A comparison of drum granulation of biochars
Drum granulation can be used to form biochar granules that could reduce dust hazards during biochar application to soils. An investigation of the effect of operational parameters using three biochar feedstock was conducted to identify the effect of biochar feedstock on granule properties. Cornstalk, birchbark and miscanthus biochar powders were successfully granulated and found to have varying granulation mechanisms, attributed primarily to differences in hydrophobic behaviour. Cornstalk granulated similarly to hydrophilic powders while birchbark had delayed granule nuclei formation resulting in larger nuclei. Miscanthus did not penetrate into the biochar powder and granulated through layering.
All three operational parameters affected granule size. An increase in liquid volume and rotational speed increased the granule size of all three biochars. Binder concentration had a negative effect on granule growth due to viscous forces that decreased granule deformation.
Granule strength was high for all three types of biochar granules and was affected by rotational speed of the drum and the liquid binder concentration. Increased binder concentration increased granule strength by promoting consolidation. Rotational speed of the drum had varying effects on granule strength due to differences in the granulation mechanisms of the biochars.
The results demonstrate that multiple biochar feedstock can be granulated using wet drum granulation, but granulation parameters must be adjusted to produce granules with specified characteristics.