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Unusual slag formation

Q: We recently ran into unusual slag buildup problems in a No. 6 fuel oil-fired utility boiler. The fuel oil contained 20-40 ppm of silica and alumina. Can you point me to references or information on the effect of Si and Al on slag formation? The dominant slag forming species are vanadium oxides and sulfur oxides (SO₂, SO₃)?

A: Slag formation occurs due to accumulation of inorganic materials such as vanadium pent oxide, alumina or silica. This is due to presence of vanadium, aluminum or silicon in the fuel oil. Presence of sulfur does not contribute to slag formation from my experience. However, it does contribute to corrosion and pollution. My suggestion for you is to have the slag analyzed for its constituents. I don’t have any published references on this subject.