Evaluation of NO_x Flue Gas Analyzers for Accuracy and Their Applicability for Low-Concentration Measurements

Abstract

The requirements of the Texas State Implementation Plan of the U.S. Clean Air Act for the Houston-Galveston Ozone Nonattainment Area stipulate large reductions in oxides of nitrogen (NO_x ) emissions. A large number of sources at Dow Chemical Co. sites within the nonattainment area may require the addition of continuous emission monitoring systems (CEMS) for online analysis of NO_x , CO, and O₂ . At the outset of this work, it was not known whether the analyzers could accurately measure NO_x as low as 2 ppm. Therefore, NO_x CEMS analyzers from five different companies were evaluated for their ability to reliably measure NO_x in the 2–20 ppm range. Testing was performed with a laboratory apparatus that accurately simulated different mixtures of flue gas and, on a limited basis, simulated a dual-train sampling system on a gas turbine. The results indicate that this method is a reasonable approach for analyzer testing and reveal important technical performance aspects for accurate NO_x measurements. Several commercial analyzers, if installed in a CEMS application with sampling conditioning components similar to those used in this study, can meet the U.S. Environmental Protection Agency’s measurement data quality requirements for accuracy.