Practical Experiences of Improvements on Board Machine by Wet End Monitoring and Controls, 1994 Papermakers Conference Proceedings

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A white water consistency control, originally developed on fine paper machines, was for the first time applied on a board machine. The goals were: to construct a white water consistency control of the inner layers of multi-layer board; to integrate this control in the mill’s automation system; and to monitor the operation of the wet end producing the inner board layers, particularly its effects on formation. The process was first monitored to get better acquainted with the system and to pinpoint any abnormally operating control loops etc. visible in the on-line measurements. Step tests were made to formulate a model describing the effects of retention chemicals on the process. The models for the two principal grades proved somewhat different. White water consistency, controlled with the retention chemical dosage, was selected as the controlled variable. Once the control solution was completed, control trials were made to monitor the control tuning and operation, and to study statistically its effects on the process. Results resembled those obtained earlier on fine paper machines; the control has considerably reduced the average consistency deviation in the short circulation of the inner layer process. This stabilisation was also clearly visible in web measurements.