Industrial Implementation of Motor Load and Freeness Control of Chemimechanical Pulp Refiners
A simple refiner control strategy aimed at minimizing variations in freeness of an ultra-high-yield sulfite (UHYS) pulp has been implemented in a newsprint mill. The feeder screw speed is being manipulated to compensate for variations in the bulk density of the chip feed and to maintain a constant motor load at the primary refiners. This ensures a more constant mass flow rate through the primary refiners, which translates into a more constant primary specific energy. This has resulted in a reduction in motor load fluctuations of about 60% and a reduction in freeness variations of 40%. The final pulp freeness is regulated by manipulating the plate gap of the secondary refiners using on-line freeness measurements made at the outlet of the latency chest. Control of the secondary plate gap has led to an additional 30% reduction of the variation in freeness. This two-stage refining control strategy has reduced the 2-sigma confidence interval for variation in pulp freeness from 48 mL to less than 14 mL, a reduction of more than 70%. The complete strategy has reduced the average refiner energy consumption per ton of pulp by 3.5% and has increased the average paper machine production by 2.5% by reducing the number of paper breaks. In addition, the strategy has compensated for changes in cooking conditions and their effect on the refining properties of the chips.
(1997). Industrial Implementation of Motor Load and Freeness Control of Chemimechanical Pulp Refiners. Hydrometallurgy, 80(12), 135-142.
Available at: http://nsuworks.nova.edu/cps_facarticles/1037