Method and apparatus for recovering c2-c4 components in methane-containing industrial gas

Abstract

Disclosed are a method and a device for recovering C2 components in methane-containing gas. The method comprises the following steps: (1) cooling a compressed methane-containing gas and performing gas-liquid separation; (2) absorbing C2 components by using an absorbent for gas to obtain a rich absorbing liquid; (3) refluxing the rich absorbing liquid to the compressed methane-containing gas or mixing the rich absorbing liquid with the liquid obtained in step (1) to obtain a mixture solution, and reducing the pressure on the mixture solultion or the rich absorbing liquid; (4) performing methane desorption on the pressure-reduced flow to obtain a rich absorbent, or performing secondary gas-liquid separation on the pressure-reduced flow, followed by methane desorption on the second liquid to obtain a rich absorbent; and (5) desorbing and separating the rich absorbent to obtain a lean absorbent and an enriched gas, and the lean absorbent is recycled and reused. The method has a high recovery rate of C2 (and above) components, as well as low overall energy consumption.

Description

Method and apparatus for recovering c2-c4 components from a methane-containing industrial gas TECHNICAL FIELD

[0001] The present invention relates to the technical field of methane desorption and recovery of C2-C4 components from a methane-containing industrial gas, including but not limited to the technical field of dry gas treatment. In particular, the present invention relates to a method and apparatus for recovering C2-C4 components from a methane-containing industrial gas, such as dry gas, and in particular to a method and apparatus for recovering carbon dioxide components from a methane-containing industrial gas, such as dry gas, and to a method and apparatus for recovering carbon dioxide and carbon trioxide components from a methane-containing industrial gas, such as dry gas. BACKGROUND

[0002] Currently, the methods for recovering carbon dioxide components (ethane, ethylene) from dry gas or for recovering carbon dioxide and carbon trioxide components from dry gas that have been industrialized mainly include:

[0003] (1) Cryogenic separation method, mature technology, high ethylene recovery rate and high purity, but requires a dryer and a propylene refrigeration device or an ethylene-propylene composite refrigeration device, large device investment and high energy consumption;

[0004] (2) Pressure swing adsorption method, simple operation, generally low energy consumption, but low product purity and low carbon dioxide component recovery rate, large device investment and land occupation when the scale of the raw dry gas treatment is large;

[0005] (3) Light oil absorption method, safe and reliable process flow, high carbon dioxide and carbon trioxide recovery rate, no requirement for sulfur content and water content in the raw gas, but the reboiler load of the absorption tower (or methane desorption tower) is large, and the low-pressure steam consumption of the entire process flow is large.

[0006] US10052581B1 discloses a method for recovering a steam cracking device raw material from FCC dry gas. The method first removes CO2, H2S, COS from the FCC dry gas by amine washing, and then removes alkyne by hydrogenation. After the above refining process, the FCC dry gas enters a pressure swing adsorption tower to remove light components such as methane and hydrogen therefrom, and finally obtains a steam cracking device raw material stream mainly composed of ethane and ethylene through a series of separation processes. Since the pressure swing adsorption tower may be operated at a condition below 0°C, in order to avoid icing, cooling and phase separation and dehydration and drying treatment are required before the dry gas enters the pressure swing adsorption tower, which requires large device investment.

[0007] CN101759516B discloses a method for separating refinery catalytic dry gas by oil absorption method, which comprises dry gas compression, absorption (re-absorption), desorption and other processes. Carbon five fraction or de-pentanizing oil is used as absorbent in the main absorption tower to absorb carbon two fraction and heavier components in the catalytic dry gas. The rich carbon five absorbent is sent to the desorption tower to obtain recovered C2 concentrated gas from the top of the desorption tower. The main absorption tower operates at a pressure of 3.5-5.5 MPaG and a tower bottom temperature of 95-115℃. The desorption tower operates at a pressure of 2-3 MPaG and a tower bottom temperature of 145-165℃, and low-pressure steam is used as heat source.

[0008] CN103159581B discloses a device for recovering carbon two in refinery dry gas by combined absorption method. It comprises a compressor, a pretreatment unit, a refinery dry gas cooling unit, an absorption unit and a rectification unit. The absorption unit comprises a gas-liquid separation tank, a carbon two absorption tower and a methane desorption tower. The rich absorbent that has absorbed carbon two components in the dry gas separates carbon two and absorbent components at the de-carbon two tower. The carbon two absorption tower operates at a pressure of 2.5-3.0 MPaG, the methane desorption tower operates at a pressure of 2.5-3.1 MPaG, and the de-carbon two tower operates at a pressure of 2.2-2.6 MPaG. The methane desorption tower needs to use a refinery heat source at about 120℃.

[0009] CN109553504A discloses a method and device for recovering refinery saturated dry gas by using shallow cold oil absorption technology. The method comprises: sequentially compressing and cooling the saturated dry gas and then sending it to a carbon four absorption tower for treatment to obtain gas phase and liquid phase which are sent to a gasoline absorption tower and a carbon four desorption tower respectively; recovering the gas phase obtained by treating the carbon four desorption tower as carbon two concentrated gas product, and returning most of the liquid phase obtained to the carbon four absorption tower for recycling; sending the liquid phase obtained by treating the gasoline absorption tower to a gasoline stabilizing tower for treatment, returning most of the liquid phase obtained to the gasoline absorption tower for recycling, and sequentially condensing and gas-liquid separating the gas phase obtained by treating the gasoline stabilizing tower to return the gas phase and liquid phase obtained to the inlet of the compressor and the gasoline stabilizing tower and the carbon four absorption tower respectively. Through two absorption-desorption processes, low-pressure steam is used as heat source.

[0010] CN106609161B discloses a method for separating refinery saturated dry gas, the saturated dry gas is subjected to phase separation after being compressed and cooled, the compressed dry gas is sent to an absorption tower, carbon four fraction is used as absorbent in the absorption tower to absorb carbon two and above heavy components in the dry gas. The absorption tower bottom liquid is sent to a carbon four desorption tower for treatment, carbon two concentrated gas is obtained from the carbon four desorption tower, and the carbon four desorption tower bottom liquid is returned to the carbon four absorption tower for recycling. The total recovery rate of carbon two and carbon three can reach 93%, the pressure of the carbon four absorption tower is 3-4.5 MPaG, the tower bottom temperature of the carbon four absorption tower is 100-160℃; the pressure of the carbon four desorption tower is 2.5-3.5 MPaG, the tower bottom temperature of the carbon four desorption tower is 100-160℃, and low-pressure steam or 145℃ hot oil outside the boundary is used as the heat source of the tower bottom reboiler of the carbon four absorption tower and the carbon four desorption tower, so the energy consumption of the device is large.

[0011] CN101759516B discloses a method for separating refinery catalytic dry gas by oil absorption, which comprises processes such as dry gas compression, absorption (reabsorption), desorption, etc. Carbon five fraction or de-pentanizing oil is used as absorbent in the main absorption tower to absorb carbon two fraction and heavier components in the catalytic dry gas, and the rich carbon five absorbent is sent to the desorption tower to obtain recovered carbon two concentrated gas from the top of the desorption tower. The operating pressure of the main absorption tower is 3.5-5.5 MPaG, the tower bottom temperature is 95-115℃, the operating pressure of the desorption tower is 2-3 MPaG, and the tower bottom temperature is 145-165℃, and low-pressure steam is used as the heat source.

[0012] CN101353286B discloses a method for separating non-deeply cooled low-carbon hydrocarbons containing light gas, which comprises the following steps: the pretreated light gas is cooled to 10 to-37℃ and then sent to a pre-cutting tower, the top of the pre-cutting tower is methane hydrogen and other light components and part of carbon two and a small amount of carbon three, the bottom of the pre-cutting tower is the remaining carbon two and heavier components, the top gas of the pre-cutting tower is sent to an absorption tower, and carbon three, carbon four, carbon five and other hydrocarbons are used as absorbents to absorb carbon two in the top gas of the pre-cutting tower. The process does not need a deep cooling tank and a de-methanizing tower, does not need to separate methane by deep cooling, and has lower energy consumption than traditional deep cooling separation. However, the process still needs propylene refrigerant at about-60℃, and the raw material gas needs to be dried and dehydrated; at the same time, the purity of the recovered carbon two component is low.

[0013] In summary, in the recovery of carbon two components or carbon two and carbon three components in the dry gas, in order to ensure the purity of the product gas and the recovery rate of carbon two or carbon two and carbon three, the existing processes generally adopt a deep cooling / intermediate cooling separation route, which needs to dry and dehydrate the raw material gas, and the device investment is large, or adopt a shallow cooling oil absorption route, which usually needs to carry out oil absorption and methane desorption processes at a high pressure, the steam consumption of the reboiler in the methane desorption process is large, the load is large, and the energy consumption of the device is high.

[0014] SUMMARY

[0015] It is an object of the present application to provide a new method and device for recovering C2-C4 components (including but not limited to carbon two components or carbon two carbon three components or carbon two carbon three carbon four components) from a methane-containing industrial gas such as dry gas, which has high purity and high recovery rate of the recovered C2-C4 components (including but not limited to carbon two components or carbon two carbon three components or carbon two carbon three carbon four components), saves device energy consumption, and does not require a dryer and a propylene refrigeration compressor. In the present application, the methane-containing industrial gas includes but is not limited to dry gas, cracking gas, natural gas, shale gas, etc., wherein the dry gas is preferably selected from at least one of refinery dry gas and coal chemical dry gas.

[0016] In a first aspect, the present application provides a method for recovering carbon two components from a methane-containing industrial gas, which comprises the following steps:

[0017] (1) compressing a raw methane-containing industrial gas, and cooling the obtained compressed gas to perform gas-liquid separation to obtain a gas phase and a liquid phase;

[0018] (2) contacting the gas phase with an absorbent to perform carbon two component absorption to obtain an absorption tail gas and an absorption rich liquid, wherein

[0019] the absorption rich liquid is returned and mixed into the compressed gas, or

[0020] the absorption rich liquid is mixed with the liquid phase obtained in step (1) or the absorption rich liquid is used as a first stream;

[0021] (3) reducing the pressure of the liquid phase obtained in step (1) or the first stream obtained in step (2);

[0022] (4) performing methane desorption on the stream after pressure reduction in step (3) to obtain a desorption gas and a rich absorbent, and the desorption gas is returned to the compression in step (1) or discharged, or

[0023] performing a second gas-liquid separation on the stream after pressure reduction in step (3) to obtain a second gas phase and a second liquid phase, the second gas phase is returned to the compression in step (1), and the second liquid phase is subjected to methane desorption to obtain a desorption gas and a rich absorbent, and the desorption gas is returned to the compression in step (1) or discharged;

[0024] (5) performing desorption separation on the rich absorbent to obtain a lean absorbent and a concentrated gas containing carbon two components, and the lean absorbent is returned and mixed into the absorbent in step (2).

[0025] In a specific embodiment of the present application, in step (2) of the method of the present application, the absorption rich liquid is returned and mixed into the compressed gas, and the liquid phase obtained in step (1) is subjected to methane desorption after pressure reduction to obtain a desorption gas and a rich absorbent.

[0026] In a specific embodiment of the present application, the first stream obtained in step (2) is depressurized in the process of the present application to obtain a second gas phase and a second liquid phase, and the second liquid phase is subjected to methane desorption to obtain a desorption gas and a rich absorbent.

[0027] Preferably, in step (2), the absorbent is selected from a carbon four fraction containing at least one of n-butane, isobutane and butene, and / or a carbon five fraction containing at least one of n-pentane, isopentane and neopentane, preferably a carbon four fraction.

[0028] Preferably, the carbon two component comprises ethane and / or ethylene.

[0029] The process according to the present application can also recover a carbon three component, preferably the carbon three component comprises propane and / or propylene.

[0030] The process according to the present application can recover a carbon two carbon three component, preferably the carbon two carbon three component comprises ethane and / or ethylene, and propane and / or propylene.

[0031] The process according to the present application can also recover a carbon four component, preferably the carbon four component comprises butane and / or butene.

[0032] In a second aspect, the present application provides a device for recovering a carbon two component from a methane-containing industrial gas, the device comprising: a compressor, a cooler, a liquid-vapor separator, an absorption column, a methane desorption column and a desorption column;

[0033] The compressor is connected to a methane-containing industrial gas pipeline, and the compressor, the cooler and the liquid-vapor separator are connected in series;

[0034] The bottom of the absorption column is connected to the top of the liquid-vapor separator and the cooler, respectively, for countercurrent contact of the gas phase discharged from the top of the liquid-vapor separator with the absorbent, the overhead of the absorption column discharges an absorption tail gas, and the bottom of the absorption column discharges an absorption rich liquid and returns to the cooler;

[0035] The upper part, the top and the bottom of the methane desorption column are connected to the bottom of the liquid-vapor separator, the compressor and the middle part of the desorption column, respectively, for methane desorption after the liquid phase discharged from the bottom of the liquid-vapor separator is depressurized, the overhead of the methane desorption column discharges a desorption gas and returns to the inlet of the compressor or between stages or is discharged externally, and the bottom of the methane desorption column discharges a rich absorbent into the middle part of the desorption column for desorption separation;

[0036] The bottom of the desorption column is connected to the top of the absorption column, for the bottom of the desorption column to discharge a lean absorbent and return to the top of the absorption column, and the overhead of the desorption column to recover a concentrated gas containing a carbon two component, such as a carbon two carbon three component.

[0037] In a third aspect, the present application provides a device for recovering carbon two components from a methane-containing industrial gas, the device comprising: a compressor, a cooler, a first liquid separator, an absorption column, a second liquid separator, a methane desorption column, and a desorption column;

[0038] The compressor is connected to a methane-containing industrial gas pipeline, the compressor, the cooler, and the first liquid separator are connected in series;

[0039] The bottom of the absorption column is connected to the top of the first liquid separator and the middle of the second liquid separator, respectively, for contacting the first gas phase discharged from the top of the first liquid separator with the absorbent in countercurrent, and discharging absorption tail gas and absorption rich liquid from the top and the bottom of the absorption column, respectively, the absorption rich liquid being mixed with the first liquid phase discharged from the bottom of the first liquid separator or the absorption rich liquid being used as a first stream, the first stream being depressurized and then entering the middle of the second liquid separator for a second gas-liquid separation;

[0040] The top and the bottom of the second liquid separator are connected to the compressor and the upper part of the methane desorption column, respectively, for discharging the second gas phase from the top of the second liquid separator and returning to the inlet or the inter-stage of the compressor, and discharging the second liquid phase from the bottom of the second liquid separator and entering the upper part of the methane desorption column for methane desorption;

[0041] The top and the bottom of the methane desorption column are connected to the compressor and the middle of the desorption column, respectively, for discharging the desorption gas from the top of the methane desorption column and returning to the inlet or the inter-stage of the compressor or discharging to the outside, and discharging the absorption rich liquid from the bottom of the methane desorption column and entering the middle of the desorption column for desorption separation;

[0042] The bottom of the desorption column is connected to the top of the absorption column, for discharging the absorption lean liquid from the bottom of the desorption column and returning to the top of the absorption column, and recovering the enriched gas containing carbon two components, such as carbon two and carbon three components, from the top of the desorption column.

[0043] The device according to the present application can further comprise a methane desorption column reboiler.

[0044] Preferably, the carbon two components comprise ethane and / or ethylene.

[0045] The device according to the present application can further recover carbon three components, preferably the carbon three components comprise propane and / or propylene.

[0046] The device according to the present application recovers carbon two and carbon three components, preferably the carbon two and carbon three components comprise ethane and / or ethylene, and propane and / or propylene.

[0047] The device according to the present application can further recover carbon four components, preferably the carbon four components comprise butane and / or butene. BRIEF DESCRIPTION OF DRAWINGS

[0048] Fig. 1 is a schematic diagram of a device for recovering carbon two components from a methane-containing industrial gas, such as dry gas, according to the present application, wherein:

[0049] BRIEF DESCRIPTION OF DRAWINGS 1 feedstock containing methane industrial gas, such as dry gas; 2 compressor; 3 cooler; 4 liquid separator; 5 absorption tower; 6 absorption tower pump; 7 methane desorption tower; 8 rich absorbent pump; 9 desorption tower; 10 enriched gas containing carbon two components; 11 absorbent circulating pump; 12 light hydrocarbon components; 13 stream; 14 absorption tail gas; 15 methane desorption tower reboiler.

[0050] Figure 2 is a schematic diagram of the device for recovering carbon two components from a methane-containing industrial gas, such as dry gas, provided by the present application, wherein:

[0051] BRIEF DESCRIPTION OF DRAWINGS 1 feedstock containing methane industrial gas, such as dry gas; 2 compressor; 3 cooler; 4 first liquid separator; 5 absorption tower; 6 desorption tower feed cooling device; 7 second liquid separator; 8 methane desorption tower; 9 methane desorption tower reboiler; 10 rich absorbent pump; 11 desorption tower; 12 absorbent circulating pump; 13 enriched gas containing carbon two components; 14 light hydrocarbon components; 15 absorption tail gas; 16 second stream. DETAILED DESCRIPTION

[0052] The specific embodiments of the present application will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely intended to illustrate and explain the present application, and are not intended to limit the present application.

[0053] The inventors of the present application have found that, by subjecting a feedstock containing methane industrial gas, such as dry gas, to absorption treatment at high pressure, followed by methane desorption treatment and absorbent desorption treatment at low pressure, the enriched gas product obtained has high purity, the recovery rate of C2-C4 components, such as carbon two components, carbon two carbon three components, carbon two carbon three carbon four components, is high, the methane desorption process tower reboiler load is low, the tower bottom temperature is low, the heat energy of this part can be completely provided by the tower bottom of the desorption tower in the device to discharge the lean absorbent, which reduces the steam consumption, and the energy consumption increase effect caused by the return of the methane desorption tower overhead desorption gas to the compressor and the energy consumption reduction effect caused by the methane desorption tower reboiler not consuming steam are considered as a whole, the optimal process flow and operating parameters are selected to minimize the overall energy consumption of the device, and a dryer and a propylene refrigeration compressor are not required.

[0054] The inventors of the present application have also found that the present application is suitable for application in the treatment process of methane-containing industrial gas to be desorbed. By independent operation and combined operation of high-pressure absorption process and low-pressure methane desorption process, effective removal of methane can be achieved with the lowest energy consumption and absorbent consumption, and high recovery rate of carbon two, carbon three, carbon four components, etc. from the methane-containing industrial gas can be achieved. Compared with the conventional shallow cold oil absorption process, the recovery rate of C2-C4 components, such as carbon two, carbon two carbon three, carbon two carbon three carbon four, etc. can reach about 95% or more, and depending on the composition of the raw material, the overall energy consumption of the device of the present application can be reduced by about 10%-30%.

[0055] In the present application, the term "methane-containing industrial gas" refers to an industrial gas from which methane can be desorbed by means of a methane desorption column from a methane-containing industrial gas to be desorbed of methane and then subjected to subsequent treatment to recover C2, C3, C4 and the like components therefrom, including but not limited to dry gas, pyrolysis gas, natural gas, shale gas and the like. In the present application, there is no specific limitation and requirement for the raw material components of the methane-containing industrial gas and their contents. As long as methane contained in the raw material methane-containing industrial gas is desorbed by means of a methane desorption column to achieve separation from C2-C4, by adjusting the process flow and operating parameters, the purpose of recovering C2, C3, C4 and the like components with high recovery rate and minimizing the total energy consumption can be achieved.

[0056] There is no specific limitation on dry gas, for example, the dry gas is selected from at least one of refinery dry gas and coal chemical dry gas. Specifically, the refinery dry gas is selected from at least one of catalytic cracking unit dry gas, delayed coking unit dry gas, PSA unit desorption gas and light hydrocarbon recovery unit dry gas, and the coal chemical dry gas is selected from at least one of methanol-to-olefins (MTO) dry gas and methanol-to-aromatics (MTA) dry gas. The dry gas in the present application is not limited thereto. There is no specific limitation on pyrolysis gas, natural gas, shale gas, for example, the pyrolysis gas includes catalytic cracking gas and steam cracking gas.

[0057] According to a preferred embodiment of the present application, when the methane-containing industrial gas includes C6 and above components with a content of less than 0.1% mol, for example, the refinery dry gas includes C6 and above components with a content of less than 0.1% mol, it is more advantageous for the recovery of C2 components in the dry gas and the minimization of the overall device energy consumption.

[0058] According to a preferred embodiment of the present application, when the methane-containing industrial gas includes C6 and above components with a content of more than 0.1% mol, for example, the refinery dry gas includes C6 and above components with a content of more than 0.1% mol, it is more advantageous for the recovery of C2 and C3 components in the dry gas and the minimization of the overall device energy consumption.

[0059] In the present application, unless otherwise specified, the pressure is gauge pressure.

[0060] In the first aspect, the present application provides a method for recovering C2 components in a methane-containing industrial gas, which comprises the following steps:

[0061] (1) compressing the raw material methane-containing industrial gas, and cooling the obtained compressed gas and then carrying out gas-liquid separation to obtain a gas phase and a liquid phase;

[0062] (2) contacting the gas phase with an absorbent to absorb C2 components, to obtain an absorption tail gas and an absorption rich liquid, wherein,

[0063] the absorption rich liquid is returned and mixed into the compressed gas, or

[0064] absorption rich liquid as a first stream;

[0065] (3) reducing the pressure of the liquid phase obtained in step (1) or the first stream obtained in step (2);

[0066] (4) subjecting the stream reduced in pressure in step (3) to methane desorption to obtain a desorbed gas and a rich absorbent, the desorbed gas being returned to the compression in step (1) or being vented, or

[0067] subjecting the stream reduced in pressure in step (3) to a second gas-liquid separation to obtain a second gas phase and a second liquid phase, the second gas phase being returned to the compression in step (1), and subjecting the second liquid phase to methane desorption to obtain a desorbed gas and a rich absorbent, the desorbed gas being returned to the compression in step (1) or being vented;

[0068] (5) subjecting the rich absorbent to desorption separation to obtain a lean absorbent and a concentrated gas containing carbon dioxide components, such as carbon dioxide and carbon trioxide components, the lean absorbent being returned and mixed into the absorbent in step (2).

[0069] In a specific embodiment of the process of the present application, the absorption rich liquid in step (2) of the process of the present application is returned and mixed into the compressed gas, and the liquid phase obtained in step (1) is reduced in pressure and subjected to methane desorption to obtain a desorbed gas and a rich absorbent.

[0070] In a specific embodiment of the present application, the present application provides a process for recovering carbon dioxide components from a methane-containing industrial gas, the process comprising the steps of:

[0071] (1) compressing a raw methane-containing industrial gas, and subjecting the compressed gas obtained after cooling to a gas-liquid separation to obtain a gas phase and a liquid phase;

[0072] (2) subjecting the gas phase to carbon dioxide component absorption by contacting with an absorbent to obtain an absorption tail gas and an absorption rich liquid, the absorption rich liquid being returned and mixed into the compressed gas;

[0073] (3) reducing the pressure of the liquid phase obtained in step (1);

[0074] (4) subjecting the stream reduced in pressure in step (3) to methane desorption to obtain a desorbed gas and a rich absorbent, the desorbed gas being returned to the compression in step (1) or being vented;

[0075] (5) subjecting the rich absorbent to desorption separation to obtain a lean absorbent and a concentrated gas containing carbon dioxide components, such as carbon dioxide and carbon trioxide components, the lean absorbent being returned and mixed into the absorbent in step (2).

[0076] Step (1) gas-liquid separation after compression and cooling of the methane-containing industrial gas

[0077] According to the present application, the compression is not particularly limited, and generally, the compression is performed in stages to increase the pressure of the feed gas containing methane to 2.5-4.6 MPaG, preferably 3-4.2 MPaG, i.e., the pressure of the compressed gas is 2.5-4.6 MPaG, preferably 3-4.2 MPaG. Further preferably, the compression is multi-stage compression, and the present application is not particularly limited in the number of stages of the compression process, and for example, the compression can be two-stage compression or three-stage compression.

[0078] According to the present application, the cooling is not particularly limited, and preferably, the temperature of the cooling is 5-40°C, preferably 10-20°C. In the present application, the compressed gas is subjected to a cooling process using a cooling medium having a temperature of 0°C or higher, and the cooling medium is selected from at least one of low-temperature water, circulating water, propylene, ammonia, and liquid nitrogen, and preferably, the cooling medium is low-temperature water; further preferably, the low-temperature water is prepared by a lithium bromide absorption refrigerator, and the temperature is 5°C or 7°C. Specifically, in the examples, 7°C low-temperature water is used, but the present application is not limited thereto.

[0079] According to the present application, preferably, the compressed gas subjected to the cooling is subjected to a gas-liquid separation to obtain a gas phase and a liquid phase, wherein the gas phase is mainly composed of hydrogen, C1-C3 hydrocarbons, and the like, and the liquid phase is mainly composed of C3-C5 hydrocarbons and the like.

[0080] Step (2) contacting the gas phase with an absorbent to absorb carbon two components

[0081] According to the present application, the absorbent is not particularly limited, and can be determined by those skilled in the art based on common knowledge in the art. Preferably, the absorbent is selected from a carbon four fraction and / or a carbon five fraction, the carbon four fraction contains at least one of n-butane, isobutane, and butene, and the carbon five fraction contains at least one of n-pentane, isopentane, and neopentane, and preferably, the absorbent is the carbon four fraction. Specifically, in the examples, mixed butane is used as the absorbent, but the present application is not limited thereto.

[0082] Preferably, the carbon two components are selected from ethane and / or ethylene. For example, ethane, ethylene, a mixture of ethane and ethylene.

[0083] According to the present application, preferably, the absorption of the carbon two components is performed in an absorption column, and more preferably, the theoretical plate number of the absorption column is 15-30, the operating pressure of the absorption column is 2.5-4.6 MPaG, preferably 3-4.2 MPaG, the top temperature of the absorption column is 10-60°C, and the bottom temperature of the absorption column is 10-70°C.

[0084] For example, in one specific embodiment, the absorbent inlet temperature is 40-50°C, the gas phase inlet temperature is about 40°C, the cooling medium in step (1) is circulating water, and the overhead temperature of the absorption tower is 40-60°C; in another embodiment, the absorbent inlet temperature is 5-20°C, the gas phase inlet temperature is 5-20°C, the cooling medium in step (1) is low-temperature water, and the overhead temperature of the absorption tower is 10-30°C.

[0085] According to one specific embodiment of the present application, the gas phase is introduced into the bottom of the absorption tower and is contacted with the absorbent at the top of the absorption tower in countercurrent, and the carbon two components and heavier fractions in the gas phase are absorbed, and the absorption tail gas is discharged from the top of the absorption tower and is sent out of the boundary region, and the absorption rich liquid is discharged from the bottom of the absorption tower and is pressurized by an absorption tower bottom liquid pump and then is returned and mixed with the compressed gas.

[0086] In the present application, the absorption rich liquid discharged from the bottom of the absorption tower is fully contacted with the compressed gas in a liquid separation tank, and a part of the C2-C4 hydrocarbons and other recombination components are pre-absorbed, the amount of the gas phase entering the absorption tower is reduced, the amount of the absorbent in the absorption tower is reduced, and the energy consumption is saved.

[0087] According to one preferred embodiment of the present application, the absorption rich liquid is first introduced into a water cooler to reduce the temperature before being returned to the cooler, the load of the cooler is reduced, and the energy consumption is saved.

[0088] Step (3) reduces the pressure of the liquid phase

[0089] According to the present application, preferably, the pressure of the liquid phase after being reduced is 0.8-3 MPaG, and more preferably 1-2 MPaG, wherein the pressure of the liquid phase after being reduced is higher than the operating pressure of the methane desorption tower, so as to ensure that the liquid phase can flow into the upper part of the methane desorption tower by itself under the action of the pressure difference.

[0090] In the present application, the pressure reduction is not particularly limited, and generally adopts the flash evaporation mode, the relative volatility between the C1-C5 hydrocarbon components is increased by reducing the pressure of the liquid phase, the load of the methane desorption tower reboiler is reduced, the temperature of the bottom of the methane desorption tower is reduced, a lower temperature heat source can be used, and the steam consumption and the energy consumption of the device are saved.

[0091] Step (4) the stream after the pressure reduction of the liquid phase is subjected to methane desorption

[0092] According to the present application, preferably, the methane desorption is carried out in a methane desorption tower, and more preferably, the theoretical plate number of the methane desorption tower is 20-50, the operating pressure of the methane desorption tower is 0.5-2.4 MPaG, the overhead temperature of the methane desorption tower is 10-60°C, and the bottom temperature of the methane desorption tower is 35-90°C.

[0093] In the preferred embodiment, the operating pressure of the methane desorption tower is 1.0-1.9 MPaG.

[0094] In a preferred embodiment, the overhead temperature of the methane desorption column is 10-20°C.

[0095] In a preferred embodiment, the bottom temperature of the methane desorption column is 40-75°C.

[0096] According to the present application, preferably, the liquid phase is depressurized and then fed into the methane desorption column, and the methane and other light components in the liquid phase are separated and removed to obtain desorption gas and rich absorbent, and the desorption gas is returned and mixed into the feed methane-containing industrial gas.

[0097] According to the present application, preferably, the desorption gas discharged from the overhead of the methane desorption column is returned to the compressor inlet or inter-stage, and the return position can be determined according to the pressure of the feed methane-containing industrial gas, the inter-stage pressure of the compressor and the pressure of the methane desorption column, so as to save the energy consumption of the compressor while ensuring that the gas at the overhead of the methane desorption column can be pressurized by the compressor.

[0098] In the present application, the methane desorption column is operated at low pressure, and the methane in the rich absorbent is evaporated at a small cost, thereby reducing the methane content in the product concentrated gas containing carbon two components. The bottom liquid of the methane desorption column is subjected to absorbent desorption treatment to obtain lean absorbent.

[0099] According to the present application, preferably, the heat source of the bottom of the methane desorption column is provided by the methane desorption column reboiler, and the heat source of the methane desorption column reboiler is a process stream. Specifically, the process stream is selected from at least one of the absorbent, the rich absorbent and the lean absorbent, and is preferably the lean absorbent.

[0100] Step (5) desorption separation of the rich absorbent

[0101] According to the present application, preferably, the desorption separation is carried out in a desorption column, and more preferably, the theoretical plate number of the desorption column is 20-50, the operating pressure of the desorption column is 1-2.8 MPaG, the overhead temperature of the desorption column is 25-70°C, and the bottom temperature of the desorption column is 90-160°C.

[0102] According to a preferred embodiment of the present application, the rich absorbent is subjected to desorption separation in a desorption column, the overhead of the desorption column recovers the concentrated gas containing carbon two components, the bottom of the desorption column discharges the lean absorbent, the lean absorbent is used as the heat source of the methane desorption, and at least part of the stream obtained after heat exchange is returned and mixed into the absorbent.

[0103] According to the present application, preferably, part of the stream obtained after heat exchange of the lean absorbent is sent out as light hydrocarbon components, and the remaining part is returned and mixed into the absorbent. The light hydrocarbon components are selected from at least one of carbon three, carbon four and carbon five hydrocarbons.

[0104] According to the present application, the concentrated gas containing carbon two components mainly contains methane, carbon two components, carbon three components and carbon four components and water.

[0105] Preferably, the content of methane is 0-5 vol%, preferably 0-2 vol%; the content of carbon di-component is 40-85 vol%, preferably 45-65 vol%; the content of carbon tri-component is 0-70 vol%, preferably 10-60 vol%; the content of carbon tetra-component and above is 0-20 vol%, preferably 0-10 vol%; and the content of water is 0-0.5 vol%, based on the total volume of the enriched gas.

[0106] Compared with the conventional shallowly cooled oil absorption process, the recovery rate of carbon di-component in the method of the present application can reach about 95% or more, and the total energy consumption of the device can be reduced by about 10%-30%.

[0107] The method for recovering carbon di-component according to the present application can be used to recover carbon di-component from methane-containing industrial gas such as dry gas at a high recovery rate, but this does not necessarily mean that the content of carbon di-component in the obtained enriched gas is necessarily higher than that of carbon tri-component. In the method, the content of carbon tri-component in the enriched gas is also related to the content of carbon tri-component in the raw material.

[0108] The method according to the present application can further comprise recovery of carbon tri-component, preferably the carbon tri-component comprises propane and / or propylene.

[0109] The method according to the present application can comprise recovery of carbon di-tri-component, preferably the carbon di-tri-component comprises ethane and / or ethylene, and propane and / or propylene.

[0110] The method according to the present application can further comprise recovery of carbon tetra-component, preferably the carbon tetra-component comprises butane and / or butene.

[0111] In a specific embodiment of the method of the present application, the mixture of the absorption rich liquid and the liquid phase obtained in step (1) or the absorption rich liquid as the first stream, and the first stream obtained after being depressurized is 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 desorption gas and a rich absorbent. Preferably, the method of the present application can further recover carbon tri-component, preferably the carbon tri-component comprises propane and / or propylene. Preferably, the method of the present application can recover carbon di-tri-component, preferably the carbon di-tri-component comprises ethane and / or ethylene, and propane and / or propylene. Preferably, the methane-containing industrial gas comprises more than 0.1% mol of carbon hexa-component and above.

[0112] In a specific embodiment of the method of the present application, the present application provides a method for recovering carbon di-component from methane-containing industrial gas, which comprises the following steps:

[0113] (1) compressing the methane-containing industrial gas, and cooling the obtained compressed gas and subjecting it to a gas-liquid separation to obtain a gas phase and a liquid phase;

[0114] (2) contacting the gas phase with an absorbent to absorb carbon dioxide components to obtain an absorption tail gas and an absorption rich liquid, and mixing the absorption rich liquid with the liquid phase obtained in step (1) or the absorption rich liquid as a first stream;

[0115] (3) reducing the pressure of the first stream obtained in step (2);

[0116] (4) performing a second gas-liquid separation on the first stream after the pressure reduction in step (3) to obtain a second gas phase and a second liquid phase, returning the second gas phase to the compression in step (1), and performing a methane desorption on the second liquid phase to obtain a desorption gas and an absorption rich liquid, and returning the desorption gas to the compression in step (1) or discharging it;

[0117] (5) performing a desorption separation on the absorption rich liquid to obtain an absorption lean liquid and a concentration gas containing carbon dioxide components, such as carbon dioxide and carbon trioxide components, and returning the absorption lean liquid to be mixed with the absorbent in step (2).

[0118] Here, the gas-liquid separation in step (1) refers to a first gas-liquid separation. The use of "first gas-liquid separation" and "second gas-liquid separation" is only to distinguish the order of the gas-liquid separation steps, and does not mean the importance of the gas-liquid separation. The first gas-liquid separation is performed after the compressed gas is cooled to obtain a first gas phase and a first liquid phase.

[0119] In a specific embodiment of the method of the present application, the present application provides a method for recovering carbon dioxide and carbon trioxide components from a methane-containing industrial gas, which comprises the following steps:

[0120] (1) compressing a raw methane-containing industrial gas, and performing a first gas-liquid separation on the compressed gas after being cooled to obtain a first gas phase and a first liquid phase;

[0121] (2) contacting the first gas phase with an absorbent to absorb carbon dioxide and carbon trioxide components to obtain an absorption tail gas and an absorption rich liquid, and mixing the absorption rich liquid with the first liquid phase or the absorption rich liquid as a first stream;

[0122] (3) reducing the pressure of the first stream in step (2);

[0123] (4) performing a second gas-liquid separation on the first stream after the pressure reduction in step (3) to obtain a second gas phase and a second liquid phase, returning the second gas phase to the compression in step (1), and performing a methane desorption on the second liquid phase to obtain a desorption gas and an absorption rich liquid, and returning the desorption gas to the compression in step (1) or discharging it;

[0124] (5) performing a desorption separation on the absorption rich liquid to obtain an absorption lean liquid and a concentration gas containing carbon dioxide and carbon trioxide components, and returning the absorption lean liquid to be mixed with the absorbent in step (2).

[0125] Step (1) compression and cooling of the methane-containing industrial gas

[0126] According to the present application, the compression is not particularly limited, and generally, the compression is carried out in stages to increase the pressure of the feedstock containing the methane industrial gas to 2.5-5 MPaG, preferably 3-4.2 MPaG. That is, the pressure of the compressed gas is 2.5-5 MPaG, preferably 3-4.2 MPaG. Further preferably, the compression is multi-stage compression, and the present application is not particularly limited to the number of stages of the compression treatment, and for example, the compression can be two-stage compression or three-stage compression.

[0127] According to the present application, the cooling is not particularly limited, and preferably, the temperature of the cooling is 5-45℃, preferably 10-20℃. In the present application, the compressed gas is subjected to a cooling treatment using a cooling medium having a temperature of 0℃ or higher, and the cooling medium is selected from at least one of low-temperature water, circulating water, propylene, ammonia and liquid nitrogen, and preferably, the cooling medium is low-temperature water; further preferably, the low-temperature water is prepared by a lithium bromide absorption refrigerator, and the temperature is 5℃ or 7℃. Specifically, in the examples, 7℃ low-temperature water is used, but the present application is not limited thereto.

[0128] According to the present application, preferably, the compressed gas subjected to the cooling 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, C1-C3 hydrocarbons and the like, and the first liquid phase is mainly composed of C3-C5 hydrocarbons and the like.

[0129] Step (2) contacting the first gas phase with an absorbent to absorb carbon two and carbon three components

[0130] According to the present application, the absorbent is not particularly limited, and can be determined by those skilled in the art based on the common sense of the prior art. Preferably, the absorbent is selected from a carbon four fraction and / or a carbon five fraction, the carbon four fraction contains at least one of n-butane, isobutane and butene, and the carbon five fraction contains at least one of n-pentane, isopentane and neopentane, and preferably, the carbon four fraction. Specifically, in the examples, n-butane is used as the absorbent, but the present application is not limited thereto.

[0131] According to the present application, preferably, the carbon two and carbon three components are absorbed in an absorption tower, and more preferably, the theoretical plate number of the absorption tower is 15-30, the operating pressure of the absorption tower is 2.5-5 MPaG, preferably 3-4.2 MPaG, the tower top temperature of the absorption tower is 10-30℃, and the tower bottom temperature of the absorption tower is 10-60℃.

[0132] Preferably, the carbon two and carbon three components include ethane and / or ethylene, and propane and / or propylene.

[0133] According to the present application, the first gas phase is subjected to the absorption at a high pressure, which is beneficial to the absorption of the carbon two and carbon three components, and reduces the amount of the absorbent.

[0134] According to a specific embodiment of the present application, the first gas phase is introduced into the bottom of the absorption tower and contacted with the absorbent at the top of the absorption tower countercurrently to absorb carbon dioxide, carbon dioxide and carbon three and heavier fractions in the first gas phase, and the absorption tail gas is discharged from the top of the absorption tower to the boundary area, and the absorption rich liquid is discharged from the bottom of the absorption tower to be mixed with the first liquid phase to obtain the first stream or the absorption rich liquid is used as the first stream.

[0135] Step (3) reducing the pressure of the first stream

[0136] Preferably, the pressure of the first stream after pressure reduction is 0.5-2.4 MPaG, preferably 0.8-2 MPaG.

[0137] In the present application, the pressure reduction process is not particularly limited, and generally adopts the flash evaporation method, by reducing the pressure of the first stream, and further increasing the relative volatility between C1-C5 hydrocarbon components, the load of the methane desorption tower reboiler is reduced, the bottom temperature of the methane desorption tower is reduced, a lower temperature heat source can be used, and steam consumption and device energy consumption are saved.

[0138] According to a preferred embodiment of the present application, the first stream is cooled before the pressure reduction process of the first stream to reduce the temperature of the first stream, and further reduce the amount of gas phase in the second liquid separation tank and the compressor load.

[0139] According to a preferred embodiment of the present application, the first stream is cooled after the pressure reduction process of the first stream to reduce the temperature of the first stream, and further reduce the amount of gas phase in the second liquid separation tank and the compressor load.

[0140] According to the present application, specifically, the cooling process is not particularly limited, and generally uses a cooler for cooling, preferably the temperature of the first stream is 5-40℃, preferably 5-15℃.

[0141] Step (4) the first stream after pressure reduction is subjected to second gas-liquid separation and the second liquid phase is subjected to methane desorption

[0142] According to a preferred embodiment of the present application, the first stream after cooling and pressure reduction is introduced into the 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 carbon two and lighter components, and the second liquid phase is mainly composed of carbon two and heavier components.

[0143] In the present application, the second liquid phase is subjected to methane desorption in the methane desorption tower, the desorption gas obtained is returned to the inlet / interstage of the compressor or discharged, and the rich absorbent is subjected to absorbent desorption separation, wherein the desorption gas is mainly composed of methane and light components, and the rich absorbent is mainly composed of absorbent containing carbon two and carbon three components.

[0144] In the present application, the return position between the second gas phase and the desorption gas returning to the compressor inlet or stage can be determined according to the pressure of the raw material containing methane industrial gas, the pressure between the compressor stages and the pressure of the methane desorption tower. While ensuring that the desorption gas discharged from the top of the methane desorption tower can be pressurized by the compressor, the energy consumption of the compressor is saved as much as possible.

[0145] According to the present application, preferably, the methane desorption is carried out in a methane desorption tower; more preferably, the theoretical plate number of the methane desorption tower is 20-50, the operating pressure of the methane desorption tower is 0.5-2.4 MPaG, the top temperature of the methane desorption tower is 10-40℃, and the bottom temperature of the methane desorption tower is 35-100℃.

[0146] In a preferred embodiment, the operating pressure of the methane desorption tower is 1.0-1.9 MPaG.

[0147] In a preferred embodiment, the top temperature of the methane desorption tower is 10-20℃.

[0148] In a preferred embodiment, the bottom temperature of the methane desorption tower is 40-75℃.

[0149] Preferably, the methane desorption tower is operated at low pressure to evaporate the methane in the second liquid phase at a small cost, thereby reducing the methane content in the enriched gas. The rich absorbent discharged from the bottom of the methane desorption tower is subjected to absorbent desorption treatment to obtain a lean absorbent.

[0150] Preferably, the heat source of the methane desorption tower is provided by a methane desorption tower reboiler, and the heat source of the methane desorption tower reboiler is a process stream. Specifically, the process stream is selected from at least one of the absorbent, the rich absorbent and the lean absorbent, and is preferably the lean absorbent.

[0151] Step (5) desorption separation of the rich absorbent

[0152] According to the present application, preferably, the desorption separation is carried out in a desorption tower; more preferably, the theoretical plate number of the desorption tower is 20-50, the operating pressure of the desorption tower is 1-2.8 MPaG, the top temperature of the desorption tower is 15-70℃, and the bottom temperature of the desorption tower is 90-200℃.

[0153] According to a specific embodiment of the present application, the rich absorbent is subjected to desorption separation in a desorption tower, the top of the desorption tower recovers the enriched gas mainly composed of carbon two and carbon three components, the bottom of the desorption tower discharges the lean absorbent to provide heat for the bottom of the methane desorption tower, and at least part of the second stream obtained by heat exchange of the lean absorbent is returned and mixed into the absorbent.

[0154] Preferably, part of the second stream obtained by heat exchange of the lean absorbent is sent out as light hydrocarbon components, and the remaining part is returned and mixed into the absorbent. The light hydrocarbon components are selected from at least one of carbon four and carbon five hydrocarbons.

[0155] According to the method of the present application, the carbon two or carbon two and three components-containing enriched gas mainly comprises methane, carbon two components, carbon three components, carbon four and above components and water;

[0156] Preferably, the content of methane is 0-5 vol%, preferably 0-2 vol%; the content of carbon two components is 30-70 vol%, preferably 40-60 vol%; the content of carbon three components is 20-70 vol%, preferably 30-60 vol%; the content of carbon four and above components is 0-20 vol%, preferably 0-10 vol%, and the content of water is 0-0.5 vol%, based on the total volume of the enriched gas.

[0157] Compared with the conventional shallow cold oil absorption process, the recovery rate of carbon two components or carbon two and three components in the method of the present application can reach about 95% or above, and the total energy consumption of the device can be reduced by about 10%-30%.

[0158] The method according to the present application can also comprise the recovery of carbon four components, which comprise butane and / or butene.

[0159] According to the present application, the two gas-liquid separation steps are suitable for the recovery of heavier methane-containing industrial gas such as dry gas. It will be understood that, based on the recovery of carbon two components or carbon two and three components according to the method of the present application, the treatment of heavier methane-containing industrial gas can be suitable by adding gas-liquid separation steps, thereby further recovering carbon four components. It will be understood that, based on the content of heavy components in the methane-containing industrial gas, the gas-liquid separation steps can be increased or decreased as needed, combined with the absorption step and the methane desorption step to recover C2-C4 components.

[0160] In a second aspect, the present application provides a device for recovering carbon two components in methane-containing industrial gas, which comprises a compressor, a cooler, a liquid separation tank, an absorption tower, a methane desorption tower and a desorption tower;

[0161] The compressor is connected to a methane-containing industrial gas pipeline such as a dry gas pipeline, and the compressor, the cooler and the liquid separation tank are sequentially connected;

[0162] The bottom of the absorption tower is connected to the top of the liquid separation tank and the cooler, respectively, for countercurrent contact of the gas phase discharged from the top of the liquid separation tank with the absorbent, the top of the absorption tower discharges absorption tail gas, and the bottom of the absorption tower discharges absorption-rich liquid and returns to the cooler;

[0163] The upper part, the top and the bottom of the methane desorption tower are connected to the bottom of the liquid separation tank, the compressor and the middle part of the desorption tower, respectively, for methane desorption after pressure reduction of the liquid phase discharged from the bottom of the liquid separation tank, the top of the methane desorption tower discharges desorption gas and returns to the inlet of the compressor or between stages or is discharged externally, and the bottom of the methane desorption tower discharges absorption-rich liquid into the middle part of the desorption tower for desorption separation;

[0164] The bottom of the desorption column is communicated with the top of the absorption column for discharging lean absorbent from the column bottom of the desorption column and returning to the top of the absorption column, and the top of the desorption column recovers a concentrated gas containing carbon di-component, such as carbon di-carbon tri-component.

[0165] According to the present application, preferably, the device further comprises: a methane desorption column reboiler; the methane desorption column reboiler is respectively communicated with the bottom of the desorption column, the lower part and the bottom of the methane desorption column, and the top of the absorption column, for supplying heat to the column bottom of the methane desorption column by discharging lean absorbent from the column bottom of the desorption column, and at least part of the stream obtained by heat exchange of the lean absorbent returns to the top of the absorption column.

[0166] Preferably, the methane desorption column reboiler is further communicated with the post-treatment unit, for sending part of the stream obtained by heat exchange of the lean absorbent discharged from the methane desorption column reboiler as a light hydrocarbon component to the post-treatment unit, and the remaining part returns to the top of the absorption column.

[0167] Preferably, the light hydrocarbon component is selected from at least one of carbon tri, carbon tetra and carbon penta hydrocarbon.

[0168] Preferably, the upper part of the methane desorption column is 1 / 20-1 / 5 of the methane desorption column.

[0169] Preferably, the lower part of the methane desorption column is 4 / 5-5 / 6 of the methane desorption column.

[0170] Preferably, the middle part of the desorption column is 1 / 6-2 / 3 of the desorption column.

[0171] The device according to the present application can also recover carbon tri-component, preferably the carbon tri-component contains propane and / or propylene.

[0172] The device according to the present application can also recover carbon tetra-component, preferably the carbon tetra-component contains butane and / or butene.

[0173] In the third aspect, the present application provides a device for recovering carbon di-component in a methane-containing industrial gas, which comprises: a compressor, a cooler, a first liquid separation tank, an absorption column, a second liquid separation tank, a methane desorption column and a desorption column;

[0174] The compressor is connected to a methane-containing industrial gas, such as a dry gas pipeline, and the compressor, the cooler and the first liquid separation tank are communicated in sequence.

[0175] The bottom of the absorption column is respectively communicated with the top of the first liquid separation tank and the middle part of the second liquid separation tank, for discharging first gas phase from the top of the first liquid separation tank to contact with the absorbent in countercurrent, and the top and the bottom of the absorption column respectively discharge absorption tail gas and absorption rich liquid, and the absorption rich liquid is mixed with the first liquid phase discharged from the bottom of the first liquid separation tank or the absorption rich liquid as a first stream, which is depressurized and enters the middle part of the second liquid separation tank for second gas-liquid separation.

[0176] The top and bottom of the second liquid separator are respectively communicated with the compressor and the upper part of the methane desorption column, for the second gas phase to be discharged from the top of the second liquid separator and returned to the inlet or inter-stage of the compressor, and for the second liquid phase to be discharged from the bottom of the second liquid separator and entered into the upper part of the methane desorption column for methane desorption;

[0177] The top and bottom of the methane desorption column are respectively communicated with the compressor and the middle part of the desorption column, for the desorption gas to be discharged from the top of the methane desorption column and returned to the inlet or inter-stage of the compressor or discharged outside, and for the rich absorbent to be discharged from the bottom of the methane desorption column and entered into the middle part of the desorption column for desorption separation;

[0178] The bottom of the desorption column is communicated with the top of the absorption column, for the lean absorbent to be discharged from the bottom of the desorption column and returned to the top of the absorption column, and for the concentrated gas containing carbon two components, such as carbon two and carbon three components, to be recovered from the top of the desorption column.

[0179] According to the present application, preferably, the device further comprises a methane desorption column reboiler; the methane desorption column reboiler is respectively communicated with the bottom of the desorption column, the lower part and the bottom of the methane desorption column and the top of the absorption column, for the lean absorbent to be discharged from the bottom of the desorption column to heat the bottom of the methane desorption column, and for at least part of the (second) stream obtained by heat exchange of the lean absorbent to be returned to the top of the absorption column.

[0180] Preferably, the methane desorption column reboiler is further communicated with a post-treatment unit, for part of the (second) stream obtained by heat exchange of the lean absorbent discharged from the methane desorption column reboiler to be sent out of the boundary area for post-treatment as light hydrocarbon components, and for the remaining part to be returned to the top of the absorption column.

[0181] Preferably, the light hydrocarbon components are selected from at least one of carbon four and carbon five hydrocarbons.

[0182] Preferably, the middle part of the second liquid separator is 1 / 3-2 / 3 of the second liquid separator.

[0183] Preferably, the upper part of the methane desorption column is 1 / 20-1 / 5 of the methane desorption column.

[0184] Preferably, the lower part of the methane desorption column is 4 / 5-5 / 6 of the methane desorption column.

[0185] Preferably, the middle part of the desorption column is 1 / 6-2 / 3 of the desorption column.

[0186] The device according to the present application can also recover carbon three components, preferably the carbon three components contain propane and / or propylene.

[0187] The device according to the present application can also recover carbon four components, preferably the carbon four components contain butane and / or butene.

[0188] The device for recovering carbon two components in methane-containing industrial gas, such as dry gas, provided by the present application will be described in detail in combination with Fig. 1. The device comprises a compressor 2, a cooler 3, a liquid separator 4, an absorption tower 5, a methane desorption tower 7 and a desorption tower 9. The compressor 2, the cooler 3 and the liquid separator 4 are connected in sequence. The compressor 2 is connected with a pipeline of methane-containing industrial gas, such as refinery dry gas 1. The bottom of the absorption tower 5 is connected with the top of the liquid separator 4 and the cooler 3 respectively, for countercurrently contacting the gas phase generated by the liquid separator with an absorbent. The top of the absorption tower 5 discharges absorption tail gas 14, and the bottom of the absorption tower 5 discharges absorption rich liquid which is pressurized by an absorption tower bottom liquid pump 6 and returned to the cooler 3. The upper part, the top and the bottom of the methane desorption tower 7 are connected with the bottom of the liquid separator 4, the compressor 2 and the desorption tower 9 respectively, for desorbing methane from the liquid phase generated by the liquid separator 4 after pressure reduction. The top of the methane desorption tower 7 discharges desorption gas which is returned to the compressor 2. The bottom of the methane desorption tower 7 discharges rich absorbent which is pressurized by a rich absorbent pump 8 and then introduced into the middle of the desorption tower 9 for desorption separation. The bottom of the desorption tower 9 is connected with the top of the absorption tower 5, for discharging lean absorbent from the bottom of the desorption tower and returning the lean absorbent to the top of the absorption tower 5. The top of the desorption tower 9 recovers concentration gas 10 containing carbon two components.

[0189] According to a preferred embodiment of the present application, the device further comprises a methane desorption tower reboiler 15, which is connected with the bottom of the desorption tower 9, the lower part and the bottom of the methane desorption tower 7 and the top of the absorption tower 5 respectively, for supplying heat to the bottom of the methane desorption tower 7 with the lean absorbent discharged from the bottom of the desorption tower 9. A part of the stream 13 obtained by heat exchange of the lean absorbent is sent out of the boundary area as light hydrocarbon components 12 for post-treatment, and the remaining part is returned to the top of the absorption tower 5.

[0190] The device for recovering carbon two components in the industrial gas containing methane, such as dry gas, provided by the present application will be described in detail in combination with FIG. 2. The device comprises a compressor 2, a cooler 3, a first liquid separator 4, an absorption tower 5, a second liquid separator 7, a methane desorption tower 8 and a desorption tower 11. The compressor 2, the cooler 3 and the first liquid separator 4 are sequentially communicated. The compressor 2 is communicated with the industrial gas containing methane, such as refinery dry gas 1. The bottom of the absorption tower 5 is respectively communicated with the top of the first liquid separator 4 and the middle of the second liquid separator 7, for contacting the first gas phase discharged from the top of the first liquid separator 4 with the absorbent in countercurrent. The top of the absorption tower 5 discharges absorption tail gas 15. The bottom of the absorption tower 5 discharges absorption rich liquid which is mixed with the first liquid phase discharged from the bottom of the first liquid separator 4 to obtain a first stream. The top and the bottom of the second liquid separator 7 are respectively communicated with the compressor 2 and the upper part of the methane desorption tower 8, for carrying out the second gas-liquid separation on the first stream after the pressure reduction and the cooling treatment by a desorption tower feed cooler 6. The top of the second liquid separator 7 discharges the second gas phase and returns to the compressor 2. The bottom of the second liquid separator 7 discharges the second liquid phase and enters the upper part of the methane desorption tower 8. The top and the bottom of the methane desorption tower 8 are respectively communicated with the compressor 2 and the middle of the desorption tower 11, for carrying out the methane desorption on the second liquid phase discharged from the bottom of the second liquid separator 7. The top of the methane desorption tower 8 discharges desorption gas and returns to the compressor 2. The bottom of the methane desorption tower 8 discharges rich absorbent which is pressurized by a rich absorbent pump 10 and enters the middle of the desorption tower 11. The bottom of the desorption tower 11 is communicated with the top of the absorption tower 5, for carrying out the desorption separation on the rich absorbent discharged from the bottom of the methane desorption tower 8. The top of the desorption tower 11 recovers the concentrated gas 13 containing carbon two components. The bottom of the desorption tower 11 discharges lean absorbent and returns to the top of the absorption tower 5.

[0191] According to a preferred embodiment of the present application, the device further comprises a methane desorption tower reboiler 9 which is respectively communicated with the lower part and the bottom of the methane desorption tower 8 and the top of the absorption tower 5, for supplying heat to the bottom of the methane desorption tower 8 with the lean absorbent discharged from the bottom of the desorption tower 11. A part of the second stream 16 obtained by the heat exchange of the lean absorbent is sent out of the boundary area as the light hydrocarbon component 14 for further treatment. The remaining part returns to the top of the absorption tower 5.

[0192] Compared with the prior art, the method and device for recovering C2-C4 components (including but not limited to carbon two components or carbon two and three components or carbon two, three and four components) in the industrial gas containing methane provided by the present application have the advantages and beneficial effects including but not limited to:

[0193] (1) The present application adopts high-pressure C2-C4 component absorption, low-pressure methane desorption and desorption separation, which not only reduces the amount of absorbent and the energy consumption of absorbent desorption, but also increases the relative volatility between C1-C5 hydrocarbon components at low pressure, reduces the load of the methane desorption column reboiler and the column bottom temperature of the methane desorption column, so that the methane desorption column reboiler only needs the process stream (depleted absorbent from the desorption column) in the device as a heat source, greatly saving steam consumption and device energy consumption.

[0194] (2) The carbon four fraction and / or carbon five fraction absorption process and the methane desorption process are independently carried out in two columns, with little mutual influence and no back mixing. The absorption process and the methane desorption process are each operated under ideal conditions, i.e., high pressure and low temperature are beneficial to absorption, the amount of absorbent is small, and the processing capacity of the steam-out column is small; low pressure is beneficial to the steam-out of methane.

[0195] (3) Since the load of the methane desorption column reboiler decreases with the decrease of the operating pressure, the desorption gas at the top of the methane desorption column can be returned to the inlet or section of the compressor, the pressure of the methane desorption column can be controlled, the reboiler of the column bottom of the methane desorption column can just use up the waste heat of the depleted absorbent from the desorption column, at the same time, the energy consumption of the compressor increases the least, and then the total energy consumption of the device is the lowest.

[0196] (4) The process stream in the device is used as the heat source of the methane desorption column reboiler, if the feed of the methane desorption column fluctuates, the change of the reboiler load has little effect on the total energy consumption of the device, which increases the operation flexibility of the device.

[0197] (5) The carbon four fraction and / or carbon five fraction is used as the absorbent to absorb the C2-C4 components in the methane-containing industrial gas in the absorption column, the raw material of the absorbent is easy to obtain and has low cost.

[0198] (6) The lowest temperature of the compression cooling, absorption and rectification operations in the process flow is 5-15°C, a propylene refrigeration compressor is not needed, a lithium bromide refrigeration unit or the like can be selected to provide cold energy, a drying device is not needed, the investment is small, the operation is simple, and the energy consumption is low.

[0199] (5) The recovery rate of the C2-C4 components reaches more than 95%, and the enriched gas containing carbon two components or the enriched gas containing carbon two and carbon three components or the enriched gas containing carbon two, carbon three and carbon four components can be used as the raw material of an ethane cracking furnace or a gas separation unit.

[0200] (6) The absorption rich solution of the absorption column is fully contacted with the compressed gas in the liquid separation tank, a part of the C2-C4 heavy components in the gas phase is pre-absorbed, the amount of the gas phase entering the absorption column is reduced, the amount of the absorbent in the absorption column is reduced, and the energy consumption is saved.

[0201] (7) The first stream after mixing the first liquid phase and the absorption rich liquid is subjected to methane desorption, a second liquid separator is arranged, the gas phase flashed out in the pressure reduction process of the first stream is separated in advance, the gas phase separation process is avoided from being performed entirely in the methane desorption tower, 50% of the gas phase space required by the methane desorption tower is saved, and equipment investment is saved.

[0202] Embodiment

[0203] In order to facilitate the understanding of the present application, the present application will be described in detail below through specific embodiments.

[0204] Embodiment 1 and Comparative Example 1

[0205] Refinery dry gas is used as a raw material in Embodiment 1 and Comparative Example 1, and the refinery dry gas is treated by the method of the present application and a typical shallow cooling oil absorption process respectively to recover a C2 component. The composition and process parameters of the refinery dry gas from a certain refinery are shown in Table 1.

[0206] Table 1 Composition and process parameters of refinery dry gas

[0207] Refinery dry gas temperature, ℃ 40.0 Pressure, MPa G 1.20 Mass flow rate, t / h 54.0 Composition, mol% H2 5.03 N2 5.47 CH4 12.11 C2H6 12.76 C3H8 12.10 C4H 10 10.32 C5+ 2.02 H2O 0.18

[0208] Embodiment 1

[0209] Embodiment 1 is used to illustrate the method and device for recovering a C2 component by oil absorption separation of dry gas according to the present application.

[0210] The device comprises a compressor 2, a cooler 3, a liquid separator 4, an absorption tower 5, a methane desorption tower 7, a desorption tower 9, and a methane desorption tower reboiler 15;

[0211] The compressor 2, the cooler 3, and the liquid separator 4 are sequentially communicated; the compressor 2 is connected to a refinery dry gas 1 pipeline;

[0212] The bottom of the absorption tower 5 is respectively communicated with the top of the liquid separator 4 and the cooler 3, for countercurrently contacting the gas phase generated by the liquid separator with the absorbent, the top of the absorption tower 5 discharges absorption tail gas 14, and the bottom of the absorption tower 5 discharges absorption rich liquid which is pressurized by an absorption tower bottom liquid pump 6 and then returned to the cooler 3;

[0213] The upper part, the top, and the bottom of the methane desorption tower 7 are respectively communicated with the bottom of the liquid separator 4, the compressor 2, and the desorption tower 9, for performing methane desorption on the liquid phase generated by the liquid separator 4 after pressure reduction, the top of the methane desorption tower 7 discharges desorption gas which is returned to the compressor 2, and the bottom of the methane desorption tower 7 discharges rich absorbent which is pressurized by a rich absorbent pump 8 and then enters the middle part of the desorption tower 9.

[0214] The bottom of the desorption column 9 is connected to the methane desorption column reboiler 15 for desorption of the rich absorbent from the column bottom of the methane desorption column 7, and the overhead of the desorption column 9 recovers the enriched gas 10 containing carbon two components, and the column bottom of the desorption column 9 discharges the lean absorbent as the heat source of the methane desorption column reboiler 15;

[0215] The methane desorption column reboiler 15 is connected to the lower part and the bottom of the methane desorption column 7 and the top of the absorption column 5, respectively, for heating the column bottom of the methane desorption column 7 with the lean absorbent discharged from the column bottom of the desorption column 9, and a part of the stream 13 obtained after heat exchange of the lean absorbent is sent out of the boundary area as the light hydrocarbon component 12 for post-treatment, and the remaining part is returned to the top of the absorption column 5.

[0216] The method comprises the following steps:

[0217] (1) The refinery dry gas with a pressure of 1.2 MPaG is introduced into a compressor, and after three-stage compression, the pressure of the compressed dry gas is 3.9 MPaG. After being combined with the absorption column absorption rich liquid (118 t / h), the pressurized dry gas is cooled to 15°C by a lithium bromide absorption refrigerator to prepare 7°C coolant water, and then sent to a liquid separation tank for gas-liquid separation. The gas phase at the top of the liquid separation tank is sent to the bottom of the absorption column, and the liquid phase at the bottom of the liquid separation tank is decompressed to 1.5 MPaG and then sent to the methane desorption column for treatment.

[0218] (2) In the absorption column, the mixed butane in the refinery is used as the absorbent (the absorbent circulation amount is 105 t / h), which is sprayed from the top of the column to absorb the carbon two fractions and heavier components in the feed gas. The theoretical plate number of the absorption column is 20, the operating pressure is 3.8 MPaG, the top temperature of the column is 17°C, and the bottom temperature of the column is 22°C. The liquid phase at the bottom of the absorption column is pressurized to 4 MPaG by an absorption column bottom liquid pump, and then combined with the gas phase at the outlet of the compressor before returning to the cooler. The tail gas not absorbed at the top of the absorption column is sent out of the boundary area to the absorbent recovery unit outside the boundary area.

[0219] (3) The liquid phase at the bottom of the liquid separation tank is decompressed to 1.8 MPaG and enters the top of the methane desorption column under the action of the pressure difference to remove the methane and other light components in the column feed. The theoretical plate number of the methane desorption column is 30, the operating pressure is 1.5 MPaG, the top temperature of the column is 13°C, and the bottom temperature of the column is 67°C. The gas phase at the top of the methane desorption column is returned to the inlet of the compressor, and the column bottom discharge of the methane desorption column is pressurized to 2.5 MPaG by a rich absorbent pump and then sent to the middle part of the desorption column.

[0220] (4) The theoretical plate number of the desorption column is 40, the operating pressure is 2.0 MPaG, the column top temperature is 56℃, and the column bottom temperature is 109℃. The desorption column is heated by low-pressure steam. The overhead of the desorption column is a concentrated gas containing carbon dioxide components, which is sent to an ethane cracking furnace as a raw material. The lean absorbent (temperature 109℃) from the bottom of the desorption column is pressurized to 4.4 MPaG by an absorbent circulating pump, and is used to heat a methane desorption column reboiler. After heat exchange, the obtained stream is returned to the absorption column for recycling, and a light hydrocarbon product mainly containing C3-C5 hydrocarbons is extracted and sent out of the boundary zone to an ethylene plant cracking furnace as a raw material.

[0221] In the method of the present embodiment, a concentrated gas containing carbon dioxide components and a light hydrocarbon component are obtained, and their compositions and process parameters are shown in Table 2, wherein the C2 recovery rate is 98.3%.

[0222] Table 2 Concentrated gas and light hydrocarbon component

[0223]

[0224] Comparative Example 1

[0225] The refinery dry gas in Table 1 is recovered by using the typical shallow cold oil absorption process of CN109553504A. The main difference between the process used in Comparative Example 1 and Example 1 is that the carbon four absorbent absorption and methane desorption process are carried out in one absorption-steam-out column, and the operating pressure is close. Since the pressure of the methane desorption process is higher, the column bottom temperature is higher, and low-pressure steam is used as the heat source of the methane desorption process column reboiler.

[0226] In the method of the present embodiment, a concentrated gas containing carbon dioxide components and a light hydrocarbon component are obtained, and their compositions and process parameters are shown in Table 2, wherein the C2 recovery rate is 98.3%.

[0227] Table 3 Concentrated gas composition

[0228] Concentrated gas composition, mol% CH4 4.22 C2H6 48.32 C3H8 40.25 C4H 10 7.12 H2O 0.09

[0229] Table 4 Comparison data of the present application and prior art

[0230]

[0231] From Table 2-4, the lowest temperature of the process stream of the present application is 5-15℃, no low temperature propylene cooling capacity is needed, no propylene refrigeration device and drying device are needed, and the equipment investment is less. Compared with the conventional shallow cooling oil absorption process, in the case of obtaining the same high carbon two recovery rate, the present application greatly reduces the energy consumption required by the process by reducing the methane desorption process pressure, and reduces the grade of the heating medium, and can use the process stream inside the device as the heating medium for the methane desorption tower, saves the consumption of low pressure steam introduced from outside the device, and reduces the total energy consumption of the device by 17.8%.

[0232] Example 2 and Comparative Example 2

[0233] Refinery dry gas is used as raw material in Example 2 and Comparative Example 2, and refinery dry gas is treated by the method of the present application and the typical shallow cooling oil absorption process respectively to recover carbon two and carbon three components. The composition and process parameters of the refinery dry gas from a certain refinery are shown in Table 5.

[0234] Table 5 Composition and process parameters of refinery dry gas

[0235] Refinery dry gas temperature, ℃ 40.0 Pressure, MPa G 1.0 Mass flow rate, t / h 54.0 Composition, mol% H2 45.03 N2 5.47 CH4 12.11 C2H6 12.76 C3H8 12.10 C4H 10 10.32 C5+ 2.02 H2O 0.18

[0236] Example 2

[0237] Example 2 is used to illustrate the method and device for recovering carbon two and carbon three components from oil absorption separation dry gas of the present application.

[0238] The device comprises: a compressor 2, a cooler 3, a first liquid separator 4, an absorption tower 5, a second liquid separator 7, a methane desorption tower 8, a methane desorption tower reboiler 9 and a desorption tower 11;

[0239] The compressor 2, the cooler 3 and the first liquid separator 4 are sequentially communicated; the compressor 2 communicates the refinery dry gas 1;

[0240] The bottom of the absorption tower 5 is respectively communicated with the top of the first liquid separator 4 and the middle of the second liquid separator 7, for contacting the first gas phase discharged from the top of the first liquid separator 4 with the absorbent countercurrently, the absorption tail gas 15 is discharged from the top of the absorption tower 5, and the first stream is obtained by mixing the absorption rich liquid discharged from the tower bottom of the absorption tower 5 with the first liquid phase discharged from the bottom of the first liquid separator 4;

[0241] The top and bottom of the second liquid separator 7 are communicated with the compressor 2 and the upper part of the methane desorption column 8 respectively, for cooling and treating the first stream after pressure reduction by the desorption column feed cooler 6, and then carrying out the second gas-liquid separation, the top of the second liquid separator 7 discharges the second gas phase and returns to the compressor 2, and the bottom of the second liquid separator 7 discharges the second liquid phase and enters the upper part of the methane desorption column 8;

[0242] The top and bottom of the methane desorption column 8 are communicated with the compressor 2 and the middle part of the desorption column 11 respectively, for carrying out the methane desorption of the second liquid phase discharged from the bottom of the second liquid separator 7, the top of the methane desorption column 8 discharges the desorption gas and returns to the compressor 2, and the column bottom of the methane desorption column 8 discharges the rich absorbent, which is pressurized by the rich absorbent pump 10 and then enters the middle part of the desorption column 11;

[0243] The bottom of the desorption column 11 is communicated with the methane desorption column reboiler 9, for carrying out the desorption separation of the rich absorbent discharged from the column bottom of the methane desorption column 8, the overhead of the desorption column 11 recovers the enriched gas 13 mainly composed of carbon two and carbon three components, and the column bottom of the desorption column discharges the lean absorbent, which is pressurized by the absorbent circulation pump 12 and then used as the heat source of the methane desorption column reboiler 9;

[0244] The methane desorption column reboiler 9 is communicated with the lower part and the bottom of the methane desorption column 8 and the top of the absorption column 5 respectively, for supplying heat to the column bottom of the methane desorption column 8 by using the lean absorbent discharged from the column bottom of the desorption column 11, and part of the second stream 16 obtained after heat exchange is sent out of the boundary area for further treatment as the light hydrocarbon component 14, and the remaining part returns to the top of the absorption column 5.

[0245] The method comprises:

[0246] (1) The refinery dry gas with a pressure of 1 MPaG is sent into a compressor, and after two-stage compression, the pressure of the compressed dry gas is 3.7 MPaG, and the pressurized dry gas is cooled to 15℃ by using 7℃ refrigerant water prepared by a lithium bromide absorption refrigerating machine, and then sent to a first liquid separator for first gas-liquid separation. The first gas phase discharged from the top of the first liquid separator enters the bottom of an absorption column, and the first liquid phase discharged from the bottom of the first liquid separator is reduced to 1.7 MPaG and then sent into a methane desorption column for treatment.

[0247] (2) In the absorption column, n-butane in the refinery is used as an absorbent (absorbent circulation amount: 120 t / h), which is sprayed from the top, to absorb carbon two, carbon three and heavier components in the compressed dry gas. The theoretical plate number of the absorption column is 20, the operating pressure is 3.6 MPaG, the overhead temperature is 17℃, and the column bottom temperature is 27℃. The tail gas not absorbed at the top of the absorption column is sent into a fuel gas pipeline network, and the column bottom of the absorption column is mixed with the first liquid phase to obtain a first stream after being reduced to 1.7 MPaG.

[0248] (3) The first stream is cooled to 15℃ in the desorption column feed cooler and then sent to the second liquid separator for the second gas-liquid separation. The second gas phase mainly contains C2 and C2+ light components and is returned to the inlet of the dry gas compressor.

[0249] (4) The second liquid phase is sent to the top of the methane desorption column to remove the light components such as methane in the second liquid phase. The desorption gas at the top of the methane desorption column is returned to the inlet of the dry gas compressor. The theoretical plate number of the methane desorption column is 30, the operating pressure is 1.5 MPaG, the top temperature is 15℃, and the bottom temperature is 55℃. The lean absorbent from the desorption column is used as the heat source for the reboiler of the methane desorption column.

[0250] (5) The rich absorbent from the bottom of the methane desorption column is pumped to the middle of the desorption column. The theoretical plate number of the desorption column is 40, the operating pressure is 1.6 MPaG, the top temperature is 55℃, and the bottom temperature is 105℃. The desorption column is heated by low-pressure steam. The concentrated gas mainly containing C2 and C3 components is obtained at the top of the desorption column and is sent to the cracking furnace of the ethylene plant as raw material. The lean absorbent from the bottom of the desorption column is pumped, heated by the reboiler of the methane desorption column, and then at least part of the second stream obtained by heat exchange is returned to the absorption column for recycling. Meanwhile, a light hydrocarbon product mainly containing C4 and C5 components is extracted and sent to the cracking furnace of the ethylene plant as raw material.

[0251] In the method of the present embodiment, the concentrated gas mainly containing C2 and C3 components and the light hydrocarbon components are obtained. Their compositions and process parameters are shown in Table 6. The recovery rate of C2 and C3 components is 98.2%.

[0252] Table 6 Concentrated gas and light hydrocarbon components

[0253]

[0254] Comparative Example 2

[0255] The typical shallow cold oil absorption process in CN106609161B is used to recover the refinery dry gas in Table 5. The main difference between the process used in Comparative Example 2 and Example 2 is that the C4 absorbent absorption and the methane desorption process are carried out in one absorption-steam-out column, and the operating pressure is close. Since the pressure of the methane desorption process is higher, the corresponding bottom temperature is higher, and low-pressure steam is used as the heat source for the reboiler of the methane desorption column.

[0256] In the method of Comparative Example 1, the concentrated gas mainly containing C2 and C3 components is obtained. Its composition is shown in Table 7. The recovery rate of C2 and C3 components is 98.2%. The comparative data of the present application and the typical shallow cold oil absorption process and the deep cold separation process technical solution are shown in Table 8.

[0257] Table 7 Concentrated gas composition

[0258] Concentrated gas composition, mol% CH4 C2H6 C3H8 C4H 10 7.42 H2O 0.09

[0259] Table 8 Comparison data of the present application and prior art

[0260]

[0261] From Tables 6-8, it can be seen that the lowest temperature of the process stream of the present application is 5-15℃, no low temperature propylene cooling capacity is needed, no propylene refrigeration device and drying device are needed, and the equipment investment is less. Compared with the conventional shallow cooling oil absorption process, in the case of obtaining the same high carbon two and carbon three recovery rate, the present application greatly reduces the energy consumption required by the process by reducing the pressure of the methane desorption process, and reduces the grade of the heating medium, can use the process stream in the device as the heat source for the methane desorption tower, saves the consumption of low pressure steam introduced from outside the device, and reduces the total energy consumption of the device by 16.8%.

[0262] As can be illustrated from the examples, compared with the conventional shallow cooling oil absorption process, the present application not only realizes high carbon two or carbon two and carbon three recovery rate, but also by using high pressure absorption and low pressure methane desorption, the methane desorption tower reboiler only needs the process stream (desorption tower bottom lean absorbent) in the device as the heat source, reduces the material consumption, greatly saves the steam consumption and the total energy consumption of the device.

[0263] The above describes in detail various embodiments of the present application, but the above description is only exemplary and the present application is not limited thereto. Various modifications can be made to the technical solutions of the present application without deviating from the technical concepts and scope of the present application, including combining each technical feature in any other suitable manner, and these modifications and combinations should also be considered as disclosed by the present application and fall within the protection scope of the present application.

Claims

1. A method for recovering carbon dioxide from methane-containing industrial gas, the method comprising: The following steps are involved: (1) compressing methane-containing industrial gas, cooling the obtained compressed gas, and performing gas-liquid separation to obtain a gas phase and a liquid phase; (2) contacting the gas phase with an absorbent to absorb the carbon two components to obtain absorbed tail gas and absorbed rich liquid, wherein: The absorption rich liquid is returned and mixed into 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 the first stream; (3) reducing the pressure of the liquid phase obtained in step (1) or the first stream obtained in step (2); (4) desorbing methane from the depressurized stream in step (3) to obtain desorbed gas and rich absorbent, wherein the desorbed gas is returned to the compression or discharge step (1), or The logistics after decompression in step (3) is subjected to a second gas-liquid separation to obtain a second gas phase and a second liquid phase, the second gas phase is returned to the compression in step (1), the second liquid phase is subjected to methane desorption to obtain desorbed gas and rich absorbent, the desorbed gas is returned to the compression in step (1) or discharged; (5) Desorbing and separating the rich absorbent to obtain a lean absorbent and an enriched gas containing carbon two components, and the lean absorbent is returned and mixed with the absorbent in step (2).

2. The method according to claim 1, wherein the methane-containing industrial gas comprises dry gas, cracked gas, natural gas, shale gas, wherein preferably the dry gas is selected from at least one of refinery dry gas and coal chemical dry gas.

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

4. The method according to claim 3, wherein the pressure of the compressed gas is 2.5-4.6 MPaG, preferably 3-4.2 MPaG; Preferably, the compression is multi-stage compression, preferably two-stage compression or three-stage compression; Preferably, the cooling temperature is 5-40°C, preferably 10-20°C, and more preferably, the cooling uses a cooling medium with a temperature above 0°C, and the cooling medium is selected from at least one of low-temperature water, circulating water, propylene, ammonia and liquid nitrogen.

5. The method according to claim 3 or 4, wherein the carbon two component absorption is carried out in an absorption tower; Preferably, the parameters of the absorption tower are include: The number of theoretical plates is 15-30, the operating pressure is 2.5-4.6MPaG, preferably 3-4.2MPaG, the tower top temperature is 10-60°C, and the tower bottom temperature is 10-70°C; Preferably, the carbon two components are selected from ethane and / or ethylene.

6. The method according to any one of claims 3 to 5, wherein the methane desorption is carried out in a methane desorption tower, Preferably, the parameters of the methane stripping tower are include: The number of theoretical plates is 20-50, the operating pressure is 0.5-2.4MPaG, the tower top temperature is 10-60℃, and the tower bottom temperature is 35-90℃; Preferably, the operating pressure of the methane stripping tower is 1.0-1.9 MPaG; Preferably, the top temperature of the methane stripping tower is 10-20°C; Preferably, the bottom temperature of the methane stripping tower is 40-75°C; Preferably, the pressure of the liquid phase after decompression is 0.8-3 MPaG, preferably 1-2 MPaG.

7. The method according to any one of claims 3 to 6, wherein the desorption separation is carried out in a desorption tower, Preferably, the parameters of the desorption tower are include: The number of theoretical plates is 20-50, the operating pressure is 1-2.8MPaG, the tower top temperature is 25-70℃, and the tower bottom temperature is 90-160℃.

8. The method according to any one of claims 3 to 7, wherein the lean absorbent is used as a heat source for the methane desorption, and at least part of the stream obtained after heat exchange is returned and mixed into the absorbent; Preferably, a portion of the stream is sent out of the restricted area as a light hydrocarbon component, and the remaining portion is returned and mixed into the absorbent; Preferably, the light hydrocarbon component is selected from at least one of C3, C4 and C5 hydrocarbons.

9. The method according to any one of claims 1 to 8, wherein the method further recovers C3 components, preferably the C3 components contain propane and / or propylene.

10. The method according to claim 1 or 2, wherein the first logistics 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 desorbed gas and rich absorbent; Preferably, the method further recovers C3 components, preferably the C3 components comprise propane and / or propylene. Preferably, the method recovers C2C3 components, preferably the C2C3 components comprise ethane and / or ethylene, and propane and / or propylene; Preferably, the methane-containing industrial gas contains more than 0.1 mol% carbon six and above components.

11. The method according to claim 10, wherein the pressure of the compressed gas is 2.5-5 MPaG, preferably 3-4.2 MPaG; Preferably, the compression is multi-stage compression, preferably two-stage compression or three-stage compression; Preferably, the cooling temperature is 5-45°C, preferably 10-20°C, and more preferably, the cooling uses a cooling medium with a temperature above 0°C, and the cooling medium is selected from at least one of low-temperature water, circulating water, propylene, ammonia and liquid nitrogen.

12. The method according to claim 10 or 11, wherein the carbon two and three components are absorbed in an absorption tower; Preferably, the parameters of the absorption tower are include: The number of theoretical plates is 15-30, the operating pressure is 2.5-5 MPaG, preferably 3-4.2 MPaG, the tower top temperature is 10-30°C, and the tower bottom temperature is 10-60°C. Preferably, the pressure of the first logistics after decompression is 0.5-2.4 MPaG, preferably 0.8-2 MPaG; Preferably, before / after the pressure reduction treatment of the first logistics, the first logistics is cooled, and the temperature of the first logistics after cooling is 5-40°C, preferably 5-15°C.

13. The method according to any one of claims 10 to 12, wherein the methane desorption is carried out in a methane desorption tower; Preferably, the parameters of the methane stripping tower are include: The number of theoretical plates is 20-50, the operating pressure is 0.5-2.4MPaG, the tower top temperature is 10-40℃, and the tower bottom temperature is 35-100℃; Preferably, the operating pressure of the methane stripping tower is 1.0-1.9 MPaG; Preferably, the top temperature of the methane stripping tower is 10-20°C; Preferably, the bottom temperature of the methane stripping tower is 40-75°C.

14. The method according to any one of claims 10 to 13, wherein the desorption separation is carried out in a desorption tower; Preferably, the parameters of the desorption tower are include: The number of theoretical plates is 20-50, the operating pressure is 1-2.8MPaG, the tower top temperature is 15-70°C, and the tower bottom temperature is 90-200°C.

15. The method according to any one of claims 10 to 14, wherein the lean absorbent is used as a heat source for the methane desorption, and at least part of the second stream obtained after heat exchange is returned and mixed into the absorbent; Preferably, a portion of the second stream is sent out of the restricted area as a light hydrocarbon component, and the remaining portion is returned and mixed into the absorbent; Preferably, the light hydrocarbon component is selected from at least one of C4 and C5 hydrocarbons.

16. The method according to claim 6 or 13, wherein the heat source of the bottom of the methane stripping tower is provided by a methane stripping tower reboiler, and the heat source of the methane stripping tower reboiler is a process stream; Preferably, the process stream is selected from at least one of the absorbent, the rich absorbent and the lean absorbent, preferably the lean absorbent.

17. The method according to any one of claims 1 to 16, wherein the absorbent is selected from a C4 fraction and / or a C5 fraction, the C4 fraction contains at least one of n-butane, isobutane and butene, and the C5 fraction contains at least one of n-pentane, isopentane and neopentane, preferably a C4 fraction.

18. The method according to any one of claims 1 to 17, wherein the method further recovers C4 components, preferably the C4 components comprise butane and / or butene.

19. The method according to claim 5, wherein the absorbent inlet temperature is 40-50°C, the gas phase inlet temperature is 40°C, the cooling medium in step (1) is circulating water, and the top temperature of the absorption tower is 40-60°C; 20. The method according to claim 5, wherein the absorbent inlet temperature is 5-20°C, the gas phase inlet temperature is 5-20°C, the cooling medium in step (1) is low-temperature water, and the top temperature of the absorption tower is 10-30°C.

21. A device for recovering carbon dioxide from methane-containing industrial gas, the device include: Compressors, coolers, separators, absorbers, methane strippers and desorbers; The compressor is connected to a methane-containing industrial gas pipeline, and the compressor, cooler and liquid separator are connected in sequence; The bottom of the absorption tower is connected to the top of the liquid separator and the cooler respectively, so as to make the gas phase discharged from the top of the liquid separator contact with the absorbent in countercurrent, the top of the absorption tower discharges the absorption tail gas, and the bottom of the absorption tower discharges the absorption rich liquid and returns it to the cooler; The upper part, top and bottom of the methane desorption tower are respectively connected to the bottom of the liquid separator, the compressor and the middle part of the desorption tower, so as to discharge the liquid phase from the bottom of the liquid separator and then depressurize it for methane desorption, the top of the methane desorption tower discharges the desorbed gas and returns it to the inlet, interstage or external discharge of the compressor, and the bottom of the methane desorption tower discharges the rich absorbent into the middle part of the desorption tower for desorption and separation; The bottom of the desorption tower is connected to the top of the absorption tower, and the bottom of the desorption tower is used to discharge the lean absorbent and return it to the top of the absorption tower. The top of the desorption tower recovers concentrated gas containing carbon 2 components, such as carbon 2 and carbon 3 components.

22. A device for recovering carbon dioxide from methane-containing industrial gas, the device include: 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 methane-containing industrial gas pipeline, and the compressor, the cooler and the first liquid separation tank are connected in sequence; The bottom of the absorption tower is connected to the top of the first liquid separator and the middle of the second liquid separator, respectively, so as to allow the first gas phase discharged from the top of the first liquid separator to be in countercurrent contact with the absorbent, and the top and bottom of the absorption tower discharge the absorption tail gas and the absorption rich liquid respectively, and the mixed liquid of the absorption rich liquid and the first liquid phase discharged from the bottom of the first liquid separator or the absorption rich liquid is used as the first logistics, and the first logistics enters the middle of the second liquid separator after decompression for the second gas-liquid separation; The top and bottom of the second liquid separator are respectively connected to the compressor and the upper part of the methane stripping tower, so that the second gas phase is discharged from the top of the second liquid separator and returned to the inlet or the stage of the compressor, and the second liquid phase is discharged from the bottom of the second liquid separator and enters the upper part of the methane stripping tower for methane stripping; The top and bottom of the methane stripping tower are respectively connected to the compressor and the middle of the stripping tower, so that the stripped gas is discharged from the top of the methane stripping tower and returned to the inlet, interstage or external discharge of the compressor, and the tower kettle of the methane stripping tower discharges the rich absorbent and enters the middle of the stripping tower for desorption and separation; The bottom of the desorption tower is connected to the top of the absorption tower, and the bottom of the desorption tower is used to discharge the lean absorbent and return it to the top of the absorption tower. The top of the desorption tower recovers concentrated gas containing carbon 2 components, such as carbon 2 and carbon 3 components.

23. The device according to claim 21 or 22, wherein the methane-containing industrial gas comprises dry gas, cracked gas, natural gas, shale gas, wherein preferably the dry gas is selected from at least one of refinery dry gas and coal chemical dry gas.

24. The device according to any one of claims 21 to 23, wherein the device further include: Methane stripper reboiler; The methane stripping tower reboiler is respectively connected to the bottom of the stripping tower, the lower part and the bottom of the methane stripping tower, and the top of the absorption tower, and is used to discharge the lean absorbent from the bottom of the stripping tower to heat the bottom of the methane stripping tower, and at least part of the stream obtained by heat exchange of the lean absorbent is returned to the top of the absorption tower; Preferably, the methane stripping tower reboiler is also connected to a post-processing unit for sending a portion of the stream discharged from the methane stripping tower reboiler as a light hydrocarbon component out of the boundary area for post-processing, and returning the remaining portion to the top of the absorption tower.

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