Patent Application
20110284428
The present invention relates generally to a process for hydrocarbon extraction from mineable deposits, such as bitumen from oil sands, and to a system for implementing such a process. Processes and systems are described for recovery of hydrocarbon associated with waste streams produced in conventional water-based bitumen extraction processes.
Methodologies for extracting hydrocarbon from oil sands have required energy intensive processing steps to separate solids and water from the products having commercial value.
Previously described methodologies for solvent extraction spherical agglomeration (SESA), have not been commercially adopted. For a description of the SESA process, see Sparks et al., Fuel 1992(71); 1349-1353. Such processes involved mixing a slurry of oil sands material with a hydrocarbon solvent (such as a high boiling point solvent), adding a bridging liquid (for example, water), agitating this mixture in a slow and controlled manner to nucleate particles, and continuing such agitation so as to permit these nucleated particles to form larger multi-particle spherical agglomerates for removal. A bridging liquid is a liquid with affinity for the solid particles (i.e. preferentially wets the solid particles) but is immiscible in the solvent. The process was conducted at about 50-80° C. (see also Canadian Patent Application 2,068,895 of Sparks et al.). The enlarged size of the agglomerates formed permits easy removal of the solids by sedimentation, screening or filtration.
Solvent recovery from the solids produced in previously described processes would be difficult, due to the nature of the solvent proposed for use in the extraction process. The proposed solvents in previously described processes have a low molecular weight, high aromatic content, and low short chain paraffin content. Naphtha was the solvent proposed for the SESA process, with a final boiling point ranging between 180-220° C., and a molecular weight of 100-215 g/mol. With such high boiling point solvents, the recovery would be energy intensive as significant energy is required to vaporize the residual hydrocarbon and to release hydrocarbon trapped within the agglomerates.
A methodology described by Meadus et al. in U.S. Pat. No. 4,057,486, involved combining solvent extraction with particle enlargement to achieve spherical agglomeration of tailings suitable for direct mine refill. Organic material was separated from oil sands by mixing the oil sands material with an organic solvent to form a slurry, after which an aqueous bridging liquid was added in small amounts. By using controlled agitation, solid particles from oil sands adhere to each other and were enlarged to form macro-agglomerates of mean diameter greater than 2 mm from which the bulk of the bitumen and solvent was excluded. This process permitted a significant decrease in water use, as compared with conventional water-based extraction processes. Solvents used in the process were of low molecular weight, having aromatic content, but only small amounts of short chain paraffins. While this may have resulted in a high recovery of bitumen, the energy intensity required for solvent recovery would be too high to be adopted in a commercial application.
U.S. Pat. No. 3,984,287 describes an apparatus for separating organic material from particulate tar sands, resulting in agglomeration of a particulate residue. The apparatus included a tapered rotating drum in which tar sands, water, and an organic solvent were mixed together. In this apparatus, water was intended to act as a bridging liquid to agglomerate the particulate, while the organic solvent dissolves organic materials. As the materials combined in the drum, bitumen was separated from the ore.
A device to convey agglomerated particulate solids for removal to achieve the process of Meadus et al. (U.S. Pat. No. 4,057,486) within a single vessel is described in U.S. Pat. No. 4,406,788.
A method for separating fine solids from a bitumen solution is described in U.S. Pat. No. 4,888,108. To remove fine solids, an aqueous solution of polar organic additive as well as solvent capable of precipitating asphaltenes was added to the solution, so as to form aggregates for removal from the residual liquid. Although the method achieved low solids content in the resulting bitumen product with this approach, the solids content in the bitumen product fell short of optimal product quality of less than 400 ppm solids on a dry bitumen basis, especially for settling times less than 1 hour.
Others have proposed sequential use of two solvents in different solvent extraction schemes. For example U.S. Pat. No. 3,131,141 proposed the use of high boiling point solvent for oil sands extraction followed by low boiling point/volatile solvent for enhanced solvent recovery from tailings in a unique process arrangement.
U.S. Pat. No. 4,046,668 describes a process of bitumen recovery from oil sands using a mixture of light naphtha and methanol. However, it is not described or suggested that a second solvent could be effectively applied to a solvent extraction process with simultaneous solids agglomeration without upsetting the agglomeration process.
U.S. Pat. No. 4,719,008 describes a method for separating micro-agglomerated solids from a high-quality hydrocarbon fraction derived from oil sands. A light milling action was imposed on a solvated oil sands mixture. After large agglomerates were formed, the milling action was used to break down the agglomerate size, but still permitted agglomerate settling and removal.
U.S. Pat. No. 5,453,133 and U.S. Pat. No. 5,882,429 describe soil remediation processes to remove hydrocarbon contaminants from soil. The processes employed a solvent and a bridging liquid immiscible with the solvent, and this mixture formed agglomerates when agitated with the contaminated soil. The contaminant hydrocarbon was solvated by the solvent, while soil particles agglomerated with the bridging liquid. In this way, the soil was considered to have been cleaned. Multiple extraction stages were proposed.
Canadian Patent Application 2,068,895 describes a method of incorporating a solvent extraction scheme into a water-based process flow sheet. The method involved a slurry conditioning process which allowed a hydrocarbon bitumen fraction, having high fines content, to be processed in a solvent extraction and solids agglomeration process to achieve higher overall bitumen recovery and reduced sludge volume.
The previously proposed process for agglomeration, as described by Govier and Sparks in “The SESA Process for the Recovery of Bitumen from Mined Oil Sands” (Proceedings of AOSTRA Oils Sands 2000 Symposium, Edmonton 1990, Paper 5), was of limited practicality partly due to the nature of the solvent which, when combined with tailings, made solvent recovery difficult. This process is referenced herein as the Govier and Sparks process. The solvent described possessed a low molecular weight and significant aromatic content, while containing only a small amount of short chain paraffins. Exemplary solvents were described as varsol or naphtha. As expected for such high boiling point solvents, bitumen recovery was consistently high. However, the energy intensity required for the solvent recovery was also high. There was no description in this document of the use of low boiling point solvents. Further, there was no suggestion in the Govier and Sparks process of how the process would have been adapted to employ a different solvent to more efficiently recover solvent, or of how appropriate feed slurry characteristics may have been achieved if a different solvent was employed.
Typically, a bottom sediment and water (BS&W) content, primarily comprised of fines, of between 0.2-0.5 wt % of solids in dry bitumen could be achieved according to the Govier and Sparks process. However, occasionally solids agglomeration would cycle unpredictably and the fines content of the agglomerator discharge stream would rise dramatically. Subsequent settling in a clarifier or bed filtration would then be required to achieve the desired product quality of 0.2-0.5 wt % BS&W. The BS&W component prepared by the process was comprised mostly of solids. Bitumen products with this composition are not fungible and can only be processed at a site coking facility or at an onsite upgrader. This would provide limited flexibility for sale or processing in a remote refinery.
The above-described agglomeration processes integrated solvent extraction and agglomeration within the same mixing vessel, which is inefficient because means of pre-conditioning and conveyance of the bituminous feed into the extraction/agglomerating unit is thus complicated. Conventional agglomeration units are large drums designed to integrate both the extraction and agglomeration aspects of the process, and are bulky and inefficient. Residence time in such agglomeration units would be lengthy, and process kinetics imposed restrictions on residence time. Dissolution time, the slow agitation required, limited slurry density, and the high containment volume required for extraction required the residence time in the agglomeration unit to be lengthy, and the process slow. Further, solvent recovery was not of concern in many previous processes, and is not addressed in most previously described processes.
The processing problems associated with recovery of water and bitumen from aqueous sources, such as from conventional water-based hydrocarbon or bitumen extraction processes, are largely due to the presence of fines in the streams. Aqueous waste streams, in particular, contain a large proportion of water, for example 60% or more by weight, which is higher than desired for solvent based hydrocarbon extraction processes. Recovery of bitumen from waste streams or intermediate streams formed in a water-based extraction process is environmentally prudent, and would increase the efficiency of the overall extraction process. Conventional attempts at de-watering streams from the water-based extraction process are typically undertaken only after the majority of hydrocarbon, or bitumen, has been removed.
Aqueous streams from water based extraction process which may undergo additional water based recovery or which may be stored as waste products include primary separation vessel middling streams, waste streams from secondary flotation tails or froth treatment, among others. Such streams have high water content, but may also have a bitumen content exceeding 15 wt % on a dry solids basis, which would be desirable to recover. There is a need for processes that can incorporate such aqueous streams into a solvent based hydrocarbon extraction process.
It is desirable to provide processes and systems that increase the efficiency of oil sands extraction, reduce water use, and/or reduce energy intensity required to produce a commercially desirable bitumen product from oil sands. Producing a product that is capable of meeting or exceeding requirements for downstream processing or pipeline transport is desirable.
Further, it is desirable to provide techniques to recover bitumen from waste streams arising from aqueous bitumen extraction, that can operate efficiently in the presence of fines, or which are largely unaffected by the presence of fines.
It is an object of the present invention to obviate or mitigate at least one disadvantage of previous processes and systems for hydrocarbon extraction from mineable deposits such as oil sands.
It is an optional object of the present invention to provide a process or system for recovery of hydrocarbon from waste streams, or to obviate or mitigate at least one disadvantage of previous methods or systems used to recover of hydrocarbon from waste aqueous streams arising from water-based oil sands extraction processes.
Solvent extraction processes to recover bitumen from oil sands are described, employing solvent extraction and sequential agglomeration of fines to advantageously simplify subsequent solid-liquid separation. The processes can produce at least one bitumen product with a quality specification of water and solids that exceeds downstream processing and pipeline transportation requirements and contains low levels of solids and water. Further, systems for implementing such processes are described.
The use of low boiling point solvents advantageously permits recovery of solvent with a lower energy requirement than would be expended for recovery of high boiling point solvents. By conducting solvent extraction and agglomeration steps independently, shorter residence times in the agglomeration unit can be achieved.
The sequential nature of the process allows for flexible design of a slurry feed system which permits high throughput from a smaller sized agglomeration unit, as well as faster bitumen production.
When the optional step of steam pre-conditioning is employed in the process, this realizes the further advantage that steam not only heats the slurry or oil sands, but adds the water necessary for the later agglomeration process.
Advantageously, the inventive process permits formation of bitumen products with an acceptable composition for sale or processing at a remote refinery, and thus these products need not be processed by an onsite upgrader.
As a result of the process, a high quality (or high grade) bitumen product is formed which is able to meet and/or exceed quality specifications of low water content and low solids content required for pipeline transport and downstream processing. The process permits premium, dry and clean bitumen to be obtained as well as a lower grade bitumen product to be obtained (which in certain cases may comprise primarily of asphaltenes) for various commercial uses. By using the process described herein, it is possible to achieve a high grade bitumen product, as well as lower grades of bitumen products. For example, a high grade bitumen product is considered to be one containing less than about 0.04 wt % solids (400 ppm), which may be obtained according to the instant process. Further, such a product formed by the process described herein may contain about 0.5 wt % or less of water+solids of the dry bitumen product. Water content may be less than or equal to 200 ppm in the final high grade bitumen product. This is an improved result compared with the 0.2-0.5 wt % of solids in dry bitumen that can be achieved according to the previously described Govier and Sparks process. Low grade bitumen products having more than 400 ppm solids, and more than 200 ppm water may additionally be obtained.
Certain embodiments of the process and system described herein advantageously permit recovery of hydrocarbon from waste water streams that were previously considered too dilute for recovery, in part due to a high fines content combined together with a high water content of over 60% by weight. By de-watering such aqueous waste streams containing bitumen to the point that the effluent contains less than 40% water, the waste stream can then be used in a process that employs agglomeration of fines.
Recycling conventionally discarded waste water is important from an environmental perspective as well as from an efficiency perspective. By decreasing water content of an aqueous waste stream to a desirable level, the stream would become more desirable for use in alternative extraction processes. Recovered water may advantageously be put to use in any aspect of bitumen production that may incorporate recycled water. By de-watering a waste stream prior to attempts to remove all hydrocarbon or bitumen, steps in a conventional aqueous process can be omitted, thereby introducing efficiencies at certain steps in the process.
A process for recovery of bitumen from oil sands is described herein. In the process, a first solvent is combined with a bituminous feed from oil sands to form an initial slurry. The initial slurry is separated into a fine solids stream and a coarse solids stream. Solids from the fine solids stream are agglomerated to form an agglomerated slurry comprising agglomerates and a low solids bitumen extract. The low solids bitumen extract is then separated from the agglomerated slurry, and a second solvent is mixed with the low solids bitumen extract to form a solvent-bitumen low solids mixture. The second solvent is selected to have a similar or lower boiling point than the first solvent. The mixture is then subjected to gravity separation to produce a high grade bitumen extract and a low grade bitumen extract. The first and second solvent can be recovered from the high grade bitumen extract, leaving a high grade bitumen product.
Further, described herein is a process for recovery of bitumen from oil sands. The process involves combining a first solvent and a bituminous feed from oil sands to form an initial slurry. The initial slurry is then separated into a fine solids stream and a coarse solids stream. Solids from the fine solids stream are agglomerated to form an agglomerated slurry comprising agglomerates and a low solids bitumen extract. A second solvent is then mixed with the agglomerated slurry to form a solvent-bitumen agglomerated slurry mixture, the second solvent having a similar or lower boiling point than the first solvent. This mixture is subjected to separation to produce a high grade bitumen extract and a low grade bitumen extract. The first and second solvent can then be recovered from the high grade bitumen extract, leaving a high grade bitumen product; and the first and second solvent can also be recovered from the low grade bitumen extract, leaving a low grade bitumen product.
Described herein is a further process for recovery of bitumen from oil sands, comprising combining a first solvent and a bituminous feed from oil sands to form an initial slurry, which is then separated into a fine solids stream and a coarse solids stream. The first solvent is then recovered from the coarse solids stream. Solids are agglomerated from the fine solids stream to form an agglomerated slurry comprising agglomerates and a low solids bitumen extract, and the low solids bitumen extract is then separated from the agglomerated slurry. A second solvent is then mixed with the low solids bitumen extract to form a solvent-bitumen low solids mixture, the second solvent having a similar or lower boiling point than the first solvent. The mixture is subjected to gravity separation to produce a high grade bitumen extract and a low grade bitumen extract; and the first and second solvent are separated from the high grade bitumen extract, leaving a high grade bitumen product.
Additionally, a process is described herein for recovery of a bitumen product from oil sands. The process comprises combining a first solvent and a bituminous feed from oil sands to form an initial slurry, and separating the initial slurry into a fine solids stream and a coarse solids stream. The first solvent is recovered from the coarse solids stream, and solids are agglomerated from the fine solids stream to form an agglomerated slurry comprising agglomerates and a low solids bitumen extract. Further, mixing a second solvent with the agglomerated slurry to form a solvent-bitumen agglomerated slurry mixture is then conducted, the second solvent having a similar or lower boiling point than the first solvent. The mixture is then subjected to separation to produce a high grade bitumen extract and a low grade bitumen extract. The first and second solvent are then recovered from the high grade bitumen extract, leaving a high grade bitumen product; and the first and second solvent are also recovered from the low grade bitumen extract, leaving a low grade bitumen product.
Additionally, there is described herein a process for recovery of bitumen from oil sands comprising combining a first solvent and a bituminous feed from oil sands to form an initial slurry and agglomerating solids from the initial slurry to form an agglomerated slurry comprising agglomerates and a low solids bitumen extract. The low solids bitumen extract is then separated from the agglomerated slurry. A second solvent is then mixed with the low solids bitumen extract to form a solvent-bitumen low solids mixture, the second solvent having a similar or lower boiling point than the first solvent. The mixture is subjected to gravity separation to produce a high grade bitumen extract and a low grade bitumen extract; and the first and second solvent are then recovered from the high grade bitumen extract, leaving a high grade bitumen product. In this process, the ratio of first solvent to bitumen in the initial slurry is selected to avoid precipitation of asphaltenes during agglomeration.
Further, there is provided herein a process for recovery of a bitumen product from oil sands. The process involves combining a first solvent and a bituminous feed from oil sands to form an initial slurry, and agglomerating solids from initial slurry to form an agglomerated slurry comprising agglomerates and a low solids bitumen extract. A second solvent is mixed with the agglomerated slurry to form a solvent-bitumen agglomerated slurry mixture, the second solvent having a similar or lower boiling point than the first solvent. The mixture is then subjected to separation to produce a high grade bitumen extract and a low grade bitumen extract comprising substantially all solids and water. The first and second solvents are then recovered from the high grade bitumen extract, leaving a high grade bitumen product; and similarly, the first and second solvents are then recovered from the low grade bitumen extract, leaving a low grade bitumen product. In this instance, the ratio of first solvent to bitumen in the initial slurry is selected to avoid precipitation of asphaltenes during agglomeration.
A system is provided for recovery of bitumen from oil sands comprising a slurry system wherein a bituminous feed is mixed with a first solvent to form an initial slurry; a fine/coarse solids separator in fluid communication with the slurry system for receiving the initial slurry and separating a fine solids stream therefrom; an agglomerator for receiving a fine solids stream from the fine/coarse solids separator, for agglomerating solids and producing an agglomerated slurry; a primary solid-liquid separator for separating the agglomerated slurry into agglomerates and a low solids bitumen extract; a gravity separator for receiving the low solids bitumen extract and a second solvent; and a primary solvent recovery unit for recovering the first solvent or the second solvent in a high grade bitumen extract arising from the gravity separator and for separating bitumen therefrom.
Additionally, a system for recovery of bitumen from oil sands is described herein, comprising a slurry system wherein a bituminous feed is mixed with a first solvent to form an initial slurry; an agglomerator for receiving the initial slurry, for agglomerating solids and producing an agglomerated slurry; a primary solid-liquid separator for separating the agglomerated slurry into agglomerates and a low solids bitumen extract; a gravity separator for receiving the low solids bitumen extract and a second solvent; and a primary solvent recovery unit for recovering the first solvent or the second solvent in a high grade bitumen extract arising from the gravity separator and for separating bitumen therefrom.
There is described herein a process for pre-treating an aqueous hydrocarbon-containing feed for downstream solvent-based extraction processing for bitumen recovery, said aqueous hydrocarbon-containing feed comprising from 60 wt % to 95 wt % water, from 0.1 wt % to 10 wt % bitumen, and from 5 wt % to 40 wt % solids, wherein said solids comprise fines, the process comprising: removing water from the aqueous hydrocarbon-containing feed to produce an effluent comprising 40 wt % water or less; and providing the effluent to a downstream solvent-based extraction process comprising fines agglomeration to recover bitumen.
Further, there is described herein a system for pre-treating an aqueous hydrocarbon-containing feed for downstream solvent-based extraction processing for bitumen recovery, said aqueous hydrocarbon-containing feed comprising from 60 wt % to 95 wt % water, from 0.1 wt % to 10 wt % bitumen, and from 5 wt % to 40 wt % solids, wherein said solids comprises fines, the system comprising: a dewatering unit for removing water from the aqueous hydrocarbon-containing feed to produce an effluent comprising 40 wt % water or less; and a conduit for providing the effluent to a downstream solvent-based extraction process comprising fines agglomeration to recover bitumen.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.
Embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures.
Generally, the present invention provides a process and system for fines capture or agglomeration and solvent extraction of bitumen from oil sands. Processing oil sands according to the invention permits high throughput and improved product quality and value.
A process and system for recovery of bitumen from oil sands is provided herein.
The term “bituminous feed” from oil sands refers to a stream derived from oil sands that requires downstream processing in order to realize valuable bitumen products or fractions. The bituminous feed from oil sands is one that contains bitumen along with other undesirable components, which are removed in the process described herein. 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 according to the process described herein. Also, recycled streams that contain bitumen in combination with other components for removal in the described process 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 contains 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, “agglomerate” refers to conditions that produce a cluster, aggregate, collection or mass, such as nucleation, coalescence, layering, sticking, clumping, fusing and sintering, as examples.
Embodiment in Which First Solvent Added Prior to Agglomeration, Second Solvent Added After Agglomerates Removed. In one embodiment of the process, a first solvent is added to agglomerate the bituminous feed, but only after the agglomerated slurry is formed is the second solvent added to extract bitumen. This embodiment comprises combining a first solvent and a bituminous feed from oil sands to form an initial slurry. The initial slurry is then separated into a fine solids stream and a coarse solids stream. The fine solids stream is subjected to agglomeration to form an agglomerated slurry, which includes agglomerates and a low solids bitumen extract. The low solids bitumen extract is separated from the agglomerated slurry, and subsequently mixed with a second solvent to form a solvent-bitumen low solids mixture. In this embodiment, the second solvent is one having a similar or lower boiling point than the first solvent. The mixture is subjected to gravity separation to produce a high grade bitumen extract and a low grade bitumen extract. The extracts are subjected to solvent recovery of both the first and second extracts, leaving a low grade bitumen product and a high grade bitumen product.
Embodiment in Which Second Solvent Added Prior to Separating Low Solids Bitumen Extract from Agglomerated Slurry. An additional process for recovery of bitumen from oil sands is provided in which the second solvent is added prior to separating low solids bitumen extract and agglomerates from the agglomerated slurry. This embodiment involves combining a first solvent and a bituminous feed from oil sands to form an initial slurry, and subsequently separating the initial slurry into a fine solids stream and a coarse solids stream. Solids from the fine solids stream are agglomerated to form an agglomerated slurry comprising agglomerates and a low solids bitumen extract. A second solvent is then mixed with the agglomerated slurry to form a solvent-bitumen agglomerated slurry mixture, the second solvent having a similar or lower boiling point than the first solvent. The mixture is then subjected to separation to produce a high grade bitumen extract and a low grade bitumen extract. The first and second solvent are then recovered from the high grade bitumen extract, leaving a high grade bitumen product. The first and second solvent are also recovered from the low grade bitumen extract, leaving a low grade bitumen product.
In this embodiment of the process, the second solvent may be added prior to separating low solids bitumen extract from the agglomerated slurry. Thus, the second solvent will contact with the agglomerates and the low solids bitumen extract to form the solvent-bitumen agglomerated slurry mixture, which is processed further into high grade and low grade products, as described in further detail herein below.
Embodiment in Which Coarse Solids are Processed Separately From Agglomeration of Fine Solids Stream. Additionally, another embodiment comprises a process for recovery of bitumen from oil sands in which a first solvent and a bituminous feed from oil sands are combined to form an initial slurry. The initial slurry is then separated into a fine solids stream and a coarse solids stream. The first solvent is recovered from the coarse solids stream, and solids are agglomerated from the fine solids stream to form an agglomerated slurry comprising agglomerates and a low solids bitumen extract. The low solids bitumen extract is separated from the agglomerated slurry, and mixed with a second solvent to form a solvent-bitumen low solids mixture. In this embodiment, the second solvent has a similar or lower boiling point than the first solvent. The mixture is then subjected to gravity separation to produce a high grade bitumen extract and a low grade bitumen extract. The first and second solvent are recovered from the high grade bitumen extract, leaving a high grade bitumen product.
In this embodiment of the process, the coarse solids stream is processed separately from the fine solids stream, to remove the solvent therefrom. Optionally, the coarse solids stream may be added back into the slurry system or separator, for subsequent processing in an iterative manner.
Embodiment in Which Coarse Solids are Processed Separately From Agglomeration of Fine Solids Stream, and the Second Solvent is Mixed With the Agglomerated Slurry. A further embodiment comprises a process for recovery of a bitumen product from oil sands comprising: combining a first solvent and a bituminous feed from oil sands to form an initial slurry; separating the initial slurry into a fine solids stream and a coarse solids stream; recovering the first solvent from the coarse solids stream; agglomerating solids from the fine solids stream to form an agglomerated slurry comprising agglomerates and a low solids bitumen extract; mixing a second solvent with the agglomerated slurry to form a solvent-bitumen agglomerated slurry mixture, the second solvent having a similar or lower boiling point than the first solvent; subjecting the mixture to separation to produce a high grade bitumen extract and a low grade bitumen extract; recovering the first and second solvent from the high grade bitumen extract, leaving a high grade bitumen product; and recovering the first and second solvent from the low grade bitumen extract, leaving a low grade bitumen product.
In this embodiment of the process, the first solvent may be recovered from the coarse solids stream separately. Optionally, the coarse solids stream may be added back into the slurry system or separator, for subsequent processing in an iterative manner.
Embodiment in Which Initial Slurry is Directed to Agglomeration Without Separation of Coarse Solids, and in Which Second Solvent is Introduced After Agglomerates are Removed. A further embodiment of the process for recovery of bitumen from oil sands is described herein in which a first solvent is combined with a bituminous feed from oil sands to form an initial slurry. Solids in the initial slurry are agglomerated to form an agglomerated slurry comprising agglomerates and a low solids bitumen extract. A low solids bitumen extract is separated from the agglomerated slurry. A second solvent is then mixed with the low solids bitumen extract to form a solvent-bitumen low solids mixture, the second solvent having a similar or lower boiling point than the first solvent. The mixture is then subjected to gravity separation to produce a high grade bitumen extract and a low grade bitumen extract. The first and second solvent are then recovered from the high grade bitumen extract, leaving a high grade bitumen product. In this embodiment, the ratio of first solvent to bitumen in the initial slurry is selected to avoid precipitation of asphaltenes during agglomeration.
In this embodiment of the process, the step of separating the initial slurry into a fine solids stream and a coarse solids stream is not conducted. Thus, the bituminous feed is combined with the first solvent to prepare the initial slurry, which can then be agglomerated without the requirement for further separation. In this embodiment, the first solvent is mixed with the bituminous feed, but the second solvent is not introduced until after the low solids bitumen extract has been separated from the agglomerates. In this way, the agglomerates need not come into contact with the second solvent.
Embodiment in Which Initial Slurry is Directed to Agglomeration Without Separation of Coarse Solids, and in Which Second Solvent is Introduced Prior to Removal of Agglomerates. A further embodiment of the process is described herein for recovery of a bitumen product from oil sands. The embodiment comprises combining a first solvent and a bituminous feed from oil sands to form an initial slurry. Solids from the initial slurry are agglomerated to form an agglomerated slurry comprising agglomerates and a low solids bitumen extract. A second solvent is then mixed with the agglomerated slurry to form a solvent-bitumen agglomerated slurry mixture, the second solvent having a similar or lower boiling point than the first solvent. The mixture is subjected to separation to produce a high grade bitumen extract and a low grade bitumen extract, in which the low grade extract comprises substantially all solids and water. The first and second solvents are then recovered from the high grade bitumen extract, leaving a high grade bitumen product. The first and second solvent are recovered from the low grade bitumen extract, leaving a low grade bitumen product. In this embodiment, the ratio of first solvent to bitumen in the initial slurry is selected to avoid precipitation of asphaltenes during agglomeration.
In this embodiment of the process, the step of separating the initial slurry into a fine solids stream and a coarse solids stream is not conducted. Thus, the bituminous feed is combined with the first solvent to prepare the initial slurry, which is then agglomerated without the requirement for further separation. In this embodiment, the first solvent is mixed with the bituminous feed, and later, the agglomeration of solids occurs. The second solvent is added to the agglomerated slurry, so as to form a mixture. In this embodiment, all components of the agglomerated slurry are contacted by both the first and the second solvent. Both solvents are then recovered from each of the high grade bitumen extract and the low grade bitumen extract.
Embodiment of a System in Which a Fine/Coarse Solids Separator and a Gravity Separator are Employed. A system is provided for recovery of bitumen from oil sands comprising a slurry system wherein a bituminous feed is mixed with a first solvent to form an initial slurry. A fine/coarse solids separator is included in the system, and is in fluid communication with the slurry system for receiving the initial slurry and separating a fine solids stream therefrom. The system additionally includes an agglomerator for receiving a fine solids stream from the fine/coarse solids separator, for agglomerating solids and producing an agglomerated slurry. A primary solid-liquid separator is present in the system for separating the agglomerated slurry into agglomerates and a low solids bitumen extract. A gravity separator is present in the system for receiving the low solids bitumen extract and a second solvent. A primary solvent recovery unit is included, for recovering the first solvent or the second solvent in a high grade bitumen extract arising from the gravity separator and for separating bitumen therefrom.
In this embodiment of the system, both a fine/coarse solids separator, and a gravity separator are employed.
Embodiment of a System in Which There is no Fine/Coarse Solids Separator Component Upstream of the Agglomerator. A further embodiment of a system for recovery of bitumen from oil sands is described herein comprising a slurry system wherein a bituminous feed is mixed with a first solvent to form an initial slurry. Further, the system includes an agglomerator for receiving the initial slurry, for agglomerating solids and producing an agglomerated slurry. A primary solid-liquid separator is used in the system for separating the agglomerated slurry into agglomerates and a low solids bitumen extract. A gravity separator is present in the system for receiving the low solids bitumen extract and a second solvent, and a primary solvent recovery unit for recovering the first solvent or the second solvent in a high grade bitumen extract arising from the gravity separator and for separating bitumen therefrom is also incorporated into the system.
In this embodiment of the system, there is no requirement for a fine/coarse solids separator, and so both fines and coarse solids may be agglomerated together in the agglomerator.
Ratio of Solvent to Bitumen in Initial Slurry. The process may be adjusted to render the ratio of the first solvent to bitumen in the initial slurry 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 solvent used, can permit the control of a ratio of solvent to bitumen in the slurry system and agglomerator. When the solvent of the invention 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 excessive solvent use.
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 during 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.
Slurry System. The slurry system in which the slurry is prepared in the system may optionally be a mix box, a pump, a pipeline, or a combination of these. By slurrying the first solvent together with the bituminous feed, and optionally with additional additives, the bitumen entrained within the feed is given an opportunity to be extracted into the solvent phase prior to the downstream separation of fine and coarse solid streams and prior to agglomeration within the agglomeration. In some prior art processes, solvent is introduced at the time of agglomeration, which may require more residence time within the agglomerator, and may lead to incomplete bitumen dissolution and lower overall bitumen recovery. The slurry system advantageously permits contact and extraction of bitumen from solids within the initial slurry, prior to agglomeration. Forming an initial slurry prior to agglomeration advantageously permits flexible design of the slurry system and simplifies means of feeding materials into the agglomerator.
Bridging Liquid. A bridging liquid is a liquid with affinity for the solids particles in the bituminous feed, and which is immiscible in the first solvent. In some embodiments, the agglomerating of solids comprises adding an aqueous bridging liquid to the fine solids stream and providing agitation. 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 solution 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.
Heating Bituminous Feed With Steam. According to an embodiment of the process, steam may be added to the bituminous feed before combining with the first solvent, to increase the temperature of the bituminous feed to a temperature of from about 0° C. to about 60° C. Steam may be of particular benefit when oil sands are mined in cold conditions, such as during winter time. The steam may be added to heat the oil sands or other bituminous feed to a temperature of from about 0° C. to about 30° C. The temperatures recited here are simply approximate upper and lower values. Because these are exemplary ranges, provided here primarily for illustration purposes, it is emphasized that values outside of these ranges may also be acceptable. A steam source for pre-conditioning the initial slurry entering the separator may be an optional component of the system of the invention. Other methods of heating the bituminous feed or the solvent (or solvent/bitumen combination) used to form the initial slurry may be incorporated into the process.
During the winter, a bituminous feed may be at a low temperature below 0° C. due to low temperature of the ambient outdoor surroundings, and the addition of steam to heat the feed to a level greater than 0° C. would be an improvement over a colder temperature. During hot summer conditions, the temperature of the bituminous feed may exceed 0° C., in which case, it may not be beneficial to heat the bituminous feed. Addition of steam may be desirable for processing efficiency reasons, and it is possible that the upper limit of the ranges provided may be exceeded.
The optional step of steam pre-conditioning of the oil sands before making contact with solvent in the slurry system has the beneficial effect of raising the temperature of the input bituminous feed. The amount of steam added is lower or equal to the amount of water required for agglomeration. Slurrying the input feed with a low boiling point solvent is promoted without the use of a pressurized mixing system. Since steam pre-conditioning permits the use of low boiling point solvents, higher levels of solvent recovery from tailings can be realized with reduced energy intensity relative to conventional processes.
During the winter, incoming oil sands may be about −3° C. At this temperature, the separation process would require more heat energy to reach the process temperatures between about 0° C. and 60° C., or more particularly for an exemplary processing temperature of about 30° C. Optimally, a solvent boiling point is less than about 100° C. For a low boiling point solvent, this heating obtained through steam pre-conditioning is adequate to meet the processing requirement. For example, by heating the oil sands in a pre-conditioning step, a temperature can be achieved that is higher than could be achieved by heating the solvent alone, and adding it to a cold bituminous feed. In this way, optimal process temperatures can be achieved without any need to use a pressurized mixing system for solvent heating. Therefore, the steam not only provides water, but also some of the heating required to bring the components of the initial slurry to a desired temperature.
Once included as steam in a pre-conditioning step, the water content of the initial slurry would optimally be about 11 wt % or less, and when expressed as a percent of solids, about 15 wt % is an upper limit to the optimal level.
The steam pre-conditioning need not occur, as it is optional. Some water may be added at the agglomeration step if it is not added through steam pre-conditioning. In instances where steam pre-conditioning is used, optimally about half of the water requirement is added as steam, and further amounts of water can be added when the fine solids stream is transferred into the agglomerator.
In embodiments in which no steam pre-conditioning is employed, a slurry comprising the bituminous feed together with the first solvent may be prepared within the slurry system. Optionally, a solvent vapor could be added to the bituminous feed in the slurry stage to capture the latent heat at atmospheric pressure without need to pressurize the mixing vessel.
Low Oxygen for Initial Slurry. The initial slurry of the process described herein may optionally be formed in a low oxygen environment. A gas blanket may be used to provide this environment, or steam may be used to entrain oxygen away from the bituminous feed prior to addition of solvent. The gas blanket, when used, may be formed from a gas that is not reactive under process conditions. Exemplary gasses include, but are not limited to nitrogen, methane, carbon dioxide, argon, steam, or a combination thereof.
Separation of Fine Solids Stream and Coarse Solids Stream. The processes described herein may involve separation of a fine solids stream from a coarse solids stream from the initial slurry after it is mixed in a slurry system. This aspect of the process may be said to occur within a fine/coarse solids separator. An exemplary separator system may include a cyclone, a screen, a filter, or a combination of these. The size of the solids separated, which may determine whether they are forwarded to the fine solids stream versus the coarse solids stream can be variable, depending on the nature of the bituminous feed. Whether a bituminous feed contains primarily small particles and fines, or is coarser in nature may be taken into consideration for determining what size of particles are considered as fine solids and directed toward agglomeration. Notably, embodiments of the process described herein do not require separation of coarse and fine solids from the initial slurry. In such instances, both coarse and fine solids will be present in the agglomerator. When separation of coarse and fine solids is desired, a typical minimum size to determine whether a solid is directed to the coarse solids stream would be about 140 microns. Fines entrainment in the coarse stream is unavoidable during this separation. The amount of fines entrained in the coarse solids stream is preferably less than 10 wt % for example, less than 5 wt %.
Fine/Coarse Solids Separator. A coarse solids stream derived from the fine/coarse solids separator may be derived from the system. When the fine/coarse solids separator is present, the coarse solids stream may be directed for combination with the agglomerated slurry arising from the agglomerator prior to entry of the slurry into the solid-liquid separator.
The feed stream entering the agglomerator unit is pre-conditioned to separate out coarse particles before entry into the agglomerator unit. Thus, the stream entering the agglomerator is predominantly comprised of finely divided particles or a “fine solids stream”. The slurry fraction containing predominantly coarse particles or the “coarse solids stream” may by-pass the agglomerator unit and can then be combined with the agglomerated slurry before the solid-liquid separation stage in which low solids bitumen is extracted from the agglomerated slurry.
A fine solids stream is processed separately from the coarse solids stream, in part because coarse solids are readily removed and need not be subjected to the processing within the agglomerator. The separator permits separation of a fine solids stream as a top stream that can be removed, while the coarse solids stream is a bottom stream flowing from the separator.
The coarse solids fraction derived from the separator may be combined with the effluent arising from the agglomerator, as the coarse solids together with the agglomerates will be removed in a later solid-liquid separation step. This would permit recovery of bituminous components that were removed in the coarse solids stream.
Re-combining Coarse Solids with Agglomerated Slurry. It is optional in the process to utilize the coarse solids stream derived from the fine/coarse solids separator by re-combining it with the agglomerated slurry prior to separating the low solids bitumen extract from the agglomerated slurry. Alternatively, the coarse solids stream may be processed separately, or added back into the slurry system for iterative processing.
Agglomeration. The step of agglomerating solids may comprise adding steam to the bituminous feed. The addition of steam may be beneficial to the bituminous feed because it may begin solids nucleation prior to the step of agglomerating.
The step of agglomerating solids may comprise adding water as bridging liquid to the fine solids stream and providing suitable mixing or agitation. The type and intensity of mixing will dictate the form of agglomerates resulting from the particle enlargement process.
Agitation could be provided in colloid mills, shakers, high speed blenders, disc and drum agglomerators, or other vessels capable of producing a turbulent mixing atmosphere. The amount of bridging liquid is balanced by the intensity of agitation to produce agglomerates of desired characteristics. As an example of appropriate conditions for a drum or disc agglomerator, agitation of the vessel may typically be about 40% of the critical drum rotational speed while a bridging liquid is kept below about 20 wt % of the slurry. The agitation of the vessel could range from 10% to 60% of the critical drum rotational speed, and the bridging liquid may be kept between about 10 wt % to about 20 wt % of solids contained in the slurry, in order to produce compact agglomerates of different sizes.
Solvents. Two solvents, or solvent systems, are sequentially employed in this process. The terms “first solvent” and “second solvent” as used herein should be understood to mean either a single solvent, or a combination of solvents which are used together in a first solvent extraction and a second solvent extraction, respectively. Accordingly, the stage of the process at which the solvent is introduced can be used to determine whether a solvent is the first or second solvent, as the sequential timing of the addition into the process results in the designations of first and second. It is emphasized that the first and second solvents are not required to be different from each other. There are embodiments in which the first solvent and second solvent are the same solvent, or are combinations which include the same solvents, or combinations in which certain solvent ingredients are common to both the first and second solvents.
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 solvents 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 included 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.
While the solvent extractions may be initiated independently, there is no requirement for the first solvent to be fully removed before the second solvent extraction is initiated.
When it is said that the first solvent and the second solvent may have “similar” boiling points, it is meant that the boiling points can be the same, but need not be identical. For example, similar boiling points may be ones within a few degrees of each other, such as, within 5 degrees of each other would be considered as similar boiling points. The first solvent and the second solvent may be the same according to certain embodiments of the invention, in which case, having “similar” boiling points permits the solvents used to have the same boiling point.
First Solvent. The first solvent selected according to embodiments of the invention may comprise an organic solvent or a mixture of organic solvents. For example, the first 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 first 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 first solvent, it may comprise a cycloalkane of 4 to 9 carbon atoms.
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%. Exemplary cycloalkanes include cyclohexane, cyclopentane, or a mixture thereof.
If the first 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.
Second Solvent. The second solvent may be selected to be the same as or different from the first solvent, and may comprise a low boiling point alkane or an alcohol. The second solvent may have an exemplary boiling point of less than 100° C. In some embodiments, the second solvent can be mixed with feed into the solid-liquid separation steps. Because the first solvent is not used in both agglomeration and the solid-liquid separation steps as described in prior art, a second solvent that is miscible with the agglomerate bridging liquid (for example, miscible with water) can be employed at the solid-liquid separation stage. In other words, the two processing steps can be conducted independently and without the solid-liquid separation disrupting the agglomeration process. Thus, selecting the second solvent to be immiscible in the first solvent, and/or having the ability to be rendered immiscible after addition, would be optional criteria.
The second solvent may comprise a single solvent or a solvent system that includes a mixture of appropriate solvents. The second solvent may be a low boiling point, volatile, polar solvent, which may or may not include an alcohol or an aqueous component. The second solvent can be C2 to C10 aliphatic hydrocarbon solvents, ketones, ionic liquids or biodegradable solvents such as biodiesel. The boiling point of the second solvent from the aforementioned class of solvents is preferably less than 100° C.
Process Temperatures. The process may occur at a wide variety of temperatures. In general, the heat involved at different stages of the process may vary. One example of temperature variation is that the temperature at which the low solids bitumen extract is separated from the agglomerated slurry may be higher than the temperature at which the first solvent is combined with the bituminous feed. Further, the temperature at which the low solids bitumen extract is separated from the agglomerated slurry may be higher than the temperature at which solids are agglomerated. The temperature increase during the process may be introduced by recycled solvent streams that are re-processed at a point further downstream in the process. By recycling pre-warmed solvent from later stages of the process into earlier stages of the process, energy required to heat recycle stream is lower and heat is better conserved within the process. Alternatively, the temperature of the dilution solvent may be intentionally raised to increase the temperature at different stages of the process. An increase in the temperature of the solvent may result in a reduced viscosity of mixtures of solvent and bitumen, thereby increasing the speed of various stages of the process, such as washing and/or filtering steps.
Solid-Liquid Separator. 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.
Secondary Stage of Solid-Liquid Separation to Wash Agglomerates. 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 according to the invention. 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.
The temperature for countercurrently washing the agglomerates may be selected to be higher than the temperature at which the first solvent is combined with the bituminous feed. Further, the temperature selected for countercurrently washing the agglomerates may be higher than the temperature at which solids are agglomerated.
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.
Recycle and Recovery of Solvent. The process involves 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 have 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. For example, in steps of the process when solvent is recovered from a low grade or high grade bitumen extract leaving a bitumen product, it is understood that some solvent may remain within that product.
The system may contain a single solvent recovery unit for recovering the first and second solvents arising from the gravity separator. The system may alternatively contain more than one solvent recovery unit. For example, another solvent recovery unit may be incorporated before the step of adding the second solvent to recover part or all of the first solvent.
In order to recover either or both the first solvent or the second solvent, conventional means may be employed. For example, typical solvent recovery units may comprise a fractionation tower or a distillation unit. A primary and/or secondary solvent recovery unit may be desirable for use in the process described herein.
Solvent recovery and recycle is incorporated into embodiments of the process. For example, the first solvent recovered from the slurry of agglomerated solids, which may contain bitumen, can be recycled in the process, such as at the slurrying or agglomerating step. Further, the second solvent may be recovered by using a solvent recovery unit and recycled for addition to the low solids bitumen extract.
Solvent recovery may be controlled to ensure that the second solvent is added at the appropriate time. For example, the first and second solvent may be recovered by distillation or mechanical separation following the solid-liquid separation step. Subsequently, the first solvent may be recycled to the agglomeration step while the second solvent is recycled downstream of the agglomerating step. In the exemplary embodiment where the second solvent is immiscible with the first solvent, the process will occur with no upset to the agglomeration process since interaction of the second solvent with the bridging liquid only occurs downstream of the agglomerating step.
Heat entrained in recycled solvent can advantageously be utilized when the solvent is added to the process at different stages to heat that stage of the process, as required. For example, heated solvent with entrained bitumen derived from washing of the agglomerates in the secondary solid-liquid separator may be used not only to increase the temperature of the initial slurry in the slurry system, but also to include a bitumen content that may be desirable to keep the solvent:bitumen ratio at a desired level so as to avoid precipitation of asphaltenes from solution during agglomeration. By including heated solvent as well as bitumen, this addition provides an advantage to the agglomeration process.
The first solvent recovered in the process may comprise entrained bitumen therein, and can thus be re-used for combining with the bituminous feed; or for including with the fine solids stream during agglomeration. 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 within the initial slurry to achieve the selected ratio within the agglomerator that avoids precipitation of asphaltenes.
Low and High Grade Bitumen Extracts and Products. Once solvent is removed from the low grade or high grade bitumen extracts, the resulting products may be used for commercial purposes. According to certain embodiments of the invention, the low grade bitumen extract is derived through gravity separation, and generally includes water and solids that may have settled into the underflow in the separation process together with bitumen and solvent. This underflow is removed and processed separately. This leaves a high grade extract as the overflow of the separation process.
The high grade bitumen extract is considered to be of a “high grade” in terms of bitumen products, as it meets and may even exceed pipeline specifications. It has been essentially de-watered, and does not contain solids removed by gravity separation, for example. The high grade bitumen product formed according to embodiments of the invention may have a low water content that is nearly undetectable, such as a content of 200 ppm. The high grade product may have a low solids content of 400 ppm or lower as a result of embodiments of the process. The low grade bitumen product may in fact be effectively similar to a “high grade” product, with very low water and solids content. This may be the case for embodiments of the invention where low water and low solids are present in the low grade bitumen extract emanating from solid-liquid separation. In some embodiments, the asphaltene content of the low grade bitumen product are high relative to the high grade bitumen product. For example, asphaltene content up to 98 wt % may be realized in the low grade bitumen product if the second solvent is paraffinic and the amount mixed with the low solids extract causes the precipitation of asphaltenes. In other embodiments, the asphaltene content of both products might in fact be similar but the low grade bitumen product is richer in polar components of the bitumen which are soluble in the solvent.
Extraction Step is Separate from Agglomeration Step. Solvent extraction may be conducted separately from agglomeration in certain embodiments of the process. Unlike prior art processes, where the solvent is first exposed to the bituminous feed within the agglomerator, the instant invention includes formation of an initial slurry in which bitumen dissolution into a solvent occurs prior to the agglomeration step. This has the effect of reducing residence time in the agglomerator, when compared to 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, pipelines, mix box or other types of conditioning systems can be employed.
Because the extraction occurs upstream of the agglomeration step, the residence time in the agglomerator is 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 slurry arriving in the agglomerator.
Dilution of Agglomerator Discharge to Improve Product Quality. The first solvent or second solvent or mixtures thereof 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(s) 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. Solvents may be added at a point source of entry, or may be added using multiple points of entry, such as multiple injection points into the slurry.
When dilution of agglomerator discharge is employed in this embodiment of the invention, the solvent to bitumen ratio of the agglomerator feed slurry 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 either the first or second solvent, or a separate dilution solvent, which may, for example, comprise an alkane.
In this embodiment, a bituminous feed (202) is provided and combined with a first solvent (209a), which may contain entrained bitumen (203a), in a slurry system (204) to form an initial slurry (205). The slurry system (204) may be any type of mixing vessel, such as a mix box, pump or pipeline or combination thereof, having a feed section with gas blanket that provides a low oxygen environment. Steam (207) may be added to the slurry system (204) so as to heat the initial slurry (205) to a level of, for example, 0 to 60° C. The initial slurry (205) is separated in a fine/coarse solids separator (206) to form a fine solids stream (208), which is directed into an agglomerator (210), as well as a coarse solids stream (212), which later, optionally, joins with the agglomerated slurry (216) arising from the agglomerator (210) for further processing. The fine/coarse solids separator (206) may be a settling vessel, cyclone or screen, or any suitable separation device known in the art.
Bitumen (203b) which may be entrained in the first solvent (209b), for example, as derived from downstream recycling of the first solvent, may be added to the agglomerator (210) in order to achieve an optimal ratio of solvent to bitumen within the agglomerator (210). Such a ratio would be one that avoids precipitation of asphaltenes within the agglomerator (210), and an exemplary ratio may be less than 2:1.
An aqueous bridging liquid (214), such as water, may optionally be added to the agglomerator (210) in the interests of achieving good adherence of fines into larger particles, and the process of agglomeration of the solids contained within the fine solids stream (208) occurs by agitation within the agglomerator (210). The agglomerated slurry (216) arising from the agglomerator (210) comprises agglomerates (217a) together with a low solids bitumen extract (220a), all of which is optionally combined with the coarse solids stream (212) in the event that the coarse solids stream is directed to be combined at this stage. The slurry (216) is then directed to the primary solid-liquid separator (218), which may be a deep cone settler, or other device, such as thickeners, incline plate (lamella) settlers, and other clarification devices known in the art.
The low solids bitumen extract (220) is separated from the agglomerated slurry within the primary solid-liquid separator (218). This extract (220) is subsequently combined in a mixer (221) with a second solvent (222a). Extract (220) may optionally be sent to a solvent recovery unit, not shown, where the first solvent is recovered from the extract, before the mixing with the second solvent (222a) is undertaken within the mixer (221).
The second solvent may be one having a low boiling point. The bitumen-containing mixture (223) obtained from the mixer (221) is separated in a gravity separator (224), which may for example be a clarifier or any other type of separator employing gravity to separate solids and water. Streams arising from the gravity separator (224) are directed either toward forming a high grade bitumen product (226) once the solvent has been extracted in a solvent recovery unit (228), or underflow may be removed as a low grade bitumen extract (230), which may then optionally have solvent removed to form a low grade bitumen product. The solvent recovery unit (228) may advantageously be used to recover any of the first solvent (209c) remaining within the effluent of the gravity separator (224), in the interests of solvent recovery and re-use. Advantageously, the second solvent (222b) is easily removed and recovered due to its volatility and low boiling point. There may be bitumen entrained in recovered solvents.
The agglomerates (217b) can also be utilized, as they leave the primary solid-liquid separator (218) and are subsequently subjected to a separation in a secondary solid-liquid separator (232), permitting recovery of the first solvent (209a) and bitumen (203a) in the process. First solvent (209c) derived from the solvent recovery unit (228) may also be recycled to the secondary solid-liquid separator (232), to wash agglomerates, for example in a belt filter using contercurrent washing with progressively cleaner solvent. Additional quantities of first solvent (209d) can be used if additional volumes of solvent are needed. Tailings may be recovered in a TSRU or tailings solvent recovery unit (234) so that agglomerated tailings (236) can be separated from recyclable water (238). Either or both the recovered first solvent (209e) derived from the TSRU (234) and/or from the solvent recovery unit (228) may be recycled in the secondary solid-liquid separator (232).
A combination containing the first solvent (209a) plus bitumen (203a) arising from the secondary solid-liquid separator (232) can be processed with the intent of achieving a bottom sediment and water (BS&W) content lower than about 0.5 wt % solid in dry bitumen. In particular, the product would have less than 400 ppm solids. This combination may also be recycled back into the process by including it in the agglomerator (210) or slurry system (204) as a way of recycling solvent, and maintaining an appropriate solvent:bitumen ratio within the agglomerator to avoid precipitation of asphaltenes.
Advantageously, such processes as outlined in
For the second solvent, a low boiling point n- or iso-alkane and alcohols or blends are candidates. Surface modifiers may be added to the alcohol if needed. With the alkanes, solvent deasphalting is achieved with concurrent cleaning of the high grade bitumen product (226) to achieve pipeline quality. Therefore, the low grade bitumen extract (230) is comprised predominantly of asphaltenes or other more polar bitumen fractions.
Another advantage is that the process forms two different grades of bitumen product from the gravity separator (224). Specifically, partial product upgrading is conducted to produce a first product of high grade bitumen product (226). The low grade bitumen extract (230) formed may also be processed to a low grade bitumen product after solvent recovery, so as to also possesses some commercial value.
This process facilitates recovery of bitumen with no need for handling more than one solvent in the tailings loop of the TSRU (234), thereby allowing for simplified solvent recovery/recycling processes.
In this embodiment, a bituminous feed (402) is provided and is combined with a first solvent (409a), which may have bitumen (403a) entrained therein, into slurry system (404) to form an initial slurry (405), optionally in the presence of steam (407) to heat the initial slurry (405). The initial slurry (405) is mixed and the first solvent (409a) is given time to contact the bituminous feed so as to extract bitumen. The slurry (405) is then directed to a separator (406) to form a fine solids stream (408) which is directed into an agglomerator (410). Further arising from the separator (406) is a coarse solids stream (412) for later processing and solid-liquid separation.
A bridging liquid (414), such as water, is added to the agglomerator (410), optionally together with bitumen (403b) which may be entrained in the first solvent (409b) as derived from downstream solvent recovery. The process of agglomeration of the solids from the fine solids stream (408) occurs by agitation of the agglomerator. The agglomerated slurry (416) arising from the agglomerator (410) comprises agglomerates (417a) together with a low solids bitumen extract 420a), all of which may be combined with the coarse solids stream (412) and directed to a mixer (421) so as to be combined prior to entry into the primary solid-liquid separator (418). The agglomerated slurry (416) is mixed with the second solvent (422a) to form a solvent-bitumen agglomerated slurry mixture (423) within the mixer, and is then separated within the primary solid-liquid separator (418), which may be a deep cone settler or any other sort of separator. Concurrently, the second solvent (422a) can be added to the primary solid-liquid separator (418). The second solvent (422a) may also be added to the mixer (421) before entry into the primary solid-liquid separator (418). The second solvent (422a) may be one having a low boiling point, such as a boiling point below 100° C., and is immiscible in the first solvent, or can be rendered immiscible in the first solvent.
The bitumen-containing mixture within the primary solid-liquid separator (418) is separated and either directed toward forming high grade bitumen product (426) once the solvent has passed through the separator (418) to form a high grade bitumen extract (425) and has been extracted in a primary solvent recovery unit (428), or can be directed toward forming a low grade bitumen product (430). Advantageously in this embodiment, the second solvent (422b, 422c) is easily removed and recovered due to its volatility, low boiling point, and optionally due to its immiscibility in the first solvent.
The agglomerates (417b) can also be processed as they leave the primary solid-liquid separator (418) and are subsequently subjected to a separation in a secondary solid-liquid separator (432), permitting recovery of the second solvent (422d), first solvent (409c) and any bitumen entrained therein in the process. Residual solvent in the tailings may be recovered in a TSRU or tailings solvent recovery unit (434) so that agglomerated tailings (436) may be separated, and optionally water (438) used in the process may be recovered and recycled.
The recovered first solvent (409d) arising from the primary solvent recovery unit (428) may be recycled for use in the process, for example when combined with the bituminous feed (402) in the separator (406). This recovered solvent may contain bitumen entrained therein. Quantities of a combination comprising recycled first solvent (409d) plus any entrained bitumen arising from the primary solid-liquid separator (418) or solvent recovery unit (428) may be directed to the agglomerator (410) for further processing. The second solvent (422b) recovered from the primary solvent recovery unit (428) may be also be recycled.
Secondary recovery of bitumen occurs within the secondary solid-liquid separator (432). The separated low grade bitumen extract (450) may be subjected to separation within a secondary solvent recovery unit (444), which may be a distillation unit, to recover and recycle the second solvent (422d) and to arrive at a low grade bitumen product (430). The low grade bitumen product (430) possesses some commercial value, as it can be processed further with the intent of achieving a bottom sediment and water (BS&W) content lower than about 0.5 wt % solid in dry bitumen.
Solvent recovered may be held in a first solvent storage (429) in the case of the first solvent (409d), or in a second solvent storage (445), in the case of the second solvent (422b) for later use in the upstream aspects of the process. High grade bitumen (431) may be added to the first solvent derived from first solvent storage (429), if there is a need to alter the solvent to bitumen ratio prior to adding a combination of solvent (409a) and bitumen (403a) to the slurry system (404). Further, additional first solvent (409e) make-up quantities or second solvent (422e) make-up quantities may be included in respective solvent storage, if the solvent volume requires replenishing. Additional second solvent (422f) may also be added to the secondary solid-liquid separator (432) if needed.
This embodiment of the process forms different grades of bitumen product and advantageously permits recovery and/or recycling of both the first solvent and the second solvent.
In this embodiment, the first solvent may be a low boiling point cyclic aliphatic solvent, such as a low boiling point cycloalkane, or a mixture of such cycloalkanes, which substantially dissolves asphaltenes. The first solvent may also be a paraffinic solvent in which the solvent to bitumen ratio is maintained at a level to avoid precipitation of asphaltenes.
The second solvent may be a polar solvent, such as an alcohol, a solvent with an aqueous component, or another solvent which is immiscible in the first solvent or which could be rendered immiscible in the first solvent. A low boiling point n- or iso-alkane and alcohols or blends of these with or without an aqueous component are candidates. Surface modifiers may be added to the alcohol if needed. Good agglomerate strength is achieved if the agglomerates are modified with hydrating agents, such as a cement, a geopolymer, fly ash, gypsum or lime during agglomeration. Optionally, the second solvent may comprise a wetting agent in an aqueous solution. A further option is to employ controlled precipitation of asphaltenes within either the agglomerator (410) or the primary solid-liquid separator (418) by employing a mixture of solvent and bitumen in a ratio that avoids precipitation of asphaltenes. For example, a ratio of solvent to bitumen of 2:1 or less may be used within the agglomerator to control asphaltene precipitation.
The embodiment depicted in
The product upgrading of low grade bitumen product (430) can be undertaken to produce a low grade product with some commercial value. If the commercial value involves alternate fuel applications, it would be possible to have a residual alcohol content remaining in the low grade bitumen product (430) from the second solvent. Generally, the low grade bitumen product (430) is comprised predominantly of asphaltenes or other more polar bitumen fractions.
A bituminous feed (602) is provided and combined with a first solvent (609a), optionally with bitumen (603a) entrained therein, in a slurry system (604) to form an initial slurry (605). Steam (607) may be added to the slurry system (604) to heat the initial slurry (605). The initial slurry (605) is then directed from the slurry system (604) to a separator (606) for separation, which may be a fine/coarse solids separator, in order to form a fine solids stream (608), which is directed into an agglomerator (610), as well as a coarse solids stream (612), which is processed separately from the agglomerated slurry (616) arising from the agglomerator (610). Additional quantities of first solvent (609b) having bitumen (603b) entrained therein, may be added to the agglomerator (610). A bridging liquid (614), such as water, may be added to the agglomerator (610), and the process of agglomeration of the solids contained within the fine solids stream (608) occurs by agitation within the agglomerator (610). The agglomerated slurry (616) arising from the agglomerator comprises agglomerates (617a) together with a low solids bitumen extract (620a). In this example, there is no combination with the coarse solids stream. Instead, the agglomerated slurry (616) itself is directed to the primary solid-liquid separator (618).
The low solids bitumen extract (620) is separated from the agglomerated slurry (616) within the primary solid-liquid separator (618). This extract (620) is subsequently combined in a mixer (621) with a second solvent (622a). Extract (620) may optionally be sent to a solvent recovery unit, not shown, where all of the first solvent contained therein is recovered from the extract, before mixing with the second solvent within the mixer (621).
The second solvent may be one having a low boiling point. The solvent-bitumen low solids mixture (623) derived from the mixer (621) is separated in a gravity separator (624), and streams arising from the gravity separator (624) are directed either toward forming a high grade bitumen product (626) once the solvent has been extracted in a solvent recovery unit (628), or toward forming a low grade bitumen extract (630). The solvent recovery unit (628) may advantageously be used to recover the majority of the first solvent (609c) remaining within the effluent, or overflow, of the gravity separator (624), in the interests of solvent recovery and re-use. Streams derived from the gravity separator (624) include high grade bitumen extract (625), and low grade bitumen extract (630) as underflow. Advantageously, the second solvent (622b) is easily removed and recovered due to its volatility and low boiling point.
The separated agglomerates (617b) can also be utilized, as they leave the primary solid-liquid separator (618) and are subsequently subjected to a separation in a secondary solid-liquid separator (632), permitting recovery of the first solvent (609c) and bitumen (603c) entrained therein in the process. Solvent (609d) derived from the solvent recovery unit (628) may also be recycled to the secondary solid-liquid separation separator (632). Additional quantities of the first solvent (609e) may be added to the secondary solid-liquid separator, if desired, for example for washing purposes. Tailings may be recovered in a TSRU or tailings separation recovery unit (634) so that agglomerated tailings (636) can be separated from recyclable water (638). Either or both the recovered first solvent (609g or 609d)) derived from the TSRU (634) and/or from the solvent recovery unit (628) may be recycled in the secondary solid-liquid separator (632).
A combination containing the first solvent (609c) plus bitumen (603c) arising from the secondary solid-liquid separator (632) can be processed with the intent of achieving a bottom sediment and water (BS&W) content lower than about 0.5 wt % solid in dry bitumen. In particular, the product may have less than 400 ppm solids. This combination containing the first solvent plus bitumen may also be recycled back into the process by including it in the agglomerator (610) or slurry system (604).
Advantageously, the process permits recovery of both the first solvent and the second solvent. In one embodiment, the first solvent may be a low boiling point solvent, such as a low boiling point cycloalkane, or a mixture of such cycloalkanes, which substantially dissolves asphaltenes. The first solvent may also be a paraffinic solvent in which the solvent to bitumen ratio is maintained at a level to avoid precipitation of asphaltenes.
For the second solvent, a low boiling point n- or iso-alkane and alcohols or blends are candidates. Surface modifiers may be added to the alcohol if needed. With the alkanes, solvent deasphalting is achieved with concurrent cleaning of the high grade bitumen product (626) to achieve pipeline quality. Therefore, the low grade bitumen extract (630) is comprised predominantly of asphaltenes or other more polar bitumen fractions.
In this embodiment, the coarse solid stream (612) derived from the separator (606) is kept segregated from the agglomerated slurry (616). Thus, the separator (606) can be reduced in size compared to the approach described with respect to
The agglomerated slurry (616) may thus enter a reduced size primary solid-liquid separator (618) and can be processed as described above in the secondary liquid-solid separator (632) and TSRU (634). Agglomerated tailings (636) can be removed using the TSRU (634). The rate determining step in solvent recovery from tailings is the time required for release of residual solvent from the pores of the agglomerated solids. With segregation, the solvent recovery from the fine particles can be optimized independent of the coarse particles. The combination of first solvent (609f) and bitumen (609f) recovered permits separation of coarse tailings (656), once drained from the secondary solid liquid separator for coarse solids (652). Coarse tailings (656) isolated from the tailings solvent recovery unit for coarse solids (654) can be sent to the primary solid-liquid separator (618) for residual fine solids removal, or may be recycled upstream of the process to form the initial slurry (605) in slurry system (604). The tailings solvent recovery unit for coarse solids (654) may be used to recover recyclable water (638) or solvent from the secondary solid-liquid separator for coarse solids (652). Coarse tailings (656) may also be removed.
Aspects of the present invention which generally relate to a process and system for recovery of hydrocarbon associated with or entrained within an aqueous stream. Such aqueous streams may be ones having in excess of 60% water. Such streams may be ones produced or rejected from water-based bitumen extraction processes, or may be streams that are directly derived from oil sands which include a high water content, but which were not necessarily intended for a water-based bitumen extraction process. Certain rejected streams from water-based bitumen extraction processes (or “waste streams”), as well as intermediate streams produced in the extraction process which were not intended as waste, may be relatively high in water content, and thus can advantageously be processed further through non-aqueous solvent extraction once the water content of the high water stream streams is reduced to a level acceptable within the non-aqueous solvent extraction process, such as for example reduced below 40% water.
Recovery of bitumen from relatively high fines aqueous feed streams may involve using a combination of non-aqueous solvent extraction and agglomeration of solids. Non-aqueous solvent extraction and agglomeration processes can employ aqueous feed streams, provided the water content is not so high as to negatively impact the agglomeration aspect. Aqueous feed streams may be used, despite a high fines content, and in this way, such aqueous streams that may have previously been considered difficult to recover because of the fines content, can be effectively utilized. High fines content is a characteristic previously considered problematic in conventional methods for extracting hydrocarbon from aqueous feed streams. For example, waste streams arising from water-based methods of hydrocarbon recovery, which may have previously been directed to tailings ponds, can be used in the solvent extraction processes described herein, provided the water content is in an appropriate range to permit use of the stream without causing excessive dilution to the solvent extraction process thereby impeding efficient agglomeration of fines. Thus, waste streams arising from conventional extraction processes, intermediate streams from conventional extraction processes, or any bituminous aqueous stream can be used in the solvent extraction process if pre-conditioned to achieve desired characteristics. The process is described herein for utilization of streams that are high in water content, which may require concentration through pre-treatment in order to be effectively used in such an extraction process.
Hydrocarbon-containing streams bearing levels of water that are not in excess of a level that would be of detriment to a non-aqueous extraction process (such as streams containing less than about 40 wt % water), can be fed directly into the non-aqueous extraction processes as described herein, without the need for concentration through a water removal pre-treatment process. Such streams that already contain water at a lower, acceptable level for non-aqueous extraction, are encompassed in the processes described herein.
One embodiment provides a process for pre-treating an aqueous hydrocarbon-containing feed for downstream solvent-based extraction processing for bitumen recovery, the aqueous hydrocarbon-containing feed comprising from 60 wt % to 95 wt % water, from 0.1 wt % to 10 wt % bitumen, and from 5 wt % to 40 wt % solids, wherein the solids comprise fines, the process comprising: removing water from the aqueous hydrocarbon-containing feed to produce an effluent comprising 40 wt % water or less; and providing the effluent to a downstream solvent-based extraction process comprising fines agglomeration to recover bitumen. The step of removing water from the aqueous hydrocarbon-containing feed may comprise: flowing the aqueous hydrocarbon-containing feed into a primary water separation system to remove water from the aqueous hydrocarbon-containing feed, producing a reduced-water stream of from 30 wt % to 60 wt % solids, and recycled water; and removing water from the reduced-water stream using a secondary water separation system to produce an effluent comprising 40 wt % water or less. The primary water separation system may comprise a clarifier, a settler, a thickener or a cyclone. Flocculant may be added to the aqueous hydrocarbon-containing feed in the clarifier. A solvent or flocculant may be mixed with the aqueous hydrocarbon-containing feed prior to water separation in the clarifier. The solvent may be mixed with the aqueous hydrocarbon-containing feed with a solvent:bitumen ratio of less than about 2:1. A low boiling point cycloalkane solvent may be mixed with the aqueous hydrocarbon-containing feed. The secondary water separation system may comprise a centrifuge with filtering capacity, a shale shaker, or one or more clarifiers. The aqueous hydrocarbon-containing feed may comprise effluent of a froth separation unit. The aqueous hydrocarbon-containing feed may comprise tailings from a tailings solvent recovery unit.
One embodiment provides a system for pre-treating an aqueous hydrocarbon-containing feed for downstream solvent-based extraction processing for bitumen recovery, the aqueous hydrocarbon-containing feed comprising from 60 wt % to 95 wt % water, from 0.1 wt % to 10 wt % bitumen, and from 5 wt % to 40 wt % solids, wherein the solids comprises fines, the system comprising: a dewatering unit for removing water from the aqueous hydrocarbon-containing feed to produce an effluent comprising 40 wt % water or less; and a conduit for providing the effluent to a downstream solvent-based extraction process comprising fines agglomeration to recover bitumen. The dewatering unit may comprise: a primary water separation system to remove water from the aqueous hydrocarbon-containing feed, producing a reduced-water stream and recycled; and a secondary water separation system for receiving the reduced-water stream and removing water therefrom to produce an effluent comprising 40 wt % water or less.
There are many sources of aqueous hydrocarbon-containing feed streams in excess of 60 wt % water which can be subjected to processing as described herein, so that hydrocarbon may be extracted. Such streams that are referred to as aqueous hydrocarbon-containing feed streams may interchangeably be referenced herein as “high water content streams”. The variety of aqueous hydrocarbon-containing feed streams which could be used as feed streams in the processes described herein possess over 60 wt % water. Thus, possible streams for processing according to the processes described include streams derived from conventional froth treatment processes, either as intermediates of the froth treatment process, or as an end-product or waste product of aqueous oil sands extraction processes. For example, streams that may normally have been considered waste streams in a conventional aqueous extraction process can now be subjected to processing, and recovery of hydrocarbon. Such streams need not be designated as waste streams per se, but may be intermediate streams which would have normally proceeded to further processing within an aqueous extraction or froth treatment process. Aqueous streams need not be derived from a water-based extraction process, but may contain water for other reasons, such as steam exposure, water-heating, or due to mixing of water with oil sands that have not yet been subjected to any extraction process, but which have been rendered aqueous for alternative reasons.
Depending on the froth treatment conducted and ore grade, bitumen content in a feed arising from such process streams may exceed 15 wt % bitumen on a dry solids basis. Although such a feed may comprise hydrocarbon of a predominantly lower grade, its bitumen content may be comparable to or higher than the original oil sands ore for the same solids throughput. However, in the integration of the non-aqueous solvent extraction and agglomeration process described herein with a conventional process, it is problematic that, except for oversized rejects, other potential feed streams have a very large proportion of water. This large proportion of water is higher than the optimum needed for effective fines agglomeration in the process. An advantage of the utilization of high water content streams, as described herein is that pre-conditioning of such streams can reduce water content to permit such streams to be used as feed streams in a non-aqueous solvent extraction process, thereby addressing this challenge. The treatment process for waste streams according to embodiments described herein permits aqueous streams with high fines content to be used as feed streams for the non-aqueous solvent extraction process, so as to permit successful recovery of bitumen that would have otherwise been lost.
Typical aqueous hydrocarbon-containing feed streams for use in the de-watering process include, but are not limited to middlings derived from a primary separation vessel (PSV), paraffinic froth treatment (PFT) tailings, floatation tails which may not yet have been directed to a tailings pond, and/or mature fine tailings (MFT), which may have already been present in a tailings pond. Appropriate aqueous hydrocarbon-containing feed streams may be ones containing bitumen and/or other hydrocarbon components, which may or may not include bitumen.
Feed streams arising as waste from conventional oil sands processing techniques are particularly attractive for pre-conditioning as described herein, to reduce water content prior to use as a feed in an agglomeration process. If conventional feed streams were fed directly into an agglomeration process, without pre-treatment as described herein, there is the problem that (except for oversize rejects) such feed streams would provide excessive dilution and decrease effectiveness and/or efficiency of the agglomeration process. The pre-conditioning process described herein would not previously have been considered as an effective way to recover waste water, nor would it have been viewed as an optimal way to recover bitumen that would have otherwise been lost. By pre-treating a waste stream in this way, in preparation for subsequent recovery in an extraction process, both a reduction in waste and an increase in recovery of bitumen can be realized.
Advantageously, the middlings from a primary separation vessel used in a conventional water-based extraction process may be processed less efficiently on the assumption that further hydrocarbon components can be recovered in downstream solvent-based extraction processes. This results in an energy saving at this step, as not all bitumen need be removed in a water based bitumen extraction process.
A mixer may be used as the aqueous stream enters a primary water separation system or vessel. One or more points of entry of the hydrocarbon-containing feed stream may be used on the way to such a primary separation vessel, so as to allow turbulence to occur. As an exemplary embodiment, multiple injection points of an aqueous hydrocarbon-containing feed are used on the way to the primary separation vessel.
Flocculants or other additives, such as coagulants or pH modifiers may be added to the aqueous hydrocarbon-containing feed streams. Typically, a pH of 8.5 is achieved, and a drop in pH may be achieved. Thus, pH may be modified from a level above pH 7 to a level below pH 7. A reduction in pH may reduce surface activities of the clays, which may result in precipitation of fines. A non-aqueous solvent may be added to the aqueous hydrocarbon-containing feed streams, for example a solvent may be used which may be lighter or heavier than water. When solvent is present, deriving recycled water may be accomplished in an appropriate way so that the recycled water may be recovered separately from the solvent. Further, small quantities of solvent may adhere to solids and thus sink to the bottom in a dewatering unit, permitting concentration of solids in the underflow.
In the primary water separation step for water removal, a clarifier, a settler, thickener, or a cyclone may be used in single or multiple units which may be in communication in serial, or employed in parallel. Thus, the dewatering unit may comprise one or more of such units. The resulting effluent may contain from 30 wt % to 60 wt % solids. The hydrocarbon content of the effluent arising from this stage of the process is enriched, relative to the initial aqueous feed. A doubling of the hydrocarbon content, or a further enriched content, may be achieved. However, the effluent from this stage is still pumpable so as to permit transport and movement through to further aspects of the process. The content of solids may in fact be above a level of 60 wt %, and water content could be lower that 40%, provided the effluent from the underflow derived from the primary water separation is still pumpable.
When present, a secondary water separation system of the dewatering unit may be employed. Similar types of apparatuses may be employed in such secondary separation, or a filter, filter centrifuge, centrifuge, or vibration filter may be employed. The system may employ a single dewatering unit, or the dewatering unit may comprise individual components, such as primary water separation system and a secondary water separation system. Each of the primary and secondary water separation systems may have multiple individual components operating in parallel or in serial.
A feed stream comprising bitumen, water and solids with or without residual solvent is pre-conditioned according to the process described herein. The feed stream may be derived from a mixture of oilsand, oversized rejects stream, and high water content streams or blends thereof. An exemplary high water content stream may be one derived from a primary separation vessel middling stream, or from secondary flotation tails and/or froth treatment tailings from a water-based extraction process. Such feed streams or blends thereof are processed via a single or dual staged water separation system (WSS) in order to be adequately pre-conditioned for use as a feed stream in the non-aqueous solvent extraction and agglomeration processes described herein, as depicted for example in
The bituminous feed (902) is passed into a primary water separation system or PWSS (904). In the PWSS, a portion of the water contained in the feed (902) is recovered as recycled water (906). The remaining portion is a reduced-water stream (908), which is then fed into a secondary water separation system or SWSS (910) to produce an effluent (912) having the consistency of a pumpable slurry, containing predominantly fine solids and hydrocarbon, and having a water content of up to 40 wt %. More recycled water (906) is recovered from the secondary water separation system (910). The effluent (912) of the secondary water separation system, having the consistency of a pumpable slurry, may be combined with oversized rejects (914) and/or recycled extract liquor (916) in proportions which permit the water content of the resulting slurry (918) to remain within the desired level for fines agglomeration or capture in later downstream processing.
The primary water separation system (904) may preferably be a clarifier unit or cyclone which takes advantage of inherent or induced high settling characteristics of the high water content feeds. In contrast to conventional extraction processes in which additives are employed to disperse fines in water and prevent slime coating of bitumen, flocculants or coagulants may optionally be used to induce the aggregation of fines and hydrocarbons within the clarifier. Large quantities of recycled water low in total suspended solids may thus be recovered. Advantageously, by recovering water at this stage, efficiencies are introduced, due to the reduced volume forwarded for downstream processing.
The secondary water separation unit (910) may be a filtering device that can provide centrifugal or vibrational force for phase separation. A slurry of coarse solids may be added to the secondary water separation system to promote efficient dewatering. In exemplary embodiments, the secondary water separation system (910) may comprise a centrifuge with filtering capacity, or a shale shaker. It may be possible in certain embodiments that the dewatering achieved in the secondary water separation system is enough to allow for direct feed of the effluent (912), without addition of oversize rejects or oil sands, into the non-aqueous solvent extraction processes described herein, and as depicted for example in
Optionally, solvent (920) may be added to the bituminous feed (902) entering the primary water separation system (904) so as to dissolve bitumen and decrease the feed density sufficiently for selective phase separation under gravity or for application of a centrifugal force field. If solvent is added, an exemplary solvent:bitumen ratio is less than 2:1.
As a further option, a flocculant (922) with selective reactivity for the fines may be added to aggregate clays contained in the bituminous feed (902) thus promoting faster settling or drainage. The flocculant may be added prior to entry of the feed (902) into the primary water separation system (904), via a mixer (921) or may be added directly into the primary water separation system. The resulting reduced-water stream (908) resulting from the primary water separation system (904) is passed through the secondary water separation system (910) and the effluent (912) may be subsequently combined with the oversize rejects (914) to produce a slurry (918) ready for processing via the non-aqueous solvent extraction process described herein, as depicted for example in
Conventional oil sands processing may include a flotation separation step, resulting in the formation of a froth. Asphaltene content in froth is typically about 5% to 15%. To separate the asphaltenes from the hydrocarbons targeted for recovery, the froth can be mixed with a solvent and subjected to one or more settling stages. An aqueous froth may be mixed with a solvent for precipitation of asphaltenes and is then subjected to one or more settling stages. The solvent can be, for example, a paraffinic hydrocarbon solvent having a chain length between about 5 and about 8 carbons. An exemplary solvent may be a mixture of pentane and hexane. This solvent is typically recovered from waste streams and recycled, to avoid release to the environment. Separation of the solvent can occur, for example, in a tailings solvent recovery unit (TSRU). Conventionally, the solvent is recycled and the tailings that exit the TSRU are disposed of as a waste product.
The bituminous feed (902) may comprise froth treatment tailings derived from an aqueous bitumen extraction of oil sands. A stream of effluent arising from a froth separation unit (FSU) underflow may be used as the bituminous feed (902) in the process described herein. Further, the bituminous feed (902) may comprise tailings from a tailings solvent recovery unit (TSRU). Advantageously, when FSU tailings are employed as the bituminous feed (902) in the instant process, this would allow exclusion of the TSRU from conventional froth treatment processes, since residual solvent recovery would occur in a later step of the non-aqueous extraction process described herein, as depicted for example in
The resulting slurry (918) may be combined with any other appropriate bituminous feed as an additional feed source (930) for later downstream processing in a process (932) capable of separating fines out of a high fines content aqueous bituminous feed, such as one capable of agglomerating tailings (934) while forming a hydrocarbon product (936).
Water is removed (1032) from the aqueous hydrocarbon-containing feed having 60 wt % to 95 wt % water, resulting in an effluent comprising 40% water or less, which goes on to be used (1034) as bituminous feed either alone or in combination with further bitumen containing sources. Other bitumen containing sources may include oversized rejects or recycled extract liquor, or any source of bitumen. The resulting mixture should have the consistency of a pumpable slurry. This mixture, including the effluent having less than 40% water, is now used as the feed for further processing. In a subsequent step, a first solvent is added (1012) to the bituminous feed to form an initial slurry. Fine solids and coarse solids are separated (1014) as a fine solids stream and a coarse solids stream from the initial slurry. Fine solids are agglomerated (1016) from the fine solids stream to form a slurry comprising agglomerates and low solids bitumen extract. A low solids bitumen extract is separated (1018) from the aggregated slurry. A second solvent is added (1020) to the low solids bitumen extract to recover a new bitumen extract essentially free of solids. In this way, a hydrocarbon product is derived from a bitumen-containing waste water stream.
In
The primary water separation system (1174) may preferably be a clarifier unit which takes advantage of inherent or induced high settling characteristics of the high water content feeds. In contrast to conventional extraction processes in which additives are employed to disperse fines in water and prevent slime coating of bitumen, flocculants or coagulants may optionally be used to induce the aggregation of fines and hydrocarbons within the clarifier. Large quantities of recycled water low in total suspended solids may thus be recovered. Advantageously, by recovering water at this stage, efficiencies are introduced, due to the reduced volume forwarded for downstream processing.
The secondary water separation unit (1180) may be a filtering device that can provide centrifugal or vibrational force for phase separation. A slurry of coarse solids may be added to the secondary water separation system to promote efficient dewatering. In exemplary embodiments, the secondary water separation system (1180) may comprise a centrifuge with filtering capacity, or a shale shaker. It may be possible in certain embodiments that the dewatering achieved in the secondary water separation system is enough to allow for direct feed of the effluent (1182), without addition of oversize rejects or oil sands, into the remainder of the processing steps.
Optionally, solvent (1190) may be added to the bituminous feed (1172) entering the primary water separation system (1174) so as to dissolve bitumen and decrease the feed density sufficiently for selective phase separation under gravity or for application of a centrifugal force field. If solvent is added, an exemplary solvent:bitumen ratio is less than 2:1.
As a further option, a flocculant (1192) with selective reactivity for the fines may be added to aggregate clays contained in the bituminous feed (1172) thus promoting faster settling or drainage. The flocculant may be added prior to entry of the feed (1172) into the primary water separation system (1174), via a mixer (1191) or may be added directly into the primary water separation system. The resulting reduced-water stream (1178) resulting from the primary water separation system (1174) is passed through the secondary water separation system (1180) and the effluent (1182) may be subsequently combined with the oversize rejects (1184) to produce a slurry (1188) ready for processing via the subsequent solvent extraction and agglomeration processing, for example as described herein and depicted in
The resulting slurry (1188) may be combined with any other appropriate feed source as a bituminous feed.
In the preceding description, for purposes of explanation, numerous details are set forth in order to provide a thorough understanding of the embodiments of the invention. However, it will be apparent to one skilled in the art that these specific details are not required in order to practice the invention.
Approximately 500 g of low grade oil sands (comprising 22 wt % fines) was mixed with 300 g cyclohexane as a first solvent (loaded with bitumen up to 40 wt %) using an impeller in a mixing vessel at 30° C. Sand grains greater than 1 mm were removed by screening. The remaining slurry was passed into an agglomerator where 30 ml of water was added. Agglomerates of sizes ranging from 0.1 mm to 1 cm were formed. The agglomerated slurry was allowed to settle for 30 minutes and a first supernatant was collected for water and solids content analysis. Solids content determined by ashing ranged between 5,000-20,000 ppm on a dry bitumen basis for this first supernatant while water content by Karl Fischer analysis was generally less than 1000 ppm. Portions of the first supernatant were mixed with normal pentane as a second solvent above the critical solvent to bitumen ratio to effect precipitation of asphaltene at 30° C. After settling for 30 minutes, a second supernatant was collected and analyzed for solids and water content. The sediment from the settling test comprised predominantly of asphaltenes and less than 20 wt % solids and was treated as the lower grade bitumen extract. Solids and water contents of the second supernatant were determined to be less than 400 ppm and 200 ppm on a dry bitumen basis, respectively. The second supernatant was a dry, clean and partially de-asphalted bitumen product suitable for transportation via a common carrier pipeline and processing in a remote refinery.
In another experiment similar to the one described in Example 1, a mixture of 30% cyclohexane and 70% heptane, by volume, was used in agglomeration as the first solvent. For the first supernatant, solids content determined by ashing range between 5,000-10,000 ppm on a dry bitumen basis while water content by Karl Fischer analysis was generally less than 1,000 ppm. Portions of the first supernatant were mixed with normal pentane as a second solvent above the critical solvent to bitumen ratio to effect precipitation of asphaltene at room temperature. The solids and water content of the resulting second supernatant was determined to be less than 400 ppm and 200 ppm on a dry bitumen basis after 30 minutes of settling.
In another experiment similar to the one described in Example 1, normal heptane loaded with 40% bitumen was used as extraction solvent (the first solvent). Solids content of the first supernatant was determined to be less than 400 ppm on a dry bitumen basis after 30 minutes of settling. Water content was less than 200 ppm. The resulting product, having less than 400 ppm of filterable solids was a high grade bitumen product.
The above-described embodiments of the invention 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 of the invention, which is defined solely by the claims appended hereto.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2,704,927 | May 2010 | CA | national |
This application claims priority from Canadian patent application number 2,704,927 filed on May 21, 2010 entitled Recovery of Hydrocarbon from Aqueous Streams, the entirety of which is incorporated by reference herein. This application contains subject matter related to PCT patent application number PCT/US2010/062312, entitled “Process and System for Recovery of Bitumen From Oil Sands,” filed on Dec. 29, 2010 and PCT patent application number PCT/US2010/056727, entitled “Process and System for Recovery of Bitumen From Oil Sands,” filed on Nov. 15, 2010.
