Method of mounting cathode section of aluminum electrolyzer

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

The invention relates to the field of non-ferrous metallurgy and can be used in the installation of aluminum electrolysis cells as major repair and capital construction.

Known widely used in industry assembling the bottom, in which the furnace hearth electrolytic cell made of carbon cathode sections of different lengths and prints interconnect seams of carbonaceous hearth mass [1]. The bottom sections of the current-carrying metal rods (Blums) inserted into the slots of coal blocks and filled with iron to create a solid mechanical and electrical contact between the steel bar and the coal block, and apply the Blums, commensurate with the length of blocks.

When mounting the steel bar with the descent of the aluminum comes out with one hand outside block, on the other hand steel bar does not reach the end of the block 100 to 150 mm and the space in the slot of the block, the so-called "sweat", score the bottom mass.

The disadvantage of this method is the occurrence of thermal stresses in the carbon block during casting of steel bar cast iron, mechanical destruction of blocks, which lead to violations of the electrolysis process and reduce the service life of the cell.

Read more the mechanism of destruction of coal blocks is as follows: coal unit with ambient temperature fills the I molten cast iron with temperature ˜ 1300°C, resulting in a thermal shock. If thermomechanical stress exceeds the tensile strength of the material block, then in it there are cracks, the formation of which is accelerated by the presence of existing microdefects. In addition, when firing the bottom cathode sections have additional thermomechanical stress due to the fact that thermal expansion coefficient of the steel bar approximately four times more than carbon. Such voltage will lead to the formation of cracks during firing or in the early stages of work that can destroy the furnace hearth baths and significantly increase the voltage drop in the cathode.

The presence of blocks of microtrain and microdefects arising as a result of thermal shock, and in the process of burning the bottom, leads to a significant reduction of the service life of the cathode of the device.

Various methods aimed at reducing harmful effects on the furnace hearth of the above phenomena, for example:

- A.S. the USSR №665025 (25 3/08) cathode is a metal rod with variable cross-section along the length of the groove carbon block, and filling the rest of the groove blocks provide bottom mass.

Current solutions have significant drawbacks:

1. Do not provide the full withdrawal (payment) heat is atragene in carbon block when mounting and heat treatment (firing-start-operation).

2. Not provide sufficient electrical contact in the system core block.

So, in the literature [2] shows that due to the absence of contact between the top of the steel bar and the groove of the block, the voltage drop in the furnace hearth is increased by 23 mV.

3. Increased labor costs and energy costs during installation and operation of the cathodic section.

It is known that temperature gradients that occur in the furnace hearth and directed into the body of the bottom block, try to bend the Central portion of the bottom up. The expansion of the carbon block caused by sodium, provides additional bending bottoms, also directed upwards. External pressure from the melt partially compensates for the bending moments in the blocks, but nevertheless absolutely rigid bottom promotes the formation of cracks, so steel steel bar should be able to slide in the slot of the block.

In this regard, is currently considered the most promising way to seal Blums using carbonaceous hearth mass or other conductive compositions having sufficient mobility in the groove of the block.

Closest to the proposed technical solution to the technical nature, the presence of similar features is the invention according to patent No. 2090659 RF "Method of mounting the cathode section aluminum electro is Ysera" (25 3/08, March 26, 1996), in which the cathode terminal is installed in the slot of the block on the layer of electrically conductive material and secured in the block by carbon paste.

In this way the main idea is differentiated approach to the choice of sealing carbonaceous materials by volume of the groove, providing contact steel bar - cathode block, to reduce the harmful effects of thermomechanical processes in the cathode section.

Namely: before installing the steel bar groove block fill with filling of the graphite powder; the gap between the side wall of the groove and the side surface of the rod to a height of 0.6 to 0.9 of the height of the rod - carbon paste with 20-30% of graphite; the upper part of the groove - carbon-based paste with low carbon content.

This approach provides a partial withdrawal of thermomechanical stresses in the cathode section due to the affinity of the material of the block and the sealing material, and also due to the mobility of graphite added.

This solution provides a better result in comparison with the known above technical solutions, namely: minimize the harmful effects of thermal expansion in the cathode section.

However, it is necessary to note significant disadvantages of the method on the prototype:

in the process of installation is violated reliability mechanical clutch Vkontakte "the bottom of the groove of the block steel bar" because of its mobility, since the filling of the graphite powder is almost not compressed, but only recorded the weight of the steel bar;

- this decision is a significant increase in labor costs and complexity of the installation process.

Object of the present invention is to improve the technical and economic indicators of 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 Electromechanical contact "conductive rod - carbon block, reducing the likelihood of penetration of molten aluminum in the body bottom.

This technical result is achieved in that in the method of mounting the cathode section of the aluminum cell, including the installation of current-carrying metal rod in the groove of the carbon block carbon layer of electrically conductive material on the surface of the groove carbon block pre-applied surfactant-based carbon, and the carbon layer of electrically conductive material is subjected to compaction by vibration, and the vibration impose on current-carrying metal rod previously in the local area, on the one hand limited by the "sweat" and off pota" distance is 1/3-1/4 of the length of the rod, contact block, while the maximum thickness of the layer of carbon-containing electrically conductive material to vibration support equal to the amount determined by the formula:

where

S - the maximum thickness of the layer of carbon-containing electrically conductive material to vibration, mm;

d_kr- maximum tolerance curvature for a metal rod, mm/p.m.;

L is the length of a metal rod, equal to the length of the cathode block minus the length pota, p.m.;

μ - the degree of compaction of the layer of carbon-containing electrically conductive material, in fractions of a unit;

K - correction factor that depends on the quality of the surface of the groove of the cathode block and variance of the geometric dimensions of the cathode block, changing in the range from 0.7 to 1.2, and the current-carrying metal rod is subjected to a preliminary mechanical processing.

In contrast to the method according to the prototype, in which before backfilling graphite powder surface grooves hearth blocks only fanned the compressed air, in the proposed method, on the surface of the groove is applied surfactant-based carbon. This solution is due to the fact that the bottom unit is a carbon-containing product, since the firing, resulting in the carbon block is ergodic in an inert state. In the absence of the active centers structuring in the process of burning the bottoms between the block and the sealing mass is practically not formed structural connections. This explains the deterioration over time of the contact bottom block sealing mass in the cell. To ensure sintering unit of mass is suggested to use a surfactant on the basis of carbon, where the carbon is in the active form and performs the role of cross-linking bridges between the carbon block and carbon putty.

Also in contrast to the method according to the prototype, in which the filling of the graphite powder is compacted by the weight of the steel bar when it is installed in the groove of the block, in the proposed decision, the seal is effected under the action of vibration imposed on the steel bar in the "Peta", and to ensure the location on one level coupling cross-section of the Blums the thickness of the layer of carbon-containing electrically conductive material to vibration correcting depending on the length of the steel bar.

The process of vibratory compaction is fundamentally different from the seal by pressing the fact that the seal is in the "boiling" layer on the principle of free self-packing to maximize the dense packing of the particles due to the redistribution of them in total. Vibration does not have a separate hour of the Itza damaging effects, the granulometric composition of the source material is not disturbed.

The compactor passes the steel bar vibro, which create a predominantly vertical component of the vibrations. At the same time, these same vibro into force of inertia and the possibility of elastic deformation of the bottom mass is called the doubling of the strength of the vertical component of the vibrations is realized resonant mode).

This creates the conditions for maximum sealing mass, namely violated automazione communications in mass, i.e. the separation of one of the particles of the filler from the other, regardless of particle size. A lot goes into a state of boiling. The result is a redistribution of particle mass with infiltration of fines into the most complicated of pores.

In the process of vibrocompaction the most active role played by dust fraction, which compacts:

firstly, the defect blocks (cracks, microtrain, pores);

- secondly, the large particles of the sealing mass due to the ingress of dust into the interior of the particles through the remote when the seal by pressing the pores, and therefore, surface porosity mud weight decreases further when firing occurs, the compaction of the particle mass in a closed volume at the expense of pyrocarbon.

The use of concrete vibration to a certain extent eliminates the defects of the block, and p is more than the density of the sintered mass. Resulting in increased mechanical contact "block-steel bar", and also reduces electroputere in the partition.

Modern electrolytic production of steel bar from the block is for long sections ˜20% of the length of steel bar, for short - ˜30%. Naturally, when mounting sections have moments of forces directed in such a way that the contact "steel bar-block" broken steel bar rises above the block in the "pota". To ensure a stable snug fit of the steel bar to the bottom of the groove after removal of a compactor for aligning torques authors proposed to establish by descent in the area of heat sealing concrete expansion joint in the form of a metal rod, which must be above the concrete fill.

The use of expansion joints is the subject of KNOW-HOW of this method.

Thus, the use of vibration compaction increases mechanical contact backupsetname mass", and the use of surfactant-based carbon provides the structural unity of the block and the sealing mass in the process of burning the bottom, resulting in a contact block mass" has a specific resistance (resistivity) is significantly lower than without the application of the aforementioned events.

Thus, the results of the tests on the Smelter showed that only the use of surfactants reduces the electrical resistivity of 13.8%. In terms of real conditions the production application of surfactant on the surface of the groove bottom of the unit will reduce the voltage drop in the cathode by at least 5 mV.

Comparative analysis of the proposed technical solutions to the prototype and other known solutions in this area revealed the following: the application of vibration to seal the bottom mass is known, for example, AS the USSR №1654380 (25 3/06) "Method of printing carbon mass of welds the bottom of the electrolytic cell for obtaining aluminium, and patent USSR No. 1790631 (25 3/06) "Method of compaction of the coal mass in the joints of the bottom aluminum cell".

In contrast to the solutions proposed in these technical solutions:

- vibration is subjected to mass interconnect seams;

- vibroplate is Vibroscreen, working body which is moved over the entire area of the sealing material.

In the proposed solution vibrating working body is steel bar, steel bar is the causative agent of vertically and horizontally oriented fluctuations in the volume of the bottom mass, when this is implemented by simultaneous application of vibration over the entire area of the groove of the block.

The authors propose to apply vibration to the local area current-carrying metal rod, namely the area bounded on one side by the "sweat" and off pota" at a distance of 1/3-1/4 of the length of the rod in contact with the block.

This area was determined experimentally, when applying vibration in the zone d is one achieves the maximum reduction of the voltage drop in the contact layer between the steel bar and the groove of the block.

Many domestic and foreign researchers have investigated the issue of improving the properties of the anode mass and anodes by introducing in the formulation of chemically active substances (Aaana "Anodes in aluminium electrolysis cells", M.: Izd. house "Ore and metals", 2001, str).

As surfactant additives known anthracene oil, glycerin tar and other additives are carbon-based. When using the positive changes in the microstructure of the composite, reducing the micro porosity and other characteristics of the paste.

As noted above, the additive surfactant in the known solutions were injected uniformly in the volume of the electrode mass. In the proposed solution the surfactant is applied evenly on the contact surface of the finished electrode of the product (block) and activate the process of structural integrity of the unit and the sealing mass. With the physico-chemical point of view, the surfactant layer is in this case a layer of structural bridges (connections).

Thus, the proposed method of mounting the cathode section, on the one hand, increases the strength of the mechanical connection "block - weight" through the use of vibration, and, on the other hand, allows us to achieve maximum structural accretion unit of mass when using SAS.

When testing for existing pots mounted on the proposed method, the pad is the voltage dropped by 20 mV. It is known that the gain in 10 mV is equivalent to a reduction of electricity consumption by 30-35 kWh per tonne of aluminium.

Currently, quite a wide range of cold-ramming mass. When choosing a weight guided by the basic requirement is the specific resistivity of the mass should be commensurate with the specific resistivity of the unit or below. So, currently used at the Smelter bottom weight brand MHTD "A" (the mass of cold-printed conductive for blast furnaces) or Mat (weight cold-printed heat-conducting contact) after firing has a resistivity equal to approximately 33-50 µohm·m And, although the electrical resistivity of the interlayer is lower than WES block (WES block is not greater than 45 µohm·m), when mounting the bottom section try to reduce the thickness of the layer. The optimal thickness of the authors recommend be determined by the formula set out in the claims. The formula for the correction factor To a given interval of variation of 0.7 to 1.2. The lower value corresponds To the minimum possible in real conditions, the deflection of the cathode blocks in geometric size, and K=1,2, respectively, for the maximum variance.

Currently, in terms of IrkAZ this method is implemented as follows.

For sealing Blums in the bottom blocks of the selected mass kholodenina conductive to the house is the R furnaces (MHTD "A") and heat-resistant concrete.

The temperature of the mass before the prints should be +25±10°C. sealing mass in the groove bottom of the block is used pad the compactor.

As an additive surfactant taken priming paste based on, for example, modified (plasticized) peck and ermantraut (dust fraction).

The compactor operates as follows.

The whole structure is rigid construction, therefore, the vibrations of the vibrator without any changes or transformations are transferred to the steel bar installed in the bottom block.

To protect the upper corners of the groove of the block from breaking under vibration compactor is provided for supporting the parts that are directly borne by the steel bar. On the other hand, the supporting parts to ensure an even distribution of vibration throughout vybiraem zone.

Preliminary preparation unit is as follows:

- the surface of the block before applying a layer of surfactant should be cleaned from dust and to have a temperature not lower than +15°C;

- additive surfactant should have a fluid state (in a particular case must be heated to 7-30°);

the surfactant layer is applied on the contact surface of the block evenly (by brush, roller) immediately before the printed mass.

On bottom of the groove previously prepared block is and along its length uniformly filled the bottom layer mass and height of 25 mm with the exception of 100 mm from both ends of the block. Across the groove of the block on the output side of the steel bar is placed compensator in the form of a steel rod and a layer of refractory concrete with a height of 15 mm No later than 1 hour after laying refractory concrete in the groove of the block place of the cathode rod and produce compaction of the lower layer of the mass using a compactor for 2-2 .5 minutes.

This time interval was determined experimentally and the optimality of a given interval is confirmed by the results of experimental-industrial tests, displayed on the graph (Fig.1-4) and in table 1.

So, for this interval is characterized by the lowest specific contact resistivity layer (figure 1), the highest mechanical strength (figure 2), the maximum density of the contact layer for unburnt and burnt mass of the layer (3, 4).

Before crimping the bottom blocks and cathode rods are heated to a temperature not below +25°C.

Seal filling in the gaps carried out by ramming.

The region of the cathode rod, the volume of the groove above the cathode rod and the "sweat" is filled with heat-resistant concrete.

After mounting section is not chantuese for at least 24 hours.

In conclusion, it should be noted that the tests conducted on the Smelter, proved the effectiveness of using vibration to compact the mass in the unit on offer is UEMOA method in conjunction with the use of surfactants in the contact areas. Therefore, this method is recommended for industrial application.

Sources of information

1. The production of aluminum. Handbook of metallurgy of nonferrous metals. M.: metallurgy, 1971, s-244.

2. Analysis of possible reasons for the high voltage drop in the furnace hearth aluminum cell. GV Arkhipov. A collection of "Aluminium of Siberia 1999" , Krasnoyarsk, 1999

1. The method of mounting the cathode section of the aluminum cell, including the installation of current-carrying metal rod in the groove of the carbon block carbon layer of electrically conductive material, wherein the surface groove of the carbon block pre-applied surfactant-based carbon, and the carbon layer of electrically conductive material is subjected to compaction by vibration, and the vibration impose on current-carrying metal rod.

2. The method according to claim 1, characterized in that the vibration is nakladivaut on current-carrying metal rod in the local area, on the one hand limited by the sweat and spaced from Peta at a distance of 1/3-1/4 the length of the rod in contact with the block.

3. The method according to claim 1, characterized in that the maximum thickness of the layer of carbon-containing electrically conductive material to vibration support equal to the amount determined by the formula

where S is the maximum thickness of the layer of carbon-containing electrically conductive material to vibration, mm;

d_kr- maximum tolerance curvature for a metal rod, mm/p.m.;

L is the length of a metal rod, equal to the length of the cathode block minus the length pota, p.m.;

μ - the degree of compaction of the layer of carbon-containing electrically conductive material, the proportion of the units;

K - correction factor that depends on the quality of the surface of the groove of the cathode block and variance of the geometric dimensions of the cathode block, changing in the range from 0.7 to 1.2.

4. The method according to claim 1, characterized in that the current-carrying metal rod is subjected to a preliminary mechanical processing.