Graphitic cathode for electrolysis of aluminum

FIELD: metallurgy; graphitic cathodes for production of aluminum.

SUBSTANCE: the invention presents a graphitic cathode for electrolysis of aluminum and is dealt with the field of metallurgy, in particular, with the graphitic cathodes used in production of aluminum by an electrolysis. The graphitic cathode for electrolysis of the aluminum is produced by graphitization of the cathodic block from a carbonaceous material. At that the cathode is made as the entire block with different specific electrical resistance along its longitudinal axis. At that the specific electrical resistance in the end areas of the cathode is more, than in its central area. The technical result - increased service life of the graphitic cathode at the expense of increased erosion resistance in the end areas of the cathode.

EFFECT: the invention ensures increased service life of the graphitic cathode at the expense of increased erosion resistance in the end areas of the cathode.

6 cl, 7 dwg, 1 tbl

 

The object of the present invention is a graphite cathode for the electrolysis of aluminium.

In the electrolysis process used in most installations for the production of aluminum electrolytic cell contains a cathode bottom, consisting of several placed side-by-side cathode blocks, metal tank, lined with refractories. This node forms the crucible, after which leakage protection lining pasta is a place of transformation electrolytic solution in the aluminium under the action of electric current. This reaction occurs at a temperature, which in the General case exceeds 950°C.

To withstand the temperature and chemical conditions prevailing during operation of the electrolytic cell, and to satisfy the need for conduction of electric current, the cathode block is made of carbon material. These materials range from poluproffesionalnye to graphitized. They are formed by extrusion or vibration compaction after mixing the following raw materials:

or a mixture of pitch, calcined anthracite and/or graphite in the case poluproffesionalnye and graphitized materials, after mixing these materials burn at approximately 1200°and graphitized cathode does not contain anthracite, Kato is made from these materials are usually referred to as a carbon cathode;

or a mixture of pitch and coke, graphite or without graphite, in the case of graphite, the material is fired at approximately 800°and then graphicsyou at temperatures above 2400°With this cathode is called a graphite cathode.

It is known the use of carbon cathodes, which, however, have moderate electrical and thermal properties, which are not suitable for continuous operation under the operating conditions of the electrolysis in the modern electrolytic cells, especially at high current. The need to reduce energy consumption and the possibility of increasing the current, in particular in modern facilities, promoted the use of graphite cathodes.

Standard processing at temperatures above 2400°in the case of graphite cathodes allows you to increase specific power and thermal conductivity, thus creating satisfactory conditions for optimized operation of the electrolytic cell. The power consumption is reduced because of the drop in the electrical resistance of the cathode. Another advantage of the fall of the electric resistance is to increase the current applied to the cell, which gives the possibility to increase the production of aluminum. Then a high value of thermal conductivity of the cathode allows to eliminate the excess heat generated by increasing the silts current. In addition, cells with graphite cathodes showed less electrically unstable, i.e., having smaller fluctuation of the electric potential than cells with carbon cathodes.

However, it was found that cell, equipped with a graphite cathodes, have a shorter life than cell equipped with carbon cathodes. Cells with graphite cathodes fail when excessive enrichment of aluminum with iron, which is a result of the influence of aluminum on the cathode rod. This metal acts on the rod as a result of erosion of a graphite block. Although the observed erosion of carbon electrodes, it is much smaller and does not affect the lifespan of cells that fail for reasons not related to the erosion of the cathode.

In contrast, the graphite electrode wear occurs quickly enough to be a major cause of failure of the cells for the electrolysis of aluminum after the premature expiration of the service life compared to life-time, registered in the case of cells, equipped with a graphite cathode. So, registered following the wear rate of various materials:

Table
The cathodeThe rate of wear (mm/year)
coal, poligraficzno the p 10-20
coal, graphitized20-40
graphite40-80

One drawing from the attached conditional drawings indicates cathode unit 3 with the cathode terminals 2 for the supply of electric current, the source profile are indicated by position 4. Profile 5 after erosion, indicated by the dotted lines, shows that this erosion is concentrated at the ends of the cathode block.

In the document FR 2117960 the essence of the cathode to produce aluminium by electrolysis. This cathode obtained from several blocks made from poluprofessionalnogo coal, which differ from each other as the specific resistance. This design is complex due to the placement of blocks side by side and electrically discontinuous, which is the result of the above-mentioned accommodation is not reducing erosion, since the cathodes of this type are not sensitive to erosion, and decrease the swelling of the bottom in the center pane.

Consequently, the rate of erosion of a graphite cathode block is its weak point, so it is attractive from an economic point of view in the context of increasing production can be disavowed if you cannot increase the service life.

The calculation of the current density in the cathode shows that they are higher in the direction of exit from the cathode of the output terminals. These density currents increase with decreasing electric resistance of the cathode. Thus, the profile of erosion of each of the cathode and, in particular, the large deterioration observed at the ends of the cathodes correspond to regions of high current densities at the cathode.

Therefore, the task is to reduce the erosion of the cathode made of graphite, in particular, in the limit areas of the cathodes.

The aim is to develop a graphite cathode with a service life increased by limiting erosion, which occurs at the ends.

To this end, the implementation of the cathode in accordance with the invention, a cathode made of graphite, is a single block, and its electrical resistivity is not the same along its longitudinal axis, and this resistivity in end regions of the cathode is greater than in the Central region of the latter. The average specific resistance of the product will correspond to the optimized operation of an electrolytic cell. Greater resistivity in end regions of the cathode generates a line current to the cell center. For this reason, reduced high-density current, generally incorporate in the direction of the exit of the cathode rods, thereby slowing the mechanism of erosion in these areas. Therefore, the service life of the cell increases. Note that to the core area of the cathode can be located for approximately from 0 to 800 mm from each end.

According to one possibility, during the operation graphitization end region of the cathode are brought to a temperature of about 2200-2500°while the Central region is brought to a temperature of about 2700-3000°C.

In accordance with the first specific embodiment, the difference in thermal treatment in the end regions and in the Central region of the cathode is obtained by limiting the insulation graphitisation furnace and/or by the location of the heatsinks in the end regions of the cathodes to increase heat loss.

In accordance with another specific embodiment, the difference in thermal treatment in the end regions and in the Central region of the cathode is obtained by local changes of the flow field, and hence as a result of the Joule effect, during the operation graphitization.

You can combine these two phenomena during the same operation graphitization.

In accordance with a specific embodiment of the cathode according to the invention, when the operation graphitization is conducted simultaneously for multiple cathodes arranged in parallel to each other inside the oven, such as oven Acheson (Acheson), in which the cathodes are separated from each other by a gasket in the form of a resistive grains, such as granules of coal or coke, the difference in treatment between the end regions and the cent is a pressing region obtained by changing the resistivity of a resistive grains between the two cathodes and/or by the location of the heatsinks in the end regions.

In any case, the invention can be better understood using the following description, given with reference to the accompanying conditional drawings showing as non-restrictive examples of the cathode in accordance with the invention, and figure 1 represents an image of the cathode with a more detailed designation erosion last after working for some time;

figure 2-4 - three species, respectively, top, front and side, graphitization Acheson furnace;

5, 6 and 7 three species, respectively, top, front and side, graphitization furnace longitudinal type.

2 to 4 depict the furnace 6 Acheson, in which several cathodes 3 are parallel to each other and between different cathodes are resistive grain 7. These resistive grain may consist, for example, pellets of coal or coke. The entire site is located within the insulating grains 8. For the operation of graphitization, into the oven down electrical energy, and the heat is a result of the Joule effect. In furnaces of this type of flow lines perpendicular to the axis of the cathode 3. To reduce heating in end regions of the cathodes 3, the resistivity of resistive grains in regions 9, the respective end areas of the cathodes 3, more than in region 10 corresponding to the Central part of the cathode. You can also reduce the thickness of the inu insulating grains 8 in end regions of the cathodes, to encourage this phenomenon limits the temperature of graphitization in these end regions due to heat losses.

Figure 5 represents the furnace 11 of the longitudinal type, in which several electrodes are placed end to end, and between adjacent cathodes is graphitization strip 12. Graphitization strips have the lowest possible resistivity, in order to avoid unwanted heating at the junction between the cathodes. In addition, the heat loss of the arrows shown are in end regions of the cathodes by providing a reduced thickness of the heat insulator 8 and/or the presence of heat sinks that can be made of graphite, but can also be located perpendicular to the cathodes and turned to the cooled areas.

From the foregoing it is obvious that the invention can significantly improve the existing technique by providing a conventional cathode structure obtained by known means, and having a specific resistance in its end areas is higher than in its Central region, which makes it possible to reduce the current density in the cathode at the ends and increase erosion resistance in these end areas.

1. Graphite cathode for electrolysis of aluminum obtained by grafitizare cathode block of carbon material, characterized in that Kato is made as a single unit with different specific electrical resistance along its longitudinal axis, this specific electric resistance in end regions of the cathode is greater than in its Central region.

2. Graphite cathode according to claim 1, characterized in that the difference in electrical resistivity in the terminal and Central regions of the cathode obtained by graphitization heat treatment at maintaining leaf areas at a temperature lower than in the Central region.

3. Graphite cathode according to claim 2, characterized in that during graphitization temperature limit areas of the cathode is 2200-2500°and the temperature of the Central region 2700-3000°C.

4. Graphite cathode according to any one of claim 2, 3, characterized in that the difference in electrical resistivity in the terminal and Central regions of the cathode is obtained by heat treatment while limiting thermal insulation graphitization furnace and/or when the location of the heat sinks facing end regions of the cathode to increase heat loss.

5. Graphite cathode according to any one of claim 2, 3, characterized in that the difference in electrical resistivity in the terminal and Central regions of the cathode is obtained by heat treatment at a local change in the flow field and result of the Joule effect during the operation graphitization.

6. Graphite cathode according to claim 5, characterized in that for graphitization multiple cathodes, RA is laid parallel to each other within the furnace, for example in a furnace Acheson, the cathodes are separated from each other by a gasket in the form of a resistive grains, such as granules or coke, and the difference in electrical resistivity between the terminal and Central regions of the cathodes obtained by heat treatment at the change of the electrical resistivity of resistive grains between the two cathodes and/or by the location of the heat sinks facing the terminal areas.



 

Same patents:

The invention relates to the electrolytic cell for obtaining aluminium, the way to maintain the cover on the side wall of the electrolytic cell for obtaining aluminium and method and regenerating electricity from one cell for obtaining aluminium

The invention relates to ferrous metallurgy and can be used in the production of aluminum by electrolysis of melts cryolithozone

The invention relates to ferrous metallurgy, in particular to the electrolytic production of aluminum, namely to design cathodic aluminum cell device

The invention relates to ferrous metallurgy, in particular to the electrolytic production of aluminum, and can be used on all types of electrolyzers

The invention relates to the field of metallurgy, namely the carbon-containing composite materials that are resistant to erosion/oxidation and capable of wetting molten aluminum used for formation of the cathodes or lining cells electrolytic recovery

The invention relates to the metallurgy of non-ferrous metals, in particular, to the design of the cathode casing aluminum cell

The invention relates to ferrous metallurgy, in particular to the electrolytic production of aluminum

The invention relates to ferrous metallurgy and can be used during installation of the lining of an aluminum reduction cell

The invention relates to the field of metallurgy, namely the production of cathodes used in electrolysis cells for the production of aluminum metal

The invention relates to ferrous metallurgy, the design of the cathode device aluminum cell

FIELD: metallurgy; graphitic cathodes for production of aluminum.

SUBSTANCE: the invention presents a graphitic cathode for electrolysis of aluminum and is dealt with the field of metallurgy, in particular, with the graphitic cathodes used in production of aluminum by an electrolysis. The graphitic cathode for electrolysis of the aluminum is produced by graphitization of the cathodic block from a carbonaceous material. At that the cathode is made as the entire block with different specific electrical resistance along its longitudinal axis. At that the specific electrical resistance in the end areas of the cathode is more, than in its central area. The technical result - increased service life of the graphitic cathode at the expense of increased erosion resistance in the end areas of the cathode.

EFFECT: the invention ensures increased service life of the graphitic cathode at the expense of increased erosion resistance in the end areas of the cathode.

6 cl, 7 dwg, 1 tbl

FIELD: metallurgy; production of graphitic cathodes.

SUBSTANCE: the invention presents an impregnated graphitic cathode for production of aluminum by electrolysis and is pertinent to the field of metallurgy, in particular, to production of the graphitic cathodes used in production of aluminum by electrolysis. The invention offers an impregnated graphitic cathode for electrolysis of aluminum and a method of its production. The cathode contains in its pores an impregnating product heat-treated. At that in the capacity of the impregnating product the cathode contains a carboniferous product heat treated under the temperature of no less than 1600°С to provide resistance to erosion at the expense of protection by the formed graphitized binding substance. The method includes production of the graphitic cathode, its impregnation by dipping into the impregnating product in vacuum and a thermal treatment. At that the graphitic cathode is produced from coke, with graphite or without it, and also from a pitch, and before impregnation it is exposed to calcination at the temperature exceeding 2400 °С. The impregnation is realized by a carboniferous product at the temperature of its viscous state and the thermal treatment of the impregnated cathode is conducted at the temperature of less than 1600 °С, but sufficient for hardening and-or sintering of the impregnating product and formation of the non-graphitized coal layer for protection of graphitizing binding substance against erosion. The technical result is an increase of service life of the graphitic cathode.

EFFECT: the invention ensures an increase of service life of the graphitic cathode.

4 cl, 2 dwg, 1 ex

FIELD: nonferrous metallurgy; production of aluminum by electrolysis of fused salts.

SUBSTANCE: the invention I pertinent to nonferrous metallurgy and may be used in a design of electrolyzers for production of aluminum by electrolysis of fused salts. The technical result of the invention is hardening of a hearth, a decrease of thickness of a metal layer on the hearth and an interpolar space, a decrease of speeds of circulatory flows of cathodic metal, a decrease of losses of current. The cathodic device contains a lined cathodic housing and a hearth made out of from carbonaceous blocks with channels of a rectangular cross section. On the surface of the hearth there is a wetted with aluminum cover and the channels have the length equal to the width of the stack of the cathodic device, and with a width equal 1,1-2,2 well of the carbonaceous block, depth, equal to 0.2-0.4 of height of the carbonaceous block and thy are formed by the lateral longitudinal surfaces of the carbonaceous blocks and the carbonaceous blocks of the lateral cathodic lining. The electro-conductive cover wetted with aluminum is made out of titanium diboride.

EFFECT: hardening of a hearth, a decrease of thickness of a metal layer on the hearth and an interpolar space, a decrease of speeds of circulatory flows of cathodic metal, a decrease of losses of current.

2 cl, 2 dwg

Aluminum cell // 2256009

FIELD: major repair of aluminum cells.

SUBSTANCE: cathode casing of aluminum cell includes lengthwise walls with windows for outlet of cathode rods, end walls, bottom and ring frames rigidly joined with walls and bottom. In order to lower labor consumption, simplify mounting and dismounting operations. Ring frames adjacent at least to one of lengthwise walls (except boundary ring frames) from their upper part till inner edge in range of height of windows for outlet of cathode rods are freely adjoined to said lengthwise wall. According to other variant of invention at least one lengthwise wall is detachable. Parting places of said wall are arranged between boundary ring frames in range of height of windows for outlet of cathode rods. In parting places members providing rigid joint of detachable wall with fixed portion of casing wall are mounted.

EFFECT: improved design, simplified works at major repair.

4 dwg

FIELD: formation of protective coatings for carbon containing components of electrolytic cell at aluminum production.

SUBSTANCE: method comprises steps of preparing liquid suspension of refractory material dispersed in solution of lignosulfonate binder; applying suspension as coating on surface of carbon containing component; drying coating.

EFFECT: improved resistance of carbon containing component against rupture at operation of electrolysis cell.

34 cl, 1 dwg, 4 tbl, 7 ex

FIELD: non-ferrous metallurgy; electrolytic production of aluminum; cathode units of aluminum electrolyzers.

SUBSTANCE: proposed side lining includes interconnected members - plates and blocks made from non-metallic refractory compounds possessing high resistance and interconnected by means of end faces in form of inversed symmetrical projections and recesses and adhesive or cementing mix. Plates and blocks are made from silicon carbide. Angular blocks are made in form of strip, 70 mm thick and 600-800 mm long which is bent at center around longitudinal axis at angle of 90° relative to vertical whose end faces are inclined at angle of 18° relative to vertical and are narrowing downward by 219 mm each. End faces are made in form of inversed symmetrical projections and recesses at radius of 14-15 mm which are parallel to vertical axis of walls of aluminum electrolyzer.

EFFECT: increased service life; enhanced strength and reliability; saving of lining material; increased useful volume of electrolyzer; increased yield of aluminum.

4 dwg

FIELD: aluminum cells, namely cathode facing for them.

SUBSTANCE: cathode facing includes carbon blocks, heat insulation layer and refractory part having two protection layers, upper layer adjoining to carbon blocks and lower layer made of powder materials. Upper protection layer includes alumosilicate composition resistant against action of electrolyte components containing 27 -35% of Al2 O3 with fraction size no more than 2.5 mm and with thickness consisting 10 - 50% of height of refractory part. Lower protection layer is made at least of one sealed metallic vessel filled with refractory material including carbon-containing composition resistant against action of melt aluminum and electrolyte components and having heat conductivity factor no more than 0.1 Wt/(mK). In lower protection layer vessels are filled with carbon black; thickness of said layer consists 50 - 90% of height of refractory part.

EFFECT: increased useful life period, improved operational characteristics of cell.

3 cl, 7 dwg, 1 tbl

FIELD: aluminum production electrolyzers of all types.

SUBSTANCE: proposed method includes mounting the heat-insulating and refractory components of electrolyzer and applying protective material on base of covalent nitrides to surface of side lining. Used as protective material is boron nitride-based material which ensures reduction of after-start period, increases electrolyzer service life, enhances aluminum grade, increases yield by current and daily productivity of electrolyzer; protective material is applied flush with top in continuous layer. Lower boundary of coat is located below "electrolyte-metal" interface. Thickness of coat is maintained within 0.1-1 mm. Open surface porosity is maintained within 2-3%. Consistency of material of coat changes from fluid to viscous-flow state. Application of coat is performed by spraying, painting or concrete-spraying method.

EFFECT: increased service life of electrolyzer; increased daily productivity of electrolyzer.

4 cl, 2 dwg, 1 tbl

FIELD: installation of aluminum electrolyzer hearth.

SUBSTANCE: proposed method includes preliminary estimation of quality of hearth modules by proximate ultrasonic inspection, mounting of complete set of hearth modules and forming of hearth; electrolyzer is equipped with hearth modules at inhomogeneity index not exceeding 0.65 relative units according to ultrasonic inspection; inhomogeneity index is determined by the following formula Iinhom = (tmax/tmin-1), where Iinhom is inhomogeneity index according to ultrasonic inspection; tmax is maximum magnitude of index of ultrasonic inspection for definite electrolyzer; tmin is minimum magnitude of index of ultrasonic inspection for definite electrolyzer; hearth is formed in such way that adjacent modules with close indices of ultrasonic inspection are mounted in longitudinal and transversal directions; modules with minimum indices of ultrasonic inspection are mounted in center of hearth at smooth increase of this index toward end faces of electrolysis bath.

EFFECT: increased service life of hearth; reduced yield of low-grade metal; reduced power requirements.

3 dwg, 1 ex

FIELD: mounting aluminum electrolyzers at major repair or in capital construction.

SUBSTANCE: current-supply metal rod is placed in slot of carbon block on layer of carbon-containing conducting material. Surface of carbon block slot is preliminarily coated with carbon-based surfactant and layer of carbon-containing conducting material is compacted by vibration applied on current-supply metal rod, thus ensuring reliable electromechanical "conducting rod-carbon block" contact and reducing probability of penetration of aluminum melt into hearth body. At application of vibration in local zone on side of flush area, maximum reduction of voltage drop is ensured in contact layer between rod and block slot. Maximum thickness of layer of carbon-containing conducting material before vibration is equal to optimal magnitude determined by definite formula.

EFFECT: enhanced efficiency.

4 cl, 4 dwg, 1 tbl

Up!