Understanding the limits of screening operation. Part 2: Characterizing the operational window

The limits of the pulp screening operation can be defined as the maximum throughput before the apertures start to plug permanently. This two-part article sought insights into the limits of screening operation. In part two, the operational window of the screen was characterized by performing a series of screening trials with different pulp furnishes, where the plugging point was conventionally measured with the pressure signal. The limits of operation, given by a slot velocity and rotor speed contour, showed a robust linear relationship at the point of plugging, which depended on the ratio of the fibre length to aperture size. For size ratios less than 1.5, the screen did not plug under the conditions tested. In addition, the plugging detection tool was conceptualized in part one based on the kurtosis of the distribution of fluctuation peaks, and it was employed here. Effectively, deviations from the Gaussian distribution of the pressure fluctuation peaks signal the onset of screen plugging. Thus, the utility of this tool was confirmed for detecting plugs using readily available pressure fluctuation data in pilot-scale screening operations.