Abstract:
A gas delivery device includes a manifold and a plurality of channels. The manifold is adapted to be connected to a source of a pressurized gas. Each of the plurality of channels is in fluid communication with the manifold through a distinct associated port. Each of the plurality of channels has a generally open bottom.

Description:
FIELD OF THE INVENTION 
       [0001]    Embodiments of this specification relate to a gas delivery device for use, for example, in supplying bubbles to inhibit fouling of an immersed filtering membrane. 
       BACKGROUND 
       [0002]    International Publication Number 2011/028341, Gas Sparger for a Filtering Membrane, describes a gas sparger that produces an intermittent flow of bubbles even if provided with a continuous gas flow. The sparger has a housing to collect a pocket of gas and a conduit to release some of the gas from the pocket when the pocket reaches a sufficient size. A large sparger can be divided into a plurality of units each having a conduit. A gas supply pipe has at least one hole aligned with each unit to deliver air to each of the units. International Publication Number 2011/028341 is incorporated by reference. 
       SUMMARY 
       [0003]    A gas delivery device is described in this specification in which a supply of gas is provided to a manifold with multiple ports. Each port discharges into a conduit that extends horizontally out from the inlet. The area of the ports is less than the area of the conduits. In an embodiment, each conduit has only one outlet for discharging bubbles. In an embodiment, the ports are located closer together than the distance between two adjacent outlets. 
         [0004]    In an embodiment, a gas delivery device has a manifold adapted to receive pressurized gas and discharging the gas into a plurality of open bottomed channels. Optionally, each channel may have a single outlet which may be formed by an open end of the channel. The manifold may also have an open bottom. Ports between the inlet manifold and the channels may be in the form of open bottom slots. In another embodiment, a gas delivery device includes a distribution plenum and a plurality of channels. The distribution plenum is adapted to be connected to a source of a pressurized gas and each of the plurality of channels is in fluid communication with the distribution plenum through a distinct associated port. Each of the plurality of channels has an outlet adapted to discharge gas. The ports have a smaller area than the channels and the ports are located close together relative to a spacing between the openings. 
         [0005]    In an embodiment, an aeration process includes: bringing a flow of pressurized gas into a tank to near or below the bottom of a membrane module; splitting the flow of pressurized gas into multiple flows of pressurized gas; directing each of the multiple flows of pressurized to a different lateral position; and releasing bubbles from the different lateral positions. In another embodiment, an aeration process includes: providing a gas delivery device with a manifold adapted to be connected to a source of a pressurized gas and a plurality of channels, each in fluid communication with the manifold through a distinct associated port and having a generally open bottom; and providing a flow of pressurized gas to the gas delivery device. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0006]      FIG. 1  is a top view of a gas delivery device according to an embodiment of the invention; 
           [0007]      FIG. 2  is a bottom view of the gas delivery device of  FIG. 1 ; 
           [0008]      FIG. 3  is a side view of the gas delivery device of  FIG. 1 ; 
           [0009]      FIG. 4A  is an isometric view of the bottom of the gas delivery device of  FIG. 1 ; 
           [0010]      FIG. 4B  is an isometric view of the top of the gas delivery device of  FIG. 1 ; 
           [0011]      FIG. 5  is a side view of the gas delivery device of  FIG. 1  in combination with an intermittent gas sparger; 
           [0012]      FIG. 6  is an isometric cross sectional view of the bottom of an alternative intermittent gas sparger according to an embodiment of the invention; and 
           [0013]      FIG. 7  is a schematic cross section of a tank having a suction driven membrane module and an aeration system immersed in the tank according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    In a gas sparger as described in International Publication Number 2011/028341, a unit of the sparger that receives a larger flow rate of input gas will produce pulses of bubbles at a higher frequency. In order to uniformly clean a membrane cassette, it may be desirable to have each unit operate at near the same frequency. The holes of the gas supply pipe are made small to help equalize the gas flow rate between holes feeding different units of the sparger. However, if the gas supply pipe is installed out of level by as few as 6 mm over a length of about 500 mm, the holes at higher elevation will have a noticeably larger gas flow rate. In addition, solids entering the gas supply pipe during maintenance periods when the gas supply is turned off can dry out or agglomerate when the gas is turned back. Occasionally, a solid particle is formed in the gas supply tube that is large or rigid enough to be lodged into one of the holes and to restrict or block the hole. A partially or completely blocked hole will in turn lead to poor distribution of gas to the membranes and allow solids to accumulate on the membranes. A gas delivery device will be described below that can be used as an alternative to such a gas supply pipe either with or without a further gas sparger. 
         [0015]      FIGS. 1 to 4  show different views of a gas delivery device  10 . Alternatively, the gas delivery device  10  may be called an aerator or a sparger. In use, the gas delivery device  10  is immersed in a liquid, for example water or activated sludge. Pressurized gas is supplied to an inlet  12  of the gas delivery device and is emitted as bubbles from a plurality of outlets  14 . The gas may be air or in some applications another gas, for example biogas, nitrogen, ozone or oxygen may be used. The gas delivery device  10  shown has four outlets  14 , but there may alternatively be more or less outlets  14 . 
         [0016]    The inlet  12  is separated from the outlets  14  by a plurality of ports  16 . Each outlet  14  communicates with a port  16  through a channel  18 . Part of the gas delivery device  10  from the inlet  12  to the ports  16  functions as a manifold  15 , alternatively called a plenum, to distribute the gas entering through the inlet  12  among the channels  18 . The inlet  12 , ports  16  and outlets  14  are located at generally the same elevation but spaced horizontally. The gas flows generally horizontally in the channels  18 . 
         [0017]    The area of the ports  16  is less than the area of the channels  18 , or less than the area of the smallest of the channels  18  if they have different areas. For example, the channels  14  may have a cross sectional area that is three times or more than the cross sectional area of the ports  16 . The ports  16  restrict the flow of gas into the channels  14 . The restriction provided by the ports  16  helps to distribute the total airflow more nearly equally among the channels  18 . Decreasing the area of the ports  16  produces a more nearly equal flow in the channels  18  but also increases head loss through the ports  16 . The ports  16  may be made all of the same area. The area of the ports  16  may be reduced until the flow is adequately distributed among the channels  18 . Optionally, a port  16  opening into a long or narrow channel  18  may be larger than a port  16  opening into a short or wide channel  18  to help equalize the flow among the channels  18 . Alternatively, one or more ports  16  may be made larger than other ports  16  to intentionally increase the relative airflow through one or more channels  18 . This may be done, for example, to provide more air to the extremities of an immersed membrane cassette to counteract a tendency for water to be lifted through the center of a cassette. 
         [0018]    As shown in  FIG. 1  and  FIG. 2 , the ports  16  are located close to each other in the horizontal direction. In this way, if the gas delivery device  10  is mounted a few degrees out of level, there is very little difference in elevation between the ports  16 . In particular, the largest horizontal distance between two ports  16  is less than the average horizontal distance between adjacent outlets  14 , or less than half of the average horizontal distance between adjacent outlets  14 . The largest horizontal distance between the ports  16  is also less than 25%, or less than 10%, of the largest distance from a port  16  to an outlet  14 . This helps produce a more nearly equal distribution of the gas among the channels  18  compared to an ordinary aerator in the form of a tube with holes when the gas delivery device  10  is mounted out of level. Because the ports  16  are primarily responsible for equalizing flow between channels  18 , the outlets  14  can be made larger, for example as large as the cross sectional area of the channels  18 , so that any solids that accumulate in a channel  18  are unlikely to block the outlet  14 . 
         [0019]    The gas delivery device  10  has its outlets  14  spaced generally in a line. Alternatively, other configurations may be used. For example, channels  18  could extend along a line but in both directions from the inlet  12 . In another example, the channels  18  could radiate from the inlet  12  like spokes from a wheel hub. 
         [0020]    Optionally, the top of the channels  18  may be pointed slightly upwards. In this way, if the gas delivery device is inadvertently mounted with a slightly downwards slant, then gas will not be trapped in the channels  18  when the supply of gas is off. A slight upwards slant may also help compensate for differences between the lengths of the channels  18 . 
         [0021]    Referring to  FIG. 7 , the gas delivery device  10  may be used, for example, to provide bubbles for scouring an immersed membrane module  50 . A device with a line of outlets  14  is particular suited for providing bubbles to membrane modules with rectangular elements such as flat sheet modules or ZeeWeed™ hollow fiber elements sold by GE Water &amp; Process Technologies. 
         [0022]    The gas delivery device  10  is immersed in a tank  52  containing one or more membrane modules  50 . The gas delivery device  10  may be mounted separately in the tank  52  or attached to the membrane modules  50 . Gas may be brought down into the tank from a riser pipe  54  and then spread horizontally through as header  56 . Saddles  58  attached to the header  56  receive gas from the header and carry the gas to a line of gas deliver devices  10  oriented perpendicularly to the header  56  in a generally horizontal plane. Optionally, a gas delivery device  10  may be connected directly to a header  56  or riser pipe  54 . Streams of bubbles  30  are discharged from the outlets  14  at various lateral positions relative to a membrane module  50 . The gas flowing to each lateral position bypasses any intermediate lateral positions. The bubbles  30  may be allowed to rise directly to the membranes to clean them or inhibit fouling. Alternatively, a transducer may be placed above the gas delivery device  10  to modify its output before the bubbles reach the membranes. For example, a diffuser may be placed over an outlet to disperse the bubbles over a wider area. 
         [0023]      FIG. 5  illustrates another transducer option in which an intermittent gas sparger  20 , for example of the type shown in International Publication Number 2011/028341, is associated with the gas delivery device. Pressurized gas  28  is split in the gas delivery device into four bubble streams  30 . Each bubble stream  30  rises into a different cavity  32  of the intermittent air sparger  20 . Gas flowing through a conduit  18  to a particular cavity  32  bypasses any intervening cavities  32 . 
         [0024]    Each cavity  32  has a discharge conduit  34 , in the form a J-shaped tube in the example of  FIG. 5 , which acts like an inverted siphon to discharge intermittent pulses of air from the cavity  32 . Bubbles emitted from the gas delivery device  10  first collect in the cavity  32  forming a pocket of gas in the top of the cavity  32 . No gas is emitted from the cavity  32  until the pocket of gas expands to reach the low point of the discharge conduit  34 . At that time, the pocket of gas empties out of the cavity  32  through the conduit  34  and the process repeats. In this way, a continuous stream of bubbles  30  from the gas delivery device  10  is converted into an intermittent flow of bubbles from the intermittent gas sparger  20 . 
         [0025]    In  FIG. 5 , the gas delivery device  10  is shown mounted separately and below the intermittent gas sparger  20 . Alternatively, the gas delivery device  10  may be mounted to the intermittent gas sparger  20 . In the example shown, the inlet  12  may be fitted into a receptacle  26  of the intermittent gas sparger  20 . A fastener (not shown) is then placed through an eyelet  22  on the gas delivery device  10  and into an abutment  24  on the intermittent gas sparger  20 . This results in the gas delivery device  10  being located partially within the intermittent gas sparger  20 . However, the outlets  14  are below the conduits  34  and still discharge into water below the lower limit of the pockets of gas in the cavities  32 . 
         [0026]      FIG. 6  is an isometric cross sectional view of the bottom of an alternative intermittent sparger  40 . In this example, multi-port conduits  42  provide two or more outlet paths extending upwards from the low point of each multi-port conduits  42 . A divider  44  between adjacent multi-port conduits  42  has a slot  46  extending from the bottom of the divider  44  to above the low point of the multi-port conduits  42 . Each cavity with a multi-port conduit  42  replaces two cavities with a single outlet conduit and so avoids a need to balance the supply of gas between the two replaced cavities. The slot  46  in the divider  44  helps equalize the air supply to the cavities. Gas may flow in either direction through the slot  46  but the net flow will be from a cavity that receives a larger gas flow to a cavity that receives a lower air flow. 
         [0027]    The gas delivery device  10  is, in a particular embodiment, an open-bottomed structure. For example, the channels  18  are formed by side walls and a top. The channels  18  are open at the bottom and, in a particular embodiment, at their ends. The outlets  14  may be defined by the open end of the channels  18 . The manifold  15  between the inlet  12  and the ports  16  is, in a particular embodiment, also open at the bottom. In a particular embodiment, the ports  16  are slots also open at the bottom of the gas delivery device  10 . In this way, solids caught anywhere in the gas delivery device  10  beyond the inlet  12  can fall or be expelled downwards out of the gas delivery device  10 . Having such a short and simple pathway for solids to leave helps prevent fouling in the gas delivery device  10 . In the event that solids somehow still accumulate in the gas delivery device, the open-bottomed structure makes it easy to locate and remove the solids, for example by spraying water into the bottom of the gas delivery device  10 . 
         [0028]    The open-bottomed construction of the gas delivery device  10  also helps accommodate a range of input gas flow rates. At low flow rates, water enters into the gas delivery device  10  and reduces the size of the ports  16 . At higher gas flow rates, less water enters into the gas delivery device  10  and the ports  16  and channels  18  increase in size. An aeration process comprising the steps of, a) providing a gas delivery device according to an embodiment of the invention; and b) providing a flow of pressurized gas to the gas delivery device. In an embodiment of the invention, the flow of pressurized gas is varied within a range of input gas flow rates. 
         [0029]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.