Optimization of Pitch Removal by Dissolved Air Flotation in a Eucalyptus Kraft Mill

Abstract Wood extractives cause production and environmental problems as well as decreasing the quality of the final product in pulp and paper manufacturing. These disturbances are commonly referred to as pitch problems in this industry. The complex composition of wood extractives is the reason why the nature of pitch problems is different for the various wood species. Also, there is a strong dependence on pulping, bleaching, and papermaking processes. Nowadays, the most common way of handling pitch is to use chemicals in order to fix the extractives to the fibers and thus remove them from the process with the final product. However, this causes serious problems in the final product and also increases problems when paper is recycled. Thus, fixation is not considered to be a sustainable operation for the future. Alternative methods to remove the extractives from the process water must be developed to overcome pitch disturbances and increase pulp quality. This is especially important in mills with closed water loops where the accumulation of extractives in the process waters can occur. In this paper an internal process water kidney, based on dissolved air flotation (DAF), is considered. The objective was to remove extractives from a kraft mill process using Eucalyptus globulus as the raw material. The results show that with the dual system, polyethylene oxide and phenol formaldehyde resin (PEO/PFR), it is possible to remove 80% of the extractive compounds by DAF. Three different techniques, hemacytometry, gas chromatography and turbidity measurement, were used to evaluate the removal efficiency. The applicability of a fast measurement, such as turbidity, to optimize the DAF operation during a future mill operation was studied. This research was carried out within the European Pitch Project (QLK5‐CT‐1999‐01357) funded by the European Commission. The authors wish to thank Beatriz Rodriguez for her skillful laboratory work and the personnel of ENCE pulp mill in Pontevedra for their cooperation.

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