Page 296 - Materials Chemistry, Second Edition

CAT3525_C09.qxd 2/8/2005 10:11 AM Page 267
Incineration of MSW 267
SOLUTION
The total area of the bag is calculated as (Reynolds et al., 2002)

A A A (9.13)
curved surface flat top
2
π Dh π D /4
2
π [(25 cm/100) (6 m) π (25 cm) / 100]/4
4.76 m 2

where D is the bag diameter and h is the length (or height).

The combined area for the 50 bags is
A (50) (4.76) 238 m 2

The filter velocity is then
V qG/A (9.14)

3
[15,000 m /60)] / 238
1.05 m/min

If we assume 100% collection efficiency, the mass collected daily is
q C (15,000)(24)(120)/3150
G i
13,714 kg/day

The advantages of the baghouse for cleaning flue gases are:

● High particle removal efficiencies over a wide range of particle sizes
● Variations in loading and flow rates do not affect removal efficiency
● Corrosion and rusting is minimized because the bags are manufactured from resistant
materials
● Simple operation and maintenance
● Flexible designs are possible
Disadvantages include:

● The adhesion and accretion of hygroscopic material. These accretions will block the fil-
ter pores and waste energy
● High temperatures, acids, and alkalis within the flue gas tend to shorten fabric life
● There is the potential for fire and explosion if oxidizable particulates accumulate in the bags
● Gases are not removed

9.5.3 GAS WASHING
Wet scrubbers have become popular for cleaning contaminated gas streams because of their ability
to remove effectively both particulate and gaseous pollutants. Wet scrubbing involves bringing a
contaminated gas stream into intimate contact with a liquid that is introduced into the scrubbing
device as a finely atomized mist. The most common low-energy scrubbers are gravity spray towers
in which liquid droplets, often simply cold water or a dilute alkaline solution, are made to fall