Coupled Multiphysics Transport-Reaction Modeling Framework for Combustion Synthesis of Cement Phases: Insights into β-C ₂ S Formation and Wavefront Dynamics

Biofuel-based combustion synthesis (BCS) processes offer low-temperature, low-carbon routes to lime and clinker production. However, they involve tightly coupled interactions between heat transfer, gas flow, and sequential solid-state reactions within reactive pellets. Experiments typically provide surface temperature evolution and final phase assemblages but give limited insight into the conversion process and the interaction between composition and process conditions. A coupled transport-reaction framework is developed here to resolve this limitation─the synthesis of β-C 2 S (belite), a major cementing phase, serving as an example. Transient conservation equations for energy, momentum, and species are solved for a porous pellet exchanging heat and mass with the furnace gas, alongside kinetic rate equations for fuel combustion, limestone calcination, and clinker-forming reactions. Kinetic parameters for fuel combustion are calibrated using dedicated experiments, and simulations are validated against measured surface temperature evolution and final phase assemblages. Furthermore, a novel wavefront propagation analysis quantifies velocities and spatial coverage of thermal, combustion, calcination, and synthesis fronts. The model reveals that internal pellet temperatures can exceed 1200 °C, enabling robust belite formation. Belite synthesis is found to be dictated by the competition between heat generation and losses than the peak temperature generated. Results indicate that a high fuel content (60% by mass) combined with a moderate porosity (∼10%) produces the optimal composition. Ultimately, the product yield is uniquely correlated to the spatial area covered by the propagating synthesis wavefront, with optimal compositions effectively covering ∼75% of the pellet cross-section. The modular treatment of transport and kinetics makes the framework extensible to other transport-reaction processes in porous media.