Particulate Emission Control - Mathematics and Statistics for the Environment - page 510

be used only for making preliminary estimates of precipitation collection efficiency. The simplest
form of the equation is

η = 1 - exp(- wA / Q ) (17.22)

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

17.4.3.2 Precipitator Example Calculations

■ EX AMPLE 17. 8
Problem: A horizontal parallel-plate electrostatic precipitator consists of a single duct 24 ft high and
20 ft deep with an 11-inch plate-to-plate spacing. Given collection efficiency at a gas flow rate of
4200 acfm, determine the bulk velocity of the gas, outlet loading, and drift velocity of this electro-
static precipitator. Also calculate revised collection efficiency if the flow rate and the plate spacing
are changed (USEPA, 1984, p. 71).

Given:
Inlet loading = 2.82 g/ft 3
Collection efficiency at 4200 acfm = 88.2%
Increased (new) flow rate = 5400 acfm
New plate spacing = 9 in.

Solution: Calculate the bulk flow (throughput) velocity V . The equation for calculating throughput
velocity is

V = Q / S

where
Q = Gas volumetric flow rate.
S = Cross-sectional area through which the gas passes.

Thus,

V = Q / S = (4200)/[(11/12) × 24)] = 191 ft/min = 3.2 ft/s

Calculate outlet loading. Remember that

Inletloading −

Inletloading

Outletloading

η (fractional) =

Therefore,

Outlet loading = Inlet loading × (1 - η) = 2.82 × (1 - 0.882) = 0.333 grains/ft 3

Calculate the drift velocity. The drift velocity is the velocity at which the particle migrates toward
the collection electrode with the electrostatic precipitator. Recall that Equation (17.22), the Deutsch-
Anderson equation, describes the collection efficiency of an electrostatic precipitator:

− wA

Q

η= − 1exp