Method of forming hearth for aluminum electrolyzer

FIELD: installation of aluminum electrolyzer hearth.

SUBSTANCE: proposed method includes preliminary estimation of quality of hearth modules by proximate ultrasonic inspection, mounting of complete set of hearth modules and forming of hearth; electrolyzer is equipped with hearth modules at inhomogeneity index not exceeding 0.65 relative units according to ultrasonic inspection; inhomogeneity index is determined by the following formula 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.

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

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The present invention relates to ferrous metallurgy and can be used when mounting the bottom of the aluminum electrolysis cell.

It is known that in the process of starting cell in the furnace hearth have significant thermo-mechanical stresses due to the temperature difference in the initial and final periods of start-up. Therefore great importance is the proximity of the physico-mechanical properties adjacent elements hearth (hearth blocks). If the neighboring blocks have a significant difference in terms of thermal expansion and mechanical strength, they are different will perceive thermal load and there will be an increased risk of fracture as an interconnect joints and blocks that, as a consequence, leads to a sharp reduction in the service life of the cell.

From all the above we can conclude that to create a quality hearth necessary equipment its bottom blocks with similar physical-mechanical properties.

The basis for evaluation of the physico-mechanical properties of the units and their furnishings must be put to one of the methods of nondestructive testing.

So, As the USSR №1696598 (25 3/20) "Method of quality control in the manufacture of cathode section aluminum cell" workmanship cathode sections aluminum cell evaluated by passing electricity is tricesimo current and measurement of the contact electrical resistance at the interface of the coal block with the metal part of the section, record a change of the contact resistance between the carbon block and the metal part of the cathode section by its heating in the temperature range 180-390°and the occurrence of defects, cracks in the coal block is judged at the moment of transition from the reduction of the electrical resistance of anxiety.

Currently, the most informative, less time consuming and cheaper NDT method is ultrasonic method.

The development of this method and its use when mounting the coal hearth aluminum cell is discussed in several works of the Ural electrode Institute:

- Ultrasonic testing of graphite electrodes (Col. metals No. 3, 1997, p.45);

- Evaluation of the ultimate tensile strength of the material hearth blocks ultrasonic method (Col. metals, 2000, No. 5, p.91).

Research many experts have found that the propagation time of the ultrasonic signal through the cross-section units correlated with many of their properties, such as strength in compression and tension, density, modulus of elasticity, coefficient of thermal expansion. In particular, the change of time t 10 µs characterizes the change of tensile elongation at ˜0.2 MPa, i.e. about 10% of its average value. Thus, the time value t is the object of the main parameter, the use of which will form the most stable for a given set of bottom blocks of the furnace hearth.

Acoustic testing of carbon products was tested at KrAZ improving the efficiency and reliability of aluminum electrolytic cells. Proceedings of YOU, Leningrad, 1988).

As the closest to the technical essence and the achieved result is described in the above-mentioned operation method selected for the prototype.

According to the prototype for quality control of baked blocks of the developed method, including the measurement of ultrasonic velocity and electrical resistivity (electrical resistivity). At the first stage of two-stage control identifies suitable blocks, and the second is rejected with high resistivity are tested for the possibility of their use at the expense of decreasing size. All carbon blocks are subjected to non-destructive control device type "Sound". According to the results of a sound control all the units in accordance with their physical and mechanical properties are divided into groups by the value of the sound index (RFI). The set of building blocks for the bottom one electrolyzer pick up the blocks to the difference in the properties of the CR, not more than 1-2 sound index. In the future perform installation hearth.

From a theoretical point of view, this method can be considered quite progressive, providing the m uniformity bottom due to the strict requirements when selecting a set of blocks on the installation of one cell, but the practical realization of this method of installation, the bottom is very difficult for the following reasons:

sort of block indexes - consuming process, this requires the modernization of storage facilities for separate storage units with different indexes;

the approach to forming the bottoms of the prototype cannot be considered effective, for example, across the body or plant, as hard selection blocks on the packaging stage leads to the fact that within a housing mounted bath life which originally laid different: bath units with low ZI has the best prerequisites to life than tub with a higher ZI;

- the installation of the bottom of the prototype is carried out randomly within the selected set of bottom blocks. But if you take into account the non-uniformity of the temperature field electrolysis cell, it is more rational to form the furnace hearth with this irregularity.

All the above-mentioned disadvantages of the prototype were considered by the authors in the proposed method, forming the bottom of the aluminum electrolysis cell.

The objective of the proposed invention is to increase the service life of the cells.

The technical result of the proposed method is the formation of a hearth with a maximum thermomechanical strength, possible DL is a specific set of blocks, as well as the creation bottoms, taking into account the unevenness of the temperature load on the furnace hearth, which allows with sufficient efficiency without compromising service life of the cell to use blocks wide range of physico-mechanical properties.

The technical result is achieved in that in the method of forming the bottom of the aluminum electrolysis cell, including a preliminary assessment of quality hearth blocks rapid method of ultrasonic testing equipment on hearth blocks for one cell according to the results of ultrasonic testing and the formation of the bottom, with the bottom of one cell is carried out hearth blocks with the index of heterogeneity not more than 0,65 ated according to the ultrasonic testing, the indicator of heterogeneity is determined by the formula

where P_nis an indicator of heterogeneity in ultrasonic testing;

t_max- the maximum rate of ultrasonic testing of a set of blocks for a particular cell, ISS;

t_minthe minimum value of ultrasonic inspection of a set of blocks for a particular cell, ISS,

and forming the bottoms carried out in such a way that adjacent blocks in the longitudinal and transverse directions set with the most similar is a simple ultrasonic testing kit for concrete cell, while the blocks with the lowest indicators of ultrasonic testing set in the center of the bottom with a gradual increase of this indicator to the ends of the electrolysis cell.

The essence of the proposed method of installation, the bottom is the following:

- for all manufacturers of hearth blocks characteristically, even within one species there is a significant fluctuation in the values of the travel time of the ULTRASONIC signal. As noted above, the index t is the most informative indicator characterizing thermomechanical behavior of the block in the furnace hearth. Therefore, to ensure the maximum possible thermo-mechanical strength of the bottom needs to adjacent blocks in the longitudinal and transverse directions was the closest indicators of ultrasonic inspection. It is known that in the bath the most termocartagena area - the center of the bottom, and less - the ends of the cell. Therefore, the authors propose to place the blocks with the lowest index t in the center of the bottom with a gradual increase of this indicator to the ends of the electrolysis cell.

From the above we can conclude that in the proposed method, as in the prototype:

paragraph 1

- quality assessment hearth blocks produced by the method of non-destructive audio control;

paragraph 2

- non-destructive testing are all, without exception blocks;

the .3

- completed deck blocks for each cell according to the results of a sound control;

item 4

- form the furnace hearth picked from hearth blocks.

But the proposed method has some fundamental differences from the prototype:

according to claim 1

Thoroughly tested technique UT (ultrasonic testing) with years of experience specialists Ural electrode of the Institute, resulting in a relative error of measuring the travel time of ultrasound (t) does not exceed 1%. UI method is the subject of KNOW-HOW of the authors.

according to claim 2, 3

The prototype upon receipt hearth blocks from the manufacturer is sound control, control all the blocks are divided into groups with ZI 19-35. Group blocks warehoused separately accumulate and form a set for one tub of groups that differ by 1-2 ZI.

In the proposed method, considering the actual conditions of production, it is possible to equip the furnace hearth cell from the whole range of available blocks.

Currently used when mounting blocks 1, 2 and 3 grades. The measure of the heterogeneity of these sorts of not more than 0,65 ated Limit value P_ndetermined on the assumption that the boundary values ultrasonic testing, characterizing the suitability of the units for the installation, is the range 220-360 ISS. B the Oka with the figures for the DCU less than 220 and 360 ISS rejected, because in the first case, the blocks are more fragile, making it difficult to transport units and installation bottoms, and in the second case differ unacceptably high "looseness"that reduces the technical-economic indicators of electrolysis in General.

Of course, it is better to pick the furnace hearth of the blocks within a single grade, which is mainly practiced, but since it is not always possible in terms of production, it is permissible to trim blocks any long set. To mitigate varietal differences as well as differences in properties within a single grade, the authors propose an original method of forming the bottom, which will be described below.

according to claim 4

In the prototype the furnace hearth form of blocks with honors in ZI in the narrow interval (1-2 CR), therefore, when mounting the bottom of the properties of the individual blocks are not taken into account and the blocks are set arbitrarily. In the proposed method and kit for one bath can hit the blocks with a significant difference between the physico-mechanical properties. Later in the section "industrial implementation of the method will be described a specific example of the practice tests of this method on the Smelter is, when the difference in the readings UT amounted to more than 40 μs.

To obtain a homogeneous furnace hearth with the greatest possible thermomechanical resistance in conditions of significant difference the indicator ultrasonic inspection units is only possible when performing installation on the proposed by the authors of the original method: the adjacent blocks in the longitudinal and transverse directions should be the closest indicators ultrasonic control of sets of blocks for a particular cell, and the blocks with the lowest indicators of ultrasonic testing set in the center of the bottom with a gradual increase of this indicator to the ends of the electrolysis cell.

Figure 1 presents a graphical presentation of the proposed method of installation, where it is apparent that when disordered placement of sections in the furnace hearth have additional thermomechanical stress, and when ordered - negative interference of adjacent blocks is smoothed, which, of course, will have a positive effect on the service life of the cell.

Figure 2 graphically presents the method of forming the bottom with a gradual increase in the DCU from one mountaineer cell to another. From the point of view of doing electrolysis process asymmetry in the properties of the bottom will cause a number of technological difficulties, so from a practical standpoint, this variant form of the bottom less interesting, although possible.

The above differences of the proposed method of forming the bottoms from the prototype allows to make a conclusion on compliance with a criterion of the invention of "novelty."

The above analysis on the technical and patent literature showed that fundamentally individual characteristics of the object are known, but the combination of known and unknown PR the characters, specified in the claims, allows you to enter a new rational level in the formation of the bottom of the aluminum electrolytic cell with the use of modern methods of quality control blocks. Thus, the proposed solution meets the criterion of "inventive step".

The following is an example of testing the proposed method in industrial electrolyzers SBM the Smelter.

Of the blocks of the Novosibirsk electrode plant were picked two similar according to the ultrasonic testing batch of blocks.

One of the parties was aimed at forming the bottom of the experimental cell by the present method. The layout of the blocks on the furnace hearth presented on figa, where two-digit numbers that correspond to the block number, and a three-digit - performance ultrasonic inspection. The second batch is aimed at the formation bath witness without ordering the blocks (figb).

From the data of figure 3 it is obvious that the degree of homogeneity bottoms, formed in accordance with the inventive method, is significantly higher than that of the bottom with a random arrangement of blocks.

Moreover, it can be argued that recommended the formation method can provide high uniformity bottoms for any given set of blocks, and without any capital cost for a small increase in labor costs.

Tests saleemul the way of ongoing and projected authors compared the cell - the prototype of the life of the pilot cell will increase by 5-20%, and will decrease the output of the low-grade metal, the energy consumption will be reduced by approximately 2%.

The method of forming the bottom of the aluminum electrolysis cell, including a preliminary assessment of quality hearth blocks rapid method of ultrasonic testing equipment on hearth blocks for one cell according to the results of ultrasonic testing and the formation of the bottom, wherein the set of the bottom of one cell is carried out hearth blocks with the index of heterogeneity not more than 0,65 ated according to the ultrasonic testing, the indicator of heterogeneity is determined by the formula

P_n=(t_max/t_min-1),

where P_nis an indicator of heterogeneity in ultrasonic testing;

t_max- the maximum rate of ultrasonic testing of a set of blocks for a particular cell, ISS;

t_minthe minimum value of ultrasonic inspection of a set of blocks for a particular cell, ISS,

and forming the bottoms carried out in such a way that adjacent blocks in the longitudinal and transverse directions set with the closest performance of ultrasonic testing of sets of blocks to spiral the aqueous electrolytic cell, while the blocks with the lowest indicators of ultrasonic testing set in the center of the bottom with a gradual increase of this indicator to the ends of the electrolysis cell.