CA2068895A1 - Conditioning of oil sands and bitumen separation therefrom - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The invention relates to a process for the conditioning of oil sands to increase the amount of high fines reject to permit separation of the oil sands into a high fines fraction comprising 5 to 25 % of the feed and a low fines fraction comprising 95 to 75 % of the feed. Having separated the feed in this manner, a hybrid Hot Water Extraction/Anhydrous Extraction process may be advantageously employed to extract bitumen from the low fines and high fines fractions, respectively.

Description

This invention relates to a process for the conditioning o~ oi~ sands and similar hydrocarbon-solids mixtures, to enable the use of hybrid Hot Water Extraction (HWE)/Anhydrous Extraction (AÆ) to improve bitumen recovery from the oil sands~
Oil sands are sand deposits impregnated with a viscous hydrocarbon, bitumen, which occur in various locations throughout the world. One of the largest deposits, and currently the only one being commercially exploited on a large scale, is located in the Athabasca region of the Province of Alberta, Canada. Athabasca oil sands consist of a three component mixture of mineral matter, bitumen and water. The valuable component, bitumen, can range from nearly O up to 20 wt~ with an average value ~eing about 10 wt%. Connate water typically runs between 3 wt% and 6 wt%. The mineral matter is composed of sands, silts and clays and usually range between about 80 wt% and 90 wt% of the deposit. The fines are those mineral materials containing the clays, silts and fine sands, of particle sizes < 44 microns and particularly < 2 microns and are responsible for a great many processing problems.
Generally the clay content increases as the oil content or ore grade decreases For a more complete fines description see R.N~ Yong and A.J. Sethi, Mineral Particle Interaction Control of Tar sand Sludge Stability. The Journal of Canadian Petroleum Technology, Volume 17, Number 4 (October December 1978).

Currently Hot Water Extraction is being used commercially to exploit the surface mineable portion of this resource. In this approach the mined sand is first mixed with steam, hot water and chemicals in large rotating vessels, known as conditioning drums or tumblers. The tumblers serve to release the bitumen from the solid matrix as aerated droplets. The conditioning drum Oversize ~representiny less than about 5% of the ore) is first separated out. The bitumen is then separated from the residual sand slurry in two stages:
- By gravity separation in the primary separation vessel (PSV).
- By flotation from the PSV middlings stream in a series of conventional flotation cells.
The process is quite efficient, with bitumen recoveries of 90-94% being the norm for oil sands containing ten weight percent or more of bitumen. However, for feed of lower grade, or any ~eed containing significant amounts of fines, processing problems arise~ owing to dispersion of these fines in the aqueous phase. The fines also increase the viscosity of the middlings fraction and inhibit the gravity separation of bitumen. In the two commercially operating hot water plants, Syncrude and Suncor, it is the fines that are largely responsible for sludge accumulation and tailings disposal problems.
Several solvent extraction processes for the recovery of bitumen from oil sands have been proposed, with the object of overcoming ~he problems inherent to the h~t water process, but to this date no commercially acceptable process has reached fruition. The propensity for fines and other small particles to impede separation of the solids and bitumen solution has been a perennial problem and many techniques to overcome this difficulty have been devised.
One technique is to slurry the oil sand in an appropriate solvent after which the mineral matter is classified into a coarse fraction and a fines fraction. By so doing, the fines are removed and treated separately. This is done in order to avoid the problems of bed plugging in subsequent processing when the coarse mineral matter is washed and the solvent recovered. A typical example of this approach may be found in Canadian Pat. No. 1,169,002 June 12/84 G. B.
Karnofsky in which the mineral matter is classified into a major coarse fraction and a minor fines fraction. Solvent is then percolated through beds of the coarse sands to extract bitumen and to wash the sands, while an elaborate series of thickener~, clarifiers and filters are used to treat separakely the fines fraction.
Another technique is to add small amounts of water to encapsulate and agglomerate the small particles so that they behave like larger particles which will not migrate through the bed. Thus the addition of a minimal amount of water can improve filtration rates and greatly reduce bed plugging. This method should be ef~ective for oil sands containing low and medium amounts of fine mineral matter.

An example of this technique, using a high grade (low ~ines) feed containing more than 10% bitumen, may be found in Canadian Pat. No. 873,852 3une 22/71 A. M. Benson in which the filtration rates of the sand solvent mixtures are improved by the addition of water. Up to a total of only 7 water was used to form a "grainy slurry", rssulting in an increased filtration rate and elimination of the clay layer usually formed on top of the filter bed.
A method in which fines and sands are separated from the extraction solvent by an agglomeration technique is disclosed in applicants Canadian Patent No. 1,249,976, filed February 14, 1989 B. D. Sparks et al. In this solvent extraction, sand agglomeration (SESA) process the fines, in conjunction with an aqueous bridging liquid, are utilised to promote binding of the particles into large or small, dense, compact agglomerates which can be easily separated from the extractant by simple screening or filtering. By these means, feed containing both high and low fines is easily handled. However, this process has not been commercialized, apparently because of high risks associated with the development of a new technology.
Accordingly, by conditioning the oil sand to increase the relative amount of Oversize, the feed oil sand may be separated into a high fines fraction and a low fines ~raction. This separation permits the use of a hybrid Hot Water Extraction/Anhydrous Extraction process to recover bitumen from the separate fractions. As will be apparent hereinafter, the low fines fraction and the high fines fraction may be advantageously treated by Hot Water Extraction and Anhydrous Extraction, respectively.
According to the invention, a process for conditioning of oil sand comprising:
(a) mixing a feed oil sand with water, steam and 0 to 1.5 lb/ton of a monovalent alkaline reagent/ at a temperature of 50 to ao c for 3 to 6 minutes, wherein the water/oil sand ratio is 0.15 to 0.35; and (b) separating the oil sand into a high fines fraction consisting of 5 to ~5 %/w of the feed oil sand and a low fines fraction consisting of 95 to 75%/w of the feed oil sand.

In the drawing which serves to illustrate the embodiments of the invention, Figure 1 is a flow sheet illustration o~ a Hot Water Extraction process used in the present invention;
Figure 2 is a flow sheet of a Solvent Extraction Sand Agglomeration process used in the present invention;

Figure 3 is a ~low sheet illustrating the improved extraction process according ~o the invention;
Figure 4 is a graph illustrating the sludge reduction according to the invention; and Figure 5 is a graph illustrating the improved bitumen recovery of the SESA versus a HWE proc~ss for di~ferent grades of oil sands.
As seen in Figure 3, the feed oil sands (bituminous tar sands oil-bearing diatomite, oil-shale, tar-saturat~d sandstone and the like) is first conditioned and separated into a high fines fraction and a low fines fraction using the conditioniny drum and screen combination typically employed in the conventional HWE process. The conditioning drum is designed to produce a pulp (slurry) by mulling tar sands with steam and water. A monovalent alkaline reagent e.g. caustic soda, sodium carbonake or sodium silicate is also included to maintain a pH of 7.5 to 9. The conditioning drum comprises a cylindrical drum rotatable approximately around its longitudinal axis and fitted with a device to allow steam to be injected into the oil sands charge. Means to control feed of oil sand and water into the drum and means to controI exit of pulp (slurry~ from the drum are also provided. The pulp (slurry) is fed by gravity from the conditioning drum onto a screen (40mm mesh) to remove from khe tar sand pulp, rocks and lumps of oil sands that were not broken down in khe drum.
This coarse fraction is known as conditioning drum oversize.

The coarse (high fines) fraction contains a disproportionately high percentage of fines (-325 mesh) relative to the feed ore whereas the remaining tar sand pulp (low fines) fraction contains a relatively smaller percentage of fines. A typical prior art example of this apparatus is described in Canadian Patent number 918,588 of M.R. Smith et al., 9 January 1973. Figure 1 taken from that Patent schematically illustrates the apparatus.
Applicant has contemplated that the relative amount of the high fines fraction may be increased by controlling various processing parameters. In general, by controlling the processing temperature, amount of caustic additive, residence time (feed rate) and water/ore ratio, 5 to 25%/w of the feed ore can be separated as a high fines fraction.
The remaining 95 to 75 %/w constitutes a low fines fraction.
As a result, the clay lumps are rejected before they can break down into fine particles and disperse in water to interfere with the subsequent floatation process.
Referring first to the processing temperature, according to the aforementioned Canadian Patent number gl8,588, conditioning is effected within the range of 54 to 89~ C, and preferably at least 77 C. Applicant has found that as the temperature is lowered within a range of 80 to 50 C, the relative amount of the high fines fraction increases. The preferred temperature range is 50 to 65 C.
Energy is also saved by operating at lower temperature.

The amount of alkaline reagent used in Canadian Patent number 918,588 is in the range of 0.1 to 3.0 lbs/ton o~ oil sand feed. The amount added is regulated to maintain the pH
of the middlings in a range of 7.5 to 9 and preferably 8.0 to 8.5. The amount of alkaline addition will also depend somewhat on the grade of the feed oil sand. Applicant contemplates caustic addition in the range of 0 to 1.5 lbs/ton of oil sand feed. The preferred caustic addition for a feed oil sand of about 12 ~/w of bitumen is 0 to 1 lb/ton.
Re~erring to the residence time, which relates to the feed r~te, applicant has found that a range of 3 to 6 minute~ is effective. These times correlate with a feed rate of 1.5 to 2.4 tonnes/h. The preferred residence time is 3 to 4.5 minutes. Thus, by increasing feed rate, the process costs are reduced by increasing plant capacity.
Further, applicant lowered the water/ore ratio ~WOR) within the range of 0.15 to 0~22 for high grade (~ 10%/w of bitumen) feed, and 0.2 to 0.35 for low grade (< 10 % of bitumen). The preferred WOR for high grada feed is 0.15 to 0.18.
It will be appreciated that it is the combined effects of controlling these parameters which results in the increased relative amount of the high ~ines fraction.
Referring again to Figure 3, the low fines pulp (slurry) is then directed to a conventional Hot Water Extraction (HWE) plant such as that illustrated in Figure 1 in order to extrac~ the bitumen. By reducing the fines content of the HWE feed stream it is expected that a significant reduction in sludge will occur. The predicted result illustrated in Figure 4 confirms this expectation.
Improved bitumen recovery is also expected because ~WE
operates more ef~ectively on higher grade low fines materials.
As seen in Figure 3, the high fines fractlon (Oversize-see Figure 1) stream is simi]arly directed to an alternative extraction plant to extract the bitumen. Any substantially anhydrous extraction plant which produces substantially dry solid~ tailings may be used. One such process is a retorting process such as the AOSTRA Taciuk Process as descrihed in AOSTRA a 15 Year Portfolio of Achievement, 1990). Various solvent extraction techniques such as the aforementioned Karnofsky process may also be employed.
Applicant prefers however, to employ his own Solvent Extraction Sand Agglomeration (S~SA) technique described above and schematically illustrated in Figure 2.
Specifically, solvent extraction and solids agglomeration are carried out concurrently in ~ rotating contactor loaded with a charge of mixing media ~steel rods which help to break down the lumps in the feed). Rotation is relatively slow and is in the range of 10-20% of the critical speed. The solvent is a recirculated stream from the solid-liquid separation step and already contains some dis~olved bitumen. Water is added in sufficient quantity to produce agglomerates in the size range 0.5-1.5mm.
Operating temperature is 50 C.
Agglomerates and bitumen solution are discharged through a trommel screen to remove any large stones and then fed to a filter via a surge hopper. On the filter, the agglomerates are drained to remove the bulk of the bitumen rich solution and then countercurrently washed through three or four stages with progressively cleaner solvent. The final wash is clean solYent, a naphtha cut with a boiling range of 80-160 C. Underflow from the first wash provides the primary extraction solvent. After final drainage on the filter the washed agglomerates are transferred to the feed hopper of the residual solvent recovery system. The bitumen rich solution can be cleaned in existing froth treatment facilities.
A rotary dryer, with external heating and using steam as a blanketing atmosphere, is used for solvent recovery.
Operating conditions will be adjusted to give solvent levels of less than 0.2wtw% while leaving 5-6 w/w% water with agglomerates. These damp aggregates are transported to the mine site where they are used as fill.
Tailings pond sludge may be used in SESA as a source of process water to improve hitumen recovery. It will be appreciated that the amount of material to be processed by the coupled SESA plant is significantly lower than the total feed. Therefore, a relatively small scale SESA plant may be used. Accordingly, the equipment and overall costs would be lower than for a full scale SESA plant. Improved bitumen recovery is expected since SESA is particularly effective on hi~h fines feed as shown in ~'igure 5.
Thus, by separating the feed oil sand into high fines and low fines fr~ctions and increasing the relative amount of the high fines fraction, applicant is able to synergistically combine the best attributes of the HWE and solvent extraction (SESA) processes.
The substantially dry solids tailings from the SESA process and the water slurry tailings (of improved settling characteristics] from the HWE process are disposed of in the usual manner.
It will be appreciated that the process may either be operated as a batch process or as a continuous process.
In the examples which follow, example 1 can be considered a base case comparable to a stand alone H~E
process and represents the useful upper limits of the processing parameters which result in a high fines (oversize~ fraction of about 5%tw of th~ feed oil sands.
For convenience sake a feed rate of 100 t/h was used in example 1. However, it will be appreciated that in practice much higher feed rates are used. Example 2 describes treatment of the same grade (average Suncor plant feed grade) of oil sands feed and represents the useful lower limits of the relevant processing parameters.

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An oil sands feed comprising 12%/w of bitumen, 85%/w mineral solids and 3~/w of water (fines content 12 t/h) is fed to a conditioning drum (of the type described in aforementioned Canadian patent number 918,588) at the rate of 100 t/h, where it is mixed with steam, hot water and about 1.5 lb/t caustic soda at a temperature of about 80 C
for a residence time of about 6 minutes. The water/ore ratio is about 0.22. The resulting slurry is then ed by gravity to a separating screen (40mm mesh).
The low fines fraction which passes through the screen is then fed at a rate of 95 t/h (including bitumen 11.8 t/h and fines 9.1 t/h) to a conventional Hot Water Extraction plant of the type described in Figure 1 to extract the bitumen. Bitumen is recovered at a recovery rate of 11.14 t/h which represPnts a percentage xecovery (efficiency) oP 94.4~. The tailings slurry produced at a rate of 72 t/h includes fines (9.3 t/h) i.e. 77.5% of total in feed.
The high fines (oversize) fraction which will not pass through the screen is concurrently fed at a rate of 5 t/h (including bitumen 0.2 t/h and fines 2.9 t/h) to a small SESA reac~or as described in Fiqure 2. Bitumen is recovered at a rate of 0.16 t/h which represents a percentage recovery (efficiency~ of 80%. The substantially dry tailings include 2.7 t/h of fines which represents 22.5 % of the total in feed. The combined bitumen recovery (efficiency) based upon the feed is 94.1%.
~XAMPLE 2 The same oil sands feed as in example 1 is processed in the same manner as described in Example 1.
However, the caustic soda addition is up to about 0.5 lb/t.
The conditioning drum operating temperature is also reduced to about 50 C and the residence time is reduced to about 3 minutes. The feed rate is thus doubled to 200t/h. The water/ore ratio is reduced to 0.15. As a result, the high fines (Oversize) fraction is increased to 20 %/w of the feed i.e. 40 t/h ~including bitumen 3.2 t/h and 19.2 t/h of fines). The low fines fraction is reduced to 80%/w of the feed i.e. 160 t/h (including bitumen 20.8 t/h and 4.8 tlh of fines). The Low fines fraction processed by HWE produces bitumen at 20.2 t/h for a recovery (efficiency) of 97.1%.
The tailings slurry includes 4.6 t/h of fines representing 19% of the total in feed. The high fines (oversize) fraction processed by SESA recovers bitumen at a (efficiency) rate of 2.88 t/h for a recovery (efficiency) of 90%. The combined bitumen recovery (efficiency) based upon the feed is 96.2%. The dry tailings include 19 t/h of fines which represents 79% of that in feed.
BXAMPhE 3 The same oil sands feed as in example 1 is processed in the same manner as described in Example 1.
However, the caustic soda addition is 0.5 to 1 lb/t. The conditioning drum operating temperature is also reduced to about 65 C and the resid~nce time is reduced to about 4 ~ 5 minutes. The feed rate is thus 150t/ho The water/ore ratio is reduced to 0.18. As a result, the high fines (Oversize) fraction is increased to 12 %/w of the feed i.e. 18 t/h (including bitumen 1.2 t/h and 7.9 t/h of fines). The low fines fraction is reduced to 88%/w of the feed i.e. 132 t/h (including bitumen 11.8 t/h and 8.1 t/h of fines). The Low fines fraction processed by HWE produces bitumen at 16.1 t/h for a recovery (efficiency) of 95.8%. The tailings slurry includes 7.8 t/h of fines representing 43% of the total in feed. The high fines (oversize) fraction processed by SESA
recovers bitumen at a (efficiency) rate of 1.02 t/h for a recovery (efficiency) of 85%. The combined bitumen recovery (efficiency~ based upon the feed is 95.1%. The dry tailings include 9.75 tlh of fines which represents 54% of that in feed.
It will thus be appreciated that the combination of reductions in temperature, amount of caustic added, residence time and water/ore ratio, result in an increase in the relative amount of the higher fines (oversize) fraction.
Also, by comparing the results of examples 1 and 2 it is apparent that on the HWE side bitumen recovery (efficiency) is increased from 94.4% to 97.1% and the fines produced decreases from 77% of total i~ feed to 19% of total in feed.
On the SESA side, the bitumen recovery ~efficiency) is also increased from 80% to 90%. The combined bitumen recovery (efficiency) is also increased from 94.1% to 96.2%.

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Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for conditioning oil sand, comprising:
(a) mixing a feed oil sand with water, steam and 0 to 1.5 lb/ton of a monovalent alkaline reagent, at a temperature of 50 to 80° C for 3 to 6 minutes, wherein the water/oil sand ratio is 0.15 to 0.35;
and (b) separating the oil sand into a high fines fraction consisting of 5 to 25 %/w of the feed oil sand and a low fines fraction consisting of 95 to 75%/w of the feed oil sand.

2. A process according to claim 1, which includes the additional steps of;
(c) extracting bitumen from the low fines fraction by hot water extraction;
(d) extracting bitumen from the high fines fraction by a substantially anhydrous separation method; and (e) disposing of the tailings from steps (c) and (d).

3. A process according to claim 2, wherein the monovalent alkaline reagent is selected from the group consisting if caustic soda, sodium carbonate and sodium silicate.

4. A process according to claim 2, wherein the conditioning temperature is 50 to 65° C.

5. A process according to claim 4, wherein the conditioning time is 3 to 4.5 minutes.

6. A process according to claim 5, wherein the water/feed oil sand ratio is .15 to .18.

7. A process according to claim 6, wherein the feed oil sand contains about 12%/w of bitumen.

8. A process according to claim 7, wherein the alkaline reagent is caustic soda in an amount of 0-1 lb/t.

9. A process according to claim 4, wherein the process is a continuous process.

10. A process according to claim 1,2,3,4,5,6,7,8, or 9 wherein step (c) the separation is effected by solvent extraction sand agglomeration.