The key objective in the production of fine paper is to produce on-specification product with minimum rework. This is achieved by maximising machine stability and hence product quality. A great deal of the variability in the Machine Direction (MD) quality parameters and machine instability can be attributed to variation in the wet-end. Stable fibre length distribution, filler content and retention are critical to achieving uniform formation of the sheet on the wire.
Perceptive Engineering delivered a Wet-End Optimisation solution on Clairefontaine's PM6. A robust model has been developed which describes the interactions between chemicals, stock and filler flows and their influence on ash, white water consistency and other stock approach variables. The model is used in an Advanced Process Control system which includes automatic broke system management. The APC also switches between sheet and headbox ash during breaks to ensure stable ash and fibre retention in all modes of machine operation.
RETURN ON INVESTMENT
The Model Predictive Controller has provided significant reductions in ash and retention variability. This includes a reduction in white water and sheet ash consistency standard deviation of 83 and 70%, respectively.
Clairefontaine have audited the knock-on benefits in machine efficiency and rework reduction over a 3 month period. By reducing lost production due to quality issues and wet-end breaks, saleable production has increased by 2.6%.
The benefits delivered a full return on investment within 6 months of commissioning, sustained via an ongoing support program provided by Perceptive.
"Before the PerceptiveAPC project, stable operation of our paper machine was difficult to achieve. Poor retention and complex wet end chemistry resulted in runnability issues. The PerceptiveAPC system uses a very good model of our machine, providing a significant improvement in stability, especially after breaks and other perturbations"
Armando Coehlo, Production Engineer, Papeteries de Clairfontaine.