Experimental investigation of particle-laden flows in an oxy-coal combustion chamber for non-reacting conditions

Abstract

Investigating the two-phase flow in close-to-realistic geometries is essential to gain a more detailed understanding of coal combustion. Particularly the slip velocity between solid fuel particles and the surrounding gas phase has a significant effect on local heat transfer and gas composition. Experimental investigations that focus on two-phase flows in combustion chambers are sparse. In this work the two-phase flow in a combustion chamber optimized for oxy-coal operation is investigated for non-reacting conditions. The aim is to advance the measurement technique and to reveal the differences of particle and gas velocities needed to estimate the instantaneous slip velocity of the particles. The investigation covers the most important regions for flame stabilization where volatiles are released: inside the quarl and directly downstream of the quarl close to the dump plane. The quarl and large parts of the combustion chamber are made of quartz glass, enabling particle image velocimetry (PIV) and particle tracking velocimetry (PTV). Two-phase PIV/PTV measurements were performed using tracer particles (0.5 µm) to track the gas flow and solid particles (40–80 µm) representing grinded coal. Using double-exposure Mie imaging, gas phase tracers and particles were simultaneously recorded and separated during post-processing. As the gas and the particle velocity fields are measured simultaneously, the slip velocity is accessible. Measurement errors are estimated and discussed in detail. Differences of gas and particle velocity fields are shown and particle trajectories are analyzed. Operation conditions covered flows for three different particle loadings with relevance for oxy-coal and air-coal combustion.