Local Deposition of Particles in a Laboratory-Scale Electrostatic Precipitator with Barbed Discharge Electrodes

The precipitation of particles in an electrostatic precipitator (ESP) results in striking dust patterns at the collecting electrodes, strongly depending on forces of the electrohydrodynamic (EHD) field in the duct. Due to precipitator geometry, electrical operation status, and process parameters, areas of high and low dust density are visible. Since latest results show a direct correlation of precipitator efficiency with the shape and size of those patterns, a better knowledge of local dust layer properties is necessary in order to improve the performance of electrostatic precipitators, e.g. by electrode optimization. For this paper experimental investigations were carried out with a laboratory scale electrostatic precipitator. In order to analyze the different characteristics of the collected dust at compressed and light dust layer regions, particle size distributions and dust layer porosity were determined with the help of a scanning electron microscope (SEM). Moreover, high accuracy weight measurements were executed to reveal prefered dust deposition along the collecting electrodes. Whereas the dust mass varies only insignificantly for short-time particle collection (e.g. 1 minute), the dust mass in high-density regions is much larger after having collected a dust layer for a longer period (e.g. 45 minutes). This phenomenon is due to a permanent dust layer erosion by forces of the gas flow. Moreover, a totally different structure of the dust layer can be observed directly opposite and between the discharge electrodes. Porosity investigations underline the observationse and prove significantly lower porosity in dust layer areas directly opposite of the coronating barbes. The different particle size distributions of dust at highand low-density regions of the dust layer show that fine particles were preferably deposited in high-density regions.