Oil and gas processing method

Abstract

The present invention relates to the technical field of oil and gas recovery, and discloses an oil and gas processing method. An oil and gas processing method, the method comprising: (1) sequentially subjecting the oil and gas to primary condensation and secondary condensation; (2) absorbing the gaseous product obtained in step (1) using a low eutectic solvent; wherein the low eutectic solvent contains at least one pair of hydrogen bond acceptor-hydrogen bond donor, the hydrogen bond acceptor being selected from one or more of choline chloride, tetrabutylammonium bromide, tetraoctylammonium chloride, menthol and thymol, and the hydrogen bond donor being an organic acid; wherein the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:0.1 to 10. In this method, the oil and gas mixture first undergoes secondary self-cascade condensation to recover the components with higher boiling points in the oil and gas; after condensation, the mixture enters the absorption system. Since the low eutectic solvent is used as the absorbent, the solvent loss caused by the volatilization of the absorbent can be avoided, thereby achieving deep recovery of VOCs.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas recovery, and in particular to an oil and gas processing method. Background Art

[0002] The oil and gas industry involves complex production, transportation, sales, storage and other links, during which a large amount of VOCs emissions are generated. Oil and gas treatment methods include destruction and recovery methods. The destruction methods mainly include thermal incineration, catalytic combustion, biological methods, etc., which decompose VOCs molecules into small molecules of water and carbon dioxide. Although the destruction method can achieve a higher VOCs treatment rate, it will produce greenhouse gases. The recovery method is to recover VOCs in oil and gas through processes such as condensation, adsorption, absorption and membrane separation. Industrial oil and gas recovery equipment often adopts a combination of multiple processes, such as condensation-adsorption and absorption-adsorption combined processes.

[0003] During the condensation process, the components in the oil and gas are gradually liquefied and recovered according to the phase change temperature from high to low. The lower the phase change temperature, the higher the corresponding energy consumption. Oil and gas usually contain certain light hydrocarbon components (C2-C4). If you want to achieve efficient recovery of light hydrocarbons, you must have an extremely low condensation temperature, so the energy consumption is huge. In order to save energy in industry, the condensation process is usually used as an oil and gas pre-treatment process, using three-stage condensation, and the condensation temperature is set at 5°C, -30°C, and -70°C. After three stages of condensation, most VOCs can be recovered, but the VOCs content at the outlet of the condensation device is still difficult to meet the emission requirements, and a combined adsorption process is required to further recover the unliquefied VOCs.

[0004] Adsorption processes typically use activated carbon as an adsorbent. Activated carbon has a large specific surface area and rich pore structure, enabling deep recovery of VOCs. Industry typically utilizes adsorption as the final step in a combined oil and gas recovery process, employing two or more adsorption tanks for switching operations. However, the adsorption process has significant thermal effects, which, on the one hand, affect adsorption and desorption efficiency and reduce the lifespan of the activated carbon. On the other hand, the heat of adsorption causes the activated carbon to heat up, which can easily lead to safety accidents. Therefore, the development of new, safe and efficient oil and gas terminal treatment processes is of great significance to the sustainable development of oil and gas recovery technology.

[0005] The absorption process involves the initial recovery of oil and gas through absorbents. This process has the advantages of simple equipment and operation, and only requires one absorption tower, resulting in low investment costs. The absorbent used in the oil and gas recovery device is generally sourced from the site, such as gasoline or diesel. Based on solubility, most of the heavier components in the oil and gas are recovered. Given the high volatility of gasoline and diesel absorbents, the absorption temperature often needs to be lowered to improve absorption efficiency. Furthermore, the amount of absorbent used is high, and the equipment scale and floor space are large. The VOCs recovery efficiency of absorption devices using gasoline and diesel as absorbents is generally less than 90%, and the VOCs content per cubic meter of gas at the device outlet is still as high as tens or even hundreds of grams. Therefore, the absorption process can currently only be used as a front-end oil and gas recovery process.

[0006] If a new type of oil and gas-specific absorbent with low volatility and high VOCs absorption performance can be developed to solve the problems of low VOCs recovery efficiency and large absorbent usage caused by the high volatility of mineral oil absorbents, the absorption method is expected to replace the adsorption method and become a safer and more efficient oil and gas end-of-pipe treatment technology. Summary of the Invention

[0007] The purpose of the present invention is to overcome the problems of high energy consumption, safety hazards, volatilization of VOCs absorbents and low VOCs adsorption rate in conventional oil and gas recovery processes in the prior art, and to provide an oil and gas treatment method. Based on the use of a specific low eutectic solvent as an absorbent, the oil and gas mixture is first subjected to a two-stage auto-cascade condensation to recover the components with higher boiling points in the oil and gas. Since an extremely low condensation temperature is not required, energy consumption and equipment investment can be reduced; after condensation, the mixture enters the absorption system. Since a low eutectic solvent is used as the absorbent, solvent loss caused by absorbent volatilization can be avoided, deep recovery of VOCs can be achieved, and the safety of the device is improved.

[0008] In order to achieve the above object, the present invention provides an oil and gas processing method, which comprises the following steps:

[0009] (1) The oil and gas are subjected to primary condensation and secondary condensation in sequence;

[0010] (2) absorbing the gaseous product obtained in step (1) using a deep eutectic solvent;

[0011] The deep eutectic solvent contains at least one pair of hydrogen bond acceptor and hydrogen bond donor, the hydrogen bond acceptor is selected from one or more of choline chloride, tetrabutylammonium bromide, tetraoctylammonium chloride, menthol and thymol, and the hydrogen bond donor is an organic acid; wherein the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:0.1 to 10.

[0012] Preferably, the organic acid is selected from levulinic acid and / or C6-C18 fatty acids;

[0013] Preferably, the C6-C18 fatty acid is one or more selected from n-hexanoic acid, n-octanoic acid, n-decanoic acid, lauric acid, palmitoleic acid and oleic acid.

[0014] Preferably, the preparation method of the deep eutectic solvent comprises: the preparation method of the deep eutectic solvent comprises: mixing a hydrogen bond acceptor and a hydrogen bond donor and then cooling.

[0015] Preferably, the mixing conditions include: temperature of 30 to 100° C.; time of 30 to 90 minutes.

[0016] Preferably, when the deep eutectic solvent contains choline chloride-levulinic acid, the molar ratio of choline chloride to levulinic acid in the choline chloride-levulinic acid is 1:2-4.

[0017] Preferably, when the deep eutectic solvent contains tetrabutylammonium bromide-oleic acid, the molar ratio of tetrabutylammonium bromide to oleic acid in the tetrabutylammonium bromide-oleic acid is 1:3-5.

[0018] Preferably, when the deep eutectic solvent contains tetraoctylammonium chloride-oleic acid, the molar ratio of tetraoctylammonium chloride to oleic acid in the tetraoctylammonium chloride-oleic acid is 1:3-5.

[0019] Preferably, when the deep eutectic solvent contains menthol-lauric acid, the molar ratio of menthol to lauric acid in the menthol-lauric acid is 1:1-3.

[0020] Preferably, when the deep eutectic solvent contains menthol-oleic acid, the molar ratio of menthol to oleic acid in the menthol-oleic acid is 1:1-3.

[0021] Preferably, the conditions for the primary condensation in step (1) include: a temperature of 2 to 5°C; the conditions for the secondary condensation in step (1) include: a temperature of -30 to -40°C.

[0022] Preferably, the refrigerants used in the primary condensation and the secondary condensation in step (1) are independently selected from one or more of polyfluoroethane, difluorochloromethane and trifluoromethane.

[0023] Preferably, the polyfluoroethane is selected from one or more of pentafluoroethane, trifluoroethane and tetrafluoroethane.

[0024] Preferably, the absorption conditions in step (2) include: temperature of 0 to 30° C. and pressure of 0.1 to 1 MPa.

[0025] Preferably, in step (2), the gas-liquid ratio of the gas-phase product to the low eutectic solvent is 2-20.

[0026] Preferably, the method further comprises: desorbing the liquid phase product obtained after absorption in step (2).

[0027] Preferably, the desorption conditions include: temperature of 30-100° C. and pressure of 0-0.1 MPa.

[0028] Preferably, the method is implemented in an oil and gas processing system, characterized in that the oil and gas processing system comprises a primary evaporator, a secondary evaporator, an absorption tower and a flash tank connected in sequence;

[0029] The bottom of the flash tank is provided with a first liquid phase outlet, the upper portion of the absorption tower is provided with a first liquid phase inlet, and a three-stage condenser is provided between the first liquid phase outlet and the first liquid phase inlet.

[0030] Preferably, a first valve is provided between the first liquid phase outlet and the third-stage condenser.

[0031] Preferably, a second liquid phase outlet is provided at the bottom of the absorption tower, a second liquid phase inlet is provided in the middle of the flash tank, and a heat exchanger is provided between the second liquid phase outlet and the second liquid phase inlet.

[0032] Preferably, a second valve is provided between the second liquid phase outlet and the heat exchanger.

[0033] Preferably, the top of the primary evaporator is provided with an oil and gas inlet, and the oil and gas from the air inlet pipeline are pressurized by an oil and gas blower and then enter the primary evaporator through the oil and gas inlet.

[0034] Preferably, the primary evaporator includes a first shell and a first cavity arranged inside the first shell, wherein the first shell is used to accommodate oil and gas; the first cavity is filled with refrigerant for condensing the oil and gas.

[0035] Preferably, the bottom of the first shell has a first condensed oil outlet, and the first condensed oil outlet is connected to the oil collecting tank through an oil collecting pipeline.

[0036] Preferably, a third valve is provided on the oil collecting pipeline between the first condensed oil outlet and the oil collecting tank.

[0037] Preferably, the secondary evaporator includes a second shell and a second cavity arranged inside the second shell, wherein the second shell is used to accommodate oil and gas from the first shell; the second cavity is filled with refrigerant for condensing the oil and gas.

[0038] Preferably, the bottom of the second shell has a second condensed oil outlet, and the second condensed oil outlet is connected to the oil collecting tank through an oil collecting pipeline.

[0039] Preferably, a fourth valve is provided on the oil collecting pipeline between the second condensed oil outlet and the oil collecting tank.

[0040] Preferably, the oil and gas processing system also includes a secondary condenser; the secondary condenser includes a third shell and a third cavity arranged inside the third shell; the third cavity has a first refrigerant inlet, and the refrigerant from the first evaporator enters the secondary condenser from the first refrigerant inlet; the third shell has a second refrigerant inlet, and the refrigerant from the secondary evaporator enters the secondary condenser from the second refrigerant inlet.

[0041] Preferably, the oil and gas processing system further comprises a first compressor, a primary condenser, a first dryer and a first expansion valve connected in sequence, and the refrigerant from the first cavity and the third cavity is processed in sequence by the first compressor, the primary condenser, the first dryer and the first expansion valve before entering the refrigerant first inlet of the secondary condenser or the first cavity of the primary evaporator;

[0042] The refrigerant from the second cavity is processed in sequence by the second compressor and the second gas-liquid separator and then enters the second refrigerant inlet.

[0043] Preferably, the first expansion valve is connected to the secondary condenser via a first connecting pipeline, and a ninth valve is provided on the first connecting pipeline;

[0044] Preferably, the first expansion valve is connected to the primary evaporator via a second connecting pipeline, and a tenth valve is provided on the first connecting pipeline.

[0045] Preferably, the primary evaporator is connected to the first compressor via a third connecting pipeline; the third cavity of the secondary condenser has a first refrigerant outlet, and the refrigerant from the first refrigerant outlet is mixed with the refrigerant from the first cavity of the primary evaporator and enters the first compressor through a fourth connecting pipeline; the third connecting pipeline and the fourth connecting pipeline have a connecting point, and a fifth valve is provided between the first compressor and the connecting point.

[0046] Preferably, the third shell of the secondary condenser has a second refrigerant outlet, and the refrigerant from the second refrigerant outlet passes through the second dryer and the second expansion valve in sequence and returns to the second cavity of the secondary evaporator.

[0047] Preferably, the oil collecting pipeline at one end of the second condensed oil outlet has a pipeline cooling section, and the refrigerant from the second cavity cools the pipeline cooling section and then enters the third cavity through the second refrigerant inlet.

[0048] Preferably, a sixth valve is provided between the pipeline cold-insulation section and the third cavity.

[0049] Preferably, the second cavity has a third refrigerant outlet, and a seventh valve, a first gas-liquid separator and an eighth valve are sequentially arranged between the third refrigerant outlet and the second refrigerant inlet.

[0050] Preferably, the oil and gas processing system includes a first control system and a second control system, which are respectively used to detect the temperature, pressure or liquid level of the first compressor and the second compressor.

[0051] The present invention adopts an absorption process using a low eutectic solvent as an absorbent as the end-of-pipe treatment process for oil and gas, and combines it with a condensation method as the front-end recovery process. That is, a two-stage auto-cascade condensation process is first adopted to achieve preliminary recovery of heavier components in oil and gas at low energy consumption. Then, an absorption process based on a low eutectic solvent is adopted to efficiently recover oil and gas, thereby improving the safety of the device, achieving deep emission reduction of VOCs, and reaching mg-level emission indicators.

[0052] The deep eutectic solvent used in the present invention is a new green solvent composed of a combination of hydrogen bond acceptors and hydrogen bond donors in a certain ratio. It has an extremely low saturated vapor pressure and can absorb VOCs in flue gas by physical absorption. Weak intermolecular interactions occur between the deep eutectic solvent and the VOCs, resulting in low energy consumption for desorption, high recovery rate, and long service life. The deep eutectic solvent used in the present invention has the advantages of being non-volatile, functionally programmable, non-flammable, environmentally friendly, and highly economical. Different functions can be designed according to different compositions. Therefore, the use of deep eutectic solvents as alternative solvents to organic solvents and ionic liquids has great development prospects.

[0053] The present invention proposes to use a low-volatility, high-VOCs absorption performance low-eutectic solvent as an absorbent to solve the problems of low VOCs recovery efficiency and large absorbent usage caused by the high volatility of mineral oil absorbents, thereby replacing the adsorption method with the absorption method to achieve safe and efficient recovery of oil and gas; and adopting a two-stage self-cascade condensation process instead of the conventional three-stage condensation process for front-end treatment of VOCs, thereby reducing the energy consumption of oil and gas recovery.

[0054] Compared with the prior art, the beneficial effects of the present invention are at least reflected in the following aspects:

[0055] 1) The present invention adopts absorption method instead of adsorption method as the oil and gas terminal treatment process, which fundamentally avoids the safety hazards of adsorption process.

[0056] 2) The present invention adopts a two-stage auto-cascade refrigeration system to recover the heavier components in the oil and gas, which has lower energy consumption and smaller footprint than the conventional three-stage condensation system.

[0057] 3) The present invention uses a deep eutectic solvent to recover light components in oil and gas. Since the deep eutectic solvent is non-volatile and non-flammable, it avoids absorbent loss, secondary pollution and explosion risks. Compared with conventional absorption processes, the amount of absorbent used and the equipment scale are reduced, and safety is improved.

[0058] 4) The deep eutectic solvent used in the present invention has the characteristic of designable functions. By adjusting its components and composition, higher light hydrocarbon absorption performance and efficient absorption of VOCs can be achieved, thereby meeting milligram-level emission indicators. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 This is the oil and gas processing system of the present invention.

[0060] Description of Reference Numerals

[0061] 1. Oil-gas blower; 2. First-stage evaporator; 3. Fifth valve; 4. First compressor; 5. First detection temperature and pressure control system; 6. First-stage condenser; 7. First dryer; 8. First expansion valve; 9. Second-stage condenser; 10. Second dryer; 11. Eighth valve; 12. First gas-liquid separator; 13. Seventh valve; 14. Second detection temperature and pressure control system; 15. Second compressor; 16. Second gas-liquid separator; 17. Second expansion valve; 18. Sixth valve; 19. Pipeline cold insulation section; 20. Second-stage evaporator; 21. Third valve; 22. Fourth valve; 23. Oil collecting tank; 24. Absorption tower; 25. Second valve; 26. Heat exchanger; 28. Flash tank; 29. ​​First valve; 30. Third-stage condenser; 31. Tenth valve; 32. Ninth valve. DETAILED DESCRIPTION

[0062] The following describes the specific embodiments of the present invention in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0063] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0064] A first aspect of the present invention provides an oil and gas processing method, the method comprising the following steps:

[0065] (1) The oil and gas are subjected to primary condensation and secondary condensation in sequence;

[0066] (2) Using a low eutectic solvent to absorb the gas phase product obtained in step (1).

[0067] The present invention adopts a combined process of condensation followed by absorption. The oil-gas mixture undergoes two-stage auto-cascade condensation (primary condensation and secondary condensation) to recover components with higher boiling points. Extremely low temperatures are not required, which can significantly reduce energy consumption. After condensation, a low eutectic solvent is used as an absorbent for absorption, which can achieve higher light hydrocarbon absorption performance and deep recovery of VOCs. Moreover, the low eutectic solvent is not easy to volatilize, so the solvent loss caused by absorbent volatilization can be avoided, and the amount of absorbent used and the equipment scale can be reduced.

[0068] According to the present invention, after the oil and gas undergo primary condensation (pre-cooling), the components with higher liquefaction temperatures in the oil and gas become condensed oil, which can be collected; the uncondensed oil and gas mixture undergoes secondary condensation, and the temperature of the secondary condensation is lower. At the lower temperature, most of the hydrocarbons above C5 in the oil and gas are liquefied, and part of C2 to C4 are liquefied, and the condensed oil can also be collected; the C2 to C4 content in the mixed gas obtained after the secondary condensation is increased, and the content of hydrocarbons above C5 is reduced. When a low eutectic solvent is used to absorb the uncondensed VOCs, due to the weak intermolecular interaction between the low eutectic solvent and the VOCs, the VOCs in the mixed gas continuously enter the low eutectic solvent, thereby efficiently absorbing the VOCs in the mixed gas.

[0069] According to the present invention, the oil and gas contain VOCs, air and water; wherein the total content of VOCs in the oil and gas is 1-1000g / m 3 .

[0070] In a specific embodiment, in order to improve the absorption efficiency, the deep eutectic solvent can be in countercurrent contact with the gas phase product to absorb the VOCs in the mixed gas.

[0071] In the present invention, a specific deep eutectic solvent is required to enhance the absorption of light hydrocarbon components in oil and gas. Specifically, the deep eutectic solvent contains at least one pair of a hydrogen bond acceptor and a hydrogen bond donor, wherein the hydrogen bond acceptor is selected from one or more of choline chloride, tetrabutylammonium bromide, tetraoctylammonium chloride, menthol, and thymol, and the hydrogen bond donor is an organic acid; wherein the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:0.1 to 10.

[0072] According to the present invention, the organic acid can be selected from various organic acids well known to those skilled in the art; specifically, the organic acid is selected from levulinic acid and / or C6-C18 fatty acids.

[0073] In some preferred embodiments, the C6-C18 fatty acid is selected from one or more of n-hexanoic acid, n-octanoic acid, n-decanoic acid, lauric acid, palmitoleic acid and oleic acid.

[0074] In the present invention, the deep eutectic solvent can be prepared according to various methods well known to those skilled in the art. Specifically, the preparation method of the deep eutectic solvent includes: mixing a hydrogen bond acceptor and a hydrogen bond donor to react, and cooling the obtained reaction product to obtain a liquid deep eutectic solvent.

[0075] Preferably, in the preparation method of the deep eutectic solvent, the reaction conditions include: the reaction temperature may be 30 to 100°C, for example, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C or 100°C; the reaction time may be 30 to 90 min, for example, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min or 90 min.

[0076] In a more specific embodiment, the preparation method of the deep eutectic solvent includes: mixing a hydrogen bond acceptor and a hydrogen bond donor, heating and stirring at 30-100° C. for 30-90 minutes to form a clear solution, and then cooling to the use temperature to keep the deep eutectic solvent in a liquid state.

[0077] In order to achieve good VOCs absorption performance, the deep eutectic solvent selected in the present invention should satisfy a VOCs absorption capacity greater than 50 g / kg, wherein the VOCs absorption capacity is obtained through a saturated solubility test.

[0078] In a more preferred embodiment, in order to improve the absorption effect of the deep eutectic solvent on VOCs in oil and gas, when the deep eutectic solvent contains choline chloride-levulinic acid, the molar ratio of choline chloride to levulinic acid in the choline chloride-levulinic acid is 1:2-4.

[0079] In a more preferred embodiment, in order to improve the absorption effect of the deep eutectic solvent on VOCs in oil and gas, when the deep eutectic solvent contains tetrabutylammonium bromide-oleic acid, the molar ratio of tetrabutylammonium bromide to oleic acid in the tetrabutylammonium bromide-oleic acid is 1:3-5.

[0080] In a more preferred embodiment, in order to improve the absorption effect of the deep eutectic solvent on VOCs in oil and gas, when the deep eutectic solvent contains tetraoctylammonium chloride-oleic acid, the molar ratio of tetraoctylammonium chloride to oleic acid in the tetraoctylammonium chloride-oleic acid is 1:3-5.

[0081] In a more preferred embodiment, in order to improve the absorption effect of the deep eutectic solvent on VOCs in oil and gas, when the deep eutectic solvent contains menthol-lauric acid, the molar ratio of menthol to lauric acid in the menthol-lauric acid is 1:1-3.

[0082] In a more preferred embodiment, in order to improve the absorption effect of the deep eutectic solvent on VOCs in oil and gas, when the deep eutectic solvent contains menthol-oleic acid, the molar ratio of menthol to oleic acid in the menthol-oleic acid is 1:1-3.

[0083] In the present invention, before the oil and gas are absorbed by the low eutectic solvent, the oil and gas are sequentially subjected to primary condensation and secondary condensation for shallow cooling and deep cooling, thereby removing components with higher boiling points in the oil and gas. In order to fully recover components with higher boiling points in the oil and gas mixture while avoiding the use of extremely low condensation temperatures, thereby reducing energy consumption and equipment investment, under preferred conditions, the conditions for the primary condensation in step (1) include: a temperature of 2 to 5°C, for example, 2°C, 2.5°C, 3°C, 3.5°C, 4°C, 4.5°C or 5°C; the conditions for the secondary condensation in step (1) include: a temperature of -30 to -40°C, for example, -30°C, -32°C, -35°C, -38°C or -40°C.

[0084] According to the present invention, a refrigerant is used to condense the oil-gas mixture during the primary condensation and the secondary condensation; the refrigerant can be a conventional choice in the art. Preferably, the refrigerants used for the primary condensation and the secondary condensation in step (1) are independently selected from one or more of polyfluoroethane, difluorochloromethane (R22), and trifluoromethane (R23). Preferably, the polyfluoroethane is selected from one or more of pentafluoroethane, trifluoroethane, and tetrafluoroethane. More preferably, the polyfluoroethane is a mixture of pentafluoroethane, trifluoroethane, and tetrafluoroethane (R404).

[0085] When the condensed oil and gas mixture is absorbed by a low eutectic solvent, in order to further improve the light hydrocarbon absorption performance and achieve deep recovery of VOCs, the absorption conditions need to be limited to an appropriate range.

[0086] In a preferred embodiment, the absorption conditions in step (2) include: a temperature of 0 to 30°C, for example, 0°C, 5°C, 10°C, 15°C, 20°C, 25°C or 30°C; and a pressure of 0.1 to 1 MPa, for example, 0.1 MPa, 0.2 MPa, 0.5 MPa, 0.8 MPa or 1 MPa.

[0087] In a more preferred embodiment, in step (2), the gas-liquid ratio (volume flow ratio) of the gas-phase product to the deep eutectic solvent is 2-20.

[0088] Compared with the existing technology, the two-stage cascade condensation and absorption combined process adopted in the present invention omits the deep cooling process above -70°C, so the energy consumption is lower and the equipment investment is less. In addition, the present invention adopts the absorption process to further process the unliquefied mixed gas, which can reduce one processing device compared with the existing adsorption process and avoid the safety risks caused by the thermal effect of the adsorbent.

[0089] Since the deep eutectic solvent of the present invention is a physical absorbent for VOCs, it has a high affinity for hydrocarbon oils that are non-polar or weakly polar substances, and thus has a high absorption capacity. At the same time, its saturated vapor pressure is low, so the deep eutectic solvent that has adsorbed VOCs can be easily regenerated for recycling.

[0090] According to the present invention, the oil and gas treatment method further comprises: desorbing the liquid phase product obtained after absorption in step (2). After the mixed gas that has not been liquefied after the secondary condensation is subjected to VOCs absorption to meet the emission standards, the deep eutectic solvent absorption liquid is desorbed and a new absorption cycle is started.

[0091] In a preferred embodiment, in order to improve the desorption efficiency of the deep eutectic solvent absorption liquid, the desorption conditions include: a temperature of 30 to 100 ° C, for example, 30 ° C, 40 ° C, 50 ° C, 60 ° C, 70 ° C, 80 ° C, 90 ° C or 100 ° C; a pressure of 0 to 0.1 MPa, for example, 0 MPa, 0.01 MPa, 0.02 MPa, 0.05 MPa, 0.08 MPa or 0.1 MPa.

[0092] This invention utilizes a combined condensation-absorption process, where the condensation system employs a nested refrigeration process with single-unit compression. Oil and gas pass through a primary evaporator and a secondary evaporator, respectively, for shallow and deep cooling, and the liquefied oil is recovered. The unliquefied mixed gas enters an absorption tower, where VOCs in the mixed gas are absorbed by a deep eutectic solvent to meet emission standards. The absorption liquid then enters a desorption tower, and the desorbed gas returns to the condensation system inlet, starting a new cycle. The oil and gas recovery system of this invention, consisting of a condensation system and an absorption and desorption system, features simple equipment, easy operation, and convenient skid-mounting.

[0093] The condensation-absorption combined process of the present invention can be implemented in a conventional system as long as it can achieve the functions of condensing VOCs in oil and gas, absorbing VOCs in oil and gas, and desorbing the absorption liquid.

[0094] According to the present invention, the oil and gas processing method is implemented in an oil and gas processing system, such as Figure 1As shown, the oil and gas processing system includes a primary evaporator 2, a secondary evaporator 20, an absorption tower 24, and a flash tank 28, which are connected in sequence. The oil and gas mixture is first pre-cooled in the primary evaporator 2 at 2-5°C to condense the VOCs components with higher boiling points in the oil and gas, and the condensed oil can be collected. The uncondensed oil and gas components are then condensed in the secondary evaporator 20. The condensation temperature in the secondary evaporator 20 is lower (-30--40°C), which can liquefy most of the C5 and above hydrocarbons in the oil and gas and partially liquefy the C2-C4 hydrocarbons. The condensed oil can also be collected. After the secondary condensation, the C2-C4 content of the mixed gas is increased and the content of hydrocarbons above C5 is reduced. The uncondensed mixed gas is passed into the absorption tower 24 to absorb the uncondensed VOCs, effectively absorbing the VOCs in the mixed gas.

[0095] In a preferred embodiment, the absorption tower 24 may be a plate tower or a packed tower, and the temperature of the absorption tower 24 may be 0 to 30° C., and the pressure may be 0.1 to 1 MPa.

[0096] In the present invention, the top of the primary evaporator 2 has an oil and gas inlet. Oil and gas from the air inlet are pressurized by the oil and gas blower 1 and then enter the primary evaporator 2 through the oil and gas inlet. The oil and gas blower 1 has both conveying and pressurizing functions. During the process of oil and gas blower 1 conveying oil and gas to the oil and gas inlet, the oil and gas volume decreases after pressurization due to the high boiling point of the oil and gas mixture, and a small amount of components in the oil and gas are liquefied.

[0097] In a specific embodiment, the primary evaporator 2 includes a first housing and a first cavity disposed within the first housing. The first housing is used to contain oil and gas, and the first cavity contains a refrigerant for condensing the oil and gas. The refrigerant and the oil and gas mixture exchange heat in the secondary evaporator 2. The oil and gas release heat, causing the higher-boiling-point VOCs to condense, while the refrigerant absorbs heat and partially evaporates.

[0098] Under preferred conditions, the primary evaporator 2 is a shell-and-tube heat exchanger, the oil-gas mixture flows through the shell side, and the refrigerant flows through the tube side, completing the heat exchange process between the refrigerant and the oil-gas mixture.

[0099] In a preferred embodiment, the bottom of the first housing has a first condensed oil outlet, which is connected to the oil collection tank 23 via an oil collection pipeline. After the oil-gas mixture is pre-cooled in the primary evaporator 2, the higher-boiling-point VOCs in the oil-gas condense to produce condensed oil, which is then collected in the oil collection tank 23 for reuse.

[0100] More preferably, a third valve 21 is provided on the oil collecting pipeline between the first condensed oil outlet and the oil collecting tank 23; when the condensed oil needs to be passed into the oil collecting tank 23, the third valve 21 can be opened to collect the condensed oil, and when the condensed oil does not need to be collected, the third valve 21 can be closed.

[0101] In a specific embodiment, the secondary evaporator 20 includes a second housing and a second cavity disposed within the second housing. The second housing is used to accommodate the oil and gas from the first housing, and the second cavity contains a refrigerant for condensing the oil and gas. Heat exchange between the oil and gas and the refrigerant continues in the secondary evaporator 20, liquefying most of the C5 and higher hydrocarbons in the oil and gas and partially liquefying the C2-C4 hydrocarbons.

[0102] Preferably, the secondary evaporator 20 is a shell-and-tube heat exchanger, in which the oil-gas mixture flows through the shell side and the refrigerant flows through the tube side, thereby completing the heat exchange process between the refrigerant and the oil-gas mixture.

[0103] In a preferred embodiment, the bottom of the second housing has a second condensed oil outlet, which is connected to the oil collection tank 23 via an oil collection pipeline. After some VOCs in the oil-gas mixture condense in the secondary evaporator 20, the resulting condensed oil enters the oil collection tank 23 for recovery and reuse.

[0104] More preferably, a fourth valve 22 is provided on the oil collecting line between the second condensed oil outlet and the oil collecting tank 23. When the condensed oil needs to be passed into the oil collecting tank 23, the fourth valve 22 can be opened to collect the condensed oil, and when the condensed oil does not need to be collected, the third valve 21 can be closed.

[0105] The present invention adopts a two-stage auto-cascade refrigeration system to recover heavier components in oil and gas, which has lower energy consumption and smaller floor space than a conventional three-stage condensation system.

[0106] According to the present invention, after the oil and gas are condensed in the primary evaporator 2 and the secondary evaporator 20, the unliquefied oil and gas mixture flowing out from the lower part of the secondary evaporator 20 enters the absorption tower 24 from the lower part, and the low eutectic solvent flows in from the upper part of the absorption tower 24. The oil and gas mixture is in countercurrent contact with the low eutectic solvent. As the gas rises, due to the weak intermolecular interaction between the low eutectic solvent and the VOCs, the VOCs in the mixture continuously enter the low eutectic solvent. After the mass transfer is completed, the VOCs in the oil and gas are absorbed, and the obtained purified gas is discharged from the top of the absorption tower 24. The low eutectic solvent absorption liquid that has absorbed the VOCs enters the flash tank 28 from the bottom of the absorption tower 24 for desorption.

[0107] In a preferred embodiment, a second liquid phase outlet is provided at the bottom of the absorption tower 24, a second liquid phase inlet is provided in the middle of the flash tank 28, and a heat exchanger 26 is provided between the second liquid phase outlet and the second liquid phase inlet. After the deep eutectic solvent absorbs VOCs in the absorption tower 24, the resulting absorption liquid has a relatively low temperature. After heat exchange in the heat exchanger 26, the temperature of the absorption liquid increases. The higher temperature absorption liquid enters the flash tank 28 and is more easily desorbed, thereby reducing desorption energy consumption.

[0108] More preferably, a second valve 25 is provided between the second liquid phase outlet and the heat exchanger 26 , and the second valve 25 can be opened and closed according to actual needs.

[0109] In a preferred embodiment, the bottom of the flash tank 28 has a first liquid phase outlet, the top of the absorption tower 24 has a first liquid phase inlet, and a three-stage condenser 30 is disposed between the first liquid phase outlet and the first liquid phase inlet. After desorption in the flash tank 28, the deep eutectic solvent absorption liquid regains its ability to adsorb VOCs. The regenerated deep eutectic solvent is cooled in the three-stage condenser 30 and then returned to the absorption tower 24 through the first liquid phase inlet for recycling. The desorbed VOCs gas is returned to the air intake pipeline through a pipeline, mixed with new oil and gas, and then enters the next round of condensation and absorption of oil and gas.

[0110] More preferably, a first valve 29 is provided between the first liquid phase outlet and the third-stage condenser 30 , and the first valve 29 can be opened or closed according to actual needs.

[0111] In a preferred embodiment, the oil and gas processing system also includes a secondary condenser 9, which includes a third shell and a third cavity arranged inside the third shell; the third cavity has a first refrigerant inlet, and the refrigerant from the first evaporator 2 enters the secondary condenser 9 from the first refrigerant inlet; the third shell has a second refrigerant inlet, and the refrigerant from the secondary evaporator 20 enters the secondary condenser 9 from the second refrigerant inlet.

[0112] More preferably, the secondary condenser is a shell-and-tube heat exchanger, wherein the refrigerant of the primary evaporator 2 flows through the tube side, and the refrigerant of the secondary evaporator 20 flows through the shell side.

[0113] In the present invention, the oil and gas processing system also includes a first compressor 4, a first condenser 6, a first dryer 7 and a first expansion valve 8 connected in sequence. The refrigerant from the first cavity and the third cavity is processed by the first compressor 4, the first condenser 6, the first dryer 7 and the first expansion valve 8 in sequence and then enters the refrigerant first inlet of the secondary condenser 9 or the first cavity of the first evaporator 2.

[0114] In this embodiment, after the refrigerant in the primary evaporator 2 pre-cools the oil and gas, a portion of the refrigerant vaporizes. This refrigerant is pressurized by the first compressor 4 and then enters the primary condenser 6 for condensation and cooling. Water is then removed in the first dryer 7 to prevent frost and blockage. The refrigerant is then throttled and cooled in the first expansion valve 8 before entering the secondary condenser 9. The refrigerant exiting the primary condenser 6, after passing through the dryer 7 and expansion valve 8, is split into two paths: one path enters the second condenser 9 for heat exchange with the refrigerant from the secondary evaporator 20; the other path enters the first evaporator 2 for the first heat exchange with the oil and gas.

[0115] In a specific embodiment, the first expansion valve 8 is connected to the secondary condenser 9 via a first connecting pipeline, which is provided with a ninth valve 32. In a specific embodiment, the first expansion valve 8 is connected to the primary evaporator 2 via a second connecting pipeline, which is provided with a tenth valve 31. The ninth valve 32 and the tenth valve 31 are used to control whether the refrigerant exiting the primary condenser 6 enters the secondary condenser 9 or the first evaporator 2.

[0116] In the present invention, the cooling method of the primary condenser 6 is air cooling. More preferably, the primary condenser 6 is an air-cooled condenser, which cools the refrigerant in the primary evaporator 2 by air convection.

[0117] Under preferred conditions, the primary evaporator 2 is connected to the first compressor 4 through a third connecting pipeline; the third cavity of the secondary condenser 9 has a first refrigerant outlet, and the refrigerant from the first refrigerant outlet is mixed with the refrigerant from the first cavity of the primary evaporator 2 and enters the first compressor 4 through a fourth connecting pipeline, and the refrigerant pressure increases; the third connecting pipeline and the fourth connecting pipeline have a connecting point, and a fifth valve 3 is provided between the first compressor 4 and the connecting point, and the fifth valve 3 can adjust the flow rate of the refrigerant entering the first compressor 4.

[0118] In the present invention, the refrigerant in the secondary evaporator 20 is divided into three branches after completing the heat exchange with the oil and gas.

[0119] In a specific embodiment, the first branch is as follows: the refrigerant from the second chamber is processed sequentially through the second compressor 15 and the second gas-liquid separator 16 before entering the second refrigerant inlet. After the refrigerant in the secondary evaporator 20 cools the oil and gas, a portion of the refrigerant vaporizes. This refrigerant is pressurized by the second compressor 15 and then enters the secondary gas-liquid separator 16 to separate into gas and liquid phases. The liquid refrigerant then returns to the second compressor 15 for pressurization and vaporization. The gaseous refrigerant then enters the third shell of the secondary condenser 9, exchanges heat with the refrigerant from the primary evaporator 2, and condenses into liquid refrigerant.

[0120] In a preferred embodiment, the third shell of the secondary condenser 9 has a second refrigerant outlet. The refrigerant from the second refrigerant outlet passes through the second dryer 10 and the second expansion valve 17 in sequence and returns to the second chamber of the secondary evaporator 20. The liquid refrigerant formed in the third shell of the secondary condenser 9 is dried by the second dryer 10 and then throttled and cooled by the second expansion valve 17. After reaching the required temperature, it returns to the secondary evaporator 20 as a condensing medium to condense the oil-gas mixture.

[0121] In a specific embodiment, the second branch is: the oil collecting pipeline at one end of the second condensed oil outlet has a pipeline cooling section 19, and the refrigerant from the second cavity cools the pipeline cooling section 19 and then enters the third cavity through the second refrigerant inlet for cooling.

[0122] Preferably, a sixth valve 18 is provided between the pipeline cold-insulating section 19 and the third cavity.

[0123] In a specific embodiment, the third branch comprises: the second chamber has a third refrigerant outlet, with a seventh valve 13, a first gas-liquid separator 12, and an eighth valve 11 disposed sequentially between the third refrigerant outlet and the second refrigerant inlet. The third branch provides overpressure protection for the system in the event of an overpressure emergency in the first branch. The refrigerant in the secondary evaporator 20 enters the first gas-liquid separator 12. After gas-liquid separation, the liquid phase enters the secondary condenser 9 and is stored in the first gas-liquid separator 12 for recycling after the overpressure in the first branch is resolved.

[0124] Preferably, the oil and gas processing system includes a first control system 5 and a second control system 14, which are used to detect the temperature, pressure or liquid level of the first compressor 4 and the second compressor 15 respectively.

[0125] This invention utilizes a combined condensation-absorption process, where the condensation system employs a nested refrigeration process with single-unit compression. Oil and gas pass through a primary evaporator and a secondary evaporator, respectively, for shallow and deep cooling, and the liquefied oil is recovered. The unliquefied mixed gas enters an absorption tower, where VOCs in the mixed gas are absorbed by a deep eutectic solvent to meet emission standards. The absorption liquid then enters a desorption tower, and the desorbed gas returns to the condensation system inlet, starting a new cycle. The oil and gas recovery system of this invention, consisting of a condensation system and an absorption and desorption system, features simple equipment, easy operation, and convenient skid-mounting.

[0126] The present invention will be described in detail below by way of examples, but the scope of protection of the present invention is not limited thereto. In the following examples, unless otherwise specified, all reagents used are commercially available.

[0127] In the following examples, the absorption capacity of VOCs was obtained by saturation solubility test.

[0128] In the following examples, R404 is a mixture of pentafluoroethane, trifluoroethane and tetrafluoroethane; R22 is difluorochloromethane; and R23 is trifluoromethane.

[0129] The oil and gas processing methods in the following embodiments are implemented in the following oil and gas processing systems:

[0130] like Figure 1As shown, the oil and gas processing system includes a primary evaporator 2, a secondary evaporator 20, an absorption tower 24 and a flash tank 28 connected in sequence; the bottom of the flash tank 28 has a first liquid phase outlet, the upper part of the absorption tower 24 has a first liquid phase inlet, and a third-stage condenser 30 is provided between the first liquid phase outlet and the first liquid phase inlet; a first valve 29 is provided between the first liquid phase outlet and the third-stage condenser 30; the bottom of the absorption tower 24 is provided with a second liquid phase outlet, the middle part of the flash tank 28 is provided with a second liquid phase inlet, and a heat exchanger 26 is provided between the second liquid phase outlet and the second liquid phase inlet; a second valve 25 is provided between the second liquid phase outlet and the heat exchanger 26; the first evaporator 2 The top is provided with an oil and gas inlet, and the oil and gas from the air inlet pipeline are pressurized by the oil and gas fan 1 and then enter the first-stage evaporator 2 through the oil and gas inlet; the first-stage evaporator 2 includes a first shell and a first cavity arranged inside the first shell, wherein the first shell is used to accommodate oil and gas, and the first cavity is filled with refrigerant for condensing the oil and gas; the bottom of the first shell is provided with a first condensed oil outlet, and the first condensed oil outlet is connected to the oil collecting tank 23 through an oil collecting pipeline; a third valve 21 is provided on the oil collecting pipeline between the first condensed oil outlet and the oil collecting tank 23; the secondary evaporator 20 includes a second shell and a second cavity arranged inside the second shell, wherein the second shell is used to accommodate the oil from the first shell. The oil and gas from the first shell, the second cavity is filled with refrigerant for condensing the oil and gas; the bottom of the second shell is provided with a second condensed oil outlet, the second condensed oil outlet is connected to the oil collecting tank 23 through an oil collecting pipeline; a fourth valve 22 is provided on the oil collecting pipeline between the second condensed oil outlet and the oil collecting tank 23; the oil and gas processing system also includes a secondary condenser 9, the secondary condenser 9 includes a third shell and a third cavity arranged inside the third shell; the third cavity has a first refrigerant inlet, the refrigerant from the first evaporator 2 enters the secondary condenser 9 from the first refrigerant inlet; the third shell has a second refrigerant inlet, the refrigerant from the secondary evaporator 20 The refrigerant enters the secondary condenser 9 from the second refrigerant inlet; the oil and gas processing system further includes a first compressor 4, a primary condenser 6, a first dryer 7 and a first expansion valve 8 connected in sequence. The refrigerant from the first cavity is processed by the first compressor 4, the primary condenser 6, the first dryer 7 and the first expansion valve 8 in sequence and then enters the first refrigerant inlet of the secondary condenser 9 or the first cavity of the primary evaporator 2; the refrigerant from the second cavity is processed by the second compressor 15 and the second gas-liquid separator 16 in sequence and then enters the second refrigerant inlet; the first expansion valve 8 is connected to the secondary condenser 9 via a first connecting pipeline, and a ninth valve 32 is provided on the first connecting pipeline;The first expansion valve 8 is connected to the primary evaporator 2 via a second connecting pipeline, and a tenth valve 31 is provided on the first connecting pipeline; the primary evaporator 2 is connected to the first compressor 4 via a third connecting pipeline; the third cavity of the secondary condenser 9 has a first refrigerant outlet, and the refrigerant from the first refrigerant outlet is mixed with the refrigerant from the first cavity of the primary evaporator 2 and then enters the first compressor 4 through a fourth connecting pipeline; the third connecting pipeline and the fourth connecting pipeline have a connection point, and a fifth valve 3 is provided between the first compressor 4 and the connection point; the third shell of the secondary condenser 9 has a second refrigerant outlet, and the refrigerant from the second refrigerant outlet passes through the second dryer 10 and the A second expansion valve 17 returns the oil to the second chamber of the secondary evaporator 20. The oil collection pipeline at one end of the second condensed oil outlet has a pipeline cold insulation section 19. Refrigerant from the second chamber is cooled by the pipeline cold insulation section 19 before entering the third chamber through the second refrigerant inlet. A sixth valve 18 is provided between the pipeline cold insulation section 19 and the third chamber. The second chamber has a third refrigerant outlet, with a seventh valve 13, a first gas-liquid separator 12, and an eighth valve 11 sequentially provided between the third refrigerant outlet and the second refrigerant inlet. The oil and gas processing system includes a first control system 5 and a second control system 14, which are used to detect the temperature, pressure, or liquid level of the first compressor 4 and the second compressor 15, respectively.

[0131] Example 1

[0132] Preparation of deep eutectic solvent:

[0133] The hydrogen bond acceptor is choline chloride and the hydrogen bond donor is levulinic acid. The hydrogen bond acceptor and the hydrogen bond donor are mixed in a molar ratio of 1:2, and stirred continuously at 50°C for 60 minutes to form a clear mixed liquid, which is then naturally cooled to 25°C. At this time, the low eutectic solvent formed is choline chloride-levulinic acid, and the molar ratio of choline chloride to levulinic acid is 1:2. It is light yellow and transparent, and is recorded as DES1. The absorption capacity of VOCs in the oil and gas to be treated in this example is 52 g / kg.

[0134] Oil and gas processing methods:

[0135] (1) The oil and gas to be treated are subjected to primary condensation and secondary condensation in the primary evaporator 2 and the secondary evaporator 20, respectively. The temperature of the primary condensation is 5°C, the temperature of the secondary condensation is -30°C, the refrigerant in the primary evaporator 2 is R404, and the refrigerant in the secondary evaporator 20 is R22. The composition of the oil and gas to be treated is shown in Table 1.

[0136] (2) the uncondensed gaseous product obtained in step (1) is passed into an absorption tower 24 and brought into countercurrent contact with the deep eutectic solvent DES1 to absorb the uncondensed gaseous product, and the obtained purified gas is discharged from the top of the absorption tower 24, wherein the absorption temperature is 10° C., the pressure is 0.8 MPa, the gas-liquid ratio of the gaseous product to the deep eutectic solvent is 2, and the packing of the absorption tower 24 is a stainless steel θ-ring random packing with a diameter of 25 mm and a height of 1.5 m;

[0137] (3) The low eutectic solvent absorption liquid obtained in step (2) is passed from the bottom of the absorption tower 24 into the flash tank 28 for desorption. The low eutectic solvent after desorption is cooled and returned to the absorption tower 24 for recycling. The VOCs gas obtained by desorption is returned to the air inlet pipeline and mixed with the new oil and gas before entering the next round of condensation absorption oil and gas treatment process, wherein the desorption temperature is 60°C and the desorption pressure is 0.01 MPa.

[0138] Example 2

[0139] Preparation of deep eutectic solvent:

[0140] The hydrogen bond acceptor is choline chloride and the hydrogen bond donor is levulinic acid. The hydrogen bond acceptor and the hydrogen bond donor are mixed in a molar ratio of 1:2, and stirred continuously at 50°C for 60 minutes to form a clear mixed liquid, which is then naturally cooled to 25°C. At this time, the low eutectic solvent formed is choline chloride-levulinic acid, and the molar ratio of choline chloride to levulinic acid is 1:2. It is light yellow and transparent, and is recorded as DES1. The absorption capacity of VOCs in the oil and gas to be treated in this example is 52 g / kg.

[0141] Oil and gas processing methods:

[0142] (1) The oil and gas to be treated are subjected to primary condensation and secondary condensation in the primary evaporator 2 and the secondary evaporator 20, respectively. The temperature of the primary condensation is 2°C, the temperature of the secondary condensation is -40°C, the refrigerant in the primary evaporator 2 is R404, and the refrigerant in the secondary evaporator 20 is R23. The composition of the oil and gas to be treated is the same as that in Example 1.

[0143] (2) the uncondensed gaseous product obtained in step (1) is passed into an absorption tower 24 and brought into countercurrent contact with the deep eutectic solvent DES1 to absorb the uncondensed gaseous product, and the obtained purified gas is discharged from the top of the absorption tower 24, wherein the absorption temperature is 10° C., the pressure is 0.8 MPa, the gas-liquid ratio of the gaseous product to the deep eutectic solvent is 2, and the packing of the absorption tower 24 is a stainless steel θ-ring random packing with a diameter of 25 mm and a height of 1.5 m;

[0144] (3) The low eutectic solvent absorption liquid obtained in step (2) is passed from the bottom of the absorption tower 24 into the flash tank 28 for desorption. The low eutectic solvent after desorption is cooled and returned to the absorption tower 24 for recycling. The VOCs gas obtained by desorption is returned to the air inlet pipeline and mixed with the new oil and gas before entering the next round of condensation absorption oil and gas treatment process, wherein the desorption temperature is 60°C and the desorption pressure is 0.01 MPa.

[0145] Example 3

[0146] Preparation of deep eutectic solvent:

[0147] The hydrogen bond acceptor is tetrabutylammonium bromide and the hydrogen bond donor is oleic acid. The hydrogen bond acceptor and the hydrogen bond donor are mixed in a molar ratio of 1:3, and stirred continuously at 50°C for 30 minutes to form a clear mixed liquid. The mixture is then naturally cooled to 25°C. At this time, the low eutectic solvent formed is tetrabutylammonium bromide-oleic acid. The molar ratio of tetrabutylammonium bromide to oleic acid is 1:3, and it is light yellow and transparent, denoted as DES2. The absorption capacity of VOCs in the oil and gas to be treated in this example is 123 g / kg.

[0148] Oil and gas processing methods:

[0149] (1) The oil and gas to be treated are subjected to primary condensation and secondary condensation in the primary evaporator 2 and the secondary evaporator 20, respectively. The temperature of the primary condensation is 3°C and the temperature of the secondary condensation is -35°C. The refrigerant in the primary evaporator 2 is R404 and the refrigerant in the secondary evaporator 20 is R23. The composition of the oil and gas to be treated is the same as that in Example 1.

[0150] (2) the uncondensed gaseous product obtained in step (1) is passed into an absorption tower 24 and brought into countercurrent contact with the deep eutectic solvent DES2 to absorb the uncondensed gaseous product, and the obtained purified gas is discharged from the top of the absorption tower 24, wherein the absorption temperature is 30° C., the pressure is 0.2 MPa, the gas-liquid ratio of the gaseous product to the deep eutectic solvent is 15, and the packing of the absorption tower 24 is a stainless steel θ-ring random packing with a diameter of 25 mm and a height of 1.5 m;

[0151] (3) The low eutectic solvent absorption liquid obtained in step (2) is passed from the bottom of the absorption tower 24 into the flash tank 28 for desorption. The desorbed low eutectic solvent is cooled and returned to the absorption tower 24 for recycling. The desorbed VOCs gas is returned to the air inlet pipeline and mixed with the new oil and gas before entering the next round of condensation and absorption oil and gas treatment process. The desorption temperature is 80° C. and the desorption pressure is 0.05 MPa.

[0152] Example 4

[0153] Preparation of deep eutectic solvent:

[0154] The hydrogen bond acceptor is tetrabutylammonium bromide and the hydrogen bond donor is oleic acid. The hydrogen bond acceptor and the hydrogen bond donor are mixed in a molar ratio of 1:3, and stirred continuously at 100°C for 90 minutes to form a clear mixed liquid. The mixture is then naturally cooled to 25°C. At this time, the low eutectic solvent formed is tetrabutylammonium bromide-oleic acid. The molar ratio of tetrabutylammonium bromide to oleic acid is 1:3, and it is light yellow and transparent, denoted as DES3. The absorption capacity of the VOCs in the oil and gas to be treated in this example is 191 g / kg.

[0155] Oil and gas processing methods:

[0156] (1) The oil and gas to be treated are subjected to primary condensation and secondary condensation in the primary evaporator 2 and the secondary evaporator 20, respectively. The temperature of the primary condensation is 3°C and the temperature of the secondary condensation is -35°C. The refrigerant in the primary evaporator 2 is R404 and the refrigerant in the secondary evaporator 20 is R23. The composition of the oil and gas to be treated is the same as that in Example 1.

[0157] (2) the uncondensed gaseous product obtained in step (1) is passed into an absorption tower 24 and brought into countercurrent contact with the deep eutectic solvent DES2 to absorb the uncondensed gaseous product, and the obtained purified gas is discharged from the top of the absorption tower 24, wherein the absorption temperature is 30° C., the pressure is 0.2 MPa, the gas-liquid ratio of the gaseous product to the deep eutectic solvent is 15, and the packing of the absorption tower 24 is a stainless steel θ-ring random packing with a diameter of 25 mm and a height of 1.5 m;

[0158] (3) The low eutectic solvent absorption liquid obtained in step (2) is passed from the bottom of the absorption tower 24 into the flash tank 28 for desorption. The desorbed low eutectic solvent is cooled and returned to the absorption tower 24 for recycling. The desorbed VOCs gas is returned to the air inlet pipeline and mixed with the new oil and gas before entering the next round of condensation and absorption oil and gas treatment process. The desorption temperature is 80° C. and the desorption pressure is 0.05 MPa.

[0159] Example 5

[0160] Preparation of deep eutectic solvent:

[0161] The hydrogen bond acceptor is tetraoctylammonium chloride and the hydrogen bond donor is oleic acid. The hydrogen bond acceptor and the hydrogen bond donor are mixed in a molar ratio of 1:4, and stirred continuously at 80°C for 90 minutes to form a clear mixed liquid, which is then naturally cooled to 25°C. At this time, the low eutectic solvent formed is tetraoctylammonium chloride-oleic acid, and the molar ratio of tetraoctylammonium chloride to oleic acid is 1:4. It is light yellow and transparent, and is recorded as DES4. The absorption capacity of VOCs in the oil and gas to be treated in this example is 197 g / kg.

[0162] Oil and gas processing methods:

[0163] (1) The oil and gas to be treated are subjected to primary condensation and secondary condensation in the primary evaporator 2 and the secondary evaporator 20, respectively. The temperature of the primary condensation is 5°C, the temperature of the secondary condensation is -40°C, the refrigerant in the primary evaporator 2 is R404, and the refrigerant in the secondary evaporator 20 is R23. The composition of the oil and gas to be treated is the same as that in Example 1.

[0164] (2) the uncondensed gaseous product obtained in step (1) is passed into an absorption tower 24 and brought into countercurrent contact with the deep eutectic solvent DES4 to absorb the uncondensed gaseous product, and the obtained purified gas is discharged from the top of the absorption tower 24, wherein the absorption temperature is 5° C., the pressure is 0.1 MPa, the gas-liquid ratio of the gaseous product to the deep eutectic solvent is 2, and the packing of the absorption tower 24 is a stainless steel θ-ring random packing with a diameter of 25 mm and a height of 1.5 m;

[0165] (3) The low eutectic solvent absorption liquid obtained in step (2) is passed from the bottom of the absorption tower 24 into the flash tank 28 for desorption. The low eutectic solvent after desorption is cooled and returned to the absorption tower 24 for recycling. The VOCs gas obtained by desorption is returned to the air inlet pipeline and mixed with the new oil and gas before entering the next round of condensation absorption oil and gas treatment process, wherein the desorption temperature is 60°C and the desorption pressure is 0.01 MPa.

[0166] Example 6

[0167] Preparation of deep eutectic solvent:

[0168] The hydrogen bond acceptor is tetraoctylammonium chloride and the hydrogen bond donor is oleic acid. The hydrogen bond acceptor and the hydrogen bond donor are mixed in a molar ratio of 1:4, and stirred continuously at 80°C for 90 minutes to form a clear mixed liquid, which is then naturally cooled to 25°C. At this time, the low eutectic solvent formed is tetraoctylammonium chloride-oleic acid, and the molar ratio of tetraoctylammonium chloride to oleic acid is 1:4. It is light yellow and transparent, and is recorded as DES4. The absorption capacity of VOCs in the oil and gas to be treated in this example is 197 g / kg.

[0169] Oil and gas processing methods:

[0170] (1) The oil and gas to be treated are subjected to primary condensation and secondary condensation in the primary evaporator 2 and the secondary evaporator 20, respectively. The temperature of the primary condensation is 5°C, the temperature of the secondary condensation is -40°C, the refrigerant in the primary evaporator 2 is R404, and the refrigerant in the secondary evaporator 20 is R23. The composition of the oil and gas to be treated is the same as that in Example 1.

[0171] (2) the uncondensed gaseous product obtained in step (1) is passed into an absorption tower 24 and brought into countercurrent contact with the deep eutectic solvent DES4 to absorb the uncondensed gaseous product, and the obtained purified gas is discharged from the top of the absorption tower 24, wherein the absorption temperature is 30° C., the pressure is 1 MPa, the gas-liquid ratio of the gaseous product to the deep eutectic solvent is 2, and the packing of the absorption tower 24 is a stainless steel θ-ring random packing with a diameter of 25 mm and a height of 1.5 m;

[0172] (3) The low eutectic solvent absorption liquid obtained in step (2) is passed from the bottom of the absorption tower 24 into the flash tank 28 for desorption. The low eutectic solvent after desorption is cooled and returned to the absorption tower 24 for recycling. The VOCs gas obtained by desorption is returned to the air inlet pipeline and mixed with the new oil and gas before entering the next round of condensation absorption oil and gas treatment process, wherein the desorption temperature is 60°C and the desorption pressure is 0.01 MPa.

[0173] Example 7

[0174] Preparation of deep eutectic solvent:

[0175] The hydrogen bond acceptor is menthol and the hydrogen bond donor is lauric acid. The hydrogen bond acceptor and the hydrogen bond donor are mixed in a molar ratio of 1:3, and stirred continuously at 60°C for 50 minutes to form a clear mixed liquid. The mixture is then naturally cooled to 25°C. At this time, the low eutectic solvent formed is menthol-lauric acid, and the molar ratio of menthol to lauric acid is 1:3. It is light yellow and transparent, and is recorded as DES5. The absorption capacity of VOCs in the oil and gas to be treated in this example is 174 g / kg.

[0176] Oil and gas processing methods:

[0177] (1) The oil and gas to be treated are subjected to primary condensation and secondary condensation in the primary evaporator 2 and the secondary evaporator 20, respectively. The temperature of the primary condensation is 3°C and the temperature of the secondary condensation is -35°C. The refrigerant in the primary evaporator 2 is R404 and the refrigerant in the secondary evaporator 20 is R22. The composition of the oil and gas to be treated is the same as that in Example 1.

[0178] (2) the uncondensed gaseous product obtained in step (1) is passed into an absorption tower 24 and brought into countercurrent contact with the deep eutectic solvent DES5 to absorb the uncondensed gaseous product, and the obtained purified gas is discharged from the top of the absorption tower 24, wherein the absorption temperature is 20° C., the pressure is 0.2 MPa, the gas-liquid ratio of the gaseous product to the deep eutectic solvent is 8, and the packing of the absorption tower 24 is a stainless steel θ-ring random packing with a diameter of 25 mm and a height of 1.5 m;

[0179] (3) The low eutectic solvent absorption liquid obtained in step (2) is passed from the bottom of the absorption tower 24 into the flash tank 28 for desorption. The desorbed low eutectic solvent is cooled and returned to the absorption tower 24 for recycling. The desorbed VOCs gas is returned to the air inlet pipeline and mixed with the new oil and gas before entering the next round of condensation absorption oil and gas treatment process, wherein the desorption temperature is 100°C and the desorption pressure is 0.1 MPa.

[0180] Example 8

[0181] Preparation of deep eutectic solvent:

[0182] The hydrogen bond acceptor is menthol and the hydrogen bond donor is lauric acid. The hydrogen bond acceptor and the hydrogen bond donor are mixed in a molar ratio of 1:3, and stirred continuously at 60°C for 50 minutes to form a clear mixed liquid. The mixture is then naturally cooled to 25°C. At this time, the low eutectic solvent formed is menthol-lauric acid, and the molar ratio of menthol to lauric acid is 1:3. It is light yellow and transparent, and is recorded as DES5. The absorption capacity of VOCs in the oil and gas to be treated in this example is 174 g / kg.

[0183] Oil and gas processing methods:

[0184] (1) The oil and gas to be treated are subjected to primary condensation and secondary condensation in the primary evaporator 2 and the secondary evaporator 20, respectively. The temperature of the primary condensation is 3°C and the temperature of the secondary condensation is -35°C. The refrigerant in the primary evaporator 2 is R404 and the refrigerant in the secondary evaporator 20 is R22. The composition of the oil and gas to be treated is the same as that in Example 1.

[0185] (2) the uncondensed gaseous product obtained in step (1) is passed into an absorption tower 24 and brought into countercurrent contact with the deep eutectic solvent DES5 to absorb the uncondensed gaseous product, and the obtained purified gas is discharged from the top of the absorption tower 24, wherein the absorption temperature is 20° C., the pressure is 0.2 MPa, the gas-liquid ratio of the gaseous product to the deep eutectic solvent is 8, and the packing of the absorption tower 24 is a stainless steel θ-ring random packing with a diameter of 25 mm and a height of 1.5 m;

[0186] (3) The low eutectic solvent absorption liquid obtained in step (2) is passed from the bottom of the absorption tower 24 into the flash tank 28 for desorption. The low eutectic solvent after desorption is cooled and returned to the absorption tower 24 for recycling. The VOCs gas obtained by desorption is returned to the air inlet pipeline and mixed with the new oil and gas before entering the next round of condensation absorption oil and gas treatment process, wherein the desorption temperature is 30°C and the desorption pressure is 0.01 MPa.

[0187] Example 9

[0188] Preparation of deep eutectic solvent:

[0189] The hydrogen bond acceptor is menthol and the hydrogen bond donor is oleic acid. The hydrogen bond acceptor and the hydrogen bond donor are mixed in a molar ratio of 1:2, and stirred continuously at 60°C for 60 minutes to form a clear mixed liquid. The mixture is then naturally cooled to 25°C. At this time, the low eutectic solvent formed is menthol-oleic acid, and the molar ratio of menthol to oleic acid is 1:2. It is light yellow and transparent, and is recorded as DES6. The absorption capacity of VOCs in the oil and gas to be treated in this example is 185g / kg.

[0190] Oil and gas processing methods:

[0191] (1) The oil and gas to be treated are subjected to primary condensation and secondary condensation in the primary evaporator 2 and the secondary evaporator 20, respectively. The temperature of the primary condensation is 2°C and the temperature of the secondary condensation is -35°C. The refrigerant in the primary evaporator 2 is R404 and the refrigerant in the secondary evaporator 20 is R23. The composition of the oil and gas to be treated is the same as that in Example 1.

[0192] (2) the uncondensed gaseous product obtained in step (1) is passed into an absorption tower 24 and brought into countercurrent contact with the deep eutectic solvent DES6 to absorb the uncondensed gaseous product, and the obtained purified gas is discharged from the top of the absorption tower 24, wherein the absorption temperature is 20° C., the pressure is 0.1 MPa, the gas-liquid ratio of the gaseous product to the deep eutectic solvent is 8, and the packing of the absorption tower 24 is a stainless steel θ-ring random packing with a diameter of 25 mm and a height of 1.5 m;

[0193] (3) The low eutectic solvent absorption liquid obtained in step (2) is passed from the bottom of the absorption tower 24 into the flash tank 28 for desorption. The low eutectic solvent after desorption is cooled and returned to the absorption tower 24 for recycling. The VOCs gas obtained by desorption is returned to the air inlet pipeline and mixed with the new oil and gas before entering the next round of condensation absorption oil and gas treatment process, wherein the desorption temperature is 60°C and the desorption pressure is 0.01 MPa.

[0194] Example 10

[0195] The hydrogen bond acceptor is menthol and the hydrogen bond donor is oleic acid. The hydrogen bond acceptor and the hydrogen bond donor are mixed in a molar ratio of 1:2, and stirred continuously at 30°C for 30 minutes to form a clear mixed liquid, which is then naturally cooled to 25°C. At this time, the low eutectic solvent formed is menthol-oleic acid, and the molar ratio of menthol to oleic acid is 1:2. It is light yellow and transparent, and is recorded as DES7. The absorption capacity of VOCs in the oil and gas to be treated in this example is 159 g / kg.

[0196] Oil and gas processing methods:

[0197] (1) The oil and gas to be treated are subjected to primary condensation and secondary condensation in the primary evaporator 2 and the secondary evaporator 20, respectively. The temperature of the primary condensation is 5°C, the temperature of the secondary condensation is -30°C, the refrigerant in the primary evaporator 2 is R404, and the refrigerant in the secondary evaporator 20 is R23. The composition of the oil and gas to be treated is the same as that in Example 1.

[0198] (2) the uncondensed gaseous product obtained in step (1) is passed into an absorption tower 24 and brought into countercurrent contact with the deep eutectic solvent DES7 to absorb the uncondensed gaseous product, and the obtained purified gas is discharged from the top of the absorption tower 24, wherein the absorption temperature is 10° C., the pressure is 0.1 MPa, the gas-liquid ratio of the gaseous product to the deep eutectic solvent is 2, and the packing of the absorption tower 24 is a stainless steel θ-ring random packing with a diameter of 25 mm and a height of 1.5 m;

[0199] (3) The low eutectic solvent absorption liquid obtained in step (2) is passed from the bottom of the absorption tower 24 into the flash tank 28 for desorption. The low eutectic solvent after desorption is cooled and returned to the absorption tower 24 for recycling. The VOCs gas obtained by desorption is returned to the air inlet pipeline and mixed with the new oil and gas before entering the next round of condensation absorption oil and gas treatment process, wherein the desorption temperature is 30°C and the desorption pressure is 0.01 MPa.

[0200] Comparative Example

[0201] Preparation of deep eutectic solvent:

[0202] The hydrogen bond acceptor is choline chloride and the hydrogen bond donor is urea. The hydrogen bond acceptor and the hydrogen bond donor are mixed in a molar ratio of 1:2, and stirred continuously at 80°C for 90 minutes to form a clear mixed liquid. The mixture is then naturally cooled to 25°C. At this time, the low eutectic solvent formed is choline chloride-urea. The molar ratio of choline chloride to urea is 1:2, and it is light yellow and transparent, denoted as DES8. The absorption capacity of the VOCs in the oil and gas to be treated in this example is 21 g / kg.

[0203] Oil and gas processing methods:

[0204] (1) The oil and gas to be treated are subjected to primary condensation and secondary condensation in the primary evaporator 2 and the secondary evaporator 20, respectively. The temperature of the primary condensation is 5°C, the temperature of the secondary condensation is -40°C, the refrigerant in the primary evaporator 2 is R404, and the refrigerant in the secondary evaporator 20 is R23. The composition of the oil and gas to be treated is the same as that in Example 1.

[0205] (2) the uncondensed gaseous product obtained in step (1) is passed into an absorption tower 24 and brought into countercurrent contact with the deep eutectic solvent DES8 to absorb the uncondensed gaseous product, and the obtained purified gas is discharged from the top of the absorption tower 24, wherein the absorption temperature is 30° C., the pressure is 1 MPa, the gas-liquid ratio of the gaseous product to the deep eutectic solvent is 2, and the packing of the absorption tower 24 is a stainless steel θ-ring random packing with a diameter of 25 mm and a height of 1.5 m;

[0206] (3) The low eutectic solvent absorption liquid obtained in step (2) is passed from the bottom of the absorption tower 24 into the flash tank 28 for desorption. The low eutectic solvent after desorption is cooled and returned to the absorption tower 24 for recycling. The VOCs gas obtained by desorption is returned to the air inlet pipeline and mixed with the new oil and gas before entering the next round of condensation absorption oil and gas treatment process, wherein the desorption temperature is 60°C and the desorption pressure is 0.01 MPa.

[0207] Test Example 1

[0208] The content of each component in the purified gas after absorption in Examples 1 to 10 and the comparative example was detected using an FID online monitor, and the total content of VOCs (non-methane total hydrocarbons) in the purified gas and the removal rate of each component were calculated. The results are shown in Tables 1 to 11.

[0209] Table 1 - Example 1

[0210]

[0211] Table 2 - Example 2

[0212]

[0213] Table 3 - Example 3

[0214]

[0215]

[0216] Table 4 - Example 4

[0217]

[0218]

[0219] Table 5 - Example 5

[0220]

[0221]

[0222] Table 6 - Example 6

[0223]

[0224]

[0225] Table 7 - Example 7

[0226]

[0227]

[0228] Table 8 - Example 8

[0229]

[0230]

[0231] Table 9 - Example 9

[0232]

[0233]

[0234] Table 10 - Example 10

[0235]

[0236]

[0237] Table 11 - Comparative Examples

[0238]

[0239] From the above analysis results, it can be seen that the deep eutectic solvent-based condensation absorption combined oil and gas recovery system of the present invention can achieve deep recovery of VOCs and meet the requirements of 120 mg / m 3 or 60 mg / m 3 Etc. VOCs mg-level emission standards.

[0240] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. An oil and gas processing method, characterized in that: The method comprises the following steps: (1) Carry out primary condensation and secondary condensation of oil and gas in sequence; (2) absorbing the gaseous product obtained in step (1) using a deep eutectic solvent; The deep eutectic solvent contains at least one pair of hydrogen bond acceptor and hydrogen bond donor, the hydrogen bond acceptor is selected from one or more of choline chloride, tetrabutylammonium bromide, tetraoctylammonium chloride, menthol and thymol, and the hydrogen bond donor is an organic acid; wherein the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:0.1 to 10; The organic acid is selected from levulinic acid and / or a C6-C18 fatty acid, and the C6-C18 fatty acid is selected from one or more of n-hexanoic acid, n-octanoic acid, n-decanoic acid, lauric acid, palmitoleic acid and oleic acid; The preparation method of the deep eutectic solvent comprises: mixing a hydrogen bond acceptor and a hydrogen bond donor and then cooling, wherein the mixing conditions include: a temperature of 30 to 100° C. and a time of 30 to 90 minutes; The conditions for the primary condensation in step (1) include: a temperature of 2 to 5°C; the conditions for the secondary condensation in step (1) include: a temperature of -30 to -40°C; The refrigerants used for the primary condensation and the secondary condensation in step (1) are independently selected from one or more of polyfluoroethane, difluorochloromethane and trifluoromethane; the polyfluoroethane is selected from one or more of pentafluoroethane, trifluoroethane and tetrafluoroethane; The absorption conditions in step (2) include: temperature of 0-30°C and pressure of 0.1-1 MPa; In step (2), the gas-liquid ratio of the gas phase product to the deep eutectic solvent is 2-20; The method further comprises: desorbing the liquid phase product obtained after absorption in step (2); the desorption conditions include: a temperature of 30-100° C. and a pressure of 0-0.1 MPa.

2. The method according to claim 1, characterized in that When the deep eutectic solvent contains choline chloride-levulinic acid, the molar ratio of choline chloride to levulinic acid in the choline chloride-levulinic acid is 1:2-4.

3. The method according to claim 1, characterized in that When the deep eutectic solvent contains tetrabutylammonium bromide-oleic acid, the molar ratio of tetrabutylammonium bromide to oleic acid in the tetrabutylammonium bromide-oleic acid is 1:3-5.

4. The method according to claim 1, wherein When the deep eutectic solvent contains tetraoctylammonium chloride-oleic acid, the molar ratio of tetraoctylammonium chloride to oleic acid in the tetraoctylammonium chloride-oleic acid is 1:3-5.

5. The method according to claim 1, wherein When the deep eutectic solvent contains menthol-lauric acid, the molar ratio of menthol to lauric acid in the menthol-lauric acid is 1:1-3.

6. The method according to claim 1, characterized in that When the deep eutectic solvent contains menthol-oleic acid, the molar ratio of menthol to oleic acid in the menthol-oleic acid is 1:1-3.

7. The method according to claim 1, wherein the method is implemented in an oil and gas processing system, characterized in that: The oil and gas processing system comprises a primary evaporator (2), a secondary evaporator (20), an absorption tower (24) and a flash tank (28) connected in sequence; The bottom of the flash tank (28) has a first liquid phase outlet, the upper portion of the absorption tower (24) has a first liquid phase inlet, and a three-stage condenser (30) is provided between the first liquid phase outlet and the first liquid phase inlet.

8. The method according to claim 7, characterized in that A first valve (29) is provided between the first liquid phase outlet and the third-stage condenser (30).

9. The method according to claim 7, characterized in that A second liquid phase outlet is provided at the bottom of the absorption tower (24), a second liquid phase inlet is provided in the middle of the flash tank (28), and a heat exchanger (26) is provided between the second liquid phase outlet and the second liquid phase inlet.

10. The method according to claim 9, characterized in that A second valve (25) is provided between the second liquid phase outlet and the heat exchanger (26).

11. The method according to claim 7 or 8, characterized in that The top of the first-stage evaporator (2) is provided with an oil and gas inlet, and the oil and gas from the air inlet pipeline are pressurized by the oil and gas blower (1) and then enter the first-stage evaporator (2) through the oil and gas inlet.

12. The method according to claim 7, characterized in that The primary evaporator (2) comprises a first shell and a first cavity arranged inside the first shell, wherein the first shell is used to contain oil and gas; and the first cavity is filled with refrigerant for condensing the oil and gas.

13. The method according to claim 12, characterized in that The bottom of the first shell is provided with a first condensed oil outlet, and the first condensed oil outlet is connected to the oil collecting tank (23) via an oil collecting pipeline.

14. The method according to claim 13, wherein: A third valve (21) is provided on the oil collecting pipeline between the first condensed oil outlet and the oil collecting tank (23).

15. The method according to claim 13, characterized in that The secondary evaporator (20) comprises a second shell and a second cavity arranged inside the second shell, wherein the second shell is used to accommodate oil and gas from the first shell; and the second cavity is filled with refrigerant for condensing the oil and gas.

16. The method according to claim 15, characterized in that The bottom of the second shell is provided with a second condensed oil outlet, and the second condensed oil outlet is connected to the oil collecting tank (23) via an oil collecting pipeline.

17. The method according to claim 16, characterized in that A fourth valve (22) is provided on the oil collecting pipeline between the second condensed oil outlet and the oil collecting tank (23).

18. The method according to claim 16, characterized in that The oil and gas processing system further includes a secondary condenser (9); The secondary condenser (9) comprises a third shell and a third cavity arranged inside the third shell; The third cavity has a first refrigerant inlet, and the refrigerant from the first-stage evaporator (2) enters the second-stage condenser (9) through the first refrigerant inlet; The third shell has a second refrigerant inlet, and the refrigerant from the secondary evaporator (20) enters the secondary condenser (9) through the second refrigerant inlet.

19. The method according to claim 18, characterized in that The oil and gas processing system further comprises a first compressor (4), a primary condenser (6), a first dryer (7) and a first expansion valve (8) connected in sequence, and the refrigerant from the first cavity and the third cavity is processed in sequence by the first compressor (4), the primary condenser (6), the first dryer (7) and the first expansion valve (8) and then enters the first refrigerant inlet of the secondary condenser (9) or the first cavity of the primary evaporator (2); The refrigerant from the second cavity is processed in sequence by the second compressor (15) and the second gas-liquid separator (16) and then enters the second refrigerant inlet.

20. The method according to claim 19, characterized in that The first expansion valve (8) is connected to the secondary condenser (9) via a first connecting pipeline, and a ninth valve (32) is provided on the first connecting pipeline.

21. The method according to claim 20, characterized in that The first expansion valve (8) is connected to the primary evaporator (2) via a second connecting pipeline, and a tenth valve (31) is provided on the first connecting pipeline.

22. The method according to claim 19, wherein The first-stage evaporator (2) is connected to the first compressor (4) via a third connecting pipeline; the third cavity of the second-stage condenser (9) has a first refrigerant outlet, and the refrigerant from the first refrigerant outlet is mixed with the refrigerant from the first cavity of the first-stage evaporator (2) and then enters the first compressor (4) through a fourth connecting pipeline; the third connecting pipeline and the fourth connecting pipeline have a connecting point, and a fifth valve (3) is provided between the first compressor (4) and the connecting point.

23. The method according to claim 18 or 19, characterized in that The third shell of the secondary condenser (9) has a second refrigerant outlet, and the refrigerant from the second refrigerant outlet passes through the second dryer (10) and the second expansion valve (17) in sequence and returns to the second cavity of the secondary evaporator (20).

24. The method according to claim 18, wherein The oil collecting pipeline at one end of the second condensed oil outlet has a pipeline cold preservation section (19), and the refrigerant from the second cavity cools the pipeline cold preservation section (19) and then enters the third cavity through the second refrigerant inlet.

25. The method according to claim 24, characterized in that A sixth valve (18) is provided between the pipeline cold-insulating section (19) and the third cavity.

26. The method according to claim 19, wherein The second cavity has a third refrigerant outlet, and a seventh valve (13), a first gas-liquid separator (12), and an eighth valve (11) are sequentially arranged between the third refrigerant outlet and the second refrigerant inlet.

27. The method according to claim 19, wherein The oil and gas processing system comprises a first control system (5) and a second control system (14), which are respectively used to detect the temperature, pressure or liquid level of the first compressor (4) and the second compressor (15).

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