Abstract:
A nozzle for use in the bowl of a disc centrifuge is provided, comprising an inner sleeve forming a longitudinally extending passageway, the inner sleeve having an elevated region at its top, the elevated region having an extended front end; and an outer sleeve for supporting the inner sleeve along most of its length, the outer sleeve having a collar with an outermost edge at its top; whereby when the inner sleeve is inserted into the outer sleeve, the elevated region of the inner sleeve extends past the collar of the outer sleeve and the extended front end of the elevated region extends towards the outermost edge of the outer sleeve collar.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to a modified external nozzle design for use in the outlet of a bowl of a disc centrifuge that reduces wear on the top surface of the nozzles. 
       BACKGROUND OF THE INVENTION 
       [0002]    Centrifugal machines of a nozzle type typically include a rotor or rotating bowl defining a separating chamber containing a stack of separating discs for effecting a two-fraction separation of a feed slurry. The feed slurry is separated into a heavy discharge slurry, or underflow fraction, which is delivered outside the rotor by a plurality of nozzles supported within the outer wall of the rotor. Generally, the plurality of nozzles are circumferentially positioned around the outermost periphery of the rotor. Each nozzle includes an inlet portion in communication with an interior area defined by the rotor bowl and an outlet to allow separated material to escape from the rotor bowl. A light fraction or separated liquid is removed from the rotor by overflow from the top end of the machine. 
         [0003]    In the oil sands industry, disc centrifuges are commonly used for de-sanding bitumen froth recovered from oil sands using a hot or warm water-based extraction process. Typically, bitumen froth comprises about 60% bitumen, 30% solids and 10% water. The bitumen froth is diluted with a solvent, such as naphtha solvent, followed by bitumen separation in a sequence of scroll and disc centrifuges. The inertial forces of the disc centrifuges cause water and solids to migrate outwardly towards the spinning bowl wall. The bitumen works its way inwardly and accumulates near the center of the disc stack, where it is removed as the light phase discharge. Thus, the water and the solids are discharged from the bowl through the plurality of nozzles, which are fitted into apertures formed in the bowl wall. 
         [0004]    Hence, in service, the nozzles are subject to high wear rates, both internally, i.e., the nozzle bore, and externally, i.e., the sleeve which enveloped the passageway or bore of the nozzle. This leads to significant replacement and repair costs. Canadian Patent No. 2,084,974 addresses the issue of internal erosion by modifying the longitudinal bore, which generally comprises two straight segments joined by an elbow, by having the surface of the bore smoothly curved and continuous through the change of direction (i.e., elbow), to prevent the eddying associated with change-of-angle linear junctions of the segments, thereby altering the flow pattern of the stream with a significant reduction in wear. 
         [0005]    As shown herein in  FIG. 1 , labeled Prior Art, the nozzle  1  of Canadian Patent No. 2,084,974, owned by the present applicant, comprises a duplex body formed by an inner sleeve  3  having a top surface  9  and a contiguous outer sleeve  4  having a protruding collar  14 . The outer sleeve  4  forms a sheath which supports the inner sleeve  3  along most of its length. Typically, the inner sleeve is formed of titanium carbide and the outer sleeve  4  of stainless steel. The inner sleeve  3  forms an internal longitudinal bore  5  comprising an inlet segment  6  and an outlet segment  7  joined by an elbow segment  8 . The surface of the elbow segment  8  is curved and smooth, being free of linear junction lines at the joinder of bore surfaces disposed at different angles. 
         [0006]    However, it was discovered that the nozzle in  FIG. 1  still showed considerable wear at the top  9  of inner sleeve  3 . The present invention addresses this issue of external erosion of disc centrifuge nozzles, in particular, at the top  9  of inner sleeve  3 . 
       SUMMARY OF THE INVENTION 
       [0007]    The present applicant used fluid dynamic modeling, e.g., Computational Fluid Dynamics or CFD, to study wear patterns on the outer surface of nozzles routinely used in disc centrifuges. Initially, it was believed that erosion problems at the top of the inner sleeve of the nozzles could be remedied simply by extending (i.e., thickening) the top of the inner sleeve to produce a nozzle having a raised or elevated portion with a blunted nose at the front end. Hence, the inner sleeve could still fit into the outer sleeve, however, it would now have an elevated region. 
         [0008]    However, it was discovered that such nozzles were still having significant erosion problems and a horse shoe-like wear pattern was observed. Such wear pattern was confirmed with the use of CFD, where stagnation was observed due to the blunted nose and the formation of a horse shoe vortex was also observed in this region. It was surprisingly discovered that by tapering the front (i.e., eliminating the blunted nose) of the elevated region of the inner sleeve to form a more wedge shaped front end (a tapered front end), i.e., making it more streamlined, the external wear of these nozzles greatly improved, as the horse shoe eddies and the like were substantially reduced. 
         [0009]    Without being bound to theory, it is believed that having a sharp transition point between the inner sleeve and the outer sleeve of the nozzle (e.g., such as a 90° transition point) causes excessive wear at that point due to the production of various eddies, such as horseshoe eddies. 
         [0010]    Thus, broadly stated, in one aspect of the invention, a nozzle for use in the bowl of a disc centrifuge is provided, comprising:
       an inner sleeve forming a longitudinally extending passageway, the inner sleeve having an elevated region at its top, the elevated region having an extended front end; and   an outer sleeve for supporting the inner sleeve along most of its length, the outer sleeve having a collar with an outermost edge at its top;   whereby when the inner sleeve is inserted into the outer sleeve, the elevated region of the inner sleeve extends past the collar of the outer sleeve and the extended front end of the elevated region extends towards the outermost edge of the outer sleeve collar.       
 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0014]    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 figures, wherein: 
           [0015]      FIG. 1  is a cross-sectional view of a prior embodiment of a disc centrifuge nozzle. 
           [0016]      FIG. 2  is a cross-sectional view of the nozzle of  FIG. 1  where the inner sleeve has an elevated region at its top with a blunted nose at its front end. 
           [0017]      FIG. 3  is a cross-sectional view of the nozzle of  FIG. 2  where the inner sleeve has an elevated region at its top with a tapered wedge shaped front end. 
           [0018]      FIG. 4  is a perspective view of the elevated region of the nozzle in  FIG. 2 . 
           [0019]      FIG. 5  is a perspective view of the elevated region of the nozzle in  FIG. 3 . 
           [0020]      FIG. 6A  is a perspective front view of the inner sleeve of the nozzle in  FIG. 3 . 
           [0021]      FIG. 6B  is a perspective side view of the inner sleeve of the nozzle in  FIG. 3 . 
           [0022]      FIG. 6C  is a perspective top view of the inner sleeve of the nozzle in  FIG. 3 . 
           [0023]      FIG. 7  shows the velocity magnitude in rotating frame of a nozzle having a blunted cap (Panel A) and a nozzle having a streamlined cap (Panel B). 
           [0024]      FIG. 8  shows the wall shear stress distribution on rotating parts for a nozzle having a blunted cap (Panel A) and a nozzle having a streamlined cap (Panel B). 
           [0025]      FIG. 9  shows the swirl in y-direction (flow direction) for a nozzle having a blunted cap (Panel A) and a nozzle having a streamlined cap (Panel B). 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0026]    The detailed description set forth below in connection with the appended drawing 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. 
         [0027]    With reference to  FIG. 2 , nozzle  101  comprises a duplex body formed by an inner sleeve  103  having a top surface  109 , the inner sleeve further comprising an elevated region or cap  116  at its top for further wear protection. Nozzle  101  further comprises a contiguous outer sleeve  104  having a protruding collar  114 . The outer sleeve  104  forms a sheath which supports the inner sleeve  103  along most of its length so that the elevated region or cap  116  of inner sleeve  103  protrudes from outer sleeve  104 . In one embodiment, cap  116  is made from the same material as inner sleeve  103  and generally cap  116  and inner sleeve  103  are formed as a unitary body. Typically, the inner sleeve  103  is formed of titanium carbide and the outer sleeve  104  of stainless steel. Cap  116  further comprises a front snubbed or blunted nose  118 . The snubbed nose  118  at the front end can be seen in a perspective view in  FIG. 4 . 
         [0028]    The inner sleeve  103  forms an internal longitudinal bore  105  comprising an inlet segment  106  and an outlet segment  107  joined by an elbow segment  108 . The surface of the elbow segment  108  is curved and smooth, being free of linear junction lines at the joinder of bore surfaces disposed at different angles. 
         [0029]    However, it was discovered that the nozzle in  FIG. 2  still showed considerable wear, in particular, at the junction  112  of inner sleeve  103  and outer sleeve  104 . The extended collar  114  and the snubbed nose  118  formed an angle (θ) of about 90° and formed a substantial step down from the top surface  109  of cap  116  and the top surface of extended collar  114 . It was observed that there was a horse-shoe wear pattern that developed at the top  109  of inner sleeve  103 . 
         [0030]    The present invention addresses this issue of external erosion of disc centrifuge nozzles, in particular, at the top  109  of inner sleeve  103 . An embodiment of the present invention is shown in  FIG. 3 . In  FIG. 3 , nozzle  201  comprises a duplex body formed by an inner sleeve  203  having a top surface  209 , the inner sleeve  203  further comprising an elevated region or cap  216  at its top for further wear protection. Nozzle  201  further comprises a contiguous outer sleeve  204  having a protruding collar  214 . The outer sleeve  204  forms a sheath which supports the inner sleeve  203  along most of its length so that the elevated region or cap  216  of inner sleeve  203  protrudes from outer sleeve  204 . In one embodiment, cap  216  is made from the same material as inner sleeve  203  and generally cap  216  and inner sleeve  203  are formed as a unitary body. Typically, the inner sleeve  203  is formed of titanium carbide and the outer sleeve  204  of stainless steel. Cap  216  further comprises an extended front end  222 , forming a tapered wedge shaped front end. The extended wedge shaped front end  222  can be seen in a perspective view in  FIG. 5 . The front end  222  covers a substantial portion of the collar  214 ; however, preferably, a portion  220  of the outer sleeve collar  214  upstream of the front end  222  remains uncovered to ensure wear occurs on the nozzle and not the bowl of the disc centrifuge. 
         [0031]    The inner sleeve  203  forms an internal longitudinal bore  205  comprising an inlet segment  206  and an outlet segment  207  joined by an elbow segment  208 . The surface of the elbow segment  208  is curved and smooth, being free of linear junction lines at the joinder of bore surfaces disposed at different angles. 
         [0032]    It was discovered that the nozzle in  FIG. 3  showed considerably reduced wear, in particular, at the junction  212  of inner sleeve  203  and outer sleeve  204 . The outer sleeve collar  214  and the extended front end  222  are secured to one another so that there is no space between the two parts. Further, the angle (θ) is much greater than 90°, e.g., in this embodiment around 150°, and substantially no step down is seen from the top surface  209  of cap  216  and the top surface of extended collar  214 . Thus, it was observed that there was little or no horse-shoe wear pattern that developed at the top  209  of inner sleeve  203 . 
         [0033]    The inner sleeve  203  is shown in three perspective views in  FIG. 6 . In particular,  FIG. 6A  shows the inner sleeve  203  looking towards the front end  222  of cap  216 .  FIG. 6B  shows inner sleeve  203  from the side which shows the extended rounded front end  222 .  FIG. 6C  shows inner sleeve  203  looking down on cap  216  and shows the extended rounded 
       EXAMPLE 1 
       [0034]    Computational fluid dynamics, usually abbreviated as CFO, is a branch of fluid mechanics that uses numerical methods and algorithms to solve and analyze problems that involve fluid flows. Computers are used to perform the calculations required to simulate the interaction of liquids and gases with surfaces defined by boundary conditions. Ongoing research yields software that improves the accuracy and speed of complex simulation scenarios such as transonic or turbulent flows. 
         [0035]    CFD was used to test nozzles  101  and  201 , as shown in  FIG. 2  and  FIG. 3 , respectively, and having caps  116  and  216 , respectively.  FIG. 7  shows the velocity magnitude in rotating frame of a nozzle having a blunted cap  116  (Panel A) and a nozzle having a streamlined cap  216  (Panel B). It can be seen that when the front of the nozzle cap is blunted, as in Panel A, there is stagnation in front of the nozzle (circle). However, when the front of the nozzle cap is extended and streamlined, as in Panel B, there is little or no stagnation in front of the nozzle (circle). 
         [0036]      FIG. 8  shows the wall shear stress distribution on rotating parts for a nozzle having a blunted cap  116  (Panel A) and a nozzle having a streamlined cap  216  (Panel B). Essentially, the radial velocity was analyzed 1 mm outside the bowl wall. It can be seen that when the front of the nozzle cap is blunted, as in Panel A, a horse shoe vortex  150  was observed (circle). However, when the front of the nozzle cap was extended and streamlined, as in Panel B, little or no horse shoe vortex was observed (circle). 
         [0037]      FIG. 9  shows the swirl in y-direction (flow direction) for a nozzle having a blunted cap  116  (Panel A) and a nozzle having a streamlined cap  216  (Panel B). Essentially, the vortex strength was analyzed 1 mm outside the bowl wall. It can be seen that when the front of the nozzle cap is blunted, as in Panel A, a horse shoe vortex  150  was also observed. However, when the front of the nozzle cap was extended and streamlined, as in Panel B, little or no horse shoe vortex was observed. 
         [0038]    Thus, it was observed that the elevated (above bowl surface) stagnation region responsible for the horse shoe vortex of the nozzle of  FIG. 2  could be corrected, i.e., substantially removed, by the addition of a more wedge shaped front end. This change in geometry reduced/eliminated the horse shoe vortex and, hence, the horse shoe vortex wear pattern. Thus, a nozzle with an extended and rounded front end on its inner sleeve cap will have less erosion on the top of the inner sleeve and therefore a greater life span. 
         [0039]    From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention. However, the scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole.