Construção e avaliação de um sistema recuperador de calor por fluxo de ar na solidificação do alumínio

Abstract

Primary and secondary aluminum industries demand large amounts of energy, being one of the main expenses inherent in the process. Most of the thermal energy is spent in the melting of the metal, being lost to the environment when the aluminum solidifies, which can represent an important fraction of the initial investment of energy in a common melting furnace. In applications where the metal is casted in permanent molds, as in the case of ingots intended for later re-melting, it is possible to extract the heat from the solidification and cooling and reintroduce it in the process in order to increase thermal efficiency, reducing energy costs and ensuring cleaner production. This work evaluates the extraction of this heat through the thermal parameters involved in an air-cooled mold, such as temperatures obtained, thermal transfer coefficients and heat extraction efficiency, comparing the available value in the solidification and cooling stages of a ingot with that achieved by the increase in the enthalpy of the flow of a known mass of air. It is also studied the possible applications of heated air in a secondary aluminum industry and its effectiveness as thermal recovery technique. The results indicate a heat extraction efficiency of 47% and a thermal energy quantity of 386 kJ for each kilogram of aluminum. The heat recovery system here assessed comes out as alternative for the development of waste heat recovery techniques in metal casting processes.