Abstract The objective of this work was to study the effect of adjustable process parameters on wood loss and bark removal in tumble drum debarking. The effect of capacity on the size distribution of the chips was studied in order to determine the optimal capacity for both the debarking and chipping sub-processes. The final aim was to propose a control strategy to optimise the processes by adapting their parameters according to the quality of the raw material. When the research started, earlier automation systems had focused on keeping the process alive, and economic values such as wood loss were not considered important. The process is usually controlled manually and shifts have different ways to manage it, which are based on trial and error. Bark removal in chemical pulp mills is usually higher than the values recommended in the literature, which in turn causes log breaking in the drum and increases wood loss. Even a small reduction in wood loss could have a substantial financial outcome. The lack of raw materials some time ago and the recession nowadays have highlighted the importance of more efficient log use. Data survey techniques were employed to reveal the interactions between drum variables from noisy measurements. Wood room data were analysed by modelling and deriving conclusions from the resulting parameters. In addition, log breaking and the size distribution of the chips were analysed under different process conditions. A pilot-scale drum was used to study residence time and the mechanical abrasion of logs. The results of this work indicated that the ratio of the volume of logs in the drum to capacity determines the residence time of the logs in the drum. Other variables influence the volume of logs in the drum, which together with capacity determine the residence time of logs in the drum, which affects wood loss and bark removal. The effect of capacity on the size distribution of the chips was not unambiguous, however, and it was therefore recommended to operate wood room at high capacity, because this reduces wood loss and increases annual production. The proposed control strategy adapts the residence time of logs in the drum to the quality of the debarked raw material by controlling the position of the closing gate. In addition, the control strategy adjusts the rotating speed of the drum using an open loop control. The results can be used to optimise the wood room process parameters. If the problem in wood room is excessive debarking, the residence time of the logs can be reduced and the rotating speed of 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 be adapted to avoid problems in the subsequent processes due to excessive bark.

Studien är gjord på uppdrag av IKEA och undersöker metoder att barka björk i smådimensioner, med syfte att belysa parametrar som inverkar vid barkning i trumma och utvärdera vilka möjliga kända metoder som finns. Studien behandlar två försök, ett förförsök i form a hydraulisk barkning och ett försök för att belysa parametrar som inverkar vid barkning i trumma. Resultaten visar på att hydraulisk barkning fungerar men vidare studier krävs för utvärdering av kostnad, vattenåtgång och vidare utveckling. Trumbarkningsförsöket visar att basning i förberedande syfte effektiviserar barkningen, virket bör vara av liknande dimension och att barken avlägsnas lättare vid savningsperioden. Inga metoder speciellt anpassade för att barka björk av mindre dimensioner hittades under studien. / he study is made on assignment of IKEA and investigates methods of debarking birch in small dimensions, with the purpose of highlighting parameters that will affect debarking in a drum and evaluating possible known methods. Two attempts is made in the study, an attempt in the form of hydraulic debarking and an attempt to highlight parameters affecting drum debarking. The results show that hydraulic barking works but further studies are required to evaluate cost, water usage and machine development. The drum debarking experiment shows that steaming in preparatory purpose makes the process more effective, logs should be of similar size and the bark will be removed more easily during the sapping season. No methods specifically adapted to debark birch of smaller dimensions was found during the study.

In many natural forests, forest managers fell and debark spruces (Picea abies) colonised by theEuropean spruce bark beetle (Ips typographus) to prevent the beetle from spreading to other tree stands. The aim of this study was to examine how this method affects the biodiversity of other saproxylic beetle species. Eclector traps were installed on debarked and non-debarked dead spruces of four different ages in four nature reserves to compare the richness and composition of saproxylic beetles. The results indicated that a significantly higher number of species and individuals emerged from standing dead trees with bark compared to debarked logs. The highest emergence of species and individuals occurred in one-year-old standing trees with bark. There was a significant interaction between the type and the age of wood, suggesting thatthe richness declined with the aging of wood with bark, while it remained constantly low in debarked logs. The species composition varied greatly between standing trees with bark and debarked logs, as well as between standing trees with bark of different ages. This study demonstrated that debarking spruces as a pest control method reduces the diversity of nontarget saproxylic beetle species. Potential reasons behind that could be the hardening and drying of consumable parts of the wood, rendering it inhabitable for many saproxylic organisms, as well as the presence of the European spruce bark beetle itself, which is associated with many other species.

There is currently a global increase in Eucalyptus pulpwood plantations. Harvesting systems traditionally utilised in the northern hemisphere are being used in Eucalyptus pulpwood plantations worldwide. However, the small tree size and complexity of debarking Eucalyptus have provided harvesting with productivity and cost challenges not previously experienced in northern-hemisphere conditions. Much research has been invested in these two harvesting methods in northern-hemisphere species and conditions. There is little research available on mechanised processing-machine productivity and costs in Eucalyptus. This investigation aimed to quantify the effect that tree and bundle size has on the productivity of different processing machines in Eucalyptus plantation pulpwood. This was done through regression analysis, whereby productivity models that included tree size and bundle size were constructed. The research also aimed to determine whether or not the multi-stem systems were more cost-effective in smaller tree sizes. The research investigated five mechanised harvesting options that forestry managers could use in Eucalyptus pulpwood plantations. These systems consisted of one CTL system, one full-tree system with single-stem processing and three full-tree systems with multi-stem processing. The CTL system used a harvester to process the trees into logs and to extract them. The full-tree system with single-stem processing used a dangle-head processor (DHP) to process trees into logs. The first full-tree system with multi-stem processing used a chain-flail debrancher debarker (CFDD) to produce debarked and debranched tree lengths, which were slashed into logs. The remaining full-tree, multi-stem systems both produced chips. The first used a chain-flail debrancher debarker chipper (CFDDC) and the second, a CFDD feeding into a stand-alone disc chipper (CFDD&C). The productivity data, measured as m3 per productive machine hour (PMH), was then statistically analysed using regression techniques. Productivity equations were formulated, considering tree size and bundle size, as well as the quadratic functions of these two variables and the interaction between them. Bundle size was only applicable to the multi-stem processing machines. The productivity equations successfully predicted processing-machine productivity, using tree size and bundle size as input variables. Apart from the 0.075 m3 tree size class, the CFDD had the highest overall productivity. The costs of the five systems were then calculated for different tree sizes. No single system was more cost-effective than the others across all tree sizes. In 0.075 m3 trees, the CFDDC system proved the most cost-effective. All systems evidenced high costs in the 0.075 m3 trees, ranging between $19.43 per m3 for the CFDDC system to $28.84 for the harvester system. In 0.40 m3 trees, the cost differences between systems were lower, ranging from $6.91 per m3 for the DHP system to $11.84 per m3 for the CFDD&C. This study confirms that the CTL system was very expensive to operate in the small tree sizes (0.075 m3). There is a cross-over point at 0.25 m3 per tree, where the CTL system costs become lower than those of the full-tree system. At the 0.40 m3 tree size, the full-tree system is slightly more expensive than the CTL system. Copyright / Dissertation (MSc)--University of Pretoria, 2012. / Plant Production and Soil Science / unrestricted