Primary Aluminum Industry - Energy and Emission Reductions: An LMD Symposium in Honor of Halvor Kvande: Energy and Emission Reductions I: An LMD Symposium in Honor of Halvor
Sponsored by: TMS Light Metals Division, TMS: Aluminum Committee
Program Organizers: Arne Ratvik, SINTEF
Wednesday 8:30 AM
March 2, 2022
Room: 208A
Location: Anaheim Convention Center
Session Chair: Guðrún Sævarsdóttir, University of Iceland; Arne Ratvik, SINTEF Industry
8:30 AM Introductory Comments
8:35 AM
Vaporization of Fluorides from Aluminium Cells. Part I: Theoretical Study on Replacement of Aluminium Fluoride and Soda: Asbjorn Solheim1; Samuel Senanu1; 1SINTEF Industry
Commercial alumina contains Na2O and CaO, which must be "neutralised" by regular additions of AlF3 to the bath in aluminium electrolysis cells. As a result, most smelters are net bath producers. The present paper suggests that part of the AlF3 can be replaced by the condensate formed by partial vacuum vaporization of tapped-off bath, thereby reducing the amounts of deposited bath. The condensate may have a composition close to the main evaporation product (NaAlF4), while the remaining bath will be rich in NaF and can be used for replacing soda. Data for vapour pressure and condensate composition are presented. A bath mass balance is derived in terms of Na2O and CaO in the alumina, comprising replacement of AlF3 with condensate from produced bath. Different process options are discussed, including repeated cycles of vaporization and condensation.
9:00 AM
Vaporization of Fluorides from Aluminium Cells. Part II: Treatment of Spent Potlining in a Laboratory Furnace: Camilla Sommerseth1; Samuel Senanu1; Henrik Gudbrandsen1; Stein Rørvik1; Per Eidem2; Asbjørn Solheim1; Morten Isaksen3; Ellen Myrvold4; 1SINTEF Industry; 2SINTEF Helgeland; 3Hydro Aluminium AS; 4Alcoa Mosjøen
Today, spent potlining (SPL) from the aluminium industry is mainly placed on landfill. In a circular economy perspective, and with limited availability for landfill sites in the future, the industry is looking into ways of cleaning the SPL to produce saleable products. Vacuum vaporization was investigated to determine its applicability for removing fluorides from the graphite rich first cut SPL. It was demonstrated that vacuum vaporization at elevated temperatures is suitable for removal of fluorides. The condensate generally contained only cryolite and NaF, in accordance with theory. At the temperatures used it was impossible remove CaF2 or alumina from the SPL, due to the low vapour pressure. Hold time at elevated temperature and vacuum affected the amount of electrolyte removed. The findings comply with the theory for vaporization of fluoride mixtures.
9:25 AM
Scale Formation in Primary Aluminium Production: Morten Isaksen1; Nancy Holt1; 1Hydro Aluminium AS
The presence of scale in process equipment during production of primary aluminium represents a factor that contributes to reduced performance. Formation of hard scale is best known in the oxide transport, operation of gas treatment units and heat exchangers. The maintenance cost of removing scale from process equipment may be significant. Studies have been carried out dealing with the formation of scale at various locations throughout the off-gas system from an electrolytic cell. Few specific hypothesis about factors leading to the formation exist. Sulfur seems to play a more important role than reported earlier. This publication covers 4 different scale types and their possible chemical formation pathways.
9:50 AM Break
10:05 AM
Sampling and Analysis Methodology Review to Report Total PFC Emissions: Luis Espinoza-Nava1; Julie Young1; 1Alcoa Technical Center
Latest International Aluminum Institute (IAI) guideline includes various methodologies to measure total perfluorocarbon (PFC) emissions. Alcoa has continued to review those methodologies in selecting and implementing procedures that give reliable sampling and analytical techniques to measure high voltage, low voltage and pot starts PFC emissions from aluminum cell operation.Canister sampling offers the simplest, cost effective method to estimate total PFC emissions. However, it is important to investigate the sampling duration and frequency that can produce reproducible PFC emissions. Alcoa has tested the canister sampling procedures and compare GC-MS, FTIR and QCL-CF4 analytical techniques at two smelters to standardize the methodology with the goal to share the results and learnings within the aluminum industry.
10:30 AM
Reflections on the Low Voltage Anode Effect in Aluminium Electrolysis Cells: Asbjorn Solheim1; 1SINTEF Industry
The paper addresses the basic mechanisms leading to the low voltage anode effect (LVAE) as well as the high voltage anode effect (HVAE) in aluminium electrolysis cells. The root cause of any anode effect is too low alumina concentration at the anode surface. By statistical treatment based on a Gaussian distribution of the alumina concentration, it was found that the onset of a HVAE takes place at higher average concentration if there is a large standard deviation. By calculating the anode potential, it was found that an LVAE can take place at a part of the anode as small as 0.001 m2 while the rest of the anode works normally, which makes the LVAE extremely difficult to discover. It was suggested that the on-and-off current pattern observed during LVAE can be explained by alternation between blocking of the surface (AE) and normal electrolysis, induced by non-stationary mass transfer of alumina.
10:55 AM Cancelled
Environmental Enhancement of Potroom Processes by Using a Machine Vision System: Alexey Zherdev1; Alexey Svoevskiy1; Vitaliy Pingin1; Yuriy Shtefanyuk1; Valentin Shakhmatov1; 1UC RUSAL
Intelligent control and digital technologies are now widely developed to improve the efficiency of aluminum production. The paper elaborates on how system is based on machine vision with training a neural network to determine the types of violations of the sealing of electrolyzers. Control commands of the system and operational analysis of their support can be used to improve or enhance the environment in a potroom. The use of machine vision and neural networks made it possible to reduce in half the time during which the cells are partly sealed, and to reduce AlF3 consumption by 3-5 kg/t Al. The in-house system was successfully tested in EcoSøderberg potrooms of Krasnoyarsk smelter. Plans are to deploy the system across all RUSAL’s smelters with Søderberg technology. Тext step of RUSAL Engineering & Technology Center is proceeded to develop a machine vision system to improve the environment in PB potrooms.