Page 215 - Air pollution and greenhouse gases from basic concepts to engineering applications for air emission control

190 6 Separation of Particles from a Gas

0.01 m and the particle has 100 element charges. The electrical mobility of the
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particle with a single charge is 1.1 × 10 −9 m /Vs.
4. A 2 mm thick home furnace filter is made of fiberglass with 3 % solidity. The
average diameter of the fiber is 20 μm. The filter is perpendicular to the face
airflow of 1.5 m/s. Assume standard room conditions and neglect the electro-
static effect, determine the filter efficiency without circulation for particles of
5 μm in aerodynamic diameter.
5. A 98 % efficient electrostatic precipitator removes fly ash from combustion
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gases flowing at 10,000 m /min. Calculate the required collection area, for an
effective precipitation velocity of 5.5 m/min.

Particle size range (μm) Mass percent in size range
0–2 10
2–12 20
12–20 25
20–40 25
40–70 15
70–100 5

6. A wire-tube electrostatic precipitator has a wire diameter of 5 mm and a tube
diameter of 50 cm. The potential between the wire and the cylinder is 5000 V.
What is the electrical field intensity at 200 mm radial position?
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7. An electrostatic precipitator has a total collection plate area of 5,500 m and
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treats 8,000 m /min of air. If the effective drift velocity is 6 m/min, calculate the
actual collecting efficiency.
8. Calculate the overall collection efficiency of a conventional Lapple cyclone with
inlet height of 1 m and width of 0.5 m. Air enters the cyclone with a flow rate of
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250 m /min. The density of particles flowing through the cyclone is 1,500 kg/m .
The size distribution of the particles is shown in table below.
9. Calculate the cut size diameter of a conventional Lapple cyclone having inlet
height of 1 m and width of 0.5 m. The standard air viscosity is 0.0072 kg/m-h.
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Air flows into the cyclone with a flow rate of 450 m /min. The density of
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particles flowing through the cyclone is 1,200 kg/m .
10. Calculate the pressure drop of a conventional Lapple cyclone having inlet height
of 0.5 m, width of 0.25 m, and body inner diameter of 0.5 m. The standard air
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containing particles flow into the cyclone with a flow rate of 150 m /min. The
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density of particles flowing through the cyclone is 1,500 kg/m and K = 16.
11. Calculate the following collection efficiencies of a single fiber per unit volume
in a filter for particles of 8 μm in aerodynamic diameter under standard density
and neglecting electrostatic effect. The filter bulk thickness is 5 mm, its solidity
is 5 %. The average diameter of the fiber is 25 μm. The face velocity is 2 cm/s.