Note: Descriptions are shown in the official language in which they were submitted.
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SYSTEMS AND METHODS FOR STEAM PRODUCTION
FIELD OF THE INVENTION
The present disclosure generally provides systems and methods for producing
steam for
use in various applications, including enhanced oil recovery processes. In
particular, the present
disclosure provides systems and methods that comprise an electrode boiler and
one or more heat
exchangers and use of such boiler and heat exchangers for steam production.
B ACK GROUND
Steam is useful in many applications, particularly in thermal enhanced oil
recovery (EOR)
technique. Thermal EOR generally involves injecting steam into an oil-bearing
formation to free
up and reduce the viscosity of the oil. Representative steam injection
techniques include cyclic,
steamflood, steam-assisted gravity drainage (SAGD), and other strategies using
vertical and/or
horizontal injection wells, or a combination of such wells, along with
continuous, variable-rate,
and/or intermittent steam injection in each well.
Thermal EOR operations often require steam production over a period ranging
from many
days to many years. During recovery of hydrocarbons from wells, water
containing some residual
hydrocarbons is also produced from the wells ("produced water"). The produced
water may have
high levels of calcium and magnesium, a high salt concentration, high organic
content in the form
of dissolved oil, and may be more acidic than other boiler feedwater that has
a pH closer to neutral
pH. Typically, this produced water can be provided to gas-fired boilers, after
minimal or no
treatment, as Boiler Feedwater (BFW) to generate the steam.
A representative gas-fired steam production system is a Once Through Steam
Generator
(OTSG), such as illustrated in, for example, US20110017449. An OTSG produces
steam by
contacting water in a single pass heat exchanger with the heat from a
combustion process. Yet
another steam generating system includes heat recovery steam generators (HRSG)
contacting the
combustion gas from a gas turbine in a single pass heat exchanger with the
water, operating in a
continuous mode. However, both rely on fossil fuel firing and hence emit CO2,
which contributes
significantly to the carbon intensity of the crude oil produced.
Concentrated solar power has been employed to generate steam through directing
sunlight
onto a pipe containing either the produced water to directly generate steam
(such as
U52020185586 or US20140318792), or a heat transfer fluid which is sent to a
heat exchanger to
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generate steam from the produced water (such as US4513733). However, the cost
of concentrated
solar technology can be relatively higher than other renewable resources.
Another representative steam production system involves electric-powered
boilers, such as
disclosed by US6205289. However, the produced water from EOR is typically not
suitable for
use as BFW for the electrode boilers referenced in this application. While the
produced water can
be treated to remove hardness, hydrocarbons, salts and other impurities, such
treatment would
usually be cost prohibitive for thermal EOR applications that often need large
quantities of
produced water to be converted to steam. While other electric boilers could be
used, like resistive
heaters, these have similar challenges as those of electrode boilers in that
extensive water clean-
up could be required, while they are also significantly less costs effective
than electrode boilers.
As such, there is still a need for steam producing systems and methods that
address these
challenges.
SUMMARY
Accordingly, the present disclosure provides a method for generating steam
comprising
providing feedwater having an electrical conductivity of less than 200 p.S/cm
to an electrode boiler,
wherein the electrode boiler has a capacity of at least 5 megawatts (MW);
converting the feedwater
to saturated steam by the electrode boiler, wherein the saturated steam has a
pressure in a range from
at least 3.5 MPa and up to 14 MPa and a temperature in a range from 240
degrees C and up to 340
degrees C; providing the saturated steam as a first fluid to a heat exchange
component; providing
water having an electrical conductivity of more than 200 p.S/cm as a second
fluid to the heat
exchanger; heating the second fluid in the heat exchange component through
indirect thermal transfer
with the saturated steam to generate wet steam having a temperature lower than
the temperature of
the saturated steam by a range from 2 degrees C and up to 30 degrees C and a
pressure in a range
from at least 0.5 MPa and up to 13 MPa; at least partially condensing the
saturated steam in the heat
exchange component through indirect thermal transfer with the second fluid to
produce a condensed
fluid; and providing at least a portion of the condensed fluid to the
electrode boiler for use as part of
the low-conductivity water to generate said saturated steam.
The present disclosure also provides for a system for generating steam
comprising an
electrode boiler configured to convert feedwater having an electrical
conductivity of less than 200
p.S/cm to saturated steam having a pressure in a range from 3.5 MPa and up to
14 MPa and a
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temperature in a range from 240 degrees C and up to 340 degrees, wherein the
electrode boiler has a
capacity of at least 5 megawatts (MW); a heat exchange component in fluid
communication with the
electrode boiler to receive the saturated steam, where said heat exchanger is
configured to receive
water having an electrical conductivity of more than 200 p.S/cm as a second
fluid to the heat exchanger
and allow indirect thermal transfer between the saturated steam and the second
fluid to convert (i) the
second fluid into wet steam having a temperature lower than the temperature of
the saturated steam
by a range from 2 degrees C and up to 30 degrees C and a pressure in a range
from at least 0.5 MPa
and up to 13 MPa and (ii) the saturated steam into a condensed fluid. The
system further comprises
a recycle line between an outlet of the heat exchanger and an inlet of the
electrode boiler to provide
at least a portion of the condensed fluid to the electrode boiler for use as
the feedwater generate the
saturated steam.
At least a portion of the wet steam may be employed for injection into a
subsurface
hydrocarbon formation for hydrocarbon recovery. The system is particularly
suitable to supply wet
steam to equipment for steam injection in thermal EOR.
BRIEF DESCRIPTION OF THE DRAWINGS
The following figures are included to illustrate certain aspects of the
present disclosure and
should not be viewed as exclusive embodiments. The subject matter disclosed is
capable of
considerable modifications, alterations, combinations, and equivalents in form
and function, as
will occur to one having ordinary skill in the art and the benefit of this
disclosure.
FIG. 1 is a schematic illustration of a system that includes an electrode
boiler and a heat
exchanger configured in accordance with an embodiment of the presently
disclosed technology.
FIG. 2 is a schematic illustration of a system that includes an electrode
boiler and two heat
exchangers configured in accordance with another embodiment of the presently
disclosed technology.
FIG. 3 is a schematic illustration of a system that includes an electrode
boiler and two heat
exchangers configured in accordance with yet another embodiment of the
presently disclosed
technology.
DETAILED DESCRIPTION
The present disclosure generally provides systems and methods for producing
steam for
use in enhanced oil recovery processes, including systems and methods
comprising an electrode
boiler and one or more heat exchangers for steam production. Specific details
of various
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embodiments of the disclosed steam production systems and methods are
described below in detail
as illustrated in the accompanying drawings. References to "one embodiment,"
"an embodiment,"
"an example embodiment," etc., indicate that the embodiment described may
include a particular
feature, structure, or characteristic, as an option but every embodiment may
not necessarily but
can include the particular feature, structure, or characteristic. Moreover,
such phrases are not
necessarily referring to the same embodiment. In some instances, well known
process steps and/or
structures may have not been described in detail in order to not unnecessarily
obscure the present
invention. The depiction of some of such features in the figures does not
indicate that all of them
are depicted. In addition, when like elements are used in one or more figures,
identical reference
characters will be used in each figure, and a detailed description of the
element will be provided
only at its first occurrence.
Pressure values are specified in units of gauge pressure.
A method is proposed for generating steam comprising providing feedwater
having an
electrical conductivity of less than 200 p.S/cm to an electrode boiler. The
feedwater is converted to
.. saturated steam by the electrode boiler. The saturated steam is provided as
a first fluid to a heat
exchange component. A second fluid, consisting of water having an electrical
conductivity of more
than 200 p.S/cm is also proficed to the heat exchange component. In the heat
exchange component,
the second fluid is heated through indirect thermal transfer with the
saturated steam, to generate wet
steam having a temperature lower than the temperature of the saturated steam
and a pressure in a
range from at least 0.5 MPa and up to 13 MPa. The saturated steam is thereby
at least partially
condensed in the heat exchange component through said indirect thermal
transfer with the second
fluid, to produce a condensed fluid. At least a portion of the condensed fluid
is provided to the
electrode boiler for use as part of the low-conductivity water to generate
said saturated steam.
The electrode boiler may have a capacity of at least 5 megawatts (MW).
The saturated steam preferably has a pressure in a range from at least 3.5 MPa
and up to 14
MPa, and a temperature in a range from 240 degrees C and up to 340 degrees C.
The wet steam
discharged from the heat exchange component may have a temperature lower than
the saturation
steam by a range from 2 degrees C and up to 30 degrees C.
Optionally, at least 50%, preferably at least 75%, or more preferably at least
99% of the
condensed fluid is provided to the electrode boiler for use to generate said
saturated steam.
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Optionally, the step of heating the second fluid in the heat exchange
component to generate
wet steam comprises providing a first portion of the saturated steam to a
first heat exchanger of the
heat exchange component; providing the second fluid to the first heat
exchanger; heating the second
fluid in the first heat exchanger through indirect thermal transfer with the
first portion of the saturated
steam to generate a pre-heated second fluid; providing the pre-heated second
fluid to a second heat
exchanger of the heat exchange component; providing a second portion of the
saturated steam to the
second heat exchanger; and heating the pre-heated second fluid in the second
heat exchanger through
indirect thermal transfer with the second portion of the saturated steam to
generate the wet steam.
The first heat exchanger may provide from 30% and up to 45% of the total
thermal energy
needed to convert the second fluid to wet steam. Preferably, the pre-heated
second fluid is in liquid
phase. In this context, a small amount of vapor, for example up to 0.1% in
mass may be acceptable.
Optionally, the step of heating the second fluid in the heat exchange
component to generate
wet steam comprises providing the second fluid to a first heat exchanger of
the heat exchange
component; heating the second fluid in the first heat exchanger through
indirect thermal transfer with
a condensed fluid from a second heat exchanger of the heat exchanger component
to generate a pre-
heated second fluid; providing the pre-heated second fluid to the second heat
exchanger; providing
the saturated steam to the second heat exchanger; heating the pre-heated
second fluid in the second
heat exchanger through indirect thermal transfer with the saturated steam to
generate the wet steam;
and at least partially condensing the saturated steam in the second heat
exchanger through indirect
thermal transfer with the pre-heated second fluid to produce the condensed
fluid.
The first heat exchanger may provide from 30% and up to 45% of the total
thermal energy
needed to convert the second fluid to the wet steam. Preferably, the pre-
heated second fluid is in
liquid phase. In this context, a small amount of vapor, for example up to 0.1%
in mass may be
acceptable.
An advantage of pre-heating the second fluid to a temperature whereby the
second fluid is
still substantially in full liquid phase, is that the control and operation of
the second heat exchanger
is decoupled from any temperature variations in the initial feed of the second
fluid. This improves
the steam quality control.
Optionally, the method further comprises providing at least a portion of the
wet steam for
injection into a subsurface hydrocarbon formation for hydrocarbon recovery.
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Optionally, the electricity powering the operation of the electrode boiler
comprises green
energy, optionally selected from a group consisting of solar photovoltaic
panels, wind turbines,
hydropower, a battery charged with any one or more of the foregoing, and any
combination thereof.
Optionally, at least a portion of the electricity is generated by one or more
solar photovoltaic panels.
Optionally, the electrode boiler is powered completely by green energy
produced by a power source
that is not connected to a public electric grid. The power source and the
electrode boiler may be
connected to one another with an islanded power grid. Optionally, the power
source comprises an
islanded solar PV microgrid.
Optionally, the method further comprises providing at least a portion of the
green energy for
.. use by the hydrocarbon recovery site.
A system for generating steam is proposed, which comprises an electrode boiler
configured
to convert feedwater having an electrical conductivity of less than 200 pS/cm
to saturated steam, a
heat exchange component in fluid communication with the electrode boiler to
receive the saturated
steam, where said heat exchanger is configured to receive water having an
electrical conductivity of
more than 200 pS/cm as a second fluid to the heat exchanger and allow indirect
thermal transfer
between the saturated steam and the second fluid to convert (i) the second
fluid into wet steam having
a temperature lower than the temperature of the saturated steam and (ii) the
saturated steam into a
condensed fluid. The system further comprises a recycle line between an outlet
of the heat exchanger
and an inlet of the electrode boiler to provide at least a portion of the
condensed fluid to the electrode
boiler for use as the feedwater generate the saturated steam.
The system is particularly suitable to supply wet steam to equipment for steam
injection in
thermal EOR. The heat exchange component may be fluidly connected to a wet
steam conduit to
receive the wet steam from the heat exchange component and route the wet steam
to equipment for
steam injection in thermal EOR. The wet steam conduit may suitably be
connected to equipment for
steam injection in thermal EOR
Optionally, the heat exchange component further comprises a first heat
exchanger in fluid
communication with the electrode boiler to receive a first portion of the
saturated steam, wherein the
first heat exchanger is configured to receive the second fluid and allow
indirect thermal transfer
between the first portion of the saturated steam and the second fluid to
generate a pre-heated second
fluid; and a second heat exchanger in fluid communication with the first heat
exchanger to receive the
pre-heated second fluid, wherein the second heat exchanger is configured to
receive a second portion
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of the saturated steam and allow indirect thermal transfer between the second
portion of the saturated
steam and the pre-heated second fluid to generate the wet steam; where the
first heat exchanger has a
heat transfer surface area less than a heat transfer surface area of the
second heat exchanger.
Optionally, the heat exchange component further comprises: a first heat
exchanger in fluid
communication with a second heat exchanger to receive a condensed fluid,
wherein the first heat
exchanger is configured to receive the second fluid and allow indirect thermal
transfer between the
condensed fluid and the second fluid to generate a pre-heated second fluid.
The second heat
exchanger is in fluid communication with the first heat exchanger to receive
the pre-heated second
fluid, wherein the second heat exchanger is configured to receive the
saturated steam and allow
indirect thermal transfer between the saturated steam and the pre-heated
second fluid to generate the
wet steam; where the first heat exchanger has a heat transfer surface surface
less than a heat transfer
surface area of the second heat exchanger.
Optionally, the heat transfer surface area of the first heat exchanger is less
than 50%
the heat transfer surface area of the second heat exchanger. Optionally, the
electricity powering the
operation of the electrode boiler comprises green energy, optionally selected
from a group consisting
of solar photovoltaic panels, wind turbines, hydropower, a battery charged
with any one or more of
the foregoing, and any combination thereof Optionally, the electrode boiler is
powered completely
by green energy produced by a power source that is not connected to a public
electric grid. The power
source and the electrode boiler may be connected to one another with an
islanded power grid.
Optionally, the power source comprises an islanded solar PV microgrid.
FIG. 1 is a partially schematic illustration of an overall system 100 used to
generate steam.
System 100 comprises at least one electrode boiler 102 (may also be referred
to as an electrode
boiler) in fluid communication with heat exchange component 104. It is
understood by one of
ordinary skill that the at least one electrode boiler can include a plurality
(i.e., two or more) of
electrode boilers connected in parallel. Electrode boiler 102 receives
feedwater, such as via line 124
and/or line 116 as further discussed below, having an electrical conductivity
of less than 200 micro
Siemens per cm (p.S/cm), preferably less than 10 p.S/cm, and most preferably
less than 5 p.S/cm, and
produces saturated steam with a pressure in a range from 3.5 MPa and up to 14
MPa, including from
3.5 MPa and up to 14 MPa, preferably from 6.5 MPa and up to 14 MPa, and more
preferably from
and up to 8.5 MPaal 4 MPa. The saturated steam has a corresponding saturated
steam temperature in
a range from 240 and up to 340 degrees C. At least a portion of the saturated
steam is provided to
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first inlet 106 of heat exchange component 104 via a suitable means, such as
line 108, which saturated
steam can be used to heat up a second fluid in heat exchange component 104 to
convert the second
fluid to wet steam. One of ordinary skill would understand that the
temperature and pressure of the
produced wet steam is lower than the temperature and pressure of the saturated
steam provided to
inlet 106 as a function of the thermal transfer that takes place in heat
exchange component 104.
Preferably, the wet steam exiting heat exchange component 104 has a
temperature lower than the
temperature of the saturated steam at inlet 106 in a range from 2 degrees C
and up to 30 degrees C,
including preferably from 5 degrees C and up to 25 degrees C lower, and more
preferably from 10
degrees C and up to 20 degrees C lower. Preferably, the wet steam exiting heat
exchange component
104 has a pressure in a range from 0.5 MPa and up to 13 MPa, including from
0.5 MPa and up to 13
MPa, preferably from 5.5 MPa and up to 13 MPa, and more preferably from 6.5
MPa and up to 13
MPa.
The second fluid can be provided to second inlet 110 of heat exchange
component 104. The
wet steam exits heat exchange component 104 in a suitable manner, such as
through first outlet 112,
and can be used in any suitable application, including being routed to
equipment for steam injection
in thermal EOR. A wet steam conduit 113 may suitably be provided to receive
the wet steam from
the first outlet 112 and to route the wet steam.
The steam quality of the produced wet steam may be limited by the content and
amount of
dissolved solids in the second fluid. Steam quality has the meaning as
understood by one of ordinary
skill, which is the mass percentage of the fluid that is in vapor phase.
Preferably, the steam quality is
kept at a predetermined value (minus a safety margin) which is determined by
the precipitation point
of solids in the second fluid, where by precipitation is avoided. The
precipitation point is generally
content-specific, and it can be determined by modeling and/or empirically. The
predetermined value
of steam quality is preferably as high as possible within the bounds of
avoiding precipitation.
The quality of the produced wet steam depends at least on the flow rate of the
second fluid
provided to second inlet 110. For instance, for a particular amount of
saturated steam, a higher flow
rate of the second liquid produces wet steam with a lower quality as compared
to a lower flow rate.
The quality of the produced wet steams also depends on the amount of saturated
steam provided to
heat exchange component 104. For instance, for a particular flow rate of the
second liquid, the greater
the amount of saturated steam in heat exchanger component 104, the higher the
quality of the wet
steam produced as compared to a lower amount of saturated steam. The amount of
saturated steam
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provided to heat exchange component 104 depends on a number of factors, one of
which is the amount
of power supplied to electrode boiler 102. Additional descriptions around the
power supply of
electrode boiler 102 is further provided in subsequent paragraphs. As such,
one of ordinary skill can
select operating parameters of the methods and systems described herein to
produce wet steam with
a steam quality in a range from 10% and up to 99%, preferably from 30% and up
to 90%, and most
preferably, at least 50%, including from 50% and up to 80%.
The rate at which the second fluid is supplied to heat exchange component 104
depends at
least on the operating conditions of electrode boiler 102 to achieve a desired
steam quality. As such,
for a given power, one of ordinary skill can adjust the second fluid flow
rate, or for a given flow rate,
one of ordinary skill can adjust the power input to one or more electrode
boilers to achieve a desired
quality of the wet steam produced in heat exchange component 104.
In heating the second fluid, the saturated steam is partially or completely
condensed in heat
exchange component 104 through indirect thermal transfer to produce a
condensed fluid that exits
heat exchange component 104 in a suitable manner, such as through second
outlet 114. As used
herein, "condensed" or "condensed fluid" means at least partially condensed,
including fully
condensed, or a fluid that is at least partially condensed (contains both
liquid and vapor), including
fully condensed (a liquid), respectively and for both as context dictates.
Because the saturated steam
does not come in direct contact with the second fluid in heat exchange
component 104, the electrical
conductivity properties of the condensed fluid remains substantially the same
as those of the feedwater
provided via line 124. As such, at least a portion of the condensed fluid can
be recycled back to
electrode boiler 102, using a suitable means such as via line 116 and pump
118, for use as part of a
portion of the feedwater used to produce the saturated steam. Optionally,
substantially most,
including all, of the feedwater provided to electrode boiler 102 consists of
the condensed fluid that
exits heat exchange component 104, such as preferably at least 50%, more
preferably at least 75%,
and most preferably at least 99% of the feedwater of electrode boiler 102
consists of the condensed
fluid. As shown in FIG. 1, in case the condensed fluid exiting second outlet
114 comprises steam that
has not condensed to liquid, prior to returning to electrode boiler 102 as
feedwater, the condensed
fluid can optionally pass through condensate vessel 120 to separate liquid
from uncondensed steam
so that liquid is fed to pump 118 for use as the feedwater for electrode
boiler 102.
Referring to FIG. 1, electrode boiler 102 is powered by electricity and
generates steam from
the feedwater by using a number of electrodes that are in contact with the
feedwater. Thermal energy
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is generated by passing an AC electrical current from an electrode to a
counter electrode using the
water as conductor, and the generated thermal energy heats up the feedwater to
generate the saturated
steam. Suitable electrode boilers include those described in W02010095954 and
can be operated to
produce saturated steam having a pressure in a range from 3.5 MPa and up to 14
MPa, including from
3.5 MPa and up to 14 MPa, preferably from 6.5 MPa and up to 14 MPa, and more
preferably from
8.5 MPa and up to14 MPa. The saturated steam has a corresponding saturated
steam temperature in
a range from 240 and up to 340 degrees C.
Because electrode boilers are powered by electricity as compared to fossil
fuel boilers, they
have the following advantages: environmentally friendly with no emissions of
products from
combustion, close to 100% efficient in converting power to heat with only a
minimal percentage of
radiation and convection loss from the exposed surfaces of the boiler, easy
control of output range
and a fast startup, as well as being more compact with smaller volume and
footprint for the same
capacity than fossil fired boilers. Another type of electric-powered boiler is
electric resistance boilers,
which uses an electrically resistive element to generate heat, which is
transferred to the feedwater,
heating it to the desired temperature. While electric resistance boilers have
similar advantages as
described above for electrode boilers and can be used as described herein,
electrode boilers are
preferred because they typically have lower costs. Optionally and preferably,
electrode boiler 102
has a capacity of at least 5 megawatts (MW), preferably at least 10 MVV, more
preferably at least 15
MVV, which corresponds to a saturated steam production capacity of
approximately at least 7 metric
tons, preferably at least 15 metric tons, and more preferably at least 23
metric tons of steam per hour.
The actual steam production rate generally depends on a number of factors,
including the efficiency
of the particular electrode boiler used, the power supplied to the electrode
boiler and the desired
quality of wet steam produced.
Feedwater having an electrical conductivity of less than 200 p.S/cm can
generally be used with
different types of electrode boilers, such as jet electrode or immersed
electrode types, as applicable.
At less than 200 p.S/cm, the feedwater is considered "low-conductivity" and
has only a minimal
amount of mineral (essentially demineralized water) to control water
conductivity to avoid arcing and
the current between the electrodes being above suitable operating conditions.
Depending on the type
of electrode boiler, lower conductivity feedwater may be preferred, such as
less than 10 p.S/cm, or
less than 5 p.S/cm.
As described, electrode boiler 102 generates saturated steam having a pressure
in a range from
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3.5 MPa and up to 14 MPa, including from 3.5 MPa and up to 14 MPa, preferably
from 6.5 MPa and
up to 14 MPa, and more preferably from 8.5 MPa and up to 14 MPa. The saturated
steam has a
corresponding saturated steam temperature in a range from 240 and up to 340
degrees C As used
herein, saturated steam has its ordinary meaning. In particular, saturated
steam occurs when the liquid
and gaseous phases of water exist simultaneously at a given temperature and
pressure. When heat is
applied to water at a particular pressure, the temperature of the water
continues to rise until it reaches
its boiling point at that pressure. Saturated steam is generated when all of
the water (that is, 100%)
has reached the boiling point at a particular pressure but has not been heated
above that boiling point.
As such, saturated steam is in equilibrium with heated water at the same
pressure. For instance,
saturated steam exists at approximately 100 C (212 F) at atmospheric pressure.
Saturated steam is
dry, meaning it does not contain any water droplets. If the temperature of
saturated steam decreases
below the boiling point at a particular pressure, however, the saturated steam
no longer exists and
reverts back to water. Wet steam occurs when at least some but less than 100%
of the water has been
converted to steam, meaning wet steam contains droplets of water. Because heat
is added to water in
electrode boiler 102, saturated steam is the product and not superheated steam
which is produced
when heat is added to steam.
Although electrode boilers have many advantages to produce steam, one
potential challenge
is the requirement for low-conductivity water, which can be costly to produce
particularly in industrial
applications such as thermal EOR, which has typically employed steam
production in in a once
through fashion using gas-fueled boilers without recycling of the feedwater.
Embodiments of the
steam production systems and methods described herein address this potential
challenge through use
of a heat exchanger to transfer the thermal energy from the saturated steam
produced by the electrode
boilers to heat water of lower quality to generate wet steam. That is, water
having an electrical
conductivity of more than 200 uS/cm is used as a second fluid that is heated
by the saturated steam
in heat exchange component 104 to become wet steam. Water with an electrical
conductivity of
more than 200 uS/cm may be referred to as "lower quality water."
Because the saturated steam does not come in direct contact with the lower
quality water in
the embodiments described herein, it maintains the electrical conductivity of
less than 200 uS/cm and
can continue to be the feedwater for producing saturated steam in the
electrode boiler. As such,
embodiments of the present systems and methods allow use of electrode boilers
to produce steam
from lower quality water with minimal need for costly purification systems to
replenish the suitable
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feedwater for such electrode boilers to meet the steam demands in various
applications, including
industrial applications that typically require steam production at large
scale, such as at least 5 MVV.
One particularly suitable source of lower quality water to be heated to wet
steam for use in
thermal EOR is water produced from the well(s) located at the site that is
using the thermal EOR to
recover hydrocarbons ("produced water"). The proximity of the available water
source provides
many advantages, particularly cost savings inherent with minimizing the need
to transport water from
a different location. This source of water for steam production would not be
available to electrode
boilers unless treated to render it suitable as feedwater, which treatment can
be cost prohibitive. This
is because the produced water has dissolved solids such as salts, dispersed
and dissolved organic
content from the hydrocarbons, and a lower pH than suitable feedwater for
electrode boilers. These
contaminants, such as salts, results in the produced water having an
electrical conductivity level
higher than the operational specifications for electrode boilers. The
dispersed oil can potentially form
foam which interferes with level measurements and/or causes a short-circuit.
The systems and methods described herein can produce steam directly from
untreated
produced water using electrode boilers, even though the option to treat the
produced water in some
manner prior to being used for steam production is available if desired.
A suitable type of heat exchanger for use as heat exchange component 104 is
the shell-and-
tube heat exchanger as known to one of ordinary skill. In general, a shell-and-
tube heat exchanger
includes a shell (usually a large pressure vessel) with a bundle of tubes
inside the shell. One fluid
runs through the tubes, and another fluid flows over the tubes (through the
shell) to transfer heat
between the two fluids. The set of tubes is called a tube bundle, and may be
composed of several
types of tubes: plain, longitudinally finned, etc. Suitably, the lower quality
water runs through the
tubes while the saturated steam from the electrode boiler flows over the tube
through the shell. It is
within the skills of one of ordinary skill in the art to select the
configurations and operating parameters
of the heat exchanger to heat the lower quality water and produce wet steam at
a pressure that is
sufficiently lower than the saturated steam provided at inlet 108 to enable
heat exchange between the
two fluids, and quality from 10% and up to 99%. Some exemplary operating
parameters include flow
rate of the saturated steam, flow rate of the lower quality water, and the
operating pressure of the heat
exchanger. Other suitable heat exchangers can include hairpin type exchangers.
Electrode boiler 102 may be at least partially or fully powered by various
types of renewable
electricity as further described in this disclosure. For embodiments in which
electrode boiler 102 is
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powered directly by a renewable electricity source that is not constantly
available, the production of
saturated steam by electrode boiler 102 can vary corresponding to the power
supply, including periods
where no power is available to operate electrode boiler 102, which periods can
occur frequently. The
potentially varying amount of saturated steam entering heat exchange component
104, particularly
during potential periods of no saturated steam in heat exchange component 104,
in turn, can introduce
frequent and/or sudden changes to the operating temperature of heat exchange
component 104. Such
potential temperature fluctuations can pose a challenge to the mechanical
integrity of heat exchange
component 104.
One option to address the potential challenge of temperature fluctuations is
shown in system
200 of FIG. 2 and system 300 of FIG. 3 in which heat exchange component 104
comprises at least
two heat exchangers: first heat exchanger 204A and second heat exchanger 204B.
As noted above,
when like elements are used in one or more figures, identical reference
characters will be used in
each figure. For purposes of brevity and ease of reading, a detailed
description of the element will
be provided only at its first occurrence, which is FIG. 1 in this instance,
and not repeated for FIGS.
.. 2 and 3.
Referring to FIGS. 2 and 3, the second fluid is heated in first heat exchanger
204A to generate
a pre-heated second fluid that enters second heat exchanger 204B for
conversion to wet steam.
Suitably, first heat exchanger 204A is configured to heat the second fluid
while maintaining it as a
liquid. In each of these embodiments, the second fluid is provided through the
second inlet 110A of
the first heat exchanger 204A.
Preferably, the second fluid is heated in first heat exchanger 204A to a
temperature that is at
least 100 degrees C, preferably at least 50 degrees C, more preferably at
least 25 degrees C, and most
preferably at least 5 degrees C, below the boiling point of water at the
operating pressure of first heat
exchanger 204A to generate pre-heated second fluid that exits first outlet
112A of first heat exchanger
.. 204A via line 222 and enters second inlet 110B of second heat exchanger
204B. The pre-heated
second fluid is then further heated in second heat exchanger 204B to generate
wet steam as described
above with respect to system 100. As with system 100, the wet steam may be
received in wet steam
conduit 113.
Suitably, pre-heating the second fluid in first heat exchanger 204A involves
less thermal
energy than generating wet steam in second heat exchanger 204B. Referring to
FIGS. 2 and 3, first
heat exchanger 204A is configured to deliver in a range from 30% and up to 45%
of the total amount
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of thermal energy (or heat duty) needed to convert the second fluid to wet
steam. First heat exchanger
204A has a heat transfer surface area that is less than the heat transfer
surface area of second heat
exchanger 204B. Suitably, first heat exchanger 204A has a heat transfer
surface area that is less than
50%, more preferably less than 30%, and most preferably less than 15%, the
heat transfer surface area
of second heat exchanger 204B.
FIG. 2 shows system 200 that employs the option of providing saturated steam
from electrode
boiler 102 to both first and second heat exchangers 204A and 204B in parallel
to generate the pre-
heated second fluid and wet steam as described. In particular, the saturated
steam from electrode
boiler 102 is provided to first heat exchanger 204A via line 108A and to
second heat exchanger 204B
via line 108B. Suitably, a range from 30% and up to 45% of the saturated steam
from electrode
boiler 102 is provided to first heat exchanger 204A via line 108A while the
remaining portion of
the saturated steam, from 55% to 70%, is provided to second heat exchanger
204B. The amount
of steam entering either first heat exchanger 204A or second heat exchanger
204B of system 200
is known to one of ordinary skill. The operating pressure of either heat
exchanger 204A or 204B
can be set using means known in the art, such as a pressure control valve
which can be placed in
line 108A or 108B, respectively, or for 204B also through the control of the
electrode boiler
pressure.
In system 200, the condensed fluid from the saturated steam remaining after
the thermal
transfer from both first and second heat exchangers 204A and 204B can be
provided to individual
.. optional condensate vessels 120A and 120B via lines 214A and 1214B,
respectively, to separate liquid
from uncondensed steam so that the liquid can be fed to pump 118 for use as
feedwater for electrode
boiler 102. Optionally, it is understood that the condensed fluid from both
exchangers 204A and
204B of system 200 can be collected via lines 214A and 214B and provided to
one condensate vessel
(not shown) rather than two as shown in FIG. 2.
FIG. 3 shows system 300 that employs the option of providing saturated steam
from
electrode boiler 102 to first and second heat exchangers 204A and 204B in
series. In particular,
the saturated steam enters second heat exchanger 204B first from electrode
boiler 102 via line 108
to further heat pre-heated second fluid to generate wet steam. The condensed
fluid remaining from
the saturated steam that exits second heat exchanger 204B is provided to first
heat exchanger 204A
via line 314 to use the remaining thermal energy in the condensed fluid to pre-
heat the second fluid
as described here. Cooled liquid remaining from the condensed fluid after the
thermal transfer can
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be routed from first heat exchanger 204A via line 214 to optional condensate
vessel 120, if desired,
to separate the liquid from any remaining steam to provide the liquid as
feedwater to electrode
boiler 102 for use to generate the saturated steam in certain embodiments
described herein.
The option of providing saturated steam from electrode boiler 102 to both heat
exchangers
.. 204A and 204B in parallel in system 200 provides a greater degree of
control over the temperature
of the pre-heated second fluid exiting first heat exchanger 204A as compared
to system 300, such
as by setting the operating pressure of either heat exchanger 204A. In system
300, the temperature
of the pre-heated second fluid exiting first heat exchanger 204A can be
influenced by configuring
the size of the heat transfer surface area of heat exchangers 204A.
The impact of the potential temperature fluctuations noted above is minimal
for first heat
exchanger 204A with its relatively smaller size while it provides a
temperature buffer for second heat
exchanger 204B. The preheated lower quality water input to second heat
exchanger 204B enables it
to be operated at more constant temperatures, thereby decreasing the impact of
the potential
temperature fluctuations, which impact can be particularly challenging from a
mechanical integrity
perspective under the operating conditions as described in this disclosure.
In each of the systems of Figs. 2 and 3, the wet steam discharged from the
first outlet 112B of
second heat exchanger 204B may be routed to equipment for steam injection in
thermal EOR. Each
of these systems may thus be comprised in a thermal EOR system. Such thermal
EOR system may
further comprise a wet steam injection line into a subsurface hydrocarbon
formation to which the
system described herein is functionally connected.
At least a portion and preferably all components of the steam production
systems and methods
described herein are powered by electricity. The source of electricity can
come from a typical
electrical power grid if access is available to the site of operation. In
large-scale steam production,
such as those employed for thermal EOR, the power requirement can be
significant, and the site of
operation may be remote so grid access may not be economically feasible or
practical.
The present disclosure provides for the option to use renewable electricity to
address some of
the foregoing challenges as well as allow for generation of "green" steam for
use in thermal EOR.
Such renewable electricity includes wind and solar energy. Use of such
renewable resources for
generating electricity releases less emissions than the combustion of fossil
fuels. The benefits of
reducing emissions from steam generation include collecting carbon credits and
meeting carbon
reduction goals currently being set by many governments and corporations.
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In addition, through the use of an islanded grid, an embodiment of the steam
production
system can optionally be "utility-grid-independent", meaning that the power
needed to operate the
system to generate steam, including the power needed to operate the electrode
boiler(s), pumps,
valves, other ancillary components, etc., does not come from a conventional
electrical utility grid
and that no electrical connection is present between the islanded grid and the
electrical utility grid.
FIGS. 1 and 2 illustrate systems 100 and 200, respectively, with islanded grid
126. One suitable
option for islanded grid 126 is a solar photovoltaic (PV) grid which comprises
a multitude of
interconnected photovoltaic cells (not shown). Another suitable option for
grid 126 is an islanded
wind grid. It is within the knowledge of one of ordinary skill to select the
size or energy production
capacity of the selected islanded grid based on the maximum power demand of
the electrode
boilers and any additional auxiliary equipment, local weather data, expected
transmission losses,
and any combination thereof. The electricity produced by islanded grid 126 is
provided at least to
electrode boiler 102, such as via line 128. Optionally, it can also be
provided to other ancillary
equipment to systems 100 or 200, and/or other nearby equipment (not shown).
Islanded grid 126 being utility-grid-independent is beneficial for remote
locations at which
electrical utility infrastructures may be limited, and as well for generating
carbon credits in some
cases. Additionally, being utility-grid-independent can reduce costs and time
to steam production
by avoiding the need for interconnection agreements that can add schedule
delays and charges
associated with utility infrastructures.
Optionally, certain embodiments of the steam production systems and methods
described in
this disclosure can be designed to run intermittently rather than on a
continuous basis. This is
particularly applicable if such embodiments are powered by renewable sources
such as wind or solar
PV that are not constant. As such, certain embodiments can be optionally
designed to supplement
existing steam production equipment, such as OTSG and EIRSG, thereby allowing
carbon offsets in
oil and gas operations by using renewable energies in the hydrocarbon recovery
processes.
While the descriptions and FIG. 1 may show one electrode boiler and one heat
exchanger, it
is understood that any number of electrode boilers and heat exchangers can be
used (such as two or
more) to meet the desired specifications, such as the total quantity of wet
steam output. The selection
of capacity, number, and type of electrode boilers and heat exchangers, as
well as pump configurations
and other ancillary equipment to achieve desired specifications, are within
the design choices known
to one of ordinary skill.
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Accordingly, referring to FIG. 1, the present disclosure provides a method for
generating wet
steam, the method comprises providing feedwater having an electrical
conductivity of less than 200
nS/cm to electrode boiler 102, which has a capacity of at least 5 MVV, and
converting the feedwater
to saturated steam by electrode boiler 102. The saturated steam has a pressure
in a range from 3.5
MPa and up to 14 MPa and a temperature in a range from 240 degrees C and up to
340 degrees C.
The method further comprises providing at least a portion of, and including up
to all of, the saturated
steam as a first fluid to first inlet 106 of heat exchange component 104 via
line 108; and providing
water having an electrical conductivity of more than 200 nS/cm as a second
fluid to heat exchange
component 104 via second inlet 110. The second fluid is heated in heat
exchange component 104
through indirect thermal transfer with the saturated steam to generate wet
steam having a temperature
lower than the temperature of the saturated steam by a range from 2 degrees C
and up to 30 degrees
C and a pressure in a range from at least 0.5 MPa and up to 13 MPa. The
saturated steam is cooled
in the heat exchanger through indirect thermal transfer with the second fluid
to produce a
condensed fluid. At least a portion of the condensed fluid is provided to
electrode boiler 102, such
as via line 116, for use as part of the low-conductivity water to generate
said saturated steam. It is
understood that the optional ranges of temperatures and pressures described
above and elsewhere are
equally applicable in this paragraph and throughout this description as
context dictates and is not
repeated here for purposes of brevity and ease of reading.
Suitably, at least 50%, preferably at least 75%, or more preferably at least
99% of the
condensed fluid is provided to electrode boiler 102 for use to generate said
saturated steam.
Optionally, referring to FIG. 2, heat exchange component 104 comprises first
heat exchanger
204A and second heat exchanger 204B. The step of providing the saturated steam
to heat exchange
component 104 preferably comprises providing a first portion of the saturated
steam to first heat
exchanger 204A, providing the second fluid to first heat exchanger 204A, and
heating the second
.. fluid in first heat exchanger 204A through indirect thermal transfer with
the first portion of the
saturated steam to generate a pre-heated second fluid. The pre-heated second
fluid and a second
portion of the saturated steam are provided to second heat exchanger 204B. The
step further
comprises heating the pre-heated second fluid in second heat exchanger 204B
through indirect
thermal transfer with the second portion of the saturated steam to generate
the wet steam.
Preferably, first heat exchanger 204A provides from 30% and up to 45% of the
total thermal energy
needed to convert the second fluid to wet steam.
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Optionally, referring to FIG. 3, heat exchange component 104 comprises first
heat exchanger
204A and second heat exchanger 204B. The step of providing the saturated steam
to heat exchange
component 104 preferably comprises providing the second fluid to first heat
exchanger 204A and
heating the second fluid in first heat exchanger 204A through indirect thermal
transfer with a
condensed fluid from second heat exchanger 204B, provided via line 314, to
generate a pre-heated
second fluid. The step further comprises providing the pre-heated second fluid
to second heat
exchanger 204B via line 222 and providing the saturated steam to second heat
exchanger 204B via
line 108. The step further comprises heating the pre-heated second fluid in
second heat exchanger
204B through indirect thermal transfer with the saturated steam to generate
the wet steam; and at
least partially condensing the saturated steam in second heat exchanger 204B
through indirect
thermal transfer with the pre-heated second fluid to produce the condensed
fluid that is provided
to first heat exchanger 204A to generate the pre-heated second fluid.
Optionally, at least a portion of the wet steam exits first outlet 112 of heat
exchange
component 104 for injection into a subsurface hydrocarbon formation for
hydrocarbon recovery.
Electricity powering the operation of electrode boiler 102 can optionally
comprise green energy,
including but not limited to solar photovoltaic panels, wind turbines,
hydropower, a battery charged
with any one or more of the foregoing, and any combination thereof, which can
be delivered via line
128. Optionally, at least a portion of the electricity is generated by one or
more solar photovoltaic
panels. Electrode boiler can be powered completely by green energy produced by
a power source
that is not connected to an electric grid, such as an islanded solar PV
microgrid. The green energy
can be provided for use by the hydrocarbon recovery site.
As described, the present disclosure provides systems and methods to produce
steam that
address various challenges noted above. The generated wet steam is primarily
intended for thermal
EOR, but other uses may be contemplated.
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