Mini-Encyclopedia of Papermaking Wet-End
Part Three: Equipment & Unit Operations
The purpose of a boil-out is to remove deposits of pitch, fibers, minerals, and biological slime from the wetted surfaces of a paper machine during a shutdown. The word "boil-out" has very little to do with boiling, except that the temperature within the paper machine usually is raised during a boil-out. The most common additives used during boil-out procedures are sodium hydroxide and detergents. Some mill operators alternate between alkaline boilouts and acidic boilouts. Enzymes also can be used to help release deposits from the surfaces of papermaking equipment. The frequency of boil-outs is widely variable. Some paper machines run for months without a boil-out. Others, due to chronic deposit problems, may require a boil-out within several hours of running. Effective use of retention aids, talc, and biocides has the potential to reduce the need for boiling out the paper machine as frequently.
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