Regulation of energy properties and thermal behavior of bio-coal from lignocellulosic biomass using torrefaction

The energy properties in bio-coal, such as proximate analysis, element composition, high heat value, colour, thermal behavior are detailed elaborated. The results show bio-coal production processes from biomass can be divided into three stages which is close to coalification through the data in energy properties. The first stage called mild torrefaction (≤220 °C) seen as biomass to peat phase during coalification in the result of unstable oxygenated functional groups in hemicellulose are decomposed and Maillard reaction induces the colour modification. Second stage called moderate torrefaction (220–260 °C) seen as lignite formation process during coalification leads to degradation of celluloses. Biomass colour from brown to sepia due to the chromophoric groups. The heating value of maple sawdust (MS) increases to 30.02 MJ/kg of MS-260. Third stage called severe torrefaction (260–300 °C) considered as metamorphic episode of lignite to bituminous coal results of covalent bond cleavage, oxygenation of lignin and condensation of aromatic carbons. As functional groups decomposition during bio-coal production, three characteristic temperatures increase with the torrefied temperature increasing read from TG and DTG curves. The MS with the highest cellulose and aliphatic C–C bonds, is effective raw materials for bio-coal production by torrefaction with the close energy properties, thermal behavior to bituminous coals.