Abstract
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.Graphic
Highlights
Global production of plastics reached 348 million tonnes in 2017 [1]
Pyrolysis has a significant advantage over other recycling processes, as it does not require an intensive sorting process, except for PET and polyvinyl chloride (PVC) removal
Three concepts of the fractionation and condensation unit of gaseous products derived from the waste plastics pyrolysis were compared
Summary
Global production of plastics (not included polyethylene terephthalate PET, polyamide PA and polyacryl-fibers) reached 348 million tonnes in 2017 [1]. Asia (50.1%) is the largest producer of plastic materials, followed by Europe (18.5%) and North American Free Trade Agreement “NAFTA” (17.7%). Due to their versatility, plastics have become important materials in strategic sectors such as packaging, building & construction, transportation, renewable energy, agriculture, medical devices or sports. I.e. thermal decomposition under anaerobic conditions in high temperature (usually 350–800 °C), is an alternative to classical plastics waste management methods [2,3,4]. During this process, chemical bonds in the polymer chains are cracked and hydrocarbons with relatively short chains are formed [5]. Plastics can be contaminated with bio-waste, which makes this method useful for recycling polyolefin fraction of municipal waste
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