This thesis reports a thermodynamic feasibility study, experimental data and modeling results for key side reactions occurring in the front-end units, i.e. the reaction furnace (RF) and the waste heat boiler (WHB), of Claus plants for sulfur recovery.

A detailed chemical reaction equilibrium study was initially performed to select thermodynamically important reactions that lead to the formation and the consumption of CO, H₂, COS and CS2 under the conditions encountered in the front-end of a Claus plant. An extensive experimental and modeling study was conducted to obtain kinetic data for the selected key side reactions. All experiments were conducted in a novel high-temperature flow-reactor system. From the modeling of the experimental data for key reactions, intrinsic kinetic rate expressions were determined.

Next, experiments on the partial oxidation of acid gas mixtures were conducted. The experimental data provided useful information on the formation of key species under oxidation conditions. Simulation and modeling studies, using detailed reaction kinetic schemes involving elementary reactions, were also conducted. A comparison of experimental data with simulation results showed that the kinetic scheme for H₂S oxidation could adequately predict gas compositions at higher temperatures (> 1100°C) but not at lower temperatures. These simulation studies also highlighted the need for the kinetics of many reactions involving sulfur containing species and carbon containing species.

Finally, modeling studies of the front-end units, the RF and the WHB of a Claus plant was conducted. The formation of COS in the tubes of an industrial WHB was simulated using new kinetics and compared with plant data. The simulation showed that up to a fifty percent reduction in COS production in the WHB may be achieved by operational and design changes. This represents a significant reduction in COS formation and has major implications on Claus plant sulfur emissions and recovery. Further, an attempt was also made to predict the gas composition from the RF using a true kinetic model. The kinetic model performed well in predicting the compositions of chemical species of interest, CO and H₂.