阅读说明：本技术 一种采用吸收-解吸的裂解气分离系统及方法 (Pyrolysis gas separation system and method adopting absorption-desorption ) 是由 田峻 李春芳 罗淑娟 张敬升 常大山 王宇飞 于 2019-10-28 设计创作，主要内容包括：本发明公开了一种采用吸收-解析的裂解气分离系统及方法。系统包括：压缩机、净化系统、脱碳四塔、吸收塔、解吸塔、脱丙烷塔、脱重塔、碳二加氢反应器,碳四加氢反应器；其中,压缩机段间依次连接净化系统和脱碳四塔,脱碳四塔顶连接压缩机后段后连接吸收塔,脱碳四塔釜连接脱重塔；脱重塔塔顶连接碳四加氢反应器,碳四加氢反应器出口管线与解吸塔塔釜出口管线合并后连接吸收塔上部；吸收塔塔釜连接解吸塔；解吸塔塔顶连接脱丙烷塔,解吸塔塔釜与碳四加氢反应器出口管线合并后连接吸收塔上部；脱丙烷塔塔顶连接碳二加氢反应器。本发明具有投资省、能耗低、效益显著的特点。(The invention discloses a pyrolysis gas separation system and method adopting absorption-desorption. The system comprises: the system comprises a compressor, a purification system, a four-decarbonization tower, an absorption tower, a desorption tower, a depropanization tower, a de-heavy tower, a carbon-two hydrogenation reactor and a carbon-four hydrogenation reactor; wherein, the compressor section is sequentially connected with a purification system and a four decarburization towers, the top of the four decarburization towers is connected with the rear section of the compressor and then connected with an absorption tower, and the kettle of the four decarburization towers is connected with a heavy component removal tower; the top of the heavy component removal tower is connected with a carbon four hydrogenation reactor, and an outlet pipeline of the carbon four hydrogenation reactor is combined with an outlet pipeline of the tower kettle of the desorption tower and then connected with the upper part of the absorption tower; the tower kettle of the absorption tower is connected with a desorption tower; the top of the desorption tower is connected with a depropanization tower, and the tower kettle of the desorption tower is combined with an outlet pipeline of the four-carbon hydrogenation reactor and then connected with the upper part of the absorption tower; the top of the depropanizing tower is connected with a carbo-hydrogenation reactor. The invention has the characteristics of investment saving, low energy consumption and obvious benefit.)

1. A cracked gas separation system using absorption-desorption, the system comprising:

the system comprises a compressor, a purification system, a four-decarbonization tower, an absorption tower, a desorption tower, a depropanization tower, a de-heavy tower, a carbon-two hydrogenation reactor and a carbon-four hydrogenation reactor; wherein the content of the first and second substances,

the purification system and the four decarburization towers are sequentially connected between the compressor sections, the four decarburization towers are connected with the rear section of the compressor and then connected with the absorption tower, and the four decarburization tower kettles are connected with the heavy component removal tower; the top of the heavy component removal tower is connected with a carbon four hydrogenation reactor, and an outlet pipeline of the carbon four hydrogenation reactor is combined with an outlet pipeline of the tower kettle of the desorption tower and then connected with the upper part of the absorption tower;

the tower kettle of the absorption tower is connected with a desorption tower; the top of the desorption tower is connected with a depropanizing towerSuction deviceThe tower kettle and the outlet pipeline of the four-carbon hydrogenation reactor are combined and then connected with the upper part of the absorption tower; the top of the depropanizing tower is connected with a carbo-hydrogenation reactor.

2. The cracked gas separation system of claim 1, wherein:

the bottom of the depropanization tower is connected with a carbon three hydrogenation reactor, the carbon three hydrogenation reactor is connected with a propylene rectifying tower, and the top of the propylene rectifying tower is connected with a compressor section.

3. The cracked gas separation system of claim 1, wherein:

a reboiler is arranged at the tower kettle of the absorption tower; and/or the presence of a gas in the gas,

the tower kettle of the desorption tower is provided with a reboiler.

4. The cracked gas separation system of claim 1, wherein:

and an outlet pipeline of the tower kettle of the desorption tower is divided into two paths, one path is extracted, and the other path is combined with an outlet pipeline of the four-carbon hydrogenation reactor and then connected with the upper part of the absorption tower.

5. A cracked gas separation method using the system as claimed in any one of claims 1 to 4, characterized in that the method comprises:

(1) after compression, pressure increase and purification, the pyrolysis gas enters a four-tower decarburization device to remove more than four carbon components;

(2) compressing the top material flow of the four decarbonization towers, then sending the material flow into an absorption tower to remove light components, and sending the kettle material flow of the four decarbonization towers into a de-weighting tower;

(3) extracting light components from the top of the absorption tower, feeding the material flow in the bottom of the absorption tower into a desorption tower, and feeding the material at the top of the desorption tower into a depropanizing tower; returning the material in the tower kettle of the desorption tower to the absorption tower;

(4) extracting a gasoline product from the tower kettle of the de-heavy tower, enabling the material flow at the top of the de-heavy tower to enter a carbon four hydrogenation reactor, combining the material flow at the outlet of the carbon four hydrogenation reactor with the material flow at the tower kettle of the desorption tower, and then enabling the combined material flow to enter an absorption tower;

(5) removing alkyne from the material at the top of the depropanizing tower by a carbo-hydrogenation reactor, and then extracting a crude ethylene product; the propane product is extracted from the tower bottom of the depropanizing tower.

6. The pyrolysis gas separation method according to claim 5, characterized in that:

the method further comprises (6),

the material in the bottom of the depropanizing tower enters a carbon-three hydrogenation reactor for reaction and then enters a propylene rectifying tower, a propylene product is extracted at the side line, a propane product is extracted at the bottom of the depropanizing tower, and the tower top returns to the space between compressor sections.

7. The pyrolysis gas separation method according to claim 5, characterized in that:

adopting five-section compression to increase the pressure of the cracking gas to 2-5 MPag, then cooling to 10-15 ℃, and then feeding into an absorption tower;

the purification is carried out between compression sections, preferably after three-section compression, the pyrolysis gas purification is carried out.

8. The pyrolysis gas separation method according to claim 5, characterized in that:

the absorbent of the absorption tower is a carbon three-fraction containing propane, a carbon four-fraction containing n-butane and isobutane, or a carbon five-fraction containing n-pentane and isopentane;

the depropanizer overhead stream controls the propylene content to be less than 0.5% mol.

9. The pyrolysis gas separation method according to claim 5, characterized in that:

the number of theoretical plates of the four decarburization towers is 25-80, and the operating pressure is 0.5-2.5 MPa;

the number of theoretical plates of the absorption tower is 25-60, the operating pressure is 2.0-6.0 MPa, and the temperature of the tower top is 10-40 ℃;

the number of theoretical plates of the desorption tower is 20-60, and the operating pressure is 1.0-4.0 MPa;

the number of theoretical plates of the depropanizing tower is 20-80, and the operating pressure is 0.5-4.0 MPa;

the number of theoretical plates of the de-heavy tower is 20-80, and the operating pressure is 0.1-2 MPa.

10. The pyrolysis gas separation method according to claim 6, characterized in that:

the number of theoretical plates of the propylene rectifying tower is 80-280, and the operating pressure is 0.1-4.0 MPa.

Technical Field

The invention relates to the technical field of pyrolysis gas separation, in particular to a pyrolysis gas separation system and method adopting absorption-desorption.

Background

A large amount of tail gas is generated in the oil refining and chemical production processes, wherein some tail gas, such as tail gas generated in the production processes of catalytic cracking, thermal cracking, delayed coking, hydrocracking and the like, contains a plurality of components of carbon and carbon, and particularly, the ethane/propane content in some tail gas is higher. At present, carbon two and three concentrated gases recovered from refinery tail gas are mainly sent to different sections of an ethylene plant to increase the yield of ethylene and propylene, however, for a refinery without an ethylene production device at the periphery, the direction of the concentrated gases is a main problem, so that carbon two and three resources in dry gases cannot be fully utilized, and great waste is caused.

The most important utilization mode of saturated alkanes such as ethane/propane is to produce high-quality basic chemical raw materials such as ethylene and propylene by thermal cracking. After being mixed with steam, cracking raw materials such as saturated alkane, light hydrocarbon, naphtha, hydrogenated tail oil, light diesel oil and the like undergo a thermal cracking reaction in a cracking furnace to generate cracking products such as hydrogen, methane, carbon two, carbon three, carbon four and the like. Separating and purifying the cracking product in a subsequent separation system to obtain fractions with different carbon atoms, and separating ethylene and propylene products from the carbon two and carbon three fractions.

At present, the separation and purification of the cracking products in the industry mainly adopts a sequential separation method, a front depropanization process, a front deethanization process and the like, and the obtained products comprise polymer-grade ethylene, polymer-grade propylene and the like. However, no matter what separation process is adopted, if a rectification method is adopted to separate out light components such as methane, a cold box is required to provide lower cold energy, the investment is large, and the energy consumption is high. In addition, the equipment quantity, energy consumption and the like required for obtaining polymer-grade ethylene products and polymer-grade propylene products are large.

For refineries without ethylene production devices around, the amount of saturated resources is not large enough, and if cracking and traditional cryogenic separation methods are adopted to utilize the resources, the investment recovery rate is low and the energy consumption is high. Therefore, it is urgently needed to develop a separation method and utilization of cracked gas to reduce the problems of large investment, high energy consumption and the like of the separation process of the cracked gas.

Disclosure of Invention

The invention provides a pyrolysis gas separation system and method adopting absorption-desorption to solve the problems of large process investment, high energy consumption and the like in the prior art. Has the characteristics of investment saving, low energy consumption and remarkable benefit.

It is an object of the present invention to provide a cracked gas separation system employing absorption-desorption.

The system comprises:

the system comprises a compressor, a purification system, a four-decarbonization tower, an absorption tower, a desorption tower, a depropanization tower, a de-heavy tower, a carbon-two hydrogenation reactor and a carbon-four hydrogenation reactor; wherein the content of the first and second substances,

the purification system and the four decarburization towers are sequentially connected between the compressor sections, the four decarburization towers are connected with the rear section of the compressor and then connected with the absorption tower, and the four decarburization tower kettles are connected with the heavy component removal tower; the top of the heavy component removal tower is connected with a carbon four hydrogenation reactor, and an outlet pipeline of the carbon four hydrogenation reactor is combined with an outlet pipeline of the tower kettle of the desorption tower and then connected with the upper part of the absorption tower;

the tower kettle of the absorption tower is connected with a desorption tower; the top of the desorption tower is connected with a depropanization tower, and the tower kettle of the desorption tower is combined with an outlet pipeline of the four-carbon hydrogenation reactor and then connected with the upper part of the absorption tower; the top of the depropanizing tower is connected with a carbo-hydrogenation reactor.

Preferably, the first and second liquid crystal materials are,

the bottom of the depropanization tower is connected with a carbon three hydrogenation reactor, the carbon three hydrogenation reactor is connected with a propylene rectifying tower, and the top of the propylene rectifying tower is connected with a compressor section.

A reboiler is arranged at the tower kettle of the absorption tower; and/or the presence of a gas in the gas,

the tower kettle of the desorption tower is provided with a reboiler.

And an outlet pipeline of the tower kettle of the desorption tower is divided into two paths, one path is extracted, and the other path is combined with an outlet pipeline of the four-carbon hydrogenation reactor and then connected with the upper part of the absorption tower.

The second purpose of the invention is to provide a method for separating cracked gas.

The method comprises the following steps:

(1) after compression, pressure increase and purification, the pyrolysis gas enters a four-tower decarburization device to remove more than four carbon components;

(2) compressing the top material flow of the four decarbonization towers, then sending the material flow into an absorption tower to remove light components, and sending the kettle material flow of the four decarbonization towers into a de-weighting tower;

(3) extracting light components from the top of the absorption tower, feeding the material flow in the bottom of the absorption tower into a desorption tower, and feeding the material at the top of the desorption tower into a depropanizing tower; returning the material in the tower kettle of the desorption tower to the absorption tower;

(4) extracting a gasoline product from the tower kettle of the de-heavy tower, enabling the material flow at the top of the de-heavy tower to enter a carbon four hydrogenation reactor, combining the material flow at the outlet of the carbon four hydrogenation reactor with the material flow at the tower kettle of the desorption tower, and then enabling the combined material flow to enter an absorption tower;

(5) removing alkyne from the material at the top of the depropanizing tower by a carbo-hydrogenation reactor, and then extracting a crude ethylene product; the propane product is extracted from the tower bottom of the depropanizing tower.

Preferably, the first and second liquid crystal materials are,

the method further comprises (6),

the material in the bottom of the depropanizing tower enters a carbon-three hydrogenation reactor for reaction and then enters a propylene rectifying tower, a propylene product is extracted at the side line, a propane product is extracted at the bottom of the depropanizing tower, and the tower top returns to the space between compressor sections.

Adopting five-section compression to increase the pressure of the cracking gas to 2-5 MPag, then cooling to 10-15 ℃, and then feeding into an absorption tower;

the purification is carried out between compression sections, preferably after three-section compression, the pyrolysis gas purification is carried out.

The absorbent of the absorption tower is a carbon three-fraction containing propane, a carbon four-fraction containing n-butane and isobutane, or a carbon five-fraction containing n-pentane and isopentane;

the depropanizer overhead stream controls the propylene content to be less than 0.5% mol.

The number of theoretical plates of the four decarburization towers is 25-80, and the operating pressure is 0.5-2.5 MPa;

the number of theoretical plates of the absorption tower is 25-60, the operating pressure is 2.0-6.0 MPa, and the temperature of the tower top is 10-40 ℃;

the number of theoretical plates of the desorption tower is 20-60, and the operating pressure is 1.0-4.0 MPa;

the number of theoretical plates of the depropanizing tower is 20-80, and the operating pressure is 0.5-4.0 MPa;

the number of theoretical plates of the de-weighting tower is 20-80, and the operating pressure is 0.1-2 MPa;

the number of theoretical plates of the propylene rectifying tower is 80-280, and the operating pressure is 0.1-4.0 MPa.

The invention can adopt the following technical scheme:

a cracked gas separation system, comprising: the system comprises a compressor, a purification system, a four-decarbonization tower, an absorption tower, a desorption tower, a depropanization tower, a de-heavy tower, a carbon-two hydrogenation reactor and a carbon-four hydrogenation reactor; wherein the content of the first and second substances,

the purification system and the four decarburization towers are sequentially connected between the compressor sections, the four decarburization towers are connected with the rear section of the compressor and then connected with the absorption tower, and the four decarburization tower kettles are connected with the heavy component removal tower; the tower kettle of the absorption tower is connected with the desorption tower; the top of the desorption tower is connected with a depropanization tower, and the tower kettle of the desorption tower is connected with the top of the absorption tower; the top of the depropanizing tower is connected with a carbo-hydrogenation reactor and then connected with a product extraction line; the top of the heavy component removal tower is connected with the carbon four hydrogenation reactor and then connected with the top of the absorption tower, and the tower kettle of the heavy component removal tower is connected with a gasoline product line.

In the invention, the tower kettle of the absorption tower and/or the tower kettle of the desorption tower are/is preferably provided with a reboiler to ensure that light components such as methane, hydrogen and the like in the tower kettle of the absorption tower are reduced below the set requirement. Wherein, the heating medium of the reboiler at the tower bottom of the absorption tower and the reboiler at the tower bottom of the desorption tower can adopt low-pressure steam or hot oil, preferably hot oil, which can not only fully utilize the abundant heat of a refinery, but also reduce the process energy consumption.

According to the invention, the material at the outlet of the four-carbon hydrogenation reactor completely enters the absorption tower, and in order to ensure the stable dosage of the absorbent in the system and prevent the accumulation of heavy components, part of the absorbent is preferably extracted from the tower kettle of the desorption tower, so that the tower kettle of the desorption tower is preferably provided with a solvent extraction pipeline.

A method of separating a cracked gas, comprising: the cracking gas enters a compressor to be pressurized, an intersegment outlet is purified and then enters a four-tower decarburization device to remove components with four or more carbons, then enters the rear section of the compressor to be compressed continuously, the compressed cracking gas enters an absorption tower to remove light components and then enters a desorption tower, the material at the top of the desorption tower enters a depropanizing tower, the material at the bottom of the depropanizing tower returns to the absorption tower, and the material at the top of the depropanizing tower is firstly removed alkyne by a carbon dioxide hydrogenation reactor and then is sent out of a battery compartment as a product. And (3) feeding a four-carbon hydrogenation reactor at the top of the de-heavy tower, hydrogenating olefin and alkadiene in the four-carbon hydrogenation reactor into alkane, returning the alkane to the absorption tower to serve as a supplementary absorbent, and extracting a gasoline product from the tower bottom.

In the present invention, the light components include methane and hydrogen.

According to a preferred embodiment of the invention, the method comprises the steps of:

(1) compression: after the pressure of the cracking gas is increased and the cracking gas is cooled, the cracking gas enters an absorption tower;

(2) purifying: purifying the cracked gas between the compression sections;

(3) and fourthly, decarburization: the purified cracking gas is cooled and then enters a decarburization four-tower, heavy components with more than four carbon atoms are extracted from a tower kettle and sent to a de-heavy tower, and the material flow at the top of the tower enters the rear section of a compressor to be continuously boosted.

(4) Absorption: cooling the boosted cracked gas to enter an absorption tower, and allowing an absorbent to enter the tower from the top of the absorption tower to absorb components C2 and above in the cracked gas; the material flow in the tower bottom of the absorption tower is sent to a desorption tower, the gas which is not absorbed in the tower top is cooled, and part of absorbent is recovered and taken out as fuel gas;

(5) desorbing: the top of the desorption tower obtains carbon dioxide three concentrated gas, the bottom of the desorption tower obtains a poor solvent, and the poor solvent returns to the top of the absorption tower after being cooled;

(6) depropanizing: sending the carbon dioxide three-concentrated gas obtained from the top of the desorption tower to a depropanizing tower, obtaining crude ethylene gas from the top of the depropanizing tower, sending the crude ethylene gas to a carbon dioxide hydrogenation reactor, removing alkyne, extracting the product, and sending the product to a styrene device to be used as a raw material.

(7) Removing weight: and (3) feeding the material at the bottom of the four-tower decarbonizing tower into a heavy component removing tower, extracting more than five carbon components from the tower bottom, feeding the four-carbon fraction at the tower top into a four-carbon hydrogenation reactor, completely hydrogenating unsaturated hydrocarbon into saturated hydrocarbon, and feeding the saturated hydrocarbon serving as a supplementary absorbent into the top of the absorption tower.

In the compression step, the number of stages to be compressed is not particularly limited in the present invention, and five-stage compression is preferably employed. Preferably, the compression specifically means that the pressure of the cracking gas is increased to 2-5 MPag, and then the gas is sent to an absorption tower after being cooled to 10-15 ℃.

In the purification step, the purification of the pyrolysis gas is performed between compression sections, preferably after three-section compression, and preferably, the purification comprises acid gas removal, drying and the like.

In the four decarburization steps, according to the invention, the number of theoretical plates of the four decarburization towers is preferably 25 to 80, and the operating pressure is preferably 0.5 to 2.5 MPa.

In the absorption step, the amount of the absorbent used in the absorption column is not particularly limited in the present invention, and can be determined by those skilled in the art based on the general knowledge of the prior art. The absorbent can be a carbon three-fraction containing propane, a carbon four-fraction containing n-butane and isobutane, or a carbon five-fraction containing n-pentane and isopentane; the carbon four-cut fraction containing n-butane and isobutane is preferred.

Preferably, the number of theoretical plates of the absorption tower is 25-60, the operating pressure is 2.0-6.0 MPa, and the tower top temperature is 10-40 ℃.

In the desorption step, the desorbed absorbent obtained at the bottom of the desorption tower can be cooled step by step and then returned to the absorption tower for recycling.

According to the invention, the number of theoretical plates of the desorption tower is preferably 20-60, and the operating pressure is preferably 1.0-4.0 MPa.

In the depropanization step, the invention has no particular limitation on the form of the carbohydrogenator and the catalyst, and the skilled person can determine the form according to the general knowledge in the prior art.

According to the invention, the number of theoretical plates of the depropanizer is preferably 20-80, and the operating pressure is preferably 0.5-4.0 MPa.

According to the present invention, preferably the depropanizer overhead stream controls the propylene content below 0.5% mol, preferably the depropanizer overhead stream is sent to the styrene plant as feed.

According to the present invention, if the cracked gas feed is high in propylene content, it is preferred to further refine the depropanizer bottoms, which preferably comprises:

(8) and (3) propylene rectification: the material at the tower bottom of the depropanizing tower firstly enters a carbon-three hydrogenation reactor and then enters a propylene rectifying tower, a propylene product is extracted at the side line, a propane product is extracted at the tower bottom, and the tower top returns to the space between compressor sections.

According to the present invention, the form and catalyst of the hydrocarbon three hydrogenation reactor are not particularly limited, and those skilled in the art can determine the form and catalyst based on the general knowledge of the prior art.

According to the invention, the number of theoretical plates of the propylene rectifying tower is preferably 80-280, and the operating pressure is preferably 0.1-4.0 MPa.

According to the present invention, preferably, the propane product is returned to the cracking furnace for use as a cracking feedstock.

In the de-heavy step, the invention has no special limitation on the form of the carbon four hydrogenation reactor and the catalyst, and the skilled person can determine the form according to the common knowledge in the prior art.

According to the invention, the theoretical plate number of the heavy component removing tower is preferably 20-80, and the operating pressure is preferably 0.1-2 MPa.

In the present invention, all the pressures are gauge pressures unless otherwise specified.

The separation method and the system of the pyrolysis gas have the following characteristics that:

(1) because the absorption-desorption method is adopted to remove light components such as methane, hydrogen and the like, a complete set of equipment such as a cold box and an ethylene refrigeration compressor is not needed, the energy consumption is saved, and the investment is obviously reduced.

(2) The carbon four fraction is fully hydrogenated and then used as a supplementary absorbent of the absorption tower, so that the supplementary absorbent is not needed to be purchased, and the device independence is strong.

(3) Because the absorption-desorption step removes light components such as methane, hydrogen and the like, the ethylene content in the crude ethylene product is high, and the obtained crude ethylene product is a high-quality raw material of a styrene device and can be continuously and finely separated. In addition, the propylene content in the product can be strictly controlled in the depropanizing step, so that the propylene content in the crude ethylene is low, the energy consumption of the device is effectively saved, and the energy consumption of the styrene device is effectively reduced.

(4) The pyrolysis gas separation method provided by the invention has the characteristics of low investment, low energy consumption and remarkable benefit.

Drawings

FIG. 1 is a schematic diagram of a cracked gas separation system of example 1;

FIG. 2 is a schematic diagram of a cracked gas separation system of example 2;

description of reference numerals:

1-1 compressor front section; 1-2 compressor rear section; 2, a purification system; 3, decarbonizing four towers; 4, an absorption tower; 5 a desorption tower; 6 a depropanizer; 7, a heavy component removing tower; 8, a hydrogenation reactor for carbon dioxide; a 9-carbon four-hydrogenation reactor; 10 a propylene rectification column; 11-carbon three-hydrogenation reactor; 20 cracking gas; 21 a crude ethylene product; 22 a propylene product; a 23 propane product; 24 a fuel gas; a 25 carbon four product; 26 gasoline products.

Detailed Description

While the present invention will be described in detail and with reference to the specific embodiments thereof, it should be understood that the following detailed description is only for illustrative purposes and is not intended to limit the scope of the present invention, as those skilled in the art will appreciate numerous insubstantial modifications and variations therefrom.

Example 1:

a cracked gas separation system as shown in fig. 1 is employed, comprising: a compressor (a compressor front section 1-1 and a compressor rear section 1-2); a purification system 2; a decarburization four tower 3; an absorption tower 4; a desorption tower 5; a depropanizer 6; a de-weighting tower 7; a carbo-hydrogenation reactor 8; a carbon four hydrogenation reactor 9.

The purification system 2 and the four decarbonization 7 towers 3 are sequentially connected between the compressor sections, the tops of the four decarbonization towers 3 are connected with the rear sections 1-2 of the compressors and then connected with the absorption tower 4, and the kettle 3 of the four decarbonization towers is connected with the de-weighting tower; the top of the heavy component removal tower 7 is connected with a carbon four hydrogenation reactor 9, and an outlet pipeline of the carbon four hydrogenation reactor 9 is combined with an outlet pipeline of the tower bottom of the desorption tower 5 and then connected with the upper part of the absorption tower 4;

the tower kettle of the absorption tower 4 is connected with a desorption tower 5; the top of the desorption tower 5 is connected with a depropanization tower 6, and the bottom of the desorption tower 5 is combined with an outlet pipeline of the four-carbon hydrogenation reactor 9 and then connected with the upper part of the absorption tower 4; the top of the depropanizer 6 is connected with a carbo-hydrogenation reactor 8.

A reboiler is arranged at the tower kettle of the absorption tower; the tower kettle of the desorption tower is provided with a reboiler.

The charge amount of the pyrolysis gas is 42000 kg/h. N-butane was chosen as absorbent.

The separation method of the pyrolysis gas comprises the following steps:

(1) compression: the cracked gas is compressed in five stages, the pressure is increased to 3.6MPag, and then the cracked gas is cooled to 15 ℃ and enters an absorption tower 4. (2) Purifying: cracked gas at the outlet of the three sections of the compressor enters a purification system 2 to remove acid gas, water and other impurities in the cracked gas.

(3) And fourthly, decarburization: the theoretical plate number of the four decarbonization towers is 40, and the operating pressure is 1 MPag. The purified cracking gas enters the middle part of a four-tower decarburization system, after more than four carbon components are removed, the gas phase at the top of the tower enters the rear section of a compressor to continuously increase the pressure, and the material at the bottom of the tower enters a heavy component removal tower.

(4) Absorption: the theoretical plate number of the absorption column 4 was 40, the operating pressure was 3.5MPag, and the column top temperature was 20 ℃. The used absorption solvent is saturated carbon four, the solvent enters the absorption tower from the top of the absorption tower 4, and the cracked gas enters from the 15 th tower plate. C2 and its heavy components in the cracked gas are absorbed by solvent and extracted from tower bottom, the tower top contains light components of methane, hydrogen, etc. and small amount of absorbent, and the absorbent is recovered through cooling and is used as fuel gas.

(5) Desorbing: the theoretical plate number of the desorption column 5 was 42, and the operating pressure was 2.3 MPag. The rich solvent absorbing the components such as C2 in the cracking gas enters a desorption tower from the 15 th tower plate, the desorbed C2 concentrated gas is extracted from the top of the tower, and after part of the lean solvent is extracted, the rest lean solvent is cooled to 15 ℃ after gradual heat exchange and returns to the absorption tower 4 for recycling.

(6) Depropanizing: the carbon two carbon three concentrated gas obtained from the top of the desorption tower 5 is sent to a depropanizer 6, the theoretical plate number of the depropanizer 6 is 35, and the operation pressure is 2.0 MPag. Crude ethylene gas is extracted from the tower top and sent to a carbon dioxide hydrogenation reactor 8 to be extracted as a crude ethylene product, and a propane product is extracted from the tower bottom.

(7) Removing weight: the theoretical plate number of the de-heavies column 7 was 39 and the operating pressure was 0.45 MPag. The material at the top of the heavy component removal tower is firstly hydrogenated into saturated hydrocarbon by a carbon four hydrogenation reactor, and then the saturated hydrocarbon is returned to the top of the absorption tower to be used as a supplementary absorbent, and the material at the bottom of the tower is extracted as a gasoline product.

The incoming pyrolysis gas composition is shown in table 1.

TABLE 1 cracked gas composition

Composition of	Wt％
		Hydrogen gas	1.15
CO	0.10
		CO2	0.02
H2S	0.01
		Methane	14.92
Acetylene	0.52
		Ethylene	29.57
Ethane (III)	3.77
		MAPD	0.86
Propylene (PA)	10.31
		Propane	0.50
Butadiene	3.09
		Butene (butylene)	1.50
Butane	1.30
		C5+	6.45
Water (W)	25.92

The composition of the crude ethylene product obtained is shown in Table 2.

TABLE 2 crude ethylene product composition

Composition of	mol％
		Methane	13
Ethylene	77.4
		Ethane (III)	8.9
Propylene (PA)	0.4

The other individual stream mass compositions are shown in table 3.

TABLE 3 Mass composition of the different streams

	20	21	22	23	24	25
							Hydrogen gas	1.15	0.00	7.58	0.00	0.00	0.00
CO	0.10	0.00	0.69	0.00	0.00	0.00
							CO2	0.02	0.00	0.00	0.00	0.00	0.00
H2S	0.01	0.00	0.00	0.00	0.00	0.00
							Methane	14.92	7.79	80.82	0.00	0.00	0.01
Acetylene	0.52	0.28	0.07	3.20	0.00	0.00
							Ethylene	29.57	81.28	0.91	0.48	0.00	0.04
Ethane (III)	3.77	10.01	0.00	1.23	0.00	0.01
							MAPD	0.86	0.00	0.24	6.83	0.46	0.01
Propylene (PA)	10.31	0.63	0.25	83.37	0.24	0.06
							Propane	0.50	0.00	0.05	4.09	0.06	0.00
Butadiene	3.09	0.00	0.00	0.00	0.00	0.08
							Butene (butylene)	1.50	0.00	0.00	0.00	0.00	0.03
Butane	1.30	0.00	9.39	0.80	99.23	0.05
							C5+	6.45	0.00	0.00	0.00	0.01	99.71
Water (W)	25.92	0.00	0.00	0.00	0.00	0.00

In this example, the ethylene recovery was 99.0%.

Example 2:

a cracked gas separation system as shown in fig. 2 is employed, comprising: a compressor (a compressor front section 1-1 and a compressor rear section 1-2); a purification system 2; a decarburization four tower 3; an absorption tower 4; a desorption tower 5; a depropanizer 6; a de-weighting tower 7; a carbo-hydrogenation reactor 8; a carbon four hydrogenation reactor 9; a propylene rectifying column 10; a carbon three hydrogenation reactor 11.

The purification system 2 and the four decarbonization 7 towers 3 are sequentially connected between the compressor sections, the tops of the four decarbonization towers 3 are connected with the rear sections 1-2 of the compressors and then connected with the absorption tower 4, and the kettle 3 of the four decarbonization towers is connected with the de-weighting tower; the top of the heavy component removal tower 7 is connected with a carbon four hydrogenation reactor 9, and an outlet pipeline of the carbon four hydrogenation reactor 9 is combined with an outlet pipeline of the tower bottom of the desorption tower 5 and then connected with the upper part of the absorption tower 4;

the tower kettle of the absorption tower 4 is connected with a desorption tower 5; the top of the desorption tower 5 is connected with a depropanization tower 6, and the bottom of the desorption tower 5 is combined with an outlet pipeline of the four-carbon hydrogenation reactor 9 and then connected with the upper part of the absorption tower 4; the top of the depropanizing tower 6 is connected with a carbo-hydrogenation reactor 8; the bottom of the depropanizing tower 6 is connected with a carbon three hydrogenation reactor 11, the carbon three hydrogenation reactor 11 is connected with a propylene rectifying tower 10, and the top of the propylene rectifying tower 10 is connected with a compressor section.

A reboiler is arranged at the tower kettle of the absorption tower; the tower kettle of the desorption tower is provided with a reboiler.

The charge amount of pyrolysis gas was also 42000kg/h, and the specific composition is shown in Table 1. N-butane was chosen as absorbent.

The specific separation steps are the same as the first seven steps of the embodiment 1, and the difference is that the method comprises the following steps:

(8) and (3) propylene rectification: the material at the bottom of the depropanizing tower is firstly fed into a carbon-three hydrogenation reactor to remove the alkyne, dialkene and other impurities, and then fed into a propylene rectifying tower 10. The theoretical plate number of the propylene rectifying column 10 was 170, and the operating pressure was 1.7 MPag. The propylene product is extracted from the side line of the propylene rectifying tower, the top of the tower returns to the space between the compressor sections, and the propane product is extracted from the bottom of the tower.

The composition of the crude ethylene product obtained is shown in Table 4.

TABLE 4 crude ethylene product composition

Composition of	mol％
		Methane	13
Ethylene	77.4
		Ethane (III)	8.9
Propylene (PA)	0.4

The composition of the propylene product obtained is shown in Table 5.

TABLE 5 propylene product composition

Composition of	mol％
		Ethylene	0.2
Propylene (PA)	99.7
		Propane	0.1

The other individual stream mass compositions are shown in table 6.

TABLE 6 Mass composition of the different streams

	20	21	22	23	24	25	26
								Hydrogen gas	1.15	0.01	0.00	0.00	7.65	0.00	0.00
CO	0.10	0.00	0.00	0.00	0.70	0.00	0.00
								CO2	0.02	0.00	0.00	0.00	0.00	0.00	0.00
H2S	0.01	0.00	0.00	0.00	0.00	0.00	0.00
								Methane	14.92	7.99	0.00	0.00	80.77	0.00	0.01
Acetylene	0.52	0.00	0.00	0.00	0.07	0.00	0.00
								Ethylene	29.57	81.16	0.13	0.00	0.94	0.00	0.04
Ethane (III)	3.77	10.21	0.00	0.00	0.00	0.00	0.01
								MAPD	0.86	0.00	0.00	0.00	0.20	0.39	0.01
Propylene (PA)	10.31	0.63	99.77	1.83	0.17	0.16	0.06
								Propane	0.50	0.00	0.10	81.72	0.04	0.04	0.00
Butadiene	3.09	0.00	0.00	0.00	0.00	0.00	0.08
								Butene (butylene)	1.50	0.00	0.00	0.00	0.00	0.00	0.03
Butane	1.30	0.00	0.00	16.44	9.47	99.41	0.05
								C5+	6.45	0.00	0.00	0.00	0.00	0.00	99.71
Water (W)	25.92	0.00	0.00	0.00	0.00	0.00	0.00

In this example, the ethylene recovery was 99.0% and the propylene recovery was 98%.

Having described embodiments of the present invention, the foregoing description is intended to be exemplary, not exhaustive, and not limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments.