Electrostatic Precipitation Technology: A Different Viewpoint

Abstract

This paper presents a viewpoint on electrostatic precipitation derived from Australian experience, particularly with fly ash collection from low sulfur coals. Thè customary expression of precipitability as an effective migration velocity calculated from the Deutsch equation is replaced by a performance line (or equation) obtained from a semi-logarithmic plot of collection efficiency against a combined function of specific collection area and operating voltage. The important effect of voltage, particle size, and carrier gas additives clearly emerge from the extended Deutsch equation, and the proper value of pilot plant testing is realized. Inclusion of particulate resistivity in the equation is straightforward, and an original calculation of loss of collection efficiency caused by high resistivities is presented. This hindrance is much less than generally thought, because the precip-itator field reduces particulate resistivity by a long-known effect hitherto ignored in precipitation technology. The operational resistivity (i.e., with the precipitator working) has been measured and is often 100-1000 times less than the so-called in situ resistivity observed at low applied field. Contrary to entrenched belief, the evidence is strongly against any general association of low sulfur in coal with poor fly ash precipitation.