CN111393248A

CN111393248A - Device and method for oil gas desulfurization and light hydrocarbon recovery

Info

Publication number: CN111393248A
Application number: CN201910636770.8A
Authority: CN
Inventors: 黄孟旗; 吴迪; 丁昱文; 李健; 姚爱智; 江盛阳
Original assignee: Sinopec Engineering Inc; Sinopec Engineering Group Co Ltd
Current assignee: Sinopec Engineering Inc; Sinopec Engineering Group Co Ltd
Priority date: 2019-07-15
Filing date: 2019-07-15
Publication date: 2020-07-10
Anticipated expiration: 2039-07-15
Also published as: CN111393248B

Abstract

The invention belongs to the field of chemical industry, and particularly discloses a device and a method for oil gas desulfurization and light hydrocarbon recovery, the method has simple flow, mild operating conditions and low cold consumption, can realize the separation and recovery of light hydrocarbon in a catalytic cracking process by using less equipment, and particularly can realize the high-efficiency separation and recovery of various components of heavy gasoline, light gasoline and light hydrocarbon, wherein the total recovery rate of a carbon two component is more than 98 wt%, the recovery rate of a carbon three component is more than 99 wt%, the content of methane in recovered carbon two is not more than 0.5 vol%, and the content of ethane in the recovered carbon three component is not more than 200 ppmv. Meanwhile, the method has wide application range, and oil gas in the processes with higher gas yield, such as catalytic cracking, delayed coking and the like, which are common in chemical production can be separated from desulfurized light oil gas by using the device.

Description

Device and method for oil gas desulfurization and light hydrocarbon recovery

Technical Field

The invention belongs to the field of oil refining and chemical engineering, and particularly relates to a device and a method for oil gas desulfurization and light hydrocarbon recovery, and more particularly relates to a device and a method for oil gas desulfurization and light hydrocarbon recovery in processes with high 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. Among them, the separation process between carbon two, carbon three and carbon four is mature, and the rectification method is usually adopted. Methane, due to its low boiling point, requires cooling to temperatures of-100 ℃ and below, i.e. cryogenic separation, if a rectification process is used to separate methane and carbon dioxide, is commonly used in ethylene plants, which is very costly and costly. Therefore, the separation of methane has been the focus of attention on the light hydrocarbon separation process, and the development of the light hydrocarbon separation process technology and the design of the process flow are all performed around the separation of methane.

The prior catalytic cracking process usually adopts absorption stabilization to recover liquefied gas (C3/C4) component to realize liquefied gas component and dry gas (H)₂/C1/C2). The catalytic cracking process has high dry gas yield, the content of the C2 component in the dry gas can reach 25-40 wt%, the dry gas mainly comprises ethylene and ethane, the ethylene can be used for producing polyethylene, styrene and the like, the ethane can be used for producing ethylene by cracking, the yield of the ethylene by cyclic cracking reaches 80%, and the ethylene is rich in hydrogen. Therefore, the recovery of C2 resource in dry gas is of great interest. The prior art focuses on recovering carbon dioxide in dry gas by adopting an absorption method, and the process method has the following defects:

(1) the dry gas and the carbon four components are separated for the second time: and the dry gas and the liquefied gas are separated in the absorption stabilizing part, the carbon four is adopted to absorb the carbon four in the carbon four recovery part, the carbon four and the dry gas are mixed again, and then the separation is carried out.

(2) The absorption stabilizing system adopts heavy gasoline as an absorbent to recover liquefied gas components, and the liquefied gas components are recycled in the catalytic cracking process due to the high yield of the liquefied gas components, so that the gasoline circulates among the gasoline absorption tower, the ethane desorption tower and the stabilizing tower, the circulating amount is large, the temperature levels of the ethane desorption tower and the stabilizing tower are high, the heat load of a reboiler at the bottom of the tower is large, and the energy consumption is high.

(3) The whole process flow is longer, and the investment and the energy consumption are correspondingly increased. The invention is provided for recovering light hydrocarbon components such as C2/C3/C4 and the like in a catalytic cracking process, simplifying a separation process and reducing investment and energy consumption.

(4) The prior art carries out desulfurization and sweetening on the dry gas and the liquefied gas which are stably absorbed, H₂S and mercaptan are circulated in the whole absorption stabilizing system, and related corrosion problems can be caused, and H exists in the whole absorption stabilizing system₂S leakage may present a safety issue.

Disclosure of Invention

The invention aims to provide a light hydrocarbon separation device and a method with simple process flow and mild operation conditions, which can realize the high-efficiency separation and recovery of components of heavy gasoline, light gasoline and light hydrocarbon, and simultaneously adopt gas phase and liquid phase to carry out desulfurization and mercaptan removal respectively, thereby having better desulfurization effect and more flexible operation.

In order to achieve the above object, the present invention provides a method for oil gas desulfurization and light hydrocarbon recovery, comprising:

(1) first gas-liquid separation: oil gas from an upstream device is condensed and cooled and then sent to a gas-liquid separation tank I for gas-liquid separation, liquid phase at the bottom of the gas-liquid separation tank I is sent to a gasoline cutting tower through pressurization, and gas phase at the top of the tank is sent to the gasoline cutting tower through pressurization of a compressor;

(2) gasoline cutting: the gas phase and the liquid phase from the step (1) enter a gasoline cutting tower, the gas phase distilled from the tower top enters a tower top reflux tank after being condensed, the gas phase at the top of the tower top reflux tank is sent to a gas-liquid separation tank II after being compressed and cooled, the liquid phase at the bottom of the tank is sent to a liquid phase impurity removal unit, and at least part of the liquid phase at the bottom of the gasoline cutting tower is taken as a heavy gasoline product to be extracted;

(3) second gas phase separation: after the gas and the liquid in the gas-liquid separation tank II are balanced, the gas phase and the liquid phase are separated again, and then the materials are respectively sent to a gas phase impurity removal unit and a liquid phase impurity removal unit for impurity removal;

(4) gas-phase impurity removal: the gas phase on the top of the gas-liquid separation tank II is subjected to pressurization, cooling and gas-liquid balance in a gas-liquid separation tank III, and then the gas phase is subjected to H removal in a rich gas desulfurization tower by taking lean amine liquid as an absorbent₂S and CO₂Removing mercaptan in a rich gas alkaline tower by taking alkali liquor as an absorbent, and then sending the rich gas alkaline tower to a cooler after optionally boosting pressure;

(5) liquid phase impurity removal: the liquid phase at the bottom of the tank from the top reflux tank, the gas-liquid separation tank II and the optional gas-liquid separation tank III of the gasoline cutting tower is correspondingly pressurized and then sequentially removed with H in the liquid hydrocarbon desulfurization tower₂S and CO₂After mercaptan is removed in the liquid hydrocarbon mercaptan removal reactor, the liquid hydrocarbon mercaptan removed is sent to a aftercooler;

(6) and (3) cooling: the gaseous light hydrocarbon after impurity removal is primarily cooled in a cooler and then is sent to a post cooler, and is mixed with the liquid light hydrocarbon in the post cooler and then is sent to a feeding tank after being cooled again;

(7) feeding: after the mixture flow from the aftercooler is mixed, pre-absorbed and gas-liquid balanced 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 separation unit;

(8) absorption: in the absorption tower, mixed C4/C5 or C4/C5/C6 is used as an absorbent to absorb components above C2 and C2 in a gas phase from the top of a feed tank, and simultaneously, part of methane is absorbed, the gas phase at the top of the absorption tower is sent to a downstream device, and a liquid phase at the bottom of the absorption tower is returned to an aftercooler;

(9) separation: the liquid phase from the bottom of the feed tank is further separated into a C2 component, a C3 component and a mixed C4/C5 or C4/C5/C6 component through a demethanizer, a depropanizer, a deethanizer and an optional propylene rectifying tower in a separation unit, wherein the C2 component and the C3 component are respectively extracted as a C2 product and a C3 product, at least one part of the mixed C4/C5 or C4/C5/C6 component is sent to an absorption tower as an absorbent, and the rest part is subjected to light gasoline separation;

(10) light gasoline separation: the liquid phase component from the bottom of the depropanizer is further separated from the mixed C4/C5 or C4/C5/C6 component in the debutanizer, the separated C4 component is extracted from the upper part of the debutanizer, and the C5 or C5/C6 component at the bottom of the depropanizer is extracted as light gasoline product.

The invention has wide application range, and the oil gas (including H) in the processes with higher gas yield such as catalytic cracking, delayed coking and the like common in petrochemical production₂C1-C4, gasoline components and minor amounts of non-hydrocarbon components) can be desulfurized using the apparatus of the invention to recover light hydrocarbons.

In the invention, oil gas from an upstream device is condensed and cooled and then sent to a gas-liquid separation tank I for gas-liquid separation, a liquid phase at the bottom of the tank is pressurized by a pump and sent to a gasoline cutting tower, and a gas phase at the top of the tank is pressurized by a compressor and then sent to the gasoline cutting tower.

In the invention, firstly, the cutting temperature of a gasoline cutting tower is controlled to preliminarily separate oil gas from an upstream device into heavy gasoline and a mixture of light hydrocarbon containing C1-C6 and rich gas, the mixture is further separated to obtain light gasoline, dry gas, C2 components, C3 components and C4 components, wherein the main components of the light gasoline, the dry gas, the C2 components, the C3 components and the C4 components are mixed with C5 or C5/C6 alkane and olefin, so that the light hydrocarbon recovery of the oil gas is realized, preferably, the dry point of a distillate gas phase at the top of the gasoline cutting tower is 60-75 ℃, and the initial boiling point of the heavy gasoline extracted from the bottom of the gasoline cutting tower is 65-80 ℃.

Because the heavy gasoline is separated in the gasoline cutting tower in advance, the heavy gasoline does not participate in the downstream light hydrocarbon separation process, the process energy consumption can be greatly reduced, and preferably, the operating temperature at the top of the gasoline cutting tower is 50-75 ℃, and the operating pressure is 0.25-0.6 MPaG; the operation temperature of the tower bottom is 145-180 ℃.

In the invention, in order to meet the requirement of related product recovery and avoid the influence of impurities in materials on a device of a light hydrocarbon recovery part, the impurities in the light hydrocarbon are removed before next separation, and the impurities are mainly eluted by amine to remove H₂S and CO₂And alkaline washing to remove mercaptans. In the invention, the light hydrocarbon is divided into a gas phase and a liquid phase and then impurity removal is respectively carried out, the form of impurity removal can be low pressure or high pressure, preferably, the gas phase at the top of the reflux tank is compressed to 1.1-1.6 MPaG, cooled to 35-45 ℃ and then sent to a gas-liquid separation tank II, and the liquid phase at the bottom of the reflux tank is pressurized to 3.0-3.5 MPaG and then sent to a liquid phase impurity removal unit. And after the gas and the liquid in the gas-liquid separation tank II are balanced, the gas phase and the liquid phase are separated again, and then the materials are respectively sent to a gas phase impurity removal unit and a liquid phase impurity removal unit for impurity removal.

In the present invention, in order to meet the requirements of the recovery of the relevant products, it is preferable that the amine elute H₂S adopts a composite solvent (namely a modified solvent based on MDEA) which can simultaneously remove H₂S and CO₂Wherein H is₂S can be removed to less than 15ppmv, CO₂The removal efficiency can reach 88 to 96 weight percent, and the CO in the material flow entering the alkaline washing mercaptan removal reactor is effectively reduced₂And further reducing the consumption of alkali liquor.

According to the invention, preferably, the operation temperature of the rich gas desulfurization tower is 35-45 ℃, and the operation pressure is 1.1-2.9 MPaG; the operation temperature of the rich gas alkaline washing tower is 35-45 ℃, and the operation pressure is 1.0-2.8 MPaG; the operating temperature of the liquid hydrocarbon desulfurization tower is 35-45 ℃, and the operating pressure is 3.0-3.5 MPaG.

According to the invention, the operating temperature of the feeding tank is preferably 5-25 ℃, and the operating pressure is 2.2-2.8 MPaG.

In the absorption tower, mixed C4/C5 or C4/C5/C6 is used as an absorbent to absorb components above C2 and C2 in a gas phase from the top of a feed tank, and part of methane is absorbed together. When the main component of the light gasoline cut from the top of the gasoline cutting tower is mixed C5/C6, the mixed C4/C5/C6 is selected as an absorbent; when the main component of light gasoline cut from the top of the gasoline cutting tower is mixed C5, mixed C4/C5 is selected as an absorbent, preferably, the operating temperature of the absorption tower is 5-25 ℃, the operating pressure is 2.1-2.7 MPaG, and the absorbent in the absorption tower is a self-balancing component in the system and does not need to be introduced from the outside of the system.

In the invention, the sequence of depropanization and deethanization in the separation step is not particularly limited and can meet the process requirements, but when the sequence of depropanization and deethanization is different, the operation conditions of a deethanization tower and the composition of recovered mixed carbon dioxide can be different, and the separation step can be specifically adjusted by one of the following two ways by a person skilled in the art according to the conventional technical means in the field:

the first method is as follows: the separating step comprises:

demethanization: removing methane from the liquid phase from the bottom of the feed tank in a demethanizer, simultaneously removing a small part of components with the weight of C2 and above C2, sending the gas phase at the top of the demethanizer to an aftercooler, and sending the liquid phase at the bottom of the demethanizer to a deethanizer;

deethanizing: separating C2 component from the liquid phase at the bottom of the demethanizer in a deethanizer, optionally passing the separated mixed C2 component at the top of the deethanizer through a carbon dioxide treatment unit, then extracting the mixed C2 product, and distributing the liquid phase components at the bottom of the deethanizer, which are more than C3 and C3, to a depropanizer;

depropanizing: separating C3 component from liquid phase component at the bottom of the deethanizer in the depropanizer, collecting separated C3 component from the upper part of the depropanizer, sending part of the bottom component to the absorption tower as mixed C4/C5 or C4/C5/C6 absorbent, and sending the rest to the debutanizer;

preferably, the separating step further comprises:

and (3) propylene rectification: c3 component extracted from the upper part of the depropanizing tower is further rectified in a propylene rectifying tower, the gas phase at the top of the propylene rectifying tower is extracted as a propylene product after being cooled, and the liquid phase at the bottom of the propylene rectifying tower is extracted as a propane product;

the second method comprises the following steps:

demethanization: removing methane from the liquid phase from the bottom of the feed tank in a demethanizer, simultaneously removing a small part of components with the content of C2 and above C2, sending the gas phase at the top of the demethanizer to an aftercooler, and sending the liquid phase at the bottom of the demethanizer to a depropanizer;

depropanizing: separating C3 component from liquid phase component at the bottom of the demethanizer in a depropanizer, sending the separated C3 component to the depropanizer after optionally drying the separated C3 component from the upper part of the depropanizer, sending part of the component at the bottom of the tower to an absorption tower as mixed C4/C5 or C4/C5/C6 absorbent, and sending the rest to the debutanizer;

deethanizing: the gas phase from the upper part of depropanization is further separated in a deethanizer, the separated tower top mixed C2 component is extracted as a mixed C2 product from the tower top of the deethanizer after optionally passing through a carbon dioxide treatment unit, and the tower bottom liquid phase is extracted as a mixed C3 component;

preferably, the separating step further comprises:

and (3) propylene rectification: the mixed C3 component from the bottom of the deethanizer is further rectified in a propylene rectifying tower, the gas phase at the top of the propylene rectifying tower is taken out as a propylene product after being cooled, and the liquid phase at the bottom of the propylene rectifying tower is taken out as a propane product.

According to the invention, preferably, the operation temperature of the top of the demethanizer is 10-40 ℃, and the operation pressure is 2.3-2.9 MPaG; the operating temperature of the propylene rectifying tower is 45-60 ℃, and the operating pressure is 1.8-2.0 MPaG.

According to the requirements of recycling and utilizing downstream carbon, when the extracted mixed C2 is sent to a downstream ethylene device, because 15-20 v% of propylene is contained in the mixed C2 product, at the moment, a drying facility is not needed to be arranged, lithium bromide is adopted for refrigeration to meet the requirements, a refrigerant with the temperature of less than-5 ℃ is not needed, and the recovered carbon is subjected to NOx and O removal by a carbon dioxide treatment unit₂And heavy metals and other related impurities are sent to an ethylene device to recover ethylene, ethane, propylene and other resources. Wherein, the removal of impurities is carried out by the person skilled in the art according to the specific situation by using the methods conventional in the artThe impurity removal method can be the hydrogenation O removal method₂Alkyne and NO_xMolecular sieve drying to remove H₂And O, removing COS by adsorption, removing mercury by adsorption and the like.

When the extracted mixed C2 is sent to ethylbenzene production, in order to reduce the content of propylene in the extracted mixed C2 product as much as possible, a drying facility needs to be arranged, a refrigerant with the temperature of-25 ℃ needs to be adopted at the top of the deethanizer, the content of propylene in the extracted mixed C2 product is controlled to be less than or equal to 0.5 wt%, then the extracted mixed C2 is directly sent to ethylbenzene production, and other impurity removal facilities do not need to be arranged.

To further recover the mixed C4/C5 or C4/C5/C6 absorbent entrained in the absorber overhead stream, preferably, the process further comprises:

(11) and (3) recovering the absorbent: in the absorbent recovery tower, part of the heavy gasoline extracted in the step (2) is used as an absorbent to absorb components of C4 and above C4 in a gas phase from the top of the absorption tower, and simultaneously absorbs a small amount of C2/C3 components, the gas phase at the top of the absorbent recovery tower mainly comprises components of methane, hydrogen, nitrogen and the like, is extracted as dry gas, and a liquid phase at the bottom of the absorbent recovery tower returns to the gasoline cutting tower; further preferably, the operating temperature of the absorbent recovery tower is 5-25 ℃, and the operating pressure is 2.1-2.7 MPaG.

In another aspect, the present invention provides an apparatus for oil gas desulfurization and light hydrocarbon recovery, the apparatus comprising: the system comprises an oil gas feeding pipeline, a gas-liquid separation tank I, a compressor I, a gasoline cutting tower, a compressor II, a cooler I, a gas-liquid separation tank II, a rich gas desulfurization tower, a rich gas alkaline tower, a liquid hydrocarbon desulfurization tower, a liquid hydrocarbon sweetening reactor, a compressor III, a cooler II, an after cooler, a feeding tank, an absorption tower, a demethanizer, a deethanizer, a depropanizer, a debutanizer and an optional compressor III, a compressor IV, a cooler III and a gas-liquid separation tank III;

the oil-gas feeding pipeline is connected with an inlet of a gas-liquid separation tank I, the top of the gas-liquid separation tank I is sequentially connected with a compressor I and a gasoline cutting tower, and the bottom of the tank is connected with the gasoline cutting tower;

the top of the gasoline cutting tower is provided with a reflux tank, the top of the reflux tank is sequentially connected with a compressor II, a cooler I and a gas-liquid separation tank II, the bottom of the tank is connected with a booster pump and then connected with a liquid hydrocarbon desulfurization tower, and the bottom of the gasoline cutting tower is provided with a heavy gasoline extraction pipeline;

the top of the gas-liquid separation tank II is sequentially connected with a compressor IV, a cooler III, a gas-liquid separation tank III, a rich gas desulfurization tower, a rich gas alkaline washing tower, a compressor III, a cooler II and an aftercooler, and the bottom of the tank is connected with a liquid hydrocarbon desulfurization tower;

the liquid hydrocarbon desulfurizing tower is connected with the liquid hydrocarbon sweetening reactor and the aftercooler in sequence;

the upper part of the rich gas desulfurization tower is provided with a lean amine liquid feeding pipeline, and the upper part of the rich gas caustic tower is provided with an alkali liquid feeding pipeline; the upper part of the liquid hydrocarbon desulfurization tower is provided with a lean amine liquid feeding pipeline;

the aftercooler is connected with the feeding tank;

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

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/C5 or C4/C5/C6 absorbent feeding pipeline;

the separation unit includes: a demethanizer, deethanizer, depropanizer, and optionally a propylene rectification column; the top of the demethanizer is connected with an aftercooler; a mixed C2 extraction pipeline is arranged at the top of the deethanizer, and a carbon dioxide treatment unit is optionally arranged on the mixed C2 extraction pipeline; a mixed C4/C5 or C4/C5/C6 product extraction pipeline is arranged at the bottom of the depropanizing tower, the mixed C4/C5 or C4/C5/C6 product extraction pipeline is divided into two branches, one branch is used as a mixed C4/C5 or C4/C5/C6 absorbent feeding pipeline, and the other branch is connected with the depropanizing tower;

the upper part of the debutanizer is provided with a C4 component extraction pipeline, and the bottom of the debutanizer is provided with a light gasoline product extraction pipeline.

According to the invention, preferably, the top of the demethanizer is connected with an aftercooler, and the bottom of the demethanizer is connected with a deethanizer;

a mixed C2 extraction pipeline is arranged at the top of the deethanizer, a carbon dioxide treatment unit is optionally arranged on the mixed C2 extraction pipeline, and the bottom of the deethanizer is connected with a depropanizer;

a mixed C3 extraction pipeline is arranged at the upper part of the depropanizing tower, the mixed C3 extraction pipeline is optionally connected with the propylene rectifying tower, a mixed C4/C5 or C4/C5/C6 extraction pipeline is arranged at the bottom of the depropanizing tower, the mixed C4/C5 or C4/C5/C6 extraction pipeline is divided into two branches, one branch is used as a mixed C4/C5 or C4/C5/C6 absorbent feeding pipeline, and the other branch is connected with the depropanizing tower;

the upper part of the debutanizer is provided with a C4 product extraction pipeline, and the bottom of the debutanizer is provided with a light gasoline extraction pipeline;

or,

the top of the demethanizer is connected with an aftercooler, and the bottom of the demethanizer is connected with a deethanizer;

the upper part of the depropanizing tower is connected with a drying unit optionally and then connected with a deethanizing tower, a mixed C4/C5 or C4/C5/C6 extraction pipeline is arranged at the bottom of the depropanizing tower, the mixed C4/C5 or C4/C5/C6 extraction pipeline is divided into two branches, one branch is used as a mixed C4/C5 or C4/C5/C6 absorbent feeding pipeline, and the other branch is connected with the debutanizing tower;

a mixed C2 produced pipeline is arranged at the top of the deethanizer, a carbon dioxide treatment unit is optionally arranged on the mixed C2 produced pipeline, a mixed C3 produced pipeline is arranged at the bottom of the deethanizer, and the mixed C3 produced pipeline is optionally connected with a propylene rectifying tower;

the upper part of the debutanizer is provided with a C4 product extraction pipeline, and the bottom of the debutanizer is provided with a light gasoline extraction pipeline; further preferably, a propylene product extraction pipeline is arranged at the top of the propylene rectifying tower, and a propane product extraction pipeline is arranged at the bottom of the propylene rectifying tower.

According to the present invention, preferably, the downstream apparatus further 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 gasoline cutting tower, and the upper part of the absorbent recovery tower is provided with a heavy gasoline absorbent feeding pipeline.

In order to maintain stable operation temperature of the whole tower, preferably, the absorption tower is provided with 2-5 middle-section refluxes, a condenser is not required to be arranged at the top of the absorption tower, a reboiler is not required to be arranged at the bottom of the absorption tower, gas phase from a feeding tank is fed from the bottom of the absorption tower, and absorbent is fed from the top of the absorption tower.

According to the invention, preferably, the top of the demethanizer is not provided with a condenser, the bottom of the demethanizer is provided with a reboiler, and the liquid phase from the feeding tank is fed from the top of the demethanizer; the light hydrocarbon separation device does not include a dehydration device.

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

(1) in the invention, the front gasoline cutting tower is adopted to separate heavy gasoline, light gasoline and components below C4 and C4 under lower pressure, so that gasoline circulation is not required to absorb liquefied gas components, the gasoline circulation amount is greatly reduced, and the energy consumption of the whole separation process is reduced.

(2) The method has the advantages of simple flow, mild operating conditions and low cold consumption, can realize the separation and recovery of light hydrocarbons in oil gas by using less equipment, and particularly can realize the high-efficiency separation and recovery of C2, C3 and C4 components; and secondary separation process does not exist between the carbon two and each component, and meanwhile, the total recovery rate of the carbon two component can be ensured to be more than 98 wt%, the recovery rate of the carbon three component can be ensured to be more than 99 wt%, the content of methane in the recovered carbon two component is not more than 0.5 vol%, and the content of ethane in the recovered carbon three component is not more than 200 ppmv.

(3) The method further separates the recovered carbon three components into propylene and propane, the recovery rate of the propylene and the propane can also reach more than 99 wt%, the purity of the propylene product is not less than 99.6 v%, and the polymer-grade propylene can be obtained without further treatment.

(4) The dry gas recovered from the top of the absorbent recovery tower has less impurities, the content of components with the purity of C2 and more than C2 is not more than 3 vol%, the pressure is 2.1-2.7 MPaG, the purity of hydrogen can reach 40-70 mol%, and the hydrogen resource can be directly recovered by a pressure swing adsorption method.

(5) According to the invention, gas phase and liquid phase are desulfurized and sweetening respectively, hydrogen sulfide and mercaptan are removed before entering the absorption tower, and are not brought to the downstream light hydrocarbon recovery part, so that the problem of corrosion related to the light hydrocarbon recovery part caused by hydrogen sulfide is avoided, meanwhile, the concentration of the downstream hydrogen sulfide is greatly reduced, and the operation safety is improved; the hydrogen sulfide and the carbon dioxide are removed in advance, the load and the energy consumption of a downstream light hydrocarbon recovery system can be reduced, and simultaneously, as CO is removed in advance₂Is removed, and the quality of downstream products can be improved.

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 oil gas desulfurization and light hydrocarbon recovery in one embodiment of the present invention.

FIG. 2 shows a process flow diagram for oil gas desulfurization and light hydrocarbon recovery in an embodiment of the present invention.

FIG. 3 shows a process flow for oil gas desulfurization and light hydrocarbon recovery in an embodiment of the present invention

Description of reference numerals:

1. a gas-liquid separation tank I; 2. a compressor I; 3. a gasoline cutting tower; 4. a compressor II; 5. a cooler I; 6. a gas-liquid separation tank II; 7. a liquid hydrocarbon desulfurization tower; 8. a liquid hydrocarbon sweetening reactor; 9. A rich gas desulfurization tower; 10. a rich gas caustic wash tower; 11. a compressor III; 12. a cooler II; 13. an aftercooler; 14. a feed tank; 15. an absorption tower; 16. a demethanizer; 17. a deethanizer; 18. a depropanizer; 19. a propylene rectification column; 20. a carbon dioxide treatment unit; 21. an absorbent recovery column; 22. a debutanizer column; 23. a compressor IV; 24. a cooler III; 25. a gas-liquid separation tank III;

s-1, oil gas from an upstream device; s-2, crude gasoline; s-3, lean amine liquid; s-4, amine-rich liquid; s-5, alkali liquor; s-6, alkali liquor to be regenerated; s-7, a carbon four absorbent; s-8, dry gas; s-9, mixing carbon two; s-10, propylene products; s-11, propane product; s-12, heavy gasoline products; s-13, preparing a carbon four product; s-14, light gasoline product.

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

Example 1

The device for oil gas desulfurization and light hydrocarbon recovery comprises:

the system comprises an oil gas feeding pipeline, a gas-liquid separation tank I1, a compressor I2, a gasoline cutting tower 3, a compressor II 4, a cooler I5, a gas-liquid separation tank II 6, a rich gas desulfurization tower 9, a rich gas alkaline washing tower 10, a liquid hydrocarbon desulfurization tower 7, a liquid hydrocarbon sweetening reactor 8, a compressor III 11, a cooler II 12, an after cooler 13, a feeding tank 14, an absorption tower 15, a demethanizer 16, a deethanizer 17, a depropanizer 18 and a propylene rectifying tower 19; an absorbent recovery column 21 and a debutanizer column 22;

the oil-gas feeding pipeline is connected with an inlet of a gas-liquid separation tank I1, the top of the gas-liquid separation tank I1 is sequentially connected with a compressor I2 and a gasoline cutting tower 3, and the bottom of the tank is connected with the gasoline cutting tower 3;

a reflux tank is arranged on the top of the gasoline cutting tower 3, the top of the reflux tank is sequentially connected with a compressor II 4, a cooler I5 and a gas-liquid separation tank II 6, the bottom of the tank is connected with a booster pump and then connected with a liquid hydrocarbon desulfurization tower 7, and a heavy gasoline extraction pipeline is arranged at the bottom of the gasoline cutting tower 3;

the top of the gas-liquid separation tank II 6 is sequentially connected with a rich gas desulfurization tower 9, a rich gas alkaline washing tower 10, a compressor III 11, a cooler II 12 and an after-cooler 13, and the bottom of the tank is connected with a booster pump and then connected with a liquid hydrocarbon desulfurization tower 7;

the liquid hydrocarbon desulfurizing tower 7 is connected with a liquid hydrocarbon sweetening reactor 8 and an after-cooler 13 in sequence;

the upper part of the rich gas desulfurization tower 9 is provided with a lean amine liquid feeding pipeline, and the upper part of the rich gas caustic wash tower 10 is provided with an alkali liquid feeding pipeline; the upper part of the liquid hydrocarbon desulfurizing tower 7 is provided with a lean amine liquid feeding pipeline;

the aftercooler 13 is connected with the feeding tank 14;

the top of the feed tank 14 is connected with the absorption tower 15, and the bottom of the feed tank is connected with the demethanizer 16;

the absorption tower 15 is provided with 2-5 middle-section refluxes, the tower top is connected with the absorbent recovery tower 21, the tower bottom is connected with the aftercooler 13, and the upper part of the absorption tower 15 is provided with a mixed C4/C5 absorbent feeding pipeline;

the top of the absorbent recovery tower 21 is provided with a dry gas extraction pipeline, the bottom of the absorbent recovery tower 21 is connected with a gasoline cutting tower 22, and the upper part of the absorbent recovery tower 21 is provided with a heavy gasoline absorbent feeding pipeline.

The top of the demethanizer 16 is connected with the aftercooler 13, the bottom of the demethanizer is connected with the deethanizer 17, and the bottom of the tower is provided with a reboiler;

a mixed C2 produced pipeline is arranged at the top of the deethanizer 17, a carbon dioxide treatment unit 20 is arranged on the mixed C2 produced pipeline, and the bottom of the deethanizer is connected with a depropanizer 18;

the upper part of the depropanizing tower 18 is connected with a propylene rectifying tower 19, 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, one branch is used as a mixed C4/C5 absorbent feeding pipeline, and the other branch is connected with the debutanizing tower;

the top of the propylene rectifying tower 19 is provided with a propylene product extraction pipeline, and the bottom of the tower is provided with a propane product extraction pipeline.

The upper part of the debutanizer 22 is provided with a C4 product extraction pipeline, and the bottom of the debutanizer is provided with a light gasoline extraction pipeline.

The oil gas desulfurization and light hydrocarbon recovery device does not comprise a dehydration device.

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

(1) first gas-liquid separation: oil gas from an upstream device is condensed and cooled and then sent to a gas-liquid separation tank I1 for gas-liquid separation, liquid phase at the bottom of the gas-liquid separation tank I1 is pressurized and sent to a gasoline cutting tower 3, and gas phase at the top of the tank is pressurized by a compressor and then sent to the gasoline cutting tower 3;

(2) gasoline cutting: the gas phase and the liquid phase from the step (1) enter a gasoline cutting tower 3, the gas phase distilled from the tower top enters a tower top reflux tank after being condensed, the gas phase (the specific composition is shown in table 3) at the top of the tower top reflux tank is compressed to 1.1-1.6 MPaG, the gas phase is sent to a gas-liquid separation tank II 6 after being cooled to 35-45 ℃, the liquid phase (the specific composition is shown in table 3) at the bottom of the tank is pressurized to 3.0-3.5 MPaG and then sent to a liquid phase impurity removal unit, and at least part of the liquid phase (the specific composition is shown in table 3) at the bottom of the gasoline cutting tower 3 is taken as a heavy gasoline product S-12; the operation temperature of the top of the gasoline cutting tower 3 is 60-85 ℃, and the operation pressure is 0.25-0.6 MPaG; the tower bottom operating temperature is 145-180 ℃;

(3) second gas phase separation: after the gas and liquid in the gas-liquid separation tank II 6 are balanced, the gas phase and the liquid phase are separated again, and then the materials are respectively sent to a gas phase impurity removal unit and a liquid phase impurity removal unit for impurity removal;

(4) gas-phase impurity removal: the gas phase on the top of the gas-liquid separation tank II 6 is sequentially subjected to H removal in a rich gas desulfurization tower 9 by taking lean amine liquid as an absorbent₂S and CO₂In the rich gas caustic tower 10, mercaptan is removed by taking alkali liquor as an absorbent, and then the rich gas caustic tower is pressurized and sent to a cooler II 12; wherein the operation temperature of the rich gas desulfurization tower 9 is 35-45 ℃, and the operation pressure is 1.1-1.6 MPaG; the operation temperature of the rich gas alkaline washing tower 10 is 35-45 ℃, and the operation pressure is 1.0-1.5 MPaG;

(5) liquid phase impurity removal: liquid-phase light hydrocarbon from the bottom of the reflux tank at the top of the gasoline cutting tower 3 and the gas-liquid separation tank II 6 is sequentially subjected to H removal in a liquid hydrocarbon desulfurization tower 7₂S and CO₂After mercaptan is removed in the liquid hydrocarbon mercaptan removal reactor 8, the liquid hydrocarbon mercaptan removed is sent to an aftercooler 13; wherein the operation temperature of the liquid hydrocarbon desulfurizing tower 7 is 35-45 ℃, and the operation pressure is 3.0-3.5 MPaG;

(6) and (3) cooling: the gaseous light hydrocarbon after impurity removal is primarily cooled in the cooler II 12 and then is sent to the after-cooler 13, and is mixed with the liquid light hydrocarbon in the after-cooler 13 and is sent to the feeding tank 14 after being cooled again;

(7) feeding: after the mixture flow from the after-cooler 13 is mixed, pre-absorbed and gas-liquid balanced in the feeding tank 14, the gas phase at the top of the tank is sent to the absorption tower 15, and the liquid phase at the bottom of the tank is sent to the demethanizer 16; wherein the operating temperature of the feeding tank 14 is 5-25 ℃, and the operating pressure is 2.2-2.8 MPaG;

(8) absorption: in the absorption tower 15, the mixed C4/C5 is used as an absorbent to absorb components with the content of C2 and above C2 in the gas phase from the tank top of the feed tank 14, and simultaneously, part of methane is absorbed, the gas phase at the tower top of the absorption tower 15 is sent to an absorbent recovery tower 21, and the liquid phase at the tower bottom is returned to the aftercooler 13; wherein the operation temperature of the absorption tower 15 is 5-25 ℃, the operation pressure is 2.1-2.7 MPaG, and the absorbent in the absorption tower 15 is a self-balancing mixed C4/C5 component in the system and does not need to be introduced from the outside of the system;

(9) separation:

demethanization: the liquid phase from the bottom of the feed tank 14 is subjected to methane removal in a demethanizer 16, and at the same time, a small part of components with the carbon number of 2 and the carbon number of more than 2 are removed, the gas phase at the top of the demethanizer 16 is sent to an aftercooler 13, and the liquid phase at the bottom of the demethanizer is sent to a deethanizer 17; wherein the operation temperature of the top of the demethanizer is 10-40 ℃, and the operation pressure is 2.3-2.9 MPaG;

deethanizing: separating C2 components from a liquid phase at the bottom of the demethanizer 16 in a deethanizer 17, extracting a mixed C2 component at the top of the separated tower as a mixed C2 product after the separated mixed C2 component passes through a carbon dioxide treatment unit 20, and distributing liquid phase components at the bottom of the tower, which are more than C3 and C3, to a depropanizer 18;

depropanizing: separating C3 component from liquid phase component at the bottom of the deethanizer 17 in the depropanizer 18, extracting the separated C3 component from the upper part of the depropanizer 18, sending part of the bottom component to the absorption tower 15 as mixed C4/C5 absorbent, and sending the rest to the debutanizer 22;

and (3) propylene rectification: c3 components extracted from the upper part of the depropanizing tower 18 are further rectified in a propylene rectifying tower 19, the gas phase at the top of the propylene rectifying tower 19 is cooled and extracted as a propylene product S-10, and the liquid phase at the bottom of the propylene rectifying tower is extracted as a propane product S-11, wherein the operating temperature of the propylene rectifying tower 18 is 45-60 ℃, and the operating pressure is 1.8-2.0 MPaG;

(10) light gasoline separation: the liquid phase component from the tower bottom of the depropanizer 18 further separates the C4 component in the debutanizer 22, the separated C4 component is extracted from the upper part of the debutanizer 22, and the tower bottom component is extracted as a light gasoline product S-14;

(11) and (3) recovering the absorbent: in the absorbent recovery tower 21, part of the heavy gasoline 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 15, and simultaneously absorbs a small amount of components of C2/C3, the gas phase at the top of the absorbent recovery tower 21 is extracted as dry gas S-8, and the liquid phase at the bottom of the absorbent recovery tower is returned to the gasoline cutting tower 3, wherein the operating temperature of the absorbent recovery tower is 5-25 ℃, and the operating pressure is 2.1-2.7 MPaG.

The composition and properties of the light and heavy gasoline, light hydrocarbon and other products separated from the oil gas by the method are shown in table 4, wherein the light and heavy gasoline is shown in table 5.

TABLE 3

Note: in the above table, PC represents a false component.

TABLE 4

TABLE 5

Example 2

The process flow chart shown in figure 1 is adopted for oil gas desulfurization and light hydrocarbon recovery.

The present embodiment differs from embodiment 1 in that:

the main components of the overhead distillate of the gasoline cutting tower comprise light hydrocarbon components of C1-C4 and alkane and olefin components of C5/C6, and mixed C4/C5/C6 is used as an absorbent in the absorption tower, wherein the main components of the distillate streams of the gasoline cutting tower are shown in a table 6, the components and properties of the separated products are shown in a table 7, and the properties of the extracted light and heavy gasoline products are shown in a table 8.

TABLE 6

Note: in the above table, PC represents a false component.

TABLE 7

TABLE 8

Example 3

the system comprises an oil gas feeding pipeline, a gas-liquid separation tank I1, a compressor I2, a gasoline cutting tower 3, a compressor II 4, a cooler I5, a gas-liquid separation tank II 6, a compressor IV 23, a cooler III 24, a gas-liquid separation tank III 25, a rich gas desulfurization tower 9, a rich gas alkaline washing tower 10, a liquid hydrocarbon desulfurization tower 7, a liquid hydrocarbon sweetening reactor 8, a cooler II 12, an after cooler 13, a feeding tank 14, an absorption tower 15, a demethanizer 16, a deethanizer 17, a depropanizer 18 and a propylene rectifying tower 19; an absorbent recovery column 21 and a debutanizer column 22;

the top of the gas-liquid separation tank II 6 is sequentially connected with a compressor IV 23, a cooler III 24 and a gas-liquid separation tank III 25, and the bottom of the tank is connected with a booster pump and then connected with a liquid hydrocarbon desulfurizing tower 7;

the top of the gas-liquid separation tank III 25 is sequentially connected with a rich gas desulfurization tower 9, a rich gas alkaline washing tower 10, a cooler II 12 and an after-cooler 13, and the bottom of the tank is connected with a booster pump and then connected with a liquid hydrocarbon desulfurization tower 7;

the aftercooler 13 is connected with the feeding tank 14;

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

(1) first gas-liquid separation: oil gas from an upstream device is condensed and cooled and then sent to a gas-liquid separation tank I1 for gas-liquid separation, a liquid phase at the bottom of the tank is pressurized and sent to a gasoline cutting tower 3, and a gas phase at the top of the tank is pressurized by a compressor and then sent to the gasoline cutting tower 3;

(2) gasoline cutting: the gas phase and the liquid phase from the step (1) enter a gasoline cutting tower 3, the gas phase distilled from the tower top enters a tower top reflux tank after being condensed, the gas phase (the specific composition is shown in table 9) at the top of the tower top reflux tank is compressed to 1.1-1.6 MPaG, the gas phase is sent to a gas-liquid separation tank II 6 after being cooled to 35-45 ℃, the liquid phase (the specific composition is shown in table 9) at the bottom of the tank is pressurized to 3.0-3.5 MPaG and then sent to a liquid phase impurity removal unit, and at least part of the liquid phase (the specific composition is shown in table 9) at the bottom of the gasoline cutting tower 3 is taken as a heavy gasoline product S-12; the operation temperature of the top of the gasoline cutting tower 3 is 60-85 ℃, and the operation pressure is 0.25-0.6 MPaG; the tower bottom operating temperature is 145-180 ℃;

(4) gas-phase impurity removal: after the gas phase at the top of the gas-liquid separation tank II 6 is sequentially pressurized by a compressor IV 23 and cooled by a cooler III 24, gas-liquid balance is carried out in a gas-liquid separation tank III 25, the gas phase at the top of the gas-liquid separation tank III 25 is sequentially subjected to H2S and CO2 removal by taking lean amine liquid as an absorbent in a rich gas desulfurization tower 9, mercaptan removal is carried out by taking alkali liquor as an absorbent in a rich gas caustic tower 10, then the gas phase is sent to a cooler II 12, and the gas phase at the bottom of the tank is sent to a liquid hydrocarbon desulfurization tower 7; wherein the operation temperature of the rich gas desulfurization tower 9 is 35-45 ℃, and the operation pressure is 2.3-2.9 MPaG; the operation temperature of the rich gas alkaline washing tower 10 is 35-45 ℃, and the operation pressure is 2.2-2.8 MPaG;

(9) separation:

The composition and properties of the light and heavy gasoline, light hydrocarbon and other products separated from the oil gas by the method are shown in table 10, wherein the light and heavy gasoline is shown in table 11.

TABLE 9

Watch 10

TABLE 11

Example 4

The process flow chart shown in fig. 3 is adopted for oil gas desulfurization and light hydrocarbon recovery, and the process flow chart is different from the process flow chart in example 1 in that:

(9) separation step

Demethanization: the liquid phase from the bottom of the feed tank 14 is subjected to methane removal in a demethanizer 16, and at the same time, a small part of components with the carbon number of 2 and the carbon number of more than 2 are removed, the gas phase at the top of the demethanizer 16 is sent to an aftercooler 13, and the liquid phase at the bottom of the demethanizer is sent to a depropanizer 18; wherein the top operating temperature of the demethanizer 16 is 10-40 ℃, and the operating pressure is 2.3-2.9 MPaG;

depropanizing: separating C3 components from the liquid phase components at the bottom of the demethanizer 16 in a depropanization 18 tower, taking out the separated C3 components from the upper part of the depropanization 18 tower, drying the components until the dew point is lower than minus 60 ℃, and sending the components to the deethanizer 17, wherein part of the components at the bottom of the tower is sent to an absorption tower 15 as a mixed C4/C5 absorbent, and the rest is sent to a debutanization tower 22;

deethanizing: the gas phase from the upper part of the depropanizing tower 18 is further separated in the depropanizing tower 17, a condenser at the top of the depropanizing tower is cooled by adopting a propylene refrigerant with the temperature of-25 ℃, the content of propylene in a mixed C2 product distilled from the top of the tower is lower, the separated mixed C2 component at the top of the tower is extracted as a mixed C2 product from the top of the depropanizing tower 17 after passing through a carbon dioxide treatment unit 20, and a tower bottom liquid is sent to a propylene rectifying tower;

and (3) propylene rectification: further rectifying the mixed C3 component extracted from the bottom of the deethanizer 17 in a propylene rectifying tower 19, cooling the gas phase at the top of the propylene rectifying tower 19, extracting the gas phase as a propylene product S-10, and extracting the liquid phase at the bottom of the propylene rectifying tower as a propane product S-11, wherein the operating temperature of the propylene rectifying tower 18 is 45-60 ℃, and the operating pressure is 1.8-2.0 MPaG;

the corresponding separation units are:

the top of the demethanizer 16 is connected with the aftercooler 13, the bottom of the demethanizer is connected with the depropanizer, and the bottom of the depropanizer is provided with a reboiler;

the upper part of the depropanizing tower is connected with the drying unit and then connected with the deethanizing tower, the bottom of the depropanizing tower is provided with a mixed C4/C5 extraction pipeline, the mixed C4/C5 extraction pipeline is divided into two branches, one branch is used as a mixed C4/C5 absorbent feeding pipeline, and the other branch is connected with the debutanizing tower;

a mixed C2 produced pipeline is arranged at the top of the deethanizer, a carbon dioxide treatment unit 20 is arranged on the mixed C2 produced pipeline, a mixed C3 produced pipeline is arranged at the bottom of the deethanizer, and the mixed C3 produced pipeline is connected with the propylene rectifying tower 19;

The composition and properties of the light and heavy gasoline, light hydrocarbon and other products separated from the oil gas by the method are shown in table 12, wherein the light and heavy gasoline is shown in table 13.

TABLE 12

Watch 13

The data in the table show that the process is simple, the operation condition is mild, the cold consumption is low, and the separation and recovery of light hydrocarbon in the catalytic cracking process can be realized by using less equipment, wherein the total recovery rate of the carbon two component is more than 98 wt%, the recovery rate of the carbon three component is more than 99 wt%, the content of methane in the recovered carbon two component is not more than 1 vol%, and the content of ethane in the recovered carbon three component is not more than 200 ppmv; meanwhile, the recovered carbon three components are further separated into propylene and propane, the recovery rate of the propylene and the propane can also reach more than 99 wt%, the recovered dry gas contains less impurities, the content of the components above C2 and C2 is not more than 2 vol%, and the purity of the hydrogen can reach more than 40 mol%. The initial boiling point of the produced heavy gasoline is 65-80 ℃, the heavy gasoline is mainly composed of six or more carbon components, the olefin content is low, the heavy gasoline mainly contains sulfides such as thiophene sulfur and the like, and the heavy gasoline can be sent to the downstream for desulfurization; the dry point of the light gasoline is 60-75 ℃, the light gasoline is mainly composed of C five or C five hexaalkane and olefin components, the olefin content of the light gasoline is high, the light gasoline mainly contains sulfides such as mercaptan and thioether, and the light gasoline can be sent to the downstream for further treatment.

The desulfurization and mercaptan removal effects of examples 1 and 3 were compared, and the results are shown in Table 14.

TABLE 14

As can be seen from Table 14, both the high-pressure desulfurization and sweetening and the low-pressure desulfurization and sweetening of the present invention can be used to remove H from light hydrocarbons₂S content of not more than 15ppmw, mercaptan sulfur content of not more than 20ppmw, CO₂The removal rate can reach 96 wt%; h in liquid-phase light hydrocarbon₂S content of 15ppmw, mercaptan sulfur content of not more than 20ppmw, CO₂The removal rate can reach 88 wt%.

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 oil gas desulfurization and light hydrocarbon recovery is characterized by comprising the following steps:

(4) gas-phase impurity removal: gas-liquid separationThe gas phase on the top of the tank separated by the tank II is subjected to pressurization and cooling optionally, and is subjected to gas-liquid balance in a gas-liquid separation tank III, and then the gas phase is subjected to H removal in a rich gas desulfurization tower by taking lean amine liquid as an absorbent₂S and CO₂Removing mercaptan in a rich gas alkaline tower by taking alkali liquor as an absorbent, and then sending the rich gas alkaline tower to a cooler after optionally boosting pressure;

(5) liquid phase impurity removal: the tank bottom liquid phases from the top reflux tank, the gas-liquid separation tank II and the optional gas-liquid separation tank III of the gasoline cutting tower are pressurized and then sequentially removed with H in the liquid hydrocarbon desulfurization tower₂S and CO₂After mercaptan is removed in the liquid hydrocarbon mercaptan removal reactor, the liquid hydrocarbon mercaptan removed is sent to a aftercooler;

(10) light gasoline separation: the liquid phase component from the bottom of the depropanizer is further separated from the mixed C4/C5 or C4/C5/C6 component in the debutanizer, the separated C4 component is extracted from the upper part of the debutanizer, and the bottom component is extracted as a light gasoline product.

2. The method of claim 1, wherein the separating step of step (9) comprises one of:

the first method is as follows: the separating step comprises:

preferably, the separating step further comprises:

the second method comprises the following steps:

preferably, the separating step further comprises:

3. The method of claim 1, further comprising:

(11) and (3) recovering the absorbent: in the absorbent recovery tower, part of the heavy gasoline 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, 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 the liquid phase at the bottom of the absorbent recovery tower is returned to the gasoline cutting tower.

4. The method of claim 1,

the dry point of the gas phase distilled from the top of the gasoline cutting tower is 60-75 ℃, and the initial boiling point of the heavy gasoline extracted from the bottom of the gasoline cutting tower is 65-80 ℃;

the operating temperature of the top of the gasoline cutting tower is 60-85 ℃, and the operating pressure is 0.25-0.6 MPaG; the tower bottom operating temperature is 145-180 ℃;

compressing the gas phase at the top of the reflux tank to 1.1-1.6 MPaG, cooling to 35-45 ℃, sending to a gas-liquid separation tank II, pressurizing the liquid phase at the bottom of the reflux tank to 3.0-3.5 MPaG, and sending to a liquid phase impurity removal unit;

the operation temperature of the rich gas desulfurization tower is 35-45 ℃, and the operation pressure is 1.1-2.9 MPaG;

the operation temperature of the rich gas alkaline washing tower is 35-45 ℃, and the operation pressure is 1.0-2.8 MPaG;

the rich gas at the outlet of the rich gas alkali washing tower is compressed to 2.3-2.9 MPaG;

the operating temperature of the liquid hydrocarbon desulfurization tower is 35-45 ℃, and the operating pressure is 3.0-3.5 MPaG;

the operating temperature of the feeding tank is 5-25 ℃, and the operating pressure is 2.2-2.8 MPaG;

the operation temperature of the absorption tower is 5-25 ℃, the operation pressure is 2.1-2.7 MPaG, and the absorbent in the absorption tower is a self-balancing mixed component C4/C5 or C4/C5/C6 in the system and does not need to be introduced from the outside of the system.

5. The method of claim 2,

the operation temperature of the top of the demethanizer is 10-40 ℃, and the operation pressure is 2.3-2.9 MPaG.

The operating temperature of the propylene rectifying tower is 45-60 ℃, and the operating pressure is 1.8-2.0 MPaG.

6. The method according to claim 3, wherein the operating temperature of the absorbent recovery tower is 5 to 25 ℃ and the operating pressure is 2.1 to 2.7 MPaG.

7. The utility model provides a device that oil gas desulfurization and lighter hydrocarbons were retrieved which characterized in that, the device includes: the system comprises an oil gas feeding pipeline, a gas-liquid separation tank I, a compressor I, a gasoline cutting tower, a compressor II, a cooler I, a gas-liquid separation tank II, a rich gas desulfurization tower, a rich gas alkaline tower, a liquid hydrocarbon desulfurization tower, a liquid hydrocarbon sweetening reactor, a compressor III, a cooler II, an after cooler, a feeding tank, an absorption tower, a demethanizer, a deethanizer, a depropanizer, a debutanizer and an optional compressor III, a compressor IV, a cooler III and a gas-liquid separation tank III;

the aftercooler is connected with the feeding tank;

8. The apparatus of claim 7,

or,

preferably, a propylene product extraction pipeline is arranged at the top of the propylene rectifying tower, and a propane product extraction pipeline is arranged at the bottom of the propylene rectifying tower.

9. The apparatus of claim 7, wherein the downstream apparatus further 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 gasoline cutting tower, and the upper part of the absorbent recovery tower is provided with a heavy gasoline absorbent feeding pipeline.

10. The apparatus of claim 7,

the absorption tower is provided with 2-5 middle-section refluxes;

a reboiler is arranged at the bottom of the demethanizer;

the apparatus does not include a dehydration apparatus.