Results of thermal changes involved during the pyrolysis of twelve US coals of various ranks in a helium atmosphere at 5.6 MPa (gauge) and temperatures up to 580 °C are reported. Thermal effects during pyrolysis of coals ranging in rank from anthracite to HVC bituminous are endothermic in nature over the temperature range investigated. Exothermic heats are observed only in the case of sub-bituminous and lignitic coals. The net thermal effects, that is the resultant of endothermic and exothermic heats, go from endothermic to exothermic with increase in carbon content, a transition occurring around 66% carbon and another in the reverse direction at about 75% carbon. A maximum in exothermicity occurs around 71% carbon and in endothermicity at about 81% carbon. Results have been compared with published DTA data on coals. The fallacy in the interpretation of published DTA thermograms of coals, where weight changes accompany thermal effects, is discussed. © 1976.
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