  Two methods of flow measurement in stacks are investigated to determine their
errors in presence of cyclonic flow. One method, based on velocity measurements
with a Pitot tube in a grid of points, is the standard reference method
according to EN ISO 16911-1. The second method, ultrasonic flow measurement, is
often used as the automated measurement system in stacks according to EN ISO
16911-2. Several typical stack configurations are considered and the flow field
in the stacks is obtained using validated computational fluid dynamics (CFD)
modelling with OpenFoam software. We show that possible errors of the standard
reference method due to the cyclonic flow are significant compared to the
requirements of the EUs Emissions Trading System. For the ultrasonic flow meter
we compare various configurations (number, orientation, position) of the
ultrasound beams and we demonstrate the flow profile pre-investigation by CFD
as prescribed in section 8.3 of EN ISO 16911-2.
