Investing in Ceramics: New Refractories for Weight Loss
Now, imagine a lightweight product with use temperatures as high as 3200 degrees F that could be used to replace some high-density kiln furniture, regardless of processing temperatures. Consider the impact on energy consumption if such materials could be used for designing or rebuilding a high-temperature kiln without the difficulties of fibrous materials. These products are available today from Cellaris, a young company based in Israel that has developed an innovative technology for ceramic foam production.
Anyone involved in kiln operation and management knows that lightweight materials for kiln furniture and setting decks can save significant energy dollars. Likewise, all kiln designers are aware that using low-mass refractory linings can save considerable amounts of energy. Now, imagine a lightweight product with use temperatures as high as 3200 degrees F that could be used to replace some high-density kiln furniture, regardless of processing temperatures. Consider the impact on energy consumption if such materials could be used for designing or rebuilding a high-temperature kiln without the difficulties of fibrous materials.
These products are available today from Cellaris, a young company based in Israel that has developed an innovative technology for ceramic foam production. The company's materials are highly refractory-typically composed of 98+% Al2O3-and are as light as a feather. The combination of excellent refractoriness and extraordinarily low mass makes this material an interesting proposition for a variety of kiln construction and furniture applications. Because energy costs have increased by 400% in the last four years, these innovative, lightweight refractories just might be the solution that many manufacturers are looking for to reduce energy consumption.
Basic Kiln Energy Economics
Fuel-fired kilns are inefficient overall; the very best tunnel kilns might approach 50% in thermal efficiency, while shuttle kilns struggle to achieve half that value.1 This efficiency is based on the total load of ware plus furniture. The story only gets worse as higher temperatures are required. In fact, energy efficiencies for periodic kilns firing in the 3000 degrees F range can be less than 10%. A significant reason for this reduced efficiency is the high thermal mass of the kiln lining and ware support furniture weight.High-temperature periodic kilns used in technical ceramic applications are often quite small, with 10- to 60-cubic-feet capacities, and small kilns have a geometry that makes the effective thermal mass of the kiln lining much heavier than the ware plus furniture loading. Kiln car refractories in these applications are usually higher in density than the walls, adding significantly to the weight of the kiln insulation. The end result is that the kiln mass consumes far more energy than the product being fired. When this mass is added to the effect of very heavy furniture, which is sometimes as much as six to eight times the weight of the fired products, it is easy to see that the energy consumed when firing these kilns is nearly independent of the ware loading.
A typical lining for high-temperature kilns firing at temperatures up to 3200 degrees F consists of a 9-in. thickness of bubble alumina brick on the hot face, backed up with 2800 grade insulating bricks (4 1/2 in.) and 1 1/2 in. of board insulation. While these are all high-quality materials, the overall wall density is very high. Using Cellaris block materials shaped into bricks, with appropriate lightweight materials as back-up insulation, can bring the average wall density down by a factor of four. Calculated fuel consumption can decrease by 40% or more when these materials are used.
A Sol-Gel-Based Solution
The ceramic foams produced by Cellaris are capable of withstanding temperatures up to 1750 degrees C (3200 degrees F). These non-fibrous, highly porous, ultra-light ceramic products, registered under the trade name Lite-Cell®, are produced by a patented technology that is based on sol-gel chemistry. This groundbreaking technology provides the next-generation platform for high-temperature applications, including furnace insulation, kiln furniture, burner blocks and other combustion systems. Other industrial applications, such as catalytic supports and filtration media, could also be developed using the new foam.The new product was incubated through research at the Israel Institute of Technology (the Technion). Following successful laboratory and pilot phases (within the framework of the Technion Incubation program) and a promising response from the marketplace, Cellaris built and commissioned an industrial pilot plant at the Bar-Lev Industrial Park in northern Israel. Delivery of commercial orders and products began in early 2005, and commercial furnaces with the new material as a hot face lining are already in operation.
The technology allows the foaming of pure and mixed oxide materials. The company currently concentrates on an alumina (Al)/silica (Si)-based system; however, it has also produced foams using zirconia and titania. The material originates as foamed pellets, which are further compressed into standard and custom shaped products. Although the bulk bodies contain about 98% highly abrasive alpha alumina, they can be easily machined into custom shapes.
Expanding Applications
So far, Cellaris has focused on the high-temperature furnace insulation market. Because the new foam is an ultra-light material with about 90% porosity, it has superior insulating properties that provide significant energy savings, along with other operational added values compared to traditional insulating materials. It is also a fiber-free product that offers a viable alternative to the potential carcinogenicity of some ceramic fibers that are currently in use. Additionally, due to its low SiO2 content and its sol-gel based processing, the product does not lead to any cristobalite formation over time.The company reports that the performance of the installed refractories has been excellent, with many products progressing past the trial stage. Standard boards (500 x 400 x 50 mm) have found use in applications involving electric, gas and microwave furnaces. In addition to being lightweight (with densities in the 0.45 g/cc range), the boards are resistant to reducing environments (H2), as well as atmospheres containing glass vapors. Additionally, standard bricks are being produced in typical brick sizes for furnace construction.
In detailed thermal studies where the new insulation was used in place of bubble alumina brick in technical alumina firing applications at temperatures of 1650 degrees C (3002 degrees F) and higher, fuel cost reductions of 40% have been achieved. These reductions translate to savings of $36,000 per year for a small 1-cubic-meter (35-cubic-foot) kiln, which is standard for this industry. Higher production throughput due to faster firing cycles with the new refractories is another benefit.
Beyond insulation products, additional developments at Cellaris include lightweight components for combustion systems and kiln furniture for special atmospheres. Setter plates have been placed in service at several locations and are being tested under excellent ware-to-furniture ratios with promising results.
And these are only some of the possibilities. Gideon Grader, chief technology officer of Cellaris, says that the company's marketing activities have only scratched the surface. "The unique properties of Lite-Cell will make it advantageous in many different applications that haven't even been considered," he says. "There is likely a place for this material in most ceramic and metal processing operations."
For more information about Cellaris, contact the company at Bar-Lev Industrial Park, P.O. Box 15, D.N. Misgav, 20179, Israel; (972) 4-9551918; fax (972) 4-9551917; e-mail Gideon Grader, CTO, at grader@cellaris.com; or visit www.cellaris.com.
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