Particulate Emission Control - Mathematics and Statistics for the Environment - page 497

= () =

2

[ ]

2

gp pp

32 2 . × 122 3 . × ( 2.5/25,400 ) × 12

− 3

v =× 12110 . ft/s

( )

18 µ

− 5

18 × 12210 . ×

Calculate the time for settling:

Outlet height
Terminal velocity

150
12110

5

t = =

− =×=

12410 . s 34.4 hr

3

. ×

Calculate the horizontal distance traveled:

Distance = Time for descent × Wind speed = (1.24 × 10 5 )(3.0/3600) = 103.3 miles

17.4 PARTICULATE EMISSION CONTROL EQUIPMENT CALCULATIONS
Different classes of particulate control equipment include gravity settlers, cyclones, electrostatic
precipitators, wet (Venturi) scrubbers (discussed in Chapter 18), and baghouses (fabric filters). In
the following section, calculations used for each of the major types of particulate control equipment
is discussed.

17.4.1 g ravity s ettlers
Gravity settlers have long been used by industry for removing solid and liquid waste materials from
gaseous streams. Simply constructed (see Figures 17.2 and 17.3), a gravity settler is actually nothing
more than an enlarged chamber in which the horizontal gas velocity is slowed, allowing particles to
settle out by gravity. Gravity settlers have the advantage of having low initial cost and are relatively
inexpensive to operate—there's not a lot to go wrong. Although simple in design, gravity settlers
require a large space for installation and have relatively low efficiency, especially for removal of
small particles (<50 µm).

17.4.1.1 Gravity Settling Chamber Theoretical Collection Efficiency
The theoretical collection efficiency of the gravity-settling chamber is given by (USEPA, 1984a,
p. 5-4)

η = ( v y L )( v x H ) (17.10)

Clean gas out

Dirty gas in

Dust hoppers

FIGURE 17.2 Gravitational settling chamber. (From USEPA, Control Techniques for Gases and Particulates ,
U.S. Environmental Protection Agency, Washington, DC, 1971.)