AN IMPROVED CONSTRUCTION OF FURNACE FOR ROASTING PYRITES
Year: 1863

page_text: LETTERS PATENT to Moritz Gerstenhöfer, of Freiberg, in the Kingdom
of Saxony, for the Invention of "AN IMPROVED CONSTRUCTION OF FURNACE
FOR ROASTING PYRITES."
Sealed the 8th December 1863, and dated the 11th September 1863.
PROVISIONAL SPECIFICATION left by the said Moritz Gerstenhöfer. at
the Office of the Commissioners of Patents, with his Petition, on the
11th September 1863.
1, MORITZ GERSTENHÖFER, of Freiberg, in the Kingdom of Saxony, do
hereby declare the nature of the said Invention for "AN IMPROVED CONSTRUC-
TION OF FURNACE FOR ROASTING PYRITES," to be as follows:-
The object of this Invention is to effect in an economical manner the roasting
of crushed pyrites for the purpose of driving off the contained sulphur therefrom
prior to its conversion into sulphuric acid. To this end I construct a furnace
or set of furnaces, into which the crushed ore is continuously supplied, and in
passing through which it is effectually exposed to the furnace heat, whereby
the rapid volatilization of the sulphur is effected. The furnace may be
described as a vertical chamber constructed of fire-brick and fitted with a series
of horizontal bearers (formed of fire-brick) distributed evenly through the body
of the furnace for the purpose of intercepting and thereby distributing the
crushed ore as it is discharged through the top of the furnace from suitable
feeding boxes. The boxes are provided with grids for arresting the descent of
large pieces of ore, and the supply is equably maintained by means of rotating

page_text: feed rollers mounted in the feed passages in the roof of the furnace. The
upper face of the bearers is made flat to receive the ore, and in accumulating
on the upper bearers it slides off on to those lower down, and so on until it
finally falls to the bottom of the furnace, at which time it is supposed to have
parted with its sulphur. In a line with these bearers stoppered openings are
provided in the front wall of the furnace for cleaning the bearers if they should
become clogged. Their rear ends rest on a hollow partition wall which divides
an air-heating flue or chamber from the furnace proper. This chamber is
provided with a series of horizontal air pipes, the upper one of which is con-
nected with the upper end of a vertical flue in the partition wall and the lower
end with a flue in connection with a cold air chamber built below the furnace.
This cold air chamber is fed by a blower or other suitable means, and is mado
capable of discharging air either into the furnace directly or into the air pipes.
Level with the floor of the furnace is an opening closed by a door for with-
drawing the burned ore, and a little way above this opening a removable grate
is fitted for heating the furnace. The temperature of the furnace having been
raised to the desired point by the consumption of fuel on this grate the grate
is withdrawn, and the opening that admitted it closed. The crushed ore is now
supplied to the furnace, and air is forced through the system of pipes and flues
described until it enters the furnace below the fire-brick bearers. In its
traverse it becomes heated, and flowing up the furnace carries off the sulphur
fumes; the mingled gases then descend the air chamber before mentioned,
heating in their descent the pipes containing the fresh supply of air; the
gases then pass off to a large chamber, where they deposit the dust which they
have carried over prior to being conducted to the sulphuric acid chambers.
SPECIFICATION in pursuance of the conditions of the Letters Patent, filed
by the said Moritz Gerstenhöfer in the Great Seal Patent Office on
the 11th March 1864.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, MORITZ
GERSTENHOFER, of Freiberg, Saxony, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent, bearing date the Eleventh day of September, in the year of our Lord
Öne thousand eight hundred and 'sixty-three, in the twenty-seventh year of Her
reign, did, for Herself, Her heirs and successors, give and grant unto me, the
said Moritz Gerstenhofer, Her special license that I, the said Moritz Gersten-
hofer, my executors, administrators, and assigns, or such others as I, the said

page_text: Moritz Gerstenhofer, my executors, administrators, and assigns, should at any
time agree with, and no others, from time to time and at all times thereafter
during the term therein expressed, should and lawfully might make, use,
exercise, and vend, within the United Kingdom of Great Britain and Ireland,
the Channel Islands, and Isle of Man, an Invention for "AN IMPROVED CON-
STRUCTION OF FURNACE FOR ROASTING PYRITES," upon the condition (amongst
others) that I, the said Moritz Gerstenhofer, by an instrument in writing under.
my hand and seal, should particularly describe and ascertain the nature of the
said Invention, and in what manner the same was to be performed, and
cause the same to be filed in the Great Seal Patent Office within six calendar
months next and immediately after the date of the said Letters Patent.
NOW KNOW YE, that I, the said Moritz Gerstenhofer, do hereby declare
the nature of my said Invention, and in what manner the same is to be
performed, to be particularly described and ascertained in and by the following
statement, reference being had to the Drawing hereunto annexed, and to the
letters and figures marked thereon (that is to say) :-
The roasting process of stamped pyrites or other sulphur ores in order to
employ them for the manufacturing of sulphuric acid has hitherto been
performed either in kilns, grate furnaces, or muffle furnaces. For roasting in
kilns the stamped ores must be brought into a compact form, which formerly
was done by mixing it either with clay, loam, vitriolic lye, or other substances
which are able to bring the ores into a plastic state, so that the mass may be
formed into lumps and dried. These pieces of pyrites are put into the kilns
in the same way as lumps of ore are, and the heat which they produce while
burning will be sufficient to heat a further supply of lumps or pieces as they
are fed in, so that the roasting process may be maintained for any length of
time without stopping.
In working stamped ores in muffle furnaces the pulverized pyrites are spread
over plates of fire-clay, which are heated by a separate fire from below, the heat
being first conducted under the plates and then led over the muffles. The ore
lying on the plates must often be stirred up or move about in order to present
a sufficient surface for the air to effect the oxydation of the metallic sulphuret.
Both these furnaces are open to objection, and the roasting of stamped ores for
the production of sulphuric acid will be at some piaces, if not impossible, at
any rate rather difficult and expensive. The forming of stamped ores.into
lumps by the addition of plastic substances, and then drying the mass for
roasting in kilns or grate furnaces is expensive; this manner of roasting is also
imperfect, and the gases produced (on account of the little sulphurous acid they
contain) will not ive a profitable yield of sulphuric acid; the effect in the lead-

page_text: :
chambers being considerably diminished by working with weak gases, and the
consumption of saltpetre being quite out of proportion to the yield of sulphuric
acid.
In working with muffle furnaces the costs of the roasting process are
augmented by the quantity of fuel that is required. Again the stirring up of
the ores involves a certain amount of labor, and after all the roasting process
is imperfect and the gases are poorer of sulphurous acid than in kilus. The
Inventor of the improved systein has endeavored to construct a furnace which
has none of the disadvantages inentioned.
The Royal Saxon Sulphuric Acid Works have made a trial with a furnace
of the improved construction with so great a success that it is now almost
exclusively employed for the roasting of pyrites at that establishment.
The principal advantages obtained by the use of this Invention are the
following 1. The ores are operated upon in a very divided state, so as to
expose a large surface to the action of the air, and this surface is always being
renewed. 2. The air which must be admitted is forced to come perfectly into
contact with the ores. 3. The ores are brought into the furnace by mechanical
means continuously in such quantities as may be required so as to maintain a
continual roasting process. 4. The air or draft is also brought into the furnace
by mechanical means in order to be able to regulate the draft according to
the quantities of ore, and also to prevent the influence of storms, which are
sometimes very troublesome in working with grate furnaces. 5. The heat
produced by the ores is not led away uselessly by the gases, but is employed to
heat the new ores and the air.
In the accompanying Drawings I have shewn various views of one of my
improved furnaces. Fig. 1 is a vertical section of the furnace through line 1, 2,
of Fig. 3; Fig. 2 is a front view of the same; Fig. 3 is another vertical section
taken in the line 3, 4, of Fig. 2; Fig. 4 is a horizontal section taken through
the line '5, 6, of Fig. 1; Fig. 5 is a horizontal section taken through the
line 7, 8, of Fig. 1; Fig. 6 is a front view of the feeding rollers; Fig. 7 is a
section taken through the air channels or passages and the air valves.
In the Drawing the furnace is shown in connection with other similar
furnaces. After drying the ores the pulverized pyrites are put into the feed
"boxes a above. These feed boxes are furnished with coarse wires or sieves b
to keep back stones, lumps, and large pieces, in order to prevent them from
breaking the feeding rollers. The bottom of these feed boxes are funnel-
shaped, and are divided into three compartments. The pulverized pyrites full
through the boxes on to the feeding rollers c, c, which are furnished each with
six ribs, and are the length of the boxes. The rollers c are made to rotate

page_text: slowly, and conduct the pulverized pyrites down to the vertical openings or slits d
through which they fall down into the main chamber of the furnace. The
inclined iron plates placed above the feeding rollers can be taken away in order in
clean the slits if necessary. The feeding rollers are actuated by screw wheels e
(Fig. 2) and the screws e', which are turned by any suitable moving power. The
stamped ores fall down through the slits d on to the upper three ore bearers f
from whence after the pyrites have reached a certain angle they will fall down on
both sides of the bearers on to the bearers below. The ore bearers are made
of fire-clay, their form being prismatic, as will be seen in the Drawings. As
the pyrites are fed in continually from above the pulverized substance will keep
falling on to the bearers below, and will pass from one to the other set of bearers
throughout the whole chamber down to the bottom of the oven. The form,
situation, and arrangement of the bearers will produce a great distribution of
the pulverized ore, so that a large amount of surface will be exposed, and the
roasting of the ore will proceed, while it is gradually passing down from top to
bottom, while the passing air is in constant motion in the opposite direction.
Again the form and situation of the bearers will be the best for the perfect
employment of the heat, because heat which is produced by the burning
ores will be taken up by the passing draft and will be reflected to the bottom
surface of the next upper bearer, from whence it will be reflected again to the
pyrites immediately below. The draft which is necessary for the roasting
process must be produced by mechanical means, either by means of blowing
engines or ventilators, partly because at some parts of the apparatus the heated
air must be forced to move downward, partly because the quantity of the air
can be more easily measured and regulated if admitted by mechanical means.
The blowing engines will force the air into the main air channel h which runs
below all the furnaces, as seen in Figs. 1 and 3, from whence it will pass through
the channel i, i, into the separate ovens; the air is then conducted to the
wind boxes (Fig. 7), from whence it will find its way by the valves, either
into the channel or the channel m. The channel leads by the shortest way
into the lower parts of the furnace, and is only to be used if too high a tem-
perature in the oven requires an admission of cold air. The channel m leads
the draft into the clay pipes n, n, (Fig. 3,) and it is forced to pass through
them from below to above one after the other. From the top pipe the drift is
forced to go downward through the channel o, which is in the middle wall, as
shewn by dots in Fig. 1, and terminates in the lower part of the oven below
the ore bearers. In the oven itself the draft must find its way through the ore
bearers, and here it will come into intimate contact with the ores on the
bearers, or with the falling ores, whereby it will increase its temperature and

page_text: take up the sulphurous acid, and when the gases arrive at the upper part of
the oven they will be perfectly ready for the process of conversion in the lead
chambers. From this upper part of the oven the gases pass off through the
wide opening p (Figs. 1 and 3) into the back part of the oven, where they are
forced to go downward and to deliver their heat to the clay pipes n through
which the fresh air is admitted as already mentioned. The warming of the
fresh air will thus be very effectually performed as it passes along as it goes in
the opposite direction to the sulphurous gases. The gases will escape through
the opening 9 (Fig. 3) at the lower part of the oven, and through the chimney r
into the wide chambers, which is intended to give an opportunity to the gases
before being brought into the lead chambers to deposit all the dust of roasted
ores, and also the arsenious acid that may have been carried off from the oven.
This chamber is provided with cast-iron plates on which the pulverized pyrites
are spread out to dry, the pyrites being sometimes delivered in a wet state
from the mining works. The roasted ores are brought out of the oven through
the tight fitting door t, which is in so high a position that the ores may come
directly into carriages or trams placed on rails, and may be withdrawn in this
manner. There is a broad slit left open in the front wall of the oven above
the door & in order to put grate bars u, u, through it to receive fuel to set the
oven on fire on commencing the operation. The front wall of the oven is built
in such a manner that there are left openings v, v, in it between every set of ore
bearers; these openings are to be shut up, either by loose stones or by iron
boxes with plugs v¹ in order to be able to reach every single bearer, and to
clean it if necessary by simply withdrawing the stones or plugs and inserting
a tool for the purpose. The interior of the oven is built of fire-clay bricks, and
some of them being of peculiar form must be made on purpose. On all parts
of the oven where a choking may happen by accumulation of dust the clearing
out of the dust is to be done through doors or openings made by removing
loose stones or bricks.
.
In beginning the roasting process the oven is set on fire by wood or other
suitable fuel placed on the grate bars u, u, and afterwards the heat is increased
by supplying coke until there is a red heat all throughout the oven; the grate
bars u, u, are then taken away, and the slit through which they are withdrawn
is shut up, and the blowing engine and feeding apparatus are started. The
roasting process will begin immediately, and will always continue uninter-
ruptedly as long as pyrites are supplied and the oven is kept from choking.
It will only be necessary to take care that the falling down of the pyrites from
one set of ore bearers to the other be maintained, and any improper accumulation
of pyrites on the bearers is to be prevented by means of a thin iron hopk, with

page_text: which the bearers are to be cleaned from time to time through the openings v, v
in the front wall. If very clean ores rich in sulphur be operated upon a
cleaving together of the sulphuret on the bearers will take place on account of
the high temperature; this is to be prevented by mixing the ores with roasted
ores in order to diminish the temperature.
Having now described my Invention of an improved construction of furnace
for roasting pyrites, and baving explained the manner of carrying the same
into effect I claim, as the Invention secured to me by Letters Patent as afore-
said, the arrangement and construction of furnace herein set forth; I claim
particularly suppyling the pulverized pyrites at the top of the oven and causing
it to trickle down in a finely divided state from one set of ore bearers to the
other until it arrives at the bottom of the oven, so that it may be brought into
intimate contact with the ascending current of air.
In witness whereof, I, the said Moritz Gerstenhofer, have hereunto set
my hand and seal, this Fourth day of March, in the year of our
Lord One thousand eight hundred and sixty-four.
Witness,
CURT MERBACH,
of Freiberg.
MORITZ GERSTENHÖFER. (L.S.)