Wasted heat energy means wasted dollars. This is why effective heat management is of the upmost importance when manufacturing high-temperature applications. Ultimately, as temperatures and process requirements increase, so does the demand for insulation products which stand as the major solution to heat energy loss.
Several factors must be taken into into consideration when choosing an insulating system, including up-front investment, insulation efficiency, energy savings, productivity, lifetime, and health, safety and environment (HSE) compliance.1Advancements in the insulation industry have led to the development of systems that use ceramic foam, such as Norfoam® by Saint-Gobain. Ceramic foam insulation provides solutions to the issues mentioned above, and thus is thought to be advantageous over conventional high-temperature insulating materials, such as insulating brick and ceramic fiber.
Refractory insulation brick, otherwise known as insulating firebrick (IFB), are traditionally used for the insulation of temperatures ranging from 1,260-1,840 °C. In general, the insulating performance of IFBs improves as the silica content of the brick increases. Unfortunately, this can negatively impact refractoriness, chemical inertness and mechanical strength of the brick, which in turn significantly restricts the use of the product in extreme environments. As insulating firebrick are machinable, any shape or design can be created using the appropriate tooling. However, because brick can be extremely abrasive towards machinery, this process is usually much more difficult than that of fiber-based products.
Refractory Ceramic Fiber
Refractory ceramic fiber (RCF), which provides effective thermal resistance, efficiency and shock resistance, has been used for insulation since the early 1950s. Unlike refractory brick, RCF is a fiber, and therefore can easily be manufactured to form any shape or design.
However, the use of RCFs for high-temperature insulation does have several limitations. For example, individual fibers tend to be mechanically weak and thus are sensitive to gas ablation. This results in fine fiber contamination that can impact downstream equipment as well as the finished product. Additionally, RCF material shrinks and crystallizes over time, producing degradation of thermal performance as the abutments of the installation widen and create thermal bridges. Finally, RCFs can be dangerous to humans and are carcinogenic under in some environments.2 The health risks associated with fibrous ceramic materials are in no doubt extremely serious and have led to strict regulations and restrictions of their use.
Figure 1. 3-D X-ray tomography of the ceramic foam.
Figure 2. Microstructure of ceramic foam (a) and fiber (b).
In light of such concerns, new bio-soluble alkaline earth silicate (AES) fibers have been developed as an alternative to conventional RCF. However, it must be considered that their composition limits their use to temperatures below 1,250 °C.
The ceramic foam is straightforward to manufacture and can be machined on-site with typical dry cutting tools or even a common wood saw. In contrast to fibers, cutting NorFoam does not release dangerous dust and hence does not require any use-restrictions. In addition, ceramic foam products can be machined with high precision. This produces very high-quality installation and further improves the furnace’s thermal efficiency.
Figure 4. Comparative thermal conductivity of ceramic foams, IFB and type 184/400 fiber.