US20150008161A1

US20150008161A1 - Method for reducing rag layer volume in stationary froth treatment

Info

Publication number: US20150008161A1
Application number: US13/933,976
Authority: US
Inventors: Yin Ming Samson Ng; Brian Knapper; George Cymerman; Tam Tran; Allan Yeung
Original assignee: Syncrude Canada Ltd
Current assignee: Syncrude Canada Ltd
Priority date: 2013-07-02
Filing date: 2013-07-02
Publication date: 2015-01-08

Abstract

A method for reducing rag layer volume in a stationary bitumen froth treatment process is provided, comprising subjecting dilfroth having a naphtha diluent to bitumen ratio of about 0.7 to gravity settling in a splitter vessel to produce an overflow stream of raw dilbit and an underflow stream of splitter tails; mixing the splitter tails with a naphtha diluent to give a mixture having a naphtha diluent to bitumen ratio of less than about 6:1 in a scrubber feed tank; and subjecting the mixture to gravity settling and agitation in a scrubber vessel to produce an overhead stream of scrubber hydrocarbons and an underflow stream of scrubber tails.

Description

FIELD OF THE INVENTION

The present invention relates to a method for reducing rag layer volume in a stationary bitumen froth treatment process by agitating naphtha diluted bitumen froth and using a low naphtha to bitumen ratio at specific treatment stages in a stationary froth treatment process.

BACKGROUND OF THE INVENTION

Oil sand, as known in the Athabasca region of Alberta, Canada, comprises water-wet, coarse sand grains having flecks of a viscous hydrocarbon, known as bitumen, trapped between the sand grains. The water sheaths surrounding the sand grains contain very fine clay particles. Thus, a sample of oil sand, for example, might comprise 70% by weight sand, 14% fines, 5% water and 11% bitumen (all % values stated in this specification are to be understood to be % by weight).
For the past 25 years, the bitumen in Athabasca oil sand has been commercially recovered using a water-based process. In the first step, the oil sand is slurried with process water, naturally entrained air and, optionally, caustic (NaOH). The slurry is mixed, for example in a tumbler or pipeline, for a prescribed retention time, to initiate a preliminary separation or dispersal of the bitumen and solids and to induce air bubbles to contact and aerate the bitumen. This step is referred to as “conditioning”.
The conditioned slurry is then further diluted with flood water and introduced into a large, open-topped, conical-bottomed, cylindrical vessel (termed a primary separation vessel or “PSV”). The diluted slurry is retained in the PSV under quiescent conditions for a prescribed retention period. During this period, aerated bitumen rises and forms a froth layer, which overflows the top lip of the vessel and is conveyed away in a launder. Sand grains sink and are 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 mixture containing fine solids and bitumen, extend between the froth and sand layers.
The wet tailings and middlings are separately withdrawn, combined 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 vessel to assist with flotation. This vessel is referred to as the TOR vessel. The bitumen recovered by flotation in the TOR vessel is recycled to the PSV. The middlings from the deep cone vessel are further processed in induced air flotation cells to recover contained bitumen.
The bitumen froths produced by the PSV are subjected to cleaning, to reduce water and solids contents so that the bitumen can be further upgraded. More particularly, it has been conventional to dilute this bitumen froth with a light hydrocarbon diluent, for example, with naphtha, to increase the difference in specific gravity between the bitumen and water and to reduce the bitumen viscosity, to thereby aid in the separation of the water and solids from the bitumen. This diluent diluted bitumen froth is commonly referred to as “dilfroth”. It is desirable to “clean” dilfroth, as both the water and solids pose fouling and corrosion problems in upgrading refineries. By way of example, the composition of naphtha-diluted bitumen froth typically might have a naphtha/bitumen ratio of 0.65 and contain 20% water and 7% solids. It is desirable to reduce the water and solids content to below about 3% and about 1%, respectively.
Separation of the bitumen from water and solids may be done by treating the dilfroth in a sequence of scroll and disc centrifuges. Alternatively, the dilfroth may be subjected to gravity separation in a series of inclined plate separators (“IPS”) in conjunction with countercurrent solvent extraction using added light hydrocarbon diluent. However, these treatment processes still result in bitumen often containing undesirable amounts of solids and water.
More recently, a staged settling process (often referred to as Stationary Froth Treatment or SFT) for cleaning dilfroth was developed as described in U.S. Pat. No. 6,746,599, whereby dilfroth is first subjected to gravity settling in a splitter vessel to produce a splitter overflow (raw diluent diluted bitumen or “dilbit”) and a splitter underflow (splitter tails) and then the raw dilbit is further cleaned by gravity settling in a polisher vessel for sufficient time to produce an overflow stream of polished dilbit and an underflow stream of polisher sludge. Residual bitumen present in the splitter tails can be removed by mixing the splitter tails with additional naphtha and subjecting the produced mixture to gravity settling in a scrubber vessel to produce an overhead stream of scrubber hydrocarbons, which stream is recycled back to the splitter vessel.
However, a rag layer tends to form between the bitumen phase and the tailings phase in the scrubber vessel during gravity settling of the splitter tails/naphtha mixture, and to a lesser extent, in the polisher vessel during gravity settling of the raw dilbit. It is believed that the rag layer may be a result of stable water-in-oil emulsions persisting, primarily due to the clay solids present in the diluted bitumen froth. The rag layer is a mixture of partially oil-wet solids, oil and water-in-oil emulsions. Much of the clay solids are kaolinite and illite. The formation of such a rag layer prevents complete separation of the diluted bitumen from the water and solids, reduces dewatering, and depresses bitumen recovery.
Accordingly, there is a need for a method of reducing and/or breaking the rag layer in stationary bitumen froth treatment processes.

SUMMARY OF THE INVENTION

The current application is directed to a method of reducing rag layer volume in stationary bitumen froth treatment processes. It was surprisingly discovered that by conducting the method of the present invention, one or more of the following benefits may be realized:
(1) Mixing of the rag layer that forms in a separation vessel significantly reduces the rag layer volume. In particular, rag layer mixing alone significantly reduces rag layer volume compared to feed (e.g., scrubber feed) mixing alone. Gentle or mild mixing is sufficient. The combined use of rag layer mixing and scrubber feed mixing is more effective in reducing the rag layer volume compared to either rag layer mixing alone or feed mixing alone.
(2) Use of a low scrubber naphtha to bitumen ratio (less than about 4:1, preferably less than about 3:1) for the scrubber feed contributes to a further reduction in rag layer volume by minimizing the precipitation of asphaltenes which normally stabilize the rag layer.
(3) Reduction in rag layer volume is optimally achieved by combining rag mixing, scrubber feed mixing, and a low naphtha to bitumen ratio for the scrubber feed, without necessitating silicate addition to the bitumen froth or rag water addition to the scrubber.
(4) Combining rag mixing, scrubber feed mixing, and a low naphtha to bitumen ratio for the scrubber feed yielded a scrubber product having a bitumen content greater than about 20 wt % and a solids content less than about 5 wt %. The enhancement in scrubber product quality reduces the amount of water and solids recycled to the splitter feed, thereby, in turn, improving splitter product quality.
(5) Agitation of the bitumen froth at various treatment stages within gravity settlers including for example, the scrubber feed tank, scrubber and polisher, may reduce the rag layer volume.
Thus, use of the present invention may improve bitumen recovery and product quality by effectively reducing the rag layer volume.
In one aspect, a method of reducing rag layer volume in a stationary bitumen froth treatment process is provided, comprising:

- subjecting dilfroth having a naphtha diluent to bitumen ratio of about 0.7 to gravity settling in a splitter vessel to produce an overflow stream of raw dilbit and an underflow stream of splitter tails;
- mixing the splitter tails with a naphtha diluent to give a mixture having a naphtha diluent/bitumen ratio of less than about 6:1; and
- subjecting the mixture to gravity settling and agitation in a scrubber vessel to produce an overhead stream of scrubber hydrocarbons and an underflow stream of scrubber tails.

In one embodiment, the method further comprises subjecting the raw dilbit to gravity settling and agitation in a polisher vessel to produce an overflow stream of polished dilbit and an underflow stream of polisher sludge.
In one embodiment, the naphtha diluent to bitumen ratio of the mixture is less than 4:1. In another embodiment, the naphtha diluent to bitumen ratio of the mixture is less than or equal to 3:1.
In one embodiment, mixing reduces the rag volume in a polisher vessel at naphtha diluent to bitumen ratio of about 0.7.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring to the drawings wherein like reference numerals indicate similar parts throughout the several views, several aspects of the present invention are illustrated by way of example, and not by way of limitation, in detail in the figures, wherein:

FIG. 1 is a graph showing, in general, one embodiment of a bitumen froth treatment process useful in the present invention.

FIG. 2 is a graph showing the rag layer volume (mL) for each test condition.

FIG. 3 is a graph showing the rag layer solids content (mass %) for each test condition.

FIG. 4 is a graph showing the rag layer water content (mass %) for each test condition.

FIG. 5 is a graph showing the rag layer bitumen content (mass %) for each test condition.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The detailed description set forth below in connection with the appended drawings is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments contemplated by the inventor. The detailed description includes specific details for the purpose of providing a comprehensive understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details.
The present invention relates generally to a method of reducing and/or breaking rag layer in a stationary bitumen froth treatment process. The method includes agitating bitumen froth and using a low naphtha to bitumen ratio at specific stages of the froth treatment process.
FIG. 1 is a general schematic of a stationary bitumen froth treatment process using gravity settlers, which can be used in one embodiment of the present invention. Bitumen froth 10 is initially received from an extraction facility which extracts bitumen from oil sand using a water extraction process known in the art. The bitumen froth 10, as received, typically comprises about 60% bitumen, about 30% water and about 10% solids.
A hydrocarbon diluent 12 is mixed with bitumen froth 10 in a suitable mixer 14 to provide diluent-diluted bitumen froth (referred to herein as “dilfroth”) 16. In one embodiment, the hydrocarbon diluent 12 is naphtha. The naphtha is supplied in an amount such that the naphtha to bitumen ratio of the dilfroth 16 is preferably in the range of 0.5 to 1.0, most preferably about 0.7.
As used herein, the term “silicate” refers to any of a wide variety of compounds containing silicon, oxygen and one or more metals with or without hydrogen, for example, a sodium silicate having the general formula xNa₂O.ySiO₂. Silicates are known to change the surface properties of fine solids, causing them to associate with the water phase, rather than the oil phase. A silicate 18 is typically added to the dilfroth 16 at a concentration ranging between about 0.0001 to about 0.1% wt/wt or more. However, in the present invention, reduction of the rag layer volume may be achieved without the addition of silicate 18. In one embodiment, addition of silicate 18 to the bitumen froth 10 is optional. The dilfroth 16 may be fed into an agitated feed tank 20, for example, a splitter feed tank.
The agitated dilfroth 22 is then pumped into the chamber of a gravity settler vessel or splitter 24 having a conical bottom 26, and underflow and overflow outlets 28, 30 at its bottom and top ends, respectively. The dilfroth 22 is temporarily retained in the splitter 24 for a sufficient length of time to allow a substantial portion of the solids and water to separate from the diluted bitumen. The splitter overflow is referred to as raw dilbit 32. Line 34 withdraws a stream of splitter tails 36 through the underflow outlet 28. Splitter overflow line 38 collects an overflow stream of raw dilbit 32.
The bottom layer of splitter tails 36 comprises mainly sand and aqueous middlings, and some hydrocarbons, and the top layer of raw dilbit 32 comprises mainly hydrocarbons containing some water and a reduced amount of fines (clay particles).
The raw dilbit 32 produced through the splitter overflow outlet 30 routinely comprises less than about 3% solids, and may be pumped to a second gravity settler vessel or polisher (40) following optional addition of a demulsifier to enhance water separation, and subjected to further gravity settling therein. The polisher is operated at naphtha to bitumen ratio of about 0.7. Water droplets coalesce and settle, together with most of the remaining fine solids. Since a rag layer may form during gravity settling, the raw dilbit 32 is thus agitated while being retained within the polisher 40 to reduce the rag layer volume. Polisher dilbit 42, comprising hydrocarbons, typically containing <3.0 wt. % water and <1.0 wt. % solids, is removed as an overflow stream from the polisher 40. Polisher sludge 44, comprising water, solids and typically between about 20-70% hydrocarbons, or 12-40% bitumen, is removed from the polisher 40 as an underflow stream.
The splitter tails 36 produced through the splitter underflow outlet 28 are pumped through line 46, to an agitated feed tank 48 or scrubber feed tank, where it may be mixed with polisher sludge 44 and naphtha 12 to produce a scrubber feed 50 preferably having a naphtha to bitumen ratio less than about 4:1. In one embodiment, the naphtha to bitumen ratio is less than about 3:1. The use of a naphtha to bitumen ratio less than about 4:1 prevents the precipitation of asphaltenes which normally stabilize the rag layer. The rag emulsion is rendered weaker and easier to break down through agitation of the scrubber feed 50 with agitator 66. In one embodiment, agitation is conducted at a speed in the range of about 700 rpm to about 1300 rpm, preferably about 700 rpm.
The agitated scrubber feed 50 is then introduced to a third gravity settler vessel or scrubber 52. The scrubber feed 50 is then temporarily retained in the scrubber 52 (for example for 20 to 30 minutes) and subjected to gravity settling therein. A stable rag layer typically forms between the diluted bitumen layer and the water layer in the scrubber 52 during gravity settling of the scrubber feed 50. The scrubber feed 50 is agitated with agitator 64 while being retained within the scrubber 52. Without being bound to theory, it is believed that agitation induces shear, which minimizes rag layer volume and breaks the gel-like rag layer, but not the water-in-oil emulsion which is present in the oil and water interface. In one embodiment, agitation is conducted at a speed in the range of about 52 rpm to about 188 rpm, preferably about 52 rpm.
Without being bound by theory, it is believed that addition of water 54 to the rag layer removes fine solids; however, in the present invention, reduction of the rag layer volume may be achieved without the addition of water 54 to the rag layer within the scrubber 52. In one embodiment, addition of water 54 to the rag layer is optional.
The scrubber overflow stream 56 of hydrocarbons, mainly comprising naphtha and bitumen, is removed through an overflow outlet 58 and in one embodiment may be recycled through line 60 to the mixer 14. Scrubber underflow stream of scrubber tails 62, comprising water and solids containing some hydrocarbons, is removed and forwarded to a naphtha recovery unit (not shown).
Exemplary embodiments of the present invention are described in the following Example, which is set forth to aid in the understanding of the invention, and should not be construed to limit in any way the scope of the invention as defined in the claims which follow thereafter.

Example 1

The flow sheet used for the evaluation of the rag volume reduction is essentially the same as that shown in FIG. 1 except that the polisher vessel was omitted to enable timely experimentation. Five variables including silicates concentration, water addition to rag layer, rag layer agitation, scrubber feed agitation and scrubber N/B ratio were evaluated using a 2^5-1fractional factorial design resulting in 16 different experimental run conditions. Table 1 summarizes the range of the independent variables and the test matrix. In addition, Table 1 includes repeat conditions and an additional run using higher rag layer agitation (Condition No. 18), resulting in a total of 20 runs completed.

TABLE 1

Test Matrix

		Water	Rag Layer
	Silicates	Addition	Agitation	Scrubber Feed	Scrubber
Condition	wt. %	(g/min)	RPM	RPM	N/B

1	0	0	0	700	>6
2	0	16	52	700	>6
3	0.1	0	52	700	>6
4	0.1	16	0	700	>6
5	0.1	16	52	1300	>6
6	0	0	52	1300	>6
7	0	16	0	1300	>6
8	0	0	52	700	<3
9	0	16	0	700	<3
10	0	0	0	1300	<3
11	0	16	52	1300	<3
12	0.1	0	52	1300	<3
13	0.1	16	0	1300	<3
14	0.1	0	0	1300	>6
15	0.1	0	0	700	<3
16	0.1	16	52	700	<3
17	0	0	0	700	>6
18	0	0	188	700	>6
19	0	0	0	700	>6
20	0.1	16	52	700	<3

In this evaluation, controlling the rag layer growth in the scrubber vessel is the primary objective. Quantifying whether the rag layer has been reduced or changed is done by measuring the rag volume and rag layer composition. It is desirable for the rag to occupy less volume in the scrubber, which directly implies that there is physically less rag layer present in the scrubber. The rag layer composition is not a concern under steady state conditions, provided the rag layer is not growing. Therefore, the following analysis focuses on the rag layer growth, i.e., the rag layer's volume and not its composition. Thus, the experimental design evaluates the effect of the five variables on rag layer volume.
The amount of rag layer produced varied considerably with the various conditions and, in some instances, there was over an order of magnitude difference in rag layer volume, from 71 to 780 mL. The volume of rag layer produced in each condition is summarized in FIG. 2. Five conditions (9, 10, 14, 17 and 19) produced the largest rag volume, wherein all five conditions did not have rag mixing. Conditions 2, 4, 8, 16, and 20 produced some of the lowest amounts of rag volume; these five conditions involved either rag mixing or rag water addition or both. The variability of the measured rag volume based on repeats was 31% relative errors. Based on 95% confidence limits, the maximum and minimum rag volumes are significantly different.
Rag layer composition appears to be more variable among the various conditions tested, as shown in FIGS. 3, 4, and 5. The results appear to indicate that the rag layer bitumen content increased when the scrubber N/B was lowered (FIG. 5). Otherwise, no particular trend of the composition with operating conditions is observed.
The effects of the five rag layer mitigation variables on the rag layer volume reduction were evaluated using an experimental design software package (Design Expert® by Stat-Ease). This software enabled the use of all experimental data, including repeats, to produce parameter estimates and determine the significant of the parameter estimates at 95% confidence limits. The empirical model representing rag volume, Y₁is:
Y ₁=310−57X ₂−110X ₃+65X ₁ X ₃+47X ₁ X ₄+72X ₂ X ₃−82X ₂ X ₅ R ²=0.91
Note that X_irepresents coded value of independent variable i. The results show that there are two main effects and four two-factor interaction effects to be significant at 95% confidence limits. The model has a R²of 91%, which means that 91% of the data variation can be explained by the model. Among these effects, rag layer mixing (X₃) has the most significant effect on the rag volume, i.e. high level of mixing reduced the rag volume. The other main effect is rag water addition, where addition of rag water reduced rag layer volume. The interpretation of two factor interaction effects is as follows:

X₁X₃: This term represents the interacting effect between the silicate and rag mixing. The interacting effect needs to be minimized to achieve a reduction in rag volume. Therefore the sign of these two variables must be opposite. Since the rag mixing has been assigned a positive value above, the silicate addition will be negative. As a result, the reduction of rag volume can be achieved through rag mixing and with no silicate addition.
X₁X₄: This term represents the interacting effect between the silicate and the Scrubber feed mixing. Similarly, the sign of the two variables needs to be opposite for rag volume reduction. Since the sign of the silicate is negative, the Scrubber feed mixing will be positive. Therefore, the reduction of rag volume required no silicate addition and high Scrubber feed mixing.
X₂X₃: This term represents the interacting effect between rag water addition and rag mixing. Again, the sign of the two variables need to be opposite to achieve the rag volume reduction. However, the main effect of these two variables suggests the sign to be the same. Under this scenario, magnitude of the three terms (X₂, X₃, and X₂X₃) required to be evaluated and optimized. If the rag volume is minimized, the results show that rag mixing must remain positive, but the sign of rag water addition will have to change to be negative.
X₂X₅: This interacting effect is between rag water addition and Scrubber N/B ratio. The sign of the two variables should be the same to allow the reduction of the rag. If the sign of rag water addition is negative, the sign of Scrubber N/B ratio should also be negative. The results suggest that a N/B ratio less than or equal to 3 should be to use to decrease the rag volume. This is not unexpected as N/B>4 would precipitate bitumen asphaltenes, which stabilize water in oil emulsion and hence the stability of the rag layer.

Based on the above evaluation, for rag volume reduction, the recommended rag mitigation variable settings are: no silicate and rag water addition, high rag and Scrubber feed mixing and low N/B ratio. Using these variables settings and the developed model (equation shown above), the rag layer volume can be estimated. Table 2 focuses on the mixing effects on rag layer volume. The standard flow sheet conditions were used, which required the N/B ratio to be greater than or equal to 6 and the scrubber feed mixing was set at 700 rpm to prevent water and solids settling in the scrubber feed tank. The rag layer volume without additional mixing introduced to the system was estimated to be 743 mL. Increasing the scrubber feed mixing from 700 to 1300 rpm reduced the rag layer volume to 649 mL. Addition of the rag layer mixing at 52 rpm significantly decreased the rag layer volume to 249 mL. The use of rag layer mixing at 52 rpm and an increase of scrubber feed mixing to 1300 rpm further decreased the rag volume to 155 mL. These results clearly demonstrated the impact of mixing on rag layer reduction.

TABLE 2

Variable	Rag volume, mL

Base case (no rag mixing and scrubber feed mixing	743
at 700 rpm)
Base case + Scrubber feed mixing (1300 rpm)	649
Base case + rag mixing (52 rpm)	249
Base case + rag mixing (52 rpm) + Scrubber feed	155
mixing (1300 rpm)

Without being bound to theory, a possible explanation as to why the recommended rag mitigation variable settings worked in the reduction of rag layer volume is offered as follows. The rag layer is comprised of multiple emulsions, which are stabilized by solids and/or bitumen asphaltenes. The majority of solids are hydrophobic solids as result of surface property change due to the interaction between the hydrophilic clays and naphthenic acid. The clays and natural surfactants are present naturally in oil sands and process water. It was proposed that addition of silicate could change the solids surface properties from hydrophobic to hydrophilic. However, it was found that silicate is not required for the rag layer volume reduction; these results may suggest that solids present in rag layer may not have originated from hydrophobic solids and they may be from the organic rich solids like humic matter. Water addition to the rag layer was hypothesized to remove the converted hydrophobic clay solids. Since the hypothesized hydrophilic clay solids do not seem present, addition of rag water is, therefore, not required. Both the scrubber feed mixing and rag layer mixing are used to break the emulsion and, hence, reduce the rag layer volume. The use of low scrubber N/B ratio prevents the precipitation of asphaltenes, hence, the rag emulsion is weaker and rag volume can be easier to break down by shear through mixing.

Example 2

An experimental condition was conducted to determine the impact of higher rag layer mixing on rag layer volume reduction. The only variable that changed was to increase the rag layer mixer speed to 188 rpm. All other rag layer mitigation variables were set at base case flow sheet conditions, i.e., no silicate or rag water addition, low scrubber feed mixer speed and high scrubber N/B ratio of greater than or equal to 6.
The rag volume comparison for the three rag mixer speeds is shown in Table 3. The rag layer volume at rag mixer speed of 52 rpm is not significantly different from the rag layer volume at rag layer mixer speed of 188 rpm. However, the rag layer volume at base case condition is significantly different from the rag layer volume at rag mixer speeds of both 52 rpm and 188 rpm.
TABLE 3

Rag

Variable Volume, ml

Base case 740

Base + rag layer mixing at 52 rpm 249

Base + high rag layer mixing at 188 rpm 273

The results in Table 3 show that rag mixing (52 to 188 rpm) did significantly reduce the scrubber rag layer volume compared with the base case. A higher rag mixer speed did not appear further reduce the rag layer volume. The impact of the shear on the scrubber rag layer was able to reduce the rag layer volume only to a certain extent. Other variables to minimize the formation of emulsion stabilizer, such as scrubber N/B ratio, are also important in the rag layer volume reduction.
The scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole, wherein reference to an element in the singular, such as by use of the article “a” or “an” is not intended to mean “one and only one” unless specifically so stated, but rather “one or more”. All structural and functional equivalents to the elements of the various embodiments described throughout the disclosure that are known or later come to be known to those of ordinary skill in the art are intended to be encompassed by the elements of the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims.

Claims

We claim:

1. A method for reducing rag layer volume in a stationary bitumen froth treatment process comprising:

subjecting dilfroth having a naphtha diluent to bitumen ratio of about 0.7 to gravity settling in a splitter vessel to produce an overflow stream of raw dilbit and an underflow stream of splitter tails;

mixing the splitter tails with a naphtha diluent to give a mixture having a naphtha diluent to bitumen ratio of less than about 6:1 in a scrubber feed tank; and

subjecting the mixture to gravity settling and agitation in a scrubber vessel to produce an overhead stream of scrubber hydrocarbons and an underflow stream of scrubber tails.

2. The method of claim 1, further comprising subjecting the raw dilbit to gravity settling and agitation in a polisher vessel at a naphtha diluent to bitumen ratio of about 0.7 to reduce and/or break rag layer and to produce an overflow stream of polished dilbit and an underflow stream of polisher sludge.

3. The method of claim 1, further comprising diluting bitumen froth with the produced scrubber hydrocarbons to form the dilfroth.

4. The method of claim 1, wherein the mixture has a naphtha diluent to bitumen ratio of less than 4:1.

5. The method of claim 1, wherein the mixture has a naphtha diluent to bitumen ratio of less than or equal to 3:1.

6. The method of claim 1, wherein agitation in the scrubber feed tank is conducted in the range of about 700 rpm to about 1300 rpm.

7. The method of claim 6, wherein agitation in the scrubber feed tank is conducted at about 700 rpm.

8. The method of claim 1, wherein agitation in the scrubber vessel is conducted in the range of 1 rpm to about 188 rpm.

9. The method of claim 8, wherein agitation in the scrubber vessel is conducted at about 52 rpm to about 188 rpm.

10. The method of claim 1, wherein agitation in the scrubber feed tank is conducted at about 1300 rpm and agitation in the scrubber vessel is conducted at about 52 rpm.

11. The method of claim 3, wherein optionally, silicate is added to the bitumen froth.

12. The method of claim 1, wherein optionally, water is added to the scrubber vessel.