CN104696700B - methane gas recovery system and recovery method - Google Patents

Abstract

The invention relates to a methane gas recovery system and recovery method. The system includes a flash evaporator, the inlet of the flash evaporator is used to receive methane gas, and the gas outlet of the flash evaporator is connected to the inlet of a compressor. , the gas outlet of the compressor is connected to the cooling device, and the cooling device is connected to the return port of the flash evaporator through a throttling valve. The invention not only has a simple gas recovery process, reduces the power consumption of methane recovery, but also has low installation and maintenance costs, high recovery rate, and the recovered product is liquefied natural gas which can be sold locally.

Description

Methane gas recovery system and recovery method

technical field

The invention relates to the technical field of gas recovery and reuse, in particular to the reliquefaction and recovery of boil-off gas (BOG) used in the storage and transportation of liquefied natural gas (LNG).

Background technique

The main component of liquefied natural gas (LNG) is methane. It is recognized as the cleanest energy source on earth. It is colorless, odorless, non-toxic and non-corrosive. Its volume is about 1/625 of the volume of the same amount of gaseous natural gas. The weight of LNG Only about 45% of the same volume of water. Liquefied natural gas is natural gas that becomes liquid after being compressed and cooled to its boiling point. Usually, liquefied natural gas is stored in a low-temperature storage tank at minus 161.5 degrees Celsius and about 0.1 MPa, transported by a special ship or tanker truck, and re-gasified when used. The burning of liquefied natural gas causes very little air pollution and releases a lot of heat, so liquefied natural gas is a relatively advanced energy source.

However, during the transportation process of LNG ships and tankers, as well as the LNG filling and unloading process, due to the heat transfer caused by the huge temperature difference between the ambient temperature and the low-temperature LNG, the pre-cooling of the gas station system and other reasons, the low-temperature LNG will continue to Boil-off gas (BOG for short) is produced when heated. Although the low-temperature container for storing LNG has a thermal insulation layer, it still cannot avoid the influence of external heat, resulting in BOG. The increase of BOG will increase the pressure of the system. Once the pressure exceeds the allowable working pressure of the storage tank, it is necessary to activate the safety protection device to release the BOG reduction. pressure.

Existing methods of methane gas recovery include converting the vaporized methane gas into the urban pipe network after heat exchange with air or using a compressor to turn the methane gas into CNG (methane gas product with a pressure greater than 20MPa). Entering the urban pipeline network scheme requires LNG filling stations to be close to the urban pipeline network, which is not suitable for ordinary LNG filling stations; the market value of CNG products is low, the storage and transportation are complicated, the compression energy consumption is high, and the equipment occupies a large area . There are also cold sources such as liquid nitrogen to cool methane, and then turn it into low-temperature methane liquid for reuse. However, this method requires a separate cooling capacity generation device, which requires high investment and operating power consumption. The process is complicated and occupies a large area. The cost of methane is high, and the recovery rate is low, which leads to the waste of energy to a certain extent.

In order to overcome the above problems, there is an installation structure of a small skid-mounted liquefied natural gas vapor re-liquefaction recovery device in the prior art, including: a low-temperature storage tank, a regenerative low-temperature refrigerator, a condensing heat exchanger; the condensing heat exchanger is installed At the cold end of the regenerative cryogenic refrigerator; between the cryogenic storage tank and the condensing heat exchanger, there are evaporation gas delivery channels and liquefied natural gas delivery channels; the liquefied natural gas at the condensing heat exchanger can flow along the liquefied natural gas The transfer channel enters the cryogenic storage tank. Although the above-mentioned documents have improved the reliquefaction efficiency and ensured the reliability and safety of equipment operation, the regenerative cryogenic refrigerator and the condensation heat exchanger must be installed above the cryogenic storage tank, so there is a problem for the installation of the equipment. Certain requirements are not easy to effectively reduce installation and maintenance costs; in addition, the gas recovery rate has not been greatly improved.

Contents of the invention

For this reason, the technical problem to be solved by the present invention is to overcome the problems of high installation and maintenance costs and low recovery rate of recovering methane in the prior art to provide a methane gas recovery system with low equipment installation and maintenance costs and high recovery rate. Recycling systems and recycling methods.

In order to solve the above technical problems, a methane gas recovery system according to the present invention, the system includes a flash evaporator, the inlet of the flash evaporator is used to receive methane gas, the gas outlet of the flash evaporator is connected to the compressor The air inlet is connected, the air outlet of the compressor is connected with the cooling device, and the cooling device is connected to the return port of the flash evaporator through a throttle valve.

In one embodiment of the present invention, the liquid outlet of the flash evaporator is connected with the product tank.

In one embodiment of the present invention, a booster pump is provided between the flash evaporator and the finished product tank.

In one embodiment of the present invention, the cooling device is a water cooling device.

In one embodiment of the present invention, the cooling device is an air cooling device.

In one embodiment of the present invention, the cooling device is a heat exchanger, and the heat exchanger includes at least two passages, one of which communicates with the pipeline between the flasher and the compressor, and the other A channel communicates with the pipeline from the compressor to the throttle valve.

In one embodiment of the present invention, the air inlet of the flash evaporator is connected with a buffer tank through a pipeline, and the flash evaporator receives the methane gas through the buffer tank.

In one embodiment of the present invention, a pressure reducing valve is provided between the buffer tank and the flash evaporator.

In one embodiment of the present invention, the components constituting the methane gas recovery system are installed together on a chassis to form a skid-mounted integrated structure.

The present invention also provides a methane gas recovery method for recovering methane gas and collecting methane liquid. The steps are as follows: step S1: compress the methane gas to form high-pressure methane gas; step S2: compress the high-pressure methane gas Methane gas is cooled to form high-pressure low-temperature methane gas; step S3: throttling the high-pressure low-temperature methane gas to form a mixture of gaseous methane and liquid methane; step S4: separating the mixture of gaseous methane and liquid methane, and The gaseous methane is returned to step S1 for recycling treatment; the liquid methane is recovered.

In another embodiment of the present invention, before the step S1, a step S0 is also included: the methane gas to be recovered is collected and buffered, and when the collected methane gas reaches a first preset amount, the steps S1-S4 are executed ; and when the collected methane gas is lower than the second preset amount, stop performing the steps S1-S4.

In another embodiment of the present invention, in the step S2, the cooling is completed by exchanging heat between the high-pressure and high-temperature methane gas and the methane gas before compression in the step S1.

The above technical solution of the present invention has the following advantages compared with the prior art:

The methane gas recovery system and recovery method described in the present invention utilize the high-grade cooling energy of the low-temperature characteristics of the released methane gas itself, the process of recovering gas is simple, the power consumption of methane recovery is reduced, the cost is low, and the product is recovered Liquefied natural gas can be sold locally.

Description of drawings

In order to make the content of the present invention more easily understood, the present invention will be described in further detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein

Fig. 1 is the schematic diagram of the methane gas recovery system described in Embodiment 1 and Embodiment 2 of the present invention;

Fig. 2 is the schematic diagram of the methane recovery system described in the third embodiment of the present invention;

Fig. 3 is a schematic diagram of the methane gas recovery system described in Embodiment 4 of the present invention;

Fig. 4 is a top view of the methane recovery device of the present invention.

detailed description

Embodiment one:

As shown in Figure 1, the present embodiment provides a methane gas recovery system, the system includes a flash evaporator 12, the inlet of the flash evaporator 12 is used to receive methane gas 10, the gas outlet of the flash evaporator 12 It is connected to the air inlet of the compressor 14 , and the air outlet of the compressor 14 is connected to the cooling device, and the cooling device is connected to the return port of the flash evaporator 12 through the throttling valve 15 .

The above is the core technical solution of the present invention. The methane gas recovery system of the present invention includes a flash evaporator 12 for receiving methane gas 10, wherein the air inlet of the flash evaporator 12 is used for receiving methane gas 10, After the methane gas enters the flash evaporator 12, it is separated into low-temperature and low-pressure methane gas and methane liquid; the gas outlet of the flash evaporator 12 is connected with the air inlet of the compressor 14 to separate The methane gas produced is pressurized to form high-pressure and high-temperature methane gas. The gas outlet of the compressor 14 is connected to a cooling device so that the high-pressure and high-temperature methane gas is cooled to form high-pressure and low-temperature methane gas. The cooling device passes through the throttling The valve 15 is connected to the return port of the flasher 12, so that the high-pressure and low-temperature methane gas is decompressed to form a mixture of gaseous methane and liquid methane, and the mixture of methane gas and liquid methane enters the flasher 12 Separation into low-temperature and low-pressure methane gas and methane liquid; wherein, the flash evaporator 12, the compressor 14, the cooling device and the throttle valve 15 form a gas circulation channel A, which is separated from the flash evaporator 12 The low-temperature and low-pressure methane gas circulates continuously in the gas circulation channel A, and the liquid outlet of the flash evaporator 12 flows out of the methane liquid to form the liquid recovery channel B, and the methane liquid separated in the flash evaporator 12 flows out from the liquid recovery channel B . The setting of the gas circulation channel A of the present invention enables the low-temperature methane gas continuously discharged from the gas outlet of the flasher 12 to be recycled, effectively improving energy utilization, avoiding energy waste, and reducing recovery power consumption; the liquid The setting of the recovery channel B enables the finished product of methane liquid to be directly collected and reused, thus improving the energy utilization rate; moreover, the present invention has a simple process flow and can be made into a skid-mounted integrated type, with low investment and operating power consumption, and the recovered product is liquefied Natural gas can be sold locally, reducing the power consumption of methane recovery, so not only the efficiency of methane recovery is greatly improved, but also the installation and maintenance costs are reduced.

In this embodiment, the liquid outlet of the flash evaporator 12 is connected with the finished product tank 16, and the liquid outlet of the flash evaporator 12 is connected with the finished product tank 16 to form a liquid recovery channel B, so that the methane liquid product can be directly It flows back into the finished product tank 16, thereby avoiding the problem of lowering the temperature of the liquid caused by the release of the finished product tank.

The following describes the working principle of the methane gas recovery system:

The methane gas enters the flash evaporator 12, and part of the liquid methane carried in the methane gas can be preliminarily separated in the flash evaporator 12, and the liquid methane is sent back to the product tank, while the low-temperature gas separated from the flash evaporator 12 Low-pressure methane gas enters the compressor 14, and is compressed by the compressor to form high-pressure methane gas. The high-pressure methane gas is cooled by the cooling device to form high-pressure low-temperature methane gas, and then throttled by the throttle valve 15. In this process, the volume of methane gas expands into low-temperature and low-pressure gaseous methane. Since methane absorbs most of the heat during the expansion process, methane becomes liquid, forming a mixture of gaseous methane and liquid methane. The mixture of gaseous methane and liquid methane flows back into the flasher 12, and is separated into methane gas and methane liquid in the flasher 12, and the methane gas is discharged from the gas outlet of the flasher 12 for recycling treatment The separated methane liquid is discharged from the liquid outlet of the flash evaporator 12, and the recovery of the methane liquid is completed through the liquid recovery channel B.

Embodiment two:

As shown in Figure 1, embodiment two is an improvement made on the basis of embodiment one. In order to improve the system for recovering methane gas, a recycling device is added to the system of embodiment one. The following details:

In this embodiment, the cooling device is a heat exchanger 13, and the heat exchanger 13 includes at least two channels, one of which communicates with the pipeline between the flasher 12 and the compressor 14, and the other A channel communicates with the pipeline between the compressor 14 and the throttle valve 15, and the low-temperature methane gas continuously discharged from the gas outlet of the flash evaporator 12 exchanges heat with the pressurized high-temperature methane gas, which is beneficial to Reduce energy loss.

The air inlet of the flash evaporator 12 is connected with the buffer tank 11 through a pipeline, and the flash evaporator 12 receives the methane gas 10 through the buffer tank 11. The present invention can be applied to LNG refueling stations to release methane The recovery utilizes the pressure characteristics of the methane gas released by the LNG filling station. The setting of the buffer tank 11 can overcome the instability of the release source of the LNG filling station and increase the time of each operation of the system.

Below in conjunction with the methane gas recovery system in the accompanying drawing 1, the working principle is described in detail:

The buffer tank 11 collects the methane gas 10 flowing into it through a pipeline. When the methane gas collected by the buffer tank 11 reaches a certain amount, the low-temperature and low-pressure methane gas in the buffer tank 11 enters the flasher 12, and the At the same time, the compressor 14 is turned on, and part of the liquid methane carried in the methane gas can be preliminarily separated in the flash evaporator 12, and the liquid methane is sent back to the finished product tank 16, and the low-temperature and low-pressure methane gas separated from the flash evaporator 12 enters the Heat exchanger 13, the low-temperature and low-pressure methane gas enters the compressor 14 after heat exchange and temperature rise in the heat exchanger 13, and the low-pressure and high-temperature methane gas is pressurized by the compressor 14 to form high-pressure methane Gas, the pressure is 8MPa and the temperature rises, the high-pressure high-temperature methane enters the heat exchanger 13 and exchanges heat with the low-pressure low-temperature methane gas discharged from the gas outlet of the flasher 12, and the high-pressure low-temperature methane gas after the full heat exchange passes through the The throttling action of the throttle valve 15 lowers the pressure and lowers the temperature and transforms it into a mixture of low-pressure and low-temperature methane gas and methane liquid at a temperature of minus 83 ° C. The mixture of low-pressure and low-temperature methane gas and methane liquid flows back into the flasher 12. The flash evaporator 12 separates the low-pressure and low-temperature methane gas from the methane liquid, wherein the methane gas is discharged from the flash gas outlet for recycling treatment; the separated methane liquid enters the LNG product tank 16 and passes through the liquid recovery channel B completes the recovery of methane liquid.

Embodiment three:

As shown in Figure 2, embodiment three is a deformation made on the basis of embodiment two. In order to improve the system for recovering methane gas, the system of embodiment two has increased recycling equipment, which will be described in detail below:

A valve can be set between the buffer tank 11 and the flash evaporator 12, and the valve is preferably a pressure reducing valve 17, so that the methane gas can be further reduced in temperature after decompression, and high-quality cold methane gas can be provided to the The flash evaporator 12 is conducive to the separation of methane gas in the flash evaporator 12, and the low-temperature and low-pressure methane gas in the buffer tank 11 is decompressed to 0.1MPa through the pressure reducing valve 17 and enters the flash evaporator 12. It is beneficial to obtain more methane liquid when the flasher 12 performs gas-liquid separation.

A booster pump 18 is provided between the flasher 12 and the finished product tank 16, for pumping the methane liquid in the flasher 12 into the finished product tank 16, which facilitates the flow of the methane liquid into the finished product Tank 16 for easy recycling.

In this embodiment, the cooling device is a water cooling device, and the outlet of the compressor 14 is provided with a water cooling system 19 for cooling the compressed methane gas, and the water cooling system 19 includes an upper circulating water 191 And the lower circulating water 192. In the gas circulation channel A, the low-temperature and low-pressure methane gas separated in the flash evaporator 12 enters the heat exchanger 13, and the low-temperature and low-pressure methane gas enters the heat exchanger 13 after heat exchange and temperature rise. In the compressor 14, when the low-pressure methane is pressurized by the compressor 14, a high-pressure methane gas is formed, the pressure is 8 MPa and the temperature rises, and the temperature is lowered through the water cooling system 19, and the high-pressure and high-temperature gas at the outlet of the compressor 14 is cooled. The methane gas is cooled to normal temperature. Specifically, the high-pressure methane gas is cooled through the upper circulating water 191 and the lower circulating water 192 shared with the compressor 14. At this time, the high-pressure and cooled methane gas enters the heat exchanger 13 It is more conducive to heat exchange with the low-pressure and low-temperature methane gas discharged from the outlet of the flash evaporator 12, which fully reduces the energy required for heat exchange. After the heat exchange is completed, the high-pressure and low-temperature methane gas expands through the throttle valve 15 Decrease the pressure and lower the temperature to transform into a mixture of low-pressure and low-temperature methane gas and methane liquid at a temperature of minus 85°C. The mixture of low-pressure and low-temperature methane gas and methane liquid enters the flash evaporator 12, and the flash evaporator 12 converts the low-pressure and low-temperature methane The mixture of gas and methane liquid is separated into methane gas and recoverable methane liquid.

As a modification, the cooling device in this embodiment can also be set as an air cooling device, and the outlet of the compressor 14 is provided with a water air cooling device, which can also cool down the compressed methane gas.

In this embodiment, the storage capacity of the buffer tank 11 is equal to the hourly processing capacity of the system.

Embodiment four:

As shown in Figure 3, Embodiment 4 is a modification made on the basis of Embodiment 3. In order to improve the system for recovering methane gas, a monitoring device for controlling the automatic recovery of gas is added to the system of Embodiment 4. The following details illustrate:

In this embodiment, the pressure reducing valve 17 is a pressure self-regulating valve, and the pressure self-regulating valve is provided with a pressure monitoring device 171 for controlling the opening and closing of the pressure self-regulating valve and the compressor 14. When the buffer tank 11 When the pressure reaches 0.6MPa, the pressure self-regulating valve is opened, and the low-temperature and low-pressure methane in the buffer tank 11 is decompressed to 0.15MPa through the pressure self-regulating valve and enters the flash evaporator 12, thereby facilitating the flow of methane gas in the The separation in flasher 12 yields more methane liquid. The low-temperature and low-pressure methane gas separated in the flash evaporator 12 enters the heat exchanger 13, and the low-temperature and low-pressure methane gas enters the compressor 14 after heat exchange in the heat exchanger 13. Methane is pressurized by the compressor 14 to form high-pressure methane gas, the pressure is 8.5MPa and the temperature rises, and the water cooling system 19 cools down, and the methane gas after high-pressure cooling enters the heat exchanger 13 for further It is beneficial to exchange heat with the low-pressure and low-temperature methane gas discharged from the gas outlet of the flash evaporator 12, thereby reducing energy loss. After the full heat exchange is completed, the high-pressure and low-temperature methane gas is transformed into The mixture of low-pressure and low-temperature methane gas and methane liquid at a temperature of minus 90° C. is beneficial for gas-liquid separation after entering the flasher 12 .

The flash evaporator 12 is provided with a liquid level monitoring device 121 that controls the opening and closing of the booster pump 18, and a liquid level self-regulating valve 122 is provided between the booster pump 18 and the finished product tank 16. The liquid level monitoring The device 121 controls the opening or closing of the booster pump 18 and the liquid level self-regulating valve 122. Specifically, when the liquid level monitoring device 121 detects that the liquid height in the flash evaporator 12 exceeds a preset value, Then the liquid level self-regulating valve 122 and the booster pump 18 will be opened, and the booster pump 18 will be used to pressurize the liquid into the finished product tank 16 . A temperature monitoring device 20 is provided between the heat exchanger 13 and the compressor 14 for monitoring the temperature of the methane gas to ensure the smooth operation of the system, including detecting the temperature of the methane gas flowing out from the outlet of the heat exchanger 13 And the temperature of the methane gas flowing to the inlet of the compressor 14 .

In this embodiment, the storage capacity of the buffer tank 11 is greater than the hourly processing capacity of the system.

Embodiment five:

This embodiment provides a methane gas recovery method, using the methane gas recovery system described in any one of embodiment one, embodiment two, embodiment three, embodiment four to recover methane gas and collect methane liquid, the steps are as follows: S1: Compress the methane gas to form high-pressure methane gas; Step S2: Cool the high-pressure methane gas to form high-pressure low-temperature methane gas; Step S3: Throttle the high-pressure low-temperature methane gas to form gaseous methane and liquid A mixture of methane; step S4: separating the mixture of gaseous methane and liquid methane, returning the gaseous methane to step S1 for recycling; recovering the liquid methane.

In the methane gas recovery method described in this embodiment, the low-temperature methane gas continuously discharged from the gas outlet of the flasher 12 can be recycled, which effectively improves energy utilization, avoids energy waste, and reduces recovery power consumption; the methane The liquid product can be directly returned to the product tank 16, the recovery process is simple, the cost is low, and the recovered product is liquefied natural gas which can be sold locally.

In this embodiment, step S0 is also included before the step S1: collecting and buffering the methane gas to be recovered, and when the collected methane gas reaches the first preset amount, the steps S1-S4 are executed to ensure that the system is as once possible The running time is long, avoiding frequent opening; and when the collected methane gas is lower than the second preset amount, the execution of the steps S1-S4 is stopped, which effectively avoids the problem of gas suffocation in the flasher 12 .

In the step S2, the cooling is completed by exchanging heat between the high-pressure and high-temperature methane gas and the methane gas before being compressed in the step S1, which can not only effectively improve the energy utilization rate, but also help reduce energy loss.

When the storage capacity of the buffer tank 11 is greater than or equal to the hourly processing capacity of the system, the methane gas can be continuously and automatically recovered, thereby facilitating the local sale of liquefied natural gas.

Embodiment six:

This embodiment provides a methane gas recovery control method, using any one of the methane gas recovery systems described in Embodiment 2, Embodiment 3, and Embodiment 4 to recover methane gas, including:

Step S1: Collect and buffer the methane gas to be recovered, use a pressure monitoring device to control the opening and closing of the pressure self-regulating valve, and when the collected methane gas reaches the first preset amount, open the pressure self-regulating valve and enter step S2: When the collected methane gas is lower than the second preset amount, close the pressure self-regulating valve, continue to collect methane gas until the methane gas reaches the first preset amount, open the pressure self-regulating valve, and enter the step S2; step S2: start the compressor, compress the methane gas to form high-pressure methane gas; step S3: cool the high-pressure methane gas to form high-pressure low-temperature methane gas; step S4: save the high-pressure low-temperature methane gas flow to form a mixture of gaseous methane and liquid methane; step S5: separating the mixture of gaseous methane and liquid methane, returning the gaseous methane to step S2 for recycling treatment; and recovering the liquid methane.

In the methane gas recovery control method described in this embodiment, a pressure detection device 171 is provided between the buffer tank 11 and the flash evaporator 12, and the pressure detection device 171 can control the pressure reducing valve 17 and the compressor. The motor switch of 14 carries out interlocking control, is conducive to prolonging the single running time of the system, and at this moment, the pressure reducing valve 17 is a pressure self-regulating valve. This method judges whether to open the recovery system by monitoring the pressure of the buffer tank 11. Once the pressure of the buffer tank 11 is higher than the first preset value, that is, the high pressure value, the pressure self-regulating valve is opened, and the whole system automatically Open, the methane gas in the buffer tank 11 enters the gas circulation channel A and the liquid recovery channel B respectively; if the pressure of the buffer tank 11 is lower than the second preset value, that is, the low pressure value, close The pressure self-regulating valve continues to collect methane gas until the methane gas reaches the first preset amount, and then opens the pressure self-regulating valve to start the system. Furthermore, the control method of the present invention, through the opening and closing of the pressure chain control system, is beneficial to prolonging the single running time of the system, avoiding the use of manpower control, and solving the problem of automatic control of methane recovery, so it not only saves labor costs but also reduces Ineffective power costs.

In this embodiment, the setting of the low pressure value is based on the pressure requirements of the subsequent system operation. If the pressure is too low, the methane gas in the buffer tank 11 will be difficult to flow into the flasher 12, and it is easy to suffocate; The setting of the high pressure value is based on the pressure of the source of the methane gas 10 released in the front section. When the high value of the pressure was higher than the pressure of the methane source gas released, enough methane gas could be collected in the buffer tank 11, so as to Ensure that the storage capacity of the buffer tank 11 is greater than or equal to the hourly recovery capacity of the system, so that the system can run as long as possible at one time and avoid frequent opening. If the pressure of the buffer tank 11 is lower than the low pressure value, the entire system is closed, and if the pressure of the buffer tank 11 is higher than the high pressure value, the entire system is opened, specifically, when the pressure of the buffer tank 11 is low When the pressure is 0.1Mpa-0.3Mpa, stop the system operation, preferably the low pressure value is 0.2Mpa, stop the system operation; open the system when the pressure of the buffer tank 11 is higher than 0.5Mpa-0.7Mpa, preferably the high pressure The value is 0.6Mpa to turn on the system.

In order to improve the automatic recovery of methane gas, in this embodiment, a temperature monitoring device 20 is provided at the outlet of the flasher 12 and the inlet pipeline of the compressor 14, wherein the temperature monitoring device 20 is provided with a temperature alarm high value and temperature parking high values. When the detected temperature is higher than the temperature alarm high value, the system will automatically alarm to detect whether the system is running normally; when the detected temperature is higher than the parking high value, close the pressure self-regulating valve and the compressor 14, and Automatic parking. The temperature monitoring device 20 is used for interlocking control of the pressure self-regulating valve and the motor of the compressor 14, which is conducive to monitoring whether the heat exchanger 13 and the compressor 14 are operating normally, and can not only effectively Monitor the operation of the system, and can achieve intrinsic safety. Wherein, the purpose of setting the high temperature alarm value is to monitor the temperature of the methane gas at the inlet of the compressor 14. If the temperature is too high, it may show that the heat exchanger 13 is faulty or the temperature of the methane gas at the outlet of the compressor 14 is too high. affect the overall operation. When the methane gas temperature between the heat exchanger 13 and the compressor 14 is higher than the temperature alarm high value, the system automatically alarms; the methane gas temperature between the heat exchanger 13 and the compressor 14 is higher than When the parking high value, the system automatically stops. Specifically, if the inlet methane gas temperature of the compressor 14 is higher than 10°C-30°C, the system will automatically alarm, preferably if the inlet methane gas temperature of the compressor 14 is higher than 15°C, the system will automatically alarm; If the outlet gas temperature of the heat exchanger 13 is higher than 20°C-40°C, the system will automatically stop, preferably if the outlet gas temperature of the heat exchanger 13 is higher than 30°C, the system will automatically stop. In the actual process setting, the temperature shutdown high value is higher than the temperature alarm high value.

In order to continuously improve the automatic recovery of methane gas, in this embodiment, the flash evaporator 12 is provided with a liquid level detection device 121 , and a liquid level self-regulating valve 122 is provided between the booster pump 18 and the finished product tank 16 . The liquid level detection device 121 is provided with a liquid level high level value and a liquid level low level value. After the methane gas in the flasher 12 is separated into methane liquid, the liquid level detection device 121 detects the liquid level of the methane liquid. , when the liquid level of the detected methane liquid is higher than the high level value of the liquid level, the booster pump 18 is started to transport the methane liquid to the finished product tank 16; when the liquid level of the detected methane liquid is lower than the low level value of the liquid level , turn off the booster pump 18, this embodiment is beneficial to prolong the single run time of the booster pump 18 by interlocking the motor switch on the booster pump 18 and the liquid level self-regulating valve 122 , to avoid the problem that the flasher 12 is full of liquid and cannot inject gas, or the problem that the liquid level is too low causes gas to flow into the booster pump 18 .

In this embodiment, the setting of the high level value of the liquid is based on the operation of the overall system. If enough methane liquid is stored and then the booster pump 18 is turned on, frequent opening of the booster pump 18 can be avoided. If the flasher 12 If the liquid level in the flasher 12 is higher than the liquid high level value, the gas space at the upper end of the flasher 12 is too small, causing the air pressure in the flasher 12 to rise. If it is higher than the pressure of the methane gas entering the flasher 12, it will As a result, the incoming gas cannot enter, and it is easy to cause gas suffocation; the setting of the low level value of the liquid is based on the consideration that once the liquid level is low, the methane gas in the flasher 12 may be mixed into the methane liquid and enter the finished product tank 16 . In order to ensure that the methane liquid separated from the flash evaporator can smoothly enter the liquid recovery channel B, the booster pump 18 is started when the liquid level in the flash evaporator 12 is higher than the high level value of the liquid level, if the flash evaporator When the liquid level in 12 is lower than the low level value of the liquid level, the booster pump 18 is closed. Specifically, when the liquid level on the flash evaporator 12 reaches 60%-80% of the total liquid height of the flash evaporator 12, start the booster pump 18, and open the liquid level self-regulating valve 122, preferably The high value of the liquid level is 70% of the total liquid height in the flash evaporator 12; when the liquid level on the flash evaporator 12 is lower than 10%-30%, close the booster pump 18 and the For the liquid level self-regulating valve 122 , preferably, the low level of the liquid level is 20% of the total liquid height of the flash evaporator 12 .

In this embodiment, between the steps S1 and S2, it also includes preliminary separation of the liquid methane carried in the methane gas, transporting the separated liquid methane to the finished product tank 16, transporting the methane gas to the compressor 14, and performing the steps S2.

In this embodiment, when the storage capacity of the buffer tank 11 is greater than or equal to the hourly processing capacity of the system, the methane gas can be continuously and automatically recovered, thereby facilitating the local sale of liquefied natural gas.

Embodiment seven:

As shown in Figure 4, this embodiment provides a methane gas recovery device according to the methane gas recovery system described in the third embodiment or the fourth embodiment, the recovery device is made into a complete set of devices, and the components that constitute the methane gas recovery system Installed on a chassis to form a skid-mounted integrated structure, thereby ensuring operational reliability and safety. The specific size can be designed according to actual operating requirements. For example, the skid-mounted body is 10 meters * 6 meters * 2.5 meters, and the length is 10 meters. meters, a width of 6 meters, and a height of 2.5 meters, wherein the distance between the buffer tank 11 and the skid-mounted inner wall along the vertical direction is 2m, and the distance between the buffer tank 11 and the skid-mounted inner wall along the horizontal direction is 1.8 meters m, the distance from the buffer tank 11 to the flash evaporator 12 in the vertical direction is 3.5 m, the distance from the flash evaporator 12 to the booster pump 18 in the vertical direction and the distance from the heat exchanger 13 to the The distance between the compressors 14 along the vertical direction is 3m, and the distance between the flasher 12 and the heat exchanger 13 along the horizontal direction is 3m.

In the present invention, the gas source of the buffer tank 11 is the LNG filling process, the release process of the LNG product tank, the pressure relief process of the LNG tanker, and the like.

In summary, the above technical solutions described in the present invention have the following advantages:

1. The present invention can be applied to the recovery of methane released from LNG filling stations, utilizes the pressure characteristics of methane gas released from LNG filling stations, the setting of the buffer tank can overcome the instability of the release source of LNG filling stations, and increase the The time of each operation of the system; the setting of the gas circulation channel enables the low-temperature methane gas continuously discharged from the gas outlet of the flasher to exchange heat with the pressurized high-temperature methane gas to reduce energy loss; the liquid recovery channel The setting of the methane liquid product can directly return to the finished product tank, thereby avoiding the problem of lowering the temperature of the liquid caused by the release of the finished product tank; moreover, the process flow of the present invention is simple, and can be made into a skid-mounted integrated type, which saves investment and operation. The power consumption is small, and the recovered product is liquefied natural gas, which can be sold locally, reducing the power consumption of methane recovery, so not only the efficiency of methane recovery is greatly improved, but also the installation and maintenance costs are reduced.

2. A decompression valve is provided between the buffer tank of the present invention and the flash evaporator, so that the methane gas can be further reduced in temperature after decompression, which is beneficial to the separation of the methane gas in the flash evaporator so as to obtain more Methane liquid; a pressurizing pump is provided between the flasher and the finished product tank, which facilitates the flow of the methane liquid into the finished product tank for easy recycling; the outlet of the compressor is provided with a water cooling system, It is beneficial to cool down the high-pressure methane gas, and it is convenient to reduce the energy required for subsequent heat exchange.

3. The decompression valve of the present invention is provided with a pressure monitoring device that controls the opening of the decompression valve and the compressor, and the pressure detection device can interlock the motor switch of the decompression valve and the compressor control, which is beneficial to prolong the single operation time of the system; the outlet of the flash evaporator and the inlet pipeline of the compressor are provided with a temperature monitoring device, which is used to control the pressure reducing valve and the compressor The interlocking control of the motor is beneficial to monitor whether the heat exchanger and the compressor are operating normally, not only can effectively monitor the system operation, but also can achieve intrinsic safety; the flash evaporator is equipped with a liquid level detection device, so A liquid level self-regulating valve is provided between the booster pump and the finished product tank. When the methane gas in the flash evaporator is separated into methane liquid, the liquid level detection device is turned on, and the motor on the booster pump is turned on. The interlocking control of the switch and the liquid level self-regulating valve is beneficial to prolong the single operation time of the booster pump, avoiding the problem that the flasher is full of liquid and cannot inject gas or the liquid level is too low to cause gas leakage. Into the booster pump problem.

4. In the methane gas recovery method of the present invention, the low-temperature methane gas continuously discharged from the gas outlet of the flasher exchanges heat with the pressurized high-temperature methane gas, which can make energy loss small, avoid energy waste, and reduce Recycling power consumption; the methane liquid product can be directly returned to the finished product tank, the recovery process is simple, the cost is low, and the recovered product is liquefied natural gas that can be sold locally.

5. The methane gas recovery control method of the present invention, in order to improve the automatic recovery of methane gas, a temperature monitoring device is provided at the outlet of the flasher and the inlet pipeline of the compressor, and the temperature monitoring device is used to monitor the The interlocking control of the decompression valve and the motor of the compressor is beneficial to monitor whether the heat exchanger and the compressor are operating normally, and not only can effectively monitor the operation of the system, but also can achieve intrinsic safety.

Apparently, the above-mentioned embodiments are only examples for clear description, and are not intended to limit the implementation. For those of ordinary skill in the art, other changes or changes in different forms can be made on the basis of the above description. It is not necessary and impossible to exhaustively list all the implementation manners here. However, the obvious changes or changes derived therefrom are still within the scope of protection of the present invention.

Claims (9)

1. A kind of 1. methane gas recovery system, it is characterised in that：The system includes flash vessel (12), and flash vessel (12) are entered Gas port is used to receive methane gas (10), and the gas outlet of the flash vessel (12) is connected with the air inlet of compressor (14), described The gas outlet of compressor (14) is connected with cooling device, and the cooling device is connected to the flash vessel by choke valve (15) (12) refluxing opening, the air inlet of the flash vessel (12) are connected with surge tank (11) by pipeline, and the flash vessel (12) is logical Cross the surge tank (11) and receive the methane gas (10), decompression is provided between the surge tank (11) and the flash vessel (12) Valve (17), the pressure-reducing valve (17) are provided with the pressure monitoring dress for controlling the pressure-reducing valve (17) and the compressor (14) keying Put (171).
2. 2. methane gas recovery system according to claim 1, it is characterised in that：The liquid outlet of the flash vessel (12) with into Product tank (16) is connected.
3. 3. methane gas recovery system according to claim 2, it is characterised in that：The flash vessel (12) and the finished pot (16) force (forcing) pump (18) is provided between.
4. 4. methane gas recovery system according to claim 1, it is characterised in that：The cooling device is water-cooling apparatus (19)。
5. 5. methane gas recovery system according to claim 1, it is characterised in that：The cooling device is air-cooling device.
6. 6. methane gas recovery system according to claim 1, it is characterised in that：The cooling device is heat exchanger (13), The heat exchanger (13) includes at least two passages, one of passage and the flash vessel (12) to the compressor (14) it Between pipeline connection, the pipeline connection between another passage and the compressor (14) to the choke valve (15).
7. 7. the methane gas recovery system according to any one in claim 1-6, it is characterised in that：Form the methane gas Each part of recovery system is installed on a chassis jointly, forms skid integral structure.
8. 8. a kind of methane gas recovery method, for reclaiming methane gas and collecting methane liquid, its step is as follows, including：

   Step S1：The methane gas that will be reclaimed is collected buffering, and the keying of pressure-reducing valve is controlled using pressure monitoring device, When the methane gas of collection reaches the first predetermined amount, the pressure-reducing valve is opened,

   Into step S2；When the methane gas of collection is less than the second predetermined amount, the pressure-reducing valve is closed, continues to collect methane gas Reach first predetermined amount to methane gas, open the pressure-reducing valve, into step S2；

   Step S2：The methane gas is compressed to form high pressure methane gas；

   Step S3：The high pressure methane gas is carried out being cooled into high pressure low temperature methane gas；

   Step S4：The high pressure low temperature methane gas is throttled, forms the mixture of gaseous methane and liquid methane；

   Step S5：The mixture of the gaseous methane and liquid methane is separated, gaseous methane return to step S2 is carried out Circular treatment；Liquid methane is reclaimed.
9. 9. methane gas recovery method according to claim 8, it is characterised in that：In the step S3, by the high pressure first Alkane gas carries out heat exchange to complete to cool down with the methane gas before being compressed in the step S2.