Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS AND SYSTEM FOR PROCESSING A PRODUCED STREAM FROM A SOLVENT HYDROCARBON
RECOVERY OPERATION
BACKGROUND
1. Field
This disclosure relates generally to hydrocarbon recovery from a reservoir
formation and more particularly
to recovery of hydrocarbons using a solvent and processing of a produced
stream from the recovery
operation.
2. Description of Related Art
Heavy oil hydrocarbon recovery from a reservoir formation may require reducing
viscosity of the heavy
hydrocarbons to increase mobility to facilitate production to the surface. The
heavy oil hydrocarbons may
include bitumen, which is generally very viscous and difficult to mobilize
within the reservoir formation.
One such recovery technique uses a solvent such as propane or butane injected
into the reservoir at
relatively low temperatures when compared to other recovery techniques such as
steam assisted gravity
drainage (SAGD). The viscosity of the heavy hydrocarbons is reduced due to
mixing with the solvent and
through a slight rise in temperature. The reduced viscosity hydrocarbons will
have improved mobility
within the reservoir formation thus facilitating production to the surface.
There remains a need for systems and processes for treating the produced
stream to recover solvent and
separate the hydrocarbon product stream from water and other produced fluids.
SUMMARY
In accordance with one disclosed aspect there is provided a process for
recovering hydrocarbons from a
reservoir formation. The process involves injecting a vaporized solvent stream
into the reservoir formation,
the solvent being operable to reduce a viscosity of the hydrocarbons to
facilitate recovery in a produced
stream including hydrocarbons, solvent, and water. The process also involves
separating a substantial
portion of the water from the produced stream to generate a dewatered stream,
and heating the
dewatered stream prior to recovering gaseous solvent from the dewatered stream
to generate a
hydrocarbon product stream. A portion of the heating is provided by extracting
heat from the gaseous
solvent recovered from the dewatered stream. The process further involves
treating the gaseous solvent to
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generate a liquefied solvent stream and to separate residual water and
reservoir gas. The process also
involves generating thermal energy through combustion of a fuel gas for
vaporizing the liquefied solvent
stream for re-injecting into the reservoir formation as the vaporized solvent
stream, the combustion of fuel
gas resulting in discharge of a hot exhaust stream. The process further
involves directing the hot exhaust
stream through a heat exchanger operably configured to cause a vaporized water
portion of the exhaust
stream to condense to a liquid thereby releasing latent energy, the released
latent energy being transferred
to a heated thermal fluid for the heating of the dewatered stream.
Injecting may involve injecting the vaporized solvent stream into the
reservoir formation at an injection
pressure, the vaporized solvent stream having a temperature at or above the
saturation point for the
vaporized solvent at the injection pressure.
The solvent may include propane and the injection temperature may be at or
above about 70 C, the hot
exhaust stream may have a temperature of at least about 120 C, and the latent
energy may be operable to
heat the thermal fluid to a temperature of at least about 80 C.
The process may involve compressing the gaseous solvent prior to extracting
heat, the compression being
operable to cause an increase in temperature of the gaseous solvent.
Generating thermal energy may involve causing a boiler to heat a thermal fluid
circulating through a heat
exchanger disposed within a vaporizer vessel, the heat exchanger being
operable to heat the liquefied
solvent.
The process may involve maintaining a pressure within the vaporizer vessel
sufficient to cause at least a
portion of solvent within the vaporizer vessel to remain liquefied and in
thermal communication with a
heat transfer surface of the heat exchanger thereby facilitating thermal
energy transfer to the liquefied
solvent portion while generating a saturated vaporized solvent stream at an
outlet of the vaporizer vessel,
and injecting the vaporized solvent stream may involve injecting the vaporized
solvent stream at a reduced
pressure less than the pressure within the vaporizer vessel to cause the
solvent to become superheated to
compensate for heat losses during injection.
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The pressure within the vaporizer vessel may be selected based on a maximum
enthalpy of the vaporized
solvent stream at saturation thereby preventing development of a liquid phase
when injecting the
vaporized solvent stream at the reduced pressure.
The solvent may include propane and the pressure within the vaporizer vessel
may be in the range of
between about 2750 kPa and about 3000 kPa.
Reducing the pressure of the vaporized solvent stream may involve reducing the
pressure to between
about 2000 kPa and about 2200 kPa.
The process may involve treating a water stream including at least one of the
portion of water separated
from the produced stream and the residual water separated from the recovered
solvent to remove
entrained hydrocarbons and to generate a treated water stream.
Treating the water stream may involve causing mixing between the water stream
and an injected gas in a
flotation vessel at a pressure high enough to cause the injected gas to induce
flotation of entrained
hydrocarbons within the water stream, the induced flotation being operable to
cause hydrocarbons to
separate from the water stream and float upwardly within the flotation vessel
to facilitate collection while a
treated water stream having reduced hydrocarbon content is drawn off from the
vessel.
The injected gas may include a fuel gas and the process may further involve
recovering at least a portion of
the fuel gas from the collected hydrocarbons in a subsequent process.
The flotation vessel may include a plurality of separation zones each zone
being operably configured to
cause mixing between the water stream and the injected gas and having an
outlet for drawing off collected
hydrocarbons, and the water stream remaining at each zone may form an inlet
stream to the next zone for
providing successive treatment of the water stream through the flotation
vessel.
The solvent may include one of propane and butane.
In accordance with another disclosed aspect there is provided a process for
recovering hydrocarbons from a
reservoir formation. The process involves injecting a vaporized solvent stream
into the reservoir formation,
the solvent being operable to reduce a viscosity of the hydrocarbons to
facilitate recovery in a produced
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stream including hydrocarbons, solvent, and water. The process also involves
separating a substantial
portion of the water from the produced stream to generate a dewatered stream,
and heating the
dewatered stream to a temperature above a critical temperature associated with
the solvent. The process
further involves receiving the dewatered stream in a first separation vessel
operated under supercritical
conditions, the separation vessel being operable to facilitate separation of
the dewatered stream by density
into a supercritical liquefied solvent and a hydrocarbon stream. The process
further involves treating the
supercritical liquefied solvent to separate reservoir gas and to generate a
liquefied solvent stream, and
vaporizing the liquefied solvent stream for re-injecting into the reservoir as
the vaporized solvent stream.
The process may involve discharging the hydrocarbon stream from the separation
vessel, receiving the
hydrocarbon stream in a second separation vessel operated at a pressure lower
than the supercritical
pressure and being operable to cause further solvent to vaporize for
collection as a gaseous solvent, and
discharging a remaining hydrocarbon portion as a hydrocarbon product stream.
The process may involve causing production of the produced stream at a
pressure above the critical
pressure associated with the solvent and maintaining the pressure above the
critical pressure while
generating the dewatered stream.
Vaporizing the liquefied solvent stream may involve causing a boiler to heat a
thermal fluid circulating
through a heat exchanger disposed within a vaporizer vessel, the heat
exchanger being operable heat the
liquefied solvent.
The process may involve maintaining a pressure within the vaporizer vessel
sufficient to cause at least a
portion of solvent within the vaporizer vessel to remain liquefied and in
thermal communication with a
heat transfer surface of the heat exchanger thereby facilitating thermal
energy transfer to the liquefied
solvent portion while generating a saturated vaporized solvent stream at an
outlet of the vaporizer vessel,
and injecting the vaporized solvent stream may involve injecting the vaporized
solvent stream at a reduced
pressure less than the pressure within the vaporizer vessel to cause the
solvent to become superheated to
compensate for heat losses during injection.
The pressure within the vaporizer vessel may be selected based on a maximum
enthalpy of the vaporized
solvent stream at saturation thereby preventing development of a liquid phase
when injecting the
vaporized solvent stream at the reduced pressure.
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The solvent may include propane and the pressure within the vaporizer vessel
may be in the range of
between about 2750 kPa and about 3000 kPa.
Reducing the pressure of the vaporized solvent stream may involve reducing the
pressure to between
about 2000 kPa and about 2200 kPa.
The process may involve treating the portion of the water separated from the
produced stream to remove
entrained hydrocarbons and to generate a treated water stream.
Treating the water stream may involve causing mixing between the water stream
and an injected gas in a
vessel at a pressure high enough to cause the injected gas to induce flotation
of entrained hydrocarbons
within the water stream, the induced flotation being operable to cause
hydrocarbons to separate from the
water stream and float upwardly within the vessel to facilitate collection
while a treated water stream
having reduced hydrocarbon content is drawn off from the vessel.
The injected gas may include a fuel gas and the process may further involve
recovering at least a portion of
the fuel gas from the collected hydrocarbons in a subsequent process.
The flotation vessel may include a plurality of separation zones each zone
being operably configured to
cause mixing between the water stream and the injected gas and having an
outlet for drawing off collected
hydrocarbons, and the water stream remaining at each zone may form an inlet
stream to the next zone for
providing successive treatment of the water stream through the vessel.
The solvent may include one of propane and butane.
In accordance with another disclosed aspect, in a hydrocarbon recovery
operation in which solvent
injection is used to reduce a viscosity of hydrocarbons within a reservoir
formation to facilitate recovery in
a produced stream including hydrocarbons, solvent, and water, there is
provided a process for generating
heat for processing the produced stream. The process involves separating a
substantial portion of the
water from the produced stream to generate a dewatered stream, and heating the
dewatered stream prior
to recovering gaseous solvent from the dewatered stream to generate a
hydrocarbon product stream, a
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portion of the heating is provided by extracting heat from the gaseous solvent
recovered from the
dewatered stream.
The process may involve compressing the gaseous solvent prior to extracting
heat, the compression being
operable to cause an increase in temperature of the gaseous solvent.
The solvent may include one of propane and butane.
In accordance with one disclosed aspect, in a hydrocarbon recovery operation
in which solvent injection is
used to reduce a viscosity of hydrocarbons within a reservoir formation to
facilitate recovery in a produced
stream including hydrocarbons, solvent, and water, there is provided a system
for generating heat for
processing the produced stream. The system includes a separation vessel
operable to receive the produced
stream and to separate a substantial portion of the water from the produced
stream to generate a
dewatered stream, and a heat exchanger for heating the dewatered stream prior
to recovering gaseous
solvent from the dewatered stream to generate a hydrocarbon product stream.
The heat exchanger is
operably configured to extract heat from the gaseous solvent recovered from
the dewatered stream for
heating the dewatered stream.
The solvent may include one of propane and butane.
In accordance with one disclosed aspect, in a hydrocarbon recovery operation
in which solvent injection is
used to reduce a viscosity of hydrocarbons within a reservoir formation to
facilitate recovery in a produced
stream including hydrocarbons, solvent, and water, there is provided a process
for generating heat for
processing the produced stream. The process involves generating thermal energy
through combustion of a
fuel gas for vaporizing a liquefied solvent stream for injecting into the
reservoir as a vaporized solvent
stream, the combustion of fuel gas resulting in discharge of a hot exhaust
stream. The process also involves
directing the hot exhaust stream through a heat exchanger operably configured
to cause a vaporized water
portion of the exhaust stream to condense to a liquid thereby releasing latent
energy, the released latent
energy being transferred to a thermal fluid used for heating of the produced
stream during processing to
recover solvent and generate a hydrocarbon product stream.
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Injecting may involve injecting the vaporized solvent stream into the
reservoir formation at an injection
pressure, the vaporized solvent stream having a temperature at or above the
saturation point for the
vaporized solvent at the injection pressure.
The solvent may include propane and the injection temperature may be at or
above about 70 C, the hot
exhaust stream may have a temperature of at least about 120 C, and the latent
energy may be operable to
heat the thermal fluid to a temperature of at least about 80 C.
The solvent may include one of propane and butane.
In accordance with one disclosed aspect, in a hydrocarbon recovery operation
in which solvent injection is
used to reduce a viscosity of hydrocarbons within a reservoir formation to
facilitate recovery in a produced
stream including hydrocarbons, solvent, and water, there is provided a system
for generating heat for
processing the produced stream. The system includes a gas-fired burner
operable to generate thermal
energy through combustion of a fuel gas for vaporizing a liquefied solvent
stream for injecting into the
reservoir as a vaporized solvent stream, the combustion of fuel gas resulting
in discharge of a hot exhaust
stream. The system also includes a heat exchanger operably configured to
receive the exhaust stream and
to cause a vaporized water portion of the exhaust stream to condense to a
liquid thereby releasing latent
energy, the released latent energy being transferred to a thermal fluid used
for heating of the produced
stream during processing to recover solvent and generate a hydrocarbon product
stream.
The solvent may include one of propane and butane.
In accordance with one disclosed aspect, in a hydrocarbon recovery operation
in which solvent injection is
used to reduce a viscosity of hydrocarbons within a reservoir formation to
facilitate recovery in a produced
stream, there is provided a process for heating solvent to an injection
temperature. The process involves
generating thermal energy to heat a heat transfer surface in thermal
communication with a liquefied
solvent within a vaporizer vessel. The process also involves maintaining a
pressure within the vaporizer
vessel sufficient to cause at least a portion of solvent within the vaporizer
vessel to remain liquefied and in
thermal communication with the heat transfer surface thereby facilitating
thermal energy transfer to the
liquefied solvent portion while generating a saturated vaporized solvent
stream at an outlet of the
vaporizer vessel. The process further involves injecting the vaporized solvent
stream at a reduced pressure
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less than the pressure within the vaporizer vessel to cause the solvent to
become superheated to
compensate for heat losses during injection.
The pressure within the vaporizer vessel may be selected based on a maximum
enthalpy of the vaporized
solvent stream at saturation thereby preventing development of a liquid phase
when injecting the
vaporized solvent stream at the reduced pressure.
The solvent may include propane and the pressure within the vaporizer vessel
may be in the range of
between about 2750 kPa and about 3000 kPa.
Reducing the pressure of the vaporized solvent stream may involve reducing the
pressure to between
about 2000 kPa and about 2200 kPa.
The solvent may include one of propane and butane.
In accordance with one disclosed aspect, in a hydrocarbon recovery operation
in which solvent injection is
used to reduce a viscosity of hydrocarbons within a reservoir formation to
facilitate recovery in a produced
stream, there is provided a system for heating solvent to an injection
temperature. The system includes a
vaporizer vessel operably configured to receive a liquefied solvent, the
vaporizer vessel having a heat
transfer surface disposed in thermal communication with the liquefied solvent.
The system also includes a
heat source operable to generate thermal energy for heating the heat transfer
surface while maintaining a
pressure within the vaporizer vessel sufficient to cause at least a portion of
solvent within the vaporizer
vessel to remain liquefied and in thermal communication with the heat transfer
surface thereby facilitating
thermal energy transfer to the liquefied solvent portion while generating a
saturated vaporized solvent
stream at an outlet of the vaporizer vessel. The system further includes a
solvent injector operably
configured to inject the vaporized solvent stream into the reservoir formation
at a reduced pressure less
than the pressure within the vaporizer vessel to cause the solvent to become
superheated to compensate
for heat losses during injection.
The solvent may include one of propane and butane.
In accordance with one disclosed aspect, in a hydrocarbon recovery operation
in which solvent injection is
used to reduce a viscosity of hydrocarbons within a reservoir formation to
facilitate recovery in a produced
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stream including hydrocarbons, solvent, and water, there is provided a process
for separating solvent from
the produced stream. The process involves separating a substantial portion of
the water from the
produced stream to generate a dewatered stream, heating the dewatered stream
to a temperature above a
critical temperature associated with the solvent, and receiving the dewatered
stream in a separation vessel
operated under supercritical conditions, the separation vessel being operable
to facilitate separation of the
dewatered stream by density into a supercritical liquefied solvent and a
hydrocarbon stream.
The process may involve discharging the hydrocarbon stream from the separation
vessel, receiving the
hydrocarbon stream in a second separation vessel operated at a pressure lower
than the supercritical
pressure and being operable to cause further solvent to vaporize for
collection as a gaseous solvent, and
discharging a remaining hydrocarbon portion as a hydrocarbon product stream.
The process may involve causing production of the produced stream at a
pressure above the critical
pressure associated with the solvent and maintaining the pressure above the
critical pressure while
generating the dewatered stream.
The solvent may include one of propane and butane.
In accordance with one disclosed aspect, in a hydrocarbon recovery operation
in which solvent injection is
used to reduce a viscosity of hydrocarbons within a reservoir formation to
facilitate recovery in a produced
stream including hydrocarbons, solvent, and water, there is provided a system
for separating solvent from
the produced stream. The system includes a separation vessel operably
configured to separate a
substantial portion of the water from the produced stream to generate a
dewatered stream. The system
also includes a heat exchanger operably configured to heat the dewatered
stream to a temperature above
a critical temperature associated with the solvent, and a supercritical
separation vessel operably configured
to receive the dewatered stream, the supercritical separation vessel being
operated under supercritical
conditions and being operable to facilitate separation of the dewatered stream
by density into a
supercritical liquefied solvent and a hydrocarbon stream.
The solvent may include one of propane and butane.
Other aspects and features will become apparent to those ordinarily skilled in
the art upon review of the
following description of specific disclosed embodiments in conjunction with
the accompanying figures.
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BRIEF DESCRIPTION OF THE DRAWINGS
In drawings which illustrate disclosed embodiments,
Figure 1 is a block diagram of a system for recovering and processing
hydrocarbons from a reservoir
formation;
Figure 2 is a schematic view of a system for system for implementation
of a dewatering and degassing
process and solvent recovery process in accordance with one disclosed
embodiment;
Figure 3 is a schematic view of a system for implementation of the
dewatering and degassing process
and solvent recovery process in accordance with an alternative disclosed
embodiment;
Figure 4 is a schematic view of a system for implementation of a
solvent treatment process in
accordance with one disclosed embodiment;
Figure 5 is a schematic view of a system for implementation of a
solvent treatment process in
accordance with another disclosed embodiment;
Figure 6 is a schematic view of a system for implementation of a solvent
vaporization process in
accordance with one disclosed embodiment; and
Figure 7 is a schematic view of a system for implementation of a water
treatment process in
accordance with one disclosed embodiment.
DETAILED DESCRIPTION
Referring to Figure 1, a system for recovering hydrocarbons from a reservoir
formation 100 is shown
generally at 102. In this embodiment two horizontally drilled wellbores extend
into the reservoir formation
100, including an upper wellbore 104 and a lower wellbore 106. A vaporized
solvent stream 108 is
introduced into the upper wellbore 104 via an injection process 110. The
vaporized solvent stream 108 will
generally be at a higher temperature than the reservoir formation 100 and
mixes with in-situ hydrocarbons.
The solvent is operable to reduce a viscosity of the hydrocarbons by causing
an increase in temperature and
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by dissolving in the hydrocarbons. In one embodiment the temperature of the
vaporized solvent stream
108 is selected such that when the solvent reaches the hydrocarbons within the
reservoir formation 100,
the vaporized solvent condenses thus releasing latent heat. In one embodiment
the solvent may be
propane, but in other embodiments butane, diluent, and/or other solvents may
make up the vaporized
solvent stream 108.
In one embodiment, the temperature of the vaporized solvent stream 108 may be
significantly lower than
steam temperatures required in thermal in-situ hydrocarbon recovery processes
such as, but not limited to,
steam-assisted gravity drainage (SAGD) and cyclic steam stimulation (CSS)
hydrocarbon recovery processes.
The lower temperature reduces losses during injection through an overburden
118 between the surface
116 and the reservoir formation 100, reducing the energy required to recover
the hydrocarbons from the
reservoir formation 100.
In embodiments where the reservoir formation 100 includes deposits of heavy
hydrocarbons such as
bitumen, the increased viscosity provided by the solvent increases the
mobility of the heavy hydrocarbons
to facilitate recovery in a produced stream 114. The produced stream 114 is
produced to the surface 116 of
the reservoir formation 100 via a production process 112. In one embodiment an
electric submersible
pump is operated within the lower wellbore 106 to pump the produced stream 114
to the surface. The
produced stream 114 will generally include hydrocarbons, water, condensed
liquid solvent, entrained
gaseous solvent and reservoir gas. Asphaltenes, sulphur, and metals within the
reservoir formation 100
may be more difficult to mobilize and at least a portion of these undesirable
products would
advantageously remain in the reservoir formation 100. The water in the
produced stream 114 may be
connate water from the reservoir formation 100. In other embodiments, steam
may be injected into the
reservoir formation 100 via the upper wellbore 104 to establish conditions
suitable for production prior to
injection of the vaporized solvent stream 108. In such cases the water portion
of the produced stream 114
may include recovered water previously injected as steam.
In other embodiments, recovery of
hydrocarbons may be only through solvent injection i.e. a solvent only
recovery process.
A surface facility for processing the produced stream 114 to remove water and
separate and treat the
solvent for re-injection into to the reservoir formation 100 is shown in
Figure 1 at 120 as a series of
processing steps. Water and solvent are separated from the produced stream 114
leaving a hydrocarbon
product stream 122, which may be transported by pipeline or other means to a
refining facility. It is
desirable to recover a significant proportion of the solvent from the produced
stream 114 to reduce the
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amount of solvent required for the recovery operation and to prevent
transportation of entrained solvent
within the hydrocarbon product stream 114. A small proportion of entrained
solvent may remain in the
hydrocarbon product stream 122 and may be substantially vented while
accumulating the hydrocarbon
product stream in, for example, a sales oil tank, prior to transportation.
The produced stream 114 initially goes through a dewatering and degassing
process 124, in which a
substantial portion of the water, some gaseous phase solvent, and other
reservoir gasses and water vapor
are separated from the produced stream 114 to generate a dewatered stream 126.
The water is discharged
as separated water 130, which may still include hydrocarbons, some solvent,
and other impurities and may
be subjected to a water treatment process 132. The water treatment process 132
may involve further de-
oiling of the water, for example in a skim tank, and results in a treated
water stream 134. The treated
water stream 134 may be used in other hydrocarbon recovery operations or may
be accumulated in a pond
for further settlement. Vaporized solvent and other reservoir gasses are
separated in a gaseous stream
128. In some embodiments the dewatering and degassing process 124 may be
implemented using a three-
phase separation vessel commonly known as a free water knock out (FWKO).
The dewatered stream 126 may still include a substantial portion of liquid
solvent and entrained gaseous
solvent still to be removed in a solvent recovery process 136. In one
embodiment, solvent is recovered
through one or more flash evaporation processes in a flash vessel where the
dewatered stream undergoes
a reduction in pressure causing liquid solvent to vaporize for removal as
recovered solvent 138. The
recovered solvent 138 will generally also include a smaller proportion of
reservoir gas and water vapor. The
remaining hydrocarbons may be subjected to a further flash evaporation
processes at further reduced
pressure to drive off a remaining portion of the solvent, leaving the
hydrocarbon product stream 122. The
hydrocarbon product stream 122 may be suitable for transport or may be further
treated, for example by
addition of a diluent, to make the product stream suitable for pipeline
transport.
The recovered solvent 138 in the gaseous phase may include some water vapor
and/or reservoir gasses
such as methane and hydrogen sulfide. The recovered solvent 138 is subjected
to a solvent treatment
process 140, in which the gaseous solvent is pressurized to generate a
liquefied solvent stream 142. During
pressurization, water vapor within the recovered gaseous solvent 138 also
condenses and is collected as
residual water 144 for processing in the water treatment process 132.
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The solvent treatment process 140 may further include treatment to separate
reservoir gas 146 such as
methane and hydrogen sulfide from the solvent. Methane has a substantially
lower vaporization
temperature than a solvent such as propane, and in proportions greater than
about 1% to 2% may
dominate the vapor space of the vaporized solvent stream 108, thus reducing
the efficacy of the solvent for
increasing hydrocarbon viscosity on injection into the upper wellbore 104. In
one embodiment, the solvent
treatment process 140 may further include treatment to separate the hydrogen
sulfide in the reservoir gas
stream 146 from methane, which can be used as a combustible fuel source for
other processes. Hydrogen
sulfide when combusted in the presence of oxygen produces Sulphur dioxide, a
sulfuric acid precursor that
acts as an acid rain contributor. The hydrogen sulfide may be treated with a
specialty chemical from a
group of chemicals known as triazines, which bind irreversibly to hydrogen
sulfide acting as a sulfide
removal agent. Alternatively, the hydrogen sulfide may be treated to form a
solid of sulfur, if there are
sufficient quantities of hydrogen sulfide in the reservoir gas stream 146.
Alternatively, other suitable
hydrogen sulfide removal processes may be implemented.
The liquefied solvent stream 142 then goes through a solvent vaporization
process 148, in which the
solvent stream is heated to a target injection temperature causing
vaporization of the solvent. Vaporized
solvent is collected and forms the vaporized solvent stream 108 for injection
into the reservoir formation
100. Heating of the liquefied solvent stream 142 may be provided through
combustion of a fuel gas 150. In
one embodiment the fuel gas 150 may be natural gas provided at least in part
through recovery of methane
during the solvent treatment process 140.
Heat integration
Referring to Figure 2, a system for implementation of the dewatering and
degassing process 124 and
solvent recovery process 136 in accordance with one embodiment is shown
generally at 200. The system
200 includes a three phase separation vessel 202, which receives the produced
stream 114 at an inlet 204.
The separation vessel 202 provides for separation by density between a less
dense hydrocarbon portion
206 and a more dense water portion 208 of the produced stream 114. The
hydrocarbon portion 206 is
discharged at an outlet 210 as the dewatered stream 126, which still includes
solvent. The water portion
208 is discharged through a lower outlet 212 as separated water 130 for
further treatment.
In one embodiment, the produced stream 114 may be received at a production
pressure of between about
2000 kPa and 2500 kPa. The production pressure is generated in the production
process 112, for example
by operation of the downhole electric submersible pump (not shown). The
produced stream 114 may have
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been heated to a temperature of about 70 C, depending on the solvent
injection temperature which may
be above 70 C for a propane solvent. In one embodiment the separation vessel
202 may be operated at a
pressure similar to the production pressure. Under these conditions some of
the condensed liquid solvent
may evaporate from the surface of the hydrocarbon portion 206 and along with
reservoir gas and water
vapor is discharged at an outlet 214 as the gaseous stream 128. For a produced
stream temperature of
about 70 C, the collected gaseous solvent and other reservoir gas may be
discharged at the outlet 214 at a
temperature of about 70 C and at a pressure similar to the produced pressure.
The system 200 also includes a valve 216 in communication with the outlet 210.
The dewatered stream 126
is fed through a pressure letdown valve, which reduces the pressure of the
dewatered steam. The pressure
letdown causes vaporization of a portion of the liquid solvent in the
dewatered stream and the resulting
Joule-Thomson effect will reduce the temperature of this stream. In one
embodiment the dewatered
stream after the valve 216 may be at a pressure of about 1200 kPa and under
these conditions the
temperature of the dewatered stream may reduce from about 70 C to about 30 C.
The system 200 also includes a first heat exchanger 226 and a second heat
exchanger 228, which are used
to reheat the dewatered stream prior to recovering gaseous solvent from the
dewatered stream in a high
pressure flash evaporator vessel 218. The flash evaporator vessel 218 has an
inlet 220 for receiving the
heated dewatered stream, an outlet 222 for discharging vaporized solvent, and
an outlet 224 for
discharging a liquid stream. In the flash evaporator vessel 218, a liquid
portion 230 accumulates and the
let-down pressure causes liquid solvent within the liquid portion to vaporize
to accumulate above a surface
of the liquid portion. Vaporized solvent is discharged from the outlet 222 and
the system 200 includes a
compressor 232 for compressing the vaporized solvent to a pressure similar to
the produced pressure. The
work done by the compressor 232 in compressing the vaporized solvent increases
the temperature, in one
embodiment to about 70 C. The liquid stream discharged from the outlet 224
will include hydrocarbons
but would still include some liquid solvent portion for recovery.
In the embodiment shown in Figure 2, the system 200 also includes a low
pressure flash evaporator vessel
234 having an inlet 236 for receiving the liquid stream from the outlet 224 of
the flash evaporator vessel
218, an outlet 238 for discharging vaporized solvent, and an outlet 240 for
discharging the hydrocarbon
product stream 122. The liquid stream discharged from the flash evaporator
vessel 218 at the outlet 224
passes through a pressure letdown valve 242 and is heated by a heat exchanger
244 before being received
at the inlet 236 of the low pressure flash evaporator vessel 234. In one
embodiment the pressure in the
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flash evaporator vessel 218 may be at about 1200 kPa and the pressure in the
low pressure flash
evaporator vessel 234 may be in the region of about 200 kPa. The pressure
reduction in this specific case
would be about 1000 kPa, but in other embodiments may be between about 200 kPa
and 2000 kPa. In the
flash evaporator vessel 234, a liquid portion 246 accumulates and the let-down
pressure causes further
liquid solvent within the liquid portion to vaporize to accumulate above a
surface of the liquid portion. The
vaporized solvent is discharged from the outlet 238. The system 200 also
includes a compressor 248 for
compressing the vaporized solvent at the outlet 238 to a pressure similar to
the produced pressure. The
work done by the compressor 248 in compressing the vaporized solvent increases
the temperature, in one
embodiment to about 70 C.
Following the low pressure flash evaporation in the flash evaporator vessel
234, a significant proportion of
the liquid solvent will have been recovered. The stream discharged at the
outlet 240 should thus have only
a small proportion of entrained liquid solvent and provides the hydrocarbon
product stream 122.
In the embodiment shown, a portion of the heating for the first heat exchanger
226 may be provided by
extracting heat from the recovered gaseous solvent at the outlet 214, the
compressor 232, and the
compressor 248. These recovered gaseous solvent streams are combined to form
the recovered solvent
138, which as described above goes through a further solvent treatment process
140. However, in this
embodiment the combined stream is also used to act as a thermal fluid for
heating the dewatered stream
.. passing through the first heat exchanger 226. In one embodiment the first
heat exchanger 226 may be
implemented as a shell and tube heat exchanger, in which the thermal fluid
(i.e. recovered solvent 138) is
channeled through tubes in a shell vessel and transfers thermal energy from
the recovered gaseous solvent
to the dewatered stream passing through the shell. The recovered solvent 138
will also generally include a
significant water vapor portion with which to provide heating through
condensation within the first heat
exchanger 226. Since the recovered solvent 138 will generally be cooled during
the solvent treatment
process 140 (shown in Figure 1) the excess thermal energy associated with the
recovered solvent would be
otherwise dissipated. Use of the excess thermal energy thus reduces the
overall thermal heating
requirement for operating the system 200, in some embodiments by about 15 %
based on process design
simulations for the disclosed system.
In the embodiment shown in Figure 2, the first heat exchanger 226 heated by
the recovered solvent 138
only provides a portion of the required heating for the dewatered stream 126
prior to processing in the
flash evaporator vessel 218. The second heat exchanger 228 and the heat
exchanger 244 for heating the
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stream being received at the inlet 236 of the low pressure flash evaporator
vessel 234 are heated by a
thermal fluid 250 such as circulating glycol or heating oil that is heated by
a heat source such as a boiler or
by other means as described later herein.
Supercritical solvent separation
Referring to Figure 3, a system for implementation of the dewatering and
degassing process 124 and
solvent recovery process 136 in accordance with an alternative embodiment is
shown generally at 300. The
system 300 includes a three phase separation vessel 302, which receives the
produced stream 114 at an
inlet 304 and operates generally as described above discharging the dewatered
stream 126 at an outlet 306
and separated water 130 at an outlet 308. However, in this embodiment, the
produced stream 114 is
received at an elevated production pressure above a critical pressure
associated with the solvent. For the
example of a propane solvent, the critical pressure is in the region of 4500
kPa and in this case the
production process 112 may involve operating an electric submersible pump at
the elevated pressure to
cause production of the produced stream 114 at a pressure above the critical
pressure. The three phase
separation vessel 302 thus operates a pressure above the critical pressure
while generating the dewatered
stream 126. The temperature of the dewatered stream 126 would still be
commensurate with the
temperature of the produced stream 114 (for example 70 C for a propane
solvent) and would thus remain
under sub-critical conditions.
Recovered solvent 310 is discharged from the three phase separation vessel 302
at an outlet 312, but in this
embodiment the recovered solvent will be at the elevated pressure. Similarly,
the dewatered stream 126
at the outlet 306 will be at the elevated pressure.
The system 300 also includes a heat exchanger 314 for heating the dewatered
stream 126 to a temperature
above a critical temperature associated with the solvent. The heat exchanger
314 is heated by a thermal
fluid 316 such as oil or glycol, and in one embodiment may heat the dewatered
stream 126 to above 100 C
for a propane solvent.
The system 300 also includes a supercritical separation vessel 318 having an
inlet 320 for receiving the
dewatered stream 126, which in this case is at supercritical pressure and
temperature. The supercritical
separation vessel 318 thus operates under supercritical conditions and
facilitates separation of the
dewatered stream 126 by density into a less dense supercritical liquefied
solvent, which is discharged at an
outlet 322, and a more dense liquid hydrocarbon stream, which is discharged at
an outlet 324.
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In the embodiment shown, the system also includes a heat exchanger 326 which
extracts heat to reduce
the temperature of the supercritical liquefied solvent discharged at the
outlet 322. The heat exchanger 326
is also configured to cause a letdown in pressure causing the solvent 328 to
remain in the liquid phase, but
at sub-critical conditions due to the reduction to sub-critical temperature
and pressure. A cooling medium
330 provided to the heat exchanger 326 will be heated by the supercritical
liquefied solvent and may be
used to provide other heating requirements for the system 300.
In the embodiment shown in Figure 3, the system 300 also includes a low
pressure flash evaporator vessel
332 having an inlet 334 for receiving the liquid hydrocarbon stream from the
outlet 324 of the flash
evaporator vessel 318, an outlet 336 for discharging vaporized solvent, and an
outlet 338 for discharging
the hydrocarbon product stream 122. The liquid hydrocarbon stream discharged
from the outlet 324 of the
flash evaporator vessel 218 passes through a pressure letdown valve 340 and is
heated by a heat exchanger
344 before being received at the inlet 334 of the low pressure flash
evaporator vessel 332. In the flash
evaporator vessel 334, a liquid portion 346 accumulates and the let-down
pressure causes further liquid
solvent within the liquid portion to vaporize to accumulate above a surface of
the liquid portion. The
vaporized solvent is discharged from the outlet 336. The system 300 also
includes a compressor 348 for
compressing the vaporized solvent at the outlet 336 to produce a recovered
solvent stream 350.
In one embodiment the recovered solvent stream 350 is compressed to an
elevated pressure at which
liquefaction of the solvent would occur. The recovered solvent 310 from the
three phase separation vessel
302 would also be at elevated pressure in this embodiment. The streams 310,
328 and 350 together make
up the recovered solvent 138 that will still undergo the solvent treatment
process 140 shown in Figure 1
and described in more detail below.
In other embodiments, the produced stream 114 may be produced at a pressure
lower than the
supercritical pressure for the solvent, and processing through the three phase
separation vessel 302 and
heat exchanger 314 may be at the lower pressure, the supercritical
pressurization being provided by an in-
line charge pump (not shown) between the heat exchanger 314 and the
supercritical separation vessel 318.
Following the low pressure flash evaporation in the vessel 332, a significant
proportion of the liquid solvent
will have been recovered. The stream discharged at the outlet 338 should thus
have only a small
proportion of entrained liquid solvent and provides the hydrocarbon product
stream 122.
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One advantage associated with the system 300 is that a substantial portion of
the solvent is removed as a
supercritical liquid, avoiding the need to vaporize and compress vaporized
solvent. This embodiment thus
eliminates the compressor 232 in the Figure 2 embodiment, thus reducing the
requirement for rotating
equipment.
Solvent treatment
Referring to Figure 4, a system for implementation of the solvent treatment
process 140 in accordance with
one embodiment is shown generally at 400. The system 400 is configured for
treatment of the recovered
solvent 138 made up by the streams 310, 328, and 350 generated by the solvent
recovery system shown in
Figure 3. In this embodiment the recovered solvent streams 310 and 350 are
processed differently to the
recovered solvent stream 328, which is generated under supercritical
conditions. The recovered solvent
streams 310 and 350 include vaporized solvent, water vapor, and reservoir
gases.
The system 400 includes an air cooler 402 and a three phase separation vessel
404. The streams 310 and
350 are received at an inlet 406 of the separation vessel 404 following
cooling by the air cooler 402. The
stream received at the inlet 406 following cooling comprises liquefied and
vaporized solvent, liquid water,
and reservoir gases. For a propane solvent at about 4000 kPa and 40 C, the
solvent will be primarily
liquefied and the separation vessel 404 separates liquid water from the liquid
solvent and discharges the
liquid water at an outlet 408. The water from the outlet 408 may be sent to
the water treatment process
132 for further processing. The liquid solvent is discharged at an outlet 412,
while a remaining gaseous
phase portion is vented via an outlet 410. The gaseous phase portion at the
outlet 410 will be primarily
reservoir gasses such as methane and hydrogen sulfide.
The system 400 also includes a distillation column 414, which has an inlet 416
for receiving the liquid
solvent from the outlet 412 of the separation vessel 404. The distillation
column 414 also includes an inlet
418 for receiving the recovered solvent stream 328. In one embodiment, both of
the streams received at
the inlets 416 and 418 will be primarily liquid phase solvent having some
entrained vaporized solvent and
reservoir gas. The distillation column 414 separates the vapor phase including
reservoir gasses from the
liquefied solvent. The vapor phase is discharged from an outlet 420. The
distillation column 414 includes a
reboiler 422 for re-boiling liquid at the bottom of the column and liquefied
solvent is discharged from an
outlet 424 as the liquefied solvent stream 142 for further processing in the
solvent vaporization process
148.
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The gaseous streams at the outlet 410 of the separation vessel 404 and the
outlet 420 of the distillation
column 414 are combined and processed through a scavenger 426 to remove
hydrogen sulfide, leaving
primarily methane for use as fuel gas 150.
Referring to Figure 5, a system for implementation of the solvent treatment
process 140 in accordance with
another embodiment is shown generally at 500. The system 500 is configured for
treatment of the
recovered solvent stream 138 generated by the system 200 shown in Figure 2. In
an embodiment where
the solvent is propane, the recovered solvent 138 may be at a pressure of
about 1500 kPa and a
temperature below 70 C following heating of the first heat exchanger 226 as
shown in Figure 2. The
system 500 includes an air cooler 502 and a three phase separation vessel 504.
The recovered solvent 138
is received at an inlet 506 of the separation vessel 504 following cooling by
the air cooler 502. The stream
received at the inlet 506 comprises vaporized solvent, liquefied solvent,
liquid water, and reservoir gases.
The air cooler 502 further cools the recovered solvent 138 prior to being
received in the separation vessel
504, which separates liquid water from the liquid solvent and discharges the
liquid water at an outlet 508.
The stream received at the inlet 506 may have a temperature of about 40 C and
a pressure of 1500 kPa.
The water from the outlet 508 may be sent to the water treatment process 132
for further processing. The
liquid solvent is discharged at an outlet 512, while a remaining gaseous phase
portion is vented via an
outlet 510. The gaseous phase portion at the outlet 510 includes vaporized
solvent and reservoir gasses
such as methane and hydrogen sulfide.
The system 500 also includes a compressor 514, which further compresses the
gaseous phase portion at
the outlet 510 and feeds the compressed stream through a cooler 516 before
undergoing a second
separation stage in a separation vessel 518. In the embodiment shown the
coolers 502 and 516 are shown
as air coolers, but in other embodiments a cooling medium other than air may
be used. The separation
vessel 518 receives a compressed cooled stream from the cooler 516 at an inlet
520. The stream received
at the inlet 520 comprises liquefied and vaporized solvent, liquid water, and
reservoir gases and for a
propane solvent at a pressure of about 4000 kPa and a temperature of about 40
C, would be primarily
liquefied. The separation vessel 518 again separates liquid water from the
liquid solvent and discharges the
liquid water at an outlet 522. The water from the outlet 522 may be sent to
the water treatment process
132 for further processing. The liquid solvent is discharged at an outlet 524.
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As in the Figure 4 embodiment, the system 500 includes a distillation column
526 having an inlet 528 for
receiving the liquid solvent from the outlet 524 of the separation vessel 518.
The distillation column 526
also includes an inlet 530. Liquid solvent separated in the separation vessel
504 at the outlet 512 is fed
through a charge pump 532 to provide an increased pressure liquid solvent
stream at the inlet 530. In one
embodiment the charge pump 532 pressurizes the liquid solvent to a pressure of
about 4000 kPa. The
streams received at the respective inlets 528 and 530 will be primarily liquid
phase solvent having some
entrained vaporized solvent and reservoir gasses. The distillation column 526
separates the vapor phase
including reservoir gasses from the liquefied solvent. The vapor phase is
discharged from an outlet 534 and
processed through a scavenger 540 to remove hydrogen sulfide, leaving
primarily methane for use as fuel
gas 150. The distillation column 526 includes a reboiler 536 for re-boiling
liquid at the bottom of the
column and liquefied solvent is discharged from an outlet 538 as the liquefied
solvent stream 142 for
further processing in the solvent vaporization process 148.
Condensing boiler
Referring to Figure 6, a system for implementation of the solvent vaporization
process 148 in accordance
with one embodiment is shown generally at 600. The system 600 includes a
boiler 602, having a burner 604
that generates thermal energy through combustion of fuel gas 150 for
vaporizing the liquefied solvent
stream 142 for re-injecting into the reservoir formation 100. The boiler
includes a tubing circuit 608 heated
by the burner 604.
The system 600 includes a vaporizer vessel 610 having in inlet 612 for
receiving the liquefied solvent stream
142. During recovery operations some of the solvent will be lost, for example
through discharge in the
treated water stream, entrainment in the hydrocarbon stream or separated
reservoir gasses, or dissipation
within the reservoir formation. In this embodiment, losses are compensated by
introducing make up
solvent 616 as required. The vaporizer vessel 610 includes a heat exchanger
618 disposed within the
vaporizer vessel and being operable to heat liquefied solvent received at the
inlet 612 and accumulated
within the vessel. The heat exchanger 618 is heated by a thermal fluid that
circulates through the heat
exchanger and is returned via a pump 620 to the tubing circuit within the
boiler 602. The heat exchanger
618 heats the liquefied solvent causing vaporization, and vaporized solvent is
discharged at an outlet 622 to
.. form the vaporized solvent stream 108 for injection into the reservoir
formation 100 via the injection
process 110.
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The combustion of fuel gas in the burner 604 results in discharge of a hot
exhaust stream 606 via a flue 624
of the boiler 602. The flue 624 channels the hot exhaust stream 606 through a
condensing section 626.
The hot exhaust stream 606 includes a significant water vapor portion due to
combustion of the fuel gas
150. In one embodiment the hot exhaust stream may be at a temperature above
100 C, which maintains
the water in the vapor phase. The condensing section 626 includes a heat
exchanger 628, which receives
the hot exhaust stream 606 and causes a vaporized water portion of the exhaust
stream to condense to a
liquid thereby releasing latent energy. The released latent energy is
transferred to the thermal fluid 250
circulating through the heat exchanger 628, which may be used for heating
requirements within the various
disclosed systems herein. For example, the thermal fluid 250 is used for
heating the second heat exchanger
228 and heat exchanger 244 shown in Figure 2. Condensed water may be collected
from the condensing
section 626 at an outlet 630 and treated in the water treatment process 132.
Solvent vaporization
The vaporizer vessel 610 shown in Figure 6 may be maintained at a pressure
sufficient to cause at least a
portion of solvent within the vessel to remain liquefied, as shown at 632. The
liquefied solvent remains in
thermal communication with a heat transfer surface of the heat exchanger 618,
thereby facilitating thermal
energy transfer to the liquefied solvent portion while generating a saturated
vaporized solvent stream at
the outlet 622 of the vaporizer vessel. In one embodiment sufficient heating
is provided by the heat
exchanger 618 to cause the vaporized solvent stream at the outlet 622 to have
a temperature at the
saturation point for the vaporized solvent at the injection pressure.
However in other embodiments, it may be desired to cause the vaporized solvent
to be superheated for
injection into the reservoir formation 100 to compensate for any injection
heat losses. Superheating a
vaporized solvent within the vaporizer vessel 610 would however require a
significantly larger heat transfer
area than the heat exchanger 618 required for heating the liquefied solvent to
lower than superheated
temperatures. Rather than attempt to superheat the vaporized stream, the
vaporized solvent stream may
be injected at a reduced pressure, less than the pressure within the vaporizer
vessel 610, causing the
vaporized solvent to become superheated to compensate for heat losses during
injection. In one
embodiment the pressure within the vaporizer vessel 610 is selected based on a
maximum enthalpy of the
vaporized solvent stream at saturation thereby preventing development of a
liquid phase when injecting
the vaporized solvent stream at the reduced pressure. As an example, for a
propane solvent the pressure
may be in the region of 2750 kPa to 3000 kPa, facilitating generation of a
substantially saturated vaporized
solvent (i.e. having a vapor quality x=1). In the embodiment shown in Figure
6, the system 600 includes a
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solvent injector 634 operable to implement the injection process 110. An
injection pressure produced in
the solvent injector 634 may be reduced to between about 2000 kPa and about
2200 kPa, causing a
vaporized solvent stream 636 to be superheated at the lower pressure for
injection into the upper wellbore
104 of the system 102 shown in Figure 1.
Water Treatment
Referring to Figure 7, a system for implementation of the water treatment
process 132 in accordance with
one embodiment is shown generally at 700. The system includes a flotation
vessel 702 and a reject
separator vessel 704. The flotation vessel 702 has a water inlet 706 for
receiving the separated water
stream 130 and/or residual water stream 144 generated in the respective
dewatering and degassing
process 124 and solvent treatment process 140. In the embodiment shown, the
water inlet 706 is disposed
to cause a generally tangential flow within the flotation vessel as indicated
by the arrow 708. The flotation
vessel 702 also includes a gas inlet 710 for injecting a gas into the
flotation vessel. In one embodiment the
gas injected at the gas inlet 710 may be a fuel gas such as methane. The
flotation vessel 702 also includes a
water outlet 712 disposed at the bottom of the vessel for discharging the
treated water stream 134 and an
outlet 714 at the top of the vessel for discharging a separated hydrocarbon
stream 720.
The water streams 130 and 144 will generally include some dissolved gasses
such as gaseous solvent and
reservoir gasses and may also include significant impurities in the form of
dissolved solids such as silica,
hardness ions such as calcium and magnesium, other salts and dissolved organic
compounds.
The water 130, 144 received at the water inlet 706 combines with the injected
gas at the gas inlet 710
causing mixing between the water stream and the injected gas in a flotation
region 716. The flotation
vessel 702 is maintained at a pressure high enough to cause the injected gas
to induce flotation of
entrained hydrocarbons within the water stream 130, 144. The induced flotation
in combination with
flotation provided by dissolved gasses entrained within the water stream
causes hydrocarbons to separate
from the water stream and float upwardly within the flotation vessel 702. The
hydrocarbons being less
dense than the water accumulate in a region 718 above the flotation region
716, facilitating collection by
the outlet 714 as the separated hydrocarbon stream 720. The separated
hydrocarbon stream 720 may
include solvent, fuel gas, and liquid hydrocarbon products. Within a treated
water region 722 below the
region 716, the water has a reduced hydrocarbon content and may be drawn off
via the water outlet 712 as
the treated water stream 134.
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The treated water region 722 may be sized to permit bubbles generated by the
injected gas to float
upwardly through the flotation region 716 thereby reducing the dissolved gas
content in the treated water
at the water outlet 712. In one embodiment the flotation vessel 702 may
include guide vanes 724 between
the flotation region 716 and the treated water region 722 to provide
separation between the regions and to
direct the injected gas upwardly within the flotation vessel 702.
The reject separator vessel 704 has an inlet 726 for receiving the separated
hydrocarbon stream 720, an
outlet 728 for collecting a separated gaseous portion and an outlet 730 for
drawing off a hydrocarbon
portion. The less dense gaseous portion separates from the hydrocarbon portion
within the reject
separator vessel 704 to produce a gaseous stream 732. The gaseous stream 732
may include vaporized
solvent and reservoir gasses, and may be combined with recovered solvent 138
generated in either of the
systems 200 or 300 described above. A hydrocarbon portion 734 drawn off at the
outlet 730 may be
further processed in the solvent recovery process 136 to remove further
solvent.
While the separated water 130 and residual water 144 may be conventionally
treated in a skim tank at low
pressures near atmospheric pressure, gaseous hydrocarbons would generally need
to be collected and
compressed rather than vented. To permit sufficient settling and residence
time, the skim tank would thus
need to be relatively large. The flotation vessel 702 provides a compact
alternative to a skim tank and the
injection of the fuel gas causes rapid separation of hydrocarbons through the
induced flotation thus
reducing a residence time in the flotation vessel. In some embodiments a multi-
stage flotation vessel
having a plurality of separation zones may be used. Each zone would be
configured generally as shown in
Figure 7 to cause mixing between the water stream and the injected gas and
would have an outlet for
drawing off collected hydrocarbons. The water stream remaining at each zone
would form an inlet stream
to the next zone for providing successive treatment of the water stream
through the flotation vessel to
provide several stages of separation within a single compact flotation vessel.
While specific embodiments have been described and illustrated, such
embodiments should be considered
illustrative of the invention only and not as limiting the invention as
construed in accordance with the
accompanying claims.
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