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METHOD FOR DETERMINING THE EFFECT OF DIFFUSION AND
FILTRATION MECHANISMS OF METHANE TRANSPORT ON THE DURATION OF DESORPTION
FROM COAL SAMPLES
V.O. Vasylkivskyi1*,
S.P. Mineev2, O.M. Molchanov1,
L.I. Stefanovich1, O.V. Chesnokova1
1Institute for Physics of Mining Processes
of the National Academy of Sciences of Ukraine, Dnipro, Ukraine
2Institute of Geotechnical Mechanics named by N. Polyakov of National Academy of Science of Ukraine, Dnipro, Ukraine
*Corresponding author:
e-mail: lod.vasylkivskyi@ukr.net
Physical and
technical problems of mining production, 2021, (23), 5-19.
https://doi.org/10.37101/ftpgp23.01.001
full
text (pdf)
ABSTRACT
Purpose. To develop
a physically substantiated
algorithm for determining the characteristic time of filtration and diffusion processes to assess the relative contribution of these processes
to the duration of gas desorption from a porous sorbing substance.
Methods. The volumetric
method was used for measurements.
In the experiments, the change in methane
pressure in a storage vessel (SV) of a known volume was recorded in the process of methane desorption. The measurement data became the information basis for determining the values of the characteristic
desorption time from coal samples
in large and small granules.
Preparation for measurements consists of several stages: 1st - drying
of coal at a temperature of 345 K, 2nd - saturation
of coal with methane, 3rd
- preliminary discharge
of free compressed methane into the atmosphere
from a container with coal after
its saturation, and 4th - picking
up the methane emitted from coal into
a storage vessel. When measuring in a coal mine,
the above operations are unnecessary. The analysis of the experimental results was carried out within the framework of the model of
diffusion-filtration mass
transfer in a sorbing porous substance. In such a model, coal is a collection
of small dense formations - blocks, the volume between which is the
volume of open pores and cracks. These pores communicate with the outer surface
of the coal and serve
as pathways for gas filtration
after diffusion from the blocks.
To solve this problem, the previously discovered feature of the gas
kinetics is involved, namely: in the final
stage of desorption, the characteristic desorption time is a linear
combination of two parameters - the characteristic times of filtration
and diffusion.
Results. Formulas are obtained for the numerical
calculation of the characteristic filtration and diffusion times to estimate the relative contribution of these processes to the duration
of gas desorption from coal. A technique and algorithm for performing measurements in laboratory and mine conditions have been developed.
The measurements showed a high sensitivity of the characteristic time of the
filtration process to structural disturbances in coal. It was
found that geological disturbances in the formation
structure lead to a decrease in the filtration
time by almost an order
of magnitude. The effect is explained by an increase
in coal permeability due to an increase
in fracture gaping. The influence of geological disturbances on the characteristic
time of diffusion processes in coal was
not found.
Originality. The possibility
of experimental determination the contribution for each process - filtration and diffusion - to the duration of gas desorption
from coal has been theoretically
substantiated and experimentally proved.
Practical implications. Such
studies, carried out in laboratory
conditions or directly in the mine, make
it possible to predict the gas-dynamic hazard during mining operations in outburst-hazardous coal seams.
Keywords: characteristic
time, desorption, filtration, diffusion, coal, volumetric method, methane pressure, coal blocks
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