Patent Application
20160348008
The present invention relates generally to a paraffinic bitumen froth treatment process using centrifugation to produce a fungible bitumen product.
Oil sand generally comprises water-wet sand grains held together by a matrix of viscous heavy oil or bitumen. Bitumen is a complex and viscous mixture of large or heavy hydrocarbon molecules which contain a significant amount of sulfur, nitrogen and oxygen. Oil sands processing involves extraction and froth treatment to produce diluted bitumen which is further processed to produce synthetic crude oil and other valuable commodities. Extraction is typically conducted by mixing the oil sand in hot water and aerating the resultant slurry to promote the attachment of bitumen to air bubbles, creating a lower-density bitumen froth which floats and can be recovered in a separator such as a gravity separator or cyclonic separator. Bitumen froth may contain about 60 wt % bitumen, about 30 wt % water and about 10 wt % solid mineral material, of which a large proportion is fine mineral material. The bitumen which is present in a bitumen froth comprises both non-asphaltenic material and asphaltenes.
Froth treatment is the process of significantly reducing the aqueous and solid contaminants from the bitumen froth to produce a clean diluted bitumen product (i.e., “diluted bitumen” or “dilbit”) which can be further processed to produce a fungible bitumen product that can be sold or processed in downstream upgrading units. It has been conventional to dilute this bitumen froth with a hydrocarbon solvent to reduce the viscosity and density of the oil phase, thereby accelerating the settling of the dispersed phase impurities by gravity or centrifugation. This diluted bitumen froth is commonly referred to as “dilfroth.” It is desirable to “clean” dilfroth, as both the water and solids pose fouling, corrosion and erosion problems in upgrading refineries.
Either a paraffinic or naphthenic type diluent may be used. The difference in the bitumen produced by use of either a paraffinic or naphthenic type diluent can be attributed largely to the presence of aromatics in naphthenic-type diluents. Aromatics have the ability to hold asphaltenes in solution, whereas paraffinic type diluents cause asphaltene precipitation. The use of naphthenic type diluents results in a relatively high bitumen recovery (generally greater than about 98%), but in a diluted bitumen product which has relatively high water (about 2 to 4 wt %) and solids (about 0.5 to 1.0 wt %) concentrations. The combined water and solids concentration typically is greater than about 2.5 wt %. Due to the level of contamination, which pose fouling, corrosion and erosion problems, the diluted bitumen is not suitable for direct pipelining to conventional refineries, cannot be sold to the open market, and must be upgraded using processes such as a coker or hydroprocessing. The upgraded products are then hydrotreated to produce synthetic crude oil.
Use of paraffinic type diluents results in a relatively lower overall bitumen recovery (generally about 90%), but in a bitumen product which is dry, light, and has a relatively low total water and solids concentration (less than about 0.5 wt %). However, paraffinic type diluents precipitate a major proportion of asphaltenes from the bitumen froth, resulting in not only the trapping of water and solids by the asphaltenes, but also high asphaltenic hydrocarbon losses (about 8%) to froth treatment tailings. There are both environmental incentives and economic incentives for recovering all or a portion of this residual asphaltenic hydrocarbon.
To separate the bitumen from water and solids, naphtha-treated bitumen froth is commonly subjected to 1 g gravity separation in inclined plate separators in series with high g centrifugation. Paraffinic-treated bitumen froth is typically subjected to phase separation and 1 g gravity separation, with sufficient space needed to accommodate large gravity separation vessels.
However, treatment processes using a naphthenic type diluent may still result in bitumen often containing undesirable amounts of solids and water. Product solids lead to increased wear of downstream equipment, higher maintenance costs, and unplanned capacity losses and outages. In addition, hydrocarbon may also be lost to tailings due to inefficient separation. Recovery of the solvent from the diluted bitumen product is required before the dry fungible bitumen may be delivered to a refinery for further processing.
Solvent and precipitated asphaltenes may also be lost to the tailings. Since the rejected asphaltenes (7-8 wt % of the original bitumen in froth) can be used as fuel or feedstock for various applications, the disposal of asphaltenes in the tailings pond is wasteful. Recovery of solvent is desirable to avoid discarding flammable, carcinogenic solvent in a tailings pond and to minimize expenditures for fresh solvent.
Accordingly, there is a need for a method of improving the quality of diluted bitumen product in bitumen froth treatment processes.
The present invention relates generally to a paraffinic bitumen froth treatment process using a decanter centrifuge to produce a fungible bitumen product. It was surprisingly discovered that by using the process of the present invention, one or more of the following benefits may be realized:
(1) The paraffinic bitumen froth treatment process of the present invention uses a decanter centrifuge to produce a fungible bitumen product amenable to downstream upgrading processes. Since a decanter centrifuge is used rather than multiple large gravity separation vessels, plot space requirements are reduced by about 70% and capital costs by about 50%.
(2) The hydrocarbon and fine solids loading on the tailings pond from froth treatment is reduced since the decanter centrifuge solids byproduct stream can be further processed in a flotation cell to recover asphaltenic hydrocarbon and fine solids.
(3) Precipitated asphaltenes in the form of a dry granulated powder are recovered and recycled at particular steps within the process for use as feedstock or fuel for various applications rather than being lost to tailings. This processable asphaltene byproduct may yield a saleable hydrocarbon liquid stream at a yield of about 40%.
(4) By recovering this asphaltenic hydrocarbon, diluent losses are reduced by about 20%. Recovery and recycling of paraffinic solvent at multiple steps within the process minimizes expenditures for fresh solvent makeup and reduces the losses of flammable, carcinogenic solvent in a tailings pond.
Thus, broadly stated, in one aspect of the present invention, a process for cleaning bitumen froth produced from an oil sands extraction process is provided, comprising:
In one embodiment, the ratio of paraffinic solvent to raw froth by weight percentage ranges from about 0.5 to about 4.5.
In one embodiment, the centrifuge is a decanter centrifuge. In one embodiment, the decanter centrifuge is operated to generate a g-force ranging from about 1000 to about 5000.
In one embodiment, the process further comprises processing the water byproduct stream to recover residual bitumen and paraffinic solvent.
In one embodiment, the process further comprises processing the solids byproduct stream to prepare a dry granulated powder comprising asphaltenes and fine solids.
For the purposes of the present invention, the term “fungible bitumen” is defined as a bitumen product wherein the sum of water and solids content is less than about 0.5 vol % to allow the hydrocarbon product to be able to be shipped down a pipeline to a conventional refinery.
The term “high g” decanter centrifuge is defined as a decanter centrifuge which is operated to generate a g-force ranging from about 1000 to about 5000.
Additional aspects and advantages of the present invention will be apparent in view of the description, which follows. It should be understood, however, that the detailed description and the specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
The invention will now be described by way of an exemplary embodiment with reference to the accompanying simplified, diagrammatic, not-to-scale drawing:
The detailed description set forth below in connection with the appended drawing is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments contemplated by the inventor. The detailed description includes specific details for the purpose of providing a comprehensive understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practised without these specific details.
The present invention relates generally to a paraffinic bitumen froth treatment process using a high g decanter centrifuge to produce a fungible bitumen product amenable to downstream upgrading processes. To meet specification requirements, the fungible bitumen product must have a total water and solids concentration of less than about 0.5 vol %.
In the process of the invention shown in
A diluent 16 is introduced via pump 18 into the in-line flow of raw froth 10. As used herein, the term “in-line” flow means a flow contained within a continuous fluid transportation line such as a pipe or other fluid transport structure which preferably has an enclosed tubular construction. In one embodiment, the diluent 16 is a paraffinic solvent. As used herein, the term “paraffinic solvent” (also known as aliphatic) means solvents containing normal paraffins, isoparaffins and blends thereof in amounts greater than 50 wt %. Presence of other components such as olefins, aromatics or naphthenes counteract the function of the paraffinic solvent and hence should not be present more than 1 to 20 wt % combined and preferably, no more than 3 wt % is present. The paraffinic solvent may be a C4 to C20 paraffinic hydrocarbon solvent or any combination of iso and normal components thereof. In one embodiment, the ratio of paraffinic solvent to raw froth (by wt %) ranges from about 0.5 to about 4.5.
Optionally, asphaltenes 20 in particulate form (i.e., asphaltene scavenger seed) may also be introduced via pump 22 into the in-line flow of raw froth 10 following addition of the diluent 16. As used herein, the term “asphaltenes” means hydrocarbons, which are the n-heptane insoluble, toluene soluble component of a carbonaceous material such as crude oil, bitumen or coal. Generally, asphaltenes have a density of from about 0.8 grams per cubic centimeter (g/cc) to about 1.2 g/cc. Asphaltenes are primarily comprised of carbon, hydrogen, nitrogen, oxygen, and sulfur as well as trace vanadium and nickel. The carbon to hydrogen ratio is approximately 1:1.2, depending on the source.
The mixture of raw froth 10, diluent 16, and/or asphaltenes 20 may then bypass or optionally, pass through a contactor 24 before being subjected to centrifugal separation. Mixing is conducted for a sufficient duration in order to allow the raw froth 10, diluent 16, and/or asphaltenes 20 to combine properly. Mixer settlers or columns are commonplace in the art and are exemplified by apparatuses including, but not limited to, stirred liquid-liquid extraction columns such as, for example, rotating disc contactors and the like. In one embodiment, the rotating disc contactor 24 is a mechanically agitated column which separates components of a mixture by adding to the mixture a suitable liquid solvent which dissolves or dilutes one or more components of the mixture, thereby facilitating their separation.
The mixture of raw froth 10, diluent 16, and/or asphaltenes 20 is subjected to centrifugal separation to yield a product stream comprising a diluted bitumen product 26 in line 36; and two byproduct streams, one comprising a separate water byproduct stream contaminated with trace diluent and hydrocarbon 28 in line 58; and the other comprising a solids byproduct stream 30 (sands, clays, asphaltenes) in line 80. In one embodiment, centrifugal separation is conducted using a three-phrase decanter centrifuge 32.
The operation of three-phase decanter centrifuges is commonly known to those skilled in the art and will not be discussed in detail. Briefly, the three-phase decanter centrifuge 32 separates solids and two liquid streams from a mixture thereof. The three-phase decanter centrifuge 32 comprises an elongated bowl mounted for rotation along its longitudinal axis. A helical screw conveyor is coaxially mounted within the bowl. A back drive features a direct drive gearbox for automatically controlling the differential speed between the bowl and the conveyor in order to maintain a balance between liquid clarity and solids dryness, irrespective of variations in the feed mixture. Since the bowl and conveyor are caused to rotate at controlled different, speeds, solids sedimented against the bowl wall are conveyed along the inner annular surface thereof to solids discharge openings provided at the tapered end of the bowl. The clarified liquid from which the solids have been removed is decanted into a chamber where two liquid phases with different specific gravities (e.g., a heavy liquid phase, a light liquid phase) may be separated. The liquids are separated in the liquid zone and decanted through separate discharge systems to prevent cross-contamination. In one embodiment, the three-phase decanter centrifuge 32 is operated to generate a g-force ranging from about 1000 to about 5000.
The product stream comprises the diluted bitumen product 26 which contains bitumen, diluent, and trace amounts of residual water and solids (possibly less than about 0.5 wt % total). The diluted bitumen product 26 is transferred from the decanter centrifuge 32 to a diluent recovery unit (“DRU”) 34 via line 36. Diluent 38 is recovered from the DRU 34 via line 40, and transferred to line 42 where it can be combined with make-up diluent 43 and/or diluent 16.
The bitumen product (“dry bitumen”) 44 free of water and mineral matter is recovered from the DRU 34 via line 46. As used herein, the term “dry bitumen” refers to dry or fungible bitumen having a solids content less than about 0.5 wt %. The dry bitumen 44 is transferred to either a storage unit 48 to be stockpiled for future use, a unit 49 for direct sale, or a fluid coker or ebullating-bed hydrocracker (“LC-Finer”) 50 for further processing into a synthetic crude oil product by means not shown but disclosed in the art. In general, fluid cokers upgrade heavy hydrocarbons to lighter products by removing carbon by thermal cracking. LC-Finers upgrade hydrocarbons in an ebullating catalyst bed by adding hydrogen in a hydroprocessing reaction. Virgin light gas oil (“LGO”) 52 is recovered from the DRU 34 via line 54, and further processed in downstream hydroprocessing units 56.
The water byproduct stream 28 comprises water, and residual hydrocarbon, diluent, and fine solids. The water stream 28 exits the decanter centrifuge 32 through line 58 and may then bypass or optionally, pass through a high speed disc stack centrifuge 60 before being subjected to a final cleanup in a solvent recovery unit (“SRU”) 62. The disc stack centrifuge 60 may be used in the event that the water stream 28 contains a significant amount of bitumen, light hydrocarbon, and solids.
The operation of disk stack centrifuges is commonly known to those skilled in the art and will not be discussed in detail. Briefly, the disc stack centrifuge 60 separates bitumen from water and solids using extremely high centrifugal forces. When the heavy phase (i.e., water and solids) is subjected to such forces, the water and solids are forced outwards against the periphery of the rotating centrifuge bowl, while the lighter phases (i.e., hydrocarbon) forms concentric inner layers within the bowl. Plates (i.e., the disc stack) provide additional surface settling area, which contributes to speeding up separation. The bitumen and diluent 64 is transferred from the disc stack centrifuge 60 to the DRU 34 via line 66 for separation and processing as previously described.
The water and residual diluent having residual hydrocarbon contaminants (nozzle plus heavy phase water) 68 is transferred from the disc stack centrifuge 60 to the SRU 62 via line 70. The SRU 62 separates the residual diluent from the water and fine solids by steam stripping to produce a diluent stream 72 which may be combined with diluent 16 prior to addition to the froth feed 10 in line 14. The SRU 62 also produces a water and fine solids stream 74 which is disposed via pump 76 to a tailings pond 78.
The solids stream 30 comprises asphaltenes, coarse and fine solids, residual diluent, and hydrocarbon. The solids stream 30 is slurried with hot water upon exiting the decanter centrifuge 32 through line 80 and enters a flotation cell 82 for separation of an overflow hydrocarbon rich with fine solids stream 84 and an underflow stream of clean coarse solids 86. The hydrocarbon rich with fine solids stream 84 is treated with diluent 88 in line 90 before being further combined in a mixer 92 and transferred to a spray drier 94 which uses nitrogen 96 as the hot gas for drying. Within the spray drier 94, the asphaltene-diluent mixture is pumped through high delta P atomizing nozzles to form a spray pattern of fine droplets. As these droplets form, any diluent is flashed off, leaving behind asphaltenes and fine solids in the form of dry granulated powdered solids 98 at the bottom of the spray drier 94. The solids 98 may be transferred to a storage unit 100 to be stockpiled for various future uses.
In one embodiment, the solids 98 may be combined with diluent 110 prior to addition to the froth feed 10 in line 14 (i.e., as asphaltene scavenger seed 20). The diluent 110 can be a combination of water with paraffinic or aromatic diluent.
In one embodiment, the solids 98 may be combined with bitumen 112 in a mixer 114, heated in a heater 116, and thermally upgraded in a fluid bed or delayed coker 118.
In one embodiment, the solids 98 may be injected into a fluidized bed gasifier or fluid bed boiler 120 which converts the solids 98 into a syngas which can be further processed to produce a synthetic natural gas or to produce liquid fuels.
In one embodiment, the solids 98 may be used as fuel for utility boilers which convert water into steam for electricity generation and process applications.
In one embodiment, the solids 98 may be directed to a land storage facility 122 to be stockpiled for future use as an energy supply.
The flashed overhead vapour comprising diluent and water 124 is condensed in an overhead exchanger system comprising an OVH condenser 126 and decanter 128 to separate the diluent 130 from the water 132. The diluent 130 is transferred via pump 134 into line 136 which connects with line 42 going to the diluent storage tank 16. The diluent 130 may be combined with diluent 72 from the SRU 62 prior to routing to the diluent storage tank 16. The water 132 may bypass or optionally, be pumped via pump 138 to pass through the SRU 62 for recovery of any residual diluent before disposal in the tailings pond 78.
Experiments were conducted to investigate the ability of a three-phase decanter centrifuge to separate a light phase product having a water content below about 2.0 wt % from naphthenic diluted froth. To mimic separation in a decanter centrifuge, a benchtop Hotspin™ centrifuge was run at particular speeds and spin times. Samples of naphthenic diluted froth contained bitumen (44 wt %), naphtha (26 wt %), water (22 wt %), and solids (8 wt %), with the N:B ratio being about 0.6. The samples were maintained at 80° C. and spun at 1500 rpm for 1, 2, 4, and 8 mins. Two samples were prepared for each spin time. The reported values are the average values between the two samples at each spin time.
Three distinguishable interfaces between light phase, heavy phase and solids were achieved in each sample after each centrifugation interval. The separated heavy phase became less turbid when spun longer, while the overall combined volume of heavy phase and solids remained relatively constant.
The amount of water present in the separated light phase was measured using Karl Fisher titration. The water content (wt %) in the light phase after the tested spin times (min at 1500 RPM) is shown in
With use of a three-phase decanter centrifuge, the light phase of the froth separated from the heavy phase and solids relatively quickly, while the solids separated from the heavy phase over a longer time frame. After initial separation, the water content of the light phase was less than about 2.0 wt %. Volumetrically, a significant amount of the solids were removed from the light phase. Based on these results, a three-phase decanter centrifuge is suitable for producing a light phase which meets froth treatment product specifications of less than about 2.0 wt % water.
An experiment was conducted to assess the feasibility of a three-phase decanter centrifuge to convey separated solids in a paraffinic diluted froth treatment process. Pentane (C5H12) and undiluted froth were mixed in diluent to bitumen (D/B) ratios of about 1.8, 2.8, 3.5, and 4.5 by weight. These samples were poured into 8 oz jars and cold spun (room temperature) for 20 minutes at about 2,000 RPM. After spinning in the centrifuge, the liquid phase was poured out leaving only the solids.
It was expected that separating paraffinic solids trapped in viscous medium might be challenging in a decanter centrifuge. However, it was observed that the paraffinic solids became more brittle and lost their cohesive or gummy texture with increasing D/B ratios (
From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. Thus, the present invention is not intended to be limited to the embodiments shown herein, but is to be accorded the full scope consistent with the claims, wherein reference to an element in the singular, such as by use of the article “a” or “an” is not intended to mean “one and only one” unless specifically so stated, but rather “one or more”. All structural and functional equivalents to the elements of the various embodiments described throughout the disclosure that are known or later come to be known to those of ordinary skill in the art are intended to be encompassed by the elements of the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims.
All publications mentioned herein are incorporated herein by reference (where permitted) to disclose and describe the methods and/or materials in connection with which the publications are cited. The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates, which may need to be independently confirmed.
