Safe and Efficient Refractory Furnace Lining Solution
Dilllinger turns to low-biopersistent fiber to take advantage of benefits such as improved worker safety, reduced costs and little to no maintenance.
Lining iron and steel furnaces is critical in order to extend the life of the furnace and to protect the purity of the metals being heat treated. Therefore, choosing the best material to meet these needs is crucial. For many years, the first-choice material for the industry has been refractory ceramic fiber (RCF), also known as aluminosilicate wool (ASW), which can withstand the extreme temperatures within the furnace and features strong resistance to pollutants.
However, RCF comes with environmental, health and safety (EHS) concerns. After numerous studies, RCF was classified as a category 1b carcinogen in Europe and is considered a substance of very high concern (SVHC) under REACH (Registration, Evaluation, Authorization and Restriction of Chemicals).
There’s already pressure from European legislators to find safer alternatives; Under the Carcinogens Directive, where technically possible, substitutes to RCF should be used. RCF is currently under consideration for further regulation in Europe, which will make the use of RCF more difficult; constraints and stringent controls are likely to come into force.
These issues are compounded by the increasing commitment of major industrial companies and trade associations to improve “green” standards, placing the onus on the fiber industry to find alternatives that match the performance of RCF without adverse effects. Recently, successful trials have confirmed that Superwool® XTRA low-biopersistent (LBP) fiber delivers a viable alternative to RCF materials used in furnace linings.
Case in Point
Superwool XTRA has been extensively tested by Dillinger at its mill for heavy plates in Germany. Superwool XTRA is an alkali metal silicate fiber, especially combined to deliver a beneficial combination of RCF and LBP properties. It is resistant to high temperatures and pollutants, and is exonerated from any carcinogenic classification under nota Q of directive 97/69EC.
At Dillinger’s mill, as well as the pusher-type furnaces used for slab reheating, three shuttle kilns operate for ingot reheating and support of the pusher-type furnaces that are on maintenance or heavy load. This environment was chosen for testing because of the high temperatures and high levels of impurities in their atmospheres, including sodium, potassium, iron, and chromium. Over time, these impurities weaken the lining, leading to high shrinkage and surface degradation. In turn, this increases thermal conductivity and heat losses, often leading to damage of the furnace’s steel infrastructure.
A small section of wall in shuttle kiln No. 2 was selected for an initial feasibility test because the risk of any problems resulting in long downtime issues was considered to be low. Tested against the existing lining material used in this application, Superwool XTRA showed 50% less shrinkage compared RCF after six months of firing. Where the existing lining material was hard, full of cracks and had discolored noticeably into a dark brown, the surface of Superwool XTRA remained softer, with no surface cracks and little change in color.
This success led Dillinger to reline half of the roof of shuttle kiln No. 3 for further testing, with similarly positive results. The company has decided to switch entirely to the new Superwool XTRA grade due to the product’s non-regulated status and its superior chemical resistance and shrinkage performance relative to RCF.
Dillinger’s refractory maintenance department has since presented Superwool XTRA to the company’s EHS department as a working alternative to RCF. The key message in their presentation was that Superwool XTRA will reduce risks for workers while also reducing costs for installation, wrecking, and disposal. Additional benefits mentioned included little or no maintenance for the filling of any shrinkage gaps, as well as no reduction in insulating performance. As a result, Dillinger decided to set Superwool XTRA as its new standard, replacing the formerly used fiber product.
The demand from industry has been for a material that balances the performance of RCF with more stringent environmental safety. This is a significant challenge, because RCF has strong characteristics that make it ideal for use in chemical processing, iron and steel processing, and ceramic factories. For example, RCF is resistant to attack by alkai-based pollutants, which is something that needs to be considered when developing a viable alternative.
With a classification temperature of 1,450°C, Superwool XTRA offers a performance equal (or superior) to RCF. For example, the fiber expands when heated up to close shrinkage gaps at high temperatures; this is reversible, so the shrinkage gaps return and are visible when the fiber cools down. Once reheated, it expands again and closes the gaps. As a result, it is not necessary to fill shrinkage gaps with blanket (the normal practice for RCF). With 2% shrinkage, open gaps with RCF normally require an installer to fill these gaps with thin blanket, which is not only time consuming but more costly since additional material is required.
Another key benefit is that Superwool XTRA does not form crystalline silica, a common byproduct when many refractories are heated to high temperatures. Having a fiber that produces no crystalline silica enhances EHS compliance.
A Safer Alternative
EHS concerns are an increasingly important driver in terms of meeting legislative compliance, and Superwool XTRA has been shown to offer high performance alongside low bio-persistence and no formation of crystalline silica. From a commercial standpoint, the bigger benefit of this low-biopersistent fiber is that it matches—and even exceeds—the established performance of RCF.