TYPICAL INSTALLATIONS FOR GRAIN
The pneumatic principle has been applied to the handling of grain in
bulk to a much greater extent than to any other material. As previously
stated, the original successful plant invented and designed by Mr.
Frederic Duckham was for the handling of wheat for the Millwall Docks
Co., and the success of this plant was such that it was imitated by
engineers in this country and abroad with equally satisfactory results.
Grain lends itself admirably to pneumatic transport because it is
easy of flow, regular in size, and practically self-feeding. Also,
the removal of dust, which is incidental to pneumatic conveying, is
a special advantage where grain is concerned. Figs. 17 and 18 show
clearly the advantages of pneumatic conveying in point of simplicity
and labour saving.
=Typical Quayside Plant.= Fig. 19 shows a typical lay-out for a
comparatively small plant handling 50 tons per hour. The diagram is
almost self explanatory.
_A_ represents the special suction nozzle through which the grain
enters the system, together with the “free air” which acts as the
conveying medium.
[Illustration: FIG. 17.—ANCIENT.]
[Illustration: FIG. 18.—MODERN.]
[Illustration: FIG. 19.—TYPICAL GRAIN-HANDLING PLANT; 50 TONS PER
HOUR.]
_B_ is a length of flexible pipe to enable the nozzle to sweep the
width of the barge, the length being dealt with by moving the boat to
within the radius of the swivel arm _E_.
_C_ is a permanent pipe carried on the jib arm which is mounted on
a swivel joint; _B_ is another short flexible pipe to permit of the
swivelling already mentioned.
_F_ indicates the receiver into which the grain is deposited, and _G_
the special rotary valves, for releasing the material from the system
without interfering with the vacuum of the conveying line.
_H_ illustrates the twin air filters which are provided with valves,
so that each of the filters can be isolated in turn from the rest of
the plant for cleaning of the fabric tubes, without interrupting the
continuous working of the plant.
_J_ indicates the connecting pipes between the receiver, air filters,
and pump, and it should be noted they are considerably larger than
those on the suction end _C_, this being necessary to allow for the
expansion of the air under vacuum.
_K_ is the reciprocating air pump, driven electrically by the motor
_M_ through large helical gear wheels, which act as flywheels and are
helpful in equalizing the torque required by the pump.
_L_ is the outlet pipe for the air as it is exhausted from and by the
pump.
[Illustration: FIG. 20.—FLOATING PNEUMATIC TRANSPORT PLANT; 200-250
TONS PER HOUR.]
[Illustration: FIG. 21.—PORTABLE PNEUMATIC PLANT ON RAILWAY TRUCK.]
This plant is simple, but every possible modification can be added
that circumstances make desirable; such as discharging on to a belt
conveyor, for feeding the silos or other storage bins.
Where grain is bought by bulk it would be necessary to check the
weight, and in this case an automatic weigher would be installed, into
which the material would be discharged from the receiver. With a bag
filter the collected dust can also be weighed, the total weight being
then obtained by addition.
=Typical Floating Plant.= The most popular development of the above
type of plant is the floating plant, designed for erection on a hulk,
or barge, and intended to suck grain from an ocean-going steamer
and discharge it into barges or lighters on the other side of the
discharging plant, as indicated in Fig. 20. The plant shown is one
of many in actual operation and its construction may be followed
by reference to the description of the plant shown in Fig. 19, the
same index letters being used in each case. One great advantage of
floating plants is that the difference in height due to tides is of no
consequence.
=Portable Plants.= Still another modification consists of a complete
quay-side plant mounted like a travelling crane, so that it can be
moved longitudinally along steel rails on the quay-side. This plant is
particularly useful where large cargo ships have to be emptied and then
allowed to remain at their berth until reloaded with another cargo.
[Illustration: FIG. 22.—PORTABLE RAILWAY PLANT IN OPERATION.]
Complete plants have also been mounted on railway trucks, the engine
and pump in this case being on a second waggon (see Figs. 21, 22). In
such a case the plant has to be mounted very low, and it is necessary
to lift from the under-side of the truck to, say, a railway waggon, by
means of an adjustable belt or bucket elevator (shown at the extreme
left of Fig. 21).
Many other applications will suggest themselves to the reader, and
sufficient has been said to prove that for the handling of wheat the
pneumatic system is distinctly flexible and convenient; also, it
effects a great saving in labour, which is an important consideration
nowadays. “Bushelling,” conveying, and weighing by hand used to cost
well over a shilling per ton, which figure was reduced to just over
1½d. per ton by pneumatic conveying; these are pre-war costs in both
instances, but the relative saving effected by pneumatic conveying is
certainly not less under present conditions.
All the previous remarks also apply to linseed and cotton seed in
bulk, maize, oats, and in fact all cereals. Such materials have to be
accepted as and when the ships arrive irrespective of convenience, and
it is an important advantage of pneumatic conveying that the material
can be lifted and discharged in the most convenient position; also,
when the barge or ship has departed the same apparatus can be utilized
to lift the material from its position in store to the cleaning or
grinding plant.