Evaluation of CaO-decorated Fe2O3/Al2O3 as an oxygen carrier for in-situ gasification chemical looping combustion of plastic wastes

Abstract

The use of solid waste such as plastic waste in Chemical Looping Combustion (CLC) becomes interesting, with potential advantages of exploiting new energy sources, suppressing pollutants, and capturing carbon dioxide. However, the emission of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) which as toxic matter has aroused increasing attention during the utilization process of these solid wastes, especially for plastic waste which contains a high chlorine content. Through applying CaO decoration to Fe-based oxygen carrier (OC) is it possible to realize effective dechlorination during chemical looping processes. In this study, a 5wt.% CaO-decorated Fe2O3/Al2O3 as OC was used for in-situ gasification chemical looping combustion (iG-CLC) of plastic waste, and the reactivity of the decorated OC particles was tested in a batch fluidized-bed reactor, compared with that of raw Fe2O3/Al2O3 OCs. Operation conditions, including reaction atmosphere, supply oxygen ratio and reaction temperature, were investigated to explore their influence on carbon conversion, maximum instantaneous rate of fuel conversion and CO2 yield. Results indicated that CaO decoration results in a lower reactivity of OC particles. However, by optimizing these operation conditions the undesirable influence of CaO decoration can be mitigated. The stability of OC reactivity was evaluated through 10 redox cycles, where stable carbon conversion, maximum instantaneous rate of fuel conversion and CO2 yield were observed. These used OC particles were characterized by a surface area and porosity analyzer and an Environment Scanning Electron Microscope coupling with Energy Dispersive X-ray spectroscopy (ESEM–EDX). The specific surface area (BET) result indicated that CaO-decorated OC particles present lower BET and pore volume after 10 redox cycles, and the ESEM–EDX result also demonstrated little ash deposition on the surface of OC particles, which both contribute to the slight deterioration of OC reactivity. It was also observed from ESEM–EDX that there is the accumulation of Cl element on OC surface, providing sound evidence for dechlorination during the iG-CLC of plastic waste.