Patent Application
20140034553
This application claims the benefit of Canadian patent application number 2,738,194 filed on Apr. 27, 2011 entitled METHOD OF PROCESSING A BITUMINOUS FEED USING AN EMULSION, the entirety of which is incorporated herein.
The present disclosure relates generally to the field of hydrocarbon extraction from mineable deposits, such as bitumen from oil sands.
Methodologies for extracting hydrocarbon from oil sands have required energy intensive processing steps to separate solids from the products having commercial value.
Solvent extraction processes for the recovery of the hydrocarbons have been proposed as an alternative to water extraction of oil sands. However, the commercial application of a solvent extraction process has, for various reasons, eluded the oil sands industry. A major challenge to the application of solvent extraction to oil sands is the tendency of fine particles within the oil sands to hamper the separation of solids from the hydrocarbon extract. Solids agglomeration is a technique that can be used to deal with this challenge.
Solids agglomeration is a size enlargement technique that can be applied within a liquid suspension to assist solid-liquid separation. The process involves agglomerating fine solids, which are difficult to separate from a liquid suspension, by the addition of a second liquid. The second liquid preferentially wets the solids but is immiscible with the suspension liquid. With the addition of an appropriate amount of the second liquid and a suitable agitation, the second liquid displaces the suspension liquid on the surface of the solids. As a result of interfacial forces between the three phases, the fines solids consolidate into larger, compact agglomerates that are more readily separated from the suspension liquid.
Solids agglomeration has been used in other applications to assist solid-liquid separation. For example, the process has been used in the coal industry to recover fine coal particles from the waste streams produced during wet cleaning treatments (see for example, U.S. Pat. Nos. 3,856,668 (Shubert); 4,153,419 (Clayfield); 4,209,301 (Nicol et al.); 4,415,445 (Hatem) and 4,726,810 (Ignasiak)). Solids agglomeration has also been proposed for use in the solvent extraction of bitumen from oil sands. This application was coined Solvent Extraction Spherical Agglomeration (SESA). A more recent description of the SESA process can be found in Sparks et al., Fuel 1992(71); pp 1349-1353.
Previously described methodologies for SESA have not been commercially adopted. In general, the SESA process involves mixing oil sands with a hydrocarbon solvent, adding a bridging liquid to the oil sands slurry, agitating the mixture in a slow and controlled manner to nucleate particles, and continuing such agitation to permit these nucleated particles to form larger multi-particle spherical agglomerates for removal. The bridging liquid is preferably water or an aqueous solution since the solids of oil sands are mostly hydrophilic and water is immiscible with hydrocarbon solvents.
The SESA process described by Meadus et al. in U.S. Pat. No. 4,057,486, involves combining solvent extraction with solids agglomeration to achieve dry tailings suitable for direct mine refill. In the process, organic material is separated from oil sands by mixing the oil sands material with an organic solvent to form a slurry, after which an aqueous bridging liquid is added in the amount of 8 to 50 wt. % of the feed mixture. By using controlled agitation, solid particles from oil sands come into contact with the aqueous bridging liquid and adhere to each other to form macro-agglomerates of a mean diameter of 2 mm or greater. The formed agglomerates are more easily separated from the organic solvent compared to un-agglomerated solids. This process permitted a significant decrease in water use, as compared with conventional water-based extraction processes. The multi-phase mixture need only be agitated severely enough and for sufficient time to intimately contact the aqueous liquid with the fine solids. The patent discloses that it is preferable that the type of agitation be a rolling or tumbling motion for at least the final stages of agglomeration. These types of motion should assist in forming compact and spherical agglomerates from which most of the hydrocarbons are excluded. The formed agglomerates are referred to as macro-agglomerates because they result from the consolidation of both the fine particles (sized less than 44 μm) and the coarse particles (sized greater than 200 μm) found in the oil sands.
U.S. Pat. No. 3,984,287 (Meadus et al.) and U.S. Pat. No. 4,406,788 (Meadus et al.) both describe apparatuses for extracting bitumen from oil sands while forming macro-agglomerates for easy solid-liquid separation. U.S. Pat. No. 3,984,287 (Meadus et al.) describes a two vessel agglomeration apparatus. The apparatus comprises a mixing vessel for agitating the oil sands, the bridging liquid, and the solvent to form a slurry with suspended agglomerates. The slurry is screened in order to remove a portion of the hydrocarbon liquid within which the bitumen product is dissolved. The agglomerates are then directed to a tapered rotating drum where they are mixed with additional solvent and bridging liquid. The additional solvent acts to wash the excess bitumen from the agglomerates. The additional bridging liquid allows the agglomerates to grow by a layering mechanism and under the increasing compressive forces produced by the tapered rotating drum bed depth. The compressive forces act to preferentially remove hydrocarbon liquid from the pores of the agglomerates such that, when optimal operating conditions are imposed, the pores of the agglomerates end up being filled with only the bridging liquid, and the solvent that remains on the surface of the agglomerates is easily recovered. U.S. Pat. No. 4,406,788 (Meadus et al.) describes a similar apparatus to that of U.S. Pat. No. 3,984,287 (Measdus et al.), but where the extraction and agglomeration processes occurs within a single vessel. Within this vessel, the flow of solvent is counter-current to the flow of agglomerates which results in greater extraction efficiency.
The above-mentioned patents describe methods of using the fines within oil sands and an aqueous bridging liquid to promote the consolidation of the coarse oil sands particles into compact macro-agglomerates having minimal entrained hydrocarbons and which are easily separated from the hydrocarbon liquid by simple screening. This macro-agglomeration process may be suitable for oil sands feeds comprising greater than 15 wt % fines. For oil sands with a lesser amount of fines, the resulting agglomerates show poor strength and a significant amount of hydrocarbons entrained within their pores. The inability of the macro-agglomeration process to produce agglomerates of similar solid-liquid separation characteristics regardless of oil sands feed grade, is a limitation. This limitation can be mitigated by using a water and fine particle slurry as the bridging liquid. U.S. Pat. No. 3,984,287 (Meadus et al.) reveals that middlings of a primary separation vessel of a water-based extraction process or sludge from the water-based extraction tailings ponds may be used as the bridging liquids with high fines content. It has been shown that when sludge is used as the bridging liquid, the addition of the same amount of sludge per unit weight of oil sands feed may result in the production of agglomerates of the same drainage properties regardless of oil sands quality. The use of sludge, however, introduces other challenges such as the fact that the appropriate sludge may not be readily available at the mine site. Furthermore, the use of sludge as the bridging liquid leads to larger agglomerates that are more prone to entrapment of bitumen.
U.S. Pat. No. 4,719,008 (Sparks et al.) describes a process to address the agglomeration challenge posed by varying ore grades by means of a micro-agglomeration procedure in which the fine particles of the oil sands are consolidated to produce agglomerates with a similar particle size distribution to the coarser grained particles of the oil sands. Using this micro-agglomeration procedure, the solid-liquid separation behavior of the agglomerated oil sands will be similar regardless of ore grade. The micro-agglomeration process is described as occurring within a slowly rotating horizontal vessel. The conditions of the vessel favor the formation of large agglomerates; however, a light milling action is used to continuously break down the agglomerates. The micro-agglomerates are formed by obtaining an eventual equilibrium between cohesive and destructive forces. Since rapid agglomeration and large agglomerates can lead to bitumen recovery losses owing to entrapment of extracted bitumen within the agglomerated solids, the level of bridging liquid is kept as low as possible commensurate with achieving economically viable solid-liquid separation.
The micro-agglomeration process described in U.S. Pat. No. 4,719,008 (Sparks et al.) has several disadvantages that have thus far limited the application of the technology. Some of these disadvantages will now be described.
In previously described SESA processes, the bridging liquid is either added directly to the dry oil sands or it is added to the oil sands slurry comprising the oil sands and the hydrocarbon solvent. In the former scenario, bitumen extraction and particle agglomeration occurs simultaneously. For this reason, the growth of agglomerates may hamper the dissolution of the bitumen into the solvent, it may lead to trapping of bitumen within the agglomerates, and it may result in an overall increase in the required residence time for bitumen extraction. In the scenario where the bridging liquid is added to the oil sands slurry, excessive agglomeration may occur in the locations of bridging liquid injection. These agglomerates will tend to be larger than the desired agglomerate size and result in an increase in the viscosity of the slurry. A higher slurry viscosity may hamper the mixing needed to uniformly distribute the bridging liquid throughout the remaining areas of the slurry. Poor bridging liquid dispersion may result in a large agglomerate size distribution, which is not preferred.
An important step in the agglomeration process is the distribution of the bridging liquid throughout the liquid suspension. Poor distribution of the bridging liquid may result in regions within the slurry of too low and too high binging liquid concentrations. Regions of low bridging liquid concentrations may have no or poor agglomeration of fine solids, which may result in poor solid-liquid separation. Regions of high bridging liquid concentration may have excess agglomeration of solids, which may result in the trapping of bitumen or bitumen extract within the large agglomerates. In the process described in U.S. Pat. No. 4,719,008 (Sparks et al.), the milling action of the rotating vessel acts to both breakup large agglomerates and distribute the bridging liquid throughout the vessel in order to achieve uniform agglomerate formation. In a commercial application, the rotating vessel would need to be large enough to process the high volumetric flow rates of oil sands. Accomplishing uniform mixing of the bridging liquid in such a large vessel would require a significant amount of mixing energy and long residence times.
Coal mining processes often produce aqueous slurries comprising fine coal particles. Solids agglomeration has been proposed as a method of recovering these fine coal particles, which may constitute up to 30 wt. % of the mined coal. In the solids agglomeration process, the hydrophobic coal particles are agglomerated within the aqueous slurry by adding an oil phase as the bridging liquid. When the aqueous slurry, with bridging liquid, is agitated, the coal particles become wetted with an oil layer and adhere to each other to form agglomerates. The hydrophilic ash particles are not preferentially wetted by the oil phase and, as a result, remain un-agglomerated and suspended in the aqueous phase. The agglomerated coal material, with reduced ash content, is readily separated from the aqueous slurry by mechanical methods such as screening.
U.S. Pat. No. 3,856,668 (Shubert) and U.S. Pat. No. 4,209,301 (Nicol et al.) describe a coal agglomeration process where the oil is first emulsified in water to form an oil-in-water emulsion before the oil is added to the aqueous slurry. Having the bridging liquid in the form of an emulsion allows for faster and more uniform agglomerate formation. The required amount of mixing energy needed for agglomeration is also significantly reduced compared to the case where the bridging liquid is added directly to the aqueous slurry. Additionally, the amount of bridging liquid needed for effective agglomeration of the coal particles is reduced.
U.S. Pat. No. 4,153,419 (Clayfiled et al.) describes a process for the agglomeration of coal fines within an aqueous slurry by staged addition of a bridging liquid to the aqueous slurry. Each agglomeration stage comprises the addition of a bridging liquid to the slurry, agitation of the mixture, and removal of agglomerates from the aqueous slurry. The inventors found that performing the agglomeration process in at least two stages yielded higher agglomeration of the coal particles as compared to the case where the same amount of bridging liquid was added in one agglomeration stage.
U.S. Pat. No. 4,415,445 (Van Hattem et al.) describes a process for the agglomeration of coal fines within an aqueous slurry by the addition of a bridging liquid and the addition of seed pellets that are substantially larger than the coal fines. The presence of seed pellets induces agglomerate growth to occur predominately by a layering mechanism rather than by a coalescence mechanism. Since the rate of agglomeration occurs much faster by layering compared to coalescence, the process described therein allows agglomerates to form very quickly so that, for a given residence time, a higher throughput of agglomerates can be obtained compared to the throughput obtainable in the absence of seed pellets.
It would be desirable to provide an alternative or improved method for processing a bituminous feed.
The present disclosure relates to a method of processing a bituminous feed. The bituminous feed is contacted with a bridging liquid-in-extraction liquor emulsion to form a slurry. Solids in the slurry are agglomerated, using agitation, to form an agglomerated slurry comprising agglomerated solids and a low solids bitumen extract. The agglomerates are then separated from the low solids bitumen extract. Emulsifying the bridging liquid prior to contacting it with the bituminous feed may reduce the amount of energy required for the agglomeration process. Other potential benefits may include the production of smaller and more uniform agglomerates. The former may lead to higher bitumen recoveries and the latter may improve the solid-liquid separation rate.
In a first aspect, the present disclosure provides a method of processing a bituminous feed, the method comprising: a) contacting the bituminous feed with a bridging liquid-in-extraction liquor emulsion, to form a slurry, wherein the extraction liquor comprises a solvent; b) agglomerating solids within the slurry, using agitation, to form an agglomerated slurry comprising agglomerates and a low solids bitumen extract; and c) separating the agglomerates from the low solids bitumen extract.
Other aspects and features of the present disclosure will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments in conjunction with the accompanying figures.
Embodiments of the present disclosure will now be described, by way of example only, with reference to the attached Figures.
The present disclosure relates to a method of processing a bituminous feed using a bridging liquid-in-extraction liquor emulsion. This method may be combined with aspects of other solvent extraction processes, including, but not limited to, those described above in the background section, and those described in Canadian Patent Application Serial No. 2,724,806 (“Adeyinka et al.”), filed Dec. 10, 2010 and entitled “Processes and Systems for Solvent Extraction of Bitumen from Oil Sands”.
Prior to describing embodiments specifically related to the emulsion, a summary of the processes described in Adeyinka et al. is provided in the following paragraph.
To extract bitumen from oil sands in a manner that employs solvent, a solvent is combined with a bituminous feed derived from oil sands to form an initial slurry. Separation of the initial slurry into a fine solids stream and coarse solids stream may be followed by agglomeration of solids from the fine solids stream to form an agglomerated slurry. The agglomerated slurry can be separated into agglomerates and a low solids bitumen extract. Optionally, the coarse solids stream may be reintroduced and further extracted in the agglomerated slurry. A low solids bitumen extract can be separated from the agglomerated slurry for further processing. Optionally, the mixing of a second solvent with the low solids bitumen extract to extract bitumen may take place, forming a solvent-bitumen low solids mixture, which can then be separated further into low grade and high grade bitumen extracts. Recovery of solvent from the low grade and/or high grade extracts is conducted, to produce bitumen products of commercial value.
As outlined in the summary section, and now with reference to
The term “bituminous feed” refers to a stream derived from oil sands that requires downstream processing in order to realize valuable bitumen products or fractions. The bituminous feed is one that comprises bitumen along with undesirable components. Such a bituminous feed may be derived directly from oil sands, and may be, for example raw oil sands ore. Further, the bituminous feed may be a feed that has already realized some initial processing but nevertheless requires further processing. Also, recycled streams that comprise bitumen in combination with other components for removal as described herein can be included in the bituminous feed. A bituminous feed need not be derived directly from oil sands, but may arise from other processes. For example, a waste product from other extraction processes which comprises bitumen that would otherwise not have been recovered, may be used as a bituminous feed. Such a bituminous feed may be also derived directly from oil shale oil, bearing diatomite or oil saturated sandstones.
In one embodiment, dry oil sands (214) are first contacted with an extraction liquor (216) that is free of any bridging liquid in a slurry system (217). The mixture is well mixed in order to dissolve all (or nearly all) of the bitumen within the oil sands. This oil sands slurry (212) is then mixed with the emulsion (208) to agglomerate the fine particles. In this embodiment, the bitumen is first extracted from the oil sands (214) prior to agglomeration in order to prevent (or limit) the agglomeration process from hampering the dissolution of bitumen into the extraction liquor. The composition of the extraction liquor used to produce the oil sands slurry (212) may be the same or different from the extraction liquor used to produce the emulsion. In another embodiment, the emulsion may be directly mixed (218) with the oil sands (214) and potentially additional extraction liquor (216) so that extraction and agglomeration occur simultaneously.
The agglomerated slurry (220), comprising agglomerates and a low solids bitumen extract, is sent to a solid-liquid separator (222) to produce a low solids bitumen extract (224) and agglomerates (226). The low solids bitumen extract is sent to a solvent recovery unit (228) to recover solvent (230) leaving a bitumen product (234). The agglomerates are sent to a tailings solvent recovery unit (236) to recover solvent (238) leaving dry tailings (240).
The agglomerated slurry (320), comprising agglomerates and a low solids bitumen extract, is sent to a solid-liquid separator (322) to produce a low solids bitumen extract (324) and agglomerates (326). The low solids bitumen extract (324) is sent to a solvent recovery unit (328) to recover solvent (330) leaving a bitumen product (334). The agglomerates (326) are sent to a desolventizer (336) to recover solvent (338) leaving dry tailings (340). Make-up extraction liquor may also be added.
The solvent (330) removed from the low solids bitumen extract (324) is used in the solid-liquid separator (322). The solid-liquid separator (322) produces extraction liquor (304) for addition to the emulsifier (306), as described above.
The agglomerated slurry (420), comprising agglomerates and a low solids bitumen extract, is sent to a solid-liquid separator (422) to produce a low solids bitumen extract (424) and agglomerates (426). The low solids bitumen extract (424) is sent to a solvent recovery unit (428) to recover solvent (430) leaving a bitumen product (434). The agglomerates (426) are sent to a desolventizer (436) to recover solvent (438) leaving dry tailings (440).
The solvent (430) removed from the low solids bitumen extract (424) is used in the solid-liquid separator (422). The solid-liquid separator (422) produces extraction liquor (404) for addition to the emulsifier (406) or the slurry system (417), as described above. Make-up extraction liquor may also be added.
The emulsion comprises a bridging liquid dispersed in an extraction liquor, both of which are described below. The emulsion may be formed with various known liquid-in-liquid emulsifiers. Exemplary devices include, but are not limited to, tubular mixers, static mixers, blenders, and liquid jet mixers. In one embodiment, the emulsion forming device is an ultrasonic emulsifier. This device is expected to produce micron size bridging liquid droplets with a lower power requirement than a conventional homogenizer. In one embodiment, the bridging liquid droplets within the emulsion are 1 to 100 μm in size, or 1 to 10 μm in size. In one embodiment, at least 80 wt. % of the bridging liquid droplets within the emulsion are 1 to 100 μm in size, or are 1 to 10 μm in size.
Using such an emulsion may enable the formation of macro-agglomerates or micro-agglomerates from the solids of the bituminous feed. Macro-agglomerates are agglomerates that are predominantly greater than 2 mm in diameter. These agglomerates comprise both the fine particles (less than 44 μm) and sand grains of the oil sands. Micro-agglomerates are agglomerates that are predominately less than 1 mm in diameter and they principally comprise fine particles of the oil sands. It has been found that for the SESA process described above, the formation of micro-agglomerates are more suitable for maximizing bitumen recovery for a range of oil sands grades. In one embodiment, the agglomerated slurry has a solids content of 20 to 70 wt. %. In one embodiment, a ratio of emulsion to slurry is in a range of 1.5 to 0.1 by weight.
In one embodiment, an unstable emulsion is used. An unstable emulsion may reduce the energy needed for the bridging liquid to contact and attach with the solid particles. It has been shown that for stable emulsions, kinetic restriction from such factors as electrical double layer interactions and film thinning considerations can lead to increased power consumption in the solids agglomeration process [see Int. J. of Min. Proc. Vol. 4 pp 173-184]. An “unstable emulsion”, as used herein, means an emulsion that begins to segregate during the agglomeration process. However, it is not desirable to have the unstable emulsion segregate much faster (for instance an order of magnitude faster) than the agglomeration process, since this would defeat the purpose of using an emulsion. The time scale of agglomeration, in one non-limiting example, may be on the order of minutes, for instance 2 to 5 minutes.
In another embodiment, a stable emulsion is used. In this embodiment, a stable emulsion is desirable in order to keep the bridging liquid droplets within the emulsion small and discreet during the agglomeration process. The stability of the emulsion may be provided by the interaction between the bridging liquid and the asphaltenes dissolved within the extraction liquor. Additional stabilizing agents may include alkaline additives such as NaOH, Na2CO3 and NH4OH. Residual solids fines, which may be found in the extraction liquor, may also act as emulsion stabilizers. Such fines may also serve as nuclei for solids agglomeration. A “stable emulsion”, as used herein, means an emulsion that will not segregate during the agglomeration process. The “stable emulsion” may be thermodynamically or kinetically stable.
A surfactant may be added to the emulsion.
Agglomeration is assisted by some form of agitation. The form of agitation may be mixing, shaking, rolling, or another known suitable method. The agitation of the feed need only be severe enough and of sufficient duration to intimately contact the emulsion with the solids in the feed. Exemplary rolling type vessels include rod mills and tumblers. Exemplary mixing type vessels include mixing tanks, blenders, and attrition scrubbers. In the case of mixing type vessels, a sufficient amount of agitation is needed to keep the formed agglomerates in suspension. In rolling type vessels, the solids content of the feed is, in one embodiment, greater than 40 wt. % so that compaction forces assist agglomerate formation.
The extraction liquor comprises a solvent used to extract bitumen from the bituminous feed. The term “solvent”, as used herein, should be understood to mean either a single solvent, or a combination of solvents.
In one embodiment, the extraction liquor comprises a hydrocarbon solvent capable of dissolving the bitumen. The extraction liquor may be a solution of a hydrocarbon solvent(s) and bitumen, where the bitumen content of the extraction liquor may range between 10 to 50 wt. %. It may be desirable to have dissolved bitumen within the extraction liquor in order to increase the volume of the extraction liquor without an increase in the required inventory of hydrocarbon solvent(s). In cases where non-aromatic hydrocarbon solvents are used, the dissolved bitumen within the extraction liquor also increases the solubility of the extraction liquor towards dissolving additional bitumen.
The solvent used in the process may include low boiling point solvents such as low boiling point cycloalkanes, or a mixture of such cycloalkanes, which substantially dissolve asphaltenes. The solvent may comprise a paraffinic solvent in which the solvent to bitumen ratio is maintained at a level to avoid or limit precipitation of asphaltenes.
While it is not necessary to use a low boiling point solvent, when it is used, there is the extra advantage that solvent recovery through an evaporative process proceeds at lower temperatures, and requires a lower energy consumption. When a low boiling point solvent is selected, it may be one having a boiling point of less than 100° C.
The solvent selected according to certain embodiments may comprise an organic solvent or a mixture of organic solvents. For example, the solvent may comprise a paraffinic solvent, an open chain aliphatic hydrocarbon, a cyclic aliphatic hydrocarbon, or a mixture thereof. Should a paraffinic solvent be utilized, it may comprise an alkane, a natural gas condensate, a distillate from a fractionation unit (or diluent cut), or a combination of these containing more than 40% small chain paraffins of 5 to 10 carbon atoms. These embodiments would be considered primarily a small chain (or short chain) paraffin mixture. Should an alkane be selected as the solvent, the alkane may comprise a normal alkane, an iso-alkane, or a combination thereof. The alkane may specifically comprise heptane, iso-heptane, hexane, iso-hexane, pentane, iso-pentane, or a combination thereof. Should a cyclic aliphatic hydrocarbon be selected as the solvent, it may comprise a cycloalkane of 4 to 9 carbon atoms. A mixture of C4-C9 cyclic and/or open chain aliphatic solvents would be appropriate.
Exemplary cycloalkanes include cyclohexane, cyclopentane, or a mixture thereof.
If the solvent is selected as the distillate from a fractionation unit, it may for example be one having a final boiling point of less than 180° C. An exemplary upper limit of the final boiling point of the distillate may be less than 100° C.
A mixture of C4-C10 cyclic and/or open chain aliphatic solvents would also be appropriate. For example, it can be a mixture of C4-C9 cyclic aliphatic hydrocarbons and paraffinic solvents where the percentage of the cyclic aliphatic hydrocarbon in the mixture is greater than 50%.
Extraction liquor may be recycled from a downstream step. For instance, as illustrated in
The solvent may also include additives. These additives may or may not be considered a solvent per se. Possible additives may be components such as de-emulsifying agents or solids aggregating agents. Having an agglomerating agent additive present in the bridging liquid and dispersed in the first solvent may be helpful in the subsequent agglomeration step. Exemplary agglomerating agent additives include cements, fly ash, gypsum, lime, brine, water softening wastes (e.g. magnesium oxide and calcium carbonate), solids conditioning and anti-erosion aids such as polyvinyl acetate emulsion, commercial fertilizer, humic substances (e.g. fulvic acid), polyacrylamide based flocculants and others. Additives may also be added prior to gravity separation with the second solvent to enhance removal of suspended solids and prevent emulsification of the two solvents. Exemplary additives include methanoic acid, ethylcellulose and polyoxyalkylate block polymers.
A bridging liquid is a liquid with affinity for the solids particles in the bituminous feed, and which is immiscible in the solvent. Exemplary aqueous liquids may be recycled water from other aspects or steps of oil sands processing. The aqueous liquid need not be pure water, and may indeed be water containing one or more salts, a waste product from conventional aqueous oil sand extraction processes which may include additives, aqueous solutions with a range of pH, or any other acceptable aqueous solution capable of adhering to solid particles within an agglomerator in such a way that permits fines to adhere to each other. An exemplary bridging liquid is water.
The bridging liquid may be added to the extraction liquor in a concentration of less than 50 wt. % of the emulsion. In another embodiment, the bridging liquid is added to the extraction liquor in a concentration of less than 25 wt. %. In one embodiment, the bridging liquid is added in a concentration of between 5 wt. % and 50 wt. % or between 10 wt. % and 25 wt. %. In one embodiment, the bridging liquid may comprise fine particles (sized less than 44 μm) suspended therein. These fine particles may serve as seed particles for the agglomeration process. In one embodiment, the bridging liquid has a solids content of less than 40 wt. %.
The process may be adjusted to render the ratio of the solvent to bitumen in the agglomerator at a level that avoids precipitation of asphaltenes during agglomeration. Some amount of asphaltene precipitation is unavoidable, but by adjusting the amount of solvent flowing into the system, with respect to the expected amount of bitumen in the bituminous feed, when taken together with the amount of bitumen that may be entrained in the extraction liquor used, can permit the control of a ratio of solvent to bitumen in the agglomerator. When the solvent is assessed for an optimal ratio of solvent to bitumen during agglomeration, the precipitation of asphaltenes can be minimized or avoided beyond an unavoidable amount. Another advantage of selecting an optimal solvent to bitumen ratio is that when the ratio of solvent to bitumen is too high, costs of the process may be increased due to increased solvent requirements.
An exemplary ratio of solvent to bitumen to be selected as a target ratio during agglomeration is less than 2:1. A ratio of 1.5:1 or less, and a ratio of 1:1 or less, for example, a ratio of 0.75:1, would also be considered acceptable target ratios for agglomeration. For clarity, ratios may be expressed herein using a colon between two values, such as “2:1”, or may equally be expressed as a single number, such as “2”, which carries the assumption that the denominator of the ratio is 1 and is expressed on a weight to weight basis.
The slurry system may optionally be a mix box, a pump, or a combination of these. By slurrying the extraction liquor together with the bituminous feed, and optionally with additional additives, the bitumen entrained within the feed is given an opportunity to become extracted into the solvent phase prior to agglomeration within the agglomerator.
As described above, the agglomerated slurry may be separated into a low solids bitumen extract and agglomerates in a solid-liquid separator. The solid-liquid separator may comprise any type of unit capable of separating solids from liquids, so as to remove agglomerates. Exemplary types of units include a gravity separator, a clarifier, a cyclone, a screen, a belt filter, or a combination thereof.
The system may contain a solid-liquid separator but may alternatively contain more than one. When more than one solid-liquid separation step is employed at this stage of the process, it may be said that both steps are conducted within one solid-liquid separator, or if such steps are dissimilar, or not proximal to each other, it may be said that a primary solid-liquid separator is employed together with a secondary solid-liquid separator. When a primary and secondary unit are both employed, generally, the primary unit separates agglomerates, while the secondary unit involves washing agglomerates.
Non-limiting methods of solid-liquid separation of an agglomerated slurry are described in Canadian Patent Application Serial No. 2,724,806 (Adeyinka et al.), filed Dec. 10, 2010.
As a component of the solid-liquid separator, a secondary stage of separation may be introduced for counter-currently washing the agglomerates separated from the agglomerated slurry. The initial separation of agglomerates may be said to occur in a primary solid-liquid separator, while the secondary stage may occur within the primary unit, or may be conducted completely separately in a secondary solid-liquid separator. By “counter-currently washing”, it is meant that a progressively cleaner solvent is used to wash bitumen from the agglomerates. Solvent involved in the final wash of agglomerates may be re-used for one or more upstream washes of agglomerates, so that the more bitumen entrained on the agglomerates, the less clean will be the solvent used to wash agglomerates at that stage. The result being that the cleanest wash of agglomerates is conducted using the cleanest solvent.
A secondary solid-liquid separator for counter-currently washing agglomerates may be included in the system or may be included as a component of a system described herein. The secondary solid-liquid separator may be separate or incorporated within the primary solid-liquid separator. The secondary solid-liquid separator may optionally be a gravity separator, a cyclone, a screen, or belt filter. Further, a secondary solvent recovery unit for recovering solvent arising from the solid-liquid separator can be included. The secondary solvent recovery unit may be a conventional fractionation tower or a distillation unit.
When conducted in the process, the secondary stage for counter-currently washing the agglomerates may comprise a gravity separator, a cyclone, a screen, a belt filter, or a combination thereof.
The solvent used for washing the agglomerates may be solvent recovered from the low solids bitumen extract, as described with reference to
The process may involve removal and recovery of solvent used in the process.
In this way, solvent is used and re-used, even when a good deal of bitumen is entrained therein. Because an exemplary solvent:bitumen ratio in the agglomerator may be 2:1 or lower, it is acceptable to use recycled solvent containing bitumen to achieve this ratio. The amount of make-up solvent required for the process may depend solely on solvent losses, as there is no requirement to store and/or not re-use solvent that has been used in a previous extraction step. When solvent is said to be “removed”, or “recovered”, this does not require removal or recovery of all solvent, as it is understood that some solvent will be retained with the bitumen even when the majority of the solvent is removed.
The system may contain a single solvent recovery unit for recovering the solvent(s) arising from the gravity separator. The system may alternatively contain more than one solvent recovery unit.
Solvent may be recovered by conventional means. For example, typical solvent recovery units may comprise a fractionation tower or a distillation unit. Solvent recovered in this fashion will not have bitumen entrained therein. This clean solvent may be used in the last wash stage of the agglomerate washing process so that the cleanest wash of the agglomerates is performed using the cleanest solvent.
The solvent recovered in the process may comprise entrained bitumen therein, and can thus be re-used as the extraction liquor for combining with the bituminous feed. Other optional steps of the process may incorporate the solvent having bitumen entrained therein, for example in countercurrent washing of agglomerates, or for adjusting the solvent and bitumen content prior to agglomeration to achieve the selected ratio within the agglomerator that avoids precipitation of asphaltenes.
Extraction Step May be Separate from Agglomeration Step
Solvent extraction may be conducted separately from agglomeration in certain embodiments of the process. Unlike certain prior processes, where the solvent is first exposed to the bituminous feed within the agglomerator, certain embodiments described herein include contact of the extraction liquor with bituminous feed prior to the agglomeration step. This has the effect of reducing residence time in the agglomerator, when compared to certain previously proposed processes which require extraction of bitumen and agglomeration to occur simultaneously. The instant process is tantamount to agglomeration of pre-blended slurry in which extraction via bitumen dissolution is substantially or completely achieved separately. Performing extraction upstream of the agglomerator permits the use of enhanced material handling schemes whereby flow/mixing systems such as pumps, mix boxes or other types of conditioning systems can be employed. Additionally, performing extraction upstream of the agglomerator prevents (or limits) the agglomeration process from hampering the dissolution of bitumen into the extraction liquor.
Because the extraction may occur upstream of the agglomeration step, the residence time in the agglomerator may be reduced. One other reason for this reduction is that by adding components, such as water, some initial nucleation of particles that ultimately form larger agglomerates can occur prior to the agglomerator.
Solvent may be added to the agglomerated slurry for dilution of the slurry before discharge into the primary solid-liquid separator, which may be for example a deep cone settler. This dilution can be carried out in a staged manner to pre-condition the primary solid-liquid separator feed to promote higher solids settling rates and lower solids content in the solid-liquid separator's overflow. The solvent with which the slurry is diluted may be derived from recycled liquids from the liquid-solid separation stage or from other sources within the process.
When dilution of agglomerator discharge is employed in this embodiment, the solvent to bitumen ratio of the feed into the agglomerator is set to obtain from about 10 to about 90 wt. % bitumen in the discharge, and a workable viscosity at a given temperature. In certain cases, these viscosities may not be optimal for the solid-liquid separation (or settling) step. In such an instance, a dilution solvent of equal or lower viscosity may be added to enhance the separation of the agglomerated solids in the clarifier, while improving the quality of the clarifier overflow by reducing viscosity to permit more solids to settle. Thus, dilution of agglomerator discharge may involve adding the solvent, or a separate dilution solvent, which may, for example, comprise an alkane.
There may be advantages of embodiments described herein as compared to SESA. It is believed that the bridging liquid to solids contact, which is needed for agglomeration, can be enhanced if the bridging liquid is first emulsified in the extraction liquor prior to mixing it with the oil sands solids. Similar advantages have been realized in the agglomeration of coal fine particles (see U.S. Pat. No. 3,856,668 (Shubert) and U.S. Pat. No. 4,209,301 (Nicol et al.)).
Previous solids agglomeration processes have required large energy inputs. Embodiments described herein are expected to reduce the total energy needed to form the agglomerates. The reduction in energy may be a result of both a reduction in the required time and the required power needed for the agglomeration process. A reduction in residence time may translate to smaller and less expensive vessels. A reduction in the power requirement means that that the torque requirements of motors used in certain types of agglomeration vessels can be reduced. In the case of rotating type vessels, the required amount of milling may be reduced. Furthermore, the wear of the internals of the vessels may be reduced due to a reduction in the required mixing intensity.
The emulsified bridging liquid is expected to more quickly and more uniformly distribute within the oil sands slurry. For this reason, the amount of bridging liquid needed to agglomerate the fine particles within oil sands slurry is expected to be less than that which would be required if the bridging liquid was not emulsified. A reduced amount of bridging liquid may result in smaller agglomerates which have been shown to result in higher bitumen recovery values. The improved distribution of bridging liquid within the oil sands slurry is also expected to result in a narrower particle size distribution for the agglomerates. Agglomerates that are more uniform in size may have higher drainage rates for solid-liquid separation methods such as filtration and screening.
In the preceding description, for purposes of explanation, numerous details are set forth in order to provide a thorough understanding of the embodiments. However, it will be apparent to one skilled in the art that these specific details are not required.
The above-described embodiments are intended to be examples only. Alterations, modifications and variations can be effected to the particular embodiments by those of skill in the art without departing from the scope, which is defined solely by the claims appended hereto.
Experiments were conducted to test the effectiveness of using a bridging liquid-in-extraction liquor emulsion to agglomerate oil sand solids within a slurry. The liquid drainage rate of the formed agglomerates was used as the experimental measurement to determine the effectiveness of the agglomeration process. The agglomerates were also visually inspected for their size and uniformity.
Athabasca oil sand was treated in a Soxhlet extractor, with toluene as the extraction solvent, to remove bitumen and water from the solids. The oil sand solids were dried overnight in an oven (100° C.) and then used as the solids in the agglomeration process. Pure cyclohexane was used as the extraction liquor and distilled water was used as the bridging liquid. Bitumen was excluded from the solids and the solvent in order to allow for visual inspection of the agglomeration process. For each experiment, a total of 350 g of solids, 311.5 g of cyclohexane, and 38.5 g of water were used. This composition translated to a solids content of 50 wt. % and a water to solids ratio of 0.11 for the agglomerated slurry.
A Parr reactor (series 5100) (Parr Instrument Company, Moline, Ill., USA) was used as the agglomerator. The reactor vessel was made of glass that permits direct observation of the mixing process. A turbine type impeller powered by an explosion proof motor of 0.25 hp was used. The mixing and agglomeration speed of the impeller were set to 1000 rpm. This rotation speed allowed the slurry to remain fluidized at all conditions of the experiments. The agglomeration experiments were conducted at room temperature (22° C.).
350 g of oil sand solids and 311.5 g of cyclohexane were placed into the Parr reactor vessel. The solids and solvent were mixed at 1000 rpm for 1 minute to fully homogenize the mixture. After 1 minute of mixing, water was quickly pored into the vessel through a sample port. The mixture was then mixed at 1000 rpm for an additional 2 minutes to agglomerate the solids.
After the agglomeration process, the impeller was turned off and the agglomerates were allowed to settle for over 1 minute. The supernatant was pored into a separate container and the wet solids were transferred to a Buchner funnel. The solids rested on a filter paper with a nominal pore size of 170 μm. The filter's effective area was approximately 8 cm2. The solids bed height was 10.8 cm. A portion of the collected supernatant was pored on top of the solids until a liquid height of 1.9 cm formed above the solids surface. A light vacuum was then applied to the Buchner funnel and the initial drainage rate of the liquid was recorded. The initial drainage rate for solids agglomerated by adding bridging liquid directly to the solids slurry was 0.37 mL/(cm2sec).
Experiment 2: Agglomeration by First Emulsifying Bridging Liquid with Solvent and then Adding Emulsion to Solids Slurry
38.5 g of water was added to 115.5 g of solvent in a glass bottle. The mixture was then emulsified by placing the glass bottle in an ultrasonic bath for 10 minutes. 350 g of oil sand solids and 196 g of cyclohexane were placed into the Parr reactor vessel. The solids and solvent were mixed at 1000 rpm for 1 minute to fully homogenize the mixture. After 1 minute of mixing, the emulsion was quickly pored into the vessel through a sample port. The mixture was then mixed at 1000 rpm for an additional 2 minutes to agglomerate the solids.
After the agglomeration process, the impeller was turned off and the agglomerates where allowed to settle for over 1 minute. The supernatant was pored into a separate container and the wet solids were transferred to a Buchner funnel. The solids rested on a filter paper with a nominal pore size of 170 μm. The filter's effective area and the funnel's cross-sectional area were approximately 8 cm. The solids bed height was 10.8 cm. A portion of the collected supernatant was pored on top of the solids until a liquid height of 1.9 cm formed above the solids surface. A light vacuum was then applied to the Buchner funnel and the initial drainage rate of the liquid was recorded. The initial drainage rate for solids agglomerated by first emulsifying the bridging liquid with solvent and then adding emulsion to solids slurry was approximately 2.1 mL/(cm2sec). This drainage rate was approximately 5.7 times greater than that of agglomerates formed without first emulsifying the bridging liquid.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2738194 | Apr 2011 | CA | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US12/28557 | 3/9/2012 | WO | 00 | 10/8/2013 |
