Control Technology for Short Sequence Bleaching, 1991 Pulping Conference Proceedings

With the constraints pulp mills face today, it is increasingly important to achieve consistent bleaching quality while minimizing chemical consumption, effluent volume, and toxic discharges. One way to help overcome these difficulties is to use advanced bleaching-control techniques in the real-time redundant environment of a distributed control system (DCS). The advanced control strategies discussed here are part of a technology package that controls and coordinates the process stages within the bleach plant to minimize variations in brightness development and chemical consumption. The specific strategy within each stage is based on a hierarchical series of sensor/instrument-supported ratio and flow control loops that provide efficient control of the lignin removal reactions. System capability includes coordination of production rate and grade changes, process modeling and pulp tracking, and sensor calibration and compensation, along with specific modules for controlling each of the bleaching stages and their associated washers.