IMPROVEMENTS IN TREATING AND UTILIZING SPENT TAN AND OBTAINING USEFUL PRODUCTS THEREFROM
Year: 1874

page_text: PROVISIONAL SPECIFICATION left by Hunter Henry Murdoch at the
Office of the Commissioners of Patents, with his Petition, on the
17th October 1874.-A communication from abroad by Modeste
Léonard Honnij, of Chatelineau, Belgium, Manufacturer.
I, HUNTER HENRY MURDOCH, of No. 7, Staple Inn, in the County of
Middlesex, Patent Agent, do hereby declare the nature of the said
Invention for "IMPROVEMENTS IN TREATING AND UTILIZING SPENT TAN AND
OBTAINING USEFUL PRODUCTS THEREFROM," to be as follows:-
In most places where leather is tanned a quantity of spent tan
accumulates without the tanners having the means of utilizing it. Now
the object of this Invention is to utilize spent tan by a process for
quickly drying and carbonising the same, and obtaining therefrom divers
useful products as herein-after described.
The processes in general use for carbonizing wood are inapplicable to
spent tan, for if the carbonization of spent tan out of contact of air were
attempted, the ignited tan would be extinguished instead of becoming
carbonized, the idea of carbonizing spent tan like charcoal by kindling a
fire in it must therefore be abandoned.

page_text: According to this Invention the carbonization of spent tan is effected
in apparatus somewhat analogous to what is used in the manufacture of
coal gas. The said apparatus produces from the said spent tan a gas
which is first purified by passing through water; secondly by cooling so
as to deprive it of the vapour it contains; and thirdly by being caused to
pass through lime. The said apparatus consists of a furnace in which
are mounted one or more tubes or retorts projecting slightly at one end
out of the said furnace, where they are fitted with a door or plate which
may be opened to charge in the spent tan. At the upper side of the
projecting end of each of the said retorts is an aperture or hole to which
is connected a suitable pipe, through which the smoke or vapour emitted
by the tan in the retort escapes, and is conducted to a tank containing
water, in which the said pipe is immersed to a depth of four or five inches.
The said smoke produces tar and gas which may be employed usefully.
The tar mixing with the water in the tank is deposited at the bottom of
the tank, and passes out of the said tank through a suitable pipe, the gas
filters through the water, and by accumulating passes through an outlet
in the upper part of the said tank, the said outlet.being provided with a
suitable pipe which conducts the tan gas to an iron tank partly filled
with water, and having above the water a grating on which is placed a
quantity of coke. The gas passing through the water is further purified
of the tar and other impurities it still contains. The said tar and other
matters are deposited in the water whilst the gas passes through the
layer of coke, is purified thereby, and then passes through another pipe
to a series of double refrigerating tubes bent in pairs and opening into a
closed chest partly filled with water, one leg of the said tubes dipping
into the water whilst the other leg opens above the water.
The tan gas
passes through the said tubes and through the water contained in tho
said chest, and thence passes through a suitable pipe to the purifier
which consists of a vessel of a conical shape tapering slightly from top to
bottom, and provided with a suitable cover. In the said purifier are
layers of trelliswork one over the other, each layer of trelliswork being
covered with a layer of moss covered over with lime; the tan gas passes
through the said trelliswork and the moss and lime and is further
purified. If very pure gas is required, a second purifier or several other
similar purifiers may be used. From the last purifier the gas is made
to pass into a suitable holder or gasometer for use.
The drying and carbonization of spent tan in ordinary retorts or
receptacles is a matter of considerable difficulty especially when the dri

page_text: fibrous materials are applied, such as the manufacture of paper pulp,
statuary, pasteboard, and other articles, for the tan being greatly
charged with moisture owing to its having remained for a length of
time in the tanner's pit emits when heat is applied to it a largo
quantity of steam which is unable to escape by the outlet of the
retort.
A supply of air which would be injurious to the carbonization of wood
or other matters inasmuch as it would cause them to ignite and burn
away, is useful or even necessary for the treatment of tan, and according
to this Invention the vapour produced by the tan is utilized in preventing
the ignition of the gases emitted by the tan when air is admitted into the
retort to hasten the drying operation, which drying operation and also
the carbonization is accelerated by the introduction of air into the retort
without loss of the gases evolved even when great heat is used. For this
purpose according to this Invention a fan placed behind the retort is used
to force a blast of air directly into the said retort, or through a perforated
pipe inside the retort; the said blast which may be regulated at pleasuro
blows out the steam as soon as it is produced and contributes greatly to
dry the tan, and the said tan being subjected to the double action of the
fire outside of the retort and the blast of air inside is speedily dried and
carbonized.
Either a hot or a cold blast may be used, the hot blast being preferable
as accelerating the operation. Or an agitator consisting of a shaft
provided with flat or curved or helical blades or wings may be used to
stir the tan, the said agitator being mounted in the retort and caused to
revolve either by hand or by power. The said agitator may be used with
or without the blast above mentioned, or by making the shaft of the
agitator hollow and perforating it with holes within the retort. The blast
may be made to pass through the said shaft into the retort, or the wings
or arms of the said agitator may be combined with tubes perforated on
one side so as to receive the blast from the hollow shaft and discharge it
within the retort. Or the retort itself may be made capable of oscil-
lating or revolving so as to increase the stirring up of the tan and the
emission of steam. The winged shaft or agitator in this case may be
either rotatory or stationary. If there should be reason to fear that the
agitator will melt or bend from the great heat, a small jet of water may

page_text: be caused to flow into the agitator shaft by means of a small pipe in
connection with a water tank.
Motion is given to the agitator and other acting parts by any suitable.
mechanical means. If preferred the steam from the retort may
be drawn out by suction instead of being forced out by blast.
By operation upon spent tan, according to this Invention, the following
products or results may be obtained :—
First. A gas suitable for lighting or heating purposes. When used
for heating purposes the said gas need not be purified by passing through
the purifiers and refrigerators herein-before described, it being sufficiently
cleansed for use by passing through the water in the first water tank. If
the gas be intended for lighting purposes all the smoke and vapour may
be evaporated till the tan is thoroughly dry, thus avoiding any mixture
of air with the gas. This evaporation though necessary when the gas is
to be used for lighting is unnecessary when it is to be used for
heating. If desired the vapour may be conducted to a second wator
tank.