Dry gas low-temperature purification and separation process and system

Abstract

The invention discloses a dry gas low-temperature purification and separation process. The process comprises the following steps: absorbing and condensing dry gas through low-temperature absorption oil to obtain absorption tail gas and rich absorption oil; the rich absorption oil is subjected to flash evaporation, and flash evaporation gas and flash evaporation oil are obtained; carrying out steam stripping separation on the flash oil in a regeneration tower to obtain regenerated gas and lean absorption oil; the lean absorption oil is pressurized, subjected to heat exchange and cooled and then circulated back into the absorption tower to serve as absorption oil; enabling the flash steam and the regenerated gas to enter an adsorption tank, and removing carried absorption oil components; the adsorption tail gas enters an amine liquid absorption tower for desulfurization and decarburization, and C2 + light hydrocarbon components are obtained. According to the method, specific absorption oil and lower operation pressure are selected, effective recovery and removal of C2 + hydrocarbon, hydrogen sulfide and carbon dioxide in the dry gas can be realized only through primary absorption, the absorption operation is greatly simplified, and the energy consumption of C2 + resource recovery is reduced.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of energy saving technology, and relates to a refinery dry gas low-temperature purification separation process and system, in particular to a refinery dry gas low-carbon hydrocarbon, hydrogen sulfide and carbon dioxide efficient low-energy consumption purification separation process and system. BACKGROUND

[0002] In the petroleum refining process, a large amount of light hydrocarbon dry gas is produced in the refining and chemical plants, and the main components are methane, ethane, ethylene, propane, propylene, etc., and also contain H2, N2, H2S and other non-hydrocarbon components. At present, 80% of the refinery dry gas is burned as fuel, causing a large amount of C1, C2, H2 resource waste. Dry gas chemical application is mainly used for purifying and separating hydrogen and ethylene and as a chemical raw material. Dry gas as a raw material includes dry gas preparation of ethylbenzene, ethylene oxide, dichloroethane, vinyl chloride, etc. Except for the dry gas preparation of dichloroethane process, the remaining dry gas chemical application has a high requirement for the raw gas, so the purification and separation of the refinery dry gas is also the premise of most refinery dry gas chemical applications. In recent years, various enterprises have successively implemented refinery dry gas comprehensive utilization projects, direct synthesis of chemical products and fuel oil, PSA desorption gas as ethylene raw material, recovery of hydrogen as hydrogen production raw material and other projects. With the increasing shortage of petroleum resources, recycling and utilization of dry gas has become an important means for integrated refining and chemical enterprises to reduce the production cost of ethylene and realize resource comprehensive utilization. Recycling and utilization of refinery dry gas will simultaneously solve the problems of environmental protection and cost reduction in the refinery. Because the refinery dry gas contains a large amount of H2, O2, N2, CO2 and H2S and other non-hydrocarbon components, which account for about 30-60% of the total amount of dry gas, there are problems such as high energy consumption in the process and large equipment scale when the dry gas is recycled.

[0003] The refinery dry gas light hydrocarbon recovery process mainly includes cryogenic separation, oil absorption separation, adsorption separation, hydrate separation and membrane separation. At present, the main methods that have realized industrial application are cryogenic separation, oil absorption separation and pressure swing adsorption separation (PSA). Among them, the cryogenic separation process has been industrialized in foreign countries since the 1970s. Subsequently, in order to overcome the shortcomings of high energy consumption and high investment of the cryogenic separation process, the oil absorption separation method and the adsorption separation process were developed and successfully realized industrial application; the membrane separation method and the hydrate separation method are still in the laboratory research or industrial test stage, and further research and development are needed to realize industrial application.

[0004] Domestic research has always been mainly based on physical oil absorption method. Because the refinery dry gas generally contains a large amount of H2, N2 and methane and other light components, the volume fraction of these components is as high as 70%, and the partial pressure of C2 and above components is low. In order to achieve high recovery rate, a large amount of absorbent is needed. The heating load of the absorption tower, the desorption tower reboiler and the condensation load of the desorption tower overhead condenser are large, so the energy consumption of the shallow cold oil process is high, and the energy consumption of the device is generally 3910 MJ / t of raw material.

[0005] The adsorption separation process is based on the different molecular forces of different types of gas molecules on the internal surface of the solid adsorbent. Under pressure conditions, the C2 components with larger adsorption force are adsorbed in the adsorption bed, and the components with smaller adsorption force such as hydrogen, methane, nitrogen, etc. are discharged. Under reduced pressure conditions, the adsorption bed discharges the adsorption components, and the adsorbent is regenerated. In industrial applications, a multi-tower pressure swing adsorption-desorption cycle process is used to achieve continuous operation of the process and achieve the purpose of purification and separation. This process has low energy consumption and is environmentally friendly. The energy consumption is low, and the energy consumption of most industrial devices is about 1675 MJ / t of raw materials. However, this method requires a large equipment, a complex control system, a high mechanical failure rate, a low ethylene purity, and a low recovery rate. To obtain polymer-grade ethylene, multiple pressure swing adsorption is usually required, which increases the land area and equipment investment.

[0006] Patent CN202110537997.4 discloses a method for recovering light hydrocarbons from refinery dry gas. The method includes compressing, desulfurizing and decarburizing, re-compressing, and cooling the refinery saturated dry gas, and then using a combined sequential absorption process with a "three-tower absorption, six-tower process" to recover light hydrocarbons from the refinery dry gas. Three types of absorbents are used for sequential absorption: the first absorbent is used to absorb C2+ components in the refinery dry gas; the second absorbent is used to absorb the first absorbent entrained in the overhead dry gas of the first absorption tower; and the third absorbent is used to absorb the second absorbent entrained in the overhead dry gas from the second absorption tower. While increasing the recovery rate of light hydrocarbons (ethane, propane) in the refinery dry gas, the method can effectively solve the problems of high energy consumption, high investment, and "non-dry" dry gas in the existing refinery dry gas light hydrocarbon recovery process. The recovered rich ethane gas has a low heavy component content (C4+≯1.5 mol%), which is suitable for direct use as a raw material for the gas cracking furnace of an ethylene cracking device. However, this process has the problems of complex process, high system investment, etc.

[0007] The journal "Refining Technology and Engineering" paper "Application of two-stage pressure swing adsorption and product gas purification technology in catalytic cracking dry gas ethylene concentration device" introduces the application of two-stage pressure swing adsorption and product gas purification technology in a 30 dam 3 / h catalytic cracking dry gas ethylene concentration device. The average ethylene recovery rate is 87%, which needs to be further improved. The process uses 16 towers for adsorption operation, and the process flow is complex. SUMMARY

[0008] In view of the deficiencies of the existing dry gas purification and separation technology, the present application provides a dry gas low-temperature purification and separation process and system. The system has the characteristics of low energy consumption, simple system, safety and energy saving, etc.

[0009] According to the first object of the present application, the present application provides a dry gas cryogenic purification separation process.

[0010] Specifically, the dry gas cryogenic purification separation process comprises the following steps: (1) providing a dry gas cryogenic purification separation system, which comprises a low-temperature absorption tower, a cooler, a flash tank, a heat exchanger, a circulating pump, a regeneration tower, a compressor, an adsorption tank and an amine liquid absorption tower; (2) dry gas from a pipe network is used as the purification object, and the dry gas is absorbed and condensed in the absorption tower by low-temperature absorption oil, and the absorbed and condensed gas is the absorption tail gas, which is discharged from the top of the absorption tower through an absorption tail gas pipeline; the absorption oil is fed from the upper end of the absorption tower and is countercurrently absorbed and condensed with the dry gas fed from the lower end of the absorption tower to condense C2+, hydrogen sulfide and carbon dioxide, and the absorption oil after absorbing and condensing the dry gas becomes rich absorption oil, which is the first stream; (3) the first stream is discharged from the bottom of the absorption tower, is sent to the flash tank by the pressure in the absorption tower, is flashed at 0.1-0.3 MPaG in the flash tank, and gas phase is obtained as the second stream and liquid phase is obtained as the third stream; the second stream is discharged from the top of the flash tank, and the third stream is discharged from the bottom of the flash tank; (4) the third stream enters the regeneration tower by self-pressure and is stripped and separated in the regeneration tower to strip out hydrogen sulfide, carbon dioxide and C2+ and other components absorbed and condensed by the absorption oil, and the fourth stream is discharged from the top of the regeneration tower; the lean absorption oil after regeneration is discharged from the bottom of the tower, which is the fifth stream; (5) the fifth stream is pressurized by a circulating pump and then enters the heat exchanger to exchange heat with the third stream discharged from the bottom of the flash tank, the lean absorption oil is cooled to -30--10℃ after heat exchange, which is the sixth stream; the third stream is heated to 60-90℃ and then enters the regeneration tower for regeneration; (6) the obtained sixth stream is cooled to -65--50℃ in the cooler and enters the absorption tower as the absorption oil of the absorption tower; (7) the gas phase second stream discharged from the top of the flash tank is mixed with the gas phase fourth stream discharged from the top of the regeneration tower, and is pressurized to 0.2-0.5 MPaG to enter the adsorption tank to adsorb the absorption oil components entrained in the second stream and the fourth stream; (8) the adsorption tail gas obtained in step (7) mainly comprises C2+ light hydrocarbon, hydrogen sulfide and carbon dioxide, and the adsorption tail gas enters the amine liquid absorption tower to absorb and remove hydrogen sulfide and carbon dioxide components to obtain C2+ light hydrocarbon components.

[0011] Further, the separation process of the present application further comprises step (9): the adsorption tank in step (7) is regenerated, and the obtained regeneration gas is separated to obtain recovered absorption oil, and the recovered absorption oil is mixed with optional additional absorption oil and then returned to step (2).

[0012] Further, the dry gas feedstock according to the present application generally contains 1-3% (v) hydrogen sulfide, 1-3% (v) carbon dioxide and the like impurities, 10-20% (v) C2+ content, and other components are methane, nitrogen and hydrogen.

[0013] Further, the main components of the absorbed tail gas are methane, nitrogen and hydrogen, wherein the hydrogen sulfide content is less than 10 ppm, the carbon dioxide content is less than 10 ppm, and the C2+ content is less than 5% (v).

[0014] Further, the operating temperature of the absorption tower is -65 to -50 ℃, the absorption pressure is 0.9-1.5 MPaG, and the liquid-gas ratio is 40-200 L / m 3 , preferably 40-120 L / m 3 .

[0015] Further, the absorption oil used in the absorption tower is selected from at least one of toluene, ethylbenzene, heptane and isooctane. The absorption oil selected by the present application is significantly different from the existing low-temperature absorption process, and has low freezing point, low saturated vapor pressure and high boiling point, and is not easy to evaporate.

[0016] Further, the flash evaporation is constant-temperature flash evaporation. The flash evaporation tank is generally provided with a jacket. The temperature control of the flash evaporation tank is -45 to -30 ℃, and the operating pressure of the flash evaporation tank is generally 0.1-0.3 MPaG.

[0017] Further, the operating conditions of the regeneration tower are well known to those skilled in the art. For example, the regeneration temperature at the bottom of the regeneration tower is 80-120 ℃, preferably 90-115 ℃; the operating temperature at the top of the regeneration tower is -10 to 10 ℃, preferably -5 to 5 ℃; the operating pressure of the regeneration tower is normal pressure operation or slightly positive pressure operation; the reflux ratio of the regeneration tower is 0.5-2, preferably 0.8-1.5.

[0018] Further, the adsorption pressure of the adsorption tank is 0.2-0.5 MPaG, and generally it is normal temperature adsorption. The adsorption tank is used to capture the absorption oil components carried in the tail gas discharged from the regeneration tower, i.e. the fourth stream, to reduce the supplement of the absorption oil. The adsorption tank is filled with an adsorbent. The adsorbent is selected from one or more of activated carbon, molecular sieve, zeolite and the like.

[0019] Further, the operation of the amine liquid absorption tower in step (8) is a conventional operation in the art. The organic amine absorption liquid (absorbent) is generally selected from MDEA, MEA, DEA and the like organic solutions.

[0020] Further, the adsorption tank in step (9) is generally provided with at least two, one for adsorption operation and the other for regeneration operation. The regeneration of the adsorption tank can use conventional operations in the art, such as steam regeneration. The regeneration temperature of the adsorption tank is 120-150 ℃, and the regeneration pressure is generally normal pressure.

[0021] Further, the absorption oil refrigeration technology, heat exchange technology and the like in the present application are well known to the skilled in the art.

[0022] According to the second object of the present application, the present application further provides a dry gas cryogenic purification separation system.

[0023] Specifically, the dry gas cryogenic purification separation system comprises: a cryogenic absorption tower, in which the dry gas is contacted with the cryogenic absorption oil, and the hydrogen sulfide, carbon dioxide and C2+ contained therein are absorbed and condensed, and the rich absorption oil is obtained; the cryogenic absorption tower comprises a dry gas feeding pipeline, a cryogenic absorption oil feeding pipeline, an absorption tail gas removal pipeline and a rich absorption oil removal pipeline; a flash tank, in which the rich absorption oil obtained from the cryogenic absorption tower is isothermally flashed; the flash tank comprises a feeding port for feeding the rich absorption oil into the flash tank, a removal pipeline for removing the flash gas, and a removal pipeline for removing the flash tank bottom oil; a regeneration tower, in which the flash tank bottom oil is subjected to a regeneration operation; the regeneration tower comprises a feeding pipeline for feeding the flash tank bottom oil into the regeneration tower, a removal pipeline for removing the regenerated gas, and a removal pipeline for removing the regeneration tower bottom oil; an adsorption tank, in which the flash gas and the regenerated gas are subjected to an adsorption treatment; the adsorption tank comprises a feeding pipeline for feeding the flash gas and the regenerated gas into the adsorption tank, and a pipeline for removing the adsorption tail gas; an amine liquid absorption tower, in which the obtained adsorption tail gas is subjected to a desulfurization and decarbonization operation; the amine liquid absorption tower comprises a feeding pipeline for feeding the adsorption tail gas and the amine liquid into the amine liquid absorption tower, a removal pipeline for removing the rich amine liquid, and a removal pipeline for removing the absorption tail gas.

[0024] Further, the adsorption tank further comprises a steam feeding pipeline for feeding steam into the adsorption tank, and a pipeline for removing the regenerated gas of the adsorption tank.

[0025] Further, the adsorption tank is usually provided with at least two, one of which is used for adsorption operation, and the other is used for regeneration operation of the adsorption tank. Further, the adsorption tank is filled with an absorbent.

[0026] Further, the cryogenic absorption oil feeding pipeline is further provided with a cooler for cooling the circulating lean absorption oil and the supplemental absorption oil to the feeding temperature.

[0027] Further, the system further comprises a heat exchanger, in which the flash tank bottom oil and the regeneration tower bottom oil are subjected to heat exchange.

[0028] Further, a booster pump is arranged on the feed line of the absorption tank to boost the mixed gas of the flash tank overhead gas and the regeneration tower overhead gas to the operating pressure of the absorption tank.

[0029] Further, the low-temperature absorption tower is a spray tower, which is provided with a gas inlet at the lower end, a rich absorption oil outlet at the bottom, a gas outlet at the top, and a lean absorption oil inlet at the upper end.

[0030] Further, the regeneration tower is a plate tower, which can be a sieve plate tower or a bubble cap tower, and has 5-15 tower plates, preferably 8-12 tower plates.

[0031] Further, in the low-temperature purification and separation system of dry gas, the dry gas pipeline is connected to the gas inlet at the lower end of the low-temperature absorption tower, the gas outlet at the top of the absorption tower is connected to the absorption tail gas pipeline to send the absorption and purification dry gas to the dry gas pipeline network for utilization.

[0032] Further, the inlet of the cooling device is connected to the absorption oil supplement pipeline.

[0033] In the present application, the cooling device and the heat exchanger can adopt a shell-and-tube heat exchanger or a plate heat exchanger, and the flash tank and the circulating pump are all well-known to those skilled in the art.

[0034] Compared with the prior art, the present application has the following beneficial effects: 1. In the dry gas low-temperature purification separation process of the present application, a specific absorption oil is selected as the absorbent, the operating temperature of the low-temperature absorption tower is selected to be -65~-50 ℃, and the absorption condensation operation is carried out at a lower absorption pressure (0.9~1.5 MPa), which more efficiently absorbs C2+ low-carbon hydrocarbons in the dry gas, effectively removes hydrogen sulfide and carbon dioxide in the dry gas, and realizes a C2+ recovery rate of greater than 95% (v) and a hydrogen sulfide and carbon dioxide concentration of less than 10 ppm. Compared with the existing low-temperature absorption process, by selecting a specific absorption oil and a lower operating pressure, the effective recovery and removal of C2+ hydrocarbons, hydrogen sulfide and carbon dioxide in the dry gas is realized by only one stage of absorption, greatly simplifying the absorption operation and reducing the energy consumption of C2+ resource recovery.

[0035] 2. By selecting a constant-temperature flash tank, the rich absorption oil obtained from the low-temperature absorption tower is subjected to flash operation, and 15~30% (v) of the C2+, hydrogen sulfide and carbon dioxide absorbed by the absorption oil is subjected to primary separation, which is equivalent to purifying the feed to the regeneration tower, reducing the feed amount of the rich absorption oil from the absorption tower for direct regeneration operation, and reducing the energy consumption of the regeneration tower operation; the flash (tank bottom) oil obtained is heated with the lean absorption oil discharged from the bottom of the regeneration tower and then enters the regeneration tower, further resolving the dissolved hydrogen sulfide, carbon dioxide and C2+ therein, thereby obtaining lean absorption oil and recycling.

[0036] 3. The resolved gas obtained from the top of the regeneration tower is mixed with the flash tank top gas, and after being pressurized, it enters the adsorption tank for recovering the absorption oil components carried by each. The absorption tail gas obtained from the adsorption tank enters the downstream amine liquid desulfurization unit for acid gas (including hydrogen sulfide and carbon dioxide) purification operation, and obtains purified C2+ hydrocarbons. In the present application, after the dry gas is subjected to low-temperature absorption and condensation separation, the C2+, hydrogen sulfide and carbon dioxide in the dry gas are condensed and absorbed by the absorption oil, and then the absorption oil regeneration gas (i.e. the feed gas of the regeneration tower) is obtained after flash tank flashing and regeneration tower stripping. Compared with the gas amount of direct desulfurization and decarburization of dry gas, the gas amount of absorption oil regeneration gas for desulfurization and decarburization is reduced by more than 70%, greatly reducing the energy consumption of amine liquid desulfurization and decarburization of dry gas.

[0037] 4、The dry gas low-temperature purification separation system of the present application, the absorption oil is recycled, compared with the existing shallow cold oil absorption, adsorption method separation low carbon hydrocarbon process flow and system simple, has the advantages of low system investment, low energy consumption. The existing shallow cold oil absorption process needs to adopt primary C4 absorption, secondary gasoline absorption process, and the absorption operation pressure is high, the system is complex, generally set after the existing amine liquid absorption desulfurization and decarburization device, the amine liquid treatment device is large in scale; the adsorption method separation low carbon hydrocarbon process needs to adopt multi-stage adsorption tank series adsorption, the adsorption equipment is much, the adsorbent consumption is large, the investment is high, generally set after the existing amine liquid absorption desulfurization and decarburization device, the amine liquid treatment device is large in scale. The present application absorbs the primary absorption, the absorption pressure is the dry gas system pressure, can be set before the existing amine liquid absorption desulfurization and decarburization device, the amine liquid treatment device is small in scale. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 It is the dry gas low-temperature purification separation process flow diagram of the present application.

[0039] Among them, 101-dry gas pipeline, 102-low temperature absorption tower, 103-cooler, 104-flash tank, 105-heat exchanger, 106-circulating pump, 107-regeneration tower, 108-compressor, 109-adsorption tank, 110-absorption tail gas pipeline, 111-absorption oil liquid supplement pipeline, 112-regeneration steam pipeline, 113-regeneration gas pipeline, 114-amine liquid absorption tail gas pipeline, 115-lean amine liquid pipeline, 116-rich amine liquid pipeline, 117-amine liquid absorption tower.

[0040] Figure 2 It is the process flow diagram of the prior art shallow cold oil absorption process.

[0041] Figure 2 Among them, 201-dry gas pipeline, 202-amine liquid absorption tower, 203-rich amine liquid pipeline, 204-lean amine liquid pipeline, 205-compressor, 206-cooler, 207-C4 absorption tower, 208-absorption oil cooler, 209-lift pump, 210-regeneration tower, 211-gasoline absorption tower, 212-rich absorption oil pipeline, 213-methane hydrogen gas pipeline, 214-absorption gasoline pipeline, 215-rich C2 gas pipeline. DETAILED DESCRIPTION

[0042] The specific situation of the present application will be further illustrated by specific examples below, but not limited to the following examples.

[0043] Combined Figure 1 The dry gas low-temperature purification separation process flow of the present application is as follows: The dry gas is condensed by low-temperature absorption oil in the absorption tower 102, and the condensed gas is an absorption tail gas, which is discharged from the top of the absorption tower 102 through an absorption tail gas pipeline; the absorption oil is fed from the upper end of the absorption tower 102, and absorbs and condenses C2+, hydrogen sulfide and carbon dioxide in the absorption tower 102 countercurrently with the dry gas fed from the lower end of the absorption tower 102, and the absorption oil after absorbing and condensing the dry gas becomes rich absorption oil. The rich absorption oil is discharged from the bottom of the absorption tower 102, and is sent to the flash tank 104 by the pressure in the absorption tower 102, and is flashed at 0.1-0.3 MPaG in the flash tank; the liquid phase discharged from the bottom of the flash tank 104 enters the regeneration tower 107 by self-pressure, and is stripped and separated in the regeneration tower 107, so that the components of hydrogen sulfide, carbon dioxide and C2+ absorbed and condensed by the absorption oil are stripped out and discharged from the top of the regeneration tower 107; the lean absorption oil after regeneration is discharged from the bottom, pressurized by the circulating pump 106, and enters the heat exchanger 105, and exchanges heat with the liquid stream discharged from the bottom of the flash tank, and the lean absorption oil is cooled to -30--10℃ after heat exchange, and is further cooled to -65--50℃ in the cooler 103, and then enters the absorption tower 102 as absorption oil of the absorption tower; at the same time, the liquid phase discharged from the bottom of the flash tank 104 is heated to 60-90℃, and then enters the regeneration tower 107 for regeneration.

[0044] The gas phase discharged from the top of the flash tank 104 is mixed with the gas phase discharged from the top of the regeneration tower 107, and is pressurized to 0.2-0.5 MPaG, and then enters the adsorption tank 109 to adsorb the absorption oil components entrained in the mixed gas; the adsorption tail gas obtained after adsorption in the adsorption tank 109 mainly consists of C2+ light hydrocarbon, hydrogen sulfide and carbon dioxide, and the adsorption tail gas enters the amine liquid absorption tower 117 to absorb and remove the components of hydrogen sulfide and carbon dioxide, and obtains the C2+ light hydrocarbon component. The adsorption tank 109 is regenerated, and the regenerated gas obtained is separated to obtain recovered absorption oil, which is mixed with optional additional absorption oil and returned to the low-temperature absorption tower 102 as absorption oil for further use.

[0045] Further, the dry gas raw material generally contains 1-3 v% (v) hydrogen sulfide, 1-3% (v) carbon dioxide and other impurities, the C2+ content is 10-20% (v), and other components are methane, nitrogen and hydrogen.

[0046] Further, the main components of the absorption tail gas are methane, nitrogen and hydrogen, wherein the content of hydrogen sulfide is less than 10 ppm, the content of carbon dioxide is less than 10 ppm, and the content of C2+ is less than 5% (v).

[0047] Further, the operating temperature of the absorption tower 102 is -65--50 ℃, the absorption pressure is 0.9-1.5 MPaG, and the liquid-gas ratio is 40-200 L / m 3 , and the liquid-gas ratio is preferably 40-120 L / m 3 .

[0048] Further, the absorption oil used in the absorption tower 102 is selected from at least one of toluene, ethylbenzene, heptane and isooctane. The absorption oil is obviously different from the existing low-temperature absorption process, and has a low condensation point, a low saturated vapor pressure and a high boiling point, and is not easy to evaporate.

[0049] Further, the flash is constant-temperature flash. The flash tank 104 is usually provided with a jacket. The temperature of the flash tank 104 is controlled at -45~-30℃, and the operating pressure of the flash tank 104 is generally 0.1~0.3MPaG.

[0050] Further, the operating conditions of the regeneration tower 107 are known to those skilled in the art. For example, the bottom regeneration temperature of the regeneration tower 107 is 80~120℃, preferably 90~115℃; the operating temperature of the top of the regeneration tower 107 is -10~10℃, preferably -5~5℃; the operating pressure of the regeneration tower 107 is normal pressure operation or slightly positive pressure operation; and the reflux ratio of the top of the regeneration tower 107 is 0.5~2, preferably 0.8~1.5.

[0051] Further, the adsorption pressure of the adsorption tank 109 is 0.2~0.5 MPaG, and generally normal-temperature adsorption. The adsorption tank 109 is used to capture the absorption oil components carried in the tail gas-fourth stream discharged from the regeneration tower, so as to reduce the supplement of the absorption oil. The adsorption tank 109 is filled with an adsorbent. The adsorbent is selected from one or more of activated carbon, molecular sieve, zeolite and the like.

[0052] Further, the operation of the amine liquid absorption tower 117 is a conventional operation in the art. The organic amine absorption liquid (absorbent) is usually selected from one or more of MDEA, MEA, DEA and other organic solutions.

[0053] Further, the adsorption tank 109 is usually provided with two, one of which is used for adsorption operation, and the other is used for regeneration operation. The regeneration of the adsorption tank 109 can adopt a conventional operation in the art, such as steam regeneration. The regeneration temperature of the adsorption tank 109 is 120~150℃, and the regeneration pressure is generally normal pressure.

[0054] Further, the absorption oil refrigeration technology, heat exchange technology and the like in the present application are well known to those skilled in the art.

[0055] In combination Figure 1 The dry gas low-temperature absorption system provided by the present application comprises: a low-temperature absorption tower 102, in which dry gas is contacted with low-temperature absorption oil, hydrogen sulfide, carbon dioxide and C2+ contained therein are absorbed and condensed, and rich absorption oil is obtained; the low-temperature absorption tower 102 comprises a dry gas feeding pipeline 101, a low-temperature absorption oil feeding pipeline, an absorption tail gas removal pipeline 110 and a rich absorption oil removal pipeline; a flash tank 104 for flash evaporation of the rich absorption oil from the low temperature absorption column 102; the flash tank 104 includes a feed inlet for feeding the rich absorption oil into the flash tank 104, a removal pipeline for removing the flash gas, and a removal pipeline for removing the bottom oil of the flash tank 104; a regeneration column 107 for regenerating the bottom oil of the flash tank 104; the regeneration column 107 includes a feed pipeline for feeding the bottom oil of the flash tank 104 into the regeneration column 107, a removal pipeline for removing the regenerated gas, and a removal pipeline for removing the bottom oil of the regeneration column; an adsorption tank 109 for adsorbing the flash gas and the regenerated gas from the regeneration column 107; the adsorption tank 109 includes a feed pipeline for feeding the flash gas and the regenerated gas into the adsorption tank, and a pipeline for removing the adsorption tail gas and a regenerated gas pipeline 113; an amine liquid absorption column 117 for desulfurization and decarbonization of the adsorption tail gas; the amine liquid absorption column includes a feed pipeline for feeding the adsorption tail gas into the absorption column, a lean amine liquid feed pipeline 115, a pipeline 116 for removing the rich amine liquid, and a pipeline 114 for removing the amine liquid absorption tail gas.

[0056] Further, the adsorption tank 109 further includes a steam inlet pipeline 112 for feeding steam into the adsorption tank, and a pipeline 113 for removing the regenerated gas.

[0057] Further, the adsorption tank 104 is usually provided with at least two, one of which is used for adsorption operation, and the other is used for regeneration operation of the adsorption tank. Further, the adsorption tank 104 is filled with an absorbent.

[0058] Further, the low temperature absorption oil feed pipeline is further provided with a cooler 103 for cooling the circulating lean absorption oil and the absorption oil from the absorption oil supplement pipeline 111 to the feed temperature.

[0059] Further, the system further includes a heat exchanger 105 for heat exchange between the flash tank bottom oil and the regeneration column bottom oil.

[0060] Further, the feed pipeline of the absorption tank 104 is further provided with a compressor 108 for pressurizing the mixed gas of the flash tank top tail gas and the regeneration column top tail gas to the operating pressure of the absorption tank.

[0061] Further, the low temperature absorption column 102 is a spray tower, which is provided with a gas inlet at the lower end, a rich absorption oil outlet at the bottom, a gas outlet at the top, and a lean absorption oil inlet at the upper end.

[0062] Further, the regeneration tower 107 is a plate tower, which can be a sieve plate tower, a bubble cap tower, etc. The regeneration tower has 5-15 tower plates, preferably 8-12 tower plates. The regeneration tower 107 is provided with a feed inlet, which is located at the middle section of the tower, preferably 2-6 plates for feeding; the bottom of the regeneration tower 107 is provided with a lean absorption oil outlet, and the top is provided with a gas outlet.

[0063] Further, the dry gas pipeline 101 is connected to the gas inlet at the lower end of the low-temperature absorption tower 102, and the gas outlet at the top of the absorption tower is connected to the absorption tail gas pipeline 110 to send the absorption and purification dry gas to the dry gas pipeline network for utilization. The lean absorption oil for the low-temperature absorption tower 102 is introduced from the lean absorption oil inlet at the upper end of the tower, and is absorbed and condensed countercurrently with the dry gas in the tower. The lean absorption oil becomes rich absorption oil, and the rich absorption oil outlet at the bottom of the low-temperature absorption tower 102 is communicated with the inlet of the flash tank 104. The gas outlet at the top of the flash tank 104 is combined with the gas outlet at the top of the regeneration tower 107 and connected to the gas inlet of the compressor 108. The gas outlet of the compressor 108 is connected to the gas inlet of the adsorption tank 109, and the adsorption separation and recovery of heavy components are carried out in the adsorption tank 109. The gas outlet of the adsorption tank 109 is connected to the amine liquid absorption tower 117 for desulfurization and decarburization of the adsorption tail gas, and a high-concentration low-carbon hydrocarbon component is obtained, which can be used as an ethylene raw material. The liquid outlet at the bottom of the flash tank is connected to the regeneration tower 107 feed inlet through a pipeline after being communicated with the heat exchanger 105. The lean absorption oil outlet of the regeneration tower 107 is communicated with the heat exchanger 105 and the cooler 103 in sequence, and then connected to the lean absorption oil inlet of the absorption tower 102. Example 1

[0064] According to the process and system described in the present application, using the dry gas composition in Table 1 as raw material, and using a mixture of toluene and ethylbenzene oil as absorption liquid, the dry gas is absorbed at -60℃ and 0.9MPaG. After the C2+ resources are recovered, the dry gas is used as fuel gas. The hydrogen sulfide content in the fuel gas is less than 10ppm, the carbon dioxide content is less than 10pmm, the C2+ content is less than 2% (v), and the C2+ recovery rate is 95.3%. The rich absorption oil is further flashed at -40℃ and 0.1MPaG, and then the rich absorption oil is regenerated at normal pressure and 110℃. The regenerated liquid is recycled after being cooled by heat exchange, and the regenerated gas and the flash gas are further adsorbed into the absorption oil at normal temperature and 0.5MPa pressure. The regenerated gas after removing the absorption oil components is finally desulfurized and decarburized by amine liquid absorption. The volume of the desulfurized and decarburized gas is greatly reduced compared with the volume of the dry gas raw material, and the amine liquid absorption gas treatment capacity is reduced by 72.5% compared with the existing technology. The C2+ recovery energy consumption is 55.4kg of standard oil per ton of dry gas raw material. The simulation results of the Aspen Plus software are shown in Table 1.

[0065] Table 1 Dry gas raw material and product gas composition in the present application

[0066] Comparative Example 1 In the paper "Simulation of Saturated Dry Gas Recovery in Refinery by Light Oil Absorption Process", the dry gas in Table 2 was used as raw material, and the absorption effect and energy consumption of the process were calculated by light oil absorption. Figure 2 In the process, the dry gas is first introduced into the amine liquid absorption tower 202 through the dry gas pipeline 201 for desulfurization and decarburization, and the lean amine liquid is introduced into the amine liquid absorption tower through the lean amine liquid pipeline 204 after washing the dry gas, and then discharged from the amine liquid absorption tower through the rich amine liquid pipeline 203; the dry gas after desulfurization and decarburization is compressed to 3.85 MPaG by the compressor 205, and then cooled to 10-15℃ by the cooler 206; the cooled dry gas is introduced into the C4 absorption tower 207 for first-stage absorption, and then introduced into the gasoline absorption tower 211 for second-stage absorption; the second-stage absorption tail gas is discharged from the gasoline absorption tower top methane hydrogen gas pipeline 213, the absorption gasoline is introduced into the gasoline absorption tower 211 through the absorption gasoline pipeline 214, and the rich absorption oil of the gasoline absorption tower is discharged from the tower bottom rich absorption oil pipeline 212 and introduced into the refinery device for recycling. The C4 absorption tower 207 bottom absorption oil is self-pressured into the regeneration tower 210 for stripping and regeneration, and then the lean C4 absorption oil after regeneration is pressurized by the booster pump 209, sent to the absorption oil cooler 208 for cooling, and then introduced into the C4 absorption tower 207 for recycling C2+ resources. The regeneration gas at the top of the regeneration tower is the recycled C2+ resources, which is discharged from the rich C2 gas pipeline 215.

[0067] As can be seen from Table 2, the dry gas raw material is first desulfurized and decarburized, and the dry gas after purification and recycling of C2+ resources is used as fuel gas, the C2+ content in the fuel gas is less than 3% (v), and the energy consumption of C2+ light oil absorption recovery is 77.8 kg of standard oil / t of dry gas raw material.

[0068] Table 2 Dry gas raw material and product gas composition in light oil absorption process

Claims

1. A dry gas cryogenic purification separation process characterized by, The application relates to a dry gas low-temperature purification separation system. (1) the dry gas from a pipe network is taken as a purification object, the dry gas is absorbed and condensed by low-temperature absorption oil in an absorption tower, the gas after absorption and condensation is tail gas, and the tail gas is discharged from the top of the absorption tower through a tail gas pipeline; the absorption oil is fed from the upper end of the absorption tower and is countercurrently absorbed and condensed with the dry gas fed from the lower end of the absorption tower to condense C2+, hydrogen sulfide and carbon dioxide in the absorption tower, and the absorption oil after absorption and condensation of the dry gas becomes rich absorption oil, which is a first stream; (3) the first stream is discharged from the bottom of the absorption tower, is sent to a flash tank by the pressure in the absorption tower, is flashed at 0.1-0.3 MPaG in the flash tank, and is obtained as a second stream in a gas phase and a third stream in a liquid phase; (4) the third stream enters a regeneration tower by self-pressure, is stripped and separated in the regeneration tower, hydrogen sulfide, carbon dioxide and C2+ components absorbed and condensed by the absorption oil are stripped out, and the fourth stream is discharged from the top of the regeneration tower; the lean absorption oil after regeneration is discharged from the bottom of the tower and is the fifth stream; (5) the fifth stream is pressurized by a circulating pump, enters a heat exchanger, exchanges heat with the third stream discharged from the bottom of the flash tank, is cooled to-30--10 DEG C after heat exchange, and is the sixth stream; the third stream is heated to 60-90 DEG C and then enters the regeneration tower for regeneration; (6) the obtained sixth stream is cooled to-65--50 DEG C in a cooler and enters the absorption tower as absorption oil of the absorption tower; (7) the second stream in a gas phase discharged from the top of the flash tank is mixed with the fourth stream in a gas phase discharged from the top of the regeneration tower, is pressurized to 0.2-0.5 MPaG, and enters an adsorption tank to adsorb absorption oil components entrained in the second stream and the fourth stream; (8) the adsorption tail gas obtained in the step (7) mainly comprises C2+ light hydrocarbon, hydrogen sulfide and carbon dioxide, the adsorption tail gas enters an amine liquid absorption tower to absorb and remove hydrogen sulfide and carbon dioxide components, and C2+ light hydrocarbon components are obtained. The dry gas contains 1-3 v% of hydrogen sulfide, 1-3 v% of carbon dioxide and 10-20 v% of C2+, and other components are methane, nitrogen and hydrogen. The main components of the tail gas obtained in the step (2) are methane, nitrogen and hydrogen, the content of hydrogen sulfide is less than 10 ppm, the content of carbon dioxide is less than 10 ppm, and the content of C2+ is less than 5 v%.

2. The cryogenic purification separation process of claim 1, wherein, The temperature of the flash tank is-45--30 DEG C, and the operating pressure of the flash tank is 0.1-0.3 MPaG; and / or 3. The cryogenic purification separation process of claim 1, wherein, The regeneration temperature at the bottom of the regeneration tower is 80-120 DEG C, the operating temperature at the top of the regeneration tower is-10-10 DEG C, the operating pressure of the regeneration tower is normal pressure operation or slightly positive pressure operation, the reflux ratio of the regeneration tower is 0.5-2, and / or 4. The cryogenic purification separation process of claim 1, wherein, ​ 5. The cryogenic purification separation process of claim 1, wherein, The operating temperature of the absorption tower is -65~ -50 ℃, the absorption pressure is 0.9~1.5 MPaG, the absorption liquid gas ratio is 40~200 L / m 3 , preferably 40~120 L / m 3 ; and / or the absorption oil is selected from at least one of toluene, ethylbenzene, heptane and isooctane.

6. The cryogenic purification separation process of claim 1, wherein, ​ ​ The adsorption pressure of the adsorption tank is 0.2-0.5 MPaG.

7. The cryogenic purification separation process of claim 1, wherein, The adsorbent filled in the adsorption tank is selected from one or more of activated carbon, molecular sieve and zeolite.

8. The cryogenic purification separation process of claim 2, wherein, Two adsorption tanks are provided in step (9), one for adsorption operation and the other for regeneration operation.

9. The cryogenic purification separation process of claim 8, wherein, The regeneration of the adsorption tank is steam regeneration, and the regeneration temperature of the adsorption tank is 120-150 DEG C, and the regeneration pressure is normal pressure.

10. A dry gas cryogenic purification separation system characterized by, It comprises: a low-temperature absorption tower, in which dry gas is contacted with low-temperature absorption oil, hydrogen sulfide, carbon dioxide and C2+ contained therein are absorbed and condensed, and rich absorption oil is obtained; the low-temperature absorption tower comprises a dry gas feeding pipeline, a low-temperature absorption oil feeding pipeline, an absorption tail gas removal pipeline and a rich absorption oil removal pipeline; a flash tank, in which the rich absorption oil obtained from the low-temperature absorption tower is isothermally flashed; the flash tank comprises a feeding port for feeding the rich absorption oil into the flash tank, a removal pipeline for removing flash gas, and a removal pipeline for removing the bottom oil of the flash tank; a regeneration tower, in which the bottom oil of the flash tank is subjected to regeneration operation; the regeneration tower comprises a feeding pipeline for feeding the bottom oil of the flash tank into the regeneration tower, a removal pipeline for removing regeneration tail gas, and a removal pipeline for removing the bottom oil of the regeneration tower; an adsorption tank, in which the flash gas and the regeneration tower tail gas are subjected to adsorption treatment; the adsorption tank comprises a feeding pipeline for feeding the flash gas and the regeneration tower tail gas into the adsorption tank, and a pipeline for removing adsorption tail gas; an amine liquid absorption tower, in which the obtained adsorption tail gas is subjected to desulfurization and decarburization operation; the amine liquid absorption tower comprises a feeding pipeline for feeding the adsorption tail gas and amine liquid into the amine liquid absorption tower, a removal pipeline for removing rich amine liquid, and a removal pipeline for removing absorption tail gas.

11. The dry gas cryogenic purification separation system of claim 10 wherein, The adsorption tank further comprises a steam feeding pipeline for feeding steam into the adsorption tank, and a pipeline for removing regeneration gas.

12. The dry gas cryogenic purification separation system of claim 10 wherein, The adsorption tank is provided with at least two, one of which is used for adsorption operation, and the other is used for regeneration operation of the adsorption tank.

13. The dry gas cryogenic purification separation system of claim 10 wherein, A cooler is further provided on the low-temperature absorption oil feeding pipeline, which is used for cooling the circulating lean absorption oil and the supplementary absorption oil to the feeding temperature.

14. The dry gas low temperature purge separation system of claim 10, wherein, The system further comprises a heat exchanger, in which the bottom oil of the flash tank and the bottom oil of the regeneration tower are subjected to heat exchange.

15. The dry gas cryogenic purification separation system of claim 10 wherein, A booster pump is further provided on the feeding pipeline of the absorption tank, which is used for boosting the mixed gas of the flash tank top tail gas and the regeneration tower top tail gas to the operating pressure of the absorption tank.

16. The dry gas cryogenic purification separation system of claim 10 wherein, The low-temperature absorption tower is a spray tower, which is provided with a gas inlet at the lower end, a rich absorption oil outlet at the bottom, a gas outlet at the top, and a lean absorption oil inlet at the upper end.

17. The dry gas cryogenic purification separation system of claim 10 wherein, The regeneration tower is a plate tower, and the regeneration tower plate is 5-15; the regeneration tower is provided with a feeding port, which is located in the middle section of the tower, and preferably 2-6 plates are fed; the bottom of the regeneration tower is provided with a lean absorption oil outlet, and the top is provided with a gas outlet.

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