Environmental Engineering FOURTH EDITION

408 ENVIRONMEN7ALENGINEERING

point is always the farthest up the process line. Most effective control is achieved at
the beginning of the process or, better yet, by finding a less polluting alternative to
the process: mass transit as a substitute for cars, for example, and energy conserva-
tion instead of infinite expansion of generating capacity. Such considerations are good
engineering and economics practice, as well as sensible and enlightened.

PROBLEMS

20.1 Taking into account cost, ease of operation, and ultimate disposal of

residuals, what type of control device would you suggest for the following emissions?

a. Dust particles with diameters between 5 and 10 pm.

b. Gas containing 20% SO2 and 80% N2.

c. Gas containing 90% HC and 10% 02.

20.2 An industrial emission has the following characteristics: 80% N2, 15% 02,

5% CO. What type of air pollution control equipment would you recommend?

20.3 A whiskey distillery has hired you as a consultant to design air pollution

control equipment for a new facility, to be built upwind from a residential area. What

problems would you encounter and what would be your control strategy?

20.4 Dust has specific gravity of 1.2 and particle size analysis as follows:

Mean diameter (Fm) % of particles by weight

0.05

0.1

0.5

1 .o

5.0

10

20

25

35

10

The dust is trapped by a cyclone with diameter 0.51 m, inlet width of 15 cm, and an

inlet length of 25 cm, operating at five effective turns and 2.0 m3/s air flow.

a. What is the removal efficiency?

b. What is the pressure drop at air temperature of 20°C and 1 atm?

c. What is the separation factor? Is this a high-efficiency cyclone?

20.5 Aplate-type electrostatic precipitator is to remove particles having a diameter

of 0.5 pm at a flow rate of 2.0 m3/s. The 40 plates are 5 cm apart and 3 m high. Ideally,

how deep must the plates be to achieve removal?

20.6 Dust has particles with a drift velocity of 0.15 ds. For a total air flow of

60 m3/s, what must be the number of 10 x 10 m2 collecting plates needed to achieve

90% removal?

20.7 Calculate the removal efficiencies for the dust described in Problem 20.4 for

a standard cyclone, an electrostatic precipitator, and a fabric filter, using the curves of

Fig. 20-12.