PELLETISING
INDUSTRY NEWS
Energy reduction in wood-fuel pellet production
By Dr Magnus Ståhl, Dr Jonas Berghel, Stefan Frodeson and Dr Roger Renström*
The unique
pellet production unit at Karlstad University.
T
he production and use of wood-fuel pellets, preferably made from sawdust
or shavings, have increased significantly worldwide in recent years. The increased use of biomaterials has resulted in raw material competition and higher raw material prices. The
The cost of raw
material, together with the energy demanding process of drying the bio-fuels, represents the main cost factor in pellet production
cost of raw material, together with the energy demanding process of drying the bio- fuels, represents the main cost factor in pellet production. The current pelletising technology also demands energy and it is therefore of uttermost importance to decrease the energy used and the cost throughout the wood-fuel pellet chain. In addition, there are increased demands on pellet quality due to increased trade and use of pellets by small-scale customers. Therefore, decreasing the energy used in pelletising should be done without affecting the quality of pellets negatively. One solution is to use additives, which in turn can be used for different purposes. Partly, they are used to facilitate the use of new raw materials to increase the raw material base, and partly, they are used to decrease the energy use in the pelletising process. They are also used to increase quality parameters such
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as pellet durability. Consequently, it is necessary to do research that systematically investigates the consequences of using additives. However, the cost of the additive used has to be accounted for, especially since the raw material cost is already a main cost factor in pellet production. In this work, it is investigated how different types of additive affect the energy use of the pelletising equipment and also how it affects the durability of pellets.
Method
The raw material used for the production of pellets was fresh sawdust of Norway spruce (Picea abies) produced at a local sawmill that uses frame saws (for the rapeseed tests the raw material was Scots Pine (Pinus Sylvestris)). The wet sawdust was dried until it reached about 11% wet base (wb). The first additive tested was rapeseed cake (pulverous) with moisture content of 6.6–7.3% (wb). The rapeseed cake came
from the production of Ecoil that is chemically unmodified oil refined from cold-pressed rape oil and the level of rape oil in the rapeseed cake was 18% (wb). The second additive consisted of four different starch grades: native wheat and potato starch, oxidised corn starch and oxidised potato starch. Solam GmbH supplied the starches. Native starches from potato and a cereal, like wheat or corn, were compared with oxidised starches, which have other sizes and shapes than does native starches. The third additive tested consisted of kraft lignin from the LignoBoost process (Metso). This way of extracting lignin by pulping black liquor, producing a material with high energy density and low ash content, has been developed by Innventia AB and Chalmers University of Technology in Sweden. The pellet additives used for this work are both dried lignin, < 10% moisture (wb), and lignin as it is received directly from the LignoBoost process, 30–40% moisture (wb).
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