BE607004A - - Google Patents

Description

       

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    Process for the direct reduction of metal oxides by a reducing gas, such as carbon monoxide or a gas mainly constituted by it.



   The present invention relates to a process for the direct reduction of metal oxides such as iron ores or
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 others, in the corresponding metals, reduction carried out in ,,.,. with two stages, that is to say a first stage, a reaction zone at relatively low temperature and a second stage in a reaction zone at relatively high temperature, by means of a reducing gas consisting mainly of carbon monoxide.



  The reduction process according to the invention is essentially characterized in that on the one hand the major part of the metal oxide, such as an iron ore, is reduced at a relatively low temperature situated in the range of. 400 to

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 5CC C to a product consisting of partially reduced oxide and containing carbon formed during the reaction, and that further said product of the first reducing stage is transported to the second reaction zone where it flows. the second stage of the reducing treatment at a relatively high temperature in the range of 800 to 1700 C and where the oxide restan + is reduced to the corresponding metal.



   The various direct reduction processes of metal oxides, such as -The iron oxides and others, into the corresponding metals, -reduction implicating the formation of carbon from carbon monoxide - allowing themselves to be grouped according to their reduction mechanism in the following two types; the Stelling process (see CTTC STEIILMG; Jernkontcrets Annalar, 147,237- 60,1957) and the Phönix Kheinrohr process (see WICHE et al .: Stani und Eisen, 79,129-134,1959).



   In the first of said direct reduction methods, i.e. the Stelling process, the reduction of iron oxide (Fe2O3) to metallic iron is first carried out at a temperature of 750 C, while inhibiting the decomposition of carbon monoxide, i.e. the formation of combined or free carbon, and the reaction product is then transported to the reaction zone at 6 ° C, where combined carbon is formed for the above-mentioned first stage.



   In the second of said methods, ie. the Phönix process, the reduction and the decompositbn of carbon monoxide are carried out simultaneously at a temperature of about 53 ° C. according to a method completely different from the previous method.



   Cr, the present invention relates to a new improved direct process for the reduction of metal oxides to the corresponding metals, which process differs from the above two processes by its mechanism of reduction and carbon deposition.



   In the method according to the invention, the temperature is

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 maintained between the limits of 4CC and 5CC C in the first reaction zone (zone where the first stage of the treatment is
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 reducing agent) and between the limits of CCG and 17Ci C in 1 second reaction zone (zone where the second stage of the reducing treatment takes place).

   In the first reaction zone (prem: st stage
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 of the redacting treatment) the iron oxide is partially reduced with simultaneous deposition of carbon. the formation of carbon in the said first stage, c. to d. during the partial reduction of
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 iron oxide is controlled so that the amount of forced hull is stoichiometrically bivalent to the remaining amount of reduced iron oxide. This carbon, con- stitutes chiefly by cerbone combines - expression se
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 generally containing carbon in the form of 1: 2 Dtalli carbides such as cementite;

   and others, and ewpbyée in the present -es-
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 crirtion to distinguish this cc..rbone from cerbcne liter - se ':: t-, c ::: e ... Â /' l- on the surface and even inside the iron oxide rrticles
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 partially reduced containing di, car4ce. the reduct from this first reducing stage is then transferred to the second reaction zone, where the temperature is maintained at a relatively high level between ECC and 17CC C and where the iron oxide / unreduced in the reaction zone. first zone is reduced because carbon, c. to d. through
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 Carbon mainly constitutes because of the combined carbon deposited in said unreduced oxide, and without it, there is no need to resort to a reducing gas. The end product is metallic iron.



   An object of the present invention is therefore a method
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 Direct improved for the reduction of mF-t-1--7-li oxides, such as iron oxides or others, allowing a rapid and complete reduction of the latter in two stages, c. to d. a first . stage in a relatively low temperature reaction zone and a second stage in a second relatively high temperature reaction zone.

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  Another object of the present invention is a method
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 direct improved for the reduction of metal oxides, followed by which said reduction is / in part carried out in a / first reaction zone (first reducing stage) at a relatively low temperature between 40C and 500C, so as to considerably facilitate the reducing treatment in question and to make the installations required for this treatment appreciably simpler and less expensive.



   A further object of the invention is an improved direct process for the reduction of metal oxides by means of a reducing gas, mainly constituted by carbon monoxide, this reduction being carried out with a maximum yield in two successive stages, vs. to d. a first stage at a relatively low temperature followed by a second stage at a relatively high temperature, making it possible to significantly increase the efficiency of the reducing treatment, ie. the percentage of metal obtained, even with a relatively simple and small installation.

   the characteristics and advantages of the present invention will emerge more clearly from an examination of the attached plonches, in which, FIG. 1 represents the well-known equilibrium diagram of the iron-cementite-carbon monoxide-carbon dioxide system (curves representing the concentration carbon monoxide and carbon dioxide as a function of temperature); FIG. 2 is the graphic representation of a part of the reduction rate (percentage of reduced oxide) as a function of temperature (reduction of iron oxide by carbon monoxide according to the process according to the present invention), and on the other hand of the proportion of carbon monoxide decomposed into barbon deposited, also as a function of the temperature;

   and Figure 3 is a schematic representation of a

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 preferred example of execution of the installation serving to practice the method according to the invention.



   The following is a detailed description of the reduction process in question, compared with the reduction processes applied heretofore.



   In general, in processes for the reduction of iron oxides by carbon monoxide, the formation of free carbon by decomposition of carbon monoxide and the formation of combined carbon (iron carbides) from carbon monoxide and carbon. reduced iron (metallic iron) or iron oxide do simultaneously with the reducing reaction.



   With regard to the force with which the reactions in question proceed - a force depending on the difference between the concentration of carbon monoxide in the reducing gas and the equilibrium concentration - it is clear from the diagram of figure 1 that 'at temperatures above 720 C the strength of the reducing reaction is greater than that of the decomposition reaction of carbon monoxide, unlike this happens at temperatures below this level.



  Needless to point out, however, that these reactions vary as a function of temperature according to complicated laws, as well as according to the aforementioned force, kinetic constants, and
The invention is the fruit of research undertaken by the author with a view to elucidating the aforementioned relations and to determine; the fastest, most efficient and complete reduction process. The results of this research are summarily represented by the curves in Figure 2.



   Curve 1 of FIG. 2 represents the relation which exists between the reduction rate and the reduction temperature at the start; of the reaction or 10 minutes after the start of the reaction.



  It can be seen that the quantity in question, that is to say the rate of reduction, increases with the temperature in the range of 350 to 500 ° C. to become constant beyond this limit. Note,.

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 however, that during this time hardly any deposited carbon is formed at temperatures above 35C C.



   Curve 2 in Figure 2 represents the relationship between the reduction rate and the reduction temperature
50 minutes after the start of the reaction. We see that the size in question, c. to d. the rate of reduction reaches a maximum at a temperature of about 450 C, to drop to a minimum at a temperature of about 550 C and tends towards a plateau of a height practically equal to the height of the curve at maximum point at 450 C, plateau practically reached at temperatures above 600 C. It clearly follows that the application of high temperatures of the order of 750 C, as in the usual Stelling process, does not necessarily lead to to an acceleration of the reducing reaction,

   nor to an increase in the reduction rate, but, on the contrary, to a decrease in the thermal efficiency and to a concretion of the products which considerably hinders subsequent treatments. On the other hand, said usual process has the disadvantage of having to apply temperatures below 600 ° C. for the formation of carbides. Now, the process according to the present invention is much more advantageous than the said usual processes, because it makes it possible to achieve the high speed and the high reduction rate of the usual Stelling process at temperatures appreciably lower than those applied in this process. process, i.e. at temperatures of around 450 C, and this with a simultaneous deposition of carbon of the same magnitude.



   On the other hand, as shown by curve 2 in figure
2, the decomposition of carbon monoxide, i.e. the formation of free carbon, or of combined carbon, takes place only at temperatures equal to or lower than 720 C and the force of the reducing reaction decreases with temperature, but, due to the decrease in the kinetic constant of said reducing reaction

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 the amount of deposited carbon or, in other words, the amount of carbon monoxide decomposed in the formation of said deposited carbon reaches its maximum at the temperature of 55CoC.



   Regarding the proportion of combined carbon or free carbon formed, this magnitude varies according to the reduction rate. The higher the latter, the faster the combined carbon formation.



   At elevated temperatures the reaction between iron oxide and combined carbon is faster than that between iron oxide and free carbon and, in the first of said reactions, the intervention of reducing gas is. extremely efficient because almost all of the carbon is involved in the reaction.



   It is clear from these results, at temperatures up to 530 C, the temperature applied in the Phönix process, the speed and the reduction rate decrease and the proportion of deposited carbon and therefore that of decomposed carbon monoxide increase (see figure 2).



   As indicated above, the carbon deposited during the reducing reactions at a relatively low rate is mainly constituted by free carbon, a certain proportion of which does not participate in the reaction and is therefore found when the reducing reaction at relatively high temperature is completely terminated, or is lost as fine dust carried away with the exhaust gases. To avoid these losses, the amount of carbon deposited must be greater than the stoichiometric amount, which obviously results in an extension of the reaction time in the usual Phönix process. These losses of free carbon have considerable drawbacks such as a substantial reduction in the efficiency of the application of carbon monoxide, etc.



   Unlike the usual direct reduction methods, reduction according to the method according to the present intention -

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 completely new process and very high efficiency - is carried out in two successive stages, ie. a first stage in a relatively low temperature zone and a second stage in a relatively high temperature zone. In said first zone the first stage of the reducing treatment takes place at a relatively low temperature situated in the range of 400 to 5 ° C without risk of concretion of the materials involved and without it being necessary to make an excessive choice. severity of the materials used in the construction of the reactor apparatus.

   In this reaction zone, a partially reduced product is obtained containing carbon deposits, mainly consisting of carbon in the combined state (combined carbon) in a stoichiometric proportion sufficient for the subsequent reduction of the part not yet reduced. said partially reduced product is then transported to the zone where the second stage of the reducing treatment takes place at a higher temperature, ie. at a temperature in the range of 800 to 17CC C. This second stage, c. to d. the reduction of the part not reduced in the first stage, flows at a speed and a higher efficiency than that of the first stage.



   Here are the reactions which take place at the first stage at a temperature in the range of 4 ° C to 500 ° C;
3Fe2O3 + CO = 2Fe3O4 + C02
Fe3O4 + 400 = 3Fe + 4C02
2CO = C + CO2
As a result of these reactions, a partial, reduced product is formed, containing carbon in the form of carbides, resulting from the solid phase reaction of the carbon generated by the reaction mentioned above with Fe, Fe203 or Fe3O4. or the reaction in gaseous phase of carbon monoxide with Fe, Fe2O3 or Fe3C4 'In the second reaction zone where flows0

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 the second stage of the reducing treatment at temperatures higher than those of the first zone, ie.

   at a temperature of 800 to 1700 C, the partially reduced product generated in the first zone is reduced to metallic iron without the application of a reducing gas, and then removed. quite simply by the carbon formed by the reaction mentioned above, carbon mainly constituted by combined carbon.Here are the diagrams of the reactions in question:
Fe 0 + C = Fe + cu x y (FexOy unreduced oxide)
Fe 0 + FenC = Fe + CG x y n (FexCy: unreduced oxide;

   FenC; iron carbide)
Said partially reduced carbon-containing product formed in the first zone where the first stage of the reducing treatment according to the invention takes place can be used as raw material in powder metallurgy, instead of being transported to the plant. zone where the second stage of the reducing treatment takes place. It goes without saying that the incompletely reduced metal oxide in question can also be reduced to metallic iron transformed into sheets or bars by cold or hot rolling .



   The raw materials treated in the process according to the invention consist of iron gold, such as
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 many iron ores, the converted dust, waste from Usinag% t, and the ga7, zeductor applied in the process in question need not be of a high degree. purity, but may contain a certain proportion (up to about 20%) of other gases such as nitrogen, hydrogen, methane, etc. Needless to say that the carbon dioxide content (002) of the gas re - driver employed in the first zone, ie.

   in the zone where the first stage of the reducing treatment takes place at a relatively low temperature, must be less than the equilibrium concentration at the temperature of

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 reduction.



   It should be noted that in the process according to the invention the application of a preliminary reduction makes it possible to increase the thermal efficiency of the treatment, a preliminary reduction carried out in a preheater, where the raw materials ( iron ore) are heated by the hot waste gases evacuated from the installation, before being taken to the area where the first stage of the reduction treatment takes place.

   FIG. 3 gives a schematic representation of the installation employed for the implementation of a preferred code of execution of the invention, the finely ground iron ore (50 to 15C meshes per inch tonbe in the hopper 1 provided with bottom of a supply hatch ± which regulates the supply of the first reactor ± (first reducing treatment stage) in the mire by the intermediary of pipe 3. the bottom of said reactor 4. is matured with a grid er i '-:

  The perforated plate 15 by which a sufficient quantity of reducing gas is blown from the bottom up into the apparatus in order to completely melt the raw materials which are present therein:;. the operation of the apparatus is adjusted so as to achieve the most uniform possible mixture of the reducing gas blown in by the case and the finely divided raw materials introduced at the top, as well as the most uniform possible distribution of the temperature.

   Although in the exemplary embodiment described and shown here, a liquid bath reactor is employed in the first zone (first stage of the reducing treatment), of standard types of reactors, such as those with solid reacting mass, rotary kilns, etc., can also be successfully applied. In the first reactor 4, the temperature of the ore is maintained at a level of 400 to 500 C. The reducing gas, preheated in the apparatus 14 to 400 to 500 C., is blown from below into said reactor 4. The finely divided ore is

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 melted and reduced in a ratio of 4C-C; (reduction lights).



  At the same time, carbon is formed, mainly in the combined state (combined carbon), in a stoichiometric proportion sufficient for the subsequent reduction of the unrelated part.
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 pick up the waste gas discharged from the premie; reactor 4, feels ics3ièrés in cyclone J5 and the ore dust thus s = rsree of said gases is reintroduced into reactor 4¯. The waste gases evacuated from this reactor are cooled in :: "'- c! 8.r' [eur of heat IC by heating the? prrific er ci- culation. extremely fine mineral dust interferes with it. the,., - az evacuated from reactor 4, are completely precipitated from the electrostatic perar2.tor II. -Gas c; 1; ri:

  fj -s sent alcrs led to cor-1-cres, -eur 12. the certain proportion of said gases released from the reactor
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 - must be evacuated from the system before being driven to the conirres- tight in order to ensure an impeccable circulation of the reducing gas and to avoid any accumulation of gases, such as nitrogen,
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 xvrene, methane or others, which do not participate in the reaction or may interfere with it. the gases evacuated from the system (rural gas) contain a high proportion of gas
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 combustible and can therefore be used as a fuel in the installation itself or elsewhere.

   The gas compressed by the compressor to a pressure of up to 2 to 3 atmospheres - compression necessary to remedy the pressure losses produced in the pipes and the purification devices is led to the purification device 13, where the The concentration of carbon dioxide (CO2) generated during the reactions is reduced to about 1% by means of a suitable absorbent. the purified gas passes with new reducing gas through the heat exchanger 10 and is heated in the apparatus 14 before being introduced into the first reactor 4.

   the finely divided ore partially reduced in the

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 first reactor! (first stage of the reducing treatment) is then taken to the second reactor 9 (second stage of the reducing treatment) via the overflow pipe.



   By heating in the second reactor the partial ore-Mare reduced to 600-1700 C, it is completely reduced to metallic iron. Said partially reduced carbon containing ore formed in the first reactor can also be employed in powder metallurgy. Like the gases leaving the second reactor. 9. contain about 90% carbon monoxide, it is advisable to use them as reducing gases after washing in a water scrubber 16 and dusting
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 siérage in an electrostatic separator 11. Said gases er ", exits aït 71r, 8acharger can also be used directly as reducing gases by introducing them into a pipe 8 (see interrupted line 18 of FIG. 3).



  Example.



   62% iron Venezolan iron ore is finely ground to a 50-150 mesh per inch sieve powder, and loaded into the feed hopper, from where it is continuously fed into the first. reactor at a rate of 3.5 kg per hour. A reducing gas composed of 95% of 00.2% of H2, 2% of N2 and 1% of CO 2 (volumetric proportions) is also introduced into said reactor at a flow rate of 1.8 mo / h. The reactor in question has an internal diameter of 12 cm and a height of 100 cm and is maintained at a temperature of 450 C.

   The reaction, which flows in this first. reactor (first stage of the reducing treatment), generates a product partially reduced at a reduction rate of 70%, a product containing deposited carbon, mainly consisting of ... combined carbon, in a stoichiometric proportion sufficient for the subsequent reduction of . the part not reduced in the first stage of treatment. Said partially resulting product

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 is then introduced into the second reactor (second stage of the reducing treatment), where. it reduces to metallic iron with a yield of 95% (plant capacity 2.5 kg of iron per hour).
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  RVEP: ICA2IOlY-S
1.- Direct reduction process for metal oxides, such; as iron ores or other, by means of a reducing gas, such as carbon monoxide or a gas mainly consisting of carbon monoxide, reduction carried out in two stages, c. to d. a first stage in which said oxides are treated at a temperature of 400 to 50 ° C. for the formation of a partially reduced product containing carbon, and a second stage in which said partially reduced product formed in the first stage is heated to a temperature of 800 to 1700 C for its complete reduction to metallic iron.



   2.- Method of direct reduction of metal oxides, such as iron ores or others, by means of a reducing gas, such as carbon monoxide or a gas mainly constituted by carbon monoxide, reduction carried out in two stages; vs. to d. a first stage in which the said oxides are treated at a temperature of 400 to 500 ° C. to form a partially reduced product with a spongy structure and containing carbon in the state of uniform dispersion, the main carbon a mixture consisting of combined carbon, in a stoichiometric proportion sufficient for the subsequent reduction of non-reduced oxides at the first stage of the reducing treatment,

   and a second stage at which said partially reduced product is heated to a temperature of 800 to 1700 C for its complete reduction to metallic iron.
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  3.- Direct reduction process, dc> -xides, @ ketallics -.1 such as iron ores or. others, by means of #d, 'reductive gas', such as by âu mDnoxydé dyd cabône. otzu; gas, ri.npaémen3- '; "constituted ¯ by; du mondxyâc - ': cPé carbonëësdita'ôS3es'' 'é' {; àh'tti'ài-

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 in a first stage at a temperature of 400 to 500 C to form a partially reduced product with a spongy structure and containing carbon in the state of uniform dispersion, carbon consisting mainly of combined carbon, in a sufficient stoichiometric proportion for the subsequent reduction of the oxides not reduced at this first stage.



   4 - A method of direct reduction of metal oxides according to claims 1-3, allowing the treatment of all kinds of iron ores, converter dust, oxidized machining waste, etc., as well as mixtures of these materials raw, instead of powdered iron ore.



   5. - A method of direct reduction of metal oxides according to claims 1-3, wherein the carbon monoxide used as reducing gas may contain impurities, such as nitrogen, hydrogen, methane or others, in a proportion of not more than 20%.



   6. A method of direct reduction of metal oxides according to claims 1-3, wherein an oven for preheating the ores is provided for a preliminary reduction of said ores prior to their reducing treatment at a temperature of 400 to 500 C .



   7. A direct reduction process for metal oxides according to claims 1-3, wherein the reduction at 400-500 C is carried out in a liquid bath (molten bath), a solid layer or a rotary kiln.



   8.- A method of direct reduction of metal oxides, such as iron ores or others, by means of a reducing gas, such as carbon monoxide or a gas mainly consisting of carbon monoxide, in which said oxides are treated at a first stage at a temperature of 400 to 500 C with a view to forming a partially reduced product with a spongy structure and containing carbon in the state of uniform dispersion,

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 carbon mainly consisting of combined carbon, in a stoichiometric proportion sufficient for the subsequent reduction of unreduced oxides, said product being transformed into sheets or bars by cold or hot rolling.
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