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.
Highlights
The use of biomass as fuel is a good option for domestic heating systems and power plants to reduce net CO2 emissions
The pressure applied to the biomass during pelletising and briquetting has a significant impact on product density and durability, as well as on the energy consumption of the process. This process parameter had been subject of many studies (Adapa et al 2009; Carone et al 2011; Gilbert et al 2009; Kaliyan and Morey 2009; Mani et al 2006; Odogherty and Wheeler 1984; Smith et al 1977; Stelte et al 2011)
The piston was stopped, namely the maximal set oil pressure was reached, after a maximum of 16 subsequent raw material layers in the case of all active segments made from carbon steel and a maximum of 34 layers in the case of two small segments made from carbon steel and one segment made from POM
Summary
The use of biomass as fuel is a good option for domestic heating systems and power plants to reduce net CO2 emissions. The pressure applied to the biomass during pelletising and briquetting has a significant impact on product density and durability, as well as on the energy consumption of the process. This process parameter had been subject of many studies (Adapa et al 2009; Carone et al 2011; Gilbert et al 2009; Kaliyan and Morey 2009; Mani et al 2006; Odogherty and Wheeler 1984; Smith et al 1977; Stelte et al 2011). Pressures typically used in most of the studies were above 50 MPa in the case of open form pelletising (Adapa et al 2009; Mani et al 2006; Stelte et al 2011). Holm et al (2007) measured the back pressure needed to press pellets
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