Measurement of the concentration of ammonia and ethene in the combustion chamber of a circulating fluidised-bed boiler

This paper presents the results of measuring the ammonia and ethene concentration profiles in the combustion chamber of a circulating fluidised-bed boiler. The boiler was operated in three air-staging conditions with peat as fuel, and with the addition of lime. Two sampling techniques were used for the analysis of ammonia: gas-sampling probe connected to a Fourier transformed infra-red (FTIR) instrument, and a gas-quenching (GQ) probe where the sample was quenched directly in the probe tip by a trapper solution. Both techniques are accurate enough to distinguish the influence on air staging of the level of ammonia in the combustion chamber. Comparison of the concentration profiles for ammonia measured by the two procedures shows similar results. The levels of ammonia and ethene measured by FTIR follow each other in the combustion chamber for all three staging conditions. The FTIR spectra were evaluated by three methods: spectral subtraction, differential absorbance and the multiple variable analysis method named 'partial least square' (PLS). Almost equal levels of concentration of ammonia and ethene were found, regardless of the method employed. The measurement error from reactions with ammonia at the GQ probe tip was estimated in a simple model.