Note: Descriptions are shown in the official language in which they were submitted.
CA 02535386 2006-02-07
TITLE: A GAS BUBBLE MIXER
FIELD OF THE INVENTION
[001] The present invention relates to the field of liquid circulation
devices, and more
specifically to gas piston-bubble mixers (hereafter referred to as "gas bubble
mixers")
that promote liquid circulation and anaerobic digestion in bodies of waste
sludge.
BACKGROUND OF THE INVENTION
[002] Gas bubble mixers for improving the performance of anaerobic digestion
of
waste sludge, are known in the art. Such gas bubble mixers generally comprise
two
main components; namely, a large stack pipe and a gas piston-bubble generator
(hereafter referred to as a "gas bubble generator") that is located adjacent
to the stack
pipe.
[003] In use, both the stackpipe and the bubble generator are completely
submerged
within the body of waste sludge, with the stackpipe positioned in a vertical
configuration. The stackpipe has a liquid intake opening at its base and a
gas/liquid
discharge opening at its upper end. The stackpipe further includes a gas
bubble inlet at
its lower end that is in communication with the gas bubble generator. The gas
bubble
generator is thus operative for producing gas bubbles that are supplied to the
stackpipe
through the gas bubble inlet.
[004] Gas bubble generators typically include gas accumulation chambers in
which gas
is received from a gas supply line, and a stand pipe through which the
accumulated gas
exits the bubble generator into the stackpipe. Once a sufficient amount of gas
has
accumulated within the gas accumulation chambers, the gas is naturally
siphoned out of
the bubble generator through the stand pipe and into the stackpipe, thereby
forming a
large gas bubble within the stackpipe. As this bubble rises, it creates a
piston-like effect
that both pushes and pulls the liquid containing dissolved and suspended
solids upwards
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through the stackpipe. By effecting this simultaneous two-phase flow, the gas
bubbles
that travel through the stack pipe produce a strong pumping action, which
continually
mixes the body of liquid. This continuous mixing aids in the anaerobic
digestion
process of transforming organic solids into a gaseous state by maintaining a
uniformity
of the incoming solids within the mixture, and by helping to maintain the body
of liquid
at a constant temperature.
[005] Although gas bubble mixers of the type outlined above are known in the
art,
most gas bubble mixers that are currently in use today contain many
deficiencies that
render them inefficient and difficult to work with.
[006] One of the major deficiencies with existing gas bubble mixers is that
they often
get clogged after start-up, and are then very difficult and inconvenient to
clean. Keeping
in mind that most gas bubble mixers are placed in large tanks of waste sludge
that
contain organic solids and a smaller portion of non-biodegradable solids such
as grit,
hair, paper, plastics, small stones, sand, and other difficult-to-degrade
debris, it is not
surprising that after a period of use this debris gets inside the gas bubble
mixers and
causes them to clog. Obviously, when such clogging happens, the bubble
generators
need to be cleaned out and unclogged so that they can return to normal
function. While
some bubble generators include flushing passages that are able to flush out
and unclog
some of their chambers, there are many parts of the bubble generators that can
only be
cleaned out by emptying the tank of the waste sludge, and then manually
cleaning out
the bubble generators. This cleaning process causes significant expense due to
the effort
required to empty the tank, as well as the significant down-time caused by
this cleaning,
during which time the anaerobic digestion system is not in use.
[007] A further deficiency with existing bubble generators lies in their
inefficient
bubble generation. Due to the size and internal configuration of many bubble
generators, they create bubbles that are either too large or too small to
effectively create
an efficient and effective pumping action through the stackpipe. Producing
bubbles that
are too large renders the system inefficient, since it increases the energy
costs associated
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with the operation of the bubble mixers, and producing bubbles that are too
small yields
inadequate pumping action.
[008] A further deficiency with existing bubble mixers lies in their poorly
designed
hydraulic braking orifices. Many existing bubble mixers are ineffective at
producing
adequate gas bubbles due to poor bubble frequency control. If the frequency of
bubble
emission is not properly calibrated, the accumulated gas volume within the
bubble
generator will either break into many smaller bubbles on entry into the
stackpipe or it
will generate an inefficient, fluctuating pumping action. Both scenarios cause
an
ineffective pumping action and poor liquid circulation through the stackpipe.
Furthermore, hydraulic braking orifices that are positioned between the second
gas
accumulation chamber and the stand pipe often create incomplete flushing of
the gas
contained within the gas accumulation chambers. This incomplete flushing can
lead to
debris deposition and build-up inside the gas accumulation chambers and the
stand pipe,
which will cause clogging to occur more rapidly.
[009] A still further deficiency with many gas bubble mixers is that the
stackpipe is
supported with supporting legs that surround the stackpipe's liquid intake
opening. The
congestion caused by these supports restricts liquid flow into the stackpipe.
This in turn
can prevent the gas bubble mixers from effectively and uniformly mixing the
liquid/waste sludge contained within the tank.
[010] In light of the above, it can be seen that there is a need in the
industry for a gas
bubble mixer that integrates an improved gas bubble generator that alleviates,
at least in
part, the deficiencies of the prior art, and improves on the overall
efficiency of the gas
bubble mixer.
SUMMARY OF THE INVENTION
[011] In accordance with a first broad aspect, the present invention provides
a gas
bubble generator suitable for being submerged within a body of liquid and for
being
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positioned adjacent to the stack pipe. The gas bubble generator comprises a
first gas
accumulation chamber, a second gas accumulation chamber and a stand pipe. The
stand
pipe has a lower end in communication with the second gas accumulation chamber
and
an upper end having an exit through which gas exits the bubble generator. The
gas
bubble generator further comprises a continuous passageway between the second
gas
accumulation chamber and the stand pipe through which gas can travel from the
first
and second gas accumulation chambers to the gas outlet. The continuous
passageway is
absent a hydraulic braking orifice. The bubble generator further comprises a
hydraulic
braking opening in proximity to the upper end of the stand pipe.
[012J In accordance with a second broad aspect, the present invention provides
a gas
bubble generator suitable for being attached to a stackpipe, or its supports,
and
submerged within a body of liquid. The gas bubble generator comprising a first
gas
accumulation chamber, a second gas accumulation chamber, a stand pipe, a gas
inlet
and a flushing inlet. The first gas accumulation chamber and the second gas
accumulation chamber are separated by a first wall and the second gas
accumulation
chamber and the stand pipe are separated by a second wall. The flushing inlet
is
positioned above one or both of the first gas accumulation chamber and the
stand pipe,
and is operative for directing flushing fluid into the second gas accumulation
chamber,
stand pipe, and stack pipe,
[013] In accordance with another broad aspect, the present invention provides
a gas
bubble generator suitable for being submerged within a body of liquid and for
being
positioned adjacent a stackpipe. The stackpipe has an upper discharge opening,
a lower
inlet opening and a tubular passage through which gas bubbles can travel. The
gas
bubble generator comprises a first gas accumulation chamber, a second gas
accumulation chamber and a stand pipe. The stand pipe comprises a gas outlet
in
communication with the lower, side inlet opening of the stackpipe for
releasing gas
bubbles into the tubular passage and a back wall. At least a portion of the
back wall
being positioned within the tubular passage of the stackpipe.
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[014] In accordance with another broad aspect, the present invention provides
a gas
bubble generator suitable for being submerged within a body of liquid and for
being
positioned adjacent to a stackpipe. The gas bubble generator comprises a
housing
having a top wall and at least one side wall and a hydraulic braking hood. The
housing
contains a first gas accumulation chamber, a second gas accumulation chamber
and a
stand pipe that comprises a gas outlet through which gas exits the gas bubble
generator.
The hydraulic braking hood is positioned above the gas outlet and comprises a
front
wall connected between the stackpipe and the top wall of the housing, two side
edges
and at least one bottom portion, wherein at least one of the side edges and
the bottom
portion are open to the body of liquid.
[015] In accordance with another broad aspect, the present invention provides
a gas
bubble mixer suitable for use in a tank containing a body of liquid. The gas
bubble
mixer comprises a stackpipe suitable for being submerged in the body of liquid
and a
gas bubble generator. The stackpipe comprises an upper section having an upper
discharge opening, a lower section having a bubble inlet opening. The gas
bubble
generator is attached to the lower section of the stackpipe and is operative
for supplying
gas bubbles to the bubble inlet opening. The gas bubble mixer further
comprises at least
three legs for mounting the stackpipe to the tank. The at least three legs are
attached to
said stackpipe.
[016] These and other aspects and features of the present invention will now
become
apparent to those of ordinary skill in the art upon review of the following
description of
specific embodiments of the invention and the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[017] In the accompanying drawings:
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[018] Figure 1 shows a schematic diagram of an anaerobic digestion system
comprising
a tank containing a body of liquid and two gas bubble mixers that are in
accordance
with a non-limiting example of implementation of the present invention;
[019] Figure 2 shows a top plan view of a stackpipe and gas bubble generator
in
accordance with a non-limiting embodiment of the present invention;
[020] Figure 3 shows a top cross sectional view of the gas bubble generator of
Figure
2;
[021] Figure 4 shows a side cross sectional view of the gas bubble generator
of Figures
2 and 3;
[022] Figure 5 shows a bottom plan view of the gas bubble generator of Figures
2, 3
and 4;
[023] Figure 6 shows a front perspective view of the gas bubble generator of
Figures 2,
3,4and5;
[024] Figure 7A-7C show schematic outlines of hydraulic braking hoods in
accordance
with non-limiting examples of implementation of the present invention;
[025] Figure 8 shows the gas bubble generator of Figures 2-5 that is supported
from
two of the tripod legs;
[026] Figure 9 shows a perspective view of a gas bubble generator in
accordance with
an alternative non-limiting embodiment of the present invention;
[027] Figure 10 shows top plan view of the gas bubble generator of Figure 9;
and
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[028] Figure 11 shows a perspective view of a gas bubble generator in
accordance with
yet another alternative non-limiting embodiment of the present invention.
[029] Other aspects and features of the present invention will become apparent
to
those ordinarily skilled in the art upon review of the following description
of specific
embodiments of the invention in conjunction with the accompanying figures.
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DETAILED DESCRIPTION
[030] Shown in Figure 1 is an anaerobic digestion system 10 for treating waste
sludge
containing bio-solids. The system 10 includes a large tank 12 having a cover
11, and a
pair of gas bubble mixers 20 for treating a body of liquid 14 (which will be
referred to
interchangeably as waste sludge throughout this description) contained in the
tank 12.
Although only two gas bubble mixers 20 are shown in Figure 1, it should be
appreciated
that any number of gas bubble mixers 20 can be included within the anaerobic
digestion
system 10 without departing from the spirit of the invention. A person of
skill in the art
would be able to establish the appropriate number of gas bubble mixers 20 to
include
within the tank 12 depending on certain parameters such as the volume of the
tank, the
rate of mixing desired, etc...
[031 ] Anaerobic digestion systems of the type shown in Figure 1 are used to
decompose industrial and municipal waste sludge into substances that can
safely re-
enter the environment. The body of liquid 14 (i.e. the waste sludge) generally
contains
in the order of 92-98% waste liquid and 2-8% waste solids. The gas bubble
mixers 20
are operative for continually circulating the body of liquid 14 in the tank
12, which
helps to keep the waste sludge at a uniform concentration of suspended solids
and at a
constant temperature throughout the body of liquid 14. Both of these factors
are
important in improving process performance in anaerobic digestion systems.
[032] As shown in Figure l, the gas bubble mixers 20 include a stackpipe 22
and a gas
bubble generator 24. Both the stackpipe 22 and the gas bubble generator 24 are
submerged within the body of liquid 14, such that the stackpipe 22 is
positioned in a
vertical orientation. The stackpipe 22 includes a generally tubular body with
a liquid
intake opening 16 at its bottom end, and a gas/liquid discharge opening 18 at
its upper
end. The stackpipe 22 further includes an opening (not shown in Figure 1) for
receiving
gas bubbles generated from the gas bubble generator 24. In the embodiment
shown in
Figure 1, the stackpipe 22 is mounted to the base of the tank via three legs
26, which
will be described in more detail further on in the description.
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[033] Although the stackpipe 22 shown in Figure 2 has a generally cylindrical
shape, it
should be appreciated that a stackpipe 22 having other shapes, such as an
oval, square or
octagonal cross section, can also be used without departing from the spirit of
the
invention.
[034] In order to keep the body of liquid 14 circulating within the tank 12,
the gas
bubble generators 24 create gas bubbles 27 which are released into openings in
their
respective stackpipes 22. Once released, the gas bubbles 27 travel up through
the
stackpipe 22 thereby pushing and pulling all liquid contained in the stackpipe
upwards.
This liquid exits out of gas/liquid discharge opening 18. As the gas bubble 27
moves up
through the stackpipe 22, more liquid from the tank 12 is pulled into the
lower end of
the stackpipe 22 through the liquid intake opening 16. In this manner, the
bubbles form
a "piston-type" pumping action for pumping the liquid contained in the tank 12
through
the stackpipe 22.
[035] A non-limiting embodiment of a gas bubble generator 24 in accordance
with the
present invention will now be described in more detail with reference to
Figures 2-5.
[036] Shown in Figure 2 is a top plan view of the stackpipe 22, the gas bubble
generator 24 and the three legs 26 of a gas bubble mixer 20. The gas bubble
generator
24 includes a housing 30, which in the non-limiting embodiment shown, is of a
generally rectangular shape. The housing 30 includes a top wall 32 and three
side walls
34a, 34b and 34c. The gas bubble generator 24 further includes a hydraulic
braking
hood 36 positioned above the housing 30, which will be described in more
detail further
on in the description. Extending into the top wall 32 of the housing 30 is a
gas supply
line 25 and a flushing line 27.
[037] The interior chambers of the gas bubble generator 24 are shown in more
detail in
Figures 3 and 4, wherein figure 3 shows a cross sectional view of the gas
bubble
generator 24 as taken along line A-A of Figure l, and Figure 4 shows a cross
sectional
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view of the gas bubble generator 24 as taken along line B-B of Figure 1. As
shown in
these two Figures, contained within the housing 30 are three interior
chambers; namely
a first gas accumulation chamber 38, a second gas accumulation chamber 40 and
a stand
pipe 42. Positioned on either side of the second gas accumulation chamber 40
and the
stand pipe 42 are empty chambers 37 that form no part of the functionality of
the gas
bubble generator 24 and can be open to the body of liquid 14 from the top
and/or
bottom. These empty chambers 37 exist simply as a result of the shape of the
housing
30. As will be shown further on in the specification, gas bubble generators
that do not
have a substantially rectangular housing 30 do not include these empty
chambers 37.
[038] Separating the first gas accumulation chamber 38 from the second gas
accumulation chamber 40 is a first wall 50, and separating the second gas
accumulation
chamber 40 from the stand pipe 42 is a second wall 52. As best shown in Figure
3, the
second gas accumulation chamber 40 is bounded by the first wall 50, the second
wall 52
and two side walls 49a and 49b that taper inwards from the f rst wall 50 to
the second
wall 52. As such, the cross sectional area of the first gas accumulation
chamber 38 is
larger than the cross sectional area of the second gas accumulation chamber
40.
Likewise, the cross sectional area of the second gas accumulation chamber 40
is larger
than the cross sectional area of the stand pipe 42. In accordance with a non-
limiting
example of implementation, the first gas accumulation chamber 38 has a width
of 20"
and a depth of 10", the second accumulation chamber 40 has a with of 16" (at
its widest
point) and a depth of 8" and the standpipe has a width of 6" and a depth of
6".
[039] The dimensions of the three chambers 38, 40 and 42, as well as the
length of the
vertical stroke "s", which is defined between the edge 61 of the first wall 50
and the
edge 60 of the second wall 52, and the physical arrangement of the hood 36 and
its
hydraulic openings (to be described further on), control the size of the gas
bubbles that
are generated by the gas bubble generator 24.
[040] In the non-limiting embodiment shown in Figures 3 and 4, a portion of
the stand
pipe 42 is positioned within the tubular passage of the stackpipe 22. The
stand pipe 42
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is defined by wall 52, two side walls 51 a and 51 b and a back wall 54. The
two side
walls 51a and 51b intersect the stackpipe 22, such that the back wall 54 is
positioned
within the tubular passage of the stackpipe 22. By positioning a portion of
the standpipe
42, within the tubular passage of the stackpipe 22, the injection of the gas
piston
bubbles into the stackpipe 22 are more centralized. This reduces piston-bubble
slippage
and thus renders the pumping action more efficient. Furthermore, by
positioning a
portion of the stand pipe 42 within the stackpipe 22, the stackpipe 22 can
have a greater
diameter than if the stand pipe 42 was positioned completely outside of the
stackpipe
22.
[041] As shown in Figure 4, the back wall 54 of the stand pipe 42 is
positioned at an
angle in relation to a longitudinal axis of the stackpipe 22. In accordance
with a non-
limiting example, the back wall 54 of the stand pipe can be positioned at an
inclination
of between 5° -10° in relation to the longitudinal axis of the
stackpipe 22. However, it
should be understood that the back wall 54 of the stand pipe 42 can be
positioned at any
angle in relation to the stackpipe 22 without departing from the spirit of the
invention.
The angled stand pipe 42 provides for smoother transition of back wall 52 into
stack
pipe 22, which reduces sludge flow friction in stack pipe 22.
[042] Referring now to Figure 4, the second gas accumulation chamber 40
includes an
upper end 41 and a lower end 43, wherein the upper end 41 includes a
passageway 45
that is in communication with the first gas accumulation chamber 38 and the
lower end
43 includes a continuous passageway 47 that is in communication with the stand
pipe
42. In accordance with a non-limiting embodiment of the present invention, the
upper
end 41 of the second gas accumulation chamber 40 can include a curved wall
section 35
for facilitating the passage of gas and liquid flow through passageway 45. The
passageway 47 between the second gas accumulation chamber 40 and the stand
pipe 42
is formed between the second wall 52 and a curved wall 56 that extends from
the first
wall 50 to the back wall 54 of the stand pipe.
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[043] The passageway 47 that extends between the second gas accumulation
chamber
40 and the stand pipe 42 is continuous and absent of any hydraulic braking
orifices. For
the purposes of the present application, the term continuous means without any
obstructions or orifices that could affect the flow of gas and/or liquid
through the
passageway 47. The continuous passageway 47 is therefore a smooth passageway
that
promotes the easy passage of gas from the second gas accumulation chamber 40
to the
stand pipe 42.
[044] Shown in Figure 5, is a bottom plan view of the gas bubble generator 24.
As
shown, the curved wall 56 of the passageway 47 can include a small hole 29
that
facilitates the drainage of the gas bubble generator 24 in the case where the
gas bubble
generator 24 is removed from the tank 12 for cleaning. Such a hole 29 would
not have
any impact on the frequency regulation of the bubbles travelling through the
bubble
generator 24. As such, the continuous passageway 47 may include one or several
small
holes that can be plugged except for drainage purposes, so long as they do not
obstruct,
or in anyway affect the flow of gas/liquid through the passageway 47.
[045] Due to the fact that the cross section of the second gas accumulation
chamber 40
is larger than the cross section of the stand pipe 42, the curved wall 56
forms an
asymmetrical return bend, wherein it is wider at its connection to the first
wall 50 and
narrower at its connection to the back wall 54. More specifically, and as
shown in
Figure 5, the width of the curved wall 56 tapers as it extends from the first
wall 50
towards the back wall 54. In this manner, the gas from the second gas
accumulation
chamber 40 is funnelled into the stand pipe 42.
[046] The curved wall 56 can be a separate component from walls 50 and 54,
such that
it is connected to these two walls via mechanical connection methods.
Alternatively, the
curved wall 56 could be continuous with one or both of walls 50 and 54. In
other words,
these walls could all be made out of the same component material, and simply
bent into
the U-shape that the combination of walls 50, 56 and 54 create. In the case
where walls
50, 56 and 54 are separate pieces, they can be connected together using any
connection
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means known in the art, such as by welding, soldering, rivets, bolts, etc...
Likewise, the
other walls of the housing 30 and of the interior chambers 38, 40 and 42 can
also be
connected together using such connection methods. All connection methods
should
create a water tight seal.
S
[047] Referring back to Figure 4, the gas supply line 2S enters the first gas
accumulation chamber 38 through a gas inlet 46, such that gas is able to enter
the gas
bubble generator 24. In addition, the flushing line 27 enters the first gas
accumulation
chamber 38 through a flushing inlet 44, such that flushing fluid is also able
to enter the
gas bubble generator 24. The first gas accumulation chamber 38 further
includes an
opening 48 that is open to the body of liquid 14 contained in the tank 12. In
the
embodiment shown, the opening 48 is positioned at the opposite end of the
first gas
accumulation chamber 38 from the gas inlet 46 and the flushing inlet 44. In
this manner,
as gas enters the first gas accumulation chamber 38 through the gas supply
line 2S, any
1S fluid contained in the first gas accumulation chamber 38 is pushed out
through the
opening 48.
[048] In addition, as gas enters through gas inlet 46, the gas accumulates in
both
chambers 38 and 40. Since chambers 38, 40 and 42 are interconnected, the gas
introduced into chambers 38 and 40 displaces liquid via both opening 48 and
the gas
outlet S8 in the stand pipe 42.
[049J The gas outlet S8 in the stand pipe 42 is the opening through which gas
bubbles
from the gas bubble generator 24 are released into the stackpipe 22. These gas
bubbles
2S flow from the gas outlet S8 into the opening 80 in the stackpipe 22. The
process of
generating these bubbles will now be described in more detail.
[050) During operation, the bubble generator 24 receives a continuous flow of
digester
bio-gas or other gases depending on the municipal or industrial application,
from the
gas supply line 2S. In a non-limiting example, the bio gas may include a
combination of
C02 (30-40%) and Methane (70-60%). Other gases can include air, inert gases
such as
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nitrogen, or natural gas where process conditions require it. In the
embodiment shown,
the gas enters the first gas accumulation chamber 38 via the gas supply line
25 that
enters through the gas inlet 46. As the gas enters the gas bubble generator
24, it begins
to fill both the first gas accumulation chamber 38 and the second gas
accumulation
chamber 40. As mentioned above, while this is happening, any of the liquid
that was
previously contained in these two accumulation chambers 38 and 40 is pushed
out
through opening 48 in the first gas accumulation chamber 38 and through the
gas outlet
58 in the stack pipe 42. Once a sufficient amount of gas has accumulated
within the first
and second gas accumulation chambers 38 and 40, meaning that the gas level has
reached the bottom edge 60 of the second wall 52, the gas in the two
accumulation
chambers 38 and 40 automatically slips into the stand pipe 42 through the
passageway
47. A natural siphoning action takes place, diverting most of the accumulated
gas in
chambers 38 and 40 into the stand pipe 42. This gas then travels through the
stand pipe
42 and is released into the stackpipe 22 through gas outlet 58. At this stage,
the gas from
the gas supply line 25 once again begins to fill the first and second gas
accumulation
chambers 38 and 40, and the cycle is repeated.
[051] As shown in Figure 6, positioned above the housing 30 of the gas bubble
generator 24 is a hydraulic braking hood 36. As such, the gas bubble generator
includes
hydraulic openings in proximity to the upper end of the stand pipe 42.
Specifically, the
hydraulic braking hood 36 is positioned over the gas outlet 58 of the stand
pipe 42. In
accordance with a non-limiting embodiment, the hood 36 has a width greater
than that
of the gas outlet 58. As such, the hydraulic braking hood 36 extends past the
gas outlet
58 on either side. It should, however, be appreciated that the hood 36 may be
of the
same width as the gas outlet 58.
[052] In the non-limiting embodiment shown in Figure 6, the hydraulic braking
hood
36 includes two front walls 60a and 60b, and two side edges 62 and 64. Each of
the two
side edges 62 and 64 includes a hydraulic opening 66 that is exposed to the
body of
liquid 14. These openings 66 create hydraulic braking for controlling the
frequency of
the gas bubbles that enter the stackpipe 22. In addition, these openings 66
prevent the
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bubbles produced by the gas bubble generator 24 from splitting into multiple
bubbles as
they enter the stackpipe 22. In the case where the hydraulic brake is not
present, liquid
movement in the stack pipe creates suction in the side opening 80, which would
pull the
liquid or gas from the gas bubble generator. Under normal operating conditions
about
5% of the liquid flow enters the stack pipe via opening 80, while 95% of
liquid is pulled
in from the bottom opening 16.
[053] In the non-limiting embodiment shown, only a portion of the side edges
62 and
64 are open to the body of liquid 14, such that the side edges 62 and 64
include wall
portions 62a and 64a. As such, the openings 66 are not as big as the side
edges 62 and
64. Alternatively, the entire side edges 62 and 64 of the hydraulic braking
hood 36 could
be open, such that the hydraulic openings 66 are of the same size as the side
edges 62
and 64. In such a case, there would be no wall portions 62a and 64a. In the
embodiment
shown, the openings 66 are of a substantially truncated triangular shape,
however, it
should be appreciated that these openings 66 can be of any shape without
departing
from the spirit of the invention. For example, the openings could be of a
trapezoidal, or
circular shape.
[054] As shown in Figure 6, the front walls 60a and 60b of the hydraulic
braking hood
36 connect between the stackpipe 22 and the top wall 32 of the housing 30. In
addition,
the hydraulic openings 66 are positioned in a substantially vertical
orientation in relation
to the bottom of the tank 12. During normal operation of the anaerobic
digestion
system, biosolids that are suspended in the waste sludge, tend to settle
downwards due
to gravity. Advantageously, having the hydraulic openings 66 positioned in a
substantially vertical orientation avoids such bio-solid debris from falling
into the
hydraulic brake openings 66 as it settles. This helps to prevent unnecessary
clogging of
the gas bubble generator 24.
[055] Positioned underneath the front walls 60a and 60b of the hydraulic
braking hood
36 are bottom portions 68. Given that the width of the top walls 60a and 60b
is greater
than the width of the gas outlet 58, these bottom portions 68 are positioned
underneath
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the front walls 60a and 60b on either side of the gas outlet 58. In the
embodiment shown
in Figure 6, these bottom portions 68 are walls formed by portions of the top
wall 32 of
the housing 30. However, in an alternative embodiment (not shown in Figure 6),
these
bottom portions 68 can be open to the liquid, such that they form hydraulic
openings. In
the case where the gas bubble generator 24 has a substantially rectangular
housing 30,
as shown in the embodiment of Figures 3, 5 and 6, these hydraulic openings
would
extend into the empty chambers 37.
[056] Shown in Figures 7A-7C are cross-sectional views of hydraulic braking
hoods
36 that include different arrangements of hydraulic openings. For the purposes
of these
Figures, like parts are denoted with like numerals. Shown in Figure 7A, is a
cross
sectional view of the hydraulic braking hood 36 shown in Figure 6, wherein the
hydraulic braking hood 36 includes only the hydraulic openings 66 at the side
portions
62 and 64. Shown in Figure 7B is a cross sectional view of a hydraulic braking
hood
that includes only hydraulic openings 69 that are positioned along the bottom
portions
68. And finally, shown in Figure 7C is a hydraulic braking hood that includes
both
hydraulic openings 66 at the side portions 62 and 64, and hydraulic openings
69 at the
bottom portions 68.
[057] Referring back to Figure 4, the gas bubble generator 24 includes both a
gas inlet
46, for receiving a continuous supply of gas from the gas supply line 25, and
a flushing
inlet 44 for receiving flushing fluid from the flushing line 27. Although two
inlets are
shown; namely the gas inlet 46 and the flushing inlet 44, in an alternative
embodiment,
the gas bubble generator 24 may include only one inlet, wherein both gas from
the gas
supply line 25 and flushing fluid from the flushing line 27 enter through this
one inlet.
[058] The gas supply line 25 may be operative to supply both gas, and flushing
fluid to
the gas bubble generator 24, such that if needed, there are two flushing lines
for
cleaning the gas bubble generator 24. During the course of normal operation,
some of
the bio-solids and other debris contained in the waste sludge accumulate
within the
chambers of the gas bubble generator 24. As such, it is advantageous to be
able to flush
16
CA 02535386 2006-02-07
out this debris without having to go through the expensive process of removing
the
bubble generator 24 from the tank 12.
(059] In the non-limiting embodiment shown in Figure 4, both the gas supply
line 25
and the flushing line 27 are positioned over the first gas accumulation
chamber 38. It
should be appreciated that one or both of the gas supply line and the flushing
line could
also be positioned above the second gas accumulation chamber 40. In addition,
the
flushing line could also be positioned over the standpipe. At least one of the
gas supply
line 25 and the flushing line 27 is operative for injecting flushing fluid
into the first gas
accumulation chamber 38. In the non-limiting embodiment shown, it is the gas
supply
line 25 that is used to inject flushing fluid into the first gas accumulation
chamber 38 for
flushing any debris contained in that chamber out through opening 48.
[060] In addition, at least one of the gas supply line 25 and the flushing
line 27 is
operative for injecting flushing fluid into the second gas accumulation
chamber 40. In
the non-limiting embodiment shown, it is the flushing line 27 that injects
flushing fluid
into the second gas accumulation chamber 40. More specifically, the flushing
line 27 is
positioned at an angle in relation to the first wall 50 such that it is able
to inject flushing
fluid into the second gas accumulation chamber 40 from its position over the
first gas
accumulation chamber 38. In addition, as the flushing fluid travels from the
flushing
line 27 to the second gas accumulation chamber 40, it is directed in proximity
to the
edge 61 of the wall S0. In operation, much of the debris that accumulates
within the gas
bubble generator 24, accumulates around the edge 61 of wall 50. As such, by
directing
the flushing fluid against and above this edge, the flushing fluid is able to
dislodge and
flush away any debris that has accumulated in this and other areas of the
generator,
including passages 40, 42, 47, 58 and 80.
[061] As mentioned above, the passageway 47 that connects the second gas
accumulation chamber 40 to the stand pipe 42 is a continuous passageway that
provides
a smooth transition between the two chambers. As such, the flushing fluid that
is
injected into the second gas accumulation chamber 40, is able to travel
through the
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CA 02535386 2006-02-07
second gas accumulation chamber 40 into the stand pipe 42 and out through the
gas
outlet 58. In this manner, the debris that has accumulated within chambers 40
and 42,
and passageway 47 is flushed out through the gas outlet 58.
[062] Referring back to Figures 1 and 2, the gas bubble mixer 20 is supported
via three
legs 26, in a generally tri-pod arrangement. The three legs 26 are connected
to the
stackpipe 22, and are positioned around the circumference of the stackpipe 22
in a
substantially equidistant relationship. The three legs 26 can be connected to
the
stackpipe 22 in any suitable way known in the art, such as by bolts, rivets,
welding or
flanges, for example. In the embodiment shown in Figures 1 and 2, the three
legs 26 are
operative for supporting the stackpipe 22 within the tank, and the stackpipe
22 is
operative for supporting the gas bubble generator 24. The gas bubble generator
24 is
mounted adjacent to the stackpipe 22, such that the majority of the gas bubble
generator
24 is positioned exterior to the stackpipe 22. As such, the gas bubble
generator 24 is not
supported by any additional legs that are positioned between it and the floor
of the tank
12.
[063] The three supporting legs 26 extend outwardly from the stackpipe 22 such
that
they are positioned farther away from the liquid intake opening 16 than if
they were
abutted and extended straight down from the sides of the stackpipe 22. By
extending
away from the liquid intake opening 16, the legs 26 avoid blocking the liquid
flow into
the stackpipe 22, which helps to improve the overall performance of the mixer
10. In the
non-limiting embodiment shown, the three legs 26 include two branches; namely
branch
26a and branch 26b that are positioned at an angle in relation to each other.
The branch
26a is connected to the stackpipe 22 and the branch 26b is connected to the
base of the
tank 12. The branch 26a is positioned at an angle in relation to the
longitudinal axis of
the stackpipe 22, for extending the legs 26 away from the liquid intake
opening 16 of
the stackpipe 22. It should be understood that legs 26 having any other
configuration
that allows them to extend away from the stackpipe 22, are also included
within the
scope of the present invention.
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CA 02535386 2006-02-07
[064] Although Figure 1 depicts the tank 12 as having a substantially flat
bottom, in
most situations, the bottom surface of the tank forms a cone or a one-sided
slanted slab,
with drainage positioned in the lowest portion of the tank bottom. As such,
the bottom
surface of the tank is not flat, and instead slants downwards towards the
lowest portion
of the tank bottom. In light of this, in order to mount the standpipe 22 in
the tank 12
such that it is positioned in a substantially vertical orientation, the three
legs 26 that are
used to mount the standpipe are not necessarily of the same length. Instead,
their length
may vary depending on the degree of slope of the bottom surface of the tank.
In
accordance with a non-limiting embodiment, the legs 26 may be adjustable in
length,
such that their length can be adjusted while the stack pipe 22 is being
installed in the
tank 12. For example, the legs 26 may include sliding components, or
telescopic
components that are able to be adjusted at the time of installation.
[065] In general, the branches 26b of the legs 26 are attached to connection
points (not
shown) on the bottom surface of the tank via bolts. However, other connection
mechanisms known in the art could also be used without departing from the
spirit of the
invention, for mounting the legs 26 to the surface of the tank 12.
[066] In yet a further alternative arrangement, the legs 26 of the tri-pod
support can be
used to suspend the stackpipe 22 from the cover 11 of the tank. In such an
arrangement,
the legs 26 do not interfere with the intake opening 16 at the lower end of
the stackpipe
22, thus providing greater free space at the intake opening 16. More
specifically, this
arrangement leaves the bottom of the stackpipe 22 free from any supports that
could
interfere with liquid/sludge flow into the stackpipe 22. With this "roof '
mounted
arrangement, it should be understood that a minimum of three legs 26 can be
used to
secure the stackpipe 22 to the cover 11.
[067J Referring now to Figure 2, in the non-limiting embodiment shown, the gas
bubble generator 24 is mounted adjacent to the stackpipe 22 such that it is
positioned
between two of the legs 26. In such an embodiment, it is the stackpipe 22 that
supports
the gas bubble generator 24. It should, however, be appreciated that in an
alternative
19
CA 02535386 2006-02-07
embodiment, such as that shown in Figure 8, the gas bubble generator 24 could
also
include supports 82 that attach to two of the legs 26 for providing additional
support for
the gas bubble generator 24. In such an embodiment, the bubble generator 24 is
mounted to the stackpipe 22 supports.
[068] Although the gas bubble generator 24 shown in Figures 1 through 8
includes a
substantially rectangular housing 30, it should be understood that gas bubble
generators
having different shapes are included within the scope of the present
invention.
[069] Shown in Figure 9 is a gas bubble generator 90 in accordance with an
alternative, non-limiting embodiment of the present invention. The gas bubble
generator
90 does not include extra walls that define a housing surrounding the interior
chambers.
Instead, the gas generator 90 simply includes the walls that define the three
interior
chambers.
[070] Gas bubble generator 90 includes a hydraulic braking hood 92 that
includes
hydraulic openings 94 along its two side portions, 96 and 98, and hydraulic
openings
100 underneath the front walls 102. Given that the gas bubble generator 90
does not
include any empty chambers, the hydraulic openings 100 are open to the liquid
in the
tank 12.
[071] Figure 10 shows a cross sectional view of the gas bubble generator 90
shown in
Figure 9.
[072] Shown in Figure 11 is a gas bubble generator 110 in accordance with yet
another
alternative, non-limiting embodiment of the present invention. The gas bubble
generator
110 includes a housing 114 that has a top wall 116 and side walls (not shown).
In this
embodiment, the hydraulic braking hood 112 is integrally formed with the
housing 114,
such that the front wall of the hydraulic braking hood 112 is also the top
wall 116 of the
housing 114. In this embodiment, the hydraulic braking hood 112, includes
hydraulic
openings 118 positioned on its side edges.
CA 02535386 2006-02-07
[073] Although the present invention has been described in considerable detail
with
reference to certain preferred embodiments thereof, variations and refinements
are
possible without departing from the spirit of the invention. Therefore, the
scope of the
invention should be limited only by the appended claims and their equivalents.
21
