Environmental impact of mineral transformations undergone during coal combustion

The mineral transformations undergone by high sulfur coal ash were studied. An X-ray diffraction (XRD) experiment was carried out to reproduce experimentally the mineral transformations produced during coal combustion in coal-fired power stations. We have verified that the anhydrite is the main crystalline phase that contains sulfur in the solid combustion waste from 500°C until its decomposition at 1060±10°C. Thus, this calcium sulfate is the main crystalline phase involved in the sulfur retention in the combustion wastes at high temperatures. Therefore, a considerable proportion of the sulfur would not be emitted into the atmosphere at temperatures lower than 1060°C. Taking as a reference the annual coal consumption of the Teruel Mining District (6 million tons), the mean sulfur content and the anhydrite content at 900°C, it was shown that the SO₂ emissions could be reduced by approximately 13 percent (83,000 ton/yr) provided that the combustion temperature was 900°C.