New Control Concept for High-Density Chest Consistency Control, 1998 Process Control, Electrical & Info. Conference Proceedings

This paper presents a new control concept for HD chest consistency control. The system was implemented at Union Camp’s Franklin, Virginia mill in mid-1996. Deinked stock is stored in the HD chest and is supplied directly to the blend chests of the mill’s six paper machines. The control requirements are stringent since there are not any low density chests to provide a second stage of consistency control. The total stock pull varies from 0 to 2000 gpm. A fuzzy logic mid-ranging control strategy is used to control the major (base) dilution flow to maintain the minor (trim) dilution flow in control range. Stock flow is recirculated to the dilution zone in the HD chest and to the suction of the stock pump.

This system has been in service for nearly two years. The consistency setpoint is 4.2% and the consistency has been held to within ±0.1% of the target 99.0% of the time. All control loops have been left in the intended “mode” 100% of the time. There has only been one instance of line pluggage in two years of operation.