Numerical Investigation of Alternative Fuel Combustion in a Cement Riser Duct Considering Tertiary Air Injection Locations

This study presents a numerical investigation of alternative-fuel combustion in the riser duct of a cement clinker production installation, with particular emphasis on the locations of the tertiary-air inlets. Computational fluid dynamics (CFD) was used to identify favorable tertiary-air inlet positions and establish an appropriate configuration for subsequent analyses of combustion and calcination processes. The numerical model was developed using an Eulerian–Lagrangian approach, in which the gas phase was described within an Eulerian framework and the motion of solid particles was tracked using a Lagrangian approach. The model incorporates the standard k–ε turbulence model, heat-transfer mechanisms, and the P1 radiation model. At this stage of the study, simplified fuel properties were assumed, whereas limestone-meal particles and their calcination were included in the numerical model to provide a more realistic representation of the thermal and physicochemical conditions within the industrial riser duct. The CFD simulations enabled the determination of velocity fields, temperature distributions, and gas-flow structures inside the riser duct. Particular attention was devoted to the recirculation zones and mixing conditions resulting from the different tertiary-air injection configurations. The results demonstrate that the locations of the tertiary-air inlets significantly influence the combustion environment and may affect the subsequent calcination process and the overall thermal efficiency of the installation. The proposed numerical approach provides a basis for the further development of advanced multiphase models incorporating more detailed representations of alternative-fuel conversion, calcination kinetics, and pollutant formation in modern cement kiln systems.