RU2307878C1 - Method for preparing aluminum cell to operation - Google Patents

Abstract

FIELD: non-ferrous metallurgy.

SUBSTANCE: method for preparing aluminum cells with fired anodes arranged crosswise in housing of cell to operation with high electric current intensity (more than 250 kA) comprises steps of heating bottom of cell and firing seams by means of outer heat source; mounting anodes, pouring electrolyte. Anodes are mounted at increasing height of anode base plane at outlet side of cell relative to plane of anode base at inlet side of cell along vertical line from cell bottom. Value of said shift for increasing height is equal to 0.6 - 3 cm or it consists of 0.01 - 0.04 of relation of electric current intensity (kA) to number of anode struts.

EFFECT: uniform electric current distribution of anodes at inlet and outlet sides in after-starting period of aluminum cells.

2 cl, 2 dwg, 1 tbl

Description

The invention relates to non-ferrous metallurgy, in particular to methods of preparation for starting electrolytic cells for producing aluminum with calcined anodes for a large current strength (over 250 kA) with a transverse arrangement in the electrolysis body.

There are many ways to prepare for the launch of aluminum electrolytic cells, differing in methods of firing, installing anodes, pouring melts into the cell of electrolytic cells.

A known method of preparation for launching an aluminum electrolyzer of any type, according to which the preparation is carried out in two stages. At the first stage, the bottom of the cell is fired and heated to a temperature not lower than 750 ° C due to the heat from the organized combustion of atomized fuel distributed evenly into the space between the inner surface of the cathode shaft and the lower surface of the anode. In this case, the lower surface of the anode is level with the cathode side. At the second stage, the electrolyte superheated to 970-1010 ° С is poured and the cathode and lining are continued to operate at operating temperatures (USSR Author's Certificate No. 659645, С25С 3/06, 1979).

There is a method of thermal preparation for starting any type of aluminum electrolysis cell, which consists in heating the bottom of the cell due to the organized burning of liquid fuel (for example, diesel fuel, fuel oil) inside an enclosed space formed by the cathode lining, the lower surface of the anode and temporary covers between the anode and the sides of the cell. (USSR author's certificate No. 765403, C25C 3/06, 1980).

A known method of firing and starting the electrolyzer to produce aluminum, which includes mounting anode cells with insulating side walls and an electrically conductive bottom on the bottom of the electrolyzer, installing electric heating elements, loading the anode mass, heating and forming a self-firing anode with a series current, pouring the melt, setting the operating voltage on the cell . As the anode burns, the self-firing anode cells are replaced with fired anodes. (USSR Author's Certificate No. 1740499, С25С 3/06, 1992).

The disadvantage of the above methods of preparing electrolyzers for start-up, with respect to electrolyzers with a large current strength with a transverse arrangement in the case, is overheating in the post-launch period of the “output” in the direction of the current in the series of sides compared to the “input” due to the installation of the sole of all anodes on one horizontal level.

A known method of preparing for launching an aluminum electrolyzer, including laying on the bottom of the electrolyzer, made of blocks, a protective layer of a mixture of cryolite with oxides and fluorides of an alkali metal, heating the bottom of the cell and firing the seams with an external heat source, installing anodes, filling the electrolyte. Firing the joints is carried out up to 550-600 ° C in three steps with holdings at 200 ° C for 3.5-4 hours, 350-400 ° C for 4.0-5.0 hours and at 550-600 ° C within 3.5-4 hours, with the subsequent installation of the anodes to a height of 0.25-0.35 of the height of the mixture layer (USSR Author's Certificate No. 5449510, C25C 3/06, 1974).

By appointment and the presence of similar significant features, this decision was made as a prototype.

The disadvantage of the method of preparation for the launch of the aluminum electrolytic cell of the prototype is the imbalance of the temperature fields along the longitudinal sides of the cell due to the installation of the sole of all anodes in a plane parallel to the bottom of the cell. In the post-start period in the electrolyzer, at a large current strength with a transverse arrangement in the housing, the “output” side (in the direction of the current in the series) of the cell overheats compared to the “input” side due to the higher current load of the anodes located on the “output” side compared to the current load anodes on the "input" side. This fact is due to the fact that in the transverse arrangement of electrolyzers with anode risers on the "input" side, the skew of the metal surface has a specific shape. The current in the anode risers is directed up, and in the melt - down. The longitudinal component of the magnetic field B _y from the anode risers, when it interacts with the vertical current component in the metal I _z , creates a field of transverse electromagnetic forces F in the metal. The magnitude of the component B _y on the “input” side is greater than on the “output” side, respectively, and electromagnetic forces on the "input" side are greater.

The objective of the proposed solution is to increase the technical and economic indicators of the operation of electrolyzers in the post-launch period and to increase the service life of electrolyzers.

The technical result is to ensure uniform distribution of current across the anodes on the "input" and "output" sides and the same temperature of the side surfaces of the casing on the "input" and "output" sides in the post-launch period of aluminum electrolysis cells.

The problem is solved in that, in the method of preparing for starting an aluminum electrolyzer for high current strength with calcined anodes with a transverse arrangement in the electrolysis body, including heating the hearth and firing the seams with an external heat source, installing anodes, filling the electrolyte, according to the proposed solution, the installation of anodes is performed with the displacement of the plane of the sole of the anodes on the "output" side of the cell compared with the plane of the sole of the anodes on the "input" side, higher vertically relative to the bottom of the cell .

The invention is complemented by private distinctive features, also aimed at achieving the task.

The plane of the sole of the anodes on the "output" side is set higher relative to the bottom of the cell compared with the plane of the sole of the anodes on the "input" side by an amount L equal to 0.6-3 cm, which is 0.01-0.04 of the ratio of the current expressed in kA to the number of anode risers.

With a relative displacement of the planes of the sole of the anodes on the “output” and “input” sides of less than 0.6 cm, a uniform distribution of current across the anodes on the “input” and “output” sides will not be achieved. With a relative displacement of the planes of the sole of the anodes on the “output” and “input” sides of more than 3 cm, the opposite effect will occur - overheating of the “input” side relative to the “output” side.

As a result of comparing the proposed solution not only with the prototype, but also with other technical solutions in the art, there are no signs distinguishing the claimed solution from the prototype, which makes it possible to conclude that the criteria of "novelty" and "inventive step" are met.

The invention is illustrated graphic material.

The figure 1 shows the field of transverse forces in the metal with a transverse arrangement of the electrolyzer with risers on the "input" side, creating a bias shifted to the "output" side, where 1 are the lines of force of the magnetic field, 2 are the anode risers of the adjacent electrolyzer, 3 is the considered cell , 4-anode risers of the electrolyzer under consideration, B _y and B _x are the directions of the horizontal longitudinal and transverse components of the magnetic field induction vector, respectively, F is the direction of the shear force vector, I is the direction of the current in the series.

Figure 2 shows the implementation of the method, where 5 are the anodes on the "input" side, 6 are the anodes on the "output" side, 7 is the bottom of the cell, I is the direction of the current in the series.

Thus, the risers themselves, their inclined parts, as well as the conductors connecting the anode bars to each other, form a force field in the metal, which shifts the metal to the "output" side.

This assumption is confirmed by the results of measurements of the distribution of current strength (kA) over the anodes when starting the electrolyzer, presented in the table.

Table day off 36 35 34 33 32 31 thirty 29th 28 27 26 25 24 23 22 21 twenty 19 Total: 9,4 8.6 9.5 9.8 13 12 eleven 10 7.1 8.6 eleven 10 10 9.7 7.5 7.5 7.2 7.5 169.4 input 10 8.1 7.0 8.0 9.5 8.4 8.7 8.3 9.0 9.1 8.5 8.3 8.7 5.9 5.1 6.3 6.5 7.2 142.6 one 2 3 four 5 6 7 8 9 10 eleven 12 13 fourteen fifteen 16 17 eighteen

As you can see, the total current strength at the anodes on the "output" side is 26.8 kA more than on the "input" side, which is due to overheating of the "output" side.

Thus, after pouring the electrolyte and metal into the starting electrolyzer in it, under the influence of electromagnetic forces, the surface of the metal is skewed with a shift to the “output” side. If during annealing of the cell the sole of all anodes is placed in a plane parallel to the bottom of the cell, the distance between the aluminum mirror and the sole of the anodes (MPR) on the “output” side becomes less than MPR on the “input” side.

Therefore, it is proposed that when starting electrolyzers with baked anodes at a high current strength with a transverse arrangement in the housing, to prevent overheating, use such an arrangement of the anodes relative to the bottom of the cell, in which the MPR would be the same on both sides of the cell.

Installing the sole of the anodes on the “output” side in a plane higher than the plane of the sole of the anodes on the “input” side will compensate for the difference in the MPR associated with the distortion of the metal under the influence of electromagnetic forces for the anodes on the “input” and “output” parties in the post-launch period.

Claims (2)

1. A method of preparing for starting an aluminum electrolytic cell at high amperage with baked anodes with a transverse arrangement of electrolyzers in the electrolysis body, including heating the hearth and firing the seams with an external heat source, installing anodes, filling the electrolyte, characterized in that the anodes are mounted with the sole plane shifted anodes on the output side of the cell as compared with the plane of the sole of the anodes on the input side are higher vertically relative to the bottom of the cell. 2. The method according to claim 1, characterized in that the vertical displacement of the planes of the sole of the anodes of the input and output sides relative to each other is 0.6-3 cm, which is 0.01-0.04 ratio of current strength, expressed in kA , to the number of anode risers.

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