Firing and Drying / Refractories

5 Tips for Achieving Furnace Lining Efficiency

Furnace linings must be properly maintained for a smooth production process.

September 3, 2013

An efficient furnace lining is key to reducing overall maintenance costs and ensuring that facilities run reliably without undue revenue loss due to downtime. These five tips can keep your furnace lining running efficiently.

1. Evaluate the furnace lining by using infrared (IR) thermography inspection.

Infrared thermography scans are an essential step for evaluating the quality of the furnace lining. Lining quality is critical to protecting the steel from heat, limiting heat loss and promoting overall furnace efficiency. The scan typically involves pointing an IR camera at several points on the furnace 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 painted surfaces.

Obviously, scanning from the outside is beneficial because the unit can continue to operate. In many cases, specially trained applications engineers conduct the IR imaging, analyze the scans, and provide recommendations for the most appropriate repair options.

2. Use on-line maintenance repair.

With traditional repairs, the furnace must be shut down and cooled until it is safe for maintenance personnel to enter and repair the lining with fiber blankets, pumpables or monolithics. On-line repairs, however, are advantageous, especially when issues arise relating to temperature, accessibility to a particular area, or the size of the hot spot.

Most maintenance managers prefer the on-line repair option because it is reliable, fast and economical. After all, furnaces generate revenue, so it is helpful if repairs can be made while the unit is on-line. This avoids revenue loss from the unit in question, as well as the consequential losses from shutting down additional connected units, processes or an entire plant.

For example, where IR scans indicate that on-line repairs are recommended, high-temperature ceramic fiber-based insulation can be pumped from the outside of the furnace or boiler, filling cracks and voids caused by deterioration. These products are ideal for providing improved thermal insulation efficiencies behind boiler tubes in sidewalls, seals and floors as well as repairs of ovens, furnaces and process equipment.

3. Choose the right material for furnace rebuilds.

When IR scans indicate that the area of concern is too large for on-line repairs, the unit must be shut down for a furnace repair or reline. Material selection is key to a successful furnace rebuild that will improve efficiency and reliability, and lower maintenance costs. Material properties, including density, mechanical resistance and insulating factor, may vary depending on the furnace’s application. Selection of the proper material is frequently done by using a heat flow analysis software program in which temperature and ambient operating factors are inputted to obtain information on the best materials to be used (see Figure 1).

Keep in mind that many units have old-style insulation but need to operate in today’s world. Since so many new, more efficient insulation types are now on the market, consider upgrading when you have to reline the furnace. For example, some types of fiber offer up to 20% lower thermal conductivity and are therefore more energy efficient than traditional refractory ceramic fiber (RCF) and any other alkaline earth silicate (AES) insulations. A breakthrough in advanced manufacturing control has allowed products to be engineered to maximize fiber content. Low bio-persistence is also beneficial for those looking to move away from RCF insulation.

4. Carefully consider engineering design.

After selecting the proper materials, be sure that the engineering design is suitable. Engineering is extremely important when it comes to ensuring that the furnace relining lasts as long as possible.

Make sure the materials have adequate anchoring studs to hold them in place and have sufficient joints for expansion. For instance, installing a brick lining without the proper expansion joints could actually cause the brick to grow and end up pushing the entire lining off the furnace wall.

5. Proper installation is critical for success.

Be sure that installation of furnace lining material is done properly and that those doing the job have the proper skills for the task. A variety of products are available, and each one 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 be difficult to place and will not develop the expected properties. The bottom line is that poor installation is as bad as a faulty design or the wrong material choice.

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