Numerical investigation of MSW combustion influenced by air preheating in a full-scale moving grate incinerator

Air preheating is generally used to improve moisture evaporation and boiler efficiency in waste incineration systems. This study employs FLIC-FLUENT coupling procedure to investigate the influence of primary air preheating on municipal solid waste (MSW) combustion characteristics in a moving grate incinerator. The MSW properties, incinerator specifications and operating parameters were acquired from an incineration plant in Zhejiang Province, China. The MSW combustion modelling was carried out with air preheating temperatures in a range of 453–513 K. The simulation results were compared with measurements data from the incinerator and literature. It was found that higher primary air temperature caused a larger layer of evaporation at the bottom of the bed. When the evaporation layer comes in contact with the ignition front, the remaining mass burned instantaneously, resulting in a faster complete combustion. Peak bed temperature was observed during the complete combustion, it was highly influenced by heat flux from the primary air and the combustion. Higher primary air temperature also resulted in increased devolatilization rate and peak flame temperature. The peak flame temperature reached 1961 K under 513 K air temperature. Boiler efficiency increased by 5.6% when remaining flue gas heat was utilized to preheat the air to 453 K compared to the unutilized. However, high primary air temperatures also have negative influences, for example, accelerated thermal NOx generation and locally high bed temperature. Condensation of acid gases could also occur if the remaining flue gas heat was over-utilized. Therefore, the determination of the suitable primary air temperature is essential.