CN112029529A

CN112029529A - Device and method for separating and recovering liquefied gas from light hydrocarbon

Info

Publication number: CN112029529A
Application number: CN201910482282.6A
Authority: CN
Inventors: 黄孟旗; 丁昱文; 余龙红; 吴迪; 刘凯祥
Original assignee: Sinopec Engineering Inc; Sinopec Engineering Group Co Ltd
Current assignee: Sinopec Engineering Inc; Sinopec Engineering Group Co Ltd
Priority date: 2019-06-04
Filing date: 2019-06-04
Publication date: 2020-12-04
Anticipated expiration: 2039-06-04
Also published as: CN112029529B

Abstract

The invention belongs to the field of chemical industry, and particularly discloses a device and a method for separating and recovering liquefied gas from light dydrocarbon, wherein gasoline, C4 and components below C4 are separated in advance before light dydrocarbon separation, so that gasoline is not required to be adopted to absorb liquefied gas components in the subsequent flow, the consumption of absorbent circulation is saved, meanwhile, gas at the outlet of a debutanizer is desulfurized, and the material flow does not contain H in the light dydrocarbon separation process₂S, the material requirement of a light hydrocarbon separation and recovery system is reduced, and H is reduced₂The risk possibly brought by S leakage ensures the safety of the whole process; meanwhile, the invention has simple process flow, mild operation condition and less energy consumption.

Description

Device and method for separating and recovering liquefied gas from light hydrocarbon

Technical Field

The invention belongs to the field of oil refining and chemical engineering, and particularly relates to a device and a method for separating and recovering liquefied gas from light hydrocarbon, and more particularly relates to a device and a method for separating and recovering liquefied gas from light hydrocarbon in processes with higher gas yield, such as catalytic cracking, delayed coking and the like.

Background

Light hydrocarbon refers to the components of methane, ethane, ethylene, propane, propylene, carbon and the like obtained in the petrochemical process, and the light hydrocarbon separation process is always the key point of attention of the petrochemical process. The existing process with high gas yield such as catalytic cracking, hydrocracking, delayed coking and the like usually adopts absorption stabilization to recover liquefied gas (C3/C4) components to realize liquefied gas components and dry gas (H)₂/C1/C2) and stabilizing the gasoline to ensure the qualified vapor pressure of the gasoline.

The absorption stabilizing process mainly comprises four towers: the absorption tower, the reabsorption tower, the desorption tower and the stabilizing tower, wherein the recovery rate of the liquefied gas is controlled by the absorption tower and the reabsorption tower, and the specification of the liquefied gas is ensured by the desorption tower (controlling the content of carbon five) and the stabilizing tower (controlling the content of carbon five). The main characteristic is that under a certain pressure (1.3 MPaG-1.6 MPaG) and normal temperature, most of liquefied gas components and a small amount of carbon dioxide in the rich gas are absorbed, then the light components of carbon, etc. are desorbed under proper conditions, and after cooling, the light components are returned to the absorption tower. Thus, the carbon two and the carbon three are separated by adopting an absorption and desorption method under a mild operation condition, the carbon two and the carbon three are prevented from being separated by adopting a rectification method (the pressure is high, the temperature is low, refrigeration is required), and the investment and the energy consumption are reduced; the cost is that the top gas of the desorption tower contains a certain amount of heavy components such as liquefied gas and the like besides carbon dioxide, and the desorbed gas returns to the absorption tower again, so that the circulation of the components of the liquefied gas between absorption and desorption is caused, and the energy consumption of an absorption stabilizing system is increased.

The prior absorption stabilization process method has the following defects:

(1) the absorption stabilizing system adopts stable gasoline as an absorbent to recover liquefied gas components, the liquefied gas components are absorbed at the normal temperature of 40 ℃, refrigeration is not carried out, and the gasoline circulation amount is large in order to ensure the liquefied gas recovery rate.

(2) Gasoline circulates among the gasoline absorption tower, the desorption tower and the stabilizing tower, the temperature of the bottoms of the ethane desorption tower and the stabilizing tower is higher, the thermal load of a reboiler at the bottom of the tower is larger, and the energy consumption is higher.

(3) The stabilizing tower (debutanizer) is arranged at the tail end, the flow path of the gasoline is long, and the energy consumption is high;

(4) the desulfurization is arranged on a dry gas and liquefied gas product line, and an absorption stabilizing system contains H₂S, the requirement on the material is high, and potential safety hazards may exist.

Disclosure of Invention

The invention aims to provide a device and a method for separating and recovering liquefied gas from light hydrocarbon, which have simple process flow and mild operation conditions, can realize the high-efficiency separation and recovery of C three and C four components, and does not contain H in the recovery process₂S, the material requirement of the light hydrocarbon recovery system is reduced, and the method is safer.

In order to achieve the above object, the present invention provides a method for separating and recovering liquefied gas from light hydrocarbons, comprising:

(1) gas-liquid separation: oil gas from an upstream device is condensed and cooled and then sent to a gas-liquid separation tank for gas-liquid separation, a liquid phase at the bottom of the tank is sent to a debutanizer, and a gas phase at the top of the tank is compressed and then sent to the debutanizer;

(2) removing butane: the gas phase and the liquid phase from the step (1) enter a debutanizer, the gas phase at the top of the tower is distilled out from the top of the tower, and then is sent to a cooler after being desulfurized and alkali washed, and the liquid phase at the bottom of the tower is taken as a stable gasoline product to be extracted;

(3) and (3) cooling: the light hydrocarbon after desulfurization and alkali washing is primarily cooled in a cooler, then sent to a post cooler for further cooling, and sent to a feeding tank;

(4) feeding: after the gas-liquid balance of the material flow from the after cooler is carried out in a feeding tank, the gas phase at the top of the tank is sent to an absorption tower, and the liquid phase at the bottom of the tank is sent to a deethanizer;

(5) absorption: in the absorption tower, mixed C4 is used as an absorbent to absorb components above C3 and C3 in a gas phase from the top of a feed tank, meanwhile, light components below C2 and C2 are absorbed together, the gas phase at the top of the absorption tower is sent to a downstream device to further recover the absorbent, and a liquid phase at the bottom of the absorption tower is returned to an aftercooler;

(6) deethanizing: separating C2 components from the liquid phase at the bottom of the feed tank in a deethanizer, collecting the separated mixed C2 components from the top of the deethanizer and returning the components to an aftercooler, and delivering the liquid phase components at the bottom of the deethanizer, which are C3 and more than C3, to a depropanizer;

(7) depropanizing: further separating liquid phase components from the bottom of the deethanizer in a depropanizer, collecting separated C3 components from the top of the depropanizer, sending the C3 components to a propylene rectifying tower for further rectification, sending at least part of the tower bottom components to an absorption tower as a mixed C4 absorbent, and collecting the rest of the C4 mixed products;

(8) and (3) propylene rectification: the gas phase from the top of the depropanizing tower is further rectified in the propylene rectifying tower, the gas phase at the top of the propylene rectifying tower is taken as a propylene product, and the liquid phase at the bottom of the propylene rectifying tower is taken as a propane product.

According to the present invention, preferably, the method further comprises:

(9) and (3) recovering the absorbent: in the absorbent recovery tower, at least part of the stable gasoline product extracted in the step (2) is used as an absorbent to absorb components of C4 and above C4 in the gas phase from the top of the absorption tower, and simultaneously absorb a small amount of components of C2/C3, the gas phase at the top of the absorbent recovery tower is extracted as dry gas, and the liquid phase at the bottom of the absorbent recovery tower is returned to the debutanizer.

The step (9) may preferably be:

(9) and (3) recovering the absorbent: in the absorbent recovery tower, circulating oil from the top of the catalytic cracking unit fractionating tower is used as an absorbent to absorb components of C4 and above C4 in a gas phase from the top of the absorption tower, a small amount of C2/C3 components are absorbed at the same time, the gas phase at the top of the absorbent recovery tower is extracted as dry gas, and a liquid phase at the bottom of the absorbent recovery tower is returned to the catalytic cracking unit fractionating tower to be used as top circulation.

In the invention, preferably, the pressure of the absorbent recovery tower is 0.8-1.4 MPaG, and the temperature is 5-25 ℃.

The invention has wide application range, and the oil gas (including H) in the common processes with higher gas yield such as catalytic cracking, delayed coking and the like in chemical production₂C1-C4, gasoline components and a small amount of non-hydrocarbon components) can be separated by the device of the invention to recycle liquefied gas.

In order to avoid the need of using a large amount of gasoline for cyclic absorption in the prior art liquefied gas recovery, the method firstly uses a debutanizer to separate gasoline from components with the temperature of C4 and the temperature of C4, and according to the method, the top temperature of the debutanizer is preferably 40-55 ℃, the pressure is 1.0-1.6 MPaG, and the bottom temperature is preferably 170-220 ℃.

According to the invention, preferably, the pressure of the absorption tower is 0.9-1.5 MPaG, and the temperature is 5-25 ℃.

Because the main recovery target of the invention is C3/C4 components, propylene with the purity not lower than 99.6 v% is further separated, and C2 components are not required to be recovered, according to the principle that the saturated vapor pressure of the C3/C4 components is lower, under the process operation condition adopted by the invention, a larger part of C3/C4 components can be condensed by directly adopting one-time gas-liquid separation, then the condensate is subjected to deethanization and depropanization processes in turn, and finally the propane and propylene products are obtained by rectifying propylene.

According to the invention, the temperature of the feeding tank is preferably 5-25 ℃ and the pressure is preferably 0.9-1.5 MPaG.

In the invention, the circulating carbon four is taken as an absorbent, the carbon four components circulate among the absorption tower, the deethanizer and the depropanizer, and the boiling point of the carbon four components is lower, so that the temperature of the bottoms of the deethanizer and the depropanizer is low, the load of a reboiler at the bottom of the tower is reduced, and the energy is saved. According to the invention, preferably, the temperature at the top of the deethanizer is 15-40 ℃, the pressure is 1.1-1.7 MPaG, and the temperature at the bottom of the deethanizer is 60-80 ℃; the temperature of the top of the depropanizing tower is 40-50 ℃, the pressure is 1.6-2.2 MPaG, and the temperature of the bottom of the depropanizing tower is 95-120 ℃; the temperature of the top of the propylene rectifying tower is 40-50 ℃, the pressure is 1.8-2.2 MPaG, and the temperature of the bottom of the propylene rectifying tower is 55-65 ℃.

In the invention, the deethanizer is only provided with a stripping section and no rectifying section, the tower top is not provided with a condenser, and the liquid phase from the upstream gas-liquid separation tank directly enters the first tower plate at the tower top of the deethanizer so as to reduce the consumption of the whole process on cold energy.

In another aspect, the present invention provides a device for separating and recovering liquefied gas from light hydrocarbons, the device comprising: a light hydrocarbon feeding pipeline, a gas-liquid separation tank, a compressor, a debutanizer, a desulfurizing tower, an alkaline washing tower, a cooler, a post cooler, a feeding tank, an absorption tower, a deethanizer, a depropanizer and a propylene rectifying tower;

wherein, the light hydrocarbon feed pipeline is connected with the inlet of the gas-liquid separation tank, the top of the gas-liquid separation tank is sequentially connected with the compressor and the debutanizer, and the bottom of the gas-liquid separation tank is connected with the debutanizer;

the top of the debutanizer is sequentially connected with a desulfurizing tower and an alkaline washing tower, the alkaline washing tower is directly connected with a cooler, a post cooler and a feeding tank, and the bottom of the debutanizer is provided with a stable gasoline product extraction pipeline;

the top of the feeding tank is connected with the absorption tower, and the bottom of the feeding tank is connected with the deethanizer; the top of the absorption tower is connected with a downstream device, the bottom of the absorption tower is connected with an aftercooler, and the upper part of the absorption tower is provided with a mixed C4 absorbent feeding pipeline;

the top of the deethanizer is connected with the aftercooler, the bottom of the deethanizer is connected with the depropanizer, and a mixed C2 component extraction pipeline is arranged at the top of the deethanizer;

the upper part of the depropanizing tower is connected with the propylene rectifying tower, the bottom of the depropanizing tower is provided with a mixed C4 product extraction pipeline, the mixed C4 product extraction pipeline is divided into two branches, and one branch is used as a mixed C4 absorbent feeding pipeline;

the upper part of the propylene rectifying tower is provided with a propylene product extraction pipeline, and the bottom of the tower is provided with a propane product extraction pipeline.

According to the invention, preferably, the downstream device comprises an absorbent recovery tower, the top of the absorbent recovery tower is provided with a dry gas extraction pipeline, the bottom of the absorbent recovery tower is connected with a debutanizer, the upper part of the absorbent recovery tower is provided with a stabilized gasoline absorbent feeding pipeline, the stabilized gasoline product extraction pipeline of the debutanizer is divided into two branches, and one branch is used as the stabilized gasoline absorbent feeding pipeline; or a dry gas extraction pipeline is arranged at the top of the absorbent recovery tower, the bottom of the absorbent recovery tower is connected with the catalytic cracking unit, and a stable gasoline absorbent feeding pipeline is arranged at the upper part of the absorbent recovery tower and is connected with a stable gasoline extraction pipeline of the catalytic cracking unit.

In the invention, the compressor can be divided into a plurality of sections, and an intersegment liquid phase extraction pipeline is connected with the debutanizer.

According to the invention, preferably, the bottom of the debutanizer is provided with a reboiler.

Compared with the prior art, the invention has the following advantages:

(1) the invention can directly condense the larger part of the liquefied gas components by adopting one-time gas-liquid separation at lower temperature and higher pressure by using less equipment, and simultaneously, the uncondensed liquefied gas components are recycled in the absorption tower by adopting the circulating carbon IV, thereby realizing high recovery rate of the liquefied gas components; the invention can ensure that the recovery rates of the carbon three component and the carbon four component are both more than 99 wt%, and the content of C2 in the obtained propylene product is not more than 2000 ppmv.

(2) In the invention, before the light hydrocarbon separation, the gasoline, the C4 and the components below C4 are separated in advance, so that the gasoline is not required to be adopted to absorb the liquefied gas components in the subsequent flow, the consumption of the absorbent circulation is saved, meanwhile, the gas at the outlet of the debutanizer is desulfurized, and the material flow does not contain H any more in the light hydrocarbon separation process₂S, the material requirement of the light hydrocarbon separation and recovery system is reduced, and the safety of the process is ensured.

(3) In the invention, because the temperature level at the bottom of the deethanizer is low, the load of the reboiler at the bottom of the deethanizer is reduced, and the energy is saved.

(4) The invention has simple process flow, mild operation condition and low energy consumption.

Additional features and advantages of the invention will be set forth in the detailed description which follows.

Drawings

The above and other objects, features and advantages of the present invention will become more apparent by describing in more detail exemplary embodiments thereof with reference to the attached drawings, in which like reference numerals generally represent like parts throughout.

FIG. 1 shows a process flow diagram for separating and recovering liquefied gas from catalytically cracked light hydrocarbons in an embodiment of the present invention.

Fig. 2 shows a process flow diagram for separating and recovering liquefied gas from catalytically cracked light hydrocarbon in another embodiment of the present invention.

Description of reference numerals:

1. a gas-liquid separation tank; 2. a compressor section; 3. a second compressor section; 4. a debutanizer column; 5. a desulfurizing tower; 6. an alkaline washing tower; 7. a cooler; 8. an aftercooler; 9. a feed tank; 10. an absorption tower; 11. a deethanizer; 12. a depropanizer; 13. a propylene rectification column; 14. an absorbent recovery column;

s-1, gas phase at the top of a catalytic cracking fractionating tower; s-2, crude gasoline; s-3, mixing with a C4 absorbent; s-4, dry gas; s-5, propylene products; s-6, a propane product; s-7, stabilizing the gasoline product; s-8, mixing with a C4 product; s-9, fractionating tower top circulating oil by a catalytic cracking unit; s-10, circulating rich absorption oil at the top of a fractionating tower of the catalytic cracking unit.

Detailed Description

Preferred embodiments of the present invention will be described in more detail below. While the following describes preferred embodiments of the present invention, it should be understood that the present invention may be embodied in various forms and should not be limited by the embodiments set forth herein.

The properties of the feed oil and gas in the following examples are shown in table 1, and the properties of the C5+ component in the oil and gas are shown in table 2:

TABLE 1

TABLE 2

Item	Numerical value
		Density, 20 deg.C	0.8167
En-type distillation (D-86) and C	Percent distilled off, v%
		0	42
10	91
		30	99
50	129
		70	145
90	162
		100	187

Example 1

Light hydrocarbon separation and recovery liquefied gas device:

the device comprises a light hydrocarbon feeding pipeline, a gas-liquid separation tank 1, a compressor section 2, a compressor section 3, a debutanizer 4, a desulfurizing tower 5, an alkaline washing tower 6, a cooler 7, an after cooler 8, a feeding tank 9, an absorption tower 10, a deethanizer 11, a depropanizer 12 and a propylene rectifying tower 13;

wherein, the light hydrocarbon feed pipeline is connected with the inlet of the gas-liquid separation tank 1, the top of the gas-liquid separation tank 1 is sequentially connected with the first compressor section 2, the second compressor section 3 and the debutanizer 4, and the bottom of the tank is connected with the debutanizer 4; a liquid phase extraction pipeline between a first section 2 of the compressor is connected with a debutanizer 4;

a reboiler is arranged at the bottom of the debutanizer 4, the top of the debutanizer is sequentially connected with a desulfurizing tower 5 and an alkaline washing tower 6, the alkaline washing tower 6 is directly connected with a cooler 7, an after-cooler 8 and a feeding tank 9, and two stable gasoline product extraction pipelines are arranged at the bottom of the debutanizer 4;

the top of the feeding tank 9 is connected with the absorption tower 10, and the bottom of the tank is connected with the deethanizer 11;

the top of the absorption tower 10 is connected with an absorbent recovery tower 14, the bottom of the absorption tower is connected with an aftercooler 8, and the upper part of the absorption tower 10 is provided with a mixed C4 absorbent feeding pipeline;

the top of the deethanizer 11 is connected with the aftercooler 8, the bottom of the deethanizer is connected with the depropanizer 12, and the top of the deethanizer is provided with a mixed C2 component extraction pipeline;

the upper part of the depropanizing tower 12 is connected with a propylene rectifying tower 13, a mixed C4 product extraction pipeline is arranged at the bottom of the tower, the mixed C4 product extraction pipeline is divided into two branches, and one branch is used as a mixed C4 absorbent feeding pipeline;

a propylene product extraction pipeline is arranged at the upper part of the propylene rectifying tower, and a propane product extraction pipeline is arranged at the bottom of the propylene rectifying tower;

the top of the absorbent recovery tower 14 is provided with a dry gas extraction pipeline, the bottom of the absorbent recovery tower 14 is connected with the debutanizer 4, the upper part of the absorbent recovery tower 14 is provided with a stable gasoline absorbent feeding pipeline, and one of the stable gasoline product extraction pipelines of the debutanizer 4 is used as a stable gasoline absorbent feeding pipeline.

The light hydrocarbon is separated by adopting the device, and the separation flow is shown in figure 1:

(1) gas-liquid separation: oil gas from an upstream device is condensed and cooled and then sent to a gas-liquid separation tank 1 for gas-liquid separation, a liquid phase at the bottom of the tank is sent to a debutanizer 4, and a gas phase at the top of the tank is compressed and then sent to the debutanizer 4;

(2) removing butane: the gas phase and the liquid phase from the step (1) enter a debutanizer 4, the gas phase at the top of the tower is distilled from the top of the tower, then the gas phase is subjected to desulfurization and alkali washing treatment and then sent to a cooler, and the liquid phase at the bottom of the tower is taken as a stable gasoline product to be extracted, wherein the temperature at the top of the debutanizer 4 is 40-55 ℃, the pressure is 1.0-1.6 MPaG, and the temperature at the bottom of the tower is 170-220 ℃;

(3) and (3) cooling: the light hydrocarbon after desulfurization and alkali washing is primarily cooled in a cooler 7, then sent to a post cooler 8 for further cooling, and sent to a feeding tank 9;

(4) feeding: after the gas-liquid balance is carried out on the material flow from the after cooler 8 in a feeding tank 9, the gas phase at the top of the tank is sent to an absorption tower 10, and the liquid phase at the bottom of the tank is sent to a deethanizer 11, wherein the temperature of the feeding tank 9 is 5-25 ℃, and the pressure is 0.9-1.5 MPaG;

(5) absorption: in the absorption tower, mixed C4 is used as an absorbent to absorb components above C3 and C3 in a gas phase from the top of a feed tank 9, meanwhile, light components below C2 and C2 are absorbed together, the gas phase at the top of the absorption tower 10 is sent to an absorbent recovery tower 14 to further recover the absorbent, and a liquid phase at the bottom of the absorption tower is returned to an aftercooler 8; wherein the pressure of the absorption tower is 0.9-1.5 MPaG, and the temperature is 5-25 ℃;

(6) deethanizing: separating a C2 component from a liquid phase at the bottom of a feed tank 9 in a deethanizer 11, collecting a separated mixed C2 component from the top of the deethanizer 11 and returning the component to an aftercooler 8, and delivering liquid phase components at the bottom of the deethanizer 11, wherein the temperature of the top of the deethanizer 11 is 15-40 ℃, the pressure of the liquid phase components is 1.1-1.7 MPaG, and the temperature of the bottom of the deethanizer is 60-80 ℃;

(7) depropanizing: further separating liquid phase components from the bottom of a deethanizer 11 in a depropanizer 12, collecting separated C3 components from the top of the depropanizer 12, sending the separated C3 components to a propylene rectifying tower 13 for further rectification, sending at least part of the tower bottom components to an absorption tower 10 as a mixed C4 absorbent S-3, and collecting the rest of the tower bottom components as a mixed C4 product S-8, wherein the temperature of the top of the depropanizer 12 is 40-50 ℃, the pressure is 1.6-2.2 MPaG, and the temperature of the bottom of the tower is 95-120 ℃;

(8) and (3) propylene rectification: further rectifying the gas phase from the top of the depropanizing tower 12 in a propylene rectifying tower 13, wherein the gas phase at the top of the propylene rectifying tower 13 is taken out as a propylene product S-5, and the liquid phase at the bottom of the propylene rectifying tower 13 is taken out as a propane product S-6, wherein the temperature at the top of the propylene rectifying tower 13 is 40-50 ℃, the pressure is 1.8-2.2 MPaG, and the temperature at the bottom of the propylene rectifying tower is 55-65 ℃;

(9) and (3) recovering the absorbent: in the absorbent recovery tower 14, at least part of the stable gasoline product extracted in the step (2) is used as an absorbent to absorb components of C4 and above C4 in the gas phase from the top of the absorption tower 10, and simultaneously absorbs a small amount of components of C2/C3, the gas phase at the top of the absorbent recovery tower 14 is extracted as dry gas S-4, and the liquid phase at the bottom of the absorbent recovery tower 14 is returned to the debutanizer 4, wherein the pressure of the absorbent recovery tower 14 is 0.8-1.4 MPaG, and the temperature is 5-25 ℃.

The light hydrocarbons in the catalytic cracking reaction were separated by the above method, and the composition and properties of each product were separated as shown in table 3.

TABLE 3

Example 2

Light hydrocarbon separation and recovery liquefied gas device:

a reboiler is arranged at the bottom of the debutanizer 4, the top of the debutanizer is sequentially connected with a desulfurizing tower 5 and an alkaline washing tower 6, the alkaline washing tower 6 is directly connected with a cooler 7, an after-cooler 8 and a feeding tank 9, and a stable gasoline product extraction pipeline is arranged at the bottom of the debutanizer 4;

the top of the absorbent recovery tower 14 is provided with a dry gas extraction pipeline, the bottom of the absorbent recovery tower 14 is connected with the catalytic cracking unit, and the upper part of the absorbent recovery tower 14 is provided with a stable gasoline absorbent feeding pipeline which is connected with a stable gasoline extraction pipeline of the catalytic cracking unit.

Adopt above-mentioned device to carry out light hydrocarbon separation, the separation flow is as shown in figure 2:

(5) absorption: in the absorption tower, mixed C4 is used as an absorbent to absorb components above C3 and C3 in a gas phase from the top of a feed tank 9, and simultaneously absorb light components below C2 and C2, the gas phase at the top of the absorption tower 10 is sent to an absorbent recovery tower 14 to further recover the absorbent, and a liquid phase at the bottom of the absorption tower is returned to an aftercooler 8; wherein the pressure of the absorption tower is 0.9-1.5 MPaG, and the temperature is 5-25 ℃;

(9) and (3) recovering the absorbent: in the absorbent recovery tower 14, circulating oil S-9 from the top of the catalytic cracking unit fractionating tower is used as an absorbent to absorb components with the concentration of C4 and above C4 in a gas phase from the top of the absorption tower 10, and a small amount of C2/C3 components are absorbed at the same time, the gas phase at the top of the absorbent recovery tower 14 is taken out as dry gas S-4, a liquid phase at the bottom of the tower is returned to the catalytic cracking unit and is used as the circulating rich absorption oil S-10 at the top of the catalytic cracking unit fractionating tower, wherein the pressure of the absorbent recovery tower 14 is 0.8-1.4 MPaG, and the temperature is 5-25 ℃.

The light hydrocarbon in the catalytic cracking reaction is separated by the method, the composition and the property of each separated product are shown in table 4, wherein the recovery rate of the propylene can reach 99.4 wt%.

TABLE 4

The data in the table 3-4 show that the process is simple, the operation condition is mild, the energy consumption is low, less equipment is utilized, the recovery of liquefied gas in oil gas of catalytic cracking, catalytic cracking and delayed coking can be realized, wherein the recovery rates of the recovered three-carbon component and four-carbon component are both more than 99 wt%, and the content of C2 in the propylene product obtained by further separation is not more than 2000 ppmv.

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 method for separating and recovering liquefied gas from light hydrocarbon is characterized by comprising the following steps:

2. The method of claim 1, further comprising:

3. The method of claim 1, further comprising:

4. The method of claim 1, wherein the hydrocarbons of the upstream plant contain H₂C1-C4 hydrocarbons, gasoline components and minor amounts of non-hydrocarbon components, the upstream unit preferably being at least one of a catalytic cracker, a catalytic cracker and a delayed coker.

5. The method according to claim 1, wherein the temperature at the top of the debutanizer is 40 to 55 ℃, the pressure at the top of the debutanizer is 1.0 to 1.6MPaG, and the temperature at the bottom of the debutanizer is 170 to 220 ℃; the temperature of the feeding tank is 5-25 ℃, and the pressure is 0.9-1.5 MPaG.

6. The method according to claim 2 or 3, wherein the pressure of the absorption tower is 0.9 to 1.5MPaG, and the temperature is 5 to 25 ℃; the pressure of the absorbent recovery tower is 0.8-1.4 MPaG, and the temperature is 5-25 ℃.

7. The method according to claim 1, wherein the temperature at the top of the deethanizer is 15-40 ℃, the pressure is 1.1-1.7 MPaG, and the temperature at the bottom of the deethanizer is 60-80 ℃; the temperature of the top of the depropanizing tower is 40-50 ℃, the pressure is 1.6-2.2 MPaG, and the temperature of the bottom of the depropanizing tower is 95-120 ℃; the temperature of the top of the propylene rectifying tower is 40-50 ℃, the pressure is 1.8-2.5 MPaG, and the temperature of the bottom of the propylene rectifying tower is 55-65 ℃.

8. A device for separating and recovering liquefied gas from light hydrocarbon is characterized by comprising: a light hydrocarbon feeding pipeline, a gas-liquid separation tank, a compressor, a debutanizer, a desulfurizing tower, an alkaline washing tower, a cooler, a post cooler, a feeding tank, an absorption tower, a deethanizer, a depropanizer and a propylene rectifying tower;

the top of the feeding tank is connected with the absorption tower, and the bottom of the feeding tank is connected with the deethanizer;

the top of the absorption tower is connected with a downstream device, the bottom of the absorption tower is connected with an aftercooler, and the upper part of the absorption tower is provided with a mixed C4 absorbent feeding pipeline;

9. The apparatus of claim 8, wherein the downstream apparatus comprises an absorbent recovery column;

the top of the absorbent recovery tower is provided with a dry gas extraction pipeline, the bottom of the absorbent recovery tower is connected with a debutanizer, the upper part of the absorbent recovery tower is provided with a stable gasoline absorbent feeding pipeline, the stable gasoline product extraction pipeline of the debutanizer is divided into two branches, and one branch is used as the stable gasoline absorbent feeding pipeline; alternatively, the first and second electrodes may be,

the top of the absorbent recovery tower is provided with a dry gas extraction pipeline, the bottom of the absorbent recovery tower is connected with the catalytic cracking unit, and the upper part of the absorbent recovery tower is provided with a stable gasoline absorbent feeding pipeline which is connected with a stable gasoline extraction pipeline of the catalytic cracking unit.

10. The apparatus of claim 8 or 9, wherein a reboiler is provided at the bottom of the debutanizer column;

the compressor is divided into a plurality of sections, and the sections are connected with the debutanizer through a liquid phase extraction pipeline.