Abstract:
The present invention provides a method for extracting bitumen from an oil sand stream that includes the steps of: providing an oil sand stream; contacting the oil sand stream with a liquid comprising a solvent thereby obtaining a solvent-diluted oil sand slurry; separating the solvent-diluted oil sand slurry, thereby obtaining a solids-depleted stream and a solids-enriched stream; increasing the S/B weight ratio of the solids-enriched stream thereby obtaining a solids-enriched stream having an increased S/B weight ratio and a liquid stream; filtering the solids-enriched stream having an increased S/B weight ratio, thereby obtaining bitumen-depleted sand. In another embodiment, the invention is a system for practicing this method.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/603,018 filed Feb. 24, 2012, which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a method for extracting bitumen from an oil sand. 
         [0003]    BACKGROUND TO THE INVENTION 
         [0004]    Various methods have been proposed in the past for the recovery of bitumen (sometimes referred to as “tar” or “bituminous material”) from oil sands as found in various locations throughout the world and in particular in Canada such as in the Athabasca district in Alberta and in the United States such as in the Utah oil sands. Typically, oil sand (also known as “bituminous sand” or “tar sand”) comprises a mixture of bitumen (in this context also known as “crude bitumen”, a semi-solid form of crude oil; also known as “extremely heavy crude oil”), sand, clay minerals and water. Usually, oil sand contains about 5 to 25 wt. % bitumen (as meant according to the present invention), about 1 to 13 wt. % water, the remainder being sand and clay minerals. 
         [0005]    As an example, it has been proposed and practiced at commercial scale to recover the bitumen content from the oil sand by mixing the oil sand with water and separating the sand from the aqueous phase of the slurry formed. Disadvantages of such aqueous extraction processes are the need for extremely large quantities of process water (typically drawn from natural sources) and issues with removing the bitumen from the aqueous phase (whilst emulsions are being formed) and removing water from the bitumen-depleted sand. 
         [0006]    Other methods have proposed non-aqueous extraction processes to reduce the need for large quantities of process water. Example of such a non-aqueous extraction process are disclosed in e.g. U.S. Pat. No. 3,475,318 and US 2009/0301937, the teaching of which is hereby incorporated by reference. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    In one embodiment, the present invention provides a method for extracting bitumen from an oil sand stream, the method comprising at least the steps of:
   (a) providing an oil sand stream;   (b) contacting the oil sand stream with a liquid comprising a solvent thereby obtaining a solvent-diluted oil sand slurry;   (c) separating the solvent-diluted oil sand slurry, thereby obtaining a solids-depleted stream and a solids-enriched stream;   (d) increasing the solvent-to-bitumen weight ratio of the solids-enriched stream thereby obtaining a solids-enriched stream having an increased S/B weight ratio and a liquid stream;   (e) filtering the solids-enriched stream having an increased S/B weight ratio, thereby obtaining bitumen-depleted sand.   
 
         [0013]    It has now surprisingly been found according to the present invention that it results in significantly reduced filtration times when compared with a process that does not apply an intermediate step of increasing the solvent-to-bitumen weight ratio of the solids-enriched stream (viz. step (d)). 
         [0014]    According to the present invention, the providing of the oil sand in step (a) can be done in various ways. Typically, before contacting the dry oil sand (which may contain some water being present in the oil sand) with the solvent the oil sand particles are reduced in size, e.g. by crushing, breaking and/or grinding, to below a desired size upper limit. Experience in large scale operations shows that the achievable size upper limit for such size reduction is currently about 8 inch. 
         [0015]    The contacting in step (b) of the oil sand with the liquid comprising a solvent thereby obtaining a solvent-diluted oil sand slurry is not limited in any way. As an example, the liquid may be added before, during or after the size-reducing step (if available) of the oil sand. Further size reduction in the presence of the liquid (comprising the solvent) may be performed; part of the size reduction may take place by dissolution of bitumen present in the oil sand, but further size reduction e.g. by using screens and/or again crushers, breaker or grinders may be performed, if desired. Typically, the solvent forms the major part of the liquid and is preferably present in an amount of from 50 wt. % up to 100 wt. %, preferably above 60 wt. %, more preferably above 70 wt. %, even more preferably above 80 or even above 90 wt. %, based on the amount of the liquid. 
         [0016]    The solvent as used in the method of the present invention may be selected from a wide variety of solvents, including aromatic hydrocarbon solvents and saturated or unsaturated aliphatic (i.e. non-aromatic) hydrocarbon solvents; aliphatic hydrocarbon solvents may include linear, branched or cyclic alkanes and alkenes and mixtures thereof. Preferably, the solvent in step (b) comprises an aliphatic hydrocarbon having from 3 to 9 carbon atoms per molecule, more preferably from 4 to 7 carbons per molecule, or a combination thereof. Especially suitable solvents are saturated aliphatic hydrocarbons such as propane, butane, pentane, hexane, heptane, octane and nonane (including isomers thereof), in particular butane, pentane, hexane and heptane. It is preferred that the solvent in step (b) comprises at least 90 wt. % of the aliphatic hydrocarbon having from 3 to 9 carbon atoms per molecule, preferably at least 95 wt. %. Also, it is preferred that in step (b) substantially no aromatic solvent (such as toluene or benzene) is present, i.e. less than 5 wt. %, preferably less than 1 wt. %. Herewith, the asphaltene content of the bitumen in the bitumen-depleted sand remains relatively high when compared with the asphaltene content of the bitumen in the original oil sand stream. 
         [0017]    Preferably, the particles of the solvent-diluted oil sand slurry obtained in step (b) are screened or reduced in size to have a diameter below 5.0 cm, preferably below 3.0 cm, more preferably below 2.0 cm. As the screening or size reduction is performed in the presence of solvent (rather than size reduction under dry conditions), this helps breaking down the larger particles and dissolving the bitumen thereby avoiding the formation of sticky lumps. Additionally, by mixing the oil sand stream with the solvent before the filtration (in step (e)), an increased filtration rate is obtained. 
         [0018]    Preferably, the solvent-diluted oil sand slurry obtained in step (b) has a solvent-to-bitumen (S/B) weight ratio of from 0.5 to 4.0, preferably from 0.7 to 3.0, more preferably from 0.9 to 2.5. In some embodiments, the slurry obtained in step (b) may have an S/B weight ratio above 1.0, or even above 1.2. 
         [0019]    Further it is preferred that the solvent-diluted oil sand slurry obtained in step (b) comprises from 10 to 60 vol. % of solids, preferably from 20 to 40 vol. %, more preferably from 25 to 35 vol. %. 
         [0020]    After contacting the oil sand with the solvent in step (b), the solvent-diluted oil sand slurry is separated in step (c), thereby obtaining a solids-depleted stream and a solids-enriched stream. Typically, the solvent is removed from the solids-depleted stream obtained in step (c) thereby obtaining a bitumen-enriched stream. This bitumen-enriched stream may be sent to a refinery or the like for further upgrading. Preferably, the solids-enriched stream obtained in step (c) comprises from 30 to 65 vol. % of solids, preferably from 40 to 55 vol. %, more preferably from 45 to 55 vol. %. Typically, the solids-enriched stream obtained in step (c) has about the same S/B weight ratio as the solvent-diluted oil sand slurry obtained in step (b), hence from 0.5 to 4.0, preferably from 0.7 to 3.0, more preferably from 0.9 to 2.5. 
         [0021]    In step (d), the S/B weight ratio of the solids-enriched stream is increased thereby obtaining a solids-enriched stream having an increased S/B weight ratio and a liquid stream; hence, the solids-enriched stream having an increased S/B weight ratio obtained in step (d) has an S/B weight ratio that is higher than the S/B ratio of the solids-enriched stream obtained in step (c). Typically, the liquid stream obtained in step (d) will also have an S/B weight ratio that is higher than the S/B ratio of the solids-enriched stream obtained in step (c). 
         [0022]    The person skilled in the art will readily understand that step (d) can be achieved in various ways. As an example, the solids-enriched stream obtained in step (c) may be contacted with a stream having a higher S/B weight ratio (such a stream may include pure solvent). Such contacting may for instance take place in counter-current decanters, counter-current hydrocyclones or counter-current wash columns. 
         [0023]    According to an especially preferred embodiment of the present invention, at least part of the liquid stream obtained in step (d) is used in the contacting of step (b), as solvent. 
         [0024]    Preferably, the solids-enriched stream having an increased S/B weight ratio obtained in step (d) has an S/B weight ratio of from 1.5 to 8.0, preferably from 2.0 to 7.0, more preferably from 2.2 to 6.0. Typically, the solids-enriched stream having an increased S/B weight ratio obtained in step (d) has about the same amount of solids as the solids-enriched stream obtained in step (c), i.e. from 30 to 65 vol. % of solids, preferably from 40 to 55 vol. %, more preferably from 45 to 55 vol. %. 
         [0025]    In step (e), the solids-enriched stream having an increased S/B weight ratio is filtered thereby obtaining bitumen-depleted sand. Usually, the bitumen-depleted sand is dried, thereby obtaining a dried bitumen-depleted sand stream containing less than 500 ppmw, preferably less than 300 ppmw, of the solvent. 
         [0026]    Typically, in step (e) one (e.g. the below-mentioned first or second filtrate) or more filtrate streams (optionally including one or both of the below-mentioned first and second filtrates) are obtained as well, which may be recycled to other parts of the process. 
         [0027]    Preferably, in step (e) a (“first”) bitumen-enriched filtrate is obtained, which is at least partly reused in the contacting of step (b). Typically, this bitumen-enriched filtrate has an S/B weight ratio of from 1.2 to 8.0, preferably from 2.0 to 7.0, more preferably from 2.2 to 6.0. 
         [0028]    Further it is preferred that in step (e) a (“second”) bitumen-depleted filtrate is obtained, which is at least partly reused in the washing of step (d). Preferably, this bitumen-depleted filtrate has an S/B weight ratio of above 3.0, preferably above 5.0 and typically below 200. 
         [0029]    The person skilled in the art will readily understand that the filtering in step (e) can be performed in many different ways. Although some fresh solvent may be used at the start-up of the process of the present invention, the addition of fresh solvent later on is preferably kept to a minimum; most of the solvent used in the filtration step is recycled from downstream of the process. Also, the splitting of the one or more filtrates in the first and/or second (and optionally further) filtrates can be performed in various ways. Typically, the first filtrate obtained in step (e) leaves the filter cake earlier than the second filtrate obtained in step (e). 
         [0030]    In another aspect the present invention provides a system for performing the method according to the present invention, the system at least comprising: 
         [0031]    a mixer for contacting the oil sand stream with a liquid comprising a solvent, the mixer having an inlet for the oil sand stream and an outlet for a solvent-diluted oil sand slurry; 
         [0032]    a solid/liquid separator for separating the solvent-diluted oil sand slurry, the separator having a first outlet for a solids-depleted stream and a second outlet for a solids-enriched stream; 
         [0033]    a washer for increasing the S/B weight ratio of the solids-enriched stream, the washer having a first outlet for a solids-enriched stream having an increased S/B weight ratio and a second outlet for a liquid stream; and 
         [0034]    a filter for filtering the solids-enriched stream having an increased S/B weight ratio, the filter having an outlet for a bitumen-depleted sand. 
     
    
     
       BRIEF DESCRIPTION OF FIGURES 
         [0035]      FIG. 1  schematically shows a process scheme of a first embodiment of the method in accordance with the present invention; 
           [0036]      FIG. 2  schematically shows a process scheme of a second embodiment of the method in accordance with the present invention; and 
           [0037]      FIG. 3  schematically shows a process scheme of a third embodiment of the method in accordance with the present invention. 
       
    
    
       [0038]    For the purpose of this description, a single reference number will be assigned to a line as well as a stream carried in that line. Same reference numbers refer to the same or similar elements. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0039]      FIG. 1  schematically shows a simplified process scheme of a first embodiment according to the present invention for extracting bitumen (i.e. in the context of the invention a bituminous and/or extremely heavy crude oil like material) from an oil sand stream. The process scheme is generally referred to with reference number  1 . The process scheme  1  shows a crusher  2 , a de-oxygenation unit  3 , a mixer  4 , a solid/liquid separator (such as a settler)  5 , a washer  6 , a filter  7 , a dryer  8 , a clarifier  9 , a SRC (solvent recovery column)  11 , and a fresh solvent source  12 . 
         [0040]    During use of the process scheme of  FIG. 1 , an oil sand stream  10  is provided and fed to the mixer  4 . Typically, before entering the mixer  4 , the oil sand stream  10  has been crushed (e.g. in crusher  2 ) or treated otherwise, to reduce the size of the larger oil sand lumps to below a pre-determined upper limit. Experience in large scale operations shows that the achievable size upper limit for such size reduction is currently about  8  inch. Further, the oil sand stream is usually de-oxygenated (e.g. in de-oxygenation unit  3 ), in particular when a non-aqueous solvent is subsequently used for the bitumen extraction. 
         [0041]    In the embodiment of  FIG. 1 , the oil sand stream  10  is contacted in the mixer  4  with solvent stream  60  (preferably containing an aliphatic hydrocarbon solvent and a certain amount of bitumen) recycled from downstream of the process (and with stream  80  which is further discussed below) thereby obtaining a solvent-diluted oil sand slurry  20 . Usually, in the mixer  4  (or in a separate unit, if needed), the particles of the solvent-diluted oil sand slurry obtained are reduced in size, typically to have a diameter below 5.0 cm. Any undesired materials (such as rocks and woody material) that may hinder downstream processing may be removed by using screens or the like (preferably in the presence of solvent) and the remaining oil sand particles are reduced in size in the presence of the solvent, e.g. by crushing, breaking and/or grinding. Typically the contacting step in mixer  4  is executed at about ambient temperatures, preferably at a temperature in the range from 0-40° C., preferably 5-25° C., and at about atmospheric pressure. 
         [0042]    The slurry stream  20  exiting the mixer  4  is fed (using a pump) into the settler  5  and allowed to settle, thereby obtaining (as an overflow) a solids-depleted stream  30  and (as an underflow) a solids-enriched stream  40 . The solids-depleted stream  30  may be further processed in clarifier  9  to remove fines; the overflow of the clarifier  9  may be sent as stream  100  to a SRC  11 , whilst the underflow  110  of the clarifier  9  may be combined with the solids-enriched stream  50  having an increased S/B weight ratio (discussed below) and/or with the solids-enriched stream  40  (not shown). In the SRC  11 , solvent is removed from the overflow  100  of the clarifier  9  thereby obtaining a bitumen-enriched stream  120 ; the solvent recovered in the SRC  11  may be recycled in the process, e.g. as wash solvent stream  130  to the filter  7 . 
         [0043]    The solids-enriched stream  40  exiting the settler  5  is fed into the washer  6  and contacted with a solvent containing stream. The washer  6  may be any device for increasing the S/B weight ratio of the solids-enriched stream  40  and usually is a counter-current decanter, a counter-current hydrocyclone or a cyclowash hydrocyclone. A suitable washer is for example Krebs CycloWash obtainable from FLSmidth A/S (Valby, Denmark). 
         [0044]    In the embodiment of  FIG. 1 , a filtrate stream  90  obtained in the filter  7  is used for increasing the S/B weight ratio in the washer  6 ; it goes without saying that other streams may be used as well, instead or in addition (including pure solvent), to increase the S/B weight ratio of the solids-enriched stream  40 . Used liquid is removed from the washer  6  as (an overflow) stream  60  and reused as solvent in the mixer  4 . Further a solids-enriched stream  50  having an increased S/B weight ratio is removed from the washer  6  (optionally combined with stream  110  from the clarifier  9 ) and fed to the filter  7  for filtration. 
         [0045]    In the filter  7 , the solids-enriched stream  50  having an increased S/B weight ratio is filtered, thereby obtaining a bitumen-depleted sand stream  70 ; typically this bitumen-depleted sand stream  70  is the “filter cake” as used in the filter  7 . This bitumen-depleted sand stream  70  may be sent to a dryer  8  and removed as dried stream  140 ; this dried stream  140  would in the art be referred to as “tailings”. The dried stream  140  can be used for land reclamation. Of course, if needed, further removal of solvent from the dried stream  140  may be performed. A recovered solvent stream  150  may be recycled from the dryer  8  to e.g. the filter  7 . 
         [0046]    In the embodiment of  FIG. 1 , a first bitumen-enriched filtrate (removed as stream  80 ) and a second bitumen-depleted filtrate (removed as stream  90 ) are obtained as well in the filter  7 . It goes without saying that further filtrate streams may be generated in the filter  7 . The first bitumen-enriched filtrate  80  is recycled to the mixer  4  and the second bitumen-depleted filtrate  90  is sent to the washer  6 ; in  FIG. 1  an optional additional solvent stream  170  is shown, which may combined with stream  90  (or directly fed into washer  6 ). The solvent stream  170  may originate from e.g. recycled solvent stream  150  or from fresh solvent stream  160  (both discussed below). 
         [0047]    As shown in the embodiment of  FIG. 1 , a stream  160  of fresh solvent may be fed from the fresh solvent unit  12  to the filter  7 , instead of or in addition of recycled solvent streams  130  (from the SRC  11 ) and  150  (from the dryer  8 ); of course other sources of solvent recycle streams may be used as well. 
         [0048]      FIGS. 2 and 3  schematically show a simplified process scheme of a second and third embodiment according to the present invention for extracting bitumen from oil sand. 
         [0049]    In  FIG. 2 , recycling of a filtrate stream ( 90  in  FIG. 1 ) from the filter  7  to the washer  6  does not take place and the full filtrate  80  is sent to the mixer  4 . Fresh solvent  170  (for example originating from stream  160 ) alone may be used for increasing the S/B weight ratio in washer  6 . 
         [0050]    In  FIG. 3  recycling of a filtrate stream ( 80  in  FIG. 1 ) from the filter  7  to the mixer  4  does not take place. 
         [0051]    The person skilled in the art will readily understand that many modifications may be made without departing from the scope of the invention. 
         [0052]    The present invention is described below with reference to the following Examples, which are not intended to limit the scope of the present invention in any way. 
       EXAMPLE 1 
       [0053]    A 753.3 g sample of an Athabasca oil sand (having a bitumen content of 9.7 wt. %; the particles having a diameter below 5.0 cm), 104.7 g solvent (n-pentane; “S1”) and 188 g of diluted bitumen were mixed for 2.5 minutes under ambient conditions using a mixer at 500 rpm to obtain a slurry having a target S/B weight ratio of 1.6. The diluted bitumen as used in this Example was bitumen (containing 11 wt. % asphaltenes) diluted with n-pentane. The purpose of adding diluted bitumen was to adjust the solids volume fraction of the slurry to about 37 vol. % to mimic the actual bitumen extraction process (see in this respect also the recycle streams 60 and 80 in the Figures). 
         [0054]    The slurry was then transferred to a 1400 ml settle tube and allowed to settle for 10 minutes, after which a solids-depleted stream (supernatant liquid; stream 30 in Figures) having an S/B weight ratio of 1.5 was removed. The solids-enriched fraction remaining in the settle tube was transferred to a tumbler (Reax 20, obtainable from Heidolph (Schwabach, Germany), at 15 rpm setting) and contacted (whilst mixing) during 5 minutes with 149 g fresh solvent (“S2”) and transferred again to the settle tube and allowed to settle, wherein the supernatant liquid (stream  60  in the Figures; having an S/B weight ratio of 2.8) was removed. The resulting solids-enriched stream (stream  50  in the Figures) had an increased S/B weight ratio. 
         [0055]    The solids-enriched stream having an increased S/B weight ratio was transferred to a filtration vessel (diameter of the filter was 78 mm), allowed to settle, and the surface of the filter cake levelled (height of the filter cake was about 9 cm). The supernatant liquid on top of the filter cake was pushed through the filter cake until only a thin (1 mm) layer of supernatant liquid remained (the pressure drop across the filter cake was 0.8 bar). 
         [0056]    81.3 g of fresh solvent was added as a wash solvent on top of the filter cake and pushed through the filter cake until only a thin (1 mm) layer of supernatant liquid remained. The collected filtrate (including the supernatant liquid on top of the filter cake) had an S/B weight ratio of 2.8. The time taken for the filtration was 16 seconds. 
       EXAMPLE 2  
       [0057]    Following the same procedure and equipment of Example 1, a 756.6 g sample of the same Athabasca oil sand as used in Example 1 was treated, whilst using the amounts and S/B weight ratios as indicated in Table 1. The time taken for the filtration was 23 seconds. 
       COMPARATIVE EXAMPLES 1 AND 2   
       [0058]    In order to show the effect of the intermediate contacting step (step (d)) according to the present invention and the resulting increased S/B weight ratio of the solids-enriched stream (stream  50  in the Figures, which is the filter feed stream) on the filtration time, Comparative Examples 1 and 2 were performed (see Table 1 for amounts and S/B weight ratios used). In Comparative Examples 1 and 2 the same Athabasca oil sand was used, but no contacting step was performed to increase the S/B weight ratio (as in step (d); but the other steps were kept the same); hence in Comparative Examples 1 and 2 the filtration step was performed with the same S/B weight ratio as during the contacting step. 
         [0059]    Table 1 below shows the results obtained for Examples 1 and 2 and Comparative Examples 1 and 2. The “delta p” is the pressure difference across the filter cake as applied by pressurized nitrogen above the filter cake. “t1” represents the time from beginning of feeding of the solids-enriched stream having an increased S/B weight ratio until any liquid on top of the filter cake was filtered through the bed and the top surface of the filter cake became visible. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Ex. 1 
                 Ex. 2 
                 C. Ex. 1 
                 C. Ex. 2 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Oil sand [g] 
                 753.3 
                 756.8 
                 751.1 
                 753.4 
               
               
                 Solvent S1 [g] 
                 104.7 
                 145.1 
                 101.2 
                 145.6 
               
               
                 Target S/B weight ratio of 
                 1.6 
                 2.35 
                 1.6 
                 2.35 
               
               
                 slurry 
               
               
                 Actual S/B weight ratio of 
                 1.5 
                 2.1 
                 1.3 
                 2.1 
               
               
                 stream 30 
               
               
                 S/B weight ratio of stream 60 
                 2.8 
                 4.35 
                 — 
                 — 
               
               
                 S/B weight ratio of stream 50 
                 2.8 
                 4.35 
                 1.3 
                 2.1 
               
               
                 (filter feed) 
               
               
                 Solvent S2 [g] 
                 149.0 
                 167.3 
                 — 
                 — 
               
               
                 Wash solvent for filtration 
                 81.3 
                 153.8 
                 82.4 
                 153.2 
               
               
                 [g] 
               
               
                 Delta p [bar] 
                 0.8 
                 0.8 
                 0.8 
                 0.8 
               
               
                 Collected filtrate [g] 
                 170.9 
                 244.8 
                 167.2 
                 253.6 
               
               
                 t1 [s] 
                 16 
                 22 
                 49 
                 49 
               
               
                 S/B weight ratio of collected 
                 2.8 
                 5.3 
                 1.5 
                 2.7 
               
               
                 filtrate 
               
               
                   
               
             
          
         
       
     
         [0060]    As can be learned from the Examples, the Examples 1 and 2 according to the present invention resulted in a significantly reduced filtration time (t1 in Table 1) when compared with Comparative Examples 1 and 2 wherein no washing step was used. This means that according to the present invention the filtration can be performed faster; also lower filter CAPEX (Capital Expenses) is needed.