Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR WATER mREATMENT
SUMMARY OF THE INVENTION
The present invention relates to the
purification of water which contains contaminants. More
specifically, it relates to water purification wherein
water is treated with ozone and is filtered to remove
solids.
Over the years, numerous devices have been used
to purify water by contact with ozone and/or by
filtration. It has been a problem with such devices
that they tend be bulky, particularly if ozonation
equipment is added to a standard filter system. It has
also been a problem that ozone generators produce heat
which must be dissipated and that ozone-bearing water is
corrosive to normal steel tankage.
A system where ozone generation is effectively
integrated with a filtration process has now been
discovered. In its various aspects, the system includes
equipment that is compact, that cools the ozone
generator, that allows standard steel tanks to be used
for filtration operations, and that operates
automatically.
One of the features disclosed is an apparatus
wherein ozone generation tubes are submerged for cooling
in the water being treated.
Another feature is the positioning of such ozone
generation tubes upstream of filtration beds and '
downstream of the point where water treatment chemicals
are added to the water. By properly arranging the tubes
in an array, the tubes will serve as a static mixer.
Water that passes through the array is agitated, thereby
mixing the additive chemicals into the water prior to
filtration.
An additional feature is the use of a tower
upstream of a filtering apparatus to provide a hydraulic
head that is sufficient to cause the water to flow
through downstream filtering stages by gravity. Most
advantageously, the tower comprises an upflow column
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a return or downflow column, the two columns
being joined at the top. With this arrangement, ozone
can be injected into water in the upflow column and then
removed from the water at the top of the columns. Ozone
is thus removed from the process water before it enters
the filtration system.
These and other features of the invention will
be further understood with reference to the following
description and drawings.
Brief Description of the Drawings
In the drawings:
FIG. 1 is a perspective schematic view of a
filter system according to the present invention;
FIG. 2 is a sectional view taken along line 2--2
of FIG. 1; and
FIG. 3 is a front elevational view of the system
shown in FIG. 1.
Detailed Descrintion
A filtration system according to the present
invention is shown in the drawings, wherein the flow of
water is illustrated by arrows. These drawings show an
example of a system for treating a stream of water by
contact with ozone in a vessel 10. Solids are then
removed by passing the stream of water through a two-
stage filter system 12 downstream of the vessel 10. The
illustrated filter system 12 includes an upstream
roughing filterin series with a downstream filter.
In the illustrated embodiment, water to be
purified is fed to a gas contactor vessel 10 that is in
the configuration of a tower. Located inside the vessel
is a vertical divider 20 which separates the interior of
the vessel into first and second chambers 22, 24. These
are, respectively, an upflow zone 22 containing an
upflow water column and a downflow zone 24 containing a
return column. Water enters the upflow zone 22 through
a process flow water inlet 26, then flows upwardly to
the top of the divider 20. The water then flows over a
weir 28 at a top portion 29 of the divider 20 and into
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the return column 24. The weir 28 controls the flow
rate. The water then flows downwardly through the
second chamber 24 by gravity and leaves the tower 10
through an outlet 30 located at an elevation below the
weir 28. The region 62 over the weir thus serves as the
outlet of the first chamber and the inlet of the second
chamber. One portion of the vessel 10 thus serves as an
contact tower 60, sometimes referred to herein as an
upflow tower with reference to the illustrated
embodiment. A second portion of the vessel 10 serves as
a return tower 61, sometimes referred to herein as a
downflow tower with reference to the illustrated
embodiment.
Water leaving the tower 10 through the outlet 30
is passed directly into a solids separation system. In
the illustrated embodiment, the solids separation system
is the filtration system 12 which includes an upflow
clarifier device 34 provided in an upflow filter
compartment defined by a vessel 35. The clarifier
device 34 includes a bed 36 of particulate material or
media that is retained beneath a screen 38 and that is
buoyant in the water inside the vessel 35. The
clarifier 34 is followed by a downflow filter 40,
including a bed 41 of nonbuoyant particulate material or
media, provided in a downflow filter compartment defined
by a vessel 42. The vessels 35, 42 are provided by a
rectangular tank which is separated by an internal
upright wall 44. The vessels communicate via clarifier
outlets 46, which also serve as inlets for the vessel
42. Examples of suitable solids separation systems can
be seen in U.S. Patents Nos. 4,547,286, 4,608,181 and
4,793,934 and in numerous other prior patents.
In a typical water treatment plant, water
systems are provided in tandem. Therefore, when the
filters in one system are being cleaned, the filters in
the other are operational so that the plant continuously
treats water. Such a second system is shown in broken
lines at the back of FIG. 1.
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The illustrated apparatus, as shown in FIGS. 2
and 3, includes an ozone injection system for contacting
ozone with water in the upright upflow or contact tower
60. A gas diffuser 52 serves as an inlet for ozone-
containing gas 53 and is positioned to inject the gas
into water in the column 22. The diffuser 52 is preferably located near the
bottom of the column 22,
either above or below the inlet 26. Most conveniently,
the diffuser may be made of a porous ceramic material
which facilitates the production of numerous small
bubbles. Ozone is continuously supplied to the diffuser
52 via a supply line 54 which is connected to an ozone
generator system 56. The rate of ozone injection is set
so that the concentration of ozone in the column 22 does
not exceed 3 ppm.
It should be appreciated that there are other
mechanical arrangements for injecting ozone into process
water. For example, if it is necessary to treat water
having an ozone demand greater than 3 ppm, the apparatus
could comprise a single large vessel containing multiple
vertical dividers that define multiple contact zones
containing multiple columns of water. Water could be
directed to flow through the various chambers,
preferably in a serpentine path, upwardly and
downwardly, while ozone is injected into more than one
of the water columns. Similarly, multiple return
columns could be provided if needed. Also, although it
is highly advantageous to use a unitary tower with one
or more internal dividers as illustrated, multiple
separate vessels could be used to define plural chambers
or zones for columns of water. The flow direction
pattern could be modified, e.g. so that water flows
downwardly in a tower and then directly into a cooling
vessel from the bottom of the tower; this would not be
convenient for gas separation, but scavenger chemicals
could be added to the water to react with any residual
ozone.
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The ozone generation equipment is of
conventional design and may, for example, be assembled
from OZOTEC brand equipment manufactured by Hankin Atlas
Ozone Systems Ltd, Scarborough, Ontario, Canada. The
ozone generator 56 includes a number of ozone production
elements 58. In the illustrated embodiment, these
elements are tubes that are made of stainless steel and
that are electrically grounded. Each stainless steel
tube surrounds an inner dielectric tube (not shown) so
that there is a gap between the outer and inner tube.
The inner tube is made of glass and is coated on its
interior surface with an electrically conductive
material. Ozone is generated by electrical discharge
through dried air or oxygen that is pumped through the
gap between the outer and inner tubes and, from there,
to the diffuser 52.
During such generation of ozone, a considerable
amount of heat is generated inside the ozone generator
tubes. This heat is dissipated by positioning at least
a portion of at least some of the tubes in the flow path
of the water to be treated, such as in one of the
chambers 22, 24 of the vessel 10, so that heat is
transfered to the passing water.
The embodiment shown in the drawings is a
particularly advantageous arrangement wherein the ozone
generator tubes 58 are located inside a cooling vessel
70 and the cooling vessel has an inlet 72 that
communicates with, and in the illustrated embodiment
corresponds to, the outlet of the upright return tower
61. It will be appreciated that the ozone generator
tubes could alternatively be positioned in the column of
water 24 inside the return tower 61 or at other
locations in the path of the water being purified.
Although, it is advantageous for the ozone inlet 52 to
be positioned upstream of ozone generation elements 58
in the water flow path.
From the drawing, it will be appreciated that
the illustrated cooling vessel 70 is a lateral extension
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of the bottom region of the return tower 61. An opening
iin the wall which defines the second chamber 24 is also
the inlet 72 for the cooling vessel 70. Because the
opening is large in the illustrated embodiment, the
walls of the return tower 61 and cooling vessel 70 can
be said to define a single chamber that has a reservoir
region 74 that corresponds to the portion of the return
column 24 that is located above the top of inlet 72 and
a cooling region 76 below the top of the inlet 72. The
cooling vessel 70 also has an outlet which, in the
illustrated embodiment, corresponds with the inlet 30 of
the filtration system.
The illustrated cooling vessel 70 is
particularly advantageous when used downstream of a
chemical feed mechanism. It is common practice to add
filtration-enhancing chemicals, particularly coagulants,
to water which is to be filtered. These chemicals must
be thoroughly mixed with water to have the best effect.
The illustrated system includes a coagulant injection
system. Water treatment chemicals, including
coagulants, are added through inlet ports 78 upstream of
the cooling vessel 70. The resulting mixture of water
and chemicals must thus pass through the cooling vessel
70 prior to filtration. Inside the cooling vessel 70,
the ozone generation tubes 58 are arranged in an array,
such as the illustrated three rows of four tubes each,
so that the combined water and chemicals flflw in a
tortuous pass through the generator tubes 58. The
generator tubes thus serve as a static mixer which
blends the injected chemicals with the water being
treated, and the cooling vessel 70 thus also serves as a
mixing vessel, with the inlet 72 serving as a mixing
vessel inlet. After passing through the array of tubes
58; ozone-depleted coagulant-containing water flows
through the outlet 30, which serves as the mixing vessel
outlet, and into the filtration system 12 as previously
mentioned.
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A mixture of ozone and water is corrosive to
mild steel. Accordingly, the tower apparatus 10,
particularly the walls of the upflow column 22, are made
of a corrosion resistant material such as stainless
steel. It would be unduly expensive to make the entire
apparatus of such a material. AccOrdingly, a mechanism
is provided for removing ozone from the water before it
enters the filtration stages of the system. In the
illustrated embodiment, gas entrained in the process
water is collected in a gas collection chamber or region
62 at the top of the tower before the water reaches the
ozone generation elements 58. Gas, including any
unreacted ozone, is removed via a gas collector system
63. The gas collector system includes a demister 64
which is connected to a catalytic off-gas destruction
system (not shown). A pump (not shown) connected to the
demister 64 maintains the gas separation region 62 at a
slightly subatmospheric pressure to encourage the
separation of gas from water at the tops of the columns
22, 24.
A detection system is provided to be sure that
substantially all ozone is removed before water enters
the filtration sections of the apparatus. This system
can include a device 66, such as an OZOMETER brand
residual ozone analyzer manufactured by Hankin Atlas,
positioned to test"water at a location downstream of the
gas collection chamber 62 and then signal if the ozone
content of the tested water exceeds a predetermined
amount. A gas supply controller unit 67, including a
device such as an OZOMICRO brand controller manufactured
by Hankin Atlas, is adapted to respond to a signal from
the ozone detector 66 and, in response to the signal, to
reduce the rate of ozone injection through the diffuser
52 when the ozone content of the sampled water exceeds
the predetermined amount. Most conveniently, this is
accomplished by signaling the power supply of the
controller unit 67 to reduce the electrical current
supplied to the electrodes of the ozone generation
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elements 58. Reducing the current in turn reduces the
percentage of ozone in=the gas injected via the diffuser
52. Instead of-using an ozone analyzer, gas removed via
the demister can be tested for ozone content by an ozone
analyzer 68. And, if the ozone content exceeds a
predetermined amount, the gas supply controller 67 is
signaled to reduce the rate of ozone injection. Other
methods of testing for residual ozone can be used, and
will be familiar to those who are experienced in this
art.
The drawings show a tower that is much higher
than other parts of the apparatus. This serves two
purposes. It is beneficial for the upflow or contactor
column.22 to be a tall to ensure complete ozone contact.
Having a tall return column 24 is helpful since it
provides the hydraulic head necessary to drive the
water, by gravity, through the downstream filtration
system. To provide sufficient head, the height of the
weir 28 is greater than the water levels required for
operation of both the subsequent filtration stages 34,
40. In particular, the weir 40 is at a higher elevation
than the upper surfaces 80, 81 of the beds 36, 41 of
particulate media in both filter stages and is higher
than the bottoms of the clarifier outlets 46.
For best operation, the surface 82 of water in
the column 24 should be maintained within a
predetermined elevation range. The surface 82 should be
at a higher elevation than the tops of the beds 36, 41
of particulate media in both filter stages and should be
higher than the bottoms of-the clarifier outlets 46.
The purface 82 should also be at least three inches
below the.top of the weir 28 so that water will fall
freely for a distance after passing over the weir. The
free falling water creates turbulence when it contacts
the surface of water in the column 24. This agitation
facilitates the release of gas from the water to the gas
collection region 62 over the weir 28.
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The level of water in the column 24 will rise as
filter elements become clogged. Accordingly, an
automatic apparatus is provided for sensing when the
level of water in'the column 24 exceeds a predetermined
height. This apparatus can take a number of forms. In
the illustrated embodiment, a float switch 84, provided
near the top of the return,column 24, serves as a level
sensor. If the water in the return column rises to a
height sufficient to trip the float switch, cleaning of
the clarifier bed 36 will commence automatically in
response. Other devices, such as pressure sensors (not
shown),, can.be used for a similar task as the float
switch 84. The cleaning mechanism for the clarifier 34
will advantageously include an air injection system 86
below the bed 36 oP particulate material. When the
sensor detects a condition of water in the return tower
61, which condition indicates that the level of the
water column 24 exceeds the pr@determined level, the
sensor signals an electronic controller (not show). The
controller responds by operating fluid flow control
valves to initiate cleaning, e.g. to initiate.a flow of
air into the air injection system 86.
To operate the illustrated apparatus, water that
contains contaminants is directed to flow upwardly
through the contact tower 60 while operating the ozone
generation system to inject ozone via the diffuser 52.
At the top of the column 22, any residual ozone
is separated from the water. Water at the top of the
column 22 the surface of the water is in.contact with
gas that is maintained at a slightly subatmospheric
pressure, preferably from one to four inches of vacuum,
in the region 62. The negative pressure maintained in
the separation region 62 urges separation of gasses from
the water.
Periodically, measurements are taken to ensure
that the no appreciable amount of water-borne ozone
enters the filter system 12. If more than a
predetermined maximum amount of ozone is detected, the
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rate of ozone injection through the diffuser 52 is
reduced.
After water reaches the-top of the column 22, it
flows over the weir 28 and then downwardly inside the
return tower 61-where it joins a pilar 24 of water that
provides a'hydraulic head sufficient to drive water
through downstream filtration units 34, 40 by gravity.
Before it enters the filtration units, water is
passed through an array of ozone generation elements to
cool the elements. In the illustrated embodiment, water
passes through an array of ozone generation tubes 58.
Filtration aids, particularly coagulants, are added at a
location 78 upstream of the ozone generation tubes, so
that the mixture of water and filter aids is agitated as
it flows through the array of tubes. After agitation,
the hdated mixture of water and filter aid chemicals is
passed through a vessel 35 containing a bed 36 of
particulate material to separate solids from the water.
If during the filtering operation it is sensed
that the water level in the return column 24 has
exceeded a predetermined height, automatic cleaning of
the filter bed 36 is commenced in response.
Having described a preferred embodiment of the
invention, it should be understood by one skilled in the
art that one can deviate from the preferred elements of
the invention and still be within the concept of the
invention described herein.
