Note: Descriptions are shown in the official language in which they were submitted.
CA 02455127 2003-12-24
SYSTEM AND METHOD
FOR REMOVING CONTAMINANTS FROM LIQUID
RELATED APPLICATION
This application claims priority from United States Provisional
Application Serial No. 60/300,768, filed June 25, 2001.
BACKGROUND OF THE INVENTION
The present invention generally relates to liquid separation
components, systems and methods. More particularly the present invention
relates to liquid flotation separation components, systems and methods that
employ one or more gasses for separating particulate matter and other
contaminants from carrier liquid streams.
It is often necessary to remove contaminants from liquid. For example,
the need to remove particles, colloids, solvent and oil from wastewater is
desirable in many settings.
Typically, such contaminants are water borne. These streams are
typically treated using coagulants and flocculants to form sludge, which is
separated from the liquid.
Dissolved air flotation (DAF) systems are often used to separate
particulate material from liquids such as wastewater. The systems typically
employ the principle that bubbles rising through a liquid attach to and carry
away particles suspended in the liquid. As bubbles reach the liquid surface,
the attached particles coalesce to form a froth that is collected.
Traditional DAF systems typically introduce small air bubbles into the
lower portion of a relatively large tank filled with the liquid to be treated.
The
air bubbles rise through the liquid and attach to particles in it. The tank
ZPM-40045
-1- UTILITY APP
CA 02455127 2003-12-24
includes an outlet through which treated liquid passes at a flow rate
consistent
with the inlet rate of the liquid plus a fraction for air entrainment.
DAF system processing times and contaminant removal efficiencies
typically depend on the residence time of the bubbles in the solution. The
residence time, in turn, is affected by bubble size, bubble buoyancy, the
depth
of the bubbles within the liquid, and the amount of turbulence in the liquid.
As
footprint increases, the probability increases that particles will contact the
bubbles during the residence time available within the tank. In addition,
relatively large footprints allow the bubbles sufficient time to rise through
the
depth to reach the free liquid surface. As a result, traditional DAF systems
employ relatively large and costly tanks having correspondingly large
"footprints".
The very size of such systems increases the period of time between
control adjustment and effect. This is because water going by the adjustment
point, for example a polymer inlet upstream of the DAF, requires over half an
hour, and usually over an hour, to reach the outlet of the DAF. Thus, there is
a substantial delay .(i.e. %2 to 1 hour response time) before the effect of
the
adjustment can be ascertained so as to inform the next adjustment. Thus,
these systems lack real-time or even near real-time control. In the event the
processing produces a treated effluent stream that is outside operating
requirements, the long response time results in production of many gallons of
out-of-specification wastewater.
This is especially true under circumstances in which the DAF unit
receives flows from several dissimilar processes. This is a common
occurrence. Many times the separate flows make up varying fractions of the
total flow entering the DAF unit. Floor drains from a canning floor, for
example, may carry a fairly small quantity of drained liquid most of the time
and large flows during wash downs. Although the normal flow may be similar
to the flow from the boiler operation, during wash downs it will exceed the
boiler flow. Thus, the character of the composite flow that reaches the DAF
can commonly change from one minute to the next. Unless adjustments are
made to the DAF process, usually via adjustment of chemical dosages, the
ZPM-40045
-2- UTILITY APP
CA 02455127 2003-12-24
contaminant removal efficiency will vary and may degrade below
requirements. A need exists for the ability to make real time or near real
time
adjustments that respond to shifts in the character of the streams to be
treated. The large tank size of the typical DAF tank is in part due to the
need
to flatten these stream variations.
In an effort to reduce the tank size for a DAF system, one proposal
disclosed in U.S. Patent No. 4,022,696 employs a rotating carriage and floc
scoop. The carriage directs an inlet solution substantially horizontally along
a
flow path to increase the path length for bubble travel, and correspondingly
increasing the residence time. However, the rotating carriage and scoop
create turbulence that slows bubble rise. Unfortunately, while the tank size
reduction is set forth as an advantage, the problem with performance tied to
residence time still remains.
Another proposal, disclosed in U.S. Patent No. 5,538,631, seeks to
address the turbulence problem by incorporating a plurality of spaced apart
and vertically arrayed baffles. The baffles include respective vanes angularly
disposed to re-direct the flow of liquid from an inlet positioned at the
bottom of
the tank. Liquid flowing through the tank deflects upwardly as it traverses
the
vanes, purportedly reducing the extensity and intensity of turbulence
generated near the inlet to the tank.
While this proposal purports to reduce the turbulence problem relating
to bubble residence time, the redirected fluid still appears to affect bubbles
rising in other areas of the tank, and influences the residence time of such
bubbles. Moreover, the proposal fails to address the basic problem of DAF
performance being dependent on the need to accomplish bubble-to-particle-
adhesion during bubble rise. This increases the residence time needed to
complete separation.
In an effort to overcome the limitations in conventional DAF systems,
air-sparged hydrocyclones (ASH) have been proposed as a substitute for DAF
systems. One form of air-sparged hydrocyclone is disclosed by Miller in U.S.
Patent No. 4,279,743. The device typically utilizes a combination of
centrifugal force and air sparging to remove particles from a fluid stream.
The
ZPM-40045
-3- UTILITY APP
CA 02455127 2003-12-24
stream is fed under pressure into a cylindrical chamber having an inlet
configured to direct the fluid stream into a generally spiral path along a
porous
wall. The angular momentum of the fluid generates a radially directed
centrifugal force related to the fluid velocity and indirectly with the radius
of
the circular path. The porous wall is contained within a gas plenum having
gas pressurized to permeate the porous wall and overcome the opposing
centrifugal force acting on the fluid.
In operation, the unit receives and discharges the rapidly circulating
solution while the air permeates through the porous wall. Air passing through
the walls of the porous tube is sheared into the fluid stream by the rapidly
moving fluid flow. Micro-bubbles formed from the shearing action combine
with the particles or gases in the solution and float them toward the center
of
the cylinder as a froth in a vortex. The centrally located froth vortex is
then
captured and exited through a vortex finder disposed at the upper end of the
cylinder while the remaining solution exits the bottom of the cylinder.
In operation, however, a substantial portion of the froth tends to
become re-entrained on the liquid leaving the hydrocyclone instead of exiting
the top. In addition, froth exiting the top usually has a substantial fraction
of
water that must then be subjected to lengthy dewatering for decanting back
into the process upstream of the hydrocyclone.
One variation in the general ASH construction, as described in U.S.
Patent Nos. 4,838,434 and 4,997,549, includes employing a froth pedestal at
the bottom of the cylinder to assist directing the froth vortex through the
vortex
finder. Another ASH modification includes replacing the vortex finder and
froth pedestal with a fixed splitter disposed at the bottom of the cylinder
and
having a cylindrical knife edge. The edge is positioned to split the helically
flowing solution into components dependent upon the specific gravity of the
components. As above, the ASH systems tend to suffer from relatively large
amounts of solution typically remaining in the froth, and significant particle
concentrations often remaining in the solution.
Morse, et al, disclosed in U.S. Patent No. 6,106,711 a system using a
hydrocyclone that differs from the above by the absence of a froth pedestal
ZPM-40045
-4- UTILITY APP
CA 02455127 2003-12-24
and vortex finder and by the fact that both the froth and the liquid exit the
hydrocylone together. In addition, the system relies on a downstream tank
with vanes that are slanted from the vertical so as to separate the bubble-
particle aggregates from the mass of the liquid stream. Morse, et al, also
disclosed in U.S. Patent No. 6,171,488 a system using a hydrocyclone that
differs from U.S. Patent No. 6,106,711 in that the hydrocyclone makes a
submerged entry into the downstream tank.
Although for both of these patents the assembly is small compared to
DAF systems, and so provides for near-real-time control, the assembly is a
single unit that requires a sizeable location and is large enough to require
special equipment to move. It also cannot accommodate the sequential
introduction of more than one additive that must be thoroughly mixed with the
stream before the introduction of the next additive. For example, it is
desirable to adjust pH before adding polymeric flocculants so that high doses
of the latter are avoided. In addition, a higher number of extremely fine
bubbles would improve flotation. For these Morse inventions, there are not
many variables that can be adjusted to optimize performance, so the
manufacture of the systems often must be customized to the waste stream to
be treated.
In addition, there can be problems scaling up to flows over 100 gallons
per minute. At such flows, the momentum of the water is such that bubbles
form that are over '12 inch in diameter. These bubbles interfere with
flotation
by being too large to aggregate with flocs and by creating cavitation, noise
and vibration in the piping. In addition, the bubble size distribution begins
at
20+ microns and does not bond to the small particles.
Therefore, the prior art has not solved the essential problems of large
footprints, process control, flexibility, and small (nanometer) bubble size.
Thus, a continuing need exists for a flotation separation system with
components that need not be near one another so that space constraints can
be accommodated. The need also exists for a method of simply and
economically creating large quantities of the optimal size bubble needed at
each step of the flocculation and flotation process. The need also exists to
be
ZPM-40045
-5- UTILITY APP
CA 02455127 2003-12-24
able to easily vary the types and order of additives to minimize doses and
interference with downstream additives. An additional need exists for a
separation system that reduces the amount of additives needed per unit
volume of liquid to be treated, which would reduce ongoing operational costs.
The flotation separation system and method of the present invention satisfies
these needs and provides other related advantages.
SUMMARY OF THE INVENTION
The fluid conditioning system and method of the present invention
provides an efficient and cost-effective way of treating liquids. This is
accomplished in part through low cost and small footprint components,
including the use of a final separation tank. In addition, advantages are
achieved by enabling of in-line mixing of additives into the liquid to be
treated
in a way in which strategies that cannot be utilized under established designs
can be employed.
This is also accomplished in part by minimizing bubble residence time
as a factor in flotation system performance. Further, system performance is
enhanced by maximizing particle-bubble contact, in part by increasing the
number of bubbles of sizes most effective for flocculation and separation.
Reduction of the need for residence time allows for smaller flotation
components, which in turn significantly reduces floor space and material
construction costs. In addition, near real-time process control can be
achieved when there is little residence time (and hence response time)
between process adjustments. Substantial space flexibility is also achieved
through a unique design that allows some components to be physically
remote from one another. Substantial reduction in the amount of high cost
additives is obtained by sequencing the mixing processes and a unique
choice of introduction points.
The present invention generally resides in a method for removing
contaminants from a liquid comprising the steps of mixing the liquid to be
ZPM-40045
-6- UTILITY APP
CA 02455127 2003-12-24
1 !
treated with additives, pressurizing the liquid, dissolving gas into the
liquid,
thereafter reducing the pressure of the liquid, allowing the dissolved gas to
exit the liquid uniformly throughout the homogenous contaminants from the
liquid by mixture of liquid and particles and contact the particles
continuously
while they grow to the most effective contact adhesion size.
The liquid to be treated is initially screened for objects with any
dimension greater than the smallest dimension of any aperture in any
hydrocyclone component of the invention.
Additives, such as pH adjusting chemicals, reducing agents, polymeric
coagulants, flocculants, or absorbers are then mixed with the liquid to be
treated. The initial additive mixing step can be accomplished using the
following devices or systems:
1. a batch tank equipped with a mixer;
2. a series of hydrocyclones;
3. a flock tube having multiple bends; or
4. in-line mixers.
The gasification step is accomplished by using a gasification device.
Preferably a vessel of the device is at least three times as tall as its
diameter.
Upstream of the gasification device, the liquid to be treated is pressurized.
Compressed gas (usually air) is added at a pressure slightly above the liquid
line pressure. The liquid enters the vessel through a hydrocyclone head at
the top of the vessel. Liquid exits the vessel at or near the bottom. A
hydrocyclone accelerator head creates a helical flow around the inside
diameter of a barrel forming the exit of the hydrocyclone and passing through
the top of the vessel. The barrel extends almost to the bottom of the vessel.
Concentric with the barrel is an "uptube" of larger diameter. Liquid flows
upward from the bottom of the barrel through the annular space formed
between the barrel and the uptube. It exits the uptube near the top of the
vessel. The vessel contains a head space above a liquid level. Large
bubbles rise immediately to the head space and are not entrained in the liquid
as it moves downward toward the vessel exit. In this way, the large bubbles
are removed from the liquid passing to the rest of the process. In contrast,
ZPM-40045
-7- UTILITY APP
CA 02455127 2003-12-24
small bubbles, those most useful for forming bubble-particle aggregates, do
pass into the downstream components. A tube connects the headspace of
the vessel to the top of the hydrocyclone. The liquid leaving the exit near
the
bottom of the vessel contains more gas than at the inlet, and most of the gas
is dissolved.
Additives, typically anionic flocculants, can be added to the liquid after
the dissolving, gasification step.
The next step of the invention is forcing of the liquid through at least
one pressure drop. This controls bubble formation and matches bubble rise
to the task at hand. This may be accomplished using either an orifice plate or
a hydrocyclone.
The final step is separation by stratification, preferably in a multi-
chamber tank that takes advantage of flotation forces in a specific way. The
liquid from the pressure drop device enters near the bottom of the tank
preferably opposite the sludge exit port of the tank. The bottom entrance
directed toward the top operates to reduce the turbulence from the pressure
drop and provide time for additive-based chemical reactions to occur. In
some applications, the first chamber is equipped with a baffle to enhance
conversion from chaotic flow into more linear upward flow.
The primary path of the liquid is horizontally across the top of the tank.
As the liquid travels from the entrance end of the tank, the flocs float to
the
surface and are removed by a mechanical skimmer that pushes them onto a
beach and into sludge handling equipment. When the liquid reaches the far
wall in its traverse across the top of the tank, it flows primarily downward
and
circulates back toward the first chamber. At the bottom of the second
chamber and substantially adjacent to the first chamber is one or more outlets
for the treated liquid. The approach to the outlet is baffled,in a way that
accomplishes deflection of the circulating current upward and maintains a
density layer separation insuring the cleanest portion of the liquid exits the
tank. Water level in the tank is maintained by any suitable means, for
example, by using a weir. Cleaned water flows out of the flotation tank below
the water level to its next use or to disposal.
ZPM-40045
-$- UTILITY APP
CA 02455127 2003-12-24
The liquid conditioning method and system of the present invention
provides for in-line managed mixing that adds and sequences initial additives
to adjust the characteristics of the liquid to optimize flocculation and
separation; provides for addition of gas in a way that evenly and finely
distributes the gas within the liquid being treated, even at flows higher than
100 gpm, reduces the pressure in a manner which causes formation of
bubbles of the size most needed at each point in the process; provides for
rapid separation and consolidation of the bubble-particle aggregates; and
produces sludge with superior separability and handling characteristics and
enables near-real-time process control.
Other features and advantages of the present invention will be
apparent from the following detailed description when read in conjunction with
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings illustrate the invention. In such drawings
FIGURES 1A and 1B are block diagrams of the liquid contaminant
removal method and related systems of the invention;
FIGURE 2 is a component diagram of the form of the invention utilizing
a batch tank for mixing initial additives, a gasification vessel, and an
orifice as
a pressure drop;
FIGURE 3 is a component diagram of the form of the invention utilizing
hydrocyclones for mixing additives, and a hydrocyclone as a pressure drop;
FIGURE 4 is an axial cross-sectional view of a hydrocyclone utilized in
accordance with the present invention;
FIGURE 5 is a component diagram of the form of the invention utilizing
a bent floc tube for mixing additives, a gasification device, and a pressure
drop device;
FIGURE 6 is a vertical cross-sectional view of the gasification device
used in accordance with the present invention;
ZPNI-40045
-9- UTILITY APP
CA 02455127 2003-12-24
FIGURE 7 is a detailed vertical cross-sectional view of the gasification
device of the present invention;
FIGURE 8 is an axial cross-sectional view of a hydrocyclone
component of the gasification device;
FIGURE 9 is a perspective cutaway view of an accelerator head of the
hydrocyclone of FIG. 8;
FIGURE 10 is vertical cross-sectional view of a flotation separation
tank of the present invention; and
FIGURE 11 is a top plan view of the flotation tank.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As shown in the drawings for purposes of illustration, the present
invention resides in a method and system, generally referred to by the
reference number 10, which removes contaminants from a liquid so as to treat
the liquid for disposal or subsequent use. With reference to FIG. 1A, the
method of the present invention generally comprises filtering or screening
objects from the liquid having a relatively large dimension with respect to
the
apertures and tubes within the system of the present invention. The liquid to
be treated is then mixed with various additives 12, as will be more fully
described below. The mixed liquid is then pressurized and gasified 14 to
dissolve gas into the liquid. The pressurized liquid then experiences a
pressure drop 16 which causes bubbles of gas within the liquid to expand and
floccules to aggregate and associate with the bubbles. The contaminants are
then separated from the liquid by a floatation and stratification process 18.
Referring to Figure 1 B, the invention consists of the following
components or subsystems, each of which is novel and innovative in its own
right: a mixing system 12a, as will be more fully disclosed below, for
introducing a sequence of additives, a gasification device 14a for adding gas
to the liquid, a pressure drop device 16a for creating the bubbles required,
ZPM-40045
-10- UTILITY APP
CA 02455127 2003-12-24
and a separation tank 18a for harvesting the cleaned liquid. All components
are composed of materials resistant to degradation by constituents of the
liquid to be treated, the additives, or any reaction product thereof.
A. Initial Additive Mixing Step:
To remove particulate and other suspended contaminants from liquids,
it is frequently necessary to mix into the liquid to be treated substances
that
cause contaminants to aggregate. The choice of additives and the order in
which they are added is tailored to the liquid to be treated. However, the
invention uses the following methods for determining the identity and order of
additives.
Liquids containing contaminants frequently have a pH that must be
adjusted to make efficient use of coagulants and flocculants. Accordingly,
the pH of the liquid to be treated is adjusted before introduction of such
additives to minimize the quantity of such additives needed. If the pH of the
liquid is not optimal to take advantage of the isoelectric point, the pH is
adjusted by adding an acid or a base. The dosage necessary to achieve a
given pH adjustment may be determined in any well-known manner.
If substantial chlorine is present in the liquid to be treated, a reducing
agent such as NaHSO3 is mixed in before introduction of polymeric
coagulants and flocculants. Chlorine may otherwise reduce the effectiveness
of the polymeric additives and necessitate higher doses.
If petroleum compounds are present, the next additive is a powdered
absorbent such as bentonite clay. Solvents and oils will tend to be absorbed
by the clay, especially if they are hydrophobic. In this way, these non-
particulate suspended contaminants are converted to particles that can be
flocculated and separated. Preferably, a porous, lightweight, hydrophilic
material with particle diameter less than 100 microns and a high surface area
to volume ratio (e.g. expanded perlite) is added also. Preferably, the clay
and
perlite-like-substance are mixed with the same water. The combination tends
to keep the perlite in suspension.
ZPM-40045
_11- UTILITY APP
CA 02455127 2010-02-11
Next, if the liquid to be treated is responsive to coagulants as
determined through standard "jar testing", a coagulant is added.
Alternatively,
in many cases coagulant will not be necessary using this system.
Lastly, one or more flocculants can be optionally added. In many
cases, two flocculants are added, a cationic flocculant and an anionic
flocculant. In many cases, it is preferable to mix in the cationic flocculant
immediately after mixing in the coagulant. In some cases, reduced flocculant
consumption can be achieved by dividing the dose of cationic flocculant and
adding it in discreet doses before the gasification step. Preferably, the
anionic
flocculant is added after the gasification process and immediately before the
pressure is reduced. Alternatively, anionic flocculant is not always
necessary.
Also, alternatively, cationic flocculant is most beneficial when added after
gasification for certain streams, such as those containing protein.
Referring now to Figure 2, a batch tank embodiment 10a for additive
mixing is disclosed. Mixing by batch tank 20 uses a container 22 equipped
with any suitable mixer 24. Additives 26 are prepared and added according to
the characteristics of the liquid to be treated, as described above. Addition
of
additives to the batch tank 20 can be automated using any suitable dosing
system. If continuous processing is desired, two batch tanks can be used so
that the process is fed from one while additives are mixed into the other.
Referring now to Figure 3, a hydrocyclone-based mixing system 10b is
disclosed. In this subsystem of the invention, the liquid is fed by a booster
pump 28 through a series of hydrocyclones 30. One or more additives 26 are
added at each hydrocyclone 30. In some cases, compatible additives 26 may
be added to a single hydrocyclone 30. Usually, a booster pump 28 is needed
after every two hydrocyclones 30 to restore liquid pressure to between 20 and
80 psi at the inlet of the next hydrocyclone 30.
Referring now to Figure 4, each hydrocyclone 30 is comprised of an
accelerator head 32 coupled at its outlet to a barrel 34. Liquid to be treated
is
fed under pressure into the accelerator head 32 through an inlet 33 in an
orientation substantially tangential to its interior wall. The liquid is
thereby
forced into a substantially helical path along the inside wall of the head 32
and
-12-
CA 02455127 2003-12-24
,I c
flows into the barrel 34. For hydrocyclones 30 between one inch and six
inches in diameter, the length of the barrel 34 should be at least
approximately 24 inches, the distance necessary for the standard pipe
velocity profile to be reestablished prior to entry into the next hydrocyclone
30.
This will depend on the feed pressure of the liquid to the hydrocyclone 30 and
the volume throughput (gpm) of the system 1 Ob.
The accelerator head 32 may be closed to atmosphere, or, preferably,
equipped with a device 36 that opens when the vacuum within the air space of
the head 32 reaches a predetermined value. For example, a spring-loaded
valve 38 may be configured to lift from its seat when the pressure inside the
head 32 is sufficiently below atmospheric to benefit from additional air. In
this
way, the layer of liquid swirling on the interior walls is kept sufficiently
thin to
optimize mixing.
The accelerator head 32 is equipped with one or more inlets 40 for
introduction of liquid or gaseous additives into the liquid flow. An inlet 40
may
be located in the top of the head 32. Inlets 40 may also be oriented through
the wall of the head so as to introduce additives substantially tangentially
to
the flow of the liquid to be treated, as shown in Figure 9. Alternatively, the
inlets 40 in the wall may be oriented radially to the axis of the head, as
shown
in Figure 4. The barrel 34 may also have wall inlets 42 in these orientations.
If there is a need for multiple inlets 42 in the barrel 34, a collar (not
shown)
equipped with inlets may be used. The collar has the same internal diameter
as the head 32 and the barrel 34. It is shorter than the barrel 34 and
contains
inlets in either tangential or radial orientations as already described.
Referring now to Figure 5, a floc tube system 1 Oc may be used to
accomplish mixing. This established method uses approximately six floc
tubes 44 having 90 degree bends to mix each additive. Additives are
prepared and dosed according to the characteristics of the liquid to be
treated.
Addition of additives can be automated using any suitable dosing system.
Some streams are suitable for use of in-line mixers (not shown), an
additional established method. Additives are prepared and dosed according
ZPM-40045
-13- UTILITY APP
CA 02455127 2003-12-24
to the characteristics of the liquid to be treated. Once again, addition of
additives to the mixers can be automated using any suitable dosing system.
B. The Gasification Step:
The gasification step 14 is accomplished using a hydrocyclone-
equipped device 46. If necessary, a booster pump 28 may be added between
the additive addition step and the gasification device 46.
Referring to Figures 2, 3 and 5, the gasification device 46 defined by
an outer vessel 48 with an inlet at the top for entry of the liquid to be
treated.
Upstream of the gasification device 46, the liquid to be treated is
pressurized.
Compressed gas (usually air) is added at a pressure slightly above the liquid
line pressure. The vessel 48 is at least three times as tall as its diameter,
and
the liquid exits the vessel 48 at or near the bottom. The vessel 48 contains
the liquid to be treated and a head space 50 above the surface of the liquid.
The capacity of the vessel 48 is between 5 seconds and 3 minutes of flow.
With particular reference now to Figures 6-8, the inlet of the gasification
device 46 is a hydrocyclone 52 composed of an accelerator head 54 and a
barrel 56 of substantially equal and constant internal diameter. The barrel 56
is preferably between 30 and 100 diameters long. The liquid to be treated is
forced into the vessel 48 through an inlet 58, the accelerator head 54, which
creates a substantially helical flow 60 around the inside wall of the head and
the barrel 56 coupled to it.
Referring again to Figures 6 and 7, the barrel 56 of the hydrocyclone
52 is positioned to enter the top of the vessel 48. The barrel 56 extends
almost to the bottom of the vessel 48. Concentric with the barrel 56 is an
"uptube" or baffle 62 of larger diameter. Liquid flows upward from the bottom
of the barrel 56 through the annular space 64 formed between the barrel 56
and the uptube 62. The liquid exits the uptube 62 near the top of the vessel
48. Large bubbles 66 rise immediately to the head space 50 and are not
entrained in the liquid as it moves downward toward the vessel exit 68. In
this
way, the large bubbles 66 are removed from the liquid passing to the rest of
the process. Large bubbles reduce the effectiveness of the downstream
ZPM-40045
-14- UTILITY APP
CA 02455127 2003-12-24
devices. In contrast, small bubbles 76, those most useful for forming bubble-
particle aggregates, do pass into the downstream components. A tube 70
connects the headspace 50 of the vessel 48 to the top of the hydrocyclone 52.
The pipe 70 that a!lows gas that enters the headspace 50 from the liquid to be
reused to gasify the liquid.
The liquid leaving the exit 68 near the bottom of the vessel 48 contains
more gas than at the inlet 58, and most of the gas is dissolved. While the
liquid is maintained at pressure over 20 psi, the gas remains dissolved.
The height of the head space 50 is between 1 and 50 inlet
hydrocyclone diameters. To maintain the position of the liquid level, the flow
of the compressed gas supply to the headspace is adjusted. The vessel may
be equipped with an automated level sensor 72 that provides a signal to
control a valve 74 regulating the supply of compressed gas.
An alternative for the coagulation and gasification steps employs
electrolysis (not shown). The liquid is passed through the annular space
between an electrically conductive tube and an insulating coaxial tube or bar.
The conductive tube is the outer tube. In the annular space is a metal coil.
The coil is not rigid, but is designed not to come in contact with the outer
tube.
The outer tube and metal coil are preferably the cathode and anode,
respectively, although the polarity may be reversed in some applications. A
voltage is set up across the coil and the outer tube. The liquid to be treated
is
passed through the annular space. In this way, it flows over the coil and is
subjected to an electrical field. Coagulation, especially of proteins, occurs
without prior pH adjustment and flocculation can be accomplished with
approximately one third the dose of flocculant. In addition, the energized
coil
vibrates and thereby resists fouling, a prime disadvantage of the
electrocoagulation of prior art.
ZPM-40045
1 5- UTILITY APP
CA 02455127 2003-12-24
C. Addition of Late Stage Additives
Referring back to Figures 1-5, the third step of the invention is addition
of late stage additives, for example, a polymeric flocculant, usually an
anionic
flocculant . This is accomplished using any pump 78 and fitting suitable to
the
liquid additive, for example, a positive displacement pump for viscous
polymeric flocculants.
D. Pressure Drop Step
The fourth step of the invention is forcing of the liquid through at least one
pressure drop. The invention releases the gas dissolved within the liquid,
initially in the form of small bubbles. It is known that small bubbles attach
most readily to particles. Further, the size of the bubbles produced by the
pressure drop component can be controlled to apply the size most needed at
each step of the flotation process. This is accomplished by adjusting the
pressure on the liquid upstream of the pressure drop device 16a.
The invention may employ either a orifice 80 or a hydrocyclone 82 to
drop the pressure. When the liquid and the freshly introduced anionic
polymer pass through the pressure drop device 16a, floccules form and
increase in size. Simultaneously, gas flashes and forms small bubbles. The
bubbles attach to particles and flocs in the liquid.
Referring now to Figure 2, the orifice option for achieving the desired
effect is disclosed. The pressure drop device preferably utilizes a single
orifice plate 80. Control is achieved by varying the pressure developed by the
pump 28, 78 upstream of the gasification device 46. The ratio between the
diameters of the orifice and the pipe is irrelevant.
Surprisingly it has been found that the use of such a high shear
passage does not degrade the performance of high molecular weight
polymeric flocculants. This is the opposite of what would be expected from
established teachings in the state of the art that high shear environments
degrade the effectiveness of such additives. For example, for an industrial
laundry stream, treatment using the orifice disclosed herein consumed less
than half of the cationic flocculant predicted by jar testing even though the
ZPM-40045
-16- UTILITY APP
CA 02455127 2003-12-24
cationic flocculant and its partially formed flocs were passed through a
minimum of two hydrocyclones 30, a pump 28 and an orifice plate 80.
Referring now to Figure 3, the second option for achieving the desired
pressure drop effect is shown using a hydrocyclone 82. This hydrocyclone 82
fits the description of the hydrocyclone(s) 30 described above, except that
the
barrel length is usually longer.
E. Separation by Stratification:
Referring to Figures 1-3, and 5, the fifth step, separation by
stratification, primarily through flotation, is disclosed. This step is
preferably
accomplished using a tank 18a configured to slow and diffuse the flow of
liquid and allow flocs to rise rapidly to the surface and accumulate. The tank
18a is downstream of the pressure drop device 16a and is referred to herein
as the flotation tank.
Referring now to Figures 10 and 11, the flotation tank 18a is preferably
a multi-chamber container that takes advantage of flotation forces in a
specific
way. The tank 1 8a is equipped with an entry 84 for the liquid from the
pressure drop device 16a (FIGS. 1 B and 5) . The entry 84 is near the bottom
of a first chamber 86 of the flotation tank 18a. The first chamber 86 has a
cross section of area at least ten times that of the feed pipe 84.
Accordingly,
the liquid slows. In the process, the kinetic energy in the liquid is reduced,
pressure drops further, small bubbles 88 expand, flocs 90 continue to form
and flocs are buoyed more effectively by the additional and larger bubbles.
The flow "blooms" in the first chamber 86 and rises through it with the flow
of
the liquid. The first chamber 86 is optionally equipped with a baffle or
diffuser
(not shown) to convert the kinetic energy from passage through the orifice 84
into more laminar upward flow. In this relatively quiescent upper portion of
the
first chamber, bubble-particle agglomerations become fully formed and robust.
The flocs 90 float to the surface and are swept toward a beach 96
located at the far wall 98 of the first chamber 86. As the liquid flows across
the first chamber 86, it propels flocs 90 rising and already at the surface
toward the beach 96. In addition, a mechanical skimmer 100 pushes
ZPM-40045
-17- UTILITY APP
CA 02455127 2003-12-24
accumulated flocs onto a beach 96 and into sludge handling equipment 102
(FIG. 2). When the liquid reaches the far wall 98 in its traverse across the
top
of the chamber 86, it has deposited the vast majority of its flocs 90 and
contaminants at the free surface.
The liquid bubble mixture then circulates back, wherein the water
turning downward carries particles with insufficient buoyancy to overcome the
horizontal velocity of the top layer of liquid across the chamber 86. Thus,
these particles remain entrained in the liquid bubble mixture. The flow splits
into two main paths at this point, one remaining in a shallow layer (arrows
with
fine dotted fill pattern in Fig. 10) beneath the outward flowing layer, and a
second flow (arrows with clear fill pattern in Fig. 10) deeper into the
chamber
86. The backflowing portion of the shallow layer moves faster and
substantially perpendicular to the deeper backflow and transports the
particles
with inadequate buoyancy back to the area at the top of the first chamber 86,
This area is populated by rising bubbles 88 and flocs 90. Particles swept into
this area attach to bubbles 88, increase their buoyancy, and are swept
outward again toward the far wall 98 of the chamber 86 in the top layer. If
their buoyancy is adequate, they are captured by the surface tension of the
free surface. If not, they are recirculated indefinitely for additional
exposure to
bubbles 88 that will eventually carry them to the surface.
At the bottom of the chamber 86 is a perforated plate 104 that
distributes the flow of clean water uniformly into an intermediate chamber
106.
Evacuation of the clean portion of the liquid in the chamber 86 is
accomplished by drawing off the bottom of the tank 18a as far out of the path
of the semi-buoyant particles as possible. The intermediate chamber is in
fluid communication with an inlet to a second chamber 108.
Preferably, the residence time in the first chamber 86 is between 1 and
4 minutes.
From the intermediate chamber 106, the treated liquid flows into a final
or second chamber 108. The liquid rises through the final chamber 108. The
liquid level in the final chamber 108 is controlled using any suitable means,
ZPM-40045
-18' UTILITY APP
CA 02455127 2003-12-24
. ,I Y
such as an adjustable weir 110. The water in the final chamber 108 is
directed using any suitable means to its next use or to disposal.
From the beach 96, the invention directs sludge 112 to a dewatering
system 102. The water that separates from the sludge 112 can be
recirculated back into the system. Sludge 112 produced using this method
dewaters rapidly.
It will be understood by those having skill in the art that the present
invention constitutes a flotation process adjustable in real time. The entire
stream is loaded with dissolved gas for later controlled release to float
solids.
The present invention may be used in connection with an existing treatment
liquid treatment system, Alternatively, the invention may be incorporated into
an entirely new liquid treatment system. Of particular significance is the
capability of retrofitting existing treatment systems to become more efficient
in
removing contaminants from liquids, while at the same time requiring few
modifications to the existing system. Additionally, by introducing rapid
bubble-
particle formation, flotation can be used to remove contaminants. The novel
and unobvious use of shapes and surfaces makes the invention one in which
the only moving parts are the pumps, gas compressor, mechanical skimmer,
and vacuum relief valve.
Although several embodiments of the present invention have
been described in detail for purposes of illustration, various modifications
of
each may be made without departing from the spirit and scope of the
invention. Accordingly, the invention is not to be limited, except as by the
appended claims.
ZPM-40045
-19- UTILITY APP
