Evolution of biomass particles during pelletization process

Abstract

Pulverizing is an essential unit operation in co-firing biomass with coal. Pulverizers are only compatible with pellet forms of fibrous biomass materials and crush them down to their original forming particle sizes. That is why the data on the size distribution of the particles forming a biomass pellet is crucial to achieving optimum combustion conditions. The current study determines the internal particle size distribution of pellets after wet disintegration, following ISO 17830 standard, and aims to suggest improvements to the mentioned standard based on new measured evidence. Experiments were carried out on white wood pellets (no bark) and brown wood pellets containing bark at four water temperatures: 20, 40, 60, and 95 °C, with or without stirring. The particle size distribution of the pre-pelletizer wood particles was also measured and compared with particles in the formed pellets. Ambient water temperature of 20 °C was found to be adequate for the complete disintegration of pellets, and no mechanical stirring was required. About 30% of particles in the disintegrated pellets were 0.5–1.0 mm. Pelletization changes the particle size distribution to smaller particles. The disintegrated bark pellets contained more fines than white pellets.