Experimental verification of novel pellet model using a single pelleter unit

Pelletization of biomass for bioenergy purposes has established itself as an important step toward a reduction in the emissions of greenhouse gases. A novel pellet model describing the pressure forces in a press channel of a pellet mill has previously been published. The model gives a theoretical explanation of how the biomass-specific parameters, such as the friction coefficient and Poisson's ratio, influence the pelletizing pressure. The model showed that the pelletizing pressure increases exponentially as a function of the channel length. In the present paper, the pellet model is verified experimentally. When the back pressure needed to press pellets of different lengths out of the press channel is measured, it is shown that the pelletizing pressure does increase exponentially as a function of the pellet length. Second, the back pressures of the hardwood beech are higher than the corresponding pressures of the softwood pine for all tested pellet lengths. Least-squares fit of the model to the data shows that the fitted parameters are in agreement with values from the literature. The procedure for using a single pelleter unit as a means for simulating an industrial pelletizing process in a controllable way is described.