Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21B—MANUFACTURE OF IRON OR STEEL
  • C21B13/00—Making spongy iron or liquid steel, by direct processes
  • C21B13/08—Making spongy iron or liquid steel, by direct processes in rotary furnaces
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21B—MANUFACTURE OF IRON OR STEEL
  • C21B13/00—Making spongy iron or liquid steel, by direct processes
  • C21B13/10—Making spongy iron or liquid steel, by direct processes in hearth-type furnaces
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/10—Reduction of greenhouse gas [GHG] emissions
  • Y02P10/134—Reduction of greenhouse gas [GHG] emissions by avoiding CO2, e.g. using hydrogen
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/20—Recycling

Definitions

• the present invention relates to a process for the reduction of metal oxides, in particular iron oxides, and to a device for carrying out the process.
• Document LU-60981 -A (Institute des Minerais) describes a process for manufacturing an iron sponge comprising the use of a continuous rotary hearth reactor with a displacement of material from the periphery to the center, supplied first in charcoal and then, after the charcoal has been coked, with iron ore in "pellets" or in pieces preheated to reaction temperature. Fixed scrapers move the coal to the center of the furnace and mix the coked coal with the ore as the rotary hearth rotates. After reaction, the charge is discharged through a central well.
• the object of the present invention is to provide a process for the reduction of metal oxides using more effectively the reducing capacities of the volatile constituents of a carbonaceous reducing agent.
• this objective is achieved by a process for the reduction of metal oxides in a rotary hearth furnace in the shape of a crown in which a carbonaceous reducing agent and metallic oxides are deposited in a strip on part of said hearth rotating and are then transported in a movement substantially in helical form to an evacuation device, characterized in that a first part of the reducer is preheated and mixed with the metal oxides preheated before and / or during deposition in a mixture on the rotating floor, in that a second part of the reducing agent is deposited on the mixture, and in that the volatile components of the carbon reducing agent and carbon monoxide are used to reduce the metal oxides.
• the process according to the invention at least part of the volatile constituents of the carbonaceous reducing agent, in particular hydrogen and methane, are used for their reducing capacity.
• the process according to the invention makes it possible to increase the reaction rates by mixing the metal oxides and the carbonaceous reducing agent by effectively using the reducing capacities of the volatile constituents of the carbonated reducing agent by their forced passage through the preheated mixture which constitutes the charging the oven.
• One of the advantages of this process lies in the fact that the volatile components, i.e. the distillation gases of the carbonaceous reducing agent are used in a first phase to reduce the metal oxides whereas in known processes, these gases are burnt and are used to heat the solid materials.
• the reduction of metal oxides is therefore done in two phases respectively by at least two different chemical reactions. These reaction phases can take place simultaneously or successively.
• the first reduction phase is carried out using hydrogen and / or methane released during the heating of the carbon reducer.
• the reaction kinetics of these reactions are more favorable than those of carbon monoxide at temperatures below 900 ° C.
• the above-mentioned volatile constituents are gradually released and come into contact with the metal oxides deposited on the hearth of the furnace, under operating conditions such that, in particular as regards the reaction temperature, they participate in the reduction of these .
• the metal oxides and the reducing gases released come into contact at temperatures as high as possible, without however disturbing the progress of the reduction process.
• the second part of the reducing agent deposited on the layer consisting of a mixture of reducing agent and metal oxides makes it possible to avoid reoxidation of the reduced metal oxides during their stay in the oven.
• the quantity of volatile components of the reducing agent which escape from the deposited layer is minimized without reacting with the metal oxides.
• a layer rich in reducing elements is maintained in contact with the upper surface of the filler, which minimizes the reoxidation of the metal oxides already partially reduced during their stay in the oven, and the formation of fayalite on the surface is also minimized.
• the second part of the carbon reducer deposited on the load is subdivided into several fractions. These fractions are advantageously heated before their deposition.
• fractions advantageously constitute up to 20% of the total amount of reducing agent used, this amount being a function of the oxides and of the reducing agent used and the reaction conditions.
• the second part of the carbon reducer is subdivided for example into two fractions each comprising up to 10% of the total amount of reducing agent used.
• At least a fraction of the second part of the reducing agent can be mixed with metal oxides before being deposited or during its deposition.
• This mixture can comprise between 60 and 100% of carbonaceous reducing agent and between 0 and 40% of metal oxides, preferably between 80 and 100% of carbonaceous reducing agent and between 0 and 20% of metal oxides, these values being a function of the nature of the metal oxides, the reducing agent used and the reaction conditions.
• the carbon reducer of the first and / or of the second part is preferably preheated to a temperature up to 200 ° C while the metal oxides are preferably preheated to a temperature up to 850 ° C.
• the components are preheated preferably by means of the heat recovered from the combustion gases discharged from the furnace in heat exchangers.
• This process also has the advantage of evacuating less dust out of the oven by controlling the speed of these gases while keeping the volume of the oven minimal.
• the metallic sponge obtained has a better homogeneity in the degree of reduction in mass than the products resulting from known techniques.
• an excess of at least 10% in carbonaceous reducing agent is used, this excess being defined relative to the theoretical quantity necessary for the reduction of the oxides.
• a method for the direct reduction of metal oxides in a rotary hearth furnace, in which a so-called hearth furnace portion is deposited over a certain width of the crown, which depends on the diameter and the capacity of the oven, a load comprising several layers. These layers can be deposited simultaneously or successively.
• the content of metal oxides and carbon reducer in the layers may be different.
• the content of metal oxides in the upper layers is greater than the content of metal oxides in the lower layers.
• the lower layers advantageously contain an excess of carbon reducer.
• the content of carbon reducer in the upper layers is therefore lower than that in the lower layers.
• there is a kind of gradient of concentration in metallic oxides concentration which increases from the sole towards the upper surface of the load. A greater quantity of volatile constituents is therefore released in the deep layers and these gases diffuse through the layers towards the upper surface of the charge where these volatile constituents meet a higher concentration of metal oxides.
• the volatile constituents of the carbonaceous reducing agent are gradually released in the lower layers and meet during their diffusion towards the upper surface of very hot metallic oxides.
• the upper layers are warmer than the lower layers, on the one hand because these upper layers contain a higher concentration of metal oxides preheated to higher temperatures than the carbon reducer and on the other hand because these layers are in contact with the atmosphere of the oven.
• the volatile constituents therefore participate more effectively in the reduction of metal oxides.
• the content of carbonaceous reducing agent in the lower layer is between the theoretical content necessary for the complete reduction of the metal oxides and a content of 100% by weight, preferably between 30% and 70% by weight and particularly preferably between 35% and 60% by weight.
• the content of carbonaceous reducing agent in the upper layer is preferably less than 25% by weight and in a particularly preferred manner is less than 16% by weight.
• the charge is heated inside the oven to a temperature of 900-1250 ° C and preferably from 1050 to 1150 ° C.
• the mixture of carbon reducer and metal oxides, respectively, the charge is inverted and mixed progressively during its stay inside the oven.
• a profiled surface is formed on the surface of the charge by forming mounds respectively to promote heat exchange between the upper part of the furnace and the charge by increasing the efficiency of the radiation. from the oven and by increasing the heat exchange surface with the atmosphere of the oven.
• the slope of the grooves respectively of the mounds is usually between 20 ° and 65 ° and preferably between 40 ° and 65 °.
• a sawtooth surface is created on the surface of the load.
• the fraction (s) of the second part of the reducer can be loaded either in the hollow of the grooves or on the crests of the silions.
• the load respectively the mixture is loaded (e) on an inner part of the sole in the shape of a crown and is transferred (e) in a substantially helical movement towards the outer part of the sole and after reaction , it (it) is evacuated (e) by the external part of the crown.
• the mixture is usually removed after four or more rounds.
• At least a fraction of the second part of the carbonaceous reducing agent is deposited on the mixture at least one revolution before the evacuation of said mixture.
• the layer (s) of mixture of carbonaceous reducing agent and metal oxides is (are) deposited (s) preferably on a part corresponding to 1/4 or less of the width of the crown.
• the second part of the carbon reducer is deposited on a part of the rotary hearth corresponding to a maximum of 1/4 of the width of the crown.
• the bulk density or bulk density of the load decreases, i.e. as its volume increases.
• the flow properties of the load vary and in particular the dumping angle or the slope angle increases, i.e. that the slope mounds respectively grooves can become increasingly stiff as the load progresses inside the rotary hearth furnace.
• the increase in its apparent volume can be compensated for by modifying one or more of the following parameters: the width of the strip , the width of the base of the furrows, the number of furrows and the slope of the furrows.
• Postcombustion of the gases released during the reduction is preferably carried out in the inner part of the crown of the furnace.
• the evacuation of the gases and the displacement of the charge inside the furnace are done radially against the current.
• the preheating of the reducer and of the metal oxides is commonly done by means of the heat recovered from the combustion gases and from the post-combustion gases.
• lime generally contributes to the desulfurization of the pig iron and to the formation of slag or more fluid slag.
• the layer of the mixture of metal oxides / carbon reducer consists of a layer of pellets including these constituents.
• metal oxides includes both metal ores, in particular iron ore, as well as metal oxides to be recycled from the steel and foundry industries, for example from blast furnaces, steelworks, electric furnaces or of the rolling mills, than a mixture of these oxide sources with coke fines or with coal, if necessary in the form of pellets.
• carbon reducer means any carbon material in the solid or liquid state such as, for example, coal, lignite and petroleum derivatives.
• the reducing agent is carbon with a content of volatile constituents as high as possible within the framework of the process, preferably with a content greater than 15% of volatile constituents.
• a rotary hearth furnace for the reduction of metal oxides comprising a rotary hearth in the form of a crown subdivided into:
• the charging zone comprising a device for depositing on a strip of the rotary hearth a load comprising one or more layers of a mixture of metal oxides and of a reducing agent
• the intermediate zone as well as possibly the oven charging zone comprising a device allowing progressive mixing of an upper part and an underlying part of the load while displacing the load radially as and when of the rotation of the sole,
• the intermediate zone as well as possibly the unloading zone of the oven comprising a device for depositing on the load one or more layers of a reducing agent optionally mixed with metal oxides;
• the unloading zone comprising an unloading device making it possible to evacuate the metallized charge at one or more unloading points.
• the oven comprises a device creating on the surface of the deposited layer grooves or mounds so as to obtain an essentially sawtooth surface.
• the device for depositing one or more layers of a mixture of metal oxides and a reducing agent as well as the device for depositing on the load one or more layers of a reducing agent optionally mixed with metal oxides on the first mixture of metal oxides and a reducing agent optionally include an apparatus for hot mixing the carbon reducing agent and the metal oxides before, after or during the deposition of the layers.
• the oven advantageously comprises an equipment making it possible to carry out the stirring which comprises rakes provided with plowshares arranged in the manner of the teeth of a rake, said rakes being fixed and arranged radially in the oven.
• These rakes preferably include plowshares penetrating the layer by moving the mixture radially towards the discharge side of the crown.
• the coulters are generally offset, that is to say slightly staggered relative to the furrows or mounds formed by the plowshares of the previous rake, so as to remove or plane a sloping side of each furrow and thus form a new furrow .
• equipment makes it possible, by a first action, to bring down the tops of the saw teeth which are the warmest part of the grooves in the hollow of the grooves, and by a second action, to bring back a face of each sawtooth on one face of the adjacent sawtooth so as to cover the material brought in by the first action.
• the angle of attack of the coulters is preferably between 20 ° and 30 ° relative to the tangent of the grooves.
• the angle of attack of the coulters can at any time be adapted to reverse the direction of radial movement of the load and to increase the residence time of the latter inside the oven.
• the plowshares are formed so as to cause the load to overturn.
• the unloading device comprises an endless screw or a deflector.
• the width of the crown of the oven may be greater than if a worm is used. Indeed, given the high temperatures prevailing inside the oven, the worm beyond a certain length is mechanically too loaded.
• Such an unloading device preferably comprises one or more devices planing the tops of the furrows or mounds in order to obtain a substantially flat surface and one or more deflectors. .
• the deflectors are then regularly placed in the evacuation zone of the oven.
• the opening angle and / or the penetration depth of each deflector are chosen according to their relative position with respect to the rotating floor.
• the oven advantageously comprises burners installed in the outer walls of the movable hearth oven and / or in the outer ring of the vault in order to maintain the oven at a temperature of the order of 1200 to 1550 ° C, preferably of the order of 1400 ° C.
• Figure 1 shows a schematic horizontal projection of a rotary kiln with a distribution of rakes in a rotary kiln.
• Figure 2 shows a vertical projection of a section of the rotary kiln.
• Figure 3 shows the grooves formed upon loading.
• Figure 4 shows the grooves resulting from the first action of the coulters, arranged on fixed rakes, in the load.
• FIG. 5 represents the furrows resulting from the second action of the plowshares, arranged on fixed rakes, in the load.
• FIG. 6 represents a schematic view of a vertical projection of a section of a rake and of a ploughshare with an arm for fixing to the rake.
• FIGS. 1 and 2 the first loading area 1, the second loading area 20 and the evacuation area of the rotary hearth 3 are illustrated with several deflectors 2, the hearth 3 performing a movement in the counterclockwise direction. of a watch represented by the arrow 4 around the axis of the furnace 5.
• the burners fixed in the external wall of the furnace are represented by 6, the combustion gases are extracted by the interior walls of the furnace at 7 and sent to the heat exchangers by 8.
• the rakes supporting the coulters have received the reference mark 9. It should be noted that one of the rakes upstream of the unloading area is equipped over the width corresponding to that of the unloading area, with a device planing the tops of the load furrows.
• the oxygen injectors have received the mark 10 while the mark 11 denotes the charge.
• FIG. 3 represents the grooves 12 before the coulters pass.
• Figure 4 shows the planing of the top 13 of the grooves, before the action of the coulters.
• FIG. 5 represents the planing 14 of the grooves, resulting from the second action of the coulters.
• FIG. 6 illustrates a schematic view of a vertical projection of a section of a rake 15 with its external thermal insulation 16 and an interior water cooling chamber 17 as well as a ploughshare 18 with an arm for fixing to the rake 19.
• the action of the double action coulters is explained in more detail below.
• the oven entrance is provided with equipment that creates triangular section grooves on the surface of the load in order to obtain a sawtooth surface.
• the oven includes complementary double-action equipment which, by a first action, causes the material constituting the top of each sawtooth to fall into the adjacent hollow in order to prevent the material of the tops, which are very quickly heated, does not reach the agglomeration and / or melting temperature, which would make it more difficult to mix with the load and the reduction of metal oxides.
• the furnace has similar double-action equipment, which allows, by a first action to remove the tops of the saw teeth and to bring this part into the adjacent hollow.
• a second action it is obtained that one face of each saw tooth is removed to the bottom, the removed part being brought back to one face of the adjacent saw tooth by covering the material brought by the first action.
• the load is moved radially as the sole rotates to be removed after several turns, preferably after 4 turns or more, towards the part of the crown opposite to the charging part.
• the two zones can also include identical equipment.
• the operating conditions are chosen so as to achieve a compromise between, on the one hand, the need to achieve as quickly as possible a high and uniform temperature of the load and, on the other hand, the need gradually bringing into contact with the layer of metal oxides or the upper layer of the metal oxide / carbon mixture only the upper part of the underlying layer, avoiding incorporating cooler lower layers therein, so that the temperature of the new mixture formed thus obtained is greater than 600 ° C, in particular of the order of 700 ° C to 800 ° C.
• the rotational speed of the hearth is chosen according to the diameter of the oven. It can be between 3 and 16 revolutions / hour and preferably, it is from 8 to 12 revolutions / hour.
• the relative speed of the load with respect to the coulters is preferably between 10 and 50 cm / s and advantageously between 15 and 30 cm / s.
• the deposition of a second part of the carbonaceous reducing agent on the surface layer makes it possible to maintain a layer rich in reducing elements in contact with the surface layer of the filler, which minimizes the reoxidation of the metal oxides already partially reduced during their stay. in the oven, and the formation of fayalite on the surface is also minimized.
• means such as rakes ensure rapid mixing of the surface layer in the immediately underlying layer.
• the elaboration time is determined by the coldest point of the filler, a metal sponge having better characteristics of homogeneity compared to the sponges produced by the techniques reduction of the state of the art, the latter generally having the disadvantage of causing the production of a product with variable reduction rates of metal oxides.
• the first part of the reducer is placed in the interior contour of the crown, the small circle, preferably on 1/6 to 1/12 of the width of the crown,
• the unloading takes place on the outer part of the crown by means of one or more deflectors of a length corresponding respectively to the width or to a fraction of the loading width,
• - burners are arranged in the side walls of the oven above the level of the hearth, mainly in the outer walls of the crown, on the large circle and / or in the outer ring of the vault,
• the gases are evacuated against the movement of the material through the walls of the inner sides of the crown, on the small circle.
• the double action coulters of different dimensions and shapes are arranged so that the coulters of the first intermediate zone gradually stir the load at lower and lower levels until the sole while the coulters of the second intermediate zone, where the charge is not yet agglomerated and is still easily mixable, have an appropriate shape different from that of the first coulters and stir the furrows and their base. This avoids the appearance on the surface of the charge of a thick and resistant reduced metal oxide plate, difficult to break up and difficult to remove.
• These rakes are fixed and arranged radially in the oven, the first rake being arranged in the first intermediate zone in extension of the charging area, that is to say the oven supply.
• the rake coulters are fixed and offset, that is to say arranged slightly at an angle with respect to the grooves formed by the coulters of the preceding rake, for example 50 mm, so as to remove a sloping side from each groove or Sawtooth.
• the movement of the material on the hearth causes mixing (that is to say, mixing) and the formation of a new groove or sawtooth.
• the coulters create triangular section grooves over the entire surface of the load, which increase the area of the load at the interface with the furnace atmosphere by 20 to 65%, thereby achieving greater transfer. from the oven to the load.
• the first and second types of double action coulters are designed so that each time the load is passed, part of it is turned over, the upper layer of the load in contact with the atmosphere of the oven, at the start consisting of metal oxides then of the metal oxides / carbon mixture and finally of reduced metal oxides, being lowered while the underlying layer is raised.
• the end of the coulters is shaped so as to cause the material to turn over so that the mantle of the groove, the warmest part, is found at the heart of the base of the new groove created, in order to ensure better homogenization.
• This end of the coulters can be cooled by an internal circulation of a cooling liquid for example.
• the distribution of rakes in the different areas of the oven can be done linearly over the passage length in one area of the oven. It will preferably be non-linear and will be dependent on the surface temperature as well as the temperature gradient in the load.
• One of the rakes upstream of the unloading zone has, over a width corresponding to that of the unloading zone, a device making it possible to plane the tops of the profiled surface in order to obtain a substantially flat surface. This facilitates unloading from the oven.
• the quantity of carbonaceous reducing agent is determined by the stoichiometric quantity necessary to bring about the complete reduction of the metal oxides present, reduced by an amount corresponding to the reducing action of the volatile elements, and possibly increased by a quantity necessary for the fusion of the 'sponge and subsequent alloy.
• the better thermal conductivity of the layer of metal oxides present at the start in a single layer in the upper part of the load and then gradually in the mixture contributes to better heat transfer than that of multi-layer processes, without the the reducing agent, in this case carbon, which is a less good thermal conductor, does not disturb this process; the gradual mixing of the layers constituting the charge allows rapid homogenization of the temperature of this charge;
• the metal oxides very quickly reach high temperatures where their reactivity is stronger, which increases the efficiency of the reduction process and decreases the operating time;
• the furnace is generally maintained at a dome temperature of the order of 1300 to 1450 ° C, preferably of the order of 1400 ° C, by burners installed in the external walls of the hearth furnace and / or in the 'outer ring of the vault and with afterburner in the inner side of the crown.
• the techniques used also make it possible to increase the homogenization of the charges made up of pellets, which contributes to a considerable increase in the thickness of the charge, to a faster and more efficient operating procedure, to a smaller size of the oven and optimization of heat exchanges.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Manufacturing & Machinery (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Manufacture Of Iron (AREA)
• Tunnel Furnaces (AREA)

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• 1999
  • 1999-07-28 AU AU52894/99A patent/AU5289499A/en not_active Abandoned
  • 1999-07-28 CN CN99816824A patent/CN1361832A/zh active Pending
  • 1999-07-28 BR BR9917437-5A patent/BR9917437A/pt not_active Application Discontinuation
  • 1999-07-28 WO PCT/EP1999/005438 patent/WO2001009394A1/fr not_active Application Discontinuation
  • 1999-07-28 JP JP2001513649A patent/JP2003505602A/ja active Pending
  • 1999-07-28 KR KR1020027001164A patent/KR20020019957A/ko not_active Application Discontinuation
  • 1999-07-28 EP EP99938375A patent/EP1204768A1/de not_active Withdrawn
  • 1999-07-28 CA CA002379267A patent/CA2379267A1/fr not_active Abandoned
  • 1999-07-28 MX MXPA02000930A patent/MXPA02000930A/es unknown

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