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462 Lawerence K. Wang et al.

Fig. 6. Schematic of a charged-particle scrubbing system.

4.3.3.2. TYPES OF CHARGED WET SCRUBBER
There are numerous arrangements and configurations of CWSs that can be used for col-
lecting submicron particles. In charged drop scrubber (CDS) units, all particles can have
either a positive or negative charge, with all the water drops having the opposite charge.
A variation of this is that the drops are bipolar (a mixture of both charges) to reduce the
self-precipitation of drops. In this case, the particles can be either unipolar or bipolar.
Other arrangements include systems that charge particles only and not the drops. The
collection in these devices has not been as effective as in the CDS. The space-charge
precipitator is an example of this arrangement. In this unit, collection relies on precipi-
tation on walls caused by self-fields induced by charged particles. Another example is
the self-agglomerator, which increases the size of particles.
Systems that use solid collectors rather than liquid collectors include the electro-
fluidized and electro-packed beds. These systems could be very useful and are considered
wet scrubbing systems when a scrubbing liquid is used.
A charged-particle scrubbing system can be represented schematically (see Fig. 6).
Physically, several of the boxes could be a single pieces of equipment. Conversely, a sin-
gle box could represent several pieces of equipment. Systems noted as A, C, and D repre-
sent fairly conventional techniques. In system B, drops could be charged as produced. They
also could be charged by ion impaction as in a conventional ESP or a system using similar
precipitator technology. Interaction step C and separation of the drops with the collected
particles from the gas step D could represent many of the standard wet scrubbing devices.
Production of charged drops consists of drop formation and drop charging.
Currently, it is most common to generate the drops by mechanical atomization, by
pneumatic atomization, by a combination of these, or by condensation. The main source
for energy from drop formation would therefore be mechanical or thermodynamic. An