Particle density determination of pellets and briquettes

Several methods and procedures for the determination of particle density of pellets and briquettes were tested and evaluated. Round
robin trials were organized involving five European laboratories, which measured the particle densities of 15 pellet and five briquette
types. The test included stereometric methods, methods based on liquid displacement (hydrostatic and buoyancy) applying different
procedures and one method based on solid displacement.
From the results for both pellets and briquettes, it became clear that the application of a method based on either liquid or solid
displacement (only tested on pellet samples) leads to an improved reproducibility compared to a stereometric method. For both, pellets
and briquettes, the variability of measurements strongly depends on the fuel type itself.
For briquettes, the three methods tested based on liquid displacement lead to similar results. A coating of the samples with paraffin did
not improve the repeatability and the reproducibility.
Determinations with pellets proved to be most reliable when the buoyancy method was applied using a wetting agent to reduce surface
tensions without sample coating. This method gave the best values for repeatability and reproducibility, thus less replications are
required to reach a given accuracy level. For wood pellets, the method based on solid displacement gave better values of repeatability,
however, this instrument was tested at only one laboratory.