Characteristics of Continuous Analyzers for Nitrogen Oxides in Flue Gas from Municipal Incinerators

Abstract

Characteristics of various continuous analyzers for nitrogen oxides in flue gas (NO_x analyzers) were investigated in municipal incinerators. The investigated NO_x analyzers were non-dispersive infrared absorption (NDIR), chemiluminescence and ultraviolet absorption (UV), respectively.
There were slight differences among the observed values of the NO_x analyzers by NDIR, chemiluminescence and UV.
CO₂ and H₂O were expected to influence the observed values of the NO_x analyzers by NDIR and chemiluminescence. HCl and NH₃ were expected to influence the observed values of the NO_x analyzer by UV. However, HC1 and NH₃ were easily dissolved and removed in condensed water in the dryer in the sampling system, therefore those gases did not interfere with actual measurement.
It was estimated that the differences between the observed values of the NO_x analyzers were dependent on the imperfect correction of the influence of CO₂ or H₂O. It is required to minimize the influence of CO₂ as follows: NO and CO₂ concentrations in the span caliblation gas should be controlled at the average concentration in flue gas, or electrical correction should be added for the average CO₂ concentration at the average NO_x concentration, or the NOx analyzer with CO₂ compensating detecter should be used. It is strongly recommended to maintain the dryer condition perfectly to minimize the influence of H₂O in the sample gas.