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 efficiency of sulfur capture and sorbent use. In this study an unreacted shrinking core model with variable effective diffusivity is applied to sulfidation test data from a pressurized thermogravimetric apparatus (P-TGA) for a set of physically and chemically different limestone and dolomite samples. The particle size was 250-300 μm for all sorbents, which were characterized by chemical composition analysis, particle density measurement, mercury porosimetry, and BET internal surface measurement. Tests were done under typical conditions for a pressurized fluidized-bed gasifier, i.e., 20% CO₂, 950 °C, 20 bar. At these conditions the limestone remains uncalcined, while the dolomite is halfcalcined. Additional tests were done at low CO₂ partial pressures, yielding calcined limestone and fully calcined dolomite. The generalized model allows for determination of values for the initial reaction rate and product layer diffusivity.