Patent Application
20140209512
This application claims the priority benefit of Canadian Patent Application 2,753,811 filed Sep. 29, 2011 entitled METHOD OF PROCESSING TAILINGS FROM SOLVENT-BASED HYDROCARBON EXTRACTION, the entirety of which is incorporated by reference herein.
The present disclosure relates generally to the field of hydrocarbon extraction from mineable deposits, such as bitumen from oil sands. More particularly, the present disclosure relates to the processing of tailings from solvent-based hydrocarbon extraction.
Oil sands are sand deposits which, in addition to sand, comprise clays, connate water, and bitumen. Depending on the geographic location, bitumen may be recovered by mining and extraction methods or by in-situ recovery methods.
Oil sands ore in a mining and extraction operation is typically processed using mechanical and chemical techniques to separate the bitumen from the sands. In general, water-based extraction and solvent-based extraction are the two processes that have been proposed or used to extract bitumen from mined oil sands. In the case of water-based extraction, water is the dominant liquid in the process and the extraction occurs by having water displace the bitumen on the surface of the solids. In the case of solvent-based extraction, the solvent is the dominant liquid and the extraction of the bitumen occurs by dissolving bitumen into the solvent.
The commercial application of a solvent-based extraction process has, for various reasons, eluded the oil sands industry. A major challenge to the application of solvent-based extraction to oil sands is the tendency of fine particles within the oil sands to hamper the separation of solids from the bitumen extract. Solvent extraction with solids agglomeration is a technique that has been proposed to deal with this challenge. The original application of this technology was coined Solvent Extraction Spherical Agglomeration (SESA). A more recent description of the SESA process can be found in
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. It has been found that the bridging liquid used in the process can be water with both a high fines and salt content. In fact, in certain embodiments of the SESA process, it may be preferable to have aqueous bridging liquid with either high fines content and/or high dissolved solid content.
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 extract compared to un-agglomerated solids. The organic extract free agglomerates can be sintered at high temperatures to make useful construction material. For example, halide salts such as NaCl, KCl, and CaCl2 can be dissolved in the aqueous bridging liquid to form agglomerates that, when sintered at elevated temperatures, produce very strong aggregates.
The oil sands industry has become relatively adept at handling aqueous tailings streams from water-based bitumen extraction. These tailings are sorted by size in a variety of operations, and bitumen and minerals can then be extracted. For instance, settlers and cyclones are currently used for aqueous tailings to separate particular streams by particle size distribution; the coarser fraction can be pumped into place and rapidly drained, making it an excellent construction material.
Oil sands tailings are unique among mining tailings in that they comprise residual hydrocarbons. They often also comprise metals, clays, and sands. In a water-based extraction process, oil sand tailings comprise water. Because of this water content, the tailings are pumpable and easily fed into separation units common in the oil industry. In this way, metals can be extracted from the aqueous tailings, bitumen can be skimmed from floating mats on tailings ponds, and coarse and fines fractions can be separated by gravity or enhanced gravity separation All of these separations of aqueous tailings currently take place in the oil sands industry.
While one solution to treating solid tailings could be to wet the tailings and subject them to the same processes as aqueous tailings this solution greatly diminishes the value of a process that produces dry tailings in the first place.
Outside of the oil sands mining industry, solids handling and separation is common in the mining industry. In particular, several mechanisms exist for the dry beneficiation of coal, as described by Lockhart, “Dry Beneficiation of Coal”, Powder Technology 40 (1984) 17-42 and also by Dwari and Rao, “Dry Beneficiation of Coal—A Review”, Mineral Processing and Extractive Metallurgy Review 28 (2007) 177-234. These techniques are applied to ores, which are routinely separated and classified, and the methods listed above, such as cyclones, sieves, magnets, etc., are established technologies.
B. D. Sparks and F. W. Meadus, “A Combined Solvent Extraction and Agglomeration Technique for the Recovery of Bitumen from Tar Sands”, Canadian Chemical Engineering Conference, Calgary: Energy Processing: Tar Sands Technology, 1979 describes the production of solid agglomerates, and refers to the storage of these materials without containment.
U.S. Patent Publication No. 2010/0258478 Moran et al. describes a method for separating aqueous oil sand tailings into a bitumen rich stream and a dry mineral stream, but separation of the dry mineral stream is not mentioned.
Newman and Arnold, in “Dry stack tailings design for the Rosemont Copper project”, Proceedings of the 14th International Conference on Tailings and Mine Waste 2010, Vail, Colo., describe a dry tailings project requiring a buttress and a cover requirement for the tailings facility.
Lupo and Hall, in “Dry stack tailings—design considerations”, ibid, describe that tailings could be distributed in a stack based on their moisture content exiting the extraction process to reduce flow of fluid tailings and dyke strength requirements. No separation is mentioned; instead, drier tailings resulting from the primary process are deposited in one way while process upset tailings are deposited in another.
U.S. Pat. No. 4,240,897 (Clarke) describes a method of producing dry tailings and recommends that these tailings be mixed with overburden and used as backfill for reclamation. No separation of tailings is mentioned.
U.S. Pat. No. 7,695,612 (Erasmus) describes a method of recovering heavy minerals from aqueous oil sands tailings.
Described is a method of processing a bituminous feed. The bituminous feed is solvent extracted to form a bitumen-rich stream and a bitumen-lean stream. Solvent is recovered from the bitumen-rich stream to form a bitumen product. Solvent and water are recovered from the bitumen-lean stream to form dry tailings with a moisture content of less than 40 wt. %. The dry tailings are separated into at least two streams, each stream having a moisture content of less than 40 wt. %, based on at least one physical or chemical property. At least one of the at least two streams is then used at an oil sands mine site. In this way, the dry tailings may be used more effectively.
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.
As used herein, 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.
As used herein, the term “agglomerate” refers to conditions that produce a cluster, aggregate, collection or mass, such as nucleation, coalescence, layering, sticking, clumping, fusing and sintering, as examples.
As used herein, the term “dry tailings” refers to tailings with a moisture content of less than 40 wt. %.
Dry tailings are not common in the oil sands industry. Where produced, dry oil sands tailings have been seen as an end state rather than as a composition suitable for further processing and use. Additionally, solid-solid separation is not common in the oil sands industry. As described herein, dry tailings from solvent-based extraction may be processed for advantageous use.
As described in the summary section, the present disclosure relates to a method of processing a bituminous feed. The bituminous feed is solvent extracted to form a bitumen-rich stream and a bitumen-lean stream. Solvent is recovered from the bitumen-rich stream to form a bitumen product. Solvent and water are recovered from the bitumen-lean stream to form dry tailings with a moisture content of less than 40 wt. %. The dry tailings are separated into at least two streams, each stream having a moisture content of less than 40 wt. %, based on at least one physical or chemical property. At least one of the at least two streams is then used at an oil sands mine site.
Suitable solvent-based extraction processes may include solvent-based extraction processes that uses an aqueous stream in the extraction process. Exemplary solvent-based extraction processes include, but are not limited to, those described in the background section, those described below, and those described in Canadian Patent Application Serial No. 2,724,806 (“Adeyinka et al.”) filed Dec. 10, 2010 and entitled “Process and Systems for Solvent Extraction of Bitumen from Oil Sands”.
One method of extracting bitumen from oil sands in a manner that employs solvent extraction with solids agglomeration is described by Adeyinka et al. In this process, 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 a coarse solids stream may be followed by mixing a bridging liquid with the fine solid stream and 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. The agglomerates may be sent to a tailings solvent recovery unit to recover solvent and water, leaving dry tailings. Additional details of a solvent-based extraction process are described below.
Processing of Tailings from Solvent-Based Extraction
Dry tailings from solvent-based bitumen extraction may be separated into at least two streams, each stream having a moisture content of less than 40 wt. %. These streams may be suitable for different uses. At least one stream may be suitable for use at the oil sands mine site, or another oil sands mine site, including an water-based bitumen extraction mine site. The separation is effected by leveraging a physical or chemical property of the tailings.
Characteristics to be leveraged for the dry oil sands tailings separation may include, but are not limited to size, density, dipole moment, permeability, shape, magnetism, adhesiveness, wettability, attrition, strength, solubility, inductiveness, and electric charge.
Suitable methods or devices for separating dry oil sands tailings may include, but are not limited to a screen, a sieve, a blower (for instance an air blower), gravity separation or enhanced gravity separation (for instance using a cyclone, centrifuge, or settler), filtration, electrostatic precipitation, a magnet, a shaker, a grinder, milling, and rolling.
Separation may also be achieved naturally without using a device, i.e. by consolidation over time. In one embodiment, the dry tailings are rolled down an incline such as a hill or mine face. The tailings separate themselves according to size and/or density. Materials at the top are of a lighter density and/or a smaller size. In another embodiment, first and second streams are separated from one another by a sieve, screen, or a blower. In another embodiment, the tailings are separated in a cyclone. In another embodiment, they are separated according to their electrostatic charge. In another embodiment, they are separated by a magnetic field. In another embodiment, the tailings are separated by their tendency to cling to a surface. In another embodiment, the tailings are separated by their strength. In another embodiment, the tailings are separated by being selectively crushed in a mill.
A first of the separated streams may be used as a construction material while a second is used for mine backfill. In this embodiment, the first stream may be a coarser stream. The second stream may be comprised of a finer fraction of particles. The separation into these streams would allow the coarser stream to be mixed with water because it would rapidly drain. The coarser material could subsequently be pumped into place, allowing construction according to the general practice in the industry, for instance for construction of a mine form at the oil sands site, such as a dyke or a road.
At least one of the at least two streams may be used drainage, as foundation, as a road, for reclamation, or as a dyke, at the oil sands mine site, or is used in a deposit for growing vegetation.
A stream of finer particle sized tailings may be separated from a stream of coarser particle sized tailings. The finer particles are used in the lining of a tailings cell to reduce its permeability to water. The tailings could be placed at the bottom of, along the walls of, and/or on the cap of a tailings deposit.
The streams may be separated by charge or magnetism. An incoming tailings stream is subjected to a magnetic moment or an electrostatic charge. The portion of the incoming tailings stream that responds to this force is captured separately from the portion that does not respond to the force. The mineral composition of the tailings being different, one of the tailings streams, rich in one or more minerals, is used in a mineral extraction process to recover the valuable minerals. Another stream is used for mine backfill. In another embodiment, the mineral poor stream is placed in a deposit closer to potential contact with water. The mineral rich tailings are placed farther away from potential contact with water. In another embodiment, the mineral rich stream is placed under water, and the mineral poor stream is placed in or over the water table.
The separation may be used to produce streams of differing sizes or densities, which can be used in different capacities in mine backfill. The lighter stream may be more prone to dusting, and may be covered with another material, such as a coarser stream of tailings. The heavier stream may be used as a capillary barrier. In this application, the coarser stream has a low hydraulic wicking potential while dry as compared to the finer stream. A material may be selectively moved from the deposit based on its materials properties.
The tailings may be separated into streams that differ by their chemical composition into a chemically active stream and a chemically inert stream. The tailings may be separated into a stream that can be heat treated to form a cementitious material. The tailings may be separated into a stream that can be mixed with a chemical binder and another stream that is not mixed with a chemical binder.
As described above, the term “dry tailings” refers to tailings with a moisture content of less than 40 wt. %. In another embodiment, the dry tailings may have a moisture content of less than 30 wt. %.
The heavier stream 108 may be a coarser material and may be suitable for use as a construction material, such as for roads or containment. In an example where both streams are used at the mine site, as illustrated in
For dry sands tailings, many uses may favor a particular fraction of the tailings rather than the whole tailings. Furthermore, some fractions of the tailings may be preferred over other fractions of the tailings. Examples include construction materials for dykes or roads, as backfill within the mine, or as a recycle stream to aid in extraction. An example of a recycle stream aiding in the extraction process is as follows. It has been previously shown that increasing the solids content, or more preferably the fines content, of a slurry may improve the solvent extraction with solids agglomeration process. Thus, a fines solids stream produced by a process described herein may be redirected back to the solvent extraction process to aid in solids agglomeration. More uses can be envisioned, such as mineral extraction from a mineral rich stream, as a pH buffer in a tailings pond, or as an absorption stream to enhance the solids content of fluid tailings, as described above. One example is to use the fines streams as an impermeable layer. Such an impermeable layer can be used as liner for mature fine tailings produced in an aqueous-based extraction process.
The moisture content of the tailings may be reduced prior to separation, for instance by drying, extraction, or agglomeration.
At least one of the at least two streams may be mixed with an additive comprising a polymer, gypsum, alum, or a resin.
At least one of the at least two streams may be mixed with tailings generated from an aqueous-based bitumen extraction process.
At least one of the at least two streams may be grinded.
One or more heavy metals may be recovered from at least one of the at least two streams. The heavy metals may be titanium, strontium, or vanadium, or a combination thereof.
At least one of the at least two streams may be recycled into the solvent extraction of step a).
The dry tailings may have a water:solids mass ratio of less than 0.15:1.
The oil sands mine site may be mine site employing aqueous-based bitumen extraction or a mine site employing solvent-based bitumen extraction.
In one embodiment, the formed agglomerates are sized on the order of 0.1-1.0 mm, or on the order of 0.1-0.3 mm. In one embodiment, at least 80 wt. % of the formed agglomerates are 0.1-1.0 mm, or 0.1 to 0.3 mm in size. The rate of agglomeration may be controlled by a balance between intensity of agitation within the agglomeration vessel, shear within the vessel which can be adjusted by for example changing the shape or size of the vessel, fines content of the slurry, bridging liquid addition, and residence time of the agglomeration process. The agglomerated slurry may have a solids content of 20 to 70 wt %.
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 agitation of the slurry has an impact on the growth of the agglomerates. In the case of mixing type vessels, the mixing power can be increased in order to limit the growth of agglomerates by attrition of said agglomerates. In the case of rolling type vessels the fill volume and rotation rate of the vessel can be adjusted in order to increase the compaction forces used in the comminution of agglomerates. These agitation parameters can be adjusted in the control system described herein.
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 and 70 wt %, or 10 and 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 extraction liquor may be mixed with the bituminous feed to form a slurry where most or all of the bitumen from the oil sands is dissolved into the extraction liquor. In one embodiment, the solids content of the slurry is in the range of 10 wt % to 75 wt %, or 50 to 65 wt %. A slurry with a higher solids content may be more suitable for agglomeration in a rolling type vessel, where the compressive forces aid in the formation of compact agglomerates. For turbulent flow type vessels, such as an attrition scrubber, a slurry with a lower solids content may be more suitable.
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 hydrocarbons in the mixture is greater than 50%.
Extraction liquor may be recycled from a downstream step. For instance, as described below, solvent recovered in a solvent recovery unit, may be used to wash agglomerates, and the resulting stream may be used as extraction liquor. As a result, the extraction liquor may comprise residual bitumen and residual solid fines. The residual bitumen increases the volume of the extraction liquor and it may increase the solubility of the extraction liquor for additional bitumen dissolution.
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 salt, 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 total amount of bridging liquid added to the slurry may be controlled in order to optimize bitumen recovery and the rate of solid-liquid separation. By way of examples, the total amount of bridging liquid added to the slurry may be such that a ratio of bridging liquid plus connate water from the bituminous feed to solids within the agglomerated slurry is in the range of 0.02 to 0.25, or in the range of 0.05 to 0.11.
The bridging liquid may be added in a concentration of less than 50 wt % of the oil sands feed, or less 25 wt %.
In one embodiment, the bridging liquid may comprise fine particles (sized less than 44 pm) 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.
Measurement of the solvent and bitumen content of the extraction liquor and/or bitumen extract could occur directly or by proxy. Direct measurement of solvent and bitumen content could involve evaporating off the solvent and measuring the mass of both liquids, or use of a gas chromatograph, mass balance, spectrometer, or titration. Indirect measurement of solvent and bitumen content could include measuring : density, the index of refraction, opacity, or other properties.
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.
The resulting slurry from the slurry system may have a solid content in the range of 20 to 65 wt %. In another embodiment, the slurry may have a solid content in the range of 20 to 50 wt %. In another embodiment, the slurry may have a solid content in the range of 40 to 65 wt %. In the case of mixing type vessels, a lower solid content may be preferred since that will assist in the proper mixing of the bridging liquid and reduce the mixing energy needed to keep the slurry well mixed. In the case of rolling type vessels, a higher solid content may be preferred since that will increase the compaction forces used in the comminution of agglomerates. Additionally, the increased compaction forces may reduce the amount of hydrocarbons that remain in the agglomerates and produce stronger agglomerates.
The preferred temperature of the slurry is in the range of 20-60° C. An elevated slurry temperature is desired in order to increase the bitumen dissolution rate and reduce the viscosity of the slurry to promote more effective sand digestion and agglomerate formation. Temperatures above 60° C. are generally avoided due to the complications resulting from high vapor pressures.
The residence time of the extraction process may be greater than 5 minutes, or may be greater than 10 minutes, or may be greater than 15 minutes, or may greater than 30 minutes. Depending on the desired level of agglomeration, the residence time of the agglomeration process may be in the range of 15 seconds to 10 minutes. In order to maximize bitumen recovery, the residence time of the agglomeration process may be in the range of 1 to 5 minutes.
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 countercurrently 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 “countercurrently 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 countercurrently 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 countercurrently 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 in Canadian Patent Application Serial No. 2,724,806 (Adeyinka et al.). A second solvent may alternatively or additionally be used as described in Canadian Patent Application Serial No. 2,724,806 (Adeyinka et al.) for additional bitumen extraction downstream of the agglomerator.
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. The solvent recovered in this fashion will not contain bitumen entrained therein. This clean solvent is preferably used in the last wash stage of the agglomerate washing process in order that the cleanest wash of the agglomerates is conducted 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.
The agglomerates may be sent to a tailings solvent recovery unit to recover solvent and water, leaving dry tailings.
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.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2753811 | Sep 2011 | CA | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US12/49978 | 8/8/2012 | WO | 00 | 1/29/2014 |
