Utilizing disc springs in vertical axis operated pellet mills and pressure regulation

Primary fuels used in meeting energy needs of humanity are fossil energy sources. However, decreasing reserve in time and environmental effects impel people alternative and renewable energy sources at an increasing rate. One of the important kind of alternative energy sources is biomass. Biomass needs to be volumetrically densified for solid fuel usage. Most common and basic technique used in this process is pelletizing. In pelletizing technique, ground biomass is extruded through a perforated die by the compression of rotating rollers on. Due to the instability of working conditions of pelletizing machines, operating issues as pressure irregularity, overloading, choking, and deformation of die/roller occur. In this study, solution of this problem is examined by integrating disc spring to pelletizing machines. Firstly a single disc spring, subsequently parallel stacked two disc springs are integrated to vertical axis operated pelletizing system used in this study. In both cases force-deformation, stress-deformation relations and accordingly resulting pelletizing pressures are determined utilizing commonly used Almen-Laszlo algorithm and finite element analysis methods. Disc springs with 125 mm outer diameter, 71 mm inner diameter, 2,9 mm cone height and 8mm thickness are utilized in the pelletizing machine. When mounting, disc springs are deformed 0,25 times as its cone height and expected to deform maximum 0,75 times as its cone height in working conditions. Hertz pressure values are calculated via forces applied to press rollers by disc springs. In the case a single disc spring used approximately 153-265 MPa, when parallel two springs used 222-390 Mpa interval of pelletizing pressure occurring determined.