PNEUMATIC COAL-HANDLING PLANTS
The writer was directly interested in the erection and installing of
one of the first plants installed in this country for the elevation and
conveying of coal, and a description of the various details may give a
good idea of a complete plant, handling coal on a commercial scale.
The conditions to be complied with are as follows: 20 tons of “slack”
per hour, to be raised 90 ft. above canal level or 80 ft. above road
level.
The coal is brought alongside the power-house by canal barges of 25
tons capacity, or by tipping steam waggons from the railway sidings,
a distance of one mile away. In both cases the coal is required to be
elevated into overhead bunkers of 600 tons capacity placed vertically
over the boilers.
[Illustration: FIG. 23.—PNEUMATIC UNLOADING OF COAL AT MESSRS. BOOTS,
LTD. (NOTTINGHAM).]
In the first case, immediately the barge is alongside, the flexible
suction pipe is lowered into the barge (Fig. 23), and coal immediately
begins to rise in the pipe and is discharged as required. Little or
no handling of the coal is required after the suction nozzle has once
reached the bottom of the barge; all that it is necessary to do is to
bring the barge gradually up to the nozzle, the coal then “avalanching”
down to the nozzle. Fig. 24 shows the discharger placed on girders
over the bunkers into which it discharges continuously. The coal enters
at _A_ and the major portion of the fuel is discharged through the
rotary valves _B_.
The _coal discharger_ itself consists of a cast iron vessel with two
King’s patent rotating valves. These are designed in the form of a
slightly conical taper divided into four sections, one portion of
the circular valve being under vacuum, and the other under ordinary
atmospheric pressure. The outlet of the valves is larger than the inlet
to allow the coal which is in the valve to drop out easily. Over each
valve is also provided a four-armed sweeper to prevent any damp coal
from forming a cone inside. The discharger is provided with two inlets
with full-way bored valves, so that the coal can be drawn either from
the water side or from the land side at will. After the coal has been
deposited in the main discharger, there is provided a supplementary
discharger consisting of a vessel 6 ft. high by 30 ins. diameter, with
two inlet pipes of 8 ins. diameter, to provide a contra-flow, so that
any particles of coal dust in the air will meet one another in the 30
ins. box at equal velocity and be deposited. The small particles are
delivered by a supplementary rotary discharge valve which is set to run
very much slower than the main discharger valves.
[Illustration: FIG. 24.—DISCHARGER FOR COAL CONVEYING PLANT.]
The main discharger valves are driven by worm gearing, the latter
having one right-hand thread and one left-hand thread, so that the end
thrust on the worms is neutralized. Ball bearings are provided and
the small motor which drives all three valves is coupled up with an
electrical device designed by the author. This device ensures that if
anything happens to the top discharge valves—so that the 3 h.p. motor
driving them cuts out, owing to an overload or other cause—then the
main motor also is cut out by the opening of its circuit breaker. This
prevents any “flooding” of the pipes and dischargers.
It may be mentioned that the valves are so designed that a portion of
the weight of each valve is carried by the vacuum, so that the vertical
wearing lift on the valves when at work is very slight.
The _intake pipes_ for the coal are 5 ins. diameter, and they are
provided with heavy cast iron bends, having extra thick metal on the
outside radius to allow for the wearing effect of coal passing at the
rate of 20 tons per hour.
The pipe into the barge is provided with a flexible steel pipe at the
suction nozzle end, for convenience of handling. India-rubber piping
has been tried, but the extra cost does not justify its continued use.
The nozzle is made as light as possible for convenience of handling,
and is fitted with a special “free air” inlet for the regulation of the
amount of air necessary to blend with the coal.
=Ash Handling.= In addition to unloading coal, the above plant is
capable of dealing with hot ashes which are first crushed in a
portable clinker breaker, electrically driven, which runs under all
the ash hoppers of the boilers. The ash when crushed gravitates into
funnel-topped tee-pieces, inserted in the main ash-conveying pipe,
whence it is immediately sucked up into an overhead ash hopper to await
the convenience of the waggons which dispose of it on the “tips.”
=Flue Cleaning.= A 3 in. suction pipe has been run round the
boiler-house in such positions that flexible hose can be attached
for flue cleaning purposes. In this case the cleaners simply use an
enlarged nozzle such as is supplied with a domestic equipment and the
dust is removed from the flues, economizer soot chambers, etc., into
the ash hopper without trouble or dust.
The success of this plant is best indicated by the fact that, at
the moment of writing, a duplicate plant is being erected. Owing to
the growth of the business, and its demand for power and steam, the
original plant has to be worked continuously on coal, so that the ash
and flue dust problem has become acute again.
=Portable Floating Plant.= A third plant ordered by the same firm is
of considerable interest. This is intended to be mounted in a barge
so as to be portable. Owing to lack of space in close proximity to
the power-house, considerable difficulty is found in keeping adequate
stocks of coal on the site except the 600 tons in the overhead bunkers.
In order to secure continuity of working, it is essential that as much
fuel as possible be stored, and for this purpose a coal pile has been
made about half a mile away from the works, adjoining the canal. Ashes
can be disposed of on certain fields a few miles outside the city in
swamps and pools caused by subsidences, due to colliery workings.
The portable plant is therefore arranged to operate as follows: the
barge is self-propelled by a 30 h.p. paraffin engine which can be
coupled by clutches to either the propeller or a Roots blower, the
latter being the exhauster for the portable suction plant.
The barge is loaded with ashes for disposal, and then proceeds under
its own power to the site where they are to be dumped. The clutch is
operated disconnecting the propeller and operating the blower. The
suction side of the blower is coupled up with the pipe line in the
boat and the barge feeds the plant by means of the flexible hose: the
discharge pipe is raised over the towing path so as not to interfere
with passing traffic, and the ashes are blown out into the swamps
previously mentioned. It will readily be recognized how simple this
unloading becomes compared with trying to dig out the ashes with either
a spade or a fork.
The empty barge then returns to the coal pile and takes up a load of
coal in a similar manner, then proceeding to the power-house under
its own power and being unloaded by the original fixed pneumatic
installation in the ordinary way.
The coal arriving by road is tipped into a concrete hopper excavated
below the ground level, and so designed with sloping sides that it is
self feeding into a suction pipe connected to the bottom of the hopper.
The same procedure occurs except that in this case the coal enters the
main discharger at the top (_E_, Fig. 24).
It is interesting to note that the very fine dust collected from the
air filter is eagerly sought after by the foundry trade, and what would
at first appear to be a waste product impossible to burn, is actually a
valuable by-product of the plant.