2008-11-27 - Ayreshire-based UPM Caledonian Paper has achieved closer control of its paper manufacturing process thanks to enhanced measurement accuracy delivered by ABB’s new AC-Master AC excitation flow meter.
UPM Caledonian Paper uses electromagnetic flow meters to measure water, chemicals and stock flow of varying consistency. Flow measurements are a crucial part of the production process. The new meter is used in online control of the thick stock flow to a paper machine, this measurement being critical in ensuring the paper is produced at the correct grade and quality. If the flow meter is unstable it can result in irregularities in the basis weight of the paper.
A previously installed 20 year old pulsed DC excitation meter was struggling to cope with the high levels of electrical noise inherent in stock flow measurement following a change to Wet End chemistry, resulting in high process noise, sluggish response to flow conditions and impaired accuracy. DC meters typically require long damping times to smooth their output to an acceptable level. This results in slow response times and ultimately waste and quality issues.
To solve the problem, ABB, via its Glasgow-based Alliance Partner JWF Process Solutions, supplied an AC-Master flow meter to replace the existing instrument. The new meter features increased coil excitation frequency and digital signal processing technology (DSP) to optimise the flow signal to the noise ratio. Where backflow can occur, flow is measured bi-directionally with any reverse flow being automatically logged and forward flow compensated for accordingly.
Gary Merrilees, Measurement and Control Engineer for UPM Caledonian Paper says, “In an industry dependant on product quality and consistency, we are always on the look out for new instrumentation that can help ensure our high standards. After consulting JWF and ABB, we realised that an AC meter would be a logical choice for ensuring accurate flow measurement.”
Compared to pulsed DC meters, the AC-Master not only has a high signal-to-noise ratio in noisy flow applications, but also delivers high frequency sinusoidal excitation to the magmeter coils resulting in the measured electrode signal being of a higher quality and lower inherent noise. The ability of AC meters to cope with process-generated noise created by varying conductivities and slurries make them ideal for most pulp and paper, slurry and high solids applications as well as dosing applications where conventional pulsed DC meters could not be used as effectively.
“Recent improvements in AC excitation electromagnetic flow meters now provide users with better performance, quicker response, and noise-free outputs not possible with pulsed DC technology”, says Mark Allinson, ABB’s Process Flow Manager. “These improvements can lead to increased efficiency, improved quality and conservation of raw materials as well as enhanced profitability through reduced energy costs.”
Since the DN300 Mag-SM has been installed, UPM has seen immediate benefits. The new meter has seen measurement accuracy improved by 90%. Previously UPM was running at a measurement accuracy of ±5 litres per second. This has now been dramatically reduced to ±0.5 litres per second, providing enhanced flow measurement which can then be used to control the process more closely.
The data that is collated from the flow meter is part of a closed loop system and is automatically fed into the plant’s control system, which uses the data to regulate the process.
“The new meter means that accurate Basis Weight control is achievable and the overall production line is not being hampered by fluctuations,” says Merrilees. “Any irregularities or imbalances recorded will self-adjust through the valve system. This not only optimises production time but avoids the financial pitfalls of negative customer feedback caused by poor quality product.”
The new meters are the latest in a long line of ABB equipment supplied to UPM Caledonian Paper. “We have a long standing relationship with ABB,” says Merrilees. “ABB’s meters are used as standard within the mill. We are able to rely on ABB for a diverse spectrum of expertise and its interchangeable flow meters offer invaluable flexibility.”