Bitumen Extraction And Asphaltene Removal From Heavy Crude Using High Shear

PATENT
Bitumen Extraction And Asphaltene Removal From Heavy Crude Using High Shear
United States Patent Application 20120241390
Inventors:
Hassan, Abbas (Sugar Land, TX, US)
Hassan, Aziz (Sugar Land, TX, US)
Viswanathan, Krishnan (Houston, TX, US)
Borsinger, Gregory G. (Chatham, NJ, US)
Anthony, Rayford G. (College Station, TX, US)
Application Number:
13/434288
Publication Date:
09/27/2012
BACKGROUND
1. Technical Field
The present invention relates to systems and methods for enhanced recovery and processing of heavy crude and/or bitumen. More particularly, the present invention relates to the high shear removal of asphaltenes from feeds comprising bitumen and/or heavy crude oil and the high shear separation of water and mineral solids from tailings conventionally sent to a tailings pond.

2. Background of the Invention
Large deposits of heavy hydrocarbon sometimes referred to as bitumen are located in many countries around the world. Bitumen may be recoverable by means of secondary or tertiary recovery processes that involve heating, solubilization or mobility control. Many of these heavy hydrocarbon deposits contain high concentrations of asphaltenes that contribute to difficulties in recovery, transporting and upgrading. Oil sands, also, known as tar sands, are heavy hydrocarbons found in the United States, Canada, Russia, Venezuela, and various countries in the Middle East. Deposits in the oil sands of Alberta Canada are the single-largest known source of petroleum in the world. These oil sands contain bitumen and as much as 17 wt % asphaltenes. The Orinoco oil belt in Venezuela is another large accumulation of bitumen. Additionally, heavy crudes produced all over the world typically contain some amount of asphaltenes.

Heavy crude oil or crude bitumen extracted from the earth is in a viscous, solid or semi-solid form that does not flow easily at normal oil pipeline temperatures, making it difficult to transport and expensive to process into gasoline, diesel fuel, and other products. The economic recovery and utilization of heavy hydrocarbons, including bitumen, is a significant energy challenge. The demand for heavy crudes, such as those extracted from oil sands, has increased significantly due to dwindling reserves of conventional lighter crude. These heavy hydrocarbons, however, are typically located in geographical regions far removed from existing refineries. Consequently, the heavy hydrocarbons are often transported via pipelines to refineries. In order to transport heavy crudes in pipelines they must meet pipeline quality specifications.

Extraction techniques utilized to recover bitumen may be broken down into three major categories: (1) those which employ water, either hot or cold, to float the bitumen oils away from the tar-sands, (2) those which employ an organic solvent to dissolve the bitumen oils, and (3) those that involve heat. Extraction of bitumen may be either by removing the deposits from the ground and extracting the bitumen externally or by in situ extraction, where only the bitumen is removed and the mineral components are left in the ground. Processes utilizing water often involve air floatation, and typically involve the utilization of an alkaline material. Due to the formation of stable emulsions containing fine tar-sands ore particles, water and bitumen oils, water-based processes are not particularly efficient, especially on ore of lower bitumen content. The treatment of emulsions comprising large volumes of water, bitumen oils and fine tar-sands ore particles has proven challenging.

Extraction of bitumen using heat can be done with electric, steam or other form of heaters as described, for example, in U.S. Pat. App. Nos. 2008/0135253 and 2009/0095480 by Vinegar et al. Various combinations of extraction techniques can be used to extract bitumen in situ. It is generally believed that in situ extraction will be more cost effective than surface mining, although the predominant method of bitumen extraction used today is surface mining. Another solvent extraction technique under development involves the utilization of solvents (in the absence of water) and is similar to techniques utilized in oil seed extraction processes. Percolation and immersion-type extractors have been used, but the need for special designs and scale-up for processing of abrasive tar-sands make economical extraction difficult. For example, the solvent to bitumen ratio needed for efficient extraction is generally high, up to 10:1, producing concomitantly high capital and utilities costs for recovery of the solvent via, for example, distillation. For economy of solvent utilization, spent sands must be stripped of residual solvent prior to disposal. Stripping of residual solvent is a capital and energy intensive undertaking.

Existing solvent extraction methods for dissolving bitumen oils from tar-sands, for example, as disclosed in U.S. Pat. No. 4,160,718 issued to Rendall, typically involve environmentally unacceptable losses of solvent and additional problems associated with the hazards posed by the necessary storage of large solvent inventories and the need for large quantities of water. Other solvent, hot water, and combination extraction processes are disclosed in U.S. Pat. Nos. 4,347,118 to Funk et al. and 3,925,189 to Wicks, III. These methods all have commercial and/or ecological drawbacks, rendering them undesirable. A method that utilizes both solvent and hot water for extraction of bitumen from tar-sands is the subject of U.S. Pat. No. 4,424,112 to Rendall.

Bitumen extraction techniques that do not involve solvent conventionally utilize truck and shovel operations. In such operations, the oil sand is first mined and then is delivered to a crusher. In one such process, bitumen separation and recovery from the oil sand is accomplished by following what is known as the Clark hot water extraction process. In the front end of this process, crushed oil sand is mixed with hot water and caustic in a rotating tumbler or conditioned in a pipeline to produce aqueous slurry. In the tumbler or pipeline, bitumen globules contact and coat air bubbles that are entrained in the slurry. The slurry is then screened to remove large rocks and the like. The screened slurry is diluted with additional water and the product is then temporarily retained in a primary separation vessel (PSV). In the PSV, the buoyant bitumen-coated air bubbles rise through the slurry and form bitumen froth. The sand in the slurry settles and is discharged from the base of the PSV, together with some water and bitumen. This stream or portion is referred to as the ‘PSV underflow’ or tailings. A ‘middlings’ portion comprising water, non-buoyant bitumen and fines may be collected from the middle of the PSV. The froth overflows the lip of the PSV and is recovered as the primary froth and typically comprises ˜60 wt. % bitumen, ˜30 wt. % water and ˜10 wt. % particulate solids.

The PSV underflow is introduced into a deep cone vessel, referred to as the tailings oil recovery vessel (‘TORV’). Here the PSV underflow is contacted and mixed with a stream of aerated middlings from the PSV. Again, bitumen and air bubbles contact and unite to form buoyant globules that rise and form froth. This ‘secondary’ froth overflows the lip of the TORV and is recovered. The secondary froth typically comprises ˜45 wt. % bitumen, ˜45 wt. % water and ˜10 wt. % solids. The middlings from the TORV is withdrawn and processed in a series of sub-aerated, impeller-agitated flotation cells. Secondary froth, typically comprising ˜40 wt. % bitumen, ˜50 wt. % water and ˜10 wt. % solids, is produced from these cells.

The primary and secondary froth streams are typically combined to yield a product froth stream, often comprising ˜60 wt. % bitumen, ˜32 wt. % water and ˜8 wt. % solids. The water and solids in the froth are contaminants which need to be reduced in concentration before the froth can be treated in a downstream refinery-type upgrading facility. This cleaning operation is generally carried out using what is referred to as ‘froth treatment.’

While there are a variety of froth treatment processes, all of these processes include deaeration of the combined froth product followed by dilution with sufficient solvent, typically naphtha, to provide a solvent to froth (‘S/F’) ratio of about 0.40 (w/w). This is done to increase the density differential between the diluted bitumen on the one hand and the water and solids on the other. By way of example, Kizior (U.S. Pat. No. 4,383,914), Guymon (U.S. Pat. No. 4,968,412), Shelfantook et al. (Canadian Pat. No. 1,293,465), Birkholz et al. (Canadian Pat. No. 2,232,929), Tipman et al. (Canadian Pat. No. 2,200,899), Tipman et al. (Canadian Pat. No. 2,353,109), Mishra et al. (U.S. Pat. No. 6,019,888), Cymerman et al. (U.S. Pat. No. 6,746,599), Beetge et al. (U.S. Pat. App. 20060196812, and Graham et al. (U.S. Pat. No. 5,143,598) describe ways of processing and treating the froth produced during the extraction process.

A serious problem, however, in using a solvent extraction process to remove bitumen from such a carbonaceous solid is that fines, primarily particles less than 50 microns in diameter, are carried over in the solvent-dissolved bitumen extract. Failure to remove the fines results in an undesirable high-ash bitumen product as well as problems with plugging of equipment used in the separation process, especially, for example, filtration equipment. Similar problems arise when other carbonaceous liquids besides bitumen, such as coal liquid or shale oil, are used. Removal of the fines during recovery of the bitumen from a carbonaceous solid or from a previously recovered carbonaceous liquid is therefore important in providing a desirable low-ash liquid product and minimizing fouling and plugging of equipment used in the process. It would be highly desirable to develop an extraction method for recovering bitumen from the aforesaid carbonaceous solids and for removing fines from the aforesaid carbonaceous liquids which would permit control of the solvency power of the extraction solvent so as to maximize the amount of bitumen or other carbonaceous liquid recovered and to minimize the fines content therein.

Following extraction of bitumen, a diluent such as light naphtha is often added for transportation. The naphtha must be distilled and recycled, adding to energy costs. Changes in temperature and/or composition may cause the asphaltenes to fall out of solution, necessitating pipeline cleaning. Typically, removal of asphaltenes desirably removes some of the heavy metals and sulfur associated with crude oil. It is well known that asphaltenes can be separated from bitumen or asphaltenic crude oil by precipitation with paraffinic solvents such as pentane or heptanes (see, for example, U.S. Pat. App. 2006/0260980 to Yeung; U.S. Pat. App. 2008/0245705 to Siskin et al.; U.S. Pat. No. 5,326,456 to Brons et al.; U.S. Pat. No. 5,316,659 et al.; U.S. Pat. No. 4,699,709 to Peck et al.; and U.S. Pat. No. 4,596,651 to Wolff et al.). Additionally, various settling aids and/or flocculants have been utilized to enhance separation of asphaltenes (see, for example, U.S. Pat. App. 2006/0196812 to Beetge et al.).

It is conventionally believed that a high solvent to oil ratio (e.g., on the order of 40:1 by volume) is required to separate substantially-pure asphaltenes from bitumen or asphaltic crude oil. At lower solvent levels, commonly used in solvent deasphalting, substantial non-asphaltenic material precipitates with the asphaltenes, resulting in undesirable oil losses. Furthermore, solvent deasphalting relies on multiple theoretical stages of separation of barely immiscible hydrocarbon liquids, such stages are intolerant to the presence of water. The oil yield of solvent deasphalting is also limited by the high viscosity of the resultant asphaltic materials, particularly for high viscosity bitumen feeds. It is thus difficult to obtain high quality oil with high oil yield due to the difficulties in achieving clean separation of the oil and asphaltic fractions. In solvent deasphalting, asphalt (essentially asphaltenes with residual oil) is produced as a very viscous hot liquid, which forms glassy solids when cooled. This viscous liquid must be heated to a high temperature in order to be transportable, causing fouling and plugging limitations.

Another technique for removal of asphaltenes involves breaking a froth of extra heavy oil and water with heat and a diluent solvent such as naphtha. In the case of paraffinic naphtha, partial asphaltene removal results. However, only about 50% of the asphaltenes may be readily removed with this treatment even with multiple stages and complete removal of asphaltenes is thus not practical. As a result, the resulting oils must still be processed by capital intensive technology that is relatively tolerant to asphaltenes.

Despite the development of the above mentioned froth and solvent extraction processes, there remains a need for improved systems and processes of extracting bitumen of higher quality, for example, containing less water, less solids, less asphaltenes and/or less diluent. It would be desirable if the enhanced systems and processes would allow increased bitumen recovery, for example, by reducing oil losses during asphaltene removal and/or reduced oil losses in the tailings. There is also a need in the art for a method of selectively and efficiently removing asphaltenic contaminants from heavy oil, which mitigates the above-mentioned difficulties of the prior art. It would be even further desirable if the systems and processes would allow bitumen extraction and/or asphaltene removal without requiring high solvent and/or water-to-bitumen ratios, long residence times or numerous or expensive processing units. Such systems and processes should desirably facilitate recycle and thus economy of utilization of process water and/or conditioning agents, such as base (e.g., caustic) and/or bicarbonate.

SUMMARY
Herein disclosed is a method of removing at least one component from a feed comprising tailings, asphaltenic oil or a combination thereof, the method comprising: subjecting the feed to high shear in the presence of carbon dioxide to produce a high shear-treated product; and separating the at least one component from the high shear-treated product to produce a component-reduced product. Subjecting the feed to high shear in the presence of carbon dioxide may further comprise subjecting the feed to a shear rate of at least 10,000 s−1. In embodiments, subjecting the feed to high shear in the presence of carbon dioxide comprises a shear rate of at least 20,000 s−1. In embodiments, subjecting the feed to high shear comprises introducing the feed and carbon dioxide into a high shear device comprising at least one rotor and at least one complementarily-shaped stator. High shear may comprise a shear rate of at least 10,000 s−1, wherein the shear rate is defined as the tip speed divided by the shear gap, and wherein the tip speed is defined as πDn, where D is the diameter of the at least one rotor and n is the frequency of revolution. In embodiments, high shear comprises a shear rate of at least 20,000 s−1. In embodiments, subjecting the feed to a shear rate of at least 10,000 s−1 produces a local pressure of at least about 1034.2 MPa (150,000 psi) at a tip of the at least one rotor. In embodiments, subjecting the feed to high shear comprises providing a tip speed of the at least one rotor of at least about 23 msec, wherein the tip speed is defined as πDn, where D is the diameter of the at least one rotor and n is the frequency of revolution.

In embodiments, the high shear-treated product comprises a dispersion of carbon dioxide bubbles. The carbon dioxide bubbles may have an average bubble diameter of less than about 1 micron. In embodiments, the carbon dioxide bubbles have an average bubble diameter of less than about 0.5 micron.

In embodiments, the feed comprises tailings from a caustic bitumen extraction process and the component-reduced product comprises water having less than 10 wt % impurities. The method may further comprise recycling at least a portion of the water to the bitumen extraction process. Separating the at least one component may comprise separating solids from the high shear-treated product to produce a solids-reduced product and separating an oil phase from the solids-reduced product to produce the component-reduced product, wherein the component-reduced product comprises water. In embodiments, the tailings are obtained from a tailings pond of a bitumen extraction process. In embodiments, at least a portion of the tailings are produced by: mixing tar sand and water in a tumbler or a hydrotransport line to form a froth; introducing the froth into a separation cell; and removing the at least a portion of the tailings from the separation cell. In embodiments, at least a portion of the tailings are produced by introducing a middlings portion from a separation cell of a bitumen extraction process into a secondary separation unit and extracting the at least a portion of the tailings from the secondary separation cell.

In embodiments, at least a portion of the tailings are produced by introducing a bitumen froth from a separation cell of a bitumen extraction process into one or more centrifuge and extracting the at least a portion of the tailings from the one or more centrifuge. In embodiments, subjecting the feed comprising tailings to high shear in the presence of carbon dioxide reduces the pH to less than about 6. In embodiments, subjecting the feed to high shear converts the caustic in the tailings to sodium bicarbonate, enhancing the rate of separation of water from the tailings relative to conventional tailings treatment processes.

In embodiments, the feed comprises asphaltenic oil, the at least one product comprises asphaltenes and the component-reduced product comprises asphaltene-reduced oil. The asphaltenic oil may be selected from the group consisting of bitumen comprising at least some percentage of asphaltenes, heavy crude oil comprising at least some percentage of asphaltenes, and combinations thereof. Separating the at least one component from the high shear-treated product to produce a component-reduced product may comprise introducing the high shear-treated product into a centrifuge operated to separate asphaltenes from asphaltene-reduced product oil.

In embodiments, the asphaltenic oil feed is subjected to high shear in the presence of water. In embodiments, the feed has an API gravity of less than about 10 and the asphaltene-reduced product oil has an API gravity of greater than about 10. In embodiments, the asphaltene-reduced product oil comprises at least about 90 wt % bitumen. In embodiments, the asphaltene-reduced product oil comprises less than about 10 wt % asphaltenes. In embodiments, the asphaltene-reduced product oil comprises less than about 5 wt % water, less than about 1 wt % solids, or both.

Also disclosed herein is a method of removing asphaltenes from asphaltenic oil, the method comprising: subjecting the asphaltenic oil to a shear rate of at least 10,000 s−1 in the presence of carbon dioxide to produce a high shear-treated product; and separating asphaltenes from the high shear-treated product to produce an asphaltene-reduced product oil. In embodiments, the asphaltenic oil is selected from bitumen and heavy crude oils. The method may further comprise separating carbon dioxide from the high shear-treated product and recycling the separated carbon dioxide to the subjecting step. In embodiments, the asphaltene-reduced oil product comprises less than about 10 wt % asphaltenes.

Also disclosed, is an improvement in an aqueous bitumen extraction process comprising forming a bitumen froth by tumbling tar sand with water and base in a tumbler or hydrotransporting tar sand with water and base in a transport pipeline; and separating the bitumen froth from tailings in a separation cell; the improvement comprising: subjecting the tailings to high shear in the presence of carbon dioxide to produce a high shear-treated product; separating solids from the high shear treated product to produce a solids-reduce product; separating water from the solids-reduced product; and recycling the water to the froth forming step. The water may comprise less than about 10, 5, 3, or 1 wt % impurities. Separating solids from the high shear treated product to produce a solids-reduce product may be performed with at least one centrifuge. Separating water from the solids-reduced product may be performed with at least one settling tank. In embodiments, an oil phase is removed from an upper portion of the settling tank and the water from a lower portion of the settling tank. In embodiments, subjecting the tailings to high shear in the presence of carbon dioxide produces a high shear-treated product having a pH of less than about 6.

Also disclosed is a system for removing at least one component from a feed comprising tailings, asphaltenic oil or a combination thereof, the system comprising: at least one high shear device comprising at least one rotor and at least one complementarily-shaped stator and configured to subject the feed to high shear in the presence of carbon dioxide and produce a high shear-treated product, wherein the at least one high shear device is configured to subject the contents therein to a shear rate of at least 10,000 s−1, wherein the shear rate is defined as the tip speed divided by the shear gap, and wherein the tip speed is defined as πDn, where D is the diameter of the at least one rotor and n is the frequency of revolution; and at least one separation unit configured to separate a component from the high shear-treated product, providing a component-reduced product. In embodiments, the at least one rotor is configured to provide a tip speed of at least about 23 msec. In embodiments, the at least one rotor is configured to provide a tip speed of at least about 40 msec. In embodiments, the at least one rotor is separated from the at least one stator by a shear gap of less than about 5 μm, wherein the shear gap is the minimum distance between the at least one rotor and the at least one stator.

In embodiments, the feed comprises tailings from a bitumen extraction process, the at least one component comprises solids and oil and the system comprises a first separation unit configured to separate solids from the high shear-treated product producing a solids-reduced product and a second separation unit configured to separate oil from the solids-reduced product providing substantially pure water as component-reduced product. The system may further comprise a tailings pond from which the feed is obtained. In embodiments, the first separation unit is a centrifuge and the second separation unit is a settling tank. In embodiments, the feed comprises asphaltenic oil, the at least one component comprises asphaltenes, and the component-reduced product comprises asphaltene-reduced oil. The feed may have an API gravity of less than 10 and the asphaltene-reduced product may have an API gravity of greater than 10. In embodiments, the asphaltene-reduced oil comprises less than about 10 wt % asphaltenes. In embodiments, the asphaltene-reduced oil further comprises less than about 5 wt % solids, less than 5 wt % water or both.

Also disclosed is a method of removing at least one component from a feed stream comprising tar sands tailings, asphaltenic oil, or a combination thereof, that may include the steps of subjecting the feed stream to high shear separation in a high shear device to produce a high shear-treated product stream; and substantially separating the at least one component from the high shear-treated product stream to produce a component-reduced product stream. In embodiments, the feed stream may be liquid phase, the feed may have the at least one component suspended therein, and/or wherein the high shear device may operate to subject the feed to a shear rate of at least 20,000 s−1. The tar sands tailings may result from a caustic bitumen extraction process, and wherein the component-reduced product may have water therein having less than 10 wt % impurities. The component-reduced product stream may include asphaltene-reduced oil.

In some aspects, the feed stream may be substantially liquid phase, wherein subjecting the feed stream to high shear may include introducing the feed stream to a high shear device that may be configured with at least one rotor and at least one complementarily-shaped stator.

The step of substantially separating the at least one component may further include separating solids from the high shear-treated product to produce a solids-reduced product and separating an oil phase from the solids-reduced product to produce the component-reduced product, wherein the component-reduced product comprises water. The step of substantially separating the at least one component from the high shear-treated product to produce a component-reduced product may further include introducing the high shear-treated product into a centrifuge operated to separate asphaltenes from asphaltene-reduced product oil. In an embodiment, the asphaltene-reduced product oil may include less than about 5 wt % water, less than about 1 wt % solids, or both.

Yet other embodiments of the disclosure include in an aqueous bitumen extraction process comprising treating a bitumen froth, the process improvement including subjecting the bitumen froth to high shear in a substantially gas-free environment to produce a high shear treated product; separating solids from the high shear treated product to produce a solids-reduced product; separating water from the solids-reduced product; and recycling the water to the high shear step.

Yet other embodiments disclosed include a system for removing at least one component from a feed stream comprising tar sand tailings, asphaltenic oil, or a combination thereof, the system including at least one high shear device comprising at least one rotor and at least one complementarily-shaped stator and configured to subject the feed stream to high shear and produce a high shear-treated product, wherein the at least one high shear device is configured to subject the contents therein to a shear rate of at least 10,000 s−1; and at least one separation unit configured to separate a component from the high shear-treated product, providing a component-reduced product.

The feed stream may include tar sand tailings produced from a bitumen extraction process. The at least one component may include solids and oil. The system may also include a first separation unit configured to separate solids from the high shear-treated product producing a solids-reduced product and a second separation unit configured to separate oil from the solids-reduced product providing substantially pure water as component-reduced product.

In accordance with other embodiments disclosed, a method for removing contaminants from feedwater may include the steps of subjecting the feedwater to high shear separation in a high shear device to produce a high shear-treated product; and using a separator to remove at least some contaminants from the high shear-treated product to produce a contaminant-reduced product. feedwater may include waste water, surface water, groundwater, or a combination thereof.

In still yet other embodiments, a system for treating feedwater to remove contaminants therefrom, the system including at least one high shear mixing device comprising at least one generator comprising a rotor and a stator separated by a shear gap, wherein the shear gap is the minimum distance between the rotor and the stator, and wherein the high shear mixing device is capable of producing a tip speed of the rotor of greater than 22.9 m/s (4,500 ft/min); and a pump configured for delivering feedwater to the high shear mixing device.

The system may include a tank from which treated water is extracted, an inlet of the tank fluidly connected to the outlet of the high shear device. The high shear device may include at least two generators. In an embodiment, the shear rate provided by one generator may be greater than the shear rate provided by another generator.

According to embodiments of this disclosure, a high shear device is used to improve the recovery and processing of heavy crude bitumen. In one aspect of the present invention a high shear device is used in combination with reactive gas (e.g. carbon dioxide) to enhance the separation of clay and other inorganic mineral solids from the bitumen once it is extracted from the ground. In another aspect of the present invention a high shear device is used in combination with carbon dioxide to enhance the separation of asphaltenes and other undesirable elements of bitumen following removal of inorganic contaminants, thus allowing for easier transportation and downstream processing of the recovered bitumen.

Certain embodiments of the above-described methods or systems potentially provide overall cost reduction by reducing the size and/or number of downstream purification apparatus/steps, providing oil having reduced levels of impurities including, but not limited to, asphaltenes, sand, silt, solids, sulfur and/or other heavy metals, and/or water, permitting operation at low temperature and/or pressure relative to conventional heavy crude oil or bitumen processing, and/or reducing capital and/or operating costs of bitumen extraction or heavy crude oil processing. These and other embodiments and potential advantages will be apparent in the following detailed description and drawings.
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