Patent Grant
10544369
The present invention relates generally to a bitumen froth treatment process for removing contaminants, namely water, asphaltenes and particulate solids, to produce a variety of deasphalted oil (DAO) products which can be directly upgraded in a conventional oil refinery.
Oil sand, as known in the Athabasca region of Alberta, Canada, comprises water-wet, coarse sand grains having flecks of a viscous hydrocarbon, known as bitumen, trapped between the sand grains. The water sheaths surrounding the sand grains contain very fine clay particles. Thus, a sample of oil sand, for example, might comprise 70% by weight sand, 14% fines, 5% water and 11% bitumen. (All % values stated in this specification are to be understood to be % by weight.) The bitumen recovered from Athabasca oil sand is generally very viscous and has an API gravity of less than 10 due to the large amount of heavy ends, such as residue and asphaltenes.
For the past 25 years, the bitumen in Athabasca oil sand has been commercially recovered using a water-based process. In the first step of this process, the oil sand is slurried with process water, naturally entrained air and, optionally, caustic (NaOH). The slurry is mixed, for example in a tumbler or pipeline, for a prescribed retention time, to initiate a preliminary separation or dispersal of the bitumen and solids and to induce air bubbles to contact and aerate the bitumen. This step is referred to as “conditioning”.
The conditioned slurry is then further diluted with flood water and introduced into a large, open-topped, conical-bottomed, cylindrical vessel (termed a primary separation vessel or “PSV”). The diluted slurry is retained in the PSV under quiescent conditions for a prescribed retention period. During this period, aerated bitumen rises and forms a froth layer, which overflows the top lip of the vessel and is conveyed away in a launder. Sand grains sink and are concentrated in the conical bottom. They leave the bottom of the vessel as a wet tailings stream containing a small amount of bitumen. Middlings, a watery mixture containing solids and bitumen, extend between the froth and sand layers.
The wet tailings and middlings are separately withdrawn, combined and sent to a secondary flotation process. This secondary flotation process is commonly carried out in a deep cone vessel wherein air is sparged into the vessel to assist with flotation. This vessel is referred to as the TOR vessel. The bitumen recovered by flotation in the TOR vessel is recycled to the PSV. The middlings from the deep cone vessel are further processed in induced air flotation cells to recover contained bitumen.
The froths produced by the PSV and flotation cells are then combined and subjected to further froth cleaning, i.e., removal of entrained water and solids, prior to upgrading. Typically, bitumen froth comprises about 60% bitumen, 30% water and 10% solids. It is understood, however, that these values can vary depending upon the grade (e.g., bitumen content and/or fines content) of the mined oil sand ore. There are currently two commercially proven processes to clean bitumen froth. One process involves dilution of the bitumen froth with a naphtha solvent, followed by bitumen separation in a sequence of scroll and disc centrifuges. Alternatively, the naphtha diluted bitumen may be subjected to gravity separation in a series of inclined plate separators (“IPS”) in conjunction with countercurrent solvent extraction using added naphtha, or some combination of both.
While the hydrocarbon recovery is very high when using naphtha dilution (˜98%), there remains an undesirable amount of contaminants in the product bitumen comprised of mostly solids and water (e.g., 1% and 2%, respectively) and asphaltenes. It is understood that these values can vary depending upon the quality of the bitumen froth. These contaminants contained therein pose a risk to the downstream upgrading operation; the chlorides in the residual water present a corrosion risk to processing equipment while the solids and asphaltenes foul the upgrading equipment and reduce catalyst life. Thus, the majority of the bitumen product must first be upgraded using fluid coking units. The requirement to thermally crack the majority of this product stream comes with additional drawbacks in the last phase of the upgrading process (e.g., hydrotreating/hydroprocessing); the thermally cracked coker products now require significantly higher catalyst addition rates due to fouling of the catalyst active sites, hydrotreating intensity requirements are much higher for cracked product streams and more hydrogen per barrel of feed is required to complete the final upgrading step. Finally, the conventional froth treatment naphtha process produces Fluid Fine Tailings (FFT), which is difficult to reclaim, and has significant losses of solvent (naphtha) to the tailings pond.
The other commercial process involves diluting the bitumen froth with a paraffinic solvent, for instance a mixture of iso-pentane and n-pentane, followed by gravity separation. When paraffinic solvent is used, a portion of the asphaltenes in the bitumen is also rejected by design, thus achieving solid and water levels that are lower than those in the naphtha-based froth treatment. Thus, some of the product streams by-pass the fluid coker primary upgrading step. Also, a moderate reduction in hydrotreating intensity would be expected in processing partially DAO product streams.
However, with the paraffinic process there is a much lower hydrocarbon recovery (˜92%), with significant losses of volatile solvent (pentane) to tailings. The process also produces FFT, which, as mentioned, is difficult to reclaim.
Broadly stated, in one aspect of the invention, a process is provided for treating bitumen froth whereby a deasphalted oil (DAO) product is produced that qualifies as “fungible bitumen”, i.e., bitumen of a pipelineable quality, which is suitable for upgrading in most conventional refineries. More particularly, a process for treating a bitumen froth comprising bitumen, solids and water to produce a deasphalted oil product is provided, comprising:
In one embodiment, a solvent is added to the raw or diluted bitumen froth and the raw or diluted bitumen froth is separated in an extraction vessel operating at a temperature and a pressure so that the solvent is at or near supercritical conditions.
As used herein, “diluent” generally refers to a hydrocarbon diluent such as naphtha or paraffin.
In one embodiment, the solvents useful for supercritical extraction includes CO2, water, toluene, methanol, naphtha, C3 to C5 alkanes and the like and mixtures thereof. In one embodiment, the solvents are C4 and C5 alkanes and mixtures thereof. Generally, extraction vessels of the present invention are operated at a temperature of about 32-250° C. and at a pressure of about 3-24 MPa so that the solvent acts as a supercritical solvent or an “anti-solvent”. Of course, it is understood that the temperature and pressure of the extraction vessel will depend upon the solvent or solvent mixture used, as well as the solids concentration present.
The term “supercritical solvent” or “anti-solvent” means a solvent or mixture of solvents in a supercritical state whereby the solvent (or mixture of solvents) exhibits properties of both a gas and a liquid; liquid-like in terms of its density and gas-like in terms of its diffusivity and viscosity.
It was discovered that certain solvents at supercritical state disrupt the solubility of asphaltenes (and to some extent maltenes) and essentially cause the bitumen to reject them.
In one embodiment, the asphaltene-solids by-product is processed in a fluid or delayed coker, or a gasifier. In another embodiment, the asphaltene-solids by-product can be processed in a combustor for steam or power production. In another embodiment, the asphaltene by-product can be stockpiled for future use.
One or more of the following advantages may be realized when practicing an embodiment of the invention:
In one aspect, the invention is concerned with a process for treating a bitumen froth comprising bitumen, solids and water to produce a deasphalted oil product, thereby eliminating the need for extensive bitumen froth cleanup. A cleaner product, e.g., less solids and water, is produced for upgrading which reduces many of the problems associated with the conventional froth treatment processes utilizing naphtha as a diluent. Further, the hydrocarbon losses are less than when using the paraffinic froth treatment process.
With reference now to
The raw or diluted bitumen froth (bitumen froth S100) is introduced into a separation vessel (Concentrator P101), which Concentrator may be a supercritical solvent extraction process, which is described in more detail in
The heavy bitumen fraction S103 and a solvent S109 (which may include CO2, water, toluene, methanol, naphtha, C3 to C5 alkanes or mixtures) is introduced into an extraction vessel (Purifier P102), which Purifier operates at a particular temperature and pressure so that the vessel operates as a supercritical solvent extraction vessel. Thus, the solvent S109 acts as a supercritical solvent to separate the components present in the heavy bitumen fraction S103. For example, if the solvent is CO2, extraction conditions are above the critical temperature of 31° C. and critical pressure of 74 bar.
In the Purifier P102, the heavy bitumen fraction S103 may be separated into a variety of deasphalted oil (DAO) products, if needed be, such as a heavy gas oil S104, a light DAO S105 and a heavy DAO S106, and byproduct streams of a dry asphaltenes-solids S108 and water S107. The DAO products can be further treated, if needed be, in hydroprocessing units or refinery processing units. The by-product water S107 can be reused in the oil sands operations. The by-product asphaltenes-solids S108 can be processed in a fluid or delayed coker, or a gasifier, or a combustor for steam or power production. The by-product asphaltenes-solids S108 can also be stockpiled for future use.
In one embodiment, as shown in
The light bitumen fraction S205 is removed from the top of the extraction vessel V201 and fed to a heating device H203 (which may be a heater or heat exchanger) and heated to a desired temperature. The heated light bitumen fraction S207 is introduced into an extraction vessel V202, where light bitumen fraction S209 (comprises light gas oil) is produced. Light gas oil can be further treated, if need be, in a hydrotreating unit (not shown). The overhead stream S208, which may comprise diluent and solvent, of the extraction vessel V202 is introduced to a separating device V203 (which may be a fractionator or splitter). A stream of solvent S210 is produced which can be reused as solvent stream S201 to dilute more bitumen froth. A diluent stream S211 (if using diluted bitumen froth) is also produced which can be reused to dilute bitumen froth from the extraction process (not shown).
In one embodiment, as shown in
In the extraction vessel V301, the feed is separated into two phases: a light phase S306 comprising solvent and extractable oil product and containing primarily oils and resins and a heavy phase S307 comprising the asphaltenes by-product, which contains most of the organometallics and coke-forming carbonaceous matters, fine solids, water and some solvent.
In one embodiment, as shown in
In one embodiment, as shown in
In another embodiment shown in
In another embodiment shown in
Additional supercritical solvent is added to the second heavy ends stream S503′ and the second heavy ends stream S503′ is then treated in a third extraction vessel V503 (referred to as supercritical fluid clean-up), which vessel is also operated at an elevated temperature and pressure to maintain supercritical conditions. Some deasphalted oil (DAO) (Stream S522) is produced (Products) and most of the dry asphaltenes-solids and water (Stream S524) are produced (By products). Both the DAO Products and the By-products can be further treated as discussed above.
The supercritical solvent can be recovered from all three extraction vessels and reused in the process.
Small scale batch experiments were performed using Supercritical CO2 with and without co-solvents that included water, naphtha, toluene, methanol, pentane and mixtures thereof, to determine the solubility of bitumen in the supercritical fluid. Table 1 shows the solubility data obtained using supercritical CO2 with different co-solvents at 60° C. and 20 MPa. Replicate experiments were performed for each case.
Table 1 shows that of the solvents tested, bitumen was most soluble in the supercritical mixture of CO2, methanol and toluene, which suggests that this combination of solvents would work well in a supercritical froth treatment process.
The following table was published in Reid, Robert C., J. M. Prausnitz, and Bruce E. Poling. 1987. The Properties of Gases and Liquids. New York: McGraw-Hill and gives critical properties for components commonly used as supercritical fluids.
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.
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