Note: Descriptions are shown in the official language in which they were submitted.
1057~
THIS INVENTION concerns a rotary surface
aerator of the kind which is adapted to be rotated
in the surface of a liquid for the purpose of
agitating and aerating same, and particularly,
. 5 though by no means exclusively, suitable for use
in the aeration of sewage liquors in the so-called
activated sludge process. ~ `
. An aerator is known which comprises a
support. member in the form of an inverted conical
: 10 shell having a plurality of angularly spaced blades : ~ .
.~ secured to its undersi~e and each extending ~:~
`. ~ tangentially from a circular locality at the centre :~
.~ of the support member towards the outer periphery :
thereof, there being a plate secured to the lower
edge of each said blade and extending~on.both sides
thereof along at least a part of the length of the
~ blade beneath said shell from the outer end of the .
: blade towards the centre of the aerator.
:
The rotation of aerators at high speeds
~ 20 is becoming increasingly popular as means of ~ ~:
:~ reducing the cost of the gear boxes which must be
~ provided between the aerators and the driving motors
~ therefor. This is particularly true in the case of
1 the larger sizes of aerator when the torque to be
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transmitted is such that the gear boxes can
account for up to half of the total cost of an
aerator installation.
: We have fcund that an aerator as described
above, whilst highly satisfactory at low rotational
speeds, develops problems at higher speeds, when
.: complex power consumption/oxygen tranfer character- .
istics occur, making control extremely difficult
. having regard to other variable parameters such
; 10 as the oxygen demand of the liquid being treated
. and the depth of immersion of the aerator in the
.. surface of the liquid being treated.
'.~, .
~,~ It is an object of the present invention .
.s to provide an aerator capable of being operated at
high speeds and without the disadvantages aforesaid.
1 According to the present invention, an
.. ~ aerator comprises a support member in the form of
,~ a flat plate which is adapted when the
i aerator is in use to lie in a horizontal plane and
~, 20 to be rotated about its central vertical axls, a ~ '
.. l plurality of angularly spaced blades secured to ~ ~'
. the underside of said plate and each extending : ~:
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radially from a central region thereof towards its :-
periphery, each said blade having a maximum depth
beneath a horizontal datum at a position inter-
mediate its ends, and being provided with a plate
secured to its lower edge and extending on both
sides of the blade along at least a portion of
that part of the length of the blade between its
outer end and the position of maximum depth.
~ :::
. We have found that an aerator embodying the
` 10 invention will perform in a particularly satisfactory
manner at higher rotational speeds when baffle means .
., is provided therebeneath for the purposes of
preventing rotational flow or swirling of the - ;
liquid being aerated immediately beneath the : ~
position of the aerator. ~ :: ~:
. . '~ ~
s~ Thus, the invention also includes an :
: installation for the aeratlon of a liquid comprising
the combination of an aerator as aforesaid with
~ baffle means mounted therebeneath and so arranged
.1~ 20 as to prevent rotational flow of the liquid in a -;
region immediately beneath the position of the
: aerator. ~ :
~ ; ~: :'' '; ;' '' .
`i The invention will be further apparent from .
the following description with reference to the
several figures of the accompanying drawings :~
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which show, by way of example only~ one form of
rotary surface aerator embodying the inventlon.
,, .
Of the drawings:-
,
Fig. 1 shows a side elevation of the
aerator;
'',~
Fig. 2 shows a plan view of the aeratorof Fig. l;
J, Fig. 3 shows a cross-section through the
aerator on the line III-III of Fig. 2;
3j
~`~ 10 and Fig. 4 shows a perspective view of the
aerator of Fig. 1 in position in an ~ ~
aeration tank with baffle means mounted ~ ;
~' therebeneath.
," . . , ~
Referring now to the drawings, and more
~ 15 particularly Figs. 1 to 3 inclusive, it will be
J~ seen that the aerator essentially comprises a
support member 10 in the form of a ~lat circular
disc, which, when the aerator is in use, lies in
a horizontal plane, and which can be rotated by
means of a shaft 11 which is secured centrally to
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, the disc 10 so as to extend upwardly therefrom.
Extendlng downwardly from the underside of the
disc 10 at its centre is a circular boss 12 formed
from tube and closed at its lower end by a
circular plate 13.
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Secured to the underside of the support
member 10 are a plurality of angularly spaced
, blades 15 each disposed in a vertical plane.
'j As best seen from Fig. 2, each of the blades 15
extends radially and outwardly from the periphery
f of the circular boss,12 to terminate at a position
lying beyond~the peripheral edge of the support
member 10. Each blade 15 is profiled, as best .
seen from Fig. 3, so as to have à maximum depth ~ .
jff ~ ~ : 15; beneath a horizontal datum at a position inter-
~! ~ : mediate lts ends, the depth of the blade on either
side of this position reducing gradually. As
, also best seen from Fig. 3 the upper edge o~ each~
.f ~ ~ blade 15 extends continuously from the periphery
1 20 of the support member 10 in contact with the ,- ,
underside thereof to the circular boss 12.
f~ Likewise the;inner edge of each blade 15 extends ," ,.
:f ` ~ . continuously downwardly in contact with the perlphery
~ of the boss 12 for a distance not substantially less ~ ,
;l 25 than the depth of the boss 12. The outermost edge
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; of each blade 15 is of substantially less height
than the inner edge thereof.
,
Secured to the lower edge of each blade
15 between the position of maximum depth thereof
and the outer end of the blade is a plate 16
which extends on both sides of the blade normal
thereto, as clearly seen from Figs. 1 and 2.
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In use, the aerator is rotated in the - -
, surface of a liquid which is to be agitated and
aerated. It will be understood that liquid is
thrown outwardly by centrifugal action through
the duct ~defined on the leading side of each
~; ~lade with~respect to the direction of rotation
y the support membar 10, blade 15 and plate 16
and that air is drawn down the duct on the trailing
ide of each blade with respect to the dlreotion of
rotation and defined by the same parts. This air
is drawn lnto the region of maximum turbulence thus
~nsuring a good transfer of oxygen to the liquid
~;; 20 ~eing aerated.
~ 1 :
1~ When the aerator is to be rotated at
~1~ he higher end of its useful speed range, as is
; )referred, it is desirable to ~rovide baffle ; ~-
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j means to prevent rotational flow or swi~ling of
the liquid at a position immediately beneath the
aerator. As can clearly be seen from Fig. 4,
such baffle means may conven~ently be comprised
by four plates lying in vertical planes and
forming a cross whose axis is coincident with
the rotary axis of the aerator.
~' . ~ ~ ~
~ Tests with aerators having the contruction
`~ described above have shown that there is a simple ;
relationship between oxygen transfer and power 1
consumption regardless of speed of rotation and
depth of immersion, thus making control of the
aerator on site particularIy straightforward. ~; ;
;-s ~ ;
?, 1~ We have also observed that aerators ~
embodying the present invention do not have a ~ ;
great tendency to cause the liquid being aerated
~to surge, and thus have a consequent~tendency to
allow the power input to remain constant during
~;~ operation.
. .
20 ` It will be appreciated that it is not
intended to limit the invention to the above
example only, many variations, such as might
~l ~ readily occur to one skilled in the art, being
possible without departing from the scope thereof,
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Thus, for example, the blades 15 need
.~ not extend from the periphery of a circular boss
; and may all meet at the vertical axis of the
: machine.
:,
Again, for example, the plates 16 need
not extend from the outer ends of the blades 15
but ~rom positions inwardly of such ends.
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Yet again, for example, the blades 15
need not extend outwardly beyond the periphery of ~ .
the disc 10 but may terminate at the periphery
.l or even at positions radially and inwardly thereo~.
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~ Still again, for example, the disc 10
~ ~ may be replaced by a plate of other than circular :
. shape. I
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