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Through a critical review of recent literature on aluminum smelting cell energy balance, this paper defines specific energy constraints which govern the feasibility of cell operation in practice. Using these constraints as a basis, the objective of reducing energy consumption per kilogram of aluminum produced was examined, again with reference to published data and modern cell developments over the last 5 years. Both incremental and quantum steps in cell design are considered in this analysis, in pursuit of a pathway to lower energy consumption in a process where energy efficiency has not yet risen above 50 pct. In Section V and VI of this work, a generic high amperage cell technology is examined using a computational model of the cell energy balance, in which the resultant electrolyte phases and their thermal, electrical, and physical states can be determined. Using a series of trial energy balances, a feasible operating point emerges, and the possibility of flexible cell amperage and production rate is tested in a preliminary way. The specific energy consumption and market implications of this new technology direction are examined. I. RECENT RESEARCH IN THE FIELD OF SMELTING CELL ENERGY BALANCEUNDERSTANDING and improvement of the energy balance of aluminum smelting cells continue to be a limiting factor in both cell design and operation and in final performance. Modern, high amperage cell designs still suffer habitually from localized sidewall failures due to lack of understanding or control of the rate of thermal convection to the walls. Cathode deposits build up on modern cell cathodes causing horizontal currents and electromagnetic instability, increasing energy usage, and reducing efficiency. Why this is the case now, after more than one hundred years of publications and excellent industry developments and training on this subject ? The answer can only be that the problem of achieving an acceptable energy balance is extremely difficult, especially in the context of the need to constantly increase production rate and reduce electrical energy consumption. The mind set of constantly increasing production is one which needs to be questioned in the context of international and local market signals, and this has been discussed in a recent market analysis.[1] This analysis concludes that structural oversupply and growing available stocks of aluminum will continue to drive lower prices despite healthy demand for the metal.Recent studies of cell energy balance [2,3] have focused on building superior three dimensional hydrodynamic field models to predict heat transfer coefficients for the electrolyte and metal phases.[2] This excellent computational work has confirmed previous experimental studies [4] in terms of the magnitude of heat transfer coefficients from the electrolyte, but unfortunately, the resultant electrolyte conditions (temperature field and superheat) were not determined in these models-rather they were inputs to the simulation. The result is an unrealistic sidewall heat flux and ledge profile becaus...

The lifetime of aluminum reduction cells is driven primarily by the lifetimes of two components of the cell lining: the carbon cathode and the sidewall refractory material. The current state‐of‐the‐art sidewall material is a silicon nitride bonded silicon carbide (SNBSC) refractory and its corrosion mechanisms in the aluminum reduction cell environment have been examined in this study. Microstructural analysis of commercial SNBSC materials identified variations in porosity and α/β Si3N4 ratio in the binder phase, with higher porosity levels and β Si3N4 content found in the interior part of the block. Unreacted metallic silicon was observed only as a crystalline phase encapsulated inside SiC grains and not in the binder phase. The effects on the corrosion rate of porosity levels, amount of binder, α/β Si3N4 ratio, and different factors in the environment, were examined in laboratory scale trials. High corrosion rates were associated with high porosity levels and a high β Si3N4 fraction in the binder. The crystal morphology of β Si3N4 is suggested as the main reason for the higher reactivity of this material. This morphology presents a higher surface area compared with α Si3N4 crystals. A corrosion mechanism for SNBSC materials in the aluminum reduction cell atmosphere is suggested.

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The widely used Si3N4-SiC sidewall refractories for aluminum smelting cells, and β SiAlON-SiC composites that can be potentially used for this purpose, have been produced by reaction bonding and their corrosion performance assessed in simulated aluminum electrochemical cell conditions. The formation of the Si3N4 and SiAlON phases were studied by reaction bonding of silicon powders in a nitrogen atmosphere at low temperatures to promote the formation of silicon nitride, followed by a higher heating step to produce β SiAlON composites of different composition. The corrosion performance was studied in a laboratory scale aluminum electrolysis cell where samples were exposed to both liquid attack from molten salt bath and corrosive gas attack. The corrosion resistance of the samples was shown to be dependent on the composition but more importantly on the environment during corrosion, with samples in the gas phase showing higher corrosion.