1300

THE COLLIERY GUARDIAN

December 24, 1915.

THE GASES IN COAL.*

By N. H. Darton.

(Continued from page 1239J

Variation in Volume from Different Coals.

Porter and Ovitz recently tested coals of various kinds
from several places in the United States, and found
that methane and small amounts of carbon dioxide are
given off by coal for an extended period under ordinary
atmospheric pressure, the amount of gas and its rate of
escape being nearly the same as when the coal is kept in
a vacuum. They ascertained, also, that oxygen was
absorbed rapidly by fresh coal, but in quantities too
small to account for the volume of carbon dioxide
liberated, if the latter be assumed to result from slow
combustion of the coal. They found great variation in
the proportion of methane liberated. A Kentucky cannel
coal yielded only a trace of methane in nine months,
whereas coal from Harrisburg, Illinois, gave off one-
fourth of its volume in four days, and a coal from
Monongah, West Virginia, yielded one-third of its
volume in the same time. A sample of Pocahontas
(Virginia) coal yielded little gas, yet mines in the
western part of the Pocahontas district contain much
gas at times. They found, in general, that at first gas
escapes rapidly from coal, then in less and less amounts,
with complete cessation in three to 18 months.

An investigation of occluded gases in Illinois coals by
Parr and Barker gave results that throw additional light
on the volume of gas, and the conditions of its emana-
tion. Samples were collected from the working faces.
Each sample was divided into two parts; one was placed
in a jar in air, and the other was kept under water in a
jar. The samples were allowed to stand for seven
months, with the following results :—

Volumes of Methane Given off in Seven Months
by Illinois Coals.

Relative volume of
methane to coal

No. of sample-	Mine.	(coal	=
		Dry	Coal under
			
		coal.	water.
1	Lebanon 		0'00	0 036
2	Bennett 		0'00	0*017
3	O’Fallon		0'66	0T47

The percentages of methane in the gas given off were
as follow:—No. 1, wet, 56; No. 2, wet, 35-4; No. 3,
dry, 11-8; and No. 3, wet, 90-3. Small amounts of
carbon dioxide were given off by Nos. 2 and 3, dry.

Tests to determine the effect of oxygen absorption
were made with some samples that had been partly air-
dried, after having been kept sealed 10 months. They
were placed in open jars. Two samples were from the
Sangamon mine at Springfield, one was from the Chicago
and Big Muddy mine near Marion, one from the Davis
mine near Duquoin, one from the Suburban mine near,
Belleville, one from O’Fallon mine No. 2, one from
O’Gara mine No. 8, near Eldorado, and one from the
Squirrel Ridge mine near Herrin. Only the two latter
gave off methane, the coal from the No. 8 mine yield-
ing 0-38 volume, or a little more than one-third, and
the Squirrel Ridge coal 0-17 volume, or a little less than
one-fifth.

Effect of Oxidation.

The early experiments of Von Meyer showed that
although coal lost most of its gases, especially methane,
when partly exposed, a considerable amount of gas was
evolved, or could be extracted for years afterwards. A
series of tests that were made by Parr and Barker to
determine the effect of oxidation of coal, showed con-
siderable variation in the amount of methane given off.
All three samples were taken from the Squirrel Ridge
mine.

Condition
of
sample.

2	...	Ditto

3	... Fresh drillings

4	...	Ditto

5	...	Ditto

Conditions
of
test.

2 © 00

o a.g

o

d <D

° II 2 £
d S S
w □ fl 2

Ph *

o

15

Per c.

1

Partly air-dried...Air from sealed con-...0* 166... 2’2
sample 2 yiars tainer in which sample
old	had been kept for two

years

Sealed in air 2 days and . 0'000... 0'0
air and gas pumped
off

.Sealed 14 days and air...0'252... 21'8
and gas pumped off

Sample in vacuum 12...O'253...86'4
days after test 3 and
gas pumped off

Sample sealed in air...O'112... 14'1
for 7 days after test 4

Tests were also made of samples taken from this and
other mines two years before. The samples were quar-
tered, reduced to buckwheat size, and air dried, and
although they yielded considerable nitrogen, oxygen,
and carbon dioxide, they gave off no methane. The
proportion of carbon dioxide varied from 2 to 8 per cent,
in most of the first tests, to 18 to 55 per cent, in the
later tests, one sample from Springfield yielding as much
as 80-5 per cent. Some of the material was from work-
ing faces not far from long-standing exposures, the
mines having been idle some time.

Screenings from the Westville mine that were 15 and
two months old yielded no methane in the first test, but
two samples of gas removed by vacuum in later tests
contained 0-002 and 0-008 volume respectively. Two
months old screenings from the Sangamon mine, near
Springfield, yielded 0-009 volume of methane in the first
test, and 0-035 volume in a second test. These screen-
ings had been stored outside of the mine. A sample
of outcrop coal near Marion, exposed a year, gave 0-006
volume of methane in the first test, and 0-001 volume

* From Bulletin 72 of the United States Department of
the Interior, Bureau of Mines.

additional in later tests; the proportions of methane in
gases given off in the two tests were 0-54 and 1-05 per
cent, respectively.

Amount of Methane in Mine Air.

Much information is on record as to the volume of gas
contained in the return air of coal mines. Many tests
have been made in mines in Europe, some of them for
protracted periods. The results of the author’s investi-
gations of numerous mines in the Pennsylvania and
Illinois coal fields show great variation in the total
volume of methane emanation from different mines,
and also from different beds and workings in the same
mine. Some parts of mines and some mines that have
the most marked manifestations of gas from blowers
and local accumulations show smaller total methane
emanation than those where the gas is given off gener-
ally and continuously.

The proportion of methane in the return air of a
mine depends not only on the total volume of gas given
off, but also on the volume of air used for ventilation;
therefore the most useful figures for comparison are
those indicating the volume of methane. Even when
the air current is of uniform volume from day to day,
the usual condition, the proportion of methane varies,
and this variation is sometimes closely related to the
amount of coal mined, diminishing in marked degree
during a cessation of mining, even for a day. Usually,
however, the variation in the volume of methane in the
return air is due directly to the variation in the quantity
given off by the coal from place to place, increasing as
gaseous areas are opened, and diminishing as they are
drained. Squeezes and outbursts are also important
factors. There has been considerable discussion as to
what is a gaseous mine, and most classifications pro-
posed have been based on the amount of methane and
carbon dioxide in the main returns. This is not a safe
basis of comparison, as the danger from gas in a mine
depends less on the steady outflow, even if it is large,
than on the liability to outbursts and large volume given
off in the fresh chambers and headings. Most authori-
ties agree that more than 2 per cent, of methane in the
return air is an indication of a very gaseous mine.

In most beds of coal there are variations in texture
and hardness, and in the trend and number of joint
planes large and small. The water content in the pores
and crevices also varies greatly in different places. These
factors all have important bearing on the variation of
the volume of methane contained in coal and the rate of
its emanation. The more porous coal may or may not
contain a larger volume, but it gives off methane more
rapidly. The difference between the total volume of
gas given off by the coal, and the rate of emanation is
usually overlooked in discussing the gas problem. Ordi-
narily, the coal is regarded as most gaseous that gives
the most gas in fresh headings while it is being
uncovered, but a more compact coal may contain more
gas, and give it off gradually, and for a long time.

The return air in many mines regarded as non-gaseous
contains only 0-01 per cent, or less of methane, whereas
in some gaseous mines main return air currents of
200,000 cu. ft. per minute carry 2 per cent, or more of
methane. Mines near Wilkes-Barre, Pennsylvania, dis-
charge 2,000 to 3,000 cu. ft. of methane a minute, or
nearly 3,000,000 cu. ft. in 24 hours; the air in the main
upcasts of these mines carries 1 to 2 per cent, of
methane.

Percentages in Prussian Mines.

Schondorff has given some interesting figures of per-
centages of methane in returns in some Prussian mines.
In several mines in the Saarbriicken basin, the methane
content ranged from 0-05 to 1-46 per cent.; in the
Aachen basin, from 0-65 to 1-56 per cent.; in the lower
Rhenish-Westphalia basin, from 0-002 to 1-428 per cent.;
and in the lower Silesian basin, from 0-27 to 0-92 per
cent.

The total daily volumes of methane from several
especially fiery mines were as follow : Neu-Iserlohn mine,
No. 2 shaft, Lower Rhenish-Westphalia, 897,600 cu. ft.;
Neu-Iserlohn mine, No. 1 shaft, Lower Rhenish-West-
phalia, 305,000 cu. ft.; Westphalia mine, Kaiserstuhl
shaft, near Dortmund, 503,700 cu. ft.; Albert shaft,
Saarbriicken, 330,000 cu. ft.; Gouley - Gemeinschaft-
Konigisgrube, Aachen, 295,000 ± cu. ft.; Friedenshoff-
nung mine, southern section, Lower Silesia, 256,500
cu. ft.; Schaumburger mine, No. 3 shaft, Wealden,
280,000 ± cu. ft.

Percentages in Austrian Mines.

The Austrian Commission made analyses of the return
air in many mines, and obtained a great variety of
results. One of the most important series is from the
very gaseous mines of the Karwin-Ostrau district, the
results being: Methane, 0-68—3-53 per cent.; carbon
dioxide, 0-06—0-18 per cent.; oxygen, 19-53—20-27 per
cent.

Percentages in Russian Mines.

Kotsowsky has given the results of a series of analyses
of return air in the Donetz basin in Russia. The figures
vary greatly as to components, the methane ranging
from 0-13 to 2-93 per cent., and the carbon dioxide from
0-18 to 1-36 per cent. In the central pit of the Youse
mines the methane ranged from 0-32 to 2-50 per cent.,
and in No. 10 of the Rikowsky mines the air from one
gallery carried 2-93 per cent, of methane, whereas air
at the working face in mine No. 14 contained only 0-13
per cent. The main upcast of the Usine pit carried
0-22 per cent, of methane.

Percentages in Scotch Mines.

Gray has given 85 analyses of return air from repre-
sentative coal and shale mines in Scotland. The depths
ranged from 36 to 2,221| ft., and the air currents had
volumes of 1,200 to 46,860 cu. ft. a minute, some of
them being total returns and others splits. Most of the
coal mine samples contained 0-05 to 0-5 per cent, of

methane, the content varying without relation to depth,
except that some of the very shallow workings were less
gaseous than deeper ones. Returns from deep workings
in Fifeshire, however, showed no trace of methane. The
largest volume of methane was in the main return from
the Diamond mine, which carried 185 cu. ft. a minute.
In general, the shale mines gave off somewhat less
methane and carbon dioxide, the volume of methane in
the most gaseous return being 93 cu. ft. a minute. The
carbon dioxide content was as high as 1 per cent, in
more than half of the returns.

Relation of Volume of Methane to Amount of Coal Mined
or Exposed.

As the proportion of methane in coal is variable, there
is great variation in the amount given off in mining and
in preparing coal. An extensive investigation of this
branch of the subject was made in the Saarbriicken
basin, Germany. Twenty-three mines were examined,
and 652 analyses made. The volume of methane varied
from 16| to 1,060 cu. ft. per ton of coal mined, or from
one-half to 30 times the volume of the coal, and in one
case the volume of gas was 2,160 cu. ft. per ton. The
methane emanation from the 23 mines varied from 8,870
to 732,566 cu. ft. a day, and the total in a year was
nearly 2billion cu. ft., or 44,000 tons of methane.

Several mines in the anthracite region near Wilkes-
Barre, Pennsylvania, producing about 2,000 tons of coal
a day, each gave off 2,000 to 3,000 cu. ft. of methane
per minute, or 1,500 to 2,500 cu. ft. per ton of coal
mined, and the rate of emanation was not diminished
greatly after mining had ceased for 30 days. Other
mines, however, working the same beds, and producing
an equal tonnage, give off only 20 to 100 cu. ft. a minute,
or 15 to 75 cu. ft. per ton of coal mined. The latter,
however, are shallower mines, and the coal may have
contained originally as much gas as in the deeper part
of the basin.

Winkler has presented a series of interesting analyses
indicating the difference between volume and composi-
tion of the ingoing and the outcoming air used in the
ventilation of some mines in Saxony. As an example,
may be cited the Van Arnim mine, where the following
figures were obtained :—

Total Me- Carbon Oxy-	Nitro- Mois-

volume. thane, dioxide, gen.	gen.	ture.

Cu. ft.	Cu. ft.	Cu.ft.	Cu. ft.	Cu. ft.	Cu.ft.

Upcast.... 19,866	...	3	...	205	..	3,717	...	15,489	... 4$0

Intake.... 17,894	...	—	7	...	3,717	...	14,018	... 150

Difference 1,972	...	3	...	198	...	—	...	1,471	... 300

The Austrian Firedamp Commission found that in
districts containing much gas the emanation of methane
averaged 7,469 cu. ft. per ton (21 to 22 cu. ft.) of coal
mined, whereas in the areas most free from gas the
average was 519 cu. ft. of methane per ton mined. The
effect of the amount of coal mined was evident, but the
volume of methane did not vary inf direct ratio with it,
and a variation in the tonnage had to continue for some
time to have much effect on the volume of methane.

The Prussian Firedamp Commission found that 357 to
2,400 cu. ft. of gas was given off per ton of coal mined.
Chesneau found 1,377 cu. ft. at the Herin mine at
Anzin, and 883 cu. ft. at the Ronchamp mine. In a
Westphalian mine it was found that in a bed giving
off gas at a moderate rate and without blowers, the
volume emitted was closely proportionate to the area of
freshly exposed coal surface. From his experience in
English mines, Thomas was convinced that most of the
gas in freshly exposed coal is given off in the first three
or four hours.

The following figures have been given by Hilt as to
the methane given off per ton in mining coal in the
Gemeinschaft and the Ath-Gouley mines :—

Cu. fr. per ton.

Gemeinschaft, return 2 ....... 1,060	to 1,152

Ath-Gouley, return 1 ......... 2,171	to 3,360

Gemeinschaft, lower workings ...	409 to 632

Gemeinschaft, Meister bed .... 2,470	to 2,640

The relation of gas emanation .to the area of coal
exposed is well illustrated in the Gemeinschaft mine in
the Grosslangenberg bed, which is gaseous throughout.
In the anthracite part much of the gas comes from the
sandstone roof, and a gas emanation may last 10 years,
beginning generally with a roof fall. The area is
divided by a fault, east of which the bed is “ flame ”
coal, where most of the gas drains off in three years.
In 1882 the anthracite workings of this bed gave off
200,000 cu. ft. of methane a day. The area of anthracite
exposed by workings was 3,300,000 sq. ft., and for every
1,000 sq.ft, of this surface 60 cu. ft. of methane was
emitted daily, equal to 219,000 cu. ft. in 10 years. If
the entire thickness of coal and sandstone be taken as
40 ft., for each cubic foot of material there must have
been 6 cu. ft. of gas to have sustained this emanation.

In the “ flame ” coal district, where the daily volume
of methane was 130,000cu. ft., the area of surface
exposed in three years of mining was 2,109,000 sq. ft.
The thickness of material holding gas is about 4} ft.,
and with methane emission of about 60 cu. ft. for each
1,000 sq. ft. of area, the total volume of methane from
the entire mass of 65,700 cu. ft. would be 13’8 cu. ft. per
cubic foot of coal. This is believed to indicate that in
the “ flame ” coal district the gas in the coal must have
had an average pressure of 207 lb. to the square inch.

In October 1882, in the Westphalia mine near
Dortmund, the workings connected with the Kaiserstuhl
shaft, which were in a fiery bed, had an exposed surface
of 110,000 sq. ft. It was found that for every cubic
foot of solid coal removed 9*7 cu. ft. of gas was produced,
or 875 cu. ft. for every ton mined, and 81 cu. ft. of
methane for every square foot of coal surface exposed.
On the other hand, on January 30, 1884, in the old
Westphalia shaft of the same mine, for every ton of coal
raised daily only 54cu.ft. of gas was given off (in one
district the volume of methane was 60 cu. ft.). In one