1072

THE COLLIERY GUARDIAN

December 1, 1916.

ECONOMIC APPLICATION OF ELEC-
TRICITY TO MINING.*

By J. H. Pease.

Electricity is to a great many, practically speaking, a
new power, and, like all other innovations, has to break
down that wall of prejudice which confronts every new
power or mechanism entering the industrial world; and
it is this prejudice which in a great many instances con-
demns anything new, whether it be a system or a
mechanism, before even it has been tested or given a
trial. So it is with electrical power. In some collieries,
where it would prove the ideal method of applying and
transmitting energy, one will see uncovered steam pipes
radiating in all directions, with their wasteful condensa-
tion of steam, small .steam units with their own boilers,
etc., in various places, each one, in most cases, wasting
more steam than it uses; and the whole constituting
nothing but an exhibition of power waste and ineffi-
ciency. In others, one will see an endeavour to apply
power, not by one system, but two, and even three and
four systems; you will probably see electric cables,
steam pipes, compressed air, and even transmission by
water, and all within a small radius of one another. The
following will be an endeavour to show the mistake of
generating and applying energy by a number of systems
close together.

Installation Considerations.

In the installation of a system, the selector is often
influenced by pre-conceived ideas and opinions. He
may have spent a number of years in association with a
particular system, and seen it operate economically and
successfully, and become imbued with the idea that it
can be applied universally, irrespective of the conditions
under which it may have to operate. Another point is
that, in most of the large power stations, the govern-
ing principle of economical operation, and one which is
seldom practised in collieries, is that the greatest
economy and efficiency are obtained when the maximum
of energy is generated by a minimum of units. Taking
as an example a colliery handling, say, 2,000 tons per
day, would it be more economical to have instead four
collieries handling 500 tons each per day? Now, apply
the simile and call the colliery the unit and the coal the
energy, and it will represent the maximum amount of
energy generated by the minimum number of units,
which is more economical than the same amount of
energy generated by a greater number of units, or by
a number of systems. The larger the unit, the more
economically and efficiently it will operate. For
instance, in 1901, a large power station in America
installed a number of 7,500 kw. reciprocating sets, and
four years later, although these represented the highest
development in engine manufacture, four of them were
taken out, broken up for scrap, and turbines put in their
places, each having a capacity of 30,000 kw. There-
fore, four turbine units were generating the same
amount of energy as 16 reciprocating units. So that a
summary of the above would point to a colliery gener-
ating the whole of its power by one system, and in as
large a unit as possible.

The Most Suitable Boiler.

In dealing with the individual parts of the system,
the boiler will be the first step in the generation of
energy. In connection with the boiler, the fact must
not be lost sight of that the ultimate economy will
depend to a great extent on the condition under which
it will have to operate. Lancashire boilers are not used
on steamships; but while they cannot compete with the
tubular boiler under these particular conditions, many
collieries use tubular boilers under colliery conditions.
Under marine conditions, the disadvantages of the
tubular boiler are compensated for by its other merits;
but under colliery conditions they disappear consider-
ably, and it is then that the Lancashire boiler shows its
superiority, having low maintenance cost, large steam
capacity, accessibility of parts; it can also be fed with
comparatively inferior water, and there is no danger of
wet steam.

Efficient Combustion of Fuel.

Of all the important parts of a power plant that seem
to have made little, if any, improvement in its economy
must be classed that of the efficient combustion of fuel
under the boiler. Even with the most rigid economy in
large power stations, there is still 15 to 20 per cent, of
the power wasted owing to the necessity of having the
flue gases, between 500 and 600degs. Fahr., to main-
tain the draught; while in average colliery practice, this
waste will amount to 25 to 55 per cent, of the power.
Every lb. of coal requires 12 lb. of air for its complete
combustion, but owing to the incomplete distribution
of the air, this amount is usually increased to 221b.
Since all this surplus air tends to reduce the tempera-
ture of combustion, any system that will obviate it
will tend to a better economy. This.has been gained to
a certain extent by forced draught; but a system that
commends itself as being more economical and efficient
is that of induced draught. Objections have been raised
against it, some contending that the hot flue gases
destroy the fan blades, but it will be easily seen that
these gases can be reduced to such a temperature as to
be rendered quite ineffective by absorbing the heat from
them with the air necessary for the combustion of the
fires, besides the heat absorbed by the use of econo-
misers, etc. Now, the temperature of combustion
under average conditions will be about 2,000 degs. Fahr,
and the temperature of the flue gases 700 to 800 degs.
Fahr., while under power station conditions the com-

* From a paper read before the Ipswich (Queensland) and
District Mining Institute.

bustion temperature will be about 2,500de^s. Fahr.,
and the flue gases about 550 degs. Fahr.

The waste in the first case would be	— 37 percent.

ZjVVV

The waste in the second case would be ^2 x =22 percent.
2,500

The waste with induced draught.... ^9 * *99 = 6'9 percent.

2,600

The fixed cost per annum at 10 % for chimney stack = £15

The fixed cost per annum at 14 % for induced draught =	8

£17 16s.

£6 16s.

£7 0s.

£2 10s.

£4 10s.

Difference = £7

Cost per annum at 0'2d. per boiler horse-power hours for
chimney draught would be ??2L^^i2L?»999 -= 143 x 7 = £150.

12 x 20

Cost per annum at 0’2d. per boiler horse-power hour for
induced draught would be	- £18.

12 x 20

Net annual economy for 100 kw. plant = £150 — £18=£132.

Economy of Feed Pumps.

In examining the economies of feed pumps, one might
think at first sight that such a detail would not pay for
the investigation, but the ultimate efficiency of a power
plant can only be gained and kept in a high state by the
rigid examination of all power losses, no matter how
small they may be, and the taking advantage of all
modern apparatus which tends to keep that efficiency in
a high state. The ordinary reciprocating feed pump is,
perhaps, the most simple and the most popular pump in
and about collieries for that purpose, but simplicity does
not necessarily mean efficiency. As an instance, the
duplex-feed pump is about the most expensive piece of
machinery about a colliery, when considered from the
point of view of steam consumption. As an example :
For a 100 kw. plant, the power cost per annum for
duplex as compared with a turbine-driven pump would
be for the duplex :—

.150 x 3	15 x 2,000 x 0'2d.

As------- =-------------------...	=

30	12 x 20

The turbine40/ 3 = 4_L--2-’0002L9^-........ =

30	12 x 20

The fixed costs per annum at 14% for the turbine
pump will be..................................

The fixed costs per annum at 14% for the duplex
pump will be..................................

The difference will equal ....................

Net economy per annum for 100 kw. plant with turbine
pumps = £17 16s. - (£6 16s. + £4 10s.) = £6 10s.

Question of a Condenser.

In the laying out of a plant, a question that is often
raised is : Will it pay to include a condenser? As far as
a good many collieries are concerned, the question seems
to have been answered in the negative; in fact, some
consider it an altogether superfluous piece of machinery
—something, in fact, that, as far as a colliery is con-
cerned, is nothing more than a fad. Considering the
question on a 100 kw. basis, and taking the following
data, steam pressure (gauge) 801b., and steam tempera-
ture, 323 degs. Fahr. :—

Fixed costs per annum at 13% will be 300 x 0'13 = £39.

Power cost per annum to work auxiliaries will be 300 x 0'04
= £12.

Horse-power hours saved with 24 in. vacuum will be

P.S. A. V.P.

560 x 200 * 12 i ,
-------------- — 40 n.p. hours.

33,000	F

Net economy per annum with power at 0'5d. per unit will be

H.P.	A.H.

40 X * 2’Q00 = ■£165 ~ •£39 + "®12 = •£114-
OdjVVV

Return on capital expended will be	9 = 38per cent.

Uncovered Pipe Radiation.

One of the easiest remediable losses in a colliery, and
one which shows the greatest return for capital expended,
is that of uncovered pipe radiation. Taking, as an
example, a 4 in. pipe, 100 ft. in length, and steam at
801b. (gauge), temperature steam 323degs. Fahr.,
and temperature of atmosphere at 80 degs. Fahr., the
thermal units in the steam will be :—

323 + 886 temperature of steam plus latent heat of
evaporation at that temperature — 1,209.

A. T. T1 C.

Thermal units radiated per hour will be 100 x (323 - 80) 2'7
= 65,600.

Thermal units radiated with average lagging = 12,000.
Therefore, units saved will equal 65,600 — 12,000 = 53,600.
Fixed costs per annum at 12 per cent, will be £18s.

Annnal cost of power wasted by radiation 0'5d. per horse-
power hour will be	0‘5d. x 2,000 =

1,209 x 30 x 12 x 20

Economy due to lagging 100 ft. of piping = £6 - £1 8s. =
£4 12s. per annum.

Size of Conductor.

In the transmission of power electrically in and about
collieries, it is seldom that much attention is given to
the most economical siz-e of conductor. Although the
special rules limit the scope of anything being done in
this direction underground by specifying the size of
cable to be used for a given current, these are not neces-
sarily the most economical sizes; and, while they have
to be adhered to in places where specified, they should
not be taken as a cast iron guide when not necessary.
All these sizes, as specified in the rules, have been cal-
culated for a 10 degs. Fahr, temperature, which is an
absurdly low limit, especially for main roads under-
ground; and, when we consider that a motor situated in
the most dangerous place is allowed to reach any tem-
perature short of taking fire, then a temperature rise
of only 10 degs. Fahr, seems somewhat of an extreftie.
The result is that larger and more costly cables have to
be put in.

Questions of Capacity.

It sometimes happens in a colliery installation that a
generator is not of sufficient capacity to take care of the
peak loads, although there is ample margin at all other
times of the load, and the installation of another unit or

a battery system is out of the question. The method
which suggests itself as getting over the trouble, provid-
ing the mechanical unit is sufficiently powerful to cope
with the overload, is to pass 3,000 to 4,000 cu. ft. of
air per minute over the windings by closing one end
of the generator and connecting a 24 in. suction fan
with air brought from outside the engine room. The
total cost of apparatus would be about £30, and 50 per
cent, overload could be gained for one hour, the annual
value of which would more than pay. for the fan
installation.

A phase of economy relative to the transmission of
power, and one that is of especial importance to coal
cutters, haulage motors, etc., is that of maintaining an
efficient voltage at the motor terminals. Nothing is
more disastrous to the life and efficient working of a
motor than having a low voltage at its terminals, for
it can be seen that a motor exerting a given horse-power,
and its voltage dropped (say, for example) 50 per cent.,
then in order to exert the same horse-power, it must
double its current, and therefore double the stress on

its shaft and gearing, although it is only exerting the
same horse-power as in the first case. Perhaps this

can be better illustrated in the following way :—

Supposing a belt transmitting 1 horse-power, and
having a velocity of 33,000 ft. per minute, the tension
on the belt would be lib.; then, if the velocity was

lowered to 1 ft. per minute, the tension on the belt to
x u u	u u 33,000	7~

still transmit 1 horse-power would be ———= 14 tons
r	2,240

These are extremes, of course, but they serve to illus-
trate the importance of keeping an efficient voltage at
the motor. To do this economically is not always an
easy matter, especially when the radius of transmission
has increased to some considerable distance from the

power house. The only method open under existing
conditions of most installations is to duplicate of increase
the area of the copper. A better and far more econo-
mical method is to provide for the increased radius of
transmission by keeping the underground supply unit
separate from the surface supply. The advantage and
economy of this system will be apparent from the follow-
ing considerations :—

Assuming the transmission of a 100 kw., size of cable
37/10, resist at 1 mile radius = 0'089 x 2 = 0-178 ohm,
the terminal voltage at | mile radius will be 232 (7 per
cent., or 18 volt drop), but by the time the working has
increased to a radius of 1 mile the voltage at the motor
will have fallen to 178 (drop 28 per cent., or 78 volts).
To bring 'this terminal voltage back up 213 volts would
necessitate the duplication with another cable 0-51
sq. in. in area. 61/12 area, 0'51 sq. in. area of 37/10,
0'47; area of cable to give 213, or 15 per cent., at motor
= 0-95 91/11. The cost of 2 miles of this cable would
be £2,080 installed; but by having the underground
supply separate from the surface supply, and then
increasing the voltage 14 per cent, at the power house,
or 285 volts, we then get 213 at the motor without any
additional expense of cable. The saving of £2,080 more
than compensates for two separate units.

Another phase of electrical economy, although it may
not be obvious at first sight, is that of deciding the size
of motor for a given amount of work to be done. Some
would probably consider that for, say, 20 horse-power
of work to be done, the correct thing would be to have
a 20 horse-power motor; but a little consideration will
show that this is not quite so correct as it may seem.
Most makers give a guarantee that the temperature rise
of their motors will not exceed a certain amount after
having run at full load for a stated time. This is usually
70 degs. Fahr, temperature rise above engine room tem-
perature after a period of six hours’ full load in one.
This is an absurd specification, inasmuch that it does
not take into consideration the climatic conditions under
which the motor may have to operate. For instance,
the standard engine room temperature upon which this
temperature rise is based is only 50degs. Fahr., while
the average summer engine room temperature in this
climate is easily 100 degs. Fahr. This means that
instead of an ultimate temperature of 120 degs. Fahr,
at full load, it will be 170 degs. Fahr. Now, the life
of a motor will certainly not be 25 years if it is run very
long at this temperature. Many a motor which has
broken down under full load conditions has been con-
demned as a poor class of motor, when the breakdown
has been probably due to the fact of not having allowed
sufficient margin of power to compensate for the
increased temperature conditions. Given a fair margin,
and a motor will run its 25 years without giving much
trouble; but with failure to observe this it will probably
be on the scrap heap before many years of its life have

run.

Application of Electricity to Coal Cutting.

In the application of electricity to coal cutting, it is
generally conceded that, unless the conditions are
abnormal to usual mining methods, it is an economic
proposition. The mechanical cutting of coal is one that
has always been looked upon with a great deal of pre-
judice. At the time of the inception of coal-cutting
machines in New South Wales, it was frequently
remarked that they would soon be taken out of the
collieries again; but instead of being taken out, the
number was increased, and there is hardly a colliery of
any note that has not its system of mechanical coal
cutting. The vital question is that it is not so much a
question of whether it will pay or not, as an intelligent
study of the existing conditions and the selection of the
proper type of machine that will give the maximum
economy under those conditions. A case could be
quoted where a top cutting chain machine saved its
operating expense in the timber alone, not to speak of
the greater safety conditions. Here, then, is an example
where the selection of the proper type of machine suc-
cessfully solved the problem. Then, again, the selec-
tion of a chain machine, either breast or short wall, would
not be a payable proposition in a thick seam that parted