Embodiments disclosed herein relate to processes for recovering bitumen from oil sand and, more particularly, to processes for polishing diluted bitumen product, particularly that following paraffinic froth treatment processes, to remove residual impurities therefrom. BACKGROUND

Oil sands extracted from deposits, such as those found in Alberta, Canada, comprise water-wet sands that are held together by a matrix of viscous heavy oil or "bitumen". Various processes are required to liberate and separate the bitumen from its associated contaminants (e.g. water, sand, and clay), and to produce a marketable diluted bitumen ('dilbit') product having acceptable sediment specifications for pipeline transportation and downstream refining requirements.

Industrial separation of bitumen from its associated contaminants in froth treatment processes can involve the use of separators at various stages of the process. Typically after primary separation cell extraction, the resulting froth is treated to separate the bitumen from the water and solids. Naphthenic and paraffinic froth treatment process are employed.

In naphthenic froth treatment, separation typically requires the use of a plethora of various separation equipment, including counter-current decanters, cyclones, centrifuges and inclined plate separators, significantly adding to both capital and operating costs of the process in order to achieve minimum sediment requirements. Indeed, given a liquid density of dilbit of about 550-700 gm/liter and residual solid densities varying between 1400 to over 2700 gm/liter, some of the solids are not readily separable using conventional gravity separators. Thus, expensive and high maintenance centrifuges are usually required.

In high temperature paraffinic froth treatment processes, at least partial asphaltene precipitation occurs, bitumen-water emulsions being more effectively destabilized, resulting in improved separation. Regardless, the paraffinic processes still require the use of multi-stage and sizable froth separation units (FSUs) having high flux rates for rapid extraction of solids and water so as to meet minimum requirements.

As such, and notwithstanding that minimum sedimentation requirements are met, industry standard dilbit product contains residual small impurities that fail to settle out during known froth treatment processing. The presence of the residual small impurities impacts on the marketability of the product and increases the risk to downstream operation, including fouling of solvent recovery units, upgraders and refineries.

There is interest in providing apparatus and methodologies for rapidly purifying dilbit, following known froth treatment processes, to remove residual contaminants therefrom, producing a premium quality dilbit, improving marketability and reducing impact on downstream operations. SUMMARY

Embodiments of a process taught herein subject a dilbit product, which has been produced from a conventional process, and which may already meet downstream processing requirements, to a High-G force environment for further removal or substantial elimination of residual impurities, such as water and fine solids, therefrom. The resulting polished dilbit product may have impurities at least an order of magnitude less than the initial dilbit feedstream. Additional stages of polishing may be used.

In a broad aspect, a process for removing residual impurities in a dilbit product of a conventional oil sands paraffinic froth treatment process for treating the dilbit product comprising mainly hydrocarbons and the residual impurities for producing a polished dilbit product comprises feeding the dilbit product to an inlet of a separation chamber. The dilbit product is subjected to centrifugal forces sufficient to separate the impurities from the hydrocarbons, the impurities including at least water and non-mineral and mineral solids having a size less than about 70 microns. The polished dilbit product is removed as an overflow from the separation chamber. The separated impurities are removed as an underflow from the separation chamber.

In embodiments, the separation chamber is in a polisher vessel. The centrifugal force is 10-G or within the separation chamber. In other embodiments, the centrifugal force is 50-G or greater within the separation chamber.

Removal of the polished dilbit product is generally continuous. Removal of impurities from the underflow outlet can be semi-continuous or can be a batch discharge. A solids lock fluidly connected to the underflow outlet and/or the formation of a quiescent centrifugal area above the underflow outlet permits removal of the impurities, such as water and fine solids, when sufficient impurities are collected, without loss of valuable dilbit product. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 A is a flow chart illustrating flow of conventional, contaminated dilbit product from upstream froth separation processes to a polishing step, using a polisher such as a cyclone, prior to further downstream operations;

Figure 1 B is a partial sectional view of a conical bottom of the polisher of Fig. 1A illustrating a solids lock fluidly connected to an outlet at the conical bottom for periodic discharge of underflow therefrom, the solids lock being shown in dotted lines as being in addition to or alternate to a quiescent or low centrifugal area formed above a discharge outlet;

Figure 2 illustrates two stages of the polisher according to Fig. 1 A; and Figure 3 illustrates a polisher according to Fig. 1A having a recycle of polished dilbit product to the initial dilbit feedstream circuit.

DETAILED DESCRIPTION

In accordance with the present description, apparatus and methodologies, a process is provided for the removal of residual impurities from diluted bitumen or 'dilbit' product following known froth treatment processes, particularly paraffinic froth treatment. The process achieves a higher removal rate of such impurities than conventional froth separation processes. As described herein, the dilbit product is generally understood to be a partially de-asphalted bitumen product from froth separation units (FSU) used in known paraffinic froth separation processes. The dilbit product typically comprises about 99.5% or greater hydrocarbon and 0.5 wt% or less impurities, which include, but are not limited to water and mineral or non-mineral solids in the order of 70 microns and less in size.

Results from a particle size distribution of conventional dilbit product following conventional bitumen extraction processes show that at least some residual impurities, remaining following paraffinic froth treatment processes, comprise fine solids having particle sizes between approximately 0.01 microns to approximately 70 microns. Given their small size, extremely slow conventional settling processes, for example operated at an upward flux rate of about 20 mm/min, have generally been required to achieve separation of the fine solids from the dilbit product. FSUs used to achieve such low flux rates are typically very large and costly. Further, at such flux rates, Brownian motion and convection become relevant factors and can prevent separation in a 1 -G environment.

Further, despite the controls over the FSU operation, there can be periodic breakthroughs to the FSU overflow, carrying at least fine solids over to the dilbit product. These fine solids carryovers, though periodic can result in spot degradation or cumulative diminishment of the dilbit product.

While centrifuges and cyclones are known in oil sands processing, they are typically applied for removal of residual oil in tailings streams, such as from inclined plate setters (IPS), rather than to clean a final bitumen product. Cyclones are typically used in situations where the feedstream comprises at least 10% water, either as free water or in an emulsion, which is not the case for a conventional dilbit product.

Embodiments of apparatus and methodologies taught herein receive, as a feedstream, a conventionally cleaned dilbit product from known paraffinic froth treatment processes that meet minimum sedimentation standards. The conventional dilbit product is rapidly further purified or "super-cleaned" by the removal of residual impurities or periodic surge or carryovers of fine solids and water from the FSU, according to processes taught herein.

In embodiments, high-centrifugal forces (or High-G forces) are applied to the conventional dilbit product for successful separation of purified diluted bitumen from residual impurities including fine solids. In embodiments, such separation can be achieved at dilbit inlet velocities at about 0.7 m/s and greater. The initial circulation rate of the feed is at a minimum of about 1 cycle per second.

In embodiments described herein, a polisher, such as a cyclonic separator, operable at high gravitational forces (High-G force), receives the conventional dilbit feedstream containing residual impurities, for example, in the size range of about 0.01 to about 70 microns. Typically, dilbit product from conventional processes comprises about 0.5 wt% impurities or less and greater amounts periodically upon spontaneous carryover on upset or statistical periodicity. The High-G force is applied to the conventional dilbit for separating the feedstream into a purified dilbit product, for example having in the order of about 0.02 wt% solids or less. An underflow of the impurities is removed. A continuous feedstream- through-to-purified dilbit product process is advantageously coupled with a batch or semi-continuous fine solids waste or underflow removal for minimal dilbit product loss with the waste.

The term "high", with respect to the centrifugal or gravitational forces imparted by the polisher, is intended to mean an acceleration sufficient to apply a force to remove water and fine solids, such as having a size of less than about 70 microns, from the dilbit for producing a polished or super-cleaned product. More particularly, the impurities separated from the dilbit product have a size from about 0.01 microns to about 70 microns.

In embodiments, the polisher described herein is capable of providing a minimum High-G force environment of about 10-G. In other embodiments, the High-G force environment is about 50-G or greater.

The above-mentioned and other features of the present apparatus and methodology will be best understood by reference to the following description of the embodiments.

In the following description, "diluted bitumen product" or "dilbit product" refers to a partially de-asphalted, paraffinic froth treatment bitumen product, having been diluted with a suitable paraffinic solvent. The dilbit product is substantially free of water and a majority of mined solids, resulting from known paraffinic froth treatment processes. The initial dilbit product may comprise greater than approximately 99.5 wt% hydrocarbon and less than approximately 0.5 wt% of residual impurities (e.g. water, mineral, or non-mineral solids in the order of 70 microns or less). It is contemplated the initial dilbit product may already have sediment specifications that satisfy conventional, standard pipeline and refinery requirements.

FSU operation is also periodically subject to process upset or spontaneous carryover of at least fine solids which can result in off-spec impurities in the dilbit product. Embodiments provided herein describe final "polishing" processes for cleaning the dilbit product to further remove or substantially eliminate the residual impurities, mainly water and fine solids, therefrom. For example, apparatus and methodology taught herein may be used to produce a polished diluted bitumen, containing for example in the order of about 0.02wt% fine particles or less. The High-G force removes about 95% of the impurities at steady state and acts to intercept most of any carryover amounts.

With reference to Fig. 1A, and according to an embodiment, dilbit product from a paraffinic froth treatment process 10 is delivered as a dilbit feedstream 18 to a dilbit polishing apparatus or process, termed herein as a bitumen polisher 20. In the bitumen polisher 20, the dilbit feedstream 18 is subjected to High-G centrifugal forces for separation of residual impurities therefrom. The bitumen polisher 20 can be a low retention-time separator, capable of rapid extraction of in the order of 0.5wt% fine impurities therefrom, such as water, non-mineral or mineral particles. The non-mineral or mineral particles have, for example, mean particle sizes up to about 70 microns, and preferably have an average particle size of approximately 20 microns. In one embodiment, the high- centrifugal action of the bitumen polisher 20 may produce a polished, dilbit product 22 having impurities an order of magnitude less that in the initial dilbit feedstream 18.

With further reference to Fig. 1A, the bitumen polisher 20 may comprise apparatus having a separation chamber 23 having at least one feed inlet 24 for receiving the dilbit feedstream 18, a clean product outlet 26 at a top 25 of the chamber 23 for removing the polished diluted bitumen product 22, and an impurities or underflow outlet 28, such as at a conical bottom 27 of the chamber 23. The underflow outlet 28 is available for continuous or periodic removal of an accumulated and separated fine solids waste stream 30 extracted from the dilbit feedstream 18.

In one embodiment, said at least one feed inlet 24 may be in direct or indirect fluid communication with the bitumen extraction process 10.

In operation, the bitumen polisher 20 may be operated in a semi- continuous or semi-batch manner. For example, the dilbit feedstream 18 may be fed to the bitumen polisher 20 via the at least one feed inlet 24 substantially continuously for treatment, for subsequent, and substantially continuous, discharge from clean product outlet 26 as the polished diluted bitumen product 22 for transport to downstream operations, such as to a refinery 40. However, also continuously, or in a batch discharge only when sufficient impurities, generally water and fine solid particles S have accumulated in the chamber 23 to reach a pre-determined discharge threshold, the accumulated impurities may be discharged from the chamber 23 at underflow outlet 28 as the fine solids waste stream or underflow 30.

Open underflow, High-G cyclonic separators would not be suitable due to a continuous loss of hydrocarbon product with the collected impurities.

Herein, configurations include rotary locks, and screw conveyance devices for controlled removal of underflow streams therefrom. The batch, or periodic discharge of the underflow 30 has an advantage wherein loss of product or recovery of the polished diluted bitumen product 22 is minimized compared to some continuous solids waste underflow processes. In effect, a low centrifugal or quiescent zone Q, and, or in the alternative, a solids lock is provided at or adjacent the underflow outlet 28

Having reference to Fig. 1 B, in an alternate embodiment, the bitumen polisher 20 may comprise a High-G centrifugal separator, such as a cyclone, having the periodic or batch solids lock 32 fluidly connected to the underflow outlet 28. A periodic purge of the solids lock 32 discharges only settled impurities, such as fine solids and water, without disturbing the valuable polished diluted bitumen product 22 thereabove. With the solids lock 32 at the underflow outlet 28, only the impurities and potentially a small amount of product 22 are discharged, and only when enough impurities are collected to be purged. Thus, the batch solids lock 32 minimizes loss of valuable polished diluted bitumen product 22, as described above.

As shown in Fig. 2, the efficiency of removal can be improved with multiple stages of high-centrifugal force separators or polishers 20. As shown a first stage polisher 20a, routes the first stage polished diluted bitumen 22a to a second stage polisher 20b for removal of residual impurities therefrom to produce a second stage polished diluted bitumen product 22b. Underflow streams 30 are discharged from the first and second stage polishers 20a, 20b separately or can be combined.

Having reference to Fig. 3, a slipstream 36 of the polished bitumen product 22 from outlet 26 of polisher 20 can be recycled to the feedstream 18 for improving fines removal.

It is desirable that the bitumen polisher 20 be configured without any moving mechanical parts, thereby having lower capital costs, operational costs and maintenance costs. It is understood that while various elements required to operate the bitumen polisher 20 have been described herein, many additional, known elements, such as valves, pumps and other tanks interconnected with the bitumen polisher 20 not described herein can be used in the operation of the bitumen polisher 20.

Although a few embodiments have 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. The terms and expressions used have been used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding equivalents of the features shown and described or portions thereof.

Applicant tested an embodiment of the system, as shown in Fig. 1A, using a dilbit product from a conventional paraffinic froth treatment process as a feedstream 18. For the testing, a Lakos (Fresno, California) High-G separator with a solids purge transfer system was suitable. Solids S were collected in the bottom of the polisher 20 for discharge from the underflow outlet 28. While the resolution of solids removal was measured in mere ppm, the testing evidenced tangible collection and removal of solids with polisher purge indicating further removal of solids S from the dilbit product, resulting in improved downstream processing thereof.