Selecting Air Pollution Control Systems:
Comparing an Electrostatic Precipitator (Wet ESP)
with Alternatives for Submicron Particulate,
Including Diesel Soot

Q. What makes submicron particulate such as diesel soot
so difficult and costly to control?

A. When drops of water are suspended in a stream of air containing particles,
such as in wet scrubbers or venturis, the air must go around the drops to pass through
the device. This creates streamlines of higher velocity air near each drop. For particles
to be captured, they must push through these streamlines to the surface of the drop.

Particles such as diesel soot, that are under 1 micron, are hardest to control because they
tend to follow the streamlines and avoid contact with the drop. As particle size decreases,
more energy is needed to force contact with the drops. This makes conventional scrubbers
ineffective below a few micons, or pressure drop too high to be practical in a venturi.

ESP technology has different challenges. In general, Dry ESP is inefficient on submicron
particulate such as diesel soot because of inherent equipment limitations on the voltage and
amperage that can be applied, and restrictions on the resistivity and loading density of
the pollutant. Wet ESP can use much higher power levels, at a high energy cost, but is
limited by the difficulty of placing a charge on the astronomical number of submicron
particles in even a light loading concentration. This severely limits the loading concentration.
Among other serious issues for a wet ESP is the intrinsic minimization of corona
charging in the submicron size range due to the physics of corona charging.

The Cloud Chamber Scrubber has overcome these difficulties. CCS charges only the
water drops, not particles. Corona charging is not used. The CCS does not require
the very high voltage and amperage of wet ESP.

The CCS uses billions of water drops to scrub particles such as diesel soot like conventional
scubbers or venturis. But unlike the conventional approaches, the CCS drops are highly charged.
The charge on the drops pulls the particles through the streamlines into contact with the
surface of the drops, thus collecting the particles. The CCS can handle high load
concentrations with little influence on capture efficiency.

Q. How does the typical 500 – 3000 watts per 1000 cfm required
by Wet ESP for charging compare with the CCS?

A. The CCS uses less than 10 watts per 1000 cfm for charging. A proprietary and patented
method is used to charge the water droplets. For example, charging droplets to treat 10,000 cfm
draws the same amount of energy as a 100 watt light bulb. The other two sources of electrical
power draw are the I.D. fan (often unnecessary) with a relatively small draw because system
pressure drop is less than 1.5” w.g., and the recirculation pumps with a moderate draw.
The cumulative result is that the CCS system is very energy-efficient compared to other
technologies, particularly Wet ESP.

Q. How is the CCS air pollution control system so different from
an electrostatic precipitator?

A. An electrostatic precipitator (wet ESP) tries to charge particles with corona discharge and
collect them on a ground plate or collector wall. CCS technology does not charge particles –
only droplets. Unlike particles, the droplets are a receptive medium, and the charging
mechanism operates under consistent steady-state conditions. While the CCS offers a
high turn-down ratio of 10 to 1 in changes in the air flow (unlike wet ESP) that accommodates
process changes or variations, the charging of the droplets remains constant and predictable.

The CCS will also simultaneously scrub the soluble gases in the emissions stream. This is
particularly important for applications such as diesel soot, which is comingled with numerous
gaseous components. Wet ESP requires the addition of a conventional wet scrubber to
scrub these gases.

Q. How does a diffusion candle collector compare with a CCS?

A. Candles require 16” to 20” w.g. to operate – and can only handle soluble particulate.
The CCS operates at under 1.5” w.g. and can handle both soluble and insoluble particulate.

Q. How does the CCS operate?

A. Please see the main CCS page for an overview.

Q. How does the CCS air pollution control system compare
with a high-energy venturi?

A. First, the basic mechanism is different. Venturis try to increase the relative velocity of
drops and particles in order to force them together.

Second, a venturi typically operates at 40” to 70” w.g. pressure drop with high operating costs.

Q. What is the best air pollution control system when a plant generates
both submicron particulate such as diesel soot and particulate that is
over 5 microns?

A. The CCS air pollution control system is 99%+ efficient for the collection of all types of
particulate, from 0.1 to 300+ microns. If the emission streams are separate, an excellent
option is a CCS for submicron particulate and a Whirl Wet for the collection of particulate
3+ microns and larger. Please visit the Whirl Wet page.

Q. Is there an air pollution control system for small particulate that
simultaneously removes fumes and gases?

A. CCS is a unique air pollution control system, in that it removes fumes and gases,
including HCl, HFl, HNO3, H2SO4, SO2, Cl2, NH3 and others simultaneously with all types
of particulate, including diesel soot. See the CCS page for detail. This is important because
now there's a single air pollution control system that can simultaneously handle submicron
particulate and hazardous fumes.

Q. How can one air pollution control system scrub submicron
particulate and fumes?

A. Charged droplets of common polarity instantly disperse in each CCS chamber,
providing optimum distribution of billions of fine droplets. The combined surface area
of the drops is extremely large. The gas molecules, if soluble, will be captured. This large
surface area, being charged, is critical for the capture of fine particles such as diesel soot.
This produces the collection of submicron particulate and the simultaneous scrubbing of gases.

Q. Is there an air pollution control system for small particulate such as
diesel soot, that doesn’t need packing, pads, or filters?

A. The CCS air pollution control system does not use any of these high-maintenance items.
The items you mention are also the source of high pressure drop. Since the charged droplets
are the collectors, there is no need for collector plates, bags, or cartridges.

This information is for general information purposes only.
For specific applications, please consult Tri-Mer.

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