Particulate Emission Control - Mathematics and Statistics for the Environment - page 502

TABLE 17.2
Collection Efficiency
for Each Particle Size

d p (µm) η (%)

94 100

90 92

80 73

60 41

40 18.2

20 4.6

10 1.11

Determine the actual flow rate in acfs. In order to calculate the collection efficiency of the system
at the operating conditions, the standard volumetric flow rate of contaminated air of 70.6 scfs is
converted to actual volumetric flow of 130 acfs:

Q a = Q s ( T a / T s ) = 70.6(446 + 460)/(32 + 460) = 130 acfs

Express the collection efficiency in terms of d p with d p in feet. Also express the collection efficiency
in terms of d p with d p in microns. Use the following equation, substituting values for p p , g , B , L , µ,
and Q in consistent units. Use the conversion factor for feet to microns. To convert d p from ft 2 to µ 2 ,
d p is divided by (304,800) 2 :

()

2

×× ()

2

gp d 32 2 . × 165 41 . × 008 15 . d p

BL
Q =

× ()

pp 2

− 4

η = = 1 134 . 10 d p

( ) ××

− 5 2

36 µ 36 × 17510 . × 130 ( 304 800 , )

where d p is in µm. Calculate the collection efficiency for each particle size. For a particle diameter
of 10 µm:

η = (1.134 × 10-4)( d p ) 2 = (1.134 × 10 -4 )(10) 2 = 1.1 × 10 -2 = 1.1%

Table 17.2 provides the collection efficiency for each particle size. The size efficiency curve for the
settling chamber is shown in Figure 17.4. Read off the collection efficiency of each particle size
from Figure 17.4, and calculate the overall collection efficiency (Table 17.3):

∑ w ii
(0.027

η = η

= × 1.1) + (0.069 × 7.1) + (0.094 × 14.0)) 0.105 + × 23.0) + (0.105 × 34.0)

+ (0.095 × 48.0) + 0.070 ( × 64.0) + (0.095 × 83.0) + (0.340 × 100.0)

= 59. 0%

17.4.2 C yClones
Cyclones—the most common dust removal devices used within industry (Strauss, 1975)—remove
particles by causing the entire gas stream to flow in a spiral pattern inside a tube. They are the col-
lector of choice for removing particles greater than 10 µm in diameter. By centrifugal force, the
larger particles move outward and collide with the wall of the tube. The particles slide down the