History of Charged Droplet Scrubbing
of Fine Particulate
Background
The concept of using charged droplets of water to scrub fine particulate was explored in the 1970s,
when the EPA funded research into charged droplet scrubbing for removal of fine particulate
at MIT and the University of Washington.
The results of this early research were mixed. While theory predicted removal efficiencies far
greater than those of electrostatic precipitators, laboratory and pilot scale tests showed poor
performance. Because of these disappointing initial results, the EPA curtailed spending on
charged-droplet fine particulate research. Researchers in other countries, particularly in France, continued efforts to build charged-droplet
scrubbers for fine particulate, but none of these efforts led to successful commercial applications. Between 1950 to 1980, many U.S. and foreign patents were issued for devices that claimed
to use charged droplets to remove aerosol particles. However, none of these devices
achieved commercial success. There were four fundamental reasons for the poor performance of
these previous experimental efforts and patented devices:
- The charge per droplet was too low.
- The density of charged droplets was not high enough.
- The energy required to charge the droplets was too high.
- The mechanical components were unreliable,
expensive, and not amenable to scaling.
Until the development of the Cloud Chamber system, the cleaning potential of charged-droplet
scrubbing of fine particulate remained unrealized. The important technological breakthrough of the
Cloud Chamber system is in its ability to economically generate large quantities of droplets that
are precisely right in size and high charge.
Development of the Cloud Chamber for
Fine Particulate Scrubbing
Dr. Clyde Richards, the atmospheric physicist who holds the patents for Cloud Chamber
technology, began his research into charged droplets during graduate studies at the
University of Arizona.
While investigating the role of charged droplets in initiating lightning, a corollary question arose
about how thunderstorms clean the air of fine suspended particles. Dr. Richards’ approach was
to develop a complete understanding of the microphysics of this natural scrubbing process,
then imitate, and improve upon it. For twelve years he worked independently, eventually establishing his own research company,
Atmospheric Physics, Inc. He developed a computer simulation that calculates the trajectory
of a particle as it passes a charged droplet and corroborated the simulation results with results
from previous charged droplet research.
Using simulation, Dr. Richards was able to calculate the fine particulate collection efficiency of
a single droplet while varying droplet size, droplet charge, droplet speed, particle size,
particle charge, and ambient electric field.
Based on these data, he applied scaling laws to accurately predict fine particulate removal
efficiencies for different conditions and configurations. The results of these predictions permitted the
optimization of droplet size and droplet charge that is unique to the Cloud Chamber Scrubber. The most significant results were the discovery of the optimal droplet size and charge; and
the mechanism by which even submicron neutral particles (the majority of naturally produced
fine particulate) could be effectively removed. Upon completion of the theoretical research, attention was turned to finding a means of
producing large quantities of optimally sized, highly charged droplets, and of thoroughly
mixing the droplets and exhaust gas. During the development phase, the main task was to produce a reliable system that provided
the necessary residence time and liquid-to-gas ratio. Insight into growing ultrafine particles
also came out of the research. A final stroke of physics insight yielded an inexpensive and
reliable method of producing the charged droplets.
Pilot tests and patents followed, shortly leading to numerous successful commercial
installations of Cloud Chamber technology for fine particulate. These installations have
been operating continuously for more than 5 years at efficiencies over 99% on
submicron particulate matter, while requiring virtually no maintenance.
WATCH: Cloud Chamber Scrubber animation
CCS Named in "Top 10 Technologies for 2007" by Pollution Engineering
Have a potential application? Tell us about it . . .
We can help you with some guidelines.
For more information contact:
Kevin Moss (801) 294-5422
kevin.moss@tri-mer.com
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