Replacement gas recovery system for low-temperature storage tank

Abstract

The utility model relates to the technical field of low-temperature storage tanks, in particular to a low-temperature storage tank replacement gas recovery system which comprises a low-temperature storage tank, a compressor, a water cooler and a condensate tank. The low-temperature storage tank is connected with a medium gas inlet pipeline, a gas phase outlet in the top of the low-temperature storage tank is sequentially connected with the compressor, the water cooler and the condensate tank through pipelines, the bottom of the condensate tank is connected with a backflow pipeline, a liquid phase medium in the condensate tank returns to the low-temperature storage tank through the backflow pipeline, and the top of the condensate tank is connected with a torch discharging pipeline. And gas in the condensate tank is discharged to the torch system through the torch discharging pipeline. Nitrogen and BOG mixed gas at the top of the low-temperature tank is sucked by starting the BOG gas compressor, medium gas is converted into a liquid phase from a gas phase through operations such as pressure boosting of the compressor, condensation of the water cooler and gas-liquid separation of the condensate tank, all the medium gas is recycled and returned to the low-temperature storage tank, and the nitrogen is still in a gas phase after being compressed and is discharged, so that the low-temperature storage tank is completely recycled. And zero emission of medium gas can be realized.

Description

Technical Field

[0001] The utility model relates to the technical field of cryogenic storage tanks, in particular to a replacement gas recovery system for cryogenic storage tanks. 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., with large storage capacity, low operating pressure and low operating temperature. Different media in the storage tank have different boiling points, and the temperature of conversion from gas phase to liquid phase is also different. For example, under normal pressure conditions, the liquefaction temperature of propane is -42℃ (boiling point temperature), while the liquefaction temperature of butane is about -2℃.

[0003] During the construction and commissioning of cryogenic storage tanks, large-capacity cryogenic storage tanks need to be replaced by nitrogen to replace oxygen, and medium gas (BOG) to replace nitrogen. When replacing the nitrogen in the tank, a large amount of medium gas needs to be added to the tank, and the mixture of medium gas and nitrogen is discharged to the flare for combustion, so as to meet the requirements of high purity of medium gas and low nitrogen content in the cryogenic tank. To replace the nitrogen in a large-capacity tank, it is necessary to discharge 3 times the volume of medium gas to the flare system. If the volume of a cryogenic tank is 160,000 m³, the medium gas (BOG) that needs to be discharged to replace the nitrogen inside is 450,000 m³. Not only is the medium loss large, but it is also dangerous, and the carbon dioxide produced by combustion pollutes the environment. Utility Model Content

[0004] In view of the deficiencies in the prior art, the utility model provides a cryogenic storage tank replacement gas recovery system, which can recover the propane gas medium generated during the start-up replacement process of the cryogenic storage tank, which not only reduces medium loss but also is safe and environmentally friendly.

[0005] The utility model adopts the following technical scheme: a low-temperature storage tank replacement gas recovery system, comprising a low-temperature storage tank, a compressor, a water cooler and a condensate tank; the low-temperature storage tank is connected to a medium air inlet pipeline, the tank top gas phase outlet of the low-temperature storage tank is sequentially connected to the compressor, the water cooler and the condensate tank through a pipeline, the bottom of the condensate tank is connected to a reflux pipeline, the liquid phase medium in the condensate tank is returned to the low-temperature storage tank through the reflux pipeline, the top of the condensate tank is connected to a flare discharge pipeline, and the gas in the condensate tank is discharged to the flare system through the flare discharge pipeline.

[0006] Furthermore, the cryogenic storage tank is connected to a discharge pipeline, and the discharge pipeline is connected to a flare system.

[0007] Furthermore, a vent valve is provided on the discharge pipeline.

[0008] Furthermore, a condensate tank top pressure control valve for controlling the gas pressure in the condensate tank is provided on the flare discharge pipeline.

[0009] Furthermore, a condensate tank hydraulic control valve is provided on the reflux pipeline.

[0010] Furthermore, two compressors are arranged in parallel, and one of the two compressors is started and the other is in standby or is started at the same time.

[0011] The beneficial effects of the utility model are as follows: in the start-up phase of the low-temperature storage tank, when the medium gas replaces the nitrogen in the low-temperature tank, the nitrogen and BOG mixed gas on the top of the low-temperature tank are sucked by starting the BOG gas compressor, and the medium gas is converted from gas phase to liquid phase and fully recovered and returned to the low-temperature storage tank after the compressor pressure is increased, the water cooler condenses, and the condensate tank gas-liquid separation and other operations are performed, while the nitrogen is still discharged in the gas phase after compression. In this way, the gas discharged from the top of the condensate tank is nitrogen, and zero discharge of the medium gas can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a process flow chart of the low-temperature storage tank replacement gas recovery system of the utility model;

[0013] In the figure: 1. Cryogenic storage tank, 2. Discharge pipeline, 3. BOG gas compressor, 4. Water cooler, 5. Condensate tank top pressure control valve, 6. Condensate tank, 7. Condensate tank hydraulic control valve, 8. Medium air inlet pipeline, 9. Reflux pipeline, 10. Flare pipeline, 11. Vent valve. DETAILED DESCRIPTION

[0014] 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.

[0015] Example 1

[0016] See attached Figure 1A low-temperature storage tank replacement gas recovery system comprises a low-temperature storage tank 1, a BOG gas compressor 3, a water cooler 4 and a condensate tank 6; the low-temperature storage tank 1 is connected to a medium air inlet pipeline 8, the tank top gas phase outlet of the low-temperature storage tank 1 is connected to the BOG gas compressor 3, the water cooler 4 and the condensate tank 5 in sequence through a pipeline, the bottom of the condensate tank 6 is connected to a reflux pipeline 9, the liquid phase medium in the condensate tank 6 returns to the low-temperature storage tank 1 through the reflux pipeline 9, a condensate tank liquid control valve 7 is arranged on the reflux pipeline 9, the top of the condensate tank is connected to a flare discharge pipeline 10, the gas in the condensate tank 6 is discharged to the flare system through the flare discharge pipeline 10, and a condensate tank top pressure control valve 5 for controlling the gas pressure in the condensate tank is arranged on the flare discharge pipeline 10.

[0017] In this embodiment, the cryogenic storage tank 1 is connected to a discharge pipeline 2 , and the discharge pipeline 2 is connected to a flare system; a vent valve 11 is provided on the discharge pipeline 2 .

[0018] In this embodiment, two BOG gas compressors 3 are arranged in parallel, and one of the two compressors is started and the other is in standby or started at the same time.

[0019] The low temperature storage tank replacement gas recovery system of the utility model is mainly used for replacing nitrogen with medium gas after the low temperature storage tank is built. It includes a low temperature storage tank 1, a BOG gas compressor 3, a compressor outlet water cooler 5 and a condensate tank 6. The top of the low temperature storage tank 1 is provided with a vent valve 11 connected to the flare combustion. The gas phase at the top of the low temperature storage tank 1 is connected to the inlet of the BOG gas compressor 3 through a pipeline.

[0020] The inlet pipeline of the BOG gas compressor 3 is connected to the gas phase pipeline at the top of the cryogenic storage tank 1, and the outlet pipeline of the BOG gas compressor is connected to the water cooler 4. The main function of the BOG gas compressor is to compress and increase the pressure of the BOG gas phase at the top of the cryogenic storage tank, and then send it to the compressor outlet water cooler 4.

[0021] The compressor outlet water cooler 4 uses circulating water as a cooling medium to cool the hot medium at the compressor outlet, and then sends it to the condensate tank through a pipeline.

[0022] The condensate tank 6 receives the medium from the outlet of the upstream water cooler 4 and separates the gas and liquid phases in the condensate tank 6. In the selection and control of the operating pressure, the BOG gas phase should be completely condensed into liquid at the current operating temperature. The liquid phase medium is sent to the low-temperature storage tank 1 through a pipeline; the gas phase is discharged to the torch through the set condensate tank top pressure control valve 5.

[0023] In the above technical solution, there are two BOG gas compressors 3, one is in operation and the other is in standby mode under normal circumstances. When the pressure of the cryogenic storage tank 1 increases and one compressor cannot meet the demand, two compressors can be operated.

[0024] During operation, when the medium enters the cryogenic storage tank 1 through the cryogenic storage tank medium inlet pipeline 8 and starts to replace the nitrogen in the storage tank, the pressure of the cryogenic storage tank 1 increases. At this time, it is not necessary to open the vent valve 2 to discharge through the discharge pipeline. The BOG gas compressor 3 can be opened first to extract the nitrogen and medium gas at the top of the cryogenic storage tank 1 from the top of the cryogenic storage tank 1 and enter the BOG gas compressor 3. The gas-liquid mixture after compression and condensation is separated in the condensate tank 6. The liquid phase medium of the condensate tank 6 returns to the cryogenic storage tank 1 again through the condensate tank liquid control valve 7. The uncondensed gas in the condensate tank 6 is discharged into the flare system through the condensate tank top pressure control valve 5 for combustion.

[0025] In operation, the medium enters the water cooler 4 from the outlet of the BOG gas compressor 3, and the low temperature should be controlled as much as possible. The lower the temperature, the greater the amount of the medium that changes from the gas phase to the liquid phase.

[0026] The pressure control valve 5 on the top of the condensate tank should control the pressure as close to the set pressure value of the safety valve as possible. For example, if the set pressure value of the safety valve on the top of the condensate tank is 2.0MPa, then the pressure of the condensate tank is controlled at 1.85MPa. The higher the pressure, the more conducive it is for the medium to change from gas phase to liquid phase, and the more conducive it is for the liquid medium to be recovered. After the operating pressure is increased, the medium gas content contained in the gas discharged to the flare system is reduced through the pressure control valve 5 on the top of the condensate tank, and the medium loss is reduced.

[0027] The recovery system of the utility model converts the medium gas from gas phase to liquid phase and recovers all of it back to the cryogenic storage tank 1 through the operations of boosting pressure in the compressor 3, condensing in the water cooler 4, and gas-liquid separation in the condensate tank 6, while the nitrogen is still discharged in the gas phase after compression. In this way, the gas discharged from the top of the condensate tank 6 is nitrogen, and zero emission of the medium gas can be achieved. In the prior art, in the process of replacing the nitrogen in the newly built and put into use cryogenic storage tank with medium gas, the mixed gas is only discharged to the flare system at the top of the cryogenic storage tank for replacement, and the nitrogen and medium gas in the tank are transported to the flare system for combustion through the venting pipeline, and the replacement is continued until the medium concentration in the cryogenic storage tank meets the requirements. According to the prior art method, a storage tank with a volume of 160,000 m³ needs to discharge 480,000 m³ of medium gas to be qualified for replacement, but after using this method, the discharged medium gas is zero emission.

[0028] It should be noted that the parts not described in detail in the present invention are prior art.

[0029] 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.

[0030] The above examples are only the best embodiments of the present invention. Obviously, the present invention is not limited to the above examples, and there are many variations. All variations that can be directly derived or associated with the contents disclosed by a person skilled in the art should be considered as the protection scope of the present invention.

Claims

1. A storage tank replacement gas recovery system, characterized in that: It includes a low-temperature storage tank, a compressor, a water cooler and a condensate tank; the low-temperature storage tank is connected to a medium air inlet pipeline, the gas phase outlet on the top of the low-temperature storage tank is connected to the compressor, the water cooler and the condensate tank in sequence through a pipeline, the bottom of the condensate tank is connected to a reflux pipeline, the liquid phase medium in the condensate tank is returned to the low-temperature storage tank through the reflux pipeline, the top of the condensate tank is connected to a flare exhaust pipeline, and the gas in the condensate tank is discharged to the flare system through the flare exhaust pipeline.

2. A storage tank replacement gas recovery system according to claim 1, characterized in that: The cryogenic storage tank is connected with a discharge pipeline, and the discharge pipeline is connected to a flare system.

3. A storage tank replacement gas recovery system according to claim 2, characterized in that: The discharge pipeline is provided with a vent valve.

4. A storage tank replacement gas recovery system according to claim 1, characterized in that: The flare discharge pipeline is provided with a condensate tank top pressure control valve for controlling the gas pressure in the condensate tank.

5. A storage tank replacement gas recovery system according to claim 1, characterized in that: The reflux pipeline is provided with a condensate tank hydraulic control valve.

6. A storage tank replacement gas recovery system according to claim 1, characterized in that: Two compressors are arranged in parallel, and one of the two compressors is started and the other is in standby or started at the same time.

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