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Title:
RECOVERY OF HYDROCARBONS, ENERGY AND WATER FROM TAILINGS SOLVENT RECOVERY UNIT UNDERFLOW
Document Type and Number:
WIPO Patent Application WO/2012/126114
Kind Code:
A1
Abstract:
In the field of oil sands processing, a process recovers asphaltenes from an tailings underflow stream of a tailings solvent recovery unit associated with a paraffinic froth treatment (PFT) operation. The process includes the steps of subjecting the tailings underflow stream to floatation to produce an asphaltene- rich froth and an asphaltene-depleted stream; filtering the asphaltene-rich froth to remove a first portion of gas and water therefrom to produce a wet asphaltene concentrate and an aqueous filtrate stream; drying the wet asphaltene concentrate to remove residual moisture therefrom to produce an asphaltene concentrate fuel; and combusting the asphaltene concentrate fuel in a fluid bed combustor to generate energy. The asphaltene-depleted stream may be subjected to thickening and the resulting water stream may be recovered. The energy and the water stream may be reused in the PFT operation.

Inventors:
FOULDS, Gary (24 Edgepark Crt. N.W, Calgary, Alberta T3A 4C4, CA)
Application Number:
CA2012/050171
Publication Date:
September 27, 2012
Filing Date:
March 19, 2012
Export Citation:
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Assignee:
FORT HILLS ENERGY L.P. (Petro-Canada Oil Sands Inc, P.O. Box 2844 150-6th Avenue S, Calgary Alberta T2P 3E3, CA)
FOULDS, Gary (24 Edgepark Crt. N.W, Calgary, Alberta T3A 4C4, CA)
International Classes:
C10C3/00; B03D1/02; B03D1/08; C10G1/04
Domestic Patent References:
WO2007102819A1
Foreign References:
US20100126395A1
US4572781A
US20090294328A1
Attorney, Agent or Firm:
ROBIC, LLP (1001 Square-Victoria - Bloc E - 8th floor, Montreal, Québec H2Z 2B7, CA)
Download PDF:
Claims:
CLAIMS

A process for recovering asphaltenes from an tailings underflow stream of a tailings solvent recovery unit associated with a paraffinic bitumen froth treatment operation, the process comprising:

subjecting the tailings underflow stream to floatation to produce an asphaltene-rich froth and an asphaltene-depleted stream;

filtering the asphaltene-rich froth to remove a first portion of gas and water therefrom to produce a wet asphaltene concentrate and an aqueous filtrate stream;

drying the wet asphaltene concentrate to remove residual moisture therefrom to produce an asphaltene concentrate fuel; and

combusting the asphaltene concentrate fuel in a fluid bed combustor to generate energy.

The process of claim 1 , comprising reusing at least a portion of the energy in the paraffinic bitumen froth treatment operation.

The process of claim 1 or 2, comprising thickening the asphaltene-depleted stream to produce a thickened tailings and recovered hot water.

The process of claim 3, comprising reusing the recovered hot water in the paraffinic bitumen froth treatment operation.

The process of any one of claims 1 to 4, wherein the floatation is performed in a sealed vessel.

The process of any one of claims 1 to 5, wherein the floatation is performed using an inert gas.

The process of claim 6, wherein the inert gas comprises nitrogen, C02 or a combination thereof.

8. The process of any one of claims 1 to 7, comprising subjecting flue gas generated by the combusting of the asphaltene concentrate fuel to desulphurization.

9. The process of any one of claims 1 to 8, comprising combining the aqueous filtrate stream with the asphaltene-depleted stream.

10. The process of any one of claims 1 to 9, wherein the tailings underflow stream contains about 10 wt% to about 15 wt% of hydrocarbons comprising asphaltenes and bitumen, and about 25 wt% to about 35 wt% mineral solids, about 55 wt% to about 65 wt% water.

1 1 . The process of claim 10, wherein the tailings underflow stream also contains up to about 0.5 wt% of residual paraffinic solvent.

12. The process of any one of claims 1 to 1 1 , wherein the tailings underflow stream is supplied to the floatation at about 605C to about 705C.

13. The process of any one of claims 1 to 12, wherein the floatation is performed in one or more floatation cells configured in series or parallel or a combination thereof.

14. The process of any one of claims 1 to 13, comprising recuperating released gas from the floatation, the filtering or the drying or a combination thereof.

15. The process of claim 14, comprising recovering paraffinic solvent contained in the released gas.

16. The process of claim 14 or 15, comprising recovering floatation gas contained in the released gas.

17. The process of any one of claims 1 to 16, wherein the floatation comprises agitation.

18. The process of any one of claims 1 to 17, wherein the filtering comprises belt filtering.

19. The process of any one of claims 1 to 18, wherein the asphaltene concentrate fuel is transported via a conveyor system.

20. The process of any one of claims 1 to 19, comprising feeding the asphaltene concentrate fuel into a hopper prior to the combusting.

21 . The process of any one of claims 1 to 20, wherein the combusting comprises addition of limestone for control of sulphur dioxide.

22. The process of any one of claims 1 to 21 , wherein the asphaltene concentrate fuel comprises at least about 20 wt% asphaltenes on a dry basis.

23. The process of any one of claims 1 to 22, wherein the asphaltene concentrate fuel comprises at least about 25 wt% asphaltenes on a dry basis.

24. The process of any one of claims 1 to 23, wherein the asphaltene concentrate fuel comprises at least about 30 wt% asphaltenes on a dry basis.

25. The process of any one of claims 1 to 24, wherein the asphaltene concentrate fuel comprises at least about 50 wt% asphaltenes on a dry basis. 26. The process of any one of claims 1 to 25, wherein the asphaltene concentrate fuel comprises up to about 50 wt% minerals on a dry basis.

27. The process of any one of claims 1 to 26, wherein the asphaltene concentrate fuel comprises an amount of minerals sufficient to facilitate operation of the fluid bed combustor.

28. The process of any one of claims 1 to 27, wherein the asphaltene concentrate fuel comprises an amount of sand sufficient to act as a fluidizing medium for fluid bed combustor.

29. The process of any one of claims 1 to 28, comprising collecting gases emitted from the floatation, the filtering or the drying or a combination thereof.

30. The process of claim 29, comprising recycling at least a portion of the collected gases as flotation gas for the floatation.

31 . The process of any one of claims 1 to 30, comprising adding a flocculent to the asphaltene-depleted stream.

32. The process of any one of claims 1 to 31 , comprising disposing of the thickened tailings in a tailings pond.

33. The process of any one of claims 1 to 32, comprising subjecting the thickened tailings to a belt filtering treatment or a drying treatment or a combination thereof to produce a dried tailings material.

34. The process of claim 33, comprising segregating the dried tailings material into subcomponents.

35. The process of any one of claims 1 to 34, wherein the floatation is conducted between about 4 minutes and about 20 minutes equivalent residence time.

36. The process of claim 35, wherein the floatation is conducted between about 7 minutes and about 16 minutes equivalent residence time.

37. The process of claim 36, wherein the floatation is conducted between about 10 minutes and about 13 minutes equivalent residence time.

38. The process of any one of claims 1 to 37, comprising controlling an amount of maltenes contained in the asphaltene-rich froth to a level sufficient to reduce or avoid binding of the asphaltene concentrate.

Description:
RECOVERY OF HYDROCARBONS, ENERGY AND WATER FROM TAILINGS SOLVENT RECOVERY UNIT UNDERFLOW

FIELD OF THE INVENTION

The present invention relates to the recovery of solvent from solvent diluted tailings derived from a bitumen froth treatment operation and more particularly to treatment of the underflow from a tailings solvent recovery unit (TSRU).

BACKGROUND

In bitumen froth treatment processes, solvent or diluent is added to a bitumen froth to separate a diluted bitumen stream for further processing. In a paraffinic bitumen froth treatment process, for example, bitumen froth derived from oil sands is combined with paraffinic solvent and then supplied to a settling vessel in which a bitumen rich fraction is separated from a bottoms fraction rich in asphaltenes, water, solvent and solids as well as residual amounts of bitumen. This bottoms fraction is often referred to as solvent diluted tailings or froth treatment tailings.

Solvent diluted tailings are preferably treated to recuperate the paraffinic solvent, which is subject to environmental discharge regulations and a valuable commodity, prior to disposal of the resulting solvent recovered tailings containing primarily water and solids. Solvent diluted tailings may be treated in tailings solvent recovery units that include flash vessels.

Flash vessels conventionally used to recover diluent from froth treatment tailings are specified for a feed flow and feed temperature so that, at the stage column pressure with optional stripping, steam vaporizes the diluent for recovery in the overhead condensing system. The tailings solvent recovery unit produces an overhead solvent stream which is further processed before returning for reuse as diluent in the froth settling vessels and solvent depleted underflow. The solvent depleted underflow is often discarded as tailings and sent to tailings ponds.

Some processes have been proposed for treating the underflow from a tailings solvent recovery unit. Some processes have been described in US patent application published under No. 2010/0258478, international PCT patent application published under No. WO 2007/102819 and US patent application published under No. 2010/0126395. These processes have a number of challenges and drawbacks including complexity, inefficiency and applicability mainly to tailings derived from naphthenic solvent treated froth.

There is indeed a need for a technology that overcomes or responds to the at least some of the challenges or drawbacks of known techniques.

SUMMARY OF THE INVENTION

The present invention responds to the above-mentioned need by providing a process and system for recovering hydrocarbons from TSRU underflow.

In one embodiment, there is provided a process for recovering asphaltenes from an tailings underflow stream of a tailings solvent recovery unit associated with a paraffinic bitumen froth treatment operation, the process comprising subjecting the tailings underflow stream to floatation to produce an asphaltene-rich froth and an asphaltene-depleted stream; filtering the asphaltene-rich froth to remove a first portion of gas and water therefrom to produce a wet asphaltene concentrate and an aqueous filtrate stream; drying the wet asphaltene concentrate to remove residual moisture therefrom to produce an asphaltene concentrate fuel; and combusting the asphaltene concentrate fuel in a fluid bed combustor to generate energy. In one aspect, the process includes the step of reusing at least a portion of the energy in the paraffinic bitumen froth treatment operation.

In another aspect, the process includes the step of thickening the asphaltene- depleted stream to produce a thickened tailings and recovered hot water.

In another aspect, the process includes the step of reusing the recovered hot water in the paraffinic bitumen froth treatment operation.

In another aspect, the floatation is performed in a sealed vessel.

In another aspect, the floatation is performed using an inert gas.

In another aspect, the inert gas comprises nitrogen, C0 2 or a combination thereof.

In another aspect, the process includes the step of subjecting flue gas generated by the combusting of the asphaltene concentrate fuel to desulphurization.

In another aspect, the process includes the step of combining the aqueous filtrate stream with the asphaltene-depleted stream.

In another aspect, the tailings underflow stream contains about 10 wt% to about 15 wt% of hydrocarbons comprising asphaltenes and bitumen, and about 25 wt% to about 35 wt% mineral solids, about 55 wt% to about 65 wt% water.

In another aspect, the tailings underflow stream also contains up to about 0.5 wt% of residual paraffinic solvent.

In another aspect, the tailings underflow stream is supplied to the floatation at about 60 5 C to about 70 5 C.

In another aspect, the floatation is performed in one or more floatation cells configured in series or parallel or a combination thereof.

In another aspect, the process includes the step of recuperating released gas from the floatation, the filtering or the drying or a combination thereof. In another aspect, the process includes the step of recovering paraffinic solvent contained in the released gas.

In another aspect, the process includes the step of recovering floatation gas contained in the released gas.

In another aspect, the floatation comprises agitation.

In another aspect, the filtering comprises belt filtering.

In another aspect, the asphaltene concentrate fuel is transported via a conveyor system.

In another aspect, the process includes the step of feeding the asphaltene concentrate fuel into a hopper prior to the combusting.

In another aspect, the combusting comprises addition of limestone for control of sulphur dioxide.

In another aspect, the asphaltene concentrate fuel comprises at least about 20 wt% asphaltenes on a dry basis.

In another aspect, the asphaltene concentrate fuel comprises at least about 25 wt% asphaltenes on a dry basis.

In another aspect, the asphaltene concentrate fuel comprises at least about 30 wt% asphaltenes on a dry basis.

In another aspect, the asphaltene concentrate fuel comprises at least about 50 wt% asphaltenes on a dry basis.

In another aspect, the asphaltene concentrate fuel comprises up to about 50 wt% minerals on a dry basis.

In another aspect, the asphaltene concentrate fuel comprises an amount of minerals sufficient to facilitate operation of the fluid bed combustor.

In another aspect, the asphaltene concentrate fuel comprises an amount of sand sufficient to act as a fluidizing medium for fluid bed combustor. In another aspect, the process includes the step of collecting gases emitted from the floatation, the filtering or the drying or a combination thereof.

In another aspect, the process includes the step of recycling at least a portion of the collected gases as flotation gas for the floatation.

In another aspect, the process includes the step of adding a flocculent to the asphaltene-depleted stream.

In another aspect, the process includes the step of disposing of the thickened tailings in a tailings pond.

In another aspect, the process includes the step of subjecting the thickened tailings to a belt filtering treatment or a drying treatment or a combination thereof to produce a dried tailings material.

In another aspect, the process includes the step of segregating the dried tailings material into subcomponents.

In another aspect, the floatation is conducted between about 4 minutes and about 20 minutes equivalent residence time.

In another aspect, the floatation is conducted between about 7 minutes and about 16 minutes equivalent residence time.

In another aspect, the floatation is conducted between about 10 minutes and about 13 minutes equivalent residence time.

The present invention also provides a corresponding system comprising a floatation unit, a filtration unit, a drying unit and a fluid bed combustion unit.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig 1 is a block flow diagram of a hydrocarbon recovery process from TSRU tailings, according to an embodiment of the present invention.

Fig 2 is a graph of asphaltene recovery versus floatation time over different runs. Fig 3 is a graph of asphaltene grade versus asphaltene recovery over different runs.

DETAILED DESCRIPTION

Referring to Fig 1 , in a preferred embodiment of the present invention, the process allows recovery of asphaltenes from TSRU tailings a boiler fuel that produces energy and hot water from TSRU tailings for reuse in the plant.

The process treats TSRU tailings 10 that are derived from a tailings solvent recovery unit from a paraffinic froth treatment operation. The TSRU tailings thus contain water, particulate mineral material, residual amounts of paraffinic solvent and residual bitumen of which asphaltenes are the major hydrocarbon component.

As illustrated in Fig 1 , the TSRU tailings 10 are supplied to an asphaltene floatation apparatus 12. The asphaltene floatation apparatus 12 has a tailings inlet 14 for supplying the TSRU tailings 10 and a gas inlet 16 for supplying a floatation gas 18 to at least one floatation chamber 20. The floatation gas 18 enters the chamber 20 and contacts the TSRU tailings 10 preferably counter- currently to contact asphaltenes and cause them to rise and separation from a predominantly water and mineral fraction of the TSRU tailings. The asphaltene floatation apparatus 12 also has an underflow outlet 22 for releasing floatation tailings 24. The asphaltene floatation apparatus 12 also has an overflow system 26 comprising a froth outlet 28 for releasing an asphaltene-rich froth 30. The asphaltene floatation apparatus 12 also has a gas outlet 32 for releasing vent gas 34 which may contain residual paraffinic solvent.

In one aspect, the asphaltene floatation apparatus 12 is preferably sealed and the floatation gas 18 is inert, e.g. preferably nitrogen though C0 2 may also be used. The floatation gas 18 performs two main functions: firstly, the asphaltenes/bitumen attach to the rising gas bubbles for recovery thereof and, secondly, the gas further aids stripping residual solvent from the TSRU tailings stream.

The TSRU tailings 10 are preferably derived from flash or stripping vessel used in the upstream TSRU. TSRU tailings 10 may contain about 9 wt% to about 15 wt% bitumen which is primarily asphaltenes. For instance, without the asphaltenes the bitumen content would be about 1 wt%. The TSRU tailings also contain about 55 wt% to about 75 wt% water, optionally 55 wt% to about 65 wt%; about 15 wt% to about 35 wt% mineral solids, optionally about 16 wt% to about 22 wt%; and up to about 0.5 wt% paraffinic solvent, optionally less than about 0.1 wt% or between about 0.01 wt% and about 0.03 wt%. The TSRU tailings may be provided at various flowrates depending on the upstream froth treatment and TSRU conditions and throughputs, optionally about 1000 t/hr to about 2000 t/hr, or between 1350 t/hr and about 1550 t/hr. The TSRU tailings 10 are pumped at a temperature of about 60°C to about 80°C, preferably from about 74°C to about 77°C, into the asphatlene floatation apparatus 12, which may include one or more flotation vessels, arranged in series or in parallel. The configuration of the flotation vessels between series and parallel depends on the capacity of the given flotation vessels.

Referring to Fig 2, asphaltene recoveries of 80% may be achieved with floatation times up to about 15 minutes, which may vary due to variations in gas injection rates, agitation rates and mixing effectiveness that are attributes of specific flotation apparatuses.

It is also noted that the TSRU tailings may contain some unrecovered maltenes due to non optimal bitumen recovery performance in the froth settling vessel. The maltene component of bitumen can act as a binder in certain circumstances. More regarding this will be discussed herein-below.

The floatation unit may be configured, sized and operated according to TSRU tailings characterization including bitumen, solids, water, asphaltene, particle sizes and distribution, water chemistry, settling rates and clay activity, for example. The floatation unit or its floatation vessels may be periodically cleaned using water wash with optional rougher. The feed density, temperature and pH of the TSRU tailings may also be controlled to optimize the floatation performance. For example, the feed density may be modified by water addition to achieve a desired density in the floatation vessels for bubble floatation performance. The flow rate of inlet floatation gas, agitator speed, additives, and the like, may be used and controlled to enhance performance.

It is noted that the floatation step helps not only to recover asphaltenes but can also enable recovery of additional fugitive solvent unrecovered in the TSRU. Referring back to Fig 1 , the overflow of asphaltene-rich froth 30 is further processed by feeding it to a filtration unit 36 to produce a filtered asphaltene-rich concentrate 38 which is gas and water depleted along with a filter gas stream 40 and a filter slurry stream 42. The filter slurry stream 42 may be returned and combined with the floatation tailings 24 for further processing as will be described herein-below. The filtration unit 36 thus removes gas and water from the froth to produce the filtered asphaltene-rich concentrate 38, which is fed to a drying unit 44. The drying unit 44 performs final water removal and produces a dried asphaltene-rich concentrate 46 and a drying gas stream 48. The drying unit 44 is preferably operated at drying temperature and conditions to remove the residual water from the asphaltene concentrate without inducing pre-mature combustion, gasification, reaction or physiochemical changes in the concentrate that would disturb or aggravate operations.

The drying gas stream 48 may be combined with one or more other vent gas streams including the floatation gas stream 34 and/or the filter gas stream 42 to form a combined vent gas 50, if desired. The individual or combined vent gas stream may be subjected to processing to separate various components thereof for reuse in the process of the PFT plant. For instance, the inert floatation gas may be recovered for recycling back as inlet floatation gas 18 and the paraffinic solvent may be recovered for reuse as diluent in the bitumen froth treatment vessel in the PFT plant. Gases from the flotation, filtering and drying operations may be collected and may be subjected to cooling to condense solvent for recycle to the PFT plant, recompression to minimize floatation gas import with purge provisions to ensure the system remains well outside the explosive envelope due to oxygen accumulation.

A variety of specific equipment may be used to filter and dry the asphaltene concentrate. During processing, the asphaltene concentrate develops limited fluidity and thus conveyor systems may be used in conjunction with the filtering and drying, e.g. employing belt filtering and drying to a hopper (not illustrated) which would feed the combustion unit.

The filtration unit may be provided with a filtering surface or structure having pore sizes in accordance with the particle sizes of the asphlatene-mineral composite in the asphaltene-rich froth.

Still referring to Fig 1 , the dried asphaltene-rich concentrate 46 is supplied to a fluidized bed combustion unit 52. The fluidized bed combustion unit 52 allows burning the asphaltene-rich concentrate 46 as a fuel. The asphaltene-rich concentrate 46 has relatively high mineral content and thus the fluidized bed combustion unit 52 is advantageously used. In one preferred aspect, the bed combustion unit 52 has a fluid bed 54 where the combustion takes place, an exhaust outlet 54 for releasing combustion gas 55, a desulphurization module 56 coupled to the exhaust 54 or in fluid communication therewith for capturing sulphur evolved from burning the asphaltene-based fuel and a solid water outlet 58 for releasing combustion solid waste 60. The fluidized bed combustion unit 52 thus produces energy 62 which can be used in a number of ways, for heating process streams and reactors in oil sands processing plants and units and the power may also be sold to the grid.

In some optional aspects, the power generated by the combustion is used to create steam which may be used in heat exchangers, for heating water for mining oil sands, for in situ hydrocarbon recovery purposes such as a SAGD operation, for electrical power used in the in situ, mining, extraction, upgrading or other uses. In a preferred aspect, the fluid bed combustion unit is located proximate to where the power is used. In one aspect, the power is used in a PFT plant to power various pieces of equipment. It is noted that in the field of oil sands processing, many process streams are slurries requiring powerful pumps at operating flow rates. For instance, slurry pumps that transport oil sands tailings from extraction or PFT operations may be required to pump the tailings many kilometers for disposal or further treatment, often about 5 Km to 10 Km or more. The high dilbit pumps used to pump the overflow from froth settling vessel of the PFT plant also have high power requirements, often in the range of about 2000 to about 5000 horsepower. The bitumen froth feed pumps of the PFT plant also have high power requirements to provide pressure of about 800 to about 900 kPa. PFT plants also have high steam requirements at various stages and units, including heat exchangers and direct steam injection e.g. into bitumen froth for pre-heating. In addition, there may also be power requirements for steam tracing for pipelines or electrical tracing for pipelines. The recuperation of the energy contained in the rejected asphaltenes provides advantageous operation and efficiency by minimizing the external energy imported into the PFT plant or oil sands operation in general often derived by natural gas sources.

In one aspect, the asphaltene combustion is coupled with a carbon capture and storage system in order to comply with emissions regulations or recuperate combustion gases for reuse.

The combustion unit may be constructed, designed and operated in a number of ways depending on the desired combustion and the properties of the asphaltene concentrated to be used as fuel. In one aspect, limestone may be added for control of sulfur dioxide and the sand used in the fluid bed combustor is largely mineral from the asphaltene concentrate itself, e.g. on a dry basis about 50/50 asphaltene/mineral. In another aspect, the combustion unit may be configured or comprise a module for capturing C0 2 and/or other gases, which could be reused or sequestered underground.

Referring to Fig 3, the asphaltene-rich froth recovered from the floatation unit is relatively consistent at about 30 wt% asphaltene with asphaltene recoveries up to about 85%. The "grade" of the asphaltene-rich froth is used to indicate its asphaltene content and thus its usefulness and properties as a fuel. The asphaltene-rich froth is subsequently dehydrated and the asphaltene concentrate fuel thus has a higher asphaltene concentration often around 50 wt%.

Referring back to Fig 1 , the asphaltene-rich concentrate 46 may have a variety of applications. The asphaltene-rich concentrate 46 may be used for alternative processing such as gasification for hydrogen production, marketed directly as an asphalt product or back blending into heavy crude to produce on-spec material for certain asphalt products.

The asphaltene concentrate to be used as fuel may be conditioned, handled or stockpiled prior to subjecting to combustion. The properties of the asphaltene concentrate is dependent on the upstream PFT plant operating conditions and bitumen froth properties, including asphaltene rejection, bitumen mixing and bitumen recovery levels.

In one aspect, the asphaltene concentrate contains a sufficient amount of minerals to facilitate processing in the fluidized bed combustion unit.

The asphaltene concentrate fuel, which may also be referred to as an asphaltene-mineral composite, preferably has a bitumen component which comprises over 80%, optionally over 83%, asphaltene. Asphaltene is an advantageous secondary energy source due to its high calorific content. The asphaltene-mineral composite fuel may contain about 70% asphaltene and about 30% mineral solids on a wet basis. The process may be adapted for improved handling of the asphaltene-mineral composite fuel in accordance with several characteristics. In one aspect, the asphaltene-mineral composite has a flowability, cohesive strength, wall friction properties and compressibility that determine the handling strategy. For instance, the minimum outlet size may be provided based on the cohesive strength of the asphaltene-mineral composite to prevent arching and ratholing. In addition, critical hopper angles may be provided to achieve required or preferred mass flow based on the wall friction properties of the asphaltene-mineral composite. Furthermore, critical chute angles may be provided to maintain flow after impact and prevent pluggage. In addition, in terms of storage issues, the handling and storing of the asphaltene-mineral composite may be provided to minimize stagnation and degradation potential. The compressibility of the asphaltene-mineral composite may also drive the configuration and operation of the process steps.

In one aspect, the asphaltene concentrate fuel is combusted to produce solid waste ash 60 into which certain compounds are present and may be extracted if desired. For instance, various metals are bound with the asphaltene composite and require thermal breakdown of the asphaltenes to be removed. After combustion the metals have been removed from the asphaltene fuel and report to the solid waste stream. It may be preferable to recuperate the metals from the solid waste stream to other recuperation methods. It is also noted that the asphaltene rejection from bitumen froth which is enabled by PFT improves downstream operations and upgrading. For instance, refineries benefit from asphaltene rejection since the asphaltenes remove the metals from the bitumen froth to produce a cleaner bitumen product that can be upgraded. Having a lower amount of metals in the bitumen reduces poisoning of refining catalysts. Thus, the metals removed from the bitumen froth and carried with the asphaltenes do not enter the refining processes but may be rejected as part of a solid waste stream for optional recuperation. The ash may also contain gypsum which could be separated for use in various applications.

As briefly mentioned above, the maltene component of the TSRU tailings may have downstream effects on embodiments of the process. For instance, part of the maltene component may be carried over with the asphaltene-rich froth and, through the subsequent process steps, the maltenes may act as a binder between asphaltene concentrate which may be in a generally particulate form. It is worth mentioning at this juncture that in the PFT process, the asphaltenes first precipitate out of the bitumen froth in the form of floes and make up a component of the solvent diluted tailings which are supplied to the TSRU. Upon injection into the TSRU, the asphaltene floe structures are broken down due to the nozzles as they release solvent. Thus, the asphaltenes in the TSRU tailings are broken down aggregates. The asphaltene-rich froth 46 thus contains asphaltenes in the form of such broken down aggregates. Through the subsequent filtration and drying steps, maltenes present in the froth may act as a binder of the asphaltene aggregates which can create difficulties for handling. In one aspect, the maltene or bitumen component in the TSRU tailings is maintained or controlled below a level sufficient to reduce or avoid binding of the asphaltene aggregates in the asphaltene concentrate. This can improve materials handling as well as filtration and drying performance.

Referring now to Fig 1 , the tailings underflow 24 from the floatation unit 12 and possibly the filtering tailings stream 42 from the filtration unit 36, are further treated in a thickening unit 64. The thickening unit 64 includes a tailings inlet 66 for receiving the floatation underflow 24, a bottoms outlet 68 for releasing thickened tailings 70 and a liquid outlet 72 for releasing recovered hot water 74.

Thus, the thickening unit 64 recovers hot water from the asphaltene-stripped TSRU tailings stream and the dense tailings are disposed. The disposal of the dense tailings may include further dewatering, flocculation, beaching and drying operations, if desired, disposal into a tailings pond or other consolidation or disposal methods. The thickened tailings may be disposed through the overall tailings system of an oil sands facility. Optionally, the thickened tailings, which may have limited flowrates, may be subjected to a belt filter and drying to facilitate production of a dry tailings product. This dry product may be further processed to recover titanium, zirconium, vanadium or other compounds for their value or to enhance environmental reclamation activities. Accordingly, the dry tailings stream may be produced so as to be segregatable.

The thickening unit 64 permits an additional efficiency option by producing hot water 70 for reuse. In addition, the thickening unit 64 can be operated with greater efficiency due to the asphaltene-depleted feed supplied thereto. With a lower amount of asphaltenes, the minerals separate easier, settling reate increase and the effect of flocculents for flocculating clays is increased as they are not competed with, deactivated or adsorbed by the hydrocarbon phase.

The thickening unit may be configured and operated to have a given flow rate, rake speed, feed and underflow compositions, pH, bed height, temperature and settling rate. It is noted that the thickener as described in Canadian patent application No. 2,454,942 may be used, preferably as the separate thickener 64 and alternatively as a floatation unit and thickener combination.

In addition, various thickening and flocculating agents may be used in conjunction with the thickening unit, with addition either upstream of the thickening unit or within it.

It is also noted that various recirculation and/or return lines may be incorporated for the underflow streams of the process. For instance, a portion of the underflow of the floatation unit may be recycled back as a recycled underflow stream into the floatation vessel itself or into the floatation feed which can stabilize flow. A portion of the underflow of the thickening unit may also be recycled back as a recycled underflow stream into the thickening unit or into the feed thereto which can stabilize flow.

Finally, it should be noted that the aspects and embodiments described or illustrated herein should not limit the scope of the present invention.