Dynamic Model For Controlling The LD Process By Off-Gas Analyzing

Based on the metallurgical thermodynamics, kinetics and transport theory, the refining process of combined-blown converter is comprehensively investigated. The oxidation mechanism of the impurity elements in steel bath and the rate-control step in the oxidation process are analyzed. A dynamic mathematics model based on off-gas analysis to describe the refining process of converter is developed. The relationship between the carbon content and the off-gas flow rate and composition, and the relationship between the temperature and the carbon content and decarburization rate, the relationship between the oxygen content and the temperature and decarburization rate, the various impurity in the bath and the variations rules of the various impurity element, and the relation between the variation of the off-gas composition with the condition of BOF were obtained.The variations of the compositions and temperatures in the bath during refining process are calculated with the mathematics model. Good agreement between prediction and production result was obtained. Through adjusting the model parameters, the simulation of the relations between different oxygen supplying rates and the variations of compositions, and the relations between the initial condition and the oxygen distribution can be realized. The following conclusions are obtained according to the variation trends and characteristics of the off-gas compositions.(1) With mass balance, the variations of carbon content in the bath can be calculated accurately by the mathematic model based on the on-lined off-gas data. The hit rating can be reached 93% on the range±0.03% with moderating the relation parameter.(2) The bath temperature is a combined function of the carbon content and the decarburization rate. So the temperature variations can be monitored from time to time even under abnormal refining conditions through the abnormal off-gas compositions. The results of calculated coincides with the true temperature in the metal. The hit rating is 60% on the range±10℃,and can be reached 90% on the range±20℃.(3)It can be knew with the model that the product of oxygen content and carbon content, which is in the range of 0.0015-0.0060 during most of the refining time, is the combined function of the temperature and the pc o. It is hardly influenced by temperature, but varies mainly with the pc o, especially at the initial and at the end of point.(4) The oxygen content, a function of the temperature and the decarburization rate ,simulated by the model closed to that in liquid steel at the end point in combined-blown converter.(5) The variations curve with the time of Mn and P in the metal is similar with blowing time with the model .