Westar Energy has found a better way to see through flames while monitoring for slag problems at its St. Marys, KS electric generating plant. Traditionally, operators would wear protective visors to check through inspection ports in the three boilers that drive three 800 MW generators, attempting to look through the flames for signs of slag buildup on the boiler tubes.

"That's typical practice in the utility industry, and we make multiple inspections per day," says Carl Schultz, senior PdM analyst for thermography at Westar. "We thought there should be a better way and began exploring the use of an infrared camera to capture what was happening with slag inside the boiler." The largest electric utility in Kansas, Westar Energy services about 659,000 customers. The St. Marys facility is one of 11 Westar power plants that together provide nearly 6,000 MW of electric generating capacity.

The Research Phase

Westar started by researching cameras specifically developed for through-the-flame capability in the 3.9 µm band. In the search process it learned about an innovative new development, an 8-14 µm band bolometer camera that utilizes proprietary filtering to operate also in through-the-flame mode.

"This gave us the potential for getting double-duty service from our camera investment," says Schultz. "We could use it for varied thermal inspections as well as monitoring what was happening with slag inside the boiler. It sounded good, but we needed convincing." (Pictured here, the MikroScan 7400 with radiation shield for high-temp applications.)

Westar brought in a variety of cameras for evaluation, he notes, including the multiduty design from Mikron Infrared. At the end of the evaluations, Westar selected the portable, dual-range MikroScan 7400 as delivering the best combination of functionality, economy, and versatility.

The camera offers three selectable temperature ranges, including a high-temperature (400-1,600°C) range needed for infrared imaging inside the boilers, where combustion temperatures can exceed 1,100°C.

Patented infrared filtering on the MikroScan 7400 allows dual spectral band operation -- 8.0-14 µm long-wave mode, or mid-wave with 3.9 µm microfilter for through-the-flame imaging. "This lets us use the camera for a wider range of applications, such as predictive maintenance monitoring in the long-wave band on motors, bearings, and electrical cabinets in the ambient to 400°F range," says Schultz. "Then we can switch to the 3.9 µm band and high-temperature range to image the boiler tubes for slag condition."

Imaging Slag Buildup

The camera's primary role is imaging the slag buildup on boiler tubes. The boilers are fired with powdered coal from the Powder River Basin, but unburned waste material can build up around tubes as slag. This reduces heat transfer efficiency, while too much buildup can keep ash from falling to the bottom of the boiler, he explains.

"In this application, we're not trying to precisely measure temperatures, but rather view what's happening inside the boiler furnace," notes Schultz.

Operators do periodic thermal inspections throughout the day. The camera lens is inserted into a 5 x 10 in. inspection door in the furnace wall to do the thermal imaging. Inspection doors, platforms, and decks are located at various intervals and heights on the massive boiler. Operators are exposed to ambient temperatures of 100-120 deg on the outside of the furnace.

The boiler is 85 ft wide by 14 stories tall, divided down the middle by a center wall. Each side produces 1.5 million hp. The Mikron camera allows thermal images to be captured through flame and particulate matter the full depth from inspection door to the center wall.

"The camera has telephoto capability, letting us image an area of about 225 sq ft at the 43 ft distance," says Schultz. Compact, portable design allows comfortable one-handed point-and-shoot operation while taking step-by-step scans across the huge structure.

The MikroScan 7400 was purchased in mid-2004 and has operated without problems through its first year at the St. Marys plant, reports Schultz. The camera is the first Westar has purchased from Mikron Infrared. He rated the camera maker's application engineering assistance and service as very good.

The Camera's Capabilities

According to Jon Chynoweth, Mikron Infrared marketing director, the company makes the industry's only uncooled, microbolometer, long-wave infrared (8-14 µm) cameras with midwave (3-5 µm) imaging capability. The 8-14 µm capability is ideal for typical PdM applications because it is unaffected by sunlight or smoke in a plant. Mikron Infrared's proprietary technology enables a bolometer camera to image other very narrow spectral bands at high temperatures, he says.

"In this case, we can deliver 3.9 micron through-flame capability along with general purpose 8-14 micron utility," he says. "We call this spectral tuning." (Image shows slag accumulating on boiler tubes; 10 color palette choices are available with Mikron software for ease in analyzing thermal images.)

The camera is also available with a radiation shield and protective window assembly to allow temperature measurement inside a furnace without interference from combustion flames.

The battery-operated MikroScan 7400 is self-contained in a rugged, IP54-rated metal case for simple, point-and-shoot versatility. It includes onboard digital voice recording and can simultaneously record high-definition 14-bit thermal images with digital visual images. It comes standard with extensive onboard image processing software and stores images and data to PCMCIA cards. Images can also be viewed in real-time via video output or optional built-in IEEE 1394 (Firewire®) interface.