The performance evaluation of a cassava pelletizer

Abstract

This paper reports on the development and performance evaluation of a machine for cottage level production of pellets from cassava mash. Cassava flour was produced by peeling, grating and drying freshly harvested cassava tubers. Experiments were conducted to determine the physical properties, such as moisture content, particle size distribution and bulk density and the chemical composition of the flour. The flour was mixed with water at different blend ratios to form cassava mash of different moisture contents. A cassava pelletizer was then developed incorporating relevant properties of the flour. The pelletizer consists of a barreled screw auger, which compresses cassava mash against a perforated end plate, through which the pellets are extruded. The barrel is encased in a co-axial counter flow heat exchanger to provide cooling for the system. The performance of the pelletizer was evaluated in terms of the density, durability, crushing strength and cyanide content of the pellets, and the throughput of the machine, against the moisture content of the mash (18, 20 and 22 % w.b.), die size (4, 6 and 8 mm) and the auger speed (90, 100 and 120 rpm). Test results showed that the bulk density and the durability of pellets decreased while the moisture content increased significantly (p<0.05) and separately with increasing die size and moisture content of cassava mash. The pellets with the best quality attributes were obtained from cassava mash at 18% moisture content (w.b.) extruded through the 4 mm die at 90 rpm and a maximum throughput of 54 kg/hr. The pellets exhibited a bulk density of 635 kg/m3 , 15% moisture content (w.b.) crushing strength of 34.24 MPa and a high durability (85.7%). The machine, thus, provides a significant leverage in the utilization of cassava as pelletized animal feed.