Improvements in Apparatus for Drying Coffee, Withering and Finishing Tea, and for other Drying Purposes, and in the Production of Hot Air for Use in such Apparatus.
Year: 1889

page_text: COMPLETE SPECIFICATION.
Improvements in Apparatus for Drying Coffee, Withering and
Finishing Tea, and for other Drying Purposes, and in the
Production of Hot Air for Use in such Apparatus.
I WILLIAM ALFRED GIBBS, of Gilwell Park, Sewardstone, in the county of Essex,
Gentleman, do hereby declare the nature of this invention and in what manner
the same is to be performed to be particularly described and ascertained in and by
the following statement :-
My invention relates firstly to an improved method of working the furnace
described in the Specification of former Letters Patent granted to me dated April 21st
1888 No. 5980 for producing practically pure air from the combustion of coal, wood
or other smoke producing fuel or coke, the said hot air being applicable for drying
purposes; secondly, to an improved arrangement of coffee dryer; thirdly, to an
improved tea witherer, and, lastly, to an improved tea finisher.
The manner of working my furnace is as follows:-
The fire box is first charged either with coke only or is partly filled with pieces of
fire brick, chalk or pure limestone with an upper stratum of coke, and then some
lighted charcoal or wood is fed onto the top of the coke and the fan is set in move-
ment. When the coke is ignited, coal, wood or other fuel is periodically fed into the
chamber and without further attention, a powerful blast of practically pure air is
delivered from the fan into the drying cylinder or other chamber wherein tea, coffee
or other produce is placed to be dried.
Sometimes when small coal is required to be used I adjust a feeding tunnel at the
back of the fire box containing bars actuated by eccentrics or cranks for slowly
pushing forward the ignited fuel into the fire box.
Great economy of fuel is obtained by this arrangement, as practically the whole of
the gaseous products arising from the combustion are utilized without the usual loss of
from 25 to 50 per cent. of heat wasted in producing chimney draught, besides which
the water contained in the coal, wood or other fuel is converted into hydrogen and
oxygen by passing through the incandescent mass in the fire-box; and these gases
besides destroying all the noxious products of combustion give a large accession of
heat to the air.
In order to regulate the heat of the furnace, I vary the depth of the filter of chalk
or the like, the least heat being obtained when the chamber is nearly full.
Instead of ordinary suction-fans I sometimes adjust at the exit end of my furnace
a chamber or reservoir into which the hot air from the furnace can pass. In this
chamber I adjust a series of induction tubes like those adopted for Körting's steam-
jet only of much larger diameter. To the smallest of these tubes projecting from
one side of the said chamber, I apply either a steam jet or the pipe from a blower
or air-compressor and by forcing the steam or compressed air through this and the
other tubes the air from the furnace is drawn in at the spaces between the tubes and
delivered from the largest of the tubes which projects out of the chamber at the other
side. From thence it can be delivered into air ducts or other drying apparatus. Where
compressed air is otherwise obtainable, a jet of such compressed air driven through
induction tubes in a chamber as above described acts in the same way as the air from
a pressure blower.
My improvements relating to the drying of coffee, maize, peas and other similar
products are illustrated in Figures 1, 2 and 3 of the accompanying drawing which
represents various arrangements of drying cylinders and air ducts.
According to this part of my invention 1 construct cylinders coned both at the feed
and discharge ends, so as to retain a large charge of produce under the action of
the hot air for so long a period as may be needful to effect perfect desiccation.

page_text: In these cylinders I adjust air ducts of various sections, so that the hot air from
my furnace or other sources shall be evenly distributed through the said cylinders
and shall not escape out of the said cylinders until it has taken up its full charge
of moisture.
These air ducts can either be stationary or have an oscillating or rotatory move-
ment. One section of the said air-ducts is shewn at Figure 1, wherein a, b are
two air-ducts contained in one cylinder c. Each air-duct is perforated with
holes d, d, d covered by louvres e, e, e. The air-duct a has also a line of holes
at covered with a guard of wire gauze or finely perforated plate. The cylinder c
is provided with lipped shelves 9, 9 the action of which is to bring the produce
up as the cylinder rotates and pour it over the louvres e, e between the two air-ducts.
Another section of cylinder is shewn in Figure 2, wherein one air-duct only is
used with ridge and furrow louvres over the face having air outlets at the junctions
of the louvres. Above these louvres I sometimes adjust an endless band with
scrapers to ensure the passage of the produce and also to retard and regulate the
speed. The under part of this air-duct is constructed of corrugated plates with
holes h, has shown. But whatever section of air-duct I employ instead of
carrying the said air-ducts through the whole length of the cylinder I prefer to
reduce that length so as to allow the produce to be lifted up by the shelves and
let fall in a continuous shower without being intercepted by air-ducts for a certain
length of the cylinder. The effect of this is to secure more complete utilization of
the hot air, because in this arrangement, the wet produce is fed in to the cylinder at
the opposite end to that from which the hot air enters, which air after being partially
saturated by the half dried portion of the said product has to pass through the con-
tinuous shower of the wetter product and thus takes up its full charge of moisture
before escaping from the cylinder. This advantage will be better understood when
contrasted with the adjustment and action of the air-ducts of my former patents. In
these, as heretofore positioned, the circular side of the air-duct wasted heat by radia-
tion without acting on the produce, because in practice I have found that the shelves.
of the cylinders delivered their whole charge on to the flat face of the air-duct, and
passed round the semi-circular side of the said air-duct quite empty, but now by
reversing the rotation of the cylinder the shelves are always full of produce, as they
pass round the semi-circular side of the air-duct and the radiated heat therefrom acts
directly upon such produce. This beneficial action can be further increased by the
emission of hot air from perforations in this semicircle.
Furthermore by carrying the air-ducts as in my former patents to the extreme
end of the cylinder a large quantity of hot air escapes from the holes and louvres
near the end of the said air-duct in an almost dry state from not having to pass
through a sufficient bulk of the wet produce.
Moreover by the old arrangement it was essential to rotate the cylinder at not less
than 8 revolutions per minute, so as to keep the flat face of the air-duct covered, and
this higher speed of rotation not only caused a waste of power but was injurious to
delicate products such as nearly dried tea.
I prefer to construct the drying and withering cylinders in the following inexpen-
sive manner, that is to say, I form a cylinder composed of two sets of laths or slats
of wood or metal arranged spirally relative to the axis of the cylinder, the laths of
one set crossing those of the other set so as to form a kind of lattice work. This
lattice work is so constructed as to shut up into a very small compass for export or
transport, and when it is to be erected, it is expanded and bolted to iron hoops or
bands, which hoops or bands are adapted to run in grooved pulleys so that the cylinder
can be rotated with little friction. From the inner circumference of the cylinder
converging towards the centre, I adjust shelves, fixed at such an angle as to carry
the leaves up and deliver them on to a central cylinder and from thence back again
to the lower shelves. I cover the cylinder either with native Indian coarse cloth or
canvas, having an open mesh of about one sixteenth of an inch, or of plain or per-
forated metal plates, or of wire gauze, and I form the aforesaid shelves of the same
materials. I give movement to the cylinder either by bevil gear or by a band driven

page_text: from any convenient motor, which band runs upon a turned hoop affixed to the
cylinder, preferably about the centre of its entire length; this cylinder is not intended
to make more than one revolution in five to fifteen minutes so as to avoid all danger
of bruising the leaves and it is placed at such an angle as shall be found sufficient to
ensure the due withering of the leaf in the once passing through from the feed to the
discharge end.
When warmth is needful for the withering process I adjust in the central cylinder
or underneath the outer cylinder one or more pipes, such pipes being perforated for
the emission of hot air and I connect such pipes to the mouth of a blast and exhaust
fan, the inlet of which is attached to my improved smokeless furnace. By simply
charging the fuel-box of the said furnace with a stratum of chalk, limestone, or
broken pieces of fire brick of greater or less depth underneath the fuel, it will supply
the fan and pipes with air warmed to any desired temperature ranging from 98°
upwards. It is not advised to let such air exceed 110° unless the leaf is exceptionally
wet.
For completely finishing the drying of tea I use plain metal cylinders (not perforated)
and I reduce the angle of the shelves of the said cylinders as shown in Figure 3, so
that instead of lifting the tea up and letting it down on to a central air-duct or
cylinder, the said shelves merely raise the tea in the lower segments of the cylinder
and let it slide gently down from one shelf to another. Instead of rotating the
cylinder at 8 to 10 revolutions per minute, I reduce the speed to one or two revolu-
tions per minute.
In place of the D-shaped air-duct of my former patent with its holes and
louvres I now employ the section shewn in Figure 3 of the accompanying drawing or
other convenient section.
The objects of this section of air-duct are, first, to direct all the air downward on to
the surface of the tea as it slides from shelf to shelf and, secondly, to collect and
partially retain any dust that may be driven in with the air.
The cylinder and air-duct thus described can be used as a separate machine for
drying and finishing or for finishing the drying of any tea which has been partially
dried in any other dryer, but I prefer to adjust it to the discharge end of my drier in
the following manner: I first detach the air-duct of the present drier from the fan
mouth of the fan and remove the cylinder and air-duct to a sufficient distance to
make room for any desired length of the tea-finisher; secondly, I attach the air-
duct to the said tea-finisher to the fan mouth at one end and to the air-duct of
my drier at the other; thirdly, I adjust the cylinder of the finisher which should
be of considerably larger diameter than the drier in such a manner that it can be
driven by a band and pulleys from one end of the fan shaft at say from one to
two revolutions per minute whilst the drier is driven (as hitherto) from the other
end of the said shaft at its present speed of 6, 8 or 10 revolutions per minute.
The action of the combined machine will therefore be continuous and complete ;
the half dried tea falls from the drying cylinder into the finishing cylinder, which
from its greater capacity and slower and gentler movement holds a large bulk of
tea under the action of the hot air and avoids all risk of breaking or greying"
the tea when arriving at the brittle condition of perfect dryness.
Where products of very delicate kind are to be dried the hot air from my furnace
can be used to give only transmitted heat through a pipe or pipes contained in the
cylinder.
When used in this way, I prefer to adjust a bend on to the inner pipe and connect
this bend with a return pipe passing along under the exterior of the outer cylinder,
which pipe is perforated with holes or furnished with jets in such a manner as that
the hot air from the said holes or jets impinges on the exterior of the said outer
cylinders so as to give a moderate heat to the produce contained therein without
allowing the air itself to come in contact with such produce.
By this arrangement, part of the heat obtained from the fuel is diffused through
the cylinder by radiation from the internal pipe or pipes and then its remaining
heating power is applied to the exterior of the said outer cylinder with the same

page_text: uniformity and evenness that is obtained by the use of jets of gas but with far
greater security against any risk of scorching.
By this mode of producing and applying hot air I obtain most of the advantages
which are obtained by heating with gas and with still greater safety from undue
heat. The said hot air is also obtainable from coal direct without any of the costly
machinery required for the production of gas.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is :
My improvements relating to drying cylinders and air-ducts and to the production
of hot air for the same, substantially as herein before described and illustrated in the
accompanying drawing.
1
35
100
G. F. REDFERN & Co.,
4, South Street, Finsbury, London, Agents for the Applicant.