Slag foaming:

Foam is a dispersion of gas bubbles in a liquid. A liquid is said to be foaming when gas bubbles could not escape through the liquid and as a result height of the liquid increases. In steelmaking, slag foaming can occur due to the following reactions:

                                                                                  
This reaction occurs within the slag. The other reaction

 
                                                                                                    
This reaction occurs at the gas/metal interface. In both the cases when the CO gas bubbles are unable to escape through the slag, the slag is said to be foaming. If the reaction between carbon and oxygen occurs deep into the bath i.e. reaction 2 then gas bubbles have enough time to grow in size and can easily escape through the slag layer as compared to when the gas bubbles are produced by reaction 2. The reaction 2 occurs within the slag

Is slag foaming desirable? Yes to the extent that slag should not flow out of the reactor. Slag foaming enhances the reaction area. In electric steelmaking foamy slag practice prevents the transfer of heat of the arch to the refractory lining.

Operational advantages: A foaming slag

• Shields molten steel against atmospheric oxidation
• Acts as a thermal barrier to prevent heat losses
• Shields the refractory lining particularly in electric arc furnace
• Control heat transfer from the post combustion flame