CA3010123C - Bitumen recovery from coarse sand tailings - Google Patents

Abstract

A method includes providing a coarse sand tailings stream (CST) comprising sand, fines, clay, water, and bitumen; mixing the CST to liberate the bitumen from the sand and disperse the bitumen in the water to form a mixed CST stream; and separating the sand from the bitumen to form a bitumen-rich stream.

Description

BITUMEN RECOVERY FROM COARSE SAND TAILINGS
BACKGROUND
Field of Disclosure [0001] The disclosure relates generally to the field of oil sand tailings.
Description of Related Art

[0002] This section is intended to introduce various aspects of the art, which may be associated with the present disclosure. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present disclosure.
Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.

[0003] Modern society is greatly dependent on the use of hydrocarbon resources for fuels and chemical feedstocks. Hydrocarbons are generally found in subsurface formations that can be termed "reservoirs". Removing hydrocarbons from the reservoirs depends on numerous physical properties of the subsurface formations, such as the permeability of the rock containing the hydrocarbons, the ability of the hydrocarbons to flow through the subsurface formations, and the proportion of hydrocarbons present, among other things.
Easily harvested sources of hydrocarbons are dwindling, leaving less accessible sources to satisfy future energy needs. As the costs of hydrocarbons increase, the less accessible sources become more economically attractive.

[0004] Recently, the harvesting of oil sand to remove heavy oil has become more economical. Hydrocarbon removal from oil sand may be performed by several techniques.
For example, a well can be drilled to an oil sand reservoir and steam, hot air, solvents, or a combination thereof, can be injected to release the hydrocarbons. The released hydrocarbons may be collected by wells and brought to the surface.

[0005] In another technique, strip or surface mining may be performed to access the oil sand, which can be treated with water, steam or solvents to extract the heavy oil.

[0006] Oil sand extraction processes are used to liberate and separate bitumen from oil sand so that the bitumen can be further processed to produce synthetic crude oil or mixed with diluent to form "dilbit" and be transported to a refinery plant. Numerous oil sand extraction processes have been developed and commercialized, many of which involve the use of water as a processing medium. Where the oil sand is treated with water, the technique may be referred to as water-based extraction (WBE). WBE is a commonly used process to extract bitumen from mined oil sand.

[0007] One WBE process is the Clark hot water extraction process (the "Clark Process").
This process typically requires that mined oil sand be conditioned for extraction by being crushed to a desired lump size and then combined with hot water and perhaps other agents to form a conditioned slurry of water and crushed oil sand. In the Clark Process, an amount of sodium hydroxide (caustic) may be added to the slurry to increase the slurry pH, which enhances the liberation and separation of bitumen from the oil sand. Other WBE
processes may use other temperatures and may include other conditioning agents, which are added to the oil sand slurry, or may operate without conditioning agents. This slurry is first processed in a Primary Separation Cell (PSC), also known as a Primary Separation Vessel (PSV), to extract the bitumen from the slurry.

[0008] In one bitumen extraction process, a water and oil sand slurry is separated into three major streams in the PSC: bitumen froth, middlings, and a PSC underflow (also known as primary separation tailings or coarse sand tailings (CST)).
100091 Regardless of the type of WBE process employed, the process will typically result in the production of a bitumen froth that requires treatment with a solvent.
For example, in the Clark Process, a bitumen froth stream comprises bitumen, solids, and water. Certain processes use naphtha to dilute bitumen froth before separating the product bitumen by centrifugation. These processes are called naphthenic froth treatment (NFT) processes. Other processes use a paraffinic solvent, and are called paraffinic froth treatment (PFT) processes, to produce pipelineable bitumen with low levels of solids and water. In the PFT
process, a paraffinic solvent (for example, a mixture of iso-pentane and n-pentane) is used to dilute the froth before separating the product, diluted bitumen, by gravity. A portion of the asphaltenes in the bitumen is also rejected by design in the PFT process and this rejection is used to achieve reduced solids and water levels. In both the NFT and the PFT
processes, the diluted tailings (comprising water, solids and some hydrocarbon) are separated from the diluted product bitumen.
[0010] Solvent is typically recovered from the diluted product bitumen component before the bitumen is delivered to a refining facility for further processing.
[0011] The PFT process may comprise at least three units: Froth Separation Unit (FSU), Solvent Recovery Unity (SRU) and Tailings SRU (TSRU). Mixing of the solvent with the feed bitumen froth may be carried out counter-currently in two stages in separate froth separation units. The bitumen froth comprises bitumen, water, and solids. A
typical composition of bitumen froth is about 60 wt. % bitumen, 30 wt. % water, and 10 wt. % solids.
The paraffinic solvent is used to dilute the froth before separating the product bitumen by gravity. The foregoing is only an example of a PFT process and the values are provided by way of example only. An example of a PFT process is described in Canadian Patent No.
2,587,166 to Sury.
[0012] From the PSC, the middlings, comprising bitumen and about 10-30 wt.
% solids, or about 20-25 wt. % solids, based on the total wt. % of the middlings, is withdrawn and sent to the flotation cells to further recover bitumen. The middlings are processed by bubbling air through the slurry and creating a bitumen froth, which is recycled back to the PSC. Flotation tailings (FT) from the flotation cells, comprising mostly solids and water, are sent for further treatment or disposed in an external tailings area (ETA). CST may be, for instance, released directly to tailings ponds or be subjected to a combination of flotation and hydrocyclone processes to recover bitumen and then desand the mixture.
[0013] In ETA tailings ponds, a liquid suspension of oil sand fines in water with a solids content greater than 2 wt. %, but less than the solids content corresponding to the Liquid Limit are called Fluid Fine Tailings (FFT). FFT settle over time to produce Mature Fine Tailings (MFT), having above about 30 wt. % solids.

[0014] It would be desirable to have an alternative method of recovering bitumen from coarse sand tailings (CST).
SUMMARY
[0015] According to one aspect, there is provided a method including providing a coarse sand tailings stream (CST) comprising sand, fines, clay, water, and bitumen;
mixing the CST
to liberate the bitumen from the sand and disperse the bitumen in the water to form a mixed CST stream; and separating the sand from the bitumen to form a bitumen-rich stream.
[0016] The foregoing has broadly outlined the features of the present disclosure so that the detailed description that follows may be better understood. Additional features will also be described herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] These and other features, aspects and advantages of the disclosure will become apparent from the following description, appending claims and the accompanying drawings, which are briefly described below.
[0018] It should be noted that the figures are merely examples and no limitations on the scope of the present disclosure are intended thereby. Further, the figures are generally not drawn to scale, but are drafted for purposes of convenience and clarity in illustrating various aspects of the disclosure.
[0019] Figure 1 is a schematic of a bitumen extraction method including a method for recovering bitumen from coarse sand tailings (CST).
[0020] Figure 2 is a chart of the effect of mixing on bitumen recovery from CST.
[0021] Figure 3 is a chart of the effect of mixing on the percentage of undigested bitumen in CST.
DETAILED DESCRIPTION
[0022] For the purpose of promoting an understanding of the principles of the disclosure, reference will now be made to the features illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended. Any alterations and further modifications, and any further applications of the principles of the disclosure as described herein are contemplated as would normally occur to one skilled in the art to which the disclosure relates.
It will be apparent to those skilled in the relevant art that some features that are not relevant to the present disclosure may not be shown in the drawings for the sake of clarity.
[0023] At the outset, for ease of reference, certain terms used in this application and their meaning as used in this context are set forth below. To the extent a term used herein is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in at least one printed publication or issued patent. Further, the present processes are not limited by the usage of the terms shown below, as all equivalents, synonyms, new developments and terms or processes that serve the same or a similar purpose are considered to be within the scope of the present disclosure.
[0024] Throughout this disclosure, where a range is used, any number between or inclusive of the range is implied.
[0025] A "hydrocarbon" is an organic compound that primarily includes the elements of hydrogen and carbon, although nitrogen, sulfur, oxygen, metals, or any number of other elements may be present in small amounts. Hydrocarbons generally refer to components found in heavy oil or in oil sand. However, the techniques described are not limited to heavy oils but may also be used with any number of other reservoirs to improve gravity drainage of liquids. Hydrocarbon compounds may be aliphatic or aromatic, and may be straight chained, branched, or partially or fully cyclic.
[0026] "Bitumen" is a naturally occurring heavy oil material. Generally, it is the hydrocarbon component found in oil sand. Bitumen can vary in composition depending upon the degree of loss of more volatile components. It can vary from a very viscous, tar-like, semi-solid material to solid forms. The hydrocarbon types found in bitumen can include aliphatics, aromatics, resins, and asphaltenes. A typical bitumen might be composed of:
19 weight (wt.) aliphatics (which can range from 5 wt. % - 30 wt. %, or higher);
19 wt. % asphaltenes (which can range from 5 wt. % - 30 wt. %, or higher);

30 wt. % aromatics (which can range from 15 wt. % - 50 wt. %, or higher);
32 wt. % resins (which can range from 15 wt. % - 50 wt. %, or higher); and some amount of sulfur (which can range in excess of 7 wt. %), based on a weight of the bitumen.
In addition, bitumen can contain some water and nitrogen compounds ranging from less than 0.4 wt. % to in excess of 0.7 wt. %, based on a weight of the bitumen. The percentage of the hydrocarbon found in bitumen can vary. The term "heavy oil" includes bitumen as well as lighter materials that may be found in a sand or carbonate reservoir.
[0027] "Heavy oil" includes oils which are classified by the American Petroleum Institute ("API"), as heavy oils, extra heavy oils, or bitumens. The term "heavy oil"
includes bitumen.
Heavy oil may have a viscosity of about 1,000 centipoise (cP) or more, 10,000 cP or more, 100,000 cP or more, or 1,000,000 cP or more. In general, a heavy oil has an API gravity between 22.3 API (density of 920 kilograms per meter cubed (kg/m3) or 0.920 grams per centimeter cubed (g/cm3)) and 10.00 API (density of 1,000 kg/m3 or 1 g/cm3).
An extra heavy oil, in general, has an API gravity of less than 10.0 API (density greater than 1,000 kg/m3 or 1 g/cm3). For example, a source of heavy oil includes oil sand or bituminous sand, which is a combination of clay, sand, water and bitumen. The recovery of heavy oils is based on the viscosity decrease of fluids with increasing temperature or solvent concentration. Once the viscosity is reduced, the mobilization of fluid by steam, hot water flooding, or gravity is possible. The reduced viscosity makes the drainage or dissolution quicker and therefore directly contributes to the recovery rate.
[0028] "Fine particles" or "fines" are generally defined as those solids having a size of less than 44 microns (um), that is, material that passes through a 325 mesh (44 micron).
[0029] "Coarse particles" are generally defined as those solids having a size of greater than 44 microns (m).
[0030] "Clays" are generally defined as those solids having a size of less than 2 microns, but some clays may be larger. Clays may include ceramics like aluminum and silicon oxide species like kaolinite and illite, and they may also include fine particles of other species such as iron oxides and quartzes.

[0031] A "bitumen extract" is generally defined as bitumen that has been extracted from oil sand.
[0032] A "bitumen product stream" or "bitumen product" is generally defined as a high grade bitumen product that may be suitable for transport within pipelines and processing within downstream refineries. A high grade bitumen product stream may have a solids content of less than 1 wt. %, or less than 0.1 wt. %, on a dry bitumen basis.
[0033] The term "solvent" as used in the present disclosure should be understood to mean either a single solvent, or a combination of solvents.
[0034] The terms "approximately," "about," "substantially," and similar terms are intended to have a broad meaning in harmony with the common and accepted usage by those of ordinary skill in the art to which the subject matter of this disclosure pertains. It should be understood by those of skill in the art who review this disclosure that these terms are intended to allow a description of certain features described and claimed without restricting the scope of these features to the precise numeral ranges provided. Accordingly, these terms should be interpreted as indicating that insubstantial or inconsequential modifications or alterations of the subject matter described and are considered to be within the scope of the disclosure.
[0035] The articles "the", "a" and "an" are not necessarily limited to mean only one, but rather are inclusive and open ended so as to include, optionally, multiple such elements.
[0036] "At least one," in reference to a list of one or more entities should be understood to mean at least one entity selected from any one or more of the entity in the list of entities, but not necessarily including at least one of each and every entity specifically listed within the list of entities and not excluding any combinations of entities in the list of entities. This definition also allows that entities may optionally be present other than the entities specifically identified within the list of entities to which the phrase "at least one" refers, whether related or unrelated to those entities specifically identified. Thus, as a non-limiting example, "at least one of A
and B" (or, equivalently, "at least one of A or B," or, equivalently "at least one of A and/or B") may refer, to at least one, optionally including more than one, A, with no B present (and optionally including entities other than B); to at least one, optionally including more than one, B, with no A present (and optionally including entities other than A); to at least one, optionally including more than one, A, and at least one, optionally including more than one, B
(and optionally including other entities). In other words, the phrases "at least one," "one or more," and "and/or" are open-ended expressions that are both conjunctive and disjunctive in operation. For example, each of the expressions "at least one of A, B and C,"
"at least one of A, B, or C," "one or more of A, B, and C," "one or more of A, B, or C" and "A, B, and/or C"
may mean A alone, B alone, C alone, A and B together, A and C together, B and C together, A, B and C together, and optionally any of the above in combination with at least one other entity.
[0037] A method may comprise: providing a coarse sand tailings stream (CST) comprising sand, fines, clay, water, and bitumen; mixing the CST to liberate the bitumen from the sand and disperse the bitumen in the water to form a mixed CST stream; and separating the sand from the bitumen to form a bitumen-rich stream.
[0038] By "liberate", it is meant to detach bitumen from sand.
[0039] By "disperse" it is meant to distribute liberated bitumen in the water.
[0040] The mixing may be any suitable mixing which liberates the bitumen from the sand and disperses the bitumen in the water to form a mixed CST stream, to a sufficient extent to that the mixed CST may be separated in the separation step. By "mixing", it is meant to provide sufficient shear in the aqueous slurry to liberate bitumen from the sand and increase a concentration of air bubbles in the system to facilitate bitumen flotation.
The shear may be, for instance, 2000-14000 s-1. The mixing may comprise mixing in an inline mixing unit, a mixing tank, or a length of pipe with pumps.
[0041] The method may further comprise adding a dilution water stream to the CST prior to or during the mixing to further disperse the bitumen. Dilution water is added to further reduce density and viscosity of the CST stream. The dilution water stream may be added to the CST in any suitable amount, for instance 10-30 vol. %, or about 20 vol. %, based on a volume of the CST.

[0042] The method may further comprise adding a gas to the CST prior to or during the mixing to further liberate the bitumen from the sand. The method may further comprise adding a gas to the mixed CST prior to of during the separating to further liberate the bitumen from the sand. The gas may be any suitable gas, and may comprise air, a nitrogen rich stream, CO2, a flue gas, or a combination thereof. The air may be dissolved in water or injected as a vapor.
[0043] The separating may comprise separating in any suitable unit, for instance a flotation vessel, a fluidized bed, an aerated fluidized bed, a hydrocyclone, or a combination thereof.
[0044] The bitumen-rich stream may comprise 0.1 to 4 wt. % bitumen.
[0045] The method may further comprise concentrating the bitumen-rich stream to form a concentrated bitumen-rich stream. The concentrating may be effected by any suitable means, for instance by flotation. The concentrating may be effected using any suitable unit, for instance a mechanical flotation cell, a flotation column, or a downcomer-type flotation unit.
[0046] The CST may have a sand content of 40 to 80 wt. %, or 50 to 70 wt.
%. The CST
may have a D50 of 150-350 microns, or 200 to 300 microns. The CST may have a temperature of 45 to 55 C. The CST may have a bitumen content of 0.05 to 4 wt.
%, or 0.1 to 3 wt. %. The CST may be from a bottom of a primary separation vessel (PSV).
[0047] Fig. 1 is a schematic of a bitumen extraction method including a method for recovering bitumen from coarse sand tailings (CST). An oil sand slurry stream (102) comprising mined bituminous ore and water is introduced into a primary separation vessel (PSV) (104). The PSV produces bitumen froth (106) for further processing, middlings (108), and coarse sand tailings (CST) (110). The middlings (108) are introduced into flotation cells (112) producing fine tailings (FT) (114) and recycle froth (116). The FT are passed through thickeners (118 and 120) forming thickened tailings (122 and 124), which are sent to tailings ponds (126). A recycle stream (128) is also formed, combined with the recycle froth (116), and recycled to the PSV (104).

- 9 -[0048] The coarse sand tailings stream (CST), comprising sand, fines, clay, water, and bitumen, is mixed in a mixer (130) to liberate the bitumen from the sand and disperse the bitumen in the water to form a mixed CST stream (132), and is passed to a separation unit (134) separating the sand from the bitumen to form a bitumen-rich stream.
[0049] Lab-scale experiments were conducted to investigate the effect of mixing on bitumen recovery. A known amount of CST was diluted with 20 vol. % process water. The mixture was then exposed to shear for 5 to 10 minutes in a mixing cell equipped with impellers. The mixture was then exposed to 5 to 10 minutes of air injection and mixing in the same tank. The recovered bitumen in the froth layer was then removed from the top of the vessel for bitumen content analysis. The remaining of the mixture was removed from the bottom for bitumen content analysis. This test was conducted at two different mixing rate.
The purpose of the mixing is to disperse the bitumen in the water so that the bitumen follows the water through the separation step. The results are illustrated in Figures 2 and 3. Figures 2 is a chart of the effect of mixing on bitumen recovery from CST. Figure 3 is a chart that shows the effect of mixing on the percentage of undispersed bitumen in CST.
Higher shear increases bitumen liberation and decreases the amount of undispersed bitumen.
The benefit of mixing for this purpose is illustrated by Figure 3.
[0050] It should be understood that numerous changes, modifications, and alternatives to the preceding disclosure can be made without departing from the scope of the disclosure. The preceding description, therefore, is not meant to limit the scope of the disclosure. Rather, the scope of the disclosure is to be determined only by the appended claims and their equivalents.
It is also contemplated that structures and features in the present examples can be altered, rearranged, substituted, deleted, duplicated, combined, or added to each other. The scope of the claims should not be limited by particular embodiments set forth herein, but should be construed in a manner consistent with the specification as a whole.

- 10 -

Claims (17)

CLAIMS:

1. A method comprising:
a) providing a coarse sand tailings stream (CST) comprising sand, fines, clay, water, and bitumen;
b) mixing the CST to liberate the bitumen from the sand and disperse the bitumen in the water to form a mixed CST stream; and c) separating the sand from the bitumen to form a bitumen-rich stream.

2. The method of claim 1, wherein the mixing comprises mixing in an inline mixing unit, a mixing tank, or a length of pipe with pumps.

3. The method of claim 1 or 2, further comprising adding a dilution water stream to the CST prior to or during the mixing to further disperse the bitumen.

4. The method of claim 3, wherein the dilution water stream is added to the CST in an amount of 10-30 vol. %, based on a volume of the CST.

5. The method of any one of claims 1 to 4, further comprising adding a gas to the CST
prior to or during the mixing to further liberate the bitumen from the sand.

6. The method of any one of claims 1 to 4, further comprising adding a gas to the mixed CST prior to of during the separating to further liberate the bitumen from the sand.

7. The method of claim 5 or 6, wherein the gas comprises air, a nitrogen rich stream, CO2, a flue gas, or a combination thereof.

8. The method of claim 7, wherein the air is dissolved in water or is injected as a vapor.

9. The method of any one of claims 1 to 8, wherein the separating comprises separating in a flotation vessel, a fluidized bed, an aerated fluidized bed, a hydrocyclone, or a combination thereof.

10. The method of any one of claims 1 to 9, further comprising concentrating the bitumen-rich stream to form a concentrated bitumen-rich stream.

11. The method of claim 10, wherein the concentrating is effected by flotation.

12. The method of claim 10, wherein the concentrating is effected using a mechanical flotation cell, a flotation column, or a downcomer-type flotation unit.

13. The method of any one of claims 1 to 12, wherein the CST has a sand content of 50 to 70 wt. %.

14. The method of any one of claims 1 to 13, wherein the CST has a D50 of 200 to 300 microns.

15. The method of any one of claims 1 to 14, wherein the CST has a temperature of 45 to 55 C.

16. The method of any one of claims 1 to 15, wherein the CST has a bitumen content of 0.1 to 3 wt. %.

17. The method of any one of claims 1 to 16, wherein the CST is from a bottom of a primary separation vessel (PSV).