Effect of weathering on physico-chemical properties and combustion behavior of an Indian thermal coal

Abstract

An open air stockpile of conical shape was formed with 3.5\xa0m base diameter and 5\xa0m height using 500 tons of −\u2009200\xa0mm size ROM thermal coal on a concrete floor. Coal sample from the stockpile were collected at 30\xa0days interval for analysis of various chemical properties like; proximate analysis, ultimate analysis, gross calorific value (GCV) and various combustion related properties such as ignition temperature, peak temperature, burnout temperature, maximum combustion rate, ignition index, burnout index, combustion performance index and combustion rate intensity index. Experimental results show that, due to weathering of coal fixed carbon decreased from 35.6% to 19.9%, elemental carbon (C) decreased from 46.6% to 28.6%, hydrogen (H) decreased from 3.3% to 2.9% and GCV decreased by up to 55% of original value during 330\xa0days of storage of coal in an open atmosphere. Ash content of coal increased form 29.2% to 46.6% due to loss of combustibles. Sulfur (S) of coal was found to get increased from 0.33% to 1.08% during storage. The activation energy of coal combustion increased from 22\xa0kJ/mol to 54\xa0kJ/mol. Variation in combustion parameters signifies that weathering has significant negative impact on coal combustion properties as coal become difficult to ignite.