Recovery Of Oil From Tar Sand By An Improved Extraction Process

Abstract

An improved process for extracting oil from tar sand containing fines using extraction and phase separation techniques. A closed-cycle, single-stage process uses only one extraction vessel in which tar sand is contacted by an extractant, such as water containing a wetting agent and/or a solvent, and recycle water in a fluidized bed condition which avoids disturbing fines attached to the tar sand particles. Fines exiting the extraction vessel in a water phase are agglomerated and reintroduced to the bottom of the extraction vessel where they are filtered out by the extracted sand passing downward in the vessel. The solvent may be vaporized to enhance contact and assure complete recovery. Steam is advantageously introduced to the extraction vessel to scour the sand particles free of solvent. The usual process control additives may be included in the recycle water. The sand and fines tailings are essentially free of pollutants.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the extraction of oil from bituminous-containing sands. More particularly, this invention relates to a method of removing oil from tar sands by an improved extraction process carried out in a closed cycle system to yield an oil phase containing a reduced amount of contaminants without the need for excessive process water requirements, high extractant losses and discharge of polluted waste streams.

Tar sands, also known as bituminous sands and oil sands, are primarily aggregates of sand, clay, oil and water capable of being surface mined. There are large known reserves of heavy petroleum locked up in tar sand deposits in various parts of the world, the best known of which is the Athabasca Tar Sands in Alberta, Canada, which has estimated recoverable reserves in excess of 250 billion barrels of oil. The significance of this quantity is apparent from the fact that the proven world-wide oil reserves as of early 1973 were 667 billion barrels. Currently, increasing world dependence upon petroleum for energy and for the manufacture of petroleum-based products coupled with a diminishing supply of petroleum suggests that the tremendous tar sand deposits of oil be exploited provided that suitable processing methods are available.

The tar or bitumen content of tar sand varies from natural deposit to natural deposit and contains 5 to 20 percent heavy oil, by weight. On the average this constitutes about one barrel of oil per 2 tons of sand. In addition to the sand component of the mineral, there are usually fine particles of clay and silt the quantity of which also varies and can range from 1 to 50 percent, by weight. Tar sand may also contain 1 to 10 percent, by weight, water in the form of a film around the sand grains. Prior to being useful in ordinary oil refining processes, the petroleum must be separated from the tar sand and various procedures for accomplishing this have been suggested.

2. Description of the Prior Art

Among the best known prior art methods for separating the oil from the sand are those utilizing water extraction processes and known as the "hot water method" and the "cold water method." In the hot water method, the tar sand is treated with steam and thoroughly mulled and aerated in large rotating drums with a minimal amount of hot water at a controlled temperature. The pulp is then dropped into a turbulent stream of circulating hot water and carried to a separation cell. In the separation cell, sand settles to the bottom, oil rises to the top in the form of a frothy mixture of minerals and oil and an aqueous middlings layer comprising clay and silt is formed between the sand and the frothy layer.

Cold water processes have involved adding a hydrocarbon diluent, such as kerosene, soda ash and a wetting agent to the tar sand followed by charging the mixture to a ball mill for mixing and grinding. The mixture is then mixed with large amounts of water in a settling zone. Most of the sand settles out and a frothy bituminous emulsion is floated to the top in a manner similar to the hot water method. Other cold water processes involve the use of agitation followed by classification and thickening to encourage settling of the sand. Still other processes involve shearing in water in a through-type kneader.

The water extraction processes possess several serious disadvantages. In particular, tar sand having a high clay and silt content results in poor oil separation and larger amounts of the oil remain with the middlings layer. Consequently, a scavenger step is required for further treatment of the middlings layer to recover this unseparated oil. See, for example, U.S. Pat. No. 3,401,110. Such a process also requires considerable slurry pumping and handling with the result that the abrasiveness of the sand takes a heavy toll on material handling equipment. The greater the clay and silt fines content, the greater also the process water required. The amount of water thus required is related to the fines content and may run as high as 150 to 250 gallons per ton of tar sand processed when 30 percent of the mineral is below 44 microns in size, a size below which fines are the greatest contaminant problem. Not only does such an amount of water represent large process water requirements, but, in addition, loss of heated water results in large heat losses as well as disposal problems.

In the attempt to overcome some of aforementioned drawbacks there have been proposed ion exchange systems to reduce fresh water requirements, U.S. Pat. No. 3,496,093, as well as techniques for desirably determining accurate water process requirements based on sand aluminum content, U.S. Pat. No. 3,558,469. The use of a flocculation zone following a sand separation zone subsequent to the scavenger zone in the hot water process in order to remove fines from the water stream has also been suggested. See U.S. Pat. No. 3,487,003. However, the aforementioned processes do not reduce the simplicity of the process or equipment required but rather either add another process step or require the use of chemical additives with a concomitant increase in complexity of handling requirements and cost.

Cold water methods may be essentially solvent extraction processes in which the tar sands are mixed with a hydrocarbon solvent slurry followed by removal of the fat solvent by filtration, centrifuging or other similar means. The main objections of this approach include the hazards involved in the slurrying of the tar sand with hydrocarbon solvent as well as the loss of solvent with the sand tailings, thus making the process uneconomical. As an aid to separation of the water from the bituminous emulsion in the water extraction processes, the use of chelating agents, U.S. Pat. No. 3,522,168, as well as the adjustment of the pH of the aqueous phase, U.S. Pat. No. 3,542,666, have been suggested. Control of viscosity conditions has also been suggested as an aid to separation. See U.S. Pat. No. 3,399,765. Controlled velocity to separate bitumen from bituminous sand in a dense slurry has also been proposed. See U.S. Pat. No. 3,556,981.

Other prior art extraction processes utilize primarily a hydrocarbon solvent to extract the oil from bituminous sands. See, for example, U.S. Pat. No. 3,553,099. In such processes tar recovery is good; however, solvent losses constitute a serious drawback because of the high cost of solvent. Since a high quantity of sand must be processed in order to recover relatively small quantities of oil, even a small percentage of solvent in the sand tailings cannot be tolerated as a loss since the overall amount will be great relative to the oil recovered. As a consequence, multi-stage recovery equipment and processes utilizing filtration or centrifugal separation have been proposed, as for example in U.S. Pat. No. 3,553,099. While solvent recovery may be enhanced in such systems, the capital cost of equipment as well as operating costs tend to be high. Alternatively, special treatment involving control of viscosity and differential velocity and utilizing high volumes of water to minimize solvent loss have been proposed. See U.S. Pat. No. 3,553,098.

Thus, it can be seen that many and diverse methods for separating the oil from bituminous sands by fluid extraction followed by separation have been proposed. Thus, there have resulted various proposed methods including hot water flotation, gravity separation, cold water flotation, centrifugal separation, solvent extraction and various combinations thereof. However, a serious drawback has remained in that the hydrocarbon product recovered by these processes, that is, the oil or bitumen and sometimes solvent, commonly contains, after the initial separation from the bullk of the sand, significant amounts of water, mineral matter, and sometimes air or gas in an emulsion or froth. In addition, process requirements of important resources such as water are high and losses of expensive solvents cannot be economically tolerated. A further disadvantage of the prior art processes is the fact that waste streams from these processes frequently contain pollutants that give rise to serious environmental concerns. Yet, the economical elimination of such contaminants must be achieved if a process is to be commercially exploited.

SUMMARY OF THE INVENTION

The present invention overcomes many of the disadvantages associated with the prior art processes and provides an efficient and relatively economical process yielding oil containing reduced amounts of contaminants from tar sand. Thus, prior art drawbacks involving material handling problems due to pumping of erosive sand slurries, high mineral contamination of separated oil, hazards in solvent handling, loss of solvents, high requirements of process water, high heat requirements and disposal problems due to polluted effluents, are overcome by the process of my invention which provides a closed-cycle single-stage system that offers the advantages of the hot water and solvent extraction processes while at the same time remaining physically and economically attractive.

My invention is an improvement on both the water and the solvent extraction type processes and overcomes the disadvantages of the prior art by providing a closed-cycle, single-stage extraction process requiring no reprocessing and repumping of the tar sand for high extraction recovery. In addition, the heat requirements of the process of my invention are minimal because the sand and fines tailings are discharged at essentially the same temperature as the incoming tar sand and the liquid media remains within the system and is recycled rather than discharged. Thus, the hazards of solvent handling are minimized, solvent losses are negligible and pollution reduced.

The process according to my invention involves the following steps. Tar sand is pretreated with hot water from a process recycle stream, described below, to make it sufficiently free flowing for removal of oversized material. The mixing of the tar sand with hot water should be sufficiently gentle to avoid disruption of the clays attached to the sand particles. The tar sand is then fed into the top of an extraction vessel designed so as to allow adequate contact time between the rising extraction liquid medium and the slowly down-flowing solid sand bed. The extraction may be hot water, containing a wetting or dispersing agent facilitating the extraction of oil from the sand, if desired, or solvent may be introduced into the lower section of the down-flowing sand bed. With the up-flowing extraction liquid, the system functions as a countercurrent extraction system minimizing extractant, water or solvent, use to that required for viscosity control of the oil. The point of tar sand feed to the top of extraction is to a level at least below the collected solvent-oil layer.

The rate of flow of the liquid medium in the extraction vessel should be adjusted to maintain the sand particles in a fluidized form but also sufficiently gentle to prevent the disruption of the clays attached to the sand particles. This rate of liquid flow also allows flocculated fines to be filtered out by the sand bed prior to discharge, as described below. Steam is also introduced into the bottom of the extraction vessel, either directly or indirectly, in order to heat any remaining solvent occluding on the sand to vaporize it. Solvent vapors condense on the cooler down-falling oil-rich sand above it. This vaporization of the solvent provides quicker and more complete dissolution of the tar on the sand and assures complete removal of solvent from the discharging sand. A recycle stream of water is also introduced at the bottom of the extractor.

The oil-solvent layer collects at the top of the extraction vessel and is there withdrawn. Below this layer is a layer of water and fines which is recycled first to a water storage and treatment vessel and then to the bottom of the extraction process. In the recirculating water system there may be incorporated, in addition to the storage and treatment tank, means for adding treatment chemicals for pH control, wetting agents, dispersing agents, and flocculants for agglomerating the fine particles. The system also permits the addition of salts, such as sodium chloride, for increasing the gravity if it is advantageous to increase the buoyancy of the oil.

The spent sands and the flocculated fines are removed from the extractor by a suitable drag conveyor such as a screw conveyor. In addition, the hot water contained in the sand may be replaced by cold make-up water introduced countercurrent to the sand flow to assure removal of soluble chemicals and the inert solids can be dumped. Alternatively, if it is advantageous to dispose of the sand as a slurry, means may be provided for pumping instead of drag removal of the sand.

Accordingly, it is a feature of my invention to provide a process for the solvent extraction of oil from tar sand in a single-stage, closed-cycle process which essentially eliminates extractant loss and minimizes sand slurry pumping requirements.

It is a further feature of my invention to provide an improved process for extracting oil from tar sand by utilizing an extractant, such as a solvent, which is essentially recovered in the process.

A still further feature of my invention is the provision of a tar sand extraction process which results in removal of chemicals in sand tailings and in the absence of polluted effluent waste streams.

Another feature of this invention is the provision of a tar sand extraction and recovery process which results in the production of a hydrocarbon product free of significant amounts of contaminants such as sand silt and other mineral matter.

The foregoing features and other features of this invention will become apparent from the following description of a preferred embodiment thereof.

BRIEF DESCRIPTION OF THE DRAWING

The drawing shows a schematic representation of a suitable process flow arrangement for carrying out a preferred embodiment of the process of my invention. The illustration represents conventional process equipment that is known to the art and readily commercially available. For simplicity, details, such as pumps and valves, have not been shown although it is understood that those skilled in the art will be able to supply the necessary equipment to carry out the process functions taught herein. The legends on the drawing aid in understanding thereof and characterize the process steps.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The process of my invention is best understood by reference to the drawings. Tar sand is fed into the processing system, shown at 10, into a mixer 14 which may be of the simple low energy type such as a rotary cement mixer. Hot water from the water recycle system is also fed into the mixer through a line 12. Sufficient hot water, plus steam if needed, is added to form a fluid slurry. The temperature within the mixer is preferably maintained at the lowest possible temperature for suitable fluidity. Within the mixer 14 gentle mixing to prevent disruption of the clays and other fines attached to the sand particles takes place. That the mixing be sufficiently gentle to avoid displacement of the fines is important in my process and is in distinction from previously known processes which deliberately mull, aerate or grind the tar sand. The tar sand-water slurry flows from the mixer 14 to a screen 18 via the line 16. On the screen 18 over-size material may be removed and discarded via a conveyor 20. It is also important that this screening not disrupt the clays and other fines attached to the sand particles. The screened slurry is then fed through a line 22 to the top of the extractor vessel 24. Within the extraction vessel an internal downcomer 26 assures that the tar sand-water slurry is fed to a level below the oil-solvent collection layer (hydrocarbon phase) and preferably to a point below the water-contaminants layer.

The extraction liquid, or extractant, may be hot water, or it may be water to which has been added wetting agent, dispersing agent and the like in order to facilitate extraction of the oil. Also, solvent of the type customarily used in such extraction processes may desirably be introduced to the extraction vessel 24 via a line 28 at a point near the lower portion of the extraction vessel. Steam is also introduced, indirectly or directly, into the extraction vessel 24 at a point near the bottom of the vessel via a line 30 which is located below the point of introduction of the solvent. After start up, once the process has reached steady-state operation, there exists a recycle stream containing water and contaminants such as clay and other fines from the extraction process. This recycle stream may also contain slight amounts of additives, such as wetting agents, dispersing agents, flocculants, and caustic for pH control, used for process control. This recycle stream is introduced to the extraction vessel 24 at a point below the points of introduction of the solvent and steam through a line 32.

The extraction process within the extraction vessel operates as follows: The up-flowing extractant liquid, including the recycled water, adjusted for the most suitable pH and containing wetting or dispersing agents, and dissolved salts, if necessary, for increased density, and solvent acts to release the tar or heavy oil from the sand and cause it to rise to an upper oil-solvent liquid layer in the extraction vessel. This hydrocarbon phase is shown schematically and referenced by the numeral 100. Since the extraction is countercurrent, the tar sand becomes more depleted in oil as it continues in its downward path in the extraction vessel while becoming exposed to leaner solvent and solvent vapor until practically all oil is removed and the sand is wetted with the solvent only.

As the sand continues its downward path in the extraction vessel 24 below the point of solvent introduction via the line 28, it is heated by steam introduced via the line 30. The heating by steam may be accomplished directly or indirectly; however, the introduction of live steam is preferred because it allows for the use of induction nozzles which provide an intimate mix with the sand particles. The steam scours the remaining solvent and other chemcials off of the sand particles and the amount of steam necessary to accomplish this is used. Should this scouring be insufficient to remove all solvent, additional steam is added until the sand temperature is above the boiling point temperature of the solvent, which has a boiling point temperature lower than the boiling point temperature of the circulated liquid, in order to vaporize the solvent.

The solvent vapor rises with the flowing liquid and condenses on the cooler down-coming sand. The oil-solvent phase constitutes the uppermost layer in the extraction vessel and is removed as a relatively clean hydrocarbon phase containing a reduced amount of contaminants via the line 34. This hydrocarbon phase may then be further refined, if desired, and separated into a solvent fraction and a product tar fraction for a refinery feed. The solvent fraction from such further refining may then be reintroduced to the system as make-up solvent entering via the line 28. The water phase containing fines such as silt and clay and other contaminants in addition to additives is an intermediate layer, shown at 200, between the oil-solvent phase and the sand extraction zone. This phase, which may also contain some dispersed hydrocarbon, is removed via a line 36 to a storage and treatment tank 38.

In the storage and treatment tank 38 this recycle material is sampled and its pH, wetting agent and salt content, and flocculating agent composition adjusted, if needed. This adjustment is accomplished through the introduction of additives from suitable supply tanks illustrated generally by the representative tank 40 feeding into the water storage and treatment tank 38 via a line 42. The water storage and treatment tank 38 is selected so as to provide sufficient retention time for agglomeration of the fines in a quescent zone incorporated in the tank. The agglomerated fines concentrated in the recycle waste are represented at 600. The length of time of agglomeration will, of course, be dependent upon the particular clays and other fines found in the tar sand and may vary. Agglomeration is aided through the addition of flocculating agents. The incidence of collision of the particles to improve adherence in agglomeration may be enhanced by the incorporation of a vibrator, such as a sonic vibrator, as is known in the art. The treated liquid containing concentrated agglomerated fines exits the storage and treatment tank 38 via a line 32 for reintroduction into the extraction system. Under some circumstances the tank may not be required and agglomeration in the layer will be sufficient. As previously mentioned, hot water may be removed from an upper phase in the water storage and treatment tank 38 via a line 12 for addition to the tar sand in the mixer 14. Also, any minor amount of oil dispersed in the water phase may be permitted to separate here and withdraw from the top, if desired.

The tar sand is contacted with the up-flowing stream including all of the solvent, recycle water and steam introduced to the extraction vessel as is shown generally at 300. Here the relative velocities of the down-flowing sand and up-flowing steam should be such that the tar sand is fluidized sufficiently to permit good effective tar sand-extractant contact but insufficiently active to dislodge fines which are attached to the sand particles. This is an important aspect of my process since it reduces the amount of fines which must be removed in the water phase and helps assure that the hydrocarbon phase has a minimum of fines. Thus, many fines can remain with the sand as fines attached to the sand particles.

The sand, which is free of solvent and soluble chemicals following the steam scouring, continues its down-flow against the incoming recycle water containing concentrated agglomerated clay and silt fines. As shown at 400, the sand particles are merely sufficiently suspended and fluidized to act as a filter medium for removing agglomerated fines from the recycle steam. The fluid velocity in the extraction vessel will vary with the other process conditions which are dependent upon the composition of the tar sand and the nature of the extractant fed to the system. In any event, the velocity should be great enough only to permit uniform distribution of the extractant and desirably kept as low as possible for good extraction contact.

The sand containing the filtered silt, clay and other agglomerated fines settles to the bottom of the extraction vessel 24 where it is represented at 500. Here it may be removed either by a drag type conveyor 44, such as a screw conveyor, or pumped away as a slurry. The drag type conveyor is preferred in that it allows the removal of sand tailings containing a minimum amount of water and avoids the need for pumping abrasive slurries. Furthermore, any water remaining with the sand is likely to be hot and contain the additives of the system. These can be recovered by adding a cold water back wash to the conveyor via a line 46 at the point of discharge of sand and agglomerated fines via a line 48. As a consequence, not only are heat and conditioning chemicals retained in the system, but the sand and agglomerated fines tailings disposed of are free of possible pollutants.

It will be appreciated by those skilled in the art that process variables such as the degrees of bed fluidization, process liquids flow rates, as well as composition of additives in the system will be governed by the mined tar sand to be processed. These operating parameters can be determined according to known procedures by those skilled in the art. In particular, considerable flexibility is possible in the use of alkali for pH control, quantity of oil extraction affecting agents such as wetting agents, dispersing agents, gravity affecting salts and amounts of solvents because of the closed-cycle feature in which all additives are recycled. For example, if large quantities of solvent are required, the vapors, which would collect in a vapor phase in the top of the extraction vessel 24 may be compressed or condensed and recycled. The requirements for pH, type and quantity of wetting agent, dispersing agent, density of liquid media and amount of solvent will vary according to the quality of the tar sand fed to the system. Thus, it is likely that some or all additives, which are known in this art, may not be required to obtain the degree of extraction desired.

Thus there has been provided a process for extracting tar from tar sand which is an improvement on the solvent-extraction procedure. In particular, the system is highly advantageous in that it requires only one extraction vessel and provides waste effluents which are pollution free. Water process requirements are reduced and, by virtue of using a closed system, solvent losses are minimized and essentially negligible, thus contributing to economies of operation. In addition, capital equipment costs are decreased since this process does not require repumping and further separation vessels such as elutriation vessels, phase separators, particle separators, centrifuges, filter beds and the like.

Claims

I claim:

1. In a process for recovering oil from tar sand by extraction and phase separation, the improvement of a closed-cycle process comprising:

introducing the tar sand to a single-stage extraction vessel,

flowing a liquid extraction stream including water countercurrent to the tar sand to maintain it in a fluidized bed condition,

separating an oil phase above the tar sand fluidized bed,

separating a water phase above the tar sand but below the oil phase,

withdrawing a water stream from the water phase in the extraction vessel,

recycling the water stream to the extraction vessel at a point below the top of the tar sand fluidized bed,

withdrawing the spent sand from the extraction vessel, and

withdrawing an oil stream from the oil phase in the extraction vessel.

2. The improved process as claimed in claim 1, further including:

introducing steam to the extraction vessel at a point below the fluidized bed, and

steam scouring the sand particles to remove therefrom essentially all extraction stream constituents except inert solids.

3. The improved process as claimed in claim 1, wherein the tar sand is introduced into the reaction vessel at a point below the oil phase.

4. The improved process as claimed in claim 1, wherein the tar sand contains fines and the process further includes:

maintaining the fluidized bed condition of the tar sand such that effective tar sand-liquid extraction stream contact is provided and the sand is sufficiently suspended to act as a filter media for agglomerated fines, but insufficiently active to dislodge any fines which may be attached to the sand particles,

collecting the unattached fines in the separated water phase,

withdrawing the fines in the water phase along with the water stream,

recycling the water-fines stream to the vessel through introduction thereto at a point below the top of the fluidized bed,

removing the fines in the water-fines recycle stream by passing the stream through the sand in the fluidized bed condition to filter them,

withdrawing the sand and filtered fines from the vessel, and

withdrawing an oil stream, from the oil phase, with reduced content of contaminants such as fines.

5. The improved process as claimed in claim 1, wherein the liquid extraction stream includes dissolved oil extraction control agents selected from the group consisting of wetting agents and dispersing agents.

6. The improved process as claimed in claim 1, wherein the liquid extraction stream includes solvent which is fed to the extraction vessel at a point near the bottom of the fluidized bed and an oil-solvent phase is separated above the fluidized bed.

7. The improved process as claimed in claim 4 further including:

passing the withdrawn water-fines stream to a storage and treatment vessel, and

agglomerating the fines in the water-fines stream within the storage and treatment vessel prior to recycling the stream of the extraction vessel.

8. The improved process as claimed in claim 1 further including:

feeding a solvent to the extraction vessel at a point near the bottom of the fluidized bed,

vaporizing the solvent within the extraction vessel, and

separating an oil-solvent phase above the fluidized bed.

9. The improved process as claimed in claim 7, further including back washing the sand and fines withdrawn from the extraction vessel prior to dumping the same as tailings in order to assure that they are pollutant-free.

10. The improved process as claimed in claim 4, further including mixing the tar sand with hot water prior to introduction into the extraction vessel, the mixing to be sufficiently gentle to assure that any fines attached to the sand particles are not dislodged therefrom.

11. A closed cycle process for recovering oil from tar sand by extraction and phase separation comprising:

introducing the tar sand to a single stage extraction vessel;

flowing a liquid extraction stream countercurrent to the tar sand to maintain it in a fluidized bed condition;

separating an oil phase above the tar sand fluidized bed;

withdrawing an oil stream from the oil phase in the extraction vessel; and

withdrawing spent sand from the extraction vessel.