Optical diagnostics of ignition and combustion behavior and NOx emission reduction analysis of single-particle excavated waste in MILD-oxy combustion conditions

Abstract

The excavation and incineration of aged landfill waste have been increasingly considered to alleviate landfill space constraints and improve energy recovery efficiency. However, the ignition and flame characteristics of excavated waste (EW) differ from those of conventional municipal solid waste (MSW), potentially leading to higher emissions of NOx and CO₂. This study established MILD-oxy combustion conditions for single-particle EW and optical diagnostics were employed to capture instantaneous images of flames. The results show that under N₂-O₂ atmospheres, only one ignition mode, homogeneous ignition, is observed. Under CO₂-O₂ atmospheres, three ignition modes are identified: at low oxygen concentration (10 %), heterogeneous ignition predominates with a longer ignition delay time (5–10 s). As the oxygen concentration increases (21 %), homogeneous ignition gradually occurs with a significantly shorter ignition delay time (3–6 s). Further increases in oxygen concentration (30 %) and environmental temperature (1000–1100 °C) reduce the ignition delay time even further, resulting in a hetero-homogeneous ignition mode. This reveals that the high heat capacity of CO₂ allows both homogeneous and heterogeneous ignition of EW to occur on the same time scale. Additionally, NOx emissions are significantly lower in CO₂-O₂ atmospheres than in N₂-O₂ atmospheres, with the lowest NOx emissions at 10 % oxygen concentration.