A BOG recycling efficiency enhancement system

Abstract

This utility model discloses a BOG (Bottle-Off Gas) recovery and utilization efficiency enhancement system, comprising an ambient air vaporizer, a buffer tank, a multi-stage compressor unit, multiple interstage cooling units, an interstage gas-liquid separation unit, a return pipeline, and a metering device connected sequentially via pipelines. The inlet of the ambient air vaporizer is connected to the BOG gas source pipeline; the inlet of the buffer tank is connected to the outlet of the ambient air vaporizer; the inlet of the multi-stage compressor unit is connected to the outlet of the buffer tank, and the multi-stage compressor unit includes at least two compression units; an interstage cooling unit and an interstage gas-liquid separation unit are disposed between two adjacent compression units; one end of the return pipeline is connected to the outlet pipeline of the final compression unit. This utility model is a recovery system that can stably compress BOG to the required pressure and then return it to the feed gas pipeline network without impacting the downstream LNG liquefaction process.

Description

Technical Field

[0001] This invention relates to the field of liquefied natural gas (LNG) processing technology, specifically to a BOG (Bottle-Off Gas) recycling and efficiency enhancement system. Background Technology

[0002] BOG is an abbreviation for Boil-Off Gas, referring to the vaporized gas generated in liquefied natural gas (LNG) storage tanks due to external heat intrusion; it is also called flash vapor. After a high-temperature LNG skid completes its delivery, the storage tank typically retains 2-4 bar of pressure, and can reach up to 4.5 bar. A single trip results in a loss of 200-400 cubic meters of natural gas. Directly releasing BOG to the flare without utilizing it would cause enormous waste and environmental pollution.

[0003] Currently, the common method for handling BOG generated at the filling end is to directly discharge it into the atmosphere or flare system through a venting pipeline. For a scattered gas project with an annual processing capacity of 200,000 cubic meters, the maximum BOG generation of this part can reach 500 cubic meters per hour, and direct venting would lead to significant energy waste and environmental pollution.

[0004] Existing technologies are mostly focused on BOG (Boiled Gas) processing at LNG receiving terminals or user-end storage tanks, where the gas source, pressure, and volume characteristics differ significantly from those of BOG generated at the filling stage. If existing solutions are directly applied to the filling process, the drastic and intermittent fluctuations in the filling BOG volume will impact the stable operation of downstream LNG production systems, leading to malfunctions in cold container conditions and hindering stable recovery. Utility Model Content

[0005] The purpose of this invention is to provide a BOG recycling and efficiency enhancement system that can stably compress BOG to the required pressure and then return it to the feed gas pipeline network without impacting the downstream LNG liquefaction process.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by this utility model is as follows:

[0007] A BOG recycling efficiency enhancement system includes the following components connected sequentially via pipes:

[0008] An ambient air vaporizer, with its air inlet connected to the BOG gas source pipeline;

[0009] A buffer tank, the air inlet of which is connected to the air outlet of the ambient temperature vaporizer;

[0010] A multi-stage compressor unit, wherein the air inlet of the multi-stage compressor unit is connected to the air outlet of the buffer tank, and the multi-stage compressor unit includes at least two compression units;

[0011] Multiple interstage cooling units and interstage gas-liquid separation units are provided, with one interstage cooling unit and one interstage gas-liquid separation unit located between two adjacent compression units;

[0012] The return pipe is connected at one end to the outlet pipe of the final stage compression unit and at the other end to the inlet of the buffer tank or the inlet pipe of the first stage compression unit.

[0013] A metering device is installed on the outlet pipe of the final stage compression unit to measure the flow rate of the output gas.

[0014] Furthermore, the multi-stage compressor unit is a four-stage compressor unit, including a first-stage compressor, a second-stage compressor, a third-stage compressor, and a fourth-stage compressor connected sequentially by pipelines.

[0015] Furthermore, the interstage cooling unit is an air cooler, including a first-stage air cooler, a second-stage air cooler, a third-stage air cooler, and a fourth-stage air cooler, which are respectively installed at the outlet of the corresponding compression unit.

[0016] Furthermore, the interstage gas-liquid separation unit is a separator, including a primary separator, a secondary separator, a tertiary separator, and a quaternary separator. The air inlet of the separator is connected to the air outlet of the corresponding air cooler, and the liquid phase outlet is connected to the sewage discharge system.

[0017] Furthermore, a pneumatic regulating valve is provided on the return pipe to adjust the return flow rate according to the pressure of the buffer tank or the intake pressure of the multi-stage compressor unit.

[0018] Furthermore, an emergency shut-off valve is also provided on the pipeline between the ambient temperature vaporizer and the buffer tank.

[0019] Furthermore, the entire system is integrated on a skid, and the ambient air vaporizer, buffer tank, multi-stage compressor unit, interstage cooling and separation unit are connected and fixed to the skid via pipes and valves.

[0020] Furthermore, a pressure sensor and a liquid level sensor are provided on the buffer tank.

[0021] Furthermore, each stage of the compression unit has a pressure sensor and a temperature sensor installed on its outlet pipe.

[0022] Furthermore, the system also includes a control unit electrically connected to the multi-stage compressor unit, the pneumatic regulating valve on the return pipe, and various pressure and temperature sensors, and is configured to: receive data from the sensors and stabilize the system pressure by controlling the opening of the pneumatic regulating valve and / or the rotational speed of the multi-stage compressor unit.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] This invention utilizes the physical volume of a buffer tank to provide a gas buffer space, transforming intermittent, large-amplitude fluctuations in intake air flow into minute pressure changes within a short period. The return pipe and regulating valve form a negative feedback control system. When a sudden decrease in intake air volume causes a downward trend in the buffer tank pressure, the controller reduces the opening of the regulating valve, decreasing the return flow and forcing more gas output, thereby maintaining pressure stability. Conversely, when the intake air volume increases suddenly, the valve opens wider to increase the return flow, consuming excess gas and preventing overpressure. This closed-loop control keeps the output pressure fluctuation range within ±0.2 MPa.

[0025] The proactive pressure stabilization mechanism ensures that the pressure and flow rate of the feed gas delivered to the downstream LNG liquefaction cold box are extremely stable, completely avoiding the water hammer effect caused by drastic pressure fluctuations in the multi-stream heat exchange conditions within the cold box, thus guaranteeing the continuity and safety of the main unit's operation.

[0026] This invention employs a multi-stage compression, cooling, and compression process, making the entire compression process closer to an isothermal process and reducing power consumption compared to single-stage compression. Interstage cooling lowers the inlet gas temperature and increases its density at each stage, improving the compressor's volumetric efficiency. The interstage separator, based on the principle of gravity settling, promptly removes liquid water and heavy hydrocarbons precipitated during compression and cooling, effectively preventing liquid from being carried into the next stage compressor and causing potential mechanical damage from liquid slugging.

[0027] This invention pre-integrates all equipment, pipelines, instruments, and control units in the factory onto a single steel skid, forming a fully functional independent module. This significantly shortens the on-site construction cycle, reduces installation costs, and decreases reliance on on-site technical personnel. The compact design saves floor space, making it suitable for space-constrained, scattered gas well sites. It also boasts excellent mobility, allowing for relocation according to gas field production needs. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of this utility model, the drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this utility model and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0029] Figure 1 This is the overall schematic diagram of the present invention.

[0030] Figure label:

[0031] 101-Ambient vaporizer, 102-Buffer tank, 103-First stage compressor, 104-First stage air cooler, 105-First stage separator, 106-Second stage compressor, 107-Second stage air cooler, 108-Second stage separator, 109-Third stage compressor, 110-Third stage air cooler, 111-Third stage separator, 112-Fourth stage compressor, 113-Fourth stage air cooler, 114-Fourth stage separator. Detailed Implementation

[0032] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the present invention. Therefore, the drawings and description are considered exemplary in nature and not restrictive. Embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0033] Example 1:

[0034] See Figure 1 This embodiment discloses a BOG recycling efficiency enhancement system, comprising the following components connected sequentially via pipelines:

[0035] Ambient air vaporizer 101, the air inlet of ambient air vaporizer 101 is connected to BOG gas source pipeline;

[0036] Buffer tank 102, the air inlet of buffer tank 102 is connected to the air outlet of ambient temperature vaporizer 101;

[0037] A multi-stage compressor unit, wherein the air inlet of the multi-stage compressor unit is connected to the air outlet of the buffer tank 102, and the multi-stage compressor unit includes at least two compression units;

[0038] Multiple interstage cooling units and interstage gas-liquid separation units are provided, with one interstage cooling unit and one interstage gas-liquid separation unit located between two adjacent compression units;

[0039] The return pipe is connected at one end to the outlet pipe of the final stage compression unit and at the other end to the inlet of the buffer tank 102 or the inlet pipe of the first stage compression unit.

[0040] A metering device is installed on the outlet pipe of the final stage compression unit to measure the flow rate of the output gas.

[0041] Furthermore, the multi-stage compressor unit is a four-stage compressor group 112, including a first-stage compressor 103, a second-stage compressor 106, a third-stage compressor 109 and a fourth-stage compressor 112 connected sequentially by pipelines.

[0042] Furthermore, the interstage cooling unit is an air cooler, including a first-stage air cooler 104, a second-stage air cooler 107, a third-stage air cooler 110, and a fourth-stage air cooler 113, which are respectively disposed at the outlet of the corresponding compression unit.

[0043] Furthermore, the interstage gas-liquid separation unit is a separator, including a primary separator 105, a secondary separator 108, a tertiary separator 111, and a quaternary separator 114. The air inlets of the separators are connected to the air outlets of the corresponding air coolers, and the liquid phase outlets are connected to the sewage discharge system.

[0044] Furthermore, a pneumatic regulating valve is provided on the return pipe to adjust the return flow rate according to the pressure of the buffer tank 102 or the intake pressure of the multi-stage compressor unit.

[0045] Furthermore, an emergency shut-off valve is also provided on the pipeline between the ambient temperature vaporizer 101 and the buffer tank 102.

[0046] Furthermore, the entire system is integrated on a skid, and the ambient air vaporizer 101, buffer tank 102, multi-stage compressor unit, interstage cooling and separation unit are connected and fixed to the skid via pipes and valves.

[0047] Furthermore, a pressure sensor and a liquid level sensor are provided on the buffer tank 102.

[0048] Furthermore, each stage of the compression unit has a pressure sensor and a temperature sensor installed on its outlet pipe.

[0049] Furthermore, the system also includes a control unit electrically connected to the multi-stage compressor unit, the pneumatic regulating valve on the return pipe, and various pressure and temperature sensors, and is configured to: receive data from the sensors and stabilize the system pressure by controlling the opening of the pneumatic regulating valve and / or the rotational speed of the multi-stage compressor unit.

[0050] To facilitate a better understanding of this invention by those skilled in the art, the invention will be further described below in conjunction with specific implementation schemes.

[0051] A BOG (Bottle-Off Gas) recovery and utilization efficiency enhancement system is disclosed for use in the LNG filling process. The core equipment, piping, instruments, and control units are all modularly designed and integrated onto a carbon steel skid measuring approximately 12m × 2.5m × 3m (length × width × height), forming a functional module that can be transported and hoisted as a whole. The skid is pre-installed with a raw material BOG inlet, a recovered gas outlet, an instrument air interface, a power interface, and a wastewater collection port.

[0052] The specifications, models, and key design parameters of each device in the system are as follows:

[0053] Ambient air vaporizer 101: It adopts aluminum alloy finned tube type, with a design pressure of 1.6MPaG and a design heat exchange of 150kW, which can reheat BOG at -120℃ to no less than 5℃.

[0054] Buffer tank 102: Vertical pressure vessel, designed pressure 1.0 MPaG, volume 2 m³ / s. 3 The material is Q345R.

[0055] Compressor unit: Uses an oil-free reciprocating compressor with four-stage compression.

[0056] First-stage compressor 103: Inlet pressure 0.02~0.05MPaG, exhaust pressure 0.7MPaG, rated power 45kW.

[0057] Two-stage compressor 106: Inlet pressure 0.65MPaG, exhaust pressure 2.5MPaG, rated power 55kW.

[0058] Three-stage compressor 109: Inlet pressure 2.4MPaG, discharge pressure 5.5MPaG, rated power 75kW.

[0059] Four-stage compressor 112: Inlet pressure 5.3MPaG, exhaust pressure 4.5~5.0MPaG (adjustable according to downstream pipeline pressure), rated power 90kW.

[0060] Interstage coolers: All are forced-draft air coolers.

[0061] The first-stage air cooler 104 is designed to exchange 80kW of heat, cooling the gas from about 150°C to 50°C.

[0062] Secondary air cooler 107: Designed to exchange 70kW of heat, cooling the gas from about 130°C to 50°C.

[0063] Three-stage air cooler 110: designed for heat exchange of 60kW, cooling gas from approximately 120°C to 50°C.

[0064] Four-stage air cooler 113: designed for heat exchange of 50kW, cooling gas from approximately 110°C to 45°C.

[0065] Interstage separators: all are vertical gravity separators, with a design pressure consistent with the discharge pressure of the corresponding compressor.

[0066] Each separator stage has a volume of 0.15m³. 3 The material is Q345R, and all are equipped with a level gauge and an automatic drain valve.

[0067] Metering device: Turbine flow meter, DN50 diameter, accuracy class 1.0, measuring range 50-500m. 3 / h.

[0068] Control valve and actuator:

[0069] Pneumatic control valve: Model is pneumatic V-type ball valve, diameter DN65, valve authority is calculated to be greater than 0.3, used for precise control of backflow.

[0070] Emergency shut-off valve: It is a pneumatic O-type shut-off ball valve that closes when air is lost, with a response time of less than 2 seconds.

[0071] meter:

[0072] Pressure sensor: mounted on buffer tank 102, measuring range 0-0.6MPaG, 4-20mA signal output.

[0073] Liquid level sensor: Installed on buffer tank 102, it is a radar liquid level gauge with a range of 0-2m.

[0074] Pressure sensors: There are 4 sensors on each compressor outlet pipeline, with ranges of 0-1.0MPaG, 0-3.0MPaG, 0-6.0MPaG, and 0-6.0MPaG respectively.

[0075] Temperature sensors: 4 units in total, Pt100 resistance temperature detectors, with a range of 0-200℃, are located on the outlet pipes of each compressor.

[0076] Control unit: A Siemens S7-1200 series PLC is used as the core controller and is integrated into a skid-mounted explosion-proof control box.

[0077] BOG (temperature -110℃, pressure approximately 20kPaG) from the LNG loading area first enters the ambient temperature vaporizer 101, where it is reheated to 10℃. The reheated gas then enters the buffer tank 102 via pipeline and emergency shut-off valve.

[0078] After the system starts, the control unit reads the pressure value of the pressure sensor in buffer tank 102 as the core control parameter.

[0079] Normal operating conditions: When the pressure in buffer tank 102 stabilizes near the set value (e.g., 0.3 MPaG), the pneumatic regulating valve remains at a preset opening (e.g., 30%).

[0080] The gas flows sequentially through a primary compressor 103, a primary air cooler 104, a primary separator 105, a secondary compressor 106, a secondary air cooler 107, a secondary separator 108, a tertiary compressor 109, a tertiary air cooler 110, a tertiary separator 111, a quaternary compressor 112, a quaternary air cooler 113, and a quaternary separator 114, and is finally compressed to 4.8 MPaG. After being metered by a metering device, it is transported to the raw material gas pipeline network.

[0081] When the BOG supply decreases: When the BOG supply decreases due to the interval between loading operations, the pressure in buffer tank 102 shows a downward trend. The PLC's PID control module calculates this rate of change and outputs a control signal to linearly reduce the opening of the pneumatic regulating valve, for example, from 30% to 15%, thereby reducing the amount of backflow gas and using more gas for external output to maintain the stability of the pressure in buffer tank 102.

[0082] When the BOG (Bottle-Off Gas) supply increases: When a large number of tank trucks fill simultaneously, causing a sudden increase in the BOG supply, the pressure in buffer tank 102 will show an upward trend. The PLC will then output a control signal to linearly increase the opening of the pneumatic regulating valve, for example, from 30% to 50%, so that more compressed gas flows back to the inlet of buffer tank 102, consuming the excess gas, preventing overpressure in buffer tank 102 and compressor overload, thereby maintaining system stability.

[0083] The condensate separated by each stage of the separator is automatically discharged into the main drain pipe at the bottom of the skid on a regular basis.

[0084] Although preferred embodiments of the present invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the present invention.

[0085] The above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. It should be noted that any modifications, equivalent substitutions and improvements made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. A BOG recycling enhancement system, characterized by, Including those connected sequentially via pipes: An ambient air vaporizer, with its air inlet connected to the BOG gas source pipeline; A buffer tank, the air inlet of which is connected to the air outlet of the ambient temperature vaporizer; A multi-stage compressor unit, wherein the air inlet of the multi-stage compressor unit is connected to the air outlet of the buffer tank, and the multi-stage compressor unit includes at least two compression units; Multiple interstage cooling units and interstage gas-liquid separation units are provided, with one interstage cooling unit and one interstage gas-liquid separation unit located between two adjacent compression units; The return pipe is connected at one end to the outlet pipe of the final stage compression unit and at the other end to the inlet of the buffer tank or the inlet pipe of the first stage compression unit. A metering device is installed on the outlet pipe of the final stage compression unit to measure the flow rate of the output gas.

2. The BOG recycling augmentation system of claim 1, wherein: The multi-stage compressor unit is a four-stage compressor unit, including a first-stage compressor, a second-stage compressor, a third-stage compressor, and a fourth-stage compressor connected sequentially by pipelines.

3. The BOG recycling augmentation system of claim 2, wherein: The interstage cooling unit is an air cooler, including a primary air cooler, a secondary air cooler, a tertiary air cooler, and a quaternary air cooler, which are respectively located at the outlet of the corresponding compression unit.

4. The BOG recycling augmentation system of claim 3, wherein, The interstage gas-liquid separation unit is a separator, including a primary separator, a secondary separator, a tertiary separator, and a quaternary separator. The air inlet of the separator is connected to the air outlet of the corresponding air cooler, and the liquid phase outlet is connected to the sewage discharge system.

5. The BOG recycling augmentation system of claim 1, wherein: A pneumatic regulating valve is installed on the return pipe to adjust the return flow rate according to the pressure of the buffer tank or the intake pressure of the multi-stage compressor unit.

6. The BOG recycling augmentation system of claim 1, wherein: An emergency shut-off valve is also provided on the pipeline between the ambient temperature vaporizer and the buffer tank.

7. The BOG recycling augmentation system of claim 1, wherein: The entire system is integrated on a skid, and the ambient air vaporizer, buffer tank, multi-stage compressor unit, interstage cooling and separation unit are connected and fixed to the skid via pipes and valves.

8. The BOG recycling augmentation system of claim 1, wherein: The buffer tank is equipped with a pressure sensor and a liquid level sensor.

9. The BOG recycling augmentation system of claim 2, wherein, Each stage of the compression unit has a pressure sensor and a temperature sensor installed on its outlet pipe.

10. The BOG recycling augmentation system of claim 1, wherein: The system also includes a control unit electrically connected to the multi-stage compressor unit, the pneumatic regulating valve on the return pipe, and various pressure and temperature sensors, and is configured to: receive data from the sensors and stabilize the system pressure by controlling the opening of the pneumatic regulating valve and / or the rotational speed of the multi-stage compressor unit.

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