Effect of Coal Cleaning on Ash Composition and its Fusion Characteristics for a High-Ash Non-Coking Coal of India

Indian coals are usually blended or beneficiated prior to being fed to utility boilers. These coals often satisfy the heat-value requirement of the boilers but may not be ideal from an ash-composition perspective. The ash compositions of beneficiated coals can significantly differ from that of the original coals thereby affecting the fusion characteristics. To have a better understanding of the variation of ash compositions due to coal cleaning, the present investigation focused on the study of ash composition in different size and density fractions of a high-ash non-coking coal. A run-of-mine coal (58.5% ash) was crushed to -75 mm and screened into six size fractions. The individual size fractions and the composite coal -75 +0.5 mm were subjected to density separation. The ash composition and ash fusion characteristics of size and density fractions were determined. The basic components of ash enriched in the lower density fractions while acidic oxides concentrated in the higher density fractions. Ash-fusion temperature and gross calorific value showed linearity with density. No such variations were observed for the size fractions. The results also indicated that cleans (20% ash) and middlings (42% ash) may be efficiently utilized for direct reduction of iron and pulverized coal power generation, respectively.