Note: Descriptions are shown in the official language in which they were submitted.
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MANIFOLD ASSEMBLY AND METHOD OF USE
The present invention relates to a manifold
assembly and a method of its use, particularly in a tailings
solvent recovery unit for recovering solvent from an oil
sands tailings stream.
In a typical oil sands operation, the oil sand is
mixed with water to obtain a bitumen froth comprising
bitumen, water and solids. Bitumen may be recovered from an
oil sand froth using a variety of methods. One method
employs solvent extraction of the bitumen, including, for
example, by using a paraffinic solvent. Paraffinic froth
treatment methods have been previously described in, for
example, Canadian patent Nos. 2,149,737; 2,217,300; and
2,232,929 and Canadian patent application Nos. 2,521,248;
2,353,109; and 2,502,239, as well as elsewhere.
In a typical solvent extraction, solvent is mixed
with the oil sands froth followed by gravity separation of
the resulting mixture into a bitumen enriched, water and
solids depleted upper fraction and a bitumen depleted, water
and solids enriched lower fluid fraction. Fractions may be
recovered, and may be subjected to one or more further
treatments. For example, the lower fluid fraction may be
subjected to further solvent extraction to recover residual
bitumen.
Solvent may be recovered at one or more stages in
the solvent extraction process, including from the underflow
stream of a final separation step. The final underflow
stream, or "tailings stream", usually comprises water,
solids (e.g., mineral particles, asphaltene particles) and
residual solvent.
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Solvent may be recovered from a tailings stream in
a Tailings Solvent Recovery Unit (TSRU), which typically
comprises an inlet means for the tailings stream, a vessel
for separation of solvent from the remainder of the tailings
stream, an outlet means for solvent recovery, and an outlet
means for the remainder of the tailings stream. One or more
TSRU in series may be used in solvent recovery.
The tailings stream in a conventional TSRU is
normally pressurized and heated to just below the bubble
point temperature of the solvent in the inlet means. (The
bubble point temperature is the temperature at which solvent
begins to boil or bubbles begin to form at a given
pressure.) The bubble point temperature increases with
increasing pressure. At temperatures below the bubble point
temperature, the solvent is a liquid. Also, the solvent is
a liquid at pressures above the bubble point pressure.
(Bubble point pressure is the pressure at which a solvent
begins to boil or bubbles begin to form at a given
temperature.) In the vessel, the pressure should be
maintained below the bubble point pressure to cause
vaporization of the solvent so that it can be separated from
other components of the tailings stream.
The inlet means normally comprises one or more
manifold assemblies that introduce the tailings stream into
the vessel. A manifold assembly typically comprises an
inlet and one or more outlets, with the inlet and the one or
more outlets being in fluid communication via a chamber.
Each outlet normally comprises a nozzle, which may be
installed on a retractable lance. The nozzles comprise a
nozzle inlet for receiving the tailings stream, a nozzle
outlet for introducing the tailings stream into the vessel
and usually a swirl chamber disposed between the nozzle
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inlet and nozzle outlet. The swirl chamber is used to
atomize the tailings stream, and create a well-defined spray
pattern.
Due to the pressure differential between the TSRU
inlet means and the vessel, flashing of the solvent may
occur in the manifold assembly, including in the swirl
chamber of a nozzle. The skilled person will be able to
determine whether flashing is occurring in a manifold
assembly using methods known in the art. For example, one
nozzle in a manifold assembly can be blinded, and if there
is no observed change in the flow rate at a given driving
pressure, then this is evidence that flashing is occurring
in the manifold assembly.
Nozzles are typically designed to produce the
required mass flow rate for single-phase liquid flow.
Flashing, however, reduces the mass flow rate of a tailings
stream through the outlet of a nozzle to less than the
design flow rate. Flashing of solvent creates a gas-liquid
flow that can result in choking of the nozzle outlet and
reduced mass flow rates. Observed mass flow rates of a
tailings stream through a conventional nozzle where the
tailings stream is exhibiting gas-liquid flow are smaller
than the observed mass flow rate for a reference
single-phase liquid where the driving pressure level through
the nozzle is the same in both instances. The mass flow
rate of a tailings stream has, in some cases, been observed
to be reduced by about 30% over nozzle design
specifications, which are based on a single-phase liquid in
which there is no flashing. This reduction in mass flow
rate is largely caused by flashing inside the conventional
nozzle. If flashing is prevented, flow rates can be
calculated more accurately.
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Flashing in the TSRU inlet means may also be
compounded by the creation of a low pressure core in the
swirl chamber of a nozzle caused by the swirl motion of
fluids in the swirl chamber.
Flashing may also result in erosion of the
interior surface of the nozzles. It has been observed that
levels of erosion in a conventional nozzle are higher than
otherwise expected. Without using costly, wear-resistant
materials, the lifetime of conventional nozzles is short,
usually not exceeding a couple of weeks. The increased
erosion of interior surfaces of the nozzles is likely due to
mineral solids in the tailings mixture being subjected to a
higher velocity than would exist absent solvent flashing.
With solvent flashing, the velocity of the tailings stream
in the nozzle increases, usually by about an order of
magnitude. Solids in the tailings stream are therefore
subjected to higher local velocities than absent solvent
flashing.
Solvent flashing therefore contributes to
decreased TSRU throughput, and equipment wear.
According to one broad aspect of the present
invention, a manifold assembly is provided comprising a
chamber having a cross-sectional area that is larger than
the combined surface area of its outlets. In practice, this
would normally be an increase of about a factor of 2, or
more. (See, for example, Ref. Equation (6-15) in Perry's
Chemical Engineers' Handbook 7th ed. McGraw-Hill, 1997,
assuming an orifice discharge coefficient of 0.61.) In an
exemplary embodiment, the cross-sectional area is larger by
about an order of magnitude or more. By increasing the
cross-sectional area of the chamber by, for example, about
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an order of magnitude or more, then the resulting fluid
velocities in the chamber can be decreased by, for example,
about an order of magnitude or more compared to the fluid
velocity in the outlets. The fluid in the chamber is
therefore more evenly distributed over the outlets of the
manifold assembly. A design in accordance with this
exemplary embodiment provides a pressure drop over the
outlets, which, in normal operation, will then be larger by
about two orders of magnitude or more than the pressure
variations in the chamber of the manifold assembly. A
manifold assembly of the present invention can therefore be
used to eliminate solvent flashing.
According to one embodiment of the present
invention, there is provided a tailings solvent recovery
unit comprising: (a) inlet means for receiving a tailings
stream containing a solvent; (b) a vessel for inducing
separation of the solvent from the tailings stream; and (c)
outlet means for recovering the solvent, wherein: the inlet
means comprises a manifold assembly comprising an inlet and
one or more outlets, wherein the inlet and the one or more
outlets are in fluid communication via a chamber having a
cross-sectional area that is larger than the combined
surface area of the one or more outlets.
According to another embodiment of the present
invention, there is provided a method for recovering solvent
from a tailings stream comprising separating a solvent from
the tailings stream using a tailings solvent recovery unit
comprising: (a) inlet means for receiving the tailings
stream containing the solvent; (b) a vessel for inducing
separation of the solvent from the tailings stream; and (c)
outlet means for recovering the solvent, wherein: the inlet
means comprises a manifold assembly comprising an inlet and
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one or more outlets, wherein the inlet and the one or more
outlets are in fluid communication via a chamber having a
cross-sectional area that is larger than the combined
surface area of the one or more outlets.
According to a further embodiment of the present
invention, there is provided a manifold assembly comprising
an inlet and one or more outlets, wherein the inlet and the
one or more outlets are in fluid communication via a chamber
having a cross-sectional area that is larger than the
combined surface area of the one or more outlets.
In a further embodiment of the invention, the
cross-sectional area of the chamber is larger than the
combined surface area of the outlets by about an order of
magnitude or more.
In a further embodiment, each of the one or more
outlets of the manifold assembly comprises a nozzle having a
nozzle inlet, a nozzle outlet and a swirl chamber disposed
between the nozzle inlet and the nozzle outlet.
An exemplary embodiment of the present invention
is shown in Figure 1. Figure 1 is a representative diagram
of an inlet means of a TSRU according to one embodiment of
the present invention. In Figure 1, the manifold assembly
comprises a full bore pipe (10) as the manifold chamber.
Flange (20) connects a first end (30) of the pipe (10) to a
retractable lance (not shown) though which the tailings
stream flows. Flange (40) connects a second end (50) of the
pipe (10) to a blind (not shown) to stop fluid flow. One or
more nozzles (60) are located along pipe (10) for injection
of the tailings stream into a TSRU vessel (not shown).
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Although the foregoing invention has been
described in some detail by way of illustration and example
for purposes of clarity of understanding, it is readily
apparent to those of ordinary skill in the art in light of
the teachings of this invention that certain changes and
modifications may be made thereto without departing from the
spirit or scope of the appended claims.
It must be noted that as used in the
specification, including in the appended claims, the
singular forms of "a", "an" and "the" include plural
reference unless the context clearly indicates otherwise.
By way of example, reference is made throughout this
specification to a manifold assembly having "an" inlet-this
should be understood as also encompassing a manifold
assembly having more than one inlet.
Unless defined otherwise all technical and
scientific terms used herein have the same meaning as
commonly understood to one of ordinary skill and the art to
which this invention belongs.
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