THE RELEASE OF IRON DURING THE COMBUSTION OF ILLINOIS NO-6 COAL

A series of investigations of iron release during the combustion of an Illinois No. 6 coal are reported. Experimental measurements are described in which 40% - 70% of the iron in the coal is released within a 25-ms period immediately following coal devolatilization. This iron release dominates the evolution of all other inorganic elements in this coal (excluding sulfur) on a mass basis. The release is consistently observed in controlled combustion environments over a particle size range from 75 to 125-mu-m and a gas oxygen concentration range of 6%-12%. Statistical uncertainty of the results is also reported and is small compared with the measured effect. Further experiments and analysis were conducted to determine the mechanism of iron release. Forms of iron with sufficient volatility to explain the results as a vaporization process were investigated. None was found that could reasonably be expected to form under the experimental conditions. Further experimentation suggests that the mechanism is related to the chemical reactivity of the iron species with oxygen and that the release proceeds through the chemical formation of an iron fume.