Simulations of circulating fluidized-bed (CFB) reactors applied to the modified Claus process were performed to assess their potential for eliminating the costly tail gas clean-up unit (TGCU) from a Claus plant. The TGCU could be eliminated by achieving very high H2S conversions in the catalytic reactors. Both the CFB regimes of pneumatic transport and fast fluidization were examined. Moreover, a newly developed CFB model accounting for the downflow of both the gas and solids in the annulus was applied to the fast fluidization regime. Recently published intrinsic reaction kinetics were employed for the hydrolysis of the problematic COS and CS2 compounds on the Kaiser 201 alumina catalyst. The simulation results were compared to the work of Birkholz et al. (1987, Can. J. Chem. Engng 65, 778-784), who simulated the use of conventional gas fluidized-bed converters in a Claus plant. The simulated three reactor, adiabatic CFB system operating in the pneumatic transport regime was able to achieve an overall sulfur recovery of 96.2%. Removal of H2O before each reactor improved the recovery to over 99%.