A Study On The High Temperature Desulfurization Behaviour Of Iron-Cerium Oxides Sorbents Supported On Coal Ash

The desulfurization and clean-up of hot coal gases was regarded as one of the key techniques in based coal gasification combined production process. In this paper, iron and cerium oxides sorbents supported by gangue power plant coal ash were prepared, and the desulfurization properties of different sorbents in simulated hot coal gases were studied.The coal ash from gangue power plant was composed mainly of silicon, aluminum and iron oxides except for partly calcium, magnesium oxides, rudimental coal, volatiles and other compositions. The characteristics of coal ash were studied in detail by close analysis its consistuent elements, magnetic particles, granularity feature, XRD, SEM character, carbon and volatiles. The coal ash with different particle size was chosed as support of iron-cerium oxides sorbents and their sulfurization properties were compared at 420-620℃.The concentration of hydrogen sulfur from a simulated coal gases was 4700ppm at the entrance. The desulfurization results of different sorbents at 620℃indicated: the sorbent supported on coal ash can reduce hydrogen sulfur to lower concentration than the unsupported sorbent. The reason was that the coal ash increased the surface area and spread around the actived component of the sorbent during calcinations. The results of the same sorbent sulfurizated at different elevated temperature from 420℃to 620℃illustrated that the sorbents can favourably resist pulverization at 620℃. Compared the different sulfurization curves of the same sorbent, the breakthrough time was shorter at 520℃than 620℃, the sulfur capacity at 520℃was also lower than 620℃. But the breakthrough time and sulfur capacity at 520℃increased obviously than 420℃. Results of all the sulfurization experiments for diffferent sorbents at 620℃indicated the sulfur capacity greater than the value calculated by supposing all Fe₂O₃ transformed into FeS and all CeO₂ transformed into Ce₂O₂S, this showed portion of Fe₂O₃ transformed into FeS_x (x >1). The sulfurization experiment of iron and cerium oxides with different mol ratio indicated that the iron and cerium sorbent of 8:2 mol ratio had longer breakthrough time(21.5h) than that of 1:1 mol ratio(8.4h), and greater sulfur capacity. These results are related with the possible sulfurization product of FeS_x (x >1) or the CeO₂ little to Ce₂O₂S at low temperature. Compared with the sulfurized results of sorbents supported with different granularity coal ash at the same condition, a conclusion can be obtained that the sorbent supported by 112-154um coal ash, which had the greatest value of carbon and volatiles, showed the most excellent ability of sulfurization and greatest breakthrough time and sulfur capacity. The breakthrough time and sulfur capacity were 36.5h and 29.5% at 620℃.However, the sorbents supported by 224-280μm coal ash or 112-154μm magnetic coal ash had breakthrough time 35h or 36h and sulfur capacity 29.4% or 28.1% at 620℃. The results indicated the micropores developed and great surface area formed by calcination at high temperature were one of the main factors which could improve the sulfurization ability of the sorbents in hot coal gases.The experimental results showed also that the COS concentration related with the H₂S concentration. The relation was achieved by reactions between H₂S and CO or CO₂ to COS and H₂ or H₂O. Therefore, it can be obtained that the sorbents can effectively removed COS at the same time removing H₂S at high temperature.