Note: Descriptions are shown in the official language in which they were submitted.
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REMOVAL of HYDROCARBON AND OIL FROM WATER
The present invention relates to methods and systems for removal of
hydrocarbon and oil from
water to increase the potential for reuse of de-oiled water or enable
discharge of de-oiled water to
surface water bodies.
BACKGROUND OF THE INVENTION
Water that contains significant amounts of hydrocarbon and oil is commonly
referred to as oily
water. Oily water can occur from a number of different industrial processes as
well as occurring in
flowback and produced water from oil and gas operations including hydraulic
fracturing operations. Oily
water can emit harmful vapours and odours. Oily water stored in open tanks or
ponds represents a
hazard to waterfowl. Oily water also presents a potential deleterious
substance if released to
waterbodies including streams or ponds. Oily water also entraps dissolved and
suspended compounds
that can be deleterious to the reuse of water.
It would be desirable to be able to use de-oiled water for a number of
beneficial uses. However
conventional methods of de-oiling water do not cost-effectively reduce the
hydrocarbon or oil content
to levels that are low enough to meet surface discharge criteria. Likewise,
conventional methods of de-
oiling water do not achieve low enough concentrations of oil or hydrocarbons
to meet standards for
other beneficial uses including feed water softening, boiler feed water, once-
through steam generation
plants for steam assisted gravity drainage processing or oil sand mining and
separation facilities.
There are a number of ways of separating oil and hydrocarbon from water but
many do not
achieve low enough levels of oil or hydrocarbon. These methods do not
sufficiently remove tiny (sub-
micron) oil droplets to allow reuse or discharge and consist of either
filtration or flotation. Filtration
systems rely on hydrophobic membranes that are vulnerable to plugging and do
not remove the
smallest (submicron) oil droplets. Flotation systems rely on the addition of
large numbers of small
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bubbles that collide with oil droplets, combine and rise to the surface.
Conventional flotation systems
struggle to remove the tiniest (submicron) oil droplets because gas bubbles
need to be of similar size to
collide and attach to the oil and hydrocarbon droplets. Conventional air
bubble generators do not
produce sufficient quantity of submicron sized or larger air bubbles nor do
they achieve sufficient
number of air-oil bubble collisions plus attachments to achieve full removal
of oil and hydrocarbon.
Thus, there is a need for an efficient and less-costly method and system for
removing oil and
hydrocarbon from water.
SUMMARY SPECIFICATION OF THE INVENTION
In the first aspect, a method of removing oil from oily water is provided,
comprising providing
water containing a first amount of oil; adding a refrigerant that is oil-
soluble at a temperature and
pressure at which the refrigerant exists in liquid form, mixing the liquid to
ensure contact between the
oil and condensed vapour; separating the lower density liquid droplets without
reducing the pressure or
de-pressuring the mixture to allow the condensed vapour that has dissolved in
the oil to re-vapourize
forming bubbles directly on or within the oil droplets; allowing these bubbles
to rise to the surface to
accumulate as a scum or skim or froth referred to as a float; and separating
this layer from the water,
the water product containing a second amount of oil that is less than the
first amount of oil.
In the second aspect, a system for removing oil from oily water is provided
comprising a feed
inlet for supplying water containing a first amount of oil; raising its
pressure to allow the addition of a
refrigerant that exists as a liquid; at least one mixer for mixing the oily
water and refrigerant while
holding pressure to preserve the liquid phase; at least one separator
downstream at the same or lower
pressure to separate the oily froth from the water produced.
Thus in the present application a system for removing oil from water is
provided. Water
containing oil is pressurized and combined with a refrigerant, for example,
butane, pentane, propane,
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freons, liquefied petroleum gas, refrigerants or other vapours or combinations
of vapours that are oil-
soluble when condensed to form a mixture. There is a preference to
refrigerants that are partially water
soluble to enhance the absorption of the condensed vapour into the oil
droplets. The refrigerant may be
added before, during or after the pressuring stage as either a vapour or a
liquid. When the refrigerant is
added as a vapour, the oily water absorbs the latent heat of condensation and
condenses the vapour.
The vapour may be added to the oily water stream either through a compressor
or introduced through
the suction of the oily water pump.
The mixture is pumped through a pressurized mixer stage to apply sufficient
turbulence and
time to allow the condensed vapour to be diluted and diffused into the oil
droplets. Mixing may be
accomplished using pipes, coalescing elements, static mixers, throttling
valves or mechanically-driven
mixer. The mixture is then maintained at pressure or depressurized into at
least one three-phase
separator. The de-pressuring may be achieved by reduction in static head,
control valve or the mixing
elements themselves. The depressurizing separator operates at a lower pressure
that allows the
condensed vapour to grow out of the oil droplet as a bubble thereby ensuring
intimate contact between
the bubble and the oil droplet, thereby lifting the oil droplets to the
surface of the water. The system
benefits from the enormous change in volume when a condensed liquid changes
phase into a vapour.
The system operates with a once-through flow of refrigerant or a combination
of once-through
flow of refrigerant supplemented by refrigerant recovered from the three phase
separator.
The method allows for the use of one or more refrigerants in combination or
separately to
achieve optimum removal, depending upon the physical and chemical
characteristics of the oily water
including temperature, salinity, density or other compounds that are present.
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BRIEF DESRIPTION OF THE DRAWINGS
Referring to the drawings wherein like reference numbers indicate similar
parts throughout the
several views, several aspects of the present invention are illustrated by way
of example, and not by way
of limitation, in detail in the figures, wherein:
Figure 1 is a process diagram of a system for removing oil from water.
DESCRIPTION OF VARIOUS EMBODIMENTS
The detailed description set forth below in conjunction with the appended
drawing is intended
as a description of the various embodiments of the present invention and is
not intended to represent
the only embodiment contemplated by the inventor. The detailed description
includes specific details
for the purpose of providing a comprehensive understanding of the present
invention. However, it will
be apparent to those skilled in the art that the present invention may be
practiced without these
specific details.
Figure 1 is a schematic illustration of a system for removing oil from water.
The system includes
an oily water feed inlet 1, a oily water pressurizer 100, a mixer 200, a
pressure reducer 300, a three
phase separator 400, a vapour re-compressor 500, a number of valves 50A, 50B
and 50C, a de-oiled
water outlet 2, an oily float outlet 3, a refrigerant vapour outlet 4, a
refrigerant makeup inlet 5A or 5B,
and a refrigerant purge 6.
Oily water (water containing a first amount of hydrocarbon and oil) is
introduced into the
system through the feed inlet 1. The oily water can be from an industrial
process such hydraulic
fracturing, primary oil extraction, groundwater extraction for steam
injection, medicine formulation,
food processing, refinery, hydrocarbon upgrading process.
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The oily water may first pass through a pressurizer 100 that increases the
pressure high enough
to allow the refrigerant to exist as a liquid.
In one embodiment, the pressurizer is a centrifugal pump. The refrigerant can
be fed into the
oily water through 50A, one of three valves. Valve 50A allows the refrigerant
to be injected upstream
of the pressurizer 100. The pressurizer therein increases the pressure of both
the oily water and
refrigerant as a two phase mixture.
In another embodiment, the pressurizer is a microbubble generator. Valve 50B
allows the
refrigerant to be injected directly into the pressurizer. The pressurizer
therein increases the pressure of
both the oily water and refrigerant as a two phase mixture.
In another embodiment, refrigerant is injected into the pressurized oily water
through Valve 50C
downstream of pressurizer 100 where it condenses.
The combined oily water and refrigerant is thoroughly mixed in Mixer 200. The
mixer can be any
type of mixer for sufficiently agitating the mixture so as to provide adequate
turbulence and time for
refrigerant to blend into the oil droplets. The mixer can be static mixers
that are used for mixing two
fluids and typically contain mixer elements or baffles that agitate the two
fluids as they are passed
through the static mixer. An example of a static mixer that can be used is
SulzerTM Mixer SMV but other
static mixers known in the art can be used. The oily water and refrigerant can
also be blended by
simultaneously coalescing them onto a oil-wettable surface of a coalescing
element. The mixer can be a
length of pipe that offers sufficient residence time. The mixer can be a
mechanical mixer. The mixer can
be a valve.
The oily water and refrigerant mixture is de-pressured in Pressure Reducer 300
to allow the
refrigerant to re-vapourize and grow bubbles both within and outside the oil
droplets. One embodiment
of the pressure reducer is a simple throttling valve. Another embodiment is a
reduction in static head
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within a pipe or vessel. One embodiment of the pressure reducer is to utilize
Mixer 200 to both mix and
reduce pressure.
Another embodiment is not to reduce the pressure once the refrigerant has been
added to the
oily water, but to let the lower density liquid droplets separate naturally.
The depressurized oily water and refrigerant mixture is routed into Separator
400 where it
separates into three phases. The de-oiled water phase is removed from the
bottom of the Separator
through Outlet 2. The float phase containing oil and residual refrigerant is
skimmed from the surface
through either simple weir, floating weir, bucket and weir assembly, skim box,
mechanical paddles. The
float phase is then routed through Oily Float Outlet 3. The vapourized
refrigerant is removed through
Refrigerant Vapour Outlet 4 for recovery through recycling.
One embodiment of the Separator is to utilize a horizontal or vertical
cylindrical vessel. A
pressure vessel allows for the separation of oil and refrigerant from high-
temperature water or the use
of a high pressure refrigerant at lower temperatures.
One embodiment of the Separator is to use a vertical cylindrical tank.
One embodiment of the Separator is to use a rectangular tank at atmospheric
pressure.
The recovered refrigerant vapour can be recycled into the oily water through
Valve 50A or 50B.
The recovered refrigerant vapour can be compressed in Re-Compressor 500 and
recycled into the oily
water through Valve 50C. An example of the Re-Compressor can be a liquid-ring
compressor or sliding
vane compressor or scroll compressor.
During normal operation, some refrigerant is dissolved in the water and is
lost through De-oiled
Water Outlet 2. During normal operation, some refrigerant remains in the float
and is lost through Oily
Float Outlet 3. During normal operation, some refrigerant may be recovered
from the de-oiled water
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and float by passing each through a flash vessel operating under partial
vacuum, compressed and added
to the refrigerant vapour recovered in Separator 400.
During normal operation, some refrigerant may be contaminated with non-
condensable
components and require purging through Refrigerant Purge 6.
To compensate for the loss of refrigerant, replacement refrigerant may be
added through
Refrigerant Makeup Inlets at 5A, 5B or combination thereof.
Example 1.
An example of 1 liter of oily water containing 100 mg/I of API 14 oil present
as micron-sized
droplets at a temperature of 4 to 12 degrees centigrade is fed into Oily Water
Feed Inlet 1 and
pressurized to 11 psig. A refrigerant quantity of 100 m/I butane is injected
through valve 50A,
compressed to 11 psig and injected into the oily water where it condenses. The
condensing
temperature of butane at this pressure is 15 degrees centigrade, therefore it
condenses within the oily
water. The combined oily water and refrigerant mix is fed through a static
mixer and the oil droplets
become saturated with butane. The water-oil-refrigerant mix is then
depressurized to atmospheric
pressure (0 psig) where the refrigerant inside the oil droplets partially re-
vapourizes. The vapour
pressure of pure butane at 4 degrees centigrade is 2.7 psig, therefore at
atmospheric pressure
approximately 50% of the butane will re-vapourize and expand. At 1 atmosphere
pressure, the density
of butane liquid is 0.601 kg/litre and the density of butane vapour is .0027
kg/litre, therefore the volume
occupied by butane increases by 221 times when it re-vapourizes increasing the
droplet size by 6 times
and reducing its density to that of butane vapour, therefore allowing the
larger and less dense oil
droplet to float to the surface. The resultant de-oiled water can contain as
little as 5 mg/I or less oil.
The previous description of the disclosed embodiments is provided to enable
any person skilled
in the art to make or use the present invention. Various modifications to
those embodiments will be
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readily apparent to those skilled in the art, and the generic principles
defined herein may be applied to
other embodiments without departing from the spirit or scope of the invention.
Thus, the present
invention is not intended to be limited to the embodiments shown herein, but
is to be accorded the full
scope consistent with the claims, wherein reference to an element in the
singular, such as by use of the
article "a" or "an" is not intended to mean "one and only one" unless
specifically so stated, but rather
"one or more". The invention described herein can be applied as a single stage
or one of multiple stages
with each further reducing the oil content of the de-oiled water. In a multi-
stage installation, for
example, the makeup refrigerant can be added to the last stage while the most-
contaminated
refrigerant can be purged at the first stage.
All structural and functional equivalents to the embodiments described
throughout the
disclosure that are known or later come to be known by those of ordinary skill
in the art are intended to
be encompassed by the elements of the claims. For example, in a multistage
unit, each stage need not
be identical with regards to how the refrigerant vapour is recycled. Moreover,
nothing disclosed herein
is intended to be dedicated to the public regardless of whether such
disclosure is explicitly recited in the
claims.
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