Causticizing Plant Slaker Computer Control

The increasing demand for coordinated control of the total paper mill has placed a greater demand for a higher standard of control of the recausticizing area. This paper presents the development and implementation of a computer control strategy for the slaker in the causticizing process. The objective of the strategy was to produce uniform white liquor exiting the primary and main slaker while minimizng the effects of unregulated load changes and the dead load of unreacted lime or sodium carbonate in the process. The control strategy relies upon practical field measurements and an energy and mass balance around the primary and main slakers. The manipulated variables are the green liquor temperature, lime flow, and green liquor flow. The controlled parameters are the slaker temperature, the ratio of lime to green liquor, causticizing efficiency, and the slaker throughput. The control was designed for and implemented in a microprocessor based controller. An analysis of the control sensitivity to measured and unmeasured parameters is made.