An Improved Method of and Apparatus for Utilizing the Waste Gases and Heat from Electric Furnaces.
Year: 1899

page_text: Date of Application, 20th Feb., 1899-Accepted, 25th Mar., 1899
COMPLETE SPECIFICATION.
An Improved Method of and Apparatus for Utilizing the Waste Gases
and Heat from Electric Furnaces.
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 the working of electric furnaces, more especially those employed for the
manufacture of carbide, attempts are sometimes made to discharge the product from
the furnace in a liquid state, for which purpose, some funaces are heated externally
in addition to internal electric heating. Other furnaces have been so constructed
(and this again applies to the manufacture of carbide) that a given quantity of the
carbide is allowed to accumulate in a solidified form within the fusing chamber, in
order that the finished block may be subsequently withdrawn from the furnace,
or allowed to fall therefrom.
The importance of carrying out the reaction in electric furnaces by excluding
the air, and utilizing the evolved waste gases for heating purposes, has also been
recognized.
All furnaces and working methods, however, heretofore known, present the
following disadvantages.
The carbide discharged from the furnace, in a heated condition, is liable to
become partially burnt."
Portions of the charge fall out of the furnace together with the discharged carbide
blocks, which are of comparatively large bulk, and the carbon in such portions
of the charge is consumer, so that when re-utilizing such charge. fresh carbon
must be added thereto, whereby more impurities than necessary find their way from
the carbon ashes into the carbide.
The cases on leaving the furnace carry off with them a considerable amount of
floating dust containing carbon particles which, being combustible, add the danger
of fire to the inconvenience resulting from the floating dust, as such.
The amount of power consumed in the manufacture of carbide is unduly high,
notwithstanding previous attempts to re-heat the furnaces by burning the waste
gases, or to heat the charge by the latter.
Now, the object of the present invention is to overcome these disadvantages, and
for this purpose I employ furnaces, such as illustrated in the accompanying
drawings, in which both resistance heating and arc-heating have proved satisfactory.
Fig. 1 represents in vertical section one form of my improved resistance heating
furnace.
Fig. 2 is a transverse vertical section of the same, taken on the line r, x, of Fig. 1,
Fig. 3 is a horizontal section taken on the line w. y of Fig. 1.
Fig. 4 represents one form of furnace for arc-heating.
Figs. 5 and 6 are sectional views hereinafter referred to.
The smelting or fusing chamber S, that is to say the electric furnace proper,

page_text: which is formed with thin walls and is provided with a water jacket D, is arranged
inside such jacket after the manner of a furnace in a steam generator.
In the resistance-heating furnace represented in Fig. 1, the electrodes E are
inserted in a suitable manner, for opposite sides, into the furnace.
In the arc-heating furnace represented in vertical section in Fig. 4, one electrode
is inserted vertically through the hopper and the other vertically from below
through a hinged bottom or hearth H capable of turning up or down, and when
opened allowing the cooled carbide block to be removed from the furnace. This
hinged bottom is secured in its closed position by a level M provided with a
counterweight.
The electrodes E, for enabling the current to traverse the charge, consist of carbon
rods or plates between which either the heating resistance W, consisting of a solid
carbon body, or of a core of rammed in pulverized carbon, is inserted. Or the
said rods or plates may be so arranged that between them a voltaic arc can be
struck (see Figs. 4, 5 and 6). The said electrodes are properly insulated at the
places where they traverse the furnace walls.
"
The charge, as far as it is not rammed into the furnace, and as far as supple-
mentary feeding is necessary, is fed from a feed hopper T filled with pulverized
material to such an extent as to prevent escape of gas.
In the interior of the furnace, is an inclined perforated metal plate or. dia-
phragm B, arranged at the natural angle of repose of the surface of the charge.
The space above this diaphragm is filled with wood debris or shavings, coarsely
granulated charcoal, or other vegetable or animal fibrous or porous material F
of a similar nature capable of retaining dust particles. This dust retaining filter
is, in order to prevent its destruction, arranged; as shewn, upon those parts of the
charge which remain comparatively cool.
From what is generally known about electric furnaces and the method of charg-
ing and discharging furnaces of the construction in question, no further explana-
tion is necessary.
When the furnace is at work, the gases escaping from the charge (which by
preference should not be too finely granulated) pass through the above mentioned
filter in the upper part of the furnace, where the floating dust is retained. Thence
the said gases, practically free from dust, pass through a suitably arranged gas
discharge pipe R into a collecting receptacle, or directly into a feed pipe from
which they may be taken, say for working gas engines.
The size of the furnace and the quantity of the charge, are so adjusted that,
after the carbide block has been entirely fused, it will still be enclosed on all sides
insufficiently thick layers of undecomposed charge. Owing to the latter being
in contact with the walls (kept cooled by the surrounding water) the said charge
remains electrically non-conductive during the whole period of work, so that not-
withstanding the metal walls of the furnace, the insulation of the electrodes
and of the smelting products causes no difficulty.
After the working is completed, the finished carbide block is left for several
hours in the furnace, as owing to the high temperature, a considerable amount of
heat still remains accumulated therein which, as it gradually passes off, may be
utilized for the generation of steam. With properly constructed furnaces, the
generation of steam commences when one such furnace has been at work for two
'hours. If, therefore, a series of furnaces of this kind be arranged in one com-
paratively large steam boiler, in which one furnace is worked after another
ecessively, and if the carbide blocks be allowed to cool down therein, the genera-
tion of steam will go on continuously and may be utilized for the generation of
power.
A diagrammatic arrangement of this kind is represented in longitudinal section
in Fig. 5, and in transverse section in Fig. 6.
The method of cooling the carbide block in the closed furnace, apart from the
nossibility of utilizing the excess of heat, offers the further advantage that any
undecomposed charge which naturally falls out of the furnace, or is withdrawn there-

page_text: from together with the finished carbide block, is so cold that the carbon contained
therein is no longer consumed, as was heretofore. believed to be unavoidable.
Experiments have proved that by utilizing the waste gases and the excess heat
existing in the finished carbide, theoretically more than a third-in practice more
than a fourth of the power, heretofore used for the manufacture of carbide, is
saved, and that none of the charge becomes covered with or choked by dust; also,
that the excess of charging material employed for protecting the furnace wall
admits of being used again at any time, without further carbon being added thereto.
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 I
claim is:-
1. The method of utilizing the waste gases and heat from electric furnaces, con-
sisting in effecting the electric smelting or reduction in the interior of a steam
generator in the presence of an excess of the charge which remains undecomposed,
freeing the gases generated in the furnace from dust particles by passing them
through a filtering medium, and then allowing the molten product to cool down
in the furnace, substantially as and for the purposes described.
2. For carrying out the above claimed method, a closed thin-walled water-
jacketed electric furnace provided with means for filtering the gases evolved, and
with gas discharge pipes, substantially as described.
3. In apparatus, as under Claim 2, the arrangement, in a steam generator, of a
comparatively large number of electric furnaces working successively, substan-
tially as and for the purpose described.
4. In an electric furnace as under Claims 1 and 2, the filtering device for retain-
ing the particles of carbon carried off by the waste gases, consisting of a perforated
metal plate or diaphragm covered with vegetable or animal fibres, or other porous
body, and located over that portion of the charge which remains comparatively
cool, to avoid said filtering medium being destroyed by the heat, substantially as
described.
5. My improved method of utilizing the waste gases and heat from electric
furnaces, substantially as herein before described.
6. The apparatus substantially as described and shewn with reference to Figs. 1
to 3, and to Fig. 4, of the annexed drawings, and for the purposes set forth.
7. The apparatus substantially as described and shewn with reference to Figs. 5
and 6 of the annexed drawings, and for the purpose set forth.
Dated this 20th day of February 1899
ERNEST DE PASS,
Chartered Patent Agent,
78, Fleet Street, London, and
5*, Market Street, Nottingham,
Agent for the Applicant.