To understand the turbulent flow and mass transfer occurring inside a continuous casting (CC) mold machine, a multiphase CFD model is currently under development. This model will be used in subsequent studies to calculate the mass transfer coefficients of different species across the interface between liquid steel and slag. Those coefficients are necessary to predict slag composition and viscosity during the casting of steels. To validate the CFD model, some investigations to measure the velocity field in the region close to the interface, where the mass transfer between liquid steel and slag takes place, were carried out. Three fluids were considered, respecting main similarity criteria but not all: water to simulate the liquid steel, silicon oil to simulate the melted flux powder and air in the atmosphere domain. The velocity field was obtained by means of a Laser Doppler Anemometry (LDA) technique in the CC water model. Some parameters were evaluated regarding their effects on the interface behavior. Two different kinematic viscosities of oil were tested: 20 and 350 cSt. To evaluate the effect of water flow rate, it was set two flow rates: 1.6 and 2.0 m³/h. Oil layer thickness was either 4 mm or 15 mm. It was observed that slag viscosity has a strong effect on the flow near the interface: with the most viscous oil, the interface tangential velocity gradient in water was increased. The increase of shear stresses with the water flow rate was also quantified, which is important to better assess the possibility of slag entrainment during the casting.
The pressure to reduce greenhouse gas (GHG) emissions in the steel industry is resulting in a massive transformation in the traditional way steel is produced. Many steel players are paving the road to large investments for shifting from the blast furnace (BF) and basic oxygen furnace (BF-BOF) route towards the direct reduction (DR) with electric furnaces (DR-EAF) for primary steel production. The implementation of this route shifting assumes that direct reduction reactors can be adapted to operate with increasingly hydrogen enriched natural gas, as low-carbon hydrogen becomes available. Another key assumption most steelmakers are using to support their decisions is that, prior to using green hydrogen, they will be able to use blue hydrogen produced from steam methane reforming with carbon capture and storage, the so-called blue hydrogen. This assumption is supported by the allegation that blue hydrogen is a lower CO2 equivalent emitter than the traditional natural gas used in the direct reduction processes. However, life cycle assessments of blue hydrogen production have shown that blue hydrogen may only be about 10% less polluting than natural gas, due to the inefficiencies associated with the carbon capture systems, and upstream and downstream methane leakage. In this paper, the GHG footprints of different decarbonization alternatives for the steel industry are evaluated. One important conclusion is that the generally accepted reduction claim of 43% in CO2eq emission from the migration of BF-BOF route to natural gas-based DR-EAF (NG-DRI-EAF) may be reduced to only 22%, when methane leakage is considered. Hence, only DR-EAF with green hydrogen and renewable energy supply could lead to the production of truly low GHG footprint steel, with less than 600kg of CO2eq emission per ton of crude steel.
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