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The vacuum circulation or RH process is widely used to produce ultra-low carbon steels. Besides decarburisation, it also comprises hydrogen and nitrogen removal under vacuum. The course of the decarburisation treatment can be observed, in principle, on the basis of off-gas measurement data, while this is not possible for the removal of nitrogen and hydrogen.
This has led to the development of a dynamic process model based on thermodynamics and reaction kinetics. It includes the calculation of the C, O, H, and N contents and of the steel temperature. With the aid of the model it is possible to simulate and analyse the process behaviour as a means of optimising the design and operation of RH degassers.
The model is utilised for the on-line observation of the current process status and for predicting the course of the treatment. This prediction serves as the basis for calculating set-points for the supply of oxygen via a lance or tuyeres for the purpose of forced decarburisation and chemical heating.
Accuracy of the process model
(standard deviation of the modelling error)
Carbon content
Oxygen content prior to
deoxidation
Nitrogen content
Hydrogen content |
6 ppm
30 ppm
8 ppm
0.2ppm |
| Temperature |
5 K |
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Structure of the process model and required input variables
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