Particulate Emission Control - Mathematics and Statistics for the Environment - page 511

where
η = Fractional collection efficiency.
A = Collection surface area of the plates.
Q = Gas volumetric flow rate.
w = Drift velocity.

Calculate the collection surface area ( A ). Remember that the particles will be collected on both sides
of the plate.

A = 2 × 24 × 20 = 960 ft 2

Calculate the drift velocity w . Because the collection efficiency, gas flow rate, and collection surface
area are now known, the drift velocity can easily be found from the Deutsch-Anderson equation:

− wA

Q

η= − 1 exp

=− −×

960
4200

w

0 882 . 1 exp

Solving for w ,

w = 9.36 ft/min

Calculate the revised collection efficiency when the gas volumetric flow rate is increased to 5400
cfm. Assume the drift velocity remains the same.

wA
Q

960 936
5400

.

−

=− −×

=

η= − 1 exp 1 exp 0 812 . = 81 2 . %

Does the collection efficiency change with changed plate spacing? No. Note that the Deutsch-
Anderson equation does not contain a plate-spacing term.

■ EXAMPLE 17.9
Problem: Calculate the collection efficiency of an electrostatic precipitator containing three ducts
with plates of a given size, assuming a uniform distribution of particles. Also, determine the collection
efficiency if one duct is fed 50% of the gas and the other passages 25% each (USEPA, 1984, p. 73).

Given:
Volumetric flow rate of contaminated gas = 4000 acfm
Operating temperature and pressure = 200°C and 1 atm
Drift velocity = 0.40 ft/s
Size of the plate = 12 ft long and 12 ft high
Plate-to-plate spacing = 8 in.

Solution: What is the collection efficiency of the electrostatic precipitator with a uniform volumetric
flow rate to each duct? Use the Deutsch-Anderson equation to determine the collection efficiency
of the electrostatic precipitator:

− wA

Q

η= − 1exp