EP0240527A1 - 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 consists in introducing a first part of the fraction of the recycled overhead gases at the base of the lower part (23) of the furnace to ensure primary cooling of the coke; and introducing the remainder of the fraction of the recycled overhead gases in the form of a secondary cooling stream flowing against the current of the mass of coke coming from the lower part (23) of the furnace in a zone (34) connected by sealingly at the outlet of the lower part (23); the secondary cooling stream then being drawn off (40) from the zone (34) and reintroduced at the top of the furnace to dilute the gases produced and to maintain the means of recovery (15a and 15b) of these gases, at a temperature high enough to prevent any condensation; and the cold coke being evacuated from the zone (34) by a sealed airlock (46). The invention also relates to a method and an electrical heating device using a fluid-conducting granulated bed.

Description

 Method for manufacturing coke molded by electric heating in a shaft furnace and shaft furnace for manufacturing such coke and method of electric heating using a granulated fluid-conducting bed.

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 granulated fluid-conducting 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 provide 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 solid mass of coke is not uniformly heated. Indeed the coke undergoes in walls a Excessive and too rapid overheating which is detrimental to the mechanical strength of the balls (bursting and cracking) and to their metallurgical quality (reactivity). Various publications, namely patents

FR-A-628.168, US-A-2.127.542, DE-A-409.341 and FR-A2.529.220 proposed, to solve these problems, to bring the heat energy of coking directly into the zone concerned, by conduction electric in the solid mass of hot balls, by generating electric currents between diametrically opposite electrodes, separated by the solid mass of coking balls.

In patent FR-A-2,529,220, the shaft 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 lateral 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, for one 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 ob held by compaction. However, excessive locality or generalized compaction of this bed constitutes an obstacle to the "fluid" flow of 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 the 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 optimal 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 evacuating the coke and means for introducing a gaseous current, in which a recycled gaseous current 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 furnace, then to a carbonization and coking stage in a second zone corresponding to the middle part of the furnace, and a step of cooling the coked balls in a third zone corresponding to the lower part of the oven; the overhead gases produced by the distillation and coking of the coals are recovered at the top of the furnace; and a fraction of these overhead gases is recycled to form the recycled gas stream, characterized in that a first part of the fraction of the recycle overhead gases is introduced at the base of the third zone 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 current circulating countercurrently to the mass of coke coming from the third zone, in a fourth zone connected in leaktight manner to the outlet of the third zone, the secondary cooling current then being withdrawn from the fourth zone and reintroduced at the top of the furnace to dilute the gases produced and to 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

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 bed of balls which have become conductive, up to the desired final temperature. Recycled gas, stove fairies by heat exchange during the primary cooling of the balls, are overheated 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 electric conduction in the moving bed of coked molded balls of a current generated between at least two diametrically opposed 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.

A further subject of the invention is 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, 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 metal 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 of silica powders which must be recycled for the production of ferro-silicon.

The invention further relates to a tank furnace for the manufacture of molded coke in the form of a substantially tubular enclosure deli using a first preheating zone corresponding to the upper part of the enclosure, a second carbonization and coking zone corresponding to the middle 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 discharging coke and means for admitting a recycled gas stream, the intake means being connected, outside the oven, to the means for recovering the 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 fourth sealed secondary cooling zone connected upstream to the means for evacuating the third zone and in downstream to a leak-proof airlock, the fourth zone comprising at its base at least one supply line for secondary gaseous cooling current connected to the recycling means, and at its top, at least one line for returning the cooling gases secondary 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 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 comprise a rotating and mobile 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 electric 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 and very conductive balls on the electrode which 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 cooking zone and from the gases of the recycled gas stream, very hot at this level. This results in a decrease in heat losses and a 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 suitable for large diameter ovens, the oven has an internal enclosure in the shape of a warhead made of material. refractory 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 electric 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 .

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 from the oven wall in the area of an electrode. Fig. 5 is a view in radial and vertical section along line 5-5 of 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 furnace 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 the 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 gradual 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 850ºC and the balls then become conductors of electricity. 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, ground 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 shielding 1 provided on its internal face with a refractory lining 2 delimiting a substantially tubular enclosure 3, 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 watertight means for introducing the raw molded balls, which comprise a rotary 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 11a, 11b of purging with a neutral gas. The airlock 10 is closed at its lower part opening into the oven, by a distribution bell 12 whose opening 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 are constituted by 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 via the lines 15a, 15b is sent to a primary purification installation shown diagrammatically at 16 to undergo a treatment of cooling, washing, taring and summary condensation 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 diagrammatically in 19. The enclosure 3 of the oven 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 are installed the electric heating means 22, 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 gas stream coming from the primary purification installation 16. These means comprise a set pipes 24 for admission of the primary recycled current 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 line 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 line 26 is adjusted to maintain the temperature detected by the sensors 28 at a predetermined set point, to avoid condensation of the tars on the baked balls and on the internal walls of the oven.

The oven comprises at its base means for evacuating 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 height adjustment cylinder 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 produced gases takes place and opening into it by 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 current and a secondary current, on the one hand the optimization of the thermal profile of the oven in the carbonization zone by adjusting the primary current , 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 150ºC, and the entrainment of these tars by dilution in the secondary current extract from the fourth cooling zone.

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

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

The coke balls descend into the lower part of the furnace 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 furnace. After cooling, the coke balls continuously extracted from the third zone by means of a rotating hearth are evacuated 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 through 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. 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 species, coke dust, petroleum coke and the substitution of melting fuses with binders, such as pitches, tars and asphalt residues. - 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). - The reduction in investment costs of more than 20%, for the same production.

- A much higher thermal efficiency since the overhead gases come out at around 150ºC and the balls are extracted cold from the shaft oven while in a conventional battery, the gases exit at 500ºC, the coke is discharged at more than 1000ºC, and the fumes are at more than 400ºC at 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 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 zones: smoke extraction and pre-cooking, 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: 1300ºC), blast coke with adjusted reactivity . - The choice of coke size.

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

- The low inertia of the oven. The rapid electrical 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 locally 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 electric heating of the conduction type, the internal wall of the refractory lining 2 delimiting the enclosure 3, forms a narrowing of the inner section for passage of the bed of molded balls at the lower part 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 profile in vertical section extend along each side of the shoulder 58 so that one of the branches of 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 of internal circulation of cooling fluid disposed 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 small diameter ovens, for example less than or equal to 2 m, a two-phase supply is produced, as illustrated in FIGS. 2A and 28, 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 38. the three pairs of electrodes marked 1, 1b are supplied with power; 2, 2b; 3, 3b; according to the three-phase diagram of FIG. 38.

The electrodes 59 made up of circular segments, the section of which is L-shaped, rest inside the furnace on a cooled refractory edge 67 (FIG. 4). There is formed on each of these electrodes, a natural embankment of highly graphitized balls (by local over-coking caused by the prolonged residence time of the balls at high temperature) and very conductive, which protect the electrodes 59 and distribute the current densities 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 increases so as to loosen the ball of balls, to increase the electrical resistances of contact between the balls and avoid stray currents in the cooling zone where they would heat the already coked balls 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 head of the furnace and 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 crossing 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 can be moved 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 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 bottom of the furnace through a cooled, insulated conductor 90 housed in the hollow axis of the rod 84. The column 85 is mounted to slide, for example by a system of grooves not shown, in a conical ring gear 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 gearmotor unit 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 rotation speed of the dosing hearth and the height thereof.

The cathode 81 is cooled by circulation from a pipe 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 of the power density

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

In particular, the induction fields being 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 effectiveness 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, in 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 favor a peripheral flow of the balls (rotary sole 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 in the vicinity of the furnace axis. The refractory material constituting the enclosure 111 may be, for example, made of silicon carbide bonded to silicon nitride, the electrical insulation properties of which are sufficient for the envisaged application and the resistance to abrasion and to thermal shock is excellent. .

These means can consist of a set of mild steel cores, vertically laminated 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 coaxially 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 passes through the rotary hearth of the oven 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 ensured by a pipe coaxial and external to the pipe 119.

Cores 120 vertically laminated 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 horizontally passing through 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 marked 1, so that the magnetic field passes radially through the tank, that is to say that the end faces facing 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 of 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 shown in FIGS. 12 and 13, the oven further comprises an internal enclosure 140 in the shape 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 131a.

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 mild steel cores, vertically laminated 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. 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: - an 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 a single-phase source or direct current source) of the ball bed 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 heating by conduction between a central electrode and a peripheral electrode, also makes it possible to cause the rapid rotation of the conduction currents by the action on these currents of the field lines created by the external coil. .

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

Inductive heating uses variable fluxes generated by induction coils totally 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.

We can combine the effects of several coils so as to control the lines of induction flux in the electric coking zone. These possibilities allow uniform distribution of 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 m3 of hot and coked balls, while it is considerably lower by conduction.

This electrical power, greater than the only thermal requirement of 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 balls.

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.

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, dust from dedusting installations, 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 into 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 ball bed at the start temperature of electric coking, that is 850ºC to 900ºC.

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 electrical 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 is made of refractory and sufficiently conductive materials, in calibrated pieces, in grains, in full or hollow and tubular cylindrical elements, in rings, in balls or pellets, 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 of 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.

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 to H ₂ and CO of the H ₂ O and CO ₂ contained in the gas, on a coke bed at 800-1000ºC; - cracking and oxidation of the heavy hydrocarbons contained in the raw and wet coke oven gas on a coke bed at 900-1100ºC, to carry out in one step the "purification" thermal of the raw and hot coke oven gas, and eliminating all condensable products; - overheating at 1200ºC of reducing gases, intended for the “direct” reduction of iron oxides, on a bed of coke; overheating at high temperature of 1200-1350ºC of preheated air, possibly under pressure and superoxygenated like the wind from a blast furnace on a bed of tubular conductive elements in silicon carbide or molybdenum silicide in the form of rings. b) - heating of liquids, conductors or insulators, flowing over 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; - pasteurization of milk. c) - Fusion of non-conductive solids, for example from slag, or glass "composition" on a "grid" of red coke. The viscous liquid flowing over 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

CLAIMS 1. 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 balls of coals previously molded by compaction (5 to 13) and means for recovery of the gases produced (15a, 15b); and at its lower part, sealed means for discharging the cooled coke, and means for introducing (24 to 27) a gas stream; in which a stream of recycled gas is circulated in an upward flow, counter-current to the downward charge of molded coal balls constituting a downward moving bed; the molded coal balls are subjected to a preheating and devolatilization step in a first zone (20) corresponding to the upper part of the furnace, then to a carbonization and coking stage in a second zone (21) corresponding to the part median of the oven and a step of cooling the coked balls in a third zone (23) corresponding to the lower part of the oven; the overhead gases produced by the distillation and coking of the coals are recovered at the top of the furnace; and a fraction of these head gases is recycled to constitute the recycled gas stream, characterized in that a first part of the fraction of the recycled head gases is introduced at the base of the third zone (23) to ensure cooling coke primer; and the remainder of the fraction of the recirculated overhead gases is introduced, in the form of a secondary cooling current flowing against the current of the mass of coke coming from the third zone, in a fourth zone (34) tightly connected to the exit from the third zone; the secon cooling current daire then being withdrawn (40) from the fourth zone and reintroduced at the top of the furnace to dilute the gases produced and to maintain the means of recovery (15a and 15b) of these gases, at a temperature high enough to prevent any condensation; and the cold coke being discharged from the fourth zone (34) by a sealed airlock (46).

2. Method according to claim 1, characterized in that the carbonization and coking are carried out by supplying electrical energy (22) to the moving bed of precoke balls, and transfer of this energy by a recycled gas stream.

3. Method according to claim 2, characterized in that the supply of electrical energy is carried out by electrical conduction in the moving bed of balls of a current generated between at least two electrodes placed in the walls of the tank at the second zone.

4. Method according to claim 2, characterized in that the supply of electrical energy is carried out by induction of electric currents in the moving bed of balls crossing the second zone.

5. Method for manufacturing metallized molded coke, characterized in that a method according to any one of the preceding claims cokes a charge of molded balls prepared by compacting a paste consisting of a single or mixed binder, and 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.

6. Method according to claim 5. characterized in that the material based on the metallic element consists of iron oxides, ore of manganese and dust from ferro-manganese production, chromite concentrates for the production of ferro-chromium, silica fines and quartz recycled in the production of ferro-silicon.

7. Bowl furnace for the manufacture of molded coke in the form of a substantially tubular enclosure (3) delimiting a first preheating zone (20) corresponding to the upper part of the enclosure, a second zone (21) of carbonization and coking corresponding to the middle zone of the enclosure and a third zone (23) for cooling the coke corresponding to the lower part of the enclosure, the oven comprising at its top sealed means for introducing a charge formed raw molded balls and means for recovering (15a, 15b) the gases produced; and at its base, sealed means for evacuating the coke and inlet means (24, 25, 26, 27) of a recycled gas stream, the inlet means being connected, outside the oven, to the recovery means (15a, 15b) of the gases produced by recycling means (17, 29), and electric heating means (22) arranged at the base of the second carbonization and coking zone, characterized in that the furnace comprises a fourth sealed secondary cooling zone (34) connected upstream to the evacuation means of the third zone and downstream to a sealed evacuation lock (46), the fourth zone (34) comprising at its base at least a secondary cooling current supply line (35) connected to the recycling means, and at its top, at least one return cooling gas return line (40) connected to the upper part of the furnace in the vicinity of the recovery of gases produced by the distillate ion and of coal coking.

8. Oven according to claim 7, characterized in that the sealed means for introducing the charge consist of a sealed airlock (10) for feeding the charge opening at its lower part into the first zone (20) of the oven by a distribution bell (12), the supply airlock (10) being itself supplied by a rotary hopper (5).

9. Oven according to claim 7, characterized in that the means for evacuating the coke from the third zone comprise a rotary hearth (30) which is movable in vertical translation opening out via a sealed airlock (33) in the fourth secondary cooling zone (34).

10. Oven according to any one of 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), disposed in the wall of the second zone (21) of the oven enclosure, said wall forming in this zone a constriction of the internal passage section of the bed of molded balls delimited by a shoulder (58) against which the electrodes are housed.

11. Oven according to claim 10, characterized in that the electrodes (59) consist of segments whose vertical section profile is L-shaped extending along each side of the shoulder (58) so that 'one of the branches of L is horizontal.

12. Oven according to claim 11, characterized in that the tank is of circular section and the segments of circular electrodes are separated from each other. others by an intermediate wall (66) of refractory material in the form of an inclined plane corresponding to the slope of the shoulder (58) delimited by the L-shaped profile of the electrodes.

13. Oven according to any one of claims 10 to 12, characterized in that it comprises an internal enclosure (80) in the form of a warhead made of a refractory material provided with a central electrode (81) cooperating with a peripheral electrode. (82) flowing along the internal wall of the enclosure.

14. Oven according to claim 13, characterized in that the internal enclosure (80) in the form of a warhead is mounted adjustable in height by means (84, 87) passing through the rotary hearth (86).

15. Oven according to any one of claims 10 and 11, characterized in that the tank is of rectangular section and the electrode segments (74) are linear and rest on copings (75) disposed on opposite sides of the rectangular section.

16. Oven according to any one of 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 with the tank and housed in the refractory lining (2) of the oven.

17. Oven according to claim 16, characterized in that it comprises an interior enclosure (111) in the form of a warhead of a refractory material in which is housed an internal laminated magnetic core (112).

18. Oven according to claim 17, characterized in that an internal induction coil (113) coaxial with the external induction coil (110) is in rolled around the internal magnetic core and supplied in phase with it.

19. Oven according to any one of claims 7 to 9, characterized in that the induction heating means consist of a set of pairs of induction coils (130, 131) arranged radially in the refractory wall (2 ) of the oven, defining an external inductor generating a rotating field horizontally passing through the tank.

20. Oven according to claim 19, characterized in that it comprises an internal enclosure (140) in the form of a warhead of refractory material in which is housed an internal inductor consisting of a set of radial coils (130a, 131a) arranged opposite the coils of the external inductor (130, 131) and determining a set of pairs of coupled coils (130, 130a, and 131, 131a) which cooperate to generate a rotating field between the external inductor and the internal inductor .

21. Oven according to any one of claims 7 to 9, characterized in that the electric heating means consist of the combination of at least one pair of electrodes as described in claim 13 generating heating by conduction, and at least one coil as described in claim 16 generating an induction heating.

22. Oven according to claim 21, characterized in that the induction heating means comprise, in addition to the coil described in claim 13, an internal laminated magnetic core as described in claim 17.

23. Method for heating a granulated bed having a certain thermal conductivity and ru by a fluid in an enclosure, characterized in that the heating of the granulated bed is carried out by means of heating by induction or conduction as described in claims 10 to 22.

24.- A device for heating a granulated bed having a certain thermal conductivity and traversed by a fluid in an enclosure, characterized in that it comprises means of heating by induction or conduction as described in claims 10 0 22.