Continuous alumina feeder

An apparatus suitable for continuously feeding particulate alumina to an electrolytic cell for the production of aluminium by the electrolysis of alumina comprising:

• a hollow elongate housing positioned over an aperture in an alumina hopper, the alumina hopper being located above the electrolytic cell,
• the housing having one or more longitudinal slots to allow the passage of alumina through the housing and out of the hopper via the aperture,
• alumina feed control means mounted within the housing, the alumina feed control means comprising an orifice member located in close proximity to the aperture, a flow control valve member which is insertable into the orifice member and has varying cross-sectional area over at least a portion of its length, positioning means to which the flow control valve member is connected, the positioning means being effective to move the flow control valve member in a longitudinal direction relative to the orifice member and to control the position of the flow control valve member,
• an inner elongate hollow body disposed or disposable in a substantially upright position within the hopper, the body having the orifice member mounted in its lower end and the positioning means mounted to its upper end, the flow control valve member being located within the inner elongate hollow body, the elongate hollow body including at least one passage located to allow alumina to flow into the body above the orifice member, the inner elongate hollow body being sized and located to assist in aligning the flow control valve member with the orifice member,
• wherein in use alumina flows through the one or more longitudinal slots in the housing and the at least one passage in the inner elongate hollow member and thereafter through the orifice, and the flow control valve member is positioned relative to the orifice member to permit a continuous flow of alumina at a desired flow rate, the flow control valve member being moved relative to the orifice to alter the area available for flow of alumina through the orifice to effect any required change in the flow rate of alumina.

A method of continuously feeding alumina to an electrolytic cell for the production of aluminum by electrolysis of alumina dissolved in a molten electrolyte and of maintaining the concentration of alumina in the electrolyte substantially at a predetermined level or substantially within a range of concentrations during the production process, the method comprising the steps of:

• supplying alumina to a hopper located over the cell and having a bottom opening for discharge of the alumina from the hopper to the cell;
• obtaining a measure of the concentration of the alumina dissolved in the molten electrolyte in the cell;
• comparing the measured concentration obtained with the level or range;
• and operating alumina feed control means associated with the bottom aperture of the hopper wherein the alumina feed control means includes a flow control valve member having varying cross-sectional area along its length, said flow control valve member being adapted to be moved longitudinally relative to a discharge aperture to change the area of the aperture available for flow of alumina and thereby change the flow rate of the alumina to permit a continuous discharge of alumina at any set rate within a range of flow rates to permit a continuous discharge of alumina from the hopper to the cell at a flow rate within a range of flow rates so as to maintain the alumina concentration in the electrolyte substantially at the level or within the range.