Stack emission monitoring using non-dispersive infrared spectroscopy with an optimized nonlinear absorption cross interference correction algorithm

摘要

In this paper, we present an optimized analysis algorithmfor non-dispersive infrared (NDIR) to in situ monitor stack emissions. Theproposed algorithm simultaneously compensates for nonlinear absorption andcross interference among different gases. We present a mathematicalderivation for the measurement error caused by variations in interferencecoefficients when nonlinear absorption occurs. The proposed algorithm isderived from a classical one and uses interference functions to quantifycross interference. The interference functions vary proportionally with thenonlinear absorption. Thus, interference coefficients among different gasescan be modeled by the interference functions whether gases are characterizedby linear or nonlinear absorption. In this study, the simultaneous analysisof two components (CO and CO) serves as an example for the validationof the proposed algorithm. The interference functions in this case can beobtained by least-squares fitting with third-order polynomials. Experimentsshow that the results of cross interference correction are improvedsignificantly by utilizing the fitted interference functions when nonlinearabsorptions occur. The dynamic measurement ranges of CO and CO areimproved by about a factor of 1.8 and 3.5, respectively. A commercialanalyzer with high accuracy was used to validate the CO and COmeasurements derived from the NDIR analyzer prototype in which the newalgorithm was embedded. The comparison of the two analyzers show that theprototype works well both within the linear and nonlinear ranges.