Back in the 1980s when I first started working in refractories, an old refractory foreman at Bethlehem Steel told me, “There are no bad refractories; you just put them in the wrong spot.” Now all these years later, I’ve come to realize he was right. There are no bad refractories … and 50 isn’t old.
In part 1 we covered classification of high-temperature insulation wool, and we will now discuss the application of same.
High-Temperature Insulation Wool (HTIW)
Industrial furnace engineering is undoubtedly one of the main applications for products made of ALSITRA and ALTRA® HTIWs. Compared to heavy linings made of dense, shaped and unshaped refractories, HTIW constructions feature key advantages both in the installation and operation of industrial furnaces.
- The lower weight of the HTIW products enables the construction of a steel structure to meet lower static requirements than for conventionally insulated industrial furnaces and installations.
- Smaller foundations can be incorporated in the design of the furnace.
- Handling and installation of the HTIW products is simpler and faster.
- Following installation, the furnace can be put into operation immediately because no drying times are required as, for example, in the case of concrete linings.
- Faster installation, repair and maintenance increase the availability and capacity of a furnace.
- The possibility of heating up and cooling down a furnace more quickly also increases its availability and therefore the productivity of an installation. This enables more flexible operation, including weekend shutdowns, and accordingly considerable savings in energy and labor costs (Fig. 1). An example is a forging furnace/shuttle kiln (Fig. 2) using Combi-Modules.
The theoretical furnace temperature is approximately 1250°C (2280°F), and the theoretical flue-gas temperature can exceed this considerably, reaching temperatures just below 1420°C (2560°F). This application clearly shows that, on account of the general operating conditions, the use of alumino-silicate modules with a classification temperature of 1400°C is not possible without incurring damage.
As explained earlier, the maximum application temperature of such a material is around 1200°C to maximum 1250°C. On a continual basis, no satisfactory furnace operation can be guaranteed with this material. In contrast, a lining with modules made of polycrystalline wool (PCW) are not acceptable because of the high capital investment. The optimal technical and economic solution is a combination of polycrystalline wool on the hot face and alumino-silicate wool on the cold face in the form of ALTRA/ALSITRA Combi-modules (Fig. 3, simplified view). An insulating thickness of the two HTIW materials optimally designed for the maximum application temperature and furnace parameters guarantees trouble-free and long-lasting operation of the furnace.
In addition to the ultra-lightweight modules made of HTIW for the roof and wall of industrial furnaces, new burner technologies (RECU burners, etc.) require the production of burner blocks from this material in order to ensure an integrated ultra-lightweight lining concept for the entire furnace – from wall/roof through the burner block to the insulation of the recuperator. The ALTRA burner block (ABB) or vacuum-formed KVS 164 burner blocks bring all the advantages of HTIW products to the burner blocks (Fig. 4). Advantages include:
- Same material (with equally good properties) in the burner block as in the wall and roof of the furnace
- Low weight (around 1/10) compared to conventional burner blocks made of refractory castables
- Easy installation (both for relining or repairs) to the walls and roof
- Possibility of a smaller size (cheaper) steel structure for the furnace
Roller-Hearth Furnace Applications
Besides being used as a refractory lining for the walls and roof of industrial furnaces, special products made of polycrystalline HTIW (ALTRA) are used increasingly in applications where the components are exposed to high thermomechanical loads. One example is roller-hearth furnaces in thin-slab casting plants (compact strip production – CSP).
Especially in the moving furnace sections – ferry transfer points (in tandem roller-hearth furnaces) – and for the insulation of the water-cooled transport rollers, in addition to being exposed to a thermal load up to 1350°C (2460°F) and chemical attack as a result of scaling, any insulation must withstand a considerable thermomechanical load caused by torsion and vibration. Torsion and vibration result in jolting caused by the movement of the ferry and the transport of the slabs through the furnace. These extreme conditions present challenges for the highly flexible, refractory HTIW material.
The side walls and roof of the roller-hearth furnace exposed to the high thermomechanical and thermal stresses at the ferry transfer points are insulated with polycrystalline HTIW modules (ALTRA Mod 72/140). The outstanding properties of this material, especially with regard to its resilience and flexibility even after many years of use in field conditions, make it predestined for use under such extreme conditions. Figure 5 shows the roof made of ALTRA Mod 72/140 in ferry transfer zone after a service period of more than two years. In other parts of the CSP-furnace with lower technical challenges, Combi-modules (ALTRA/ALSITRA) or ALSITRA 1400 modules are used as a less-expensive alternative.
The substantial and lasting energy savings and a considerable reduction in the running costs for maintenance and repairs of the rollers in this roller-hearth furnace could be achieved by the implementation of a customized and optimized lining and insulating system made of HTIW (in this case, ALTRA Mod 72/160) for the water-cooled transport rollers.
The use of prefabricated HTIW modules (ALTRA Mod 72/160), which are fitted between the support/carrying rings, results in numerous advantages.
- High energy savings of up to 30% compared to conventional linings on the basis of lightweight castables (depending on the geometry and the operational mode of the furnace).
- Much shorter installation time for the insulation of the rollers thanks to prefabricated modules.
- The rollers can be used immediately after fitting of the insulating material (i.e., without further treatment necessary – no drying, no tempering, no firing, no hardening, etc.).
- Better durability and longer service lifetime of the HTIW insulation compared to materials based on lightweight castables.
The combination of all these advantages results in considerable savings in primary energy, a reduction in the associated CO2 emissions, lower costs for maintenance and repairs, and less downtime.
An increase in the plant availability and the efficiency of the plant, an improved and more consistent product quality and a lower cost of the overall production process confirm the effectiveness of ALTRA Mod 72/160, Combi Mod (Altra/Alsitra) or Alsitra 1400 Mod insulating materials produced on the basis of HTIW.
With regard to the enormous technical developments in the construction of industrial furnaces and the energy savings that have only been made possible thanks to the application of high-temperature insulation wool products in different industrial sectors, thermal insulation for progressive companies with state-of-the-art processes and temperatures exceeding 900°C (1650˚F) would be unthinkable without these materials.[7,8]
Adopting an integrated approach, especially with consideration of technical, economic and environmental aspects, it becomes clear why HTIW products have become indispensable for industry and thermal-process engineering.
The many advantages of these products with regard to the consumption and saving of primary energy, investment cost, plant availability and operational reliability, help safeguard and strengthen the competitiveness and production base of the user industry.
- Routschka, G., Feuerfeste Baustoffe, Essen: Vulkan Verlag, 1997
- VDI-Richtllinie 3469 ”Emissionsminde - rung – Herstellung und Verarbeitung von faserhaltigen Materialien – Hochtempe – raturwollen,” Blatt 5, 03/2007
- DIN EN 1094
- Technische Regel für Gefahrenstoffe 619, ”Substitution für Produkte aus Alumini-umsilikatwolle (TRGS 619),” Ausgabe February 2007
- Sonnenschein, G., Werkstoffe zur Wär - medämmung unter Berücksichtigung des Einsatzes von Keramikfasern; Gefahr - stoffe Reinhaltung der Luft, 5/2003
- Wimmer, H., ”Hochtemperaturwolle, Vernachlässigte Innovation im Feuerfest-bau”, Gaswärme 5 (2004)
- Mendheim, J., Refractory Materials in Ceramic Kiln Construction: Past, Present, and Future CN Refractories Vol. 5/2001
- Klinger, W., ”Moderne Wärmedämm-stoffe im Industrieofenbau;” Fachtagung der Deutschen Gesellschaft für Feuer-fest- und Schornsteinbau, Düsseldorf; 6/2003