Impact of torrefaction process temperature on the energy content and chemical composition of stool tree (Alstonia congenisis Engl) woody biomass

Abstract

Torrefaction process temperature has been identified as one important factor that can enhance energy content of Alstonia congenisis wood-dust biomass. Wood biomass, being the principal feedstock for solid fuel needs to be subjected to optimum process conditions that will increase its energy content. Therefore, physico-chemical analyses were carried out both on the torrefied and untorrefied samples of Alstonia congenisis wood-dust biomass in order to understand effects of torrefaction treatment on chemical and energy compositions of the biomass. Torrefaction was performed at varying process temperatures of 200 ​°C, 250 ​°C and 300 ​°C under a resident time of 45 ​min with an improvised laboratory scale torrefier designed with steel container. The results showed thattorrefied samples were remarkably different in colour compared to the untorrefied. It was observed that as the process temperature increases, the higher heating value (HHV) increased and energy yield decreased. The thermal stability of lignin, cellulose and hemicellulose was discovered to be in the following order: hemicellulose ˂ cellulose ˂ lignin. The fixed carbon and ash contents increased with increase in temperature. The result of elemental composition showed that torrefaction enhanced the fuel properties of the Wood-dust. Grindability and hydrophobicity tests indicated that torrefaction process increased the fragility and water-hating properties of the biomass. The observed decrease in moisture content greatly improved the fuel properties of the biomass as solid fuel. Hence, torrefaction process was confirmed as a value-added thermo-chemical conversion process for Alstonia congenisis wood dust biomass.