Double funnel with baffle cascade aeration unit

Abstract

Cascade Aeration mixing guns for oxygenating sewage are known in the art but cannot be properly scaled up, or paralleled in one unit. A double cascaded unit which incorporates integral baffles is shown so that capacity can be greatly increased, while maintaining efficiency.This invention relates to aerators of the double funnel cascade type, as described in Canadian Pat. No. 937, 610 issued on Dec. 4, 1973 in the name of Jan W. Romanowski.To reduce capital costs in any installation it is generally desirable to increase the size and reduce the numbers of aerators. Unfortunately the size of the aerator - the 12 inch diameter tube - of the above mentioned patent represents a good typical compromise of maximum aeration capacity and maximum aeration efficiency, on oxygen transfer. These quantities are to some extent interdependent, and tests show that both depend upon the depth of submersion. The abbreviated table below is an extract based on test results for such a 12 inch diameter unit.______________________________________Values of Liquid Depth 10' 12' 16' 20'______________________________________ 12 1.52 1.76 2.98 2.57Free 16 1.94 2.23 2.78 3.29AirFlow 20 2.33 2.69 3.33 3.94SCFM 24 2.47 2.85 3.54 4.19 28 2.55 2.94 3.65 4.31______________________________________Figures in the table are oxygen transfer rates in lbs. per hour.Attempts to increase the throughput by scaling up the unit are very unsatisfactory. Superficially, to double the capacity would seem, erroneously, merely to require doubling all areas - a size increase from 12 diameter to 18 inches ought to give ample margin. In practice this does not happen and the momentum of the increased air jet is such that proper mixing does not take place; doubling the depth helps somewhat, but the efficiency is still low; moreover, as increased excavation is expensive, doubling depth is a theoretical laboratory type suggestion rather than a practical expedient. Attempts at making twin parallel cascade funnels within a single tube gives disappointing results also.Accordingly, this invention comprises an assembly adapted to aerate sewage comprising: oxygen-containing gas supply means having two delivery orifices to form two streams of gas; two first funnels converging downstream and secured downstream from and cooperating with said orifices so that oxygen-containing gas issuing from the orifice can entrain liquid and become mixed therewith; two second funnels converging downstream and spaced downstream from the first funnels; baffle means in the flow path between the exit from the first funnels and to the second funnels; means securing the first funnels, the baffle means and the second funnel together so that the mixture of oxygen-containing gas and sewage streaming from the exit of the first funnels impinges on the baffle means before entering the second funnels.The invention will best be understood by reference to the drawings which illustrate by way of example a unit incorporating the invention.

Description

Claims

1. An assembly adapted to aerate sewage comprising:

oxygen-containing gas supply means having two delivery orifices to form two streams of gas;

two first funnels converging downstream and secured downstream from and cooperating with said orifices so that oxygen-containing gas issuing from the orifice can entrain liquid and become mixed therewith;

two second funnels converging downstream and spaced downstream from the first funnels;

baffle means in the flow path between the exit from the first funnels and the entry to the second funnels; and

means securing the first funnels, the baffle means and the second funnels together so that the mixture of oxygen-containing gas and sewage streaming from the exit of the first funnels impinges on the baffle means before entering the second funnels.

2. An assembly as claimed in claim 1 wherein the baffle means comprises

a skirt joining the two second funnels together.

3. An assembly as claimed in claim 1 wherein said securing means comprises a tube extending both upstream and downstream from said second funnels, said tube having cutouts both upstream and downstream of the inlet to the two second funnels, whereby the upstream openings allow access of unmixed liquid sewage to the inlet of the two second funnels, together with the mixture issuing from the two first funnels, and the downstream openings allow access of further unmixed sewage whereby the downstream extending portion forms an exit tube in which further mixing occurs.

4. An assembly as claimed in claim 3 wherein the tube has a minimum diameter of at least 18 inches.

5. An assembly as claimed in claim 2 wherein each of the two second funnels are asymmetrically flared at the upstream end so as to blend into the skirts and form a circular section therewith.