Mikron Infrared cameras allows energy company to monitor boilers through flames
Westar Energy found a better way to see through flames in monitoring for slag problems in three boilers that drive three 800 MW generators at its St. Marys, Kansas electric generating plant. Traditionally, operators would wear protective visors to check through inspection ports, attempting to look through flames for signs of slag build-up 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.
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 also operate 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."
Westar brought in a variety of cameras for evaluation, he notes, including the multi-duty 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 C - 1600 C) range needed for infrared imaging inside the boilers where combustion temperatures can exceed 1100 C.
Patented infrared filtering on the MikroScan 7400 allows dual spectral band operation - 8.0 to 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," notes Schultz.
The camera's primary role is imaging the slag build up 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 build-up 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 inch x 10 inch 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° on the outside of the furnace.
The massive boiler is 85 feet 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 in taking step-by-step scans across the huge structure.
The MikroScan 7400 was purchased in mid-2004 and has operated without problem through its first year at the St. Marys plant, reports Schultz. The camera is the first purchased by Westar from Mikron Infrared. He rated the camera maker's application engineering assistance, service and service as very good.
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. More to the point, Chynoweth emphasizes, microbolometer cameras are affordable. "Depending on the resolution of the detector array, commonly 320x240 pixels, microbolometer-based cameras are available in a range of $11,995-$43,000," he explains. "Typical mid-wave cameras that would otherwise be needed for this boiler application are based on a cryogenically cooled (approximately -200 C) detector. Such cameras are larger, heavier and less portable. They cost $50,000-80,000, consume batteries at a rapid rate, and require service costing up to $15,000 if the cooling system fails."
Mikron Infrared perfected proprietary technology to enable 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."
Along with the specialized infrared filtering capabilities, 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 MikroScan 7400 is battery-operated and self-contained in a rugged, IP54-rated metal case for simple, point-and-shoot versatility. It includes on-board 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.
The Westar generating plant employs various means to deal with slag build up when detected. Blowers and water cannons can be applied to dislodge the slag, says Schultz. During nighttime hours, when electrical demand is lowest, the generating load can be dropped, in effect "cooling" the unit which can induce slag to slough off as well. As boiler pressure is reduced and the saturation temperature of the water decreases, the tubes shrink, helping the slag to break loose, he explains.
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 megawatts of electric generating capacity.