GB2034755A

GB2034755A - Reduction of Metal Oxides

Info

Publication number: GB2034755A
Application number: GB7932022A
Authority: GB
Original assignee: Danieli and C Officine Meccaniche SpA
Current assignee: Danieli and C Officine Meccaniche SpA
Priority date: 1978-09-19
Filing date: 1979-09-14
Publication date: 1980-06-11
Also published as: AU5034079A; DD146190A5; ES484139A1; IT1109109B; SE7906778L; ZA794281B; DE2935466A1; FR2436822A1; IT7869153A0; FR2436822B3

Abstract

Process for the reduction of metal oxide(s), preferably in the form of pellets, by heating such in the presence of a solid reducing agent, e.g. pit-coal, in a retort (S) and causing the gaseous reaction product(s) to move at least partially in co-current flow with the direction of flow of the charge (K). An apparatus for carrying out the process comprising at least one retort (S) which has an inlet (25, 26) at the top for admission of the charge (K), an outlet (36, 37) at the bottom of the retort (S) for discharge of the spent charge (K) and a gas outlet (33, 20), separate from the outlet (36, 37), at the bottom of the retort for discharge of gas(es). <IMAGE>

Description

SPECIFICATION A Process and Apparatus for the Reduction of Metal Oxide(s) The present invention relates to an improvement in a process for the reduction, with a solid reducing agent, of metal oxides, preferably ores and materials prepared as tablets or pastilles commonly called "pellets".

A great number of processes concerning the deoxidization of minerals and pellets essentially formed by metal oxides and particularly iron oxides, is known to metallurgists. Various solutions suggest operative techniques wherein these oxides are treated at a high temperature with reducing agents such as carbon monoxide, hydrogen (gaseous reducing agents) or carbon (solid reducing material).

The common base of all the known processes is the production of an atmosphere comprising suitable mixtures of these gases (CO and H2) obtained from the hydrocarbons of various composition or from coal, and the treatment of the oxides with these gas mixtures at the highest possible temperature compatible with the softening point of the oxides or the ashes or gangue combined with the oxides. This is in order to avoid the agglomeration of the charge which prevents its extraction. Among the processes having an advantageous industrial application there are comprised the ones defined as those "with solid deoxidizer" (coal) due to their relative simplicity, to the great availability of coal in comparison with other energy resources as well as to the particular reducing effectiveness of carbon brought at a high temperature when in direct contact with the oxides to be reduced.

In the above described processes, the reducing action is therefore effected in two ways: directly, by intimate contact of the carbon and the oxygen linked to the oxides to be treated, and indirectly between the carbon oxide gas formed in the direct reducing reaction and the other oxygen contained in the oxides. As, in these processes, an excess of coal is always present and the temperature is always near 1 000o1 2000C, the carbon dioxide forming from the reaction of the carbon monoxide (indirect reduction) will again split into carbon monoxide according to the known reaction scheme CO2+Co2CO. It follows that with the indirect reaction, the generation of other carbon monoxide will also proceed.

Of course, the carbon dioxide which may form from the direct reduction reaction (between the carbon and the oxide oxygen) will also contribute to the formation of a carbon monoxide reducing gas, as already mentioned in the preceding paragraph.

The reduction treatment proceeding in a known vertical retort furnace will be better understood from Figure 1 of the accompanying drawings which shows in a vertical section such a known type of furnace. Reference numeral 1 indicates the inflow of the charge formed by a mixture of minerals or coal "pellets" and, if needed, desulphurizer. In the zone indicated by 2, there is effected the drying of the charge with formation of vapour, the preheating of the same charge and the distillation of the volatile parts contained, or still contained, in the coal. Further, within said zone, the gas produced by the reduction reactions occurring in the remaining of the retort, passes through the charge.

In the zone indicated by 3, there is effected the real reduction by the direct action of the carbon and the indirect action of the carbon monoxide.

Unless, through special contrivances, hydrogen or hydrogen-containing gas has been introduced through a duct 13, along the whole retort, in zones 4 and 3, there will be present only carbon monoxide gas and the carbon oxide level which will be allowed by the kinetics of the reaction CO2+C2CO. It is useful to note at that moment, that in said operative conditions, at the retort base, the gas will be in a nearly stationary state and its analysis will depend oh the reactivity of the oxides under treatment while its pressure will be determined by the retort height and geometry, by the granulometry of the charge and, obviously, by the gas quantity which must be expelled from the top as a function of the quantity as it is generated in the various retort sections.

Therefore, the reaction gas motion will be directed upwardly in countenflow with respect to the descending motion of the charge, and the lapping speed of same will increase when proceeding from down to up.

From the preceding considerations, it follows that the oxides will be as such at the throat of the retort and in the descending motion they will transfer the oxygen they contain to the solid reducer and the reaction gases which act as carriers between the interior of the minerals or "pellets" and the reducing carbon which is always present in the charge up to the retort base; in other words, the oxides will be in intimate contact with a considerable carbon charge and an appreciable gaseous current incoming from the retort in the initial phase of the treatment (high zone) and, conversely, they will be in the presence of a small quantity of carbon and a nearly stationary gaseous phase, at the base of the retort.

It must be further observed that the gas quantities involved in the process are relatively small and that the contribution to the preheating of the charge in the high section of the retort, is quantitatively negligible.

Following the examination of the known structural arrangement of Figure 1 it may be seen how the heating of the charge and the supply of the heat required by the reaction, are provided by means of burners 9 so that by extracting the combustion products from the top, through a duct (not shown) at the top of the retort F, the contribution of heat will be very high at its top and becomes lower and lower proceeding downwardly. In effect, the combustion products of all the burners which are below the top will contribute to the heating of the retort, in addition to the heat radiating from the single burners considered. In the zone indicated by 4, the charge is cooled in order to prevent successive new oxidation and allow the separation of the excess coal residue.In zone 5, there is provided for the extraction of the charge with a suitable gastight system and in zone 6, through a suitable manifold 8, the charge is discharged onto a scavenging carrier 7. Arrow 14 indicates the descending motion of the charge and arrow 11 the upward motion of the reaction gases and, finally, arrow 10 indicates the whole of reaction gases, vapours from the charge drying and coal distillation, which are discharged into the atmosphere to be burned as a torch or otherwise used.

For a more complete understanding of the present invention it is only necessary to make a careful examination of the gases 10 emitted by the retort F, and such an examination must be effected on the preliminary understanding that theory and experimental practice have indicated.

The most suitable solid reducing material for such reduction processes is the youngest pitcoals which therefore have the highest percentage of volatile elements. It must then be considered that the total analysis of the volatile parts of such coals would indicate the presence of a high quantity of hydrogen, methane and other hydrocarbons which, at a high temperature, have the tendency to split up into hydrogen and active carbon.

From the examination of the many known solutions which in the years have been concentrated on this subject-matter, an unequivocal appreciation is found for the properties of the above said coals, and particularly, of their volatile parts, as the presence of hydrogen in the reducing gas considerably enhances their efficacy.

As concerning the above stated matter, many known inventions provide in various ways the capture of the reaction gases, their treatment and injection by compression at the base of the retort after their pre-heating, if needed. Even if all this is technically possible, it requires very complex means for the plant and the management, particularly in view of the nature of the reduction process whose optimization requires operation at temperatures at the limits of the charge sintering.

Further, it must be remembered that the load losses, and therefore the pressure, at the retort base are quadratic functions of the relative capacity, and, hence, in order to not raise the said value too much with a detrimental effect on the gastight properties of the retort, instead of a quantitative efficacy it is opportune to have recourse to a qualitative efficacy of the reducing gas.

The present invention, starting from the notion of the known solutions to this problem and the above stated considerations, has as its essential object to obtain, with the most simple technology, the complete and rational utilization of the reducing features of the used coals, leaving an operative freedom as the utilization of the reaction gas(es) which will be expelled and for which the re-use, for the heating of same installation, may or may not be effected.

The fundamental concept of present invention is to provide a flow of distillation and reaction gas(es) having the same direction as that of the charge, leaving out of consideration the selected operative techniques, which may therefore be with retorts and positive gas pressure, or with retorts and negative pressure.

When retorts with positive gas pressure are used, the charge is generally effected through a double chamber with gastight valves and the output of gases will occur naturally, due to the spontaneous equilibrium, as known in the existing plants, but the discharge opening will be located at the retort base in an opportunely selected position. When retorts with negative gas pressures are used, preferably a ventilator apparatus will provide the necessary vacuum to have no gas outlet from the charging throat.

According to another variant directed to improve the reliability and security of the plants, a gastight system may be further provided in the charging zone by the injection of a noncombustible gas.

The present invention is capable of realising one or more of the following important advantages: 1. Any water contained in the charge, even if this is not preheated, will be transformed into steam and hence into water gas, a very good combustible and particularly a very good reducing agent.

2. All the coal distillation products, prevalently formed of hydrogen, will efficaciously contribute to reduce the oxides and the treatment will occur during the whole reduction cycle.

3. All increases of the "washing" metal oxides to be reduced is obtained, proportionately to the decrease of their reducibility.

4. An increase of the reducing gas(es)/coal exchange is obtained as a function of the lower quantity of coal present in the charge during its descent.

5. An increase of the thermal exchange is obtained in the zones of a greater reaction.

6. It is possible to obtain, at the retort base, a gas having a good calorific value and in such a quantity as to make up, if desired, for all the energy necessities of the same plant.

According to one aspect of the invention there is provided a process for the reduction of metal oxide(s) comprising heating metal oxide(s) in the presence of a solid reducing agent in a retort, and causing the gaseous reaction product(s) to move at least partially in co-current flow with the direction of flow of the charge. Generally the metal oxide(s) is/are in the form of pellets. In one expedient form of process embodying the invention hereinafter referred to as process (a) the charge is passed downwardly through a substantially gas-tight retort with a gas outlet at the base thereof, the discharge of gas(es) through the gas outlet being caused at the base of the retort.In another expedient form of process embodying the invention hereinafter referred to as process (b) the charge is passed downwardly through a retort having a reduced pressure therein provided by an extracting ventilator located at the base of the retort. In a further expedient form of process embodying the invention hereinafter referred to as process (c) non-combustible gas is injected into a charging zone at the top of the retort to render the top of the retort gastight.

The solid reducing agent may, for instance, comprise pit-coal and/or reactive coke. In a process embodying the invention wherein the charge contains water and steam derived from drying of the charge is forced to pass in co-current flow through the whole charge contained in the retort, thereby allowing the transformation of the steam into a reducing and combustible water gas.

If desired, the gas(es) discharged from the retort may be used as a combustion gas in another application.

According to another aspect of the invention there is provided an apparatus for carrying out the process, the apparatus comprising at least one retort which has an inlet at the top for admission of the charge, a gas outlet at the bottom of the retort for discharge of gas(es) and an outlet at the bottom of the retort, separate from the said gas outlet, for the spent charge. Preferably the said gas outlet extends upwardly and away from the outlet for the spent charge.

An example of an apparatus for carrying out process (a) is an apparatus comprising: at least one retort which has an inlet at the top for admission of the charge; a first and a second charge chamber disposed at the top of said retort; a first and a second gastight valve disposed at the bottom of said first and second charge chambers, respectively; a gas discharge duct at the base of the or each said retort for the spontaneous outlet of gas(es) flowing therethrough in co-current flow with the charge; heating means for heating the or each said retort; cooling means for cooling the charge issuing from the or each said retort, and discharge means for the substantially gastight extraction and discharge of the charge.

Preferably the discharge means comprises: a screw feeder; a first discharge chamber disposed at the outlet of said screw feeder; a second discharge chamber disposed at the outlet of said first discharge chamber; a first gastight discharge valve disposed between said first and second discharge chambers, and a second gastight discharge valve disposed at the outlet of the said second discharge chamber.

An example of an apparatus for carrying out process (b) is an apparatus comprising: at least one retort having an open charging throat at the top thereof; charge means for directly feeding charge, by gravity, into the charge throat of the or each said retort; a gas discharge duct disposed at the base of the or each said retort; an extracting ventilator disposed within said gas discharge duct; heat exchange means disposed in said gas discharge duct upstream of the said ventilator for refrigeration of the gas(es) passing therethrough; shutter means for control of the pressure at the retort charging throat; heating means for heating the or each said retort; cooling means for cooling the charge issuing from the or each said retort, and discharge means for substantially gastight extraction and discharge of the charge.

Preferably the discharge means comprises: a screw feeder; a first discharge chamber disposed at the outlet of the said screw feeder; a second discharge chamber disposed at the outlet of the said first discharge chamber; a first gastight discharge valve disposed between said first and second discharge chambers, and a second gastight discharge valve disposed at the outlet of said second discharge chamber.

An example of an apparatus for carrying out process (c) is an apparatus comprising: at least one retort; a charging duct connected to the top of the or each said retort by means of a tight expansion coupling; a charging hopper disposed at the inlet of said charging duct; a pipe opening into said charging duct; injection means for injecting non-combustible gas through the said pipe into the or each said retort; heating means for controllably heating the or each said retort; cooling means connected to the base of the or each said retort in a gastight manner for cooling the charge issuing from the or each said retort; a gas discharge duct disposed in the area of the said cooling means; depression means within said gas discharge duct for creating a controllable depression within said duct, and discharge means for the gastight extraction and discharge of the charge.

Preferably the said discharge means comprises a screw feeder, at least one accumulation and discharge chamber and a scavenging valve connected to each of the said accumulation and discharge chambers. The apparatus may include at least one lateral gas discharger connected to the top of the or each said retort for use in the event of over-pressures within the or each said retort. The apparatus may include an interception and partializing valve means in the or each said gas discharger for moderating and controlling the quantity of reaction gas sent downward within the or each said retort. Preferably the said depression means comprises an aspirator and detection means for automatically piloting said aspirator dependent upon the pressure detected at the base of the or each said retort. For instance, the said aspirator may be a water ejector.The apparatus may include an antiburst valve within said gas discharge duct and washing means for washing gas(es) passing through said gas discharge duct and evacuating means for evacuating the mud washed therefrom.

By way of example preferred forms of the invention will now be described in detail with reference to Figures 2 to 4 of the accompanying drawings, wherein: Figure 2 is a sectional view of a first form of vertical retort furnace suitable for carrying out a reduction process embodying the present invention; Figure 3 is a sectional view similar to Figure 2 showing a modified form of furnace embodying the present invention, and Figure 4 also is an axial sectional veiw of a vertical retort furnace according to another embodiment of the present invention.

With reference, firstly, to Figure 2, a technological solution is described concerning a process embodying the present invention with the gases flowing in the same direction as the charge, wherein gas under pressure is evolved within the retort and the outlet occurs naturally through a duct 20 which may be advantageously disposed in the cooling jacket 21 of a container 32. From an upper duct, the charge K is drawn into compartment 22, which is gastight and provided with a valve 23. When the desired quantity 24 has been received into compartment 22, valve 23 will be closed and valve 25 of a lower compartment 26, will be opened. Lower compartment 26 is defined by walls 27 having a refractory lining. This operation may occur with timed or otherwise automatic devices as a function of the desired level of charge.

The descending charge arrives successively in the retort S. In the first part 28 of the retort the charge is gradually brought to a high temperature and completely dried and hence distilling the coal volatile parts. The whole of the gases and vapours, having no other vent, is driven downward passing through the whole charge of the retort, at suitable temperatures that will be imposed on the same by burner batteries 29, 30, 31, in a furnace F corresponding with the various zones of the retort.

A suitable "Eiffel tower" profile given to the retort may minimize the loss of load along the same, giving a passage section of increasing width with gas fiux increase and increase of the charge compactedness. Further, the increase of the charge lapping speed by the gases may significantly improve the thermal conductivity of the mass, just in the zone wherein a temperature homogeneity is more required.

At the base of the retort, the charge will be cooled in container 32, provided with a water jacket 21, in which a manifold 33 is provided to drive the gases into said duct 20 to feed them to a pre-established destination. The extraction of the finished product at the end of the process may be effected in any suitable manner, e.g. with a screw extractor 33 feeding a gastight chamber 34 provided with a valve 35 followed by a subsequent gastight chamber 36 provided with a valve 37 which rhythmically feeds a suitable scavenging device 38.

The above described solution with gas pressure requires obviously the provision of retorts having a good gas-tightness and resistance to the pressure generated in them by the whole of the gas-producing reaction.

The gas present at the discharge opening of the duct 20 will, however, have a pressure sufficient to utilize it for various appliances and may contain all the sensitive heat at its disposal compatible with the particular features of the evacuation duct(s) used.

The Figure 3 embodiment, wherein the parts, similar or corresponding to those of the preceding Figure 2 embodiment are indicated by the same reference numerals, concern an operating scheme wherein the same flowing direction of the gases and the charge is obtained by means of an extraction ventilator 42 with suitable features, located at the retort base. With respect to the solution described with reference to Figure 2, it must be observed that the greatest simplification of Figure 3 is the charge K feeding which maintains the desired level in the retort S by a simple gravity load, being directly fed into an upper charging throat BC of the retort. However, the reaction gases issuing from the lower duct 20 must be ultimately cooled in a suitable exchanger 39 fed by the cooling fluid incoming at 40 and discharged at 41 to be sent to regeneration.This is because the extraction ventilator 42 presents low operating temperature limits. It will be further indispensable to instal onto the extraction manifold a shutter 43, controlled by a suitable device, which imposes on the cha;ging throat BC of the retort a predetermined pressure very near to zero.

With the above described embodiment, it is nearly impossible to have a loss of reducing gases towards the combustion chamber while, in case of an ineffective tightness of the retort, the reducing gases would be diluted by the combustion products of the heating burners 29, 30, 31. The necessity for cooling the discharge gases causes a loss of sensitive heat of same and a rather sophisticated control of the retort depression. In return, ventilator 42 can confer on the gases a pressure sufficient for their transfer to even distant users.

The embodiment of Figure 4 has the object of creating a flow of gases in the same direction as the charge without the intervention of mechanical valves which may present difficulties of adequate closing due to their probable incrustation and danger in case of excess pressures in the retorts.

According to this embodiment, there is obtained an artificial counterpressure in the high zone of the retort, that is, in the charging zone, by the injection of a suitable quantity of a noncombustible gas. At the same time there is created a small depression to make easier the inflow of the reaction gases from the inside of the retort.

Figure 4 shows that the charge K is fed, through a suitable metering distributor 50, to a hopper 51 whose shape allows the same charge to be conveyed into a sufficiently narrow vertical duct 52. Duct 52 is connected to the upper part of the retort S through a tight coupling G which allows the free vertical expansion of the retort without carrying on it the load of the hopper 51.

Level detectors (not shown) will be provided to programme the material calls and to ensure the continuity of the retort feeding. The upper part of the retort is further provided with a side venting burner 54 provided, in turn, with a partializing and intercepting shutter 54a controlled by an automatic oleodynamic system 54b. From burner 54, small quantities of reaction gases may issue, and, for ecological reasons, they are kept burning as a torch. The charge K, after its passage into the upper part of the retort S and having been dried and preheated follows downward while being heated by the burners of furnace F, and the combustion products proceed upwardly to be directed into a duct 55 through smoke intakes 56 and 57 which are partializable and interceptable in order to control the heating in the high zone of the retort; the combustion products are then conveyed to chimney 58.

Corresponding with the furnace base, after the treatment in the retort, the charge is passed into cooling jackets 59 and continuously extracted by a screw feeder. All the material accumulates on a valve 61 and it is thence evacuated from container 62 by means of another valve 63 and a belt conveyor 64.

In the high zone of the hopper, intercepted by valve 61, a vertical duct 65 is arranged and provided with an antiburst valve 65a. This duct is kept in a slight depression by an ejector 67 operating by inlet of water through nozzle 68. The depression is controlled with the greatest accuracy by a special control valve 69 receiving the signal from a probe 70 immersed at the retort base. The reaction gases are therefore withdrawn and washed in the ejector 67 and the dust falls into the channel 66, provided with a transferring member, and separated from the muds. The gases pass towards duct 71 and are sent at 72 for utilization as desired.

With the just described embodiment, the following advantages are generally obtained: the possible control, relatively easy, of the pressure conditions at the top and base of the retort in order to impose a total or partial cocurrent flow stream; the absence of mechanical sealing members in the retort top; the greatest simplicity of the passage from the conventional flow of gases from down to up to the co-current flow by simply lifting the liquid in channel 66 and opening of shutter 54a, and possible control of the thermic load by interception of valves 56 and 57.

Claims

1. A process for the reduction of metal oxide(s) comprising heating metal oxide(s) in the presence of a solid reducing agent in a retort, and causing the gaseous reaction product(s) to move at least partially in co-current flow with the direction of flow of the charge.

2. A process according to Claim 1 or Claim 2, wherein the metal oxide(s) is/are in the form of pellets.

3. A process according to Claim 1 or Claim 2, wherein the charge is passed downwardly through a substantially gastight retort with a gas outlet at the base thereof, the discharge of gas(es) through the gas outlet being caused by spontaneous equilibrium conditions at the base of the retort.

4. A process according to Claim 1 or Claim 2, wherein the charge is passed downwardly through a retort having a reduced pressure therein provided by an extracting ventilator located at the base of the retort.

5. A process according to Claim 1 or Claim 2, including injecting non-combustible gas into a charging zone at the top of the retort to render the top of the retort gastight.

6. A process according to any preceding claim, wherein the solid reducing agent comprises pit coal and/or reactive coke.

7. A process according to any preceding claim, wherein steam derived from drying of the charge is forced to pass in co-current flow through the whole charge contained in the retort, thereby allowing the transformation of the steam into a reducing and combustible water gas.

8. A process according to any preceding claim, wherein the gas(es) discharged from the retort is/are used as a combustion gas in another application.

9. A process according to Claim 1 substantially as herein described with reference to any one of Figures 2-4 of the accompanying drawings.

10. Metal which has been reduced and/or gas(es) which has or have been produced by the method claimed in any preceding claim.

11. An apparatus for carrying out the process claimed in Claim 1, comprising at least one retort which has an inlet at the top for admission of the charge, a gas outlet at the bottom of the retort for discharge of gas(es) and an outlet at the bottom of the retort, separate from the said gas outlet, for the spent charge.

12. An apparatus according to Claim 11, wherein the said gas outlet extends upwardly and away from the outlet for the spent charge.

1 3. An apparatus for carrying out the process claimed in Claim 3, comprising: at least one retort which has an inlet at the top for admission of the charge; a first and a second charge chamber disposed at the top of said retort; a first and a second gastight valve disposed at the bottom of said first and second charge chambers, respectively; a gas discharge duct at the base of the or each said retort for the spontaneous outlet of gas(es) flowing therethrough in co-current flow with the charge; heating means for heating the or each said retort; cooling means for cooling the charge issuing from the or each said retort, and discharge means for the substantially gastight extraction and discharge of the charge.

14. An apparatus in accordance with Claim 13, wherein the said discharge means comprises: a screw feeder; a first discharge chamber disposed at the outlet of said screw feeder; a second discharge chamber disposed at the outlet of said first discharge chamber; a first gastight discharge valve disposed between said first and second discharge chambers, and a second gastight discharge valve disposed at the outlet of the said second discharge chamber.

1 5. An apparatus for carrying out the process claimed in Claim 4, comprising: at least one retort having an open charging throat at the top thereof, charge means for directly feeding charge, by gravity, into the charge throat of the or-each said retort; a gas discharge duct disposed at the base of the or each said retort; an extracting ventilator disposed within said gas discharge duct; heat exchange means disposed in said gas discharge duct upstream of the said ventilator for refrigeration of the gas(es) passing therethrough; shutter means for control of the pressure at the retort charging throat; heating means for heating the or each said retort; cooling means for cooling the charge issuing from the or each said retort, and discharge means for substantially gastight extraction and discharge of the charge.

1 6. An apparatus in accordance with Claim 15, wherein the said discharge means comprises: a screw feeder; a first discharge chamber disposed at the outlet of the said screw feeder; a second discharge chamber disposed at the outlet of the said first discharge chamber; a first gastight discharge valve disposed between said first and second discharge chambers, and a second gastight discharge valve disposed at the outlet of said second discharge chamber.

1 7. An apparatus for carrying out the process claimed in Claim 5, comprising: at least one retort; a charging duct connected to the top of the or each said retort by means of a tight expansion coupling; a charging hopper disposed at the inlet of said charging duct; a pipe opening into said charging duct; injection means for injecting non-combustible gas through the said pipe into the or each said retort; heating means for controllably heating the or each said retort: cooling means connected to the base of the or each said retort in a gastight manner for cooling the charge issuing from the or each said retort; a gas discharge duct disposed in the area of the said cooling means; depression means within said gas discharge duct for creating a controllable depression within said duct, and discharge means for the gastight extraction and discharge of the charge.

18. An apparatus in accordance with Claim 17, wherein the said discharge means comprises a screw feeder, at least one accumulation and discharge chamber and a scavenging valve connected to each of the said accumulation and discharge chambers.

1 9. An apparatus in accordance with Claim 1 7 or Claim 18, which includes at least one lateral reaction gas discharger connected to the top of the or each said retort for use in the event of overpressures within the or each said retort.

20. An apparatus in accordance with Claim 19, including an interception and partializing valve means in the or each said gas discharger for moderating and controlling the quantity of reaction gas sent downward within the or each said retort.

21. An apparatus in accordance with any one of Claims 1 7 to 20, wherein the said depression means comprises an aspirator and detection means for automatically piloting said aspirator dependent upon the pressure detected at the base of the or each said retort.

22. An apparatus in accordance with Claim 21, wherein the said aspirator is a water ejector.

23. An apparatus in accordance with any one of Claims 1 7 to 22, including an antiburst valve within said gas discharge duct and washing means for washing gas(es) passing through said gas discharge duct and evacuating means for evacuating the mud washed therefrom.

24. An apparatus for carrying out a process for the reduction of metal oxide(s) substantially as herein described and illustrated by any one of Figures 2 to 4 of the accompanying drawings.