In a high turnaround mill environment all aspects of production need to run smoothly. Achieving accurate flow measurement can contribute towards the reduction of downtime, lowering production costs and enhancing safety.
With over 1500 customers in 100 countries efficiency is essential for leading Swedish manufacturer of strong primary fiber-based packaging BillerudKorsnäs.
At its paper mill in Gävle, Sweden, the company’s pulp digester processing stage was previously using a magnetic flow meter to measure the flow of white liquor used in a pulp digester. This technology is frequently used for this type of application; however, it was unsuccessful in this case because the flowmeter was occasionally subjected to a significant vacuum that partially collapsed the liner.
Reduced digester performance
This caused the magmeter to read a higher flow rate, resulting in too little alkali input which reduced digester performance. As the process could not be stopped outside the scheduled shutdown period, it was not possible to replace the meter immediately. “When the flow measurement was inaccurate, unreliable, or completely failed, the alkali-to-wood ratio could not be accurately controlled,” said Peter Hallenberg, project leader for process automation, BillerudKorsnäs. “Replacing the meter tied up our maintenance team and incurred a cost of about €3,400 (US$4,500) per unit.
Since the pulp digester is a critical part of the production process, the company tried other technologies to overcome these issues including using an ultrasonic flowmeter. However, this trial proved to be unsuccessful as the solids and fibers in the liquor would build up on the meter walls, causing unpredictable flow readings.
The mill solved this flow measurement challenge by installing a Rosemount 8800 Vortex flowmeter from Emerson Process Management, which is not affected by the high liquor temperature, vacuum, coating, or suspended solids in the flow. Vortex flowmeters are not typically considered for this application, as the fluid contains solids and fibers that would clog the crevices and ports common to traditional vortex flowmeters, impacting the meter performance.
However, the design of the Rosemount 8800 Vortex eliminates crevices and ports while preventing the risk of clogging. In addition, the 8800 is balanced so it is not affected by vibrations in the pipes that are typical in mill applications. The resulting flow measurement is accurate, stable and reliable.
Consistent pulp quality
For BillerudKorsnäs, the more accurate flow measurements translated to more consistent pulp quality and a lower cost per tonne of pulp. The mill has also reduced maintenance costs by eliminating the need to remove and clean the failed flowmeter.
This has also enhanced safety at the plant because operators no longer need to maintain faulty equipment. In addition, the reliability of the vortex flowmeter has enabled BillerudKorsnäs to detect that a decrease in the flow reading was being caused by progressive plugging of the heat exchanger. Operators are now able to proactively take corrective action, increasing process efficiency.
Hallenberg concluded. “The flowmeter has improved pulp digester process efficiency. In addition, process availability has increased and maintenance costs reduced.”