Background/aims: One main purpose of vacuum degassing is the removal of nitrogen and hydrogen from the liquid steel. The progress of dehydrogenation and denitrogenation during degassing cannot be observed on‐line from measured waste gas values. It is therefore usual to elongate the vacuum treatment more than necessary to be sure that the aim values are reached. To overcome the uncertainty in the required degassing duration, a dynamic process model for dehydrogenation and denitrogenation was developed. Results and conclusions: The dynamic process model for denitrogenation and dehydrogenation is based on the principles of thermodynamics and reaction kinetics. It was applied to the vacuum tank degassing (VD) and the vacuum circulation (RH) process. The model was validated by comparison of simulation results with measured process data. The resulting simulation accuracy is about 8 ppm for nitrogen and 0.2 ppm for hydrogen. A simplified version of the process model is used for on‐line observation of the current nitrogen and hydrogen content.

A dynamic matbematical model of the vacuum circulation process for steel decarburization was developed. [t comprises the process parts of steel circulation decarburization reaction, adjustment of vessel pressure with its influence on the carbon equilibrium content, and the oxygen pickup from the ladle slag. The model allows to simulate the behaviour of all important process values with good accuracy and can be used for optimization of plant construction and operation as well as for improvement of process control.

Based on the principles of thermodynamics and reaction kinetics, a dynamic model for the vacuum circulation (RH) process was developed. It comprises decarburisation, oxygen removal, dehydrogenation, denitrogenation and the course of steel temperature. The process model was validated by comparison of simulation results with measured process data from the RH/1 plant of Voest Alpine Stahl Linz (VASL). At this plant, it is used for on-line observation of the contents of carbon, oxygen, hydrogen and nitrogen as well as the steel temperature. Based on cyclically measured values of vessel pressure, lift gas flow rate as well as waste gas flow rate and composition, the current heat status is calculated reliably. The accuracy of the carbon balance with measured waste gas values was improved remarkably by a model-based correction calculation. The on-line process observation system provides the operator with valuable information on the progress of vacuum treatment. Dynamisches Modell zur on-Iine-Beobachtung des aktuellen ProzeBzustands wiihrend derEntgasung in der RH-Anlage. Basierend auf thermodynamischen und reaktionskinetischen Grundlagen wurde ein dynamisches Modell tur die Vakuum-Umlauf-(RH-) Entgasung entwickelt. Es umfaBt die Entkohlung, den Sauerstoffabbau, die Dehydrierung, die Entstickung und den Verlauf der Stahltemperatur. Das ProzeBmodell wurde uber den Vergleich von Simulationsergebnissen mit ProzeBmeBwerten der RH/1-Anlage der Voest Alpine Stahl Linz verifiziert. An dieser Anlage wird das Modell zur on-line-Beobachtung der Gehalte von Kohlenstoff, Sauerstoff, Wasserstoff und Stickstoff sowie der Stahltemperatur genutzt. Anhand der zyklisch erlaBten MeBwerte fur GefaBdruck, F6rdergasdurchfluB sowie Abgas-durchfluB und -analyse wird der aktuelle ProzeBzustand zuvsrlasslq berechnet. Die Genauigkeit der Kohlenstoffbilanz uber die Abgas-meBwerte konnte durch eine modellbasierte Korrekturrechnung deutlich verbessert werden. Die on-line-ProzeBbeobachtung stellt dem Bediener Informationen uber den Verlauf der Vakuumbehandlung zur Verfuqunq.

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