The present invention relates to a process for treating an aqueous oil sand slurry to enhance the probability of bitumen droplet contact and coalescence.
Oil sand, as known in the Fort McMurray region of Alberta, comprises water-wetted sand grains having viscous bitumen flecks trapped between the grains. It lends itself to separating or dispersing the bitumen from the sand grains by slurrying the as-mined oil sand in heated water so that the bitumen flecks disperse into the aqueous phase.
The bitumen in McMurray oil sand has been commercially recovered at applicant's plant for the past 25 years. Initially this was done using the following general scheme (referred to as the “hot water process”):
A fairly recent change with respect to this procedure involved:
It needs to be understood that the composition and processability of oil sand varies, often significantly. As a consequence, we have noted that, from time to time, the pipelined oil sand slurry produces unsatisfactory primary froth yield in the PSV. We believe that one reason for this may be that the residence time in the pipeline may be too short for that particular oil sand and that the bitumen droplets do not coalesce and grow to a size suitable for aeration and flotation.
With this background in mind, we have devised an apparatus and process for treating an aqueous aerated oil sand slurry to increase the probability that bitumen droplets will contact and coalesce to grow in size. In addition, small non-aerated droplets may coalesce and grow to a size that will readily aerate.
More particularly:
The preparation of slurry, pipelining and bitumen/sand separation of an aqueous oil sand slurry is known technology in the oil sand industry. Typically, the as-mined oil sand is pre-crushed to −24 inches using a double roll crusher 1. The crushed oil sand is then mixed with heated water and air and partly conditioned in a mixer 2. Oversize material is rejected by passing the slurry through a screen 3. The aerated slurry is collected in a pump box 4 and is then pumped through a pipeline 5, thereby advancing conditioning, and is introduced into a sand/bitumen separator 6, such as a cycloseparator.
In accordance with the present invention, a coalescer 7 is connected with the pipeline 5, upstream of the separator 6.
The coalescer 7 is an elongate, closed, preferably cylindrical vessel 8 forming an interior chamber 9 of circular cross-section. The vessel 8 has a tangential inlet 10 at one end. The inlet 10 is connected with the pipeline 5. At its opposite end, the vessel 8 has an outlet 11, preferably axial, which is connected with the separator 6.
In use, pipeline slurry is injected under pressure into the chamber 9 through the tangential inlet 10. The slurry rotates as it proceeds to advance longitudinally through the chamber 9. Under the influence of centrifugal force, the lighter bitumen and water migrate inwardly and the heavier sand migrates outwardly. The entire stream, now somewhat stratified, is expelled through the outlet 11 and is introduced back into the pipeline 5 and eventually into the separator 6 for separation of the bitumen and sand.
By centrally concentrating the bitumen droplets in the stream moving through the coalescer 7, a greater opportunity or probability is provided whereby the individual bitumen droplets may contact, coalesce and grow into larger droplets better able to unite with air bubbles to form buoyant bitumen. As a result, the performance of the separator 6 may be enhanced.
Although a preferred embodiment has been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims.
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Number | Date | Country | |
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20050082205 A1 | Apr 2005 | US |