Note: Descriptions are shown in the official language in which they were submitted.
. =
Processes And Systems For Generating Steam From Produced Water
Field Of The Invention
The invention relates to processes and systems for treating produced water and
more specifically to processes and systems for treating produced water
sufficiently such
that the treated water may be used to generate steam in hydrocarbon recovery.
Background
In hydrocarbon recovery (or production) operations steam is used, for example,
in
extracting heavy oil through cyclic steam stimulation, steam flooding, or
steam-assisted
gravity drainage (SAGD). The cost of steam generation, the capital and
operating
Jo expenditures for the water treatment and steam generation facility and
the associated
generation of emissions each impact the viability of a hydrocarbon recovery
operation.
Water produced from a hydrocarbon production facility, referred to as produced
water or production water, may be treated and recycled for use in steam
generation.
Recycling of produced water requires overall removal of suspended solids,
dissolved
solids and of scale-forming chemicals, among other ions and chemical
compounds, that
affect the operation of steam generating systems. Conventional processes are
complex
and expensive when handling the specific chemistry of produced water and other
oil and
gas effluents.
Produced water is typically received at a high temperature and pressure, both
of
which must be reduced before being treated using conventional processes and
systems.
This typically involves the use of heat exchangers to reduce the temperature
of the
produced water before treatment to remove oil and emulsions, suspended solids,
dissolved solids and scale-forming chemicals such as calcium, magnesium and
silica,
before the treated water is then re-heated and re-pressurized in advance of
steam
generation. The cooling, re-heating and the re-pressurization of the treated
water requires
significant energy consumption and equipment to carry out.
The current economic climate, with low oil prices, is driving the need to
lower the
cost of hydrocarbon production. More stringent environmental regulations on
carbon
emissions and waste streams further underscore the need for new technologies
that will
increase productivity without significantly impacting the bottom line, and
reduce the
CA 2972383 2018-07-20
facilities operation costs by simplifying facilities, decreasing pipe network,
increasing
modularization and/or shortening construction cycles.
Summary Of The Invention
In one illustrative embodiment, the present invention provides for a process
for generating
steam from produced water in a hydrocarbon recovery system, the processing
comprising:
inputting a produced water stream having an initial concentration of unwanted
components [UC]i at an initial temperature (Ti) above 80 C and an initial
pressure (Pi)
above atmospheric pressure,
treating the produced water stream to produce a treated water stream having a
treated concentration of unwanted components [UC]t, a treated temperature (Tt)
and a
treated pressure (Pt), wherein treating the produced water stream comprises:
separating oil emulsion from the produced water stream to produce a
separated produced water stream; and
removing oil from the separated produced water stream using a column
flotation unit (CFU) to produce the treated water stream having a [UC]t lower
than
[UC]i; and
generating steam from the treated water stream in a steam generator,
wherein:
[UC]t is lower than [UC]i;
Tt is within 50 C or 40% of Ti; and
Pt is within 10% or 0.2 MPa of Pi.
In a further embodiment of the process or processes outlined above, Ti is
above 130 C
and Pi is >1MPa and Tt is above 80 C.
In a further embodiment of the process or processes outlined above, Ti is from
130-220 C
and Pi is >1MPa and up to 3.1 mPa and Tt is greater than 130 C and Pt is
>1MPa.
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In a further embodiment of the process or processes outlined above, the Pt is
at least at
the steam saturation pressure.
In a further embodiment of the process or processes outlined above, the
unwanted
components are in the form of oil and grease, total suspended solids,
turbidity, silica,
hardness, soluble organics and/or total dissolved solids.
In a further embodiment of the process or processes outlined above, the [UC]i
for oil and
grease is 200 mg/L or more.
In a further embodiment of the process or processes outlined above, the [UC]t
for oil and
grease is about 2 mg/L or less.
In a further embodiment of the process or processes outlined above, the [UC]i
for total
suspended solids is about 100 mg/L or more.
In a further embodiment of the process or processes outlined above, the [UC]t
for total
suspended solids is about 5 mg/L or less.
In a further embodiment of the process or processes outlined above, the [UC]i
for turbidity
is about 250 NTU or more.
In a further embodiment of the process or processes outlined above, the [UC]t
for turbidity
is about 5 NTU or less.
In a further embodiment of the process or processes outlined above, the [UC]i
for silica is
about 250 mg/L or more.
In a further embodiment of the process or processes outlined above, the [UC]t
for silica is
about 50 mg/L or less.
In a further embodiment of the process or processes outlined above, the [UC]i
for hardness
is about 25 mg/L or more.
In a further embodiment of the process or processes outlined above, the [UC]t
for
hardness is about 15 mg/L or less.
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In a further embodiment of the process or processes outlined above, the [UC]i
for soluble
organics is about 500 mg/L.
In a further embodiment of the process or processes outlined above, the [UC]t
for soluble
organics is about less than about 500 mg/L.
In a further embodiment of the process or processes outlined above, the
process or
processes further comprise using an ion exchange reaction to remove unwanted
components in the form of iron and/or hardness.
In a further embodiment of the process or processes outlined above, the
process is free
of a cooling step for reducing the initial temperature of the produced water
stream and is
to free of a de-pressurization step for reducing the initial pressure of
the produced water
stream.
In a further embodiment of the process or processes outlined above, the steam
generator
generates steam from the treated water stream having a steam quality of at
least 80%,
90% or 100%.
In a further embodiment of the process or processes outlined above, the steam
generator
is a once-through steam generator (OTSG) or a flash steam generator (FSG).
In a further embodiment of the process or processes outlined above, treating
the produced
water stream further comprises exposing the treated water stream to a
flocculation
reaction to further remove unwanted components.
In another illustrative embodiment, the present invention provides for a
system for treating
produced water and generating steam using the treated water for use in
hydrocarbon
recovery, wherein the produced water has an initial concentration of unwanted
components [UC]i at an initial temperature (Ti) above 80 C and an initial
pressure (Pi)
above atmospheric pressure, and wherein the treated water has a treated
concentration
of unwanted components [UC]t, a treated temperature (Tt) and a treated
pressure (Pt),
the system comprising:
a produced water input;
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a treatment device for treating the produced water to reduce the concentration
of
unwanted components [UC]i, wherein the treatment device comprises a column
flotation
unit (CFU) for treating the produced water; and
a steam generator for producing steam using the treated water;
wherein
[UC]t is lower than [UC]i;
Tt is within 50 C or 40% of Ti; and
Pt is within 10% or 0.2 MPa of Pi.
In a further embodiment of the system outlined above, the treatment device
further
comprises an electro-flocculation system in communication with the CFU.
In one illustrative embodiment, the present invention provides for a facility
for treating
produced water to provide treated water and for generating steam for use in
hydrocarbon recovery from the treated water, wherein the produced water has
received
emulsion treatment, wherein the produced water has an initial concentration of
unwanted
components ([UC]i), an initial temperature (Ti) that is above 80 C, and an
initial pressure
(Pi) that is above atmospheric pressure, and wherein the treated water has a
treated
concentration of unwanted components ([UC]t), a treated temperature (Tt), and
a treated
pressure (Pt), the facility comprising:
a produced water input;
a treatment device comprising a flotation type unit for treating the produced
water to
reduce the concentration of the unwanted components; and
a steam generator for generating steam from the treated water,
wherein:
the facility is free of a lime softening unit and occupies a reduced
footprint,
[UC]t is lower than [UC]i,
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CA 2972383 2018-07-20
Tt is within 50 C or 40% of Ti, and
Pt is within 10% or 0.2 MPa of Pi.
In one illustrative embodiment, the present invention provides for a process
for
generating steam from produced water in a hydrocarbon recovery system, the
processing comprising:
inputting a produced water stream into a treatment device comprising a
flotation type
unit , wherein the produced water stream has received emulsion treatment, and
wherein
the produced water stream has an initial concentration of unwanted components
([UC]i)
and an initial temperature (Ti) which is above the normal boiling point of the
produced
water at an inlet to the flotation type unit;
producing a treated water stream from the produced water stream by passing the
produced water stream through the treatment device, the treated water stream
having a
treated concentration of unwanted components ([UC]t) and a treated temperature
(Tt);
and
generating steam from the treated water stream in a steam generator;
wherein producing the treated water stream comprises passing the produced
water
stream through the flotation type unit such that the [UC]t for silica is
between about 30
ppm and about 300 ppm and the treated water stream is compatible with the
steam
generator without requiring a lime softening step.
In one illustrative embodiment, the present invention provides for a system
for treating
produced water to provide treated water and for generating steam from the
treated water
for use in hydrocarbon recovery, wherein the produced water has received
emulsion
treatment, wherein the produced water has an initial concentration of unwanted
components ([UCli), and wherein the treated water has a treated concentration
of
unwanted components ([UC]t), the system comprising:
a produced water input;
a treatment device comprising a flotation type unit for treating the produced
water
to reduce the concentration of unwanted components; and
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CA 2972383 2018-07-20
a steam generator for producing steam using the treated water;
wherein:
the produced water has an initial temperature (Ti) which is above the normal
boiling
point of the produced water at an inlet to the flotation type unit,
the treated water has a treated temperature (Tt), and
the treatment device comprising the flotation type unit is configured such
that the [UC]t
for silica is between about 30 ppm and about 300 ppm and the treated water
stream is
compatible with the steam generator without requiring a lime softening unit.
In one illustrative embodiment, the present invention provides for a facility
for treating
produced water to provide treated water and for generating steam for use in
hydrocarbon recovery from the treated water, wherein the produced water has
received
emulsion treatment, wherein the produced water has an initial concentration of
unwanted
components ([UC]i), and wherein the treated water has a treated concentration
of
unwanted components ([UC]t), the facility comprising:
a produced water input;
a treatment device comprising a flotation type unit for treating the produced
water to
reduce the concentration of unwanted components; and
a steam generator for generating steam from the treated water,
wherein:
the facility is free of a lime softening unit and occupies a reduced
footprint,
the produced water has an initial temperature (Ti) which is above the normal
boiling
point of the produced water at an inlet to the flotation type unit,
the treated water has a treated temperature (Tt), and
the treatment device comprising the flotation type unit is configured such
that the [UC]t
for silica is between about 30 ppm and about 300 ppm and the treated water
stream is
compatible with the steam generator without requiring a lime softening unit.
5b
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In one illustrative embodiment, the present invention provides for a process
for
generating steam from produced water in a hydrocarbon recovery system, the
processing comprising:
inputting a produced water stream into a treatment device comprising a
flotation type
.. unit , wherein the produced water stream has received emulsion treatment,
and wherein
the produced water stream has an initial concentration of unwanted components
([UC]i)
and an initial temperature (Ti) which is below the normal boiling point of the
produced
water at an inlet to the flotation type unit;
producing a treated water stream from the produced water stream by passing the
io produced water stream through the treatment device, the treated water
stream having a
treated concentration of unwanted components ([UC]t) and a treated temperature
(Tt);
and
generating steam from the treated water stream in a steam generator;
wherein producing the treated water stream comprises passing the produced
water
stream through the flotation type unit such that the [UCjt for silica is
between about 30
ppm and about 300 ppm and the treated water stream is compatible with the
steam
generator without requiring a lime softening step.
In one illustrative embodiment, the present invention provides for a system
for treating
produced water to provide treated water and for generating steam from the
treated water
for use in hydrocarbon recovery, wherein the produced water has received
emulsion
treatment, wherein the produced water has an initial concentration of unwanted
components ([UC]i), and wherein the treated water has a treated concentration
of
unwanted components ([UC]t), the system comprising:
a produced water input;
a treatment device comprising a flotation type unit for treating the produced
water
to reduce the concentration of unwanted components; and
a steam generator for producing steam using the treated water;
wherein:
5c
CA 2972383 2018-07-20
õ
the produced water has an initial temperature (Ti) which is below the normal
boiling point
of the produced water at an inlet to the flotation type unit,
the treated water has a treated temperature (Tt), and
the treatment device comprising the flotation type unit is configured such
that the [UC]t
for silica is between about 30 ppm and about 300 ppm and the treated water
stream is
compatible with the steam generator without requiring a lime softening unit.
In one illustrative embodiment, the present invention provides for a facility
for treating
produced water to provide treated water and for generating steam for use in
hydrocarbon recovery from the treated water, wherein the produced water has
received
emulsion treatment, wherein the produced water has an initial concentration of
unwanted
components ([UC]i), and wherein the treated water has a treated concentration
of
unwanted components ([UC]t), the facility comprising:
a produced water input;
a treatment device comprising a flotation type unit for treating the produced
water to
reduce the concentration of unwanted components; and
a steam generator for generating steam from the treated water,
wherein:
the facility is free of a lime softening unit and occupies a reduced
footprint,
the produced water has an initial temperature (Ti) which is below the normal
boiling point
of the produced water at an inlet to the flotation type unit,
the treated water has a treated temperature (Tt), and
the treatment device comprising the flotation type unit is configured such
that the [UC]t
for silica is between about 30 ppm and about 300 ppm and the treated water
stream is
compatible with the steam generator without requiring a lime softening unit.
5d
CA 2972383 2018-07-20
_
Brief Description Of The Drawings
Embodiments of the present invention will be described, by way of example,
with
reference to the drawings and to the following illustrative description, in
which:
Figure 1 is a schematic illustrating a prior art embodiment for treating
produced
water for steam generation;
Figure 2 is a schematic illustrative of one embodiment of a process for
treating
produced water and generating steam utilizing a compact flotation unit (CFU);
Figure 3 is a schematic illustrative of a further embodiment of a process for
treating produced water and generating steam utilizing a compact flotation
unit (CFU);
Figure 4 is a schematic illustrative of one embodiment of a process for
treating
produced water and generating steam utilizing an electro-flocculation (EF)
reaction;
Figure 5 is a schematic illustrating a pilot system for testing the CFU as
described in Example 1;
Figure 6 is a schematic illustrating a pilot system for testing WLS removal
described in Example 1; and
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CA 2972383 2018-07-20
Figure 7 is a schematic illustrating a pilot system for testing the EF unit
described
in Example 2.
Detailed Description
Described herein are processes, systems, apparatuses, techniques and
embodiments suitable for treating producing water by removing unwanted
components
such that the treated produced water is suitable for use in steam generation
in a
hydrocarbon production facility. It will be appreciated that the processes,
systems,
apparatuses, techniques and embodiments described herein are for illustrative
purposes
to intended for
those skilled in the art and are not meant to be limiting in any way. All
reference to dimensions, capacities, embodiments, substitutions,
modifications, optional
features or examples throughout this disclosure, including the Figures, should
be
considered non-limiting and a reference to an illustrative and non-limiting
embodiment or
an illustrative and non-limiting example. For simplicity and clarity of
illustration, reference
is numerals may be
repeated among the Figures to indicate corresponding or analogous
elements. Numerous details are set forth to provide an understanding of the
embodiments
and examples described herein. The embodiments and examples may be practiced
without these details. In other instances, well-known methods, procedures, and
components are not described in detail to avoid obscuring the examples
described. All
20 ranges referred
to herein are intended to be interpreted as being a reference to all values
of the range and should be considered a disclosure of all values with each
referred to
range. The description and claims are not to be considered as limited to the
scope of the
examples described herein.
Produced water contains unwanted components which should be removed before
25 the treated
water may be recycled and used in steam production. In conventional
treatment methods, the treatment includes the cooling and depressurization of
the
produced water followed by the removal of various unwanted components such as
oil and
grease, total hardness including calcium and magnesium, silica and total
organic carbon,
before being re-pressurized and re-heated for steam generation. A person of
skill in the
30 art will
appreciate that water entering a steam generator may also be referred to as
boiler
feed water (BFW).
6
CA 2972383 2018-07-20
Removal of a portion of these unwanted components is necessary to allow for
steam generation without substantial scale formation. Scale formation often
leads to
operability problems, for example producing an insulating effect which in turn
may result
in frequent shut downs and boiler tube failures. In order to reduce the
overall energy
expenditure as well as reduce the footprint of the hydrocarbon production
facility it is
desirable to avoid, or at least reduce the need, for cooling and de-
pressurizing the
produced water before unwanted components are removed. This reduces the
magnitude
of the energy required to re-heat and re-pressurize the treated water.
After emulsion is recovered from a hydrocarbon reservoir and treated for
coarse
to oil-water separation, produced water is typically obtained at
temperatures of between
about 80 - 250 C at various points in the process and contains unwanted
components that
should be removed before the produced water may be recycled and used in steam
generation. In a conventional system 100, such as that shown in Figure 1, the
produced
water from emulsion treatment 102 is cooled, using for example a series of
heat
exchangers 104, before it is subjected to de-oiling 106 and water treatment
108. Emulsion
treatment 102 typically comprises units such as degassers, treaters and free
water
knockout (FWKO). De-oiling 106 typically comprises several units, such as a
skim tank for
gravity separation, a flotation type unit, such as an Induced Gas Flotation
(IGF), for further
removal of suspended solids, and a filtration type unit such as an oil removal
filter (ORF).
Water treatment 108 typically includes a warm lime softener (WLS) which
increases the
pH of the water, may remove hardness in the form of calcium and magnesium as
carbonate precipitates, and removes silica. The WLS is typically followed by
an ion
exchange unit where additional removal of Ca", Mg" and iron ions occurs. The
decrease
in temperature of the produced water stream entering de-oiling 106 is
necessary in
conventional systems and processes for several reasons, for example, operation
of the
various treatment/filtration units (e.g. Skim tank, IGF and WLS) at high
pressure would be
economically unfavorable when compared to operation at atmospheric pressure.
As well,
many of the treatment units require lower temperature for effective operation.
A heat
recovery step 110 is then employed, for example, with a number of heat
exchangers, to
recover at least some of the enthalpy lost from the prior cooling steps
through heat
integration. The pressure is also increased through pumping. As is clearly
evident, a
significant input of energy and equipment is required to re-heat the treated
water exiting
the water treatment 108 and to re-pressurize the treated water before being
input into the
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CA 2972383 2018-07-20
steam generator. Typical feedwater in a steam generator is usually between
about 180-
200 C. Steam generation 112 often includes a once-through steam generator
(OTSG)
followed by a steam separator.
It has been determined that a process may be used that permits the treatment
of
produced water to remove unwanted components at or near initial produced water
temperatures and pressures thereby allowing for the use of the treated
produced water in
steam generation while significantly conserving the enthalpy in the system and
meeting
desirable boiler feed water specifications.
In various embodiments, the present invention provides for processes and
systems
for treating produced water for eventual use in steam generation that do not
require the
need for a significant reduction in temperature and/or pressure before
unwanted
components are removed thus avoiding the need for significant re-
pressurization and re-
heating of the treated water before being fed into a steam generator. These
processes
allow for the produced water to be treated at temperatures and pressures at or
near those
of the initial produced water temperature and initial produced water pressure.
Compact Flotation Unit & Removal of Lime Softener
In a series of embodiments of processes encompassed by the present invention,
a flotation type unit such as but not limited to, a compact flotation unit
(CFU) is used to
replace the skim tank, ISF/IGF and ORF thereby reducing the overall equipment
footprint
and complexity of the de-oiling operation central processing facility (CPF).
Leveraging
flotation type technology for de-oiling of the produced water has been shown
to be capable
of achieving all, or at least substantially all, the functionalities of the
individual conventional
units and replaces the skim tank, ISF/IGF and ORE with a single piece of
equipment, for
example the CFU. In addition, by utilizing a flotation unit such as a CFU, the
produced
water can be processed and treated at temperatures and pressures greater than
about
80 C and atmospheric pressure. This in turn means that produced water entering
the de-
oiling section of the facility no longer requires cooling and as a result, may
be processed
at or near the initial temperatures and initial pressures of the produced
water. The CFU
enables the throughput of a produced water containing both silica and having
hardness to
be treated, where the hardness is later removed, if required, through a
hardness removal
unit such as an ion exchange unit. Achieving suitable oil and turbidity
removal, while
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CA 2972383 2018-07-20
_
maintaining the produced water stream at an elevated pressure and temperature
in a
multistage flotation unit, allows for the simplification of the conventional
process scheme
and corresponding facility. In some embodiments, the flotation unit may also
be utilized in
debottlenecking existing operations where oil removal targets from the
produced water
stream are not consistently met, or where hydraulic capacity may be limited.
An example
of such a facility is shown with reference to Figure 2 detailing an embodiment
of a central
processing facility (CPF) system 200 encompassed by the present invention. As
shown
in Figure 2, a high efficiency flotation unit, for example, a CFU 205, has
replaced the skim
tank, ISF/IGF and ORF. It will be appreciated by those skilled in the art that
the section of
the CPF containing these units is often termed the de-oiling section. The
system 200
enables the removal of heat exchangers 104 that were previously required prior
to the de-
oiling of the produced water. In some embodiments, heat exchangers 207 may be
desirable to increase the temperature of the treated water exiting one of the
CFU 205 or
a hardness removal unit 209. For example, heat exchangers 207, in a heat
integration
step, may employ enthalpy from another location within the process, for
example an
emulsion cooling step (not shown) prior to emulsion treatment 202.
It is a widely held belief within the SAGD industry that in order to re-use
produced
water as boiler feed water, both silica and hardness need to be removed prior
to steam
generation in order to prevent scaling in steam generators, for example OTSGs.
The most
widely accepted practice in industry is to use a Lime Softener (LS) such as a
warm lime
softener (WLS) to achieve removal of these contaminants. However, and without
wishing
to be bound by theory, it is theorized by the inventors that silica may not
cause severe
scaling issues, particularly if minimal hardness is present. A LS operation is
expensive
due to chemical consumption, disposal treatment, and the use of high
maintenance
equipment. Elimination of the LS can reduce: the capital cost for new facility
phases, the
volume of required waste disposal, chemical and maintenance costs, and the
overall
facility environmental footprint. Detailed in the examples below are the
results of various
experiments performed to challenge the industry's belief that silica removal
to the
generally accepted level of about 50 ppm is required prior to steam
generation. Generally,
about 100-300 ppm silica is observed in produced water returning from
reservoir, and
validate that more efficient produced water treating can be achieved without
lime softening
at high temperature and high pressure produced water treatment conditions.
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CA 2972383 2018-07-20
Due to the current industry standard of 76-82% steam quality mode of operation
of the OTSGs for steam generation downstream of the water treatment system,
the
hardness removal unit 209 (for example an ion exchange unit or an EF reactor)
may still
be used for the removal of Ca2+ and Mg2+ ions. To prevent the silica from
precipitating out
of the solution, a high pH should be maintained in the range of 7-12. Removing
hardness
from the produced water tends to keep the silica in solution since the silica
generally reacts
with hardness to produce species with low solubility and as such the silica
will now not
react and produce highly water insoluble compounds.
By redesigning of the conventional processing template by removing the
traditional
de-oiling system as well as the conventional water treatment system which
includes lime
softening, to instead now utilize a CFU 205 in conjunction with the removal of
lime
softening, the system 200 can be operated at temperatures and pressures
greater than
80 C and atmospheric pressure, respectively. It will be appreciated by those
skilled in the
art that a CFU could be replaced by other flotation type units that could
achieve similar
performance to that described herein. Flotation units, such as a CFU, may also
be
described as high efficiency flotation units.
In another embodiment, as shown in Figure 3, the ion exchange unit may be
eliminated from the system 300, by leveraging a different steam generation
technology
downstream, such as flash steam generation 312 (FSG). FSG comprises higher
pressure
heat exchange decoupled from the phase change process (occurring in the flash
tank) to
produce dry steam at pressure for steam-assisted gravity drainage (SAGD)
operations. In
this embodiment, it is possible to eliminate a conventional system of water
treatment 108
as described above all together with this steam generation technology because
boiling of
produced water and the accompanying deposit of scale is eliminated or
significantly
reduced from the equipment while still achieving high quality steam
production. A person
of skill in the art will appreciate that a number of options exist for steam
generation from
de-oiled produced water without need for additional water treatment ,in
addition to flash
steam generation which has previously been described.
It will be appreciated that modifications, amendments and/or alterations to
the
systems, methods and concepts described herein may be carried out and are
intended to
be within the scope and spirit of the invention.
CA 2972383 2018-07-20
Electro-flocculation
In a further series of embodiments of processes of the invention, an electro-
flocculation (EF) process is applied, thereby treating the produced water at
high
temperature and pressure to remove the majority of unwanted components
(contaminants) and enabling recycling of the treated water for use in steam
generation.
In electro-flocculation (EF), or electro-coagulation (EC), an electrical
current is
applied to cause metallic ions, such as Fe2+ or AP, to dissolve in an aqueous
solution
and then form hydroxide, or other, flocs at an appropriate pH, usually without
the need of
polymer addition. These flocs serve to remove the contaminants in the water by
various
to mechanisms, such as absorption. Contaminants include scale forming
minerals, such as
calcium, magnesium, SiO2 and insoluble organics, hydrocarbons, suspensions and
emulsions, in the quantities observed in SAGD produced water as understood by
those
familiar in the art.
In a typical EF unit, there are a series of metal sheets referred to as
electrodes,
which generally are arranged in pairs of two, one anode and one cathode. At
least one of
the anode or cathode is sacrificial and is made from materials such as iron,
aluminum,
zinc, or magnesium. The ions thereof migrate into the electrolyte and bond
with or adhere
to the impurities to floc, or precipitate, these impurities with suitable pH
changes. The
primary reaction occurring at the anode is metal dissolution, as well as the
potential
oxidation of the metal ion to a higher oxidation state when exposed to oxygen.
The main
cathodic reaction is hydrogen evolution. It will be appreciated that the main
reactions in
electro-flocculation utilizing iron (Fe) anodes are as follows:
Fe(s) 4 Fe2+0q) + 2e- (1)
2H20(I) + 2e- -3 H2(g) + 20H(at) (2)
Fe2+(aq) + 20H-0q) 4 Fe(OH)2(s) (3)
A person skilled in the art will appreciate that Ohm's and Faraday's laws
provide
the basic operational and essential framework for EF. One embodiment of the
process
and system of the present invention involves integration of the EF technology
into a SAGD
facility to remove contaminants in produced water prior to entering a steam
generator.
An EF process as referred to in this application comprises an electro-chemical
or EF
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CA 2972383 2018-07-20
reactor, pH adjustments, mixing, and separation stage. Potential embodiments
are
detailed below and are intended to be illustrative of aspects of the invention
and are not
intended to be limiting:
In one embodiment, shown in Figure 4, the system 400 includes an EF unit 414
downstream of the emulsion treatment 402. The system 400, enables the removal
of heat
exchangers 104 that were previously required prior to the de-oiling of the
produced water,
such that the produced water entering the system 400 is at an elevated
temperature and
pressure as compared with the conventional system described in Figure 1 above.
Produced water flows into the EF unit 414, for example an iron reactor, where
Fe2+
to dissolves in
the produced water. The pH is adjusted to facilitate the formation of
hydroxide
flocs, which bind to the contaminants within the produced water. The reaction
may require
a suitable residence time with optional mixing, within a residence unit 416.
The residence
unit 416 may be piping or an additional vessel. These flocs are removed in a
separation
vessel 418. The separation vessel 418 may include filtration or flotation or
other
separation methods. In another embodiment, the separation vessel 418 may be a
high
efficiency flotation unit such as a CFU. Optionally, the system 400 may
further include a
hardness removal unit 409 such as ion exchange vessels (e.g., SAC/WAC), and a
unit
420 for removing excess iron and/or organics, as EF has been shown to increase
the iron
concentration in produced water and doesn't reduce soluble organic
contaminants. While
zo Figure 4 shows
unit 420 after the separation vessel 418, this unit may also be positioned
after the separation vessel. In one embodiment, unit 420 may be a two-stage
process
where excess iron is removed through an ion exchange unit and organics are
removed
using a chemical oxidation process. A skilled person in the art would
understand there
are numerous suitable options for both iron and organics removal.
In a further embodiment, where the produced water entering the system 400
comprises large quantities of free floating oil, an additional oil removal
unit (not shown)
may be included upstream of the EF unit 414. In some instances, free floating
oil in the
produced water may inhibit electro-flocculation because free oil may form a
layer on the
electrode surface. This layer may inhibit iron solubility at the electrodes.
The system shown in Figure 4 is operable at or near the initial produced water
temperature and pressure conditions, thereby obviating the need to cool and de-
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pressurize the produced water entering the system 400 and then re-heat and re-
pressurize
the treated water prior to inputting for use in steam generation 412,
In addition, the EF processes and systems described herein allow for both high
temperature / high pressure de-oiling and high temperature / high pressure
treatment of
the produced water. Implementation of the electro-flocculation systems and
processes
described herein also allows for a significant reduction in the CPF footprint
by removing
extraneous equipment, for example decreasing the reliance on storage tanks and
various
treatment vessels. This can also reduce both capital and operating expenses. A
person
of skill in the art will appreciate that operation of EF processes and systems
could be
reconfigured and continue to operate at high pressure and high temperature as
described
herein.
Examples
Example 1 - Compact Flotation & Removal of Warm Lime Softener
CFU Test Skid:
A portable compact flotation unit (CFU) test skid containing several flotation
stages was used to demonstrate the oil removal capabilities under varying test
conditions. The type of CFU utilized in this skid is described in Advances in
Compact
Flotation Units (CFUs) for Produced Water Treatment by hatnagar, M. &
Sverdrup, C.
J. Offshore Technology Conference Asia held in Kuala Lumpur, Malaysia, 25-28
March
2014 (OTC-24679-MS). A person of skill in the art will appreciate that other
CFUs may
also be used. A low shear pump at the inlet to the skid was utilized for a
lower pressure
and temperature test, but was not utilized during a higher pressure and
temperature test.
A series of hoses connected the test skid to an existing SAGD central
processing facility
(CPF) at Foster Creek in Northern Alberta. A chemical injection pump enabled a
variety
of flocculants to be dosed into the skid unit. The test skid also allowed for
a variety of
flotation gases to be tested. The separated oil and gas were recycled back to
the CPF
for processing separately from the de-oiled water. Sample valves and tubing
allowed for
the sampling of process fluid at different locations within the test skid.
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In the de-oiling process using the CFU testing skid, the produced water input
into
the skid had the following compositional characteristics:
Pressure: ranged from atmospheric to greater than 1000 kPag
Temperature: ranged from about 90 C to about 150 C
Oil content: ranged from about 0 ppm to about 500 ppm of oil in water during
normal operation, at upset conditions oil content could reach up to about
5,000
ppm
Turbidity: ranged from about 1 NTU to about 300 NTU during normal operation,
at upset conditions turbidity could reach up to about 1,000 ppm
As described in the application above, the use of a multi-stage flotation type
unit that
is capable of removing oil in water at high temperature and high pressure
operations can
either substitute for or eliminate skim tanks, gas flotation units and oil
removal filters. A
substantial reduction in land footprint is possible compared to the
conventional de-oiling
facility design.
Trial locations were selected in the de-oiling area of the plant and
downstream of the
FWKO, as shown in Figure 5 which depicts the CFU test skid installation 610 in
the
facility. Several CFU trials were completed using samples taken at various tie
points
downstream of the free water knock out (FWKO) in the existing CPF to
demonstrate the
ability to remove oil and turbidity at high temperature and pressure. The
following
parameters were adjusted to determine suitable operating parameters of the
CFU:
1. Number of stages in operation was varied by controlling flotation gas
injection.
2. Type, temperature and flow rate of the flotation gas
3. Reject water flow rate
4. Inlet water flow rate
5. Flocculant injection: chemical type and concentration
Oil removal and removal efficiency was demonstrated for each of the produced
water samples that were analyzed for oil in water concentration as measured by
a TD-
500 hand held analyzer (supplied by Turner Designs Hydrocarbon Instruments).
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Test samples were taken at the following tie in points: FWKO outlet 630,
treater
outlet 640, skim tank inlet 650, and ISF inlet 660. Typically, the duration of
each test
was about 1-2 weeks. The dotted line on Figure 5 illustrates the various tie
in points
from the CPF system to the test skid 610.
The conventional de-oiling process is able to reduce the oil in water to less
than
ppm and turbidity to less than 10 NTU under typical operation conditions and
the
current system responds well to upset conditions. Comparatively, the tested
multi-stage
compact flotation unit was able to achieve both similar oil removal efficiency
and turbidity
reduction at the outlet 670 as the current entire conventional de-oiling
process.
10 In particular, comparable oil removal to the conventional de-oiling
train shown in
Figure 1 was seen at conventional operational temperatures and pressures,
while
improved oil removal was seen at higher temperatures and pressures. Operating
at
higher pressure and temperature required slightly higher dosage of flocculent
compared
to operation at the current lower temperature and pressure conditions, likely
due to
polymer degradation at higher temperatures and higher oil demand. A person of
skill in
the art will appreciate that any of a number of established polymers,
flocculants, or a
combination thereof, for CFUs may be used in the processes and systems
described
herein.
Removal of Lime Softening (LS):
While the testing procedure and theory focused mainly on silica concentration,
the
follow-on effects of LS unit elimination were also investigated. The LS unit
affects the
concentration of other compounds and elements such as magnesium (added to LS
as
Mg(OH)2 for silica removal), calcium (added as Ca(OH)2 for pH adjustment in
LS) and also
total organic carbon (TOG), to name a few. The testing discussed below allowed
for the
observation of secondary and tertiary effects as well as reactions that are
difficult to
account for theoretically. Additionally, the chemical composition of boiler
feed water
derived from the typical water treatment train in a conventional CPF and
boiler feed water
derived from a CPF with the LS absent was monitored. In theory, where there is
no LS,
the boiler feed water will react differently when exposed to the conditions at
which steam
is produced. Some or all of the scale composition, deposition rate and
formation
mechanism will most likely show different characteristics.
CA 2972383 2018-07-20
A systematic and controlled testing procedure was developed in order to
validate
the concepts behind the theory mentioned above. The testing procedure employed
several
step changes (phases) as silica concentration in a water stream intended for
steam
generation was increased to develop a better understanding of the chemistry
and
operability of the system. As mentioned previously, though silica is the main
factor
controlled for in each phase of testing, other chemical effects were also
monitored. A pilot
system 700 for testing LS removal, in this case warm LS (WLS), is shown in
Figure 6. The
pilot system took advantage of low and high silica source tie points to
achieve overall
targeted silica concentrations between about 40 ppm and 300 ppm measured as
SiO2 for
delivery to an OTSG.
A low silica source water was derived from the existing water treatment train
that
employs a WLS to reduce the silica concentration to a range typically between
about 30
ppm and about 50 ppm. More specifically this tie point 780 is located
immediately following
the WLS, which ensures that only the effects of the WLS unit were considered
and not
additional water treatment units preceding it. A high silica source was
derived from a tie
point 790 prior to the WLS tank; this source stream is also known as de-oiled
produced
water as known to those skilled in the art and the industry. To target a
certain concentration
for each phase of testing the two source streams (pre- and post-WLS) were
mixed at
various ratios.
A WLS test skid 710 was set up to replicate the unit operations that follow
WLS in
a typical water treatment train. This includes a filtration unit and several
ion exchange unit
steps that together decrease the total suspended solids (TSS) and hardness of
the mixed
high silica produced water. The test skid 710 enabled control over the test
parameters, as
well as allowed for isolation of the test skid 710 from central processing
facility operations.
Currently, conventional thinking suggests that controlling hardness
concentration is critical
as it is directly associated with the scale formation rate. In addition, for
preventing silica
based deposition, the control of ion exchange operations is also considered
critical.
The filter prior to the ion exchange units was included in the test skid 710
for the
removal of TSS, turbidity and to some extent 'free' oil, as known to those
skilled in the art.
The hardness level was controlled to levels below what are currently targeted
in the
existing water treatment facility that employs a LS unit for example, <0.5
ppm. Even if the
LS is eliminated, hardness may be maintained at <0.5 ppm. The heightened
levels of
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substrates (e.g., silica, sodium silicate) that could bind with hardness to
produce
precipitation will push the reaction towards the product side, thus, even
fairly low levels of
hardness could be detrimental to control of scale deposition. Nevertheless,
the rate of
scale formation, operation time between mechanical cleaning (pigging) cycles
of the
boilers and cost savings observed from the elimination of LS from operations
were all
considered for setting success criteria.
The results have shown flexibility in the level of silica control which
suggests that
the current level of silica control practiced in the industry is unnecessary.
The results have
shown that a relaxing of current silica control practices and full by-pass of
the WLS are all
to possible without causing detrimental effects to the operability of the
CPF. A person of skill
in the art will appreciate that other combinations of filters, ion exchange
units, and other
equipment could be used as an alternative to the test set-up described herein
and shown
in Figure 6.
Testing began by passing a low silica stream (30-50ppm) from existing
facilities
through the WLS test skid, providing boiler feed water for steam generation
and
establishing a baseline (over a 2 week period) for steam generation at an
inlet
temperature of about 125 C to about 130 C. Samples of boiler feed water (BFW)
and
blowdown (BD) from the steam generator were regularly acquired and analyzed
for
content including silica, iron, hardness, pH, conductivity, oil & grease,
carbonate/bicarbonate, total dissolved solids, chlorides/sodium, turbidity,
TOC, dissolved
organic carbon, sulfates and TSS. Infrared thermal scans were completed after
two
weeks of baseline operation, and at least as frequently as incremental step
changes of
silica concentration were made.
Once the baseline data was gathered as described above, the OTSG feed was
switched incrementally (about every 3 months) to higher silica concentration
water blends
(e.g., 100 ppm, 150 ppm silica). The OTSG continued operating at the same
conditions
as set out in the baseline operation. Chemicals (chelant and sulfite) were
dosed as per
rates equivalent to the current conventional facilities practice, as will be
understood by a
person of skill in the art.
The OTSGs were inspected after boiler feedwater streams with the varying
silica
concentrations were tested for steam generation. The OTSG scale load was
measured
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CA 2972383 2018-07-20
to be more than what is observed in existing facility operations. However,
given that the
integrity and functionality of the OTSG was not compromised, BFW having
increased silica
concentrations was shown to successfully generate steam.
The produced water entering the inlet of the test skid unit was shown to have
average values ranging from 10-1000 ppm oil and grease, 20-1000 NTU Turbidity
and
hardness of 1-50 ppm. The treated water at the outlet of the test skid prior
to entering an
OTSG was shown to have average values below about 5 ppm oil and grease, 10 NTU
Turbidity, and 0.2 ppm hardness.
The concentration of silica at the inlet and outlet of the test skid was
essentially
1() unchanged. Testing of variations in the silica concentration of BFW
ranging from 100ppm
to a maximum concentration of about 300pm will be tested in further
experiments.
However, as noted above, higher silica concentrations in BFW have been shown
to
successfully generate steam indicating that the improved system 200 can be
successfully
implemented.
In experiments performed, it was observed that the boiler can be operated at
commercial conditions for 250 days under a 90 ppm ¨ 280 ppm range of silica
concentrations, compared to industry's practice of operating at a
concentration of about <
50 ppm silica. All monitored parameters and inspections indicated that the
test boiler
utilized for the experiments was in good condition with no integrity issues.
The boiler tube
conditions remained consistent with those obtained prior to LS removal. The
treated water
at the outlet of the test skid prior to entering the OTSG showed the same
quality as the
treated water in the existing water treatment train that employs a WLS (the
exception being
the higher silica concentrations tested), with average treated water outlet
values below
about 5 ppm oil and grease, 10 NTU turbidity, and 0.2 ppm hardness.
Example 2 - Electro-flocculation
A trial was performed at a SAGD facility at Foster Creek in Northern Alberta
to
confirm that the EF technology described in Figures 4 can remove the necessary
contaminants found in SAGD produced water to a similar degree as the current
de-oiling
water treatment process at atmospheric conditions. A pilot system 800 for
testing an EF
.. unit 810 in a CPF is shown in Figure 8. Using an EF test skid 810,
operating on the
theoretical principles previously described, we were able to successfully
treat a source of
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produced water over the course of 2 weeks of testing period with typical
industry
contaminant concentrations for SAGD produced water, e.g., 0-500 mg/L oil, 1-
300 NTU,
100-800 mg/L TSS, 100-300 mg/L silica, 10-50 mg/L hardness (as CaCO3), 400-600
mg/L
soluble organics (TOC). A person of skill in the art will appreciate that
typical contaminant
concentrations will vary depending on the type of reservoir and hydrocarbon
recovery
operations. The EF test skid 810 was configured for testing atmospheric
conditions and at
a temperature between about 20-60 C, lower than the about 90 C operating
temperature
of the facility, and so the produced water was let cool prior to entering the
EF unit 810.
Contaminant removal was successfully demonstrated at these conditions.
The test skid and process described herein, was comprised mainly of a pH pre-
adjustment, an EF unit (also referred to as an iron reactor in this example),
pH after-
adjustment, a mixing chamber, and filtration to remove flocs. When in the
reactor, iron(II)
enters the solution and forms iron(II) hydroxide flocs. A person of skill in
the art will
appreciate that some iron(III) may be produced by oxidation of iron with air
at the surface
of the basin. Microbubbles are also formed which attach to the flocs and float
them to the
top of the reactor. A rectifier produced a constant current across the
electrode plates within
the reactor. The operating voltage is generally between about 4 and 10 V.
Variation in the
conductivity of the feed water is compensated for by changes in the voltage
during normal
operation. The number of electrodes was varied depending on conductivity of
the feed
water being tested, with more electrodes used for lower conductivity water
feeds. pH
adjustments varied as appropriate to facilitate floccing. pH was pre-adjusted
between 6-8
by dosing with acid (e.g., HCI) when applicable for proper iron dissolution
and pH after-
adjustment to between 9 and 10 was performed by dosing with caustic (e.g.,
NaOH) to
facilitate large Fe(OH)2 floc formation without the addition of other
chemicals.
Inlet produced water was comprised of the following approximate contaminant
concentration ranges during testing: 200-500 mg/L oil, 100-800 mg/L TSS, 100-
300
mg/L silica, 10-50 mg/L hardness (as CaCO3), 400-600 mg/L soluble organics
(TOC).
The conductivity of the produced water was between 2-4 mS/cm. These levels may
vary
during normal process operation. The testing demonstrated average oil removal
of
>99%, TSS removal of 98%, silica removal of 96%, hardness removal of 72%, and
TOC
removal of 50%, generating a treated water suitable for steam generation. A
person of
skill in the art will appreciate that water contamination parameters targeted
for steam
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CA 2972383 2018-07-20
generation will vary depending on the particular source water and hydrocarbon
recovery
operations being performed.
Testing supports the feasibility of designing and building a process system
incorporating EF technology as shown in Figures 4. EF technology provides a
number
of advantages over current practices, including a significant reduction in
capital and
operating expenditures.
Based on results from the on-site tests, electro-flocculation is suitable for
replacing the conventional de-oiling and water treatment equipment up to WAC
polishers, working at atmospheric pressure. Such a configuration is shown in
Figure 4.
to The Applicants predict based on the testing conducted to date, that
solubility of
almost all inorganic salts (i.e., Fe(OH)2) will change only slightly when
temperature
increases to about 135 C or more making operation at high temperature and high
pressure feasible. (Yoshio Nishi, Robert Doermig, Handbook of Semiconductor
Manufacturing Technology (2007); Selji Sawamura, High-pressure investigations
of
solubility, Pure Appl. Chem., Vol. 79, No. 5, pp. 861-874, (2007); and L. M.
Dorfman, G.
E. Adams; Reactivity of the Hydroxyl Radical in Aqueous Solutions, Ohio State
University, Columbus, Ohio 43210, (1973). Based on this understanding and the
test
data described above, EF may be implemented under high temperature, high
pressure
operating conditions (as shown in Figure 4).
It will be appreciated that various modifications, changes, adaptations and
substitutions may be made to the embodiments disclosed and claimed herein
without
departing from the scope and spirit of the invention and such modifications,
changes,
adaptations and substitutions are intended to be captured by the scope and
spirit of the
disclosure and claims. The disclosure provides embodiments for the purposes of
illustrating the invention and is not intended to limit the scope of the
claims.
CA 2972383 2018-09-07
