BOG gas recovery system in low-temperature storage tank

Abstract

The utility model relates to the technical field of low-temperature storage tanks, in particular to a BOG gas recovery system in a low-temperature storage tank, which comprises a low-temperature storage tank, a BOG compressor system, a water cooler, a condensate tank and a flash tank, the low-temperature storage tank is connected with a medium feeding pipeline; the BOG compressor system is connected with the low-temperature storage tank; the water cooler is connected with an outlet of the BOG compressor system; the condensate tank is connected with the water cooler, and the condensate tank is connected with a condensate tank top discharge pipeline; the flash tank is connected with the condensate tank, the flash tank is connected to an inlet of the BOG compressor system through a flash tank top discharge pipeline, and the flash tank is connected to the low-temperature storage tank through a liquid backflow pipeline. In the operation process, BOG gas is compressed and condensed through the compressor to become liquid, the liquid medium is pressed and fed back to the low-temperature storage tank again after passing through the separation tank, the BOG gas medium is recycled, and the pressure of the low-temperature storage tank is reasonably controlled.

Description

Technical Field

[0001] The utility model relates to the technical field of cryogenic storage tanks, in particular to a BOG gas recovery system in a cryogenic storage tank. Background Art

[0002] Existing large-capacity cryogenic storage tanks are mainly used for the storage and transportation of liquid media such as LNG, propane, butane, etc. They have large storage capacity, low operating pressure, and low operating temperature. Different media in the storage tank have different boiling points, and the temperature at which they are converted from gas phase to liquid phase is also different. For example, under normal pressure conditions, the liquefaction temperature of LNG gas is about -180℃, the liquefaction temperature of cryogenic propane is -45℃, and the liquefaction temperature of cryogenic butane is -5℃.

[0003] When storing cryogenic media such as LNG, propane, butane, etc., some gas will flash out from the surface of the liquid in the cryogenic tank, which is called BOG gas. How to reasonably recycle this part of the flashed BOG gas and control the pressure of the cryogenic tank is an urgent problem to be solved. Utility Model Content

[0004] In view of the defects of the prior art, the utility model provides a BOG gas recovery system in a cryogenic storage tank. During its operation, the BOG gas is compressed and condensed by a compressor to become liquid, and the liquid medium is "pressurized" back to the cryogenic storage tank after passing through a separation tank. Not only the BOG gas medium is recovered, but also the pressure of the cryogenic storage tank is reasonably controlled.

[0005] In order to achieve the above-mentioned purpose, the technical solution provided by the utility model is a BOG gas recovery system in a cryogenic storage tank, which includes a cryogenic storage tank, a BOG compressor system, a water cooler, a condensate tank and a flash tank; the cryogenic storage tank is connected to a medium feed pipeline; the BOG compressor system is connected to the cryogenic storage tank; the water cooler is connected to the outlet of the BOG compressor system; the condensate tank is connected to the water cooler, and the condensate tank is connected to a condensate tank top discharge pipeline; the flash tank is connected to the condensate tank bottom discharge pipeline of the condensate tank, the flash tank is connected to the inlet of the BOG compressor system through the flash tank top discharge pipeline, and the flash tank is connected to the cryogenic storage tank through a liquid reflux pipeline.

[0006] Furthermore, the BOG compressor system includes two BOG compressors connected in parallel, and the two BOG compressors are started one and kept on standby or started at the same time.

[0007] Furthermore, the condensate tank top discharge pipeline is provided with a condensate tank top pressure control valve.

[0008] Furthermore, the condensate tank bottom discharge pipeline is provided with a condensate tank bottom liquid control valve.

[0009] Furthermore, the condensate tank top discharge pipeline is connected to a flare system.

[0010] Furthermore, the flash tank top discharge pipeline is provided with a flash tank top pressure control valve.

[0011] Furthermore, the liquid reflux pipeline is provided with a flash tank liquid control valve.

[0012] Furthermore, the inlets of the two BOG compressors are respectively provided with a first manual valve and a second manual valve.

[0013] Furthermore, the medium feed pipeline is provided with a medium feed valve.

[0014] During operation, the liquid medium enters the cryogenic storage tank through the medium feed pipeline, and the pressure of the cryogenic storage tank increases. At this time, the BOG compressor system can be turned on first, and the gaseous medium at the top of the cryogenic storage tank is extracted from the top of the cryogenic storage tank and enters the BOG compressor system. After compression and pressure increase, the gas-liquid mixture is condensed by the water cooler, and the gas-liquid separation is carried out in the condensate tank. The liquid medium in the condensate tank enters the flash tank, and the uncondensed gas in the condensate tank is discharged into the flare system for combustion. After the flash tank receives the liquid medium in the condensate tank, it is flashed in the flash tank, and the liquid medium in the flash tank returns to the cryogenic storage tank again, and the gas medium flashed out of the flash tank is discharged into the inlet of the BOG compressor system.

[0015] The beneficial effects of the utility model are as follows: during its operation, the BOG gas is compressed and condensed by the compressor to become liquid, and the liquid medium is "pressurized" back to the low-temperature storage tank after passing through the separation tank, which not only recovers the BOG gas medium but also reasonably controls the pressure of the low-temperature storage tank. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a process flow chart of a BOG gas recovery system in a cryogenic storage tank in one embodiment of the utility model;

[0017] Figure 2 This is a process flow chart of a BOG gas recovery system in a cryogenic storage tank in another embodiment of the utility model;

[0018] In the figure:

[0019] 100. Low temperature storage tank, 110. Medium feed pipeline, 111. Medium feed valve,

[0020] 200, BOG compressor system, 210, outlet, 220, inlet, 230, first BOG compressor, 231, first manual valve, 240, second BOG compressor, 241, second manual valve,

[0021] 300, water cooler,

[0022] 400, condensate tank, 410, condensate tank top discharge pipeline, 411, condensate tank pressure control valve, 420, condensate tank bottom discharge pipeline, 421, condensate tank bottom hydraulic control valve;

[0023] 500. Flash tank. 510. Flash tank top discharge pipeline. 511. Flash tank top pressure control valve. 520. Liquid reflux pipeline. 521. Flash tank liquid control valve. DETAILED DESCRIPTION

[0024] In order to make the above-mentioned purposes, features and advantages of the utility model more obvious and easy to understand, the specific implementation methods of the utility model are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the utility model. However, the utility model can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the utility model, so the utility model is not limited by the specific embodiments disclosed below.

[0025] See also Figure 1 , shows a BOG gas recovery system in a cryogenic tank in an embodiment of the present invention, which is applied to the cold exchange equipment at the outlet of LNG gas compressor, propane gas compressor and butane gas compressor, and includes a cryogenic tank 100, a BOG compressor system 200, a water cooler 300, a condensate tank 400 and a flash tank 500. The cryogenic tank 100 is connected with a medium feed pipeline 110; the BOG compressor system 200 is connected with the cryogenic tank 100; the water cooler 300 is connected with the outlet 210 of the BOG compressor system 200; the condensate tank 400 is connected with the water cooler 300, and the condensate tank 400 is connected with a condensate tank top discharge pipeline 410; the flash tank 500 is connected with the condensate tank bottom discharge pipeline 420 of the condensate tank 400, the flash tank 500 is connected to the inlet 220 of the BOG compressor system 200 through the flash tank top discharge pipeline 510, and the flash tank 500 is connected to the cryogenic tank 100 through the liquid reflux pipeline 520.

[0026] During operation, when the liquid medium enters the cryogenic storage tank 100 through the medium feed pipeline 110, the pressure of the cryogenic storage tank 100 increases. At this time, the BOG compressor system 200 can be first turned on to extract the gaseous medium at the top of the cryogenic storage tank 100 from the tank top of the cryogenic storage tank 100 and enter the BOG compressor system 200. After compression and pressure increase, the gas-liquid mixture is condensed through the water cooler 300, and gas-liquid separation is performed in the condensate tank 400. The liquid phase medium of the condensate tank 400 enters the flash tank 500 through the condensate tank bottom discharge pipeline 420, and the uncondensed gas of the condensate tank 400 is discharged into the flare system through the condensate tank top discharge pipeline 410 for combustion. After the flash tank 500 receives the liquid medium of the condensate tank 400, it is flashed in the flash tank 500, and the liquid phase medium of the flash tank 500 returns to the cryogenic storage tank 100 again, and the gaseous medium flashed out of the flash tank 500 is discharged into the inlet 220 of the BOG compressor system 200.

[0027] The BOG compressor system 200 in the BOG gas recovery system in the above-mentioned low-temperature storage tank has an inlet pipeline connected to the gas phase pipeline at the top of the low-temperature storage tank 100, and the outlet pipeline of the BOG compressor system 200 is connected to the water cooler 300. The main function of the BOG compressor system 200 is to compress and increase the pressure of the BOG gas phase at the top of the low-temperature storage tank 100, and then send it to the water cooler 300 at the compressor outlet. The cooling medium of the water cooler 300 is circulating water, and the main function of the water cooler 300 is to use water to reduce the outlet medium temperature of the BOG compressor system 200. During operation, the circulating water flow rate and low temperature should be controlled as much as possible. The lower the temperature, the more the medium is converted into the liquid phase, the less the gas phase medium, and the lower the pressure of the condensate tank 400, which is more conducive to operation. The water cooler 300 uses circulating water to cool the hot medium at the outlet of the BOG compressor system 200, and the cooled medium is sent to the condensate tank 400 through a pipeline. After the condensate tank 400 receives the medium from the outlet of the upstream water cooler 300, the gas-liquid two-phase separation is performed in the condensate tank 400. The liquid phase medium is sent to the flash tank 500 through the condensate tank bottom discharge pipeline 420, and a small amount of gas phase medium is discharged to the torch through the set condensate tank hydraulic pressure control valve 411. After the flash tank 500 receives the liquid phase medium from the outlet of the upstream condensate tank 400, the gas-liquid two-phase separation is performed in the flash tank 500. The liquid phase medium is sent to the low-temperature storage tank 100 through the pipeline for recovery, and the gas phase enters the inlet of the BOG compressor system 200 through the set flash tank top pressure control valve 511 and the flash tank top discharge pipeline 510 for gas phase medium circulation.

[0028] It should be noted that the lower the temperature of the medium in the cryogenic storage tank 100 is controlled, the better, but it cannot be lower than the design temperature. The lower the temperature, the less the medium evaporates, which is more conducive to the pressure control of the cryogenic storage tank 100. When the pressure of the cryogenic storage tank 100 does not rise, the BOG compressor system 200 can be stopped. When the pressure of the cryogenic storage tank 100 rises to a certain pressure, the BOG compressor system 200 is turned on again. Since the BOG compressor system 200 runs intermittently, the water cooler 300, condensate tank 400, flash tank 500 and other equipment and facilities at the outlet of the BOG compressor system 200 also run intermittently, making the load controllable. The pressure control of the condensate tank 400 should be as high as possible, but it cannot exceed the design. The higher the pressure, the more conducive it is to convert the medium from gas phase to liquid phase for recovery, reducing losses.

[0029] In one embodiment, the BOG compressor system 200 includes two BOG compressors connected in parallel, namely, a first BOG compressor 230 and a second BOG compressor 240, and the two BOG compressors are one on and one on standby or are activated at the same time. It should be noted that during the operation of the system, turning on the first BOG compressor 230 can usually meet the design pressure requirements of the cryogenic storage tank 100. If the pressure of the cryogenic storage tank 100 still increases, the first BOG compressor 230 and the second BOG compressor 240 can be turned on and operated at the same time to reduce the pressure of the cryogenic storage tank 100. In addition, the purpose of reducing the pressure of the cryogenic storage tank 100 can also be achieved by reducing the feed flow in the medium feed pipeline 110, that is, adjusting the medium feed valve 111 set in the medium feed pipeline 110. In this embodiment, the two BOG compressors are set to one on and one on standby, and the water cooler 300, condensate tank 400, and flash tank 500 through which the outlets of the two BOG compressors pass are only set as one set. In this embodiment, the water cooler 300, the condensate tank 400, the flash tank 500, each device and associated facilities are provided as one set, and no spare equipment is required. Compared with the technical solution of providing two sets of the water cooler 300, the condensate tank 400, and the flash tank 500 at the same time, it can not only meet the original design and production needs, but also save equipment investment, reduce equipment floor space, and reduce equipment maintenance costs, which is beneficial to design, procurement, construction and other aspects.

[0030] In one embodiment, the condensate tank top discharge pipeline 410 is provided with a condensate tank pressure control valve 411. In this embodiment, the medium flow rate of the condensate tank top discharge pipeline 410 is adjusted by controlling the condensate tank pressure control valve 411.

[0031] Furthermore, in one embodiment, the condensate tank top discharge line 410 is connected to the flare system. In this embodiment, the liquid phase medium is sent to the flash tank 500 through the condensate tank bottom discharge line 420, and a small amount of gas phase medium is discharged to the flare through the set condensate tank pressure control valve 411.

[0032] In one embodiment, the flash tank top discharge pipeline 510 is provided with a flash tank top pressure control valve 511. In this embodiment, the medium flow rate of the flash tank top discharge pipeline 510 is adjusted by controlling the flash tank top pressure control valve 511.

[0033] In one embodiment, the liquid return pipeline 520 is provided with a flash tank liquid control valve 521. In this embodiment, the medium flow rate of the liquid return pipeline 520 is adjusted by controlling the flash tank liquid control valve 521.

[0034] In one embodiment, the inlets of the two BOG compressors are respectively provided with a first hand valve 231 and a second hand valve 241. Thus, if the pressure of the cryogenic storage tank 100 is very high, the first hand valve 231 and the second hand valve 241 can be opened at the same time, and the first BOG compressor 230 and the second BOG compressor 240 can be started and operated at the same time to reduce the pressure of the cryogenic storage tank 100.

[0035] In one embodiment, the medium feed pipeline 110 is provided with a medium feed valve 111. If the pressure of the cryogenic storage tank 100 is very high, in addition to adjusting the BOG compressor system 200, the medium feed valve 111 provided on the medium feed pipeline 110 can also be adjusted to reduce the feed flow in the medium feed pipeline 110, thereby achieving the purpose of reducing the pressure of the cryogenic storage tank 100.

[0036] In terms of operation, it is required that the feed flow rate from the medium feed pipeline 110 into the cryogenic storage tank 100 should not exceed the design flow rate, so as to prevent a large flow of liquid medium from entering the cryogenic storage tank 100 and causing excessive evaporation of the gas phase medium in the tank, which will eventually cause the pressure of the cryogenic storage tank 100 to rise too quickly.

[0037] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0038] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present utility model, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0039] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0040] In the present utility model, unless otherwise clearly specified and limited, the first feature "above" or "below" the second feature may be that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature "above", "above" and "above" the second feature may be that the first feature is directly above or obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. The first feature "below", "below" and "below" the second feature may be that the first feature is directly below or obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature. It should be noted that when an element is referred to as "fixed to" or "set on" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected" to another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "up", "down", "left", "right" and similar expressions used herein are for illustrative purposes only and do not represent the only implementation method.

Claims

1. A BOG gas recovery system in a cryogenic storage tank, characterized in that: include A cryogenic storage tank connected to a medium feed pipeline; A BOG compressor system connected to the cryogenic storage tank; a water cooler connected to an outlet of the BOG compressor system; A condensate tank connected to the water cooler, wherein the condensate tank is connected to a condensate tank top discharge pipeline; A flash tank is connected to the condensate tank bottom discharge pipeline of the condensate tank, the flash tank is connected to the inlet of the BOG compressor system through a flash tank top discharge pipeline, and the flash tank is connected to the low-temperature storage tank through a liquid reflux pipeline.

2. The BOG gas recovery system in a cryogenic storage tank according to claim 1, characterized in that: The BOG compressor system includes two BOG compressors connected in parallel, and the two BOG compressors are one on and one on standby or are started at the same time.

3. The BOG gas recovery system in a cryogenic storage tank according to claim 2, characterized in that: The inlets of the two BOG compressors are respectively provided with a first manual valve and a second manual valve.

4. A BOG gas recovery system in a cryogenic storage tank according to claim 1 or 2, characterized in that: The condensate tank top discharge pipeline is provided with a condensate tank top pressure control valve.

5. A BOG gas recovery system in a cryogenic storage tank according to claim 1 or 2, characterized in that: The condensate tank bottom discharge pipeline is provided with a condensate tank bottom liquid control valve.

6. A BOG gas recovery system in a cryogenic storage tank according to claim 1 or 2, characterized in that: The condensate tank top discharge pipeline is connected to the flare system.

7. A BOG gas recovery system in a cryogenic storage tank according to claim 1 or 2, characterized in that: The flash tank top discharge pipeline is provided with a flash tank top pressure control valve.

8. A BOG gas recovery system in a cryogenic storage tank according to claim 1 or 2, characterized in that: The liquid reflux pipeline is provided with a flash tank liquid control valve.

9. A BOG gas recovery system in a cryogenic storage tank according to claim 1 or 2, characterized in that: The medium feed pipeline is provided with a medium feed valve.

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