806

THE COLLIERY GUARDIAN

April 27, 1917.

The coal is delivered from the overhead bunkers,
whether large or small, by chutes, valves, or measur-
ing “ drums ” being fixed between the bunker and the
top of the chute. At the earlier stations—Brakpan
and Simmerpan—measuring drums of a known capa-
city were fitted ; a counter was attached, so that the
measured quantity of coal passed per shift or per day
was known. These proved unsatisfactory, as the duff
coals do not run freely, especially when wet, so that
the drums did not fill properly. As a consequence, no
reliance whatever could be placed upon them, and all
subsequent bunkers were provided with the well-known
Babcock and Wilcox coal valve. The chutes are usually
about 10 in. diameter, and have splayed bottoms,
where they discharge the coal into the stoker hoppers.
It is found that the makers usually provide these of
too thin a plate—J in. or in.—and, as a result, they
are rapidly corroded away on the bottom side, especi-
ally when dealing with wet coal. At Vereeniging the
coal chutes are of rectangular section, which renders
them much easier to repair. The bottom plate can
easily be renewed, this being impossible when the
chutes are of round section. In the earlier installa-
tions the discharge end was splayed to about half the
width of the stoker hopper. This was found to give
an unequal distribution of coal, the peas or larger
pieces of coal falling to the sides, and the duff and
powder falling in the centre, resulting in uneven fires.
An improvement has been effected by making the
width of the splayed bottom equal to the full width
of the stoker hopper, and as the chutes are replaced
this design is being adopted ; but even with these there
is a tendency for the larger particles of coal to fall
to the side and make a somewhat uneven fire.

Ash Handling.

At all stations except Vereeniging the ashes are
dumped over the back of the grate through ash tipping
plates into open hoppers below, from which they are
discharged into coco-pans pushed by natives through
the ash basement. They are then switched to the
haulage, and taken up to the dump, very similar in
shape and arrangement to the mine dumps. The ash
haulage ropes last up to about two years. Side
jockeys are used, as with the ordinary jockey there is
the risk of the rope being burnt.

At Brakpan the average percentage of ash in the
coal as fired is about 27 per cent., at Vereeniging about
18-5 per cent., and at Rosherville and Simmerpan
about 17 per cent.

The average maintenance cost of ash haulage is
0-50d. per ton of coal burnt. This includes the main-
tenance of tracks, repairs and replacement of coco-
pans, haulage ropes, and repairs to reduction gears
and motors.

The above system of ash haulage was also installed
at Vereeniging, but owing to the fact that this station
is run at a high load factor, the coal consumption is
about 1,400 tons per day with 18 boilers steaming, and
when burning anything over 1,000 tons of coal per day
it was almost a physical impossibility for the natives
to keep the basement clear of ashes. In fact, this was
the factor limiting output at that station. To over-
come this, a Zimmer vibrating conveyor has been
installed, and, so far, has been a success. Certain
mechanical defects had to be overcome, but these have
been met, and the plant is working fairly well. A con-
veyor is erected under each line of five boilers, these
conveyors discharging on to a cross conveyor, which
discharges the ashes into a bin, from which they are
fed into coco-pans and taken up to the dump by a rope
haulage. It is found essential to saturate the ashes
with water as they fall from the hopper on to the con-
veyor troughs; unless this is done the troughs become
overheated and badly buckled. The troughs under
each row of boilers are 24 in. wide, and the cross con-
veyor is 24 in. and 30 in. wide. The installation of
this conveyor has, in addition, made it possible to
reduce the natives in the ash basement from 48 boys on
eight hours shifts to 12 boys on 12 hours shifts, and the
temperature in the basement is now quite reasonable,
and as the ashes are thoroughly wetted, there is very
little dust. The plant has not been running long
enough to enable any reliable figures for maintenance
costs to be put forward.

The provision for dealing with ashes is often an
after-thought in station design, but the efficient hand-
ling is a matter of the utmost importance at a power
station running at a high load factor and burning any
considerable tonnage of coal, and especially is this the
case where it contains a high percentage of ash. The
boiler house floor should preferably be supported by
steel columns and girders rather than by brickwork, as
it is of the utmost importance to allow all possible
ventilation in the ash basement. It is found that if
the boiler house is supported on brickwork piers and
walls, the ventilation is seriously interfered with.
It is to be hoped that in veers to come there will be no
necessity to handle ashes at the power stations, as
by-product recovery plants will be working, and the
boilers will be gas-fired.

Midland Miners’ Relief Society. — At the 34th annual
meeting of the Midland District Miners’ Fatal Accident
Relief Society on Tuesday, the Duke of Devonshire was
re-elected president, and the Duke of Portland, the Duke
of Rutland, Earl Carnarvon, Lord Middleton, and . Mr.
E. S. W. Sitwell were re-appointed vice-presidents. Mr.
E. Overton (Bolsover) was re-elected as one of the delegates
to the annual conference of the Central Association of
Miners’ Permanent Relief Societies, and Mr. J. Shooter
(Rufford) and Mr. H. Tatham (Ibstock) were chosen in
place of Mr. Saxton, deceased, and Mr. S. Hancock,
resigned.

MINE GAS.

VIEWS OF A RUSSIAN ENGINEER.

A work has just been published in Petrograd,
written by N. N. Chernitzyn, mining engineer, on
mine gas, the condition of its liberation, its proper-
ties, and the methods for coping with it. The author
deals at considerable length with his subject, begin-
ning with the theoretical genesis of coal gas, then
following its theoretical phases of development, pass-
ing under review the investigations and analyses
carried out by others as well as by himself, and finally
submitting for consideration the methods by which it
may be countered in its dangerous manifestations. He
observes in his preface that the question of mine gas
has agitated the practical and theoretical mining
world for over 100 years, during which period many
investigations have taken place which have cleared up
with almost exhaustive completeness several aspects
of this great problem. But, as frequently happens in
other departments of life, the bottom question of the
conditions of the formation of mine gas, and the forms
in which the mutual relations established between coal
and the gas exist, have been but imperfectly handled.
The old idea of the simple mechanical entrance of the
gas into the pores of the coal mass does not answer to
the present position of the question, as many data have
been accumulated which testify to the existence of a
connection between coal and methane in other forms.
To this particular question he devotes the first of the
three parts of his work. In the second part he deals
with the available data on mine gas and its explosive-
ness, whilst the third or last part is occupied by a
recapitulation of methods adopted for countering coal
gas or its effects in underground workings.

A perusal of the work brings the reader into contact
with a large quantity of tabular matter taken from
the works of other authorities on the subject, as well
as a large number of tables and comments on the
same to illustrate the very wide and useful experi-
ments and analyses made by himself, which he sub-
mits and compares with the others quoted, in a prac-
tical and easily understood manner.

He is able to say that a considerable amount of
investigation work has taken place in the Donetz
basin, the development of which is, however, young.
In his earlier chapters, after examining the known
theories of the formation of mine gas, its metamor-
phosis, and so on, and quoting copiously from inves-
tigation reports made in various parts of the world, he
says, making room for exceptions, the chief source of
mine gas, as has always been acknowledged, is coal.
And the normal and predominant part of that gas is
methane. Secondary and unimportant associates of
methane, in point of quantity, will be carbonic acid
and nitrogen, ethane, ethylene, carbon monoxide, and
hydrogen. The recognition of the latter constituents
in mine gas has met with various objections from a
number of- quarters, which induces him to submit a
considerable part of the data on the analyses of mine
gas which he is able to produce.

Dealing with blower gases liberated at atmospheric
pressure, after sampling and analysis, he says all the
analyses of mine gas obtained from coal at normal
temperature and atmospheric pressure show that the
combustible constituent of these gases does not undergo
any observable change in passing from anthracite to
gas coal. It consists almost exclusively of methane.
In some blowers probably ethylene is also present, but
in very small quantities. Carbonic acid and nitrogen
are constant associates of methane. Hydrogen, oxide
of carbon, and ethane have also been observed. Refer-
ring to gases extracted from coal in vacuum after
many experiments in many parts made by himself, he
says: u Under these conditions, too, the presence of
carbon monoxide and ethane was observed along with
methane in coals of the Kuznetz, the Caucasus, and
other basins. But in these cases the gases now
referred to were very rarely met with in important
quantities.”

Not satisfied with the conclusions of the American
chemist, Chamberlin, as conclusive on the question of
the form in which the gas is held in the beds, he made
some laboratory tests to learn the process of the libera-
tion of gas from coal. Samples were taken from mines
working different coals.

A special apparatus was used, consisting of a glass
jar of 730 c.c. capacity, with thick rubber stopper,
into which a glass tube was fixed to let out the gas,
also a steel rod ending below in a massive round disc
of 4 cm. diameter. The rod was combined with a
special muff with stuffing box, which gave an imper-
meability to the combination during the movement of
the rod whilst the coal was being crushed in the jar.
The glass tube was connected by means of a three-
way cock to a graduated vessel filled with mercury and
a water gauge. Before the test 100 grms. of coal was
placed in a jar in lumps; the sample was pressed close,
and the level of the water in the gauge was reduced to
zero. On the coal being crushed, the jar was con-
nected to the gauge and the graduated vessel, in which
gas was sucked, until the atmospheric pressure was
reached. When the test was finished the volume of
the liberated gas was taken at 760 mm. and 20 degs.
Cent. And the coal powder obtained was sifted
through various sized meshes in order to somewhat
equalise the crushing condition. The volume of gas
was calculated again on the coal that passed through
the sieve with 1 sq. mm. openings. The anthracite was
not nearly so finely ground, but it liberated consider-
ably more gas than the other coals; perhaps because

it was more solid, and was freer from cracks and
pores. Unfortunately, all the samples were not taken
at the same time. The chief constituent of the gases
obtained was methane.

On the question of the occlusion of gases, he bases
his view on a number of his own experiments and the
reports of other authorities, and comes to the follow-
ing conclusions, which, he says, confirm those of
Chamberlin: u The process of the liberation of gas
from lumps of coal and the walls of mine workings,
taking place in the pillars, continues over a long
period of time, up to half a year for some of the beds
investigated by me. With the increase in volatile
substances in the coal, and, consequently, with the
complexity of its constitution, the duration of the
process referred to increases notably. The quantity
of gas liberated by different coals when kept in jars
does not turn out to be in simple dependence on the
quantity of volatile substances. During the time the
coal is kept in jars the gas it contains is not all liberated.
The balance of it may be removed by a subsequent
grinding of the small pieces. Very finely ground coal
and coal dust all the same possesses, if even to only a
small degree, the power of yielding gas. From the
coal that has ceased to liberate gas at atmospheric
pressure, a further quantity of gas may be extracted
by means of applying intense exhaustion. Coal that
has ceased to liberate gas in contact with pure methane
liberates an additional quantity of gas when placed in
a jar with air or oxygen.”

On the question of the hypothesis of the nature of
the occlusion and liberation of gases in coal, he con-
cludes that the absorption of methane by coal gener-
ally takes place, that this absorption proceeds con-
siderably more intensively with an increase of the
outside pressure, and that the methane once absorbed
may find its way into the atmosphere at a reduced
pressure, and that besides methane, oxygen and
nitrogen also may be absorbed by coal, whilst it may
under certain conditions assist in the liberation of the
previously occluded methane.

On the absorption of methane by coal, based on a
series of tables oh tests which he quotes, he says these
tables show that the process of the absorption of
methane proceeded considerably more rapidly than
might have been expected from the reduction of pres-
sure in the jars, since simultaneously with the absorp-
tion of the methane, the liberation of nitrogen also
went on. The formation of nitrogen may be explained
thus: the coal, while it lay in the air (all the samples
of coal were investigated after lying 11 months in the
laboratory), absorbed a considerable quantity of this
gas, and now, being put into a medium not contain-
ing nitrogen, liberates it. The quantity of methane
absorbed in 10 days reached one-third of the volume of
the quantity of coal taken. The absorption of
hydrogen being quantitatively considerably less,
thanks to the smaller content of hydrogen in the gas,
proceeded at about the same rate as the methane. The
formation of carbonic acid was very unimportant, and
then only in one case; the liberation of nitrogen in
one case reached one-third of the volume of the coal,
and in two others it amounted to one-seventh and
one-eighth part of the volume of the coal.

Dealing with earth tremors and microseisms and
their influence on the liberation of gases, he states that
observations made at the Makeieff rescue station, which
has a seismic station of the first order on the ground,
do not support the hypothesis of the influence of
microseisms. The Ivan shaft, in which tests were made,
stood at a distance of about a verst from the station,
which made the data obtained particularly suitable for
comparison. Between the microseisms of the first order
and the liberation of gas no connection could be
observed. Between the microseisms of the second order
and the volumes of gas some connection was noted, but
the microseismic variations of this series appeared to
be connected, according to Yuvenalieff, with changes
in the barometer.

On the influence of the quantity of coal produced
on the liberation of gas, he shows, by a table of the
tests made in the Ivan shaft, that the process of
separation of gas and the content of the methane may
differ at various hours of the day, for the work is not
always carried on with the same intensity.

On the relative gas-containing capacity of coal beds,
he states that in Russia, according to official data, this
factor was considered in 1878 in the Donetz basin,
when the first explosion occurred there; and at the
beginning of 1880 at the Egoshinsky mines of the
Ural. The committee in 1898 observed the largest
liberation of gas in the mines of the Donetz basin, to
the extent of 6-6 cu. m. per ton. In 1903 Prof.
Skotchinsky found a higher number, 12-7 cu. m., in
shaft No. 8 of the Chukovsky mine. But, by this
time, the figure has been exceeded in a good many
mines.

The quantity of gas contained in a bed depends in
the first place on the nature of the coal: that is, on
the constitution of the original vegetable remains, the
positions of their first decomposition and metamor-
phosis, and also on the quantity of volatile substances
contained at a given moment in the coal. All these
factors will influence more or less the content of
methane in the coal. Its retention in the bed, how-
ever, depends on other causes: the depth at which the
bed is found, the strength and porosity of the over-
lying rock, the extent of later dislocations, their
greater or lesser liability to fissure, the presence of
cracks due to thrusts, the connection between the bed
and the surface, etc.

Following on a study of the geological growth of
beds, and their richness in gas, the author says that
at the moment there are known to be 110 or more
gassy mines in the Donetz basin, although the data in
his hands enabled him to classify 78 only. On the dis-