CN113755198A - Method for recovering carbon dioxide and heavier components in refinery dry gas, system and application thereof - Google Patents

Abstract

The invention relates to the field of gas organic matter recovery, and discloses a method for recovering carbon dioxide and heavier components in refinery dry gas, and a system and application thereof. The method comprises the following steps: compressing the light refinery dry gas; compressing the heavy refinery dry gas; cooling the compressed dry gas in the heavy refinery, and then carrying out gas-liquid phase separation to obtain a first gas phase and a first liquid phase; mixing the compressed dry gas of the light refinery with the first gas phase, compressing, cooling, feeding into the middle part of an absorption tower, carrying out countercurrent contact with an absorbent, feeding the second liquid phase obtained at the tower bottom of the absorption tower into the middle part of a desorption tower, carrying out desorption, feeding the crude concentrated gas obtained at the tower top of the desorption tower into the bottom of a decarbonization tower, contacting with a decarbonization agent, obtaining a third gas phase at the tower top of the decarbonization tower, and obtaining a third liquid phase at the tower bottom of the decarbonization tower; and combining the first liquid phase and the third gas phase to obtain concentrated gas. The method can simultaneously recover the carbon dioxide and heavier components in the dry gas of the light refinery and the dry gas of the heavy refinery, and can obviously reduce the energy consumption of a recovery system.

Description

Method for recovering carbon dioxide and heavier components in refinery dry gas, system and application thereof

Technical Field

The invention relates to the field of recovery of gas organic matters, in particular to a method and a system for recovering carbon dioxide and heavier components in refinery dry gas and application of the method or the system in recovery of the refinery dry gas.

Background

The refinery dry gas from the oil refining chemical plant, such as catalytic cracking dry gas, delayed coking dry gas, PSA (pressure swing adsorption) gas, hydrocracking dry gas, PX (para-xylene) disproportionation fuel gas, PX isomerization fuel gas, reforming dry gas and the like, usually contains more carbon dioxide and heavier components, and if the carbon dioxide and the heavier components in the dry gas are recovered and sent to an ethylene plant cracking furnace or a subsequent separation unit to be used as raw materials, the economic benefit is remarkable. The refinery dry gas represented by catalytic dry gas, coking dry gas, PSA desorption gas and the like has a large content of light components such as hydrogen, methane, nitrogen and the like, and has a carbon content of about 10-20% vol, which is hereinafter referred to as light refinery dry gas. The refinery dry gas represented by the cracking dry gas, the aromatic dry gas (including PX disproportionation fuel gas, PX isomerization fuel gas and the like) and the like has higher content of carbon two and above components, for example, the content of ethane in the PX disproportionation fuel gas can reach 25-70% vol when the molar content is higher, and the sum of the content of carbon two and the content of carbon three components in the hydrocracking dry gas can exceed 50% vol, which is hereinafter referred to as heavy refinery dry gas.

At present, methods for recovering carbon dioxide and heavier components from refinery dry gas mainly comprise a cryogenic separation method, a pressure swing adsorption method, a shallow cold oil absorption method and the like. The cryogenic separation method has mature process, high ethylene recovery rate and purity, but large investment, and higher energy consumption for recovering the dilute ethylene; the pressure swing adsorption method has simple operation, low energy consumption, low product purity, low ethylene recovery rate and large occupied area.

The shallow cold oil absorption method mainly separates gas mixture by utilizing different solubility of each component in the gas by an absorbent, generally firstly absorbs heavy components above C2 and C2 by the absorbent at shallow cold temperature (5-20 ℃), separates out non-condensable gas such as methane, hydrogen and the like, and then separates each component in the absorbent by a rectification method. The method has the characteristics of high recovery rate of C2C3, safe production, reliable operation, strong adaptability to raw material gas and the like, and is one of the existing competitive technologies. However, the conventional shallow cold oil absorption process does not generally distinguish raw material dry gas, and if the raw material contains light refinery dry gas and heavy refinery dry gas, the light refinery dry gas and the heavy refinery dry gas are mixed together and sent into the main absorption tower after being pressurized and cooled by the compressor. The carbon dioxide and heavier components in the heavy refinery dry gas are also subjected to an absorption-desorption process, and finally are sent out of the battery limit area from the top gas phase of the desorption tower or the extracted absorbent. In the process, the load of a main absorption tower and a desorption tower is large, and the steam consumption of a reboiler at the tower bottom is high.

CN101063048A discloses a method for separating refinery dry gas by adopting an intercooled oil absorption method, which comprises the steps of compression, acid gas removal, drying and purification, absorption, desorption, cold quantity recovery, rough separation and the like, and has the advantages of low absorbent cost, low loss and the like. However, the process needs to cool the dry gas to-30 ℃ to-40 ℃, which belongs to an intercooling separation process, so the investment is large and the energy consumption is high.

CN103087772A discloses a device and a method for separating dry gas by an oil absorption method, wherein the method comprises the steps of carbon four absorption, carbon four desorption, gasoline absorption and the like, and carbon four is used as an absorbent to recover carbon two and carbon three fractions in the dry gas. And recovering carbon four in the tail gas by adopting a gasoline absorbent. The process has high carbon recovery rate. When the dry raw gas contains both light refinery dry gas and heavy refinery dry gas, the two dry gases (possibly multiple strands of raw gas) need to be mixed at the inlet of a compressor or between sections, and the C2+ component in the heavy refinery dry gas is diluted and then sent to an absorption tower and a desorption tower for concentration. The carbon four absorption tower and the carbon four desorption tower have larger load and higher energy consumption.

CN106609161A discloses a method for separating refinery saturated dry gas, which comprises compressing refinery saturated dry gas, cooling, and separating gas from liquid, wherein the compressed dry gas and the compressed condensate after gas-liquid separation are respectively sent to a carbon four absorption tower for absorption or sent to a gasoline stabilizer for rectification. The process comprises a gasoline stabilizer used for treating the gasoline-rich solvent and the compressed condensate in the gasoline absorption tower kettle. When the raw dry gas contains both light refinery dry gas and heavy refinery dry gas, the two dry gases (possibly multiple) need to be mixed at the inlet or between the sections of the compressor. The C2+ component in the heavy refinery dry gas is diluted, so that the amount of compression condensate separated out after subsequent compression, cooling and phase separation is reduced. Most of C2+ components in the heavy refinery dry gas still enter the carbon four absorption tower and the desorption tower. The two towers have larger load and higher energy consumption.

CN104560194A discloses a refinery saturated dry gas recovery system and a recovery method, and the system comprises an absorption tower, a desorption tower, a reabsorption tower, a compressor and a heat exchanger, and is provided with a condensate stripper. And (3) delivering compressed condensate obtained after the refinery dry gas is compressed, cooled and separated into liquid to a condensate stripper for treatment, and discharging from the kettle of the condensate stripper to be extracted as a product. When the raw dry gas contains both light refinery dry gas and heavy refinery dry gas, the C2+ component in the heavy refinery dry gas is diluted, resulting in a reduced amount of compressed condensate entering the condensate stripper, and a lot of C2+ component in the heavy refinery dry gas still undergoes the carbon four absorption-desorption process. The absorption tower and the desorption tower have larger load and higher energy consumption.

In summary, when the raw dry gas contains both light refinery dry gas (containing less carbon dioxide and heavier components) and heavy refinery dry gas (containing more carbon dioxide and heavier components) during the recovery of the carbon dioxide and heavier components in the refinery dry gas, the conventional light cold oil absorption process mixes the light refinery dry gas and the heavy refinery dry gas in the gas compression stage, and most of the C2+ components in the heavy refinery dry gas are diluted and still undergo the subsequent absorption-desorption process. The reboiler load of the main absorption tower and the tower kettle of the desorption tower is increased, and the total energy consumption of the system is increased.

Disclosure of Invention

The invention aims to solve the problem of overhigh energy consumption caused by the mixing of light refinery dry gas and heavy refinery dry gas in the prior art, and provides a method for recovering carbon dioxide and heavier components in the refinery dry gas, a system and an application thereof.

In order to achieve the above object, a first aspect of the present invention provides a method for recovering carbon dioxide and heavier components from refinery dry gas, characterized in that the method comprises the steps of:

(1) compressing dry gas of a light refinery: compressing the dry gas of the light refinery;

(2) compressing dry gas in a heavy refinery: compressing the heavy refinery dry gas;

(3) cooling and phase splitting of dry gas in heavy refineries: cooling the compressed dry gas obtained in the step (2), and performing gas-liquid phase separation to obtain a first gas phase and a first liquid phase;

(4) cooling dry gas: mixing the light refinery compressed dry gas obtained in the step (1) with the first gas phase obtained in the step (3) to obtain mixed dry gas, and compressing and cooling the mixed dry gas;

(5) carbon four and carbon five absorption: feeding the cooled dry gas obtained in the step (4) into the middle part of an absorption tower, and carrying out countercurrent contact with an absorbent from the top of the absorption tower, so as to obtain a second gas phase at the tower top of the absorption tower and obtain a second liquid phase at the tower kettle of the absorption tower;

(6) desorbing: feeding the second liquid phase obtained in the step (5) into the middle part of a desorption tower for desorption, obtaining crude concentrated gas at the tower top of the desorption tower, and obtaining lean absorbent at the tower kettle of the desorption tower;

(7) decarbonization: feeding the crude extraction concentrated gas obtained in the step (6) into the bottom of a decarbonizing tower, contacting with a decarbonizing agent from the top of the decarbonizing tower, obtaining a third gas phase at the top of the decarbonizing tower, and obtaining a third liquid phase at the tower kettle of the decarbonizing tower;

and (3) combining the first liquid phase in the step (3) and the third gas phase in the step (7) to obtain concentrated gas.

In a second aspect, the present invention provides a system for recovering carbon dioxide and heavier components from refinery dry gas, the system comprising: the system comprises a first compressor section, a second compressor, a first cooler, a second cooler, a liquid separation tank, a compressor section tank, an absorption tower, a desorption tower and a decarbonization tower;

the first compressor section is used for compressing the dry gas of the light refinery and is communicated with the compressor section inter-tank;

the second compressor, the first cooler and the liquid separating tank are communicated in sequence and are used for compressing, cooling and gas-liquid phase separation of the dry gas of the heavy refinery;

the compressor section inter-tank is respectively communicated with the first compressor section and the top of the liquid separation tank and is used for mixing the light refinery compressed dry gas from the first compressor section and the first gas phase from the top of the liquid separation tank to obtain mixed dry gas;

the compressor section inter-tank, the first compressor section, the second cooler, the absorption tower, the desorption tower and the decarbonization tower are communicated in sequence;

the first compressor section and the second cooler are used for compressing and cooling the mixed dry gas from the top of the compressor section inter-tank;

the middle part of the absorption tower is communicated with a second cooler and is used for enabling the compressed mixed dry gas cooled by the second cooler to be in countercurrent contact with an absorbent, and a second gas phase and a second liquid phase are respectively discharged from the tower top and the tower kettle of the absorption tower;

the middle part of the desorption tower is communicated with the bottom of the absorption tower and is used for desorbing the second liquid phase discharged from the bottom of the absorption tower, the top of the desorption tower obtains crude concentrated gas, and the bottom of the desorption tower obtains lean absorbent;

the bottom of the decarbonizing tower is communicated with the top of the desorption tower and is used for enabling the crude extraction concentrated gas discharged from the top of the desorption tower to be in countercurrent contact with a decarbonizing agent, a third gas phase is obtained at the top of the decarbonizing tower, and a third liquid phase is obtained at the tower kettle of the decarbonizing tower;

and mixing the third gas phase with the first liquid phase from the bottom of the liquid separation tank to obtain concentrated gas.

In a third aspect, the present invention provides a use of the above method or system in refinery dry gas recovery.

Through the technical scheme, the method for recovering the carbon dioxide and heavier components in the refinery dry gas, the system and the application thereof provided by the invention have the following beneficial effects:

(1) in the invention, the light refinery dry gas and the heavy refinery dry gas are respectively compressed and cooled, part of the carbon dioxide and heavier components in the heavy refinery dry gas enter a liquid separation tank liquid phase and are directly merged into the product concentrated gas without undergoing an absorption-desorption process, so that the consumption of an absorption tower and a reboiler of a desorption tower is saved and the energy consumption of a system is reduced on the basis of ensuring the recovery rate of the carbon dioxide.

(2) In the invention, most of light components such as hydrogen, methane, nitrogen and the like in the heavy refinery dry gas are compressed and then sent into the absorption tower, and are separated from the carbon two components in the absorption-desorption process, so that the content requirement of the light components in the final product concentrated gas is ensured.

(3) In the invention, the content of carbon dioxide and hydrogen sulfide in the dry gas of the heavy refinery is less, so that the compressed cooling condensate of the dry gas of the heavy refinery is directly merged into the product gas, and the treatment capacity of the decarburization unit can be reduced on the basis of ensuring the content requirements of the carbon dioxide and the hydrogen sulfide in the product, thereby saving the equipment investment.

(4) In the invention, the compression pressure and the cooling temperature of the dry gas of the heavy refinery are related to the composition of the dry gas, the compression pressure and the cooling temperature can be selected to meet the requirement, the first gas phase quantity is as small as possible to reduce the total energy consumption of the device, and meanwhile, after the first liquid phase is mixed with the crude extraction concentrated gas after decarburization, the content of light components such as methane hydrogen in the obtained concentrated gas product is sufficiently small to ensure the product quality.

(5) In the preferred embodiment of the invention, in the method, the lowest temperature of the operations of compression, cooling, absorption and desorption is 5-15 ℃, a propylene refrigeration compressor is not needed, a lithium bromide refrigeration unit can be selected to provide refrigeration capacity, a drying system is not needed, the investment is low, the operation is simple, and the energy consumption is low.

(6) The method obviously improves the recovery rate of the carbon two and heavier components in the product concentrated gas, particularly, the recovery rate of the carbon two component in the concentrated gas is more than 92 percent, and the recovery rates of the carbon three and the heavier components are more than 92 percent, so that the product can be used as a raw material of a cracking furnace or a subsequent separation unit of an ethylene device.

Drawings

FIG. 1 is a schematic flow diagram of the process of the present invention for recovering carbon dioxide and heavier components from light and heavy refinery dry gas using oil absorption.

Description of the reference numerals

1, light refinery dry gas; 2a first compressor section; 3 a first compressor section; 4, heavy refinery dry gas; 5 a second compressor; 6 a first cooler; 7, separating a liquid tank; 8 compressor inter-stage tank; 9 a second cooler; 10 an absorption tower; 11 a desorption tower; 12 an absorbent circulation pump; 13 an absorbent cooler; 14, a decarbonizing tower; a 15 carbon four carbon five absorbent; 16 a decarbonizing agent; 17, a rich decarbonizing agent; 18 concentrating gas; 19 a second gas phase; 20, coarse concentration gas.

Detailed Description

The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.

The invention provides in a first aspect a method for recovering carbon dioxide and heavier components from refinery dry gas, characterised in that the method comprises the steps of:

(1) compressing dry gas of a light refinery: compressing the dry gas of the light refinery;

(2) compressing dry gas in a heavy refinery: compressing the heavy refinery dry gas;

(3) cooling and phase splitting of dry gas in heavy refineries: cooling the compressed dry gas obtained in the step (2), and performing gas-liquid phase separation to obtain a first gas phase and a first liquid phase;

(4) cooling dry gas: mixing the light refinery compressed dry gas obtained in the step (1) with the first gas phase obtained in the step (3) to obtain mixed dry gas, and compressing and cooling the mixed dry gas;

(5) carbon four and carbon five absorption: feeding the cooled dry gas obtained in the step (4) into the middle part of an absorption tower, and carrying out countercurrent contact with an absorbent from the top of the absorption tower, so as to obtain a second gas phase at the tower top of the absorption tower and obtain a second liquid phase at the tower kettle of the absorption tower;

(6) desorbing: feeding the second liquid phase obtained in the step (5) into the middle part of a desorption tower for desorption, obtaining crude concentrated gas at the tower top of the desorption tower, and obtaining lean absorbent at the tower kettle of the desorption tower;

(7) decarbonization: feeding the crude extraction concentrated gas obtained in the step (6) into the bottom of a decarbonizing tower, contacting with a decarbonizing agent from the top of the decarbonizing tower, obtaining a third gas phase at the top of the decarbonizing tower, and obtaining a third liquid phase at the tower kettle of the decarbonizing tower;

and (3) combining the first liquid phase in the step (3) and the third gas phase in the step (7) to obtain concentrated gas.

In the invention, the dry gas of a light refinery and the dry gas of a heavy refinery are compressed and pressurized respectively, the dry gas of the heavy refinery is compressed and then is cooled and subjected to gas-liquid phase separation treatment, the gas phase of a liquid separation tank is sent to a compressor intersegmental tank of the dry gas of the light refinery, and is further compressed and cooled and then is sent to a downstream absorption tower for absorption-desorption and decarburization treatment; and directly merging the liquid phase of the liquid separating tank at the outlet of the dry gas compressor of the heavy refinery into the concentrated gas product after decarburization, and sending the concentrated gas product out of the battery limits. By adopting the method, the carbon dioxide and heavier components in the dry gas of the heavy refinery can be prevented from being diluted, the load of a reboiler of the absorption tower and the desorption tower is reduced, the energy consumption is saved on the basis of ensuring the recovery rate of the carbon dioxide, and a dryer and a propylene refrigeration compressor are not needed.

In the present invention, the pressure is a gauge pressure unless otherwise specified.

In the present invention, the light refinery dry gas may be a light refinery dry gas conventional in the art, for example, derived from at least one of catalytic dry gas, coker dry gas, and PSA desorption gas.

According to the invention, the light refinery dry gas comprises hydrogen, methane, carbon dioxide, hydrogen sulphide, oxygen, nitrogen, a carbon two component, a carbon three component, a carbon four component and heavier components.

Preferably, the content of the carbon two component is 10-20 vol%, the total content of the hydrogen and the methane is 30-75 vol%, the content of the carbon dioxide is 0-20 vol%, the content of the hydrogen sulfide is 0-20 vol%, the content of the carbon three component is 0-20 vol%, and the content of the carbon four and heavier components is 0-10 vol%, based on the total volume of the light refinery dry gas.

In the present invention, the refinery-related dry gas may be a refinery-related dry gas conventional in the art, such as at least one derived from a cracked dry gas, a PX disproportionation fuel gas, and a PX isomerization fuel gas.

According to the invention, the heavy refinery dry gas comprises hydrogen, methane, a carbon two component, a carbon three component, a carbon four component and heavier components.

Preferably, the total content of the hydrogen and the methane is 5-40 vol%, the content of the carbon two component is 20-80 vol%, and the total content of the carbon three, the carbon four and heavier components is 5-80 vol% based on the total volume of the heavy refinery dry gas.

In the invention, the carbon two component refers to a hydrocarbon component with two carbon atoms, including ethane and ethylene; the carbon three component refers to hydrocarbon components with three carbon atoms, and comprises propane and propylene; the carbon four component refers to hydrocarbon component with four carbon atoms, including butane and butylene.

According to the invention, in step (1), the light refinery dry gas compression is a multi-stage compression, preferably a two-stage compression or a three-stage compression.

Preferably, the pressure of the light refinery dry gas is increased to 3-5MPaG, preferably 3.6-4.2 MPaG.

In the invention, in order to ensure that carbon and heavier components in the dry gas of the heavy refinery enter the first liquid phase in the step (3) to reduce the total energy consumption of the device, and meanwhile, light components such as hydrogen, methane, nitrogen and the like in the dry gas of the heavy refinery enter the first liquid phase in the step (3) to avoid the reduction of the content of the light components in the final recovered product concentrated gas, the inventor researches the lifting pressure of the dry gas of the heavy refinery in the step (2), and researches show that the requirements can be simultaneously met when the pressure of the dry gas of the heavy refinery is increased to 1-2 MPaG.

Furthermore, when the pressure of the dry gas in the heavy refinery is increased to 1.5-2MPaG, the comprehensive effect is more excellent.

According to the invention, in step (2), the heavy refinery dry gas compression is one-stage compression or two-stage compression.

According to the invention, in step (3), the heavy refinery compressed dry gas is cooled to 5-30 ℃, preferably 10-20 ℃.

In the present invention, the gas-liquid separation may be carried out in an apparatus capable of effecting gas-liquid separation which is conventional in the art, for example, the gas-liquid separation is carried out in the dry gas-liquid separation tank described in the present invention.

In the invention, the liquid-gas ratio of the liquid separation tank in the step (3) is determined by the composition of the refinery dry gas, the operation pressure and the cooling temperature, and preferably, the volume ratio of the carbon dioxide and heavier components in the first liquid phase to the carbon dioxide and heavier components in the refinery dry gas is more than 3: 10, preferably 5: 10-7: 10.

in the invention, the gas-liquid ratio of the liquid separation tank refers to the ratio of the gas phase discharge quantity at the top of the liquid separation tank to the liquid phase discharge quantity at the bottom of the liquid separation tank.

According to the invention, in the step (4), the pressure of the mixed dry gas is increased to 3-5MPaG, and the mixed dry gas is cooled to 5-30 ℃.

Preferably, the pressure of the mixed dry gas is increased to 3.6-4.2MPaG and cooled to 15-20 ℃.

In the present invention, in both step (3) and step (4), the cooling step may be performed by a refrigerant supplied from a lithium bromide absorption refrigerator.

In the invention, the refrigerant provided by the lithium bromide absorption refrigerator is adopted to cool the compressed gas, and the lithium bromide refrigerator takes waste heat steam from a refinery or hot water at 96-100 ℃ as a heat source.

In the present invention, the refrigerant may be a refrigerant conventional in the art, for example, cold water of 7-12 ℃ is selected as the refrigerant.

According to the invention, in step (5), the absorbent is a carbon four and/or carbon five fraction, preferably at least one of n-butane, isobutane, ether carbon four and pentane.

In the present invention, the amount of the absorbent used is not particularly limited, and may be adjusted according to the actual need.

According to the invention, the theoretical plate number of the absorption column is from 25 to 50, preferably from 30 to 40.

According to the invention, the operating pressure of the absorption column is between 3 and 5MPaG, preferably between 3.6 and 4.2 MPaG.

According to the invention, the top temperature of the absorption column is between 10 and 30 ℃ and preferably between 15 and 25 ℃.

According to the invention, the temperature of the tower kettle of the absorption tower is 80-150 ℃, and preferably 100-130 ℃.

According to the invention, the method further comprises feeding the second gaseous phase in step (5) to a fuel gas network for plant-wide fuel balancing.

In one embodiment of the invention, compressed and cooled mixed dry gas is introduced into the middle part of the absorption tower and is in countercurrent contact with an absorbent from the top of the absorption tower to absorb carbon dioxide and fractions above in a first gas phase, a second gas phase at the top of the absorption tower is sent out of a boundary zone, and a second liquid phase at the bottom of the absorption tower is sent to a desorption tower for treatment.

According to the invention, the theoretical plate number of the desorber is from 20 to 50, preferably from 30 to 40.

According to the invention, the operating pressure of the desorber is between 1 and 2.8MPaG, preferably between 1.2 and 2 MPaG.

According to the invention, the temperature at the top of the desorption column is between 15 and 70 ℃, preferably between 18 and 55 ℃.

According to the invention, the temperature of the bottom of the desorption tower is 90-200 ℃, preferably 100-130 ℃.

According to the invention, the method also comprises the step of returning the lean absorbent obtained in the bottom of the desorption tower in the step (6) to the absorption tower.

In the present invention, in the step (7), the decarbonizing agent is a decarbonizing agent conventional in the art, such as MDEA decarbonizing solvent.

In the present invention, the amount of the decarbonizing agent is not particularly limited, and can be determined by those skilled in the art based on the general knowledge of the prior art. The decarbonizing column is a typical absorption column, and there is no particular requirement for the number of theoretical plates and the operating pressure, and those skilled in the art can determine the number of the theoretical plates and the operating pressure based on the general knowledge of the prior art.

According to the invention, the method also comprises the step of introducing the concentrated gas into a cracking device for cracking reaction.

In the invention, the method also comprises the step of heating the concentrated gas to the normal temperature (30 ℃) by adopting a heater and then sending the concentrated gas out of the boundary area.

According to the invention, the enriched gas comprises hydrogen, methane, a carbon two component, a carbon three component and more than four carbon components.

According to the invention, the hydrogen is present in an amount of 0 to 1 vol%, preferably 0 to 0.1 vol%, based on the total volume of the concentrate gas; the content of methane is 1-5 vol%, preferably 1-3 vol%; the content of the carbon dioxide component is 50-85 vol%, preferably 60-80 vol%; the content of the carbon three component is 0-40 vol%, preferably 10-22 vol%; the content of the carbon four or more component is 0 to 20 vol%, preferably 8 to 15 vol%.

Step (7) further comprises passing the third liquid phase outside the battery limits for regeneration of a rich MDEA solution comprising carbon dioxide and hydrogen sulfide.

In a second aspect, the present invention provides a system for recovering carbon dioxide and heavier components from refinery dry gas, the system comprising: the system comprises a first compressor section, a second compressor, a first cooler, a second cooler, a liquid separation tank, a compressor section tank, an absorption tower, a desorption tower and a decarbonization tower;

the first compressor section is used for compressing the dry gas of the light refinery and is communicated with the compressor section inter-tank;

the second compressor, the first cooler and the liquid separating tank are communicated in sequence and are used for compressing, cooling and gas-liquid phase separation of the dry gas of the heavy refinery;

the compressor section inter-tank is respectively communicated with the first compressor section and the top of the liquid separation tank and is used for mixing the light refinery compressed dry gas from the first compressor section and the first gas phase from the top of the liquid separation tank to obtain mixed dry gas;

the compressor section inter-tank, the first compressor section, the second cooler, the absorption tower, the desorption tower and the decarbonization tower are communicated in sequence;

the first compressor section and the second cooler are used for compressing and cooling the mixed dry gas from the top of the compressor section inter-tank;

the middle part of the absorption tower is communicated with a second cooler and is used for enabling the compressed mixed dry gas cooled by the second cooler to be in countercurrent contact with an absorbent, and a second gas phase and a second liquid phase are respectively discharged from the tower top and the tower kettle of the absorption tower;

the middle part of the desorption tower is communicated with the bottom of the absorption tower and is used for desorbing the second liquid phase discharged from the bottom of the absorption tower, the top of the desorption tower obtains crude concentrated gas, and the bottom of the desorption tower obtains lean absorbent;

the bottom of the decarbonizing tower is communicated with the top of the desorption tower and is used for enabling the crude extraction concentrated gas discharged from the top of the desorption tower to be in countercurrent contact with a decarbonizing agent, a third gas phase is obtained at the top of the decarbonizing tower, and a third liquid phase is obtained at the tower kettle of the decarbonizing tower;

and a tower top pipeline of the decarbonization tower is communicated with a bottom pipeline of the liquid separation tank, so that the third gas phase is mixed with the first liquid phase from the bottom of the liquid separation tank to obtain the concentrated gas.

According to the invention, the system further comprises an absorbent circulation pump and an absorbent cooler;

the absorbent circulating pump and the absorbent cooler are communicated with the bottom of the desorption tower and used for boosting and cooling the lean absorbent obtained at the tower bottom of the desorption tower and at least partially returning to the top of the absorption tower.

Preferably, the theoretical plate number of the absorption column is 25 to 50, more preferably 30 to 40.

Preferably, the number of theoretical plates of the desorber is from 20 to 50, more preferably from 30 to 40.

In the invention, the system also comprises a cracking device which is used for carrying out cracking reaction by taking the recovered concentrated gas as a raw material.

In a third aspect, the present invention provides a use of the above method or system in refinery dry gas recovery.

The method and system of the present invention are further described with reference to fig. 1.

The pressure of the light refinery dry gas 1 is boosted to 1.5-2MPaG through a first compressor section 2, and the compressed dry gas is sent to a compressor section inter-tank 8;

the pressure of the dry gas 4 of the heavy refinery is increased to 1-2MPaG by a second compressor, the dry gas is cooled to 5-30 ℃ in a first cooler 6, the dry gas is sent into a liquid separation tank 7 for gas-liquid phase separation, the obtained first gas phase is sent into a compressor intersegment tank 8, and the first liquid phase is merged into a concentrated gas 18;

the pressure of the mixed dry gas in the compressor inter-stage tank 8 is increased to 3-5MPaG through the first compressor second stage 3, and is cooled to 5-30 ℃ through the second cooler 9; feeding the gas to the middle part of an absorption tower 10, and making the gas be in countercurrent contact with an absorbent 15 from the top of the absorption tower to absorb the carbon dioxide fraction and heavier components in the dry gas, and feeding a second gas phase 19 containing methane and hydrogen which is not absorbed at the top of the tower to a fuel gas pipe network or other uses;

feeding the second liquid phase from the tower bottom of the absorption tower 10 into the middle part of a desorption tower 11 for desorption, obtaining a crude concentrated gas 20 at the tower top of the desorption tower 11, and feeding the crude concentrated gas into a decarbonization tower 14; the poor absorbent obtained from the bottom of the desorption tower 11 is pressurized by an absorbent circulating pump 12, and is returned to the absorption tower 10 for recycling after being cooled by an absorbent cooler 13.

Feeding the crude concentrated gas 20 from the top of the desorption tower into the bottom of a decarbonizing tower 14, contacting with a decarbonizing agent 16 from the top of the decarbonizing tower 14 to remove carbon dioxide and hydrogen sulfide in the crude concentrated gas, combining a third gas phase obtained from the top of the decarbonizing tower 14 with a first liquid phase of a heavy refinery dry gas liquid separation tank 7 to be used as a concentrated gas 18 product, and feeding the concentrated gas to an ethylene device to be used as a raw material; the rich decarbonizer 17 obtained from the tower bottom of the decarbonization tower 14 is sent out of the battery limits.

The present invention will be described in detail below by way of examples. In the following examples, the carbon dioxide recovery was calculated as: x 100% of (ethane + ethylene) in the concentrated gas, (ethane + ethylene) in the light refinery dry gas and (ethane + ethylene) in the heavy refinery dry gas); the calculation formula of the carbon recovery rate is as follows: the x is 100% of (propane + propylene) in the concentrated gas, (propane + propylene) in the light refinery dry gas and (propane + propylene) in the heavy refinery dry gas).

In example 1 and comparative example, the compositions of the light and heavy refinery dry gases are shown in table 1. The gas composition was tested using the standard ASTM D1945.

TABLE 1 refinery Dry gas flow and composition

	Light refinery dry gas	Heavy refinery dry gas
			Temperature, C	40.0	40.0
Pressure, MPaG	0.60	0.30
			Mass flow, t/h	50.0	20.0
Composition in mol%
			H2	40.80	6.99
H2S	0.06	0.00
			CO	0.75	0.00
CO2	0.57	0.00
			O2	0.83	0.00
N2	11.12	0.00
			CH4	20.15	3.94
C2H6	16.43	60.12
			C2H4	0.25	0.00
C3H8	5.11	19.01
			C3H6	0.05	0.00
C4H10	2.50	6.21
			C4H8	0.02	0.00
C5+	1.27	3.72
			H2O	0.07	0.00

Example 1

The method for recovering the carbon and heavier components in the dry gas of the light and heavy refineries by adopting the oil absorption method is adopted to separate and recover the dry gas of the refineries.

The specific process comprises the following steps:

the light refinery dry gas, with the composition shown in table 1 and pressure of 0.6MPaG, enters the first compressor stage, increases the pressure to 2MPaG, and is sent to the compressor stage tank.

The heavy refinery dry gas, with a composition as shown in table 1, at a pressure of 0.3MPaG, enters the second compressor, raising the pressure to 2 MPaG. And (3) cooling the pressurized compressed dry gas of the heavy refinery to 15 ℃ in a first cooler, then sending the cooled compressed dry gas into a liquid separation tank for gas-liquid phase separation, sending the first gas phase at the top of the liquid separation tank into a compressor intersegmental tank, combining the first liquid phase at the bottom of the liquid separation tank into a concentrated gas product, and sending the concentrated gas product out of a boundary region.

The gas phase on the top of the compressor section tank passes through the first compressor section and the second compressor section, the pressure is increased to 3.8MPaG, and the gas phase is cooled to 15 ℃ by the second cooler and sent to the middle part of the absorption tower.

In the absorption tower, carbon four and carbon five fractions (45 vol% of n-butane, 22 vol% of isobutane and 33 vol% of pentane) are used as an absorbent (the circulation amount of the absorbent is 165t/h), and are sprayed from the top of the tower to absorb the carbon two fraction and heavier components in the dry gas. The number of theoretical plates of the absorption tower is preferably 40, the operating pressure is 3.7MPaG, the temperature at the top of the tower is 18 ℃, and the temperature at the bottom of the tower is 121 ℃. The tower kettle at the top of the absorption tower adopts low-pressure steam for heating, the unabsorbed second gas phase at the top of the tower is discharged into a fuel gas pipe network, the second liquid phase at the bottom of the tower is sent into a desorption tower for treatment, wherein, the volume ratio of the carbon dioxide and heavier components in the first liquid phase to the carbon dioxide and heavier components in the dry gas of a heavy refinery is 6.1: 10.

the second liquid phase from the bottom of the absorption tower enters the middle part of the desorption tower. The theoretical plate number of the desorption tower is 40, the operation pressure is 2MPaG, the tower top temperature is 56 ℃, and the tower bottom temperature is 130 ℃. The desorption tower is heated by low-pressure steam, crude concentrated gas is obtained at the tower top and is sent to the decarbonization tower, lean absorbent obtained from the desorption tower is boosted by an absorbent circulating pump, and the lean absorbent returns to the absorption tower for recycling after being cooled to 15 ℃ by an absorbent cooler.

And (3) feeding the crude concentrated gas from the top of the desorption tower into the bottom of a decarbonizing tower, and injecting the crude concentrated gas into the decarbonizing tower from the top of the decarbonizing tower by taking an MDEA decarbonizing solvent as a decarbonizing agent (the flow of the decarbonizing agent is about 60t/h) to absorb carbon dioxide and hydrogen sulfide in the crude concentrated gas. And combining the third gas phase at the top of the decarbonizing tower with the first liquid phase at the bottom of the heavy refinery dry gas liquid separation tank, heating to 45 ℃, taking the gas as a concentrated gas product, sending the gas out of a boundary zone, and sending the gas to an ethylene device cracking furnace as a raw material.

In this example, the composition of the product concentrate is shown in table 2, where the carbon two recovery is 95.8% and the carbon three recovery is 97.4%.

TABLE 2

	Concentration gas
		Temperature, C	45.0
Pressure, MPaG	1.82
		Mass flow, t/h	43.4
Composition in mol%
		H2	0.05
CH4	2.72
		C2H6	65.13
C2H4	0.40
		C3H8	20.69
C3H6	0.10
		C4H10	9.08
C5+	1.45
		H2O	0.38

Example 2

TABLE 3 refinery Dry gas flow and composition

The flow rates and compositions of the light and heavy refinery dry gases in this example are shown in table 3. The gas composition was tested using the standard ASTM D1945

The method for recovering the carbon and heavier components in the dry gas of the light and heavy refineries by adopting the oil absorption method is adopted to separate and recover the dry gas of the refineries.

The specific process comprises the following steps:

the light refinery dry gas, with the composition shown in table 3 and pressure of 0.6MPaG, enters the first compressor stage, increases the pressure to 1.2MPaG, and is sent to the compressor stage tank.

The heavy refinery dry gas, with a composition as shown in table 3, was fed to the second compressor at a pressure of 0.2MPaG, increasing the pressure to 1.2 MPaG. And (3) cooling the pressurized dry gas to 20 ℃ in a first cooler, then sending the dry gas into a liquid separation tank for gas-liquid phase separation, sending the first gas phase at the top of the liquid separation tank into a compressor intersegmental tank, combining the first liquid phase at the bottom of the liquid separation tank into a concentrated gas product, and sending the concentrated gas product out of a boundary region.

The gas phase on the top of the compressor section tank passes through the first compressor section and the second compressor section, the pressure is increased to 4.2MPaG, and the gas phase is cooled to 20 ℃ by the second cooler and sent to the middle part of the absorption tower.

In the absorption tower, carbon four and carbon five fractions (n-butane 50 vol%, isobutane 19 vol% and pentane 31 vol%) are used as an absorbent (the circulation amount of the absorbent is 150t/h), and are sprayed from the top of the tower to absorb the carbon two fraction and heavier components in the dry gas. The number of theoretical plates of the absorption tower is preferably 30, the operating pressure is 4.0MPaG, the temperature at the top of the tower is 19 ℃, and the temperature at the bottom of the tower is 128 ℃. The tower kettle at the top of the absorption tower adopts low-pressure steam for heating, the unabsorbed second gas phase at the top of the tower is discharged into a fuel gas pipe network, the second liquid phase at the bottom of the tower is sent into a desorption tower for treatment, wherein, the volume ratio of the carbon dioxide and heavier components in the first liquid phase to the carbon dioxide and heavier components in the dry gas of a heavy refinery is 5.5: 10.

the second liquid phase from the bottom of the absorption tower enters the middle part of the desorption tower. The theoretical plate number of the desorption tower is 30, the operation pressure is 1.2MPaG, the tower top temperature is 40 ℃, and the tower kettle temperature is 100 ℃. The desorption tower is heated by low-pressure steam, crude concentrated gas is obtained at the tower top and is sent to the decarbonization tower, lean absorbent obtained from the desorption tower is boosted by an absorbent circulating pump, and the lean absorbent returns to the absorption tower for recycling after being cooled to 15 ℃ by an absorbent cooler.

And (3) feeding the crude concentrated gas from the top of the desorption tower into the bottom of a decarbonizing tower, and injecting the crude concentrated gas into the decarbonizing tower from the top of the decarbonizing tower by taking an MDEA decarbonizing solvent as a decarbonizing agent (the flow of the decarbonizing agent is about 50t/h) to absorb carbon dioxide and hydrogen sulfide in the crude concentrated gas. And combining the third gas phase at the top of the decarbonizing tower with the first liquid phase at the bottom of the heavy refinery dry gas liquid separation tank, heating to 45 ℃, taking the gas as a concentrated gas product, sending the gas out of a boundary zone, and sending the gas to an ethylene device cracking furnace as a raw material.

In this example, the composition of the product concentrate is shown in table 4, where the carbon two recovery is 96.4% and the carbon three recovery is 97.9%.

TABLE 4

	Concentration gas
		Temperature, C	45.0
Pressure, MPaG	1.16
		Mass flow, t/h	43.8
Composition in mol%
		H2	0.05
CH4	2.54
		C2H6	51.44
C2H4	0.42
		C3H8	33.32
C3H6	0.11
		C4H10	9.85
C5+	1.90
		H2O	0.37

Comparative example 1

The dry gas shown in table 1 was recovered according to the typical shallow cold oil absorption process scheme of CN103087772A, wherein the feed conditions and carbon dioxide recovery rate were the same as in example 1, and the composition of the obtained product concentrate gas is shown in table 5, and the process conditions and energy consumption are shown in table 6.

TABLE 5

	Concentration gas
		Composition in mol%
CH4	3.03
		C2H6	68.42
C2H4	0.43
		C3H8	21.73
C3H6	0.11
		C4H10	5.83
H2O	0.45

Comparative example 2

The dry gas shown in Table 1 was recovered by a cryogenic separation process, wherein the feed conditions and the carbon dioxide recovery rate were the same as in example 1, and the process conditions are shown in Table 6.

TABLE 6

As can be seen from tables 2-6, the lowest temperature of the process stream of the process is 5-15 ℃, the propylene refrigeration capacity at a low temperature position is not needed, a propylene refrigeration system and a drying system are not needed, and the equipment investment is low. Compared with the conventional shallow cold oil absorption process, the process has the advantages that the light and heavy refinery dry gases are respectively compressed and cooled, most of the carbon dioxide and the heavy components in the heavy refinery dry gases are directly merged into a concentrated gas product along with a compressed condensate, so that the load of an absorption tower and a reboiler of an desorption tower is reduced, the energy consumption of a system is reduced, the water content in the concentrated gas is lower, and the risk of freezing and blocking of an external delivery pipeline is reduced.

The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.

Claims (12)

1. A method for recovering carbon dioxide and heavier components from refinery dry gas, comprising the steps of:

(1) compressing dry gas of a light refinery: compressing the dry gas of the light refinery;

(2) compressing dry gas in a heavy refinery: compressing the heavy refinery dry gas;

(3) cooling and phase splitting of dry gas in heavy refineries: cooling the compressed dry gas obtained in the step (2), and performing gas-liquid phase separation to obtain a first gas phase and a first liquid phase;

(4) cooling dry gas: mixing the light refinery compressed dry gas obtained in the step (1) with the first gas phase obtained in the step (3) to obtain mixed dry gas, and compressing and cooling the mixed dry gas;

(5) carbon four and carbon five absorption: feeding the cooled dry gas obtained in the step (4) into the middle part of an absorption tower, and carrying out countercurrent contact with an absorbent from the top of the absorption tower, so as to obtain a second gas phase at the tower top of the absorption tower and obtain a second liquid phase at the tower kettle of the absorption tower;

(6) desorbing: feeding the second liquid phase obtained in the step (5) into the middle part of a desorption tower for desorption, obtaining crude concentrated gas at the tower top of the desorption tower, and obtaining lean absorbent at the tower kettle of the desorption tower;

(7) decarbonization: feeding the crude extraction concentrated gas obtained in the step (6) into the bottom of a decarbonizing tower, contacting with a decarbonizing agent from the top of the decarbonizing tower, obtaining a third gas phase at the top of the decarbonizing tower, and obtaining a third liquid phase at the tower kettle of the decarbonizing tower;

and (3) combining the first liquid phase in the step (3) and the third gas phase in the step (7) to obtain concentrated gas.

2. The method of claim 1, wherein the light refinery dry gas comprises hydrogen, methane, carbon dioxide, hydrogen sulfide, oxygen, nitrogen, a carbon two component, a carbon three component, a carbon four component, and heavier components;

preferably, the content of the carbon two component is 10-20 vol%, the total content of the hydrogen and the methane is 30-75 vol%, the content of the carbon dioxide is 0-20 vol%, the content of the hydrogen sulfide is 0-20 vol%, the content of the carbon three component is 0-20 vol%, and the content of the carbon four and heavier component is 0-10 vol% based on the total volume of the light refinery dry gas;

preferably, the heavy refinery dry gas comprises hydrogen, methane, a carbon two component, a carbon three component, a carbon four component and heavier components;

more preferably, the total content of hydrogen and methane is 5-40 vol%, the content of the carbon two component is 20-80 vol%, and the total content of the carbon three, carbon four and heavier components is 5-80 vol%, based on the total volume of the heavy refinery dry gas.

3. The process according to claim 1 or 2, wherein in step (1), the light refinery dry gas compression is a multi-stage compression, preferably a two-stage compression or a three-stage compression;

preferably, the pressure of the light refinery dry gas is increased to 3-5MPaG, preferably 3.6-4.2 MPaG.

4. The method according to any one of claims 1-3, wherein in step (2), the heavy refinery dry gas compression is one-stage compression or two-stage compression;

preferably, the pressure of the heavy refinery dry gas is increased to 1-2MPaG, preferably 1.5-2 MPaG.

5. The process according to any one of claims 1 to 4, wherein in step (3), the heavy refinery compressed dry gas is cooled to 5 to 30 ℃, preferably 10 to 20 ℃;

preferably, the step of cooling is performed by a refrigerant provided by a lithium bromide absorption refrigerator;

preferably, the volume ratio of carbon dioxide and heavier components in the first liquid phase to carbon dioxide and heavier components in the refinery dry gas is greater than 3: 10, preferably 5: 10-7: 10.

6. the method according to any one of claims 1 to 5, wherein, in the step (4), the pressure of the mixed dry gas is increased to 3 to 5MPaG, and is cooled to 5 to 30 ℃;

preferably, the pressure of the mixed dry gas is increased to 3.6-4.2MPaG and cooled to 15-20 ℃.

7. The process according to any one of claims 1 to 6, wherein in step (5) the absorbent is a carbon four and/or carbon five fraction, preferably at least one of n-butane, isobutane, post-etheric carbon four and pentane;

preferably, the theoretical plate number of the absorption tower is 25 to 50, preferably 30 to 40;

preferably, the operating pressure of the absorption column is from 3 to 5MPaG, preferably from 3.6 to 4.2 MPaG;

preferably, the tower top temperature of the absorption tower is 10-30 ℃, preferably 15-25 ℃;

preferably, the temperature of the tower kettle of the absorption tower is 80-150 ℃, and preferably 100-130 ℃;

preferably, the method further comprises: and (5) feeding the second gas phase into a fuel gas pipe network.

8. The process according to any one of claims 1 to 7, wherein in step (6), the theoretical plate number of the desorber is from 20 to 50, preferably from 30 to 40;

preferably, the operating pressure of the desorber is from 1 to 2.8MPaG, preferably from 1.2 to 2.2 MPaG;

preferably, the temperature of the top of the desorption tower is 15-70 ℃, preferably 18-55 ℃;

preferably, the temperature of the bottom of the desorption tower is 90-200 ℃, preferably 100-130 ℃;

preferably, the method further comprises returning the lean absorbent obtained in the bottom of the desorption tower in the step (6) to the absorption tower.

9. The method of any one of claims 1-8, further comprising passing the enriched gas to a cracking unit for a cracking reaction;

preferably, the concentrated gas comprises hydrogen, methane, a carbon two-component, a carbon three-component and more than four carbon components;

more preferably, the hydrogen is present in an amount of 0 to 1 vol%, preferably 0 to 0.1 vol%, based on the total volume of the concentrate gas; the content of the methane is 1-5 vol%, preferably 1-3 vol%; the content of the carbon dioxide component is 50-85 vol%, preferably 60-80 vol%; the content of the carbon three component is 0-40 vol%, preferably 10-22 vol%; the content of the carbon four or more component is 0 to 20 vol%, preferably 8 to 15 vol%.

10. A system for recovering carbon dioxide and heavier components from refinery dry gas, the system comprising: the system comprises a first compressor section, a second compressor, a first cooler, a second cooler, a liquid separation tank, a compressor section tank, an absorption tower, a desorption tower and a decarbonization tower;

the first compressor section is used for compressing the dry gas of the light refinery and is communicated with the compressor section inter-tank;

the second compressor, the first cooler and the liquid separating tank are communicated in sequence and are used for compressing, cooling and gas-liquid phase separation of the dry gas of the heavy refinery;

the compressor section inter-tank is respectively communicated with the first compressor section and the top of the liquid separation tank and is used for mixing the light refinery compressed dry gas from the first compressor section and the first gas phase from the top of the liquid separation tank to obtain mixed dry gas;

the compressor section inter-tank, the first compressor section, the second cooler, the absorption tower, the desorption tower and the decarbonization tower are communicated in sequence;

the first compressor section and the second cooler are used for compressing and cooling the mixed dry gas from the top of the compressor section inter-tank;

the middle part of the absorption tower is communicated with a second cooler and is used for enabling the compressed mixed dry gas cooled by the second cooler to be in countercurrent contact with an absorbent, and a second gas phase and a second liquid phase are respectively discharged from the tower top and the tower kettle of the absorption tower;

the middle part of the desorption tower is communicated with the bottom of the absorption tower and is used for desorbing the second liquid phase discharged from the bottom of the absorption tower, the top of the desorption tower obtains crude concentrated gas, and the bottom of the desorption tower obtains lean absorbent;

the bottom of the decarbonizing tower is communicated with the top of the desorption tower and is used for enabling the crude extraction concentrated gas discharged from the top of the desorption tower to be in countercurrent contact with a decarbonizing agent, a third gas phase is obtained at the top of the decarbonizing tower, and a third liquid phase is obtained at the tower kettle of the decarbonizing tower;

and a tower top pipeline of the decarbonization tower is communicated with a bottom pipeline of the liquid separation tank, so that the third gas phase is mixed with the first liquid phase from the bottom of the liquid separation tank to obtain the concentrated gas.

11. The system of claim 10, wherein the system further comprises an absorbent circulation pump and an absorbent cooler;

the absorbent circulating pump and the absorbent cooler are communicated with the bottom of the desorption tower and used for boosting and cooling the lean absorbent obtained at the tower bottom of the desorption tower and at least partially returning to the top of the absorption tower.

12. Use of the method of any one of claims 1 to 9 or the system of claim 10 or 11 in refinery dry gas recovery.

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