Company News THE FUTURE OF KILN LINING FIBRES Lining iron and steel furnaces is critical 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 RCF, which can withstand the extreme temperatures within the furnace and has strong resistance to pollutants.
However, RCF has 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,
Restriction of Chemicals). There’s
already pressure Authorisation and 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
with constraints and stringent controls likely to come into force.
This is compounded by the increasing commitment of major industrial companies and trade associations to improve ‘green’ standards, placing the onus on the fibre industry to find alternatives that match the performance of RCF without adverse effects.
Backed by almost 10 years of research and development and more than 30 months in trials at customer furnaces, the Thermal Ceramics business has launched Superwool® XTRA, a material that delivers the performance of RCF without the inherent EHS risks associated with it.
Since the 1990s, the Superwool® brand has been a mark of quality in creating low bio- persistent (LBP) fibres that minimise health risk to furnace installers, operators and other factory employees. Major advances have been achieved in the performance of LBP fibres through Superwool® HT™ and Superwool® Plus™ grades. The evolution of the Superwool® family of materials has been recognised with the Queen’s Award for Enterprise: Innovation (2003), as the insulating fibre experts have continued to innovate to meet – and anticipate – market demand.
This demand is now for a material that balances the performance of RCF with more stringent environmental challenge,
safety. This is a significant because RCF has really strong 12 ENGINEER THE REFRACTORIES
characteristics that make it ideal for use in chemical processing, iron and steel processing and ceramics factories. For example, RCF is very resistant to attack by alkai-based pollutants, something that needs to be considered when developing a viable alternative.
That’s why, in recent years, the focus at the Fibre Centre of Excellence in Bromborough, UK has been to challenge the assumptions in LBP chemistry. Rather than keep trying to make marginal gains in LBP performance, the approach was flipped, and the RCF itself was revisited. The industry needs an RCF equivalent that has low bio-persistence, so that’s how development was approached.
Superwool® XTRA is an Alkali Metal Silicate fibre, especially
combined to deliver the
optimum combination of RCF and LBP properties.
when many refractories are heated to high temperatures. Having a fibre that produces no crystalline silica is a major breakthrough for the industry, which enhances EHS compliance.
A Class of Its Own Superwool®
XTRA has been extensively
tested by Dillinger, at its mill for heavy plates in Germany. At the mill, as well as the pusher type furnaces used for slab reheating, three shuttle kilns are existing for ingot reheating and for support of the pusher type furnaces 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. This in
turn A Different Fibre
Superwool® XTRA delivers the strength that industrial applications need, both in terms of its resistance to high temperatures and pollutants, but also its improved EHS credentials.
With a classification temperature of 1450°C, Superwool® XTRA offers a performance equal – and in many cases superior – to RCF. The fibre is unusual in that it expands when heated up to close shrinkage gaps at high temperatures, this is reversible so when it cools down the shrinkage gaps return and are visible. Once heated again it expands and closes the gaps again.
This means there is no reason to fill the shrinkage gaps with blanket – the normal practice for RCF. With a 2% shrinkage, open gaps with RCF normally require an installer to fill these gaps with thin blanket, this is not only time consuming but more material is required adding to costs.
In terms of EHS qualities, Superwool® XTRA is exonerated from any carcinogenic classification under nota Q of directive 97/69EC.
A key benefit is that Superwool® XTRA does not form crystalline silica, a common by-product
increases thermal conductivity and
increases heat losses and often damage to the steel infrastructure of the furnace.
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
used in this application, after six months of firing, Superwool® XTRA showed 50% less shrinkage compared RCF. Where the existing lining material was hard, full of cracks and had discoloured noticeably into a dark brown, the surface of Superwool® XTRA remained softer, with no surface cracks and there was little change in colour. This proves that the material is
outperforming existing RCF solutions in environments with high pollutant levels.
This success led the customer to reline half of the roof of shuttle kiln No. 3 for further testing, with similarly positive results. The customer has now decided to switch entirely to the new Superwool® XTRA grade, for the benefit of both the non-regulated status of this product and its
superior chemical resistance shrinkage performance, relative to RCF.
The refractory maintenance department has since presented Superwool® XTRA to Dillinger’s EHS Department as a working alternative to
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