Marine LNG engine gas supply system

Abstract

The application discloses a marine LNG engine gas supply system, which comprises a storage tank for storing natural gas, a gasifier and a first compressor for compressing gaseous natural gas, the first compressor comprises a first compressor suction port and a first compressor discharge port, the first compressor discharge port is used for connecting a natural gas engine, and the marine LNG engine gas supply system further comprises a reliquefaction system, the reliquefaction system comprises at least one second compressor for compressing gaseous natural gas, at least one heat recovery heat exchanger and a throttling valve. The marine LNG engine gas supply system has the advantages that the heat recovery heat exchanger is provided, the heat discharged by the reliquefaction system can be used to heat and gasify liquid natural gas, the cold source quality of the reliquefaction system and the heat source quality of the gas supply system can be improved, the size of the heat exchanger is small, and the exhaust temperature of the gas supply system can be improved.

Description

Technical Field

[0001] This invention relates to the field of engine air supply systems, and more specifically to a marine LNG engine air supply system. Background Technology

[0002] Compared to engines using conventional fuels, natural gas engines emit fewer pollutants. However, when ships use natural gas engines, they need to carry large storage tanks for storing cryogenic liquefied natural gas. These tanks inevitably absorb heat from the outside environment, causing the liquefied natural gas to vaporize. Therefore, they must be reliquefied periodically using a reliquefaction unit. At the same time, when liquefied natural gas is supplied to the engine, it must first be vaporized into gaseous natural gas before being transferred to the engine. Both the reliquefaction unit and the vaporization unit include one or more heat exchangers, which not only occupy a large amount of ship space and have high costs, but also have low overall thermal efficiency. Summary of the Invention

[0003] The present invention mainly addresses the technical problems existing in the prior art, thereby providing a marine LNG engine gas supply system with a heat recovery heat exchanger that can use the heat emitted from the reliquefaction system to heat and vaporize liquefied natural gas. This system can improve both the cold source quality of the reliquefaction system and the heat source quality of the gas supply system, resulting in a smaller heat exchanger size and increased exhaust temperature of the gas supply system.

[0004] The present invention solves the technical problems existing in the prior art through the following technical solution:

[0005] A marine LNG engine gas supply system includes a storage tank for storing natural gas, a booster pump, a vaporizer, and a first compressor for compressing gaseous natural gas. The booster pump delivers the liquefied natural gas stored in the storage tank to the vaporizer. The liquefied natural gas in the vaporizer can absorb heat from the outside and vaporize through the vaporizer. The first compressor includes a first compressor intake port and a first compressor exhaust port. The first compressor exhaust port is connected to the natural gas engine. The marine LNG engine gas supply system also includes a reliquefaction system. The vaporization system includes at least one second compressor for compressing gaseous natural gas, at least one heat recovery heat exchanger, and a throttle valve. The throttle valve includes a throttle valve inlet and a throttle valve outlet. The second compressor includes a second compressor suction port and a second compressor discharge port. The outlet of the booster pump is connected to one end of the vaporizer, and the other end of the vaporizer is connected to the suction port of the second compressor. This allows the vaporizer to draw liquefied natural gas from the storage tank and transfer the heat absorbed by the vaporizer from the outside to the liquefied natural gas, causing the liquefied natural gas to vaporize and be sent to the second compressor.

[0006] The heat recovery heat exchanger includes a first flow channel and a second flow channel. Each of the first and second flow channels has an inlet and an outlet. The fluid in the two flow channels can transfer heat through the heat recovery heat exchanger. The exhaust port of the second compressor is fluidly connected to the inlet of the first flow channel, the outlet of the first flow channel is fluidly connected to the inlet of the throttle valve, and the outlet of the throttle valve is fluidly connected to the storage tank. Natural gas is throttled to a low temperature and low pressure state in the throttle valve and then returns to the storage tank.

[0007] The outlet of the booster pump is also fluidly connected to the inlet of the second flow channel of the heat recovery heat exchanger, and the outlet of the second flow channel of the heat recovery heat exchanger is fluidly connected to the suction port of the first compressor; so that when the liquefied natural gas flows through the second flow channel, it can absorb heat from the gaseous natural gas in the first flow channel and vaporize into gas before entering the first compressor.

[0008] As a preferred technical solution of the present invention, the reliquefaction system includes at least two second compressors connected in series and a number of heat recovery heat exchangers equal to the number of the second compressors. The inlet of the first flow channel of each heat recovery heat exchanger is in fluid communication with the inlet of the second compressor. The second flow channels of the multiple heat recovery heat exchangers are arranged in series, so that the high-temperature gaseous natural gas discharged from the exhaust port of each second compressor can release heat into the natural gas in the second flow channel through the heat recovery heat exchanger and liquefy into liquid in the first flow channel of the last heat recovery heat exchanger. Thus, the liquid natural gas discharged from the storage tank into the second flow channel of the heat recovery heat exchanger gradually absorbs heat and vaporizes in the second flow channel of the heat recovery heat exchanger and enters the first compressor after reaching a superheated state.

[0009] As a preferred technical solution of the present invention, the marine LNG engine gas supply system further includes a gas-liquid separator and an ejector. The gas-liquid separator includes an inlet, a liquid outlet, and a gas outlet. A sprayer is arranged inside the storage tank. The ejector includes an ejector inlet, an ejector outlet, and an ejector port. The outlet of the throttle valve is fluidly connected to the inlet, the liquid outlet is fluidly connected to the sprayer, and the gas outlet is fluidly connected to the ejector port. The outlet of the booster pump is connected to one end of the vaporizer through a one-way valve. The outlet of the booster pump is also fluidly connected to the inlet of the second flow channel of the heat recovery heat exchanger through a one-way valve.

[0010] The advantages of the marine LNG engine gas supply system of the present invention are: it is equipped with a heat recovery heat exchanger, which can use the heat emitted by the reliquefaction system to heat and vaporize liquefied natural gas, thereby improving both the cold source quality of the reliquefaction system and the heat source quality of the gas supply system, making the heat exchanger smaller in size, and also increasing the exhaust temperature of the gas supply system. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0012] Figure 1 This is a schematic diagram of the gas supply system for a marine LNG engine according to the present invention;

[0013] in:

[0014] 1. Storage tank; 11. Sprayer;

[0015] 2. Vaporizer;

[0016] 3. First compressor; 31. First compressor intake port; 32. First compressor exhaust port;

[0017] 4. Second compressor; 41. Second compressor intake port; 42. Second compressor exhaust port;

[0018] 5. Heat recovery heat exchanger;

[0019] 6. Throttling valve; 61. Throttling valve inlet; 62. Throttling valve outlet;

[0020] 7. Gas-liquid separator; 71. Inlet; 72. Liquid outlet; 73. Gas outlet;

[0021] 8. Ejector; 81. Ejector inlet; 82. Ejector outlet; 83. Ejector port. Detailed Implementation

[0022] The preferred embodiments of the present invention will be described in detail below so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more explicit definition of the scope of protection of the present invention.

[0023] The advantages of the marine LNG engine gas supply system of the present invention are: it is equipped with a heat recovery heat exchanger, which can use the heat emitted by the reliquefaction system to heat and vaporize liquefied natural gas, thereby improving both the cold source quality of the reliquefaction system and the heat source quality of the gas supply system, making the heat exchanger smaller in size, and also increasing the exhaust temperature of the gas supply system.

[0024] like Figure 1 As shown, a marine LNG engine gas supply system includes a storage tank 1 for storing natural gas, a booster pump, a vaporizer 2, and a first compressor 3 for compressing gaseous natural gas. The booster pump is used to send the liquefied natural gas stored in the storage tank 1 into the vaporizer 2. The liquefied natural gas located in the vaporizer 2 can absorb heat from the outside and vaporize through the vaporizer 2. The first compressor 3 includes a first compressor intake port 31 and a first compressor exhaust port 32. The first compressor exhaust port 32 is used to connect to the natural gas engine. The first compressor 3 compresses the low-pressure natural gas discharged from the first compressor intake port 31 to a high-pressure state and supplies it to the natural gas engine for use.

[0025] The LNG engine gas supply system also includes a reliquefaction system, which comprises two second compressors 4 connected in series for compressing gaseous natural gas, two heat recovery heat exchangers 5, and a throttle valve 6. The throttle valve 6 includes a throttle valve inlet 61 and a throttle valve outlet 62. The second compressors 4 include a second compressor suction port 41 and a second compressor discharge port 42. One end of the vaporizer 2 is connected to the liquefied natural gas in the storage tank 1, and the other end of the vaporizer 2 is connected to the second compressor suction port 41, so that the vaporizer 2 can draw gas from the storage tank 1. Liquid natural gas is taken and the heat absorbed from the outside by the vaporizer 2 is transferred to the liquid natural gas to vaporize it and then sent to the second compressor 4. The second compressor 4 compresses the gaseous natural gas into a high temperature and high pressure state and then sends it to the heat recovery heat exchanger 5 connected to its exhaust port to release heat and simultaneously cool and depressurize it. It is worth mentioning that the high temperature, high pressure, low temperature and low pressure states referred to in this invention do not refer to absolute high temperature, high pressure, low temperature or low pressure, but rather to the relative high temperature, high pressure, low temperature or low pressure state in the marine LNG engine gas supply system disclosed in this invention, which will not be elaborated further. The reliquefaction system in this embodiment includes two second compressors 4 and two heat recovery heat exchangers 5. In other embodiments, the reliquefaction system may also include only one second compressor 4 and one heat recovery heat exchanger 5, or the reliquefaction system may have three or more second compressors 4 and more heat recovery heat exchangers 5. The number of heat recovery heat exchangers 5 may also be more than the number of second compressors 4. The purpose is to use the second compressor 4 to compress the low-temperature and low-pressure gaseous natural gas into a high-temperature and high-pressure state so that heat can be released and liquefied in the heat recovery heat exchanger 5.

[0026] The heat recovery heat exchanger 5 includes a first flow channel and a second flow channel, each with an inlet and an outlet. The fluids in the two flow channels can transfer heat through the heat recovery heat exchanger 5. The exhaust port 42 of the second compressor is fluidly connected to the inlet of the first flow channel, and the outlet of the first flow channel is fluidly connected to the inlet 61 of the throttle valve. The outlet of the booster pump is fluidly connected to the vaporizer 2 and the inlet of the second flow channel through a three-way valve, so that only one booster pump can be used to feed liquid natural gas into the vaporizer 2 and the second flow channel of the heat recovery heat exchanger 5. To prevent natural gas from flowing between the vaporizer 2 and the second flow channel of the heat recovery heat exchanger 5, one-way valves can also be arranged before the inlet of the vaporizer 2 and before the inlet of the second flow channel of the heat recovery heat exchanger 5.

[0027] The outlet of the second flow channel is in fluid communication with the suction port 31 of the first compressor, so that the liquid natural gas discharged from the storage tank into the second flow channel of the heat recovery heat exchanger 5 gradually absorbs heat and vaporizes in the second flow channel of the multiple heat recovery heat exchangers 5 and enters the first compressor 3 after reaching a superheated state.

[0028] The reliquefaction system of this invention delivers liquefied natural gas from storage tank 1 to a vaporizer, allowing the liquefied natural gas in the reliquefaction system loop to absorb a large amount of heat from the outside and vaporize. The vaporized gas is then compressed and heated by the second compressor 4 in the reliquefaction system, significantly improving the quality of the external heat supply. Since liquefied natural gas must first absorb heat and vaporize into a gaseous state before being supplied to the first compressor 3, requiring a large amount of heat absorption during vaporization, it can serve as a better cold source. Therefore, the reliquefaction system in the marine LNG engine gas supply system disclosed in this invention has a better cold source, and the gas supply system itself also has a better heat source. The high quality of both the heat and cold sources allows for a smaller size of the heat recovery heat exchanger 5, reducing valuable space on the ship. The better heat source quality also increases the exhaust temperature of the gas supply system, which is beneficial for improving engine thermal efficiency. The better cold source also allows the vaporized natural gas in the reliquefaction system to be liquefied again and returned to storage tank 1.

[0029] The reliquefaction system includes at least two second compressors 4 connected in series and a number of heat recovery heat exchangers 5 equal to the number of second compressors 4. The inlet of the first flow channel of each heat recovery heat exchanger 5 is in fluid communication with the inlet of the second compressor 4. The second flow channels of the multiple heat recovery heat exchangers 5 are arranged in series, so that the high-temperature gaseous natural gas discharged from the exhaust port of each second compressor 4 can release heat into the second flow channel through the heat recovery heat exchanger 5 and liquefy into liquid in the first flow channel of the last heat recovery heat exchanger 5. Thus, the liquid natural gas discharged from the storage tank 1 into the second flow channel of the heat recovery heat exchanger 5 gradually absorbs heat and vaporizes in the second flow channel of the heat recovery heat exchanger 5 and enters the first compressor 3 after reaching a superheated state.

[0030] The marine LNG engine gas supply system also includes a gas-liquid separator 7, an ejector 8, a first one-way valve 101, a second one-way valve 102, and a third one-way valve 103; the outlet of the booster pump and one end of the vaporizer 2 form a one-way fluid communication structure through the first one-way valve 101; the outlet of the booster pump and the inlet of the second flow channel of the heat recovery heat exchanger 5 also form a one-way fluid communication structure through the second one-way valve 102; the purpose of setting the first one-way valve 101 and the second one-way valve 102 is to prevent the natural gas in the pipeline from flowing back when the compressor 3 fluctuates. The gas-liquid separator 7 includes an inlet 71, a liquid outlet 72, and a gas outlet 73. A sprayer 11 is arranged inside the storage tank 1. The ejector 8 includes an ejector inlet 81, an ejector outlet 82, and an ejector port 83. The outlet 62 of the throttle valve is in fluid communication with the inlet 71. The liquid outlet 72 and the fluid of the sprayer are connected in a one-way fluid communication structure through the third one-way valve 103. The gas outlet 73 is in fluid communication with the ejector port 83. When the load on the marine LNG engine increases and it requires more natural gas, it sends a signal to the marine LNG engine gas supply system that it needs more natural gas. The marine LNG engine gas supply system then controls the first compressor 3 to increase its load so that the first compressor 3 can supply more natural gas. This will increase the flow rate of natural gas in the second flow channel of the heat recovery heat exchanger 5, while the flow rate of natural gas in the first flow channel of the heat recovery heat exchanger 5 will not increase. This will cause a mismatch in the flow rates in the two flow channels of the heat recovery heat exchanger 5. This will not only prevent the system from fully utilizing the thermal capacity of the vaporizer and supplying the LNG engine with higher-temperature natural gas, but may also cause the natural gas flowing through the second flow channel of the heat recovery heat exchanger to carry liquid, thereby damaging the first compressor 3 and the external LNG engine.By setting up the ejector 8, the first compressor 3 can directly extract natural gas flowing through the first channel of the heat recovery heat exchanger 5 with minimal cost increase. This allows the flow rates in the first and second channels of the heat recovery heat exchanger 5 to be matched. Specifically, the greater the load on the first compressor 3, the greater the flow rate at its exhaust port, and the greater the flow rate through the ejector 8. This allows more natural gas to be extracted from the gas-liquid separator 7. The outlet of the gas-liquid separator 7 is connected to the sprayer 11 located in the storage tank 1 via a third one-way valve 103. Natural gas in the storage tank 1 cannot enter the gas-liquid separator 7 through the sprayer 11 and the third one-way valve 103. When more natural gas is drawn out of the gas-liquid separator 7, the outlet pressure of the throttle valve 1 decreases. The larger pressure difference across the throttle valve 6 naturally increases the flow rate through it. Since all the natural gas flowing through the throttle valve 6 originates from the first flow channel of the heat recovery heat exchanger 5, the flow rate of natural gas through the first flow channel of the heat recovery heat exchanger 5 naturally increases, thus matching the increase in the flow rate of natural gas through the second flow channel of the heat recovery heat exchanger 5. Similarly, when the load on the first compressor 3 decreases, the outlet flow rate of the first compressor 3 decreases, and the flow rate of natural gas drawn out of the gas-liquid separator 7 through the ejector 8 also decreases, which also leads to a reduction in the flow rate of natural gas through the first and second flow channels of the heat recovery heat exchanger 5, respectively. In summary, by setting up the ejector 8, the flow rates of the first and second channels of the heat recovery heat exchanger 5 can be better matched. This not only fully utilizes the heat absorption capacity of the vaporizer 2 but also prevents the natural gas in the second channel of the heat recovery heat exchanger 5 from carrying liquid when entering the first compressor 3. Of course, there are other ways to achieve this technical effect. For example, a corresponding control module can be added to the marine LNG engine gas supply system and corresponding logic can be written. When the load of the first compressor 3 increases, the control device can control the load of the second compressor to increase accordingly, thereby matching the flow rates through the first and second channels of the heat recovery heat exchanger 5. However, this method is costly. When there are multiple second compressors in the marine LNG engine gas supply system, the complexity of the control logic in this implementation will increase significantly, the cost will increase significantly, and the system reliability will be lower.

[0031] The above are merely some of the design ideas for the embodiments of the present invention. Where the system allows, the present invention can be extended to simultaneously connect more functional modules, thereby maximizing its functionality.

[0032] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions conceived without inventive effort should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A gas supply system for a marine LNG engine, comprising a tank (1) for storing natural gas, a booster pump, a vaporizer (2) and a first compressor (3) for compressing gaseous natural gas, said booster pump being arranged to feed liquid natural gas stored in said tank (1) into said vaporizer (2), liquid natural gas in said vaporizer (2) being capable of absorbing heat from the surroundings through said vaporizer (2) and vaporizing, said first compressor (3) comprising a first compressor suction port (31) and a first compressor discharge port (32), said first compressor discharge port (32) being arranged to be connected to a natural gas engine, characterized in that: The LNG engine air supply system for ships further comprises a reliquefaction system, the reliquefaction system comprises at least one second compressor (4) for compressing gaseous natural gas, at least one heat recovery heat exchanger (5), and a throttling valve (6), the throttling valve (6) comprises a throttling valve inlet (61) and a throttling valve outlet (62), the second compressor (4) comprises a second compressor suction port (41) and a second compressor discharge port (42), the outlet of the booster pump is in communication with one end of the vaporizer (2), and the other end of the vaporizer (2) is in communication with the second compressor suction port (41), so that the vaporizer (2) can extract liquid natural gas from the storage tank (1) and transfer the heat absorbed by the vaporizer (2) from the outside to the liquid natural gas to vaporize the liquid natural gas and then send it into the second compressor (4). The heat recovery heat exchanger (5) comprises a first flow channel and a second flow channel, each of the first flow channel and the second flow channel has an inlet and an outlet, and the fluids in the two flow channels can transfer heat through the heat recovery heat exchanger (5), the second compressor discharge port (42) is in fluid communication with the inlet of the first flow channel, the outlet of the first flow channel is in fluid communication with the throttling valve inlet (61), and the throttling valve outlet (62) is in fluid communication with the storage tank (1), and the natural gas is throttled to a low-temperature and low-pressure state in the throttling valve (6) and then returned to the storage tank (1). The outlet of the booster pump is also in fluid communication with the inlet of the second flow channel of the heat recovery heat exchanger (5), and the outlet of the second flow channel of the heat recovery heat exchanger (5) is in fluid communication with the first compressor suction port (31), so that the liquid natural gas can absorb heat from the gaseous natural gas in the first flow channel and vaporize into a gaseous state when flowing through the second flow channel and then enter the first compressor (3).

2. Marine LNG engine gas supply system according to claim 1, characterized in that: The reliquefaction system comprises at least two second compressors (4) connected in series and heat recovery heat exchangers (5) consistent with the number of the second compressors (4), the inlet of the first flow channel of each heat recovery heat exchanger (5) is in fluid communication with the inlet of the second compressor (4), and the second flow channels of the plurality of heat recovery heat exchangers (5) are arranged in series, so that the high-temperature gaseous natural gas discharged from the discharge port of each second compressor (4) can release heat to the natural gas in the second flow channel through the heat recovery heat exchanger (5), and the liquid natural gas discharged from the storage tank (1) into the second flow channel of the heat recovery heat exchanger (5) gradually absorbs heat, vaporizes, and reaches a superheated state in the second flow channel of the heat recovery heat exchanger (5) and then enters the first compressor (3).

3. Marine LNG engine gas supply system according to claim 2, characterized in that: The marine LNG engine gas supply system further comprises a gas-liquid separator (7), an ejector (8), a first one-way valve (101), a second one-way valve (102) and a third one-way valve (103); the outlet of the booster pump and one end of the gasifier (2) are in one-way fluid communication through the first one-way valve (101); the outlet of the booster pump and the inlet of the second flow channel of the heat recovery heat exchanger (5) are in one-way fluid communication through the second one-way valve (102); the gas-liquid separator (7) comprises an inlet (71), a liquid outlet (72) and a gas outlet (73); a sprayer (11) is arranged in the storage tank (1); the ejector (8) comprises an injection inlet (81), an injection outlet (82) and an injection port (83); the throttling valve outlet (62) is in fluid communication with the inlet (71); the liquid outlet (72) and the sprayer are in one-way fluid communication through the third one-way valve (103); and the gas outlet (73) is in fluid communication with the injection port (83).

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