Morten Karlsen

New Aerated Distribution (ADS) and Anti Segregation (ASS) Systems for Alumina

Two tonnes of alumina is required to produce one tonne of aluminium. The logistics of alumina therefore represent an important part of the aluminium production, including unloading of ships, internal transport and storage, fume treatment and finally distribution into the electrolysis pots. Over the last 20 years several automated distribution systems utilizing pneumatic conveying have been developed. These systems are closed, resulting in less dusting. However, due to the erosive properties of alumina and relatively high transport velocities, such systems require high maintenance frequencies. Problems also arise because secondary alumina forms scales when conveyed pneumatically.

Experimental investigation of load exerted on a double-cone insert and effect of the insert on pressure along walls of a large-scale axisymmetrical silo

Applications of flow aid devices such as inserts improve the silo discharging mode. Considerable effort has been made in finding the best configurations between inserts and silos to achieve optimal functional results. In the present investigation, experiments were carried out to measure the loads imposed on a double-cone insert by particulate solids (free-flowing sand) when it was fitted within an axisymmetrical large-scale silo. Concentric filling/discharging was implemented to carry out such measurements. Pressures along the walls of the silo were also measured. Analyses of the measurement results showed that: (1) the loads on the insert were rather stable in total, but appeared to be asymmetrical at the end of filling; (2) a sudden increase of the loads on the insert was observed at the transition from filling to discharging, but this increase lasted only for a short moment; and (3) the loads on the insert decreased slowly but remained rather high for a large part of the discharge. Effects of the double-cone insert on the pressures along the silo walls were discussed.

Factors Influencing Cell Hooding and Gas Collection Efficiencies

In modern aluminium electrolysis cells the hooding and gas collection efficiencies are important design parameters to improve productivity and reduce environmental pollution. Hooding efficiency is the result of a variety of design parameters for the anode superstructure. The factors that determine the gas collection efficiency are described by simple physical models. Measurements of HF emission rates into the potroom were made with our self-developed HF monitor. Forced gas suction rate during cell operations will in general reduce the HF emission from the potroom. By optimising the gas suction rate and operational routines it may be possible to reduce emissions from the anode changing operation by approximately 75%. Ventilation rates through the potroom were found to have a significant influence on the emission level, depending on the suction rate employed in the cells.

Handling CO2EQ from an Aluminum Electrolysis Cell

The increased focus on reduction of energy consumption and preserving our environment will affect a lot of industries in the coming years, and this will indeed be the case also for the aluminum industry. Hydro believes that aluminum is a part of a sustainable future and wants to take an active part in developing a more environmentally friendly production process. Most of Hydro’s electricity used for aluminum production is based on water power, but the plants in Kurri Kurri, Australia and Neuss, Germany are based on coal power and our new smelter in Qatar will be based on gas power. This paper gives an insight in Hydro’s plans for reduction of the carbon footprint from their primary production plants around the world by keeping their focus aiming at elimination of AE and production of CF gases. Hydro also has developed a gas suction technology enabling partial CO2 capture from their electrolysis cells, as well as reduction of the net gas suction volume, with promising results.

A system for the reduction of air current segregation in silos

Air current segregation, which often results in fluctuations in the dust content of the discharged material, can lead to severe downstream problems with equipment depending on fluidization for their operation, such as air slides and volumetric feeding devices. Investigations carried out in aluminium plants have shown that the consequences of such periodic fluctuations in quality are anode effects and temporary shutdown of distribution systems. To reduce the scale of the problem, a device called an Anti Segregation Tube (AST) has been developed for use when filling silos. The AST has a specially designed inlet section, and a patented distribution system called ASS (Anti Segregation System) and is equipped with self-activating flap-valves along its height. The silos are filled via one or more of these tubes (depending on the silo diameter) and initially only the lowest valve opens. When it is partially covered the next valve above opens, and so on. Using ASTs reduces dusting during filling dramatically. This chapter describes the results obtained from an AST installed in a pilot plant, and the design of a system of 6 tubes installed in each of two 6000 t silos.

Alumina Handling in the Smelter — From Port to Pot

Alumina is the main raw material for primary aluminium production and the smelters rely on continuous, steady streams of alumina to the pots. At the pot, variations in the alumina quality shall be minimized. Fluoride content, particle size distribution, attrition, segregation, powder flowability and impurities all are important parameters that are affected and partly controlled by the alumina handling and treatments including the alumina silo storage, transport, screening and gas treatment /alumina enrichment systems upstream the pots.

Using real-time particle size analysis to optimise aluminium smelting

Abstract The Hall–Héroult electrolytic process used throughout the world to produce aluminium from alumina is highly energy intensive. Norsk Hydro ASA is a major player in this market. At the companys sites in Norway a plentiful supply of hydroelectric power lightens the environmental burden associated with production, but energy consumption remains a major concern. Thus understanding and improving the performance of the electrolysis circuit remains an important operational objective.