A NEW OR IMPROVED PROCESS OF EXTRACTING METALLIC ZINC FROM ITS ORES AND OXIDES, AND IMPROVEMENTS IN FURNACES OR APPARATUS CONNECTED THEREWITH
Year: 1876

page_text: LETTERS PATENT to John Henry Johnson, of 47, Lincoln's Inn Fields, in the
County of Middlesex, Gentleman, for the Invention of "A NEW OR IMPROVED
PROCESS OF EXTRACTING METALLIC ZINC FROM ITS ORES AND OXIDES, AND
IMPROVEMENTS IN FURNACES OR APPARATUS CONNECTED THEREWITH."
communication from abroad by Frank Laurent Clerc, of Bethlehem, Penn-
sylvania, United States of America.
A
Sealed the 12th December 1876, and dated the 11th July 1876.
PROVISIONAL SPECIFICATION left by the said John Henry Johnson at the
Office of the Commissioners of Patents on the 11th July 1876.
JOHN HENRY JOHNSON, of 47, Lincoln's Inn Fields, in the County of Middlesex'
Gentleman. "A NEW OR IMPROVED PROCESS OF EXTRACTING METALLIC ZINC FROM
ITS ORES AND OXIDES, AND IMPROVEMENTS IN FURNACES OR APPARATUS CON-
NECTED THEREWITH." A communication from abroad by Frank Laurent Clerc, of
Bethlehem, Pennsylvania, United States of America.
The principal object of this Invention is to save fuel and labor by making the
process of reduction a continuous one, and dispensing with the use of retorts or
muffles, thereby applying the fuel more economically and generating the heat in
the charge where it is required instead of transmitting it through walls of fire-clay.
The process, according to this Invention, consists of the following operations,
namely:-
The reduction of the metal in the form of a gas.
The protection of metallic vapor from re-oxidation.
The condensation of the metallic vapor to a liquid form.
The removal of the residues of the ore and ashes of the fuel.
These operations are carried on continuously and simultaneously in the following
manner :-
First. Feeding a charge of calcined ore, fuel, and flux mixed together and crushed,
say, to about the size of a pea, into a properly constructed furnace, such, for example,
as that herein-after described, in such a manner that the charge is thoroughly
dried and heated before reaching the furnace, and is always covered in the furnace
by a layer of heated carbonaceous fuel. By these means the oxidation of the dis-
tilling zinc vapors is prevented whilst at the same time the deoxidation of the
carbonic acid gas is ensured.

page_text: Second. Injecting through the tuyeres into and through the charge a blast of
air heated to a temperature above the melting point of zinc. Drawing off the
gases from the top of the furnace at a temperature considerably above the melting
point of zinc, and causing them to pass slowly through condensing flues of fire-brick
which are not allowed to fall below that temperature.
Third. Fusing the residue of the ore with the ashes of the fuel by means of a
suitable flux, and running them out at the bottom of the furnace.
The gases are withdrawn from the condensing flues after they have become
cooled below the temperature of melting zinc and are rapidly cooled in iron pipes,
after which whatever zinc has escaped condensation is washed out of them in the
form of a netallic dust, known as blue powder, in the manner herein-after described.
The resultant blue powder is dried and returned to the furnace in a subsequent
charge.
In the working of the process it is preferred to use a furnace and apparatus
constructed substantially in the following manner :-The furnace is made in the
form of an inverted frustum of a widely glaring conc resting on a cylindrical shaft
called the hearth. It is arched over by a dome having a large central opening and
lateral openings or transverse passages. In the hearth of the furnace are openings
for the insertion of tuyeres, a slag eye, and in special cases an additional tapping
hole.
The feeding apparatus consists of a shaft, the lower portion of which is of fire-
brick, extending through the dome into the furnace and terminating at the top in
a hopper, through which descends into the shaft an inner shaft supported by arms.
The condenser is placed over and around the furnace, and consists of fire-brick
flues, say, for example, twelve in number passing over the dome of the furnace.
These flues communicate with each other at the top in sets of four through the trans-
verse passages before mentioned and lead into three chimneys. At the bottom they
are connected together in sets of two adjacent flues uniting to form around the
furnace receptacles for the collection of the condensed metal, the bottoms of these
receptacles being inclined towards each other and converging to the tapping holes.
The sides of the flues are formed by a number of arched radial walls, say, for
example, twelve, extending over and across the furnace, but interrupted in the
centre to admit the feeding shaft. These walls also support the dome of the furnace
and the lower portion of the feeding shaft, and are continued above the flues to
carry the superstructure to the furnace. The dome of the furnace forms the bottom
common to all the flues. The condenser carrying with it the dome of the furnace,
feeding shaft, and otlier contiguous parts is built on an annular iron bed plate, which
may be supported by a double row of pillars.
The washing apparatus consists of a series of vertical pipes connected near the
top with the chimneys by means of cooling pipes. These vertical pipes communicate
with an upper water tank, and each pipe is covered with a finely perforated plate.
The lower ends of the pipes enter a covered water tank, the bottom of which is
divided into a series of receptacles, the sides of the latter converging to a series of
discharging orifices. The cover is so constructed as to form an air chamber above
the level of the water from which the trapped gases pass off through suitable pipes.
The operation of the furnace after it has been dried and lighted in the manner
common to blast furnaces is as follows:-The charge consists of an intimate mixture
of calcined ore crushed, say, to about the size of a pea, or of oxide of zinc, artificially
prepared with proper proportions of flue and flux, to which may be added the blue
powder recovered in the washer from a previous charge. About half of the coal
should be crushed as fine as the ore, the remainder may be somewhat larger. Quick-
lime, iron, or the oxides of manganese are generally applicable as fluxes. With
rich ores, a fusible slag, and a highly heated blast a weight of coal equal to one half
the weight of the charge will be found sufficient. The charge is fed into the inner
hopper as fast as it sinks in the shaft, and at the same time some charcoal or soft
coke easily acted upon by carbonic acid is fed into the interior hopper. As they
descend together they unite in a solid column and are gradually heated before

page_text: reaching the furnace, on entering which they spread out, falling with a natural
"talus
to the outer wall of the furnace. The charcoal being on the outside is
thrust upwards, forming a layer on the top of the charge, where as it is deposited
gradually and in close proximity with the heated dome of the furnace it is maintained
at a sufficiently high temperature to reduce the issuing gases. As the oxide of
zine descends in the furnace the metal is reduced, and being liberated in the form of
a gas it rises with the other gases, passes through the layer of heated charcoal or its
equivalent, (in which operation whatever carbonic acid there may be remaining in
the accompanying gases is effectually reduced to carbonic oxide, and escaping from
its free surface issues into the condenser through the passage ways. In passing
through the condensing conduits it parts slowly with its heat and condenses into
drops, which run together and collect in the receptacles before mentioned, from which
it is withdrawn from time to time. After leaving the condenser the gases are
rapidly cooled by passing them through the cooling pipes before they reach the
washer which they enter near the top of the vertical pipes and descend along with
a shower of water from the water-tank above into the covered tank. The cooling
pipes should be constructed so as to be capable of being replaced by duplicate pieces
when they become obstructed. The blue power is washed out and is withdrawn
through orifices at the bottom, and the washed gases pass off through pipes to be
burned, as in the iron furnace for heating the blast and other purposes. When the
ore contains any metal, such, for example, as copper, manganese, or iron, which is
not volatile at the temperature obtained, and which does not flux with the
"
gangue in the reducing atinosphere to which it is exposed, it may be collected at
the bottom of the furnace and run out through a lower tapping hole in the form of
a metal, matte, or spiegeleisen,
*
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said John Henry Johnson in the Great Seal Patent Office on the 11th
January 1877.
JOHN HENRY JOHNSON, of 47, Lincoln's Inn Fields, in the County of Middlesex,
Gentleman. "A NEW OR IMPROVED PROCESS OF EXTRACTING METALLIC ZINC FROM
ITS ORES AND OXIDES, AND IMPROVEMENTS IN FURNACES OR APPARATUS CON-
NECTED THEREWITH." A communication from abroad by Frank Laurent Clerc, of
Bethlehem, Pennsylvania, United States America.
The principal object of the said Invention is to save fuel and labour by making
the process of reduction a continuous one, and dispensing with the use of retorts
or muffles, thereby applying the fuel more economically and generating the heat
in the charge where it is required instead of transmitting it through walls of
fire-clay.
The process, according to the said Invention, consists of the following operations,
namely:-
The reduction of the metal in the form of a gas.
The protection of metallic vapour from re-oxidation.
The condensation of the metallic vapour to a liquid form.
The removal of the residues of the ore and ashes of the fuel.
These operations are carried on continuously and simultaneously in the following
manner :-
First. Feeding a charge of calcined ore, fuel, and flux mixed together and crushed,
say, to about the size of a pea, into a properly constructed furnace, such, for example,
as that herein-after described, in such a manner that the charge is thoroughly dried
and heated before reaching the furnace, and is always covered in the furnace by a
layer of heated carbonaceous fuel.
Second. Injecting through tuyeres into and through the charge a blast of air
heated to a temperature above the melting point of zinc. Drawing off the gases

page_text: from the top of the furnace at a temperature considerably above the melting point
of zinc, and causing them to pass slowly through condensing flues of fire-brick
which are not allowed to fall below that temperature.
Third. Fusing the residues of the ore with the ashes of the fuel by means of a
suitable flux, and running them out at the bottom of the furnace.
The gases are withdrawn from the condensing flues after they have become
cooled below the temperature of melting zinc and are rapidly cooled; in iron pipes,
after which whatever zinc has escaped condensation is washed out of them in the
form of a metallic dust, known as blue powder, in the manner herein-after described.
The resultant blue powder is dried and returned to the furnace in a subsequent
charge.
In the working of the process it is preferred to use a furnace and apparatus
constructed substantially as illustrated by the accompanying Drawings, to which I
shall now proceed to refer.
Figure 1 of the Drawings represents a vertical section of the furnace, condenser,
and feeding, shaft; Figure 2 is a sectional plan of the same taken along the line
1-2, Figure 1; and Figure 3 represents a perspective view of a washing apparatus
to be connected with the furnace.
The furnace A is made in the form of an inverted frustum of a widely flaring
cone resting on a cylindrical shaft A¹ called the hearth. It is arched over by a
dome a having a large central opening and lateral openings c, as clearly shewn
in Figure 1. In the hearth of the furnace are the openings e for the insertion
of tuyeres, the slag eye a, and in special cases the additional tapping hole y.
The feeding apparatus B, Figure 1, consists of a shaft, the lower portion of
which is of fire-brick, extending through the dome a into the furnace and termi-
nating at the top in a hopper B', through which descends into the shaft B an inner
shaft D supported by arms D¹.
The condenser is placed over and around the furnace, and consists of fire-brick
flues C (twelve being employed in the present example), passing over the dome
of the furnace. These flues communicate with each other at the top in sets of four
through the transverse passages c and lead into chimneys F, three of which are
assumed to be employed. At the bottom they are connected together in sets of
two adjacent flues, uniting to form around the furnace the receptacles & for the
collection of the condensed metal, the bottoms of these receptacles being inclined
towards each other and converging to the tapping holes f. The sides of the flues
are formed by twelve arched radial walls g extending over and across the furnace,
but interrupted in the centre to admit the feeding shaft B. These walls also
support the dome of the furnace and the lower portion of the feeding shaft, and
are continued above the flues to carry the superstructure to the furnace. The
dome of the furnace forms the bottom common to all the flues. The condenser
carrying with it the dome of the furnace, feeding shaft, and other contiguous parts
is built on an annular iron bed plate, which in the present example is supported
by a double row of pillars C¹, as shewn.
The washing apparatus shewn in the perspective view, Figure 3, consists of a
series of vertical pipes I connected near the top with the chimneys F (Figure 1)
by means of the cooling pipes J. These vertical pipes communicate with the upper
water tank h, and each pipe is covered with a finely perforated plate i. The lower
ends of the pipes enter the covered water tank K, the bottom of which is divided
into a series of receptacles, the sides of the latter converging to a series of discharging
orifices. The cover is so constructed as to form an air chamber above the level of
the water from which the trapped gases pass off through the pipes n.
The operation of the furnace after it has been dried and lighted in the manner
common to blast furnaces is as follows:-The charge consists of an intimate mixture
of calcined ore crushed, say, to about the size of a pea, or of oxide of zinc, artificially
prepared with proper proportions of fuel and flux, to which may be added the blue
powder recovered in the washer from a previous charge. About half of the coal
should be crushed as fine as the ore, the remainder may be somewhat larger. The

page_text: proper proportions of coal and flux will vary in accordance with the character of
the ore and fuel, temperature of blast, and other conditions. They can be approxi-
mately determined in any case by a preliminary analysis of the fuel and ores, and
accurately adjusted so as to secure the best results by careful experimental working.
Quicklime, iron, or the oxides of manganese, are generally applicable as fluxes.
With rich ores, a flexible slag, and a highly heated blast a weight of coal equal to
one half the weight of the charge will be found sufficient. The charge is fed into
the inner hopper as fast as it sinks in the shaft, and at the same time some charcoal
or soft coke easily acted upon by carbonic acid is fed into the interior hopper. As
they descend together they unite in a solid column, and are gradually heated before
reaching the furnace, on entering which they spread out, falling with a natural
"talus" to the outer wall of the furnace. The charcoal being on the outside is
thrust upwards, forming a layer on the top of the charge, where as it is deposited
gradually and in close proximity with the heated dome of the furnace, it is main-
tained at a sufficiently high temperature to reduce the issuing gases. As the oxide
of zinc descends in the furnace the metal is reduced, and being liberated in the
form of a gas, it rises with the other gases, passes through the layer of heated
charcoal or its equivalent (in which operation whatever carbonic acid there may
be remaining in the accompanying gases is effectually reduced to carbonic oxide)
and escaping from its free surface issues into the condenser through the passage
ways c. In passing through the condensing conduits its part slowly with its heat
and condenses into drops, which run together and collect in the receptacles d, from
which it is withdrawn from time to time. After leaving the condenser the gases
are rapidly cooled by passing them through the cooling pipes J before they reach
the washer, which they enter near the top of the vertical pipes I, and descend
along with a shower of water from the water tank above into the covered tank K.
The blue powder is washed out and is withdrawn through the orifices, and the
washed gases pass off through the pipes n to be burned as in the iron furnace for
heating the blast and other purposes. When the ore contains any metal, such,
for example, as copper, manganese, or iron, which is not volatile at the temperature
obtained, and which does not flux with the "gangue" in the reducing atmosphere
to which it is exposed, it may be collected at the bottom of the furnace and run
out through a lower tapping hole in the form of a metal, matte, or spiegeleisen.
In order to insure the satisfactory working of the furnace it is essential, first,
that command should be had of a sufficient pressure and volume of blast to be able
to regulate the rate of combustion and the temperature of different parts of the
furnace; second, the blast should be heated as hot as is consistent with the durability
of the furnace and blast apparatus, in order that it may compensate as much as
possible for the heat withdrawn by taking the gases out of the furnace and counter-
act the cooling effect in the upper part of the furnace due to reduction, without
unduly increasing the amount of the consumed and consequently the volume of
gases with which the zinc vapour is diluted. The temperature absolutely required
in any case will depend upon the nature of the fuel; it will be less with
charcoal and soft coke than with hard coke or anthracite. The temperature must
be sufficient to kindle the fuel whenever it comes in contact with it, and to ensure
the perfect conversion of the oxygen of the blast to carbonic oxide in passing
through even a thin layer of the fuel. It is also essential that the ore, fuel, and
flux should be thoroughly dry before entering the furnace, and free from volatile
constituents capable of oxidizing the zinc vapour if given off at the top of the
furnace, for this reason the ore and flux should be carefully calcined, and only such
fuel as anthracite coke or charcoal containing but a small quantity of volatile matter
should be employed. Even when anthracite or hard coke is used it is desirable to
mix with it a proportion of charcoal sufficient to effect reduction.
The satisfactory working of the washing apparatus will depend upon the
thoroughness with which the gases are deoxidized before leaving the furnace, since
the presence of even a small proportion of oxide of zinc in the gases is sufficient to
choke the pipes and obstruct the working of the apparatus.

page_text: The cooling pipes should be made of iron, and as light as possible, and should
be so constructed as to be capable of being replaced by duplicate pieces in case they
become choked, as they are liable to do when the furnace is working irregularly.
These pipes also serve to indicate the temperature at which the gases leave the
condenser. The gases should not remain after they have cooled below the tem-
perature of melting zinc, lest the condensing conduits become filled with blue
powder, nor should they leave the condenser while condensation is still possible.
The height of the feeding shaft will depend upon the pressure of the blast and the
fineness of the charge, it must be sufficient to prevent the gases from escaping
upwards through it instead of passing into the condenser. The large open chambers
of the condenser are constantly filled with a gas which will explode when mixed
with air, hence the necessity for adopting precautions to prevent such a mixture.
So long as the blast is continued there is an outward pressure at all parts of the
furnace, and no air can enter; but should the blast be suddenly interrupted the
cooling of the gases might induce air to enter the furnace; but this danger is
greatly lessened by the intimate connection between the condenser and the washer,
through which only the burnt gases and aqueous vapour could be drawn into the
furnace, neither of which can cause an explosion with carbonic oxide.
The principle advantages claimed for the process over any heretofore used are a
saving of fuel and labour, the more perfect extraction of the metal from the ores,
and its adaptation to ores which cannot be treated directly by any other process.
Having now described and particularly ascertained the nature of the said In-
vention, and the manner in which the same is or may be used or carried into
effect, I would observe in conclusion that what I consider to be novel and original,
and therefore claim as the Invention secured to me by the herein-before in part
recited Letters Patent, is-
First. The mode or process of extracting metallic zinc from its ores and oxides
by injecting a blast of superheated air into and through a charge of calcined ore, fuel,
and flux, causing the gases evolved to pass through heated charcoal or soft coke,
and finally condensing the zinc vapour at a temperature above the melting point of
zine, all substantially as herein-before described.
Secondly. The process of preventing the oxidation of the distilling zinc vapours and
securing the deoxidation of the carbonic acid gas by charging the furnace in such a
manner that a hot layer of superposed carbonaceous fuel is always presented to the
outgoing gases and vapours at the time of their exit from under the furnace dome,
substantially as herein-before described.
Thirdly. The process of washing the gases evolved from the furnace, that is to
say, causing them to pass with a shower or showers of water into a tank, hercin-
before described.
Fourthly. A zinc furnace, in which are combined the following elements, namely,
a hearth A, a furnace proper A, made in the form of an inverted frustum of a
cone, the dome a, central feeder B, and passages and flues, all substantially as
herein-before described and illustrated by the accompanying Drawings.
Fifthly. The combination of the feeding shaft B and its hopper B¹ with the
inner feeder D and its hopper, all substantially as herein-before described and
illustrated by the accompanying Drawings.
In witness whereof, I, the said John Henry Johnson, have to this my Speci-
fication set my hand and seal, this Tenth day of January, in the year
of our Lord One thousand eight hundred and seventy-seven.
J. HENRY JOHNSON. (L.S.)