Improvements in Apparatus for Drying Tea Leaf or other Substances.
Year: 1898

page_text: Date of Application, 12th Mar., 1898-Accepted, 16th Apr., 1898
COMPLETE SPECIFICATION.
Improvements in Apparatus for Drying Tea Leaf or other
Substances.
I, SAMUEL CLELAND DAVIDSON, of Sirocco Engineering Works, Belfast, Ireland,
Merchant, 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 :-
This invention has reference to drying apparatus of the type in which the tea
leaf or other substance to be dried is exposed on superimposed sieves or trays of
foraminous material in a drying chamber, to the action of heated or dried air, which
is drawn or forced through the trays and the substance thereon, and the invention
relates. more particularly to the form of drying apparatus described in a former
Specification of Letters Patent granted to me and dated 12th January 1893 No. 722
(hereinafter referred to as the previous: Specification).
In the said previous Specification the column of trays employed therein has each
fresh tray with the moist substance on it introduced at the exhaust end of the
drying chamber, that is to say the end further from that at which the fresh hot or
dried air is admitted; and by suitable-appliances the said trays are moved inter-
mittently and in successive order in the direction contrary to the flow of the heated
or dried air through same, so that the substance on the freshly introduced tray is
firstly subjected to the more or less moisture-laden air which has previously passed
through the substance on the trays constituting the column of superimposed trays
already in the drying chamber. I have found however, that in the drying of some
substances, and more especially tea leaf, it is more desirable to have the fresh leaf
subjected to the action of the fresh hot air immediately on its being introduced into the
drying chamber, so as to get a portion of its moisture evaporated rapidly at the
start of its desiccation, and its tendency to further fermentation thereby checked,
and the object of my invention is to accomplish the drying of tea leaf or other
substance in accordance with the above indicated modified system, and so that the
same may be capable of operation in a practically efficient manner.
According to the present invention, a separate receiving compartment (herein-
after called the primary compartment) is constructed in a drying chamber such as
that described in the previous Specification, and in which the air current through
the chamber operates with preferably a downward flow. Into this primary com-
partment the fresh tray (hereinafter called the primary tray) containing the moist
leaf or other material is firstly introduced through a special port, and receives a
quick and partial or primary drying. The said primary compartment is situated
between the inlet of the fresh hot or dried air to the drying chamber and the column
of superimposed and successively ascending trays (hereinafter called the main
column), so that before the said downwardly flowing current of hot or dried air
reaches the main column of trays, it passes through the fresh tea leaf on the.
primary tray. The primary tray with the tea leaf thereon is kept in the primary
compartiment until a tray of fully dried tea leaf is removed from the top of the main.
column; the primary tray is then removed from the primary compartment through
the port by which it was introduced, and is then inserted in the bottom place of the

page_text: main column, from which position it is subsequently intermittently moved in rotation
until it reaches the top place in the main column. It is then immediately below the
tray which for the time being is in the primary compartment, and on its desiccation
being completed it is in turn removed from the apparatus ..th
When a primary tray has been removed from the primary compartment and
inserted into the bottom place of the main column, another fresh primary tray of
material is at once inserted into the primary compartment. By this arrangement
as the air acting on the material on the top and finishing tray of the main column
has previously passed through the fresh material on the primary tray, the intensity
of its heat is so considerably reduced thereby that it is not liable to injure (or
"over-fire" as it is termed) the desiccated material on the said top tray of the
main column, while as the material on the primary tray has still a considerable
percentage of moisture remaining in it, up to the time of its removal therefrom,
evaporation continues to take place from it rapidly, in consequence of which it is
not liable to over-firing either. On being afterwards inserted into the bottom place
of the main column, the material thereon has so much heat stored up in it that the
moisture in the air current, which at this place is considerably further cooled by
having passed through the upper trays in the main column, does not become
deposited thereon, and the vapour which the stored-up heat in the material causes
it to give off, mixes with the air current passing through it, without producing over-
saturation therein.
Among the advantages of this system of drying are that the hot air employed
can be used at a higher initial temperature without danger of over-firing or
injuring the, material, than if the first impact of the fresh: hot air operated as
hitherto ordinarily has been the case, direct on the fully desiccated material, and
. consequently the improved apparatus does moro drying work in a. given time,
while, in the case of tea leaf, the quality of the dried tea is superior, owing to its
being subjected to a sharp high temperature while in a damp state, whereby its
tendency to further fermentation is almost instantaneously arrested, and to
its complete desiccation being effected at a comparatively low and moderate
temperature, whereby the contained volatile oils are less volatilized than when
:same is completed at relatively high temperatures.
The accompanying drawings represent an apparatus constructed according to
the present invention.
Figure 1 is a front elevation; with part in section, of a drying chamber. Figure 2
is a side elevation, with part in section, of the same.
a is the primary compartment. b represents the primary tray in position. c is
the port through which the primary tray is inserted into and withdrawn from the
primary compartment. dd represent the main column of trays. e is the port at
the bottom of the main column through which the primary tray is inserted after its
removal from the primary compartment a. f the port through which the
topmost tray of. the column with the completely desiccated material thereon is
removed. is a lever and hh pawls by means of which the trays of the main
column are from time to time lifted up one stage; these appliances are fully
described in the previous Specification. i is the inlet air duct, and k the exhaust
duct below the drying chamber. The arrows shown in Figure 1 indicate the
direction of the air current.
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
1. In apparatus for drying tea leaf or other substances in which the substance
to be dried is exposed to the action of a current of heated or dried air on a series
of superimposed trays or sieves of foraminous material in a drying chamber, the
combination with a series of trays (hereinbefore called the main column) in a drying
compartment having a tray-inlet port at one end of the column and a tray-outlet port
at the other end of the column, and having also means for moving the trays of the
:

page_text: said column intermittently and in successive order towards the outlet port, of
another drying compartment, herein before called the primary compartment, and
of a port to this compartment for the insertion of a tray containing the fresh
substance to be dried, and for the withdrawal of this tray for removal to the further
end of the other compartment, whereby the fresh hot air after entering the
apparatus passes first through the moist substance on the tray in the primary
compartment and then through the more or less completely dried substance on the
trays in the other compartment, through which the trays with the substance they
contain pass in successive order, the final desiccation of the substance on each
tray being thus effected when the tray reaches the position which is nearest to
the primary compartment, substantially as and for the purpose herein before
described.
1111 1
1 1000
J. C. MEWBURN & ELLIS,
*55 and 56, Chancery Lane, London, Chartered Patent Agents.