A fine paper mill with a coated paper machine has installed a three (3) stage thick stock screening system for the removal of very fine particles, mainly plastic. Rather than modifying their existing headbox screening equipment, which would have required extensive piping changes, and additional screens, the mill opted for a screening system to operate at 3.0+% consistency, located between the blend chest and the machine chest. Earlier trial work with a pressure screen in the primary position, only, having a slotted screening cylinder with 0.008" (0.20mm) wide slots removed over 75% of the small rejects. This efficiency was quite adequate, the pulp quality improvement was evident in the operation of the paper machine. A complete, three (3) stage system was designed, and installed.The new screens, all equipped with cylinders having 0.008" (0.20mm) wide slots, have satisfactorily removed over 75% of the small debris. From an operational point of view, the holes per reel of paper have been reduced, the number of breaks on the machine have decreased, and the finished paper quality has improved. The screens have performed well at over 3.0% consistency, and the deflaking capability of the "high" consistency rotor has resulted in cleaner pulp and reduced sewer losses.
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