A Numerical Study of Gas Production and Bubble Dynamics in a Hall-Héroult Reduction Cell

Cubeddu, A.; Nandana, Varchasvi; Janoske, Uwe

doi:10.1007/978-3-030-05864-7_75

Cited by 6 publications

(4 citation statements)

References 10 publications

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“…The cathode block with the cast iron and the collector bars conducts the current out of the cell [4]. The current rating is up to 600 kA with a typical voltage of 4-5 V [5].…”

Section: Introductionmentioning

confidence: 99%

Long-term heat treatment of collector bars for aluminium electrolysis: impact on microstructure and electrical properties

et al. 2020

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In order to identify possible optimizations regarding the electrical energy efficiency of an aluminium electrolysis cell, the impact of service temperature on microstructure and electrical properties of the cell cathode was investigated. The investigations include experiments regarding the chemical composition, especially the content of carbon, the electrical conductivity and the microstructure at selected positions. Thermodynamic calculations were used to estimate local service temperatures and explain phase transformations and formations. It was found that due to the increased service temperature diffusion processes of carbon took place to a particular extent between cast iron and collector bar. As a result, the carbon content in the collector bar changed from 0.06 to 1.05–1.4 wt%, while in the cast iron a reduction from 3.47 to < 1.50 wt% took place. These processes led to isothermal phase transformations and formations, that changed the matrix of the collector bar from austenitic with low content of ferrite to an austenitic matrix accompanied by precipitation of secondary, predominantly allotriomorphic cementite at service temperature. It was then shown that this has a negative effect on collector bar and decreases the electrical conductivity by up to 26 %. It was also discovered that graphite spheroidization within the grey cast iron has a positive effect on its electrical conductivity, which has increased by 52 %. The results provide the basis to gain an understanding of the carbon diffusion related processes within the cathode of an electrolysis cell and reveal further potential to increase the energy efficiency of primary aluminium production.

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“…The cathode block with the cast iron and the collector bars conducts the current out of the cell [4]. The current rating is up to 600 kA with a typical voltage of 4-5 V [5].…”

Section: Introductionmentioning

confidence: 99%

Long-term heat treatment of collector bars for aluminium electrolysis: impact on microstructure and electrical properties

et al. 2020

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“…The typical operating temperature of such a cell ranges between 950 and 970 °C [2] and relies completely on electrical energy. Therefore, it consumes about 15 kWh per kg of pure aluminium [3] at an operating voltage of only 4 V-5 V and currents up to 600 kA [4]. Because of the costly energy carrier and the high demand on production, optimization of the cell efficiency is a crucial aspect to increase the productivity of aluminium production.…”

Section: Introductionmentioning

confidence: 99%

Investigation of phase transformation related electrical conductivity of long-term heat treated aluminium electrolysis cathodes

et al. 2022

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This study presents an investigation on the specific electrical conductivity of the cathode materials used in an aluminium electrolysis cell over a temperature range between room temperature and 950 °C. Those materials are subjected to a diffusion related aging process due to the high operating temperature of the cell, leading to a change in chemical composition and microstructure. The materials were investigated both in the initial state before use in an aluminium electrolysis cell and after an operating period of 5 years. It is shown that the changes in chemical composition and thus also in microstructure over the service life at elevated operating temperature exert an effect on the electrical conductivity. In addition, calculations based on thermodynamic data were used to relate phase transformations to the changes in electrical conductivity. On the one hand, the electrical conductivity of the collector bar at 950 °C is reduced by about 11% after 5 years of service. On the other hand, the ageing process has a positive influence on the cast iron with an increased conductivity by about 41% at 950 °C. The results provide an understanding how diffusion related processes in the cathode materials affect energy efficiency of the aluminium electrolysis cell.

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“…In particular, hydrogen generation from electrochemical water-splitting is a promising source of future renewable energy [9][10][11]. Bubbles unavoidably form on the electrodes of many important gas-evolving electrochemical processes, such as water electrolysis, the chlor-alkali process and the Hall-Heroult process [12][13][14][15][16][17][18][19]. The importance of understanding how electrolytic bubbles impact the mass transfer and energy efficiencies of electrochemical cells is reflected in the growing number of publications on the topic [20,21].…”

Section: Introductionmentioning

confidence: 99%

Potential response of single successive constant-current-driven electrolytic hydrogen bubbles spatially separated from the electrode

Raman

Peñas

Meer

et al. 2022

Preprint

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In gas-evolving electrolytic processes, the presence of bubbles can heavily alter the mass transport of gaseous products and can induce severe overpotential penalties at the electrode through the action of bubble coverage (hyperpolarization) and electrolyte constriction (Ohmic shielding). However, bubble formation can also alleviate the overpotential by lowering the concentration of dissolved gas in the vicinity of the electrode. In this study, we investigate the latter by considering the growth of successive hydrogen bubbles driven by a constant current in alkaline-water electrolysis and their impact on the half-cell potential in the absence of hyperpolarization. The bubbles nucleate on a hydrophobic cavity surrounded by a ring microelectrode which remains free of bubble coverage. The dynamics of bubble growth does not adhere to one particular scaling law in time, but undergoes a smooth transition from pressure-driven towards supply-limited growth. The contributions of the different bubble-induced phenomena leading to the rich behaviour of the periodic fluctuations of the overpotential are identified throughout the different stages of the bubble lifetime, and the influence of bubble size and applied current on the concentration and Ohmic overpotential components is quantified. We find that the efficiency of gas absorption, and hence the concentration-lowering effect, increases with increasing bubble size and also with increasing current. However, the concentration-lowering effect is always eventually countered and overcome by the effect of Ohmic shielding as the bubble size outgrows and eclipses the electrode ring beneath.

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A Numerical Study of Gas Production and Bubble Dynamics in a Hall-Héroult Reduction Cell

Cited by 6 publications

References 10 publications

Long-term heat treatment of collector bars for aluminium electrolysis: impact on microstructure and electrical properties

Long-term heat treatment of collector bars for aluminium electrolysis: impact on microstructure and electrical properties

Investigation of phase transformation related electrical conductivity of long-term heat treated aluminium electrolysis cathodes

Potential response of single successive constant-current-driven electrolytic hydrogen bubbles spatially separated from the electrode

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