1186

THE COLLIERY GUARDIAN.

December 6, 1918.

Fig. 1.—Diagrammatical Elevation of

Draper Washer.

DIRT £.\eVaT0Px

Washed CoaiTShoot

Air Vessel

X) Water sealed
c > Revolving

sScaapk.9 for Dirj

Inspection Window

Sampling Tubc

Regulating Valve.

COAk elevator

revolving

Screen

water &.aled \
REVolviimqX DELIvAy VALV£

tan a.

Slurry Tank.

THE DRAPER WASHER.*

By Prof. G. Knox, F.G.S., M.I.M.E.

Although the process of separating fine particles of
mineral < res from each other or from their accom-
panying vein stuff, has for many years been the subject
of careful investigation in metalliferous mining,
resulting in the adoption of innumerable methods of
classification, it is only within comparatively recent
years that the application of the processes successfully
adapted for the dressing of fine minerals has been
extended to the separation of fine coal from shale, etc.

There are various reasons to account for this dilatori-
ness on the part of coal mining engineers, chief among
them being :—>(1) The assumed worthlessness of very
fine coal previous to the application of modem coking
processes ; (2) the
large quantity of
fine coal material
to be treated in
comparison with the
output of metal-
liferous ores; and
(3) the compara-
tively slight differ-
ence in specific
gravity between fine
coal and its accom-
panying shales.

Since it has been
discovered that the
fine coal in slurry
from coal-washing
machines, and the
sweepings of coal
dust from under-
ground roadways
when cleaned, are
just as valuable for
coking purposes as
similar quality nuts
and peas, various
attempts have been
made to devise a
suitable process of
cleaning this very
fine coal which
cannot otherwise be
separated from the
shale by any form
of jig washing.

Liihrig, after many years experience of jig washing
in the dressing of fine ores, set out in 1864 to adapt this
plant to coal separation below in. diameter. After three
years experimenting he devised his now famous and
generally used feldspar washer. This was a great
improvement on the ordinary jig washer, but in spite
of the numerous improvements which, dining the past
50 years, have been made on the Liihrig feldspar
washer, it has not yet been found possible to f-eparate
the finer sizes of coal and shales.

During this period n any other methods of classifica-
tion have been devised for v ashing the larger sizes of
co.il, but little attention being given to cleaning the
finer, varieties. Recently a new type of fine coal
classifier has been put on the market by Mr. J. M.
Draper, of the Rhondda Engineering and Mining
Company, Bridgend, which promises to effectively solve
this very difficult problem.

This washer is the most modern development of the
principle of upward current classification, and although
originally designed to recover fine coal from slurry, etc.,
has been.adapted to deal with all sizes of small coal.
The original plant erected at Glamorgan Colliery,
Llwynypia, was designed to deal with the fine coal
carried away by the water as slurry from the jig
washer, together with the fine coal dust sweepings from
underground.

The coal to be washed is elevated from the slurry
tank into a revolving screen (fig. 1) which separates the
wet coal into sizes from to 0 in. The over size
passes into.a separate washing compartment and the
under size is only what passes through a mesh,
which averages about 2 per cent. This revolving screen
is partially immersed in water, which enables the finest
sizes being treated without clogging.

The various sizes pass through water-sealed revolving
star delivery valves, and through the feeder launders,
into the washer, where they meet an upward current of
water regulated in velocity so as to float the lighter
coal particles and at the same time allow the heavier
particles of shale to fall. This is accomplished by a
very simple device, consisting of an inverted plain or
perforated cone g (fig. 2) attached to a straight length
of pipe h in which the greater water velocity creates
a zone of maximum lifting effect, below which only the
heavier particles can desc -nd; and in the cone itself
the decreasing velocity produces a minimum lifting
effect, which is just sufficient to float the lighter
particles over the. sill into the shoot d. It is
evident that only a short fall is necessary against the
upward current to effect separation, because the velocity
is too low at the bottom of the cone to prevent the
gravity velocity of the falling heavy particles of shale
descending, though too high to permit of the coal
reaching the tube h, and just sufficient to carry it over
into the shoot d.

Fig. 1 is a diagrammatic section of one of the
washing units, and fig. 2 is a detailed section of the
wascer proper, and consists of a vertical pipe a, into
which the cone is fitted. This vertical pipe has two
branches the ©ne b for the f< ed water being connected
to an overhead tank (fig. 1), and fitted with a regulating
valve capable of adjusting the velocity flow of the
upward current, so as to produce the separation of
small pa» tides with only a slight difference in specific
gravity. The other branch pipe c is connected to the
lower end of a, and acts as a balancing column in
the event of irregular feeding tending to choke the
cone. The pipe a being filled with water to the top of

* From a paper read before the South Wales Institute
of Engineers on November 30.

the sill at d, the feed water passes from b through a
to h, where it ascends to the cone. Below h the
water is still, so that particles of shale, falling slowly
through h, have their velocity accelerated in the still
water. The unwashed coal is fed in through the shoot
e with the hopper f, and thence to the cone g In
order that the coal and water may be properly mixed in
g, a division plate is inserted between the hopper and
the overflow.

Inspection windows are provided whereby the charge-
man can determine whether the npwa d current has
been properly adjusted, and immediat Iv underneath a
special sampling tube is fitted to facilitate sampling of
the shale. This is a most important part of the plant,
as it enables constant and systematic', sampling to be
carried on while the plant is running, thus ensuring the
best economic results. This valve is merely a sliding

hollow tube fitted into a suitable chamber, and having
an opening made in the upper side capable of collecting
a stream of falling particles. When the tube is pulled
out and inverted the sample falls out, and the tube
is then pushed back ready to collect a further sample.
By the combined use of the inspection windows and
samples, the chargeman can regulate the flow of water
as desired.

If the feeding of the unwashed coal is irregular, there
is a tendency for the cone to become choked up. To
overcome this difficulty the column c, which is fitted
with an air-vessel at top, comes into action automati-
cally. This column is filled with water to the level of
the sill d and above that point with air at atmospheric
pressure. Should too much coal be fed into the cone
there is a momentary check to the upward current of
water, and part of the pressure is taken up by the air
in the air vessel and immediately released to assist the
water in opening up the particles in the cone and pro-
ducing separation.	*

Laboratory experiments and experience with the
washers erected ^haie enabled Mr. Draper to devise a

os fit







Fig. 3,—Plant for Washing Four

scale of openings in the water-discharge valve for given
sizes of coal, so that the chargeman has only to make
any finer adjustment necessary as a result of sampling
due to changes in the quality of coal being washed.

Underneath the sampling tube there is a revolving
water sealed star-discharge valve, which deliveis the
shale through the still water into a screw conveyor, and
from this it passes into the boot of the dirt elevator and
thence into the trams.

Any number of units may be added, according to the
capacity required, and one great advantage of this
system is that, with an 8 in. cone and 4 in. diameter
stem, all sizes of coal can be alternately washed in the
same tube, by simply altering the velocity flow of the
water. This will enable small colliery companies to
wash their coal, which would be otherwise impossible

if a large capital expenditure, bad to be incurred for a
jig washer.

In designing this apparatus, the best use has been
made of the principle of upward-current classificatio n
to effect separation; and being perfectly automatic and
continuous in action, it is a great advance on anything
previously attempted. It is in

fact the first successful

UNWASHED COAL

Vessel

Air

e

Inspection Windows

evolving Discharge Valv

Fig. 2.—Washer Cone.

SAMPLING

Tube

WATEK

DRAPER WASHERj

	
	OF A
WASHING PlArV :	F'OR ULAl/MG
WHO	y/a'S	Of CCAL •

Sizes of Coal.

attempt that has yet been made to wash coal less than
in. in diameter.

To give an example of how close this apparatus will
separate grains having nearly equal specific gravities,
an experiment was made with a mixture of equal weights
of bituminous coal (1’27 specific gravity) and steam
coal (1’33 specific gravity) of T\T in. diameter, which
was passed through the separator with a current
velocity of 4J in. per second.
of like falling bodies in

. The ratio of diameters
this case would be very
close, e.g.—
D -133-1	,Q

D; 127-1	12

The separator de-
livered 56 per cent,
of the mixture having
an average specific
gravity of 1’28, and 44
per cent. having
an average specific
gravity of 1’32. This
shows that the appa-
ratus can be worked
with considerable ex-
actitude. As a rule,
the ratio of diameters
of like falling bodies
of coal and shale
varies from 4 : 1 to
5:1; there is there-
fore a large range
to work upon in
separating even the
finest sizes.

The capacity of
each unit is remark-
able when compared
with other forms of
washing, in relation
to their size, as the
dimensions of the
washery at Glamorgan
Colliery indicate. This
high, and contains a
tons of the finest coal

building is 25 x 20 X 45 ft
plant capable of washing 30
per hour. This plant is worked by one man, whilst
another workman is employed to look after the
delivery into the wagons. A 20 horse-power motor was
installed to work it, but including the 5 hor?e-power
for centrifugal pump, the load on the motor never exceeds
10 horse-power; as shown by the figure, the coal is
delivered directly into wagons ; and in three hours the
water content is, on the average, not more than 8 per
cent. This effective drainage is due to the purity of
the washed coal by the elimination of hygroscopic
shale, and the water given off is quite clear.

The following figures have been calculated as a guide
to the quantity of water required and coal washed per
hour:—