Washing oil, one of the important distillation cut of coal tar, consists of a series of high value-added components which can form azetropic and eutectic system, making it impossible to separate certain components completely by normal distillation. In this work, a scheme coupling distillation with crystallization to deal with this cut for pure chemicals is simulatively investigated before an industrial design. By the aid of this research, a 25Kt/a pilot scale unit was successfully designed which is now running with alpha-methyl-naphthalene, beta-methyl-naphthalene, fluorene, dibenzofuran and acenaphthylene in high purity as main products and naphthalene fraction, medium washing oil (dimethylnaphthalene) and heavy washing oil as by-products.

A computational fluid dynamics (CFD) model was developed for describing the flow patterns and hydraulics of triangular fixed valve tray. The gas and liquid phase, as two interpenetrating phases, were modeled in the Eulerian framework. Based on the clear liquid height obtained by experiments, a new correlation for liquid hold-up was adopted, and the interphase momentum transfer source was also calculated. Several simulations were carried out for a triangular fixed valve tray with varying operational conditions. Velocity distributions, clear liquid height, froth height, and phase hold-up were predicted for various combinations of gas and liquid flow rates, and the results were found to be in reasonable agreement with the experimental data.