Method and apparatus for recovering C2-C4 components from methane-containing industrial gases.

Abstract

The present invention discloses a method and apparatus for recovering C2 components from a methane-containing industrial gas. The method includes: (1) cooling a compressed methane-containing industrial gas and performing gas-liquid separation; (2) absorbing the C2 components in the gas phase using an absorbent to obtain an absorption-rich liquid; (3) returning the absorption-rich liquid to the compressed state in step (1) or mixing the absorption-rich liquid with the liquid phase obtained in step (1) to obtain a mixed liquid, and depressurizing the mixed liquid or the absorption-rich liquid; (4) performing methane desorption on the depressurized stream to obtain a rich absorbent, or performing a second gas-liquid separation on the depressurized stream, followed by methane desorption on the second liquid phase to obtain a rich absorbent; and (5) desorbing and separating the rich absorbent to obtain a lean absorbent and an enriched gas, and recycling and reusing the lean absorbent. This method has a high recovery rate of C2 or heavier components and low overall energy consumption.

Description

Detailed Description of the Invention

[0001] [Technical field] The present invention relates to the technical field of methane desorption and C2-C4 component recovery from methane-containing industrial gas, including but not limited to the technical field of dry gas processing. Specifically, the present invention relates to a method and apparatus for recovering C2-C4 components in methane-containing industrial gas such as dry gas, in particular, to a method and apparatus for recovering C2 components in methane-containing industrial gas such as dry gas, and to a method and apparatus for recovering C2 and C3 components in methane-containing industrial gas such as dry gas.

[0002] [Background technology] At present, already industrialized processes for recovering C2 components (ethane, ethylene) from dry gas or for recovering C2 and C3 components from dry gas mainly include: (1) Cryogenic separation method: this method has a mature process and can achieve high ethylene recovery and high purity, but it requires a dryer and a propylene cooling device or an ethylene-propylene combined cooling device, which requires large investment and high energy consumption; (2) Pressure swing adsorption: this method is simple in operation and generally requires low energy consumption, but the purity of the product is low, the recovery rate of C2 components is low, and when the raw material dry gas processing is large-scale, the equipment requires large investment and space occupation; (3) Shallow oil absorption method: This method has a safe and reliable process flow, a high recovery rate of C2 and C3 components, and no requirements on the sulfur content and water content in the raw gas. However, in this method, the tower kettle reboiler of the absorption tower (or methane desorption tower) bears a high load, and a large amount of low-pressure steam is consumed during the whole process.

[0003] US10052581B1 discloses a process for recovering steam cracker feed from FCC dry gas. In this process, FCC dry gas is first separated into CO 2 , H 2The dry gas is subjected to an operation of eluting S, COS with amine, and then to a hydrodealkyning operation. After the above purification process, the FCC dry gas is passed through a pressure swing adsorption tower to remove methane, hydrogen and other light components therein, and then undergoes a series of separation processes to finally obtain a feed stream for a steam cracker mainly composed of ethane and ethylene. In this process, the pressure swing adsorption tower may have an operating condition below 0°C during the operation process, so in order to avoid freezing, it is necessary to carry out cooling, phase separation, dehydration and drying processes before the dry gas is allowed to flow into the pressure swing adsorption tower, and as a result, the device requires a relatively large investment.

[0004] CN101759516B discloses a process for separating catalytic dry gas in an oil refinery by oil absorption. The process includes dry gas compression, absorption (reabsorption), desorption and other processes. In the main absorption tower, C5 fraction or depentanized oil is used as an absorbent to absorb the C2 fraction and heavier components in the catalytic dry gas, and the C5 rich absorbent is delivered to the desorption tower, and the recovered C2 enriched gas is obtained from the top of the desorption tower. The operating pressure of the main absorption tower is 3.5-5.5 MPaG, the temperature of the tower kettle is 95-115 ° C, the operating pressure of the desorption tower is 2-3 MPaG, the temperature of the tower kettle is 145-165 ° C, and low pressure steam needs to be used as a heat source.

[0005] CN103159581B discloses an apparatus for recovering C2 in refinery dry gas by a composite absorption method, including a compressor, a pretreatment unit, a refinery dry gas cooling unit, an absorption unit and a rectification unit. The absorption unit includes a gas-liquid separation tank, a C2 absorption tower and a methane desorption tower, and the rich absorbent absorbing the C2 components in the dry gas is separated into C2 components and absorbent components in the C2 removal tower. The operating pressure of the C2 absorption tower is 2.5-3.0 MPaG, the operating pressure of the methane desorption tower is 2.5-3.1 MPaG, and the operating pressure of the C2 removal tower is 2.2-2.6 MPaG. The methane desorption tower needs to use a heat source of about 120°C in the refinery.

[0006] CN109553504A discloses a method and apparatus for recycling saturated dry gas in an oil refinery plant by adopting shallow-cooling oil absorption technology. The method includes compressing and cooling the saturated dry gas in sequence, then sending it to a C4 absorber for processing, and sending the resulting gas and liquid phases to a gasoline absorber and a C4 desorber; recovering the gas phase obtained by the processing in the C4 desorber as a C2-enriched gas product, and returning most of the resulting liquid phase to the C4 absorber for recycling; sending the liquid phase obtained by the processing in the gasoline absorber to a gasoline stabilization tower for processing, returning most of the resulting liquid phase to the gasoline absorber for recycling, and subjecting the gas phase obtained by the processing in the gasoline stabilization tower to concentration and gas-liquid separation processing in sequence, and respectively returning the resulting gas and liquid phases to the inlet of the compressor and sending them to the gasoline stabilization tower and the C4 absorber for processing. Two degrees of absorption-desorption are carried out, and low-pressure steam is used as the heat source.

[0007] CN106609161B discloses a method for separating saturated dry gas in a refinery plant. The saturated dry gas is subjected to compression and cooling, and then gas-liquid phase separation, and the compressed dry gas is sent to an absorption tower, where the C4 fraction is used as an absorbent to absorb the C2 and heavier components in the dry gas. The liquid in the absorption tower kettle is sent to the C4 desorption tower for processing, C2-enriched gas is obtained from the C4 desorption tower, and the liquid in the C4 desorption tower kettle is returned to the C4 absorption tower for recycling. The total recovery rate of C2 and C3 in this process can reach 93%, the pressure of the C4 absorption tower is 3-4.5 MPaG, the temperature of the tower kettle of the C4 absorption tower is 100-160 ° C; the pressure of the C4 desorption tower is 2.5-3.5 MPaG, and the temperature of the tower kettle of the C4 desorption tower is 100-160 ° C. Both the C4 absorber and the C4 desorber require the use of low pressure steam or 145° C. hot oil outside the battery limit as the heat source for the tower kettle reboiler, and therefore the units consume a relatively large amount of energy.

[0008] CN101759516B discloses a method for separating catalytic dry gas in an oil refinery by oil absorption. The method includes dry gas compression, absorption (reabsorption), desorption and other processes. In the main absorption tower, C5 fraction or depentanized oil is used as an absorbent to absorb the C2 fraction and heavier components in the catalytic dry gas, and the C5 rich absorbent is delivered to the desorption tower, and the recovered C2 enriched gas is obtained from the top of the desorption tower. The operating pressure of the main absorption tower is 3.5-5.5 MPaG, the temperature of the tower kettle is 95-115 ° C, the operating pressure of the desorption tower is 2-3 MPaG, the temperature of the tower kettle is 145-165 ° C, and low pressure steam needs to be used as a heat source.

[0009] CN101353286B discloses a non-cryogenic separation method for low hydrocarbons containing light gas, in which the pre-treated light gas is cooled to 10℃~-37℃, and then fed to a pre-cut tower, the top of the pre-cut tower is light components such as methane and a part of C2, as well as a small amount of C3, and the bottom of the pre-cut tower is the remaining C2 and heavier components, and the top gas of the pre-cut tower is fed to an absorption tower, in which C3, C4, C5 and other hydrocarbons are used as absorbents to absorb the C2 in the top gas of the pre-cut tower. This process does not have a cryogenic cold box and demethanizer, does not require cryogenic separation of methane, and therefore consumes less energy than traditional cryogenic separation. However, during this process, propylene refrigerant at about -60℃ is still required, and the raw gas also needs to be dried and dehydrated, and at the same time, the recovered C2 components have low purity.

[0010] In summary, when recovering C2 components or C2 and C3 components in dry gas, in order to ensure the purity of the produced gas and the recovery rate of C2 or C2 and C3, the existing processes usually adopt a cryogenic / intermediate cooling separation route (in this route, the raw gas needs to be dried and dehydrated, and the equipment requires large investment), or a shallow cooling oil absorption route (in this route, the oil absorption and methane desorption process usually need to be carried out under higher pressure), in which the reboiler in the methane desorption process consumes a large amount of steam and has a large load, and the equipment has a higher energy consumption.

[0011] Summary of the Invention The object of the present invention is to provide a novel method and apparatus for recovering C2-C4 components (including but not limited to C2 components, or C2 and C3 components, or C2, C3 and C4 components) from methane-containing industrial gases such as dry gas. The C2-C4 components (including but not limited to C2 components, or C2 and C3 components, or C2, C3 and C4 components) recovered by the method and apparatus have high purity and high recovery rate, the energy consumption of the apparatus is saved, and a dryer and a propylene cooling compressor are not required. In the present invention, the methane-containing industrial gas includes, but is not limited to, dry gas, cracked gas, natural gas, shale gas, etc., and the dry gas is preferably at least one selected from the group consisting of refinery dry gas and coal chemical dry gas.

[0012] In a first aspect, the present invention provides a method for recovering C2 components in a methane-containing industrial gas, the method comprising the steps of: (1) compressing a raw methane-containing industrial gas, and cooling the resulting compressed gas before gas-liquid separation to obtain a gas phase and a liquid phase; (2) contacting the gas phase with an absorbent to absorb the C2 components to obtain an absorption tail gas and an absorption rich liquid, wherein the absorption rich liquid is returned to and mixed with the compressed gas, or a mixture of the absorption rich liquid and the liquid phase obtained in step (1) or the absorption rich liquid is used as a first stream; (3) reducing the pressure of the liquid phase obtained in step (1) or the first stream obtained in step (2); (4) subjecting the reduced pressure stream in step (3) to methane desorption to obtain a desorbed gas and a rich absorbent, and returning the desorbed gas to the compression in step (1) or venting it to the outside; or subjecting the reduced pressure stream in step (3) to a second gas-liquid separation to obtain a second gas phase and a second liquid phase, returning the second gas phase to the compression in step (1), subjecting the second liquid phase to methane desorption to obtain a desorbed gas and a rich absorbent, and returning the desorbed gas to the compression in step (1) or discharging it to the outside; (5) The rich absorbent is subjected to desorption separation to obtain a lean absorbent and an enriched gas containing C2 components, and the lean absorbent is returned to and mixed with the absorbent in step (2).

[0013] In a particular embodiment of the present invention, in step (2) of the process of the present invention, the absorption rich liquid is returned into and mixed with the compressed gas, and the liquid phase obtained in step (1) is depressurized and then subjected to methane desorption to obtain a desorbed gas and a rich absorbent.

[0014] In a particular embodiment of the present invention, in the process of the present invention, the first stream obtained in step (2) is depressurized and then subjected to a second gas-liquid separation to obtain a second gas phase and a second liquid phase, and the second liquid phase is subjected to methane desorption to obtain a desorbed gas and a rich absorbent.

[0015] Preferably, in step (2), the absorbent is selected from the group consisting of a C4 cut and / or a C5 cut, the C4 cut comprising at least one of n-butane, isobutane and butenes, the C5 cut comprising at least one of n-pentane, isopentane and neopentane, and the C4 cut being preferred.

[0016] Preferably, the C2 components include ethane and / or ethylene.

[0017] The process of the present invention may also include recovering C3 components, preferably said C3 components comprising propane and / or propylene.

[0018] The process according to the invention may include recovering C2 and C3 components, preferably said C2 and C3 components comprising ethane and / or ethylene, and propane and / or propylene.

[0019] The process of the present invention may also include recovering C4 components, preferably said C4 components comprising butanes and / or butenes.

[0020] In a second aspect, the present invention provides an apparatus for recovering C2 components in a methane-containing industrial gas, the apparatus comprising a compressor, a cooler, a liquid separation tank, an absorber, a methane desorption tower and a desorption tower; The compressor is connected to a pipeline of methane-containing industrial gas, and the compressor, the cooler and the liquid separation tank are connected in series; the bottom of said absorption tower is connected to the top of said liquid separation tank and said cooler respectively to countercurrently contact the gas phase discharged from the top of said liquid separation tank with an absorbent, and an absorption tail gas is discharged from the top of said absorption tower, and an absorption rich liquid is discharged from a tower kettle of said absorption tower and returned to said cooler; The methane desorption tower has its upper, top and bottom connected to the bottom of the liquid separation tank, the compressor and the middle part of the desorption tower, respectively, for desorption of methane in liquid phase discharged from the bottom of the liquid separation tank after depressurization; the desorbed gas is discharged from the top of the methane desorption tower and returned to the inlet or interstage of the compressor or discharged to the outside; the rich absorbent is discharged from the tower kettle of the methane desorption tower and then passed through the middle part of the desorption tower for desorption separation; The desorption tower has its bottom connected to the top of the absorption tower, wherein lean absorbent is discharged from the tower kettle of the desorption tower and returned to the top of the absorption tower, and enriched gas containing C2 components, such as C2 and C3 components, is recovered from the top of the desorption tower.

[0021] In a third aspect, the present invention provides an apparatus for recovering C2 components in a methane-containing industrial gas, the apparatus comprising a compressor, a cooler, a first liquid separation tank, an absorption tower, a second liquid separation tank, a methane desorption tower, and a desorption tower; The compressor is connected to a pipeline of a methane-containing industrial gas, and the compressor, the cooler and the first liquid separation tank are connected in series; the bottom of the absorption tower is connected to the top of the first liquid separation tank and the middle part of the second liquid separation tank, respectively, for contacting the first gas phase discharged from the top of the first liquid separation tank with an absorbent in countercurrent flow; the absorption tail gas and the absorption rich liquid are discharged from the top of the absorption tower and the tower kettle, respectively; the mixture of the absorption rich liquid and the first liquid phase discharged from the bottom of the first liquid separation tank or the absorption rich liquid is used as a first stream; the first stream is depressurized and then passed to the middle part of the second liquid separation tank for second gas-liquid separation; the second liquid separation tank has its top and bottom connected to the compressor and the top of the methane desorption tower, respectively, wherein a second gas phase is discharged from the top of the second liquid separation tank and returned to the inlet or interstage of the compressor, and a second liquid phase is discharged from the bottom of the second liquid separation tank and passed to the top of the methane desorption tower for methane desorption; the top and bottom of the methane desorption tower are connected to the compressor and the middle part of the desorption tower, respectively, wherein the desorbed gas is discharged from the top of the methane desorption tower and returned to the inlet or interstage of the compressor or discharged to the outside, and the rich absorbent is discharged from the tower kettle of the methane desorption tower and passed to the middle part of the desorption tower for desorption separation; The desorption tower has its bottom connected to the top of the absorption tower, wherein lean absorbent is discharged from the tower kettle of the desorption tower and returned to the top of the absorption tower, and enriched gas containing C2 components, such as C2 and C3 components, is recovered from the top of the desorption tower.

[0022] The apparatus of the present invention may further include a methane desorber reboiler.

[0023] Preferably, the C2 components include ethane and / or ethylene.

[0024] The apparatus according to the invention may also recover C3 components, preferably said C3 components comprising propane and / or propylene.

[0025] The apparatus according to the present invention recovers C2 and C3 components, preferably said C2 and C3 components comprising ethane and / or ethylene, and propane and / or propylene.

[0026] The apparatus according to the invention may also recover C4 components, preferably said C4 components comprising butanes and / or butenes.

[0027] BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of an apparatus for recovering C2 components in methane-containing industrial gases, such as dry gas, provided by the present invention: Explanation of symbols: 1. Raw material methane-containing industrial gas (such as dry gas); 2. Compressor; 3. Cooler; 4. Liquid separation tank; 5. Absorption tower; 6. Absorption tower kettle liquid pump; 7. Methane desorption tower; 8. Rich absorbent pump; 9. Desorption tower; 10. Enriched gas containing C2 components; 11. Absorbent circulation pump; 12. Light hydrocarbon components; 13. Stream; 14. Absorption tail gas; 15. Methane desorption tower reboiler.

[0028] FIG. 2 is a schematic diagram of an apparatus for recovering C2 components in methane-containing industrial gases, such as dry gas, provided by the present invention: Explanation of symbols: 1. Raw material methane-containing industrial gas (such as dry gas); 2. Compressor; 3. Cooler; 4. First liquid separation tank; 5. Absorption tower; 6. Desorption tower feed cooler; 7. Second liquid separation tank; 8. Methane desorption tower; 9. Methane desorption tower reboiler; 10. Rich absorbent pump; 11. Desorption tower; 12. Absorbent circulation pump; 13. Enriched gas containing C2 components; 14. Light hydrocarbon components; 15. Absorption tail gas; 16. Second stream.

[0029] Detailed Description of the Invention Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, but are not used to limit the present invention.

[0030] As a result of investigation, the inventors of the present invention have found the following: by subjecting raw material methane-containing industrial gas such as dry gas to absorption treatment under high pressure, and then continuously performing methane desorption treatment and absorbent desorption treatment under low pressure, the obtained enriched gas product has high purity, the recovery rate of C2 to C4 components such as C2 components, C2 and C3 components, and C2, C3 and C4 components is high, the load of the tower kettle reboiler in the methane desorption process is low, the tower kettle temperature is low, and this part of the thermal energy is generated in the tower kettle of the desorption tower in this device. the methane desorption tower kettle reboiler does not consume steam, and an optimized process flow and operating parameters are selected by comprehensively considering the effect of increasing energy consumption due to the desorbed gas at the top of the methane desorption tower being returned to the compressor, and the effect of reducing energy consumption due to the methane desorption tower kettle reboiler not consuming steam, so that the energy consumption of the entire apparatus is minimized and a dryer and a propylene cooling compressor are not required.

[0031] In addition, the inventors of the present invention have found that the present invention is suitable for a process for treating methane-containing industrial gases with methane to be desorbed. By independently operating the high-pressure absorption process and the low-pressure methane desorption process, and by operating them in combination, methane can be effectively removed with minimal energy consumption and consumption of materials such as absorbents, thereby achieving a high recovery rate of C2, C3, C4 and other components from methane-containing industrial gases. Compared with the conventional shallow oil absorption process, under the circumstances where the recovery rate of C2 to C4 components such as C2, C2 and C3, and C2, C3 and C4 reaches about 95% or more, the total energy consumption of the apparatus of the present invention can be reduced by about 10% to 30% depending on the composition of the raw material.

[0032] In the present invention, the term "methane-containing industrial gas" refers to a methane-containing industrial gas from which methane is desorbed by a methane desorption tower, and the industrial gas is then subjected to subsequent processing to recover C2, C3, C4 and other components, including but not limited to dry gas, cracked gas, natural gas, shale gas, etc. In the present invention, there are no particular limitations and requirements on the components and their contents of the raw methane-containing industrial gas. As long as the methane contained in the raw methane-containing industrial gas is desorbed by a methane desorption tower to achieve separation from C2 to C4, the objective of recovering C2, C3, C4 and other components with a high recovery rate and minimizing the total energy consumption can be achieved by adjusting the process flow and operation parameters.

[0033] The dry gas is not particularly limited, but is at least one selected from the group consisting of refinery dry gas and coal chemical dry gas. Specifically, the refinery dry gas is at least one selected from the group consisting of catalytic cracker dry gas, delayed coker dry gas, PSA unit desorption gas, and light hydrocarbon recovery unit dry gas, and the coal chemical dry gas is at least one selected from the group consisting of methanol-olefins (MTO) dry gas and methanol-aromatics (MTA) dry gas. The dry gas in the present invention is not limited to the above. The cracked gas, natural gas, and shale gas are not particularly limited, but the cracked gas includes catalytic cracked gas and steam cracked gas.

[0034] According to a preferred embodiment of the present invention, when the methane-containing industrial gas contains less than 0.1% molar C6 or heavier components (i.e., components having 6 or more carbon atoms), for example when the dry gas contains less than 0.1% molar refinery dry gas having C6 or heavier components, this contributes even more to the recovery of C2 components in the dry gas and the lowest overall energy consumption of the apparatus.

[0035] According to a preferred embodiment of the present invention, when the methane-containing industrial gas contains more than 0.1% molar C6 or heavier components, for example when the dry gas contains more than 0.1% molar refinery dry gas having C6 or heavier components, this contributes even more to the recovery of C2 and C3 components in the dry gas and the lowest overall energy consumption of the device.

[0036] In the present invention, unless otherwise specified, pressures are gauge pressures.

[0037] In a first aspect, the present invention provides a method for recovering C2 components in a methane-containing industrial gas, the method comprising the steps of: (1) compressing a raw methane-containing industrial gas, and cooling the resulting compressed gas before gas-liquid separation to obtain a gas phase and a liquid phase; (2) contacting the gas phase with an absorbent to absorb the C2 components to obtain an absorption tail gas and an absorption rich liquid, wherein the absorption rich liquid is returned to and mixed with the compressed gas, or a mixture of the absorption rich liquid and the liquid phase obtained in step (1) or the absorption rich liquid is used as a first stream; (3) reducing the pressure of the liquid phase obtained in step (1) or the first stream obtained in step (2); (4) subjecting the reduced pressure stream in step (3) to methane desorption to obtain a desorbed gas and a rich absorbent, and returning the desorbed gas to the compression in step (1) or venting it to the outside; or subjecting the reduced pressure stream in step (3) to a second gas-liquid separation to obtain a second gas phase and a second liquid phase, returning the second gas phase to the compression in step (1), subjecting the second liquid phase to methane desorption to obtain a desorbed gas and a rich absorbent, and returning the desorbed gas to the compression in step (1) or discharging it to the outside; (5) The rich absorbent is subjected to desorption separation to obtain a lean absorbent and an enriched gas containing C2 components (e.g., C2 and C3 components), and the lean absorbent is returned to and mixed with the absorbent in step (2).

[0038] In a particular embodiment of the present invention, in step (2) of the process of the present invention, the absorption rich liquid is mixed back into the compressed gas and the liquid phase obtained in step (1) is depressurized and then subjected to methane desorption to obtain a desorbed gas and a rich absorbent.

[0039] In a particular embodiment of the present invention, the present invention provides a method for recovering C2 components in a methane-containing industrial gas, the method comprising the steps of: (1) compressing a raw methane-containing industrial gas, and cooling the resulting compressed gas before gas-liquid separation to obtain a gas phase and a liquid phase; (2) contacting the gas phase with an absorbent to absorb the C2 component to obtain an absorption tail gas and an absorption rich liquid, and returning the absorption rich liquid to the compressed gas and mixing it; (3) reducing the pressure of the liquid phase obtained in step (1); (4) subjecting the reduced pressure stream in step (3) to methane desorption to obtain desorbed gas and rich absorbent, and returning the desorbed gas to the compression in step (1) or discharging it to the outside; (5) subjecting the rich absorbent to desorption separation to obtain lean absorbent and an enriched gas containing C2 components (e.g., C2 and C3 components), and mixing the lean absorbent back into the absorbent in step (2).

[0040] Step (1) Gas-liquid separation of methane-containing industrial gas after compression and cooling According to the present invention, the compression is not particularly limited, and in order to increase the pressure of the raw material methane-containing industrial gas to 2.5 to 4.6 MPaG, preferably 3 to 4.2 MPaG, a compression step is usually adopted. That is, the pressure of the compressed gas is 2.5 to 4.6 MPaG, preferably 3 to 4.2 MPaG. More preferably, the compression is a multi-stage compression, and in the present invention, there is no particular limit to the number of stages of the compression process, and for example, the compression may be a two-stage compression or a three-stage compression.

[0041] According to the present invention, the cooling is not particularly limited, and preferably, the temperature of cooling is 5 to 40°C, preferably 10 to 20°C. In the present invention, a cooling medium having a temperature of 0°C or higher is used to cool the compressed gas, and the cooling medium is at least one selected from the group consisting of low-temperature water, circulating water, propylene, ammonia and liquid nitrogen, preferably low-temperature water; more preferably, the low-temperature water is prepared by a lithium bromide absorption cooling device and has a temperature of 5°C or 7°C. Specifically, low-temperature water at 7°C is used in the examples, but the present invention is not limited thereto.

[0042] According to the invention, preferably, the cooled compressed gas is subjected to gas-liquid separation to obtain a gas phase and a liquid phase, wherein the gas phase is mainly composed of hydrogen and C 1 ~C 3 It is composed of light components such as hydrocarbons, and the liquid phase is mainly C 3 ~C 5 It is composed of heavy components such as hydrocarbons.

[0043] Step (2) Contacting the gas phase with an absorbent to absorb the C2 component According to the present invention, the absorbent is not particularly limited and can be determined by those skilled in the art according to the well-known knowledge in the prior art.Preferably, the absorbent is selected from C4 fraction and / or C5 fraction, the C4 fraction comprises at least one of n-butane, isobutane and butene, the C5 fraction comprises at least one of n-pentane, isopentane and neopentane, and the C4 fraction is preferred.Specifically, mixed butane is used as the absorbent in the embodiment, but the present invention is not limited thereto.

[0044] Preferably, the C2 components are selected from ethane and / or ethylene, for example ethane, ethylene, mixtures of ethane and ethylene.

[0045] According to the present invention, the absorption of the C2 component is preferably carried out in an absorption tower, and more preferably, the number of theoretical plates of the absorption tower is 15 to 30, the operating pressure of the absorption tower is 2.5 to 4.6 MPaG, preferably 3 to 4.2 MPaG, the temperature at the top of the absorption tower is 10 to 60°C, and the kettle temperature of the absorption tower is 10 to 70°C.

[0046] For example, in a particular embodiment, the temperature of the absorbent entering the tower is 40-50°C, the temperature of the gas phase entering the tower is about 40°C, the cooling medium in step (1) is circulating water, and the temperature at the top of the absorption tower is 40-60°C; in another embodiment, the temperature of the absorbent entering the tower is 5-20°C, the temperature of the gas phase entering the tower is 5-20°C, and the cooling medium in step (1) is low-temperature water, so that the temperature at the top of the absorption tower is 10-30°C.

[0047] According to a particular embodiment of the present invention, the gas phase is fed to the bottom of the absorber and is in countercurrent contact with the absorbent at the top of the absorber, thereby absorbing the C2 components and heavier fractions in the gas phase, the absorption tail gas is discharged from the top of the absorber and pumped out of the boundary region, and the absorption rich liquid is discharged from the tower kettle of the absorber, pressurized by the absorber kettle liquid pump, and then returned to be mixed with the compressed gas.

[0048] In the present invention, the absorption rich liquid discharged from the tower kettle of the absorption tower is fully contacted with the compressed gas in the liquid separation tank, and a part of the C2-C4 hydrocarbons and other heavy components are pre-absorbed therein, thereby reducing the amount of gas phase entering the absorption tower, reducing the amount of absorbent used in the absorption tower, and saving energy consumption.

[0049] According to a preferred embodiment of the present invention, the absorption rich liquid is first passed through a water cooler to be cooled before being returned to the chiller, thereby reducing the load on the chiller and saving energy consumption.

[0050] Step (3) Decompression of liquid phase According to the present invention, preferably, the pressure of the liquid phase after decompression is 0.8-3 MPaG, more preferably 1-2 MPaG, wherein the pressure of the liquid phase after decompression is higher than the operating pressure of the methane desorption tower, thereby ensuring that the liquid phase can naturally flow into the upper part of the methane desorption tower under the action of the pressure difference.

[0051] In the present invention, the pressure reduction is not particularly limited. Generally, the pressure of the liquid phase is reduced by the method of flash evaporation, thereby improving the relative volatility between the C1-C5 hydrocarbon components. As a result, the reboiler of the methane desorption tower bears a lower load, and the tower kettle temperature of the methane desorption tower is reduced, therefore, a heat source with a lower temperature level can be used, and the steam consumption and energy consumption of the equipment are saved.

[0052] Step (4) Methane desorption from the stream after depressurization of the liquid phase According to the present invention, preferably, methane desorption is carried out in a methane desorption tower, and more preferably, the number of theoretical plates of the methane desorption tower is 20 to 50, the operating pressure of the methane desorption tower is 0.5 to 2.4 MPaG, the tower top temperature of the methane desorption tower is 10 to 60°C, and the tower kettle temperature of the methane desorption tower is 35 to 90°C.

[0053] In a preferred embodiment, the operating pressure of the methane desorption tower is 1.0 to 1.9 MPaG.

[0054] In a preferred embodiment, the temperature at the top of the methane desorption tower is 10 to 20°C.

[0055] In a preferred embodiment, the tower kettle temperature of the methane desorption tower is 40 to 75°C.

[0056] According to the present invention, preferably, after depressurization, the liquid phase is passed into a methane desorption tower for separation and removal of light components such as methane in the liquid phase, thereby obtaining a desorbed gas and a rich absorbent, and the desorbed gas is returned and mixed into the raw methane-containing industrial gas.

[0057] According to the present invention, preferably, the desorbed gas discharged from the top of the methane desorption tower is returned to the inlet or interstage of the compressor, and the return position can be determined according to the pressure of the raw methane-containing industrial gas, the interstage pressure of the compressor, and the pressure of the methane desorption tower. While ensuring that the top gas of the methane desorption tower can be pressurized by the compressor, the energy consumption of the compressor shall be saved as much as possible.

[0058] In the present invention, the methane desorption tower is operated at low pressure to distill off the methane in the absorption rich liquid at little cost, thereby reducing the methane content in the product rich gas containing C2 components. The kettle liquid of the methane desorption tower is subjected to absorbent desorption treatment to obtain lean absorbent.

[0059] According to the present invention, the heat source of the tower kettle of the methane desorption tower is preferably provided by the reboiler of the methane desorption tower, and the heat source of the reboiler of the methane desorption tower is a process stream. Specifically, the process stream is at least one selected from the group consisting of an absorbent, a rich absorbent and a lean absorbent, and is preferably a lean absorbent.

[0060] Step (5) Desorption and separation of rich absorbent According to the present invention, desorption separation is preferably carried out in a desorption tower, and more preferably, the number of theoretical plates of the desorption tower is 20 to 50, the operating pressure of the desorption tower is 1 to 2.8 MPaG, the tower top temperature of the desorption tower is 25 to 70°C, and the tower kettle temperature of the desorption tower is 90 to 160°C.

[0061] According to a preferred embodiment of the present invention, the rich absorbent is desorbed and separated in a desorption tower, the enriched gas containing C2 components is recovered from the top of the desorption tower, the lean absorbent is discharged from the tower kettle of the desorption tower, the lean absorbent is used as a heat source for methane desorption, and at least a portion of the stream obtained after heat exchange is returned into and mixed with the absorbent.

[0062] According to the present invention, preferably, a part of the stream obtained after the heat exchange of the lean absorbent is sent out of the boundary region as a light hydrocarbon component, and the remaining part is returned to and mixed in the absorbent, where the light hydrocarbon component is at least one selected from the group consisting of C3, C4 and C5 hydrocarbons.

[0063] According to the present invention, the C2-rich gas contains primarily methane, C2 components, C3 components, C4 or heavier components (ie, components having 4 or more carbon atoms), and water.

[0064] Preferably, based on the total volume of enriched gas, the methane content is 0-5 vol.%, preferably 0-2 vol.%; the C2 component content is 40-85 vol.%, preferably 45-65 vol.%; the C3 component content is 0-70 vol.%, preferably 10-60 vol.%; the C4 or heavier component content is 0-20 vol.%, preferably 0-10 vol.%; and the water content is 0-0.5 vol.%.

[0065] Compared with the conventional shallow-cooled oil absorption process, the method of the present invention can achieve a recovery rate of C2 components of about 95% or more, and can reduce the total energy consumption of the device by about 10% to 30%.

[0066] The method for recovering C2 components according to the present invention can be used to recover C2 components from methane-containing industrial gases such as dry gas at a high recovery rate. However, this does not necessarily mean that the content of C2 components in the resulting enriched gas must be higher than the content of C3 components. In this method, the content of C3 components in the enriched gas is also related to the content of C3 components in the raw material.

[0067] The process according to the invention may further comprise recovery of C3 components, preferably said C3 components comprising propane and / or propylene.

[0068] The process according to the invention may include the recovery of C2 and C3 components, preferably said C2 and C3 components comprising ethane and / or ethylene, and propane and / or propylene.

[0069] The process according to the invention may further comprise recovery of C4 components, preferably the C4 components comprise butanes and / or butenes.

[0070] In a particular embodiment of the process of the present invention, the mixture of the absorption rich liquid and the liquid phase obtained in step (1) or the absorption rich liquid is used as the first stream, the first stream obtained is depressurized and then subjected to a second gas-liquid separation to obtain a second gas phase and a second liquid phase, and said second liquid phase is subjected to methane desorption to obtain a desorbed gas and a rich absorbent. Preferably, the process of the present invention can also recover C3 components, preferably said C3 components comprising propane and / or propylene. Preferably, the process of the present invention can recover C2 and C3 components, preferably said C2 and C3 components comprising ethane and / or ethylene, and propane and / or propylene. Preferably, the methane-containing industrial gas comprises more than 0.1% molar C6 or heavier components.

[0071] In a particular embodiment of the method of the present invention, the present invention provides a method for recovering C2 components in a methane-containing industrial gas, the method comprising the steps of: (1) Compressing a methane-containing industrial gas and cooling the resulting compressed gas prior to gas-liquid separation to obtain a gas phase and a liquid phase; (2) contacting the gas phase with an absorbent to absorb the C2 component to obtain an absorption tail gas and an absorption rich liquid, and using a mixture of the absorption rich liquid and the liquid phase obtained in step (1) or the absorption rich liquid as a first stream; (3) reducing pressure on the first stream obtained in step (2); (4) after depressurizing the first stream in step (3), subjecting the stream to a second gas-liquid separation to obtain a second gas phase and a second liquid phase, returning the second gas phase to compression in step (1), subjecting the second liquid phase to methane desorption to obtain a desorbed gas and a rich absorbent, and returning the desorbed gas to compression in step (1) or discharging it to the outside; (5) The rich absorbent is subjected to desorption separation to obtain a lean absorbent and an enriched gas containing C2 components (e.g., C2 and C3 components), and the lean absorbent is returned to and mixed with the absorbent in step (2).

[0072] Here, the gas-liquid separation in step (1) refers to the first gas-liquid separation. The terms "first gas-liquid separation" and "second gas-liquid separation" are used only to distinguish the order of the gas-liquid separation steps, and do not imply the importance of the gas-liquid separation. After the compressed gas is cooled, the first gas-liquid separation is performed to obtain a first gas phase and a first liquid phase.

[0073] In a particular embodiment of the method of the present invention, the present invention provides a method for recovering C2 and C3 components in a methane-containing industrial gas, the method comprising the steps of: (1) compressing a feed methane-containing industrial gas and cooling the resulting compressed gas before performing a first gas-liquid separation to obtain a first gas phase and a first liquid phase; (2) contacting the first gas phase with an absorbent to absorb C2 and C3 components to obtain an absorption tail gas and an absorption rich liquid, and using a mixture of the absorption rich liquid and the first liquid phase or the absorption rich liquid as a first stream; (3) reducing pressure on the first stream obtained in step (2); (4) subjecting the first stream depressurized in step (3) to a second gas-liquid separation to obtain a second gas phase and a second liquid phase, returning the second gas phase to compression in step (1), subjecting the second liquid phase to methane desorption to obtain a desorbed gas and a rich absorbent, and returning the desorbed gas to compression in step (1) or discharging it to the outside; (5) subjecting the rich absorbent to desorption separation to obtain lean absorbent and enriched gas containing C2 and C3 components, and the lean absorbent is returned to and mixed with the absorbent in step (2).

[0074] Step (1) Compression and cooling of methane-containing industrial gases According to the present invention, the compression is not particularly limited, and in order to increase the pressure of the raw material methane-containing industrial gas to 2.5 to 5 MPaG, preferably 3 to 4.2 MPaG, compression is usually performed in stages. That is, the pressure of the compressed gas is 2.5 to 5 MPaG, preferably 3 to 4.2 MPaG. More preferably, the compression is a multi-stage compression, and in the present invention, there is no particular limit to the number of stages of the compression process. For example, the compression may be a two-stage compression or a three-stage compression.

[0075] According to the present invention, the cooling is not particularly limited, and preferably, the temperature of cooling is 5 to 45°C, preferably 10 to 20°C. In the present invention, a cooling medium having a temperature of 0°C or higher is used to cool the compressed gas, and the cooling medium is at least one selected from the group consisting of low-temperature water, circulating water, propylene, ammonia and liquid nitrogen, and is preferably low-temperature water; more preferably, the low-temperature water is prepared by a lithium bromide absorption cooling device and has a temperature of 5°C or 7°C. Specifically, low-temperature water at 7°C is used in the examples, but the present invention is not limited thereto.

[0076] According to the present invention, preferably, the cooled compressed gas is subjected to a first gas-liquid separation to obtain a first gas phase and a first liquid phase, wherein the first gas phase is mainly composed of hydrogen and C 1 ~C 3 The first liquid phase is composed of light components such as hydrocarbons, and is mainly composed of C 3 ~C 5 It is composed of heavy components such as hydrocarbons.

[0077] Step (2) Contacting the first gas phase with an absorbent to absorb the C2 component. According to the present invention, the absorbent is not particularly limited and can be determined by a person skilled in the art according to the well-known knowledge in the prior art.Preferably, the absorbent is selected from C4 fraction and / or C5 fraction, the C4 fraction comprises at least one of n-butane, isobutane and butene, the C5 fraction comprises at least one of n-pentane, isopentane and neopentane, and the C4 fraction is preferred.Specifically, butane is used as the absorbent in the embodiment, but the present invention is not limited thereto.

[0078] According to the present invention, the absorption of the C2 and C3 components is preferably carried out in an absorption tower, and more preferably, the number of theoretical plates of the absorption tower is 15 to 30, the operating pressure of the absorption tower is 2.5 to 5 MPaG, preferably 3 to 4.2 MPaG, the top temperature of the absorption tower is 10 to 30°C, and the kettle temperature of the absorption tower is 10 to 60°C.

[0079] Preferably, the C2 and C3 components include ethane and / or ethylene, and propane and / or propylene.

[0080] According to the invention, the first gas phase is absorbed under high pressure, which is advantageous for the absorption of C2 and C3 components and for reducing the amount of absorbent used.

[0081] According to a particular embodiment of the present invention, the first gas phase is fed to the bottom of the absorber and is in countercurrent contact with the absorbent at the top of the absorber, thereby absorbing the C2, C2, and C3 fractions and heavier fractions in the first gas phase. The absorption tail gas is discharged from the top of the absorber and sent out of the boundary region, and the absorption rich liquid is discharged from the tower kettle of the absorber to obtain a first stream, which is mixed with the first liquid phase or is used as the first stream.

[0082] Step (3) Depressurizing the first stream Preferably, the pressure of the first stream after decompression is 0.5 to 2.4 MPaG, preferably 0.8 to 2 MPaG.

[0083] In the present invention, the decompression treatment is not particularly limited. Generally, the pressure of the first stream is reduced by the method of flash evaporation, thereby improving the relative volatility between C1-C5 hydrocarbon components. As a result, the reboiler of the methane desorption tower bears a lower load, and the tower kettle temperature of the methane desorption tower is reduced, therefore, a heat source with a lower temperature level can be used, and the steam consumption and energy consumption of the equipment are saved.

[0084] According to a preferred embodiment of the present invention, prior to the depressurization treatment of the first stream, the first stream is subjected to a cooling treatment to reduce the temperature of the first stream, thereby reducing the vapor phase volume of the second liquid separation tank and the load on the compressor.

[0085] According to a preferred embodiment of the present invention, after the first stream is depressurized, the first stream is subjected to a cooling process to reduce the temperature of the first stream, thereby reducing the vapor phase volume of the second liquid separation tank and the load on the compressor.

[0086] According to the present invention, specifically, the cooling treatment is not particularly limited, and generally, a cooler is used for cooling, and preferably, the temperature of the first stream is 5 to 40°C, preferably 5 to 15°C.

[0087] Step (4) Second gas-liquid separation of the depressurized first stream and desorption of methane from the second liquid phase. According to a preferred embodiment of the present invention, the first stream after cooling and depressurization is fed to a second liquid separation tank for second gas-liquid separation to obtain a second gas phase and a second liquid phase, the second gas phase is returned to the inlet or interstage of the compressor, and the second liquid phase is subjected to methane desorption; wherein the second gas phase is mainly composed of light components having C2 or lighter components, and the second liquid phase is mainly composed of heavy components having C2 or heavier components.

[0088] In the present invention, the second liquid phase is subjected to methane desorption in a methane desorption tower, the obtained desorbed gas is returned to the inlet / interstage of the compressor or discharged to the outside, and the rich absorbent is subjected to absorbent desorption separation, where the desorbed gas is mainly composed of light components such as methane, and the rich absorbent is mainly composed of absorbent containing C2 and C3 components.

[0089] In the present invention, the second gas phase and the desorbed gas are returned to the inlet or interstage of the compressor, and the return position can be determined according to the pressure of the raw methane-containing industrial gas, the interstage pressure of the compressor and the pressure of the methane desorption tower. While ensuring that the desorbed gas discharged from the top of the methane desorption tower can be compressed by the compressor, the energy consumption of the compressor shall be saved as much as possible.

[0090] According to the present invention, preferably, methane desorption is carried out in a methane desorption tower; more preferably, the number of theoretical plates of the methane desorption tower is 20-50, the operating pressure of the methane desorption tower is 0.5-2.4 MPaG, the tower top temperature of the methane desorption tower is 10-40°C, and the tower kettle temperature of the methane desorption tower is 35-100°C.

[0091] In a preferred embodiment, the operating pressure of the methane desorption tower is 1.0 to 1.9 MPaG.

[0092] In a preferred embodiment, the temperature at the top of the methane desorption tower is 10 to 20°C.

[0093] In a preferred embodiment, the tower kettle temperature of the methane desorption tower is 40 to 75°C.

[0094] Preferably, the methane desorption tower is operated at low pressure to distill off the methane in the second liquid phase at little cost, thereby reducing the methane content in the enriched gas. The rich absorbent discharged from the tower kettle of the methane desorption tower is subjected to an absorbent desorption process to obtain a lean absorbent.

[0095] Preferably, the heat source of the tower kettle of the methane desorber is provided by the reboiler of the methane desorber, and the heat source of the reboiler of the methane desorber is a process stream. Specifically, the process stream is at least one selected from the group consisting of an absorbent, a rich absorbent, and a lean absorbent, and is preferably a lean absorbent.

[0096] Step (5) Desorption and separation of rich absorbent According to the present invention, desorption separation is preferably carried out in a desorption tower, and more preferably the number of theoretical plates of the desorption tower is 20 to 50, the operating pressure of the desorption tower is 1 to 2.8 MPaG, the tower top temperature of the desorption tower is 15 to 70°C, and the tower kettle temperature of the desorption tower is 90 to 200°C.

[0097] According to a particular embodiment of the invention, the rich absorbent is desorbed and separated in a desorption tower, an enriched gas composed mainly of C2 and C3 components is recovered from the top of the desorption tower, the lean absorbent is discharged from the tower kettle of the desorption tower to provide heat for the tower kettle of the methane desorption tower, and at least a portion of the second stream obtained after heat exchange of the lean absorbent is returned into the absorbent and mixed.

[0098] Preferably, a portion of the second stream obtained after the heat exchange of the lean absorbent is sent out of the boundary region as a light hydrocarbon component, and the remaining portion is returned to and mixed in the absorbent, where the light hydrocarbon component is at least one selected from the group consisting of C4 and C5 hydrocarbons.

[0099] According to the method of the present invention, the enriched gas containing C2 and C3 components comprises primarily methane, C2 components, C3 components, C4 or heavier components, and water.

[0100] Preferably, based on the total volume of enriched gas, the methane content is 0-5 vol.%, preferably 0-2 vol.%; the C2 component content is 30-70 vol.%, preferably 40-60 vol.%; the C3 component content is 20-70 vol.%, preferably 30-60 vol.%; the C4 or heavier component content is 0-20 vol.%, preferably 0-10 vol.% and the water content is 0-0.5 vol.%.

[0101] Compared with the conventional shallow-cooled oil absorption process, the method of the present invention can achieve a recovery rate of about 95% or more of C2 components or C2 and C3 components, and can reduce the total energy consumption of the device by about 10% to 30%.

[0102] The process of the present invention may further include recovery of C4 components, including butanes and / or butenes.

[0103] According to the present invention, the two gas-liquid separation steps are suitable for the recovery of heavier methane-containing industrial gases, such as dry gas. It will be understood that by adding a gas-liquid separation step based on the method for the recovery of C2 components or C2 and C3 components according to the present invention, it is suitable for the treatment of heavier methane-containing industrial gases, thereby further recovering C4 components as required. It will be understood that depending on the amount of heavy components in the methane-containing industrial gas, the gas-liquid separation step can be increased or decreased, and combined with the absorption step and the methane desorption step to recover C2 to C4 components as required.

[0104] In a second aspect, the present invention provides an apparatus for recovering C2 components in a methane-containing industrial gas, the apparatus comprising a compressor, a cooler, a liquid separation tank, an absorber, a methane desorption tower and a desorption tower; the compressor is connected to a pipeline of methane-containing industrial gas, such as dry gas, the compressor, the cooler and the liquid separation tank being connected in series; the bottom of said absorption tower is connected to the top of said liquid separation tank and said cooler respectively to countercurrently contact the gas phase discharged from the top of said liquid separation tank with an absorbent, and an absorption tail gas is discharged from the top of said absorption tower, and an absorption rich liquid is discharged from a tower kettle of said absorption tower and returned to said cooler; The methane desorption tower has its upper, top and bottom connected to the bottom of the liquid separation tank, the compressor and the middle part of the desorption tower, respectively, for desorption of methane in liquid phase discharged from the bottom of the liquid separation tank after depressurization; the desorbed gas is discharged from the top of the methane desorption tower and returned to the inlet or interstage of the compressor or discharged to the outside; the rich absorbent is discharged from the tower kettle of the methane desorption tower and then passed through the middle part of the desorption tower for desorption separation; The desorption tower has its bottom connected to the top of the absorption tower, lean absorbent is discharged from the tower kettle of the desorption tower and returned to the top of the absorption tower, and enriched gas containing C2 components, such as C2 and C3 components, is recovered from the top of the desorption tower.

[0105] According to the present invention, preferably, the apparatus further includes a methane desorption tower reboiler; the methane desorption tower reboiler is respectively connected to the bottom of the desorption tower, the lower and bottom parts of the methane desorption tower, and the top of the absorption tower, so as to provide heat for the tower kettle of the methane desorption tower by using lean absorbent discharged from the tower kettle of the desorption tower, and at least a part of the stream obtained after heat exchange of the lean absorbent is returned to the top of the absorption tower.

[0106] Preferably, the methane desorber reboiler is also connected to a post-treatment unit, which is used to send a part of the stream obtained after heat exchange of the lean absorbent discharged from the methane desorber reboiler out of the boundary region as a light hydrocarbon component for post-treatment, and the remaining part is returned to the top of the absorber.

[0107] Preferably, the light hydrocarbon component is at least one selected from the group consisting of C3, C4 and C5 hydrocarbons.

[0108] Preferably, the upper part of the methane desorption tower is 1 / 20 to 1 / 5 of the methane desorption tower.

[0109] Preferably, the lower part of the methane desorption tower is 4 / 5 to 5 / 6 of the methane desorption tower.

[0110] Preferably, the intermediate portion of the desorption tower is 1 / 6 to 2 / 3 of the desorption tower.

[0111] The device according to the invention is also capable of recovering C3 components, preferably said C3 components comprising propane and / or propylene.

[0112] The device according to the invention is also capable of recovering C4 components, preferably said C4 components comprising butanes and / or butenes.

[0113] In a third aspect, the present invention provides an apparatus for recovering C2 components in a methane-containing industrial gas, the apparatus comprising a compressor, a cooler, a first liquid separation tank, an absorption tower, a second liquid separation tank, a methane desorption tower, and a desorption tower; the compressor is connected to a pipeline of methane-containing industrial gas, such as dry gas, and the compressor, the cooler and the first liquid separation tank are connected in series; the bottom of the absorption tower is connected to the top of the first liquid separation tank and the middle part of the second liquid separation tank, respectively, for contacting the first gas phase discharged from the top of the first liquid separation tank with an absorbent in countercurrent flow; the absorption tail gas and the absorption rich liquid are discharged from the top of the absorption tower and the tower kettle, respectively; the mixture of the absorption rich liquid and the first liquid phase discharged from the bottom of the first liquid separation tank or the absorption rich liquid is used as a first stream; the first stream is depressurized and then passed to the middle part of the second liquid separation tank for second gas-liquid separation; the second liquid separation tank has its top and bottom connected to the compressor and the top of the methane desorption tower, respectively, a second gas phase is discharged from the top of the second liquid separation tank and returned to the inlet or interstage of the compressor, and a second liquid phase is discharged from the bottom of the second liquid separation tank and passed to the top of the methane desorption tower for methane desorption; the top and bottom of the methane desorption tower are connected to the compressor and the intermediate section of the desorption tower, respectively; the desorbed gas is discharged from the top of the methane desorption tower and returned to the inlet or interstage of the compressor or discharged to the outside; the rich absorbent is discharged from the tower kettle of the methane desorption tower and passed to the intermediate section of the desorption tower for desorption separation; The desorption tower has its bottom connected to the top of the absorption tower, lean absorbent is discharged from the tower kettle of the desorption tower and returned to the top of the absorption tower, and enriched gas containing C2 components, such as C2 and C3 components, is recovered from the top of the desorption tower.

[0114] According to the present invention, preferably, the apparatus further comprises a methane desorption tower reboiler; the methane desorption tower reboiler is connected to the bottom of the desorption tower, the lower and bottom parts of the methane desorption tower, and the top of the absorption tower, respectively, to provide heat for the tower kettle of the methane desorption tower by using the lean absorbent discharged from the tower kettle of the desorption tower, and at least a part of the (second) stream obtained after heat exchange of the lean absorbent is returned to the top of the absorption tower.

[0115] Preferably, the methane desorber reboiler is also connected to a work-up unit, which is used to send out a part of the (second) stream obtained after heat exchange of the lean absorbent discharged from the methane desorber reboiler outside the boundary region as a light hydrocarbon component for work-up, and the remaining part is returned to the top of the absorber.

[0116] Preferably, the light hydrocarbon component is at least one selected from the group consisting of C4 and C5 hydrocarbons.

[0117] Preferably, the middle part of the second liquid separation tank is 1 / 3 to 2 / 3 of the second liquid separation tank.

[0118] Preferably, the upper part of the methane desorption tower is 1 / 20 to 1 / 5 of the methane desorption tower.

[0119] Preferably, the lower part of the methane desorption tower is 4 / 5 to 5 / 6 of the methane desorption tower.

[0120] Preferably, the intermediate portion of the desorption tower is 1 / 6 to 2 / 3 of the desorption tower.

[0121] The device according to the invention is also capable of recovering C3 components, preferably said C3 components comprising propane and / or propylene.

[0122] The apparatus according to the present invention is also capable of recovering C4 components, preferably the C4 components include butanes and / or butenes.

[0123] The apparatus for recovering C2 components in methane-containing industrial gas, such as dry gas, provided by the present invention will be described in detail by referring to FIG. 1. The apparatus includes a compressor 2, a cooler 3, a liquid separation tank 4, an absorption tower 5, a methane desorption tower 7 and a desorption tower 9. The compressor 2, the cooler 3 and the liquid separation tank 4 are connected in sequence; the compressor 2 is connected to a pipeline of methane-containing industrial gas 1, such as refinery dry gas; the absorption tower 5 has its bottom connected to the top of the liquid separation tank 4 and the cooler 3, respectively, to contact the gas phase generated by the liquid separation tank with the absorbent in countercurrent flow; the absorption tail gas 14 is discharged from the top of the absorption tower 5; the absorption rich liquid is discharged from the tower kettle of the absorption tower 5, pressurized by the absorption tower kettle liquid pump 6, and then returned to the cooler 3; the methane desorption tower 7 is connected to the liquid separation tank 4 after depressurization, and the liquid separation tank 4 is connected to the top of the absorption tower 5 and the cooler 3 ... For liquid-phase methane desorption, its top, top and bottom are connected to the bottom of the liquid separation tank 4, the compressor 2 and the desorption tower 9, respectively; the desorbed gas is discharged from the top of the methane desorption tower 7 and returned to the compressor 2; the rich absorbent is discharged from the tower kettle of the methane desorption tower 7, pressurized by the absorbent pump 8, and then passed to the middle part of the desorption tower 9 for desorption separation; the desorption tower 9 has its bottom connected to the top of the absorption tower 5; the lean absorbent is discharged from the tower kettle of the desorption tower and returned to the top of the absorption tower 5; and the enriched gas 10 containing C2 components is recovered from the top of the desorption tower 9.

[0124] According to a preferred embodiment of the present invention, the apparatus further includes a methane desorption tower reboiler 15; the methane desorption tower reboiler 15 is respectively connected to the bottom of the desorption tower 9, the lower and bottom parts of the methane desorption tower 7, and the top of the absorption tower 5, so as to provide heat for the tower kettle of the methane desorption tower 7 by using the lean absorbent discharged from the tower kettle of the desorption tower 9, and a part of the stream 13 obtained after the heat exchange of the lean absorbent is sent out of the boundary region as the light hydrocarbon component 12 for post-treatment, and the remaining part is returned to the top of the absorption tower 5.

[0125] The apparatus for recovering C2 components in methane-containing industrial gas, such as dry gas, provided by the present invention will be described in detail by referring to Fig. 2. The apparatus includes a compressor 2, a cooler 3, a first liquid separation tank 4, an absorption tower 5, a second liquid separation tank 7, a methane desorption tower 8 and a desorption tower 11; the compressor 2, the cooler 3 and the first liquid separation tank 4 are connected in series, and the compressor 2 is connected to a methane-containing industrial gas 1, such as refinery dry gas; the absorption tower 5 has its bottom connected to the top and bottom of the first liquid separation tank 4, so as to contact the first gas phase discharged from the top of the first liquid separation tank 4 with the absorbent in countercurrent flow. and the middle part of the second liquid separation tank 7, respectively; the absorption tail gas 15 is discharged from the top of the absorption tower 5, and the absorption rich liquid is discharged from the tower kettle of the absorption tower 5 and mixed with the first liquid phase discharged from the bottom of the first liquid separation tank 4 to obtain a first stream; the second liquid separation tank 7 has its top and bottom connected to the compressor 2 and the methane desorption tower 5 for second gas-liquid separation of the depressurized first stream after cooling by the desorption tower feed cooler 6. The second gas phase is discharged from the top of the second liquid separation tank 7 and returned to the compressor 2, and the second liquid phase is discharged from the bottom of the second liquid separation tank 7 and passed to the top of the methane desorption tower 8; the top and bottom of the methane desorption tower 8 are connected to the compressor 2 and the middle part of the desorption tower 11, respectively, for the methane desorption of the second liquid phase discharged from the bottom of the second liquid separation tank 7, and the desorbed gas is discharged from the top of the methane desorption tower 8. and returned to the compressor 2; the rich absorbent is discharged from the tower kettle of the methane desorption tower 8, pressurized by the rich absorbent pump 10, and passed to the middle part of the desorption tower 11; the desorption tower 11 has its bottom connected to the top of the absorption tower 5 for desorption and separation of the rich absorbent discharged from the tower kettle of the methane desorption tower 8, the enriched gas 13 containing C2 components is recovered from the top of the desorption tower 11, and the lean absorbent is discharged from the tower kettle of the desorption tower 11 and returned to the top of the absorption tower 5.

[0126] According to a preferred embodiment of the present invention, the apparatus further includes a methane desorption tower reboiler 9, which is respectively connected to the lower and bottom of the methane desorption tower 8 and the top of the absorption tower 5, for providing heat for the tower kettle of the methane desorption tower 8 by using the lean absorbent discharged from the tower kettle of the desorption tower 11, and a part of the second stream 16 obtained after the heat exchange of the lean absorbent is sent out of the boundary region as the light hydrocarbon components 14 for post-treatment, and the remaining part is returned to the top of the absorption tower 5.

[0127] Compared with the prior art, the advantages and beneficial effects of the method and apparatus for recovering C2-C4 components (including but not limited to C2 components, or C2 and C3 components, or C2, C3 and C4 components) in methane-containing industrial gases provided by the present invention include, but are not limited to: (1) By adopting C2-C4 component absorption at high pressure, methane desorption and desorption separation at low pressure, the present invention not only reduces the amount of absorbent and reduces the energy consumption of absorbent desorption, but also reduces the load of the methane desorption tower reboiler and the tower kettle temperature of the methane desorption tower due to the relative volatility improvement between C1-C5 hydrocarbon components under low pressure. As a result, the methane desorption tower reboiler only needs the process stream (lean absorbent from the desorption tower kettle) in the equipment as a heat source, which greatly saves the steam consumption and energy consumption of the equipment.

[0128] (2) The C4 and / or C5 fraction absorption process and the methane desorption process are carried out independently in two columns, with little mutual influence and no backmixing. The absorption process and the methane desorption process are operated under ideal conditions, respectively, i.e., high pressure and low temperature are favorable for absorption, the absorbent is used in small amounts, and the throughput of the distillation column is small; low pressure is favorable for the distillation of methane.

[0129] (3) The load of the methane desorber reboiler decreases with the decrease of the operating pressure, so that the pressure of the methane desorber can be controlled with respect to returning the desorbed gas at the top of the methane desorber to the inlet of the compressor or between stages. As a result, the methane desorber reboiler only consumes the waste heat of the lean absorbent in the desorber kettle, and at the same time, the energy consumption of the compressor is increased to a minimum, thereby minimizing the total energy consumption of the unit.

[0130] (4) The process stream in the unit is used as the heat source for the methane desorber reboiler. When the feed to the methane desorber is varied, the change in the reboiler load has little effect on the total energy consumption of the unit, which increases the flexibility of the unit's operation.

[0131] (5) The C2 to C4 components in the methane-containing industrial gas are absorbed in an absorption tower by using a C4 fraction and / or a C5 fraction as an absorbent, and the absorbent raw material is easily available and low cost.

[0132] (6) The process flow has a minimum temperature of 5-15°C for compression and cooling, absorption and rectification operations, does not require a propylene refrigeration compressor, and can use a lithium bromide refrigeration unit to provide cooling capacity, does not require drying equipment, has low investment, simple operation, and low energy consumption.

[0133] (5) The recovery rate of C2 to C4 components can reach 95% or more, and the obtained enriched gas containing C2 components, enriched gas containing C2 and C3 components, or enriched gas containing C2, C3 and C4 components can be used, for example, as a raw material for an ethane cracking furnace or a gas separation unit.

[0134] (6) The absorption-rich liquid in the absorption tower is fully contacted with the compressed gas in the liquid separation tank, and pre-absorbs part of the C2-C4 and other heavy components therein, thereby reducing the amount of gas phase entering the absorption tower, reducing the amount of absorbent in the absorption tower, and saving energy consumption.

[0135] (7) Before the first stream obtained after mixing the first liquid phase and the absorption rich liquid is subjected to methane desorption, the second liquid separation tank is arranged to pre-separate the gas phase flashed from the first stream in the depressurization process, thereby preventing the whole gas phase separation process from proceeding in the methane desorption tower, thereby saving 50% of the gas phase space required by the methane desorption tower and saving equipment investment.

[0136] [Example] In order to facilitate understanding of the present invention, the present invention will be described in detail below with reference to specific examples.

[0137] Example 1 and Comparative Example 1 In Example 1 and Comparative Example 1, refinery dry gas was used as the feedstock, which was treated by the method of the present invention and a typical shallow oil absorption process, respectively, to recover C2 components. The composition of the dry gas from the refinery and the process parameters are shown in Table 1.

[0138] [Table 1]

[0139] Example 1 Example 1 was used to illustrate the method and apparatus for dry gas oil absorption and separation to recover C2 components of the present invention.

[0140] The apparatus includes a compressor 2, a cooler 3, a liquid separation tank 4, an absorption tower 5, a methane desorption tower 7, a desorption tower 9, and a methane desorption tower reboiler 15; A compressor 2, a cooler 3 and a liquid separation tank 4 are connected in series; the compressor 2 is connected to a pipeline of refinery dry gas 1; The absorber 5, the bottom of which is connected to the top of the liquid separation tank 4 and the cooler 3 respectively, is used to contact the gas phase generated by the liquid separation tank with the absorbent in countercurrent flow, the absorption tail gas 14 is discharged from the top of the absorber 5, and the absorption rich liquid is discharged from the tower kettle of the absorber 5 and returned to the cooler 3 after being pressurized by the absorber kettle liquid pump 6; The methane desorption tower 7 has its upper, top and bottom connected to the bottom of the liquid separation tank 4, the compressor 2 and the desorption tower 9 respectively, which is used for desorption of the liquid phase methane produced by the liquid separation tank 4 after depressurization, the desorbed gas is discharged from the top of the methane desorption tower 7 and returned to the compressor 2, the rich absorbent is discharged from the tower kettle of the methane desorption tower 7 and entered into the middle part of the desorption tower 9 after being pressurized by the rich absorbent pump 8; The desorption tower 9 is connected at its bottom to the methane desorption tower reboiler 15, and is used for desorption and separation of the rich absorbent discharged from the tower kettle of the methane desorption tower 7, the enriched gas 10 containing the C2 component is recovered from the top of the desorption tower 9, and the lean absorbent is discharged from the tower kettle of the desorption tower 9 and supplied as a heat source for the methane desorption tower reboiler 15; The methane desorption tower reboiler 15 is connected to the lower and bottom of the methane desorption tower 7 and the top of the absorption tower 5, respectively, and is used to provide heat for the tower kettle of the methane desorption tower 7 using the lean absorbent discharged from the tower kettle of the desorption tower 9, and a part of the stream 13 obtained after the heat exchange of the lean absorbent is sent out from the boundary region as the light hydrocarbon component 12 for post-treatment, and the remaining part is returned to the top of the absorption tower 5.

[0141] The method included the following steps: (1) Refinery dry gas with a pressure of 1.2 MPaG was fed into the compressor. After three-stage compression processing, the compressed dry gas had a pressure of 3.9 MPaG. After combining with the absorption rich liquid (118 t / h) of the absorption tower, the pressurized dry gas was cooled to 15°C through a cooler with 7°C cooling water prepared by a lithium bromide absorption chiller, and sent to the liquid separation tank for gas-liquid separation. The gas phase at the top of the liquid separation tank was sent to the bottom of the absorption tower, and the liquid phase at the bottom of the liquid separation tank was depressurized to 1.5 MPaG, and then sent to the methane desorption tower for processing.

[0142] (2) In the absorber, refinery mixed butane was used as the absorbent (absorbent circulation rate was 105 t / h) and injected from the top of the tower to absorb the C2 fraction and heavier components in the feed gas. The absorber had 20 theoretical plates, an operating pressure of 3.8 MPaG, a tower top temperature of 17°C, and a tower kettle temperature of 22°C. The liquid phase in the absorber kettle was pressurized to 4 MPaG by the absorber kettle liquid pump and combined with the gas phase from the compressor outlet before returning to the cooler. The unabsorbed tail gas at the top of the absorber was pumped out of the boundary zone and sent to an absorbent recovery unit outside the boundary zone.

[0143] (3) The liquid phase at the bottom of the liquid separation tank was depressurized to 1.8 MPaG and fed to the top of the methane desorption tower under the action of pressure difference to remove light components such as methane in the tower feed. The methane desorption tower had a theoretical plate number of 30, an operating pressure of 1.5 MPaG, a tower top temperature of 13°C, and a tower kettle temperature of 67°C. The gas phase at the top of the methane desorption tower was returned to the inlet of the compressor, and the material discharged from the tower kettle of the methane desorption tower was pressurized to 2.5 MPaG by the rich absorbent pump and sent to the middle part of the desorption tower.

[0144] (4) The desorption tower had a theoretical number of 40, an operating pressure of 2.0 MPaG, a tower top temperature of 56°C, and a tower kettle temperature of 109°C. The desorption tower was heated by low-pressure steam, and an enriched gas containing C2 components was obtained at the top of the tower and sent to the ethane cracking furnace as a feedstock; the lean absorbent in the desorption tower kettle (having a temperature of 109°C and pressurized to 4.4 MPaG by the absorbent circulation pump) provided heat for the methane desorption tower reboiler, and the stream obtained after heat exchange was returned to the absorption tower for recycling; at the same time, a stream of light hydrocarbon products mainly composed of C3-C5 hydrocarbons was withdrawn and sent out of the boundary region and sent to the cracking furnace of the ethylene facility as a feedstock.

[0145] In the method of this example, an enriched gas containing C2 components and light hydrocarbon components was obtained, and its composition and process parameters are shown in Table 2. Here, the C2 recovery rate was 98.3%.

[0146] [Table 2]

[0147] Comparative Example 1 The refinery dry gas in Table 1 was recovered by using a typical shallow oil absorption process in CN109553504A. The method adopted in Comparative Example 1 was mainly different from Example 1 in that the absorption by C4 absorbent and the methane desorption process were carried out in one absorption-steaming tower, and the operating pressures were close. Since the methane desorption method involved a relatively high pressure, the tower kettle temperature was relatively high, and low-pressure steam was used as the heat source of the tower kettle reboiler in the methane desorption process.

[0148] In the method of Comparative Example 1, an enriched gas containing C2 components was obtained, and its composition is shown in Table 3. Here, the C2 recovery rate was 98.3%. The comparison data between the present invention and the technical solutions of the typical cryogenic oil absorption process and cryogenic separation method in the prior art are shown in Table 4.

[0149] [Table 3]

[0150] [Table 4]

[0151] As can be seen from Tables 2-4, the minimum temperature of the process stream of the present invention is 5-15°C, and neither low-temperature level propylene cooling capacity nor propylene cooling equipment and drying equipment are required, so the equipment investment is low.Compared with the conventional shallow-cooling oil absorption process, under the condition of obtaining the same high C2 recovery rate, by reducing the pressure of the methane desorption process, the present invention can greatly reduce the energy consumption required for the process, and at the same time, lower the grade of the heat medium, and use the heat process stream in the device to provide all the heat of the methane desorption tower, thereby saving the consumption of low-pressure steam introduced from outside the device, and reducing the total energy consumption of the device by 17.8%.

[0152] Example 2 and Comparative Example 2 In Example 2 and Comparative Example 2, refinery dry gas was used as the raw material and was processed by the method of the present invention and a typical shallow oil absorption process, respectively, to recover C2 and C3 components. The composition and process parameters of the dry gas from the refinery are shown in Table 5.

[0153] [Table 5]

[0154] Example 2 Example 2 was used to illustrate the method and apparatus for dry gas oil absorption and separation to recover C2 and C3 components of the present invention.

[0155] The apparatus includes a compressor 2, a cooler 3, a first liquid separation tank 4, an absorption tower 5, a second liquid separation tank 7, a methane desorption tower 8, a methane desorption tower reboiler 9, and a desorption tower 11; A compressor 2, a cooler 3 and a first liquid separation tank 4 are connected in series, and the compressor 2 is connected to the refinery dry gas 1; the absorber tower 5, the bottom of which is connected to the top of the first liquid separation tank 4 and the middle of the second liquid separation tank 7 respectively, is used to contact the first gas phase discharged from the top of the first liquid separation tank 4 with the absorbent in countercurrent flow, the absorption tail gas 15 is discharged from the top of the absorber tower 5, and the absorption rich liquid is discharged from the tower kettle of the absorber tower 5 and mixed with the first liquid phase discharged from the bottom of the first liquid separation tank 4 to obtain a first stream; the second liquid separation tank 7, the top and bottom of which are connected to the compressor 2 and the top of the methane desorption tower 8, respectively, is used for a second gas-liquid separation of the depressurized first stream after cooling by the desorption tower feed cooler 6, the second gas phase is discharged from the top of the second liquid separation tank 7 and returned to the compressor 2, and the second liquid phase is discharged from the bottom of the second liquid separation tank 7 and enters the top of the methane desorption tower 8; The methane desorption tower 8 has its top and bottom connected to the compressor 2 and the middle part of the desorption tower 11, respectively, and is used for the methane desorption of the second liquid phase discharged from the bottom of the second liquid separation tank 7, the desorbed gas is discharged from the top of the methane desorption tower 8 and returned to the compressor 2, and the rich absorbent is discharged from the tower kettle of the methane desorption tower 8, pressurized by the rich absorbent pump 10, and enters the middle part of the desorption tower 11; The desorption tower 11 is connected at its bottom to the methane desorption tower reboiler 9 and is used for desorption and separation of the rich absorbent discharged from the tower kettle of the methane desorption tower 8, the enriched gas 13 mainly composed of C2 and C3 components is recovered from the top of the desorption tower 11, and the lean absorbent is discharged from the tower kettle of the desorption tower, pressurized by the absorbent circulation pump 12, and used as the heat source of the methane desorption tower reboiler 9; The methane desorption tower reboiler 9 is connected to the lower and bottom of the methane desorption tower 8 and the top of the absorption tower 5, respectively, and is used to provide heat for the tower kettle of the methane desorption tower 8 using the lean absorbent discharged from the tower kettle of the desorption tower 11, and a part of the second stream 16 obtained after heat exchange is sent out of the boundary region as the light hydrocarbon component 14 for post-treatment, and the remaining part is returned to the top of the absorption tower 5.

[0156] The method included the following steps: (1) Refinery dry gas with a pressure of 1 MPaG was entered into the compressor. After two-stage compression processing, the compressed dry gas had a pressure of 3.7 MPaG. The pressurized dry gas was passed through a cooler and cooled to 15°C with 7°C cooling water prepared by a lithium bromide absorption cooler, and sent to the first liquid separation tank for first gas-liquid phase separation. The first gas phase discharged from the top of the first liquid separation tank entered the bottom of the absorption tower, and the first liquid phase discharged from the bottom of the first liquid separation tank was depressurized to 1.7 MPaG, and then sent to the methane desorption tower for processing.

[0157] (2) In the absorption tower, refinery n-butane was used as the absorbent (the circulation amount of the absorbent was 120t / h) and injected from the top of the tower to absorb the C2 and C3 fractions and heavier components in the dry gas. The absorption tower had a theoretical plate number of 20, an operating pressure of 3.6MPaG, a tower top temperature of 17°C, and a tower kettle temperature of 27°C. The unabsorbed tail gas at the top of the absorption tower was sent to the fuel gas pipe network, and the absorption rich liquid in the tower kettle of the absorption tower was depressurized to 1.7MPaG, and then mixed with the first liquid phase to obtain a first stream.

[0158] (3) The first stream was cooled to 15°C in the desorption tower feed cooler and then sent to a second liquid separation tank for a second gas-liquid separation. The second gas phase, composed mainly of light components below C2, was returned to the inlet of the dry gas compressor.

[0159] (4) To remove light components such as methane in the second liquid phase, the second liquid phase entered the top of the methane desorption tower, and the desorbed gas at the top of the methane desorption tower was returned to the inlet of the dry gas compressor. The methane absorption tower had a theoretical plate number of 30, an operating pressure of 1.5 MPaG, a tower top temperature of 15°C, and a tower kettle temperature of 55°C. The methane desorption tower reboiler selected the lean absorbent from the desorption tower kettle (having a temperature of 105°C and pressurized by the absorbent circulation pump) as the heat source of the methane desorption tower reboiler.

[0160] (5) The rich absorbent discharged from the tower kettle of the methane desorption tower was pressurized by the rich absorbent pump and sent to the middle part of the desorption tower. The desorption tower had a theoretical number of 40, an operating pressure of 1.6 MPaG, a tower top temperature of 55°C, and a tower kettle temperature of 105°C. The desorption tower was heated by low-pressure steam, and a rich gas mainly composed of C2 and C3 components was obtained at the top of the tower and sent to the cracking furnace of the ethylene unit as a feedstock; the lean absorbent discharged from the tower kettle was pressurized by the absorbent circulation pump to provide heat for the methane desorption tower reboiler; then, at least a part of the second stream obtained after heat exchange was returned to the absorption tower for recycle; at the same time, a stream of light hydrocarbon products mainly composed of C4 and C5 was withdrawn and sent out of the boundary region and sent to the cracking furnace of the ethylene facility as a feedstock.

[0161] In the method of this example, an enriched gas mainly composed of C2 and C3 components and light hydrocarbon components was obtained, and its composition and process parameters are shown in Table 6. Here, the recovery rate of C2 and C3 components was 98.2%.

[0162] [Table 6]

[0163] Comparative Example 2 The refinery dry gas in Table 5 was recovered by using a typical shallow oil absorption process in CN106609161B. The method adopted in Comparative Example 2 was mainly different from Example 2 in that the absorption by C4 absorbent and the methane desorption process were carried out in one absorption-steaming tower, and the operating pressures were close. Since the methane desorption method involved a relatively high pressure, the corresponding tower kettle temperature was relatively high, and low-pressure steam was used as the heat source of the tower kettle reboiler in the methane desorption process.

[0164] In the method of Comparative Example 1, an enriched gas mainly composed of C2 and C3 components was obtained, and its composition is shown in Table 7. Here, the recovery rate of C2 and C3 components was 98.2%. The comparison data between the present invention and the technical solutions of the typical cryogenic oil absorption process and cryogenic separation method in the prior art are shown in Table 8.

[0165] [Table 7]

[0166] [Table 8]

[0167] As can be seen from Tables 6-8, the minimum temperature of the process stream of the present invention is 5-15°C, and neither low-temperature level propylene cooling capacity nor propylene cooling equipment and drying equipment are required, so the equipment investment is low.Compared with the conventional shallow-cooling oil absorption process, under the condition of obtaining the same high C2 and C3 recovery rate, by reducing the pressure of the methane desorption process, the present invention can greatly reduce the energy consumption required for the process, and at the same time, lower the grade of the heat medium, and use the heat process stream in the device to provide all the heat of the methane desorption tower, thereby saving the consumption of low-pressure steam introduced from outside the device, and reducing the total energy consumption of the device by 16.8%.

[0168] Compared with the traditional shallow-cooled oil absorption process, the present invention not only achieves high recovery rate of C2, or C2 and C3, but also enables the methane desorption tower reboiler to only require the process stream in the equipment (lean absorbent in the desorption tower kettle) as the heat source by adopting high-pressure absorption and low-pressure methane desorption, thereby reducing material consumption and greatly saving the consumption of steam and the total energy consumption of the equipment, which can be illustrated by examples.

[0169] Although various embodiments of the present invention have been described in detail above, the above description is merely illustrative, and the present invention is not limited thereto. Various modifications can be made to the technical solutions of the present invention, including combining various technical features in other suitable ways, without departing from the technical concept and scope of the present invention, and these modifications and combinations should also be considered as the contents disclosed in the present invention, and all of them belong to the protection scope of the present invention. [Brief description of the drawings]

[0170] [Figure 1] FIG. 1 is a schematic diagram of an apparatus for recovering C2 components in a methane-containing industrial gas, such as dry gas, provided by the present invention: Key to symbols: 1. Raw methane-containing industrial gas (such as dry gas); 2. Compressor; 3. Cooler; 4. Liquid separation tank; 5. Absorption tower; 6. Absorption tower kettle liquid pump; 7. Methane desorption tower; 8. Rich absorbent pump; 9. Desorption tower; 10. Enriched gas containing C2 components; 11. Absorbent circulation pump; 12. Light hydrocarbon components; 13. Stream; 14. Absorption tail gas; 15. Methane desorption tower reboiler. [Diagram 2]FIG. 2 is a schematic diagram of an apparatus for recovering C2 components in a methane-containing industrial gas, such as dry gas, provided by the present invention: Key to symbols: 1. Raw methane-containing industrial gas (such as dry gas); 2. Compressor; 3. Cooler; 4. First liquid separation tank; 5. Absorption tower; 6. Desorption tower feed cooler; 7. Second liquid separation tank; 8. Methane desorption tower; 9. Methane desorption tower reboiler; 10. Rich absorbent pump; 11. Desorption tower; 12. Absorbent circulation pump; 13. Enriched gas containing C2 components; 14. Light hydrocarbon components; 15. Absorption tail gas; 16. Second stream.

Claims

1. A method for recovering C2 components in a methane-containing industrial gas, the method comprising the steps of: (1) compressing the methane-containing industrial gas and cooling the resulting compressed gas prior to gas-liquid separation to obtain a gas phase and a liquid phase; (2) contacting the gas phase with an absorbent to absorb the C2 components to obtain an absorbed tail gas and an absorbed rich liquid; Here, the absorption rich liquid is returned to and mixed with the compressed gas, or The mixture of the absorption rich liquid and the liquid phase obtained in step (1) or the absorption rich liquid is used as a first stream; (3) reducing the pressure of the liquid phase obtained in step (1) or the first stream obtained in step (2); (4) subjecting the reduced pressure stream in step (3) to methane desorption to obtain desorbed gas and rich absorbent, and returning the desorbed gas to the compression in step (1) or venting it to the outside; or subjecting the reduced pressure stream in step (3) to a second gas-liquid separation to obtain a second gas phase and a second liquid phase, returning the second gas phase to the compression in step (1), subjecting the second liquid phase to methane desorption to obtain a desorbed gas and a rich absorbent, and returning the desorbed gas to the compression in step (1) or discharging it to the outside; (5) The rich absorbent is subjected to desorption separation to obtain a lean absorbent and an enriched gas containing C2 components, and the lean absorbent is returned to and mixed with the absorbent in step (2).

2. 10. The method of claim 1, wherein the methane-containing industrial gases include dry gas, cracked gas, natural gas, and shale gas.

3. 3. The method according to claim 1 or 2, wherein in step (2), the absorption rich liquid is returned into and mixed with the compressed gas, and the liquid phase obtained in step (1) is depressurized and then subjected to methane desorption to obtain a desorbed gas and a rich absorbent.

4. The pressure of the compressed gas is 2.5 to 4.6 MPaG; said compression being a multi-stage compression; The method according to claim 3, wherein the cooling temperature is 5 to 40° C., the cooling uses a cooling medium having a temperature of 0° C. or higher, and the cooling medium is at least one selected from the group consisting of low-temperature water, circulating water, propylene, ammonia, and liquid nitrogen.

5. The absorption of the C2 components is carried out in an absorption tower; 4. The method of claim 3, wherein the parameters of the absorber tower include a theoretical number of 15 to 30, an operating pressure of 2.5 to 4.6 MPaG, a tower top temperature of 10 to 60°C, and a tower kettle temperature of 10 to 70°C.

6. The absorption of the C2 component is carried out in an absorption tower; 5. The method of claim 4, wherein the parameters of the absorber include a theoretical number of 15 to 30, an operating pressure of 2.5 to 4.6 MPaG, a column top temperature of 10 to 60°C, and a column kettle temperature of 10 to 70°C.

7. The methane desorption is carried out in a methane desorption tower; The parameters of the methane desorption column include a theoretical number of 20 to 50, an operating pressure of 0.5 to 2.4 MPaG, a column top temperature of 10 to 60° C., and a column kettle temperature of 35 to 90° C.; and The method according to any one of claims 3 to 6, wherein the pressure of the liquid phase after decompression is 0.8 to 3 MPaG.

8. The desorption separation is carried out in a desorption tower, 8. The process of claim 3, wherein the desorption column parameters include a theoretical number of 20 to 50, an operating pressure of 1 to 2.8 MPaG, a column top temperature of 25 to 70° C., and a column kettle temperature of 90 to 160° C.

9. 9. The method according to any one of claims 3 to 8, wherein the lean absorbent is used as a heat source for the methane desorption, and at least a portion of the stream obtained after heat exchange of the lean absorbent is returned into and mixed with the absorbent.

10. The method of any one of claims 1 to 9, wherein the method further comprises recovering C3 components, the C3 components comprising propane and / or propylene.

11. 3. The method according to claim 1 or 2, wherein the first stream obtained in step (2) is depressurized and then subjected to a second gas-liquid separation to obtain a second gas phase and a second liquid phase, and the second liquid phase is subjected to methane desorption to obtain a desorbed gas and a rich absorbent.

12. The pressure of the compressed gas is 2.5 to 5 MPaG; The compression is a multi-stage compression; The method according to claim 11, wherein the cooling temperature is 5 to 45° C., and the cooling uses a cooling medium having a temperature of 0° C. or higher, and the cooling medium is at least one selected from the group consisting of low-temperature water, circulating water, propylene, ammonia, and liquid nitrogen.

13. Absorption of C2 and C3 components is carried out in an absorption tower; The parameters of the absorption tower include a theoretical number of 15 to 30, an operating pressure of 2.5 to 5 MPaG, a tower top temperature of 10 to 30° C., and a tower kettle temperature of 10 to 60° C.; the pressure of the first stream after reduction in pressure is 0.5 to 2.4 MPaG; 13. The method according to claim 11 or 12, wherein before / after the depressurization of the first stream, the first stream is subjected to a cooling treatment, and the temperature of the first stream after cooling is from 5 to 40°C.

14. The methane desorption is carried out in a methane desorption tower; The parameters of the methane desorption tower include a theoretical number of 20 to 50, an operating pressure of 0.5 to 2.4 MPaG, a tower top temperature of 10 to 40° C., and a tower kettle temperature of 35 to 100° C.; The method according to any one of claims 11 to 13.

15. The desorption separation is carried out in a desorption tower, 15. The process of any one of claims 11 to 14, wherein the parameters of the desorption column include a number of theoretical stages of 20 to 50, an operating pressure of 1 to 2.8 MPaG, a column top temperature of 15 to 70°C, and a column kettle temperature of 90 to 200°C.

16. 16. The method according to any one of claims 11 to 15, wherein the lean absorbent is used as a heat source for the methane desorption, and at least a portion of the second stream obtained after heat exchange of the lean absorbent is returned into the absorbent.

17. 15. The method of claim 7 or 14, wherein the heat source for the tower kettle of the methane desorber is provided by a methane desorber reboiler, and the heat source for the methane desorber reboiler is a process stream; and the process stream is at least one selected from the group consisting of the absorbent, the rich absorbent, and the lean absorbent.

18. 18. The method according to any one of claims 1 to 17, wherein the absorbent is selected from a C4 cut and / or a C5 cut, the C4 cut comprising at least one selected from the group consisting of n-butane, isobutane and butenes, and the C5 cut comprising at least one selected from the group consisting of n-pentane, isopentane and neopentane.

19. 19. The method of any one of claims 1 to 18, wherein the method further comprises recovering C4 components, the C4 components comprising butanes and / or butenes.

20. 7. The method according to claim 6, wherein the temperature of the absorbent entering the tower is 40-50° C., the temperature of the gas phase entering the tower is 40° C., the cooling medium in step (1) is circulating water, and the tower top temperature of the absorption tower is 40-60° C.

21. 7. The method according to claim 6, wherein the temperature of the absorbent entering the tower is 5 to 20° C., the temperature of the gas phase entering the tower is 5 to 20° C., the cooling medium in step (1) is low temperature water, and the tower top temperature of the absorption tower is 10 to 30° C.

22. An apparatus for recovering C2 components in a methane-containing industrial gas, the apparatus including a compressor, a cooler, a liquid separation tank, an absorption tower, a methane desorption tower and a desorption tower; The compressor is connected to a pipeline of methane-containing industrial gas, and the compressor, the cooler and the liquid separation tank are connected in series; The bottom of the absorption tower is connected to the top of the liquid separation tank and the cooler, respectively, to countercurrently contact the gas phase discharged from the top of the liquid separation tank with the absorbent, and the absorption tail gas is discharged from the top of the absorption tower, and the absorption rich liquid is discharged from the tower kettle of the absorption tower and returned to the cooler; The methane desorption tower has its upper, top and bottom connected to the bottom of the liquid separation tank, the compressor and the middle part of the desorption tower, respectively, for desorption of methane in liquid phase discharged from the bottom of the liquid separation tank after depressurization; the desorbed gas is discharged from the top of the methane desorption tower and returned to the inlet or interstage of the compressor or discharged to the outside; the rich absorbent is discharged from the tower kettle of the methane desorption tower and then passed through the middle part of the desorption tower for desorption separation; The desorption tower has its bottom connected to the top of the absorption tower, lean absorbent is discharged from the tower kettle of the desorption tower and returned to the top of the absorption tower, and enriched gas containing C2 components, such as C2 and C3 components, is recovered from the top of the desorption tower.

23. An apparatus for recovering C2 components in a methane-containing industrial gas, the apparatus including a compressor, a cooler, a first liquid separation tank, an absorption tower, a second liquid separation tank, a methane desorption tower, and a desorption tower; The compressor is connected to a pipeline of methane-containing industrial gas, and the compressor, the cooler and the first liquid separation tank are connected in series; The bottom of the absorption tower is connected to the top of the first liquid separation tank and the middle part of the second liquid separation tank, respectively, for contacting the first gas phase discharged from the top of the first liquid separation tank with an absorbent in countercurrent flow; the absorption tail gas and the absorption rich liquid are discharged from the top of the absorption tower and the tower kettle, respectively; the mixture of the absorption rich liquid and the first liquid phase discharged from the bottom of the first liquid separation tank or the absorption rich liquid is used as a first stream; the first stream is depressurized and then passed to the middle part of the second liquid separation tank for second gas-liquid separation; the second liquid separation tank has its top and bottom connected to the compressor and the top of the methane desorption tower, respectively, a second gas phase is discharged from the top of the second liquid separation tank and returned to the inlet or interstage of the compressor, and a second liquid phase is discharged from the bottom of the second liquid separation tank and passed to the top of the methane desorption tower for methane desorption; The top and bottom of the methane desorption tower are connected to the compressor and the middle part of the desorption tower, respectively, the desorbed gas is discharged from the top of the methane desorption tower and returned to the inlet or interstage of the compressor or discharged to the outside, and the rich absorbent is discharged from the tower kettle of the methane desorption tower and passed to the middle part of the desorption tower for desorption separation; The desorption tower has its bottom connected to the top of the absorption tower, lean absorbent is discharged from the tower kettle of the desorption tower and returned to the top of the absorption tower, and enriched gas containing C2 components, such as C2 and C3 components, is recovered from the top of the desorption tower.

24. 24. The apparatus of claim 22 or 23, wherein the methane-containing industrial gases include dry gas, cracked gas, natural gas, and shale gas.

25. The apparatus further includes a methane desorber reboiler; the methane desorption tower reboiler is connected to the bottom of the desorption tower, the lower and bottom parts of the methane desorption tower, and the top of the absorption tower, respectively, to provide heat for the tower kettle of the methane desorption tower using lean absorbent discharged from the tower kettle of the desorption tower, and at least a portion of the stream obtained after heat exchange of the lean absorbent is returned to the top of the absorption tower; Apparatus according to any one of claims 22 to 24.

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