Numerical Simulation of Cocombustion of Medical Waste in a Municipal Solid Waste Incinerator and Air Distribution Optimization

Abstract To address the industry challenges of continuously increasing medical waste (MW) production in China and the insufficient emergency disposal capacity of traditional rotary kilns, and to fill the scientific gap where existing coincineration research predominantly focuses on pollutant emission verification at low blending ratios while lacking optimization strategies for furnace air distribution under high-ratio cofiring conditions, this study established a coupled numerical model integrating the Fluid Dynamic Incinerator Code (FLIC) bed solid-phase model with the ANSYS FLUENT furnace gas-phase model for an 850 t · d − 1 reverse-acting mechanical grate municipal solid waste (MSW) incinerator in Beijing. The model was validated against on-site measurements of furnace temperature and outlet oxygen concentration, with relative errors within ± 10 % . Based on the validated model, the influence mechanism of MW blending ratios ranging from 0% to 18% on the in-furnace combustion process was analyzed, followed by a multicondition air distribution optimization study. The results indicate that MW cofiring advances the endpoint of moisture evaporation on the grate bed by approximately 0.3 m, with a corresponding forward shift in the peak position of volatile release. Under a constant total air flow rate, 12% was identified as the maximum safe blending ratio. Under this condition, volatile release is most complete and combustion efficiency is optimal. Increasing the blending ratio to 18% leads to incomplete combustion due to an insufficient primary air excess coefficient, resulting in a significant decrease in combustion efficiency. The optimal air distribution scheme features a primary-to-secondary air ratio of 0.65 ∶ 0.35 and a front-to-rear wall secondary air ratio of 0.4 ∶ 0.6 . This configuration effectively optimizes the flow field organization within the furnace, enhances temperature distribution uniformity, and mitigates the risk of overheating caused by high-temperature gas adherence to the walls. This study elucidates the evolution of combustion characteristics during high-ratio MW coincineration, defines the safe cofiring boundary, and provides theoretical support and data references for the engineering design and safe operation of MSW incinerators coprocessing MW.