Cathode facing to aluminum cell

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

 

The invention relates to the field of non-ferrous metallurgy, in particular to the electrolytic production of aluminum, in particular to the design of the cathode lining of an aluminum reduction cell.

Known cathode lining of an aluminum reduction cell (Patent Hungary No. 154854, IPC 25 3/08), which contains carbon blocks, insulating layer, two protective layers, one of which is made of oxides and/or fluorides of CA, Mg, Na, or mixtures thereof, and the other in the form of a metallic sheet.

Known design increases service life of the cell, but does not provide complete protection of the lining against the penetration of aluminum and Tortola in the insulating layer, which degrades its quality and reduces the performance of the cell. Another disadvantage lining is that the connection components of the electrolyte with oxides and/or fluorides of CA, Mg, Na, or their mixtures have a low viscosity. The metal plate under the action of the electrolyte components and particularly molten aluminum dissolved, resulting in reduced service life of the lining.

Closest to the claimed cathode lining to the technical essence and the achieved result is the lining of the cathode casing aluminum cell (Patent RF №2125621 IPC With 25 3/08, 1999). In the cathode lining, including carbon blocks, nicerspro the config cap, consisting of layers of insulation and refractory parts of the two protective layers, the upper protective layer, representing the compacted quartz sand thickness of 10-60 mm, particle size of 0.4 to 0.15 mm and lower. The lower protective layer is composed of two steel sheets that are stacked horizontally one above the other with a gap of 1-3 mm, filled with alumina, or from a layer of ceramic material. As the ceramic material can be used red brick.

The disadvantage of the prototype is that these layers do not provide sufficient protection against the penetration of cryolite-alumina melt and liquid aluminum. As compacted quartz sand is not a barrier either for aluminum and sodium, which it is easily restored, nor for fluoride melts, because the resulting sodium silicate does not contribute to the formation of glassy phase and also has a lower solidus temperature. In addition, alumina is placed between the steel sheets, in the case of the destruction of the latter (as is often observed in practice), will interact with sodium fluoride with a significant increase (to 6.5%). The interaction products are characterized by low viscosity and low regional contact angle on the border with refractory material that promotes the front propick the back cap with damage to the insulating layers.

The basis of the invention is the development of cathode lining of an aluminum reduction cell, the construction of which would increase the service life of the cell, improving its performance by eliminating the ingress of Tortola and molten aluminum on the insulating layers.

The problem is solved in that in the cathode lining of an aluminum reduction cell, including carbon blocks, insulating layer and the refractory part, consisting of two protective layers - top, adjacent to the carbon blocks and the bottom, made of powder-like material, according to the proposed solution, the upper protective layer consists of an aluminosilicate material that is resistant to electrolyte components. The lower protective layer lined airtight metal containers, one or more filled with refractory material that is resistant to molten aluminum and electrolyte components, carbon-containing composition with a thermal conductivity of not more than 0.1 W/(m·).

The proposed method is complementary to private distinctive features aimed at solving the problem.

The upper protective layer is made from a material with a content of Al2O3from 27 to 35%, a particle size of not more than 2.5 mm and a thickness of from 10 to 50% of the height of Agnew the priori part.

In the lower protective layer containers filled with soot and its thickness ranges from 50 to 90% of the height of the refractory part.

Comparative analysis of the characteristics of the proposed solutions and features analog and prototype demonstrates compliance solutions to the criterion of "novelty".

The implementation of the upper protective layer in the refractory part of the powder with a maximum particle size less than 2.5 mm and aluminosilicate having a composition containing Al2O3from 27 to 35% with a thickness from 50 to 10% of the height of the refractory part attributable to the following:

Special studies have shown that cryolithological is defined as the average pore size and density of the material. With decreasing particle size decreases the size of the channel pore and growing cryolithological, but decreases the density value. Therefore, there is an optimal particle size, while maintaining the density value and the maximum cryolithological. As you know, for more dense packing of the distribution of the particle sizes must follow the curve of the ideal distribution. With this in mind, the maximum particle size must not exceed 2.5 mm If the size of the particles will be greater than the specified value, it is truncated surface interaction with penetrating components of the electrolyte, increasing the size of the pores that result is to increase the penetration and the degree of interaction. If the maximum particle size is less than 2.5 mm, then decreases the density of the refractory material.

Particles are highly reactive layer should have the aluminosilicate composition with a content of Al2About3from 27 to 35%. First, it is the cheapest material, and secondly, it forms a layer of nepheline according to reaction (1), which promotes the formation of albite, inhibiting infiltration of electrolyte components:

If enough moderate intake of NaF nepheline reacts with silicon dioxide according to reaction (2) with the formation of albite, NaAlSi3O8that will be in the viscous glassy molten state:

When the content of Al2O3less than 27% will be difficult the formation of nepheline. With more than 35%, the content of Al2O3reduced reactivity and reaction takes place education β-alumina (3):

However, due to the significantly lower density β-alumina below α-alumina can occur volumetric changes in the lining, leading to the rise bottoms.

The execution of a lower protective layer of soot thickness of from 50 to 90% of the height of the refractory part due to the fact that carbon has unique properties such as high resistance, nesma Iwamoto percolate and low coefficient of thermal conductivity at temperatures up to t ˜ 800°C.

The proposed construction of the cathode of the device in comparison with the prototype allows to increase his life span by slowing down the speed of penetration of the components of the cryolite-alumina melt in heat-insulating portion of the cap and the preservation of thermophysical properties of the latter. In addition, the stabilization of the heat balance will reduce specific energy consumption.

The invention is illustrated in the following graphic material, where:

figure 1 shows a diagram of the cathode lining of an aluminum reduction cell;

figure 2 - results of studies on cryolithological;

figure 3 - view of the formed soot sample after testing, the direct effect of the electrolyte;

figure 4 - dependence of the conductivity of carbon black from temperature;

figure 5 - temperature distribution along the height of the base;

figure 6 - temperature field and the shape of the working space (FER) of the cell when using the prototype;

figure 7 - temperature field and the FER of the cell when using the proposed solutions.

Depicted in figure 1, the lining consists of the alignment of the pillow 1, two layers of insulating material 2, the lower protective layer 3 of refractory metal containers filled with soot, the upper protective layer 4 refractory parts, made of al is mosilikatse material, having high reactivity to the components of the electrolyte penetrating through the furnace hearth, consisting of carbon blocks 5. The anode 6 is placed in the electrolysis bath. Bottom weight 7 fills the space between the carbon blocks 5 and the onboard unit 8. Steel bar 9 through the seal 10 is connected with the carbon block 5. In the lower part of the electrolysis bath is installed compensator 11. View of the formed soot sample after testing, the direct effect of the electrolyte is shown in figure 3, where the electrolyte 12 is on the lower protective layer 3. The sample is placed in the crucible 13.

As shown by the results of studies on cryolithological (figure 2), the grinding particles can reduce the amount of unreacted material. There is a reduction in the share of material reacted with the components of Tortola from 23 to 14-15%.

Tests of soot in the tests on cryolithological showed that soot is not wetted and does not interact with the components of the electrolyte (figure 3). Carbon has unique properties such as high resistance, nesmachivaemost percolate and low coefficient of thermal conductivity to temperatures up to 800°C.

Comparative analysis of the temperature fields in the cathode device, obtained using three-dimensional mathematical models of the prototype, where the height of the refractory part C is being dry barrier mixtures (SBS) is 90 mm, below the carbon blocks and the prototype, where the height of the lower protective layer is 30 mm, and the top - 60 mm, showed the following characteristic features (table. and figure 5).

Laying soot layer thickness of 30 mm, placed in a metal container, leads to the increase in temperature on the furnace hearth in the center of the cell with respect to the prototype with 968,5 to 975°C. due to this sharply reduced the length of nastily under the projection of the anode (from 215 to 165 mm) and decreases the thickness of the crust. The temperature directly under the bottom blocks will increase by 15°C. Therefore, the upper layer of SBS will have a higher temperature, and hence a slightly higher probability of interaction with components of the penetration of the electrolyte.

Table
The measurement parameterUnit.Value
the placeholderdeclare
MNRmm5149
Temperature:
Center MPR°976977
PBA cell°960962
On the furnace hearth in the center of the cell°C968,5975
Under bottom-block°C952967
Under SBS°C876943
Under soot or concrete°C-524
Under 1 number of bricks fireclay°C850505
Under 2 number of bricks fireclay°C820485
Under 1 number of bricks vermiculite°C545326
Under 2 number of bricks vermiculite°C11468
The bottom (center)°C9257
The length has nastily under the projection of the anode:mm215165
The minimum thickness of the crust:mm186178

At the same time, because of the low conductivity carbon black layer has high thermal resistance, which provides a large temperature gradient along its height. Therefore penetrating the molten electrolyte cools, forming a crust, impervious lagazuoi and liquid phases.

Another positive factor of the proposed technical solution is that the upstream bottom block in the case of the use of carbon black will be in a more uniform temperature field. Thus, the temperature difference across the height of the bottom block of the prototype is 16.5°and in the proposed version is only 8°C. the period of heating and firing the bottom this factor determines the integrity of the hearth, as if the warm-up temperature difference in height is massive hearth block decreases. During the soaking hearth blocks components of the electrolyte due to capillary forces decrease of the temperature gradient at their height helps reduce the amount of penetration of sodium fluoride. But the most notable in the case of application of the proposed solution is sharp (356° (C) reducing the temperature in the lower layers. As a result of this (while maintaining the properties of soot under the action of the electrolyte components, in particular sodium vapor) offer the possibility of reducing the number of materials used in the basement, which entails economic effect. The foregoing is illustrated by the paintings of the temperature distribution and the FER aluminum cell (Fig.6 and 7).

Using the above cathode lining will increase the average service life of each aluminum is about pot 1 year, that will lead to an increase in aluminium production by about 400 so the achieved reduction of specific power consumption for 125 thousand kW·h

1. Cathode lining aluminum cell that includes a carbon blocks, insulating layer and the refractory part, consisting of two protective layers - top, adjacent to the carbon blocks and the lower protective layer made of powder materials, characterized in that the upper protective layer consists of an aluminosilicate material that is resistant to electrolyte components, and the lower protective layer lined airtight metal containers, one or more filled with refractory material that is resistant to molten aluminum and electrolyte components, carbon-containing composition with a thermal conductivity of not more than 0.1 W/(MK).

2. The lining according to claim 1, characterized in that the upper protective layer is made from a material with a content of Al2O3from 27 to 35%, a particle size of not more than 2.5 mm and a thickness of from 10 to 50% of the height of the refractory part.

3. The lining according to claim 1, characterized in that the lower protective layer containers filled with soot and its thickness ranges from 50 to 90% of the height of the refractory part.



 

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