Four coals containing iron mineral pyrite (FeS2) and siderite (FeCO3) were combusted in a laboratory drop tube furnace at temperatures of 1300, 1450, and 1600 °C under oxidizing and reducing conditions. Results for the behavior of pyrite mineral were in agreement with the established literature. The behavior of siderite mineral was determined and comparisons made. Coals containing pyrite minerals were determined to have potential to produce ash deposition and slagging at lower temperatures than coals containing siderite mineral. Reducing conditions were determined to lower the temperature at which ash deposition and slagging may occur for coals containing iron minerals compared to oxidizing conditions. With respect to ash deposition and slagging, it was determined that the iron levels in a coal are not definitive, but rather the iron mineral type (pyrite or siderite), mineral association (included or excluded), degree of association of included minerals, and the type of included alumino−silicate minerals have important roles.

A model for the prediction of iron-based slagging precursors from the combustion of ironcontaining coals is detailed. The model accounts for the form of iron (pyrite or siderite), the distribution of iron within the pulverized coal, temperature, and oxidizing or reducing conditions. The input required for the model is a CCSEM analysis of the pulverized coal. For oxidizing conditions, the index predicts similar behavior for pyrite, and siderite-containing coals, with iron alumino-silicate ash particles becoming sticky at temperatures greater than 1400°C. This suggests that for oxidizing conditions, the extent of included iron minerals is the most important factor. For reducing conditions, the index predicts sticky ash particles are formed at lower temperatures, as low as 1000°C for pyrite-containing coals as a result of the decomposition and partial oxidation of pyrite-forming sticky particles, and 1100°C for siderite-containing coals. For reducing conditions, the level of excluded pyrite mineral for pyrite-containing coals and the level of included iron-containing minerals associated with clays for siderite-and pyrite-containing coals are the most important factors determining slagging.

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