The Coal Pyrolytic And Gasification Behaviors And Sulfur Transformation Under The Effect Of Ca-based Additives

Experiments were performed on a fixed bed reactor, the effect of two Ca-based additives (Ca(OH)2 and CaCO3)on slow pyrolytic behaviors of three bituminous coals were investigated by methods of gas chromatograph(GC),gas chromatograph-mass spectrometer(GC-MS)and fourier transform infrared spectroscopy(FTIR). The results showed that Ca-based addtives promoted cracking of tar and accelerated cracking of macromolecular structure in coal, resulted in reduction of the tar and char yield, and increase of the gas yield. Ca-based addtives promoted cracking of tar by facilitating the dehydrogenation and demethanation of tar,cracking of long chain hydrocarbons,decomposing of side group richer aromatics and the formation of BTX. The swelling property of coal appeared to influence the activity of calcium additive on the cracking reactions of tar. Overall, the effect of Ca (OH) 2 was superior to CaCO3.By methods of GC,X-ray diffraction (XRD) and X-ray absorption near edge structure (XANES), we researched the sulfur transformation and the forms of sulfur in coal during coal pyrolysis, above all, the effect of Ca-based additives was also studied. It was found that, YST raw coal consisted of inorganic sulfur (mainly include pyrite and melanterite) and organic sulfur (mainly include thiophenic sulfur,sulphone and sulfoxide). H2S and COS were the main sulfur-containing gases. Ca(OH)2 promoted the decomposition of FeS, which was the decomposition product of FeS2, and fixed more sulfur in char by CaS. Moreover, adding Ca(OH)2 made the maximum evolution of H2S moved to the high temperature. By means of acid-washing and method of XANES, it was found that, Ca(OH)2 promoted the generation of disulfide, which might be the second reaction product of sulfur.The effect of Ca-based additives on catalytic gasification,sulfur transformation and forms of sulfur was also studied, it was found that, Ca-based additives contributed to catalytic gasification(K2CO3 as catalyst). Besides, after adding Ca(OH)2, K2SO4 as the gasification production existed in ash, which showed that Ca not only had much effective on sulfur-fixing, but also in favor of recycling of K.