CN112760120B

CN112760120B - Oil gas recovery method and device

Info

Publication number: CN112760120B
Application number: CN201911061380.9A
Authority: CN
Inventors: 黄孟旗; 余龙红; 吴雷; 江盛阳; 丁昱文; 吴迪
Original assignee: Sinopec Engineering Inc; Sinopec Engineering Group Co Ltd
Current assignee: Sinopec Engineering Inc; Sinopec Engineering Group Co Ltd
Priority date: 2019-11-01
Filing date: 2019-11-01
Publication date: 2022-04-15
Anticipated expiration: 2039-11-01
Also published as: CN112760120A

Abstract

The invention belongs to the field of chemical industry, and particularly discloses a method and a device for recovering oil gas, wherein the method has the advantages of simple process, mild operating conditions and low cold consumption, can realize the high-efficiency separation and recovery of gasoline, carbon two, carbon three and carbon four components by using less equipment, and particularly can realize the high-efficiency separation and recovery of the carbon two, the carbon three and the carbon four components; the invention adopts gas phase and liquid phase to desulfurize and desulfurize mercaptan respectively, and the gas phase desulfurizes and desulfurize mercaptan under high pressure, and the invention has smaller equipment volume, lower investment and good desulfurization effect.

Description

Oil gas recovery method and device

Technical Field

The invention belongs to the field of oil refining and chemical engineering, and particularly relates to a method and a device for recovering oil gas, in particular to a device and a method for recovering oil gas 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) components and realize the liquefied gas components 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. Generally, the carbon dioxide resource returned can be sent to an ethylene plant separation unit to obtain ethylene and ethane, and can also be sent to a downstream plant to prepare ethylbenzene/styrene. 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 stable gasoline as an absorbent to recover liquefied gas components, and the catalytic cracking process has the advantages that the yield of the liquefied gas components is high, 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.

(4) When the recovered carbon dioxide product is sent to an ethylene plant separation unit, part of heavy components such as propylene and the like in the carbon dioxide product can be recovered through the ethylene separation unit; however, when the recovered carbon dioxide product is sent to the downstream ethylbenzene production, the propylene component contained in the recovered carbon dioxide product can bring a plurality of adverse effects to the ethylbenzene production, and not only can the adverse effects be brought to the ethylbenzene productionGreatly increases the consumption of benzene and can directly influence the quality of ethylbenzene and styrene products. Due to the low boiling point of the carbon-two component, the separation of the carbon-two and carbon-three components usually requires temperatures of-5 to-20 ℃ to be reached, for which dehydration and CO removal are required₂The treatment is carried out, and a refrigerant with lower temperature grade is needed, so the investment and the energy consumption are large.

(5) 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.

The invention is provided for recovering light hydrocarbon components such as C2/C3/C4 and the like in a catalytic cracking process under mild operating conditions, simultaneously leading the recovered carbon two components to be basically free of propylene, simplifying a separation process and reducing investment and energy consumption.

Disclosure of Invention

The invention aims at providing a method and a device for recovering oil gas, which have simple process flow and mild operation conditions, and can realize the high-efficiency separation and recovery of stable gasoline, carbon two, carbon three and carbon four components; meanwhile, the gas phase and the liquid phase are respectively adopted for desulfurization and mercaptan removal, so that the desulfurization effect is better, and the operation is more flexible.

In order to achieve the above object, the present invention provides a method for oil and gas recovery, the method 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, a liquid phase at the bottom of the tank is pressurized and sent to a debutanizer, and a gas phase at the top of the tank is pressurized by a compressor 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 distilled from the tower top enters a tower top reflux tank after condensation, the gas phase at the top of the tower top reflux tank is sent to a gas-liquid separation tank II after compression and cooling, the liquid phase at the bottom of the tank is sent to the gas-liquid separation tank II after pressurization, and at least part of the liquid phase at the bottom of the debutanizer is taken as a stable gasoline product to be extracted;

(3) second gas phase separation: after the materials are mixed and gas-liquid balanced in the gas-liquid separation tank II, the gas phase and the liquid phase are separated again, and then impurities are respectively removed; simultaneously separating sulfur-containing sewage and sending the sulfur-containing sewage to sewage steam stripping;

(4) gas-phase impurity removal: the gas phase on the top of the gas-liquid separation tank II is sequentially subjected to H removal in a rich gas desulfurization tower by taking lean amine liquid as an absorbent₂S and CO₂In the gas-rich alkaline washing tower, alkali liquor is used to remove mercaptan and small amount of H₂S and CO₂Then sending the mixture to a cooler;

(5) liquid phase impurity removal: the liquid phase at the bottom of the tank separated by the gas-liquid separation tank II is sequentially subjected to H removal by lean amine liquid in a liquid hydrocarbon desulfurization tower₂S and CO₂In the liquid hydrocarbon sweetening reactor, alkali liquor is used to remove mercaptan and small quantity of H₂S and CO₂Then sending the mixture to a cooler;

(6) and (3) cooling: mixing and cooling the gaseous light hydrocarbon and the liquid light hydrocarbon which are subjected to impurity removal in a cooler, and then sending the mixture to a feeding tank;

(7) feeding: after the mixture flow from the cooler 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, the mixed C4 is used as an absorbent to absorb components with the content of C2 and above 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 a cooler;

(9) separation: the liquid phase from the bottom of the feeding tank is separated from light hydrocarbon in a separation unit, and the light hydrocarbon separation method comprises one of the following three modes:

the first method is as follows:

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

depropanization I: separating liquid phase components from the bottom of the demethanizer in a depropanizer I, sending a separated tower top gas phase to a deethanizer, sending at least one part of the tower bottom liquid phase to an absorption tower as a mixed C4 absorbent, and extracting the rest part of the tower bottom liquid phase as a C4 product;

deethanizing: the gas phase from the tower top of the depropanizing tower I is separated into C2 components in the depropanizing tower by taking propane as an absorbent, the separated mixed C2 component at the tower top is optionally subjected to impurity treatment and then extracted as a mixed C2 product, and the liquid phase at the tower bottom is sent to a depropanizing tower II for further separation;

depropanization II: the liquid phase from the bottom of the deethanizer is further separated in a depropanizer II, the separated gas phase at the top of the deethanizer is taken out as a C3 product, the liquid phase at the bottom of the deethanizer is taken out as a C4 product, or at least a part of the liquid phase is taken as a mixed C4 absorbent and sent to an absorption tower, and the rest is taken out as a C4 product;

the second method comprises the following steps:

deethanizing: the gas phase from the tower top of the depropanizing tower I is separated into C2 components in a deethanizing tower by taking mixed C4 as an absorbent, the separated mixed C2 components at the tower top are optionally subjected to impurity treatment and then extracted as a mixed C2 product, and the liquid phase at the tower bottom is sent to a depropanizing tower II for further separation;

depropanization II: further separating the liquid phase from the bottom of the deethanizer in a depropanizer II, extracting the separated gas phase at the top of the deethanizer as a C3 product, heating a part of the liquid phase at the bottom of the deethanizer, conveying the heated part of the liquid phase to the deethanizer and an optional absorption tower as a propane absorbent, and extracting the rest of the liquid phase as a C4 product;

the third method comprises the following steps:

depropanization I: separating liquid phase components from the bottom of the demethanizer in a depropanizing tower I, sending a gas phase at the top of the separated tower to a deethanizing tower, sending at least one part of the liquid phase at the bottom of the tower to an absorption tower as a mixed C4 absorbent, sending one part of the liquid phase as a mixed C4 absorbent to the deethanizing tower after cooling, and extracting the rest part of the liquid phase as a C4 product;

depropanization II: and further separating the liquid phase at the bottom of the deethanizer in a depropanizer II, taking the separated gas phase at the top of the deethanizer as a C3 product, taking the liquid phase at the bottom of the deethanizer as a C4 product, or taking at least one part of the liquid phase as a mixed C4 absorbent to an absorption tower, and taking the rest part of the liquid phase as a C4 product.

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 minor amounts of non-hydrocarbon components) can be recovered using the apparatus of the present invention.

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 debutanizer, a gas phase at the top of the tank is pressurized by a compressor and then sent to a gas-liquid separation tank II, wherein the compressor is divided into a plurality of sections. The method comprises the following steps that stable gasoline is separated from oil gas in a debutanizer, so that gasoline products are separated in advance, the gasoline products do not enter a downstream light hydrocarbon separation system, the heat of rich gas after two-stage compression is fully utilized, and the process energy consumption can be greatly reduced, wherein preferably, the operating temperature of the top of the debutanizer is 55-85 ℃, the operating temperature of the bottom of the debutanizer is 160-210 ℃, and the operating pressure is 1.0-1.35 MPaG; the initial boiling point of the stable gasoline is 30-45 ℃, and the saturated vapor pressure at 40 ℃ is 55-85 kPaA.

In the invention, in order to meet the requirement of related product recovery, impurity removal is required before next separation, and the impurity removal mainly comprises amine elution H₂S and CO₂And alkaline washing to remove mercaptan. Because the effects of gas phase desulfurization and mercaptan removal are better under high pressure, and the volume of desulfurization equipment under high pressure is smaller, the compressed gas phase in the gas-liquid separation tank II and the pressurized liquid phase are mixed and subjected to gas-liquid equilibrium, the gas phase and the liquid phase are separated again, and then impurities are respectively removed. Preferably, the operating temperature of the gas-liquid separation tank II is 35-45 ℃, and the operating pressure is 2.3-2.9 MPaG. After gas-liquid equilibrium is carried out again, because the content of heavy hydrocarbons (C3 and C4) in the separated gas phase is low, the amount of heavy hydrocarbons condensed into the amine liquid is low during desulfurization, the problems of amine liquid foaming and the like of a desulfurization unit can be effectively avoided, and the stable operation of the device is ensured.

In the present invention, in order to meet the requirements of the recovery of the relevant products, it is preferred that the amine in the gas phase and the liquid phase elute H₂S and CO₂All adopt a compound amine liquid solvent (namely a modified solvent based on MDEA) and carry out H simultaneously₂S and CO₂In which H is₂S can be removed to less than 10ppmw, CO₂The removal efficiency can reach 90-95 wt%, and CO in material flow entering the alkaline washing mercaptan removal reactor is effectively reduced₂And further reducing the consumption of alkali liquor. After amine washing, the gas phase and the liquid phase are sent to alkali washing to further remove impurities, and H can be removed₂S is removed to 1ppmw, mercaptan sulfur is removed to 10ppmw, and CO is removed₂Removing to 100-200 ppmw.

According to the invention, preferably, the operation temperature of the rich gas desulfurization tower is 35-45 ℃, and the operation pressure is 2.2-2.8 MPaG; the operating temperature of the liquid hydrocarbon desulfurization tower is 35-45 ℃, and the operating pressure is 3.0-3.5 MPaG.

In the invention, the gas-phase component and the liquid-phase component after impurity removal are cooled before being sent into the feeding tank, and the cooled liquid phase and the cooled and compressed gas phase are both sent into the feeding tank, preferably, the operating temperature of the feeding tank is 5-25 ℃, and the operating pressure is 2.2-2.8 MPaG.

According to the invention, the operation temperature of the absorption tower is preferably 5-25 ℃, and the operation pressure is preferably 2.1-2.7 MPaG. In the invention, the absorbent mixed with the C4 absorbent adopted by the absorption tower comes from the bottom of the depropanization tower, is a self-balanced C4 component in the system and does not need to be introduced from the outside of the system.

In the invention, a secondary depropanization process is adopted, the depropanization tower I adopts fuzzy separation, the separation precision requirement of the carbon three/carbon four components is reduced, and part of the carbon four components are separated to the tower top, so that the reflux ratio of the depropanization tower I can be reduced, thereby reducing the energy consumption; and meanwhile, heavy carbon four components mainly comprising n-butane and butene-2 (including maleic and fumaric) and light carbon four components mainly comprising isobutane, isobutene and butene-1 can be obtained from the bottoms of the depropanizing tower I and the depropanizing tower II respectively, wherein the heavy carbon four components can be mixed with the light carbon four components to be used as carbon four products or can be independently used, the heavy carbon four components can be sent to a downstream carbon four processing device for superposition and the like for utilization, and the light carbon four components can be sent to a downstream alkylation device for utilization.

When the deethanizer adopts a propane absorbent or a mixed C4 absorbent to separate C2 components, the separated C2 components basically do not carry propylene, and only contain 15-18 mol% of propane or 10-13 mol% of C4, at the moment, the lowest temperature at the top of the deethanizer is only 15 ℃, a refrigeration system and a drying facility with lower temperature level are not needed, and the conventional lithium bromide refrigeration can meet the requirements. Because the content of propylene in the C2 component is greatly reduced, the propylene can be directly sent to the preparation of ethylbenzene without arranging other impurity removal facilities, and preferably, the operation temperature at the top of the deethanizer is 15-30 ℃, and the operation pressure is 2.6-3.2 MPaG; the propane absorbent and/or mixed C4 absorbent comes from self-balancing propane and/or mixed C4 components in the system and does not need to be introduced from the outside of the system.

In the present invention, preferably, the separation in step (9) further includes rectification of propylene, and the separated mixed C3 component may be further rectified to obtain a propylene product and a propane product, and the separation mode includes one of the following two modes:

in the first mode:

and (3) propylene rectification: the gas phase from the top of the depropanizing tower II is further rectified in a propylene rectifying tower, the gas phase at the top of the propylene rectifying tower is cooled and then extracted as a propylene product, at least one part of the liquid phase at the bottom of the tower is extracted as a propane product, and the rest part of the liquid phase is heated and then sent to a deethanizing tower as a propane absorbent;

in the second and third modes:

and (3) propylene rectification: and (3) further rectifying the gas phase from the top of the depropanizing tower II in a propylene rectifying tower, cooling the gas phase at the top of the propylene rectifying tower, and then extracting the gas phase as a propylene product, wherein the liquid phase at the bottom of the propylene rectifying tower is extracted as a propane product.

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

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

(10) and (3) recovering the absorbent: in the absorbent recovery tower, a part of the stable gasoline product extracted in the step (2) 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, and simultaneously absorbs a small amount of components with the concentration of C2/C3, 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 debutanizer, further preferably, the operating temperature of the absorbent recovery tower is 15-40 ℃, and the operating pressure is 2.1-2.7 MPaG.

In another aspect, the present invention provides an apparatus for recovering oil and gas, the apparatus comprising: the system comprises an oil-gas feeding pipeline, a gas-liquid separation tank I, a compressor I, a debutanizer, a compressor II, a cooler I, a gas-liquid separation tank II, a rich gas desulfurization tower, a rich gas alkaline washing tower, a liquid hydrocarbon desulfurization tower, a liquid hydrocarbon sweetening reactor, a cooler II, a feeding tank, an absorption tower and a separation unit;

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 debutanizer, and the bottom of the tank is connected with the debutanizer;

a reflux tank is arranged at the top of the debutanizer, 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 debutanizer is connected with a booster pump and then connected with the gas-liquid separation tank II, and a stable gasoline extraction pipeline is arranged at the bottom of the debutanizer;

the top of the gas-liquid separation tank II is sequentially connected with a rich gas desulfurization tower, a rich gas alkaline washing tower and a cooler II, and the bottom of the tank is sequentially connected with a liquid hydrocarbon desulfurization tower, a liquid hydrocarbon sweetening reactor and the cooler II;

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 cooler II 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 a cooler II, and the upper part of the absorption tower is provided with a mixed C4 absorbent feeding pipeline;

the separation unit includes: a demethanizer, a deethanizer, a depropanizer I and a depropanizer II; the connection mode of the separation unit comprises one of the following three modes:

the first method is as follows:

the top of the demethanizer is connected with a cooler II, and the bottom of the demethanizer is connected with a depropanizer I;

the upper part of the depropanizing tower I is connected with a deethanizing tower, a mixed C4 product extraction pipeline is arranged at the bottom of the depropanizing 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 mixed C2 produced pipeline is arranged at the top of the deethanizer, an impurity treatment unit is optionally arranged on the mixed C2 produced pipeline, the bottom of the deethanizer is connected with a depropanizer II, and a propane absorbent feeding pipeline is arranged at the upper part of the deethanizer;

the top of the depropanizer II is provided with a C3 extraction pipeline, the bottom of the depropanizer II is provided with two extraction pipelines, one of the two extraction pipelines is connected with a mixed C4 absorbent feeding pipeline;

the second method comprises the following steps:

a mixed C2 produced pipeline is arranged at the top of the deethanizer, an impurity treatment unit is optionally arranged on the mixed C2 produced pipeline, the bottom of the deethanizer is connected with a depropanizer II, and a mixed carbon four absorbent feeding pipeline is arranged at the upper part of the deethanizer;

a C3 extraction pipeline is arranged at the top of the depropanizer II, three extraction pipelines are arranged at the bottom of the depropanizer II, one of the three extraction pipelines is connected with a mixed C4 absorbent feeding pipeline, and the other extraction pipeline is connected with a propane absorbent feeding pipeline;

the third method comprises the following steps:

the upper part of the depropanizing tower I is connected with a deethanizing tower, the bottom of the depropanizing tower I is provided with a mixed C4 product extraction pipeline, the mixed C4 product extraction pipeline is divided into three parts, one part is used as a mixed C4 absorbent feeding pipeline, the other part is connected with a mixed C4 absorbent feeding pipeline, and the other part is used as a mixed C4 extraction pipeline;

a mixed C2 produced pipeline is arranged at the top of the deethanizer, an impurity treatment unit is optionally arranged on the mixed C2 produced pipeline, the bottom of the deethanizer is connected with a depropanizer II, and a mixed C4 absorbent feeding pipeline is arranged at the upper part of the deethanizer;

and a C3 extraction pipeline is arranged at the top of the depropanizer II, two extraction pipelines are arranged at the bottom of the depropanizer II, and one of the two extraction pipelines is connected with a mixed C4 absorbent feeding pipeline.

According to the present invention, preferably, the separation unit further comprises a propylene rectification column; in the first connection mode, the top of the depropanizing tower II is connected with a propylene rectifying tower, a propylene product extraction pipeline is arranged at the top of the propylene rectifying tower, a propane product extraction pipeline is arranged at the bottom of the propylene rectifying tower, the propane product extraction pipeline is divided into two branches, and one branch is used as a propane absorbent feeding pipeline; in the second connection mode and the third connection mode, the top of the depropanizing tower II is connected with a propylene rectifying tower, 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 debutanizer, the upper part of the absorbent recovery tower is provided with a stabilized gasoline absorbent feeding pipeline, the bottom of the debutanizer is divided into two stabilized gasoline extraction pipelines, and one of the two stabilized gasoline extraction pipelines is used as the stabilized gasoline absorbent feeding pipeline.

In order to maintain the operating temperature of the whole tower uniform and ensure the absorption effect, the absorption tower is preferably 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, the gas phase from a feeding tank is fed from the bottom of the absorption tower, and the 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 apparatus does not include a dehydration apparatus.

According to the invention, the material at the tower bottom of the depropanizer I is mainly heavy four-carbon components such as n-butane, maleic and fumaric, the material at the tower bottom of the depropanizer II is mainly light four-carbon components such as isobutane, n-butene and isobutene, the two different carbon four components can be mixed to be used as a mixed four-carbon product, and can also be respectively used as four groups of heavy four-carbon components and light four-carbon components to be distributed to devices for superposition, alkylation and other four-carbon processing devices for further utilization according to downstream requirements. Therefore, the technical advantages of the present invention will be more apparent when the separation of four components of light carbon and heavy carbon is required.

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

(1) in the invention, the front-mounted debutanizer is adopted, components below C4 and C4 are firstly separated from gasoline components, and gasoline circulation is not required to absorb liquefied gas components, so that the gasoline circulation amount is greatly reduced, and the energy consumption of the whole separation process is reduced.

(2) The invention adopts a secondary depropanization process, the depropanization tower I adopts fuzzy separation, the separation precision requirement of the carbon three/carbon four components is reduced, and part of the carbon four components are separated to the tower top, so that the reflux ratio of the depropanization tower I can be reduced, thereby reducing the energy consumption; meanwhile, the heavy carbon four components and the light carbon four components can be respectively obtained at the bottoms of the depropanizing tower I and the depropanizing tower II, and comprehensive utilization of the carbon four components is facilitated.

(3) 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, particularly can realize the high-efficiency separation and recovery of C2, C3 and C4 components, and does not have a secondary separation process between carbon dioxide and each component; meanwhile, the total recovery rate of the carbon two components can be ensured to be more than 98 wt%, the recovery rate of the carbon three components can be more than 99 wt%, the content of methane in the recovered carbon two components is not more than 1 vol%, and the content of ethane in the recovered carbon three components is not more than 200 ppmw.

(4) The deethanizer of the invention adopts propane or mixed C4 absorbent to separate C2 component, the separated C2 component contains no propylene basically, and can be directly sent to a downstream device to prepare ethylbenzene/styrene, and the propane or mixed C4 absorbent is from the inside of the system, and does not need to be introduced from the outside of the system, thus saving energy consumption.

(5) The invention realizes the high-efficiency recovery of components such as carbon dioxide, propylene and the like under the condition of shallow cooling, and the recovered carbon dioxide product is basically free of propylene; the recovered carbon dioxide product can be directly sent to downstream ethylbenzene/styrene production, so that the energy consumption of the downstream ethylbenzene/styrene production can be reduced, the benzene consumption is reduced, and the quality of ethylbenzene and styrene products is ensured. Meanwhile, dehydration and CO removal are not needed under the condition of shallow cooling₂And the impurities and the refrigerant with lower temperature level are not needed, so that the investment and the consumption can be further reduced.

(6) The dry gas recovered from the top of the absorbent recovery tower has less impurities, the content of components with the concentration of C2 and more than C2 is not more than 2 vol%, the pressure of hydrogen is 1.9-3.4 MPa, the purity can reach 40-70 mol%, and the hydrogen resource can be directly recovered by a pressure swing adsorption method.

(7) The invention can respectively desulfurize the gas phase and the liquid phase and remove mercaptan, and the gas phase is desulfurized under higher pressure, so the equipment volume is smaller, the investment is lower, and the desulfurization effect is good; meanwhile, the content of heavy hydrocarbon in the gas phase is reduced, the heavy hydrocarbon can be prevented from being condensed into the amine liquid, foam entrainment of a desulfurization device caused by the foaming of the amine liquid can be effectively avoided, and the stable operation of the device is ensured.

(8) According to the invention, hydrogen sulfide and mercaptan are removed before entering the absorption tower, and cannot be brought to the light hydrocarbon recovery part, so that the problem of corrosion related to the light hydrocarbon recovery part caused by hydrogen sulfide is avoided, and meanwhile, the concentration of downstream hydrogen sulfide is greatly reduced, and the safety is improved. Because the hydrogen sulfide and the carbon dioxide are separated in advance, the load and the energy consumption of a light hydrocarbon recovery system are reduced, and simultaneously, because of CO₂Is removed, and the quality of the extracted product is 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 and gas recovery in example 1 of the present invention.

FIG. 2 shows a process flow diagram for oil and gas recovery in example 2 of the present invention.

FIG. 3 shows a process flow diagram for oil and gas recovery in example 3 of the present invention.

Description of reference numerals:

1. a gas-liquid separation tank I; 2. a first section of a compressor I; 3. a second section of the compressor I; 4. a debutanizer column; 5. a compressor II; 6. a cooler I; 7. a gas-liquid separation tank II; 8. a rich gas desulfurization tower; 9. a rich gas caustic wash tower; 10. a liquid hydrocarbon desulfurization tower; 11. a liquid hydrocarbon sweetening reactor; 12. a cooler II; 13. a feed tank; 14. an absorption tower; 15. a demethanizer; 16. a depropanizer I; 17. a deethanizer; 18. an impurity processing unit; 19. a depropanizer II; 20. a propylene rectification column; 21. an absorbent recovery column;

s1, oil gas; s2, lean amine liquid; s3, an amine-rich solution; s4, alkali liquor; s5, regenerating alkali liquor; s6, C4 absorbents; s7, refluxing propane; s8, dry gas; s9, mixing C2 product; s10, propylene products; s11, propane product; s12, stabilizing the gasoline product; s13, C4 products.

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 ℃ C.), g/cm³	0.753
D86 curve, v%	Temperature, C
		0	35.0
5	44.1
		10	52.0
30	73.0
		50	95.0
70	128.0
		90	177.0
95	188.7
		100	200.0

Example 1

The oil gas recovery device comprises:

the system comprises an oil gas feeding pipeline, a gas-liquid separation tank I1, a compressor I, a debutanizer 4, a compressor II 5, a cooler I6, a gas-liquid separation tank II 7, a rich gas desulfurization tower 8, a rich gas alkaline washing tower 9, a liquid hydrocarbon desulfurization tower 10, a liquid hydrocarbon sweetening reactor 11, a cooler II 12, a feeding tank 13, an absorption tower 14, a demethanizer 15, a depropanizer I16, a deethanizer 17, an impurity treatment unit 18, a depropanizer II 19, a propylene rectifying tower 20 and an absorbent recovery tower 21;

wherein, the oil gas feed line is connected with the inlet of a gas-liquid separation tank I1, the top of the gas-liquid separation tank I1 is connected with a compressor I and a debutanizer 4 in turn, and the bottom of the tank is connected with the debutanizer 4;

a reflux tank is arranged on the top of the debutanizer 4, the top of the reflux tank is sequentially connected with a compressor II 5, a cooler I6 and a gas-liquid separation tank II 7, the bottom of the tank is connected with a booster pump and then connected with the gas-liquid separation tank II 7, a stabilized gasoline extraction pipeline is arranged at the bottom of the debutanizer 4, the extraction pipeline is divided into two branches, and one branch is used as a stabilized gasoline absorbent feeding pipeline;

the top of the gas-liquid separation tank II 7 is sequentially connected with a rich gas desulfurization tower 8, a rich gas alkaline washing tower 9 and a cooler II 12, and the bottom of the tank is sequentially connected with a liquid hydrocarbon desulfurization tower 10, a liquid hydrocarbon sweetening reactor 11 and the cooler II 12;

the upper part of the rich gas desulfurization tower 8 is provided with a lean amine liquid feeding pipeline, and the upper part of the rich gas caustic wash tower 9 is provided with an alkali liquid feeding pipeline;

the cooler II 12 is connected with the feeding tank 13;

the top of the feeding tank 13 is connected with the absorption tower 14, and the bottom of the tank is connected with the demethanizer 15;

the top of the absorption tower 14 is connected with an absorbent recovery tower 21, the bottom of the absorption tower is connected with a cooler II 12, and the upper part of the absorption tower 14 is provided with a mixed C4 absorbent feeding pipeline;

the top of the demethanizer 15 is connected with a cooler II 12, and the bottom of the demethanizer is connected with a depropanizer I16;

the upper part of the depropanizing tower I16 is connected with a deethanizing tower 17, the bottom of the depropanizing tower I 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;

a mixed C2 produced pipeline is arranged at the top of the deethanizer 17, an impurity processing unit is arranged on the mixed C2 produced pipeline, the bottom of the deethanizer is connected with a depropanizer II 19, and a propane absorbent feeding pipeline is arranged at the upper part of the depropanizer II 19;

the top of the depropanizing tower II 19 is connected with the propylene rectifying tower 20, the bottom of the depropanizing tower II is provided with two extraction pipelines, one of which is connected with a mixed C4 absorbent feeding pipeline;

a propylene product extraction pipeline is arranged at the top of the propylene rectifying tower 20, a propane product extraction pipeline is arranged at the bottom of the propylene rectifying tower, the propane product extraction pipeline is divided into two branches, and one branch is used as a propane 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 the debutanizer 4, and the upper part of the absorbent recovery tower 21 is provided with a stable gasoline absorbent feeding pipeline.

The oil gas recovery is carried out by adopting the device, and the recovery 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, a liquid phase at the bottom of the tank is pressurized and sent to a debutanizer 4, and a gas phase at the top of the tank is pressurized by a compressor 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 distilled from the tower top enters a tower top reflux tank after condensation, the gas phase at the top of the tower top reflux tank is sent to a gas-liquid separation tank II 7 after compression and cooling, the liquid phase at the bottom of the tank is sent to the gas-liquid separation tank II 7 after pressurization, and at least part of the liquid phase at the bottom of the debutanizer 4 is taken as a stable gasoline product S12 to be extracted; the operation temperature of the top of the debutanizer 4 is 55-85 ℃, the operation temperature of the bottom of the debutanizer 4 is 160-210 ℃, and the operation pressure is 1.0-1.35 MPaG; the initial boiling point of the stable gasoline is 30-45 ℃, and the saturated vapor pressure at 40 ℃ is 55-85 kPaA;

(3) second gas phase separation: after the materials are mixed and gas-liquid balanced in the gas-liquid separation tank II 7, the gas phase and the liquid phase are separated again, and then impurities are respectively removed; the operating temperature of the gas-liquid separation tank II 7 is 35-45 ℃, and the operating pressure is 2.3-2.9 MPaG;

(4) gas-phase impurity removal: the gas phase on the top of the gas-liquid separation tank II 7 is sequentially subjected to H removal in a rich gas desulfurization tower 8 by taking lean amine liquid S2 as an absorbent₂S and CO₂Removing mercaptan from the gas-enriched caustic tower 9 by using alkali liquor S4 as an absorbent, and then sending the gas-enriched caustic tower to a cooler II 12; the operation temperature of the rich gas desulfurization tower 9 is 35-45 ℃, and the operation pressure is 2.2-2.8 MPaG;

(5) liquid phase impurity removal: the liquid phase at the bottom of the gas-liquid separation tank II 7 is sequentially subjected to H removal in a liquid hydrocarbon desulfurization tower 10 by adopting lean amine liquid S2₂S and CO₂Removing mercaptan in a liquid hydrocarbon mercaptan removal reactor 11 by adopting alkali liquor S4, and then sending the liquid hydrocarbon mercaptan removal reactor to a cooler II 12; the operating temperature of the liquid hydrocarbon desulfurization tower 10 is 35-45 ℃, and the operating pressure is 3.0-3.5 MPaG;

(6) and (3) cooling: the gaseous light hydrocarbon and the liquid light hydrocarbon after impurity removal are mixed and cooled in a cooler II 12 and then are sent to a feeding tank 13;

(7) feeding: after the mixture flow from the cooler II 12 is mixed, pre-absorbed and gas-liquid balanced in the feeding tank 13, the gas phase at the top of the tank is sent to the absorption tower 14, and the liquid phase at the bottom of the tank is sent to the demethanizer 15; the operating temperature of the feeding tank 13 is 5-25 ℃, and the operating pressure is 2.2-2.8 MPaG;

(8) absorption: in the absorption tower, the mixed C4 is used as an absorbent to absorb components with the carbon number of 2 and the carbon number of 2 and above in a gas phase from the top of the feed tank 13, and simultaneously, part of methane is absorbed, the gas phase at the top of the absorption tower 14 is sent to an absorbent recovery tower 21, and a liquid phase at the bottom of the absorption tower is returned to a cooler II 12; the operation temperature of the absorption tower 14 is 5-25 ℃, and the operation pressure is 2.1-2.7 MPaG;

(9) separation:

demethanization: removing methane from the liquid phase at the bottom of the feed tank 13 in a demethanizer 15, removing a small part of components with the carbon number of C2 and the carbon number of more than C2, cooling the gas phase at the top of the demethanizer 15, returning the gas phase to the feed tank 13, and sending the liquid phase at the bottom of the tower to a depropanizer I16;

depropanization I: separating liquid phase components from the bottom of the demethanizer 15 in a depropanizer I16, sending a separated tower top gas phase to a deethanizer 17, sending at least one part of the tower bottom liquid phase to an absorption tower 14 as a mixed C4 absorbent, and taking the rest as a C4 product S13;

deethanizing: the gas phase from the top of the depropanizing tower I16 is separated into C2 components in the depropanizing tower 17 by taking propane as an absorbent, the separated mixed C2 component at the top of the depropanizing tower is taken out as a mixed C2 product S9 after being subjected to impurity treatment, and the liquid phase at the bottom of the depropanizing tower II 19 is sent to be further separated; the operation temperature at the top of the deethanizer 17 is 15-30 ℃, and the operation pressure is 2.6-3.2 MPaG;

depropanization II: the liquid phase from the bottom of the deethanizer 17 is further separated in a depropanizer II 19, the separated gas phase at the top of the tower is sent to a propylene rectifying tower 20, and the liquid phase at the bottom of the tower is all extracted as a C4 product S13;

and (3) propylene rectification: the gas phase from the top of the depropanizing tower II 19 is further rectified in a propylene rectifying tower 20, the gas phase at the top of the propylene rectifying tower 20 is cooled and then taken out as a propylene product S10, at least one part of the liquid phase at the bottom of the tower is taken out as a propane product S11, and the rest part of the liquid phase is cooled and then sent to a deethanizing tower 17 as a propane absorbent; the operating temperature of the propylene rectifying tower 20 is 45-60 ℃, and the operating pressure is 1.8-2.0 MPaG;

(10) and (3) recovering the absorbent: in the absorbent recovery tower 21, a part of the stabilized gasoline product S12 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 14, and simultaneously absorbs a small amount of C2/C3 components, the gas phase at the top of the absorbent recovery tower 21 is extracted as dry gas S8, and a liquid phase at the bottom of the tower is returned to the debutanizer 4; wherein the operating pressure of the absorbent recovery tower is 2.1-2.7 MPaG at 15-40 ℃.

In this example, the four carbon components were separated into four light carbon components and four heavy carbon components, and there was no mixing between the four light carbon components and the four heavy carbon components. Wherein, the compositions and the flow rates of the recovered products are shown in the following tables 3 and 4:

TABLE 3

TABLE 4

Example 2

The oil gas recovery process flow shown in fig. 2 is different from the process flow of example 1 in that: in the separation step, demethanization: removing methane from the liquid phase at the bottom of the feed tank 13 in a demethanizer 15, removing a small part of components with the carbon number of C2 and the carbon number of more than C2, cooling the gas phase at the top of the demethanizer 15, returning the gas phase to the feed tank 13, and sending the liquid phase at the bottom of the tower to a depropanizer I16;

deethanizing: the gas phase from the top of the depropanizing tower I16 is separated into C2 components in the depropanizing tower 17 by taking mixed C4 as an absorbent, the separated mixed C2 components at the top of the depropanizing tower are treated by impurities and then extracted as a mixed C2 product S9, and the liquid phase at the bottom of the depropanizing tower II 19 is sent to be further separated; the operation temperature at the top of the deethanizer 17 is 15-30 ℃, and the operation pressure is 2.6-3.2 MPaG;

depropanization II: further separating the liquid phase at the bottom of the deethanizer 17 in a depropanizer II 19, sending the separated gas phase at the top of the tower to a propylene rectifying tower 20, cooling a part of the liquid phase at the bottom of the tower, sending the cooled liquid phase as an absorbent to the deethanizer 17, and extracting the rest of the liquid phase as a C4 product S13;

and (3) propylene rectification: the gas phase from the top of the depropanizing tower II 19 is further rectified in a propylene rectifying tower 20, the gas phase at the top of the propylene rectifying tower 20 is cooled and then taken out as a propylene product S10, and the liquid phase at the bottom of the tower is taken out as a propane product S11; the operating temperature of the propylene rectifying tower 20 is 45-60 ℃, and the operating pressure is 1.8-2.0 MPaG.

In this embodiment, the four carbon components are separated into four light carbon components and four heavy carbon components, and the four light carbon components and the four heavy carbon components are mixed, so that only one mixed four carbon product is obtained. The composition, flow rate and properties of each recovered product are shown in tables 5 and 6.

TABLE 5

TABLE 6

Item	Numerical value
		Density (20 ℃ C.), g/cm³	0.7538
D86 curve, v%	Temperature, C
		0	35.1
5	44.3
		10	52.0
30	72.5
		50	96.0
70	127.6
		90	177.0
95	188.7
		100	199.7

Example 3

The oil gas is recovered by adopting the process flow shown in figure 3, which is different from the process flow in the embodiment 1 in that: in the separation step, demethanization: removing methane from the liquid phase at the bottom of the feed tank 13 in a demethanizer 15, removing a small part of components with the carbon number of C2 and the carbon number of more than C2, cooling the gas phase at the top of the demethanizer 15, returning the gas phase to the feed tank 13, and sending the liquid phase at the bottom of the tower to a depropanizer I16;

depropanization I: separating liquid phase components from the bottom of the demethanizer 15 in a depropanizer I16, sending a separated tower top gas phase to a deethanizer 17, sending at least one part of the tower bottom liquid phase to an absorption tower 14 as a mixed C4 absorbent, sending one part of the tower bottom liquid phase to the deethanizer 17 as a mixed C4 absorbent after cooling, and collecting the rest part of the tower bottom liquid phase as a C4 product S13;

and (3) propylene rectification: the gas phase from the top of the depropanizing tower II 19 is further rectified in a propylene rectifying tower 20, the gas phase at the top of the propylene rectifying tower 20 is cooled and then taken out as a propylene product S10, and the liquid phase at the bottom of the tower is taken out as a propane product S11.

In this embodiment, the four carbon components are separated into four light carbon components and four heavy carbon components, and the four light carbon components and the four heavy carbon components are mixed, so that only one mixed four carbon product is obtained. Wherein the compositions, flow rates and properties of the recovered products are shown in tables 7 and 8

TABLE 7

TABLE 8

The data in the table show that the process is simple, the operation conditions are mild, the cold consumption is low, the separation and recovery of gasoline and light hydrocarbon in oil gas can be realized by using less equipment, particularly the high-efficiency recovery of components such as carbon dioxide and propylene under the shallow cold condition can be realized, and the recovered carbon dioxide product is basically free of propylene; and secondary separation process does not exist between the carbon two and each component, and meanwhile, the total recovery rate of the carbon two can be ensured to be more than 98 wt%, the recovery rate of the propylene component can be more than 99 wt%, the content of methane in the recovered carbon two is not more than 1 vol%, and the content of ethane in the recovered carbon three is not more than 200 ppmw; the recovered dry gas contains less impurities, the content of components of C2 and above C2 is not more than 2 vol%, and the purity of the hydrogen can reach above 40 mol%.

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 of oil and gas recovery, the method comprising:

(3) second gas phase separation: after the materials are mixed and gas-liquid balanced in the gas-liquid separation tank II, the gas phase and the liquid phase are separated again, and then impurities are respectively removed;

(4) gas-phase impurity removal: the gas phase on the top of the gas-liquid separation tank II is sequentially 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 washing tower by using alkali liquor, and then sending the rich gas alkaline washing tower to a cooler;

(5) liquid phase impurity removal: the liquid phase at the bottom of the tank separated by the gas-liquid separation tank II is sequentially subjected to H removal by lean amine liquid in a liquid hydrocarbon desulfurization tower₂S and CO₂Removing mercaptan in a liquid hydrocarbon mercaptan removal reactor by adopting alkali liquor, and then conveying the liquid hydrocarbon mercaptan removal reactor to a cooler;

the first method is as follows:

depropanization II: the liquid phase from the bottom of the deethanizer is further separated in a depropanizer II, the separated gas phase at the top of the deethanizer is taken out as a C3 product, the liquid phase at the bottom of the deethanizer is taken out as a C4 product, or a part of the liquid phase is taken as a mixed C4 absorbent and sent to an absorption tower, and the rest is taken as a C4 product;

and (3) propylene rectification: the gas phase from the top of the depropanizing tower II is further rectified in a propylene rectifying tower, the gas phase at the top of the propylene rectifying tower is cooled and then taken out as a propylene product, at least one part of the liquid phase at the bottom of the propylene rectifying tower is taken out as a propane product, and the rest part of the liquid phase is cooled and then taken as an absorbent to be sent to a deethanizing tower;

the second method comprises the following steps:

depropanization II: the liquid phase from the bottom of the deethanizer is further separated in a depropanizer II, the separated gas phase at the top of the tower is taken out as a C3 product, at least one part of the liquid phase at the bottom of the tower is heated and then sent to the deethanizer and an optional absorption tower as a propane absorbent, and the rest part is taken out as a C4 product;

and (3) propylene rectification: the gas phase from the top of the depropanizing tower II is further rectified in a propylene rectifying tower, the gas phase at the top of the propylene rectifying tower is cooled and then extracted as a propylene product, and the liquid phase at the bottom of the propylene rectifying tower is extracted as a propane product;

the third method comprises the following steps:

depropanization I: separating liquid phase components from the bottom of the demethanizer in a depropanizing tower I, sending a gas phase at the top of the separated tower to a deethanizing tower, sending at least one part of the liquid phase at the bottom of the tower to an absorption tower as a mixed C4 absorbent, sending one part of the liquid phase to the deethanizing tower as the absorbent after cooling, and extracting the rest of the liquid phase as a C4 product;

depropanization II: the liquid phase from the bottom of the deethanizer is further separated in a depropanizer II, the separated gas phase at the top of the deethanizer is taken out as a C3 product, the liquid phase at the bottom of the deethanizer is taken out as a C4 product or at least a part of the liquid phase is taken as a mixed C4 absorbent and sent to an absorption tower, and the rest part is taken as a C4 product;

(10) and (3) recovering the absorbent: in the absorbent recovery tower, a 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 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 debutanizer.

2. The method of claim 1,

the operation temperature of the top of the debutanizer is 55-85 ℃, the operation temperature of the bottom of the debutanizer is 160-210 ℃, and the operation pressure is 1.0-1.35 MPaG;

the initial boiling point of the stable gasoline is 30-45 ℃, and the saturated vapor pressure at 40 ℃ is 55-85 kPaA;

the operating temperature of the gas-liquid separation tank II is 35-45 ℃, and the operating pressure is 2.3-2.9 MPaG;

the operation temperature of the rich gas desulfurization tower is 35-45 ℃, and the operation pressure is 2.2-2.8 MPaG;

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

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 C4 component in the system and does not need to be introduced from the outside of the system;

the operation temperature at the top of the deethanizer is 15-30 ℃, and the operation pressure is 2.6-3.2 MPaG; the propane absorbent and/or mixed C4 absorbent comes from propane and/or mixed C4 components from self-balancing within the system, and does not need to be introduced from outside the system.

3. The method of claim 1,

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

4. The method of claim 1,

the operating pressure of the absorbent recovery tower is 2.1-2.7 MPaG at 15-40 ℃.

5. An apparatus for use in the method of any one of claims 1 to 4, the apparatus comprising: the system comprises an oil gas feeding pipeline, a gas-liquid separation tank I, a compressor I, a debutanizer, a compressor II, a cooler I, a gas-liquid separation tank II, a rich gas desulfurization tower, a rich gas alkaline washing tower, a liquid hydrocarbon desulfurization tower, a liquid hydrocarbon sweetening reactor, a cooler II, a feeding tank, an absorption tower, a separation unit and a propylene rectifying tower;

the cooler II is connected with the feeding tank;

the first method is as follows:

the top of the depropanization tower II is connected with the propylene rectifying tower, a propylene product extraction pipeline is arranged at the top of the propylene rectifying tower, a propane product extraction pipeline is arranged at the bottom of the propylene rectifying tower, the propane product extraction pipeline is divided into two branches, and one branch is used as a propane absorbent feeding pipeline;

the second method comprises the following steps:

the top of the depropanization tower II is connected with the propylene rectifying tower, 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;

the third method comprises the following steps:

the upper part of the depropanizing tower I is connected with a deethanizing tower, the bottom of the depropanizing tower I is provided with a mixed C4 product extraction pipeline, the mixed C4 product extraction pipeline is divided into three parts, one part is connected with a mixed C4 absorbent feeding pipeline of the absorption tower, the other part is connected with a mixed C4 absorbent feeding pipeline of the deethanizing tower, and the other part is used as a C4 product extraction pipeline;

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 debutanizer, the upper part of the absorbent recovery tower is provided with a stabilized gasoline absorbent feeding pipeline, the bottom of the debutanizer is divided into two stabilized gasoline extraction pipelines, and one of the two stabilized gasoline extraction pipelines is used as the stabilized gasoline absorbent feeding pipeline.

6. The apparatus of claim 5,

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

the top of the demethanizer is not provided with a condenser, and the bottom of the demethanizer is provided with a reboiler;

the apparatus does not include a dehydration apparatus.