System and method for re-liquefying ammonia vapor from a ship

Abstract

A system and method for re-liquefying ammonia vapor on a vessel is disclosed. [Solution] The ammonia evaporative gas re-liquefaction system for a ship of the present invention comprises a compression unit which compresses the evaporative gas generated from ammonia in a storage tank installed on the ship, and a second compressor which further compresses the evaporative gas compressed by the first compressor, thereby compressing the evaporative gas in multiple stages; a condenser which cools the evaporative gas compressed through the compression unit; and a re-liquefaction gas recovery line which sends the ammonia cooled and condensed by the condenser to the storage tank, and is characterized in that ammonia is branched off from the re-liquefaction gas recovery line and supplied to the compression unit, thereby adjusting the temperature of the evaporative gas in the compression unit.

Description

[Technical Field]

[0001] The present invention relates to a system and method for re-liquefying an ammonia evaporative gas for a ship, and more particularly to a system and method for re-liquefying an ammonia evaporative gas for a ship that uses ammonia as fuel for its onboard engine, by compressing and cooling the evaporative gas generated from an ammonia storage tank. [Background technology]

[0002] As global warming becomes more serious, efforts are being made around the world to reduce greenhouse gas emissions. With the 1997 Kyoto Protocol, which stipulated greenhouse gas reduction obligations for developed countries, set to expire in 2020, the Paris Climate Change Accord was adopted at the 21st Conference of the Parties to the United Nations Framework Convention on Climate Change held in Paris, France in December 2015, and came into effect in November 2016. Under this agreement, 195 signatory countries agreed to take various measures to reduce greenhouse gas emissions.

[0003] In line with this global trend, there is growing interest in renewable energy (or regenerative energy) such as wind power, sunlight, solar heat, bioenergy, tidal power, and geothermal energy as non-polluting alternatives to fossil fuels and nuclear power, and various technological developments are being carried out in these fields.

[0004] Liquefied gases such as liquefied natural gas are environmentally friendly fuels that can remove or reduce air pollutants during the liquefaction process and emit fewer air pollutants when burned. As a result, the consumption of liquefied gases such as liquefied natural gas (LNG) and liquefied petroleum gas (LPG) has been rapidly increasing worldwide in recent years. Liquefied gases, which are gases liquefied at low temperatures, have a significantly reduced volume compared to their gaseous state, which has the advantage of improving storage and transportation efficiency.

[0005] Liquefied natural gas (LNG) is a colorless, transparent liquid obtained by liquefying natural gas, which is primarily composed of methane, at approximately -162°C, and its volume is approximately 1 / 600 of that of its gaseous state. This makes liquefied natural gas very efficient to transport.

[0006] The liquefaction temperature of liquefied petroleum gas (LPG) varies depending on the composition, but petroleum gas, which is mainly composed of propane, is liquefied at a low temperature of approximately -42°C at normal pressure, and can be stored in liquid form at approximately 45°C at 18 bar and 20°C at 7 bar.

[0007] Meanwhile, conventional LPG carriers and other vessels use fuel supply systems that use heavy fuel oil, such as bunker C oil, which is relatively inexpensive as propulsion fuel for ships. However, as international exhaust gas emission regulations for the use of heavy fuel oil have become stricter, these heavy fuel fuel supply systems require the installation of a separate low-sulfur residual fuel oil (LSHFO) tank, creating a need for an environmentally friendly fuel supply system that meets international environmental regulations.

[0008] In recent years, the use of fuel supply systems that use LPG or LNG and the vapor generated from them as propulsion fuel has increased on LPG or LNG carriers, and with the trend toward stricter exhaust gas emission regulations internationally, the number of general ships that use LNG and other fuels as propulsion fuel is also increasing, in addition to LPG and LNG carriers.

[0009] Typical marine engines that use LNG as fuel include gas-fueled engines such as DFDE, X-DF engines, and ME-GI engines.

[0010] The DFDE is a four-stroke engine that uses the Otto Cycle, in which relatively low-pressure natural gas of approximately 5.5 barg is injected into the combustion air inlet and pressurized as the piston rises.

[0011] The X-DF engine is a two-stroke engine that uses approximately 15 barg natural gas as fuel and employs an Otto cycle.

[0012] The ME-GI engine is a two-stroke engine that uses a diesel cycle in which high-pressure natural gas of approximately 300 barg is injected directly into the combustion chamber near the top dead center of the piston.

[0013] However, although LNG and LPG are considered to be more environmentally friendly fuels than other fossil fuels used in conventional ships, they still produce carbon dioxide when burned, and ships that use them as fuel still emit carbon dioxide during operation. Summary of the Invention [Problem to be solved by the invention]

[0014] The International Maritime Organization (IMO) is a specialized agency of the United Nations established to standardize ship routes, traffic regulations, port facilities, etc. It has set a goal of reducing greenhouse gas emissions by 50% compared to 2008 levels by 2050, and by 100% (GHG Zero Emissions) by 2100, and is expected to see stronger regulations in each country and region in response.

[0015] According to the Energy Efficiency Design Index (EEDI), the IMO's mandatory carbon dioxide reduction regulations for newly constructed ships, the initial EEDI announcement called for EEDI Phase 1, which would reduce carbon dioxide emissions by 10% from 2015, based on carbon dioxide emissions from 2013 to 2015. The regulations were then gradually strengthened every five years, with EEDI Phase 3 scheduled to be applied in 2025. However, for LPG carriers, EEDI Phase 3 will be applied ahead of schedule, starting in 2022, two years after the application of EEDI Phase 2. Because regulations on carbon dioxide emissions from ships are being tightened so rapidly, it may be difficult to meet the carbon dioxide emission regulations simply by using LNG or LPG as fuel.

[0016] As a result, various researches have been conducted on environmentally friendly marine fuels that can reduce carbon dioxide emissions, and recently, research and development has been conducted on technology for marine engines that can use ammonia as fuel along with fuels such as LNG and LPG.

[0017] Ammonia (NH3) is a substance in which three hydrogen atoms are bonded to one nitrogen atom. Because it forms strong hydrogen bonds between molecules, it is easily liquefied, and its boiling point at normal pressure is -33.34°C and its melting point is -77.73°C.

[0018] Ammonia is easier to store than LNG and has slightly lower specific energy and energy density than conventional HFO, but it does not emit carbon dioxide, so it is attracting attention as an environmentally friendly marine fuel in light of strengthened international standards on greenhouse gas emissions.

[0019] Ammonia has a boiling point of -33.34°C, which is higher than that of LNG, but because its boiling point is higher than that at room temperature, evaporation gas is generated from storage tanks that store ammonia as fuel for ships.

[0020] The present invention proposes a system that effectively re-liquefies the evaporative gas generated from ammonia supplied as fuel, thereby preventing fuel waste and safely maintaining pressure in the storage tank. [Means for solving the problem]

[0021] In order to solve the above-mentioned problems, one embodiment of the present invention provides a compression unit that compresses evaporated gas in multiple stages, the compression unit including a first compressor that receives and compresses evaporated gas generated from ammonia in a storage tank provided on a ship, and a second compressor that additionally compresses the evaporated gas compressed by the first compressor;

[0022] a condenser for cooling the evaporative gas pressurized through the compression unit; and

[0023] a re-liquefaction gas recovery line that sends the ammonia cooled and condensed in the condenser to a storage tank;

[0024] A reliquefaction system for ammonia evaporated gas on a ship is provided, characterized in that ammonia in a reliquefaction gas recovery line is branched off and supplied to a compression unit, and the evaporated gas temperature of the compression unit is adjusted.

[0025] Preferably, the system further comprises: a temperature adjustment line that branches off ammonia from the reliquefaction gas recovery line, compresses it in the first compressor, and supplies the evaporated gas to be sent to the second compressor as evaporated gas; a heat exchanger that is provided in the reliquefaction gas recovery line and additionally cools the ammonia condensed in the condenser; and a first pressure relief valve that is provided in the temperature adjustment line and reduces the pressure of the ammonia branched off from the reliquefaction gas recovery line; and the ammonia depressurized by the first pressure relief valve passes through the heat exchanger to exchange heat with ammonia in the reliquefaction gas recovery line, and is then mixed with the evaporated gas downstream of the first pressure relief valve.

[0026] Preferably, the first pressure relief valve is controlled in a cascade control manner by comparing the discharge temperature of ammonia downstream of the first pressure relief valve in the temperature adjustment line with the discharge temperature of ammonia downstream of the heat exchanger in the reliquefaction gas recovery line.

[0027] Preferably, the compression unit is a three-stage multi-stage compressor further including a third compressor to which the evaporated gas compressed through the first and second compressors is supplied and compressed, and further includes an intercooler to which the evaporated gas compressed by the second compressor is supplied, cooled, and then supplied to the third compressor.

[0028] Preferably, the system further comprises: a side stream line that branches off the ammonia in the reliquefied gas recovery line and sends it as evaporated gas to the first compressor of the compression unit; a heat exchanger that is provided in the reliquefied gas recovery line and that additionally cools the ammonia condensed in the condenser; and a first pressure relief valve that is provided in the side stream line and that reduces the pressure of the ammonia branched off from the reliquefied gas recovery line; and the ammonia depressurized by the first pressure relief valve is passed through the heat exchanger to exchange heat with the ammonia in the reliquefied gas recovery line, and then mixed with the evaporated gas upstream of the compression unit and supplied to the first compressor.

[0029] Preferably, the first pressure relief valve is controlled in a cascade control manner by comparing the discharge temperature of ammonia downstream of the first pressure relief valve in the side stream line with the discharge temperature of ammonia downstream of the heat exchanger in the reliquefied gas recovery line.

[0030] Preferably, the compressor further comprises an intercooler which receives and cools the evaporated gas compressed by the first compressor and then supplies the cooled evaporated gas to the second compressor.

[0031] Preferably, the system further comprises: a receiver provided in the reliquefied gas recovery line between the condenser and the heat exchanger and for storing the ammonia cooled by the condenser; a vent line for discharging the gas separated from the receiver; and a control valve provided in the vent line, wherein the control valve is controlled in accordance with the ammonia level detected in the receiver to adjust the ammonia level inside the receiver.

[0032] Preferably, the system further comprises a second pressure relief valve provided in the reliquefied gas recovery line for reducing the pressure of the ammonia that has been additionally cooled through the heat exchanger, and the second pressure relief valve is controlled in accordance with a value selected from the discharge pressure of ammonia downstream of the compression unit and the pressure of ammonia upstream of the second pressure relief valve.

[0033] Preferably, the system further includes a knock-out drum that receives the evaporated gas discharged from the storage tank and supplies it to the first compressor of the compression unit, and liquid contained in the evaporated gas is separated and discharged from the knock-out drum.

[0034]

[0035] Another embodiment of the present invention is a method for compressing evaporated gas generated from ammonia in a storage tank installed on a ship in multiple stages using a compression unit including a first compressor and a second compressor,

[0036] The evaporated gas compressed through the compression unit is condensed in a condenser and sent to the storage tank along a re-liquefied gas recovery line;

[0037] A method for reliquefying ammonia evaporated gas from a ship is provided, in which ammonia in a reliquefaction gas recovery line is branched off and supplied to a compression unit, and the temperature of the evaporated gas in the compression unit is adjusted.

[0038] Preferably, the ammonia in the reliquefaction gas recovery line is branched to a temperature adjustment line, compressed by the first compressor, and then sent to the second compressor as evaporated gas, and the temperature of the evaporated gas sent to the second compressor is adjusted, the reliquefaction gas recovery line is provided with a heat exchanger that additionally cools the ammonia condensed in the condenser, the temperature adjustment line branches off from the reliquefaction gas recovery line upstream of the heat exchanger, and the ammonia branched to the temperature adjustment line is depressurized by a first pressure relief valve, passes through the heat exchanger to exchange heat with the ammonia in the reliquefaction gas recovery line, and then is mixed with the evaporated gas downstream of the first compressor.

[0039] Preferably, the ammonia in the reliquefied gas recovery line is branched off into a side stream line and sent to the first compressor of the compression unit as evaporated gas, and the temperature of the evaporated gas sent to the compression unit is adjusted, the reliquefied gas recovery line is provided with a heat exchanger that additionally cools the ammonia condensed in the condenser, the side stream line branches off from the reliquefied gas recovery line upstream of the heat exchanger, the ammonia branched off into the side stream line is depressurized by a first pressure relief valve, passes through the heat exchanger and exchanges heat with the ammonia in the reliquefied gas recovery line, and is then mixed with the evaporated gas upstream of the compression unit and supplied to the first compressor.

[0040] Preferably, the first pressure relief valve is controlled in a cascade control manner by comparing the ammonia discharge temperature downstream of the first pressure relief valve with the ammonia discharge temperature downstream of the heat exchanger in the re-liquefied gas recovery line. [Effects of the Invention]

[0041] In the present invention, ammonia, which is an environmentally friendly fuel, is supplied as fuel for a ship's engine, thereby reducing greenhouse gas emissions when the ship is operating and making it possible to meet regulatory standards set forth in international agreements.

[0042] In particular, the evaporated gas generated in the storage tank where ammonia is stored is pressurized, cooled, and re-liquefied, and then recovered or supplied as fuel, thereby safely maintaining the pressure in the storage tank and preventing the waste of ammonia fuel.

[0043] Furthermore, a portion of the condensed ammonia is branched off and re-liquefied to form a main ammonia stream, which is then heat exchanged in a heat exchanger and sent between the first and second compressors again to adjust the temperature of the compressed ammonia evaporative gas, or sent upstream of the compression unit to adjust the temperature of the ammonia evaporative gas supplied to the first compressor. This maximizes the efficiency of sidestream cold heat recovery and reduces the system installation and operation costs. [Brief explanation of the drawings]

[0044] [Figure 1] 1 is a schematic diagram showing a re-liquefaction system for an ammonia evaporated gas of a ship according to a first embodiment of the present invention.

[0045] [Figure 2] FIG. 4 is a schematic diagram showing a re-liquefaction system for an ammonia evaporated gas on a ship according to a second embodiment of the present invention. Means for carrying out the invention

[0046] For a full understanding of the operating advantages and objects attained by the embodiments of the present invention, reference should be made to the accompanying drawings and the contents thereof, which illustrate the embodiments of the present invention.

[0047] The structure and operation of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that, when referring to components in the drawings of this specification, the same components are denoted by the same reference numerals whenever possible, even if they appear in different drawings.

[0048]

[0049] Hereinafter, the term "ship" as used in the present invention refers to any ship equipped with an engine that uses ammonia as fuel, and includes ships capable of self-propulsion such as LPG carriers, LNG carriers, liquid hydrogen carriers, ammonia carriers, container carriers, crude oil carriers, bulk carriers for minerals and grains, special ships such as offshore wind turbine installation vessels, and roll-on / roll-off ships (Roll-on / Roll-off ships), as well as floating marine structures that do not have self-propulsion capabilities.

[0050] "Ammonia-fueled engines" include both engines for propulsion of ships and engines for power generation, including those that are simultaneously fueled with other marine fuels such as LNG, LPG, HFO, MGO, and diesel oil, as well as those that are fueled solely with ammonia. Two or more propulsion engines and two or more power generation engines may be provided as necessary.

[0051] Furthermore, this embodiment can be applied to a reliquefaction system for any liquefied gas that is liquefied at a cryogenic temperature, transported, and generates evaporated gas during storage. Examples of such liquefied gases include LNG (Liquefied Natural Gas), LEG (Liquefied Ethane Gas), LPG (Liquefied Petroleum Gas), liquefied ethylene gas, and liquefied propylene gas. In the following embodiment, ammonia, one of the typical liquefied gases, will be used as an example.

[0052]

[0053] FIG. 1 is a schematic diagram showing a re-liquefaction system for an ammonia evaporated gas on a ship according to a first embodiment of the present invention.

[0054] As shown in FIG. 1, the ammonia vapor re-liquefaction system of the first embodiment of the present invention is configured to re-liquefy ammonia vapor generated from a storage tank T installed on a ship, which stores ammonia to be supplied as fuel for the ship's engines, and recover the ammonia vapor in the tank or supply it as fuel. Because ammonia gas is toxic, classification society regulations require that the design pressure of the storage tank be increased or that a treatment system for the vapor generated in the storage tank be installed so that the system can be operated without venting even at room temperature. The system of this embodiment is a system for re-liquefying ammonia vapor, in which ammonia vapor generated in the storage tank is compressed in a compression unit 100 via a knock-out drum 400, cooled and condensed in a condenser 200, and then recovered via a receiver 250, a heat exchanger 300, etc.

[0055] As shown in Figure 1, the system of the present invention includes a compression unit 100 that compresses the evaporated gas in multiple stages, including a first compressor 100A that is supplied with and compresses the evaporated gas generated from ammonia in a storage tank T installed on a ship, and a second compressor 100B that further compresses the evaporated gas compressed by the first compressor, a condenser 200 that cools the evaporated gas compressed by the compression unit 100, a re-liquefaction gas recovery line RL that sends the ammonia cooled and condensed by the condenser 200 to the storage tank, and a temperature adjustment line TL that branches off the ammonia from the re-liquefaction gas recovery line RL, compresses it in the first compressor, and then sends it to the second compressor as evaporated gas.

[0056] The ammonia vapor discharged from the storage tank T is supplied to the first compressor 100A of the gas-only compression unit via the knock-out drum 400. The liquid (condensate) contained in the vapor is separated from the knock-out drum and discharged to the bottom of the drum.

[0057] The compression unit 100 may be a three-stage multi-stage compressor including a first compressor 100A that receives and compresses the evaporative gas, a second compressor 100B that additionally pressurizes the evaporative gas compressed by the first compressor, and a third compressor 100C that further compresses the evaporative gas compressed by the second compressor and sends it to a condenser. The compression unit may be, for example, a three-stage centrifugal compressor including the first to third compressors, or a three-stage reciprocating compressor with reciprocating pistons. The number of stages in the compression unit may be increased as necessary.

[0058] The evaporated gas compressed through the compression unit 100 is supplied to the condenser 200 and cooled. In the condenser 200, the evaporated gas compressed in the compression unit 100 is cooled and re-liquefied by, for example, heat exchange with a cold heat source, thereby cooling the ammonia evaporated gas.

[0059] The ammonia cooled and condensed in the condenser 200 is received in a sub-cooled state along the re-liquefaction gas recovery line RL in the receiver 250. Since the ammonia sent to the receiver 250 is in a sub-cooled state, basically no evaporated gas is generated, but some vapor may be generated due to nitrogen or air, so the gas is separated from the condensed ammonia in the receiver and vented through the vent line CL, and the liquid is sent to a storage tank along the re-liquefaction gas recovery line RL.

[0060] The vent line CL is equipped with a control valve CV, which is controlled according to the ammonia level detected in the receiver. By controlling the control valve, the gas discharged through the vent line is adjusted, and the ammonia level inside the receiver is also adjusted.

[0061] A heat exchanger 300 is provided downstream of the receiver in the reliquefied gas recovery line RL, and additionally cools the ammonia condensed in the condenser. The heat exchanger in the system of this embodiment may be, for example, a plate heat exchanger or a diffusion-bonded printed circuit heat exchanger (PCHE).

[0062] To ensure a cold source for the heat exchanger 300, a temperature control line TL branches off from the reliquefied gas recovery line RL upstream of the heat exchanger. A first pressure relief valve JTV1 is provided in the temperature control line TL to depressurize the ammonia branched from the reliquefied gas recovery line. A side stream of ammonia branched from the temperature control line TL, depressurized and cooled by the first pressure relief valve JTV1, is supplied to the heat exchanger 300 and exchanges heat with the main stream of ammonia flowing along the reliquefied gas recovery line RL. That is, in the heat exchanger 300, the ammonia in the reliquefied gas recovery line RL exchanges heat with the ammonia branched from the temperature control line TL and cooled by depressurization by the first pressure relief valve JTV1. The ammonia that passes through the heat exchanger 300 along the temperature control line TL joins the first compressor 100A of the compression unit downstream, is mixed with the evaporated gas compressed by the first compressor, and is sent to the second compressor 100B. In this way, the reliquefaction system of the present invention utilizes a plate heat exchanger or a diffusion-bonded printed circuit heat exchanger (PCHE) to cool ammonia by heat exchange between the side stream and the mainstream without a quenching operation, thereby maximizing cycle efficiency.

[0063] The first pressure relief valve JTV1 is controlled by a cascade control method by comparing the ammonia discharge temperature T1 downstream of the first pressure relief valve in the temperature adjustment line with the ammonia discharge temperature T2 downstream of the heat exchanger in the reliquefaction gas recovery line. This makes it possible to adjust the temperature of the evaporated gas compressed by the first compressor and sent to the second compressor without providing a separate intercooler between the first and second compressors.

[0064] Therefore, the evaporative gas compressed by the first compressor 100A of the compression unit is branched off through the temperature adjustment line TL and mixed with the decompressed ammonia to adjust the temperature, and then supplied to the second compressor 100B where it is compressed. An intercooler 150 is provided between the second and third compressors of the compression unit, and the evaporative gas compressed by the second compressor is cooled by the intercooler 150 before being compressed by the third compressor. In this way, the system of the present invention uses a three-stage multi-stage compressor, but a side stream is provided between the first and second stage compressors, and an intercooler is provided between the second and third stage compressors to adjust the temperature of the evaporative gas while preventing overheating.

[0065] The ammonia evaporated gas compressed through the compression units up to the third compressor 100C is supplied to the condenser 200 where it is cooled and condensed, and passes through the receiver 250 and the heat exchanger 300.

[0066] The reliquefied gas recovery line RL is provided with a second pressure relief valve JTV2 that depressurizes the ammonia that has been additionally cooled through the heat exchanger 300. The second pressure relief valve JTV2 is controlled by a pressure value (pressure control), and is controlled according to a select function selected from ammonia discharge pressure PT1 downstream of the compression unit, i.e., the third compressor, and ammonia pressure PT2 upstream of the second pressure relief valve.

[0067] After being cooled by the heat exchanger 300, the ammonia is decompressed through the second pressure relief valve JTV2 and collected in the storage tank T, sent to the fuel supply line, and immediately supplied as fuel to the engine.

[0068] As described above, in the first embodiment of the present invention, the evaporation gas generated from the ammonia supplied as fuel is reliquefied, thereby maintaining the pressure of the storage tank and preventing ammonia waste. In particular, a portion of the condensed ammonia is branched off and heat exchanged with the main stream of reliquefied ammonia in a heat exchanger, and then sent back between the first and second compressors to use for adjusting the temperature of the compressed ammonia evaporation gas. This maximizes the efficiency of recovering cold energy from the side stream, reduces the amount of equipment in the system, lowers installation costs, and contributes to securing space on board the ship.

[0069]

[0070] Next, FIG. 2 is a schematic diagram showing a re-liquefaction system for ammonia evaporated gas on a ship according to a second embodiment of the present invention.

[0071] As shown in FIG. 2, the ammonia evaporative gas re-liquefaction system of the second embodiment of the present invention is configured to re-liquefy ammonia evaporative gas generated from a storage tank T installed on a ship that stores ammonia to be supplied as fuel for the ship's engines, and recover the ammonia evaporative gas in the storage tank or supply it as fuel. Because ammonia gas is toxic, classification society regulations require that the design pressure of the storage tank be increased or that a treatment system for the evaporative gas generated in the storage tank be installed so that the system can be operated without venting even at room temperature. The system of this embodiment is a system for re-liquefying ammonia evaporative gas, in which ammonia evaporative gas generated in the storage tank is compressed in a compression unit 100 via a knock-out drum 400, cooled and condensed in a condenser 200, and then recovered via a receiver 250, a heat exchanger 300, etc.

[0072] As shown in Figure 2, the system of the present invention is equipped with a compression unit 100 that compresses the evaporated gas in multiple stages, including a first compressor 100A that is supplied with and compresses the evaporated gas generated from ammonia in a storage tank T provided on the ship, and a second compressor 100B that additionally compresses the evaporated gas compressed by the first compressor, a condenser 200 that cools the evaporated gas compressed by the compression unit 100, a re-liquefied gas recovery line RL that sends the ammonia cooled and condensed by the condenser 200 to the storage tank, and a side stream line BL that branches off the ammonia from the re-liquefied gas recovery line RL and supplies it to the first compressor as evaporated gas upstream of the compression unit.

[0073] The ammonia vapor discharged from the storage tank T is supplied to the first compressor 100A of the gas-only compression unit along the gas delivery line GL via the knock-out drum 400. The liquid contained in the vapor may be separated from the knock-out drum and discharged to the bottom of the drum.

[0074] The compression unit 100 may be a two-stage multi-stage compressor including a first compressor 100A that receives and compresses the evaporative gas, and a second compressor 100B that additionally compresses the evaporative gas compressed by the first compressor. The compression unit may be, for example, a two-stage centrifugal compressor including first and second compressors, or a two-stage reciprocating compressor with reciprocating pistons. The number of stages in the compression unit may be increased as necessary.

[0075] The evaporated gas compressed by the compression unit 100 is supplied to the condenser 200 and cooled. The condenser 200 cools and re-liquefies the evaporated gas compressed by the compression unit 100, and exchanges heat with a cold source to cool, for example, ammonia evaporated gas.

[0076] The ammonia cooled and condensed in the condenser 200 is received in a sub-cooled state along the re-liquefaction gas recovery line RL in the receiver 250. Since the ammonia sent to the receiver 250 is in a sub-cooled state, essentially no evaporated gas is generated, but some vapor may be generated due to nitrogen or air, so the receiver separates the gas from the condensed ammonia and vents it through the vent line CL, and the liquid is sent to a storage tank along the re-liquefaction gas recovery line RL.

[0077] The vent line CL is equipped with a control valve CV, which is controlled according to the ammonia level detected in the receiver. By controlling the control valve, the amount of gas discharged through the vent line is adjusted, and the ammonia level inside the receiver is also adjusted.

[0078] The reliquefied gas recovery line RL is provided with a heat exchanger 300 downstream of the receiver to additionally cool the ammonia condensed in the condenser. The heat exchanger in the system of this embodiment may be, for example, a plate heat exchanger or a diffusion-bonded printed circuit heat exchanger (PCHE).

[0079] To ensure a cold source for the heat exchanger 300, a side stream line BL branches off from the reliquefied gas recovery line RL upstream of the heat exchanger. A first pressure relief valve JTV1 is provided on the side stream line BL to depressurize the ammonia branched off from the reliquefied gas recovery line. The ammonia stream (side stream) branched off to the side stream line BL, depressurized and cooled by the first pressure relief valve JTV1, is supplied to the heat exchanger 300 and exchanges heat with the main stream of ammonia flowing along the reliquefied gas recovery line RL. That is, in the heat exchanger 300, the ammonia from the reliquefied gas recovery line RL is heat exchanged with the ammonia branched off to the side stream line BL, depressurized and cooled by the first pressure relief valve JTV1. The ammonia that passes through the heat exchanger 300 along the side stream line BL is sent to the upstream stage of the compression unit, where it is mixed with the vaporized gas flowing from the storage tank through the knockout drum and introduced into the first compressor 100A of the compression unit, and then introduced into the first compressor. Thus, the reliquefaction system of the present invention utilizes a plate heat exchanger or a diffusion-bonded printed circuit heat exchanger (PCHE) without a quenching operation to cool ammonia by heat exchange between the side stream and the main stream, thereby maximizing cycle efficiency, and sending the side stream back upstream of the compression unit to adjust the temperature of the evaporated gas supplied to the compression unit.

[0080] The first pressure relief valve JTV1 is controlled using a cascade control method by comparing the ammonia discharge temperature T1 downstream of the first pressure relief valve in the temperature adjustment line with the ammonia discharge temperature T2 downstream of the heat exchanger in the reliquefaction gas recovery line.

[0081] As a result, the evaporative gas that has passed through the knockout drum is branched off via side stream BL and mixed with decompressed ammonia, allowing its temperature to be adjusted, and then compressed in first compressor 100A. An intercooler 150 is provided between the first and second compressors of the compression unit, and the evaporative gas compressed in the first compressor is cooled through intercooler 150 before being supplied to the second compressor. In this way, the system of the present invention uses a two-stage multistage compressor, and is provided with a side stream that is supplied from a side stream line upstream of the compression unit, and an intercooler is provided between the first and second stage compressors to adjust the temperature of the evaporative gas while preventing overheating.

[0082] The ammonia vapor compressed through the compression unit is supplied to the condenser 200 where it is cooled and condensed, and then passes through the receiver 250 and the heat exchanger 300 .

[0083] The reliquefied gas recovery line RL is provided with a second pressure relief valve JTV2 that depressurizes the ammonia that has been additionally cooled through the heat exchanger 300. The second pressure relief valve JTV2 is controlled by a pressure value (pressure control), and is controlled according to a select function selected from the ammonia discharge pressure PT1 downstream of the compression unit, i.e., the third compressor, and the ammonia pressure PT2 upstream of the second pressure relief valve.

[0084] After being cooled in the heat exchanger 300, the ammonia passes through the second pressure relief valve JTV2 and is compressed, recovered in the storage tank T, sent to the fuel supply line, and immediately supplied as fuel to the engine.

[0085] As described above, the second embodiment of the present invention re-liquefies the evaporative gas generated from ammonia supplied as fuel, thereby preventing ammonia waste while maintaining the pressure in the storage tank. In particular, a portion of the condensed ammonia is branched off and heat-exchanged with the main stream of re-liquefied ammonia in a heat exchanger. The branched ammonia is then returned to the upstream stage of the compression unit and used to adjust the temperature of the ammonia evaporative gas introduced into the compression unit. This maximizes the efficiency of cold recovery from the sidestream, prevents overheating in the compression unit, reduces the amount of equipment required in the system, and contributes to reducing installation costs and securing space on board the ship. By returning the branched ammonia to the first and second compressors and using it to adjust the temperature of the compressed ammonia evaporative gas, this maximizes the efficiency of cold recovery from the sidestream, reduces the amount of equipment required in the system, and contributes to securing space on board the ship.

[0086]

[0087] 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 modifications and changes can be made without departing from the technical gist of the present invention.

Claims

1. a compression unit that compresses the evaporated gas in multiple stages, the compression unit including a first compressor that is supplied with and compresses evaporated gas generated from ammonia in a storage tank provided on the ship, and a second compressor that additionally compresses the evaporated gas compressed by the first compressor; a condenser for cooling the evaporative gas compressed through the compression unit; and a re-liquefaction gas recovery line that sends the ammonia cooled and condensed in the condenser to a storage tank; The ammonia in the re-liquid gas recovery line is branched and supplied to the compression unit, and the evaporation gas temperature of the compression unit is adjusted. Ammonia vapor re-liquefaction system for ships.

2. a temperature adjustment line for branching off the ammonia in the re-liquefied gas recovery line, compressing it in the first compressor, and then supplying the evaporated gas to be sent to the second compressor as evaporated gas; and a heat exchanger provided in the reliquefied gas recovery line for additionally cooling the ammonia condensed in the condenser; and a first pressure relief valve provided in the temperature adjustment line to reduce the pressure of the ammonia branched off from the reliquefied gas recovery line; The ammonia decompressed by the first pressure relief valve is heat exchanged with the ammonia in the reliquefied gas recovery line through the heat exchanger, and then mixed with the evaporated gas downstream of the first pressure relief valve.

2. The system for re-liquefying ammonia evaporated gas on a ship according to claim 1.

3. the first pressure relief valve is controlled by a cascade control method by comparing the discharge temperature of ammonia downstream of the first pressure relief valve in the temperature adjustment line with the discharge temperature of ammonia downstream of the heat exchanger in the reliquefaction gas recovery line, 3. The system for re-liquefying ammonia evaporated gas on a ship according to claim 2.

4. the compression unit is a three-stage multi-stage compressor further including a third compressor to which the evaporated gas compressed through the first and second compressors is supplied and compressed, The refrigerant supply system further includes an intercooler that supplies the evaporated gas pressurized by the second compressor to the third compressor after cooling the evaporated gas.

4. The system for re-liquefying ammonia evaporated gas on a ship according to claim 3.

5. a side stream line for branching off the ammonia from the re-liquefied gas recovery line and sending it as evaporated gas to the first compressor of the compression unit; and a heat exchanger provided in the reliquefied gas recovery line for additionally cooling the ammonia condensed in the condenser; and a first pressure relief valve provided in the side stream line to reduce the pressure of the ammonia branched off from the re-liquefied gas recovery line; The ammonia decompressed by the first pressure relief valve is heat exchanged with the ammonia in the reliquefied gas recovery line through the heat exchanger, and then mixed with the evaporated gas upstream of the compression unit and supplied to the first compressor.

2. The system for re-liquefying ammonia evaporated gas on a ship according to claim 1.

6. the first pressure relief valve is controlled by a cascade control method by comparing ammonia discharge temperature downstream of the first pressure relief valve in the side stream line with ammonia discharge temperature downstream of a heat exchanger in the reliquefied gas recovery line.

6. The system for re-liquefying ammonia evaporated gas on a ship according to claim 5.

7. The compressor further includes an intercooler that receives and cools the evaporated gas compressed by the first compressor and then supplies it to the second compressor.

7. The system for re-liquefying ammonia evaporated gas on a ship according to claim 6.

8. a receiver provided in the reliquefied gas recovery line between the condenser and the heat exchanger, for receiving the ammonia cooled by the condenser; and a vent line for discharging separated gas from the receiver; and a control valve provided in the vent line; The control valve is controlled in accordance with the ammonia liquid level detected in the receiver, and the ammonia liquid level inside the receiver is adjusted.

10. The system for re-liquefying ammonia evaporated gas on a ship according to claim 2 or 5.

9. a second pressure relief valve provided in the reliquefied gas recovery line to reduce the pressure of the ammonia that has been additionally cooled through the heat exchanger; The second pressure relief valve is controlled in response to a value selected from a discharge pressure of ammonia downstream of the compression unit and a pressure of ammonia upstream of the second pressure relief valve.

9. The system for re-liquefying ammonia evaporated gas on a ship according to claim 8.

10. The apparatus further includes a knock-out drum that receives the evaporated gas discharged from the storage tank and supplies the evaporated gas to the first compressor of the compression unit, and liquid contained in the evaporated gas is separated and discharged from the knock-out drum.

10. The system for re-liquefying ammonia evaporated gas on a ship according to claim 9.

11. The evaporated gas generated from the ammonia in the storage tank provided on the ship is compressed in multiple stages by a compression unit including a first compressor and a second compressor, The evaporated gas compressed through the compression unit is condensed in a condenser and sent to the storage tank along a re-liquefied gas recovery line; The ammonia in the reliquefied gas recovery line is branched off and supplied to the compression unit, and the temperature of the evaporated gas in the compression unit is adjusted. A method for re-liquefying ammonia vapor from a ship.

12. The ammonia in the reliquefaction gas recovery line is branched to a temperature adjustment line, compressed by the first compressor, and then sent to the second compressor as evaporated gas, and the temperature of the evaporated gas sent to the second compressor is adjusted; The re-liquefied gas recovery line is provided with a heat exchanger for additionally cooling the ammonia condensed in the condenser, The temperature adjustment line branches off from the reliquefied gas recovery line upstream of the heat exchanger, and the ammonia branched off to the temperature adjustment line is decompressed by a first pressure relief valve, passes through the heat exchanger, exchanges heat with the ammonia in the reliquefied gas recovery line, and is then mixed with the evaporated gas downstream of the first compressor. The method for re-liquefying ammonia evaporated gas from a ship according to claim 11.

13. branching the ammonia in the re-liquid gas recovery line to a side stream line and sending it as evaporated gas to a first compressor of the compression unit; adjusting the temperature of the evaporated gas sent to the compression unit; The re-liquefied gas recovery line is provided with a heat exchanger for additionally cooling the ammonia condensed in the condenser, the side stream line branches off from the reliquefied gas recovery line upstream of the heat exchanger; the ammonia branched to the side stream line is decompressed by a first pressure relief valve, passes through the heat exchanger to exchange heat with the ammonia in the reliquefied gas recovery line, and is then mixed with the evaporated gas upstream of the compression unit and supplied to the first compressor. The method for re-liquefying ammonia evaporated gas from a ship according to claim 11.

14. The first pressure relief valve is controlled by a cascade control method by comparing the ammonia discharge temperature downstream of the first pressure relief valve with the ammonia discharge temperature downstream of the heat exchanger of the re-liquefied gas recovery line. The method for re-liquefying ammonia evaporated gas from a ship according to claim 12 or 13.

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