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The vacuum tank degassing or VD process is used to remove carbon, hydrogen, nitrogen and sulphur from steel melts. At many degassers it is not possible to carry out measurements and sampling under vacuum. This has led to the development of a dynamic process model, based on thermodynamics and reaction kinetics, for observing the current process status on-line. It includes the calculation of C, O, H, N and S contents and of the steel temperature. The model has been verified within the scope of several research projects with the aid of process data from numerous vacuum tank degassers.
At present the model is being used on-line to calculate the liquid steel's hydrogen content and thereby determine individually, for each melt, the point in time when the required end content has been reached and the vacuum treatment can consequently be terminated. Thus a measurement of the attained hydrogen content, which is expensive and error-prone, is no more necessary.
Accuracy of the process model
(standard deviation of the modelling error)
Carbon content Oxygen content
prior to deoxidation
Nitrogen content
Hydrogen content |
8 ppm
50 ppm
8 ppm 0.25 ppm |
| Temperature |
7 K |
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Structure of the process model and required input variables
 Example: On-line observation for calculating the hydrogen content and steel temperature |
