J. Niinimäki and T. Stoor (Finland)
log breakage, wood loss, bark content
Logs used in pulp and papermaking are debarked prior to processing. Drum debarking as a unit process is a simple system where debarking degree and wood losses are crucial factors affecting the technical and economical performance of a pulp or paper mill. Wood properties, rotation frequency of a drum, capacity and filling degree are the main debarking variables having an effect on debarking degree and wood losses. It is not possible, however, to simulate wood losses with these main parameters, because many disturbing variables and some, such as wood properties and filling degree are too difficult to measure. This study aimed to find out new measures for controlling debarking drum. Based on the knowledge on crucial effect of wood breakage on the wood losses, we suggest minimum breakage principle to be used as control basis. This means that optimal debarking result can be achieved using maximal debarking efficiency, which results as minimum amount of broken logs. In the case of rugged logs, the maximum filling degree with the lowest rotation speed should be used in order to avoid wear of logs' ends. With thin, long wood which cuts easily, large number of weak wood contacts gives the lowest wood loss. This can be achieved keeping drumming power constant by increasing rotation speed and simultaneously lowering the filling degree.
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