Optimizing the Production Process of Fuel Pellets from Swine Dung Compost

Interest in producing fuel pellets from animal manure compost has increased due to a sharp rise in oil prices. This study has aimed to optimize the pellet production process by determining the physical characteristics of fuel pellets produced from swine manure compost with either wood bark or sawdust added. Prior to the pelleting process, the physical properties of compost with wood bark added were examined after mixing with industrial oil at different weight ratios of 0%, 1%, 3%, or 6%, or with rice hull meal at weight ratios of 5% or 10%, while controlling the moisture content to 10%, 15%, or 20%. The physical properties of compost with sawdust added were also examined after the compost was sieved through 1, 2, 3, or 5 mm diameter mesh and mixed with a 1% ratio of oil, while controlling its moisture content to a range between 17% and 18%. The two highest calorific values of 14,876 and 15,086 kJ kg-1 were observed for the pellet made from compost mixed with 1% oil and 10% water content, and with 0% oil and 15% water content, respectively. The pellet durability index (PDI) decreased with increasing oil content above 1%. Both the specific gravity and apparent density decreased with increasing oil mixing ratio and moisture content. Mixing with rice hull meal resulted in higher durability during the pelleting process compared to mixing with oil. The durability was greater than 98% when the compost was sieved through a 1, 2, or 3 mm diameter mesh, whereas the durability was 96% when the compost was sieved through a 5mm diameter mesh. The results indicate that an optimal fuel pellet can be obtained by controlling the moisture content of the swine dung compost to between 15% and 20%, mixing with oil at a ratio of 1% or lower, and sieving through a mesh with a 3 mm or smaller diameter. The overall and net efficiencies of a boiler were higher using pellets made from the compost with wood bark than those with the pellets made from the compost with sawdust.