Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1065'765
The present invention relates to a sludge removal
system in combination with a sludge settling tank to remove sludge
which settled out at the bottom of the tank, particularly a biolo-
gical settling basin, and to a method of removing sludge from the
bottom of the settling tank.
Sewage, which has solids suspended therefrom, is cus-
tomarily introduced into a basin, in which the solids can settle
out. A sludge forms at the bottom of the basin wnich can be re-
moved by means of a suction apparatus, such as a suction nozzle,
secured to a transport bridge located above the basin and arranged
to travel over the basin to carry the nozzle along. The sludge or
mud which has settled out from the sewage can then be removed over
a pipe or duct arrangement connected to the suction nozzle.
Sewage treatment plants, and sludge settling tanks
or basins, should be as simple as possible, so that, in operation,
maintenance of the apparatus associated therewith is simplified.
It is particularly important that the mechanical arrangements
should be as simple as possible, and that portion of the apparatus
which is movable over the level of liquid in the tank or basin
should preferably not have electrical apparatus thereon, so that
cable or open-wire connections to the electrical apparatus carried
on the movable bridge can be avoided. Preferably, electrical
drives for all apparatus used in connection with such settling
. tanks or basins should be fixed and located at non-movable posi-
tions. To avoid a drive on the movable bridge, it has -
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previously been proposed to move the bridge itself by means
of a cable drive, the cable itself being moved by a motor
in fixed location. It has also been proposed to construct
essentially circular basins, and to rotate the bridges by
means of a mechanical drive located, for example,in the center
of the basin, the bridge extending radially from a center
support to the edge or rim thereof. Motor drives may,
however, be required for the pumps to remove sludge and
deposits through the nozzle. Such pumps, located on the
bridge, are subject deterioration due to corrosion resulting
from gases and vapors rising from the sewage in the settling
tank. Movable electrical connections to pump apparatus at
~i the bridge are also subject to deterioration and require
excessive maintenance. Mechanical pumps located on the bridge
can be avoided by using syphons to remove the precipitated
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solids from the bottom of the tank. The syphons are secured
to the bridge to sweep across the bottom of the tank or ba~in
and to remove the solids together with some liquid by
introducing them into a duct or channel for further transport
of the sludge, for example by means of a pump. Syphons
introduce additional problems. Reliable operation of the
, syphons can be ensured only if the suction nozzle or pick-up
;l element actua~y removing the sludge, and the ducts connected
thereto, do not plug- up or clog. If necessary, counterflow
should be possible to provide for back-flushing of the nozzle
and connected pipes. Such counterflow can be obtained by
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rais~ng the level of liquid in the removal duct above the
level of liquid in the basin. Additional apparatus must,
however, sti~ be used to remove air and gas from the liquid
which is passed through the ducts or pipes, usually in form
S of large bubbles. Such bubbles or gas contents greatly
decrease the quantity of sludge and liquid being removed and
may,at times, interrupt the liquid column within the syphon.
The vacuum in the syphon can be re-established by locating
a v cuum pump in connection with the connecting ducting; such
a vacuum pump must, however, again be located on the bridge,
`` requiring yet another power supply thereto.
In some installations it is practically impossible to
avoid deposits of solids in the suction nozzle and in the
associated syphon ducts. It is practically impossible to
prevent such deposits and re-establish flow by dropping the
level in the collecting duct, or back-flushing the piping
and the suction nozzle by raising the level in the collecting
!~ duct over the level of the settling basin, since change in
level of the collecting duct can be done only within a very
limited range, and the initial difference in level between
the liquid in the settling tank and the liquid in the
; collecting duct is small.
Some sewage disposal plants use a single settling
tank only. In such plants, sewage is introduced into the
: 25 settling tank with all its contaminants, which have not yet
been removed by a prior pre-cleaning apparatus including
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mechanical cleaning systems such as rakes, or the like. The dan-
ger of plugging or stoppages in the suction system is particularly
high in single-stage installations. Back-flushing the suction
nozzle and asqociated piping, to provide for self-cleaning, was
possible only with additional apparatus.
It is an object of the present invention to provide
a sludge removal system for combination with a settling tank which
can be easily cleaned by back-flushing under high pressure, and
which does not require motor drives on a movable bridge.
According to the present invention, there is provided
a sludge removal system in combination with a sludge settling tank
to remove sludge which settled out at the bottom of the tank com-
prising a support bridge located above the tank and movable in a
path over the tank; means removing the sludge from the bottom of
the tank, as the bridge is moving while excluding access of air at
ambient pressure to said sludge and forming an hydraulically clo-
sed suction fluid conduit to remove said sludge, including a `~
suction nozzle and a suction riser pipe supported from the bridge
and extending into the tank to sweep the bottom of the tank upon
movement of the bridge in its path; a fixed sludge removal pipe
located at least in part below the hottom of the tank, fixed with
respect to the tank, immovably secured thereto and having a verti-
cally extending fixed pipe portion; a connecting pipe means sup-
ported from and moving with the bridge including a horizontal
portion located above the highest liquid level joined to the suc-
tion riser pipe and an end portion extending vertically down-
wardly, and aligned with the vertically extending portion of the
fixed sludge removal pipe; and a movable joint which is substan-
tially liquid-tight and tight with respect to subatmospheric
pressure connecting the vertical end portion of the connecting -~
pipe meanS and the sludge removal pipe; and a pump located later-
ally wlth respect to the tank and having a suction inlet
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connection connected to the sludge re~ v~l pipe, and hence to the
hydraulically closed fluid conduit to provide a suction fluid cir-
cuit which is hydraulically closed from the nozzle below the liquid
level through the pipe portion above the liquid level and then to
the laterally located pump while permitting relative movement of
the nozzle in itQ path over the sludge settling tank.
According to the present invention, there is also
provided method to remove sludge from the bottom of a settling
tank having a movable nozzle in fluid communication with the bot-
tom of the tank, and a closed fluid piping conduit connected tothe movable nozzle including a fixed sludge removal pipe from
which the sludge is discharged extending transversely of the tank
and located below the tank, a movable riser extending from the
movable nozzle to above the operating liquid level of the tank, a
' movable transverse connecting pipe located above the highest level
of the tank and extending transversely of the tank, and an essen-
) tially liquid-tight, suction-tight rotary joint connecting the
movable transverse connecting pipe and a fixed downwardly exten-
ding pipe jointed to said fixed transversely extending pipe to
provide an eQsentially hydraulically completely suction-tigh~
closed fluid conduit from the nozzle to the terminal end of the
transversely extending pipe, comprising the steps of moving the
nozzle, and removing sludge from the bottom of the tank as the
nozzle is moving while excluding access of air at ambient pressure
to the sludge by applying suction to the transversely extending
pipe in excess of the pressure head generated by the level of li-
quid in the tank to apply the suction in the closed fluid conduit -
as said nozzle is moving.
The invention will be described by way of example
with reference to the accompanying drawings, wherein:
Fig. 1 is a schematic vertical sectional view through
half of a circular settling basin with a radially located brJdge
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spanning the basin and having a central liquid-introducing struc-
ture;
and Fig. 2 is a schematic piping diacram illustrat-
ing selective sludge removal under forced flow conditions, or
back-flushing also under forced flow conditions while providing
single-direction pump operation.
A settling basin, generally shown at 1 in Fig. 1,
has a circular outline when viewed from the top. An inlet struc-
ture 2 is located centrally therein. Inlet structure 2 is a
hollow col D 3 formed with openings 4 adjacent the bottom there-
of. The basin 1 has an outer circular wall 5. An overflow trough
7 is secured to the outer wall 5 so that cleared liquid can be
skimmed off the top level 6 and introduced into the clear-liquid
trough 7, for removal from _
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the tank 5, trough 7 passing through a suitable opening
(not shown) of the side wall 5 of the basin, or being in
communication with a suction pump.
The upper edge or crown of wall 5 is s~tably shaped
to guide rollers 9 supporting bridge 8 which extends
radially from the center structure 2 across the basin. The
bridge 8 is supported on center structure 2 by a hollow
pipe-like cylindrical structure lO on which a gear ll is
secured. Gear ll and, with it, cylindar~ 10 are guided
by means of radial and axial or thrust-bearings (not shown)
supported on~ a socket 12 and secured to spaced brackets
~ 13 which, in turn, are secured to cylinder 3. Rather than
;. using brackets, a support ring may also be usedj located,
for example, at the inside of the hollow cylinder 3 of the
inlet structure 2. Drive motor 15, secured to the inlet
structure 2 and having a spur gear secured thereon in an
engagement with gear 11, drives the bridge 9 in rotary
movement about the basin 1.
~` Various other drive or support arrangements may be
used; for example bridge 8 may be constructed as a cantilever-
ed structure, freely extending across basin 1, 80 that further
support, such as ro~ers 9 on the outer wall 5, is not
necessary. The elements 11, 14, 15 drive bridge 8 over
basin 1.
Two suction nozzles 17 are supported by means of
riser ducts 18 from bridge 8. Suction nozzles 17 are
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located to just clear the bottom of basin 1. They move along
with the bridge 8. The risers 18 both terminate in a
horizontal connecting line 19. Line 19 is located beneath
bridge 8 to just clear the upper liquid level 6 of liquid
in the basin 1. Connecting line 19 is suspended from bridge
8 by means of suspension holders 21. Preferably, a flow
indicator, such asa transparent pipe section, or a deflecting
vane with an external indicator, is located in the risers 18
at a readily visible position to indicate flow through the
: 10 risers, which can be individually controlled by valves 22. .
The flow indicators are not shown in the drawings for
. simplicity. - .
: Connecting line 19 extends horizontally, supported
from bridge 8, and terminates at the center of rotation of ~ ~.
: 15 bridge 8 in a vertically downwardly extending end portion 23,having a terminal end 24. End 24 is flush with the end 25 . .
of a verticallyupwardly extending pipe 26 ~hich is fixed in
position. The ends 24, 25 of pipes 19, 26 are thus movable
with respect to each other and,to prevent leakage,they are
covered by an external sleeva 27, engaging the respective . ~ .
pipe ends 24, 25 for example with o-rings. Connecting line
26 extends through the bottom of the inlet str~cture 2 of
`................ the basin 1, and extends outwardly of the basin 1 to terminate
i at a pumping station 28.
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The joint formed by ends 24, 25 and collar or sleeve
27, forms a movable joint which connects the two pipes 19, 26
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essentially liquid-tight, but permits free movement of the
pipe elements 17, 18, 19, 23 with respect to the fixed pipe
26.
Line 26, which i9 used as the sludge removal pipe,
is connected to the suction inlet of a pump 29 located in
pump chamber 28.
The vertical part 30 of the sludge removal pipe 26
i8 coaxial with the center of rotation of bridge 8. It is
surrounded by a wider pipe 31 forming the inlet for sewage
to be cleared in the settling tank or basin. Pipe 31 merges
at its upper end in a funnel-shaped enlargement 32. Pipe 31
extends through the bottom of the inlet structure 2 and is
connected to a pipe duct 33 forming the inlet line for basin
1.
Operation: Sewage introduced through line 33 flows
out of funnel 32, and through the center structure 2, to
enter the basin 1 at the bottom openings 4. To remove
sludge which has precipitated at the bottom of the basin 1,
pump 29 is started. Pump 29 preferably has a variable,
controllable through-put. Bridge 8 is started by starting
motor 15. The entire bottom wall of basin 1 is thus
continuously cleaned.
If the through-put through the pump changes
substantially - which can be sensed, for example, by sensing
pump-operating characteristics - or by observing flow through
flow indicators or transparent pipe sections, pump 28 can be
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80 operated that the sludge removal line 26 is used as a
pressure or flushing or cleaning line. Interruption or
substantial decrease of flow through the pump may be due to
deposits at the nozzles or anywhere in the system of pipes
17, 18, 19, 23, 26. Referring to Fig. 2: Pipe 26 is
connected to the inlet of pump 29 through a normally open
inlet valve 34. The outlet from pump 29 is conducted to a
sludge storage or further settling basin through a normally
open outletvalve 33. The pump can be reverse-connected,
however, by opening two normally closed valves 35, 36,
connected between the outlet of valve 33 and the inlet of
pump 29, and the outlet of pump 29 and the inlet to valve 34, -
respectively. Under normal operating conditions, sludge will
flow through pipe 26, as indicated in solid lines in Fig. 2, -
through normally open valve 34, pump 29, and normally open
valve 33. For reverse flushing, however, flushing liquid
is introduced from the outlet pipe through the then opened
normally closed valve 35, the suction inlet of pump 29 and
the then opened normally closed valve 36 to flow as ~dicated
in broken line arrows in reverse connection through the
piping system 26, 23, 19, 18, 17. The through-put direction
of the pump 29 remains the same regardless of the mode of
operation - sludge removal or reverse flushing, as indicated
; by the fixed directional triangle within the pump symbol.
Pressurized cleaning or flushing liquid can thus be
supplied both through the fixed as well as the movable portio~
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of the ducting system, to flush out any depo~its and to
clear blockages. The flow indicator (not shown) within one
of the pipes can be u~ed to determine the quantity or
velocity of flow of flushing liquid through the respective
risers 18. If the indicator should show that one of the lines
does not receive its proper share of back-flushing liquid,
then the other one of the lines can be shut off by means of
valve 22, 80 that flushing liquid at full pumping pressure
will be applied to the one line which is partly or wholly
plugged,to clear that specific line of solids which caused
the obstructi~n~ and stoppage. Since the direction of
flushing flow is counter the removal direction, any stoppages
are more readily cleared than the application of high-preæsure
in flow direction. Persistent stoppages are effectively
avoided. The pump permits back-flushing not only of the
of
fixed portion of the piping system, but also/the movable
portion. The movable joint 27 is essentially tight, and
permits application of pressurized fluid through the movable
joint, thus ensuring reliable interruption-free operation.
In normal operation, however, the fixed, as well as the
movable piping system, provide~ the connection to the
suction inlet of the pump.
; Pwmping station 28 can be so arranged that the line26 operates as a syphon ter~ating in a pump sump in
communication with the basin 1, from which solids removed
from the basin can then be further transported or pumped.
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An auxiliary pump i8 preferably provided in such
arrangements as well, which permits back-flushing of the
fixed as well as of the movable piping, as described in
connection with pump 29.
The movable joint is so constructed that it is
capable of accepting over-pressure (for pressurized back-
flushing) as well as being tight with respect to under-
pressure, that is, for normal, suction operation. Sealing
the movable joint 27 with respect to under-pressure is
facilitated by locating the movable joint 27 below the
operating level 20 of the settling basin 1.
' The nwm~er of suction nozzles 17 depends largely on
the size of the basin 1; depending on its size, one, or more
; of the ~uction nozzles can be used; two have been shown as
an example. The suction nozzles are directly connected to a
fixed suction line, preferably to the suction line directly
connected to pump 29 without intermediate open vessels or
troughs. Removal efficiency tnus is similar to that other-
wise obtainable only with fixed nozzles. The arrangement,
particularly as shown in Fig. 2, permits use of a single
pump 29 which can be located essentially at random with
respect to the operating level 20 of the liquid in the basin
1, and for example below the level of the basin 1, 80 that
pressure will exist at the suction side of the pump, thus
increasing the operating reliability of the system.
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Inlet pipe 31 is located to surround the vertical
portion 30 of the removal line 26. This permits symmetrical
flow of the sewage introduced into the basin 1, and
similarly essentially symmetrical distribution of the sewage
S through the openings 4 into the basin 1.
The invention has been described with respect to a
circular basin. The arrangement of the piping having a -~
movable, sealed joint between a fixed pipe part and a movable
part effectively makes the suction nozzle 17 the suction
opening for a fixed pumping station 28 located outside of
the basin 1. In similar manner, a basin having a rectangular
outline can be used; connection between the ixed and movable
piping portions can then be obtained by telescoping pipes,
for example, with the same advantages as those which are
o ffl ainable with a circular basin as specifically described
; in connection with Fig. l.
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Various changes and modifications may be made within
the scope of the inventive concept.
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