A system and method for the production of propylene by dry gas disproportionation in a refinery

Abstract

The present application belongs to the field of refinery dry gas utilization, and discloses a system and method for preparing propylene by disproportionation of refinery dry gas. The system comprises a raw material pretreatment unit, a disproportionation reaction unit and a product separation unit. The raw material pretreatment unit comprises, in sequence, an alkali washing package, a dry gas compressor, a dry gas absorption tower, a first desorption tower, a second desorption tower and a circulating carbon four cooler. The disproportionation reaction unit comprises a disproportionation reactor inlet-outlet heat exchanger, a disproportionation reactor and a reaction outlet cooler. The product separation unit comprises a deethanizer, a propylene rectification tower, a reaction separation tail gas absorption tower and a remaining carbon four cooler. The system and method can reduce the consumption of carbon four raw material, improve the recovery rate of ethylene in refinery dry gas and reduce consumption.

Description

Technical Field

[0001] This invention belongs to the field of refinery dry gas utilization, and more specifically, relates to a system and method for disproportionating refinery dry gas to produce propylene. Background Technology

[0002] Refinery dry gas mainly consists of hydrogen, nitrogen, oxygen, methane, ethylene, ethane, carbon monoxide, carbon dioxide, propane, and propylene. In most cases, dry gas is directly burned as fuel. This represents a significant waste of valuable gases, such as ethylene and ethane.

[0003] CN102372573A describes a technical solution that uses C4 ether and ethylene as raw materials, and includes the following steps: (1) Raw material I, which removes water, alcohol, ether and sulfur-containing impurities from the raw materials, and ethylene stream II, are mixed and then treated with an isomerization catalyst to obtain stream III containing butene-2 ​​by weight greater than 80%; (2) Stream III reacts under the action of a disproportionation catalyst and an isomerization catalyst to generate reaction product stream IV containing ethylene, propylene, butene and trace C5 components; (3) Stream IV is deethyleneized by a deethyleneization tower to obtain stream V containing propylene, butene and trace C5; (4) Stream V is separated by a depropyleneization tower to obtain propylene product and stream VI containing butene and trace C5; (5) Stream VI is debutaneized by a butaneization tower to remove trace C5 and above hydrocarbons to obtain stream VII containing butene. This solution can be used in the industrial production of propylene from C4 ether and ethylene.

[0004] As can be seen from the technology disclosed in the above patent application, the method for producing propylene by C4 disproportionation mentioned in CN102372573A uses adsorption treatment for the raw materials, and it is aimed at the process of disproportionating propylene from pure ethylene, and does not involve the process of producing propylene by disproportionation of refinery dry gas.

[0005] In view of the above-mentioned technological status, there is an urgent need to propose a method and system for producing propylene from refinery dry gas disproportionation. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing a method and system for producing propylene from refinery dry gas through disproportionation. The system and method of this invention can reduce the consumption of C4 feedstock, increase the ethylene recovery rate from refinery dry gas, and reduce the grade requirements and consumption of the overhead refrigerant in the de-ethaner tower.

[0007] To achieve the above objectives, the present invention provides a system for producing propylene by disproportionation of refinery dry gas, the system comprising a feed pretreatment unit, a disproportionation reaction unit, and a product separation unit.

[0008] The raw material pretreatment unit includes an alkaline washing bag, a dry gas compressor, a dry gas absorption tower, a primary desorption tower, a secondary desorption tower, and a circulating C4 cooler connected in sequence.

[0009] The disproportionation reaction unit includes a disproportionation reactor feed heat exchanger, a disproportionation reactor, and a reaction discharge cooler;

[0010] The product separation unit includes an ethane stripper, a propylene refining tower, a reaction separation tail gas absorption tower, a reaction separation tail gas desorption tower, and a residual C4 cooler.

[0011] The inlet of the alkali washing bag is connected to the refinery dry gas feed pipeline, and the bottom outlet of the secondary desorption tower is connected to the circulating C4 cooler and then connected to the top inlet of the dry gas absorption tower and the top inlet of the primary desorption tower respectively.

[0012] The top outlet pipeline of the secondary desorption tower merges with the fresh C4 feed pipeline and the top outlet pipeline of the reaction separation tail gas desorption tower, and is then connected in sequence to the cold side inlet of the disproportionation reactor feed heat exchanger and the inlet of the disproportionation reactor; the outlet of the disproportionation reactor is connected in sequence to the hot side inlet of the disproportionation reactor feed heat exchanger, the reaction discharge cooler, and the deethanerization tower.

[0013] The top gas phase outlet of the deethaner is connected to the bottom inlet of the reaction separation tail gas absorption tower, and the bottom outlet of the deethaner is connected to the propylene refining tower; the bottom outlet of the reaction separation tail gas absorption tower is connected to the top inlet of the reaction separation tail gas desorption tower.

[0014] The lower discharge pipeline of the propylene refining tower is divided into two paths. One path is connected to the cold side inlet of the feed heat exchanger of the disproportionation reactor, and the other path is connected to 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 C4 cooler.

[0015] In this invention, the alkaline washing package is used to remove acidic gaseous impurities such as carbon dioxide and hydrogen sulfide from dry gas, which is a conventional operation in the art. As a preferred embodiment, the alkaline washing package is an alkaline washing tower.

[0016] According to the present invention, preferably, the outlet of the alkaline washing package is connected to the bottom inlet of the dry gas absorption tower via the dry gas compressor; the bottom outlet of the dry gas absorption tower is connected to the middle inlet of the primary desorption tower; the bottom outlet of the primary desorption tower is connected to the middle inlet of the secondary desorption tower; a hydrogen-rich dry gas discharge pipeline is provided at the top of the dry gas absorption tower; and a hydrogen-lean dry gas discharge pipeline is provided at the top of the primary desorption tower.

[0017] According to the present invention, preferably, the bottom of the reaction separation tail gas desorption tower is provided with an ethane-rich C4 discharge pipeline.

[0018] According to the present invention, preferably, a methane-rich gas outlet pipeline is provided at the top of the reaction separation tail gas absorption tower.

[0019] According to the present invention, preferably, the top of the propylene refining tower is provided with a polymer-grade propylene product discharge pipeline, and the bottom of the tower is provided with a heavy component discharge pipeline.

[0020] According to the present invention, preferably,

[0021] The raw material pretreatment unit also includes a fresh C4 absorbent feed line and a fresh C4 absorbent cooler connected in sequence; the discharge line of the fresh C4 absorbent cooler merges with the discharge line of the remaining C4 cooler and is connected to the top inlet of the secondary desorption tower and the top inlet of the reaction separation tail gas absorption tower.

[0022] Alternatively, the raw material pretreatment unit further includes an absorbent regeneration tower; the bottom outlet of the secondary desorption tower and the ethane-rich C4 discharge pipeline are also connected to the middle inlet of the absorbent regeneration tower, and the lower outlet of the absorbent regeneration tower is connected to the top inlet of the secondary desorption tower and the top inlet of the reaction separation tail gas absorption tower through the residual C4 cooler; the product separation unit further includes a butane removal tower; the lower discharge pipeline of the propylene refining tower is connected to the middle inlet of the butane removal tower, and the bottom discharge pipeline of the butane removal tower is divided into two paths, one path is connected to the cold side inlet of the disproportionation reactor feed heat exchanger, and the other path is connected to the top inlet of the secondary desorption tower and the top inlet of the reaction separation tail gas absorption tower through the residual C4 cooler.

[0023] According to the present invention, preferably, the primary desorption tower, the secondary desorption tower and the reaction separation tail gas desorption tower are each independently provided with a reboiler.

[0024] According to the present invention, preferably, the propylene refining tower and the absorbent regeneration tower are each independently provided with a top condenser and a bottom reboiler.

[0025] According to the present invention, preferably, the butane dehydrogenator is provided with a top condenser and a bottom reboiler.

[0026] According to the present invention, preferably, the deethaner is provided with a top condenser, a top gas-liquid separator, and a bottom reboiler.

[0027] According to the present invention, preferably, the number of theoretical plates in the dry gas absorption tower is 10 to 40.

[0028] According to the present invention, preferably, the theoretical number of trays of the primary desorption tower is 10 to 40, and the theoretical feed trays are the 5th to 25th trays from the top of the tower (counting from the top of the tower).

[0029] According to the present invention, preferably, the theoretical number of trays in the secondary desorption tower is 20 to 100, and the theoretical feed trays are the 10th to 70th trays from the top of the tower (counting from the top of the tower).

[0030] According to the present invention, preferably, the theoretical number of plates in the reaction separation tail gas absorption tower is 10 to 40.

[0031] According to the present invention, preferably, the theoretical number of plates in the reaction separation tail gas desorption tower is 10 to 40.

[0032] According to the present invention, preferably, the theoretical number of plates of the deethaner column is 40 to 100, and the theoretical feed plate is the 20th to 80th plate from the top of the column (counting from the top of the column).

[0033] According to the present invention, preferably, the theoretical number of trays of the propylene refining tower is 20 to 100, and the theoretical feed trays are the 10th to 80th trays from the top of the tower (counting from the top of the tower).

[0034] According to the present invention, preferably, the theoretical number of trays of the absorbent regeneration tower is 20 to 100, and the theoretical feed trays are the 10th to 70th trays from the top of the tower (counting from the top of the tower).

[0035] According to the present invention, preferably, the theoretical number of butane removal plates is 10 to 50, and the theoretical feed plates are the 5th to 30th plates from the top of the column (counting from the top of the column).

[0036] Another aspect of the present invention provides a method for producing propylene from refinery dry gas by disproportionation, the method employing the aforementioned system for producing propylene from refinery dry gas by disproportionation, and comprising the following steps:

[0037] S1: The refinery dry gas is processed sequentially through the alkaline washing bag, dry gas compressor, dry gas absorption tower, primary desorption tower and secondary desorption tower. Ethylene-rich dry gas is obtained at the top of the secondary desorption tower and ethylene-lean C4 is obtained at the bottom of the tower. A portion of the ethylene-lean C4 is cooled by a circulating C4 cooler and sent to the top of the dry gas absorption tower and the top of the primary desorption tower respectively.

[0038] S2: The ethylene-rich dry gas and fresh C4 feed are heat-exchanged by the inlet and outlet heat exchanger of the disproportionation reactor and then enter the disproportionation reactor to react and obtain reaction products. The reaction products are then heat-exchanged by the inlet and outlet heat exchanger of the disproportionation reactor and cooled by the reaction outlet cooler before entering the de-ethane tower.

[0039] S3: In the deethaner, the cooled reaction product from step S2 is separated to obtain the top gas phase and the bottom product of the deethaner; the top gas phase of the deethaner is processed sequentially through the reaction separation tail gas absorption tower and the reaction separation tail gas desorption tower, obtaining ethylene-rich circulating gas at the top of the reaction separation tail gas desorption tower and ethylene-rich C4 at the bottom, the ethylene-rich circulating gas and ethylene-rich dry gas are mixed and enter the feed heat exchanger of the disproportionation reactor; the bottom product of the deethaner enters the propylene refining tower, and is separated to obtain polymer-grade propylene, heavy component product and residual C4; a portion of the residual C4 is mixed with ethylene-rich dry gas and enters the feed heat exchanger of the disproportionation reactor, the remaining portion passes through the residual C4 cooler and enters the top of the secondary desorption tower and the top of the reaction separation tail gas absorption tower as feed.

[0040] According to the present invention, preferably, hydrogen-rich dry gas is obtained at the top of the dry gas absorption tower.

[0041] According to the present invention, preferably, hydrogen-poor dry gas is obtained at the top of the primary desorption tower.

[0042] According to the present invention, preferably, the temperatures of the top feed of the dry gas absorption tower, the top feed of the primary desorption tower, the top feed of the secondary desorption tower, and the top feed of the reaction separation tail gas absorption tower are each independently 0 to 30°C.

[0043] According to the present invention, preferably, the proportion of the feed from the top of the dry gas absorption tower to the bottom discharge of the secondary desorption tower is 30% to 80%; and the proportion of the feed from the top of the primary desorption tower to the bottom discharge of the secondary desorption tower is 5% to 30%.

[0044] According to the present invention, preferably, the gas phase at the top of the deethaner is cooled to obtain a gas phase portion and a liquid phase portion. The gas phase portion enters the reaction separation tail gas absorption tower, and the liquid phase portion is refluxed to the deethaner for distillation circulation.

[0045] According to the present invention, preferably, the top of the reaction separation tail gas absorption tower yields methane-rich gas, and the bottom yields methane-lean C4 gas; the methane-lean C4 gas enters the reaction separation tail gas desorption tower for treatment.

[0046] According to the present invention, preferably:

[0047] The remaining portion of the ethylene-deficient C4 is discharged externally;

[0048] The ethane-rich C4 efflux;

[0049] The remaining portion of the remaining C4, along with the cooled fresh C4 absorbent feed, enters the top of the secondary desorption tower and the top of the reaction separation tail gas absorption tower as feed.

[0050] The proportion of residual C4 entering the feed heat exchanger of the disproportionation reactor is 0% to 80% of the total residual C4; the proportion of residual C4 as the top feed of the secondary desorption tower is 30% to 60% of the total residual C4; and the proportion of residual C4 as the top feed of the reaction separation tail gas absorption tower is 40% to 70% of the total residual C4.

[0051] The proportion of fresh C4 absorbent used as the top feed of the secondary desorption tower is 30% to 60% of the total amount of fresh C4 absorbent; the proportion of fresh C4 absorbent used as the top feed of the reaction separation tail gas absorption tower is 40% to 70% of the total amount of fresh C4 absorbent.

[0052] According to the present invention, preferably:

[0053] The remaining portion of the lean ethylene C4 is fed into the absorbent regeneration tower to obtain regenerated absorbent. After cooling, the regenerated absorbent is used as the top feed of the secondary desorption tower and the top feed of the reaction separation tail gas absorption tower. Preferably, the lean ethylene C4 fed into the absorbent regeneration tower accounts for 10% to 50% of the bottom effluent of the secondary desorption tower. Preferably, the regenerated absorbent used as the top feed of the secondary desorption tower accounts for 30% to 60% of the total regenerated absorbent; and the regenerated absorbent used as the top feed of the reaction separation tail gas absorption tower accounts for 40% to 70% of the total regenerated absorbent.

[0054] The remaining C4 first enters the butane de-butanizer for processing, resulting in butene-lean C4 at the top of the butane de-butanizer and butene-rich C4 at the bottom of the butane de-butanizer; the butene-lean C4 at the top of the butane de-butanizer is discharged externally; a portion of the butene-rich C4 at the bottom of the butane de-butanizer is mixed with ethylene-rich dry gas and enters the feed heat exchanger of the disproportionation reactor, while the remaining portion enters the top of the secondary desorption tower and the top of the reaction separation tail gas absorption tower as feed;

[0055] The proportion of butene-rich C4 at the bottom of the butane degassing tower entering the feed heat exchanger of the disproportionation reactor is 0% to 80%; the proportion of butene-rich C4 at the bottom of the butane degassing tower, which is the top feed of the secondary desorption tower, is 30% to 60% of the total butene-rich C4 at the bottom of the butane degassing tower; and the proportion of butene-rich C4 at the bottom of the butane degassing tower, which is the top feed of the reaction separation tail gas absorption tower, is 40% to 70% of the total butene-rich C4 at the bottom of the butane degassing tower.

[0056] According to the present invention, preferably, the source of the refinery dry gas is at least one of the processes of crude oil distillation, catalytic cracking, thermal cracking, coking, hydrocracking, catalytic reforming, hydrorefining, and steam cracking to produce ethylene.

[0057] According to the present invention, preferably, the fresh C4 feed is at least one selected from propane, propylene, isobutane, n-butane, 1-butene, isobutene, and 2-butene.

[0058] According to the present invention, preferably, the top operating pressure of the dry gas absorption tower is 1.0 to 4.0 MPaA and the top operating temperature is -20 to 60°C; preferably, the top operating pressure of the dry gas absorption tower is 2.0 to 3.5 MPaA and the top operating temperature is 10 to 40°C.

[0059] According to the present invention, preferably, the top operating pressure of the primary desorption tower is 0.5 to 3.0 MPaA and the top operating temperature is -20 to 60°C; preferably, the top operating pressure of the primary desorption tower is 1.5 to 2.0 MPaA and the top operating temperature is 10 to 40°C.

[0060] According to the present invention, preferably, the top operating pressure of the secondary desorption tower is 1.5 to 4.0 MPaA and the top operating temperature is 40 to 140°C; preferably, the top operating pressure of the secondary desorption tower is 2.0 to 3.0 MPaA and the top operating temperature is 60 to 90°C.

[0061] According to the present invention, preferably, the top operating pressure of the reaction separation tail gas absorption tower is 1.0 to 3.0 MPaA, and the top operating temperature is -20 to 60°C.

[0062] According to the present invention, preferably, the top operating pressure of the reaction separation tail gas desorption tower is 1.0 to 3.0 MPaA, and the top operating temperature is 0 to 60°C.

[0063] According to the present invention, preferably, the top operating pressure of the deethanizer is 1.0 to 4.0 MPaA, and the top operating temperature is -30 to 20°C.

[0064] According to the present invention, preferably, the top operating pressure of the propylene refining tower is 1.0 to 3.0 MPaA, and the top operating temperature is 20 to 60°C.

[0065] According to the present invention, preferably, the top operating pressure of the absorbent regeneration tower is 1.0 to 3.0 MPaA, and the top operating temperature is 20 to 60°C.

[0066] According to the present invention, preferably, the top operating pressure of the butane dehydrogenator is 0.4 to 2.0 MPaA, and the top operating temperature is 20 to 60°C.

[0067] The beneficial effects of the technical solution of the present invention are as follows:

[0068] (1) The process of this invention is simple. The dry gas from the refinery is pretreated by the raw material pretreatment unit, which can remove hydrogen, oxygen, nitrogen, carbon monoxide and methane. Propane and propylene are removed simultaneously without the use of propylene refrigerant, so that the product separation unit after the disproportionation reaction does not need to separate propane and propylene.

[0069] (2) The present invention uses the remaining C4 obtained after the disproportionation reaction as the absorbent in the dry gas pretreatment unit of the refinery, which can reduce the consumption of C4 raw materials.

[0070] (3) This invention achieves the recovery and utilization of ethylene by sending all the separation tail gas (top gas phase of the deethaner) obtained after the disproportionation reaction into the reaction separation tail gas absorption tower and then returning it to the disproportionation reaction unit for treatment, thereby improving the ethylene recovery rate in refinery dry gas. At the same time, it achieves the removal of methane from the separation tail gas (top gas phase of the deethaner). The removal of methane reduces the operating temperature at the top of the deethaner after the reaction, which can reduce the grade requirements of the top refrigerant. It also achieves the removal of ethane from the separation tail gas (top gas phase of the deethaner). The removal of ethane reduces the load on the deethaner after the reaction, which can reduce the consumption of the top refrigerant.

[0071] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0072] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the invention.

[0073] Figure 1 A schematic diagram of a system for producing propylene by disproportionation of refinery dry gas is shown in Embodiment 1 of the present invention.

[0074] Figure 2 A schematic diagram of a system for producing propylene by disproportionation of refinery dry gas is shown in Embodiment 2 of the present invention.

[0075] Figure 3 A schematic diagram of a system for producing propylene from refinery dry gas, provided as a comparative example of the present invention, is shown.

[0076] The annotations in the attached figures are explained as follows:

[0077] 1-Dry gas compressor; 2-Alkali scrubbing tower; 3-Dry gas absorption tower; 4-First-stage desorption tower; 5-Second-stage desorption tower; 6-Disproportionation reactor feed heat exchanger; 7-Disproportionation reactor; 8-Reaction discharge cooler; 9-Ethylene removal tower; 10-Propylene refining tower; 11-Reaction separation tail gas absorption tower; 12-Circulating C4 cooler; 13-Residual C4 cooler; 14-Refinery dry gas feed line; 15-Dry gas discharge line from dry gas compressor; 16-Dry gas discharge line from alkali scrubbing tower; 17-Ethylene-rich C4 discharge line; 18-Hydrogen-rich dry gas discharge line; 19-Lean hydrogen dry gas discharge line; 20-First-stage desorption C4 discharge line; 21-Second-stage desorption tower top outlet line; 22-Lean ethylene C4; 23-Lean 24 - Remaining C4 of ethylene; 25 - Top feed to dry gas absorber; 26 - Top feed to primary desorption tower; 27 - Top feed to reaction separation tail gas absorber; 28 - Cold side discharge from disproportionation reactor inlet / outlet heat exchanger; 29 - Discharge from dry gas disproportionation reactor; 30 - Discharge from reaction discharge cooler; 31 - Top gas phase outlet of deethaner; 32 - Methane-rich gas; 33 - Methane-lean C4; 34 - Bottom discharge from deethaner; 35 - Polymer-grade propylene product discharge line; 36 - Heavy component discharge line; 37 - Remaining C4; 38 - Top feed to secondary desorption tower; 39 - Fresh C4 feed line; 40 - Remaining C4 recycled into the disproportionation reactor inlet / outlet heat exchanger.

[0078] 41-Butane removal tower; 42-Butane removal tower top butene-lean C4; 43-Butane removal tower bottom butene-rich C4; 44-Absorbent regeneration tower; 45-Absorbent regeneration tower top discharge; 46-Absorbent regeneration tower bottom discharge; 47-Regenerated absorbent;

[0079] 48 - External discharge pipeline; 49 - Reaction separation tail gas circulation section; 50 - Reaction separation tail gas desorption tower; 51 - Top outlet pipeline of reaction separation tail gas desorption tower; 52 - Fresh C4 absorbent feed pipeline; 53 - Fresh C4 absorbent cooler; 54 - Fresh C4 absorbent cooler outlet pipeline; 55 - Residual C4 discharged externally; 56 - Ethane-rich C4 outlet pipeline. Detailed Implementation

[0080] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0081] Example 1

[0082] This embodiment provides a system for producing propylene from refinery dry gas disproportionation, such as... Figure 1 As shown, the system includes a raw material pretreatment unit, a disproportionation reaction unit, and a product separation unit;

[0083] The raw material pretreatment unit includes an alkaline washing tower 2, a dry gas compressor 1, a dry gas absorption tower 3, a primary desorption tower 4, a secondary desorption tower 5, and a circulating C4 cooler 12 connected in sequence.

[0084] The disproportionation reaction unit includes a disproportionation reactor inlet and outlet heat exchanger 6, a disproportionation reactor 7, and a reaction outlet cooler 8;

[0085] The product separation unit includes an ethane stripper 9, a propylene refining tower 10, a reaction separation tail gas absorption tower 11, a reaction separation tail gas desorption tower 50, and a residual C4 cooler 13.

[0086] The refinery dry gas feed line 14 is connected to the bottom inlet of the alkali washing tower 2; the top outlet of the alkali washing tower 2 is connected to the bottom inlet of the dry gas absorption tower 3 through the dry gas compressor 1; the bottom outlet of the dry gas absorption tower 3 is connected to the middle inlet of the primary desorption tower 4; the bottom outlet of the primary desorption tower 4 is connected to the middle inlet of the secondary desorption tower 5; a hydrogen-rich dry gas discharge line 18 is provided at the top of the dry gas absorption tower 3; a hydrogen-lean dry gas discharge line 19 is provided at the top of the primary desorption tower 4; the bottom outlet of the secondary desorption tower 5 is connected to the circulating C4 cooler 12 and then connected to the top inlet of the dry gas absorption tower 3 and the top inlet of the primary desorption tower 4 respectively.

[0087] The top outlet pipeline 21 of the secondary desorption tower merges with the fresh C4 feed pipeline 39 and the top outlet pipeline 51 of the reaction separation tail gas desorption tower, and is then connected in sequence to the cold side inlet of the disproportionation reactor feed heat exchanger 6 and the inlet of the disproportionation reactor 7; the outlet of the disproportionation reactor 7 is connected in sequence to the hot side inlet of the disproportionation reactor feed heat exchanger 6, the reaction discharge cooler 8, and the deethanerization tower 9.

[0088] The top gas phase outlet 31 of the deethaner 9 is connected to the bottom inlet of the reaction separation tail gas absorption tower 11, and the bottom outlet of the deethaner 9 is connected to the propylene refining tower 10; the bottom outlet of the reaction separation tail gas absorption tower 11 is connected to the top inlet of the reaction separation tail gas desorption tower 50; an ethane-rich C4 discharge pipeline 56 is provided at the bottom of the reaction separation tail gas desorption tower 50; and a methane-rich gas discharge pipeline 32 is provided at the top of the reaction separation tail gas absorption tower 11.

[0089] The lower discharge pipeline of the propylene refining tower 10 is divided into two paths. One path connects to the cold side inlet of the disproportionation reactor inlet / outlet heat exchanger 6, and the other path, after passing through the residual C4 cooler 13, connects to the top inlet of the secondary desorption tower 5 and the top inlet of the reaction separation tail gas absorption tower 11, respectively. The raw material pretreatment unit also includes a fresh C4 absorbent feed pipeline 52 and a fresh C4 absorbent cooler 53 connected in sequence. The discharge pipeline 54 of the fresh C4 absorbent cooler merges with the discharge pipeline of the residual C4 cooler and connects to the top inlet of the secondary desorption tower and the top inlet of the reaction separation tail gas absorption tower.

[0090] The propylene refining tower 10 is equipped with a polymer-grade propylene product discharge pipeline 35 at the top and a heavy component discharge pipeline 36 at the bottom.

[0091] The primary desorption tower 4, the secondary desorption tower 5, and the reaction separation tail gas desorption tower 50 are each independently equipped with a reboiler (not shown);

[0092] The propylene refining tower 10 is equipped with a top condenser and a bottom reboiler (both not shown);

[0093] The ethane removal column 9 is equipped with a top condenser, a top gas-liquid separator, and a bottom reboiler (all not shown);

[0094] The theoretical number of trays in the alkaline washing tower 2 is 30;

[0095] The theoretical number of plates in the dry gas absorption tower 3 is 30;

[0096] The theoretical number of trays in the primary desorption tower 4 is 30, and the theoretical feed tray is the 15th tray at the top of the tower.

[0097] The theoretical number of trays in the secondary desorption tower 5 is 60, and the theoretical feed tray is the 30th tray at the top of the tower.

[0098] The theoretical number of plates in the reaction separation tail gas absorption tower 11 is 30;

[0099] The theoretical number of trays in the reaction separation tail gas desorption tower 50 is 30;

[0100] The theoretical number of trays in the ethane removal column 9 is 80, and the theoretical feed tray is the 50th tray at the top of the column.

[0101] The theoretical number of trays in the propylene refining tower 10 is 60, and the theoretical feed tray is the 30th tray at the top of the tower.

[0102] The method for producing propylene by disproportionation of refinery dry gas using the above system includes the following steps:

[0103] S1: Refinery dry gas is sequentially processed through the alkaline scrubbing tower 2, dry gas compressor 1, dry gas absorption tower 3, primary desorption tower 4, and secondary desorption tower 5; hydrogen-rich dry gas is obtained at the top of the dry gas absorption tower 3; hydrogen-lean dry gas is obtained at the top of the primary desorption tower 4; ethylene-rich dry gas is obtained at the top of the secondary desorption tower 5, and ethylene-lean C4 22 is obtained at the bottom; a portion of the ethylene-lean C4 22 is cooled by the circulating C4 cooler 12 and sent to the top of the dry gas absorption tower 3 and the top of the primary desorption tower 4 respectively, and the remaining portion 23 of the ethylene-lean C4 is discharged.

[0104] The dry gas from the refinery is sourced from the catalytic cracking process;

[0105] The temperatures of the top feed 24 of the dry gas absorption tower, the top feed 25 of the primary desorption tower, the top feed 38 of the secondary desorption tower, and the top feed 26 of the reaction separation tail gas absorption tower are each independently 10°C.

[0106] The proportion of the top feed 24 of the dry gas absorption tower to the bottom discharge (lean ethylene C4 22) of the secondary desorption tower is 70%; the proportion of the top feed 25 of the primary desorption tower to the bottom discharge of the secondary desorption tower is 18%.

[0107] S2: The ethylene-rich dry gas and fresh C4 feed are heated by the disproportionation reactor feed heat exchanger 6 and then enter the disproportionation reactor 7 to react and obtain the reaction product (dry gas disproportionation reactor effluent 28). The reaction product is heated by the disproportionation reactor feed heat exchanger 6 and cooled by the reaction effluent cooler 8 before entering the de-ethane tower 9.

[0108] The fresh C4 feed is a mixture of isobutane, n-butane, 1-butene, isobutene, and 2-butene;

[0109] S3: In the deethanizer 9, the reaction product after cooling in step S2 is separated to obtain the top gas phase of the deethanizer and the bottom product 34 of the deethanizer; the top gas phase of the deethanizer is cooled to obtain a gas phase portion and a liquid phase portion:

[0110] The gas phase portion enters the reaction separation tail gas absorption tower 11 and the reaction separation tail gas desorption tower 50 for treatment. The top of the reaction separation tail gas absorption tower 11 yields methane-rich gas 32, and the bottom yields methane-lean C4 33. The methane-lean C4 33 enters the reaction separation tail gas desorption tower 50, the top yields ethylene-rich recycle gas 51, and the bottom yields ethane-rich C4 56. The ethylene-rich recycle gas 51 is mixed with ethylene-rich dry gas and enters the disproportionation reactor feed heat exchanger 6. The ethane-rich C4 56 is discharged.

[0111] The liquid phase is returned to the ethane removal tower 9 as tower reflux.

[0112] The bottom product 34 of the de-ethane tower enters the propylene refining tower 10, where it is separated to obtain polymer-grade propylene, heavy component product, and residual C4 37. A portion of the residual C4 37 is mixed with ethylene-rich dry gas and enters the feed heat exchanger 6 of the disproportionation reactor, while the remaining portion, together with the cooled fresh C4 absorbent feed, enters the top of the secondary desorption tower 5 and the top of the reaction separation tail gas absorption tower 11 as feed.

[0113] The proportion of residual C4 40 entering the feed heat exchanger 6 of the disproportionation reactor to the residual C4 37 is 0%; the proportion of residual C4 37 as the top feed of the secondary desorption tower is 45%; and the proportion of residual C4 37 as the top feed of the reaction separation tail gas absorption tower is 55%.

[0114] The proportion of fresh C4 absorbent as the top feed of the secondary desorption tower is 45% of the total amount of fresh C4 absorbent; the proportion of fresh C4 absorbent as the top feed of the reaction separation tail gas absorption tower is 55% of the total amount of fresh C4 absorbent.

[0115] The alkaline washing tower 2 operates at a top pressure of 2.0 MPaA and a top temperature of 40°C; the dry gas absorption tower 3 operates at a top pressure of 3.0 MPaA and a top temperature of 10°C; the primary desorption tower 4 operates at a top pressure of 2.0 MPaA and a top temperature of 16°C; the secondary desorption tower 5 operates at a top pressure of 3.0 MPaA and a top temperature of 70°C; the reaction separation tail gas absorption tower 11 operates at a top pressure of 2.8 MPaA and a top temperature of 20°C; the reaction separation tail gas desorption tower 50 operates at a top pressure of 2.7 MPaA and a top temperature of 20°C; the ethane removal tower 9 operates at a top pressure of 2.9 MPaA and a top temperature of 0°C; and the propylene refining tower 10 operates at a top pressure of 1.8 MPaA and a top temperature of 40°C.

[0116] Example 2

[0117] This embodiment provides a system for producing propylene from refinery dry gas disproportionation, such as... Figure 2 As shown, the only difference between this system and the system in Example 1 is that:

[0118] The raw material pretreatment unit also includes an absorbent regeneration tower 44; the bottom outlet of the secondary desorption tower 5 and the ethane-rich C4 discharge pipeline 56 are also connected to the middle inlet of the absorbent regeneration tower 44, and the lower outlet of the absorbent regeneration tower 44 is connected to the top inlet of the secondary desorption tower 5 and the top inlet of the reaction separation tail gas absorption tower 11 through the residual C4 cooler 13.

[0119] The product separation unit also includes a butane removal tower 41; the lower discharge pipeline of the propylene refining tower 10 is connected to the middle inlet of the butane removal tower 41, and the bottom discharge pipeline of the butane removal tower 41 is divided into two paths, one of which is connected to the cold side inlet of the disproportionation reactor feed heat exchanger 6, and the other of which is connected to the top inlet of the secondary desorption tower 5 and the top inlet of the reaction separation tail gas absorption tower 11 through the residual C4 cooler 13.

[0120] The absorbent regeneration tower 44 is equipped with a top condenser and a bottom reboiler (both not shown);

[0121] The butane removal column 41 is equipped with a top condenser and a bottom reboiler (both not shown);

[0122] The theoretical number of trays in the absorbent regeneration tower 44 is 70, and the theoretical feed tray is the 30th tray at the top of the tower.

[0123] The theoretical number of plates for the debutane 41 is 30, and the theoretical feed plate is the 15th plate at the top of the column.

[0124] The method for producing propylene from refinery dry gas using the above system differs from Example 1 only in that:

[0125] In step S1:

[0126] The remaining portion 23 of the lean ethylene C4 is fed into the absorbent regeneration tower 44 for processing to obtain regenerated absorbent 47. After cooling, the regenerated absorbent 47 is used as the top feed of the secondary desorption tower 5 and the top feed of the reaction separation tail gas absorption tower 11.

[0127] The top feed 24 of the dry gas absorption tower accounts for 70% of the bottom discharge of the secondary desorption tower 5; the top feed 25 of the primary desorption tower accounts for 18% of the bottom discharge of the secondary desorption tower 5. The lean ethylene C4 fed into the absorbent regeneration tower 44 accounts for 12% of the bottom discharge of the secondary desorption tower 5. The regenerated absorbent, as the top feed of the secondary desorption tower, accounts for 45% of the total regenerated absorbent; the regenerated absorbent, as the top feed of the reaction separation tail gas absorption tower, accounts for 55% of the total regenerated absorbent.

[0128] In step S3:

[0129] The remaining C4 37 first enters the butane de-butanizer 41 for processing, resulting in butene-lean C4 42 at the top of the butane de-butanizer and butene-rich C4 43 at the bottom of the butane de-butanizer; the butene-lean C4 42 at the top of the butane de-butanizer is discharged; a portion of the butene-rich C4 43 at the bottom of the butane de-butanizer is mixed with ethylene-rich dry gas and enters the feed heat exchanger 6 of the disproportionation reactor, and the remaining portion enters the top of the secondary desorption tower 5 and the top of the reaction separation tail gas absorption tower 11 as feed;

[0130] The proportion of butene-rich C4 at the bottom of the butane degassing tower entering the feed heat exchanger of the disproportionation reactor is 0%; the proportion of butene-rich C4 at the bottom of the butane degassing tower, which is the top feed of the secondary desorption tower, is 45% of the total butene-rich C4 at the bottom of the butane degassing tower; and the proportion of butene-rich C4 at the bottom of the butane degassing tower, which is the top feed of the reaction separation tail gas absorption tower, is 55% of the total butene-rich C4 at the bottom of the butane degassing tower.

[0131] The absorbent regeneration tower 44 has an operating pressure of 2.0 MPaA at the top and an operating temperature of 40°C at the top; the butane removal tower 41 has an operating pressure of 1.0 MPaA at the top and an operating temperature of 40°C at the top.

[0132] Comparative Example 1

[0133] This comparative example provides a system for producing propylene from refinery dry gas disproportionation, such as... Figure 3 As shown, the system includes a raw material pretreatment unit, a disproportionation reaction unit, and a product separation unit;

[0134] The raw material pretreatment unit includes an alkaline washing tower 2, a dry gas compressor 1, a dry gas absorption tower 3, a primary desorption tower 4, a secondary desorption tower 5, and a circulating C4 cooler 12 connected in sequence.

[0135] The disproportionation reaction unit includes a disproportionation reactor inlet and outlet heat exchanger 6, a disproportionation reactor 7, and a reaction outlet cooler 8;

[0136] The product separation unit includes an ethane removal tower 9 and a propylene refining tower 10.

[0137] The refinery dry gas feed line 14 is connected to the bottom inlet of the alkali washing tower 2; the top outlet of the alkali washing tower 2 is connected to the bottom inlet of the dry gas absorption tower 3 via the dry gas compressor 1; the bottom outlet of the dry gas absorption tower 3 is connected to the middle inlet of the primary desorption tower 4; the bottom outlet of the primary desorption tower 4 is connected to the middle inlet of the secondary desorption tower 5; the fresh C4 absorbent feed line 52 is connected to the top inlet of the secondary desorption tower 5 via the fresh C4 absorbent cooler 53; a hydrogen-rich dry gas outlet line 18 is provided at the top of the dry gas absorption tower 3; a hydrogen-lean dry gas outlet line 19 is provided at the top of the primary desorption tower 4; the bottom outlet of the secondary desorption tower 5 is connected to the circulating C4 cooler 12 and then to the top inlet of the dry gas absorption tower 3 and the top inlet of the primary desorption tower 4, respectively.

[0138] The top outlet pipeline 21 of the secondary desorption tower merges with the fresh C4 feed pipeline 39 and is then connected in sequence to the cold side inlet of the disproportionation reactor feed heat exchanger 6 and the inlet of the disproportionation reactor 7; the outlet of the disproportionation reactor 7 is connected in sequence to the hot side inlet of the disproportionation reactor feed heat exchanger 6, the reaction discharge cooler 8, and the deethanerization tower 9.

[0139] The top gas outlet 31 of the deethanizer is divided into two paths: one path is connected to the cold side inlet of the disproportionation reactor feed heat exchanger 6, and the other path is connected to the discharge pipeline 48; the bottom outlet of the deethanizer is connected to the propylene refining tower 10.

[0140] The lower discharge pipeline of the propylene refining tower 10 is connected to the cold side inlet of the inlet and outlet heat exchanger 6 of the disproportionation reactor. The top of the propylene refining tower 10 is provided with a polymer-grade propylene product discharge pipeline 35, and the bottom of the tower is provided with a heavy component discharge pipeline 36.

[0141] The primary desorption tower 4 and the secondary desorption tower 5 are each independently equipped with a reboiler (not shown);

[0142] The propylene refining tower 10 is equipped with a top condenser and a bottom reboiler (both not shown);

[0143] The deethanizer 9 is equipped with a top condenser, a top gas-liquid separator, and a bottom reboiler (all not shown).

[0144] The theoretical number of trays in the alkaline washing tower 2 is 30;

[0145] The theoretical number of plates in the dry gas absorption tower 3 is 30;

[0146] The theoretical number of trays in the primary desorption tower 4 is 30, and the theoretical feed tray is the 15th tray at the top of the tower.

[0147] The theoretical number of trays in the secondary desorption tower 5 is 60, and the theoretical feed tray is the 30th tray at the top of the tower.

[0148] The theoretical number of trays in the ethane removal column 9 is 80, and the theoretical feed tray is the 50th tray at the top of the column.

[0149] The theoretical number of trays in the propylene refining tower 10 is 60, and the theoretical feed tray is the 30th tray at the top of the tower.

[0150] The method for producing propylene by disproportionation of refinery dry gas using the above system includes the following steps:

[0151] S1: Refinery dry gas is sequentially processed through the alkaline scrubbing tower 2, dry gas compressor 1, dry gas absorption tower 3, primary desorption tower 4, and secondary desorption tower 5; hydrogen-rich dry gas is obtained at the top of the dry gas absorption tower 3; hydrogen-lean dry gas is obtained at the top of the primary desorption tower 4; ethylene-rich dry gas is obtained at the top of the secondary desorption tower 5, and ethylene-lean C4 22 is obtained at the bottom; a portion of the ethylene-lean C4 22 is cooled by the circulating C4 cooler 12 and sent to the top of the dry gas absorption tower 3 and the top of the primary desorption tower 4 respectively, and the remaining portion 23 of the ethylene-lean C4 is discharged.

[0152] The dry gas from the refinery is sourced from the catalytic cracking process;

[0153] The absorbent in the secondary desorption tower 5 is a cooled, fresh C4 absorbent;

[0154] The temperatures of the top feed 24 of the dry gas absorption tower and the top feed 25 of the primary desorption tower are each 10°C.

[0155] The proportion of the top feed 24 of the dry gas absorption tower to the bottom discharge of the secondary desorption tower 5 is 70%.

[0156] The proportion of the feed 25 from the top of the primary desorption tower to the discharge 5 from the bottom of the secondary desorption tower is 18%.

[0157] S2: The ethylene-rich dry gas and fresh C4 feed are heated by the disproportionation reactor feed heat exchanger 6 and then enter the disproportionation reactor 7 to react and obtain the reaction product (dry gas disproportionation reactor effluent 28). The reaction product is heated by the disproportionation reactor feed heat exchanger 6 and cooled by the reaction effluent cooler 8 before entering the de-ethane tower 9.

[0158] The fresh C4 feed is a mixture of isobutane, n-butane, 1-butene, isobutene, and 2-butene;

[0159] S3: In the deethanizer 9, the cooled reaction product from step S2 is separated to obtain the top gas phase and the bottom product 34 of the deethanizer. After cooling, the top gas phase of the deethanizer is divided into a gas phase and a liquid phase. The reaction separation tail gas recirculation section 49 of the gas phase is mixed with ethylene-rich dry gas and enters the feed heat exchanger 6 of the disproportionation reactor. The remaining part is discharged through the discharge pipeline 48. The liquid phase is returned to the deethanizer 9 (not shown) as tower reflux. The bottom product of the deethanizer 9 enters the propylene refining tower 10 and is separated to obtain polymer-grade propylene, heavy component product, and residual C4 37. A portion of the residual C4 37 is mixed with ethylene-rich dry gas and enters the feed heat exchanger 6 of the disproportionation reactor. The remaining part is discharged.

[0160] The operating pressure at the top of the alkaline washing tower 2 is 2.0 MPaA, and the operating temperature at the top of the tower is 40℃.

[0161] The top operating pressure of the dry gas absorption tower 3 is 3.0 MPaA, and the top operating temperature is 10℃.

[0162] The operating pressure at the top of the primary desorption tower 4 is 2.0 MPaA, and the operating temperature at the top of the tower is 16℃.

[0163] The operating pressure at the top of the secondary desorption tower is 3.0 MPaA, and the operating temperature at the top of the tower is 70°C.

[0164] The top operating pressure of the ethane removal column 9 is 2.9 MPaA, and the top operating temperature is 0°C.

[0165] The propylene refining tower 10 has an operating pressure of 1.8 MPaA at the top and an operating temperature of 40°C at the top.

[0166] Test case

[0167] Table 1. Composition of refinery dry gas in Example 1 and Comparative Example 1

[0168]

[0169]

[0170] Table 2. Fresh C4 composition of Example 1 and Comparative Example 1

[0171] Components %wt Isobutane 47.08 n-Butane 0.50 1-Butene 12.17 Isobutylene 0.16 2-Butene 39.25 other 0.84 total 100.00

[0172] Table 3 Comparison Results

[0173]

[0174]

[0175] As can be seen from Table 3, the method for producing propylene from refinery dry gas according to the present invention can increase the ethylene recovery rate by 8 percentage points, increase the production of polymer-grade propylene by 10%, reduce the consumption of C4 olefin feedstock by 9%, and reduce the product energy consumption index (based on propylene) by 9%, thereby maximizing the utilization of raw materials while reducing energy consumption.

[0176] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A system for producing propylene from refinery dry gas disproportionation, characterized in that, The system includes a raw material pretreatment unit, a disproportionation reaction unit, and a product separation unit; The raw material pretreatment unit includes an alkaline washing bag, a dry gas compressor, a dry gas absorption tower, a primary desorption tower, a secondary desorption tower, and a circulating C4 cooler connected in sequence. The disproportionation reaction unit includes a disproportionation reactor feed heat exchanger, a disproportionation reactor, and a reaction discharge cooler; The product separation unit includes an ethane stripper, a propylene refining tower, a reaction separation tail gas absorption tower, a reaction separation tail gas desorption tower, and a residual C4 cooler. The alkali washing package inlet is connected to a refinery dry gas feed pipeline; the bottom outlet of the secondary desorption tower is connected to the circulating C4 cooler and then to the top inlet of the dry gas absorption tower and the top inlet of the primary desorption tower, respectively; the alkali washing package outlet is connected to the bottom inlet of the dry gas absorption tower via the dry gas compressor; the bottom outlet of the dry gas absorption tower is connected to the middle inlet of the primary desorption tower; the bottom outlet of the primary desorption tower is connected to the middle inlet of the secondary desorption tower; a hydrogen-rich dry gas outlet pipeline is installed at the top of the dry gas absorption tower; a hydrogen-lean dry gas outlet pipeline is installed at the top of the primary desorption tower. The top outlet pipeline of the secondary desorption tower merges with the fresh C4 feed pipeline and the top outlet pipeline of the reaction separation tail gas desorption tower, and is then connected in sequence to the cold side inlet of the disproportionation reactor feed heat exchanger and the inlet of the disproportionation reactor; the outlet of the disproportionation reactor is connected in sequence to the hot side inlet of the disproportionation reactor feed heat exchanger, the reaction discharge cooler, and the deethanerization tower. The top gas phase outlet of the deethaner is connected to the bottom inlet of the reaction separation tail gas absorption tower, and the bottom outlet of the deethaner is connected to the propylene refining tower; the bottom outlet of the reaction separation tail gas absorption tower is connected to the top inlet of the reaction separation tail gas desorption tower. The bottom of the reaction separation tail gas desorption tower is equipped with an ethane-rich C4 discharge pipeline. The top of the reaction separation tail gas absorption tower is equipped with a methane-rich gas outlet pipeline. The lower discharge pipeline of the propylene refining tower is divided into two paths. One path is connected to the cold side inlet of the feed heat exchanger of the disproportionation reactor, and the other path is connected to 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 C4 cooler. The propylene refining tower is equipped with a polymer-grade propylene product discharge pipeline at the top and a heavy component discharge pipeline at the bottom.

2. The system for producing propylene from refinery dry gas according to claim 1, wherein, The raw material pretreatment unit also includes a fresh C4 absorbent feed line and a fresh C4 absorbent cooler connected in sequence; the discharge line of the fresh C4 absorbent cooler merges with the discharge line of the remaining C4 cooler and is connected to the top inlet of the secondary desorption tower and the top inlet of the reaction separation tail gas absorption tower. Alternatively, the raw material pretreatment unit further includes an absorbent regeneration tower; the bottom outlet of the secondary desorption tower and the ethane-rich C4 discharge pipeline are also connected to the middle inlet of the absorbent regeneration tower, and the lower outlet of the absorbent regeneration tower is connected to the top inlet of the secondary desorption tower and the top inlet of the reaction separation tail gas absorption tower through the residual C4 cooler; the product separation unit further includes a butane removal tower; the lower discharge pipeline of the propylene refining tower is connected to the middle inlet of the butane removal tower, and the bottom discharge pipeline of the butane removal tower is divided into two paths, one path is connected to the cold side inlet of the disproportionation reactor feed heat exchanger, and the other path is connected to the top inlet of the secondary desorption tower and the top inlet of the reaction separation tail gas absorption tower through the residual C4 cooler.

3. The system for producing propylene from refinery dry gas according to claim 2, wherein, The primary desorption tower, the secondary desorption tower, and the reaction separation tail gas desorption tower are each independently equipped with a reboiler. The propylene refining tower and the absorbent regeneration tower are each independently equipped with a top condenser and a bottom reboiler; The butane removal column is equipped with a top condenser and a bottom reboiler. The deethane removal tower is equipped with a top condenser, a top gas-liquid separator, and a bottom reboiler.

4. The system for producing propylene from refinery dry gas according to claim 2, wherein, The theoretical number of plates in the dry gas absorption tower is 10 to 40. The theoretical number of trays in the primary desorption tower is 10 to 40, and the theoretical feed trays are the 5th to 25th trays at the top of the tower. The theoretical number of trays in the secondary desorption tower is 20 to 100, and the theoretical feed trays are the 10th to 70th trays at the top of the tower. The theoretical number of plates in the reaction separation tail gas absorption tower is 10~40; The theoretical number of trays in the reaction separation tail gas desorption tower is 10~40; The theoretical number of trays in the ethane stripper is 40 to 100, and the theoretical feed trays are the 20th to 80th trays at the top of the column. The theoretical number of trays in the propylene refining tower is 20 to 100, and the theoretical feed trays are the 10th to 80th trays at the top of the tower. The theoretical number of trays in the absorbent regeneration tower is 20 to 100, and the theoretical feed trays are the 10th to 70th trays at the top of the tower. The theoretical number of plates for butane removal is 10 to 50, and the theoretical feed plates are the 5th to 30th plates at the top of the column.

5. A method for producing propylene by disproportionation of refinery dry gas, characterized in that, This method employs the refinery dry gas disproportionation to propylene system according to any one of claims 1-4, and includes the following steps: S1: The refinery dry gas is processed sequentially through the alkaline washing bag, dry gas compressor, dry gas absorption tower, primary desorption tower and secondary desorption tower. Ethylene-rich dry gas is obtained at the top of the secondary desorption tower and ethylene-lean C4 is obtained at the bottom of the tower. A portion of the ethylene-lean C4 is cooled by a circulating C4 cooler and sent to the top of the dry gas absorption tower and the top of the primary desorption tower respectively. S2: The ethylene-rich dry gas and fresh C4 feed are heat-exchanged by the inlet and outlet heat exchanger of the disproportionation reactor and then enter the disproportionation reactor to react and obtain reaction products. The reaction products are then heat-exchanged by the inlet and outlet heat exchanger of the disproportionation reactor and cooled by the reaction outlet cooler before entering the de-ethane tower. S3: In the deethaner, the cooled reaction product from step S2 is separated to obtain the top gas phase and the bottom product of the deethaner; the top gas phase of the deethaner is processed sequentially through the reaction separation tail gas absorption tower and the reaction separation tail gas desorption tower, obtaining ethylene-rich circulating gas at the top of the reaction separation tail gas desorption tower and ethylene-rich C4 at the bottom, the ethylene-rich circulating gas and ethylene-rich dry gas are mixed and enter the feed heat exchanger of the disproportionation reactor; the bottom product of the deethaner enters the propylene refining tower, and is separated to obtain polymer-grade propylene, heavy component product and residual C4; a portion of the residual C4 is mixed with ethylene-rich dry gas and enters the feed heat exchanger of the disproportionation reactor, the remaining portion passes through the residual C4 cooler and enters the top of the secondary desorption tower and the top of the reaction separation tail gas absorption tower as feed.

6. The method for producing propylene by disproportionation of refinery dry gas according to claim 5, wherein, Hydrogen-rich dry gas is obtained at the top of the dry gas absorption tower; hydrogen-lean dry gas is obtained at the top of the first-stage desorption tower. The temperatures of the top feed of the dry gas absorption tower, the top feed of the primary desorption tower, the top feed of the secondary desorption tower, and the top feed of the reaction separation tail gas absorption tower are each independently 0~30℃; The proportion of the feed material from the top of the dry gas absorption tower to the bottom discharge of the secondary desorption tower is 30% to 80%; the proportion of the feed material from the top of the primary desorption tower to the bottom discharge of the secondary desorption tower is 5% to 30%. The gas phase at the top of the deethanizer is cooled to obtain a gas phase and a liquid phase. The gas phase enters the reaction separation tail gas absorption tower, and the liquid phase is refluxed back to the deethanizer for distillation circulation. The top of the reaction separation tail gas absorption tower is rich in methane gas, and the bottom is lean methane C4 gas; the lean methane C4 gas enters the reaction separation tail gas desorption tower for treatment.

7. The method for producing propylene by disproportionation of refinery dry gas according to claim 6, wherein, The remaining portion of the ethylene-deficient C4 is discharged externally; The ethane-rich C4 efflux; The remaining portion of the remaining C4, along with the cooled fresh C4 absorbent feed, enters the top of the secondary desorption tower and the top of the reaction separation tail gas absorption tower as feed. The residual C4 entering the feed heat exchanger of the disproportionation reactor accounts for 0% to 80% of the total residual C4; the residual C4 as the top feed of the secondary desorption tower accounts for 30% to 60% of the total residual C4; and the residual C4 as the top feed of the reaction separation tail gas absorption tower accounts for 40% to 70% of the total residual C4. The proportion of fresh C4 absorbent used as the top feed of the secondary desorption tower is 30% to 60% of the total amount of fresh C4 absorbent; the proportion of fresh C4 absorbent used as the top feed of the reaction separation tail gas absorption tower is 40% to 70% of the total amount of fresh C4 absorbent.

8. The method for producing propylene by disproportionation of refinery dry gas according to claim 6, wherein, The remaining portion of the lean ethylene C4 is fed into the absorbent regeneration tower for processing to obtain regenerated absorbent. After cooling, the regenerated absorbent is used as the top feed of the secondary desorption tower and the top feed of the reaction separation tail gas absorption tower. The lean ethylene C4 fed into the absorbent regeneration tower accounts for 10% to 50% of the bottom effluent from the secondary desorption tower; the regenerated absorbent used as the top feed of the secondary desorption tower accounts for 30% to 60% of the total regenerated absorbent; and the regenerated absorbent used as the top feed of the reaction separation tail gas absorption tower accounts for 40% to 70% of the total regenerated absorbent. The remaining C4 first enters the butane de-butanizer for processing, resulting in butene-lean C4 at the top of the butane de-butanizer and butene-rich C4 at the bottom of the butane de-butanizer; the butene-lean C4 at the top of the butane de-butanizer is discharged externally; a portion of the butene-rich C4 at the bottom of the butane de-butanizer is mixed with ethylene-rich dry gas and enters the feed heat exchanger of the disproportionation reactor, while the remaining portion enters the top of the secondary desorption tower and the top of the reaction separation tail gas absorption tower as feed; The proportion of butene-rich C4 at the bottom of the butane dehydrogenator entering the feed heat exchanger of the disproportionation reactor is 0%~80%; the proportion of butene-rich C4 at the bottom of the butane dehydrogenator, which is the top feed of the secondary desorption tower, is 30%~60% of the total butene-rich C4 at the bottom of the butane dehydrogenator; and the proportion of butene-rich C4 at the bottom of the butane dehydrogenator, which is the top feed of the reaction separation tail gas absorption tower, is 40%~70% of the total butene-rich C4 at the bottom of the butane dehydrogenator.

9. The method for producing propylene by disproportionation of refinery dry gas according to claim 8, wherein, The refinery dry gas is sourced from at least one of the following processes: crude oil distillation, catalytic cracking, thermal cracking, coking, hydrocracking, catalytic reforming, hydrorefining, and steam cracking to produce ethylene. The fresh C4 feed is at least one of propane, propylene, isobutane, n-butane, 1-butene, isobutene, and 2-butene; The operating pressure at the top of the dry gas absorption tower is 1.0~4.0 MPaA, and the operating temperature at the top of the tower is -20~60℃. The operating pressure at the top of the primary desorption tower is 0.5~3.0 MPaA, and the operating temperature at the top of the tower is -20~60℃. The operating pressure at the top of the secondary desorption tower is 1.5~4.0 MPaA, and the operating temperature at the top of the tower is 40~140℃. The operating pressure at the top of the reaction separation tail gas absorption tower is 1.0~3.0 MPaA, and the operating temperature at the top of the tower is -20~60℃. The operating pressure at the top of the reaction separation tail gas desorption tower is 1.0~3.0 MPaA, and the operating temperature at the top of the tower is 0~60℃. The top operating pressure of the ethane stripper is 1.0~4.0 MPaA, and the top operating temperature is -30~20℃. The operating pressure at the top of the propylene refining column is 1.0~3.0 MPaA, and the operating temperature at the top of the column is 20~60℃. The operating pressure at the top of the absorbent regeneration tower is 1.0~3.0 MPaA, and the operating temperature at the top of the tower is 20~60℃. The top operating pressure of the debutanizer is 0.4~2.0 MPaA, and the top operating temperature is 20~60℃.

10. The method for producing propylene by disproportionation of refinery dry gas according to claim 9, wherein, The operating pressure at the top of the dry gas absorption tower is 2.0~3.5MPaA, and the operating temperature at the top of the tower is 10~40℃.

11. The method for producing propylene by disproportionation of refinery dry gas according to claim 9, wherein, The operating pressure at the top of the primary desorption tower is 1.5~2.0 MPaA, and the operating temperature at the top of the tower is 10~40℃.

12. The method for producing propylene by disproportionation of refinery dry gas according to claim 9, wherein, The operating pressure at the top of the secondary desorption tower is 2.0~3.0 MPaA, and the operating temperature at the top of the tower is 60~90℃.

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