Behavior of Nitrogen During ADD Process

A computational model based on mass transfer and thermodynamic data as well as kinetic information from the industrial AOD process has been created in order to simulate the nitrogen content of the stainless steel melt as a function of blowing time. The model uses Butler's equation to calculate the reaction area available for nitrogen transfer between the steel and gas bubbles. Thermodynamic driving force is calculated as a function of temperature as well as stainless steel melt and gas compositions. According to the study effective surface area for nitrogen transfer achieved its maximum as well as thermodynamic driving force is also high during the 1st stage (absorption). During desorption effective reaction surface area is only approximately 7-9%. Typical initial nitrogen contents were about 400 ppm whereas the maximum values of 1000-1500 ppm were achieved before nitrogen argon switch-point. Simulations showed that desorption rate of nitrogen is low and final nitrogen contents below 400 ppm's are very difficult to be achieved economically. According to the simulations model predicts final nitrogen content of stainless steel melt after AOD process with 50 ppm accuracy.