.
From left to right: Helmut Schwarz, Line Manager for Pulp Production and Newsprint Production; Rudolf Mayböck from Andritz; Günter Flicker, Electrical Maintenance Engineer; Franz Medl, Assistant Raw Materials Supply.
Norske Skog’s Bruck an der Mur mill in Austria produces about 400,000 t/a of printing grades (newsprint on PM3 and LWC on PM4). High-grade pressurized groundwood (PGW) is an important component in the fiber mix, lending mechanical strength and surface properties to the LWC grades. The PGW plant processes about 200,000 m3 of spruce each year.
“Pulp cleanliness is absolutely critical for our grades,” says Helmut Schwarz, Line Manager for Pulp Production and Newsprint Production at Bruck Mill. “We can’t have any bark particles in the pulp, but excessive debarking is not economical. Add the seasonal fluctuations from frosted logs, and short ends or crooked logs which must be removed manually, and you find that the debarking process can be difficult to control.”
Pioneering projectBruck is making the most of its fiber resources with three innovative woodyard automation tools. On one level is BarkScan™ and LogScan™. On the optimizing level is DrumMatic™. “Bruck is truly pioneering with this degree of automation,” says Rudolf Mayböck, Senior Engineer for ANDRITZ Automation.
During construction of PM 4 in 1989, the woodyard received a facelift when an ANDRITZ debarking drum and two manual sorting lines went into operation. In 1998, Bruck installed ANDRITZ BarkScan™ and DrumMatic™ systems. BarkScan™ is a vision system which gives real-time information on the wood content remaining in the bark waste. DrumMatic™ takes this and other inputs and controls the debarking drum’s speed, filling level, and discharge gate position.
Thanks to this modernization, the mill has substantially reduced wood losses during debarking and maintains a more constant filling level in the debarking drum.
Rely on the eyes?However, there was still the situation with operator fatigue and errors. Bruck’s operators visually sorted logs for the PGW operations. Running two shifts a day, the operation was staffed with three people – two of them responsible for manning the two sorting lines at any time. Manual sorting involved removing any logs whose external appearance (length, straightness, diameter, obvious defects) did not meet requirements. Given the speed and volume of the moving logs, this task required a high level of concentration, which could only be sustained for a limited period by a single individual. “There comes a point when your eyes begin to play tricks on you,” Schwarz says. “Fatigue or lapses in concentration leads to errors which impact pulp quality.”
“The solution was to automate this laborious and error-prone visual log sorting,” Mayböck says. “Together we began a pilot project to utilize our experience in image processing systems and automated control.” This was in October 2007. The project was justified on the ability to increase throughput of the debarking line, relieve the stress burden on operators, reduce costs, and improve sorting quality.
Tools for automatic log sortingANDRITZ Automation specialists installed a LogScan™ system for automating the log sorting process on both lines. LogScan™ is based on modern image processing. It consists of a special video camera and light source mounted above the log conveyor – as well as the computerized electronics for image processing, analysis, and communications to the DrumMatic™ supervisory control system.
According to Mayböck, “The logs are made to roll while in the scanning area so that the entire surface can be scanned,” he says. “Length and diameter are determined. Shape and cleanliness after debarking are also analyzed.”
LogScan™ automatically decides where to route the log: to the pressurized grinder, back to the debarking drum for more bark removal, or to a chipper which cuts unsuitable logs into chips.
Debarking optimizedSorting with LogScan™ provides Bruck with logs that are within specifications for dimensions, shape, and cleanliness while avoiding operating disruptions in the plant, according to Schwarz. “Right after start-up we knew immediately that there was no need for vast improvements, but only for a little optimization,” he says.
Automatic sorting with LogScan™ has been operating at Bruck for over two years now. “This system has certainly lived up to expectations in terms of optimizing the debarking process,” Schwarz says.
Schwarz notes that the surface cleanliness of our logs is now greater than 99.9% with minimum wood losses. Of particular importance is the constant and largely trouble-free throughput (16,000m³ per month). “Our net operating time for the double shift has increased from 13 to 15.5 hours,” he says. “This gives us flexibility to cancel an occasional shift or use it for preventive maintenance. We also now need one operator less at the log sorting station.”
Whenever there is a need to tweak or optimize the systems (for example, adapting to changes between fresh/mature logs or winter/summer logs), ANDRITZ Automation maintains an online link to the control systems. “It is helpful that ANDRITZ has remote access to our plant so that they can assist with these small adjustments and optimization,” Schwarz says.
Much like BarkScan™, LogScan™ also communicates with the DrumMatic™ control system to optimize the entire debarking process. “Bruck is unique in having these control systems integrated into one network,” Mayböck says.
