Measurement of coal pyrolysis reaction heat by TG-DSC

Five typical Chinese coals with different ranks were sampled,then their pyrolysis reaction heats were meas- ured,in which TG-DSC was used to measure the heat flows of coal samples during pyrolysis process,and heat flow baseline was isolated or determined by empirical method and test method,respectively. Besides,the effects of pyrolysis temperature and coal rank on the coal pyrolysis reaction heat were investigated,and the pyrolysis reaction heats derived from different heat flow baseline determination methods were compared and discussed. Results show that the pyrolysis reaction heat of Shengli lignite,Shenmu long frame coal,Shendong bitumite,Datong bitumite and Taixi anthracite at a pyrolysis temperature of 1 100 ℃ measured by test method were -5 743. 11,-13 888. 42,-16 246. 20,-21 433. 89 and 3 097. 79 J / g,respectively,whereas based on empirical method the pyrolysis reaction heat of these coals were -5 963. 81,-13 839. 86,-17 792. 50,-22 871. 74 and 3 536. 47 J / g,respectively. For coal samples excluding anthracite,with the increasing degree of coal metamorphism,the heat released during coal pyrolysis shows an increasing trend,also the pyrolysis reaction heat increases and then decreases and then increases again with the increase of pyrol- ysis temperature. For Taixi anthracite,the reaction heat is always positive at each temperature range,which means that the pyrolysis reaction of anthracite is endothemic,also the reaction heat is proportional to the pyrolysis temperature. The values of pyrolysis heats measured by two methods,empirical baseline method and test method,are close except Shendong bitumite and Datong bitumite. The biggish difference between pyrolysis reaction heats of Shendong bitumite and Datong bitumite determined by empirical baseline method and test method might result from the excessively higher reaction heat of two coals in the exothermic range predicted subjectively by empirical method when determining the baseline. Thus,it is obvious that the test method has the advantage of simpler operation,higher accuracy and better re- peatability in the measurement of coal pyrolysis reaction heat than the empirical baseline method.