Reducing Blowoff in Cascade Impactor Measurements

Abstract

Fourteen fly-ash-size distributions were obtained with Meteorology Research, Inc. (MRI) cascade impactors at the outlet of a coal-fired utility boiler. To reduce errors due to particles blowing off or bouncing off larger particle impactor stages and collecting on following stages, jet velocities were kept low, sampling times were kept short, and a duplicate sixth stage was used between the usual sixth and seventh (last) stages. Significant collection of oversized particles was evident only on the last stage; this collection was highly correlated with jet velocity. Since considerable material was collected by the duplicate stage, the error in particle mass on the last stage would probably have been significantly worse without the duplicate stage.