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Fletcher Challenge Canada Limited, Crofton, BC
Process Analysis and Control Audit

Background

No.2 paper machine has been experiencing swings in the MD basis weight and moisture content since the installation of a Beloit twin wire hydraulic former. These swings cause off-grade products, sheet breaks and often force the backtender to lower moisture content target. The addition of new cleaners caused the increase of basis weight variability. Andritz Automation completed a process control audit and determined what caused the basis weight swings.

The Project

The analysis of the data collected shows the basis weight variability comes from several sources. However, the primary cause is an oscillation in the mass flow rate to the headbox. A review of the mass balance shows that the most significant change resulting from new cleaner addition is an increase in the recirculated load through the primary fan pump. This was the primary cause of the increase in basis weight variability. Several tests were performed to verify the cause and some modification of the deaerator overflow piping was recommended.

Benefits

After the modification of the deaerator overflow piping, the basis weight variability was reduced to one tenth of its previous value and off-grade products and sheet breaks were minimized.