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Electrostatistic Precipitation 179

Fig. 9. Effects of fly ash resistivity on effective migration velocity in an ESP. (From ref. 23.)

A highly resistive particle increases the occurrence of sparking in an ESP and forces
a lower operating voltage. A serious back corona can develop, which reduces both charg-
ing and collection of particles. The effects of resistivity are more significant above 10 11
Ω-cm, but can be accounted by for the design for effective migration velocity. Figure 9
illustrates the effect of fly ash resistivity on effective migration velocity of particles.
Example 7
Estimate the collecting plate area required for an ESP that is applied for removing fly ash
in the gas stream emitted from an utility power plant. Assuming that (1) the designed
3
collection efficiency is 99.5%, (2) the volumetric gas flow rate is 9,600 m /min, and (3)
9
the resistivity of fly ash is 8×10 Ω-cm.
Solution
9
3
3
Given: p = 8×10 Ω-cm and Q = 9,600 m /min = 160 m /s
From Fig. 9, w = 7.2 m/min = 0.12 m/s. Applying the Deutsch–Anderson equation
− (
1
η= − exp wA Q )
− (
0 995 = 1 − exp 0.12 160 )
.
A
(
A= ln 1 − 0.995)(160 ) (0 12. ) = 7 040, m
3.3. Internal Configuration
The design of the internal configuration of an ESP is of great importance; however,
it was usually ignored in most textbooks. The even distribution of gas flow through the