Petroleum coke combustion is different from coal and its behaviour in an FBC environment clearly illustrates this. Analysis of bed ash from the CFBC boilers owned and operated by the Nelson Industrial Steam Company Ltd. (NISCO) was examined in detail to determine the fate of calcium in the ash using a range of techniques. These analyses have shown a free lime content, which is significantly lower than expected based on the elemental analysis of the bed material. Using different methods of analyses than have been typically used for FBC ashes (coal in particular) it would appear that between 6 to 7% of the total CaO in the samples is combined in the form of acid soluble and insoluble other calcium compounds (OCC). This translates to about 30% less free lime (depending on the ash sulfur content) in the sample than would be calculated based on a standard chemical analysis of the bed ash. This current work has identified about 1% of the missing CaO in the form of acid insoluble Ca and Mg vanadates with perhaps as much as 2% of the remaining missing CaO present as soluble OCC.

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