CFD Modelling of NOx and Soot Formation in Aluminum Anode Baking Furnace

Abstract

Copyright © 2018 ASME. The cost and quality of aluminum produced by the reduction process are strongly dependent on heat treated (baked) carbon anodes. A typical aluminum smelter requires more than half a million tons of carbon anodes for producing one million ton of aluminum. The anode baking process is very energy intensive, approximately requires 2GJ of energy per ton of carbon anodes. Moreover, pollutant emissions such as NOx and soot formation are of major concern in the aluminum anode baking furnace. The current study aims at developing an accurate numerical platform for predicting the combustion and emissions characteristics of an anode baking furnace. The Brookes and Moss model, and the extended Zeldovich mechanism are employed to estimate soot and NOx concentration, respectively. Considering a fire group of three burner bridges, one after the other in the fire direction, combustion and emissions features of these three firing sections are interrelated in terms of oxidizer’s concentration and temperature. In the present study, considering this interconnection, the effect of diluted oxygen concentration at elevated oxidizer’s temperature (~1200°C), which are the key features of the moderate or intense low oxygen dilution (MILD) combustion are analyzed. It is observed that by circulating some of the exhaust gases through the ABF crossovers, oxygen dilution occurs which results in higher fuel efficiency, lower pollutant emissions, and more homogeneous flow and temperature fields.