Chipping vs grinding, net energy requirements

Biomass-derived products, in particular wood, are increasing their importance as sources of clean and renewable energy for the production of electricity or steam. The energetic aspects linked to the process of transformation, handling and transport of these materials have to be considered in order to optimize and improve these phases. This paper reports results on an additional investigation on the machine productivity and energy requirements of a grinder alternatively equipped with hammers and knives tools. In this paper, an alternative post-processing computation, based on the power and consumption net values, was applied. The previous study (Spinelli, 2011) was conducted approaching the performances indicators computation using the gross values. During the investigation fuel consumption, PTO torque and speed, processing time and weight of processed material were recorded. The machine was fed with three different feedstock types (logs, pallets and residues from park maintenance). 10 repetitions for each combination of feedstock-tool were carried out. The data collected were post-processed to obtain net values for energy requirements, fuel consumption and power. The results of this study show that, with this data, considering net or gross values changes the final results in absolute terms, but the relationships between specific values are unchanged. The knives requires, depending on the processed material, from 2 to 20% less net energy. In particular, the highest difference between tools was found in logs processing whereas the smallest was in residues of park maintenance. Furthermore the results of the investigation indicate, that, in testing conditions, the specific net fuel consumption for hammers is higher (60%) than knives.