Simulation of the Condensation and Fractionation Unit in Waste Plastics Pyrolysis Plant

The condensation and fractionation unit design affects the quantity and quality of the liquid products derived from the waste plastics pyrolysis. The oil products, if meet the standards requirements, can be used as an alternative fuel. Three configurations of this unit were studied: two condensers system with phase separators (2 CNDR), three condensers system with phase separators (3 CNDR) and as an unconventional solution in pyrolytic plant—the rectification column system (TOWR). Based on the chromatographic analysis and laboratory distillation results of the pyrolytic oil from industrial plant, the composition of the model oil was determined. This model oil was then used in simulations of the condensation and fractionation units, using ChemCad software. The comparison of the three tested configurations showed that the best separation of components was achieved in the TOWR system. Although in the simplest CNDR 2 system the desired heavy fraction yield was higher, its composition was least favourable in terms of oil properties (e.g., flash point), because more light components were condensed. Since the application of rectification column resulted in the best fractionation efficiency, the proposed TOWR configuration was examined in detail. The change of the rectification column process parameters (mainly the reflux ratio) allows for precise control of the oil fractions composition. The reflux ratio, and hence the distillate temperature, determines the heavy fraction yield. The yield and composition of the oil fractions practically do not depend on the feed stream temperature. By increasing the number of stages in the rectification column the separation of near-boiling components is improved, but the significant effect is noticeable only up to 10 theoretical stages.