An Improved Method of Obtaining High Temperatures and for Pro- ducing Calcium Carbide, Refractory Metals, and the like.
Year: 1899

page_text: Date of Application, 22nd Feb., 1899-Accepted, 22nd Apr., 1899
COMPLETE SPECIFICATION.
An Improved Method of Obtaining High Temperatures and for Pro-
ducing Calcium Carbide, Refractory Metals, and the like.
I, WILHELM BORCHERS, of 3, Lousberg Strasse, Aix la Chapelle, in the German
Empire, Professor of Metallurgy, 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, reference being had to the accom-
panying drawings and to the letters and figures marked thereon, that is to say: -
In processes of generating high temperatures by artificial heating, that is to say
by combustion, a limit has so far been reached which is dependent partly upon
the durability of the material of which the furnace is constructed, and is partly
due to the imperfection with which the combustion takes place, especially where
a gascous fuel is employed.
As regards the durability of building materials, it is well known that refractory
clays will invariably soften on reaching a temperature of 2000° C., or thereabouts.
Magnesia bricks will stand higher degrees of temperature, but are not always
applicable for furnaces of large dimensions, owing to their defective resistance
when irregularly heated. Carbon bricks, although infusible at temperatures
above 3000° C., still suffer considerably when exposed to hot gases containing
carbonic acid, water, or free oxygen.
Except for these disadvantages, it might be possible, by a preliminary heating
of the air and of the fuel in regenerating furnaces of known kinds, to slightly
raise the temperature beyond the maximum limit known to have been reached.
There is still another possibility of raising the temperature, namely by enriching
the air with oxygen, as is done for example in Linde's process. The employment
of air thus enriched, involves however other disadvantages amongst which is:
The expense caused by producing gaseous mixtures of a higher percentage of
oxygen increases in a-much higher rate than that at which the air can be enriched.
Moreover the direct combustion of gaseous fuels in which carbonic oxide,
hydrogen, and carburetted hydrogen form the most essential constituents, becomes
very imperfect at temperatures exceeding 2000° C., as the temperatures at which
the chief products of combustion, namely carbonic acid and water become dis-
sociated lie below 3000° C. Even if one were to rely upon completing the com-
bustion in regenerative furnaces it would be very difficult to obtain a durable
furnace-material and, speaking generally, the whole arrangement of the apparatus
would also involve great difficulties. The most refractory materials will fuse or
burn under these circumstances.
Even the use of carburetted hydrogen substances (hydrocarbons) as fuels,
especially and repeatedly recommended for heating carbide furnaces, has, according
to my experiments, proved to be at least unsuitable, because at high temperatures,
such as here in question, combustion can only be carried to the point at which the
carbon is burnt to form carbonic oxide, the hydrogen not being burnt at all.
Even if further oxygen were intended to be brought into the combustion chamber
for consuming the hydrogen, this oxygen either would not enter into any com-

page_text: bination at all with the hydrogen, or if such combination should take place to a
small extent, the resulting water, vapour would, when in contact with the carbon
supplied for heating, be re-converted into carbonic oxide and hydrogen.
I have now discovered certain working conditions whereby the disadvantages
above referred to may be avoided, and by which the most simple and known
apparatus may be employed for carrying out smelting processes for which, hereto-
fore, only the electric furnace seemed to be applicable.
As fuel, I use carbon in the form of charcoal or coke; hydrocarbons, on the
contrary, I only employ in case they can be obtained so cheaply as to compete
with the former fuels, or in case the mixture of unburnt hydrogen, carbonic oxide,
and nitrogen obtained therefrom as a waste gas, can be advantageously utilized.
In point of fact, even in the latter case, it is only the carbon which serves directly
for generating heat.
For the combustion of the carbon, I employ air enriched by oxygen, as may be
easily produced, for example by Linde's process.
Now I have found that by blowing air containing 75% or even 60% of oxygen
into ignited charcoal, a temperature may be easily produced at which calcium
carbide is formed. Oxygen mixtures of this percentage would, however, be hardly
applicable in practice because their production is too difficult, or, in other words,
too expensive. But the smaller the percentage of oxygen chosen, the smaller
naturally will be the temperature obtained, and the greater will be the danger of
carbonic acid, besides carbonic oxide being formed at the moment the gas enters
the furnace. Such carbonic acid has a detrimental effect as regards, the pre-
servation of the proper constitution of the charge, seeing that it consumes the
carbon contained in said charge.
By only moderately enriching the air however with oxygen, up to a percentage
varying between 30 and 50%, and by heating this oxygenized mixture, I have
found that substantially the carbon is burnt to carbonic oxide only, and this at
once, without carbonic acid being previously formed, the result being that the
charge to be treated is brought to fusion in an atmosphere as free from carbonic
acid and water vapour as possible.
In the case of oxygen mixtures of 30%. the temperature need not exceed 400° C.,
but in the case of oxygen mixtures of 40% to 50%, the temperature should remain
below 400° C.
Moreover, by a moderate preliminary heating. to about 300° C., an enriched
air mixture whose percentage of oxygen varies between 30 and 50%, is rendered
suitable for the manufacture of carbide, because, under these conditions, carbonic
oxide is generated as the first product of combustion with so little carbonic acid
that the latter has no detrimental effect upon the carbon charge.
By keeping the preliminary heating (when using oxygen mixtures not exceeding
an average percentage of 40%) within the limit of 300° C., a still further important
advantage is obtained, viz.; that metals may be employed in constructing the
apparatus in which the preliminary heating is to be effected. It will be readily
understood that if the preliminary heating were carried higher, or if a larger
percentage of oxygen were employed, the danger of metallic blast heaters being
burnt would increase considerably. The fact that metallic preliminary heating
apparatus may be employed, however, is as apparent from all the preceding
explanations, of great importance with regard to the simplicity of the operation
and of the apparatus.
Another important point for ensuring good results is the method of blowing
in the oxygen mixture. The relative position of the jets of air to the feed opening
of the furnace must be such that the air, on entering the furnace, first meets a
layer of fuel. If the air jet be blown directly towards the centrally located smelting
product, the thickness of the layer of fuel must be so chosen that the gas current
meeting the smelting product contains little or no free oxygen.
As, however, naturally, there will be a desire not to construct furnaces larger
than necessary, the air jets, the fuel, and the smelting product are preferably so

page_text: arranged that the said jets will meet the smelting product nearly tangentially.
Owing to this, the jets also travel upwardly in the layer of fuel thereby more
efficiently heating the same. Preliminary heating of the smelting product is
not to be recommended because these jets might easily have the effect of disturbing
the proportions in which the constituent parts of the smelting product are mixed.
In the case of mixtures specially sensitive in this respect, it is therefore desir-
able to enclose them in compressed hollow receptacles prior to introducing them
into the furnace. I do not intend to manufacture costly crucibles, or carbon pipes
for this purpose, seeing that charcoal or coke, such as employed as fuel, may be
simply mixed with a little tar, or other suitable binding agent, and, by slight com-
pression, be brought into the form of thin walled crucibles or tubular receptacles.
It should be borne in mind that the whole method of operation, such as I propose,
admits of a very considerable concentration of heat and of a rapid absorption of
heat, so that very small furnaces may be used while being of great efficiency,
whereby similar conditions are thus obtained with regard to the dimensions of
the smelting furnaces, as have heretofore only been obtained by working with
electricity.
In view of the fact that when the conditions above described are adhered to,
the simplest ordinary furnaces may be used, I will add descriptions of the following
furnaces that have been utilized in carrying out my experiments. These are
given merely as examples and are not in themselves novel types.
Figs. 12 and 3 represent in elevation, vertical section, and horizontal section,
respectively, an arrangement of plumbago crucible a such as has been employed
for carrying out experiments on the smallest scale. For the preliminary heating
of the enriched air, two copper coils b, c, are used running side by side and ter-
minating in two magnesite nozzles.d, e. Through these coils air is blown at a
pressure of 100 to 200 mm. of water. When experimenting on this scale, it is
preferable that, as as a fuel, charcoal reduced to grains averaging about 10 mm.
across be used, and taking as an example the manufacture of calcium carbide, the
lime or lime stone and the carbon required for forming the carbide may both
be reduced to granules of the same size, say 5 mm. across. This mixture of lime
and carbon may either be introduced centrally into the crucible in the form of
bricks, or bars, or be packed into a compressed carbon receptacle, such as before
referred to.
Fig. 4 is a horizontal section through a crucible provided with four coils and
four magnesite nozzles.
Figs. 5 and 6 represent a furnace a built on the Sefström principle. The shaft
of the furnace is made so wide that the inner wall, constructed of copper plates,
will not suffer from the flame jet. In order to protect the copper wall from being
burnt at the place where the air is discharged, long magnesite nozzles d, held in
position in the copper wall by means of properly cooled fittings are employed,
the object being to prevent the highly oxygenated air from igniting and burning
the copper between the nozzle and the outer copper casing.
The above described apparatus were used for carrying out experiments in which
the sole object was to obtain a small quantity, by weight, of the substance to be
produced, whereas the furnace illustrated in Figs. 7 and 8 has been designed for
commercial use.
In this construction the furnace wall also consists of a number of compound
copper coils b which are so bent that the shaft of the furnace expands downwards.
The reason for so constructing the apparatus, is likewise to protect those copper
paris which lie opposite the nozzles, from the action of the flame jets as well as
to prevent the respective parts of the copper coil from being too intensely heated,
and from the possibility of burning. The copper coils are, in addition, surrounded
by a gas tight sheet metal casing, in order to permit of the waste gases being
intercepted in an unconsumed state and being again used. For the blast nozzles,
I employ either cooling devices of any known kind, or magnesia nozzles held in
fittings capable of being cooled. The lower part of the furnace, namely the collect-

page_text: ing chamber h, for the molten but readily solidifying substances, is protected
from access of the outer air, and is so arranged that the solidified product can
be discharged into a box 1, after a slide or door i has been opened. For this pur-
pose, a stirring iron may, if necessary, be employed, and from the said box the
product can be subsequently discharged after the slide or door has been again
closed.
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
claim is:-
1. The improved method of producing calcium carbide refractory metals, and the
like without the employment of electricity and in apparatus of ordinary con-
struction, consisting in creating the temperature necessary for the reaction by
the combustion of carbonaceous fuels (directly surrounding the substances to be
treated and in immediate proximity thereto) in air enriched to 30 to 50 per cent.
of oxygen and previously heated to about 400°; the combustion being regulated
so that it only forms oxide of carbon and that the formation of carbonic acid
and water is avoided.
2. The herein described method for producing calcium carbide, refractory
metals, and the like, substantially as set forth.
Doted this 22nd day of February 1899
ERNEST DE PASS,
Chartered Patent Agent,
78, Fleet Street, London, and 5*, Market Street, Nottingham,
Agent for the Applicant.