CA2015784E - Low temperature version of the hot water extraction process for oil sand - Google Patents

Abstract

The hot water process for extracting bitumen from oil sand is practiced observing the following novel combination of conditions:
- no steam is used in the tumbler;
- hot water is added to the tumbler in an amount between 25 and 35% by weight of the oil sand;
- the temperature of the slurry in the tumbler is 40 to 55°C; and - the tumbler retention time is 7 to 12 minutes.
This combination of features results in a process yielding primary froth and total bitumen recoveries that are comparable to the conventional process, even though the slurry is significantly reduced in temperature.

Description

2 In one aspect, this invention relates to a 3 modification of the conventional hot water process for extracting bitumen from mined oil sand, to produce bitumen froth. In a preferred aspect of the invention, this modified extraction process is linked with a novel process for 7 purifying the obtained froth.
$ BACKGROUND OF THE INVENTION
g Oil sands in Alberta are currently being mined and processed at two separate commercial operations . Each such 11 "operation" involves a sequence of steps, namely;
12 - strip mining the oil sand;
13 - transporting the mined oil sand to an 14 extraction plant;
- extracting the bitumen from the oil sand using 16 the hot water process, to produce bitumen 17 froth;
lg - diluting the bitumen froth with a light lg hydrocarbon diluent, typically with naphtha, 2~ and separating contained water and solids from 21 the diluted froth using two stages of 22 centrifugation, to produce purified bitumen;
23 and 24 - upgrading the bitumen in a refinery to produce synthetic crude.

Oil sand itself comprises sand grains which are encapsulated in thin sheaths of connate water. Fine clay 3 like solid particles are present in the water. The bitumen 4 or oil is present in the interstices between the water-wet sand grains.
The hot water process comprises first dispersing 7 the bitumen from the solids and then recovering the bitumen 8 separately. The first step of this process involves the following, which will be referred to as "conditioning":
- The as-mined oil sand is fed into and moved 11 through the length of a rotating,slightly-12 inclined-from-horizontal drum or tumbler. Hot 13 process water and a small amount of caustic 14 are mixed with the oil sand in the tumbler .
The temperature of the added hot water is 16 about 95°C. The amount of process water 1~ added is in the order of 20~ by weight of the 18 oil sand or less. The water:solids ratio is 19 therefore about 0.2 or less. The amount of caustic used is about' 0.03$ by weight of the 21 oil sand. Steam is injected into the mixture 22 along the length of the tumbler, in an amount suf f is Tent to trim the slurry temperature to 24 ensure that it is at about 80oC when it leaves the Fumbler . The retention time in the 26 tumbler is typically about 3 minutes. The product is a slurry of porridge-like 28 consistency.

There are several mechanisms going on together during 2 conditioning. These include:
- That the caustic reacts with acidic moieties 4 of the bitumen to create surfactants that assist the bitumen to separate from the 6 solids;
- That the process water heats the bitumen, 8 thereby reducing its viscosity, so that it can 9 more easily separate from the solids;
- That the process water provides a medium 11 into which the bitumen may be dispersed away 12 from the solids, in the form of minute flecks;
13 - That the combination of the heat, obtained 14 from the water and steam, and the mechanical energy, supplied by rotation of the tumbler, 16 together work to induce ablation of the oil sand lumps. This ablation is of particular 18 importance in winter, when the as-mined oil 19 sand contains many frozen chunks. A screen is positioned at the outlet from the tumbler .
21 This screen removes remaining over-size lumps 22 from the slurry and the lumps are discarded as 23 tailings. If ablation is not complete, then 24 the oversize reject rate increases . This becomes a problem, as bitumen is lost with the 26 rejects; and 1 - That the agitation of the slurry assists in entraining air bubbles, 2 which play a necessary part in the flotation step which follows 3 conditioning.
4 Broadly stated then, the known conditioning step of the hot water process involves: mixing the oil sand with hot water using mechanical energy fi for sufficient time to disperse the bitumen from the solids and into the water, 7 ablate oil sand lumps and entrain air bubbles, to produce a conditioned slurry.
8 It is useful at this point to give some explanation as to why the industry 9 has commonly combined:
- the use of sufficient hot process water having a temperature of 11 about 95°C; and 12 - the provision of trim steam;
13 to ensure a slurry temperature of about 80°C at the tumbler outlet.
If the 14 slurry is at about 80°C, the density differential between the bitumen and water is at a maximum. This has long been felt to be desirable for the subsequent 16 flotation step. In addition, the high temperature assists in achieving complete 17 ablation in a short retention time.
18 Now, the industry has long appreciated that it would be desirable to 19 carry out conditioning at a lower temperature. The heat that is added by way of the process water and steam is not recovered, so any diminution in its 21 consumption would be desirable as long as the process die not otherwise 22 suffer side effects of such severity as to make the change impractical.

1 However, while the desirability of conducting conditioning at a lower 2 temperature was self-evident, no one, to our knowledge, has taught a 3 combination of conditions that would enable reduction of temperature to be 4 achieved in the extraction without suffering an unacceptable degree of side effects. It is an objective of this invention to provide such a combination.
5a 1 After leaving the tumbler and being screened, the slurry is diluted by the addition of more hot water. More particularly, the water content of the slurry is increased to give a water/solids ratio of about 1:1 (which equates with a total water content of about 50~ based on the weight of the 6 oil sand). This dilution is a step referred to in the industry as "flooding".
8 The diluted slurry is retained under quiescent conditions in an open-topped vessel having a cylindrical upper portion and a conical lower portion. The vessel is 11 termed a primary separation vessel or "PSV". In the PSV, the 12 sand sinks, is concentrated by the cone, and is discharged as 13 tailings from the base of the cone. The bitumen becomes 14 attached to air bubbles and rises to form a froth. The froth is recovered by overflow into a launder extending around the 16 rim of the vessel. This froth is termed "primary froth" and 17 typically analyzes at:
18 66.4 bitumen 8.9~ solids 24.7 water 21 Between the froth layer at the top and the sand 22 layer at the bottom of the PSV contents, there exists an 23 intermediate water layer containing fine solids and some non-24 buoyant bitumen. This layer is referred to as "middlings".
A slipstream of the middlings is withdrawn and introduced 26 into sub-aerated flotation cells, wherein the feed is 2~ agitated and copiously aerated to produce a "dirty" froth, 28 referred to as "secondary froth" . The secondary froth is 29 recovered and typically analyzes at:

1 23.8$ bitumen 2 . 17.5$ solids 58.7 water 4 The underflow from the secondary flotation cells is discarded as tailings.
Because the spontaneously-produced primary froth is 7 cleaner than the secondary froth produced by forced aeration, 8 it is a fundamental objective in the strategy applied to the hot water process to maximize the production of primary froth and minimize the production of secondary froth.
1.1 The secondary froth is partially upgraded by 12 holding it in a tank for a period of time to allow some of 13 the contained water and solids to settle out. The produced 14 cleaned secondary froth is then combined with primary froth 15 to yield a "combined froth", stream which is the product from 16 the extraction circuit.
17 In the conventional process, the combined froth is lg diluted with naphtha, to increase the difference in specific 19 gravity of the hydrocarbon phase relative to the water phase.
2~ This is done to facilitate separation of the phases by 21 gravity forces.
22 The diluted froth is then processed in a scroll-23 type centrifuge to remove contained coarse sand. The 24 hydrocarbon-rich product from the scroll centrifuge is 25 treated in a disc-type centrifuge to remove contained water 26 and fine solids. The so-purified product typically analyzes 27 at:

59.4$ $ by wt. bitumen 2 37.5 ~ by wt. naphtha 3 4.5$ $ by wt. water 0.4 $ by wt. solids This purified product is suitable for upgrading in a refinery-type facility to produce various hydrocarbon products. The entire process, as described, is commonly referred to as the hot water process. It is the object of 9 this invention to modify the conditioning step, including lowering the temperature at which it is conducted, but 11 without significantly lessening the primary froth and total ~2 bitumen recoveries, relative to the conventional recoveries.

14 More particularly, we have discovered a novel combination of conditions which, when applied to the 16 conventional hot water process, cause the so-modified process 17 to produce a comparable yield of primary bitumen froth with ~g less heat consumption. The conditions involved relate to the g conditioning step. They comprise:
- Conducting the conditioning step without the 2~ addition of steam and adding sufficient hot 22 process water to the tumbler to supply all of 23 the heat required to yield an oil sand slurry 24 having a temperature in the range of 40oC to 55oC; and 26 - Increasing the retention time of the slurry in %7 the tumbler to within the range of about 7-12 28 minutes.

1 Therefore, in a broad aspect of the invention, the known conditioning 2 step of the hot water process is modified by mixing sufficient hot water with 3 the oil sand to supply all of the heat required to yield an oil sand slurry having 4 a temperature in the range of 40 - 55°C, said hot water being essentially the only source of heat supplied to the slurry; and maintaining the mixing time 6 within the range of about 7 - 12 minutes.
8a 1 By "hot process water" is meant water of such 2 temperature as to give, when mixed with the oil sand feed, a 3 slurry of the desired temperature. Usually the water will 4 have a temperature in the range 70°C to 95°C.
In a preferred form of the invention, the amount of 6 hot process water added in the conditioning step is in the range of about 25-35~ by weight of the oil sand and the 8 amount added, including the flooding step, is in the range of 9 about 45- 65$.
From the foregoing, it will be noted that:
11 - No steam is used in the tumbler;
12 - The temperature of the slurry leaving the 13 tumbler is reduced relative to that of the 14 slurry produced in the conventional process;
and 16 - More water than is conventional is used in the 17 conditioning step but the total amount of hot 18 process water used in the combination of the 19 conditioning and flooding steps of the modified process is substantially the same as 21 used in the conventional process.
22 As supported by the examples following below, the 23 modified extraction process is characterized by a recovery of 24 bitumen, in the form of primary froth, generally equivalent to that obtained using conventional conditions. In addition, 26 the extent of lump ablation, as indicated by the amount of 27 bitumen lost with the rejects, is also generally equivalent.

1 The resulting process is characterized by the following 2 advantages:
3 - That the elimination of using steam reduces 4 capital and operating costs; and - That while consumption of mechanical energy is 6 increased by use of the invention, its cost is 7 less than the use of heat needed to operate at 8 80°C. Surprisingly, we have discovered that the 9 separation of bitumen is more responsive to mechanical energy than it is to thermal energy.
11 More particularly, our work has shown that 0.45 12 kJ of mechanical energy has the same effect as 61 13 kJ of thermal energy. This enables improvement 14 of the extraction process even though the retention time and mechanical energy consumption 16 are increased.
17 Broadly stated, the invention is an improvement in the 18 hot water process of extracting bitumen from as-mined oil sand, 19 some of which is present in the form of lumps, wherein the oil sand is mixed with hot water and a surfactant-producing caustic 21 process aid, in a rotating tumbler in a conditioning step, 22 whereby the lumps of oil sand are ablated, the slurry produced 23 from the tumbler is diluted with additional hot water in a 2looding step, and the diluted slurry is temporarily retained in a primary separation vessel to produce primary bitumen froth by 26 spontaneous flotation. The improvement comprises: admixing in 27 the tumbler an amount of hot water sufficient to combine with 28 the oil sand and process aid to yield a slurry having a 29 temperature at the tumbler outlet in the range of 45° - 55°C, said 1 hot water being essentially the only source of heat supplied to the slurry;
and 2 maintaining the retention time of the slurry in the tumbler within the range of 3 about 7 to 12 minutes; whereby the quanta of recovery of bitumen as primary 4 froth and the rejection of over-sized lumps of oil sand are generally equivalent to those which would have been obtained if the process had been operated 6 with a slurry exit temperature of about 80°C and transfer retention time of 7 about 3 - 4 minutes.
8 In another statement of the invention, it is an improvement in the 9 conditioning step of the hot water process for extracting bitumen from oil sand, wherein oil sand is mixed with hot water using mechanical energy for 11 sufficient time to disperse the bitumen from the solids and into the water, 12 ablate oil sand lumps and entrain air bubbles, to produce a conditioned slurry.
13 The improvement comprises: mixing sufficient hot water with the oil sand to 14 supply all of the heat required to yield an oil sand slurry having a temperature in the range of 45 - 55°C, said hot water being essentially the only source of 16 heat supplied to the slurry; and maintaining the mixing time within the range of 17 about 7 - 12 minutes.

Figure 1 is a schematic showing the pilot plant extraction circuit used to 21 develop the first aspect of the invention.

24 The invention is exemplified and delineated by the following examples.
l0a 2 -. T.his example describes the processing of an average 3 grade oil sand in a pilot plant extraction unit shown in Figure 4 1.
The oil sand composition was as follows:
6 12% by wt. bitumen 7 3.1% by wt. water 8 84.9% by wt. solids 9 Three runs are reported. In run A, no steam was used in the tumbler, retention time was extended to 8 minutes, and the 11 tumbler slurry temperature was 50°C. In run B, the same 12 conditions were used as in run A, except that the retention time 13 was increased to 12 minutes. Run C was conducted in accordance 14 with prior art conditions.
~ The pilot plant used was designed to process about 2.5 16 tons per hour of oil sand, in comparison to one train in 17 assignees' cozxmercial operation that is designed to process about 18 3250 tph. However, the pilot plant has previously been proven 19 to yield similar results to those of the commercial train when the hot water process was practiced in the two units under 21 substantially the same conditions with substantially the same oil 22 sand feed.
23 . The pilot glant comprised a feeder 1 for feeding oil 24 sand to a tumbler 2. Hot water (95°C), caustic and steam could 25, be introduced into the tumbler through suitable lines. The 26 tumbler product passed through a 1/2 inch screen 3 to remove 27 oversize material. The screened product dropped into a pump box /i 1 4 where it was diluted with additional hot water. The product 2 from the pump box was fed to a PSV 5 to produce a primary froth 3 product, a tailings underflow, and a middlings stream. The 4 middlings stream was fed to a bank of induced air flotation cells 6. The flotation cells produced a secondary froth stream and a 6 tailings underflow. The secondary froth stream was fed to a tank 7 7 to settle out water and solids and produce secondary froth., 8 Following is the data relating to runs A. R anr~ ~.
9 R~ P,~ _B C_ Conditioning Time (minute) 8 12 4 11 Ore Feed rate (G/S) 639 639 639 12 Slurry Water (Wt%) 25 25 20 13 Tumbler Speed (RPM) 13.90 13.70 13.70 14 Caustic Addition (Wt%) 0.03 0.03 0.03 Tumbler Slurry Temp. (C) 50 50 80 16 Flooded SLurry Temp. (C) 60 60 80 17 Total Water Addition (Wt%) 65 65 65 / ~L

1 Prime Froth Density (G/mL) NA 0.75 0.92 2 Ore Sample ~ Bitumen 12.0 3 ~ Water 3.1 4 ~ Solids 84.9 ~ Fines 11.5 6 PSV Froth Rate (G/S) 101 98 106 PSV Froth ~ Bitumen 67.8 71.7 65.5 8 $ Water 21.1' 17.5 25.8 9 ~ Solids 11.0 10.8 8.8 PSV Middlings Rate (G/S) 205 198 158 11 PSV Middlings ~ Bitumen 0.8 0.5 1.7 12 ~ Water 82.2 82.3 81.1 13 ~ Solids 17.0 17.2 17.1 14 pSV Tails Rate (G/S) 675 714 697 PSV Tails $ Bitumen 0.3 0.2 0.3 16 ~ Water 33.2 34.4 35.0 17 ~ Solids 66.5 65.4 64.7 18 Reject Rate (G/S) 7 8 9 19 (W/W)$ 1.1 1.3 1.4 Reject ~ Bitumen 5.9 6.0 5.2 21 $ Water 0.2 23.5 11.1 22 ~ Solids 87.0 70.6 83.8 1 Cleaner Froth Rate (G/S) 5 9 16 2 Cleaner Froth ~ Bitumen 50.3 14.1 35.5 3 $ Water 36.0 69.6 49.7 ~ Solids 13.8 16.2 14.8 Secondary Tails Rate (G/S) 200 189 142 6 Secondary Tails ~ Bitumen 0.3 0.3 0.3 7 ~ Water 83.6 84.3 84.9 8 ~ Solids 16.1 15.5 14.8 9 Combined Froth $ Bitumen 66.97 66.90 61.57 ~ Water 21.80 21.84 28.93 - ~ Solids 11.13 11.25 9.59 12 PSV Froth Bitumen (G/S) 68.48 70.27 69.43 13 PSV Tails Bitumen (G/S) 2.03 1.43 2.09 14 Cleaner Froth Bitumen (G/S) 2.52 1.25 5.0'8 Cleaner Tails Bitumen (G/S) 0.60 0.57 0.43 16 Rejects Bitumen (G/S) 0.41 0.48 0.47 17 Primary Recovery (~) 92.50 94.96 88.90 18 Secondary Recovery (~) 3.40 1.70 7.27 19 Combined Recovery (~) 95.90 96.66 96.18 Primary Tails Loss (~) 2.74 1.93 2.68 21 Secondary Tails Lcss (~) 0.81 0.77 0.55 22 Reject Loss ($) 0.56 0.65 0.60 1 Primary Recovery (Rej-Free) 93.02 95.58 89.44 2 Secondary Recovery (Rej-Free) 3.42 1.71 7.32 3 Combined Recovery (Rej-Free) 96.43 97.29 96.76 Primary Tails Loss (Rej-Free) 2.75 1.94 2.69 Secondary Tails Loss (Rej-Free) 0.82 0.77 0.55 6 From the foregoing data it will be noted that:
7 - The warm slurry runs A and B yielded primary 8 froth and total bitumen recoveries which were 9 better or comparable to those from the hot slurry run C;
11 - The bitumen losses with the tumbler and PSv 12 tailings were comparable for the warm and hot 13 slurry runs;
14 - The oversize reject rates from the three runs were comparable, indicating that the extent of 16 ablation was about the same;
17 - The total hot water consumption for the thee 18 runs was the same, yet the recoveries for the 1g runs mere comparable; and - As shown by comparing the data of runs A and 21 B, there is little improvement obtained in 22 increasing the tumbler residence time from 8 23 to 12 minutes when the slurry is only warm.

EXAMPLE II
2 This example demonstrates that operation of the hot 3 water process by reducing only the temperature of the slurry in the conditioning step gives reduced yields of primary and combined froth.
6 Hot water process runs were conducted, using the 7 pilot plant and conditions described in Example I, on two g distinct oil sand feeds. In one case, the process was g operated at 80oC and in the other it was operated at 50oC.
The relevant data was as follows:
Oil Sand Type Estuarine Marine ~2Bitumen in feed (~) 8.1 8.9 13Mean primary recovery 14at 80oC 80.3 37.2 15at 50oC 65.9 37.0 16Mean combined recovery at 80C 86.2 77.5 ~8at 50oC 81.1 67.9 20This example shows the advantage of redistributing 2~the total hot increase the amount used in water used, the to 22tumbler. The the amount bitumen lost with effect is that of 23tumbler rejects is reduced the slurry having in the case of 24increased water content in the tumbler.
All results were for 25a slurry having a temperature of 50oC.

1 Residence Slurry Water Oil Sand Bitumen lost 2 time (min) as proportion feed rate to reject ($

3 of oil sand (g/s) based on bitumen ( ~S ) in feed ) 6.16 17 445 2.34 6 5.78 22 445 1.47 7 5.45 27 445 0.55 8 4.56 17 639 3.16 9 4.30 22 639 2.29 4.07 27 639 1.42 11 3.70 17 833 3.98 12 3.50 22 833 3.11 13 3.33 27 833 2.24 14 Such reductions are not notice d at 80oC because reject rates ar e always low. At 50oC the reject rate has a 16 tendency to be high but can reduced by using more of be the 17 total water in the tumbler as slurry water.
Thereafter, a lg proportionately lower amount of water needed as flood is lg water for the resulting dilu ted slurry to give the same separation in be achieved from conventional the PSV as would 21 water distribution.

Claims (5)

1. In the hot water process of extracting bitumen from as-mined oil sand, some of which is present in the form of lumps, wherein the oil sand is mixed with hot water and a surfactant-producing caustic process aid, in a rotating tumbler in a conditioning step, whereby the lumps of oil sand are ablated, the slurry produced from the tumbler is diluted with additional hot water in a flooding step, and the diluted slurry is temporarily retained in a primary separation vessel to produce primary bitumen froth by spontaneous flotation, the improvement comprising:
admixing in the tumbler an amount of hot water sufficient to combine with the oil sand and process aid to yield a slurry having a temperature at the tumbler outlet in the range of 45° - 55°C, said hot water being essentially the only source of heat supplied to the slurry; and maintaining the retention time of the slurry in the tumbler within the range of about 7 to 12 minutes.

2. The Improvement as set forth in claim 1 wherein:
the amount of hot water added in the conditioning step is about 25 to 35% by weight of the oil sand; and the total amount of hot water added in the conditioning and flooding steps is about 45 to 65% by weight of the oil sand.

3. A process according to claim 1, wherein said retention time is about 8 minutes and the temperature of the slurry at the tumbler outlet is about 50°C.

4. A process according to claim 2, wherein said retention time is about 8 minutes and the temperature of the slurry at the tumbler outlet is about 50°C.

5. In the conditioning step of the hot water process for extracting bitumen from oil sand, wherein oil sand is mixed with hot water using mechanical energy for sufficient time to disperse the bitumen from the solids and into the water, ablate oil sand lumps and entrain air bubbles, to produce a conditioned slurry, the improvement comprising:
mixing sufficient hot water with the oil sand to supply all of the heat required to yield an oil sand slurry having a temperature in the range of 45 - 55°C, said hot water being essentially the only source of heat supplied to the slung; and maintaining the mixing time within the range of about 7 -12 minutes.