Review of efficiencies in comminuting forest fuels

Knowledge about the generalized operational efficiency of comminution machines and systems is of great interest when tailoring solid biofuel supply systems. The objectives were therefore to collect and compare data from the literature to those from machinery manufacturers on the performances of various forest biomass comminution systems, with the aim of identifying areas for further research. Our meta-analysis was based on data from 55 scientific publications and specification sheets from 566 machine models collected from manufacturer's websites. A majority, 56%, of studies were carried out at the roadside and 54% of studies examined comminuted logging residues, which thus reflects the most common materials and environments of the forest fuel supply system studied in the literature. We conclude that: (1) Chipping is more productive and requires less energy than grinding for machinery with nominal power up to 300 kW. (2) Chipping small trees or residues lowers productivities and increases energy demand compared to logs; the comminution productivity is dependent on the type of machine, the nominal power, and the material handled. (3) The energy demand is a function of the variable type of machinery (chipper, grinder), and maximum particle size produced. (4) Productivities in operational studies are clearly lower than the ones reported by the manufacturers in idealized conditions. Further investigations of equipment such as large chippers and grinders operated in terminals under controlled conditions are needed, in order to gain a better understanding of the different factors affecting the efficiencies of large equipment.