Coal Processing for Fuel Cell Utilization: Task VIII. H sub 2 S Removal by Calcium-Based Sorbents

摘要

Equilibrium calculations indicate an optimum thermodynamic limit of (H sub 2 S)/(H sub 2 0) approx. = 10 exp -3 for a typical fluidized bed gasification process using limestone or dolomite at temperatures of 1000 to 1200 exp 0 K; thus, the minimum H sub 2 S level which can be attained in the gasifier is probably near 100 ppM. Detailed kinetic investigations have shown that the kinetic rate constant for CaO with H sub 2 S is of the same magnitude as that with SO sub 2 and that the activation energy for both reactions is less than 10 exp 0 K cal/mole. The late time reactivity of H sub 2 S is higher than that of SO sub 2 because the formation of CaS does not completely obstruct the porous structure of CaO, as does the formation of CaSO sub 4 . This offers clear evidence that the sulfur deposits play a role in the late time reactivity. Hence, the next step in the modeling of sulfur cleanup by limestone must include the effects of the sulfur deposits. The first step in generating such a model is to utilize grain theory and the second step is to add sulfur deposits to the pore branching model. In addition to developing a model which includes the effects of sulfur deposits, we must determine the effects of the calcination temperature and CO sub 2 background on the pore structure. The enhancement of CaO reactivity by lower calcination temperature and higher CO sub 2 background level has been experimentally observed, although very little quantitative work has been reported. These effects are important for CaO utilization and additional empirical work is required before a theoretical model can be constructed. (ERA citation 05:005234)