Wet End Management by Controlling Consistencies and Charge, 1999 Papermakers Conference Proceedings

Timo Rantala, Jukka Nokelainen, Martti Artama
Wet end chemistry contributes essentially to dewatering, retention, and formation. The effects of these interactions on many paper quality properties, and on paper machine runnability, are well known: effective and economical paper production is secured by managing these interactions.

In order to manage the wet end chemistry on a paper machine, we aim to control sub-processes through which we can influence the operation of the entire wet end with maximum effect. This paper introduces the principle, applications, and results of a unique, comprehensive wet end control concept based on a developed measuring system. White water consistency control is first described; results and experiences from several PMs show that this control stabilizes consistencies in the short circulation by 40% to 80% and reduces the MD variation of the final product by 10% to 40%. New, comprehensive control solutions based on headbox ash Cs and thick stock ash content measurements are then described together with some practical results.

Electrokinetic processes play an important role in wet end management. This paper presents an automatic solution for wet end charge control. Its purpose is to give the process control a tool with which to react to changes that are caused by dissolved and colloidal materials entering the wet end system. A steadier charge status in the wet end makes the dosing of chemicals far easier and even helps to achieve chemical savings. An example of combining the charge and retention controls is given to demonstrate the importance of a comprehensive control strategy and to illustrate the role of each individual control in this strategy.

With the solutions described in this paper, the entire process is now much more robust to process disturbances. Charge control takes care of the dissolved and colloidal material; the consistency control concept improves wet end stability and, in combination with conventional paper ash and basis weight controls, it improves both paper quality and runnability.