Refining method for preparing ethylene through ethanol dehydration

Abstract

The invention relates to a refining method for preparing ethylene by ethanol dehydration, which comprises the following steps: (a) feeding a raw material crude ethylene into an ethylene rectifying tower to obtain an ethylene gas-phase material I at the tower top and a heavy-component liquid-phase material II at the tower kettle; (b) condensing the material I to obtain an ethylene liquid-phase material III-1 and an ethylene liquid-phase material III-2, returning the material III-1 to the ethylene rectifying tower, and feeding the material III-2 into a light component removal tower; (c) condensing a gas-phase material obtained at the top of the light component removal tower, feeding the condensed gas-phase material into a light component removal tower reflux tank, obtaining an ethylene-containing light gas-phase material IV-1 at the top of the reflux tank, obtaining a liquid-phase material IV-2 at the bottom, and returning the liquid-phase material IV-2 to the light component removal tower; (d) feeding the material II and the material IV-1 into a flash tank to obtain a gas-phase material V rich in ethylene at the top and heavy components at the bottom; (e) the material V enters a gas-liquid separation tank after being pressurized by a compressor and cooled by an outlet cooler, an ethylene-rich material is obtained at the bottom, and light components are obtained at the top; and (f) returning the bottom material of the gas-liquid separation tank to the ethylene rectifying tower. The method has the characteristics of simple process and high ethylene yield.

Description

Technical Field

[0001] The present invention relates to a refining method for ethanol dehydration to produce ethylene. Background Art

[0002] Ethylene is the basic raw material of modern petrochemical industry, and its major downstream products mainly include polyethylene, ethylene oxide, ethylene glycol, polyvinyl chloride, styrene, vinyl acetate, etc. The ethylene industry is the leading industry of petrochemical industry, and the size of its output is a symbol to measure the development degree of a country's petrochemical industry and even the national economy.

[0003] Ethanol dehydration to produce ethylene was once the main method for ethylene industrial production. Since the mid-20th century, with the rapid development of the petroleum industry, the cost of producing ethylene by thermal cracking of petroleum-based raw materials has been greatly reduced, basically replacing the process route of producing ethylene with ethanol as the raw material. However, as a traditional chemical process technology, in some special regions, due to economic, political and other reasons, this method is still considered for producing ethylene, including: regions with only a small demand for ethylene and inconvenient transportation; regions lacking petroleum resources; regions with a large number of agricultural and sideline products available for fermenting ethanol; countries aiming to reduce dependence on imported petroleum; regions lacking funds for investing in the construction of a combined device for producing ethylene by petroleum steam cracking, etc. Thereafter, with the rapid development of biochemistry technology, the production cost of biomass to ethanol has been greatly reduced, providing the possibility for developing large-scale ethanol dehydration to produce ethylene technology and device. For bioethanol, in addition to using crops such as corn and cassava as fermentation raw materials, fibrous raw materials such as crop straws, bagasse, and wood chips can also be used as fermentation raw materials to produce ethanol, which is expected to further reduce the production cost of ethanol. In addition, the third-generation bioethanol technology, by genetically modifying algae to directly convert CO 2 into bioethanol, will also enter the industrial application stage.

[0004] In the process method of ethanol dehydration to produce ethylene, the main industrial applications currently are fixed-bed processes, including isothermal fixed-bed process and adiabatic fixed-bed process. The process flow generally includes four parts: dehydration reaction system, gas washing system, compression drying system, and refining and separation system. The most important difference between the two processes lies in the dehydration reaction system, and the process flow after the reaction is basically the same. The isothermal fixed-bed process usually uses an isothermal tubular fixed-bed reactor for dehydration reaction, with great difficulty in engineering scale-up, and is generally applicable to small-scale device applications. The adiabatic fixed-bed process uses at least one adiabatic reactor for dehydration reaction, which is easy for engineering scale-up and suitable for large-scale devices.

[0005] CN102372559B introduces an ethylene separation method. In this method, the compressed and dried crude ethylene is fed into an ethylene rectification column. The overhead stream of the ethylene rectification column enters a de-light component column for separation. Light components are removed from the top of the de-light component column, and ethylene product is obtained at the bottom. The bottom material of the ethylene rectification column is fed into an adiabatic flash tank for flashing. The overhead material of the flash tank enters the lower part of the ethylene rectification column. Part of the bottom material is recycled to the middle of the flash tank, and the other part is discharged out of the boundary. This method is mainly a process improvement aimed at the loss of ethylene in the bottom material of the ethylene rectification column. By adding an adiabatic flash tank and flashing the bottom material of the ethylene rectification column, the ethylene content in the material discharged out of the boundary is reduced, so as to improve the ethylene recovery rate of the ethylene rectification column. For an ethylene rectification system composed of an ethylene rectification column and a de-light component column, there is also a considerable amount of ethylene loss in the de-light component column. This method only focuses on the ethylene loss in the ethylene rectification column and does not consider the ethylene loss in the de-light component column. Therefore, for the separation system composed of two columns, the improvement of the total ethylene recovery rate is limited.

[0006] CN103420751A introduces a method for removing light components in the process of ethanol dehydration to produce ethylene. In this method, the liquid-phase material from the top of the ethylene rectification column is fed into a light-component rectification column. The material containing ethylene and light components at the top is condensed, and the gas phase is discharged, while the liquid phase is fully refluxed to the light-component rectification column, and ethylene product is obtained at the bottom. This method uses a conventional single-column rectification process and only focuses on the ethylene loss in the light-component rectification column, without considering the ethylene loss in the upstream ethylene rectification column. CN103539606A introduces a separation method for biomass ethanol to produce ethylene. In this method, the crude ethylene is fed into an ethylene rectification column. Light components are separated from the top, ethylene product is withdrawn from the upper side line of the column, and the heavy components at the bottom enter a stripping distillation column. The gas phase at the top of the stripping distillation column returns to the ethylene rectification column, and the heavy components are discharged from the bottom. This method only focuses on the loss of ethylene contained in the heavy components at the bottom of the ethylene rectification column and does not consider the loss of ethylene contained in the light components.

[0007] CN103772102B introduces a separation and purification method for ethanol dehydration to produce ethylene. In this method, the upstream crude ethylene material is first fed into an ethylene rectification column. The ethylene containing light components obtained at the top is fed into a de-light component column, and the ethylene-rich heavy components are discharged from the bottom. The non-condensable gas of the overhead gas phase material of the de-light component column is discharged after condensation, and the condensate is returned as reflux to the de-light component column. Part of the bottom liquid material of the de-light component column is pressurized by a pump and used as reflux to the ethylene rectification column, and the rest is withdrawn as ethylene product. The ethylene-rich heavy components at the bottom of the ethylene rectification column enter a heavy-component stripping distillation column, the gas phase at the top returns to the ethylene rectification column, and the bottom obtains heavy components containing a small amount of ethylene. This method also only focuses on the ethylene loss in the ethylene rectification column and does not consider the ethylene loss in the de-light component column. Summary of the Invention

[0008] In view of the problem of low ethylene yield in the existing ethylene refining system, the present invention provides a new refining method for ethanol dehydration to produce ethylene. When refining ethylene, this method has the characteristics of simple process and high ethylene yield.

[0009] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0010] A refining method for ethanol dehydration to produce ethylene, which comprises the following steps:

[0011] (a) Feed the raw material crude ethylene into an ethylene rectification column. Ethylene gas-phase material I containing light components is obtained at the top of the column, and a heavy-component liquid-phase material II containing ethylene is obtained at the bottom of the column;

[0012] (b) Condense the ethylene gas-phase material I to obtain an ethylene liquid-phase material III. Divide the ethylene liquid-phase material III into two parts, the first part of the ethylene liquid-phase material III-1 and the second part of the ethylene liquid-phase material III-2. The first part of the ethylene liquid-phase material III-1 is returned to the ethylene rectification column as reflux liquid, and the second part of the ethylene liquid-phase material III-2 is fed into a de-lighting column as de-lighting column feed;

[0013] (c) Feed the gas-phase material obtained at the top of the de-lighting column into a de-lighting column reflux drum after condensation. The light-component gas-phase material IV-1 containing ethylene is obtained at the top of the de-lighting column reflux drum, and the liquid-phase material IV-2 at the bottom of the de-lighting column reflux drum is returned to the de-lighting column as reflux liquid;

[0014] (d) Feed the heavy-component liquid-phase material II and the light-component gas-phase material IV-1 into a flash tank. A gas-phase material V rich in ethylene is obtained at the top of the flash tank, and a heavy component with most of the ethylene removed is obtained at the bottom;

[0015] (e) After the gas-phase material V is pressurized by a compressor and cooled by a compressor outlet cooler, it enters a gas-liquid separation tank. A material rich in ethylene is obtained at the bottom of the gas-liquid separation tank, and light components are obtained at the top of the gas-liquid separation tank;

[0016] (f) Return the material rich in ethylene obtained at the bottom of the gas-liquid separation tank to the ethylene rectification column for utilization (it can be used as an ethylene raw material).

[0017] According to some embodiments of the present invention, the ratio (reflux ratio) of the first part of the ethylene liquid-phase material III-1 to the second part of the ethylene liquid-phase material III-2 is 2-7, such as 2, 3, 4, 5, 6, 7 or the range composed of any two of these values. Preferably, the ratio (reflux ratio) of the first part of the ethylene liquid-phase material III-1 to the second part of the ethylene liquid-phase material III-2 is 3-6.

[0018] According to some embodiments of the present invention, the ratio (reflux ratio) of the light-component gas-phase material IV-1 to the liquid-phase material IV-2 is 5-18, such as 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 or the range composed of any two of these values. Preferably, the ratio (reflux ratio) of the light-component gas-phase material IV-1 to the liquid-phase material IV-2 is 6-16.

[0019] According to some embodiments of the present invention, the refining method further includes discharging the heavy components with most of the ethylene removed obtained at the bottom of the flash tank to outside the plant.

[0020] According to some embodiments of the present invention, the refining method further includes discharging the light-component non-condensable gas obtained at the top of the gas-liquid separation tank to outside the plant.

[0021] According to some embodiments of the present invention, the refining method further includes that the raw material crude ethylene is the material after ethanol dehydration reaction, washing, and compression drying.

[0022] According to some embodiments of the present invention, the raw material crude ethylene contains hydrogen, methane, carbon monoxide, ethylene, ethane, propane, and C4.

[0023] According to some embodiments of the present invention, the light-component gas-phase material IV-1 enters from the bottom of the flash tank and is used to strip the heavy-component liquid-phase material II.

[0024] According to some embodiments of the present invention, the operating pressure of the ethylene distillation column is 2.3-4.0 MPaG, such as 2.3 MPaG, 2.4 MPaG, 2.5 MPaG, 2.6 MPaG, 2.8 MPaG, 3.0 MPaG, 3.2 MPaG, 3.4 MPaG, 3.8 MPaG, 4.0 MPaG or the range composed of any two of these values.

[0025] According to some embodiments of the present invention, the number of theoretical trays of the ethylene distillation column is 50-110, such as 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105 or the range composed of any two of these values.

[0026] According to some embodiments of the present invention, the operating pressure of the de-lighting column is 3.3-5.0 MPaG, such as 3.3 MPaG, 3.5 MPaG, 3.8 MPaG, 4.0 MPaG, 4.2 MPaG, 4.5 MPaG, 4.8 MPaG, 5.0 MPaG or the range composed of any two of these values.

[0027] According to some embodiments of the present invention, the number of theoretical plates of the light removal column is 5 to 40, such as 5, 8, 10, 15, 18, 20, 25, 28, 30, 32, 35, 38, 40, or the range composed of any two of these values.

[0028] According to some embodiments of the present invention, the operating pressure of the flash tank is 0.1 to 1.0 MPaG, such as 0.1 MPaG, 0.2 MPaG, 0.3 MPaG, 0.4 MPaG, 0.5 MPaG, 0.6 MPaG, 0.8 MPaG, 0.9 MPaG, or the range composed of any two of these values.

[0029] According to some embodiments of the present invention, the outlet pressure of the compressor is 4.0 to 6.5 MPaG, such as 4.3 MPaG, 4.5 MPaG, 4.8 MPaG, 5.0 MPaG, 5.2 MPaG, 5.5 MPaG, 5.8 MPaG, 6.0 MPaG, 6.2 MPaG, or the range composed of any two of these values.

[0030] According to some embodiments of the present invention, the outlet temperature of the outlet cooler of the compressor is -38 to -30 °C, such as -38 °C, -35 °C, -32 °C, or the range composed of any two of these values.

[0031] According to some embodiments of the present invention, the temperature at the top of the ethylene rectification column is not lower than -40 °C; such as -38 °C, -35 °C, -32 °C, or the range composed of any two of these values.

[0032] According to some embodiments of the present invention, the temperature at the top of the light removal column is not lower than -40 °C; such as -38 °C, -35 °C, -32 °C, or the range composed of any two of these values.

[0033] According to some embodiments of the present invention, the temperature of the refrigerant for condensing the gas-phase material at the outlet of the outlet cooler of the compressor is not lower than -40 °C; such as -38 °C, -35 °C, -32 °C, or the range composed of any two of these values.

[0034] The refining method of the present invention combines technologies such as stripping, flashing, and pressurized cooling to fully recover ethylene in the heavy components at the bottom of the ethylene rectification column and ethylene in the non-condensable gas at the top of the light removal column. The non-condensable gas at the top of the light removal column is used as the stripping gas for the heavy components at the bottom of the ethylene rectification column. At the same time, combined with the flashing effect, the mixture composed of ethylene and light components is separated from the heavy components and enters the compressor in the gas phase. Through pressurization and cooling by the cooler, the light components and ethylene are separated. The light components are discharged out of the boundary in the gas phase, and ethylene returns to the ethylene rectification column in the liquid phase. This method effectively improves the total recovery rate of ethylene and achieves good technical effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a schematic process flow diagram of the refining method for ethanol dehydration to ethylene in the present invention.

[0036] Among them: 1 is the crude ethylene from the self-compression drying unit, 2 is the gas-phase material at the top of the ethylene rectification column, 3 is the liquid-phase material in the reflux drum of the ethylene rectification column, 4 is the liquid-phase material at the bottom of the ethylene rectification column, 5 is the gas-phase material at the top of the light component removal column, 6 is the gas-phase material in the reflux drum of the light component removal column, 7 is the liquid-phase material in the reflux drum of the light component removal column, 8 is the ethylene product, 9 is the gas-phase material in the flash tank, 10 is the liquid-phase material in the flash tank, 11 is the gas-phase material in the gas-liquid separation tank at the compressor outlet, 12 is the liquid-phase material in the gas-liquid separation tank at the compressor outlet, C1 is the ethylene rectification column, C2 is the light component removal column, E1 is the condenser of the ethylene rectification column, E2 is the condenser of the light component removal column, E3 is the cooler at the compressor outlet, V1 is the reflux drum of the ethylene rectification column, V2 is the reflux drum of the light component removal column, V3 is the flash tank, V4 is the gas-liquid separation tank at the compressor outlet, K1 is the compressor, P1 is the reflux pump of the ethylene rectification column, and P2 is the reflux pump of the light component removal column. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and the drawings. The specific embodiments described herein are only used to explain the present invention and do not constitute any limitation to the present invention. In addition, in the following description, the descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present disclosure. Such structures and technologies have also been described in many publications.

[0038] According to Figure 1For the process shown, the crude ethylene 1 from the compression drying unit enters the ethylene rectification column C1. The ethylene gas-phase material 2 containing light components at the top of the column is condensed by the ethylene rectification column condenser E1 and then enters the ethylene rectification column reflux drum V1. The liquid-phase material 3 in the ethylene rectification column reflux drum is pressurized by the ethylene rectification column reflux pump P1 and then divided into two parts (the first part of the ethylene liquid-phase material and the second part of the ethylene liquid-phase material). The first part of the ethylene liquid-phase material enters the ethylene rectification column C1 as the reflux liquid, and the second part of the ethylene liquid-phase material enters the light component removal column C2. The liquid-phase material 4 at the bottom of the ethylene rectification column enters the flash drum V3. The light component gas-phase material 5 containing ethylene at the top of the light component removal column is condensed by the light component removal column condenser E2 and then enters the light component removal column reflux drum V2. The gas-phase material 6 in the light component removal column reflux drum containing light components enters the flash drum V3. The liquid-phase material 7 in the light component removal column reflux drum enters the light component removal column C2 as the reflux liquid after being pressurized by the light component removal column reflux pump P2. Ethylene product 8 is obtained at the bottom of the light component removal column. The gas-phase material 9 in the flash drum is pressurized by the compressor K1 and cooled by the compressor outlet cooler E3, and then enters the compressor outlet gas-liquid separation drum V4. The gas-phase material 11 in the compressor outlet gas-liquid separation drum containing light components is discharged to the outside of the boundary as non-condensable gas, and the liquid-phase material 12 in the compressor outlet gas-liquid separation drum returns to the ethylene rectification column C1.

[0039] The present invention will be described in detail below through embodiments.

[0040] Example 1

[0041] As Figure 1 shown, the composition (volume %) of the crude ethylene is: hydrogen 0.9%, methane 0.2%, carbon monoxide 0.2%, ethylene 97.6%, ethane 0.5%, propylene 0.2%, C4 and above 0.4%.

[0042] The number of theoretical plates of the ethylene rectification column is 80, the operating pressure is 2.4 MPaG, and the reflux ratio is 2 (the ratio of the first part of the ethylene liquid-phase material to the second part of the ethylene liquid-phase material, the same below); the number of theoretical plates of the light component removal column is 25, the operating pressure is 3.6 MPaG, and the reflux ratio is 6 (the ratio of the gas-phase material in the light component removal column reflux drum to the liquid-phase material in the light component removal column reflux drum, the same below); the operating pressure of the flash drum is 1.0 MPaG; the compressor outlet pressure is 4.5 MPaG; the temperature of the compressor outlet cooler is -35 °C.

[0043] The mass composition of ethylene in the ethylene product is 99.95%, and the recovery rate of ethylene is 99.0% (the amount of ethylene in the ethylene product / the amount of ethylene in the crude ethylene, the same below).

[0044] Example 2

[0045] As Figure 1As shown, the composition of the crude ethylene (volume %) is: hydrogen 0.9%, methane 0.2%, carbon monoxide 0.2%, ethylene 97.6%, ethane 0.5%, propylene 0.2%, C4 and above 0.4%.

[0046] The number of theoretical plates of the ethylene rectification column is 100, the operating pressure is 2.4 MPaG, and the reflux ratio is 4; the number of theoretical plates of the light component removal column is 10, the operating pressure is 4.0 MPaG, and the reflux ratio is 10; the operating pressure of the flash tank is 0.2 MPaG; the outlet pressure of the compressor is 5.0 MPaG; the temperature of the cooler at the compressor outlet is -30 °C.

[0047] The mass composition of ethylene in the ethylene product is 99.96%, and the recovery rate of ethylene is 99.2%.

[0048] Example 3

[0049] According to Figure 1 As shown, the composition of the crude ethylene (volume %) is: hydrogen 0.9%, methane 0.2%, carbon monoxide 0.2%, ethylene 97.6%, ethane 0.5%, propylene 0.2%, C4 and above 0.4%.

[0050] The number of theoretical plates of the ethylene rectification column is 60, the operating pressure is 3.0 MPaG, and the reflux ratio is 5; the number of theoretical plates of the light component removal column is 35, the operating pressure is 4.5 MPaG, and the reflux ratio is 12; the operating pressure of the flash tank is 0.5 MPaG; the outlet pressure of the compressor is 5.0 MPaG; the temperature of the cooler at the compressor outlet is -33 °C.

[0051] The mass composition of ethylene in the ethylene product is 99.97%, and the recovery rate of ethylene is 99.3%.

[0052] Example 4

[0053] According to Figure 1 As shown, the composition of the crude ethylene (volume %) is: hydrogen 1.2%, methane 0.3%, carbon monoxide 0.1%, ethylene 97.1%, ethane 0.6%, propylene 0.3%, C4 and above 0.4%.

[0054] The number of theoretical plates of the ethylene rectification column is 110, the operating pressure is 4.0 MPaG, and the reflux ratio is 7; the number of theoretical plates of the light component removal column is 8, the operating pressure is 4.8 MPaG, and the reflux ratio is 18; the operating pressure of the flash tank is 0.8 MPaG; the outlet pressure of the compressor is 6.0 MPaG; the temperature of the cooler at the compressor outlet is -33 °C.

[0055] The mass composition of ethylene in the ethylene product is 99.98%, and the recovery rate of ethylene is 99.2%.

[0056] Example 5

[0057] According toFigure 1 As shown, the composition (volume %) of the crude ethylene is: hydrogen 1.2%, methane 0.3%, carbon monoxide 0.1%, ethylene 97.1%, ethane 0.6%, propylene 0.3%, C4 and above 0.4%.

[0058] The number of theoretical plates of the ethylene rectification column is 70, the operating pressure is 3.5 MPaG, and the reflux ratio is 4; the number of theoretical plates of the light component removal column is 15, the operating pressure is 5.0 MPaG, and the reflux ratio is 16; the operating pressure of the flash tank is 0.3 MPaG; the outlet pressure of the compressor is 6.5 MPaG; the temperature of the cooler at the compressor outlet is -37°C. The mass composition of ethylene in the ethylene product is 99.97%, and the recovery rate of ethylene is 99.3%.

[0059] Example 6

[0060] As Figure 1 shown, the composition (volume %) of the crude ethylene is: hydrogen 1.2%, methane 0.3%, carbon monoxide 0.1%, ethylene 97.1%, ethane 0.6%, propylene 0.3%, C4 and above 0.4%.

[0061] The number of theoretical plates of the ethylene rectification column is 70, the operating pressure is 3.5 MPaG, and the reflux ratio is 1; the number of theoretical plates of the light component removal column is 15, the operating pressure is 5.0 MPaG, and the reflux ratio is 16; the operating pressure of the flash tank is 0.3 MPaG; the outlet pressure of the compressor is 6.5 MPaG; the temperature of the cooler at the compressor outlet is -37°C.

[0062] The mass composition of ethylene in the ethylene product is 99.90%, and the recovery rate of ethylene is 99.3%.

[0063] Example 7

[0064] As Figure 1 shown, the composition (volume %) of the crude ethylene is: hydrogen 1.2%, methane 0.3%, carbon monoxide 0.1%, ethylene 97.1%, ethane 0.6%, propylene 0.3%, C4 and above 0.4.

[0065] The number of theoretical plates of the ethylene rectification column is 70, the operating pressure is 3.5 MPaG, and the reflux ratio is 4; the number of theoretical plates of the light component removal column is 15, the operating pressure is 5.0 MPaG, and the reflux ratio is 3; the operating pressure of the flash tank is 0.3 MPaG; the outlet pressure of the compressor is 6.5 MPaG; the temperature of the cooler at the compressor outlet is -37°C.

[0066] The mass composition of ethylene in the ethylene product is 99.91%, and the recovery rate of ethylene is 99.3%.

[0067] Comparative Example 1

[0068] Under the same conditions as in Example 1, except that the light-component gas-phase material at the top of the debutanizer reflux drum and the heavy-component liquid-phase material at the bottom of the ethylene rectification column are directly discharged to the outside of the battery limit, and there is no flashing, compression, or cooling recovery process in the process. At this time, the mass composition of ethylene in the ethylene product is 99.97%, and the recovery rate of ethylene is 98.1%.

[0069] 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 technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A refining method for the production of ethylene by ethanol dehydration, comprising the following steps: (a) Feeding the raw material crude ethylene into an ethylene rectification column, obtaining ethylene gas-phase material I containing light components at the top of the column, and obtaining ethylene-containing heavy-component liquid material II at the bottom of the column; (b) Condensing the ethylene gas-phase material I to obtain ethylene liquid-phase material III, dividing the ethylene liquid-phase material III into two parts, the first part of ethylene liquid-phase material III-1 and the second part of ethylene liquid-phase material III-2, returning the first part of ethylene liquid-phase material III-1 as reflux liquid to the ethylene rectification column, and feeding the second part of ethylene liquid-phase material III-2 as the feed for the light removal column into the light removal column; (c) Condensing the gas-phase material obtained at the top of the light removal column and feeding it into the reflux drum of the light removal column, obtaining light-component gas-phase material IV-1 containing ethylene at the top of the reflux drum of the light removal column, and returning the liquid material IV-2 obtained at the bottom of the reflux drum of the light removal column as reflux liquid to the light removal column; (d) Feeding the heavy-component liquid material II and the light-component gas-phase material IV-1 into a flash tank, obtaining gas-phase material V rich in ethylene at the top of the flash tank, and obtaining heavy components with most of the ethylene removed at the bottom; (e) Pressurizing the gas-phase material V with a compressor, cooling it with a cooler at the outlet of the compressor, and then feeding it into a gas-liquid separation tank, obtaining ethylene-rich material at the bottom of the gas-liquid separation tank and obtaining light components at the top of the gas-liquid separation tank; (f) Returning the ethylene-rich material obtained at the bottom of the gas-liquid separation tank to the ethylene rectification column for utilization.

2. The method according to claim 1, characterized in that the ratio (reflux ratio) of the ethylene liquid-phase material III-1 to the ethylene liquid-phase material III-2 is 2-7, preferably 3-6; the ratio (reflux ratio) of the light-component gas-phase material IV-1 to the liquid material IV-2 is 5-18, preferably 6-16.

3. The method according to claim 1 or 2, characterized in that discharging the heavy components with most of the ethylene removed obtained at the bottom of the flash tank to the outside of the boundary; and / or discharging the non-condensable light components obtained at the top of the gas-liquid separation tank to the outside of the boundary.

4. The method according to any one of claims 1-3, characterized in that the raw material crude ethylene is the material after ethanol dehydration reaction, washing and compression drying, and / or the raw material crude ethylene contains hydrogen, methane, carbon monoxide, ethylene, ethane, propane and C4.

5. The method according to any one of claims 1-4, characterized in that the light-component gas-phase material IV-1 enters from the bottom of the flash tank and is used to strip the heavy-component liquid material II.

6. The method according to any one of claims 1-5, characterized in that the operating pressure of the ethylene rectification column is 2.3-4.0 MPaG, and the number of theoretical plates is 50-110; and / or the operating pressure of the light removal column is 3.3-5.0 MPaG, and the number of theoretical plates is 5-40.

7. The method according to any one of claims 1-6, characterized in that the operating pressure of the flash tank is 0.1-1.0 MPaG.

8. The method according to any one of claims 1-7, characterized in that, the outlet pressure of the compressor is 4.0 to 6.5 MPaG.

9. The method according to any one of claims 1-8, characterized in that, the outlet temperature of the outlet cooler of the compressor is -38 to -30 °C.

10. The method according to any one of claims 1-9, characterized in that, the temperature at the top of the ethylene rectification tower is not lower than -40 °C; and / or the temperature at the top of the light component removal tower is not lower than -40 °C; and / or the temperature of the refrigerant for condensing the gas-phase material at the outlet of the outlet cooler of the compressor is not lower than -40 °C.

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