Mini-Encyclopedia of Papermaking Wet-End
Part Two: Definitions and Concepts
White water is a term papermakers use for process water that is removed from the furnish during formation of the sheet. The water appears white in many cases due to the presence of fiber fines, filler, and air bubbles that scatter light. Even if the process water appears brown, orange, or blue, due to the presence of black liquor, dyes, etc., it is still called white water. Most white water is reused within several seconds or minutes for the dilution of thick stock at a fan pump. Experience has shown that a paper machine system runs more efficiently and produces a more uniform product if the composition of white water is stable over time. This can be accomplished by monitoring the white water solids and controlling the flow of a retention aid. Excess white water is passed to a save-all, where solids are collected either by filtration or by flotation with air bubbles. The clear white water stream may be discharged to wastewater treatment, or it may be further filtered to make it suitable for use in showers on the paper machine. The air content of white water is kept to a moderate level by the design of a "tray" and "silo." These structures allows bubble of air time to rise to the water surface. A deculator system can be used to remove more air just before the sheet is formed.
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