Performance and energy efficiency of alternative comminution principles: chipping versus grinding

Comminution is a critical process in biomass supply chains and can be conducted with either chippers or grinders. These machines use different work tools(knives and hammers, respectively) and are applied to different feedstock types, but few studies are available on the inherent differences between the two technologies. A versatile grinder, alternatively equipped with hammers and knives, was studied to investigate the effect of tool type on machine productivity, fuel consumption, and product quality.The machine was powered by an agricultural tractor rigged with a flow meter, a torque meter, and shaft revolution meter for determining fuel consumption, power output, and engine speed. Three different feedstock types were processed: discarded pallets, solid logs, and residues from park maintenance, the latter consisting of branches from ornamental tree and shrub species. Depending on feedstock type, the knife configuration was 3080% (average 50%) more productive than the hammer configuration and required 1530% (average 24%) less energy per unit of product. Fuel consumption per dry ton was 3075% (average 52%) higher for the hammer configuration. That held true for all feedstock types. Product quality was better for the knife configuration, except for park maintenance residues. In general, hammers should be limited to product with severe contamination that prevents the efficient use of knives.