Features Research & Innovation
Reduction in Quality Variation in a Continuous Kamyr Using Model Predictive Control

Rduction de la variation de la qualit dans un lessiveur Kamyr en continu par contrle prdictif base de modle (MPC)

Abstract: There is a growing need within the industry to cut operating cost by reducing variability in pulping operations and optimizing chemical and energy utilization. Better control of digester house operation is therefore considered to be at the center of pulp mill optimization, especially considering that many pulp mills are digester limited.

This paper details an implementation of a model predictive range control (MPRC) based approach on a continuous digester utilizing Honeywell’s Profit® controller. The robust range control algorithm of this controller helps to give good control despite model plant mismatch, which is inherent when using linear models to control a nonlinear process. This is particularly useful for dealing with nonlinearities due to different production rates. The goal has been to develop a solution to improve yield, reduce white liquor demand, and minimize Kappa variability. The MPRC design has focused on controlling cooking time, temperature and chemical concentration. Quality control was added by including Kappa feedback control and residual alkali feedback control.

This digester control solution has yielded excellent results in two digesters in a southeast United States mill, where we were able to meet and exceed all performance guarantees.

Paper presented at the PAPTAC 95th Annual Meeting 2009 in Montreal, Que., February 3-4, 2009.

Keywords: CONTINUOUS DIGESTER, KAMYR DIGEST-ER, PULP, MODEL PREDICTIVE CONTROL, MODEL PREDICTIVE RANGE CONTROL, MPC, MPRC, ADVANCE PROCESS CONTROL, APC, PROFIT CONTROLLER, RMPCT

Full manuscript available at www.paptac.ca.