Ignition in 40 kW co-axial turbulent diffusion oxy-coal jet flames

This paper is directed towards understanding how composition of the coal transport medium (primary CO2 and O-2) affects the observed ignition stand-off distance in 40 kW co-axial turbulent diffusion, oxy-coal flames, supported in a specially designed combustion test rig, rated at 100 kW. First, a methodology to define and quantify the observed ignition stand-off distance in laboratory combustor scale turbulent pulverized coal jets was developed and is described in detail. Results are presented in the form of probability density profiles of the measured stand-off distance, as obtained from replicate runs each consisting of six thousand photo-images. Several probability density functions showed multi-modal behavior representing semi-stable attached flames. Special tests in which the transport fluid only was interchanged between N-2 and CO2, led to additional qualitative insight into ignition of coal in practical, turbulent diffusion flames. Results show that flame stability is affected by primary P-O2, secondary preheat temperature, secondary P-O2, and transport medium. Increasing secondary P-O2 can stabilize the flame with zero P-O2 in transport stream. The results presented in this paper can also provide a basis for validation of future detailed simulations of this process. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.