24 CRISTINI


switchable loop is manually controllable and when closed, it is fully automated.


Case study on a board machine In a competitive market, successful companies are always seeking to improve. This article describes a recent case study into a multiple layer board machine, demonstrating a control strategy that allows the mill to enhance the board quality and reduce a notably the amount of energy used drives and vacuum pumps. The project was evolved into precise steps:


1) analyse the current operation and targets


2) define the sensor requirement and installation of the system


3) data collection and analysis 4) targeted trial with the purpose to explore all the ‘what if’ scenarios


5) Implementation of control loops and final assessment.


Internal bond strength (Scott type) measures the energy required to rapidly delaminate a sheet-type specimen. Fibre mix and overall quality of the raw material has a major impact on the results. On many occasions, starch is used to aim for the target value of Scott test. However, dewatering distribution has a crucial effect on the fibre distribution and the delamination position. Each single dewatering zone of the former has an impact on the internal bond strength, as shown in Figure 3.


Distribution of fines determine the weak spot in Z-direction Consistency (as measured by the FiberScaOnlin) at the pre- former in combination with


July/August 2019


Figure 4 – Internal bond strength (Scott type) measures the energy required to rapidly delaminate a sheet-type specimen


consistency at the combining points correlates with mechanical properties of the board. The mill, in cooperation with


Cristini, implemented a system to control, through a mix of open and closed loops, the consistency in the most critical position of the forming section, resulting not only in quality important achievements (more than 10 per cent of bond strength) but also in a massive energy reduction. The optimisation of the vacuum


level (controlled by the sensor cluster) on each zone has resulted in a reduction of electrical energy consumption by drives and vacuum pumps of more than 20 per cent. The vacuum has been re-


distributed to meet new needs,


such as blowers in favour of liquid ring pumps for low and medium vacuum zones and two liquid ring pumps eliminated. The balance of dewatering


between the bottom and top dewatering units has a direct impact of the fibre and filler distribution, determining the weakest link. Only an accurate and repeatable measurement of the web consistency can overcome the well-known human limits in controlling such variables. Further, the SmartScan


contactless microwave sensor in the first dryer group has helped to dispel the myth that higher dryness in the forming section leads to better press/drier efficiency. See Figure 4.


Conclusion The adoption and the daily use of the microwave measuring system significantly boosts many retro- commissioning processes within the optimisation programmes of board mills.


Quality and energy efficiency


are therefore not contradictory but go hand in hand in the big picture of sustainability Measurement is the first


step that leads to control and eventually to improvement. If something cannot be measured, it cannot be understood. If it cannot be understood, it cannot be controlled. If it cannot be controlled, it cannot be improved. *Luca Canali is development leader at Cristini Diagnostic Systems in Italy


Pulp Paper & Logistics


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