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HYDRAULIC STOWAGE OF COAL
WASTES IN COAL MINES.
The British consul-general at Dusseldorf, Mr.
Koenig, in his annual report, gives some interesting
details on the subject of "Hydraulic Stowage
of Coal Wastes in Coal Mines," says the Colliery
Guardian. He says there is at present an everincreasing
interest in hydraulic stowing of coal
waste in the coal mines of Westphalia, and it is
considered likely that the majority of the coal
mines will sooner or later be compelled to adopt
the hydraulic stowing as already introduced by a
certain number of coal mining companies. The
general idea of the method is to fill the void made
in working with material carried by water from
the surface. The object of hydraulic stowing is:
1. To support the surface and prevent buildings
from cracking.
2. To allow of the working of the whole coal in
very thick seams, thus dispensing with coal pillars.
3. To prevent surface water from flooding the
workings.
4. To support the surface carrying roads and
railways which would otherwise sink in the natural
course of time.
5. It is maintained that hydraulic stowing prevents
fire by spontaneous ignition, thus causing
greater safety to the miners.
0. Hydraulic stowing is stated to be a saving
in Ihe timber used underground.
In olden times the main thing in coal mining was
to produce large quantities of coal and thus keep
down the cost per ton. Under government regulations
certain pillars of coal had to be left to support
railways and buildings. To-day the laws as
to surface damages are very strict and claims for
compensation are very frequent. The expenditure
under this heading has become very considerable,
so that in many cases hydraulic stowing
has become a necessity. It would appear that
under the new system of hydraulic stowing the
leaving of coal pillars as supports would, to a
large extent, become superfluous. The substitution
of a complete support is one of the burning
questions of the day, especially in the thickly populated
mining and industrial district of Westphalia,
where the value of landed property and buildings
has increased so enormously.
With regard to the materials used for hydraulic
stowing, the ideal material would appear to be
sand wherever immediately available. In many
cases, however, pit waste, blast furnace slag, and
ashes are used. The slag is reduced to a sandy
state, and in this form proves to be very good
stowing material. In Westphalia sand is not
always available and substitutes have to be found.
ground down, and well mixed before being flushed
down the pipes for stowing purposes. In the
Saarbrucken State mines the material used is
THE COAL TRADE BULLETIN. 41
chiefly boiler ashes and furnace slag mixed with
brick clay. The storage there has proved so successful
that they have been able to win the pillars
of coal left to support the surface where formerly
surface damage had taken place. It is
said that in some cases in thick seams the loss of
coal under the old system, apart from safety pillars
left standing amounted to 40 to 50 per cent.,
which, it is proved, would be entirely obviated
under the new method. In many cases in Westphalia
the coal is being worked from under the
villages, and in some eases towns, where the damage
caused to the surface used to be very heavy;
the hydraulic system has been installed, and has
proved a great success, preventing further subsi
dence of the surface. It is generally considered
that hydraulic stowing does not prevent surface
damage entirely, but it has been proved to keep
down the claims caused by subsidence of the surface
to a minimum. In all cases hydraulic stowing
has been found a great improvement on the
old method, the coal output being increased, and
the costs experienced in the past from claims for
damages being vastly decreased.
With regard to the pipes used for hydraulic
stowing, steel or wrought iron is chiefly used, with
a cast iron, cast steel, or porcelain lining. The
diameter of the pipes averages about 7 inches. The
cast iron lining appears to be the one preferred,
and is less expensive than the porcelain lining.
With regard to the cost of hydraulic stowing it
appears to vary very much, according to the material
used in flushing. The cheapest material is
sand where it can be obtained on the spot, whereas
the most expensive material is that which has to
be ground down and mixed before it can be used.
The actual cost of hydraulic stowdng would appear
to be anything between 6d. and 1s. 6d. per ton of
coal.
When it is considered that under the old system
of work the loss of coal is in some cases some 40
to 50 per cent., and that the production in Germany
in 1909 amounted to 148,900.000 tons, of
which 85.000,000 tons, or nearly 60 per cent., was
produced in the mining board district of Dortmund,
and that Germany's total output in 1910
amounted to 153,000,000 tons, it would mean a dead
loss (taking 20 per cent, only as an average loss)
of coal left in the pit of about 30,000.000 tons in
one year, an enormous saving in national wealth
being possible in the adoption of the hydraulic
stowing system, which is so simple and inexpensive.
Assuming the production in the United
Kingdom to be at the very least 270,000,000 tons
per annum, there would be a saving of 54,000,000
tons per annum at least.
The advantages claimed in Westphalia are as
follow:
1. The increase of the total coal output per