Study On Cyclic CO₂ Capture Performance Of Biomass-templated CaO-based Sorbent Pellets

Based on the actual needs of CO2 capture in the calcium looping process system,an extrusion-spheronization method was adopted to prepare the biomass-templated CaO-based absorbent pellets for capturing CO2 in industrial tail gas.The paper mainly carried out the research on the decarburization performance of four kinds of agricultural herbaceous biomass(straw,rice husk,wheat straw,corn stalk)with different doping ratios(2,5,10 and 20 wt.%)and 20 wt.%microcrystalline cellulose addition.Furthermore,investigated the circulating CO2 capture performance of the modified CaO-based absorbent pellets in different calcination conditions(850?,100 vol.%N2 and 900? 40 vol.%CO2)and pre-calcination conditions(N2 pyrolysis,air calcination and pulverized coal combustion).At calcination condition of 850? and 100%N2,it was found that straw,rice husk,wheat straw and corn stalk had poorer modification effect on calcium-based absorbent particles.Among them,CH-MJ10(10 wt.%wheat straw doping,the same below)has the best modification effect of the absorbent particles,and its CO2 absorption attenuation rate is 12.35%,which is only 26.10%of the pure calcium hydroxide decay rate.At 900? and 40%CO2 calcination,the cyclic decarburization performance of the biomass-template modified absorbent particles not only failed to be effectively improved,but also the cyclic decarburization performance showed a gradual deterioration trend with the increase of the addition ratio.In particular,the decay rate per unit CO2 absorption of the 20-cycle unit mass absorbent particles of CH-YMG10,CH-DC10,and CH-DC20 particles was 79.27%,78.86%,and 78.69%,respectively.The reason for the poor decarburization effect of these modified absorbent particles is that the lignin in the biomass significantly impairs the improvement effect of the cellulose and hemicellulose on the CO2 absorption performance of the calcium-based absorbent particles.In addition,the biomass template can significantly improve the anti-wear properties of the modified absorbent particles.After 6000 r wear test,CH-MJ5 has the lowest wear rate of 0.73%;CH-DC 10 has the second,2.12%(when the undoped pellets were 6.32%).The cellulose was further selected attributed its better modification effect,and the addition ratio was 20 wt.%.It has been found that the size of the calcium-based absorbent particles has a very weak effect on their cyclic CO2 absorption properties,but smaller-sized particles can reach their maximum CO2 absorption capacity faster than large particles.Because the smaller size means shorter CO2 diffusion paths,pellets can react with more CO2 in the same time,shortening the carbonation time.Due to the similar weight loss characteristics of cellulose template with different particle sizes(<45 ?m,100-150 ?m and>300 ?m),the improvement of the pore structure of calcium-based absorbent particles is not significant.The effect on the cyclic CO2 absorption capacity and absorption rate of the calcium-based absorbent particles is weak.Compared with the N2 pyrolysis pre-calcination treatment,air calcination and blending of pulverized coal powder tend to cause deterioration of the sintering of the calcium-based absorbent particles,resulting in the decrease of circulating CO2 absorption capacity.At the same time,N2 pyrolysis can form a stable and hard framework inside the absorbent particles,maintain the stability of the pore structure of the absorbent particles in the process of cyclic decarburization,and enhance the stability of the absorption of CO2 by the absorbent particles.In addition,cellulose doped with>300 ?m has good mechanical properties in addition to good decarburization performance.