Using Low Bio-Persistent (LBP) Fibers for Kiln Linings

To extend the life of a furnace and to protect the purity of the metals being heat treated, lining iron and steel furnaces is crucial. So selecting the best material to meet these requirements is critical. The first-choice material for the industry has been RCF for a number of years, which has strong resistance to pollutants and can withstand the extreme temperatures within the furnace.

Yet, RCF has environmental, health and safety (EHS) concerns. As a result of a number of 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, Authorisation and Restriction of Chemicals).

There is mounting pressure from European legislators to discover safer alternatives. Substitutes to RCF should be utilized under the Carcinogens Directive, where it is technically possible. RCF is presently under consideration for further regulation in Europe, with constraints and stringent controls likely to come into force, the utilization of RCF will become much more difficult.

This is compounded by the growing commitment of trade associations and major industrial companies to improve ‘green’ standards, placing the responsibility on the fiber industry to acquire alternatives that match RCFs performance without adverse effects.

Backed by nearly 10 years of research and development and over 30 months in trials at customer furnaces, Superwool® XTRA has been launched. It is a material that gives the performance of RCF without the inherent EHS risks associated with it.

Reinventing RCF

The Superwool® brand has been a mark of quality in creating low bio-persistent (LBP) fibers that minimize health risk to furnace operators, installers, and other factory employees since the 1990s. Huge advances have been achieved in the performance of LBP fibers using Superwool® HT™ and Superwool® Plus™ grades.

The evolution of the Superwool® family of materials has been recognized with the Queen’s Award for Enterprise: Innovation (2003), as insulating fiber experts have continued to innovate, anticipate, and meet market demand.

Today, the demand is for a material that balances RCFs performance with more stringent environmental safety. This is an exceptional challenge, because RCF has strong characteristics that make it perfect for utilization in ceramics factories, chemical processing, and iron and steel processing. RCF is extremely resistant to attack by alkali-based pollutants for example, which is something that should be considered when developing a viable alternative.

At Morgan Advanced Material’s Fibre Centre of Excellence in Bromborough, UK, the main aim has been to challenge the assumptions in LBP chemistry. Instead of trying to make marginal gains in LBP performance, RCF itself has been revisited. What the industry needs is an RCF equivalent with low bio-persistence, so that’s how development has been approached. Superwool® XTRA is an Alkali Metal Silicate fiber, chiefly combined to provide the optimum combination of RCF and LBP properties.

A Different Fiber

Superwool® XTRA provides the strength that industrial applications require, both in terms of its resistance to pollutants and high temperatures, but also its better EHS credentials. Possessing a classification temperature of 1450°C, Superwool® XTRA gives a performance equal – and in many cases superior – to RCF.

The fiber is extraordinary because it expands when heated up to close shrinkage gaps at high temperatures, this is reversible so that when it cools down the shrinkage gaps return and can be seen. Once reheated it expands and closes the gaps again.

Using this method there is no reason to fill the shrinkage gaps with blanket, which is the typical practice for RCF. With a 2% shrinkage, open gaps with RCF usually need an installer to fill these gaps with thin blanket, which is not only time consuming but more material is needed, which adds to the costs. In terms of EHS qualities, Superwool® XTRA is exonerated from any carcinogenic classification under nota Q of directive 97/69EC.

One of the key benefits of Superwool® XTRA is that it does not form crystalline silica, a common by-product when a number of refractories are heated to high temperatures. Having a fiber that generates no crystalline silica is a huge breakthrough for the industry, which enhances EHS compliance.

A Class of its Own

Dillinger, at its mill for heavy plates in Germany, has extensively tested Superwool® XTRA. At the mill, in addition to the pusher type furnaces used for slab reheating, three shuttle kilns are present for ingot reheating and for support of the pusher type furnaces on maintenance or heavy load.

This environment was selected for testing due to the high temperatures and high levels of impurities in their atmospheres, including potassium, sodium, chromium and iron. These impurities weaken the lining over time, resulting in high shrinkage and surface degradation. This consequently heightens thermal conductivity and increases heat losses and frequently, damage to the steel infrastructure of the furnace.

A small section of wall in shuttle kiln no. 2 was chosen for an initial feasibility test, because the risk of any problems resulting in long downtime issues was seen to be minimal. After six months of firing, Superwool® XTRA showed 50% less shrinkage compared RCF, when tested against the existing lining material used in this application.

Where the existing lining material was hard, full of cracks and had discolored noticeably into a dark brown, the surface of Superwool® XTRA stayed softer, with no surface cracks and there was minimal change in color. This proves that, in environments with high pollutant levels, the material is outperforming existing RCF solutions.

The success of this test led the customer to reline half of the roof of shuttle kiln No. 3 for further assessment, with similarly positive results. The customer has now chosen to switch completely to the new Superwool® XTRA grade, for the benefit of both the non-regulated status of this product and its superior chemical resistance and shrinkage performance, relative to RCF.

The refractory maintenance department has since presented Superwool® XTRAto Dillinger’s EHS Department as a working replacement to RCF. The key messages in their presentation were that Superwool® XTRA would decrease risk for workers whilst minimizing costs for installation, wrecking and disposal.

There are extra benefits in no or small amounts of maintenance for the filling of any shrinkage gaps and no reduction in the insulating performance. Dillinger decided to set Superwool® XTRA as their new standard as a result of this, replacing the formerly utilized Cerachem® Fibre. This example confirms the capabilities of Superwool® XTRA.

In terms of meeting legislative compliance, EHS concerns are an increasingly important driver. Superwool® XTRA gives exceptional performance together with low bio-persistence and no formation of crystalline silica.

From a commercial standpoint, the bigger benefit of this breakthrough in LBP is that it equals, and even surpasses, the established performance of RCF. Superwool® XTRA is the future for applications which require high temperature fibrous insulation.

This information has been sourced, reviewed and adapted from materials provided by Morgan Advanced Materials.

For more information on this source please visit Morgan Advanced Materials.

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