Narrow stack emissions: Errors in flow rate measurement due to disturbances and swirl

European legislation continues to drive down emission limit values, making the emission measurement of narrow stacks of increasing importance. However, the applicable standards (EN ISO 16911-1 and EN 15259) are poorly validated for narrow stacks, and the effect of flow disturbances on the described methods are largely unknown. In this article, measurement errors are investigated in narrow stacks with flow disturbances and swirl, both experimentally and through computational fluid dynamics (CFD) simulations. The results indicate that measurement errors due to misalignment of the flow with typical measuring probes (pitot tubes) are small compared to errors resulting from the positioning of these probes in the measurement plane. Errors up to 15% are reported using the standardized methods, while the measurement error is both smaller and more predictable when using additional measurement points. Implications: Current international standards provide methods to measure emissions from industrial stacks. With increasingly small emission limit values, the accuracy of these measurements is becoming considerably more important. The data from this study can be used to inform revisions of these standards, in particular with respect to flow disturbances in narrow stacks, and can help law- and policy-makers to obtain insight into the uncertainties of emission measurements in these specific situations.