As a major manufacturer and distributor of uncoated free sheet papers, containerboard and corrugated containers, newsprint, and market pulp, Boise Paper Solutions, Boise, ID, markets itself as a company that provides consistent and efficient products. That is why having to go off-line for unscheduled lime kiln shutdowns at a cost of about $87,000 a year in lost production, makeup lime, and maintenance costs is disastrous.Enter Ron Blood, predictive maintenance and reliability supervisor for Boise’s 500-person Wallula, WA, plant. Shortly after joining Boise in 2001, Blood became aware of a continual build-up problem with calcium carbonate on one of its large induction (ID) fans for a lime kiln. According to Blood, particulate had a tendency to stick to the fan rotor, and this continuous, nonuniform build-up would throw the fan out of balance. This high level of vibration resulted in an average of 2.5 unscheduled shutdowns per year at a cost of $33,000-$35,000 each in lost production, makeup lime, and maintenance costs.
“When the fan started to vibrate, my coffee would actually shake in my cup as it sat on my desktop,” Blood said. “Shutting down is a serious process that typically takes 3 hours to allow the kiln to cool off, and another 3 hours to conduct the cleaning process. By the time we would get the kiln back in service, at least 10 hours of production were lost.”
In addition to lost time and production, frequent episodes of high vibration also were causing accelerated wear on the fan bearing, and the staff was often taken away from regular duties to troubleshoot vibration problems.
Searching for an answer
When faced with finding a solution to this situation, Blood remembered reading an article about a technology that might help solve his problem. After an Internet search, he located Lord Corp., Cary, NC, and called for more information. Andy Winzenz, sales manager for Lord, visited the plant and helped confirm the diagnosis.
“Bosie’s manufacturing process is dependent on the performance of the fans and their ability to maintain process air flow,” Winzenz said. “As such, when the fan was thrown out of balance because of build-up, the result was untimely and expensive shutdowns.”
After analyzing the problem, Winzenz recommended the company’s RealTime balancing technology—a permanently mounted fan balancing system that continuously monitors fan vibration levels. He recommended this balancing system because of its ability to make rapid balance corrections and to withstand the harsh environment surrounding the lime kiln ID fan.
How the balancing system works
The balancing ring of the system mounts to the fan shaft. The ring houses liquid counterweight masses that can be repositioned to offset the unbalance detected in the fan rotor. Using vibration sensors, the system monitors the fan bearing vibration. Vibration signals are received and processed by a control system, which then determines the balance adjustments that are required. The controller relocates the counterweight masses to the desired position to minimize vibration levels. This process continues until the controller senses that balance has been restored. Typical balance cycle times range from 30-120 seconds, depending on operating speed.
Lord developed and patented the actuator coil assembly used in the balancing system. The actuator coil is traditionally mounted to support brackets located on the bearing pedestal. The noncontact power supply used in the actuator coil eliminates the need for maintenance, sending power across an air gap between the stationary actuator coil and the rotating balancer ring.
Implementing the solution
According to Blood, after the balancing technology was presented to the Boise team, a capital request was made and approved, allowing for an April 2003 installation during a regular scheduled shutdown. Installation involved moving the motor out of the way, pulling the coupling and bearing off the fan shaft, installing the balance ring, reassembling the bearing and coupling, and putting the motor back in and aligning it. Some minor trimming of the stiffening ribs on the fan housing had to be done to make clearance for the balance ring. Other work, such as installing power to the controller and then mounting it in a dustproof, waterproof box near the fan, was completed in advance of the shutdown.
Since installation, the team has endured only one unscheduled shutdown and that was caused by massive particulate build-up and throw-off. Blood said that after the installation, the fan ran so smoothly that the team forgot the fact that build-up was still happening.
“We received a wake-up call several months after installation when a large chunk of build-up flew off the fan,” Blood said. “The resulting vibration was more than the balancer could compensate for, so we had to shut down and sandblast.”
Because the balancing technology stores balance history and events, data can be analyzed—greatly aiding Boise’s process of calculating the build-up rate of the particulate in order to better plan for any necessary cleaning and sandblasting.
The proof is in the numbers
According to Blood, this process improvement has added up to big savings—an estimated $87,000 in 2003. Not only is Boise able to run the lime kiln with fewer production interruptions, it is also extending the life of the equipment and has minimized wear and tear on the fan bearings. Although Boise still shuts down the lime kiln three to four times per year for routine maintenance, such occurrences are typically planned and not in response to fan unbalance.
Blood can demonstrate the smoothness of the fan operation with the addition of the balancer by balancing a nickel on the edge of a fan bearing while in operation. Even more important, the production supervisors have little worries about the fan and are afforded the opportunity to perform their daily functions without the hassle of an unscheduled shutdown. Finally, the vibration figures speak for themselves. Before installation of the balancer, the fan registered 0.3-0.8 in./sec within 30-60 days of sandblasting. Today, however, Boise reports vibration levels of 0.04-0.06-in./sec within the same timeframe thanks to the new balancing technology.
“The new balancing technology paid for itself in six months, not taking into account the expense of wear and tear on the bearings,” Blood said. “Although the installation and learning curve had some glitches, the technology has more than met our expectations. A fan that was once a chronic problem and a constant worry is now one of the smoothest running pieces of rotating equipment in the mill.” MT