GB1559868A

GB1559868A - Surface aerator for liquids

Info

Publication number: GB1559868A
Application number: GB39454/76A
Authority: GB
Original assignee: Norm AMC AG
Current assignee: Norm AMC AG
Priority date: 1975-09-24
Filing date: 1976-09-23
Publication date: 1980-01-30
Also published as: EG12940A; IT1075245B; JPS561157B2; CS189034B2; MX3697E; ATA700576A; TR19499A; ES451802A1; AT343063B; AU1799976A; NL7610424A; DE2559170C2; IE43724L; CH591278A5; PL110638B1; IE43724B1; FR2325610A1; JPS5241446A; DD126165A5; DE2559170A1

Description

(54) A SURFACE AERATOR FOR LIQUIDS (71) We, NORM A.M.C.

AKTIENGESELLSCHAFT, a joint stock company organized under the laws of Switzerland of Schulhausstrasse 10 CH6048, HORWILU, Switzerland, do hereby declare this invention for which we pray that a Patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement:- This invention relates to a surface aerator for liquids, particularly for wastewater to be purified, of the general kind having a body arranged for rotation about a vertical axis, the body having at least one array of blades diverging from a lower suction opening towards an upper discharge opening, whereby the blade array forms a number of conveying channels directed in such a manner that the liquid entering the channels from the suction opening is diverted through substantially 90" and is discharged at the circumference of the rotor in a generally radial direction.

It is known that the overall effectiveness of a surface aerator depends not only upon its capability to achieve intimate contact between the projected liquid and the overhead gas, but also upon its ability to produce strong mixing currents within the body of liquid. In the past, surface aerators which achieve excellent gas-liquid contact have been incapable of circulating liquid at sufficient rate to transfer the total required quantity of oxygen and to distribute the dissolved oxygen uniformly throughout the liquid body. Surface aerators which have possessed the desired liquid circulating capability have obtained poor contact between the projected liquid and the overhead gas. As a result, previous surface aerators have not achieved high dissolution performance per unit drive power.

It is known that in order to obtain good oxygen dissolution performance per KW drive power, waste-water surface aerators should expel the water at high rate over the surface of the body of water. It is also important that the aerator produce rapid recirculation and mixing of substantially all the water within the tank, so that the water thrown upward in contact with the gas will not already be highly enriched with dissolved oxygen, but instead will contain the lowest dissolved oxygen concentration of all the liquid in the tank. Such "liquid mixing" function is important in order to maximize the concentration driving force for oxygen dissolution, and in order to distribute the dissolved oxygen effectively to all regions of the tank.

An object of the invention is to provide a surface aerator of the above general kind which does not have the above named disadvantages and, which, with the same dimensions as known surface aerators, achieves a higher oxygen dissolution performance per unit drive power.

According to this invention, a surface aerator for the aeration of liquids comprises a body arranged for rotation about a vertical axis, the body being hollow and diverging from a lower suction opening towards an upper discharge opening, the body carrying at least one array of blades, each blade having at least one portion fixed to and extending away from the interior surface of the body and a further portion generally transverse to said one portion and spaced from and overlying said surface so that the blades and said surface define conveying channels which are open towards the interior of the body and directed in such a manner that the liquid entering these channels from the suction opening is diverted through substantially 900 and discharges at the circumference of the rotor in a generally radial direction, the ratio of the aerator outer diameter measured so as to exclude the width of an outer generally radial flow guide wall, to the suction opening diameter lying in the range between 1.3 to 1.7, and the ratio of the aerator outer diameter to the height of the aerator measured from the suction opening to said surface at the exit ends of the channels, lying in the range between 2.5 to 5.5.

Surface aerators designed in accordance with this invention possess high liquid recirculation capability despite the fact that the liquid acceleration channels between the blades are greatly shortened in length, as compared with some conventional aerators of the aforesaid general kind as a result of enlarging the inlet and reducing the height H. Moreover, the rate of curvature of the channels, from vertical orientation at the inlet to the substantially horizontal orientation at the outlet, is made much more rapid and acute in the surface aerators of this invention.

In operation, surface aerators of this invention are observed to impose no appreciable rotary motion to the liquid within the inlet zone, i.e., inside the wreath of rotating blades. The liquid motion at the inlet is primarily vertical, upward into the channels between the blades and there is no discernable vortex.

The invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a perspective view of a first embodiment of the surface aerator of the invention; Figure 2 is a perspective view, partially in cut-away, of a second embodiment of the surface aerator of the invention; Figure 3 is vertical section through a further embodiment of the surface aerator of the invention; and Figure 4 is a section along the line IV-IV in Figure 3.

The surface aerator represented in Figure 1 has a rotatable body 2 diverging from the lower suction side towards the upper exit side and carrying an array of blades 1, the array of blades thus forming a number of conveying channels 3 curved in vertical planes. By this means, the liquid entering the conveying channels 3 from the bottom is diverted by about 900 in these channels and exits at the circumference of the rotor in a horizontal direction.

For the formation of the conveying channels 3, which are open towards the interior, the blades 4 have an L-shaped profile, the free longitudinal edges of the vertical portions 5 of the L-shaped profiles being fastened to the inside of the rotational body 2.

On the upper side of the blades 4a, 4b and 4c, is fastened a support 6 which serves to connect the rotor with the drive shaft 7.

This surface aerator is intended to operate only in the direction indicated by arrow 8.

By contrast with the surface aerator represented in Figure 1, the surface aerator depicted in Figure 2 uses blades 4 with Tshaped cross-sections for the formation of conveying channels which are open towards the interior, the free longitudinal edges of the vertical portion 5 of the T-shaped profiles being fastened to the inside of the rotational body 2. The surface aerator of Figure 2 is meant to be driven in either direction of rotation.

In order to obtain high oxygen dissolution performance per unit of driving power, the ratio of the outer diameter of the surface aerator A (see Figure 2, measured without the width b of the guide wall 10) to the suction inlet diameter C lies in the range between 1.3 to 1.7 and is preferably 1.48.

The ratio of the outer diameter of the aerator A (measured without the width b of the flow guide wall 10) to the height H of the aerator from the underside of the aerator to the underside of the exit cross-sectional area 9 lies in the range between 2.5 to 5.5 and preferably is 3.7.

In order to convey the liquid leaving the surface aerator in a flat and more concentrated fashion over the surface area to be aerated, this embodiment is advantageously provided, along the underside of the -exits 9 of the conveying channels 3, with an annular flow guide wall 10 running concentric to the aerator axis and extending radially outwardly from the channel exits 9. It was found to be advantageous for the width b of the ringshaped guide wall 10 to be at least 70%, preferably 100% of the height h of the channel exits 9.

By arranging the annular flow guide wall 10 along the underside of the exits 9 of the conveying channel 3, the waste-water exiting from the latter is prevented from impinging immediately after leaving the conveying channel exits 9 against the surrounding liquid. Due to the action of the ring-shaped flow guide wall 10, the liquid leaving the conveying channels 3 is conveyed in a flat and broad manner above the liquid surface area which surrounds the surface aerator.

It was found to be advantageous if the angle of emersion (cur) of the blades lies in the range of 10 to 350 and if the radius of curvature r of the vertical portions 5 of the blade profiles, as seen from an axial direction, correspond to the aerator outer diameter A (measured without the width b of the flow guide wall) with a deviation of + 10%.

The surface aerator represented in Figure 3 and Figure 4 is equipped additionally with a further flow guide wall 11 which is arranged above the exits 9 of the conveying channels 3 concentric to the axis of the aerator and extending radially outward from the channel exits 9. By this means, the liquid leaving the conveying channels 3 is conveyed in a very flat manner above the water surface.

Claims

WHAT WE CLAIM IS:

1. A surface aerator for the aeration of liquids, comprising a body arranged for rotation about a vertical axis, the body being hollow and diverging from a lower suction opening towards an upper discharge opening, the body carrying at least one array of blades, each blade having at least one portion fixed to and extending away from the interior surface of the body and a further portion generally transverse to said one portion and spaced from and overlying said surface so that the blades and said surface define conveying channels which are open towards the interior of the body and directed in such a manner that the liquid entering these channels from the suction opening is diverted through substantially 90" and discharges at the circumference of the rotor in a generally radial direction, the ratio of the aerator outer diameter measured so as to exclude the width of an outer generally radial flow guide wall to the suction opening diameter lying in the range between 1.3 to 1.7, and the ratio of the aerator outer diameter to the height of the aerator measured from the suction opening to said surface at the exit ends of the channels, lying in the range between 2.5 to 5.5.

2. A surface aerator according to Claim I wherein the flow guide wall is annular and disposed around the exit ends of the conveying channels at the level of said surface, said guide wall being concentric to the axis of the aerator and extending radially outwardly from said exit ends.

3. A surface aerator according to Claim 2 wherein the width of the annular flow guide wall is at least 70% of the height of the exit ends of the channels.

4. A surface aerator according to Claim 1 wherein a further flow guide wall is disposed around the axially outermost extremities of the exit ends of the conveying channels, said further guide wall being concentric to the axis of the aerator and extending radially outwardly from the exit ends of the channels.

5. A surface aerator according to any one of Claims 1 to 4 wherein the angle of emersion (a) of the blades lies in the range of 10 to 350.

6. A surface aerator according to any one of Claims 1 to 5 wherein the radius of curvature of the blades as seen from an axial direction, corresponds to the outer diameter of the aerator, with a deviation of + 10%.

7. A surface aerator according to Claim 3 wherein the width of the annular flow guide wall is equal to the height of the exit ends of the channels.

8. A surface aerator according to Claim 1, wherein said ratio of the aerator outer diameter measured so as to exclude the width of said flow guide wall, to the suction opening diameter is 1.48.

9. A surface aerator according to Claim I wherein the ratio of the aerator outer diameter to the height of the aerator measured from the suction opening to said surface at said exit ends of the channels is 3.7.

10. A surface aerator according to any one of the preceding claims wherein each of the blades has an "L" or "r' shaped end profile when viewed from the periphery of the aerator.

11. A surface aerator substantially as hereinbefore described with reference to Figure 1, Figure 2, or Figures 3 and 4 of the accompanying drawings.