Optimization of Burnout Air Parameters in a Large-Scale Biomass Grate Boiler: A CFD Study with Engineering Validation

Under the context of carbon neutrality, optimizing biomass boiler efficiency is crucial. This study employed Computational Fluid Dynamics (CFD) to investigate the impact of a dedicated burnout air system on combustion in a 130 t/h biomass grate boiler. A high-fidelity model was established and validated against field measurements, with relative errors within 7%. The research systematically analyzed the effects of burnout air parameters, including outlet velocity, pipe diameter, and injection angle. Results showed that implementing the burnout air significantly enhanced combustion efficiency. Increasing the outlet velocity effectively elevated the oxygen concentration and expanded its distribution in the rear grate section, which intensified the burnout of unburned carbon particles. The char burnout ratio was remarkably improved from 76.5% (baseline) to a maximum of 87.8% under optimized conditions, representing a 14.8% relative improvement. A larger pipe diameter also improved oxygen availability and flue gas temperature, enhancing turbulent mixing. In contrast, variations in the injection angle demonstrated minimal effects. The rational adjustment of the burnout air velocity and pipe diameter is key to optimizing boiler efficiency, although these parameters require careful balancing to mitigate potential slagging risks associated with excessively high furnace outlet temperature. This work provides novel, industrially validated insights into the optimization of a dedicated burnout air system for large-scale biomass grate boilers, highlighting a critical balance between burnout enhancement and slagging suppression.