DE1433677A1 - Reduction furnace with superstructure - Google Patents

Description

Wargön Aktitbolag. .21. Guard Λ <\ (. (, V a r κ ö η / Sweden AB Sveneka ivlaekinverken Kallhäll / Sohwedtn 1.433677 Reduction furnace provided with a superstructure

The invention relates to a superstructure. Reduction furnace for high reaction temperatures, in particular for the production of τοη ferro alloys and calcium carbide Reduction of oxidic materials with coal and / or coca, with running through the ceiling of the superstructure and into the feed protruding electrodes »

dei the reduction of oxide ores with coal for production of pig iron »calcium carbide, ferromanganese, silicon metal, silicon iron and ferro-alloys in general are ao high reaction temperatures required that in the Beschiokung The main carbon contained in it comes off in the form of carbon oxide

In open furnaces is allowed because "carbon monoxide above the Besohikkungafläche the furnace" unexploited burn to carbon dioxide, which lost big> e amounts of heat. Thus shows the details below wnrmebilanz for an open 12000 kVA reduction furnace oei the Herateilung 45 '' silicon iron, that the.-Jfirme- and riner moving halt approximately of the same magnitude as that supplied to "electrically" energy, and that the / '■ ^i: rmewirkungsgrad of the furnace »only oa. 50 % is when the heat content of the furnace gases is not used.

^{16095 BATH} ORIGINAL

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909 816/0096

143367?

To led heat supply #

Electric · Energy 53.6

Energy content dee reducing agent _"r

aehl · electrode consumption 42.5

! »© thermal formation heat ·

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Verb smoked amount of heat

Sb & ® thermal © heat of reaction 43 ₉ 4

Pfeyaikallsdfeev heat content

of the alloy 5 »β

Heat loss © dmrch di® 0 £ @ & wäM® 2 _{; s} 1

through the © Besehiüku & g '. 1 ₉ &

Heat content d®s 0f @ agai @ s. 2.6 EnergieiaYes all furnace gas © ®

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deep combustion of the furnace gases go over the furnace

T © rlor®a »a © nd @ in one tatenaiv® which complicates the operation of the oven

Via the dome furnace

With Btleksioht- on the Ob pending® one has tried danacii to use part® # @ ® cabbage © moxytiahalt der Of © ngas ©, partly the heat © eiitwickluag over the oven by -Terhinderuag .der? 0rtr © Biramg; des Kohleiäoscyda, see below, "eliminate", to dieats .Zw © cfc.® mam umm. has the furnace aslbs "! with "a gas-tight Ofeerbau Tarashea and da @ under the thus formed Gewölfee @ - aaiomelte gas, welühee gewöhnlioh 70-> 90 ^ Kofel © no xji contains _g » - to be used for all fuel and / or output material for other production ⁽ see below) »Since there is no combustion of the carbon oxide under the vault, this is only reduced to the physical heat content of the Of & ngaa® and the

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Exposed thermal radiation τοη the charge. Solohe roofed stoves can of course only be used with Processes are used "the reaction temperature is so low that the temperature under the vault does not endanger the strength of the same" and that no coagulation of the load to be feared needs »as in the production τοη pig iron» ferromanganese and calcium carbide; furthermore, the operation of a hermetically sealed furnace is made considerably more difficult by its unavailability, and great demands must be placed on the quality of the incoming raw materials are provided »because disturbances of the Furnace operation with regard to the explosion and tergif dangers that are always present when working with carbon dioxide. actions are »must be avoided as far as possible«

In the reduction processes »primarily in the production of τοη high-percentage ferrosilicon and silicon metals, where sometimes a high reaction temperature is required "sometimes sintering and other difficulties arise with the charging" is the above-mentioned hermetic covering of the Furnace · practically impossible to realize, which is why one was forced to »look for other ways» to deal with the problems To finish. Attempts have been made to do this with furnace superstructures to solve "which allow a complete or partial combustion of the carbon monoxide under a vault" whereby the furnace has become more or less accessible for the furnace personnel 1st. However, the proposed constructions are such It was the way that the vaults did not show the necessary strength and operational safety, especially in continuous operation, against the extraordinarily high temperatures which the combustion of carbon oxide and sudden dislocations and deflagrations (eruption-like breakthroughs in the boom due to the under this prevailing overpressure) in the furnace loading cause. Add to that the great difficulties that The removal of the breath gases offers, as in all the processes mentioned above, large amounts of dust in the flue gases as a result

9 0 9 8 1 6/0 0 9 R BAD ORIGINAL

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τοη loss of loss, which with increased reaction temperature rise sharplyj occur. At high temperatures; which prevail under the vault, this dust has a great tendency to sinter and adhere to both the vault as well as in the flue gas duct »

The design of the vault is dependent on the fact that both the supply of the charge as an electrical current Museum seen through the electrodes through the vaulted ceiling According to the previously used construction principles one has In general, the aim was to keep the superstructure as low as possible £ U m & Qhsn »so that it has the shape of a lid. Because of this, oh you wanted to tor all the ohas seeing losses in the Electrode ρ as well as driving on an electrode break with heavy and expensive business interruption resulting therefrom * a ^^ Fail to reduce it, even if this is the case achieved profit at the expense of a! © worthy supply and Operation went · '■ _'

The invention basically gives way to τοη ä @ n conventional Design guidelines by putting on the contrary a Uplift of the superstructure advocated what by for the / peculiar Arrangement enables us »Invention

The reduction furnace of the invention is essentially thereby identified; » that the electrode holder * i.e. the the operational flow to the electrodes transferring contact bfliokea, installed under the ceiling of the superstructure sin4, and that their free distance τοη dem normalesi BeeehiokungsniTs & u, mostly near the top edge of the stove body, learn Sin bis Four "$ roughly equal to the sine content to three times that Slectrode diameter beträrl, where Aas τοη the ceiling and built on the sides of the superstructure · furnace vault essentially aisle with a water- or water-vapor-cooled cavity construction is covered, which see τοη the vaulted ceiling extends downwards, so that it also surrounds the electrodes

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433177

With this arrangement, the lsi are more likely to be unsolved problems solved »a fully functional and hostile for continuous operation ·· heat recovery system for induction processes ·· with special · to create high! temperatures, both in terms of the furnace superstructure and the extraction of the flue gases *

The elevation of the furnace vault results in a larger furnace * space than before »i.e. prerequisites for better final combustion of unburned gases (carbon oxide), possibilities for creating ample supply *» » Operating and observation opening «! in the side walls of the superstructure »which also facilitate the removal of fragments in the case of Elektrobruoh» as well as the arrangement of a large Rauohgasauelasses with the consequent profit Collection material and more effective dust separation

J) Ie attachment of the electrode holder under the ceiling of the Superstructure - which is made possible by the aforementioned lifting of the ceiling - instead of the previous attachment above the Ceiling offers the possibility of any holder mentioned to be laid close to the boiling area. As a result, the free electrode length under the holders can be reduced to a minimum are held »which is partly due to its own weight> the burn-off and the thermal stresses resulting from the stresses on the electrode material are reduced Electrode tube easily removable · short fragment · gives »partly the inductive resistance of the furnace and the between the electrode holder and BesohiokungeflÄhe high loss · »that occurs in Frag · kosuaeadea high Current strength "very considerable (BX) will" be able to, to · 1κ Lowers the minimum

Through the internal cooling of the (Jewüib ·· as well as through dl · AuSe * - Cooling of the ülektrodtn are dft ffewSl and the hectares © - the devices against impermissible use «g« »OAtitet«

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BATHROOM OBlGlNAL

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In addition, the cooling surfaces effectively prevent that Dust sintered into the vault from the hot smoke gases is »and the cooling in connection with the furnace dimensioning according to the invention enables such a temperature to be maintained in the vault that a certain agglomeration of the extremely small "dust particles can be preserved" without

Sintering etc. occur? which the operation of the heat Recovery plant and the final cleaning of the Rauchgas® «reohweren».

A great advantage of the arrangement according to the invention is also » that raw materials such as hard coal, "petroleum coke and cabbage" etc. can also be used as reducing agents " where the current value of the fleeting Beatand parts of this Can make fabrics nuts »

In the aforementioned goose roof stoves for carbon dioxide recovery lies bsi the last-mentioned reducing agent the danger of empty and pool formations in front of the gas discharge and make gas cleaning more difficult «

The invention is illustrated below in the accompanying drawings described in more detail where Hg. 1 is a front view of an embodiment of the furnace "according to the invention with partially" Section seigt · Fig. 2 is a plan view of the furnace according to Fig. Fig. 3 is a longitudinal section on a larger scale the tour of the electric speakers in the vaulted ceiling, wing 4, is one Front view »partly in section» of another design & ts Oven® with inspection of its loading »and flg. 5 is a «purely sohematisoh · front view of the R »uoh &« eausl »ss of the furnace connecting exhaust system ·

In the case of R # dukti @ as © £ ®a of the Liohtbogf® «ftderefeat type played on la Hg« 1 and 2, & ·? «Igentliea®. §F enkörpsr with 1 unl * £ # reBstt with 2 rewarded Xin this case® the overb & u 2 siiisttls w d © i> Stell® 3 Se · overbuilding angrtlftMtn »lüoliertn-

4 frelMngaad .g * meets («i · ^derQK ande ^ ee end

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The length of the tie rods can be regulated. The middle part 5 of the ceiling 3%, which is preferably designed as a double-walled sheet metal structure cooled by low pressure, has three symmetrically arranged electrodes 6, which are carried in the usual way and for regulation The electrodes 6 protrude into the charge 7 in the furnace body 1, consisting of the respective oxidic raw material as well as cabbage and / or coke, where the reduced melt is shown at 8.

The furnace part 1 is separated from the lower edge 10 of the superstructure, which is made of insulating material, by a gap 9 and is coaxial with the superstructure 2 on its base 11 rotatably mounted (not shown in more detail), so that the entire furnace body slowly - of the order of a few revolutions or fractions of a revolution per 24 hours - can be turned around by means of a suitable drive The purpose of this arrangement is evident from the following

As can best be seen from FIG. 2, the wall of the furnace body 1 has a circular horizontal section »during the /.and 12 of the superstructure 2 cut a hexagonal horizontal section has, with a sioh over on every second of the six pages the larger part of the same opening 13 is present. Each such opening is by means of - in this case two - slider 14 »15, preferably of low pressure water-cooled double jacket sheet metal construction on the inside Covered fire-resistant material, lockable, this slide at its upper edge on a horizontal support 16 are slidably mounted. Through the openings 13 can load, operate and inspect the furnace · thanks the ample openings can be done in a convenient manner.

PAD LOCAL 909816/009 Π. - ^β -

Due to the limited air supply through the adjustable gap 9 is obtained between the furnace body 1 and the superstructure 2, the burn-up of the reduction material on the surface of the Charge 7 is reduced and also a better and more even preheating of the load is achieved. For this also carries you rotation d @ ® 0 £ ®nk8rperβ 1 in relation to the Stillstahen & en electrodes 6 at what a common »and thus more evenly filling the loading through the off » nungea 13 brings about »and the rest of the operation is © r« ». eases.

First of all, the electrode routing through the middle ceiling section 5 sea superstructures will be described in one. According to . According to the invention, the electrode holder »& · &«, the contact pads 17 », which are responsible for the transfer of current, are laid for each electrode 6 on the underside of the cover 3 of the superstructure 2. The jaws 17 are kept in good contact with the electrode by means of a pressure finger 18 surrounding the jaws. In the case shown, this pressure ring is designed like a double-jacket _{sheet metal structure 9,} which is preferably cooled by low pressure water. or other "liquid serving as a hydraulic fluid can be pressed. Each jaw 17 is supported at its upper edge by a joint 19, the upper end of which is firmly connected to the lower edge of a suspension jacket 20" which in turn is not closer to the upper end manner shown worn iarl · To the upper land $ eggs contact jaw 17 are> u6h eia or several feed lines? NS? the electric current, Eweok-like in the form of copper reds "but here only indicated by a dash-dotted line 21" balanced down the outer periphery of the Druokringea ta see a "ylindriseh shield 22 extends upward through the ceiling 3 of the superstructure, resting against one in its Middle section <- '5 bordered

909 8 16 / QO9G

BATH ORIGINAL

H33I77

Cranes 23 made of ceramic material or other electrical Non-conductive material · In the annular gap formed between the electrode surface and the inside of the shield 22 run freely the named supply lines, suspension elements for contact banks 17 and pressure ring 18, pipes for cooling and possible Supply lines for hydraulic actuation of the pressure ring · The shield 22 »der aus nichtmagnetisch»! », Like austenitisohea Material consists »in order to reduce the Hyettreeieverluett» is equal to the sliders 14 »15» of the Deokenpartit 5 unA ata .Pressure ring 18 two-way like a low-pressure water-cooled Double lead construction carried out “Eohr connections specific for this are indicated at 24” Except as protection for conductors and drilling, the shield 22 is used to prevent τοη burning (in the case of so-called Söderberg electrode) or combustion (in the case of an "ordinary electrode) above the electrode holder» · Furthermore, the Sohila forms a sealing bearing against the electrode the inside of the wreath 23 "Ee is to be noted" that the Electrode with the attached scarf through if necessary their crane "can be raised for inspection" where the roof of the superstructure can serve as a work platform

You part of the bottom 22 under the Seeks is free Play sound surrounded by a coil system 25 formed from diohtiegenien cooling coils, which see above close to a Rohrschlangensyetem 26 connects, which is essentially the The furnace vaulting formed on the inside of the superstructure covers yarn, but with the exception of the Btaohiokungsuffätze 15 and of the Rauohgasaualasse described later ».

Against the intense heat that can unhindered the gap between the outside of the shield 2t in the inside tn * part 4t »Spultnsystess 25 up to the stoke, from το? "Lit" its litttlpartit be protected from excessive Wäratbeanspruohuiista "and one Diohtun & must also abroad for the dust provided stia · In? I" * 3 _f dit in jpriltrts eintn Langssohnitt by doing u stisttn krifci * ofe "m Bereiak ztict within the Sltktrotta »» Invite getignttt take-away

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Achievement of the mentioned protection as well as for the sealing of the electrodes stated »The shield 22 of each electrode6 is surrounded with a relatively large play τοη a first» low-pressure water-cooled ring channel 27 © n ₉ the one with the hanging channel of the neighboring .Blektro & is (in certain parts) common * Außenwamdp & rti® 28 has · sound below is called the channel «jet em το? the heat through the pipe coils 26 of the öewölbe & eck® and clay the sides are arranged in Hingform® blocks 29 made of refractory (ceramic) material protected »On the upper side of each Block®® 29 the crane 23 mentioned above rests over a sealing» low-pressure water-cooled ring channel 30 , whereby an insulating element 31 protruding from the lower hanging channel 27 separates the hanging channels lying therebelow from one another. The bleed constructions of the lower cooling channel · become && their * dem. The side opposite the common center of the electrodes is worn on the> @riphery of the middle part. All cave structures are made of non-magnetic lower material to avoid hysteria. Goal all applies to di @ ® the Hohrschlangen in the coil 25 and in the ceiling and on. the uewglbe apply. The pipe coils are carried clay hangers (not shown) * which are on the opposite sides of the pipe, which are directly protected by heat radiation s he cools t »uni the tone of the smoke gases absorbed» ® »· heat content of the circulating water or the ffftee®3P-I>» Bpi »MisohuBf is on ttslieh® W # i @ · in heat recovery

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BATH ORIGINAL 809816/0 09 6``. ~ 1

U33977

dl · last-mentioned arrangement in connection with the electrical The insulating suspension of the superstructure 2 and with the rotation of the furnace body 1, there is sufficient security against both the current-carrying components in the charge (e.g. the reducing agents, scrap, etc.) and in vital furnace parts as well as against personal injury caused by voltage settings in different parts of the furnace system or in parts connected to it.

In the embodiment shown, the distance a between the normal Beschiokungeneven and the inside of the Ceiling ((Jtwölbe) de superstructure 2 almost twice the electrode diameter, i.e. within the range given in the introduction value given as preferred 1.5 to 5 times the electrode length chinese er β.

In iig. 4- an alternative feeding arrangement is shown Here shafts or channels 32 are through the ceiling 3 * · » Oven superstructure 2, whereby the ropes of the channels or wear sheets protruding down in the vault are surrounded by high pressure water-cooled coils 33

As mentioned earlier, the wearing made possible by the invention large distance between the Beschiokungsflache and vaulted ceiling contributes to the greatest extent to the solution of the flue gas problem in that the opening of the flue gas outlet can be selected to be maximally large. I used to be because of the low The superstructure is dependent on small (low) outlet openings, which in turn has forced the flue gases to flow out at high speeds in order to reduce the build-up of dust in the vault. However, the high (read speeds) cause major disadvantages. This means that valuable · · material lost by the fact that the feed is carried away by the gas stream, and deaf tends to get under in the furnace to accumulate the vault * Especially at the high temperatures,

■ ί · 12 - ■■ ". ■■■■■■, ■ - ■■ ...

■ 143367?

which "occur" in processes of the type in question here, the Stamto has a strong tendency to sinter and agglomerate, which is freely unloved. Furnace and flue gas systems the superstructure, the _; Flue gas duct β and the exhaust gas boiler more or less; quite. 'clog .may. E® is particularly noteworthy that the ready. small accumulations of dust on the convection surfaces can thwart the heat transfer.-gana · *.

- earlier - mentioned: "there is no significant risk of dust getting on the Q-wolves due to the" effective cooling of the inside of the G-Qwolfe with the furnace design according to the invention. ewölbefläelien, which is why one is not bound to the previously used outflow speed of the flue gases. On the contrary, in order to achieve the dust separation described in the following, the gas speed should be largely reduced »This is due to the relatively high altitude according to the invention of the furnace superstructure, which allows an unusually large opening of the raw gas outlet »as indicated in Fig. 2 at 34 » ■ '. "■ - ■ ■. ■ -" ■ .. " ^: ■■■' - ■ - -" ■■ '■' ■ - ■..; ■; ■: ■■ '.. - - - \. - .-, .- "

In Fig. 5, the construction gas arrangement according to the invention is shown schematically. A dust pocket 35 », indicated by dash-dotted lines, also in I ¹ Ig, closes off the Rauehgasauelaß opening 34. 1 and 2 »with a dust take-off 36 at its lowest point. The pocket 35 forms an inclined bottom of a vertical cooling drum 37, which above a transverse channel 38 is attached to the upper part of a known ball-rain-cleaned (the ball-rain cleaning device is indicated at 39) vertical exhaust gas boiler 40 with tubular tubes 41 »42 Sohematically indicated convection surface B. adjoins the lower part of the boiler 40 stands above a duct 43 with the inlet of a fan M in the lower part of a chimney 45 in TerbindUÄg,

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H33S77

Following the top edge of the ^A uelaßöffnung 34 protrudes a were reading or a guide plate 46 in a to the inclined bottom of the bag 35 (the! Drum 37) in the direction substantially parallel. All sides of the spawn 35 "the vertical cooling drum 37 and the transverse channel 33 up to and above the exhaust gas boiler 40 are lined with high-pressure water-cooled bores 47 so that these pipes can belong to the same circulation system as the pipe coils arranged in the furnace vault. In the upper part of the drum 37 there is a flap 49 that can be opened against a chimney 48 and a slide 50 is provided in the transverse channel 38 Even when the system is started, the slide valve 50 is closed and the flap 49 opened in order to discharge the smoke gases directly through the chimney 46.

The described flue gas system works in the following ways » The fan 44 is adjusted to reduce the dust-mixed smoke gases flowing out from the outlet opening 34 of the furnace (Temperature of the order of 1000 °) to bring such a low speed that a large part of the dust is excreted in the dust bag 35. #ie from the with Arrows indicated gas path shows, the inclined guide plate 46 contributes to this deposition to a high degree by adding a downward kinetic energy component to the dust particles as well as a centrifugal force grant in the Current deflection can be issued upwards. It is the purpose of the vertical cooling drum 37, not just gravity itself to allow the dust particles to act as much as possible, but rather also to cool the flue gases so far that there is a risk of the remaining dust sintering together upon entry of the gases in the exhaust gas boiler 40 is very low would find the drum 37 separating dust is under the

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The Brfiniuag is nicht.- are on the gesseigtsiAusführungs sculpt be "" restricts ο but verschieden® modifications within the. Hfifemiias <Slqt It> findiaag d @ Aba3f · particular, various Element® Odei "arrangements by eq, uiralent · ersetist who · = » _{Den e} Beispi@lsw.eiae, instead of being freely suspended, the superstructure * can rest self-supporting on corresponding support structures j the sliders in the sides of the superstructure can be lifted and lifted by means of a lifting device instead of being slidable to the side on supporting beams be lowerable; the furnace superstructure can have other, equilateral * or non-equilateral polygonal cross-sections instead of the horizontal cross-section shown, or

816 / OH 9

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goose cylindrical, etc. 3Perner could instead of τοη den hoohdruok water or steam-cooled pipe coils in Oven vaults and flue gas ducts, other cooled cavity structures can be used in the case where this is practically possible and suitable with regard to the temperature maintenance «

Finally, of course, the furnace with the associated raw gas system can be used for other reduction processes than the expressly stated in the description are used «

Claims t

909 8 1

Claims (1)

^: H33677 μ ■■■■■■■■, '■■; ■ · ■■■. "■■' Patent claims: 1. A reduction furnace with a superstructure for high reaction temperatures, especially for production of ferro alloys and calcium carbide by reducing oxidic raw materials with coal and / or coke, with running through the essentially flat ceiling of the superstructure on the inside and into the charging protruding electrodes, characterized in that the "s the electrode holder, i.e. the operating current to the electrodes transferring Kohtaktbacken (.17) are attached under the ceiling (j5) of the superstructure (2), and that their free distance (a) from the normal loading level, mostly near the upper edge (at 9) of the furnace body (l) is ,, one to four, preferably one and a half to three times the electrode diameter, the Ceiling, (3) and the sides (12) of the superstructure (2) on the Inside are completely covered with a water- or water-vapor-cooled cavity construction (26,25), which are extends so far down from the vault that it also surrounds the electrodes (6), 2. Reduction furnace according to claim 1, characterized in that that the cavity structure is made of high-pressure water-cooled Coiled tubes (26,25) made of non-magnetic material, which is a in the ceiling and in the sides of the vault Form a substantially completely covering mat (26) and a tight coil (25) around the electrodes (6). 3. Reduction furnace according to claim 2, characterized in that that the pipe coils (26,25) are fastened with the help of hangers those on the pipes for direct heat radiation protected sides are welded. - 2 - %. Reduction furnace according to one of the preceding claims, characterized in that the contact jaws (17) of each electrode (6) are surrounded by a pressure ring (18), from the outer periphery of which a cylindrical shield (22) made of non-magnetic material extends downwards through a ring in the ceiling ( 3) of the superstructure enclosed, sealing rim (2/5) made of electrically insulating, for example ceramic material, the feeder (21) to the contact jaws (17), the suspension elements (19) of the jaws and the pressure ring (18), tubes for cooling and any supply lines for cooling and any supply lines for hydraulic actuation of the pressure ring (18) run freely in the annular gap formed between the shield (22) and the outer surface of the electrode (6). 5. Reduction furnace according to claim 4, characterized in that the thermal stresses exposed, for sealing between the central part (5) of the ceiling (3) of the superstructure serving the electrodes, as well as the shield (22) of each electrode (6) and optionally Pressure ring (l8) are designed as low-pressure water-cooled double-jacket sheet metal constructions. 6. Reduction furnace according to one of the preceding claims, characterized characterized in that the furnace superstructure (2) is designed as a freely suspended or cantilevered unit, wherein the furnace body (1) forms a unit which is separated from the lower edge of the superstructure (2) by a gap (9) is mounted for rotation coaxially with the superstructure (2). , 7. Reduction furnace according to claim 6, characterized in that the suspension device (4) of the superstructure (2) is designed in this way is that their position in the height direction is adjustable. ö. Reduction furnace according to claim 6 or J, characterized in that the superstructure (2). is insulated and has an electrically insulating lower edge (lo), and that in the Distribution and collecting pipes of the cooling pipes electrically non-conductive sections are inserted. ~ 9. Reduction furnace according to one of the preceding claims, characterized characterized in that the superstructure (2) has a polygonal, preferably hexagonal cross-section and on a number has loading openings (13) on the side, which extend over the greater part of the relevant pages and can be closed by means of slide (14, 15) for the purpose of actuation in the lateral or vertical direction, the slide ■ preferably as sheet metal structures cooled with low pressure water executed and on the inside with refractory material are lined "- 10. Reduction furnace according to one of the preceding claims, characterized in that the ceiling (3) of the superstructure (2) a number of feed openings with water or steam cooled feed shafts (Fig. 4) has * the preferably from the ceiling (3) of the superstructure with wear plates (22) inside covered pipe spirals (33) protrude •. 11. Reduction furnace according to one of the preceding claims, da-. characterized in that the water-cooled or steam-cooled Cavity constructions (26.25 * 33 or «18.22.5,14.15) in circulation systems for the recovery of part of the with the flue gases outgoing heat content are included. 12 .. reduction furnace according to one of the preceding claims, characterized through a flue gas outlet opening (34) provided in the side wall (12) of the superstructure (2) large dimensions in order to give the gas flow such a low exit velocity to teach that a minimum amount of dust is carried away from the furnace and that the greater Part of the dust contained in the flue gases in a dust pocket attached to the lower edge of the outlet (34) (35) is deposited. H33677 13 · Reduction furnace according to claim 9 and 12, characterized in that that the outlet opening receives substantially all of the relevant side of the wall (12) of the superstructure (2). 14. Reduction furnace according to claim 12 and 13, characterized in that that the dust bag (35) the bottom of a substantially vertical, internally cooled drum (37) forms the top via a likewise cooled transverse channel (38) to the upper part a per se known exhaust gas boiler (4o) which has been cleaned with the flue gases (at 39) and has been cleaned in cocurrent is, in which common convective surfaces (4l, 42) are built, and its lower part with a chimney (45) is in communication (at 43). 15 · Reduction furnace according to claim 14, characterized in that the dust pocket (35) is one of the lower edge of the furnace admission (34) has continuously downward sloping floor, wherein an oblique.,. 'lech (46) from the furnace outlet flowing flue gases down into the pocket (35). 16. Reduction furnace according to claim 14 or 15, characterized in that that the insides of the pocket (35), the vertical drum (37) and the transverse channel (38) are essentially whole are covered with high-pressure water-cooled pipes (47). 17. Reduction furnace according to one of claims 11-13, characterized partly by a flap (49) which is provided in the upper end of the drum (37) and which can be opened against a protective stone (48) is, partly through a flap (slide) (5o) provided in the transverse channel (38). 18. Reduction furnace according to one of claims 14-17, characterized in that that the vertical drum (37) also serves as a combustion chamber for the oil burner door additional firing. 9098 1 6/009