Abstract:
A system for treating tar sand involving a centrifuge where under centrifugal force solvent treated tar sand and water form a three layer system of wet sand, water, and petroleum, where solvent solubilized hydrocarbons are stripped from the wet sand layer, passed through the water, and into the petroleum layer. The hydrocarbons are skimmed from the hydrocarbon layer and recovered.

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application from U.S. patent application Ser. No. 11/946,043 now U.S. Pat. No. 7,985,171, filed Nov. 27, 2007, which claims priority from U.S. Provisional Patent Application 60/867,354, filed 27 Nov. 2006, which applications are hereby incorporated by reference. 
    
    
     BACKGROUND 
     Tar sands, also referred to as bituminous sands, represent a large portion of the unexploited reserve of hydrocarbon resources. A problem that has impeded their develment is the lack of economical methods for separating the hydrocarbon or petroleum portion from the “sand”, the inert mineral portion. 
     SUMMARY 
     Described is a system for processing tar sands to separate hydrocarbons associated with mineral portions or sand of a tar sand. The tar sand is treated with a solvent (such as a petroleum fraction) to solubilize the hydrocarbons associated with the sand. The treated tar sand is then continuously introduced into a spinning centrifuge to subject the tar sand to centrifugal force, which increases the force to strip the solubilized hydrocarbon from the sand. Water is present in the centrifuge so that petroleum from the tar sand (including the hydrocarbon originally in the sand and the solvent), the water, and solid portions of the tar sand (the “sand” or mineral portion) form a three layered system, a solids layer, a water layer, and a petroleum layer. 
     Petroleum from the petroleum layer is continuously removed or skimmed from the petroleum layer to form a hydrocarbon product. Sand is also continuously removed by conveying it against the centrifugal force through and out of the water layer. Where the sand is removed, petroleum is blocked or excluded to prevent the petroleum from becoming reassociated with the sand. By further continuously conveying the sand under centrifugal force, the sand is further dewatered, to produce a damp sand for disposal, such as by depositing it into previously mined out spaces. 
     An exemplary apparatus comprises a cylindrical outer shell and a perforated cylindrical inner shell within the outer shell with a space between the inner and outer shell. Attached to the inner shell within the space are one or more auger flights. Tar sand that has been treated with solvent is introduced through a feed inlet into the outer shell. A drive system spins the outer shell and the inner shell about a spin axis to produce a centrifugal force that directs tar sand to an inside wall of the outer shell. On this inside wall is formed a three-layer system with a solids layer adjacent the inside wall. This layer includes sand, water, and any hydrocarbons and solvent not yet stripped from the sand. In addition, there is an overlying petroleum layer, which includes solvent and hydrocarbon stripped from the sand. Thirdly, there is an intermediate layer of water between the solids layer and the petroleum layer. The water volume is maintained and regulated such that the perforated inner shell is within the water layer. 
     During operation hydrocarbon that has been solubilized by the solvent is stripped from the sand and travels by buoyancy through the water layer, through the perforated inner shell, and to the overlying petroleum layer. A skimmer system is used to remove petroleum from the petroleum layer and convey it to the outside of the outer shell. 
     The drive system is configured to spin or drive the outer shell and the inner shell at different rates. This is so that the auger flights, which are suitably constructed, convey the sand in the solids layer toward the bottom of the outer shell, where it can be removed through a sand outlet. 
     The system for removal may comprise a lower conical section or extension of the outer shell, with the inner shell and the auger flights extended into the conical section. The construction is such that sand is conveyed by the auger flights into the conical section and toward the spin axis, such that the sand is conveyed through and out of the water layer, and is centrifugally dewatered as it is conveyed toward the spin axis. The conical section is extended sufficiently such that after the sand leaves the water, it is subjected further to centrifugal force to dewater the sand before it is removed from the apparatus. The portion of the inner shell extending into the conical section of the outer shell is not perforated in order to block petroleum from the petroleum layer from contacting the sand being conveyed out of the water layer. 
     Optionally, the apparatus has a spinning paddle disposed near the feed inlet to impart a stripping action to the solvent treated tar sand feed, and to convey the feed toward the inside wall of the outer shell. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a flow sheet illustrating a process for separating the hydrocarbon portion from the mineral portion of tar sand. 
         FIG. 2  is a schematic diagram illustrating an example of an apparatus for separating the hydrocarbon portion from the mineral portion of tar sand. 
     
    
    
     DETAILED DESCRIPTION 
     Reference is made to  FIG. 1 , which is a flow sheet illustrating a method for processing tar sand to separate hydrocarbon portions from mineral portions. Tar sand is treated with solvent to solubilize the hydrocarbon portions, and continuously introduced to centrifugal force in the presence of water sufficient to form a layered system comprising a solids layer of sand from mineral portions, a layer of water, and a layer of petroleum of solvent and hydrocarbons from petroleum portions. Petroleum from the petroleum layer and sand are continuously removed to respectively form a hydrocarbon product stream, and a mineral tail stream. 
     EXAMPLE 
     Reference is made to  FIG. 2 , which illustrates an example of a method and apparatus for processing tar sand. The centrifuge or separator  101  comprises an outer shell  103  and an inner shell  105 . Attached to the inner shell is a helical auger flight or flights  109 . The inner and outer shells  103 ,  105  are spun or rotated on the same axis  127 . The spinning rates of the outer and inner shells are synchronized and are at different rates of rotation. 
     Tar sand that has been cut with a suitable solvent to solubilize the hydrocarbons is introduced into inlet  123 . The solvent may be any suitable solvent, such as kerosene or other petroleum extract. By means of the centrifugal action of the spinning outer shell  103  the tar sand is conveyed to the inside wall  131  of the outer shell  103 . The rates of rotation of the outer and inner shells  103 ,  105  are different and synchronized, and the construction of the flight  109  are such that the tar sand is conveyed by the flight down the inside wall  131  of the outer shell  103 . Any suitable combination of spin rates and flight construction is contemplated, as for example, having the outer shell spin slightly faster, as long as the sand conveying action of the auger flight is achieved, and sufficient centrifugal force is provided. There may be one flight or multiple flights. The synchronization of the inner and outer shells can be by any suitable system (not shown), such as, for example, by use of any of synchronized electrical motors, hydraulic motors, planetary gears, chain drives, and the like. 
     The centrifugal force induced by the spinning shells forces any solids and liquids against the inside wall  131  of the outer shell  103 . The solids form a solids layer  111  against the inside wall  131 , which includes tar sand minerals or sand from which petroleum fraction or tar and solvent is extracted. The liquids include water and extracted petroleum fraction and solvent. Water is present in the outer shell, so that a water layer is formed over the sand, which is conveyed through the outer shell within a water phase. 
     As the tar sand is conveyed down the inside wall, under influence of the centrifugal force the solubilized tar strips from the sand and forms an oil or petroleum layer  115  upon the surface of the water. The inner shell is perforated with holes  107  to allow removed hydrocarbons with solvent to “rise” against the centrifugal force by means of buoyancy inward toward the center or spin axis of the drum through the water to a petroleum layer  115 , which is over a water layer  113 . The water layer  113  is between the solids layer  111  and the petroleum layer  115 . The amount of water is such that the inner shell is within the water layer  113  so that the water/petroleum interface  116  is within the inside of the inner shell. Accordingly, the petroleum layer  115  is completely within the inner shell and can be effectively skimmed from the surface. 
     Water is introduced by any suitable means, normally with the tar sand feed. The amount of water is maintained essentially constant to maintain the proper location of the water/petroleum interface  116 . The volume can be regulated by any suitable means, such as any combination of floats, sensors, valves and make-up water lines to add water to the tar sand feedstock. In the figure is shown a sensor  117 . Water removal is continuous and in the amount required to make a damp sand tailing, which is the only “waste” water from the system. 
     Stripped hydrocarbons and solvent are skimmed or removed from the petroleum layer by any suitable system, such as an oil skimmer or scoop  119  with a petroleum outlet  121  to carry the petroleum from the interior of the shells. 
     As the sand approaches the lower end of the cylinder it becomes stripped of petroleum and solvent. The stripped sand is dewatered in a conical section of the outer shell at its lower end. The stripped sand is conveyed along a conical section  129  of the inside wall  131  of the outer shell  103 . The conical section wall extends inward toward the spin axis  127 . The inner shell  105  and auger flight  109  are constructed to extend into the conical section and match the conical construction of the outer shell  103  so as to convey sand inwardly along the inner wall  131  of the conical section  129  of the outer shell  103 . The effect is to convey the sand against the centrifugal force and bring it out of the water layer. 
     In the conical section, the inner shell  105  is not perforated so that hydrocarbons and solvent from the petroleum layer are kept within the inner shell and from the sand as it is removed from the water. The sand is thus removed from the water in the space between the inner and outer shells and is thereby dewatered. The sand is further dewatered and dried by the centrifugal force as it continues along the conical inside wall, until it is eventually passed to outside the outer shell, though an outlet  125 . 
     Optionally, a spinning paddle  135  is placed at the inlet  123 . As the tar sand is introduced into the inlet it hits the paddle, and is forcibly directed toward the inside wall. The agitation is designed to increase the stripping of the solubilized tar from the sand. A disk is placed under the paddle to prevent tar sand from falling through the shell and direct the tar sand to the upper end of the inside wall. The spinning of the paddle need not be synchronized with the spinning of the shells and is preferably rotated in the opposite direction to increase the force for stripping of hydrocarbon from the sand. The axis of spin for the paddle is preferably the same as (or near to and parallel to) the axis of spin for the inner and outer shells. However, any suitable configuration is contemplated that functions to increase the stripping action and direct the tar-sand feed toward the top of the inside wall of the outer shell. 
     While this invention has been described with reference to certain specific embodiments and examples, it will be recognized by those skilled in the art that many variations are possible without departing from the scope and spirit of this invention, and that the invention, as described by the claims, is intended to cover all changes and modifications of the invention which do not depart from the spirit of the invention.