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Technical Paper
Figure 8: Another example of high alumina bricks used in an alkali rich environment where temperatures above 1300°C were experienced. Even though slag did not form the mineralogical change from α to β- alumina caused serious damage to the refractory lining
the lining from gas penetration into the brick or lining. Figure 6 is an example of an area where the environmental conditions are the same for the two materials used, compared to Figure 7 where a definite change in conditions occurs over a very short distance in the oxidiser.
By far the biggest problem in the industry is that even till this day, people select refractory materials for the aggressive and corrosive environment in waste incinerators, based on the alumina content. Generally there is some logic to increase or decrease the alumina content based on the temperature in order to allow glass of a certain viscosity to form. However, refractories are not single component systems. It consists of grains, sometimes various types, and a matrix, keeping it all together. A high alumina grain will react completely different to a low alumina matrix and vice
versa. Natural
impurities
concentrated in the grains will react completely different to the corrosive environment than the same amount of impurities in the matrix. It is, therefore, of little use to specify materials on alumina content and based a purchase on
May 2018 Issue
Figure 9: Laboratory testing to simulate alkali attack is not nearly as efficient as inserting test samples in the unit. This image is an example of the massive difference between the old bricks and a test brick from a different quality
ENGINEER THE REFRACTORIES 21
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