Ignition and combustion characteristics of coal particles under high-temperature and low-oxygen environments mimicking MILD oxy-coal combustion conditions

• Published in: Fuel (Guildford) Vol. 253; pp. 1104 - 1113
• Main Authors: Zeng, Zhukai, Zhang, Tingyao, Zheng, Shankai, Wu, Wendong, Zhou, Yuegui
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.10.2019; Elsevier BV
• Subjects: Burning; Carbon dioxide; Carcinogens; Coal; Color; Combustion; Combustion mode; Digital cameras; Digital imaging; Dilution; Endothermic reactions; Fiber optics; Gasification; High temperature; Ignition; Ignition standoff distance; Luminosity; MILD combustion; Mimicry; Optical fibers; Oxy-coal combustion; Oxygen; Particle temperature; Particulates; Physicochemical properties; Radiation; Temperature effects; Uniformity coefficient; Particle temperature; Oxy-coal combustion; Combustion mode; Ignition standoff distance; MILD combustion
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2019.05.101

The experiments of coal particles combustion were conducted to mimic moderate and intense low-oxygen dilution (MILD) oxy-coal combustion on a diffusion-flamelet-based Hencken burner under different O2/CO2 and O2/N2 environments with the coflow temperatures of 1400–1800 K and oxygen concentrations of 5%–20%. The images of coal particles combustion flame were captured by a digital camera to determine the ignition standoff distances of coal particles. The radiation spectrums of burning coal particles at different coflow temperatures and oxygen concentrations were measured by a fiber optic spectrometer and the temperatures of burning coal particles were deduced with the two-color method. It is found that either increasing the coflow temperature or the oxygen concentration leads to brighter flame luminosity, shorter ignition standoff distance and higher burning particles temperature. The ignition standoff distance of coal particles is increased by 0.07–0.49 cm when carbon dioxide is used as diluent gas instead of nitrogen. The temperatures of the burning coal particles under O2/CO2 environments are lower by 51–185 K than those under O2/N2 environments at the same conditions due to the combined physicochemical properties of CO2 with higher heat capacity and the endothermic reaction of char gasification. Moreover, a method based on the coal particles temperature uniformity coefficient is proposed to quantitatively identify the combustion modes of MILD coal combustion and MILD oxy-coal combustion. All coal combustion flames are visible under both O2/CO2 and O2/N2 environments, and the MILD coal combustion flames under high-temperature and low-oxygen concentration conditions are weaker and more uniform with dark red color.