Abstract:
A device for dissolving a gas in a liquid. The device comprises a pressure vessel or column for receiving a gas-entrained liquid via an inlet and for injecting the gas-entrained liquid via a riser into a headspace of the vessel. A flow director is disposed in an upper portion of the vessel or column to form a swirling flow path extending into a liquid pool in a lower portion of the vessel or column. An outlet is provided to direct the liquid away from the vessel or column.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to aeration of liquid systems. 
       BACKGROUND 
       [0002]    Aeration of liquids is important in many process applications. In waste water treatment for example, various processes require effective aeration to perform efficiently. Typically, blower/diffuser systems are employed. Such systems operate at low efficiencies, and thus require air to be supplied in great excess to produce adequate aeration. There is a need for a system and process to more efficiently provide aeration to liquid systems. 
       SUMMARY OF THE INVENTION 
       [0003]    The present invention relates to a device for dissolving a gas in a liquid. The device includes a pressure vessel having an inlet disposed on the pressure vessel for receiving a gas-liquid mixture. A riser is disposed in the pressure vessel and connected to the inlet. The riser extends into a head space of the pressure vessel. The riser is adapted to receive the gas-liquid mixture from the inlet and inject the mixture into the head space. An opening is disposed in an upper end of the riser below an interior surface of the pressure vessel. Disposed in an upper portion of the pressure vessel is a flow director that forms a swirling flow path. An outlet is disposed on the pressure vessel for directing the liquid from the pressure vessel. 
         [0004]    The present invention provides a method of dissolving a gas into a liquid. The method includes mixing a gas into the liquid to form a gas-liquid mixture. The method also includes directing the mixture into a pressure vessel and into a vessel riser extending within the pressure vessel. In addition, the method includes discharging the mixture under pressure into the pressure vessel and directing the mixture along a swirling flow path and towards an outlet. The method also includes discharging the liquid under pressure from the pressure vessel. The method may further include discharging pressurized liquid with gas dissolved therein into a tank containing a liquid and forming micro bubbles in the tank. 
         [0005]    Other objects and advantages of the present invention will become apparent and obvious from a study of the following description and the accompanying drawings which are merely illustrative of such invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a schematic of an embodiment of the system for producing micro bubbles in a liquid held in a tank. 
           [0007]      FIG. 2  is a cross-sectional view of one embodiment of the pressure column of the present invention. 
           [0008]      FIG. 3  is a cross-sectional view of a second embodiment of the pressure column of the present invention. 
           [0009]      FIG. 4  is a cross-sectional view of a third embodiment of the pressure column of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    With particular reference to the drawings, a micro bubble forming system, indicated generally by the numeral  100 , is provided. Micro bubble forming system  100  includes a liquid source contained in a tank  40 . Connected to an outlet  46  of tank  40  is a pump  10 . Pump  10  is connected to a venturi device  20  to cause liquid from tank  40  to flow therethrough. Venturi device  20  includes an air inlet  22  to entrain a gas, such as air, into the liquid flow. To direct the flow of gas-entrained liquid from venturi device  20 , the venturi device is connected to inlet  32  of a pressure column, indicated generally by the numeral  30 . Outlet  34  of pressure column  30  is connected to inlet  42  of tank  40  to return the flow of liquid to the tank. It is appreciated that system  100  provides a generally closed circuit in which liquid may flow from tank  40  and be returned to the tank. In circuit, the liquid passes through venturi  20  where a gas is entrained with the liquid, transits pressure column  30  where the liquid becomes highly saturated with the gas, and returns to tank  40  where micro bubbles are formed. System  100  has utility in such areas as aerating waste water prior to treatment and enriching other fluids with oxygen. 
         [0011]    It is appreciated that micro bubble forming system  100  may, in an operable state, include any of various liquid sources. As illustrated in  FIG. 1 , the liquid source contained in tank  40 , and the tank holds a volume of liquid from which liquid is withdrawn, pumped through venturi device  20  and pressure column  30 , and returned to the tank. Alternatively, for example, the liquid source may be contained in a pipe through which a liquid is conducted under influence of a separate motive force. A portion of the liquid flowing in the pipe may be withdrawn by means of a first tap or side outlet, pumped through venture device  20  and pressure column  30 , and returned to the pipe at a second tap or side inlet. 
         [0012]    Turning now to a detailed description of pressure column  30 , and referring particularly to  FIG. 2 , the pressure column comprises generally a pressure vessel capable of withstanding operating pressures. Pressure column or vessel  30  includes a riser  36  that is fluidly connected to inlet  32 . Vessel riser  36  extends upward within pressure column  30  and has an opening disposed near an inner surface  38  of the top of the vessel. In one embodiment riser  36  extends to a height such that the upper open end is disposed a short distance down from the inner surface  38  of the top of the vessel forming a gap there between. An open upper end of riser  36  forms the opening, which faces inner surface  38  across the gap. The gap is generally about one inch or smaller. 
         [0013]    Inlet  32  to pressure column  30  is disposed at the top of inlet riser  31 , and outlet  34  is disposed at the top of outlet riser  33 . Generally, inlet riser  31  extends upwardly to about 50% of the height of vessel riser  36  while outlet riser  33  extends upwardly to about 40% of the height of the vessel riser. 
         [0014]    In a second embodiment, pressure column  30  includes a helical baffle  39  disposed in an upper portion of the pressure vessel at least partially below head space  37  near the surface of liquid pool  35 . See  FIG. 3 . Helical baffle  39  comprises about one revolution or more of a helical or screw flight and forms a helical flow path in an upper portion of liquid pool  35 . In a third embodiment, illustrated in  FIG. 4 , one or more revolutions of helical baffle  39  are disposed at least partially in head space  37 , and one or more revolutions are disposed at least partially in liquid pool  35 . Baffle  39  serves as a flow director to encourage a swirling and generally downward flow within pressure column  30 . 
         [0015]    Micro bubble forming system  100  functions as follows. The liquid is pumped through venturi device  20  where a gas is entrained. As illustrated in  FIG. 1 , environmental air may be entrained via venturi device  20 . However, a gas, such as oxygen, from a gas source or generator may be entrained alternatively or in addition to environmental air. A gas-liquid mixture is formed in venturi device  20  and directed to inlet  32  of pressure column  30  as a gas-entrained liquid flow. In response to the pump driving force, the gas-liquid mixture is directed up vessel riser  36  and injected under pressure into head space  37 . In one embodiment, the mixture is ejected under pressure from an opening in riser  36  against interior surface  38 . The ejection of the mixture against surface  38  tends to spray the mixture into head space  37 . The gas-liquid mixture is incorporated into liquid pool  35  such that the gas becomes dissolved in the liquid at a highly saturated level. 
         [0016]    In one embodiment, the apparatus for which is illustrated in  FIG. 2 , the gas-liquid mixture sprayed into head space  37  descends into liquid pool  35  where the gas dissolves in the liquid. In one embodiment, apparatus illustrated in  FIG. 3 , a swirling and generally downward movement of the mixture and the liquid in pool  35  is encouraged by helical baffle  36  disposed in an upper portion of liquid pool  35 . In one embodiment, apparatus shown in  FIG. 4 , the gas-liquid mixture descends along helical baffle  38  that is disposed at least partially in head space  37  and at least partially in liquid pool  35 . A swirling and generally downward movement of gas and liquid in pressure column  30  at least partially facilitates the gas becoming dissolved in the liquid. 
         [0017]    Sufficient pressure is maintained in pressure column  30  further encourage dissolution of the gas and to force liquid with gas dissolved therein from pool  35  through outlet  34  and thence to tank  40 . Generally, the pressure within head space  37  ranges from about 35 psi to about 60 psi. Due to the pressure drop between liquid leaving pressure column  30  and liquid in tank  40 , gas will come out of solution and form micro bubbles  44  as the liquid returns to the tank. The pressure drop preferably ranges between about 8 psi and about 10 psi. Micro bubbles formed range in diameter from about 1 micron to about 10 microns and generally less than about 5 microns. Continued operation of system  100  for a sufficient time results in a cloudy or milky appearance of the liquid in tank  40 . This cloudiness evidences extensive dispersion of micro bubbles throughout the liquid. 
         [0018]    By way of example two functional scale models are described here below. In both cases, the liquid is water and the gas is environmental air. These scale models illustrate the utility of system  100  in aerating water. 
         [0019]    Model I includes tank  40  holding  55  gallons of water. Pressure column  30  is 46½″ high formed from 8⅝″ OD×¼″ wall thickness steel tube capped on each end by a 1″ steel plate welded there to and having a capacity of 10 gallons. Risers  31 ,  33 , and  36  are formed from ¾″ schedule  40 S steel pipe. The gap between the upper end of riser  36  and surface  38  is 1″. Venturi device  20  is a Mazzei® Injector Model NK PVDF 784 (Mazzei Injector Corp. 500 Rooster Dr. Bakersfield, Calif. 93307). A 1 hp pump  30  is used and a flow rate of 10 gpm is maintained through venturi device  20 . 
         [0020]    Model II includes tank  40  holding 5 gallons of water. Pressure column  30  is 18″ high formed from 2½″ OD×¼″ wall thickness steel tube capped on each end by a 3/16″ steel plate welded there to and having a capacity of 0.24 gallons. Risers  31 ,  33 , and  36  are formed from ¼″ schedule  80 S steel pipe. The gap between the upper end of riser  36  and surface  38  is ⅜″. Venturi device  20  is a Mazzei® Injector Model NK PVDF 287. A ¼ hp pump  30  is used and a flow rate of 1 gpm is maintained through venturi device  20 . 
         [0021]    The responses of the two models are summarized in Table I. 
         [0000]    
       
         
               
               
               
             
           
               
                   
                 TABLE I 
               
               
                   
                   
               
               
                   
                 Model 
                 Time to Cloud 
               
               
                   
                   
               
             
             
               
                   
                 I 
                 4 minutes 
               
               
                   
                 II 
                 2 minutes 
               
               
                   
                   
               
             
          
         
       
     
         [0022]    A utility of the present invention is to enhance, for example, oxygen-requiring reactions in a reservoir such as tank  40 . Tank  40  may be a water treatment tank, for example, where aerobic degradation of pollutants is desired. The distribution of micro bubbles of air, for example, in such a treatment tank may enhance and accelerate the removal of such pollutants. The enhancement may result in a reduction in treatment time and/or tank size. 
         [0023]    The present invention may, of course, be carried out in other specific ways than those herein set forth without departing from the scope and the essential characteristics of the invention. The present embodiments are therefore to be construed in all aspects as illustrative and not restrictive.