Usage of Chemical Energy  

The high electrical energy costs pushed EAF steelmakers to look for alternative energy sources. One such source is the chemical energy derived from chemical reactions. In recent years the chemical energy supply amounts to 35% to 40% of the total energy in most of the modern EAFs. (See figure 16.3)



    i) Oxidation reactions

The main oxidation reactions are oxidation of iron and carbon besides oxidation of silicon and manganese. The oxidation of iron though generates more energy than oxidation of carbon but iron oxidation results in loss in productivity.

	Heat contant
	Heat contant

Hence oxygen injection must be controlled such that iron oxidation is kept minimum. For bath carbon levels above , all oxygen reacts with carbon to produce . Below , the efficiency of carbon oxidation to form drops and more and more  is generated in the slag.

For scrap carbon levels below  levels in the slag can be quite high and represents an unavoidable yield loss. Increased carbon injection is necessary to control slag  levels and to prevent excessive refractory wear. Efficiency of heat transfer from oxidation reactions is extremely high due to the fact that these reactions are occurring in the bath. Greater penetrability of oxygen jet ensures the occurrence of oxidation reactions in the bath.

    ii) Post combustion

It is a practice of generating additional energy for melting steel by using the right amount of extra oxygen to combust  and  which evolve within the EAF. Carbon monoxide is generated in an EAF by

• Partially combusted hydrocarbons entering the furnace with the scrap
• Combustion of charged and injected carbon via  
• The reduction of  by carbon during slag foaming
  
  

Hydrogen is generated by:

• The cracking of hydrocarbons (oil in scrap, methane)
• The reduction of water:  or

In EAF, carbon monoxide and hydrogen may be available at the freeboard, whereas the foaming slag contains carbon- monoxide. It must be noted that oxygen flow should have low velocity to promote mixing with the furnace gases and to avoid scrap oxidation and rebound of oxygen from the scrap to the water cooled panels. Post combustion in the slag typically aims at combustion of 20 to 30% of the  generated in slag and 70 – 80% at the free board.

For post combustion speed of oxygen injection must be low and also uniform distribution of oxygen is required.


        iii)     Oxy – fuel burner

Oxy-fuel burner uses natural gas or oil, together with pure oxygen to produce an extremely high flame temperature. Oxy- fuel burners are used to melt unmelted scrap between the electrodes and to provide heat to cold spot. On most modern UHP furnaces, the primary function of burners is to provide heat to cold spots to ensure even scrap melting and to decrease the melting time necessary to reach a flat bath. Typically industry practice indicates that 0.133 MW of burner rating should be supplied per ton of furnace capacity. Others recommend  of burner power to eliminate cold spots in a UHP furnace and 50 to  of burner power for low powered furnaces.