Desulfurization of hot coal gases by regenerative sorption

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Abstract
With an objective to contribute to the integration of coal gasifier with advanced power generation systems, such as molten carbonate fuel cells, this study has investigated h i g h t e m p e r a t u r e r e g e n e r a b l e d e s u l f u r i z a t i o n processes in which the H2S content of coal gases is reduced from 200 ppm to 1 ppm. Commercially available processes involved very low temperature scrubbing prior to use in the fuel cells and, consequently, introduce penalties in capital cost and system efficiency. As a result of a systematic thermodynamic screening, four candidates (ZnO, V2O3, Cu, and WO2) were identified for intermediate to high temperature (350‐700°C) desulfurization of fuel gases derived from coal. Of these, ZnO was experimentally studied using a bench scale, isothermal packed bed reactor. It was demonstrated that ZnO can reduce the sulfur levels to less than 1 ppm from coal gases at 650°C, and it can be completely regenerated to ZnO. However, severe decrease in sulfur capacity at high temperatures and further degradation upon regeneration were observed. Electron microscopy, microanalysis, and surface area measurements were obtained and examined in conjunction with a pore plugging model for this type of gas‐solid reactions. Major causes for the observed decrease in sulfur capacity of the sorbent were shown to be the pore plugging during sulfurization and sintering during regeneration reaction. Further research to solve these two problems is continued.

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