Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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CIRCULATING APPA~TUS FOR ~ATER TREATMENT BASINS
Bac]cground of the Invention
This invention relates to circulating apparatus for
water treatment basins and more particularly to mixing basins
and/or aerating basins having at least one blade immersing
into the basin contents and supported by a structure
transportable above the basin.
Apparatus of this type is disclosed in West German
Patent No. 16 09 004 granted on July 15, 1976 to A. Schreiber,
in the form of a bubble aerator provided at the bottom of
the basin. A rigidly mounted transport blade extends across
substantially the entire width of the basin and ensures
a circulation of the basin contents, whereby the upwardly moving
path of the bubbles is lengthened as aerated and unaerated
quantities of water are mixed together to prevent sludge deposits.
Difficulties have been encountered in starting up and in braking
or stopping such circulating apparatus because extremely strong
forces then come into action due to the acceleration or decelera-
tion of the water. For this reason circulating apparatus which
is gradually started has been employed heretofore. However, such
apparatus is expensive and prone to malfunctions and does not
prevent overloading of the motor and the transport blade securing
means since it is a positive control system. Furthermore, it
does not solve the problem of the acting forces when the bridge
is stopped. These problems are further aggravated by the fact
that, particularly in circular basins, the acting forces are
not distributed uniformly across the width of the transport
blade.
Summary of the Invention
An object of this invention is to provide circulating
apparatus of the type referred to above in which the starting
and braking, even without a starting circuit, does not lead to
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overloading of the transport blade, its securing means and its
drive means, and in which it is possible to take into consideration
flow conditions which are not uniform across the width of the
basin.
In accordance with this invention circulating apparatus
of the type referred to above is provided with a blade which is
suspended for swinging movement or is formed of a construction
which is yieldable. The blade can thus automatically escape
the forces of the current during starting and also during braking,
whereby the influence of forces acting upon the blade suspension
means and the bridge drive means is prevented. Where the blade
is supported for movement about a horizontal axis the blade,
which is loaded downwardly by its weight, exerts a transport
action upon the water in its upward pivoted position, and to
the degree to which the water velocity adapts itself to the
speed of travel, the blade sinks down into its normal operating
position, so that it fills the full cross sectional depth of
the basin and develops its full transport action.
In accordance with a further embodiment of our invention,
the blade is subdivided along its width into a plurality of
partial blades which are suspended independently of each other.
By this means, it is possible to provide particularly good
adaptation to different flow conditions and resistance forces
across the blade width, such as occurs particularly in circular
basins. The different peripheral velocities in circular basins
can be taken into consideration by giving the partial blades
located radially farther outwardly a higher weight relative to
the effective surface than those located farther inwardly.
Another unexpected advantage in our invention is that it
has been discovered that, in the case of a blade suspended for
swinging movement about a horizonlal axis, not only a circulation
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in the direction of travel of the brldge is obtained, but a
very desirable cross-current occurs, which leads to a thorough
mixing of the llquid transversely of the basin. It has been
observed that, in a circular basin, in the radially inner region
of the blade or partial blade a current occurs in front of the
blade which is directed radially and inwardly parallel to the
blade while a corresponding current is directed radially and
ouk~ardly behind the blade. By this means the air bubbles
ascending from the bottom of the basin are also diverted corres-
pondingly radially inwardly and outwardly, respectively. Aparticularly thorough mixing of aerated and unaerated water is
thus achieved in this manner. The subdivision and swinging
suspension of the blade also provides advantages in the assembly,
operation and maintenance of the apparatus. For inspection work
the blade or each partial blade can be pivoted upwardly in an
extremely simple manner. Also, individual partial blades can
be dismantled separately. When the bridge is stopped the blade
or partial blade swings in the opposite direction due to the
forward flow of the water, whereby the action of forces upon
the blade suspension means and the bridge drive means is also
prevented while the blade is in this position.
A further advantage in our improved apparatus is that by
providing blade sections or partial blades which are independently
swingable relative to each other they are at least intermittently
connected to each other and may have a particular, V-shaped or
curved, profile. Also, the horizontal pivot axis of the blade
or of the partial blade may be angled obli~uely to the direction
of travel of the ~ridge. By these measures currents transversely
or radially of the basin can be generated deliberately and the
circulation can be improved or sludge deposits in the center of
the basin can be prevented by this means.
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The invention can also be carried out by attaching the
blades or partial blades to vertical axes. In this case the
return force produced by the entrainment of the basin contents
can be exerted by suitable means such as springs. The return
force may also be generated by the blade itself, by making the
latter of flexible material, at least in the region near the
axis, and attaching it rigidly to the axis. Also, the blades
may be articulated for free swinging movement relative to the
axes and inclined relative to the vertical. The vertical plane
extending through this inclined axis is placed generally trans-
versely to the direction of travel whereby the center of gravity
of the blade which moves out of this plane upon deflection
generates a return moment of a value similar to that of a
suspension from a horizontal axis.
The invention may be applied not only to circular and annular
basins, but also to so-called arena basins which have more or
less long straight sections. The apparatus for circulating the
basin contents according to our invention may also be used in
square or rectangular basins in which the blades extend across
the entire cross-section only intermittently.
The invention is described more fully hereinafter with re-
ference to the accompanying drawings, in which Figs. 7 and 8 are
shown on the sheet of drawings having Figs. 3 and 4 thereon and
wherein:
FIG. 1 is a sectional view showing a circular basin with
circulating apparatus according to our invention;
FIG. 2 is a plan view of the apparatus shown in FIG. l;
FIG. 3 is a side elevational view showing the circulating
apparatus in side elevation with the basin being shown in section;
FIG. 4 is a fragmental perspective view showing a detail of
the circulating apparatus;
FIG. 5 is a side elevational view showing another form of
our circulating apparatus;
FIG. 6 is a plan view of the apparatus shown in FIG. 5;
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FIG. 7 is a fragmental sectional view showing the partial
blade as being V-shaped;
FIG. 8 is a fragmental sectional view showing the partial
blade as having a curved profilei
FIG. 9 is a fragmental view showing adjacent partial blades
connected together by flexible members; and
FIG. 10 is a fragmental view showing the blades as being
subdivided in height into two or more sections.
Referring now to FIGS. 1 to 3 we show a circular basin 10
having a central column 12. Annular aerating pipes 13 are laid
on the bottom of the basin 10 from which air bubbles 14 ascend.
A transportable bridge 15 is mounted for pivotal movement on
the column 12 by means of a pivot bearing 16 and is mounted for
movement on the basin crest 18 by means of a carriage 17.
Carried by the bridge 15 above the water level is a horizontal
axis 20 on which four juxtaposed blades 19 are suspended for
free swinging movement. When the bridge 15 is set in rotation
in the direction of the arrow 15' by its drive motor (not shown),
the bl.~des 19 exert a shear force upon the water and are them-
selves pivoted backwardly and upwardly by the resistance of thewater into the starting position 19' illustrated in FIG. 3. The
drive motor for the bridge 15 can therefore be started up with
full speed immediately, because overloading of the motor, for
the bridge and of the blade suspension means is prevented by
the automatic escape of the blades. Progressively as the flow
velocity of the water increases, the blades 19 swing back into
their normal working position indicated at 19'' in FIG. 3. When
the bridye 15 is stopped the blades 19 can escape from the water,
which initially continues to flow, by swinging in the opposite
direction.
The circulation of the water in the peripheral direction
of the basin generated by the blades causes the air bubbles from
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the pipes 13 to ascend obliquely with a lengthened path in
the water, as indicated at 21 in FIG. 3. Due to the swingable
arrangement of the blades 19, an additional radial circulation of
the water in the radially inner basin region occurs unexpectedly.
That ls, as shown by the arrows 22 in FIG. 2, a radially inwardly
directed current is created in front of the blades 19 in the
direction of travel and a radially outwardly directed current is
created behind the blades. By this means the ascending air
bubbles are also correspondingly diverted alternately radially
inwardly and outwardly.
In circular basins the speed of the bridge 15, and also
correspondingly the resistance exerted by the water, is greater
on the outside than on the inside, so that upon starting up, the
blades 19 located farther outwardly are pivoted into a higher
position than the inner blades, as shown in FIG. 1. To prevent
the escape of too much water through the triangular gaps pro-
duced between adjacent blades and consequently impair the
transport effect, we provide partition walls 23 at the vertical
edges of the blades 19, as shown in FIG. 4. The partition walls
23 project at right angles to the surface of the blade 19 in
position to bridge the triangular openings defined between
adjacent blades 19.
In the embodiment illustrated in FIGS. 2 to 4 the axial
center of the bridge 15 is oriented whereby it extends radially
relative to the basin 10. The horizontal swing axis 20 of the
blades is however arranged staggered with reference to the axial
center of the bridge 15 and is also oriented parallel to the
radially extending axis of the bridge 15. The swing axis 20
may also be positioned obliquely relative to the axial center
of the bridge 15. By this means additional radial components
of the circulating current can be generated deliberately in order
to prevent sludge deposits in the center of the basin 10 or to
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improve the aeration effect by increased transverse exchange.
Similar effects can be achieved by profiling the blades 19
to provide V-shaped blades or a ploughshare-like curvature for
the blades 19. The swing axis 20 may also be prolonged inwardly
beyond the center of the basin and carry one or more additional
blades 19 on the other side of the column 12.
The adjacent partial blades or blade sections 19 may be
connected together by chains 30, cables or the like in order to
limit the extent of their pivoting relative to each other.
Rigid connecting devices, such as bolts, may also be provided
for the only intermittent connection of adjacent blades.
A further modification of the invention is to provide
blades which are subdivided in height into two or more sections
articulately connected to each other. Instead of this, or
additionally, the blades or their sections may consist of flexible
material.
In the circulating apparatus shown in FIGS. 5 and 6 the
outer blades 24 are attached to vertically inclined swing axes
25 so that their center of gravity moves upwardly when they
swing out. The innermost blade 26 is attached rigidly to a
vertical support bar 27 and consists of flexible material which
gives the blade 26 an adequately powerful return force for the
entrainment of the basin contents. The swing axes 25 and the
support bar 27 are attached to the bridge 15, so that they extend
in a radial vertical plane. In order to improve the stability
of the swing axes 25, they may be additionally braced by means
of brackets 28.
