Performance evaluation of biomass pretreated by demineralization and torrefaction for ash deposition and PM emissions in the combustion experiments

Abstract

Biomass combustion is a promising method in combustion facilities to reduce CO2 emissions. Biomass fuel has unfavorable characteristics, such as low temperature ash minerals and high particulate matter (PM) emission in the combustion facility, which influences operation and creates environmental issues. In this work, different types of empty fruit bunch (EFB) and palm kernel shell (PKS) biomass samples, such as raw biomass, demineralized biomass, and its biomass pretreated by torrefaction were studied to identify their char combustion characteristics by thermogravimetric analysis (TGA) and their ash deposition behaviors and PM emissions in a drop tube furnace (DTF) experiment. Regarding the char combustion characteristic results obtained by TGA, demineralization pretreatment did not clearly influence the char combustion reactivity compared to that of raw biomass, but torrefaction pretreatment lowered the char combustion reactivity at low temperatures. In the DTF experiments, torrefaction pretreatment led to increasing ash deposition and PM emissions during biomass combustion. However, demineralization pretreatment clearly lowered the amount of ash deposition and PM emissions because potassium (K), chlorine (Cl), and sulfur (S) were significantly removed by demineralization pretreatment. In particular, scanning electron microscopy with dispersive X-ray spectroscopy (SEM-EDX) analysis results showed that the demineralized biomass samples having low K, Cl, and S components emitted relatively large PM compared to untreated biomass. Therefore, demineralization pretreatment might be a good method to produce cleaner biomass fuel.