Fluidized bed thermal degradation products of HDPE in an inert atmosphere and in air-nitrogen mixtures

Different processes involving thermal decomposition such as incineration, pyrolysis, gasification or co-combustion are becoming important for energy generation using plastic wastes as combustible materials. The thermal degradation of the material, the product distribution and consequently the economics of the process are strongly influenced by the experimental conditions used. In this work, the thermal degradation of high-density polyethylene (HDPE) has been carried out using a fluidized bed reactor under different temperature conditions. Two types of experiments have been performed, pyrolysis experiments, in which nitrogen has been used as inert gas, and gasification experiments, meaning that the thermal decomposition has been carried out in a nitrogen-air mixture with low oxygen concentration. The influence of the operating parameters on the product distribution and gas composition has been investigated using GC and MS/GC for the analysis of the gas, wax and oil fractions obtained. The results obtained show a widely differing product yield in both processes. The main objective of the paper is a comparison of pyrolysis and gasification in terms of the generation of products of high heating value, and the energy requirements for the thermal degradation and production of residues and polyaromatic compounds. An optimum interval of operation temperatures is suggested in order to obtain high yield to gases of high heating values and low yield to PAHs. (C) 2002 Elsevier B.V. All rights reserved.