Static Model

Static models are based on materials and heat balance by considering initial and final states of reactants. In the material balance, mass of all input and output elements is considered. Once mass balance is done then heat balance is done.

Sensible heat of all inputs+ Heat produced or absorbed by oxidation reaction= Heat taken out by steel, slag and exit gases and fumes+ heat losses from the converter mouth and through the lining of the converter+ any other heat losses

In making materials and heat balance some assumptions may be required for example

• iron loss in slag,
• carbon removal in the form of CO,
• complete dissolution of CaO in slag
• basicity of slag
• thermo-physical and thermo-chemical properties of slag and metal

The above are some of the assumptions, further may be added.

By coupling of mass and balance one can predict

i)   Quantity of hot metal and scrap

ii)   Amount of flux

iii)  Total quantity of oxygen required to be blown.

iv)   Amount of slag produced

v)   Volume of exit gases

It is very much important that the prediction based upon the model is verified by the actual plant data. Tuning of the model is necessary because the predictions are based on equilibrium considerations and uncertainties due to simplified assumptions.

Reliability of predictions increases when the predictions of the model are compared with the plant data for large number of heats. Statistical correlations can be developed and used to fine tune the model. For this purpose it is of utmost necessary to collect the reliable data from the reliable instruments

BOF steelmaking is a stochastic process. Oxygen blowing produces lot of turbulent in the phases during hot metal refining. The amount of droplets emulsified in the slag, amount of lime dissolution, carbon removal rate, intensity of oxygen jet impinging the bath, lance distance, bottom stirring rate due to plugging of tuyeres etc.  may vary from one heat to the other. The error in predictions may be due to

i)    Error in weighing

ii)   Differences in lime dissolution from one heat to the other

iii)  Effect of size of scrap on its dissolution. Large size will take more time to dissolve as compared       with smaller ones.

iv)  State of foaming of slag and entrained metal droplets in slag. This may vary from one  heat to other       due to behavior of oxygen jet in a dynamic surrounding as discussed in     lecture 13. Surrounding of       oxygen jet changes during the blow. As a result extent and magnitude of slag/metal reactions       might change.

v)  Converter lining profile due to wear.

vi)  Extent of mixing within the phases and between the phases.