Process for recovering carbon dioxide in waste gas
Through the combination of modified activated carbon adsorption bed and physical absorption method, the existing CO2 capture and recovery technology is solved, with complex, energy consumption and high cost, and efficient and economical CO2 recovery and purification effects are achieved.
Patent Information
- Application Number
- CN202510094430.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-21
- Publication Date
- 2025-04-25
AI Technical Summary
The existing CO2 capture and recycling technologies have problems such as complex processes, high energy consumption and high cost, especially in the separation and recycling of low-concentration CO2 gases.
A carbon dioxide recovery process in waste gas is adopted, and the carbon dioxide is further purified by a modified activated carbon adsorption bed. Modified activated carbon improves adsorption efficiency and regeneration efficiency through the modification of carbonate and alcohol amine.
It improves the recovery rate and purity of carbon dioxide, reduces the cost of adsorbents, optimizes the regeneration efficiency, and achieves efficient and economical CO2 recovery.
Smart Images
Figure CN119873822A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of resource recovery, and in particular to a process for recovering carbon dioxide in waste gas. Background Art
[0002] As one of the main greenhouse gases, how to effectively reduce CO2 emissions has become an important political and economic issue for countries around the world, and it is also a difficult task facing the world. In recent years, researchers from various countries have carried out a lot of research on CO2 emission reduction and utilization. On the one hand, by optimizing the energy structure, developing clean energy, and improving energy utilization, the goal of reducing emissions and controlling CO2 increments can be achieved; on the other hand, by capturing CO2 and utilizing it as a resource, the content of CO2 in the atmosphere can be reduced.
[0003] The methods for capturing and recovering CO2 in CCUS technology mainly include: chemical absorption, physical absorption, adsorption separation, membrane separation and cryogenic distillation. Chemical absorption is widely used to capture CO2 because of its fast absorption rate, high absorption efficiency and relatively mature technology. The chemical absorption method is to separate CO2 from other gases by selectively reacting the absorbent with CO2 in the mixed flue gas, and regenerate it with the help of the reverse reaction of the reaction to release high-purity CO2 for enrichment. The reaction principle is that weak base and weak acid react to generate a salt soluble in water, and its absorption or release of CO2 is controlled by the balance of chemical reaction. At present, the main bottleneck restricting the large-scale application of chemical absorption is its complex process, high energy consumption and high cost.
[0004] Physical absorption refers to a method of absorbing CO2 by using water, methanol, acrylate, N-methylpyrrolidone, polyethylene glycol dimethyl ether, etc. as absorbents, and utilizing the principle that the solubility of CO2 in these solvents changes with pressure. Under pressurized conditions, CO2 dissolves in the absorption liquid, but does not chemically react with the absorption liquid. When the pressure decreases or the temperature increases, the solubility of CO2 decreases, so that it can be released from the absorption liquid, realizing the separation and recovery of CO2. However, compared with the chemical absorption method, the absorption efficiency of the physical absorption method may be lower. The separation effect for low-concentration CO2 gas is not ideal; during the decompression or heating process, the release of CO2 may require additional energy.
[0005] The adsorption separation method of CO2 utilizes the selective adsorption of CO2 by the adsorbent to separate CO2 from the mixed gas. This method is based on the intermolecular attraction between the gas and the active points on the surface of the adsorbent. Commonly used adsorbents include molecular sieves, activated carbon, zeolites, metal organic framework materials, etc. These adsorbents have different pore sizes, structures and adsorption properties, and can be selected and designed according to the needs of actual applications. The adsorption separation method has a high CO2 capture efficiency, especially in the capture of low-concentration CO2. The adsorbent can be regenerated by heating or decompression, thereby achieving recycling, but the cost, regeneration efficiency and long-term stability of the adsorbent need to be further optimized and resolved. Summary of the invention
[0006] In view of this, the purpose of the present invention is to provide a process for recovering carbon dioxide in exhaust gas. In the process of recovering carbon dioxide, adsorption separation method and physical absorption method are used to selectively adsorb carbon dioxide in exhaust gas, and modified activated carbon is used as adsorbent, so as to improve the adsorption efficiency and the regeneration efficiency at the same time.
[0007] The present invention solves the above technical problems by the following technical means:
[0008] A process for recovering carbon dioxide from waste gas comprises the following steps:
[0009] S1. The waste gas is passed into a water scrubber for pretreatment to obtain waste gas after pH adjustment;
[0010] S2. Dry the waste gas after pH adjustment and send it to the modified activated carbon adsorption bed arranged in the absorption tower to circulate and adsorb the carbon dioxide in the waste gas to obtain the initially recovered carbon dioxide; S3. Analyze the initially recovered carbon dioxide, and after analysis, send it to the regeneration tower for physical absorption, and after physical absorption, analyze it to obtain refined carbon dioxide;
[0011] S4. Drying and purity testing the refined carbon dioxide to obtain recovered carbon dioxide.
[0012] According to the above technical means, by first pre-treating the waste gas containing carbon dioxide by washing with water and adjusting the pH, on the one hand, particulate matter such as hydrogen chloride, ammonia, hydrogen sulfide, dust, smoke, etc. in the waste gas can be dissolved or adsorbed, and the temperature of the waste gas can be reduced, thereby facilitating the subsequent treatment of the waste gas; by drying the pre-treated waste gas to remove moisture in the waste gas, and then circulating the adsorption through a modified activated carbon adsorption bed, the carbon dioxide in the waste gas can be fully adsorbed; the carbon dioxide adsorbed in the modified activated carbon adsorption bed is then analyzed, and after analysis, it is sent to a regeneration tower for physical absorption, thereby further purifying the carbon dioxide, and then the purified carbon dioxide is dried and tested for purity, and then carbon dioxide with higher purity can be obtained. The entire process can not only improve the adsorption efficiency and reduce the cost of using the adsorbent, but also obtain carbon dioxide with higher purity.
[0013] Preferably, in the step S1, during the pretreatment, the waste gas is firstly subjected to a pH test, and the solution is sprayed according to the pH test result.
[0014] Further preferably, when pH ≤ 6.2, an alkaline solution is sprayed, and the concentration of the alkaline solution is not greater than 0.65 mol / L; when pH ≥ 7.8, an acidic solution is sprayed, and the concentration of the acidic solution is not greater than 0.75 mol / L.
[0015] Further preferably, the alkaline solution is one or more combinations of potassium hydroxide solution, sodium hydroxide solution, sodium carbonate, potassium carbonate, and sodium bicarbonate.
[0016] More preferably, the acidic solution is one or more combinations of dilute hydrochloric acid, carbonic acid, acetic acid, and acid salts.
[0017] Preferably, in the step S2, during drying, the drying temperature is 60-80°C, the drying time is 8-12 min, and the flow rate is 20-35 L / min.
[0018] According to the above technical means, by drying the waste gas containing carbon dioxide, the moisture in the waste gas can be reduced, which is beneficial to the subsequent adsorption of carbon dioxide in the waste gas.
[0019] Preferably, in the step S2, when the carbon dioxide in the exhaust gas is cyclically adsorbed, the number of cycles is 2-5 times, and the time for each cycle is 10-30 minutes.
[0020] According to the above technical means, through cyclic adsorption, the modified activated carbon can reach adsorption saturation as much as possible, so as to adsorb as much carbon dioxide in the exhaust gas as possible to improve the recovery rate of carbon dioxide.
[0021] Preferably, in the S2 step, the modified activated carbon adsorption bed includes a first modified activated carbon layer, a second modified activated carbon layer and a third modified activated carbon layer arranged in sequence from bottom to top, and the exhaust gas circulates through the first modified activated carbon layer, the second modified activated carbon layer and the third modified activated carbon layer.
[0022] Further preferably, the modified activated carbon pore size of the first modified activated carbon layer and the third modified activated carbon layer is the same, and the modified activated carbon pore size of the second modified activated carbon layer is smaller than the modified activated carbon pore size of the third modified activated carbon layer.
[0023] According to the above technical means, by using modified activated carbon with different pore sizes, it is possible to adapt to carbon dioxide particles of different sizes, especially particles formed by the combination of carbon dioxide and other gas molecules, particulate matter, etc. By adsorbing carbon dioxide particles of different sizes, the carbon dioxide in the exhaust gas can be absorbed as much as possible, thereby improving the recovery rate.
[0024] Preferably, in step S2, the preparation of modified activated carbon comprises the following steps:
[0025] A1. The activated carbon was soaked in pure water, ultrasonically treated for 6-8 hours, and then dried to obtain the treated activated carbon;
[0026] A2. The activated carbon treated in step A1 is placed in a carbonate solution, immersed at 60-80°C for 8-10 hours, and then dried to obtain carbonate-modified activated carbon;
[0027] A3. The carbonate-modified activated carbon is placed in an alcoholamine solution, immersed for 1-2 hours, and then quickly frozen to obtain a freeze-dried mixture;
[0028] A4. Wrap a coating layer on the freeze-dried mixture to obtain modified activated carbon.
[0029] According to the above technical means, by first soaking and ultrasonically treating the activated carbon, impurities in the activated carbon can be removed as much as possible, and then the activated carbon is modified by carbonate to improve the adsorption capacity and decomposition efficiency of carbon dioxide by the activated carbon. Then, by mixing and adsorbing with an alcoholamine solution and quick freezing, modified activated carbon loaded with alcoholamine can be obtained. Finally, the modified activated carbon loaded with alcoholamine is wrapped by a coating layer. On the one hand, it is convenient for storage and transportation, and on the other hand, it will not affect the adsorption of carbon dioxide.
[0030] Further preferably, in step A1, the activated carbon is one or more combinations of coal-based activated carbon, wood-based activated carbon, and fruit shell activated carbon.
[0031] Further preferably, the activated carbon is fruit shell activated carbon, and the fruit shell activated carbon is coconut shell activated carbon.
[0032] According to the above technical means, since coconut shell activated carbon has the advantages of developed pores, good adsorption performance, high strength, easy regeneration, economy and durability, it is not only conducive to the adsorption of carbon dioxide, but also convenient for long-term use.
[0033] Further preferably, in the step A1, during the ultrasonic treatment, the ultrasonic power is 80-180 w.h; and the drying condition is at 100-120° C. for 3-5 h.
[0034] According to the above technical means, impurities in the activated carbon can be further removed through ultrasonic treatment, and then moisture and impurities in the activated carbon can be removed through drying.
[0035] Preferably, in step A2, the carbonate solution is one or more combinations of sodium carbonate solution, potassium carbonate solution, calcium carbonate solution, and basic copper carbonate solution.
[0036] Further preferably, the carbonate solution is a basic copper carbonate solution, and the basic copper carbonate solution is a copper complex formed by basic copper carbonate in an aqueous solution of ammonium chloride and sodium carbonate.
[0037] According to the above technical means, by immersing the activated carbon in a basic copper carbonate solution, metal ions and amino groups can be introduced into the activated carbon to promote the reaction and adsorption of carbon dioxide, thereby improving the absorption rate of carbon dioxide.
[0038] More preferably, in the step A2, the drying is carried out at 100-120° C. for 1-2 hours.
[0039] Preferably, in step A3, the alcoholamine solution is one or more combinations of monoethanolamine solution, diethanolamine solution, and N-methyldiethanolamine solution.
[0040] More preferably, the alcoholamine solution is N-methyldiethanolamine solution with a concentration of 6-10 mol / L.
[0041] According to the above technical means, by selecting N-methyldiethanolamine solution as the absorbent, it has a higher carbon dioxide absorption capacity, good thermal stability and chemical stability, is not easy to degrade, can reduce corrosion to equipment, and has low energy consumption during regeneration. Combined with the adsorption of carbon dioxide by modified activated carbon, it can effectively improve the recovery rate of carbon dioxide in exhaust gas.
[0042] More preferably, in the step A3, during quick freezing, the product is frozen at -5-2°C for 10-20 minutes.
[0043] According to the above technical means, N-methyldiethanolamine is loaded on activated carbon by freezing in a relatively short time. At room temperature, N-methyldiethanolamine will not volatilize and is easy to store. When in use, N-methyldiethanolamine can be released from the activated carbon by heating to absorb carbon dioxide. When analyzing after absorbing carbon dioxide, N-methyldiethanolamine can be re-adsorbed on the modified activated carbon. N-methyldiethanolamine and modified activated carbon will not react under normal conditions and will not affect the continued use of the modified activated carbon.
[0044] Further preferably, in the step A4, when the coating layer is wrapped on the freeze-dried mixture, the coating is performed by spraying, infiltration, brushing or vacuum adsorption.
[0045] Further preferably, the coating layer is one or more combinations of paraffin, beeswax, porous resin, gelatin, an aqueous solution of sodium alginate, an aqueous solution of polyvinyl pyrrolidone, an aqueous solution of silica gel or an ethanol solution of ethyl cellulose.
[0046] According to the above technical means, by using a coating layer to coat N-methyldiethanolamine and modified activated carbon, on the one hand, it is convenient for storage and transportation, and on the other hand, it will not affect the adsorption of carbon dioxide.
[0047] Preferably, in the step S2, the preparation of modified activated carbon also includes the following steps: placing the activated carbon in a pore expanding agent, treating it at 40-60°C for 2-3h by soaking, grinding or stirring, and then washing and drying to obtain the activated carbon after pore expansion.
[0048] More preferably, the pore expanding agent is one or more combinations of ferric hydroxide, ferrous hydroxide, zinc hydroxide and citric acid.
[0049] According to the above technical means, by using a pore expanding agent to expand the pores of activated carbon, activated carbon with different pore sizes can be obtained, so that the activated carbon can be used in different applications on the adsorption bed.
[0050] Further preferably, in the step S3, during the analysis, the adsorbed carbon dioxide is analyzed by alternately operating the heat exchanger and the cooler.
[0051] Preferably, in the step S3, when physical absorption is performed, the absorption liquid is one or more combinations of alkaline solution, organic amine solution, alcohol amine solution, functionalized ionic liquid, and acid salt solution.
[0052] More preferably, the absorption liquid is an acid salt, and the acid salt is one or more combinations of sodium acetate, sodium oxalate, sodium butyrate, and sodium succinate.
[0053] According to the above technical means, by using acid salt as the absorption liquid, not only the release temperature of carbon dioxide can be reduced, but also the impact on the equipment can be reduced and the service life of the equipment can be extended.
[0054] The present application adopting the above scheme has the following beneficial effects:
[0055] 1. In the present application, by first pre-treatment of the waste gas containing carbon dioxide by water washing and adjusting the pH, on the one hand, particulate matter such as hydrogen chloride, ammonia, hydrogen sulfide, dust, smoke, etc. in the waste gas can be dissolved or adsorbed, and the temperature of the waste gas can be reduced, so as to facilitate the subsequent treatment of the waste gas; by drying the pre-treated waste gas to remove the moisture in the waste gas, and then circulating the adsorption through the modified activated carbon adsorption bed, the carbon dioxide in the waste gas can be fully adsorbed; the carbon dioxide adsorbed in the modified activated carbon adsorption bed is then analyzed, and after analysis, it is sent to the regeneration tower for physical absorption, so as to further purify the carbon dioxide, and then the purified carbon dioxide is dried and purity tested, and then higher purity carbon dioxide can be obtained. The whole process can not only improve the adsorption efficiency and reduce the use cost of the adsorbent, but also obtain higher purity carbon dioxide;
[0056] 2. In the present application, when carbon dioxide is adsorbed, modified activated carbon is first used for adsorption, which can absorb as much carbon dioxide in the exhaust gas as possible, thereby improving the recovery rate, and then adsorbing and analyzing it through organic acid salts can improve the recovery purity of carbon dioxide and reduce the energy consumption of analysis; 3. In the present application, when carbon dioxide is adsorbed by modified activated carbon, carbonate is first used to modify the activated carbon, which can increase the adsorption amount and analysis efficiency of carbon dioxide by the activated carbon, and then mixing and adsorbing it with an alcoholamine solution can reduce corrosion to the equipment, and during regeneration, the energy consumption is low, further effectively improving the recovery rate of carbon dioxide in the exhaust gas. BRIEF DESCRIPTION OF THE DRAWINGS
[0057] The present application may be further illustrated by non-limiting examples given in the accompanying drawings;
[0058] Figure 1 is a flow chart of a process for recovering carbon dioxide from waste gas in an embodiment of the present application;
[0059] Figure 2 It is a schematic diagram of the absorption tower in the embodiment of the present application. DETAILED DESCRIPTION
[0060] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only 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:
[0061] Example 1, Process for Recovery of Carbon Dioxide from Waste Gas
[0062] Preparation of modified activated carbon
[0063] A1. 100 parts by weight of 20-30 mesh coconut shell activated carbon was soaked in pure water and ultrasonically treated at an ultrasonic power of 150w.h for 8h, and then dried at 120°C for 4h to obtain treated activated carbon;
[0064] A11. 30 parts by weight of coconut shell activated carbon was placed in a 0.5 mol / L citric acid solution at 52°C for 3 hours, then washed with water 3-5 times, and dried at 120°C for 4 hours to obtain activated carbon after pore expansion;
[0065] A2. 70 parts by weight of activated carbon are placed in 100 parts by weight of a basic copper carbonate solution, wherein the basic copper carbonate solution is a copper complex solution formed by basic copper carbonate in an aqueous solution of ammonium chloride and sodium carbonate, and the mixture is immersed for 10 hours at 60° C. and then dried for 5 hours at 120° C. to obtain activated carbon modified with basic copper carbonate;
[0066] A3. The activated carbon modified with basic copper carbonate is divided into several portions of equal weight, each portion is in the shape of a strip or a circle, and each portion of the activated carbon modified with basic copper carbonate is placed in a sufficient amount of 8.5 mol / L N-methyldiethanolamine solution, immersed for 2 hours, and then frozen at -5°C for 20 minutes to obtain a freeze-dried strip or spherical mixture;
[0067] A4. On each freeze-dried bar or spherical mixture, paraffin is wrapped on the bar or spherical mixture by spraying, with a coating thickness of 2-3 mm, and cooled to obtain modified activated carbon.
[0068] Recovery of carbon dioxide from exhaust gases, such as Figure 1-2 As shown;
[0069] S1. The waste gas is introduced from the bottom of the water washing tower, and the acidity and alkalinity of the waste gas are detected by a pH detector. When the pH is ≤6.2, potassium hydroxide solution is sprayed, and the concentration of the potassium hydroxide solution is 0.35 mol / L; when the pH is ≥7.8, dilute hydrochloric acid solution is sprayed, and the concentration of the dilute hydrochloric acid solution is 0.55 mol / L; the flow rate of spraying potassium hydroxide or dilute hydrochloric acid solution is determined according to the amount of waste gas introduced, which is generally 1.5-2 times the flow rate of waste gas, and a carbon dioxide-containing waste gas with a pH of 6.8-7.5 is obtained;
[0070] S2. The carbon dioxide-containing waste gas with a pH value of 6.8-7.5 is sent into the drying tower through an induced draft fan from the bottom of the drying tower, and dried at 80±5°C. The dried carbon dioxide-containing waste gas is sent into the absorption tower through an induced draft fan from the bottom of the absorption tower, and the delivery flow rate is 20-30L / min, so that the carbon dioxide-containing waste gas is S-shaped, and circulates through the first modified activated carbon layer, the second modified activated carbon layer and the third modified activated carbon layer arranged from bottom to top. The pore size of the modified activated carbon in the second modified activated carbon layer is smaller than the pore size of the modified activated carbon in the first modified activated carbon layer and the third modified activated carbon layer. The cycle is repeated 3 times, and the time for each cycle is 25 minutes. During the cycle, the absorption tower is heated by a heat exchanger. During the heating, the temperature is gradually increased to 82±2°C at a rate of 5±1°C / min, and then maintained for 2 hours to obtain the initially recovered carbon dioxide;
[0071] During the heating process, the frozen N-methyldiethanolamine solution gradually melts, and the paraffin melts. During the outflow process, the carbon dioxide in the exhaust gas is physically absorbed. As the N-methyldiethanolamine solution flows out, the pores of the modified activated carbon are exposed, and the carbon dioxide that is not absorbed by the N-methyldiethanolamine solution can be adsorbed, thereby effectively improving the adsorption rate; the unabsorbed gas is discharged as exhaust gas; S3. The initially recovered carbon dioxide is analyzed, and after analysis, it is sent to a regeneration tower for physical absorption. After physical absorption, it is analyzed to obtain refined carbon dioxide;
[0072] During this process, the heat exchanger is heated up again in a gradient manner, and the temperature is raised to 270±5°C at a rate of 15±1°C / min. During the heating process, the temperature is first maintained at 160-170°C for 30-40min; the carbon dioxide adsorbed in the N-methyldiethanolamine solution is decomposed and sent to the regeneration tower through the induced draft fan; the temperature is then raised to 270±5°C to decompose the carbon dioxide adsorbed in the modified activated carbon, and the temperature is maintained for 60-70min, and the decomposed carbon dioxide is then sent to the regeneration tower through the induced draft fan;
[0073] After analysis, the heat exchanger stops working, and the cooler starts working to perform gradient cooling, and the temperature is lowered to 260±5°C at a rate of 10±1°C / min, and maintained for 20-30min, so that the modified activated carbon after analysis absorbs the gaseous N-methyldiethanolamine, and then the temperature is lowered to 230±5°C, and maintained for 30-40min, so that the modified activated carbon absorbs the misty N-methyldiethanolamine as much as possible, and flows between the first modified activated carbon layer, the second modified activated carbon layer and the third modified activated carbon layer with the misty N-methyldiethanolamine, so that the N-methyldiethanolamine is adsorbed on the modified activated carbon as much as possible; finally, the temperature is lowered to room temperature, and the valve is opened, so that the N-methyldiethanolamine that is not absorbed on the first modified activated carbon layer, the second modified activated carbon layer and the third modified activated carbon layer forms a solution and is collected at the bottom of the absorption tower;
[0074] During physical absorption, a 3.6 mol / L mixed solution of sodium acetate and sodium oxalate is sprayed to absorb the carbon dioxide transported by the induced draft fan. After absorption, the mixture is heated to 165±5°C by a reboiler to analyze the mixed solution of sodium acetate and sodium oxalate that has absorbed the carbon dioxide. The analyzed carbon dioxide is cooled by a water cooler and separated by a steam-water separator to obtain refined carbon dioxide.
[0075] S4. The refined carbon dioxide is transported to a drying tower and dried at 110±2°C. After drying, the purity is tested. When the purity of the carbon dioxide is ≥92%, it is transported to a storage device through an induced draft fan to obtain recovered carbon dioxide. When the purity of the carbon dioxide is <92%, it is transported to a regeneration tower through an induced draft fan for physical absorption again until the purity of the carbon dioxide is ≥92%.
[0076] Example 2, Process 2 for recovering carbon dioxide from waste gas
[0077] In this embodiment, the preparation method of modified activated carbon is the same as that of Example 1;
[0078] The recovery process of carbon dioxide in the exhaust gas is as follows: Figure 1-2 As shown;
[0079] S1. The waste gas is introduced from the bottom of the water washing tower, and the acidity and alkalinity of the waste gas are detected by a pH detector. When the pH is ≤6.2, potassium hydroxide solution is sprayed, and the concentration of the potassium hydroxide solution is 0.35 mol / L; when the pH is ≥7.8, dilute hydrochloric acid solution is sprayed, and the concentration of the dilute hydrochloric acid solution is 0.55 mol / L; the flow rate of spraying potassium hydroxide or dilute hydrochloric acid solution is determined according to the amount of waste gas introduced, which is generally 1.5-2 times the flow rate of waste gas, and a carbon dioxide-containing waste gas with a pH of 6.8-7.5 is obtained;
[0080] S2. The carbon dioxide-containing waste gas with a pH value of 6.8-7.5 is sent into the drying tower through an induced draft fan from the bottom of the drying tower, and dried at 80±5°C. The dried carbon dioxide-containing waste gas is sent into the absorption tower through an induced draft fan from the bottom of the absorption tower, and the delivery flow rate is 20-30L / min, so that the carbon dioxide-containing waste gas is S-shaped, and circulates through the first modified activated carbon layer, the second modified activated carbon layer and the third modified activated carbon layer arranged from bottom to top. The pore size of the modified activated carbon in the second modified activated carbon layer is smaller than the pore size of the modified activated carbon in the first modified activated carbon layer and the third modified activated carbon layer. The cycle is repeated 5 times, and the time of each cycle is 25 minutes. During the cycle, the absorption tower is heated by a heat exchanger. During the heating, the temperature is gradually increased to 82±2°C at a rate of 5±1°C / min, and then maintained for 2 hours to obtain the initially recovered carbon dioxide;
[0081] During the heating process, the frozen N-methyldiethanolamine solution gradually melts, and the paraffin melts. During the outflow process, the carbon dioxide in the exhaust gas is physically absorbed. As the N-methyldiethanolamine solution flows out, the pores of the modified activated carbon are exposed, and the carbon dioxide that is not absorbed by the N-methyldiethanolamine solution can be adsorbed, thereby effectively improving the adsorption rate; the unabsorbed gas is discharged as exhaust gas; S3. The initially recovered carbon dioxide is analyzed, and after analysis, it is sent to a regeneration tower for physical absorption. After physical absorption, it is analyzed to obtain refined carbon dioxide;
[0082] During this process, the heat exchanger is heated up again in a gradient manner, and the temperature is raised to 270±5°C at a rate of 15±1°C / min. During the heating process, the temperature is first maintained at 160-170°C for 30-40min; the carbon dioxide adsorbed in the N-methyldiethanolamine solution is decomposed and sent to the regeneration tower through the induced draft fan; the temperature is then raised to 270±5°C to decompose the carbon dioxide adsorbed in the modified activated carbon, and the temperature is maintained for 60-70min, and the decomposed carbon dioxide is then sent to the regeneration tower through the induced draft fan;
[0083] After analysis, the heat exchanger stops working, and the cooler starts working to perform gradient cooling, and the temperature is lowered to 260±5°C at a rate of 10±1°C / min, and maintained for 20-30min, so that the modified activated carbon after analysis absorbs the gaseous N-methyldiethanolamine, and then the temperature is lowered to 230±5°C, and maintained for 30-40min, so that the modified activated carbon absorbs the misty N-methyldiethanolamine as much as possible, and flows between the first modified activated carbon layer, the second modified activated carbon layer and the third modified activated carbon layer with the misty N-methyldiethanolamine, so that the N-methyldiethanolamine is adsorbed on the modified activated carbon as much as possible; finally, the temperature is lowered to room temperature, and the valve is opened, so that the N-methyldiethanolamine that is not absorbed on the first modified activated carbon layer, the second modified activated carbon layer and the third modified activated carbon layer forms a solution and is collected at the bottom of the absorption tower;
[0084] During physical absorption, a 3.6 mol / L mixed solution of sodium acetate and sodium oxalate is sprayed to absorb the carbon dioxide transported by the induced draft fan. After absorption, the mixture is heated to 165±5°C by a reboiler to analyze the mixed solution of sodium acetate and sodium oxalate that has absorbed the carbon dioxide. The analyzed carbon dioxide is cooled by a water cooler and separated by a steam-water separator to obtain refined carbon dioxide.
[0085] S4. The refined carbon dioxide is transported to a drying tower and dried at 110±2°C. After drying, the purity is tested. When the purity of the carbon dioxide is ≥92%, it is transported to a storage device through an induced draft fan to obtain recovered carbon dioxide. When the purity of the carbon dioxide is <92%, it is transported to a regeneration tower through an induced draft fan for physical absorption again until the purity of the carbon dioxide is ≥92%.
[0086] Example 3, Process 3 for recovering carbon dioxide from waste gas
[0087] In this embodiment, the preparation method of modified activated carbon is the same as that in Example 1;
[0088] The recovery process of carbon dioxide in the exhaust gas is as follows: Figure 1-2 As shown;
[0089] S1. The waste gas is introduced from the bottom of the water washing tower, and the acidity and alkalinity of the waste gas are detected by a pH detector. When the pH is ≤6.2, potassium hydroxide solution is sprayed, and the concentration of the potassium hydroxide solution is 0.35 mol / L; when the pH is ≥7.8, dilute hydrochloric acid solution is sprayed, and the concentration of the dilute hydrochloric acid solution is 0.55 mol / L; the flow rate of spraying potassium hydroxide or dilute hydrochloric acid solution is determined according to the amount of waste gas introduced, which is generally 1.5-2 times the flow rate of waste gas, and a carbon dioxide-containing waste gas with a pH of 6.8-7.5 is obtained;
[0090] S2. The carbon dioxide-containing waste gas with a pH value of 6.8-7.5 is sent into the drying tower from the bottom of the drying tower through an induced draft fan, and dried at 80±5°C. The dried carbon dioxide-containing waste gas is sent into the absorption tower from the bottom of the absorption tower through an induced draft fan, and the delivery flow rate is 20-30L / min, so that the carbon dioxide-containing waste gas is S-shaped, and circulates through the first modified activated carbon layer, the second modified activated carbon layer and the third modified activated carbon layer arranged from bottom to top, and the modified activated carbon pore size of the second modified activated carbon layer is smaller than the modified activated carbon pore size of the first modified activated carbon layer and the third modified activated carbon layer. The cycle is repeated twice, and the time of each cycle is 25min. During the cycle, the absorption tower is heated by a heat exchanger. During the heating, the temperature is gradually increased to 82±2°C at a rate of 5±1°C / min, and then maintained for 2h to obtain the initially recovered carbon dioxide;
[0091] During the heating process, the frozen N-methyldiethanolamine solution gradually melts, and the paraffin melts. During the outflow process, the carbon dioxide in the exhaust gas is physically absorbed. As the N-methyldiethanolamine solution flows out, the pores of the modified activated carbon are exposed, and the carbon dioxide that is not absorbed by the N-methyldiethanolamine solution can be adsorbed, thereby effectively improving the adsorption rate; the unabsorbed gas is discharged as exhaust gas; S3. The initially recovered carbon dioxide is analyzed, and after analysis, it is sent to a regeneration tower for physical absorption. After physical absorption, it is analyzed to obtain refined carbon dioxide;
[0092] During this process, the heat exchanger is heated up again in a gradient manner, and the temperature is raised to 270±5°C at a rate of 15±1°C / min. During the heating process, the temperature is first maintained at 160-170°C for 30-40min; the carbon dioxide adsorbed in the N-methyldiethanolamine solution is decomposed and sent to the regeneration tower through the induced draft fan; the temperature is then raised to 270±5°C to decompose the carbon dioxide adsorbed in the modified activated carbon, and the temperature is maintained for 60-70min, and the decomposed carbon dioxide is then sent to the regeneration tower through the induced draft fan;
[0093] After analysis, the heat exchanger stops working, and the cooler starts working to perform gradient cooling, and the temperature is lowered to 260±5°C at a rate of 10±1°C / min, and maintained for 20-30min, so that the modified activated carbon after analysis absorbs the gaseous N-methyldiethanolamine, and then the temperature is lowered to 230±5°C, and maintained for 30-40min, so that the modified activated carbon absorbs the misty N-methyldiethanolamine as much as possible, and flows between the first modified activated carbon layer, the second modified activated carbon layer and the third modified activated carbon layer with the misty N-methyldiethanolamine, so that the N-methyldiethanolamine is adsorbed on the modified activated carbon as much as possible; finally, the temperature is lowered to room temperature, and the valve is opened, so that the N-methyldiethanolamine that is not absorbed on the first modified activated carbon layer, the second modified activated carbon layer and the third modified activated carbon layer forms a solution and is collected at the bottom of the absorption tower;
[0094] During physical absorption, a 3.6 mol / L mixed solution of sodium acetate and sodium oxalate is sprayed to absorb the carbon dioxide transported by the induced draft fan. After absorption, the mixture is heated to 165±5°C by a reboiler to analyze the mixed solution of sodium acetate and sodium oxalate that has absorbed the carbon dioxide. The analyzed carbon dioxide is cooled by a water cooler and separated by a steam-water separator to obtain refined carbon dioxide.
[0095] S4. The refined carbon dioxide is transported to a drying tower and dried at 110±2°C. After drying, the purity is tested. When the purity of the carbon dioxide is ≥92%, it is transported to a storage device through an induced draft fan to obtain recovered carbon dioxide. When the purity of the carbon dioxide is <92%, it is transported to a regeneration tower through an induced draft fan for physical absorption again until the purity of the carbon dioxide is ≥92%.
[0096] Example 4 (Comparative Example 1), Process 4 for Recovery of Carbon Dioxide from Waste Gas
[0097] In this embodiment, the modified activated carbon is not loaded with N-methyldiethanolamine, that is, it is not wrapped with paraffin, and the recovery process of carbon dioxide in the exhaust gas is the same as that in Example 1.
[0098] Example 5 (Comparative Example 2), Process 5 for Recovery of Carbon Dioxide from Waste Gas
[0099] In this embodiment, unmodified activated carbon is used, and the recovery process of carbon dioxide in the exhaust gas is the same as that in Example 1.
[0100] Example 6 (Comparative Example 3), Process for Recovery of Carbon Dioxide from Waste Gas
[0101] In this embodiment, in step S2, an MEA absorption tower is used to absorb and analyze carbon dioxide in the exhaust gas, and the remaining steps are the same as those in embodiment 1.
[0102] Example 7 (Comparative Example 4), Recovery Process of Carbon Dioxide in Waste Gas
[0103] In this embodiment, in steps S2 and S3, an MEA absorption tower and an MEA regeneration tower are used to absorb and analyze carbon dioxide in the exhaust gas, and the remaining steps are the same as those in Example 1.
[0104] The test was conducted using waste gas containing carbon dioxide from a smelter in Chongqing. Each liter of waste gas contained 12.8% NO X , 21.7% SO2, 33.1% CO2, 8.4% smoke particles, 23.9% water and 0.1% metal particles. The waste gas is respectively subjected to CO2 recovery by the processes in Examples 1-7. The test results are shown in Table 1:
[0105]
[0106] According to the above data, by controlling the process parameters of the present application to recover CO2 in the MEA tower as a comparison, in Examples 1-3, by using modified activated carbon loaded with N-methyldiethanolamine as an adsorption bed, the recovery rate of carbon dioxide in the exhaust gas can be effectively improved, and by controlling the process conditions of adsorption and analysis, the recovery purity of carbon dioxide can be effectively improved. Moreover, when the modified activated carbon loaded with N-methyldiethanolamine is regenerated, the regeneration time is relatively short, and the modified activated carbon and N-methyldiethanolamine can be synergistically regenerated during regeneration to improve the regeneration efficiency.
[0107] In Examples 1-3, by controlling the number of cycles of carbon dioxide in the first modified activated carbon layer, the second modified activated carbon layer and the third modified activated carbon layer during the absorption process of carbon dioxide in the absorption tower, the recovery rate of carbon dioxide can be improved by increasing the number of cycles from 3 to 5, but the purity will not be improved. Relatively speaking, it takes more time, and when the number of cycles is 2, the recovery rate and purity of carbon dioxide are reduced, indicating that increasing the number of cycles can increase the adsorption of carbon dioxide by the modified activated carbon adsorption bed.
[0108] In Example 4, when N-methyldiethanolamine is not loaded on the modified activated carbon, under the same process parameters, the recovery rate and purity of carbon dioxide are reduced, indicating that by loading N-methyldiethanolamine on the modified activated carbon, the recovery rate and purity of carbon dioxide can be effectively improved.
[0109] In Example 5, when coconut shell activated carbon is directly used, under the same process parameters, the recovery rate and purity of carbon dioxide are significantly reduced, and the reduction in CO2 recovery relative to the MEA tower is also more obvious, indicating that the selective adsorption capacity of carbon dioxide can be improved by modifying the activated carbon.
[0110] In Example 6, when sodium acetate and sodium oxalate are used as the absorption liquid in the regeneration tower, the recovery rate of carbon dioxide can be improved compared to using the MEA tower as the absorption tower and the regeneration tower, but the purity is reduced. This shows that the use of sodium acetate and sodium oxalate as the absorption liquid can improve the recovery rate of carbon dioxide, and compared with the MEA absorption tower and the MEA regeneration tower, the regeneration temperature is lower, which can save energy consumption relatively.
[0111] The above is a detailed introduction to a process for recovering carbon dioxide from waste gas provided by the present invention. The description of the specific embodiment is only used to help understand the method and core idea of the present invention. It should be pointed out that for ordinary technicians in this technical field, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.
[0112] It should be noted that if no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be purchased commercially.
[0113] The above examples are intended to provide a better understanding of the present invention, and are not intended to be limiting of the best implementation mode described herein, nor are they intended to limit the content and protection scope of the present invention. Any product identical or similar to the present invention that is derived by anyone under the inspiration of the present invention or by combining the present invention with features of other prior arts shall fall within the protection scope of the present invention.
Claims
1. A process for recovering carbon dioxide from waste gas, characterized in that: The following steps are involved: S1. The waste gas is passed into a water scrubber for pretreatment to obtain waste gas after pH adjustment; S2. Drying the waste gas after pH adjustment and sending it to the modified activated carbon adsorption bed arranged in the absorption tower to cyclically adsorb the carbon dioxide in the waste gas to obtain the initially recovered carbon dioxide; S3. The initially recovered carbon dioxide is analyzed, and after analysis, sent to a regeneration tower for physical absorption, and after physical absorption, analyzed to obtain refined carbon dioxide; S4. Drying and purity testing the refined carbon dioxide to obtain recovered carbon dioxide.
2. The process for recovering carbon dioxide from waste gas according to claim 1, characterized in that: In the step S1, during the pretreatment, the waste gas is first subjected to a pH test, and a solution is sprayed according to the pH test result; In the step S2, during drying, the drying temperature is 60-80°C, the drying time is 8-12 minutes, and the flow rate is 20-35 L / min.
3. The process for recovering carbon dioxide from waste gas according to claim 1, characterized in that: In the step S2, when the carbon dioxide in the exhaust gas is cyclically adsorbed, the number of cycles is 2-5 times, and the time of each cycle is 10-30 minutes.
4. The process for recovering carbon dioxide from waste gas according to any one of claims 1 to 3, characterized in that: In the step S2, the modified activated carbon adsorption bed includes a first modified activated carbon layer, a second modified activated carbon layer and a third modified activated carbon layer arranged in sequence from bottom to top, and the exhaust gas circulates through the first modified activated carbon layer, the second modified activated carbon layer and the third modified activated carbon layer.
5. The process for recovering carbon dioxide from waste gas according to claim 4, characterized in that: The modified activated carbon pore diameters of the first modified activated carbon layer and the third modified activated carbon layer are the same, and the modified activated carbon pore diameter of the second modified activated carbon layer is smaller than the modified activated carbon pore diameter of the third modified activated carbon layer.
6. The process for recovering carbon dioxide from waste gas according to claim 1, characterized in that: In the step S2, the preparation of modified activated carbon comprises the following steps: A1. The activated carbon was soaked in pure water, ultrasonically treated for 6-8 hours, and then dried to obtain the treated activated carbon; A2. The activated carbon treated in step A1 is placed in a carbonate solution, immersed at 60-80°C for 8-10 hours, and then dried to obtain carbonate-modified activated carbon; A3. The carbonate-modified activated carbon is placed in an alcoholamine solution, immersed for 1-2 hours, and then quickly frozen to obtain a freeze-dried mixture; A4. Wrap a coating layer on the freeze-dried mixture to obtain modified activated carbon.
7. The process for recovering carbon dioxide from waste gas according to claim 6, characterized in that: In the step A2, the carbonate solution is one or more combinations of sodium carbonate solution, potassium carbonate solution, calcium carbonate solution, and basic copper carbonate solution.
8. The process for recovering carbon dioxide from waste gas according to claim 6, characterized in that: In the step A3, the alcoholamine solution is one or more combinations of monoethanolamine solution, diethanolamine solution, and N-methyldiethanolamine solution.
9. The process for recovering carbon dioxide from waste gas according to claim 6, characterized in that: In the step S2, the preparation of modified activated carbon also includes the following steps: placing the activated carbon in a pore expanding agent, treating it at 40-60° C. for 2-3 hours by soaking, grinding or stirring, and then washing and drying to obtain the activated carbon after pore expansion.
10. The process for recovering carbon dioxide from waste gas according to claim 1, characterized in that: In the step S3, when physical absorption is performed, the absorption liquid is one or more combinations of alkaline solution, organic amine solution, alcohol amine solution, functionalized ionic liquid, and acid salt solution.