Browsing by Author "Van der Merwe, Jaco-Pierre"

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    The impact of mechanical log surface damage on fibre loss and chip quality when processing Eucalyptus pulpwood using a single-grip harvester
    (Stellenbosch : Stellenbosch University, 2014-03) Van der Merwe, Jaco-Pierre; Pulkki, R. E.; Ackerman, P. A.; Langin, D.; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.
    ENGLISH ABSTRACT: Mechanised harvesting operations are growing in popularity in South Africa, as motor-manual and manual harvesting operations pose significant health and safety risks to workers. Potential damage inflicted by single grip harvester feed rollers and delimbing knives on the log surface during debranching and debarking eucalypts, may affect fibre recovery and chip quality. Chip quality is important as it influences pulp quality and recovery in the kraft pulping process. The study investigated the influence of two mechanised debarking treatments in eucalypts (three feed roller passes and five feed roller passes along the stem surface) with feed roller induced log surface damage on chip uniformity, size, purity and wood fibre loss. The two mechanised treatments were compared against chips produced from manually debarked logs. In addition, the effect of two log drying periods (one week and two weeks) and three log sections (base, middle and top logs) on chip quality were also analysed. An economic evaluation was conducted to quantify potential recoverable pulp value losses associated with debarking treatments and log drying periods. Logs subject to manual debarking produced significantly less undesired sized chips than both three pass and five pass mechanically debarked logs. Potential recoverable pulp revenue for chips produced from five pass and three pass mechanically debarked logs were valued at R 60.54 BDt-1 and R 50.90 BDt-1 less than wood chips produced from manually debarked logs. Two week dried logs produced significantly less under-sized chips than chips produced from one week dried logs. However, two week dried logs produced wood chips with significantly more over-thick chips than logs dried for one week. The volume of undesirable sized chips produced during chipping increased with decreasing log size. Potential recoverable pulp revenue for chips produced from one week dried logs were valued at R 137.90 BDt-1 less than chips produced from two week dried logs. Manually debarked logs produced chips with significantly less bark content than three pass mechanically debarked logs (0.008 % vs 0.062 %). Five pass mechanically debarked logs produced chips with significantly less bark content than three pass mechanically debarked logs (0.018 % vs 0.062 %). Middle logs also produced chips with significantly less bark content than base logs (0.016 % vs 0.056 %). Top logs produced chips with significant less bark content than base logs (0.017 % vs 0.056 %). In all cases the bark content was considerably less than the maximum of 1.0 % generally specified by kraft pulp mills. Both three pass and five pass mechanically debarked trees caused significant fibre losses of 2.6 m3 ha-1 and 5.1 m3 ha-1 respectively. Wood fibre losses in terms of total extractable wood volume for three and five pass mechanically debarked trees were 0.8 % and 1.6 % respectively.