CA3148080C

CA3148080C - Aluminium reduction cell with a heat insulated side lining

Info

Publication number: CA3148080C
Application number: CA3148080A
Authority: CA
Inventors: Gennadiy Viktorovich ARKHIPOV; Rashid Khaliullovich MUKHAMETCHIN; Evgeniy Rashidovich SHAYDULIN; Aleksandr Vladimirovich POPOV; Yuriy Olegovich AVDEEV
Original assignee: Rusal Engineering and Technological Center LLC
Current assignee: Rusal Engineering and Technological Center LLC
Priority date: 2019-08-15
Filing date: 2020-07-24
Publication date: 2023-10-17
Anticipated expiration: 2040-07-24
Also published as: CA3148080A1; NO20220184A1; RU2714565C1; WO2021029787A1

Abstract

The invention relates to non-ferrous metallurgy, and more particularly to a design for electrolytic cells for the electrolytic production of aluminium, and can be implemented in all types of electrolytic cells. The present electrolytic cell comprises a metallic cathode shell, a heat-insulating lining and a refractory lining, a bottom made of bottom blocks with conductive cathode posts, and a side wall lining made of silicon carbide plates with an additional cast refractory layer, the latter having lower heat conductivity and being disposed between the walls of the metallic cathode shell and the silicon carbide plates. The result is: a reduction in the operating voltage of the electrolytic cell by virtue of a reduction in heat loss from the side walls thereof; stabilization of the heat balance; and an increase in the MHD stability of the electrolytic cell.

Description

ALUMINIUM REDUCTION CELL WITH A HEAT INSULATED
SIDE LINING
Field of the invention The invention relates to the non-ferrous metallurgy field, namely, to the design of reduction cells intended for the electrowinning of aluminium, and can .. be implemented in reduction cells of all types.
Background of the invention In the existing designs of reduction cells intended for the electrowinning of aluminium, the highest component of heat loss (about 35 %) falls on the longitudinal side walls (Fig. 1) (see Zhaowen Wang et al., Heat Recovery of the Aluminium Reduction Cells. Production of Aluminium: Collection of Reports of the 9th International Congress 'Non-Ferrous Metals and Minerals.' Krasnoyarsk: North-Eastern University, 2017, 209-217). This amount of heat loss negatively affects the thermal balance of the reduction cell making it necessary to recover heat losses by increasing the voltage supplied to the reduction cell, which entails increased electricity consumption and, as a result, an increase in the cost of aluminium produced.
An aluminium reduction cell with a side lining is known (application RU
94012661, C25C3/06, publication date: April 10, 1996), which allows forming stable decking and ensuring a long service life of the reduction cell. The main distinguishing feature of this design is an inclined longitudinal side wall made of side graphitised carbon blocks. In this case, the side lining of the reduction cell is inclined to the horizon at an angle of 0.3-0.9 (I), where (I) is the angle of inclination of the side wall of the cathode shell to the same plane.

Date Recue/Date Received 2022-01-19 There are known 'Aluminium reduction cell cathode device' (RU
1295786, C25C3/08, published in 1985), where the angle of inclination of the side wall is 45-66 , 'Aluminium reduction cell' (SU 1788090, C25C3/08, published in 1990), where the angle of inclination of the side wall is 20-45 , Tlectrolyser for production of aluminium' (RU 94009828, publication date:
April 10, 1996), where the angle of inclination of the side wall is 120 .
The disadvantage of these technical solutions is due to the fact that during the electrolytic reduction process, the force from the thermal expansion of the bottom graphitised carbon blocks, acting on the inclined side wall, causes a force directed perpendicular to the inclined walls of the shell. The tangential component, acting on the inclined side blocks, pushes them by a deckplate, the loads on the deckplate increase significantly resulting in destruction of the side lining. Therefore, the use of inclined side walls requires an increase in the rigidity of the cathode shell, in turn, an increase in the rigidity of the shell is associated with an increase in its weight and an increase in capital costs.
Also, the disadvantage is that with this version of the side lining, there is oxidation and destruction of coal plates as a result of their exposure to oxygen of the air entering through the bath crust resulting in leakage of the bath melt into the lining and deterioration of thermal insulation properties. As a result of leaks, forces arise that push the coal plates away from the cathode shell and subsequently destroy the side lining.
In addition, in case of inclined design of the side wall, stabilisation of the thermal balance of the reduction cell by reducing heat loss from the sides becomes possible only after the start-up period of the reduction cell, i.e., after the formation of metal ledge and slag lining. Thus, the heat loss from the sides with an inclined longitudinal wall during the start-up period will remain unchanged, which will require heat compensation by increasing the voltage supplied to the reduction cell.

2 Date Recue/Date Received 2022-01-19 A side lining of the aluminium reduction cell is known (patent RU
2072398, C25C3/06, publication date: January 27, 1997), in which a belt is made of a non-conductive ceramic material based on aluminium nitride. The belt is made of plates attached to each other by end faces with the help of asymmetric protrusions and recesses using glue with additives of refractory compounds. The disadvantage of this solution is the use of expensive materials with low barrier resistance to the effects of the bath melt.
There is a known reduction cell for producing aluminium and a method for maintaining a crust on the side wall and regenerating electricity (application RU 2002135593, C25C3/06, publication date: May 29, 2001), wherein a high-temperature, heat-resistant and heat-insulating material is located inside, on the inner part of the side walls of the steel shell, characterised in that all the side walls of the reduction cell are equipped with cooling evaporative panels. The disadvantage of this solution is that the thermal balance of the reduction cell of the claimed design depends on the metal ledge and slag lining intensively formed by cooling the sides with evaporative panels, in each case of deviation from the preset process parameters of the reduction cell operation and change of the shape of the working space, the thermal balance of the reduction cell will become unstable. The location of the cooling evaporative panels inside the cathode shell is critical, since the contact of the panels with the aggressive bath environment will significantly reduce their service life, and the protection of the panels by coating them with a heat-resistant, heat-insulating material is associated with a significant increase in capital costs.
The closest in terms of technical substance to the claimed invention is the side lining of a reduction cell (copyright certificate SU 377419, C25C3/08, publication date: April 17, 1973), wherein the side lining is made of materials with different resistance to melt, while its upper part is made of a material with increased resistance ¨ graphite plates, and its lower part is made of a material with reduced resistance ¨ baked carbon blocks. The disadvantage of this

3 Date Recue/Date Received 2022-01-19 prototype is that after sintering with an adhesive layer at a high speed of melt circulation, the insert is destroyed due to deformation shifts occurring in the upper parts of the cathode shell.
Disclosure of the invention The objective of the proposed invention is to reduce heat losses from the side walls of the reduction cell and to stabilise the thermal balance of the reduction cell, as well as to ensure formation of a stable metal ledge and slag lining, which ensures a long service life of the reduction cell, a stable behaviour of the electrolytic reduction process and allows to significantly reduce electric power consumption thanks to the operation of the reduction cell at a lower operating voltage.
The technical result consists in solving the task at hand, reducing the operating voltage of the reduction cell by reducing heat losses from the side walls of the reduction cell, stabilising the thermal balance and increasing the MHD (magnetohydrodynamic) stability of the reduction cell.
As a result of the stabilisation of the thermal balance of the reduction cell, the above technical result also includes a reduction in the electric power consumed, while an increase in MHD stability allows to increase the current efficiency, which in turn allows to reduce the cost of aluminium produced.
The task is addressed, and the technical result is achieved due to the fact that in a reduction cell intended for the electrowinning of aluminium, including a metal cathode shell, heat-insulating and refractory lining, a bottom made of bottom blocks with cathode current-carrying rods, a side lining, the novelty consists in the fact that the side lining is made of silicon carbide and/or carbon plates with an additional moulded refractory layer with lower thermal conductivity installed between the walls of the metal cathode shell and silicon carbide and/or carbon plates.
To implement the proposed invention, it is advisable to use carbon plates, silicon carbide materials, chamotte. Silicon carbide is a material obtained by

4 Date Recue/Date Received 2022-01-19 combining powdered silicon carbide with soot, characterised by high density, high degree of heat resistance, electrical conductivity and resistance to the process of scale formation.
Multi-layer structures can be used, where the first layer is formed by a silicon carbide plate or a cheaper carbon one. The material of the first layer should be erosion-resistant, with low electrical and thermal conductivity, with low porosity and high density. The refractory layer can be made of chamotte material or represent a multi-layer structure. The dimensions of the refractory layer are determined in accordance with the design of the cathode shell, and depend on the target technological parameters of the reduction process. It is important that the first silicon carbide layer is erosion-resistant to an aggressive electrolysis medium (electrolyte), and the second, for example, from chamotte, is heat-resistant to reduce heat losses.
The moulded refractory layer can be made of monolithic refractory plates and/or refractory bricks, can contain inserts of additional heat-insulating material located inside the masonry of refractory plates and/or refractory bricks, while the inserts can be made of moulded and/or unmoulded thermal insulation material.
The additional refractory layer can also be made of unformed material. In this case, the installation of the side lining provides for the manufacture of a special tooling (frame), which is filled up with the unformed material for its further ramming, drying and solidification into a refractory layer in the shape given by the tooling.
Previously, a two-layer lining was not used, i.e., there was no lining made of two different materials, either carbon lining (cheap, with low resistance to overheating, and low thermal conductivity) or silicon carbide lining (more expensive, more corrosion resistant, but also heat conducting with high heat losses) were used.
The invention essence is explained by the drawings.

5 Date Recue/Date Received 2022-01-19 Fig. 2 a) presents the results of modelling the temperature field and the shape of the working space of a reduction cell with a two-layer insulated side lining in comparison with a reduction cell of the existing serial design b);
Fig. 3 shows a reduction cell intended for the electrowinning of aluminium;
Fig. 4 shows the additional refractory layer.
Explanations of the structural elements shown in the drawings:
1 ¨ metal cathode casing;
2 ¨ heat-insulating lining;
3 ¨ refractory lining;
4 ¨ bottom made of bottom blocks;
5 ¨ cathode current-carrying rods;

6 ¨ carbide-silicon plates;

7 ¨ additional moulded refractory layer;

8 ¨ inserts of additional heat-insulating material;

9 ¨ refractory bricks/plates.
Until now, a side lining made of carbon blocks, later a side lining made of silicon carbide plates was used in the reduction cells. Carbon blocks are mostly cheap and have low thermal conductivity, which minimises heat losses from the sides of the reduction cell. At the same time, carbon blocks have relatively low erosion resistance (low resistance to high overheating, as well as to the aggressive reduction process environment ¨ the bath), which reduces the service life of the reduction cell. Expensive silicon carbide plates, on the contrary, have a high resistance to overheating and high resistance in the bath environment. A significant disadvantage of silicon carbide plates is their high thermal conductivity, which entails large heat losses from the sides of the reduction cell, which require compensation in the form of voltage to stabilise the thermal balance, which leads to increased electricity consumption ¨ an increase in the cost of aluminium.

Date Recue/Date Received 2022-01-19 The proposed heat-insulated structure of the side lining, consisting of silicon carbide plates bordering the bath and an additional refractory layer between the silicon carbide plates and the reduction cell casing, combines both high overheating resistance and high resistance to the bath, and low thermal conductivity, which ensures a long service life with a stable thermal balance of the reduction cell, which will allow implementing reduction technologies at lower voltage, with lower electric power consumption, with lower cost of aluminium produced.
Below are the results of mathematical modelling of a reduction cell with a side lining of the claimed design.
The calculation results showed that to ensure the thermal balance of a reduction cell with a two-layer (or more) heat insulated side lining, with the bath temperature of 956 C, an interpolar distance of 48.3 mm is necessary.
Under these conditions, the total heat loss from the anode device will be 106.0 kW (42.1 %), from the longitudinal walls of the cathode device ¨ 86.5 kW
(21.5 %), from the end walls of the cathode device ¨ 37.3 kW (14.9 %), from the bottom of the cathode device ¨ 22.8 kW (8.6 %). The maximum temperature of the longitudinal wall of the cathode device will be 235 C, the maximum temperature of the end wall of the cathode device will be 155 C, the maximum temperature of the bottom of the cathode device will be 70 C. The length of the metal ledge along the longitudinal wall will be 150 mm, along the end wall ¨ 162 mm under the anode. The minimum thickness of the slag lining will be 30 mm along the longitudinal wall and 64 mm along the end wall at the level of the carbon block insert. The average voltage will be 4,050 V, and the electric power will be 12,823 kWhit.
Within the framework of pilot scale tests of insulated double-layer (and more) side lining, the additional refractory layer was glued to the cathode shell of the reduction cell, a layer of silicon carbide plates was also glued to the additional refractory layer. During the installation of the two-layer side lining, Date Recue/Date Received 2022-01-19 no special requirements were imposed on the gluing materials, as well as on the laying operations. During industrial tests on an experimental reduction cell, thanks to the insulated design of the side lining, a reduction in electric power consumption by 300 kWhit was achieved compared to the existing reduction cells provided with silicon carbide side lining.

Date Recue/Date Received 2022-01-19

Claims

CLAIMS OF THE INVENTION

1. A reduction cell intended for the electrowinning of aluminium containing a metal cathode shell, a heat-insulating and refractory lining, a bottom made of bottom blocks with cathode current-carrying rods, a side lining, characterised in that the side lining is made in the form of a multilayer structure containing silicon carbide and/or carbon plates with at least one additional moulded refractory layer with lower thermal conductivity, installed between the walls of the metal cathode shell and silicon carbide and/or carbon plates.

2. The reduction cell according to claim 1, wherein the moulded refractory layer is made of monolithic refractory plates and/or refractory bricks.

3. The reduction cell according to claims 1 or 2, wherein the moulded refractory layer contains inserts of additional heat-insulating material located inside the masonry of refractory plates and/or refractory bricks.

4. The reduction cell according to claim 3, wherein the inserts are made of moulded or unmoulded heat-insulating material.
#49M9073 Date Recue/Date Received 2022-01-19