Pre-emptive control of moisture content in paper manufacturing using surrogate measurements

Abstract

Paper manufacturing consists of the sequential removal of over 90% of the water from pulp through gravity, vacuum dewatering, pressing and thermal drying. Control of moisture content is important for paper quality and energy economy. Current strategy for the control of moisture content uses a feedback sensor at the end of the process to adjust the dryers. This introduces a long dead-time and causes excessive use of the dryers, which translate to limitations in performance, robustness and inefficient energy usage. In this paper, we investigate a new control approach in which in-process moisture contents are estimated using air-flow as surrogate measurements, and the pressure settings in the vacuum dewatering boxes are adjusted according to the surrogate measurements. A pre-emptive control algorithm is developed which has the ability to decouple and eliminate the effects of the disturbances that occur upstream in the process from the downstream. Robustness analysis and simulation studies suggest that as long as the surrogate measurements are accurate, the proposed control scheme will be robust and accurate.