Geoscience Reference
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100
9 80
70
60
50
40
30
20
(0.1)
23 456789
(1.0)
234567
89
(1.0)
Particle Size Ratio, d p /(d p ) Cut
FIGURE 17.6 Lapple's curve: cyclone efficiency vs. particle size ratio. (Adapted from USEPA, Control
of Gaseous and Particulate Emissions: Self-Instructional Problem Workbook , EPA 450/2-84-007, U.S.
Environmental Protection Agency Air Pollution Training Institute, Research Triangle Park, NC, 1984.)
Solution: Determine the collection efficiency of the cyclone. Use Lapple's method, which provides
collection efficiency, values from a graph relating efficiency to the ratio of average particle diameter
to the cut diameter. Again, the cut diameter is the particle diameter collected at 50% efficiency (see
Figure 17.6). Calculate the cut diameter using the Lapple method (Equation 17.19):
05
.
9
µ
B
c
d
=
(
)
p
2
π
nv
pp
cut
ti
p
g
Determine the inlet width of the cyclone ( B c ). The permit application has established this cyclone as
conventional. The inlet width of a conventional cyclone is 1/4 the cyclone diameter:
B c = cyclone diameter/4 = 2.0/4 = 0.5 ft
Determine the value of p p - p g . Because the particle density is much greater than the gas densit y,
p p - p g can be assumed to be p p :
p p - p g = p p = 2.75 × 62.4) = 171.6 lb/ft 3
Calculate the cut diameter:
(
) ×
05
.
4
91
×
.21
×
10
05
.
9
µ
B
c
d
=
=
=
457
.
µm
(
)
p
2
π
nv
pp
24550
π
×××
.
171 6
.
cut
ti
p
g
Calculate the ratio of average particle diameter to the cut diameter:
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