Biocoal Briquettes Combusted in a Household Cooking Stove: Improved Thermal Efficiencies and Reduced Pollutant Emissions

Clean fuels are urgently needed to reduce household cooking emissions. The thermal efficiencies (eta(th)) and pollutant emission factors (EFs) of biocoal briquettes (made from a mixture of biomass and coal powder) burned in a typical cooking stove were investigated and compared with those of coal briquettes and biomass briquettes. Biocoal briquette samples were obtained by molding blends of anthracite with 10-30 wt % crop straw of various types (maize straw, wheat straw, or rice straw). The optimum proportions for energy savings and PM2.5 EF reduction were found to be 15-20 wt %. Compared with the eta(th) of coal briquettes and biomass briquettes, the eta(th) of biocoal briquettes increased by 81-127% and 88-179%, respectively, with the optimum addition ratios of crop straw, while the delivered energy-based PM2.5 EFs of the biocoal briquettes were reduced by 61-67% and 99.0-99.5%, respectively. Delivered energy-based EFs of NOX, SO2, and toxic elements (As, Se, and Pb) also showed a significant reduction. These results indicated that biocoal briquettes can serve as a promising substitute for domestic solid fuel to reduce pollutant emissions and save energy.