Mineralogical influence of mining intrusions in CFB combustion of Indian lignite

Abstract

Lignite has emerged as an additional important fuel source for thermal power generation in India. Circulating fluid bed combustion technology is applied considering the impurities, moisture, ash and sulfur content, and wide variations for large units. Lignite mineralogy greatly influences combustion behavior. Agglomeration and clogging/blockage are experienced due to sintering of lignite at lower temperature regime in which circulating fluid bed boilers operate (800°C to 900°C). At this low temperature range, the extensive knowledge built for pulverized coal combustion with respect to slagging, fouling, and high-temperature corrosion is not useful. Sintering studies using the heating microscope’s potential are applied for understanding this phenomenon. The gray clay, which occurs as intrusions/thin bands in the lignite mine, is sampled at the mine site and taken up for analysis. Morphology of sintered deposits in the bottom ash is matched with the properties of clay which is very close to halloysite mineral (kaolinite group). Sintering is avoided by selecting the operating temperature range of combustion on either side of peak sintering temperature in the sample case. With higher ashing temperature, the lignite ash loses part of its sintering tendency. This indicates to a new hypothesis that once the lignite ash undergoes transformations resulting in sintering, its sintering tendency is lowered. Conventional slagging indices are also analyzed, and correlation was derived for sintering behavior of lignite.