Recently, a new scrubber system* has been developed that features low operating costs, low energy consumption, and the ability to simultaneously handle both submicron particulate and hazardous fumes. The technology, which is based on the natural principle of cloud formation, has been implemented and proven at several major fiber optics manufacturing facilities, as well as other facilities generating submicron particulate in North America and Europe. The system has been shown to be 99%+ efficient for the collection of all types of particulate above 0.1 micron.
“Clouds are formed when water condenses on small particles of dust, or salt. Those particles naturally coagulate with larger ones—the phenomena is called Brownian motion—but in nature, the process is only about 1% efficient. The key to collecting particulate efficiently is to improve upon the action of the cloud: to ‘grow’ particulates by increasing humidity.
“At 80% relative humidity, for example, a particle that was originally .01 micron will, in seconds, double in size. At 100% humidity, it will grow to about .05 microns. Now, take it to 101% relative humidity—the point of slight super-saturation—and that particle becomes easily removable from a gas flow.”
Richards believed a technology could be developed that would use these principles to collect “earthbound” particulate. Over a 12-year period, his company, Atmospheric Physics Inc., researched and tested dozens of techniques to create the water droplet, particulate and electrical charge combination that would most efficiently allow particulate to be collected. The result was the new scrubber system, now licensed and distributed by Tri-Mer Corp.
Inside the scrubber’s collection chamber, billions of droplets are formed and electrically charged, causing droplets and uncharged particles to move continuously in relation to each other. The fact that particles are not charged is an important distinction, because the corona discharge used by ESP devices to drive particulate to a grounding plate consumes large amounts of energy. In fact, the new scrubber operates at barely 1% of the total energy required by an ESP for the same task. The new scrubber’s primary charge modules require just 600 watts of power, compared to the level of a typical electrostatic precipitator power draw of 60,000 watts or more.
With the new scrubber, as any particle passes between 10 and 20 microns of a water droplet, electrical attraction causes the particles to enter the water droplets. Each water droplet therefore becomes a “collector” of thousands of particles, constantly re-energizing with each pass through the system. Since the charged droplets are the collectors, there is no need for fibrous filters, collector plates, Venturi throats, layered pads, bags or cartridges. A schematic of the new scrubber system is shown in Figure 1.
Second, in cases where particulate is below 0.1 micron in size, a super-saturation section, interfaced into the system’s preconditioning chamber, is included in the system design. This facilitates the collection of particulate as small as 0.01 microns by allowing the particles to “grow” to a size that allows the scrubber to work successfully in ranges not possible with other technologies.
Third, the new scrubber has flexibility of application. It is alone in its ability to collect both soluble and insoluble particulate, and in its ability to scrub corrosive fumes, gases and odors simultaneously with particulate. The system can easily scrub 100 ppm of HCl to below 1 ppm, for instance, while collecting ammonium chloride, ammonium nitrate or other particulate matter, including silica dioxide and lead oxide. The system can also interface with applications requiring the reduction of SO2, Cl2, NH3, sulfuric acid, fluorine, and other gaseous emissions, which can eliminate the need for packed bed scrubbers. Due to its low pressure drop, the system can also act as a tail gas scrubber. Manufacturers can also incorporate the new scrubber with other selective catalytic reduction NOx removal systems.
The most advantageous particle size distribution for a scrubber unit is between 0.1 and 5 microns, but the system can also handle particulate hundreds of microns in size. Removal efficiencies of 99% and higher for particulate from 0.1 micron and above are achievable. The system handles inlet grain loadings in excess of 1.5 grains per dry standard cu. ft. (dscf), reducing loads to below 0.015 grains per dscf. Lower outputs are also possible, depending on site permit requirements.