Dynamic modelling of reactive absorption with the Maxwell-Stefan approach

Modelling and design of reactive absorption are based on the theoretical description of the reaction and mass transport in multicomponent systems. The multicomponent nature of these phenomena leads to complex process behaviour due to the superposition of many driving forces-multicomponent diffusion, chemical interactions, convective flows, multicomponent thermodynamic interplay, etc. For this reason, adequate theoretical description of multicomponent reactive systems calls for the application of the Maxwell-Stefan equations and, further, for the use of coupled mass transfer equations together with the relevant reaction kinetics. On this basis, a two-phase, gas-liquid reactive system is considered and a general dynamic model is developed for its design. Both the film and bulk reaction mechanisms are allowed for. This dynamic rate-based approach leads to a system of partial differential equations, which have to be discretized in the axial direction. The resulting DAE system is solved numerically. As an application example, the reactive absorption of sour gases in an air purification process with packed columns is simulated. For this case, an additional account of the electrical potential gradient is involved because of the presence of electrolytes. Simulation results are presented for the H2S scrubber with three liquid distributors and a structured packing section. For the validation of the model, pilot plant steady state experiments were carried out at Thyssen Still Otto in Duisburg, Germany. The simulation results are in good agreement with the experimental data.