerant storage tanks.

[0142] 9 to 12 are schematic diagrams showing waste heat recovery systems for exhaust gas for ships according to ninth to twelfth embodiments of the present invention, respectively.

[0143] As shown in Figures 9 to 12, the exhaust gas waste heat recovery systems of the ninth to twelfth embodiments include a heat medium circulation line RCL that is provided on a ship and through which a working fluid circulates, a vaporizer 100 that is provided in the heat medium circulation line RCL and heats and vaporizes the working fluid by heat exchange with exhaust gas discharged from an engine of the ship, a gas-liquid separator 200 that separates the working fluid heated (vaporized) in the vaporizer 100 into gas and liquid, and an expansion turbine 300 that is provided in the heat medium circulation line RCL and expands the working fluid to generate shaft power.

[0144] In the ninth to twelfth embodiments, a liquefied gas having a low flash point is supplied as fuel to an engine (not shown). The working fluid circulates through a closed-loop heat medium circulation line RCL and changes phase from liquid to gas using exhaust gas emitted from the engine that uses the liquefied gas having a low flash point as fuel as a heat source.

[0145] Ammonia and LPG have relatively high boiling points among low-flash-point liquefied gases. LPG, which is primarily composed of propane, has a flash point of −105°C and a boiling point of −42°C under standard pressure. Furthermore, the boiling point of ammonia is −33°C under standard pressure, which is higher than that of methane (LNG), which has a boiling point of −161°C under standard pressure, and hydrogen, which has a boiling point of −253°C under standard pressure. Therefore, when ammonia or LPG is supplied to an engine as fuel, only a very small amount of heat is required to heat the fuel to the required supply temperature. Therefore, the ammonia or LPG can be heated with engine coolant or the like and then supplied to the engine as fuel, without using steam generated from high-temperature exhaust gas emitted from the engine. Furthermore, since the fuel does not contain sulfur components, low-temperature corrosion is unlikely to occur, and waste heat can be recovered from exhaust gas with a temperature of 150°C or less. Therefore, in the ninth to twelfth embodiments, an organic Rankine cycle, which is suitable for recovering low-temperature waste heat, is applied to the heat medium circulation line RCL to recover waste heat from the exhaust gas discharged from the engine.

[0146] The heat medium circulation line RCL is provided with an evaporation unit 100 that heats and vaporizes the working fluid by heat exchange with exhaust gas, a gas-liquid separator 200 that separates the working fluid heated (evaporated) in the evaporation unit 100 into gas and liquid, an expansion turbine 300 that expands the gaseous working fluid separated in the gas-liquid separator 200 to generate shaft power, a condenser 400 that cools and condenses the working fluid cooled by expansion in the expansion turbine 300, a supply pump 500 that pressurizes the working fluid condensed in the condenser 400 and sends it to the evaporation unit 100, and first and second recuperators 600, 650 that heat the working fluid pressurized by the supply pump 500 and supply it to the evaporation unit 100. The first and second recuperators 600, 650 have a function of preheating the working fluid pressurized by the supply pump 500 before supplying it to the evaporation unit 100. In the first recuperator 600, heat is exchanged between the working fluid pressurized by the supply pump 500 and the working fluid that has been expanded and cooled in the expansion turbine 300 and has not yet been supplied to the condenser 400. In the second recuperators 650a, 650b, 650c, and 650d, the working fluid pressurized by the supply pump 500 is heated by waste heat supplied from a compressor, a cooling device, or the like on the ship. The liquid working fluid separated in the gas-liquid separator 200 is supplied to the heat medium circulation line RCL downstream of the expansion turbine 300 via the liquid line LL, LLc, or LLd, and is supplied to the first recuperator 600 together with the working fluid discharged from the expansion turbine 300, and then to the condenser 400.

[0147] In the systems of the ninth to twelfth embodiments, the vaporization unit 100 includes a vaporizer 110 and a superheater 120 that are arranged in accordance with the flow direction of the working fluid delivered from the supply pump 500. The exhaust gas HM supplied from the exhaust gas supply line HL is supplied to the superheater 120 of the vaporization unit 100, and then supplied to the vaporizer 110 of the vaporization unit 100. The exhaust gas supplied to the superheater 120 has a higher temperature than the exhaust gas supplied to the vaporizer 110.

[0148] 9 and 10, in the systems of the ninth and tenth embodiments, the working fluid pressurized by the supply pump 500 is preheated in the first or second recuperator 600, 650a, or 650b. The working fluid is then vaporized by heat exchange with relatively low-temperature exhaust gas in the vaporizer 110, and the vapor-liquid separation is performed in the gas-liquid separator 200. The gaseous working fluid separated in the gas-liquid separator 200 is supplied to the superheater 120 of the vaporizer 100, where it is further heated (additionally heated) by relatively high-temperature exhaust gas, and then supplied to the expansion turbine 300. In this way, in the ninth and tenth embodiments, the working fluid before being supplied to the expansion turbine 300 is additionally heated to a superheated state by the high-temperature exhaust gas in the superheater 120, thereby preventing the generation of droplets. Furthermore, the systems of the present embodiments can improve waste heat recovery efficiency and system stability.

[0149] In the systems of the ninth and tenth embodiments, a fluid having a boiling point lower than that of water can be used as the working fluid circulating through the heat medium circulation line RCL so that waste heat from low-temperature exhaust gas can also be recovered.

[0150] 9 and 10 , in the systems of the ninth and tenth embodiments, the working fluid in a liquid state condensed in the condenser 400 is pressurized by the supply pump 500 to a pressure required to drive the expansion turbine 300, and is supplied to the first or second recuperator 600, 650a, or 650b to be preheated and then supplied to the vaporizer 110 of the vaporization unit 100. The working fluid pressurized by the supply pump 500 is branched into two flows, which are supplied to the first recuperator 600 and the second recuperator 650a or 650b, respectively. In the first recuperator 600, the working fluid pressurized by the supply pump 500 is heated by heat exchange with the working fluid discharged from the expansion turbine 300 and before being supplied to the condenser 400, downstream of the junction of the heat medium circulation line RCL with the liquid line LL. In the second recuperator 650a or 650b, the working fluid pressurized by the supply pump 500 is heated by waste heat from air, cooling water, and the like discharged from other devices on the ship, such as a compressor or a cooling device. That is, in the first recuperator 600, heat is exchanged between the working fluid pressurized and discharged by the supply pump 500 and the working fluid before being supplied to the condenser 400. In addition, the second recuperator 650a or 650b recovers waste heat from other devices on the ship. The working fluid preheated in the first or second recuperator 600, 650a, or 650b and then supplied to the vaporizer 110 is supplied to the superheater 120 through the exhaust gas supply line HL and then heated and vaporized by the waste heat of the exhaust gas HM supplied to the vaporizer 110. The gaseous working fluid separated in the gas-liquid separator 200 is supplied to the superheater 120 of the vaporization unit 100. The working fluid supplied to the superheater 120 is heated to a superheated state by high-temperature exhaust gas supplied through the exhaust gas supply line HL, and then supplied to the expansion turbine 300. The gaseous working fluid expands in the expansion turbine 300 to drive the turbine and generate shaft power. The working fluid that has been partially cooled by the expansion is subjected to heat exchange in the first recuperator 600 and then supplied to the condenser 400. In the condenser 400, the working fluid is further cooled (additionally cooled) by cooling water supplied through the cooling water supply line CL, and is then condensed. The condensed liquid working fluid is then supplied to the supply pump 500.In this way, the working fluid undergoes a phase change while circulating through the closed-loop heat medium circulation line RCL, thereby recovering the waste heat of the exhaust gas and converting it into power.

[0151] In addition, in the system of the ninth embodiment, the shaft power SP generated in the expansion turbine 300 by utilizing the waste heat of the exhaust gas can be used to drive a generator to generate electricity, and the shaft power SP may also be used in a compressor to generate compressed air to be supplied to consumers on board the ship.

[0152] The system of the tenth embodiment shown in FIG. 10 differs from the system of the ninth embodiment in that a compressor 350 is additionally provided, which is connected to the expansion turbine 300 via a shaft.

[0153] As shown in FIG. 10, the system of the tenth embodiment further includes a compressor 350 that compresses air using the shaft power generated by the expansion turbine 300, and an air supply line AL that supplies air to the compressor 350.

[0154] In the system of the tenth embodiment, compressed air compressed by the compressor 350 is supplied to the second recuperator 650b through the air supply line AL to exchange heat with the working fluid, and then supplied to the consumer CS within the ship. That is, in the tenth embodiment and the system of a twelfth embodiment described below, a compressor 350 connected to the expansion turbine 300 via a shaft is provided. The compressor 350 uses shaft power to compress air to generate compressed air, and the compressed air compressed by the compressor 350 is supplied to the consumer CS within the ship. In addition, the heat of the compressed air discharged from the compressor 350 is recovered by the second recuperator 650b or 650d and used to preheat the working fluid.

[0155] Furthermore, a consumer CS within a ship to which compressed air is supplied may be, for example, an air lubrication system that injects air onto the outside bottom of the ship's hull. The air lubrication system injects air onto the outside bottom of the hull to form a continuous air layer between the hull and seawater, thereby reducing frictional resistance between the hull and seawater during operation and improving the ship's fuel efficiency.

[0156] The air lubrication system is also configured with an air compressor (not shown) for generating compressed air to be injected onto the outside bottom surface of the hull, piping for supplying the compressed air, an air injection unit (not shown), an air layer (not shown) formed on the outside surface of the bottom surface of the hull, a control unit (not shown), and other components. Compressed air generated by a waste heat recovery system can also be supplied to the air lubrication system. In this embodiment, the system compresses air using the shaft power generated by the expansion turbine 300, and the compressed air is supplied to the air lubrication system. Since the compressor of the waste heat recovery system can be used instead of the air compressor of the air lubrication system, a separate air compressor or other device is not required for the air lubrication system. Even if an air compressor is provided in the air lubrication system, a smaller-capacity air compressor can be used because the compressed air generated by the waste heat recovery system can compensate for the insufficient capacity of the air compressor. When compressed air is supplied to the air lubrication system, the compressor 350 is operated at a compression ratio of approximately 2. In this case, the compressor 350 can be configured as a single-stage centrifugal compressor.

[0157] As described above, the systems of the ninth and tenth embodiments recover waste heat from exhaust gas emitted from an engine using a low-flashpoint fuel by using the heat medium circulation line RCL provided with multiple recuperators 600, 650b and the vaporization unit 100 configured to recover waste heat in sequence according to the temperature of the exhaust gas. In addition, the recovered waste heat can be converted into electricity or compressed air and supplied to consumers on the ship, thereby improving the energy efficiency of the ship.

[0158] 11 and 12 differ from the systems of the ninth and tenth embodiments in that they additionally include a third recuperator 700 that recovers thermal energy from the liquid working fluid that is separated in the gas-liquid separator 200 and flows through the liquid line LLc or LLd, and an exhaust heat heater 130 that is provided in the vaporization section 100 and recovers exhaust heat from the low-temperature exhaust gas. Hereinafter, a description of the same configuration as the systems of the ninth and tenth embodiments will be omitted, and the following description will focus on the configuration that differs from the ninth and tenth embodiments.

[0159] 11 and 12, in the systems of the eleventh and twelfth embodiments, a third recuperator 700 is provided in the heat medium circulation line RCL to heat a working fluid that has been pressurized by the supply pump 500 and then preheated in the first or second recuperator 600, 650c, or 650d. The working fluid heated in the third recuperator 700 is supplied to the vaporizer 110. In the systems of the eleventh and twelfth embodiments, the working fluid pressurized by the supply pump 500 is branched into two streams and supplied to the first or second recuperator 600, 650c, or 650d, respectively. The working fluid discharged from the first or second recuperator 600, 650c, or 650d and joined together is heated by heat exchange with the liquid working fluid that has been separated in the gas-liquid separator 200 and flows through the liquid line LLc or LLd.

[0160] By arranging the third recuperator 700 in this manner, thermal energy can be recovered from the working fluid that remains in a liquid state without being vaporized even when heated by the waste heat of the exhaust gas in the vaporizer 110, and the working fluid discharged from the supply pump 500 and the first or second recuperator 600 or 650c or 650d can be preheated before being supplied to the vaporizer 110.

[0161] In the systems of the eleventh and twelfth embodiments, the working fluid circulating through the heat medium circulation line RCL may be, for example, an aqueous ammonia solution. When the aqueous ammonia solution is heated by heat exchange with low-temperature exhaust gas in the vaporizer 110 of the vaporization unit 100, the ammonia, which has a low boiling point, is vaporized into a gaseous state, while water may remain in a liquid state without being vaporized. The gaseous ammonia separated in the gas-liquid separator 200 is heated to a superheated state in the superheater 120 and supplied to the expansion turbine 300. Meanwhile, the water separated in the gas-liquid separator 200 is supplied to the third recuperator 700 via the liquid line LLc or LLd, where thermal energy is recovered. Thereafter, the water is supplied to the heat medium circulation line RCL downstream of the expansion turbine 300, and is supplied to the first recuperator 600 together with the ammonia discharged from the expansion turbine 300, and is then supplied to the condenser 400.

[0162] In the systems of the eleventh and twelfth embodiments, the vaporization unit 100 is further provided with a waste heat heater 130. In the waste heat heater 130, heat is exchanged between the working fluid and the low-temperature exhaust gas supplied to the superheater 120 and the vaporizer 110 via the exhaust gas supply line HL and discharged from the vaporizer 110. A portion of the working fluid that has been pressurized by the supply pump 500 and then heat-exchanged in the first recuperator 600 is branched via the branch line RCLc or RCLd, heated by the low-temperature exhaust gas in the waste heat heater 130, and then supplied to the heat medium circulation line RCL downstream of the third recuperator 700. That is, a portion of the working fluid that has been pressurized by the supply pump 500 and then preheated in the first recuperator 600 is heated in the third recuperator 700 by the fluid flow in the liquid line LLc or LLd, and a portion of the branched working fluid is heated in the waste heat heater 130 by the low-temperature exhaust gas flow. Then, these are joined together downstream of the third recuperator 700 on the heat medium circulation line RCL, and are supplied to the vaporizer 110 of the vaporization section 100. This makes it possible to further improve the amount of waste heat recovered from the exhaust gas.

[0163] Furthermore, similar to the system of the above-described tenth embodiment, the system of the twelfth embodiment is configured such that compressed air generated in the compressor 350 using shaft power is supplied to a second recuperator 650d through an air supply line AL and then supplied to a consumer CS within the ship, so that the heat of the compressed air discharged from the compressor 350 can be used to preheat the working fluid. Note that a description of the same configuration as that of the above-described eleventh embodiment will be omitted.

[0164] As described above, the system of this embodiment further improves the thermal efficiency of the ship by providing the third recuperator 700 and the exhaust heat heater 130, and can effectively recover waste heat from the exhaust gas. Furthermore, by using an aqueous ammonia solution as the working fluid of the heat transfer medium circulation line RCL, replenishment and management of the working fluid becomes easy. In particular, when the system of this embodiment is applied to an ammonia-fuel propelled ship or an ammonia carrier that uses ammonia as engine fuel, ammonia as fuel or cargo can be directly used as the working fluid of the heat transfer medium circulation line RCL, eliminating the need to install a separate refrigerant management system and reducing the installation costs of related equipment such as refrigerant storage tanks.

[0165] The present invention is not limited to the above-described embodiments, and it will be obvious to those skilled in the art to which the present invention pertains that various changes or modifications can be made without departing from the technical gist of the present invention.

Claims

1. a heat medium circulation line provided in the ship through which a working fluid circulates; and a vaporizer provided in the heat medium circulation line for heating the working fluid by heat exchange with exhaust gas discharged from an engine of the ship; and a gas-liquid separator provided in the heat medium circulation line for separating the working fluid heated by the vaporizer into gas and liquid; and an expansion turbine that expands the gaseous working fluid separated by the gas-liquid separator to generate shaft power; and a condensing heat exchanger that cools and condenses the working fluid cooled by expansion in the expansion turbine; and a supply pump provided in the heat medium circulation line to pressurize the working fluid condensed in the condensing heat exchanger and send the pressurized working fluid to the vaporizer; and a first cooling water supply line that supplies cooling water to the condensing heat exchanger to cool the working fluid; supplying a low flash point liquefied gas as fuel to the engine; the condensation heat exchanger exchanges heat among three flows: the working fluid cooled by expansion in the expansion turbine, the working fluid pressurized by the supply pump, and the cooling water in the first cooling water supply line. Exhaust gas waste heat recovery system for ships.

2. a suction pot for additionally cooling the working fluid condensed in the condensing heat exchanger before supplying it to the supply pump; and a second cooling water supply line for supplying cooling water to the suction pot for cooling the working fluid; The working fluid additionally cooled by the suction pot is supplied to the supply pump to prevent cavitation at a suction portion of the supply pump.

2. A waste heat recovery system for a marine vessel exhaust gas according to claim 1.

3. a liquid line that supplies the liquid working fluid separated by the gas-liquid separator to a side of the heat medium circulation line downstream of the expansion turbine, The liquid working fluid separated in the gas-liquid separator is supplied to the condensing heat exchanger through the liquid line together with the working fluid discharged from the expansion turbine.

3. A waste heat recovery system for a marine vessel exhaust gas according to claim 2.

4. The working fluid is a fluid that circulates through the heat medium circulation line, changes phase from a liquid to a gas using the exhaust gas as a heat source, and has a boiling point lower than that of water.

4. A waste heat recovery system for a marine vessel exhaust gas according to claim 3.

5. The present invention further comprises a recuperator provided in the heat medium circulation line, which heats the working fluid that has been pressurized by the supply pump and then heat-exchanged in the condensing heat exchanger, and supplies the working fluid to the evaporator.

4. A waste heat recovery system for a marine vessel exhaust gas according to claim 3.

6. In the recuperator, the working fluid pressurized by the supply pump and then heat-exchanged in the condensing heat exchanger is heated by heat exchange with the liquid working fluid separated in the gas-liquid separator and flowing through the liquid line.

6. A waste heat recovery system for a marine vessel exhaust gas according to claim 5.

7. Compressing air in a compressor using shaft power generated by the expansion turbine, The air compressed by the compressor is supplied to a consumer within the ship, The on-board consumer is an air lubrication system that injects air onto the outside of the bottom of the ship during operation to reduce frictional resistance with seawater.

7. A waste heat recovery system for a marine vessel exhaust gas according to claim 6.

8. The working fluid is an organic refrigerant or an aqueous ammonia solution. The waste heat recovery system for exhaust gas for a ship according to any one of claims 1 to 7.

9. The low flash point liquefied gas contains at least one of LPG and ammonia.

9. The exhaust gas waste heat recovery system for a marine vessel according to claim 8.

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