BOG (Boil Off Gas) recondensation system of dual-fuel ship

Abstract

The invention discloses a BOG recondensation system for a dual-fuel ship. The BOG recondensation system comprises a BOG pretreatment unit, a BOG recondensation unit, a low-pressure fuel gas supply unit and a high-pressure fuel gas supply unit. The BOG pretreatment unit comprises a BOG preheater, a BOG suction port tank, a compressor, a first-stage oil-gas separator, a BOG aftercooler and a second-stage oil-gas separator which are connected in sequence; the re-condensation unit comprises a secondary oil-gas separator, a BOG pre-cooler, a BOG re-condenser, a high-pressure pump and a high-pressure vaporizer which are connected in sequence; the low-pressure fuel gas supply unit comprises a low-pressure pump arranged in the fuel tank, and a fuel gas duplex filter, a BOG recondenser and a high-pressure pump which are sequentially connected with an outlet of the low-pressure pump; the high-pressure fuel gas supply unit comprises a high-pressure gasifier, a BOG pre-cooler, a high-pressure fuel gas buffer tank, an engine fuel gas supply main valve set and an engine which are sequentially connected with an outlet of the high-pressure pump. The method is low in investment cost, and fuel loss can be reduced.

Description

Technical Field

[0001] The present invention relates to a BOG recondensation system for a dual-fuel ship. Background Art

[0002] With the improvement of global environmental protection requirements, new types of ship fuels have begun to be widely used, especially liquefied natural gas (LNG) and liquefied ethane (LEG) fuels. Due to the cryogenic storage characteristics of liquefied gases, the treatment of boil-off gas (BOG) is inevitably involved.

[0003] For many refitted ships, only the engine is refitted, that is, the engine is refitted into a high-pressure dual-fuel engine. Since the inlet pressure of the high-pressure dual-fuel engine reaches 300 - 370 Barg (LNG: 300 - 325 Barg, LEG: 370 Barg), while the pressure of the fuel tank is only 0.7 - 18 Barg, the pressure of the BOG generated during ship operation is lower than the design pressure of the fuel tank, and the BOG generated in the fuel tank cannot be consumed. At this time, the excessive accumulation of BOG will cause safety accidents such as the action of the overpressure safety valve or structural damage. In order to treat the BOG, currently in the market, a high-pressure compressor is used to pressurize the BOG to the pressure required by the main engine. However, currently, only the Burkhardt compressor can be selected for the high-pressure compressor, and the cost investment is very high; in addition, a subcooler is also configured to treat the BOG and convert it into a liquid to circulate back into the fuel tank. Similarly, it depends on imported equipment, and the initial cost and the energy consumption of the ship's power grid are also relatively high. There are many operating devices for re-liquefying BOG based on land mixed refrigerants, but such devices also cause high energy consumption of the ship and high input costs; South Korea has a treatment plan of "recondensing the gas into a liquid and then directly feeding it into a high-pressure pump for pressurized gasification, and then supplying it to the main engine".

[0004] In view of the scenario where the gas users of refitted ships and newly built ships consume less or not at all, in order to ensure the safety of the fuel tank and the ship and prevent unnecessary fuel loss or structural damage caused by overpressure, it is urgent to develop a BOG recondensation system with relatively low cost. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide a BOG recondensation system for a dual-fuel ship, which not only has low input cost but also can reduce fuel loss.

[0006] The purpose of the present invention is achieved as follows: A BOG recondensation system for a dual-fuel ship includes a BOG pretreatment unit, a BOG recondensation unit, a low-pressure gas supply unit, and a high-pressure gas supply unit; wherein,

[0007] The BOG pretreatment unit includes a BOG preheater, a BOG suction tank, a compressor, a primary oil-gas separator, a BOG aftercooler, and a secondary oil-gas separator. Among them, the inlet of the BOG preheater is connected to the outlet of the fuel tank, and the outlet of the BOG preheater is connected to the inlet of the BOG suction tank. The outlet of the BOG suction tank is connected to the inlet of the compressor, and the outlet of the compressor is connected to the inlet of the primary oil-gas separator. The outlet of the primary oil-gas separator is connected to the inlet of the BOG aftercooler, and the outlet of the BOG aftercooler is connected to the inlet of the secondary oil-gas separator. The outlet of the secondary oil-gas separator is connected to the gas supply port of the low-pressure gas user on the ship and the return port of the BOG suction tank, and a compressor overpressure return valve is provided between the outlet of the secondary oil-gas separator and the return port of the BOG suction tank.

[0008] The recompression unit includes a BOG precooler, a BOG recompressor, a high-pressure pump, and a high-pressure vaporizer. Among them, the inlet of the BOG precooler is respectively connected to the fuel tank and the outlet of the secondary oil-gas separator. The inlet of the BOG recompressor is connected to the outlet of the BOG precooler through a recompression liquid flow regulating control valve. The condensate outlet of the BOG recompressor is connected to the inlet of the high-pressure pump through a condensate to high-pressure pump control valve. The condensate outlet of the BOG recompressor is also connected to the return port of the fuel tank through a condensate return to fuel tank control valve. The non-condensable gas of the BOG recompressor is connected to the inlet of the BOG preheater in the BOG pretreatment unit through a non-condensable gas release valve. The inlet of the high-pressure vaporizer is connected to the outlet of the high-pressure pump.

[0009] The low-pressure gas supply unit includes a low-pressure pump provided in the fuel tank, a gas double filter connected to the outlet of the low-pressure pump, and a BOG recompressor and a high-pressure pump respectively connected to the outlet of the gas double filter.

[0010] The high-pressure gas supply unit includes a high-pressure vaporizer and a BOG precooler respectively connected to the outlet of the high-pressure pump, a high-pressure gas buffer tank connected to the outlet of the high-pressure vaporizer, an engine gas supply main valve group connected to the outlet of the high-pressure gas buffer tank, and an engine connected to the outlet of the engine gas supply main valve group. The outlet of the BOG precooler is connected to the inlet of the high-pressure vaporizer.

[0011] In the above-mentioned BOG recompression system of the dual-fuel ship, the BOG recompression system further includes an auxiliary unit, and the auxiliary unit includes a lubricating oil circulation unit and a heat transfer medium circulation unit. Among them,

[0012] The lubricating oil circulation unit includes two lubricating oil pumps, a lubricating oil cooler, a primary oil-gas separator, a secondary oil-gas separator, and a lubricating oil double filter. Among them,

[0013] The oil discharge ports of two lubricating oil pumps are both connected to the oil inlet of the lubricating oil cooler. The oil discharge port of the lubricating oil cooler is connected to the oil inlet of the compressor through a lubricating oil temperature control valve. The outlet of the lubricating oil temperature control valve is also connected to the oil inlet of the first-stage oil-gas separator through a lubricating oil preheating circulation control valve. The oil discharge port of the first-stage oil-gas separator is connected to the oil inlet of the lubricating oil duplex filter, and the oil discharge ports of the lubricating oil duplex filter are respectively connected to the oil inlets of the two lubricating oil pumps.

[0014] The heat exchange medium circulation unit includes a high-temperature heat exchange medium connected to the heat exchange medium inlet of the high-pressure vaporizer and a low-temperature heat exchange medium connected to the heat exchange medium outlet of the high-pressure vaporizer, a low-temperature heat exchange medium respectively connected to the heat exchange medium inlets of the BOG preheater, the BOG aftercooler, and the lubricating oil cooler, and a high-temperature heat exchange medium connected to the heat exchange medium outlets of the BOG preheater, the BOG aftercooler, and the lubricating oil cooler.

[0015] In the above BOG recondensation system of a dual-fuel ship, the BOG recondensation system further includes a variable-frequency motor driving the compressor, a first differential pressure sensor provided on the gas duplex filter, a second differential pressure sensor provided on the lubricating oil duplex filter, a pressure sensor provided between the outlet of the second-stage oil-gas separator and the compressor overpressure reflux valve, a liquid level sensor provided in the BOG recondenser, a high-pressure pump outlet temperature sensor provided at the outlet of the high-pressure pump, a first flowmeter provided between the outlet of the BOG precooler and the recondensate flow regulating control valve, and a second flowmeter provided between the inlet of the engine and the recondensate flow regulating control valve.

[0016] In the above BOG recondensation system of a dual-fuel ship, the compressor adopts a normal-temperature single-stage screw compressor.

[0017] In the above BOG recondensation system of a dual-fuel ship, the BOG precooler adopts a printed circuit board heat exchanger.

[0018] In the above BOG recondensation system of a dual-fuel ship, an electric heater is provided on the first-stage oil-gas separator.

[0019] In the above BOG recondensation system of a dual-fuel ship, a liquid tank bottom injection valve or a liquid tank spray circulation valve is installed at the reflux port of the fuel tank.

[0020] The BOG recondensation system of the dual-fuel ship of the present invention has the following characteristics:

[0021] 1. Select a normal-temperature compressor, which overcomes the problem that the materials of low-temperature evaporation gas compressors need to be low-temperature resistant, provides more choices for equipment procurement, and greatly reduces the investment cost of BOG compressors.

[0022] 2. Compared with the mixed refrigerant re-liquefaction and subcooling unit, it has lower energy consumption and lower input cost.

[0023] 3. After the gas is recondensed into a liquid in the present invention, it can either go to the high-pressure pump or return to the fuel tank, which can reduce fuel loss.

[0024] 4. The present invention is applicable not only to the methane fuel supply system but also to the ethane fuel supply system. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is the principle structure diagram of the BOG recondensation system of the dual-fuel ship of the invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention will be further described below with reference to the drawings.

[0027] Please refer to Figure 1 , the BOG recondensation system for dual-fuel ships of the present invention includes a BOG pretreatment unit, a BOG recondensation unit, a low-pressure gas supply unit, a high-pressure gas supply unit, an auxiliary unit, and a monitoring and control unit.

[0028] The BOG pretreatment unit includes a BOG preheater E11, a BOG suction tank E12, a compressor E13, a primary oil-gas separator E14, a BOG aftercooler E15, and a secondary oil-gas separator E16; among them, the inlet of the BOG preheater E11 is connected to the outlet of the fuel tank 10 through a fuel supply valve V11 installed on the pipeline 101, and the outlet of the BOG preheater E11 is connected to the inlet of the BOG suction tank E12 through a pipeline 102; the outlet of the BOG suction tank E12 is connected to the inlet of the compressor E13 through a pipeline 103, and the outlet of the compressor E13 is connected to the inlet of the primary oil-gas separator E14; the outlet of the primary oil-gas separator E14 is connected to the inlet of the BOG aftercooler E15 through a pipeline 105, and the outlet of the BOG aftercooler E15 is connected to the inlet of the secondary oil-gas separator E16 through a pipeline 106; the outlet of the secondary oil-gas separator E16 is divided into three paths. The first path is connected to the gas supply port of the low-pressure gas user 20 on the ship through a pipeline 107, and a valve V14 is installed on the pipeline 107; the second path is connected to the inlet of the BOG precooler E21 through a pipeline 109, and a valve V13 is installed on the pipeline 109; the third path is connected to the return port of the BOG suction tank E12 through a return pipeline 108, and a compressor overpressure return valve V12 is installed on the return pipeline 108; the compressor E13 adopts a normal-temperature single-stage screw compressor.

[0029] The recondensation unit includes a BOG pre-cooler E21, a BOG re-condenser E22, a high-pressure pump E41 and a high-pressure vaporizer E42. Among them, the inlet of the BOG pre-cooler E21 is connected to the fuel tank 10; the inlet of the BOG re-condenser E22 is connected to the outlet of the BOG pre-cooler E21 through pipelines 201 and 202. A recondensate flow regulating control valve V21 is installed on the pipeline 202. The condensate outlet of the BOG re-condenser E22 is connected to the recondensate outlet pipeline 203. A recondensate return fuel tank control valve V22 is installed on the recondensate outlet pipeline 203; the outlet of the recondensate outlet pipeline 203 is connected to the return port of the fuel tank 10 through a pipeline 204. A liquid tank bottom injection valve V26 or a liquid tank spray circulation valve V25 is installed on the pipeline 204; the outlet of the recondensate outlet pipeline 203 is also connected to the inlet of the high-pressure pump E41 through a pipeline 205. A recondensate to high-pressure pump control valve V23 is installed on the pipeline 205; the gas outlet of the BOG re-condenser E22 is connected to the inlet of the BOG pre-heater E11 in the BOG pretreatment unit through a gas pipeline 206; the inlet of the high-pressure vaporizer E42 is connected to the outlet of the high-pressure pump E41 through a pipeline 401.

[0030] The low-pressure gas supply unit supplies low-pressure gas to the BOG re-condenser E22 and the high-pressure pump E41 and includes a low-pressure pump E31 provided in the fuel tank 10, a gas double filter E32 connected to the outlet of the low-pressure pump E31 through a pipeline 301, and the high-pressure pump E41 and the BOG re-condenser E22 respectively connected to the outlet of the gas double filter E32 through pipelines 302 and 303; a low-pressure fuel to BOG pre-cooler control valve V32 is installed on the pipeline 302.

[0031] The high-pressure gas supply unit supplies high-pressure gas to the high-pressure vaporizer E42 and the BOG pre-cooler E21 and includes the high-pressure vaporizer E42 and the BOG pre-cooler E21 respectively connected to the outlet of the high-pressure pump E41 through pipelines 401, a high-pressure gas buffer tank E46 connected to the outlet pipeline 402 of the high-pressure vaporizer E42, an engine gas supply main valve group E43 connected to the outlet of the high-pressure gas buffer tank E46 through an engine gas main valve V41, and an engine E45 connected to the outlet of the engine gas supply main valve group E43 through high-pressure gas pipelines 404 and 405; the outlet of the BOG pre-cooler E21 returns to the inlet of the high-pressure vaporizer E42 through a pipeline 403.

[0032] The auxiliary unit includes a lubricating oil circulation unit and a heat transfer medium circulation unit; among them,

[0033] The lubricating oil circulation unit supplies lubricating oil to compressor E13 and includes two lubricating oil pumps E53, E54, a lubricating oil cooler E55, a primary oil-gas separator E14, a secondary oil-gas separator E16, and a lubricating oil duplex filter E52; among which,

[0034] The oil discharge ports of the two lubricating oil pumps E53, E54 are both connected to the oil inlet of the lubricating oil cooler E55, the oil discharge port of the lubricating oil cooler E55 is connected to the oil inlet of the compressor E13 through a lubricating oil temperature control valve E56, and the outlet of the lubricating oil temperature control valve E56 is also connected to the oil inlet of the primary oil-gas separator E14 through a lubricating oil preheating circulation control valve V51; the oil discharge port of the primary oil-gas separator E14 is connected to the oil inlet of the lubricating oil duplex filter E52, and the oil discharge port of the lubricating oil duplex filter E52 is respectively connected to the oil inlets of the two lubricating oil pumps E53, E54; an electric heater E51 is provided on the primary oil-gas separator E14.

[0035] The heat exchange medium circulation unit includes a high-temperature heat exchange medium pipeline 529 connected to the heat exchange medium inlet of the high-pressure vaporizer E42 and a low-temperature heat exchange medium pipeline 530 connected to the heat exchange medium outlet of the high-pressure vaporizer E42, a low-temperature heat exchange medium pipeline 527 respectively connected to the heat exchange medium inlets 525 of the BOG preheater E11, the heat exchange medium inlet 521 of the BOG aftercooler E15, and the heat exchange medium inlet 523 of the lubricating oil cooler E55, and a high-temperature heat exchange medium pipeline 528 connected to the heat exchange medium outlets 526 of the BOG preheater E11, the heat exchange medium outlet 522 of the BOG aftercooler E15, and the heat exchange medium outlet 524 of the lubricating oil cooler E55.

[0036] The monitoring and control unit includes a variable-frequency motor connected to the driving compressor E13 through a coupling, a first differential pressure sensor provided on the gas duplex filter E32, a second differential pressure sensor provided on the lubricating oil duplex filter E52, a pressure sensor PT11 provided between the outlet of the secondary oil-gas separator E16 and the compressor overpressure reflux valve V12, a liquid level sensor LT11 provided on the BOG recooler E22, a high-pressure pump outlet temperature sensor TT21 provided at the outlet of the high-pressure pump E41, a first flowmeter E23 provided between the outlet of the BOG precooler E21 and the recirculated condensate flow regulating control valve V21, and a second flowmeter E44 provided between the inlet of the engine E45 and the recirculated condensate flow regulating control valve V21.

[0037] The working principle of the BOG pretreatment unit is:

[0038] 1.1. The BOG evaporation gas enters the BOG pre-heater E11 through the fuel supply valve V11 on the pipeline 10, pre-heats the low-temperature BOG evaporation gas, and then enters the BOG suction tank E12 through the pipeline 102; the BOG pre-heater E11 is mainly used to heat the BOG to the temperature required at the inlet of the normal-temperature compressor. The fuel supply valve V11 has an ESD function and can act according to the corresponding signals of the system;

[0039] 1.2. The heated BOG is temporarily stored in the BOG suction tank E12; the BOG suction tank E12 is used to maintain the stability of the suction pressure of the compressor E13 and perform gas-liquid separation;

[0040] 1.3. The heated BOG goes to the compressor E13 through the outlet pipeline 103 of the BOG suction tank E12. Two compressors E13 are configured. When the BOG flow rate is small, any one of the compressors E13 can be started to handle the BOG. When the BOG flow rate is large, both compressors E13 can be started simultaneously to handle the BOG; the compressor E13 adopts a normal-temperature single-stage screw compressor, and the evaporation gas can be compressed to 16 kg through a single-stage compressor, which can maximize the efficiency of BOG re-condensation and also meet the intake requirements of the low-pressure gas users 20 on the ship;

[0041] 1.4. After being compressed by the compressor E13, the BOG enters the baffle-type primary oil-gas separator E14 through the compressor discharge pipeline 104 for oil-gas separation. The primary oil-gas separator E14 can remove the lubricating oil in the gas; since the compressed BOG is in a high-temperature state, it needs to be cooled to 45 °C to meet the required temperature of the BOG pre-cooler E21 in the re-condensation system and the inlet temperature of the low-pressure gas users 20. Therefore, the BOG filtered by the primary oil-gas separator E14 enters the BOG after-cooler E15 through the pipeline 105 for cooling, and the cooled BOG enters the secondary oil-gas separator E16 for further fine filtration of oil-gas to further remove the oil in the gas; the BOG after oil-gas separation avoids the influence of lubricating oil on the engine E45 and the pollution of the gas in the fuel tank 10 when the gas is re-condensed back into the fuel tank 10.

[0042] 1.5. After being finely filtered by the secondary oil-gas separator E16, the BOG goes to the pipeline 109 and the pipeline 110 through the pipeline 107 respectively. A valve V13 is installed on the pipeline 109, and the valve V13 controls the evaporation gas to go to the BOG pre-cooler E21 for the next pre-cooling; a valve V14 is installed on the pipeline 110, and the valve V14 controls the gas to go to the low-pressure gas users 20 (optional) of the ship.

[0043] The working principle of the re-condensation unit is:

[0044] 2.1. BOG enters BOG precooler E21 through pipeline 109 to exchange heat with high-pressure gas. BOG precooler E21 uses printed circuit board heat exchanger (PCHE) for efficient heat exchange; BOG is initially cooled to about -100°C. The initially cooled BOG enters BOG recondenser E22 through pipelines 201 and 202, the first flowmeter E23 and the recondensate flow regulating control valve V21. The load regulation control of the recondensate unit is achieved by controlling the opening of the recondensate flow regulating control valve V21 based on the data of the second flowmeter E44, the first flowmeter E23 and the high-pressure pump outlet temperature sensor TT21.

[0045] 2.2. The BOG coming out of the BOG precooler E21 enters the BOG recondenser E22 through the recondensate flow regulating control valve V21, and exchanges heat with the low-pressure liquid fuel supplied to the BOG recondenser E22 by the low-pressure pump E31, so as to recondense the BOG into liquid.

[0046] 2.3. The recondensed liquid is mixed with the inlet liquid of the high-pressure pump E41 through valve V23 and enters the high-pressure vaporizer E42 to prepare fuel.

[0047] 2.4. The recondensed liquid returns to the fuel tank 10 through the valve V22. It can directly enter the fuel tank 10 through the bottom injection pipe control valve V26 as needed, or enter the fuel tank 10 after entering the spray pipe through the fuel tank spray control valve V25.

[0048] 2.5. The non-condensable gas in the BOG recondenser E22 enters the BOG preheater E11 in the BOG pretreatment unit through the non-condensable gas release valve V24 installed on the gas pipeline 206 to continue pretreatment. At the same time, the overpressure gas in the BOG recondenser E22 can also be released to the pretreatment unit through the non-condensable gas release valve V24.

[0049] The working principle of the low-pressure gas supply unit is:

[0050] The low-pressure fuel gas in the fuel tank 10 is pumped out through the low-pressure pump E31 in the fuel tank 10, passes through the valve V301 and the pipeline 301, and enters the fuel gas duplex filter E32, and then enters the high-pressure pump E41 and the BOG recondenser E22 through the valves V32 and V33 in a one-to-one correspondence; the fuel tank 10 can be a C-type or B-type fuel tank; the low-pressure pump E31 is a submersible pump or a deep well pump; the fuel gas duplex filter 32 can prevent damage caused by tiny particles entering the high-pressure pump E41, and at the same time they serve as backup for each other and can be switched to ensure the stability of the engine air supply.

[0051] The working principle of the high pressure gas supply unit is:

[0052] 4.1. The high-pressure gas formed after the low-pressure fuel is pressurized by the high-pressure pump E41 can directly go to the high-pressure vaporizer E42, and the high-pressure vaporizer E42 vaporizes the high-pressure gas to the inlet temperature required by the engine E45.

[0053] 4.2. The high-pressure gas formed after the low-pressure fuel is pressurized by the high-pressure pump E41 also enters the BOG pre-cooler E21 through the valve V42 to exchange heat with the hot BOG, and then returns to the inlet of the high-pressure vaporizer E42 through the valve V43 installed on the pipeline 403; the high-pressure pump outlet temperature sensor TT11 provides a signal to the recondensate flow regulating control valve V21.

[0054] 4.3. The high-pressure gas coming out of the high-pressure vaporizer E42 enters the high-pressure gas buffer tank E46. The high-pressure gas buffer tank E46 not only avoids the fluctuation of the supply gas pressure, but also buffers the pulse of the high-pressure pump E41.

[0055] 4.4. The high-pressure gas in the high-pressure gas buffer tank 46 is transported to the engine gas supply main valve group E43 through the engine gas main valve V41, and then enters the engine E45 through the second flowmeter E44. The engine gas main valve V41 has an emergency cut-off function to cut off the system gas supply in case of a gas supply failure; the engine gas supply main valve group E43 regulates the gas flow and pressure; the second flowmeter E44 provides a signal to the recondensate flow regulating control valve V21 and measures the gas consumption of the main engine at the same time.

[0056] The working principle of the lubricating oil circulation unit is as follows:

[0057] Before the compressor 13 starts, it is necessary to ensure the normal operation of the lubricating oil system. In order to ensure the normal start of the compressor 13 after the initial start or after a period of shutdown, the first-stage oil-gas separator 14 is equipped with an electric heater E51 for preheating the lubricating oil. The lubricating oil preheating circulation consists of pipelines 511, 512, 513, 514, 515, 516, lubricating oil duplex filter E52, lubricating oil pumps E53 / 54, lubricating oil preheating circulation control valve V51, temperature control valve E56 and lubricating oil cooler E55. When the lubricating oil temperature is qualified, the lubricating oil preheating circulation control valve V51 closes, and the lubricating oil circulates completely through the compressor E13; the temperature control valve E56 is used to regulate the flow of the lubricating oil and the flow of the lubricating oil going to the lubricating oil cooler E55; the lubricating oil duplex filter E52 is used to filter impurities in the lubricating oil to avoid impurities entering the compressor E13 and causing wear of the compressor E13. The lubricating oil duplex filter E52 is equipped with a differential pressure sensor to monitor the clogging of the filter; when one lubricating oil pump is in use, the other lubricating oil pump is in standby state, which provides the safety of the lubricating oil circulation unit; the lubricating oil pumps E53 / 54 adopt screw-type lubricating oil pumps to lubricate the compressor E13 and ensure the normal operation of the compressor E13; the lubricating oil cooler E55 is used to cool the lubricating oil to facilitate the lubricating oil circulation unit to maintain high efficiency.

[0058] The working principle of the heat exchange medium circulation unit is:

[0059] The heat exchange medium is water glycol, which is divided into low-temperature glycol and high-temperature glycol. The high-temperature glycol system enters the high-pressure gasifier E42 through pipeline 529 to heat the high-pressure fuel gas to the inlet temperature required by the engine E45. The low-temperature glycol is used to preheat the cold BOG in the fuel tank 10 to room temperature to meet the needs of the room-temperature compressor E13, and to cool the compressed high-temperature BOG and the lubricating oil of the compressor E13. The low-temperature glycol goes to three users, namely the BOG preheater E11, the BOG aftercooler E15 and the lubricating oil cooler E55.

[0060] Working principle of control and monitoring unit:

[0061] A. The first pressure difference sensor and the second pressure difference sensor are respectively provided for the gas duplex filter E32 and the lubricating oil duplex filter E52, so as to monitor whether the gas duplex filter E32 and the lubricating oil duplex filter E52 are blocked.

[0062] B. Compressor E13 controls pressure and displacement through the speed of the variable frequency motor.

[0063] C. The pressure sensor PT11 installed at the outlet of the secondary oil-gas separator E16 is used to control the opening of the compressor overpressure return valve V12 when the pretreatment unit is overpressured.

[0064] D. The liquid level sensor LT11 installed on the BOG recondenser E22 provides a signal to the liquid level control valve V24 to realize the liquid level control of the BOG recondenser E22.

[0065] E. The temperature sensor TT21 at the outlet of the high-pressure pump E41, the first flow meter E23 at the BOG precooler E21 and the second flow meter E44 at the inlet of the engine E45 jointly provide signals to the recondensing flow regulating valve V21.

[0066] The above embodiments are only used to illustrate the present invention, rather than to limit the present invention. Those skilled in the relevant technical field may make various changes or modifications without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions should also belong to the scope of the present invention and should be defined by the claims.

Claims

1. A BOG recondensation system for a dual-fuel ship, comprising a BOG pretreatment unit, a BOG recondensation unit, a low-pressure gas supply unit and a high-pressure gas supply unit; characterized in that, The BOG pretreatment unit includes a BOG preheater, a BOG suction tank, a compressor, a first-stage oil-gas separator, a BOG aftercooler and a second-stage oil-gas separator; wherein, the inlet of the BOG preheater is connected to the outlet of the fuel tank, and the outlet of the BOG preheater is connected to the inlet of the BOG suction tank; the outlet of the BOG suction tank is connected to the inlet of the compressor, and the outlet of the compressor is connected to the inlet of the first-stage oil-gas separator; the outlet of the first-stage oil-gas separator is connected to the inlet of the BOG aftercooler, and the outlet of the BOG aftercooler is connected to the inlet of the second-stage oil-gas separator; the outlet of the second-stage oil-gas separator is connected to the gas supply port of the low-pressure gas user on the ship and the reflux port of the BOG suction tank, and a compressor overpressure reflux valve is provided between the outlet of the second-stage oil-gas separator and the reflux port of the BOG suction tank; The recondensation unit includes a BOG precooler, a BOG recondenser, a high-pressure pump and a high-pressure vaporizer; wherein, the inlet of the BOG precooler is respectively connected to the fuel tank and the outlet of the second-stage oil-gas separator; the inlet of the BOG recondenser is connected to the outlet of the BOG precooler through a recondensate flow regulating control valve, the condensate outlet of the BOG recondenser is connected to the inlet of the high-pressure pump through a condensate to high-pressure pump control valve, the condensate outlet of the BOG recondenser is also connected to the reflux port of the fuel tank through a condensate return fuel tank control valve, and the non-condensable gas of the BOG recondenser is connected to the inlet of the BOG preheater in the BOG pretreatment unit through a non-condensable gas release valve; the inlet of the high-pressure vaporizer is connected to the outlet of the high-pressure pump; The low-pressure gas supply unit includes a low-pressure pump arranged in the fuel tank, a gas double filter connected to the outlet of the low-pressure pump, and a BOG recondenser and a high-pressure pump respectively connected to the outlet of the gas double filter; The high-pressure gas supply unit includes a high-pressure vaporizer and a BOG precooler respectively connected to the outlet of the high-pressure pump, a high-pressure gas buffer tank connected to the outlet of the high-pressure vaporizer, an engine gas supply main valve group connected to the outlet of the high-pressure gas buffer tank, and an engine connected to the outlet of the engine gas supply main valve group; the outlet of the BOG precooler is connected to the inlet of the high-pressure vaporizer.

2. The BOG recondensation system of the dual-fuel ship according to claim 1, characterized in that, The BOG recondensation system further includes an auxiliary unit, and the auxiliary unit includes a lubricating oil circulation unit and a heat transfer medium circulation unit; wherein, The lubricating oil circulation unit includes two lubricating oil pumps, a lubricating oil cooler, a first-stage oil-gas separator, a second-stage oil-gas separator and a lubricating oil double filter; wherein, The oil discharge ports of two lubricating oil pumps are both connected to the oil inlet of the lubricating oil cooler. The oil discharge port of the lubricating oil cooler is connected to the oil inlet of the compressor through a lubricating oil temperature control valve. The outlet of the lubricating oil temperature control valve is also connected to the oil inlet of the first-stage oil-gas separator through a lubricating oil preheating circulation control valve. The oil discharge port of the first-stage oil-gas separator is connected to the oil inlet of the lubricating oil duplex filter, and the oil discharge port of the lubricating oil duplex filter is respectively connected to the oil inlet of two lubricating oil pumps. The heat exchange medium circulation unit includes a high-temperature heat exchange medium connected to the heat exchange medium inlet of the high-pressure vaporizer and a low-temperature heat exchange medium connected to the heat exchange medium outlet of the high-pressure vaporizer. The low-temperature heat exchange medium is respectively connected to the heat exchange medium inlets of the BOG preheater, the BOG aftercooler, and the lubricating oil cooler, and the high-temperature heat exchange medium is connected to the heat exchange medium outlets of the BOG preheater, the BOG aftercooler, and the lubricating oil cooler.

3. The BOG recondensation system of the dual-fuel ship according to claim 1 or 2, characterized in that, The BOG recondensing system further includes a variable-frequency motor for driving the compressor, a first differential pressure sensor provided on the gas fuel duplex filter, a second differential pressure sensor provided on the lubricating oil duplex filter, a pressure sensor provided between the outlet of the second-stage oil-gas separator and the compressor overpressure reflux valve, a liquid level sensor provided in the BOG recondenser, a high-pressure pump outlet temperature sensor provided at the outlet of the high-pressure pump, a first flowmeter provided between the outlet of the BOG precooler and the recondensate flow regulating control valve, and a second flowmeter provided between the inlet of the engine and the recondensate flow regulating control valve.

4. The BOG recompression system of the dual-fuel ship according to claim 1 or 2, characterized in that, The compressor uses a normal-temperature single-stage screw compressor.

5. The BOG recondensation system of the dual-fuel ship according to claim 1, characterized in that, The BOG precooler uses a printed circuit board heat exchanger.

6. The BOG recondensation system of the dual-fuel ship according to claim 1 or 2, characterized in that, An electric heater is provided on the first-stage oil-gas separator.

7. The BOG recondensation system of the dual-fuel ship according to claim 1, characterized in that, A liquid tank bottom injection valve or a liquid tank spray circulation valve is installed at the return port of the fuel tank.

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