IMPROVEMENTS IN REVERBERATORY AND OTHER FURNACES FOR ROASTING ORES
Year: 1874

page_text: LETTERS PATENT to Alexander Melville Clark, of 53, Chancery
Lane, in the County of Middlesex, Patent Agent, for the In-
vention of "IMPROVEMENTS IN REVERBERATORY AND OTHER FURNACES
FOR ROASTING ORES."- A communication from abroad by Ernst
Heiligendorfer, of Eureka, in the County of Lander, and State of
Navado United States of A moving
COMPLETE SPECIFICATION filed by the said Alexander Melville Clark
at the Office of the Commissioners of Patents, with his Petition
and Declaration, on the 23rd September 1874, pursuant to the 9th
Section of the Patent Law Amendment Act, 1852.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, ALEXANDER
MELVILLE CLARK, of 53, Chancery Lane, in the County of Middlesex,
Patent Agent, send greeting...
WHEREAS I am in possession of an Invention for "IMPROVEMENTS IN
REVERBERATORY AND OTHER FURNACES FOR ROASTING ORES," and have petitioned
Her Majesty to grant unto me, my executors, administrators, and
-

page_text: assigns, Her Royal Letters Patent for the same, and have made solemn
Declaration that it has been communicated to me from abroad by
Ernst Heiligendorfer, of Eureka, in the County of Lander, and State of
Nevada, United States of America.
NOW KNOW YE, that I, the said Alexander Melville Clark, do hereby
declare that the following Complete Specification, under my hand and
seal, fully describes and ascertains the nature of the said Invention,
and in what manner the same is to be performed, in and by the following
statement, reference being had to the accompanying Sheet of Drawings,
and to the letters and figures marked thereon (that is to say) :-
In the Drawing Figures 1, 2, and 3, represent vertical longitudinal
sections through the improved reverberatory furnace as constructed for
producing a highly oxydizing fire, and the more complete roasting of
the ore.
Similar letters of reference indicating corresponding parts.
The object of the Invention is to so improve the reverberatory and
other furnaces for roasting ore, that a clear fire, free from smoke, of the
highest oxydizing power, is thrown in the screened pulp in its state of
greatest fluidity, by means of currents of heated air or other gases
which are introduced between and sidewise to the gases of combustion,
so that the furnace may be applied to work all kinds of base gold and
silver ores, galena, zinc blende, and similar ores.
The Invention consists in the introduction of partitions or air inlets of
cast iron plates or fire-bricks, intermediately and at both sides of the
grate parellel to the grate bars and the fire-place, and extending above
the fuel accumulated in them. It consists also in an improved screening
of the heated pulp, and its passage through a chlorinizing respectively
oxydizing fire in a state of greatest fluidity by passing through a shaft
and over a diagonally upward inclined fire-bridge, and lastly, in the
method of treating the pulp of gold and silver ores, first with chlorinizing
and afterwards with oxydizing gases.
Every one acquainted with blowpipe assaying is cognizant of the
importance of using a pure oxydizing flame for oxydizing processes. It
is of analogous importance on a larger scale in metallurgy, where correct
results are impossible if as in actual practice at present dark and smoky
fires are used. Smoke is reducing and works directly against oxydation.
To obtain therefore from a common grate a clear fire free from smoke
and of the highest oxydizing power, I introduce by natural draught

page_text: currents of air between and sidewise to the gases of combustion.
The
amount of oxygen introduced must not only be sufficient to consume the
smoke, but there must be beside a surplus provided for the purpose of
oxydation. Sometimes also an abundance of air may be used in order
to have a large fire of low temperature.
same.
In the Drawing A represents the furnace; B, the fire-place; C, the
grate bars; and D, the vertical partitions which form the air inlets,
being constructed of cast iron plates placed between, and at both sides
of the grate parallel to the grate bars and to the axis of the fire-place,
and extending through its full length high enough to rise above the fuel
on the grate. If for instance three partitions are arranged as indicated
in Figure 1, five different currents of gases are produced, two from the
fire, and three of fresh air which mingle between the bridge and arch of
the furnace, and throw a clear fire of superior oxydizing quality into the
The number of partitions may be increased if pine wood with
pitch or bituminous coal is burned in proportion to the smoke producing
qualities of the fuel, and also to the width of the grate. In a great
many cases however for all smaller work two air currents will be found
sufficient, which enbracing the fire from both sides form a principal point
of this Invention. The same system of air currents may be applied to
gas generators. The gases of combustion produced by a generator
cannot be burned at all without fresh air. An air current is therefore at
present introduced between the arch and fire-bridge either from below or
from above; but as this one sided air current is not sufficient to render_
the flame oxydizing and free from smoke, I therefore introduce two
air currents from both sides which suffice for smaller work and for
great fires. I also penetrate the gases with one or more inner currents.
It is obvious that every inner partition divides a grate into two
different grates, and that a wide grate divided by several inner partitions
is indeed a combination of several separate fire-places.
When one or more inner air currents shall be applied to a gas
generator, the gas can either be divided or it may be found simpler to
construct two, three, or more separate gas generators between every two
of which an air inlet can be provided for. By uniting the different.
flames over the fire-bridge an oxydizing fire of any required thickness.
can be obtained. In this manner a common grate may also be worked
in combination with one or more gas generators, by which explosions.

page_text: fire-bridge.
It is important that the least possible heat be consumed in the fire-
place, and that the greatest amount of heat produced by the fuel be
thrown into the furnace. To this end the gases of combustion and the
air currents should not mingle before arriving near the fire-bridge. If
for instance three partitions are arranged as in Figure 1, the partition on
the left side farthest from the fire-bridge may either extend near the
arch, or, better, be substituted by an air inlet in the brick wall and arch
is indicated in Figure 2, and for the same purpose, that is, to prevent a
too early mingling of air and gases of combustion, the two cast-iron plates
which form the middle partitions may have different heights. To give
these cast-iron plates more durability they may be lined with fire-bricks,
or the air inlets may be entirely constructed of fire-bricks for conducting.
the different gases in separate channels near to the fire-bridge. For the
roasting of such ores for which a mere oxydizing process is not sufficient,.
I introduce through the partitions, besides the air, also such other
roasting gases as answer the purpose especially chloric, hydrochloric, and
sulphurous gases and steam, so that this grate construction though
originally intended for the roasting furnace will be found useful for
many other purposes. In roasting the ore it has been the aim to expose
the greatest possible surface of ore to the roasting gases by screening
the dry crushed ore or pulp through a fire. The screening hitherto has
however been more or less a failure as the pulp was screened in a cold
state. Cold pulp is sticky and adhesive, but when it is heated up to
about 200 or 300° Celsius, at which temperature roasting begins, and
kept simultaneously in constant movement it becomes more and more
thin and almost as easily flowing as a liquid. This fluidity however
diminishes again from the beginning towards the end of roasting, and
after the pulp is thoroughly roasted it is not thin but drops down like
wet sand. These qualities must be taken into consideration as only then
the difficulties to the screening of pulp may be avoided. The sieve used
must be coarse or its holes would be blocked up in a short time. If
cold pulp is screened through such a coarse sieve it forms small balls,
some of which fall through the fire entirely crude. On the contrary
when the pulp is screened in its greatest fluidity it will partly by sifting
partly by falling some distance through the air form a dust rain of very
minute particles. A higher temperature of the pulp, would not only

page_text: destroy the sieve, and produce the most annoying vapors, but also would
take away the fluidity, the very object of heating up the pulp. The main.
difference in which this heating and screening process differs from those
used heretofore in other kinds of roasting furnaces lies herein, that their
previous heating is only preparatory to the following roasting with a
tendency to do as much previous roasting as possible, while the heating.
now described has for its only object to screen the pulp into fine
particles, and not to raise the temperature above the point where roasting.
begins.
The mode of roasting of this Invention is shown in Figure 3 of the
Drawing, and consists in dropping the pulp from a hopper in small and
constantly renewed quantities into the inclined and revolving cylinder E
of about 12 feet in length by a foot in diameter. The pulp is heated
during its passage through the cylinder to the desired degree of
temperature and fluidity, and passed on to the sieve F where it is spread
and screened by machinery.
The shaft G connects the sieve F with the
furnace below, and is from five to ten feet high for protecting the screen
from the fire and give the pulp a chance to drop in a fine spray or dust
rain. The pulp reaches at the mouth of the shaft the fire of the
furnace which consists as before described of alternating fire and air
currents, and eventually also of other roasting gases.
The temperature and thickness of the fire can be made to suit all the
different kinds of ores and smelting products. As the pulp during its
fall through the fire is by the draught carried away to a horizontal
distance about equal to the width of the shaft, as indicated by dotted
lines in Figure 3, the fire-bridge H is extended upwards in an inclined
diagonal direction for giving to the lower part of the fire the same
efficiency as the upper part. The diagonal shape of the fire-bridge
serves therefore to counteract the pressure of the falling pulp by the
side pressure of the current. After having passed the fire the roasted
pulp drops into the receiving space I, which is for the purpose of saving
labor provided with a trapdoor or movable bottom. This construction
of roasting furnace offers special advantages for the chlorinizing of silver
and gold ore, being based on the qualities of the minerals mixed there-
with. Silver ore is accompanied in the majority of cases with sulphur,
antimony, arsenic, iron, copper, lead, bismuth, etc. Of these the
sulphur, arsenic, and antimony may be well enough removed by the
better kinds of existing roasting furnaces, but the injurious effect of

page_text: fire to compensate both the side pressure of the gas currents, and the
vertical pressure of the falling pulp, substantially as specified.
4thly. The process herein described of roasting gold and silver ore by
heating it to the required degree of fluidity, screening it in minute
particles, and exposing it first to the action of chlorinizing, and afterwards
to the action of oxydizing gases, substantially in the manner and for the
purpose set forth.
In witness whereof, I, the said Alexander Melville Clark, have
hereunto set my hand and seal, this Twenty-third day of
September, in the year of our Lord One thousand eight hundred
and seventy-four.
Witness,
HARRY SWALES,
53, Chancery Lane,
London.
A. M. CLARK. (L.S.)