Technical Paper

just glue mullite grains together with a weak matrix. These will, and do, perform different in application.

Laboratory testing to simulate corrosive reactions, as would be expected inside the unit, is not considered to be realistic. The best method is still to install test pieces in lower risk areas for proper evaluation. This is a strategy that most production managers are very reluctant to take as it is seen to convert a production unit into an experimental unit. However, if they only realise the benefits such a strategy can have on the overall advancement of performance. When making decisions about what materials can be trialed, it is always good to perform the basic alkali resistant testing in a laboratory to ensure the risk of installing something significantly worse is eliminated.

A basic rule for designing thermal oxidisers is to stay away/keep clear/do not use, metallic anchors. Many may not agree with this statement, but being primarily


Figure 10: Leucite (KAlSi2O6) skin around the large alumina silica grains caused by reaction with potassium. At low temperatures (900 - 1000°C) it does not form a liquid and result in expansion

the cheapest supplier. Figure 9 is a very good example of such a mistake.

In some cases XRD analysis would be used to quantify the amount of mullite. Nothing wrong with the concept, but it

still requires a very

good understanding of the microstructure of the material and where this mullite is situated within the microstructure. Some of our suppliers have progressed in manufacturing very good microstructural mullite bricks, whereas others


failure analysis, anchors would come up as number one problem. Previous articles were published

describing the risks with metal

anchors. Since the time I wrote that, something came along which I don’t believe many would have known or even guessed. Figures 11 and 12 show the result of the use of Inconel (high Nickel allow metal with an extreme high melting point) anchors in a silicon carbide

Figure 11: The result after using an Inconel anchor in a silicon carbide refractory material after only a few days of operation 22 ENGINEER THE REFRACTORIES May 2018 Issue

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