Fibre losses during debranching and debarking of Eucalyptus pulp logs using a single-grip harvester

Abstract

Mechanised harvesting operations are becoming more prevalent in South Africa, with the realisation that motormanual and manual harvesting operations pose significant health and safety risks to workers. However, the potential damage caused by single-grip harvester feed rollers and delimbing knives on the log surface during debranching and debarking of eucalypts pulp logs may negatively affect fibre recovery as opposed to manually debarked logs, which show little or no log surface damage. Compared with manual debarking, this study investigated the influence of two mechanised debarking treatments on wood fibre loss on eucalypt log assortments debarked by harvester head feed rollers and delimbing knives. The two mechanised debarking treatments consisted of three and five feed roller passes along the stem surface. In addition to quantifying the magnitude of this fibre loss, a financial evaluation was done to calculate the value of these losses. The three- and five-pass debarking treatments caused significant fibre losses of 1.425 green tonnes per hectare (gt ha⁻¹) and 2.275 gt ha⁻¹, respectively, as opposed to manually debarked logs, which produced no fibre losses. Wood fibre losses in terms of total potential (or available) wood mass for three- and five-pass mechanically debarked trees were 1.06% and 1.70%, respectively. These represent a fibre value loss of R441.75 ha⁻¹ and R705.25 ha⁻¹ for three- and five-pass operations, respectively. For the 6.48 million gt y⁻¹ currently mechanically debarked for the South African pulp and paper industry, this equates to fibre value losses of R21.36 million and R34.10 million annually for three- and five-pass operations, respectively.

Keywords: Eucalyptus, fibre loss, manual debarking, mechanised debarking, pulp logs, pulpwood