CN111394120B

CN111394120B - Light hydrocarbon recovery method and device

Info

Publication number: CN111394120B
Application number: CN201910882196.4A
Authority: CN
Inventors: 黄孟旗; 吴迪; 郝少博; 姚爱智; 刘凯祥
Original assignee: Sinopec Engineering Inc; Sinopec Engineering Group Co Ltd
Current assignee: Sinopec Engineering Inc; Sinopec Engineering Group Co Ltd
Priority date: 2019-09-18
Filing date: 2019-09-18
Publication date: 2022-02-22
Anticipated expiration: 2039-09-18
Also published as: CN111394120A

Abstract

The invention belongs to the field of oil refining and chemical engineering, and particularly discloses a light hydrocarbon recovery method and a light hydrocarbon recovery device, wherein the method has the advantages of simple process, mild operating conditions and low cold consumption, can realize the separation and recovery of light hydrocarbons in a hydrocracking process by using less equipment, and particularly can realize the high-efficiency separation and recovery of four components of ethane, propane and carbon, wherein the ethane recovery rate reaches more than 97 wt%, the propane recovery rate reaches more than 98 wt%, the methane content in the recovered ethane is not more than 1 vol%, and the ethane content in the recovered propane is not more than 300 ppmv.

Description

Light hydrocarbon recovery method and device

Technical Field

The invention belongs to the field of oil refining and chemical engineering, and particularly relates to a light hydrocarbon recovery method and a light hydrocarbon recovery device, and particularly relates to a light hydrocarbon recovery device and a light hydrocarbon recovery method in a hydrocracking process.

Background

Hydrocracking is one of the main processing technologies in refineries, and the heavy distillate oil such as wax oil is subjected to a series of reactions such as hydrotreating and hydrocracking under the action of a catalyst under high pressure and hydrogen atmosphere to achieve the purpose of heavy oil lightening. Hydrocracking can produce a certain amount of C1-C4 light hydrocarbons, the yield is about 3-8 wt%, the light hydrocarbons are recovered by a conventional hydrocracking device mainly for recovering components of liquefied gas (C3/C4), the process is set perfectly, and a debutanizer, an absorption desorption tower, a stabilizer, a dry gas desulfurization tower, a liquefied gas desulfurization tower and the like are mainly arranged. A dephlegmator is usually adopted at the top of a debutanizer of a hydrocracking device, oil gas produced at the top of the tower enters a reflux tank after being condensed and cooled, a separated gas phase is sent to an absorption desorption tower, a part of a separated liquid phase is refluxed, and the rest part of the separated liquid phase is also sent to the absorption desorption tower. And (3) sending the liquid phase at the bottom of the debutanizer to a fractionating tower, and sequentially separating naphtha, diesel oil and tail oil.

The prior hydrocracking 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). Since the hydrocracking process yields the C2 component in a low yield and the C2 is all ethane, without ethylene, recovery of the C2 component is of less concern. In recent years, due to the trend of integration of oil refining and chemical engineering, the scale of a hydrocracking apparatus has been increased, the amount of ethane produced has also increased, and ethane is a high-quality ethylene feedstock, and comprehensive utilization thereof has been drawing attention. The scale of relevant process units such as reforming, aromatics and residue hydrogenation is increasing, and the amount of light hydrocarbons (C1-C4 saturated hydrocarbons) produced is also increasing. In addition, refineries such as light hydrocarbon under normal pressure and reduced pressure, PSA tail gas and the like also contain a large amount of ethane components. For ethane recovery, it is mainly necessary to save the separation between ethane and methane.

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 for light hydrocarbon separation process, and the development of light hydrocarbon separation process technology and the design of process flow are all performed around the separation of methane.

For the existing light hydrocarbon recovery process technology, the C3/C4 component is generally recovered firstly, and then the C2 component is recovered, the flow is long, secondary separation exists among the components, the investment and energy consumption are high, and the operation is complex.

In order to recover light hydrocarbon components such as C2/C3/C4 and the like in gases generated by a hydrocracking process, reforming, aromatic hydrocarbon, residual oil hydrogenation and normal and vacuum pressure, and simultaneously realize H₂S and other impurities are removed, the separation process is simplified, and the investment and the energy consumption are reduced.

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 carbon two, carbon three and carbon four components of saturated light hydrocarbon components in hydrocracking process and reforming, aromatic hydrocarbon, residual oil hydrogenation, atmospheric and vacuum processes and the like, simultaneously has less impurities in recovered dry gas, and can directly recover hydrogen by a pressure swing adsorption method.

In order to achieve the above object, an aspect of the present invention provides a method for recovering light hydrocarbons, comprising:

(1) removing butane: sending hot low-fraction oil and/or cold low-fraction oil from a hydrocracking device to a debutanizer for separation, sending a liquid phase at the bottom of the debutanizer to a fractionating tower for further separation of naphtha, diesel oil and tail oil, condensing a gas phase at the top of the tower through a condenser, and sending the gas phase at the top of the tower to a reflux tank, and respectively removing impurities from the gas phase at the top of the reflux tank and the liquid phase at the bottom of the reflux tank;

(2) low-pressure gas phase impurity removal: the gas phase on the top of the tank separated by the reflux tank is subjected to H removal in a rich gas desulfurization tower by taking lean amine liquid as an absorbent₂S and CO₂Then the mixture is compressed and cooled and then is sent to a gas-liquid separation tank;

(3) liquid phase impurity removal: removing H from the liquid phase at the bottom of the reflux tank in a liquid hydrocarbon desulfurizing tower₂S and CO₂Then the mixture is cooled and sent to a gas-liquid separation tank;

(4) gas-liquid separation: after the gas-phase light hydrocarbon and the liquid-phase light hydrocarbon subjected to impurity removal are mixed again in the gas-liquid separation tank, pre-absorbed and gas-liquid balanced, the separated gas phase and liquid phase are respectively sent to the absorption tower and the separation unit;

(5) absorption: in the absorption tower, 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 the gas-liquid separation tank, and simultaneously, part of methane is absorbed together, 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 returns to the gas-liquid separation tank after being cooled;

(6) separation: and the liquid phase from the bottom of the gas-liquid separation tank is further separated into C2, C3 and C4 components in a separation unit through a demethanizer, a deethanizer, a depropanizer I and optional depropanizer II and an isobutane tower, wherein at least part of the separated C4 components are sent to an absorption tower as a mixed C4 absorbent, and the rest is extracted as a C4 product.

According to the present invention, preferably, the light hydrocarbon recovery process further comprises:

(7) and (3) recovering the absorbent: in the absorbent recovery tower, at least part of the naphtha separated in the step (1) is used as an absorbent to recover components with the content of C4 and C4 or more in the gas phase from the top of the absorption tower, 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 absorption tower is returned to the debutanizer.

In the invention, the hot low-fraction oil and the cold low-fraction oil come from the bottom liquid phases of a hot low-pressure separator and a cold low-pressure separator in a hydrocracking reaction system respectively.

According to the invention, preferably, the operating temperature of the debutanizer is 50-80 ℃, and the operating pressure is 1.0-1.6 MPaG; the temperature of the return flow tank at the top of the debutanizer is 35-45 ℃.

In the invention, the bottom material flow of the debutanizer is sent to the fractionating tower to continuously fractionate naphtha, diesel oil and tail oil, and preferably, the initial boiling point of the separated naphtha absorbent is 25-40 ℃ and the dry point is 165-200 ℃.

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 H₂And S. In the invention, light hydrocarbon is divided into a gas phase and a liquid phase and then impurity removal is respectively carried out, preferably, the operating temperature of the rich gas desulfurization tower is 35-45 ℃, and the operating pressure is 0.9-1.5 MPaG; the operating temperature of the liquid hydrocarbon desulfurization tower is 35-45 ℃, and the operating pressure is 2.55-3.15 MPaG.

In the present invention, in order to meet the requirements of the recovery of the relevant products, the amine elution H₂S is preferably carried out in the presence of a complex amine liquid solvent (i.e., a modified MDEA-based solvent) while H is carried out₂S and CO₂In which H is₂S can be removed to less than 20ppmv, CO₂The removal efficiency can reach 90-95 wt%, and CO in the material flow is effectively reduced₂To further improve the purity of ethane component in the recovered light hydrocarbon and reduce CO brought into the cracking furnace of the ethylene unit₂Content and reduces alkali liquor consumption in alkali washing at the downstream of an ethylene unit.

In the invention, gas-phase light hydrocarbon subjected to impurity removal is subjected to pressure boosting and then is cooled and then is sent to a gas-liquid separation tank, and is mixed with liquid-phase light hydrocarbon which is directly sent to the gas-liquid separation tank after being cooled, preferably, the operating temperature of the gas-liquid separation tank is 5-25 ℃, and the operating pressure is 2.15-2.75 MPaG;

according to the invention, preferably, the operation pressure of the absorption tower is 2.1-2.7 MPaG, the operation temperature is 5-25 ℃, and the absorbent used in the absorption tower does not need to be introduced from the outside of the system and is a self-balanced C4 component in the system.

According to the present invention, preferably, the separation in step (6) comprises one of the following four ways:

in a first mode, the separating step sequentially includes:

demethanization: removing methane from the liquid phase at the bottom of the gas-liquid separation tank in a demethanizer, simultaneously removing a small part of components with the content of C2 and above C2, cooling the gas phase at the top of the demethanizer, returning the gas phase to the gas-liquid separation tank, 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, extracting the separated gas phase at the top of the deethanizer as an ethane product, and distributing the liquid phase components at the bottom of the deethanizer above C3 and C3 to a depropanizer I;

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

in a second mode, the separating step sequentially comprises:

demethanization: removing methane from the liquid phase at the bottom of the gas-liquid separation tank in a demethanizer, simultaneously removing a small part of components with the content of C2 and above C2, cooling the gas phase at the top of the demethanizer, returning the gas phase to the gas-liquid separation tank, and sending the liquid phase at the bottom of the demethanizer to an isobutane removal tower;

deisobutanizing: separating components below C3 and C3 from the liquid phase at the bottom of the demethanizer in a deisobutanizer, sending the separated gas phase at the top of the tower to the deethanizer, sending at least one part of the liquid phase at the bottom of the tower to an absorption tower as a mixed C4 absorbent, and extracting the rest part of the liquid phase as a n-butane product;

deethanizing: separating C2 component from the liquid phase at the bottom of the deisobutanizer in a deethanizer, taking the separated gas phase at the top of the deethanizer as an ethane product, and sending the liquid phase component at the bottom of the deethanizer to a depropanizer I;

depropanizing: further separating liquid phase components from the bottom of the deethanizer in the depropanizer I, extracting the separated propane product from the top of the depropanizer I, and extracting the liquid phase at the bottom of the depropanizer as an isobutane product;

in a third mode, the separating step sequentially comprises:

demethanization: removing methane from a liquid phase at the bottom of the gas-liquid separation 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 gas-liquid separation tank, and sending a liquid phase at the bottom of the demethanizer to a depropanizer I;

depropanizing: separating liquid phase components from the bottom of the demethanizer in a depropanizing tower I, extracting the separated components with the carbon number of 3 and the carbon number of less than 3 from the top of the depropanizing tower I, sending the extracted components to a deethanizing tower, sending at least one part of the tower bottom components to an absorption tower as a mixed C4 absorbent, and extracting the rest of the tower bottom components as a C4 product;

deethanizing: further separating the gas phase from the upper part of the depropanizing tower I in a deethanizing tower, and extracting the separated gas phase at the top of the tower as an ethane product and the liquid phase at the bottom of the tower as a propane product;

in a fourth mode, the separating step sequentially comprises:

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: separating the gas phase from the top of the depropanizing tower I in a deethanizing tower, taking the separated gas phase from the top of the depropanizing tower I as an ethane product, and sending the liquid phase at the bottom of the 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 overhead gas phase is taken out as a propane product, at least one part of the liquid phase at the bottom of the deethanizer is sent to the absorption tower as a mixed C4 absorbent, and the rest is taken out as a C4 product.

According to the invention, it is further preferable that the operation temperature at the top of the demethanizer is 15-40 ℃, and the operation pressure is 2.25-2.85 MPaG; the operation temperature at the top of the deethanizer is 10-40 ℃, and the operation pressure is 2.6-3.2 MPaG; the operation temperature of the top of the depropanizing tower I is 45-70 ℃, and the operation pressure is 1.4-2.0 MPaG; the operation temperature of the top of the depropanizing tower II is 45-65 ℃, and the operation pressure is 1.5-1.9 MPaG; the operation temperature of the top of the deisobutanizer is 45-65 ℃, and the operation pressure is 0.4-1.0 MPaG.

In the second method, the material flow without methane is sent to an isobutane removal tower, the absorbed ethane, propane and part of isobutane are separated, most of the n-butane component at the bottom of the tower is used as a supplementary absorbent and returns to the carbon dioxide absorption tower, and the rest is directly sent out as a product. The supplementary absorbent in the method is based on n-butane, so that the absorption effect of the carbon dioxide absorption tower can be ensured, and the content of the carbon four components in the dry gas at the top of the carbon dioxide absorption tower can be reduced. And because the scheme reduces the absorbed dose of the internal circulation of the system, the heat load of the bottom reboilers of the deethanizer and the depropanizer is further reduced, the scheme realizes the separation of isobutane and normal butane products, and also realizes the reduction of energy consumption.

In the third method, the material flow without methane is sent to a depropanizing tower, the absorbed ethane and propane components are separated, the material at the bottom of the tower is the carbon four components mainly comprising isobutane and normal butane, wherein most of the material is used as a supplementary absorbent and returns to the carbon dioxide absorption tower, and the rest of the material is directly sent out as a product. The scheme can reduce the absorption dosage of the circulation in the system, reduce the heat load of the reboiler at the bottom of the deethanizer and reduce the energy consumption.

In the fourth method, in order to further reduce the energy consumption, two depropanizing towers are adopted, the depropanizing tower I adopts fuzzy separation to separate ethane, propane and partial carbon four components firstly, most of the carbon four components at the tower bottom are used as supplementary absorbent to return to the carbon dioxide absorption tower, and the rest is directly delivered as a product. The scheme can not only reduce the absorbed dose of the internal circulation of the system, but also reduce the heat load of the reboiler at the bottom of the deethanizer and the depropanizer II and reduce the energy consumption. According to the scheme, the tower top temperature of the depropanizing tower I is increased, so that the tower top temperature of the depropanizing tower I is 45-65 ℃, and circulating water is adopted to meet the cooling requirement, so that the cold consumption of depropanizing tower I is reduced, and the purpose of reducing energy consumption is achieved.

Another aspect of the present invention provides a light hydrocarbon recovery device, comprising: the system comprises a hot/cold low oil separation feeding pipeline, a debutanizer, a fractionating tower, a rich gas desulfurization tower, a liquid hydrocarbon desulfurization tower, a compressor, a cooler, an after-cooler, a gas-liquid separation tank, an absorption tower and a separation unit;

wherein, the hot/cold low oil separation feed pipeline is connected with the debutanizer;

the debutanizer is provided with a condenser and a reflux tank, the bottom of the tower is connected with the fractionating tower, the top of the tower is sequentially connected with the condenser and the reflux tank, the top of the reflux tank is connected with the rich gas desulfurization tower, and the bottom of the reflux tank is connected with the liquid hydrocarbon desulfurization tower;

the top of the rich gas desulfurization tower is sequentially connected with a compressor, a cooler, an after cooler and a gas-liquid separation tank;

the top of the liquid hydrocarbon desulfurization tower is sequentially connected with an after cooler and a gas-liquid separation tank;

the top of the gas-liquid separation tank is connected with the absorption tower, and the bottom of the tank is connected with the separation unit;

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

the separation unit includes: a demethanizer, a deethanizer, a depropanizer I, and optionally a depropanizer II and a deisobutanizer; the separation unit is provided with two mixed C4 product extraction pipelines, wherein one pipeline is connected with a mixed C4 absorbent feeding pipeline.

According to the present invention, preferably, the separation unit includes the following four connection modes:

the first method is as follows:

the top of the demethanizer is sequentially connected with the aftercooler and the gas-liquid separation tank, and the bottom of the demethanizer is connected with the deethanizer;

an ethane extraction pipeline is arranged at the top of the deethanizer, and the bottom of the deethanizer is connected with the depropanizer I;

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

the second method comprises the following steps:

the top of the demethanizer is sequentially connected with the aftercooler and the gas-liquid separation tank, and the bottom of the demethanizer is connected with the deisobutanizer;

the top of the deisobutanizer is connected with the deethanizer, and the bottom of the deisobutanizer is provided with two extraction pipelines, wherein one of the two extraction pipelines is connected with a mixed C4 absorbent feeding pipeline, and the other extraction pipeline is used as a normal butane extraction pipeline;

a propane extraction pipeline is arranged at the top of the depropanizer I, and an isobutane extraction pipeline is arranged at the bottom of the depropanizer I;

the third method comprises the following steps:

the top of the demethanizer is sequentially connected with the aftercooler and the gas-liquid separation tank, and the bottom of the demethanizer is connected with the depropanizer I;

the top of the depropanizing tower I is connected with a deethanizing tower, the bottom of the depropanizing tower I is provided with two extraction pipelines, one of the two extraction pipelines is connected with a mixed C4 absorbent feeding pipeline, and the other extraction pipeline is used as a C4 product extraction pipeline;

an ethane extraction pipeline is arranged at the top of the deethanizer, and a propane extraction pipeline is arranged at the bottom of the deethanizer;

the method is as follows:

an ethane extraction pipeline is arranged at the top of the deethanizer, and the bottom of the deethanizer is connected with a depropanizer II;

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

According to the present invention, preferably, the downstream apparatus comprises an absorbent recovery column; a naphtha absorbent feeding pipeline is arranged at the upper part of the absorbent recovery tower, a dry gas extraction pipeline is arranged at the top of the tower, and the bottom of the tower is connected with a debutanizer; the top of the fractionating tower is provided with two naphtha extraction pipelines, and one of the two naphtha extraction pipelines is connected with a naphtha absorbent feeding pipeline.

According to the invention, preferably, 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 light hydrocarbon recovery device does not include a dehydration device.

The invention can treat light hydrocarbons of hydrocracking process, and saturated light hydrocarbons (mainly C1-C4 components) from related processes such as reforming, aromatic hydrocarbon hydrogenation, residual oil hydrogenation, atmospheric and vacuum processes and the like can also be sent to a proper position in the process of the invention for treatment, and the specific mixing position needs to be determined after optimization according to the pressure, composition, impurity content and the like of light hydrocarbons of other processes.

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

(1) in the invention, the separation of components below C4 and C4 and gasoline components is completed in the debutanizer, and the absorption of liquefied gas components by using gasoline as an absorbent is not required, and the secondary separation of components below C4 and C4 and gasoline components is also not required.

(2) The invention has simple flow, mild operation condition and low cold consumption, can realize the separation and recovery of saturated light hydrocarbon in the hydrocracking process and in the reforming, aromatic hydrocarbon, residual oil hydrogenation, atmospheric and vacuum processes and the like by using less equipment, particularly can realize the high-efficiency separation and recovery of ethane, propane and C4 components, can ensure that the ethane recovery rate reaches more than 97 wt%, the propane recovery rate reaches more than 98 wt%, the methane content in the recovered ethane is not more than 1 vol%, and the ethane content in the recovered propane is not more than 300 ppmv.

(3) By adopting the process, the optimal scheme from the first scheme to the fourth scheme can be adopted according to the composition and content of ethane, propane, isobutane and normal butane components in the light hydrocarbon to be treated, so that the investment and energy consumption are reduced.

(4) The absorbent used by the absorption tower is from the self-balanced C4 component in the system, and does not need to be introduced from the outside of the system, thereby reducing the process cost.

(5) The invention can further separate normal butane and isobutane.

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 light hydrocarbon recovery in example 1 of the present invention.

Figure 2 shows a process flow diagram for light hydrocarbon recovery in example 2 of the present invention.

FIG. 3 shows a process flow diagram for light hydrocarbon recovery in example 3 of the present invention.

FIG. 4 shows a process flow diagram for light hydrocarbon recovery in example 4 of the present invention.

Description of reference numerals:

1. a debutanizer column; 2. a fractionating column; 3. a rich gas desulfurization tower; 4. a liquid hydrocarbon desulfurization tower; 5. a compressor; 6. a cooler; 7. an aftercooler; 8. a gas-liquid separation tank; 9. an absorption tower; 10. a demethanizer; 11. a deethanizer; 12. a depropanizer I; 13. an absorbent recovery column; 14. an isobutane removal tower; 15. a depropanizer II;

s-1, cooling and separating oil; s-2, hot low oil separation; s-3, naphtha; s-4, diesel oil; s-5, tail oil; s-6, lean amine liquid; s-7, amine-rich liquid; s-8, a carbon four absorbent; s-9, dry gas; s-10, ethane production; s-11, propane product; s-12, C4 products; s-13, and producing isobutane; s-14 and a normal butane 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, the properties of the C5+ components in the oil and gas from the hydrocracking unit are shown in table 2, the properties of the composition of the extraneous light hydrocarbons are shown in table 3, and the location of incorporation of the extraneous light hydrocarbons is at the inlet of the compressor 5.

TABLE 1

TABLE 2

TABLE 3

Item	Numerical value
		Temperature of	45
Pressure MPaG	1.1
		Fraction of gasification	1
Flow rate kg/hr	125400
		Components	Composition by mass
H₂	0.0444
		CO₂	0.0007
CH₄	0.1711
		C₂H₆	0.3761
C₃H₈	0.2361
		IC₄H₁₀	0.0617
NC₄H₁₀	0.0430
		H₂S	0.0085
C₆H₆	0.0090
		IC5	0.0259
NC5	0.0235

Example 1

Light hydrocarbon recovery unit includes: the system comprises a hot/cold low oil separation feeding pipeline, a debutanizer 1, a fractionating tower 2, a rich gas desulfurizing tower 3, a liquid hydrocarbon desulfurizing tower 4, a compressor 5, a cooler 6, an after cooler 7, a gas-liquid separating tank 8, an absorption tower 9 and a separating unit;

wherein, the hot/cold low oil separation feed pipeline is connected with the debutanizer 1;

the debutanizer is provided with a condenser and a reflux tank, the bottom of the tower is connected with the fractionating tower 2, the top of the tower is sequentially connected with the condenser and the reflux tank, the top of the reflux tank is connected with a rich gas desulfurization tower 3, and the bottom of the reflux tank is connected with a liquid hydrocarbon desulfurization tower 4;

the top of the rich gas desulfurization tower 3 is sequentially connected with a compressor 5, a cooler 6, an after cooler 7 and a gas-liquid separation tank 8;

the top of the liquid hydrocarbon desulfurizing tower 4 is sequentially connected with an after-cooler 7 and a gas-liquid separating tank 8;

the top of the gas-liquid separation tank 8 is connected with the absorption tower 9, and the bottom of the tank is connected with the separation unit;

a mixed C4 absorbent feeding pipeline is arranged at the upper part of the absorption tower 9, the top of the absorption tower is connected with an absorbent recovery tower 13, and the bottom of the absorption tower is sequentially connected with the aftercooler 7 and the gas-liquid separation tank 8; 2-5 middle-section reflux is arranged in the absorption tower;

the top of the fractionating tower 2 is provided with two naphtha extraction pipelines, one of which is connected with a naphtha absorbent feeding pipeline; a naphtha absorbent feeding pipeline is arranged at the upper part of the absorbent recovery tower 13, a dry gas extraction pipeline is arranged at the top of the tower, and the bottom of the tower is connected with the debutanizer 1;

the separation unit includes: a demethanizer 10, a deethanizer 11 and a depropanizer I12;

the top of the demethanizer 10 is not provided with a condenser, the bottom of the demethanizer is provided with a reboiler, the top of the demethanizer 10 is sequentially connected with the aftercooler 7 and the gas-liquid separation tank 8, and the bottom of the demethanizer is connected with the deethanizer 11;

an ethane extraction pipeline is arranged at the top of the deethanizer 11, and the bottom of the deethanizer is connected with a depropanizer I12;

a propane extraction pipeline is arranged at the top of the depropanizer I12, two extraction pipelines are arranged at the bottom of the depropanizer I, one extraction pipeline is connected with a mixed C4 absorbent feeding pipeline, and the other extraction pipeline is a C4 extraction pipeline;

the light hydrocarbon recovery unit does not include a dehydration unit.

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

(1) removing butane: hot low-fraction oil and/or cold low-fraction oil from a hydrocracking device is sent to a debutanizer 1 for separation, a liquid phase at the bottom of the debutanizer 1 is sent to a fractionating tower 2 for further separation of naphtha, diesel oil and tail oil, a gas phase at the top of the tower is condensed by a condenser and then sent to a reflux tank, and the gas phase at the top of the reflux tank and the liquid phase at the bottom of the reflux tank are respectively subjected to impurity removal; the operation temperature at the top of the debutanizer 1 is 50-80 ℃, and the operation pressure is 1.0-1.6 MPaG; the temperature of the return tank at the top of the debutanizer is 35-45 ℃;

(2) low-pressure gas phase impurity removal: the gas phase on the top of the tank separated by the reflux tank is subjected to H removal in a rich gas desulfurizing tower 3 by taking lean amine liquid as an absorbent₂S and CO₂Then the mixture is compressed and cooled and then is sent to a gas-liquid separation tank 8; the operation temperature of the rich gas desulfurization tower 3 is 35-45 ℃, and the operation pressure is 0.9-1.5 MPaG;

(3) liquid phase impurity removal: the liquid phase at the bottom of the tank separated by the reflux tank is subjected to H removal in a liquid hydrocarbon desulfurization tower 4₂S and CO₂Then the mixture is cooled and sent to a gas-liquid separation tank 8; the operating temperature of the liquid hydrocarbon desulfurizing tower 4 is 35-45 ℃, and the operating pressure is 2.55-3.15 MPaG;

(4) gas-liquid separation: after the gas-phase light hydrocarbon and the liquid-phase light hydrocarbon subjected to impurity removal are mixed again in the gas-liquid separation tank 8, pre-absorbed and gas-liquid balanced, the separated gas phase and liquid phase are respectively sent to the absorption tower 9 and the separation unit; the operating temperature of the gas-liquid separation tank 8 is 35-45 ℃, and the operating pressure is 2.15-2.75 MPaG;

(5) absorption: in the absorption tower 9, the mixed C4 is used as an absorbent to absorb components with the content of C2 and above C2 in the gas phase from the top of the gas-liquid separation tank 8, and simultaneously, part of methane is absorbed together, the gas phase at the top of the absorption tower 9 is sent to a downstream device, and the liquid phase at the bottom of the absorption tower is cooled and then returns to the gas-liquid separation tank; the operating pressure of the absorption tower 9 is 2.1-2.7 MPaG, and the operating temperature is 5-25 ℃;

(6) separation:

demethanization: the liquid phase from the bottom of the gas-liquid separation tank 8 removes methane in the demethanizer 10, at the same time, a small part of components with the carbon number of 2 and more than 2 are removed, the gas phase at the top of the demethanizer 10 returns to the gas-liquid separation tank 8 after being cooled, and the liquid phase at the bottom of the tower is sent to the deethanizer 11; the operation temperature of the top of the demethanizer 10 is 15-40 ℃, and the operation pressure is 2.25-2.85 MPaG;

deethanizing: separating C2 components from the liquid phase at the bottom of the demethanizer 10 in a deethanizer, extracting the separated gas phase at the top of the deethanizer as an ethane product S-10, and distributing the liquid phase components at the bottom of the deethanizer above C3 and C3 to a depropanizer I12; the operation temperature at the top of the deethanizer 11 is 10-40 ℃, and the operation pressure is 2.6-3.2 MPaG;

depropanizing: further separating liquid phase components from the bottom of the deethanizer 11 in a depropanizer I12, extracting a separated propane product S-11 from the upper part of the depropanizer I12, sending at least one part of the bottom components to an absorption tower as a mixed C4 absorbent, and extracting the rest as a C4 product; the operation temperature of the tower top 12 of the depropanizer I is 45-70 ℃, and the operation pressure is 1.4-2.0 MPaG;

(7) and (3) recovering the absorbent: in the absorbent recovery column 13, the C4 and components of C4 or more in the gas phase from the top of the absorption column are recovered with at least a part of the naphtha S-3 separated in step (1) as an absorbent, the gas phase at the top of the absorbent recovery column 13 is withdrawn as a dry gas S-9, and the liquid phase at the bottom of the column is returned to the debutanizer 1.

The product compositions and properties of the dry gas, ethane, propane and C4 separated from the light hydrocarbons by the above process are shown in table 4.

TABLE 4

The composition and properties of the gasoline and diesel products obtained from the fractionator by the above process (no tail product is shown in this example) are shown in table 5.

TABLE 5

Example 2

The oil gas desulfurization and light hydrocarbon recovery are carried out by adopting the process flow chart shown in figure 2.

The present embodiment differs from embodiment 1 in that:

(6) separation:

demethanization: the liquid phase from the bottom of the gas-liquid separation tank 8 removes methane in the demethanizer 10, at the same time, a small part of components with the carbon number of 2 and more than 2 are removed, the gas phase at the top of the demethanizer 10 returns to the gas-liquid separation tank 8 after being cooled, and the liquid phase at the bottom of the tower is sent to the deisobutanizer 14; the operation temperature of the top of the demethanizer 10 is 15-40 ℃, and the operation pressure is 2.25-2.85 MPaG;

deisobutanizing: separating components below C3 and C3 from the liquid phase at the bottom of the demethanizer 10 in a deisobutanizer 14, sending the separated overhead gas phase to a deethanizer 11, sending at least one part of the liquid phase at the bottom of the tower to an absorption tower 9 as a mixed C4 absorbent, and extracting the rest part of the liquid phase as a n-butane product S-14; the operation temperature of the top of the deisobutanizer 14 is 45-65 ℃, and the operation pressure is 0.4-1.0 MPaG;

deethanizing: c2 components are separated from a liquid phase at the bottom of the deisobutanizer 14 in the deethanizer 11, a gas phase at the top of the separated tower is taken out as an ethane product S-10, and a liquid phase component at the bottom of the tower is sent to a depropanizer I12; the operation temperature at the top of the deethanizer 11 is 10-40 ℃, and the operation pressure is 2.6-3.2 MPaG;

depropanizing: liquid phase components from the bottom of the deethanizer 11 are further separated in the depropanizer I12, the separated propane product S-11 is extracted from the top of the depropanizer I12, and the liquid phase at the bottom of the depropanizer is extracted as an isobutane product S-13. The operation temperature of the top of the depropanizing tower I12 is 45-70 ℃, and the operation pressure is 1.4-2.0 MPaG.

Correspondingly, the separation unit comprises a demethanizer 10, a deisobutanizer 14, a deethanizer 11 and a depropanizer I12, and the specific connection mode is as follows:

the top of the demethanizer 10 is sequentially connected with an aftercooler 7 and a gas-liquid separation tank 8, and the bottom of the demethanizer is connected with an isobutane removal tower 14;

the top of the deisobutanizer 14 is connected with the deethanizer 11, the bottom of the deisobutanizer is provided with two extraction pipelines, one of which is connected with the mixed C4 absorbent feeding pipeline, and the other is used as a normal butane extraction pipeline;

the top of the depropanizer I12 is provided with a propane extraction pipeline, and the bottom of the depropanizer I12 is provided with an isobutane extraction pipeline.

The product compositions and properties of dry gas, ethane, propane, isobutane and C4 in the light hydrocarbons separated by the above method are shown in table 6.

TABLE 6

Example 3

The oil gas desulfurization and light hydrocarbon recovery are carried out by adopting the process flow chart shown in figure 3.

The present embodiment differs from embodiment 1 in that:

(6) separation:

demethanization: the liquid phase from the bottom of the gas-liquid separation tank 8 removes methane in the demethanizer 10, at the same time, a small part of components with the carbon number of 2 and more than 2 are removed, the gas phase at the top of the demethanizer 10 returns to the gas-liquid separation tank 8 after being cooled, and the liquid phase at the bottom of the tower is sent to a depropanizer I12; the operation temperature of the top of the demethanizer 10 is 15-40 ℃, and the operation pressure is 2.25-2.85 MPaG;

depropanizing: separating liquid phase components from the bottom of the demethanizer 10 in a depropanizer I12, collecting separated components with the C3 and the C3 or less from the top of the depropanizer I12, sending the separated components to a deethanizer 11, sending at least one part of the components at the bottom of the depropanizer to an absorption tower 9 as a mixed C4 absorbent, and collecting the rest of the components as a C4 product S-12; the operation temperature of the top of the depropanizing tower I12 is 45-70 ℃, and the operation pressure is 1.4-2.0 MPaG;

deethanizing: the gas phase from the upper part of the depropanizing tower I12 is further separated in the deethanizing tower 11, the separated gas phase at the top of the tower is taken out as an ethane product S-10, and the liquid phase at the bottom of the tower is taken out as a propane product S-10; the operation temperature at the top of the deethanizer 11 is 10-40 ℃, and the operation pressure is 2.6-3.2 MPaG.

Correspondingly, the separation unit comprises a demethanizer 10, a depropanizer I12 and a deethanizer 11, and the specific connection mode is as follows:

the top of the demethanizer 10 is sequentially connected with an after-cooler 7 and a gas-liquid separation tank 8, and the bottom of the demethanizer is connected with a depropanizer I12;

the top of the depropanizing tower I12 is connected with the deethanizing tower 11, the bottom of the depropanizing tower I12 is provided with two extraction pipelines, one of the two extraction pipelines is connected with a mixed C4 absorbent feeding pipeline, and the other extraction pipeline is used as a C4 product extraction pipeline;

an ethane extraction pipeline is arranged at the top of the deethanizer 11, and a propane extraction pipeline is arranged at the bottom of the deethanizer;

the product compositions and properties of the dry gas, ethane, propane and C4 separated out from the light hydrocarbons by the above process are shown in table 7.

TABLE 7

Example 4

The oil gas desulfurization and light hydrocarbon recovery are carried out by adopting the process flow chart shown in figure 4.

The present embodiment differs from embodiment 1 in that:

(6) separation:

depropanization I: separating liquid phase components from the bottom of the demethanizer 10 in a depropanizer I12, sending the separated tower top gas phase to a deethanizer 11, sending at least one part of the tower bottom liquid phase to an absorption tower 9 as a mixed C4 absorbent, and taking the rest part of the tower bottom liquid phase as a C4 product to obtain S-12; the operation temperature of the top of the depropanizing tower I12 is 45-60 ℃, and the operation pressure is 1.7-2.0 MPaG;

deethanizing: the gas phase from the top of the depropanizing tower I12 is separated in the deethanizing tower 11, the separated gas phase at the top of the depropanizing tower is taken out as an ethane product S-10, and the liquid phase at the bottom of the depropanizing tower II 15 is sent to be further separated; the operation temperature at the top of the deethanizer 11 is 10-40 ℃, and the operation pressure is 2.6-3.2 MPaG;

depropanization II: the liquid phase from the bottom of the deethanizer 11 is further separated in a depropanizer II 15, the separated gas phase at the top of the tower is taken out as a propane product S-11, at least one part of the liquid phase at the bottom of the tower is taken as a mixed C4 absorbent and sent to an absorption tower, and the rest part is taken out as a C4 product S-12; the operation temperature of the depropanizing tower II 15 is 50-65 ℃, and the operation pressure is 1.5-1.9 MPaG.

Correspondingly, the separation unit comprises a demethanizer 10, a depropanizer I12, a deethanizer 11 and a depropanizer II 15, and the specific connection mode is as follows:

an ethane extraction pipeline is arranged at the top of the deethanizer 11, and the bottom of the deethanizer is connected with a depropanizer II 15;

the top of the depropanizer II 15 is provided with a propane extraction pipeline, the bottom of the depropanizer II is provided with two extraction pipelines, one of which is connected with a mixed C4 absorbent feeding pipeline, and the other is used as a C4 product extraction pipeline.

The product compositions and properties of the dry gas, ethane, propane and C4 separated out from the light hydrocarbons by the above process are shown in table 8.

TABLE 8

The method has the advantages of simple process, mild operating conditions and low cold consumption, can realize the separation and recovery of saturated light hydrocarbon in the hydrocracking process and in the reforming, aromatic hydrocarbon, residual oil hydrogenation, atmospheric and vacuum processes and the like by using less equipment, particularly can realize the high-efficiency separation and recovery of ethane, propane and C4 components, can ensure that the ethane recovery rate reaches more than 97 wt%, the propane recovery rate reaches more than 98 wt%, the methane content in the recovered ethane is not more than 1 vol%, and the ethane content in the recovered propane is not more than 300 ppmv.

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

Claims

1. A light hydrocarbon recovery method is characterized by comprising the following steps:

(6) separation: c2, C3 and C4 components are further separated from a liquid phase from the bottom of the gas-liquid separation tank in a separation unit through a demethanizer, a deethanizer, a depropanizer I and optional depropanizer II and an isobutane tower, wherein at least part of the separated C4 components are sent to an absorption tower as a mixed C4 absorbent, and the rest is extracted as a C4 product;

(7) and (3) recovering the absorbent: recovering C4 and components of C4 or more in a gas phase from the top of the absorption tower by using at least part of the naphtha separated in the step (1) as an absorbent in an absorbent recovery tower;

the separation in step (6) includes one of the following four ways:

in a first mode, the separating step sequentially includes:

in a second mode, the separating step sequentially comprises:

in a third mode, the separating step sequentially comprises:

in a fourth mode, the separating step sequentially comprises:

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 propane product, at least one part of the liquid phase at the bottom of the tower is taken as a mixed C4 absorbent and sent to an absorption tower, and the rest part is taken out as a C4 product;

the operating temperature of the top of the demethanizer is 15-40 ℃, and the operating pressure is 2.25-2.85 MPaG;

the operation temperature of the top of the deethanizer is 10-40 ℃, and the operation pressure is 2.6-3.2 MPaG.

2. A light hydrocarbon recovery process as claimed in claim 1, wherein (7) the absorbent recovery further comprises: 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 returns to the debutanizer.

3. The light hydrocarbon recovery process of claim 1, wherein the debutanizer is operated at a temperature of 50 to 80 ℃ and at a pressure of 1.0 to 1.6 MPaG; the temperature of the return tank at the top of the debutanizer is 35-45 ℃;

the initial boiling point of the naphtha absorbent is 25-45 ℃, and the dry point is 165-200 ℃;

the operation temperature of the rich gas desulfurization tower is 35-45 ℃, and the operation pressure is 0.9-1.5 MPaG;

the operating temperature of the liquid hydrocarbon desulfurization tower is 35-45 ℃, and the operating pressure is 2.55-3.15 MPaG.

4. The light hydrocarbon recovery method of claim 1, wherein the gas-liquid separation tank has an operating temperature of 5 to 25 ℃ and an operating pressure of 2.15 to 2.75 MPaG; the operating pressure of the absorption tower is 2.1-2.7 MPaG, the operating temperature is 5-25 ℃, and the absorbent used in the absorption tower does not need to be introduced from the outside of the system.

5. A light hydrocarbon recovery process as claimed in claim 1,

the operation temperature of the top of the depropanizing tower I is 45-70 ℃, and the operation pressure is 1.4-2.0 MPaG;

the operation temperature of the top of the depropanizing tower II is 45-65 ℃, and the operation pressure is 1.5-1.9 MPaG;

the operation temperature of the top of the deisobutanizer is 45-65 ℃, and the operation pressure is 0.4-1.0 MPaG.

6. A light hydrocarbon recovery unit for use in the light hydrocarbon recovery process of any one of claims 1 to 5, wherein the light hydrocarbon recovery unit comprises: the system comprises a hot/cold low oil separation feeding pipeline, a debutanizer, a fractionating tower, a rich gas desulfurization tower, a liquid hydrocarbon desulfurization tower, a compressor, a cooler, an after-cooler, a gas-liquid separation tank, an absorption tower and a separation unit;

7. The light hydrocarbon recovery device of claim 6, wherein the separation unit comprises the following four connections:

the first method is as follows:

the second method comprises the following steps:

the third method comprises the following steps:

the method is as follows:

8. The light hydrocarbon recovery device of claim 6, wherein the downstream device comprises an absorbent recovery column; a naphtha absorbent feeding pipeline is arranged at the upper part of the absorbent recovery tower, a dry gas extraction pipeline is arranged at the top of the tower, and the bottom of the tower is connected with a debutanizer;

the top of the fractionating tower is provided with two naphtha extraction pipelines, and one of the two naphtha extraction pipelines is connected with a naphtha absorbent feeding pipeline.

9. A light hydrocarbon recovery device as claimed in claim 6,

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 light hydrocarbon recovery device does not include a dehydration device.