Energy costs may fluctuate up and down in the short term, but no matter which direction they are currently trending, wasted heat energy means wasted dollars. The pursuit of manufacturing excellence in high-temperature applications necessitates a focus on effective heat management. As temperatures and process requirements increase, so does the demand on the high-temperature insulation solution.
OEMs, installers and end users searching for insulating systems are looking for a middle ground that meets all of their needs. Considerations such as up-front investment; insulation efficiency; energy savings; productivity; lifetime; and health, safety and environment (HSE) compliance must all be taken into account.1 New ceramic foam insulation can address these issues, offering advantages over traditional high-temperature insulating products.
Traditional Insulating Refractory Brick
Refractory insulation brick, also called insulating firebrick (IFB), are traditional products for high-temperature insulation. The composition of these products varies and directly impacts their performance. The most commonly used insulating firebrick are used in temperatures ranging from 1,260-1,840°C. The type of brick required depends on a number of parameters, including insulating capability, refractoriness, mechanical strength and chemical inertness.
In general, as the silica content of the brick increases, its insulating performance improves. This unfortunately has a negative impact on the other three parameters (refractoriness, chemical inertness and mechanical strength), which can severely limit the applications of the product in extreme environments. Insulating firebrick are machinable, and any shape or design can be manufactured using the appropriate tooling. However, it generally takes more effort to machine brick than fiber because of the high abrasion ability toward the machining tool.
Refractory Ceramic Fiber
The use of refractory ceramic fiber (RCF) began in the early 1950s in industrial kilns. As a furnace lining, RCFs provide high thermal resistance, efficiency and shock resistance. As the material is a fiber, it can be readily formed into shapes that may be more difficult to achieve with refractory brick.
However, RCFs do have some limitations. Since the material is in a very fine fiber form, the individual fibers are mechanically weak and therefore sensitive to ablation by the gas. The result is a fine fiber contamination that can damage both downstream equipment and the finished fired product. In addition, through the lifetime use of a RCF installation, the material will continue to crystallize and shrink. The result is a degradation of thermal performance as the abutments of the installation widen and create thermal bridges.
The last and most important limitation is the health risk associated with fibrous ceramic materials. RCFs are considered to be harmful to humans and probably carcinogenic under certain conditions,2 which is leading to stricter regulations. To address these concerns, bio-soluble alkaline earth silicate (AES) fibers have been developed. These new fibers are an EHS-compliant alternative, though their composition limits their use to temperatures below 1,250°C.
New Ceramic Foam
To address the market needs for a high-performing, easily formable and health-friendly alternative, Saint-Gobain has developed NorFoam® ceramic foams. The new ceramic foam can offer a credible and efficient alternative to current solutions for temperatures above 1,250°C. The ceramic foams do not contain any fiber material or organic binders and consequently are HSE-friendly in use and application. They are currently available in different formulations specifically designed to address various high-temperature applications and needs.
A patented direct foaming process allows the production of the ceramic insulation foam from a wide range of materials, including alumina, mullite, cordierite and zirconia. It can also be easily extended to non-oxide materials such as silicon nitride or silicon carbide. The process is capable of producing board shapes with thicknesses of up to 150 mm, enabling simplified lining designs and efficient installations.
NorFoam has been designed to offer potential alternatives for replacing both refractory insulating brick and ceramic fiber. It is possible to use the foam where traditional fibers are used, as NorFoam exhibits excellent machinability, as well as alkaline and abrasion resistance.
Thanks to its engineered microstructure, the ceramic foam offers advanced properties, insulating capability, thermal shock resistance and high purity compared to insulating firebrick and refractory fibers.3 Figure 1 shows the microstructure of the foam produced by Saint-Gobain. Its microstructure was engineered to provide excellent insulating performance at high temperature while maintaining sufficient mechanical strength and dimensional stability. The complex architecture of the foams influences their thermal and mechanical properties.
Compared to refractory fibers, the ceramic foam is 100% fiber free (see Figure 2). Traditional refractory brick are also fiber free, but they suffer from much greater densities and significantly lower thermal performance. Installations using the ceramic foam require no special equipment to protect workers, the workspace or the environment from contamination from potentially dangerous fibers. This is especially true during a relining operation, where the used ceramic fiber is particularly hazardous because it is in an extremely weakened state from its lifetime in the furnace.
In addition, the ceramic foam products can be handled like brick, using mortar to join them, and require no special disposal. Shape and design opportunities would even allow using fixing systems that are usually used for fiber.
The ceramic foam is easier and faster to install compared to traditional IFB, as it is lighter and available in larger dimensions. Consequently, maintenance outages, relining or repairs can be made much faster and with less physical impact on the operating staff who are performing the installation.
Safe for the Environment
From production process to end of life, the ceramic foam causes less of an environmental impact than traditional materials. The NorFoam process is based on a food-grade system and is constituted of high-purity mineral grains. Consequently, the foam can be recycled or disposed of as conventional waste with moderate disposal fees, compared to the high costs required for fiber dumping.
Ease of Handling/Shaping
The ceramic foam can be easily machined on site with conventional dry cutting tools or even a common wood saw. Contrary to fibers, the cutting of NorFoam does not release hazardous dust and therefore does not require specific confining processes.
Due to its strong cohesion, the ceramic foam product can be machined with high precision tolerances and very complex designs. The result is an excellent fit and finish to the installation, further increasing the furnace’s thermal efficiency (see Figure 3).
The thermal conductivity and high temperature resistance of refractory insulation products are, of course, a primary performance factor for the selection of such products. Ceramic foams achieve thermal performance approaching that of ceramic fiber without sacrificing the convenience and long-term performance of a rigid brick (see Figure 4). This drastic increase in thermal performance vs. IFB allows a furnace to simultaneously lower its thermal mass and decrease its waste heat, resulting in faster ramp-ups, better temperature control, and reduced energy costs.
Ceramic foams are replacing traditional products in heat treatment and sintering furnaces for technical ceramic products, as well as in metallurgy and glass applications. For example, NorFoam XPure is running in a furnace at 1,500°C under pure nitrogen to replace mullite insulating brick. Initially lined with lightweight mullite insulating product, the alkalines released from the fired load reacted with the mullite insulation and caused severe damage of the backup layer, resulting in dangerous hot spots on the furnace’s steel shell. Following replacement of the hot face with the ceramic foam, the furnace shell temperature was reduced and no damage to the first and second refractory layer has occurred.4
The low-mass inertia of the ceramic foam product enables better temperature control of the kiln and faster heating/cooling ramps, providing a measurable productivity gain compared to traditional brick linings. In addition, installation time for the ceramic foam is shorter than the existing mullite solution. Consequently, NorFoam is actively participating to reduce maintenance efforts and costs while reducing downtime and energy consumption, leading to more stable operations, higher planning and process availability, and positive energy management.
The mechanical strength and lightweight nature of the product makes it increasingly attractive for use as setters or spacers for firing a multitude of products. Once in use, users are reporting a faster ramp rate and more homogenous temperature in the reactor, as well as reduced energy consumption. The advanced machinability of the ceramic foam associated with its mechanical strength helps to overcome critical design and operation issues of reactor parts.
The new ceramic foam products excel in applications for the metallurgy industry due to their excellent resistance to molten metals. Currently, reheating furnaces are mainly lined with insulating monolithics and fiber modules. Scale dust, atmosphere impurities, and alkalis coming from the burners attack these linings, causing aging and premature failure. Due to their intrinsic stable properties, ceramic foams prevent this premature wear. In the petrochemical industry, high chemical inertness, high specific area and pore interconnection are often requested, making the ceramic foams an option to be used in installations with catalytic reactions.
Ceramic insulating foams can provide a solution for those looking to replace refractory fibers or refractory insulating brick, whether in existing equipment or new installations. By advancing the properties and performance of the process, the new ceramic foams are able to exceed the application requirements and deliver savings in terms of operational, maintenance, and health safety costs. Among other qualities, their optimized insulating characteristics, ease of use, and fiber-free nature means that the applications where ceramic foams are used to replace fiber or insulating brick are increasing rapidly and drawing a very positive outlook of this innovative material for the future.
1. “High Temperature Insulation Materials Market–Global Trends & Forecast to 2019,” www.marketsandmarkets.com.
2. Regulation EC 1272/2008.
3. San-Miguel, L. and Schumann, M., “Fiber Free Ceramic Insulation Foam for Extreme Temperatures–A New Generation of HSE Friendly Refractory Products with Multiple Application Possibilities,” Refractories World Forum, August 2017 .
4. Roulet, F.; San-Miguel, L.; and Schumann M., “Refractory Ceramic Foam–High Temperature Insulation Solution with Potential,” DKG Jahrestagung & Symposium Hochleistungskeramik, Freiberg, Germany, March 2016.
This article was originally posted on www.ceramicindustry.com.