Speaker
Description
The steel industry is responsible for about 10% of the worlds CO2 emissions. As steel remains indispensable in our current and future society, the steel industry needs to make a rapid shift towards green steel production. Iron is the core ingredient of steel, and most of it is made by iron-making blast furnaces. The green steel production route will use a Direct Reduction Plant (DRP) in which iron ore will be reduced to iron using hydrogen or a mixture of natural gas and hydrogen.
These Direct Reduced Iron (DRI) pellets are more prone to breakage than the Blast Furnace Iron (BFI) pellets, since the DRP does not have cokes reinforcing the pellet bed and the DRI pellets are much more porous. For accurate reduction and fracture predictions, a transient 3-D single-pellet model is made, to be able to handle multicomponent mass-transfer, dynamic boundary conditions, solid-phase transformation and pellet breakage. A first step towards this goal is taken with the development of a 1-D model, with a focus on the reduction process and mass transfer, while neglecting pellet breakage. The reduction process of iron oxide to iron is complex, as it can involve up to five co-existing solid phases, a changing pellet morphology, multicomponent mass-transfer and reaction kinetics that depend heavily on the reactor conditions, thus requiring a multi-scale approach. An additional challenge is the limitation in experimental possibilities, where it is particularly difficult to isolate the effects of the previously mentioned phenomena.
Using a transient 1-D Finite-Difference approach, the direct reduction of an iron ore pellet is modelled. Syngas or methane gas is used as a reduction agent, where a multicomponent gas mixture (H2 – CO – H2O – CO2 – N2) is modeled using the Dusty Gas Model (DGM), accounting for concentration and pressure driven flow. The DGM is compared to the Wilke-Lee mixture diffusion model, in which a flux correction was applied to ensure mass conservation. Morphology evolution is implemented as the local change in porosity, and all oxidation/reduction states are solved for and tracked. Dynamic boundary conditions are applied to simulate realistic DRP conditions, and carburization reactions caused by the CO-CO2 system are included. The effect of cross-diffusion on the internal reduction profile under different conditions is investigated, as well as the importance of considering the radial molar profile of gas and solid phases. Issues with fitting and implementation of apparent kinetic rate constants are addressed, and an alternative approach is presented using more intrinsic rate constants. The model is validated against existing literature and experimental data.
| Country | Netherlands |
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