Measurements of Gas Concentrations in a Fluidized Bed Combustor Using Laser-Induced Photoacoustic Spectroscopy and Zirconia Cell Probes

Abstract

The dynamic combustion behavior of a circulating, fluidized bed boiler (CFB) was studied using two high-speed gas analysis systems during the combustion of coal, peat, and wood chips. Time-resolved concentrations of SO 2 and NO were measured by laser-induced photoacoustic spectroscopy (LIPS). A zirconia-cell based probe (λ-probe), synchronized with the LIPS probe, measured fluctuations between reducing and oxidizing conditions. The two probes were positioned in the same measurement volume on the centerline of the CFB combustion chamber. The purpose of the work was to investigate the behavior of the LIPS in a combustion chamber containing reacting gases in order to extend the previous λ-probe measurements to other gas components. Correlations between oxidizing and reducing conditions and gas species concentrations in three locations in the combustion chamber are presented. The best correlations were found in the upper part of the CFB combustion chamber. In some cases the correlation between reducing conditions and the LIPS signal was caused by unburnt hydrocarbons. Average values of [NO] and [SO 2] obtained by the LIPS system were compared with the results from a sampling probe connected to on-line analyzers. The measurements of [NO] and [SO 2] were disturbed by interfering gases during reducing conditions. During a sufficiently long time of oxidizing conditions, however, reasonable agreement was obtained between LIPS measurements of [NO] and [SO 2] and those of the on-line analyzers. On some occasions (low SO 2 concentration) the concentration of the OH radical was also measured.