Yevgen Rizaev presents his M.Sc. thesis on "Phase-Field Modeling of Microstructure Effects on Direct Reduction of Iron Ore with Hydrogen"


Primary production of metallic iron accounts for a significant share of the industrial green-
house gas emissions, and an expected growth in the demand for steel motivates the search for
alternative sustainable ways of iron ore reduction. Hydrogen-based direct reduction is a very
promising alternative technology, currently under development, with which a cutback in CO2
emissions of up to 99% is envisaged. While several full-scale demonstration reactors are be-
ing constructed, significant differences between reaction kinetics of hydrogen and conventional
reduction agents on the pellet scale have been reported. Many underlying mechanisms of this
process are not well understood, inter alia which factors determine the rate-controlling step.
Several authors connect this lack of understanding with studies on microscopical processes be-
ing sparse, and suggest filling this knowledge gap to optimize the H2-based direct reduction
on the reactor scale. One of such gaps in modeling is the transport of reaction species in the
gaseous phase, usually assumed to be only due to diffusion. Motivated by the observation of
reaction speed being dependent on average pore size, a computational model for the gas-solid
reaction that includes advective transport of reaction components in the gaseous phase has been
developed in this work. Lattice-Boltzmann method, utilized for solving the advection-diffusion
problem in gas, has been coupled with the phase-field model, which is responsible for sim-
ulating the species transport in the solid phase. Simulation results have shown a noticeable
difference in reaction kinetics between systems with mass transport due to pure diffusion in the
gaseous phase and systems with dominated advection transport. The latter has faster overall
kinetics in the earlier stages of the reaction before a layer of reduced iron is formed between the
gas and the iron ore. Later, the oxygen transport in the solid towards the reaction site becomes a
rate-limiting step. However, in the considered systems, advection supplies less hydrogen from
the bulk gas to the pores if the flow develops in such a way that the bulk gas flows tangentially
to the inlets of the pores. Still, in both cases of mass transport in gas by only diffusion or mixed
advection-diffusion, porosity provides additional reaction sites and accelerates overall reduc-
tion kinetics. Taking backward reaction into account leads to chemical reaction becoming the
rate-limiting step and slowing down reaction kinetics in all the investigated simulation setups.