PAPER MACHINE WHITE WATER DE-AERATION AND PURIFICATION IN A SELECTIVE TWO-STAGE FLOTATION ARRANGEMENT, 2010 TAPPI PEERS Conference

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Build-ups of detrimental substances that originate from deinked pulps accumulate in paper machine circulation waters in considerable amounts, thus hindering process efficiency and the quality of paper. The applicability of selective flotation to remove substances from circulation waters was investigated in a two-stage pilot-scale process where the froth formation and contaminant removal were based on the inherent surface active components of the white water. The two-stage purification process consisted of a white water de-aerating channel flow from which the reject (overflow) was floated further in a separate flotation cell. The efficiency of the flotation stages to remove ink, stickies and wood extractives were considered in relation to the total flow of water and the solid materials removed. The total efficiency of a simulated two-stage flotation process was then analyzed through mass balance calculations.

The results show that a considerable reduction of contaminant load can be obtained using the two-stage process studied. The de-aerating function of the channel flow was not affected by the feed of macro bubbles that were used to improve white water frothing and the separation efficiency of hydrophobic contaminants. Further optimization of the proposed internal white water purification scheme can provide substantial benefits to paper or board machine operations at low reject rates.