Patent Application
20140151270
The present invention relates to a process of extracting bitumen from oil sand ores by adding a combination of sodium triphosphate 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 The bitumen froth, middlings and tailings are separately withdrawn.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” 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” 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 may create undesired consequences. Caustic is toxic and corrosive, impacting health and the environment and causing scaling on equipment. 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. Caustic disperses fines, hindering fines settling and tailings treatment. Higher caustic dosages induce bitumen emulsification which impairs froth treatment.
Accordingly, there is a need for a method of minimizing the amount of caustic used in bitumen extraction.
The current application is directed to a process of extracting bitumen from mined oil sand ores by adding a combination of sodium triphosphate 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 combined use of sodium triphosphate and caustic has a synergistic effect, improving bitumen recovery and froth quality in poor (low-grade high-fines) and good ores.
(2) For good ores, the combined use of sodium triphosphate and caustic does not have any negative impact on processability.
(3) The combined use of sodium triphosphate and caustic requires a lower amount of total chemical addition than the use of caustic alone, and is more effective at much lower dosages than caustic alone.
(4) The combined use of sodium triphosphate and caustic minimizes the amount of caustic, negating problems normally encountered by use of high caustic dosages. Sodium triphosphate is non-toxic to humans, animals, and the environment; a scaling and corrosion inhibitor; reduces the chances of bitumen emulsification; and hydrolyzes such that divalent cations captured in chelating form may be released for fine solids coagulation in tailings treatment; and the hydrolyzed species (e.g., ATP which is nutritious and essential to life) may positively impact the environment and land reclamation.
Thus, use of the present invention conserves the amounts of process aids in bitumen extraction, and improves bitumen recovery and froth quality.
In one 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 wt % to about 0.05 wt % of poor oil sand ore. In one embodiment, the sufficient amount of sodium triphosphate ranges from about 0.005 wt % to about 0.05 wt % of poor oil sand ore.
In one embodiment, the amount of caustic ranges from about 0 wt % to about 0.05 wt % of good oil sand ore. In one embodiment, the amount of sodium triphosphate ranges from about 0.003 wt % to about 0.009 wt % of good oil sand ore.
In one embodiment, the caustic is sodium hydroxide.
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 triphosphate 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 triphosphate and caustic are also added to the slurry preparation unit to aid in conditioning the oil sand slurry. As used herein, the term “sodium triphosphate” means the sodium salt of the polyphosphate penta-anion which is the conjugate base of triphosphoric acid. Synonyms, abbreviations, and other names for sodium triphosphate include STP, STPP, sodium tripolyphosphate, and TPP. Sodium triphosphate has the molecular formula Na5P3O10. Triphosphate is a chelating agent which binds strongly to metal cations such as, for example, calcium and magnesium. Since polyphosphates are hydrolyzed into simpler phosphates, polyphosphates are non-toxic to humans, animals, and the environment.
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 sufficient amount of caustic ranges from about 0.01 wt % to about 0.05 wt % of poor oil sand ore. In one embodiment, the sufficient amount of caustic ranges from about 0.01 wt % to about 0.05 wt % of good oil sand ore. In one embodiment, the caustic is sodium hydroxide.
The amount of sodium triphosphate is determined by the optimal caustic dosage and type of oil sand ore. In one embodiment, the dosage for each of caustic and sodium triphosphate 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 sufficient amount of sodium triphosphate ranges from about 0.005 wt % to about 0.05 wt % of poor oil sand ore. In one embodiment, the sufficient amount of sodium triphosphate ranges from about 0.003 wt % to about 0.009 wt % of good oil sand ore.
The sodium triphosphate 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 triphosphate and caustic are added to the heated water.
Following the addition of sodium triphosphate 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 bitumen separation vessel operates under somewhat more quiescent conditions to allow the bitumen droplets to rise to the top of the vessel and form bitumen froth, which 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 Example, which is 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, sodium triphosphate alone, and a combination of caustic and sodium triphosphate 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 triphosphate alone, and in combination with caustic. The dosages for caustic or sodium triphosphate did not exceed 0.05 wt % since higher dosages are impractical in plant 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):
R
c
=R
p
+R
s (2)
The total recovery (Rt) which is the sum of the primary, secondary, and wall bitumen recoveries was calculated using equation (3):
R
t
=R
p
+R
s
+R
w (3)
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%, 0.03% was selected as the dosage for further testing with sodium triphosphate addition. When the caustic dosage was further increased to 0.05%, the primary bitumen recovery increased to 32.2%.
The primary bitumen recovery and primary froth bitumen content generally increased with increasing chemical dosage (
For the primary froth solids content, sodium triphosphate alone or in combination with caustic (0.01 wt %) resulted in lower froth solids contents than the use of caustic alone (
For a fair comparison, the total chemical dosage (caustic and sodium triphosphate dosages) should be considered. When sodium triphosphate (0.01 wt %) and caustic (0.03 wt %) were combined, the total chemical dosage was 0.04 wt %. Compared to caustic alone (0.04 wt %), the primary recovery increased from 20.2% to 28.5% and primary froth bitumen content increased from 29.4% to 37% (Table 3). The results of primary bitumen recovery and primary froth bitumen content were grouped by the total chemical dosages for oil sand AR. For every group at the same total chemical dosage, the combined use of caustic and sodium triphosphate improved the primary froth quality. The primary bitumen recovery was also improved by the combined uses of caustic and sodium triphosphate, except for the case with a total chemical dosage of 0.03 wt %, at which the primary recoveries did not differ.
Similar to the primary bitumen recovery (
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 caustic dosage of 0.02 wt % was selected based on the raw primary froth amounts obtained from test series #1. Based upon the total bitumen recoveries, it appears that 0.01 wt % should be the optimal caustic dosage; thus, the caustic dosage of 0.02 wt % used in test series #3 was higher than the optimal dosage.
Sodium triphosphate performed much better than caustic in regards to primary bitumen recovery (
For the combination of caustic and sodium triphosphate, 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 for poor ore AD were grouped by the total chemical dosage (Table 5). For every group at the same total chemical dosage, sodium triphosphate alone or in combination with caustic outperformed caustic alone.
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.
Sodium triphosphate outperformed caustic, increasing the primary bitumen recovery (
The results of the primary bitumen recovery and the primary froth bitumen content for poor ore AAX were grouped by the total chemical dosage (Table 7). For every group at the same total chemical dosage, sodium triphosphate alone or in combination with caustic (0.03 wt %) performed significantly better than caustic.
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 and sodium triphosphate, alone or in combination, had little effect on the total bitumen recovery, but improved the primary bitumen recovery and froth quality.
The primary bitumen recovery was about 88% when no process aid was used (
Without any process aid, the primary froth bitumen content was 52.9% (
The effects of sodium triphosphate alone and in combination with caustic on combined bitumen recovery are shown in
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.
