Study on the Pneumatic Lime Injection in the Electric Arc Furnace Process: An Evaluation on the Performance Benefits

Abstract

Over the years the production of steel through electric arc furnace (EAF) technology has increased more and more, allowing the EAF to compete more successfully with the integrated mills; to the will to reduce the amount of CO 2 and dust emission have further encouraged the steel production through this technology. In 2019, the EAF crude steel production reached 517 million tons, corresponding to the 27.7% of the worldwide production. [1] In Italy, the scrap-based route covers a crucial role with 37 EAF production sites and a crude steel production share of 82%. [2,3] The electric furnace process has evolved becoming a highly efficient scrap smelter, which integrate a technology able to improve energy using oxygen, gas, carbon, and lime injection. Generally, the lime charging procedure into the EAF is based on lime addition, in the form of lumps, directly within the scrap bucket through conveyor systems. This practice, however, has several issues related with lime emissions during the scrap bucket charging and an inadequate distribution of lime in the furnace, made possible instead by lime injection. [4] In recent years, the usage of pneumatic injection of lime in EAFs, due to its surprising results in terms of reduction of the specific raw material consumption, foaming benefits, operational cost benefits, and improvement in environmental aspects, has acquired interest as a viable technology for the steelmaking industry. [5] Acciaierie di Calvisano steelmaking plant, in collaboration with Unicalce S.p.A., decided to upgrade its EAF, implementing a new system of lime delivering, in place of the traditional procedure. Combining carbon and lime powder injectors, the lances are able to create a homogeneous layer of foamy slag over the whole metal bath surface. The addition of lime is essential for the proper bath chemistry and the slag foaming practice, which offers an increased energy efficiency of the furnace, since the heat from the arc is captured by the slag; a protection of the water panels and the roof from radiation and a decreased noise pollution and low nitrogen incorporation in the steel are

Influence of the Recirculation of Various by-products Generated through Electric Arc Furnace Route on EAF Slag Quality

“…Slags from shop A are characterized by wustite, larnite and brownmillerite, and to a lesser extent of chromite, being characterized by high binary basicity index (from 2.5 to 3.5) and significant iron oxide fraction. 21,22) This is also confirmed by the SEM analysis presented in the next paragraph. Samples B are mainly formed by akermanite-gehlenite, kirschsteinite and wustite.…”

Future Scenarios for Reducing Emissions and Consumption in the Italian Steelmaking Industry

“…[10][11][12] Lime is usually introduced in the process to obtain a proper bath chemistry and achieve the so called "slag foaming practice," which allows an increase of the energy efficiency of the furnace. [18,19] The heating is provided by a synergic work of the arc and the chemical reactions that take place during the melting. The electric arc provides an average energy of 360-420 kWh/t STEEL .…”

“…[ 10–12 ] Lime is usually introduced in the process to obtain a proper bath chemistry and achieve the so called “slag foaming practice,” which allows an increase of the energy efficiency of the furnace. [ 18,19 ]…”