Reaction and transport effects in the heterogeneous systems for lean gas purification

Sorption of hydrogen chloride gas by active soda and that of hydrogen sulfide gas by calcium oxide are explored by experiment as promising means of removing these detrimental contaminants from fuel gas: active Na₂CO₃ was prepared by the calcination of commercial NaHCO₃ at 200 °C; reactive CaO was formed by decomposing a fine-grained, high-calcium limestone at 830 °C. Techniques with a differential reactor were employed to explore the rate of reaction of HCl with Na₂CO₃ at 500 °C and that of H₂S with CaO at 800 °C. Time-resolved data on the sorbents’ conversion were collected as a function of mean particle size in the range between 0.285 and 1.12 mm. The surface reaction constants, deduced via the tractable model from the initial reaction rates of the two reactions, slightly increase with the increasing particle size. The proposed correlations enable to interpolate or cautiously extrapolate to other isotropic, irregularly shaped solids. The effective diffusivities educed by means of the model from the experimental curves decrease significantly with the increasing conversion and are affected by the particle size in both sorptions. The developed reaction rate equations can conveniently be applied to the design and simulation of the deep dechloridization and the bulk desulfurization of hot producer gas.