Patent Application
20100275600
The application claims priority from Canadian Patent Application number 2,610,052 which was filed on 8 Nov. 2007, which is incorporated herein by reference.
The present invention relates generally to oil sands mining. More particularly, the present invention relates to a system and method of recovering heat and water from oil sands tailings using a vacuum flash process. The water recovered from this process can be used for steam generation in thermal recovery operations, extraction, utility purposes or other processes recognized by those skilled in the art requiring the use of water, steam or a combination thereof.
Oil sands are sand deposits which in addition to sand, contain clays, connate-water and bitumen. Depending on geographic location, bitumen may be recovered by mining or in-situ thermal methods. Examples of thermal in-situ recovery processes include but are not limited to steam-assisted gravity drainage (SAGD), cyclic steam stimulation (CSS), and various derivatives thereof, such as solvent-assisted SAGD (SA-SAGD), steam and gas push (SAGP), combined vapor and steam extraction (SAVEX), expanding solvent SAGD (ES-SAGD), constant steam drainage (CSD), and liquid addition to steam for enhancing recovery (LASER), as well as water flooding and steam flooding processes. Recovering the highly viscous bitumen from the oil sand poses numerous challenges, particularly since large quantities of heat and water are required to extract the bitumen. Further, most oil sand deposits are located in remote areas (such as, for example, the Fort McMurray area of northern Alberta, Canada), which can contribute to increased costs for transportation and processing, especially in harsh weather conditions.
Oil sand ore in a mining and extraction operation is typically processed using mechanical and chemical techniques to separate the bitumen from the sands. One of the most common extraction techniques is bitumen froth flotation. Hot water, air and process aides are added to the sands, resulting in the formation of an oil-rich froth that “floats” or rises to form a distinct hydrocarbon phase that can be separated from the aqueous layer. The waste ore (sand, clay, rock, other wastes) in combination with the spent processing water and reagents from the plant are known as tailings.
The properties of tailings are dependent on the ore body being mined, the grinding and processing circuits, the reagent properties and the thickening process prior to disposal. Tailings can be disposed of or stored in a variety of different methods. Unfortunately, the overall oil sands extraction process creates a large volume of waste requiring disposal. The extraction of one barrel of bitumen requires approximately 1 m3 of water. This water is stored in the tailings pond for years before the fines settle and some of the water recycled to the extraction process. The long settling times result in large tailings ponds.
An additional improvement to the overall oil sands extraction process is to enhance the total energy efficiency. In the current process, heat is added to water for use in the hydrotransport and conditioning of ore. Tailings that are generated via the current aqueous process are subsequently released to storage ponds at warm temperatures (20° C. to 90° C.), resulting in heat loss to the environment. The loss of energy is compensated by increasing the input of energy at the front end of the system. Thus, there has been a need to reduce input energy by recovering energy from the available waste streams.
Attempts to recover heat, water and other reagents used in the oil sands extraction process have been described in the prior art. U.S. Pat. Nos. 4,343,691, 4,561,965 and 4,240,897 are directed to heat and water vapor recovery from tailings for use in the extraction process using a humidification/dehumidification cycle. Brown et. al (U.S. Pat. No. 6,358,403 B1) describes a vacuum flash process for the purpose of recovering hydrocarbon solvents used in the extraction process. Heated tailings (˜80° C.) are subjected to a mild vacuum (˜35 kPaa) in order to flash and recover naphtha or paraffinic solvents. This particular scheme also included the addition of steam to enhance hydrocarbon recovery. However, there has been a lack of recent success in achieving effective energy and resource conservation methods, despite the progress made in oil sands bitumen extraction technology and the increasing global awareness of industrial environmental impacts.
In these and other methods, the amount of heat and water recovered from tailings by these methods is low (in the range of 0-5%). This has made very little impact on the oil sand bitumen extraction process. Thus, there exists a need to more efficiently and successfully recover residual heat and water for downstream uses. A more efficient recovery method of heat and water would also reduce costs and improve environmental performance. It is, therefore, desirable to provide a cost effective and environmentally sound process to recover residual heat and water from tailings, thereby reducing the amount of required energy during the oil sands extraction process.
Generally, the present invention provides a method to recover heat and water from a warm slurry, such as warm tailings from an oil sands extraction mining operation. The method comprises providing the tailings to a vacuum vessel, removing, from the vacuum vessel, warm water vapor derived from the tailings, condensing the warm water vapor in a condenser to produce high quality water suitable as a feed source for steam generation, and recovering the water from the condenser. Cool water from any surface, subterranean or process-affected source destined for industrial use can be subsequently warmed with the heat from the condensation of the vapor for additional uses in the mining operation. Water of high quality suitable for use in steam generation can be obtained in the process. This can also be achieved using one or more flash vessels in series to produce and condense the vapor. Power can also be generated from the vapor using a turbine.
In a first aspect described herein, there is provided a method of recovering water of high quality suitable for steam generation (utilizing OTSG's, (once through steam generators) drum boiler or any other method known in the art) from a warm slurry (consisting of water, solids and hydrocarbons, for example), comprising the steps of: providing the slurry to a vacuum vessel; removing, from the vacuum vessel, warm water vapor derived from the slurry; condensing the warm water vapor in a condenser to produce liquid water; and recovering the high quality water from the condenser. Slurry remaining in the vacuum vessel after removal of the warm vapor is typically cooled and de-aerated, when compared to the added oil sands slurry.
The warm slurry feed for the process described in this invention can be any tailings stream, typically 20° C. to 90° C., generated during the oil sands extraction process. The liquid product recovered from the tailings is typically water, which when condensed is essentially pure. In the event that light hydrocarbons are present in the tailings stream, the recovered fluid may contain both high quality water and light hydrocarbon liquid.
Condensation of the vapor can be accomplished by cold water supplied to the condenser, such as from river or process-affected water sources. Alternately, cold water from any surface subterranean or industrial source or third party source may be used. The cold water absorbs the latent heat of condensation, which represents a significant percentage of the thermal energy which would be otherwise lost to the environment
Alternately, condensation of the water vapor can be achieved with any available heat sink. In certain embodiments, cold ambient air intended for combustion equipment could be used to condense the water vapor; the cold air condenses the water vapor and absorbs energy, therefore increasing the overall energy efficiency of the process. As an example, pipelined natural gas is typically throttled to a lower pressure upon entering an industrial site. This throttling causes a temperature drop according to the nature of the fuel and process conditions. The heat sink developed presents a cooling source that is independent of seasonal weather conditions. In the event where water is provided through a long pipeline, a near constant temperature is established, thus minimizing any seasonal temperature variations of the cold water supply or heat sink.
In another aspect of the present invention there is provided a method of recovering high quality water from a warm slurry (such as warm tailings, as described above) using a multistage flash process, comprising the steps of: providing the warm slurry to a first flash vessel, partially vaporizing the warm slurry in the first flash vessel to produce water vapor, condensing the water vapor in the first flash vessel via a cooling conduit (or possibly due to a rise in pressure) to form liquid, and recovering the high quality water for useful purposes.
Warm slurry not vaporized in the flash vessel can be processed in one or more additional flash vessels in series, if desired. Water vapor produced in the one or more additional flash vessels is condensed in a similar manner as in the first stage.
In a further aspect, the present invention provides a method of generating power from warm tailings obtained from an oil sands extraction process, comprising the steps of: providing the warm tailings to a vacuum flash vessel to produce water vapor, and providing the vapor to a turbine to generate power. In one embodiment, vapor from the turbine is provided to a condenser to condense the vapor, thereby producing cold water condensate.
In yet another aspect of the present invention there is provided a closed-cycle method of generating power from warm tailings obtained from an oil sands extraction process, comprising the steps of: providing the warm tailings to an evaporator containing a working fluid to produce working fluid vapor, and providing the working fluid vapor to a turbine to generate power. In one embodiment, the working fluid vapor is provided to a condenser to condense the working fluid for further use in the initial evaporation process. Rather than condensing tailings vapor, cold water is supplied to the condenser to condense the working fluid vapor, absorb the heat of condensation, and as a result increase the overall thermal efficiency of the mining operation.
The working fluid can be any suitable fluid, but is typically ammonia, ammonia-water mixtures or propylene.
In a further aspect, the present invention provides a system for recovering heat or water from an oil sands slurry comprising: a separation vessel for separating bitumen froth from the slurry; a vacuum vessel for removing warm vapor from the slurry; and a condenser for condensing the warm vapor to produce water.
In yet another aspect, the present invention provides a system for recovering heat and water from an oil sands slurry comprising: a separation vessel for separating bitumen froth from the slurry; a first flash vessel for receiving the slurry, wherein the first flash vessel vaporizes a portion of the slurry to produce a vapor; and a condenser for condensing the vapor to liquid water.
Any slurry not vaporized in the flash vessel is processed in one or more additional flash vessels in series.
In still another aspect, the present invention provides a system for generating power from an oil sands slurry, comprising: a flash chamber for vaporizing a portion of the slurry to produce vapor; and a turbine to generate power from the vapor. The system can further comprise a condenser to condense the vapor from the turbine, thereby producing a condensate.
In yet another aspect, the present invention provides a closed-cycle system for generating power from an oil sands slurry comprising: an evaporator containing a working fluid, wherein slurry added to the evaporator produces working fluid vapor; and a turbine from generating power from the working fluid vapor. The system can further comprise a condenser for condensing the working fluid vapor for further use in the evaporator.
Recovering both the water and the heat required to condense water vapor rather than allowing the low temperature heat to be lost to the atmosphere provides economic uplift by reducing makeup energy requirements for bitumen extraction, provides improved environmental performance through a reduction in greenhouse gas emissions and provides a reduction in fresh water use.
Methods in accordance with the present invention produce high quality water for bitumen extraction, boiler feedwater or other industrial purposes, thereby improving environmental performance by reducing freshwater requirements.
An added benefit to the vacuum process is the reduction in corrosion rates for pipe and equipment due to the inherent de-aerating of the tailings. Thus, non-metallic linings or coatings can be used in the piping and equipment used in the system or method of the present invention.
One advantage over direct heat recovery methods and systems known in the art (such as heat exchangers) is that no heat transfer surface contacts the tailings; the fouling and erosion/corrosion issues known to be present are virtually eliminated.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.
Embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein:
Many aspects of the present invention can be better understood with reference to the above drawings. The elements and features shown in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating principles of exemplary embodiments of the present invention. Moreover, certain dimensions may be exaggerated to help visually convey such principles. In the drawings, same reference numerals designate like or corresponding, but not necessarily identical, elements throughout the several views.
Generally, the present invention provides systems and methods for recovering heat, water or power from an oil sands slurry, but is applicable to any process utilizing or generating aqueous slurry or mine tailings.
In one aspect of the present invention there is provided a method of recovering high quality water from a warm oil sands slurry, comprising the steps of: providing the slurry to a vacuum vessel; removing, from the vacuum vessel, warm water vapor derived from the slurry; condensing the warm water vapor in a condenser to produce high quality water suitable as feed water for steam generation or the like; and recovering the water from the condenser.
In another aspect of the present invention there is provided a system for recovering heat or water from an oil sands slurry comprising: a separation vessel for separating bitumen froth from the slurry; a vacuum vessel for removing warm vapor from the slurry; and a condenser for condensing the warm vapor to produce high quality water, wherein the latent heat of condensation can be recovered.
As used herein, a “slurry” can refer to tailings obtained from an oil sands extraction process, but can be any solid-liquid mixture used or generated in mining or industrial operations from which heat and/or water can be recovered.
Typically, tailings from any source can be used. In accordance with exemplary embodiments of the present invention, tailings removed from oil sands processing methods known in the art can be used. The raw oil sands are heated and conditioned to extract bitumen from which hydrocarbon products are obtained. The tailings usually comprise residual hydrocarbons (or bitumen), sand, and water and are typically at elevated temperatures (20° C. to 90° C.) and thus contain residual heat. In most oil sands operations, tailings are discarded to open pits commonly referred to as “tailings ponds”. Residual heat is allowed to be released to the atmosphere, while process affected water is retained for potential future reuse with some loss to evaporation.
The vacuum vessel (14) can be any appropriate chamber suitable for receiving tailings or related slurries. The vacuum is established by any means known in the art—a vacuum pump (30) is shown in
The higher temperature of the vapor provides advantages by increasing the temperature difference between the vapor and cold water. This could result in a reduction in required surface area, and consequently a lower capital cost. An exemplary embodiment of the process, with the addition of a steam ejector, has features which are similar to steam-jet refrigeration cycles known in the art. There are, however, some important differences. One aspect of the present invention is to capture the heat and recover water for other useful purposes. A secondary compressor (30) can also be used in the system, to evacuate non-condensable gas to the atmosphere. While the exemplary embodiment in
The water vapor generated in the vacuum vessel (14) must be condensed to provide liquid. As the water required for the bitumen extraction process is available from surface, subterranean or process affected water sources at a cooler temperature than the vapor, this water can be used to provide a heat sink and condense the vapor and in turn is heated, reducing the energy requirements for the mining operation.
The heat required to condense the vapor is roughly the same as the heat removed from the tailings. For the typical conditions envisioned of 35° C. tailings flashed to 2 kPaa (kilo Pascal absolute), this is approximately 75 kJ per kg of water (˜4.18 kJ/kg-° C.). The energy can be absorbed by cold river water as an energy conservation method. As one example, cooling 150,000 m3 per day of water by 18° C. and concomitant heating of river or pond water can result in a financial savings of about $55,000 (Canadian Dollars)/day, at an energy cost of $5 (CAD)/GJ.
In another aspect of the present invention there is generally provided a method of recovering heat and water from a warm slurry using a flash process, comprising the steps of: providing the warm slurry to a first flash vessel; vaporizing the warm slurry in the first flash vessel to produce water vapor; condensing the vapor in the first flash vessel to remove water from the vapor; and recovering the water.
Further, the present invention provides a system for recovering heat or water from an oil sands slurry comprising: a separation vessel for separating bitumen froth from the slurry; a first flash vessel for receiving the slurry, wherein the first flash vessel vaporizes water from the slurry to produce water vapor; and a condenser for condensing the water from the vapor.
In the configuration shown in
Ideally, fresh water production from an open cycle scheme in accordance with at least one aspect of the present invention could amount to about 3% of the gross throughput, with tailings water cooled to roughly 17° C. from an initial 35° C. It is also recognized that higher water recoveries are achieved in circumstances when the tailings water exhibits a temperature greater than 35° C.
Optionally, a direct contact condenser (not shown) can be used if segregation of the condensed water is not required.
Adjusting the final flash pressure will also control the final temperature. A lower pressure provides additional vapor, and a greater net heat recovery from the tailings. If the heat sink temperature rises to where no condensing can occur due to seasonal variation, flashing to a higher pressure will still provided some heat recovery at a higher temperature. For 35° C. tailings, one could expect that the temperature could be reasonably adjusted between about 17° C. and about 29° C., for example.
Power and Fresh Water Generation
In another aspect of the present invention there is generally provided a method of generating power from warm tailings obtained from an oil sands extraction process, comprising the steps of: providing the warm tailings to a vacuum flash vessel to produce vapor; providing the vapor to a turbine to generate power, and a condenser to capture the water vapor as liquid for reuse.
Further, the present invention provides a system for generating power from an oil sands slurry, comprising: an vacuum flash vessel for vaporizing the slurry to produce vapor; and a turbine to generate power from the vapor. The system can further comprise a condenser for condensing the vapor.
Energy from heat sources has been generated in water desalination processes, such as in the Ocean Thermal Energy Conversion (OTEC) system. This system relies on the naturally occurring temperature difference between surface ocean water in the tropics and cold water from the depths to generate power and desalinated water. Many different schemes have been described in the art (such as U.S. Pat. No. 4,430,861, U.S. Pat. No. 5,582,691, U.S. Pat. No. 5,555,838, U.S. Pat. No. 4,430,861, and elsewhere). Unlike the present method, the schemes described in the art are intended to use temperature differences available in nature, and do not consider similar temperature heat sources from industrial processes. The low temperature differences imply very large low rates in order to produce useable power, and such flow rates are not common in industrial applications. In addition the application of this concept in an oil sands mining operation is significantly different in that a slurry is utilized rather than seawater. The density of the slurry may be as high as 1600 kg/m3 and the sensible heat contained in the solids will typically contribute to increased vapor production.
Due to the large volume of warm tailings water in bitumen mining operations, the heat can be used for generating power. Bitumen mines have flow rates and heat source/sink temperatures which are conducive to a favorable generation of power.
Typically, in the context of a 20° C. temperature difference, a flow rate of 4 m3/s is required to produce 1 MW of electricity. For most of the year, oil sands mining operations offer potentially available heat sinks of greater than 20° C. temperature difference. Any additional temperature gradient above 20° C. would, ideally, allow for additional electricity to be generated. For instance, mine tailings could be expected to be discharged at 35° C., and during winter months river (or pond) water would be less than 5° C., providing a net difference of 30° C.
As an alternative of the scheme exemplified in
In yet another aspect of the present invention there is provided a closed-cycle method of generating power from warm tailings obtained from an oil sands extraction process, comprising the steps of: providing the warm tailings (donor fluid) to an evaporator containing a receptor fluid to produce receptor fluid vapor; and providing the receptor fluid vapor to a turbine to generate power.
Further, the present invention provides a closed-cycle system for generating power from an oil sands slurry comprising: an evaporator vessel containing a receptor fluid, wherein a donor fluid (for instance, slurry) supplied to the evaporator vessel produces receptor fluid vapor; a turbine from generating power from the receptor fluid vapor, and a condenser for condensing the receptor fluid vapor for further use in the evaporator vessel.
The person of ordinary skill in the art would readily appreciate any source of warm water could easily be integrated into any of the schemes described herein, not only from thermal bitumen production.
Table 1 shows examples of the heat recovered from an exemplary heat/water recovery scheme in accordance with one aspect of the method of the present invention. The table shows results modeled from steam tables with no consideration of the sensible heat of solid particles.
The overall liquid recovery would provide a significant percentage of the water required for either utility purposes, or boiler feed water for a thermal recovery operation (SAGD). As an example, if the slurry volume was 150,000 m3/day, a 3.5% recovery would provide 5,250 m3/d of high quality water suitable for steam generation, while at the same time providing 12,800 GJ of recovered energy. The overall economic incentive of the process could result in the production of 1750 m3 bitumen (SOR 3:1) if the water was utilized for an in-situ thermal operation and as well as an energy cost savings exceeding $50,000/(Canadian Dollars)day (natural gas=$55 CAD/GJ).
The above-described embodiments of the present invention are intended to be examples only. Alterations, modifications and variations may be effected to the particular embodiments by those of skill in the art without departing from the scope of the invention, which is defined solely by the claims appended hereto.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2610052 | Nov 2007 | CA | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US08/79576 | 10/10/2008 | WO | 00 | 6/29/2010 |
