A simple model was developed to describe the absorption of SO2 in a circulating dry scrubbing (CDS) process, which is a semidry, lime-based, flue-gas desulfurization (FGD) process that utilizes a circulating fluidized bed arrangement for contacting a sorbent with SO2-laden flue gas under "coolside" conditions. The reaction chemistry is thought to be similar to that of spray-drying absorption. The liquid-phase mass-transfer coefficient was successfully modeled as a function of the sorbent particle spacing on the wetted surfaces. Gas-phase mass-transfer resistances were assumed to be insignificant. Due to the high surface area available in a CDS reactor, the evaporation rate of water from the slurry was modeled as "constant-rate" drying according to classic spray-dryer theory. However, the "falling-rate" and "diffusion" evaporation stages were negligible in CDS since sorbent particle bunching at the surface of the slurry is nonexistent.