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

ash from coal-fired electric power plants, Selzler and Watson (29) suggested that in the
determination of particulate migration velocity the important factors are electrical
power input to the precipitator, the particle size distribution in the entering gases, and
the sulfur-to-ash ratio of the coal burned. Based on this approach, a proposed empirical
collection efficiency equation is,
[ )( 14 06 ) 022 ]
.
.
.
.
η =− exp − ( 0 57 )(203 AQ ) (kW Q ) (S AH (52)
1
2
where A is the surface area of collecting plate (1000 ft ), Q is the flue gas volumetric
3
flow rate (1000 actual ft /min), kW is the power input to the discharge electrodes, and
S/AH is the sulfur-to-ash ratio of the coal burned (by weight).
Selzler and Watson derived the numerical parameters by the use of least-squares
regression techniques. The data used for the development of the above equation were
obtained from the US Environmental Protection Agency (US EPA) and questionnaires
sent to utility companies and the Federal Power Commission.
Frisch and Coy (30) considered Selzler and Watson’s approach as a good attempt at
a more systematic method for sizing the ESPs. However, they commented that it is
meaningless to use the sulfur-to-ash ratio as an independent variable to describe pre-
cipitator performance at elevated temperatures and that it is erroneous to assume power
density as an unconstrained independent variable. The following empirical efficiency
equation was developed (30):
[ ′ a ′ b ′ c ′ d ]
v
1
η =− exp kP A ) (A Q ) ( ) ( ) x (53)
− ( c
2
2
where P /A is the power density (W/ft ), A/Q is the specific collecting area (ft /1000
c _ _
3
actual ft /min), v is the average treatment velocity (ft/s), x is the mass median particle
diameter (µm), and k, a', b', c', and d' are empirical constants.
On the basis of theoretical considerations and a comparison of observed versus pre-
dicted collection efficiency, the use of the Frisch–Coy equation [Eq. (53)] showed
better results than the Selzler–Watson equation [Eq. (52)] in estimating the size of hot-
side precipitators. The hot-side precipitator is recently applied because it reduces particu-
late resistivity and prevents acid condensation by means of placing the precipitator in the
front of an air preheater, where flue gas temperature is much higher than that at the usual
downstream location.
Cooperman (31) and Robinson (32) have modified the Deutsch–Anderson equation
and brought the theoretical and empirical aspects of precipitation phenomena into
closer agreement. The modification takes into account the erosion of collected particles
and the nonuniformity of particle concentration over the precipitator cross-section. Soo
(33) rationalized precipitator design by providing knowledge of the equilibrium posi-
tion of a corona wire and the effect of turbulent diffusion in the electrostatic field. Soo
(34) also introduced the concept of particle–gas–surface interactions applied to the
electrostatic precipitators. Potter (35) has utilized the concept of an extended
Deutsch–Anderson equation: A semilogarithmic plot of particulate collection efficiency
against the product of specific collection area and the square of operating voltage
generates a “performance line” for a particulate–precipitator combination. Such per-