CA2428544A1 - Process for recovering hydrocarbons from tar sands - Google Patents

Abstract

An improved process for extracting hydrocarbons from tar sands and the like includes the steps of digestion, separation/flotation, and secondary flotation. The digestion step comprises the formation of a relatively thick aqueous slurry of the tar sands, which is then hydrotransported to a separation vessel, preferably under high shear conditions. At the separation vessel, the slurry is diluted and treated with an oxidant such as hydrogen peroxide to generate a gas within the slurry and to form a froth on the surface thereof. The froth entrains most of the hydrocarbon component, which are subsequently extracted. The coarse tailings are disposed of and the middlings stream is transported to a flotation tank and subjected to a second frothing process, preferably using hydrogen peroxide either alone or with additional air sparging.

Description

PROCESS F'OR RECOVERING HYDROCARBONS
FROM TAR SANDS
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
[0001] The present invention relates to an improved process of recovering hydrocarbons from tar sands and like minerals and, mare specifically, to the use of hydrogen peroxide for such recovery.
DESCRIPTION OF THE PRIOR ART

[0002] Tar sands (which are also known by other names such as oil sands, bituminous sands etc.) are sand deposits that are impregnated with dense, viscous petroleum.
One of the largest deposits of tar sands is in the Athabasca region of Alberta, Canada. This region is believed to contain more petroleum than the combined known reserves of the entire world.
Unfortunately, due to the physical characteristics of these tar sands oil reserves, and their mixture with sand and minerals, extraction of the desired hydrocarbons involves a higher cost that makes this source of oil less attractive.

[0003] Various solutions have been developed for improving the efficiency of hydrocarbon recovery from tar sands. One of these methods is the "hot water process", wherein tar sands are first subj ected to steam and alkali treatment to form an aqueous slurry. The heat treatment initially serves to separate a hydrocarbon portion comprising the mare volatile components.
Also, by forming the tar sands into a slurry, the viscosity of the hydrocarbon material is reduced so as to facilitate its transport. The slurry is then subjected to a frothing step wherein the heavier hydrocarbon material, also referred to as bitumen or bituminous material, is collected in the froth and later separated. This process, however, can result in a lower than desired yield of TDO-RED #8194326 v. l hydrocarbons as some of the bituminuous material is lost in the tailings, which is comprised mainly of sand particles. Apart from the reduced hydrocarbon yield, the resulting sand cannot be easily discarded due to environmental concerns.

[0004] Canadian patent number 1,275,063 teaches an improved hot water process wherein tar sands are treated with an oxidizing agent such as hydrogen peroxide to facilitate extraction of the heavier hydrocarbon materials. A similar method is taught in Canadian patent application number 2,177,018. Another tar sands treatment process is taught in US patent number 6,251,290. Although having improved hydrocarbon extraction efficiency, these methods involve additional cost that may render the process economically unattractive. In addition, these references relate mainly to batch processes and do not provide guidance on continuous processes.
The references also do not teach any means of optimizing the use of the H2OZ
oxidant for achieving efficient and economic operation.

[0005] Notwithstanding the improvements to the hot water process discussed above, there exists still a need for a more improved hydrocarbon extraction process wherein a higher, faster and more cost effective hydrocarbon recovery is obtained and wherein the use of the oxidizing agent is made in an effective manner.
SUMMARY OF THE INVENTION

[0006] In accordance with a preferred embodiment, the present invention provides a process for recovering hydrocarbons from tar sands comprising:
- forming a heated slurry of said tar sands by mixing said tar sands with water;
- pumping the slurry to a separation vessel;
- diluting said slurry with water and mixing said slurry with an oxidizing agent, said oxidizing agent being capable of generating gas bubbles when contacted with said slurry;

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- generating a first froth layer in said separation vessel to entrain a first hydrocarbon fraction containing hydrocarbons in said slurry;
- separating the slurry in said separation vessel into said first froth layer, a tailings layer, and a middlings layer, said tailings layer comprising solid components of said slurry and said middlings layer comprising liquid and fines components of said slurry;
- removing and transporting said first froth layer to a froth treatment station;
- removing and transporting said tailings layer to a coarse tailings treatment station; and, removing and transporting said middlings layer to a flotation tank.

[0007] In accordance with another embodiment, the present invention provides a process for recovering hydrocarbons from tar sands comprising:
- forming a heated slurry of said tar sands by mixing said tar sands with water;
- pumping the slurry to a separation vessel;
- diluting said slurry with water;
- generating a first froth layer in said separation vessel to entrain a first hydrocarbon fraction containing hydrocarbons in said slurry;
- conducting a primary hydrocarbon separation in said separation vessel, said separation resulting in said first hydrocarbon rich froth layer, a hydrocarbon lean tailings and a middlings layer;
- removing said middlings layer and transporting said layer to a flotation tank, said flotation tank including an inlet for addition of an oxidizing agent; the oxidizing agent being capable of generating gas bubbles when contacted with the middlings;
- generating a second froth layer in said flotation tank to entrain hydrocarbons contained in said middlings;
- separating and removing said second froth layer; and, - removing the remaining contents in said flotation tank.

TDO-RED #8194326 v. 1 [0008] In accordance with another embodiment, the present invention provides a process for recovering hydrocarbons from tar sands comprising:
- forming a heated slurry of the tar sands by mixing the tar sands with water;
- pumping the slurry to a separation vessel;
- diluting the slurry to increase the water to ore ratio;
mixing, or injecting, the slurry with an oxidizing agent, the oxidizing agent being capable of generating gas bubbles when contacted with the slurry;
- separating the slurry in said separation vessel into a first froth layer, a tailings layer, and a middlings layer, the first froth layer comprising a first hydrocarbon fraction of the hydrocarbons contained in the slurry, the tailings layer comprising the solid components of the slurry and the middlings layer comprising liquid and fines components of the slurry;
- removing and transporting the first froth layer to a froth treatment station;
- removing and transporting the tailings layer to a coarse tailings treatment station;
- removing and transporting the middlings layer to a flotation tank, the flotation tank including a froth generating means comprising air sparging andior injection of hydrogen peroxide;
- generating a second froth in the flotation tank to entrain a second hydrocarbon fraction containing hydrocarbons in the middlings;
- removing and transporting the second froth layer either back to the separation vessel or directly to the froth treatment station;
- removing and transporting the remaining portion in the flotation tank to a fine tailings treatment station or back into the bottom of the separation vessel.

[0009] In accordance with yet another embodiment, the invention provides a process for recovering hydrocarbons from tar sands comprising:
- forming a heated slurry of the tar sands by mixing the tar sands with water, the slurry having a water to ore ratio of about 0.2 to 0.5 by weight;

TDO-RED #8194326 v. l -q._ - pumping the slurry to a separation vessel with a hydrotransport system;
- diluting the slurry to a water to ore ratio of about 0.5 to I .6 by weight;
- mixing the slurry with hydrogen peroxide;
- separating the slurry in said separation vessel into a first froth layer, a tailings layer, and a middlings layer, the first froth layer comprising a first hydrocarbon fraction of the hydrocarbons contained in the slurry, the tailings layer comprising solid components of the slurry and the middlings layer comprising liquid and fines components of the slurry;
- removing and transporting the first froth layer to a froth treatment station;
- removing and transporting the tailings layer to a coarse tailings treatment station;
- removing and transporting the middlings layer to a flotation tank, the flotation tank including a froth generating means comprising air sparging and/or injection of hydrogen peroxide.
- generating a second froth in the flotation tank to entrain a second hydrocarbon fraction containing hydrocarbons in the middlings;
- removing and transporting the second froth layer either back to the separation vessel or directly to the froth treatment station;
- removing and transporting the remaining portion in the flotation tank to a fine tailings treatment station or back into the bottom of the separation vessel.

[0010] These and other features of the preferred embodiments of the invention will become more apparent in the following detailed description in which reference is made to the appended drawings wherein:

[0011] Figure 1 is the schematic drawing of a tar sands treatment process according to a preferred embodiment of the invention.

TDO-RED #8194326 v. 1 - S -[0012] Figure 2 is a graph illustrating the average effects of extraction variables on primary recovery of hydrocarbons from tar sands according to the present invention.

[0013] Figure 3 is a graph illustrating the average effects of extraction variables on total recovery of hydrocarbons from tar sands according to the present invention.

[0014] Figures 4 and 5 are graphs illustrating the effect of peroxide addition point on primary plus secondary recovery.

[0015] Figure 6 is a graph illustrating froth recovery as a function of time.
DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] In the following description, it will be understood that the term "tar sands" will be used to refer to tar sands, oil shales and other such naturally occurring material wherein hydrocarbons are bound or mixed with sand or other mineral deposits. Further, the terms "oil", "bitumen" or "hydrocarbons" will be used to refer to any hydrocarbon material that is contained in tar sands and which is to be recovered.

[0017] One of the objects of the present invention is to provide an improved process for hydrocarbon extraction from tar sands that results in a high hydrocarbon recovery with a reduced cost. In one of its embodiments, the present invention provides a process that has a lower demand for an oxidizing agent, such as hydrogen peroxide (HZOZ). As will be understood, such reduction in oxidant will reduce the cost associated with the hydrocarbon extraction process. In the course of this study, it has been found that one of the key factors associated with improving extraction efficiency lies in the point at which the oxidant ("peroxide") is added. It has also been found that with a select addition point of the oxidant, a lower concentration can be used.
Furthermore, it has been found that the addition of hydrogen peroxide not only improves the TDO-RED #8194326 v. I

recovery yield but also increases the recovery rate, i.e. the velocity with which bitumen froth can be recovered from tar sands. The following description discusses these aspects of the invention in more detail.

[0018] In most of the known tar sands treatment systems, the following treatment steps are followed: digestion; flotation; and scavenging (secondary flotation). In the digestion step, the tar sands are formed into a slurry and heated and mixed. It is at this stage in the prior art that an oxidant, such a hydrogen peroxide, is added to the slurry. During this step, the viscosity of the hydrocarbon material is reduced and the oxidant serves to support the release of bituminous material from the sand or mineral components. Once the slurry is formed, it is subjected to one or more frothing processes to entrain the hydrocarbon material released from the sand. The sand is then discarded as known in the art.

[0019] In the prior art, for example US Patent No. 6,251,290, it leas been postulated that the addition of an oxidant to the tar sands slurry serves to partially oxidize the hydrocarbon material and to break any polar bonds between such components and sand particles.
However, the present study has concluded that the beneficial action of the peroxide lies with its in-situ decomposition on the surfaces of the solids and the generation of oxygen bubbles, which, in turn, support the vertical flotation of oil to the surface. Once a free gas bubble is formed, the interfacial characteristics of the gas/water and bitumen/water interfaces make attachment of the oil to the bubble favourable and thus support the mechanical separation of the hydrocarbon material from the sand. A particular advantage of an in-situ bubble generating oxidant over sparged air is that gas bubbles are generated right at the bitumen/solid interface and the association of the bubbles with bitumen is enhanced by the proximity of newly formed bubbles to bitumen. These bubbles begin as microbubbles and grow to a range of sizes, which eventually provide sufficient lift to float the attached oil. Furthermore, the reaction of peroxide with the solid surfaces renders the solids more water wet, which hinders reattachment of separated !44899-320957 TDO-RED #8194326 v. I

bitumen. As such, the present invention provides an improved process wherein separation within the slurry is increased and accelerated by, among other means, the addition of an oxidizing agent at specific locations and at specif.c concentrations to maximize its functional efficiency.

[0020] Figure 1 schematically illustrates a process in accordance with the preferred embodiment of the invention. As shown, the system includes three stages labelled as I, II and III. The first stage, I, comprises the digestion or "conditioning" phase. At this stage, the tar sands are combined with preferably hot water to form a heated slurry. This step brings the tar sands into a pumpable state and reduces the viscosity of the slurry. During this stage, any volatile hydrocarbons may be released from the stream with known technologies.

[0021] Digestion of the tar sand slurry progresses as the slurry is transported with one or more pumps 12 to the second stage discussed below. In the preferred embodiment, transport of the slurry is achieved using a hydrotransport system, which is k~zown in the art. Further, in the preferred embodiment, the water to ore (w/o) ratio of the slurry in this digestion phase is about 0.2 to 0.5 on a weight basis. This results in a generally thicker slurry than that of the prior art.
For example, in US Patent 6,251,290, a w/o ratio of between 0.5 and 1.0 is taught. Due to the low water to ore ratio, high sheax forces are introduced and turbulent mixing takes place in the pipeline that breaks up clumps of sand and liberates the bitumen as the slurry is pumped to the second stage. Such high mechanical force present in a hydrotransport system especially serves to initiate the separation of the heavy hydrocarbon components from the mineral or sand components. In the preferred embodiment, the digestion stage is carried out in the hydrotransport pipeline while the tar sand slurry is transported from the mine site to a separation facility at a different location.

[0022] In the prior art, as discussed above, an oxidizing agent (i.e. hydrogen peroxide) is normally added at this digestion stage on the assumption that the partial oxidation of the TDO-RED #8794326 v. I

hydrocarbon components results in a greater hydrocarbon separation. However, according to the invention, no oxidant is added until the next stage or just ahead of the next stage discussed below. Instead, the present invention uses internally generated shear forces during the pumping process to initiate the hydrocarbon separation.

[0023] The second stage, stage II, is refe~yed to as the flotation stage. At this stage, the digested slurry is pumped into a first flotation vessel 14, also known as a primary separation vessel (PSV) or separation cell. At this stage, the slurry is further diluted by addition of water 16 to result in a slurry with a water to ore (w/o) ratio in the range of about 0.5 to 1.6, which again is a higher ratio than that taught in the prior art. In a preferred embodiment, especially for industrial scale equipment, the slurry is further diluted to result in a slurry with a water to ore (w/o) ratio of 0.6 to 1.1 by weight. This higher water content serves to aid in the formation of layers of froth, middlings and tailings. Along with the water 16, the desired oxidant 18 is also added to the slurry at this stage as well as any known flotation aids or agents. Such flotation aids generally include alcohols (e.g. methyl isobutyl carbinol, MIBC), caustic (NaOH), sodium bicarbonate (NaHC03), kerosene and other components as are apparent to persons skilled in the art. In the preferred embodiment, the oxidant is hydrogen peroxide primarily due to its lower cost. However, as discussed below, various other oxidants can be used with the invention as will be apparent to persons skilled in the art. As illustrated in Figure 1, the oxidant, dilution water and other flotation aids can be injected in-line just ahead of vessel 14 (as shown by stream 13) or into the aqueous middlings stream of the vessel 14, below the bitumen-laden froth layer (as shown by stream 15). Addition of the oxidant and water ahead of the vessel 14 (i.e. via stream 13) offers a few advantages. Firstly, from a process point of view, it is easier to mix the oxidant and water into the slurry when done in-line as opposed to directly into the vessel 14. Further, better mixing and more efficient dilution of the slurry is achieved when the oxidant is introduced in-line. The hydrogen peroxide is preferably added to result in an oxidant concentration less than 0.5%, and preferably between 0.01 % and 0.1 % by weight in the aqueous phase.

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_9-[0024] In the vessel 14, the slurry is agitated to enhance the formation of a primary froth 20 on the surface of the slurry. During this phase, the solids 22 (i.e. send etc.) settle to the bottom of the vessel. As known in the prior art, the froth 20 entrains the hydrocarbon material released from the tar sands. Once settling of the solids 22 is complete, the sand, which is essentially free of hydrocarbons, is removed as coarse tailings and taken 23 to a tailings treatment step 24, to be discarded in a manner as known in the art. The froth 20 is extracted and passed to a separate froth treatment process 26 for extracting the hydrocarbon material entrained therein. Such froth treatment methods are commonly known in the art and typically include the mixing of a paraffinic solvent (e.g. naphtha) with the froth to lower the viscosity of the bitumen, so that it can be cleaned of water and solids by centrifuging, hydrocycloning or settling.
The remaining aqueous phase 28, referred to as the middlings layer, of the vessel 14 is transported to the third phase of the system, which involves the "scavenging" process or "secondary flotation" as discussed below. The primary separation vessel 14 is generally maintained at about 25°C or higher, to allow enough heat for the hydrogen peroxide to decompose. In the preferred embodiment, the temperature of the vessel 14 is maintained at about 25°
to 65°C. This temperature range offers optimal conditions for the decomposition of I-IZO2.
Although temperatures higher than 65°C may be utilized, the energy cost to raise the temperature to such level would not be recouped. The heat of the slurry from stage I would normally be sufficient to ~ maintain the desired temperature conditions and, as such, no additional heating system is required, thereby allowing costs to be minimized.

[0025] As discussed above, one of the aspects of~ the present invention is to increase bitumen recovery of the tar sand. In the preferred embodiment, the oxidant added to the slurry during the flotation stage is one that results in the generation of a gas when added to the slurry (i.e. in-situ generation). According to a preferred embodiment, the oxidant is hydrogen peroxide (HZO2). It is known that hydrogen peroxide decomposes, upon contact with the mineral and solids fraction TDO-RED #8194326 v. I

of the tar sands slurry, into oxygen gas and water. ~.Tnder normal circumstances the decomposition is sufficiently catalyzed by the mineral and solids fraction of the tar sand and, as described ahove, the temperature of the separation vessel 14 is maintained at a value to ensure such decomposition. However, in on.e embodiment of the invention, additional decomposition catalysts such as caustic soda (I~laOH), sodium bicarbonate (NaHCO3), lime (Ca(OH)2) or heavy metal ions, preferably ferric/ferrous (Fe2+i3+) or cupric ions (Cu2+) can be added in low amounts to accelerate the decomposition kinetics. As indicated above, although temperatures of about 25°C can be used, another embodiment of the invention involves the temperature of the slurry being raised, preferably up to 35° to 65°C in order to accelerate the decomposition of hydrogen peroxide. Further, it is known that the oxygen resulting from the decomposition of HZOZ is initially formed as very small diameter bubbles ("microbubbles") having generally uniform dimensions. It has been found in the present study that the generation of these gas bubbles greatly increases and accelerates the recovery of the hydrocarbon material contained in the slurry, more so than the application of an agitating force alone. Once free gas bubbles are formed, the interfacial characteristics of~ the gas/water and bitumen/water interfaces make attachment of the bitumen to the bubbles favourable. Exposure to hydrogen peroxide also renders the solid surfaces more hydrophilic and water wet so that reattachment of separated bitumen to dispersed solids is hindered. These features altogether support the mechanical separation of the hydrocarbon material from the sand and other mineral components. As the bubbles grow in size they entrain the hydrocarbon components and carry them to the surface where the froth is formed.

[0026) With an agitator alone, wherein air rnay be sparged into the slurry, gas bubbles are generated in a single location (i.e. the base of the vessel) and in a narrow range of sizes and then rise upwardly. As such, their maximal effect is localized in a certain portion of the vessel.
Furthermore, their effect is limited upon the number of successful collisions between rising bubbles and oiI droplets in the suspension. On the other hand, with the addition of hydrogen TDO-RED #8194326 v. I

peroxide according to the invention, gas bubbles are generated irz-situ throughout almost the entire volume of the separation vessel. Even more important is the fact that they are generated right at the bitumen/solid interface (that is, where they have maximum contact with bitumen) thereby eliminating the requirement of successful collisions and maximizing the separation effect. The mechanistic advantage of in-situ generated oxygen bubbles over externally introduced air therefore lies in the higher probability of attachment of bubbles to bitumen droplets as a result of the proximity of newly formed bubbles to bitumen and the alteration in the wettability of the solid surfaces.

[0027] In the prior art, as discussed above, the oxidant is normally added upstream of the separation vessel, during the digestion phase. As such, the efficiency of the oxidant would not be maximized in such an approach since oxygen bubbles formed during digestion would not have a chance to float attached bitumen to the surface. A significant amount of bubbles would even be destroyed due to the high shear forces present in a hydrotransport line. The present invention, therefore, provides an improvement over the prior art by adding the oxidant at the most efficient location.

[0028] The third stage of the process, indicated as III in Figure 1, involves the scavenging (secondary flotation) of any remaining hydrocarbon material in the middlings 28 from the primary separation vessel 14. It will be understood that the third phase of the process is a preferred embodiment. The middlings 28 generally comprise the liquid phase of the slurry and include water in which mineral fines are suspended. The middlings 28 are transported to a second flotation tank, or secondary vessel, 30 and subjected to a further frothing step for removing any remaining hydrocarbon material. In this step, the frothing is achieved by known sparging methods. Optionally, in another embodiment, a second hydrogen peroxide solution 32 can be added to enhance the froth generation as described with reference to stage II. The peroxide solution 32 may be added together with or instead of air sparging.
The froth 34 from TDO-RED #8194326 a 1 this step, referred to as the secondary froth, is retrieved and transported 36 to the froth treatment facility 26. In another embodiment, all or a portion of the froth 34 may optionally be returned 38 to the primary separation vessel 14 to repeat the flotation process and improve froth quality. The remaining liquid and solids in the tank 30 are removed as fine tailings, 40, and taken to a fine tailings treatment step 25, to be treated in a manner known in the art.
~ptionally, in another embodiment of the present invention, clean flotation effluent from the flotation tank 30 is injected into the bottom of the primary separation vessel (PSV) 14, as shown by stream 31, to displace bitumen-bearing material to the middlings stream of the vessel 14.

[0029] As indicated above, the use of the flotation tank 30 is a preferred embodiment of the invention. It will be understood that the hydrocarbon recovery of the primary vessel 14 will be generally greater than that of the secondary vessel 30 due to the higher hydrocarbon concentration in the slurry. Extraction of hydrocarbons in the secondary tank 30 is more difficult since the middlings stream entering the tank 30 is considerably leaner than the feed stream to the primary vessel 14. For this reason, as explained above, the present invention provides an improved secondary tank 30 wherein H202 is provided as a froth generating means. The action of the peroxide, as explained above, provides an efficient hydrocarbon removal system.
[0030] The following examples are provided to illustrate the present invention and are not intended to limit the invention in any way.
Examples Example 1 [0031] Various tests were carried out in a batch extraction unit (BEU) using the process of the present invention and the data from such tests are provided in the tables below. The tests were conducted to determine if hydrogen peroxide would assist in the recovery of bitumen from TDO-RED #8194326 v. I

a sample of poorly processing Athabasca oil sand, which had been taken from the Albian Sands Energy Inc. lease, northeast of Fort McMumay, Alberta, Canada. ~i1 sand from this particular stockpile had been associated with poor processing during 20-ton per hour pilot runs on the Albian lease.

[0032] Baseline primary recoveries from this oiI sand, without peroxide as a process aid, ranged from 20 to 47%, depending on the operating conditions used. Primary recovery typically should be in the range of 80% for a typical oil sand having 8.5% bitumen content.

[0033] The results of a sensitivity analysis, as shown on Table 1 and in Figures 2 and 3, illustrate the aspects of the present invention. For this purpose several independent extraction variables were selected and a high and a low level defined for each variable.
Then, a factorial design of test program was conducted to determine the significance of effects of hydrogen peroxide on extractability and to compare the magnitude of those effects to the impact of other variables. Figure 2 illustrates the average mp 'marX recovery efficiencies, which are the recovery rates of hydrocarbons after the Stage II step (after "primary flotation") for all experiments conducted at a low and a high level of each extraction variable. Figure 3 illustrates the average total recovery efficiencies, after both the Stage II and III steps (after "scavenging") for all experiments conducted at a low and a high level of each extraction variable.

[0034] From the results, it is first noted that primary and total recoveries increased by increasing the peroxide dosage from 0.1 to 0.5% in water. Primary recovery increased on average from 30.5 to 46.6% and total recovery on average from 45.4 to 56.6%
(see Figures 2 and 3). As well, the results show that it was much more effective to add the peroxide just prior to the flotation step (Stage II) rather than during digestion (Stage I). In fact, the point in the process at which the peroxide was added was more important than the quantity, within the range of peroxide used. The average primary recovery increased from 26.9 to 50.3% and the average TOOSl3-0004-CA

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total recovery from 40.1 to 61.9% as the point of addition was moved from digestion (Stage I) to flotation (Stage II). The sensitivity analyses also revealed that only the point of addition and the peroxide concentration had an average effect on recovery at the 95% confidence level. The effects of other extraction variables were insignificant or significant at much lower statistical confidence levels (e.g. temperature).

[0035] Further analyses relating to froth quality revealed that the peroxide had no measurable effect on either the amount of solids or amount of water that floated with the bitumen.
Bitumen/solids ratios and % Bitumen contents in the primary froth and combined froths (i.e.
primary + secondary) were used as measures of these attributeso [0036] The results of additional head-to-head comparisons, where all other variables were fixed except for peroxide addition - i.e. either no peroxide added, peroxide added only during digestion, peroxide added only during flotation, or peroxide added at both stages - are shown in Table 2. It is noted that increases in primary and total recovery were generally higher when peroxide was added at the flotation stage alone or when it was added at both stages, flotation and digestion, as compared to addition at only the digestion stage. The average benefit in primary recovery for adding peroxide just prior to flotation rather than during digestion was 8.4 % and in total recovery, 9.2 %. Given the precision of the method, the results in Table 2 confirm the results of the factorial design of experiments (Table 1). On average, primary and total recovery increased from 22.2 and 37.1% respectively for the "no peroxide runs" to 38.7 and 51.2%
respectively for the "peroxide runs". When the average of runs where 0.1 %
peroxide was used is compared to the average of runs where 0.5% peroxide was used, then average primary recovery was found to increase from 30.5% to 46.7%, and average total recovery from 35.7°/~ to 56.0%.
By all measures of froth quality, that is % bitumen in primary and total froths, % solids in primary froth (shown in Table 2) and bitumen/solids ratio in the primary and total froths, there was only a marginal deterioration as a result of peroxide addition in the flotation stage.
TOOSl3-0004-CA

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Example 2 [0037] In the next series of tests the process aids hydrogen peroxide and sodium hydroxide were compared. Furthermore, it was intended to determine the impact of peroxide if it was added prior to scavenging (Stage III). In addition to the poorly processing Albian oil sand, an oxidized ore from the Athabasca Aurora site was processed. First, a baseline test with no process aids was conducted. Second, a "caustic" run was carried out using an amount required to produce a digestion slurry of pH 8.5. Then, additional two runs were made using one half and 1.5 times of this "optimum" amount of caustic. Third, a 2-level, full factorial experiment was carried out, in which the H202 addition point (prior to flotation versus prior to scavenging), the peroxide amount and the presence of induced air during scavenging were varied. Finally, two additional runs were made in which hydrogen peroxide was added prior to flotation and prior to an additional post-scavenging stage (see Table 3 and 4). This post-secondary recovery stage was carried out as a means of determining if there would be any benefit to increasing residence time at the end of the process to make use of any ongoing oxygen bubble formation.

[0038] The recovery data from the two series of runs are presented in Table 3 and 4. The comparison below shows that the "optimum" caustic process and the peroxide process yield similar recoveries both after the typical scavenging stage (column: Primary plus Secondary recovery) and after the "post-scavenging" stage (column: Total Recovery). Both processes, however, yield significantly higher recoveries than the baseline runs without a process aid.
Comparison of Optimized Caustic and Peroxide Recoveries:
Run Prianary ~ Prymary plus Total Recovery Recover Secondary Recover Albian Ore Baseline 20.0 45.1 58.8 Optimum Caustic 45.0 70.2 79.4 144899-3209.57 TDO-RED X8194326 v. I

Peroxide (Flotation)- 61.6 - 70.3 74.5 Peroxide (Scavenging)16.6 69.5 76.7 Aurora Ore Baseline 24.2 61.4 85.0 Optimum Caustic 52.3 86.8 92.3 Peroxide (Flotation)74.7 86.7 91.2 Peroxide Scavenging)30.4 84.1 90.1 [0039] The comparison indicates that even if total recovery is equivalent for the optimum caustic and hydrogen peroxide case, recovery could be moved forward to the primary flotation S stage. Consequently, on a commercial scale, there is a potential for either increased throughput or smaller sizing of vessels to achieve equivalent recoveries.

[0040] As a result of using a factorial experiment design, it was possible to isolate the effect of using peroxide prior to flotation (primary recovery) versus prior to scavenging. Figures 4 and S show that in only one out of eight head-to-head comparisons was there a significant benefit of adding peroxide prior to primary flotation rather than prior to scavenging.
However, by virtue of the fact that in all eight cases, recovery was slightly better by adding peroxide prior to primary flotation, there may be a small benefit to adding the peroxide in time to take advantage of the full extent of bubble formation.

[0041] Although primary recovery increased dramatically with peroxide addition just prior to that stage, changes in froth quality were marginal. For the Albian oil sand, the average bitumen content in the primary froth decreased from an average of 14.4% to an average of 12.6% when peroxide was used. The change in solids was not significant - the use of peroxide was associated with a minor decrease in solids content from 38.6% to 38.1%.
Example 3 TDO-RED #8194326 v.

[0042] Another series of tests was carried out in a laboratory hydrotransport loop to better measure the effect of hydrogen peroxide on total recovery and, in particular, on recovery kinetics. This continuous flow loop is intended to simulate the digestion process during slurry transport. The operation of the loop however differs from a commercial slurry transport design because the recovery vessel is built into the loop so that bitumen can be recovered even before digestion is complete. The internal diameter of the loop was 2 inches. The slurry - controlled at 50 °C - was comprised of 1 kg of oii sand and 3 kg of water. It was pumped for sixty minutes around the loop using a progressing cavity pump. A calculated amount of hydrogen peroxide was either charged in a single dose immediately at the beginning of the run (t= 0 min) or split in half and added in two portions at the beginning (t=0 min) and after 30 min into the run. In addition, the same calculated amount of hydrogen peroxide was continuously metered into the flow loop over 60 minutes. A baseline run without any additive and a run with caustic as a process aid (pH
8.5} were conducted as well for comparison purposes.

[0043] Results of the loop tests are shown in Table 5 and Figure 6. The recovery profiles depicted in Figure 6 reveal that all runs approach a total (cumulated) recovery between 80 and 90% after 60 minutes. Differences in recovery are marginal after this length of time. This similarity in recoveries is most probably attributed to the fact that all of the tests were carried to extinction after 60 minutes. However, analysis of the prof les within the first 20 minutes of the test show recovery increases in the range of 10- 20% for the "peroxide runs"
versus the "no additive" and "caustic" run. Figure 6, therefore, clearly demonstrates that peroxide addition improves the rate of recovery during the early stage of the extraction process. Closer examination of the recovery data of the "no additive", "single" and "double"
dosage runs with hydrogen peroxide suggests a linear relationship between the initial recovery rate (at t=0 min) and the hydrogen peroxide concentration.

TDO-RED #8194326 v. I

[0044] The above-mentioned improvements in $°ecovery kinetics obtained with hydrogen peroxide are unprecedented in tar sands extraction and have not been mentioned in the prior art.
These unexpected findings have significant economic implications for large-scale industrial operations. If they occur on a commercial scale, there is a potential for either faster processing and increased throughput of ore in existing installations or smaller sizing of vessels for newly designed extraction plants.

[0045] Although the invention has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art without departing from the spirit and scope of the invention as outlined in the claims appended hereto.

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Claims (25)

1. A process for recovering hydrocarbons from tar sands comprising:
- forming a heated slurry of said tar sands by mixing said tar sands with water;
- pumping the slurry to a separation vessel;
- diluting said slurry with water and mixing said slurry with an oxidizing agent, said oxidizing agent being capable of generating gas bubbles when contacted with said slurry;
- generating a first froth layer in said separation vessel to entrain a first hydrocarbon fraction containing hydrocarbons in said slurry;
- separating the slurry in said separation vessel into said first froth layer, a tailings layer, and a middlings layer, said tailings layer comprising solid components of said slurry and said middlings layer comprising liquid and fines components of said slurry; and, - removing and transporting said first froth layer to a froth treatment station.

2. The process of claim 1 further comprising:
- removing and transporting said tailings layer to a coarse tailings treatment station; and, - removing and transporting said middlings layer to a flotation tank.

3. The process of claim 2 wherein said flotation tank includes a froth generating means and wherein the process further comprises the steps of:
- generating a second froth layer in said flotation tank to entrain a second hydrocarbon fraction containing hydrocarbons in said middlings;
- separating and removing said second froth layer; and, - removing the remaining contents in said flotation tank.

4. The process of claim 3 wherein said second froth layer is generated by means of an air sparging system, a hydrogen peroxide solution, or a combination thereof.

5. The process of claim 3 wherein said second froth layer is transported to said separation vessel, said froth treatment station, or a combination thereof.

6. The process of claim 3 wherein the remaining contents in said flotation tank are transferred to a fine tailings treatment station, to the bottom of said separation vessel, or a combination thereof.

7. The process of claim 1 wherein dilution of the slurry and mixing of said oxidizing agent are conducted simultaneously.

8. The process of claim 1 wherein said oxidizing agent is hydrogen peroxide.

9. The process of claim 1 wherein said slurry is transported to said separation vessel using a hydrotransport system.

10. The process of any one of claims 1 to 9 wherein said slurry has a water to oil ratio of about 0.2 to 0.5 by weight.

11. The process of any one of claims 1 to 10 wherein said slurry in said separation vessel is diluted to a water to oil ratio of about 0.5 to 1.6 by weight, and preferably about 0.6 to 1.1 by weight.

12. The process of claim 11 wherein the temperature in said separation vessel and said flotation tank is between 25°C and 65°C.

13. The process of claim 1 wherein said slurry is provided with catalysts for accelerating the decomposition of the oxidizing agent.

14. The process of claim 13 wherein said catalysts for accelerating the decomposition of the oxidizing agent are chosen from the group consisting of caustic soda (NaOH);
sodium bicarbonate (NaHCO3); lime (Ca(OH)2); heavy metal ions; ferric/ferrous (Fe2+/3+); and cupric ions (Cu2+) or combinations thereof.

15. A process for recovering hydrocarbons from tar sands comprising:
- forming a heated slurry of said tar sands by mixing said tar sands with water;
- pumping the slurry to a separation vessel;
- diluting said slurry with water;
- generating a first froth layer in said separation vessel to entrain a first hydrocarbon fraction containing hydrocarbons in said slurry;
- conducting a primary hydrocarbon separation in said separation vessel, said separation resulting in said first hydrocarbon rich froth layer, a hydrocarbon lean tailings and a middlings layer;
- removing said middlings layer and transporting said layer to a flotation tank, said flotation tank including an inlet for addition of an oxidizing agent; the oxidizing agent being capable of generating gas bubbles when contacted with the middlings;
- generating a second froth layer in said flotation tank to entrain hydrocarbons contained in said middlings;
- separating and removing said second froth layer; and, - removing the remaining contents in said flotation tank.

16. The process of claim 15 wherein said second froth layer is transported to said separation vessel, a froth treatment station, or a combination thereof.

17. The process of claim 15 wherein the remaining contents in said flotation tank are transferred to a fine tailings treatment station, to the bottom of said separation vessel, or a combination thereof.

18. The process of claim 15 wherein dilution of the slurry and mixing of said oxidizing agent are conducted simultaneously.

19. The process of claim 15 wherein said oxidizing agent is hydrogen peroxide.

20. The process of claim 15 wherein said slurry is transported to said separation vessel using a hydrotransport system.

21. The process of any one of claims 15 to 20 wherein said slurry has a water to oil ratio of about 0.2 to 0.5 by weight.

22. The process of any one of claims 15 to 21 wherein said slurry in said separation vessel is diluted to a water to oil ratio of about 0.5 to 1.6 by weight, and preferably about 0.6 to 1.1 by weight.

23. The process of claim 15 wherein the temperature in said separation vessel and said flotation tank is between 25°C and 65°C.

24. The process of claim 15 wherein said slurry is provided with catalysts for accelerating the decomposition of the oxidizing agent.

25. The process of claim 24 wherein said catalysts for accelerating the decomposition of the oxidizing agent are chosen from the group consisting of: caustic soda (NaOH);
sodium bicarbonate (NaHCO3); lime (Ca(OH)2); heavy metal ions; ferric/ferrous (Fe2+/3+); and cupric ions (Cu2+) or combinations thereof.