98/03980 Low-NO x-emission system for boilers in Power Plant III

Abstract

Nitrous oxide (N2O) was measured in the flue gas from four wall-fired and three corner-fired 500 MW boilers, fitted with either conventional or low-NOx burners, at four C.E.G.B. power stations. Measurements were made both by on-line non-dispersive infra red (NDIR) monitors and by extractive sampling for later laboratory analysis by electron capture gas chromatography (ECD GC). It was found that the on-line and laboratory methods were in good agreement for samples analyzed within 1–3 h of sampling, but that the nitrous oxide concentration in the stored samples had a tendency to increase with time, which was dependent on the concentration of water in the sample. Experiments with synthetic mixtures showed that the increase in nitrous oxide concentration was consistent with the overall reaction2NO+SO2→N2O+SO3 in which nitric oxide is reduced by sulphur dioxide.The highest average N2O concentration measured by the on-line analyzer was 16 vpm, and for most of the boilers monitored the concentration was less than 10 vpm. There was no statistically significant difference between the measured N2O emissions from normal boilers and those fitted with low-NOx burners. It is suggested that these values are close to the true levels of N2O emissions from p.f. fired boilers and that recent reports of high levels (up to 200 vpm) are likely to be an artefact resulting from the observed generation of N2O in stored samples. A consequence of these measurements of N2O is that current estimates of the contribution of emissions from p.f. fired boilers to the global N2O budget are likely to be too high.