The use of white water closed loop consistency control to provide chemical savings and more stable wet end chemistry conditions of a newsprint machine

Increasing speeds of the forming section, development of new brighter grades of paper, stringent quality demands, more demanding printing technologies and always-important cost considerations make paper production increasingly dependent on proper application of chemical technologies. Changes in the furnish characteristics and water chemistry impact the performance of the wet end of the paper machine, including such important applications as retention, drainage and deposit control programs. The impact of this variation extends from the forming section all the way to the reel. Newsprint machines utilising mixed TMP and deinked pulp (DIP) represents a particularly difficult case. Not only are there two potential independent sources of variability, TMP and DIP processes, but also the overall system is more sensitive to system variability. Therefore, basic stability in both TMP and DIP streams must remain a constant focus of papermakers and suppliers activities. This background effort opens opportunity of stabilisation of the mass balance around the forming section of the papermachine through the application of an on-line retention, or white water consistency, control strategy. Stable white water consistency positively impacts processes both downstream and upstream, of the forming section. However, forcing a system with high intrinsic variability into an on-line consistency control strategy might require large changes in flocculant dosage, resulting in poor runnability and process quality variation. This paper describes the process of developing an on-line consistency control for a fast newsprint machine that utilises a blend of TMP and DIP pulps. Selection of control equipment, evaluation of responsiveness of a chemical program, development of control algorithms and implementation experiences are discussed together along with early benefits.