338

THE COLLIERY GUARDIAN.

February 15, 1918.

Mr. Casmey suggested that grease found its way to
that particular part of the boiler plate. If a plate
became at all greasy, the water was kept away from
the plate by the coating of grease, and then there was a
possibility of the plate becoming overheated. Then
there came in the human element.

Mr. Conway-Plumbe said it seemed to him Mr.
Casmey sought automatically to find a ratio between
the air supply and the coal supply which could not
be got away from. That might be all right where the
draught was constant, but where the draught was vary-
ing they needed some other criterion. The accepted
criterion was the percentage of C02. Was the C02
recorder used continuously in the experiments, or did
Mr. Casmey rely upon snap tests?

Mr. Casmey said the instrument he had used, and
was still using, was continuous. There was nothing to
get out of order, no rubber tube or anything to leak.
He had had it for 12 months, and believed it to be the
best means for the purpose. It was made by the
W. W. Patents Company, of Leeds. There was a
copper vessel, and inside, a porous box containing an
absorbing cartridge—dry absorbent. The gases passed
from the side flue into the copper vessel, and through
the porous box. The C02 was absorbed by the dry
agent, and the partial vacuum formed was indicated
by a water gauge. The rise and fall of the water
indicated the percentage of CO2.

Mr. Bramwell said he was interested in the removal
of the cross tubes in the flues. Years ago he came to
the conclusion that they were no good; they were
a nuisance, and he had them pulled out. In all the
new flues they put in they left the cross divisions out.
He was pleased to hear Mr. Casmey found they were
no good.

Mr. T. R. Wollaston said he did not see any reason
why they should not get any possible temperature
from a furnace and use it in a boiler, providing it was
free from scale, and, particularly, free from grease.
Mr. Bramall mentioned that he found a little dust.
If he collected a little of that dust and then got an
iron spoon and turned it over he would probably find
a strong smell of oil about it. In dozens of cases there
was absolutely no appearance of oil, but one could
detect its presence by the nose. Personally, he had
a strong belief in taking snap records of CO2. He used
one of the simplest apparatus known, the Bunte
tube; which was easy to work. On the question of the
reduced grate area he was in agreement with Mr.
Casmey, but the problem of economising coal might be
approached in a different way, and he had come to the
conclusion that the gas producer was the right way to
consume coal. The combustion of coal was a very
intricate chemical process, and one could not get the
best results in a boiler even with the use of a chain
stoker. If they could by any means gasify the fuel
first, and then burn it with secondary air, he did not
see any reason why they should not get 18 or 19 per
cent. CO2, which would mean perfect combustion. The
Lancashire boiler was a splendid piece of engineering
work, but one could not get ideal combustion in it.

The Chairman said he was interested in the question
whether it was possible to get the temperature too high
because he had experience of at least three cases of
collapsed furnace, the crowns coming down very
shortly after the temperature of the furnace had been
increased substantially through the introduction of
forced draught. He was glad to hear that, given clean
plates, one could not get the temperature too high, but
the difficulty was to have the plates always clean. They
had the human element to deal with.

THE LONDON COAL TRADE.

Thursday, February 14.

Business during the past week has been comparatively
quiet. The demand has considerably diminished at many
of the depots, but the volume of trade doing still con-
tinues fairly good. Many of the merchants, especially
in the North London district, are beginning to ease off the
pressure for fresh supplies, but in the East London depots
the urgency for supplies seems to be as keen as ever. The
market has been well attended, and evidently more coal
is offering, and in the outlying districts the demand con-
tinues strong. The wagon question is causing considerable
anxiety, and in a good many directions collieries will only
accept orders on condition of empties being set in. The
railway companies are bringing forward the loaded wagons
regularly and promptly, but the heavy delays to the
returned empties are causing a great shortage. Hard steam
coals are very difficult to obtain, and the factories on the
Thames-side are often in great straits for want of fuel.
Nutty slacks and unscreened coals are still being used
plentifully. Silkstone and best coals are easier, and all
the depots report a good stock in hand, but Derby brights
and kitchen cobbles are wanted. Bakers’ nuts and double
screened nuts are in urgent demand, and supplies are very
meagre. The seaborne market is firm, and the arrivals at
the beginning of the week showed 31 contract cargoes for
Monday’s market; on Wednesday seven arrived. The
rough weather along the coast had a good deal to do with
the diminished arrivals during the week.

From Messrs. Dinham, Fawcus and Company’s Report.

Friday, Feb. 8.—The seaborne house coal continued
quiet, with no cargoes on offer. Arrivals, 1.

Monday, Feb. 11.—There was a good demand for sea-
borne house coal, and the few cargoes available were
readily disposed of, but no quotations made known.
Cargoes, 31.

Wednesday, Feb. 13.—The seaborne coal market was
quiet, no cargoes being on offer. Cargoes, 7.

About 4,500 commercial vehicles have already been
equipped for using coal gas instead of petrol, and appli-
cations have already been made for a further 2,500 vehicles.

The Appleby Iron Company has been acquired by
Messrs. Steel, Peech and Tozer Limited, steel manufac-
turers, Sheffield.

An extraordinary situation has arisen at Liverpool docks
owing to the attitude of the bucket work coal heavers, who
suspended labour over the question of conditions of
pay. It is understood that the men claim a guaranteed
wage of 12s. per day in place of the present system of
piece payment. They resumed work, pending settlement.

COAL ECONOMY FROM A NATIONAL
STANDPOINT.*

By W. H. Casmey.

The recently published reports of the Fuel Research
Committee indicate that the future of utilisation coal
may be on the lines of carbonisation, thereby enabling
valuable by-products to be secured which, under the
existing conditions escape into the atmosphere. It is
also suggested to create a number of huge generating
stations from which electricity will be distributed and
great economy effected. Such a scheme has much in
its favour, especially where steam is not required for
industrial purposes. These lines are no doubt the right
ones, but to make such a drastic change will take many
years to accomplish, and cost much money, and even
then will not be as elastic as our present methods,
which, though wasteful, could be readily modified,
whilst, in any case, separate steam plants will be
required for practically the whole of the textile trades.
The object of the present paper is to indicate briefly
how we are wasting our coal, its general effect on the
community, and a proposed remedy or stepping stone
from the present low over all boiler efficiency of about
62 per cent, to the more scientific one which the
Research Committee will ultimately arrive at, some-
where in the region of 80 per cent, to 85 per cent.
Whereas years must elapse before truly scientific
stoking of boilers becomes general, the proposed bridge
between “Now” and “Then” could be in operation
over the whole kingdom inside one month from instruc-
tions being given for its adoption, and without practic-
ally any cost to the steam user.

Cause.

If the methods of stoking at home and in the boiler
house are examined it will be found that the losses
were primarily due to overlooking the simple fact that
air is just as essential as coal in producing heat, that
the gases liberated when a fire is first stoked will not
ignite at a lower temperature than 800 degs., and that
the first effect of stoking a fire is to reduce its tem-
perature.

Dealing first with the domestic grate, the consump-
tion of coal throughout the kingdom for such fires is
nearly 40,000,000 tons a year. The fire is allowed, as
a rule, to burn very low before mending and then a
shovelful of coal is dumped on, with the result that
its temperature is at once reduced much below the
ignition temperature, and a thick stream of smoke
flows up the chimney, depositing soot from bottom to
top and carrying the remainder of its load into the
atmosphere. That stream of smoke continues, in
gradually decreasing volume, until the temperature
of the fire returns to over 800 degs., but, meanwhile,
nearly all the gaseous part of the coal has escaped,
viz., about 25 per cent, of the total weight. There-
fore, about 10,000,000 tons escape from our home fires
in the form of smoke annually. Moreover, probably
as much, or even more, is lost with the ashes.

Boilers.

The general method of stoking steam boilers is but
a repetition of that indicated above, for instead of
watching the fires or chimney the steam gauge receives
the chief attention, and when it shows a backward
movement stoking is at once started. The natural
result is that the steam pressure rapidly falls, due to
the loss of heat taken up by the new charge of coal, and
smoke is emitted from the chimney until the furnace
temperature reaches the point where the carbon and
oxygen chemically unite, and from which point the
useful temperature of the furnace is quickly restored.
During the black smoke period, however, 10 per cent,
of . the coal thrown on the fire escapes. All losses in
the boiler house are not attributable to the fireman,
the want of uniformity in boiler grates and outlets
being a responsible factor, though not the principal
one. As an illustration, one takes three Lancashire
boilers : 30 ft. by 7 ft., 30 ft. by 8 ft. and 30 ft. by 9 ft.,
all with the standard grates, 6 ft. long, and operated
on by the same chimney draught; the proportion of
grate to outlet from the furnace flues is, respectively,
4 to 1, 3} to 1 and 2f to 1, so that the 9 ft. diameter
boiler will burn as much coal on 2| sq. ft. of grate
as the 7 ft. diameter boiler does on 4 sq. ft. In other
words, the draught in the larger boiler furnaces is
much better than in the smaller boiler.

To emphasise that very important point, we should
consider the chimney draught operating on the three
boilers as a constant equal to 1,000 ft. per minute.
The respective grate areas being 33 sq. ft., 38 sq. ft.
and 45 sq.ft., the actual air velocities through the
grates will be for the 7 ft. diameter boiler 250 ft.; 8 ft.
diameter boiler 290 ft.; 9 ft. boiler 370 ft., and the coal
burned per sq. ft. of grate will be 121b., 171b. and
201b., respectively. If the evaporation be, say, 81b. of
water per 1 lb. of coal on each boiler, the hourly
evaporation per sq. ft. of grates will be 9*6 gals., 13-6
gals, and 16 gals. Therefore, with a ratio of grate to
outlet from furnace flues of 2-75 to 1, 15 per cent, more
water is evaporated per sq. foot of grate than with a
ratio of 3-25 to 1, and 40 per cent, more than with a
ratio of 4 to 1, and yet one lays the blame on the boiler
attendant for not securing better results, whereas it
was one’s own neglect. The three boilers specified can-
not give uniform results, because, although all have
the same draught at the chimney, the smaller boilei'
can only burn 420 lb. of coal per hour, and that means
a very thin fire and, therefore, much excess air and
low efficiency. The 8 ft. diameter boiler will burn
6081b. of coal per hour, or about 61b. more per ft. of
grate. Therefore, a slightly higher efficiency is secured
and the 9 ft. diameter boiler will burn 9001b. of coal
per hour (201b. per ft. of grate), and the efficiency of
the boiler will be higher than either of the others.

Another fruitful source of adding to our coal wastage
is cross tubes in furnace flues and defective brickwork
around the boiler, or economiser; and in-leakage of
cold air into the internal flues has the same effect as

* From a paper read before the Manchester Geological
and Mining Society on February 12.

tilting the chimney of a paraffin lamp. To intercept
the heat which leaves the boiler, economisers are fixed
between the boilers and chimney and used to heat the
feed water for the boiler. Many engineers believe
that the higher the temperature of the economiser
water the higher is the boiler efficiency, and that fancy
costs many thousand tons of coal every year. Uncovered
steam pipes mean a loss of heat, and therefore a loss
of coal probably ranging from 7 to 10 per cent, of
that used in the plant; and boiler scale is a further
cause of waste, it being no uncommon thing to find the
shell and flues coated with scale % in. or more thick,
the heat-transmitting power of which is approximately
only two-thirds that of boiler plate.

Effect.

The effect of any boiler attendant ignoring the
elementary laws of combustion, is to give himself
unnecessary work, waste his employer’s money, flood
the atmosphere with dust, soot, and foul gases, and
lay the foundation for winter fogs. In one of
our largest cities, with an annual death rate of 18 per
1,000, a few days continuous fog increased it to 25,
rising in one week to 33; and that wasted 1 uel plays
a serious part is evident from the fact that, in the
Attercliffe district of Sheffield, for example, the
average monthly fall of dust per square mile in 1914
was 56 tons. Actual analysis has shown that the
gaseous and solid impurities found in the atmosphere
in foggy weather are the same as found in gases leaving
furnaces; hence the confidence in the statement that
black smoke and other products of imperfect combus-
tion are responsible for fogs.

The Remedy.

For perfect combustion, 1 lb. of coal requires (about)
12 lb. of air, and the resulting temperature is 5,000
degs. Fahr. The temperature of combustion is consis-
tent, and if more than the specified weight of air be
present, the temperature is reduced in proportion to
the weight of excess air. For steam raising purposes,
5,000 degs. Fahr, is much too high, and a mixture of
15 lb. air and 1 lb. coal gives good practical working
conditions. Therefore, it should not in any case be
exceeded. A more common practice is to supply
nearer 30 lb. of air per pound of coal, the result being
a reduction in temperature of 25 per cent., which
decreased the radiating powers of the furnaces over
50 per cent. The value of a high temperature is,
therefore, most apparent.

To obtain the best results with, say, a 30 ft. by 8 ft.
Lancashire boiler, the distance from the rear end of
the boiler to the brickwork should be the same as the
diameter of one furnace flue at the front end. The
bottom flue width should be half the diameter of the
boiler, and the depth equal to the diameter of one of
the furnace flues, front end. Along the bottom flue a
division wall should be built 9 in. thick to within 6 in.
of the boiler plates, in order to convert the convected
heat of the gases to radiant heat, and thereby enable
the boiler to secure a larger share of the heat generated
in the furnaces. In the side flues the brickwork
should not be nearer than 15 in. to the swell of the
boiler. Outer walls 18 in. thick, with a 2 in. cavity
in the centre, filled with flue dust, and there should
also be a 2 in. layer of flue dust between the top of the
concrete foundation and brickwork paving on the top
of it. The dust cavities act as a non-conductor, thus
preventing heat from escaping through the brickwork
by radiation, or being conducted into the earth;
further, in case the walls should crack from any cause,
the dust at once fills up the opening and prevents cold
air getting into the flues. All the external walls,
whether belonging to the main flue or the economiser,
shut the dust cavity. The feed water entering the
boiler should be carried to the bottom of the boiler
before liberation, this practice ensuring positive circu-
lation, and preventing the feed from minimising ebulli-
tion, and thereby reducing the rate of heat transmis-
sion from the furnace to the water.

These notes, which apply to steam boilers of the tank
type, show why the domestic fire is most wasteful as at
present used. Part of its time it merely acts as a gas
retort; for a short time it radiates a fair proportion of
heat into the room; but as it burns lower its radiating
powers decrease. To secure economy, coal must be
supplied to the room grates in small quantities whilst
the fire is still bright; thus the temperature will be
maintained, smoke minimised, and coal consumption
reduced. Cinders must be used up with the smallei'
quality of coal.

Tn a boiler furnace the conditions are more adapted
for economical combustion, but the factors of loss are
the same in both cases—too much air and stoking at
the wrong time. Taking the 7 ft. diameter Lanca-
shire boiler already referred to, it would be necessary
to provide a grate 3 ft. long instead of the standard
6ft., to secure the proportion of 2 sq. ft. of grate to
1 ft. of outlet from the internal flues, say, a total area
of 16-5 sq.ft., the chimney suction being, as before,
equal to a velocity of 1,000 ft. per minute. The reduc-
tion of the grate area will increase the draught through
the remaining parts of the furnaces, and enable the
same weight of coal to be burned on the 16’5 sq. ft. of
firebars as on 33 sq. ft., as used originally. Instead of
121b. of coal per square foot of grate, it will now burn
241b., and work with thicker fires; thereby reducing
the excess air so that the weight of air per pound of
coal will be, say, 151b. The furnace temperature will
be about 2,500 degs., or from 25 to 30 per cent, higher
than with an air supply of 25 lb. per pound of coal.
A boiler grate area of 16J sq. ft., with a ratio of 2 ft.
of grate to 1 ft. of outlet, and fed with such a mixture
of coal and air, will radiate 13 per cent, more heat than
33 sq. ft. of grate supplied with coal and air in the
proportion of 1 to 25, the ratio of grate and outlet
being 4 to 1.

Assuming that under the present arrangements the
evaporation is 81b. of water per pound of coal, that
will be increased to 9-02 lb. The quantity of coal
required to evaporate 17,9201b. of water will be
reduced from one ton (2,2401b.) to 1,9861b. A saving
of 150 tons per year will be effected in the case of a