High temperature, isothermal data on SO 2 capture were obtained as a function of temperature, SO 2 partial pressure, and Ca/S molar ratio for a pulverized dolomite (34 micron mean size) and a high purity calcite (11 micron mean size). The experimental results indicated that sulfur capture increases approximately iinearly with increasing Ca/S ratio and is relatively insensitive to SO 2 partial pressure at the conditions tested. Reaction zone temperature was found to critically influence the overall effectiveness of sulfur capture by sorbent injection; as the local temperature increases, the rates of heterogenous chemical reaction and diffusion increase but these are ultimately compensated by a decrease in initial sorbent surface area due to desurfacing during flash calcination. The results of the experimental studies were compared with theoretical predictions using a combined diffusion/heterogeneous chemical reaction model which was developed based on a grain formulation. Initial analysis of various fundamental kinetic studies suggested that the intrinsic chemistry was first order in calcium sites and near zero order in SO 2 partial pressure. Model predictions, based on measured gas temperatures and limestone surface areas without sulfur plus kinetic and diffusion rates derived from previously reported fundamental studies, showed good qualitative and quantitative agreement with experimental data. Analysis of temperature profiles from full-scale utility boilers suggests that effectiveness of dry sorbent injection will depend strongly on the quench rate within the surfation zone even if sorbent injection is optimized.