Mathematical Modeling of Nitrogen Removal from the Vacuum Tank Degasser

Abstract

The removal of nitrogen from an industrial vacuum tank degasser depends on a series of operational parameters, steel composition, and contents of surface-active elements in liquid steel, e.g., oxygen and sulfur. The effect of some specific elements on nitrogen removal in the vacuum degasser has been (well) examined. Still, it is quite challenging to assess the overall effect of the whole steel composition on the process. The focus of the present work was to predict nitrogen removal from the vacuum degasser specially taking into account the multi-component effect of steel composition. An integrated computational fluid dynamics (CFD) model for simulating nitrogen (and hydrogen) removal in industrial vacuum tank degassers was therefore developed based on theories and methods that are relatively separate in the literature. In order to include the multi-component effect, the model is coupled with an in-house thermodynamics code that can be used to determine the activity coefficient of nitrogen, oxygen, or sulfur as a function of steel composition and temperature. The code was verified by comparing the calculated activity coefficients against experimental measurements from various sources. Efforts were also put into developing an on-line use concept to control the nitrogen removal. The gas plume, flow field, and evolutions of nitrogen and hydrogen during vacuum treatment were predicted and the on-line concept was demonstrated by presenting two operating diagrams. The results showed that the final nitrogen content decreases with an increase in the chemical reaction rate constant and a decrease in the initial nitrogen content. By contrary, the final nitrogen content increases with a decrease in the chemical reaction rate constant and an increase in the initial nitrogen content. Finally, the operating diagrams were validated by industrial data and observations.

Efficiently Removing Hydrogen of H-Supersaturated Liquid Steel in the Vacuum Degasser with Various Gas Injection Modes

“…In the steel industry, the hydrogen degassing from liquid steel is usually achieved in an exclusive vacuum-degassing apparatus, such as VD or Ruhrstahl-Heraeus (RH), in which liquid steel is subjected to a combination of low pressure and argon-purging, and as a result, the dissolved hydrogen can be considerably reduced. In this direction, a great number of studies [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] have been performed to reveal the dehydrogenation behavior of liquid steel based on the thermodynamics and kinetics related to hydrogen removal in an industrial RH or VD by employing an industrial test or Computational Fluid Dynamics techniques. Steneholm et al [11] calculated the removal rates of sulfur, hydrogen, and nitrogen by collecting slag and steel samples before and after the vacuum treatment.…”

A Review of Physical and Numerical Approaches for the Study of Gas Stirring in Ladle Metallurgy

“…Based on previous work on the E-E model, the simultaneous reaction model (SRM) coded by these researchers was added to investigate the metal-slag reactions. In contrast, Yu et al [118][119][120][121][122] mainly focused on investigating the dehydrogenation and denitrogenation behaviors in an industrial vacuum tank degasser with different operating conditions. A recent work by Li et al [39] used the PBM to calculate the bubble size distribution affected by the coalescence and breakage in the plume.…”

An Integrated Methodology for Rule Extraction from ELM-Based Vacuum Tank Degasser Multiclassifier for Decision-Making

“…As the most critical step in the secondary steelmaking process, the VTD has been extensively studied through using various approaches with the goal of better understanding the cause-effect relationships of the vacuum degassing process. Several mathematical models of VTD refining have been developed [1][2][3]. These models were formulated on the basis of differential equations to describe chemical/physical reactions during the production process in the ladle.…”

“…These models were formulated on the basis of differential equations to describe chemical/physical reactions during the production process in the ladle. These mathematical models are local models, dehydrogenation [2] or denitrogenation [3], which depict only part of the property, so it is extremely hard to forecast the temperature of liquid steel using these kinds of white-box models.…”