Study On The Characteristics Of Calcium-Based Cyclic Carbonation-Calcination Reactions For CO₂ Separation

As the greenhouse effect impacts on the global climate more and more significantly, the reduction of the greenhouse gases emission, especially CO₂, has drew the high degree of attention of governments and researchers around the world. The Cyclical Carbonation-Calcination Reactions (CCRs) based on Calcium sorbent has been proved to be a promising CO₂ separation technology because of its economy and high efficiency. In this thesis, the sorbent reaction characteristics with the increasing carbonation-calcination cycles have been evaluated by experiments, theoretical calculation and comparative analysis; the sintering mechanism also its effect towards pore structure and surface area of sorbent have been verified both from the perspective of macro-and micro-depth; the improvement of the cyclic stability has been successfully carried out by the preparation of the calcium-based compound sorbents and sorbent pellets in various specifications which meet the application requirements of the fluidized bed technology have also been fabricated in a bench-scale.Multi-cyclic CO₂ capturing using PT CaCO3 and nano-CaCO3 power was studied in a fixed bed which focused on the comparison of the carbonation conversion changes. The result indicated that, the reduction of surface area and the deterioration of pore structure brought by long-time sintering was the main reason that the reactivity of calcium-based sorbent decayed with the increasing number of carbonation-calcination cycles, which had nothing to do with the kinds of sorbents. CaO and CaCO3 samples obtained in different stages of CO₂ capturing were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The grain sizes of CaO and CaCO3 were both calculated based on Scherrer formula, and the grain sizes change was used to explain the effect of sintering on the conversion and capturing capacity of CaO sorbents. The results showed severe sintering occurred in multi-cyclic CO₂ capturing was the main reason of CaO grains'growth. Therefore, CaO particles started to stick together and the size of particle grew quickly, which were responsible for the conversion decay of the sorbent during the cyclic reactions. The cyclic characteristics of calcium-based sorbent were also investigated in steam participation conditions. The research suggested that appropriate amount of steam could improve the sorbent's capturing capacity significantly while the sintering effect would be dramatically catalyzed during the long-time high temperature reactions in the presence of steam. However, sorbent's reactivity was affected little if steam presented during the calcination stage.The synthetic calcium-based sorbents CaO/La₂O₃ and CaO/Ca₁₂Al₁₄O₃₃ were prepared by the sol-gel method to enhance the performances during the cyclic reactions. The test and experimental data showed that La₂O₃ and Ca₁₂Al₁₄O₃₃ had played an important role of framework in sorbent which could remarkably reduce the adverse effect caused by sintering.Synthetic calcium-based sorbent pellets in various specifications which meet the application requirements of the fluidized bed technology were fabricated in a bench-scale by sol-gel, impregnation and pelletization based on core-in-shell model, and the minimum crushing pressure resistance was 4.73N tested by measuring equipment.