Note: Descriptions are shown in the official language in which they were submitted.
î ~5~2~
H0~ 8~/H 008
The present invention relates to process ~or making
oalcium carbide from lims(also -termed white material) and
a carbon carrier (also termed black material) in a closed
electrothermal furnace with a capaclty of more than 20
5 megawatt~ in which the electrodes are arranged symmetri-
cally so as to form the three corners o~ an equilateral
triangle~
Electrothermal furnaces have been in worldwide use for
decades. The product first made by electrothermal mea~s
10 was calcium carbide. Furnaces of relatively limited capacity
had been in operation over decades; gas which evolved was
allowed to undergo combustion on the surface of the
mixture of flux and ores (briefly termed burden herein-
after). Reaction a~d burden were under continuous visual
15 inspection so that lrregularities during operation could
be corrected at once by mechanical action. As a resultS it
wa~ unnecessary for the nature o~ the individual components
forming the burden to comply with particularly high
standards.
Since about 25 years, furnaces have been designed
and constructed which, ~or reason~ of environmental
protec~ion, are completely clo~ed and, for reasons of
economy, have been given considerably increased capacity,
furnaces with a capacity of up to 75 megawatts having
25 indeed been taken into use.
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l i 5~425
A serie~ of dif'~icul-ties have been encou~tered in
the development of these modern industrial ~urnaces.
Needless to say the furnaces no longer permit the
processes occurring therein to be directly acted upon
during operation. As a result, it is necessary to use a
burden o~ which the composition has to comply with
particularly high standards. More specifically, it is
desirable ~or the burden to have a cor~positlon permitting
reliable ~urnace operation over a period of at least some
days be~ore the mechanical removal of agglomerated material
or slag.
All these operatlonal steps have been rendered
additionally difficult by the ~act that the liability of
an unsuited burden to ~ail has increa~ed together with the
distinct increase in furnace capacity.
With the increasing capacity of electric reduction
furnaces, the permeability to gas of the covering layer
o~ burden in the reaction vessels and the exchange of
heat between ga~ and burden have to an increasing extent
become factors which critically determine the ~uccessful
operation of -those furnaces. In the event o~ the evolving
gas being irregularly removed from these vessels, very
hot furnace gas i8 liable to be ejected shockwi~e, causing
damage to the furnace cover, electrode holders and
ultimately, electrostatic dust precipitators. These
difficulties have even been found to be intensified in the
event of standard metallurgical coke grades being replaced
by such ill-reactive carbon carriers as customarily
employed anthracite, petroleum coke and/or lean coal.
To improve the burden's permeabllity to gas and
hence the exchange of heat between gas and burden, it
has heretofore been held desirable for the particle size
of the burden to vary within narrow limits, i~e. for
the burden and more speci~ically ~or the carbon carrier
particles to present a certain minimum size.
This is why the carbon carrier has pre~erentially
been used heretofore in the form o~ particles with a
size within the range 10 to 20 mm. Dust, i.e. particles
with a size of less than 6 mm has hereto~ore been screened
o~f from the burden (Ullmann~ Enzyklopadie der technischen
Chemie, 5th volume, 3rd edition, (1954), Urban und Schwarzen-
berg, Munchen-Berlin, pages 30 to 35).
Attempts ha~e also been made ~or the reason ~ust
described to use fine-particulate burden constituents
in electrothermal processes, in hollow electrodes (U.S.
Patent 2,996,360).
The quantity o~ fine particulate material allowable
in these processes is howe~er very limited~ While the
introduction o~ increasin~ quantities o~ solid material
through a hollow electrode initially has beneficial e~ects
upon furnace operation ~reduced electrode consumption per
unit time; electrodes reaching deeply into burden) the
fact remains that the introduction o~ solid material in
quantities increased beyond a certain maximum results in
the ~urnace conditions being radically impaired.
As regards black material and its chemical composition~
it is inter alia necessary for it to be practically ~ree
from volatile constituents. As a result, coke has been
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predominantly used in practice ln closed industrial furnaces.
Needless to ~ay, attemp~s have already been made to
replace the coke by other black material, especially by
anthracite and petroleum coke. During the operation of
closed industrial .~urnaces under commercial conditicns,
these two materials have however been fou~d to entail
considerable di~iculties as a result o~ th~ volatile
hydrocarbons contained therein and as a result of these
two materials30ther properties. The burden has heretofore
long been held in the art to be usable ln such caseY
only in admixture with ju~t small proportlons of anthracite,
petroleum coke or lean coal (up to a maximum o~ about 25 %,
ba ed on black material, the percentages indicated here and
hereina~ter being alway~ ma~s %~, in order to avoid serious
adverse effects upon ~urnace operation. Even thi3 however
is possible only in ~urnaceq which are wor~ing well, and
it is indeed necessary ~or the addition o~ anthracite,
petroleum coke or lean coal to be stopped immediately
upon the ~ir~t occurre~ce o~ irregularities.
~o Anthracite and petroleum coke ~or use in the prsparation
of electrode masses have long been calcined; this, however, i8
calcined mater~al which is not suitable ~or use in an electro-
therml roduction furnace~ not only for it~ electric conducti-
vity which is too high, but also for i~s reduced reactivity
which cause~ the temperature prevailing inside the ~urnace
to be increased. Increased temperatures favor side reactions
- whereby the burden becomes prematurely slagged.
The present invention now unexpectedly provides a
process permitting use to be made o~ considerable
proportions of anthracite and petroleum coke, which can be
6; 4 2 5
employed individually or in admixture with one another,
in a closed electro-thermal furnace with a capaoity of
more than 20 megawatts, whereln the electrodes are
arranged symmetrically w~th respect to each other 30 as
to form the corners of an equilateral triangle.
The in~ention provide~ more specifically for at
least 40 % of the total carbon component in the ~urnace
burden to be used in the form of a carbon carrier consisting
of anthracite, petroleum coke and/or lean coal, the carbon
carrier with an initial co~tent of volatile constituents
o~ more than 5.0 % having been subjected to thermal
pretreatment at increased temperature for as long as
necessary to establish a residual content of volatile
constituents of less than 5.0 %, preferably 1 to 3 %,
and separated into a fraction consisting of particles
with a size of 3 to 10 mm and into a fraction consisting
of particles with a size of 10 to 25 mm; the small particle
fraction being introduced into a central region inside
the ~urnace lying between the electrodes, and the large
particle fraction being introduced into a peripheral region
of the burden surface area inside the furnace which lies
outside the triangle formed and bounded by the electrodes.
It i5 pre~erable for the thermal pretreatment to be
effected at temperatures lower than 1000C, espeoially at
temperatures within the range 600 to 800C, the treatment
periods being naturally the shorter the higher the
treatment temperature and inversely being the longer
the lower -the temperature selected.
It ~s also pre~erable for up to 25 /0 of the total
mass of carbon component in the burden to be used in the
form of coke dust and ~or said coke dust to be introduced
into the furnace through hollow electrodes and simultaneously
with the anthracite or petroleum coke or mixture thereo~,
the coke dust containing up to 50 % o~ anthracite dust,
if desired~
Further preferred ~eatures of the present process
provide ~or the carbon component whlch is used in the
burden to contain the carbon carrier pretreated in
accordance with this 1nvention together with up to 60 %
of coke, or ~or it to contain the carbon carrier pretreated
in accordance with this invention together with up to 60 %
o~ a mixture consi~ting o~ coke, on the one hand, and o~
untreated anthracite, petroleum coke and/or lean coal, on
the.other hand, in a ratio o~
Still further preferred ~eatures provide ~or the
carbon component which is used in the burden to contain
the carbon carrier pretreated in accordance with this
invention together with up to 30 % of untreated anthracite,
petroleum coke and/or lean coal, or for it to consist to
an extent of 100 % of -the carbon carrier pretreated in
accordance with this invention.
It is also good practice in the overall burden to
establish a mas~ ratio of black to white material of
about 1 : 1.5 - 1.6 which gives carbide yielding 280 - 300 l
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~ 2,5
of acetylene per kg, upon reactlon wlth water. Meedle~3
to say, the invention also provides ~or the use of a
burden with a ratio other than just specified.
The following Examples are intended to illustrate
the invention which is naturally not limited thereto:
Example 1:
Anthracite with the following analytical data:
Particle size 6 - 30 mm
Water 6.3 %
Ash 12.4 %
Volatile con~tituents 9.8 %
Electric resistance at 20C107 ohms cm
was heated ~or about 90 minutes to 850C in an indirectly
heated tube ~urnace with the exclusion of air. The resulting
dry a~thracite still contained 1.9 Yo of volatile hydro-
carbons and had an electric resistance of 0.8 x 102 ohms cm.
The material so treated was screened so as to obtain two
fractions consisting of particles with a size of 3 to 10 mm
and 10 to 22 mm, respectively.
The two ~ractions were introduced into a closed type
carbide ~urnace with a maximum capacity of 55 megawatt3.
The ~i~er particle fraction was introduced into the central
region lying between the ~urnace electrodes and the
coarser particle frac-tion was introduced into the outer
(peripheral) furnace region. Anthracite and lime were
used in the ratio of 1 part anthracite to about 1.6 part
llme.
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The carbide ~urnace was equipped with hollow electrodes
through which a mixture of standard coke breeze (particle
size up to 6 mm) and ~ine lime in the ratio o~ 1 : 1.6
was in~ected, the mixture constituting an about 15 %
proportion of the overall burden. The ~urnace worked
reliably.
The ~ollowing result was obtained a~tor operation ~or
8 hours:
Consumption: 351,000 kwh (average about 44 mwh/h)
56 ton~ anthracite
10 tons coke breeze
90 tons lump lime
15 tons fine lime
Production: 110 ton~ carbide yielding 293 1 C2H2 per kg.
Under the conditions de~cribed, it was possibl~ ~or
the furnace to bç operated from one control to the next
over approximately the ame period of time as with the
use of coke, as usual.
Example 2:
The fine particle ~raction with a size of up to 3 mm
obtained on screening the anthracite was added to coke
breeze for introduction through thè hollow electrode.
The entire quantity of fine anthraclte obtained was used.
As a result, the black component introduced through
the hollow electrode consisted of an about 1 : 1 mixture
of coke breeze and anthracite.
The other conditions were as in Example 1.
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Approximately the same re~ult as in Exampl~ 1 was
obtained, within customary lirnits of error.
Example 3:
The procedure was ba.sically the same as de~cribed in
Example 1 save that the degassed anthracite was admixed
with a quantity of untreated anthracite sufficient for ~he
resulting mixture to contain about 30 % of crude anthracite.
The untreated anthracite was added to the uncooled pre-
treated an-thracite to ef~ect evaporation just of the
water present in the untreated anthracite, leaving the
hydrocarbons substantially unaffected.
The consumption o~ materials was as in Example 1,
within customary limits o~ error. The carbide o made
was, however, found to produce only 285 l C2H2 per kg.
In the ~urnace operated under these conditions,
slag was distinctly more liable to be formed at the
~urface area of the burden. As a result, it was necessary
for the working furnace to be more frequently controlled
and corrected. This resulted in frequent production stopp-
age9~ They are, however, not as ~requent as would be
necessary for them to render furnace operation commercially
unacceptable.
Example 4:
Petroleum coke which had a particle size of 6 to 35 mm
and con-tained 9.7 % volatile hydrocarbons~ 6 % water and
less than 1 % ash was placed in the furnace described in
Example 1 and heated therein for about 2 hours to 750C.
4 2 5
The coke sa treated 3-t:Lll contained 2.8 % volatile
constituen~ and had an electrical re~is-tance of 1.6 x
ohms cm. The coke was further proces~ed as described
in Example 1 and used ln the carbide furnace o~ that
Example; coke and lime were, however, employed in a ratio
of 1 : 1.5.
Standard coke breeze was introduced through the
hollow electrode~
After 8 hours, the ~ollowing result was obtained:
Consumption: 438,000 kwh (average 55 mwh/h)
11 tons petroleum coke
20 tons coke breeze
77 tons lump lime
13 tons fine lime
Production: 145 tons carbide yielding 298 l C2H2 per kg.
Furnace operation was normal. It was not necessary
for the furnace to be controlled more frequently than with
use of standard metallurgical coke.
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