Environmental Engineering FOURTH EDITION

Air Pollution Control 393

EXAMPLE 20.1. A cyclone has an inlet width of 10 cm and four effective turns (N = 4).
The gas temperature is 350 K and the inlet velocity is 10 ds. The average parti-
cle diameter is 8 pm and the average density is 1.5 g/cm3. What is the collection
efficiency?
The viscosity of air at 350 K is 0.0748 kg/m-h. We can assume that p is negligible
compared to ps:

1 lI2

9(0.0748 kg/m-h)(O.l m)

dc = [ 2n(4)(10m/s)(3600s/h)(1500kg/m3)

= 7.04 x 10-6m = 7.04 pm.

Then, using Eq. (20.10)

• 
  
  
  
  • 1.14,
    dc 7.04
  
  
  
  

and from Fig. 20-6, the expected removal efficiency is about 55%.

Fabric Filters

Fabric filters used for controlling particulate matter (Figs. 20-4 and 20-7) operate like
a vacuum cleaner. Dirty gas is blown or sucked through a fabric filter bag. The fabric
bag collects the dust., which is removed periodically by shaking the bag. Fabric filters
can be very efficient collectors for even submicrometer-sized particles and are widely

Clean gas out

Filter bags

Dirty gas in

Hopper

Discharge

F'igure 20-7. Industrial fabric filter apparatus. (Courtesy of American Lung
Association.)