(350c) Rate-Based and Equilibrium Model Approach for Absorption of Aromatic Hydrocarbons in Multicomponent Mixtures: Simulation and Experiment

The determination of the absorption of aromatic hydrocarbons from coke-oven gases is strongly influenced by the complexity of the applied washing fluid. In the case of coal tar oil the number of components (400 up to 500) present in the mixture is inhibiting the application of conventional calculation techniques by binary interaction parameters. Investigations on an industrial plant (Schwelgern, Germany) have shown that the application of available gE models offered by process simulators are not able to calculate this process in an accurate manner and therefore great deviations occur between the measured process parameters from an industrial plant and the simulation results. For a better description of the regarded process comprehensive experiments were carried out in order to determine the phase equilibrium behaviour of the main aromatics, i.e. benzene, toluene and xylenes in coal tar oil whereby the washing oil mixture is treated as one pseudo component. Based on these studies an equilibrium as well as rate-based approach are developed and implemented in FORTRAN for simulating the regarded absorption process in the commercial simulation software ChemCAD. The calculation of diffusion coefficients are according to the methods of Fuller for the gas phase and Wilke-Chang for the liquid phase. Mass transfer coefficients are calculated by the methods of Billet and Schultes. The comparisons of the calculated profiles clarify that the assumption of temperature equilibrium between the present phases in the case of the equilibrium model is also leading to wide differences in the calculated concentration profiles.

On the basis of experiments carried out in a pilot plant the concentration as well as temperature profiles are evaluated for the recovery of benzene and toluene in coal tar oil. Therefore a pilot plant equipped with 2.6 m of structured packing Mellapak 350.Y with a diameter of 0.1 m was constructed at the laboratories of the University of Technology Berlin. In order to minimize the effects of maldistribution liquid collector and distributor systems were placed each 0.85 m along the column height. Gas samples are taken at four different points along the column and the temperature profile is measured at eight points between the gas and the liquid outlets. The operation conditions were varied for liquid loads between 6.5 and 11.0 m³/m²h as well as gas loads between F = 1.3 and 1.6 in order to obtain different rates of recovery. Gas concentrations at the inlet of the column were varied between 2.0 and 15 g/m³ of benzene and 1.0 to 5 g/m³ of toluene. The evaluation of the applied models is carried out by a great number of measurements. In the presentation both models and their applicability for the complex mixture will be discussed based on experimental investigations

As a result of these investigations the industrial process of the coke oven gas purification can be simulated in a more accurate manner and therefore turns out more efficiently in operation and process design.