Study of effect of oxycoal combustion conditions on fly ash characteristics

The composition and morphology of fly ash produced by the combustion of pulverised coal are determined by source, rank of the coal and combustion conditions. Fly ash samples generated from four bituminous coals under air coal and oxycoal combustions in a pilot scale test facility have been studied using scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. Results show that temperature is the dominant parameter in determining fly ash morphology. It has been found that once oxycoal combustion thermal conditions are matched to those in air coal conditions, fly ashes have similar shape (with standard deviation of 0.02), size (with standard deviation of 2 mm) and morphology in comparison to those from air coal combustion. Oxygen enrichment shows insignificant effect in comparison to temperature on the shape and size of fly ash particles. A variety of particle shapes, such as plerospheres, cenospheres and ferrospheres, have been observed in all the samples. The results from this study suggest that particulate control systems used in air coal conditions could still be employed for oxycoal process provided that they have similar surface chemistry and the fly ash formed is still saleable to industries.