Quantification and characterisation of biomass residues for the formulation of charcoal briquettes for household use in Kenya

Abstract

Energy is the engine for economic development of any country, providing essential services to humanity. Production and consumption of global energy has been increasing since 1973 with demand for renewable energy accounting for about 15%. In Kenya 80% of the total energy requirements is derived from biomass sources. While woody biomass are diminishing rapidly, causing deforestation and degradation of water catchment areas, agro-based biomass residues are increasing without adequate innovations for their economic utilization thus causing environmental and human healthy and safety problems. The foregoing necessitated this study whose rationale was to formulate household charcoal briquettes using suitable crop residues and clay as a binder. The study area was in factories milling sugarcane, coffee cherries, macadamia nuts and round wood found in Nyanza, Central, Nairobi and Rift Valley provinces. Appraisal and rationalization studies were conducted to derive linear regression models for the estimation of quantities of biomass residues using computer-based models. The models developed were statistically tested for their suitability in application using 95% confidence limits. Physico-chemical characterisation and formulation of briquettes was carried out at KEFRI laboratories. Briquettes formulated were tested for their compliance to current charcoal specifications using SABS (2000). It was found that although enormous quantities of bagasse, coffee husks, macadamia shells and sawmilling wastes were generated annually, only less than 10% was economically exploited. The residue indices of bagasse, coffee husks, macadamia shells and sawdust residues were found to be 0.364, 0.207, 0.510 and 0.528 respectively. About 1.6 million metric tonnes of bagasse was generated annually. Except sawdust whose calorific values were low (3.950 Kcal/g), bagasse, coffee husks and macadamia shells had 5.04 Kcallg, 5.37 Kcallg and 5.99 Kcal/g respectively of energy. Bagasse had 1.85% ash content while coffee husks, macadamia shells and sawdust had 1.08%, 2.62% and 0.74% respectively. High calorific energy and ash content of bagasse and its availability in large quantities, enhanced its suitability as a major component in the formulation of briquettes. Briquettes formulated using I: 1:40 ratio for molasses, clay and bagasse respectively at 0.50 N/mm2 were found to be good, based on their physico-chemical properties. Volatile matter, ash content and calorific energy of the briquettes were 27.2%, 36.4% and 4.390 Kcallg respectively at an average Me of 4%. They were odourless and burnt with smokeless flame without sparks while they ignited easily and took relatively long to extinguish. The briquettes were recommended for production on commercial scale for household use to supplement wood charcoal thus contribute to environmental conservation.