The objective of this work was to study the effect of adjustable process parameters on wood lossand bark removal in tumble drum debarking. The effect of capacity on the size distribution of thechips was studied in order to determine the optimal capacity for both the debarking and chippingsub-processes. The final aim was to propose a control strategy to optimise the processes byadapting their parameters according to the quality of the raw material. \nWhen the research started, earlier automation systems had focused on keeping the processalive, and economic values such as wood loss were not considered important. The process isusually controlled manually and shifts have different ways to manage it, which are based on trialand error. Bark removal in chemical pulp mills is usually higher than the values recommended inthe literature, which in turn causes log breaking in the drum and increases wood loss. Even a smallreduction in wood loss could have a substantial financial outcome. The lack of raw materials sometime ago and the recession nowadays have highlighted the importance of more efficient log use.\nData survey techniques were employed to reveal the interactions between drum variables fromnoisy measurements. Wood room data were analysed by modelling and deriving conclusions fromthe resulting parameters. In addition, log breaking and the size distribution of the chips wereanalysed under different process conditions. A pilot-scale drum was used to study residence timeand the mechanical abrasion of logs. \nThe results of this work indicated that the ratio of the volume of logs in the drum to capacitydetermines the residence time of the logs in the drum. Other variables influence the volume of logsin the drum, which together with capacity determine the residence time of logs in the drum, whichaffects wood loss and bark removal. The effect of capacity on the size distribution of the chips wasnot unambiguous, however, and it was therefore recommended to operate wood room at highcapacity, because this reduces wood loss and increases annual production. The proposed controlstrategy adapts the residence time of logs in the drum to the quality of the debarked raw materialby controlling the position of the closing gate. In addition, the control strategy adjusts the rotatingspeed of the drum using an open loop control.\nThe results can be used to optimise the wood room process parameters. If the problem in woodroom is excessive debarking, the residence time of the logs can be reduced and the rotating speedof the drum lowered. In this way the logs will be damaged less and wood loss will be reduced.Bark removal requirements in mechanical pulp mills are high, and the process parameters can beadapted to avoid problems in the subsequent processes due to excessive bark.

155 s.
Tuotekoodi 014001
20,00 €