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Hydrogen-based direct reduction of industrial iron ore pellets: Statistically designed experiments and computational simulation

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Abstract

As part of efforts to reduce anthropogenic CO2 emissions by the steelmaking industry, this study investigated the direct reduction of industrially produced hematite pellets with H2 using the Doehlert experimental design to evaluate the effect of pellet diameter (10.5–16.5 mm), porosity (0.36–0.44), and temperature (600–1200°C). A strong interactive effect between temperature and pellet size was observed, indicating that these variables cannot be considered independently. The increase in temperature and decrease in pellet size considerably favor the reduction rate, while porosity did not show a relevant effect. The change in pellet size during the reduction was negligible, except at elevated temperatures due to crack formation. A considerable decrease in mechanical strength at high temperatures suggests a maximum process operating temperature of 900°C. Good predictive capacity was achieved using the modified grain model to simulate the three consecutive non-catalytic gas—solid reactions, considering different pellet sizes and porosities, changes during the reaction from 800 to 900°C. However, for other temperatures, different mechanisms of structural modifications must be considered in the modeling. These results represent significant contributions to the development of ore pellets for CO2-free steelmaking technology.

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Abbreviations

1D:

One-dimensional space

ANOVA:

Analysis of variance

CL:

Calcination loss

DR:

Direct reduction

E1:

Extra reduction experiment 1

E2:

Extra reduction experiment 2

FEM:

Finite element method

GM:

Grain model

MIDREX:

Midland-ross direct iron reduction

SCM:

Shrinking core model

TGA:

Thermogravimetric analyzer

a :

Coefficients of the polynomial

A n :

Resistances due to chemical reactions n = 1, 2, 3, s/m

B n :

Resistances due to the diffusion of the reacted solid layer of n = 1 (magnetite), 2 (wustite), and 3 (iron), s/m

\({C_{{\rm{eq}}n,{{\rm{H}}_2}}}\) :

Equilibrium concentrations of H2 for each of reactions n = 1, 2, 3, mol/m3

C H, C M, C W, C Fe :

Concentration of hematite, magnetite, wustite, and iron, respectively, mol/m3

C i :

Concentration of specie i = H2 or H2O, mol/m3

C i,bulk :

Concentration bulk of specie i = H2 or H2O, mol/m3

d p d 0 :

Pellet initial diameter, mm

D effi :

Effective diffusivity of i = H2 or H2O, m2/s

D i :

Effective intraparticle diffusivity of i = H2 or H2O, m2/s

D i,j :

Effective intraparticle diffusivity of i = H2 or H2O, m2/s

D k i :

Knudsen diffusivity of i = H2 or H2O, m2/s

D m i :

Molecular diffusivity of i = H2 or H2O, m2/s

F :

Resistance of the gas film layer, s/m

K 0 :

Effective Knudsen parameter, m

k eq,n :

Equilibrium constant of H2 for reactions n = 1, 2, 3, [-]

k g :

Mass transfer coefficient through gaseous film, m/s

k n :

Reaction rate constant for reaction n = 1, 2, 3, m/s

M :

Molecular mass, g/mol

m 0 :

Initial mass of the pellet, g

m t :

Mass of the pellet at time t, g

m ∞ :

Final mass of the pellet, g

N :

Mol of the solid product formed by one mol of solid reagent

P :

Pressure, Pa

\(\bar R\) :

Gas constant, J·mol−1·K−1

R 2 :

Coefficient of determination, [-]

r :

Radial coordinate in the pellet, m

Re :

Reynolds number

r g :

Grain radius, m

r n :

Radius of the reaction interface within each grain n = 1, 2, 3, m

r n,0 :

Initial radius of the reaction interface within each grain n = 1, 2, 3, m

R n :

Reaction rate for reactions n = 1, 2, 3 mol·m−3·s−1

r p :

Pellet radius, m

Sc :

Schmidt number, [-]

Sh :

Sherwood number, [-]

T :

Temperature, K or °C

t :

Time, s

U k :

Measure experimental values for each factor k = 1, 2, 3, mm, °C, or [-]

U ′ k :

Nominal experimental values for each factor k = 1, 2, 3, mm, °C, or [-]

U 0 k :

Centred experimental values for each factor k = 1, 2, 3, mm, °C, or [-]

v i :

Stoichiometric coefficient

y :

Mole fraction [-]

Y q :

Response q, q = 1, 2, min or N/mm2

X n :

Fractional reduction for n = 1 (magnetite), 2 (wustite), and 3 (iron), [-]

x n :

Local fractional reduction for n = 1 (magnetite), 2 (wustite), and 3 (iron), [-]

X global :

Global fractional reduction of the pellet, [-]

Z k :

Real coded values for each factor k = 1, 2, 3, [-]

Z ′ k :

Nominal coded values for each factor k = 1, 2, 3, [-]

δ k :

Maximum code value of each factor k = 1, 2, 3

ΔU k :

Experimental step value, mm, °C, or [-]

ε :

Pellet porosity, [-]

ε 0, ε s,0, ε s :

Initial porosity of the pellet, initial porosity and predicted porosity of the solids s = H, M, W, Fe, respectively, [-]

ε M, ε w, ε Fe :

Porosity of the magnetite, wustite and iron, respectively, [-]

ε f, ε s,f :

Final porosity of the pellet, predicted final porosity of the solids s = H, M, W, Fe, [-]

ρ s,0 :

Initial true molar density of the s = H, M, W, Fe, mol/m3

ρ s,f :

Final true molar density of the s = H, M, W, Fe, mol/m3

σ :

Diffusion volume of simple molecule, cm3/mol

Φ 2 :

Thiele modulus, [-]

Note: [-]:

means the variables are dimensionless.

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Acknowledgements

The authors express their gratitude to Institute of Technological Research — IPT, Fundação de Amparo ã Pesquisa do Estado de São Paulo, Brazil [Process 2019/05840-3] and Conselho Nacional de Desenvolvimento Científico e Tecnológico, Brazil [Process 167470/2018-3].

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Authors and Affiliations

  1. Chemical Systems Engineering Center, Department of Chemical Engineering, University of São Paulo, São Paulo, 05508-900, Brazil

    Patrícia Metolina & Roberto Guardani

  2. Metallurgical Process Laboratory, Institute of Technological Research, São Paulo, 05508-901, Brazil

    Patrícia Metolina & Tiago Ramos Ribeiro

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  1. Patrícia Metolina
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  2. Tiago Ramos Ribeiro
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Correspondence to Patrícia Metolina.

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Metolina, P., Ribeiro, T.R. & Guardani, R. Hydrogen-based direct reduction of industrial iron ore pellets: Statistically designed experiments and computational simulation. Int J Miner Metall Mater 29, 1908–1921 (2022). https://doi.org/10.1007/s12613-022-2487-3

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