HYDROGEN-SULFIDE CAPTURE BY LIMESTONE AND DOLOMITE AT ELEVATED PRESSURE .2. SORBENT PARTICLE CONVERSION MODELING

The physical structure of a limestone or dolomite to be used in in-bed sulfur capture in fluidized bed gasifiers has a great impact on the e fficiency of sulfur capture and sorbent use. In this study an unreacte d shrinking core model with variable effective diffusivity is applied to sulfidation test data from a pressurized thermogravimetric apparatu s (P-TGA) for a set of physically and chemically different limestone a nd dolomite samples. The particle size was 250-300 mu m for all sorben ts, which were characterized by chemical composition analysis, particl e density measurement, mercury porosimetry, and BET internal surface m easurement. Tests were done under typical conditions for a pressurized fluidized-bed gasifier, i.e., 20% CO2, 950 degrees C, 20 bar. At thes e conditions the limestone remains uncalcined, while the dolomite is h alf-calcined. Additional tests were done at low CO2 partial pressures, yielding calcined limestone and fully calcined dolomite. The generali zed model allows for determination of values for the initial reaction rate and product layer diffusivity.