Modelling of EAF Off‐Gas Post Combustion in Dedusting Systems using CFD Methods

Abstract

To comply with the increasingly strict environmental regulations, the poisonous off‐gas species, e. g. carbon monoxide (CO), produced in the electric arc furnace (EAF) must be treated in the dedusting system. In this work, gas flow patterns of the off‐gas post combustion in three different dedusting system units were simulated with a computational fluid dynamics (CFD) code: (1) post combustion in a horizontal off‐gas duct, (2) post combustion in a water cooled post combustion chamber without additional energy supply (no gas or air/oxygen injectors) and (3) post combustion in a post combustion chamber with additional energy input (gas, air injectors and ignition burner, case study of VAI‐Fuchs GmbH).All computational results are illustrated with gas velocity, temperature distribution and chemical species concentration fields for the above three cases. In case 1, the effect of different false air volume flow rates at the gap between EAF elbow and exhaust gas duct on the external post combustion of the off‐gas was investigated. For case 2, the computed temperature and chemical composition (CO, CO2 and O2) of the off‐gas at the post chamber exit are in good agreement with additional measurements. Various operating conditions for case 3 have been studied, including different EAF off‐gas temperatures and compositions, i. e. CO content, in order to optimize oxygen and burner gas flow rates. Residence time distributions in the external post combustion chambers have been calculated for cases 2 and 3. Derived temperature fields of the water cooled walls yield valuable information on thermally stressed parts of post combustion units.The results obtained in this work may also gain insight to future investigation of combustion of volatile organic components (VOC) or formation of nitrogenoxide (NOx) and permit the optimization of the operation and design of the off‐gas dedusting system units.