Particulate Emission Control - Mathematics and Statistics for the Environment - page 509

To plates

High
voltage

Clean
gas out

To wires

Discharge
electrode (wire)

Clean
gas out

Dirty
gas in

Dirty
gas in

Collection
plate

Weights

(A)

Clean
gas out

Clean
gas out

Spary

Discharge
electrode
(wire)

Dirty
gas in

Dirty
gas in

Weights

(B)

FIGURE 17.7 Typical simple fabric filter baghouse design. (From USEPA, Control Techniques for Gases
and Particulates , U.S. Environmental Protection Agency, Washington, DC, 1971.)

Migration velocity is quite sensitive to the voltage, because the electric field appears twice in
Equation 17.20. Therefore, the precipitator must be designed using the maximum electric field for
maximum collection efficiency. The migration velocity is also dependent on particle size; larger
particles are collected more easily than smaller ones. Particle migration velocity can also be deter-
mined by the following equation:

qE

p

w = (17.21)

4πµ r

where
w = Migration velocity.
q = Particle charge (charges).
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).
r = Radius of the particle (µm).

The Deutsch-Anderson equation or derivatives thereof are used extensively throughout the pre-
cipitator industry. Specifically, it has been used to determine the collection efficiency of the precipi-
tator under ideal conditions. Though scientifically valid, there is a number of operating parameters
that can cause the results to be in error by a factor of two of more. Therefore, this equation should