Mechanical and combustion properties of sawdust-Straw pellets blended in different proportions

- Pine sawdust, wheat straw and rapeseed straw were blended in different proportions.
- A series of experiments of quality and strength have been performed.
- Mechanical and combustion parameters were found dependent on proportions of ingredients.

The objective of this project was to determine the mechanical and combustion properties of pellets made of pine sawdust mixed with wheat and rapeseed straws. We determined the characteristics and quality of the pine sawdust, wheat straw and rapeseed straw agglomerates blended in different proportions, including the poured density, tapped density and the Carr compressibility index, according to standard test method ASTM D6393: 1999. To determine pellet durability, we used the Ligno tester ONORM M 7135: 2000 to perform single-pellet drop tests. We determined the strength of the pellets by diametric compression between flat plates, and measured the heat of combustion and ash content following the international standards ISO 9831: 2005 and ISO 18122: 2016, respectively. Our results reveal that the mechanical and combustion parameters are proportion-dependent. Pellet density decreased with an increased percentage of the two straw types in the mixture. An increase in compaction pressure resulted in an increase in pellet density. The mean values of the drop resistance decreased with the addition of wheat starch, and this decrease was lower for mixtures with a higher moisture content and compaction pressure. Mixtures of sawdust with ground rapeseed straw yielded pellets of higher durability and drop resistance. The swirled durability of mixtures with rapeseed straw was not dependent on the percentage contributions of rapeseed straw and moisture content. Pellet strength decreased with the addition of ground straw. We observed a decrease in strength with an increase in moisture content and an increase in strength with increasing compaction pressure. In addition, we observed a decrease in the heat of combustion with an increase in the percentage contribution of straw in the mixture.