REJECT THICKENING BEHAVIOR OF TMP SCREENING

Radiata pine thermomechanical pulps with different fibre types and deg rees of development are shown to have different reject thickening char acteristics, which have a large impact on the useful operating range o f the screen. The reject thickening changes can be accommodated by alt ering screening variables such as reject rate, aperture type and dimen sion, surface contour, rotor type and rotor speed. These variables can alter the reject thickening characteristics by a similar amount to th e furnish changes. The use of a variable speed drive allows the rotor speed to be used as a fast response to furnish changes, in addition to the reject rate. This is particularly effective with the contoured su rface baskets.