Dynamic behavior of sodium release from pulverized coal combustion by phase-selective laser-induced breakdown spectroscopy

In this paper, we examine the dynamic behavior of sodium (Na) release during the pulverized coal combustion of Zhundong lignite using a laminar, Hencken flat-flame burner technique. By utilizing the gap between the excitation energies of the gas and particle phases, a new low-intensity laser-induced breakdown spectroscopy (LIBS) is developed to distinguish the existence of sodium in the particle or gas phase along the combustion process. Within the coal flame domain, Na atomic spectra in the particle phase are clearly detected that consistently agree with the NIST database. For the first time, the in situ verification of the gas phase Na release accompanying coal devolatilization is fulfilled when the ambient temperature is high enough. The residence time, indicating Na release from particle to gas phases, is determined from the signal. By using a theoretical analysis, the Na release time approximately coincides with the characteristic pyrolysis time of lignite, further confirming the observation above. The effects of ambient temperature, coal rank and oxygen concentration are further discussed. This work may provide a basis for exploring the formation mechanism of submicron fine particulates during coal combustion. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.