EP0240527B1 - Method for producing moulded coke by electric heating in a shaft furnace and shaft furnace for producing such coke and electric heating method by means of a fluid conducting granulated bed - Google Patents

Abstract

The method according to the invention comprises the introduction of a first part of the fraction of recycled head gases at the base of the lower portion (23) of the furnace to provide for a primary cooling of the coke, and the introduction of the remainder of the fraction of recycled head gases in the form of a secondary cooling stream circulating in counter-current of the mass of coke issuing from the lower portion (23) of the furnace into a region (34) sealingly connected to the outlet of the lower portion (23); the secondary cooling stream being then tapped (40) from the region (34) and reintroduced at the top of the furnace to dilute the gases produced and maintain the recovery means (15a and 15b) of said gases at a temperature sufficiently high to prevent any condensation; the cold coke is then discharged from the region (34) through a sealed chamber (46). The invention also relates to an electric heating method and device by means of a fluid conducting granulated bed.

Description

The invention relates to a process for the production of molded coke and a shaft furnace for the production of such coke in which the heating and coking heat is supplied by an electrical energy supply and transferred by a recycled gas stream. The invention also relates to a method and an electrical heating device using a fluid-conducting granulated bed.

Processes are known for manufacturing coke molded in a shaft furnace, in which a mass of molded coal balls circulates from top to bottom, against the flow of a recycled gas stream originating from a fraction of the gas produced by the coking and taken from the top of the oven to be reintroduced at the base of the latter.

The coking of the molded balls takes place in a central zone of the furnace by gaseous contribution from the distillation.

It has been proposed to produce this heat supply, initially carried out using burners, by dissipation of electrical energy by the Joule effect, which has the consequence of avoiding the dilution of the coking gases recovered at the top of the furnace by the fumes resulting from combustion, the volume of which is large, in particular when the burners are supplied with air, and thus considerably increases the calorific value of the coking gases recovered at the top of the furnace.

In a first approach, the heat energy was provided by an external electric heating, of the resistance electric oven type, however this technique has a poor yield and efficiency because the coke block is not heated uniformly. In fact, the coke undergoes excessive and too rapid overheating in the walls, which is detrimental to the mechanical strength of the balls (bursting and cracking) and to their metallurgical quality (reactivity).

Various publications, namely the patents FR-A-628 168, US-A-2 127 542, DE-A-409 341 and FR-A-2 529220 have proposed, to solve these problems, to provide heat energy directly in the area concerned, by electrical conduction in the mass of hot balls, by generating electric currents between diametrically opposite electrodes, separated by the mass of balls to be coked.

In patent FR-A-2 529 220, the cell furnace is in the form of a column with a straight section, substantially uniform over the entire interior height of the bed of circulating molded balls, comprising, on the one hand, electrodes arranged in a median zone of the side wall of the furnace, and on the other hand, mobile electrodes, which are introduced by the upper part of the furnace into the bed of circulating balls, and arranged in an adjustable manner at a level of the furnace higher than that of fixed electrodes.

One of the major drawbacks of this type of oven lies in the difficulty of ensuring an appropriate electrical conduction of the bed of ball of molded coal in circulation, in order to regulate in a homogeneous and optimal way the calorific contribution necessary for the coking of the balls. Indeed, the electrical conductivity of the mass of balls is linked, in part, to the quality and to the reproducibility of the individual contacts of the balls between them and therefore to the distribution of the internal pressures of this mass obtained by compaction. However, localized or generalized, excessive compaction of this bed, constitutes an obstacle to the "fluid" flow of the materials and to a correct circulation of the bed, which is not admissible.

Furthermore, the localized current flow, causing local heating by the Joule effect of the mass of balls, considerably reduces the resistivity and causes a concentration of electric currents in an area which is already too hot.

This difficulty is not adequately controlled by the means described above, and the adjustment of the thermal balance of the bed of balls in circulation is not ensured, which is however necessary for controlling the quality of the cooking of the balls, (progressive, regular, homogeneous, precise).

The object of the invention is to remedy these drawbacks by providing a process for the manufacture of coke molded in a vertical tank oven, the structure of which optimizes the distribution of the supply of heat energy suitably distributed over the entire section of the oven, while by ensuring correct circulation of the coke mass and by achieving the optimum conditions for coking the molded coal balls.

It thus relates to a process for the manufacture of coke molded in a vertical tank furnace of the type comprising at its upper part sealed means for introducing a charge of raw molded balls and means for recovering the gases produced; and at its lower part, watertight means for discharging the coke and means for introducing a gaseous stream, in which a recycled gaseous stream is circulated in an upward flow against the current of the descending charge of coal balls molded constituting a descending moving bed; the molded coal balls are subjected to a preheating and devolatilization step in a first zone corresponding to the upper part of the oven; then at a stage of carbonization and coking in a second zone corresponding to the middle part of the furnace, and a stage of cooling the coked balls in a third zone corresponding to the lower part of the furnace, the overhead gases are recovered at the top of the furnace produced by the distillation and coking of coals; and a fraction of these overhead gases is recycled to constitute the recycled gas stream, characterized in that a first part of the fraction of the overhead gases recycled at the base of the third zone is introduced to ensure primary cooling of the coke and the rest of the fraction of the overhead gases recycled in the form of a secondary cooling stream flowing against the current mass of coke coming from the third zone, in a fourth zone tightly connected to the outlet of the third zone, the secondary cooling stream being then withdrawn from the fourth zone and reintroduced at the top of the furnace to dilute the gases produced and maintain the means for recovering these gases at a temperature high enough to prevent any condensation; and the cold coke being evacuated from the fourth zone by a sealed airlock.

• - La phase de cokéfaction terminale est réalisée par dissipation d'énergie électrique par effet Joule, dans le lⁱt de boulets devenus conducteurs, jusqu'à la température finale souhaitée. Les gaz recyclés, réchauffés par échange thermique lors du refroidissement primaire des boulets, sont surchauffés sur les boulets chauffés électriquement; ils transportent et transfèrent successivement cette chaleur aux boulets en cours de carbonisation, distillation et préchauffage dans les zones supérieures du four.
• - Le chauffage électrique est réalisé par conduction électrique dans le lⁱt mobile de boulets moulés cokéfiés d'un courant généré entre au moins deux électrodes diamétralement opposées, placées dans les parois de la cuve au niveau de la seconde zone.
• - Le chauffage électrique est réalisé par induction de courants électriques dans le lit mobile de boulets cokéfiés qui garnissent la partie inférieure de la deuxième zone.

According to other characteristics of the invention:

• - The terminal coking phase is carried out by dissipation of electrical energy by the Joule effect, in the l ⁱ t of balls which have become conductive, up to the desired final temperature. The recycled gases, heated by heat exchange during the primary cooling of the balls, are superheated on the electrically heated balls; they successively transport and transfer this heat to the balls during carbonization, distillation and preheating in the upper zones of the oven.
• - The electric heating is carried out by electrical conduction in the movable l ⁱ t of coked molded balls of a current generated between at least two diametrically opposite electrodes, placed in the walls of the tank at the level of the second zone.
• - The electric heating is carried out by induction of electric currents in the moving bed of coked balls which garnish the lower part of the second zone.

The subject of the invention is also a process for manufacturing metallized molded coke, characterized in that a coke, by a process as defined above, is coked with a charge of molded balls prepared by compacting a paste consisting of a binder, simple or mixed, of a mixture of suitable coals, and fine particles of a material based on the metallic element to be incorporated into the coke, in metallic or oxidized form.

The material based on the metallic element consists of iron oxides, manganese ores and dust resulting from the production of ferro-manganese, chromite concentrates for the production of ferro-chromium, quartz fines and silica powders that must be recycled for the production of ferro-silicon.

The subject of the invention is also a pot furnace for the manufacture of molded coke in the form of a substantially tubular enclosure delimiting a first preheating zone corresponding to the upper part of the enclosure, a second carbonization zone and coking corresponding to the central zone of the enclosure and a third coke cooling zone corresponding to the lower part of the enclosure, the oven comprising at its top sealed means for introducing a charge consisting of raw molded balls and means for recovering the gases produced and at its base sealed means for removing the coke and means for admitting a recycled gas stream, the intake means being connected, outside the oven, to the means for recovery of gases produced by recycling means, and electric heating means arranged in the wall of the second carbonization and coking zone, characterized in that the oven comprises a qu atrieme sealed secondary cooling zone connected upstream to the evacuation means of the third zone and downstream to a sealed evacuation airlock, the fourth zone comprising at its base at least one secondary cooling gas supply line connected the recycling means, and at its apex, at least one return pipe for the secondary cooling gases connected to the upper part of the furnace in the vicinity of the means for recovering the gases produced by the distillation and coking of the coal.

The watertight means for introducing the load consist of a sealed load supply airlock opening at its lower part into the first zone of the furnace by a distribution bell, the supply airlock being itself supplied by a rotating hopper.

The means for evacuating the coke from the third zone comprises a rotating and movable floor in vertical translation opening out, via a sealed airlock, into the fourth secondary cooling zone.

According to a first embodiment of the invention, the electrical heating means are of the conduction type and consist of at least one pair of diametrically opposite electrodes, disposed at the base of the wall of the second zone of the enclosure of the oven, said wall forming, in this zone, a constriction of the internal section of passage of the bed of molded balls delimited by a shoulder against which the fixed electrodes are housed.

In a preferred embodiment of the invention, the electrodes consist of segments, the profile of which in vertical section is L-shaped extending along each side of the shoulder so that one of the branches of L is horizontal.

In the case of a circular section tank, the electrode segments are circular and separated from the others by an intermediate wall of refractory and insulating material in the form of an inclined plane corresponding to the slope of the shoulder delimited by the L-profile. electrodes.

This L-shaped profile is preferably chosen because it causes an embankment accumulation of coked balls and very conductive on the electrode that they protect. This protective slope is constantly renewed; it extends the electrode while protecting it from abrasion from the descending molded coke bed, and it isolates it from the hot zone of cooking and gases from the recycled gas stream, very hot at this level. This results in a reduction in heat losses and better mechanical resistance of the electrodes, especially if they are made of cooled alloy copper.

According to a variant of the embodiment of the conduction heating, the oven comprises an internal enclosure in the shape of a warhead in a refractory material provided with a central electrode cooperating with a peripheral electrode circulating along the internal wall of the enclosure. The two electrodes are supplied by a direct or single-phase current source.

According to a second embodiment of the invention, the electric heating means are of the induction type and consist of an induction coil coaxial with the tank and housed in the refractory lining of the furnace.

In a variant, the oven comprises an internal enclosure in the form of a warhead made of a refractory material, in which is housed a laminated magnetic core.

The correct distribution of the heating energy is further improved by winding around this magnetic core an internal induction coil, coaxial with the external induction coil, and supplied in phase with the latter, by the same current source at medium frequency.

According to yet another variant, the induction heating means consist of a set of pairs of induction coils arranged radially in the refractory wall of the furnace, defining an external inductor generating a rotating field passing horizontally through the tank.

According to a modification of this variant adapted to large diameter ovens, the oven comprises an internal enclosure in the shape of a warhead of refractory material in which is housed an internal inductor consisting of a set of radial coils arranged opposite the coils of the external inductor and determining a set of pairs of coupled coils which cooperate to generate a rotating field between the external inductor and the internal inductor.

According to yet another mixed embodiment, the electrical heating means consist of the combination of at least one pair of electrodes as described above generating conduction heating, and at least one coil generating induction heating .

• La Fig. 1 est une vue schématique en coupe axiale d'un four de cokéfaction circulaire selon la présente invention.
• La Fig. 2A est une vue en coupe horizontale selon le plan 2 - 2 de la Fig. 1 d'une première variante, à deux paires d'électrodes alimentées par une source de courants diphasés (transformateur Scott).
• La Fig. 2B est un schéma de principe de l'alimentation des électrodes de la Fig. 2A.
• La Fig. 3A est une vue en coupe horizontale selon le plan 2 - 2 de la Fig. 1 d'une seconde variante à trois paires d'électrodes alimentées par une source de courants triphasés.
• La Fig. 3B est un schéma de principe de l'alimentation des électrodes de la Fig. 3A.
• La Fig. 4 est une vue en coupe radiale verticale selon la ligne 4 - 4 de la Fig 3A de la paroi du four dans la zone d'une électrode.
• La Fig. 5 est une vue en coupe radiale et verticale selon la ligne 5 - 5 de la Fig. 3A de la paroi du four.
• La Fig. 6 est une vue en perspective d'une batterie à trois unités de fours à coke selon l'invention dans une variante à section droite rectangulaire, avec trois paires d'électrodes opposées alimentées en courant triphasé.
• La Fig. 7 est une vue partielle, en coupe axiale, de la partie inférieure d' une variante du four de la Fig. 1, avec une alimentationen courant monophasé ou continu.
• La Fig. 8 est une vue en coupe horizontale selon le plan 8 - 8 du four de la Fig. 7.
• La Fig. 9 est une vue schématique partielle en coupe axiale verticale d'un second mode de réalisation du four selon rinvention, chauffé par induction simple.
• La Fig. 10 est une vue schématique partielle en coupe axiale verticale d'une seconde variante du four selon la Fig. 9, avec chauffage par induction extérieure et axiale.
• La Fig. 11 est une vue schématique partielle en coupe axiale verticale d'une troisième variante du four selon la Fig. 9 avec chauffage par induction extérieure de champs tournants.
• La Fig. 12 est une vue schématique partielle en coupe axiale verticale d'une quatrième variante du four selon la Fig. 9, avec chauffage par induction extérieure et intérieure de champs tournants.
• La Fig. 13 est une vue schématique en coupe horizontale selon le plan 13 -13 du four selon la Fig. 12 illustrant le principe de branchement des inducteurs.
• La Fig. 14 est une vue schématique partielle d'un mode de réalisation mixte de l'invention, avec un chauffage par conduction monophasé et par induction extérieure.

The invention will be described below in detail using the accompanying drawings which show several embodiments. In these drawings:

• Fig. 1 is a schematic view in axial section of a circular coking oven according to the present invention.
• Fig. 2A is a view in horizontal section along the plane 2 - 2 of FIG. 1 of a first variant, with two pairs of electrodes supplied by a two-phase current source (Scott transformer).
• Fig. 2B is a block diagram of the supply of the electrodes of FIG. 2A.
• Fig. 3A is a view in horizontal section along the plane 2 - 2 of FIG. 1 of a second variant with three pairs of electrodes supplied by a three-phase current source.
• Fig. 3B is a block diagram of the supply of the electrodes of FIG. 3A.
• Fig. 4 is a view in vertical radial section along line 4 - 4 of FIG. 3A of the wall of the furnace in the area of an electrode.
• Fig. 5 is a view in radial and vertical section along the line 5 - 5 in FIG. 3A from the oven wall.
• Fig. 6 is a perspective view of a battery with three coke oven units according to the invention in a variant with rectangular cross section, with three pairs of opposite electrodes supplied with three-phase current.
• Fig. 7 is a partial view, in axial section, of the lower part of a variant of the oven of FIG. 1, with a single-phase or direct current supply.
• Fig. 8 is a view in horizontal section along the plane 8 - 8 of the oven of FIG. 7.
• Fig. 9 is a partial schematic view in vertical axial section of a second embodiment of the oven according to the invention, heated by simple induction.
• Fig. 10 is a partial schematic view in vertical axial section of a second variant of the oven according to FIG. 9, with external and axial induction heating.
• Fig. 11 is a partial schematic view in vertical axial section of a third variant of the oven according to FIG. 9 with external induction heating of rotating fields.
• Fig. 12 is a partial schematic view in vertical axial section of a fourth variant of the oven according to FIG. 9, with external and internal induction heating of rotating fields.
• Fig. 13 is a schematic view in horizontal section along the plane 13 -13 of the oven according to FIG. 12 illustrating the principle of connection of the inductors.
• Fig. 14 is a partial schematic view of a mixed embodiment of the invention, with heating by single-phase conduction and by external induction.

The process of the invention consists in coking, continuously, in an electrically heated tank furnace, by conductor and / or by induction, balls of dried coal agglomerated by binders and molded in press.

The pyrolysis of the balls in the furnace causes the emission of distillation gases from the coals and binders, a large part of which is recycled at the base of the furnace, after brief purification. These recycled gases form an ascending gas stream which cools the balls in the lower part of the furnace and the progressive heating, in counter-current, of the balls which descend the upper part of the furnace.

The balls are successively preheated and dried, then smoked. The carbonization then ensures the mechanical consolidation of the balls.

The progressive heating of the balls completely eliminates the volatile matter around 850 ° C and the balls then become electrically conductive. This conductivity is used to pass electric currents through the ball bed which cause the balls to be heated by the Joule effect in their mass and at the points of contact between them. This electric heating completes the cooking and coking of the balls at the desired temperature.

The ball of balls then behaves like a heating grid which overheats against the current the ascending gas flow coming from the lower part of the oven in which the coked balls are cooled.

This overheating of the gas also has the effect of cracking the heavy hydrocarbons still contained in the gas. The ascending gas stream then essentially consists of hydrogen (and methane). By its particular thermal and electrical properties, it constitutes an excellent vector of heat exchange between the gases and the balls, which avoids the formation of arcs and discharges between the balls.

The raw molded balls are prepared by first making a paste by kneading with a mixed binder (pitch, tar, asphalt ...) of coals previously mixed, dried, crushed and preheated. The preheated dough is then compacted into balls in a tangential cylindrical hoop press.

The shaft furnace shown in FIG. 1 comprises a metal casing or shield 1 provided on its internal face with a refractory lining 2 delimiting an enclosure 3 substantially tubular, and slightly frustoconical in its upper part, in which is loaded a mass of molded balls constituting the moving bed 4. In the variant shown in FIG. 1, the enclosure 3 is of circular section, but may also have a rectangular section as illustrated in FIG. 6.

The shaft furnace is loaded at its top by sealed means for introducing the raw molded balls, which comprise a rotating hopper 5 supplied with balls by a belt conveyor 6 controlled by a charge level detector 7 placed in the hopper. The hopper 5 has at its lower part a rotating bell 8 whose opening, under the action of a jack 9, frees the introduction of the balls into a sealed lock airlock 10 comprising pipes 11 a, 11 b of purge with neutral gas. The sealed airlock 10 is closed at its lower part opening into the oven, by a distribution bell 12, the opening of which is controlled by a jack 13 according to the indications of a charge level detector 14 placed at the head of the tank. .

The bells 12 and 8 are opened in sequence according to the indications of the sensor 14.

The furnace is also provided at its top with means for recovering the gases produced, which consist of two pipes 15a, 15b, of large diameter, opening into the enclosure of the furnace on either side of the rotating distribution bell 12.

The coke oven gas recovered by the lines 15a, 15b is sent to a primary purification installation shown diagrammatically at 16 to undergo a cooling, washing, drainage and summary condensation treatment of the water and the naphthalene. The gas thus treated is recycled for a fraction of 60 to 80% to the oven by a recycling line 17 and sent for the remaining fraction by a line 18 to a storage gasometer not shown via a conventional secondary purification installation shown schematically in 19.

The oven enclosure 3 has three separate functional areas. The upper part of the enclosure corresponds to a first cooking zone 20 where the balls are progressively preheated, smoked by distillation of the coals and binders and undergo a first phase of carbonization, by the current of ascending hot gases flowing in countercurrent.

The middle part corresponds to a second zone 21 at the end of carbonization and coking at the base of which the electrical heating means 22 are installed, housed in the internal wall of the refractory lining 2.

A third zone 23 for primary cooling of the coke formed occupies the lower part of the enclosure and comprises at its base means for admitting a recycled gaseous stream coming from the primary purification installation 16. These means comprise a set of pipes 24 for admission of the primary recycled current coming from a supply circular 25, itself connected to the recycling pipe 17 by a pipe 26 on which is mounted a valve 27 for adjusting the flow rate controlled as a function of the indications supplied by temperature sensors 28 located at the head of the oven. The circulation of the recycled gas in the pipe 17 is ensured by a fan 29 and the admission flow rate of a first part of the recycled gases, corresponding to the primary current, sent in the pipe 26 is adjusted to maintain the temperature detected by the sensors 28 at a predetermined set point, to avoid condensation of gou drons on the balls in the oven and on the internal walls of the oven.

The oven comprises at its base means for evacuating the coke from the third zone 23 which comprise a rotary hearth 30 driven in rotation by a geared motor group 31 and movable in vertical translation by means of a cylinder for adjusting height 32.

The rotary hearth 30 puts the third zone 23 of the oven in communication with an airlock 33 opening itself into a fourth zone 34 for secondary cooling of the coke.

The fourth secondary cooling zone 34 has at its base inlet pipes 35 for a secondary cooling current corresponding to the remaining part of the recycled gas stream. These pipes 35 come from a circular 36 connected by a pipe 37, via a flow control valve 38, to the recycling pipe 17. The valve 38 is controlled according to the indications provided by a temperature sensor 39 measuring the average temperature of the coke present in the fourth zone 34 for secondary cooling of the coke. The flow rate of the remaining part of the recycled gases introduced in the form of a secondary cooling stream is adjusted to maintain the temperature of the coke detected by the sensor 39 at a predetermined set point, lower than the maximum normal handling temperature of the coke. .

This fourth secondary cooling zone 34 has, at its upper part, conduits 40 opening into a circular 41 collecting the secondary cooling current, itself connected by a conduit 42, on which a fan 43 is mounted, to a return circular 44 of the secondary cooling current surrounding the upper part of the furnace where the recovery of the gases produced and opening into it takes place via return pipes 45.

The fourth cooling zone 34 is connected, downstream, to a sealed lock airlock 46 provided with purge lines 47, 48 and itself connected to an evacuation hopper 49 releasing the cold coke on a strip dosing extractor 50.

The sequential and automatic opening of the valves 51, 52 and 53 for communication between the airlock 33, the fourth zone 34 and the sealed lock airlock 46, is controlled respectively by jacks 54, 55 and 56 according to the indications provided by a charge level detector 57 located at the head of the fourth zone.

The structure of the oven as previously described, by its device for recycling gases divided into a primary stream and a secondary stream, on the one hand the optimization of the thermal profile of the oven in the carbonization zone by adjusting the primary stream , and on the other hand to avoid an accumulation of condensable tars in the top of the tank thanks to the maintenance of the temperature at the top of the oven, at least 150 ° C, and to the entrainment of these tars by dilution in the secondary current extracted from the fourth cooling zone.

The balls leaving the first zone reach a temperature of about 850 ° C, from which the electrical conductivity becomes appreciable and increases considerably to cap around 1100 C.

It is in the lower part of the second zone where temperatures above 900 ° C prevail that electric currents are brought or induced which overheat the balls until the final coking temperature, adjusted from 950 to 1250 ° C depending on the reactivity of the coke that it is desired to produce (1100 ° C. for a steel coke).

The coked balls descend into the lower part of the oven corresponding to the third primary cooling zone 23, at the base of which is injected the stream of recycled cold gas which is used as a heat transfer vector in the various zones of the oven.

After cooling, the coke balls continuously extracted from the third zone by means of a rotating hearth are removed in two stages. In a fourth secondary coke cooling zone, the balls are completely cooled by a secondary stream of recycled gas, which is then returned to the top of the furnace; then, they are discharged by the final lock airlock, purged with neutral gas, which eliminates any risk of explosion. The molded coke is extracted cold and then screened before shipment.

Compared to the coke produced in a battery of conventional ovens, the manufacture of electric molded coke combines the advantages of gas coke with those of the electric process.

• - Diversification des approvisionnements en charbons et diminution du prix de revient de la pâte à coke. Le procédé permet l'utilisation massive d'anthracites,. de charbons maigres, d'inertes, de poussier de coke, de coke de pétrole et la substitution de charbons fusibles fondants par des liants, tels que brais, goudrons et résidus asphaltiques.
• - La décentralisation de la production du coke. Le procédé permet de produite du coke moulé avec des unités plus petites, adaptées aux besoins en quantité et qualité (formes, dimensions, température de cuisson et réactivité du coke).
• - La diminution des coûts d'investissements de plus de 20 %, pour une même production.
• - Une efficacité. thermique bien supérieure puisque les gaz de tête sortent à environ 150°C et les boulets sont extraits froids du four à cuve alors que dans une batterie classique, les gaz sortent à 500°C, le coke est défourné à plus de 1000°C, et les fumées sont à plus de 400°C à la cheminée.

First of all, compared to conventional coke, the manufacture of molded coke has the following advantages:

• - Diversification of coal supplies and reduction of the cost price of coke paste. The process allows the massive use of anthracites. lean coals, inert coals, coke dust, petroleum coke and the substitution of melting fuses with binders, such as pitches, tars and asphalt residues.
• - The decentralization of coke production. The process makes it possible to produce molded coke with smaller units, adapted to the needs in quantity and quality (shapes, dimensions, cooking temperature and reactivity of the coke).
• - Reducing investment costs by more than 20%, for the same production.
• - Efficiency. much higher thermal since the overhead gases come out at around 150 ° C and the balls are extracted cold from the shaft furnace while in a battery classic, the gases leave at 500 ° C, the coke is discharged at more than 1000 ° C, and the fumes are at more than 400 ° C in the chimney.

A better coke yield, because the dry cooling of the balls, in neutral gas, does not oxidize the carbon of the coke as does the steam of conventional wet quenching.

Furthermore, compared to molded coke baked in a gas flame, electric molded coke has the following advantages:

The production of a rich distillation gas, without heavy hydrocarbons, because the gas is not diluted in the combustion fumes, and recycling causes the craking of hydrocarbons. This gas can be used as furnace fuel, or to extract the hydrogen it contains.

Excellent coke yield due to the absence of any combustion and / or surface oxidation of the balls in the oven.

Control of the physical and chemical quality of coke.

The combination of electric heating and gaseous counter-current for recycling allows progressive coking with precise control of the temperature of the different smoke and pre-cooking zones, carbonization and electric coking, ball cooling.

The homogeneity of the cooking temperature ensures the regularity of the coke quality.

The cooking temperature control makes it possible to control the reactivity of the coke produced: reactive coke for electrometallurgy (cooked at low temperature), foundry coke with very low reactivity (cooked at high temperature: 1300 ° C), blast coke with reactivity adjusted.

The choice of coke size. The contribution of electrical energy to the coking front in each ball allows internal progressive cooking in the zone at high temperature. It is possible to produce larger, homogeneous cokes which are better suited to the blast furnace or cupola, since their mechanical resistance is clearly better than that of gas-fired balls.

The low inertia of the oven.

• - L'absence de pollution et des conditions de travail améliorées. L'extraction des boulets s'effectue à sec. Le four est étanche à l'enfournement et au défournement. La pollution de l'atmosphère est donc limitée et les conditions de travail sont, par conséquent, considérablement meilleures.
• - La faisabilité des petites et moyennes unités.

The rapid electric control of the heating allows adaptation to changes in pace, corrections to malfunctions (cooking) and facilitates stops and starts.

• - The absence of pollution and improved working conditions. The balls are extracted dry. The oven is sealed against loading and unloading. Air pollution is therefore limited and working conditions are therefore considerably better.
• - The feasibility of small and medium units.

Small units producing the desired quantity and quality of coke on site can be profitable because they can be automated and are not heavily penalized by a higher investment.

The heating means 22 arranged in the lower part of the second zone 21 correspond to two embodiments which will be described below.

According to a first embodiment corresponding to an electric heating of the conduction type, the internal wall of the refractory lining 2 delimiting the enclosure 3, forms a narrowing of the internal passage section of the bed of molded balls at the bottom of the second zone 21. This narrowing is delimited by a shoulder 58 formed along the wall of the enclosure 3.

As is more particularly visible in FIG. 4, electrodes 59 having an L-shaped vertical sectional profile extend along each side of the shoulder 58 so that one of the branches of the L is horizontal. The electrode 59 is made of an electrically conductive material, for example copper and fixed by a tie rod 60 which passes through it, as well as the refractory lining 2, outside the shield 1 by conventional means such as nut and against nut. The tie rod 60 is electrically isolated from the shield 1 by the interposition of an electrical insulating material in the form of discs 61. The end of the tie rod 60 outside the shield forms a terminal 62 on which is fixed an electric power cable 63 of the electrode connected to the current source 64, shown in FIG. 1.

The area of the refractory lining 2 immediately adjacent to the electrode 59 is cooled by a tube 65 for internal circulation of cooling fluid arranged in a serpentine fashion along the two faces of the electrode 59 facing the refractory lining. The electrode can also be cooled directly by internal circulation of the cooling fluid. In the case of a circular section tank shown in Figs. 2A and 3A, the electrodes 59 are in the form of diametrically opposite circular segments and separated from each other by an intermediate wall 66 of separation more clearly visible in FIG. 5. This wall 66 is in the form of an inclined plane at an inclination corresponding to the slope of the shoulder 58 against which the electrodes 59 are housed.

According to a first variant of the first embodiment using a supply at the frequency of the network, a pair of electrodes 59 are arranged around the tank per phase. The electrodes of the same phase are diametrically opposite in the tank, as shown in Figs. 2A and 3A, so as to ensure the passage of current to the center of the furnace. Their supply voltage is adjustable (phase by phase) by acting on the secondary of the supply transformer.

Depending on the size of the oven, there is room and need to have, on the periphery of the oven, two or three pairs of electrodes.

For ovens with a small diameter, for example less than, or equal to 2 m, a two-phase supply is produced, as illustrated in FIGS. 2A and 2B, using a SCOTT transformer, according to the connection diagram in Fig. 2A, which transforms a three-phase primary supply into a two-phase secondary (phases marked 1 and 1b on the one hand and 2 and 2b on the other hand) of adjustable voltage.

In the case of ovens of larger diameter, for example 3 to 4 m, illustrated in Figs. 3A and 3B, the three pairs of electrodes marked 1, 1b are supplied; 2, 2b; 3, 3b; according to the three-phase diagram in FIG. 3B.

The electrodes 59 made up of circular segments the cross section of which is L-shaped rest inside the furnace on a cooled refractory edge 67 (FIG. 4). Is formed on each of these electrodes, a ball of repose strongly graph ⁱ silly things (by local surcokéfaction driven by the long residence time at high temperature ball) and highly conductive, which protect the electrodes 59 and divided densities current in the ascending load.

Each electrode is separated from its neighbor by the insulating refractory, insulating, abrasion-resistant wall 66 (for example made of silicon carbide bricks, linked to silicon nitride) whose conicity ensures a slight progressive compression of the charge at right copper electrodes in order to improve and homogenize the electrical conductivity of the ball bed during coking.

On the contrary, under the compressed coking zone, at the entrance to the primary cooling zone 23, the diameter of the furnace rapidly expands so as to loosen the l ⁱ t of balls, to increase the electrical resistances of contact between the cannonballs and avoid stray currents in the cooling zone where they would heat already coked cannonballs in pure loss.

The developed width of the circular segments of the electrodes 59 is chosen to be approximately equal to the width of the refractory intermediate walls 66 so as to avoid preferential passages between phases or even short circuits from one phase to another on the periphery of the furnace.

The present invention has been described above with reference to an oven whose tank has a circular section. In Fig. 6 is shown a variant in which the section of the tank is rectangular.

The structure of this oven is substantially similar to that described with reference to FIG. 1 with regard to the means for introducing the charge of raw molded balls and recovery of coke, as well as with regard to the recycling of coke oven gas recovered by two collecting pipes 70 and 71 located at the top of the furnace returned to the base of the primary cooling zone by two pipes 72 and 73. In this case also the cooling of the coke takes place in two stages between which the fractions of recycled gas are divided, as previously indicated.

An essential difference resides in the linear shape of the electrodes 74 for conduction of the electric current arranged on opposite sides of the rectangular section which rest on copings 75. These electrodes also have an L-shaped profile, on which a slope accumulates. highly graphitized balls.

For an industrially interesting application in three-phase power, the ovens are grouped by three units as shown in FIG. 6. Each phase of the current supplies a pair of copper electrodes from a transformer 76. The electrodes of the same phase are arranged opposite one another along each of the large faces of the furnace and are separated from the pair of adjacent electrodes by a refractory insulating wall 77.

According to a variant of the first embodiment of the invention illustrated in FIGS. 7 and 8, the circular oven has an inner enclosure 80 in the form of a warhead made of a refractory material, while the structure of the enclosure 3 of the oven remains identical in all its peripheral parts. This enclosure 80 carries a central electrode 81, frustoconical, which ensures the return of the currents passing through the solid mass of hot balls during coking and coming from a circular peripheral electrode 82 of L-shaped section current along the interior perimeter of the tank above the edge 67.

This provision aims to avoid parasitic currents between the electrodes supplied by different phases, and to ensure the passage of current in the center of the furnace. Power is supplied between the peripheral electrode 82 connected as an anode and the central electrode 81 forming the cathode, by a direct current source, for example a rectifier 83, or a single-phase current source for a small capacity oven.

The ogival enclosure 80 is mounted on a rod 84 passing through its center a column 85 ensuring the support and the mobility of the annular rotary hearth 86.

To adjust the height of the electric coking zone, the ogival enclosure 80 is movable vertically under the action of a jack 87 placed under the rod 84. At its upper part the rod 84 is surmounted by an insulator 88 which prevents the passage of parasitic currents back along the rod 84.

The central electrode 81 in the form of a truncated cone is made of an abrasion-resistant material such as densified silicon carbide sufficiently electrically conductive to limit the localized heating of the walls of the cathode 81. The cathode 81 rests on a sleeve 89 made of a refractory insulating material. The return currents through the cathode 81 flow to the base of the furnace through a cooled, insulated conductor 90 housed in the hollow axis of the rod 84.

The column 85 is slidably mounted, for example by a system of grooves not shown, in a conical toothed crown 91 ensuring the rotational drive of the column thanks to a conical pinion 92 with which it engages. the pinion 92 being mounted at the end of the output shaft of a geared motor group 93. The vertical sliding of the column is ensured by a jack 94. The coke extraction rate, homogeneous over the entire periphery is adjusted by adjusting the speed of rotation of the metering bed and the height thereof.

The cathode 81 is cooled by circulation from a line 95 of a stream of refrigerated gas which escapes through the annular clearance formed between the ogival enclosure and the column 85 at the place where the enclosure 80 comes to style the latter.

According to a second embodiment, illustrated in detail in FIGS. 9 to 13, the electric heating is carried out by induction.

As shown in Fig. 9, the heating means arranged at the base of the coking zone 21 comprise an induction coil 100 coaxial with the enclosure 3 and housed in the refractory wall 2 of the furnace. Vertically laminated mild steel cores 101 are arranged radially around the coil 100 and channel the field return lines. The coil 100 is supplied by a generator 102 at medium frequency, between approximately 50 and 1000 Hertz.

The electrical conductor which constitutes the coil 100 is a hollow tube, in which circulates a cooling fluid introduced at 103 and withdrawn at 104, which is itself connected by conductors 105 and 106 to the generator 102.

The laminated cores 101 constitute a magnetic yoke cooled by circulation of cooling fluid introduced by the pipe 107 and withdrawn by the pipe 108.

The expression for the power density (electrical power dissipated per unit of coke volume), established for the variant in FIG. 9 shows that the radius of the tank and the conductivity of the balls have a determining influence on the powers developed locally in the bed.

In particular, since the induction fields are weak in the center of the oven, this first variant has the disadvantage of unevenly heating the balls passing through the wall and those passing through the center of the oven, which risk being insufficiently heated.

In the case of large capacity ovens (diameter of 3 meters and more) for which the ascending gaseous current will have a limited efficiency in reducing the transverse heating heterogeneities, the ball beds arranged outside will have a temperature and an electrical conductivity significantly higher than the center balls, which will lead to different end-of-coking temperatures and an uneven quality of the coke balls, at the center and at the wall.

This simple solution of FIG. 9 is therefore limited to small coking units, the extraction device of which will promote peripheral flow of the balls (rotary hearth for example).

According to a variant of the second embodiment illustrated in FIG. 10, the oven comprises means of electric induction heating which comprise, in addition to an induction coil 110 coaxial with the enclosure 3 and housed in the refractory wall 2 of the oven, an interior enclosure 111 in the form of an ogive made of a refractory material which includes means for strengthening the magnetic field near the axis of the furnace. The refractory material constituting the enclosure 111 may for example be made of silicon carbide bonded to silicon nitride, the electrical insulation properties of which are sufficient for the intended application and the resistance to abrasion and to thermal shock is excellent. .

These means may consist of a set of vertically laminated mild steel cores 112, arranged radially, housed in the warhead enclosure 111.

These means can be supplemented, as illustrated in FIG. 10, by an internal induction coil 113 coaxial with the coil 110, supplied in phase with the latter and housed in the warhead enclosure 111. The mild steel cores laminated vertically 112 and arranged radially are inserted into the coil 113 coaxial with the latter.

As in the case of FIG. 10, the induction coil 110 consists of a hollow electrical conductor with helical winding in which circulates a cooling fluid supplied at 114 and withdrawn at 115. The internal induction coil 113 is produced in a similar manner and cooled by circulation of a cooling fluid between the points of arrival 116 and of exit 117, this cooling circuit emerging outside the oven by circulation in a column 118, of smaller diameter than the enclosure in the shape of a warhead 111 and supporting the latter. Column 118 crosses the rotary hearth of the furnace as illustrated in more detail for the first embodiment of the induction heater shown in FIG. 7.

All of the laminated cores 113 constitute an internal induction cylinder head also cooled by circulation of a cooling fluid supplied by a central pipe 119 arranged along the axis of the column and opening at the top of the cores, the return of the fluid being provided by a line coaxial and external to line 119.

120 vertically laminated cores and arranged radially outside the coil 110 forming an external induction yoke cooled by a circulation of a cooling fluid supplied by a line 121 and withdrawn by a line 122.

A medium frequency generator 123 supplies the coils 110 and 113 in series via a conductor 124 connected to the input of the coil 110, then a conductor 125 connecting the output of the coil 110 to the input of the coil 113 and a conductor 126 ensuring the return of the output of the coil 113 to the generator 123.

The coils 110 and 113 placed in the furnace opposite one another make it possible to associate their respective field of induction to simultaneously and homogeneously heat the balls passing along the peripheral walls of the enclosure 3, and of the walls of the inner enclosure 111.

According to yet another variant of the second embodiment, the induction heating means consist of a set of pairs of induction coils arranged radially in the refractory wall of the furnace, thus defining an external inductor generating a rotating field passing horizontally across the tank.

In Fig. 11 two coils 130, 131 having their axes merged and arranged radially and diametrically opposite are wound on horizontally laminated magnetic steel cores forming inductors 132, 133. The coils 130 and 131 are supplied on the same phase of a polyphase current identified 1, so that the magnetic field passes radially through the tank, that is to say that the opposite end faces of the coils 130 and 131 are of opposite polarities.

In the normal case of a three-phase current, there are three pairs of diametrically opposite coils.

Each pair of coils 130, 131 which represents a phase is regularly shifted in the inductor so that the resulting field rotates at the frequency of the supply currents and generates eddy currents in the mass of the coked balls.

The inductors 132, 133 are cooled by circulation of a cooling fluid supplied by a circuit entering through the line 135 and leaving through the line 136.

A generator 137, three-phase medium frequency, supplies the coils as shown in FIG. 11 for two coils in an axial cutting plane.

The horizontal section shows the feeding which takes place as shown in Fig. 13 by considering only the inductors outside the oven enclosure.

According to yet another variant arising from that illustrated above, and represented in FIGS. 12 and 13, the oven further comprises an internal enclosure 140 in the form of a warhead, made of a refractory material, in which is housed an internal inductor constituted by a set of radial coils arranged opposite the coils of the external inductor and determining a set of pairs of coupled coils which cooperate to generate a radially rotating field between the external inductor and the internal inductor.

A coil 130 of the external inductor is associated with a coil 130a supplied in such a way that the opposite end faces of the coils are of opposite polarities. Likewise, the coil 131 is associated with a coil 131 a.

The coils 130a and 131a are wound on a horizontally laminated magnetic steel inductor traversed by a cooling circuit consisting of a central supply tube 141 and peripheral return tubes 142 (Fig. 13).

In a mixed variant illustrated in FIG. 14, the electric heating means of the oven comprise, in the coking zone, conduction heating means with L-shaped peripheral electrode 150 and central electrode 151 as described with reference to FIG. 7, supplied from a rectifier 152 and induction heating means comprising an axial coil 153, as described with reference to FIG. 9, supplied from a medium frequency current source 154, and optionally a set of vertically laminated mild steel cores 156, arranged radially, housed in the support column 157 of the electrode 151, as described with reference in Figure 10.

The axial coil 153 is then housed in the coping 155 projecting from which the electrode 150 sits and below the latter.

• - un chauffage inductif par une simple bobine coaxiale à la cuve logée dans le revêtement réfractaire du four. Cette bobine, identique à la solution de base proposée pour le chauffage inductif de la Fig. 9, assure le chauffage des couches externes.
• - un chauffage conductif (par source monophasée ou source de courant continu) du lit de boulets entre une électrode centrale et une électrode circulaire, tel qu'il a été décrit en référence à la Fig. 7. Cette disposition concerne les flux de courant de conduction vers l'électrode autour de laquelle les boulets sont chauffés car il s'y développe, par diminution de section, une densité de courant et une puissance volumique plus grandes.

This mixed assembly combining inductive heating at the periphery of the tank coupled with conductive central heating, is intended for medium and large capacity ovens. It combines:

• - inductive heating by a simple coil coaxial with the tank housed in the refractory lining of the furnace. This coil, identical to the basic solution proposed for the inductive heating of FIG. 9, provides heating for the outer layers.
• - conductive heating (by single-phase source or direct current source) of the ball of balls between a central electrode and a circular electrode, as described with reference to FIG. 7. This provision relates to the conduction current flows towards the electrode around which the balls are heated because it develops there, by reduction of section, a higher current density and power density.

This association of an induction coil with conduction heating between a central electrode and a peripheral electrode, also makes it possible to cause rapid rotation of the conduction currents by faction on these currents of the field lines created by the external coil.

In this way, we constantly renew the current lines between the two electrodes and preferential current flows are eliminated along the most conductive ball lines which lead to local overheating.

Inductive heating uses variable fluxes generated by induction coils completely external to the mass of the balls during coking and makes it possible to overcome, in large part, the problems of variation of the contact resistance between balls and in contact electrodes.

The effects of several coils can be combined so as to control the lines of induction flux in the electric coking zone. These possibilities make it possible to uniformly distribute the heating currents in the cross section, to avoid local overheating of the balls near the coils and parasitic heating currents outside the cooking zone.

Thanks to these specific advantages, the electromagnetic induction developed in a ball of balls allows density levels varying within wide limits. For an electrical gradient of 75 to 100 volts per meter, the developed power can reach 5 to 10 Megawatts per m ³ of hot and coked balls, while it is considerably lower by conduction.

This electrical power, greater than the only thermal requirement of the electrical coking developed in the mass of balls, can be used to reduce, by the carbon of the coke and by the volatile matters of the binders, fines of oxidized ores or dusts which can be incorporated into composite bullets.

These reduction reactions which develop simultaneously with electric coking regulate the temperature of electric coking of the balls and produce a very resistant metallized coke.

• - Des fines et des poussières d'oxydes de fer (concentrés, poussières d'aciéries et de gaz de haut fourneau, poussières d'installations, de dépoussiérage, d'agglomérations de minerais, etc ...)
• - Des fines de minerais de manganuse et des poussières de production de ferro-manganèse.
• - Des concentrés de chromites pour la production de ferro-chrome.
• - Des fines de silice et de quartz recyclés dans la production de ferro-silicium.

The present invention finally includes a process for manufacturing molded coke making it possible to add to the mixture of coals to be compacted into balls:

• - Iron oxide fines and dust (concentrates, steelworks dust and blast furnace gas, plant dust, dedusting, ore agglomerations, etc.)
• - Manganese ores fines and ferro-manganese production dust.
• - Chromite concentrates for the production of ferro-chromium.
• - Silica and quartz fines recycled in the production of ferro-silicon.

For these different applications, the rate of mineral fines incorporated in the coke paste is limited by the electrical conductivity of the ball bed which cannot be less than 100 mhos (electrical conductivity of the homogeneous medium equivalent to the bed of balls at the start temperature electric coking, i.e. 850 ° C to 900 ° C).

The invention, as described above, also relates to a method and a device making it possible to dissipate, in a uniform and homogeneous manner, significant volumetric electric powers, developed by the Joule effect of induced electric currents, in a medium. conductive granule which can thus be brought to high temperature.

This granulated bed having a high specific surface can be used to heat or superheat gases, liquids, melt solids, and vaporize liquids by superheating the vapors thus produced.

The conductive granulated bed consists of refractory and sufficiently conductive materials, in calibrated pieces, in grains, in solid or hollow and tubular cylindrical elements, in rings, in balls or pellets, in briquettes.

By way of examples, the refractory materials composing the conductive granulated bed can be constituted by calibrated pieces and grains of carbon, graphite, cokes, or by rings, pellets, and cylinders of silicon carbide, molybdenum silicide, diboride of zirconium or by balls, pellets, briquettes of coal paste and coking mixtures.

In view of its use, the granulated bed is chosen according to its electrical resistivity, its refractoriness, its specific surface and its permeability, and finally its resistance to oxidation and corrosion for the use which is made of it.

• a) - chauffage de gaz.
  • - chauffage et surchauffage de gaz réducteurs sur un lit de morceaux de coke calibré;
  • - régénération et génération de gaz réducteurs par conversion en H₂ et CO de l'H₂O et C0₂ contenus dans le gaz, sur un lit de coke à 800 - 1000°C;
  • - cracking et oxydation des hydrocarbures lourds contenus dans le gaz de cokerie brut et humide sur un lⁱt de coke à 900 - 1100°C, pour réaliser en une seule étape "l'épuration" thermique du gaz de cokerie brut et chaud, et éliminer tous les produ- ⁱts condensables;
  • - surchauffe à 1200°C de gaz réducteurs, destinés à la réduction "directe" d'oxydes de fer, sur un lit de coke;
  • - surchauffe à haute température de 1200 - 1350°C d'air préchauffé, éventuellement sous pression et suroxygéné comme le vent d'un haut-fourneau sur un lit d'éléments tubulaires conducteurs en carbure de silicium ou siliciure de molybdène sous forme d'anneaux.
• b) - chauffage des liquides, conducteurs ou isolants, ruisselant sur des lits granulés conducteurs inertes vis-à-vis du liquide tels que:
  • - fabrication de vapeur surchauffée sèche, sur un lit de copeaux ou tournures, d'acier inoxydable et réfractaire;
  • - surchauffe de métal liquide ruisselant sur un lit de coke;
  • - pasteurisation du lait.
• c) - Fusion de solides non conducteurs, par exemple de laitiers, ou de "composition" verrière sur une "grille' de coke rouge. Le liquide visqueux ruisselant sur le coke est chauffé et fluidisé.

Examples of use include:

• a) - gas heating.
  • - heating and superheating of reducing gases on a bed of calibrated pieces of coke;
  • - regeneration and generation of reducing gases by conversion into H ₂ and CO of the H ₂ O and C0 ₂ contained in the gas, on a coke bed at 800 - 1000 ° C;
  • - cracking and oxidation of heavy hydrocarbons contained in the raw and wet coke oven gas on a l ⁱ t of coke at 900 - 1100 ° C, to carry out in one step the thermal "purification" of the raw and hot coke oven gas, and eliminate all produ- ⁱ ts condensable;
  • - superheating at 1200 ° C of reducing gases, intended for the "direct" reduction of iron oxides, on a bed of coke;
  • - overheating at high temperature of 1200 - 1350 ° C of preheated air, possibly under pressure and superoxygenated like the wind of a blast furnace on a bed of tubular conductive elements made of silicon carbide or molybdenum silicide in the form of rings.
• b) - heating of liquids, conductors or insulators, trickling on conductive granular beds inert with respect to the liquid such as:
  • - manufacture of dry superheated steam, on a bed of shavings or turnings, of stainless steel and refractory;
  • - liquid metal overheating trickling over a coke bed;
  • - milk pasteurization.
• c) - Fusion of non-conductive solids, for example from slag, or glass "composition" on a "grid" of red coke. The viscous liquid flowing on the coke is heated and fluidized.

To carry out the gas heating process, an oven is used comprising heating means as shown in FIGS. 7 to 14.

The conductive granulated bed is compacted in the tubular enclosure of the oven whose walls are lined with insulating refractories. This granulated bed rests on a refractory grid through which the gas to be overheated is blown. It can also be placed between two layers of non-conductive material such as sand, so as to center the lines of flight.

Claims (22)

1. Process for the production of coke moulded in a vertical shaft furnace of the type having in its upper part tight means (5 to 13) for the introduction of a charge of crude moulded balls and means (15a, 15b) for recovering the gases produced and in its lower part tight means for the discharge of the coke and means (24 to 27) for introducing a gas flow, in which is circulated a recycled gas flow, which rises in countercurrent to the falling charge of moulded coal balls constituting a falling moving bed; the moulded coal balls are subject to a preheating and devolatilization stage in a first area (20) corresponding to the upper part of the furnace, then a carbonization and coking stage in a second area (21) corresponding to the median part of the furnace and a cooling stage of the coked balls in a third area (23) corresponding to the lower part of the furnace; at the top of the furnace are recovered the top gases produced by the distillation and coking of the coal; and a fraction of these top gases is recycled for forming the recycled gas flow, characterized in that a first part of the fraction of the recycled top gases is introduced at the bottom of the third area (23) in order to ensure a primary cooling of the coke and the remainder of the fraction of the recycled top gases in the form of a secondary cooling flow flowing in countercurrent with respect to the coke mass from the third area into a fourth area (34) tightly connected to the outlet of the third area, the secondary cooling flow then being drawn off (40) from the fourth area and reintroduced into the top of the furnace to dilute the gases produced and keep the recovery means (15a, 15b) for said gases at a sufficiently high temperature to prevent any condensation; and the cold coke is discharged from the fourth area (34) by a tight lock (46).

2. Process according to claim 1, characterized in that carbonization and coking are carried out by a supply of electric power (22) to the moving bed of precoked balls and the transfer of said power by a recycled gas flow.

3. Process according to claim 2, characterized in that the electric power supply is carried out by electric conduction into the moving bed of balls of a current generated between at least two electrodes placed in the walls of the shaft level with the second area.

4. Process according to claim 2, characterized in that the electric power supply is brought about by the induction of electric currents into the moving bed of balls passing through the second area.

5. Process for the production of metallized moulded coke, characterized in that, by a process according to any one of the preceding claims, coking takes place of a moulded ball charge prepared by compacting a paste constituted by a simple or mixed binder and a mixture of appropriate coals and fine particles of a material based on the metallic element to be incorporated into the coke in metallic or oxidized form.

6. Process according to claim 5, characterized in that the basic material for the metallic element is constituted by iron oxides, manganese ore and dust resulting from the production of ferro- manganese, chromite concentrates for the production of ferrochrome and recycled quartz and silica fines for ferrosilicon production.

7. Shaft furnace for the production of moulded coke in the form of a substantially tubular enclosure (3) defining a first preheating area (20) corresponding to the upper part of the enclosure, a second carbonizing and coking area (21) corresponding to the median area of the enclosure and a third coke cooling area (23) corresponding to the lower part of the enclosure, the furnace having at its top tight means for the introduction of a charge constituted by crude moulded balls and means (15a, 15b) for recovering the gases produced and at its bottom tight means for the discharge of the coke and means (24, 25, 26, 27) for admitting a recycled gas flow, the admission means being connected, outside the furnace, to means (15a, 15b) for recovering gases produced by the recycling means (17, 29), as well as electric heating means (22) located in the wall of the second carbonizing and coking area, characterized in that the furnace comprises a fourth tight, secondary cooling area (34) connected upstream to the discharge means of the third area and downstream to a tight discharge lock (46), the fourth area (34) having at its base at least one secondary cooling gas flow supply pipe (35) connected to the recycling means and at its top at least one secondary cooling gas return pipe (40) connected to the upper part of the furnace in the vicinity of the recovery means of the gases produced by the distillation and coking of the coal.

8. Furnace according to claim 7, characterized in that the tight means for introducing the charge are constituted by a tight took (10) for the supply of the charge issuing in its lower part into the first area (20) of the furnace by a distributing bell (12), the supply lock (10) being itself supplied by a rotary hopper (5).

9. Furnace according to claim 7, characterized in that the means for discharging the coke from the third area incorporate a rotary half (30) mobile in vertical translation issuing via a tight lock (33) into the fourth secondary cooling area (34).

10. Furnace according to any one of the claims 7 to 9, characterized in that the electric heating means (22) are of the conduction type and constituted by at least one pair of diametrically opposite electrodes (59) located in the wall of the second area (21) of the furnace enclosure, said wall forming in said area a constriction of the internal passage cross-section of the moulded ball bed defined by a shoulder (58) against which are located the electrodes.

11. Furnace according to claim 10, characterized in that the electrodes (59) are constituted by segments, whose vertical sectional profile is in the form of a L extending along each side of the shoulder (58), in such a way that one of the branches of the L is horizontal.

12. Furnace according to claim 11, characterized in that the shaft has a circular cross-section and the circular electrode segments are separated from one another by a refractory material, interposed wall (66) in the form of an inclined plane corresponding to the slope of shoulder (58) defined by the L-profile of the electrodes.

13. Furnace according to any one of the claims 10 to 12, characterized in that it has an ogival, refractory material, internal enclosure (80) provided with a central electrode (81) cooperating with a peripheral electrode (82) passing along the inner wall of the enclosure.

14. Furnace according to claim 13, characterized in that the ogival internal enclosure (80) is mounted in height regulatable manner by means (84, 87) passing through the rotary hearth (86).

15. Furnace according to one of the claims 10 and 11, characterized in that the shaft has a rectangular cross-section and the electrode segments (74) are linear and rest on ledges (75) disposed on opposite sides of the rectangular section.

16. Furnace according to any one of the claims 7 to 9, characterized in that the electric heating means are of the induction type and constituted by an external induction coil (100, 110) coaxial to the shaft end located in the refractory lining (2) of the furnace.

17. Furnace according to claim 16, characterized in that it has an internal ogival, refractory material enclosure (111) in which is located an internal, laminated, magnetic core (112).

18. Furnace according to claim 16, characterized in that an internal induction coil (113) coaxial to the external induction coil (110) is wound around the internal magnetic core and supplied in phase with the latter.

19. Furnace according to any one of the claims 7 to 9, characterized in that the induction heating means are constituted by a plurality of pairs of induction coils (130, 131) arranged radially in the refractory wall (2) of the furnace, defining an external inductor generating a rotary field passing horizontally through the shaft.

20. Furnace according to claim 19, characterized in that it has an internal, ogival, refractory material enclosure (140), in which is located an internal inductor constituted by a plurality of radial coils (130a, 131a) positioned facing the coils of the external inductor (130.131) and defining a plurality of pairs of coupled coils (130, 130a and 131, 131a), which cooperate in order to generate a rotary field between the external inductor and the internal inductor.

21. Furnace according to any one of the claims 7 to 9, characterized in that the electric heating means are constituted by the combination of at least one pair of electrodes, like those described in claim 13 and generating heating by conduction, and at least one coil, like that described in claim 16, generating heating by induction.

22. Furnace according to claim 21, characterized in that the induction heating means also incorporate the coil described in claim 13 end a laminated, inner magnetic core like that described in claim 17.

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