Influence of Particle Size, Structure, and Layer Thickness on the Back Discharge in Electrostatic Precipitators

Abstract

In an electrostatic precipitator the discharge electrodes are connected to the negative terminal of a direct current source. The charged dust particles move to the collection electrodes where they are held by a combination of Van der Waals, capillary, and electrical attraction forces. In the case of the high dust resistivity (>10 11 X cm), a detrimental phenomenon known as "back discharge" causes the re-entrainment of the dust particles. Besides the other important aspects, e.g., gas humidity, chemical composition of dust layer etc., particle size, structure, and layer thickness also have a major influence on the onset of back discharge.Dust resistivity of glass dusts (spherical particles) was measured using a resistivity measurement unit. A new method was applied, in which the electric conditions were current-controlled, allowing the adjustment of the back-discharge. Test samples were divided into three fractions with mean particle diameters of 75 lm, 150 lm, and 200 lm. Experiments were performed under increasing temperatures up to 250°C and subsequently decreasing it down to 70°C. Our results show that the bigger particles have a quite remarkable higher dust resistivity in the lower temperature region (<170°C) but for higher temperatures nearly the same resistivity is observed. In the next phase, one particle fraction (d = 75 lm) was grinded in a ball mill to reshape the particles from spherical to sharp-edged. The spherical particles show higher resistivity in the lower temperature regions of <170°C (see Fig.). In further experiments, the thickness of a fly ash sample (d p , 50 = 10 lm) was varied to 3, 4, 5, and 7 mm. The results will be reported. P4.02Kontrolle der Nanomorphologie in organischen Solarzellen