Page 214 - Air pollution and greenhouse gases from basic concepts to engineering applications for air emission control

6.5 Filtration 189

0:34 1:675
g sG ¼14A 1=3 Pe 0:23 N 0:052 d p þ 0:55A s N A 1 d p
8
vdw
s
d G d G
ð6:116Þ
0:24

þ 0:22N 0:053 Gr 1:11 d p
vdw
d G
Figure 6.16 shows a comparison between the TE model Eq. (6.114) and the
refined model Eq. (6.116) with the experiments. Experiments were conducted using
2-mm glass beads in dry air with a bed thickness of 12.7 cm. The corresponding air
flow rate was 65 L/min [13].
In granular filtration, particles are collected as they pass through a bed of
granules by the same mechanisms that operate in a fibrous filter. In air cleaning,
granular filtration is used primarily for sticky, corrosive, or high-temperature par-
ticles. Sometime, granules are driven to move for circulation, regeneration, and/or
low resistance to air flow.

6.6 Practice Problems

1. The size distribution and collection efficiency of a particle separator as a
function of particle size is shown in the table below. Estimate the cut size and
the overall collection efficiency of the control device.

Particle size range (μm) Mass fraction Efficiency (%)
0–20 0.11 15
20–40 0.25 25
40–60 0.35 50
60–80 0.19 75
80–100 0.10 100

2. An industrial plant is using cyclone and electrostatic precipitator in serial for air
emission control. A cyclone has an 80 % efficiency and it is followed by an
3
electrostatic precipitator. The inlet air to the cyclone has a dust load of 150 g/m .
What are the collection efficiency of the electrostatic precipitator and the
allowable concentration of fly ash in the air that exits from the electrostatic
precipitator, in order for the whole system to meet the total collection efficiency
of 99 %?
3. Find the precipitation velocity of a 1 μm particle between two parallel plates
with a potential difference of 1000 V. The distance between the two plates is