An alternative supply system for stump biomass - coarse grinding combined with sieving of the produced hog fuel

摘要

Transport costs are one of the major costs in the supply chain of stumps for fuel. Stump parts are bulky and it is impossible to achieve full tonnages on trucks and trailers even though the load space is completely full. The transport economy for stumps is also negatively affected by the large amount of contaminants in the loads. Grinding the stumps at the landing and sieving of the produced hog fuel has the potential to increase load weights and reduce both the amount of contaminants and the transport costs. To evaluate such a system a series of studies were made. Results show that coarse grinding and sieving reduced both moisture and ash content in the produced fuel, thus increasing the heating value per ton delivered fuel and transforming a soilcontaminated material to an acceptable fuel. Transport payloads increased substantially compared to transports of stump parts, but a transport distance of 110 km was needed before the coarse grinding system provided lower cost than the standard system with transports of stump parts and grinding at the heating plant. Further studies are needed to evaluate the total energy efficiency in the two systems. Coarse grinding and sieving is a feasible way to increase fuel quality and improve transport economy. However, total costs will in most cases be higher than for the loose stump system which renders the method preferable only in cases where the sieving process converts a non-acceptable material into an acceptable fuel.