Large-eddy simulation of pulverized coal combustion using flamelet model

A flamelet model for pulverized coal combustion, which considers three mixture fractions for coal moisture, volatile matter and gasified char, has been coupled with a large-eddy simulation. Its prediction accuracy for ignition and extinction has been investigated in the configurations of a lab-scale coal jet flame and a large-scale test furnace with an actual coal burner. For the lab-scale coal jet flame, the profile of the ratio of coal burnt on the central axis of the coal jet was compared with the measurement. The profile by the flamelet model well agreed with the experimental data within the measurement error. For the large-scale test furnace with the actual burner, the prediction ability for the ignition limit in a decreasing coal feed rate was examined. The present simulation reproduced an unstable flame state occurring at a lower coal feed rate. The ignition stability index, which was evaluated from the flame images, was compared with the test result. The sharp decline of the ignition stability index near the ignition limit was well-captured by the present simulation. The prediction error for the coal feed rate at the ignition limit was estimated to be within 10%.