Influence of the synergistic effects and potassium on the combustion behaviors of biomass under high heating rate

Abstract

This work aims to study the synergistic effects between lignin, hemicellulose, and cellulose, as well as potassium on the combustion behaviors of biomass at high heating rate conditions. The combustion behaviors of biomass are studied in a Hencken flat burner with a high-speed camera, and the radiant energy analysis technology is used to calculate the flame temperature. The results indicate that the ignition delay time (IDT) and the char ignition delay time (IDT-CHAR) increase with the increase of the cellulose content when the cellulose content in biomass is less than 41%, and decrease significantly when the cellulose content is more than 41%. The homogeneous ignition of the cellulose and lignin with removing alkali metals (LIG-R) mixtures is not affected by the synergistic effects between cellulose and LIG-R. The catalysis of potassium significantly promotes the synergistic effects between cellulose and lignin without removing alkali metals (LIG-NR) in the blending ratio range from 50% to 75%, and the rapid decomposition of cellulose provides hydrogen donors for the pyrolysis of lignin and accelerates the release of combustible matters in lignin, resulting in the promotion of the homogeneous ignition. The promoted homogeneous ignition results in the significant decrease in the ignition of the biomass which has higher ratios of cellulose and lignin (50%-75%) and higher cellulose content (more than 40%). The catalysis of potassium on the synergistic effects between cellulose and lignin for the biomass homogeneous ignition and char ignition need to satisfy-two conditions: (1) the mass ratio of cellulose in the mass sum of cellulose and lignin in biomass should be in the range of 50%-75%, and (2) the cellulose content should be greater than 40%.