Chemistry: electrical and wave energy – Processes and products – Processes of treating materials by wave energy
Reexamination Certificate
2000-09-01
2002-08-13
Wong, Edna (Department: 1741)
Chemistry: electrical and wave energy
Processes and products
Processes of treating materials by wave energy
C204S157440
Reexamination Certificate
active
06432279
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the production of ozone (O
3
) and decomposition of contaminants, specifically to methods and apparatus for using density differences in fluids combined with a cylindrically configured irradiation apparatus for improved production of ozone from air or oxygen and for decontamination. Ozone is used as a treatment for drinking water, wastewater, and related applications where it interacts with organic impurities to implement disinfection. Decontamination applications include removal of gaseous pollutants such as sulfur dioxide from effluent gas and volatile organic compound decomposition in water, wastewater, air and other gases.
BACKGROUND OF THE INVENTION
Currently there is only one widely used process for the generation of ozone for water treatment and other commercial uses. This process is referred to as “corona discharge” or “silent discharge”. In this process the oxygen or air is introduced to a high voltage environment where the high voltage causes the gas to “corona” at areas of concentrated electric field which leads to break down and arcing between the negative electrode (cathode) and the positive electrode (anode). The products of decomposition of the oxygen include ozone. The corona discharge devices that were first developed have been improved over the years. And now commercially available corona discharge devices can generate a pound of ozone from pure oxygen with as little as 3 kilowatt-hours of energy. Furthermore, the corona discharge process can now convert more than 10 percent of pure oxygen to ozone. Both the energy efficiency and the ozone concentration are critical to the economical production of ozone. In addition to these operating characteristics, ozone generator equipment cost and maintenance are important factors.
Although the corona discharge process has come to be the main method for ozone production, it has its disadvantages and limitations. First of all, relatively large electrode surface areas are required for the corona discharge process. This causes corona discharge reaction chambers to be relatively large and expensive. This large size can also have a significant impact on the space requirements within the user's process facility. Secondly, corona discharge devices require periodic cleaning and replacement of their corona discharge electrodes and insulators in order to minimize system failures. This not only has a labor cost impact, but also has an impact on the floor space needed for access to the system for proper cleaning as well as an impact on the available up time of these systems. Thirdly, corona discharge systems require relatively sophisticated high voltage, high frequency pulsed power supplies to operate. These systems are expensive, complicated and require access to highly qualified technical staff for servicing. And finally, the operating efficiency of the corona discharge device is highly dependent on the availability of low temperature cooling water. This means that in most locations a substantial cost for water chillers must be included in the capital equipment and operating budget for corona discharge systems. In addition, more space, power, and maintenance are required to support the chiller.
Alternative methods for the production of ozone have been reviewed and some have been shown to be viable from the aspect of overall efficiency of production. Steinberg, Beller, and Powell have discussed the advantages of using chemonuclear reactors as an efficient ozone production process. Unfortunately this process may only be cost effective from a capital equipment standpoint for the very largest of water treatment facilities. A number of studies have been made evaluating ozone production rates using either gamma or electron beam radiation. Although these studies have generally shown production efficiencies that equal or exceed corona discharge devices, the capital cost comparisons did not show any economic advantages of these alternatives except for the very largest of systems.
Several patents have been issued for electron beam devices used for the generation of ozone. U.S. Pat. No. 3,883,413 to Douglas-Hamilton (1975) discusses a pulsed discharge electron beam device that generates ozone with the same efficiency that corona discharge systems have today. However this system is not an economical alternative because of its typical ozone concentration of only 0.4%. This is well below the 10 to 15% ozone concentration levels attainable with today's corona discharge systems. U.S. Pat. No. 4,167,466 to Orr, Jr. et al. (1979) describes an electron beam generator with much higher production efficiency. This device requires as little as 0.26 kW-hours of energy to produce a pound of ozone. The patent indicates that high efficiencies are attained by moving oxygen past the beam at high velocities. However the ozone concentrations produced are still less than 1 percent for a single pass through. The patent does indicate much higher ozone production concentrations are possible by repeatedly recycling the oxygen past the beam. However there is no mention of how this can be accomplished cost effectively. U.S. Pat. No. 5,756,054 to Wong et al. (1998) describes an electron beam device that can be used to generate ozone directly from liquid oxygen. This is supported by earlier research that indicated generating ozone concentration levels of up to 10% were generated by an electron beam in liquid oxygen. However the energy dosage had to be applied slowly and the oxygen had to be cryogenically cooled to be maintained in a liquid state. U.S. Pat. No. 5,756,054 discusses an approach that uses cryogenic cooling to separate the ozone from the oxygen. In this way the oxygen not converted to ozone could continue to be processed to maximize ozone production. However it does not address the economics of this process in order to evaluate its cost relative to its benefit.
In summary, a number of corona discharge devices have been used for the production of ozone, but nevertheless they all suffer from a number of disadvantages:
(a) They are large and require considerable space within a facility
(b) They require the use of expensive pulsed or high frequency power supplies
(c) They require periodic cleaning and other maintenance to function effectively
(d) They require water chillers to operate at high efficiencies.
In addition, electron beam generators have been proposed as alternative ozone generating devices, however they also have a number of disadvantages:
(a) Proposed electron beam generators are expensive to manufacture because of their complex configuration and beam focusing requirements.
(b) Their unidirectional or bi-directional beam structure does not allow the system to have the compactness desired for processing systems.
(c) Currently proposed electron beam generators have thus far only generated low concentrations of ozone which may, to some extent be due to recycling limitations.
(d) Additional apparatus proposed for increasing ozone concentrations involving multiple recycling of the oxygen or refrigeration to precipitate ozone are relatively expensive and complicated processes.
A number of patents have been issued for the decomposition of sulfur dioxide and other pollutants using electron beam irradiation. The most important difficulties to overcome for effective irradiation have been penetration of the medium to be processed and spreading the electron beam to effectively process large waste streams. Many innovative techniques have been employed in attempts to overcome these difficulties. For example in U.S. Pat. No. 3,891,855 to Offermann (1975) and U.S. Pat. No. 4,173,719 to Tauber et al. (1979) the process fluid stream is narrowed to allow penetration with a lower energy beam. However converting the fluid stream to a wide, narrow channel can be expensive and cause substantial flow losses and process complications. Other attempts have been made including processing contaminated fluids in the vapor phase as described U.S. Pat. No. 5,319,211 to Matthews et al. (1994). Although penetration of the f
Gregory Smith & Associate
Wong Edna
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