Design of industrial reactive absorption processes in sour gas treatment using rigorous modelling and accurate experimentation

In this paper a rigorous rate-based model for the selective absorption and desorption of sour gases in packed towers within a coke oven gas purification process (VACASULF((R))-process) is presented. It considers multi-component mass transfer of CO2, H2S, NH3 and HCN in aqueous potassium hydroxide (KOH) or potash (K2CO3) solutions and the influence of chemical reactions on mass transfer using enhancement factors. A modified Pitzer model is used to estimate activity coefficients in the electrolyte solution for the calculation of the chemical and the phase equilibria as well as the reaction kinetics (Bronsted-Bjerrum equation). Using data from the literature this thermodynamically consistent approach was successfully validated for the phase equilibria and the reaction kinetic calculation. Since no experimental data for the above-mentioned chemical system in packed towers is available in the literature, own experiments were carried out in a pilot plant packed tower. A newly developed experimental method using redundant measurements and a Data Reconciliation procedure improved the accuracy of concentration profiles for the gas and the liquid phase. Using eight absorption and eight desorption experiments, as well as industrial on-site measurements of the entire plant, the model was successfully validated. In addition, the model was used for global optimization using evolutionary algorithms, revealing an optimization potential of 30% in operating costs.