Dual-solvent extraction of oil sand bitumen

Abstract

A process for extracting bitumen from oil sand is provided, comprising: contacting mined oil sand with a high-flash point heavy solvent (HS) to produce a dense oil sand slurry; mixing the dense slurry with a first light solvent (LS) stream and a second LS stream to give a heavy solvent to light solvent (HS/LS) mass ratio of about 75/25 to about 40/60; subjecting the HS/LS-diluted oil sand slurry to a first stage solid-liquid separation to produce a first liquids stream containing bitumen and a first solids stream; and washing the first solids stream with a mixed solvent having a HS/LS mass ratio of about 50/50 to about 20/80 and subjecting the solids and the mixed solvent to a second stage solid-liquid separation to produce a second liquids stream and a second solids stream.

What is claimed is: 
     
         1 . A process for extracting bitumen from oil sand, comprising:
 (a) contacting mined oil sand with a high-flash point heavy solvent (HS) to produce a dense oil sand slurry;   (b) mixing the dense slurry with a first light solvent (LS) stream and a second LS stream to give a heavy solvent to light solvent (HS/LS) mass ratio of about 75/25 to about 40/60;   (c) subjecting the HS/LS-diluted oil sand slurry to a first stage solid-liquid separation to produce a first liquids stream containing bitumen and a first solids stream; and   (d) washing the first solids stream with a mixed solvent having a HS/LS mass ratio of about 50/50 to about 20/80 and subjecting the solids and the mixed solvent to a second stage solid-liquid separation to produce a second liquids stream and a second solids stream.   
     
     
         2 . The process of  claim 1 , further comprising in step (b), mixing the dense slurry with a minimal amount of water to give a water to solids (W/S) mass ratio less than about 0.1 to flocculate solids. 
     
     
         3 . The process of  claim 1 , further comprising before step (b), preparing the dense oil sand slurry for oil sand deoxygenation and passing it through an airlock. 
     
     
         4 . The process of  claim 3 , further comprising:
 (e) mixing the second solids stream and two LS streams in a repulper prior to being subjected to a third stage solid-liquid separation to produce a third liquids stream and a third solids stream.   
     
     
         5 . The process of  claim 4 , further comprising:
 (f) washing the third solids stream with LS and subjecting the solids and LS stream to a fourth stage solid-liquid separation to produce a fourth liquids stream and a fourth solids stream.   
     
     
         6 . The process of  claim 1 , wherein in step (b), the first LS stream comprises from about 70 wt % to about 90 wt % LS. 
     
     
         7 . The process of  claim 1 , wherein in step (b), the W/S mass ratio is less than about 0.08. 
     
     
         8 . The process of  claim 5 , wherein in step (c), the first liquids stream is treated in a distillation unit to recover bitumen, LS and HS. 
     
     
         9 . The process of  claim 8 , wherein the recovered HS is the solvent used in step (a). 
     
     
         10 . The process of  claim 9 , wherein the recovered HS comprises either pure HS, or about 70 wt % HS and about 30 wt % bitumen. 
     
     
         11 . The process of  claim 8 , wherein the recovered LS is used for washing in step (f). 
     
     
         12 . The process of  claim 5 , wherein the second liquids stream is used as the second LS stream in step (b). 
     
     
         13 . The process of  claim 12 , wherein second LS stream comprises from about 45 wt % to about 65 wt % LS. 
     
     
         14 . The process of  claim 5 , wherein the third liquids stream is passed through a splitter to produce LS for use in mixing in step (b) as the first LS stream; washing in step (d); and repulping in step (e). 
     
     
         15 . The process of  claim 5 , wherein the fourth liquids stream is used for repulping in step (e). 
     
     
         16 . The process of  claim 5 , wherein the LS present in the fourth solids stream is recovered by drying the fourth solids stream in a solids dryer to produce dry tailings. 
     
     
         17 . The process of  claim 16 , wherein the fourth solids stream is pre-heated before drying. 
     
     
         18 . The process of  claim 17 , wherein the fourth solids stream is pre-heated in a jacketed screw conveyor with steam before drying. 
     
     
         19 . The process of  claim 16 , wherein the solids dryer removes and recovers greater than 99% LS from the fourth solids stream and leaves less than about 300 mg/kg of LS in solids. 
     
     
         20 . The process of  claim 16 , wherein the dry tailings are mixed with fluid fine tailings to produce trafficable solids containing about 85 wt % solids. 
     
     
         21 . The process of  claim 16 , wherein the recovered LS passes through a condenser to remove residual water before the LS is used for washing in step (f). 
     
     
         22 . The process of  claim 1 , wherein the oil sand contains fines as high as 49% in solids and bitumen as low as 6%, the bitumen recovery is at least about 95%, and the HS and LS recoveries are at least about 99%. 
     
     
         23 . The process of  claim 1 , wherein the HS is a non-volatile, high-flash point light gas oil stream, distilled from oil sand bitumen, and has a boiling range of about 130-470° C. 
     
     
         24 . The process of  claim 1 , wherein the LS is a C 6 -C 10  hydrocarbon stream produced from an oil sand bitumen upgrading unit, and has a boiling range of about 69-170° C. 
     
     
         25 . The process of  claim 24 , wherein the LS is aliphatic C 6 -C 7  and has a boiling range of about 69-110° C. 
     
     
         26 . The process of  claim 1 , wherein in step (a), the dense oil sand slurry is produced in a first slurry preparation and conditioning unit. 
     
     
         27 . The process of  claim 26 , wherein the first slurry preparation and conditioning unit comprises a rotatable tumbler. 
     
     
         28 . The process of  claim 1 , wherein in step (b), the HS/LS-diluted oil sand slurry is produced in a second slurry preparation and conditioning unit. 
     
     
         29 . The process of  claim 28 , wherein the second slurry preparation and conditioning unit comprises a baffled tank agitated with one or more impellers. 
     
     
         30 . The process of  claim 29 , wherein the one or more impellers comprise 45° pitched blade turbines. 
     
     
         31 . The process of  claim 30 , wherein the impellers have a diameter ranging from about 0.55 to about 0.7 of the tank diameter. 
     
     
         32 . The process of  claim 31 , wherein the bottom clearance ranges from about 0.01 to about 0.15 of the tank diameter. 
     
     
         33 . The process of  claim 31 , wherein the bottom clearance ranges from about 1 cm to about 5 cm for any tank diameter. 
     
     
         34 . The process of  claim 32 , wherein the power input by the one or more impellers ranges from about 1 W/kg to about 15 W/kg of slurry.