Pressure build-up and wear analysis of tapered screw extruder biomass briquetting machines

The design of efficient screw extruder biomass briquetting machines is important for the utilization of loose biomass materials from wood and agricultural wastes for the production of solid fuel. In this study, the effects of geometrical parameters (channel depth and helix angle) and operational parameters (friction coefficient, mass flow rate and speed) on the performance and design of the briquetting machine were investigated using a pressure model based on the plug flow theory. An analytical model, which utilizes the pressure model, was also developed from Archard’s wear law to investigate screw wear of biomass briquetting machines. The study on the pressure model showed that a shallow screw channel and small helix angle resulted in rapid pressure build-up along the screw extruder biomass briquetting machine. High friction at the barrel-material interface, low friction at the screw-material interface, high screw speed and high mass flow rate also resulted in rapid pressure build-up along the screw extruder biomass briquetting machine. The geometrical and operational parameters which resulted in rapid pressure build-up required shorter screw length for the briquetting machine. The wear model developed predicted the screw wear satisfactorily and showed that the screw speed and the choice of material for screw affect the screw wear. The wear volume increased exponentially towards the end of the screw where pressure is the highest. Redesigning the screw to select optimum geometry and speed with appropriate choice of material could improve the screw life and performance of the biomass briquetting machine.