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There has been little research on volatile releasing characteristics of pulverized coals under moderate or intense low-oxygen dilution (MILD) oxy-combustion (MO) conditions. For the first time, volatile releasing characteristics of bituminous coal and semi-anthracite under both MILD air-combustion (MA) and MO conditions were investigated using a flat-flame assisted entrained flow reactor. Both heating rate (~105 K/s) and residence time (65 ms) were carefully selected to mimic the conditions in typical industrial boilers. The combustion processes and properties of the volatiles were characterized through direct observation and char analysis. The results showed that the lower diffusion rate of the volatile in CO2 resulted in the decreasing of the volatile envelope flame size and a longer volatile burnout time (more than 20%). For bituminous coal (volatile content of 25%), the lower amount of apparent volatile yield under MO conditions reduced the heating value of the volatile. For semi-anthracite coal (volatile content of 7%), the short devolatilization time led to char-CO2 gasification reaction, which increased the apparent volatile yield and the heating value of the volatile by 47% and the volatile-N by 19%. This paper indeed provided new insight into the MILD oxy-combustion of solid fuels. [ABSTRACT FROM AUTHOR]

Pressurized oxy-fuel combustion technology is the second generation of oxy-fuel combustion technology and has low energy consumption and low cost. In this research, a visual pressurized flat-flame reaction system was designed. A particle-tracking image pyrometer (PTIP) system based on a high-speed camera and an SLR camera was proposed. Combining the experimental system and data-processing method developed, the ignition and combustion characteristics of a single coal particle between 69 and 133 μm in size were investigated. The results indicated that at atmospheric pressure, the ignition delay time of ShanXi (SX) anthracite coal was longer than that of ShenHua (SH) bituminous coal, while that of PRB sub-bituminous coal was the shortest. As the pressure rose, the ignition delay time of the PRB sub-bituminous coal and SX anthracite coal showed a continuous increasing trend, while the ignition delay time of SH bituminous coal showed a trend of first increasing and then decreasing. Moreover, pressure also affects the pyrolysis process of coal. As the pressure increases, it became more difficult to release the volatiles produced by coal pyrolysis, which reduced the release rate of volatiles during the ignition stage, and prolonged the release time and burning duration time of volatiles. [ABSTRACT FROM AUTHOR]