Evaluation of usher wood and karkadeh stem for charcoal in Sudan

Two unusual biomass materials Hibiscus sabdarifja var. sabdariffa (karkadeh) stem and Calotropis procera (usher) wood were investigated in the laboratory as potential raw materials for charcoal making in Sudan. The materials were characterized physically and chemically and despite the low density and high bark-to-wood ratio by volume, good yields and quality of charcoal were predicted. The carbonization trials with a laboratory retort at conditions close to those of field metal kiln gave very good charcoal yields (35% for karkadeh and 38% for usher) with high energy transformation (58% and 62%, respectively). The karkadeh charcoal, except for a somewhat high ash content, was good for domestic uses (79% fixed carbon and 30.3 MJ kg^?1 heat value). The usher charcoal was better with respect to fixed carbon (86.5%) and gross heat value (32.4 MJ kg^?1 ). Both charcoals were of low density (140–160 kg m^?3) and further assessment of their economic suitability should be carried out under field conditions. The carbonization by-products were also collected and characterized by means of gas chromatography.