WO2025031944A1 - Regenerative parallel-flow vertical shaft furnace - Google Patents

Abstract

The invention relates to a regenerative parallel-flow vertical shaft furnace comprising at least two shafts (1, 2) interconnected by a gas transfer channel (3), each of the shafts comprising, in the active or inactive position, a charging inlet (5) for charging a carbonate mineral rock at the top of the shaft, means for firing the rock, an outlet (8) for discharging the decarbonated produced calcined material at the bottom of the shaft, a cooling air inlet (7) at the bottom of the shaft for countercurrent cooling of the produced calcined material, and a central collecting element (21) that has, at its upper end, a collection opening (24) for collecting the cooling air heated by the calcined material and, at its lower end, an extraction outlet (22), each shaft further comprising a hat-shaped protective element (25) that is fixed in the shaft in a position independent of the central collecting element (21), which element covers and surrounds the upper end thereof to a level lower than the collection opening (24) so as to leave, between this upper end and the hat-shaped element (25), a free passage for collecting the heated cooling air through the collection opening (24).

Description

Regenerative parallel flow vertical straight furnace

The present invention relates to a regenerative parallel flow vertical straight furnace for the calcination of carbonate mineral rock.

The vertical parallel flow regenerative straight kiln or regenerative lime kiln called "PFRK" (Parallel Flow Regenerative Kiln) has an energy efficiency of 85% to 90%; this is the highest in the lime sector, or even in the entire energy-intensive industry sector: cement, steel, glass, etc. Around 60% of lime in Europe is produced in this type of kiln. This proportion is set to increase in Europe and worldwide, taking into account the roadmaps for the energy and ecological transition.

The classic “PFRK” furnace is a straight furnace with a double vertical tank where a fuel is injected alternately into one tank then into another for approximately 10 to 15’ with a stop period between cycles of approximately T to 2’ to reverse the air and fuel circuits. This is the “inversion” period. The two tanks are connected by a connecting flue. When one tank is in combustion (firing mode), the hot combustion fumes pass through the connecting flue (transfer path for gas) and give up part of their heat to the mineral rock to be calcined to preheat it in the other tank called in regeneration or preheating mode. The tanks of the PFRK furnace are either cylindrical or rectangular. In some cases, there are three tanks, two in preheating and one in firing.

For the purposes of the present invention, carbonate mineral rock is understood to mean in particular calcined limestone, dolomitic rock and/or magnesite. respectively in quicklime, quickdolomite and/or magnesia. The calcination equation for limestone into lime is as follows:

CaCCh (solid) + heat -> CaO (solid) + CO2 (gas)

It is a reversible endothermic reaction and the lime recombines with the CO2 at the first opportunity below 900°C, with equilibrium and kinetics more or less rapid depending on the temperature and the ambient concentration of CO2.

During this process, the initial limestone or dolomite rock therefore releases a significant volume of CO2 during its calcination into lime or dolomite. In addition, to achieve this calcination, high temperatures must be reached and to do this, fuels, often fossil fuels, are commonly burned, which in turn causes a significant release of CO2. Overall, calcination processes have the disadvantage of actively contributing to the increase in the greenhouse effect.

This very common calcination process also has the disadvantage of providing for combustion of fuel in the presence of air and cooling of the calcined product by air. This results in the release at the top of the furnace of a gaseous effluent having a high level of diatomic nitrogen, and a comparatively low level of CO2 (volume concentration of the order of 20% to 30% on dry gas), which is expensive to capture due to the high presence of dinitrogen coming from the air used. Attempts have already been made to extract from the vat in firing mode the cooling air that has been heated in contact with the decarbonated calcined material produced. In the case of circular vats, a central tubular collector element has been provided that stands vertically in the bottom of the vat and has at its top several collection openings. This central collector element generally communicates with a draft element external to the vat so as to allow, at a level below the connecting flue, an extraction from the furnace of heated cooling air (see WO2022/1 1 1817 and WO2022/2291 19).

It should be noted that this central collector element must be able to withstand the pressure of a bed of material of at least 12 m, regularly 20 m high and that it must therefore have a very robust structure. It must also withstand possible force imbalances due to a non-uniform descent of this bed of material, with the possibility of local blockages. The central collector element must therefore inevitably have minimal dimensions, which represents a major drawback, in particular for small furnaces that produce less than 400 tonnes per day, as is the case for most PFRK furnaces in Europe. Indeed, the presence of a bulky central collector element has the consequence of prejudicing the downward flow of the calcined material produced. Furthermore, the lower part of the circular tanks of these small conventional furnaces, in which the cooling of the calcined material takes place, usually has the shape of an inverted truncated cone, that is to say a truncated cone whose upper base has a larger area than the base. lower. In this configuration, the presence of a bulky central collector element is quite detrimental given the narrowness of the lower part of the tank at its lower level.

Furthermore, these central collector elements known from the prior art have the disadvantage of not being able to effectively prevent the penetration of fines from the calcined material produced through their collection openings.

In order to solve this particular problem, it has already been provided that the central collector element carries, at its top, a hat-shaped element which thus protects the collection opening from unwanted penetration of fines (see DE102023102447). Unfortunately, the addition of this element at the top of the central collector element further increases the weight that it must support in the lower part of the tank concerned and therefore requires the presence of an extremely robust and therefore even more bulky central collector element. Such a structure is not adaptable in an existing small-sized furnace where the lower part of the tank narrows more and more towards the bottom.

The present invention aims to significantly reduce the structural drawbacks and risks presented by the central collector elements of the state of the art, while retaining their functional model and therefore the efficiency of the extraction of the heated cooling air in the center of the circular tank of the oven which is in cooking mode. It is also desirable that these central collector elements are adaptable in existing small-sized ovens. To solve these problems, according to the invention, there is provided a vertical straight furnace with regenerative parallel flows, comprising at least two tanks interconnected by a gas transfer path, each of said tanks comprising, in the in-service or out-of-service position,

- at least one loading inlet of a carbonate mineral rock, at the top of the tank,

- at a level above said gas transfer path, means for cooking said carbonated mineral rock during descent from said at least one loading inlet intended to produce a charge of decarbonated calcined material,

- at least one discharge outlet for the decarbonated calcined material produced, at the bottom of the tank,

- at least one gas effluent discharge pipe at the top of the tank,

- at a level below said gas transfer path, at least one cooling air inlet at the bottom of this lower part of the tank for counter-current cooling of the decarbonated calcined material produced, and a central tubular collector element having, at its upper end, at least one collection opening through which cooling air heated by the decarbonated calcined material is collected inside the central tubular collector element and, at its lower end, at least one extraction outlet allowing collection outside the furnace of this collected heated cooling air, in which each tank further comprises a protective element in the form of a hat which is fixed in the tank in an independent position of the aforementioned central tubular collector element by covering and surrounding the upper end thereof up to a level lower than said at least one collection opening, so as to leave, between this upper end and the cap, a free passage for collection of the heated cooling air through said at least one collection opening.

In such a furnace, the load of the descending bed of material is supported solely by the hat-shaped protective element. This arrangement relieves the central tubular collector element, which can then be made in a lighter and therefore less bulky form in the narrowest area of the lower part of the tank. Advantageously, it can have the form of a simple cylindrical tube. When the furnace has tanks whose lower part is in the shape of an inverted truncated cone, the hat-shaped protective element is located in the widest area of this lower part, thus impairing the flow of material downwards as little as possible.

In addition to its mechanical function, the hat-shaped protective element creates a vacuum below it, through which the heated cooling air can pass freely inside the central collector element to exit the furnace at the bottom and not mix with the gas stream from the calcination that exits the furnace at the top. This arrangement is therefore particularly robust, simple and particularly adaptable in a small furnace where the air outlet remains proportionally large.

In a conventional manner, the furnace according to the invention comprises a system for reversing the operation of the tanks, arranged so that each tank operates, in production mode, alternately in cooking mode and in preheating mode, one tank being in cooking mode for a predetermined period of time while at least one other tank is in preheating mode, and vice versa, this inversion system controlling for this purpose said positions in service and out of service.

During the inversion time, the inversion system synchronously controls all the changes necessary to switch from one mode to the other, for example by opening the carbonate mineral rock loading inlet in the tank when it is in cooking mode and closing it when it switches to preheating mode. The inversion system therefore controls not only numerous valves and flaps, but also the operation of the loading and unloading equipment or that of various suction, pumping or injection elements.

Depending on the case, said at least one cooling air introduction inlet is thus controlled in the operating position in all the oven tanks or only in the tank in cooking mode.

By production mode, it is meant that the furnace is in its normal operation during which it continuously produces calcined material. This mode therefore does not concern the phases of starting the furnace, stopping it or maintenance in the event of a malfunction.

According to one embodiment of the invention, the tubular central collector element has, at its upper end, a single opening oriented axially upwards and an upper part of the protective element in the form of a hat is arranged above and at a distance from this single opening, flaring downwards to a cylindrical lower part which extends coaxially and at a distance from the aforementioned upper end of the tubular central collector element. By the downwardly flared shape of its upper part, the protective element facilitates the flow of the decarbonated calcined material away from the tubular central collector element, which makes it possible to avoid blockages of said collection opening as much as possible. Advantageously, the protective element is conical in its upper part and cylindrical in its lower part.

According to an advantageous embodiment of the invention, several support spacers, preferably 3 or 4 spacers, arranged between the outer wall of the tank and the hat-shaped protective element support the latter above the central tubular collector element.

Preferably, the hat-shaped protective element is traversed by at least one cooling circuit which is supplied with cold cooling fluid, for example cold air, from at least one inlet duct traversing at least one said support spacer, a heated cooling fluid being evacuated from said at least one cooling circuit by at least one outlet duct traversing at least one said support spacer. There are no ducts which connect the tubular central collector element to the hat-shaped protective element which is particularly favorable for the passage of the heated cooling air. On the other hand the cooling fluid is supplied via the spacers which are cooled in turn. This is a simple and robust system to construct and manage, in particular in a small furnace. dimension where the air outlet section remains proportionally large.

According to one embodiment of the invention, the tubular central collector element is, in a lower part, fixed to the external wall of the tank by several beams, preferably four beams, arranged horizontally. Advantageously, the hat-shaped protective element is supported centrally above the upper end of the tubular central collector element by vertical uprights supported by said horizontal beams.

Preferably, in this case, the hat-shaped protective element is traversed by at least one other cooling circuit which is supplied with cold cooling fluid, for example cold air, from at least one supply duct traversing at least one aforementioned beam and one aforementioned upright, a heated cooling fluid being evacuated from said at least one other cooling circuit by at least one evacuation duct traversing at least one aforementioned upright and one aforementioned beam.

Advantageously, the tubular central collector element is traversed by at least one refrigeration fluid circuit which is supplied with cold refrigeration fluid, for example cold air, from outside the furnace, a heated refrigeration fluid being evacuated from this circuit to the outside of the furnace. The tubular central collector element and the hat-shaped protective element are thus cooled by independent circuits. Each of these circuits can be short, which increases their efficiency compared to a circuit which should be used for cooling both elements. Indeed, in the latter case, the cooling of the element in hat shape occurs unfavorably at the end of the circuit, while it is the element which is subjected to the highest thermal conditions, of the order of 900 to 1000°C, or even up to 1200°C.

According to one embodiment of the invention, each tank is further provided with an annular collector which communicates with it via several doors located on the periphery of the tank and with an external extraction device for extracting heated cooling air from the furnace. In this way, the efficiency of the extraction is increased, it takes place both in the center of the tank and on the periphery thereof. The risk of an escape of fines from the decarbonated calcined material towards said at least one collection opening of the central collector element, with potential blockage thereof, is thus greatly reduced.

The above-mentioned means of cooking the carbonated mineral rock during descent are elements for injecting a fuel and an oxidant into the tank in cooking mode which, through combustion, make it possible to reach a calcination temperature of said rock. In a conventional furnace, the fuel may commonly be a fluid fuel, such as natural gas, or a solid fuel, such as coal or lignite powder, and the oxidant may be air. It is also very advantageous to envisage an oxidant formed from a mixture of CO2 and dioxygen.

As means of cooking the carbonate mineral rock during descent, it is also possible to envisage elements for injecting into the tank in cooking mode a gas or gas mixture brought, outside this tank, to a calcination temperature of said rock. It is possible to envisage for this fair electrical devices, for example involving plasma torches.

As can be seen, the furnace according to the invention has only a few structural modifications made to the interior of the lower part of the furnace vats. Existing and/or new furnaces can therefore be easily adapted to implement a calcination process during which the introduced cooling air can be extracted from the vats in a particularly efficient manner, without causing extreme deterioration in the flow and discharge of the calcined material produced.

Further details and features of the oven according to the invention are indicated in the appended claims.

Other features of the invention will also emerge from the description given below, without limitation and with reference to the attached drawings.

Figure 1 schematically represents a PFRK oven according to the invention.

Figures 2 and 3 show partially broken views of the lower part in the shape of an inverted truncated cone of a tank of a PFRK furnace according to the invention.

Figure 4 shows a partially broken view of the lower part in the shape of an inverted truncated cone of a tank of another PFRK furnace according to the invention.

In the figures, identical or similar elements bear the same references. Conventionally, the tank illustrated on the left in Figure 1 is in cooking mode and the tank shown on the right in preheating mode. In order not to clutter the drawings with standard elements, such as loading or unloading equipment, they are not shown or are shown very schematically.

As can be seen in Figure 1, the PFRK furnace illustrated is a straight double-shaft furnace 1, 2 where the fuel is injected alternately into one tank 1 and then into another 2 for about 12’ with a stopping period between cycles of 30 seconds to 2’ to reverse the circuits. This is the “inversion” period. The two tanks have a circular section and are provided with peripheral channels 13, 13’ which are interconnected by a connecting flue 3. The tanks are divided in height into three zones, the preheating zone A where the carbonate rock is preheated before calcination, the calcination zone B where the carbonate rock is fired and the cooling zone C where the calcined material is cooled. In this last zone, the tank with circular section here has a part in the shape of an inverted truncated cone 38.

In the illustrated example, when a tank is in cooking mode, here the tank 1, a fuel supply device in the form of lances 4 injects a fuel 9 into the tank, which, in this case, is natural gas. The carbonate rock, loaded at the top of the tank by an inlet 5 in the open position, gradually descends into it. An oxidant is introduced at the top of the tank by a supply opening 6, which allows combustion of the fuel at the outlet of the lances 4 and decarbonation of the carbonate rock into calcined material 10. The gas stream 1 1 formed by the combustion and decarbonation descends in co-current with the calcined material and, via the peripheral channel 13, passes into the connecting flue 3. Cooling air is, through a supply duct 7, introduced at the bottom of the tank, in counter-current to the calcined material, to cool it. The calcined material is discharged through the outlet 8 into an unloading equipment 26.

When a tank is in preheating mode, here tank 2, the fuel supply device is closed and the lances 4 are therefore out of service. The same applies to the inlet 5 for the carbonate rock and the opening 6 for the supply of the oxidant. On the other hand, the supply duct 7 for the cooling air and the outlet 8 for the calcined material remain in the open position. The gas stream 1 1 , coming from the connecting flue 3, reaches the tank 2 via the peripheral channel 13'. This gas stream 1 1 progresses to the top of the tank where it is evacuated from the furnace by an evacuation duct 14 and transferred to a chimney 15, advantageously passing through a draft fan and a filtration unit not shown. In the tank in cooking mode 1 , this evacuation duct 14 is closed.

The furnace comprises a schematically represented reversing system 12 which controls the operation of the tanks in a synchronized manner, during the reversal time of the tanks, and this directly or remotely. It controls the commissioning or decommissioning of all the elements of the furnace so that, in production mode, each tank operates alternately in cooking mode and in preheating mode. In some cases there are three tanks, two for preheating and one for combustion.

In the furnace illustrated in FIG. 1, a separation member 17 is provided on the discharge duct 14, capable of taking a portion of the gaseous effluent discharged from the furnace and introducing it into a recirculation circuit 18. In this circuit, the portion of gaseous effluent taken is advantageously treated in a treatment unit 19, where it can for example be filtered, cooled and/or dried. Dioxygen is supplied to the recirculation circuit 18 via the supply duct 20. This circuit 18 then conducts the oxidizing mixture formed from the recirculated fraction of gaseous effluent and O2 concentrated at the top of each of the tanks to the supply opening 6. In certain cases, it is also possible to supply this oxidizing mixture to the flue 3 or to the peripheral channels 13, 13', as shown in FIG. 1.

The operation of the PFRK furnace of Figure 1 is as follows. The separation member 17 is in continuous operation, as are the treatment unit 19 and the oxygen supply 20. As already seen, the inversion system 12 closes the exhaust duct 14 at the top of the tank in cooking mode. On the other hand, it opens, at the top of this tank, the supply opening 6 to allow the introduction of the oxidizing mixture, while it is closed at the top of the tank in preheating mode.

The oven illustrated in Figure 1 comprises according to the invention, at the bottom of each tank, a central tubular collector element 21 having, at its lower end, at least one extraction outlet 22 and, at its upper end located at a level lower than the flue 3, a collection opening 24 oriented axially upwards. Through this opening, the cooling air heated in contact with the decarbonated calcined material is collected inside the central tubular collector element 21, so as to allow its extraction from the furnace. In the example illustrated, this hot air extracted from the furnace is transferred, using a draft fan 23, to a heat exchanger 16 mounted on the recirculation circuit 18, so as to preheat the portion taken from the gaseous effluent leaving the furnace, preferably before mixing it with concentrated dioxygen.

Each tank further comprises a hat-shaped protective element 25 which, fixed in the tank in a position independent of the tubular central collector element 21, covers the upper end thereof by surrounding it up to a level below the collection opening 24. In the illustrated example an upper part of the hat-shaped protective element 25 is arranged above and at a distance from the collection opening 24, widening downwards in a conical manner to a cylindrical lower part which extends coaxially and at a distance from the upper end of the tubular central collector element 21. This arrangement thus leaves, between the upper end of the collector element 21 and the hat 25, a free passage for collecting the heated cooling air through the opening 24 of the tubular central collector element.

As shown in Figures 1 to 3, the hat-shaped protective element 25 is supported centrally in the tank by several support spacers 27, here 4 spacers. As can be seen in particular from Figure 2, the lower part in the form of an inverted truncated cone 38 is, in this example, formed of two successive truncated cone stages separated by a shoulder of the outer wall 28 on which these spacers are fixed, which makes it possible to produce with the cap 25 a very robust structure which is capable of receiving the load of the carbonate rock and the calcined material during descent. As is particularly apparent from FIG. 3, the tubular central collector element 21 can thus be designed in the form of a lighter structure which does not become cumbersome for the descent of the calcined material which takes place between the spacers 27. In the example illustrated, the central collector element 21 is fixed in the tank by four beams 34 arranged horizontally in a cross at the bottom of the tank.

Given the high temperature of the calcined material during descent, it is advantageous to cool the hat-shaped covering element 25 by a schematically illustrated cooling circuit 29, in which a cooling fluid, for example air, circulates (see in particular FIG. 2). In the illustrated example, this circuit is supplied with cold cooling fluid along the arrow F1 from an inlet duct 30 running through each of the support spacers 27. The cooling fluid heated during its passage in the circuit 29 is discharged from the latter along the arrow F2 by an outlet duct 31 running through each support spacer 27. The hat-shaped protective element, which is in contact with materials having a very high temperature, is thus cooled by a short, particularly effective cooling circuit.

Advantageously, the spacers have an upward covering in the form of a double-sloped roof 32 so as to facilitate the descent of the calcined material. Preferably, in the refractory, the spacer has an upper wall having a substantially flat shape. Indeed, a flat shape of the upper wall of the spacer at the refractory makes it possible to better support the weight of the furnace. Preferably, the spacer has an upper wall having a substantially flat shape when the spacer connects to the refractory at a pillar.

As can be seen in particular from FIG. 3, the cooling air heated in contact with the calcined material during descent is collected in the passage left free between the cap 25 and the tubular collector element 21, and this by following the path F3. This air has a very high temperature and it is therefore preferable to provide, in order to protect the tubular wall of the collector element 21, a refrigeration circuit 33 which runs through this tubular wall as shown schematically. This circuit 33 is supplied with refrigeration fluid, for example cold air, from outside the tank, then the heated fluid is evacuated therefrom.

As has just been seen above, the arrangement, provided according to the invention, between the hat-shaped protective element 25 and the central collector element 21, makes it possible to collect the cooling air which is heated by contact with the calcined material and which rises in the center of the tank. As illustrated in particular in FIG. 3, the tank can also be provided, at a level below the connecting flue 3 and the peripheral channels 13 and 13', with a collector ring 35 which communicates with the outside with a draw-off element, for example the draft fan 23, and opens into the tank through several peripheral doors 36 so as to allow a extraction from the furnace of the heated cooling air which rises around the periphery of the tank.

It is conceivable that the hat-shaped protective element 25 is, in another manner, supported in the tank independently of the tubular collector element 21. For example, as shown in FIG. 4, the hat-shaped protective element 25 is supported centrally above the upper end of the tubular central collector element 21 by vertical uprights 37 supported by the horizontal beams 34.

In this case, the hat-shaped protective element is traversed by at least one cooling circuit 29 which is supplied with cold fluid, for example cold air, from at least one supply duct traversing, according to arrow F4, a beam 34 and a vertical upright 37. The heated cooling fluid is evacuated from the cooling circuit by at least one evacuation duct traversing a vertical upright 37 and a beam 34, according to arrow F5.

It should be understood that the oven according to the invention is in no way limited to the examples described above and that many modifications can be made thereto without departing from the scope of the claims which follow.

For example, it may be provided that the inlet opening 6 for the oxidant can be used, in a shared manner, as a gaseous effluent outlet depending on whether the tank is used in cooking mode or in preheating mode. In cooking mode, the opening 6 is connected to the recirculation duct 18 and in preheating mode to the evacuation duct 14. It is also possible to consider the presence of a CO2 buffer tank in parallel with the furnace, to allow CO2 recycling during the inversion period where the furnace is stopped for a short time to reverse the operation of the tanks, to allow a supply from the downstream of the installation (concentration unit, CO2 purification for example) without having to stop the gas flow from the furnace, and to compensate for the various small daily shutdowns of the furnace due to faults, small breakdowns, by ensuring a supply from the downstream during these short shutdowns.

Claims

1. Regenerative parallel flow vertical straight furnace, comprising at least two tanks (1, 2) interconnected by a gas transfer path (3), each of said tanks comprising, in the in-service or out-of-service position, - at least one loading inlet (5) of a carbonate mineral rock, at the top of the tank, - at a level above said gas transfer path (3), means for cooking said carbonated mineral rock during descent from said at least one loading inlet (5), intended to produce a charge of decarbonated calcined material, - at least one discharge outlet (8) for the decarbonated calcined material produced, at the bottom of the tank, - at least one gaseous effluent discharge conduit (14) at the top of the tank, and - at a level below said gas transfer path (3), at least one cooling air inlet (7) at the bottom of the tank for counter-current cooling of the decarbonated calcined material produced, and a central tubular collector element (21) having, at its upper end, at least one collection opening (24) through which cooling air heated by the decarbonated calcined material is collected inside the central tubular collector element and, at its lower end, at least one extraction outlet (22) allowing collection outside the furnace of this collected heated cooling air, characterized in that each tank further comprises a cap-shaped protective element (25) which is fixed in the tank in a position independent of the aforementioned tubular central collector element (21), covering and surrounding the upper end thereof up to a level below said at least one collection opening (24), so as to leave, between this upper end and the cap (25), a free passage for collection of the heated cooling air through said at least one collection opening (24). 2. Oven according to claim 1, characterized in that, at its upper end, the tubular central collector element (21) has a single collection opening (24) oriented axially upwards and in that an upper part of the hat-shaped protective element (25) is arranged above and at a distance from this single opening, widening downwards to a cylindrical lower part which extends coaxially and at a distance from the aforementioned upper end of the tubular central collector element (21). 3. Oven according to either of claims 1 and 2, characterized in that each tank comprises an outer wall (28) from which several support spacers (27), preferably 3 or 4 spacers, centrally support the hat-shaped protective element (25) above the tubular central collector element (21). 4. Oven according to claim 3, characterized in that the hat-shaped protective element (25) is traversed by at least one cooling circuit (29) which is supplied with cold cooling fluid from at least at least one inlet duct (30) running through at least one said support spacer (27), a heated cooling fluid being discharged from said at least one cooling circuit (29) by at least one outlet duct (31) running through at least one said support spacer (27). 5. Oven according to any one of claims 1 to 4, characterized in that each tank comprises an external wall (28) and in that the central tubular collector element (21) is, in a lower part, fixed to this wall by several beams (34), preferably four beams, arranged horizontally. 6. Oven according to one of claims 1 and 2, characterized in that each tank comprises an external wall (28), in that the tubular central collector element (21) is, in a lower part, fixed to this wall by several beams (34), preferably four beams, arranged horizontally and in that the hat-shaped protective element (25) is supported centrally above the upper end of the tubular central collector element (21) by vertical uprights (37) supported by said horizontal beams (34). 7. Oven according to claim 6, characterized in that the hat-shaped protective element (25) is traversed by at least one cooling circuit (29) which is supplied with cold cooling fluid from at least one supply conduit running through at least one said beam (34) and one said upright (37), a heated cooling fluid being evacuated from said at least one cooling circuit (29) by at least one conduit evacuation running through at least one aforementioned upright (37) and one aforementioned beam (34). 8. Oven according to any one of claims 1 to 7, characterized in that the central tubular collector element (21) is traversed by at least one refrigeration circuit (33) which is supplied with cold refrigeration fluid from outside the oven, a heated refrigeration fluid being evacuated from this circuit to the outside of the oven. 9. Oven according to any one of claims 1 to 8, characterized in that each tank is further provided with an annular collector (35) which communicates with it via several doors (36) located on the periphery of the tank and with an external extraction device for extracting heated cooling air from the oven. 10. Oven according to any one of claims 1 to 9, characterized in that the tubular central collector element (21) has the shape of a cylindrical tube. 1 1. Oven according to any one of claims 1 to 10, characterized in that at the level below said gas transfer path (3), each tank has a lower part (38) in the shape of an inverted truncated cone. 12. Oven according to any one of claims 1 to 11, characterized in that said means for cooking the carbonated mineral rock during descent are injection elements (4, 6) into the tank in cooking mode of a fuel and an oxidant which by combustion make it possible to reach a calcination temperature of said rock. 13. Oven according to any one of claims 1 to 11, characterized in that said means for cooking the rock carbonated mineral during descent are elements of injection into the tank in cooking mode of a gas or gas mixture brought, outside this tank, to a calcination temperature of said rock.