Heat-flux-based 1D–3D coupling of combustion and heat transfer in rotary kilns

Rotary kilns involve strongly coupled combustion, radiation, and gas–solid heat transfer, yet most existing models rely on prescribed gas-temperature profiles, leading to inconsistencies in predicting bed thermal response and clinker formation. This study develops an OpenFOAM-based heat-flux–driven 1D–3D coupled framework, in which pulverized-fuel combustion is resolved in a 3D Eulerian–Lagrangian CFD domain and the clinker bed/wall response is modeled through an embedded 1D formulation. Unlike approaches that prescribe an axial gas-temperature profile, the present framework transfers CFD-resolved convective and radiative heat fluxes to the embedded bed/wall balances and returns the updated boundary temperatures to the 3D domain. A Robin-type semi-implicit interface treatment preserves the separate convective and radiative forcing, and the coupled fields are iterated within each solution step. The coupled simulations reveal a radiation-dominated heat-transfer regime in the sintering zone, where radiative flux accounts for the majority of energy transfer from the freeboard to the bed. A pronounced axial thermal lag between gas and solid phases is identified, together with local heat-flux reversal near the burner induced by jet–shear–recirculation structures. These effects are shown to govern the spatial heterogeneity of temperature and reaction environments. The predicted kiln-tail gas composition, shell-temperature trend, and clinker-outlet temperature are consistent with the available plant measurements. The proposed approach provides a physically consistent basis for rotary-kiln thermal diagnostics and offers a generalizable strategy for coupling multiphase reacting flows with embedded process models.