CA2350001C - Staged settling process for removing water and solids from oil sand extraction froth - Google Patents

Abstract

Diluent-diluted bitumen froth containing bitumen and naphtha diluent hydrocarbons, water, sand and fines, (collectively "dilfroth"), is fed into a vapor-tight gravity settler ('splitter') and temporarily retained to therein produce a bottom layer of tails comprising sand and middlings, a rag layer of discrete three-dimensional structures, each comprising hydrocarbons contained in a skin of fines, and a top layer of hydrocarbons containing small droplets of water and fines ('raw dilbit'). The flux in the splitter is less than 6 m3/h of dilfroth fed per m2 of horizontal cross-sectional rag area. The in-coming dilfroth is fed directly into the splitter middlings. Demulsifier is added to the overflow stream of raw dilbit and the mixture is subjected to prolonged settling in a vapor-tight polisher tank, to produce polished dilbit containing less than 1.0 wt. % water and 0.3 wt. % solids. The splitter underflow tails, containing less than 15 wt. % bitumen, is mixed with additional diluent to raise the diluent/bitumen ratio to 4:1 to 10:1 and is gravity settled in a vapor-tight scrubber. Scrubber overflow, mostly diluent containing residual bitumen stripped from the tails, is recycled to the splitter. In concept, the sand is first separated from the bitumen in the stripper. The substantially sand-free bitumen can then feasibly be treated with chemical demulsifier and subjected to prolonged settling in the polisher to reduce water and fines contents to low levels. Bitumen lost with the splitter tails is recovered in the scrubber using a high concentration of diluent. The scrubber overflow of bitumen and diluent is recycled to the stripper to conserve diluent.

Description

1 "STAGED SETTLING PROCESS FOR REMOVING WATER AND

2 SOLIDS FROM OIL SAND EXTRACTION FROTH"

4 The present invention relates to a staged gravity settling process for removing contaminants, namely water and particulate solids, from light 6 hydrocarbon diluent-diluted bitumen froth derived from water-based extraction 7 of bitumen from oil sand.

Oil sand, as known in the Fort McMurray region of Alberta, Canada, 11 comprises water-wet, coarse sand grains having flecks of a viscous 12 hydrocarbon, known as bitumen, trapped between the sand grains. The water 13 sheaths surrounding the sand grains contain very fine clay particles. In 14 summary then, oil sand comprises: bitumen; particulate solids (coarse sand and clay "fines"); and water. A sample of oil sand, for example, might 16 comprise 70% by weight sand, 14% fines, 5% water and 11 % bitumen. (All %
17 values stated in this specification are to be understood to be % by weight.) 18 When mixed with hot water, the bitumen will separate from the sand 19 grains and be dispersed into the water phase.

For the past 25 years, the bitumen in McMurray oil sand has been 21 commercially recovered using a water-based process. In the first step of this 22 process, the oil sand is slurried with hot water, steam, usually some caustic 23 and naturally entrained air. The slurry is mixed, for example in a tumbler or 24 pipeline, for a prescribed retention time, to initiate a preliminary separation or {E4160765. D0C;1 }

1 dispersal of the bitumen and solids and to induce air bubbles to contact and 2 aerate the bitumen. This step is referred to as "conditioning". The 3 conditioned slurry is then further diluted with hot water and introduced into a 4 large, open-topped, conical-bottomed, cylindrical vessel (termed a primary separation vessel or "PSV"). The diluted slurry is retained in the PSV under 6 quiescent conditions for a prescribed retention period. During this period, 7 aerated bitumen rises and forms a froth layer, which overflows the top lip of 8 the vessel and is conveyed away in a launder. Sand grains sink and are 9 concentrated in the conical bottom. They leave the bottom of the vessel as a wet tailings stream containing a small amount of bitumen. Middlings, a watery 11 mixture containing solids and bitumen, extend between the froth and sand 12 layers.

13 The wet tailings and middlings are separately withdrawn, combined 14 and sent to a secondary flotation process. This secondary flotation process is commonly carried out in a deep cone vessel wherein air is sparged into the 16 vessel to assist with flotation. This vessel is referred to as the TOR
vessel.
17 The bitumen recovered by flotation in the TOR vessel is recycled to the PSV.
18 The middlings from the deep cone vessel are further processed in induced air 19 flotation cells to recover contained bitumen.

The hot froths (80 - 85 C) produced by the PSV and flotation cells are 21 combined and subjected to cleaning, to reduce water and solids contents.

22 More particularly, it has been conventional to dilute this bitumen froth 23 with a light hydrocarbon diluent, such as naphtha, to increase the difference in 24 specific gravity between the bitumen and water and to reduce the bitumen {E4160765.DOC;1}2 1 viscosity, to thereby aid in the separation of the water and solids from the 2 bitumen. By way of example, the composition of naphtha-diluted bitumen 3 froth typically might have a naphtha/bitumen ratio of 0.65 and contain 20%
4 water and 7% solids.

This diluent-diluted bitumen froth, derived from water-based extraction 6 of bitumen from oil sand, is commonly referred to as "dilfroth".

7 Separation of the bitumen from water and solids is then carried out.
8 This may be done by treating the dilfroth in a sequence of scroll and disc 9 centrifuges. Alternatively, the dilfroth may be subjected to gravity separation in a series of inclined plate separators ("IPS") in conjunction with 11 countercurrent solvent extraction using added light hydrocarbon diluent.

12 These prior art centrifuge and IPS techniques for removing water and 13 particulate solids from dilfroth have not been entirely satisfactory.
Typically 14 the "cleaned" froth, (commonly referred to as "dilbit"), may still contain at least 1.5% water and 0.5 % solids. These contaminants cause problems in the 16 downstream refinery-type processes used to upgrade the dilbit to produce 17 useful end products. More particularly, the water contains chlorides, which 18 cause corrosion in heat exchangers. The solids plug catalysts. For these 19 reasons, the upgrading sector of these plants have specified that the dilbit should contain <1.0% water and <0.3% solids.

21 Researchers have long sought to develop a practical and viable 22 alternative process which would reliably produce dilbit having the specified 23 smaller concentrations of water and solids. It would be even more desirable 24 to reduce the contamination to levels in the order of <0.5% water and <0.2%
{E4160765.DOC;1 }3 1 solids. In addition, it would be desirable to achieve this using a system which 2 eliminates the centrifuges, as these are expensive to operate and cause 3 emulsification. However, solutions have been constrained by the following 4 realities:

= the clays and asphaltenes in the bitumen have an affinity for each 6 other. They tend to concentrate at hydrocarbons/water interfaces 7 and act to limit coalescence of water droplets into larger globules 8 that would settle rapidly to enable further reduction of water content 9 in the dilbit product;

= the loss of bitumen with tails must be minimal, as this is 11 environmentally undesirable and of course reduces oil recovery;

12 = N/B ratio in dilbit should not exceed 0.8; and 13 = given the huge volumes processed in these operations, the 14 equipment used should be simple and reasonably inexpensive to operate and additives, such as demulsifiers, should be used only 16 sparingly.

19 In accordance with one embodiment of the invention, the following steps are practised in combination:

21 = Dilfroth, preferably having a light hydrocarbon diluent/bitumen ratio 22 of 0.5:1 to 0.8:1, is fed into a gravity settler vessel, referred to as 23 the "splitter". The splitter has outlet means for withdrawal of solids 24 and aqueous phase from the bottom and outlet means for overflow {E4160765. DOC;1 }4 . ,.

1 of the hydrocarbon phase at the top. The vessel should be 2 enclosed at the top and vapor-tight to prevent escape of diluent.
3 The splitter has a feed inlet, preferably intermediate its ends. The 4 dilfroth is temporarily retained in the splitter chamber so that the froth settles to form a bottom layer of sand and aqueous middlings, 6 a rag layer and a top layer of hydrocarbons (referred to as "raw 7 dilbit"). Middlings is a mixture comprising mainly water containing 8 some fines and bitumen. An underflow stream of middlings and 9 settled sand, containing some hydrocarbon, (collectively referred to as "splitter tails"), is removed through the bottom outlet. An 11 overflow stream of splitter raw dilbit is removed through the top 12 outlet. The splitter raw dilbit comprises hydrocarbons contaminated 13 with water and solids, for example 3 - 5% water and 0.5 - 2.5%
14 solids. The solids are mainly fines. The splitter tails comprise mostly water, typically containing solids and hydrocarbons, for 16 example 10 - 25% solids and 8 - 20% hydrocarbons;

17 = In an optional or preferred feature, the dilfroth is directly introduced 18 into the splitter middlings layer, beneath the rag layer and above the 19 settled sand. The reason for this is explained below;

= In another preferred feature, the feed rate of dilfroth to the splitter, 21 per square meter of horizontal cross-sectional rag or vessel 22 chamber area, is maintained below 8 m3/h, preferably below 6 m3/h 23 of dilfroth for each m2 of rag area. More preferably, the feed rate is 24 maintained at about 4m3/h or less. Otherwise stated, the {E4160765. DOC;1 }5 , 1 hydrocarbons/water interface area loading rate or flux is preferably 2 maintained below 8 m/h , preferably below 6 m/h. It is found that the 3 thickness of the rag layer begins to increase if the flux is high, for 4 example at 8 m/h. As a result, oil loss with the tails increases and/or contamination of the dilbit also increases. The reason for 6 this is explained below;

7 = In another preferred feature, the elevation of the 8 hydrocarbon/middlings interface in the splitter chamber is 9 monitored, for example with a capacitance probe. The rate of introduction of dilfroth and rate of tails removal are preferably 11 controlled in response to the elevation of the interface, so as to 12 maintain separation of the interface from the bottom outlet by 13 keeping the interface at a generally constant elevation. This is 14 controlled, for example, so as to preferably maintain the hydrocarbon content in the tails at less than 20%, more preferably 16 less than 15%;

17 = In another preferred step, the splitter raw dilbit is introduced into a 18 large vapor-tight vessel (referred to as the "polisher") and 19 temporarily retained therein for a prolonged period (relative to the retention time in the splitter). For example, the retention time in the 21 polisher might be in the range of 5 to 24 hours;

22 = In another preferred step, demulsifier is added to the splitter raw 23 dilbit treated in the polisher. As a result of prolonged settling and 24 the use of demulsifier, water droplets coalesce and settle in the {E4160765.DOC;1}6 1 polisher chamber, together with fine solids, to produce a polished 2 dilbit overhead product which may contain less than 1.0% water 3 and 0.3% solids, more preferably < 0.5% water and < 0.2% solids, 4 and a polisher sludge underflow comprising water and fine solids;

= In another preferred step, the splitter tails are mixed with additional 6 diluent and settled in a vapor-tight vessel referred to as the 7 "scrubber". The scrubber is similar in structure to the splitter. In the 8 case of naphtha diluent, the scrubber diluent/bitumen ratio is quite 9 high, preferably in the range 4:1 to 10:1. At such a high diluent/bitumen ratio, the diluent strips residual bitumen from the 11 splitter tails, so that there is produced a scrubber overhead stream 12 which is rich in diluent and contains most of the residual bitumen.
13 This stream is preferably recycled to the splitter feed to help provide 14 the preferred splitter diluent/bitumen ratio of 0.5:1 to 0.8:1. The scrubber also produces a scrubber tails underflow which is mainly 16 sand, fines and water, typically containing, for example, less than 17 3% bitumen.

18 With respect to the foregoing, the following will be noted:

19 = That most of the sand and water originally in the dilfroth are separated in the splitter and report to the splitter underflow, leaving 21 a splitter dilbit product containing fine water droplets which are 22 difficult to coalesce and separate by settling - however the volume 23 of the splitter dilbit is now considerably reduced relative to the {E4160765.DOC;1}7 1 volume of the dilfroth feed. More importantly, virtually all coarse, 2 fast settling solids have been removed from the raw dilbit;

3 = That with respect to the splitter hydrocarbon losses with the tails are 4 found to be relatively low, for example <20% of the hydrocarbons originally in the dilfroth feed - in contrast, in the IPS system, 6 between 35 - 50% of the original hydrocarbons go into the tails;

7 = That in the polishing step, it is now viable to add demulsifier to the 8 splitter dilbit (reduced in volume and free of sand) and to use 9 prolonged retention time to coalesce and settle out the residual water and fine solids, thereby producing a polished dilbit product 11 that approaches or meets the desired specification of less than 12 1.0% water and 0.3% solids. Because the solids entering the 13 polisher are primarily fine clays, a flat-bottom, large diameter 14 enclosed tank can be used to provide the prolonged settling (for example in the order of 5 to 24 hours) needed to separate the water 16 and fines;

17 = That in the scrubbing step, a high diluent/bitumen ratio is used to 18 scrub out residual bitumen in the splitter tails to keep bitumen 19 losses to a low level. The added diluent is recycled countercurrently to use it efficiently and to help provide the desired 21 diluent/bitumen ratio in the splitter; and 22 = that the vessel chambers or zones of separation used are 23 preferably free of inclined plates.

{E4160765.DOC;1 }8 1 The invention arose from a research program in which the settling 2 behaviour of dilfroth was studied using a glass-walled test circuit.
Dilfroth was 3 fed into a glass column splitter through a glass inlet pipe connected with the 4 splitter between its top and bottom ends. The incoming stream of dilute froth was not homogeneous. It comprised easily discernible globes of 6 hydrocarbon, pockets of muddy middlings and grains of coarse sand. As the 7 dilfroth stream entered the vessel chamber, a separation process occurred 8 due to gravity settling. As a result, a lower aqueous phase of middlings and 9 an upper hydrocarbons phase were established. The incoming dilfroth was fed directly into the middlings phase. This middlings phase mainly comprised 11 a suspension of clays in water. The initial separation was rapid (a few 12 seconds). The following actions were observed:

13 = the sand grains (60 - 150pm) settled quickly through the middlings 14 to the base of the splitter chamber. The sand and some middlings were continually withdrawn and pumped to a glass column 16 scrubber, as further described below;

17 = pockets of incoming middlings, containing only traces of 18 hydrocarbon, joined the aqueous phase and became part of it; and 19 = the incoming hydrocarbons, present in the form of discrete, three dimensional structures, which we referred to as "leaky sacks", 21 floated up through the aqueous phase and collected in a rag layer 22 of other oil sacks at the interface between the middlings and the 23 layer of hydrocarbons which accumulated above.

{E4160765, DOC;1 }9 1 The leaky sacks were filled with hydrocarbons and had outer skins 2 formed of sub-micron clay particles. The composite density of the sacks was 3 lower than that of the aqueous middlings (density 1.05 - 1.1 kg/I) because 4 they would float in the middlings - but the density of the sacks was greater than that of the hydrocarbon phase above the interface, because they would 6 not float in that phase (density 0.76 - 0.8 kg/1). Hence the composite density 7 of the hydrocarbon laden sacks was apparently between 0.8 and 1.05 kg/I.
8 The density of the clay alone was 2.65 kg/I.

9 The sacks formed the intermediate rag layer, approximately 100 to 200 mm thick at the interface, between the aqueous and hydrocarbon phases.
11 The sacks in the rag layer did not coalesce into larger ones, although some of 12 them did cluster together. They did not readily burst. They appeared to 13 crowd upwardly into the rag layer.

14 Yet the sacks did not remain in the rag layer indefinitely. They appeared to penetrate the rag layer and, after residing there briefly (a minute 16 or two), they started moving downwardly through the rag layer and then sank 17 through the middlings to the bottom of the vessel chamber. This meant that 18 the sacks underwent a change in composite density and acquired a density 19 greater than that of the middlings. At the same time, the layer of hydrocarbons above the rag increased in volume and excess hydrocarbon 21 overflowed the vessel. Since there was no input of hydrocarbons to the top 22 layer, other than from the sacks, and since no sacks entered the hydrocarbon 23 phase, it follows that the sacks were leaking hydrocarbons through their 24 permeable clay skins. Hence the expression "leaky sacks".

{E4160765.DOC;1}10 1 It is our belief that the rag layer becomes a zone of compression, 2 whereby buoyancy force from the middlings compresses the sacks against 3 the layer of hydrocarbons. As a result of this compression, hydrocarbons 4 within a sack pass through the clay skin and enter the hydrocarbon phase above the rag. It is mostly the uppermost sacks in the rag layer that are 6 partially emptied of hydrocarbon by compression. These sacks increase in 7 composite density and sink to the base of the vessel chamber. However, 8 even though they are denser than the middlings, the descending sacks still 9 contain some hydrocarbons. They are only partially deflated. This is clearly visible in the glass vessel, since their shape is now different. During the initial 11 floating period, a sack is spherical and full. When a sack sinks, it is thin and 12 deflated.

13 The process of hydrocarbon release from the sacks occurs only at a 14 limited rate. We refer to it as "rate of rag permeability". That is, there is only a certain volume of hydrocarbon that can be released through a unit area of the 16 rag layer in a unit of time. If the delivery of new sacks to the bottom of the rag 17 layer exceeds the rate of rag permeability, the hydrocarbon release from the 18 sacks becomes the limiting factor and the process stalls gradually. The 19 process of emptying the sacks does not respond well to an increase in the rate of delivery. More sacks enter the rag layer from the bottom than can be 21 emptied by the gentle compression of the layer. The depth of the rag layer 22 therefore grows. This increases the depth of rag that must be penetrated by 23 new sacks and by hydrocarbon released from them. The increased rag depth 24 also hinders the removal of partially emptied sacks from the rag layer.
This {E4160765.DOC;1 } 11 1 leads to downward rag build-up with the result that rag is withdrawn by the 2 underflow pump, causing an increase in hydrocarbons loss with the splitter 3 tails.

4 As a result of considerable experimentation, we have determined a preferred limit of splitter feed rate in m3/h for each square meter of rag 6 horizontal cross-sectional area in the splitter chamber. This flux limit is less 7 than 6 m3/h of splitter feed for each m2 of rag area. More preferably the flux 8 should be less than about 4 m/h. At the high end of flux, the loss of 9 hydrocarbons with the splitter tails begins to increase. For example, at a flux of 8 m/h the loss becomes excessive and may jeopardize the performance of 11 the scrubber. This is because the diluent/bitumen ratio in the scrubber will be 12 reduced.

13 The splitter operation does not appear to be a perfect process. Some 14 small droplets of water (a few microns in diameter) also make their way into the hydrocarbon phase. The hydrocarbon layer is found to contain small 16 quantities of water (for example 3 to 5%) and clays (for example 1.5 to 2.5%), 17 present in the form of tiny droplets. Microscopic examination indicates that 18 the clays are suspended in water and the surfaces of water droplets are 19 coated with clay particles. The composite droplets resist coalescence and appear very stable. Removal or separation of these often micron-sized 21 droplets by gravity settling is very slow. However, we have shown that, by 22 prolonged settling, preferably coupled with the addition of known demulsifier 23 chemical, the composite water/clay droplets can be flocculated or coalesced {E4160765. DOC;1 } 12 1 into much larger structures which will settle out of the hydrocarbon phase over 2 a period of hours.

3 We have also shown that a scrubbing action with a high 4 diluent/bitumen ratio (for example 4:1 to 10:1) is effective to recover residual bitumen from the splitter tails and may reduce the loss of hydrocarbons with 6 the scrubber tails to less than 1.0% bitumen and less than 6% naphtha. Most 7 of the naphtha in scrubber tails can be further recovered by steam stripping in 8 a naphtha recovery unit.

9 Broadly stated, in one embodiment a process is provided for cleaning light hydrocarbon diluent-diluted bitumen froth ("dilfroth") comprising bitumen 11 and light hydrocarbon diluent hydrocarbons contaminated with water and 12 particulate solids, the solids comprising sand and fine clay particles ("fines"), 13 comprising: providing a splitter vessel forming a vapor-tight chamber for 14 gravity settling, said vessel having an overflow outlet at its upper end, an underflow outlet at its lower end and means for feeding incoming dilfroth into 16 the chamber; feeding dilfroth into the chamber through the feed means and 17 temporarily retaining it therein so that the dilfroth separates to form a bottom 18 layer of splitter tails comprising sand and aqueous middlings, said splitter tails 19 containing hydrocarbons, an intermediate layer of rag comprising water, fines and hydrocarbons collected in discrete three dimensional structures, and a 21 top layer of raw dilbit comprising hydrocarbons containing water and fines, 22 said middlings combining with the rag and dilbit to create a discernible 23 hydrocarbons/water interface; the feed means being operative to directly feed {E4160765.DOC;1)13 1 the incoming dilfroth into the middlings; removing dilbit through the overflow 2 outlet; and removing splitter tails through the underffow outlet.

3 Broadly stated, in another embodiment a process is provided for 4 cleaning light hydrocarbon diluent-diluted bitumen froth ("dilfroth") containing bitumen and diluent hydrocarbons contaminated with water and solids, the 6 solids mainly consisting of sand and fine clay particles ("fines"), comprising:
7 subjecting the dilfroth to gravity settling in an enclosed first zone of separation 8 to produce an overflow stream of raw dilbit, comprising hydrocarbons 9 containing water and fines, and an underFlow stream of tails comprising sand and aqueous middlings; and subjecting the raw dilbit to gravity settling in an 11 enclosed second zone of separation for sufficient time to produce an overflow 12 stream of polished dilbit and an underflow stream of sludge.

13 Broadly stated, in another embodiment a process is provided for 14 cleaning light hydrocarbon diluent-diluted bitumen froth ("dilfroth") containing bitumen and diluent hydrocarbons contaminated with water and solids, the 16 solids mainly consisting of sand and fine clay particles ("fines"), comprising:
17 subjecting the dilfroth to gravity settling in an enclosed first zone of separation 18 to produce an overflow stream of raw dilbit, comprising hydrocarbons 19 containing water and fines, and an underflow stream of tails, comprising sand and aqueous middlings; subjecting the raw dilbit to gravity settling in an 21 enclosed second zone of separation to produce an overflow stream of 22 polished dilbit and an underflow stream of sludge; and mixing the first zone 23 tails with diluent and subjecting the produced diluted tails to gravity settling in {E4160765.DOC;1}14 1 an enclosed third zone of separation to produce an overhead stream of 2 scrubber hydrocarbons and an underFlow stream of scrubber tails.

Figure 1 is a schematic showing a preferred embodiment of the vessels 6 and steps of the process;

7 Figure 2a is a schematic showing the laboratory pilot circuit, in 8 polishing configuration, as used to develop the data of Example I;

9 Figure 2b is a schematic showing the laboratory pilot circuit, in scrubbing configuration, as used to develop the data of Example II;

11 Figure 3 is a plot showing dilbit water content when settled over time 12 when the dilbit does not contain demulsifier; and 13 Figure 4 is a plot showing dilbit water content when settled over time 14 when the dilbit contains demulsifier.

17 The invention is concerned with a process for cleaning diluent-diluted 18 bitumen froth by reducing the content of contaminants, specifically water and 19 solids.

{E4160765.DOC;1}15 1 Bitumen froth is initially received from a plant (not shown) for extracting 2 bitumen from oil sand using the known hot water process. The froth, as 3 received, is at elevated temperature (for example 85 C) and typically 4 comprises:

bitumen - 60%
6 water - 30%
7 solids - 10%

8 A light hydrocarbon diluent, such as process naphtha 37, is mixed with 9 the froth in a mixer I to provide diluent-diluted bitumen froth 38. The naphtha is preferably at least partly supplied by recycling scrubber naphtha, produced 11 as described below.

12 The scrubber naphtha 37 is supplied in an amount such that the 13 naphtha/bitumen ratio of the diluent-diluted froth ("dilfroth") 38 is preferably in 14 the range 0.5 - 0.8, most preferably about 0.65.

The dilfroth 38 is fed by line 37 from the mixer I into the chamber 2 of 16 a gravity settler vessel, referred to as the "splitter" 3. The dilfroth 38 is fed into 17 the splitter chamber 2 through inlet means 4. The splitter 3 has a conical 18 bottom 5. It has underflow and overflow outlets 6, 7 at its bottom and top 19 ends, respectively. A pump 8 and line 9 withdraw a stream of splitter tails through the underflow outlet 6. Splitter overflow line 10 conveys away an 21 overflow stream of raw dilbit 45.

22 The rate at which dilfroth 38 is fed to the splitter chamber 2 and the 23 diameter of the cylindrical section 11 of the splitter 3 are selected to provide a 24 preferred flux of < 6 m/h, most preferably about 4 m/h.

{E4160765.DOC;I}16 1 The dilfroth 38 is temporarily retained in the splitter chamber 2 for 2 sufficient time so that gravity settling takes place to produce the following:

3 = a bottom layer 12 of splitter tails 13, comprising mainly sand 14 and 4 aqueous middlings 15, said tails containing some hydrocarbons;

= an intermediate layer 16 of rag 17, said rag comprising mainly 6 hydrocarbons associated with water and fines in discrete three 7 dimensional structures or sacks 18; and 8 = a top layer 19 of raw dilbit 20 comprising mainly hydrocarbons 9 containing some water and fines (clay particles).

The middlings 15 combine with the rag 17 to create a discernible 11 hydrocarbons/water interface 21 with the raw dilbit 20.

12 The splitter inlet means 4 delivers incoming dilfroth 38 into the 13 middlings 15 extending across the cross-section of the.splitter chamber 2, at 14 an elevation spaced below the layer of rag 17 and well above the underFlow outlet 6.

16 Means, such as a capacitance probe, not shown, may be used to 17 monitor the elevation of the hydrocarbons/water interface 21. The rates of 18 feeding dilfroth 38 and withdrawing tails 13 may be controlled in response to 19 the probe readings to maintain the elevation of the interface 21 generally constant. It is of course desirable to keep the interface 21 away from the 21 bottom of the splitter chamber 2, to minimize hydrocarbon losses with the 22 splitter tails 13. Alternatively one may monitor the composition of the splitter 23 tails 13 and vary the rates with the objective of keeping the tails hydrocarbon 24 content below a predetermined value, usually less than 15%.

{E4160765.DOC;1}17 1 The raw dilbit 20 produced through the splitter overflow outlet 7 is 2 pumped through line 10 to a flat-bottomed, vapor-tight tank, referred to as the 3 "polisher" 22, and subjected to gravity settling therein. Preferably a 4 demulsifier is added to the raw dilbit 20 as it moves through the line 10.
For example, 40 ppm of Champion MR 121-6TM demulsifier may be added for this 6 purpose.

7 The polisher 22 has a bottom underflow outlet 23 and a top overflow 8 outlet 24.

9 The raw dilbit/demulsifier mixture is temporarily retained for a prolonged period (for example, 24 hours) in the polisher chamber 25. Water 11 droplets coalesce and settle, together with fines. Polished dilbit 39 is 12 removed as an overflow stream from the polisher 22 through line 26. The 13 polished dilbit 39 is found to comprise hydrocarbons, containing low water and 14 solids concentrations, for example <1.0% water and < 0.3% solids. Polisher sludge 27, comprising water, solids and, for example, less than 15%
16 hydrocarbons, is removed from the polisher 22 as an underflow stream 17 through line 28. It is pumped through line 28 into scrubber mixer 29.

18 The splitter tails 13 produced through the splitter underflow outlet 6 are 19 also pumped through line 9 to scrubber mixer 29. Naphtha is added to the splitter tails 13 and polisher sludge 27 in the scrubber mixer 29 to produce a 21 scrubber feed 30 preferably having a naphtha/bitumen ratio in the range 4 to 22 10, more preferably 5 to 8. The scrubber feed 30 is introduced into the 23 chamber 31 of a vapor-tight vessel, referred to as the "scrubber" 32. The 24 scrubber feed 30 is temporarily retained in the scrubber chamber 31 (for tE4160765.DOC;1 } 18 1 example for 20 to 30 minutes) and subjected to gravity settling therein. A
2 scrubber overflow 33 of hydrocarbons, mainly comprising naphtha associated 3 with some bitumen, is removed through an overflow outlet 34 and recycled 4 through line 35 to splitter mixer 1. A scrubber underflow stream of scrubber tails 36, comprising water and solids containing some hydrocarbons, is 6 removed and forwarded to a naphtha recovery unit (not shown).

7 The nature and utility of the process is further demonstrated by the 8 following examples.

Example 1- Splitter and Polisher 11 This example demonstrates the results obtained when a splitter and 12 polisher were operated together in series.

13 In this experiment, two glass columns were supplied as splitter 3 and 14 polisher 22 and connected as shown in Figure 2a. Hot bituminous froth and naphtha were combined in an agitated splitter mixer 1, at naphtha/bitumen 16 ratios of 0.55/1.0 by weight. The mixture was pumped continuously, at a rate 17 of 191 g/min, to the splitter 3 (ID- 125 mm and height - 750 mm). The 18 calculated splitter flux was 0.93 m/h.

19 The separation process was clearly visible through the glass walls of the splitter column, with coarse solids 14 mainly sand) settling and 21 hydrocarbon sacks 18 floating. The full sacks 18 accumulated as a rag layer 22 16 at the hydrocarbons/water interface 21 and a deep layer 19 of hydrocarbon 23 formed above the interface. After residing in the rag layer 16 for a few 24 minutes, partially emptied sacks 41 of hydrocarbon were observed sinking {E4160765.DOC;1}19 1 and joining the settled solids as splitter tails 13 at the bottom. The rate of the 2 splitter tails withdrawal through line 9 was adjusted manually to maintain the 3 level of hydrocarbon/water interface 21 a few inches above the feed injection 4 point 4.

As shown in Table 1, the splitter overflow or raw dilbit 20 contained 6 about 4.57% water and 0.76 % solids.

7 The splitter overflow was continuously fed through line 10 into the 8 polisher 22, where the residence time was about 35 min. During this short 9 residence time, water content in the polisher overflow (polished dilbit 39) dropped to 2.91 % and solids content down to 0.36%. This polished dilbit 11 quality would not be entirely adequate for further processing in the bitumen 12 upgrading plant.

13 Table 1 14 Summary of continuous splitter/polisher operation without demulsifier Splitter Splitter Splitter Polisher Polisher Feed Overflow Underflow Overflow UnderFlow Flow Rate, mg/I 191.14 145.96 45.18 132.29 13.67 Bitumen, % 48.16 59.72 10.81 60.02 56.71 Naphtha, % 26.57 32.65 6.92 34.36 16.04 Water, % 19.97 4.57 69.68 2.91 20.72 Solids 4.77 0.76 17.75 0.36 4.58 {E4160765. DOC;1 j20 1 To improve dilbit quality, a series of experiments were conducted to 2 investigate the effects of demulsifier addition and prolonged settling. In one 3 such experiment, demulsifier was continuously injected into the splitter 4 overflow, at a dosage of 40 ppm, before it entered the polisher column. When the polisher column was completely filled with the demulsifier-treated raw 6 dilbit, the operation was stopped. At this point, both the splitter and polisher 7 columns were completely filled with dilbit. However, the first splitter column 8 contained dilbit with no demulsifier and the polisher column contained dilbit 9 with 40 ppm of demulsifier. The diluted bitumen in the two columns was allowed to stand for up to 26 h while the temperature inside the columns was 11 controlled at 80 C, by re-circulating hot water through water jackets.
Samples 12 from different depths of the two vessels were taken periodically for water 13 content analysis by Karl Fisher titration.

14 Figure 3 shows the water contents in diluted bitumen remaining in the first column, as a function of settling -time. As illustrated, the water content 16 dropped from 3.5% to 2.8% in the first hour and to 2.4% within 3 hours.
After 17 settling for 6 hours, the water content stayed at a constant level, 2.2%.
18 Further increases in settling time, up to 25 h, did not change the water content 19 at all. This indicates that the final concentration of 2.2% was very stable.
Without demulsifier, it was not possible to remove the remainder of water by 21 gravitational settling within a reasonable settling time.

{E4160765.DOC;1}21 1 However, in the second column, where 40 ppm of demulsifier were 2 present in the dilbit, the removal of water improved dramatically, as shown in 3 Figure 4. Water content dropped from 3.5% to 1.3 %, even during the 4 continuing operation, when the second column was filling up (about 30 min).
After 3 hours of settling, water content dropped to 0.8% and eventually down 6 to 0.2% over the 26 hour period. As demonstrated, the addition of demulsifier 7 to the polisher feed, combined with extended settling, can produce essentially 8 dry dilbit.

9 Figures 3 and 4 also show that the water contents at different depths are almost the same, in the range of depths studied in this work. This reveals 11 that the water separation is not a simple droplet settling process, where 12 settling velocity is controlled by the size of droplets as introduced in the feed.
13 Based on the test results, we postulate that the demulsifier de-stabilizes the 14 water emulsion and allows small droplets to form much larger aggregates.
Once the droplets agglomerate to larger formations, they settle out very 16 quickly through the entire depth of the oil phase. The residence time, required 17 in the polisher, is the time needed for the process of droplet agglomeration to 18 be completed.

19 In summary, the splitter overflow raw dilbit advantageously can be treated by the addition of suitable demulsifier and settling in a separate vessel 21 for sufficient time to achieve the desired level of water content. With addition 22 of appropriate demulsifier and given sufficient settling time, a very high quality 23 dilbit can be produced.

{E4160765.DOC;1}22 1 Example 2- Splitter and Scrubber 2 In another experiment, the same two columns were connected as 3 shown in Figure 2b and operated as splitter 3 and scrubber 32. Bituminous 4 froth was initially mixed with fresh naphtha in the feed mixer 1 and introduced to the splitter column as described in Example 1. The separation process in 6 the splitter column was the same as in experiment 1. The splitter overflow 7 stream was weighed and sampled. The stream of tailings 13 from the splitter 8 column was mixed with fresh naphtha, added at a rate of 64.35 g/minute, and 9 introduced to the scrubber column. Since the amount of bitumen remaining in splitter tails was only a small fraction of the total hydrocarbon ("HC") entering 11 the process, the N/B ratio in the scrubber column was an order of magnitude 12 higher than that in the splitter feed. As previously explained, it was 13 determined that at N/B ratios exceeding 4/1, the HC/clay structures 14 responsible for the formation of the rag become unstable.

The released HC in the scrubber column overflow 33 contained very 16 littie water and solids, whereas the scrubber underflow tails 36 contained very 17 little hydrocarbon. As soon as the scrubber overflow stream became 18 available for re-circulation, we discontinued the addition of fresh naphtha to 19 the fresh froth and replaced it with the high N/B scrubber overflow. The process continued for four hours, until we were satisfied that a steady flow 21 condition was reached. The material balance data, recorded during the 22 steady state condition, are shown in Table 2.

(E4160765.D0C;1}23 1 Table 2 2 Summary of continuous splitter/scrubber operation without demulsifier Splitter Splitter Splitter Scrubber Scrubber Scrubber Feed Overflow Underflow Feed Overflow Underflow Flow Rate, mg/I 259.59 183.55 76.03 140.38 80.60 59.78 Bitumen, % 46.57 57.77 19.51 10.56 17.10 1.75 Naphtha, % 30.05 37.69 11.59 51.97 89.95 0.78 Water, % 18.08 3.57 53.09 28.76 1.09 66.06 Solids, % 3.48 0.68 10.23 5.54 0.06 27.48 4 Bitumen and naphtha recoveries in this experiment were 99.43% and 99.14%
respectively.

{E4160765.DOC;1}24

Claims (28)

1. A process for cleaning bitumen froth comprising bitumen contaminated with water and solids, the solids comprising sand and fine clay particles, comprising:

diluting the bitumen froth with a light hydrocarbon diluent to form a dilfroth;
providing a splitter vessel forming a vapor-tight chamber for gravity settling, said vessel having an overflow outlet at its upper end, an underflow outlet at its lower end and means for feeding incoming dilfroth into the chamber;

feeding dilfroth into the chamber through the feed means and temporarily retaining it therein so that the dilfroth settles to form a bottom layer of splitter tails comprising sand, hydrocarbons and aqueous middlings, an intermediate layer of rag comprising water, fine clay particles and hydrocarbons collected in discrete three dimensional structures, and a top layer of raw dilbit comprising hydrocarbons containing water and fine clay particles, and aqueous middlings combining with the rag and dilbit to create a discernable hydrocarbons/water interface;

the feed means being operative to directly feed the incoming dilfroth into the middlings;

removing dilbit through the overflow outlet; and removing splitter tails through the underflow outlet.

2. The process as set forth in claim 1 wherein the incoming dilfroth is fed into the chamber at a rate less than 6 m3/h for each m2 of horizontal cross-sectional rag area.

3. The process as set forth in claim 1 or 2 comprising:

monitoring the hydrocarbons/water interface and controlling at least one of feeding and removing rates to maintain the interface at a generally constant elevation to limit hydrocarbon losses in the splitter tails.

4. The process as set forth in claim 1, 2 or 3 wherein:

the fed dilfroth settles to form splitter tails which contain less than 20% by weight of the hydrocarbons in the dilfroth.

5. The process as set forth in claim 1, 2, 3 or 4 wherein:

the fed dilfroth settles to form dilbit which contains less than 3 percent by weight solids and less than 8 percent by weight water.

6. The process of any one of claims 1 to 5 wherein:

the bitumen froth is diluted with sufficient diluent to produce dilfroth having a diluent/bitumen ratio in the range of about 0.5:1 to about 0.8:1.

7. A process for cleaning bitumen froth containing bitumen contaminated with water and solids, the solids comprising sand and fine clay particles, comprising:

diluting the bitumen froth with a light hydrocarbon diluent to form a dilfroth;
subjecting the dilfroth to gravity settling in an enclosed first zone of separation to produce an overflow stream of raw dilbit, comprising hydrocarbons containing water and fine clay particles, and an underflow stream of first zone tails, comprising sand and aqueous middlings; and subjecting the raw dilbit to gravity settling in an enclosed second zone of separation to produce an overflow stream of polished dilbit and an underflow stream of sludge.

8. The process set forth in claim 7 comprising:

adding demulsifier to the raw dilbit treated in the second zone of separation.

9. The process set forth in claim 7 or 8 wherein:

the raw dilbit is gravity settled in the second zone of separation for sufficient time to produce polished dilbit containing less than 1.0 percent by weight water and less than 0.3 percent by weight solids.

10. The process as set forth in claim 7, 8 or 9 wherein:

the dilfroth settles to produce raw dilbit containing less than 3 percent by weight solids and less than 8 percent by weight water and tails containing less than 15 percent by weight hydrocarbons.

11. The process as set forth in claim 7, 8, 9 or 10 wherein:

the rate of feeding incoming dilfroth into the first zone is maintained at less than 8 m3/h for each m2 of horizontal cross-sectional first zone area.

12. The process as set forth in claim 7, 8, 9, 10 and 11 wherein the dilfroth settles to produce first zone tails containing less than 20 percent by weight of the hydrocarbons in the dilfroth.

13. The process as set forth in any one of claims 7 to 12 comprising:

mixing the first zone tails with diluent and subjecting the produced diluted first zone tails to gravity settling in an enclosed third zone of separation to produce an overhead stream of scrubber hydrocarbons and an underflow stream of scrubber tails.

14. The process set forth in claim 13 comprising:
recycling scrubber hydrocarbons to the first zone.

15. The process set forth in claim 13 and 14 wherein:

sufficient diluent is added to the first zone tails to produce diluted first zone tails having a diluent/bitumen ratio in the range of about 4:1 to about 10:1.

16. A process for cleaning bitumen froth containing bitumen contaminated with water and solids, the solids comprising sand and fine clay particles, comprising:

diluting the bitumen froth with a light hydrocarbon diluent to form a dilfroth;
subjecting the dilfroth to gravity settling in a vapor-tight splitter chamber to produce an overflow stream of raw dilbit, comprising hydrocarbons containing water and fine clay particles and being substantially free of sand, and an underflow stream of splitter tails, comprising sand and aqueous middlings; and mixing the splitter tails with sufficient diluent to increase the diluent to bitumen ratio to a value in the range of about 4:1 to about 10:1;and subjecting the produced diluted splitter tails to gravity settling in a vapor-tight scrubber chamber to produce an overhead stream of scrubber hydrocarbons and an underflow stream of scrubber tails.

17. The process set forth in claim 16 wherein:
the light hydrocarbon diluent is naphtha; and the naphtha to bitumen ratio in the dilfroth is in the range of about 0.5:1 to about 0.8:1.

18. The process as set forth in claim 17 wherein:

the dilfroth settles to produce splitter tails which comprise 10 - 25 percent by weight solids and 8 - 20 percent by weight hydrocarbons.

19. The process as set forth in claim 16, 17 or 18 wherein:
scrubber hydrocarbons are recycled to the splitter chamber.

20. The process as set forth in claim 16, 17, 18 or 19 comprising:

subjecting the raw dilbit to gravity settling in a vapor-tight polisher chamber to produce an overflow stream of polished dilbit and an underflow stream of sludge.

21. The process as set forth in claim 20 comprising:

adding demulsifier to the raw dilbit treated in the polisher chamber.

22. The process as set forth in claim 21 wherein:

the raw dilbit is gravity settled in the polisher chamber for sufficient time to produce polished dilbit containing less than 1.0 percent by weight water and less than 0.3 percent by weight solids.

23. The process as set forth in any one of claims 1 to 15 wherein:
the diluent is naphtha.

24. The process set forth in any one of claims 16 to 23 comprising:

maintaining the rate of feeding incoming dilfroth to the splitter chamber at less than 6 m3/h for each m2 of horizontal cross-sectional zone area.

25. The process as set forth in any one of claims 1 to 6 wherein:

the splitter vessel chamber is free of an obstruction to fluid flow therethrough.

26. The process as set forth in any one of claims 7 to 15 wherein:

each zone is free of an obstruction to fluid flow therethrough.

27. The process as set forth in any one of claims 16 to 24 wherein:
each chamber is free of an obstruction to fluid flow therethrough.

28. The process as set forth in claims 25, 26 or 27 wherein:

said obstruction is inclined plates.