A Modern On-Line Porosity Analyzer For Paper And Board Machines

摘要

The on-line porosity analyzers have, in recent years, become a practical tool for papermakers to maximize paper quality and production profitability. The best on-line porosity analyzers have been developed to a new standard of measurement accuracy, speed and reliability to satisfy the requirements of on-line sensor technology. The PERMI, being a fast and reliable on-line porosity analyzer from ACA Systems Oy, helps papermakers to rapidly adjust all grades to specification and carry out fast paper grade changes. The monitoring of several paper grades can accurately and reliably be measured with only one single calibration. The very fast machine direction measurement enables a new kind of control of paper and paperboard processes. The effects of process adjustments can be monitored immediately after changes because it is not necessary to wait for laboratory results. Responses to test runs can be confirmed directly. In addition, the on-line analyzer measures the process 24 hours every day and 7 days a week and actual readings can be graphed and backed up for long periods. Paper quality variations in the machine direction can be reduced with greater ease when a fast real paper quality measurement is available. It is easier to track the root causes of faster variations (recipes, dosing of chemicals, screen cleanings, variation in deaerator vacuum and air content etc.) Naturally, this leads to better paper uniformity, not only in porosity but also in most of the other important quality characteristics. The refining of chemical pulp as well as the post-refining of mechanical pulp can be optimized for each paper grade in spite of quality changes in the incoming pulp. The process automation system (DCS) can be equipped with a closed loop control circuit to maintain the required porosity level. The potential to save energy and increase production is remarkable and the uniformity of paper quality improves noticeably. The dosing of paper chemicals (fixatives, retention aids, and defoamers) can be monitored and optimized so that a good combination of retention, formation and drainage, as well as better runnability on the machine, can be achieved. Overdosing and the costs of the chemicals can be reduced without any risks to the process operation. The vacuum levels in the wire section (foils, vacuum rolls, vacuum boxes) can be quickly adjusted in the grade changes and therefore a good formation and dewatering with lower energy costs can be achieved. When monitoring the operation and usability of paper machine wires and felts, the annual costs of machine clothing can be decreased. The operation of test wires and felts can be quickly observed and therefore the development time of clothing is shorter. The draw difference between the press and drying sections can be minimized with the help of the PERMI. Depending on the paper grade, the final porosity may considerably increase when the draw difference grows. This paper presents the key features of the modern on-line porosity analyzer and the real on-line porosity measurement results from some European paper machines.