A Comprehensive Review of Nitrogen Control in the Current and Future Green Steelmaking Operations

Depending on the property requirements of steel products, their allowable levels of nitrogen typically vary from 20 to 30 ppm for automotive and appliance sectors to 60 to 120 ppm for aerospace applications. The current converter steelmaking practice using the Blast Furnace–Basic Oxygen Furnace (BF–BOF) route is well suited to produce grades with wide variation of final nitrogen in crude steel, but there are still possibilities to optimize the bottom gas stirring schemes. For the future green steelmaking routes, producing low-nitrogen steel grades, starting from low-carbon input materials such as Direct Reduced Iron (DRI) or electric smelter based hot metal, can be challenging—and therefore could potentially limit the production of high-quality steel grades. The present work includes a comprehensive review of the prior work done on nitrogen control in primary steelmaking. Both the fundamental mechanism and the industrial practices for nitrogen control in the current BOF and EAF (Electric Arc Furnace) routes are reviewed. Based on our current understanding, the potential nitrogen control scenarios under future green steelmaking operations are analyzed. The future green steelmaking practices covered in this work include the Direct Reduction Plant–Electric Smelting Furnace–Basic Oxygen furnace (DRP–ESF–BOF) route and the Electric Arc Furnace (EAF) route with inputs of scrap and virgin iron inputs like Direct Reduced Iron (DRI), Hot Briquetted Iron (HBI), Pig Iron (PI), and Hot Metal (HM). A summary of the possible nitrogen sources and their contents in various stages of steelmaking, along with the key operational parameters that enable minimization of dissolved nitrogen levels in steelmaking operations, is provided. The kinetics of nitrogen absorption and desorption and the relation between the kinetic parameters with change in operating conditions are discussed by giving specific examples based on the BOF process. The current study also investigates the impact of future DRP–ESF–BOF steelmaking route on nitrogen removal from the liquid melt by using simple thermodynamics and a BOF kinetic model. The study summarizes the existing kinetic models for predicting nitrogen behavior in liquid steel bath, which suggests potential improvement in the models and outlines necessary plant trials as future work to improve our understanding and control of nitrogen under the future green steelmaking practices.