Performance analysis of the aluminum casting furnace
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I.
INTRODUCTION
THE aluminum casting furnace plays a central role in the production of primary aluminum. Its place in the process is between the potline where liquid aluminum is produced by electrolysis, and the castshop where the liquid metal, after being appropriately prepared and brought to the right temperature, is poured into the molds to make ingots or other products. The role of the furnace is to receive the liquid aluminum from the electrolytic cells, bring it to an appropriate temperature, and hold it there for alloy preparation and for casting. The furnace also receives a solid charge made of solid aluminum of various sizes such as extrusion butts, ingots, and logs, to be melted into the liquid metal. In addition to holding and melting, the aluminum also undergoes a cleaning operation by action of chlorine, known as fluxing. To improve the heat transfer, the metal is stirred by the action of a jet of inert gas such as nitrogen; and the dross formed on the surface is skimmed by mechanical action. Note that chlorine, besides its role as fluxing agent, also provides a stirring action similar to the one provided by the inert gas. This type of furnace is often called melter-holder. Melter-holders consume large amounts of energy at a low efficiency. Figures of specific consumption commonly encountered are in the order of 4.5 to 6 megajoules per kilogram of aluminum melted. Of this energy, usually no more than 20 pct actually reaches the metal either for melting or holding purpose. Fumace designers are interested in improving the design in terms of energy efficiency and productivity, while the operators will want to know what the effects of changes in the operating procedures will be. We are speaking here of changes in the sequence of operations that constitutes a batching cycle, or changes in the duration of each of these operations, or changes in the size of the charge, and also changes in the ways of performing an operation, e . g . , a continuous stirring of the liquid metal v s a discrete stirring or a closed door operation v s open door. The purpose of this work is to build a mathematical model, of relative simplicity and not too expensive to run on the computer, and capable of providing an answer to these questions. During the past months, we have endeavored to address a number of such R.T. BUI, Professor of Engineering, and J. PERRON, Graduate Student, are with the Department of Applied Science, Universit~ du Qufbec Chicoutimi, Chicoutimi, PQ, Canada G7H 2B1. Manuscript submitted June 8, 1987. METALLURGICALTRANSACTIONS B
questions using a preliminary version of the model, and the results have been presented in a technical meeting.l This paper gives the final version of the model along with its validation and applications. The number of design and operating parameters involved in the melter-holder is indeed large, in the order of 450. With such a high degree of freedom, it is difficult to make decisions based only on experience and intuition. The physical phenomena involved are conduction, convection (
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