A method for producing high purity gases using a carbon dioxide capture process

Abstract

The present application 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 capture process, comprising: collecting flue gas after combustion of helium-containing natural gas, and decarburizing the flue gas by using alkaline hydroxide to obtain decarburization tail gas and carbon-rich solution; dehydrating the decarburization tail gas to obtain dehydrated tail gas; adsorbing and separating the dehydrated tail gas to obtain nitrogen, and adsorbing and separating the nitrogen-removed tail gas to obtain helium; electrochemically regenerating the carbon-rich solution, generating hydrogen at the cathode and generating mixed gas at the anode; and performing membrane separation on the mixed gas to obtain CO2 and O2. The present application is suitable for a CO2 capture process including flue gas of a gas-fired boiler. Since the present application can realize the recycling of N2, He, H2 and O2 while regenerating CO2 in the absorbent, the present application realizes the reduction of the cost of carbon capture and helium extraction, and opens up a new way of helium extraction, and therefore has a good application prospect.

Description

TECHNICAL FIELD

[0001] The present application 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 capture process. BACKGROUND

[0002] In the carbon emission pattern in China, energy activities, i.e. the combustion of fossil fuels and the greenhouse gas emission during the exploitation of fossil fuels, account for 85.4%. In the near and medium term, the structure of fossil and coal energy in China is difficult to change fundamentally. It is urgent to carry out large-scale CO2 capture, utilization and storage (CCUS) technology. At present, China's carbon emissions have not yet peaked, and the market gap for carbon capture is still large. Among the existing carbon capture technologies, the alkaline solution (such as NaOH, KOH and Ca(OH)2) absorption combined with electrochemical regeneration method has obvious advantages due to the availability of raw materials, large absorption capacity and low regeneration energy consumption. For example: Chinese patent application No. "202110911758.0" discloses "a method and system for realizing hydrogen production, organic matter oxidation, carbon dioxide absorption and desorption, and hydroxide regeneration". The patent uses an electrochemical regeneration method to regenerate the absorption rich solution by electrolyzing carbonate solution, to realize CO2 concentration on the anode, and to obtain regenerated hydroxide absorption solution and by-product hydrogen on the cathode. Chinese patent application No. "202210184705.8" discloses "a CO2 capture and electrochemical regeneration synchronous conversion system and method". The patent uses an electrochemical regeneration device to regenerate the alkali absorbent, and introduces the CO2 regenerated on the anode into the cathode chamber to react with the cathode H2 to realize 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 to the development of the industry, and how to further reduce the cost has become a top priority.

[0003] The main methods for helium extraction from natural gas include pressure swing adsorption, absorption, membrane permeation separation and cryogenic method. The cryogenic method is the most mature and commonly used method for helium extraction from natural gas, and is currently the main method for helium extraction from natural gas. However, there are problems. The cryogenic method for extracting crude helium from natural gas requires a large amount of energy to liquefy methane, which is costly. In recent years, the liquefied natural gas industry has emerged, and the gas concentration in BOG is relatively high, with a maximum of 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 the BOG tail gas, the critical temperature of hydrogen (-253℃) is lower, and more cold energy is required for its liquefaction, resulting in higher production cost. Some studies have proposed a method of extracting helium from BOG tail gas after combustion. For example: Chinese patent application No. "202010463988.0" discloses "a method and system for recovering helium from BOG tail gas in a LNG plant". The patent removes CH4 and H2 in the BOG tail gas by combustion method, and at the same time, removes nitrogen by cryogenic method to recover helium from the BOG tail gas, avoiding the traditional direct cryogenic method for helium extraction from natural gas, reducing the cost of helium extraction, but the problem is that the amount 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 the yield of helium has become a top priority. SUMMARY

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

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

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

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

[0008] Adsorbing and separating the dehydrated tail gas to obtain nitrogen gas;

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

[0010] Membrane separation of the mixed gas to obtain CO2 and O2.

[0011] Further preferred technical solutions are: adsorption and separation, including first adsorption and separation, second adsorption and separation and third adsorption and separation, the first adsorption and separation is to remove water gas to obtain dehydrated tail gas, the second adsorption and separation is to separate nitrogen gas from the dehydrated tail gas to obtain nitrogen gas and de-nitrogenation tail gas.

[0012] A further preferred technical solution is that the third adsorption separation is helium separation from the denitrogenated tail gas to obtain helium.

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

[0014] A further preferred technical solution is that the first adsorption separation is molecular sieve dehydration using NaX or NaY.

[0015] A further preferred technical solution is that the second adsorption separation is denitrogenation using a molecular sieve or MOFs.

[0016] A further preferred technical solution is that the third adsorption separation is helium extraction using activated carbon or MOFs.

[0017] A further preferred technical solution is that the electrochemical regeneration is coupled with water electrolysis to produce hydrogen.

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

[0019] A further preferred technical solution is that the application is applied to the recovery of flue gas after combustion of helium-containing natural gas.

[0020] The beneficial effects of the present application are:

[0021] (1) The nitrogen content in the absorption tail gas is higher than that in air (about 78%), and the dry basis concentration is higher than 90%. Therefore, the adsorption separation method for purifying and separating nitrogen in the tail gas can save 12% of the nitrogen production cost.

[0022] (2) The helium extraction cost is low. Compared with traditional direct helium extraction from natural gas and direct helium extraction from BOG tail gas, the helium concentration in the gas after decarburization and denitrogenation of the flue gas of the gas-fired boiler is as high as 95%, thereby reducing the helium extraction cost. Compared with traditional direct helium extraction from natural gas, the treatment steps such as deacidification and dehydrogenation are saved, thereby saving equipment investment and operation cost. More importantly, not only waste can be turned into treasure, but also a new type of helium acquisition channel can be developed for China, and the helium production of China can be improved.

[0023] (3) The hydrogen production cost is low. The electrochemical regeneration process is essentially to regenerate the absorption rich solution and concentrate CO2 by coupling with the water electrolysis process to produce hydrogen. H2 is generated at the cathode in the electrolysis process, which has the characteristic 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. CO2 and O2 are generated at the anode during electrolysis. Based on the characteristics of the mixed gas (CO2 concentration is about 67%), high concentrations of CO2 and O2 are obtained by membrane separation.

[0025] This invention is applicable to CO2 capture processes, including those involving flue gas from gas-fired boilers. Because it can simultaneously regenerate CO2 and recover and utilize N2, He, H2, and O2, it reduces the cost of carbon capture and helium extraction, opening up a new helium extraction method and showing promising application prospects.

[0026] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 A flowchart of the method of the present invention is shown. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1

[0031] like Figure 1 As shown, the combustion flue gas from the gas-fired boiler is absorbed by a KOH alkaline solution. The absorbed tail gas then undergoes adsorption separation using NaX molecular sieves to remove moisture, followed by MOF adsorption separation to remove nitrogen. Finally, high-purity helium is extracted through activated carbon adsorption separation. The CO2-rich solution is regenerated using an electrochemical regeneration process, with pure hydrogen as a byproduct at the cathode. CO2 and O2 are produced at the anode, with the CO2 content being approximately 70%.

[0032] The nitrogen content in the absorption tail gas is higher than that in the air (about 78%), and the dry basis concentration is higher than 90%. Thus, the nitrogen in the tail gas can be purified by the adsorption separation method, thereby saving 12% of the cost of nitrogen production.

[0033] The helium extraction cost is low. Compared with the traditional direct helium extraction from natural gas and the direct helium extraction from the BOG tail gas, the helium concentration in the gas after decarburization and denitrification of the flue gas of the gas-fired boiler is as high as 95%, thereby reducing the helium extraction cost. Compared with the traditional direct helium extraction from natural gas, the helium is extracted from the carbon capture process of the boiler flue gas, thereby saving the treatment steps such as acid removal and dehydrogenation, and thus saving the equipment investment. More importantly, the helium is extracted from the tail gas after the carbon capture of the flue gas of the gas-fired boiler, which not only turns waste into treasure, but also opens up a new channel for obtaining helium in China and improves the helium production in China.

[0034] Embodiment 2

[0035] The combustion flue gas from the gas-fired boiler is absorbed by the NaOH alkaline solution, the absorption tail gas is removed of water by the NaY molecular sieve adsorption separation, then the nitrogen in the tail gas is further removed by the molecular sieve adsorption separation process, and then the high-purity helium is extracted by the activated carbon adsorption separation. The rich liquid after absorbing CO2 is regenerated by the electrochemical regeneration process, and the pure hydrogen is by-produced at the cathode. CO2 and O2 are generated at the anode, and the content of CO2 is about 70%.

[0036] The method provided by the application has low hydrogen production cost. The electrochemical regeneration process is essentially to regenerate the absorption rich liquid and concentrate CO2 by coupling the water electrolysis hydrogen production process. H2 is generated at the cathode in 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] Embodiment 3

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

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

[0040] It should be noted that the terms "first", "second", etc. in the present application are used to distinguish similar objects, and do not necessarily indicate a specific order or sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented. Although the present application is described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for producing a high purity gas using a carbon dioxide capture process, characterized by, The application relates to a method for recovering helium from helium-containing natural gas, comprising the following steps: collecting flue gas after combustion of helium-containing natural gas, and decarburizing the flue gas by using an alkaline hydroxide solution to obtain decarburized tail gas and a carbon-rich solution; the nitrogen content in the decarburized tail gas is higher than 90% in dry basis; the decarburized tail gas is subjected to first adsorption separation by using NaX or NaY, i.e. molecular sieve dehydration, to obtain dehydrated tail gas; the dehydrated tail gas is subjected to second adsorption separation by using a molecular sieve or MOFs to obtain nitrogen and denitrogenated tail gas; the denitrogenated tail gas is subjected to third adsorption separation by using activated carbon or MOFs to obtain helium; the carbon-rich solution is subjected to electrochemical regeneration, hydrogen is generated at the cathode, and composite gas is generated at the anode; the electrochemical regeneration is coupled with water electrolysis to generate hydrogen; and the composite gas is subjected to membrane separation to obtain CO2 and O2. The alkaline hydroxide is selected from any one of a potassium hydroxide solution, a sodium hydroxide solution and a calcium hydroxide solution. In the membrane separation, the separation membrane used is selected from one of a polydimethylsiloxane film and a polyimide film. The application is applied to flue gas recovery after combustion of helium-containing natural gas. ​ ​ ​ 2. The method of claim 1, wherein the method is characterized by, ​ 3. The method of claim 1, wherein the method further comprises: ​ 4. Use of a process for the production of high-purity gases from a carbon dioxide capture process according to any one of claims 1 to 3, characterized in that, ​

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