Conceptual Design for Lower-Energy Primary Aluminum

Abstract

Operating parameters have been identified such that slag melts typical of other carbothermic aluminum processes are thermodynamically unstable. This facilitates the direct reaction of carbon in carbon-saturated aluminum with alumina under dispersed-contact high-intensity conditions. A conceptual design for one million tonnes per annum (1 Mtpa) aluminum production from Bayer alumina is developed. Freestanding graphite reactors and an ancillary plant encapsulated by inert gas are totally unconstrained within refractory-lined shells. Electrical conductive heating and melt circulation in closed loops, employing a 10 vol pct dispersion of fine carbon particles in aluminum (slurry), transports sensible heat to a single pressurized metalproducing reactor (MPR) to satisfy the endothermicity. In the proposed plant, an MPR at 0.28 MPa (2.8 bar) and 2433 K (2160°C) with a hearth 2-m-wide · 190-m-long leads the melt via a barometric leg back to essentially atmospheric pressure, for further in-line processing. The impeller-stirred assimilation of fine carbon particles is followed by multistage gas-lift pumping to provide a 5.4-m total head, as required by two parallel straight-line melt-conductive heaters 1 m in diameter · 226 m in length. Overall energy-consumption figures 28.7 pct lower than today's more recently installed Hall-Heroult electrolytic plants are predicted, with 51.3 pct less purchased electricity, supplemented with 1.10 times the stoichiometric elemental carbon.

Improved Energy Efficiency in the Aluminium Industry and its Supply Chains

“…No values for the energy efficiency improvements were found for any of the indirect carbothermic reductions, which makes a comparison with electrolysis impossible. Direct carbothermic reduction has the disadvantage of higher demand for reaction material (carbon) compared to electrolysis (theoretically about 0.67 tonnes C/tonne Al [149] for direct carbothermic reduction compared to about 0.46 tonnes C/tonne Al in industrial applications [49] and a theoretical value of about 0.33 tonnes C/tonne Al for electrolysis [94]). Lorentsen [167] estimated that more than 100 million tonnes of bio-coke per year would be needed to replace the aluminium production in 2014 with direct carbothermic reduction.…”

Review of measures for improved energy efficiency in production-related processes in the aluminium industry – From electrolysis to recycling

“…Despite this, the proposed processes have not been commercialised [107]. For the direct carbothermic reduction, there have been problems with extreme operating conditions, yield [107], the formation of aluminium carbide, high temperatures [108][109][110], energy delivery for reaching the temperatures [108,109,111], aluminium volatiles [108][109][110][111], the formation of undesired by-products [112,113] and complicated back-reaction [110]. More knowledge about the reaction mechanisms and kinetics of alumina reduction is needed to overcome these problems [108,109].…”

Towards Zero CO2 Continuous Steelmaking Directly from Ore

“…On the other hand, carbon pellets are needed in the author's proposed new technology for reducing the energy consumption in primary aluminum production. [15] In an effort to make an unbiased comparison, standard enthalpies of reaction at 298 K (25°C) have been utilized in the knowledge that such values do not vastly change with temperature. Assuming that reduction endothermicity is provided by electrical conductive heating within an ironmaking melt circulation loop without any contribution by post combustion, as indeed is outlined in the Appendix, Fe 2 O 3 electrolysis consumes about 1.5 times the energy of natural gas-based steelmaking.…”