Combustion characteristics of modified plant biomass pellets

The main objective of this experimental study is to investigate the thermo-chemical conversion of modified biomass pellets of different origin (spruce, aspen and wheat straw). The modification of biomass pellets includes the microwave (mw) pre-treatment of these biomass samples and spraying of waste cooking and mineral oils on the surface of the mw pre-treated pellets. The initial and modified pellets were characterized in terms of the elemental composition, heating values, energy density (bulk), moisture, and ash contents. The results show that for all biomass types mw pre-treatment as well as spraying of waste oils on the surface of pre-treated pellets results in an increase of the carbon content and heating values of the samples relative to the original biomass pellets with direct impact on the gasification and combustion characteristics of these pellets. The experimental study of the effect of biomass pellets modification on their gasification/combustion characteristics includes complex time-dependent measurements of the biomass weight loss rate, temperature, heat production rate, combustion efficiency and products composition. Due to the variations of the elemental composition and heating values of the produced biomass pellets, a correlating increase of the volume fraction of CO₂ and produced heat energy at thermo-chemical conversion of biomass was observed. The results of the complex experimental measurements allow to conclude that the proposed modification of plant biomass pellets including their mw pre-treatment with further spraying of waste oils is an effective tool to convert biomass into a fuel with improved combustion characteristics.