KR890004535B1 - Minimum-energy process for carbothermic reduction of alumina - Google Patents

Abstract

A carbothermic reduction process for Al prodn. is characterized by producing Al from the material mainly composed of Al oxide and carbon in reduction furnace by carbothermic process. The gas evolved during reduction is made to flow upward through the charged material in the furnace, and in postreaction region, chemical compounds producing or exothermic reaction occurs and the chemical compounds recirculate to the reduction region with the charged material. This process comprises (a) reduction of alumina and slag contg. carbonized Al with enough heat input in the hearth, (b) making of additive Al and gas without reactive C, (c) prodn. of preliminary reduced prodt. by transporting the gas from a and b, (d) Al gaining process.

Description

Carbothermal process for manufacturing aluminum

1 is a cross-sectional view of a decarburization furnace connected to a moving bed shaft carbothermal reduction furnace having a hearth shoulder as a charge entry control device and a closed recirculation system shown schematically.

FIG. 2 is a cross-sectional view of the carbosic reduction furnace of FIG. 1 connected to a decarburization furnace which is part of the schematic recirculation recirculation system.

Figure 3 shows a carbosics connected to tantalum, which is part of a closed recirculation system shown schematically, with a separate charging column of alumina and carbon mixtures in which the separated vapors are parallel and countercurrent through the charging material. Section of the reduction furnace.

4 is a cross-sectional view of a carbosmic reduction furnace having a mixture of alumina and carbon as the main component in the two fluidized beds (the mixture containing the alumina and carbon as the main component is discharged separately into the reduction furnace, and also the scrubber of the furnace steam) I play a role.)

5 is a cross-sectional view of a moving bed carbothermal reduction furnace which is not equipped with a subgrade shoulder and which is connected to the final stripping furnace and which is part of the closed recirculation system shown schematically.

* Explanation of symbols for main parts of the drawings

10: first lane 12: refractory brick

13: hearth 14: graphite stub (stub)

15: fireproof lining 16: fireproof roof (roof)

16 ': shoulder 17: space

18 electrode 19 plenum and opening

21: charging slot 22: tapping

23 liquid slack layer 24 reactive charges

25: liquid metal layer 28: charging column

30: second lane (tantalo) 31: insulator

32: inside fireproof lining 33: charging opening

34: charging and tapping outlet 35: product tapping

36 electrode 37 jack means

38: slack layer 39: liquid metal layer

40: decarburization furnace 41: line

42: dust collector 44,46: line

48: charge reserve device 49, 51, 52: line

50: third furnace (finishing furnace) 62: insulating refractory material

63 inner side image 68 electrode

69: electrical insulation means 72: tapping hole

73: molten slack layer 74: alumina

75 molten metal layer 76 charge

118: dust separation apparatus 121,122: reserve bin reduction

123: charging control means

The present invention relates to a method for producing aluminum from a material mainly composed of aluminum oxide and carbon in a reduction furnace, wherein in the reduction furnace, alumina and carbon are reacted by a carbothermic process to produce a small amount of aluminum carbide. This mixed aluminum is produced.

Looking at the prior art documents and patent documents it can be seen that there have been many attempts to develop a thermal process that can compete with the conventional electrolysis method of aluminum. It is well-known that in the prior art, there is a lot of theoretical advantages in using aluminum heat reduction instead of electrolysis in producing aluminum.

These useful points are of increasing importance in situations where energy costs are on the rise. Unfortunately, most aluminum production methods, such as the carbosmic process, do not produce pure aluminum.

Conventional methods fail because a mixture of aluminum metal and aluminum carbide is produced. When a mixture of 10-20% carbide or more dehydrated is cooled to about 1400 ° C., aluminum carbide forms a cellular structure that traps the liquid aluminum, making it difficult to pour the mixture. As a result, the purification of the mixture is not impossible, but very difficult, unless it is maintained at extremely high temperatures throughout the entire process step.

The difficulty in producing aluminum by the thermal process is not in the formation of aluminum through the reduction of minerals containing alumina, but in recovering aluminum in a pure state. Conventional technical documents and patent documents fully explain the theory and explanation of various back reactions occurring between aluminum and various carbon-containing compounds.

For example, U.S. Patent No. 3,971,653 uses a slag having an alumina mole fraction (N ^* = Al ₂ O ₃ mol / (Al ₂ O ₃ mol + Al ₄ O ₃ mol)) of 0.85 at 2100 ° C. and a slag of reduction temperature. The dross containing Al ₄ C ₃ is recycled. However, the overall reaction to produce aluminum takes place at the alumina mole fraction N ^* = 0.85, which means that the vaporization load is very large and power consumption is very high.

U.S. Pat.Nos. 2,794,032 and 2,828,961 describe typical results predicted in carbosmic reduction of stoichiometric charges of alumina and carbon in conventional electric furnaces. The aluminum produced by the former patent method contains 20-37% Al ₄ C ₃ , and the aluminum produced by the latter patent method contains 90% Al ₄ C ₃ . The methods described in these two patents limit the usage limitations because at least one of the reacted carbon and aluminum carbide always comes in contact with the produced aluminum and also has the time to allow the aluminum to react with the carbon to dissolve the carbide up to its solubility limit. Receive.

One method of solving the general problem of obtaining very pure aluminum from carbosmic processes is described in US Pat. No. 3,607,221. According to this patent, it is possible to produce almost pure aluminum, but the operating temperature is extremely high, which can cause problems with the constituent materials of the installation. Another method for obtaining very pure aluminum by carbothermal processes is also described in U.S. Patent No. 3,929,465, which also uses a carbothermal process to produce very pure aluminum but is charged to prevent incorporation of aluminum carbide. It is necessary to closely control the heating method of water.

Most prior art for producing high purity aluminum has been concerned with the process of treating the products of furnaces containing 20-35% by weight of aluminum carbide. Therefore, the prior art has a method of fluxing a furnace product with a metal salt to reduce the entry and exit of aluminum carbide.

Unfortunately, the molten salt is mixed with the carbide so removed, which is expensive to remove the carbide from the molten salt and recycle it to the furnace. Without this recirculation step, power consumption and furnace dimensions are more economical than conventional methods used to produce aluminum.

U. S. Patent No. 3,975, 187 describes a process for gas treating a product of a furnace to reduce the content of aluminum carbide in aluminum produced by a carbosmic process. It can be easily separated. This process is very effective in conserving the energy given to the production of aluminum carbide, but this process requires a recycling process due to the energy loss associated with the processing of the material.

According to US Pat. No. 4,099,959, the liquid alumina sock is circulated alternately through the tube into the low temperature region and the high temperature region, and the resistance is heated in a relation that is inversely proportional to the cross-sectional area of the tube. The low temperature region is a temperature sufficient to produce aluminum carbide. The off gas passes through a first charge column containing only carbon and then a second containing only alumina to preheat the charge without forming a viscous charge due to the partial melting of aluminum oxycarbide. It is first washed through the charge column. The low temperature zone and the high temperature zone operate within the melting range of the slag with an N ^* value of 0.82-0.85.

U.S. Patent No. 3,929,456 and U.S. Patent No. 4,033,757 describe a process for producing aluminum containing less than 20% Al ₄ Cl ₃ , i.e. 5-10% Al ₄ C ₃ , by a carbothermal process. Includes a method of intermittently applying open arcs to a portion of the surface of the charge to be reduced.

Today, however, the technological advances have made it possible to produce aluminum of commercial purity by treating aluminum incorporating about 20% of aluminum carbide. For example, U.S. Patent No. 4,216,010 can produce aluminum containing Al ₄ C ₃ (less than 20% (e.g. 10%)), which contains Al ₄ C ₃ as a product containing Al ₄ C ₃ . It is valuable as the best technology of the prior art by providing commercial competitiveness over the conventional carbothermal process that produces aluminum in the non-existent state.

It is now clear that technology development should be focused on limiting the energy losses associated with vaporization products, regardless of the method used to produce aluminum containing less than 20% Al ₄ C ₃ at a rapid rise in energy costs. The energy loss due to vaporization depends on the amount of steam produced in the reduction and decarburization stages, and the amount of steam that can be supplied into the system for use in the pre-reduction reaction, with the heat released and recovered from the post-reaction which sometimes releases heat. In addition, the amount of by-product aluminum and by-products need to be minimized, which are emitted from the hearth to minimize the energy losses involved. It also allows the vaporized material to circulate into the reduction zone before undesirable reactions (eg Al ₄ O and oxygen reactions) occur, maximizing the proportion of Al ₄ C ₃ formed outside the reduction zone. There is a need.

The process of US Pat. No. 4,216,010 is effective in the treatment of incorporation of aluminum carbide at greater than about 2% by weight. However, as already pointed out, unless special methods are used, for example, US Pat. Nos. 3,607,221 and 3,929,465, the amount of aluminum carbide incorporation produced in a conventional reduction furnace ranges from about 20-35% by weight. Becomes

U.S. Patent No. 4,216,010 relates to a method of treating aluminum incorporating about 10-20% by weight of aluminum carbide conventionally produced by carbosmic reduction reactors. However, this method can also be used to treat aluminum incorporating about 2-10% by weight of aluminum carbide produced in a furnace primarily used for aluminum production, as described in US Pat. Nos. 3,607,221 and 3,292,456. .

The process of US Pat. No. 4,216,010 reduces the furnace product of aluminum carbide by heating the furnace product in which aluminum carbide is mixed with a molten slag containing a large amount of alumina to react the aluminum carbide in the furnace product with the alumina in the slack. It is to let. Here, "to cause aluminum carbide to react with alumina in the slag" is an expression to describe the reaction of various modes. The reaction between the alumina in the slag and the aluminum carbide in the furnace product can be at least bivalent. However, it is not necessarily limited to these two types of reactions.

One of the above reaction modes may be referred to as a "reduction mode", which is a reaction mode in which alumina in slag generates aluminum by reaction between aluminum carbide in the furnace product under reducing conditions. One way to identify this reaction pattern is to check for the occurrence of carbon monoxide.

Another reaction mode can be expressed as a "rextraction mode," which is a non-metal slag such as aluminum tetraoxy carbide as opposed to the production of liquid aluminum by the reaction between alumina in the slag and aluminum carbide in the furnace product. It is a reaction mode that produces a compound.

The above "extraction form" may also occur with the "reduction form".

In general, for the operation of the "reduction mode" in the reduction zone under atmospheric pressure, a temperature of at least 2050 ° C is required. Under any given pressure, the decrease in the concentration of aluminum carbide in aluminum increases the temperature required for the "reduction mode" operation, on the contrary, the "extraction mode" operation can occur at temperatures below 2050 ° C.

Furnaces having a roof forming a bed shoulder supporting the charge column at the top of the furnace provide a means of controlling the amount of charge entering the furnace but a method of controlling the amount of charge entering the furnace. Generally more is needed. Moreover, this control method is very useful for controlling the amount of charges entering the hearth in furnaces of various shapes.

SUMMARY OF THE INVENTION An object of the present invention is to provide an aluminum production method for producing aluminum by carbothermal reduction of alumina and at the same time limiting the energy loss due to the increase to, for example, an amount corresponding to 10-20% vaporization of the supplied aluminum. It is.

It is a further object of the present invention to provide a gas that flows from the hearth to the incoming charge to recover a large amount of sensible heat, reducing heat and vaporizing material without impairing the air permeability of the incoming charge. To provide a way to capture.

It is yet another object of the present invention to provide a production method by a carbothermal process which can obtain an aluminum product containing a small amount of aluminum carbide.

The method for limiting steam and losses provides for the maintenance of one or more oxidant zones and pre-reduced compound zones where the gaseous product will post-react to produce alumina and aluminum carbide. This method includes the step of limiting the ratio (L / S) of the liquid phase in the tandem post-reaction zone to maintain an atmosphere in which the necessary post-reaction is possible. In extreme cases, the method includes charging feed carbon only at the top of the charge column and charging reducing alumina on the furnace.

The method of limiting vaporization loss includes limiting the production of vaporization material in the production of molten aluminum. This step increases the amount of reduction as much as possible while simultaneously contacting the solid aluminum carbide with the slag in the reduction zone, until the furnace product is decarburized to contain a predetermined amount of carbide, preferably less than 10% of carbide. The reduction reaction is terminated by decomposing the slag containing aluminum carbide and solid solution alumina.

In one embodiment of the present invention, the last step above uses the reduction decarbonization method described in US Pat. No. 3,216,010, because the composition of the slag is less than 25% Al ₄ C by the process of decomposing the slag. This is because the composition becomes rich in alumina to the extent necessary to maintain equilibrium with the metal containing ₃ .

The carbothermal process of the present invention for producing aluminum containing the selected small amount of aluminum carbide includes the following steps.

A. reacting a mixture of solid aluminum carbide and carbon with a liquid slag comprising alumina and aluminum carbide while providing sufficient heat input to produce liquid aluminum containing aluminum carbide, B. reaction Decomposing the slack in the absence of carbon and solid aluminium carbide to produce additional aluminum and carbon monoxide; C. passing the gas produced in A and B into at least one region, ie, the region in which the gas reacts with the region to produce alumina, aluminum tetraoxycarbite and aluminum carbide; D. combining the product of step C with said charge mixture for reaction with axon slack; E. recovering aluminum from step B containing a predetermined minimum amount of aluminum carbide.

The resulting aluminum recovered in step E usually contains 4-12% Al ₄ C ₃ . Part of the alumina that is stoichiometrically required for the production of alumina is added to step A, and another part is added to step C to control the L / S ratio and the aeration of the charge. The gas after passing through the charge material exits the device as a residual gas containing fume. It is preferred to add the charges to the insert column through which the increase can pass, but the charges can also be added to one or more fluidized bed reactors where heat transfer, reaction of by-products and branching of residual gas can be carried out.

It is also desirable to selectively take the following measures in the carbothermal process.

a) controlling the entry of the reactants into step A to reduce the reaction carbon in the slack of steps A and B.

b) Take action to reduce the alumina and aluminum carbide as described in US Pat. No. 4,216,010.

c) by heating aluminum containing aluminum carbide in the range of 4-10% in the absence of carbon, and heating the slag containing alumina to react the alumina dissolved in the aluminum with the carbide mixture. Measures to further generate aluminum and carbon monoxide at temperatures suitable for the operation of "reduction mode".

In particular, it is possible to produce the aluminum as the uihamyeo how Al of the invention ₄ C ₃ of carbonyl seomik final product as containing an Al ₄ C ₃ of less than 15% by the reduction reaction of aluminum and at the same time energy of the gas generator The loss can be limited to a level equivalent to the vaporization of more than 20% of the aluminum contained in the total furnace feed material. The method of the present invention comprises the following steps.

A. Producing aluminum as the first product of aluminum furnace containing 20-37% by weight of Al ₄ C ₃ by reacting alumina, carbon and recycle material according to the following steps, 1) the upper part of the electrode, reduction region Providing a reducing charge entry means disposed in the reducing zone having access to the reducing zone and at the same time bypassing the charge entry means, 2) 80-97% by weight in the reducing zone Forming a liquid slack layer containing Al ₂ O ₃ , 3) preparing a feedstock mixture comprising a portion of the alumina, recycle material, and carbon, which is stoichiometrically required to produce the initial product of an aluminum furnace. 4) providing at least one post-reaction zone capable of venting the vapor connected to the reduction zone by means of a charge entry means, and 5) adding stoichiometrically equivalent amounts of carbon to the final product of the aluminum furnace. Transferring the containing feedstock mixture from the post-reaction zone to the reduction zone via the charge entry means, 6) a bulk comprising alumina having a stoichiometric approximately equivalent amount of aluminum contained in the final product of aluminum furnace Adding alumina to the portion of the alumina entering the slack layer through the charge entry means directly to the reduction zone through the charge, 7) generating sufficient heat by energizing the current between the electrodes Dangy's charge mixture reacts with the slag layer to produce an initial product of aluminum furnace on the slag layer as a liquid side separated from the slag layer; B. The post-reaction zone is slumped by limiting the L / S ratio in the post-reaction zone and by varying the proportion of feed alumina selectively supplied to the post-reaction zone and directly supplied to the reduction zone. slumping) and keeping the steam aerated; C. terminating the reduction reaction to produce the final product according to the following steps, i.e. 1) by operating the charge entry means so that no further carbon as a charge mixture is supplied to the reduction zone and at the same time the reduction reaction 2) heating the slag layer until the reaction temperature in the reduction zone rises, and the slag is decomposed to produce the product of the final aluminum furnace as a separated liquid phase layer; D. Terminating the aluminum production cycle by removing the product of the final aluminum furnace.

The final product is processed in a finishing furnace to produce pure aluminum product and dross which is skimmed. Alternatively, the final product may be treated according to the technique of US Pat. No. 4,216,010, or by simply heating the final product in the absence of semi-annealed and aluminum-containing slag at a temperature of "reduction form" to obtain pure aluminum product and steam. There is also a method of producing and supplying the generated steam to the post-reaction zone.

The method also includes repeating steps 5) -7) of step A and adding the steps B-D to an additional production cycle.

The vaporization product contains Al, Al ₂ O ₃ , and CO. Recycled material includes CO, and aeration of the furnace collected from some or all of the dross collected from the finished furnace. The dust and dross are preferably mixed with carbon and a portion of the alumina supplied through the post reaction zone, followed by carbon coating to form briquetles and to minimize dissolution in the post reaction zone.

The production of aluminum is initiated on the slag side with composite alumina having a molar fraction of 0.4-0.6 as the starting material and continued while the solid Al ₄ C ₃ is in contact with the slag containing alumina having a molar fraction of about 0.775. Purification of the production method provides heat from an electrode placed on liquid aluminum to cause aluminum carbide in the aluminum layer to react with alumina in the slack layer so that the mole fraction of alumina in the slack layer is about 0.91-0.93, and the aluminum layer is It continues until it contains about 9.5-4% aluminum carbide and 12% alumina.

The L / S ratio in the charge column ranges from 27/73 to 52/48 when the temperature of the post reaction zone is 2000 ° C., preferably about 1970 ° C.

The post reaction zone may consist of a single charge column surrounding the electrode and in which the hearth that houses the post reaction zone is exposed at the top. However, it consists of a pair of insert columns located outside the furnace and connected to a pair of charge openings leading to the hearth, the charging mixture is added to the first charge column, and the mixing ratio with carbon is 80:20 in weight ratio. Particularly satisfactory when adding alumina having from 90 to 10 to the second charge column.

It is also possible to form a post reaction zone as a fluidized bed in a pair of charge columns by adding a powdered prereact compound to the charge column. The first and second charge columns each independently discharge into the furnace but enter the vaporization product first charge column and then into the second charge column as flowing gas. For example, about 30% of the feed alumina and all of the carbon are added to the fluidized bed in the first charge column and converted to Al ₄ C ₃ in the wetting copper bed and the remaining feed alumina is the fluidized bed in the second charge column. When preheated in the furnace and added to the furnace, the L / S ratio in the first charge column is about 45/55.

Features of the present invention may be described in comparison with US Pat. No. 4,099,959. The patented process is a continuous process involving changes in composition occurring at different locations in the system to produce metal over a narrow slack composition range of N ^* = 0.83-0.85. This process produces a total Al ₄ C ₃ for reduction in the slack and produces metal by reacting Al ₄ C ₃ in the slack solution with Al ₂ O ₃ of the solution in the slack. The patent process involves passing the vapor through a charge preheating column containing only carbon from the metal product and at a temperature such that the aluminum in parallel with the carbon produces more than 20% aluminum carbide. Under temperature the metal product in the carbon liquid is held in contact. Finally, the process of US Pat. No. 4,099,959 transfers liquid slack from one vessel to another.

In contrast, in the process of the present invention, the reduction step and the decarburization step are bath processes, and the change in composition occurs at different times at the same location in the system. The process of the present invention adds the reactant complex in a hearth having a wide range of N ^*, i.e., N ^* of 0.4-0.94 to produce metal. In the process of the invention most Al ₄ C ₃ is produced for reduction in the charge column. In fact, by adding about 67% or less of alumina directly to the hearth for the reduction reaction, all reduction reactions Al ₄ C ₃ can be prepared in the charge column.

Moreover, as much metal as possible can be produced by reacting Al ₂ O ₃ and solid Al ₄ C ₃ in the solution in the slack of the present invention. The reaction occurs during some stages of the metal production stage where the N ^* of the roadbed complex is about 0.775-0.4.

The present invention also removes the reaction carbon from the metal product during the final metallization step, producing a metal containing as little as 2% of Al ₄ C ₃ entry. The gas generated during the production of the metal flows into the charge preheating column and the charge pre-reduction column loaded with reducing carbon and some alumina.

In one embodiment of the invention, about one quarter of the reducing alumina is added to the charge column with carbon and about three quarters is added directly to the hearth.

In the present invention, it is preferable to maintain the liquid slack on one position, that is, on the primary furnace.

The aluminum production method of the present invention can be described based on five device examples (three single column examples, one twin column example and one fluidized bed column example). That is, 1) the charge contains dust, dross, carbon and alumina. 2) All dust, some or all of the dross, some or all of the alumina, and some or all of the carbon are intimately mixed in briquette mode (except fluid and column examples).

3) The remaining alumina and the remaining dross are fed to the furnace containing the molten slack layer in the reduction zone.

4) Alumina is supplied in an optional balance so that the charging column is kept gas ventilated and at the same time as much Al ₄ C ₃ can be formed in the charging column.

5) For the three single column embodiments, the charge is placed directly on the hearth.

6) Two columns of the twin column embodiment and the fluid bed column embodiment are arranged on top of the side of the hearth.

7) In all examples except fluidized bed examples, the gas produced from the reactions generated in the hearth is supplied to one charge column or multiple charge columns, transferring heat to the downwardly moving charge material, and The temperature becomes high as it approaches the post-reaction zone and the reduction zone.

8) The gas transfers heat to the charge material while passing through the gap between the charge materials, and the temperature of the charge material becomes high temperature as it approaches the post-reaction zone and the reduction zone.

9) In a number of post-reaction zones, a number of reactions occur between the charge and gas components and the heat of reaction is released to the charge.

10) The product of the reaction includes Al ₄ O ₄ C and Al ₄ C ₃ which are intermediates of alumina production.

11) Residual gas discharged from the post-reaction zone is fed to a device that separates the dust from this residual gas and sends the separated dust to the charge-processing unit.

12) In all embodiments, a sufficient amount of carbon-containing material is supplied to the furnace at the beginning and in the beginning of the production cycle in order to produce the large amount of aluminum required for the production cycle.

13) When the electrode is placed in contact with the liquid phase in the hearth, and a current is supplied to the electrode, the temperature generally does not rise to about 2000 ° or more, and if carbon is used to form Al ₄ C ₃ , aluminum is present. No metal is produced in large quantities.

14) All carbons react and at the point just before the temperature reaches 2080 ° C., the N ^* value of the material on the hearth drops to 0.4.

15) After carbon is consumed and the temperature reaches about 2080 ° C., a liquid aluminum layer formed by the reaction of alumina and solid Al ₄ C ₃ in the solution in the slag is formed on the liquid slack layer.

16) The reduction reaction continues until the N ^* value of the composition on the hearth is about 0.775.

17) As the N ^* value changes from about 0.775 to about 0.91-0.93, the electrode remains in contact with the fluid, and as the N ^* value approaches 0.93, the temperature rises to about 2130 ° C to 4-10%. Liquid aluminum containing Al ₄ C ₃ is produced.

18) Then, in the first extraction (alumina is supplied) or in the second (alumina is supplied and the slag is recycled in the reverse direction of the flow of aluminum) until the N ^* value is about 0.96. Dewanization reaction occurs.

19) Subsequently, further decarburization is carried out in conventional rice fields to produce aluminum having a commercial level of purity.

The reactions occurring in the post reaction zone and the reduction zone are as follows depending on the temperature conditions.

The method of the present invention is also characterized by the following steps occurring at the top of the charging column at a particular zone and at a particular time.

(Step I) The charge is preheated. Particulate dust in the particulate scrubber is returned to the scrubber as charged material. The only chemical reaction that takes place at this stage is the oxidation of Al ₂ O, which leaves the top of the long column and enters the scrubber.

(Step II) At the top of the charge column, solid alumina and carbon react to form Al ₄ O ₄ C and Al ₂ O vapor reacts according to Scheme R ₈ , wherein steam is carbon according to Scheme R ₁₁ . The first preliminary reduction step takes place, which reacts with to form an aluminum solid Al ₄ C ₃ .

(Step III) At the bottom of the charge column, the remaining Al ₂ O ₃ or carbon (used at the end) reacts to form a solid Al ₄ C ₃ , wherein Al ₂ O vapor is reacted according to Scheme R ₉ . The second preliminary reduction phase takes place. The aluminum vapor in contact with Al ₄ C ₃ condenses and liquid aluminum falls from the bottom of the charge column with the charge to the hearth.

(Step IV) Charges falling from the bottom of the charge column containing carbon and / or Al ₄ C ₃ and / or Al ₄ O ₄ C and or Al are mixed with alumina added to the furnace or to the slack. A mixing step occurs.

The slack was recycled to the hearth in the previous step to control the composition and to obtain a balanced metal product. If there is unreacted carbon, the above reaction formula R ₄ occurs.

(Step V) The material in the hearth reduction zone comprises a liquid slack, generally having an N ^* value of about 0.77-0.78, mixed with the solid and the pre-reduced product of step Al ₄ C ₃ . The composition of the composite has a N ^* value in the range of about 0.5 to about 0.775, starting at an N ^* value of 0.4 and increasing to about 0.775 as the reduction reaction continues and solid aluminum carbide is removed from the composition.

(Step VI) As the decarburization reaction to produce aluminum with an N ^* value of 0.775 or more occurs while the electrode is spaced from the metal on the hearth, the N ^* value is determined according to the reduced decarburization mode described in US Pat. No. 4,216,010. Will have the final value of. This stage is the final stage of the first furnace.

(Step iii) The decarburization step of the "extraction form" is accomplished according to the "extraction mode" as defined in US Pat. No. 4,216,010. The furnace for carrying out this decarburization step can be "DECARB Furnace" if the furnace is separated from the first lane.

(Step VII) Further decarburization is achieved by conventional cracking by separating the liquid product of the previous stage into two parts, the dross part containing some aluminum, some aluminum carbide and some slack and the product metal part. Run as a job.

Gas treatment of the furnace product as described in US Pat. No. 3,975,187 promotes the separation into the liquid aluminum product portion and / or the dross portion as described above, which requires 80% by volume of nitrogen, 10% by volume. It is particularly useful to use "Tri-gas" consisting of chlorine and volume% carbon monoxide.

It is one of the main objects of the present invention to provide control means for controlling the% of liquid phase in the upper region of the charge column in order to be able to control the vaporization losses in the primary furnace. One way to do this is to resupply the dross of step VII to the furnace in the first furnace, which is released by the post-reaction of Al ₂ O, although the% of the liquid phase at the end of step II is very low. This method has a high energy loss since no heat can be used to heat the dross.

It is an important feature of the present invention to provide a means for controlling the entry of carbon-containing charges into the hearth, such as a shoulder formed by the upper surface of the roof of the hearth in the two single column embodiments described above. As long as both the carbon and alumina components are present under the temperature of the furnace lower than 2000 ° C., slag is formed in the furnace but aluminum is not produced in a large amount. To solve this problem, the entry of the charges should be controlled so that the hearth completely consumes free carbon before step V begins. The furnace shoulder is installed to provide a charge column which controls the entry of such charges and at the same time releases useful heat by the post reaction of steam.

If the electrodes are in contact with the slag or the charge material mixed with the slack as in step VI, the temperature will be very uniform throughout the entire reaction zone and will not be above the temperature required for the progress of the reduction reaction. In order to provide the conditions for the decarburization during step VI, there is excess aluminum on the hearth. As long as free carbon is present, reaction R ₁ and reaction R ₃ proceed, whereby the temperature is limited to a temperature of at least 75 ° C. which is below the temperature required for the production of metal.

Problems such as "preemptive-heat absorption" by the slack-generating reaction can be solved by applying sufficient superheat to the stage by means such as an open arc. However, the steam generation rate of the open arc reduction method throughout step V is lower than that of the submerged-arc reduction method.

Hereinafter, the above-described five device embodiments will be described. The device of the first embodiment is a device comprising a first lane with a hearth shoulder, which is a three component device as shown in FIG. The apparatus of the second embodiment is the same as the apparatus of the first embodiment, but, unlike the apparatus of the first embodiment, a further "reduction form" decarburization reaction is carried out in the first lane, and the decablo of the "extraction form" is omitted. Alumina, which is not added to the top of the charge, is added to the furnace of the first furnace, and the alumina-rich liquid slag on the furnace of the primary furnace has a pair of devices as shown in FIG. A charge column. The apparatus of the fourth embodiment, ie the fluidized bed embodiment, includes a fluidized bed column as shown in FIG. The apparatus of the fifth embodiment, which is also a single column embodiment, includes a moving bed shaft furnace as shown in FIG. All charge columns except the fluidized bed column of FIG. 3 are supported to allow gas to be vented to allow countercurrent (reverse flow) of the reactant gas from the hearth.

For the five process implementations, the five apparatus embodiments described above are used as follows.

Example 1

From the decarburization furnace (Dicabro) to the first lane of FIG. 1, some alumina in the form of slack is supplied in counter current.

Example 2

Some alumina is supplied only to the reduction zone of the hearth in the first furnace of FIG.

Example 3

The entire charge is fed into a twin column which is supported for venting in FIG.

Example 4

The entire charge is fed to the fluidized bed twin column of FIG.

Example 5

A part of alumina is supplied to the reduction zone of the hearth in the first furnace of FIG.

Unlike Example 1, [Example 2] does not require recycling of alumina-rich slacks.

[Example 1] includes three processes. That is, in the first lane, crude aluminum containing about 9.5% Al ₄ C ₃ and 12% Al ₂ O ₃ is produced (first step); Decarburizing the crude aluminum in a decarburization furnace supplied with a large amount of alumina to form about 2% of Al ₄ C ₃ and slag (second step); Finishing, ie, decarburization in a gas fluxing furnace, produces practically pure aluminum and dross (third process). The term "counterflow" is a suitable term in the case of the present [Example 1], because the slack from the decarburization furnace is supplied to the first lane and moves countercurrent to the flow direction of aluminum.

Only two processes are required in the remaining four examples [2] [3] [4] [5], which in this example use some primary decarburization treatment to produce crude aluminum. Therefore, in Examples [2] [3] [4], aluminum containing 4-10% of Al ₄ C ₃ was produced (first step). In this case, aluminum containing about 2% of Al ₄ C ₃ is prepared (first step). As the decarburization treatment (second step), almost all suitable decarburization methods can be used except for the slack production method of [Example 1].

In the above embodiment, a pair of electrodes (for example, carbon electrodes) are used as heat generating means for reduction and decarburization, but a plasma torch may also be used as described in US Pat. No. 3,153,133. (Cathode emitter) and an anodic ring element of the plasma torch.

The closed recirculation system of FIG. 1 is lined with a refractory brick 12, which is an insulator, comprising a primary furnace 10 and a carbon furnace 3, which is provided with a graphite stub 14. Via an electrical bus.

The fire lining 15 and the inner roof 16 are formed in the inner side, and the upper surface of the inner loop 16 forms the shoulder 16 ', the inner loop 16 and the electrode. A space 17 is formed between the 18 and the gas phase electrode 18 is connected in parallel to the second side of the electric circuit.

The plenum and opening means 19 allow carbon monoxide to flow inward to prevent aluminum from condensing on the inner wall, thereby preventing electrical shorts between the roof 16 and the hearth 13. Numeral 21 is a tapping hole, and numeral 22 is a charging slot.

In the second lane 30, the insulator 31 has an internal (non-carbonaceous) fireproof lining 32, a charging inlet 33 for particulate matter, and tapping and moving for moving the liquid material between the first lane. The inlet 34 and the tapping-out hole 35 for tapping a product are comprised. The electrode 36 is for applying heat to the melt in the furnace 30.

37 is a jacking means for lifting the furnace 30, wherein when the furnace 30 is lifted, the melt is pulled from the tapping and charging hole 34 to the first lane 10 through the charging hole 21. Is transferred to). The product of the first lane flows into the tapping and charging hole 34 through the tap opening 22 of the first lane. The second furnace 30 is called a decarb furnace.

The dust collector device 42 is for separating aftershocks and residual gas discharged from the first lane 10 through the line 41, and the separated dust can be added to the charge of the first lane. Is transferred to the charge reserve device 48, and the purified residual gas is discharged to the atmosphere via the line 46.

The third furnace 50 is called a finishing furnace, which is in the form of a conventional cracking furnace, and has means for injecting fluxing gas at the lower side of the charging hole, the tapping hole and the melt. The final product aluminum is discharged through line 51 and the dross is transferred via line 52 to charge reserve 48.

In the charge preparation device 48, coke, alumina, lead, dross and pitch are mixed to produce a briquette-type charge and sent to the first lane 10 through the line 49.

Example 1

The briquettes 28 of the briquettes of the composition A and the composition B were prepared. Composition A (see US Patent Nos. 3,723,093, p. 8, lines 50-65) is transformed into alumina powder by applying 600-1000 ° C heat to aluminum hydroxide powder drawn according to Bayer method, This alumina powder and petroleum coke powder pulverized to pass through a 100 mesh sieve are mixed in a weight ratio of 85:15.

The composition B is prepared by petroleum coke, petroleum and coal tar pitch, the dust of the furnace tangled in the dust collector, dross removed from the finishing furnace 50, the briquette of the composition B is 800 The dust was removed by heating to 0 ° C.

The start-up operation for operating the first lane in the normal operating state is carried out in the following manner.

As in the start of the operation of a silicon furnace, the furnace is heated by energizing a pulverized coke bed from the electrode. When the hearth is properly heated according to the operation mode with silicon, sufficient alumina is added to form the liquid layer 23 on the hearth. The composition of the liquid layer 23 is a composition such as a fusion of alumina and aluminum carbide containing 80 to 97% by weight of alumina. Preferred compositional positions are 85-90% Al ₂ O ₃ and the remainder Al ₄ C ₃ .

At this point, the charge of composition A is added and the electrode is raised to an open arc to form a liquid layer 23 about 12 inches deep. When the charge is further added, alumina is further added to maintain the weight ratio of Al ₂ O ₃ : Al ₄ C ₃ in the liquid layer 23 within the range of 80: 20-97: 3 (parts by weight). In order to form the liquid layer 23 which is a slack layer to a predetermined depth, only the briquette of the composition A is sufficiently added. If the content of Al ₄ C ₃ in the slack layer is too small, the content can be adjusted by adding coke to continue heating under an open arc state.

Once the molten slack layer of the desired composition is formed, a charge of composition B is fed to form a charge column 28 by surrounding the electrode on top of the loop 16. In this charge column 28, vapor products react to release heat. A certain amount of charge from the charge column 28, which is stoichiometrically equivalent to the metal to be tapped, is heated to fall on the slack layer 23 to form a reactive charge in the hearth and on the hearth. Subsequently, the electrode is sufficiently lowered to be in electrical contact with the liquid phase, and a current is supplied to the liquid phase layer 23 to generate sufficient heat so that the reactive charge 24 reacts with the liquid slack layer 23. At this point in the cycle, the slag from the furnace (30) is added to the reactive charge (24).)

As the reduction reaction (step V) proceeds, aluminum containing 30-35% Al ₄ C ₃ is formed and is present as a liquid metal layer 25 separated on the slack layer 23. At the same time, a small amount of aluminum vapor and aluminum monoxide gas (Al ₂ O) are produced.

The aluminum vapor and the aluminum gas under monoacid are mixed with CO generated by the aluminum production reaction to rise upward through the charge column 28 in which the reaction occurs after exotherm, releasing heat and generating a compound. The resulting compound is lowered with the charge to produce aluminum carbide as the temperature rises. The gas and vapor continue to rise through the charge column to cool down and react until it reaches the top of the charge column 28 and the remaining gas proceeds to line dust collector 42 via line 41 where Clean residual gas from which dust is removed at is discharged to the outside through the line 46. The heat generated in the charge column 28 by the flow of the steam is used to preheat the charge and to cause the charge of composition B to produce Al ₄ O ₄ C.

At high temperatures, such as the bottom of the charge column 28 and loop 16, the charge of composition B reacts with the recycled vaporization product to produce Al ₄ C ₃ .

Step V is followed by the molar fraction N ^* (Al ₂ O ₃ ) of the composite composition (slack + charge) on the hearth until almost all the reaction carbon in the charge column 28 has been consumed with the electrode in contact with the charge or melt. Mole + Al ₄ C ₃ mole)) until about 0.775.

To change the metal product of step V containing 30-35% Al ₄ C ₃ to a product containing 10% Al ₄ C ₃ , the decarburization reaction according to step VI is used, which desorbs the electrode into the liquid phase. It is performed by raising to the top of the metal layer 25 to bring it into an open arc heating state. This open arc heating requires a higher voltage than when the electrode is in contact with the melt, but the total power input can operate at a reduced current equal to, or somewhat less than, step V where the electrode proceeds to an ecological contact with the liquid layer. Voltage is sufficient.

Open arc heating in step VI is continued until the molar fraction N ^* of the slack layer is 0.91 using reduced decarburization as defined in US Pat. No. 4,216,010.

At this point, the metal contains about 9.5% Al ₄ C ₃ and about 12% Al ₂ O ₃ . The temperature of the liquid metal portion in which the arc collides is a high temperature of about 2400 ° C., but the temperature of the liquid slack is about 2100 ° C. Both of these temperatures are sufficient to allow the metal to be present as an immiscible layer on the slack layer.

The metal is then transferred to the decarburization furnace 30 to complete step VI. An additional Al ₄ C ₃ charge from the pre-reduction zone is dropped onto the slack layer of the first lane 10, additional recycled slack is added onto the slack layer, and the electrode is brought into contact with the furnace melt. Repeat step V.

The heat intensity transferred from the arc to the charge must be limited, otherwise the vaporization will be so large that preheating and pre-reduction reactions in the charge column 28 will not be able to absorb the post reaction heat. In such a situation, the furnace becomes thermally unstable and unreacted vapor product is ejected from the top of the charge column to the outside, releasing excess heat and preventing useful reactants.

In the second lane, the liquid metal layer 39 on top of the slack layer 38 with N ^* = 0.96 of metal containing about 9.5% Al ₄ C ₃ and 12% Al ₂ O ₃ from step VI of the first lane. Rises as. The slack layer 38 also contains 15% CaO and is denser than the Al ₄ C ₃ -Al metal layer when operating at a temperature of about 1650 ° C. and is a liquid phase that does not mix with this metal layer. Most alumina, which is stoichiometrically required for aluminum products, is added to the decarburization furnace 30 to form an insulating cover, and finally into the slack, ie, the slack layer 38, to extract the method of US Pat. No. 4,216,010. After Al ₄ C ₃ is extracted from the metal to maintain the N ^* value of the slack layer 0.96.

When the metal layer 39 has adequate fluidity and the concentration of Al ₄ C ₃ is about 2%, the decarburization furnace 30 is inclined by the jack means 37 so that the molten metal is slack layer of the decarburization furnace 30 ( 38) to the finishing furnace (50). The slack generated during the extraction process of step VII of the second furnace 30 is recycled to the hearth of the first furnace and mixed with the reactive charge 24 dropped from the charge column 28.

According to step iii, all the alumina and aluminum carbide present in the metal product of step iv are in the melt with Tri-gas or other commonly used aluminum fluxing gas until it floats as dross on the surface of aluminum. It is blown into and refine | purified. This purification takes place at a temperature of about 900 ° C. The floated dross is skimmed and mixed without delay to the primary charging briquettes in the charge reserve device 48 via line 52 to prevent the aluminum carbide from hydrolyzing. The process of step VII is then completed by tapping the final aluminum product of commercial purity from the finishing furnace 50.

The molar fraction of the complex of the reaction stage from the mass balance and the energy balance of the embodiment described above is from N ^* = 0.51 at the end of step II to the end of step III N ^* = 0 (100% Al ₄ C). ₃ ) until N ^* = 0.468 at the end of Step IV, N ^* == 0.775 at the end of Step V, to N ^* = 0.910 at the end of Step VI, and N ^* = 0.96 at the end of Step VII I can see that.

Thus, the% of the liquid phase in the charge column is 35% at the end of step II, 0% at the end of step III and 46% at the end of step IV.

The resulting aluminum is 100㎏ when, in the step Ⅵ 12 pounds of Al ₂ O and 12㎏ aluminum vapor is generated, in step Ⅴ the Al ₂ O and Al vapors 9㎏ of 38㎏ is generated, at step 14 Ⅳ Kg of Al ₂ O is produced. In steps II and III, 48 kg of Al ₂ O and 16 kg of aluminum vapor were recovered by post-reaction. The heat generated is used as a driving source for the pre-reduction reactions of steps II and III, with the pure process heat required for the reaction in the charge column being 0.77 KWH per kilogram of aluminum produced.

The net energy loss of the 83 kg vaporization product produced in steps IV, V and VI is the amount associated with 4 kg of aluminum vapor leaving step II at the top of the 15 kg Al ₂ O and charge column. Table I summarizes the mass balance and energy balance for each of the eight steps.

The maximum allowable Al ₄ C ₃ content in the product of step VI of open arc heating to obtain mass balance in the extraction operation of step VII is about 9.5%. If it is above 9.5% and the extraction of step VII is in equilibrium, then the alumina charge must be added to step VII, and more slack is generated in step VII than is needed in the first lane. If the open-arc heating product of step VI contains 9.5% or less of Al ₄ C ₃ , the amount of alumina added required for the extraction operation of step VII becomes small, thus increasing the amount of alumina added to step IV. That is, alumina is added to the charge of the adjustment B.

The initial amount of slack in stage IV should be kept to a minimum in order to provide the alumina required for stage V, thereby keeping the N ^* value of the composite of stage V below 0.775 for as long as possible.

The addition of alumina in place of the charge of composition B to the furnace in the decarburization furnace or primary furnace reduces the% of the liquid phase in step II to 35%, which is about 79% when all alumina is added to the charge of composition B. It is very low. Keeping the carbon content in the charge of composition B as high as possible and coating the alumina with dross with pitch coke results in less sintering between briquettes and less slump in the charge column 28. As a result, the charge column can maintain a vapor permeability state, and thus, when Al ₂ O vapor permeates the charge column, a post reaction occurs to maintain an equilibrium state, thereby minimizing energy loss due to vaporization.

Example 2

인치메시의 그린(green) 석유코우크스로서 장입된다. 모든 알루미나는 환원 전해조에 장입되는 전형적인 알루미나 입도 분호를 가지는 금속학적 등급의 알루미나로서 장입된다.At the same time as using the apparatus shown in FIG. 2, briquettes A and B in the form of briquettes were prepared as in the countercurrent alumina feed system of Example 1, which differs from Example 1 to form briquettes of composition B. Is to mix the recycle material with the pitch. All coke needed for the reduction reaction

It is charged as green petroleum coke of inch mesh. All aluminas are charged as metallurgical grade aluminas with typical alumina particle size loading into a reducing electrolyzer.

As in the alumina countercurrent feed system, pre-reduction (in unreacted coke or Al ₄ O ₄ C and Al ₄ C ₃₎ , which is stoichiometrically required to produce aluminum that is tapping at the end of the aluminum production cycle. The production cycle is initiated by dropping the charge on the loop onto the furnace to provide all of the carbon (in compound form). The additional coke then feeds recycle material to the top of the charge column 28 to an appropriate level to provide a reaction zone in which the post-vaporation reaction takes place during subsequent production cycles.

If some of the slag is tapped together with the metal in the preceding production cycle, the charge is dropped to an additional charge above the amount stoichiometrically required to produce the metal in order to restore the carbon content in the slack to the desired start-up level. You have to.

The charge shown in FIG. 2 during the production cycle is then followed by the addition of alumina below the equivalent of the equivalent alumina content of the charge consisting of the pre-reduced product to be dropped to the alumina required to supplement the slag required at the start of the production cycle. Provided via 21 provides alumina which is stoichiometrically required to produce the metal to be tapped.

The electrode 18 is lowered to contact the charge 24, and electricity is supplied between the electrode and the hearth. As heat is generated, unreacted carbon reacts with the slack to produce Al ₄ C ₃ in the slack solution. After carbon is changed to Al ₄ C ₃ , the temperature rises to about 2100 ° C., and the production of metal begins. The greater the amount of metal produced, the greater the amount of aluminum supplied through the charging inlet 21, the better the fluidity of the metal, and the electrode needs to be raised to a low voltage arc condition. When all the alumina required for the production cycle is supplied and all the power for the reduction reaction during the production cycle is used, the metal is decarburized to the extent that it contains 4-10% of Al ₄ C ₃ when the metal is cooled. .

No further carbon is supplied to the hearth throughout the production cycle, and the vaporization product is post-reacted in the charge column to generate the heat necessary to produce Al ₄ O ₄ C and Al ₄ C ₃ . These materials then fall on the hearth during the next production cycle.

When using this embodiment without employing an alumina countercurrent feed system, the decarburization furnace 40 requires a special decarburization method such as that required to decarburize the product of the primary furnace containing 4-10% Al ₄ C ₃ . It doesn't. However, the decarburization method should not be the slack decarburization method of "extraction mode". Any decarburization method can be used in which the concentration of Al ₄ C ₃ is 2% or less without supplying additional alumina to the decarburization furnace. Usually, the product of a primary furnace is decarburized by the following method. That is, (a) dilution with pure aluminum followed by fluxing with gas, (b) the reaction of chlorine directly with the product of the primary furnace, or (c) the reaction carbon as described above. A method of simply heating the product of the primary furnace to a reduction temperature in a vessel not to be used.

It was observed that the product of the first furnace prepared according to this example contains 4-10% Al ₄ C ₃ and about 12% Al ₂ O ₃ . Alumina contained in the primary product may react with Al ₄ C ₃ in the product to produce Al, Al ₂ O ₂ and CO. If the above reaction occurs in the absence of reactive carbon, the metal is decarburized according to the decarburization method of (C) above.

Example 3

This embodiment employing an external charging method is shown in FIG. This embodiment, unlike the first and second embodiments, does not have a charge column in the furnace, but installs one or more plug-flow post-reaction vessels outside the furnace. Each post-reaction vessel contains a reactive material as a charge column, through which the vapor generated during the reduction and decarburization step proceeds to cause post-reaction, and the pre-reduced product from the post-reaction vessel is charged with one or more charges. By supplying water to the reduction zone by the water entry device, the carbon in the slag can be consumed at a predetermined cycle. In the case of this embodiment, it is preferable to have two charge columns, and it is necessary to supply the whole charge to the container 81,82.

The furnace 60 is composed of an insulating refractory 62 and a hearth 63 on the inside, and side and roof linings 65 made of carbon. The hearth 63 is connected to the electric bus via a graphite stub 64.

Electrical insulation means 69 is provided around each electrode 68, and the insulation means is installed such that carbon monoxide gas flows downward along the electrode so that aluminum does not condense around the top of each electrode. This prevents a short circuit between the electrode 68 and the hearth 63. 72 shows a hot water outlet. The liquid slack layer 73 is located under the liquid metal layer 73 containing aluminum and aluminum carbide. The electrodes 68 are connected in parallel and are in contact with the liquid metal layer 75. Heat is generated by energizing a current through the slack layer 73 between the electrode 68 and the hearth 63.

Vessel 81 is a vessel provided for preheating alumina using the heat generated by the reaction of aluminum and aluminum monoxide with the CO produced in furnace 60, wherein vessel 82 is subjected to a reduced vaporization product later A vessel is provided for preheating and reducing the contents containing coke, alumina and recycle products using the heat released upon coagulation. Feed means 83 and 84 are installed to control the amount of material supplied and the supply time of the furnace 60.

The slack layer 73 is formed in accordance with the method described in the first embodiment. The flow rate of the reducing steam and the flow rate of the CO gas through the containers 81 and 82 can be controlled using the valves 85 and 86 to prevent overheating and melting of the alumina in the container 81.

Forms charged briquettes containing dross from petroleum coke, recirculation and decarburization. When the briquette is charged into the container 82, the coke component in the briquettes undergoes a preliminary reduction reaction using heat generated by the post-reaction of steam from the reduction furnace 60. Heat transfer to briquettes is achieved by passing CO gas through the vessel 82.

To begin the production cycle, the equivalent mole fraction of the slack is adjusted so that the N ^* value is about 0.91 by first adding alumina from the vessel 81 or the charge from the vessel 82. Subsequently, the stoichiometric amount of charge 76 is supplied from the container 82 to the slack layer 73 with respect to the metal to be tapped at the end of the production cycle. At the same time, the calculated amount of alumina 74 is supplied from the container 81 to the slack layer so as to yield a stoichiometric compensation amount of the charge supplied from the container 82.

Continue to supply generation level power throughout the generation cycle. Initially the temperature of the slag is reduced and the composition of the slag changes toward N ^* = 0.775 as the unreacted carbon in the charge 76 reacts with the slag. After the free carbon has been consumed, the temperature naturally rises to the reduction temperature and metal production begins. Metals containing about 4-10% Al ₄ C ₃ are produced until the composition of the slag returns to N ^* = 0.91. Tapping this metal completes the production cycle.

According to the method described above, the liquid / solid ratio in the container 82 is the lowest. In some cases, if it is necessary to increase the% of the liquid phase in the container 82, alumina required for the reduction reaction can be added to the briquettes. Another effect obtained by adding alumina to briquettes is that a greater amount of Al ₄ C ₃ is formed in the vessel 82 and the tendency of carbon to directly reduce in the hearth region is reduced.

Unlike the method of US Pat. No. 4,099,959, the method of the present invention uses a conventional furnace, does not require circulation of the slag between two temperature zones, and provides a means for consuming slag in reactive carbon at the charge feed point. and has a very wide range up to N ^* = 0.91 from the mole fraction of the time of generation of the metal furnace top alumina N ^* = 0.39.

The addition of the three charges according to Example 3 and the operation of the furnace are summarized in Table II.

Example 4

As shown in FIG. 4, the furnace 100 is composed of an internal furnace 103 having an insulating refractory 102 and a side and roof lining 106 of carbon. The hearth 103 is connected to the electric bus via a graphite stub 104. The furnace 100 is also provided with electrical insulation means 109 on the periphery of each electrode 108. The electrical insulation means 109 is designed to allow the carbon monoxide gas to flow downward along each electrode. Aluminum can be prevented from condensing on the top, thereby preventing the occurrence of a short circuit between the electrode 108 and the hearth 103. The furnace 100 is provided with a tap and the electrode 108 is connected in parallel.

The pre-reduction vessels 121 and 122 are connected in series with the inlet gas via lines 115, 116 and 117. Residual gas passes through line separation device 118 through line 125 and then through lines 126 and 127. Some of the gas is recycled to vessel 121 via lines 128 and 116, and some of the gas (the same amount of gas in line 115) exits through line 127. The total amount of gas circulating through the containers 121 and 122 keeps the contents in the container in a flow state.

Alumina is charged in the vessel 122 and carbon and recirculating dross particles are charged in the vessel 121 which are separated in line 125 and enter through line 119. Preheated alumina from vessel 122 then enters furnace 100 via line 124, and the preheated and pre-reduced charge from vessel 121 is passed through furnace 124. Enter As a result, the charge 144 is combined with the alumina from the container 122.

The first lane 100 is provided with a liquid slack layer 113 at the beginning of operation as in the first and second embodiments. The vessel 122 is filled with Al ₂ O ₃ , and the vessel 121 is filled with a mixture of granular coke, recycled Al ₂ O ₃ , dust, Al ₄ C ₃ and Al. A typical charge for producing 100 kg of aluminum in each production cycle is 71.9 kg of carbon, 25.3 kg of Al ₂ , O ₃ , 18.5 kg of Al ₄ C ₃ from the recycle dross and 66.7 kg from the recycle dross Al is 182.4 kg in total, and these contents are supplied to the container 121.

In each production cycle for producing 100 kg of aluminum, the charge control means 123 was operated to produce 1.4 kg of Al ₂ O ₃ , 203.6 kg of Al ₄ C ₃ and 43.7 kg of Al from the vessel 121. Enters the slack layer 113 of the hearth and also activates the supply means 124 to drop 189.2 kg of Al ₂ O ₃ from the vessel 122 onto the hearth to complete the formation of the charge 114. It forms part of the mixing stage IV.

When the reducing current is energized while the electrode 108 is in contact with the slack layer 113, steps IV and V occur in the furnace 100.

The reduction reaction proceeds while the temperature of the hearth is maintained at 2000 ° C. until carbon in the composition of the hearth is depleted to form Al ₄ C ₃ in a sufficient amount for the N ^* value to approach 0.39.

Subsequently, the Al ₂ O ₃ and Al ₄ C ₃ react in the slack layer 113 to raise the temperature to 2100 ° C. to form the metal layer 105 according to Scheme R5. 121) After passing through the charge in 122, the residual gas enters the dust collector through the valve.

When a sufficient amount of Al ₄ C ₃ is consumed according to Scheme R5, the N ^* value of the liquid slack layer 113 approaches 0.91, and the metal layer 105 contains 4-10% of Al ₄ C ₃ . This metal layer is then transferred to a finishing process as described in Example 2, where the dross and 100 kg of produced aluminum are recycled to the pre-reduction vessel 121 to be used in subsequent steps. The operation of the furnace of Example 4 is summarized in Table III.

Example 5

The fifth embodiment is the same as the first and second embodiments in which a single charge column is disposed directly on the hearth, but differs from the first and second embodiments in that there is no hearth shoulder serving as the charge entry means. Instead, the conditions of operation are carefully manipulated to ensure that the contents have their own support.

As shown in FIG. 5, the first furnace 130 is a high voltage, polyphase AC furnace used for the production of silicon. However, the furnace is equipped with means for direct entry of alumina into the hearth and an insulator designed to maintain the interfacial temperature between the carbonaceous lining at 1980 ° C when the liquid slack is maintained at a temperature of 2000 ° C in the hearth chamber. .

The first lane 130 has an insulator 132 made of a refractory brick, an inner wall made of carbon, and a hearth. The electrode 138 is connected to the AC three-phase Y array, so there is no need to conduct current through the hearth.

The crucible F inside is formed by cooling 90% or more of Al ₂ O ₃ and the remainder from alumina from the slag containing Al ₄ C ₃ .

The liquid slack layer 143 is formed in the crucible F, and the liquid aluminum layer 145 containing Al ₄ C ₃ floats on the slack layer 143.

A semi-reduced compound (D) is present around the isotherm at 1970 ° C, while Al ₄ C ₃ and Al ₂ O ₃ or carbon-containing material (C) at 2000-2050 ° C is located near the heat source. Is formed at a temperature of.

The inlet 141 is an alumina charging means that allows the alumina to be loaded onto the furnace without contacting the non-reactant charge in the region C or D or the moving bed shaft A.

In addition, there is a tapping hole 142, which is connected to the electric means having a transformer connected to the neutral circuit of the power supply device of the electrode, it is necessary to open the tapping opening 142 In this case, it is possible to help dissolve the crucible (F) around the tapping hole (142).

The furnace 160 is a conventional aluminum crack furnace, which contains a spout, means for releasing the fluxing gas out of the upper surface of the melt, skimmer and solid dross from the top surface of the resulting aluminum. Ejector means are provided.

The dust collector 152 is for accommodating residual gas leaving the furnace 13 through the line 151, and the collected dust is sent to the charging preliminary device 158 via the line 154, where the recovered dust is collected. The particles are mixed with petroleum coke, petroleum or Kltar pitch, alumina and the draw down recovered from the finishing furnace 160 to produce briquettes.

Furnace 130 can be started by the method described in Example 1, liquid slack layer 143 consisting of 95% Al ₂ O ₃ and 5% Al ₄ C ₃ according to the method of Example 1 (melting point Silver is about 1980 ° C.). Initially, the depth of the liquid slack layer is dimensioned to be equal to the maximum expected height of the metal layer 145 to be produced. Subsequently, a sufficient amount of slag is tapped to form a solidified slag crucible F while the upper surface of the liquid slack layer 143 is positioned at the bottom of the tap.

The pre-reduced charge (C) containing the stoichiometrically required carbon in the form of Al ₄ O ₄ C, Al ₄ C, or C in the metal to be tapped is dropped onto the slack layer 143 to make the reactive charge 144 ) And charge briquettes are added to the charge column 148 to maintain that level.

Current flows between the electrodes through region C, flows from the electrodes to the metal or slag and then to the adjacent electrodes.

When heat is transferred, the reaction between the reactive charge 144 and the slack 143 proceeds to form aluminum containing 30-35% Al ₄ C ₃ .

At the same time aluminum vapor and aluminum oxide (Al ₂ O) gas are produced. These gases are mixed with CO gas formed by the aluminum formation reaction and flow upward through zone C and the charge column 148 where post-reaction occurs to release heat and produce compounds. The fished compound is recycled with the charge to produce a mixture of Al ₂ O ₃ , Al ₄ C ₃ and Al ₄ O ₄ C at about 1970 ° C. in zone D. In the high temperature C region, Al ₄ C ₃ reacts with carbon to form Al ₄ C ₃ .

Al ₄ C ₃ formed in the region C forms a sintered roof to prevent unreacted carbon from entering the sulfur source region for the remainder of the production cycle.

As the production cycle progresses, a certain amount of alumina is supplied through the inlet 141 which is stoichiometrically required for the production of aluminum but not added to the charge briquettes. A generation cycle continues and, according to haejum supply additional alumina slack-water reactive charged composition of the mole fraction of the alumina from the N ^* N ^* of about 0.06 to about 0.92 is changed. The metal is decarburized to about 4% A1 ₄ C ₃ according to the reduction pattern of decarburization described in US Pat. No. 4,216,010.

The level of power is then reduced to the extent that the production of metal can be stopped (which can be seen by the significant decrease in the production of CO gas), and the furnace is held for about 1 hour in this state. During this period, the slag temperature is maintained at about 2000 ° C, the alumina solidifies slightly to remove the reactive carbon in contact with the slag, and the metal is about 2% according to the decarburization method of the extraction form described in US Pat. No. 4,216,010. Is further decarburized to Al ₄ C ₃ .

The metal is then tapped into the furnace 160 where the trigas is blown in and the temperature is lowered to about 900 ° C. so that about 20% of the aluminum and all Al ₂ C ₃ and Al ₄ housed in the furnace 130 are provided. Dry dross containing C ₃ is formed. The dross is skimmed and recycled through line 162 to charge reserve device 158 where it is mixed with the charged briquettes of the primary lane without delay to afford room for hydrolysis. The aluminum produced in commercial purity is then tapped from the finishing furnace.

Immediately after tapping the metal of the furnace 130, the production cycle is repeated by moving the material from zone C to reduction zone E.

The preferred percentage of alumina added to the charged briquettes is 20-30%. This alumina facilitates the fall of the material by creating a liquid phase in zone C, while keeping the% of the liquid phase low in zone D so as not to impair the permeability necessary for post-reaction of vapor and gas.

Table IV summarizes the energy balance and the step-by-step mass balances for the processes described above. The industry may be described as including a charge bridging preheating stage including a lead recovery unit and a recycle. As the charge column A descends the shaft of the furnace 130, semi-liquid compounds are produced in zone D and sintered bodies (mainly Al ₄ C ₃ ) are produced in zone C. In zone E, mixing, pre-reduction and decarburization occur sequentially. Decarburization then occurs in furnace 160.

TABLE I

Overview of Materials and Energy Balances

TABLE II

Overview of Materials and Energy Balances

TABLE III

Overview of Materials and Energy Balances

Table IV

Overview of Materials and Energy Balances

Claims (21)

Alumina and carbon react in the reduction zone in the furnace to produce aluminum containing aluminum carbide, and the gas produced during the reduction reaction can flow upward through the charging material charged into the furnace in the post reaction zone. In the reaction zone, an exothermic reaction and a reaction to generate a compound occur, and the compound is recycled to the reduction zone together with the charged material, wherein in the carbothermal process for aluminum manufacturing, (A). A mixture containing solid aluminum carbide and carbon was added to the liquid phase including alumina and aluminum carbide in the furnace of the furnace under applying a heat input sufficient to produce the gas and sufficient heat input to produce aluminum carbide containing liquid. Reacting with slack; (B). Decomposing the slack in the absence of reactive carbon and solid aluminum carbide to produce additional aluminum and gas; (C). Generating a pre-reduction product by passing the gas generated in steps (A) and (B) through a post-reaction zone; (D). Using the pre-reduction product of step (C) as part of the mixture of step (A); (E). Carbothermal process for producing aluminum, characterized in that consisting of recovering the product aluminum containing aluminum carbide from the step (B). The process of claim 1 wherein at least some of the alumina stoichiometrically required for the production of aluminum is supplied to the hearth of the furnace without passing through step (C). The process of claim 2, wherein the gas released in the reaction of step (C) is used to preheat the alumina supplied to the furnace without passing the step (C). The process of claim 2 or 3, wherein a portion of all carbon and alumina that is stoichiometrically equivalent to the carbon contained in the product aluminum is fed to step (C) together with the charged material, and the portion of the alumina Carbothermic process for producing aluminum, characterized in that the total amount of part of the alumina supplied to the furnace without passing the step (C) is the amount of alumina which is stoichiometrically equivalent to the aluminum recovered in the step (E). The post-reaction according to claim 2, wherein the ratio of the total alumina demand supplied to the furnace without passing through step (C) is controlled to be 67% or less, thereby controlling the ratio of liquid / solid phase in the post-reaction zone of step (C). A carbothermal process for producing aluminum, wherein the material in the zone is maintained at a rate that ensures non-slumping and vapor venting conditions. 6. The liquid / solid phase ratio in this zone is 27 / 27-52 / 48, preferably in the range of 35 / 65-45 / 55 when the temperature in the vapor-permeable region is below 2000 ° C. Carbothermal process for producing aluminum, characterized in that. The process of claim 2 wherein the entry of said mixture into said step (A) is controlled to consume reactive carbon in the slack for the purpose of said step (B). 8. The method of claim 7, wherein the ingress of the mixture is controlled by a hearth shoulder forming an inner loop for the reduction zone disposed above the hearth and below the charge column providing the post reaction zone. Carbothermal process for producing aluminum. The process of claim 7 wherein the entry of the mixture is controlled by a pair of charges in the loop of the furnace and the post reaction zone is provided by at least one column of the corresponding pair of charge columns outside of the furnace. And a carbothermal process for producing aluminum, which is connected to the charging hole. 10. The process of claim 9 wherein each post-reaction zone terminates as a fluidized bed in a pair of charge columns and is added to the charge in powder form. A charge material according to claim 9 or 10, wherein a charge material containing carbon and some of the alumina is supplied to one charge column, wherein the reaction of step (C) takes place, and the other charge column contains the remaining alumina. Wherein the alumina is preheated before entering the hearth of the furnace in the other charge column. 8. The process of claim 7, wherein the entry of the mixture is controlled by adjusting the proportion of total alumina supplied to the furnace to 70-80% without going through step (C), whereby the bottom of the charge material in the post reaction zone is reduced. Carbothermal process for producing aluminum, characterized in that it has sufficient strength to form a sintered loop for the region, The method of claim 2, wherein the product aluminum is moved to a second lane to react with the slag containing alumina to further reduce the carbide content of aluminum, and the portion of the alumina supplied without the step (C) is A carbothermal process for producing aluminum, which is added to a slag in a second furnace and recycled to the hearth of the first furnace. The method of claim 1, wherein the heat input of step (A) is provided by an electrode in contact with the fusion layer of the hearth, and the electrode is provided in the hearth to provide open arc heating in step (B). A carbothermal process for producing aluminum, which is spaced apart from the melt. The process of claim 1, further comprising the step of further decomposing the slack layer at a temperature causing the generation of carbon monoxide until the carbide in the slack layer is further depleted after step (B). fair. The process of claim 1, wherein the steps (A)-(E) are cyclically repeated. The liquid slag of step (A) contains 80-97% by weight of alumina, and the liquid aluminum produced by step (A) contains 20-37% by weight of aluminum carbide. Carbothermal process for producing aluminum, characterized in that the aluminum product recovered in step (E) contains not more than 15% by weight, preferably 2-12% by weight of aluminum carbide. The method according to claim 1, wherein the alumina mole fraction (N ^* ) at the start of step (A) is at least 0.4, preferably 0.5-0.6, and is raised to 0.77-0.78 when no solid aluminum carbide is present, and step (B). The carbothermal process for manufacturing aluminum, characterized in that it is raised to 0.91-0.93 at the end of the step, and is raised to 0.94-0.96 in a subsequent step of the step (B) in which the reaction between the aluminum product and the alumina containing slag occurs. The process of claim 1 wherein the aluminum product is further treated in a finishing furnace to produce pure aluminum and dross, which dross is recycled to the charge material after coating with carbon. 2. The method of claim 1, wherein the flow of carbon monoxide into the reduction zone is maintained to prevent aluminum from condensing on the furnace wall or the heating electrode, thereby preventing short circuit of the heating electrode. Carbothermal process. The alumina and carbon react in the reduction zone in the furnace to produce aluminum containing aluminum carbide, and the gas generated during the reduction reaction can flow upward through the charging material charged into the furnace in the post reaction zone. In the reaction zone, an exothermic reaction and a reaction to generate a compound occur, and the compound is recycled together with the charged material to a reduction zone in the carbothermal process for producing aluminum, wherein the carbon is stoichiometrically equivalent to the carbon contained in the aluminum product. After the reaction charge material containing the reaction is moved to the furnace of the furnace to react with the liquid slack layer containing alumina, at least a part of the alumina to be reacted is directly supplied to the furnace, the at least some alumina and the post-reacted The total amount of alumina contained in the charge material is contained in the aluminum product. Carbothermal process for producing aluminum, characterized in that the stoichiometric amount of aluminum.

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