CA1290275C - Microbubble flotation process for the separation of bitumen from an oilsands slurry - Google Patents

Abstract

"MICROBUBBLE FLOTATION PROCESS FOR THE SEPARATION
OF BITUMEN FROM AN OIL SANDS SLURRY"
ABSTRACT OF THE DISCLOSURE
An improvement is provided to the known hot water process for extracting bitumen from mined oil sand. More particularly, a methodology is provided for the production of microbubbles of air, and it has been found that the so-produced microbubbles can be used in the primary flotation/settling step of the hot water process to yield increased bitumen recovery. More particularly, a steam stream and an air stream in admixture are injected via a submerged nozzle into a flowing aqueous stream. A plurality of finely dispersed microbubbles are formed. These microbubbles have a diameter less than about 100 microns.
The stream of microbubbles is injected into the diluted aqueous tar sand slurry formed in the hot water process. The injection is practiced following the conditioning step and prior to the introduction of the slurry into the flotation/settling step.

Description

~x 90~75 1 FIELD OF THE INVENTIO~

2 The invention relates to an improvement to the

3 known hot water process for extracting h~drocarbons (commonLy

4 referred to as 'bitumen') from mined oil sand. More particularly, the invention relates to a form of improved 6 aeration in the process.

8 Geological depositions of oil sand, also known as 9 tflr or bituminous sand, occur for example in the Athabasca region of Alberta, Canada.
11 Commercial processes for extracting and refining 12 the bitumen to yield useful hydrocarbon products fro~ the oil 13 sand have long been in operation.
14 In these operations, the basic procedure involves re~oving the overburden and mining the oil sand. The 16 hydrocarbon is then extracted from the oil sand utilizing a 7 process known as the hot water process. The recovered l8 hydrocarbon is upgraded in a hydrotreating facility to 19 convert it to a refineable product.
It is the physical nature of the oil sand per se 21 which renders it amenable to successful processing using the 22 hot water extraction process .
23 The composition of oil sand comprlses bitumen, 2~ water, quartz sand and clays. The quartz sand forms the major component. The clay particles are contained in a water 26 matrix which forms a film around each sand grain. The 27 bitumen is disposed in the interstices between the water-2a sheathed grains. The presence of the water envelope, , .

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~Z90~5 1 interposed between the hydrocarbon globules and sand grains, 2 provides the basis whereby the bitumen may be separated from 3 the sand by means of a water addition mechanism.
4 In order to successfully carry out the hot water process, it is necessary to first separate the bitumen from 6 the solids particles and then selectively aerate the bitumen 7 g].obules so that the latter float upwardly as a recoverable 8 upper froth layer.
9 Thus the process relies on the density differentials within an aqueous slurry of the solids, water 11 and bitumen, and the use of a selective separatory froth 12 flotation process ~herein the solids sink and the bitumen 3 rises to form the froth.
4 More specifically, the first step of the hot water process involves an operation referred to as 'conditioning'.
16 In this step, the mined oil sand is mixed in a horizontal 17 rotating drum, or 'tumbler', with hot water and process aid 18 ttypically sodium hydroxide). The amounts of reagents added 19 are in the following proportions- oil sand - 3250 tons; hot water - 610 tons; and NaOH - 4 tons. The hot water is 21 typically at a temperature of about 90 C. Steam is sparged 22 into the drum contents at intervals along the length thereof 23 to trim the temperature so that the slurry exit temperature 24 iB about 80 C. The residence time in the drum is about four minutes.
26 The conditioning operation is undertaken for 27 several reasons. The water is added to dlsplace the bitumen 28 and solids particle away from each other. The hot water and 29 steam cooperate to raise the temperature of the slurry. This ~ 30 will lower the viscoslty of the bitumen and thus enhance its :: :

~.290~75 1 displacement from the solids by ~ater. The higher 2 temperature also increases the density differential between 3 the bitumen and water. This facilitates the separation 4 therebetween in the subsequent flotation/separation stage which follows conditionin~. Additionally, as the slurry 6 undergoes agitation in the tumbler, beneficial entrainment of 7 air bubbles therein results.
8 Following conditioning, the thick aqueous slurry is 9 screened to remove rocks, oversi~.e oil sand and clay lumps.
The screened slurry is then diluted or 'flooded' with 1l additioual hot water before being pumped into the 12 flotation/settling vessel(commonly referred to as the 3 'primary separation vessel' or 'PSV'). The thus diluted 4 slurry will be referred to hereinafter as 'the diluted aqueous slurry'. The slurry at a point prior to its 16 dilution will be referred to hereinafter as 'the slurry'.
17 The composition of the diluted aqueous slurry 18 typically comprises 7% wt. bitumen; 43~ wt. water; and 50 19 solids.
The diluted aqueous slurry is then pumped into the 21 PSV. This open-topped vessel comprises a cylindrical upper 22 section and a conical lower section. The aqueous slurry is 23 retained in ~he PSV under quiescent conditions for a period 24 of time, typically in the order of twenty-five minutes. The solids, largely sand, sink to the vessel bottom, are 26 concentrated by the conical wall, and are withdrawn from the 27 vessel as an underflow stream termed 'primary tailings'. A
28 major portion of the bltumen, present in the form of 29 suspended globules filmed over entrained air bubbles, rises rapidly to the top of the PSV to form bitumen-rich froth.

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~ 4 ~(32~5 1 This froth is termed 'primary froth'. Primary froth 2 typically has a hydrocarbon content in excess of 60% wt.
3 Less buoyant or inherently less floatable bitumen, 4 together with a subst&ntial portion of the clay particles, remains in aqueous suspension between the settled sand and 6 the floating froth layers. This suspension is referred to as 7 'middlings'. The aqueous phase of the suspension is termed 8 'process water'.
9 The hot water process further includes a secondary 0 recovery circult. More particularly, a stream of middlings 11 is withdrawn from the PSV and passed through ons or more 12 serially connected sub-aerated flotation cells. The middlings 13 are subjected therein to vigorous agitation and aeration.
14 Bitumen-rich froth, termed 'secondary froth', is produced and recovered from the upper surfaces of the cells. The 16 recovered secondary froth, usually having a hydrocarbon 7 content of about 25%, is subsequently retained in a settling 18 tank for a period of time to allow some contained water and 19 solids to settle out. The remaining 'cleaned' secondary froth is then admixed with the primary froth to produce 8 combined 21 froth product.
22 The secondary froth is considerably more 23 contaminated with water and solids than is the case with the 24 primary froth. More particularly, the primary froth might typlcally contain about: 66.4% wt. bitumen; 8.9Z wt. solids;
26 and 24.7% water. The secondary ~roth typically might contain 27 about: 23.8% wt. bitumen; 17.5% solids; and 58.7Z water.
28 It is, therefore, an objectlve in the operation of 29 the hot water process to seek to maximize the recovery of the bitu-en contained in the oil ssAd in the Eort oi pri~ary :~ .
' ~IL2~3027S

1 froth. That is to say, it is desirable that the bitumen 2 report as primary froth rather than secondary froth. One 3 also seeks always to maximi~e total bitumen recovery.
4 Before the combined froth can be advanced to the upgrading operation, it is first necessary to remove most of 6 the water and solids therefrom. This is conventionally 7 accomplished by means of a two-stage centrifuging circuit.
8 In this circuit, the combined froth stream is first diluted 9 with naphtha and then fed to a scroll centrifuge to sepàrate lo off the bulk of the coarse solids. The product stream, 11 comprising water, bitumen and fine solids, is then passed 12 through a high-speed disc centrifuge to recover the bitumen.
13 Whilst many of the hot water process parameters 14 have heretofore been extensively researched, relatively little research has been directed to the addition of air and 16 its effects on primary froth recovery. This omission was 7 perhaps a consequence of early development work, undertaken 18 by the present assignee. Air injected into the primary 13 separAtion vessel had resulted in an increase in the contamination by solids and water of the prlmary froth.
21 Additionally, researchers had injected air into the tumbler, 22 without finding any significant increase in primary froth 23 recoveries. At the time of the present invention it was, 24 therefore, the widely held belief in applicants' laboratory that air addition (as opposed to air entrainment in the 26 tumbler) was either mildly deleterious to the process or was 27 not a critical parameter either way.

~2~2~j SUMMA~Y OF T}~E INVENTION
2 In the early work leading up to the present 3 invention, applicant commenced by injecting air alone into 4 the slurry line carrying the diluted aqueous slurry. It was found that the oil content of the mi~dlings was depressed a 6 small amount (which is favorabl~), but the improvement was 7 only minor and the total bitumen recovery was not 8 significantly improved. It was postulated that the formed 9 bubbles, (whose diameters were in the order of 4 mm, as derived from photographic studies) might be too large for 11 efficient attachment with the minute bitumen globules.
12 Applicant postulated that if microbubbles of air 13 could be introduced into the flowing diluted aqueous slurry 14 stream, improved attachment between the bitumen globules and air might take place. This in turn could result in improved 16 froth quality coupled with increased yield. However,`
17 heretofore, the techniques and equipment utilized for the) 18 generation of microbubbles typically involved mechanical \
19 spargers and the like. Whilst suitable for use in clean systems, such devices would rapidly become plugged and 21 inoperative in the oily and high solids content fluids 22 involved in the hot water process.
23 In accordance with one aspect of the present 24 invention, therefore, a particularly methodology is provided for the production of microbubbles of air. This technique 26 was found to yield minute air bubbles using equipment that 27 would not plug. More specifically, a steam stream and an air 28 stream in admixture are injected via a submerged nozzle into 29 a flowing aqueous stream. A gaseous jet is formed at the outlet of the nozzle. At the boundaries of the jet, the .~

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~.29~;~75 1 eddies create vortices which entrain fluid into the jet. The 2 steam and air stream is broken up into small bubbles which 3 mix with the fluid. The steam component thereof condenses, 4 leaving a plurality of minute, finely dispersed, uncondensed air bubbles. Typically, the diameter of these 'microbubbles' 6 is of the order of less than about lOO~m. The microbubble 7 size range may be varied by adjustment of the steam to air 8 ratio and by selection of a suitable jet.
9 In another broad aspect of the present invention, it has been discovered that when a profusion of microbubbles 11 of air are injected into the diluted aqueous slurry formed in 12 the hot water process after the conditioning step, and prior 3 to the introduction thereof into the flotation/settling zone, 14 increased recovery of bitumen as primary froth may be obtained. Preferably the microbubbles are generated as 16 previously described.
17 The gist of the invention therefore involves the 18 combination of:
19 - mixing steam and air in a chamber;
- discharging the mixture as a pressurized jet 21 into the diluted aqueous slurry of the hot 22 water process, with resulting production of a 23 dlsperslon of a multitude of minute air bubbles;
24 - practicing the aeration step on the diluted aqueous slurry be~ore it enters the PSV; and 26 - discovering that the foregoing improves the 27 yleld of primary fro~h.
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1 Broadly stated, the invention is an improvement in 2 the hot water process, for extracting bitumen from mined oil 3 sand in an extraction circuit, comprising conditioning the 4 oil sand by admixing said oil sand with hot water and steam and an alkaline process aid and agitating the resultant 6 slurry, diluting said slurry with additional hot water, 7 passing the diluted aqueous slurry to a primary separation 8 vessel and retaining the diluted aqueous slurry in the 9 primary separation vessel under quiescent conditions to produce an underflow stream of tailings, an overflow stream 11 of primary Eroth and a suspension of middlings therebetween.
12 The improvement comprises injecting microbubbles of air into 3 said diluted aqueous slurry after conditioning and prior to 4 the introduction thereof into the primary separation vessel to thereby increase the recovery of primary froth, said 16 microbubbles of air being generated by admixing a steam 17 stream and an air stream and injecting said steam and air 18 mixture into the diluted aqueous slurry stream whereby, as 19 the steam component condenses, residual microbubbles of air are formed.
21 As a result of practicing the improvements 22 described herein the following advantages were derived.
23 First, the yield of bitumen in the form of primary froth was 24 increased. Additionally, the methodology aclopted for creating microbubbles involved the use of equipment which is 26 not sub~ect to plugging.

28 Figure l is a schematic of the extraction circuit 2' employed in the hot water process;

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~ ~ 9 ~290275 1 Figure 2 is a sectional view of the equipment used 2 for the injection of stearn/air mixture into the diluted 3 slurry.

4 DESCRIPTION OF THE PREFERRED ENBODIMENTThe invention is an improvement on the known hot 6 water extraction process for extracting bitumen from tar sand 7 ores. More specifically, the invention involves aeration of 8 the diluted aqueous slurry stream following condition:Lng and g prior to the introduction of the slurry into the PSV.
The experimental work underlying the~ invention was ll carried out in a continuous pilot-scale hot water extraction 12 circuit operating at a rate of about 2,270 kg/h. Results l3 derived from the pilot plant, which is illustrated in Figure 14 l, are correlatable to applicant's comMercial plant operation. This experimental work and the results arising l6 therefrom will now be described.
l7 Oil sand feed, was fed by conveyor l to tumbler 2, 18 wherein it was mixed with process aid tNaOH) and hot water l9 (90 - 95 C) from conduit 3 to produce a slurry. The rate of oil sand addition was about 2.5 tonnes per hour. The rate of 21 water addition was about 1.5 tonnes per hour. The sodium 22 hydroxide was added at the rate of 0.02 wt. ~, expressed as 23 a percentage of oil sand feed, Steam was introduced to the 24 slurry contained in tuMbler l through sparglng valves 4 to trim the exit temperature of the slurry to about 80C. The 26 residence time of the slurry in tumbler 2 was approximately 27 3-l/2 minutes.

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l The slurry, prepared and conditioned in tumbler 2 , 2 was withdrawn by gravity flow through outlet line 5. It was 3 then screened through a vibrating screen 6, sized to reject 4 +1/4 inch material and permit selective passage of the slurry therethrough. A continuous hot water wash from spray 7 was 6 provided. Oversize reject material remaining on the screen 7 was discarded.
8 The screened slurry was then diluted further with 9 hot water added at pump box 8 to produce a diluted slurry containing about 50% solids by weight.
ll The diluted aqueous slurry was led from the pump 12 box 8 and pumped through a conduit 9, into which l3 microbubbles of air were introduced co-currently therewith.
l4 The generation of microbubbles was carried out as ~ollows:
16 A stream of steam was supplied via line 10. This line 10 included a variable control valve 10a and a check 18 valve 10b. The steam supplied by line 10 was jetted through 19 nozzle 12a into the mixing chamber 12b of a mixing tube 12.
A stream of air was supplied via line 13 to the mixing 21 chamber 12b at the outlet of the nozzle 12a. Line 13 22 included a control valve 13a and a check valve 13b. In 23 mixing chamber 12b, the steam and air commingled in a 24 controlled ratio. From mixing chamber 12b, the steam air mixture passed through an orlfice 12c, a line lS, having a 26 check valve 16, and through a nozzle 17. The nozzle 17 was 27 positloned at an elbow of the ~lurry line 9. The outlet 17a 28 of the nozzle 17 was in communication with the interior of 29 the line 9.

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~L29027~

1 The dimensions of the equipment used were as 2 follows:
3 inside diameter of line 9 - 25 mm 4 inside diameter of line 10 - 9.4 mm inside diameter of mixing tube 12 - 10 mm 6 diameter of outlet of nozzle 12a - 3 mm 7 orifice diameter - 6 mm 8 inside diameter of tube 15 - 9.4 mm 9 inside diameter of nozzle 17 - 2 mm diameter of outlet 17a of nozzle 17 - 1.5 mm 1l Typically, the steam and air to oil sands ratios 12 were 2.7 gm of 550 kPa steam and 0.1 L of air at STP per kg 13 of oil sand.
14 The air bubbles obtained with the equipment and materials described were generally less than 100~ m in 16 diameter. This was determined by photographic method.
7 Following aeration, the slurry was passed into the prlmary separation vessel or PSV 18. The slurry was retained 19 in PSV 18 under quiescent conditions to permit development of the bitumen-rich primary froth 19, the settled solids primary 21 taillngs 20 and the middlings 21. The primary froth 19 was 22 conducted off through line 19a to a froth purification 23 circuit ~not shown). The primary tailings 20 were withdrawn 24 and discarded. A stream of mlddlings was continuously withdrawn through middlings outlet line 21a and advanced to 26 the secondary recovery circuit 22.
27 The secondary recovery circuit 22 comprised 28 serially connected sub-aeration and flotation cells 23, of 29 conventional design. Each cell 23 was provided with an ~ 12 ~, ;

~29~X75 1 agitator and inlet distributor (not shown). Underflow reject 2 from the first cell was progressively advanced as feed to the 3 adjacent cell. Underflow from the final cell was discarded 4 as a tailings stream. Secondary froth was led from the cells 23 via conduit 24 to a settler 25, wherein some solids and 6 water settled out to leave cleaned secondary froth.
7 The following examples, which are derived from 8 experiments conducted in the above-described continuous pilot 9 plant, are included to demonstrate the present invention.
Example 1 ll This example provides a comparison between the 12 standard hot water process and the steam/air microbubble 13 injection process of the invention, carried out on an oil 14 sand containing 10.6% oil and 30% fines. The resttlts of runs, conducted in accordance with the foregoing, are given 16 in Table 1 herebelow:
Table 1 l8 % Oil in % Oil in % Primary Process Utilized l9 Middlings Primary Froth Tailings Recovery 2l 3.2 0.5 81 no air injection 22 (standard hot water 23 process) 2~ 2.0 0.5 86 air injection alone into the aqueous 26 slurry conduit 27 0,7 O.~ 93 steam/air mi~ture 28 injection into the 29 aqueous slurry conduit .~

l Example 2 2 This example shows a comparison between a case 3 wherein the process is conducted without the benefit of air 4 injection and a case wherein the process is conducted with S steam/air injection i.e. injection of microbubbles of air 6 into the slurry transfer pipe, for an oil sand different in 7 composition than that of Example 1 and with a change in the 8 rate of air addition. More particularly, the oil sand 9 contained 8.7Z oil and 33Z fines. A mixture of steam/air was used in the following proportions: 2.7 g steam and 0.1 1 of ll air per 1 kg of oil sand feed. The results obtained are set 12 forth in Table 2 following herebelow:
13 - Table 2 14% Oil in % Primary % Total Process l5 Primary Recovery Recovery Utilized 16Tailin~s 7 1.3 32 73 ~standard hot l8 water process l9 - no air injection) 2l 1.1 53 79 (injection of 22 microbubbles 23 of air into 24 the slurry pipe) ~ ,~
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Claims (4)

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

1. In the hot water process for extracting bitumen from mined oil sand in an extraction circuit said process comprising conditioning the oil sand by admixing said oil sand with hot water and steam and an alkaline process aid and agitating the resultant slurry, diluting the so conditioned slurry with additional hot water, passing the diluted aqueous slurry to a primary separation vessel and retaining the diluted aqueous slurry in the primary separation vessel under quiescent conditions to produce an underflow stream of tailings, an overflow stream of primary froth and a suspension of middlings therebetween, the improvement which comprises:
injecting microbubbles of air into said diluted aqueous slurry after conditioning and prior to the introduction thereof into the primary separation vessel to thereby increase the recovery of primary froth, said microbubbles of air being generated by admixing a steam stream and an air stream and injecting said steam and air mixture into the diluted aqueous slurry stream whereby as the steam component condenses, residual microbubbles of air are formed.

2. The improvement as set forth in claim 1 wherein the microbubbles have a diameter less than about 100 microns.

3. The improvement as set forth in claim 1 or 2 wherein said steam and air mixture is injected co-currently with the flow of diluted aqueous slurry into said separation vessel.

4. The improvement as set forth in claim 2 wherein the mixture of steam and air is injected through a nozzle into the diluted aqueous slurry.