Ship BOG compressor parallel operation system and control method thereof

Abstract

The invention discloses a ship BOG compressor parallel operation system and a control method thereof.The ship BOG compressor parallel operation system is characterized in that when a ship main engine gas mode is initially started, one compressor is adopted for independently supplying gas to a ship main engine, and the other compressor is adopted for independently supplying gas to a gas combustion unit for use; by adopting the control strategy, waste caused by direct combustion of natural gas is reduced, stable operation of a fuel gas mode of the marine main engine can be guaranteed, and the marine main engine is more stable in fuel gas mode. BOG formed by natural volatilization of the fuel tank or the liquid cargo tank is used for main engine combustion to the maximum extent, BOG combustion is avoided or reduced as much as possible, and therefore the operation economical efficiency of the LNG liquid cargo ship or the fuel ship is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of shipbuilding, and particularly to a parallel operation system for a ship BOG compressor and a control method thereof. Background Art

[0002] During the operation of an LNG tanker or a fuel ship, after the LNG cargo tank or the LNG fuel tank is loaded, due to the disturbance of the loading process and related equipment, the BOG (Boil-Off Gas) volatilized from the LNG cargo tank or the LNG fuel tank is far greater than the amount of NBOG (Natural Boil-Off Gas). In addition, during the LNG transportation process, the long transportation distance of the ship, the change of climate during the voyage, and the shaking of the ship itself will cause the cargo tank or the fuel tank to absorb heat, causing the LNG in the cargo tank to evaporate into a large amount of NBOG.

[0003] Since the pressure of the BOG directly volatilized from the LNG cargo tank or the LNG fuel tank is relatively low and does not meet the intake pressure operation requirements of the dual-fuel main engine and the generator in the gas mode, it is necessary to boost the pressure through a BOG compressor and then transport it to the dual-fuel main engine and the generator for use. Considering the early construction cost of the LNG tanker or the fuel ship, the single capacity of the BOG compressor selected by the owner usually does not meet the full-load operation requirements of the dual-fuel main engine and the generator, and the BOG volatilized from the above-mentioned LNG cargo tank or the LNG fuel tank will exceed the single capacity of the BOG compressor. In addition, considering the ship safety factor, it is necessary to control a certain pressure in the LNG cargo tank or the LNG fuel tank. At present, the mainstream design of major LNG tanker or LNG fuel ship building shipyards is to supply these BOGs or NBOGs to the dual-fuel main engine and the generator through one BOG compressor, and the remaining BOGs or NBOGs are supplied to the gas combustion unit through another BOG compressor for combustion. This design cannot meet the economic indicators during the operation of the LNG tanker or the fuel ship, resulting in a large waste of BOG; if the single capacity of the BOG compressor is simply increased, the early construction cost of the LNG tanker or the fuel ship will be significantly increased. Summary of the Invention

[0004] In view of this, the present invention provides a parallel operation system for a ship BOG compressor and a control method thereof to solve the problems of a large waste of BOG and a significant increase in the early construction cost.

[0005] A parallel operation system for a ship BOG compressor includes an LNG cargo tank or a fuel tank, a BOG gas transmission pipeline, a BOG gas main pipeline, a first BOG compressor intake pipeline, a second BOG compressor intake pipeline, a first BOG compressor supply pipeline, a second BOG compressor supply pipeline, a gas combustion unit intake pipeline, a ship main engine intake pipeline, a first BOG compressor, and a second BOG compressor.

[0006] At least one LNG cargo tank or fuel tank is provided, and each LNG cargo tank or fuel tank is connected to a BOG gas transmission pipeline. Each BOG gas transmission pipeline converges and is connected to a BOG gas main pipeline. The BOG gas main pipeline is respectively connected to the intake pipeline of the first BOG compressor and the intake pipeline of the second BOG compressor. The intake pipeline of the first BOG compressor is connected to the intake port of the first BOG compressor, and the intake pipeline of the second BOG compressor is connected to the intake port of the second BOG compressor;

[0007] Both the first BOG compressor and the second BOG compressor are used to compress BOG gas. The gas supply port of the first BOG compressor is connected to the first BOG compressor gas supply pipeline. The first BOG compressor gas supply pipeline is respectively connected to the gas combustion unit intake pipeline and the ship main engine intake pipeline. The gas supply port of the second BOG compressor is connected to the second BOG compressor gas supply pipeline. The second BOG compressor gas supply pipeline is respectively connected to the gas combustion unit intake pipeline and the ship main engine intake pipeline. The gas combustion unit intake pipeline is connected to the gas combustion unit through a gas valve group, and the ship main engine intake pipeline is connected to the ship main engine through a gas valve group.

[0008] Preferably, when the ship main engine gas mode is just started, the gas compressed by the first BOG compressor is only supplied for use by the ship main engine, and the gas compressed by the second BOG compressor (12) is only supplied for use by the gas combustion unit;

[0009] After the ship main engine gas mode runs stably, gradually reduce the amount of compressed gas from the second BOG compressor to the gas combustion unit and increase the amount of compressed gas to the ship main engine, so as to gradually incorporate the gas compressed by the second BOG compressor into the ship main engine intake pipeline. After the first BOG compressor and the second BOG compressor operate in parallel stably, close the gas combustion pipeline to stop supplying gas to the gas combustion unit.

[0010] Preferably, during the stable operation of the ship main engine gas mode, if the sum of the BOG amounts output by the first BOG compressor and the second BOG compressor is greater than the total amount required for all ship main engines to operate at full load, then open the gas supply pipeline of the gas combustion unit while keeping the ship main engines operating at full load, and direct a part of the gas compressed by the two BOG compressors to the gas combustion unit for combustion.

[0011] Preferably, the first BOG compressor gas supply pipeline includes a first BOG compressor gas supply pipe 1 and a second BOG compressor gas supply pipe 2. A first control valve for controlling the opening and closing of this branch pipe is installed on the first BOG compressor gas supply pipe 1, and a second control valve for controlling the opening and closing of this branch pipe is installed on the second BOG compressor gas supply pipe 2.

[0012] The second BOG compressor supply pipeline includes a first second BOG compressor supply pipe and a second second BOG compressor supply pipe. A third control valve for controlling the opening and closing of this branch pipe is installed on the first second BOG compressor supply pipe, and a fourth control valve for controlling the opening and closing of this branch pipe is installed on the second second BOG compressor supply pipe.

[0013] Preferably, there are two LNG cargo tanks or fuel tanks.

[0014] Preferably, the ship is an LNG cargo ship or a fuel ship, and the ship's main engine includes a dual-fuel main engine and a dual-fuel generator.

[0015] A control method for the above-mentioned system specifically includes the following steps:

[0016] Open the BOG gas transmission pipelines on each LNG cargo tank or fuel tank, and at the same time open the BOG gas main pipeline, the first BOG compressor supply pipeline, the second BOG compressor supply pipeline, the pipeline of the first BOG compressor supply pipeline connected to the ship's main engine intake pipeline, the pipeline of the second BOG compressor supply pipeline connected to the gas combustion unit intake pipeline, the gas combustion unit intake pipeline, and the ship's main engine intake pipeline. Keep other pipelines closed and select the natural gas mode for the ship's operation mode;

[0017] When the ship's main engine gas mode is just started, the gas compressed by the first BOG compressor is only supplied for use by the ship's main engine, and the gas compressed by the second BOG compressor is only supplied for use by the gas combustion unit;

[0018] After the ship's main engine gas mode runs stably, gradually reduce the gas supply volume of the pipeline of the second BOG compressor supply pipeline connected to the gas combustion pipeline, and at the same time increase the gas supply volume of the pipeline of the second BOG compressor supply pipeline connected to the ship's main engine intake pipeline. Gradually incorporate the gas compressed by the second BOG compressor into the ship's intake connection pipeline. After the first BOG compressor and the second BOG compressor operate in parallel stably, close the gas combustion unit intake pipeline to stop supplying gas to the gas combustion unit.

[0019] Preferably, during the stable operation of the ship's main engine, if the sum of the BOG volumes output by the first BOG compressor and the second BOG compressor is greater than the total consumption required for all ship's main engines to operate at full load, then gradually open the gas combustion unit intake pipeline while keeping the ship's main engine operating at full load to direct the excess BOG gas to the gas combustion unit for combustion.

[0020] The beneficial effects of the present invention are:

[0021] 1. The present invention uses two compressors to operate in parallel to supply gas to the ship's main engine, which can reduce the equipment capacity of a single compressor, effectively reduce the procurement cost of the compressor. Compared with the traditional technology, the present invention not only reduces the waste caused by direct combustion of natural gas, but also increases the economy of the ship, and at the same time reduces carbon emissions, which has important positive significance for environmental protection.

[0022] 2. When the gas mode of the ship's main engine is initially started, the present invention uses one compressor to supply gas to the ship's main engine alone and the other compressor to supply gas to the gas combustion unit alone. When the gas mode of the ship's main engine operates stably, the gas supply to the gas combustion unit is gradually reduced to gradually transition to both compressors supplying gas to the ship's main engine. By adopting this control strategy, not only the waste caused by direct combustion of natural gas is reduced, but also the stable operation of the gas mode of the ship's main engine can be ensured, so that the BOG formed by natural evaporation of the fuel tank or liquid cargo tank is maximally used for main engine combustion, and BOG combustion is avoided or reduced as much as possible, thereby realizing the operation economy of the LNG liquid cargo ship or fuel ship. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required to be used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0024] Figure 1 It is a system schematic diagram in the early stage of parallel operation of the ship's BOG compressor.

[0025] Figure 2 It is a system schematic diagram in the stable parallel operation stage of the ship's BOG compressor.

[0026] The meanings of the reference numerals in the drawings are as follows:

[0027] 1 is the LNG liquid cargo tank or fuel tank,

[0028] 2 is the BOG gas transmission pipeline, 21 is the control valve of the BOG gas transmission pipeline,

[0029] 3 is the BOG gas main pipeline, 31 is the control valve of the BOG gas main pipeline,

[0030] 4 is the first BOG compressor intake pipeline, 41 is the control valve of the first BOG compressor intake pipeline,

[0031] 5 is the second BOG compressor intake pipeline, 51 is the control valve of the second BOG compressor intake pipeline,

[0032] 6 is the supply gas pipeline for the first BOG compressor, 61 is the first supply gas pipe for the first BOG compressor, 62 is the first control valve, 63 is the second supply gas pipe for the first BOG compressor, 64 is the second control valve,

[0033] 7 is the supply gas pipeline for the second BOG compressor, 71 is the first supply gas pipe for the second BOG compressor, 72 is the third control valve, 73 is the second supply gas pipe for the second BOG compressor, 74 is the fourth control valve,

[0034] 8 is the inlet gas pipeline for the gas combustion unit, 81 is the control valve of the inlet gas pipeline for the gas combustion unit,

[0035] 9 is the inlet gas pipeline for the ship's main engine, 91 is the control valve of the inlet gas pipeline for the ship's main engine,

[0036] 10 is the first BOG compressor,

[0037] 11 is the gas valve group,

[0038] 12 is the second BOG compressor,

[0039] 13 is the ship's main engine,

[0040] 14 is the gas combustion unit. Specific embodiments

[0041] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be described below through specific embodiments shown in the drawings. However, it should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, the descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present invention.

[0042] The terms used in the present disclosure are only for the purpose of describing specific embodiments and are not intended to limit the present disclosure. The singular forms "a", "the" and "said" used in the present disclosure and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0043] It should be understood that although the terms first, second, etc. may be used in the present disclosure to describe various information, such information should not be limited to these terms and should not be construed as indicating or implying relative importance. These terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of the present disclosure, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Depending on the context, the word "if" as used herein may be interpreted as "when" or "while" or "corresponding to determining".

[0044] To better understand the technical solution of the present invention, the present invention will be described in detail below with reference to the accompanying drawings.

[0045] The present invention provides a parallel operation system for a ship BOG compressor, which includes an LNG cargo tank or fuel tank 1, a BOG gas transmission pipeline 2, a BOG gas main pipeline 3, a first BOG compressor intake pipeline 4, a second BOG compressor intake pipeline 5, a first BOG compressor supply pipeline 6, a second BOG compressor supply pipeline 7, a gas combustion unit intake pipeline 8, a ship main engine intake pipeline 9, a first BOG compressor 10, and a second BOG compressor 12.

[0046] At least one LNG cargo tank or fuel tank 1 is provided, and each LNG cargo tank or fuel tank 1 is connected to a BOG gas transmission pipeline 2. The BOG gas transmission pipeline 2 is used to transport the BOG gas formed by volatilization in the LNG cargo tank or fuel tank. Each BOG gas transmission pipeline 2 converges and is connected to the BOG gas main pipeline 3. In this embodiment, as Figure 1 shown, two LNG cargo tanks or fuel tanks 1 are provided. Each of the two LNG cargo tanks or fuel tanks 1 is connected to a BOG gas transmission pipeline 2. A control valve 21 for controlling the pipeline switch is provided on each BOG gas transmission pipeline 2. The two BOG gas transmission pipelines 2 are both connected to the BOG gas main pipeline 3.

[0047] The BOG gas main pipeline 3 is respectively connected to the first BOG compressor intake pipeline 4 and the second BOG compressor intake pipeline 5. The first BOG compressor intake pipeline 4 is connected to the intake port of the first BOG compressor 10, and the second BOG compressor intake pipeline 5 is connected to the intake port of the second BOG compressor 12. A control valve 31 for controlling the pipeline switch is provided on the BOG gas main pipeline 3, a control valve 41 for controlling the pipeline switch is provided on the first BOG compressor intake pipeline 4, and a control valve 51 for controlling the pipeline switch is provided on the second BOG compressor intake pipeline 5. The BOG gas converging to the BOG gas main pipeline 3 is transported along the BOG gas main pipeline 3 and is respectively fed into the first BOG compressor intake pipeline 4 and the second BOG compressor intake pipeline 5 at the end of the BOG gas main pipeline 3, and then enters the first BOG compressor 10 and the second BOG compressor 12 for compression.

[0048] Both the first BOG compressor 10 and the second BOG compressor 12 are used to compress BOG gas. The air supply port of the first BOG compressor 10 is connected to the first BOG compressor air supply pipeline 6, and the first BOG compressor air supply pipeline 6 is respectively connected to the gas combustion unit intake pipeline 8 and the ship main engine intake pipeline 9. The air supply port of the second BOG compressor 12 is connected to the second BOG compressor air supply pipeline 7, and the second BOG compressor air supply pipeline 7 is respectively connected to the gas combustion unit intake pipeline 8 and the ship main engine intake pipeline 9. The gas combustion unit intake pipeline 8 is connected to the gas combustion unit through a gas valve group, and the ship main engine intake pipeline 9 is connected to the ship main engine through a gas valve group.

[0049] Specifically, the first BOG compressor air supply pipeline 6 includes a first BOG compressor air supply pipe 61 and a first BOG compressor air supply pipe 63. The first BOG compressor air supply pipe 61 is connected to the ship main engine intake pipeline 9, and a first control valve 62 for controlling the opening and closing of this branch pipe is installed on its pipeline. The first BOG compressor air supply pipe 63 is connected to the gas combustion pipeline 8, and a second control valve 64 for controlling the opening and closing of this branch pipe is installed on its pipeline.

[0050] The second BOG compressor air supply pipeline 7 includes a second BOG compressor air supply pipe 71 and a second BOG compressor air supply pipe 73. The second BOG compressor air supply pipe 71 is connected to the ship main engine intake pipeline 9, and a third control valve 72 for controlling the opening and closing of this branch pipe is installed on its pipeline. The second BOG compressor air supply pipe 73 is connected to the gas combustion unit intake pipeline 8, and a fourth control valve 74 for controlling the opening and closing of this branch pipe is installed on its pipeline.

[0051] A control valve 81 for controlling the opening and closing of its pipeline is installed on the gas combustion unit intake pipeline 8, and a control valve 91 for controlling the opening and closing of its pipeline is installed on the ship main engine intake pipeline 9. The end of the gas combustion unit intake pipeline 8 is connected to the gas combustion unit 14 through a gas valve group, and the end of the ship main engine intake pipeline 9 is also connected to the ship main engine 13 through a gas valve group 11.

[0052] When the gas mode of the ship main engine is just started, the gas compressed by the first BOG compressor 10 is only supplied for use by the ship main engine 13, and the gas compressed by the second BOG compressor 12 is only supplied for use by the gas combustion unit 14.

[0053] After the gas mode of the ship's main engine runs stably, gradually reduce the gas volume of the second BOG compressor 12 leading to the gas combustion unit and increase the gas volume leading to the ship's main engine, so as to gradually incorporate the gas compressed by the second BOG compressor 12 into the intake pipeline 9 of the ship's main engine 13. After the first BOG compressor 10 and the second BOG compressor 12 operate in parallel stably, close the intake pipeline 8 of the gas combustion unit to stop supplying gas to the gas combustion unit 14.

[0054] During the stable operation of the gas mode of the ship's main engine, if the sum of the BOG volumes output by the first BOG compressor 10 and the second BOG compressor 12 is greater than the total consumption required for all ship's main engines 13 to operate at full load, then while keeping the ship's main engine operating at full load, gradually open the gas combustion pipeline 8 to lead the excess BOG gas to the gas combustion unit 14 for combustion.

[0055] The ship mentioned above is an LNG liquid cargo tank or a fuel ship, and the ship's main engine 14 includes a dual-fuel main engine and a dual-fuel generator.

[0056] In this embodiment, all the above control valves can be any one of manual, hydraulic, pneumatic, and explosion-proof electric valves.

[0057] The present invention also provides a control method for a parallel operation system of the ship's BOG compressor, which specifically includes the following steps:

[0058] Open the BOG gas transmission pipeline 2 on each LNG liquid cargo tank or fuel tank 1, and at the same time open the BOG gas main pipeline 3, the intake pipeline 4 of the first BOG compressor, the intake pipeline 5 of the second BOG compressor, the pipeline of the supply pipeline 6 of the first BOG compressor connected to the intake pipeline 9 of the ship's main engine, the pipeline of the supply pipeline 7 of the second BOG compressor connected to the intake pipeline 8 of the gas combustion unit, the intake pipeline 8 of the gas combustion unit, and the intake pipeline 9 of the ship's main engine, and keep other pipelines closed, that is, as Figure 1 shown, Figure 1 in the valves 21, 31, 41, 51, 62, 74, 81, and 91 are opened, the valves 64 and 72 are kept closed, and select the ship operation mode as the natural gas mode;

[0059] When the gas mode of the ship's main engine is just started, the gas compressed by the first BOG compressor 10 is only supplied for use by the ship's main engine, and the gas compressed by the second BOG compressor 12 is only supplied for use by the gas combustion unit;

[0060] After the gas mode of the ship's main engine runs stably, gradually reduce the gas supply volume of the pipeline of the second BOG compressor supply pipeline 7 connected to the gas combustion unit intake pipeline 8, and at the same time increase the gas supply volume of the pipeline of the second BOG compressor supply pipeline 7 connected to the ship's main engine intake pipeline 9 (that is, keep the valve openings of valves 21, 31, 41, 51, 62, 74, and 91 unchanged, gradually open valve 72, and gradually close valve 81), gradually incorporate the gas compressed by the second BOG compressor 12 into the ship's main engine intake pipeline 9. After the first BOG compressor 10 and the second BOG compressor 12 operate in parallel stably, close the gas combustion unit intake pipeline 8 to stop supplying gas to the gas combustion unit (that is, completely close valve 81).

[0061] During the stable operation of the ship's main engine, if the sum of the BOG volumes output by the first BOG compressor 10 and the second BOG compressor 12 is greater than the consumption required for the ship's main engine to operate at full load, then while keeping the ship's main engine operating at full load, gradually open the gas combustion unit intake pipeline 8 to direct the excess BOG gas to the gas combustion unit for combustion (that is, appropriately open valve 81 so that the gas combustion unit can consume the excess BOG gas).

[0062] It should be clear that the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

Claims

1. A parallel operation system for a ship BOG compressor, characterized in that, Comprising an LNG cargo tank or fuel tank (1), a BOG gas transfer pipeline (2), a BOG gas main pipeline (3), a first BOG compressor intake pipeline (4), a second BOG compressor intake pipeline (5), a first BOG compressor supply pipeline (6), a second BOG compressor supply pipeline (7), a gas combustion unit intake pipeline (8), a ship main engine intake pipeline (9), a first BOG compressor (10) and a second BOG compressor (12), At least one LNG cargo tank or fuel tank (1) is provided, and a BOG gas transfer pipeline (2) is connected to the upper part of each LNG cargo tank or fuel tank (1). Each BOG gas transfer pipeline (2) converges and is connected to the BOG gas main pipeline (3). The BOG gas main pipeline (3) is respectively connected to the first BOG compressor intake pipeline (4) and the second BOG compressor intake pipeline (5). The first BOG compressor intake pipeline (4) is connected to the intake port of the first BOG compressor (10), and the second BOG compressor intake pipeline (5) is connected to the intake port of the second BOG compressor (12); Both the first BOG compressor (10) and the second BOG compressor (12) are used to compress BOG gas. The air supply port of the first BOG compressor (10) is connected to the first BOG compressor supply pipeline (6). The first BOG compressor supply pipeline (6) is respectively connected to the gas combustion unit intake pipeline (8) and the ship main engine intake pipeline (9). The air supply port of the second BOG compressor (12) is connected to the second BOG compressor supply pipeline (7). The second BOG compressor supply pipeline (7) is respectively connected to the gas combustion unit intake pipeline (8) and the ship main engine supply pipeline (9). The gas combustion unit intake pipeline (8) is connected to the gas combustion unit through a gas valve group, and the ship main engine supply pipeline (9) is connected to the ship main engine through a gas valve group.

2. The BOG compressor parallel operation system for ships according to claim 1, characterized in that, When the ship main engine gas mode is just started, the gas compressed by the first BOG compressor (10) is only supplied for the use of the ship main engine, and the gas compressed by the second BOG compressor (12) is only supplied for the use of the gas combustion unit; After the ship main engine gas mode runs stably, gradually reduce the amount of compressed gas of the second BOG compressor (12) leading to the gas combustion unit and increase the amount of compressed gas leading to the ship main engine, so as to gradually incorporate the gas compressed by the second BOG compressor (12) into the ship main engine supply pipeline (9). After the first BOG compressor (10) and the second BOG compressor (12) operate in parallel stably, close the gas combustion unit intake pipeline (8) to stop supplying gas to the gas combustion unit.

3. The BOG compressor parallel operation system for ships according to claim 2, characterized in that, During the stable operation of the ship main engine, if the sum of the BOG amounts output by the first BOG compressor (10) and the second BOG compressor (12) is greater than the total consumption required for all ship main engines to operate at full load, then gradually open the gas combustion unit intake pipeline (8) while keeping the ship main engine operating at full load, and the excess BOG gas is directed to the gas combustion unit for combustion.

4. The BOG compressor parallel operation system for a ship according to claim 2, wherein, The first BOG compressor gas supply pipeline (6) includes a first BOG compressor gas supply pipe one (61) and a first BOG compressor gas supply pipe two (63). A first control valve (62) for controlling the on / off of this branch pipe is installed on the first BOG compressor gas supply pipe one (61), and a second control valve (64) for controlling the on / off of this branch pipe is installed on the first BOG compressor gas supply pipe two (63). The second BOG compressor gas supply pipeline (7) includes a second BOG compressor gas supply pipe one (71) and a second BOG compressor gas supply pipe two (73). A third control valve (72) for controlling the on / off of this branch pipe is installed on the second BOG compressor gas supply pipe one (71), and a fourth control valve (74) for controlling the on / off of this branch pipe is installed on the second BOG compressor gas supply pipe two (73).

5. The BOG compressor parallel operation system for ships according to claim 1, characterized in that, There are two LNG cargo tanks or fuel tanks (1).

6. The BOG compressor parallel operation system for ships according to claim 1, characterized in that, The ship is an LNG cargo tank or fuel ship, and the ship's main engine includes a dual-fuel main engine and a dual-fuel generator.

7. A control method for the system according to any one of claims 1-6, characterized in that, Specifically, it includes the following steps: Open the BOG gas transmission pipelines (2) on each LNG cargo tank or fuel tank (1), and at the same time open the BOG gas main pipeline (3), the first BOG compressor intake pipeline (4), the second BOG compressor intake pipeline (5), the pipeline of the first BOG compressor gas supply pipeline (6) connected to the ship's main engine intake pipeline (9), the pipeline of the second BOG compressor gas supply pipeline (7) connected to the gas combustion unit intake pipeline (8), the gas combustion unit intake pipeline (8) and the ship's main engine intake pipeline (9). Keep other pipelines closed and select the natural gas mode for the ship's main engine and generator operation; When the ship's main engine gas mode is just started, the gas compressed by the first BOG compressor (10) is only supplied for the use of the ship's main engine, and the gas compressed by the second BOG compressor (12) is only supplied for the use of the gas combustion unit; After the ship's main engine gas mode runs stably, gradually reduce the gas supply volume of the pipeline of the second BOG compressor gas supply pipeline (7) connected to the gas combustion pipeline (8), and at the same time increase the gas supply volume of the pipeline of the second BOG compressor gas supply pipeline (7) connected to the ship's main engine intake pipeline (9). Gradually incorporate the gas compressed by the second BOG compressor (12) into the ship's main engine intake pipeline (9). After the first BOG compressor (10) and the second BOG compressor (12) operate in parallel stably, close the gas combustion unit intake pipeline (8) to stop supplying gas to the gas combustion unit.

8. The control method according to claim 7, wherein During the stable operation of the ship's main engine gas mode, if the sum of the BOG volumes output by the first BOG compressor (10) and the second BOG compressor (12) is greater than the total consumption required for all ship's main engines to operate at full load, then gradually open the gas combustion unit intake pipeline (8) while keeping the ship's main engine operating at full load to direct the excess BOG gas to the gas combustion unit for combustion.

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