Automatic Control of Additives with Modern Online Measurement Technology Raises Papermaker Productivity

摘要

In recent years, paper machines have undergone remarkable changes in terms of speeds and usable widths to meet ever-increasing demands on paper quality. This development has necessitated novel techniques for monitoring the stock properties. Today, lab-scale measurements alone fail to efficiently monitor PM processes because the latter are extremely difficult to simulate. Instead, online/inline measuring procedures have to be applied. After the introduction of online measurement, the next and decisive step is to implement closed-loop control. This is the only way to achieve targeted chemical dosages to ensure a sustainable improvement of paper properties. As far as deaerator chemicals are concerned, the installation of control loops successfully achieves the desired advancement. At Holmen Paper, deaerator control achieved a 37% reduction in the consumption of this chemical. Advanced, low-maintenance sensors enable retention control via effective consistency control in the white water. Once Inline Retention Control had been installed at the Braviken mill, the white water consistency was kept more constant than had been possible with the previous sensor. Owing to it's lower maintenance requirements, sensor availability was increased. The trials at Braviken were intended to study the impact of charge on wet end processes. Specifically, the charge variation caused by DIP and TMP as furnish components was studied. It was found that the measured fluctuations are also seen in subsequent process steps, where they may be successfully controlled. At Braviken, a fixative control loop was installed ahead of the blend chest, i.e. before starch dosage.