Improved Screen Removal of Stickies, 1998 Pulping Conference Proceedings

Separation of small particles, particularly those that are sticky and deformable, is a difficult task since size, specific gravity, and other properties are similar to those of paper fibers. This paper discusses several factors which influence the efficiency of particle removal by screens to help users make good decisions in adding screen capacity or improving operation.

Near the inlet side of the screening surface, pulp and contaminants are more concentrated than in the feed flow. Turbulences generated in this zone assures mobility of the fibers to allow passage through the openings, while lots or holes block the way for the contaminants. With today’s contaminants, the slot width and slot profile details are the governing variables for removal efficiency. Average velocity through holes or slots and rotor design have noticeable but secondary influences.

With smaller slots, fractionation must be avoided to assure reliable operation of a screening system despite variations in the incoming secondary fiber pulps. Once reliable operation is established, the screen cylinder and rotor details can be optimized.