Cryogenic reliquefaction device utilizing natural gas cold energy

Abstract

The invention discloses a cryogenic reliquefaction device utilizing natural gas cold energy. The cryogenic reliquefaction device comprises a compressor, an expansion machine and a motor used for driving the compressor and the expansion machine to rotate. The compressor is sequentially connected with the water cooler, the backheating heat exchanger, the expansion machine and the supercooling heat exchanger through pipelines to form a cooling loop; a cooled loop is formed between the supercooling heat exchanger and the liquefied natural gas storage device; at least one refrigerant side inlet of the backheating heat exchanger is communicated with the liquefied natural gas storage device, and an outlet of the backheating heat exchanger is communicated with the boil-off gas collecting facility. When the reliquefaction device works, natural gas cold energy can be fully utilized, part of heat exchange loss of the heat exchanger is offset, the inlet and outlet temperature of the compressor is improved, the compression efficiency is greatly improved, meanwhile, the use amount of cooling water can be reduced, and therefore the comprehensive efficiency of the reliquefaction device is improved. And the device has high economic and practical values in occasions where natural gas is needed.

Description

Technical Field

[0001] The present invention relates to a liquefaction device, in particular to a cryogenic reliquefaction device utilizing cold energy of natural gas. Background Art

[0002] As the world's energy demand and environmental awareness continue to increase, natural gas is becoming more and more important in the energy structure of various countries. There are many ways to transport natural gas. With the rapid development of natural gas trade, the most common way for long-distance ocean transportation is liquefied natural gas (LNG).

[0003] LNG is transported at sea by large LNG carriers. Due to problems such as heat leakage in the cargo tank during transportation, LNG will inevitably undergo low-temperature liquid gasification, producing boil-off gas (BOG). As the amount of boil-off gas increases, the temperature and pressure of the cargo tank will gradually increase. In order to ensure transportation safety and reduce energy waste and economic losses, BOG needs to be reliquefied and recovered. At present, the cryogenic reliquefaction technology based on the reverse Brayton cycle can supercool LNG and then return it to the cargo tank, and directly condense BOG through a spray device. This BOG treatment device and method has relatively outstanding advantages in terms of safety, efficiency, reliability, installation and maintenance, and has a better market prospect. However, for the BOG treatment system of large LNG carriers, in order to quickly cool down (such as pre-cooling process) or maintain the system at a low temperature (such as standby process), the system must be started quickly at high power or run for a long time at low power, which requires a certain amount of operation and maintenance time and cost, and the flexibility needs to be further improved.

[0004] On the other hand, the power system of LNG carriers usually adopts dual-fuel engines, mainly using natural gas naturally evaporated from LNG cargo tanks, namely BOG, as fuel. If the gas demand is high, it can be supplemented by pumping LNG gasification, and traditional marine diesel can also be used. However, the storage temperature of LNG is -163℃, while the temperature of natural gas used in the power system is the ambient temperature, usually 20-45℃. The vaporization and heating process from -163℃ to ambient temperature will release about 850kJ / kg of cold energy. At present, this part of cold energy can be used for air conditioning, cold storage and cold energy power generation. Among them, the cooling capacity required for ship air conditioning and cold storage is very small, and the cold energy power generation process is too complicated and difficult to promote on ships. Therefore, this part of cold energy has not been fully utilized, resulting in a large amount of cold energy waste. Summary of the invention

[0005] Purpose of the invention: The purpose of the present invention is to provide a cryogenic reliquefaction device that utilizes the cold energy of natural gas, which can not only fully utilize the cold energy of natural gas, but also improve the comprehensive efficiency of the reliquefaction device and effectively reduce operation and maintenance investment.

[0006] Technical solution: The deep-cold reliquefaction device utilizing the cold energy of natural gas described in the present invention comprises a compressor, an expander, and a motor for driving the compressor and the expander to rotate; the compressor and the water cooler, the heat recovery heat exchanger, the expander, and the subcooling heat exchanger are sequentially connected by pipelines to form a cooling circuit; a cooled circuit is formed between the subcooling heat exchanger and the liquefied natural gas storage device; at least one refrigerant side inlet of the heat recovery heat exchanger is connected to the liquefied natural gas storage device, and its outlet is connected to the evaporated gas collection facility.

[0007] Wherein, the liquefied natural gas storage device includes at least one storage tank for containing liquefied natural gas, and the storage tank includes at least one lower area for containing liquefied natural gas and at least one upper area for containing evaporated gas of liquefied natural gas; the heat medium side inlet of the subcooling heat exchanger is connected to the lower area; the heat medium side outlet of the subcooling heat exchanger is connected to the upper area.

[0008] Among them, at least one refrigerant side inlet of the heat recovery heat exchanger is connected to the lower area of ​​the storage tank through a first branch, and its outlet is connected to the gas using device through a second branch.

[0009] Among them, at least one refrigerant side inlet of the heat exchanger is connected to the upper area of ​​the storage tank through the third branch, at least one refrigerant side outlet of the heat exchanger is connected to the evaporator compressor through the fourth branch, and the evaporator compressor is connected to the gas using device through the fifth branch.

[0010] The storage tank is provided with a delivery pump for delivering the liquefied natural gas in the storage tank to the heat medium side inlet of the subcooling heat exchanger, and a spraying device connected to the heat medium side outlet of the subcooling heat exchanger for spraying the liquefied natural gas in a subcooled state back to the storage tank.

[0011] The delivery pump is installed in the lower area of ​​the storage tank and is used to pressurize and deliver the LNG; the spray device is installed in the upper area of ​​the storage tank.

[0012] Wherein, the evaporative gas collecting device comprises at least one gas using device, and the refrigerant side outlet of the heat recovery heat exchanger is connected to the gas using device through an evaporative gas compressor.

[0013] Wherein, the compressor and the expander are coaxially arranged through the motor for driving.

[0014] In this process, low temperature is provided at the subcooling heat exchanger via a closed refrigerant circuit.

[0015] The refrigerant is a mixture of one or more gases selected from the group consisting of helium, nitrogen, neon and argon.

[0016] Beneficial effects: Compared with the prior art, the present invention achieves the following significant effects:

[0017] (1) The deep-cold reliquefaction device utilizing the cold energy of natural gas provided by the present invention makes effective and direct use of the cold energy of liquefied natural gas or its evaporated gas, thereby avoiding the problem of excess cold energy in situations where natural gas is required (such as LNG transport ships powered by LNG), and at the same time eliminating the need for a traditional BOG evaporator and heater or BOG preheater; (2) The present invention can offset part of the heat exchange loss of the heat exchanger while the reliquefier is working, and improve the inlet and outlet temperatures of the compressor, thereby greatly improving the compression efficiency, while reducing the amount of cooling water, reducing the overall power consumption, and saving the cooling time of the reliquefaction device; (3) The present invention only adds a refrigerant side flow channel to the heat exchanger, so the process is simple and the offshore adaptability is strong. At the same time, the overall efficiency is higher and the operation and maintenance investment is less. The present invention is very suitable for situations where both reliquefaction of natural gas and utilization of natural gas are required, and has higher economic and practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of one structure of the device of the present invention;

[0019] Figure 2 Another structural schematic diagram of the device of the present invention. DETAILED DESCRIPTION

[0020] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0021] like Figure 1 As shown, the present invention provides a cryogenic reliquefaction device utilizing cold energy of natural gas, comprising a compressor 21, an expander 22, and a motor 23 for driving the compressor 21 and the expander 22 to rotate; the compressor 21 and the water cooler 24, the heat recovery heat exchanger 25, the expander 22, and the subcooling heat exchanger 26 are sequentially connected by pipelines to form a cooling circuit; a cooled circuit is formed between the subcooling heat exchanger 26 and the liquefied natural gas storage device 1; at least one refrigerant side inlet of the heat recovery heat exchanger 25 is connected to the liquefied natural gas storage device 1, and its outlet is connected to the evaporation gas collection device 3.

[0022] The liquefied natural gas storage device 1 of this embodiment includes a storage tank 11 for containing liquefied natural gas, and the storage tank 11 includes a lower area 113 for containing liquefied natural gas and an upper area 112 for containing boil-off gas of liquefied natural gas; the heat medium side inlet of the subcooling heat exchanger 26 is connected to the lower area 113; the heat medium side outlet of the subcooling heat exchanger 26 is connected to the upper area 112. The number of storage tanks 11 can be set as needed, and the upper area 112 and the lower area 113 in the storage tank 11 can be set in multiples.

[0023] The refrigerant side inlet of the regenerative heat exchanger 25 of this embodiment is connected to the lower area 113 of the storage tank 11 through the first branch R31, and the outlet is connected to the gas using device 31 through the second branch R32. Figure 1 The refrigerant side inlet of the regenerative heat exchanger 25 of this embodiment can also be arranged to be connected to the upper area 112 of the storage tank 11 through the third branch R33. At this time, the refrigerant side outlet of the regenerative heat exchanger 25 is connected to the evaporation gas compressor 32 through the fourth branch R34, and the evaporation gas compressor 32 is connected to the gas user 31 through the fifth branch R35. Figure 2 shown.

[0024] The storage tank 11 of this embodiment is provided with a delivery pump 12 for delivering the liquefied natural gas in the storage tank 11 to the heat medium side inlet of the subcooling heat exchanger 26, and a spray device 13 connected to the heat medium side outlet of the subcooling heat exchanger 26 for spraying the liquefied natural gas in a subcooled state back to the storage tank 11. The delivery pump 12 is installed in the lower area 113 of the storage tank 11, and is used for pressurizing and delivering the LNG; the spray device 13 is installed in the upper area 112 of the storage tank 11.

[0025] The evaporation gas collecting device 3 of the present embodiment includes an air-using device 31. The refrigerant-side outlet of the heat recovery heat exchanger 25 is connected to the air-using device 31 through an evaporation gas compressor 32. The number of the air-using devices 31 can be set according to needs.

[0026] The compressor 21 of this embodiment is a centrifugal compressor; the expander 22 is a turbine expander; the motor 23 used for driving is a magnetic levitation motor; the compressor 21 and the expander 22 are coaxially arranged through the motor 23 used for driving; the water cooler 24 is a shell and tube heat exchanger; the heat recovery heat exchanger 25 and the subcooling heat exchanger 26 are plate-fin heat exchangers.

[0027] In this embodiment, a closed refrigerant circuit is used to provide low temperature at the subcooling heat exchanger 26. The refrigerant is a mixture of one or more gases selected from helium, nitrogen, neon and argon.

Claims

1. A cryogenic reliquefaction device utilizing cold energy of natural gas, comprising a compressor (21), an expander (22), and a motor (23) for driving the compressor (21) and the expander (22) to rotate; characterized in that: The compressor (21) is connected in sequence with a water cooler (24), a heat recovery heat exchanger (25), an expander (22), and a subcooling heat exchanger (26) via pipelines to form a cooling circuit; a cooled circuit is formed between the subcooling heat exchanger (26) and the liquefied natural gas storage device (1); at least one refrigerant side inlet of the heat recovery heat exchanger (25) is connected to the liquefied natural gas storage device (1), and its outlet is connected to the evaporated gas collection facility (3).

2. The cryogenic reliquefaction device utilizing natural gas cold energy according to claim 1, characterized in that: The liquefied natural gas storage device (1) comprises at least one storage tank (11) for containing liquefied natural gas, wherein the storage tank (11) comprises at least one lower region (111) for containing liquefied natural gas and at least one upper region (112) for containing evaporated gas of the liquefied natural gas; the heat medium side inlet of the subcooling heat exchanger (26) is connected to the lower region (111); and the heat medium side outlet of the subcooling heat exchanger (26) is connected to the upper region (112).

3. The cryogenic reliquefaction device using natural gas cold energy according to claim 2, characterized in that: At least one refrigerant side inlet of the heat recovery heat exchanger (25) is connected to the lower area (111) of the storage tank (11) through a first branch (R31), and its outlet is connected to the gas using device (31) through a second branch (R32).

4. The cryogenic reliquefaction device using natural gas cold energy according to claim 2, characterized in that: At least one refrigerant side inlet of the heat exchanger (25) is connected to the upper area (112) of the storage tank (11) through a third branch (R33), and at least one refrigerant side outlet of the heat exchanger (25) is connected to the evaporator compressor (32) through a fourth branch (R34), and the evaporator compressor (32) is connected to the gas using device (31) through a fifth branch (R35).

5. The cryogenic reliquefaction device utilizing natural gas cold energy according to claim 2, characterized in that: The storage tank (11) is provided with a delivery pump (12) for delivering the liquefied natural gas in the storage tank (11) to the heat medium side inlet of the subcooling heat exchanger (26), and a spraying device (13) connected to the heat medium side outlet of the subcooling heat exchanger (26) for spraying the liquefied natural gas in a subcooled state back to the storage tank (11).

6. The cryogenic reliquefaction device using natural gas cold energy according to claim 5, characterized in that: The delivery pump (12) is installed in the lower area (111) of the storage tank (11) and is used to pressurize and deliver the LNG; the spray device (13) is installed in the upper area (112) of the storage tank (11).

7. The cryogenic reliquefaction device using natural gas cold energy according to claim 1, characterized in that: The evaporative gas collecting device (3) comprises at least one gas using device (31), and the refrigerant side outlet of the heat recovery heat exchanger (25) is connected to the gas using device (31) via an evaporative gas compressor (32).

8. The cryogenic reliquefaction device using natural gas cold energy according to claim 1, characterized in that: The compressor (21) and the expander (22) are coaxially arranged via the motor (23) for driving.

9. The cryogenic reliquefaction device using natural gas cold energy according to claim 1, characterized in that: A low temperature is provided at the subcooling heat exchanger (26) through a closed refrigerant circuit.

10. The cryogenic reliquefaction device using natural gas cold energy according to claim 9, characterized in that: The refrigerant is a mixture of one or more gases selected from the group consisting of helium, nitrogen, neon and argon.

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