PROCESS MODELING OF ALUMINUM SCRAPS MELTING IN MOLTEN SALT AND METAL BATH IN A ROTARY FURNACE

摘要

During secondary aluminum recovery, aluminum scraps are melted and refined often in a rotary melting furnace. The feed is normally a complex combination of aluminum scraps with different sizes, shapes, compositions, and contaminations. During the process, the scraps are charged into the rotary furnace, heated by the combustion of natural gas, melted and refined under a molten salt layer. Efficient melting of the scraps is a critical issue in order to achieve higher metal recovery, lower energy and salt consumption, and less environmental impact. To study the scrap melting behavior, a furnace process model has been developed based on a Computational Fluid Dynamics (CFD) framework, coupled with a user-developed scrap-melting sub-model. The furnace model consists of a gas region with turbulent flow and combustion as well as radiative heat transfer in the upper part of the furnace, and a solid-liquid region of salt and aluminum metal in the lower part of the furnace. The melting sub-model implemented in the CFD framework was modified from a user developed melting model for a single aluminum particle in molten melts. To represent the distributed nature of the scrap feed, aluminum scraps were classified into several groups depending on their properties, e.g. size of the scraps. The melting behavior of aluminum scrap was simulated with the exchange of information between the melting sub-model and the CFD calculations. Heat sink due to scrap melting was calculated by the sub-model and fed back to the CFD model as source term of the energy equation. Gas flow in the top combustion space and temperature distributions in the furnace calculated by the CFD model was used to calculate the melting rate of aluminum scrap in the sub-model. The influence of scrap size distribution on melting behavior was studied.