914

THE COLLIERY GUARDIAN.

November 1, 1918.

diately below the South Reef pillar, is largely un-
payable, so that there is no probability of its being
removed, and no danger is anticipated from this
source, as experience has shown that the large rock
bursts do not occur when an excavation exists either
above or below a block of ground; but if it were neces-
sary to remove this other shaft pillar, it would be
taken out in a similar manner. From the solid nature
of the pillar which was observed during the course
of removal, there is little room for doubting that if
it had been allowed to remain further rock bursts
would most certainly have occurred.

Severe earth tremors are still being felt on the mine,
and the most violent yet recorded at the Observatory,
that of November 15, 1917, while damaging some of
the lower levels, did not cause the slightest movement
near the shaft.

In the light of the experience of the Village Main
Reef and other neighbouring mines that have suffered
in a similar manner, it seems probable that more
attention might profitably be given to the subject of
shaft pillars. The general tendency in European coal
mines is to leave very large supports for the shaft,
and in some of the deeper mines pillars having an
area of over 130 acres have been left. In South
African mines the size of the pillar is too often deter-
mined by the gold contents of the ore, a generous
measure of protection being given where low grade
rock surrounds the shaft, but with rich rock a much
smaller support is deemed sufficient. In the new mines
of the East Rand special precautions will have to
be taken if creep and crush are to be avoided, as the
soft slate footwall of our eastern mines is very similar
to that found below the coal measures, and unless
pillars are left of large area, the main arteries of
the mines will certainly suffer from creep and crush
even more than the central mines have done.

Some mining engineers have gone so far as to state
that shaft pillars are neither necessary nor desirable,
and that an excavation should be started from the
shaft bottom and extended outwards to the boundaries
of the claim area, the space round the shaft being
packed as tightly as possible with stone packing. In
this way settlement would not be so great and would
be more even, and the shaft would not be so liable to
get out of plumb. Gob fires in coal mines due to
crushing would also be avoided. .

MAXIMUM PRICES OF FRENCH
COALS.

The following maximum prices per ton for French
coals (f.o.r. at colliery) are now fixed for the under-
mentioned collieries. The figuies in brackets represent
ash percentages:—

Charbonnages du Centre.—Anthracite, picked nuts,
55-80 mm. (under 15), 7915 fr.; washed beans,
25-55 mm. (17), 79 15 fr.; washed nuts, 15-25 mm. (20),
72T5 fr.; washed beans, 5-15 mm. (18), 67T5 fr.;
unwashed small, 0-5 mm. (21), 4515 fr.; washery
sludge (30), 30-15 fr.; briquettes (19), 7915 fr.

Mines de Saint-Agnes.—Through and through (32),
43 fr.

Soc. Nouvelle de la Condemine (Mines des PlamoresJ.—
Large screened, over 25 mm. (under 28),41fr.; medium
screened. 25 mm. (35), 32fr.; washed, small, 0*25 mm.
(26), 30 fr., 0'25 (32), 25 fr.; extra large, 40 mm. (30),
37*50 fr.; large, 40 mm. (35), 31*50 fr.; large beans,
15-40 mm. (30), 32*50 fr., 15-40 mm. (35), 27*50 fr.;
small, 0*15mm. (83), 26*50 fr.; through and through
(35), 22 fr. (at pit head).

Soc. Anon, des Mines de Charbon des Alpes.—Lean
cobbles, 40 mm. (18), 36*50 fr.; lean screened, 25 mm.
(20). 30*50 fr.; bituminous screened, 25 mm. (25),
30*50fr.; through and through, with one-third lean
screened (23). 28fr.; bituminous through and through,
with one-third screened (25), 28 fr.; lean or bituminous
small, 0*25 (25). 26*50 fr.; through and through
unwashed (25), 26*50 fr.

Soc. Anon, des Mines de la Loire.—Large (under 10),
64 fr.; large gas cobbles, 45 mm. (10), 60*50 fr.; cobbles,
45 mm. (10), 59 50 fr.; small cobbles, 35 m.m. (25),
43*50 fr.; peas or small, 12 mm. (15), 51 fr.; washed
beans, 12-30 mm. (16), 48 fr.; washed gas cobbles,
30-45 mm. (18), 54 fr.; washed cobbles, 30-45 mm. (18),
53 fr.; washed smithy nuts, 6-45 mm. (10), 60 fr.; rough
smithy small (10), 57 fr.; rough gas small (15), 46 fr.;
small (15), 45 fr., (35), 26 fr.; washed gas small, 0-12 mm.
(15), 45 fr.; washed smithy small, 0-12 mm. (10),
50*50 fr.; gas slack, 0-35 mm. (15), 43*50 fr.; coking
srpall, 0-42 mm., 42 fr.; washed small, 0-35 mm. (28),
29 fr ; washery sludge, 21*50-25*50 fr.; briquettes (15),
63*50 fr.

Mines des Methamis (Charbonnages du Vaucluse).—
Through and through (28), 36 fr. (at pit head).

Italian Coal Supply.—Official information states that
during September the arrival of coal was slightly less than
the quota assigned to Italy. England delivered by sea in
British vessels more coal than was promised. The shortage
was in French coal, which was to be delivered by land, and
was due to obstacles of a military character. With im-
proved transport Italy expects to receive during November
considerably more than 160,000 tons, which is the quota
allotted to her.

South African Coal Output.—The annual report of the
Union Department of Mines and Departments states that
the actual output of marketable coal in 1917 was 10,949,186
short tons. The quantity sold (10,382,920 short tons)
realised £3,275,608, compared with the £2,739,665 for
10,007,502 tons in 1916. The average price obtained for
the coal last year in the Transvaal was 4s. 9-32d., in
the Orange Free State 5s. l-86d., in Natal 10s. l-76d., and
in the Cape 14s. 4-05d. The higher price obtained for
coal in the Cape is largely due to the absence of com-
petition as met with in other parts of the Union, and
not to any superiority of quality over the coal of the
other provinces. Of the 15,372 tons of coke produced,
15,361 tons were sold for £28,648. No returns of tar are
available.

FUEL OIL AND ITS APPLICATIONS.*

By A. F. Baillie.

Apart from its superiority to coal for marine pro-
pulsion, the use of coal on railways is advantageous
in countries which are not favourably situated in
respect of coal supply. A typical instance is that
of the Mexican Railway, where conversion from coal to
oil has resulted in reductions of 32 per cent, in the
weight of fuel consumed per train kilometre and of
40 per cent, in the cost of fuel. The oil can be handled
from tank cars to storage tanks, and thence to loco-
motives for about 0-015d. per ton, while the average
cost of handling coal is about 2^d. per ton. The
wastage in handling between shipment and consump-
tion (estimated at 8 per cent, to 10 per cent, with
coal) is eliminated. No men are required to load up
the engine or clean out ashpans; there are no ashpit;
to empty or ashes to be loaded up and hauled away.

In the comparative tests carried out by the
Tehuantepec National Railway, the following infor-
mation was obtained: —

The gross weight of train being approx.... 500 tons.

Time getting up 1801b. steam from cold—

coal 150 mins.

Do. do.	do. oil 70 „

Improved speed with oil over coal (average) 16*2 p c.

Do. evaporation per lb. fuel...	5 *62 lb. or 90 p.c.

Pounds of coal per JOO-ton miles . 20*8

Do. oil do. do................. ]0*3

The grades on this railway vary from level to 2-15
per cent., with many curves up to 11-5 degs., where
the train speed is limited to 15 miles per hour.

Land Steam Plants.

In the author’s opinion the output of boilers
could be augmented by 30 per cent, to 100 per cent,
by substituting oil for coal. Where used as an
auxiliary equipment to coal-fired boilers to meet re-
curring peak loads, its use not only enables the plant
to meet sudden and heavy demands, as in the case of
electrical power stations, but may obviate the neces-
sity of putting down additional boilers with the
growth of the average output of current.

The perfect smokeless combustion of oil fuel would
prevent or abate the smoke nuisance in closely popu-
lated districts. The -Public Health Act of 1871 made
it an offence to emit black smoke from factory
chimneys, and in many instances the local authorities
insist on its provisions being carried out, but much
remains to be done, as is shown by the statement that
in the Administrative County of London 76,000 tons
of soot descend every year.

On. a comparative test run at Wallsend Slipway on
coal and oil on a Scotch marine multitubular type
boiler, the following results were obtained : —

Fuel oil—

Specific gravity at 60degs. Fahr.... 0*953

Viscosity at 100 degs. Fahr. (Red.

No. 1).......................... 2,130 secs.

Flash point (close) .............. 160 degs. F. (above)

Calorific value in B.Th.U......... 18,430

Water evaporated—

Pounds of water per lb. of oil ... 12*15

Pounds of water per lb. of oil (from

and at 212 degs. Fahr.)......... 14*38

Boiler efficiency ................ 73*37 per cent.

Coal -

Calorific value in B.Th. U........ 14,432

Water evaporated—

Pounds of water per lb. of coal...	7’76

Pounds of water per lb. of coal (from

and at 212 degs. Fahr.) ........ 9*31

Boiler efficiency ................ 62*28 per cent.

Efficiencies as high as 84*5 per cent, have been
obtained on Scotch marine type boilers using Mexican
fuel oil with the pressure system of oil burning.

At a large London factory Lancashire boilers have
been converted and the following comparative figures
obtained : —

Fuel oil.	Coal.

Calorific value ...... 18,750 B.Th.U. ... 11,451 B.Th.U.

Evaporation per lb ... 14 44 1b.	... 7*22 lb.

Do. per sq. foot

of heating surface ... 7 lb.	... 3*33 lb.

In the United States a large series of actual working
temperature tests have shown that with coal the
thermal efficiency of boilers varies from 66-6 to 68-1
per cent., with oil from 80-6 to 81*5 per cent.

In this country fuel oil is mainly used in industrial
furnaces for such processes as billet heating, metal
melting, riveting, bolt and nut making, and the
manufacture of glass bottles. Of the three systems of
burners for oil fuel, the pressure jet system, in which
the atomising agent is pump pressure and steam
temperature, has been developed during the last ten
years to such an extent that it is now recognised as
the most economical system for use under land and
marine boilers, and is being rapidly developed for
locomotive purposes. The oil is drawn from the
storage tanks by a steam pump through suction
strainers, and delivered through heaters and discharge
strainers to the oil fuel burners.

A point which usually appeals- to every works
manager is the fact that when utilising oil fuel the
size of the furnace is reduced by 30 per cent., and
the working area occupied by a furnace and its ad-
jacent machines is only about 50 per cent, of that of
a coal fired furnace, -where a stack of coal occupies
a certain amount of space in front, and the ashes
another space behind. Another interesting feature
is that many metal melting manufacturers have either
scrapped their coke fired furnaces or converted them
to gas or oil. The principal metals being melted at

* From a paper read before the Manchester Association
of Engineers.

the present moment are aluminium (used for aero-
planes and motor car purposes) and what is known
as 70/30 brass (principally used for cartridges).

Auxiliary to Coal and Gas.

In the early years of this century a French engineer
introduced the subject of oil as an auxiliary. The
main advantages of auxiliary firing, he claimed, lay
in being able to obtain at will a large increase in the
power of boilers. The combustion of the petroleum
does not in any way prejudicially affect that of coal;
in fact, by the introduction of jets of petroleum the
condition and efficiency of combustion are improved
by a more complete mixture of the gases. It is therefore
not correct to consider the evaporative power of coal
as indentical when passing from ordinary to auxiliary
firing.

Admitting this as a principle, and supposing the
quantity of water evaporated by the coal to he con-
stant, the extra evaporation, due to the better mixing
of gases, is credited to the petroleum.

In several evaporative trials made on the same
boiler of a French Navy ship, when coal alone was
burnt at the rate of 18-8 lb. per sq. ft. of grate area
per hour, the water evaporated per lb was 9-05 lb.
With a mixture of coal and 45 per cent, oil, the corre-
sponding figure was 11 34 lb. ; with a mixture of the coal
and 64 per cent, oil, 14-12 lb. In this last test the
efficiency of the mixture was higher than when burn-
ing petroleum only.

These tests served as a basis for further experiment,
about four years ago, by power station engineers.
Their theory was that a poorer class of coal could
be used in conjunction with oil feul. When used
alone, the inferior coal tended to cake on the links
of the chain grate stokers, thereby retarding the neces-
sary quantity of air from being drawn through the
bars to complete combustion. The result was a
smouldering mass, which travelled slowly along the
bars and was dumped into the ashpit as a partly con-
sumed coal. On analysis this ash would probably be
found to contain a very high percentage of com-
bustible matter. Therefore a very much higher
quantity of coal was burned per hour to maintain, say,
rated evaporation.

The theory was that when fuel oil was applied, the
combustible gases rising from the coal fuel bed were
quickly ignited, causing the top of this mass to become
much more incandescent, and thereby tending to aerate
the bottom mass, which would allow sufficient air to
be drawn through to complete the combustion of the
inferior coal.

Sufficient interest was taken in this theory for a
large London power station to give their sanction for
tests to be carried out under a coal fired Stirling
water tube boiler. One burner was introduced into
each side of the boiler, approximately about 25 per
cent, from the back of the grate, the burners being
opposite one another. The oil was stored in an over-
head tank capable of holding three or four days’
supply. It gravitated to the burners, which were of
the Kermode steam-jet type, operating with steam as
an atomising agent at a pressure of about 25 lb.
per sq. in.

The first test was carried out on a nutty slack
having a calorific value of 10,400 B.Th.U., and a
boiler efficiency of 69-25 per cent, was obtained. The
temperature of the combustion chamber was 2,648
degs. Fahr, and uptake 660 degs. Fahr.

The final of a series of experimental mixed burning
tests was carried-out on a mixture of a nutty slack hav-
ing a calorific value of 10,300 B.Th.U., with Mexican
fuel oil having a calorific value of 18,750 B.Th.U. A
boiler efficiency of 74 per cent, was obtained. The tem-
perature of the combustion chamber was 2,850 degs.
Fahr., and uptake 628 degs. Fahr. The proportion of
oil to coal on a B.Th.U. basis was 8 per cent., and on
a weight basis 4-96 per cent. The comparative cost,
were—with coal only, 2-8; with the mixture men-
tioned, 2-62, showing a monetary saving of 6 per cent.

The tests showed that with oil at a cost of 2| times th^
cost of coal, and burning in the aforementioned per-
centages, a saving is effected which should induce
power station engineers to consider adopting this
method of firing in the super-power stations of the
future.

As an example of the saving effected, the following
figures have been given by a well-known firm of bolt
and nut makers in the- Manchester district: —

Gas costs Is. per 1,000 cubic feet less 5 per cent.; con-
sumption 450 cubic feet per hour ; temperature in furnace
1,750 degs.; size of bolts j in. dia. to | in. dia.; calorific
value, gas, equal 660 B.Th.U. per cu. ft.

Comparing with oil on B.Th.U. basis for ten hours’

working: —

Then 450 -10- X-e60 = 158*5 lb. oil........... =	16*7 gals.

18,750

Cost of gas for 10 hrs. =	= ^ess 5 % = 51*3d.

Cost of oil at say 2|d. per gal. = 16*7 x 2*75 ... = 45*Pd.
Saving per day by using oil = 5*4d.

Saving per year of 300 days = £6 15s. per furnace.

Bolt Making.

Figures given by a firm in the Manchester
district: —

One furnace feeds two bolt-making machines.

The output of these two machines is four tons per day.

£ s. d.

To. obtain this output, 1 ton 10 cwt. of coal

is used at 12s. per ton ...	...	...	0 18 0

Using oil at 5 gals, per hour (10 hours per

day) at 2fd. per gal. = 1/2 x 10	...	0 11 8

They have seven furnaces in operation.

This means that they pay out for coal
in six days per week :—

12s. per ton coal : One furnace burns

1 ton 10 cwt. = 18s. x 7 x 6 = coal 37 16 0

Oil consumption per week of 55 hours at

5 gals, per hour (seven furnaces =

5 x 55 x 7 = 1,925 gals.

1,925 gals, at 2|d. per gal. Oil ...	... 22 1 1

Saving in favour of oil 15 14 10