CLIAMS:NA ,TagSPECI:The present disclosure provides an electrolytic cell including a collector bar.
BACKGROUND
Aluminium is produced by the Hall-Heroult process in an electrolytic cell. The Hall–Héroult process involves dissolving alumina in molten cryolite, and electrolysing the same in an electrolytic cell. The molten mixture of cryolite and alumina is electrolyzed by passing low voltage (3-5V) direct current through the cell. Specifically, the current enters the cell through the anode and then passes through the molten cryolite bath (electrolytic bath), molten aluminium and enters the carbon cathode. This facilitates deposition of liquid aluminium metal at the cathode and production of carbon dioxide at the anode by combination of oxygen from the alumina with carbon from the anode. The electrical current is carried out of the cell by collector bars.
In general, the current passes through the cryolite bath at a voltage loss which is directly proportional to the length of the current path, i.e. the interpolar distance between the anode and the cathode. Reduction in this spacing is limited because of Magneto hydrodynamics (MHD) instability, which arises due to electromagnetic forces generated from interaction of vertical magnetic field and horizontal component of current. Also any increase of the anode to cathode spacing restricts the maximum power efficiency of the electrolytic cell.
Further, substantial voltage drop through an electrolytic cell occurs in the electrolyte and is due to electrical resistance of the electrolyte, or electrolytic bath, across the anode-cathode distance. The electrical resistance or voltage drop in cells for the electrolytic reduction of alumina includes a decomposition potential, i.e., energy used in producing aluminum, and an additional voltage due to heat energy generated in the inter-electrode spacing by the bath resistance.
Multiple steel cathode collector bars extending from the external bus bars through each side of the electrolytic cell into the carbon cathode blocks are known in the art. The steel cathode collector bars are attached to the cathode blocks in such a manner that it facilitates electrical contact between the carbon cathode blocks and the steel cathode collector bars.
The flow of electrical current through the carbon cathode and collector bar follows the path of least resistance. The resistance of the current path between the collector bar and the nearest external bus is lower because of which the flow of current through the molten aluminium, cathode and collector bar gets concentrated towards the exit of the collector bar thereby generating a horizontal current component as illustrated in Fig. 1 (Resistance: R1 < R2). Such horizontal current component interacts with the vertical component of the magnetic field results in MHD instability and adversely affects efficient cell operation, thus limiting the reduction in inter-electrode distance.
Therefore, there is a need to an electrolytic cell for aluminium production which has reduced energy consumption and voltage drop in inter-electrode gap as well as in the cathode and collector bar assembly. Further, there is a need of an improved collector bar which facilitates least or no generation of horizontal current component thereby providing uniform current distribution in the cell.
BRIEF DESCRIPTION OF DRAWINGS
Fig. 1: Cross-sectional view of aluminium smelter showing two different resistance path and current distribution (prior art)
Fig. 2: Cross-sectional view of aluminium smelter showing collector bar design and its impact on current distribution in accordance with the present disclosure.
Fig. 3: Single cathode block with collector bar(s) in accordance with the present disclosure.
Fig. 4: Isometric view of new design single collector bar having a slot filled with copper in accordance with the present disclosure.
Fig. 5: Long side view of new design single collector bar having a slot filled with copper in accordance with the present disclosure.
Fig. 6: Top view of new design single collector bar having a slot filled with copper in accordance with the present disclosure.
DETAILED DESCRIPTION
For the purpose of promoting an understanding of the principles of the invention, reference will now be made to embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the disclosed process, and such further applications of the principles of the invention therein being contemplated as would normally occur to one skilled in the art to which the invention relates.
It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof.
Reference throughout this specification to “one embodiment” “an embodiment” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrase “in one embodiment”, “in an embodiment” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.
The present description provides a collector bar with reduced electrical resistance and an electrolytic cell including the same.
As illustrated in Fig 1, the electrolytic cell comprises of an anode (carbon), electrolytic bath (mixture of cryolite and alumina), cathode (carbon) and a collector bar. Temperature within the cell is maintained via electrical resistance. Oxidation of the carbon anode increases the electrical efficiency at a cost of consuming the carbon electrodes and producing carbon dioxide. While solid cryolite is denser than solid aluminium at room temperature, liquid aluminium is denser than molten cryolite at temperatures around 1,000 °C (1,830 °F). The aluminium sinks to the bottom of the electrolytic cell, where it is periodically collected. Alumina is added to the cells as the aluminum is removed. The current flows from the anode through the electrolytic bath to the cathode. The collector bar collects the electric current from cathode and passes the same to the next electrolytic cell connected in series.
In accordance with an aspect, the collector bar is provided with an angular insert consisting of a material of high electrical conductivity. The angular insert has a substantially greater depth near the center than the edges. In accordance with an embodiment, the collector bar is provided with a slot having a substantially greater depth near the center than the edges, which is filled with a material of higher conductivity as compared to the material of the collector bar. By way of example, the slot may be a V-shaped, U-shaped, curved or even have a flat base. The slot is illustrated in Fig. 2 wherein the slot is filled with higher electrically conductive material than steel (indicated in grey). By way of example, the slot of the collector bar is filled with copper and the collector bar is made of steel (as illustrated in Fig. 4, 5 and 6). In accordance with an embodiment, the depth of the slot near the center is half of the height (H) of the collector bar (as illustrated in fig.5). Further, the length (l) of the slot is about 2/3rd of collector bar’s length (L) (as illustrated in Fig.6). In the embodiments illustrated in Figure 4, 5 and 6, a V-shaped angular insert is used.
The collector bar having a slot filled with a material of higher conductivity as compared to the material of the collector bar provides variable electrical conductivity along the length of collector bar (increasing towards the mid length of bar). This affects the electrical resistance path in the cathode and the collector bar assembly making it more uniform thereby facilitating substantially uniform current distribution in the molten metal region of electrolytic cell. Such uniform current distribution facilitates least or no generation of horizontal current component and provides stability to metal-electrolyte interface in the cell.
INDUSTRIAL APPLICABILITY
The present disclosure provides an electrolytic cell including a collector bar with increased electrical conductivity which helps in establishing substantially uniform current distribution in molten metal region (electrolytic bath) with least generation of horizontal current component. Further, reduced horizontal current provides stable metal-electrolyte interface resulting in lowering of inter-electrode gap thereby reducing the energy consumption in the electrolytic cell.

Dated this 22nd day of August, 2014

Aparna Kareer
Of Obhan & Associates
Agent for the Applicant
Patent Agent No. 1359