The effect of water chemistry and fibre-size distribution on dissolved air flotation efficiency

Abstract: The purpose of this diploma work was to investigate the problem of insufficient fibre recovery in the dissolved air flotation-cell at the new thermomechanical pulping-line at Braviken Paper Mill. An investigation of the effect of process parameters on the removal efficiency in the micro-flotation process was undertaken. The experiments were carried out for two setups at the Noss pilot plant with a small-scale flotation unit. Factorial design helped plan the experiments and four factors were controlled; temperature, fibre-size distribution, water quality and feed concentration. Three samples, feed, overflow and filtrate, were taken from each experiment and concentration measurements were made. The results were analyzed using the software MODDE. The results from showed an influence from the fibre-size distribution. To see if the fibre-size distribution really had an effect on the results, follow-up experiments were carried out. These experiments showed no influence from temperature, fibre-size distribution or water quality. This concludes that none of those three factors influenced the results significantly. Additional experiments were done to examine the influence from concentration and fibre-size distribution on the flotation efficiency and these showed an influence from the feed concentration. When increasing the feed concentration the efficiency of the flotation process decreased.