Semi – dynamic model  
  
The above features make static control models inadequate. Hence improvements are required. Static model predictions can be improved by measurements on temperature and composition of slag and metal by a sub lance during the blow.

Immersion type sensors can also be used to measure carbon and oxygen concentration during the blow. All these data are collected and fed into the computer which compares the model predictions to suggest the action to be taken by the operator. These are semi-dynamic model. It must be noted that error in carbon measurement may need to over blow the heat when end carbon measured is greater than specified carbon. Also if end point carbon measured is lower than the specified, carburization has to be done in the ladle for carbon adjustment.

Determination of carbon by a sub lance is indirectly done by measuring the temperature of steel through a sample collected by the sub lance during the flow.

Dynamic Models

Static models do not calculate the variation of blowing parameters as a function of time. For this purpose continuous measurement of some representative parameter is required during the blow. In a preprogrammed model, these values are fed continuously and corrections can be done during the blow. Dynamic models contain all features of static model; in addition it includes reaction kinetics and process dynamics. In steelmaking major reactions are oxidation of carbon and iron.  In a dynamic model rate of decarburization and  consumed are determined from exit analysis. Computation of  is then done.

Dynamic control requires measurements continuously. Exit gas temperature and its composition can be measured continuously and the data can be fed to computer. From the exit gas composition and temperature carbon, oxygen in bath can be determined as a function of time. From carbon balance, decarburization rate can be determined. Oxygen balance provides the following information:

Enthalpy balance based on exit gas temperature and composition and amount gives information on energy leaving the system.

Slag height can also be determined by measuring the acoustic sound produced by the slag during the blow. Sonic meter measures the intensity of sound. Intensity of sound is fed to computer which in turn adjusts the lance height, oxygen flow rate and bottom stirring rate to control the slag/metal height.

It must be mentioned that large number of literature is available on the process control models in steelmaking. It is not possible to cover in one lecture. The interested reader may go through the references given at the end of the lecture. Some references are given. You may find more.