Patent Grant
9469814
The present invention relates generally to a process of extracting bitumen from oil sand ores by adding sodium citrate or a combination of sodium citrate and caustic (sodium hydroxide) to condition the oil sand slurry.
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. The Athabasca oil sand deposits may be efficiently extracted by surface mining which involves shovel-and-truck operations. The mined oil sand is trucked to crushing stations for size reduction, and fed into slurry preparation units where hot water and caustic (sodium hydroxide) are added to form an oil sand slurry. The oil sand slurry may be further conditioned by transporting it using a hydrotransport pipeline to a primary separation vessel (PSV) where the conditioned slurry is allowed to separate under quiescent conditions for a prescribed retention period into a top layer of bitumen froth, a middle layer of middlings (i.e., warm water, fines, residual bitumen), and a bottom layer of coarse tailings (i.e., warm water, coarse solids, residual bitumen). The bitumen froth, middlings and tailings are separately withdrawn. The bitumen froth is de-aerated, heated, and treated to produce diluted bitumen which is further processed to produce synthetic crude oil and other valuable commodities.
“Fines” are particles such as fine quartz and other heavy minerals, colloidal clay or silt generally having any dimension less than about 44 μm. “Coarse solids” are solids generally having any dimension greater than about 44 μm. Oil sand extraction typically involves processing ores which are relatively high in bitumen content and low in fines content. However, there exists an abundance of “poor ores”, also referred to as “poor processing ores”, which alone yield poor bitumen recovery and consequently cannot be processed unless a high proportion of high-grade, good ores are blended into these dry ore feeds. “Poor ores” are oil sand ores generally having low bitumen content (about 6 to about 10%) and/or high fines content (greater than about 30%). In comparison, “good ores” or “good processing ores” are oil sand ores generally having high bitumen content (about 10 to about 12% or higher) and/or low fines content (less than about 20%).
Caustic is used in bitumen extraction to improve bitumen recovery and froth quality. Caustic promotes the release of natural surfactants from bitumen to the aqueous phase, precipitates divalent cations such as calcium and magnesium, modifies the electrical surface potential of bitumen and solids, adjusts the pH, and makes solids more hydrophilic, leading to better bitumen-solids separation. For an oil sand ore, there is normally an optimal caustic dosage at which the highest bitumen recovery can be obtained and the optimal dosage appears to be determined by both the fines content (Sanford, E., 1983, Can. J. Chem. Eng. 61:554-567) and the ore grade.
However, the use of caustic creates undesired consequences. Caustic is toxic and corrosive, impacting health and the environment and causing scaling on equipment due to precipitation of divalent cations when it is added to the slurry water for slurry preparation. Compared to the caustic dosage for good ores, a higher caustic dosage is required for poor ores, but does not necessarily improve bitumen recovery and froth quality. Poor ore feed often results in high PSV middlings' density and viscosity, leading to low recovery and poor bitumen froth quality. The current solution is to reduce the feed rate and to add more water at the price of lowering production. However, for some poor ores, the use of caustic alone does not provide sufficient improvement in processability. Caustic disperses fines, hindering fines settling and tailings treatment. Higher caustic dosages induce bitumen emulsification which impairs froth treatment.
Due to these problems, it is desirable to replace caustic with an alternative chemical, or to reduce the amount of caustic used in the extraction process. A great number of chemicals have been tested as an alternative for caustic, but were not as effective and economic as caustic.
Accordingly, there is a need for a method of minimizing the amount of caustic used in bitumen extraction while improving overall extraction performance, especially for poor processing ores.
The current application is directed to a process of extracting bitumen from mined oil sand ores by adding sodium citrate or a combination of sodium citrate and caustic to condition the oil sand slurry. It was surprisingly discovered that by conducting the process of the present invention, one or more of the following benefits may be realized:
(1) The use of comparable dosages of sodium citrate to sodium hydroxide that is currently used by the applicant generally resulted in higher overall bitumen recovery (%), in particular, when poor ore was used.
(2) The combined use of sodium citrate and caustic has a synergistic effect, improving bitumen recovery and froth quality in poor (low-grade high-fines) and good ores.
(3) For good ores, the combined use of sodium citrate and caustic does not have any negative impact on processability.
(4) The combined use of sodium citrate and caustic requires a lower amount of total chemical addition than the use of caustic alone, and was more effective at much lower dosages than caustic alone.
(5) The combined use of sodium citrate and caustic minimizes the amount of caustic, negating problems normally encountered by use of high caustic dosages. Sodium citrate is non-toxic to humans, animals, and the environment; a buffering agent or acidity regulator which can resist changes in pH; and a chelating agent which binds strongly to metal cations.
Thus, in one aspect, use of the present invention may conserve the amounts of process aids used in bitumen extraction and improve bitumen recovery and froth quality.
In one aspect, a process for extracting bitumen from an oil sand ore having a fines content up to about 60% and a bitumen content higher than about 6% is provided, comprising:
In one embodiment, the dosage of sodium citrate ranges from about 0.001 to about 0.1 wt % of the oil sand ore. In another embodiment, the dosage of sodium citrate ranges from about 0.01 to about 0.05 wt % of oil sand ore.
In one embodiment, the process further comprises adding a dosage of caustic (e.g., sodium hydroxide) to the process either prior to or during the mixing step or prior to or during the conditioning step or both.
In one embodiment, the dosage of caustic ranges from about 0.001 to about 0.1 wt % of the oil sand ore. In another embodiment, the dosage of caustic ranges from about 0.01 to about 0.05 wt % of oil sand ore.
In one embodiment, when the bitumen content of the oil sand ore ranges from about 6% to about 10% and the fines content of the oil sand ore is greater than about 25%, the caustic dosage ranges from about 0.01 wt % to about 0.05 wt % and the sodium citrate dosage ranges from about 0.003 wt % to about 0.05 wt %.
In another aspect, a process of extracting bitumen from oil sand ores having a fines content up to about 60% and a bitumen content higher than about 6% is provided, comprising:
In one embodiment, the amount of caustic ranges from about 0.01 wt % to about 0.05 wt % of oil sand ore. In one embodiment, the amount of sodium citrate ranges from about 0.003 wt % to about 0.05 wt % of oil sand ore. In one embodiment, the oil sand ore is poor processing ore having a bitumen content of about 6 to about 10% or a fines content greater than about 30% or both.
In one embodiment, the amount of caustic is about 0.01 wt % of good processing ore. In one embodiment, the amount of sodium citrate ranges from about 0.003 wt % to about 0.03 wt % of good processing ore.
In one embodiment, when the bitumen content of the oil sand ore ranges from about 6% to about 10% and the fines content of the oil sand ore is greater than about 25%, the caustic amount ranges from about 0.01 wt % to about 0.05 wt %, and the sodium citrate amount ranges from about 0.003 wt % to about 0.05 wt %.
In one embodiment, the caustic is sodium hydroxide.
In one embodiment, the sodium citrate is trisodium citrate.
Referring to the drawings wherein like reference numerals indicate similar parts throughout the several views, several aspects of the present invention are illustrated by way of example, and not by way of limitation, in detail in the figures, wherein:
The detailed description set forth below in connection with the appended drawings 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 practiced without these specific details.
The present invention relates generally to a process of extracting bitumen from mined oil sand ores by adding a combination of sodium citrate and caustic to condition the oil sand slurry.
In one embodiment of the process of the present invention useful in extracting bitumen from oil sand ores, oil sand is mined from an oil sand rich area such as the Athabasca Region of Alberta. The oil sand ore may comprise a fines content up to about 60% and a bitumen content greater than about 6%.
In addition to the oil sand and water, sodium citrate and caustic are also added to the slurry preparation unit to aid in conditioning the oil sand slurry. As used herein, the term “sodium citrate” means any sodium salt of citric acid including monosodium citrate, disodium citrate, and trisodium citrate. Synonyms, abbreviations, and other names for sodium citrate include citrosodine, citric acid trisodium salt dehydrate, 2-hydroxy-1,2,3-propanetricarboxylic acid trisodium salt, citnatin, citrosodine, citrine, and natrocitral. In one embodiment, sodium citrate comprises trisodium citrate having the molecular formula Na3C6H5O7.
In one embodiment, the process aids are added to the heated water. In another embodiment, the process aids are added directly to the slurry preparation unit. In another embodiment, the process aids are added prior to the conditioning step.
In one embodiment, the process aids comprises sodium citrate. The dosage of sodium citrate generally ranges from about 0.001 to about 0.1 wt %, depending upon the grade of oil sand ore (i.e., poor processing oil sand ore versus good processing oil sand ore). In one embodiment, the dosage of sodium citrate ranges from about 0.01 to about 0.05 wt %.
In one embodiment, the process aids comprises a combination of sodium citrate and caustic. The amount of caustic is determined by initially testing varying caustic dosages to elucidate the optimal caustic dosage which yields a desired primary bitumen recovery. In one embodiment, the amount of caustic ranges from about 0.01 wt % to about 0.05 wt % of poor oil sand ore. In one embodiment, the amount of caustic is about 0.01 wt % of good oil sand ore. In one embodiment, the caustic is sodium hydroxide.
The amount of sodium citrate is generally determined by the optimal caustic dosage and type/grade of oil sand ore. In one embodiment, the dosage for each of caustic and sodium citrate does not exceed 0.05 wt % since higher dosages are impractical in industrial operations due to costs and efforts to conserve process aids. In one embodiment, the amount of sodium citrate ranges from about 0.003 wt % to about 0.05 wt % of poor oil sand ore. In one embodiment, the amount of sodium citrate ranges from about 0.003 wt % to about 0.03 wt % of good oil sand ore.
The sodium citrate and caustic may be added to the water prior to mixing with oil sand, directly into the slurry preparation unit during mixing, or to the oil sand slurry prepared prior to hydrotransport/slurry conditioning. Preferably, the sodium citrate and caustic are added to the water.
Following the addition of sodium citrate and caustic, the oil sand slurry may be screened through a screen portion, where additional water may be added to clean the rejects (e.g., oversized rocks) prior to delivering the rejects to a rejects pile. The screened oil sand slurry is collected in a vessel such as pump box where the oil sand slurry is then pumped through a hydrotransport pipeline (slurry conditioning), which pipeline is of a adequate length to ensure sufficient conditioning of the oil sand slurry, e.g., thorough digestion/ablation/dispersion of the larger oil sand lumps, coalescence of released bitumen flecks and aeration of the coalesced bitumen droplets.
The conditioned oil sand slurry is then fed to a bitumen separation vessel (also referred to as a primary separation vessel or PSV), which operates under somewhat quiescent conditions to allow the bitumen droplets to rise to the top of the vessel and form bitumen froth. The froth over flows to the launder and is collected for further froth treatment. Tailings are either discarded or further treated for additional bitumen recovery.
Exemplary embodiments of the present invention are described in the following Examples, which are set forth to aid in the understanding of the invention, and should not be construed to limit in any way the scope of the invention as defined in the claims which follow thereafter.
Samples of three poor ores and one good ore were tested (Table 1). The three poor ores had bitumen contents ranging from 8.7% to 9.6%, with fines contents from 26% up to 39%. The good ore had a bitumen content of 11.9% and a fines content of 16%.
Batch extraction unit testing was conducted, using blended process water, conducting conditioning at 50° C., and testing different dosages of caustic alone, and a combination of sodium citrate and caustic to assess whether a combination of process aids might have a synergistic effect. The dosages were based upon the dry oil sand weight (500 g for each test). Initial tests involving addition of caustic alone were conducted to find an optimal caustic dosage for each ore, followed by subsequent tests involving addition of sodium citrate and caustic in combination. The dosages for sodium citrate or caustic did not exceed 0.05 wt % since higher dosages are impractical in industrial operations due to costs and efforts to conserve process aids.
The data were reconciled for material balance using the Bilmat™ program, Version 9.2, 2006 (Algosys Inc., Quebec, CA). The extraction performance was indicated by the primary, secondary, and wall bitumen recoveries (Rp, Rs, Rw), which were calculated using equation (1):
where R denotes bitumen recovery; M is the mass; X is the mass fraction; the subscript i represents either primary (p), secondary (s), or wall (w); and the subscripts f, B, and os stand for froth, bitumen, and oil sand, respectively.
The combined recovery (Rc) which is the sum of the primary and secondary recoveries was calculated using equation (2):
Rc=Rp+Rs (2)
The total recovery (Rt) which is the sum of the primary, secondary, and wall bitumen recoveries was calculated using equation (3):
Rt=Rp+Rs+Rw (3)
Poor Ore AR
For poor ore AR, the primary bitumen recovery was 11.6% when no process aid was used (Table 2). The addition of caustic improved processability. As the primary bitumen recovery did not substantially change when the caustic dosage was increased from 0.03 to 0.04 wt %, 0.03 wt % was selected as the dosage for further testing with sodium citrate addition. When the caustic dosage was further increased to 0.05 wt %, the primary bitumen recovery increased to 32.2%. The primary bitumen recovery and primary froth bitumen content generally increased with increasing chemical dosage (
For a fair comparison, the total chemical dosage (caustic and sodium citrate dosages) should be considered. The results of primary bitumen recovery and primary froth bitumen content grouped by the total chemical dosages for oil sand AR are summarized in Table 3. When sodium citrate (0.009 wt %) and caustic (0.03 wt %) were combined, the total chemical dosage was about 0.04 wt %. Compared to caustic alone (0.04 wt %), the primary bitumen recovery increased from 17.9% to 34.6% and primary froth bitumen content increased from 29.4% to 43.8% (Table 3). Even the lowest dosage of sodium citrate (0.003 wt %) in combination with caustic (0.03 wt %) improved the primary bitumen recovery and froth bitumen content compared to caustic alone.
For every group at the same/similar total chemical dosage, the combined use of sodium citrate and caustic improved both the primary bitumen recovery and primary froth bitumen content. However, it is preferred that the sodium citrate dosage be less than about 0.02 wt %.
Similar to the primary bitumen recovery (
Poor Ore AD
Poor ore AD processed reasonably well with a primary recovery of 70.2% and a total recovery of 87.7% when no process aid was used (Table 4). The addition of caustic improved processability. The caustic dosage of 0.03 wt % was selected based on the results obtained from test series #1.
For the combination of sodium citrate and caustic, the performance was generally better than caustic. Significant increases were observed for the primary bitumen recovery (
The results of primary bitumen recovery and froth bitumen content were grouped by the total chemical dosage (Table 5). For every group at the same total chemical dosage, the combination of sodium citrate and caustic outperformed caustic alone.
Pore Ore AAX
Ore AAX was a very poor processing ore. The primary bitumen recovery was low at 13.0% coupled with a low primary froth bitumen content at 19.7% when no process aid was used (Table 6). Even at the highest caustic dosage (0.05 wt %), the primary recovery remained low at 26.7%, and did not appear to change with the increased caustic dosage from 0.02 wt % to 0.04 wt %. The dosage of 0.03 wt % was thus not necessarily the optimal dosage.
The combination of sodium citrate and caustic outperformed caustic alone, increasing the primary bitumen recovery (
The combination of caustic and sodium citrate improved the combined bitumen recovery (
The results of the primary bitumen recovery and the primary froth bitumen content for pore ore AAX were grouped by the total chemical dosage (Table 7). For every group at the same total chemical dosage, the combination of caustic (0.03 wt %) and sodium citrate at varying dosages (0.003-0.02 wt %) performed significantly better than caustic alone.
Good Ore AR12
Testing of a good ore was conducted to confirm whether any of the process aids might have negative effects on the processability. Ore AR12 was a good processing ore, yielding a total recovery of 97.5% when no process aid was used (Table 8). Caustic alone (0.005-0.03 wt %), sodium citrate alone (0.003-0.03 wt %), and the combination of sodium citrate (0.003-0.03 wt %) and caustic (0.01 wt %) had little effect on the total bitumen recovery, but the combined use improved the primary bitumen recovery and froth quality.
The primary bitumen recovery was 88% when no process aid was used (
Without the use of any process aid, the primary froth bitumen content was 52.9% (Table 8). The primary froth bitumen content increased with increasing caustic dosage, reaching 61.7% at the highest caustic dosage (0.03 wt %). With sodium citrate (0.02 wt %), the bitumen content was 64%. With caustic (0.01 wt %) and sodium citrate (0.03 wt %), the primary froth bitumen content reached 70.3%. For the primary froth solids content (
The effects of sodium citrate alone and in combination with caustic on combined bitumen recovery are shown in
The results of the primary bitumen recovery and the primary froth bitumen content were grouped by the total chemical dosage (Table 9). For every group at the same total chemical dosage, the combination of caustic and sodium citrate at varying dosages performed significantly better than caustic alone.
Synergistic Effect of Caustic and Sodium Citrate
The combined use of sodium citrate and caustic is preferred due to having a synergistic effect. For each of the poor ores (AD, AAX and AR) and good ore (AR12), the overall performance was improved with the combination of reagents which enhanced the primary bitumen recoveries and froth bitumen contents compared to use of caustic alone (Table 10). Even a relatively low dosage of sodium citrate (0.003 wt %) may improve both the primary bitumen recovery and froth bitumen content compared to caustic alone. The combined use of sodium citrate and caustic required a lower amount of total chemical addition than the use of caustic, and was more effective at much lower dosages than caustic. The combined use of sodium citrate and caustic minimizes the amount of caustic.
The flowsheet is operated under two conditions as follows:
where WSEP stands for warm slurry extraction process and HUF stands for heat upfront process.
Samples of two poor ores and one average ore were tested (Table 11). The two poor ores had bitumen contents of 9.8% and 9.0%, with fines contents of 40.3% and 42.7%, respectively. The average ore had a bitumen content of 10.1% and a fines content of 29.5%.
Poor Ore AW-14-04-13
Poor Ore AW-14-04-13 was processed using the flowsheet pilot plant under both the heat upfront process (HUF) and the warm slurry extraction process (WSEP).
Poor Ore AT-14-06-19
Poor Ore AT-14-06-19 was processed using WSEP. As can be seen in
Average Ore AC-14-04-26
Average Ore AC-14-04-26 was processed using WSEP. As can be seen in
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