Patent Application
20090139906
The present invention relates to processes and systems for processing oil sands from mining the ore to cleaning the produced bitumen. Specifically the present invention relates to isoelectric separation of oil sand and the associated use of an oleophilic endless belt formed from one or more endless cable systems wrapped in spaced configuration a multitude of times around two or more drums. Accordingly, the present invention involves the fields of process engineering, chemistry, and chemical engineering.
According to some estimates, oil sands, also known as tar sands or bituminous sands, may represent up to two-thirds of the world's petroleum. Oil sands resources are relatively untapped. Perhaps the largest reason for this is the difficulty of extracting bitumen from the sands. Mineable oil sand is found as an ore in the Fort McMurray region of Alberta, Canada, and elsewhere. This oil sand includes sand grains having viscous bitumen trapped between the grains. The bitumen can be liberated from the sand grains by slurrying the as-mined oil sand in water so that the bitumen flecks move into the aqueous phase for separation. For the past 40 years, bitumen in McMurray oil sand has been commercially recovered using the original Clark Hot Water Extraction process, along with a number of improvements. Karl Clark invented the original process at the University of Alberta and at the Alberta Research Council around 1930 and improved it for over 30 years before it was commercialized.
In general terms, the conventional hot water process involves mining oil sands by bucket wheel excavators or by draglines at a remote mine site. The mined oil sands are then conveyed, via conveyor belts, to a centrally located bitumen extraction plant. In some cases, the conveyance can be as long as several kilometers. Once at the bitumen extraction plant, the conveyed oil sands are conditioned. The conditioning process includes placing the oil sands in a conditioning tumbler along with steam, water, and caustic soda in an effort to disengage bitumen from the sand grains of the mined oil sands. Further, conditioning is intended to remove oversize material for later disposal. Conditioning forms a hot, aerated slurry for subsequent separation. The slurry can be diluted for additional processing, using hot water. The diluted slurry is then pumped into a primary separation vessel (PSV). The diluted hot slurry is then separated by flotation in the PSV. Separation produces three components: an aerated bitumen froth which rises to the top of the PSV; primary tailings, including water, sand, silt, and some residual bitumen, which settles to the bottom of the PSV; and a middlings stream of water, suspended clay, and suspended bitumen. The bitumen froth can be skimmed off as the primary bitumen product. The middlings stream can be pumped from the middle of the PSV to sub-aeration flotation cells to recover additional aerated bitumen froth, known as a secondary bitumen product. The primary tailings from the PSV, along with secondary tailings product from flotation cells are pumped to a tailings pond, usually adjacent to the extraction plant, for impounding. The tailings sand can be used to build dykes around the pond and to allow silt, clay, and residual bitumen to settle for a decade or more, thus forming non-compacting sludge layers at the bottom of the pond. Clarified water eventually rises to the top for reuse in the process.
The bitumen froth is treated to remove air. The deaerated bitumen froth is then diluted with naptha and centrifuged to produce a bitumen product suitable for upgrading. Centrifuging also creates centrifugal tailings that contain solids, water, residual bitumen, and naptha, which can be disposed of in the tailings ponds.
After the process became commercial, about 40 years of research and many millions of dollars have been devoted to improving the Clark process by several commercial oil sands operators, and by the Alberta government. Research has largely been focused on improving the process and overcoming some of the major pitfalls associated with the original Clark process. Some of the major pitfalls are:
1. Major bitumen losses from the conditioning tumbler, from the PSV and from the subaeration cells.
2. Reaction of hot caustic soda with mined oil sands result in the formation of naphthenic acid detergents, which are extremely toxic to marine and animal life, and require strict and costly isolation of the tailings ponds from the environment for at least many decades.
3. Huge energy losses due to the need to heat massive amounts of mined oil sands and massive amounts of water to achieve the required separation, which energy is then discarded to the ponds.
4. Loss of massive amounts of water taken from water sources, such as the Athabasca river, for the extraction process and permanently impounded into the tailings ponds that can not be returned to the water sources on account of its toxicity. For example, to produce one barrel of oil requires over 2 barrels of water from the Athabasca River.
5. The cost of constructing and maintaining a large separation plant.
6. The cost of transporting mined oil sands from a remote mining location to a large central extraction plant by means of conveyors. Additionally, the conveyors can be problematic.
7. The cost of dilution centrifuging.
8. The cost of naphtha recovery.
9. The cost of maintaining and isolating huge tailings ponds.
10. The cost of preventing leakage of toxic liquids from the tailings ponds.
11. The cost of government fines when environmental laws are breached.
12. The eventual cost of remediation of mined out oil sands leases and returning these to the environment in a manner acceptable to both the Alberta and the Canadian government.
13. The environmental impact of the tailings ponds.
Some major improvements have been made that included lowering the separation temperature in the tumbler, the PSV, and the flotation cells. This reduced the energy costs to a degree but may also require the use of larger tumblers and the addition of more air to enhance bitumen flotation. Another improvement eliminated the use of bucket wheel excavators, draglines and conveyor belts to replace these with large shovels and huge earth moving trucks, and then later to replace some of these trucks with a slurry pipeline to reduce the cost of transporting the ore from the mine site to the separation plant. Slurry pipelines eliminate the need for conditioning tumblers but require the use of oil sand crushers to prevent pipe blockage and require cyclo-feeders to aerate the oil sand slurry as it enters the slurry pipeline, and may also require costly compressed air injection into the pipeline. Other improvements included tailings oil recovery units to scavenge additional bitumen from the tailings, and naptha recovery units for processing the centrifugal tailings before these enter the tailings ponds.
More recent research is concentrating on reducing the separation temperature of the Clark process even further and on adding gypsum or flocculants to the sludge of the tailings ponds to compact the fines and release additional water. Most of these improvements have served to increase the amount of bitumen recovered and reduce the amount of energy required, but have increased the complexity and size of the commercial oil sands plants.
One particular problem that has vexed commercial mined oil sands plants is the problem of fine tailings disposal. In the current commercial process, mined oil sands are mixed and stirred with hot water, air, and caustic soda to form a slurry that is subsequently diluted with cooler water and separated in large separation vessels. In these vessels, air bubbles attach to bitumen droplets of the diluted slurry and cause bitumen product to float to the top for removal as froth. Caustic soda serves to disperse the fines to reduce the viscosity of the diluted slurry and allows the aerated bitumen droplets to travel to the top of the separation vessels fast enough to achieve satisfactory bitumen recovery in a reasonable amount of time. Caustic soda serves to increase the pH of the slurry and thereby imparts electric charges to the fines, especially to the clay particles, to repel and disperse these particles and thereby reduce the viscosity of the diluted slurry.
Without caustic soda, for most oil sands the diluted slurry would be too viscous for effective bitumen recovery. It can be shown from theory or in the laboratory that for an average oil sand, it takes five to ten times as long to recover the same amount of bitumen if no caustic soda is added to the slurry. Such a long residence time would make commercial oil sands extraction much more expensive and impractical.
While caustic soda is beneficial as a viscosity breaker in the separation vessels for floating off bitumen, it is environmentally very detrimental. At the high water temperatures used during slurry production it reacts with naphthenic acids in the oil sands to produce detergents that are highly toxic. Not only are the tailings toxic, but also the tailings fines will not generally compact. Tailings ponds with a circumference as large as 20 kilometers are required at each large mined oil sands plant to contain the fine tailings. Coarse sand tailings are used to build huge and complex dyke structures around these ponds.
Due to the prior addition of caustic soda, the surfaces of the fine tailings particles are electrically charged, which in the ponds, causes the formation of very thick layers of microscopic card house structures that compact extremely slowly and take decades or centuries to dewater. Many millions of dollars per year have been and are being spent in an effort to maintain the tailings ponds and to find effective ways to dewater these tailings. Improved mined oil sands processes must be commercialized to overcome the environmental problems of the current plants. One such alternate method of oil sands extraction is the Kruyer Oleophilic Sieve process invented in 1975.
Like the Clark Hot Water process, the Kruyer Oleophilic Sieve process originated at the Alberta Research Council and a number of Canadian and U.S. patents were granted to Kruyer as he privately developed the process for over 30 years. The first Canadian patent of the Kruyer process was assigned to the Alberta Research Council and all subsequent patents remain the property of Kruyer. Unlike the Clark process, which relies on flotation of bitumen froth, the original Kruyer process used a revolving apertured oleophilic wall (trademarked as the Oleophilic Sieve) and passed the oil sand slurry to the wall to allow hydrophilic solids and water to pass through the wall apertures whilst capturing bitumen and associated oleophilic solids by adherence to the surfaces of the revolving oleophilic wall.
Along the revolving apertured oleophilic wall, there are one or more separation zones to remove hydrophilic solids and water and one or more recovery zones where the recovered bitumen and oleophilic solids are removed from the wall. This product is not an aerated froth but a viscous liquid bitumen.
A bitumen-agglomerating step may be required to increase the bitumen particle size before the slurry passes to the apertured oleophilic wall for separation. Attention is drawn to the fact that in the Hot Water Extraction process the term “conditioning” is used to describe a process wherein oil sands are gently mixed with controlled amounts water in such a manner as to entrain air in the slurry to eventually create a bitumen froth product from the separation. The Oleophilic Sieve process also produces a slurry when processing mined oil sands but does not “condition” it. Air is not required, nor desired, in the Oleophilic Sieve process. As a result, the slurry produced for the Oleophilic Sieve, as well as the separation products, are different from those associated with the conventional Hot Water Extraction process. The Kruyer process was tested extensively and successfully implemented in a pilot plant with high grade mined oil sands (12 wt % bitumen), medium grade mined oil sands (10 wt % bitumen), low grade oil sands (6 wt % bitumen) and with sludge from commercial oil sands tailings ponds (down to 2% wt % bitumen), the latter at separation temperatures as low as 5° C. A large number of patents are on file for the Kruyer process in the Canadian and U.S. Patent Offices. These patents include: CA 2,033,742; CA 2,033,217; CA 1,334,584; CA 1,331,359; CA 1,144,498 and related U.S. Pat. No. 4,405,446; CA 1,141,319; CA 1,141,318; CA 1,132,473 and related U.S. Pat. No. 4,224,138; CA 1,288,058; CA 1,280,075; CA 1,269,064; CA 1,243,984 and related U.S. Pat. No. 4,511,461; CA 1,241,297; CA 1,167,792 and related U.S. Pat. No. 4,406,793; CA 1,162,899; CA 1,129,363 and related U.S. Pat. No. 4,236,995; and CA 1,085,760.
While in a pilot plant, the Kruyer process has yielded higher bitumen recoveries, used lower separation temperatures, was more energy efficient, required less water, did not produce toxic tailings, used smaller equipment, and was more movable than the Clark process. There were a number of drawbacks, though, to the Kruyer process. One drawback to the Kruyer process is related to the art of scaling up. Scaling up a process from the pilot plant stage to a full size commercial plant normally uncovers certain engineering deficiencies of scale such as those identified below.
Commercial size apertured drums that may be used as revolving apertured oleophlilic walls require very thick perforated steel walls to maintain structural integrity. Such thick walls increase retention of solids by the bitumen and may degrade the resulting bitumen product. Alternately, apertured mesh belts may be used as revolving apertured oleophilic walls. These have worked well in the pilot plant but after much use, have tended to unravel and fall apart. This problem will likely be exacerbated in a commercial plant running day and night. Rugged industrial conveyor belts are available. These are made from pre-punched serpentine strips of flat metal and then joined into a multitude of hinges by cross rods to form a rugged industrial conveyor belt. Other industrial metal conveyor belts are made from flattened coils of wire and then joined into a multitude of hinges by cross rods to form the belts. Both types of metal belts were tested and have stood up well in a pilot plant. However, it was difficult and energy intensive to remove most of the bitumen product in the recovery zone from the surfaces of the belts before these revolved back to the separation zone.
Bitumen agglomerating drums using oleophilic free bodies, in the form of oleophilic balls that tumbled inside these drums worked very well in the pilot plant. However commercial size agglomerators using tumbling free bodies may require much energy and massive drum structures to contain a revolving bed of freely moving heavy oleophilic balls with adhering viscous cold bitumen to achieve the desired agglomeration of dispersed bitumen particles.
While the chemistry of oil sand separation is very complex and has been studied for over 60 years a simplified description is here provided explaining the unique features whereby the systems disclosed and claimed in the instant invention can overcome some of the problems of the prior art developed by Karl Clark and improved by subsequent researchers.
As explained, the Clark process relies on bitumen flotation to separate oil sand slurries. However, bitumen has the same density as water at room temperature and, as such, unaided bitumen droplets or flecks will not rise in an aqueous environment. Bitumen expands more rapidly than water with increasing temperature and only after the slurry is brought to an elevated temperature will bitumen have a tendency to float to the top of a separation vessel. But without the use of a caustic process aid, most oil sand slurries are so viscous that the rate of ascent of bitumen droplets through a diluted viscous slurry in the separation vessels of the Clark process is so slow that inordinately long residence times would be required in the separating equipment to achieve acceptable bitumen recoveries.
Sodium hydroxide, the process aid normally used in small amounts during slurry preparation generally results in dispersed slurries with a pH of about 8.5 and gives commercially acceptable bitumen flotation recoveries for most oil sands. As part of the slurry making process, air normally is trapped in the form of tiny bubbles to which bitumen droplets or flecks attach themselves to help in their ascent. Also air may be added elsewhere in the process. The resulting product is a bitumen froth, which rises to the top of the vessels and is skimmed off for further clean up and processing.
Salts, chemicals, humic matter, minerals and heavy minerals have a tendency to reduce the effectiveness with the Clark process, either by interfering with the slurry dispersion mechanism or by inclusion in or adhesion to bitumen droplets or flecks, making these droplets too heavy to float and causing them to report to the tailings, thereby reducing overall bitumen recovery. Clay particles and heavy minerals, for example, titanium and zirconium oxides widely distributed in Alberta oil sands have a tendency to adhere to bitumen and, when there is insufficient attachment of bitumen to air bubbles which aid in the flotation process, such deficiency can result in significant loss of bitumen to the tailings. This is particularly true for low-grade oil sand ores rich in fines.
The process aid required in the Clark process for most oil sands has a detrimental effect on the tailings or effluents. During processing at elevated temperatures sodium hydroxide (caustic) releases and reacts with naphthenic acids naturally present in oil sand ores and causes the tailings to become highly toxic. As a result, tailings water from the Clark process, according to current Alberta environmental law, may not be returned to the environment but must be impounded.
After the fines of an oil sand slurry are dispersed, and bitumen froth has been recovered in the Clark process, the fines in the resulting toxic tailings remain dispersed and must be kept isolated from the environment. Accordingly the tailings flow into a tailings pond where coarse sand drops out on a gently sloping beach and is scraped up to form huge dykes to contain the remaining water and fines. Some dykes may be up to hundreds of meters high. Fines settle in the pond water and, after months or years, form microscopic gel like card house structures of electrically charged platelets. These structures can take decades or centuries to compact and thereby trap and retain large amounts of water. Hence, the result of adding a caustic process aid in the Clark process is the accumulation of huge single or multiple tailings ponds beside each mined oil sand plant; some of which may encompass a total area 20 kilometers in circumference. Clarified water will eventually rise to the top of a tailings pond and may be reused by the oil sands plant but normally only after years of operation.
A recent commercial trend is to allow the fines to settle in the pond and then, after maturing for a decade or more to pump the mature settled fines from the pond and mix these with gypsum in an effort to compact the card house structures to release some of the trapped water. Coarse sand may then be mixed with these compacted fines to form a wet mixture that may be disposed into the mined out portions of the oil sands lease. The released water may be toxic still and is hard water containing calcium and normally would require treatment before it can be reused in the commercial plant.
Although, froth flotation is a commercially accepted method of bitumen recovery from mined oil sands, it is not environmentally friendly. It requires many steps, vessels, controls and processes to achieve acceptable bitumen recovery and subsequently requires many steps controls and processes to isolate or overcome the environmental problems that were generated to achieve this acceptable bitumen recovery. As a result, environmental remediation of a mined out oil sands lease is very costly and may never be fully accomplished.
As will be described in more detail below, the systems and processes of the present invention allow for the elimination of caustic, process aids, and added air. The system disclosed and claimed in the instant invention overcomes many of the problems described above. Environmentally it is a more beneficial system, e.g. the tailings water is not toxic and can be reused in the process without major treatment. The system generally requires less energy, less water, less chemicals, fewer steps and less equipment to achieve the same or better bitumen recovery.
Bitumen flotation is not used and caustic process aid is not used. Instead of by flotation, the oil sand slurry is separated by screening out bitumen by an oleophilic endless belt formed by multiple wraps of an endless cable formed of a suitable oleophilic material such as, but not limited to, steel, carbon fiber, plastic or other material having sufficient mechanical strength and abrasion resistance. Bitumen adheres to the cable whilst water, sand and fines pass through the slits or spaces between the cable wraps to dewatering, to disposal or to further optional processing. The adhering bitumen is subsequently removed from the cable wraps in a recovery zone, not as bitumen froth but as viscous liquid bitumen. The liquid bitumen may then be cleaned effectively in one or more subsequent system steps.
In summary, the system of the instant invention approaches oil sands separation from a completely different angle than the commercial Clark process. Instead of using air to float bitumen from dispersed slurry, and instead of using a caustic process aid that results in major environmental concerns downstream from the plant, the instant invention screens the bitumen out of oil sand slurry at or close to isoelectric conditions using long lasting abrasion resistant endless cables. That means the fines do not have to be dispersed by increasing the natural pH of the oil sand ore. Bitumen droplets or flecks are not encouraged to float and air entrainment is not required since flotation is not used. Naphthenic acids naturally present in oil sands are not released by nor reacted with sodium hydroxide and the resulting tailings are much less toxic. Tailings water produced by the present invention will do much less damage to the environment. Gel like card-house structures of tailings fines in tailings ponds or during dewatering are reduced or eliminated. Tailings dewater more rapidly and water from the tailings is readily recycled in the process without major treatment. Over the lifespan of an oil sands plant, fresh water requirements for processing oil sands are significantly lower. For example, in the current commercial bitumen flotation processes about two barrels of water are removed from the environment to produce one barrel of bitumen. In the process of the instant invention, due to process water recycle, the water requirements on a quarterly basis are less than one barrel of water per barrel of bitumen produced. Additional water may be recovered and re-used as tailings dewatering continues thereafter to further reduce these water requirements. Large tailings ponds can also be eliminated. The costs of oil sand lease environmental remediation are lower. Less energy is lost to the tailings ponds. Carbon dioxide production is well below 30 kilograms of carbon dioxide per barrel of bitumen produced as compared with 45 kilograms for the Clark process for mined oil sands and 95 kilograms for recovering bitumen from deep deposits by the steam assisted gravity drainage (SAGD) process. The Kruyer process is simpler, more portable, and is useful for separations at the surface or for partial separations underground in a mineshaft or under overburden. Water requirements are lower and the costs to recover a barrel of bitumen from oil sands is lower than for the Clark process.
In one embodiment of the instant invention, isoelectric or nearly isoelectric separation of an oil sand slurry can include mining of the oil sand ore, on the surface or underground. The mined ore can be transported to a crusher, where the ore can be crushed to a size suitable for unobstructed pipeline slurry transport. Coarse rocks and large lumps can be screened, if required, and the resulting material can be mixed with water to form a slurry. The slurry can be transported through a pipe or pipeline, a portion of which optionally includes a sinusoidal pipe or pipeline configured to digest the slurry into discrete bitumen and solids particles dispersed in an aqueous medium. The digested slurry can be further subjected to coarse screening to remove large rocks and undigested lumps, if needed, prior to entry into one or more hydrocyclones. The digested and/or screened slurry can be passed through one or more hydrocyclones to produce an aqueous underflow of coarse solids including sand and a generally de-sanded aqueous overflow of bitumen droplets and fine solids. The underflow can be dewatered, either with a revolving belt filter or by allowing water to be run off and to be collected at a short term tailings pond. Furthermore, the overflow can be passed to and/or through a revolving endless oleophilic belt formed from multiple wraps of one or more endless cables to produce continuous phase viscous liquid bitumen product containing dispersed water, oleophilic and hydrophilic solids, while yielding a generally de-sanded tailings product for dewatering and disposal. The de-sanded tailings product can be dewatered, either with a revolving belt filter or by use of a short term tailings pond. System water collected from the underflow and from the de-sanded tailings can be optionally reused. The continuous phase viscous liquid bitumen product can be processed further to remove hydrophilic solids. This is done by dispersing the viscous liquid bitumen product in water using one or more pumps and pipes including one or more static mixers such as sinusoidal pipes. The resulting dispersed bitumen product in a continuous water phase can be passed to and/or through a revolving endless oleophilic belt formed from multiple wraps of one or more endless cables to produce a viscous bitumen product from which a large portion of its hydrophilic solids has thus been removed, yielding tailings that have passed through the belt gaps for disposal.
Various optional pumps, static mixers and hydrocyclones can be used, in addition, to further mix and process viscous liquid bitumen product with paraffinic hydrocarbon to remove water, solids and heavy asphaltenes from the viscous liquid bitumen product of the endless cable belt of the instant invention and make it suitable for long distance pipeline transport or for upgrading to synthetic crude oil.
There has thus been outlined, rather broadly, various features of the invention so that the detailed description thereof that follows may be better understood, and so that the present contribution to the art may be better appreciated. Other features of the present invention will become clearer from the following detailed description of the invention, taken with the accompanying claims, or may be learned by the practice of the invention.
a is a side view and
It will be understood that the above figures are merely for illustrative purposes in furthering an understanding of the invention. Further, the figures are not drawn to scale, thus dimensions and other aspects may, and generally are, exaggerated or changed to make illustrations thereof clearer. Therefore, departure can be made from the specific dimensions and aspects shown in the figures in order to produce the separation system using endless cables of the present invention.
Before the present invention is disclosed and described, it is to be understood that this invention is not limited to the particular structures, process steps, or materials disclosed herein, but is extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.
It must be noted that, as used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a splice” includes one or more of such splices, reference to “an endless cable” includes reference to one or more of such endless cables, and reference to “the material” includes reference to one or more of such materials.
Definitions
In describing and claiming the present invention, the following terminology will be used in accordance with the definitions set forth below.
As used herein, the term “endless cable” refers to a cable having no beginning or end, but rather the beginning merges into an end and vice-versa, to create an endless or continuous cable. The endless cable can be, e.g., a wire rope, a plastic rope, a single wire, compound filament (e.g. sea-island) or a monofilament which is spliced together to form a continuous loop, e.g. by long-splicing.
As used herein, “conditioning” in reference to mined oil sand is consistent with conventional usage and refers to mixing a mined oil sand with water, air and caustic soda to produce a warm or hot slurry of oversize material, coarse sand, silt, clay and aerated bitumen suitable for recovering bitumen froth from said slurry by means of froth flotation. Such mixing can be done in a conditioning drum or tumbler or, alternatively, the mixing can be done as it enters into a slurry pipeline and/or while in transport in the slurry pipeline. Conditioning aerates the bitumen for subsequent recovery in separation vessels. Likewise, referring to a composition as “conditioned” indicates that the composition has been subjected to such a conditioning process.
As used herein, “bitumen” refers to a viscous hydrocarbon that may include maltenes and asphaltenes that is found in oil sands ore interstitially between sand grains. In a typical oil sands plant, there are many different streams that may contain bitumen.
“Agglomeration drum” refers to a revolving drum containing oleophilic surfaces that is used to increase the particle size of bitumen in oil sand slurries prior to separation. Bitumen particles flowing through said drum come in contact with the oleophilic surfaces and adhere thereto to form a layer of bitumen of increasing thickness until the layer becomes so large that shear from the flowing slurry and from the revolution of the drum causes a portion of the bitumen layer to slough off, resulting in bitumen particles that are much larger than the original bitumen particles of the slurry.
As used herein, “fluid” refers to flowable matter. Fluids, as used in the present invention typically include a liquid, gas, and/or flowable particulate solids, and may optionally further include amounts of solids and/or gases dispersed therein. As such, fluid specifically includes slurries (liquid with solid particulate), flowable dry solids, aerated liquids, gases, and combinations of two or more fluids. In describing certain embodiments, the term slurry and fluid may be used interchangeably, unless explicitly stated to the contrary.
The term, “central location” refers to a location that is not at the periphery. In the case of a pipe, a central location is a location that is neither at the beginning of the pipe nor the end point of the pipe and is sufficiently remote from either end to achieve a desired effect, e.g. washing, disruption of agglomerated materials, etc.
As used herein, “velocity” is used consistent with a physics-based definition; specifically, velocity is speed having a particular direction. As such, the magnitude of velocity is speed. Velocity further includes a direction. When the velocity component is said to alter, that indicates that the bulk directional vector of velocity acting on an object in the fluid stream (liquid particle, solid particle, etc.) is not constant. Spiraling or helical flow-patterns are specifically defined to have substantially constant or gradually changing bulk directional velocity.
The “isoelectric point” (pI) is defined as the pH at which a particular molecule or surface carries no net electrical charge and thus is not encouraged to disperse from other molecules or surfaces in an aqueous medium. With respect to oil sand separation, isoelectric separation of oil sand or oil sand slurry is separation in which the pH is such that, on average, the clay particles in aqueous slurry produced from the oil sand are at or close to or substantially at the isoelectric point. Since oil sands vary in composition from location to location and may also contain a variety of clay types at each location, and each clay type has its own isoelectric point, isoelectric separation of an oil sand slurry would by necessity be defined as separation taking place at a suitable average isoelectric point such as to minimize dispersion of the clay particles before and after separation and to minimize the trapping of water in gel like microscopic clay card house structures in tailings effluents upon settling.
The term, “multiple wrap endless cable” as used in reference to separations processing refers to an endless cable that is wrapped around two or more drums and/or rollers a multitude of times to form an endless belt having spaced cables. Movement of the endless cable belt can be facilitated by at least two guide rollers or guides that prevent said cable from rolling off an edge of the drum and guide the cable back to the opposite end of the same or other drum. The spacing in the endless belt is formed by the slits or gaps between sequential wraps. The endless cable can be a wire rope, a plastic rope, a single wire, compound filament (e.g. sea-island) or a monofilament which is spliced together to form a continuous loop, e.g. by long splicing. As a general guideline, the diameter of the endless cable can be as large as 3 cm and as small as 0.001 cm, although other sizes might be suitable for some applications. An oleophilic endless cable belt is a cable belt made from a material that is oleophilic under the conditions at which it operates.
As used herein, “single wrap endless cable” refers to an endless cable which is wrapped around two or more cylindrical members in a single pass, i.e. contacting each roller or drum only once.
The term “cylindrical” indicates a generally elongated shape having a circular cross-section. Therefore, cylindrical includes cylinders, conical shapes, and combinations thereof. The elongated shape has a length referred herein also as a depth as calculated from one of two points - the open vessel inlet, or the defined top or side wall nearest the open vessel inlet.
As used herein, “digested slurry” refers to a slurry from which bitumen particles have been at least partially (and in many cases primarily) disengaged from sand grains of the original oil sand ore. Oil sand ore comprises mainly sand grains in which the voids between the sand grains are filled with bitumen. An oil sand slurry may be produced by thoroughly mixing the oil sand ore with water in such a manner that the sand grains and the bitumen form discrete particulates individually dispersed in an aqueous medium. Thus, in such a slurry most of the bitumen particles have disengaged from and are separate from the sand grains.
As used herein, “recovery yield” refers to the percentage of material removed from an original mixture or composition. Therefore, in a simplified example, a 100 kg mixture containing 45 kg of water and 40 kg of bitumen where 38 kg of bitumen out of the 40 kg is removed would be a 95% recovery yield.
As used herein, the term “confined” refers to a state of substantial enclosure. A path of fluid may be confined if the path is, e.g., walled or blocked on a plurality of sides, such that there is an inlet and an outlet and direction of the flow is directed by the shape and direction of the confining material.
As used herein, “retained on” refers to association primarily via simple mechanical forces, e.g. a particle lying on a gap between two or more cables. In contrast, the term “retained by” refers to association primarily via active adherence of one item to another, e.g. retaining of bitumen by an oleophilic cable. In some cases, a material may be both retained on and retained by one or more cables.
The term “roller” indicates a revolvable cylindrical member or drum, and such terms are used interchangeably herein.
As used herein, “wrapped” or “wrap” in relation to a cable wrapping around an object indicates an extended amount of contact. Wrapping does not necessarily indicate full or near-full encompassing of the object.
The term “metallic” refers to both metals and metalloids. Metals include those compounds typically considered metals found within the transition metals, alkali and alkali earth metals. Examples of metals are Ag, Au, Cu, Al, and Fe. Metalloids include specifically Si, B, Ge, Sb, As, and Te. Metallic materials also include alloys or mixtures that include metallic materials. Such alloys or mixtures may further include additional additives.
As used herein, the term “substantially” refers to the complete or nearly complete extent or degree of an action, characteristic, property, state, structure, item, or result. For example, an object that is “substantially” enclosed would mean that the object is either completely enclosed or nearly completely enclosed. The exact allowable degree of deviation from absolute completeness may in some cases depend on the specific context. However, generally speaking the nearness of completion will be so as to have the same overall result as if absolute and total completion were obtained. The use of “substantially” is equally applicable when used in a negative connotation to refer to the complete or near complete lack of an action, characteristic, property, state, structure, item, or result.
As used herein, a plurality of components may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary.
Concentrations, amounts, volumes, and other numerical data may be expressed or presented herein in a range format. It is to be understood that such a range format is used merely for convenience and brevity and thus should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. As an illustration, a numerical range of “about 1 inch to about 5 inches” should be interpreted to include not only the explicitly recited values of about 1 inch to about 5 inches, but also include individual values and sub-ranges within the indicated range. Thus, included in this numerical range are individual values such as 2, 3, and 4 and sub-ranges such as from 1-3, from 2-4, and from 3-5, etc. This same principle applies to ranges reciting only one numerical value. Furthermore, such an interpretation should apply regardless of the breadth of the range or the characteristics being described.
It has been found that effective oil sand slurry separation can be achieved by passing the slurry to and through a revolvable oleophilic device having gaps or apertures. Such an oleophilic device can take the form of an apertured drum, an apertured belt, a mesh belt or an endless cable that is formed into an oleophilic belt by wrapping the endless cable a multitude of times over two or more drums or rollers as described in the co-pending Endless Cable Application.
Separating oil sand slurry using such an oleophilic device is not a flotation operation but represents a screening operation in which water and hydrophilic solids pass through the gaps and/or apertures of the device whilst bitumen and oleophilic solids adhering to the bitumen are captured by and retained on the surfaces of the revolvable oleophilic device for subsequent recovery. Unlike the commercial Clark flotation process, this method of separation does not require the addition of a caustic process aid, does not require air bubbles to which bitumen can adhere to achieve flotation and does not require dispersion of the fines of the slurry. The bitumen product is not a froth but a viscous flowable liquid no or substantially no air and the resulting oil sands tailings product is not toxic and neither is the resulting tailings water.
The separation is carried out at or near the isoelectric point of the fines of the oil sand slurry and, under those conditions, the resulting tailings generally do not form microscopic card house structures. Therefore, tailing produced by the processes and systems of the present invention can be readily recycled within the recovery operation or released to the environment with minimal treatment.
Separation of oil sand slurries by means of an oleophilic endless belt formed from one or more endless cables has certain advantages and certain disadvantages. Abrasion of the equipment by sharp sand grains or damage from gravel or rocks is one of the disadvantages. For that reason oil sand slurry can be de-sanded before it comes in contact with the oleophilic wall device. A suitable hydrocyclone for such de-sanding is disclosed in the co-pending Hydrocyclone Application.
Oil sand can be mined, crushed, mixed with water and pumped into one or more pipes which are configured to form a digested slurry after required screening to remove oversize material to prevent conduit blockage. The digestion pipe transport system can include straight pipe, serpentine conduits, or other suitable system which allows for digestion of the slurry, often without introduction of a surfactant, caustic soda, or other processing fluids other than water. For example, slurry can be at least partly digested in a straight pipe under turbulent flow if the pipe is longer than 1 kilometer and if the slurry temperature is high enough, e.g. from about 30° C. to about 80° C. Alternatively, or in addition, serpentine conduits can be included along the digestion pipe transport system. Suitable serpentine or sinusoidal conduits can include a plurality of angles which create a shear mixing and turbulent environment within the slurry flow. Such serpentine conduits are described in more detail in the co-pending Sinusoidal Mixing Application. Optionally, a plurality of pipes can be used in parallel in order to provide increased capacity, as back-up pipes, and/or to reduce required pump sizes.
The digested slurry is passed through one or more hydrocyclones to separate the slurry into an aqueous underflow containing coarse solids and a de-sanded overflow containing an aqueous mixture of dispersed bitumen and fine solids. The overflow is passed to and through an oleophilic revolving device which in one embodiment can include one or more endless cables wrapped a multitude of times around two or more rollers. An agglomerator may be used to agglomerate the bitumen particles to make them larger prior to passage to the oleophilic members (e.g. endless cables, apertured wall, etc.) of the device. At the oleophilic wall, water and fine solids pass through the gaps or apertures and bitumen adheres to the oleophilic wall for subsequent removal as a liquid bitumen product containing little or no air.
Bitumen product, a viscous liquid, removed from the oleophilic wall contains entrained water and hydrophilic and oleophilic solids. Before such bitumen can be pipelined over extended distances or upgraded to synthetic crude oil it should usually be cleaned to remove water and solids. One method of removing hydrophilic solids from viscous liquid bitumen is illustrated in
One method of cleaning up bitumen is shown in
General
Referring back to
Wash water 60 is optionally added through a pipe 61 and injected into the confined helical path 19 to encourage bitumen to report to the overflow 24 of the open vessel 20. This overflow from the first hydrocyclone can flow into a second hydrocyclone situated in
The overflow 33 from the open vessel 25 of the second hydrocyclone flows in the direction shown by the arrow 34 into a distribution device 35. The distribution device can be any device such as, but not limited to, a screen, vibrator, or the like, that distributes the thus de-sanded slurry onto a top flight 36 of an oleophilic endless belt formed from multiple wraps of one or more endless cables. The arrow 37 shows the direction of movement of the belt. Water and hydrophilic solids pass through gaps between adjacent wraps of the cable on the top flight 36 and bitumen is captured by the top flight, e.g. by adherence to the cable. The top flight passes between two squeeze rollers 39 and 40 to removed captured bitumen, which also contains some solids and water, although other mechanisms could be used to remove bitumen from the cables. The squeezed off bitumen 41 is collected in a pipe or vessel (not shown) as a primary bitumen product.
Water and hydrophilic solids passing through the gaps of the top flight fall onto and into an agglomerator 43 which contains oleophilic baffles 44. A deflecting baffle 42 prevents water and solids from contacting a bitumen recovery or squeeze roller 47. Residual bitumen not recovered by the top flight 36 flow through the top flight gaps with water and hydrophilic solids into the agglomerator 43 where bitumen comes in contact with oleophilic baffles 44. Bitumen adheres to these baffles in increasing thickness until shear from the flowing water and hydrophilic particulates strip bitumen from these baffles 44. The resulting mixture of water, solids and enlarged bitumen particulates leaves the agglomerator 43 and flows to the bottom flight 38 where most of the agglomerated bitumen is captured and remaining water and solids flow into a vessel 46 to become the de-sanded tailings 49. Vessel walls or baffles 45 collect spillage or drippings and direct these to the de-sanded tailings 49. Adhering bitumen is removed from the bottom flight 38 using squeeze rollers 47 and 48 to remove captured bitumen. Alternatively, adhering bitumen can be removed by any suitable approach such as, but not limited to, combs, heating, or the like. The squeezed off bitumen 50 is collected in a pipe or vessel (not shown) as a secondary bitumen product. Both bitumen products 41 and 50 can be further processed separately or in combination. Various other suitable methods for separating bitumen from an aqueous mixture are described in the co-pending Endless Cable application.
Referring now to
Referring again to
When a tailings pond is not desired, a mechanical process may be used to dewater the tailings. Such mechanical processes are often more expensive and less effective but will require less room than a tailings pond. One dewatering option involves the use of a revolving dewatering filter described with
In contrast, the underflow of
Tailings Pond Bitumen Recovery
In yet another embodiment of the present invention, the endless cable device can be used to recover bitumen from conventional caustic tailings found in tailings ponds associated with the Clark process or other similar processes. Current commercial developers of the Clark process see a tailings pond as a means for storing toxic tailings and recovering water for reuse in the commercial process but generally do not use a pond as part of the process for recovering bitumen. As a result, the current commercial plants go to great lengths and expense recover bitumen from the warm tailings before they flow into the ponds and loose their elevated temperatures. However, in accordance with the present invention, a large amount of additional bitumen may be recovered as such a tailings pond is incorporated into a bitumen recovery process utilizing the endless cable devices of the present invention. At current commercial tailings ponds, sand and silt settle out of the tailings and water floats to the top, leaving a sludge containing bitumen, clay fines and water present in a bitumen-rich middlings portion of the pond (e.g. below the water rich layer and above the sand and silt layer). The percent bitumen content of this sludge can be an order of magnitude greater than the bitumen content of the tailings flowing into the pond. In some cases, on a dry basis percentage, sludge may contain as much bitumen as mined oil sand ore. As long as the ponds are not abandoned, this bitumen is not lost but collects in the ponds and may be recovered by oleophilic devices described in this or in the Endless Cable application. Such separation may be carried out at very low temperatures, even approaching zero degrees centigrade when centrifugal tailings (or tailings from other types of hydrocarbon bitumen clean up) are blended with primary and secondary tailings flowing into the pond thereby reducing the viscosity of bitumen of primary and secondary tailings by residual solvent contained in the centrifugal tailings. Without such blending, the separation of sludge from primary and secondary tailings may be carried out by oleophilic means around 10° C. to 20° C. The bitumen rich sludge can be collected using a suitable mechanism, such as but not limited to, pumping with an intake set at the appropriate depth. The collected sludge can then be directed to the endless cable as either the sole feed (optionally mixed with water or other additives to control flowability) or in combination with a crushed sands slurry or other materials as discussed previously.
When a tailings pond becomes part of the bitumen recovery process of a commercial oil sands plant, and oleophilic means can be used to recover this bitumen. Allowing bitumen to accumulate and concentrate in tailings ponds and then recovering this bitumen at a later date can effectively increase overall annual commercial plant bitumen recovery after the commercial plant has been in operation for some time. Since caustic process aid is used in the current commercial plants, the debitumenized sludge left after recovering bitumen from a current commercial tailings pond (e.g. using the Clark process or its equivalent) remains toxic.
Removal of Hydrophilic Solids
Bitumen product recovered from oil sand or from pond sludge by the present invention normally is a continuous phase viscous liquid bitumen that contains dispersed water, fine grained hydrophilic solids and fine grained oleophilic solids but very little or no air. It is liquid bitumen and not an aerated froth. The oleophilic solids generally adhere tightly to bitumen but water and hydrophilic solids generally are trapped as dispersed water droplets and water wet solids in the bitumen product. A large portion of these hydrophilic solids may be removed by washing this bitumen product with water.
One such water washing method is shown in
Alternately a different system, such as illustrated in
Heavy Minerals
Precious metals and non-precious heavy minerals have an affinity for bitumen and are or become oleophilic upon contact with bitumen. When bitumen product contains heavy minerals such as gold and silver and ores of titanium and zirconium, it can be advantageous to first beneficiate these oleophilic heavy minerals by the method of
Geologically it is generally accepted that in times past oil migrated into porous sediments of sand and silt to eventually form oil sand deposits after such porous sediments had been established. Precious and other minerals often are found in many sediments along riverbanks as the result of minerals weathering upstream of such rivers. When oil sands were formed in riverbed sites due to such oil migration, bitumen recovered from such sites will most likely contain precious and other heavy minerals due to the oleophilic attraction of such minerals for bitumen. This may explain why significant concentrations of precious minerals only are found in oil sands in a few locations. The Alberta oil sands contain a greater abundance of titanium and zirconium ores in the form of small particulates, which are widely distributed through the deposit. When bitumen is separated from the Alberta oil sands it nearly always contains titanium and zirconium ore particulates due to the affinity of these heavy minerals for bitumen.
It is well known in the oil sands industry that heavy minerals, including ilmenite, rutile and zircon adhere to bitumen froth in aqueous oil sand separation methods, such as the Clark process, and many authors in this industry have concluded that essentially all the heavy minerals found in mined oil sands end up in the centrifugal tailings of commercial oil sands plants.
However, the present inventor has found that heavy minerals also accumulate in the tailings ponds from primary and secondary tailings of at least one of the current commercial mined oil sands plants. This was determined from the large amount of heavy minerals in bitumen produced from the sludge of a tailings pond that primarily received primary and secondary tailings and rarely any centrifugal tailings from the commercial plant. These results were obtained from a pilot plant operated for about 9 months with tailings pond sludge being separated with an apertured oleophilic wall at a rate of 1 tonne of sludge per hour. Sludge had been formed by settling in this pond after sand and silt dropped out of the primary and secondary tailings and water rose to the top of the pond. By dropping out tailings sand and water, this tailings pond in effect served to concentrate bitumen in tailings pond sludge in the form of dispersed bitumen and in the form of bitumen mats. Bitumen and bitumen mats are found in many oil sand tailings ponds. The sludge from this pond contained up to 10 weight percent bitumen and, after water washing, the bitumen product from the pilot plant averaged about 8 weight percent heavy minerals. The heavy minerals recovered from this bitumen product were very high in rutile, a preferred ore of titanium. The composition of bitumen product from his pilot plant did not vary much from sludge collected and processed at various times from various locations within the pond.
This abundance of heavy minerals in pond sludge from primary and secondary tailings was a surprising discovery. Without being bound by theory this abundance may be explained by considering the probable behavior of bitumen droplets rising in a flotation vessel, when heavy minerals weigh down these droplets. In a commercial froth flotation plant tiny particles of mineral adhere to and are part of the bitumen droplets that rise in the separation vessels aided by air bubbles. Bitumen droplets that contain a small amount of mineral matter, but are attached to air bubbles, will float to the top fast enough to be skimmed off from the separation vessels as froth. Bitumen droplets that are loaded more heavily, especially when air is not abundant in the slurry, will rise slower in these vessels and may never reach the top before this bitumen leaves with the tailings. This discovery that this tailings pond sludge was high in heavy minerals content may explain why the commercial Clark process can at times have high bitumen losses to the tailings. These losses may be the result of minerals, and especially heavy minerals, loading down some bitumen droplets sufficiently to prevent their desired flotation, especially when there is a shortage of flotation air. By the same token, any particulate matter, heavy or not so heavy, may reduce or prevent bitumen flotation if this particulate matter adheres to bitumen droplets or flecks in sufficient amounts.
Unlike froth flotation, when an oleophilic wall device as in the present invention, for example, an oleophilic endless cable belt, is used to process oil sand slurries, the density of bitumen droplets is only a small consideration in the separation process. A large amount of heavy minerals can be collected along with the bitumen product without being concerned about bitumen density. Bitumen recovery is very high because both light bitumen and heavy bitumen are recovered without being influenced to a significant degree by minerals content. As explained with
Another benefit of washing a bitumen product with water is that it may reduce corrosion of subsequent bitumen clean up or transportation equipment by removing chlorides or other undersirable components. Since the present invention does not use caustic soda the water dispersed in the bitumen product may contain chlorides and other salts or acids that could damage such equipment. Washing bitumen with clean water will reduce the amount of such substances in the bitumen product. Reagents to neutralize such substances may even be added to the wash water if desired.
Bitumen Clean Up
Bitumen product from an oleophilic device, such as bitumen product from an oleophilic endless cable belt, may be cleaned up by means of processing the product with a paraffinic hydrocarbon. This clean up involves the removal of water, solids and the heaviest asphaltenes from the bitumen product. Particularly beneficial for subsequent upgrading is the removal of the heavy asphaltenes that contain undesirable metals which tend to react with or interfere with catalysts used in the upgrading process of bitumen to synthetic crude oil. Paraffinic hydrocarbons that may be used for bitumen clean up include, but are not limited to, butane, pentane, hexane, heptane, octane, nonane or mixtures thereof, or natural gas condensate containing at least 50% by weight mixtures of some of these alkanes. As explained, the clean up may be done after hydrophilic solids have been removed from the bitumen product. Alternately, bitumen produced by the endless cable belt may be cleaned up with paraffinic hydrocarbons without prior hydrophilic minerals removal.
One configuration of such a method is illustrated in
One static mixer and one hydrocyclone may be sufficient or the process may be enhanced by the use of a second static mixer and hydrocyclone. In that case, the underflow 98 from the first hydrocyclone flows through a pipe 104 to a pump 105 where it is increased in pressure and may then be introduced into a second static mixer or serpentine conduit to keep the asphaltenes finely dispersed as the underflow enters the confined helical path of a second hydrocyclone. Alternately, the underflow 98 may be pumped directly into the helical confined path 107 of the second hydrocyclone. Unlike the hydrocyclones of the present invention (which are more fully described in co-pending Hydrocyclone application), conventional hydrocyclones do not do not have confined helical paths and in that case the flow is directly into the hydrocyclones in stead of through the confined helical confined paths. The overflow 110 from the second hydrocyclone consists of residual paraffinic hydrocarbon and clean bitumen and an underflow 109 of water, solids, and dispersed heavy asphaltenes flowing to disposal. The overflow 110 passes into a still 111 or distillation tower where it is separated into clean bitumen flowing from the bottom outlet 114 and a gaseous overhead 112 of paraffinic hydrocarbons which are condensed and reused in the process. Since the flow in both hydrocyclones is adjusted to eliminate all or nearly all dispersed heavy asphaltenes, solids and water, conventional stills or distillation apparati may be used to recover the paraffinic hydrocarbon provided these are designed to accommodate a small amount of solid asphaltenes. A defoaming agent may be added to the bitumen/paraffin feed or to the overflows 97 and 110 to enhance the distillation. Heating coils 101 and 113 are shown in the drawing by way of illustration to indicate that the overflows or the stills/towers are heated to achieve the separation. When only one hydrocyclone is used, underflow 98 from this hydrocyclone flows to a suitable disposal site, tailings pond or the like.
It should be noted that, while the system of
Of course, it is to be understood that the above-described arrangements, and specific examples and uses, are only illustrative of the application of the principles of the present invention. Numerous modifications and alternative arrangements may be devised by those skilled in the art without departing from the spirit and scope of the present invention and the appended claims are intended to cover such modifications and arrangements. Thus, while the present invention has been described above with particularity and detail in connection with what is presently deemed to be the most practical and preferred embodiments of the invention, it will be apparent to those of ordinary skill in the art that numerous modifications, including, but not limited to, variations in size, materials, shape, form, function and manner of operation, assembly and use may be made without departing from the principles and concepts set forth herein.
This application is related to U.S. patent application Ser. No. 11/939,978 entitled “Sinusoidal Mixing and Shearing Apparatus and Associated Methods,” filed Nov. 14, 2007 (hereinafter referred to as “Sinusoidal Mixing Application”), Ser. No. 11/940,099 entitled “Hydrocyclone and Associated Methods,” filed Nov. 14, 2007 (hereinafter referred to as “Hydrocyclone Application”), and Ser. No. 11/948,816 entitled “Endless Cable System and Associated Methods,” filed Nov. 30, 2007 (hereinafter referred to as “Endless Cable Application”) which are each incorporated herein by reference.
