Abstract:
A method for entraining and mixing gas with liquids within a conduit or drop structure, comprising the channeling of one or more liquid flows into spiral flows of predetermined radius (radii), reducing the predetermined radius (radii) to increase the centrifugal forces acting upon the spiral flow(s) as the spiral flow(s) enter the conduit, and allowing gas access to the conduit to mix with and entrain within the spiral flow within the conduit or drop structure. The method can facilitate the mixing of gas with one or more fluid flows and/or reduce the release of gas emissions from the fluid(s) into the surrounding environment.

Description:
This application claims the benefit of U.S. patent application Ser. No. 09/561,999 filed May 1, 2000, now U.S. Pat. No. 6,419,843 which claimed the benefit of provisional patent application No. 60/135,476 filed May 24, 1999. 
    
    
     FIELD OF USE 
     The invention relates generally to applications whereby it is desirous to introduce or reintroduce gas with liquid flowing through pipes, and/or mix two fluids within a pipe. In particular, this method can be used, but is not so limited, to mix and entrain air and other odorous gas emissions into sewage to reduce odorous gas emissions and to reduce hydrogen sulfide corrosion and abrasive wear in waste water conveyance, collection and treatment systems. 
     BACKGROUND OF THE INVENTION 
     Throughout past decades, sewers have been utilized to efficiently transport waste water or sewage from locations where it was generated to waste water treatment plants and other destinations. These sewers consist generally of pipelines locate below ground level and oriented with a slight downward grade in the direction of the sewage flow. Gravity acts upon the sewage to cause it to flow within the pipelines toward its ultimate destination. These pipelines are sometimes interconnected by “drop structures” that allow the sewage to flow from one line into the drop structure, drop vertically therewithin, and then to flow out of the drop structure into additional pipes or other structures. 
     One problem that occurs during the transport of sewage is the release of sulfides from the sewage. Sulfides form as a result of bacterial reduction of sulfates within the sewage in an anaerobic environment. As sewage ages, the level of sulfides increases. Drop structures within a sewer system can provide a beneficial aeration of the sewage flow by introducing additional dissolved oxygen into the flow. The dissolved oxygen reacts with the sulfides, resulting in less chemical volatility in the sewage. This aeration is particularly beneficial where the sewage is fresh and contains a relatively small amount of dissolved sulfides, such as hydrogen sulfide (H 2 S). 
     Unfortunately, in most practical applications, sewage contains a significant amount of potentially volatile dissolved molecular hydrogen sulfide gas. Turbulence within the sewage flow can cause this dissolved gas to be released into the surrounding air. Significant sources of turbulence in sewage flow, and hence the emission of hydrogen sulfide gas in a sewer, occur in drop structures such as interceptor drop maintenance holes, joint structures, forcemain discharges and wet well drops in sewer pumping stations. Thus, while drop structures can reintroduce dissolved oxygen into the sewage flow, lowering the level of hydrogen sulfide gas, they can also cause the release of hydrogen sulfide gas. The hydrogen sulfide emissions often cause corrosion with the drop structures and adjacent sewer lines, and cause odor problems even the most elegant, pristine neighborhoods. 
     One known type of drop structure comprises an influent line, a maintenance hole and an effluent line. The influent line runs almost horizontally at a relatively shallow depth below the ground surface in the form of a pipe. The maintenance hole is located below the street level maintenance hole manhole cover. The maintenance hole is generally cylindrical in shape with a vertical longitudinal axis. The effluent line is another almost horizontal pipe that exits slightly above the bottom of the maintenance hole. Turbulent waste water flow is created when the sewage, which has a substantial amount of potential energy, exits from the influent line near the top of the maintenance hole and tumbles down like a waterfall to the side wall and base of the maintenance hole. Then the sewage pools and eventually flows out the effluent line. This turbulent action releases hydrogen sulfide gas into the air. To reduce the problem of gas release, while still allowing beneficial aeration of the sewage, the potential and kinetic energy in the sewage must be dissipated. 
     One known method is to create a wall hugging spiral flow down the maintenance hole to dissipate the energy by friction. The spiral flow is generated by the insertion of a vortex form connected to the influent line near the top of the maintenance hole. The vortex form is generally helical in shape and is placed directly below the manhole cover near the top of the maintenance hole. The vortex form channels and diverts the flow from its languid state into a spiral flow descending down the cylindrical wall of the maintenance hole. The vortex form can be made of concrete with applied protective coating, or made of a noncorrosive material, metal or plastic, such as PVC, High Density Polyethylene (HDPE) or other like materials. The vortex form may be manufactured at the factory or on-site. 
     Two problems remain to be solved when applying this known method of using a vortex form in a drop structure for sewage flows. First, the upstream flow velocities within the influent line are usually not large enough to create a stable spiral flow on the vertical wall of a typical maintenance hole. Thus, the flow, rather than continuing to spiral down the cylindrical wall of the maintenance hole, will generally revert to a turbulent descending flow similar to waterfall, losing the effective energy dissipation of the spiral flow and releasing significant amounts of hydrogen sulfide gas into the air. Second, quite often the maintenance hole is used for additional lateral influent connections at elevations lower than the main influent pipe. Consequently, the lateral influent connections disrupt the spiral flow and create a turbulent waterfall of sewage to the bottom of the maintenance hole, again releasing significant amounts of hydrogen sulfide gas into the air. The additional influent pipe may run in any direction, but at a lower depth than the main influent pipe. 
     SUMMARY OF INVENTION 
     It, therefore, is an object of this invention to provide a method for reducing gas emissions of a fluid through the entraining and mixing of gas with the liquid. 
     It is also an object of this invention to provide a method for mixing gas with one or more fluids in a conduit. 
     Another object of this invention is to provide a method for use in sewer drop structures that significantly reduces odorous gas emissions from the sewer. 
     A further object of the invention is to reduce hydrogen sulfide corrosion in waste water conveyance, collection and treatment systems. 
     A benefit of this invention is the improved way in which the method helps to protect conveyance or collection systems from abrasive wear. 
     Another benefit is the way the invention in particular improves the quality of wastewater by wastewater aeration. 
     The foregoing objects and benefits of the present invention are provided by a method for reducing gas emission and for entraining and mixing gas with liquids. The method comprises channeling a fluid flow though one or more pipes, introducing the flow from the pipe(s) into a conduit or chamber through the use of spiral flows of predetermined radii, reducing such radii to increase centrifugal forces acting upon the flow, introducing gas into the reduced radius flow and continuing the reduced radius flow within the conduit until the gas is substantially entrained within the flow. This method can be implemented through the use of a maintenance hole and an influent line for carrying liquid to the maintenance hole, a vortex form which accepts the liquid from the influent line, the vortex form comprising a spiral channel of decreasing radius disposed substantially within the maintenance hole, and a conduit also disposed within the maintenance hole and fluidly connected to the vortex form and extending substantially downwardly from the vortex form to a flow exit near the maintenance hole base. The fluid flowing from the influent line enters the vortex form and is channeled by the vortex form into a spiral flow with a radius smaller than the maintenance hole wall radius. The reduction in the radius of the channel outer wall causes the centrifugal forces acting upon the fluid flow to increase, forcing the flow to continue in intimate contact with the outer wall of the channel. The fluid then flows from the reduced radius of the vortex channel into the conduit and, aided by gravity and the flow&#39;s acquired rotational velocity, continues its spiral descent towards the maintenance hole base, in substantially intimate contact with the conduit wall. The spiral flow then exits the conduit near the maintenance hole base into an energy dissipating pool. 
     The method creates an accelerated fluid flow sufficient to create substantial intimate contact with the vortex form and conduit wall throughout the fluid flow&#39;s descent in the maintenance hole. This intimate contact creates frictional forces that reduce the kinetic energy of the flow and inhibit turbulent flow. The reduction in turbulent flow in turn reduces the release of gases, including hydrogen sulfide. In addition, the spiral flow in the conduit creates an air core with reduced pressure in the center of the conduit, inhibiting the escape of any hydrogen sulfide gas into the environment and encouraging the reintroduction of any escaped gas back into the spiral flow and the energy dissipating pool. 
     In another embodiment of the invention, two influent lines may be used to channel the same or separate flows into the same conduit at two different but proximate locations. The influent lines can originate from a single line or from two distinct lines and may contain the same or different fluids. The flows are then introduced into the conduit through reducing-radius vortices in opposing rotational direction. 
     In certain embodiments of the invention, it may be advantageous to utilize a vortex form channel with a downwardly sloping base sufficient to create an accelerating spiral flow. The method may also utilize a vortex form incorporating an entrance flume designed to accept the fluid flow from the influent line and more gently direct the flow into the vortex channel. This entrance flume may also incorporate a slope to create an accelerating flow into the vortex channel. 
     The invention also contemplates utilizing in certain applications of the invention various conduit base configurations for allowing the fluid flow to exit the conduit into the energy dissipating pool. These flow exit paths vary based on the desired fluid flow rates, the energy dissipating pool depth, and the existence and configuration of any effluent lines running from the conduit. 
     While this invention is particular useful in wastewater conveyance systems, it is not so limited, and can be applied to any system where one desires to mix and entrain one or more gases, including air, into one or more fluid flows within a conduit. Additional applications for the present invention include aeration and/or purification of water in wastewater treatment plants, fishery basins, and natural streams, lakes and bays, and heat transfer in power plant cooling basins. This invention may also be applied to mix food and beverage liquids; to mix constituents in pharmaceutical applications, including applications to suspensions and emulsions; and to mix construction materials including insulation materials, fillers, and high-air concentration mortars and concrete. Thus, the particular embodiments discussed below are not exhaustive and are not intended to limit the scope of this invention. 
    
    
     BRIEF DESCRIPTION 
     Other objects, features, and advantages of the present invention will become more fully apparent from the following detailed description of certain embodiments, the appended claims, and the accompanying drawings in which: 
     FIG. 1 is a side elevation, cross-sectional, view of one embodiment of the present invention with a portal-type flow exit; 
     FIG. 2 is the cross-sectional view A—A of the embodiment illustrated in FIG. 1; 
     FIG. 3 is perspective view of another embodiment of the present invention with a flow exit comprising a plurality of legs; 
     FIG. 4 is a side elevation view of an additional embodiment of the present invention with a suspended flow exit; 
     FIG. 5 is a top plan view of a portion of an influent line and a vortex form; 
     FIG. 6 is a perspective view of one embodiment of the vortex form; 
     FIG. 7 is a perspective view of another embodiment of the present invention using two vortex forms from a single influent line; 
     FIG. 8 is a perspective view of another embodiment of the present invention using two vortex forms from two influent lines. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates in a side elevation view one embodiment of a sewer apparatus  10  constructed in accordance with the present invention. Referring to FIG. 1, the sewer apparatus  10  includes an influent line  12 , a vortex form  20 , a maintenance hole  30 , a conduit  40 , a flow exit  50 , and an effluent line  60 . 
     The maintenance hole  30  in which the vortex form  20  is disposed may be identified from street level as being below a manhole cover  32 . FIG. 1 shows the maintenance hole  30  as being cylindrical in shape and oriented vertically. A lateral line  33  for inputting additional city sewer flowage into the maintenance hole  30  may be disposed below the influent line  12 . The base  34  and walls  36  of the maintenance hole  30  are generally concrete. An energy dissipating pool  72 , comprised of sewage, forms at the base  34  of the maintenance hole  30 . An effluent line  60  is connected to the maintenance hole  30  near the top level of the energy dissipating pool  72 . 
     As illustrated in FIG. 1, sewage flows from the influent line  12  into the vortex form  20  near the top of a maintenance hole  30 . The influent line  12  is generally a cylindrical pipe running slightly below the ground surface. To create an accelerated flow of sewage, a portion of the influent line  12  can be set at a predetermined downward sloping orientation. Such an orientation is shown in FIG.  3 . The slope necessary to create a constant or accelerating velocity is known as the critical or supercritical slope, respectively. A critical slope in which the velocity of the sewage flow would remain constant is identified as having a Froude Number (Fr) equal to one. A supercritical slope in which the sewage flow is accelerating is identified as having a Froude Number greater than one (Fr&gt;1). The Froude Number is calculated using the formula Fr=V/(g*d){fraction (1/2,)} where V represents average sewage flow velocity, d represents flow depth and g represents acceleration due to gravity, approximately 32.2 feet per second squared. Each of these factors can effect the critical slope of the influent line  12 . While the critical slope will generally occur around one to three percent, it is envisioned that the desired slope could vary anywhere from one percent or more. In the embodiment illustrated in FIG. 3, the influent line  12  descends at a supercritical slope of about ten percent slope to create an accelerated flow. 
     Referring again to FIG. 1, the influent line  12  connects to the vortex form  20  and maintenance hole  30  near the top of the maintenance hole  30 . The vortex form  20  is disposed within the maintenance hole  30  for receiving the sewage from the influent line  12  and is generally shaped to create a descending spiral flow. FIG. 2 presents the cross-sectional view A—A of FIG. 1, illustrating the vortex form in further detail. Referring to FIG. 2, the vortex form  20  includes a vortex channel  24 , and may in certain embodiments also include an entrance flume  22 . In the embodiment of the present invention shown in FIG. 1, the entrance flume  22  is fluidly connected to the influent line  12 . The entrance flume  22  can take on any shape capable of transporting the sewage from the influent line  12  to the vortex channel  24 . In the embodiment illistrated in FIG. 1, the entrance flume  22  consists of a base  21  and side walls  23 . The vortex channel  24  is fluidly connected to the entrance flume  22  and comprises a base  25 , an outer wall  26 , and an inner wall  27 . While the specific vortex channel shown utilizes a flat base  25  with substantially vertical side walls  26  and  27 , it is envisioned that these structures could take on any shape capable of transporting the sewage in a spiral flow. 
     The vortex form  20  may be made of concrete with applied protective coating, or made of a noncorrosive material, metal or plastic, such as PVC, High Density Polyethylene (HDPE) or other like materials . The vortex form  20  may be made in advance at the factory or on-site. As shown in FIGS. 3 and 4, the entrance flume  22  and/or vortex channel  24  may be manufactured and oriented with their bases having a supercritical slope, allowing the sewage to accelerate as it flows through the vortex form  20 . The selected slopes of the influent line  12 , the entrance flume base  21 , the vortex channel base  25  will not necessarily be the same. In the embodiment illustrated in FIG. 1, the influent line  12  is substantially horizontal, while the entrance flume base  21  and the vortex channel base  25  have a supercritical slope of about ten percent. 
     As noted, while the embodiment shown in FIGS. 1 and 2 illustrate a vortex form containing an entrance flume  22 , other embodiments of the present invention may fluidly connect the vortex channel  24  directly to the influent line  12 , omitting the use of the entrance flume  22 . Examples of such embodiments are shown in FIGS. 3,  4 , and  5 . 
     Referring to FIG. 2, the vortex channel  24  directs the sewage flow into a substantially spiral flow. The vortex channel  24  also reduces the radius of this spiral flow in order to increase the centripetal forces acting upon the flow. This is accomplished through the reduction in radius of the outer wall  26 , which will increase the centripetal forces applied by the outer wall  26  on the spiral flow. In the embodiment shown in FIG. 2, a radius transition section  28  supports the outer wall  26  and reduces the radius of the spiral flow created by the vortex channel  24  (shown in FIG. 2 as R 1 ) to the radius of the conduit  40  (shown as R 2 ). The radius transition section  28  also aids in directing the flow from the vortex channel  24  into the conduit  40 . The radius transition section  28  is generally made of a noncorrosive metal or plastic with concrete or a foam fill material. 
     To allow the sewage flow to enter the conduit  40 , inner wall  27  must include a height transition section  29  (identified on FIGS. 2,  4 , and  6  as section A-B) which allows the sewage flow to enter the conduit  40 . It is envisioned that this transition section could take many forms, including a sharp vertical cut or a gradual decrease in wall height. It has been found to be advantageous, however, to fabricate inner wall  27  such that its height profile reflects an axial flow velocity distribution. This type of cut is illustrated in FIG.  6 . 
     Referring again to FIG. 1, conduit  40  is disposed within maintenance hole  30  and fluidly connected to vortex channel  24 . Conduit  40  comprises a pipe wall  45  having a radius smaller than maintenance hole  30  and extending substantially downwardly from vortex form  20 . Conduit  40  further comprises a base  46 , and a flow exit path  50  near said maintenance hole base. The upper portion of the pipe wall  45  may be constructed integrally with inner wall  27 . 
     Still referring to FIG. 1, the sewage spirals and falls from vortex channel  24  into conduit  40 , along the inner surface  47  of pipe wall  45 . This flow continues to descend along the inner surface  47  of pipe wall  45  in a substantially spiral fashion until the sewage nears the conduit base  46 . The conduit base  46  is disposed below the surface of the energy dissipating pool  72  and at or above the base  34  of the maintenance hole  30  to create a flow exit path  50 . The sewage flow accumulates in the conduit base where it eventually flows through the flow exit path  50 , located at or near the conduit base  46 , into the energy dissipating pool  72  near the bottom of the maintenance hole  30 . 
     The flow exit path  50  may comprise any structure that allows the sewage flow to exit the conduit  40  at a predetermined flow rate. One example of a flow exit path is shown in FIG. 1, comprising a portal  56  in the conduit base  46 . The portal  56  allows the sewage flow that has accumulated in the conduit base  46  to exit into the energy dissipating pool  72 . Additional embodiments of the flow exit path  50  are shown in FIGS. 3 and 4. In FIG. 3, the flow exit path  50  comprises a plurality of legs  52  connected to and supporting the conduit base  46 . The plurality of legs  52  are themselves supported by the maintenance hole base  34 . The plurality of legs  52  allows the sewage flow within the conduit base  46  to be fluidly connected to the energy dissipating pool  72  and allows the sewage flow to exit the conduit base  46  at a predetermined flow rate. In FIG. 4, the flow exit path  50  comprises a suspended conduit support  80 . The suspended conduit support  80  includes a conduit anchor  82  and a vortex form base support  84 . The vortex form base support  84  is connected to both the maintenance hole side wall  36  and the maintenance hole base  34 , and supports the vortex form  20  and conduit  40  in a suspended fashion. The conduit anchor  82 , comprising a rigid structure capable of securing the conduit  40 , is connected to the maintenance hole side wall  36  and provides horizontal support for the conduit  40 . The conduit support  80  allows the conduit  40  to be suspended above the maintenance hole base  34 , thus allowing the sewage flow to exit the conduit  40  at the conduit base  46  and enter the energy dissipating pool  72 . 
     Once the flow has reached the energy dissipating pool  72 , it may be drawn away for further transport though an effluent line  60 , as shown in FIG.  1 . In another embodiment, shown in FIG. 4, the sewage flow may be drawn into a treatment pool  62  for further treatment. 
     As illustrated in FIG. 3, the present invention may utilize an air relief  70  to equalize substantially the air pressure within the maintenance hole  30  above the vortex form  20  with the air pressure within the maintenance hole  30  below the vortex form  20  and within the effluent line  60 . Air relief  70  comprises a pipe connecting the top portion of the effluent line  60  with the maintenance hole  30  above the vortex form  20 . The air relief  70  substantially equalizes the air pressures in the upper influent line  12  and the lower effluent line  60 , drawing the air from the higher pressure influent line  12  downward to the lower pressure effluent line  60 . This pressure equalization, by drawing the air through the air relief  70  into the effluent line  60 , further prevents the leakage of noxious gases not absorbed by the sewage flow within the maintenance hole  30 . These gases, dragged by the influent flow and not consumed by the spiral flow, would otherwise rise and emit from the improved sewer apparatus into the neighborhood. As illustrated in FIG. 5, in another embodiment the air relief  70  comprises a pipe extending through the vortex form, providing a path for the air to travel from the higher pressure area above the vortex form  20  to the lower pressure area below the vortex form  20 . The air relief  70  of this embodiment acts in the same fashion as the previously described embodiment to prevent the leakage of noxious gases not absorbed by the sewage flow within the maintenance hole  30 . 
     Referring to the embodiment illustrated in FIG. 1, in operation, incoming sewage at a small slope enters the vortex form  20  at the entrance flume  22  and descends through the vortex channel  24 . The supercritical slope of the entrance flume  22  and the vortex channel  24  provides rising flow velocities with a partial potential energy transition into kinetic energy. Even though sewage flow encounters a narrowing of the cross-section of the entrance flume  22 , the water level generally does not rise due to the flow acceleration created by the supercritical slope of the base  21 . The flow is then directed within the vortex channel  24  by the radius transition section  28  and the height reduction section  29  of the inner wall  27  into a smaller radius conduit  40 . 
     The sewage flow then spirals downwardly against the inside wall of the conduit  40 , creating a low pressure air core running longitudinally in the center of the conduit  40 . The low pressure air core draws air from the maintenance hole  30  above the vortex form  20  into the conduit  40 . Some of the oxygen in the air core mixes with and becomes entrained in the sewage flow, reacting with the potentially volatile dissolved hydrogen sulfide gas (H 2 S) in the liquid sewage to produce hydrogen sulfate (H 2 SO 4 ) in the solution. This reaction prevents hydrogen sulfide gas from being released into the air and then onto sewer surfaces where corrosion can occur or into the above ground neighborhood as a foul gas. The conduit  40  also helps to dissipate the high velocities and kinetic energy of the sewage flow by friction between the descending spiral flow and the conduit wall  45 . This energy reduction through friction reduces flow turbulence and thus hydrogen sulfide gas emission from the waste water liquid into the surrounding air. Without losing the flow&#39;s integrity, the gravity flow is transformed into a flow with combined gravity and centrifugal forces. 
     The sewage flow completes its downward spiral near the conduit base  46 , where the most intensive processes of flow mixing and aeration occur. The sewage air-flow mixture then flows out of the conduit base  46  through a flow exit  50  into an energy dissipating pool  72  for further internal mixing and friction. At the top surface of the energy dissipating pool  72  is a generally tranquil flow that leaves the maintenance hole  30  via the effluent line  60 . 
     As shown in FIGS. 7 and 8, other embodiments of the invention can also be used to mix and entrain gas in fluid flow within a conduit  120 . In FIG. 7, flow is channeled through influent line  12  into separate vortex forms  102  and  112 . Influent line  12  is generally a cylindrical pipe, but can take any cross-sectional shape. Depending upon the flow acceleration desired in the vortex forms  102  and  112 , the influent line  12  and the vortex forms  102  and  112  can be oriented at a variety of slopes. In addition, fluid flow pumps (not shown), known in the prior art, can be utilized to accelerate the flow within the influent line  12 . In FIG. 7, the influent line  12  is shown substantially horizontal. 
     The influent line  12  is fluidly connected to both vortex forms  102  and  112 . Each vortex form  102  and  112  is positioned to receive a portion of the flow from influent line  12  and each is generally shaped to create a spiral flow about the centerline  122  of conduit  120 . Vortex form  112  is positioned proximate to and downstream of vortex form  102 . In practice, it is beneficial to direct the spiral flow of vortex form  112  in a direction opposing the spiral flow created in vortex form  102 . As described in the previous embodiments, the vortex form  102  directs the fluid into a spiral of a predetermined radius (shown as R 3 ) greater than the radius (shown as R 7 ) of the conduit  120  and subsequently reduces the radius of the spiral flow (shown as R 4 ) to be equal to or less than radius R 7  of the conduit  120  to increase the centrifugal forces acting upon the fluid. Vortex form  112  directs the flow in a similar manner, creating spiral flow of predetermined radius (shown as R 5 ) and reducing the radius of a that spiral flow (shown as R 6 ). 
     Conduit  120  is fluidly connected to vortex forms  102  and  112  and extends downstream away from the vortex forms  102  and  112 . The downstream extension of conduit  120  may be oriented in any position from substantially horizontal to downwardly vertical, depending upon the application. Conduit  120  may also extend upstream of vortex form  102 . Conduit  120  includes an air intake  124  upstream of vortex form  102  that allows air or other gases to enter into conduit  120  and mix with flows delivered by vortex forms  102  and  112  within conduit  120 . In FIG. 7, the air intake  124  is a pipe, but could in other embodiments take any form allowing the flow of air or gases into the conduit  120  upstream of vortex form  102 . The spiral flows created by vortex forms  102  and  112  create a column of air or gas that is drawn through the air intake  124  and causes a portion of the air or gas to mix with and become entrained in the fluid flow. The conduit  120  must extend far enough downstream to allow such mixing and entrainment. 
     The embodiment in FIG. 8 also uses vortex forms  102  and  112  to create two spiral flows. However, in FIG. 8, each vortex form  102  and  112  receives fluid from separate influent lines  130  and  132 . The influent lines  130  and  132  may deliver the same or different fluids, and the densities of each fluid may differ. Conduit  126  is disposed within conduit  120  about centerline  122 , and receives flow from vortex form  102 . Conduit  126  can be formed separate from or integral with vortex form  102 . Conduit  126  ends proximate to vortex form  112 . Gas mixes with the spiral flow from vortex form  102  within conduit  126 . The spiral flow and gas within conduit  126  then empty into conduit  120  and mix with the spiral flow created by vortex form  112 . It is again beneficial to direct the spiral flows from vortex forms  102  and  112  in opposing directions to enhance the mixing and entrainment of the gas and fluids. 
     This description is intended to provide specific examples of individual embodiments which clearly disclose the present invention. By way of example only, and without limitation, the present invention could find use in drop structures having other than a circular or cylindrical configuration, thus freeing designers to construct such structures according to need. This invention can also be used in non-sewer applications where one seeks to mix gas and fluid within a conduit. Accordingly, the invention is not limited to the described embodiments, or to the use of the specific elements described therein. All alternative modifications and variations of the present invention which fall within the spirit and broad scope of the appended claims are covered.