Diffusion and Flow of CO 2 in Carbon Anode for Aluminium Smelting
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nship between the gas bubble generations of carbon anodes related to ohmic voltage drop has attracted much attention, both due to the energy saving possibilities and the possible cell stabilizing effects for the smelting process. The bubble nucleation reaction takes place in the interface between active electrolysis sites and the porous anode with approximately 15 to 25 pct interconnected pores.[1] Despite the important role of the bubble layer, the details of bubble nucleation behavior and the gas
EPMA PUTRI is with the Faculty of Science, Engineering and Technology, Swinburne University of Technology, Hawthorn, VIC 3122, Australia and also with the CSIRO, Mineral Resources, Clayton, VIC 3169, Australia. Contact email: [email protected] GEOFFREY BROOKS is with the Faculty of Science, Engineering and Technology, Swinburne University of Technology. GRAEME A. SNOOK is with the CSIRO, Mineral Resources. INGO EICK is with the Hydro Aluminium Deutschland GmbH, 41468 Neuss, Germany. LORENTZ PETTER LOSSIUS is with the Hydro Aluminium AS, 6882 Øvre A˚rdal, Norway. Manuscript submitted May 15, 2018. Article published online February 5, 2019. 846—VOLUME 50B, APRIL 2019
transport mechanism for this process are not completely understood. Einarsrud et al.[2] proposed two possibilities for the gas path, namely, transport through pores in the anode or transport through the bath. However, there are limited data in the literature for gas diffusion measurements in both media, and the correlations between anode and bath properties, such as composition, porosity, and permeability of anode material, are poorly understood. A previous study by Golovina[3] measured the CO2 diffusion coefficient in coal at a temperature ranging from 273 K to 873 K, where the average pore size was not investigated and the diffusion transfer was not complicated by chemical reactions. The value obtained from their experiments ranged from 2.25 9 107 to 1.51 9 106 m2/s. Investigation for the CO2 diffusion coefficient above this temperature range is important, especially at the Hall–He´roult cell operating temperature (960 C). The voltage drop caused by bubble formation contributes ~0.25 V of the total cell voltage 4.19 V.[2] These data play an important role in describing and understanding the bubble nucleation behavior and, consequently, allow for possible energy efficiency improvements via optimization of bubble size and its distribution on the underside of the anode. The purpose
METALLURGICAL AND MATERIALS TRANSACTIONS B
of this study is to measure the diffusion rate of CO2 in a porous carbon anode by performing anode characterization using mercury intrusion porosimetry (MIP) and porous solid gas diffusion measurements. The results will lead to further understanding of gas diffusion behavior in relation to the anode porosity characteristics. The research, in general, will provide not only fundamental background in relation to gas transport mechanisms but also provide experimental data for the simulation of bubble formation and transport.
II.
THEORETICAL BACKGROUN
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