In
this paper, the reactive properties of coals associated with low-temperature
oxidation were studied using thermogravimetric analysis (TGA). Coal
samples were pulverized into a size fraction of <106 μm and
analyzed using two non-isothermal thermogravimetric methods. The “adsorption
of oxygen” test consisted of exposing coal samples to slow
heating rates in air while measuring the weight increase produced
by the oxygen adsorption. Two heating ramps were used (3 and 5 °C
min–1), recording the net mass increases from 20
to 250 °C. Results range from 0.0 to 4.4% weight gain, with the
lowest heating rate giving the highest levels of adsorption. A second
thermogravimetric test for spontaneous ignition potential (TGspi) was developed, which focused on the linear segment of
the weight derivative curve between 150 and 350 °C at different
ramp rates in air (3, 5, 7, 10, and 20 °C min–1). From these results, a relationship between the mass loss rate
and temperature was obtained (TGspi index), where high
values were produced by highly reactive coals. The “oxygen
adsorption” test related to the chemisorption step, which precedes
“spontaneous combustion”. The “TGspi” test was more related to the combustion process, post-ignition.
These results also agreed with the known behavior for the samples
studied, indicating that these tests could be useful tools to identify
coals prone to self-oxidation.
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