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Online vibration monitoring prevents unexpected shutdowns due to bearing failures on boiler fans

09 June 2006

Emerson Process Management has significantly reduced the number of unplanned shutdowns at the Mondi Business Papers’ Richards Bay Mill, South Africa, using Emerson’s CSI 4500 Machinery Health Monitor. The online system detects changes in fan behaviour alerting the operators and prompting a remedial response that prevents unexpected fan failures and boiler shutdown.

“In just seven months, Emerson’s Machinery Health technologies have prevented seven incidents due to fan imbalance and early bearing defects that could have shut us down,” said Nico Groenewald, senior mechanical technician, Condition Monitoring. “We estimate that the savings in lost revenue from these incidents would have been €424,539. Not only are we more productive, but this is a safer work place because of Emerson’s predictive technologies.”

The uneven build-up of deposits on the runners of fans providing air to the recovery boilers changes the balance of these fans, causing numerous problems. Bearing failure on the primary and secondary air fans can result in a shutdown of the recovery boilers for at least six to eight hours. The cost of the recovery boiler being down is approximately €13,562 per hour, not including the cost of repairing damaged equipment.

Online monitoring using Emerson’s CSI 4500 Machinery Health Monitor, a component of Emerson’s PlantWeb digital plant architecture, provides a continuous flow of information on the condition of the fans and the operators are made immediately aware of any changes. The faulty fan can then be shut down for cleaning or repairs before failure occurs.

An additional benefit of the system is the ability to trend fan behaviour over time using Emerson’s AMS™ Suite: Machinery Health Manager software. This enables the condition of assets to be remotely monitored using the Wide Area Network at the site. AMS Machinery Manager incorporates multiple diagnostic technologies into a common database and enables operators to correlate trends with changes in boiler condition. This information is useful in reducing incidents of deposit build-up on the fans. Knowledge of vibration behaviour over time can also be useful in the early detection of bearing problems and misalignment leading to failure. It can also be used as a quality control factor after maintenance interventions.

These fans were previously monitored as part of a routine vibration monitoring program, so sudden changes in vibration levels might go undetected for several days or until the next scheduled measurement. The additional loading/stress on fan bearings when running in an unbalanced condition for an extended period sometimes resulted in reduced bearing life along with the downtime and material costs associated with bearing failures. The unpredictable nature of the build-up on these fans also posed a potential safety hazard.

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