Putting IR on Slag PatrolDecember 1, 2005 By: Stephanie vL Henkel, Sensors Sensors
Westar Energy's electric generating plant at St. Mary's, KS, is the largest in the state. Its three coal-fired boilers, 85 ft. wide and 14 stories high, are vertically divided by an interior center wall. Each side produces 1.5 million hp, and together they drive three 800 MW generators.
An ongoing—and expected—problem is the slag that continuously builds up around the boiler tubes. Blowers, water cannons, and off-hour cooling can remove it, but first you have to find it. Operators wearing protective visors have traditionally handled this job by periodically squinting through inspection ports to see what's going on behind the flames. Carl Schultz, Westar's senior predictive maintenance analyst for thermography, went looking for a better way. He wound up selecting the MikroScan 7400, Mikron Infrared's portable, battery-operated, dual-range IR camera, industry's only uncooled microbolometer-based, long-wave (8–14 μm band) IR device with midwave (3–5 μm) imaging capability. Spectral tuning, along with three user-selectable temperature ranges, would let it serve two purposes.
To search for slag deposits, an operator inserts the camera lens into various 5 x 10 in. inspection doors on the boilers for a one-handed point-and-shoot inspection. Proprietary filtering and a through-the-flame mode (3.9 μm band) give the imager a good look at conditions inside the furnace. Its telephoto capability can view an ~225 sq. ft. area at field depths of 43 ft. for step-by-step scans of the areas of interest. The operator is exposed to sweaty but safe external temperatures of 100°F–120°F; the fire inside can exceed 2012°F. "In this application," says Schultz, "we're not trying to precisely measure temperatures, but rather view what's happening inside the boiler furnace."
Schultz also finds the long-wave mode handy for predictive maintenance of motors, bearings, and electrical cabinets whose temperatures range from ambient to 400°F. Moreover, the 8–14 μm band is unaffected by sunlight or smoke in the facility. Other features include onboard digital voice and thermal image recording, processing, software,and storage capabilities. Real-time viewing is also available via video output or Firewire interface.
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