Modelling of $${\text{NO}}_{{X}}$$ Mitigation Strategies for Hydrogen Shrouded Supersonic Coherent Jets for Steelmaking Furnaces

Abstract Supersonic coherent jets are crucial in steelmaking, not only for injecting oxygen for metallurgical purposes but also to serve as a heat source during scrap heating. In steelmaking furnaces, hybrid coherent jets are often used, allowing the injection mode to be adjusted based on metallurgical requirements. In the Electric Arc Furnace (EAF), commonly used for recycling steel, these coherent jets can switch between generating flames, injecting supersonic oxygen, and adding carbon and lime. Most of these jets currently run on natural gas, but with the steel industry focusing on decarbonisation, replacing natural gas with hydrogen is a promising option, as hydrogen combustion produces only water vapour $$({\text{H}}_{2}\text{O})$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mo>(</mml:mo> <mml:msub> <mml:mtext>H</mml:mtext> <mml:mn>2</mml:mn> </mml:msub> <mml:mtext>O</mml:mtext> <mml:mo>)</mml:mo> </mml:mrow> </mml:math> . However, hydrogen flames are known to form oxides of nitrogen $$({\text{NO}}_{\text{x}})$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mo>(</mml:mo> <mml:msub> <mml:mtext>NO</mml:mtext> <mml:mtext>x</mml:mtext> </mml:msub> <mml:mo>)</mml:mo> </mml:mrow> </mml:math> which have significantly higher $${\text{CO}}_{2}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mtext>CO</mml:mtext> <mml:mn>2</mml:mn> </mml:msub> </mml:math> equivalent impact. In this study, the $${\text{NO}}_{\text{x}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mtext>NO</mml:mtext> <mml:mtext>x</mml:mtext> </mml:msub> </mml:math> emissions from three commonly used types of coherent jets were modelled and compared using computational fluid dynamics (CFD). Then, the effects of water injection in supersonic combustion coherent jets were also analysed to predict $${\text{NO}}_{\text{x}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mtext>NO</mml:mtext> <mml:mtext>x</mml:mtext> </mml:msub> </mml:math> levels. The CFD model shows that the NO mass fraction, which is predominant amongst the oxides of nitrogen, for a standard coherent jet can reach up to 1078 PPM, However, introducing hydrogen fuel through the outer port of the jet reduces NO emissions to 610 PPM and for a combustion coherent jet further to 526 PPM. Adding water vapour to the hydrogen fuel in the combustion coherent jet reduces NO emissions even more, with levels dropping to 474 PPM and 424 PPM when 5 and 10 pct water vapour, respectively, are added to the fuel. However, the CFD results predict that the potential core length of the jet decreases due to these modifications in the supersonic coherent jet.