Modelling of uncertainties of an emission concentration measurement in stacks

This contribution describes a research of measurement uncertainty of industrial emissions flowing through vertical stacks and its dependence on different geometrical configurations and physical conditions. Since the legislative requirements for emission limits from industrial processes are decreasing, the higher measurement accuracy is becoming more important and new uncertainty standards needs to be implemented. This contribution is a part of the research project 18NRM04 Heroes under European Metrology Program for Innovation and Research (EMPIR). CFD modelling is used to analyse particle distributions in stacks with three different geometries of a supply pipe, different size of the particles and several concentrations. Vertical stack with a circular cross section of a diameter of 0.75 m is considered with the supply pipe containing none, one or two bends. The number of particles entering the stack defines the initial volumetric concentration from 0.1 to 10 mg·m -3 with the particle size from 10 to 50 μm. Concentration fields in several cross-sections were compared and the particle distributions were analysed as functions of the physical conditions and the chosen geometry of the stack. The results show not very high sensitivity of the concentration profiles on the initial concentrations. On the other hand, significant changes of the concentration fields are observed when the stack geometry or the particle diameter is changed. This should be taken into account in the iso-kinetic sampling practise where the overall concentrations are calculated from measurements in several points.