Determination of radial pressure distribution on the wall of the press channel of a novel biomass single die pelletiser

Abstract Pressure is an important process parameter that greatly influences the density of biomass pellets. The positive number of Poisson's ratio of biomasses makes pelletising possible in ring die and flat die types of pelletisers, because as a consequence of the longitudinal direction of load, the material strains into the radial direction. The radial strain is obstructed by the channel wall and therefore radial pressure and wall friction occur, which supports (backs) the compression of the further sequentially loaded biomass. A novel test device consisting of a single pelletising unit and a novel sensor, a back pressure measurement disc was developed and calibrated. Pelletising experiments were carried out with a flat die pelletising machine and with the single pelletiser unit with ground post agglomerated (GPA)-spelt chaff (chaff of triticum spelta) samples. The body density and radial pressure values in different pelletising unit segments were measured. The equations introduced for dimensionless relative density and for radial pressure as a function of the relative position equations fit the measured data well.