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Volume 112
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Effect of particle agglomeration in iron oxide reduction – A CFD-DEM approach (Open Access)
Juan G. Ramírez a b, Y. Tang a c, Martin van Sint Annaland a b, Niels G. Deen a c, Ivo Roghair a b d *
a Eindhoven Institute for Renewable Energy Systems (EIRES), Eindhoven University of Technology, Eindhoven, the Netherlands
b Chemical Process Intensification, Department of Chemical Engineering & Chemistry, Eindhoven University of Technology, Eindhoven, the Netherlands
c Power and Flow Group, Department of Mechanical Engineering, Eindhoven University of Technology, Eindhoven, the Netherlands
d Complex Fluids and Interfaces, Department of Chemical Engineering & Chemistry, Eindhoven University of Technology, Eindhoven, the Netherlands
10.1016/j.partic.2026.02.026
Volume 112, May 2026, Pages 260-270
Received 3 December 2025, Revised 6 February 2026, Accepted 24 February 2026, Available online 13 March 2026, Version of Record 26 March 2026.
E-mail: i.roghair@tue.nl
Highlights

• A sintering model and iron reduction kinetics are integrated into a CFD-DEM framework.

• Agglomeration effects on reduction efficiency were studied for inflow temperatures ranging from 630 °Cto 980 °C.

• Temperatures above 630 °C cause rapid defluidization due to particle sintering.

• Above 770 °C, sintering lowers reduction efficiency by over 20 %.

• Sintering-driven channeling increases significantly the product heterogeneity.


Abstract

Iron powders are a promising carbon-neutral energy carrier via closed oxidation-reduction cycles, offering a unique solution to long-duration storage and long-distance transport of renewable energy. After releasing energy through oxidation, the iron must be regenerated (reduced) from the oxidation product (iron oxide), ideally using renewable energy sources such as green hydrogen. However, this high-temperature reduction process, typically carried out in fluidized beds, is strongly hindered by particle agglomeration caused by sintering of solid materials at elevated temperatures. In this work, a Computational Fluid Dynamics–Discrete Element Method (CFD-DEM) framework is employed to investigate how agglomeration affects reduction efficiency at different operating temperatures. Chemical reduction is modeled using a shrinking-core formulation, while sintering is represented through a solid-bridge model based on surface-diffusion mechanisms. The results show that operating temperatures above 630 °C lead to rapid defluidization. If the temperature is increased beyond 840 °C, the overall reduction degree is decreased, despite the higher reactivity. This is due to intensified sintering. This behavior is likely linked to gas channeling within the bed, which not only lowers reduction efficiency (by more than 20% for T > 840 °C) but also significantly increases the heterogeneity in the final reduction state of the product.

Graphical abstract
Keywords
Direct reduced iron; Sintering; Fluidized beds; CFD-DEM; Shrinking core model; Metal fuels
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