12 ABB
Pulp Paper & Logistics
Giovanni Pruscini, assistant production manager at the Rossano Veneto mill
3
a minute in the entire 45 minute cycle.”
With the normal control loop (see Figures 1 and 2), the FSD reacts to fluctuations in the drainage caused by variations in the pulp and the influx of already refined material. Mounted on the refiner the control loop shows that if the amount of water goes up by X the refining power goes down by Y, so the threshold is larger than the noise in the signal from the sensor. For each paper the set point is
controlled manually and when the batch is running satisfactorily the set point is set at the actual condition. Because of the time
Figure 1
FSD signal, pink setpoint, green actual value
delay in the control system the amount of water on the felt goes up slightly as the retention values rise. In other words the system never catches up completely. This control loop is running
satisfactorily with reduced variations in quality and improved control of dryline when making watermarked paper. There are also savings made in refining costs. Stock preparation is as follows: 1. The mixing chest is filled and
the contents pumped into the resting chest 2. After around 45 minutes, when the level drops below threshold, pumping into the resting chest stops and new
Figure 2: FSD signal in green (grams H2
batch starts 3. At end of the batch the level
falls, and the new batch enters 4. Pumping into the resting
chest starts and new batch enters, but will be different in composition because of variations in consistency, filler and colorants 5. When changing the tank the
drainage characteristics will be different. The change in composition of the new batch results in a different retention value, and this can cause quality problems when making watermarked paper. Also with coloured paper a large change in retention value may change the colour because of different
O/m2
), refiner signal in pink (drops from 22% to 17%, i.e almost a third)
colourants and ash content. To keep the retention values equal in these conditions the control loop tries to compensate for a change in consistency and filler by a change in the refining power.
The normal control loop greatly
reduces the problem, with the bump in quality being reduced in time (to one minute from two) and in amplitude, being reduced to 30-50 per cent of the original variation.
QCS signal, blue ashes, pink refiner
Since the installation of the L&W FSD sensor overall on- target production is now running at more than 80 per cent, said Pruscini. “The quality consistency ensures both the mill and its customers trust in the products being produced,” he said. “With watermarked paper production we would have around 10 to 12 per cent waste, but since the sensor’s installation this has been reduced to three per cent, and falls well within the operational tolerances for this kind of product.” More information from Lars
QCS signal, pink moisture
Kånge, Product Manager at Lorentzen & Wettre, Viderögatan 2, Box 4, SE 164 93 Kista, Sweden. Tel: 46 8 477 90 00. Fax: 46 8 477 91 99. Email:
info@l-w.com Web:
www.lorentzen-wettre.com
May 2013
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