A BOG recovery device suitable for LNG liquefaction plants

Abstract

The application discloses a BOG recovery process of an LNG liquefaction plant, which comprises an improved BOG inlet buffer tank, an LNG circulating pump, a BOG compressor, an automatic valve group and a pipeline system. The improved BOG inlet buffer tank is a vertical pressure vessel, which has the functions of basic compressor inlet gas buffering, gas-liquid contact filling, BOG cooling and liquid level monitoring. The BOG recovery process can be used to recover BOG in the LNG liquefaction plant.

Description

Technical Field

[0001] This invention belongs to the field of LNG technology, specifically relating to a BOG recovery device for an LNG liquefaction plant. Background Technology

[0002] LNG, as a clean energy source, is mainly composed of CH4 and is characterized by high calorific value and low combustion pollutants. BOG (Boiled Gas) is LNG gas formed through evaporation during cryogenic storage. Currently, conventional BOG recovery methods involve setting up desuperheaters, compressors, and BOG recondensers to reliquefy the BOG, which is then transported to liquid LNG export pipelines. After being amplified by high-pressure LNG export pumps, it is finally vaporized and exported by an LNG vaporizer. This method is characterized by a variety of equipment and a complex process flow.

[0003] The BOG (Boiled Ocean Gas) reprocessing technology in LNG liquefaction plants refers to the process of pressurizing BOG gas in LNG storage tanks using a BOG compressor and returning it to the LNG liquefaction plant in a gaseous state for reliquefaction. Conventional BOG processing technologies are not entirely suitable for the LNG liquefaction plant scenario. This invention proposes a novel BOG reprocessing technology to meet the BOG reprocessing requirements of LNG liquefaction plants. Summary of the Invention

[0004] This invention provides a BOG recovery process suitable for LNG liquefaction plants, in order to solve the technical problems of existing technologies, such as the large variety of equipment, complex operating processes, and inability to be fully applied to LNG liquefaction plants.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A BOG (Boiled Gas) recovery device suitable for LNG liquefaction plants includes a BOG inlet buffer tank, an LNG circulating pump, a compressor, a self-regulating valve assembly, and a piping system. The BOG inlet buffer tank is a vertical pressure vessel that, in addition to basic compressor inlet gas buffering functions, is equipped with gas-liquid contact packing, an LNG spray pipe, an LNG injection port, and an LNG circulating pump inlet. The gas-liquid contact packing is located at the top outlet of the BOG inlet buffer tank; the LNG injection port is located on the tank wall below the gas-liquid contact packing; the LNG spray pipe is located on the tank wall above the gas-liquid contact packing; and the LNG circulating pump is located at the bottom of the BOG inlet buffer tank.

[0007] By installing gas-liquid contact packing, LNG spray pipe, LNG injection port, and LNG circulation pump port on the BOG inlet buffer tank, BOG de-temperature cooling and BOG inlet buffer tank liquid level monitoring can be achieved.

[0008] The gas-liquid contact packing is located at the top outlet of the BOG inlet buffer tank. The packing is in the form of Boulder rings to provide sufficient gas-liquid contact area. An LNG spray pipe is installed above the gas-liquid contact packing, and a regulating valve is installed on the LNG spray pipe to spray liquid LNG from top to bottom. The BOG gas flows upwards and contacts the gas-liquid contact packing in a counter-current manner, achieving mass and heat transfer and cooling. This maintains a stable compressor inlet temperature.

[0009] The LNG injection port pipeline is equipped with a regulating valve. The main inlet is located below the gas-liquid contact packing, and an LNG circulation pump is installed at the bottom outlet of the BOG inlet buffer tank. The LNG spray pipe regulating valve, the LNG injection port pipeline regulating valve, the LNG circulation pump, and the BOG inlet buffer tank are interlocked to maintain a stable liquid level in the containers.

[0010] Preferably, the BOG inlet buffer tank is a vertical pressure vessel with an operating pressure of 5–15 kPag. It must meet the requirements for residence time, as well as the design pressure and design temperature of the BOG system.

[0011] Preferably, the BOG inlet buffer tank is equipped with gas-liquid contact packing in the gas outlet section of the container, and the packing is in the form of Boulder rings. This provides sufficient contact area for LNG and BOG gas. Due to the low operating pressure of the container, LNG undergoes flash evaporation after entering the improved BOG inlet buffer tank, forming low-temperature gas-liquid miscible LNG. By spraying the gas-liquid miscible LNG, the BOG cooling function is achieved with the help of the sufficiently large contact area provided by the packing layer.

[0012] Preferably, the BOG inlet buffer tank is equipped with a level monitoring system to monitor the container level in real time, preventing LNG from overflowing and entering the downstream BOG vapor phase pressurization system, which could cause compressor failure. The BOG inlet buffer tank level monitoring system controls the LNG circulation pump outlet flow rate, stabilizing the tank level.

[0013] Preferably, the BOG inlet buffer tank gas phase outlet pipeline is equipped with a temperature monitoring system, which stabilizes the gas phase outlet temperature by recirculating part of the BOG compressor outlet gas, thereby avoiding fluctuations in the BOG compressor inlet temperature.

[0014] Preferably, the BOG inlet buffer tank is a cryogenic operating device. BOG processing is an intermittent operation. When the BOG system is shut down, a liquid LNG circulation pump located at the bottom of the BOG inlet buffer tank maintains the container temperature by circulating liquid LNG.

[0015] The beneficial effects of this invention are as follows:

[0016] Gas-liquid separation can be achieved by setting up an improved BOG inlet buffer tank; sufficient gas-liquid contact area can be provided by setting up a packing layer to cool the BOG gas; liquid level monitoring can prevent liquid phase from entering the BOG compressor; and liquid level monitoring and LNG circulation pumps can be used to maintain stable container liquid levels and cold circulation. This meets the BOG recycling requirements of LNG liquefaction plants. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a BOG recovery device suitable for LNG liquefaction plants according to the present invention.

[0018] The attached diagram is labeled as follows: 1-BOG inlet buffer tank, 2-packing layer, 3-BOG compressor, 4-LNG circulating pump, 5-liquid level monitoring sensor, 6-liquid level monitoring sensor, 7-LNG inlet emergency shut-off valve, 8-LNG circulating regulating valve, 9-LNG spray regulating valve, 10-temperature monitoring sensor, 11-BOG compressor reflux regulating valve, 12-LNG circulating pump flow control regulating valve. Detailed Implementation

[0019] The implementation of the technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0020] like Figure 1 The illustrated BOG recovery device for LNG liquefaction plants includes a BOG inlet buffer tank 1, an LNG circulation pump 4, a BOG compressor 3, automatic control valve groups 8, 9, and 11, and a piping system. The BOG inlet buffer tank is a vertical pressure vessel equipped with a gas-liquid contact packing layer 2, liquid level monitoring devices 5 and 6, an emergency shut-off valve 7, and a temperature monitoring sensor 10 for the vessel outlet pipeline. This patent enables BOG recovery within LNG liquefaction plants through this BOG recovery device.

[0021] The operating pressure of the BOG inlet buffer tank 1 is 5–15 kPag. The outlet pipe temperature monitoring sensor 10 of the BOG inlet buffer tank 1 can monitor the outlet BOG temperature. Because the BOG reprocessing process is intermittent, the outlet temperature will be higher than the set value when the BOG processing system is first put into operation. This temperature signal will interlock and open the LNG spray regulating valve 9, allowing LNG to enter the container from the top of the improved BOG inlet buffer tank 1. Due to the low operating pressure of the improved BOG inlet buffer tank 1, LNG flashes after entering the BOG inlet buffer tank, forming cryogenic gas-liquid miscible LNG.

[0022] The BOG inlet is positioned below the outlet of the LNG spray regulating valve 9. Under the suction of the BOG compressor 3, the BOG and the aforementioned cryogenic LNG droplets exchange heat in a counter-current manner before entering the packing layer 2. The packing layer 2 provides a sufficiently large gas-liquid contact area, ensuring that the gas and liquid become cryogenic gas after passing through the packing layer 2, thereby achieving the BOG cooling function.

[0023] When the temperature signal from the temperature monitoring sensor 10 on the outlet pipeline of the BOG inlet buffer tank 1 is lower than the set value, the BOG compressor reflux regulating valve 11 is interlocked and opened. By refluxing a portion of the high-temperature BOG gas at the compressor outlet, the compressor inlet temperature is maintained stable.

[0024] When the BOG processing capacity is lower than the minimum allowable operating flow rate of the BOG compressor, the BOG compressor reflux regulating valve 11 is opened to maintain the compressor's normal processing capacity through self-circulation. Due to the introduction of additional high-temperature BOG, the temperature monitored by the BOG inlet buffer tank 1 outlet pipeline temperature monitoring sensor 10 will be higher than the set value. The temperature is maintained at the set value by controlling the opening of the LNG spray regulating valve 9.

[0025] The BOG inlet buffer tank 1 is equipped with a liquid level monitoring sensor 6. When the liquid level is detected to be higher than the set value, the emergency interlock closes the feed emergency shut-off valve 7 to prevent liquid LNG from entering the BOG booster system and causing compressor failure.

[0026] The BOG inlet buffer tank 1 is equipped with a level monitoring sensor 5 and an LNG circulation pump 4. The level signal interlocks with the LNG circulation pump 4 outlet LNG circulation pump flow control valve 12 to maintain the improved BOG inlet buffer tank 1 by adjusting the pump flow rate.

[0027] The BOG inlet buffer tank 1 operates at a cryogenic temperature. When the BOG processing system is shut down, the LNG circulation regulating valve 8 and the LNG circulation pump 4 are opened. Cryogenic LNG is injected into the bottom of the BOG inlet buffer tank 1, and the LNG circulation pump 4 pumps it out to maintain the improved BOG inlet buffer tank 1 liquid level and cryogenic operating conditions.

[0028] The above are merely typical embodiments of the present invention. It should be noted that those skilled in the art can make several improvements or substitutions without departing from the principles described in the present invention, and these improvements or substitutions should also be considered within the scope of protection of the present invention.

Claims

1. A BOG recovery device suitable for LNG liquefaction plants, comprising a BOG inlet buffer tank, an LNG circulating pump, a compressor, a self-controlled valve assembly, and a piping system, characterized in that: The BOG inlet buffer tank is a vertical pressure vessel. In addition to basic compressor inlet gas buffering functions, it is also equipped with gas-liquid contact packing, LNG spray pipe, LNG injection port, and LNG circulation pump port. The gas-liquid contact packing is located at the top outlet of the BOG inlet buffer tank. The LNG injection port is located on the tank wall of the BOG inlet buffer tank, below the gas-liquid contact packing. The LNG spray pipe is located on the tank wall of the BOG inlet buffer tank, above the gas-liquid contact packing. The LNG circulation pump is located at the bottom of the BOG inlet buffer tank.

2. The BOG recycling device according to claim 1, characterized in that: The gas-liquid contact packing is located at the top outlet of the BOG inlet buffer tank, and the packing is in the form of Boolean rings.

3. The BOG recycling device according to claim 1, characterized in that: A regulating valve is installed on the LNG spray pipe to spray liquid LNG from top to bottom.

4. The BOG recycling device according to claim 1, characterized in that: The LNG injection port pipeline is equipped with a regulating valve, and the main inlet is located below the gas-liquid contact packing.

5. The BOG recycling device according to claim 1, characterized in that: The BOG inlet buffer tank is a vertical pressure vessel with an operating pressure of 5–15 kPag.

6. The BOG recycling device according to claim 1, characterized in that: The BOG inlet buffer tank is equipped with a liquid level monitoring system to monitor the container liquid level in real time and prevent LNG from overflowing.

7. The BOG recycling device according to claim 1, characterized in that: A temperature monitoring system is installed on the gas phase outlet pipeline of the BOG inlet buffer tank.

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