Wet scrubber unit

Details Wet scrubber unit Wet scrubber unit

1998-11-09

2001-05-15

Simmons, David A. (Department: 1724)

Gas separation: apparatus

With gas and liquid contact apparatus

C096S355000, C261S078200, C261S118000, C055S342000

Reexamination Certificate

active

06231648

ABSTRACT:

BACKGROUND OF INVENTION
1. Field of Invention
This invention relates generally to air pollution control devices, and more particularly to a wet electrostatic scrubber unit for extracting particulate matter entrained in a polluted air stream, whereby emerging from the unit is an environmentally-acceptable air stream.
2. Status of Prior Art
The concern of this invention is with air pollution resulting from the emission into the atmosphere of particulate matter and other contaminants. As noted in the Federal Register of Dec. 27, 1996 (Vol. 61, No. 25), “The primary goal of the Clean Air Act is to enhance the quality of the Nation's air resources and to promote the public health and welfare and the productive capacity of its population.”
The same volume of the Federal Register deals with reducing emissions of hazardous air pollutants (HAP) from plants that manufacture flexible polyurethane foam. The HAP emitted by these plants include methylene chloride, toluene diisocyanate and several other compounds. However methylene chloride accounts for over 98 percent of the total HAP.
In my above-identified copending patent application there is disclosed a wet scrubber that is particularly applicable for use in industrial plants that emit hazardous air pollutants, such as plants producing flexible polyurethane foam.
The wet scrubber disclosed in my copending application integrates the normal action of a wet scrubber in which pollutants in a gaseous stream are contacted with water, and the action of an electrostatic precipitator in which pollutants are extracted electrostatically.
A conventional electrostatic precipitator passes a polluted gas stream between spaced electrodes across which is applied a high direct voltage, such as 15,000 VDC. The resultant electrostatic field acts to charge particles entrained in the gaseous stream and to cause them to migrate toward one of the electrodes and be collected thereby. The main drawback of a conventional electrostatic precipitator, apart from requiring a high voltage supply, is that the contaminants collected on the collecting electrode tend to adhere thereto. This makes it necessary, on occasion, to shut down the precipitator in order to scale off the accumulated dirt.
Wet electrostatic precipitators are known having a curtain of water flowing down the collecting electrode to wash away dirt particles, thereby preventing the particles from adhering to this electrode. But should water be sheared off this curtain by the gas stream being blown through the precipitator, then sparking will occur, making it necessary to shut down the precipitator or to reduce the velocity of the air stream.
In a wet scrubber of the type disclosed in my copending application, an electrostatic charge is produced in a treatment station not by a high voltage as in an electrostatic precipitator, but by a triboelectric action arising from friction produced when a beam of water collides with a hard surface in the station. The force of this collision is such as to generate negative ions which electrostatically charge the turbulent mist resulting from the collision, thereby capturing particulate matter entrained in the polluted air stream intercepting the mist.
The treatment station disclosed in my copending application has a rectangular configuration, with a row of nozzles mounted on one wall of the station which project multiple beams of water that strike a parallel wall to produce a turbulent mist that is electrostatically charged as a result of ions generated by the collision. However, the turbulent mists and the ions generated in the rectangular station are not dispersed throughout the station, particularly at the four right-angle corners which are effectively dead spots.
Of prior art interest are the wet scrubbers disclosed in the Sibley et al. U.S. Pat. No. 4,609,386 and in the Clark U.S. Pat. No. 2,802,542. In these scrubbers, pollutants are removed from a gaseous or air stream by passing the polluted air through a scrubber chamber in a tortuous path, the flowing air being contacted by water sprayed into the chamber by nozzles. This action causes pollutants to be transferred from the polluted air to the water, thereby cleaning the air.
The reason wet scrubbers of the type heretofore known do not triboelectrically generate ions even though water projected from nozzles mounted on one wall of the scrubber strike another wall thereof is that the collision of the water with the wall does not have sufficient force to provide the friction necessary to generate a significant amount of ions. Thus in the Clark patent the water projecting from each nozzle flares out, so that when striking a wall it then has little impact force.
Wet scrubbers of the type heretofore known transfer the particulate matter extracted from the polluted gaseous stream to the water, as a consequence, of which the water emerging from the scrubber is contaminated. While the usual practice is to feed water discharged from a wet scrubber into a sewer line, in doing so one may violate existing environmental protection regulations.
If the contaminants in the water discharged from the wet scrubber are innocuous, the discharge is then “sewerable”. But if the contaminants carried by the water are hazardous, the water may not be sewerable. Hence the fact that the wet scrubber is highly effective in removing contaminants from the gaseous stream being discharged into the atmosphere does not overcome the problem of discharging water-borne hazardous contaminants into a sewer line.
SUMMARY OF INVENTION
In view of the foregoing, the main object of this invention is to provide a wet electrostatic scrubber unit for extracting from a polluted air stream the particulate matter entrained therein by creating an electrostatically charged mist which captures the particulate matter, whereby emerging from the unit is an environmentally-acceptable air stream.
More particularly, an object of this invention is to provide a unit of the above type in which the electrostatically charged mist is produced by projecting a beam of water at high velocity toward the hard surface of a duct through which is blown the polluted air stream, the beam colliding with this surface with sufficient force to triboelectrically generate negative ions that cause the mist to acquire an electrostatic charge.
A significant feature of the invention is that the negative ions generated in the unit react with oxygen in the air stream to produce ozone that acts as a germicidal agent to destroy microorganisms carried by the air stream and to oxidize the particulate matter captured by the mist whereby the water emerging from the scrubber which carries this oxidized particulate matter is sewerable.
Also an object of the invention is to provide a wet electrostatic scrubber unit that operates efficiently and reliably, and can be manufactured at a relatively low cost.
Briefly stated, these objects are attained in a wet electrostatic scrubber unit for extracting from a polluted air stream particulate matter entrained therein, whereby emerging from the unit is an air stream that is environmentally acceptable. The unit includes a treatment station having a cylindrical duct through which is blown the polluted air stream. Coaxially disposed within the duct is a water delivery pipe having nozzles along its length from each of which is projected toward the duct a radial beam of water.
The radial beam collides with the inner surface of the duct to create a turbulent mist which is intercepted by the polluted air stream flowing through the duct. The velocity of the radial beam is such as to cause it to collide with the duct surface with sufficient force to triboelectrically generate negative ions. These cause the mist to acquire an electrostatic charge to capture the contaminates entrained in the polluted air stream. The negative ions also react with oxygen in the air stream to produce ozone that oxidizes the particulate matter captured by the mist. As a consequence, the water carrying the oxidized particulate matter can safely be discharged into a sewer.


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