Method and device for preparing polymer grade ethylene by recovering C2 component in dry gas and application

Abstract

The invention relates to the technical field of dry gas treatment, and discloses a method and a device for preparing polymer grade ethylene by recovering C2 components in dry gas and application, the method comprises the following steps: (1) compressing the raw material dry gas and carrying out gas-liquid separation to obtain a gas phase and a liquid phase; (2) contacting the gas phase with an absorbent for C2 component absorption to obtain absorption tail gas and an absorption rich solution; (3) performing methane desorption on the liquid phase to obtain desorbed gas and a rich absorbent; (4) desorbing and separating the rich absorbent to obtain a lean absorbent and concentrated gas; (5) the concentrated gas is subjected to acid gas removal, dehydration and impurity removal and then sent to a deethanizer for separation of light components and heavy components, and a gas phase at the top of the tower serves as feed to enter an ethylene rectifying tower for separation of ethylene and ethane; and (6) extracting a polymer-grade ethylene product from the side of the body of the ethylene rectifying tower. The C2 component recovered by the method has the advantages of high purity, high recovery rate, simple process, low steam consumption, no need of a deoxidation reactor and a demethanizer, and low energy consumption of the device.

Description

Technical Field

[0001] This invention relates to the field of dry gas treatment technology, and more specifically, to a method, apparatus, and application for recovering C2 components from dry gas to produce polymer-grade ethylene. Background Technology

[0002] Currently, the main industrial-scale methods for recovering ethane and ethylene components from dry gas are:

[0003] (1) Cryogenic separation method, which is a mature process with high ethylene recovery rate and high purity, but requires a dryer and propylene refrigeration unit or ethylene-propylene composite refrigeration unit, which requires a large investment and high energy consumption.

[0004] (2) Pressure swing adsorption is simple to operate and generally has low energy consumption, but the product purity is low and the recovery rate of C2 components is low. When the scale of raw material dry gas treatment is large, the investment in the equipment and the land area are large.

[0005] (3) Shallow cold oil absorption method: The process is safe and reliable, with high C2 and C3 recovery rates. It has no requirements on the sulfur 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 whole process is large.

[0006] CN112725032B discloses a method and apparatus for recovering C2 components from dry gas. The method includes: (1) compressing the raw dry gas, cooling the resulting compressed gas, and then performing gas-liquid separation to obtain a gas phase and a liquid phase; (2) contacting the gas phase with an absorbent to absorb C2 components, obtaining an absorption tail gas and an absorption-rich liquid, wherein the absorption-rich liquid is returned and mixed into the compressed gas; (3) depressurizing the liquid phase and then performing methane desorption to obtain a desorbed gas and a rich absorbent, wherein the desorbed gas is returned to the compression step (1) or discharged; (4) desorbing and separating the rich absorbent to obtain a lean absorbent and a concentrated gas mainly composed of C2 components, wherein the lean absorbent is returned and mixed into the absorbent. This method achieves high C2 component recovery rate and low overall energy consumption of the apparatus.

[0007] CN103159581B discloses an apparatus for recovering C2 from refinery dry gas using a combined absorption method. It includes a compressor, a pretreatment unit, a refinery dry gas cooling unit, an absorption unit, and a distillation unit. The absorption unit comprises a gas-liquid separator, a C2 absorption tower, and a methane desorption tower. The absorbent rich in C2 components absorbed from the dry gas separates C2 from the absorbent components at the desorption tower. The operating pressure of the C2 absorption tower is 2.5-3.0 MPaG, the operating pressure of the methane desorption tower is 2.5-3.1 MPaG, and the operating pressure of the desorption tower is 2.2-2.6 MPaG. The methane desorption tower requires a heat source of approximately 120°C from the refinery.

[0008] CN 111320523B discloses a method and apparatus for separating ethylene from refinery dry gas. The separation method includes steps such as compression, purification, cooling, absorption, propane removal, methanation removal, and ethylene refining. Separating ethylene from refinery dry gas involves purifying the gas after pressurization. The purified gas is cooled and then fed into an oil absorption tower. The stream from the bottom of the absorption tower enters a propane removal tower. The top gas from the propane removal tower is sent to a methanation removal tower. The top gas from the methanation removal tower is returned to the compressor section or sent outside the boundary zone. The bottom stream from the methanation removal tower is sent to an ethylene distillation tower. The stream from the methanation removal tower enters the ethylene distillation tower, thus achieving the direct extraction of polymer-grade ethylene from refinery dry gas.

[0009] CN111320522B discloses a method and apparatus for separating ethylene from refinery dry gas. The separation method includes steps such as compression, purification, cooling, absorption, demethanization, depropanization, and ethylene refining. This method involves pressurizing the refinery dry gas and then purifying it, including but not limited to removing acidic gases, oxygen, drying, arsenic, mercury, and carbon. For refinery dry gas containing oxygen and water, deoxygenation and drying are necessary.

[0010] In summary, when recovering C2 components from dry gas to produce polymer-grade ethylene, existing processes require deoxygenation and dehydration of all raw gas, or the installation of a dedicated demethanizer, resulting in significant investment and high energy consumption.

[0011] Therefore, it is of great significance to research and develop a method and apparatus for recovering the C2 component from dry gas to produce polymer-grade ethylene. Summary of the Invention

[0012] The purpose of this invention is to overcome the shortcomings of existing technologies in the production of polymer-grade ethylene from C2 components in dry gas. These technologies require deoxygenation and dehydration of all raw gas or the installation of a dedicated demethanizer, resulting in high investment and energy consumption. This invention provides a method, apparatus, and application for recovering C2 components from dry gas to produce polymer-grade ethylene. This method recovers high purity and high recovery rate of C2 components, has a simple process, low steam consumption, eliminates the need for deoxygenation reactors and demethanizers, and has low energy consumption.

[0013] To achieve the above objectives, a first aspect of the present invention provides a method for recovering C2 components from dry gas to produce polymerization-grade ethylene, wherein the method comprises:

[0014] (1) The raw material dry gas is compressed, and the resulting compressed gas is cooled and then separated into gas and liquid phases to obtain gas and liquid phases;

[0015] (2) The gas phase is contacted with the absorbent phase to absorb C2 components, resulting in absorption tail gas and absorption rich liquid. The absorption rich liquid is returned and mixed into the compressed gas.

[0016] (3) After depressurizing the liquid phase, methane is desorbed to obtain desorbed gas and rich absorbent. The desorbed gas is returned to the compression or discharge in step (1).

[0017] (4) The rich absorbent is desorbed and separated to obtain a lean absorbent and a concentrated gas mainly composed of C2 components. The lean absorbent is returned and mixed into the absorbent.

[0018] (5) The enriched gas, which is mainly composed of C2 components, is sent to the de-ethanizer tower after being treated by deacidification, dehydration and impurity removal. The gas phase at the top of the tower is fed into the ethylene distillation tower to separate ethylene and ethane. The liquid phase at the bottom of the tower is returned to the absorption system in step (2) as an absorbent.

[0019] (6) The non-condensable gas at the top of the ethylene distillation column is returned to the compressor in step (1), and ethane product with ethane as the main component is obtained in the bottom of the column. Polymer-grade ethylene product is extracted from the side stream of the column.

[0020] The second aspect of the present invention provides an apparatus for recovering carbon-two components from dry gas to produce polymer-grade ethylene, wherein the apparatus comprises: a compressor 2, a cooler 3, a separator 4, an absorption tower 5, a methane desorption tower 7, a desorption tower 9, a purification system, an ethane removal tower 12, and an ethylene distillation tower 13.

[0021] The refining system includes an alkali washing tower 10 and a dryer 11. The upper part of the alkali washing tower 10 is connected to fresh alkali solution 17, which is used to remove acidic gases from the concentrated gas 16 to a lower content. The dryer 11 is used to remove water from the concentrated gas 16.

[0022] The de-ethane tower 12 is connected to the outlet of the dryer 11, the top of the tower is connected to the ethylene distillation tower 13, and the bottom of the tower is connected to the absorption tower 5, for separating the C2 component from the C3 and above heavy components in the enriched gas 16;

[0023] The top of the ethylene distillation column 13 is connected to the compressor 2, which is used to separate the light components from the carbon-rich distillate and return them to the compressor 2. The bottom of the column yields ethane product 21, which is mainly composed of ethane, and the polymer grade ethylene product 20 is collected from the middle of the column.

[0024] A third aspect of the present invention provides the application of the aforementioned apparatus in the aforementioned method for recovering carbon-two components from dry gas to produce polymer-grade ethylene.

[0025] The above-described technical solution, employing the technical solution of the present invention, has the following beneficial effects:

[0026] (1) The present invention adopts high pressure carbon two-component absorption, low pressure methane desorption and desorption separation, which reduces the amount of absorbent and the energy consumption of absorbent desorption. Furthermore, due to the increase in relative volatility among C1-C5 hydrocarbon components under low pressure, the load of the methane desorption tower reboiler and the bottom temperature of the methane desorption tower are reduced, so that the methane desorption tower reboiler only needs the process stream in the unit as a heat source, which greatly saves steam consumption and unit energy consumption.

[0027] (2) The rich absorbent liquid and compressed gas in the absorber are in full contact in the separator, pre-absorbing a portion of the heavy components such as C2-C4, reducing the amount of gas phase entering the absorber, reducing the amount of absorbent used in the absorber, and saving energy.

[0028] (3) The process flow inside the unit is used as the heat source for the reboiler of the methane desorption tower. If the feed to the methane desorption tower fluctuates, the change in the load of the reboiler has little impact on the total energy consumption of the unit, thus increasing the operational flexibility of the unit.

[0029] (4) The present invention uses low-pressure methane desorption and desorption separation, resulting in a lower methane content in the enriched gas. This eliminates the need for a demethanizer tower for subsequent separation, simplifying the process and reducing energy consumption.

[0030] (5) The present invention uses high pressure carbon two-component absorption, low pressure methane desorption and desorption separation. Oxygen, as a difficult-to-absorb component, is difficult to absorb and is more easily desorbed under low pressure methane desorption conditions. The oxygen content in the enriched gas is lower, which can eliminate the need for a subsequent deoxygenation reactor, simplify the process and reduce energy consumption.

[0031] (6) The recovery rate of C2 component is greater than 95%, and polymer-grade ethylene products can be obtained. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the apparatus provided by the present invention for recovering carbon two components from dry gas to produce polymer-grade ethylene;

[0033] Figure 2 This is a schematic diagram of the apparatus for recovering carbon-two components from dry gas to produce polymer-grade ethylene, provided in Comparative Example 1 of this invention.

[0034] Explanation of reference numerals in the attached figures

[0035] 1. Raw material dry gas 2. Compressor 3. Cooler

[0036] 4. Separating tank; 5. Absorption tower; 6. Absorption tower bottom liquid pump.

[0037] 7. Methane desorption tower; 8. Absorbent-rich pump; 9. Desorption tower

[0038] 10 Alkali washing tower; 11 Dryer; 12 Ethane removal tower

[0039] 13 Ethylene distillation column 14 Lean absorbent 15 Absorption tail gas

[0040] 16. Concentrated gas 17. Fresh lye solution 18. Waste lye solution

[0041] 19 Refined and concentrated gas; 20 Ethylene products; 21 Ethane products

[0042] 22 Deoxygenation reactor 23 Hydrogen Detailed Implementation

[0043] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0044] As previously stated, the first aspect of the present invention provides a method for recovering C2 components from dry gas to produce polymerization-grade ethylene, wherein the method comprises:

[0045] (1) The raw material dry gas is compressed, and the resulting compressed gas is cooled and then separated into gas and liquid phases to obtain gas and liquid phases;

[0046] (2) The gas phase is contacted with the absorbent phase to absorb C2 components, resulting in absorption tail gas and absorption rich liquid. The absorption rich liquid is returned and mixed into the compressed gas.

[0047] (3) After depressurizing the liquid phase, methane is desorbed to obtain desorbed gas and rich absorbent. The desorbed gas is returned to the compression or discharge in step (1).

[0048] (4) The rich absorbent is desorbed and separated to obtain a lean absorbent and a concentrated gas mainly composed of C2 components. The lean absorbent is returned and mixed into the absorbent.

[0049] (5) The enriched gas, which is mainly composed of C2 components, is sent to the de-ethanizer tower after being treated by deacidification, dehydration and impurity removal. The gas phase at the top of the tower is fed into the ethylene distillation tower to separate ethylene and ethane. The liquid phase at the bottom of the tower is returned to the absorption system in step (2) as an absorbent.

[0050] (6) The non-condensable gas at the top of the ethylene distillation column is returned to the compressor in step (1), and ethane product with ethane as the main component is obtained in the bottom of the column. Polymer-grade ethylene product is extracted from the side stream of the column.

[0051] The inventors of this invention discovered that because the methane desorption tower operates under low pressure, the content of light components such as methane, hydrogen, and oxygen in the enriched gas is low. After the ethane desorption tower separates the C3 and higher heavy components, the methane content in the refined enriched gas can be less than 1% (v), preferably 0-0.6% (v). The oxygen content is less than 5 ppm (v), preferably 0-5 ppm, more preferably 0-3 ppm. Therefore, there is no need to set up a demethanizer tower for separating methane from C2 and higher components, nor is there a need to set up a deoxygenation reactor to remove oxygen. This simplifies the process, reduces energy consumption, and saves investment.

[0052] In the method of this invention, the dry gas is not particularly limited, and 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 dry gas from catalytic cracking / catalytic pyrolysis units and dry gas from delayed coking units, and the coal chemical dry gas is selected from at least one of dry gas from methanol-to-olefins (MTO) and dry gas from methanol-to-aromatics (MTA). The dry gas used in this invention is not limited to these.

[0053] According to the present invention, there is no particular limitation on the compression. Generally, a step-by-step compression is used to increase the pressure of the raw material dry gas to 2.5-4.6 MPaG, preferably 3-4.2 MPaG, and more preferably 3.9-4.2 MPaG; that is, the pressure of the compressed gas is 2.5-4.6 MPaG, preferably 3-4.2 MPaG, and more preferably 3.9-4.2 MPaG. Further preferably, the compression is a multi-stage compression. The present invention does not particularly limit the number of stages of the compression process; for example, it can be a two-stage or three-stage compression.

[0054] According to the present invention, preferably, the pressure of the liquid phase after depressurization is 0.8-3 MPaG, more preferably 1-2 MPaG, and even more preferably 1.5-2 MPaG. In this invention, by reducing the pressure of the liquid phase, the relative volatility among the C1-C5 hydrocarbon components is increased, thereby reducing the load on the reboiler of the methane desorption tower and lowering the bottom temperature of the methane desorption tower. This allows the use of a lower temperature heat source, saving steam consumption and equipment energy consumption. Furthermore, the increased difference in relative volatility between the components makes it easier for light components such as hydrogen, methane, and oxygen to separate from the C2-C5 components, further reducing the content of light components in the bottom liquid phase of the methane desorption tower. In this invention, the methane desorption tower operates at low pressure, distilling off light components such as methane, hydrogen, and oxygen from the rich absorbent solution at a lower cost, reducing the content of light components such as methane, hydrogen, and oxygen in the enriched gas, which is mainly composed of C2 components.

[0055] According to the present invention, the cooling in step (1) is not particularly limited. Preferably, the cooling temperature is 5-40°C, and more preferably 10-20°C. In step (1) of the present invention, the compressed gas is cooled using a cooling medium with a temperature above 0°C. The cooling medium is selected from at least one of cryogenic water, propylene, ammonia, and liquid nitrogen, preferably cryogenic water. More preferably, the cryogenic water is prepared by a lithium bromide absorption chiller at a temperature of 5°C or 7°C. Specifically, 7°C cryogenic water is used in the embodiments, but the present invention is not limited thereto.

[0056] According to the present invention, steps (5)-(6) further include a step of cooling the compressed gas, wherein the cooling is not particularly limited, but preferably, the cooling temperature is -40°C to 0°C, more preferably -36°C to -10°C. In steps (5)-(6) of the present invention, the compressed gas is cooled using a cooling medium with a temperature below -10°C, wherein the cooling medium is selected from at least one of cryogenic water, propylene, ammonia and liquid nitrogen, preferably propylene.

[0057] According to the present invention, there is no particular limitation on the absorbent, which can be determined by those skilled in the art based on common knowledge of the prior art. In the present invention, the absorbent is selected from C4 fraction and / or C5 fraction, preferably C4 fraction; wherein the C4 fraction contains at least one of n-butane, isobutane and butene; the C5 fraction contains at least one of n-pentane, isopentane and neopentane; specifically, the embodiments use mixed butane as absorbent, but the present invention is not limited thereto.

[0058] According to the present invention, the C2 component is selected from ethane and / or ethylene. For example, ethane, ethylene, or a mixture of ethane and ethylene. Preferably, the polymer-grade ethylene product meets the enterprise standard Q / SH 012.01.12-1999, and the quality indicators can be superior grade or first grade, as shown in Table 1.

[0059] Table 1

[0060]

[0061] According to the present invention, preferably, the absorption of the C2 component is carried out in an absorption tower; more preferably, the number of theoretical plates in the absorption tower is 15-30, and more preferably 20-25; the operating pressure of the absorption tower is 2.5-4.6 MPaG, preferably 3-4.2 MPaG, and more preferably 3.8-4 MPaG; the top temperature of the absorption tower is 10-60°C, preferably 17-55°C; and the bottom temperature of the absorption tower is 10-70°C, preferably 22-65°C.

[0062] According to a specific embodiment of the present invention, the gas phase is introduced into the bottom of the absorption tower and comes into countercurrent contact with the absorbent at the top of the absorption tower to absorb the C2 component in the gas phase. The absorption tail gas is discharged from the top of the absorption tower and sent out of the boundary area. The absorption rich liquid discharged from the bottom of the absorption tower is pressurized by the bottom liquid pump and returned and mixed with the compressed gas.

[0063] In this invention, the absorbent liquid discharged from the bottom of the absorption tower comes into full contact with the compressed gas in the separator, pre-absorbing a portion of the heavy components such as C2-C4 hydrocarbons, reducing the amount of gas phase entering the absorption tower, reducing the amount of absorbent used in the absorption tower, and saving energy.

[0064] According to the present invention, preferably, the methane desorption is carried out in a methane desorption tower; more preferably, the number of theoretical plates in the methane desorption tower is 20-50, and more preferably 30-45; the operating pressure of the methane desorption tower is 0.5-2.4 MPaG, and more preferably 1.5-2 MPaG; the top temperature of the methane desorption tower is 10-60°C, and more preferably 15-55°C; the bottom temperature of the methane desorption tower is 35-90°C, and more preferably 40-77°C.

[0065] According to the present invention, preferably, the liquid phase is depressurized and then fed into a methane desorption tower to separate and remove light components such as methane from the liquid phase, thereby obtaining desorbed gas and rich absorbent. The desorbed gas is returned and mixed into the raw material dry gas.

[0066] According to the present invention, preferably, the desorbed gas discharged from the top of the methane desorber is returned to the compressor inlet or inter-stage. The return location can be determined according to the raw material dry gas pressure, the compressor inter-stage pressure and the methane desorber pressure, so as to save compressor energy consumption as much as possible while ensuring that the top gas of the methane desorber can be pressurized by the compressor.

[0067] According to the present invention, preferably, the heat source of the bottom of the methane desorption tower is provided by the reboiler of the methane desorption tower, and the heat source of the reboiler of the methane desorption tower is the process stream. Specifically, the process stream is selected from at least one of the absorbent, the rich absorbent, and the lean absorbent, preferably the lean absorbent.

[0068] According to the present invention, preferably, the desorption separation is carried out in a desorption tower; more preferably, the theoretical plate number of the desorption tower is 20-50, and more preferably 30-40; the operating pressure of the desorption tower is 1-2.8 MPaG, and more preferably 2-2.5 MPaG; the top temperature of the desorption tower is 25-70°C, and more preferably 45-65°C; the bottom temperature of the desorption tower is 90-160°C, and more preferably 119-155°C.

[0069] According to a preferred embodiment of the present invention, the rich absorbent is desorbed and separated, the absorbent is discharged from the bottom of the desorption tower, the lean absorbent serves as the heat source for the methane desorption, and at least a portion of the stream obtained after heat exchange is returned and mixed into the absorbent.

[0070] According to the present invention, preferably, the refining system includes an acid gas removal system and a dryer; the acid gas removal system includes an alkaline scrubbing tower, etc., which uses NaOH solution to remove the acid gas completely; the dryer uses molecular sieves to remove moisture from the concentrated gas. Preferably, when the carbon dioxide and hydrogen sulfide content in the concentrated gas is high, an amine decarbonization system can also be set up to remove most of the acid gas first, and then the acid gas is completely removed by the alkaline scrubbing tower. In the present invention, the decarbonization system and / or the alkaline scrubbing tower and dryer are operated in a conventional manner. The alkaline scrubbing tower 10 operates at a pressure of 1.9-2.4 MPaG and a top temperature of 40-45°C; the alkaline scrubbing tower 10 uses NaOH solution to remove the acid gas to less than 5 ppm. The dryer 11 operates at a pressure of 1.8-2.3 MPaG.

[0071] According to the present invention, preferably, the deethanizer is used to separate light components of C2 and below from heavy components of C3 and above; more preferably, the theoretical plate number of the deethanizer is 25-55, preferably 35-50; the operating pressure of the deethanizer is 1.5-3.8 MPaG, preferably 1.8-3.5 MPaG; the top temperature of the deethanizer is -20°C to 0°C, preferably -25°C to 0°C; and the bottom temperature of the deethanizer is 50-160°C, preferably 50-150°C.

[0072] According to the present invention, the ethylene distillation column mainly separates ethylene from ethane. More preferably, the theoretical plate number of the ethylene distillation column is 60-105, the operating pressure of the ethylene distillation column is 1.5-2.5 MPaG, preferably 1.7-2.5 MPaG; the top temperature of the ethylene distillation column is -38°C to -30°C, preferably -35°C to -30°C; and the bottom temperature of the ethylene distillation column is -20°C to -10°C.

[0073] The second aspect of the present invention provides an apparatus for recovering carbon-two components from dry gas to produce polymer-grade ethylene, wherein the apparatus comprises: a compressor 2, a cooler 3, a separator 4, an absorption tower 5, a methane desorption tower 7, a desorption tower 9, a purification system, an ethane removal tower 12, and an ethylene distillation tower 13.

[0074] The refining system includes an alkali washing tower 10 and a dryer 11. The upper part of the alkali washing tower 10 is connected to fresh alkali solution 17, which is used to remove acidic gases from the concentrated gas 16 to a lower content. The dryer 11 is used to remove water from the concentrated gas 16.

[0075] The de-ethane tower 12 is connected to the outlet of the dryer 11, the top of the tower is connected to the ethylene distillation tower 13, and the bottom of the tower is connected to the absorption tower 5, for separating the C2 component from the C3 and above heavy components in the enriched gas 16;

[0076] The top of the ethylene distillation column 13 is connected to the compressor 2, which is used to separate the light components from the carbon-rich distillate and return them to the compressor 2. The bottom of the column yields ethane product 21, which is mainly composed of ethane, and the polymer grade ethylene product 20 is collected from the middle of the column.

[0077] According to the present invention, the compressor 2, the cooler 3 and the liquid separator 4 are connected in sequence.

[0078] According to the present invention, the bottom of the absorption tower 5 is connected to the top of the separator 4 and the cooler 3 respectively, for countercurrent contact between the gas phase discharged from the top of the separator 4 and the absorbent, the absorption tail gas 15 is discharged from the top of the absorption tower 5, and the absorption rich liquid is discharged from the bottom of the absorption tower 5 and returned to the cooler 3.

[0079] According to the present invention, the upper part, top and bottom of the methane desorption tower 7 are respectively connected to the bottom of the liquid separator 4, the compressor 2 and the middle part of the desorption tower 9, for depressurizing the liquid phase discharged from the bottom of the liquid separator 4 for methane desorption, the desorbed gas discharged from the top of the methane desorption tower 7 is returned to the inlet or inter-section of the compressor 2 or discharged externally, and the absorbent discharged from the bottom of the methane desorption tower 7 enters the middle part of the desorption tower 9.

[0080] According to the present invention, the bottom of the desorption tower 9 is connected to the top of the absorption tower 5, and is used to desorb the rich absorbent discharged from the bottom of the methane desorption tower 7 for desorption separation. The top of the desorption tower 9 recovers the concentrated gas 16, which is mainly composed of C2 components. The bottom of the desorption tower 9 discharges the lean absorbent 14 and returns it to the top of the absorption tower 5.

[0081] According to the present invention, the top of the alkaline washing tower 10 is connected to the dryer 11.

[0082] According to the present invention, the lower part of the alkaline washing tower 10 is connected to the top of the desorption tower 9.

[0083] According to the present invention, the bottom of the alkali washing tower 10 is connected to the waste alkali solution 18.

[0084] The alkaline washing tower 10 in the acid gas removal system is connected to the fresh alkaline solution 17, the dryer 11, the top of the desorption tower 9, and the waste alkaline solution 18 collection pipe at its upper, top, lower, and bottom parts, respectively.

[0085] The top and bottom of the dryer 11 are respectively connected to the top of the alkaline washing tower 10 and the middle of the ethane stripping tower 12, and are used to remove moisture from the concentrated gas after the acid gas has been removed.

[0086] According to the present invention, the middle, top and bottom of the deethaner 12 are respectively connected to the bottom of the dryer 11, the middle of the ethylene distillation column 13 and the absorbent, for separating the C3 and above heavy components in the enriched gas 16 for continued use as absorbent.

[0087] According to the present invention, the theoretical number of plates of the deethaner 12 is 25-55.

[0088] According to the present invention, the middle part of the deethaner 12 is 1 / 6 to 2 / 3 of the deethaner.

[0089] According to the present invention, the middle, top, upper middle and bottom of the ethylene distillation column 13 are respectively connected to the de-ethanizer column 12, compressor 2, ethylene product collection system and ethane product collection system, for separating ethylene and ethane, and collecting polymer-grade ethylene product from the upper middle side stream of the column.

[0090] According to the present invention, the upper part of the methane desorption tower is 1 / 20 to 1 / 5 of the size of the methane desorption tower.

[0091] According to the present invention, the lower part of the methane desorption tower is 4 / 5 to 5 / 6 of the methane desorption tower.

[0092] According to the present invention, the middle part of the desorption tower is 1 / 6 to 2 / 3 of the total length of the desorption tower.

[0093] According to the present invention, the middle part of the deethaner is 1 / 6 to 2 / 3 of the length of the deethaner.

[0094] According to the present invention, the theoretical plate number of the ethylene distillation column (13) is 75-105; the middle part of the ethylene distillation column (13) is 1 / 5-1 / 3 of the ethylene distillation column, and the upper middle part of the ethylene distillation column (13) is 1 / 10-1 / 5 of the ethylene distillation column.

[0095] According to a preferred embodiment of the present invention, the invention will be described below in conjunction with... Figure 1This invention provides a device for recovering C2 components from dry gas. The device includes: a compressor 2, a cooler 3, a separator 4, an absorption tower 5, a methane desorption tower 7, a desorption tower 9, an alkaline washing tower 10, a dryer 11, an ethane removal tower 12, and an ethylene distillation tower 13. The compressor 2, cooler 3, and separator 4 are connected sequentially. The compressor 2 is connected to a refinery dry gas pipeline 1. The bottom of the absorption tower 5 is connected to the top of the separator 4 and the cooler 3, for countercurrent contact between the gas phase generated in the separator 4 and the absorbent. Absorption tail gas 15 is discharged from the top of the tower. The rich absorbent discharged from the bottom of the absorption tower 5 is pressurized by the bottom liquid pump 6 and returned to the cooler 3. The upper part, top, and bottom of the methane desorption tower 7 are respectively connected to the bottom of the separator 4, the compressor 2, and the desorption tower 9, and are used to depressurize the liquid phase of the separator 4 for methane desorption. The desorbed gas discharged from the top of the methane desorption tower 7 is returned to the compressor 2. The rich absorbent discharged from the bottom of the methane desorption tower 7 is pressurized by the rich absorbent pump 8 and enters the middle of the desorption tower 9. The bottom of the desorption tower 9 is connected to the bottom of the cooler 3. The top of the absorption tower 5 is used to desorb the rich absorbent discharged from the bottom of the methane desorption tower 7 for desorption separation. The top of the desorption tower 9 recovers the concentrated gas 16, which is mainly composed of C2 components. The bottom of the desorption tower 9 discharges the lean absorbent 14 and returns it to the top of the absorption tower 5. The alkaline washing tower 10, dryer 11, ethane removal tower 12, and ethylene distillation tower 13 are connected in sequence. The lower part and the top of the alkaline washing tower 10 are respectively connected to the top of the desorption tower 9 and the dryer 11, removing acidic gases such as carbon dioxide and hydrogen sulfide from the concentrated gas 16 to less than 5 ppm. The bottom is connected to the waste alkali outlet 18; the middle, top and bottom of the de-ethane tower 12 are respectively connected to the dryer 11, the middle of the ethylene distillation tower 13 and the top of the absorption tower 5, to separate the C3 and above components in the concentrated gas 16 and return them to the absorption tower 5, and the light components of C2 and below are collected from the top of the tower; the middle, top and bottom of the ethylene distillation tower 13 are respectively connected to the top of the de-ethane tower 12, the compressor 2 and the ethane product 21 collection system, and the middle and upper part of the ethylene distillation tower 13 is connected to the ethylene product collection system, which is used to separate ethylene from components such as ethane to obtain polymer-grade ethylene product 20.

[0096] A third aspect of the present invention provides the application of the aforementioned apparatus in the aforementioned method for recovering carbon-two components from dry gas to produce polymer-grade ethylene.

[0097] The present invention will be described in detail below through embodiments.

[0098] In the following examples and comparative examples:

[0099] In this invention, unless otherwise stated, the pressure is gauge pressure.

[0100] In this invention, "MPaG" means that MPa is a pressure unit, representing gauge pressure, megapascal; and G refers to the standard pressure state.

[0101] In this invention, the composition of dry gas from a certain refinery is shown in Table 2.

[0102] Table 2

[0103] Refinery dry gas Temperature, °C 40.0 Pressure, MPaG 1.20 Mass flow rate, t / h 15.0 Composition, mol% <![CDATA[H2]]> 24.71 <![CDATA[N2]]> 18.50 <![CDATA[O2]]> 1.82 <![CDATA[H2S]]> 20ppm CO 0.45 <![CDATA[CO2]]> 3.14 <![CDATA[CH4]]> 25.53 <![CDATA[C2H4]]> 12.28 <![CDATA[C2H6]]> 12.39 <![CDATA[C3H6]]> 0.52 <![CDATA[C3H8]]> 0.15 <![CDATA[C4]]> 0.03 C5+ 0.03 <![CDATA[H2O]]> 0.45

[0104] Example 1

[0105] This embodiment illustrates the method and apparatus for oil absorption, separation of dry gas, and recovery of C2 according to the present invention.

[0106] The device includes: compressor 2, cooler 3, separator 4, absorber 5, methane desorption tower 7, desorption tower 9, alkaline washing tower 10, dryer 11, ethane removal tower 12, and ethylene distillation tower 13;

[0107] The method includes:

[0108] (1) Refinery dry gas 1 (as shown in Table 3) with a pressure of 1.2 MPaG is fed into compressor 2. After compression, the pressure of the compressed dry gas is increased to 3.9 MPaG. After merging with the rich liquid absorbed by absorber 5, the pressurized dry gas is cooled to 15°C by propylene from propylene refrigeration unit at 7°C in cooler 3 and sent to separator 4 for gas-liquid phase separation to obtain gas and liquid phases. The gas phase at the top of separator 4 is sent to the bottom of absorber 5, and the liquid phase at the bottom of separator 4 is depressurized to 1.5 MPaG and then sent to methane desorption tower 7 for treatment.

[0109] (2) In absorber 5, refinery mixed butane is used as the absorbent (absorbent circulation rate 60t / h), injected from the top of the tower to absorb the C2 fraction and heavier components in the feed gas. Absorber 5 has a theoretical plate number of 20, an operating pressure of 3.8MPaG, a top temperature of 17℃, and a bottom temperature of 22℃. The liquid phase of absorber 5 is pressurized to 4MPaG by absorber bottom liquid pump 6 and returned to cooler 3, where it merges with the outlet gas phase of compressor 2. The unabsorbed tail gas 15 at the top of absorber 5 is sent out of the boundary area.

[0110] (3) The bottom liquid phase of the separator 4 enters the top of the methane desorption tower 7 under the action of pressure difference to remove light components such as methane from the tower feed, obtaining desorbed gas and rich absorbent. The theoretical number of plates in the methane desorption tower is 30, the operating pressure is 1.5 MPaG, the top temperature is 15℃, and the bottom temperature is 77℃. The top gas phase of the methane desorption tower 7 returns to the inlet of the compressor 2, and the bottom product of the methane desorption tower 7 is pressurized by the rich absorbent pump 8 and sent to the middle of the desorption tower 9.

[0111] (4) The rich absorbent is desorbed and separated in desorption tower 9 (to obtain lean absorbent 14 and concentrated gas 16 mainly composed of C2 components). Desorption tower 9 is heated by low-pressure steam. The concentrated gas 16 mainly composed of C2 components is obtained at the top of the tower. The lean absorbent 14 at the bottom of desorption tower 9 is used to heat the reboiler of the methane desorption tower. The stream obtained after heat exchange is returned to absorption tower 5 for recycling. The theoretical plate number of desorption tower 9 is 40, the operating pressure is 2.0 MPaG, the top temperature is 45°C, and the bottom temperature is 119°C.

[0112] (5) The refining unit is equipped with an alkaline washing tower 10 and a dryer 11. The refined concentrated gas 19, which is mainly composed of C2 components, is sent to the ethane stripping tower 12 after being treated by deacidification, dehydration and impurity removal to separate the light components of C2 and below from the heavy components of C3 and above. The gas phase at the top of the tower is fed into the ethylene distillation tower 13 to separate ethylene from ethane. The liquid phase at the bottom of the tower is returned to the absorption system of step (2) as an absorbent.

[0113] The alkaline washing tower 10 operates at a pressure of 1.9 MPaG and has a top temperature of 45℃. NaOH solution is used in the alkaline washing tower 10 to remove acidic gases to less than 5 ppm.

[0114] The dryer 11 operates at a pressure of 1.8 MPaG.

[0115] Among them, the theoretical plate number of the deethaner 12 is 35, the operating pressure is 1.8 MPaG, the top temperature is -25℃, and the bottom temperature is 50℃.

[0116] (6) Non-condensable gas from the top 13 of the ethylene distillation column is sent to the inlet of the compressor 2. The theoretical number of plates in the ethylene distillation column 13 is 60, the operating pressure is 1.7 MPaG, the temperature at the top of the column is -35℃, and the temperature at the bottom of the column is -10℃. Polymer-grade ethylene product 20 is collected from the 10th plate at the top of the column and sent out of the boundary area, and ethane product 21 is collected from the bottom of the column and sent out of the boundary area.

[0117] In the method of this embodiment, the composition of the enriched gas, which is mainly composed of C2 components, and the ethylene and ethane products are shown in Table 3, wherein the C2 recovery rate is 98%.

[0118] Table 3

[0119]

[0120] As shown in Table 3, in step (5), the content of light components such as methane, hydrogen, and oxygen in the enriched gas is low. After the heavy components of C3 and above are separated by the deethanizer 12, the methane content in the refined enriched gas 19 is less than 0.1%, so there is no need for a dedicated deethanizer, which can meet the feed requirements of the ethylene distillation tower. In addition, the content of light components such as methane, hydrogen, and oxygen in the enriched gas is low. After the heavy components of C3 and above are separated by the deethanizer, the O2 content in the refined enriched gas 19 is 3 ppm, so there is no need for dedicated deoxygenation, which can meet the feed requirements of the ethylene distillation tower.

[0121] Example 2

[0122] (1) Refinery dry gas 1 (same as in Example 1) with a pressure of 1.2 MPaG is fed into compressor 2. After compression, the pressure of the compressed dry gas is increased to 3.9 MPaG. After merging with the rich liquid absorbed by absorber 5, the pressurized dry gas is cooled to 15°C by propylene from propylene refrigeration unit at 7°C in cooler 3 and sent to separator 4 for gas-liquid phase separation to obtain gas and liquid phases. The gas phase at the top of separator 4 is sent to the bottom of absorber 5, and the liquid phase at the bottom of separator 4 is depressurized to 1.5 MPaG and then sent to methane desorption tower 7 for treatment.

[0123] (2) In absorber 5, refinery mixed butane is used as the absorbent (absorbent circulation rate 70t / h), injected from the top of the tower to absorb the C2 fraction and heavier components in the feed gas. Absorber 5 has a theoretical plate number of 20, an operating pressure of 3.8MPaG, a top temperature of 16℃, and a bottom temperature of 21℃. The liquid phase of absorber 5 is pressurized to 4MPaG by absorber bottom liquid pump 6 and returned to cooler 3, where it merges with the outlet gas phase of compressor 2. The unabsorbed tail gas 15 at the top of absorber 5 is sent out of the boundary area.

[0124] (3) The bottom liquid phase of the separator 4 enters the top of the methane desorption tower 7 under the action of pressure difference to remove light components such as methane from the tower feed, obtaining desorbed gas and rich absorbent. The theoretical number of plates of the methane desorption tower is 25, the operating pressure is 1.3 MPaG, the top temperature is 16℃, and the bottom temperature is 85℃. The top gas phase of the methane desorption tower 7 returns to the inlet of the compressor 2, and the bottom product of the methane desorption tower 7 is pressurized by the rich absorbent pump 8 and sent to the middle of the desorption tower 9.

[0125] (4) The rich absorbent is desorbed and separated in desorption tower 9 (to obtain lean absorbent 14 and concentrated gas 16 mainly composed of C2 components). Desorption tower 9 is heated by low-pressure steam. The concentrated gas 16 mainly composed of C2 components is obtained at the top of the tower. The lean absorbent 14 at the bottom of desorption tower 9 is used to heat the reboiler of the methane desorption tower. The stream obtained after heat exchange is returned to absorption tower 5 for recycling. The theoretical plate number of desorption tower 9 is 40, the operating pressure is 2.0 MPaG, the top temperature is 42℃, and the bottom temperature is 125℃.

[0126] (5) The refining unit is equipped with an alkaline washing tower 10 and a dryer 11. The refined concentrated gas 19, which is mainly composed of C2 components, is sent to the ethane stripping tower 12 after being treated by deacidification, dehydration and impurity removal to separate the light components of C2 and below from the heavy components of C3 and above. The gas phase at the top of the tower is fed into the ethylene distillation tower 13 to separate ethylene from ethane. The liquid phase at the bottom of the tower is returned to the absorption system of step (2) as an absorbent.

[0127] The alkaline washing tower 10 operates at a pressure of 1.8 MPaG and has a top temperature of 45℃. The alkaline washing tower 10 uses NaOH solution to remove acidic gases down to 1 ppm.

[0128] The dryer 11 operates at a pressure of 1.7 MPaG.

[0129] Among them, the theoretical plate number of the deethaner 12 is 40, the operating pressure is 1.65 MPaG, the top temperature is -29℃, and the bottom temperature is 45℃.

[0130] (6) Non-condensable gas from the top 13 of the ethylene distillation column is sent to the inlet of the compressor 2. The theoretical number of plates in the ethylene distillation column 13 is 60, the operating pressure is 1.6 MPaG, the temperature at the top of the column is -38℃, and the temperature at the bottom of the column is -7℃. Polymer-grade ethylene product 20 is collected from the 10th plate at the top of the column and sent out of the boundary area, and ethane product 21 is collected from the bottom of the column and sent out of the boundary area.

[0131] In the method of this embodiment, the composition of the enriched gas, which is mainly composed of C2 components, and the ethylene and ethane products are shown in Table 4, wherein the C2 recovery rate is 97%.

[0132] Table 4

[0133]

[0134]

[0135] As shown in Table 4, in step (5), the content of light components such as methane, hydrogen, and oxygen in the enriched gas is low. After the heavy components of C3 and above are separated by the deethanizer 12, the methane content in the refined enriched gas 19 is less than 0.1%, so there is no need for a dedicated deethanizer, which can meet the feed requirements of the ethylene distillation tower. In addition, the content of light components such as methane, hydrogen, and oxygen in the enriched gas is low. After the heavy components of C3 and above are separated by the deethanizer, the O2 content in the refined enriched gas 19 is 1 ppm, so there is no need for dedicated deoxygenation, which can meet the feed requirements of the ethylene distillation tower.

[0136] Comparative Example 1

[0137] This comparative example illustrates a conventional method for recovering polymer-grade ethylene from dry gas by oil absorption and separation.

[0138] like Figure 2As shown, the device includes: compressor 2, cooler 3, separator 4, absorber 5, desorption tower 9, alkaline washing tower 10, dryer 11, ethane removal tower 12, ethylene distillation tower 13, deoxygenation reactor 22, and hydrogen 23.

[0139] Refinery dry gas 1 is pressurized and sent to absorption tower 5, where mixed butane is used as the absorbent to absorb the C2 components from the dry gas. Separation then occurs in desorption tower 9, with enriched gas obtained at the top. This enriched gas passes through alkaline scrubbing tower 10 and enters deoxidation reactor 22. The oxygen content in the enriched gas is 30 ppm. The enriched gas is preheated to 120-230°C with steam, mixed with a certain amount of hydrogen, and then sent to the deoxidation reactor. A precious metal deoxidizer is used to remove trace amounts of oxygen from the enriched gas to less than 5 ppm. The enriched gas exiting the reactor is cooled by circulating water and then sent to dryer 11.

[0140] The energy consumption of the deoxygenation system is shown in Table 5.

[0141] Table 5

[0142]

[0143]

[0144] As shown in Table 5 above, for the conventional refinery dry gas to polymerization process, due to the high oxygen content in the enriched gas, a special deoxygenation system is required to remove the oxygen. The enriched gas needs to be heated and cooled, consuming 10.37 kg of standard oil / t of enriched gas.

[0145] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for recovering C2 components from dry gas to produce polymer-grade ethylene, characterized in that, The method includes: (1) The raw material dry gas is compressed, and the resulting compressed gas is cooled and then separated into gas and liquid phases to obtain gas and liquid phases; (2) The gas phase is contacted with the absorbent phase to absorb C2 components, resulting in absorption tail gas and absorption rich liquid. The absorption rich liquid is returned and mixed into the compressed gas. (3) After depressurizing the liquid phase, methane is desorbed to obtain desorbed gas and rich absorbent. The desorbed gas is returned to the compression or discharge in step (1). (4) The rich absorbent is desorbed and separated to obtain a lean absorbent and a concentrated gas mainly composed of C2 components. The lean absorbent is returned and mixed into the absorbent. (5) The enriched gas, which is mainly composed of C2 components, is sent to the de-ethanizer tower after being treated by deacidification, dehydration and impurity removal. The gas phase at the top of the tower is fed into the ethylene distillation tower to separate ethylene and ethane. The liquid phase at the bottom of the tower is returned to the absorption system in step (2) as an absorbent. (6) The non-condensable gas at the top of the ethylene distillation column is returned to the compressor in step (1), and ethane product with ethane as the main component is obtained in the bottom of the column. Polymer-grade ethylene product is extracted from the side stream of the column.

2. The method according to claim 1, wherein, In step (5), after the heavy components of C3 and above are separated by the de-ethane tower, the methane content in the refined concentrated gas can be less than 0.1%, preferably 0-0.6%; And / or, in step (5), after the heavy components of C3 and above are separated by the deethaner, the O2 content in the purified gas is less than 5 ppm, preferably 0-5 ppm, and more preferably 0-3 ppm.

3. The method according to claim 1 or 2, wherein, The alkaline washing tower operates at a pressure of 1.9-2.4 MPaG and has a top temperature of 40-45℃. And / or, the acidic gas in the alkaline washing tower is removed to less than 5 ppm using NaOH solution; The dryer operates at a pressure of 1.8-2.3 MPaG.

4. The method according to claim 1, wherein, The operating pressure of the deethanizer is 1.5-3.8 MPaG, the top temperature of the deethanizer is -20℃ to 0℃, and the bottom temperature of the deethanizer is 50-160℃.

5. The method according to claim 1, wherein, The operating pressure of the ethylene distillation column is 1.5-2.5 MPaG, the top temperature of the ethylene distillation column is -38℃ to -30℃, and the bottom temperature of the ethylene distillation column is -20℃ to -10℃.

6. The method according to claim 1, wherein, The pressure of the compressed gas is 2.5-4.6 MPaG, preferably 3-4.2 MPaG; And / or, the pressure after the liquid phase depressurization is 0.8-3 MPaG, preferably 1-2 MPaG; And / or, the operating pressure of the absorption tower is 2.5-4.6 MPaG, the top temperature is 10-60℃, and the bottom temperature is 10-70℃; And / or, the operating pressure of the methane desorption tower is 0.5-2.4 MPaG, the top temperature is 10-60℃, and the bottom temperature is 35-90℃; And / or, the operating pressure of the desorption tower is 1-2.8 MPaG, the top temperature is 25-70℃, and the bottom temperature is 90-160℃; And / or, the absorbent is selected from C4 fraction and / or C5 fraction; preferably, the C4 fraction contains at least one of n-butane, isobutane and butene; preferably, the C5 fraction contains at least one of n-pentane, isopentane and neopentane; And / or, the C2 components are selected from ethane and / or ethylene.

7. An apparatus for recovering C2 components from dry gas to produce polymer-grade ethylene, characterized in that, The device includes: a compressor (2), a cooler (3), a separator (4), an absorption tower (5), a methane desorption tower (7), a desorption tower (9), a purification system, an ethane removal tower (12), and an ethylene distillation tower (13); The refining system includes an alkaline washing tower (10) and a dryer (11). The upper part of the alkaline washing tower (10) is connected to fresh alkaline solution (17) to remove acidic gases from the concentrated gas (16) to a lower content. The dryer (11) is used to remove water from the concentrated gas (16). The de-ethane tower (12) is connected to the outlet of the dryer (11), the top of the tower is connected to the ethylene distillation tower (13), and the bottom of the tower is connected to the absorption tower (5), which is used to separate the C2 component from the C3 and above heavy components in the enriched gas (16); The top of the ethylene distillation column (13) is connected to the compressor (2) for separating the light components from the carbon-rich distillate and returning them to the compressor (2). Ethane product (21), mainly composed of ethane, is obtained from the bottom of the column, and polymer-grade ethylene product (20) is collected from the middle of the column.

8. The apparatus according to claim 7, wherein, The top of the alkaline washing tower (10) is connected to the dryer (11); And / or, the lower part of the alkaline washing tower (10) is connected to the top of the desorption tower (9); And / or, the bottom of the alkali washing tower (10) is connected to the waste alkali solution (18).

9. The apparatus according to claim 7, wherein, The middle, top and bottom of the de-ethane tower (12) are respectively connected to the bottom of the dryer (11), the middle of the ethylene distillation tower (13) and the absorbent, and are used to separate the C3 and above heavy components in the concentrated gas (16) for continued use as absorbent; And / or, the theoretical plate number of the deethaner (12) is 25-55; And / or, the middle part of the deethaner (12) is 1 / 6 to 2 / 3 of the deethaner.

10. The apparatus according to claim 7, wherein, The middle, top, upper middle and bottom of the ethylene distillation column (13) are respectively connected to the de-ethane column (12), compressor (2), ethylene product collection system and ethane product collection system, for separating ethylene and ethane; And / or, the theoretical plate number of the ethylene distillation column (13) is 75-105; And / or, the middle section of the ethylene distillation column (13) is 1 / 5 to 1 / 3 of the length of the ethylene distillation column; And / or, the upper middle part of the ethylene distillation column (13) is 1 / 10 to 1 / 5 of the ethylene distillation column.

11. The apparatus according to claim 7, wherein, The compressor (2), the cooler (3), and the liquid separator (4) are connected in sequence; And / or, the bottom of the absorption tower (5) is connected to the top of the separator (4) and the cooler (3) respectively, for discharging the gas phase discharged from the top of the separator (4) into countercurrent contact with the absorbent, discharging the absorption tail gas (15) from the top of the absorption tower (5), and discharging the rich absorption liquid from the bottom of the absorption tower (5) and returning it to the cooler (3); And / or, the upper part, top and bottom of the methane desorption tower (7) are respectively connected to the bottom of the liquid separator (4), the compressor (2) and the middle part of the desorption tower (9), for depressurizing the liquid phase discharged from the bottom of the liquid separator (4) for methane desorption, the desorbed gas discharged from the top of the methane desorption tower (7) is returned to the inlet or inter-section or external discharge of the compressor (2), and the absorbent discharged from the bottom of the methane desorption tower (7) enters the middle part of the desorption tower (9); And / or, the bottom of the desorption tower (9) is connected to the top of the absorption tower (5) for desorption separation of the rich absorbent discharged from the bottom of the methane desorption tower (7), the top of the desorption tower (9) recovers the enriched gas (16) mainly composed of C2 components, and the bottom of the desorption tower (9) discharges the lean absorbent (14) and returns it to the top of the absorption tower (5).

12. The use of the apparatus according to any one of claims 7-11 in the method for producing polymer-grade ethylene from the recovery of carbon-two components in dry gas according to any one of claims 1-6.

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