THE HANDLING OF GRAIN
THE ELEVATOR--THE SUCTION PNEUMATIC GRAIN-LIFTER--THE PNEUMATIC BLAST
GRAIN-LIFTER--THE COMBINED SYSTEM
THE ELEVATOR
On or near the quays of our large seaports, London, Liverpool,
Manchester, Bristol, Hull, Leith, Dublin, may be seen huge buildings of
severe and ugly outline, utterly devoid of any attempt at decoration.
Yet we should view them with respect, for they are to the inhabitants
of the British Isles what the inland granaries of Egypt were to the
dwellers by the Nile in the time of Joseph. Could we strip off the
roofs and walls of these structures, we should see vast bins full of
wheat, or spacious floors deeply strewn with the material for countless
loaves. The grain warehouses of Britain--the Americans would term them
"elevators"--have a total capacity of 10,000,000 quarters. Multiply
those figures by eight, and you have the number of bushels, each of
which will yield the flour for about forty 2-lb. loaves.
In these granaries is stored the grain which comes from abroad. With
the opening up of new lands in North and South America, and the
exploitation of the great wheat-growing steppes of Russia, English
agriculture has declined, and we are content to import five-sixths of
our breadstuffs, and an even larger proportion of grain foods for
domestic animals. It arrives from the United States, India, Russia,
Argentina, Canada, and Australia in vessels often built specially for
grain transport; and as it cannot be immediately distributed, must be
stored in bulk in properly designed buildings.
These contain either many storeys, over which the grain is spread to
get rid of superfluous moisture which might cause dangerous heating; or
huge bins, or "silos," in which it can be kept from contact with the
air. Experiments have proved that wheat is more successfully preserved
if the air is excluded than if left in the open, provided that it
is dry. The ancient Egyptians used brick granaries, filled from the
top, and tapped at the bottom, in which, to judge by the account of a
grievous famine given in the book of Genesis, their wheat was preserved
for at least seven years. During last century the silo fell into
disrepute; but now we have gone back to the Egyptian plan of closed
bins, which are constructed of wood, brick, ferro-concrete, or iron,
and are of square, hexagonal, or round section. They are set close
together, many under one roof, to economise space; as many as 2,985,000
bushels being provided for in the largest English storehouse.
Such vast quantities of grain require well-devised machinery for their
transport from ship to bin or floor, weighing, clearing, and for
their transference to barges, coasting vessels, or railway trucks.
The Alexander Grain Warehouse of Liverpool may be taken as a typical
example of a well-equipped silo granary. It measures 240 by 172 feet,
and contains 250 hexagonal bins of brickwork, each 80 feet deep and
12 feet in diameter. The grain is lifted from barges by four elevators
placed at intervals along the edge of the quay. The elevator is a
wooden case, 40 or 50 feet high, in which an endless band furnished
with buckets travels over two rollers placed at the top and bottom.
These are let down into the hold and scoop up the grain at the rate
of from 75 to 150 tons per hour, according to their size. As soon as
a bucket reaches the top roller it empties its charge into a spout,
which delivers the grain into a bin, whence it is lifted again 32
feet by a second elevator to a bin from which it flows by gravity to
a weighing hopper beneath; and as soon as two tons has collected, the
contents are emptied automatically into a distributing hopper. After
all this, the grain still has a long journey before it; for it is now
shot out on to an endless, flat conveyer belt moving at a rate of 9
to 10 feet per second. It is carried horizontally by this for some
distance along the quay, and falls on to a second belt moving at right
angles to the first, which whisks it off to the receiving elevators of
the storehouse. Once more it is lifted, this time 132 feet, to the top
floor of the building, and dropped on to a third belt, which runs over
a movable throwing-off carriage. This can be placed at any point of the
belt's travel, to transfer the grain to any of the spouts leading to
the 250 bins.
Here it rests for a time. When needed for the market it flows out at
the bottom of a bin on to belts leading to delivery elevators, from
which it may be either passed back to a storage bin after being well
aired, or shot into wagons or vessels. From first to last a single
grain may have to travel three miles between the ship and the truck
without being touched once by a human hand.
The vertical transport of grain is generally effected by an endless
belt, to which buckets are attached at short intervals. The grain,
fed to the buckets either by hand or by mechanical means, is scooped
up, whirled aloft, and when it has passed the topmost point of its
travel, and just as the bucket is commencing the descent, it flies by
centrifugal force into a hopper which guides it to the travelling belt,
as already described.
Of late years, however, much attention has been paid to pneumatic
methods of elevating, by which a cargo is transferred from ship to
storehouse, or from ship to ship, through flexible tubes, the motive
power being either the pressure of atmospheric air rushing in to fill
a vacuum, or high-pressure air which blows the grain through the tube
in much the same way as a steam injector forces water into a boiler.
Sometimes both systems are used in combination. We will first consider
these methods separately.
THE SUCTION PNEUMATIC GRAIN-LIFTER
is the invention of Mr. Fred E. Duckham, engineer of the Millwall
Docks, London. The ships in which grain is brought to England often
contain a "mixed" cargo as well; and that the unloading of this may
proceed simultaneously with the moving of the wheat it is necessary
to keep the hatches clear. As long as the grain is directly under
a hatchway, a bucket elevator can reach it; but all that is not so
conveniently situated must be brought within range of the buckets. This
means a large bill for labour, even if machinery is employed to help
the "trimming." Mr. Duckham therefore designed an elevator which could
easily reach any corner of a ship's interior. The principal parts are
a large cylindrical air-tight tank, an engine to exhaust air from the
same, and long hoses, armoured inside with a steel lining, connected at
one end to the tank, and furnished at the other with a nozzle. These
hoses extend from the receiving tank to the grain, which, when the air
has been exhausted to five or six pounds to the square inch, flies
up the tubes into the tank. At the bottom of the tank are ingenious
air-locks, to allow the grain to pass into a bin below without
admitting air to spoil the vacuum. The locks are automatic, and as soon
as a certain quantity of grain has collected, tip sideways, closing the
port through which it flowed, and allowing it to drop through a hinged
door. Two locks are attached together, the one discharging while the
other is filling. An elevator of this kind will shift 150 tons or more
an hour. Mr. Duckham claims for his invention that it has no limit in
capacity. It is practically independent of everything but its own steam
power; and the labour of one man suffices to keep its flexible suckers
buried in grain. No corner is inaccessible to the nozzle. The pipes
occupy only a very small part of the hatchway. They can be set to work
immediately a vessel comes alongside. As many as a quarter of a million
bushels are handled daily by one of these machines.
The pneumatic elevator is often installed on a floating base, so that
it may be moved about in a dock.
THE PNEUMATIC BLAST GRAIN-LIFTER
differs from the system just described in that the grain is _driven_
through the pipes or hoses by air compressed to several pounds above
atmospheric pressure. A small tube attached to the main hose conveys
compressed air to the nozzle through which grain enters the tube. The
nozzle consists of a short length of metal piping which is buried
in the grain. One half of it is encased by a jacket into which the
compressed air rushes. As the air escapes at high speed past the inner
end of the piping into the main hose, it causes a vacuum in the piping
and draws in grain, which is shot up the hose by the pressure behind
it. As already remarked, the action of this pneumatic elevator is
similar to that of a steam injector.
THE COMBINED SYSTEM
Under some conditions it is found convenient to employ both suction
and blast in combination: suction to draw the grain from a vessel's
hold into elevators, from which it is transferred to the warehouse by
blast. Special boats are built for this work, _e.g._ the _Garryowen_,
which has on board suction plant for transferring grain from a ship to
barges, and also blowing apparatus for elevating it into storehouses
or into another ship. The _Garryowen_ has the hull and engines of an
ordinary screw steamer, so that it can ply up and down the Shannon and
partly unload a vessel to reduce its draught sufficiently to allow it
to reach Limerick Docks. Floating elevators of this kind are able to
handle upwards of 150 tons of grain per hour.