Lime Kiln Induction Fan in Balance as Boise Wallula Adopts New Technology

Pulp & Paper, Oct 2004 by Kayler, Kimberly

Washington paper mill eliminates $87,000 in unscheduled downtime costs with the installation of a permanently mounted fan-balancing system

As a major manufacturer and distributor of uncoated free-sheet papers, Containerboard and corrugated containers, newsprint, and market pulp, Boise Paper Solutions markets itself as a company that provides consistent and efficient products that aids its customers in making their own great products. That is why having to go offline for unscheduled lime kiln shutdowns at a cost of about $87,000/yr in lost production, makeup lime, and maintenance costs is disastrous.

Shortly after joining Boise in 2001, Ron Blood, predictive maintenance and reliability supervisor for Boise's 500-person Wallula, Wash., mill, became aware of a continual build-up problem with calcium carbonate on one of the mill's large induction (ID) fans for a lime kiln. According to Blood, paniculate had a tendency to stick to the fan rotor, and this continuous, non-uniform buildup would actually 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 to $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," describes Blood. "Shutting down is a serious process that typically takes three hours to allow the kiln to cool off and another three hours to conduct the cleaning process. By the time we would get the kiln back in service, at least 10 hours of production was 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 a quick internet search, Blood located and contacted Lord Corp., which specializes in the management of vibration, motion, and noise.

"Boise's manufacturing process is dependent on the performance of the fans and their ability to maintain process air flow," says Andy Winzenz, sales manager for Lord Corp., who helped confirm the diagnosis. "As such, when the fan was thrown out of balance because of buildup, the result was untimely and expensive shutdowns."

After analyzing the problem, the recommendation was a permanently mounted fan-balancing system called RealTime that continuously monitors fan vibration levels. This system was recommended because of its ability to make rapid balance corrections and withstand the harsh environment surrounding the lime kiln ID fan.

The system is set up to monitor fan bearing vibration levels and the vibration phase angle in order to automatically correct for unbalanced conditions. This is done while the fan is running at operating speed, eliminating costly downtime to clean and manually balance the fan. Once levels reach a preset high trip point, the system switches on, commanding balance mass inside the shaft-mounted system to adjust as needed to counteract the unbalance and reduce the vibration.

The balancing ring of the RealTime balancing 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. Utilizing vibration sensors, the system monitors the fan-bearing vibration.

Vibration signals are received and processed by an "Adaptive Influence Coefficient" control system, which then determines the balance adjustments that are required. The controller relocates the counterweight masses to the desired position to minimize the vibration levels. This process continues until the controller senses that balance has been restored. Typical balance cycle times range from 30- to 120-sec, depending on operating speed.

Lord Corp. developed and patented the actuator coil assembly used in the RealTime balancing system. The actuator coil is traditionally mounted to support brackets located on the bearing pedestal. The non-contact 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 quickly 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 dust-proof, waterproof box near the fan, was completed in advance of the shutdown.