Proof of concept to recover thermal wastes from aluminum electrolysis cells using Stirling engines

• Published in: Energy conversion and management 2018-09, Vol.172, p.497-506
• Main Authors: Cascella, F., Gaboury, S., Sorin, M., Teyssedou, A.
• Format: Article
• Language: English
• Subjects: Aluminum; Cells; Computational Fluid Dynamic; Computational fluid dynamics; Computer applications; Conduction; Conduction heating; Conductive heat transfer; Convection; Electrolysis; Electrolytic cells; Energy conversion efficiency; Energy demand; Energy efficiency; Heat engines; Heat exchangers; Heat flux; Heat recovery; Heat transfer; Low temperature; Mining; Power efficiency; Radiation; Recovery; Smelters; Stirling engine; Stirling engines; Thermal wastes; Thermodynamics; Wastes; Working conditions
• ISSN: 0196-8904; 1879-2227
• DOI: 10.1016/j.enconman.2018.07.048

•Overall description of energy consumption of aluminum smelters.•Evaluation of the thermal wastes of electrolysis cells by means of CFD.•Validate CFD prediction with analytical results.•Feasibility of using Stirling engines to convert recovered thermal wastes. The production of aluminum is a low energy-efficient industrial process. In fact, almost half of its energy demand is lost under the form of heat along the production line. For this reason, aluminum producers are interested in improving energy efficiency of their smelters by recovering the thermal losses. It is well known that a significant loss of energy occurs across the sidewalls of the electrolysis cells. This paper proposes a proof of concepts where the sidewall thermal wastes are used to drive Low Temperature Differential (LTD) Stirling engines. To estimate the losses, a heat transfer study is implemented; heat conduction coupled with mixed convection and radiation is evaluated by using the OpenFOAM Computational Fluid Dynamic (CFD) software. Then, a parametric study is performed to analyse cell working conditions under which thermal wastes could be recovered. The heat flux and the temperature of the thermal wastes are used to judge the utilization of possible Stirling engine technologies. Two scenarios are studied: (i) a plane heat collector coupled to the radiative sidewall and (ii) a plane heat collector in direct thermal contact with the cell sidewall. It is demonstrated that the recovery of the wastes by radiation is technically feasible and it does not threaten the safety of the smelter; furthermore, the losses can power some Stirling engines given in the open literature. Therefore, the recovery of the radiative wastes and the further conversion by means of the Stirling engine is an interesting solution to improve the aluminium smelter energy efficiency.