Measurements of Pressure Pulses from a Solid Core Screen Rotor, 2002 Fall Technical Conference

Pulp screens use hydrodynamic elements on a rotor to produce pressure pulses that backflush screen apertures and clear them of pulp accumulations. The shape and magnitude of the pulses produced by a rotor determines the minimum aperture size and hence the pulp quality improvements and capacity available from a screen. To better understand the factors affecting the pulse characteristics, a laboratory pressure screen was outfitted with a pressure transducer and shaft position sensor to measure pressure traces produced by the rotor elements. Rotor elements were made using CNC machining which enables prototype elements to be rapidly designed, built and tested.

This study examined the effect of rotor speed, gap between the rotor and screen cylinder, and pulp consistency on the pulse form. The positive pressure peak was located just before the leading edge of the rotor element. The negative pressure peak occurred immediately following the maximum height of the element. The pressure coefficient, non-dimensionalized by the rotor tip-speed, was shown to be approximately independent of rotor speed. As gap decreased, the magnitude of the pressure pulse increased but the pulse shape remained constant. Increases in the pulp consistency caused the pressure pulse to decrease and this relationship was approximately linear for consistencies below 2%.