July 28, 1916.

THE COLLIERY GUARDIAN.

161

“British Baum” Coal Washing Plant.

(SPECIALLY CONTRIBUTED.)

The ordinary accepted theory of coal washing is that
the coal must first be sized, so that the particles of coal
and dirt to be separated are approximately equal in
cubic content. This theory is based upon the fact that
two such particles of different densities placed in still
• water would sink with different velocities, or, in other
words, the heavy piece of dirt would fall through the
water at a quicker rate than the lighter piece of coal.
Knowing the density, then, and the size of the particles,
the rate of fall can be calculated; and in washing
minerals this fact is recognised, by arranging or design-
ing the washer box so as to give an upward flow of
water at such a rate that, whilst allowing the heavy
particles 'to sink, the lighter particles’—e.g., coal, in a
coal washer—would remain on the surface of the water
and flow off with it. Hence, in the ordinary design of
a washery, the wash boxes are made in units, and each
unit is arranged to deal with a certain size of coal.

The “ Baum ” patent washer box, however, has quite
upset this theory, inasmuch as there is no classification
before washing, 'the different sizes from 3 in. cubes to
nothing all passing through the same washer box. It is
true that perfect results are not obtained, so far as
regards the very fine coal, say, coal particles below in.,
when these are being washed with coal up to 3 in. cube;
but it is mainly a question of degree as to the required
ash content of the washed product, and this again
depends upon the relative proportions of large and fine
coal. If, for instance, the proportion of very fine coal
is not high, then, in all probability, quite satisfactory
results can be obtained .by a single washing. On the
other hand, if a very considerable proportion of the coal
is fine, and a minimum ash content is required, it may
be necessary to re-wash this fine coal.

Womb well Washery.

The washery at Wombwell Colliery is of the latter
type, the coal dealt with being all from 1| in. to nothing,
all below f in. being used for coking.

In the ordinary type of washer box, the rise and fall
of the water is obtained by means of pistons or plungers
operated by eccentrics, or sometimes by means of levers,
whereby the piston may receive a quick downstroke and
a slow upstroke. In the “ Baum,’’ however, as is now
well known, the pulsation of the water in the washer box
is obtained by means of compressed air, furnished by
an eccentrically-driven four-blade blower, which supplies
air at a pressure of about 2 lb. per square inch /at the
valve. The washer box consists of a tank divided into
two chambers : one an air chamber, with the air valve
fitted on top; the other the washing chamber, provided
with a gauze or perforated plates, upon which the mix-
ture of coal and dirt is received. The mixture is flushed
with water into the washer box at one end, and is sub-
jected both to the pulsation set up in the water by the
action of the compressed air, and to the flow of water
across the washer box to the outlet at the other end.
It would appear that the effect of this cross-flow of
water was not sufficiently considered in arriving at the
theory above mentioned, as the results obtained in the
“ Baum ’’ washer box conclusively prove that different-
sized cubes can be efficiently dealt with in the same box.

At Wombwell Colliery all the coal passing through a
mesh of 1| in. is washed, but as 30 per cent, of this is
below one-fiftieth of an inch, and it is necessary to reduce
the ash content to 'the lowest possible amount, the fine
coal below f in. is re-washed. The washery is placed
close to the screens, and, as will be seen from the accom-
panying plans, is built over the railway lines, one of
which is the main locomotive road, which had to be
kept open during the whole period of erection.

The coal is received direct from the screens by means
of conveyor belts, and delivered to the hopper B at A,
section C.C., from whence it is raised by means of the
elevator to the washer box D. This box consists of two
sections, Dx and D2—the coal entering at Dx and passing
off at D2—and is also provided with two dirt elevators,
Sx and S2, one at each end. Most of the dirt passes
off the perforated plate through a gate into the elevators,
but the fine dirt which passes through /the perforations
is caught in a spiral conveyor at the bottom of the box,
and carried into the dirt elevator. The whole action,
therefore, is absolutely automatic, and there are no
levers or valves to be constantly manipulated by the
attendant.

After being washed, the coal is conveyed in a canal to
the revolving screen E, where it is sized into two classes
of nuts, viz., If in. to 1 in. and 1 in. to fin., all below
f in. being raised by the elevator H into the washer box
D3, where it is re-washed, and afterwards conveyed in
a canal—shown by the dotted lines in the plan I—I.—to

the draining screen J, section A—A, and to the slurry
refiner 0. This latter consists of a set of very fine mesh
vibrating screens, set at a slight inclination towards the
delivery end. The coal and water pour on to the lower
end of these screens, and the effect of the vibration is
to shake out the water, the coal gradually creeping up
the screen, and becoming, at the same time, drier and
drier, until it is delivered, over the end of the screen, as
pure fine smudge coal, containing only 15 to 20 per
cent, of moisture. The drainage water and fine slurry
saturated with coal dust from the screen J is collected
in the sump L, and is pumped up, by means of the
pump M, into the large conical settling tank N.

This consists of a large concrete structure, set upon
a square base, with railway lines passing underneath.
The diameter at the top is about 40 ft., and at the
bottom it is fitted with a 10 in. diameter pipe and valve.
The fine coal dust settles to the bottom of this cone, and,
in the form of slurry, is delivered through pipes to the
smudge or slurry refiner previously described.

The small coal from the screen J is delivered into a
large draining conveyor K, fitted with a perforated
bottom, and moving forward at the rate of from 12 to
18 in. per minute. This conveyor is constructed in such
a manner that the division plates alternately close
together and open outwards, which has the effect of
first compressing or squeezing the coal, and then loosen-
ing it, thus breaking it up, so to speak, and allowing
moisture, which would be retained in 'the solid or fixed
type of bucket, to escape. The fine smudge from the
slurry refiner is delivered on top of the coal in this con-
veyor, and the coal is discharged at the top into the
disintegrators Px and P2, with approximately 12 per
cent, of moisture. From these disintegrators or
crushers the coal is delivered on to a rubber belt con-
veyor, and carried to the coke oven service bunker;

All the water from the draining conveyor flows back
to the sump L, from whence it is pumped to the settling
tank.

Returning to the revolving screen, which, as already
explained, separates the two sizes of nuts from the fine
coal which passes to the re-washer, the nuts, after being
separated, are flushed down canals with “ glass ’’
bottoms to “ jigging ” draining tables, the large nuts to
table Fo and the small nuts to Fx (section C—C), where
the water is drained off, and the nuts are delivered into
the bunkers Gx and G2 respectively. A third bunker,
G3, is provided for the storage of coal for coking, and is
fed by a shoot from the bottom of the crusher casing.
From these bunkers the coal is delivered into wagons
as required. It will also be noticed that the bunkers for
the nut coal are provided with spiral shoots, to mini-
mise breakage.

Provision is also made for discharging coal from rail-
way wagons into the raw coal bunker B, as is shown in
plans I—I and 2—2.

The water for washing is used over and over again,
and the only addition of fresh water necessary is for
replacing that carried away by the coal and dirt in the
shape of moisture, most of it going off with the coking
coal and fine dirt. The fact that the water can be used
repeatedly is due to the great efficiency of the
drainage system, viz., the slurry refiner and the drainage
conveyor, ass the water draining through the coal is also
filtered, and is therefore quite clean as it flows back to
the sump. So clean, in fact, is the water, that
the nut coals are discharged straight into the
bunkers from the revolving screen quite bright, and do
not require the usual subsequent spraying wd'th clean
water.

The dirt from the dirt elevators is deposited in the
bunkers T, and T2. The elevators are provided with
perforated buckets, from which the water is drained.

The plant forms an imposing structure, and the
machinery works smoothly and continuously, only a
minimum of labour being required. Where possible,
all shafting and journals, are fitted with some suitable
form of self-lubrication, depending upon the position
and speed of rotation of the shaft. The bucket chains
in the large elevator, instead of working on slides, as is
the usual arrangement for this type of elevator, run
on rollers, the axles of which are self-lubricated.
There is an absence of vibration, as no moving pistons
or plungers are used in the washer boxes. The
only moving piece of machinery is the air-con-
trolling valve, which consists of a sleeve piston
operated by an eccentric. The number of pulsations
depends upon the number of strokes of the valve; the
height of the stroke, or rise of the water in the washing
compartment, is regulated by simply adjusting the
quantity as well as the pressure of the air to the air
compartment. There is considerable elasticity in the
use of air for causing the pulsations. By adjusting the
valve, air may be admitted to cause a short and ener-
getic upward stroke of water through the perforated
plate and washer bed, and exhausted slowly and gently,
so as to give ample time for the mixed coal and dirt
to separate according to their specific gravities. The
dirt elevators are open, and may be inspected frequently,
so that any irregularities can be detected, and the defec-
tive working traced out and put right.

The slurry refiner is really an excellent piece of
apparatus, and well worth the attention of those who
have difficulties in satisfactorily draining fine coal—
especially in connection with coke ovens, "it gets rid at
once of the unsightly settling ponds, which not only

occupy considerably space, but involve heavy expense
in recovering the coal after settling.

The contractors for the plant are Messrs. Simon-
Carves Limited, of Manchester, who kindly supplied
the drawing from which the accompanying illustrations
were prepared, and obtained the necessary permission
from the owners of the washery—Messrs, the Womb well
Colliery Company Limited—for the writer to inspect the
plant for the purpose of this article.

SOCIETY OF CHEMICAL INDUSTRY.

Our Coal Supply.

At the annual meeting of the Society of Chemical
Industry in Edinburgh last week, Dr. Charles
Carpenter, of the South Metropolitan Gas Company,
London, presiding, Prof. Henry Louis, Newcastle, con-
tributed a paper on “ Waste in Coal Production.’’ (Sec
next page.)

In the course of the discussion, Prof. H. E.
Armstrong asked whether one source of waste was not
the decaying of pit props, which might well be treated
with some preservative.—Mr. W. F. Reid suggested that
reinforced concrete props could be substituted; but Prof.
Louis said that these had been tried, and had proved
insufficiently resilient. Moreover, they gave no warn-
ing of approaching collapse. If wood became much
dearer, it might prove worth while to use steel props.

Fuel Economy.

Prof. H. E. Armstrong, F.R.S., Durham, submitted
a paper on “ Fuel Economy : A National Policy
Required.” He said that not only was coal dear beyond
all expectations, and procurable with difficulty, but we
were in face of an absolute shortage of liquid fuel for
internal combustion engines, and of a shortage of the
dyestuffs that were made from various products of the
destructive distillation of coal—partly because of a lack
of raw material. Should they not memorialise Govern-
ment at once to foreshadow legislation prohibiting the
use of raw coal, as a fuel, at no distant date? He was
told that the use of raw coal was stopped in Germany at
an early period of the war. There were many problems
connected with the economical use of coal which must
be fully enquired into. It wa^ essential that both the
funds and the machinery for such enquiry should be
provided without delay. The appointment of a central
national fuel board to initiate and supervise all neces-
sary enquiries would seem to be the first step that was
called for, and no better way of obtaining funds could
well be suggested than that of a small tax on all coal
raised in the country.

Discussion.

The Chairman commented on the anomaly of per-
mitting so much of the nitrogen content of coal to be
wasted at a time, when efforts were being made to estab-
lish a synthetic nitrogen industry in this country.—Dr.
E. F. Armstrong argued that manufacturers should
endeavour to economise coal, instancing one firm which
employed the whole services of a skilled chemist in
studying the economy of fuel and water supply, with
excellent results.—References were made to the smoke
abatement work of certain corporations. One or two
members mentioned the objectionable amount of ash
produced by smokeless fuel.—Dr. Dunn suggested that
the smokeless fuel might be gasified, and the gas used
more readily.—It was generally agreed that the time
was not ripe for the prohibition of the use of solid fuel.
—Mr. Roberts said that for the purposes of the pottery
industry, solid fuel was an absolute necessity. Gas
firing was of no use owing to the rapid deterioration of
the kilns.—Prof. Armstrong, in neplying, said that the
ash difficulty was non-existent if a good coal washer
was used. He urged the society to take some common
action, and assert their authority on this question. He
was confident that the general adoption of low tempera-
ture distillation was at hand, and he recommended the
gas industry to put its house in order.

Dr. G. P. Lishman read a paper on “ Some Recent
Improvements in Coke Oven Practice.” (See page 163.)

Presidential Address.

Dr. Carpenter, in his presidential address, said there
never existed so suitable a problem for a round-table
conference as that of the utilisation of the fuel supplies
of the kingdom. Our coal resources were the most
important of our capital assets. Yet the bulk of the
country was busily engaged either in squandering that
capital or bartering it away and living on the proceeds.
Should the development and utilisation of our coal
resources be left unrestrictedly to the individual or group
of individuals acquiring mining rights, generating
energy, or warming their dwellings, or should such
matters be subject to State supervision and control?

War and the Tar Industry.

Mr. W. H. Coleman, Glasgow, submitted a paper on
“ The Influence of the European War on the Tar Dis-
tillation Industry.” After the war the price of pitch
fell considerably, due to the stoppage of exports.
Several proposals had been made to find outlets for the
surplus; and he thought that the briquette making
industry held out considerable promise. In this country
the tar industry had suffered from a lack of co-operation
among the workers. He quite realised the difficulties
in the way of such co-operation, but felt sure if we were
to recapture the fine chemical and colour trade from
Germany we must be prepared to give a good deal more
scientific attention to the tar industry than had been
the case in the past.

The Coal Tar Colour Industry.

Air. C. AL Whittaker, B.Se., of British Dyes Limited,
gave a paper on “ The British Coal Tar Colour Industry
and its Difficulties in War Time.” In the early days
of the industry Germany was dependent on outside
countries, particularly Great Britain,for the iaw material
of the industry, but the modern coke oven recovery plant