Lukashova Lidiya Sergeevna
Possibility of Locating Heat Source of Spontaneous Combustion of Coal by the Electric Potential
The Individual Task
"The computerised subsystem of diagnostics and monitoring
of a condition of the mountain machine
(on an example of coal-mining combine 1KDK500)"
THE METHANE RATING SYSTEM TO DETERMINE COAL FACE METHANE CONDITIONS
Methane
Rating was developed from a need in South Africa to measure coal seam
gas contents, as well as emission rates into the cutting zone for mechanical
miners. These are then combined and compared to the average and normal
conditions to provide a risk assessment tool for continuous miner operations.
The last two years have seen widespread acceptance of Methane Rating as
a practical and simple means of identifying seam gas contents and emission
rates during mining, and of rating the changing methane conditions. The
system uses proven direct methods of methane measurement to quantify the
contents and emissions, combined with an innovative rating system. Each
new result is compared with the expected average or normal conditions
to determine its Methane Rating between 1 and 5.
METHANE RATING
Methane
Rating (MR) measures the methane content and emission rate from newly
cut coal samples, plots these against each other, and rates the conditions
1 to 5 against the available database. A rating of MR1 is lowest risk,
with content and emission below average, and MR 5 is the highest risk
with content and emission both above average.
The selected database can vary between individual sections, mines, coalfields,
coal seams, and all national results, so the Methane Rating of any sample
can also vary. For example a high risk MR5 on a low gas mine indicates
high risk conditions for that mine, but it may well be MR1, lowest risk
on a coalfield or national scale.
Figure 1 shows the Methane Rating graph of gas content against emission
rate, The averages and the Normal Operating Range are calculated for the
selected database and the new sample is plotted against these on the graph
. An example for a selected database would be to compare all results for
Highveld coalfield, No.4 seam, devolatilised coal.
Methane Rating was designed to be simple and practical, using intentionally
low technology and straightforward calculations. It was developed from
internationally acceptable direct methods of methane content measurement,
modified to calculate an emission rate during mining as well as content,
and to be suitable for the variable and relatively low gas contents of
South African seams.
Underground
Equipment and methods used underground have been kept simple. One or two
direct volume displacement readings are required to measure methane being
emitted from newly mined coal samples, which are normally collected from
shuttle cars. This takes no more than a few minutes at each location.
Any normal and acceptable direct method equipment can be used, but due
to the relatively low methane contents and low initial gas volume were
released, a practical innovative new measurement kit has been developed.
Software
All calculations are performed by the data base software, using the underground
and laboratory results as input values. A new software release has taken
into account the user and industry feedback from the previous version,
with each result now being stored as a file. This means any individual
result can be recalled as it was at the time of sampling, and also then
recalculated to present database conditions. calculations, with only the
addition of the database results, so can also be done by hand or spreadsheet
without the Methane Rating software. It is the Browse Areas page that
allows the user to review all the mines in the database, leading to individual
samples and information already stored about a particular mine
Gas Content
The gas content is the total volume of gas contained in the coal as it
was mined. It is given in cubic metres per ton (m3/t), and is calculated
from the standard direct methods of calculation, considering all the gas
given off during underground sampling, further desorbing and laboratory
milling.
Methane
Emission Rate
The emission rate is in litres per ton mined per minute. This emission
is for the coal as a continuous miner, or coal cutter is actually cutting,
and is calculated from what is usually termed the lost gas. The lost gas
volume is taken as a rate over the time between cutting the coal and sealing
it in the canister.
Methane
Ratings
The Methane Rating value is comparative against the results in the database.
A new result is plotted for gas content and emission rate against the
average of these for the database. One standard deviation is added to
and subtracted from the averages to plot the Normal Operating Range.
The Normal Operating Range accounts for the expected variations in results
that will occur in any database, and accepts that although a result may
be above average conditions, it may not be unexpected for that particular
mine or area or coalfield. The increased Methane Rating of MR5 is for
samples not only above average, but also outside of the Normal Operating
Range
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