Torrefaction of biomass and plastic from municipal solid waste streams and their blends: Evaluation of interactive effects

Abstract

This paper investigated the interactive effects between biomass and plastic, derived from municipal solid wastes, during co-torrefaction of their mixtures. Mango branches (MBr), waste newspaper (Np), low-density polyethylene (LDPE) and their blends were torrefied at 300 °C at a constant heating rate of 10 °C/min for 30 min using a bench-scale reactor. Statistically significant interactions were found between MBr and Np during torrefaction of MBr-Np and MBr-Np-LDPE blends. The synergistic behaviour in torrefied MBr-Np accounted for its improved energy density, reduced volatile matter content, increased carbon content and higher fuel ratio than expected. During co-torrefaction with plastic, melted LDPE limited mass transfer, which resulted in higher char yield and energy content. Analysis of combustion indices revealed that waste blending ratio of torrefied biomass-LDPE blends should be limited to 5 wt%, due to the high volatile matter content of LDPE. This study elucidates that among the different torrefied blends, synergistic interactions during co-torrefaction of waste biomass (MBr-Np) generated a char with improved fuel characteristics that allowed co-firing of biomass at higher blending ratios (20 wt%).