Design, fabrication, and testing of biomass pelleting machine for coffee wastes

Abstract

A biomass pelletizer was designed and fabricated to produce pellets using coffee husks and spent coffee grounds. The pelletizer works on a principle of a rotating roller pellet mill in which power from the prime mover is transmitted to the rotating spindle at a reduced speed, and causes the roller dies to drift and press the pellet mixture through the thick perforated die plate. An unsharpened knife attached to the spindle facilitates easy detachment of pellets from the die plate upon extrusion and the perforated pellet chute separates the nonpelletized particles and fines from the pellets itself. The performance evaluation of the machine revealed an average pelleting capacity and efficiency of 1.50 kgh-1 and 92.49 percent, respectively, suitable for small-scale pellet production and also a low percentage losses (5%). The physical characteristics of the pellets produced were found to have high uniformity with an average length of 9.86±0.63 mm, diameter of 5.71±0.41 mm, mass per pellet of 0.12 g, moisture content (dry basis) of 16.65 percent, and a bulk density of 850 kg m-3. The researchers recommend that the performance of the pelleting machine be optimized by attaching a feed controller on the hopper and manipulating the speed of the roller dies. Furthermore, it will also be best to analyze the thermochemical properties of the pellets including the proximate and ultimate composition employing standard test methods.