SU600214A1 - Aluminium electrolyzer - Google Patents

Description

I

The invention relates to the field of non-ferrous metallurgy, in particular, to the design of an electrolyzer for producing aluminum from molten media.

With an increase in the power of the electrolyzers, both as a result of an increase in the current density and as a result of an increase in the area of the anode (especially its width), a clear increase in the temperature of the electrolyte is observed. Since an increase in the electrolyte temperature lowers the main process indicators (for example, the current efficiency decreases by 2.3% for thirsty 10% temperature increases), this significantly slows down the growth of the unit capacity of the electrolyzers.

There are a number of methods for reducing the electrolyte temperature: increasing the thickness of the molten aluminum layer, intermittent destruction of the alumina crust, raising the electrolyte level above the side lining (by increasing the outer crust), introducing components into the electrolyte that lower its solidification temperature and increase its electrical conductivity, etc.

Due to a number of reasons (shortage and high cost of additives, inconvenience in servicing electrolyzers, increasing labor costs, etc.), none of the methods mentioned above proved to be highly effective in practical application.

Also known is an electrolytic cell for the production of aluminum, including a lined bath with an anode introduced into it and cooling elements made in the form of pipes. The cooling system is located outside the cathode housing of the electrolyzer 1.

The known cooling system provides an increase in heat loss and thus allows an increase in the current strength on it, but due to the inevitable decrease in the temperature of the lower part of the bottom, crystallization of the diffused melt directly beneath the bottom occurs. The latter causes a significant increase in the vertical pressure at the bottom bottom and accelerates its destruction. An increase in the temperature gradient along the bottom thickness increases its bending, also accelerates destruction, and causes swelling on the bottom. The cooling of the sides of the TaKHve electrolyzer allows for increased heat transfer, however, it cannot provide a decrease in the temperature of the electrolyte and control. Moreover, due to the increase in heat flux from the melt to the lateral naslyan, the temperature of the electrolyte in its central zones even increases.

The purpose of the invention is to increase the heat removal from the electrolyte, facilitate adjustment of its temperature and increase the service life of the bottom of the bath.

For this, cooling elements are placed between the bottom bath and the level of the anode base.

In a number of cases, cooling elements can be placed between the side walls of the bath and the anode under the anchor below the level of the anode base.

The cooling elements can be made of a material selected from soils containing graphite, siliconized graphite, graphite e coated with boron carbon graft and silicon carbide.

In addition, the cooling elements can be made of two-layer with an inner layer of heat-resistant steel to the outer, made of the above materials. This gives the cooling elements an increase in the carrying capacity and the protection of their internal cavities from oxidation.

FIG. 1 shows the proposed electrolyzer, a longitudinal section; in fig. 2 - the same cross section.

The electrolyzer contains horizontally positioned anode 1 and hearth 2, the space of which is filled with melt "s electrolyte 3 in the upper part and aluminum 4 in the bottom. In the aluminum melt placed the cooling elements 5 of one or more pipes (depending on the type and power of the electrolyzer). The cross section of pipes is determined by the thermal load. For example, for electrolyzers with an upper current lead at current GyO kA, a decrease in electrolyte temperature from 965 ° C to 955 ° C is provided by a cooler from 3 parallel to the longitudinal axis of the electrolyzer graphite pipes with an internal diameter of 40 mm and a thick wall of 30 mm. The coolant flows through the pipes. To simplify the construction and its operation, the most acceptable coolant is reduced or fan air. Modern technology has a number of materials that can be applied to cooling elements. Along with traditional graphite, silicon carbide, more resistant to molten aluminum and fluorine salts, can be used in the form of strong graphite or self-bonded graphite with an outer coating of boron carbonitride. In addition, for example, a thin-walled metal pipe can be used to protect the internal cavity of the pipes from oxidation. To ensure sufficient mechanical strength, the cooling tubes are made of two layers: the inner layer is made of heat-resistant steel, and the outer layer is made of a material that is chemically resistant to molten aluminum. The ratio of the diameters of these pipes is selected taking into account the coefficients of thermal expansion, so that at 950-1000 ° C, both pipes are in sufficient contact with each other. It is permissible to leave an annular gap between the outer and the inner tube with filling it with high thermal conductivity powder, for example

graphite. Pipes can be located both along and across the longitudinal axis of the electrolyzer. Taking into account that heat should first of all be removed from the most heated electrolyte zones, at the radial position, the cooling tubes are located closer to the longitudinal axis of the electrolyzer. In order to ensure a sufficiently uniform cooling of the metal over the length of the cooling pipes, the coolant can be supplied in opposite directions along adjacent pipes. In order to rely on the bottom and fix the height of the location of the pipes in the shaft of the bath, each pipe has two or three supports 6 made of a material that is resistant to melt.

The joining of pipe elements along the length is carried out by one of the known methods (on threaded couplings, etc.). Coolant tubes are introduced into the cathode metal

through a layer of molten electrolyte (through the knee, bent at an angle of 90 ° C) or laterally through the side lining.

Prn operation of the electrolyzer reduced or fan air enters

from one end of each pipe and out through the other. In this case, part of the heat is removed from the molten aluminum, its temperature is reduced. Due to its inherent high thermal conductivity, molten aluminum will cool the electrolyte in the reaction zone. The intensity of the cooling is controlled by the amount of air flowing. The use of modern materials that are highly resistant to molten aluminum makes it possible to rely on the service life of the cooling elements, equal to the duration of the electrolysis cell's overhaul campaign, but if necessary, the elements can be removed from the electrolyzer and replaced

new ones. The heat taken from the melt can be disposed of using one of the known methods.

The use of cooling elements placed in the space between the bottom and

anode, maintains the temperature of the electrolyte in the reaction zone of the electrolyzer in the optimal range. This is achieved by improving the main technical and economic indicators, primarily output

current. Stabilizing the electrolyte temperature opens up the possibility of a significant increase in the current load and, consequently, the performance of the electrolyzers. The economic effect of manufacturing is not

less than 100 thousand rubles for each typical electrolysis building, which in the industry will be at least 7.5 million rubles.

Claims (1)

1. An electrolyzer for producing aluminum, including a lined bath with an anode inserted into it and cooling elements made in the form of pipes, with about one lump and so that, in order to increase heat removal from electrolyte, making it easier to adjust