Abstract
In 1991, Canadian Occidental undertook the development of a new process designed for efficient extraction of bitumen from oil sands which would be suitable for employment at remote sites. The new process, Sand Reduction Technology (SRT), is based on the separation of solids from an oil sand slurry in a system of hydrocyclones. The sand and day in the slurry exit as a concentrated tails stream containing 70 to 75 percent solids. The remaining bitumen, water, and fine solids form an overhead stream containing 5 to 15 percent bitumen. The objective of this new program was to test process concepts for efficient removal of water from this stream to produce a concentrated bitumen product stream containing 40 to 75 percent bitumen.
Following a series of laboratory investigations, a small scale process development unit (PDU) was constructed in Canadian Occidental's laboratory in Tulsa to test the bitumen concentration process. The PDU was sized to feed 10 Ibs/min of oil sands to a slurry preparation unit which consisted of a heated tumbler. The slurry was screened to remove oversize solids and unconditioned oil sands and was then pumped to a one-inch hydrocyclone for separation of most of the slurry solids. The overhead stream from the hydrocyclone was tested in several process options to concentrate the contained bitumen, which averaged about 8 percent in this stream. Oil sands feed for this project was obtained from Syncrude Canada Ltd. and consisted of two grades described as "typical grade" and "low grade".
Twenty-two PDU runs were made from November 1993 through June 1994. The operating plan for each run included a start-up period in which process conditions were established, followed by a one-hour material balance period. Two basic bitumen concentration concepts were evaluated, with several variations of each. The first process concept was based on the flotation of bitumen from the cyclone overhead stream. A four-cell Denver flotation unit was employed for this phase of the project, which included eight PDU runs. Good bitumen recovery was achieved in the flotation tests with up to 99 percent retention of bitumen in this part of the process. The bitumen was also concentrated, with bitumen concentration in the flotation froth averaging greater than 40 percent during optimal run periods.
The second class of concentration concepts was based on the coalescence of the bitumen contained in the overhead stream to increase the average droplet size, followed by a rapid separation step. Laboratory tests showed that the small bitumen droplets in the overhead stream could be caused to coalesce with the application of shear under certain conditions. The first PDU tests of this concept utilized a two stage attrition scrubber which was used to apply shear energy to the dilute bitumen stream. A simulated bitumen recycle stream was blended with the overhead stream to increase the bitumen concentration which has been shown to enhance the coalescence operation. The product from the attrition scrubber was separated in a batch vessel from which bitumen was withdrawn and analyzed as a function of time and vessel depth. Bitumen concentrations up to 85 percent were achieved, but data regarding bitumen recovery could not be achieved in this type oftest.
A simpler variation of the coalescence concept was tested using a "static coalescer" which consisted of a series of static mixers through which the overhead stream and the simulated recycle stream were pumped. The coalesced product stream was then separated in the batch separation vessel, as in the earlier tests. Similar bitumen concentration results were obtained using the static coalescer as compared to those achieved in the attrition scrubber.
To improve the analysis of this process concept, a continuous separation vessel was constructed and utilized in the last series of six PDU runs.
Excellent bitumen concentration results were observed, with concentrations up to 72 percent in the overhead stream from the separator while 95 to 98 percent of the bitumen in the feed stream to the separator was recovered.
In summary, promising concepts were found for bitumen concentration. When these concepts are used in conjunction with the SRT process, the potential exists for a process which can be used to recover bitumen at remote sites relative to existing operations, thereby increasing the economically recoverable reserves of Canadian oil sands. Further work on this project should include development and testing of the static coalescence concept with full implementation of bitumen recycle. Additional laboratory evaluation of chemical additives which promote the coalescence of bitumen is also needed. Field tests of the combined SRT and bitumen concentration processes are dependent on future economic evaluations and the availability of funding.
