SU1548268A1 - Method of pre-start preparation of aluminium electrolyzer - Google Patents

Abstract

The invention relates to the production of aluminum by the electrolysis of cryolite-alumina melt and can be used on all types of electrolyzers in preparing them for operation after construction or major repairs. The purpose of the invention is to increase the service life of the aluminum electrolysis cell. On the interblock and peripheral hem seams lay a protective layer of the following composition, wt.%: Alkali metal oxide 30-45

alkali metal fluoride 18-27

cryolite 35-45. As the alkali metal oxide used oxide CA or MG. Laying is carried out in the following sequence: alkali metal oxide, alkali metal fluoride, cryolite to the ratio of the area of the bottom block to the area of the base of the layer equal to (3.0-3.5): 1, and the ratio of the height of the layer to its width equal to (1 , 5-3,0): 1. The firing of seams is carried out up to 550-600 ° C in three steps with exposures at 200 ° C for 3.5-4 hours at 350-400 ° C for 4.0-5.0 hours and at 550-600 ° C in for 3.5-4 hours, followed by installation of the anodes to a height of 0.25-0.35 of the height of the mixture layer. This method allows to increase the service life of the electrolyzer by improving the quality of firing interblock and peripheral bottom welds. 1 hp f-ly.

Description

one

(21) 4448045 / 23-02

(22) 05-04088

(46) 07.03.90. Bul Number 9

(71) Sana Aluminum Plant

(72) A.M. Ivanov, V "V, Strigo,

S.A. Bochkarev, Yu.A. Bagaev, V.V. Ber-Stenev, V.V.Samodurov and V.V.Korobko

(53) 669.713.72 (088.8)

(56) USSR Copyright Certificate No. 549510, kp. C 25 C 3/06, 1974.

(54) METHOD OF PREPARATION FOR START-UP OF ALUMINUM ELECTROLYZER

(57) The invention relates to the production of aluminum by the electrolysis of a cryolite-clay-earth melt and can be used on all types of electrolyzers in preparing them for operation after construction or major repairs. The purpose of the invention is to increase the service life of the aluminum electrolysis cell. On the interblock and peripheral hem seams lay a protective layer of the following composition, wt.%: The alkali metal oxide 30-45; alkali metal fluoride 18-27; cryolite 35-45. As the alkali metal oxide, Ca or Mga oxide is used. Laying is carried out in the following sequence: alkali metal oxide, alkali metal fluoride, cryolite to a ratio of the bottom unit to the base area of the layer equal to (3.0-3.5): 1, and the ratio of the height of the layer to its width, equal to (1.5-3.0): 1. The firing of seams is carried out up to 550-600 ° C in three steps with exposures at 200 ° C for 3.5-4 hours, at 350-400 ° C for 4.0-5.0 hours and at 550-600 ° C for 3.5-4 hours, followed by installation of the anodes to a height of 0.25-0.35 of the height of the mixture layer. This method allows to increase the service life of the electrolyzer by increasing the firing quality of the interblock and peripheral heatsinks of 1 hp. f-ly.

WITH/

The invention relates to the production of aluminum by electrolysis of a cryolite-alumina melt and can be used on electrolyzers of all types in preparing them for operation after construction or major repairs.

The purpose of the invention is to increase the service life of the cell.

As a protective layer using a mixture containing, may. %: Alkali Oxide 30-45

Alkali metal fluoride18-27 Cryolite 35-45 Laying of the mixture is carried out on interblock and peripheral bottom seams in the sequence: alkali metal oxide, alkali metal fluoride and cryolite, to a ratio of the area of the bottom block to the base area of the layer equal to (3.0-3.5 ): 1, and the ratio of the layer height to its width, equal to (1.5-3.0): 1, the firing of interblock and peripheral seams is carried out up to 550-600

with holdings at 200 ° C for 3.5-4 hours, at 350-400 ° C for 4-5 hours and at 550-600 ° C for 3.5-4 hours, the installation of the anodes is carried out on a honeycomb constituting 0.25-0.35 the height of the mixture layer.

Calcium or magnesium oxide is used as alkali metal oxide.

The method of preparing for start-up for electrolysis of an aluminum electrolysis cell is carried out as follows.

On the interblock and peripheral hem seams, the mixture is loaded in the following sequence: magnesium oxide (MgO) or calcium oxide (CaO), then a layer of calcium fluoride or sodium fluoride and cryolite ;. The mixture is laid at a height of the mixture layer of 50-120 mm with the exit of the backfill area beyond the interblock and peripheral joints by 70-80 mm. The heating of the bottom and the burning of interconnect seams are carried out by an external source of heat generated from the combustion of sprayed fuel distributed evenly in the space between the inner surface of the bottom and the lower surface of the anode. The bottom heating with simultaneous burning of interconnect seams is carried out in three stages until the bottom temperature reaches 550-600 ° C with holding at 200 ° C for 3.5-4 hours, at 350-400 ° C for 4-5 hours and at 550-600 ° C for 3.5-4 hours during 11-13 hours.

After heating the hearth to the required temperature of 550-600 ° C, the anode array is lowered to a height of 30-35 mm from the upper layer of the mixture, as well. the starting cell is loaded into the shaft of the electrolyzer along the periphery of the electrolyzer. Before the electrolyte is poured on the bottom, a cushion of circulating electrolyte is laid out with overfilling with starting raw material to a height of 100-120 mm from the bottom surface so that the electrolyte stream does not directly fall on the bottom blocks in order to avoid their thermal shock. After the electrolyte is poured into the cell shaft, the electrolyzer is connected to an electric furnace. The additional firing of the seams takes place under a layer of the mixture that is in the electrolyte until the operational temperatures of the bottom are reached.

The layer of the mixture covering the interblock and peripheral seams is its

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in the initial period of warming up the hearth from burning out a thin layer of the bonding upper surface of the interblock seam, which is especially important in the initial period of heating the bottom. Due to the fact that the bottom mass of the upper layer of the interblock seam, protected by the mixture layer, has not yet coked, the temperature deformation of the bottom blocks caused by the temperature difference of their warming up takes place without destroying the bond of the block material with the bottom mass of the interblock seams.

The determined sequence of laying the layer of the mixture: calcium oxide or magnesium oxide, calcium fluoride or sodium fluoride, cryolite on top, allows you to place the more dense and viscous components of the mixture directly on the surface of the interblock seam, as well as on the surface of the bottom block. Thus, the interblock seams, as well as the contact surfaces of the seam - block, covered with a softened consistency of the lower layer of the mixture, fill first of all the cracks and pores formed, protecting the interblock bottom seams from penetration of the aluminum melt into them.

The upper layer of cryolite, melted from above when the hearth is heated, forms a dense crust with a glaze surface over the entire area of the backfill. Thus, a sufficiently tight volume is created in which the coking process takes place without air access, which is a necessary and necessary condition for the normal course of the firing process of the bottom mass of the seams. Since the evolving volatiles create some pressure under the hermetic layer of the mixture, the rate of removal of the newly formed volatile is slowed down, which reduces the porosity of the bottom material, thereby increasing its strength.

In addition, the crust forming a dense glaze prevents not only the material of the interblock seams from oxidizing, but also the block - seam contacting surface, which is important for increasing the strength of these surfaces, since it is the main channel for filtering the melt through the interlock seams. Volatile emissions from

the inner regions of the interblock seam on the more hot outer surfaces of the interblock seams undergo secondary decomposition reactions. The resulting secondary coke contributes to additional compaction of the outer surface of the interblock seam, which reduces porosity and shrinkage, and thereby increases the strength of the interblock seams and their interconnection with the bottom blocks. Due to the coating of interblock and peripheral seams with a layer of this mixture, the temperature of the bottom mass of the seams is 200-250 ° C below the bottom temperature at which its heating ends. Full coking of the hearth mass of interblock joints at this temperature does not end, therefore compensation for mechanical stresses arising in the body of the bottom hearth blocks takes place in this case without disrupting the bonds of adhesion of the interblock material to the block body.

Heating and holding at the indicated temperatures contribute to the most uniform heating of the hearth and equalization of its temperature both in terms of area and height of the bottom blocks.

Laying the mixture layer on the interblock and peripheral seams with a ratio of the bottom surface of the backfill located on the bottom blocks and the seam to the area of the bottom block that is smaller (3.0-3.5): 1 does not allow to obtain the required quality of interblock and peripheral seams. In addition, the seam-block phase boundary is therefore not sufficiently protected by a layer of this mixture, as a result of which it undergoes oxidation. Applying a layer of the mixture with a ratio greater than (3.0-3.5): 1 increases the width of the bedding mixture on the bottom block, creating additional resistance to the passage of electric current, which leads to increased power consumption.

Lowering the anodes to a height of less than 0.25 the height of the backfill layer does not provide sufficient heat

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electrolyzer. When the anodes are located at a height of more than 0.35, the height of the backfill layer causes an additional influx of heat, which adversely affects the heating of the hearth and the quality of coking of interblock and peripheral joints.

Claims (2)

1. A method of preparing for the start-up of an aluminum electrolysis cell, including laying on the bottom, made of blocks, a protective layer of the mixture, heating the bottom and firing of the seams with an external heat source, installing anodes, pouring electrolyte, characterized in that, in order to increase the service life of the electrolyzer, as a protective layer using a mixture containing, may. %: Alkali Metal Oxide30-45 Alkali Metal Fluoride18-27 Cryolite 35g45 Laying of the mixture is carried out on interblock and peripheral bottom seams in the sequence - alkali metal oxide, alkali metal fluoride and cryolite, to a ratio of bottom area, block to backfill base area, equal to (3 , 0-3.5): 1, and the ratio of the layer height to its width, equal to (1.5-3.0): 1, the firing of interblock and peripheral seams is carried out up to 550-600С with soaking at 200 ° C for 3.5-4.0 h, at 350-400 ° C for 4-5. H and at 550-600 ° C for 3.5-4.0 h, the installation of the anodes is carried out at a height of 0.25-0.35 of the height of the mixture layer. 2. A method according to claim, characterized in that calcium oxide or magnesium oxide is used as an alkali metal oxide.