SE200035C1 - - Google Patents

Description

Inventors: S Lindblom, S TjernstrOm, and S Hellman The present invention relates to a superstructure reduction furnace for high reaction temperatures, especially for the production of ferroalloys and calcium carbide by reduction of oxidic materials with carbon and / or coke, with through the roof of the superstructure and in the mission projecting electrodes.

Reduction of oxidic ores with carbon for the production of pig iron, calcium carbide, ferromanganese, silicon metal, silicon and ferro-alloys In general, such high reaction temperatures are required that the carbon present in the charge is mainly emitted in the form of carbon monoxide.

When opening furnaces, the unused carbon monoxide is allowed to burn to carbon dioxide. Over the oven's charging surface, whereby large heaters are wasted. Salunda shows the following heat balance, taken from an open 12000 kVA reduction furnace in the production of% ferrosilicon, that the heat and energy content of the furnace gases is of approximately the same order of magnitude as the supplied electrical energy, and that the furnace's heat efficiency is only about 50%. the heat content of the furnace gases is not utilized.

SUPPLY HEAT QUANTITY Electrical energy Energy content of the reducing agent, including electrode consumption Exothermic heat of formation 100.0 CONSUMPTED HEAT QUANTITY Endothermic heat of reaction43.4 Physical heat content of the alloy 5.6 Heat losses through the furnace cradles2,1 Radiation losses. at 21 h: 16/30; 18 b: 5/52 The physical heat content of the furnace gas 2.6 The energy content of the furnace gas, 44.7 100.0 Through the combustion of the furnace gases Not only large amounts of heat were lost in the furnace, but an intense heat developed, which defends the furnace's dishes and to a large extent oven details Above the oven.

In view of the above, efforts have been made to take advantage of the carbon dioxide content of the furnace gases and to eliminate the heat development over the furnace by preventing the combustion of carbon dioxide. For this purpose, the furnace itself was then provided with a gas-fired superstructure and the gas collected under the vault thus formed was discharged, usually containing 70-90% carbon monoxide, to be used as fuel and / or starting material for other production. Since no combustion of the carbon monoxide takes place under the vault, it is only exposed to the physical heat content of the furnace gases and the heat radiation from the charge. However, such furnaces can of course only be used in processes which occur at such a reaction temperature that the temperature under the vault does not compromise its firmness, and that sintering of the charge does not have to be feared, as in the production of pig iron, ferromanganese and calcium carbide. Furthermore, the bulkhead of a hermetically sealed oven is largely defended by its inaccessibility, and great demands must be placed on the quality of the raw materials, as disturbances in the oven operation must be avoided as far as possible in view of the explosive and poisoning risks which always concern the hand. carbon monoxide.

Vic; the reduction processes, primarily the production of high percentage of ferrosilicon and silicon metal, where high reaction temperature is required, and sintering and other similarities with the mission occur, are thus the above-mentioned hermetic filling of the furnace is not practical. possible, why one. forced to seek other ways to get to grips with the problems ,. Attempts to loosen these have been made on furnace superstructures, which have allowed full or partial combustion of the carbon monoxide under the vault, whereby the furnace has become more or less accessible to the furnace personnel. The proposed constructions have, however, been of such a nature that the arches have not shown the required half-strength and reliability, especially in continuous operation against the extremely high temperatures, such as the combustion of carbon monoxide and instantaneous settling and blowing (ie eruption-like breakthrough of the loading layer due to this). radiating overpressure) in the oven coating give rise to. Harlin come the great responsibilities which the very extraction of the flue gases offer, .because in all the above-mentioned processes..large amounts of dust are obtained in the flue gases through waste losses; which rise sharply with increasing reaction temperature. At the high temperatures, which are below the vault, ..this dust has a great tendency to sintering and adhering to both the vault and the flue gas duct.

The design of the vault depends on the delay, that, as well as the transmission of the charge as the electric current via the electrodes, must pass through the vault roof. One of the design principles applied so far has generally been strived for: Ora the carcass said. lag sorn possible, ie. -denim hay got the character ... ay lock. Harigenom avgag nan. presented to reduce as much as possible the unheard-of losses in the electrodes, as well as the risks of electrode failure with such responses and costly interruptions of operation, even if the profit achieved by harigenoni was made at the expense of flexibility in mission and taxation.

The invention radically deviates from the conventional design guidelines in that, on the contrary, it advocates an elevation of the superstructure, which is made possible by the special arrangement of the invention. The reduction furnace according to the invention can be characterized mainly by the fact that the electrode holders, i.e. the operating current to the contact jaws opposite the electrodes is located under the roof of the superstructure, the free distance from the nominal loading level, usually near the upper edge of the furnace body, is between 1 and 4, preferably between 1.5 and 3.0 times the electrode diameter. and sides formed of the furnace vault are essentially completely thanked with a water- or water-cooled cavity construction, which extends from the vaulted roof to the surroundings of the junction electrodes.

. This arrangement solves in one fell swoop the hitherto unsolved problems of achieving a continuously operational and economical thermal theater extraction system for reduction operation at particularly high temperatures, as far as the furnace oyster building and the emission of flue gases are concerned.

The raising 'of the furnace vault gives a previously larger fireplace room, ie. prerequisites for better final combustion of unburned gases (carbon monoxide), possibilities' to arrange - abundant missions.7., skOitsel-_ and inspection- openings ,. in the side cradles of the superstructure, which also facilitate the removal of fragments in the event of electrode rupture, as well as the provision of a large flue gas outlet with accompanying gain in mission material and more efficient dust separation, as will be described later.

The placement of the electrode halls under the roof of the superstructure - which enables the said raising of the roof - in the place of the previous placement above the roof gives free rein to the relocation of; said holder arbitrarily near the mission surface. Through it can the -free. the length of the electrode under the halls is kept at a minimum, which partly reduces them from the dead weight, the burn and the heat stresses, while the packing of the electrode material () eh in the event of an electrode break gives removable short fragments, and at a minimum reduces the oven's inductive resistance as well as between the electrode holders and the transmitting surface obnisk Minsters, which In the case of the high current controllers in question can be highly ignored (RI2) .- - Gendm the internal cooling of the vault, as well as the reduction of the cooling around the electrodes protects the vault and the electrode arrangements against unauthorized packing. In addition, the cooling surfaces effectively prevent dust from them. the hot flue gases are sintered in the vault, as well as the cooling compound with the furnace dimensioning according to the invention tilting a. such a temperature in the selection, that some agglomeration of the extremely small dust particles can be obtained, without sinks, etc., arising, which defend the protection of the varineater extraction plant and the final purification of the shaving gases.

A great advantage of the arrangement according to the invention is also that as a reducing agent it is also possible to use such materials as coal, petroleum coke and coke, etc., in order to be able to utilize the heat content in the volatile constituents of these materials.

In the case of the previously mentioned fully ignited furnaces I Or carbon dioxide recovery, there is a risk of tar and pitch formations in the latter reduction material, which can defend gas discharge and gas purification.

The invention is described in more detail below with reference to. attached drawings, where Fig. 1 shows a vertical view of an embodiment of the furnace according to the invention with certain parts cut away, Fig. 2 a plan view of the furnace in Fig. 1, Fig. 3 in stone scale a vertical section through the electrode bushing in the vaulted roof Fig. 4 is a vertical view, partly in section, of an alternative embodiment of the furnace with respect to its charge, and Fig. 5 is a highly schematic vertical view of the exhaust system connecting to the flue gas outlet of the furnace.

In the reduction furnace shown in Figs. 1 and 2, which is of the light bag resistance type, the actual furnace body is generally denoted by 1, and the superstructure by 2. In this case, the superstructure 2 is supported free-hanging by means of engaging, insulating drawbars 4 at the superstructure roof 3. , the second spirit of which is anchored to an overhead construction not shown. The drawbars can be adjustable to their length. Extending through the center portion 5 of the roof 3 preferably as a double-jacketed, low-pressure water-cooled plate structure, three symmetrically placed electrodes 6 extend, which are at one time supported and arranged for regulating the layer of electrodes in the furnace. The electrodes 6 shoot down into the charge 7 consisting of the oxidic material and carbon and / or coke in question in the furnace body 1, where the reduced melt is shown at 8.

The oven part. 1 is through a gap 9 separated from the lower edge 10 of the superstructure consisting of insulating material and there rotatably mounted (not shown in more detail) on its base 11, coaxial with the superstructure 2, so that the whole furnace body slowly - of the order of some vary or fractions of vary per day - can be turned around by means of a suitable drive device. The purpose of this arrangement is as follows.

As can be seen from Fig. 2, the cradle of the furnace body 1 has a circular horizontal section, while the cradle 12 of the superstructure 2 has a hexagonal horizontal section, on each of the six sides there is an over most of this extending opening 13. Each such opening is dr. closable by means in this case two. doors 14, 15 are preferably of double-jacketed, low-pressure water-cooled plate construction with the inside coated with refractory material, which at their upper edge are slidably mounted on a horizontal bar beam 16. Through said openings 13, loading, maintenance and inspection of the oven can take place on convenient salt. increased dimensions.

Due to the limited air supply, which is obtained via the adjustable gap 9 between the furnace body 1 and the superstructure 2, burning of the reduction material on the surface of the charge 7 is reduced, and furthermore a better and more even preheating of the charge is obtained. The life of the furnace body 1 relative to the stationary electrodes 6 contributes to this, the silk entails a more scattered and thus more even filling of the charge via the openings 13, as well as the dish is otherwise omitted.

Next, the electrode lining through the central roof portion 5 of the 8-building shall be described in detail. According to the invention, the electrode holder, i.e. the current transfer is provided by the contact jaws 17, for each electrode 6 located on the underside of the roof 3 of the superstructure 2. The jaws 17 are lined in good contact with the electrode by means of one. the jaws, surrounding pressure ring 18, which in the case shown challenges as a double-sheathed plate construction, preferably low pressure water cooled. The contact pressure can be achieved through membranes inserted in the inner cradle of the pressure ring (not shown), which are pressed against the respective contact jaws 17 through the low-pressure water or other liquid serving as hydraulic medium. Each jaw 17 is supported in its upper edge by a long 19, the upper edge of which is firmly joined to the leading edge of a suspension jacket 20, which in turn takes on the upper edge which is supported on no further proof that. To each contact jaw, 17 above, one or more conductors for the electric current are also drawn down, apparently in the form of copper tubes, but have only been indicated by a dotted line 21. From trycli.- ;. the outer periphery of the ring 18 extends a cylindrical shield 22 up through the roof 3 of the superstructure during abutment against a ring 23 of ceramic material or included in its center portion 5. other electrically non-conductive material. In the annular gap formed between the electrode surface and the inside of the shield 22, there are freely formed conductors; suspension means for contact jaws 17 and pressure ring 18 tubes and any leads for hydrant action of the pressure ring. The shield 22, which consists of non-magnetic as well as austenitic reduction of the hysteresis losses, Sr, like the ports 14, 15, the roof portion 5 and the pressure ring 15, is suitably challenged as a double-jacketed, low-pressure water-cooled construction; Halls intended iror connections "are indicated • at 24. In addition to protecting conductors and tubes, the shield 22 serves to prevent. Brawling (at the so-called Soderberg electrode) rasp. Combustion (at the" wring "electrode) above the electrode holder. Furthermore, the shield forms an increasing storage. of the electrode towards the inside of the ring 23. It should be noted that an electrode with an attached shield can, if necessary, be hoisted through its ring for supervision, whereby the roof of the superstructure can serve as a working plan.

With free play, the portion of the shield 22 is surrounded under the arch by a spiral basket 25 formed by tangled cooling pipes, which at the top joins a ripple system 26, which essentially completely thanks the furnace arch formed by the inside of the superstructure, of course with the exception of the mission openings 43 and the latter described flue gas outlet. Against the intense heat, which via the column the outside of the shield 22 and. The inside of the spiral basket can reach the roof without hindrance, especially the center part of which must be cut towards 4 - too large heat packs, as well as sealing outside the ragas dust. Fig. 3, which on a larger scale shows a vertical section through the most critical area within the electrodes, shows suitable measures for providing nanind protection as well as for the electrodes to drain. The shield 22 of each electrode 6 is surrounded by a relatively large clearance of a first, low pressure water cooled annulus 27, which has an outer wall portion 28 common to the annulus of the adjacent electrode. Underhill ', said duct system is protected from heat by vaulted tubes 26 and frail sides by annular blocks 29 of refractory (ceramic. On the upper side of each block 29, the previously mentioned ring 23 rests via a tangent, low-pressure water-cooled ring channel 30, an insulating element 31 projecting from the lower ring channel 27 separating the above-mentioned ring channels from each other. As can be seen from the figure, the inside of the wreath 23 adjoins closely to the mantle surface of the shield 22. The plate constructions of the lower cooling channels are supported (not shown) at their common center point of the electrodes opposite side of the bar beams arranged at the periphery of the center portion 5. All hall constructions are suitably challenged by non-magnetic material to avoid hysteresis losses. Above all, this applies to the rudder loops in the basket 25 and on the roof and sides of the arch. The rudder loops are supported by hangers (not shown), which are welded to the sides of the rudder protected against direct heat radiation. The entire rudder system is high-pressure water or ang-water cooled by forced circulation, and the heat input of the circulating water or water-ang mixture is usually accommodated in heat theater extraction apparatus, which may also be the case with the double-jacketed plate constructions. In both the high-pressure and low-pressure cooling system distribution and collection pipes are electrically Conductive sections inserted. In this context, it should be noted that the latter arrangement in conjunction with the electrically insulating suspension of the superstructure 2 saint of the furnace body 1 provides a reassuring certainty against all card closures between current-carrying components in the mission (such as reducing agents, scrap, etc.) and vital furnace parts such as injuries. by voltage settings in different parts of the furnace system or parts connected to it.

In the embodiment shown, the distance a between the normal loading level and the inside of the roof of the superstructure 2 (the vault) is closer to twice the electrode diameter, ie. However, the values given in the preamble of the description as preferred are 1.5-3 times the electrode diameter.

Fig. 4 shows an alternative mission arrangement. In this case, saw holes or gutters 32 are passed through the roof 3 of the furnace superstructure 2, the parts of the gutters projecting downwards in the vaulting space resp. the wear plates are surrounded by high-pressure water-cooled pipe loops 33.

As previously stated, the large distance between the loading surface and the vault roof made possible by the invention contributes to the greatest extent to the solution of the flue gas problem in that the opening of the flue gas outlet can be chosen to a maximum size. Previously, due to the low superstructure height, it has been referred to its & (low) outlet openings, which in turn has forced high outflow velocities on the natural gases to reduce dust deposition in the vault. However, the high gas velocities entail major disadvantages. Thus, waste of valuable material is obtained by pulling particles in the charge by the gas stream, and dust tends to accumulate in the furnace under the vault. Especially at the high temperatures, which occur in processes of this kind, the dust acquires a strong tendency to sintering and agglomeration, which in ordinary furnace and ragas systems can more or less completely clog superstructures, flue gas ducts and exhaust boilers. In particular, it should be noted that even minor adhesions of dust on the convection surfaces can damage the heat transfer.

As previously mentioned, in the furnace construction according to the invention, due to the efficient cooling of the inside of the arch, there is no significant risk of dust being deposited on the arch surfaces, so that one does not become bound to the previously used high flow rate of the flue gases. On the contrary, in order to achieve the effective dust separation described below, one seeks to reduce the gas velocity to a high degree. This is made possible by the relatively large height d of the furnace superstructure according to the invention, which allows an unusually large opening for the flue gas outlet, which is indicated in Fig. 2 at 34.

Fig. 5 schematically shows the flue gas arrangement according to the invention. Adjoining the flue gas outlet opening 34 is a dust pocket 35 with dotted lines indicated also in Figs. 1 and 2 with a dust outlet 36 next to its lowest point. The pocket 35 forms a sloping bottom for a vertical cooling drum 37, which at the top via a transverse channel 38 connects to the upper part of a per se co-current carbon black (carbon black device is indicated at 39) vertical exhaust boiler 40 with convection surfaces schematically indicated as rudder loops 41, 42. The boiler 40 stands in its lower part via a channel 43 in connection with the inlet to a flat 44 in the lower part of a chimney. 45.

In connection with the upper edge of the outlet opening 31, a nose or guide plate 46 projects in a substantially parallel direction with the threats sloping with the pocket 35 (drum 37). All sides of the pocket 35, the vertical cooling drum 37 and the transverse channel 38 at the front. Over the exhaust boiler 40 are completely filled with high-pressure water-cooled tubes 47, which can not be in the same circulation system as the pipe loops arranged in the furnace vault. At the top of the drum 37 a slat 49 which can be opened towards a chimney 48 is inserted, just as a sliding slat 50 is inserted into the transverse channel 38. During unsteady operation, of course, the slat 49 is kept closed and the slat 50 iippet. When inspecting the exhaust boiler, possibly also at the start of the plant, the damper 50 is closed and the damper 49 is opened to release the shaving gases directly through the chimney 48.

The described flue gas plant operates in the following way. The flat 44 is installed to impart to the exhaust furnace outlet 34 of the Iran furnace, dust-bound ragas (temperature of the order of 1000 °) at such a low speed that a large part of the dust falls out of the dust pocket 35. As can be seen from the arrows indicated by arrows, the inclined guide plate 46 contributes degree to this separation effect by imparting to the dust particles a downward directional energy component as well as a cent of rifugal force addition at the upwardly tightening of the strut. The task of the vertical cooling drum 37 is, in addition to letting the gravity of the most dusty man Ora gall on the dust particles, to cool the shaving gases to such an extent that the risk of sintering of the remaining dust is minimal when the gases enter the exhaust boiler 40. Pa. the settling dust of the drum 37 will, under the influence of gravity, collapse to the point of threat, so that the accumulations accumulate a sufficiently large mass, whereupon the drum is self-cleaning.

After the shaving gases have passed the carbon blacked boiler 40 and thereby left the larger part of its heat content to the coils 41, 42 for further transport to heaters, the gases (temperature of the order of now a few hundred degrees) flow out into the chimney 46, largely freeing dust, which to a great extent facilitates complete dust separation of the exhaust gases in gas purification devices.

The vertical drum 37 can be arranged to serve as a fire chamber for oil burners for additional firing and the like.

From the above it appears that the furnace and the flue gas system adjoining it together form a plant which, as an excellent choice, is lit, in particular the production of high percentage of ferrosilicon and silicon metals by reduction by means of coal and / or coke during continuous operation and with viii recovery of the developed heat. , at the same time as great operational and personal safety is obtained and the dust problem is solved satisfactorily.

The invention is not limited to the embodiments shown, but various modifications can be considered within the scope of the invention. In particular, various details or arrangements shown can be replaced with equivalent ones. As an example, it can be stated that the storage building in the stable is allowed to be free-hanging, free-standing can rest on corresponding support structures; the gates in the sides of the superstructure can instead be slidable laterally on bar beams and can be shark and sank by means of lifts; oven, the superstructure in the stable of the shown hexagonal horizontal section may have another polygonal, equilateral or dissimilar section or be completely cylindrical; etc. Furthermore, instead of the high-pressure water- or ang-water-cooled pipe loops in furnace vaults and flue gas ducts, other cooled hall space constructions could be used, in case this is practically possible and appropriate with regard to the temperature conditions.

Finally, of course, the furnace with associated flue gas plant can be used for other reduction processes than those explicitly described in the description. specified.

Claims (19)

Patent claim: 1. A suction furnace equipped with a superstructure obtains high reaction temperatures, in particular the production of ferroalloys and calcium carbide by reducing oxidative materials with carbon and / or coke, but substantially through the superstructure on the inside. flat roofs patching and in the mission projecting electrodes, can be characterized by the fact that the electrode halls, ie. the operating currents to the electrodes leading to the contact jaws (17), are located under the roof (3) of the superstructure (2), the free distance (a) of which is the nominal loading level, which is usually near the upper edge of the furnace body (1) (at 9), amounts to - between 1 and 4, preferably between 1.5 and 3.0, times the electrode diameter, the roof (3) and sides (12) of the superstructure (2) being substantially completely inside with a water- or water-cooled hall space construction ( 26, 25) which frail the vaulted roof extends neatly to the onagivande of jamval electrodes (6). 2. Reduction furnace according to claim 1, characterized in that the cavity construction consists of high-pressure water-cooled coil loops (26, 25) of non-magnetic material, which in the roof and sides of the arch form a substantially thanking mat (26) and form tat spiral baskets (25) around the electrodes (6). ). 3. A reduction furnace according to claim 2, characterized in that the rudder loops (26, 25) are fixed by means of hangers which are welded to the tube on their sides protected from direct heat radiation. 4. A reduction furnace according to any one of the following patent claims, characterized in that the contact jaws (17) of each electrode (6) are surrounded by one. pressure ring (18), from the outer periphery of which a cylindrical shield (22) of non-magnetic material extends upwards through a recessive 6— -limbs (23) of electrically insulating, for example ceramic material enclosed in the roof (3) of the superstructure (3), the conductors (21 ) to the contact jaws (17), their and the pressure ring (18) suspension means (19), tubes for cooling and any leads for cooling and any leads for hydraulic action of the pressure ring (18) free running & in the Indian shield (22) and the electrode (6 ) mantle surface formed ring gap. 5. Reduction furnace according to claim 4, characterized in that the center portion (5) of the superstructure roof (3), which is exposed to heat between the electrodes, as well as the shell (22) of each electrode (6) and any pressure ring (18) challenge sludge double-jacketed, low-pressure water-cooled plate constructions. 6. A reduction furnace according to any one of the preceding patent claims, characterized in that the furnace superstructure (2) is challenged as a free-hanging or cantilevered unit, the furnace body (1) forming a unit separated from the lower edge of the superstructure (2) by a slot (9) stored for rotation coaxial with the superstructure (2). 7. Reduction furnace according to claim 6, characterized in that the suspension device (4) of the superstructure (2) is designed so that its height is adjustable in height. Reduction furnace according to claim 6 or 7, characterized in that the superstructure (2) is insulatingly suspended and has an electrically insulating lower edge (10), and that electrically non-conductive sections are inserted in the distribution and collecting pipes of the pipe. 9. Reduction furnace according to any one of the foregoing patent claims, characterized in that the '45 superstructure (2) has a polygonal, preferably hexagonal horizontal section, and on a number of sides has loading openings - (13), which extend over most of the sides in question. and are closable with sliding gates (14, 15) for lateral or vertical maneuvering, preferably challenging as low-pressure water-cooled plate constructions and on the inside clad with refractory material. 10. Reduction furnace according to any one of the preceding patent claims, characterized in that the roof (3) of the superstructure (2) has a number of loading openings with water- or water-cooled loading shafts (Fig. 4), preferably from the roof of the roof (3) projecting into with wear plates (32) internally notched rudder coils (33). 11. A reduction furnace according to any one of the preceding claims, characterized in that the water- or finger-water-cooled filament structures (26, 25, 33 and 18, 22, 5, 14, 15, respectively) are not in circulating systems for recovery - of a part a * part, with the flue gases leaving the heat content. 12. Reduction furnace according to any one of the preceding patent claims, characterized by a flue gas outlet opening (34) arranged in the superstructure (2) of the superstructure (2) with sufficiently large dimensions to provide the gas stream with such a low output speed that a minimum of dust is entrained from the furnace and - most of the dust contained in the flue gases is deposited in a dust pocket (35) connecting to the lower edge of the outlet (34). 13. Reduction furnace according to claims 9 and 12, characterized in that the outlet opening (34) occupies substantially the entire side of the superstructure (2) of the superstructure (2). A reduction furnace according to claims 12 and 13, characterized in that the dust pocket (35) forms the bottom of a substantially vertical, internally cooled drum (37), which at the top is connected via an equally cooled cross channel (38) to the upper part of an i and fOr itself kand, co-current carbon black (at 39) exhaust boiler (40), in which gingse convective surfaces (41, 42) were built-in, and whose lower part is connected (at 43) with a chimney (45). 15. A reduction furnace according to claim 14, characterized in that the dust pocket (35) has a continuously sloping bottom from the lower edge of the furnace outlet (34), a sloping guide plate (46) being arranged to direct the flue gases flowing from the furnace outlet into the pocket. ). Reduction furnace according to claim 14 or 15, characterized in that the insides of the pocket (35), the vertical drum (37) and the transverse channel (38) are substantially completely filled with high-pressure water-cooled pipes (47). 17. Reduction furnace according to any one of the patent claims 1113, characterized by, on the one hand, a damper (49) inserted over the drum (37), openable to a chimney (48), and on the other hand a damper (50) inserted in the transverse channel (38). 18. A reduction furnace according to any one of claims 14-17, characterized in that the vertical drum (37) above is arranged to serve as a fire chamber for oil burners for additional firing. Request publications: Patentskrifter! Rein Sverige 151 884; Norway 86 817; Germany 1,055,025, 1,090,696; USA 2 931 7 19.