Effects of alternate fuels. Report No. 3. Analysis of high-duty fireclay refractories degraded by residual oil combustion products

Abstract

High-duty fireclay brick (approximately 39 wt% Al/sub 2/O/sub 3/) used for only six months in the soot hopper of a residual-oil-fired steam boiler, where the refractory operated at about 1400/sup 0/C was analyzed. The refractory loss of this firebrick was about 30 mm and the reaction zone in the firebrick extended to a depth of 80 mm toward the brick cold end. The rate of the refractory material loss was 5 mm/month and the reaction zone front proceeded at a rate of 18 mm/month. In a natural-gas-fired boiler, this type of refractory has a typical service life of three years. The service time of the refractory was drastically shortened by reactions involving firebrick constituents with sodium and vanadium derived from the fuel oil plus calcium and magnesium from the fuel oil additives. Four principal reactions between the impurities derived from residual fuel oil and oil additives and the high-duty firebrick during service were identified. Both sodium and vanadium played an important role in the refractory degradation. The magnesia- and dolomite-based additives used in the fuel oil for retarding metal boiler tube corrosion did not impede the refractory corrosion. Zircon and corundum phases in the firebrick appear inert to reactions withmore » fuel oil impurities and additives. Increasing the aluminia content of the refractory may produce a more viscous glassy phase to reduce fuel oil impurity-refractory reaction rate and/or introduce more corundum into the refractory to increase its resistance to fuel oil impurity corrosion.« less