Kappa Number Estimation, Control and Management in the Pulping Process

Abstract

The primary goal of this work is to develop a uniform method and implementation for the control of pulping reactions. Specifically, the desired pulp Kappa number and black liquor residual alkali are provided for, under the various operating conditions of different mills. A general model is developed which accommodates parameter estimation for different charging and cooking procedures. Having physical meaning, these parameters are measurable and readily available from the mill's process knowledge and information base. For this general and multivariable model, a supervisory control strategy is developed to maintain the desired Kappa number and residual alkali concentration. This is accomplished by coordinating and simultaneously setting of the two primary reaction inputs, namely, the initial alkali charge and cook time/temperature targets. Prior to implementation of any supervisory control scheme, measures are first taken to stabilize the underlying process. Actual implementation of the controller is then done on an incremental basis. This design is highly manageable and provides good performance despite significant modelling error. Further, the system also incorporates on-line statistical process control analysis for real-time closed loop actuation. Implementation of the control stratgegy is discussed including the distributive microprocessor algorithms. The supervisory pulp quality controller functions as the highest level of an integrated pulp mill control system coordinating with other elements to optimize process production, yield and efficiency. In total, the system provides a cost-effective means of realizing significant process economic benefits and, consequently, a high rate of return on investment.