Particulate Emission Control - Mathematics and Statistics for the Environment - page 499

Because the density of particle p p is usually much greater than the density of gas p a , the quantity
p p - p a reduces to p p . The velocity can be written as

V = Q / BL (17.13)

where
Q = Volumetric flow.
B = Chamber width.
L = Chamber length.

Equation 17.12 is reduced to

05 .

() =

Q
gp BL

18 µ *

d (17.14)

p

p

The efficiency equation can also be expressed as

=

gp BLN
Q ()

2

p c

η d (17.15)

p

18 µ

where N c is the number of parallel chambers: 1 for simple settling chamber and ( N trays + 1) for a
Howard settling chamber. Equation 17.15 can be written as

gp BLN
Q ()

2

p c

η = 05 . d (17.16)

p

18 µ

and the overall efficiency can be calculated using

= ∑

η η

w

(17.17)

tot i

where
η tot = Overall collection efficiency.
η i = Fractional efficiency of specific size particle.
w i = Weight fraction of specific size particle.

When flow is turbulent, Equation 17.18 is used:

−

Lv
Hv

y
x

η= exp (17.18)

When using Equations 17.10 to 17.16, note that Stokes' law does not work for particles greater than
100 µm.

17.4.1.2 Minimum Particle Size
Most gravity settlers are precleaners that remove the relatively large particles (>60 µm) before the
gas stream enters a more efficient particulate control device such as a cyclone, baghouse, electro-
static precipitator, or scrubber.