The Gorgas Steam Plant is located on the Mulberry Fork of the Warrior River, some 35 miles northwest of Birmingham, Alabama. Its first unit began operation in 1917. It is the oldest coal-fired plant at Alabama Power system, a Southern Company subsidiary. Today, units 6,7,8,9 and 10 provide about 1,250 MW.
In 2002, a selective catalytic reduction (SCR) unit for control of nitrogen oxides was installed on Unit 10, a 750-MW super-critical unit. An Advatech flue gas desulfurization (FGD) system, or “scrubber,” was added in 2007 in the first worldwide attempt to scrub multiple units through one system.
In the Unit 10-B Pulverizer, the vertical shaft thrust bearing supports the weight of the mill rotating parts and the downward grinding force exerted by the grinding rolls. The thrust bearing isn’t designed to withstand any radial loading.
“Lubrication contamination is a big problem,” says James “Pete” Peterson, condition-based maintenance specialist at Alabama Power. “Most of our units are from the ’50s, ’60s and ’70s. A good lubrication program, that includes on-site oil analysis, enables you to trend data on your equipment,” says. “It provides for a rapid response, if needed, and can save big dollars. When combined with other technologies, it can help a plant be the best that it can be.”
The plant uses the CSI 5200 Machinery Health Oil Analyzer from Emerson Process Management with a microscope attachment to check for debris.
“Routine oil analysis revealed a high ferrous index on the 10-B Pulverizer gearbox,” explains Peterson. “We have six 8-ft gearboxes; one of them is redundant. The software screen that comes with the 5200 went from zero to 352 reading for ferrous. And the next day it was 443. The fact that the previous month’s analysis showed zero ferrous told me we had a problem. After calling for help from my more experienced colleague, Harold Dobbins, it was determined that the system owner should be brought into the discussion. A major outage was to begin in the next day or two on Unit 10, so the CE Pulverizer man was already on the plant site and it was decided to let him look at the data.”
After draining the gearbox and examining the internals, it was found that the thrust bearing had deteriorated to the extent that failure of the gearbox was imminent and that the 10-B Pulverizer would not have made it into peak season.
When Alabama Power experienced a similar problem in 1999, prior to its on-site lab setup, it resulted in catastrophic failure of the gearbox, which required a total rebuild and cost more than $400,000. With the ability to catch this before a catastrophic failure could occur, the cost was $20,000 for the bearing and $10,000 for the installation.