Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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LIQITID BASED BOILER
CROSS RE1-iERF.NCF. TO RELATED APPLICATIONS
[00011 This application claims benefit of U.S. Patent Application
Ser. No. 61/983,742 filed
April 24, 2014 entitled "LIQUID BASED BOILER," which is hereby incorporated by
reference.
FIELD OF THE INVENTION
10021 '1'he invention relates to method and system for generating
steam with minimal or
eliminated fouling resulting largely liorn the use of contaminated feedwaters.
The invention
limits fouling problem by spraying dirty feedwater directly onto a hot
hydrocarbon for steam
generation.
BACKGROUND
[00031 Steam Assisted Gravity Drainage (SAGD) is an enhanced oil
recovery technology for
producing heavy crude oil and bitumen. It is an advanced fonn of steam
stirnulati011 wherein a
pair of horizontal wells are drilled into the oil reservoir, one a few meters
above the other. High
pressure steam is continuously -injected into = thc upper wellbore to beat the
oil and re,ducc its
viscosity, causing the heated oil and any condensed steam (hot water) to
gravity drain into the
lower wellbore, where it can be pumped to the surface. The produced oil is a
mixture of heated
oil plus water.. Because water is as precious a resource as oil, the "produced
water" is then
cleaned and returned to the boiler, where it is converted into steam and
injected back into the
ground.
[0004] Due to. the recycling of water in SACiD operations, and the
fact that the water
= encounters petroleum deposits as well as any additives used in
production, the leedwater usecl to
make steam is typically far from pure. Produced water and brackish well water
are the main
boiler feedwater sources for SAGD and other steam based oil recovery process.
The water at
time or being generated into thc steam may still contain: at, least about 500
parts per million
(ppm), at least 1000 ppm, al least 10,000 ppm or at least 45,000 ppm total
dissolved solids; at
least 100 ppm, at least 500 ppm, at least 1000 ppm or at least 15,000 ppm
organic compounds or
,
organics; and at least 1000 ppm free oil. =
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[00051
"Fouling" is the contamination of heating surfaces by these mineral scales,
and the
build-up of scale eventually decreases the heat-flux and thus the heating
efficiency. Therefbre,
the boiler has to be shut down several times a year to remove the [baling
layer arid/or repair the
tubing. In addition to the repair cost, the down-time further increases the
cost of the SA(II
operation, To minitnize fouling, boiler feed-water (.1-114W) quality is
critical because dissolved
solids are the major cause of boiler failure and efficiency losses. Therefbre,
the total dissolved
solids (TDS) fbr BFW needs to bc controlled under a certain level to prevent
or alleviate the
scaling issue, and this is usually done by pre-treating feedwater prior to use
to reduce TDS.
[00061
The two most common types of steam generators used for oil sands recovery arc
once
through steam generators (OTSG) and drum boilers, which are also called water
tube boilers.
Coal-fired stetun generators, downholc steam generators, fluidized bed
combustion boilers and
vapor therm steam generators have previously been reported to be used in
Alberta fields, but they
arc no longer found in recent field applications.
= [0007.1 The=OTS0 is a large continuous tube type steam generator
wherein steam is produced
at the outlet of the continuous tube, as shown in in FIG. l. Feedwater
supplied at one cold end of
the tube undergoes the preheating-evaporation cycle as it travels along the
continuous tube, As =
steam is produced in a traditional OTSG, the steam quality is usually around
75-80%, i.e. not all
the fee,clwater vaporizes.
10008) In
drum type steam generators, in contrast, preheated water evaporates as it
circulates
in heated tubes between the steam drum and the feedwater drum, as shown in
FIG. 2. Saturated
= steam and water rises into the steam ]rum due to the lowered density
compared with the water in
downcomer tube. Saturated steam is drawn off the top of the drum and sent to
the superheater
section.
[0009J
OTSO systems require fie,iquent cleaning, which leads to the increased down-
time and
costly repair. Fouling also reduces the thermal efficiency 1% to 15% depending
on the amount
of deposits, as they act as an insulating layer on the heating tubes. The
shutdown to clean the
scale increases operating costs, and the pre-treatments needed to de-oil and
clean the fecdwater
belbre use also contributes significantly to cost.
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[00101 Therefore, there is a need for an improved steam
production scheme that can
minimize fouling issues and reduce the downtime ancl reduce both operating and
initial capital
costs for SAG l) and other steam based oil recovery operations.
SUMMARY 011 T.U.E DISCI ..0SURE
[00111 Embodiments of the invention use a hot liquid, such as the
produced heated
hydrocarbons, or fractions thereof, to directly vaporize non-treated boiler
feedwater. This hot
hydrocarbon receives its thermal energy from another hot fluid, such as Molten
sodium, molten
sodium-potassium, or another hydrocarbon that may include butane, DOWTHERMTm
or
TT-IF.RMTNOLTm heal transfer fluid, within coils in a closed circulation loop
traveling froni a
standard heater to the vessel containing thc hot hydrocarbon. Contaminants
from the: water being
vaporized may thus buildup in the hot liquid requiring treatment Of the hot
liquid. The fluid in
the coils transfers heat to the hot liquid without relying on transfer of the
hot liquid to the heater.
Thus, the fluid ill the coils circulates to maintain a desired heat balance
providing a benefit by
enabling &coupled circulation of the hot liquid for treatment, such EIS
desalting, at a rate wanted
= for removal of the contaminants independent of a flow needed for the
heating.
100121 The use of a hot hydrocarbon such as DOWTHERMTm enables
more conventional
met2dlurgies to be used for the coils, thus minimizing CAPEX costs. Further,
thc contaminants
remain in the hot liquid outside the coils without passing to the heater to
avoid problems inside
the circulation loop.
[00131 'The hydrocarbon heat steam generation system is a
replacement to the current OTSGs
de-oiling and water treatment facilities, which are otherwise essential to
prevent rapid fouling
= and tube corrosion that occurs in either drum boilers or OISC.4 systems.
Use of thc oil and
desalting of the oil mitigates contaminant concentration buildup in the oil
and tholing within the
steam generation system.
[0014j The hot hydrocarbon may giye up sonic lighter molecular
weight elements to the
steam, thus providing a ,sinall amount or solvent, and essentially converting
the SAW) process to
an ES-SAGD process, which may reduce steam usage since the solvent has the
effect of diluting
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and thinning the heavy oil or bitumen. Typically, Cl -05 hydrocarbons, and
even C6-C8
hydrocarbons, may vaporize and be carried along with the steam, albeit in low
amounts.
[0015] The invention produces high pressure steam or steam-plus-solvent
which can be used
in a SAGD reservoir or in other steam stimulation processes, such as cyclic
steam generation
(CSS) or steam drive (SD) also called steam flooding, and combinations and
variations thereof.
[00(61 Of course, the hot hydrocarbon picks up the dissolved solids and
any entrained oil in
the dirty feedwater, but the oils are not a problem, arid the dissolved solids
(which may no longer
be dissolved) can be removed in a cleaning loop using known technology.
Treatment units can
include one or more of a variety of treatment units, including e.g.., a
filter, coalescer, desalter,
dehydrator, visbreaker OT electrostatic separator,
[0017] Salts in crude oil feedstocks can cause severe problems
downstream, including
corrosion. by acids formed by chloride salt decomposition in fractionator
overhead equipment,
fouling of heat exchangers by salt deposition, and poisoning of catalysts in
down-strefun
Therefore, crude is typically desalted before being charged to the
distillation train. Crude can
also contain suspended solids, such as sand, clay, and iron oxidc particles.
,
.
[0018] The two most typical methods of crude-oil desalting, chemical
and electrostatic
separation, use hot water as the extraction agent. In chemical desalting,
water and chemical
surfactant (demulsi tiers) are added to the crude, heated so that salts and
other impurities dissolVe
into the water or attach to the water, and then held in a tank where they
settle out. Electrical
desalting is the application of high-voltage electrostatic charges to
concentrate suspended water
globules in the bottom of the settling tank. Surfactants are added only when
the crude has a large
amount of suspended solids. Both methods &desalting are continuous. A third
and less-common
process involves filtering heated crude using diatomaceous eaith.
I0019J For example, an. electrostatic dehydration system i.s an
efficient method to remove
high salinity formation water from thc crude oil stream. This process relies
on establishing a high
voltage AC electrical field in the oil phase of dehydratoridesalter vessels.
The electrical field
imposes an electrical charge on water droplets entrained in the oil stream,
thus causing them to
oscillate as they pass through the electrodes. During this oscillation the
droplets are stretched or
elongated and then contra.cted during reversal of the imposing AC electrical
field. During this
4
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= .1. AL Mk = BB. .A= ..==11 .= J = ==/k / MB. =.=.== t === =
CA 02887935 2015-04-13
agitation, the water droplets co-mingle and coalesce into droplets of
sufficient size to migrate, by
gravity, back into the lower water phase of the vessel for disposal.
[0020] Alternatively, Ultrafiltration (IN) can be used primarily to remove
the emulsified oil
droplets, followed by the removal of total dissolved solids (TDS) via reverse
osmosis (LC)).
[0021] The liquid boiler system described herein improves SAGD economies
by:
= Eliminating the need for dc-oiling, water pre-treatment plants and
conventional steam
boiler plants.
= Enhancing the heavy oil recovery by including lower molecular weight
hydrocarbons
.combined with the produced stearn. These hydrocarbons aid in reducing the
heavy oil
viscosity in the reservoir along with the steam, thus, enhancing oil
production.
= Overall SAGD steain demand may also decrease due to the -presence of
hydrocarbon
= within the steam, in much the same ma.nner that ES-SAGD reduces steam
requirements.
[0022] The invention includes onc or more of the following embodiments, in
any
ccnnbination thereof
100231 A steam generator system for heavy oil production, comprising: a
vessel comprising a
hot hydrocarbon; a pump tbr.pressurizing a dirty feedwater stream fluidly
connected to nozzles
in said vessel, said nozzles .spraying said dirty feedwater onto said hot
hydrocarbon; and an exit
port near a top of said vessel tbr collecting pressurized steam and
transporting said pressurized
steam to a wellhead injection system for injecting steam into an oil
reservoir; wherein these
elements are fluidly connected_=
[0024] A closed heat transfer fluid circulation loop that passes in part
through said vessel can
be used to heat said hot hydrocarbon. 'Hie closed heat transfer fluid
circulation loop can
comprise a heat transfer fluid, a heater, and a pump, circulating through
closed coils which pass,
in part, through the liquid boiler vessel.
100251 The liquid boiler vessel can also e-omprise a hot hydrocarbon
treatment loop in fluid
connection with said vessel, wherein said hot hydrocarbon treatment loop
either clean or
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upgrades the hot hydrocarbons. Exemplary treatments include filtering,
desalting, dehydrating,
coalescing, visbreaking, electrostatic separating, and thc like.
100261 A liquid stetun generator, comprising u vessel comprising
a hot hydrocarbon in a
lower portion of said vessel; a closed heat transfer fluid circulation loop
containing a heat
transfer fluid, said loop passing in part through said lower half of said
vessel to heat said hot
hydrocarbon, the remainder passing to a heater and a pump to heat and
circulate said heat
transfer fluid; a hot hydrocarbon treatment loop for cleaning said hot
hydrocarbon, said hot
hydrocarbon treatment loop including a pump anti a desalter; a pump for
pressurizing a dirty
fecdwater stream .fluidly connected to nozzles in an upper portion of said
vessel, said nozzles
spraying said dirty fcedwater onto said hot hydrocarbon; and an exit port near
a top of said vessel
for collecting pressurized steam and transporting said pressurized steam to a
wellhead. injeetion
system for injecting steam into an oil reservoir wherein the elements (except
for the closed
circulation loop) arc fluidly connected.
[0027] , Exemplary hydrocarbon heat transfer fluids are selected from butane,
molten sodium,
molten sodium-potassi Lirfl, DOWTHERM or THERMINOL.
100281 The dirty feedwater can be any water that is not
pretreated before use, including
produced water, brackish water, well water, brine, surface water and
combinations thereof. The
dirty feedwater may be produced water originating from any convenient source.
100291 The hot hydrocarbon fluid can be any conveniently
available hot hydrocarbon,
especially being a produced hydrocarbon separated from said produced water, or
a fraction
thereof.
[0030] The liquid boiler can produce a pressurized stetun that
is a mixture of steam and low
molecular weight hydrocarbons, such as butane, pentane, arid the like.
[0031] One embodiment is an improved method of steam assisted
gravity drainage (SA OD),
the method comprising preireating produced water ler a steam generator to
remove oil and salts,
making pressurized steam li-om said pretreated watcr, pumping said pressurized
steam into a
= wellborc in an amount sufficient to mobilize heavy oil, and gravity
draining said. mobilized
heavy oil to a production well, the improvement comprising spray injecting
pressurized dirty
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water into a vessel containing a hot heavy oil and collecting pressurized
steam for use in SAGD,
without said water prctreating step.
[0032] Another improved method of steam production for the
mobilization of heavy oil, the
method comprising pre,treating. produced water for a steam generator to.
remove oil and salts,
= making pressurized steam from said pretreated water, pumping said
pressurized steam into at
wellbore in am amount sufficient to mobilize heavy oil, and producing said
mobilized heavy oil,
the improvement comprising spray injecting pressurized dirty water into a
vessel containing a
hot hydrocarbon and collecting pressurized steam for usc in mobilizing heavy
oil, without said
water pretreating step, .wherein said hot hydrocarbon is heated with a closed
circulation loop
comprising a pump and a furnace to circulate a heat transfer fluid through
said closed circulation
loop.
100331 Hy "dirty water" what is meant is that the water can bc
recycled from oil recovery
processes and used as is, without expensive de-oiling or desalting pre-
treatments applied to it.
= [00341 Thc use of the word "a" or "an" when used in conjunction
with the term "comprising"
in the claims or the specification means one or more than one, unless the
context dictates
otherwise.
10035] The term "about" means the stated value plus or tninus the
margin of' error of
measurement or plus or tninus 10% iftio method of measurement is indicated.
100361 The use of the term "or" in the claims is used to mean
"and/or" unless explicitly .
indicated to refer to alternatives only or if the alternatives are mutually
exclusive.
= 100371 The terms "comprise", "have", "include". and
"contain" (and their variants) are open-
ended linking verbs and allow the addition of other elements when used in a
claim.
[0038] The phrase "consisting of' is closed, and excludes all
additional elements.
100391 Tile phrase "consisting essentially of" excludes
additional material elements, but
allows the inclusions of non-material elements that do not substantially
change the nature of the
invention.
7.
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[0040] The following abbreviations arc used herein:
ABBREVIATION TERM
ATM Atmosphere
BFW Boiler feed-water
CAPEX Capitol expenses
. = = . . .__._... . ________ _
CPF Central processing facility
_
QS Cyclic steam stimulation
_
ES-SAGD Expanding solvent SAGD
-
OPEX = Operating expenses
OTSG Once-through steam generator
Reverse osmosis
SAGD Steam-assisted gravity drainage
. .
SD Steam drive
TDS total dissolved solids
-Ts Saturation temperature
UF Ultrafiltration
=
=
BRIEF DESCRIPTION OF THE DRAWINGS
100411 FIG. 1 illustrates a highly simplified view of a modem OTSG system
and used for
SA.GI) steam production.
[0042] FIG. 2 presents a simplified drum boiler system.
[0043] FIG. 3 illustrates a simplified schematic of the liquid boiler
system of the invention,
which can be beneficially used with SAGD and other steam-based enhanced oil
recovery
methods
[0044] FIG. 4 is a schematic of an alternative arrangement to contact a
mixture of water and
oil with more of the oil that has been heated to thus Vaporize the water and
potentially result in
visbreaking of the oil, according to one embodiment of the invention.
= 8
=
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DETAILED DESCRIPTION
[00451 The disclosure provides a novel method for generating steam with
minimized or
eliminated finding. The disclosure also provides a novel system for
implementing the method.
[00461 In general, an impnived method of generating steam for SAGD and
other heavy oil
production uses is provided, wherein a hot liquid hydrocarbon is used to
convert water to steam,
and wherein the steam may thus contain lower molecular weight components
stripped from the
hot liquid hydrocarbon.
100471 FIG. 3 gives one example of a liquid boiler process for SACiD_ As
seen in the figure,
dirty feedwater 101 that is not de-oiled or pre-treated to remove dissolved
solids enters the
system. Pump 103 brings the dirty water to high pressure and then it is
injected via spray
nozzles 105 into the liquid boiler vessel 109. Since the water is pressurized
thereis little fouling
of the components up to this point.
[00481 Hot liquid 113 (e.g., produced heavy hydrocarbons, etc.)
vaporizes the dirty boiler
feed water sprayed into the vessel. The resulting produced stearn (with
potentially some
hydrocarbons in it) exits 111 out the top of the liquid-boiler and is sent by
line 113 to the SAGD
reservoir. Any dissolved solids or oil from the dirty feedwater remains with
the hot 'liquid
hydrocarbons_
=
[00491 The hot liquid receives its thermal energy li-om another heat
transfer fluid in a closed
circulation loop 157 via heat transfer within coils 155. The heat transfer
fluid (such as butane,
molten sodium, molten sodium-potassium, DOWTHERM or THERMINOL) within the
coils
receives its heat via an external furnace 151, and in that sense the boiler is
kin indirect boiler, heal
coming from an outside source. in some embodiments, the heat transfer fluid,
such as butane,
may be condensed for pumping prior to being vaporized in the furnace 151 and
circulated
= through the coils 155 in the vessel J 09. To the extent that produced
hydrocarbons are used in the
process, they already have a certain heat, decreasing initial heating costs. J
he hot hydrocarbons
used to vaporize the produced water may be treated by an external hydrocarbon
treatment unit
.173, such as a clesalter, to remove the accumulating contaminants from the
dirty feedwater.
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[0050] The ine,thod allows the boiler to produce steam with non-
treated (dirty) boiler feed
water_ This, therefbre, reduces the CAPEX and OPEX costs associated with de-
oiling anti water
treatment plants. Using a liquid such as DOWTHERM or TITERMINOI., as the heat
transfer
liquid allows for conventional coil inetallurgy, thus, minimizing the CAPEX
Ibr the indirect
boiler, as well as minimizing any fouling of these coils. =
10051] F1G. 4 illustrates a hot hydrocarbon-based system with a
steam generator vessel 200,
an injection well 201 and a production well 202 that are operated for steam
generation. A feed
pump 216 pressurizes the dirty fccdwatcr mixture 204 that can optionally be
preheated in
furnace or heat exchanger 217 prior to introduction into the vessel 200. In
some embodiments,
the mixture 204 may receive pre-heat from a sales portion 210 of the
hydrocarbons.
[0052] Upon entry into the vessel 200, some flashing of the
water in the mixture 204 may
occur upon expansion into relative lower pressure conditions of the vessel
200. llowever, most
of the water in the mixture 204 vaporizes tipon contact with hot hydrocarbon
220 collected in the
lower half of the vessel 200. The hydrocarbons 220 may be partially heated, if
for example,
produced hydrocarbons ate used, and/or can be further heated in closed
circulation loop 257
consisting of furnace 251, pump 253 and heating coils 255 that pass through
the hot hydrocarbon
220.
[0053-1 A second circulation loop 222 contains El recycle pump
221 that passes the, hot
hydrocarbon 220 from the vessel 200 to a treatment unit 223 before returning
the hot
= hydrocarbon 220 to the vessel 200. Treatment unit 223 can include one or
more of a variety of
treatment units, including e.g., a filter, coalescer, desalter, dehydrator,
visbreaker or electrostatic.
separator. The desalter or other treatment unit 223 removes inorganic.
material from the hot
hydrocarbon 220. Some of the hot hydrocarbon 220 exiting thc &salter 223 can
provide the
sales portion 210 of the hydrocarbons for pipeline or transport to a refinery
for further
processing.
[0054] For sonic embodiments, overhead from the vessel 200
passes through a separation
.1
device 229 that may include demisters, separators, liactionators and/or
particulate filters. 'The
device 229 removes entrained liquids and/or solids 233 and/or condensable
hydrocarbons 231
vaporized by the hot hydrocarbon 220 or resulting from cracking of the hot
hydrocarbon 220.
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The condensable hydrocarbons 231 may mix back into the sales portion 210 of
the hydrocarbons
or have a portion mixed back for injection into the formation as a solvent.
However, it is
anticipated that the overhead steam can be used as is, and that any light
hydrocarbons that may
have evaporated along with the steain (e.g., naptha), will reduce the steam
oil ratio (SOR) needed
to produce a barrel of oil.
100551
Steam 230 cxits the device 229 and is conveyed to the injection well
201. Since
separation of the mbaure 204 occurs with the vessel 200, this approach
eliminates need for
independent de-oiling equipment.
[0056.1
Residence time of the hot hydrocarbon 220 in the vessel 200 may even
provide
sufficient soak time for visbrcaking of the hydrocarbon 220. A vishreakff
thermally cracks large
hydrocarbon molecules in' the oil by heating in a furnace to reduce its
viscosity and to produce
small quantities of light hydrocarbons (LPG and gasoline). The process name of
"visbreaker"
refers to the fact that the process reduces (i.e., breaks) the viscosity of
the residual oil, and =
generally the process is non-catalytic.
[0057]
Alternatively, a visbreaker can be provided in the second circulation
loop 222.
Exemplary soaking times may range from 5 minutes to 1 hour with the bitumen
heated in the
visbreaker to at least 385 C. The circulation loop 222 may incorporate
various approaches to
enhance the vishreaking, such as radiation thermal cracking or hydrodynamic
cavitation. The
vishreaking lowers viscosity and density of the heavy oils or biturne-n 220
and hence the sales
portion 210 making the sales portion 210 more valuable and easier to transport
while requiring
= less diluents than the bitumen without such upgrading.
100581
In some embodiments, the water supplied lbr generation of the steam may
include
boiler blowdown from another steam generator, such as a once-through steam
generator.
methods disclosed herein may provide for treatment of such blowdown. Further,
the steam
generated by such treatment may bc al pressures lower than desired for
injection and may be
recycled for mixing with boiler lecd water prior to generation of steam tin-
injection.
[0059]
Based on the above illustrations, it is clearly shown that the methods
and systems
herein described pressurize the feedwater before it enters the heating
mechanism and thereby
avoids the nucleate boiling phase that directly conlributes to ibuling.
Downtime tbr
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pigging/rc,pairing the boiler and pipes can be greatly reduced, therefore
cutting clown the
operation cost.
[00601 The following documents are incorporated by reference in
their entirety:
Gwak et al., A Review of Steam Generation for In-Situ Oil Sands, Projects,
Oeosystem
Engineering, 13(3), 111-118 (September 2010).
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