Gerdau Midlothian Successfully Starts Up Lime/Dololime Sidewall Injection System from MORE
Gerdau Midlothian operates a technologically advanced steel mill that produces over 2 million tons per year of bar and structural steel products by recycling scrap steel recovered from life-expired automobiles via the largest and most productive shredded facility in the world. The site has two electric arc furnaces (EAF A=134 t/151 st; EAF B=141 t /156 st) with continuous casters, a bar mill, a structural mill, and a large beam mill that enables the company to produce a broader array of steel products than traditional mini mills. Production includes beams, reinforcing bars, special bar quality rounds, channels, and merchant quality rounds.
In 2012 Gerdau Midlothian awarded MORE for the supply of the complete chemical injection system (oxygen, carbon and lime injection) for both EAFs. The first step of the project was the supply of MORE pneumatic lime/dololime injection system includes four MOLI dispensers each of 3000 liters/792 gal capacity for pneumatic injection of lime and dololime from the storage silos to the EAFs; two LIMEJET units for each EAF shell (one for lime and one for dololime pneumatic injection); oxygen and natural gas valves stands. The LIMEJET is a combined 4 MW burner/lime injector with innovative MSF-Mixed Swirl Flame technology for high efficiency scrap melting and lime injection.
MORE has also supplied the innovative SOS-Slag Optimization Software that calculates the isothermal stability diagram (ISD) for a particular slag composition, where the conditions for optimum slag foaming can be achieved. Based on the slag chemical analysis received from the slag analyzer and the target of the slag basicity/FeO percent, it calculates the quantity of fluxes that should be added to the current melting process in order to keep the slag within targets of basicity, FeO, MnO and MgO saturation optimizing the material consumption. Lime injection, when associated with oxygen and carbon injection, delivers the best benefits especially when injected during last scrap bucket meltdown and during superheat. This practice favors refractory side bank protection and steady slag foaming and viscosity control. Injection of lime, into the slag, increases substantially its recovery and the use of fine particles makes the solution faster and more reactive. It must also be mentioned that injection of powder reactants will generate a much cleaner shop environment and the abandonment of dusty, maintenance demanding belt conveyor handling system.
Before the installation of MORE lime/dololime pneumatic injection system, the material was charged via conveyor belts from the fifth hole. Now with MORE system in operation, there has been a dramatic increase of injected material and foaming slag is stable and repeatable. Moreover, thanks to the precise MOLI transportation air flow control system, the material is able to be transferred to the LIMEJET injectors from the main silos installed more than 90 m (295 ft) from the EAF.
With MORE pneumatic lime injection, there has been a decrease of 3% on the electrical energy consumption and a 7% decrease of power-on time.
This project reconfirms MORE as a reliable and innovative manufacturer of equipment needed in the steelmaking industry. Presently, MORE has a scorecard of 52 lime/dololime pneumatic transportation/injection systems in operation or under manufacturing worldwide.