Bearings That Can Handle The Heat

The bearings on the dampers controlling airflow to two 535-MW coal-fired units at a power plant couldn’t handle the heat. High-temperature bearings solved the problem.

The inlet-air section of a utility boiler is a harsh environment for the dampers that control the flow of preheated air into the combustors. Over time, the hot air dries out the lubricant in the metal bearings, or roller elements, that control the movement of the dampers, causing the dampers to seize.

This was a problem at the Sioux Power Plant of Ameren UE (Union Electric), near St. Louis. The plant has two 535-MW, coal-fired units, each of which has 10 cyclone burners. There are two dampers on each burner -- a control damper and a shut-off -- for a total of 40 secondary air dampers. “On average, we had a bearing problem about every two months,” says James Riegerix, general supervisor at the plant.

Ameren has solved the problem by replacing the lubricated steel bearings with self-lubricating bearings made from GRAPHALLOY®, a graphite/metal alloy by Graphite Metallizing Corp., Yonkers, N.Y. All of the bearings for one boiler were replaced in the spring of 2004, and those in the other unit were replaced a year later. Both installations were completed during planned plant outages, which normally are scheduled every two years. So far, there have been no problems with the new bearings, says Riegerix.

He adds that when the changeover was done, the installers found a single bearing from Graphite Metallizing that had been put in a few years earlier. It was still in such good condition it was not changed.

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