Modelling plastic heating and melting in a semi-batch pyrolysis reactor

Plastic pyrolysis is a solution for the dilemma of enormous plastic waste accumulation and an alternative source of energy, which converts plastic wastes into a wide range of fuels and chemicals by thermal decomposition. The concept is widely validated and applied at lab-scale in terms of characterisation of the process and its by-products. On the other hand, numerical modelling and optimizing of the process for the sake of developing and efficient implementation at the industrial scale are seldom reported in literature. And since there exist different phenomena involved during this process (starting from feeding with raw material until the recovery of products), the aim of this work is to model and validate heating and melting phenomena of plastics, using finite element method, inside a semi-batch reactor as a first step preceding the cracking phenomenon. First, sensible heat transfer within the reactor, empty or loaded with solid and liquid materials, is modelled by coupling the energy and the momentum equations, where the results are validated experimentally at different heating rates. Moreover, a modified apparent heat capacity method (AHCM) is used to model the melting phenomena of plastics, which revealed good capability. As a result, the model is validated through temperature profiles measured at different points on the semi-batch reactor and by addressing energy balance on the whole experiment. Whereas, the average relative error between experimental and simulated results, at different heating rates didn't exceed 8%. Finally, the validated model has paved the way for modelling the whole pyrolysis process of plastics.

Automated summary

Plastic pyrolysis, as a method to convert plastic waste into fuels and chemicals, has been widely validated and applied at the lab scale, but there is limited literature on numerical modeling and optimization for industrial implementation. This study models and validates the heating and melting phenomena of plastics inside a semi-batch reactor using finite element method, laying the foundation for modeling the entire pyrolysis process.