Microwave Velocity Based Consistency Measurement Enables New Process Optimization Possibilities, 1997 Process Control, Electrical & Info. Conference Proceedings

This paper introduces KAJAANI MCA, the new consistency measurement method based on the measurement of microwave velocity changes that are linearly related to the stock consistency. The measurement principle and its main features are described. Being unaffected by flow rate changes and totally independent on fiber based stock properties like pulp grade, wood species, fiber length, stock type (chemical/mechanical) and including also the fillers to the measurement result the method overcomes these most severe short comings of the conventional (shear force, optical) consistency measurement methods. This makes it possible to improve the overall consistency management in pulp and paper processes and to actively use more efficient consistency control methods like feedforwad mode control. This improves directly the process runnability and product quality. Further it is possible to cost efficiently optimize the use of raw materials in paper and board furnishes with simultaneous improvement in product quality.

The operation of the meter is studied at actual mill site installation as a function of process variables like freeness and flow rate. Further included are mill site case studies featuring basis weight control on paper machines where the measurement is used to stabilize the thick stock feed to the paper machines. The measurement is used there in feed forward mode of control which effectively eliminates the rapid consistency changes which cannot be handled with the conventional basis weight control due to the slowness of the basis weight measurement and consequential control.

Also included is a study on optimizing the furnish of a board machine using the developed method resulting to a 10 % reduction in chemical pulp consumption per produced ton of board and considerable improvement in process runnability. These cases demonstrate that considerable savings can be reached by utilizing the new microwave based consistency measurement method.