Combustion performance and emissions from torrefied and water washed biomass using a kg-scale burner

Abstract

This study investigates wastes and biomass as alternative fuels in a kg-scale burner in terms of combustion characteristics and emissions. Water washing, torrefaction, and their combination are used to improve the properties of the wastes and biomass. The air pollutants in the exhaust of the burner are also analyzed. It could be concluded that the reactivity and average heat supply from the pretreatment are improved significantly. The improvement ratio of average heat supply can be up to 103.5 %, stemming from water-soluble ash removal during water washing. Torrefaction can lift the average heat supply due to the increment of fixed carbon content in the fuels, but it reduces the reactivity owing to the decrement of volatile matters. Most of the raw or pretreated materials can be directly combusted, as a result of lower regulated air pollutants (e.g., NOx, SO2, CO) from them than from coal. Water washing can successfully remove chlorine in the wastes by dissolution since most of the chlorine in the wastes are in salt form. The chlorine reduction significantly reduces the HCl concentration (55–58 % reduction efficiency) and the toxicity concentration of polychlorinated dibenzo-p-dioxins and dibenzofurans (78–84 %), while torrefaction increases the toxicity concentration owing to the de novo synthesis.