Adding Value to the Papermaking Process by Automating Control of Wet End Chemicals

摘要

In most paper manufacturing processes, wet end chemicals are dosed in fixed amounts. The dosages are usually optimized for a specific process condition regardless of variations originating from changing qualities of the incoming raw materials. These inconsistent qualities lead to varying requirements of wet end chemicals. Process stability and paper quality can, however, be improved by automatically dosing these chemicals based on online measurement results. Almost all of these applications have a high cost cutting potential. This paper outlines a way towards a controlled wet end. The procedure followed to meet this objective makes use of online measuring technology in the wet end of a paper machine. The first step is to gain a theoretical insight into the process by means of a standardized questionnaire. With this information on hand, lab instruments are used to measure charges, retention and drainage in order to conduct a practical survey of the process. This theoretical and practical information combined with in-depth application experience enables the origins of problems and optimum sampling points for online measurement to be assessed. Once online devices have been installed, the measurement results are monitored together with relevant process and quality parameters along a defined period of time. Based on the results obtained during this period, the control loops for chemicals are closed and optimized. After operating the control loops for another defined period of time, the results of both periods are compared to enable direct calculation of the payback of the instruments. Two cases are presented where this method has been applied. The first example illustrates the process, quality and economic results achieved by a linerboard manufacturer who established closed loop retention aid control. The second example describes the results obtained by a newsprint producer on his two paper machines. In this latter case, fixatives, retention aids and deaerator chemicals are automatically controlled on the basis of online measurement results.