Dust Resistivity

A major factor affecting ESP performance is the electrical resistivity of dust. If the resistivity is low (high conductivity), the charge on a particle leaks away quickly as particles collect on the plate. Thus, reentrainment becomes possible. As van der Waals' forces may be insufficient to bind the particles, the particles hop or creep through the pre-cipitator. Conversely, if the particle resistivity is high, a charge builds on the collected dust. This charge reduces field strength, reducing ionization and the migration velocity of particles through the gas.

A plot of resistivity versus temperature shows a maximum resistivity between 250 and 350°F (see Figure 5.17.6). This relationship is unfortunate because operators cannot reduce the ESP temperature below 250°F without risking condensation of H2SO4 on the plate surfaces.

y = 0 (Plate and Boundary layer)

FIG. 5.17.5 Top view of wire-plate precipitator.

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