Added Soap Contact Time with Recycled Pulp Improves Flotation Deinking Efficiency and Reduces Cost, 2013 PEERS Conference

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Optimisation of the fatty acid soap addition points increased the soap contact time with the recycled pulp prior to flotation. This, in turn, resulted in improved ink removal efficiencies for three of four types of commercial flotation cells. Mill A was able to save 25% in fatty acid flotation collector dosage while maintaining the same brightness gain and ink removal efficiency. In Mill B, increasing the soap contact time improved the aeration of one line of flotation cells which in turn led to a one point brightness improvement of deinked pulp (DIP) and savings in bleaching chemistry. Both mills showed a 30-54% lower carry-over of saturated fatty acids from the flotation collector to newsprint made from DIP and thermomechanical pulp (TMP). Flotation cells with longer residence times and aeration injectors in good order did not show any improvement in aeration nor flotation efficiency. Soap contact times with pulp whether prior or during flotation should be in the order of 9-20 min to assure maximal flotation efficiency. Increasing the soap contact time prior to flotation to 45-60 min did not show further improvements in flotation efficiency.