Modeling of emission measurement error due to uneven distribution of particulate matter in stacks

Legislative requirements for emission limits from industrial processes are becoming increasingly stringent and therefore a lower uncertainty of measurement of emissions released to the atmosphere is needed and possible sources of measurement errors need to be reconsidered. In this paper, we investigate a measurement error of industrial emissions of particulate matter from stacks caused by the selection of sampling positions in stacks with uneven particle distribution and we determine its dependence on different flow fields inside the stacks and on the size of the particles. CFD modeling is used to analyze particle distributions in stacks with a diameter of 0.75m and with three different shapes of a supply pipe (straight, one or two bends) generating different flow fields, considering sizes of the particles from 10μm to 50μm (Stokes numbers from 0.007 to 0.18). Concentration fields in several cross-sections are compared and significant changes of the particle distribution are observed when the shape of the supply pipe or the emission particle diameter are changed. The error of the emission mass flow rate as it would be determined according to the EN 15259 standard can reach about 30% for particle diameters of 20μm. Larger particles and the presence of bends lead to stronger particle clustering and near-wall accumulation which tend to increase the error. This should be taken into account in the iso-kinetic sampling practice.<i>Implications</i>: This study highlights the significant impact of particulate matter distribution on the accuracy of emission measurements in industrial stacks. The findings demonstrate that uneven particle distribution, particularly in setups with bends causing stronger particle clustering and near-wall accumulation, can introduce measurement errors of up to 50% depending on flow conditions. These results suggest that current standard sampling methods (e.g., EN 15259) may not always provide accurate emission mass flow rate estimations, especially for larger particles. The study underscores the need for improved sampling strategies or mixing devices to ensure reliable regulatory compliance in emission monitoring.