Steady State and Dynamic Modeling of the Modified Claus Process as part of an IGCC Power Plant

The Modified Claus Process is one of the most common methods for sulfur recovery from acid gas streams. An extensive survey of the open literature has been carried out to collect rate expression and experimental data for the reactions of the Claus reaction furnace. For the instances that no rate expression could be found, rate expressions were derived from the available published experimental data. Additionally, data fitting of the rate parameters of key reactions in the Claus furnace was carried out. This resulted in a significantly better agreement of the model with the published industrial data in comparison to the available models in the open literature. With these and other rate expressions, a steady-state model of the Claus plant and hydrogenation unit was developed. With this kinetic model, an optimization study was carried out to minimize the power requirement in the Claus unit and other associated units as a result of the Claus unit operation. The optimization study shows that for low costs of hydrogen sulfide recovery, optimal H 2S/SO2 ratio is larger than two so as to maximize hydrogen production. As the cost of hydrogen sulfide recovery is increased, optimal H2S/SO2 ratio nears two, increasing single-pass conversion. This steady state model then served as the basis of a dynamic pressure-driven simulation of the Claus and hydrogenation units. With this simulation, models where identified between the oxygen flow to the Claus furnace (input) and H2S/SO2 ratio (output) and between the H2S concentration in the feed to the Claus unit (disturbance)) and the H 2S/SO2 ratio. With these identified models, a feedforward control strategy was developed and implemented in Aspen Plus Dynamics. This control strategy resulted in a much improved dynamic performance than conventional PI control under changing acid gas composition