Patent Application
20160310872
The present invention relates generally to a feedwell system for separation vessels such as those used for separating bitumen from an oil sand/water slurry and, more particularly, to a feedwell system having a bottom deflector pate.
Separation vessels such as gravity separation vessels, thickeners, and the like, are used in various fields to separate solid particles from liquid in a slurry. For example, gravity separation vessels are used in the oil sands industry to separate bitumen and water from solids in an oil sand slurry.
Bitumen extracted from oil sand, such as oil sand mined in the Fort McMurray region of Alberta, is generally made up of water-wet sand grains and viscous bitumen. To eventually produce a commercial petroleum product from oil sand, the bitumen must be removed from the sand. To remove the bitumen from the sand/bitumen mixture, the oil sand is often crushed and then mixed with water to form an oil sand/water slurry. This slurry can then be subjected to what is commonly referred to as “pipeline conditioning” by pumping the slurry some distance through a pipeline, commonly called a hydrotransport pipeline. The conditioned slurry is then typically diluted with a fluid, such as water, to form a diluted slurry. By diluting the slurry, the density of the slurry can be altered to a more desirable density for separation of the bitumen in the slurry. The diluted slurry is then fed to a gravity separation vessel such as a primary separation vessel (PSV) where the relatively quiescent conditions and entrained air in the bitumen allows a significant portion of the bitumen to float towards the top of the gravity separation vessel and collect in a layer of froth, commonly called primary bitumen froth. This primary bitumen froth can be recovered and further treated to eventually be made into a commercial petroleum product.
In addition to the bitumen froth layer, typically a middlings layer and a tailings layer are also formed in the gravity separation vessel. The middlings layer forms below the bitumen froth layer and the tailings layer forms at the bottom of the gravity separation vessel. The middlings and tailings layers are removed and often further treated to extract out additional bitumen that remains in these layers. However, the bitumen in these layers is not as easily recoverable.
To try and increase the quality of the bitumen froth that collects in the bitumen froth layer, an underwash layer is often purposely formed above the middlings layer and below the bitumen froth layer in the PSV. The underwash layer is typically formed by introducing heated liquid, such as water, in between the middlings layer and the bitumen froth layer. The heated liquid in the underwash layer can help to increase the temperature of the bitumen froth produced. The heated underwash water can also replace the middlings in the bitumen froth as it is formed, thereby reducing the amount of solids in the froth.
To enhance gravity separation, quiescent conditions need to be maintained in the PSV. One of the main factors affecting these quiescent conditions is the introduction of the slurry to the gravity separation vessel. Typically, these gravity separation vessels are operated as a continuous process with slurry continuously being introduced into the vessel while end products, such as bitumen froth, a tailings stream, etc. are continuously being removed from the vessel. The introduction of slurry can have a detrimental effect on these quiescent conditions due to the high velocity of the feed and the recirculation currents formed by the separation of the coarse solids from the slurry. Additionally, the introduction of the slurry can have a detrimental effect on the underwash layer, with swirling and vortices created in the gravity separation vessel by the introduction of the slurry affecting the stability of the underwash layer and causing an erosion of the underwash layer.
It has been discovered using both laboratory and computational fluid dynamics (CFD) simulations that coarse solids present in an oil sand slurry flowing out of conventional feedwells in primary separation vessels (PSV) create a plunging flow pattern underneath the feedwell. This flow pattern has strong downward velocities which can entrain bitumen droplets and carry them into the PSV underflow, resulting in bitumen losses.
It was discovered that bitumen losses from the PSV could be significantly reduced by minimizing the plunging flow pattern beneath the feedwell seen in
In one embodiment, the feedwell system further comprises an extension pipe attached to the opening to divert the flow of the feed stream from the opening directly onto the center or apex of the conical deflector plate. The extension pipe favors an axisymmetric down-flow which impacts onto the apex producing a circumferentially uniform discharge. It is understood that the opening must be of a sufficient size to allow the passage of the entire feed stream, including any lumps that may be present therein.
In another embodiment, the feedwell further comprises at least one substantially vertical baffle located within the substantially cylindrical chamber for reducing the momentum of the feed stream as it enters the substantially cylindrical chamber. In one embodiment, the width of the baffles may increase in the rotation direction as you move away from the inlet with the thinnest baffle position directly in line with the feed stream inlet, thus, preventing excessive erosion of the baffles located closest to the feed inlet point. It is understood that baffles can be different shapes as known in the art, for example, L shaped baffles can be used.
In one embodiment, the deflector plate comprises a plurality of apertures in the form of slots along the perimeter of the deflector plate. In one embodiment, there are four slots. In one embodiment, the deflector plate has a substantially horizontal outer periphery and the at least one aperture extends to the substantially horizontal outer periphery.
In another aspect, a feedwell system for a separation tank is provided, comprising:
In one embodiment, the second deflector plate comprises a plurality of apertures in the form of slots along the perimeter of the deflector plate. In one embodiment, there are four slots. In one embodiment, the second deflector plate has a substantially horizontal outer periphery and the at least one aperture extends to the substantially horizontal outer periphery. In another embodiment, the first deflector plate also has a substantially horizontal outer periphery.
It is understood that the space between the first and second deflector plates should be sufficient to allow any large lumps in the feed stream to pass therebetween. For example, when the feed is oil sand slurry, it is possible to have lumps therein having a diameter of up to 4 inches. In one embodiment, the first and second deflector plates are substantially parallel. However, it is understood that the plates can be either convergent or divergent, provided, however, that the narrowest space between the plates is sufficient to allow the passage of the largest lumps in the feed stream therebetween.
Referring to the drawings wherein like reference numerals indicate similar parts throughout the several views, several aspects of the present invention are illustrated by way of example, and not by way of limitation, in detail in the following figures. It is understood that the drawings provided herein are for illustration purposes only and are not necessarily drawn to scale.
The detailed description set forth below in connection with the appended drawings is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments contemplated by the inventor. The detailed description includes specific details for the purpose of providing a comprehensive understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details.
Bottom floor 66 of the substantially cylindrical chamber 52 of the feedwell system 50 has an opening 64 which can have an extension pipe 68 extending therefrom. The opening 64 can be positioned in the center of the bottom plate 66 of the substantially cylindrical chamber 52 and can be sized so that it constrains the amount of slurry exiting the feedwell 50. In one embodiment, the opening 64 has a substantially smaller area than the area of the bottom floor 66. By sizing the opening 64 based on the flow rate that will be used for the slurry entering the feedwell 50 through the inlet 62, the feedwell 50 can be designed so that a desired level of slurry can be maintained in the feedwell 50. If an extension pipe 68 is provided, the extension pipe 68 can help to cause a uniform axisymmetric down-flow in the slurry exiting the substantially cylindrical chamber 52 through the opening 64
A deflector assembly 70 can be provided below the opening 64 in the bottom floor 66. The deflection assembly 70 can have a deflector plate 76 positioned spaced below the opening 64 in the bottom floor 66 or below extension pipe 68. In one aspect, the deflector plate 76 can be generally conically-shaped with a apex 77 of the deflector plate 76 positioned spacedly below the opening 64 in the bottom plate 66 so that slurry discharged out of the substantially cylindrical chamber 52 of the feedwell 50 is deflected by the apex 77 of the deflector plate 76 to follow the downward slant of the deflector plate 76.
The feedwell 50 may further have a lid 59 at the upper perimeter edge 53 having an opening 61, to prevent the slurry feed from splashing out while still allowing venting.
Deflector plate 76 further comprises apertures 48. The apertures 48 in this embodiment are in the form of circular openings or cutouts at or near the outer periphery of the deflector plate 76. In one embodiment, the apertures can be any shaped opening or cutout. In one embodiment, the apertures may extend inwardly from the periphery of the conically-shaped deflector plate 76.
Thus, in the embodiments shown in
As shown in
In the embodiment shown in
In this embodiment, there are four inwardly extending apertures 148 in the form of slots (15° cutouts), which slots are evenly spaced around the periphery of the substantially horizontal periphery portion 178. The apertures 148 can be seen more clearly in
In one aspect, a number of baffles can be provided in the substantially cylindrical chamber to reduce swirling of slurry in the substantially cylindrical chamber of the feedwell system.
A deflector assembly 270 can be provided below the opening 264 in the bottom floor 266. The deflection assembly 270 can have a first deflector plate 272 and a second deflector plate 276. In one aspect, the first deflector plate 272 has a generally frusto-conical shape and an opening 274, which opening 274 is positioned immediately below opening 264 of the bottom floor 266. In one embodiment, the opening 274 is connected to opening 264 by an extension pipe 268. The second deflector plate 276 can be generally conically-shaped with a apex 277 of the deflector plate 276 positioned spacedly below the opening 274 of the first deflector plate 272 so that slurry 209 discharged out of the walled member 252 flows in between the space formed between the two deflector plates 272 and 276. Thus, the feed is deflected by the apex 277 of the second deflector plate 276 to follow the downward slant of the second deflector plate 276. A substantially horizontal periphery portion 278 of the second deflector plate 276 can extend outwards to attempt to redirect the flow of slurry horizontally. A similar substantially horizontal periphery portion 273 may extend from the first deflector plate 272.
The first deflector plate 272 and the second deflector plate 276 act in conjunction to direct at least a substantial portion of the flow of slurry entering a separator vessel from the feedwell system 250 outwardly in a substantially horizontal direction. However, as previously discussed, the slurry flowing through the opening 264 to the deflection assembly 270 can create a plunging flow pattern. This flow pattern has strong downward velocities which can, for example, entrain bitumen droplets and carry them into the PSV underflow, resulting in bitumen losses. Thus, the second deflector plate 276 can be provided with at least one aperture 248, and an embodiment of which aperture 248 can be seen more clearly in the perspective view of feedwell system 250 in
It can be seen in
The second deflector plate 276 can be generally conically-shaped with a apex 277 of the deflector plate 276 positioned spacedly below the opening 274 of the first deflector plate 201 so that slurry 209 discharged out of the walled member 252 flows in between the space formed between the two deflector plates 201 and 276. Thus, the feed is deflected by the apex 277 of the second deflector plate 276 to follow the downward slant of the second deflector plate 276. A substantially horizontal periphery portion 278 of the second deflector plate 276 can extend outwards to attempt to redirect the flow of slurry horizontally. A similar substantially horizontal periphery portion 273 may extend from the first deflector plate 201. The first deflector plate 201 and the second deflector plate 276 act in conjunction to direct at least a substantial portion of the flow of slurry entering a separator vessel from the feedwell system 250 outwardly in a substantially horizontal direction.
However, as previously discussed, the slurry flowing through the opening 264 to the deflection assembly 370 can create a plunging flow pattern. This flow pattern has strong downward velocities which can, for example, entrain bitumen droplets and carry them into the PSV underflow, resulting in bitumen losses. Thus, the second deflector plate 276 can be provided with at least one aperture 248, which at least one aperture can be a circular or other shaped cutout or a slot as shown in
Computational fluid dynamics (CFD) simulations were performed for five different feedwell systems. Each feedwell system comprised a top deflector plate and a bottom deflector plate.
The five designs tested were as follows:
By using CFD, it was discovered that the best performing feedwell system was the one having a bottom deflector plate with a horizontal periphery portion that increased its radius by 50% and that had four apertures, i.e., four slots (15° cutouts). The CFD results for this design can be seen in
Bitumen recovery and sand recovery were also determined for each feedwell design described above. The feedwells were used in primary separation vessels (PSVs) and the feed used was oil sand slurry.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to those embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments. Reference to an element in the singular, such as by use of the article “a” or “an” is not intended to mean “one and only one” unless specifically so stated, but rather “one or more”. Nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims.
