The utilisation of SKF sealed bearings, combined with upgraded internal modifications, reconditioning and locally manufactured custom seals, has increased the average mean time between failures (MTBF) of scraper idlers on a customer’s submerged scraper conveyor (SCC) from between three and six months, up to between 12 and 18 months..
The submerged scraper idlers convey water-quenched hot coarse ash to the front of the SSC, which then collects and dewaters the boiler bottom ash (BBA) before discharging it at a controlled rate in the downstream plant. The SSC’s water-filled top trough, which works in conjunction with the dipper plates, provides boiler sealing by preventing air ingress into the boiler via the SSC.
The cost of frequent plant downtime to replace the failed scraper idlers was also exacerbated by the need for regular purchasing of new units. SKF proposed the supply of sealed spherical roller bearings (SRBs), a quality reconditioning procedure on the scraper idlers, and an overall redesign of the internal sealing arrangement. Senior application engineer, Cody Petersen explains that the highly contaminated operating conditions merited the use of sealed bearings. These bearings eliminated the possibility of contaminant ingress, thus increasing overall bearing life expectancy, equipment availability, and application running time. SKF supplied 28 units, each unit comprising two bearings, thus giving a total of 56 bearings.
“We proposed a complete redesign of the internal sealing arrangement due to the fact that the existing units were lasting for only approximately six months after installation, before either getting stuck due to guide wheel seizure, or leaking prematurely,” he says. “The SKF team carried out a redesign of the entire internal geometry, shaft, hub and guide wheel. We also manufactured custom seal cartridges to house custom seals manufactured by SKF locally, and we partnered with an accredited SKF supplier to recondition the housings.
“Our solution has created tremendous value for our customer on several levels. In addition to a significant decrease in plant downtime, the prevention of water/ash slurry leakage has, most importantly, resulted in a safer working environment. Alongside cost savings, the reconditioning and reuse of the housings also saved the customer time due to a faster overall turnaround time while lowering CO2 emissions, ultimately benefiting the environment.”
Since the installation of the first units, SKF has received a great deal of positive feedback from the customer, who has placed further orders for reconditioned units. “We have established an excellent working relationship with our valued customer, and we are continually implementing improvements in the current design to deliver the most optimal solution,” concludes Petersen.
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| www: | www.skf.co.za |
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