Investigation of additives in combustion of wheat straw pellets in a small scale boiler

Crop residues could provide a local, sustainable, and low-cost solid fuel alternative to woody biomass for heat supply in the agricultural community. However, utilization of crop residues on a small scale is associated with increased pollutant emissions, as well as ash-related operational problems. There is ongoing research on fuel conditioning measures, such as fuel leaching, fuel blending, and using mineral additives, as a manner to mitigate these issues. The purpose of this study is to investigate the applicability of additives in the combustion of crop residues under everyday conditions. To this end, wheat straw pellets were combusted in a 30 kW boiler with and without additives (kaolinite and MgO, 2 wt. % and 4 wt. %). Carbon monoxide (CO) and particulate matter (PM) emissions have been monitored during combustion experiments, as well as changes in bottom ash behavior and composition. The results have shown that additives slightly decrease the heating value of the fuel (3%-6%). During experiments with additized wheat straw pellets, higher emissions of CO were observed. Combustion of pure not additized wheat straw pellets resulted in a PM emission of 568 mg/Nm(3), which decreased with additives. Both researched additives increase the four characteristic ash deformation temperatures.