Cyclonic stack flow measurement uncertainties and impact on annualised mass emission measurements

Measurements of emissions of air pollutants are typically performed in accordance with CEN standards, which are being referred to as Standard Reference Methods. To determine emissions of air pollutants, concentration and flow measurements need to be performed within the stack. Standard EN ISO 16911-1 is employed as the Standard Reference Method for flow measurements. We perform validation measurements for this method in narrow stacks with cyclonic flows. To traceably determine the uncertainty of cyclonic flow in realistic field conditions, we use a stack simulator. We use a traceably calibrated wind tunnel to provide the stack with a welldefined input flow. We perform velocity measurements with a traceably calibrated L-Pitot tube in a stack simulator with two configurations: one with a straight stack entrance, the other with an elbow just before the stack entrance. In both cases, we measure the velocity at planes at several hydraulic diameters downstream from the stack entrance, namely 3, 4, 5, 6, and 7 diameters downstream of the stack entrance. We also characterize the velocity profile at the stack entrance. We show that in both configurations, the flow profile deviates significantly from fully developed turbulent pipe flow, even at 7 diameters downstream of the stack entrance. In case of cyclonic flow, the effect is more pronounced. Future work will focus on comparing the flow measurements with computational fluid dynamics modelling to gain further insight into the additional flow measurement uncertainty.