| Research Abstract |
The effect of the alkali metal compounds on the desulfurization characteristics was elucidated quantitatively and theoretically in this study. The desulfurization experiments by adding some alkali metal compounds and chlorides to limestone were carried out, using a thermobalance. The mechanism on the enhancement of desulfurization characteristics were elucidated, based on the chemical and physical change of structure due to alkali metal compounds addition as well as structure change of CaO calculated by molecular dynamics simulation. Obtained results show that addition of NaCl into the limestone was found to be the most effective on improving the desulfurization efficiency. In order to elucidate in details the effect of the NaCl-doping on such structure change, the crystal structures of calcined seashell, limestone and NaCl-doped limestone were analyzed by X-ray diffraction (XRD), Consequently, CaO in both seashell and NaCl-doped limestone was crystallized, whereas CaO in the calcined
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limestone was disordered. Therefore, NaCl-doping can change the CaO crystal structure. From those experimental facts, the desulfurization characteristics are influenced by result of the crystal structure of samples after calcination. Next, the crystal structures for pure CaO and NaCl-doped CaO were simulated, using molecular dynamics simulation, in order to confirm the effect of NaCl-doping on the CaO structure theoretically. The results show that NaCl-doping into CaO contributes to the crystallization of CaO even at the temperatures of formation of amorphous structure for the pure CaO. Additionally, KC1 and LiCl-doped CaO was simulated under the same calculation conditions and procedures. Finally, only NaCl stably exists as the CaO crystal, while NaCl-doping showed predominant effect on the CaO crystallization. These tendencies depend on the difference of the potential energy and ionic radius of each alkali metal chloride. The experimental and simulation results obtained suggested that NaCl-doping contributed to crystallizing the CaO molecules. Less
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