Efficiency of Integrated Grinding and Screening of Stump Wood for Fuel at Roadside Landing with a Low-Speed Double-Shaft Grinder and a Star Screen

Impurities in harvested stumps are a quality problem because high levels of mineral contaminants decrease the effective heating value of the stump wood, and can also affect ash melting behaviour during combustion, leading to sintering and drift problems. The aim of this case study was to clarify the productivity and screening efficiency of the Kompetech Crambo 6000 low-speed double-shaft grinder equipped with a Komptech star screen, in the integrated grind ing and screening of Norway spruce and Scots pine stumps for fuel at a roadside landing, when using two different sieve sizes (250 x 320 mm and 180 x 180 mm screen baskets). Fur thermore, we studied the fuel consumption of the Crambo 6000 grinder, ash content and particle size distribution of ground stump wood, and ash content and particle size distribution of the screening reject. In addition, the heating value of the produced hog fuel and screening reject were analysed. During the time of the studies, both the grinder and star screen were operating well and there were no delays due to machine breakdowns. The mobile Crambo 6000 grinder was also capable of operating well in constricted roadside landings. The quality of the produced hog fuel was high, due to low ash content (0.4–2.3%), and this highlights the signifi cance of screening to guarantee sufficient quality when processing stump fuel. The ash content of the screening reject was 32.4–74.7%, and the effective heating value was 5.2–13.4 MJ/kg. The effective heating value of the produced hog fuel was 17.9–19.9 MJ/kg. The average grinding productivity, when using the 250 x 320 mm screen basket, was 162 loose m 3 per effective hour, and the fuel consumption of the grinder was 0.44 litres per loose m 3 . With a narrower screen, the average grinding productivity was 101 loose m 3 per effective hour, and the fuel consump tion of the grinder was 0.75 litres per loose m 3 .

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