Technical evaluation of non-woody biochar feedstocks as charcoal dust alternatives in production of carbonised briquettes

Abstract

The increasing deforestation in Uganda due to charcoal production has heightened the need for sustainable alternatives in briquette manufacturing. This study investigates the potential of biochar derived from non-woody feedstocks such as water hyacinth, sugarcane bagasse, coffee husks, and corn cobs as substitutes for charcoal dust in carbonised briquette production. Biochar characterisation included proximate analysis and calorific value assessment. Corn cobs biochar exhibited the highest calorific value (28.08 MJ/kg), whereas water hyacinth biochar had the lowest (7.18 MJ/kg). Briquette characterisation revealed reduced calorific values compared to raw biochar, except for water hyacinth, where the binder contributed to an increase. Bulk density was highest for charcoal dust briquettes (370.49 kg/m³), followed by water hyacinth briquettes (321.31 kg/m³). Combustion performance tests assessed ignition time, water boiling time, thermal efficiency and fuel consumption. Corn cob and sugarcane bagasse briquettes ignited fastest (4 minutes), while water hyacinth and charcoal dust took longer (6 minutes). Under cold-start conditions, corn cob briquettes took 13 minutes longer than charcoal dust to boil 5 litres of water, but under hot-start conditions, the gap reduced to 2- 3 minutes, indicating efficiency during sustained cooking compared to the other briquettes. Water hyacinth briquettes yielded inconsistent boiling results with unrealistically high thermal efficiency, making their thermal performance inconclusive. Corn cob briquettes showed the lowest specific fuel consumption in both cold and hot start tests, indicating high combustion efficiency likely due to their higher volatile matter content. In contrast, coffee husk briquettes consumed more fuel, potentially due to lower fixed carbon. Economically, corn cob briquettes (UGX 1,199/kg) are nearly as affordable as charcoal dust (UGX 1,128/kg), while coffee husk and bagasse remain viable alternatives; water hyacinth (UGX 5,916/kg) is currently unfeasible without improved supply logistics. The findings suggest that corn cobs and sugarcane bagasse are the most viable, sustainable alternatives to charcoal dust, offering comparable calorific value, faster ignition, and combustion efficiency. This study concludes that integrating these feedstocks into briquette production can mitigate deforestation pressures while providing an efficient, eco-friendly energy solution for Uganda.