Development and characterization of composite briquettes for domestic cooking application

Abstract

One of the main challenges affecting the adoption of carbonized briquettes in Uganda is their inefficiency in transferring heat. Composite briquette materials enable the strengths of each constituent raw material to become amplified. For example, rice husks have high ash content and are lightweight but coffee husks have good ignition properties. This work aimed at producing composite briquettes from three common agricultural residues in Uganda, namely rice husks, coffee husks, and groundnut shells. A low-pressure technique and cassava starch binder were employed in the briquette development process. The physical properties of the developed composite briquettes were determined by using thermogravimetric analysis (TGA). The mechanical integrity of the briquettes was determined using the drop tests and particle density. Developed composite briquettes from this study had improved properties compared to those developed previously from individual bio-chars. More so, the carbonization process significantly improved the fixed carbon contents and these later were verified by the increased calorific values of the developed briquettes after carbonization. The calorific values of the developed briquettes ranged between 13134.5 MJ/kg and 19199.5 MJ/kg. Drop strengths ranged between 43.8% and 100.0% while particle densities ranged between 409.46 kg/m3 and 707.25 kg/m3. This means that the developed briquettes will withstand forces during transportation and storage more than briquettes developed from individual bio-chars. TGA confirmed that the developed briquettes have high residuals and thus high fixed carbon contents. The lowest total percentage weight loss at the highest combustion temperature was 68.3%, obtained by briquette 10. This work showed that calorific values have no linear relationship with drop strength and particle density, even though it varies with them. The results provide vital information that shows composite briquettes have higher potentials for use as fuel for cooking purposes and also serve as a measure in curbing the environmental hazard posed by poor methods of agricultural waste disposal in addition to reducing the popular use of charcoal which harms our environment (deforestation). There is however need to explore the use of different binders with better binding abilities, most preferably those not associated with food.