SOLIDS FLOCCULATION/AGGLOMERATION IN SOLVENT EXTRACTION OF BITUMEN FROM OIL SAND

Abstract

A process and apparatus is provided for flocculating and/or agglomerating oil sand solids during solvent extraction, the process using a mixing tank comprising a vertical baffle-free cylindrical vessel having at least one impeller mounted vertically therein.

Claims

1. A process for flocculating and agglomerating oil sand solids during solvent extraction of bitumen from oil sand ore, comprising: (a) treating the oil sand ore with at least one solvent to produce an oil sand and solvent slurry; (b) feeding the oil sand and the at least one solvent slurry into a mixing tank and adding a bridging liquid to the mixing tank to flocculate or aggregate solids present in the oil sand and at least one solvent slurry to produce a flocculated and/or aggregated slurry; and (c) removing the flocculated/aggregated slurry from the mixing tank and subjecting the flocculated/aggregated slurry to a separation step to separate liquid from solids; whereby the mixing tank comprises a vertical baffle-free cylindrical vessel having at least one impeller mounted vertically therein.

2. The process as claimed in claim 1, wherein the at least one solvent is a heavy solvent (HS).

3. The process as claimed in claim 1, wherein a heavy solvent (HS) and a light solvent (LS) is used to produce the oil sand and solvent slurry.

4. The process as claimed in claim 1, wherein the at least one solvent is a light solvent (LS).

5. The process as claimed in claim 1, wherein the oil sand ore is pre-crushed oil sand ore.

6. The process as claimed in claim 1, wherein the at least one impeller has a diameter of about 0.5 to 0.8 times that of the cylindrical vessel diameter.

7. The process as claimed in claim 1, wherein the at least one impeller comprises a plurality of blades or vanes.

8. The process as claimed in claim 7, wherein the blades are down-pumping blades or up-pumping blades or both.

9. The process as claimed in claim 1, wherein the at least one impeller comprises a pitched blade turbine (PBT) mixing impeller or a flat blade turbine mixing impeller.

10. The process as claimed in claim 9, wherein the PBT is a 45° PBT.

11. The process as claimed in claim 1, wherein the oil sand and at least one solvent slurry is added to the mixing tank so that a height of the oil sand and at least one solvent slurry is about 0.2 to 0.8 times the cylindrical vessel diameter.

12. The process as claimed in claim 1, wherein the at least one vertically mounted impeller is mounted at a height of about 0.01 to about 0.1 times the cylindrical vessel diameter from the bottom of the cylindrical vessel.

13. The process as claimed in claim 1, wherein a plurality of mixing tanks are used to produce the flocculated and/or agglomerated slurry.

14. The process as claimed in claim 13, wherein two mixing tanks are used in parallel and the two mixing tanks are connected through an opening.

15. The process as claimed in claim 14, wherein the opening is about 0.2 to about 1.0 of the mixing tanks diameter.

16. The process as claimed in claim 13, whereby four mixing tanks are used in two parallel trains and the four mixing tanks connected to one another through an opening.

17. The process as claimed in claim 16, wherein the opening is about 0.2 to about 1.0 of the mixing tanks diameter.

18. The process of either claim 14 or claim 16, whereby the directions of slurry motion are the same at each mixing tank connection.

19. The process of either claim 14 or 16, whereby the directions of motion are different at each mixing tank connection.

18. A mixing tank useful for flocculating and/or aggregating oil sand solids present in an oil sand and solvent slurry, comprising: (a) a cylindrical vessel having a closed top having a lid, a closed bottom and vessel diameter; and (b) at least one essentially vertical impeller having a diameter of about 0.5 to about 0.8 times the vessel diameter for mixing the oil sand and solvent slurry and flocculating or aggregating the oil sand solids therein; whereby the cylindrical vessel does not have any vertical baffles.

19. The mixing tank as claimed in claim 18, wherein the at least one impeller has a bottom clearance of about 0.01 to about 0.1 of the mixing tank diameter.

20. The mixing tank as claimed in claim 18, wherein the at least one impeller comprises 45° pitched-bladed turbines (PBT).

21. The mixing tank as claimed in claim 18, further comprising a slurry discharge at or near the bottom of the mixing tank.

22. The mixing tank as claimed in claim 18, wherein the at least one impeller is a down-pumping PBT.

23. The mixing tank as claimed in claim 18, wherein the at least one impeller is an up-pumping PBT.

24. The mixing tank as claimed in claim 18, wherein the at least one impeller is a flat blade turbine.

25. The mixing tank as claimed in claim 18, wherein the bottom of the mixing tank is dished shaped.

26. The mixing tank as claimed in claim 18, wherein the bottom of the mixing tank is flat.

27. The mixing tank of claim 18, further comprising at least one horizontal tube or plate positioned above the vertical impeller.

28. The mixing tank of claim 27, wherein the at least one horizontal tube or plate is adapted to provide heat to the mixing tank.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The process and apparatus will now be described by way of an exemplary embodiment with reference to the accompanying simplified, diagrammatic, not-to-scale drawings:

[0022] FIG. 1 is a schematic process flow diagram of one embodiment of a solvent extraction process.

[0023] FIG. 2 is a schematic diagram of one embodiment of a mixing tank useful in a solvent extraction process.

[0024] FIG. 3 is a schematic diagram of the top view of another embodiment of a mixing tank useful in a solvent extraction process.

[0025] FIG. 4 is a schematic diagram of the top view of another embodiment of a mixing tank useful in a solvent extraction process.

[0026] FIG. 5 is a schematic diagram of two mixing tanks of FIG. 1 arranged in series in a single train.

[0027] FIG. 6 is a schematic diagram of four mixing tanks of FIG. 1 arranged in a series of two parallel trains.

DETAILED DESCRIPTION

[0028] The detailed description set forth below in connection with the appended drawings is intended as a description of various embodiments and is not intended to represent the only embodiments contemplated by the inventors. The detailed description includes specific details for the purpose of providing a comprehensive understanding of the process and apparatus herein.

[0029] A solvent extraction process is provided and, more particularly, a mixing tank useful in flocculating/agglomerating solids present in oil sand/solvent slurries during solvent extraction of bitumen from oil sand ore is provided.

[0030] As previously mentioned, one key challenge of solvent extraction processes for extracting bitumen from oil sand is the removal of the oil sand solids from an oil sand/solvent slurry. Thus, presented herein is a process and apparatus for flocculating and/or agglomerating oil sand solids present in an oil sand/solvent slurry.

[0031] As previously mentioned, “flocculation” refers to a process for making oil sand solid aggregates of smaller than 1 mm in size and “agglomeration” refers to a process to make oil sand solid aggregates of larger than 1 mm in size.

[0032] As used herein, “heavy solvent (HS)” means a light gas oil stream, for example, a distillation fraction of oil sand bitumen, comprising a mixture of C.sub.9 to C.sub.32 hydrocarbons with a boiling range within about 130° C. to about 470° C. The light end boiling below about 170° C. should be less than 5 wt %. It has a flash point of about 90° C. in air.

[0033] As used herein, “light solvent (LS)” means a hydrocarbon stream comprising C.sub.6-C.sub.10 hydrocarbons with a boiling range of 60-170° C. The preferred LS is aliphatic C.sub.6-C.sub.7 with a boiling range of 69-110° C. It has a flash point below 0° C. in air.

[0034] With reference now to FIG. 1, an embodiment of the steps of a solvent extraction process for oil sands are illustrated. As mined oil sand ore 10 is mixed with hot solvent 20 in a slurry preparation and conditioning unit 30 to form a solvent/oil sand slurry. The oil sand ore 10 may have been crushed in a two-stage sizer/crusher. The hot solvent stream 20 may contain recycled bitumen from the downstream units, e.g. stream 80. The unit 30 may comprise a rotating tumbler. Longitudinal lifters may be present in the tumbler to assist in the further comminution of large oil sand lumps by lifting and dropping them on other oil sand lumps. The solids content in the solvent/oil sand slurry is about 60-75 wt % and the bitumen concentration is generally about 50 wt %. The slurry temperature is preferably around 50° C. In one embodiment, the source of heat comes primarily from the hot solvent stream 20. In one embodiment, the solvent used is a HS. In another embodiment, the solvent used is a LS. In yet another embodiment, the solvent used is a mixture of HS and LS.

[0035] The slurry stream 40 is then subjected to a solids flocculation/agglomeration step 50, where water is added to the slurry to aggregate the fines with sand grains. This minimizes the fines liberation into the hydrocarbon phase. The aggregation of fines with sand grains forms aggregates of near 0.3 mm or larger which are characterized as having a funicular structure with a greater amount of water molecules filling the spaces among the solids, and more securely bridging the solids together. The percentage of pore filling by the bridging water ranges from about 45% to about 95%. The size of aggregates mostly depends on water dosage and mixing time. As used herein, “flocs” and “agglomerates” refer to particles of different sizes, namely, smaller than 1 mm in size and larger than 1 mm in size, respectively, while “aggregate” is a general term for either flocs or agglomerates.

[0036] The solids flocculation/agglomeration step 50 uses a mixing tank 150, which will be described in more detail below. After solids flocculation and/or agglomeration has occurred, the flocculated/agglomerated slurry is then subjected to the step of solid-liquid separation 70, such as filtration, to provide solid aggregates 90 and a hydrocarbon product 80 having substantially reduced solids therein.

[0037] One embodiment, mixing tank 150, is shown in FIG. 2. Mixing tank 150 comprises a cylindrical vessel 152 having a vessel diameter (T) and at least one essentially vertical impeller 154 having a diameter (D) of about 0.5 to about 0.8 times the vessel diameter (D/T), which is driven by a drive motor (not shown), for mixing the oil sand and solvent slurry and flocculating or aggregating the oil sand solids therein. Cylindrical vessel 152 has smooth walls 153. The bottom clearance (C) of the vertical impeller 154 is about 0.01-0.1 of the tank diameter (T) (C/T). The slurry 156 height (H) is 0.2-0.8 of the tank diameter (T). The impeller comprises 45° pitched-blade turbines 158. It is understood, however, flat blade turbine, down-pumping pitch-blade turbines or up-pumping pitch blade turbines or other design of impellers known in the art can also be used. It is further understood that the mixing tank may comprise more than one impeller. In the embodiment shown in FIG. 2, the closed bottom 164 of mixing tank 150 is flat but it is understood that the bottom of a mixing tank useful in the solvent extraction process can also be dished. In one embodiment, the slurry discharge is at the bottom 164 of the tank. In another embodiment, the slurry discharge is at the top of the slurry layer 162 in the tank. The top 163 is closed with lid 165.

[0038] It can further be seen from FIG. 2, that mixing tank 150 is free from any vertical baffles. It was surprisingly discovered by the present applicant that the power input of impeller 154 necessary to bring about near optimal flocculation/agglomeration of the solids present in the oil sand/solvent slurry was about half of that in a mixing tank with the identical configuration but with standard vertical baffles. It is understood that using mixing tanks with lower energy requirements will greatly reduce the cost of running a commercial plant.

[0039] Vertical baffles are generally included in mixing tanks to promote the upward movement of the slurry. Such baffles are usually considered essential for proper mixing. However, a significant amount of energy is necessary for this solids uplifting motion. It was surprising, however, to discover that the flocculation/agglomeration of oil sand solids in oil sand/solvent slurries does not require the drastic upward movement aided by vertical baffles. Small vertical movement of the slurry driven by the 45° PBT and the rise and fall of the slurry along the tank wall was discovered to be able to generate sufficient up and down mixing action and shear to enable solids flocculation/agglomeration. Removal of the baffles brings in significant energy savings. Most importantly, without vertical baffles, slurry moves at a higher tangential velocity everywhere in the mixing tank that minimizes harmful solids buildup or deposition when processing oil sand.

[0040] With reference now to FIG. 3, in another embodiment, the mixing tank 250 further comprises at least one partially circumferential horizontal plate or tube 268 placed near the slurry surface, especially near the circumference of the tank, to minimize rise of the slurry along the tank wall and reduce the size of a central vortex. A large vortex causes slurry aeration and reduces mixing energy input. In one embodiment, the at least one plate or tube 268 further provides a heat-exchanging surface to provide heat to the slurry. In FIG. 3, it can be seen that there are four such horizontal plates or tubes 268 provided. As can further be seen in FIG. 3, these partially circumferential plates or tubes 268 only cover approximately ¾ of the total circumference of the cylindrical vessel 252. The other ¼ of the total circumference of the cylindrical vessel acts as a feeding area 272 for feeding the oil sand/solvent slurry 274 into the mixing tank 250. It is understood, however, that the feeding area 272/total cross-section area can range between about 0.1 to about 0.3.

[0041] In the embodiment shown in FIG. 3, if tubes are used, the tubes generally have a diameter (W/T) of about 0.001 to about 0.1. When plates are used, the plates have a width (W/T) of about 0.001 to about 0.1 and a thickness (X/W) of about 0.1 to about 0.5. The thickness X is not shown in FIG. 3. The gap width (G/T) between each plate or tube ranges from 0 to about 0.1. The central hole diameter (O/T) ranges from about 0.1 to about 0.5.

[0042] With reference now to FIG. 4, in another embodiment, the mixing tank 350 further comprises at least one completely circumferential horizontal plate or tube 368 placed near the slurry surface, above the impeller(s), and especially near the circumference of the tank, to minimize rise of the slurry along the tank wall and development of a central vortex. In one embodiment, the at least one plate or tube 368 further provides a heat-exchanging surface to provide heat to the slurry. In FIG. 4, it can be seen that there are four such completely circumferential horizontal plates or tubes 368 provided.

[0043] In the embodiment shown in FIG. 4, if tubes are used, the tubes generally have a diameter (W/T) of about 0.001 to about 0.1. When plates are used, the plates have a width (W/T) of about 0.001 to about 0.1 and a thickness (X/W) of about 0.1 to about 0.5. The thickness X is not shown in FIG. 4. The gap width (G/T) between each plate or tube ranges from 0 to about 0.1. The central hole diameter (O/T) ranges from about 0.1 to about 0.5.

[0044] In one embodiment, horizontal plates or tubes of FIGS. 3 and 4 are placed near the slurry surface, especially near the circumference of the mixing tank to provide heat to the slurry. Further, having the horizontal plates or tubes near the slurry surface, especially near the circumference of the tank, minimizes the rise of the slurry along the tank wall and reduces the size of the central vortex.

[0045] With reference now to FIG. 5, FIG. 5 shows two mixing tanks 450 of any of the mixing tank embodiments discussed above connected in series. Each mixing tank 450 has its own impeller 454 and drive motor (not shown). The two tanks are connected through a large opening on the bottom parts of their walls via connector 488. The size of the opening on the bottom parts of their walls is about 0.2 to about 1 of the tank diameter. The opening may be of a square or a round shape. Because of higher tangential velocity of slurry in baffle-free tanks, slurry readily exchanges from one tank to another through the opening. It saves slurry transfer pumps and level controls when multiple tanks must be used in large-scale operations. The oil sand/solvent slurry 478 is fed into the left tank and slurry discharge 482 is discharged from the right tank. Arrow 484 shows that the left mixing tank is operating clockwise and the arrow 486 shows that the right mixing tank is operating counter clockwise. In one embodiment, the impeller rotational directions in any tanks are different. In one embodiment, the left tank in FIG. 5 contains horizontal plates or tubes as shown in FIG. 3, and the right tank in FIG. 5 contains horizontal plates or tubes as shown in FIG. 4.

[0046] With reference now to FIG. 6, FIG. 6 shows four mixing tanks 550 of any of the mixing tank embodiments discussed above whereby the top left and the bottom left mixing tanks are connected in parallel via connector 588. The left and right mixing tanks on top and on bottom are both connected in series via connector 588. Each mixing tank 550 has its own impeller 554 and drive motor (not shown). The tanks 550 are connected through large openings on the bottom parts of their respective walls. The size of the opening is 0.2-1 of the mixing tank diameter. The opening may be of a square or a round shape. Because of higher tangential velocity of slurry in baffle-free tanks, slurry readily exchanges from one tank to another through the opening. It saves slurry transfer pumps and level controls when multiple tanks must be used in large-scale operations. The slurry 578 is fed into the two tanks on the left and slurry discharge 582 is discharged from the two tanks on the right. With respect to the top two mixing tanks, arrow 592 shows that the left mixing tank is operating clockwise and the arrow 594 shows that the right mixing tank is operating counter clockwise. Similarly, with respect to the bottom two mixing tanks, arrow 596 shows that the left mixing tank is operating counter clockwise and the arrow 598 shows that the right mixing tank is operating clockwise. In one embodiment, the impeller rotational directions in any tanks are different. In one embodiment, the left two tanks in FIG. 6 contain horizontal plates or tubes as shown in FIG. 3, and the right two tanks in FIG. 6 contain horizontal plates or tubes as shown in FIG. 4.

EXAMPLE 1

[0047] In the following example, the oil sand used contained 10.3 wt % bitumen, 3.6 wt % water and 86.1 wt % solids. The fines (<44 μm) content in the solids was 17 wt %. 750 g of this oil sand was used with 22.5 g added water and a bitumen-in-light naphtha solution containing 18 wt % bitumen and 82 wt % light naphtha in each test. As used herein, “light naphtha” is a hydrocarbon solvent comprising mainly aliphatic C.sub.6-C.sub.9 hydrocarbons with a boiling range of about 60° C. to about 160° C. The added water came from an oil sand tailings pond with pH 8.5. The hydrocarbon phase in the slurry prior to the first filtration step comprised about 33 wt % bitumen and 67 wt % light naphtha. The solids content in the slurry was about 53 wt %.

[0048] The solids were flocculated in a batch mixing tank of 13 cm in diameter (T) at about 50° C. The impeller was a 6-blade 45° PBT of 7.6 cm in diameter (D). The bottom clearance (C) was about 0.3 cm. The approximate slurry height was 6 cm. The impeller was turned to pump down at 1100 rpm for 5.5 min. In test #1, four standard vertical baffles were inserted into the mixing tank. In test #2, no baffles were used. Other parameters were identical. The mixed slurry was transferred to a top-loading batch filter with about −16.7 kPa g pressure in its filtrate receiver. The cake thickness was about 5 cm. After 1.sup.st-stage drainage, 225 g of light naphtha was added to the filter cake for washing and 2.sup.nd-stage drainage. Both drainage stages were timed. 5 and 10 s drying time was allowed after 1.sup.st- and 2.sup.nd-stage drainage, respectively. Vacuum and filtrate flow were turned off after drying time. The total amount of time under vacuum was used to calculate the filter process rate. The cake was then analyzed for its bitumen content, which was used to calculate the bitumen recovery. The results are shown in Table 1, below.

TABLE-US-00001 TABLE 1 Results of solids flocculation tests #1 and #2 Filter Water-to- Bitumen Energy Test Baffle Process Rate Solids Recovery Input No. Number (t/m.sup.2h) Mass Ratio (%) (W/kg) #1 4 12.7 0.061 93.8 12.1 #2 0 12.2 0.057 94.1 6.5

[0049] The results shown in Table 1 indicated that both filter process rates and bitumen recoveries are almost identical in two tests with and without baffles. Standard baffles caused significant increase in energy input without any benefits in bitumen extraction or filtration.

[0050] References in the specification to “one embodiment”, “an embodiment”, etc., indicate that the embodiment described may include a particular aspect, feature, structure, or characteristic, but not every embodiment necessarily includes that aspect, feature, structure, or characteristic. Moreover, such phrases may, but do not necessarily, refer to the same embodiment referred to in other portions of the specification. Further, when a particular aspect, feature, structure, or characteristic is described in connection with an embodiment, it is within the knowledge of one skilled in the art to affect or connect such module, aspect, feature, structure, or characteristic with other embodiments, whether or not explicitly described. In other words, any module, element or feature may be combined with any other element or feature in different embodiments, unless there is an obvious or inherent incompatibility, or it is specifically excluded.

[0051] It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for the use of exclusive terminology, such as “solely,” “only,” and the like, in connection with the recitation of claim elements or use of a “negative” limitation. The terms “preferably,” “preferred,” “prefer,” “optionally,” “may,” and similar terms are used to indicate that an item, condition or step being referred to is an optional (not required) feature.

[0052] The singular forms “a,” “an,” and “the” include the plural reference unless the context clearly dictates otherwise. The term “and/or” means any one of the items, any combination of the items, or all of the items with which this term is associated. The phrase “one or more” is readily understood by one of skill in the art, particularly when read in context of its usage.

[0053] The term “about” can refer to a variation of ±5%, ±10%, ±20%, or ±25% of the value specified. For example, “about 50” percent can in some embodiments carry a variation from 45 to 55 percent. For integer ranges, the term “about” can include one or two integers greater than and/or less than a recited integer at each end of the range. Unless indicated otherwise herein, the term “about” is intended to include values and ranges proximate to the recited range that are equivalent in terms of the functionality of the composition, or the embodiment.

[0054] As will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges recited herein also encompass any and all possible sub-ranges and combinations of sub-ranges thereof, as well as the individual values making up the range, particularly integer values. A recited range includes each specific value, integer, decimal, or identity within the range. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, or tenths. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc.

[0055] As will also be understood by one skilled in the art, all language such as “up to”, “at least”, “greater than”, “less than”, “more than”, “or more”, and the like, include the number recited and such terms refer to ranges that can be subsequently broken down into sub-ranges as discussed above. In the same manner, all ratios recited herein also include all sub-ratios falling within the broader ratio.