Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Process and Apparatus for Separating
Immiscible Liquids from Aqueous Fluids
SPECIFICATION:
FIELD OF THE INVENTION
This invention relates to a process and apparatus for separating immiscible
liquids such as oil and
hydrocarbon based liquids from an aqueous fluid. Oil and hydrocarbon based
liquids as defined herein
refer to any liquid which is attracted to an oleophilic surface, and are
collectively referred to as oil.
BACKGROUND AND PRIOR ART
Oil is found throughout industry both as naturally occurring and synthetic
based products. When these
come in contact with aqueous fluids a variety of different types of oily
mixtures can be formed. These
include free floating oil, oil-in-water emulsions and water-in-oil emulsions.
Emulsions can be
mechanically or chemically created, with the former being caused by fluid
agitation where oil in the fluid
is mechanically broken up into very small dispersed particles, and the latter
being caused by contact with
a surfactant where oil is chemically dispersed as very small oil particles in
the fluid. In both cases the
oil particles typically won't separate from the aqueous fluid very quickly by
gravity due to their small
size. It has consequently become necessary to develop alternate oil removal
technologies to deal with
these smaller oil dispersions.
Many different processes and types of equipment have been developed over the
years to do this
including density separation, adsorption/absorption systems, chemical removal,
coalescing processes and
filtration processes.
Density separation generally uses centrifugal force to separate liquids of
different densities using
equipment such as hydro-cyclones. In these machines centrifugal force is
applied to the contaminated
fluid causing higher density products to move to the outside of the water
column while lower density
products move to the inside. This allows a target liquid to be separated from
the other fluid and removed.
This process is generally restricted in the size of oil particle it can remove
to approximately 5-10 microns
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or larger. Other processes are usually required to remove smaller particles.
Adsorption and absorption based processes use oleophilic media to attract oil
particles from the fluid
to a fixed surface as the carrier fluid passes through. One common application
of this technology is in
the use of disposable oil adsorbing filters. One disadvantage of these systems
is that saturation of the
media with oil generally requires that it be replaced with new product, and
the used media disposed as
a waste product. It also doesn't permit recovery of the oil for re-use or re-
cycling. In the following
discussion `adsorbent' products generally refer to products which weakly
attract oil to the surface of a
media while `absorbent' products generally refer to products which strongly
bind or trap oil in the media
matrix. For purposes of discussion herein, `adsorbent' products and
`absorbent' products are collectively
to referred to as `adsorbent' materials.
Chemical treatment processes require addition of chemicals to the fluid,
usually requiring substantial
residence time for the treated product in a large contact chamber, and often
have high operating and
maintenance costs.
Coalescing systems use oleophilic media to attract oil particles to its
surface where they are encouraged
to coalesce and then release from the media as larger droplets downstream.
Filtration systems generally use membranes which are designed to have pore
spaces so small that the
membrane can strain out large oil particles from the fluid while letting
smaller water molecules pass
through. Due to the small pore size of membrane required for this process to
be effective, this solution
is very sensitive to the presence of particulate matter in the fluid stream,
and can quickly be plugged
up with such matter, requiring frequent cleaning and maintenance.
The fields to which this invention most applies are the adsorbing, coalescing
and gravity separation
processes noted above. The purpose of the invention is to provide a process
and apparatus which allows
adsorbent type media to be used much longer before it requires replacement,
thereby reducing
replacement costs substantially while at the same time allowing oil in the
fluid to be recovered for re-use
rather than being disposed as a waste product..
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Prior patents and patent applications of relevance to the current invention in
this area are listed below:
Patent Application #CA 2,582,585; US Patent Application #20080210635, US Pat.
#7,264,721, US Pat.
#6,475,393; US Pat. #4,493,772; US Pat. #3,937,662; US Pat. #3,878,094; US
Pat. #3,738,492 and US
Pat. #3,558,482.
METHOD BY WHICH THE PRESENT INVENTION OVERCOMES PRIOR ART PROBLEMS
It is an object of this invention to provide an oil separation process and
apparatus which greatly increases
the volume of oil that can be processed through a treatment system before the
adsorbent media in the
system needs to be replaced, thereby reducing treatment costs significantly.
It is a further object of this invention to provide a process and apparatus
which permits most of the oil
in the aqueous fluid to be recovered for re-use rather than having to be
disposed as a waste stream.
It is a further object of this invention to provide a process and apparatus
which can treat aqueous fluids
containing wide ranges of oil concentrations ranging from 1 mg/1 to1,000,000
mg/1.
To accomplish this, three treatment stages are used in the process consisting
of a coalescing stage, a
gravity separation stage and an adsorption stage. In the first stage, a fluid
pervious oleophilic media
attracts and coalesces oil particles in the fluid and subsequently releases
them downstream as larger oil
droplets.
The second stage consists of a gravity separation area where the larger oil
droplets discharging from the
coalescing stage can float up, or sink depending on their density relative to
the carrier fluid, and thereby
be separated, removed and recovered from the carrier fluid.
The third stage consists of an oil adsorbing fluid pervious media which
attracts and retains remaining
oil particles in the fluid onto its substrate, while letting the other fluid
pass through as clean product.
Under the above process, media used in the first stage of the treatment
operation is designed to become
saturated with oil as part of the coalescing and consequently does not require
replacement when it
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becomes saturated. The second stage of the process consists of a simple open
area designed to allow
coalesced oil particles to settle out by gravity, and thus has no moving or
replaceable parts requiring
maintenance. The third stage of the process is the only stage where saturation
of media with oil
necessitates replacement of the media. Because of the system configuration
however, by the time the
aqueous fluid reaches this stage most of the oil has been removed by earlier
stages, so the length of time
required between media replacements is greatly increased.
Disposable oil adsorption filters are widely used in industry to remove trace
amounts of oil from aqueous
fluids. One apparatus commonly used to accomplish this consists of a product
which is commonly
referred to as oil `filters' These aren't actually `filters' from a technical
standpoint as they don't rely on
their pore spaces to strain out large oil molecules and let others pass
through. Instead they work on the
adsorption principle noted earlier whereby the `filter' contains an oleophilic
substrate which has an
affinity for oil, causing oil to preferentially attach to the substrate. One
feature common to these products
is that the media being used to attract the oil typically has a maximum
retention capacity for oil which
determines how much it can hold before becoming saturated. This capacity is a
significant operating
consideration in many treatment applications, as it largely determines the
feasibility and economics of
using the technology for different oil removal applications. For purposes of
discussion herein, the term
`oil filter' is used to refer collectively to any oleophilic media which is
being used to attract oil.
In testing it was found that the life of these filters can be increased
significantly by using a process and
apparatus which combines a specific configuration of coalescing filters
upstream, adsorbent filters
downstream and a gravity stage in between. It has been found in this regard
that coalescing and gravity
separation processes by themselves cannot normally remove all dispersed oil
particles from an aqueous
fluid, generally leaving a visible oil sheen on the treated discharge fluid.
Conversely, adsorption filters
alone can generally remove all oil from an aqueous fluid, but become saturated
very quickly if significant
concentrations of oil are present, necessitating frequent media replacement.
It has been found however,
that combining the above processes in a manner which seeks to maximize oil
recovery in the second stage
results in most of the oil being removed by the system before it can reach the
final stage, thereby
extending the life of the adsorption filter substantially. Since the
downstream adsorption filter is the only
consumable item in the system, this will allow users to greatly reduce the
operating cost of such a
treatment process. The process also allows most of the oil in the fluid to be
recovered, providing an
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additional environmental advantage over current oil treatment practices.
One of the key aspects to making this process work involves maximizing the
size of droplets being
released by the coalescing stage. By maximizing the size of these droplets,
the downstream gravity stage
is more effective for removing the droplets from the fluid. In this regard it
was found that this can be
accomplished by passing contaminated fluids sequentially through more than one
coalescing filter
arranged in series prior to reaching the gravity separation stage. Each filter
so arranged was found to
further increase the size and number of large oil droplets being discharged
downstream, thereby allowing
them to be recovered easier by the gravity separation stage. Maximizing the
amount of oil recovered in
this manner is a key to also maximizing the life of the downstream absorption
filter, which is the primary
aim of the invention.
A practical application of the invention can be illustrated by referring to
the current practice of using
small disposable fabric type filter cartridges to remove oil from water. One
such filter currently used for
this purpose consists of a 2.5 in dia. x 10 in long cylindrical filter
cartridge which is installed in a hand
tightened filter cartridge housing. This arrangement allows a filter cartridge
to be quickly and easily
replaced by simply unscrewing the filter housing and installing a new
cartridge. These filters are typically
used in many low flow `under-the-counter' type applications for the purpose of
removing oil from a piped
fluid stream. When the filter cartridges become saturated with oil they are
replaced with new units and
the old ones disposed of as waste products. Regarding oil retention capacity
of these filters, US Pat.
#7,264,721 describes tests carried out on one such type of filters to
ascertain this. Test results presented
therein found that two such filters, when processing a fluid containing an oil
concentration of 3000 ppm
and non-emulsified No.2 oil, were capable of capturing and retaining 85 gms
and 185 gms of oil per filter
respectively before oil concentrations in the discharge exceeded 5 ppm. US
Pat. # 6,475,393 also lists
test results for another filter where the oil retention capacity was found to
be approximately 165 gms prior
to an oil sheen being detectable in the discharge. In typical industrial
applications, these results (85 - 185
gms/filter and 165 gms/filter) would generally represent the approximate point
at which the filter would
need to be replaced in order to maintain a suitable water discharge quality.
Treatment of a fluid stream
containing high oil concentrations with such units would require replacement
efforts and costs
proportionate to their retention abilities.
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Under the process described in this invention, these results can be improved
upon significantly before a
filter cartridge would need to be replaced. Tests carried out to demonstrate
this used similar 2.5 in dia.
x 10 in oil filters made of spun wound polypropylene, with test parameters as
described below:
Test Set-Up - Preliminary tests indicated that installing multiple coalescing
filters in series significantly
increased the volume and number of larger oil droplets that could be generated
in the discharge effluent
and subsequently removed in the gravity separation stage. The preferred number
of filters to use in this
regard depended on the type of fluid being processed, with additional
coalescing filters generating more
such oil particles. From a practical standpoint, a point will be reached in
most applications where adding
further filters isn't warranted by the extra improvement that such additions
provide, and the number to
use becomes a field decision based on various considerations such as effluent
quality required, space
restrictions at the site, etc. In general however, it was found that arranging
the coalescing stage in a
manner which could reduce emulsified oil content going to the adsorbent filter
of 50 ppm or less had
the desired effect of increasing filter longevity to a point where replacement
costs would no longer be a
significant problem in most applications. The number of coalescing filters
needed to achieve this can be
determined on a site by processing a trial sample of contaminated fluid
through a series of small portable
filters. The emulsified oil content of fluid passing each filter can quickly
define the level of oil reduction
being achieved, and consequently the optimum number of coalescing filters
needed to fit a specific
application from a life cycle cost standpoint.
For purposes of the performance test described below, three 2.5 in dia. x 10
in long spun wound
polypropylene filter cartridges were used which had been pre-treated with an
oleophilic compound to
make them act as coalescing filters. These cartridges were installed in series
to represent a three filter
coalescing stage in the system. Immediately downstream of the coalescing
filters was installed a 5 in dia.
empty inverted filter housing to represent the gravity separation stage of the
process where coalesced oil
droplets discharging from the first stage could separate and float to the
surface by gravity. Downstream
of the gravity separation chamber a single 2.5 in dia. x 10 in long oil
adsorbent spun wound
polypropylene filter cartridge was installed which had been pre-treated with
an oleophilic compound to
make it adsorb oil, representing the third and final stage of the oil removal
process. This test arrangement
is depicted in Fig. #1.
Test Methodology - The filters and gravity separator noted above were
connected together by piping
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which allowed test fluids to be injected through an inlet pipe into the first
coalescing filter of stage one,
following which it flowed through coalescing filter #2, then coalescing filter
#3, then the gravity
separation chamber, then the oil adsorbing filter #4 and finally to discharge.
Test fluids consisted of diesel
fuel (sp. gravity = 0.84) and fresh water which were mechanically mixed in a
17 litre container to form
mechanical emulsions. This fluid was pumped through the test set up using a
centrifugal submersible
pump installed in the raw fluid container. The test mixture contained an
average oil concentration of 1421
ppm. When the injection pump was engaged, test fluid flowed through the test
set-up until the raw fluid
container was empty, following which it was refilled with similar fluid and
the test resumed. This
arrangement was used to simulate actual field conditions expected to be
encountered if treating
contaminated water on a boat or in an industrial operation where oil in the
water would likely be pre-
emulsified by an Owner's submersible pump before reaching the treatment
system. To ensure that
longevity results for filter #4 were not affected by any oil retention
capacity offered by the three
coalescing filters, the coalescing filters were first pre-conditioned with oil
and water before the filter
#4 longevity test began. This involved pumping oily water through the first
three coalescing filters and
the gravity chamber until all three filters were saturated with oil. Such
saturation was deemed to have
occurred when coalesced oil droplets began discharging from the third
coalescing filter and rising in the
gravity separation chamber. Filter #4 was only added to the system after this
saturation process was
complete. The longevity test for filter #4 then commenced to identify how much
oil could be injected into
the system before filter #4 would become saturated with oil and need to be
replaced. This was defined
as the point at which a detectable oil sheen could be seen discharging from
filter #4. Results of the test
were as follows:
= Test #1 - To provide a reference point for assessing longevity results of
filter #4 when used in this
system, it was first necessary to identify what the oil retention capacity of
filter #4 would have
been if it was installed in a conventional set-up and required to process this
type of fluid. To do
this, three filter cartridges were taken from the same batch of filter
material as filter #4, and were
then tested to determine their oil retention capacity in a conventional oil
filter set-up (i.e.- without
the coalescing or gravity separation stage used herein). Results of these
tests indicated that filter
#4 had an average oil retention capacity of 96.2 gms of oil per filter in the
absence of using the
new process described herein;
= Test #2 - The test was then done using the new set-up described herein,
consisting of three
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saturated coalescing filters arranged in series, a gravity separation chamber
and adsorption filter
#4. Test results confirmed that 1517 gms of oil could be pumped through the
system before a
detectable oil sheen began discharging through filter #4, representing an
improvement of
approximately 1400% in filter longevity by using the process.
As part of this test, it was also noted that coalesced oil droplets rose
quickly in the gravity
separation chamber as planned, and joined together at the top of the chamber
to form a layer of
free oil which could be easily removed by opening a discharge port at the top
of the container
Based on the above results, the length of time the system could operate before
filter #4 would have to be
replaced was increased by a factor of more than 14 times, which would
translate into substantial cost
savings for users. It was noted during the test as well that while the oil
droplets were being coalesced as
intended during the coalescing stage, the system would have generated even
better longevity results if the
gravity separation chamber had been larger. Because of the small size of the
chamber used in the test set-
up, it was found that some of the larger coalesced oil droplets were still
being drawn down into filter #4
rather than floating up due to fluid turbulence in the chamber. A larger
gravity chamber, or one configured
to reduce this turbulence, would eliminate this effect, resulting in a further
increase in the downstream
the longevity of filter #4.
The bulk of the oil injected into the system was recovered as free oil at the
top of the gravity chamber,
allowing it to be re-used or re-cycled.
Thus it may be seen that the process described allows a significant
improvement in oil removal
performance over conventional adsorption type processes, and a proportionate
decrease in the cost of
replacing filters in such applications. It also allows a significant reduction
in the amount of waste material
generated from such systems by allowing the oil to be recovered for re-use.
The above example is provided only for the purpose of illustrating how the
process and apparatus works.
For those skilled in the art it will be evident from the preceding description
that the process can be applied
to any type of oil treatment application which uses an adsorption/absorption
stage. As such, many
equipment arrangements can be deduced to take advantage of the improved
performance offered ranging
from small filter systems described above, to large systems such as those
typically used in the oil
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production industry.
The invention differs from the process described in US Pat. #3,558,482 in that
it works for pollutants
heavier than water as well as lighter than water, it works for `oil-in-water
emulsions' as well as `water-in-
oil emulsions', it provides an improved and definable means of optimizing
results through proper design
and configuration of the coalescing stage and it doesn't require the use of a
back-washable granular filter
bed.
LIST OF FIGURES AND DESCRIPTION OF THE INVENTION
In drawings which illustrate embodiments of the invention, Figure 1 is a cross-
sectional view through the
invention as it would apply to one preferred embodiment.
The invention as illustrated consists of an initial coalescing stage
comprising three coalescing oil filters
installed in series (1), (2), (3), a gravity separation chamber (5), and an
adsorption/absorption chamber
(4) containing a single oil adsorbing/absorbing filter (15). Contaminated
inlet fluid enters the first
coalescing chamber (1) through a pipe or other means of conveyance (6). In the
coalescing chamber (1)
the fluid passes through a fluid pervious oleophilic coalescing media (7)
which causes oil dispersions in
the fluid to attach to the surface of the media and coalesce into larger oil
particles. These particles grow
in size until they release from the media (7) and re-enter the fluid flow (14)
as larger oil droplets. The
coalesced oil droplets and carrier fluid from filter #1(14) then pass through
the second coalescing
chamber (2) in a similar manner and finally through third coalescing chamber
(3), each time increasing
the size of oil droplets for removal by the next stage of the process. The
coalesced oil droplets and carrier
fluid then enter a gravity separation area (5) through a pipe or other means
of conveyance (9) where the
coalesced oil droplets (10) separate from the carrier fluid and float to the
top of the container. The oil
droplets which float to the top of the chamber (5) coalesce there to form a
free oil layer at the top (11)
which can be removed through a discharge outlet (12) provided for that
purpose. The remaining aqueous
fluid (13), with most of the oil now gone, then flows to a final
adsorption/absorption chamber (4) where
remaining oil in the fluid is captured and removed by a fluid pervious
oleophilic media (15) which is
capable of attracting oil from the carrier fluid and affixing it to its media
surface or substrate. The carrier
fluid, now free of oil, discharges from the system as clean fluid through a
pipe (8) or other means of
conveyance.
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In the above illustration, the treatment chambers consisted of individual
circular filter housings which
were pre-formed to allow the bottom part of the housing to be screwed to a top
manifold for ease of
installing filter cartridges. The oleophilic media used in the system
consisted of pre-treated spun wound
circular filter cartridges which fit inside the filter housings. Those skilled
in the art will recognize that
there are many different types, sizes and shapes of process chambers and media
other than illustrated in
fig. 1 which can be used with this process without departing from the intent
of the invention, such as use
of larger or multiple media chambers in the coalescing stage to increase the
amount of oil which can be
removed in the next stage; using more than one gravity separation chamber to
increase the size range of
oil droplets which can be removed using the process; using larger or multiple
adsorption/absorption
media units in the final stage to increase media longevity or facilitate media
replacement without having
to shut down the system, etc. All such modifications are included in the
process described herein as long
as the concept of a coalescing stage, gravity separation stage and
adsorption/absorption stage is utilized.
In another embodiment of the invention, the coalescing stage may consist of
any shape or size of
container which promotes the movement of aqueous fluid from one side of the
fluid pervious coalescing
media to the opposite side, including pressurized and non-pressurized vessels.
In another embodiment of the invention the coalescing media (7) may be any
shape, size, type or
configuration as long as it is effective for coalescing dispersed oil into
larger droplets as the fluid passes
through the media. Such media may be naturally occurring or pre-treated to
provide it with enhanced oil
attraction abilities.
In another embodiment of the invention the coalescing media (7) may be used in
single or multiple units,
and placed in one container or a plurality of containers.
In a preferred embodiment of the invention, the gravity separation stage (5)
would be designed in
accordance with Stoke's Law to maximize the amount of oil that can be removed
in a given time period.
Stoke's Law can be used to determine how big the gravity separation chamber
would need to be to
facilitate floating or sinking of particles based on their size and relative
density in a given time frame. A
larger container offering a longer residence time, or a container geometry
which minimizes fluid velocity
opposite in direction to the direction the oil particle is floating or
sinking, will allow smaller size oil
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droplets to separate from the carrier fluid and maximize the amount of oil
which can be removed in the
gravity separation stage (5). The size and shape of container to be used for
this stage will thus depend on
specific project applications such as space restrictions and cost
considerations. This includes
configurations where the gravity separation area is attached to or located
within the same container as the
coalescing media, or multiple gravity separation stages such as a separate
ones for each coalescing
chamber.
In another embodiment of the invention, the adsorption/absorption stage (4)
may comprise any shape or
size of container which promotes the movement of fluid from one side of the
fluid pervious media to the
opposite side, including pressurized and non-pressurized containers
In another embodiment of the invention the adsorption/absorption media (15)
may be any shape, size or
configuration that is effective in capturing dispersed oil from the fluid and
removing it from the fluid flow
as fluid passes through the media.
In another embodiment of the invention the adsorption/absorption media (15)
may be installed in
individual or multiple units and in one container or a plurality of
containers..
In another embodiment of the invention, the adsorption/absorption media (15)
may be a naturally
occurring oleophilic material, or a material that has been pre-treated to make
it oleophilic or more
oleophilic, as long as the final material is effective in capturing oil and
removing oil from the fluid stream
as fluid passes through the media.
In another embodiment of the invention, a re-circulation feature may be added
to any stage of the process
to allow treated or partially treated fluid from one stage to be returned to a
previous stage for additional
treatment to increase longevity of the adsorption/absorption media (15).
In another embodiment of the invention, the system may be equipped with
pressure guages, oil sensors,
discharge valves, solenoid valves, motorized valves, back-washing mechanisms
and the like for the
purpose of automating operation of the system, allowing it to be cleaned
remotely, or allowing oil to be
collected or discharged from the system automatically.
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ONE INTENDED USE OF THE INVENTION
One preferred use of the invention is for use in treatina oily water generated
by small oily water
--enerating operations such as machine shops, car washes and boats where
improved filter lone'evity
would reduce operatinc, costs significantly.
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