A liquid nitrogen cooled BOG gas liquefaction recovery system

Abstract

The utility model discloses a kind of liquid nitrogen cooling BOG gas liquefaction recovery systems, it includes LNG storage tank, primary heat exchanger, primary liquid nitrogen storage tank, primary liquid nitrogen storage tank gasifier, primary gas-liquid separator and primary heat exchanger rear gasifier;The diffusion port of the LNG storage tank is equipped with pressure relief valve, the diffusion port is sequentially communicated with the heat exchange passage of one primary heat exchanger and the inlet of primary gas-liquid separator, the liquid outlet of primary gas-liquid separator is communicated with LNG storage tank;The primary liquid nitrogen storage tank gasifier is connected between the gasification outlet and gasification inlet of primary liquid nitrogen storage tank, the liquid ammonia outlet of primary liquid nitrogen storage tank is communicated with another heat exchange passage of primary heat exchanger, the heat exchange passage outlet is communicated with the inlet of primary heat exchanger rear gasifier, and the gas outlet of primary heat exchanger rear gasifier is communicated with gaseous nitrogen pipe network.This system reduces equipment investment cost, and operation cost is also low, and liquid nitrogen price is cheap, with the characteristics of saving power consumption, low investment, remarkable economic benefits.

Description

Technical Field

[0001] This utility model relates to the field of liquefied natural gas recovery technology, and in particular to a liquid nitrogen-cooled BOG liquefaction and recovery system. Background Technology

[0002] Boil-off gas (BOG) is the vaporized gas produced when liquefied natural gas (LNG) partially transforms from a liquid state to a gaseous state during storage or transportation due to temperature increases. The typical process for recovering BOG from LNG storage tanks involves using a BOG compressor to vaporize the BOG gas in a vaporizer to ambient temperature before it is drawn back into the liquefaction process. To ensure process continuity, one BOG compressor needs to be on standby. The cooling capacity of the BOG is wasted during vaporization, and the BOG compressor cylinders require regular maintenance and spare parts replacement, consuming significant amounts of electricity. This results in high investment costs, uneconomical operation (high electricity consumption), and expensive spare parts replacements. Utility Model Content

[0003] The technical problem to be solved by this utility model is to provide an energy-saving and efficient liquid nitrogen cooling BOG gas liquefaction and recovery system.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by this utility model is as follows: it includes an LNG storage tank, a primary heat exchanger, a primary liquid nitrogen storage tank, a primary liquid nitrogen storage tank vaporizer, a primary gas-liquid separator, and a post-vaporizer of the primary heat exchanger; the vent of the LNG storage tank is equipped with a pressure relief valve, which is sequentially connected to one heat exchange passage of the primary heat exchanger and the inlet of the primary gas-liquid separator, and the outlet of the primary gas-liquid separator is connected to the LNG storage tank; the primary liquid nitrogen storage tank vaporizer is connected in series between the vaporization outlet and the vaporization inlet of the primary liquid nitrogen storage tank, the liquid ammonia outlet of the primary liquid nitrogen storage tank is connected to another heat exchange passage of the primary heat exchanger, the outlet of which is connected to the inlet of the post-vaporizer of the primary heat exchanger, and the outlet of the post-vaporizer of the primary heat exchanger is connected to the gaseous nitrogen pipeline network.

[0005] Furthermore, the LNG storage tank is equipped with an LNG storage tank pressure monitoring instrument; the primary liquid nitrogen storage tank is equipped with a primary liquid nitrogen storage tank pressure monitoring instrument; and a primary liquid nitrogen flow regulating valve is installed on the pipeline between the primary liquid nitrogen storage tank vaporizer and the primary liquid nitrogen storage tank.

[0006] Furthermore, the primary liquid nitrogen flow regulating valve is interlocked with the pressure relief valve.

[0007] Furthermore, a temperature monitoring instrument for the first-stage heat exchanger is installed on the pipeline between the first-stage heat exchanger and the first-stage gas-liquid separator.

[0008] Furthermore, the temperature monitoring instrument after the primary heat exchanger controls the opening of the primary liquid nitrogen flow regulating valve.

[0009] Furthermore, the system includes a secondary heat exchanger, a secondary liquid nitrogen storage tank, a secondary liquid nitrogen storage tank vaporizer, a secondary gas-liquid separator, a secondary heat exchanger post-vaporizer, and a secondary gas-liquid separator post-vaporizer. The outlet of the primary gas-liquid separator is sequentially connected to one heat exchange path of the secondary heat exchanger and the inlet of the secondary gas-liquid separator. The outlet of the secondary gas-liquid separator is connected to the secondary gas-liquid separator post-vaporizer, and the liquid outlet of the secondary gas-liquid separator is connected to the LNG storage tank. The secondary liquid nitrogen storage tank vaporizer is connected in series between the vaporization outlet and the vaporization inlet of the secondary liquid nitrogen storage tank. The liquid ammonia outlet of the secondary liquid nitrogen storage tank is connected to another heat exchange path of the secondary heat exchanger, and the outlet of this heat exchange path is connected to the inlet of the secondary heat exchanger post-vaporizer. The outlets of both the secondary heat exchanger post-vaporizer and the secondary gas-liquid separator post-vaporizer are connected to a gaseous nitrogen pipeline network.

[0010] Furthermore, the secondary liquid nitrogen storage tank is equipped with a secondary liquid nitrogen storage tank pressure monitoring instrument; a secondary liquid nitrogen flow regulating valve is installed on the pipeline between the secondary liquid nitrogen storage tank vaporizer and the secondary liquid nitrogen storage tank.

[0011] Furthermore, the secondary liquid nitrogen flow regulating valve is interlocked with the pressure relief valve.

[0012] Furthermore, a temperature monitoring instrument for the secondary heat exchanger is installed on the pipeline between the secondary heat exchanger and the secondary gas-liquid separator.

[0013] Furthermore, the temperature monitoring instrument after the secondary heat exchanger controls the opening degree of the secondary liquid nitrogen flow regulating valve.

[0014] The beneficial effects of adopting the above technical solution are as follows: In the LNG storage tank described in this invention, the BOG gas exchanges heat with liquid nitrogen through a heat exchanger. After liquefaction, it is separated by a gas-liquid separator. The liquid LNG flows back to the LNG storage tank, while the gaseous nitrogen and part of the BOG gas are cooled again to liquefy LNG, which then flows back to the LNG storage tank. This cycle can be repeated multiple times until the methane content in the nitrogen is low. The nitrogen in the BOG gas and the nitrogen after heat exchange are combined and reused in the industrial nitrogen pipeline network. This invention eliminates the need for a BOG compressor, resulting in energy savings, low investment, and significant economic benefits.

[0015] The system provided by this utility model can start and stop processing BOG gas at any time, and has good adaptability to changes in operating conditions; it reduces equipment investment costs and operating costs, and liquid nitrogen is inexpensive; the system has high operational safety, and the liquid nitrogen is recycled instead of being emitted after cooling the BOG gas; this system can effectively overcome the shortcomings of existing technologies and has the characteristics of saving power consumption, low investment, and significant economic benefits. Attached Figure Description

[0016] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0017] Figure 1 This is a schematic diagram of the system structure of this utility model.

[0018] In the diagram: LNG storage tank 1; LNG storage tank pressure monitor 2; LNG storage tank pressure relief valve 3; primary heat exchanger 4-1; secondary heat exchanger 4-2; primary liquid nitrogen storage tank 5-1; secondary liquid nitrogen storage tank 5-2; primary liquid nitrogen flow regulating valve 6-1; secondary liquid nitrogen flow regulating valve 6-2; primary liquid nitrogen storage tank vaporizer 7-1; secondary liquid nitrogen storage tank vaporizer 7-2; primary liquid nitrogen storage tank pressure monitor 8-1; secondary liquid nitrogen storage tank pressure monitor 8-2; temperature monitor after primary heat exchanger 9-1; temperature monitor after secondary heat exchanger 9-2; primary gas-liquid separator 10-1; secondary gas-liquid separator 10-2; vaporizer after primary heat exchanger 11-1; vaporizer after secondary heat exchanger 11-2; vaporizer after secondary gas-liquid separator 11-3; gaseous nitrogen pipeline network 12. Detailed Implementation

[0019] This liquid nitrogen cooling BOG gas liquefaction and recovery system can be configured as a single-stage or multi-stage recovery system. Figure 1 The diagram shows the structure of a two-stage recycling system, which will be explained in detail below.

[0020] Figure 1 As shown, this liquid nitrogen cooling BOG gas liquefaction and recovery system includes an LNG storage tank 1, a primary heat exchanger 4-1, a primary liquid nitrogen storage tank 5-1, a primary liquid nitrogen storage tank vaporizer 7-1, a primary gas-liquid separator 10-1, a primary heat exchanger post-vaporizer 11-1, a secondary heat exchanger 4-2, a secondary liquid nitrogen storage tank 5-2, a secondary liquid nitrogen storage tank vaporizer 7-2, a secondary gas-liquid separator 10-2, a secondary heat exchanger post-vaporizer 11-2, and a secondary gas-liquid separator post-vaporizer 11-3.

[0021] Figure 1As shown, in this liquid nitrogen cooling BOG gas liquefaction and recovery system, the LNG storage tank 1 has a pressure relief valve 3 at its vent, which is the vent valve of the LNG storage tank 1. The vent is connected to the inlet of one heat exchange path of the primary heat exchanger 4-1, and the outlet of this heat exchange path is connected to the inlet of the primary gas-liquid separator 10-1. The outlet of the primary gas-liquid separator 10-1 is connected to the LNG storage tank 1. The primary liquid nitrogen storage tank 5-1 has a vaporization outlet at the bottom and a vaporization inlet at the top. The primary liquid nitrogen storage tank vaporizer 7-1 is connected in series between the vaporization outlet and the vaporization inlet of the primary liquid nitrogen storage tank 5-1. The liquid ammonia outlet of the primary liquid nitrogen storage tank 5-1 is connected to another heat exchange path of the primary heat exchanger 4-1, and the outlet of this heat exchange path is connected to the inlet of the downstream vaporizer 11-1. The outlet of the downstream vaporizer 11-1 is connected to the gaseous nitrogen pipeline 12. When a single-stage recovery system structure is adopted, the outlet of the first-stage gas-liquid separator 10-1 is connected to the gas-liquid separator and then to the gaseous nitrogen pipeline 12; when a multi-stage recovery system structure is adopted, the outlet of the first-stage gas-liquid separator 10-1 is connected to the next stage recovery system.

[0022] Figure 1 As shown, in this liquid nitrogen cooling BOG gas liquefaction and recovery system, the outlet of the primary gas-liquid separator 10-1 is connected to the inlet of a heat exchange path of the secondary heat exchanger 4-2, and the outlet of this heat exchange path is connected to the inlet of the secondary gas-liquid separator 10-2. The outlet of the secondary gas-liquid separator 10-2 is connected to the LNG storage tank 1. The secondary liquid nitrogen storage tank 5-2 has a vaporization outlet at the bottom and a vaporization inlet at the top. The secondary liquid nitrogen storage tank vaporizer 7-2 is connected in series between the vaporization outlet and the vaporization inlet of the secondary liquid nitrogen storage tank 5-2. The liquid ammonia outlet of the secondary liquid nitrogen storage tank 5-2 is connected to another heat exchange path of the secondary heat exchanger 4-2, and the outlet of this heat exchange path is connected to the inlet of the vaporizer 11-2 after the secondary heat exchanger. The outlet of the vaporizer 11-2 after the secondary heat exchanger is connected to the gaseous nitrogen pipeline 12. When a two-stage recovery system structure is adopted, the outlet of the secondary gas-liquid separator 10-2 is connected to the vaporizer 11-3 after the secondary gas-liquid separator, and then connected to the gaseous nitrogen pipeline 12; when a three-stage recovery system structure is adopted, the outlet of the secondary gas-liquid separator 10-2 is connected to the next stage recovery system, until the outlet of the last stage gas-liquid separator is connected to the gaseous nitrogen pipeline 12 after the gas-liquid separator is connected.

[0023] Figure 1As shown, in this liquid nitrogen cooling BOG gas liquefaction and recovery system, the LNG storage tank 1 is equipped with an LNG storage tank pressure monitor 2; the primary liquid nitrogen storage tank 5-1 is equipped with a primary liquid nitrogen storage tank pressure monitor 8-1; a primary liquid nitrogen flow regulating valve 6-1 is installed on the pipeline between the primary liquid nitrogen storage tank vaporizer 7-1 and the primary liquid nitrogen storage tank 5-1. The secondary liquid nitrogen storage tank 5-2 is equipped with a secondary liquid nitrogen storage tank pressure monitor 8-2; a secondary liquid nitrogen flow regulating valve 6-2 is installed on the pipeline between the secondary liquid nitrogen storage tank vaporizer 7-2 and the secondary liquid nitrogen storage tank 5-2. A primary heat exchanger post-temperature monitor 9-1 is installed on the pipeline between the primary heat exchanger 4-1 and the primary gas-liquid separator 10-1. A secondary heat exchanger post-temperature monitor 9-2 is installed on the pipeline between the secondary heat exchanger 4-2 and the secondary gas-liquid separator 10-2.

[0024] In this liquid nitrogen cooling BOG gas liquefaction and recovery system, the primary liquid nitrogen flow regulating valve 6-1 is interlocked with the pressure relief valve 3, and the secondary liquid nitrogen flow regulating valve 6-2 is also interlocked with the pressure relief valve 3. Thus, opening the pressure relief valve 3 simultaneously opens both the primary and secondary liquid nitrogen flow regulating valves 6-1 and 6-2. The temperature monitoring instrument 9-1 after the primary heat exchanger controls the opening of the primary liquid nitrogen flow regulating valve 6-1, using the temperature detected by the instrument. Similarly, the temperature monitoring instrument 9-2 after the secondary heat exchanger controls the opening of the secondary liquid nitrogen flow regulating valve 6-2, using the temperature detected by the instrument.

[0025] Figure 1 As shown, the working process of this liquid nitrogen cooling BOG gas liquefaction and recovery system is as follows: 1) When the LNG storage tank pressure monitoring instrument 2 detects a tank pressure > 21 kPa, it indicates that the LNG storage tank is an atmospheric pressure tank. When the tank pressure > 22.5 kPa, the top vent valve will automatically open, which means the LNG storage tank pressure relief valve 3 will open. 2) The BOG gas in LNG storage tank 1 is about -160°C. After exchanging heat with the first-stage heat exchanger 4-1 through the pipeline, it enters the first-stage gas-liquid separator 10-1. 3) When the LNG storage tank pressure relief valve 3 is opened, the interlocked primary liquid nitrogen flow regulating valve 6-1 is also opened; 4) The liquid nitrogen flowing out from the bottom of the primary liquid nitrogen storage tank 5-1 is vaporized by the primary liquid nitrogen storage tank vaporizer 7-1 and then returned to the top of the primary liquid nitrogen storage tank 5-1; 5) The pressure monitoring instrument 8-1 in the primary liquid nitrogen storage tank 5-1 detects an increase in pressure, and the liquid nitrogen is forced out from the bottom of the tank to the primary heat exchanger 4-1 to exchange heat with BOG gas; 6) After the BOG gas heats up, the temperature is monitored by the temperature monitoring instrument 9-1 after the first-stage heat exchanger, and the temperature is controlled at -164℃.

[0026] 7) In the first-stage gas-liquid separator 10-1, LNG flows back from the bottom to the LNG storage tank 1; 8) Nitrogen and some gaseous natural gas in the first-stage gas-liquid separator 10-1 re-enter the second-stage heat exchanger 4-2 and then enter the second-stage gas-liquid separator 10-2; 9) When the LNG storage tank pressure relief valve 3 is opened, the interlocked primary liquid nitrogen flow regulating valve 6-2 is also opened; 10) The liquid nitrogen flowing out from the bottom of the secondary liquid nitrogen storage tank 5-2 is vaporized by the secondary liquid nitrogen storage tank vaporizer 7-2 and then returned to the top of the secondary liquid nitrogen storage tank 5-2; 11) The pressure monitoring instrument 8-2 in the secondary liquid nitrogen storage tank 5-2 detects an increase in pressure, and the liquid nitrogen is forced out from the bottom of the tank to the secondary heat exchanger 4-2 to exchange heat with the nitrogen and some gaseous natural gas in the primary gas-liquid separator 10-1; 12) After heat exchange between nitrogen and part of the gaseous natural gas, the temperature is monitored by the temperature monitoring instrument 9-2 after the secondary heat exchanger, and the temperature is controlled at -164℃; 13) In the secondary gas-liquid separator 10-2, LNG flows back from the bottom to the LNG storage tank 1; 14) Nitrogen and a smaller amount of gaseous natural gas in the secondary gas-liquid separator 10-2 re-enter the next cycle.

[0027] 15) Until the nitrogen content in the gas coming out of the top of the gas-liquid separator meets the requirement of ≥99.5% nitrogen content in GB / T 3864-2008.

[0028] 16) The nitrogen gas coming out of the first-stage heat exchanger 4-1, the second-stage heat exchanger 4-2 and the second-stage gas-liquid separator 10-2 is vaporized and reheated to room temperature after passing through the first-stage heat exchanger vaporizer 11-1, the second-stage heat exchanger vaporizer 11-2 and the second-stage gas-liquid separator vaporizer 11-3, and then connected to the gaseous nitrogen pipeline 12.

Claims

1. A liquid nitrogen-cooled BOG gas liquefaction and recovery system, characterized in that: It includes an LNG storage tank (1), a primary heat exchanger (4-1), a primary liquid nitrogen storage tank (5-1), a primary liquid nitrogen storage tank vaporizer (7-1), a primary gas-liquid separator (10-1), and a post-vaporizer (11-1) of the primary heat exchanger; the vent of the LNG storage tank (1) is equipped with a pressure relief valve (3), which is sequentially connected to a heat exchange passage of the primary heat exchanger (4-1) and the inlet of the primary gas-liquid separator (10-1), the primary gas-liquid separator (10-1)... -1) The outlet of the liquid nitrogen tank is connected to the LNG storage tank (1); the vaporizer (7-1) of the first-stage liquid nitrogen storage tank is connected in series between the vaporization outlet and the vaporization inlet of the first-stage liquid nitrogen storage tank (5-1). The liquid ammonia outlet of the first-stage liquid nitrogen storage tank (5-1) is connected to another heat exchange passage of the first-stage heat exchanger (4-1). The outlet of this heat exchange passage is connected to the inlet of the vaporizer (11-1) after the first-stage heat exchanger. The outlet of the vaporizer (11-1) after the first-stage heat exchanger is connected to the gaseous nitrogen pipeline (12).

2. The liquid nitrogen cooling BOG gas liquefaction and recovery system according to claim 1, characterized in that: The LNG storage tank (1) is equipped with an LNG storage tank pressure monitoring instrument (2); the primary liquid nitrogen storage tank (5-1) is equipped with a primary liquid nitrogen storage tank pressure monitoring instrument (8-1); and a primary liquid nitrogen flow regulating valve (6-1) is installed on the pipeline between the primary liquid nitrogen storage tank vaporizer (7-1) and the primary liquid nitrogen storage tank (5-1).

3. The liquid nitrogen cooling BOG gas liquefaction and recovery system according to claim 2, characterized in that: The primary liquid nitrogen flow regulating valve (6-1) is interlocked with the pressure relief valve (3).

4. The liquid nitrogen cooling BOG gas liquefaction and recovery system according to claim 2, characterized in that: A temperature monitoring instrument (9-1) is installed on the pipeline between the primary heat exchanger (4-1) and the primary gas-liquid separator (10-1).

5. The liquid nitrogen cooling BOG gas liquefaction and recovery system according to claim 4, characterized in that: The temperature monitoring instrument (9-1) after the first-stage heat exchanger controls the opening degree of the first-stage liquid nitrogen flow regulating valve (6-1).

6. A liquid nitrogen-cooled BOG gas liquefaction and recovery system according to any one of claims 1-5, characterized in that: It also includes a secondary heat exchanger (4-2), a secondary liquid nitrogen storage tank (5-2), a secondary liquid nitrogen storage tank vaporizer (7-2), a secondary gas-liquid separator (10-2), a post-vaporizer of the secondary heat exchanger (11-2), and a post-vaporizer of the secondary gas-liquid separator (11-3); the outlet of the primary gas-liquid separator (10-1) is sequentially connected to a heat exchange passage of the secondary heat exchanger (4-2) and the inlet of the secondary gas-liquid separator (10-2), and the outlet of the secondary gas-liquid separator (10-2) is connected to the post-vaporizer of the secondary gas-liquid separator (11-3). The outlet of the first-stage gas-liquid separator (10-2) is connected to the LNG storage tank (1); the second-stage liquid nitrogen storage tank vaporizer (7-2) is connected in series between the vaporization outlet and vaporization inlet of the second-stage liquid nitrogen storage tank (5-2), and the liquid ammonia outlet of the second-stage liquid nitrogen storage tank (5-2) is connected to another heat exchange path of the second-stage heat exchanger (4-2), the outlet of which is connected to the inlet of the vaporizer (11-2) after the second-stage heat exchanger; the outlets of the vaporizer (11-2) after the second-stage heat exchanger and the vaporizer (11-3) after the second-stage gas-liquid separator are both connected to the gaseous nitrogen pipeline network (12).

7. The liquid nitrogen cooling BOG gas liquefaction and recovery system according to claim 6, characterized in that: The secondary liquid nitrogen storage tank (5-2) is equipped with a secondary liquid nitrogen storage tank pressure monitoring instrument (8-2); a secondary liquid nitrogen flow regulating valve (6-2) is installed on the pipeline between the secondary liquid nitrogen storage tank vaporizer (7-2) and the secondary liquid nitrogen storage tank (5-2).

8. The liquid nitrogen cooling BOG gas liquefaction and recovery system according to claim 7, characterized in that: The secondary liquid nitrogen flow regulating valve (6-2) and the pressure relief valve (3) are interlocked.

9. A liquid nitrogen-cooled BOG gas liquefaction and recovery system according to claim 7, characterized in that: A temperature monitoring instrument (9-2) is installed on the pipeline between the secondary heat exchanger (4-2) and the secondary gas-liquid separator (10-2).

10. A liquid nitrogen-cooled BOG gas liquefaction and recovery system according to claim 9, characterized in that: The temperature monitoring instrument (9-2) after the secondary heat exchanger controls the opening degree of the secondary liquid nitrogen flow regulating valve (6-2).

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