Figure 1. An infrared camera is used to detect hot spots or other problems with the lining.
An efficient furnace lining is key to reducing overall maintenance costs and ensuring that facilities run smoothly without undue revenue loss due to downtime. Follow the five tips below to keep your furnace lining running efficiently.
1. Evaluate Using Infrared Thermography inspection
Infrared thermography scans are an essential step for evaluating the quality of the furnace or high temperature heating vessel lining. Lining quality is critical to protecting the equipment structure from heat and also to limiting heat loss and promoting overall furnace efficiency. Typically, the scan involves pointing an infrared camera at several points on the casing to analyze the outside temperature and identify hot spots where the unit is leaking heat or experiencing design issues that may not be visible from the outside. This is a particular issue with a painted surface.
Obviously, scanning from the outside is of great benefit because the unit can continue to operate. Figure 1 shows an infrared camera detecting hot spots or other problems with the lining. In many cases, specially trained applications engineers conduct the infrared imaging, analyze the scans and provide recommendations on the most appropriate repair options.
2. Use Online Maintenance Repair
Depending upon the temperature, the difficulty of getting to a particular area or how big the hot spot is, conduct online repairs wherever possible. Most maintenance managers prefer the online repair option because it is reliable and fast. After all, boilers and process units are generating revenue, so it is of great value if repairs can be made while the unit is online. This avoids revenue loss from the unit in question as well as the consequential losses from shutting down additional connected units.
3. Choose the Right Material for Furnace Rebuilds
Figure 2. Material selection is key to a successful furnace rebuild that will improve efficiency and reliability and lower maintenance costs.
When infrared scans indicate that the area of concern is too large for online repairs, the unit must be shut down for a furnace reline or process heater reline.
Material selection is key to a successful furnace rebuild that will improve efficiency and reliability and lower maintenance costs. Material properties, including hardness, density, mechanical resistance or insulating factor, may vary depending upon the furnace’s application. Selection of the proper material frequently is done by using a heat flow analysis software program in which temperature and use factors are input to obtain information on the best materials to be used.
Keep in mind that many units have old style insulation. Because there are many more efficient insulation types now available, consider upgrading when you have to reline the furnace. For example, some fibers have up to 20 percent lower thermal conductivity than current insulations, which are up to 17 percent more energy efficient than traditional refractory ceramic fiber (RCF) and any other alkaline earth silicate (AES) insulations. Figure 2 shows materials used in furnace rebuilds.
4. Carefully Consider Engineering Design
After selecting the proper materials, be sure that the engineering design is suitable. Engineering is extremely important to ensuring that the furnace relining will last as long as possible. Make sure the materials have enough studs to hold them in place and have sufficient joints for expansion or shrinkage. For instance, if you install a brick lining without the proper expansion joints, the brick could actually grow and end up pushing the entire lining off the furnace wall.
5. Proper Installation Is Key to Success
Be sure that installation of furnace lining material is done properly and those doing the job have the proper skills for the task. There are many products available and each has different installation requirements. For example, with concrete products, if the concrete is not mixed with the right amount of water at the proper temperature, the material will not develop, will be difficult to place and will not reach expected properties.
The bottom line is that if you do not install it right, it is as bad as not having a good design and not making a good material choice.