Improvements in Electrical Furnaces.
Year: 1898

page_text: COMPLETE SPECIFICATION.
Improvements in Electrical Furnaces.
We, SIEMENS BROTHERS & Co. LIMITED, of 12, Queen Anne's Gate, Westminster,
S.W., Electrical Engineers, do hereby declare the nature of this invention
(which has been communicated to us from abroad by Siemens & Halske Aktien-
Gesellschaft, of Markgrafen Strasse No. 94, Berlin, S. W., Electrical Engineers)
and in what manner the same is to be performed to be particularly described
and ascertained in and by the following statement :-
If electrical furnaces are so constructed that the outer air can penetrate to the
electric arc through the layer of material to be treated, several disadvantages
arise. Firstly the consumption of the carbon electrodes is considerable, because
they not only crumble away, but are also burnt; secondly, if a combustible gas,
such as carbonic oxide is produced in the electric arc, this gas, in entering into
combustion, penetrates through the layer of material and carries considerable
quantities thereof upward, producing objectionable fumes and wasting the material;
thirdly, in consequence of the large quantity of air gaining access to the electric
arc, this, as also the incandescent carbon electrodes, are considerably cooled.
According to the present invention these several defects are obviated, firstly by
employing a layer of the pulverulent material to be treated of such a depth that
neither the external air can penetrate through the same from the outside, nor can
the gas produced by the electric arc penetrate through the same from the inside;
secondly, by employing as the upper moveable carbon electrode, a carbon tube
extending up through the layer of material, so that the gases produced escape
through the same without entering into combustion.
The carbon tube is provided at its upper end with an iron cover having several
openings, to which are connected flexible metal tubes, at the ends of which the
gases escaping through them enter into combustion with the outer air, the tubes
being made of such a size that the flames cannot strike back through them, even
when, for the purpose of tapping the furnace, air penetrates into the carbon tube
from below.
The use of tubes of carbon or of a non conductor in electrical furnaces is not
in itself new, such use having been described in the Specification to Patent
No. 21879 of 1894 and in the Zeitschrift für Elektrochemie 1897 page 14; in both
cases however an indifferent or reducing gas is passed downwards through the
tube into the electric arc, and is led thence upward through the layer of material
into the open air, for the purpose of keeping the outer air away from the electric
With the present invention on the other hand, the same object is attained
without the use of a special supply of gas.
arc.
Electrical furnaces have also been constructed with a hermetically closed furnace

page_text: casing into which the outer air cannot penetrate, and from which the gas produced is
led off. The present invention has however the advantage over these of entirely
dispensing with an enclosing air-tight casing, the air tight enclosure being effected
in the crucible itself, where the layer of pulverulent material forms, as it were, a
shifting air-tight packing, passing continuously downward to the electric arc, and
continually supplied with fresh material at top.
For discharging the product produced by the electric arc, we employ a simple
tapping hole, if the liquid product does not solidify too rapidly; in the case of
calcium carbide and other rapidly solidifying products, we employ a roof-like
shield covered by the material, which allows the liquid product to flow off, but
prevents the material above from following in the same direction.
We adopt this arrangement for periodically tapping, by arranging the shield to
be vertically moveable by means of a lever, and by keeping the tapping hole
generally closed, but opening the same from time to time by the lowering of the
shield in order to remove also the solid products formed in the electric arc.
The present invention constitutes therefore a continuously acting electric
furnace without enclosing casing, and operating without emission of fumes or
flames, in which the material is continuously supplied from above, while the
product formed in the electric arc is discharged at bottom, and in which the outer
air is kept away from the electric arc, and the gases produced therein are
discharged in an unburnt condition.
On the accompanying drawing are shown by way of example electrical furnaces
constructed according to the above described invention.
In the arrangement shewn in vertical section in Figure 1, and in sectional plan
on line 2-2 in Figure 2, K is the carbon tube, constituting the upper electrode, C
the crucible lined at bottom with carbon plates and provided with the tapping hole O,
D a roof-shaped shield covered with the material treated and made vertically
moveable by means of a lever D¹. The gas rising up through the carbon tube, if of
a combustible nature, is led off through the flexible metal tubes M into the annular
space R at the bottom of the crucible where it is ignited and serves for heating up
the crucible externally, the air supply necessary for the combustion entering the
space R through holes P while the products of such combustion' are discharged
through a pipe S into a chimney.
The said combustible gases might also be used for working a gasmotor engine, or
if it be not desired to utilise the gases, they may be led by the pipes M to a chimney
and there burnt.
The above described electrical furnace can also be used as a distilling furnace if
the carbon tube constituting the moveable electrode be connected to a receiver, serv-
ing to condense the vapours generated by the distilling process, and if the layer of
material to be treated be made sufficiently deep. The receiver may be arranged
directly over the carbon tube and be enclosed in such manner by the material
treated that the condensing chamber will be subject to the exact temperature
necessary for the condensation of the vapours produced in the electric arc.
According to the laws of the conduction of heat, the temperature of the layer of
material will decrease in a uniform ratio from the bottom of the crucible to the top
of the layer, and at the latter point there will always exist the same temperature,
even with a considerable variation in the thickness of the layer.
If therefore the temperatures existing at the bottom of the crucible and at the
top of the layer of material be determined by a few experiments, it will be easy to
determine, for a certain length of the carbon tube, the length of the condensing
chamber and the height of the layer of material necessary for insuring in the former
the required temperature for condensing the vapour or fumes of a certain sub-
stance.
Thus, if for example, the temperature at the bottom of the crucible be taken
at 1800° C. and that at the upper surface of the layer of material at 100° C., and if
the condensing chamber is required to have the temperature at from 500° to 900°

page_text: such as is required for zinc distillation, theu, as shewn in the diagram Figure 3,
if 2 L represent the length of the carbon tube, the length of the condensing
chamber inust be taken as equal to L while the layer of material must extend up
beyond the chamber to the extent of ths L.
The heigth of the layer of material can also be so modified in the event of the
carbon tube being shortened by burning that the whole of the vapour or fumes will
be condensed in the condensing chamber and no portion thereof in the tube. Thus
if the carbon tube be shortened by one half, therefore L as indicated in the
diagram Figure 4, while the condensing chamber retains its length L, then
the layer of material is only made to extend to fo ths of the height of the
chamber.
The lower end of the latter will then have a temperature of 900° C. and the upper
end about 100° namely, the same as the upper surface of the layer of material. In
Figures 3 and 4 K represents the length of the carbon tube. V that of the con-
densing chamber and X the height of the layer of material.
Figure 5 shows a vertical section of an electrical distilling apparatus of the above
described kind, K is the carbon tube, H an iron collar thereon, V the condensing
chamber, W W the trays between which the vapours or fumes rise and on which
the product is condensed, G tube lengths, of which one is fixed to each tray and
which are fitted one upon the other with the interposition of packing rings, these
being all secured together by bolts F, E is the discharge pipe for the uncondensed
gases Z Z the holders from which the carbon tube and condensing chamber are
suspended, and by which they are raised or lowered for regulating the electric arc
in the known manner, X is the layer of material treated, C the walls of the crucible,
T the carbon, bottom thereof, to which the electric current is supplied, Q the
melted product, O the tapping hole and B the electric arc.
When the chamber V is fully charged with condensation products, which will be
shewn by the decrease of pressure of the issuing gases, the screws N are removed
and the condensing chamber V and tube E are drawn out and replaced by fresh
ones, the carbon tube K and the casing D' remain in the crucible. The bolts F of
the extracted chamber having been removed, the tube lengths G with the trays are
separated for the removal of the condensation products therefrom. It will be seen
that the above.described distilling furnace admits of easier and simpler manipula-
tion tban electrical distilling furnaces of existing construction, where the entire
furnace casing requires to be made air tight and has an external con-
densing chamber which, according to circumstances, may require to be specially
heated.
Having now particularly described and ascertained the nature of this inven-
tion and in what manuer the same is to be performed we declare that what we
claim is
1. An electrical furnace having a carbon tube as the upper inoveable electrode,
wherein the charge of pulverulent material to be treated is made to constitute an
air tight packing, preventing the access of the outer air to the electric arc while
the gases generated by the electric arc are discharged through the tubular electrode
and conveyed away through a pipe or pipes to wherever required, substantially as
required.
2. In an electric furnace such as is referred to in the first claim, the com-
bination with the carbon tube of a receiver or condensing chamber for condens-
ing the vapours or fumes produced by the electric arc, which chamber is embedded
in the charge of material to be treated, substantially as and for the purposes herein
described.
3. An electrical furnace having a carbon tube as the upper moveable electrode,
combined and operating as herein described with reference to Figure 1 of the
drawings.
4. An electrical furnace having a carbon tube as the upper moveable electrode

page_text: arranged for distilling substances and condensing the products and operating as
herein described with reference to Figure 5 of the drawings.
ABEL & IMRAY,
Agents for the Applicants.