A device for treating non-condensable gases in LPG cargo boil-off gas used on ships

Abstract

A device for processing non-condensable gases in boil-off gas of LPG cargo on a ship, comprising a first liquid collector, a second liquid collector and a heat exchanger; the first gas outlet end of the first liquid collector is connected to the first refrigerant side inlet end of the heat exchanger; the first liquid outlet end of the first liquid collector is connected to the liquid cargo tank through a main pipeline, the second liquid outlet end of the second liquid collector is connected to the second refrigerant side inlet end of the heat exchanger through an auxiliary pipeline, and a first throttle valve is provided on the auxiliary pipeline; the second gas outlet end and the second liquid outlet end connected to the liquid cargo tank are provided on the second liquid collector; the first refrigerant side outlet end of the heat exchanger is connected to the second liquid collector. The non-condensable gas processing device can utilize the cold energy of the liquid cargo itself to liquefy and recover useful non-condensable gases with low boiling points such as ethane, and at the same time separate and discharge useless non-condensable gases with high boiling points such as nitrogen and carbon dioxide, thereby preventing non-condensable gases from accumulating in the reliquefaction system and affecting the normal operation of the reliquefaction system, and does not consume extra energy, saving energy and being environmentally friendly.

Description

Technical Field

[0001] The present invention relates to the field of ships, and in particular to a device for processing non-condensable gas in boil-off gas of LPG cargo used on ships. Background Art

[0002] For refrigerated or fully refrigerated LPG ships, liquid cargo is transported at a temperature far below the ambient temperature. During transportation, external heat will continuously enter the cargo tank, generating boil-off gas, which will cause the pressure in the tank to increase. Therefore, LPG ships for ocean transportation are usually equipped with a reliquefaction system to reliquefy the boil-off gas.

[0003] The boil-off gas from LPG ships usually contains non-condensable gases. This is because after the inert gas (mainly nitrogen and carbon dioxide) in the cargo tank is exhausted with cargo vapor before loading, there is usually some inert gas remaining. A small amount of inert gas is also introduced when the pipeline is purged after loading. In addition, when the transported cargo is commercial propane (propane containing a small amount of ethane), ethane is difficult to liquefy due to its low boiling point and will also become a non-condensable gas after evaporation. During the operation of the reliquefaction system, non-condensable gases such as inert gases and ethane will gradually accumulate in the gas area at the top of the cargo tank due to their lower density than cargo vapor, resulting in a large amount of non-condensable gases in the boil-off gas inhaled by the reliquefaction system.

[0004] Due to the low boiling point of non-condensable gases, reliquefaction systems often struggle to liquefy and recover them. The presence of non-condensable gases can reduce the condenser's heat exchange performance, thereby reducing the reliquefaction system's refrigeration capacity. Simultaneously, the system's condensing pressure and temperature increase, leading to higher compressor exhaust temperatures, increased power consumption, lower refrigeration efficiency, and even carbonization of the compressor's lubricating oil, affecting lubrication and, in severe cases, damaging the compressor. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the prior art, the technical problem to be solved by the present invention is to provide a device for treating non-condensable gases in boil-off gas of LPG cargo for ships.

[0006] The present invention proposes a device for processing non-condensable gases in evaporated gas of marine LPG cargo, comprising a first liquid collector connected to a liquid supply end, a second liquid collector and a heat exchanger; the first liquid collector is provided with a first gas outlet end and a first liquid outlet end, the heat exchanger is provided with a first refrigerant side and a second refrigerant side, the first gas outlet end of the first liquid collector is connected to the first refrigerant side inlet end of the heat exchanger; the first liquid outlet end of the first liquid collector is connected to the liquid cargo tank through a main pipeline, the first liquid outlet end of the first liquid collector is connected to the second refrigerant side inlet end of the heat exchanger through an auxiliary pipeline, and a first throttle valve is provided on the auxiliary pipeline; the second liquid collector is provided with a second gas outlet end and a second liquid outlet end connected to the liquid cargo tank; the first refrigerant side outlet end of the heat exchanger is connected to the second liquid collector, and the second refrigerant side outlet end of the heat exchanger is connected to the liquid cargo tank.

[0007] Preferably, a second throttle valve is connected between the main pipeline and the liquid cargo tank, and a third throttle valve is connected between the second liquid outlet end of the second liquid collector and the liquid cargo tank.

[0008] Preferably, the second throttle valve and the third throttle valve are float throttle valves, and the first throttle valve is a thermal expansion valve.

[0009] Preferably, a regulating valve one is provided between the first air outlet end of the first liquid collector and the first refrigerant side inlet end of the heat exchanger, and a regulating valve two is provided between the first refrigerant side outlet end of the heat exchanger and the second liquid collector; a regulating valve three is provided between the second refrigerant side outlet end of the heat exchanger and the liquid cargo tank, and a regulating valve four is provided at the second liquid outlet end of the second liquid collector.

[0010] Preferably, the first liquid outlet end of the first liquid collector is connected to the first refrigerant side inlet end of the heat exchanger, the second refrigerant side outlet end of the heat exchanger is connected to the second liquid collector, and the first refrigerant side outlet end of the heat exchanger is connected to the liquid cargo tank.

[0011] Preferably, the second gas outlet end of the second liquid collector is connected to the high-pressure stage inlet of the marine compressor.

[0012] Preferably, a regulating valve five is provided between the first liquid outlet end of the first liquid collector and the first refrigerant side inlet end of the heat exchanger, a regulating valve six is ​​provided between the second refrigerant side outlet end of the heat exchanger and the second liquid collector, and a regulating valve seven is connected between the first refrigerant side outlet end of the heat exchanger and the liquid cargo tank.

[0013] Preferably, a throttle valve is connected between the first refrigerant side outlet end of the heat exchanger and the liquid cargo tank.

[0014] Preferably, a pressure measuring device is installed in the first liquid collector to determine the content of non-condensable gas in the first liquid collector.

[0015] As described above, the present invention relates to a device for processing non-condensable gases in boil-off gas of LPG cargo on board a ship, which has the following beneficial effects: when the content of non-condensable gases is large, the device can utilize the cold energy of the liquid cargo itself to liquefy and recover useful non-condensable gases with low boiling points such as ethane, while separating and discharging useless non-condensable gases with even lower boiling points such as nitrogen and carbon dioxide, thereby preventing the accumulation of non-condensable gases in the reliquefaction system and affecting the normal operation of the reliquefaction system, and does not consume additional energy, thus saving energy and being environmentally friendly; at the same time, when the content of non-condensable gases is small, the device can be used as an intermediate cooling device to cool the superheated steam entering the high-pressure stage of the compressor and at the same time supercool the cargo liquid entering the liquid cargo tank, thereby improving the refrigeration efficiency of the system, thereby enabling the reliquefaction system to be equipped with one less set of intermediate cooling devices, saving equipment investment costs, improving economy, and reducing the deck space occupied by the reliquefaction system. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The present invention is a schematic diagram of a device for treating non-condensable gases in boil-off gas from LPG cargo used on ships.

[0017] Description of reference numerals:

[0018] 100. First liquid collector; 110. First air outlet; 120. First liquid outlet; 200. Second liquid collector; 210. Second air outlet; 220. Second liquid outlet; 300. Heat exchanger; 310. First refrigerant side; 311. First refrigerant side inlet; 312. First refrigerant side outlet; 320. Second refrigerant side; 321. Second refrigerant side inlet; 322. Second refrigerant side outlet; 400. Main pipeline; 410. Auxiliary pipeline; 500. First throttle valve; 510. Second throttle valve; 520. Third throttle valve; 600. Control valve one; 610. Control valve two; 620. Control valve three; 630. Control valve four; 640. Control valve five; 650. Control valve six; 660. Control valve seven; 670. Control valve eight; 680. Control valve nine. DETAILED DESCRIPTION

[0019] The following describes the implementation of the present invention through specific embodiments. People skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification.

[0020] It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for understanding and reading by those familiar with this technology, and are not used to limit the conditions for implementation of the present invention. Therefore, they have no substantial technical significance. Any modification of the structure, change in the proportional relationship, or adjustment of the size should still fall within the scope of the technical content disclosed by the present invention without affecting the efficacy and purpose that can be achieved by the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle", etc. quoted in this specification are only for the convenience of description and are not used to limit the scope of implementation of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of implementation of the present invention without substantially changing the technical content.

[0021] like Figure 1 As shown, the embodiment provided by the present invention is a non-condensable gas treatment device in LPG cargo boil-off gas for ships, comprising a first liquid collector 100 connected to a liquid supply end, a second liquid collector 200 and a heat exchanger 300; the first liquid collector 100 is provided with a first gas outlet end 110 and a first liquid outlet end 120, the heat exchanger 300 is provided with a first refrigerant side 310 and a second refrigerant side 320, the first gas outlet end 110 of the first liquid collector 100 is connected to the first refrigerant side 310 and the first refrigerant side inlet end 311 of the heat exchanger 300; the first liquid outlet end of the first liquid collector 100 120 is connected to the liquid cargo tank through the main pipeline 400, the first liquid outlet end 120 of the first liquid collector 100 is connected to the second refrigerant side inlet end 321 of the heat exchanger 300 through the auxiliary pipeline 410, and the auxiliary pipeline 410 is provided with a first throttle valve 500; the second liquid collector 200 is provided with a second gas outlet end 210 and a second liquid outlet end 220 connected to the liquid cargo tank; the first refrigerant side 310 first refrigerant side outlet end 312 of the heat exchanger 300 is connected to the second liquid collector 200, and the second refrigerant side outlet end 322 of the heat exchanger 300 is connected to the liquid cargo tank.

[0022] When the non-condensable gas processing device is in operation, the gas-liquid mixture at the liquid supply end enters the first liquid collector 100. The gaseous portion overflows from the first gas outlet 110 of the first liquid collector 100. This separated gas is a mixture of lower-boiling-point non-condensable gases such as nitrogen and carbon dioxide, low-boiling-point non-condensable gases such as ethane, and evaporated cargo vapor, resulting in a high-temperature, high-pressure gas mixture containing non-condensable gases. The liquid portion of the cargo then flows out of the first liquid outlet 120 of the first liquid collector 100 and is divided into two paths, flowing through the main pipeline 400 and the auxiliary pipeline 410, respectively. The liquid flowing through the main pipeline 400 flows to the cargo tank. The liquid flowing through the auxiliary pipeline 410 is cooled and pressured by the first throttle valve 500 and flows into the second refrigerant side 320 of the heat exchanger 300. It should be noted that at this point, the high-temperature, high-pressure gas mixture flows into the first refrigerant side 310 of the heat exchanger 300. After absorbing heat, the liquid on the second refrigerant side 320 becomes a gas-liquid two-phase state and flows directly into the cargo tank. Meanwhile, the higher-boiling-point cargo vapor and low-boiling-point non-condensable gases, such as ethane, in the mixed gas on the first refrigerant side 310 are condensed and liquefied, while the lower-boiling-point non-condensable gases remain in a gaseous state and enter the second liquid collector 200 for further gas-liquid separation. The lower-boiling-point non-condensable gases are discharged into the atmosphere through the second gas outlet 210 at the top of the second liquid collector 200, while the liquefied ethane and cargo are cooled and decompressed to cargo tank pressure through the throttle valve at the bottom of the second liquid collector 200 before returning to the cargo tank. At this point, undesirable non-condensable gases, such as nitrogen and carbon dioxide, are discharged into the atmosphere, while useful non-condensable gases, such as ethane, are recovered and returned to the cargo tank. It should be noted that to ensure that the liquid in the first liquid collector 100 can flow smoothly into the second liquid collector 200, the pressure in the second liquid collector 200 should be 3-4 bar lower than that in the first liquid collector 100. The heat exchanger may be a shell and tube heat exchanger, wherein the first refrigerant side 310 is the shell side and the second refrigerant side 320 is the tube side.

[0023] like Figure 1 As shown, a second throttle valve 510 is connected between the main pipeline 400 and the cargo tank, and a third throttle valve 520 is connected between the liquid outlet of the second liquid collector 200 and the cargo tank. The second throttle valve 510 and the third throttle valve 520 respectively cool and reduce the temperature and pressure of the liquid flowing out of the first liquid outlet 120 of the first liquid collector 100 and the second throttle valve 510 to the pressure and saturation temperature of the cargo tank before the liquid is transferred to the cargo tank. Specifically, the second throttle valve 510 and the third throttle valve 520 are float throttle valves, while the first throttle valve 500 is a thermal expansion valve.

[0024] like Figure 1As shown, a regulating valve 1 600 is provided between the first gas outlet 110 of the first liquid collector 100 and the first refrigerant-side inlet 311 of the heat exchanger 300. A regulating valve 2 610 is provided between the first refrigerant-side outlet 312 of the first refrigerant-side 310 of the heat exchanger 300 and the second liquid collector 200. A regulating valve 3 620 is provided between the second refrigerant-side outlet 322 of the heat exchanger 300 and the liquid cargo tank. A regulating valve 4 630 is provided at the second liquid outlet 220 of the second liquid collector 200. Each regulating valve can adjust the flow of liquid or gas in each pipeline as needed, controlling the connection and disconnection of each pipeline.

[0025] The first liquid outlet end 120 of the first liquid collector 100 is connected to the first refrigerant side inlet end 311 of the first refrigerant side 310 of the heat exchanger 300, the second refrigerant side outlet end 322 of the heat exchanger 300 is connected to the second liquid collector 200, and the first refrigerant side outlet end 312 of the first refrigerant side 310 of the heat exchanger 300 is connected to the liquid cargo tank.

[0026] like Figure 1 As shown, when the non-condensable gas entering the first liquid collector 100 from the liquid supply end is low and does not affect the normal operation of the reliquefaction system, the device functions as an intermediate cooling device. Specifically, the second throttle valve 510, regulating valve 1 600, regulating valve 2 610, regulating valve 3 620, regulating valve 4 630, and regulating valve 8 670 can be closed. The cargo liquid in the first liquid collector 100 flows out of the first liquid outlet 120 in two ways: one way enters the first refrigerant side 310 of the heat exchanger 300, and the other way enters the second refrigerant side 320 of the heat exchanger 300 through the auxiliary pipeline 410 after being cooled and reduced in pressure by the first throttle valve 500, serving as a cooling source. The liquid passing through the first refrigerant side 310 is cooled by the cooled liquid in the second refrigerant side 320 before flowing into the cargo tank. The cargo flowing through the second refrigerant side 320 absorbs heat and becomes a gas-liquid two-phase state before entering the second liquid collector 200. The saturated liquid stored in the second liquid collector 200 evaporates into saturated steam and then overflows from the second gas outlet 210 of the second liquid collector 200. In this process, the first liquid collector 100 can not only adjust and stabilize the circulation volume of the cargo liquid to adapt to the needs of changing working conditions, but also play a liquid sealing role to prevent high-pressure cargo vapor from escaping into the low-pressure system pipeline.

[0027] like Figure 1As shown, preferably, the second gas outlet 210 of the second liquid collector 200 can be connected to the compressor high-pressure stage inlet, where it mixes with the superheated vapor from the compressor low-pressure stage within the pipeline before entering the compressor high-pressure stage inlet together. This reduces the temperature of the superheated vapor entering the compressor high-pressure stage, thereby reducing compressor power consumption and improving system cooling efficiency. In this embodiment, the second gas outlet 210 is connected to two parallel pipelines, one connecting to the atmosphere and the other to the compressor high-pressure stage inlet. A regulating valve 8 670 is provided between the second gas outlet 210 and the atmosphere, and a regulating valve 9 680 is provided between the second gas outlet 210 and the compressor high-pressure stage inlet.

[0028] like Figure 1 As shown, preferably, a regulating valve five 640 is provided between the first liquid outlet end 120 of the first liquid collector 100 and the first refrigerant side inlet end 311 of the first refrigerant side 310 of the heat exchanger 300, a regulating valve six 650 is provided between the second refrigerant side outlet end 322 of the heat exchanger 300 and the second liquid collector 200, and a regulating valve seven 660 is connected between the first refrigerant side outlet end 312 of the first refrigerant side 310 of the heat exchanger 300 and the liquid cargo tank.

[0029] A throttle valve is connected between the first refrigerant-side outlet port 312 of the heat exchanger 300 and the liquid cargo tank. In this embodiment, the throttle valve may be the third throttle valve 520 .

[0030] like Figure 1 As shown, preferably, a pressure measuring device is installed in the first liquid collector 100 to determine the content of non-condensable gas in the first liquid collector 100. During the operation of the reliquefaction system, when its internal pressure is normal, it indicates that the content of non-condensable gas in the system is relatively low. This device is used as an intermediate cooling device. At this time, the second throttle valve 510, regulating valve 1 600, regulating valve 2 610, regulating valve 3 620, regulating valve 4 630, and regulating valve 8 670 are all closed, and the remaining valves are all open. When the internal pressure rises to exceed the predetermined value, it indicates that the system contains a large amount of non-condensable gas. At this time, regulating valve 5 640, regulating valve 7 660, regulating valve 6 650, and regulating valve 9 680 are all closed, and the other valves are all open. This device is used as a non-condensable gas treatment device. In this way, not only the non-condensable gas treatment function is increased, but also one less intermediate cooling device is required, which saves equipment investment costs, improves economy, and reduces the space occupied by the reliquefaction system deck.

[0031] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A device for treating non-condensable gases in LPG cargo boil-off gas for marine use, characterized in that: The invention comprises a first liquid collector (100) connected to a liquid supply end, a second liquid collector (200) and a heat exchanger (300); the first liquid collector (100) is provided with a first gas outlet end (110) and a first liquid outlet end (120); the heat exchanger (300) is provided with a first refrigerant side (310) and a second refrigerant side (320); the first gas outlet end (110) of the first liquid collector (100) is connected to the first refrigerant side inlet end (311) of the heat exchanger (300); the first liquid outlet end (120) of the first liquid collector (100) is connected to the liquid cargo tank through a main pipeline (400); The first liquid outlet (120) of the first liquid collector (100) is connected to the second refrigerant side inlet (321) of the heat exchanger (300) via an auxiliary pipeline (410), and the auxiliary pipeline (410) is provided with a first throttle valve (500); the second liquid collector (200) is provided with a second gas outlet (210) and a second liquid outlet (220) connected to the liquid cargo tank; the first refrigerant side outlet (312) of the heat exchanger (300) is connected to the second liquid collector (200), and the second refrigerant side outlet (322) of the heat exchanger (300) is connected to the liquid cargo tank.

2. The device for treating non-condensable gases in LPG cargo boil-off gas for marine use according to claim 1, characterized in that: A second throttle valve (510) is connected between the main pipeline (400) and the liquid cargo tank, and a third throttle valve (520) is connected between the second liquid outlet end (220) of the second liquid collector (200) and the liquid cargo tank.

3. The device for treating non-condensable gases in LPG cargo boil-off gas used on ships according to claim 2, characterized in that: The second throttle valve (510) and the third throttle valve (520) are float throttle valves, and the first throttle valve (500) is a thermal expansion valve.

4. The device for treating non-condensable gases in LPG cargo boil-off gas used on ships according to claim 3, characterized in that: A regulating valve one (600) is provided between the first air outlet end (110) of the first liquid collector (100) and the first refrigerant side inlet end (311) of the heat exchanger (300), and a regulating valve two (610) is provided between the first refrigerant side outlet end (312) of the heat exchanger (300) and the second liquid collector (200); a regulating valve three (620) is provided between the second refrigerant side outlet end (322) of the heat exchanger (300) and the liquid cargo tank, and a regulating valve four (630) is provided at the second liquid outlet end (220) of the second liquid collector (200).

5. The device for treating non-condensable gases in LPG cargo boil-off gas used on board a ship according to claim 4, characterized in that: The first liquid outlet end (120) of the first liquid collector (100) is connected to the first refrigerant side inlet end (311) of the heat exchanger (300), the second refrigerant side outlet end (322) of the heat exchanger (300) is connected to the second liquid collector (200), and the first refrigerant side outlet end (312) of the heat exchanger (300) is connected to the liquid cargo tank.

6. The device for treating non-condensable gases in LPG cargo boil-off gas used on ships according to claim 5, characterized in that: The second gas outlet end (210) of the second liquid collector (200) is connected to the high-pressure stage inlet of the marine compressor.

7. The device for treating non-condensable gases in LPG cargo boil-off gas used on ships according to claim 5, characterized in that: A regulating valve five (640) is provided between the first liquid outlet end (120) of the first liquid collector (100) and the first refrigerant side inlet end (311) of the heat exchanger (300), a regulating valve six (650) is provided between the second refrigerant side outlet end (322) of the heat exchanger (300) and the second liquid collector (200), and a regulating valve seven (660) is connected between the first refrigerant side outlet end (312) of the heat exchanger (300) and the liquid cargo tank.

8. The device for treating non-condensable gases in LPG cargo boil-off gas used on ships according to claim 5, characterized in that: A throttle valve is connected between the first refrigerant side outlet end (312) of the heat exchanger (300) and the liquid cargo tank.

9. A device for treating non-condensable gases in LPG cargo boil-off gas for use on ships according to any one of claims 1 to 8, characterized in that: A pressure measuring device is installed in the first liquid collecting container (100) for determining the content of non-condensable gas in the first liquid collecting container (100).

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