Method for extraction of carbon dioxide and unit for its implementation

Abstract

FIELD: gas processing; oil refining and petrochemical industries.SUBSTANCE: group of inventions relates to the separation of carbon dioxide and can find application in organizing the purification of raw gas from acidic components. The method consists of primary separation and subsequent chemical absorption with an aqueous solution of a hydrogen sulphide-selective absorbent based on methyldiethanolamine and its regeneration with the formation of an acid gas; the gas flow after the chemical absorption stage is fed to the first stage of membrane gas separation. The first stage retentate, which is purified commercial gas, is removed from the plant for further processing; the first stage permeate is first compressed to a pressure of no more than 6.5 MPa and then sent to the second stage of membrane gas separation. The separated permeate of the second stage, which is a highly concentrated separated stream of carbon dioxide, is removed from the unit as a marketable product, and the retentate of the second stage is returned back to the first stage of membrane gas separation. The unit comprises a separator, a chemical absorption unit, which includes an absorber, a desorber, the first and second pumps, a recuperative heat exchanger, the first and second air coolers, a reboiler, an expander, an acid gas separator, and a two-stage membrane extraction unit, consisting of the first and second membrane gas separation units, a compressor, and a separator.EFFECT: simplifying the process flow diagram for purifying raw gas from acidic components, reducing the consumption of an aqueous solution of amine absorbent and energy costs for its regeneration with a guaranteed quality of the resulting product.2 cl, 1 dwg, 1 tbl

Description

[0001] The group of inventions relates to the separation of carbon dioxide and can find application in the gas processing, oil refining and petrochemical industries in organizing the purification of raw gas from acidic components.

[0002] A method for processing natural gas is known (RU Patent No. 2576738, IPC F25J 3 / 08, published March 10, 2016). The method involves a sequential two-stage purification of raw separation gas from acidic components: first, hydrogen sulfide is removed using an absorbent with selective hydrogen sulfide selectivity, which is an absorbent containing polyethylene glycol dimethyl ether, then carbon dioxide is removed using supersonic separation.

[0003] This method requires significant energy consumption during carbon dioxide separation due to the operation of the main equipment, which operates at high pressures and low temperatures. It is also quite complex to operate, including due to the need to maintain the temperature of the two-phase flow exiting the supersonic separator above the CO2 crystallization temperature. It also suffers from low reliability during long-term industrial operation due to erosive wear of the supersonic separator blades. Periodic blade replacement increases costs and reduces the economic efficiency of the unit. The above-described disadvantages could potentially significantly limit the operation and implementation of this method in industrial settings.

[0004] A known method for separating acid gas into components - hydrogen sulfide and carbon dioxide (RU Patent 2750797, IPC B01D 53 / 14, published on July 2, 2021), consists of a two-stage sequential absorption of hydrogen sulfide with a selective absorber in two absorption columns (an aqueous solution of methyl diethanolamine (hereinafter MDEA) - 60% by weight and diethylene glycol - 12% by weight) and one common desorption stage, which makes it possible to obtain two process streams (carbon dioxide and hydrogen sulfide) of high concentration, due to the separation of acid gas with a concentration ratio of hydrogen sulfide to carbon dioxide in the acid gas equal to 1:1.

[0005] The disadvantages of the known method are its significant energy costs associated with the operation of three additional sorption columns, which also leads to an increase in metal consumption and, accordingly, capital costs for the implementation of the known method.

[0006] A known method for separating carbon dioxide from exhaust gas using membrane separation stages based on purging and absorption (RU Patent No. 2534075, IPC B01D 53 / 14, published November 27, 2014), consists of first dividing the flue gas flow into two parts and then purifying them by absorption capture of carbon dioxide and membrane separation, organized in parallel. The invention ensures efficient purification of flue gases.

[0007] The disadvantage of the known method is the impossibility of using such a technical solution for the separation of carbon dioxide during the purification of natural gas containing hydrocarbons and hydrogen sulfide.

[0008] A known technology for combined acid gas purification from carbon dioxide (Maddox Rand., MJ. Gas conditioning and processing. Vol. 4. Gastreating and sulfur recovery. - 2008. No. 3) consists of sequentially conducting first single-stage membrane gas separation, followed by absorption amine purification. Single-stage membrane gas separation before the amine purification stage reduces operating costs at the absorption stage, but does not solve the problem of isolating a highly concentrated stream of commercial-quality carbon dioxide, due to the similar permeability coefficients of hydrogen sulfide and carbon dioxide through the membrane, which is its drawback.

[0009] The closest analogue of the claimed invention (prototype) is a method for purifying natural gas from carbon dioxide and hydrogen sulfide (RU Patent No. 2547021, IPC B01D 53 / 14, published on 10.04.2015), which consists in sequentially purifying gas in two absorption stages, each of which has its own absorbent circulation circuit and at each absorption stage, acid gas of varying composition is separated from the gas. In this case, an aqueous solution of MDEA with a content of 40-60% or its modification with additives that weaken the absorption with respect to carbon dioxide is used as an absorber at the first stage, and at the second stage - a solution of MDEA mixed with DEA ​​in different ratios or each of them separately, including their modifications and additives that enhance the absorption effect with respect to carbon dioxide.

[0010] The disadvantage of the above technical solution is that the amine absorbent primarily extracts hydrogen sulfide in the first stage of chemical absorption, and carbon dioxide in the second stage. This disadvantage leads to a decrease in the efficiency of carbon dioxide separation from the feed gas during its purification, due to the additional consumption of expensive absorbent in the second stage of chemical absorption for carbon dioxide absorption and the associated additional energy costs for its regeneration.

[0011] A device is known for implementing a method for purifying natural gas (RU Patent No. 2576738, IPC F25J 3 / 08, published 03 / 10 / 2016), containing a unit for extracting hydrogen sulfide with an absorbent with selective selectivity for hydrogen sulfide, consisting of absorption and desorption columns, heat exchange and injection equipment, interconnected by pipelines, and a supersonic separation unit, which includes heat exchange, separation, pumping and compressor equipment, a fractionation column, a supersonic separator.

[0012] The disadvantages of the known device are:

[0013] - high energy costs during the release of a carbon dioxide flow associated with the operation of the main equipment operating at high pressures and low temperatures;

[0014] - Low reliability during long-term industrial operation due to erosive wear of the supersonic separator blades. Periodic blade replacement increases costs and reduces the economic efficiency of the unit.

[0015] The closest to the proposed method for sequentially cleaning gas using two stages of absorption and the installation for its implementation (prototype) is the method and installation for cleaning natural gas from carbon dioxide and hydrogen sulfide (RU Patent No. 2547021, IPC B01D 53 / 14, published on 10.04.2015). The method includes two stages of absorption: at the first stage, selective cleaning with respect to carbon dioxide is carried out with the release of acid gas, in which the carbon dioxide content does not exceed 30-40%, and purified gas with a hydrogen sulfide content of no more than 5-7 mg / m 3 , sent further to the second stage of absorption to obtain purified gas with a carbon dioxide content of no more than 50-200 mg / m3 3and a complete absence of hydrogen sulfide and acid gas with a hydrogen sulfide content of no more than 200 mg / m3 3 , wherein the saturation of the alkylamine absorbent at each stage of absorption with acidic components does not exceed 0.4 mol / mol, while natural gas has a hydrogen sulfide to carbon dioxide ratio of 1.0, but not more than 1.5, and a hydrogen sulfide concentration of 3.5 to 8.0 vol.%. The installation includes two sequential gas absorption purification units, consisting of an absorber, a regenerator, pumps, a refrigerator, a recuperative heat exchanger, a boiler, a tank and pipelines piping the apparatus of the gas absorption purification units.

[0016] The disadvantages of the above technical solution are the absorption of predominantly hydrogen sulfide at the first stage of the process, and carbon dioxide at the second stage of the process, which leads to an increase in the amount of necessary process equipment, an increase in metal consumption and a complication of the overall process flow diagram.

[0017] The task that the claimed group of inventions is aimed at solving is the development of an effective method for separating carbon dioxide and an installation for its implementation, which makes it possible to separate carbon dioxide while organizing the purification of raw gas from acidic components.

[0018] The technical result that the group of inventions is aimed at achieving is an increase in the productivity of carbon dioxide emission.

[0019] The technical result according to the subject of the invention - the method is achieved in that in the method of separating carbon dioxide from raw gas, including carrying out primary separation, after which chemical absorption is carried out with an aqueous solution of an absorbent selective with respect to hydrogen sulfide based on methyldiethanolamine and its regeneration with the formation of acid gas, what is new is that the gas stream after the chemical absorption stage with a pressure of up to 6.0 MPa and a temperature of up to 55 ° C is fed to the first stage of membrane gas separation, while the retentate of the first stage, which is purified commercial gas, is removed from the plant for further processing, the permeate of the first stage is first compressed to a pressure of no more than 6.5 MPa, and then sent to the second stage of membrane gas separation, the separated permeate of the second stage is a highly concentrated separated stream of carbon dioxide, which is removed from the plant as a commercial product,and the retentate from the second stage is returned back to the first stage of membrane gas separation.

[0020] The technical result according to the subject of the invention - the device is achieved in that the installation for separating carbon dioxide contains a separator, a chemical absorption unit, which includes an absorber, a desorber, first and second pumps, a recuperative heat exchanger, first and second air cooling devices, a reboiler, an expander, an acid gas separator, connecting pipelines, and a two-stage membrane extraction unit, consisting of first and second membrane gas separation units, a compressor and a separator-condenser, interconnected by pipelines.

[0021] The elements of the claimed installation are interconnected as follows: a pipeline for feeding raw gas is connected to the lower part of the absorber, the top of the absorber is connected by a pipeline for feeding gas purified from hydrogen sulfide to the first membrane gas separation unit, the high-pressure cavity of which is connected to the first stage retentate discharge pipeline, and the low-pressure cavity of which is sequentially connected by the first stage permeate discharge pipeline through a compressor and a separator-condenser to the second membrane gas separation unit, the high-pressure cavity of which is connected by the second stage retentate discharge pipeline to the pipeline for feeding gas purified from hydrogen sulfide, and the low-pressure cavity of which is connected by the second stage permeate discharge pipeline.The top of the desorber is connected in series via a pipeline through the first air cooler and an acid gas separator, the outlet of which is connected via the first pump to the top of the desorber, with an acid gas removal pipeline. The bottom of the absorber is connected by pipelines first to the expander, then to the recuperative heat exchanger, and then to the desorber. The bottom of the desorber is connected to the reboiler, the top of which is connected to the bottom of the desorber, and the bottom of which is connected via a second pump to the top of the absorber through the recuperative heat exchanger and the second air cooler.

[0022] The essence of the claimed invention is explained by the drawing.

[0023] The drawing shows a basic flow chart of the installation in which the claimed method of carbon dioxide extraction is carried out.

[0024] The installation (see drawing), in which the claimed method is carried out, consists of the following elements:

[0025] - separator (not shown in the drawing) for primary separation of raw gas, which is a cylindrical horizontal apparatus in which mechanical impurities and hydrocarbon liquid are separated from the gas mixture;

[0026] - pipeline for feeding raw gas 1 after primary separation;

[0027] - acid gas discharge pipeline 18;

[0028] - pipeline for supplying gas purified from hydrogen sulfide 2;

[0029] - absorber 10, which is a vertical apparatus equipped with a packing in which the absorption of predominantly hydrogen sulfide by a selective absorbent occurs;

[0030] - desorber 20, which is a vertical type apparatus in which the regeneration of a saturated solution of a selective absorbent occurs due to a reverse chemical reaction when the pressure decreases and the temperature of the absorbent solution increases;

[0031] - recuperative heat exchanger 4 for recovering the heat of the regenerated absorbent solution returned back to the chemical absorption stage;

[0032] - reboiler 8 to maintain the required temperature regime of the desorber;

[0033] - expander 25 for removing physically dissolved hydrocarbons from a saturated absorbent solution before feeding it for regeneration;

[0034] - acid gas separator 6 for separating acidic water (phlegm) from the gas flow, which is returned for irrigation back to the desorber;

[0035] - the first and second air cooling devices 5, 11 to ensure the required temperature regime of process flows;

[0036] - the first and second pumps 7, 9, which are dynamic centrifugal pumps for ensuring the circulation of liquid flows;

[0037] - the first and second membrane gas separation units 30, 40, which are devices in which a semi-permeable membrane is installed, dividing it into high and low pressure cavities;

[0038] - compressor 12 for increasing the pressure of the permeate gas flow directed to the input of the second membrane gas separation unit;

[0039] - separator-condenser 13, which is a vertical metal apparatus in which condensed water is separated from the gas flow;

[0040] - first stage retentate discharge pipeline 17;

[0041] - first stage permeate discharge pipeline 21;

[0042] - second stage retentate discharge pipeline 22;

[0043] - second stage permeate discharge pipeline 23.

[0044] In this case, the elements of the installation for implementing the method for separating carbon dioxide in accordance with the drawing are interconnected as follows: the pipeline for feeding raw gas 1 is connected to the lower part of the absorber 10, the top of the absorber 10 is connected by a pipeline for feeding gas purified from hydrogen sulfide 2 to the first membrane gas separation unit 30, the high-pressure cavity of which is connected to the first stage retentate discharge pipeline 17, and the low-pressure cavity of which is connected by the first stage permeate discharge pipeline 21 in series through the compressor 12 and the separator-condenser 13 to the second membrane gas separation unit 40, the high-pressure cavity of which is connected by the second stage retentate discharge pipeline 22 to the pipeline for feeding gas purified from hydrogen sulfide 2, and the low-pressure cavity of which is connected by the second stage permeate discharge pipeline 23,wherein the top of the desorber 20 is connected in series through a pipeline via the first air-cooling apparatus 5 and the acid gas separator 6, the outlet of which is connected via the first pump 7 to the top of the desorber 20, with the pipeline for removing acid gas 18. The bottom of the absorber is connected in series by pipelines first to the expander 25, then to the recuperative heat exchanger 4 and is connected to the desorber 20. The bottom of the desorber is connected to the reboiler 8, the top of which is connected to the bottom of the desorber 20, and the bottom of which is connected via the second pump 9 to the top of the absorber 10 in series through the recuperative heat exchanger 4 and the second air-cooling apparatus 11.

[0045] The method for isolating carbon dioxide is as follows.

[0046] Feed gas enters the primary separation separator, where mechanical impurities and hydrocarbon liquid are separated from the gas mixture. Next, the feed gas from the separator, at a temperature no higher than 30°C and a pressure of up to 6.0 MPa, is sent through pipeline 1 to absorber 10 for purification from acidic components. Due to countercurrent contact between the vapor and liquid phases, hydrogen sulfide is primarily absorbed by a selective absorbent based on an aqueous MDEA solution.

[0047] Before being fed through pipelines by centrifugal pump 9 to absorber 10, the regenerated selective absorbent solution passes through heat exchanger 4 and air cooling apparatus 11, where it is cooled to a temperature of no more than 55°C.

[0048] The gas purified from hydrogen sulfide is withdrawn from the top of the absorber 10 and fed through pipeline 2 to the membrane gas separation, and the MDEA solution saturated with acid gases is withdrawn through a pipeline from the bottom of the absorber 10. Next, the amine solution saturated with hydrogen sulfide and carbon dioxide is fed through a pipeline to the expander 25, where physically dissolved hydrocarbons are removed from it in the form of an expansion gas, and then through the recuperative heat exchanger 4, where it is heated due to the heat of the regenerated amine solution flow, it enters the desorber 20. The temperature of the top of the desorber 20 is no more than 112 °C, and the temperature in the bottom of the desorber 20 is no more than 130 °C, controlled by sensors with the readings displayed on the computer. The bottom part of the desorber 20 is equipped with a reboiler 8 to maintain the temperature regime of the column.

[0049] In the internal contact devices of desorber 20, hydrogen sulfide and carbon dioxide are separated from the saturated amine solution by the ascending vapor flow. Acidic components are separated in the desorber by contact between the ascending vapors from the bottom of the column and the descending flow of the saturated amine solution.

[0050] A mixture of hydrogen sulfide, carbon dioxide and water vapor is discharged from the top of desorber 20 and cooled in air cooling unit 5, where most of the water vapor condenses, while the temperature of the acid gas at the outlet of the air cooling unit does not exceed 60°C.

[0051] The vapor-liquid mixture after the air cooling unit 5 enters the acid gas separator 6, where acidic water is separated from the acid gas, which enters the intake of the pump 7 and is fed as reflux for irrigation to the stripper 20. The exhaust acid gas, enriched with hydrogen sulfide, from the separator 6 is sent through the pipeline 18 to the sulfur recovery units using the Claus method.

[0052] The gas, purified from hydrogen sulfide and enriched with carbon dioxide, from the upper part of the absorber 10 is mixed through pipeline 2 with a pressure of up to 6.0 MPa and a temperature of up to 55°C with the return flow of the retentate of the second stage 22 and is sent through pipeline 24 to the two-stage membrane extraction of carbon dioxide in the first membrane gas separation unit 30, where, under the action of a pressure drop, the gas mixture is separated due to the selective penetration of its components (mainly CO2) through the polymer membrane.

[0053] The polymer membrane divides the first membrane gas separation unit 30 into two cavities - high and low pressure, wherein the permeate of the first stage is a gas flow enriched in carbon dioxide that has passed through the polymer membrane into the low-pressure cavity, and the retentate is a gas flow that has not passed through the polymer membrane and remains in the high-pressure cavity.

[0054] Due to the mass transfer of gases through the polymer membrane in the first membrane gas separation unit 30, a first-stage retentate is formed in the high-pressure cavity, which is a gas purified from acidic components with a hydrogen sulfide content of no more than 0.007 g / m3 3and a molar fraction of carbon dioxide of no more than 2.5%, which is removed from the plant via a pipeline for further processing, and in the low-pressure cavity, first-stage permeate is formed, which is removed via a pipeline and sent to compressor 12 to compress the permeate flow before the second membrane gas separation unit.

[0055] The gas stream, compressed in compressor 12 to a pressure of 6.5 MPa, is fed through separator-condenser 13, where a portion of the condensed moisture is separated, via a pipeline to the second membrane gas separation unit 40. In the high-pressure cavity of this unit, a second-stage retentate is formed, which is returned to the first membrane gas separation unit, and in the low-pressure cavity of this unit, a second-stage permeate is formed, which is a highly concentrated gas stream of carbon dioxide. The stage permeate recovered in the second membrane gas separation unit 40 is discharged from the unit as a marketable product.

[0056] A distinctive part of the claimed method is the organization of purification of raw gas using a combined absorption-membrane scheme, where after absorption of hydrogen sulfide, carbon dioxide is extracted in two membrane stages, which ensures its high concentration in the released stream and additional purification from residual hydrogen sulfide until commercial quality is achieved.

[0057] Due to the fact that the entire volume of hydrogen sulfide is selectively extracted at the stage of chemical absorption, the organization of membrane extraction of carbon dioxide from the exhaust gas of amine purification is guaranteed to ensure the production of two marketable products of the required consumer qualities, both purified natural gas without loss of its quality with a low content of hydrogen sulfide and carbon dioxide in accordance with the required standards (STO Gazprom 089-2010 https: / / gktgs.ru / assets / files / sto / sto-gazprom-089-2010-gaz-goruchy-transportiruemy-po-magistralnim-truboprovodam.pdf), and the target product - carbon dioxide with a high mass content of carbon dioxide.

[0058] Compared to the prototype, the replacement of the second stage of chemical absorption with a two-stage membrane extraction of carbon dioxide leads to the complete elimination of energy costs for the regeneration of the saturated amine absorbent in the second stage of chemical absorption from energy consumption items, and also significantly simplifies the process flow diagram, including reducing its metal consumption.

[0059] The proposed technical solution solves the problem of isolating a highly concentrated stream of commercial-quality carbon dioxide without losing the quality of natural gas purification, reduces the metal consumption of the installation’s process flow diagram relative to known solutions, due to the use of small-sized membrane blocks, and also reduces energy costs due to a significant reduction in the consumption of absorbent (due to the elimination of the second stage) and thermal energy for its regeneration.

[0060] The implementation of the claimed method is illustrated by the following example.

[0061] Example. Separation of carbon dioxide during the purification of natural gas from acidic impurities according to the proposed invention.

[0062] Component composition of purified natural gas, mol%: H2S - 4.45; CO2 - 5.84; CH4 - 78.95; C 2+ - the rest.

[0063] The feed rate of the absorber is 5455.1 kmol / h. The absorber is supplied with regenerated selective absorbent solution at a rate of 190.0 t / h at a temperature of 51°C.

[0064] Selective absorbent composition, mass %: MDEA - 49.4; water - the rest.

[0065] The absorber top temperature is 51°C, the bottom temperature is 73°C, the column pressure is 6.0 MPa.

[0066] The top temperature of the desorber is 104°C, the bottom temperature is 128°C, the pressure in the column is 0.2 MPa.

[0067] The chemical absorption unit generates 930.5 kmol / h of acid gas containing 41.9 mol% carbon dioxide and 51.6 mol% hydrogen sulfide, and 2005.0 m 3 / h of natural gas purified from hydrogen sulfide, in which the carbon dioxide content is 5.3 wt.%.

[0068] The gas from the upper part of the absorber, purified from hydrogen sulfide and enriched with carbon dioxide, at a temperature of 51°C and a pressure of 5.95 MPa, is sent through a pipeline to the membrane gas separation units using a polymer membrane for carbon dioxide extraction.

[0069] Table 1 shows the main operating parameters of the two-stage membrane extraction unit adopted in the example of the component composition of the gas during its purification according to this invention.

[0070] The table data shows that purified natural gas leaves the plant with a carbon dioxide content of 1.55 mol.% and hydrogen sulfide of 0.005 g / m3 3 , which complies with the requirements of STO Gazprom 089-2010, and the emitted carbon dioxide flow in the amount of 3.41 t / h is characterized by a high concentration of CO2 equal to 94.7 mass%.

[0071] Thus, the developed method and installation for the extraction of carbon dioxide are highly efficient and ensure the achievement of the technical result claimed in the invention.

[0072]

Claims

1. A plant for separating carbon dioxide, comprising a separator, a chemical absorption unit that includes an absorber, a desorber, first and second pumps, a recuperative heat exchanger, first and second air cooling devices, a reboiler, an expander, an acid gas separator, connecting pipelines and a two-stage membrane extraction unit consisting of first and second membrane gas separation units, a compressor and a separator, wherein the pipeline for feeding raw gas is connected to the lower part of the absorber, the top of the absorber is connected by a pipeline for feeding gas purified from hydrogen sulfide to the first membrane gas separation unit, the high-pressure cavity of which is connected to the first stage retentate discharge pipeline, and the low-pressure cavity of which is sequentially connected by the first stage permeate discharge pipeline through the first compressor and the first separator to the second membrane gas separation unit,the high-pressure cavity of which is connected by a pipeline for removing the retentate of the second stage with a pipeline for feeding gas purified from hydrogen sulfide, and the low-pressure cavity of which is connected by a pipeline for removing the permeate of the second stage, the top of the desorber is connected in series through a pipeline through the first air-cooling apparatus and an acid gas separator, the outlet of which is connected through the first pump to the top of the desorber, with a pipeline for removing the acid gas, the bottom of the absorber is connected by pipelines in series first with the expander, then with the recuperative heat exchanger and is connected to the desorber, the bottom of the desorber is connected to the reboiler, the top of which is connected to the bottom of the desorber, and the bottom of which is connected through the second pump to the top of the absorber in series through the recuperative heat exchanger and the second air-cooling apparatus.

2. A method for separating carbon dioxide using the plant according to paragraph 1, which consists of carrying out primary separation, then carrying out chemical absorption with an aqueous solution of a hydrogen sulfide-selective absorbent based on methyldiethanolamine and regenerating it with the formation of acid gas, characterized in that the gas stream after the chemical absorption stage with a pressure of up to 6.0 MPa and a temperature of up to 55°C is fed to the first stage of membrane gas separation, wherein the retentate of the first stage, which is purified marketable gas, is removed from the plant for further processing, the permeate of the first stage is first compressed to a pressure of no more than 6.5 MPa, and then sent to the second stage of membrane gas separation, the separated permeate of the second stage is a highly concentrated separated stream of carbon dioxide, which is removed from the plant as a marketable product, and the retentate of the second stage is returned back to the first stage of membrane gas separation.

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