IR camera technology provides new perspective on furnace inspection routines
A few years ago, managers at a US-based oil refinery called in an expert to inspect their oil furnaces with an infrared (IR) camera.
A few years ago, managers at a US-based oil refinery called in an expert to inspect their oil furnaces with an infrared (IR) camera. The inspector identified “cool” spots that suggested a problem. Rather than relying on what could be seen with the IR camera, the managers checked their thermocouples, saw no issues and continued to operate as before. It was not long before a preheater tube burst, forcing the refinery to shut down. It was a costly lesson learned.
Regular furnace inspections are crucial to avoiding hydrocarbon processing problems, such as variations in product quality, process line shutdowns and physical damage to the equipment itself. However, many of the monitoring and inspection tools commonly used in the past are inadequate for identifying potential sources of failure before processing problems become critical. These tools include arrays of thermocouples installed at various points inside furnaces to monitor temperatures.
When industry standard is not enough
Although thermocouples are an industry standard, they are of limited utility in identifying potential sources of failure because they are single-point measurement devices. If thermocouples are not located near a trouble spot, then emerging problems can go unnoticed for extended periods. Thermocouple readings simply cannot paint a complete picture of the inside of a furnace or boiler. In addition, welds that keep thermocouples in place—and even the thermocouples themselves—can deteriorate over time, leaving even larger gaps in coverage.
Although inspection ports in furnaces allow for the observation of some internal parts, flames, combustion gases and ash can easily obscure the view. When inspectors are unable to achieve adequate visibility into emerging furnace problems, the chances for product quality problems, process line shutdowns, or catastrophic equipment or facility damage expand rapidly.
Thermal imaging aids furnace inspection
Fortunately, inspectors at a growing number of companies are using thermal imaging technology with the ability to “see” through flames to keep their furnaces and boilers in good operating condition (Fig. 1). In IR cameras, lens extenders are often used to provide better viewing angles of furnace tubes when inspecting furnaces with small viewports. Better angles mean improved safety, more accurate measurements and more comprehensive scans. Detachable heat shields can be used to protect the camera and camera operator by reflecting heat.
FIG. 1. IR cameras are increasingly popular for high-temperature (up to 2,000°C) industrial furnace applications, particularly in the chemical, petrochemical and utility industries.
One reason IR cameras are gaining popularity in refineries is their efficacy in detecting product quality problems early, allowing facility managers to schedule repairs and avoid emergency shutdowns. More importantly, these cameras allow refineries to avoid costly, catastrophic damage to the furnace or boiler, or to the facility as a whole.
A variety of mechanisms can lead to furnace and boiler equipment failures, including coking that plugs the inside of tubes and impedes the flow of feedstock. Other common problems include slag buildup on the exterior of tubes, clinker damage, under- and over-heating, and flame impingement on tubes as a result of burner misalignment. Feedstock leaks can ignite and damage the equipment. The latest generation of IR cameras can detect most of these equipment problems early (Fig. 2).
FIG. 2. IR imaging can reveal emerging furnace issues, such as internal coking and external scaling, allowing facility managers to avoid tube overheat failures and ensure proper planning of unit shutdowns and decoking procedures.
For furnace control and inspection routines that still include thermocouple monitoring, a thermal imaging camera offers an accurate way to validate the thermocouple temperature readings. IR cameras can identify buildup or damage, and can even detect non-functioning burners. The results of the camera readings offer facility managers the tools needed to make a better assessment of the level of coking, slag buildup, etc. Plants can continue operating safely, or prepare for an orderly shutdown and component replacement, thereby minimizing downtime, reducing maintenance costs and preventing production losses.
Spectral waveband sensitivity enhances detection
IR cameras that can see through flames have a spectral waveband filter that allows only thermal radiation of specified wavelengths to pass through to the camera’s photodiode detector. For furnace and boiler inspection applications, the flame filter restricts the spectral sensitivity to a bandpass centered at 3.9 µm.
Since the IR energy from the flames is largely filtered out, the energy from objects behind the flames, such as tubes and burner parts, can pass through to the camera’s focal plane array detector. The detector’s highly sensitive response is the result of being actively cooled to cryogenic temperatures through a closed-cycle Stirling process. The IR cameras are calibrated to measure ultra-high temperatures and to store real-time video and imagery data for documentation purposes.
This specialized filtering enables IR cameras to detect a wide range of furnace faults, including degradation or refractory issues, which can cause damage to burners and tubes. The filters are also useful for evaluating flame shape and detecting dust deposits on tubes, which can cause poor heat transfer and reduce product temperature. IR cameras are often used to check for oxidation, which can eventually peel off, leaving a weakened area behind. They can also simplify the detection of unlit burners or burners that are causing flame impingement on the tubes. The latest IR cameras offer a cost-effective way to manage these assets responsibly. HP
The Author
Boccella, M. - FLIR Systems, Inc., Wilsonville, Oregon
Mark Boccella is the Americas Business Development Manager for Optical Gas Imaging at FLIR Systems Inc. He holds a BS degree in electrical engineering from Texas A&M University in College Station, Texas, and has 10 years of experience with infrared technology. Mr. Boccella is also responsible for supporting the growth of FLIR’s Optical Gas Imaging business.
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