Kinetics of mn-based sorbents for hot gas desulfurization: Task 2 - exploratory experimental studies. Quarterly report, March 15, 1996--June 15, 1996

The objective of this project is to develop a pellet formulation which is capable of achieving low sulfur partial pressures and a high capacity for sulfur, loaded from a hot fuel gas and which is readily regenerable. Furthermore the pellet must be strong for potential use in a fluidized bed and regenerable over many cycles of loading and regeneration. Regeneration should be in air or oxygen-depleted air to produce a high-concentration sulfur dioxide. Fixed-bed tests were conducted with several formulations of manganese sesquioxide and titania, and alumina They were subject to a simplified fuel gas of the oxygen-blown Shell type spiked with a 30,000ppmv concentration of H{sub 2}S. Pellet crush strengths for 4 and 2mm diameter pellets was typically 12 lbs per pellet and 4 lbs per pellet, respectively. For the most favorable of the formulations tested and under the criteria of break-through at less than 100ppmv H2S and loading temperatures of 500{degrees}C and an empty-bed space velocity of 4,000 per hour, breakthrough occurred an effective loading of sulfur of 27 to 29% over 5 loading and regeneration cycles. At 90% of this saturation condition, the observed level of H{sub 2}S was below 10ppmv. For regeneration, a temperature of 900{degrees}C is required to dissociate the sulfide into sulfur dioxide using air at atmospheric pressure. The mean sulfur dioxide concentration which is achieved during regeneration is 8% with empty-bed space velocities of 700/hr. TGA tests on individual pellets indicate that bentonite is not desirable as a bonding material and that Mn/Ti ratios higher than 7:1 produce relatively non-porous pellets. Whereas the reactivity is rapid below 12% conversion, the kinetics of conversion decreases significantly above this level. This observation may be the result of plugging of the pellet pores with sulfided product creating inaccessible pore volumes or alternately an increase m diffusional resistance by formation of MnS