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CN-117654217-B - System and method for preparing propylene by disproportionation of refinery dry gas

CN117654217BCN 117654217 BCN117654217 BCN 117654217BCN-117654217-B

Abstract

The invention belongs to the field of refinery dry gas utilization, and discloses a system and a method for preparing propylene by disproportionating refinery dry gas. The system comprises a raw material pretreatment unit, a disproportionation reaction unit and a product separation unit, wherein the raw material pretreatment unit comprises an alkaline washing bag, a dry gas compressor, a dry gas absorption tower, a primary desorption tower, a secondary desorption tower and a circulating carbon four cooler which are sequentially communicated, the disproportionation reaction unit comprises a disproportionation reactor feeding and discharging heat exchanger, a disproportionation reactor and a reaction discharging cooler, the product separation unit comprises a deethanizer, a propylene refining tower, a reaction separation tail gas absorption tower and a residual carbon four cooler, and the system and the method can reduce the consumption of the carbon four raw materials, improve the recovery rate of ethylene in the dry gas of a refinery and reduce the consumption.

Inventors

  • ZHU CHAO
  • BAI YAN
  • WANG XINQUAN

Assignees

  • 中国石油化工股份有限公司
  • 中国石化工程建设有限公司

Dates

Publication Date
20260512
Application Date
20220825

Claims (12)

  1. 1. A system for preparing propylene by disproportionating refinery dry gas is characterized by comprising a raw material pretreatment unit, a disproportionation reaction unit and a product separation unit; The raw material pretreatment unit comprises an alkaline washing bag, a dry gas compressor, a dry gas absorption tower, a primary desorption tower, a secondary desorption tower and a circulating carbon four cooler which are sequentially communicated; The disproportionation reaction unit comprises a disproportionation reactor feeding and discharging heat exchanger, a disproportionation reactor and a reaction discharging cooler; The product separation unit comprises a deethanizer, a propylene refining tower, a reaction separation tail gas absorption tower, a reaction separation tail gas desorption tower and a residual carbon four cooler; The alkaline washing bag inlet is connected with a refinery dry gas feeding pipeline, the outlet at the bottom of the second-stage desorption tower is connected with the circulating carbon four cooler and then is respectively communicated with the inlet at the top of the dry gas absorption tower and the inlet at the top of the first-stage desorption tower, the outlet of the alkaline washing bag is communicated with the inlet at the bottom of the dry gas absorption tower through the dry gas compressor, the outlet at the bottom of the dry gas absorption tower is communicated with the inlet at the middle of the first-stage desorption tower, the outlet at the bottom of the first-stage desorption tower is communicated with the inlet at the middle of the second-stage desorption tower, the top of the dry gas absorption tower is provided with a hydrogen-rich dry gas discharging pipeline, and the top of the first-stage desorption tower is provided with a hydrogen-lean dry gas discharging pipeline; The outlet pipeline at the top of the secondary desorption tower is converged with a fresh carbon four feed pipeline and the outlet pipeline at the top of the reaction separation tail gas desorption tower and then is sequentially communicated with the cold side inlet of the disproportionation reactor in-out heat exchanger and the disproportionation reactor inlet; The gas phase outlet at the top of the deethanizer is communicated with the inlet at the bottom of the reaction separation tail gas absorption tower, and the discharge outlet at the bottom of the deethanizer is communicated with the propylene refining tower; The bottom of the reaction separation tail gas desorption tower is provided with four discharge pipelines rich in ethane and carbon; the top of the reaction separation tail gas absorption tower is provided with a methane-rich gas discharge pipeline; The lower discharge pipeline of the propylene refining tower is divided into two paths, one path is communicated with the cold side inlet of the disproportionation reactor feeding and discharging heat exchanger, and the other path is respectively communicated with the top inlet of the secondary desorption tower and the top inlet of the reaction separation tail gas absorption tower after passing through the residual carbon four cooler; the top of the propylene refining tower is provided with a polymerization-stage propylene product discharge pipeline, and the tower kettle is provided with a heavy component discharge pipeline.
  2. 2. The system for preparing propylene by disproportionating refinery dry gas according to claim 1, wherein, The raw material pretreatment unit further comprises a fresh carbon four absorbent feeding pipeline and a fresh carbon four absorbent cooler which are sequentially connected, wherein a discharging pipeline of the fresh carbon four absorbent cooler is communicated with a top inlet of the secondary desorption tower and a top inlet of the reaction separation tail gas absorption tower after being converged with a discharging pipeline of the residual carbon four cooler; the raw material pretreatment unit further comprises an absorbent regeneration tower, wherein the bottom outlet of the secondary desorption tower and the four-discharging pipeline rich in ethane are further communicated with the middle inlet of the absorbent regeneration tower, the bottom outlet of the absorbent regeneration tower is communicated with the top inlet of the secondary desorption tower and the top inlet of the reaction separation tail gas absorption tower through the residual four-carbon coolers, the product separation unit further comprises a debutanizer, the lower discharging pipeline of the propylene refining tower is communicated with the middle inlet of the debutanizer, the discharging pipeline at the bottom of the debutanizer is divided into two paths, one path is communicated with the cold side inlet of the disproportionation reactor inlet and outlet heat exchanger, and the other path is respectively communicated with the top inlet of the secondary desorption tower and the top inlet of the reaction separation tail gas absorption tower through the residual four-carbon coolers.
  3. 3. The system for preparing propylene by disproportionating refinery dry gas according to claim 2, wherein, The first-stage desorption tower, the second-stage desorption tower and the reaction separation tail gas desorption tower are respectively and independently provided with a tower kettle reboiler; the propylene refining tower and the absorbent regeneration tower are respectively and independently provided with an overhead condenser and a tower kettle reboiler; The debutanizer is provided with a tower top condenser and a tower kettle reboiler; The deethanizer is provided with a tower top condenser, a tower top gas-liquid separation tank and a tower kettle reboiler.
  4. 4. The system for preparing propylene by disproportionating refinery dry gas according to claim 2, wherein, The theoretical plate number of the dry gas absorption tower is 10-40; The theoretical plate number of the primary desorption tower is 10-40, and the theoretical feeding plate is the 5 th plate to the 25 th plate of the tower top; the theoretical plate number of the secondary desorption tower is 20-100, and the theoretical feeding plate is the 10 th plate to the 70 th plate of the tower top; the theoretical plate number of the reaction separation tail gas absorption tower is 10-40; The theoretical plate number of the reaction separation tail gas desorption tower is 10-40; The theoretical plate number of the deethanizer is 40-100, and the theoretical feeding plate is the 20 th plate to the 80 th plate of the tower top; The theoretical plate number of the propylene refining tower is 20-100, and the theoretical feeding plate is the 10 th plate to the 80 th plate of the tower top; the theoretical plate number of the absorber regeneration tower is 20-100, and the theoretical feeding plate is the 10 th plate to the 70 th plate of the tower top; The theoretical plate number of the debutanized is 10-50, and the theoretical feeding plate is the 5 th plate to the 30 th plate of the tower top.
  5. 5. A method for preparing propylene by disproportionating refinery dry gas, which is characterized in that the method adopts the system for preparing propylene by disproportionating refinery dry gas according to any one of claims 1-4, and comprises the following steps: The method comprises the following steps of S1, treating refinery dry gas sequentially by an alkaline washing bag, a dry gas compressor, a dry gas absorption tower, a first-stage desorption tower and a second-stage desorption tower, obtaining ethylene-rich dry gas at the top of the second-stage desorption tower, and obtaining ethylene-poor C-IV at the bottom of the second-stage desorption tower; S2, enabling the ethylene-rich dry gas and fresh carbon four feed to enter a disproportionation reactor for reaction after being subjected to heat exchange through a disproportionation reactor feed-in and feed-out heat exchanger to obtain a reaction product, and enabling the reaction product to enter the deethanizer after being subjected to heat exchange through the disproportionation reactor feed-in and feed-out heat exchanger and cooling through the reaction discharge cooler in sequence; And S3, separating the cooled reaction product in the step S2 to obtain a deethanizer top gas phase and a deethanizer bottom discharge, sequentially passing through the reaction separation tail gas absorption tower and the reaction separation tail gas desorption tower to treat the deethanizer top gas phase, obtaining an ethylene-rich circulating gas at the reaction separation tail gas desorption tower top, mixing the ethylene-rich circulating gas with an ethylene-rich dry gas and entering a disproportionation reactor feeding and discharging heat exchanger, feeding the deethanizer bottom discharge into the propylene refining tower to obtain polymerization grade propylene, heavy component discharge and residual carbon four through separation, mixing a part of the residual carbon four with the ethylene-rich dry gas and entering the disproportionation reactor feeding and discharging heat exchanger, and feeding the rest of the residual carbon four into the top of the secondary desorption tower and the reaction separation tail gas absorption tower after passing through the residual carbon four coolers.
  6. 6. The method for preparing propylene by disproportionation of refinery dry gas according to claim 5, wherein, Obtaining hydrogen-rich dry gas at the top of the dry gas absorption tower, and obtaining hydrogen-poor dry gas at the top of the primary desorption tower; The temperatures of the dry gas absorption tower top feed, the primary desorption tower top feed, the secondary desorption tower top feed and the reaction separation tail gas absorption tower top feed are respectively and independently 0-30 ℃; the top feed of the dry gas absorption tower accounts for 30% -80% of the bottom discharge of the secondary desorption tower, and the top feed of the primary desorption tower accounts for 5% -30% of the bottom discharge of the secondary desorption tower; the gas phase at the top of the deethanizer is cooled to obtain a gas phase part and a liquid phase part, the gas phase part enters the reaction separation tail gas absorption tower, and the liquid phase part flows back to the deethanizer for rectification circulation; and the methane-rich gas is obtained at the top of the reaction separation tail gas absorption tower, the methane-poor carbon four is obtained at the bottom of the reaction separation tail gas absorption tower, and the methane-poor carbon four enters the reaction separation tail gas desorption tower for treatment.
  7. 7. The method for preparing propylene by disproportionation of refinery dry gas according to claim 6, wherein, The remainder of the ethylene-depleted carbon four is discharged; The four carbon-rich ethane is discharged; The residual part of the residual carbon four enters the top of the secondary desorption tower and the top of the reaction separation tail gas absorption tower together with the cooled fresh carbon four absorbent feed to be used as the feed; The proportion of the residual carbon four entering the feeding and discharging heat exchanger of the disproportionation reactor to the total amount of the residual carbon four is 0% -80%, the proportion of the residual carbon four serving as the top feed of the secondary desorption tower to the total amount of the residual carbon four is 30% -60%, and the proportion of the residual carbon four serving as the top feed of the reaction separation tail gas absorption tower to the total amount of the residual carbon four is 40% -70%; The fresh carbon four absorbent fed at the top of the secondary desorption tower accounts for 30% -60% of the total amount of the fresh carbon four absorbent, and the fresh carbon four absorbent fed at the top of the reaction separation tail gas absorption tower accounts for 40% -70% of the total amount of the fresh carbon four absorbent.
  8. 8. The method for preparing propylene by disproportionation of refinery dry gas according to claim 6, wherein, The rest part of the ethylene-poor carbon four is sent into the absorbent regeneration tower to be treated to obtain a regenerated absorbent, the regenerated absorbent is cooled and then used as top feed of the secondary desorption tower and top feed of the reaction separation tail gas absorption tower, the ethylene-poor carbon four which is sent into the absorbent regeneration tower to be treated accounts for 10% -50% of the bottom discharge of the secondary desorption tower, the regenerated absorbent which is used as the top feed of the secondary desorption tower accounts for 30% -60% of the total amount of the regenerated absorbent, and the regenerated absorbent which is used as the top feed of the reaction separation tail gas absorption tower accounts for 40% -70% of the total amount of the regenerated absorbent; The method comprises the steps of enabling the residual carbon four to enter a debutanizer for treatment to obtain a butene-lean carbon four at the top of the debutanizer and a butene-rich carbon four at the bottom of the debutanizer, wherein the butene-lean carbon four at the top of the debutanizer is discharged outside; The ratio of the butene-rich carbon four at the bottom of the debutanizer, which enters the feeding and discharging heat exchanger of the disproportionation reactor, to the butene-rich carbon four at the bottom of the debutanizer is 0% -80%, the ratio of the butene-rich carbon four at the bottom of the debutanizer, which is used as the top feed of the secondary debutanizer, to the butene-rich carbon four at the bottom of the debutanizer is 30% -60%, and the ratio of the butene-rich carbon four at the bottom of the debutanizer, which is used as the top feed of the reaction separation tail gas absorber, to the butene-rich carbon four at the bottom of the debutanizer is 40% -70%.
  9. 9. The method for preparing propylene by disproportionation of refinery dry gas according to claim 8, wherein, The source of the refinery dry gas is at least one of crude oil distillation, catalytic cracking, thermal cracking, coking, hydrocracking, catalytic reforming, hydrofining and steam cracking to prepare ethylene; The fresh carbon four feed is at least one of propane, propylene, isobutane, n-butane, 1-butene, isobutene and 2-butene; the top operation pressure of the dry gas absorption tower is 1.0-4.0 MPaA, and the top operation temperature is-20-60 ℃; The tower top operation pressure of the primary desorption tower is 0.5-3.0 MPaA, and the tower top operation temperature is-20-60 ℃; The tower top operation pressure of the secondary desorption tower is 1.5-4.0 MPaA, and the tower top operation temperature is 40-140 ℃; The operation pressure of the top of the reaction separation tail gas absorption tower is 1.0-3.0 MPaA, and the operation temperature of the top of the reaction separation tail gas absorption tower is-20-60 ℃; The operation pressure of the top of the reaction separation tail gas desorption tower is 1.0-3.0 MPaA, and the operation temperature of the top of the tower is 0-60 ℃; the top operation pressure of the deethanizer is 1.0-4.0 MPaA, and the top operation temperature is-30-20 ℃; The operation pressure of the top of the propylene refining tower is 1.0-3.0 MPaA, and the operation temperature of the top of the propylene refining tower is 20-60 ℃; The tower top operation pressure of the absorbent regeneration tower is 1.0-3.0 MPaA, and the tower top operation temperature is 20-60 ℃; The overhead operating pressure of the debutanizer is 0.4-2.0 MPaA, and the overhead operating temperature is 20-60 ℃.
  10. 10. The method for producing propylene by disproportionation of refinery dry gas according to claim 9, wherein the top operation pressure of the dry gas absorption tower is 2.0 to 3.5mpa and the top operation temperature is 10 to 40 ℃.
  11. 11. The method for producing propylene by disproportionation of refinery dry gas according to claim 9, wherein the top operation pressure of the primary desorption tower is 1.5-2.0 mpa, and the top operation temperature is 10-40 ℃.
  12. 12. The method for producing propylene by disproportionation of refinery dry gas according to claim 9, wherein the overhead operating pressure of the secondary desorption tower is 2.0 to 3.0mpa and the overhead operating temperature is 60 to 90 ℃.

Description

System and method for preparing propylene by disproportionation of refinery dry gas Technical Field The invention belongs to the field of refinery dry gas utilization, and particularly relates to a system and a method for preparing propylene by disproportionating refinery dry gas. Background The main components of the refinery dry gas comprise hydrogen, nitrogen, oxygen, methane, ethylene, ethane, carbon monoxide, carbon dioxide, propane, propylene and the like. In most cases, the dry gas is burned directly as fuel gas. This is a great waste of valuable gases, of which ethylene and ethane are representative. CN102372573A is prepared from C-IV and ethylene through removing water, alcohol, ether and S-contained impurities, mixing, treating by isomerisation catalyst to obtain the stream III containing butene-2 (80 wt.%), reacting under the action of disproportionation catalyst and isomerisation catalyst to obtain the resultant stream IV containing ethylene, propylene, butene and trace C-V, removing ethylene from stream IV, separating by de-allyl tower to obtain propylene product, butene and trace C-V, removing hydrocarbon from stream VI, and removing hydrocarbon from stream VI. As can be seen from the technology disclosed in the above patent application, CN102372573a refers to a process for producing propylene by carbon four disproportionation, wherein the raw material treatment method adopts adsorption treatment, and the process of disproportionating propylene by pure ethylene is aimed at, and the process of producing propylene by disproportionating refinery dry gas is not involved. In view of the above state of the art, it is desirable to provide a method and system for producing propylene by disproportionating refinery dry gas. Disclosure of Invention The invention aims at overcoming the defects of the prior art and provides a method and a system for preparing propylene by disproportionating refinery dry gas. The system and the method can reduce the consumption of the carbon four raw materials, improve the recovery rate of ethylene in the refinery dry gas and reduce the grade requirement and consumption of the top refrigerant of the deethanizer. In order to achieve the above object, in one aspect, the present invention provides a system for preparing propylene by disproportionating refinery dry gas, which comprises a raw material pretreatment unit, a disproportionation reaction unit and a product separation unit; The raw material pretreatment unit comprises an alkaline washing bag, a dry gas compressor, a dry gas absorption tower, a primary desorption tower, a secondary desorption tower and a circulating carbon four cooler which are sequentially communicated; The disproportionation reaction unit comprises a disproportionation reactor feeding and discharging heat exchanger, a disproportionation reactor and a reaction discharging cooler; The product separation unit comprises a deethanizer, a propylene refining tower, a reaction separation tail gas absorption tower, a reaction separation tail gas desorption tower and a residual carbon four cooler; the inlet of the alkaline washing bag is connected with a refinery dry gas feeding pipeline, and the outlet of the bottom of the secondary desorption tower is connected with the circulating carbon four cooler and then is respectively communicated with the inlet at the top of the dry gas absorption tower and the inlet at the top of the primary desorption tower; The outlet pipeline at the top of the secondary desorption tower is converged with a fresh carbon four feed pipeline and the outlet pipeline at the top of the reaction separation tail gas desorption tower and then is sequentially communicated with the cold side inlet of the disproportionation reactor in-out heat exchanger and the disproportionation reactor inlet; The gas phase outlet at the top of the deethanizer is communicated with the inlet at the bottom of the reaction separation tail gas absorption tower, and the discharge outlet at the bottom of the deethanizer is communicated with the propylene refining tower; The lower discharging pipeline of the propylene refining tower is divided into two paths, one path is communicated with the cold side inlet of the disproportionation reactor feeding and discharging heat exchanger, and the other path is respectively communicated with the top inlet of the secondary desorption tower and the top inlet of the reaction separation tail gas absorption tower after passing through the residual carbon four cooler. In the invention, the alkaline washing bag is used for removing acid gas impurities such as carbon dioxide, hydrogen sulfide and the like in the dry gas, and is a conventional operation in the field. Preferably, the alkaline washing bag is an alkaline washing tower. According to the invention, preferably, the caustic wash bag outlet is communicated with the bottom inlet of the dry gas absorption tower through the dry gas compressor, the bottom outlet of the dry gas