MEASUREMENTS OF GAS CONCENTRATIONS IN A FLUIDIZED-BED COMBUSTOR USINGLASER-INDUCED PHOTOACOUSTIC-SPECTROSCOPY AND ZIRCONIA CELL PROBES

The dynamic combustion behavior of a circulating, fluidized bed boiler (CFB) was studied using two high-speed gas analysis systems during th e combustion of coal, pear, and wood chips. Time-resolved concentratio ns of SO2 and NO were measured by laser-induced photoacoustic spectros copy (LIPS). A zirconia-cell based probe (lambda-probe), synchronized with the LIPS probe, measured fluctuations between reducing and oxidiz ing conditions. The two probes were positioned in the same measurement volume on the centerline of the CFB combustion chamber. The purpose o f the work was to investigate the behavior of the LIPS in a combustion chamber containing reacting gases in order to extend the previous h-p robe measurements to other gas components. Correlations between oxidiz ing and reducing conditions and gas species concentrations in three lo cations in the combustion chamber are presented. The best correlations were found in the upper part of the CFB combustion chamber. In some c ases the correlation between reducing conditions and the LIPS signal w as caused by unburnt hydrocarbons. Average values of [NO] and [SO2] ob tained by the LIPS system were compared with the results from a sampli ng probe connected to on-line analyzers. The measurements of [NO] and [SO2] were disturbed by interfering gases during reducing conditions. During a sufficiently long time of oxidizing conditions, however, reas onable agreement was obtained between LIPS measurements of [NO] and [S O2] and those of the on-line analyzers. On some occasions (low SO2 con centration) the concentration of the OH radical was also measured. (C) 1998 by The Combustion Institute.