Aluminum electrolysis cell cathode shunt design

Abstract

The invention relates to electrowinning of aluminum from cryolite-alumina melts, and can be used in the shunt design of a cathode assembly. In an aluminum electrolysis cell, cathode vertical metal shunts, are designed such that their top part is melted aluminum, and the bottom part is solid aluminum. Shunts are located in conduits made in a hearth slab lining which has a widening in the middle part which is wider than both parts of the shunts. The widening in the shunt conduit can be filled with a composite material, i.e. titanium diboride-carbon. The shunts can be designed as a tube, and the widening in the conduit and the space inside the tube can be filled with the composite material titanium diboride-carbon. The invention makes it possible to increase the electrical efficiency due to the absence of contact assemblies, reduced current loss, and achieving an effective current distribution and current shunting.

Claims

1. An aluminum electrolysis cell cathode shunt and conduit system, the system comprising: a vertical metallic cathode shunt carrying electric current from an aluminum melt to a cathode bus structure, the shunt comprising a shunt upper part consisting of molten aluminum and a solid shunt lower part, wherein the shunt upper part and the shunt lower part contact at an interface; and a shunt conduit within a hearth slab lining, wherein the shunt is within the shunt conduit, wherein the shunt conduit comprises a conduit upper part, a conduit lower part, and a conduit middle part between the conduit upper part and the conduit lower part, the conduit middle part comprising a central region surrounded radially by an annular region which is wider than both the conduit upper part and the conduit lower part, wherein the central region of the conduit middle part has a vertical cylinder shape with an outer edge, wherein the annular region of the conduit middle part surrounds the outer edge of the vertical-cylinder-shaped central region, and wherein the interface between the molten aluminum shunt upper part and solid shunt lower part is within the conduit middle part.

2. The aluminum electrolysis cell cathode shunt and conduit system according to claim 1, wherein the annular region of the conduit middle part is filled with a composite material based on titanium diboride-carbon and the shunt passes through the central region of the conduit middle part but not into the annular region.

3. The aluminum electrolysis cell cathode shunt and conduit system according to claim 1, wherein the shunt consists of aluminum.

4. An aluminum electrolysis cell cathode shunt and conduit system, the system comprising: a vertical metallic cathode shunt carrying electric current from an aluminum melt to a cathode bus structure, the shunt consisting of a shunt upper part consisting of molten aluminum and a solid shunt lower part, wherein the shunt upper part and the shunt lower part contact at an interface; and a shunt conduit within a hearth slab lining, wherein the shunt is within the shunt conduit, wherein the shunt conduit comprises a conduit upper part, a conduit lower part, and a conduit middle part between the conduit upper part and the conduit lower part, the conduit middle part comprising central region surrounded radially by an annular region which is wider than both the conduit upper part and the conduit lower part, wherein the central region of the conduit middle part has a vertical cylinder shape with an outer edge, wherein the annular region of the conduit middle part surrounds the outer edge of the vertical-cylinder-shaped central region, and wherein the interface between the molten aluminum shunt upper part and solid shunt lower part is within the conduit middle part.

5. An aluminum electrolysis cell cathode shunt and conduit system, the system comprising: a vertical metallic cathode shunt carrying electric current from an aluminum melt to a cathode bus structure, the shunt comprising a tube-shaped shunt upper part and a tube-shaped shunt lower part each having a cavity, the shunt upper part consisting of molten aluminum and the shunt lower part being solid, wherein the shunt upper part and shunt lower part contact at an interface, and wherein the cavity within the shunt upper part and the cavity within the shunt lower part are each filled with a composite material based on titanium diboride-carbon; and a shunt conduit within a hearth slab lining, wherein the shunt is within the shunt conduit, wherein the shunt conduit comprises a conduit upper part, a conduit lower part, and a conduit middle part between the conduit upper part and the conduit lower part, the conduit middle part comprising a central region surrounded radially by an annular region which is wider than both the conduit upper part and the conduit lower part, wherein the central region of the conduit middle part has a vertical cylinder shape with an outer edge wherein the annular region of the conduit middle part surrounds the outer edge of the vertical-cylinder-shaped central region, and wherein the interface between the molten aluminum shunt upper part and solid shunt lower part is within the conduit middle part.

6. The aluminum electrolysis cell cathode shunt and conduit system according to claim 5, wherein the annular region of the conduit middle part is filled with a composite material based on titanium diboride-carbon and the shunt passes through the central region of the conduit middle part but not into the annular region.

7. An aluminum electrolysis cell cathode shunt and conduit system, the system comprising: a vertical metallic cathode shunt carrying electric current from an aluminum melt to a cathode bus structure, the shunt comprising a shunt upper part consisting of molten aluminum and a solid shunt lower part, wherein the shunt upper part and the shunt lower part contact at an interface; and a shunt conduit within a hearth slab lining, wherein the shunt is within the shunt conduit, wherein the shunt conduit comprises a conduit upper part, a conduit lower part, and a conduit middle part between the conduit upper part and the conduit lower part, the conduit middle part comprising central region surrounded radially by an annular region which is wider than both the conduit upper part and the conduit lower part, wherein the shunt comprises a middle region comprising the lower portion of the upper part of the shunt and the upper portion of the lower part of the shunt, wherein the middle region is wider than both the upper portion of the shunt upper part and the lower portion of the shunt lower part and corresponds to the annular region of the shunt conduit, whereby the middle region carries electric current from the aluminum melt to the cathode bus structure across a larger cross-sectional area for transmission of electric current than the cross-sectional areas of the upper portion of the shunt upper part or the lower portion of the shunt lower part.

Description

(1) The essence of the invention is explained by the graphic material.

(2) FIG. 1 shows the cathode of an aluminum electrolysis cell with the proposed shunts, shown with a quarter cut-away;

(3) FIG. 2 shows a bottom block with conduits for the shunts;

(4) FIG. 3 shows a bottom block in assembled form with the shunts, with a cut-away view;

(5) FIG. 4 shows a bottom block in assembled form with the shunts according to claim 2;

(6) FIG. 5 shows a bottom block in assembled form with the shunts according to claim 3.

(7) The cathode assembly of an aluminum electrolysis cell with inert anodes includes a steel cathode casing 1; bottom blocks 2 made of high-alumina concrete (Al.sub.2O.sub.3 at least 90%); aluminum shunts installed in conduits 3 of the bottom block 2, with a solid 4 and a liquid 5 part; a current-carrying collector 6 made from an aluminum plate with a part 7 extending to the outside; seams 8 between the blocks, made of high-alumina concrete; edge blocks 9; layers of refractory, for example, made from fire clay, high-alumina magnesia periclase-carbonaceous brick, and thermal insulating materials 10, which can be made from lightweight fire clay, vermiculite, foam diatomite, calcium silicate; and a composite 11 based on titanium diboride/carbon to fill the conduits 3 of the bottom block 2.

(8) The bottom blocks 2 of the cathode assembly have conduits 3 for the shunts with solid 4 and liquid parts 5, uniformly distributed over the working surface of the bottom block 2. The conduits 3 can be made by machining of the blocks or during the forming of the bottom blocks 2. First of all, a connection is made between the solid parts 4 of the shunts and the current-carrying collector 6, made of aluminum. The connection is made by welding. Next, the current-carrying collector 6 assembled as a whole unit with the shunts is installed in the bottom block 2 and secured there by tacking the installation rods to the shunts projecting from the bottom block. After this, the assembled bottom block 2 is mounted in the cathode. It should be noted that supplemental preparatory steps for the fabrication of the cathode shunting conduits and the shunts and the costs of these steps are negligibly small in relation to the results achieved during the operation of the electrolysis cell.

(9) The electrolysis cell works as follows. The cathode of the electrolysis cell prior to being started is heated to temperatures of 850-900? C. by means of gas or liquid burners or electric heaters. The upper part of the shunts is melted and becomes the liquid part of the shunt 5, and the widening in the conduit 3 (the forming cavity) becomes filled. The further draining of aluminum from the conduit 3 is prevented by the removal of heat accomplished by the collector 6, which causes the liquid aluminum to crystallize around the shunt and thereby fill the cavity existing between the conduits 3 and shunts.

(10) After the warm-up of the cathode of the electrolysis cell, liquid aluminum is poured into the vat to create a layer of 120-150 mm on the hearth slab; this layer of aluminum joins as a single whole with the liquid part 5 of the shunts and forms a closed electric circuit. The resulting circuit effectively transmits the current load from the anodes to the cathode, with subsequent applying of the current load to the next electrolysis cell in the current path of the electrolysis bank. The transmission efficiency of the current load is dictated by the use of liquid and solid aluminum as conductors, the absence of electrical contacts of heterogeneous metals in the circuit, and the absence of electrical resistance in the material of the hearth lining.

(11) Making the conduit 3 with a widening will substantially increase the contact area of the liquid 5 and solid parts 4 of the shunt and ensure its stable electrical contact over the course of the entire operating life of the electrolysis cell.

(12) Moreover, the widening in the conduit 3 of the bottom block 2 can be filled with composite material 11 based on titanium diboride-carbon. This solution works as follows. The composite material 11 becomes wetted with liquid aluminum and prevents the penetration of electrolyte between the liquid 5 and solid 4 parts of the shunt. Over time, the composite material 11 itself having a porosity on the order of 30-40% becomes impregnated with aluminum and forms internal pores, capillaries, channels, and cavities filled with metal of the same composition as is being deposited at the cathode. The use of such a solution can lower the risk of aluminum leakage into the base of the vat during startup, since the cavity in the conduit of the bottom block is initially filled with the composite material, preventing the penetration of aluminum.

(13) Furthermore, the shunt can be made in the form of a tube, the internal cavity of which is filled with the composite material 11, which in the space of a short time is entirely impregnated by liquid aluminum.

(14) One of the benefits of this solution is a lowering of the costs of fabrication of the shunts, since the upper part of the shunt will be more or less molten, so it is perfectly logical to use a hollow tube of aluminum instead of a solid aluminum rod. This will enable a savings on the order 25-30% in the fabrication of the shunts.

(15) Thus, there is a stabilization of the electrical and technological parameters of the electrolysis cell, an effective current distribution, a more reliable operation of the metallic cathode shunts (i.e., electrical contact in the shunt between its liquid and solid parts) and longer operating life for them, a longer service life for the electrolysis cell, and consequently better technical and economic parameters of the process.

(16) The lining of an aluminum electrolysis cell with inert anodes is assembled as follows.

(17) First of all, the bottom blocks 2 are assembled, for which the previously connected current-carrying collector 2 provided with conduits 3 is placed in the shaped bottom block 2, the previously connected current-carrying collector 6 with shunts 4 (vertical tubes) are secured there, and then the bottom block 2 is transported to the site of installation of the lining.

(18) After assembly and installation of the steel cathode casing 1, its bottom is lined with refractory and thermal insulating materials 11, after which the surface of the refractory layer is covered with a layer of loose material, playing the role of a leveling cushion, on which the bottom blocks are set, with a certain spacing, so as to have a gap of 30-50 mm between adjacent blocks, in order to create the seam 8 between blocks. After this, the side lining or brim is laid, situated along the perimeter of the cathode casing between the bottom blocks and the lower part of the walls of the cathode casing and consisting of a layer of thermal insulating material, packed against the walls of the casing, and refractory material packed against the thermal insulating material. The projecting parts of the current-carrying collectors are clad with the side lining, ensuring tightness of the brim while at the same time not impeding the thermal expansion of the aluminum collectors. The brim is the base for installation of the side lining 9; the installing of the edge blocks of nonmetallic refractory compounds is done in a single row along the walls of the cathode casing 1, gluing them to the walls of the casing, and lubricating all of the bearing and joining surfaces. One can use as the adhesive or cementing composition gunite, mortar, or refractory concrete containing silicon carbide powder

(19) The culminating and critical operation in the assembly of the lining is the filling of the seams 8 between the bottom blocks 2.

(20) Use of the proposed technical solution enables a substantial boosting of the efficiency of use of electricity thanks to the absence of contact assemblies with heterogeneous materials in the cathode shunt, the lowering of the current losses, and the assurance of an effective current distribution and effective current shunting.