Note: Descriptions are shown in the official language in which they were submitted.
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HEATING FOR INDIRECT BOILING
FIELD OF THE INVENTION
[0001]
Embodiments of the invention relate to methods and systems for generating
steam which may be utilized in applications such as bitumen production.
BACKGROUND OF THE INVENTION
[0002] Several
techniques utilized to recover hydrocarbons in the form of bitumen
from oil sands rely on generated steam to heat and lower viscosity of the
hydrocarbons
when the steam is injected into the oil sands. One common approach for this
type of
recovery includes steam assisted gravity drainage (SAGD). The hydrocarbons
once
heated become mobile enough for production along with the condensed steam,
which is
then recovered and recycled.
[0003] Costs
associated with building a complex, large, sophisticated facility to
process water and generate steam contributes to economic challenges of oil
sands
production operations. Such a facility represents much of the capital costs of
these
operations. Chemical and energy usage of the facility also contribute to
operating costs.
[0004] Past
approaches rely on once through steam generators (OTSGs) to produce
the steam. However, boiler feed water to these steam generators requires
expensive de-
oiling and treatment to limit boiler fouling problems. Even with this
treatment, fouling
issues persist and are primarily dealt with through regular pigging of the
boilers. This
recurring maintenance further increases operating costs and results in a loss
of steam
production capacity, which translates to an equivalent reduction in bitumen
extraction.
[0005]
Therefore, a need exists for methods and systems for generating steam that
enable efficient hydrocarbon recovery from a formation.
BRIEF SUMMARY OF THE DISCLOSURE
[0006] In one
embodiment, a method of vaporizing water includes introducing a
gaseous fluid into a first vessel and in contact with solid particulate within
the first vessel
to transfer heat from the gaseous fluid to the solid particulate. Upon
recovering and then
reheating the gaseous fluid from the first vessel, the gaseous fluid
circulates back into the
first vessel for continued heating of the solid particulate that is
circulating between the
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first vessel and a second vessel. The water introduced into the second vessel
contacts the
solid particulate heated to a temperature that results in vaporizing the water
into steam,
which is then separated from the solid particulate.
[0007] For one embodiment, a system for vaporizing water includes a first
vessel
having an inlet and an outlet for a gaseous fluid and containing solid
particulate in
contact with the gaseous fluid that passes from the inlet to the outlet for
transference of
heat from the gaseous fluid to the solid particulate. A heater coupled to the
inlet and the
outlet of the first vessel reheats the gaseous fluid that is recovered from
the outlet of the
first vessel and circulated back to the inlet of the first vessel for
sustained heating of the
solid particulate. A second vessel couples to the first vessel by conduits
through which
the solid particulate is circulated between the first vessel and the second
vessel. An
injection line coupled to the second vessel supplies the water into the second
vessel and
in contact with the solid particulate heated to a temperature that results in
vaporization of
the water into steam. A steam output line coupled to the second vessel conveys
the steam
that is separated from the solid particulate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] A more complete understanding of the present invention and benefits
thereof
may be acquired by referring to the following description taken in conjunction
with the
accompanying drawings.
[0009] Figure 1 is a schematic of a steam generating system that includes
dual vessels
arranged to alternate between heating and steam generation cycles, according
to one
embodiment of the invention.
[0010] Figure 2 is a schematic of a steam generating system with an
exemplary
heating vessel through which solid particulate circulates to regain thermal
energy used to
vaporize water, according to one embodiment of the invention.
[0011] Figure 3 is a schematic of a steam generating system with a heating
vessel in
which heat is transferred to solid particulate via recycled gaseous fluid,
according to one
embodiment of the invention.
[0012] Figure 4 is a schematic of a steam generating system with a heating
vessel in
which heat is transferred to solid particulate via recycled gaseous fluid that
is condensed
before reheating, according to one embodiment of the invention.
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[0013] Figure
5 is a schematic of a steam generating system with a heating vessel
having an internal heat exchanger to transfer heat to solid particulate from
hot fluids
without direct contact, according to one embodiment of the invention.
[0014] Figure
6 is a schematic of a steam generating system with a single vessel for
vaporizing water upon contact with fluidized solid particulate disposed in the
vessel and
in thermal contact with a heat exchanger, according to one embodiment of the
invention.
[0015] Figure
7 is a schematic of the steam generating system shown in Figure 3 and
in a side-by-side vessel configuration, according to one embodiment of the
invention.
DETAILED DESCRIPTION
[0016] Turning
now to the detailed description of the preferred arrangement or
arrangements of the present invention, it should be understood that the
inventive features
and concepts may be manifested in other arrangements and that the scope of the
invention
is not limited to the embodiments described or illustrated.
[0017]
Embodiments of the invention relate to systems and methods for vaporizing
water into steam, which may be utilized in applications such as bitumen
production. The
methods rely on indirect boiling of the water by contact with a substance such
as solid
particulate heated to a temperature sufficient to vaporize the water. Heating
of the solid
particulate may utilize pressure isolated heat exchanger units or a hot gas
recirculation
circuit at a pressure corresponding to that desired for the steam. Further,
the water may
form part of a mixture that contacts the solid particulate and includes a
solvent for the
bitumen in order to limit vaporization energy requirements and facilitate the
production.
[0018] In any
embodiments disclosed herein, the water may come from separated
production fluid associated with a steam assisted gravity drainage (SAGD)
bitumen
recovery operation. The water at time of being generated into the steam may
still
contain: at least about 1000 parts per million (ppm), at 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.
Injecting the steam through an injection well into the formation during the
bitumen
recovery operation thus enables sustainable recycle of the water without
stringent
treatment requirements of conventional boiler feed.
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[0019] Figure
1 illustrates a steam generating system that includes a first vessel 101
and a second vessel 102 that each contains solid particulate. As used herein,
examples of
the solid particulate include sand, metal spheres, cracking catalyst and
mixtures thereof
In some embodiments, fluidization of the solid particulate keeps the solid
particulate
moving within the vessels 101, 102 during operation to generate steam. Such
fluidization
may involve circulation of the solid particulate and may rely on addition of
supplemental
steam.
[0020] Each of
the vessels 101, 102 couples to a water injection line 104 and a heat
source line 106. A manifold system controls flow through the vessels 101, 102
to a steam
output 108 and an exhaust 110 and includes first through eighth valves 111-
118. In
operation, the valves 111-118 alternate between heating and steam generation
cycles with
the first vessel 101 being shown in the steam generation cycle while the
second vessel
102 is in the heating cycle.
[0021] As
shown, the first and fifth valves 111, 115 on the water injection line 104
and the steam output 108 thus remain open to flow of the water through the
first vessel
101 to generate the steam while the third and seventh valves 113, 117 block
flow of the
water through the second vessel 102. The steam exits the first vessel 101
through the
steam output 108, which may couple to the injection well, and is separated
from the solid
particulate that remains in the first vessel 101 and may be trapped by filters
or cyclones.
The second and sixth valves 112, 116 block flow from the heat source line 106
to the first
vessel 101 at this time while the fourth and eighth valve 114, 118 are open to
flow of
oxygen and fuel, such as methane, from the heat source line 106 through the
second
vessel 102 to the exhaust 110. As thermal load of the solid particulate in the
first vessel
101 becomes depleted, position of each of the valves 111-118 switches such
that steam is
generated in the second vessel 102 while the solid particulate is reheated in
the first
vessel 101.
[0022] The
oxygen and fuel passing through the second vessel 102 combusts to
reheat the solid particulate. During such combustion, contaminants, such as
organic
compounds deposited on the solid particulate from the water, may partially or
fully
convert into carbon dioxide and water, and some salts deposited on the solid
particulate
from the water may come off and be swept out of the second vessel 102. The
combustion
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heats the solid particulate to a temperature that results in vaporizing the
water upon
contact therewith in the steam generation cycle that follows.
[0023] Not all
embodiments rely on such cleaning of the solid particulate. Surface
area of the solid particulate provides enough dispersion of the deposits to
limit heat
transfer interference. As needed over time, replacing some or part of the
solid particulate
may ensure desired performance is maintained at minimal cost and with limited
to no
interruption. For example, a lockhopper system employed with embodiments where
the
solid particulate is always in a pressurized environment can enable such
withdrawal and
replacement while in continuous operation.
[0024] Due to
the first and second vessels 101, 102 with the manifold system, the
heat source line 106 can supply the oxygen and fuel without compression to
pressures
desired for the steam to be injected into the formation. This relative lower
pressure
combustion facilitates economic production of the steam. Alternating each of
the vessels
101, 102 between the steam generation cycle and the heating cycle also
eliminates need
for conveying the solid particulate to units dedicated to one particular
cycle.
[0025] In some
embodiments, the water mixes with a solvent 120 for the bitumen
prior to vaporization due to contact with the solid particulate. The solvent
120 (common
reference number depicted in all figures) thus may flow as a liquid into the
water supply
line 104 to form a resulting mixture of the water with the solvent 120.
Vaporization of
the water along with the solvent 120 results in the steam output 108 also
containing both
water and solvent vapors, as may be desired for injection into the formation.
[0026] The
solvent 120 may include hydrocarbons having between 3 and 30 carbon
atoms, such as butane, pentane, naphtha and diesel. Temperatures associated
with the
indirect boiling described herein limit potential problems of cracking the
hydrocarbons,
which can tend to occur if passed through direct fired boilers that may thus
require
injection of any wanted solvents into steam rather than boiler feed. Such
injection of the
solvent into the steam instead of the water feed may either cause loss of some
steam due
to condensation or require superheating of the steam. Conventional
superheating of the
steam also suffers from fouling problems. Therefore, the solvent 120 may flow
into
steam superheated by steam generation methods described herein in some
embodiments
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since the fouling issues from the superheating are overcome in the same manner
as those
associated with steam generation.
[0027] The
mixture in the water supply line 104 may include between 5 and 30
percent of the liquid hydrocarbon by volume. The mixture may further provide
an energy
requirement for vaporization that is at least 10 percent lower than water
alone. For
example, a 28:72 ratio of butane to water reduces steam generator duty by 22
percent as
compared to water alone.
[0028] Figure
2 shows a steam generating system with a steam generating riser 200
and/or vessel 201 and a heating vessel 202 through which solid particulate are
circulated.
Similar to the system in Figure 1, a heat source line 206 supplies reactants
for combustion
within the heating vessel 202 in order regain thermal energy used to vaporize
water. Flue
gases from the combustion exit the heating vessel 202 through exhaust 210
following any
filtering to retain the solid particulate. Multiple alternating heating
vessels with flow
control similar to Figure 1 or lockhoppers may enable operation of the heating
vessel 202
at a lower pressure than the steam generating riser 200 and/or vessel 201.
[0029] In some
embodiments, the solid particulate heated in the heating vessel 202
transfers to the steam generating vessel 201 by gravity since the heating
vessel 202 is
disposed above the steam generating vessel 201. A water supply line 204 then
inputs the
water into contact with the solid particulate that is heated to result in
vaporizing the water
and providing a steam output 208. Some of the steam output 208 may provide
lift for the
solid particulate being returned up the riser 200 to the heating vessel 202.
For some
embodiments, the water vaporizes in the riser 200 such that the steam
generating vessel
201 is not even required and the steam is recovered at a riser output 209.
[0030] Figure
3 illustrates a steam generating system with a heating vessel 302 in
which heat is transferred to solid particulate via recycled gaseous fluid
circulating in a
circuit. Similar to systems in other figures, the solid particulate once
heated transfers to a
steam generating vessel 301 where water 304 is input to contact the solid
particulate and
generate steam 308. Embodiments may therefore implement various features and
attributes explained in detail with respect to another particular figure or
elsewhere herein
without being repeated in order to be as succinct as possible.
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[0031] The
gaseous fluid that exits the heating vessel 302 through an outlet 310
passes through heat exchanger(s) 350 and a fin-fan cooler 352, if necessary.
The heat
exchanger 350 may transfer heat with the gaseous fluid post compression
boosting and/or
with the water 304 being input into the steam generating vessel 301. Such heat
exchange
helps maintain efficiency while bringing the temperature of the gaseous fluid
below
temperature limits of a compressor 358 through which the gaseous fluid is sent
downstream in the circuit.
[0032] A purge
354 allows removal of a portion of the gaseous fluid, which may pick
up contaminants, such as from cracking or entrainment. Makeup gas 356 combines
with
the gaseous fluid to replace that purged. In some embodiments, the gaseous
fluid
includes an inert gas such as nitrogen and may also include air or oxygen for
burning of
the deposits. Methane may provide the gaseous fluid for some embodiments and
may be
desired due to its relative higher thermal capacity.
[0033] The
compressor 358 only boosts pressure of the gaseous fluid circulating
through the circuit. For example, the compressor may provide between 50 and
150
kilopascals (kPa) boost in pressure, which is achievable without making steam
generation
uneconomical by requiring levels of compression needed to increase atmospheric
pressure to above 2500 kPa. The gaseous fluid in the circuit may thus always
remain
above 2500 kPa, in some embodiments.
[0034] The
gaseous fluid from the compressor 358 then flows through the circuit to a
furnace 360. The furnace 360 burns fuel to reheat the gaseous fluid that
reenters the
heating vessel 302 through a heat source line 306 for sustained heating of the
solid
particulate within the heating vessel 302. The heating vessel 302 may include
multiple
(e.g., 6 as shown) bed stages 362 or trays such that the solid particulate
passing through
the heating vessel 302 counter current with the gaseous fluid achieves
efficient heat cross
exchange.
[0035]
Pressure of the steam desired for injection into the formation dictates
pressure
inside the steam generating vessel 301. With the recycled gaseous fluid
circulating in the
circuit to reheat the solid particulate, both the steam generating vessel 301
and the
heating vessel 302 may operate at this pressure, such as above 2500 kPa,
provided there
may be sufficient differences in pressure in the vessels 301, 302 or other
such
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arrangements described herein to maintain fluid flows. For some embodiments, a
slipstream 364 of the gaseous fluid also at necessary pressure provides lift
for
transporting the solid particulate from the steam generating vessel 301 to the
heating
vessel 302.
[0036] Figure
4 shows a steam generating system with a heating vessel 402 in which
heat is transferred to solid particulate via recycled gaseous fluid that is
circulating in a
circuit and condensed before reheating. While shown as being recycled, the
gaseous
fluid in some embodiments passes once through the vessel 402 and may then be
utilized
in another application. Like the system in Figure 3, the solid particulate
once heated
transfers to a steam generating vessel 401 where water 404 is input to contact
the solid
particulate and generate steam 408. The gaseous fluid that exits the heating
vessel 402
through an outlet 410 passes through heat exchanger(s) 450 that transfer heat
from flow
along the circuit post pumping and/or with the water 404 being input into the
steam
generating vessel 401. The heat exchange 450 condenses the gaseous fluid, such
as
propane, butane or naphtha, to a liquid phase for pressurization by a pump
458. Before
the pump 458, a separator 454 may enable venting off gasses that are not
condensed, such
as may result from cracking of the gaseous fluid.
[0037] Outflow
from the pump 458 and any makeup 456 then flows through the
circuit to a furnace 460. The furnace 460 burns fuel to vaporize and reheat
the gaseous
fluid that reenters the heating vessel 402 through a heat source line 406 for
sustained
heating of the solid particulate within the heating vessel 402. While pressure
in the
circuit again stays at a level similar to that desired for the steam to be
injected into the
formation, the pump 458 may influence efficiency if used in place of
compression. Use
of the pump 458 with the gaseous fluid that is condensed may further enable
economic
once through heating (i.e., without the circuit) at the desired pressure
similar to
approaches depicted in Figures 1 or 2 (i.e. replace oxygen and methane for
combustion
with a higher hydrocarbon pumped and then heated as in Figure 4) except that
resulting
exhaust may have further application for its energy content.
[0038] Figure
5 illustrates a steam generating system with a heating vessel 502
having an internal heat exchanger 562 to transfer heat to solid particulate
from hot fluids
without direct contact. Similar again to systems in other figures, the solid
particulate
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once heated transfers to a steam generating vessel 501 where water 504 is
input to contact
the solid particulate and generate steam 508. Both the steam generating vessel
501 and
the heating vessel 502 may operate in open pressure communication with one
another at
an internal pressure desired for injection of the steam into a formation while
pressure
isolated flow through the heat exchanger 562 may be at a lower pressure.
[0039] In
operation, oxygen and fuel react in a combustor 560 to generate a flue gas
conveyed to the heat exchanger 562 by a heat source line 506. The flue gas
passes
through the heat exchanger 562 and exits via an exhaust 510. A thermally
conductive
material forms the heat exchanger 562 such that heat from the flue gas
transfers to the
solid particulate in the heating vessel 502. In some embodiments, the
thermally
conductive material forms a tube of the heat exchanger. The tube may coil
within the
heating vessel 510 to provide the heat exchanger 562 with either the solid
particulate
flowing through an inside of the tube or the flue gas flowing through the
inside of the
tube.
[0040] For
some embodiments, a fluidization gas, such as air, passes through the
inside of the heating vessel 502. This gas may help remove contaminants from
the solid
particulate as well. Use of the gas for only fluidization while relying on
heating by the
heat exchanger 562 limits quantity and compression requirements for the gas
whether the
gas is used once through or circulated in a circuit.
[0041] Figure
6 shows a steam generating system with a single vessel 600 for
vaporizing water upon contact with fluidized solid particulate disposed in the
single
vessel 600 and in thermal contact with a heat exchanger 662. The solid
particulate heated
by the heat exchanger 662 contacts water 604 that is input into the single
vessel to
generate steam 608. In operation, a circulating liquid, such as sodium or
sodium and
potassium, passes through the heat exchanger 662, exits the heat exchanger via
an outlet
610 and is pumped by an pump 658 to a furnace 660 that reheats the circulating
liquid
prior flowing back to the heat exchanger 662 via inlet 606.
[0042] The
heat exchanger 662 transfers heat from the circulating liquid to the solid
particulate and may have a design such as described with respect to the heat
exchanger
562 shown in Figure 5. Vaporization of the water 604 still occurs upon
contacting the
solid particulate that is heated. While the solid particulate thus should
receive deposits
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from the water 604, movement of the solid particulate along the heat exchanger
662
provides abrasion to ensure that the heat exchanger 662 does not become
fouled.
[0043] The
heat exchangers 562, 662 in Figures 5 and 6 may each operate with either
the flue gas or the circulating liquid as described herein providing hot fluid
thereto. In
some embodiments, systems may incorporate both the heat exchanger 662 where
the
steam is being generated along with additional heating of the solid
particulate such as
provided in the heating vessel 302 shown in Figure 3. Sharing this thermal
load may
enable efficient operation.
[0044] Figure
7 shows the system illustrated in Figure 3 with the steam generating
vessel 301 disposed at a common elevation with the heating vessel 302 as
opposed to a
stacked vertical arrangement. This side-by-side configuration limits or
eliminates need to
use lift gas for transfer of the solid particulate. The solid particulate
transfers between the
steam generating vessel 301 and the heating vessel 302 via dense phase gravity
drain as a
result of such at least partial overlapping height. As shown, an upper outlet
of the steam
generating vessel 301 couples to a relative lower inlet of the heating vessel
302 for flow
from the steam generating vessel 301 to the heating vessel 302. In a similar
manner, a
bottom outlet of the heating vessel 302 couples to a relative lower inlet of
the steam
generating vessel 301 for flow from the heating vessel 302 to the steam
generating vessel
301.
[0045] Overall
volumetric gas flow rate reduces as demand for the lift gas decreases.
This flow rate reduction enables utilizing smaller recycle power requirement
of the
compressor 358 and cross exchanger surface area defined by the heating vessel
302,
which both lower costs. Further, these benefits may facilitate selection of
the gaseous
fluid that otherwise may lack suitable thermal properties for heating the
solid particulate.
[0046]
Although the systems and processes described herein have been described in
detail, it should be understood that various changes, substitutions, and
alterations can be
made without departing from the spirit and scope of the invention as defined
by the
following claims. Those skilled in the art may be able to study the preferred
embodiments and identify other ways to practice the invention that are not
exactly as
described herein. It is the intent of the inventors that variations and
equivalents of the
invention are within the scope of the claims, while the description, abstract
and drawings
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are not to be used to limit the scope of the invention. Each and every claim
below is
hereby incorporated into this detailed description or specification as
additional
embodiments of the present invention. The invention is specifically intended
to be as
broad as the claims below and their equivalents.
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