A New Flotation Aid in a Paper Mill
White Water System
D. J. HAHN, Engineer
Environmental Control Section
J. J. JENDE, Technical Engineer
Paper Equipment Section
T. F. RICH, Chemical Engineer
Process Development Department
The Procter&Gamble Company
Cincinnati, Ohio
F. J. TREMEL, Assistant Pollution Control Engineer
The Charmin Paper Products Company
Green Bay, Wisconsin
INTRODUCTION
Dissolved-air flotation units or, as they are more commonly called, flotation
save-alls have been extensively employed for paper mill white water clarification
since World War 1(1). The Sveen-Pederson system was one of the first flotation
savealls to appear in the paper industry and, therefore, today many people refer to a
paper mill flotation unit as a sveen.
The Sveen-Pederson, and most of the other flotation systems utilized by the
paper industry, incorporate the total pressurization approach. Figure 1 schematically
shows this system. The entire stream of water to be treated is pumped into the
retention tank at pressures varying from 25 to 80 psi. There, with the addition of air
under pressure, the water becomes nearly saturated for the retention pressure with
dissolved air. As the water flows from the retention tank to the flotation unit, the
pressure of the water is reduced to nearly atmospheric. This pressure drop causes
very fine bubbles of air to be formed as the dissolved air comes out of solution. The
flotation compartment where solid-liquid separation occurs is normally preceded by
an inlet compartment. The purpose of this inlet compartment is to provide a zone for
floe development and to prevent hydraulic short circuiting in the flotation unit. The
suspended solids with the fine bubbles attached to them are then buoyed up to the
water surface where they are scraped off with the skimmers. The clarified water is
generally drawn off near the bottom of the flotation compartment through collector
pipes. These collector pipes extend horizontally across the width of the flotation
unit. The liquid level in the flotation compartment is controlled by the height of the
vertical riser pipes connected to the collector pipes. The clarified water is then either
reused in the paper mill or is sewered. The float scraped off the flotation units is
either directed to dewatering equipment for disposal or is pumped to the paper mill
to recover fiber and fillers.
The flotation units in the mills of the Charmin Paper Products Company,
wholly owned subsidiary of the Procter & Gamble Company, Cincinnati, Ohio, are
employed largely for pollution control. Our paper mills manufacture tissue grade
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