Investigation On CO₂Capture Through Calcination/Carbonation Reactions With Ca-based Sorbents

As one of the post-combustion CO2capture technologies, the process of calcination/carbonation reactions (CCRs) with Ca-based sorbents to capture CO2from flue gases has been paid more attentions, due to its more economics than that of the amine scrubbing technology. This paper is focused on the process of carbonation/calciantion reactions (CCRs) with Ca-based sorbents to capture CO2from flue gases. Four different aspects were investigated in this paper, including the mechanism and the effect of different experimental conditions on the cyclic carbonation/calcination characteristics of Ca-based sorbents, the influence of SO2and steam on CCRs for Ca-based CO2sorbent and the effect of alcohol solution on Ca-based sorbents for CO2sequestration.The cyclic carbonation/calcination characteristics of Ca-based sorbents and the effects of carbonation temperature, calcination temperature, particle size, CO2concentration, effect of SO2and moisture, and different carbonation stages on the sorbent cyclic conversion were investigated experimentally on a lab-scale fixed bed reactor and a thermo-gravimetric analyzer (TGA). Based on the experimental results, the mechanism of the decay of sorbent conversions is obtained, and the variation of surface structure is explained from the microscopic aspect.The effect of SO2and moisture on reaction characteristics of Ca-based sorbents CaCO3was studied, The influence of SO2on carbonation reaction、calcination reaction and cycling stability in calcination/carbonation reaction was obtained. The possible reason was deduced by comparison of SEM results for the sorbents used in cycling calcination/carbonation reaction. The results show that the CO2capture capacity of CaCO3decreased with the increasing of the cycling number in cycling calcination/carbonation reaction, and the additive of SO2will result in the lower capacity of CO2capture. After10th cycling, the carbonation conversion (XN) were25.5%(0%SO2),16.9%(0.1%SO2) and5.2%(0.2%SO2) respectively. The possible reason is that the sulfate products generated on the surface of CaCO3particle block the holes at surface of sorbent and result in difficult diffusion of CO2into the sorbent. The conversions of the CaO is increased as the steam is introduced to the carbonation process.Repetitive calcination-carbonation of Ca-based CO2sorbents with adding steam was perfomed experimentally to investigate the effect of steam on the cyclic characteristics of Ca-based CO2sorbents. The influence of steam on carbonation reaction and cycling stability in calcination/carbonation reaction was obtained. The results show that the CO2capture capacity of CaCO3decreased with the increasing of the cycling number in cycling calcination/carbonation reaction, the additive of steam results in the higher capacity of CO2 capture. When the steam concentration is greater than20%, the influence of steam on sorbent will no longer be enhanced. The possible reasons is that the water could be adsorbed on the solid surface, this multilayer might show a liquid-like behavior, it can reduce the energy barriers of solid surface, and the CO2will spread even more rapidly.Modification of CaO calcined from CaCO3with alcohol solution to improve the capture of CO2in flue gas was carried out and the new sorbent with excellent capture properties was obtained by calcining. The results show that the carbonation conversion of CaO modified by alcohol solution was much higher than that of CaO hydrated by distilled water with the increasing of cyclic reaction times. After10th cyclics, the carbonation conversion of30%、50%、70%and90%alcohol solution modified sorbent are each35.2%、43.4%、48.8%and50.5%. The higher the alcohol concentration in solution, the higher the carbonation conversion of modified CaO, and the better the anti-sintering performance was achieved. The possible reason is deduced that alcohol molecule enhances affinity and penetrability of H2O molecule to CaO in hydration reaction and improve the pores structure and characteristics in modified Ca-based sorbent after calcination.