Title of Invention

AN ELECTROLYTIC CELL FOR ALUMINIUM PRODUCTION

Abstract

An electrolytic cell (4) for aluminum production, including a cell wall (7, 18), a bus bar (46, 48), a carbonaceous cathode block (10), and a collector bar (30) connecting the bus bar with the cathode block. The collector bar comprises a ferrous metal body including a solid spacer (32) and a sheath (33) defining a cavity (34) containing a copper insert (40). The spacer has an external end portion (35) connected with the bus bar and an internal end portion (36) that is preferably spaced inwardly of the cell wall. The spacer separates the copper insert from the bus bar, thereby reducing heat loss from the cell.

Full Text

ORIGINAL IN/PCT/2001/560/MUM FORM 2 THE PATENTS ACT 1970 [39 OF 1970] COMPLETE SPECIFICATION [See Section 10] "AN ELCTROLYTIC CELL FOR ALUMINIUM PRODUCTION BALANCE" ALCOA INC., a corporation organised under the laws of the State of Pennsylvania, of Alcoa Corporate Center, 201 Isabella Street, Pittsburgh, Pennsylvania 15212-5858, United States of America, The following specification particularly describes and ascertain the nature of the invention and the manner in which it is to be performed :- According to the present invention there is provided an electrolytic cell for aluminum production. This invention relates to electrolytic cells. In one aspect, this invention relates to cathode collector bars of electrolytic reduction smelting cells 5 used in the production of aluminum. Aluminum is produced by an electrolytic reduction of alumina in an electrolyte. The aluminum produced commercially by the electrolytic reduction of alumina is referred to as primary aluminum. Electrolysis involves an electrochemical oxidation-reduction 10 associated with the decomposition of a compound. An electrical current passes between two electrodes and through molten Na3AlF6 cryolite bath containing dissolved alumina. Cryolite electrolyte is composed of a molteJs#Ja3AlF6 cryolite bath containing alumina and other materials, e.g., such as fluorspar, dissolved in the electrolyte. A metallic constituent of the compound is reduced together with a 15 correspondent oxidation reaction. Electrical current is passed between the electrodes from an anode to a cathode to provide electrons at a requisite electromotive force to reduce the metallic constituent which usually is the desired electrolytic product, such as in the electrolytic smelting of aluminum. The electrical energy expended to produce the 20 desired reaction depends on the nature of the compound and the composition of the electrolyte. Hall-Heroult aluminum reduction cells are operated at low voltages (e.g. 4-5 volts) and high electrical currents (e.g. 70,000-325,000 amps). The high electrical current enters the reduction cell through the anode structure and then 25 passes through the cryolite bath, through a molten aluminum metal pad, and then enters a carbon cathode block. The electrical current is carried out of the cell by cathode collector bars. As the electrolyte is traversed by electric current, alumina is reduced electrolytically to aluminum at the cathode, and carbon is oxidized largely to carbon 30 dioxide at the anode. The aluminum, thus produced, accumulates at the molten aluminum pad and is tapped off periodically. Commercial aluminum reduction cells are operated by maintaining a minimum depth of liquid aluminum in the cell, the surface of which serves as the actual cathode. The minimum aluminum depth is about 2 inches and may be 20 inches. The alumina-cryolite bath is maintained on top of the molten aluminum metal pad at a set depth. The current passes through the cryolite bath at 5 a voltage loss directly proportional to the length of the current path, i.e., the interpolar distance gap between the anode and molten aluminum pad. A typical voltage loss is about 1 volt per inch. Any increase of the anode to cathode spacing restricts the maximum power efficiency and limits the efficiency of the electrolytic cell operation. 10 Much of the voltage drop through an electrolytic cell occurs in the electrolyte and is attributable to electrical resistance of the electrolyte, or electrolytic bath, across the anode-cathode distance. The bath electrical resisfance or voltage drop in conventional Hall-Heroult cells for the electrolytic reduction of alumina dissolved in a molten cryolite bath includes a decomposition potential, i.e., energy 15 used in producing aluminum, and an additional voltage attributable to heat energy generated in the inter-electrode spacing by the bath resistance. This latter heat energy makes up 35 to 45 percent of the total voltage drop across the cell, and in comparative measure, as much as twice the voltage drop attributable to decomposition potential. 20 An adverse result from reducing anode-cathode distance is a significant reduction in current efficiency of the cell when the metal produced by electrolysis at the cathode is oxidized by contact with the anode product. For example, in the electrolysis of alumina dissolved in cryolite, aluminum metal produced at the cathode can be oxidized readily back to alumina or aluminum salt 25 by a close proximity to the anodically produced carbon oxide. A reduction in the anode-cathode separation distance provides more contact between anode product and cathode product and significantly accelerates the reoxidation or "back reaction" of reduced metal, thereby decreasing current efficiency. The high amperage electrical current passing through the electrolytic 30 cell produces powerful magnetic fields that induce circulation in the molten aluminum pad leading to problems such as reduced electrical efficiency and "back reaction" of the molten aluminum with the electrolyte. The magnetic fields also WE CLAIM:- 1. An electrolytic reduction cell for aluminum production, comprising a cell wall, a bust bar external to said cell wall, an anode, a carbonaceous cathode block separated from said anode, and a collector bar connecting said bus bar with said cathode block, said collector bar comprising: (a) a ferrous metal body comprising 1) a solid, ferrous metal spacer having an external end portion connected with said bus bar and an internal end portion spaced inwardly of said external end portion, and 2) a ferrous metal sheath defining a cavity and an air vent for relieving pressure from said cavity; and (b) a copper insert inside said cavity and a steel plug enclosing the copper insert, an expansion allowance space is provided in said cavity between the copper insert and the steel plug, said copper insert having an external end adjacent said spacer. 2. The cell as claimed in claim 1, wherein said cathode block defines a slot and said collector bar is seated in said slot. 3. The cell as claimed in claim 1, comprising means in said slot for joining said collector bar to said cathode block 4. The cell as claimed in claim 3, wherein said means in said slot comprises an electrically conductive material. 5. The cell as claimed in claim 1, wherein said means in said slot is selected from the group consisting of cast iron, carbonaceous glue, and rammed carbonaceous paste. 6. The cell as claimed in claim 1, wherein said cavity has a polygonal transverse cross-section and said copper insert has a polygonal transverse cross-section. 7. The cell as claimed in claim 1, wherein said cavity has a generally circular transverse cross-section and said copper insert has a generally circular transverse cross-section. 8. The cell as claimed in claim 1, wherein said cathode block comprises about 30-100 wt.% graphite or a graphitized cathode block. 9. The cell as claimed in claim 1, wherein said ferrous metal sheath is integral with said spacer. 10. The cell as claimed in claim 1, wherein said internal end port of the spacer is spaced inwardly of said cell wall. 11. An electrolytic reduction cell for aluminum production substantially as herein described with reference to the accompanying drawings. Dated this 16th day of May, 2001 (RITUSHKA NEGI) OF REMFRY & SAGAR ATTORNEY FOR THE APPLICANTS

Documents:

abstract1.jpg

in-pct-2001-560-mum-cancelled pages(02-12-2004).pdf

in-pct-2001-560-mum-claims(granted)-(02-12-2004).pdf

in-pct-2001-560-mum-correspondence(09-08-2007).pdf

in-pct-2001-560-mum-correspondence(ipo)-(13-10-2006).pdf

in-pct-2001-560-mum-drawing(02-12-2004).pdf

in-pct-2001-560-mum-form 13(09-08-2007).pdf

in-pct-2001-560-mum-form 1a(09-08-2007).pdf

in-pct-2001-560-mum-form 2(granted)-(02-12-2004).pdf

in-pct-2001-560-mum-form 3(03-12-2001).pdf

in-pct-2001-560-mum-form 5(16-05-2001).pdf

in-pct-2001-560-mum-form-pct-isa-210(16-05-2001).pdf