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CN-122010674-A - Method and device for preparing polymerization grade ethylene by recycling carbon two components in dry gas and application

CN122010674ACN 122010674 ACN122010674 ACN 122010674ACN-122010674-A

Abstract

The invention relates to the technical field of dry gas treatment, and discloses a method and a device for preparing polymerization grade ethylene by recycling carbon two components in dry gas and application thereof, wherein the method comprises the steps of (1) compressing raw dry gas and separating gas from liquid to obtain gas phase and liquid phase; the method comprises the steps of (1) contacting a gas phase with an absorbent to absorb carbon two components to obtain absorption tail gas and absorption rich liquid, (3) desorbing methane from the liquid phase to obtain desorption gas and rich absorbent, (4) desorbing and separating the rich absorbent to obtain lean absorbent and enriched gas, (5) feeding the enriched gas to a deethanizer to separate light components from heavy components after deacidification gas and dehydration and impurity removal, and feeding the gas phase at the top of the tower into an ethylene rectifying tower as a feed to separate ethylene from ethane, and (6) collecting a polymerization grade ethylene product from the side line of the body of the ethylene rectifying tower. The method has the advantages of high purity of the recovered carbon two components, high recovery rate, simple flow, low steam consumption, no need of a deoxidizing reactor and a demethanizer, and low energy consumption of the device.

Inventors

  • LIU ZHIXIN
  • ZHANG CHANG
  • SHAO HUAWEI
  • HU ZHIYAN
  • LI YAN
  • ZHANG WEIHONG
  • ZHENG ZEJIA
  • WANG YANNA
  • Hou Zhuoya
  • LI YAN

Assignees

  • 中国石油化工股份有限公司
  • 中石化(北京)化工研究院有限公司

Dates

Publication Date
20260512
Application Date
20241111

Claims (12)

  1. 1. A method for preparing polymer grade ethylene by recovering carbon two components in dry gas, which is characterized by comprising the following steps: (1) Compressing raw material dry gas, cooling the obtained compressed gas, and performing gas-liquid separation to obtain gas phase and liquid phase; (2) The gas phase is contacted with an absorbent to absorb carbon two components, so as to obtain absorption tail gas and absorption rich liquid, and the absorption rich liquid returns and is mixed into the compressed gas; (3) Methane desorption is carried out after the liquid phase is depressurized, so that desorption gas and rich absorbent are obtained, and the desorption gas returns to the compression or the discharge in the step (1); (4) Desorbing and separating the rich absorbent to obtain a lean absorbent and a concentrated gas mainly comprising carbon two components, wherein the lean absorbent returns and is mixed with the absorbent; (5) The concentrated gas mainly comprising the carbon two components is sent to a deethanizer for separating light components with carbon two and below and heavy components with carbon three and above after being treated by deacidification gas and dehydration impurity removal, the gas phase at the top of the tower is used as a feed to enter an ethylene rectifying tower for separating ethylene from ethane, and the liquid phase at the bottom of the tower is returned to the absorption system of the step (2) to be used as an absorbent; (6) And (3) returning the noncondensable gas at the top of the ethylene rectifying tower to the compressor in the step (1), and obtaining an ethane product mainly comprising ethane at the tower bottom, and obtaining a polymerization-grade ethylene product at the side line of the tower body.
  2. 2. The process of claim 1 wherein in step (5) after separation of carbon three and more heavy components by the deethanizer, the methane content of the refined concentrate may be less than 0.1%, preferably 0-0.6%; And/or, in the step (5), after separation of three or more heavy components from the deethanizer, the content of O 2 in the refined concentrate is less than 5ppm, preferably 0 to 5ppm, more preferably 0 to 3ppm.
  3. 3. The process according to claim 1 or 2, wherein the caustic scrubber operating pressure is 1.9-2.4MPaG and the overhead temperature is 40-45 ℃; and/or, the alkali washing tower adopts NaOH solution to remove acid gas to less than 5ppm; And/or paste, said dryer operating pressure is 1.8-2.3MPaG.
  4. 4. The process of claim 1, wherein the deethanizer is operated at a pressure of 1.5-3.8mpa g, the deethanizer is operated at a head temperature of-20 ℃ to 0 ℃, and the deethanizer is operated at a foot temperature of 50-160 ℃.
  5. 5. The process of claim 1, wherein the operating pressure of the ethylene rectification column is from 1.5 to 2.5mpa g, the overhead temperature of the ethylene rectification column is from-38 ℃ to-30 ℃, and the bottoms temperature of the ethylene rectification column is from-20 ℃ to-10 ℃.
  6. 6. A process according to claim 1, wherein the compressed gas has a pressure of 2.5-4.6MPaG, preferably 3-4.2MPaG; and/or the pressure of the liquid phase after depressurization is 0.8-3MPaG, preferably 1-2MPaG; and/or the operating pressure of the absorption tower is 2.5-4.6MPaG, the tower top temperature is 10-60 ℃, and the tower bottom temperature is 10-70 ℃; and/or the operating pressure of the methane desorption tower is 0.5-2.4MPaG, the tower top temperature is 10-60 ℃, and the tower bottom temperature is 35-90 ℃; and/or the operation pressure of the desorption tower is 1-2.8MPaG, the tower top temperature is 25-70 ℃, and the tower bottom temperature is 90-160 ℃; And/or the absorbent is selected from a carbon four fraction and/or a carbon five fraction, preferably the carbon four fraction contains at least one of n-butane, isobutane and butene, preferably the carbon five fraction contains at least one of n-pentane, isopentane and neopentane; and/or the carbon bi-component is selected from ethane and/or ethylene.
  7. 7. The device for preparing the polymerization grade ethylene by recycling the carbon two-component in the dry gas is characterized by comprising a compressor (2), a cooler (3), a liquid separating tank (4), an absorption tower (5), a methane desorption tower (7), a desorption tower (9), a refining system, a deethanizer (12) and an ethylene rectifying tower (13); the refining system comprises an alkaline washing tower (10) and a dryer (11), wherein the upper part of the alkaline washing tower (10) is connected with fresh alkali liquor (17) and is used for removing acid gas in the enriched gas (16) to a lower content, and the dryer (11) is used for removing water in the enriched gas (16) cleanly; The deethanizer (12) is connected with the outlet of the dryer (11), the top of the tower is connected with the ethylene rectifying tower (13), and the bottom of the tower is connected with the absorption tower (5) and is used for separating the carbon two components from the carbon three and more heavy components in the enriched gas (16); The top of the ethylene rectifying tower (13) is connected with the compressor (2) and is used for separating light components from the carbon-rich two components and returning the light components to the compressor (2), an ethane product (21) mainly comprising ethane is obtained at the tower bottom, and a polymerization-grade ethylene product (20) is extracted from the middle part of the tower body.
  8. 8. The device according to claim 7, wherein the top of the caustic scrubber (10) is connected to the dryer (11); and/or the lower part of the alkaline washing tower (10) is connected with the top of the desorption tower (9); And/or the bottom of the alkaline washing tower (10) is connected with the waste lye (18).
  9. 9. The apparatus of claim 7, wherein the middle, top and bottom of the deethanizer (12) are respectively connected to the bottom of the dryer (11), the middle of the ethylene rectification column (13) and the absorbent for separating out the heavy components of three or more carbon atoms in the enriched gas (16) for further use as absorbent; And/or the theoretical plate number of the deethanizer (12) is 25-55; And/or the middle part of the deethanizer (12) is 1/6-2/3 of the deethanizer.
  10. 10. The apparatus of claim 7, wherein the middle, top, middle upper and bottom of the ethylene rectification column (13) are in communication with the deethanizer (12), compressor (2), ethylene product collection system and ethane product collection system, respectively, for separating ethylene and ethane; And/or the theoretical plate number of the ethylene rectifying tower (13) is 75-105; and/or the middle part of the ethylene rectifying tower (13) is 1/5-1/3 of the ethylene rectifying tower; and/or the middle and upper part of the ethylene rectifying tower (13) is 1/10-1/5 of the ethylene rectifying tower.
  11. 11. The apparatus of claim 7, wherein the compressor (2), the cooler (3) and the knock-out pot (4) are in communication in sequence; And/or the bottom of the absorption tower (5) is respectively communicated with the top of the liquid separating tank (4) and the cooler (3), and is used for enabling the top exhaust gas phase of the liquid separating tank (4) to be in countercurrent contact with the absorbent, absorbing tail gas (15) is discharged from the top of the absorption tower (5), absorbing rich liquid is discharged from the tower bottom of the absorption tower (5) and returned to the cooler (3); And/or the upper part, the top and the bottom of the methane desorption tower (7) are respectively communicated with the bottom of the liquid separation tank (4), the compressor (2) and the middle part of the desorption tower (9), and are used for performing methane desorption after the liquid phase discharged from the bottom of the liquid separation tank (4) is depressurized, the desorption gas discharged from the top of the methane desorption tower (7) is returned to the inlet or the interval or the outer discharge of the compressor (2), and the rich absorbent discharged from the tower 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 communicated with the top of the absorption tower (5) and is used for discharging a rich absorbent from the tower kettle of the methane desorption tower (7) for desorption separation, the concentrated gas (16) mainly containing carbon two components is recovered from the top of the desorption tower (9), and the lean absorbent (14) is discharged from the tower kettle of the desorption tower (9) and returned to the top of the absorption tower (5).
  12. 12. Use of the apparatus of any one of claims 7 to 11 in a process for the production of polymer grade ethylene from carbon bi-component recovered dry gas as claimed in any one of claims 1 to 6.

Description

Method and device for preparing polymerization grade ethylene by recycling carbon two components in dry gas and application Technical Field The invention relates to the technical field of dry gas treatment, in particular to a method and a device for preparing polymer grade ethylene by recycling carbon two components in dry gas and application thereof. Background The method for industrially recycling ethane and ethylene components from dry gas at present mainly comprises the following steps: (1) The cryogenic separation method has mature process, high ethylene recovery rate and high purity, but needs a dryer and a propylene refrigerating device or an ethylene-propylene composite refrigerating device, and has larger device investment and higher energy consumption; (2) The pressure swing adsorption method is simple to operate, generally has lower energy consumption, but has low product purity and low recovery rate of carbon two components, and when the treatment scale of raw dry gas is larger, the investment of equipment and the occupation of land are larger; (3) The shallow cold oil absorption method has the advantages of safe and reliable process flow, high recovery rate of carbon two and carbon three, no requirement on sulfur content and water content in raw material gas, larger load of a tower kettle reboiler of an absorption tower (or a methane desorption tower), and larger low-pressure steam consumption in the whole process flow. CN112725032B discloses a method and apparatus for recovering carbon two components in dry gas. The method comprises the steps of (1) compressing raw material dry gas, cooling the obtained compressed gas, performing gas-liquid separation to obtain a gas phase and a liquid phase, (2) contacting the gas phase with an absorbent to perform carbon two-component absorption to obtain absorption tail gas and absorption rich liquid, returning the absorption rich liquid and mixing the absorption rich liquid into the compressed gas, (3) depressurizing the liquid phase, performing methane desorption to obtain desorption gas and rich absorbent, returning the desorption gas to the compression or the discharge of the step (1), and (4) performing desorption separation on the rich absorbent to obtain a lean absorbent and a concentrated gas mainly comprising carbon two components, and returning and mixing the lean absorbent into the absorbent. The recovery rate of the carbon two components obtained by the method is high, and the total energy consumption of the device is low. CN103159581B discloses a device for recovering carbon two in refinery dry gas by combined absorption method. Comprises a compressor, a pretreatment unit, a refinery dry gas cooling unit, an absorption unit and a rectification unit. The absorption unit comprises a gas-liquid separation tank, a carbon two absorption tower and a methane desorption tower, and the carbon two and absorbent components are separated at the decarburization tower by the rich absorbent which absorbs the carbon two components in the dry gas. The operating pressure of the carbon two absorption tower is 2.5-3.0MPaG, the operating pressure of the methane desorption tower is 2.5-3.1MPaG, and the operating pressure of the decarbonization two tower is 2.2-2.6MPaG. The methane desorption tower needs to use a heat source of about 120 ℃ in a refinery. CN 111320523B discloses a method and apparatus for separating ethylene from refinery dry gas, the separation method comprises the steps of compression, purification, cooling, absorption, depropanization, demethanization, ethylene refining, etc. Separating ethylene from refinery dry gas involves purifying the refinery dry gas after pressure boosting. The purified gas is cooled and then sent into an oil absorption tower, the material flow from the bottom of the oil absorption tower enters a depropanization tower, the gas at the top of the depropanization tower is sent into the depropanization tower, the gas at the top of the depropanization tower returns to the compressor section or is sent out of the boundary zone, and the material flow at the bottom of the tower is sent to an ethylene rectifying tower. The material flow from the demethanizer kettle enters an ethylene rectifying tower, so that a polymerization grade ethylene product is directly obtained from refinery dry gas. CN111320522B discloses a method and apparatus for separating ethylene from refinery dry gas, the separation method comprises the steps of compression, purification, cooling, absorption, demethanization, depropanization, ethylene refining, etc. The method comprises the steps of pressurizing the refinery dry gas, purifying the refinery dry gas, including but not limited to deacidification gas, oxygen removal, drying, arsenic removal, mercury removal, decarburization and the like, and deoxidizing and drying the refinery dry gas containing oxygen and water. In summary, when the polymerization grade ethylene is prepared by recycling the carbon two com