Particulate Emission Control - Mathematics and Statistics for the Environment - page 508

d p /[ d p ] cut = 7.5/4.57 = 1.64

Determine the collection efficiency utilizing Lapple's curve (see Figure 17.6):

η = 72%

Calculate the required collection efficiency for the approval of the permit:

Inletloading Outletloading
Inletloading

−

×= −

05 01
05

. .

×=

η= 100 100 80 %

.

Should the permit be approved? Because the collection efficiency of the cyclone is lower than the
collection efficiency required by the agency, the permit should not be approved.

17.4.3 e leCtrostatiC p reCipitators
The electrostatic precipitator (ESP) has been used as an effective particulate-control device for many
years. It is usually used to remove small particles from moving gas streams at high collection effi-
ciencies. ESPs are used extensively where dust emissions are less than 10 to 20 µm in size with a
predominant portion in the submicron range (USEPA, 1984a, p. 7-1). Widely used in power plants
for removing fly ash from the gases prior to discharge, an electrostatic precipitator applies electrical
force to separate particles from the gas stream. A high voltage drop is established between electrodes,
and particles passing through the resulting electrical field acquire a charge. The charged particles
are attracted to and collected on an oppositely charged plate, and the cleaned gas flows through the
device. Periodically, the plates are cleaned by rapping to shake off the layer of dust that accumulates,
and the dust is collected in hoppers at the bottom of the device (see Figure 17.7). Although elec-
trostatic precipitators have the advantages of low operating costs, capability for operation in high-
temperature applications (to 1300°F), low pressure drop, and extremely high particulate (coarse and
fine) collection efficiencies; they have the disadvantages of high capital costs and space requirements.

17.4.3.1 Collection Efficiency
The ESP collection efficiency can be expressed by the following two equations (USEPA, 1984a,
p. 7-9):

• Migration velocity equation
• Deutsch-Anderson equation

The migration velocity ( w ) (sometimes referred to as the drift velocity ) represents the parameter at
which a group of dust particles in a specific process can be collected in a precipitator and is

dEE
po p

w = (17 . 20)

4πµ

where
w = Migration velocity.
d p = Diameter of the particle (µm).
E o = Strength of field in which particles are charged, volts per meter (represented by peak
voltage).
E p = Strength of field in which particles are collected, volts per meter (normally the field close
to the collecting plates).
µ = Viscosity of gas (Pa-s).