1. Environmental and Chemical Engineering Research Unit, Control Engineering , 6370 University of Oulu , P.O. Box 8000 , University of Oulu , Finland
2. Automation Technology and Mechanical Engineering, Faculty of Technical Sciences , 7840 Tampere University , P.O. Box 692 , Tampere , Finland
3. Valmet Automation Inc. , P.O. Box 237 , Tampere , Finland