Method of mounting side lining of cathode device for aluminum electrolyzer

IPC classes for russian patent Method of mounting side lining of cathode device for aluminum electrolyzer (RU 2270887):

C25C3/08 - Cell construction, e.g. bottoms, walls, cathodes

Another patents in same IPC classes:

Cathode facing to aluminum cell / 2266983
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.

Side lining of aluminum electrolyzer / 2263162
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.

Method of forming protective coating for carbon containing components of electrolysis cell / 2257425
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.

Aluminum cell / 2256009
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.

Cathodic device of aluminum electrolyzer / 2245397
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.

Impregnated graphitic cathode for electrolysis of aluminum / 2245396
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.

Graphitic cathode for electrolysis of aluminum / 2245395
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.

Method of mounting side lining of cathode device for aluminum electrolyzer / 2270887
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.

Method of forming hearth for aluminum electrolyzer / 2270888
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 I_inhom = (t_max/t_min-1), where I_inhom is inhomogeneity index according to ultrasonic inspection; t_max is maximum magnitude of index of ultrasonic inspection for definite electrolyzer; t_min 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.

Method of mounting cathode section of aluminum electrolyzer / 2270889
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.

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

The present invention relates to non - ferrous metals, in particular, to the production of aluminum electrolytic method. In this area you can use in electrolytic cells of all known types when put into commercial operation.

It is known that in the process of preparing cells for operation (firing and start) its cathode part in the most heavily exposed to aggressive factors, which leads to various kinds of destruction of the cathode.

Destruction of the lateral lining is the most common and dangerous form of destruction.

The main reason for the destruction of the lateral erosion of the lining caused by the influence of various factors in equal periods of life of the bath, namely:

oxidation and thermal destruction of the carbon lining during firing of the cathode;

active diffusion of alkali metal vapor, mainly Na and K, in the carbon lining in the start-up;

- erosion of the carbon lining under the action of the circulating flow of the metal and the electrolyte in the post-launch period.

In the absence of lateral skull coal blocks lateral lining collapse under the influence of the metal and the electrolyte with considerable speed. From literary sources ("Light Metals, 1982, PP 299/309) this speed is 1 mm per day. If you do not stop this process, it is possible Loka is lnoe the destruction side of the lining, dissolution of steel casing and, eventually, a breakthrough of the melt, generally at the level of the interface of the metal-electrolyte".

The mechanism of destruction of the lateral carbon lining can be represented as follows. At the time of the start side of the coal lining through the open pores exposed to the active influence of sodium-potassium pairs of electrolyte, loosening the surface layer of the lining and providing high wettability of carbon cryolite. The process of penetration of cryolite is until complete saturation of the lining, from 4 to 200 days, depending on the material of the block (200 days for amorphous graphite). Once there is a full impregnation, the cathode becomes permeable to melt, which continues to "leak" through the cathode due to the liquid static pressure on him.

In practice this process, at best, is terminated at the moment of attainment of equilibrium in the system "impregnated carbon lining - reacted refractory materials", but there may be emergency - breakthrough melt.

Therefore, it is very important to ensure good protection of the side lining at all times during operation of the electrolyzer, and especially in the period of commissioning.

To increase the strength of the lining using reagents such as boron, are in the firing process and start under the influence of Ter is practical and electrical loads, interacting with the material lining, metal and electrolyte, to form a coating that increases durability of the lining to the aluminum and the electrolyte.

For example, the famous "method of applying a coating on the cathode substrate from the supersaturated solution" for U.S. patent No. 5227045 (25 3/06), according to which the cathode surface is formed boride coating of electrolyte enriched in the boron compounds.

Known "Cathode device aluminum cell" for U.S. patent No. 3764509 (CL-243R, publ.: 1974), according to which all or part of the cathode surface is covered by plates or other elements of pure TiB₂or from a composite material containing at least 30% TiB₂. Or maybe deposition TiB₂or composite material based on the whole or part of the cathode surface. It is also possible introduction TiB₂in carbon paste.

The above solution from the point of view of implementation, not tech, expensive and time-consuming. The metal stable quality on these technologies are possible only in the presence of advanced instrumentation techniques and technologies, allowing to quickly intervene in the process of electrolysis according to the results of Express-analysis.

Closest to the proposed technical solution the technical essence of the tee, the presence of similar features is the invention according to the patent of Russian Federation №2133302 (25 3/06) "Lining for electrolytic cell for aluminum production", in which the side lining has a cladding layer of a ceramic material selected from the group comprising boron carbide having a density of at least 95% of theoretical density and having at least a closed porosity.

This solution is based on the use of ceramics with virtually missing open porosity, which prevents the penetration of the melt into the lining of the bath. This material is applied as a cladding film.

From a theoretical point of view, this solution is ideal, but practically to obtain ceramics with no external pores and in the quantity required for industrial applications, not really because of the high cost and technical complexity of the process. Moreover, when mounting the facing inevitable joints, sealing them in the conditions of the electrolysis shop will not allow you to get the junction with the qualitative characteristics similar to the characteristics of the ceramics.

Thus, from ceramics offer to get a cladding, completely prevent the penetration of the melt into a carbon lining, is almost impossible.

The task of the invention is to increases the techno-economic performance of the electrolysis, reducing the cost of installation of cathodic section, increasing the service life of the cells.

The technical result of the proposed method is:

- reliable protection of the side lining of the cell from the effects of aggressive factors in different periods of life of the bath (firing, launch, post-launch and operational phases);

- the possibility of reducing the interpolar distance through improved magnetohydrodynamic situation in the electrolysis bath by reducing the horizontal component of the current density in the melt;

- increase the working space of the cell due to the possibility of varying the thickness of the crust in a wide range.

This technical result is achieved in that in the method of installation of the side lining cathode device aluminum cell, including the installation of thermal insulation and refractory elements, coating the surface of the side lining protective material on the basis of covalent nitrides, as the material of the protective coating on the basis of covalent nitrides use material based on boron nitride and put it on 0,3-1,0 height of the side lining flush with its top solid layer, and the lower border of the coatings perform below the boundary between the electrolyte-metal, and the thickness of the coating is kept in the range of 0.1-1 m is, this open surface porosity of the coating is maintained within the range of 2-3%, and the consistency of the coating material changing from a fluid to viscous-fluid state and put its coating, painting, spraying method with control of the size of the open pore channels covering, and, if appropriate, the coating of the lateral lining and the furnace hearth electrolytic cell is subjected to simultaneous thermal treatment.

In contrast to the method according to the prototype, in which the coating material serves ceramics based on silicon carbide, silicon nitride and boron carbide, the proposed technical solution uses material based on boron nitride with unique properties from the point of view of application in the cell with the aggressive melt.

To explain the choice of material is given in table 1.

Table 1. Properties of covalent nitrides
Name	Density, g/cm³	T plvl., °	T decomp. °	UD. e/comp., ASM
AlN	3,05	>2200	2200	10⁸-10¹⁰(20°)
BN	2,34	3000	2500	10¹³(20°)
Si₃N₄	3,18-3,21	1780-1820	1780-1820	10⁵(350°)

From table 1 it is seen that the boron nitride is an excellent insulator in a wide temperature range (up to 2000°). Low density BN compared to other covalent nitrides allows to provide maximum protection lining with a minimum coating thickness. Under normal conditions, the boron nitride has a hexagonal structure of graphite, which provides good adhesion to the carbon material based on it.

The coating material is a dense porous composite ceramic material based on boron nitride and aluminum oxide in a ratio of ˜1:6 and is characterized by a homogeneous macrostructure consisting of irregularly dispersed agglomeration of alumina various random shapes and sizes and fibrous, like a sponge electroconductive grid having a size less than 1 micron grains BN, forming a tight contact with these agglomerations of aluminum oxide.

This material with the carbon lining reacts substitution with the formation of overlapping spatial structures, which explains the high adhesion of the coating to the side lining.

It should be noted the fact that the coating of the specified material acquisition is em high protective properties after natural drying during the day, the only requirement is that the ambient temperature should not be below 10°C. For the coating material characterized by high thermal stability with rapid and frequent temperature changes. Up to 2000°With boron nitride retains a high resistance against oxidation, the action of molten metals, hot acids, various corrosive gases.

Material based on boron nitride, as noted above, has a high heat resistance and heat resistance, while it is characterized by a moderate coefficient of thermal expansion, making refractory nitride coating has a high hardness, wear resistance, corrosion resistance.

Materials based on covalent nitrides known widely enough. Therefore, the authors do not claim to be the composition of the coating material, as the object of the invention.

The authors propose a method of applying a coating of this kind of materials applied to the electrolytic production of aluminum.

Currently coatings based on nitride or not widely industrial applications due to the high cost of this material.

The authors, based on extensive practical experience of operating electrolytic cells, as well as theoretical knowledge in the field of electrolytic production of aluminum, offer a method of applying a coating to the side ft is roku with a minimum consumption of the coating material. moreover, depending on the economic capabilities of the enterprise in the implementation of the method, the flow rate of the coating material can be reduced by approximately three times. This point is reflected in the claims intervals "...from 0.3 to 1.0 height of the side lining flush with its top".

This interval is due to the following:

The most effective from the point of view of the gain in performance of the electrolysis process to apply the coating over the entire height of the side lining. When this is implemented as a protecting lining from damage and minimize the horizontal component of the current density in the melt with all the ensuing advantages in technology. But even when the coating of 0.3 of the height of the lining, just below the boundary between the electrolyte-metal"effect of protection lining from destruction will appear in full, but at the same time, current flows in the bath will improve slightly. Therefore, depending on the financial capacity of the plant, i.e. the amount of the coating material, the height of the protective coating of the side lining may vary, but lower coverage limit should be lower boundary of the metal-electrolyte".

In the claims also claimed the interval thickness 0.1-1 mm change in the thickness of the coating in such a wide range is caused by the instability of the quality of the carbon is s blocks of the side lining. According to the technical conditions of the plate should have a porosity of not more than 24%do not have any mechanical damage and chipping. For the coating of the plates of this quality enough to cover it with one layer of material on the basis of boron nitride, which provides a thickness of 0.1 mm

For reliable protection can be applied to the lining of two or more layers, and without changing the total thickness of the coating due to changes in the consistency of the coating material. The optimum thickness of the coating is selected on the basis of the following positions: on the one hand, the thickness should be sufficient to protect the side of the lining from the effects of the electrolyte, and on the other hand, does not interfere with heat transfer from the bath to prevent overheating of the melt and, consequently, erosion of the skull. This is especially important for electrolytic high power. Therefore, the authors give an upper limit of the thickness is 1 mm When selecting the thickness of the coating should be guided by the indicator open surface porosity, the authors recommend that to maintain this rate in the range of 2-3%.

The proposed method for protection of the side lining for all its simplicity is a major advantage as the leading technology of electrolysis and technical-economic indicators of the process, namely:

1. Reduction of post-launch period with the introduction of e is ctrainer in commercial operation.

This period represents the period of time from the start to establish a normal process conditions and is characterized by low output aluminum current, and low grade of the produced metal. During the post-launch period on the inner side surface mine cathode of the cell and on the periphery of the bottom leads to the formation of the crust, which is a layer of frozen electrolyte, which forms the workspace.

The coating on the proposed method, having high electrical insulating properties, virtually eliminates the occurrence of horizontal currents in the melt or at least reduces them to a minimum. Due elektroprovodnosti lateral lining is not heated warmth of its ohmic resistance and the crust freezes faster. On the other hand, forming the crust is subjected to less active degradation of flow of the melt due to the reduction in the speed of circulation of the melt in the practical absence of horizontal currents.

In the post-launch period can be reduced to 7 days.

2. Increased service life of the cell.

The film of the coating material formed on the lateral lining, has a minimum open porosity (ideally free), and the cross-section of the pore of the channel is comparable or maneeratana aggressive ions and molecules of the melt, therefore, the film coating is a reliable barrier to the penetration of the molten electrolyte and the metal in the side lining.

As a result, the service life of the cell is increased by 5-20 months.

3. The increase in grade aluminum and increase current output.

Reduce the speed of circulation of the melt by reducing the horizontal component of the current in the melt stabilizes and reduces the longitudinal misalignment of the mirrors of the metal during the entire period of operation of the bath, which allows to minimize the MNR (interpolar distance) and practically does not change it.

As a result, increases the quality of the produced aluminum, as well as increases the current output (approximately 1-2%).

4. The increase in the average daily performance of the cells.

If coating is available for the proposed method it is possible to work at reduced thickness of the crust, as the side lining is protected. Moreover, while ensuring the passage of the current, mainly vertically through the furnace hearth creates a continuous vertical profile of the heat loss, which significantly reduces the thickness of the upper layer of solidified cryolite, which is very important in electrolyzers equipped with APG (automated alumina point feeders).

In addition, technologists the opportunity to vary the temperature in over the wide range.

As a result of increasing the working space of the cell, and thus increases its performance.

Comparative analysis of the proposed technical solutions to the prototype and other known solutions in this area revealed the following:

- the use of covalent nitrides for protection cathodic bath is known, for example, AS the USSR №631560 "Electrolyzer for the production of metals and alloys" (25 3/16, g.), according to which the boron nitride layer is introduced into the interconnect joints bottoms to prevent their destruction. The proposed technical solution, the material based on boron nitride is deposited only on the side lining, since its introduction into the furnace hearth reduces its conductivity;

- there are various ways to reduce the horizontal component of the current density in the melt. Thus, AS the Russian Federation No. 1788091 (25 3/08) "electrolytic Cell for aluminium production" (12.03.91,) it is proposed to create at the bottom of the electrolyzer discrete tokoprovodyascheho zone by mounting on the bottom carbon blocks of bars of insulating material along the front and deaf sides of the electrolyzer. This leads to a periodic change in the direction of the horizontal component of the current density in the melt, which, in turn, affect the frequency of changing the direction of the longitudinal p is recos mirror metal which leads to the reduction of the resulting amplitude of the longitudinal bias and stabilization of the process of electrolysis. But, unlike the technical solutions, the proposed method tokoprovodyaschaya zone (lateral lining) is continuous, therefore the longitudinal misalignment of the mirror metal is stable during the entire period of operation of the bath.

In contrast to the known solutions in the field of protection of the juice lining the height of the coating can be changed in the range of 0.3-1.0 height, but be sure the following requirements are met: the lower bound of the coverage must be below the boundary between the electrolyte-metal", and the top is flush with the top of the lining, and the coating is applied in a continuous layer.

A new collection of characteristics both known and unknown in their close relationship allows us to obtain the technical result of a higher level.

Currently, in terms of IrkAZ this method is passed the preliminary tests.

Tests were conducted on industrial electrolyzers SB, SBM, C3. As the coating material used high temp paint on the basis of boron nitride. The coating material is prepared in advance and depending on the requirements for coating thickness consistency can vary from fluid to viscous-fluid state.

The method is implemented as follows.

After mounting the electrolysis cell the inner surface of the side liner paint brush, roller or spray. Dried during the day when ambient temperatures. Then shall start according to the instruction manual of the Smelter.

In the process baths coated on the proposed method periodically carried out supervision of the obtained metal to boron and titanium in the metal. At the same time carried out the sampling with bath witness (without coating).

Control of Bor and titanium was carried out for the confirmation of the stability of the coating in the melt, since it is known that boron refines the cathode metal from impurities Ti and V by education him fine borides.

The testing results are presented in figure 1 and 2.

From figure 1 it is evident that the experienced baths content of titanium is higher than that of witnesses. This means that boron coating racks in the melt does not come.

This fact is confirmed by figure 2. The boron content in the experimental tubs and baths-witnesses are practically identical.

In conclusion, it should be noted that the tests conducted on the Smelter, proved the efficiency of the coating on the proposed method. Therefore, this method is recommended for industrial application.

1. The method of installation of the side lining cathode device is aluminum the th cell, including the installation of thermal insulation and refractory elements, coating the surface of the side lining protective material on the basis of covalent nitrides, characterized in that the material of the protective coating on the basis of covalent nitrides use material based on boron nitride and put it on 0,3-1,0 height of the side lining flush with its top solid layer, and the lower border of the coatings perform below the boundary between the electrolyte-metal, and the thickness of the coating is kept in the range of 0.1 to 1 mm.

2. The method according to claim 1, characterized in that the open surface porosity of the coating is maintained within the range of 2-3%.

3. The method according to claim 1, characterized in that the lining is applied protective coating consisting of two or more layers due to changes in the consistency of the material from a fluid to a plastic state.

4. The method according to claim 1, characterized in that the coating is performed by painting, spraying, spraying method.