Aeration apparatus by means of vortex action
BACKGROUND AND SUMMARY OF THE INVENTION 
     The invention concerns an apparatus for promoting dissolution of gas into liquid by entraining gas from the liquid surface and dispersing it into the liquid body. A particularly useful application of the invention is in the aeration of wastewater for the aerobic treatment process. Up to date there are three principal methods used in activated sludge process: the submerged diffuser method, the submerged turbine method, and the surface aeration method. 
     In the first method, submerged diffusers are used. The gas phase is compressed and then introduced to the liquid near the bottom of the tank through a porous diffuser head. It is known that the efficiency is generally low. Besides, the cost of maintenance is high due to the clogging problem of the porous head. The second method is using a submerged turbine. The gas is compressed and let out through a conduit near the bottom of the tank. The submerged turbine is placed above the gas outlet. The rotating motion of the turbine produces kinetic energy and turbulence for dispersing and mixing the discharged gas with the liquid. With this method the absorption efficiency is higher and there is less clogging problem. However, it not only requires a gas compressor but also a rotating turbine and therefore the initial cost is high and there are more components to maintain. 
     The last method is known as surface aeration which utilizes a rotating body with vanes for spraying the liquid into droplets. The droplets contact with the gas phase while traveling in the air. Surface aeration is a very effective method and mechanically it is simple. However, there are many disadvantages such as inadequate local mixing, limitation in tank depth due to poor mixing and contamination of the atmosphere around the system. 
     BRIEF STATEMENT OF THE INVENTION 
     Utilizing energy more economically, the object of this mechanically simple invention is to provide a more efficient method for dissolving gas into liquids. The basic operating principle of this invention is to entrain gas into the liquid at the surface and then disperse it in the liquid body through a pumping device. 
     The gas entraining assembly is comprised of multiple vertical tubes with both ends open. The upper ends of the tubes are submerged just below the top of the liquid surface. The lower ends of the tubes are surrounded by the flow-confining barrel, which is vertically mounted. The pumping device is disposed below the vertical tubes and within the flow-confining barrel. As the pumping device induces a downward flow within the flow-confining barrel, the liquid is drawn through the tubes. The suction action at the upper ends of the tubes generates a vortex in each of the tubes. The velocities in the vertical tubes and in the flow confining barrel are determined to be at least higher than the bubble rising velocity relative to the liquid. The gas is then entrained into the tubes through the vortex action. The liquid with entrained gas continues down into the flow-confining barrel by the pumping device and is subsequently discharged to the liquid body through the lower end of the flow-confining barrel. The dispersed gas bubbles continue to be in contact with the tank liquid and promote efficient gas liquid mass transfer. The rate of gas entrainment depends on the depth of the submergence of the upper end of the vertical tubes. Therefore, the gas flow can be controlled at the desired rate by adjusting the position of the vertical tubes; through this adjustment the maximum efficiency of mass transfer can be achieved. While the invention has a primary application to aerate waste water, the invention can also be used to advantage for other purposes: chlorination and ozonization of water, direct contact gas liquid heat exchange and many other applications pertaining to gas liquid mixing operation. 
    
    
     DESCRIPTION OF DRAWING 
     The drawing is a perspective view of the apparatus in accordance with this invention. 
    
    
     With reference to the drawing, flow confining means (10) is submerged in the liquid (11) and is vertically oriented. A group of vertical tubes (12) is placed at the upper end of the flow confining means (10). The tops of these tubes (13) are positioned a short distance below the liquid surface (14), and the lower ends (15) are open to and enclosed in the flow confining means (10). The tubes (12) are attached to a plate (16) at the top end of the flow confining means (10) restricting the flow path only into the tubes (12) at their open ends (13). An impeller (17) at the end of a rotating shaft (18) is driven by a motor (19). The impeller is positioned in the flow confining means (10) below the vertical tubes (12). The impeller (17) rotates and induces a downward flow which draws the liquid into the vertical tubes (12) and into the flow confining means (10). The downward action of the flow generates vortices in the tubes and lowers the liquid surface (14) thereby entraining gas into the vertical tubes (12) through the centers of the vortices. The liquid and the gas mix in tubes (12); the flow continues downward into the flow confining means. The rotating impeller drives the gas liquid mixture further downward and subsequently disperses it into the liquid body (11) through the lower end (20) of the flow confining means (10). A flow deflector (21) is disposed underneath the lower end (20) of the flow confining means for directing the discharged flow in a desired direction.