Note: Descriptions are shown in the official language in which they were submitted.
CA 02937392 2016-07-29
APPARATUS, SYSTEM, AND METHOD FOR SEPARATING OIL FROM A FLUB)
MIXTURE
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED
RESEARCH OR DEVELOPMENT
[0002] Not applicable.
BACKGROUND
[0003] Field of the Disclosure
[0004] This disclosure relates generally to separating oil from a mixture that
contains oil and
water. More particularly, it relates to an apparatus and system for separating
oil from produced
water from an oil well that contains a mixture of oil and water,
[0005] Background to the Disclosure
[0006] Oilfield wastewater and produced water are created in fracturing
("frac") flowback and/or
in both land-based and offshore oil production operations. The wastewater and
produced water
are processed to extract oil as best as is possible. The wastewater or
produced water is a fluid
mixture that contains water and oil laden with residual solids. Water
processing facilities
commonly receive the fluid mixture either by pipeline or by truck.
Conventional facilities are
designed to receive the fluid mixture into an offload or de-sand tank. The
fluid mixture is then
pumped to a "vertical gun barrel" separation tank, then through a water leg
which holds a
constant level on the vertical gun barrel, and then into water storage tanks.
Some of the oil
remains and accumulates in the water storage tanks. This system is plagued
with certain
problems which include: build of solids in the storage tank, poor recovery of
oil from the water,
and difficulty in removing oil from the water storage tanks. Improvements have
been achieved
with a newer system that includes a "horizontal gun barrel" (HUB) separation
tank, which has a
longer flow path, but operations difficulties continue, including difficulty
in removing oil from
the water storage tanks. An apparatus or system that provides operational
improvements would
be useful to the oil field industry.
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BRIEF SUMMARY OF THE DISCLOSURE
[0007] These and other needs in the art are addressed in one embodiment by a
system for
extracting oil from a fluid mixture that includes oil and water. In an
embodiment, the system
comprises a separation vessel having an internal chamber that extends upwardly
to a chamber
elevation, an inlet port, a water outlet port, and an oil outlet port;
wherein, the oil outlet port is
disposed at an elevation that is greater than the elevation of the water
outlet port. In addition, the
system includes a first liquid storage tank having an internal chamber
extending to a tank
elevation, an inlet port, an upper outlet port that is disposed at an upper
outlet elevation, and a
lower outlet port disposed below the upper outlet. Further, the system
includes a first conduit
system interconnecting the water outlet port of the separation vessel and the
inlet port of the first
liquid storage tank and comprising a top conduit segment that is positioned at
an elevation equal
to the upper outlet elevation of the upper outlet port in the first liquid
storage tank. Still further,
the system includes a second conduit system interconnecting the first conduit
system and the
inlet port of the first liquid storage tank, the second conduit system
intersecting with the first
conduit system at an elevation that is less than the upper outlet elevation
and greater than the
chamber elevation. The system also includes a pump in fluid communication with
the upper
outlet port of the first storage tank and configured to pump fluid exiting the
upper outlet port to
the inlet port of the separation vessel.
[0008] In another embodiment, a system for extracting oil from a fluid mixture
that includes oil
and water includes a separation vessel comprising: an internal chamber that
extends upwardly to
a chamber elevation, an inlet port, a water outlet port, and an oil outlet
port; wherein, the oil
outlet port is disposed at an elevation that is greater than the elevation of
the water outlet port. In
addition, the system includes a plurality of liquid storage tanks, each
comprising: an inlet port, an
upper outlet port that is disposed at an upper outlet elevation that is
substantially the same for all
tanks, a lower outlet port disposed below the upper outlet port, and an
internal chamber
extending to a tank elevation that is greater than the upper outlet elevation,
the internal chamber
in fluid communication with the inlet port, the upper outlet port, and lower
outlet port. Further,
the system includes a conduit system interconnecting the water outlet port of
the separation
vessel with the inlet ports of the liquid storage tanks to allow fluid
communication there
between, the conduit system comprising: a first conduit segment in fluid
communication with the
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water outlet port of the separation vessel and extending upward, and a top
conduit segment in
fluid communication with the first conduit segment and with the inlet ports of
the liquid storage
tanks, the top conduit segment positioned at an elevation equal to the upper
outlet elevation. Still
further, the system includes a second conduit system interconnecting the first
conduit segment
and the inlet ports of the liquid storage tanks, the second conduit system
intersecting the first
conduit segment at an elevation that is less than the upper outlet elevation
and greater than the
chamber elevation. Moreover, the system includes a return conduit system
interconnecting the
upper outlet ports of the liquid storage tanks with the inlet port of the
separation vessel for fluid
communication.
[0009] In another embodiment, a system for extracting oil from a fluid mixture
that includes oil
and water includes a separation vessel comprising: an internal chamber having
a vertical span
that extends upvlardly to a chamber elevation and having a horizontal span
that is greater than its
vertical span, an inlet port, a water outlet port separated horizontally from
the inlet port by a
distance greater than the vertical span of the internal chamber, and an oil
outlet port; wherein, the
oil outlet port is disposed at an elevation that is greater than the elevation
of the water outlet port.
In addition, the system includes a first liquid storage tank comprising: an
inlet port, a lower
outlet port, and an internal chamber extending to a tank elevation, the
internal chamber in fluid
communication with the inlet port and lower outlet port. Further, the system
includes an oil
storage tank comprising an oil inlet port disposed at an oil inlet elevation
that is less than the tank
elevation. Still further, the system includes a conduit system interconnecting
the water outlet
port of the separation vessel with the inlet port of the first liquid storage
tank for fluid
communication, the conduit system comprising: a first conduit segment in fluid
communication
with the water outlet port of the separation vessel and extending upward, and
a top conduit
segment in fluid communication with the first conduit segment and with the
inlet port of the first
liquid storage tank, the top conduit segment positioned at a top elevation
greater than the oil inlet
elevation. Moreover, the system includes a third conduit system
interconnecting the oil outlet
port of the separation vessel with the oil inlet port of the oil storage tank,
the third conduit
system including an air bleed valve disposed at an elevation above the chamber
elevation.
[0010] These and other needs in the art are addressed in an embodiment by a
method for
extracting oil from a fluid mixture that includes oil and water. In an
embodiment, the method
comprises conveying the fluid mixture into a separation tank configured to
separate the fluid
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mixture into an intermediate fluid including water and a lighter fluid
including oil, distinguished
by specific gravity. In addition, the method includes conveying a first
portion of the
intermediate fluid to a first storage tank through a first conduit system.
Further, the method
includes skimming oil from the first storage tank and conveying it back to the
separation tank.
Still further, the method includes conveying a second portion of the
intermediate fluid to a
second storage tank through a second conduit system that is in fluid
communication with the first
conduit system at an intersection and has a top segment disposed above the
intersection.
[0011] Thus, embodiments described herein include a combination of features
and
characteristics intended to address various shortcomings associated with
certain prior devices,
systems, and methods. The various features and characteristics described
above, as well as
others, will be readily apparent to those of ordinary skill in the art upon
reading the following
detailed description, and by referring to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] For a detailed description of the disclosed exemplary embodiments,
reference will now
be made to the accompanying drawings, wherein:
[0013] Figure 1 shows an elevation view, in schematic form, of an embodiment
of a system for
extracting oil from a fluid mixture in accordance with principles described
herein; and
[0014] Figure 2 shows a diagram of a method for extracting oil from a fluid
mixture in
accordance with principles described herein.
NOTATION AND NOMENCLATURE
[0015] The following description is exemplary of certain embodiments of the
disclosure. One of
ordinary skill in the art will understand that the following description has
broad application, and
the discussion of any embodiment is meant to be exemplary of that embodiment,
and is not
intended to suggest in any way that the scope of the disclosure, including the
claims, is limited to
that embodiment.
[0016] The drawing figures are not necessarily to scale. Certain features and
components
disclosed herein may be shown exaggerated in scale or in somewhat schematic
form, and some
details of conventional elements may not be shown in the interest of clarity
and conciseness. In
some of the figures, in order to improve clarity and conciseness, one or more
components or
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aspects of a component may be omitted or may not have reference numerals
identifying the
features or components. In addition, within the specification, including the
drawings, like or
identical reference numerals may be used to identify common or similar
elements.
[0017] As used herein, including in the claims, the terms "including" and
"comprising," as well
as derivations of these, are used in an open-ended fashion, and thus are to be
interpreted to mean
"including, but not limited to...." Also, the term "couple" or "couples" means
either an indirect
or direct connection. Thus, if a first component couples or is coupled to a
second component, the
connection between the components may be through a direct engagement of the
two components,
or through an indirect connection that is accomplished via other intermediate
components,
devices and/or connections. The recitation "based on" means "based at least in
part on."
Therefore, if X is based on Y, then X may be based on Y and any number of
other factors.
DETAILED DESCRIPTION OF THE DISCLOSED EXEMPLARY EMBODIMENTS
[0018] Referring to Figure 1, in an exemplary embodiment, an oil-water
separation system 50 is
configured to extract oil from a fluid mixture containing oil and water. The
fluid mixture may be
wastewater or produced water from a land-based or an offshore oil production
operation. System
50 includes a separation vessel 60, a plurality of liquid storage tanks 90, an
oil storage tank 110,
a plurality of conduit systems 120, 140, 150, 160, 180 and a control system
198. In Figure 1, the
several fluid containers and tanks are shown to be mounted at a common base
elevation 52,
which will be used as a datum plane for measuring the elevations of various
components or
features. Three storage tanks 90 are shown, but any practical number of
storage tanks may be
used, such as 2, 4, 10, 29, 50, etc., as may be feasible based on technical or
economic
considerations. Some other embodiments may have a single storage tank. In
various
embodiments, one or more of the several vessels and tanks 60, 90, 110 may be
mounted on a
different elevation, but the common base elevation 52 would continue to serve
as a datum plane
for measuring the disclosed and the claimed elevations. As used herein and in
the claims, the
elevation of component, such as a conduit (e.g. a piece of tubing or pipe), a
tank, a vessel, or a
chamber, refers to the portion of that component that is configured to contain
a process fluid.
[0019] In this embodiment, the separation vessel 60 is generally cylindrical
and has a nominal
vessel length L60 extending horizontally and a nominal vessel diameter D60
extending
vertically, making vessel 60 a horizontal cylinder. The horizontal span of
vessel 60, i.e. length
CA 02937392 2016-07-29
L60, is greater than its vertical span, i.e. diameter D60, providing shorter
distance through which
the oil must rise in order to separate from the water, as compared to certain
previous separation
vessels, such as a vertical gun barrel that is vertically elongate and
therefore requires that the
lighter fluid (e.g. oil) travel a greater distance before separating from the
heavier fluid (e.g.
water).. Consequently, the horizontally elongate vessel 60 is configured to
provide greater
separation efficiency for a given dwell time within the vessel. Greater
separation efficiency
means that more of oil from the inlet flow is removed before the intermediate
fluid (e.g. partially
cleaned water) exits the vessel. Some embodiments of the current disclosure
are even operated
with a lower dwell time as compared to a vertically elongate separation vessel
that may achieve
the lower separation efficiency or, at most, a similar separation efficiency.
Some embodiments
of the disclosed system that have lower dwell time also have a higher
throughput rate.
[0020] Vessel 60 may also be called a horizontal gun barrel (HGB). Vessel 60
includes an
internal chamber 62 having a horizontal span and a vertical span that are
equal to or
approximately equal to the nominal length L60 and nominal diameter D60,
respectively. Internal
chamber 62 extends vertically up to a chamber elevation E62 above the base
elevation 52. In an
example, vessel length L60 is 30 feet, and vessel diameter D60 is 8 feet.
Vessel 60 includes an
inlet port 64 to receive a fluid mixture to be processed, a water outlet port
66 distal the inlet 64
and near the bottom of vessel 60, an oil outlet port 68 also distal the inlet
64 but near the top of
vessel 60, a solids removal port 70 near the bottom of vessel 60, and a
plurality of vertical baffles
72 located proximal the inlet port 64 to distribute the flow laterally and to
encourage solids to
drop to the bottom. The example of Figure 1 includes two baffles 72. Vessel 60
may also
include an automated or semi-automated solids removal system (not shown) to
aid in the removal
of solids through port 70. Water outlet port 66 is separated horizontally from
the inlet port 64 by
a distance greater than the vertical span of the internal chamber 62, i.e. a
distance greater than the
vertical span diameter of vessel 60. Oil outlet port 68 is located at an
elevation E68 that is
greater than the elevation E66 of water outlet port 66. In Figure 1, the
elevation E68 of Oil
outlet port 68 is equal to or greater than the chamber elevation E62.
[0021] Typically, the fluid to be processed is a mixture that includes oil and
water and may
contain other fluids and particulate matter such as dirt, rock fragments, or
sand. The water may
be salt water, fresh water, brackish water, etc., as examples. The fluid
mixture may come from a
land-based oil well or from an off-shore oil well, as examples. In the example
of Figure 1, a
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mixture that includes oil and water is received from a tank truck 80 and is
moved by a pump 85
through inlet port 64 into vessel 60. In at least one embodiment, pump 85 is a
low-shear pump,
configured to minimize the amount of blending or emulsification of oil and
water that may occur
when the fluid mixture passes through the pump. In at least one embodiment,
pump 85 is a
progressive cavity pump.
[0022] During normal operation, chamber 62 of vessel 60 is completely filed
with fluid and an
oil-water interface 74 develops therein. The baffles 72 and gravity separate
the incoming fluid
mixture in to an upper layer of lighter fluid, a lower portion of intermediate
fluid, and solids that
settle to the bottom. In typical operation, the lighter fluid is oil, and the
intermediate fluid
includes water and some residual oil or other contaminants and exits through
the water outlet
port 66.
[0023] Each liquid storage tank 90 includes an internal chamber 92 extending
from the bottom of
tank 90 vertically upward at least to a nominal tank height, which is located
at a tank elevation
E92, an inlet port 94 located proximal the bottom of chamber 92, a lower
outlet port 96 located
proximal the bottom of chamber 92, a vent port 98 located proximal the top of
chamber 92, and
an upper outlet port 100 located proximal the top of chamber 92 at an upper
outlet elevation
E100. Ports 94, 96, 98, 100 are in fluid communication with chamber 92.
Elevation E100 is less
than tank elevation E92, less than the elevation of vent port 98, and greater
than the elevation of
the lower outlet port 96. The elevations E100 of the upper ports 100 on all
tanks 90 are the same
or substantially the same. In the exemplary embodiment of Figure 1, the bottom
oftank 90 is at
base elevation 52, tank elevation E92 is 25 feet; upper outlet elevation E100
is two feet less than
tank elevation E92; the elevation of vent port 98 is 24.5 feet; tank 90 has a
tank diameter of 12
feet; and lower outlet port 96 is horizontally separated from inlet port 94 by
the tank diameter.
Vent port 98 may be employed to bleed a gas, such as air, from the top of tank
90. Alternatively,
vent port 98 may be employed as another liquid outlet port for oil. In some
embodiments; the
port 98 may be closed. In some embodiments, vent port 98 is located on the
roof of tank 90.
[0024] Oil storage tank 110 includes an oil inlet port 112 and an outlet port
114. Inlet port 112 is
located at an oil inlet elevation E112 that is less than the upper outlet
elevation El 00 of the upper
ports 100 on liquid storage tanks 90.
[0025] An intermediate fluid conduit system 120 interconnects the water outlet
port 66 of the
separation vessel 60 with the inlet ports 94 of the storage tanks 90 to allow
fluid communication
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of the intermediate fluid. Conduit system 120 has various conduit segments,
including an initial
segment 122, an inverted U-tube 124, and a completion segment 132. Inverted U-
tube 124
includes an upward segment 126 extending upward, a top segment 128 that
achieves a top
elevation equal to upper outlet elevation E100 of tanks 90, a vent port 129
rising above top
segment 128, and a downward segment 130 extending down toward the elevations
of tank inlet
ports 94. U-tube 124 may also be called a U-leg 124, Completion segment 132
has multiple
terminating portions, each with a tank inlet valve V1 and each extending to
one of the tank inlet
ports 94. Thus each tank inlet port 94 is serviced by a dedicated inlet valve
Vito allow or
inhibit fluid communication, selectively, between (at least) downward segment
130 of inverted
U-tube 124 and the corresponding tank 90. Each inlet valve V1 is configured at
least for an open
position and a closed position. Gate valves, ball valves, and butterfly valves
may all serve as
inlet valves 135, as examples. In various embodiments, inlet valves V1 may be
configured for
manual or for powered operation and may be controlled locally or via remote
control. Valve V1
may also be configured both for manual operation and for powered operation, as
may be selected
by an operator. Vent port 129 on U-leg 124 is vented to atmosphere, but in
some embodiments,
vent port 129 is plumbed to communicate fluidly with the top of a tank 90,
above the liquid level
in that tank, and communicates with the tank's vent port 98.
[0026] As used herein, including the claims, the term "conduit segment" means
and includes any
number of conduit segments or runs that are in fluid communication with one
another and that
cooperate to convey fluid from one point to another. As examples, a claim may
use the term
"first conduit segment" to refer to a conduit run that includes initial
segment 122 and upward
segment 126, or the term may refer to initial segment 122 or upward segment
126 alone.
[0027] Still referencing Figure 1, a by-pass conduit system 140 interconnects
the upward
segment 126 of inverted U-tube 124 with the inlet ports 94 of the storage
tanks 90 to provide
fluid communication, by-passing the top segment 128 and the downward segment
130. By-pass
conduit system 140 is configured to provide a flow of the intermediate fluid
from vessel 60 in
order to push-out or skim the oil that collects at the top of storage tanks 90
during normal
operation. Thus, conduit system 140 can be used as a clean-out system. Conduit
system 140 has
multiple conduit segments, including an initial segment 142 that extends from
the U-tube upward
segment 126 at an intersection 143, a check valve CV1 coupled to initial
segment 142, and a
completion segment 146 extending downward toward the elevations of tank inlet
ports 94.
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Completion segment 146 has multiple terminating portions, each with a by-pass
valve V2 and
each coupling to one of the tank inlet ports 94. Thus each tank inlet port 94
is serviced by a
dedicated valve V2 to allow or inhibit fluid communication, selectively,
between by-pass conduit
system 140 and the corresponding tank 90. Each by-pass valve V2 is configured
like any of the
options described for inlet valves V1 and may also be called an inlet valve
V2. Check valve
CV1 is oriented to allow fluid to travel only from the upward segment 126 to
completion
segment 146 and to inhibit fluid flow in the reverse direction. A portion of
completion segment
146 that is located beyond inlet valve V2 and a portion of completion segment
132 that is located
beyond inlet valve V1 intersect each other in order to couple to tank inlet
port 94. In other
embodiments, each tank 90 includes two inlet ports 94, one for each completion
segment 132,
146.
[0028] Initial segment 142 of by-pass conduit system 140 intersects upward
segment 126 at a by-
pass elevation E142 that is below top segment 128 of the inverted U-tube 124.
Thus, by-pass
elevation E142 is less than the upper outlet elevation E100 of the upper
outlet ports 100 of the
storage tanks 94. In at least one embodiment, the by-pass elevation E142 is
greater than the
chamber elevation E62 of separation vessel 60. Each component 142, CV1, 146,
V2 of the by-
pass conduit system 140 includes a flow passage that cooperates in providing
fluid
communication between upward segment 126 and the tanks 90. The internal flow
passages of the
by-pass conduit system 140 are located below the elevation E100; however, in
some
embodiments a portion of system 140 located beyond the intersection 143 may
rise above and
drop below the upper outlet ports 100 before reaching tank inlet 94.
[0029] A cleaned water discharge conduit system 150 includes an outlet valve
V3 at each lower
outlet port 96 of each tank 90 and includes a piping manifold 156 to connect
the outlet valves V3
to a common discharge pipe. Conduit system 150 is provided to remove and
transport the
cleaned water that accumulates at the bottom storage tanks 90. The cleaned
water may contain
contaminants and even some oil.
[0030] Continuing to reference Figure 1, an oil conduit system 160
interconnects the oil outlet
port 68 of the separation vessel 60 with the oil inlet port 112 of the oil
storage tank 110 to
provide fluid communication there between. Conduit system 160 includes
multiple conduit
segments and components, including a control valve V4 coupled to outlet port
68, a level sensor
LS1 coupled to vessel 60 and electrically coupled to valve V4. Conduit system
160 includes an
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initial segment 166 extending from control valve V4 opposite the port 68, and
a completion
segment 168 extending to oil inlet port 112. Conduit system 160 also includes
an air bleed valve
V5 coupled at the highest location along initial segment 166. In the example
of Figure 1, initial
segment 166 includes portions (i.e. smaller segments) that rise above vessel
60, extend parallel to
base 52, drop down to base 52, and rise up toward the elevation E112 of oil
inlet port 112 to
couple to completion segment 168. In at least one embodiment, initial segment
166 rises above
vessel 60 and extends horizontally toward oil inlet port 112 without dropping
toward base 52. In
at least one embodiment, conduit system 160 is located entirely below the
elevation El 00 of the
upper ports 100.
[0031] Level sensor LS1 is configured to monitor the oil-water interface 74
within vessel 60 and
to open valve V4 when interface 74 moves to a location below a selected,
target elevation,
allowing excess oil at the top of vessel 60 to exit through oil conduit system
160 and travel to oil
storage tank 110. In various embodiments, level sensor LS1 is a level switch
configured to
produce a binary response. In other embodiments, sensor LS1 may be a level
transducer
configured to transmit measurement data. During normal operation, the vessel
chamber 62 and
the portion of conduit system 120 from water outlet port 66 up to the top
segment 128 remain
filled with fluid, up to the upper outlet elevation E100. Of course, in some
conditions, an air
pocket may develop in vessel 64 or conduit system 120. Thus filled with fluid,
the upward
segment 126 of U-tube 124 exerts a hydrostatic pressure head on the fluid in
vessel chamber 62,
and provides a motive force for pushing oil through conduit system 160 and
into tank 110 when
valve V4 is opened. The amount of pressure head available is equal to the
difference in elevation
between upper outlet elevation E100 and the elevation E112 of oil inlet port
112.
100321 A return conduit system 180 interconnects the upper outlet ports 100 of
the storage tanks
90 with the inlet port 64 of the separation vessel 60 to provide fluid
communication there
between. Conduit system 180 includes various conduit segments and components,
including an
initial segment 182 having portions coupled to each of the upper outlet ports
100, a downward
segment 184 extending toward base elevation 52 and coupled to the suction port
186 of a transfer
pump 185, and a completion segment 192 extending between the pump's discharge
port 188 and
inlet port 64. The various conduit segments 182, 184, 192 may also be called
return segments.
Conduit system 180 further includes a fluid sensor 194 coupled to downward
segment 184,
located below the upper outlet ports 100, proximal base elevation 52 and pump
185. Fluid
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sensor 194 is positioned and coupled to sense the presence and the absence of
a fluid, for
example oil, in in at least a portion of downward segment 184 and to send a
signal to activate or
to deactivate transfer pump 185 as appropriate. In the example of Figure 1,
fluid sensor 194
comprises a pair of sensors: a pressure sensor PS1 and a flow sensor FS1. In
various
embodiments, pressure sensor PSI is a pressure switch configured to produce a
binary response.
Alternatively, switch PSI is a pressure transducer configured to transmit
measurement data.
Similarly, in various embodiments, flow sensor FS1 is a flow switch configured
to produce a
binary response or is a flow rate transducer configured to transmit
measurement data. Pump 185
is configured to activate and pump fluid when the pressure sensor PS1 detects
that the pressure
head of a fluid in the downward segment 184 is greater than a predetermined
threshold pressure
value, indicating a quantity of fluid in segment 184. As examples, the
predetermined threshold
pressure value may correspond to the pressure head that results when downward
segment 184 is
full of oil up to the elevation E100 or is half full or two-thirds full of
oil. The pump is
configured to deactivate and cease pumping fluid when the flow sensor FS1
senses a flow rate in
the downward segment 184 that is less than a threshold flow rate value. In at
least one
embodiment, pump 185 is a low-shear pump, configured to minimize the amount of
blending or
emulsification of oil and water that may occur when such a fluid mixture
passes through the
pump. In at least one embodiment, pump 185 is a progressive cavity pump. The
statement that
pump 185 is configured to activate or to deactivate based on a sensor PSI, FS1
means that
circuitry and logic in pump 185, in a sensor PS1, FS1, or in control system
198 monitors the
sensors PSI, FS1 and causes pump 185 to turn-on or turn-off at an appropriate
time.
[0033] Referring still to Figure 1, control system 198 is configured to
monitor or regulate the
pumps, the sensors, and the valves of oil-water separation system 50 and to
provide an operator
with information and with control features. Control system 198 communicates
with the pumps,
the sensors, and the valves through wired connections, through wireless
connections, or a
combination of wired and wireless connections. The amount of monitoring and
regulating
performed by control system 198 varies with different embodiments of system
50. In various
embodiments, the purging of oil from the top of a tank 94 is automatically
actuated by control
system 198 through the sequencing of inlet valve V1, by-pass valve V2, outlet
valve V3, and
transfer pump 185. The operation of pump 185 is based on signals or data
received from
pressure sensor PSI and flow sensor FS1. In various embodiments, the purging
of oil from the
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top of separation vessel 60 is automatically actuated by control system 198
through interactions
between level sensor LS1 and control valve V4.
[0034] During a normal mode of operation of oil-water separation system 50, a
fluid mixture
that includes oil and water enters separation vessel 60 through inlet port 64
and fills chamber 62.
A first portion of the oil rises to the top, and the intermediate fluid
remains toward the bottom of
chamber 62, generating the oil-water interface 74. The flow of the fluid
mixture into vessel 60
may be driven by pump 85 or by gravity. The first portion of oil is removed to
tank 110 by oil
conduit system 160 as explained above. The intermediate fluid flows through
outlet port 66 and
through the inverted U-tube 124 of conduit system 120. Typically, this
intermediate fluid
contains some residual oil. During operation, the inlet valve V1 and outlet
valve V3 are open for
at least a first water storage tank 90, and corresponding by-pass valve V2
remains closed for the
same water storage tank 90. With inlet valve V1 open, some or all the
intermediate fluid enters a
first tank 90, with any remainder going to another tank 90 if another valve VI
is open, and the
fluid in the first tank rises or remains steady at some level below the upper
outlet port 100. The
term "normal-flow configuration" for any particular tank 90 will refer to the
configuration in
which the inlet valve V1 and the outlet valve V3 are open and the by-pass
valve V2 is closed for
that tank 90. Continuing to discuss the operation of the first tank 90, over
time, some or all
residual oil separates from the water in the first tank 90. The residual oil
rises and accumulates in
a layer above the water, creating an oil-water interface 102 in tank 90. The
water that settles
below interface 102 will also be called "cleaned water," although it may
continue to contain
some of the oil or other contaminants of the intermediate fluid that entered
inlet port 94. At
planned intervals, or at another selected time, the oil in the first tank 90
is removed through
upper outlet port 100 by closing the tank's inlet valve VI and outlet valve V3
and opening the
by-pass valve V2, causing the fluid level in first tank 90 to rise to the
upper outlet elevation
El 00. This removal of oil from the top of a tank 90 will also be called
"skimming" and may be
initiated by an operator or by pre-established programing in control system
198, using a time
criterion. During typical skimming, additional fluid mixture continues to
enter vessel 60 from
pump 85 or another source, and the intermediate fluid continues to exit
through the vessel outlet
66.
[0035] Once initiated, the skimming of oil from the top surface of fluid in
the first tank 90 (or
any selected tank 90) may be performed without supervision by an operator and
without
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CA 02937392 2016-07-29
supervision by control system 198 by maintaining an inlet valve V1 on at least
one other tank 90
open. While the fluid mixture flows into vessel 60, some of the intermediate
fluid (water and its
residual oil or other contaminants) from vessel 60 flows to the other tank or
tanks 90. To skim
the first tank 90 without supervision, its outlet valve V3 is closed as
mentioned above, its inlet
valve V1 is closed, and its by-pass valve V2 is opened; this is the skimming
configuration for the
first tank. In this configuration, some intermediate fluid from vessel 60
enters the first tank 90
via the by-pass conduit system 140, This intermediate fluid) fills the first
tank 90 up the upper
outlet port 100. The pressure of the fluid head that exists in the inverted U-
tube 124 between the
intersection 143 and in the top segment 128 governs the flow of the
intermediate fluid through
the open by-pass valve V2 and governs the steady-state elevation of the oil-
water interface 102
in the first tank 90 and the release of oil through upper outlet port 100, as
will be explained next.
[0036] Typically, water, exclusive of any oil, has a specific gravity of 1.0
or greater. The water
may be saltwater or "fresh water," as examples. The oil at the top of vessel
60 and at the top of
tank 90 has a lower specific gravity, for example, a specific gravity of about
0.7. This difference
causes the cleaned water and the residual oil in first tank 90 (and in the
other tanks 90) to
separate and form the oil-water interface 102. Separation is also aided by the
polar and non-
polar molecular difference between water and oil. The intermediate fluid in
the inverted U-tube
124, including the top segment 128 includes water and a small fraction of oil
and, has a specific
gravity that is equal or nearly equal to the specific gravity of the cleaned
water in the tanks 90
and is greater than the specific gravity of oil. The fluid head in the
inverted U-tube 124 ,
including top segment 128, drives the oil-water interface 102 upward, causing
the less dense oil
layer in the first tank 90 to rise above the upper outlet elevations E100 and
exit through upper
outlet port 100. This rise of oil-water interface 102 continues until it
reaches an elevation equal
to or somewhat below the top segment 128. The pressure head of the
intermediate fluid in top
segment 128 is able to drive oil through upper outlet port 100, but when the
level of the cleaned
water reaches the upper outlet elevation El 00 the water in tank 90 balances
with the level of
water in top segment 128, reducing or stopping the flow of fluid through upper
outlet port 100.
In this mariner, the skimming from the first tank 90 may continue
indefinitely. The first tank can
remain in the skimming configuration indefinitely, without supervision, while
fluid continues to
enter vessel 60, and intermediate fluid passes through the intermediate fluid
conduit system 120.
At least some of intermediate fluid from separation vessel 60 continues to
pass to the one or
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CA 02937392 2016-07-29
more other tank 90, or the flow from vessel 60 may stop or restart, as may
occur if inlet pump 85
is deactivated and later reactivated. In at least some situations, when the
height of oil-water
interface 102 in the first tank 90 rises to the location where it balances
with the height of the
intermediate fluid in the U-tube, intermediate fluid stops entering inlet port
94 and fluid (e.g. oil)
stops exiting through upper port 100. As a result, flow sensor FS1 detects a
cessation or
reduction of fluid flow in downward segment 184 of return conduit system 180,
and transfer
pump 185 is deactivated. With no intermediate fluid entering first tank 90,
all the flow of
intermediate fluid passes to the other tank or tanks 94 having an open inlet
valve Vi. After a
selected time period, the first tank 90 may be returned to the normal-flow
configuration in which
its valves V1, V3 are open and by-pass valve V2 is closed. Optionally, in a
supervised mode of
operation, first tank 90 may be returned to the normal-flow configuration
after flow sensor FS1
detects a cessation of oil flow in downward segment 184. In some other
embodiments, the
activation of pump 185 may be based on a rising signal from flow sensor FS1,
and the
deactivation of pump 185 may be based on a falling signal from pressure sensor
PS1. Skimming
of the same first tank 90 may be repeated at a later time.
[00371 In some embodiments, during a single session of skimming before first
tank 90 is
returned to the normal-flow configuration, pump 185 may be reactivated to pump
oil after being
deactivated if the pressure sensor PSI again detects a sufficient pressure
head of a fluid, i.e. oil
or water, in the downward segment 184.
100381 Any of the storage tanks 90 can be skimmed periodically with or without
supervision
while at least one other tank 90 is in the normal-flow configuration,
configured to receive
intermediate fluid through its inlet valve Vi. Depending on the flow rate of
fluid mixture into
vessel 60 and the flow rate of intermediate fluid leaving vessel 60, it may be
appropriate to keep
a plurality of tanks 90 in the normal-flow configuration while skimming a
tank. When multiple
=
tanks 90 are in normal-flow configuration, they are in fluid communication
through completion
segment 132 of conduit system 120, and the oil-water interfaces 102 or a fluid
level in the
communicating tanks 90 may become balanced, possibly achieving a common
elevation,
depending on the ratio of water and oil in each tank 90. Optionally, a
plurality of storage tanks
90 can be skimmed simultaneously while at least one other tank 90 is in the
normal-flow
configuration.
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CA 02937392 2016-07-29
[0039] In various embodiments or instances of this operational sequence, the
timing and
operation of the valves and pumps may be controlled by control system 198,
using pre-
established criteria or programing. Alternately, the timing and operation of
the valves and
pumps may be directly controlled by an operator through control system 198 or
by manually
manipulating the valves, when system 50 is equipped for manual operation.
Optionally, the
operation of the valves and pumps may be shared between the operator and
control system 198.
[0040] As described above, for at least some embodiments, the skimming of oil
from the top of a
tank 90 continues without supervision. "Without supervision" means that the
decision to change
a tank 90 from the normal-flow configuration to the skimming configuration or
vice versa is
achieved based on a time criterion or another criterion unrelated to the
amount of oil in the tank
90or unrelated to the amount of oil leaving port 100. Unsupervised skimming of
oil from the top
of a tank 90 is accomplished without using a level indicating device. In
Figure 1, tanks 90 are
configured without a level sensor. Unsupervised skimming is possible based on
the balancing
effect that occurs as a result of these three factors: (1) the top of U-tube
124 being filled with
intermediate fluid and having the same elevation as the upper outlet port 100
of tank 90, (2) the
presence of oil-water interface 102 in tank 90, and (3) of the different
specific gravities (or
densities) of the oil above the interface 102 and the cleaned water below the
interface 102.
[0041] Alternatively, the skimming process may be supervised; meaning that the
decision to
change a tank 90 from the normal-flow configuration to the skimming
configuration or vice
versa is governed based on process parameters rather than based solely on a
time period or
arbitrary decision. Supervised operation of the skimming process may utilize
knowledge of one
or more of these process parameters: the location of the of the oil-water
interface 102, the
location of the top of the oil layer in the tank 90, or the amount of oil in
the tank 90, as might be
achieved by the use of level indicating device, such as a dip stick, an
electrically coupled level
sensor, or another technology known in the art. For some embodiments or some
operation
scenarios, supervision of the skimming process can be achieved using the
signals of pressure
sensor PS1 or flow sensor FS1.
[0042] Some of these embodiments include a level sensor or another technology
coupled to the
tank 90 to detect and indicate the location of the oil-water interface 102 or
the amount of oil in
the tank 90, and some of these embodiments operate the skimming process in a
supervised mode
based on a response signal from the level sensor. Even so, one or more of
these embodiments
CA 02937392 2016-07-29
having a level sensor may perform the skimming process without supervision,
that is to say,
without responding to the information from the level sensor. Even so, the
information from the
level sensor may be collected for evaluation of the effectiveness of the
skimming process or for
another purpose. Various embodiments include a dip stick on a tank 90, while
others do not.
[0043] Figure 2 shows a method 300 for extracting oil from a fluid mixture
that includes oil and
water in accordance with the principles described herein. At block 302, method
300 includes
conveying a fluid mixture into a separation tank configured to separate the
fluid mixture into an
intermediate fluid including water and a lighter fluid including oil,
distinguished by specific
gravity. Block 304 includes conveying a first portion of the intermediate
fluid to a first storage
tank through a first conduit system. Block 306 includes skimming oil from the
first storage tank
and conveying it back to the separation tank. Block 308 includes conveying a
second portion of
the intermediate fluid to a second storage tank through a second conduit
system that is in fluid
communication with the first conduit system at an intersection and has a top
segment disposed
above the intersection. Block 310 includes isolating the first storage tank
from a completion
segment of the second conduit system. In some embodiments of method 300,
skimming oil is
performed free of level detection in the first storage tank. Various actions
of method 300 may be
performed by control system 198. Various embodiments of method 300 may include
fewer
operations than described, and other embodiments of method 300 include
additional operations
based on the concepts disclose herein.
[0044] While various vessels and tanks have been described as cylinders, in
some embodiments,
a vessel or tank or corresponding internal chamber may instead have another
cross-sectional
shape: such as a square, a rectangle, a hexagon, another type of polygon as
examples, or a vessel
or tank may be spherical as another example. While separation vessel 60 in the
example of
Figure 1 is oriented horizontally, some embodiments have a separation vessel
that is oriented
differently, such as vertically. In an example, a vertically oriented,
cylindrical separation vessel
may be called a vertical gun barrel (VGB). Some embodiments include a
separation vessel
having a diameter that is greater than or equal to its length. In some
embodiments, the water
outlet port 66 is separated horizontally from the inlet port 64 by a distance
less than or equal to
the vertical span of the internal chamber 62 of the vessel.
[0045] Referring again to Figure 1, although the inlet port 94 of each tank 90
is shown to be
proximal the bottom of chamber 92, in other embodiments, one or more tanks 90
may include an
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CA 02937392 2016-07-29
inlet port 94 that is positioned at another elevation that is less than upper
outlet elevation E100.
For example, the inlet port 94 may be located any vertical location below
elevation E142.
[0046] Referring again to Figure 1, in some embodiments, at least one tank 90
has a tank
elevation E92 or a tank diameter that varies from another of the tanks 90.
However, all tank
elevations E92 will be greater than the common elevation E100 shared by each
upper outlet port
100 of all the tanks 90.
[0047] While exemplary embodiments have been shown and described,
modifications thereof
can be made by one of ordinary skill in the art without departing from the
scope or teachings
herein. The embodiments described herein are exemplary only and are not
limiting. Many
variations, combinations, and modifications of the systems, apparatus, and
processes described
herein are possible and are within the scope of the disclosure. Accordingly,
the scope of
protection is not limited to the embodiments described herein, but is only
limited by the claims
that follow, the scope of which shall include all equivalents of the subject
matter of the claims.
The inclusion of any particular method step or operation within the written
description or a
figure does not necessarily mean that the particular step or operation is
necessary to the method.
If feasible, the steps or operations of a method may be performed in any
order, except for those
particular steps or operations, if any, for which a sequence is expressly
stated. In some
implementations, when feasible, two or more of the method steps or operations
may be
performed in parallel, rather than serially.
17
