Remotely controllable vehicle-mounted mobile device for recovering and emptying natural gas by using liquid nitrogen cold energy

Abstract

The invention discloses a vehicle-mounted mobile device capable of being remotely controlled and recycling and emptying natural gas by using liquid nitrogen cold energy. The system comprises a liquid nitrogen storage tank, a centrifugal pump, a throttle valve, a plate-fin heat exchanger, a temperature controller and an LNG storage tank, carrying out liquefaction treatment on the vented natural gas by adopting low-temperature liquid nitrogen; liquid nitrogen stored in the liquid nitrogen storage tank is pressurized by the pump and enters the heat exchanger to exchange heat with recycled natural gas, the liquid nitrogen is discharged into air after losing cold energy, and the liquefied natural gas enters the LNG storage tank through the throttling valve to be temporarily stored and then can be injected into an LNG pipeline or directly sold. The process is simple, an expansion machine is not needed, the equipment investment cost is low, the size is small, and vehicle-mounted movement can be achieved; remote dynamic control can be realized, and workers do not need to stay beside the device for a long time; the pressure range of the recovered and vented natural gas comprises but is not limited to 0.2-4 MPa, the liquefaction efficiency is stable, and the minimum liquefaction rate is 98.2%; the device is suitable for gas compression stations and gas transmission stations which are small in emptying amount, large in gas pressure fluctuation range, scattered in gas source distribution, high in methane content and free of operations such as light hydrocarbon removal.

Description

Technical Field

[0001] The invention relates to the technical field of petrochemical environmental protection, and in particular to a vehicle-mounted mobile device which can be remotely controlled and can utilize liquid nitrogen cold energy to recover and vent natural gas, and is suitable for gas transmission stations and gas compression stations. Background Art

[0002] The main component of natural gas is methane. Studies have shown that the greenhouse effect of methane is 25 times that of carbon dioxide, and the warming effect of methane will increase dramatically over time. Within 20 years, the warming effect of methane will be 84 times that of carbon dioxide. Gas transmission stations will release some natural gas during overhaul or maintenance of normal operation. The release of natural gas will not only cause great economic losses to the station and processing units, but also damage the environment, which does not meet the requirements of national safety and environmental protection.

[0003] At present, the utilization technologies of natural gas venting and recovery at home and abroad mainly include the following aspects: liquefied natural gas (LNG), natural gas power generation (GTW), adsorbed natural gas (ANG), compressed natural gas (CNG), natural gas hydrate (NGH) and lithium bromide direct-fired engine. The application of liquefied natural gas technology to recycle vented natural gas has advantages and disadvantages. The advantage is that the required equipment occupies a relatively small area, the transportation and transportation of natural gas are relatively simple, and the vented natural gas can be directly liquefied into LNG and injected into the LNG pipeline or sold directly; the disadvantage is that the equipment and process required for this technology are relatively complex, and the various investment costs of the equipment are relatively high.

[0004] The existing equipment for recovering vented natural gas using liquefied natural gas technology occupies a large area, which is not conducive to movement within the station; the equipment investment is too large, the process is complicated, the equipment investment recovery period is long, and the equipment later maintenance costs are high; the liquefaction rate is unstable and is greatly affected by the pressure of the recovered natural gas. Because the existing technology has inconveniences and defects in practical applications, it is necessary to improve it. Liquid nitrogen is used as a refrigerant to make full use of the cold energy of liquid nitrogen to liquefy the recovered vented air. Since liquid nitrogen is cheap and its source is very wide, the temperature of liquid nitrogen is -196℃ at normal pressure, which is much lower than the temperature of LNG, which can simplify the liquefaction process and increase profits. Summary of the invention

[0005] In order to solve the problems of low mobility, unstable liquefaction efficiency, and excessive equipment investment in existing vented natural gas recovery devices, the present invention provides a vehicle-mounted mobile device that can be remotely controlled and utilizes liquid nitrogen cold energy to recover vented natural gas.

[0006] A remotely controlled vehicle-mounted mobile device for recovering vented natural gas using liquid nitrogen cold energy comprises: a liquid nitrogen storage tank, a centrifugal pump, a throttle valve, a plate-fin heat exchanger, a temperature controller, and an LNG storage tank; low-temperature liquid nitrogen is used to liquefy the vented natural gas, and the device can be transported on a vehicle and dynamically controlled; the liquid nitrogen stored in the liquid nitrogen storage tank is pressurized by a pump and enters a heat exchanger to exchange heat with the recovered natural gas, and the liquid nitrogen is discharged into the air after losing its cold energy, and the liquefied natural gas passes through a throttle valve and enters an LNG storage tank for temporary storage, and can then be injected into an LNG pipeline or sold directly.

[0007] The liquefaction treatment is achieved by using a plate-fin heat exchanger; a centrifugal pump is used to allow liquid nitrogen to enter the cold medium channel of the plate-fin heat exchanger, and the hot medium channel of the plate-fin heat exchanger is introduced into the vented natural gas; the flow rate of liquid nitrogen is controlled by a throttle valve so that the temperature of the natural gas after the liquefaction treatment is not lower than -152°C.

[0008] In the vented natural gas recovery device, the liquefied natural gas passes through the outlet of the cold medium channel of the plate-fin heat exchanger and passes through the throttle valve to enter the LNG storage tank for temporary storage; after the liquid nitrogen loses its cold energy, it is discharged into the atmosphere through the outlet of the hot medium channel of the plate-fin heat exchanger.

[0009] The dynamic control is implemented by using a temperature controller; the dynamic control sets the range of the natural gas outlet temperature through the temperature controller, thereby adjusting the opening of the throttle valve to adjust the liquid nitrogen flow rate, so that the natural gas outlet temperature is controlled within the range of -152°C to -175°C.

[0010] The equipment of the present invention is simple, and the expansion machine is omitted, which saves costs. The plate-fin heat exchanger is used to reduce the floor space, improve the liquefaction efficiency, and make full use of the cold energy of liquid nitrogen to liquefy the vented natural gas. It is convenient for vehicle-mounted movement and can be dynamically controlled. After the liquid nitrogen loses its cold energy, it is discharged into the air. The liquefied natural gas can be injected into the LNG pipeline or sold directly. When the pressure of the vented natural gas is between 1MPa and 4MPa, the liquefaction rate is 100%, and when it is between 0.2MPa and 1MPa, the minimum liquefaction rate is 98.23%. It is suitable for compressor stations and gas transmission stations with small venting volume, large air pressure fluctuation range, scattered gas source distribution, high methane content, and no need to remove light hydrocarbons. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a schematic diagram of the process flow of recovering vented natural gas using liquid nitrogen cold energy.

[0012] In the figure: liquid nitrogen storage tank 1, centrifugal pump 2, throttle valve 3, plate-fin heat exchanger 4, throttle valve 5, temperature controller 6, LNG storage tank 7. DETAILED DESCRIPTION

[0013] The present invention will be further described in detail below with reference to the accompanying drawings and in combination with embodiments. The following embodiments are intended to explain the present invention but the present invention is not limited to the following embodiments.

[0014] See also Figure 1 The embodiment of the present invention provides a vehicle-mounted mobile device that can be remotely controlled to utilize liquid nitrogen cold energy to recover and vent natural gas. The small device includes: a liquid nitrogen storage tank 1, a centrifugal pump 2, a throttle valve 3, a plate-fin heat exchanger 4, a throttle valve 5, a temperature controller 6, and an LNG storage tank 7. The liquid nitrogen stored in the liquid nitrogen storage tank 1 is pressurized by the centrifugal pump 2 and enters the heat exchanger 4 to exchange heat with the recovered natural gas. After the liquid nitrogen loses its cold energy, it is discharged into the air. The liquefied natural gas passes through the throttle valve 5 and enters the LNG storage tank 7 for temporary storage.

[0015] In this embodiment, the liquefaction treatment is achieved by using a plate-fin heat exchanger 4; a centrifugal pump 2 is used to allow liquid nitrogen to enter the cold medium channel of the plate-fin heat exchanger 4, and the hot medium channel of the plate-fin heat exchanger 4 is passed through the vented natural gas; the flow rate of liquid nitrogen is controlled by a throttle valve 3 so that the temperature of the natural gas after the liquefaction treatment is not lower than -152°C.

[0016] In this embodiment, in the venting natural gas recovery device, the liquefied natural gas passes through the cold medium channel outlet of the plate-fin heat exchanger 4 and the throttle valve 5 to enter the LNG storage tank 7 for temporary storage; the liquid nitrogen loses its cold energy and is discharged into the atmosphere through the hot medium channel outlet of the plate-fin heat exchanger 4.

[0017] In this embodiment, the dynamic control is implemented by a temperature controller 6; the dynamic control sets the range of the natural gas outlet temperature through the temperature controller 6, thereby adjusting the opening of the throttle valve 3 to adjust the liquid nitrogen flow rate, so that the natural gas outlet temperature is controlled within the range of -152°C to -175°C.

[0018] The technical solution of this embodiment is used to recover and process the vented natural gas at a station on the Shaanxi-Beijing line, wherein the components and molar fractions of the vented natural gas before recovery and processing are 97% methane and 3% ethane.

[0019] When the vented natural gas at a station on the Shaanxi-Beijing line is recovered and processed, the vented natural gas is first collected and then sent to a plate-fin heat exchanger for liquefaction. The temperature of the natural gas sent to the plate-fin heat exchanger is 30°C, the natural gas pressure is 0.2MPa~4MPa, and the temperature of the liquefied natural gas is -154°C~-171°C; the liquefaction rate of the treated natural gas is as low as 98.23%, as shown in Table 1; it can be seen from the table that the liquefaction rate of the vented natural gas recovered by this small device is very high.

[0020] Table 1

[0021] Case Natural gas inlet pressure (kPa) Liquefaction rate Heat exchanger minimum temperature difference (℃) Natural gas outlet temperature (℃) Case 1 200 0.9823 11.1067 -161.3609 Case 2 400 0.9867 14.5251 -154.3047 Case 3 600 0.9911 17.1933 -155.0308 Case 4 800 0.9956 19.4391 -155.7558 Case 5 1000 1.0000 21.4936 -156.4828 Case 6 1200 1.0000 23.4461 -157.2127 Case 7 1400 1.0000 23.8974 -159.0025 Case 8 1600 1.0000 27.1487 -158.6818 Case 9 1800 1.0000 27.0866 -160.5414 Case 10 2000 1.0000 28.7090 -160.1630 Case 11 2200 1.0000 26.7613 -162.1108 Case 12 2400 1.0000 27.2165 -161.6556 Case 13 2600 1.0000 25.1567 -163.7153 Case 14 2800 1.0000 23.2342 -165.6378 Case 15 3000 1.0000 24.9588 -163.9132 Case 16 3200 1.0000 22.6739 -166.1981 Case 17 3400 1.0000 20.5122 -168.3599 Case 18 3600 1.0000 22.6823 -166.1897 Case 19 3800 1.0000 20.0411 -168.8310 Case 20 4000 1.0000 17.5190 -171.3530

[0022] The small-scale device for recovering vented natural gas provided in the embodiment of the present invention adopts liquid nitrogen as a cold source to liquefy the vented natural gas. The process is simple, the device is easy to move on a vehicle, the device can be remotely dynamically controlled, and the operation management and maintenance are simple. The device can realize efficient recovery and utilization of the vented natural gas, and economically and effectively solve the problems of environmental pollution and waste of resources caused by vented natural gas. The device is suitable for compressor stations and gas transmission stations with small venting volume, large pressure fluctuation range, scattered gas source distribution, high methane content, and no need to remove light hydrocarbons.

[0023] The specific embodiments described above have detailed descriptions of the objectives, technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A mobile vehicle-mounted device that can be remotely controlled and utilizes liquid nitrogen cold energy to recover vented natural gas, characterized in that: include: Liquid nitrogen storage tank (1), centrifugal pump (2), throttle valve (3), plate-fin heat exchanger (4), throttle valve (5), temperature controller (6), LNG storage tank (7); low-temperature liquid nitrogen is used to liquefy the vented natural gas, which can be transported on a vehicle and can be remotely dynamically controlled; the liquid nitrogen stored in the liquid nitrogen storage tank is pressurized by a pump and enters the heat exchanger to exchange heat with the recovered natural gas. The liquid nitrogen loses its cold energy and is discharged into the air. The liquefied natural gas passes through the throttle valve and enters the LNG storage tank for temporary storage, and can then be injected into the LNG pipeline or sold directly; It is suitable for compressor stations and gas transmission stations with small venting volume, large pressure fluctuation range, scattered gas source distribution, high methane content, and no need to remove light hydrocarbons.

2. The vented natural gas recovery device according to claim 1, characterized in that: The liquefaction treatment is achieved by using a plate-fin heat exchanger (4) without an expander; a centrifugal pump (2) is used to allow liquid nitrogen to enter the cold medium channel of the plate-fin heat exchanger (4), and the hot medium channel of the plate-fin heat exchanger (4) is introduced into the vented natural gas; the flow rate of the liquid nitrogen is controlled by a throttle valve (3) so that the temperature of the natural gas after the liquefaction treatment is not lower than -152°C.

3. The vented natural gas recovery device according to claim 1, characterized in that: The liquefied natural gas passes through the outlet of the cold medium channel of the plate-fin heat exchanger (4) and passes through the throttle valve (5) to enter the LNG storage tank (7) for temporary storage; and the liquid nitrogen loses its cold energy and is discharged into the atmosphere through the outlet of the hot medium channel of the plate-fin heat exchanger (4).

4. The vented natural gas recovery device according to claim 1, characterized in that: The dynamic control is implemented by using a temperature controller (6); the dynamic control sets the range of the natural gas outlet temperature through the temperature controller (6), thereby adjusting the opening of the throttle valve (3) to adjust the liquid nitrogen flow rate, so that the natural gas outlet temperature is controlled within the range of -152°C to -175°C.

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