Page 493 - Air Pollution Control Engineering

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Emerging Pollution Control Technologies 465

Fig. 9. TRW charged-droplet scrubber general arrangement. (Courtesy of TRW Inc.)

arrangement through the electrodes as shown. Dirty gas enters at the lower right and
cleaned gas leaves at the top.

4.4. Use of Chemicals
It has been noted that many particle collection systems use liquids in the process to
either serve directly as the collection medium or to assist indirectly by washing out the
collected material. Water is the most common liquid used. The collected matter or addi-
tion of chemicals can change the collection efficiency of wet systems. For example, in
Venturi scrubbers, wetting agents (surfactants) can improve collection efficiency by
reducing the surface tension of the water. This changes the quality of atomization and
enables hydrophobic material to become more easily wetted and collected. The collection
efficiency of fly ash, which is slightly hydrophobic, can be improved compared with
that predicted by Eq. (23) up to the amount predicted by (13)
C /C ≅ 8.42 × 10 −8 V 3.87 A 0.157 (ρ / ∆P) 1.92 (37)
o i t g
4.5. Simultaneous Particle–Gas Removal Interactions
Wet scrubbing is useful for both particle removal by impaction and gas removal by
absorption. If a chemical reaction occurs in addition to physical absorption, it is called
chemical absorption. The absorption rate of a gas simultaneous with wet inertial
impaction removal of particulates can be expressed using the Chilton and Colburn (16)
concept of transfer units: