Natural gas dealkylation system for offshore oil and gas field

Abstract

The invention relates to a natural gas dealkylation system for an offshore oil and gas field. The gas-liquid separation module receives an oil-gas mixture, and separated natural gas enters the low-temperature dealkylation module to reduce the hydrocarbon dew point of the natural gas; the low-temperature dealkylation module condenses heavy hydrocarbon components in the natural gas by utilizing the throttling, pressure reducing and temperature reducing principle of a J-T valve, heavy hydrocarbon is separated through a low-temperature separator, and light components and the natural gas are subjected to heat exchange through a heat exchanger and then enter the pressurization and output module; qualified natural gas in the pressurization output module is pressurized through two dry gas compressors and then is output; pressure is monitored through a pressure sensor in front of a J-T valve, the opening degree of the J-T valve is adjusted according to the flow, the temperature of the low-temperature separator is monitored through a temperature sensor, the opening degree of a temperature control valve is adjusted through a temperature control instrument, and then the temperature of the low-temperature separator is adjusted. When a single dry gas compressor is shut down in normal production of an offshore oil and gas platform, the opening degree of the J-T valve can be accurately adjusted according to the flow change of natural gas, and production shut-off is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of low-temperature hydrocarbon removal from natural gas, and more specifically, to a natural gas hydrocarbon removal system for offshore oil and gas fields. Background Art

[0002] During the normal production of an offshore platform, after natural gas is produced from the formation, it undergoes preliminary dehydration and hydrocarbon removal through the production treatment device on the offshore platform, and is pressurized by a dry gas compressor to be transported through the subsea natural gas pipeline. The J-T valve and the low-temperature separator are important equipment in the oil and gas treatment process. After natural gas is produced from the formation, it undergoes throttling and temperature reduction through the J-T valve, and the separation of natural gas and heavy hydrocarbons is achieved by gravity in the low-temperature separator. Currently, for the natural gas hydrocarbon removal system in offshore oil and gas fields: since the J-T valve is controlled by the upstream pressure, when a single dry gas compressor shuts down, the opening of the J-T valve will maintain its original opening. According to this control method, it will cause overpressure in the low-temperature separator. ① This will cause the low-temperature separator to trigger pressure protection and cannot meet the requirement of not triggering production shutdown; ② Since the pressure difference before and after the J-T valve becomes smaller, the hydrocarbon removal effect becomes worse, and it cannot meet the requirement that the quality of the exported natural gas does not exceed the standard. Summary of the Invention

[0003] The purpose of the present invention is to overcome the deficiency that production shutdown is likely to occur when a single dry gas compressor shuts down in the prior art, and to provide a natural gas hydrocarbon removal system for offshore oil and gas fields, which can effectively avoid the occurrence of production shutdown.

[0004] To solve the above technical problems, the technical solution adopted by the present invention is:

[0005] Provide a natural gas hydrocarbon removal system for offshore oil and gas fields, including a gas-liquid separation module, a low-temperature hydrocarbon removal module, and a pressurization and export module; the gas-liquid separation module receives the oil and gas mixture from underwater, and the separated natural gas enters the low-temperature hydrocarbon removal module to reduce the hydrocarbon dew point of the natural gas; the low-temperature hydrocarbon removal module uses the throttling and pressure reduction and temperature reduction principle of the J-T valve to condense the heavy hydrocarbon components in the natural gas, and separates the heavy hydrocarbons through a low-temperature separator. The light components and the natural gas enter the pressurization and export module after heat exchange through a heat exchanger; in the pressurization and export module, the qualified natural gas is pressurized by two dry gas compressors and then output; among them, the pressure is monitored by a pressure sensor before the J-T valve, the opening of the J-T valve is adjusted according to the flow rate, the temperature of the low-temperature separator is monitored by a temperature sensor, and the opening of the temperature control valve is adjusted according to the temperature monitored by the temperature sensor, so as to adjust the temperature of the low-temperature separator.

[0006] A natural gas dehydrocarbonization system for offshore oil and gas fields of the present invention can, when a single dry gas compressor shuts down during normal production of an offshore oil and gas platform, accurately adjust the opening of the J-T valve according to the change in the flow rate of natural gas, avoid the need to upgrade from unit shutdown to production shutdown, and thus avoid the need for unqualified hydrocarbon dew point in the exported gas.

[0007] Furthermore, when a single dry gas compressor suddenly shuts down, the opening of the J-T valve is adjusted according to the magnitude of the natural gas flow rate. During the operation of two dry gas compressors in an offshore oil and gas field, in the case of a sudden shutdown of a single compressor, the opening of the J-T valve of the dehydrocarbonization system is calculated and adjusted through the change in the flow rate of the exported flowmeter to meet the control mode of the exported flow rate of a single dry gas compressor.

[0008] Furthermore, the natural gas flow rate and the opening of the J-T valve are calculated according to the following formula (1):

[0009]

[0010] In the formula, represents the mass flow rate; ΔP represents the pressure difference before and after the J-T valve, op represents the opening of the J-T valve; Cvmax represents the valve flow coefficient Cv value when the J-T valve is fully open; ρ i represents the fluid density at the inlet of the J-T valve. In the present invention, the logical control mode of the J-T valve of the dehydrocarbonization system establishes this logical control model from the relationship between the J-T valve flux and the opening, and adjusts the opening of the J-T valve according to the magnitude of the flow rate. Based on the above formula (1), the influence of the magnitude of the natural gas flow rate on the opening of the J-T valve can be accurately calculated.

[0011] Furthermore, the gas-liquid separation module includes a slug catcher, a first pressure sensor connected to the slug catcher, and a vent PV valve. The oil-water mixture is input into the slug catcher to separate natural gas. The pressure of the slug catcher is monitored by the pressure sensor, and the opening and closing of the vent PV valve are controlled by the pressure control instrument to vent and relieve the overpressure part of the slug catcher.

[0012] Furthermore, the low-temperature dehydrocarbonization module includes a heat exchanger, a low-temperature separator, a temperature sensor and a second pressure sensor connected to the low-temperature separator, and a pre-valve pressure sensor; part of the natural gas A output from the gas-liquid separation module is directly input into the low-temperature separator, and another part of the natural gas B is input into the heat exchanger. After heat exchange in the heat exchanger, it converges with natural gas A and is input into the low-temperature separator. The natural gas processed by the low-temperature separator is input into the heat exchanger again, and after heat exchange in the heat exchanger, it is output to the booster and export module; among them, the J-T valve and the pre-valve pressure sensor are both arranged on the pipeline where natural gas A and natural gas B converge, and the temperature control valve is arranged on the pipeline for transporting natural gas A.

[0013] Furthermore, the pressurized export module includes two dry gas compressors, and each dry gas compressor is equipped with an anti-surge system.

[0014] Furthermore, the pipeline for inputting into the pressurized export module is communicated with the output pipeline of the pressurized export module through an auxiliary gas pipeline, and a reflux PV valve is arranged on the auxiliary gas pipeline. The opening degree of the reflux PV valve is controlled by a pressure control instrument, so as to realize the regulation of the inlet pressure of the dry gas compressor unit.

[0015] Furthermore, when one dry gas compressor suddenly shuts down, calculate the opening degree of the J-T valve according to formula (1), and adjust the opening degree of the J-T valve through a pressure control instrument, so that the pressure of the low-temperature separator reaches the peak value and then continuously drops to a safe value.

[0016] Furthermore, when both dry gas compressors are operating normally, the opening degree of the J-T valve remains unchanged.

[0017] The present invention also provides a control method for the J-T valve of a natural gas dehydrocarbonization system in an offshore oil and gas field. Using the above-mentioned natural gas dehydrocarbonization system in an offshore oil and gas field, calculate the opening degree of the J-T valve according to formula (1), and adjust the opening degree of the J-T valve through a pressure control instrument, so that the pressure of the low-temperature separator reaches the peak value and then continuously drops to a safe value.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] The natural gas dehydrocarbonization system in an offshore oil and gas field of the present invention can meet the requirement that when a single dry gas compressor shuts down during the normal production of an offshore oil and gas platform. This dehydrocarbonization system can accurately adjust the opening degree of the J-T valve according to the change of the natural gas flow rate, avoid the situation that the unit shutdown is upgraded to production shutdown, and thus avoid the situation that the dew point of the exported hydrocarbon is unqualified. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic structural diagram of a natural gas dehydrocarbonization system in an offshore oil and gas field;

[0021] In the drawings: 1, slug catcher; 2, heat exchanger; 3, low-temperature separator; 4, dry gas compressor; 5, J-T valve; 6, pre-valve pressure sensor; 7, temperature sensor; 8, pressure controller; 9, temperature control instrument; 10, temperature control valve; 11, first pressure sensor; 12, venting PV valve; 13, second pressure sensor; 14, reflux PV valve; 15, anti-surge valve. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] The present invention will be further described below in conjunction with specific embodiments. Among them, the attached drawings are only for illustrative purposes, showing only schematic diagrams rather than physical diagrams, and should not be construed as a limitation on the present invention; in order to better illustrate the embodiments of the present invention, some components in the attached drawings will be omitted, enlarged or reduced, and do not represent the size of the actual product; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the attached drawings may be omitted.

[0023] In the attached drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", etc. indicating the orientation or positional relationship, they are based on the orientation or positional relationship shown in the attached drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the attached drawings are only for illustrative purposes and should not be construed as a limitation on the present invention. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0024] Embodiment 1

[0025] This embodiment is the first embodiment of a natural gas dehydrocarbon system for an offshore oil and gas field, including a gas-liquid separation module, a cryogenic dehydrocarbon module, and a pressurization and export module; the gas-liquid separation module receives the oil and gas mixture from underwater, and the separated natural gas enters the cryogenic dehydrocarbon module to reduce the hydrocarbon dew point of the natural gas; the cryogenic dehydrocarbon module uses the throttling pressure reduction and temperature reduction principle of the J-T valve 5 to condense the heavy hydrocarbon components in the natural gas, and separates the heavy hydrocarbons through the cryogenic separator 3. The light components and the natural gas enter the pressurization and export module after heat exchange through the heat exchanger 2; the qualified natural gas in the pressurization and export module is pressurized by two dry gas compressors 4 and then output; among them, the pressure is monitored by the pressure sensor 6 in front of the J-T valve 5, and the opening of the J-T valve 5 is adjusted according to the flow rate and through the pressure control instrument 8. The temperature of the cryogenic separator 3 is monitored by the temperature sensor 7, and the opening of the temperature control valve 10 is adjusted through the temperature control instrument 9, so as to adjust the temperature of the cryogenic separator 3.

[0026] In the prior art, the opening of the J-T valve 5 on the offshore platform is controlled by the pressure before the valve, and the pressure of the low-temperature separator 3 is controlled by the reflux valve of the dry gas compressor 4 unit. During normal production, the platform starts two dry gas compressors 4 to pressurize and export the dehydrated and dehydrocarbonated natural gas. However, during the oil and gas treatment process, if one of the dry gas compressors 4 shuts down, the pressure before the J-T valve 5 will remain unchanged, and the opening of the J-T valve 5 will remain unchanged. However, since one of the dry gas compressors 4 has shut down, the remaining one dry gas compressor 4 will bear natural gas with twice its own flow rate, which will quickly cause the pressure of the low-temperature separator 3 to be extremely high (PAHH), resulting in the shutdown of production on the offshore platform and causing losses in natural gas production. If the J-T valve 5 can respond quickly when one of the dry gas compressors 4 shuts down and timely reduce the flow rate of natural gas reaching the low-temperature separator 3, so that the pressure of the low-temperature separator 3 does not quickly rise to the extremely high pressure (PAHH) set point, it can effectively avoid the shutdown of production on the offshore platform and reduce losses in natural gas production. At the same time, since the natural gas produced by the offshore platform will be directly supplied to the downstream power plant for power generation, the quality requirements for the exported natural gas are very strict. When one of the dry gas compressors 4 shuts down, due to the obvious fluctuation of the J-T valve 5, the temperature of the low-temperature separator 3 will fluctuate violently, resulting in unqualified dew points of the exported hydrocarbons. When the J-T valve 5 undergoes a rapid action process, it will also cause a sharp fluctuation in the pressure upstream of the J-T valve 5, which may cause a large amount of venting of the upstream equipment, bringing risks to the safe production of the platform. At present, there are mainly two types of control logics for the J-T valve 5 in the academic community. One is to control the opening of the J-T valve 5 through the pressure before the valve, and the pressure of the low-temperature separator 3 is controlled by the reflux valve of the dry gas compressor 4 unit. The second is to control the opening of the J-T valve 5 by the pressure difference before and after the J-T valve 5, and the pressure of the low-temperature separator 3 is controlled by the reflux valve of the dry gas compressor 4 unit. Under the second control logic, when one of the dry gas compressors 4 shuts down, the pressure of the low-temperature separator 3 will rise. Therefore, in order to ensure that the pressure difference before and after the J-T valve 5 remains unchanged, the J-T valve 5 will gradually close, causing the upstream pressure to build up to maintain the pressure difference. However, this control method cannot effectively give the valve closing time during emergency shutdown, and may not be able to respond quickly in case of emergencies, still causing the pressure of the low-temperature separator 3 to be extremely high (PAHH) to be triggered.

[0027] In this embodiment, when one of the dry gas compressors 4 suddenly shuts down, the opening of the J-T valve 5 is adjusted according to the magnitude of the natural gas flow rate. During the operation of two dry gas compressors 4 in the offshore oil and gas field, in the case of sudden shutdown of one compressor, the opening of the J-T valve 5 of the dehydrocarbonation system is calculated and adjusted through the change in the flow rate of the export flowmeter to meet the control mode of the export flow rate of one dry gas compressor 4. Among them, the natural gas flow rate and the opening of the J-T valve 5 are calculated according to the following formula (1):

[0028]

[0029] In the formula, represents the mass flow rate; ΔP represents the pressure difference before and after the J-T valve, op represents the opening degree of the J-T valve; Cvmax represents the Cv value of the valve flow coefficient when the J-T valve is fully open; ρ i represents the density of the fluid at the inlet of the J-T valve.

[0030] Based on this formula, the influence of the size of the natural gas flow rate on the opening degree of the 5th J-T valve can be accurately calculated. The purpose is to calculate and adjust the opening degree of the J-T valve 5 in the dehydrocarbonization system to meet the control mode of the external output flow rate of a single dry gas compressor 4 during the operation of two dry gas compressors 4 in an offshore oil and gas field in the event of a sudden shutdown of a single compressor.

[0031] Under normal operating conditions, the control is still carried out according to the pressure before the valve. In this mode, the opening degree of the J-T valve 5 remains unchanged.

[0032] When a single dry gas compressor 4 suddenly shuts down, calculate the opening degree of the J-T valve 5 according to formula (1), and adjust the opening degree of the J-T valve 5 through the pressure control instrument 8. After the pressure of the low-temperature separator 3 reaches the peak value, it continues to decline and does not trigger a high-high pressure. Eventually, the pressure of the low-temperature separator 3 will return to the set value, which can effectively avoid the shutdown of platform production and the normal external output of dry gas.

[0033] A natural gas dehydrocarbonization system for an offshore oil and gas field provided in this embodiment can meet the situation when a single dry gas compressor 4 shuts down during the normal production of an offshore oil and gas platform. This dehydrocarbonization system can accurately adjust the opening degree of the J-T valve 5 according to the change of the natural gas flow rate, avoiding the situation of upgrading from unit shutdown to production shutdown, and thus avoiding the situation of unqualified dew point of the exported hydrocarbons.

[0034] Embodiment 2

[0035] This embodiment is the second embodiment of a natural gas dehydrocarbonization system for an offshore oil and gas field. This embodiment is similar to Embodiment 1. In this embodiment, the gas-liquid separation module includes a slug catcher 1, a first pressure sensor 11 and a vent PV valve 12 connected to the slug catcher 1. The oil-water mixture is input into the slug catcher 1 to separate natural gas. The pressure of the slug catcher 1 is monitored by the pressure sensor, and the opening and closing of the vent PV valve 12 is controlled by the pressure control instrument 8 to vent and relieve the overpressure part of the slug catcher 1.

[0036] In this embodiment, the low-temperature hydrocarbon removal module includes a heat exchanger 2, a low-temperature separator 3, a temperature sensor 7 and a second pressure sensor 13 connected to the low-temperature separator 3, and a pre-valve pressure sensor 6. A part of the natural gas output from the gas-liquid separation module, namely natural gas A, is directly input into the low-temperature separator 3, and another part of the natural gas B is input into the heat exchanger 2. After heat exchange in the heat exchanger 2, it converges with natural gas A and then is input into the low-temperature separator 3. The natural gas processed by the low-temperature separator 3 is input into the heat exchanger 2 again, and after heat exchange in the heat exchanger 2, it is output to the boosting and external transportation module. Among them, the J-T valve 5 and the pre-valve pressure sensor 6 are both arranged on the pipeline where natural gas A and natural gas B converge, and the temperature control valve 10 is arranged on the pipeline for transporting natural gas A.

[0037] In this embodiment, the boosting and external transportation module includes two dry gas compressors 4. Each dry gas compressor 4 is equipped with an anti-surge system, and each anti-surge system is configured with an anti-surge valve 15. The pipeline for inputting the boosting and external transportation module is connected to the output pipeline of the boosting and external transportation module through an auxiliary gas pipeline, and a reflux PV valve 14 is arranged on the auxiliary gas pipeline. The opening of the reflux PV valve 14 is controlled by a pressure controller 8 meter, so as to realize the regulation of the inlet pressure of the dry gas compressor 4 unit.

[0038] Embodiment III

[0039] This embodiment is an embodiment of a control method for the J-T valve 5 of a natural gas hydrocarbon removal system in an offshore oil and gas field. This embodiment uses the natural gas hydrocarbon removal system of Embodiment I or Embodiment II, calculates the opening of the J-T valve 5 according to formula (1), and adjusts the opening of the J-T valve 5 through the pressure controller 8 meter, so that the pressure of the low-temperature separator 3 reaches the peak value and then continuously drops to a safe value.

[0040] When a single dry gas compressor 4 shuts down and the remaining one dry gas compressor 4 undertakes twice the flow rate, the opening control mode of the J-T valve 5 adopts the method of this embodiment and is regulated by the external transportation flow rate. The J-T valve 5 is adjusted to the opening calculated by formula (1). After the pressure of the low-temperature separator 3 reaches the peak value, it continuously drops, and the pressure of the low-temperature separator 3 returns to the set value, thus effectively avoiding the shutdown of system production and enabling the normal external transportation of natural gas.

[0041] The control method for the J-T valve 5 of the natural gas hydrocarbon removal system in the offshore oil and gas field provided in this embodiment can meet the situation when a single dry gas compressor 4 shuts down during the normal production of an offshore oil and gas platform. This hydrocarbon removal system can accurately adjust the opening of the J-T valve 5 according to the change of natural gas flow rate, avoid the situation of upgrading from unit shutdown to production shutdown, and thus avoid the situation of unqualified external transportation hydrocarbon dew point.

[0042] In the specific content of the above specific embodiments, the technical features can be combined arbitrarily without contradiction. For the sake of brevity of description, not all possible combinations of the above technical features are described. However, as long as the combinations of these technical features do not exist in contradiction, they should all be considered as within the scope described in this specification.

[0043] Obviously, the above embodiments of the present invention are merely examples given to clearly illustrate the present invention, rather than limitations on the embodiments of the present invention. For those of ordinary skill in the art, other different forms of changes or variations can be made on the basis of the above description. It is not necessary and impossible to enumerate all the embodiments here. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A natural gas dehydrocarbonization system for offshore oil and gas fields, characterized in that, it includes a gas-liquid separation module, a cryogenic dehydrocarbonization module, and a pressurization and export module; the gas-liquid separation module receives the oil and gas mixture from underwater, and the separated natural gas enters the cryogenic dehydrocarbonization module to reduce the hydrocarbon dew point of the natural gas; the cryogenic dehydrocarbonization module uses the throttling pressure reduction and temperature reduction principle of the J-T valve to condense the heavy hydrocarbon components in the natural gas, and separates the heavy hydrocarbons through a cryogenic separator. The light components and the natural gas enter the pressurization and export module after heat exchange through a heat exchanger; the qualified natural gas in the pressurization and export module is pressurized by two dry gas compressors and then output; among them, the pressure is monitored by a pressure sensor before the J-T valve, the opening of the J-T valve is adjusted according to the flow rate, the temperature of the cryogenic separator is monitored by a temperature sensor, and the opening of the temperature control valve is adjusted according to the temperature monitored by the temperature sensor, so as to adjust the temperature of the cryogenic separator.

2. The natural gas dehydrocarbonization system for offshore oil and gas fields according to claim 1, characterized in that, when a single dry gas compressor suddenly stops, the opening of the J-T valve is adjusted according to the size of the natural gas flow rate.

3. The natural gas dehydrocarbonization system for offshore oil and gas fields according to claim 2, characterized in that, the natural gas flow rate and the opening of the J-T valve are calculated according to the following formula (1): In the formula, represents the mass flow rate; ΔP represents the pressure difference before and after the J-T valve, and op represents the opening degree of the J-T valve; Cvmax represents the Cv value of the valve flow coefficient when the J-T valve is fully open; ρ i represents the fluid density at the inlet of the J-T valve.

4. The natural gas dehydrocarbonization system for offshore oil and gas fields according to claim 3, characterized in that, the gas-liquid separation module includes a slug catcher, and a first pressure sensor and a vent PV valve connected to the slug catcher. The oil-water mixture is input to the slug catcher to separate the natural gas. The pressure of the slug catcher is monitored by the pressure sensor, and the opening and closing of the vent PV valve are controlled by a pressure control instrument to realize the venting and pressure relief of the overpressure part of the slug catcher.

5. The natural gas dehydrocarbonization system for offshore oil and gas fields according to claim 3, characterized in that, the cryogenic dehydrocarbonization module includes a heat exchanger, a cryogenic separator, a temperature sensor and a second pressure sensor connected to the cryogenic separator, and a valve front pressure sensor; the natural gas output by the gas-liquid separation module, part of the natural gas A is directly input to the cryogenic separator, and another part of the natural gas B is input to the heat exchanger. After heat exchange through the heat exchanger, it converges with the natural gas A and is input to the cryogenic separator. The natural gas processed by the cryogenic separator is input to the heat exchanger again, and after heat exchange through the heat exchanger, it is output to the pressurization and export module; among them, the J-T valve and the valve front pressure sensor are both arranged on the pipeline where the natural gas A and the natural gas B converge, and the temperature control valve is arranged on the pipeline for transporting the natural gas A.

6. The natural gas dehydrocarbonization system for offshore oil and gas fields according to claim 3, characterized in that, the pressurization and export module includes two dry gas compressors, and each dry gas compressor is equipped with an anti-surge system.

7. The natural gas dehydrocarbonization system for offshore oil and gas fields according to claim 6, characterized in that, the pipeline for inputting the pressurization and export module is communicated with the output pipeline of the pressurization and export module through an auxiliary gas pipeline, and a reflux PV valve is arranged on the auxiliary gas pipeline, and the opening of the reflux PV valve is controlled by a pressure control instrument, so as to realize the adjustment of the inlet pressure of the dry gas compressor unit.

8. The natural gas dehydrocarbonization system for offshore oil and gas fields according to any one of claims 3 to 7, characterized in that, when a dry gas compressor suddenly shuts down, the opening of the J-T valve is calculated according to formula (1), and the opening of the J-T valve is adjusted through a pressure control instrument so that the pressure of the low-temperature separator continuously drops to a safe value after reaching the peak value.

9. The natural gas dehydrocarbonization system for offshore oil and gas fields according to claim 8, characterized in that, when both dry gas compressors are operating normally, the opening of the J-T valve remains unchanged.

10. A control method for the J-T valve of a natural gas dehydrocarbonization system for offshore oil and gas fields, characterized in that, using the natural gas dehydrocarbonization system for offshore oil and gas fields according to any one of claims 3 to 9, the opening of the J-T valve is calculated according to formula (1), and the opening of the J-T valve is adjusted through a pressure control instrument so that the pressure of the low-temperature separator continuously drops to a safe value after reaching the peak value.

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