A variety of lime products are used in the production of steel. Melting of scrap and DRI in an electric arc furnace (EAF), creates oxides that are detrimental to refractory performance and energy consumption. Lime is critical in producing a slag through the “mass balance” approach to assure the correct chemistry for the ideal slag basicity.
In the EAF process, it is common to see high calcium pebble lime and dolomitic pebble lime being charged through the roof, over the roof in a bucket or injection lime through the sidewall using a “co-jet” type injection directly into the slag/metal interface for optimization of foamy slag characteristics and refractory protection.
Electric arc furnace steel production accounts for 60% of all steel produced in the United States. Electrical consumption for a million tons per year plant is approximately the same as a small city.
- High Calcium pebble lime is key to neutralizing “acid oxides” from the oxidation of silicon and aluminum in scrap during melting. It is the CaO/SiO2 relationship that influences the MgO demand of the slag.
- Dolomitic pebble lime additions provide the MgO saturation for basicity conditions to provide the refractory protection and foamy slag performance for reduction of energy in the EAF. The slag contains dissolved calcium compounds and acidic compounds that cause MgO to dissolve from refractory brick into the slag. MgO will dissolve into the slag based on relationships of FeO content, basicity and temperature. The lower the slag basicity, the higher the MgO requirement for slag.
- FerroDolime is a specialized product that provides the same benefits as dolomitic lime but due to the di-calcium ferrite coating on the pebble it provides additional environmental benefits due to its mechanical strength from the coating and provides protection from hydration.
- Injectolime has a specific sizing for high calcium lime and dolomitic lime that is finer than pebble lime. This provides faster dissolution and accurate additions without losses through the emission evacuation system in the EAF. This technology is replacing the older lime charging systems and is environmentally beneficial.