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184 Chung-Shin J. Yuan and Thomas T. Shen

representative parameter. The typical range of the overall power density is 10–20 W/m 2
(27). By substituting Eq. (50) (wA = k′P ) into the Deutsch–Anderson equation, the
c
corona power can be related to the collection efficiency:
′ 
 kP c
1
η =− exp  −  (51)
 Q 
3
Equation (51) with k' = 0.015 for P /Q in units of W/(m /s) [or k' = 0.55 for P /Q in
c c
3
units of W/(ft /s)] is reasonably accurate for particulate collection efficiencies up to
approx 98.5% (28). For collection efficiencies above 98.5%, the required corona power
increases rapidly for an increase in collection efficiency, as shown in Fig. 11.
Example 9
3
An electrostatic precipitator is designed to treat 9000 m /min of gas stream to remove
99.8% of particles.
Solution
3
3
Given: Q = 9000 m /min = 333,333 ft /min and η= 99.8%
From Fig. 11, P /Q = 330 W/(1000 acfm) and
c
P = (
,
c
c P Q Q )( ) = (330 1 000 )(333 333, )(1 1 000, ) =110 kW
3.6. Gas Flow Systems
The design of the gas flow system is commonly based on model studies with large
systems. The best operating conditions for an electrostatic precipitator occur when the
gas velocity ranges between 0.6 and 2.4 m/s (2–8 ft/s) and is uniformly distributed (13,
19). Because conveying velocities within flue systems are too high for particle precip-
itation, it is necessary to reduce the gas flow rate by careful design of the connecting
systems. In practice, it is almost impossible to achieve a completely uniform velocity
distribution in a practical duct system. However, it is possible to approach an accept-
able quality of flow at the precipitator inlet by the use of splitters, strengtheners, vanes,
baffles, and diffusion plates. The purpose of these designs is to achieve a nearly uniform
gas flow rate, using the best duct design procedures plus field corrective measures as
required (13).
A nonuniform gas flow rate can result in excessive deposits of particles as well as
variation of flow pattern in the ducts and gas flow system. It changes the velocity dis-
tribution across the ESP and consequently alters the designed residence time of the
gas stream in each duct. Although the increasing of residence time in some ducts might
enhance the collection efficiency of particles, the decreasing of residence time in
other ducts would definitely reduce the collection efficiency of particles. The combi-
nation of these two effects, however, results in the reduction of particulate removal
efficiency in an ESP.
3.7. Precipitator Housing

The precipitator housing is built of weatherproof gastight materials, suitable for
outdoor or indoor installations. Major housing parts include the shell, hopper, inlet and