Method of forming protective coating for carbon containing components of electrolysis cell

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

 

The technical field to which the invention relates.

The present invention relates to the production of protective coatings for carbon-containing components of the electrolyte (electrolytic) cells used in the production of aluminum. More specifically the invention relates to opaque compositions providing during electrolysis protect these components from destruction or damage, and to components containing such compounds.

The level of technology

Manufacturer of aluminum is usually carried out by means of electrolytic recovery process Hall-Heroult in which alumina is dissolved in molten cryolite and electrolyzed at temperatures of about 900-1000° C. the process is carried out in regenerative cell containing, typically, a steel shell provided with an insulating lining of suitable refractory material. In turn, this lining is provided with a lining of carbon in contact with the molten components. To the positive pole of the DC source connected to one or several anodes, made usually of baked carbon blocks. The anodes are located inside a cell in limbo. In the carbon cathode substrate forming the bottom of the cell, is mounted one or more conductive rods connected to the negative pole of the DC source. In the cathodic substrate upon application of a current becomes the cathode.

Baked anodes used in aluminum production, contain aggregates of petroleum coke with resin as a binder. Carbon lining, as a rule, design of the system annealed cathode blocks connected with each other into one unit by means of a mixture that usually contains anthracite, tar and coal godonou resin.

Aluminum in the form of melt produced in the electrolysis cell as a result of the following reaction:

2l2O3+3C→ 4l+3SD2.

In the case of conventional devices of cells of the Hall-Heroult molten aluminium collects at the base of the cell. When oxygen is released and reacts with available carbon on the anode surface, forming gaseous carbon dioxide. Theoretically, one kilogram of aluminum produced according to the above reactions, spend 0,334 kg of anode carbon. However, the real consumption of the anode by 25-35% more.

Excessive consumption of baked anodes is the result of a series of secondary reactions, which can be summarized as follows:

I) air oxidation: oxidation reactions proceed under the influence of oxygen in the air in contact with the upper part of the anode, and, if you leave the anode unprotected accession reactions is with the formation of carbon dioxide;

II) reaction of the Boudoir (Boudouard): the oxidation of carbon flow under the influence of CO2at the surface of the anode immersed in the electrolyte and produces carbon monoxide (a process known as balance Boudoir), and

III) dust: pitch coke oxidation, selective with respect to petroleum coke, results in the release of carbon particles, generating dust, which has a negative impact on the process.

Losses due to such secondary reactions in the electrolytic cell reaches approximately 10% of the cost of aluminum production.

Further, the economic inefficiency of aluminium production can be associated with deterioration (damage or destruction) carbon lining or material of the cathode of the electrolytic cell as a result of erosion and penetration of electrolyte and molten aluminum, as well as the formation of layers of metallic sodium.

Although currently for aluminium production process of the Hall-Heroult is the most reliable, is the need for its continuous improvement. Due to the economic consequences of the ineffectiveness of this process, significant efforts were directed at developing improved components of an electrolytic cell capable of withstanding critical conditions peculiar to the ele is tralize aluminum.

For example, in U.S. patent No. 3852107 considered impervious protective coating for the electrodes, which contains a matrix with a melting point above 1000° and refractory filler, dissolved or suspended in a liquid medium such as water. As an example, the component matrix of the coating is specified material capable of wetting the graphite, such as boric acid, and/or the material forming the glaze, such as aumontzey fluoride. The list of proposed refractory fillers include oxides, carbides, nitrides or borides. For certain situations to improve wetting of graphite were offered the use of the modifying agent, such as chrome ore, with a suitable value of the surface tension.

In U.S. patent No. 4624766 described specially designed for use in electrolysis cells cured carpigiani cathode material capable of wetting by aluminum. The material contains particulate refractory material in a carbonaceous matrix, which includes carbon-containing filler and carbon fiber are associated Nagravision amorphous carbon. While this matrix has the speed of erosion is essentially equivalent to the rate of wear and dissolution of refractory hard material in the operational environment of ACE the key.

In the international application WO 98/17842 published 30.04.1998, describes a method of applying a refractory boride components aluminium electrolytic cells by forming a slurry of refractory boride, pre-formed in powder form in colloidal carriers, at least two levels, followed by drying. These carriers are selected from the group consisting of colloidal aluminum oxide (alumina), yttrium, cerium, thorium, zirconium, magnesium, lithium, monoaluminate phosphate, cerium acetate and mixtures thereof. While it is preferable that both colloidal media represented the same colloid. Two levels of colloidal carriers have average particle sizes differing from each other by approximately 10-50 nm.

U.S. patent No. 5486278 to improve fracture resistance during operation of the cell provides a method of impregnation of the carbonaceous component of the cell with a solution containing boron. In that case, when the solvent for the specified solution used water to achieve acceptable processing time required surfactant. In the alternative, the solvent can be selected from methanol, ethylene glycol, glycerol and mixtures thereof. This method required the introduction of the solution containing boron, which is protected compo is UNT to a depth of 1-10 see In addition, this patent States that the carbon-containing components, thus treated, the air oxidation was comparable with the total expenditure of such components, treated with conventional coatings protecting the aluminum.

Despite the above attempts, most often still use the usual techniques of conducting electrolysis of aluminum. This implies that more sophisticated from a technical point of view or cost-effective way of dealing with the destruction of carbon-containing components of the cell are not known.

As a binder in many industries, but not in aluminum electrolysis cells, for a long time used lignosulfonates, such as ammonium lignosulfonate.

The invention

The problem to which the present invention is directed, is to develop an efficient and economical method of processing components of electrolytic cells for aluminum production with the aim of protecting them from damage or destruction during operation of the cell.

In its broadest aspect the invention relates to a method for processing carbon-containing component of an electrolytic cell for the production of aluminum, to improve the resistance component damage or destruction during R the bots cells. The method includes preparing a liquid suspension of refractory material dispersed in the solution lignosulfonate binder, and applying the suspension as a protective coating on the carbon-containing component of the cell, followed by drying of the coating. Refractory material you can choose from a broad range of refractory compounds, such as compounds of boron, zirconium, vanadium, hafnium, niobium, tantalum, chromium and molybdenum.

As a byproduct of the production of pulp and paper, lignosulfonate simultaneously redefinition and relatively cheap. It was shown that in harsh environments aluminum electrolysis cell, it is extremely effective as a binder.

According to one embodiments of the invention lignosulfonate binder is used in the coating composition of the carbon sintered anodes. For this purpose prepare a liquid suspension of aluminum fluoride, lignosulfonate binder, for example ammonium or calcium lignosulfonate, and boron compounds such as boric acid, boron oxide, hydrated oxide of boron or borax. The above suspension is applied to the anode as a protective coating, and, as a rule, on those parts of the anode, which during operation of the cell exposed to the atmosphere. After application, the coating is dried, for example, what redstem drying air at room temperature. To increase the strength of the coating suspension can include a binder in the form of phenolic polymer.

According to the following variant of the invention lignosulfonate binder is used to cover structures of carbon cathodes in aluminium electrolysis cells. With this purpose, prepare a liquid suspension of refractory boride, such as titanium diboride, lignosulfonate binder and binder in the form of phenolic polymer (phenolic resin). Then, this liquid suspension is applied as a protective coating on the structure of the cathode, followed by drying.

As the basis of the composition of liquid suspensions of the present invention, lignosulfonate functions as a dispersant for dispersing in the liquid phase, the wetting agent for uniform coating and binding when creating a continuous layer of suspended solid phases, effectively adhering to the carbon surface.

One of the main reasons for the excess of the total consumption of carbon oxidation is upstream of the baked anodes during operation of the cell. In General, these anodes to protect them from oxidation by air is covered with alumina, crushed material of the bath or mixtures thereof. Practice drawing alumina coatings on components of the anode in the cell Hall-Heroult to reduce / min net and air oxidation is widely used in the manufacture of aluminum. However, when the total consumption of carbon approximately 410-460 kg/t Al this practice is not optimal, not to mention the excessive costs associated with these coatings.

One of the preferred embodiments of the present invention uses a mixture of aluminum fluoride and boron compounds such as boric acid, boron oxide, hydrated oxide of boron or borax. The mixture is dispersed in lignosulfonate binder and has the form of a viscous liquid. In this form, the liquid can be applied on the surface of the anode through atomization (sputtering). After drying, forms a protective coating that can withstand destruction of the anode during its oxidation. This viscous liquid can be applied to the upper portion of the sintered anode, having a size of one-half to one-third of the anode, when the ambient temperature air through the injector at a pressure of 8.2× 105PA and give it a chance to dry at room temperature for about 3 hours. The coating is preferably applied to a total thickness lying in the range 0.5 to 2 mm, Most preferably a coating thickness of about 1 mm.

Viscous opaque liquid usually contains about 20-60 wt.% of lignosulfonate (50% solution), 25-60 wt.% boric acid and 0-25 wt.% aluminum fluoride. The preferred composition comprises 20-40% of lignosulfonate (5% solution), 30-55% boric acid and 0-15% aluminum fluoride. Particularly preferred interval in the range of 25-35% of lignosulfonate (50% solution), 35-55% of boric acid and 0-10% aluminum fluoride. Opaque liquid may also contain up to 20 wt.% phenolic polymer.

During the process occurring in the aluminum electrolysis cell, the temperature of the upper part of the anode of the cell is approximately 550-650° C. Covered viscous opaque liquid and dried anodes due to the formation in them of the coating containing boron and aluminum oxide, are protected from oxidation.

For components of the anode having a protective coating according to the present invention, there has been a significant decrease in the total consumption of carbon. It is calculated that coverts the composition according to the invention provides savings of approximately 3 dollars per tonne of metal for each percentage reduction of the total consumption of carbon.

Another preferred embodiment of the invention relates to a method for protecting the surface of the cathode blocks subjected to stress in an aluminum electrolysis cell, through the coating, which contains titanium diboride dispersed in a mixture of lignosulfonate and phenolic polymer (phenolic resin). This coating provides the wetting properties and the match is erosion, and significantly slows down the destruction of the upper layers, which occur due to the penetration of sodium and bath filler. This coverts the mixture usually contains about 5-40 wt.% of lignosulfonate (50% solution), about 5-40 wt.% phenolic polymer, about 20-70 wt.% of titanium diboride and 0-5 wt.% anthracite (or graphite). The preferred composition contains about 14-20 wt.% of lignosulfonate (50% solution), about 14-20 wt.% phenolic polymer, about 50-70 wt.% of titanium diboride and 2-5 wt.% anthracite (<74 μm). Although the preferred material for this purpose is bored titanium, you can apply a wide range of borides, such as boric zirconium, vanadium, hafnium, niobium, tantalum, chromium or molybdenum.

This coverts the mixture is preferably applied to a thickness of about 1-3 mm through air injector at a pressure of 8.2× 105PA, and first subjected covered with the cathode air drying at room temperature for about 10 hours. However, you can increase the service life of the coating by increasing its thickness of 10-15 mm by applying a large number of covering layers. After applying each layer, the coating can be dried by heating the system at about 100-150° C. Then coated cathode is subjected to preliminary heating, which is part of the normal running of the cell. In preparation for the preliminary heating of the Kato is covered with a layer of coke (not a filler bath) 10 cm thick, as the anodes are lowered until then, until they hit a layer of coke. Next, pass the current, and in such conditions the temperature of the coating is approximately 1000° for approximately 25 hours.

The above composition provides a surface capable of wetted metal, and not only protects exposed to the effects of the cathode surface from damage, but also reduces the absorption of sodium facing the cathode as a whole and oxidation units side walls in the coating composition in these areas.

The drawing is a graph showing time dependence of the number TiB2drawn from the aluminum electrolysis process.

Information confirming the possibility of carrying out the invention

EXAMPLE 1

The liquid suspension was prepared by mixing 30 wt.% H3IN330 wt.% AlF3and 40 wt.% the ammonium lignosulfonate. Lignosulfonate was a 50% liquid preparation (NORLIG TSFL™ )obtained from the company Borregaard Lignotech, USA. Liquid lignosulfonate has a pH in the range of 4-5 and contains a total of 47.5-51.5% of the solid phases. H3IN3and AlF3had the form of powders.

Using the jet injector at a pressure of 8.2× 105PA, sprayed liquid suspension on top of the baked anodes on a plot of approximately half-a third of the height of the anodes.

EXAMPLE 2

Profilesare test for oxidation, using the examples of the anode material having a small size, designed for laboratory conditions and coated with various coating compositions, whose main binder was lignosulfonate. As in example 1 was again used NORLIG TSEL™ . The coating was applied to a thickness of approximately 2 mm, using a jet injector at a pressure of 8.2× 105PA, followed by drying at room temperature for about 3 hours.

To test for oxidation of coated samples were subjected to high temperatures in the furnace size 33 cm × 18 cm × 25 see the Furnace was heated from room temperature to 600° for a period of 4 hours, and kept at 600° C for 12 h.

Each sample was weighed before and after exposure and expected percentage loss of mass. Coating formulations and the results obtained are presented in the following Table 1.

H3IN3(%)
Table 1

The compounds tested for oxidation, and the obtained results
SAMPLE # COMPOSITIONOXIDATION (% weight loss)
BinderSolid phase
LCA**(%)Phenolic polymerIn2About3(%)Additive (%)
Proof test0 00060-90
F-3840 1563SiC24
F-3940 1581 SiC 
E-4040 1563AlF338
E-4140 1581AlF329
E-42*40 1563 SiO238
F-4440 1563 SiC40
E-4540 1581 SiC22
E-4640 1563 AlF325
E-4740 1581 lF329
E-8 *40 1563 SiO215
E-49*40 1581 SiO218
*measurements include weight coating

* *LCA - ammonium lignosulfonate

EXAMPLE 3

The procedure of example 2 was repeated using a more diverse set covering formulations. Applied coating formulations and the results of oxidation are presented in the following Table 2:

Table 2

The compounds tested for oxidation, and the obtained results
SAMPLE # COMPOSITIONOXIDATION (% weight loss)
BinderSolid phase
LCA**(%)Phenolic polymerIn2O3(%)H3IN3(%)Additive (%)
Proof test0 00060-90
E-6040  1572 SiC7
E-6140 1572 SiC1
E-62*40 1572 SiO21
E-63*40 1572 SiO22
E-7840 -3030 AlF30
E-7940 -3030 AlF30
E-8040 22830 AlF30
E-8140 22830 AlF30
E-7640 --60 AlF339
E-7740 --60 AlF341
*measurements include weight coating

Ȁ * *LCA - ammonium lignosulfonate

EXAMPLE 4

For these test coatings were prepared and applied in the same manner as in example 2. Some coatings contain a binder in the form of phenolic polymer (DURITE Phenolic Resin RL-2360B). For carrying out high-temperature tests on the oxidation of the samples was placed on a substrate of alumina powder. Thereby more closely reproduce the actual production conditions as to cover the anodes during operation of the cell used alumina powder, which is the raw material supplied to the electrolysis cell for production of aluminum metal.

Mineral compositions and the results obtained are presented in Table 3.

Table 3.

The compounds tested for oxidation, and the obtained results
SAMPLE # COMPOSITIONOXIDATION (% weight loss)
BinderSolid phase
LCA (%)Phenolic polymerIn2About3(%)H3IN3(%) powderAdditive (%)
Proof test00  0060-90
E-9840- 3030 IMTV*14
E-10040- 2040 IMTV*23
E-10640- 3030 IMTV*11
E-10540- 4020 AlF34
E-10840- 4020 AlF35
O-160382 3030 AlF37
O-161355 3030 AlF35
O-162355 4020 AlF30
O-163382% CaO 3030 AlF38
*IMT = crushed solid material baths

As a control, each oxidation test included a sample of the anode without any protective coating according to the present invention. These unprotected samples showed a weight loss of 60 to 90 wt.%.

EXAMPLE 5

The following tests were conducted using samples of the anode material, the same as in example 2, with the use of lignosulfonate and phenolic polymer from examples 2 and 4. Source AlF3used finely ground solid material of the bath, extracted from the cells. This material contained about 50% AlF3and 50% Al3About3.

Coated samples were subjected to high-temperature oxidation in a furnace as in example 2. The results obtained are presented in Table 4. For composition 0-175 spent the industrial test.

Table 4

The compounds tested for oxidation, and the obtained results
SampleLignosulfonate (50%)Phenolic polymerH3IN3*Finely ground filler baths% weight loss
Control000060-90
0-1743118 -0
0-175291737170
*pellets - 100% activity

EXAMPLE 6

Prepared a series of opaque compositions for application to the structure of the cathodes. Used the same lignosulfonate and phenolic polymer, as in the previous example. The composition contained 60 wt.% of titanium diboride, 5 wt.% anthracite (<74 μm), 17.5 wt.% phenolic polymer and 17.5 wt.% solution (50 wt.%) the ammonium lignosulfonate. Some formulations also contained anthracite with a particle size of <200 mesh. The compositions prepared in the form of a viscous dispersion systems, is enough fluid for spray application.

Using the jet injector at a pressure of 8.2× 105PA, sprayed structures on the surface of the cathodes subjected to impacts. The coating has dried, pre-heated and subjected to electrolysis tests at 900° C for 100 hours. After the test, the entire surface is covered with the sample cathode was dipped aluminum and did not show signs of erosion.

EXAMPLE 7

Conducted industrial trials using 6 full-scale electrolysis cell with the following coating composition: 17.5% of phenolic polymer, a 17.5% solution (50%) of ammonium lignosulfonate, 60% TiB2and 5% anthracite (<74 μm). Stand rnost cathode (bottom blocks, monolithic sealing paste and block side) plated coating, total weight for all of the tested cells was about 60-70 kg. Thickness of this coating was close to 1 mm, in order To determine the service life of the coating during operation of the cell the concentration of Ti In the aluminium produced six test cells, compared with the corresponding levels in six of the control cells. On the basis of these results, the lifetime of the coating, having a thickness of 1 mm, approximately 350-400 days. It is known that during operation of the cell, the rate of erosion of the carbon cathode uncoated approximately 15-30 mm per year. Figure 1 shows the cumulative number of TiB2derived from subjects of cells defined on the basis of the concentrations of Ti and aluminium. Industrial test shows that the rate of erosion is covered with the cathode blocks below 1 mm/year, which is significantly less than the rate of erosion for the uncovered blocks.

1. The method of processing carbon-containing component of an electrolytic cell for production of aluminum, designed to improve the resilience of the specified component destruction during operation of the cell and providing for the preparation of liquid suspensions of refractory material dispersed in the solution lignosulfonate binder, applying the suspension as the aircraft is Oia on the surface of the specified carbon-containing component and then drying the coating.

2. The method according to claim 1, characterized in that the refractory material is a compound of boron, zirconium, vanadium, hafnium, niobium, tantalum, chromium or molybdenum.

3. The method according to claim 2, characterized in that the liquid suspension further comprises a binder in the form of phenolic polymer.

4. The method according to any one of claims 1 to 3, characterized in that the liquid suspension contains a boron compound, aluminum fluoride and lignosulfonate binder.

5. The method according to claim 4, characterized in that the boron compound is a boric acid, boron oxide or hydrated oxide of boron.

6. The method according to claim 1, characterized in that the refractory material is a titanium diboride.

7. The method according to any one of claims 1 to 6, characterized in that lignosulfonate binder contains ammonium or calcium salt.

8. The method according to claim 4, characterized in that the specified component is a carbon anode, a liquid suspension is applied as a protective coating, at least over a portion of the anode which is exposed to the atmosphere during operation of the cell, with subsequent drying of the coating.

9. The method of claim 8, wherein the suspension contains 25-65% boric acid, 0-25% aluminum fluoride and 20-60% lignosulfonate binder (50%solution).

10. The method according to claim 9, wherein the suspension additionally contains up to 20% with sousage in the form of phenolic polymer.

11. The method according to claim 8, characterized in that the suspension is applied to the anode brush, rolling or spraying.

12. The method according to claim 1, characterized in that it envisages the preparation of a liquid suspension of refractory boride, lignosulfonate binder and binder in the form of phenolic resin and applying a liquid suspension as a protective coating on the structure of the carbon cathode aluminum electrolysis cell, followed by drying.

13. The method according to item 12, wherein the refractory Board is bored titanium, zirconium, vanadium, hafnium, niobium, tantalum, chromium or molybdenum.

14. The method according to item 12, wherein the refractory Board is a titanium diboride.

15. The method according to 14, wherein the suspension contains 55-65% of titanium diboride, 0-5% anthracite, 15-20% lignosulfonate binder and 15-20% of the binder in the form of a phenolic polymer.

16. The method according to item 12, wherein the suspension is applied on the structure of the cathode brush, rolling or spraying.

17. Composition for coating carbon-containing component of an electrolytic cell for production of aluminum, designed to improve the resilience of the specified component destruction during operation of the cell and containing a liquid suspension of refractory material dispersed in the solution lignosulfonates the binder.

18. The composition according to 17, wherein the refractory compound is a compound of boron, zirconium, vanadium, hafnium, niobium, tantalum, chromium or molybdenum.

19. The composition according to 17, characterized in that the liquid suspension contains boric acid, boron oxide or hydrated oxide of boron.

20. The composition according to 17, characterized in that the refractory material is a titanium diboride.

21. The composition according to any one of p-20, characterized in that lignosulfonate binder contains ammonium or calcium salt.

22. The composition according to 17, characterized in that it is arranged to use as the coating of the carbon anode in aluminum electrolysis cells and contains a liquid suspension of boron compounds, aluminum fluoride and lignosulfonate binder.

23. The composition according to item 22, wherein the suspension contains 25-60% boric acid, 0-25% aluminum fluoride and 20-60% lignosulfonate binder (50%solution).

24. The composition according to item 22, wherein the suspension additionally contains up to 20% of binder in the form of phenolic polymer.

25. The composition according to 17, characterized in that is made use of as a cover structures of the carbon cathode aluminum electrolysis cell and contains the liquid suspension of refractory boride, lignosulfonate binder and phenolic poly the EPA.

26. The composition A.25, characterized in that the refractory Board is a titanium diboride.

27. The composition A.25, wherein the suspension contains 20-70% of titanium diboride, 5-40% lignosulfonate binder and 5-40% of a binder in the form of phenolic polymer.

28. The composition according to any one of p-27, characterized in that it further comprises 0-5% Antracite coal.

29. Carbon-containing component for use in the electrolysis of aluminum, which is based coating composition described in 17.

30. Carbon-containing component according to clause 29, wherein the specified component is an anode.

31. Carbon-containing component according to item 30, wherein the coating has a thickness of 0.5-2 mm.

32. Carbon-containing component according to clause 29, wherein the specified component is a cathode.

33. Carbon-containing component b, characterized in that the coating has a thickness of 0.5-15 mm

34. Carbon-containing component b, characterized in that the coating has a thickness of 1-3 mm



 

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