Biomass briquettes offer a promising solution to meet the increasing energy demands of households and industries, while mitigating environmental challenges associated with waste disposal and deforestation. However, their combustion is often limited by low calorific value and high ash content. For instance, biomass materials, including wheat straw, maize straw, rice straw, and rice husk, have ash contents of up to 10.21%, 6.87%, 14.83%, and 19.6%, respectively. Heterogeneity, which involves blending biomass materials at varying proportions to produce heterogeneous briquettes, offers one of the sustainable solutions to this problem. This review aims to determine the effect of heterogeneity on the combustion of briquettes. A narrative review approach was employed, involving thorough literature searches in Scopus and Google Scholar, encompassing articles between 2005 and 2025 in English, peer-reviewed journals, conference proceedings, and case studies. Findings revealed that heterogeneity improves calorific value and thermal efficiency. For instance, the calorific value of blended onion peels and tamarind shells with cassava starch binder increased to 21.05 MJ/kg from 18.24 MJ/kg for onion peels and 18.34 MJ/kg for tamarind shells briquettes. The thermal efficiency of a blend of coconut and groundnut shell improved to 92.35% from 66.86% for groundnut shell briquettes. Despite these enhancements, limited information is available on the optimal composition of biomasses, environmental and economic aspects that hinder the scalability and acceptability of heterogeneous briquettes. Future research should focus on optimizing biomass composition, analyzing comprehensive combustion behavior, and conducting environmental and economic assessments for the real-world applications of heterogeneous briquettes. Mixing waste from different plants into solid fuel makes them burn better and more efficiently than single-source fuels. Blended solid fuels show big gains in energy output and cooking efficiency, and are cleaner for household and industrial use. For wider adoption, more work is needed to find the best mixes, assess costs, and environmental impacts.
Walozi et al. (Mon,) studied this question.