Method for lining a cathode of a reduction cell for production of primary aluminum

Abstract

The present invention relates to nonferrous metallurgy, in particular to the process equipment for electrolytic production of primary aluminum, namely to methods for lining cathode assemblies of reduction cells. A method for lining a cathode of a reduction cell for production of aluminum includes filling a cathode device shell with a thermal insulation layer and leveling said layer; filling, leveling and compacting a refractory layer; installing bottom and side blocks followed by sealing joints therebetween with a cold ramming paste. Prior to filling a shell bottom with the thermal insulation layer, a layer of fine carbonized particles is formed. The inventive method for lining a cathode assembly of a reduction cell for production of primary aluminum allows to reduce the cost of lining materials and energy consumption for reduction cell operation by means of improved heat resistance of a base and to increase the service life of reduction cells.

Claims

1. A method for lining a cathode of a reduction cell for production of aluminum, the method comprising: filling a bottom of a cathode device shell with a layer of fine carbonized particles, wherein the fine carbonized particles consist of carbonized woodflour, carbonized hardwood sawdust, or carbonized softwood sawdust; filling and leveling a thermal insulation layer on the layer of fine carbonized particles; filling, leveling and compacting a refractory layer; and installing bottom and side blocks followed by sealing joints therebetween with a cold ramming paste, wherein the fine carbonized particles are compacted to a height of 5-25% of the total height between the cathode device shell and the cathode, wherein the layer of fine carbonized particles has a density of 250 to 600 kg/m.sup.3.

2. A method for lining a cathode of a reduction cell for production of aluminum, the method comprising: filling a bottom of a cathode device shell with a layer of fine carbonized particles; filling and leveling a thermal insulation layer on the layer of fine carbonized particles; filling, leveling and compacting a refractory layer; and installing bottom and side blocks followed by sealing joints therebetween with a cold ramming paste, wherein the fine carbonized particles are compacted to a height of 5-25% of the total height between the cathode device shell and the cathode, wherein the layer of fine carbonized particles has a density of 250 to 600 kg/m.sup.3.

3. A method for lining a cathode of a reduction cell for production of aluminum, the method comprising: filling a bottom of a cathode device shell with a layer of fine carbonized particles, wherein the fine carbonized particles consist of carbonized woodflour, carbonized hardwood sawdust, or carbonized softwood sawdust; filling and leveling a thermal insulation layer on the layer of fine carbonized particles; filling, leveling and compacting a refractory layer; and installing bottom and side blocks followed by sealing joints therebetween with a cold ramming paste.

Description

(1) The essence of the invention will be better understood upon studying following drawings:

(2) FIG. 1 shows findings concerning the impact of carbonization temperature on a relative volumetric shrinkage and a thermal conductivity coefficient of woodflour having different densities.

(3) FIG. 2 shows calculation results for temperatures in a reduction cell bottom for production of primary aluminum.\

(4) When non-shaped materials are used to install cathode assemblies, compaction of a thermal insulation layer together with a refractory layer leads to compaction of both upper and lower layers and the thermal conductivity coefficient thereof is increased. A layer of fine carbonized particles, such as woodflour particles, makes the space under the cathode more heat resistant because a thermal conductivity coefficient of woodflour is lower than that of partially carbonized lignite. Moreover, providing an elastic layer of fine carbonized particles (FCPs) directly on a bottom of a cathode assembly contributes to the reduction of the relative shrinkage of thermal insulation layers arranged above.

(5) Parameters of heights and densities of FCPs layers according to the present invention are optimal. As can be seen in FIGS. 1 and 2, incompletely compacted fine carbonized particles creating a layer height of more than 25% of the total height of the space under the cathode increase the risk of compaction of the FCPs layer and structural elements arranged above, as well as the reduction cell breakdown. The over-compacted FCPs resulting in a layer height less than 5% of the total height of the space under the cathode increase a thermal conductivity coefficient and reduce the technical effect which is caused by the low heat resistance.

(6) Experiments on the compaction process and compacted material behavior were carried out using a laboratory bench. The packed density of FCPs was 76 kg/m3. Fractional composition of FCPs is shown in Table 1.

(7) TABLE-US-00001 TABLE 1 Particle +2 2/+1 1/+0.63 0.63/+0.315 0.315/+0.1 0.1 size, mm Percent- 23.15 24.95 9.55 26.85 14.85 0.65 age, %

(8) The pyrolysis reaction of FCPs was carried out in a reducing environment (in the filling of partially carbonized lignite) during 7 hours at different temperature values (from 200 to 800 C.). For pyrolysis purposes, samples were compacted to obtain the densities of 245 kg/m3 and 640 kg/m3, and the filling height for such compaction rate was reduced in 3.2 and 8.42 times, respectively.

(9) These researches have shown significant shrinkage of samples at pyrolysis temperatures above 300 C. The strength of the samples was significantly reduced too, and at the pyrolysis temperatures above 400 C. it was no more than 0.3 MPa. In addition, the higher rate of FCPs compaction reduces the relative shrinkage which is more obvious at pyrolysis temperatures of no more than 200 C. Generally, according to the experimental results the following conclusions can be made: for hard wood materials a thermal conductivity coefficient is higher than for soft wood materials; at higher pyrolysis temperatures FCPs thermal conductivity is lower; fine wood materials (e.g., woodflour) have lower thermal conductivity values than more coarse FCPs (5 mm).

(10) At the maximum compaction rate (640 kg/m3) a thermal conductivity coefficient is 0.203 W/(m.Math.K). However, when pyrolysis temperature is about 200 C., the thermal conductivity is lowered to 0.116 W/(m.Math.K). Accordingly, the use of fine carbonized materials within non-shaped materials under a thermal insulation layer will be highly efficient.

(11) Moreover, additional experiments were carried out where the use was made of compaction rates which can be achieved during reduction cell lining Results for FCPs of various origins and particle sizes are shown in Table 2.

(12) TABLE-US-00002 TABLE 2 Relative Packed shrinkage density, Compaction under pressure No FCPs type kg/m.sup.3 coefficient of 1.5 MPa, % 1 Soft wood (5 mm) 161 2 15 2 Soft wood (woodflour) 172 27 3 Hard wood (5 mm) 160 19 4 Hard wood (woodflour) 191 20

(13) At the compaction coefficient equal 2 the lowest compaction (of 15%) have demonstrated soft wood FCPs. This value is a little bit higher than the desired compaction rate under the pressure of 1.5 MPa (10%). To obtain the desired compaction rate (less than 10%) a compaction coefficient has to be increased up to 2.2.

(14) The advantage of soft wood FCPs under satisfactory thermal and physical characteristics is in its affordability.

(15) Industrial tests for the said method for lining with non-shaped materials of reduction cells have confirmed the main principles of the inventive method.

(16) The inventive method for lining a cathode assembly of a reduction cell for production of primary aluminum allows, in comparison to the prototype, to reduce the cost of lining materials and energy consumption for reduction cell operation by means of improved heat resistance of a base and to increase the service life of reduction cells.