Characteristic feature of converter steelmaking

Supply of oxygen in the form of free gas jet is an important feature of converter steelmaking both in pure and different versions of combined blown ones. In this form of oxygen supply, the total time of blowing of oxygen is almost independent of converter capacity, oxygen blowing rate and bottom stirring. This was reflected by evaluating dimensionless momentum flow rate vs. ratio of time of blowing  blowing time   for different converter capacities ranging from 40-400 tons. (See reference at the end). Dimensionless momentum flow rate was correlated as

 

Where

It is illustrated in lecture 13 that dimensionless momentum flow rate describes the action of free oxygen jet produced by constant volume flow rate of oxygen at various lance distances. The dimensionless momentum flow rate number increases with the decrease in lance distance. Decrease in lance distance makes the blow hard and increase in lance distance makes the blow soft. Lance profile can be considered to generate soft blow initially and progressively harder blow with the progress of the blow.

The fundamental requirements of the lance profile in all converter steelmaking are formation of FeO rich slag in the initial stage and then removal of carbon and phosphorus by progressively increasing the availability of oxygen in the bath to avoid over oxidation of slag. The first requirement is achieved by “soft blow” (shallow penetration of jet) and the other requirement is achieved by hardening the blow (deep penetration of jet into bath) progressively. Thus soft and hard blow are essential requirement of refining of hot metal by impinging oxygen jet irrespective of the converter capacity and type of converter steelmaking practices (pure top blowing combined blowing) as a result the total oxygen blow time remains more or less same.

Environmental issues in oxygen steelmaking  

• Control of emissions during transfer of hot metal to desulphurization station.
• Disposition of slag
• Capture and removal of contaminants in hot and dirty exit gas from the converter.
• Particulate matter exiting with the exit gas.
• Emission of CO. for this purpose sufficient excess air must be used at the hood to burn CO.

Causes of high turnover rates of BOF

• Energetic supply of oxygen: This method ensures.
• Availability of oxygen where it is needed during refining
• Faster mechanism of mass transfer by producing droplets and slag/metal emulsion.
• Bottom stirring
• A basic and limy slag of required basicity is formed at the early stages of the blow.