No-Hassle, Low-Mass Kiln Cars
Low-mass kiln car designs offer significant fuel savings in tunnel kiln furnaces because of the low heat loss and heat storage properties of refractory ceramic fiber. Until recently, anchored and bonded ceramic fiber module systems were considered state-of-the-art for kiln car refits and repairs. However, many kiln cars feature support piers, making extensive field cutting necessary when installing ceramic fiber blanket or modules.
A gunnable foam/fiber insulation system1 is quickly gaining ground as an easier, more cost-effective alternative. The system combines high fuel and energy savings, fast installation and overall cost savings, making it an important innovation in high-temperature technology for low-mass kiln car applications.
Benefits of the SystemThe foam/fiber insulation system comprises three components: specially conditioned bulk ceramic or soluble fibers, an inorganic binder, and an organic foaming binder. The bulk fiber material is combined with the binders in a patented mixing mechanism, creating a homogeneous foam/fiber mixture. The installation machinery propels this mixture through a feed hose and nozzle, and the material is then gunned onto the target surface.
The insulation can be installed at rates in excess of 1000 board feet per hour, which can be two to six times faster than traditional installation techniques. Unlike conventional installations, which often require five or more installers, a three-person installation crew is all that is required with this new technology.
The application system is also specially designed to control airborne fiber levels. Unlike “sprayable fiber” technologies, which feed dry fiber and binder in separate streams that are partially combined once the product leaves the installation nozzle, the fiber in the new insulation system is completely coated within the foaming binder solution while in the mixing chamber, significantly reducing the potential for airborne fiber release into the surrounding environment. While measurable airborne fiber levels with the new system can vary according to the specific application, tests have shown that the average real-time exposures to airborne fiber levels with this technology are similar to or less than those experienced during conventional blanket or module installations. Additionally, because the insulation is installed much faster than conventional methods, the duration of exposure is significantly decreased.
In addition to the patented mixing chamber and proprietary binder system, a dust collection hood is located on top of the fiber feed hopper to further control the release of airborne fiber. A vacuum is drawn on the fiber hopper hood, which keeps the bulk fiber chamber under negative pressure during operation. Limit switches installed on the binder mixing chamber also prevent discharge of fiber prior to complete mixing with the foam binder.
The insulation’s interlocking network of fibers creates a strong, uniform monolithic structure that provides:
• speed and ease of installation,
• low rebound during installation,
• low thermal conductivity,
• low thermal shrinkage,
• low heat storage,
• excellent thermal shock resistance and
• good chemical resistance.
Proven PerformanceTo reduce its kiln car mass, Saint-Gobain Abrasives in Worcester, Mass., began using fiber modules several years ago. However, the modules had to be cut and fitted around the support piers of the cars—a time- and labor-intensive process. Additionally, the insulation exhibited shrinkage at the module-to-module joints after service, reducing its performance.
In July 2002, the company decided to try the gunnable foam/fiber insulation system on two of its kiln cars, which were used in a tunnel kiln with an operating temperature of 2300 degrees F (1260 degrees C) in the soak zone. The application consisted of 10 in. (250 mm) of a 2600 degrees F-rated foam/fiber insulation2 with a density of 8 pounds per cubic foot (PCF) (128 Kg/m3) applied to each low-mass car. Lee Jacques, sales engineer for Atlantic Contracting & Specialties Inc., and Jim Mitchell, senior pyrometric technician for Saint-Gobain Abrasives, supervised the project.
The first step in the installation was to gun the foam/fiber insulation into the car body tightly around the refractory support piers and against the refractory perimeter blocks.* After the insulation was gunned into place, a wet trowel was used to work the material around the support piers and smooth the surface of the car deck. Finally, to provide a denser surface that could be easily cleaned, a high-density ceramic fiber-based topcoat material3 was troweled a 1⁄4 in. thick over the insulation.
The entire installation was completed in less than two hours, from start to finish, compared to the full day of installation required using other types of low-mass products. The result was a seamless, monolithic, energy-efficient insulation system that was installed very quickly, and that allowed Saint-Gobain Abrasives to return the car to service in less than 24 hours. Due to the low heat loss and heat storage properties of the refractory ceramic fiber, fuel efficiency was optimized. In addition, Saint-Gobain Abrasives’ ability to obtain all of the required materials, equipment and installation as a complete package provided a definite advantage.
“The gunnable foam/fiber insulation system offers significant advantages for low-mass kiln car designs,” Mitchell said. “Due to its unique method of installation, the insulation was easy to install as a monolithic ceramic fiber system around the kiln car support structures. After seven months of service, the kiln car shows no sign of shrinkage and is meeting all of our expectations. This insulation will be a key component in our ongoing efforts to upgrade the performance and efficiency of our kiln car system.”
Extending the AdvantagesIn addition to its applications in low-mass kiln cars, the gunnable foam/fiber insulation can also be used to repair or upgrade existing furnace linings in a fraction of the time required for conventional blanket or module linings. The system offers energy savings, installation speed and improved lining performance for upgrades of existing fiber linings, linings over hard refractory, and furnace lining patches or refits.
Perhaps the greatest benefit of the foam/fiber system is that the end user realizes energy savings immediately after the product is installed and the kiln car or furnace is put back into service. When installed as a lining upgrade or lining over existing refractory, the insulation has demonstrated a substantial improvement in thermal performance, saving thousands of dollars in energy costs. The payback period in terms of energy savings for an installation over an existing hard refractory lining with this technology is typically less than six months. Applying several inches of the foam/fiber insulation over a partially deteriorated furnace lining can also extend the furnace lining life and improve furnace efficiency. The system can also be used as a hot face veneer or full thickness lining in kilns and furnaces operating at temperatures up to 2450 degrees F.
References:1. Foamfrax Insulation, supplied by Unifrax Corp., Niagara Falls, N.Y.
2. Foamfrax Grade II Fiber, supplied by Unifrax Corp., Niagara Falls, N.Y.
3. Fiberfrax TopCoat 2600, supplied by Unifrax Corp., Niagara Falls, N.Y.
*Lining the entire car perimeter with either hard refractory or ceramic fiber modules is required to ensure a successful installation in any kiln car application.