CN112707787B

CN112707787B - Pyrolysis gas separation system with purification function and utilization method

Info

Publication number: CN112707787B
Application number: CN201911020269.5A
Authority: CN
Inventors: 李东风; 罗淑娟; 李琰; 李春芳; 邹弋; 舒展
Original assignee: Sinopec Beijing Research Institute of Chemical Industry; China Petroleum and Chemical Corp
Current assignee: Sinopec Beijing Research Institute of Chemical Industry; China Petroleum and Chemical Corp
Priority date: 2019-10-25
Filing date: 2019-10-25
Publication date: 2022-09-20
Anticipated expiration: 2039-10-25
Also published as: CN112707787A

Abstract

The invention discloses a pyrolysis gas separation system with purification and a separation method. The system comprises: the system comprises a compressor, a purification system, a de-weighting tower, an absorption tower, a desorption tower and a carbon dioxide hydrogenation reactor; the purification system and the de-heavy tower are sequentially connected between the compressor sections, the top of the de-heavy tower is connected with the rear section of the compressor and then connected with the absorption tower, and the tower kettle of the absorption tower is connected with the desorption tower; the top of the desorption tower is connected with the carbon dioxide hydrogenation reactor and then is connected outside, and the tower kettle of the desorption tower is connected with the upper part of the absorption tower. The system and the method have the characteristics of low investment, low energy consumption and remarkable benefit.

Description

Pyrolysis gas separation system with purification function and utilization method

Technical Field

The invention relates to the technical field of cracking separation, in particular to a cracking gas separation system with purification and a utilization method.

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 are subjected to 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, if saturated resources are cracked and the cracked gas is separated by adopting the traditional cryogenic separation method, 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

In order to solve the problems in the prior art, the invention provides a pyrolysis gas separation system with purification and a utilization method. The system and the method have the characteristics of low investment, low energy consumption and remarkable benefit.

One of the purposes of the invention is to provide a pyrolysis gas separation system with purification.

The method comprises the following steps:

the system comprises a compressor, a purification system, a de-weighting tower, an absorption tower, a desorption tower and a carbon dioxide hydrogenation reactor;

the purification system and the de-heavy tower are sequentially connected between the compressor sections, the top of the de-heavy tower is connected with the rear section of the compressor and then connected with the absorption tower, and the tower kettle of the absorption tower is connected with the desorption tower; the top of the desorption tower is connected with the carbon dioxide hydrogenation reactor and then is connected outside the battery limits, and the tower kettle of the desorption tower is connected with the upper part of the absorption tower.

The system further comprises: a depropanizing tower, a carbon-three hydrogenation reactor and a propylene rectifying tower;

the tower kettle of the de-heavy tower is connected with a depropanization tower; the top of the depropanizing tower is connected with a C-III hydrogenation reactor, the C-III hydrogenation reactor is connected with a propylene rectifying tower, and the kettle of the depropanizing tower is connected with a C-IV product line; the side line of the propylene rectifying tower is connected with a propylene product line, the gas phase at the top of the tower returns to the space between compressor sections, and the tower kettle is connected with a propane product line.

Among them, preferred are:

the heavy component removing tower is a high-pressure heavy component removing tower and a low-pressure heavy component removing tower;

the high-pressure heavy component removing tower and the low-pressure heavy component removing tower are connected in series; the tower kettle of the high-pressure heavy-duty tower is connected with the low-pressure heavy-duty tower, the top of the low-pressure heavy-duty tower is connected with the rear section of the compressor and then is connected with the cooler and the gas-liquid separation tank, the gas phase is connected with the absorption tower, the liquid phase is connected with the upper part of the high-pressure heavy-duty tower, and the top of the high-pressure heavy-duty tower is connected with the absorption tower.

The absorption tower kettle and/or the desorption tower kettle are/is provided with a reboiler;

the absorption tower is provided with an absorbent makeup line.

The second purpose of the invention is to provide a method for utilizing the pyrolysis gas by adopting the system.

The method comprises the following steps:

(1) purification and compression: purifying the cracked gas between the compression sections;

(2) removing weight: the purified and cooled cracking gas enters a de-heavy tower, heavy components with more than three carbon atoms are extracted from a tower kettle, and the tower top material flow enters the rear section of a compressor to be continuously boosted;

(3) 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 kettle of the absorption tower is sent to a desorption tower, and gas which is not absorbed at the tower top is taken as fuel gas to be extracted;

(4) desorption: crude ethylene gas is obtained from the top of the desorption tower and is sent to a carbon dioxide hydrogenation reactor, and the crude ethylene gas is taken out as a product after acetylene hydrocarbon is removed; the lean solvent obtained from the tower bottom returns to the absorption tower.

Preferably, the method further comprises the following steps:

(5) the material at the tower bottom of the heavy component removal tower is sent to a depropanizing tower, the carbon three components are extracted from the tower top of the depropanizing tower and enter a carbon three hydrogenation reactor, and the carbon four product is extracted from the tower bottom of the depropanizing tower;

(6) and (3) propylene rectification: feeding the material of the C-III hydrogenation reactor into a propylene rectifying tower, extracting a propylene product from the side line of the propylene rectifying tower, and extracting a propane product from the tower kettle; the top of the propylene rectifying tower returns to the space between the compressor sections.

Among them, preferred are:

and (1) purifying the pyrolysis gas between compression sections, preferably purifying the pyrolysis gas after three sections of compression.

A step (2) of carrying out a treatment,

the overhead stream of the de-heavy tower controls the content of propylene to be lower than 0.5% mol;

the number of theoretical plates of the de-heavy tower is 20-80, and the operating pressure is 1.0-6.0 MPa;

when the heavy component removing tower is a high-pressure heavy component removing tower and a low-pressure heavy component removing tower which are connected in series,

the purified cracking gas enters a high-pressure de-weighting tower, the liquid phase at the tower bottom enters a low-pressure de-weighting tower, and the material at the tower bottom of the low-pressure de-weighting tower enters a depropanizing tower; after the gas phase at the top of the low-pressure heavy component removal tower enters the rear section of the compressor to be continuously boosted, cooling gas-liquid separation is carried out, the gas phase enters the absorption tower, the liquid phase enters the high-pressure heavy component removal tower, and the gas phase at the top of the high-pressure heavy component removal tower enters the absorption tower;

the number of theoretical plates of the high-pressure de-heavy tower is 10-40, and the operating pressure is 1.5-6.0 MPa;

the theoretical plate number of the low-pressure de-heavy tower is 25-80, and the operating pressure is 1.5-6.0 MPa.

Respectively controlling the high-pressure heavy component removal tower, wherein the content of propylene in the gas phase at the top of the low-pressure heavy component removal tower is lower than 0.5% mol.

Step (3), increasing the pressure of the cracked gas to 2-5 MPag, then cooling to-20-40 ℃, and then sending the gas-phase cracked gas to an absorption tower;

when a high-pressure heavy-duty removal tower and a low-pressure heavy-duty removal tower are adopted, two materials enter an absorption tower, one material is the top of the high-pressure heavy-duty removal tower and does not need to be cooled again, the temperature of the materials is lower, the other material is the top of the low-pressure heavy-duty removal tower, the materials are firstly pressurized by a compressor and then cooled again, the temperature is reduced to about-20 to-40 ℃, gas and liquid are separated, a gas phase enters the absorption tower, and a liquid phase returns to the high-pressure heavy-duty removal tower.

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 ℃;

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 0.1-4.0 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:

the pyrolysis gas enters a compressor to be pressurized, an intersegment outlet is purified and then enters a de-heavy tower to remove heavy components, then the pyrolysis gas enters a rear section of the compressor to be compressed continuously, the compressed pyrolysis gas enters an absorption tower to remove light components and then enters a desorption tower, and the material on the top of the desorption tower is removed of alkyne through a carbon-two hydrogenation reactor and then is taken as a product to be extracted. The tower bottom material returns to the absorption tower. Directly discharging the tower bottom material of the heavy component removal tower out of a boundary region, or sending the tower bottom material to a depropanizing tower, removing more than four carbon components in the depropanizing tower, feeding the tower top material into a carbon-three hydrogenation reactor, and then feeding the tower top material into a propylene rectifying tower; the material at the top of the propylene rectifying tower returns to the space between the compressor sections, the polymerization-grade propylene product is collected at the side line, and the propane product is collected at the bottom of the tower.

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, the cracking gas enters an absorption tower;

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

(3) removing weight: the purified cracking gas is cooled and then enters a de-heavy tower, heavy components with more than three carbon atoms are extracted from a tower kettle, and the tower top material flow 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: crude ethylene gas is obtained from the top of the desorption tower and is sent to a carbon dioxide hydrogenation reactor, acetylene hydrocarbon is removed and then the crude ethylene gas is taken as a product to be extracted, and the product can be sent to a styrene device to be taken as a raw material. Obtaining a lean solvent at the tower bottom, and returning the lean solvent to the top of the absorption tower after cooling;

the material in the tower bottom of the de-heavy tower can be directly discharged outside the boundary area and can also be sent to a depropanizing tower, if the material in the tower bottom of the de-heavy tower enters the depropanizing tower, the method also comprises the following steps:

(6) a hydrogenation reactor and a tower kettle are taken out as carbon four products;

(7) and (3) propylene rectification: the polymerization grade propylene product is extracted from the side of the propylene rectifying tower, and the propane-rich product is extracted from the tower bottom.

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 de-heaving step, according to the present invention, one column may be used for operation, or two columns may be used for operation, preferably two columns, one of which is at high pressure, referred to as the high pressure de-heaving column, and one of which is at low pressure, referred to as the low pressure de-heaving column. Preferably, the gas phase of the pyrolysis gas enters the high-pressure de-heavy tower, the liquid phase of the pyrolysis gas enters the low-pressure de-heavy tower, and the liquid phase at the top of the low-pressure de-heavy tower returns to the high-pressure de-heavy tower.

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 alkane such as propane, butane or pentane, and can also be carbon three fraction containing propane, carbon four fraction containing n-butane and isobutane, or carbon five fraction containing n-pentane and isopentane; the carbon four-cut fraction containing n-butane and isobutane is preferred.

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.

In the desorption step, the present invention does not specifically limit the form of the carbon hydrogenation reactor and the catalyst, and those skilled in the art can determine the form according to the general knowledge of the prior art.

In the depropanization step, the invention has no special limitation on the form of the carbon triple 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 present invention, preferably, the propane product is returned to the cracking furnace for use as a cracking feedstock.

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) 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 tower top can be strictly controlled by the de-heavy tower, 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.

(3) The product quality is high, and the economic benefit is obvious.

(4) The absorbent has good selectivity, and each absorbent has ideal absorption effect, and the most suitable absorbent can be selected according to the conditions of different manufacturers.

(5) 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 the cracked gas separation system of example 2.

Description of the reference numerals:

1-1 compressor front section, 1-2 compressor rear section; 2, a purification system; 3, a de-weighting tower; 4, an absorption tower; 5 a desorption tower; 6, a hydrogenation reactor for carbon dioxide; 7 a depropanizer; an 8-carbon three-hydrogenation reactor; 9, a propylene rectifying tower; 20 cracking gas; 21 supplementing an absorbent; 22 a crude ethylene product; 23 a propylene product; 24 heavy components; 25 propane product; 26 fuel gas.

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); 2, a purification system; 3, a de-weighting tower; 4, an absorption tower; 5 a desorption tower; 6, a hydrogenation reactor for carbon two;

the heavy component removing tower adopts two towers, namely a high-pressure heavy component removing tower and a low-pressure heavy component removing tower.

The compressor section is connected with the purification system 2 and the high-pressure de-heavy tower in sequence and then connected with the absorption tower 4. The tower kettle of the high-pressure de-weighting tower is connected with the low-pressure de-weighting tower, the top of the low-pressure de-weighting tower is connected with the rear section 1-2 of the compressor and then connected with the cooler and the gas-liquid separation tank, the gas-phase outlet of the gas-liquid separation tank is connected with the absorption tower 4, the liquid-phase outlet of the gas-liquid separation tank is connected with the upper part of the high-pressure de-weighting tower, the top of the high-pressure de-weighting tower is connected with the absorption tower 4, and the tower kettle of the absorption tower 4 is connected with the desorption tower 5; the top of the desorption tower 5 is connected with a carbon hydrogenation reactor 6 and then is connected with a crude ethylene product extraction line; the tower kettle of the desorption tower 5 is connected with the absorption tower 4; the absorber 4 is provided with a make-up absorber line 21.

The charge of cracked gas is about 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 4MPag, and the cracked gas 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) Removing weight: cooling the purified material to-35 deg.C, separating gas phase from liquid phase, feeding the gas phase into high-pressure de-weighting tower, and feeding the liquid phase into low-pressure de-weighting tower. The theoretical plate number of the high pressure de-heaving tower is 15, the operating pressure is 3.8MPag, the theoretical plate number of the low pressure de-heaving tower is 40, and the operating pressure is 1.7 Mpag. The material in the tower bottom of the high-pressure heavy component removing tower directly enters the low-pressure heavy component removing tower, and the gas phase at the tower top enters the absorption tower 4. Taking the tower bottom material of the low-pressure de-weighting tower as a heavy component, raising the pressure of the tower top material, cooling the tower top material to 3MPag, cooling the tower top material to-20 ℃, separating gas and liquid, feeding the gas phase into an absorption tower 4, and returning the liquid phase to the high-pressure de-weighting tower.

(4) Absorption: the theoretical plate number of the absorption column 4 was 40, the operation pressure was 3.4MPag, 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, and the tower top contains light components of methane, hydrogen, etc. and small amount of absorbent.

(5) Desorption: the theoretical plate number of the desorption column 5 was 42, and the operation pressure was 2.1 Mpag. The rich solvent absorbing the components of C2 and the like in the cracking gas enters a desorption tower from the 15 th tower plate, and the desorbed C2 concentrated gas is extracted from the top of the tower and enters a carbon dioxide hydrogenation reactor, and is extracted as a product after acetylene hydrocarbon is removed. The lean solvent in the bottom of the desorption tower is cooled to 15 ℃ after being subjected to gradual heat exchange and then returns to the absorption tower 5 for recycling.

The incoming pyrolysis gas composition is shown in table 1.

TABLE 1 cracked gas composition

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

TABLE 2 crude ethylene product composition

Composition of	mol％
		Methane	17.6
Ethylene	71.8
		Ethane (III)	8.8
Butane	1.7

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

TABLE 3 Mass composition of the different streams

In this example, the ethylene recovery was 96.5%.

Example 2:

a cracked gas separation system comprising: a compressor (a compressor front section 1-1 and a compressor rear section 1-2); a purification system 2; a de-weighting tower 3; an absorption tower 4; a desorption tower 5; a carbo-hydrogenation reactor 6; a depropanizer 7; a carbon three hydrogenation reactor 8; a propylene rectifying column 9.

The compressor section is connected with the purification system 2 and the high-pressure de-heavy tower in sequence and then connected with the absorption tower 4. The tower kettle of the high-pressure de-weighting tower is connected with the low-pressure de-weighting tower, the top of the low-pressure de-weighting tower is connected with the rear section 1-2 of the compressor and then connected with the cooler and the gas-liquid separation tank, the gas-phase outlet of the gas-liquid separation tank is connected with the absorption tower 4, the liquid-phase outlet of the gas-liquid separation tank is connected with the upper part of the high-pressure de-weighting tower, the top of the high-pressure de-weighting tower is connected with the absorption tower 4, and the tower kettle of the absorption tower 4 is connected with the desorption tower 5; the top of the desorption tower 5 is connected with a carbon hydrogenation reactor 6 and then is connected with a crude ethylene product extraction line; the tower kettle of the desorption tower 5 is connected with the absorption tower 4; the absorption tower 4 is provided with a make-up absorbent line 21. The material at the bottom of the de-heavy tower 3 is connected with a de-propanizer 7, the top of the de-propanizer 7 is connected with a carbon three hydrogenation reactor 8 and then connected with a propylene rectifying tower 9, and the bottom of the de-propanizer 7 is connected with a heavy component product line; the side line of the propylene rectifying tower 9 is connected with a propylene product line, the tower kettle is connected with a propane product line, and the tower top is connected with a compressor section.

The steps 1 to 5 described in this example are the same as in example 1, except that the bottom material of the low-pressure de-heavy column enters the depropanizer 7,

(6) depropanizing: the theoretical plate count of the depropanizer 7 was 40 and the operating pressure was 0.7 MPag. The material in the bottom of the low-pressure de-heavy tower enters a depropanizing tower, heavy components are extracted from the tower bottom, and the material in the top of the tower enters a hydrogenation reactor to remove alkyne and dialkene in the material, and then enters a propylene rectifying tower 9.

(7) And (3) propylene rectification: the number of theoretical plates of the propylene rectifying column 9 was 170, and the operating pressure was 1.7 MPag. The polymerization grade propylene product is extracted from the side line, the propane product is taken from the tower bottom, and the gas phase at the tower top returns to the space between the compressor sections.

The pyrolysis gas composition is shown in table 1.

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

TABLE 4 crude ethylene product composition

Composition of	mol％
		Methane	12.4
Ethylene	78.3
		Ethane (III)	8.9
Propylene polymer	0.3

TABLE 5 propylene product composition

Composition of	mol％
		Ethylene	0.18
Propylene polymer	99.7
		Propane	0.12

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

TABLE 6 Mass composition of the different streams

In this example, the ethylene recovery was 98% 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.

Claims

1. A cracked gas separation system with purification, the system comprising:

the purification system and the de-heavy tower are sequentially connected between the compressor sections, the top of the de-heavy tower is connected with the rear section of the compressor and then connected with the absorption tower, and the tower kettle of the absorption tower is connected with the desorption tower; the top of the desorption tower is connected with the carbon dioxide hydrogenation reactor and then is connected with the outside, and the tower kettle of the desorption tower is connected with the upper part of the absorption tower.

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

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

the heavy component removing tower comprises a high-pressure heavy component removing tower and a low-pressure heavy component removing tower;

the high-pressure heavy component removing tower and the low-pressure heavy component removing tower are connected in series; the tower kettle of the high-pressure heavy-duty tower is connected with the low-pressure heavy-duty tower, the top of the low-pressure heavy-duty tower is connected with the rear section of the compressor and then is sequentially connected with the cooler and the gas-liquid separation tank, the gas-phase outlet of the gas-liquid separation tank is connected with the absorption tower, the liquid-phase outlet of the gas-liquid separation tank is connected with the upper part of the high-pressure heavy-duty tower, and the top of the high-pressure heavy-duty tower is connected with the absorption tower.

4. The cracked gas separation system as claimed in any one of claims 1 to 3, wherein:

a reboiler is arranged at the tower kettle of the absorption tower and/or the tower kettle of the desorption tower; and/or

The absorption tower is provided with an absorbent makeup line.

5. A method for utilizing a cracked gas using the system as claimed in any one of claims 1 to 4, said method comprising:

(3) absorption: cooling the boosted cracked gas, allowing the cooled cracked gas to enter an absorption tower, allowing an absorbent to enter the tower from the top of the absorption tower, and absorbing C2 and above components in the cracked gas; the material flow in the tower kettle of the absorption tower is sent to a desorption tower, and the gas which is not absorbed in the tower top is taken as fuel gas to be extracted;

(4) desorbing: crude ethylene gas is obtained from the top of the desorption tower and is sent to a carbon dioxide hydrogenation reactor, and the crude ethylene gas is taken out as a product after acetylene hydrocarbon is removed; and returning the lean solvent obtained from the tower bottom to the absorption tower.

6. The utilization method according to claim 5, characterized in that the method comprises:

(5) the material in the tower bottom of the de-heavy tower is sent to a depropanizing tower, the top of the depropanizing tower extracts the carbon three components, the carbon three components enter a carbon three hydrogenation reactor, and the tower bottom of the depropanizing tower extracts a carbon four product;

7. The utilization method according to claim 5, characterized in that:

and (1) purifying the mixture in a compression section.

8. The utilization method according to claim 7, characterized in that:

and (1) after three-stage compression, carrying out pyrolysis gas purification.

9. The utilization method according to claim 5, characterized in that:

controlling the content of propylene in the overhead stream of the de-heavy tower to be lower than 0.5% mol;

the theoretical plate number of the heavy component removing tower is 20-80, and the operating pressure is 1.0-6.0 MPa.

10. The utilization method according to claim 5, characterized in that:

step (2), when the heavy component removing tower is a high-pressure heavy component removing tower and a low-pressure heavy component removing tower which are connected in series,

the purified cracking gas enters a high-pressure de-weighting tower, the liquid phase at the tower bottom enters a low-pressure de-weighting tower, and the material at the tower bottom of the low-pressure de-weighting tower enters a depropanizing tower; the gas phase at the top of the low-pressure heavy-component removal tower enters the rear section of the compressor to be continuously boosted and enters the high-pressure heavy-component removal tower, and the gas phase at the top of the high-pressure heavy-component removal tower enters the absorption tower;

the number of theoretical plates of the high-pressure de-heavy tower is 10-40, and the operating pressure is 1.0-6.0 MPa;

the number of theoretical plates of the low-pressure de-weighting tower is 25-80, and the operating pressure is 1.0-6.0 MPa;

11. The utilization method according to claim 5, characterized in that:

and (3) increasing the pressure of the cracking gas to 2-5 MPag, cooling to-20-40 ℃, and conveying to an absorption tower.

12. The utilization method according to claim 5, characterized in that:

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 ℃;

13. The utilization method according to claim 6, characterized in that: