Abstract:
A method of solvent recovery from oil sand extraction plant tailings, using 180 degree opposing steam-assisted accelerating nozzles, impacting on each other&#39;s high velocity jets, thus creating an impact area at the point of collision, creating an exceedingly large number of small droplets having a very large surface area exposed to the depressurized environment inside the vessel in which the nozzles are mounted. The diluent thus escaping from the tiny droplets is collected from the vessel space and recovered by condensation in a surface condensor and returned to the process.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention is based on Provisional Application entitled Method and Apparatus for Recovery of Lost Diluent in Oil Sands Extraction Tailings, filed Jul. 28, 2000, application No. 60/221,373, and claims the priority filing date of that application.  
         BACKGROUND OF THE INVENTION  
         [0002]    A diluent is used to reduce the viscosity of the recovered bitumen from oil sands. The viscosity must be reduced to make it possible to remove the residual impurities like water and fine minerals from the bitumen.  
           [0003]    The diluent that is used is mixed with the recovered bitumen, at a certain ratio with the bitumen, to arrive at a workable viscosity of the diluted bitumen.  
           [0004]    When the impurities are removed, as for example by centrifugation, a certain percentage of the original diluent is lost along with the water and fine solids.  
           [0005]    The present methods of stripping the diluents from the tailing stream is to use vacuum distillation with overhead vapour recovery. These methods are only partially successful in recovering the diluent. This results in substantial economic loss.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention provides a method and apparatus for diluent recovery from extraction tailings that is more effective than existing procedures.  
           [0007]    According to one aspect of the invention streams of extraction tailings Are directed through a nozzle at an impaction target. Next, saturated steam is injected into the stream of extraction tailings to produce a confluent stream of steam and extraction tailings. Rapid expansion of the steam causes acceleration of the composite stream resulting in a violent collision with the impaction target. The expanding steam dramatically increases the impact velocity. By utilizing this technique impact velocities approaching 7,000 feet per minute can be achieved. It is preferred to use a plurality of nozzles positioned in a common horizontal plane with a stream of one of the nozzles serving as the impaction target for the other of the nozzles. A preferred configuration is to position two nozzles in 180 degree opposed orientation.  
           [0008]    Utilizing the above principles of operation there is provided an apparatus for diluent recovery which is comprised of a containment vessel having a top, a bottom, and peripheral side walls. A plurality of inlet nozzles are secured in a common horizontal plane to the peripheral side walls. Each nozzle has a first inlet for receiving a first fluid, a second inlet for receiving a second fluid and a single outlet for discharging a mixed stream of the first and second fluids. The mixed discharge stream of one of the nozzles is focused at the mixed discharge stream of the other of the nozzles, such that the mixed discharge streams impact each other. Means is provided positioned adjacent the top of the containment vessel for drawing off the vapors resulting from the impact. An outlet is positioned adjacent the bottom of the containment vessel for removing extraction tailings which have been stripped of diluent.  
           [0009]    Although there are a variety of configurations that can be used in terms of the number of nozzles, it is preferred to use two nozzles oriented in a common plane disposed in confronting relation 180 degrees apart.  
           [0010]    While there are a variety of nozzles that are capable of handling a mixed stream of steam and extraction tailings, it is preferred that the nozzle enhance the accelerating effect of the rapidly expanding steam. Even more beneficial results may be obtained when each nozzle includes a body having a passage leading to the outlet and the first inlet has an extension portion disposed in the passage. A steam chamber communicates with the first inlet and circumscribes the second inlet. The steam chamber has a short spiral that surrounds the second inlet, imparting to the steam flow a spiraling motion at the outlet of the nozzle. The rotating and accelerating steam flow will tend further to increase the intensity of the impact when the opposing jets meet. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    These and other features of the invention will become more apparent from the following description in which reference is made to the appended drawings, wherein:  
         [0012]    [0012]FIG. 1 is a front sectional elevation of apparatus for recovering diluent from extraction tailings constructed in accordance with the teachings of this invention.  
         [0013]    [0013]FIG. 2 is a plan view of the nozzle orientation when installed in the apparatus for solvent recovery from oil sand tailings. In this view, two additional nozzles have been shown in dotted lines to indicate the possibility of using a plurality of opposed nozzles. For purposes of explanation only one set of nozzles will be considered.  
         [0014]    [0014]FIG. 3 is a side elevation view of the nozzles shown in FIG. 2, to illustrate the formation of the fine droplets produced as a result of the high velocity impact when the streams meet at mid-vessel.  
         [0015]    [0015]FIG. 4 is a side elevation view showing the shed deck and doughnut deck arrangements for final heating of the oil sands tailings.  
         [0016]    [0016]FIG. 5 is a side elevation of the wetted plate separator arrangement. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]    Referring now to FIG. 1 of the drawing there is shown a system for diluent recovery from oil sand extraction tailings. Apparatus  10  comprises a containment vessel  12  having a top  14 , a bottom  16 , and peripheral side walls  18 . Referring to FIG. 3 each nozzle  20  and  22  has a first inlet  24  for receiving a first fluid, a second inlet  26  for receiving a second fluid and a single outlet  28  for discharging a confluent stream of the first fluid and the second fluid. As seen in FIG. 1 nozzles  20  and  22  are oriented in 180 degree opposed relation such that their discharge streams are directed to impact with each other. An eductor  30  is used as means for drawing vapors from containment vessel  12 . Eductor  30  is positioned at the top of vessel  12 . Vapors pass through a wetted plate separator and a demister pad  31  to eductor  30 . An outlet  32  is positioned adjacent bottom  16  of vessel  12  for removing the stripped oil sand tailings. Saturated steam passes through flow line  38  where it is diverted by a series of secondary flow lines. Secondary flow line  40  controlled by valve  42  brings saturated steam to eductor  30 . Secondary flow lines  44  and  46  controlled by valves  48  and  50  bring saturated steam to nozzles  20  and  22 . Secondary flow line  52  controlled by valve  54  brings saturated steam to steam sparger  56  positioned within and in spaced relation from the bottom  16  of vessel  12 . Outlet  32  is connected to a pump-out line  74  having a branch line controlled by valve  76 . The drain valve  76 , the use of which, is to effect cleaning of the containment vessel is also used to obtain samples of the cleaned tailings. Referring to FIG. 3, the preferred form of nozzles  20  and  22  includes a body having a first inlet  24  and a second inlet  26  in addition to a common outlet  28 . First inlet  24  of nozzle  22  communicates with oil sand tailings line  36  and second inlet  26  communicates with steam flow line  46 . Nozzle  20  is similarly connected. Referring to FIG. 5, the rising vapors and small droplets generated by the impact when the jet streams meet, are drawn through plates  72  of a plate separator. It is inevitable that some fine mineral particles will be entrained in the upflow and will stick to the plate surfaces. A continuous fine hot water spray will be provided to wash the plates clean and prevent the growth of particles on the plates.  
         [0018]    The use and operation of apparatus  10 , as illustrated in FIGS. 1 through 5, will now be described in relation to the preferred method of operation for which such apparatus was developed. Two nozzles  20  and  22  are positioned in 180 degrees opposed relation in a common horizontal plane such that the jet stream from one nozzle forms an impaction target for the jet stream from the opposed nozzle. Additional paired nozzles can be added if desired, as shown by way of example, in dotted lines in FIG. 2. With the nozzles so positioned oil sand tailings are directed through flow lines  36  to the first inlet  24  of nozzles  20  and  22 . Saturated steam is then injected via steam flow lines  44  and, as seen in FIG. 1, into the second inlets  26  of nozzles  20  and  22  to produce at the outlet of the nozzles a confluent stream of steam and oil sand tailings. Referring to FIGS. 2 and 3 saturated steam flowing through secondary inlet  26  is passed through coiled tubing  29  to impart to the steam a spiral component of velocity before it mixes with oil sand tailings pumped through first inlets  24 . Oil sand tailings pass from first inlet  24  into an extension of the nozzle just inside the nozzle outlet  28 . Outlet  28  is so shaped that the high velocity spiraling steam flow meets with the oil sand tailings just inboard of nozzle outlet  28 . When a mixed stream of steam and oil sand tailings is created, as described, an expansion of the steam causes an acceleration of each of the mixed streams resulting in a violent collision of the streams. By having the steam and tailing flows meet just short off the outlet  28  the steam pushes the stream of oil sand tailings further enhancing the impact velocity. With this method of operation impact velocities approaching 7000 feet per minute can be attained.  
         [0019]    The method of operation as it applies to solvent recovery from oil sand tailings will now be summarized. High velocity oil sand tailings streams are emitted from diametrically opposed nozzles  20  and  22 . The streams are accelerated through the use of steam injections. The mixed streams impact each other to produce a violent collision in which solvent is ejected in the form of solvent vapors. The vapors are removed from the top  14  of containment vessel  12  by a vacuum generated by eductor  30 . The solvent vapors will be evacuated from inside containment vessel  12  along with low pressure steam. To achieve the high velocities required saturated steam at approximately 150 pounds per square inch is allowed to expand when entering nozzles  20  and  22 . As previously noted, steam velocities can reach speeds as high as 7000 feet per minute, depending on the back pressure inside containment vessel  12 . When the mixed streams collide kinetic energy will be converted to potential energy, or pressure energy. The pressure change will be rapid squeezing out the solvent vapors in a solution state from inside the host structure. A very large spray of small droplets is generated surrounding the impact area. The solvent vapors remaining inside the droplets are presented with a second opportunity to escape through the surface area of the droplets since the pressure of containment vessel  12  is kept low by eductor  30  thus assisting in escape of the solvent vapors out of the droplets.  
         [0020]    There is one more area where solvent vapors can be removed from the tailings host. As seen in FIG. 4 the droplets generated in the impact zone will drop down and gather as a thin layer on top of shed-deck  64   a  from which area they flow onto a doughnut deck  64   b  located below the sheddeck. The underside of these decks are kept hot by a sparging steam delivered by sparger ring  62 . From this point the oil sand tailings continue on their way down to the collecting sump  84  as seen in FIG. 1. Solvent vapors that escape will rise to the top of the containment vessel  12  where they are evacuated through the demister pad  31  and ejector  30 .  
         [0021]    In sump  84  where the treated oil sands tailings eventually come to rest there is a final steam sparger  56 . The main function of the sparger is to ensure that the tailings keep sufficiently warm so that the slurry remains fluid enough to pump out through nozzle  32  located at the bottom  16  of the containment vessel. The result is that steam sparger  56  not only keeps the tailings host hot but also additionally assists in the removal of trace amounts of the solvent. The expansion of the steam will cause the temperature of the host tailings to drop. The main function of the steam sparger  56  is to keep the oil sands tailings from becoming too viscous when the temperature drops to permit their removal by pump. There is also a potential danger that small quantities of bitumen from the upstream process could accumulate in the sump  84  and make evacuation by pump impossible if the temperature drops below 60 degrees centigrade. The oil sand tailing minus the solvent is withdrawn through outlet  32  at a fixed rate and under control of a pump to a storage unit not shown.  
         [0022]    As a last point in the solvent recovery process the solvent vapors that accumulate at the top  14  of the vessel are removed through a plate separator  72 . The plates are kept wet with hot water by sparger  80  located above the plates. The solvent vapors will escape through the plate spaces and through the demister  31  to be evacuated by eductor  30  and delivered to an overhead condenser, (not shown), where the solvent is recovered and returned to the process.  
         [0023]    It will be apparent to one skilled in the art that modifications may be made to the illustrated embodiment without departing from the scope of the invention as hereinafter defined in the appended claims.