Method for preparing high-purity gas by using carbon dioxide trapping process

Abstract

The invention belongs to the field of multi-component gas concentration, and particularly relates to a method for preparing high-purity gas by using a carbon dioxide trapping process, which comprises the following steps: collecting flue gas after combustion of helium-containing natural gas, and decarbonizing the flue gas by using basic hydroxide to obtain decarbonized tail gas and a carbon-rich solution; dehydrating the decarbonized tail gas to obtain dehydrated tail gas; carrying out adsorption separation on the dehydrated tail gas to obtain nitrogen, and carrying out adsorption separation on the denitrified tail gas to obtain helium; the carbon-rich solution is subjected to electrochemical regeneration, a cathode generates hydrogen, and an anode generates mixed gas; and carrying out membrane separation on the mixed gas to obtain CO2 and O2. The device and the method are suitable for the CO2 trapping process of the flue gas of the gas-fired boiler. The regeneration of the absorbent CO2 and the recycling of N2, He, H2 and O2 can be realized at the same time, so that the carbon capture and helium extraction cost is reduced, a new helium extraction mode is developed, and the method has a better application prospect.

Description

Technical Field

[0001] The invention belongs to the field of multi-component gas concentration, and in particular relates to a method for preparing high-purity gas by utilizing a carbon dioxide capture process. Background Art

[0002] In my country's carbon emission pattern, energy activities, namely the combustion of fossil fuels and greenhouse gas emissions during fossil fuel mining, account for 85.4%. In the near and medium term, my country's structural form dominated by fossil and coal energy is unlikely to change fundamentally. It has become a top priority to develop large-scale CO2 capture, utilization and storage (CCUS) technology. At this stage, my country's carbon emissions have not yet peaked, and there is still a large market gap for carbon capture. Among the existing carbon capture technologies, alkaline solution (such as NaOH, KOH and Ca(OH)2) absorption combined with electrochemical regeneration has significant advantages due to its easy availability of raw materials, large absorption capacity, and low regeneration energy consumption. For example: Chinese patent application number "202110911758.0" discloses "a method and system for realizing hydrogen production, organic oxidation, carbon dioxide absorption and desorption, and hydroxide regeneration". The patent adopts an electrochemical regeneration method to achieve absorption rich liquid regeneration by electrolyzing carbonate solution, achieve CO2 concentration on the anode, obtain regenerated hydroxide absorption liquid on the cathode, and produce hydrogen as a by-product. Chinese patent application number "202210184705.8" discloses "a CO2 capture and electrical regeneration synchronous conversion system and method". The patent uses an electrochemical regeneration device to achieve the regeneration of the alkaline solution absorbent, and at the same time introduces the anode regenerated CO2 into the cathode chamber to react electrochemically with the cathode H2 to achieve the directional preparation of CO2 into different high value-added products such as methane, methanol, and formic acid. However, the high cost of carbon capture is still a key challenge restricting the development of the industry, and how to further reduce costs has become a top priority.

[0003] The main methods for extracting helium from natural gas are pressure swing adsorption, absorption, membrane permeation separation and cryogenics. Cryogenics is the most mature and commonly used method for extracting helium from natural gas, and it is also the main method for extracting helium from natural gas at present. However, the problem is that the use of cryogenics to extract crude helium from natural gas requires a lot of energy to liquefy methane, which is costly. In recent years, the liquefied natural gas industry has emerged. The gas concentration in BOG is high, up to 15%, and the composition is relatively simple, mainly He, CH4, N2, H2, O2, Ar, etc., which is a very economically valuable helium resource. However, due to the high hydrogen content in BOG tail gas and the low critical temperature of hydrogen (-253°C), it requires more cold to liquefy it, and its production cost is higher. Some studies have proposed a method for extracting helium after burning BOG tail gas. For example: Chinese patent application number "202010463988.0" discloses "a method, system and recovered helium for recovering helium from BOG tail gas of LNG plant". This patent removes CH4 and H2 from BOG tail gas by combustion, and combines it with cryogenic denitrification to recover helium from BOG tail gas, avoiding the traditional direct cryogenic helium extraction from natural gas and reducing the cost of helium extraction. However, the problem is that the volume of helium extracted from BOG is not large enough to obtain a large amount of helium. How to reduce the cost of helium extraction, break the passive situation, and increase helium production has become a top priority. Summary of the invention

[0004] In view of the above problems, the present invention provides a method for preparing high-purity gas by utilizing a carbon dioxide capture process, comprising:

[0005] Collecting flue gas after natural gas combustion, and decarbonizing the flue gas with alkaline hydroxide to obtain decarbonized tail gas and carbon-rich solution;

[0006] Dehydrating the decarbonized tail gas to obtain dehydrated tail gas;

[0007] Adsorbing and separating the dehydrated tail gas to obtain nitrogen;

[0008] Adsorbing and separating the denitrification tail gas to obtain helium;

[0009] Electrochemically regenerating the carbon-rich solution, producing hydrogen at the cathode and a mixed gas at the anode;

[0010] The mixed gas is subjected to membrane separation to obtain CO2 and O2.

[0011] Its further preferred technical scheme is: adsorption separation, including the first adsorption separation, the second adsorption separation and the third adsorption separation. The first adsorption separation is to remove water vapor to obtain dehydrated tail gas, and the second adsorption separation is to separate nitrogen from the dehydrated tail gas to obtain nitrogen and denitrogenated tail gas.

[0012] A further preferred technical solution is: a third adsorption separation is to separate helium from the denitrification tail gas to obtain helium.

[0013] A further preferred technical solution is that the alkaline hydroxide is selected from any one of potassium hydroxide solution, sodium hydroxide solution and calcium hydroxide solution.

[0014] A further preferred technical solution is: the first adsorption separation is to use NaX or NaY for molecular sieve dehydration.

[0015] A further preferred technical solution is: the second adsorption separation is to use molecular sieves or MOFs for denitrification.

[0016] A further preferred technical solution is: the third adsorption separation is to use activated carbon or MOFs to extract helium.

[0017] A further preferred technical solution is: electrochemical regeneration, i.e. coupled water electrolysis to produce hydrogen.

[0018] A further preferred technical solution is that in membrane separation, the separation membrane used is selected from one of a polydimethylsiloxane film, an inherent microporous polymer membrane and a polyimide membrane.

[0019] A further preferred technical solution is: application in flue gas recovery after combustion of helium-containing natural gas.

[0020] Beneficial effects of the present invention:

[0021] (1) Compared with the nitrogen content in air (about 78%), the nitrogen content in the absorbed tail gas is higher, with a dry basis concentration of more than 90%. Therefore, using the adsorption separation method to purify and separate nitrogen from the tail gas can save 12% of the nitrogen production cost.

[0022] (2) Low helium extraction cost. Compared with traditional direct helium extraction from natural gas and BOG tail gas, the helium concentration in the flue gas of gas boilers after decarbonization and denitrification is as high as 95%, thus reducing the cost of helium extraction; compared with traditional direct helium extraction from natural gas, it saves the deacidification, dehydrogenation and other processing links, thus saving equipment investment and operating costs. More importantly, it can not only turn waste into treasure, but also open up new helium acquisition channels for my country and increase my country's helium production.

[0023] (3) Low cost of hydrogen production. The electrochemical regeneration process essentially realizes absorption of rich liquid regeneration and CO2 concentration by coupling the water electrolysis hydrogen production process. H2 is generated at the cathode during the electrolysis process, which has the characteristics of high product purity. Compared with the existing single water electrolysis hydrogen production technology, the hydrogen produced in the carbon capture process has significant economic value.

[0024] (4) Purification and recovery of oxygen. During the electrolysis process, CO2 and O2 are generated at the anode. Combined with the characteristics of the mixed gas (CO2 concentration is about 67%), high-concentration CO2 and O2 are obtained by membrane separation.

[0025] The present invention is applicable to the CO2 capture process including gas boiler flue gas. Because it can regenerate CO2 while recycling N2, He, H2 and O2, it can reduce the cost of carbon capture and helium extraction, open up a new way of helium extraction, and has good application prospects.

[0026] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] Figure 1 The technical flow chart of the method of the present invention is shown. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Example 1

[0031] like Figure 1 As shown in the figure, the combustion flue gas from the gas boiler is absorbed by the KOH alkaline solution, the absorbed tail gas is separated by NaX molecular sieve adsorption to remove moisture, and then the nitrogen in the tail gas is further removed by MOFs adsorption separation process, and then high-purity helium is extracted by activated carbon adsorption separation. The rich liquid after absorbing CO2 is regenerated by electrochemical regeneration process, and pure hydrogen is produced as a by-product at the cathode. CO2 and O2 are produced at the anode, and the CO2 content is about 70%.

[0032] Compared with the nitrogen content in air (about 78%), the nitrogen content in the absorbed tail gas is higher, with a dry basis concentration of more than 90%. Therefore, using the adsorption separation method to purify and separate nitrogen in the tail gas can save 12% of the nitrogen production cost.

[0033] The cost of helium extraction is low. Compared with the traditional direct helium extraction from natural gas and BOG tail gas, the helium concentration in the flue gas of gas boilers after decarbonization and denitrification is as high as 95%, thus reducing the cost of helium extraction; compared with the traditional direct helium extraction from natural gas, helium is extracted from the carbon capture process of boiler flue gas, which saves the deacidification, dehydrogenation and other treatment links, thus saving equipment investment. More importantly, the use of tail gas after carbon capture of gas boiler flue gas for helium extraction can not only turn waste into treasure, but also open up new helium acquisition channels for my country and increase my country's helium production.

[0034] Example 2

[0035] After the combustion flue gas from the gas boiler is absorbed by the NaOH alkaline solution, the absorbed tail gas is separated by molecular sieve adsorption to remove moisture, and then the nitrogen in the tail gas is further removed by molecular sieve adsorption separation process, and then high-purity helium is extracted by activated carbon adsorption separation. The rich liquid that has absorbed CO2 is regenerated by electrochemical regeneration process, and pure hydrogen is produced as a byproduct at the cathode. CO2 and O2 are produced at the anode, and the CO2 content is about 70%.

[0036] The method provided by the present invention has low hydrogen production cost. The electrochemical regeneration process is essentially to achieve absorption of rich liquid regeneration and CO2 concentration by coupling the water electrolysis hydrogen production process. H2 is generated at the cathode during the electrolysis process, and has the characteristics of high product purity. Compared with the existing single water electrolysis hydrogen production technology, the hydrogen produced in the carbon capture process has significant economic value.

[0037] Example 3

[0038] After the combustion flue gas from the gas boiler is absorbed by the NaOH alkaline solution, the absorbed tail gas is separated by molecular sieve adsorption to remove moisture, and then the nitrogen in the tail gas is further removed by molecular sieve adsorption separation process, and then high-purity helium is extracted by MOFs adsorption separation. The rich liquid after absorbing CO2 is regenerated by electrochemical regeneration process, and pure hydrogen is produced as a by-product at the cathode. CO2 and O2 are produced at the anode, and the CO2 content is about 70%.

[0039] The method provided by the present invention can effectively purify and recycle oxygen. During the electrolysis process, CO2 and O2 are generated at the anode. Combined with the characteristics of the mixed gas (CO2 concentration is about 67%), high-concentration CO2 and O2 are obtained by membrane separation, which is simple, convenient and highly efficient.

[0040] It should be noted that the terms "first", "second", etc. in this application are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so as to describe the embodiments of the present application described herein. Although the present invention has been described in detail with reference to the aforementioned embodiments, a person of ordinary skill in the art should understand that it is still possible to modify the technical solutions described in the aforementioned embodiments, or to replace some of the technical features therein by equivalents; and these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing high-purity gas using a carbon dioxide capture process, characterized in that: include: Collecting flue gas after natural gas combustion, and decarbonizing the flue gas with an alkaline hydroxide solution to obtain decarbonized tail gas and a carbon-rich solution; Dehydrating the decarbonized tail gas to obtain dehydrated tail gas; Adsorbing and separating the dehydrated tail gas to obtain nitrogen; Adsorbing and separating the denitrification tail gas to obtain helium; Electrochemically regenerating the carbon-rich solution, producing hydrogen at the cathode and composite gas at the anode; The composite gas is subjected to membrane separation to obtain CO2 and O2.

2. The method for preparing high-purity gas by utilizing the carbon dioxide capture process according to claim 1, characterized in that: The adsorption separation includes a first adsorption separation, a second adsorption separation and a third adsorption separation. The first adsorption separation is for removing water vapor to obtain dehydrated tail gas, and the second adsorption separation is for removing nitrogen to obtain denitrogenated tail gas.

3. The method for preparing high-purity gas by utilizing the carbon dioxide capture process according to claim 2, characterized in that: The third adsorption separation is to perform a third adsorption separation on the denitrification tail gas to obtain helium.

4. The method for preparing high-purity gas by utilizing the carbon dioxide capture process according to claim 1, characterized in that: The alkaline hydroxide is selected from any one of potassium hydroxide solution, sodium hydroxide and calcium hydroxide solution.

5. The method for preparing high-purity gas by utilizing the carbon dioxide capture process according to claim 2, characterized in that: The first adsorption separation is to use NaX or NaY for molecular sieve dehydration.

6. The method for preparing high-purity gas by utilizing the carbon dioxide capture process according to claim 2, characterized in that: The second adsorption separation is performed by using molecular sieves or MOFs for the first adsorption separation.

7. The method for preparing high-purity gas by utilizing the carbon dioxide capture process according to claim 2, characterized in that: The third adsorption separation is to use activated carbon or MOFs for the second adsorption separation.

8. The method for preparing high-purity gas by utilizing the carbon dioxide capture process according to claim 1, characterized in that: The electrochemical regeneration is to produce hydrogen by coupling water electrolysis.

9. The method for preparing high-purity gas by utilizing the carbon dioxide capture process according to claim 1, characterized in that: In the membrane separation, the separation membrane used is selected from one of a polydimethylsiloxane film, an intrinsic microporous polymer membrane and a polyimide membrane.

10. The use of a method for preparing high-purity gas by utilizing a carbon dioxide capture process according to any one of claims 1 to 9, characterized in that: The application is in the recovery of flue gas after the combustion of helium-containing natural gas.

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