Foam Control on Closed Water Loops and High Temperature Paper Machines, PaperCon 2010 Conference

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Paper makers encounter various problems due to poor foam control. The scope of foam related troubles is rather broad. Reduced production rates can be caused by poor drainage on the forming table or cavitating pumps. Foam problems can also adversely impact paper quality and cause sheet defects which include pin holes, uneven distribution of fiber and fillers, and wet end chemicals. Poor pulp mill foam control also leads to problems in the paper mill such as; increased undesirable anionic trash, increased hydrophobic material, furnish with a higher foaming tendency, and sizing issues on the paper machine. Excessive foam also frequently causes housekeeping and safety challenges. Closure of mill water loops has exacerbated foam control efforts through increased operating temperatures and by build up of foam causing and stabilizing materials.

The higher machine temperatures of modern mills have impacted foam control strategies in two ways. First, the surface tension of water decreases with increased temperature, this makes the system foamier. Secondly it impacts the type of defoamer products that are capable of controlling foam. In the past, water based defoamers offered efficient, process friendly chemistries. Unfortunately these technologies had an upper temperature efficacy limit with a marked decrease in performance above 130° F (54° C). A common approach to higher paper machine temperatures and foaming tendencies is the use of oil based defoamer chemistry. Oil based defoamers, if misapplied can cause problems with sizing and VOC’s, among other things.