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EFFECT OF WATER VAPOR ON THE PROCESS OF METHANE
DESORPTION FROM COAL
L.I. Stefanovich1*,
E.P. Feldman1, O.Yu. Mazur1
1Institute for Physics of Mining Processes
of the National Academy of Sciences of Ukraine, Dnipro, Ukraine
*Corresponding author:
e-mail: listef2591@gmail.com
Physical and
technical problems of mining production, 2021, (23), 20-39.
https://doi.org/10.37101/ftpgp23.01.002
full
text (pdf)
ABSTRACT
Purpose. To analyze
theoretically the effect of water
vapor on the desorption of methane from the surface
of open voids of a coal sample.
Methods. Using Langmuir's
assumptions: the monomolecularity of adsorption and the constancy of the heat
of adsorption, the equations for the monomolecular
adsorption of a binary mixture of gases: methane
and water vapor are derived
by methods of statistical physics.
Findings. The dependences
of the degree of coverage
of the adsorption layer with methane and water molecules
are obtained in a situation when the partial
pressure of water vapor changes linearly in the chamber
where the coal sample is placed. Within the framework of the quasi-static approximation, the kinetics of desorption of methane molecules from the adsorption
layer and the adsorption of water molecules
is traced, if the process
of moistening the sample in time proceeds
according to a linear law and when it
is described by a smooth step function. The situation corresponding to the process of methane adsorption in dry coal and
in samples with different degrees of natural moisture is analyzed theoretically. It is shown that
with an increase in moisture content, the process of methane adsorption on the surface of open cracks
and pores slows down, and the amount
of adsorbed methane decreases significantly.
Originality. It is shown that the main reason
for the desorption of methane from open cracks and pores in
moistened coal is the competition
for sites due to the
presence of a limited number of active adsorption
centers and the difference in the binding
energies of methane and water molecules with the coal
surface.
Practical implications. The
studies carried out allow us
to conclude that the procedure
for their moistening can be successfully applied for degassing coal seams.
Keywords: open cracks
and pores, degree of coverage,
activation centers, desorption of methane, adsorption of water molecules,
binding energy, competition for places, quasi-static approximation
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