EP0098771B1 - Process for the production of form coke in a shaft furnace, and shaft furnace for carrying out the process - Google Patents

Abstract

1. Process for producing moulded coke in a shaft oven with a vertical axis (1), which is supplied in its upper part (3) with a burden of coal for coking in the form of ovoids, forming a movable bed descending in the shaft (1) in counter flow to gas circulating from the bottom upwards and passing successively from the top downwards through a preheating zone, a coking zone and a cooling zone, the rising stream of gas being formed by the gases released by the coal during its heating and coking and by some of the gases recovered in the upper part of the oven and recycled in the lower part after washing and dust extraction, heat being supplied by circulation of electrical current through the bed of solid materials between electrodes (8) located on two opposite sides of the wall (2) of the oven (1), characterized in that the electrical heating is carried out in a controlled way over a specific height in the middle part (C) of the oven (1), electric currents, the intensities of which can be regulated, being passed through the burden in several staggered horizontal planes, and in that, by adjustment of the circulation of the gases and of the electrical power distributed to the various levels of electrodes according to the heat requirements and the electrical resistance of the burden, a progressive and uniform heating of the latter is controlled during its descent in the oven according to a law of heating selected as a function of the type of coal, to preserve the shape of the ovoids, in such a way that the temperature of the bed of solid material is between 600 degrees C and 850 degrees C at the entrance of the middle zone (C) of electrical heating and that coking is carried out completely in this zone (C) at a temperature remaining between 950 degrees C and 1150 degrees C, the coke ovoids subsequently being cooled in the lower part of the oven (1).

Description

The invention relates to a method for manufacturing coke molded in a shaft furnace and the corresponding shaft furnace.

A process is known for manufacturing coke molded in a tank furnace where coal balls are introduced into the tank furnace, at its upper part, to constitute a bed circulating from top to bottom through the furnace over its entire height.

During their circulation inside the oven, these coal balls are in contact with hot gases passing through the oven from bottom to top.

The upper part of the oven constitutes a balanced exchanger in which the bed of solids is dried and heated to a certain temperature and the circulating gases cooled before their exit to the upper part of the oven.

The middle part of the oven constitutes the coking zone in which heat is supplied to the bed of circulating solid materials, for example by means of burners.

This addition of heat can be carried out by combustion of part of the gases circulating in the shaft furnace, by means of oxidizing air introduced at the level of the central zone.

In this case, at least part of the gases escaping from the top of the shaft furnace are recycled after taring and dusting, by reinjecting these gases at the lower end of the outlet for solid products, at the base of the shaft furnace.

The lower part of the shaft furnace, below the middle zone, constitutes a second balanced heat exchanger where the solid materials coked in the middle zone are cooled by the gases injected into the lower part of the shaft furnace. The gases are therefore at a high temperature when they reach the middle zone of heating and coking.

Coal balls liberate in particular at the time of their coking combustible gases coming from volatile materials of coal.

These gases have great industrial value, since they can be recovered, treated and reused either in the shaft furnace itself, or for other uses.

However, the injection of combustion air to cause the combustion of part of the gases circulating in the shaft furnace is the reason for the presence in the gases recovered from the furnace top of a large proportion of nitrogen which decreases the calorific value of the gas. It is also necessary to treat larger quantities of gas, which entails a higher cost of this recovered gas. Thus, for each tonne of coke produced, we are in the presence of an excess of gas due to the volatile matter of the coal and the injected air, of approximately 680 m ³ to 800 m ³ depending on the nature treated coals.

On the other hand, control of the process, as far as thermal adjustment is concerned, is relatively difficult to obtain.

It is indeed necessary to adjust the temperature in the coking zone in a relatively precise manner and to prevent the air introduced for the combustion of the gas and the heat supply in the central zone of the furnace from oxidizing part of the carbon of the balls, this which would be at the expense of the efficiency and effectiveness of the coking operation.

It has therefore been proposed for the simultaneous production of coke and combustible gas to carry out the supply of heat in the shaft furnace by means of electrodes passing through the walls of the furnace and coming into contact with the bed of circulating solid materials. A strong electric current can thus cross the bed of solid materials and produce a heat release by Joule effect.

Such a process is described for example in French patent 997,058 where an electric heating zone is provided in the oven, below the coking zone. The coke produced is thus brought to very high temperature by electrical heating and the gases coming from the base of the furnace which pass through this zone heat up strongly in contact with the coke at very high temperature and are capable of causing the coking of coal in the zone. oven located above the electric heating zone.

This process has the drawback of requiring the coke to overheat up to a temperature in the region of 1,400 ° C.

By way of comparison, the coke temperature in conventional coke ovens does not exceed 1,200 ° C.

The FR.A. patent has also been proposed. 628 168, to use electrically heated ovens, with gas circulation against the current of solid materials, for cooking coke in order to manufacture electrodes.

However, such processes require temperatures much higher than the temperatures necessary for coking.

There are also known processes for treating coke, for example for its desulphurization, which use both electric heating and the passage of gas through the mass of coke brought to high temperature.

However, such processes are carried out very differently from a coking process and are only intended for the treatment of the coke itself, however, there is no point in bringing the coke to temperatures which may exceed 1.400 ° C because the metallurgical quality of coke is affected and its reactivity, among other things, decreases.

In patent US-A-2,127,542, the electrodes are placed at the level of the coking zone but, in this case also, the passage of the current takes place in coke which is charged at the same time as coal to the upper part of the shaft furnace forming an annular layer which surrounds the coal charge and descends with it. it is therefore in this layer of coke that the Joule effect produces a supply of heat which is transmitted by conduction to the adjacent coal which transforms into coke and in turn lets the current flow. The carbonization process therefore extends radially inwards during the descent of the charge and the degree of carbonization of the pieces of coal depends, at each level, on their distance from the wall of the furnace.

The invention proposes, on the other hand, a process for manufacturing mold coke in which the heating of the charge is carried out by observing a heating law determined according to the nature of the coal so as to avoid the formation of clusters and to preserve the shape of the balls until the end of the treatment, in particular by avoiding their bursting and their overheating.

For this purpose, a known kiln is used, at the top of which coking charcoal balls are introduced which constitute a moving bed descending into the furnace against the gas flow passing through the furnace from bottom to top. , part of which consists of gases recovered at the top of the oven and recycled at its bottom and another part of which consists of the gases released by the coal during its heating and coking, a supply of heat being effected by passing electric currents through the bed of solids.

In accordance with the invention, electrical heating is carried out in a controlled manner, in the central zone of the furnace over a determined height, by passing electrical currents, the intensities of which can be individually adjusted, in several horizontal planes of the load, by adjusting the heat exchanges between the solid charge and by adjusting the gas circulation and the electric power distributed over the different electrode levels according to the heat requirements and the electrical resistance of the charge, progressive heating is controlled and homogeneous thereof during its descent into the oven according to a heating law chosen according to the nature of the coal to maintain the shape of the balls, so that the temperature of the bed of solid material is between 600 ° C. and 850 ° C at the entry of the central zone (C) of electric heating and that the coking reaction is carried out completely in this zone (C) at a e remaining temperature included. between 950 ° C and 1150 ° C, the coke balls thus produced are then cooled in the lower part of the oven.

According to another important characteristic, in the upper preheating zone of the furnace, an adjustable flow rate of the rising current of hot gases is derived, so as to control a gradual rise in temperature of the materials at a speed chosen according to the nature of the coal for avoid melting or sticking of the balls.

Preferably, the electrical resistance of the charge is increased after leaving the central coking zone by decompressing the charge in the cooling zone, capable of increasing the contact resistances between the balls.

To encourage the passage of electric current in the middle coking zone, to make electric heating homogeneous and to facilitate the electric adjustment of the power consumed, the charcoal balls introduced into the upper part of the oven are mixed with particles of small coke or any other electrically conductive product, unalterable at temperatures reached in the oven and being in the form of grains of dimensions smaller than those of the coal balls, said grains being distributed homogeneously in the interstices between the balls.

The cell furnace for implementing the method according to the invention comprises at least two pairs of superposed electrodes, placed in horizontal planes spaced apart from one another and whose electrical supply voltages are individually adjustable by pair.

In a preferred embodiment, the electrodes placed in at least one of the horizontal planes are mounted movable horizontally and each connected to alternate advancing and reversing means, each electrode exerting constant pressure on the charge by progressive advancement towards the interior of the oven to a determined position from which a rapid reverse is controlled accompanied by a descent of the load and followed by a new advancement.

• La figure 1 représente schématiquement un four à cuve suivant l'invention dans une vue en coupe par un plan vertical.
• La figure 2 représente une section du four suivant Il Il de la figure 1.
• La figure 3 représente la partie inférieure des électrodes du premier ensemble représenté à la figure 1, dans une vue à plus grande échelle.
• La figure 4 représente un mode de réalisation plus perfectionné d'un four à cuve selon l'invention.
• La figure 5 est un diagramme représentant la loi de chauffe de la charge.

In order to clearly understand the invention, we will now describe, by way of nonlimiting example, with reference to the attached figures, an example of implementation of the method according to the invention in the case of an oven with tank fitted with a double set of electrodes.

• Figure 1 shows schematically a tank furnace according to the invention in a sectional view through a vertical plane.
• FIG. 2 represents a section of the furnace along II Il of FIG. 1.
• FIG. 3 represents the lower part of the electrodes of the first assembly represented in FIG. 1, in a view on a larger scale.
• FIG. 4 represents a more improved embodiment of a cell oven according to the invention.
• FIG. 5 is a diagram representing the heating law of the load.

In Figure 1, we see the tank furnace 1 having a double insulating wall 2 and the upper part of which constitutes a chute 3 for charging charcoal balls.

This mouthpiece is of a type similar to that of blast furnace mouths and allows, by means of a device 4, the recovery of gases at the upper part of the shaft furnace. The gueulard is completely waterproof and avoids the entry of atmospheric air.

At the bottom of the shaft furnace, hoppers and rotary evacuators 5 allow a regular outlet of the coke reaching the bottom of the furnace.

A moving bed 6 of solid materials moves continuously in the oven. The upper surface 60 of this bed of solids is maintained at a substantially constant level by introduction of coal balls thanks to the jaw 3 at a flow rate identical to the coke outlet flow rate.

In the example shown in Figure 1, a first set of electrodes 7 is introduced into the furnace through its upper part. These electrodes can be adjusted in height, so that the level of the plane AA in which electric currents of horizontal direction circulate between the electrodes can be adjusted by vertical displacement of all of the upper electrodes.

As can be seen in FIGS. 2 and 3, these electrodes comprise a conductive part 10 constituted by a graphite plate crimped in a piece of refractory steel 11. The pieces 11 of refractory steel are connected to support tubes 12 also in refractory steel constituting conductors serving to bring the current to the end of the electrodes 7. Cooling air possibly circulates inside these tubes and comes to cool, at their lower part, the part 11 for fixing the conductive part 10.

Blocks of refractory material 14 make it possible to isolate the suspension and supply tubes from the current 12 from the bed of solid materials and from the high temperature gases circulating in the furnace.

The electrodes 7 plunge into the bed of solid materials to a depth of approximately 1.5 meters below the surface of the level 60. This depth of introduction of the electrodes can be adjustable.

In Figure 2, we see the rectangular section of the oven in which are arranged six electrodes 7 allowing a flow of current between the electrodes in horizontal directions. The electric current passes from one electrode to another following a horizontal path by crossing the bed of solids having at the level of the electric heating zone a certain conductivity.

A second set of electrodes 8 disposed at a level B lower than the level of the plane A, pass horizontally through the double wall 1, 2 of the furnace. These electrodes consist of blocks of graphite housed in the refractory located between the two walls 1 and 2 of the furnace and slightly projecting in the interior space of the furnace.

Preferably, these electrodes are movable horizontally so as to exert a constant thrust on the load.

To this end, as shown schematically in Figure 1, each electrode 8 can be mounted on a carriage 81 movable horizontally for example by means of a jack 82 at constant pressure. The forward movement towards the inside of the furnace is limited in its course so that the electrodes 8 extend a few centimeters beyond the internal face of the wall 2 of the furnace. The jack 82 then commands a rapid retreat of the electrode which is accompanied by a descent of the mstières located above and the advance movement can resume. An easy-to-design system compensates for the wear of electrode 8.

Outside the oven, a gas recovery and treatment circuit 15 is connected on the one hand to the gas recuperator 4 at the upper part of the oven and on the other hand to the lower part of the oven by an injection pipe. 18.

On this gas circuit are arranged a gas washing unit 16 where the gas is dusted and tared as well as a circulation and injection pump 17. In addition, the circuit can advantageously include equipment 19 limiting the vapor content water from the recycled gas and constituted for example by an exchanger lowering the dew point of the gas by cooling.

A valve 20 makes it possible to regulate the injection of gas at the base of the furnace and to direct a part of this gas towards a storage tank or a circuit of use.

In a more perfected embodiment shown in FIG. 4 the oven comprises several nivesux of electrodes 8 placed in horizontal planes staggered along the middle zone C and the power supply of which, not shown in the figure, can be adjusted individually in each plane, depending on the electrical power desirable for the realization of the heating law.

The required area of electrodes is determined by the intensity of the electric current to be circulated in the mass so as to avoid overheating.

The total surface area of the electrodes is therefore significant. But it is necessary that a ball does not stay too long under a strong intensity. There will therefore be a number of electrodes constituting horizontal planes and of small thickness. The current voltage can be adjusted by group of electrodes according to the heating law.

Furthermore, the furnace 1 has a rectangular section allowing the modular production of an installation made up of adjoining cells.

In the upper preheating zone P the furnace is provided with means making it possible to divert part of the ascending current of hot gases and which can for example consist of a double side wall 21 providing a space for the circulation of gases which is effected by the difference in pressure drop between the two internal and peripheral circuits respectively thus formed.

A shutter system makes it possible to adjust the pressure drop and therefore the gas flow in the main circuit.

In the lower cooling part R, the oven has a greater width and is further crossed by horizontal bars 22 lined with refractory and possibly internally cooled and which extend from one wall to the other. The extraction of the products at the base 5 of the furnace therefore ensures a decompression of the charge at the outlet of the coking zone C. 11 this results in an increase in the resistances of contact which reduces the flow of electric current from the start of the cooling zone. This limits downward the electric heating zone C.

We will now describe the operation of the furnace for the production of molded coke and high calorific gases.

FIG. 5 gives an example of a heating law and of the respective temperatures of the materials (indicated on the abscissa) according to the height of the oven (indicated on the ordinate). The solid line curve gives the temperature of the solids and the dotted line the gas temperature.

Is introduced into the oven, via the gueulard 3 a charcoal charge consisting of briquettes or balls of usual dimensions (for example: 40 x 25 x 20 mm) mixed with small coke with a particle size ranging from 5 to 15 mm . This small coke is previously distributed homogeneously in the balls, in a suitable proportion, for example: 10% by weight or 19% by volume. (The small coke could be replaced by any equivalent product, of the same size, that is to say conductive of electricity and unalterable at the temperatures practiced in the gaseous medium considered).

This small coke is partially lodged between the coal balls, occupying the interstices of the charge.

The charcoal balls consist of a mixture of lean or flaming dry coal associated with fatty or flaming coals mixed with a binder consisting of pitch (possibly mixed with tar).

The homogenized mixture descends into the oven against the flow of gases and reaches the lower part of the upper exchanger of the oven at a temperature close to 850 ° C. The coal balls are therefore dried and then heated so that their temperature is close to 800 ° C. at the outlet of the upper exchanger from the shaft furnace.

The gas flow rate and the heating of the furnace are regulated according to the flow rate of solid materials to obtain the adequate heat exchanges.

As can be seen in FIG. 5, by deriving an adjustable part of the hot gases between the levels E and F of the upper preheating zone, it is possible to control the heating law of the load, in particular between 400 and 700 ° C. so as to avoid the fusion of the balls.

In the operating conditions, the temperature of the balls at the outlet of the upper exchanger P must, in practice, be higher than 700 ° C. so that the flow of the current occurs in a suitable manner and not exceed 850 ° C. for that the thermal efficiency of the operation is good.

When the bed of solids comprising the agglomerated coal balls and the coke reaches plane A of the first set of electrodes, a current flows through this bed of materials and produces a rise in temperature inside the balls by the Joule effect.

The particles of small coke inserted between the coal balls favor the passage of the current in the bed of solid matter circulating in the furnace by multiplying the points of contact.

Raw balls as introduced into the shaft furnace are not very conductive of electricity. However, from a certain degree of devolatilization, the internal resistivity of these balls quickly decreases. For example at 800 ° C the measurements have shown that these balls have an internal resistivity which does not exceed 1500 σ / 0m. Thus, by controlling the temperature rise of the balls in the preheating zone P, one limits upwards the zone C of electric heating.

It is also necessary to avoid too high locsle temperature increases which would cause an excessive cracking of gaseous hydrocarbons circulating in the furnace and a carbon-black deposit between the electrodes, which would create short circuits, this carbon-blsck being conductive.

However, the method according to the invention makes it possible to reduce the risk of overheating since it is easier to regulate the temperature of the electric heating by distributing it in several successive horizontal sections of the oven.

The small coke mixed with the balls of raw coal before being introduced into the oven is recovered at the base of the oven by screening the coke balls produced. This small coke has not undergone any transformation throughout its passage through the furnace. Its role is limited to reducing the contact resistances between the carbon balls and obtaining a more homogeneous heating of the load.

On entering the central electric heating zone of the furnace lying essentially between the two planes A and B of the electrodes, the bed of solids has a very uniform temperature, on the one hand because of the movement of the charge of solids crossing the electrode area and subjected to Joule heating of the currents which cross it, resulting from the multiple contacts established by the grains of small coke distributed in the balls and which constantly change position, and on the other hand because of the circulation gases in this area.

In the case of a shaft furnace having a square section whose side measures 3.50 meters, and whose coke production is approximately 350 tonnes per day, electrodes arranged as shown in FIG. 4 are used. ie about 3.5 m apart.

These electrodes are supplied with a voltage which is preferably continuous and regulated for a power kept constant and give off a total power of 1,500 kw for example. This power is distributed between the various levels of electrodes so as to obtain the desired heating law.

This thermal power of electrical origin makes it possible to increase the temperature of the solid materials from 800 to 1,050 ° C. approximately in zone C of electric heating.

Full coking of coal occurs in this zone, the coke at 1000 ° C entering the lower exchanger through the upper part thereof. The gases circulating in the furnace heat up in contact with the coke and the coal being coked in the electric heating zone and their flow rate increases by volatilization of a part of the products contained in the coal balls.

The gases injected at the base of the furnace through line 18 make it possible to cool the coke produced from the outlet temperature from the middle zone, that is to say a temperature close to 1000 ° C. to a temperature close to 150 ° vs.

For the oven mentioned above, about 1000 m ³ of gas per tonne of solid matter circulating in the oven is injected at the base of the oven, which ensures balanced exchanges at the bottom and at the top of the oven.

The gas produced in the oven is recovered at the top, dusted and tared before being introduced into the oven through line 18.

In addition, an excess quantity of combustible gas is produced depending on the nature of the charcoals used, for example 500 m ³ per tonne of coke produced. The calorific value of this gas is around 18810J / m ³ (4500 calories per m ³ ),

Electric power consumption is around 150 kWh per tonne of coke produced.

Coking therefore occurs at a relatively moderate temperature and generally a little lower than the coking temperature in conventional coke ovens.

The setting of the electric heating according to the flows of solids and gases may vary somewhat but to obtain a good thermal efficiency and optimal coking conditions, the maximum temperature of the bed of solids in the electric heating zone should not exceed a value between 950 and 1150 ° C.

By distributing the electric power on several levels, we obtain a progressive heating and adapted to all types of coal, which would not be the case if we used a single set of electrodes allowing a passage of current in a single plane horizontal.

The balance concerning the energy consumption in the process according to the invention is entirely favorable if it is compared to what it is for conventional coke ovens.

Indeed, such coke ovens consume approximately 800 therms per tonne of coke produced while the consumption of electrical energy in the shaft furnace according to the invention would correspond approximately to a consumption of 150 kWh per tonne of coke produced.

It can therefore be seen that the main advantages of the process according to the invention are to allow a reduction in the energy consumption for the production of coke and the recovery of a gas with high calorific value which can be produced continuously.

In addition, the thermal adjustment of the process can be carried out in a simple manner, so that the exchanges between the gases and the solid materials are balanced and that the calorific contribution by electrical energy is used practically only to compensate for the heat losses of the furnace and the heat of endothermic reactions that can occur in the oven. The flexibility of this type of oven makes it possible to modulate the consumption of electric current with load shedding during peak hours.

Finally, the complete tightness of the oven makes it possible to avoid any gas leaks, which avoids any pollution of the environment.

It is obvious that the invention is not limited to the process and to the device described in a nonlimiting manner, but that they include all variants thereof.

Thus, depending on the operating conditions and the quality of the coals used, the thermal adjustment conditions may vary within the intervals mentioned.

The shape of the straight section of the oven is not necessarily square or rectangular but can also be circular.

The shape of the electrodes, their arrangement and their spacing can be variable depending on the shape of the oven and the desired heating conditions.

The gases recovered at the top of the furnace undergo treatments which depend on their end use.

Claims (12)

1. Process for producing moulded coke in a shaft oven with a vertical axis (1), which is supplied in its upper part (3) with a burden of coal for coking in the form of ovoids, forming a movable bed descending in the shaft (1) in counter flow to gas circulating from the bottom upwards and passing successively from the top downwards through a preheating zone, a coking zone and a cooling zone, the rising stream of gas being formed by the gases released by the coal during its heating and coking and by some of the gases recovered in the upper part of the oven and recycled in the lower part after washing and dust extraction, heat being supplied by circulation of electrical current through the bed of solid materials between electrodes (8) located on two opposite sides of the wall (2) of the oven (1), characterized in that the electrical heating is carried out in a controlled way over a specific height in the middle part (C) of the oven (1), electric currents, the intensities of which can be regulated, being passed through the burden in several staggered horizontal planes, and in that, by adjustment of the circulation of the gases and of the electrical power distributed to the various levels of electrodes according to the heat requirements and the electrical resistance of the burden, a progressive and uniform heating of the latter is controlled during its descent in the oven according to a law of heating selected as a function of the type of coal, to preserve the shape of the ovoids, in such a way that the temperature of the bed of solid material is between 600°C and 850°C at the entrance of the middle zone (C) of electrical heating and that coking is carried out completely in this zone (C) at a temperature remaining between 950°C and 1150°C, the coke ovoids subsequently being cooled in the lower part of the oven (1).

2. Process for producing moulded coke according to Claim 1, characterized in that, in the preheating zone (P), an adjustable flow rate of the rising stream of hot gases is derived so as to control a progressive increase in temperature of the materials at a speed selected as a function of the type of coal, to prevent the fusion or caking of the ovoids.

3. Process for producing moulded coke according to one of Claims 1 and 2, characterized in that the electrical resistance of the burden is increased after it leaves the coking zone (C), by producing a decompression of the burden in the cooling zone (R), which is capable of increasing the contact resistances between the ovoids.

4. Process for producing moulded coke according to Claim 1, characterized in that the coal ovoids introduced into the upper part (3) of the oven (1) are mixed with particles of small sized coke or any other product in the form of electrically conductive grains resistant to the temperatures reached in the oven and of dimensions less than those of the ovoids, the said grains being distributed uniformly in the gaps between the coal ovoids and assisting the passage of electrical current through the middle coking zone (2), making the heating uniform and facilitating the electrical adjustment of the power consumption.

5. Process for producing moulded coke according to Claim 4, characterized in that the size of the particles of small sized coke is between 5 and 15 mm.

6. Shaft oven for producing coke by means of the process according to one of Claims 1 to 5, consisting of a shaft (1) of vertical axis having, in its upper part, a throat (3) for introducing a burden of coal in the form of ovoids and gas recovery means and, in its lower part, a component for discharging the solid materials and gas injection means, and equipped in its middle part with electrodes (8) making it possible to pass an electric current through the burden, characterized in that it possesses at least two pairs of electrodes (8) located one below the other in two horizontal planes (A, B) spaced from one another, and means of individually adjusting the electrical supply to each pair of electrodes.

7. Shaft oven according to Claim 6, characterized in that it is associated with elements for assisting the passage of electric current and constituted by particles of a conductive and resistant product, such as small sized coke having dimensionsless than those of the ovoids and distributed uniformly between these.

8. Shaft oven according to Claim 6, characterized in that it has at least one pair of electrodes (8) mounted so as to be horizontally movable and each connected to means of alternate advance and retraction (81, 82), each electrode (8) exerting a constant thrust on the burden as result of a progressive advance towards the interior of the oven (1), up to a specific position, from which a rapid retraction is controlled, this being accompanied by a descent of the burden, and so on and so forth.

9. Shaft oven according to Claim 6, characterized in that it possesses a first set of electrodes (10) located at the upper level (A) and suspended on vertical conductors (12), the position of which is adjustable according to the height of the oven, and at least one second set of electrodes (8) extending horizontally at a lower level (B) through the lateral wall of the oven (1).

10. Shaft oven according to Claim 9, characterized in that the vertical conductors allowing the suspension and displacement of the movable electrodes (10) are constituted by tubes (12) surrounded with refractory material and connected in their upper part to a device for blowing in cooling air for the electrodes.

11. Shaft oven according to one of Claims 6 to 10, characterized in that it possesses a meansfor decompressing the burden at the outlet of the coking zone (C), consisting of a widening of the cross-section of the oven in the cooling zone (R) below the middle coking zone (C).

12. Shaft oven according to Claim 11, characterized in that it is equipped with horizontal bars passing through the burden in the cooling zone (R).

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