Comparative Evaluation of Alternative Reactor Configurations for Flash (Intra)-Carbonization of Sawdust with Minimal External Fuel Use​

Alternative reactor designs to improve thermal efficiency and product quality of intra-carbonisation of sawdust were evaluated. Configurations tested include a cylindrical reactor with an internal combustion chamber, a conical reactor with both internal and external combustion chambers with varying feedstock packing regimes. Results indicate that reactor geometry and air/fuel dynamics critically affect conversion rate, carbon yield, and briquette quality. The best conversion of ~ 95% and a yield of 46% was achieved using a stratified conical reactor + combustion chamber (SCCC) where there was quick and uniform heat transfer in 8hrs. Conical reactor systems using an external combustion chamber had very low conversions and yields, particularly in mixed feedstock scenarios compared to stratified, due to reduced initial aeration. The conical reactor with internal combustion chamber (both SCCC and OCCC) achieved faster carbonization, reaching over 90% conversion in 8-10 hours. The two also had the best quality of charred biomass of between 23.33MJ/kg and 23.41MJ/kg gross calorific value; while the least converted with low yields of 4-5%, particularly from the cylindrical reactor, had the least values for calorific value of 17.91-17.94MJ/kg, close to raw biomass. Closing the reactor top generally encouraged heat retention though in some cases it compromised convective transfer. The competent reactor configurations offer promising alternatives for sustainable bio char and activated carbon production from loose waste biomass in low-income and rural settings.