Observation of Detailed Structure of Turbulent Pulverized-Coal Flame by Optical Measurement (Part 1, Time-Averaged Measurement of Behavior of Pulverized-Coal Particles and Flame Structure)

Abstract

The purpose of this study is to elucidate of the primary air combustion zone in pulverized-coal combustion by means of advanced laser-based diagnostics with high temporal and spatial resolutions. An open-type burner is fabricated to apply various optical measurement techniques. Detailed and overall evaluation is performed by applying various optical measurement techniques to the flame, such as the velocity and shape of nonspherical pulverized-coal particles, temperature, and light emissions from a local point in the flame. It is observed that the particle mean diameter increases as the distance from the burner increases, and this is found to be caused by the decrease in the diameters of small particles and the increase in the diameters of large particles, which result in the char reaction and the particle swelling due to devolatilization, respectively. The size-classified streamwise velocities of pulverized-coal particles in the central region of the jet exhibit the same magnitude, whereas those in the outer region are different depending on the particle size. The behavior is well explained in terms of the particle inertia.

Eulerian–Eulerian multi-fluid methods for pulverized coal flames with nongray radiation

“…It should be noted that the minimal remaining O 2 along the centerline is still more than three times the extra oxygen introduced by replacing nitrogen and sulfur with oxygen in the coal. Although the central jet is fuel-rich, particles collected downstream revealed large amounts of incomplete combustion [3]. The incomplete combustion was also observed in previous simulations because of insufficient oxygen.…”

“…However, the predictions on burn-out are close between the two devolatilization models. The original experiments reported a low combustion efficiency of 38.3%, a volatile release of 44.6% and remaining fixed carbon of 65% [3]. In comparison, the simulations suggest complete devolatilization using either Kobayashi's or Ubhayakar's models.…”

“…The target flame for validation purposes is a pulverized coal ignition jet flame piloted by a methane flame [2][3][4]. The fuel injector, as shown in Fig.…”

“…In the original flame measurements [2][3][4], the particle temperature was inferred from a two-color pyrometer operating at 0.9 and 1.0 lm. Such a pyrometer measures flame radiation at two wavelengths along line-of-sight.…”

“…The accuracy of a model set in a simulation is validated through the comparison of model predictions to experimental measurements. For example, the target flame of this study [2][3][4] investigated coal ignition processes in a methane pilot. An accurate simulation of coal flames demands a high-fidelity comprehensive approach to multiple physics, which include turbulence, multiphase flow, chemical reactions and heat transfer together with their interactions [1].…”