Note: Descriptions are shown in the official language in which they were submitted.
~;~3~
FUl~ACE
'~his invention relates to the art of preventing a
refractory furnace lining from wear by applying an elect-
ric field. More particularly, it relates to industrial
furnaces u~ed in metallurgy and glass production.
Major reaso~s for refractory lining wear are u3ually
heat load~ and high-temperature corrosion induced b~ melts
a~d gase~ accompanying the burning of a fuel, as well as
by ~he liquid and gaseous melting products.
Heat loads exerted on the lining are di~tinguished by
non-uniform heat ~luxes and temperature patterns, as well
a~ by ~requent -temperature v~riation3, resul-ting in mecha-
nic~l ~trains in the lining and eventually in ~pallin~
thereof.
Corro~ion affects the structure of the lining working
~urface in contact with the melt and furnace ga~eou~ at-
mosphere to re~ult in deterioration o~ i-ts ~trength and in
turn in a considerable a¢celeration o~ spalllne.
Du~ing furnace operation -the surface of the refractory
material ba~ed on such heat-resi~ta~t metal oxides as
~1203, CaO, MgO, ZrO a~d the like is impregnated with
various substance~, particularly molten metal~ and sla~ in
melting furnaces, molten heat-transfer medium in hea-ting
furnQces, and in mo~t cases with g~seous products. This
gives rise to the formation o~ an area of complex chemical
composition, which may h~ve the proper-tie~ of both semicon-
du¢tors and solid electrolytes. ~he temperature of this
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area in non-uniform at various points; that i~ ~ome
areas are heated more than the others. In tu~n, -thi~
promotes the appearance of a thermoelectromotive ~orce
(thermal em~), which induces an electric current in the
lining to cause an excessive electrochemical corrosion of
the refractory.
~ he magnitude and direction of this electromotive
force depend on t~e chemical compo~ition of the refractory
lining impreg~ated with the ~urnace produc-ts, and on the
temperature difference. If the temperature difference is
ne~ligeable, it can be con~i~ered that that E = ~ ~ T,
wh~re E is the magnitude of the thermal emf between two
pointa, ~ r is the temperature di~ferenoe between the~e
points, and ~ i~ a constant eoefficient -takîng into
account the compo~ition of the refrac-tory material. l~ormal-
ly, the ~urnace operation i~ accomp~nied by a thermal emf
of botweerl 0.5 and 2.0 V.
~ he n~ture and rate of elecSrochemical corrosion vary
a~d depend o~ the conductivit~ of the area throu~h which
the electric current pa~es. As a rule, both conduction by
electrons and ionio co~duotion take place.
A multitude of techniques are employed for fighting
Gorrosion of the furnace refractory lining.
; One such -technique involves immer~io~ in a melt bath
o~ at least one electrode o~ a aurable material, wherea~
the zirconium~o~ide b~sed re~ractoriea to be protected are
brought into contact with metal conductors for a continuous
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em~ produced by an ex-ternal ~ource to ari~e between the~e
conductors and the electrodes immersed in the bath,
whereby an electric current ~low~ from -the electrode to
the refractories to be corrosion-protected. ~he em~ is
adjusted so as to provide an electrolytic current having
a den~ity ~t the surface o~ the refractory on the order of
10 mA/cm2.
~ here~ore, corrosion is inhibited due to ionic
exch~nge c~used by a difference between the chemic~l po-
te:ntials o~ the molten sub~tance and the surface of the
refractory.
Inherent in the above technique is a di~advantage
re~iding in that it i~ applicable exclusively to re~rac-
torie~ based on zirconium o~ide. In addition, it ~ails
to provide for a substantial increase in the durability
of the refractory lining, since i-t ac-t~ to defer only one
rather than all kinds of corrosion. Another di~adva~tage
i~ that the qu~lity o:f glas~ melt tend~ to deteriorate in
p~].ae~ maklng furnace~ due to electrolytic decompo~ition
of the melt under -the action of a current havine a.den~ity
10 mA/cm2 .
; According to another known technique~ corrosion
protection is effected by means of electrodes i~ner~ed in
a melt and current-conducting elements ~ecured in ~n inter-
medi~te glazed coating made on the refractory material,
these current-conducting elements being oonnected to the
oppo3ite pole~ of a direc-t ourrent ~ource; the emf of the
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~L~365(3~
direct curren-t source being adju~ted ~o -that -the current
den~ity at the surface of con-t~ct of the melt with the
re~:ractory material would be les~ than 1 mAi~cm .
This solution of the problem likewise ~ails to ensure
a substantial increase in the service life o~ the lining,
because it slow~ down only electrolytic corrosion oi the
working ~ur~ace o~ the refrac-tory in the location where
it i~ brough-t in contact with the melt.
~ here is further kno~n a furnace conætruction which
to some extent solves the problem of extending the service
life of the refractory lining, which compri~es a bath
lined with a refractory material and containing a qilicate
melt, and current-conducting elementæ arranged inside the
lining to e~it on the working surface thereof below and
above the melt level -to be connec-ted, respectively, -to
positive and negatiYe poles of a direot ourrent source.
hlæ arrangement ¢ompensateæ for the thermal emf
be~ween v~rlou~ portio~s o* the worki~e surface of the
re~ractory linin~.
'rherefore, currents pasæing alon~ the ~urface and
: cauæing corrosion o~ the refraotory lining are reduced.
However, other causes of corroæion remain, while the 3ust
described arrangement is not capable of combatting them
to re~ult in a failure to attain a æufficient e~tension
of the service life of the re~rac-tory lining.
The principle object of the invention i~ to provide
a de~ign of the industrial furnace snd arrangemen-t of
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current-conducting element~ which woulcl be able to ensure
a prolonged service life of the re-fractory lining as well
as to increase the furnace capacity due to reducing repair
works downtime.
The ob3ect is attained by that in a furnace compris-
ing a bath lined with a refractory material and contain-
ing a melt and having current-conducting elements arranged
in the lining to exit on its working surface below and
ahove the level of the melt, these current-conducting ele-
ments being connected to opposi-te pole of a direct current
source, according to the invention, there are provided
addi-tional current-conducting elements arranged in the
linin~ short of e~iting on its working surface and con-
nected to the pole pieces o~ the direct current source o~
opposite polarity relative -to the connection of the our-
rent-conducting elemeIlts of -the correspondln~ working
surface.
Preferably, at least three ourrent-conduc-ting ele-
rnents are disposed below the melt level, -two of these
element~ e~iting on the working surface of -the lining a-t
different hei~ht, whereas the third i~ interposed between
these two short of e~iting on the ~vorkin~ surface of the
lining.
~ or a more ef~ective protection from oorrosion it
is preferable that substan-tially below the melt level the
current-conducting elements exitin~ on the working surface
o~ -the bath wall llning would be arranged at a dis-tance
from the melt level and the bottom of the ba-th equal to
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between 0.1 and 0.2 the linin~ -thicknes~ 7 whercas the
current-conduc-ting element failing to exi-t on -the working
surface of the linin~ would be.spaced at equal distances
from said elements~
The aforedescribed ernbodiment o~ the invention opti-
mizes condi-tions for the protection of refractory lining
from corrosion and extends the furnace lining service
life~
The es~ence of -the invention resides in as follows.
~ urnace o~eration is accompanied by a substan-tial
temperature difference between the working ~urface of the
refractory lining and its inner body to result in a thermo-
electromotive ~orce and, a~ a consequence, elsctric cur-
rent. ~his current -tend~ to cause accelera-tion in electro-
chemical corro~ion in the lining body, which in turn lead~
to structural defects in the thick boundary layers clo~e
to the workin~ ~urface o~ the lining and a ~ubsequent los~
of ~trength -to a ~ubstan-tial depth of the linin~.
Re~earch has ~hown that the provision in the lining
of additional current-conducting elements which do not
exi-t on the working surface thereof a~d which are con~ect-
ed to -the poles of the direct current ~ource of opposite
polarit~ rela-tive to the connection of the current-con-
ducting elements of the corre,sponding workin~ surface make
-the bulk of the lining less prone to corrosiorl.
It has also been established that this i~ ~ccompanied
by a le~s pronounced pene-tratio~ into the refrac-tory o~
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the melt, as well as of the products o~ ~lelting and fuel
combustion to thereby hamper the course of changing the
chemical an~ mineralogical composition of the refractory
and slow down the rate o~ formation of the s-tructural
zones in the liningO Structural defects also appear at a
much slower rate. In view of -the foregoing, the refractory
retain~ sufficien-t stren~th through a longer service life,
spalling o~ the lining is prevented, and ~ining durability
is thu.s improved.
~ he provision below the melt level of a-t least three
current-conducting elements of which two exit on the work-
ing sur~ace of the lining at different heigh-ts, and one
is interposed between the first two short of exiting on
the working ~urface of the lining make~ it possible to
di~tribu-te the electric ~ield produced by an external
source ~lon~ the hoight of the bath wall~ and thereby com-
pletely protect the lining of the bath wall~ from oorro~
~ion throughout its height.
~ he po~itioning of the current-conductin~ elements
exiting on the working sur~ace of the bath wall lining a-t
a distance from the level of melt and bottom of the bath
equal -to between 0~1 and 0,2 the thicknes~ of the lining,
anA the arran~ement of -the curre~t-conducting element
failing to exit on the working ~urface of the lining at an
equal distance from the two firstmentioned elements ènables
to produce such a field pattern,which ensures irl the best
po~ible manner protection from corrosion o~ those parts
of the bath walls which are most prone to corro~ion,
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particularly the parts adjacent the upper and lower melt
boundary where vigorous physical and ohemical processes
take placeO ~niform protection of the bath wall lining at
-the remaining height thereof is al~o ~ssured.
~ he proposed arrangement makes furnace refractory
lining 1.5 to 2 times more dur~ble. Production capacity
of the ~urnace is thus enhanoed due to e~tended operating
oycle, and reduoed do~ntime required for relining. Another
attendin~ advantage is that modification of furnaces in
line with the features of the present ~nvention is in-
e~pensi~e, because no structural remaking of the furnace
associated with high capital costs is required. Also,
repair expenditures are sub~ta-~tially reduced. One more
advantage is operating ~implicity of the proposed design.
~ he invention will be more fully understood from a
more detailed d2scription that follows taken in corljunc-
tion with the accompanying dr~wln~s 7 in which:
~ ig. 1 i~ a oross-sectional view o~ an industrial
gl~ss Inaking furnace provided with additional current-con-
ducting elements, and a diagr~l showin~ connection of
these elements to a current source; and
~ i~. 2 is sub~tantially the same as illustrated in
~ig. 1~ the difference being in that the current-conduot-
in~ elements are located below the melt level so that -two
of these element e~i-t on the working surface of the
refractory lining, while the third is interposed between
the first two.
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With reference to ~igs. 1 and 2, a furnace accord-
ing to the invention comprii~es a bath 1 defined by walls 2
and a hearth 3 of lined with i3 re~ractory material, a
glass melt 4, wiallis 5 of the upper section of the ~urnace,
and a roof 6 also lined wi-th a refractory material. The
refractory linin~ of the roof 6 and walls 5 overlying
the level of the molten glass includei~ current~conduct-
ing elemen-ts 7 exiting on the working surface o~ the
lining, and additional current-conducting elements 8
failing to exi-t on -the working su.rface of the lining.
In the lining Oe- the hearth 3 and wallis 2 of -the
bath 1 below the molten glass level 4 there are provided
current-conducting elements ?a exiting on the working
isurface, and addi-tional current-conducting elementis 8a
withou-t exit on the working surface, A ishown in ~ig. 2,
in the lining of the hearth and w~ s of the.bath 1
below the level o~ the mol-ten glasis there are provided at
least three curxent-conductin~ elemerlt~ two o-f these
elements indicated at 7a exit on the work~n~ iYur~ce o~
the lining, whereas one additional current-conducting
element 8a fails to exit on the worki~g surface of the
lining and is interposed between these elements 7a.
The current-conducti~g elements 7a exiting on the
working surface of the linin~ made on the walls 2 of the
ba-th 1 a.re arranged at a distance fro~ the level o~ the
melt 4 and the bottom 3 of the`ba-th 1 which makes 0.1 to
0.2 the lining -thickness, whereais the current-conductir
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~7~36S~9
elemen-t 8a not exiting on the working sur~ace of the
lining is spaced at equal distance from the elernent~ 7a.
All the current-conducting elements are generally
stainless steel pl~tes between 1.5 and 2.0 ~m in thick-
ness; al-ternatively, these elements may be ~bricated from
other known and available durable materials, such a~
platinum, molybden~n, and the like.
The proposed ~urnace design al~o includes a source 9
of direct current with a po~itive polarity terminal 10 and
a negative polarity termin~1 11. ~he current-conduc-ting
elements 7a and 8 are connected to the terminal 10~ whereas
-the current-conducting elements 7 and 8a are wired to the
terminal 11, wires 12 being u~ed for such a connection.
The fur~ace according to the invention operates ag
f`ollows,
The proce~s of making the gla~s rnelt 4 i~ accomp~nied
by the ~ppearance of a -therrnal emf in the refractory li~-
lng o~ th~ walls 2 and 5, bottom 3, and roo~ 6 of -the
~urnace between the working surEace o~ the lining and its
body, this em~ being induced by virtue of a temperature
dif~erence therebetween and al~o due to difference~ in the
chemical composition thereof caused by i~pre~nation of the
re~rac-tory lining with the melt and the gaseous melt
products in the furnace atmosphere, as well a~ due to the
structural differences between the surface and deeper
layers of the lining. A thermal emf also tends to be
induced between the working surface of the linin~ above
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~23~5~9
the level of the ~elt and below that level, this emf being
caused pxima:rily by a difference in the chemical compo~i-
tion Or the furnace products tending to lmpregnate the
lining sur~ace~ in the~e area~ herewit~l, the ~urface of
the wall~ 5 and roof 6 above -the level of the melt and the
interior lining Gf the wall~ 2 below the melt level will
be charged positively with respect to both the charge of
the interior o~ -the walls 5 ana roo~ 6 above the melt
level and ~he charg~ o~ the ~urface of -the walls 2 below
the mel -t level. The pot en t i al differenc e amoun t ~ to
between 0.7 and 1.0 V.
Subsequent to connecting all the current-conducting
element~ 7, 7a, 8, and 8a to the terminals 10 and 11 o~
the direct current ~ource by mean~ of the connecting wires
11 as shown in ~i~s~ 1 and 2, a voltage of from 3.0 to
4.0 V i~ applie~ -to the current-conducting element~.
An electric ~ield induced thereby in the lining by
the current~conducting element~ i~ op~osed -to -the thermal
emf throughout the lining areas.
.
~hanks to that the current ~ource produce~ a volta~e
, . ,
in exce~s of the magnitude of the thermal em~, a ~ ld
cre~ted by the current-conducting elements is quite suf-
~icient for reliably ~uppres~ing corrosion-inducing cur-
rents de pite of the di~crete arrangement o~ -the current-
-conductint~ elements in the lining and a c~rtain voltage
drop in the connecting wires, whereby damage o~ the re~rac-
tory lining is delayed.
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~36S~)9
In view of the foregoing, the proposed device offers
substantial advantage~ over the prior art, since i-t enables
to extend the service lif'e of the re~ractory lining of the
~urnace to thus make it more economically ef~ici.ent.
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