The
dynamic thermal process for methane sorption in coal has not
been quantitatively studied, and the temperature change induced by
the heat of adsorption on the sorption equilibrium state has not been
confirmed by tests. In order to probe the temperature evolvement and
its effect on methane adsorption in coal, the temperature of the coal
sample is measured using a digital temperature gauge during methane
isothermal adsorption in coal. Isothermal adsorption tests for methane
in coal under six different temperatures (50, 40, 30, −10,
−20, and −30 °C) are conducted. Blind experiments
show that the temperature increase of the tested coal sample induced
by external energy brought via the filled methane and the possible
Joule–Thomson effect is within 0.5 °C in this test and
thus will not be considered during methane adsorption in coal. Both
real test and modeling results show that the temperature of the coal
sample induced by the heat of adsorption can go up to 13.79 °C
during the methane adsorption process in coal, and the methane adsorption
in coal is not an isothermal process in the initial sorption stage.
During the methane adsorption process in coal, the temperature induced
by the heat of adsorption first increases to the peak sharply, then
decreases gradually with time, and finally drops down to the environmental
temperature prior to reaching sorption equilibrium. The closer the
distance of the monitoring point is from the wall of the steel sample
canister, the smaller the peak temperature value is and the shorter
the time needed. This can be attributed to the different heat transfer
efficiency in the different places inside the sample canister. The
total specific power decreases exponentially with time, which can
work as one index to model the heat transfer behavior of the coal
sample in different places inside the canister. Temperature influence
on the sorption equilibrium state induced by the heat of adsorption
can be neglected because the temperature variation stage only lasts
a short time in the initial sorption stage.
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