Liquefied natural gas production shutdown gas recovery system

Abstract

The utility model belongs to the technical field of gas recovery, and particularly relates to a liquefied natural gas production shutdown gas recovery system which comprises a natural gas long-distance conveying pipeline and a natural gas purification unit which are sequentially communicated, and further comprises a first control valve, a second control valve and a third control valve. The natural gas purification unit is communicated with a natural gas long-distance transportation pipeline through a second control valve and a third control valve in sequence, and the natural gas purification unit is externally connected with a first control valve. When the natural gas recovery device is shut down, the remaining natural gas can be effectively recycled, and energy is saved.

Description

Technical Field

[0001] The utility model belongs to the technical field of gas recovery, and particularly relates to a gas recovery system for liquefied natural gas production shutdown. Background Art

[0002] In the production of liquefied natural gas (hereinafter referred to as LNG), natural gas in the long-distance pipeline needs to be processed through devices such as pressurization, acid removal, dehydration, heavy hydrocarbon removal, and mercury removal, and then sent to a cold box to be cooled to about -160°C to obtain the product LNG for storage or market sales. However, during the LNG production process, due to equipment failures, maintenance, regular inspections, etc., the devices need to be shut down, and the high-pressure natural gas stored in the dynamic and static equipment and pipelines needs to be emptied or burned in the flare, resulting in certain economic losses and increasing greenhouse gas emissions to pollute the environment.

[0003] Currently, for the recovery of the gas existing during the shutdown of liquefied natural gas production, referring to the Chinese patent document with the reference publication number CN215676068U, a low-temperature flash gas recovery and liquefaction device includes a heat exchanger, a normal-temperature compressor, and a cold box. The heat exchanger is used to cool or reheate the pressurized feed gas from the low-temperature compressor. The outlet of the heat exchanger is connected to the inlet of the normal-temperature compressor, and the outlet of the normal-temperature compressor is connected to the cold box. The temperature of the pressurized feed gas from the outlet of the low-temperature compressor may be below 0°C or above 40°C. This part of the pressurized feed gas is first cooled or reheated by the heat exchanger and then enters the normal-temperature compressor for pressurization and cooling, and then enters the cold box. It can prevent the normal-temperature compressor from being damaged and increase the operating condition stability and economy. However, the existing recovery mainly focuses on the recovery and utilization of low-temperature flash gas (with a pressure of 10KPaG - 20KPaG), and there is no effective recovery of the natural gas and liquefied natural gas (with a pressure ≥ 100KPaG) remaining inside the production device, resulting in energy waste. Summary of the Utility Model

[0004] Aiming at the technical problem in the background art that there is no effective recovery of the natural gas and liquefied natural gas remaining in the production device, resulting in energy waste, the utility model provides a gas recovery system for liquefied natural gas production shutdown.

[0005] The utility model effectively recovers and utilizes the remaining natural gas during shutdown by setting a first control valve, a second control valve, and a third control valve, thereby saving energy.

[0006] To achieve the above object, the technical solution adopted by the utility model is:

[0007] A liquefied natural gas production shutdown gas recovery system includes a natural gas long-distance pipeline and a natural gas purification unit connected in sequence, and also includes a first control valve, a second control valve, and a third control valve; the natural gas purification unit is connected to the natural gas long-distance pipeline through the second control valve and the third control valve in sequence, and a first control valve is also externally connected to the natural gas purification unit.

[0008] Further defined, a first check valve is also provided between the natural gas purification unit and the second control valve.

[0009] Further defined, the liquefied natural gas production shutdown gas recovery system also includes a buffer tank and a normal temperature natural gas compressor. One end of the buffer tank is respectively connected to the first check valve and the natural gas purification unit, the other end of the buffer tank is connected to the normal temperature natural gas compressor, and the normal temperature natural gas compressor is respectively connected to the second control valve and the third control valve.

[0010] Further defined, the liquefied natural gas production shutdown gas recovery system also includes a second check valve and a fourth control valve; one end of the second check valve is connected to the buffer tank through the fourth control valve, and the other end of the second check valve is respectively connected to the first check valve and the natural gas purification unit.

[0011] Further defined, the liquefied natural gas production shutdown gas recovery system also includes a fifth check valve and a seventh control valve. One end of the seventh control valve is connected to the normal temperature natural gas compressor through the fifth check valve, and the other end of the seventh control valve is respectively connected to the second control valve and the third control valve.

[0012] Further defined, the liquefied natural gas production shutdown gas recovery system also includes a liquefaction device; the natural gas purification unit is connected to the liquefaction device through the first control valve.

[0013] Further defined, the liquefied natural gas production shutdown gas recovery system also includes a vaporizer; the liquefaction device is connected to the buffer tank through the vaporizer.

[0014] Further defined, the liquefied natural gas production shutdown gas recovery system also includes a third check valve and a fifth control valve; the liquefaction device is connected to the vaporizer through the third check valve and the fifth control valve in sequence.

[0015] Further defined, the liquefied natural gas production shutdown gas recovery system also includes a fourth check valve and a sixth control valve; the vaporizer is connected to the buffer tank through the fourth check valve and the sixth control valve in sequence.

[0016] The beneficial effects of the present utility model are:

[0017] 1. The utility model realizes the recovery of the remaining natural gas in the liquefied natural gas production and saves energy by setting the first control valve, the second control valve and the third control valve, which are simultaneously connected to the natural gas purification unit, and the second control valve is also connected to the natural gas long-distance pipeline through the third control valve.

[0018] 2. By setting a buffer tank and a normal-temperature natural gas compressor, the utility model can boost the low-pressure gas through the normal-temperature natural gas compressor and then realize the recovery and utilization of the remaining natural gas in the natural gas purification unit during the liquefied natural gas production.

[0019] 3. By setting a vaporizer and connecting the liquefaction device to the buffer tank through the vaporizer, the utility model can first heat up and vaporize the remaining liquid natural gas in the liquefaction device and then recover and utilize it, with a more thorough recovery.

[0020] 4. The recovery system provided by the utility model can effectively recover and utilize the natural gas with different pressures and different forms remaining during the liquefied natural gas production according to actual needs by setting three recovery pipelines, thus saving energy.

[0021] 5. In the utility model, control valves are set on the recovery pipeline and can be switched according to actual needs, which is flexible and convenient. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the gas recovery system for natural gas production shutdown provided by the utility model Figure 1 ;

[0023] Figure 2 Schematic diagram of the gas recovery system for liquefied natural gas production shutdown provided by the utility model Figure 2 ;

[0024] Wherein:

[0025] 1 - Natural gas long-distance pipeline; 2 - Natural gas boosting device; 3 - Acid removal device; 4 - Dehydration device; 5 - Heavy hydrocarbon removal device; 6 - Mercury removal device; 7 - First control valve; 8 - Liquefaction device; 9 - LNG storage device; 10 - First check valve; 11 - Second control valve; 12 - Third control valve; 13 - Second check valve; 14 - Fourth control valve; 15 - Third check valve; 16 - Fifth control valve; 17 - Vaporizer; 18 - Fourth check valve; 19 - Sixth control valve; 20 - Buffer tank; 21 - Normal-temperature natural gas compressor; 22 - Fifth check valve; 23 - Seventh control valve; 24 - Natural gas purification unit. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The technical solution protected by the present utility model will be described in detail below in conjunction with the accompanying drawings and embodiments. However, it is obvious that the described embodiments are part of the embodiments of this application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of this application without creative work belong to the scope of protection of this application.

[0027] Unless otherwise defined, the technical terms or scientific terms used in this application shall have the ordinary meaning understood by those of ordinary skill in the field to which this application belongs. The "first", "second" and similar terms used in this application do not indicate any order, quantity or importance, but are only used to distinguish different components. The terms such as "including" or "comprising" mean that the elements or objects appearing before this word cover the elements or objects listed after this word and their equivalents, without excluding other elements or objects.

[0028] See Figure 1 , the existing liquefied natural gas (hereinafter referred to as LNG) production system includes: a natural gas long-distance pipeline 1, a natural gas pressurization device 2, a natural gas purification unit 24, a liquefaction device 8 and an LNG storage device 9 that are connected in sequence. The production process of liquefied natural gas (hereinafter referred to as LNG) is as follows: The natural gas in the production area is transported into the natural gas long-distance pipeline 1. After the natural gas is pressurized, it is purified and then sent into the liquefaction device 8 to obtain the product LNG at about -160 °C and stored in the LNG storage device 9. However, during shutdown, there is natural gas remaining in the connecting pipelines and containers between the natural gas purification unit 24, the liquefaction device 8 and the LNG storage device 9. These natural gases cannot be effectively recycled, resulting in waste of resources. The purpose of the present utility model is to recover the natural gas remaining in the pipelines and containers.

[0029] See Figure 2 , preferably, the natural gas purification unit 24 includes a deacidification device 3, a dehydration device 4, a deheavy hydrocarbon device 5 and a mercury removal device 6 that are connected in sequence. The mercury removal device 6 is connected to the liquefaction device 8, and the natural gas long-distance pipeline 1 is connected to the deacidification device 3 through the natural gas pressurization device 2.

[0030] Embodiment 1

[0031] See Figure 1 , the liquefied natural gas production shutdown gas recovery system provided in this embodiment includes a natural gas long-distance pipeline 1 and a natural gas purification unit 24 that are connected in sequence, and also includes a first control valve 7, a second control valve 11 and a third control valve 12; the natural gas purification unit 24 is connected to the natural gas long-distance pipeline 1 through the second control valve 11 and the third control valve 12 in sequence, and a first control valve 7 is also externally connected to the natural gas purification unit 24.

[0032] In this embodiment, a first check valve 10 is further provided between the natural gas purification unit 24 and the second control valve 11. The first check valve 10 only allows conduction towards one end of the second control valve 11, preventing the reverse flow of natural gas back into the natural gas purification unit 24.

[0033] In this embodiment, the liquefied natural gas production shutdown gas recovery system further includes a liquefaction device 8; the natural gas purification unit 24 is connected to the liquefaction device 8 via a first control valve 7.

[0034] In this embodiment, three branches are separated from the natural gas purification unit 24. The first branch is the normal production pipeline of natural gas formed by connecting the natural gas purification unit 24 and the natural gas long-distance transmission pipeline 1. The second branch is the pipeline connecting the natural gas purification unit 24 and the liquefaction device 8. Both of these branches are for the production of liquefied natural gas and are normal production pipelines for liquefied natural gas. The third branch (the newly added first recovery pipeline) is that the natural gas purification unit 24 is connected to the natural gas long-distance transmission pipeline 1 via a first check valve 10, a second control valve 11, and a third control valve 12 in sequence. This branch is mainly used to recover and utilize the natural gas stored in the natural gas purification unit 24 when the pressure of the natural gas remaining in the natural gas purification unit 24 > the pressure of the natural gas in the natural gas long-distance transmission pipeline 1 during shutdown.

[0035] During implementation, a first control valve 7 is provided between the natural gas purification unit 24 and the liquefaction device 8. When the pressure of the natural gas remaining in the production system > the pressure of the natural gas in the natural gas long-distance transmission pipeline 1, the first check valve 10, the second control valve 11, and the third control valve 12 are opened, and at the same time, the first control valve 7 is closed. The natural gas remaining in the natural gas purification unit 24 is transported to the natural gas long-distance transmission pipeline 1 through the first check valve 10, the second control valve 11, and the third control valve 12 until the pressure of the natural gas remaining in the production system ≤ the pressure of the natural gas in the natural gas long-distance transmission pipeline 1. At this time, the first check valve 10 and the second control valve 11 are closed.

[0036] Embodiment 2

[0037] See Figure 1 , based on Embodiment 1, the liquefied natural gas production shutdown gas recovery system provided in this embodiment further includes a buffer tank 20 and a normal temperature natural gas compressor 21. One end of the buffer tank 20 is respectively connected to the first check valve 10 and the natural gas purification unit 24, and the other end of the buffer tank 20 is respectively connected to the second control valve 11 and the third control valve 12 after passing through the normal temperature natural gas compressor 21.

[0038] In this embodiment, the liquefied natural gas production shutdown gas recovery system further includes a second check valve 13 and a fourth control valve 14; one end of the second check valve 13 is communicated with the buffer tank 20 through the fourth control valve 14, and the other end of the second check valve 13 is respectively communicated with the first check valve 10 and the natural gas purification unit 24.

[0039] In this embodiment, the liquefied natural gas production shutdown gas recovery system further includes a fifth check valve 22 and a seventh control valve 23. One end of the seventh control valve 23 is communicated with the normal temperature natural gas compressor 21 through the fifth check valve 22, and the other end of the seventh control valve 23 is respectively connected to the second control valve 11 and the third control valve 12.

[0040] In this embodiment, a new branch (i.e., the fourth branch) is further separated from the natural gas purification unit 24. After coming out of the natural gas purification unit 24, this new branch (the newly added second recovery pipeline) is successively communicated with the natural gas long-distance pipeline 1 through the second check valve 13, the fourth control valve 14, the buffer tank 20, the normal temperature natural gas compressor 21, the fifth check valve 22, the seventh control valve 23 and the third control valve 12. The purpose of this new branch is to recover and utilize the natural gas existing in the production system when the pressure of the natural gas remaining in the natural gas purification unit 24 ≤ the pressure of the natural gas in the natural gas long-distance pipeline 1 during shutdown.

[0041] During implementation, when the pressure of the natural gas remaining in the production system ≤ the pressure of the natural gas in the natural gas long-distance pipeline 1, open the second check valve 13, the fourth control valve 14, the fifth check valve 22, the seventh control valve 23 and the third control valve 12, and at the same time close the first control valve 7; start the normal temperature natural gas compressor 21, and send the natural gas remaining in the production system into the buffer tank 20 through the second check valve 13 and the fourth control valve 14. After the natural gas is pressurized by the normal temperature natural gas compressor 21, it is sent to the natural gas long-distance pipeline 1 through the fifth check valve 22, the seventh control valve 23 and the third control valve 12 until the pressure at the inlet of the normal temperature natural gas compressor 21 is lower than the starting pressure of the normal temperature natural gas compressor 21, then the normal temperature natural gas compressor 21 stops working, close the fourth control valve 14, and recover the natural gas in the liquefaction device 8.

[0042] Embodiment 3

[0043] See Figure 1 , on the basis of Embodiment 2, the liquefied natural gas production shutdown gas recovery system further includes a vaporizer 17; the liquefaction device 8 is communicated with the buffer tank 20 through the vaporizer 17.

[0044] In this embodiment, the liquefied natural gas production shutdown gas recovery system further includes a third check valve 15 and a fifth control valve 16; the liquefaction device 8 is successively communicated with the vaporizer 17 through the third check valve 15 and the fifth control valve 16.

[0045] In this embodiment, the liquefied natural gas production shutdown gas recovery system further includes a fourth check valve 18 and a sixth control valve 19; the vaporizer 17 is communicated with the buffer tank 20 through the fourth check valve 18 and the sixth control valve 19 in sequence.

[0046] In this embodiment, a branch is led out from the liquefaction unit 8. This branch (the newly added third recovery pipeline) is specifically that the liquefied natural gas coming out of the liquefaction unit 8 passes through the third check valve 15, the fifth control valve 16, the vaporizer 17, the fourth check valve 18 and the sixth control valve 19 and then is communicated into the buffer tank 20. This branch is mainly used for recycling the natural gas in the liquefaction unit 8.

[0047] In this embodiment, when recovering the natural gas in the liquefaction unit 8, open the third check valve 15, the fifth control valve 16, the fourth check valve 18, the sixth control valve 19, the fifth check valve 22 and the seventh control valve 23, and at the same time close the first control valve 7; start the normal temperature natural gas compressor 21. The remaining natural gas (liquid state) in the liquefaction unit 8 enters the vaporizer 17 through the third check valve 15 and the fifth control valve 16, is heated and vaporized, then enters the buffer tank 20 through the fourth check valve 18 and the sixth control valve 19, and finally is pressurized by the normal temperature natural gas compressor 21 for the natural gas (vaporized), and is transported to the natural gas long-distance pipeline 1 through the fifth check valve 22, the seventh control valve 23 and the third control valve 12 until the pressure at the inlet of the normal temperature natural gas compressor 21 is lower than the starting pressure of the normal temperature natural gas compressor 21, then the normal temperature natural gas compressor 21 stops working, and close the third check valve 15, the fifth control valve 16, the fourth check valve 18 and the sixth control valve 19 to complete the recovery of the natural gas in the liquefaction unit 8.

[0048] To sum up, for the liquefied natural gas production shutdown gas recovery system provided by the present utility model, when performing gas recovery, there are three relatively optimal implementation methods. First, recover the gaseous natural gas, and at the same time compare the pressure of the remaining natural gas in the production system with the pressure of the natural gas in the natural gas long-distance pipeline 1, and the gas recovery control is flexible; then recover the liquefied natural gas. First, heat and vaporize the liquefied natural gas, and then realize its recovery. During implementation, according to the actual environment and recovery requirements, control the valves on the corresponding recovery pipelines to realize the effective recovery and utilization of the remaining natural gas in the production system during the shutdown of liquefied natural gas production, avoid waste of resources and save costs.

[0049] The specific embodiments described above have further elaborated in detail the purpose, technical solution and beneficial effects of the present utility model. It should be understood that the above description is only the specific embodiments of the present utility model, and is not used to limit the protection scope of the present utility model. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present utility model shall be included within the protection scope of the present utility model.

Claims

1. A liquefied natural gas production shutdown gas recovery system, comprising a natural gas long-distance pipeline (1) and a natural gas purification unit (24) connected in sequence, characterized in that: It also comprises a first control valve (7), a second control valve (11) and a third control valve (12); the natural gas purification unit (24) is connected to the natural gas long-distance pipeline (1) via the second control valve (11) and the third control valve (12) in sequence, and the natural gas purification unit (24) is also externally connected to the first control valve (7).

2. The liquefied natural gas production shutdown gas recovery system according to claim 1, characterized in that: A first check valve (10) is also provided between the natural gas purification unit (24) and the second control valve (11).

3. The liquefied natural gas production shutdown gas recovery system according to claim 2, characterized in that: The liquefied natural gas production shutdown gas recovery system further comprises a buffer tank (20) and a normal temperature natural gas compressor (21), one end of the buffer tank (20) being respectively connected to a first check valve (10) and a natural gas purification unit (24), the other end of the buffer tank (20) being connected to a normal temperature natural gas compressor (21), and the normal temperature natural gas compressor (21) being respectively connected to a second control valve (11) and a third control valve (12).

4. The liquefied natural gas production shutdown gas recovery system according to claim 3, characterized in that: The liquefied natural gas production shutdown gas recovery system further comprises a second check valve (13) and a fourth control valve (14); one end of the second check valve (13) is connected to the buffer tank (20) via the fourth control valve (14), and the other end of the second check valve (13) is connected to the first check valve (10) and the natural gas purification unit (24), respectively.

5. The liquefied natural gas production shutdown gas recovery system according to claim 4, characterized in that: The liquefied natural gas production shutdown gas recovery system further comprises a fifth check valve (22) and a seventh control valve (23); one end of the seventh control valve (23) is connected to the normal temperature natural gas compressor (21) via the fifth check valve (22); and the other end of the seventh control valve (23) is connected to the second control valve (11) and the third control valve (12), respectively.

6. The liquefied natural gas production shutdown gas recovery system according to claim 3, characterized in that: The liquefied natural gas production shutdown gas recovery system further comprises a liquefaction device (8); the natural gas purification unit (24) is connected to the liquefaction device (8) via a first control valve (7).

7. The liquefied natural gas production shutdown gas recovery system according to claim 6, characterized in that: The liquefied natural gas production shutdown gas recovery system further comprises a vaporizer (17); the liquefaction device (8) is connected to the buffer tank (20) via the vaporizer (17).

8. The liquefied natural gas production shutdown gas recovery system according to claim 7, characterized in that: The liquefied natural gas production shutdown gas recovery system further comprises a third check valve (15) and a fifth control valve (16); the liquefaction device (8) is connected to the gasifier (17) via the third check valve (15) and the fifth control valve (16) in sequence.

9. The liquefied natural gas production shutdown gas recovery system according to claim 8, characterized in that: The liquefied natural gas production shutdown gas recovery system further comprises a fourth check valve (18) and a sixth control valve (19); the gasifier (17) is connected to the buffer tank (20) via the fourth check valve (18) and the sixth control valve (19) in sequence.

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