Refractory Ceramic Fiber: The Refractory “PC”
For industrial refractory technology, a strong case can be made that refractory ceramic fiber (RCF) and its subsequent derivatives – such as low bio-persistence fibers (LBP) – may be viewed as the industrial equivalent of the personal computer for owners and operators of high-temperature thermal-processing equipment.
The invention of RCF recently celebrated its 70th anniversary. A simple experiment that involved exposing a molten mixture of alumina and silica to air pressure with the intent of creating a “bubbled” refractory instead gave way to white, fluffy fibers. J.C. “Charlie” McMullen, a research engineer with Carborundum Company (now Unifrax I LLC) in Niagara Falls, N.Y., who was conducting this experiment, is generally credited with inventing these fluffy fibers that are now commonly referred to as RCF (Fig. 1).
Over the next two decades, many advances in fiber production methods and expanding product forms brought RCF to market, which then began to displace traditional refractories and other insulation materials in many applications. The inherent physical properties of RCF, such as low heat storage and low heat loss along with significant weight reductions, resulted in substantial benefits for users of industrial furnaces.
The use of RCF has resulted in the savings of millions of dollars in energy costs along with the associated reduced carbon footprint. Today, this material is also commonly used in automotive pollution-control assemblies and passive fire protection. The net result is that this relatively innocuous invention at the time, has made our world a greener, cleaner and safer place to live today.
Greener Process Operation
The use of RCF as a replacement for traditional dense refractories provides significant energy savings and reduced greenhouse-gas (GHG) emissions. It stands to reason that complete replacement of dense refractories with an RCF product form provides the most savings in this regard. Using RCF as backup insulation or as a hot-face veneer over an existing refractory lining, however, affords significant energy savings as well.
Product and installation advancements such as Foamfrax® technology and specialized materials such as the Silplate® technology platform provide a means for end users and installers to apply the unique thermal properties of RCF for use in common high-temperature industrial applications. Figure 2 indicates the potential energy savings by incorporating RCF in some capacity into a refractory system. Regardless of the method employed (full thickness, backup or veneer), the net result is an energy-saving, greener operation of high-temperature industrial process equipment.
With increased emission standards for combustion engines, ceramic-based catalytic converters have become a standard component of almost all exhaust systems. Exhaust temperatures commonly reach a point where a ceramic material is required to insulate the various metallic components of the exhaust system. Specific material and product forms have been engineered that incorporate RCF in order to solve these challenging applications. The most common application in this regard is a ceramic mounting mat around the catalytic converter that provides a tight seal to force the pollutants through the catalytic converter. The mat also provides thermal insulation for the surrounding metallic components (Fig. 3).
RCF furnace linings significantly reduce heat loss through furnace walls and, therefore, reduce cold-face temperatures providing a more comfortable and safer working environment. RCF and LBP product forms have been successfully tested and qualified for use in passive fire-protection applications common to everyday life. Examples of these are grease ducts found in commercial food preparation and ventilation air ducts in commercial buildings/apartments, marine vessels and railroad tank cars (Fig. 4).
Greener, Cleaner, Safer
Seventy years after Charlie McMullen’s original invention of RCF, Unifrax is supplying and manufacturing many different types of inorganic specialty glass fibers. These inorganic specialty glass fibers differ in chemistry and/or product form, but all have the same fundamental end-user benefits that have been outlined. Through innovation and understanding our customer’s requirements, Unifrax is providing solutions using inorganic specialty fibers that help save energy, reduce pollution and improve fire safety. IH
For more information: Contact Brian Bradley, Sr. Engineering Manager, Furnace Related Products or Virginia Cantara, Manager, Marketing Communications for Unifrax I LLC, 2351 Whirlpool Street, Niagara Falls, NY 14305; tel: 716-278-3800; e-mail: firstname.lastname@example.org; web: www.unifrax.com
Thermal Management Solutions: Save Time, Save Energy
Both Foamfrax® and Silplate® technologies provide customers with specialized materials and installation advancements that save time and energy.
Foamfrax insulation is a monolithic insulation system used to insulate metal, refractory or ceramic-fiber surfaces at temperatures up to 2800˚F (1538˚C). A principle application of Foamfrax insulation is to insulate or upgrade the efficiency of a deteriorated furnace lining. Installation rates in excess of 1,000 board-feet/hour dramatically reduce downtime, and have provided substantial improvements in thermal performance, furnace efficiency and energy costs in numerous applications (Fig. 5).
The Foamfrax installation process combines the bulk fiber material with the inorganic and organic binders in a patented mixing mechanism. The fibers and binders are combined within the mixing chamber to create a homogeneous foam/fiber mixture that is gunned onto the target surface using the Foamfrax installation machinery. The interlocking network of fibers provides a strong, uniform monolithic structure having excellent thermal-insulating properties, low heat storage, excellent resistance to thermal shock and good chemical resistance.
Silplate structural insulation board – a unique product withrevolutionary characteristics – is able to withstand high temperatures, has high compressive strength, resists attack by molten metal and maintains low thermal conductivity (Fig. 6). Its physical properties do not change, even under the highest operating temperatures, ensuring physical stability to the complete refractory system. Silplate Mass 1500 is an extension of the Silplate family of high-temperature, fiber-based insulation products. This product is a hot-face coating material for use over fiber modules, castables and refractory bricks for application at temperatures up to 2732˚F (1500˚C). It may be applied on fiber lining systems as well as hard refractory surfaces. Benefits are increased abrasion resistance and durability, protection from shrinkage and/or chemical attack, minimizing heat loss and overall energy efficiency.
These high-performance products save both time and energy while providing ideal solutions for a variety of demanding applications.
Fig. 5. Foamfrax insulation
Fig. 6. Silplate board application