Thick or Thin? Selection and Application of Fine Screening Equipment for Contaminant and Stickies Removal, 1999 Pulping Conference Proceedings

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May Fursey
Voith Sulzer Paper Technology
North America, Inc.

Fine slotted screening continues to be the solution for the removal of fine contaminants and stickies. During process installations or upgrades of fine screening equipment, economic considerations often affect the selection, location, and operating consistency. Apparently however, least expensive option may turn out to be the most costly, when additional equipment has to be installed in another location to further deal with the stickies problem.

This paper reviews the operating parameters of the fine screen such as; slot width, passing velocity, reject rate, and in particular, operating consistency and rotor speed.

The pressure and shear forces required to operate the fine slotted screen at higher consistency can lead to deformation and disintegration of macro stickies. Known laboratory measurements (Tappi pick-up-method, T277, pm 99) may show a reduction in macro stickies concentration. However, the stickies material may have just been disintegrated and shifted to another location, causing problems elsewhere in the system or on the paper machine.

Pilot plant data and mill experiences compare the results of high (3 to 4%) and low (1 to 2%) consistency screening and can help guide us to the correct selection and application of the fine screening equipment.