Experimental Study on Ignition and Combustion Characteristics of Pyrolyzed Char in an O2‑Enriched Atmosphere with Multiple Optical Diagnostic Techniques

A flat-flame entrained-flow pulverized coal/char reactor (EFR) was designed to study the ignition and combustion characteristics of pyrolyzed bituminous (PB) char particle stream of 53–80 μm size. A highly volatile content bituminous pulverized coal (Shenhua bituminous) was also tested for comparison. The OH planar laser-induced fluorescence, CH* chemiluminescence, visible light, and three-color high-temperature pyrometer studies were performed to determine the PB char ignition process, flame structure, and particle temperature. In the EFR, the heat-up and ignition of the PB char were retarded with a decrease in both ambient oxygen concentration from 30% to 5% and ambient temperature from 1800 to 1600 K. As the O2 concentration is enriched, a decreased trend in the duration of the volatile flame is observed; the total combustion time and fixed carbon residual ratio decrease to about 1/2. In the range from 20% to 30% oxygen concentration, PB char combustion was particularly intensified and numerous small fragments trailing from the char particles appeared in the flame. PB char particle temperatures and combustion intensity are enhanced apparently in oxygen-enriched environments. At high O2 concentrations, the ratios of volatile flame time in total flame time for PB char are about 1/3 to 1/2 of bituminous coal. The initial rapid volatile evolution appeared to have little effect on PB char ignition, and the heterogeneous combustion mode is dominant in the pyrolyzed char particle flame.