Patent Application
20150101962
Embodiments disclosed herein relate to feed delivery systems for separation vessels and, more particularly, to a high velocity feedwell for a froth separation vessel.
Separation vessels are well known in a variety of industries, such as for separation of solid particles from a liquid phase. Gravity separators typically separate solids by gravity settling, creating a generally quiescent environment in the vessel so as to minimize bulk fluid flux for minimizing the effect of terminal velocities of the components therein. The solids are generally discharged from a bottom of the vessel and the clarified fluid is discharged from a top of the vessel.
In the case of extraction of bitumen from mined oil sands, the oil sand is typically mixed with water, which may be hot, for forming a slurry. The slurry is conditioned and delivered to a primary settling cell (PSC). Droplets of bitumen separate from the majority of the solids therein which settle by gravity and rise to the top of the PSC as a froth. Typically about 10% of the slurry feed stream becomes froth. The froth typically comprises about 55 wt % bitumen, 35 wt % water and 10 wt % fine solids. The froth is thereafter removed from the PSC for further treatment to remove the water and the fine solids. As is well understood in the industry, the froth is diluted with a solvent, naphthenic or paraffinic, and is separated in a froth settling unit (FSU) to produce diluted bitumen as the product stream. Typically, about 80% of the feed stream to the FSU becomes diluted bitumen.
It is known by those skilled in the art that, in paraffinic froth treatment, asphaltenes are precipitated and form aggregates, prior to reaching the FSU, which may trap some of the fine solids therein. The negatively buoyant aggregates, as well as the coarser solids and water settle within the FSU and the cleaned, solvent-diluted bitumen product (dilbit) is removed from the top of the FSU.
It is also well known to deliver a feedstream to separation vessels using a feedwell. Conventional feedwells for delivering feed to the separation vessel are often a single, vertical pipe design with a deflector plate spaced from the discharge end for distributing the slurry feed radially to the vessel.
In the case of PSCs, feedwells are known for delivering the conditioned slurry feedstream, which typically comprises bitumen, water and both coarse solids (≧44 um) and fine solids, (≦44 um). As one of skill in the art will appreciate, the feed stream, being the conditioned slurry, has significantly different settling properties than the solvent-diluted froth. Generally the slurry, which comprises the about 55% bitumen, 10% solids and 35% water, does not contain solvent or asphaltenes and is primarily the result of an effort to separate bitumen from tailings and is not directed, at this stage, to product quality.
In the case of Canadian Patent 2,734,811, to Imperial Oil Resources, a PSC feedwell comprises a centrally located feedwell, typically positioned near a top of the vessel. The PSC feedwell has a bottom deflector plate and a protector plate to improve the underwash layer stability. The protector plate has ventilation openings which reduce the discharge velocity, limit the formation of an adverse pressure gradient and encourage circumferential distribution. Thus, energy in the feed is dissipated within the feedwell and the feed is delivered radially outwardly therefrom rather than being directed downward toward the vessel underflow before separation of the froth from the tailings can occur.
In Canadian patent application 2,809,959 to Syncrude, a central PSC feedwell is designed to deliver slurry toward the center of a plurality of inclined plate assemblies.
In the case of delivery of solvent-diluted froth to an FSU, Canadian patent 2,672,004 to Imperial Oil Resources Limited (IOL) teaches delivering the feed to the FSU through one or more side wall ports in the FSU, preferably situated about half the height of the vessel and entering normal thereto, which deliver the feed such that it flows down the inside wall of the vessel. The feed delivery is at low velocity and is characterized by a Richardson number of greater than 1.0. The gentle flow of the feed to the FSU vessel is purported to mitigate upward flux of the smaller particles, such as mineral solids, by trapping the smaller particles below the larger particles, such as the asphaltene aggregates which formed as a result of dilution with a paraffinic solvent in the feed line prior to the FSU. The minerals solids are thus carried to the discharge of the vessel by the larger particles. Further, efforts were made by IOL to design the side-inlets in such a way as to have a reduced Reynolds number, about 2500 to 35000, at the vessel.
Conventionally, large scale settler, typically clarifiers or thickeners, have a low height to diameter aspect ratio, such as about 1:10, wherein energy dispersion and creation of a zero vertical flux zone are key to effective settling therein. As such, turbulence, if formed in the vessel, may result in ejecting bulk fluid from the vessel without separation. FSU height to diameter ratio is typically between about 1:0.5 to 1:2.
Clearly there is interest in apparatus for feeding a bitumen-rich feed to a separation vessel so as to support the separation of solids and liquids in the vessel for producing a product overflow stream which is substantially free of fine solids and water, while at least minimizing the cross-sectional area of the vessel required to do so.
Embodiments of FSU taught herein deliver feed to a separation zone within the FSU vessel at a Richardson number less than about unity for maximizing the flow path in the separation zone. In embodiments, the feed is discharged into the separation zone at a Richardson number between about 0.001 to about 0.8.
In one broad aspect, a method for treating a bitumen-containing, paraffinic froth feed containing a solvent-diluted bitumen, water, solids and asphaltenes in a froth settling vessel comprises delivering the feed to a separation zone within the vessel. The feed is discharged into the separation zone, through one or more inlets, each inlet discharging the feed at a high velocity for forming a coherent stream along a flow path generally horizontally toward a boundary and having a Richardson number less than about unity for maximizing the flow path in the separation zone. The flow velocity of the flow path dissipates adjacent the boundary for separating the feed into a diluted bitumen and solvent product which rises to a top of the vessel and a waste stream comprising water, solids and asphaltenes which settles by gravity to a bottom of the vessel.
In another broad aspect, a system for separating a feed into a diluted bitumen and solvent product stream and a waste stream comprises a settling vessel having an upper cylindrical portion and a conical bottom portion, the product stream being discharged as an overflow therefrom and the waste steam being discharged as an underflow therefrom. A feedwell, having one or more inlets to the vessel, delivers the feed to a separation zone within the vessel for discharging the feed into the separation zone through one or more inlets, each inlet discharging the feed at a high velocity, having a Richardson number less than about unity. A coherent stream is formed along a flow path generally horizontally toward a boundary for maximizing the flow path in the separation zone. The velocity dissipates at about the boundary for separating the feed into the product stream which rises to a top of the vessel and the waste stream comprising water, solids and asphaltenes which settles by gravity to a bottom of the vessel.
Un-coalesced water droplets are carried above the separation zone and are coalesced in a coalescing zone above the separation zone. The coalesced water droplets fall by gravity through the separation zone, to settle at the bottom of the vessel, carrying suspended solids associated therewith.
The inlets which discharge feed into the vessel are arranged about the center or axis of the vessel for directing the feed outwardly toward the perimeter of the vessel. Alternatively, the inlets are arranged at the perimeter of the vessel for directing the feed inwardly toward the axis. The inlets can be normal to an inlet pipe or angled or tangential relative to the inlet pipe.
FSU according to embodiments taught herein have a reduced footprint as well as reduced costs associated therewith. Costs are reduced including one or more of reducing the foundation structure required to support the vessel weight, including the weight of the contents, lowering the amount of solvent inventory required, reducing the de-inventory storage facility size and better controlling of the system having a smaller size vessel and reduced residence time.
The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.
FIG. 6A1 is a vertical slice of a CFD (Computational Fluid Dynamics—ANSYS® fluent) simulation, illustrating a vertical velocity component in mm/min, ranging from −3000 to +3000, feed being introduced to the vessel from inlets at about a center of the vessel and directed toward a perimeter wall of the vessel;
FIG. 6A2 is a line drawing representative of FIG. 6A1;
FIG. 6C1 is a vertical slice of a CFD simulation illustrating a vertical velocity component in mm/min, ranging from −3000 to +3000, feed being introduced to the vessel from inlets at about the perimeter wall of the vessel and directed toward the center of the vessel;
FIG. 6C2 is a line drawing representative of FIG. 6C1;
Generally, the term “feedwell” implies a structure, such as a chamber which is positioned within a vessel, such as a settling vessel, the chamber having inlets therefrom to the vessel. In embodiments described herein, the term “feedwell” is used interchangeably to refer to a structure which provides the inlets to the vessel and to the inlets themselves.
Embodiments of a feedwell 10 for a froth settling unit (FSU) or vessel 12 are described herein and, in contradistinction to the prior art, a diluted bitumen froth F is delivered to the FSU in a vigorous manner and along a flow path characterized by a low Richardson number Ri, being less than about unity. The froth F may carry at least some insoluble asphaltenes therewith. The Richardson number Ri in a vessel is related to the fluid properties, spatial arrangement and the feed inlet velocity.
A low Richardson number is generally understood to represent a flow having sufficient kinetic energy that the feed stream exiting the inlet to the vessel is coherent and generally unaffected by buoyancy. Therefore, one can determine the discharge parameters for the feed F to achieve the Richardson number Ri given characteristics of the feed F, the velocity of discharge and the areal influence on the feed F once delivered to the FSU vessel.
More particularly, as discussed herein, the Richardson number for the incoming feed or feed jet is based on a feedwell outlet diameter (d), a feed density (ρ-feed), a fluid density surrounding the feed zone (ρ_fluid), a velocity of the feed jet (u) and gravitational acceleration (g) as represented in the following equation:
Ri=d*g*(ρ_feed−ρ_fluid)/ρ_fluid/u2
In embodiments, the Richardson number is in the range of 0.001 to 0.8. In embodiments, the Richardson number may be from about 0.001 to about 0.5, and more particularly from about 0.001 to about 0.125.
The feed F is discharged from the feedwell 10 generally horizontally and across the FSU vessel 12 for utilizing a substantial portion of the vessel's cross-section and achieving effective separation. Substantially maximum utilization of the vessel occurs at low Richardson numbers. The substantially 100% utilization results from local upward velocities which approach average upward velocities in the clarification zone. The feedwell discharges the bitumen-containing feed through one or more feed inlets 14 at a relatively high velocity resulting in the low Richardson number and the coherent, generally horizontal feed stream until such time as the kinetic energy is dissipated and bulk separation can occur. Use of a large portion of the FSU vessel 12 enables use of smaller vessels for the same feed stream, or more effective separation and higher capacity than in conventionally sized FSU vessels. Applicant believes that the lower the Richardson number, at the feed inlet, particularly within the range of about 0.001 to about 0.8, the more the hydraulics of the fluid flow in the vessel 12 approach average for the whole clarification zone and thus, the smaller the resulting FSU vessel 12 cross sectional area. Thus, FSU vessels 12 utilizing feedwells 10, according to embodiments taught herein, are capable of efficiently separating diluted bitumen and solvent from water, solids and asphaltenes in the feed F and have a reduced footprint as well as reduced costs associated therewith.
In embodiments, for example, where the froth F is diluted with pentane (C5), the hydrocarbon phase may comprise from about 30% to about 95% of the froth feed F. In embodiments where the froth F is diluted with butane (C4) the hydrocarbon phase may comprise about 20% to about 95% of the feed F. Fine particles are typically distributed in both the hydrocarbon rich phase and the aqueous phase. In the FSU 12, as the aqueous phase has a higher density (920-1400 g/L) than the hydrocarbon phase (550-750 g/L), the aqueous phase settles to a bottom 16 of the vessel 12 with the coarse particles and carries the suspended fine particles therewith toward a vessel underflow 18. The FSU 12 is typically operated at between about 65° C. and about 150° C.
Any coarse solids in the feed F are caused to separate under gravity as the energy in the feed F, discharged from the feed inlets 14 and resulting from the relatively high velocity, is dissipated along the flow path across an extent of the FSU vessel 12. Separated coarse and fine solids are recovered at the underflow 18 and may comprise between about 0% to about 75% hydrocarbon, 0% to about 75% trapped water or a combination thereof. The hydrocarbon, when diluted with a paraffinic solvent, contains asphaltenes. The hydrocarbon in the solid phase contains about 20% to about 99% asphaltenes.
As one of skill in the art will appreciate, in embodiments taught herein, the term “inlet” refers to any type of inlet 14 which is capable of delivering feed F to the vessel 12 in a stream at a velocity to result in the specified range of Richardson number. In embodiments, the inlet 14 can be an open pipe, a nozzle or other such fluid feed delivery apparatus, as is well understood in the art.
In an embodiment, as shown in
The separation horizon or zone is at or about a discharge of the feedwell 10 which is positioned in the vessel 12 such that the one or more inlets 14 are immersed in fluid contained within the vessel wherein the fluid contains about 60% of the aqueous phase and about 40% of the hydrocarbon phase, regardless the height of the vessel 12. The FSU vessel 12 has a conical bottom 16 and a cylindrical upper portion 24 extending upwardly therefrom. The conical bottom 16 of the vessel 12 typically has an angle of between about 45° to about 75°. In embodiments, a height of the cylindrical portion 24 of the vessel 12, above the one or more inlets 14 in the separation zone Z, is about a height equivalent to a diameter of the vessel 12.
In the embodiment shown in
Having reference to
As shown in
As shown in
Applicant further contemplates embodiments wherein the feed F enters the vessel 12 through one or more inlets 14 which extend through the perimeter wall 22 of the FSU vessel 12, spaced about a circumference thereof. The feed F enters the vessel 12 at the high velocity, having the Richardson number of less than unity and more particularly between 0.001 and 0.8. As in the case of
Having reference to
As shown in FIGS. 6A1 to 6D, Computational Flow Dynamics (CFD) simulations illustrate the separation and the formation of a relatively uniform clarification zone 40 above the one or more inlets 14. In embodiments, the vessel 12 has a height to diameter aspect ratio of greater than about 0.5. In embodiments, a height of the cylindrical portion 24 of the vessel 12 above the one or more inlets 14 is about the diameter of the vessel 12.
Having reference to FIGS. 6A1, 6A2 and 6B, in embodiments wherein the one or more inlets 14 are positioned at or near the center of the vessel 12, feed F exits the one or more inlets 14 to the vessel 12 at the separation horizon or zone Z in the vessel 12 as a coherent stream which is directed to the boundary P, being at or adjacent the perimeter wall 22. As can be seen, the lightest components and most dense components of the feed F, may begin to rise or fall, respectively, before the majority of the coherent stream of feed F reaches the boundary P. Thereafter, at the boundary P of the separation zone Z, when the energy is dissipated therefrom, dense components, such as water W, solids S and asphaltenes A, plunge generally downward in the vessel 12, under the effect of gravity, for settling to the bottom 16 of the vessel 12. The less dense components, such as solvent V and bitumen B, rise in the vessel 12.
The upward and downward flows are generally segregated from the incoming coherent stream of feed F, such as in areas within the vessel 12, between the coherent feed streams F. As one of skill will appreciate, as constituents of the feed F begin to separate within the vessel 12, the constituents largely avoid the more violently mixed areas of the vessel, such as near the incoming coherent streams of feed F, by rising and falling in the areas of the vessel between the incoming feeds.
In embodiments taught herein, the segregation of the upward and downward flows occurs without the need for baffles or other mechanical internals which are prone to mechanical failure, plugging and which may not be robust with respect to variances in operating parameters affecting the sizes of the upward and downward flows.
As will be understood by those of skill in the art, light components may be carried downward with heavier components as they separate and further, some heavier components may be carried upward with the solvent and diluted bitumen rising in the vessel 12. More particularly, as the upward flow of lighter components passes the incoming coherent stream of feed F, an upward impetus or flux is created which is sufficient to carry some un-coalesced water droplets W therewith above the separation zone Z and into the clarification zone 40 thereabove. As the water droplets W in the clarification zone 40 coalesce, such as in a water coalescing zone WC above the incoming coherent feed streams, the coalesced water droplets W therein achieve a terminal velocity sufficient to counteract the upward flux. Thereafter, the coalesced water droplets W fall through the separation zone Z, between the incoming coherent feed streams F to a water-rich zone 42 below the inlets 14, carrying solids S suspended in the water W therewith. Similarly, any solvent V and diluted bitumen B which is carried downward with the denser components, such as the bulk of the water W, solids S and asphaltenes A, as they plunge in the vessel 12 separates from the denser components below the separation zone Z and rises through the separation zone Z between the incoming coherent feed streams F.
FIGS. 6C1, 6C2 and 6D illustrate an embodiment wherein the one or more inlets 14 are positioned in, at or adjacent the perimeter wall 22 of the, feed F exiting the one or more inlets 14 to the vessel 12 at the separation zone Z in the vessel 12 as a coherent stream of feed F which is directed to the boundary P, being at or adjacent the center C of the vessel 12. Separation occurs generally as described for FIGS. 6A1, 6A2 and 6B.
By way of example, an ideal FSU vessel 12 has a superficial flux rate approaching the settling rate. The superficial flux rate is defined herein as the average upward velocity of the diluted bitumen and solvent toward the top 34 of the vessel 12. The superficial flux rate is generally calculated as flowrate divided by cross-sectional area of the FSU 12. The settling rate is defined herein as a terminal settling velocity to achieve a product being 99.5% pure within the vessel.
Having reference to
More particularly,
The results of
In designing an FSU vessel 12, the flowrate is fixed, thus the higher the superficial flux rate, the smaller the vessel 12. By way of example, if the settling rate for solids in the ideal FSU vessel 12 is determined to be 260 mm/min and the output is designed to be 3000 m3/hr of product, being 99.5% pure solvent-diluted bitumen, the cross-sectional area of the ideal FSU vessel 12 would be 192.3 m2.
The size of the vessel 12 required to achieve the desired characteristics is then calculated for various Richardson numbers, as shown in Table A, based upon the relationships shown in
Having reference to
When the capacity is turned down to 30%, the operating line is below the design line which indicates the vessel 12 can still perform for turn down rates.
It is clear to one of skill in the art that as the feed flow rate of the FSU vessel decreases, the Richardson number increases and the tolerable vertical flux decreases, however even at 30% capacity the resulting flux is below the Richardson's adjusted tolerable flux and therefore, Applicant believes that embodiments described herein are effective even when the operating rate of the vessel is less than 100% of the design capacity.
This application claims the benefit of U.S. Provisional Patent application Ser. No. 61/889,692, filed, Oct. 11, 2013, the entirety of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61889692 | Oct 2013 | US |
