CA2866923C - Methods for processing diluted bitumen froth or froth treatment tailings - Google Patents

Abstract

A method for processing diluted bitumen froth or froth treatment tailings including bitumen and solvent. The method includes forming a settler overflow and a settler underflow by gravity separating the diluted bitumen froth or the froth treatment tailings in a settler; forming a hydrocyclone overflow and a hydrocyclone underflow by separating the settler underflow in a hydrocyclone; and recycling the hydrocyclone overflow to the settler.

Description

METHODS FOR PROCESSING DILUTED BITUMEN FROTH OR FROTH
TREATMENT TAILINGS
BACKGROUND
Field of Disclosure [0001] The disclosure relates generally to the field of oil sand processing. More specifically, the disclosure relates to methods for processing diluted bitumen froth or froth treatment 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. 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. 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.

[0005] In an example of WBE, mined oil sands are mixed with water to create a slurry suitable for extraction. Caustic may be added to adjust the slurry pH to a desired level and thereby enhance the efficiency of the separation of bitumen.

[0006] Regardless of the type of WBE employed, the extraction process will typically result in the production of a bitumen froth comprising bitumen, water and fine particles and a tailings stream comprising coarse particles and some fine particles and water.
The tailings stream may consist essentially of coarse particles and some fine particles and water. A typical composition of bitumen froth may be about 60 weight (wt.) % bitumen, 30 wt. %
water, and wt. % solids. The water and solids in the froth are considered as contaminants. The contaminants may be substantially eliminated or reduced to a level suitable for feed to an oil refinery or an upgrading facility, respectively. Elimination or reduction of the contaminants may be referred to as a froth treatment process. Elimination or reduction of the contaminants may be achieved by diluting the bitumen froth with a solvent. The solvent may comprise any suitable solvent, such as an organic solvent. For example, the organic solvent may comprise naphtha solvent and/or paraffinic solvent. Diluting the bitumen with solvent (also referred to as dilution) may increase the density differential between bitumen and water and solids.
Diluting the bitumen with solvent may enable the elimination or reduction of contaminants using multi-stage gravity settlers. Use of the multi-stage gravity settlers may result in a "diluted bitumen froth" and another tailings stream. The another tailings stream may be commonly referred to as the froth treatment tailings. The froth treatment tailings may comprise residual bitumen, residual solvent, solids and water. The froth treatment tailings stream may be further processed to recover residual solvent, for instance in a tailings solvent recovery unit (TSRU). If the solvent is paraffinic solvent, the froth treatment tailings may be referred to as "paraffinic froth treatment tailings".

[0007] It is desirable to reduce the amount of bitumen and solvent in the diluted bitumen froth or the froth treatment tailings sent to gravity settlers, such as gravity settlers positioned after the first gravity settler of the multi-stage gravity settlers, and to the TSRU. In particular, the quantity of bitumen and solvent in the diluted bitumen froth and froth treatment tailings directly impacts the amount of bitumen and solvent lost to tailings and has a substantial impact on the design requirements of the TSRU. Bitumen in the tailings is either lost, impacting overall bitumen recovery of the bitumen recovery process, or requires additional processing equipment to recovery bitumen from the tailings. The size and cost of processing equipment to recover solvent from the tailings is directly related to the quantity of solvent in the tailings. The performance of a TSRU may be improved by reducing the fraction of solvent in the froth treatment tailings. The gravity settlers positioned after the first gravity settler of the multi-stage gravity settlers may be referred to as subsequent gravity settlers.

[0008] Existing schemes to reduce the amount of bitumen and solvent in froth treatment tailings generally rely on additional gravity settling stages or large recycle loops to reduce the bitumen and solvent carry-under from the gravity settlers to the TSRU. Additional gravity settling stages have high capital, operating, and maintenance costs.
Large recycle loops increase pump power requirements, increase piping sizes, increase erosional wear, increase the downward flux rate of the settlers and decrease residence time in the settlers. The downward rate may be a nominal downward velocity from an inlet of the settler to a bottom outlet of the settler. Residence time may be an average amount of time that an average particle resides within a settler prior to exiting a bottom of the settler.
Increased downward flux rate and lower residence time have negative implications on performance and vessel sizing requirements.

[0009] In view of the aforementioned disadvantages, there is a need for alternative or improved methods for processing diluted bitumen froth or froth treatment tailings.

SUMMARY

[0010] It is an object of the present disclosure to provide methods for processing diluted bitumen froth or froth treatment tailings.

[0011] Disclosed is a method for processing diluted bitumen froth or froth treatment tailings comprising bitumen and solvent. The method may comprise forming a settler overflow and a settler underflow by gravity separating the diluted bitumen froth or the froth treatment tailings in a settler; forming a hydrocyclone overflow and a hydrocyclone underflow by separating the settler underflow in a hydrocyclone; and recycling the hydrocyclone overflow to the settler.

[0012] 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

[0013] 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.

[0014] Figure 1 is a flow chart of a method for processing diluted bitumen froth or froth treatment tailings.

[0015] Figure 2 is a flow chart of a method for processing diluted bitumen froth or froth treatment tailings.

[0016] 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.

DETAILED DESCRIPTION

[0017] 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.

[0018] 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.

[0019] Throughout this disclosure, where a range is used, any number between or inclusive of the range is implied.

[0020] 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.

[0021] "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. %).
In addition, bitumen can contain some water and nitrogen compounds ranging from less than 0.4 wt. % to in excess of 0.7 wt. %. 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.

[0022] "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 10.0 API (density of 1,000 kg/m3 or 1 g/cm3). An extra heavy oil, in general, has an API gravity of less than 10.00 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.

[0023] "Fine particles" 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).

[0024] "Coarse particles" are generally defined as those solids having a size of greater than 44 microns (m).

[0025] The term "solvent" as used in the present disclosure should be understood to mean either a single solvent, or a combination of solvents.

[0026] 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.

[0027] 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.

[0028] The term "paraffinic solvent" (also known as aliphatic) as used herein means solvents comprising normal paraffins, isoparaffins or blends thereof in amounts greater than 50 wt. %. Presence of other components such as olefins, aromatics or naphthenes may counteract the function of the paraffinic solvent and hence may be present in an amount of only 1 to 20 wt. % combined, for instance no more than 3 wt. %. The paraffinic solvent may be a C4 to C20 Or C4 to C6 paraffinic hydrocarbon solvent or a combination of iso and normal components thereof. The paraffinic solvent may comprise pentane, iso-pentane, or a combination thereof. The paraffinic solvent may comprise about 60 wt. %
pentane and about 40 wt. % iso-pentane, with none or less than 20 wt. % of the counteracting components referred above.

[0029] A settler can separate diluted bitumen froth or froth treatment tailings, comprising bitumen and solvent, by gravity, into a settler overflow and a settler underflow.
The settler overflow has a higher liquid content (by weight) and a lower solid content (by weight) than the settler underflow. Settlers may be arranged in series with a settler underflow from one settler passed as a feed to the next settler in the series. A settler underflow flow-rate may be controlled to maintain a hydrocarbon continuous ¨ aqueous slurry interface level in the settler. Controlling the aqueous slurry interface level in the settler may be maintained in conjunction with processing a settler underflow from a final settler in a hydrocyclone. A final settler may be a settler last in a series of settlers. The hydrocyclone may produce a hydrocyclone overflow and a hydrocyclone underflow. The hydrocyclone overflow has a higher liquid content (by weight) and a lower solid content (by weight) than the hydrocyclone underflow. The hydrocyclone overflow flow-rate may be controlled to a fixed flow-rate or flow ratio with respect to the hydrocyclone underflow flow-rate. The fixed flow-rate or flow ratio may be optimized to balance equipment, piping size requirements, piping wear, and/or pump power requirements, with incremental recovery of solvent and bitumen from the tailings. The hydrocyclone inlet flow-rate may be maintained at a fixed volume flow-rate.
The hydrocyclone inlet flow-rate may be maintained at the fixed volume flow-rate by modulating the hydrocyclone overflow flow-rate. The hydrocyclone inlet flow-rate may be maintained at the fixed volume flow-rate by adding water to the underflow from the final settler vessel. Maintaining the hydrocyclone inlet flow-rate at the fixed volume flow-rate may be advantageous because a fixed speed pump may be used upstream of the hydrocyclone and the hydrocyclone geometry may be optimized for a single inlet flow- rate.
Control of the overflow, underflow, and water flow-rates may be achieved using control valves, variable speed pumps, or a combination thereof.

[0030]
Figures 1 and 2 are flow charts of a method for processing diluted bitumen froth or froth treatment tailings. The diluted bitumen froth or froth treatment tailings (1) may be the result of WBE followed by dilution by solvent, and froth separation in the case of the tailings. For example, mined oil sand may undergo WBE to form bitumen froth.
The bitumen froth may be diluted with solvent and, in the case of the tailings, undergo froth separation by gravity in a settler (referred to herein as a preliminary settler). An overflow from the preliminary settler may comprise bitumen and solvent and may be passed to solvent recovery. An underflow from the preliminary settler may form the froth treatment tailings (1). The froth treatment tailings (1) may comprise water, mineral matter, precipitated asphaltenes, solvent, and/or some unrecovered bitumen. The froth treatment tailings may comprise precipitated asphaltenes if the solvent is paraffinic. Where two or more preliminary settlers are used, they may be arranged in series or in parallel.

[0031] The method may comprise forming (202) a settler overflow (3) and a settler underflow (5) by gravity separating the diluted bitumen froth or froth treatment tailings (1) in a settler (2). The settler (2) may be any suitable gravity settler. The settler (2) may comprise a vertical tank (14) above a conical bottom (15). The settler underflow (5) may be withdrawn from the bottom of the settler (2). The bottom of the settler (2) may be within the conical bottom (15). Where two or more settlers (2) are used, they may be arranged in series or in parallel.

[0032] Solvent may be recovered from the settler overflow (3). For example, the settler overflow (3) may be passed through a solvent recovery unit (SRU) or other suitable apparatus in which the solvent is flashed off and condensed in a condenser associated with the solvent flashing apparatus and recycled/reused in the process. The SRU may be any suitable SRU, such as but not limited to a fractionation vessel.

[0033] Due to the structure of asphaltene aggregates, when the solvent is paraffinic, in the diluted bitumen froth or froth treatment tailings (1) and the incremental recovery of solvent and solvent-soluble bitumen from the settler underflow (5) (described below), the settler underflow (5) may approach a maximum packing ratio of a transportable slurry. As the maximum packing ratio is approached, a pressure drop may increase through a hydrocyclone (6) and piping leading into and out of the hydrocyclone (6), which may decrease solid-liquid separation efficiency in the hydrocyclone (6). Water (4) may be added to the settler underflow (5) to reduce the packing ratio. For example, water (4) may be added to the settler underflow (5) in a water: settler underflow volume ratio of 1:5 or less, or of 1:50 to 1:5. The amount of water (4) that may be added may depend on the water content of the diluted bitumen froth or froth treatment tailings (1). The water content of the diluted bitumen froth or froth treatment tailings (1), may vary depending for instance on the oil sand composition and/or WBE parameters. The addition of the water (4) may reduce the bulk viscosity of the settler underflow (5). Reducing the bulk viscosity of the settler underflow (5), may improve separation efficiency in the hydrocyclone (6).

[0034]
The method may comprise forming (204) a hydrocyclone overflow (7) and a hydrocyclone underflow (8) by separating the settler underflow (5) in a hydrocyclone (6).
The settler underflow (5) may be pumped into the hydrocyclone (6) using a pump (10). This pumping of the settler underflow (5) may increase a pressure of the settler underflow (5).
Increasing the pressure of the settler underflow (5) may allow for overcoming pressure losses in the hydrocyclone (6). Increasing the pressure of the settler underflow (5) may enable the hydrocyclone overflow (7) to be recycled back to the settler (2).
Where two or more hydrocyclones (6) are used, they may be arranged in series or in parallel.
Solvent may be recovered from the hydrocyclone underflow (8), for example in a subsequent TSRU of a tailings solvent recover unit (TSRU) (9). The hydrocyclone (6) reduces the bitumen and solvent content in the settler underflow (5). Reducing the bitumen and solvent content in the settler underflow (5) may reduce the amount of bitumen and solvent in tailings which may be sent to the subsequent gravity settler or the TSRU (9).

[0035]
Cyclonic separation of the diluted bitumen froth or froth treatment tailings (5) may increase bitumen and solvent recovery by using centrifugal force rather than gravity.
Due to the enhanced separation of bitumen and solvent in the hydrocyclone (6), bitumen and solvent recovery may be improved in the settler (2) without an unacceptable increase in a downward flux rate in the settler (2). Due to the enhanced separation of bitumen and solvent in the hydrocyclone (6), bitumen and solvent recovery may be improved in the settler (2) without inducing a detrimental circulation pattern in the settler (2). A
detrimental circulation pattern is a flow pattern internal to the settler (2) that results in either (a) solids and/or water being carried-over into the settler overflow (3) or (b) higher entrainment of solvent and solvent-soluble bitumen into the settler underflow (5).

[0036]
The method may comprise recycling (206) the hydrocyclone overflow (7) to the settler (2). The hydrocyclone overflow (7) has a higher hydrocarbon liquid (bitumen and solvent) content than the settler underflow (5). The hydrocyclone overflow (7) may be kept _ to, for example but not limited to 10-30 wt. % hydrocarbon liquid, for assisting bitumen and solvent recovery. The hydrocarbon liquid may be combined bitumen and solvent.
By limiting the hydrocarbon liquid content in the hydrocyclone overflow (7) from the hydrocyclone (6) to, for instance 10-30 wt. %, separation of the lighter hydrocarbon liquid from the water and solids may be improved. In particular, drawing more water and solids into the hydrocyclone overflow (7) may reduce the amount of lighter hydrocarbon liquid in the hydrocyclone underflow (8), in contrast to trying to achieve the most efficient separation in both the hydrocyclone overflow (7) and the hydrocyclone underflow (8).
Adjusting the overflow rate from the hydrocyclone (6) may permit optimization of solvent and bitumen recovery in the settler (2).

[0037] The settler (2) may recover bitumen and solvent-soluble bitumen from the hydrocyclone overflow (7) that is recycled. The hydrocyclone overflow that is recycled may be referred to a recycled hydrocyclone overflow. The hydrocyclone overflow (7) may be introduced into the settler (2) below an inlet for receiving the diluted bitumen froth or froth treatment tailings (1). The hydrocyclone overflow (7) may be recycled adjacent and above the conical bottom of the settler (2). The hydrocyclone overflow (7) may be pumped into the settler (2) using a pump (11). Pumping the hydrocyclone overflow (7) into the settler (2) may overcome pressure losses in the hydrocyclone (6) to enable the recycling of the hydrocyclone overflow (7) to the settler (2).

[0038] 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.

Claims (14)

CLAIMS:

1. A method for processing diluted bitumen froth or froth treatment tailings comprising bitumen and solvent, the method comprising:
a) forming a settler overflow and a settler underflow by gravity separating the diluted bitumen froth or the froth treatment tailings in a settler;
b) forming a hydrocyclone overflow and a hydrocyclone underflow by separating the settler underflow in a hydrocyclone; and c) recycling the hydrocyclone overflow to the settler.

2. The method of claim 1, wherein the hydrocyclone overflow comprises 10-30 wt. %
combined bitumen and solvent.

3. The method of any one of claims 1-2, further comprising reducing a packing ratio of the settler underflow by adding water to the settler underflow.

4. The method of claim 3, wherein the water is added to the settler underflow in a water: settler underflow volume ratio of 1:50 to 1:5.

5. The method of any one of claims 1-4, wherein the hydrocyclone overflow is recycled into the settler below an inlet that receives the diluted bitumen froth or the froth treatment tailings.

6. The method of any one of claims 1-5, wherein the settler comprises a conical bottom and a vertical tank above the conical bottom, and wherein the hydrocyclone overflow is recycled adjacent and above the conical bottom.

7. The method of any one of claims 1-6, further comprising pumping the settler underflow into the hydrocyclone.

8. The method of any one of claims 1-7, further comprising pumping the hydrocyclone overflow into the settler.

9. The method of any one of claims 1-8, further comprising recovering the solvent and/or the bitumen from the hydrocyclone underflow.

10. The method of any one of claims 1-9, wherein the hydrocyclone comprises more than one hydrocyclone arranged in one of series and parallel.

11. The method of any one of claims 1-9, further comprising recovering the solvent from the settler overflow.

12. The method of any one of claims 1-11, wherein step a) comprises gravity separating the diluted bitumen froth.

13. The method of any one of claims 1-11, wherein step a) comprises gravity separating the froth treatment tailings.

14. The method of claim 13, wherein the froth treatment tailings comprise paraffinic froth treatment tailings.
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