Experimental and Theoretical Investigation into Sulfate Formation in the Regeneration of Zinc Ferrite Sorbents. Final Report

摘要

The high temperature desulfurization of coal gas for use in molten carbonate fuel cells requires a regenerable sorbent such as zinc ferrite. In this program the regeneration of spent zinc ferrite sorbent using air-steam gas mixtures in the temperature range of 550 sup 0 to 900 sup 0 C was studied. Thermodynamic calculations show and experimental measurements confirm that zinc sulfate is formed in the regeneration process. The formation of the sulfate requires the simultaneous presence of SO sub 2 and O sub 2 . Hence, it reaches a maximum level under conditions when the sulfides in the spent sorbent have been nearly oxidized. Sulfate formation is enhanced by lower temperatures and higher oxygen pressures in the feed gas. The formation of sulfate is promoted by the presence of iron oxide in the zinc ferrite and also by added chromium oxide. The analyses of residual sulfate present in sorbents regenerated in a laboratory scale fixed-bed reactor were used to derive a linear equation that predicts the sulfate level as a function of process variables. During subsequent desulfurization, the zinc sulfate present in the regenerated sorbent releases SO sub 2 and SO sub 3 into the hot coal gas stream. These undesirable contaminants can be removed by another bed of zinc ferrite, provided that a sufficient concentration of hydrogen is available in the coal gas stream. 20 refs., 35 figs., 19 tabs. (ERA citation 11:021858)