| The essences of removing CO2by using regenerable alkali metal sorbents is to use alkiali carbonate salts mixed with CO2in the flue gas, and react to form alkiali bicarbonate salts, the salts will decompose to regenerate for releasing CO2under certain conditions, which to achieve the separation of CO2and flue gas. Compared with removeing CO2by chemisorptions, the dry CO2absorption by using regenerable alkali metal sorbents with the advantages of low energy consumption, high recycling efficiency, no corrosion to equipment and no secondary pollution has become a research hotspot. This paper focuses on studying regeneration reaction characteristics and regeneration reaction kinetics characteristics of pure bicarbonate potassium and bicarbonate potassium based fly ash sorbents.The K2CO3with structure of hexagonal crystal is selected as the active components of potassium based fly ash sorbents by comparing specific surface area, pore diameter and volume of the hexagonal crystal K2CO3with the monoclinic crystal K2CO3, which is obtained from calcined of KHCO3. The thermal decomposition characteristics of KHCO3is studied in different atmosphere, heating rate and reaction temperature by thermogravimetric analysis tests. The results show that the KHCO3hardly produces decomposition reaction below100℃, the KHCO3begins to decompose slowly when the temperature is more than125℃. The KHCO3were fully decomposed in atmosphere of air and nitrogen and the atmosphere of air is good at regeneration reaction. The optimum reaction terminal temperature is about200℃, the best heating rate is15～20℃/min. The power plant coal fly ash is selected as the carrier material of sorbents through to the carrier material abrasion resistance, particle shape and smoothness, particle size distribution, porosity and cost aspects. Compared particle size distribution of the Jiangsu jiangyinligang power plant coal fly ash and Shanghai minhang power plant coal fly ash, Shanghai minhang power plant coal fly ash is choosed as the carrier material of dry CO2sorbents. The potassium based coal fly ash sorbents is mainly composed of active components, the carrier material and adhesive, etc. And the active components is KHCO3the carrier material is Shanghai minhang power plant coal fly ash, the adhesive is liquid sodium silicate. The preparation of sorbents includes grinding, mixing, drying and calcination etc. The regeneration characteristics of potassium based fly ash sorbents is studied in different atmosphere, heating rate and reaction temperature by thermogravimetric analysis tests. The results show that the potassium based fly ash sorbents begin to decompose between100℃and150℃, the regeneration reaction is over between225℃and275℃. The optimum reaction terminal temperature of the potassium based fly ash sorbents is about200℃, the best heating rate is15～20℃/min. The regeneration reaction of the potassium based fly ash sorbents is running at final temperature of200℃in the atmosphere of air and nitrogen. The results show that the regeneration reaction rate of sorbents is faster in the atmosphere of air and the maximum reaction rate is about1.1mg/min, and the maximum reaction rate is about0.6mg/min in the atmosphere of nitrogen. Therefore, air is good at sorbents regeneration reaction at the same final temperature. The microstructure, pore size and volume of the regenerated potassium based fly ash sorbents were analyzed by the scanning electron microscopy and nitrogen adsorption characterization. The material composition was analyzed by the XRD diffraction spectrum after the regeneration and carbonization of potassium based fly ash, the results show that carbide or regeneration products besides K2CO3and KHCO3, also forms KA1(CO3)2(OH)2, K2Mg(CO3)2, K2Mg(CO3)2-4H2O, K2Ca(CO3)2and Ca(OH)2, etc. Based on non-isothermal kinetic method, the regeneration kinetics characteristics of KHCO3and the potassium based fly ash sorbents for CO2capture were studied in different atmosphere and different heating rate. The results show that the most probability regeneration mechanism function is random nucleation and subsequent growth.The general integral method is used to solve the regeneration reaction kinetics characteristics.The regeneration reaction activation energy of KHCO3is between85.7kJ/mol and92.0kJ/mol in atmosphere of nitrogen, and it is between85.3kJ/mol and117.2kJ/mol in atmosphere of air. The regeneration reaction activation energy of potassium based fly ash sorbents for CO2capture is between27.1kJ/mol and69.4kJ/mol in atmosphere of nitrogen, and it is between24.8kJ/mol and59.8kJ/mol in atmosphere of air. Compared with regeneration reaction activation energy of pure KHCO3and fly ash load potassium for CO2capture, regeneration reaction activation energy of potassium based fly ash sorbents is lower. |
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