Abstract:
A method and apparatus for stripping a volatile compound from waste water comprises creating a high velocity spray of air and stream of water at a first inlet to a first expansion chamber to volatize the compound, recombining the water and air flow through a second and successive expansion chambers and recreating a spray at each such chamber, whereby additional volatile compounds are released from the water at each stage to steadily reduce the contamination of the water. The decontaminated water and volatile compound-laden air are separately collected after exiting the last expansion chamber.

Description:
This application is based on my U.S. Provisional Patent Application Ser. No. 60/108,839, filed Nov. 18, 1998. 
    
    
     This invention relates to a method of and device for stripping volatile organic and similar compounds from a non-volatile liquid such as water that is contaminated with such compounds, in order to enable the liquid to be reused for purposes where any remaining contamination is acceptable for such use. 
     BACKGROUND OF THE INVENTION 
     Water has long been recognized as one of the earth&#39;s most precious resources. Recent scientific reports have indicated that the population of the earth may double by the year 2050, placing severe stress on the supply of fresh water available for human use, crops, livestock and other needs where only relatively clean water is acceptable to meet the requirements. In many areas, the demand for fresh water already exceeds the supply, and the situation is only expected to worsen. Desalinization is not always an option, because it ordinarily requires that a nearby source of salt water be available. Cost also continues to be comparatively excessive. Desalinization is customarily confined to areas where fresh water is either scarce or unavailable. 
     Many industrial uses of water result in contamination with volatile organic compounds (VOC&#39;s) such as oils, gasoline, benzene, etc., to the extent that the degraded water is no longer fit for other purposes. A number of methods of treatment of VOC-contaminated waste water have been in use for a considerable period. They typically involve aerating the waste water to cause separation of the VOC&#39;s from the water by providing for their molecular attachment to air, discharging the separated VOC&#39;s and air and letting the water flow by gravity or by being pumped to a collection point for the now-decontaminated liquid Examples of apparatus for practicing the method are illustrated in U.S. Pat. Nos. 4,544,488, 5,266,208, 5,470,478, 5,685,976 and 5,069,796. This prior art demonstrates various types of towers and tanks in which forced air is passed upwardly through descending water moving by gravity from one perforated, shallow tray to another or through a bed of particulate material, ordinarily by bubbling the air through the water from below to create a froth of the contaminant, and then separately collecting the then-contaminated air and decontaminated water. Other of these systems utilize charcoal or carbon to finally adsorb the last-remaining organic materials when the water is to be stripped completely of contaminants. Typically, while such systems are effective to one degree or another, they generally suffer to some extent from being labor-intensive in requiring frequent disassembly and cleaning and from being complex in structure. Obviously, decontamination of a processed liquid cannot be performed satisfactorily by equipment that collects contaminant internally during processing and retains some of the contaminating substance within the equipment after processing. None of the equipment of the above-mentioned prior art systems can be said to be self-cleaning. 
     Additionally, it is typical to provide demisting apparatus with conventional air strippers, increasing the overall cost of the equipment and necessitating that the demisting means also require periodic disassembly and cleaning. 
     SUMMARY OF THE INVENTION 
     A method of and apparatus for stripping a volatile compound from waste water combine a high velocity stream of air and water to create a spray at a first inlet to a first expansion chamber to volatize the compound and commences air/water blending, and thereafter recombine the water and air flow through a second and further successive expansion chambers while recreating a blended spray at each such chamber, whereby additional volatile compounds are released from the water at each stage to steadily reduce the contamination of the water as stripping progresses. The decontaminated water and volatile compound-laden air are automatically demisted and separately collected after exiting the last expansion chamber. The apparatus is essentially self-cleaning and thus requires only nominal, occasional maintenance. Down time for disassembly and cleaning of the equipment is essentially eliminated, but in any event, is kept to a minimum. The structure is such that, even in the occasional instances where cleaning is required, it can be accomplished easily, quickly and efficiently. 
     While demisting apparatus is ordinarily required at the collection point of air and water of prior art air stripping systems, I provide for automatic demisting of the air within a collection or separation chamber itself, thereby eliminating the need for a conventional large equipment stack for that purpose. 
     It is a principal object of this invention to provide an air stripping method and apparatus that operates to more effectively reduce organic contaminants from water than known systems. 
     A major benefit from this invention is achievement of the principal object with an apparatus which is essentially self-cleaning. 
     Another object is to provide an apparatus that can be easily constructed from conventional, relatively low cost materials, without requiring use of easily-cloggable, fine nozzles and orifices. 
     Still another object is to provide a single vertical air stripping tank which can be divided into a plurality of separate, individual expansion chambers by means of a drop-in unitary set of spaced and interconnected impingement and focusing plates. 
     Another object is to enable the construction of the primary apparatus of my invention either as a single tall vertical unit or a low sequentially-segmented unit in which short interconnected segments are arranged parallel horizontally and stacked vertically. 
     Other objects and advantages will become apparent from the following description, in which reference is made to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a simplified elevational cross-sectional view of a preferred form of air stripping apparatus for practicing the method of my invention. 
     FIG. 2 is an enlarged fragmentary view of a portion of the apparatus contained within the dot-dash circle  2  of FIG.  1 . 
     FIG. 3 is a simplified elevational view of another form of air stripping apparatus for practicing the method of my invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the embodiment of my invention illustrated in FIG. 1, a vertical PVC tube forms a columnar tank  10  which may be between six and twelve inches in diameter. The tank has end caps  12  and  14  secured thereto. The tube illustrated is shown to provide four different separated expansion chambers  16 ,  18 ,  20  and  22 . The number of expansion chambers is dependent upon the liquid being decontaminated and the type and amount of contaminants to be removed. Contaminated water is introduced into the tank through a water inlet  24 . High velocity air is introduced into an air inlet  26  adjacent the water inlet  24 . The water and air volumes and velocities will vary depending on the particular liquid being decontaminated, the extent of the contamination and the desired end purity of the liquid upon completion of the decontaminating process. The mixture at the inlets  24  and  26  creates a coarse spray pattern that thoroughly blends the air and water and forms a highly efficient air/water interface. 
     For purposes of understanding this invention, let us assume that water is contaminated with an unacceptable amount of gasoline in the amount of 100 parts of gasoline to 1,000,000 parts of water (100 ppm), and that an acceptable decontamination for the intended next use of the decontaminated water will be in the reduced range of 6-8 ppm. The air flow can come from a conventional high velocity centrifugal blower (not shown) or, if desired, can be from a source of vacuum (not shown) connected to an exit end  28  for contaminant-laden air leaving the system. The air and water inlets are simple tubes which form a nozzle that has sufficiently large orifices to effectively avoid clogging due to mineralization and contaminant collection. The air velocity in the illustrative example is 5000 feet per minute (fpm) at the inlet  26  and the water infeed into the inlet  24  is 10 gallons per minute (gpm). Addressing what results within the expansion chambers before discussing how it occurs, approximately 50% of the 100 ppm contaminant will be removed from the water and become airborne by molecular attraction to the air in each chamber. This means that each successive chamber will result in reducing the contaminants in the water to 50 ppm as it exits from chamber  16 , 25 ppm after exiting chamber  18 , 12.5 ppm after exiting chamber  20  and finally 6.25 ppm after the water leaves chamber  22 . Therebeyond, the mist of air and water leaves the tank  10  through a tube  30  and enters the bottom of an air/water separation chamber  32 . Contaminant-laden air and water bubbling through water  34  in separation chamber  32  leaves through the air exit end  28 , while decontaminated water leaves through a water discharge pipe  36  to wherever it is to be conveyed. Assuming the percentage of removal were to be exactly 50% at each chamber, water leaving at pipe  36  will contain 6.25 ppm of gasoline, while 93.75 parts of gasoline will have been extracted along with the air passing through exit end  28 . That contaminated air can be treated in conventional ways not directly pertinent to this invention, and has therefore not been shown nor will it be described. This broadly describes the process in connection with the apparatus of FIG. 1, now let us refer to how the system functions at each individual expansion chamber. 
     As high velocity air and water leave their respective inlets  26  and  24  and enter the expansion chamber  16 , the two are combined and converted to a spray illustrated by dotted lines. This immediately causes a portion of the contaminating substance in the water to blend molecularly with the air as the mixture enters chamber  16 . The spray then contacts an impingement plate  38  located centrally of the chamber. Impingement acts to further convert the spray into a finer blending mist, which then tends to reflect back upwardly somewhat toward the spray entrance, but is inhibited from doing so by continued entry of spray through the inlets  24  and  26 . The finer spray spreads outwardly to deposit water droplets on the inside surface of the chamber  16 . Water runs and is then forced downwardly toward a central opening  40  in a focusing plate  42 . The water flows to the inside peripheral edges of the opening  40 . The downward air flow in the now-pressurized chamber  16  causes contaminant-laden air to flow through the center of the opening  40 , again combining the water and air at the opening  40  to create a further spray as they enter the next-following expansion chamber  18 . The opening  40  thus acts as a further large nozzle orifice. It can be seen from FIG. 1 that this action is repeated in as many expansion chambers as are provided. For this reason, the impingement action and the recombination and the further recombining of air and water to create a new spray at each successive opening in each focusing plate will not be further described. It should be understood that the entire apparatus between the inlets  24  and  24  and the exit end  28  are fully enclosed and thus pressurized. 
     Assuming the percentage reduction of contamination actually takes place as stated previously, water exiting from tank  10  into tube  30  has but about 6 ppm of the original 100 ppm contaminant remaining. The other  94  ppm has become airborne at that point, and is caused, along with the water, to enter the bottom of the separation chamber  32 . An attempt is made via the drawing to illustrate that the air flow during the processing of the contaminated water is such that only a small amount of water is contained at the bottom of the tube  30 . The air and water are forced by pressure into the separation chamber, and the air bubbles to the water surface. This action results in a demisting of the bubbles, eliminating the need to supply a demisting stack intermediate the separation tank and the exhaust system that extracts the contaminant-laden air. It also provides for additional contaminant removal. The level of water within the separation chamber  32  can be maintained by any known means to any desired height to produce the most effective results. Water is constantly drawn off at the water discharge pipe  36  as the process progresses and is conveyed therefrom to a reservoir or disposal where decontaminated water is transported. 
     FIG. 2 is an enlargement of a portion of the tank  10  showing the manner in which the impingement and focusing plates  38  and  42  are interconnected by means of threaded alignment rods  44  and nuts  46 . The enlargement corresponds to that portion of FIG. 1 contained within the dot-dash circle  2 . The plates  38  and  42  are provided with drilled holes to enable the rods to pass through them inside the outer edges of the impingement plates  38  and just outwardly of the openings  40  in the focusing plates  42 . The diameter of the impingement plates  38  and their spacing relative to the focusing plates is optional to perform whatever is found to best provide for appropriate flow of water and air through the expansion chambers. I have found that a circular impingement plate that is one-third the diameter of the tank  10  performs well. The focusing plates are annular and of an outside diameter that allows clearance between their outer peripheries and the inside cylindrical wall of the tank to accommodate natural build-up of iron and minerals on the inside wall. The clearance should be sufficient to allow plates  38  and  42  and their interconnecting alignment rods  44  to be easily installed and removed axially as a unit, even with mineral build-up. If desired, a gasket (not shown) may be provided between each focusing plate periphery and the tank wall. For example, the clearance could be as much as a quarter of an inch, and a flat, annular gasket or washer applied to each focusing plate  42 . When the unit is installed or removed, the edges of the gaskets would flex, making removal easier and facilitating resealing upon reinstallation. To accommodate such removal, the tank may be disconnected between its ends at any convenient location, shown here simply as a dotted-line coupling  47  at the upper end of the tank  10 . When the coupling  47  is decoupled, the upper end of the tank  10  may be removed and the entire assembly of rods  44  and plates  38  and  42  lifted upwardly. While the construction of nozzles or orifices through which contaminated water must pass is of such large size that internal cleaning is seldom required, provision is made so that the function can be simply and easily accomplished if necessary. The unitary interconnection of plates  38  and  42  allows cleaning to be done without much equipment down time. The system is essentially self-cleaning during processing of contaminated water and thus requires little or only nominal maintenance. The enlarged view of FIG. 2 shows what occurs as water recollects at the bottom of each expansion chamber, as visually observed in a test unit having a transparent tank wall. 
     An alternate apparatus for performing the claimed method is illustrated in FIG.  3 . This construction preceded the design of FIG. 1 in time and is designed for a low, compact air stripper where vertical space is at a premium. It consists of three separate expansion chambers  16 ′,  18 ′ and  20 ′ that are interconnected by separate piping  48  for air and  50  for water in which the air and water flow recombines between adjacent chambers. As air and water enter the first chamber  16 ′, they are converted to a spray. Spray droplets recollect into a liquid about ½ inch deep at the bottom of each chamber and drain through the piping  50  through the combined force of gravity and chamber air pressure. Contaminant-laden air in the chamber is forced by the air pressure through the piping  48  to a point where a second nozzle is formed at the juncture of water passing from the lower end of piping  50 . This new spray created at the entrance to the expansion chamber  18 ′ causes the entire contaminant-reduction process to be repeated. As noted earlier, repetition reduces the contaminated organic compound by approximately 50% in each chamber. The discharge from the last of the expansion chambers can be like that exiting from tube  30  of FIG. 1, from which the air/water flow would go into a separation chamber and water and air collectors, respectively. With chamber diameters of perhaps six to eight inches in the FIG. 3 construction and the collection apparatus at one side thereof, the entire unit can be kept to a height of as low as three feet or less. This compares to an apparatus of six or more feet high for an average size operation of the FIG. 1 design. If desired, impingement plates may be provided in any or all of chambers  16 ′,  18 ′ and  20 ′ and each expansion chamber may be constructed to enable disassembly. The piping  48  and  50  of the FIG. 3 design performs a function essentially like that of the focusing plates  42  of the FIG. 1 design. 
     While I have illustrated two different designs of apparatus for carrying out the method of air stripping according to my invention, various other changes within the scope of my invention and claims will become apparent to those skilled in this art. Also, while the method and apparatus were described solely in connection with removal of volatile organic compounds from waste water, their use for other types of contaminants and liquids other than water will be apparent to persons skilled in this art.