CA2573633C

CA2573633C - Bitumen froth treatment process

Info

Publication number: CA2573633C
Application number: CA2573633A
Authority: CA
Inventors: William L. Strand
Original assignee: William L. Strand; B & N Resources Inc.
Current assignee: B & N Resources Inc
Priority date: 2007-01-10
Filing date: 2007-01-10
Publication date: 2010-11-23
Anticipated expiration: 2027-01-10
Also published as: CA2573633A1

Abstract

A process for treating a bitumen froth comprising bitumen, water and a mineral material which includes subjecting a first mixture of the bitumen froth and added diluent to first gravity separation to produce a first overflow stream and a first underflow stream, subjecting a second mixture of the first underflow stream and added diluent to second gravity separation to produce a second overflow stream and a second underflow stream, and subjecting a third mixture of the second underflow stream and added diluent to third gravity separation to produce a third overflow stream and a third underflow stream, wherein the first overflow stream is a bitumen product stream. The process may also include subjecting a fourth mixture of the first overflow stream and added diluent to fourth gravity separation to produce a fourth overflow stream and a fourth underflow stream so that the fourth overflow stream is the bitumen product stream.

Description

BITUMEN FROTH TREATMENT PROCESS
FIELD OF INVENTION

The present invention relates to a process for treating a bitumen froth comprising bitumen, water and a mineral material using a diluent and gravity separation techniques.
BACKGROUND OF INVENTION

Oil sand is essentially a matrix of bitumen, water and mineral material. The bitumen component of oil sand consists of viscous hydrocarbons, including asphaltenes, which behave much like a solid at normal in situ temperatures and which act as a binder for the other components of the oil sand matrix. The mineral material component of oil sand typically consists largely of sand, but may also include rock, silt, clay and heavy metals. Sand and rock are considered to be coarse mineral material, while clay and silt are considered to be fine mineral material, where fines are defined as mineral material having a particular size of less than 44 microns. The water component of oil sand consists essentially of a film of connate water surrounding the sand in the oil sand matrix, and may also contain particles of fine mineral material within it.
A typical deposit of oil sand will contain about 10% to 12% bitumen and about 3% to 6% water, with the remainder of the oil sand being made up of mineral material.
Typically the mineral material component in oil sand will contain about 14% to 20% fines, measured by weight of total mineral material contained in the deposit, but the amount of fines may increase to about 30% or more for poorer quality deposits. Oil sand extracted from the Athabasca area near Fort McMurray, Alberta, Canada, averages about 11 %
bitumen, 5% water and 84% mineral material, with about 15% to 20% of the mineral material being made up of fines.

Oil sand deposits are mined, and oil sand extraction processes are performed, for the purpose of liberating or separating the bitumen from the oil sand, which bitumen may subsequently be upgraded to produce synthetic crude oil. Accordingly, various oil sand extraction processes have been developed for separating the bitumen from the oil sand.

One well known oil sand extraction process is the Clark Process, which is often referred to as the "hot water process". The hot water process utilizes both aggressive thermal action and aggressive mechanical action to liberate and separate bitumen from the oil sand and is typically a three step process which produces a number of product streams.

In the hot water process, the oil sand is first conditioned by mixing it with hot water at about 95 Celsius and steam in a conditioning vessel which vigorously agitates the resulting slurry in order to completely disintegrate the oil sand. Once the disintegration is complete, the slurry undergoes a primary separation process. The primary separation process separates the slurry by allowing the sand and rock to settle out to provide a "coarse tailings"
stream, while the bitumen, having air entrained within it, floats to the top of the slurry and is withdrawn as a "bitumen froth stream". The remainder of the slurry, which is referred to as the "middlings stream", is then treated further or scavenged by froth flotation techniques to recover bitumen that did not float to the top of the slurry during the primary separation process. The bitumen recovered from the middlings stream may be returned to the primary separation process or may be combined with the bitumen froth stream.
Various alternative oil sand extraction processes have been developed, including but not limited to the inventions described in: Canadian Patent No. 1,085,761 issued on September 16, 1980 to Rendall; United States of America Patent No. 4,512,956 issued on April 23, 1985 to Robinson et al; United States of America Patent No. 4,533,459 issued on August 6, 1985 to Dente et al; United States of America Patent No. 4,414,117 issued on November 8, 1983 to Yong et al; United States of America Patent No. 4,225,433 issued September 30, 1980 to Liu et al.; Canadian Patent Application No. 2,030,934 published on May 28, 1992 by Strand;
Canadian Patent Application No. 2,124,199 published on June 11, 1992 by Strand; and Canadian Patent No. 2,123,076 issued November 17, 1998 to Strand et. al.

Regardless of which oil sand extraction process is used, such processes typically produce a bitumen froth stream which is comprised of bitumen, water and mineral material.
The bitumen froth stream from the oil sand extraction process is typically subjected to further processing in order to remove amounts of water and mineral material in order to produce a bitumen product which is suitable either for upgrading or for pipelining to an upgrading facility.
For example, in order to be suitable for upgrading, the bitumen product may be required to contain at least about 95 percent hydrocarbons by weight, while in order to be suitable for pipelining, the bitumen product may be required to contain at least about 99.5 percent hydrocarbons by weight.

Thus, the bitumen froth stream obtained from an oil sand extraction process must typically undergo one or more treatment processes in order to remove water and mineral material therefrom. A number of different bitumen froth treatment processes have been proposed in the prior art.

Canadian Patent No. 1,239,371 issued July 19, 1988 to Angelov et. al. provides a process for de-emulsifying and de-asphalting a heavy oil/water emulsion. The emulsion is first mixed with a solvent comprising a paraffinic composition, whereby the oil is dissolved by the solvent while the water and asphaltics coalesce as fast settling particles. The particles are then separated from the oil/solvent phase for further treatment.

Canadian Patent No. 1,267,860 issued April 19, 1990 to Hann describes a process in which the bitumen froth is diluted with a light hydrocarbon diluent prior to the passing of the diluted bitumen froth through an inclined plate separator. The inclined plate settler is controlled by varying the underflow withdrawal rate from the separator in response to the hydrocarbon content of the separator overflow. Subsequently, the settler underflow is conducted to a "conventional" centrifuge treatment circuit, while the settler overflow, after diluent recovery, is conducted to an upgrading process.

Canadian Patent No. 1,293,465 issued December 24, 1991 to Shelfantook et. al.
relates to a counter-current process for treating bitumen froth which utilizes three stages of inclined plate separators. In particular, the bitumen froth is passed through a circuit of the serially connected inclined plate settlers, while a light hydrocarbon diluent moves countercurrently through the circuit.

Canadian Patent No. 2,012,305 issued March 21, 1995 to Lechnick et. al.
describes the preparation of a tar sands extract comprising bitumen, a "non-specific" solvent capable of dissolving all of the bitumen components and mineral fines, and mixing the extract with a "specific" solvent which is generally not capable of dissolving all of the bitumen components such as the asphaltenes, in order to form agglomerates comprising asphaltenes and mineral fines. The agglomerates are then gravitationally separated from the balance of the tar sands extract using a "lamella separator."

Canadian Patent Application No. 2,000,068 by Hall, published April 2, 1991 relates to a bitumen froth treatment process which involves separating bitumen from the froth using gravity settling. The bitumen is removed from the bitumen froth utilizing a gravity separator which is heated to a temperature of between about 250 F and about 450 F while maintaining the froth under sufficient pressure to prevent the vaporization of the water and bitumen. The process is intended to be performed without the addition of diluent to the bitumen froth.

Canadian Patent No. 2,021,185 issued September 15, 1998 to Tipman et, al.
relates to a process which passes the bitumen froth through a plurality of separation stages in series for gravity separation of the water and solids from the bitumen. Each separation stage further involves the heating of the bitumen froth to a temperature of between about 80 C to about 300 C under a sufficient pressure to maintain the hydrocarbon component in a liquid state. Further, a low molecular weight hydrocarbon diluent may be mixed with the bitumen froth for preconditioning of the froth prior to each gravity separation stage.

Canadian Patent No. 2,217,300 issued August 20, 2002 to Long et. al. and Canadian Patent No. 2,149,737 issued March 2, 1999 to Tipman et. al. both provide methods for the cleaning of a bitumen froth. The methods include adding a sufficient amount of a paraffinic solvent to the froth to induce inversion, mixing the froth and the solvent for a sufficient time to disperse the solvent in the froth, and subjecting the mixture to gravity or centrifugal separation.

Canadian Patent No. 2,400,258 issued January 11, 2005 to Madge et. al. and Canadian Patent Application No. 2,527,058 by Garner et. al., published March 19, 2004 describe froth treatment circuits in which a bitumen froth feed stream is diluted with a solvent and supplied to a primary inclined plate separator stage. The underflow from the primary inclined plate separator is further processed by a primary cyclone stage, a secondary inclined plate separator stage and a secondary cyclone stage. The solvent or diluent may be naphtha or a paraffinic or alkane hydrocarbon solvent. The expressed intention of the circuits is to treat the bitumen froth without the need for centrifuge equipment.

Canadian Patent Application No. 2,435,113 by Walker et. al., published January 11, 2005 describes the treatment of a bitumen-water emulsion, such as a bitumen froth, with a mixture comprised of a naphtha and a light solvent, particularly a C3 or C4 aliphatic hydrocarbon. The treatment destabilizes the emulsion and results in the precipitation of some of the asphaltenes in the bitumen. The amount of precipitation is controlled to produce a product of a specified asphaltene content. More particularly, the asphaltene content is controlled by adjusting the ratio of the naphtha to the light solvent and/or the ratio of the light solvent to the bitumen. The combined bitumen froth and mixture of naphtha and light solvent are fed to a phase separator.

Canadian Patent Application No. 2,493,677 by Romero et. al., published June 28, 2005 utilizes a counter-current bitumen froth treatment circuit. The treatment circuit includes a primary inclined plate separator, a secondary inclined plate separator and a primary cyclone connected in series. A diluent is added to each of the primary and secondary inclined plate separator stages, and a diluent is optionally added to the cyclone stage.

United States of America Publication No. US2005/0150844 Al by Hyndman et.
al., published July 14, 2005 describes a process for treating a bitumen froth which includes adding a diluent solvent to the bitumen froth to produce a diluted bitumen froth. The diluted bitumen froth is subjected to a separating step to separate the bitumen from the remaining diluted tailings component. The separating step is performed by a separator apparatus comprised of first and second separator vessels connected in series and configured to operate in a countercurrent manner, wherein the diluent solvent is added to the bitumen froth in the second separator vessel. Further, the solvent is subsequently recovered from the diluted tailings component such that it may be recycled within the process.

There remains a need for an alternative process for treating bitumen froth which requires relatively low energy input to operate and which provides for a relatively efficient use of diluent.
SUMMARY OF INVENTION

The present invention is a process for treating a bitumen froth comprising bitumen, water and a mineral material. The process is comprised of subjecting the bitumen froth and a diluent to gravity separation.

More particularly, the process is comprised of a plurality of stages of gravity separation. In a first stage of gravity separation, a mixture comprising the bitumen froth and a first added amount of the diluent is subjected to gravity separation. In subsequent stages of gravity separation, mixtures comprising streams derived from the bitumen froth and further added amounts of the diluent are subjected to gravity separation. The added amounts of the diluent at each stage of gravity separation are controlled in order to control the amount of the diluent which is present in each of the mixtures which are subjected to gravity separation.

In one preferred aspect, the process is comprised of three stages of gravity separation. In another preferred aspect, the process is comprised of four stages of gravity separation. The invention may, however, be comprised of fewer than three stages of gravity separation or more than four stages of gravity separation.

In a particular preferred aspect, the invention is a process for treating a bitumen froth comprising bitumen, water and a mineral material, the process comprising:

(a) subjecting a first mixture comprising the bitumen froth and a first added amount of a diluent to first gravity separation in a first gravity separation apparatus, thereby producing a first overflow stream and a first underflow stream;
(b) subjecting a second mixture comprising the first underflow stream and a second added amount of the diluent to second gravity separation in a second gravity separation apparatus, thereby producing a second overflow stream and a second underflow stream; and (c) subjecting a third mixture comprising the second underflow stream and a third added amount of the diluent to third gravity separation in a third gravity separation apparatus, thereby producing a third overflow stream and a third underflow stream.
The mixtures which are subjected to gravity separation in the practice of the invention each have a diluent-to-bitumen ratio.

The bitumen which is contained in the mixtures may be present as maltenes, dissolved asphaltenes, and precipitated asphaltenes. Diluent-to-bitumen ratio as used herein is the ratio by weight of the amount of diluent in the mixture to the amount of bitumen in the mixture, wherein the amount of bitumen includes maltenes and dissolved asphaltenes, but does not include precipitated asphaltenes.

The diluent-to-bitumen ratio of each of the mixtures is controlled in the practice of the invention in order to provide a desired result for each of the stages of gravity separation, preferably while avoiding the use of excessive amounts of diluent.

Preferably there is a trend toward increasing the diluent-to-bitumen ratio of successive mixtures which are subjected to the gravity separation. Preferably a first diluent-to-bitumen ratio of the first mixture is between about 0.5 and about 1.1.
Preferably a second diluent-to-bitumen ratio of the second mixture is between about 2 and about 4.
Preferably a third diluent-to-bitumen ratio of the third mixture is between about 3 and about 8.
As used herein, "gravity separation" includes any process which utilizes gravity in order to achieve separation of a mixture of substances having different densities, and is therefore distinguishable from other separation processes such as molecular sieve processes, absorption processes, adsorption processes, magnetic processes, electrical processes, etc.
As used herein, "gravity separation" is also distinguishable from "enhanced gravity separation processes" such as centrifuge processes, cyclone processes etc. Enhanced gravity separation processes are generally not suitable for use in the invention because they may unnecessarily disrupt or interfere with the components of the bitumen froth, resulting in less selective separation, and because they generally require higher energy input than gravity separation processes.

One or more different gravity separation processes may be used to perform the gravity separation in the invention. Preferably the gravity separation processes used in the invention are relatively low intensity processes, thereby minimizing disruption and/or interference with the components of the bitumen froth and minimizing the required energy input.

The gravity separation processes may be performed using any suitable gravity separation apparatus or suitable combination of gravity separation apparatus.

Preferably, gravity settling vessels and/or inclined plate settling apparatus are used as the gravity separation apparatus to perform the gravity separation.

Gravity settling vessels are typically comprised of tanks or other vessels into which a material to be separated may be introduced for a residence time in order to facilitate separation of the material due to gravity into two or more components having different densities. Gravity settling vessels may have any shape, size and/or configuration which is suitable for achieving gravity separation. Gravity settling vessels may include internal structures such as weirs, sumps, launders, baffles, distributors etc. and may include internal mechanical devices such as rakes, conveyors, augers etc.

Inclined plate settling apparatus are typically comprised of a plurality of inclined plates onto which a material to be separated may be introduced so that the material flows downward along the plates in order to facilitate separation due to gravity into two or more components having different densities.

Inclined plate settling apparatus may be preferred over gravity settling vessels in circumstances where space is limited and a relatively small "footprint" for the gravity separation apparatus is required.
In preferred embodiments, a combination of gravity settling vessels and inclined plate settling apparatus are used as the gravity separation apparatus to perform the gravity separation.

An objective of each of the stages of gravity separation is to produce an overflow stream and an underflow stream, wherein the overflow stream contains a relatively higher amount of bitumen than the underflow stream and wherein the underflow stream contains a relatively higher amount of water and mineral material than the overflow stream.

Each of the stages of gravity separation is performed for a length of time which is sufficient to provide an effective amount of separation having regard to the limitations of the gravity separation apparatus, the bitumen froth and the diluent. Preferably each of the stages of gravity separation is designed to achieve a balance between a desired amount of separation and the time required to achieve the desired amount of separation.

Where the gravity separation apparatus is comprised of a gravity settling vessel, preferably the average residence time of the mixture in the gravity settling vessel is at least about 30 minutes. Where the gravity separation apparatus is comprised of an inclined plate settling apparatus, the apparatus may be sized to provide a desired level of separation at a desired throughput of material to be separated.
The diluent may be comprised of any diluent which is suitable for use in treating a bitumen froth. For example, the diluent may be comprised of what is recognized in the art as a naphtha diluent or may be comprised of what is recognized in the art as a paraffinic diluent.
Naphtha diluents may include aromatic compounds while paraffinic diluents may include relatively short-chain aliphatic compounds (such as, for example, C5 to C8 aliphatic compounds).

Preferably the diluent is either a naphtha type diluent or a paraffinic type diluent.
A naphtha type diluent is comprised of a sufficient amount of a naphtha diluent (or an equivalent thereof) so that the naphtha type diluent essentially exhibits the properties of a naphtha diluent. A naphtha type diluent may therefore be comprised of a mixture of a naphtha diluent and one or more other substances.

A paraffinic type diluent is comprised of a sufficient amount of a paraffinic diluent (or an equivalent thereof) so that the paraffinic type diluent essentially exhibits the properties of a paraffinic diluent. A paraffinic type diluent may therefore be comprised of a mixture of a paraffinic diluent and one or more other substances. One exemplary diluent which may be suitable for use as a paraffinic type diluent is natural gas condensate, which may be comprised of a large percentage of relatively short-chain aliphatic compounds together with small amounts of other hydrocarbons which may include naphtha compounds.

An important distinction between naphtha diluents and paraffinic diluents is that asphaltenes are generally soluble in naphtha diluents, while asphaltenes exhibit a tendency to precipitate in paraffinic diluents under certain conditions. In particular, asphaltenes tend to precipitate in paraffinic diluents when the diluent-to-bitumen ratio is at or above a critical asphaltene precipitation diluent-to-bitumen ratio. At diluent-to-bitumen ratios above the critical asphaltene precipitation diluent-to-bitumen ratio, the extent of asphaltene precipitation in paraffinic diluents generally increases as the diluent-to-bitumen ratio increases.

The critical asphaltene precipitation diluent-to-bitumen ratio varies depending upon the composition of the bitumen, the composition of the diluent, and other conditions such as temperature and pressure. The critical asphaltene precipitation diluent-to-bitumen ratio for a particular combination of bitumen and diluent may be determined experimentally, but is typically about 1.1.

It is known that asphaltenes tend to attract each other and agglomerate together as they precipitate. During this process, water and mineral material become associated with the asphaltenes and tend to precipitate with the asphaltenes. As a result, precipitation of asphaltenes has been found to produce a cleaning effect on bitumen froth by assisting in the separation of bitumen from the water and mineral material which are components of the bitumen froth.

Furthermore, it is generally recognized that asphaltenes which include the highest concentrations of undesirable constituents such as sulphur and heavy metals are most susceptible to precipitation in paraffinic diluents and are therefore the first asphaltenes to precipitate in paraffinic diluents. Consequently, although precipitation of asphaltenes generally results in a loss of hydrocarbons from the bitumen, precipitation of a small amount of asphaltenes also assists in removing undesirable constituents from the bitumen.

As a result, the cleaning effects of asphaltene precipitation in paraffinic diluents are twofold. First, precipitation of asphaltenes assists in separating water and mineral material from the bitumen due to the agglomeration of asphaltene particles. Second, precipitation of a small amount of asphaltenes removes undesirable constituents such as sulphur and heavy metals from the bitumen.

In some aspects of the invention, the diluent is preferably a naphtha type diluent.
In other aspects of the invention, the diluent is preferably a paraffinic type diluent. In either case, the amount of the diluent which is present in each of the mixtures which are subjected to gravity separation (i.e., the diluent-to-bitumen ratio) may be controlled in order to achieve a specific result from the gravity separation. Where the diluent is a naphtha type diluent, the amount of the diluent may be controlled to achieve a desired composition of the overflow streams and the underflow streams. Where the diluent is a paraffinic type diluent, the amount of the diluent may be controlled to selectively avoid the precipitation of asphaltenes or to cause the precipitation of asphaltenes, as well as to achieve a desired composition of the overflow streams and the underflow streams.

In either case, one of the functions of the diluent is to dilute the bitumen which is contained in the bitumen froth, thereby increasing the mobility of the bitumen and reducing the density of the combined diluent and bitumen so that it is more easily separated from the water and mineral material which are contained in the bitumen froth.

Each of the overflow streams produced by the invention is comprised of an overflow amount of bitumen, diluent, water and mineral material. Similarly, each of the underflow streams produced by the invention is comprised of an underflow amount of bitumen, diluent, water and mineral material.

Where the diluent is a naphtha type diluent, a first goal of the first gravity separation is to produce a first overflow stream which is an acceptable bitumen product, and a second goal of the first gravity separation is to limit to an acceptable amount the amount of bitumen and diluent which is contained in the first underflow stream.

In order to achieve the first goal of the first gravity separation using a naphtha type diluent, the first diluent-to-bitumen ratio is preferably selected having regard to the other operating parameters of the process and the characteristics of the gravity separation apparatus so that the water and the mineral material in the first overflow stream together comprise less than about 10 percent by weight of the first overflow amount. The first diluent-to-bitumen ratio is more preferably selected so that the water and the mineral material in the first overflow stream together comprise less than about 7 percent by weight of the first overflow amount. The first diluent-to-bitumen ratio is most preferably selected so that the water and the mineral material in the first overflow stream together comprise less than about 5 percent by weight of the first overflow amount.

In order to achieve the second goal of the first gravity separation using a naphtha type diluent, the first diluent-to-bitumen ratio is preferably selected having regard to the other operating parameters of the process and the characteristics of the gravity separation apparatus so that the bitumen and the diluent in the first underflow stream together comprise less than about 25 percent by weight of the first underflow amount. The first diluent-to-bitumen ratio is more preferably selected so that the bitumen and the diluent in the first underflow stream together comprise less than about 20 percent by weight of the first underflow amount. The first diluent-to-bitumen ratio is most preferably selected so that the bitumen and the diluent in the first underflow stream together comprise less than about 15 percent by weight of the first underflow amount.
Where the diluent is a naphtha type diluent, a goal of the second gravity separation is to recover additional bitumen from the second mixture.

In order to achieve this goal of the second gravity separation, the diluent-to-bitumen ratio of the second mixture may be increased relative to the diluent-to-bitumen ratio of the first mixture, thereby increasing the density differential of the combined diluent and bitumen relative to the water and mineral material and decreasing the bitumen concentration in the combined diluent and bitumen.

More particularly, in order to achieve this goal of the second gravity separation using a naphtha type diluent, the second diluent-to-bitumen ratio is preferably selected having regard to the other operating parameters of the process and the characteristics of the gravity separation apparatus so that the water and the mineral material in the second overflow stream together comprise less than about 10 percent by weight of the second overflow amount. The second diluent-to-bitumen ratio is more preferably selected so that the water and the mineral material in the second overflow stream together comprise less than about 8 percent by weight of the second overflow amount. The second diluent-to-bitumen ratio is most preferably selected so that the water and the mineral material in the second overflow stream together comprise less than about 6 percent by weight of the second overflow amount.

More particularly, in order to achieve this goal of the second gravity separation using a naphtha type diluent, the second diluent-to-bitumen ratio is preferably selected having regard to the other operating parameters of the process and the characteristics of the gravity separation apparatus so that the bitumen and the diluent in the second underflow stream together comprise less than about 20 percent by weight of the second underflow amount. The second diluent-to-bitumen ratio is more preferably selected so that the bitumen and the diluent in the second underflow stream together comprise less than about 18 percent by weight of the second underflow amount. The second diluent-to-bitumen ratio is most preferably selected so that the bitumen and the diluent in the second underflow stream together comprise less than about 15 percent by weight of the second underflow amount.
Where the diluent is a naphtha type diluent, a goal of the third gravity separation is to maximize the amount of bitumen which is contained in the third overflow stream and thus minimize the amount of bitumen which is contained in the third underflow stream. This goal is particularly important where the third gravity separation is the last stage of gravity separation, since the third underflow stream will in such circumstances represent a tailings stream, with the result that bitumen contained in the third underflow stream will be lost to the tailings stream.
As a result, selective rejection of water and mineral material is typically less important than bitumen recovery in the performance of the third gravity separation.

In order to achieve this goal of the third gravity separation, the diluent-to-bitumen ratio of the third mixture may be increased relative to the diluent-to-bitumen ratio of the second mixture, thereby increasing the density differential of the combined diluent and bitumen relative to the water and mineral material and decreasing the bitumen concentration in the combined diluent and bitumen.

More particularly, in order to achieve this goal of the third gravity separation using a naphtha type diluent, the third diluent-to-bitumen ratio is preferably selected having regard to the other operating parameters of the process and the characteristics of the gravity separation apparatus so that the water and the mineral material in the third overflow stream together comprise less than about 10 percent by weight of the third overflow amount. The third diluent-to-bitumen ratio is more preferably selected so that the water and the mineral material in the third overflow stream together comprise less than about 8 percent by weight of the third overflow amount. The third diluent-to-bitumen ratio is most preferably selected so that the water and the mineral material in the third overflow stream together comprise less than about 6 percent by weight of the third overflow amount.
More particularly, in order to achieve this goal of the third gravity separation using a naphtha type diluent, the third diluent-to-bitumen ratio is preferably selected having regard to the other operating parameters of the process and the characteristics of the gravity separation apparatus so that the bitumen and the diluent in the third underflow stream together comprise less than about 15 percent by weight of the second underflow amount.
The third diluent-to-bitumen ratio is more preferably selected so that the bitumen and the diluent in the third underflow stream together comprise less than about 13 percent by weight of the second underflow amount. The third diluent-to-bitumen ratio is most preferably selected so that the bitumen and the diluent in the third underflow stream together comprise less than about 10 percent by weight of the third underflow amount.

Where the diluent is a paraffinic type diluent, the process is preferably further comprised of subjecting a fourth mixture comprising the first overflow stream and a fourth added amount of the diluent to fourth gravity separation in a fourth gravity separation apparatus, thereby producing a fourth overflow stream and a fourth underflow stream.

Each of the mixtures which is subjected to gravity separation is comprised of bitumen. The bitumen is comprised of asphaltenes and maltenes. All or a portion of the asphaltenes may be present as dissolved asphaltenes.

Dissolved asphaltenes are asphaltenes that are dissolved in the diluent and/or the maltenes. Where the diluent is a paraffinic type diluent, a general goal of the process is to control the precipitation of dissolved asphaltenes during each of the stages of gravity separation in order to achieve a very high quality bitumen product and an efficient use of the diluent.

Where the diluent is a paraffinic type diluent, a goal of the first gravity separation is to separate a large portion of the water and mineral material from the bitumen without causing any, or any significant precipitation of the first mixture dissolved asphaltenes which are contained in the first mixture.

In order to achieve the goal of the first gravity separation using a paraffinic type diluent, the first diluent-to-bitumen ratio is selected so that it is less than the critical asphaltene precipitation diluent-to-bitumen ratio, thereby minimizing precipitation of the first mixture dissolved asphaltenes when the first mixture is subjected to the first gravity separation.

Where the diluent is a paraffinic type diluent, a first goal of the fourth gravity separation is to produce a fourth overflow stream which is a high quality bitumen product, and a second goal of the fourth gravity separation is to limit to an acceptable amount the amount of bitumen and diluent which is contained in the fourth underflow stream.

In order to achieve these goals of the fourth gravity separation using a paraffinic type diluent, the fourth diluent-to-bitumen ratio is selected to be greater than the critical asphaltene precipitation diluent-to-bitumen ratio in order to take advantage of the bitumen cleaning effects of asphaltene precipitation, but is preferably controlled so that a desired amount of the fourth mixture dissolved asphaltenes are precipitated when the fourth mixture is subjected to the fourth gravity separation.

The desired amount of asphaltene precipitation will depend upon the desired quality of the bitumen product (which is enhanced by asphaltene precipitation) and the desired level of bitumen recovery (since the precipitation of asphaltenes results in lost bitumen).

The fourth diluent-to-bitumen ratio is preferably selected so that no greater than about 70 percent by weight of the fourth mixture dissolved asphaltenes are precipitated when the fourth mixture is subjected to the fourth gravity separation. This limit will provide a very high quality bitumen product at the expense of bitumen recovery. The fourth diluent-to-bitumen ratio is more preferably selected so that no greater than about 20 percent by weight of the fourth mixture dissolved asphaltenes are precipitated when the fourth mixture is subjected to the fourth gravity separation. This limit will provide significant cleaning effects from asphaltene precipitation with significantly lower bitumen loss.

In addition, the fourth diluent-to-bitumen ratio is preferably selected so that at least about 5 percent by weight of the fourth mixture dissolved asphaltenes are precipitated when the fourth mixture is subjected to the fourth gravity separation, in order to achieve some measurable cleaning effects from asphaltene precipitation. In particular, precipitation of at least about 5 percent by weight of the fourth mixture dissolved asphaltenes should typically result in the removal of a large percentage of the water and minerals with the precipitated asphaltenes and will also result in removal from the bitumen of at least some of the asphaltenes which contain the highest concentrations of undesirable constituents.

Stated in other terms, the fourth diluent-to-bitumen ratio is preferably between the critical asphaltene precipitation diluent-to-bitumen ratio and about 1.8.
The fourth diluent-to-bitumen ratio is more preferably between the critical asphaltene precipitation diluent-to-bitumen ratio and about 1.5. The fourth diluent-to-bitumen ratio is most preferably between the critical asphaltene precipitation diluent-to-bitumen ration and about 1.2.

Where the diluent is a paraffinic type diluent, a goal of the second gravity separation is to dilute further and selectively clean the second mixture by providing a combined density of the diluent and bitumen which is reasonably favourable for selective bitumen recovery and by utilizing further the cleaning effects of asphaltene precipitation. As a result, the second diluent-to-bitumen ratio is preferably greater than the fourth diluent-to-bitumen ratio. Controlling the amount of asphaltene precipitation during the second gravity separation is less important than in the fourth gravity separation since the amount of asphaltenes contained in the second mixture is relatively small in comparison with the amount of asphaltenes contained in the fourth mixture. As a result, more asphaltene precipitation may typically be tolerated during the second gravity separation than during the fourth gravity separation.

In order to achieve this goal of the second gravity separation using a paraffinic type diluent, the second diluent-to-bitumen ratio is preferably selected so that no greater than about 80 percent by weight of the second mixture dissolved asphaltenes are precipitated when the second mixture is subjected to the second gravity separation. The second diluent-to-bitumen ratio is more preferably selected so that no greater than about 30 percent by weight of the second mixture dissolved asphaltenes are precipitated when the second mixture is subjected to the second gravity separation. The second diluent-to-bitumen ratio is more preferably selected so that no greater than about 20 percent by weight of the second mixture dissolved asphaltenes are precipitated when the second mixture is subjected to the second gravity separation.

Stated in other terms, the second diluent-to-bitumen ratio is preferably between the critical asphaltene precipitation diluent-to-bitumen ratio and about 3.
The second diluent-to-bitumen ratio is more preferably between the critical asphaltene precipitation diluent-to-bitumen ratio and about 2.5.

Where the diluent is a paraffinic type diluent, a goal of the third gravity separation is to dilute further and selectively clean the third mixture by providing a combined density of the diluent and bitumen which is favourable for bitumen recovery and by utilizing even further the cleaning effects of asphaltene precipitation. As a result, the third diluent-to-bitumen ratio is preferably greater than the second diluent-to-bitumen ratio.

Controlling the amount of asphaltene precipitation during the third gravity separation is less important than in either the fourth gravity separation or the second gravity separation since the amount of asphaltenes contained in the third mixture is relatively small in comparison with the amount of asphaltenes contained in either the fourth mixture or the second mixture. As a result, more asphaltene precipitation may typically be tolerated during the third gravity separation than during either the fourth gravity separation or the second gravity separation.

In order to achieve this goal of the third gravity separation using a paraffinic type diluent, the third diluent-to-bitumen ratio is preferably selected so that no greater than about 80 percent by weight of the third mixture dissolved asphaltenes are precipitated when the third mixture is subjected to the third gravity separation. The third diluent-to-bitumen ratio is more preferably selected so that no greater than about 40 percent by weight of the third mixture dissolved asphaltenes are precipitated when the third mixture is subjected to the third gravity separation.

Stated in other terms, the third diluent-to-bitumen ratio is preferably between the critical asphaltene precipitation diluent-to-bitumen ratio and about 6.

One or more of the gravity separation stages may be assisted with the use of one or more suitable process aids. Suitable process aids may include, but are not limited to, flocculants and coalescing agents. In preferred embodiments, an amount of a flocculant may be used to assist the gravity separation stages. The flocculant may be comprised of any suitable substance or combination of substances.
The process of the invention may be configured to produce a plurality of bitumen product streams and/or a plurality of tailings streams.

Preferably, however, the process of the invention is configured to produce a single bitumen product stream and a single tailings stream. Where the process is comprised of three gravity separation stages which are configured as described above, the bitumen product stream is preferably the first overflow stream and the tailings stream is preferably the third underflow stream. Where the process is comprised of four gravity separation stages which are configured as described above, the bitumen product stream is preferably the fourth overflow stream and the tailings stream is preferably the third underflow stream.
As a result, preferably the second overflow stream and the third overflow stream are each recycled so that they are added to one or more of the mixtures which are subjected to gravity separation. Where the process is comprised of four gravity separation stages, preferably the fourth underflow stream is also added to one or more of the mixtures for further processing by gravity separation.

The second overflow stream and the third overflow stream may be added to any of the mixtures. Preferably, however, the second overflow stream is added to the first mixture so that the first mixture is further comprised of the second overflow stream, and the third overflow stream is added to the second mixture so that the second mixture is further comprised of the third overflow stream.

Similarly, the fourth underflow stream may be added to any of the mixtures.
Preferably, however, the fourth underflow stream is added to the second mixture so that the second mixture is further comprised of the fourth underflow stream.

Either or both of the bitumen product stream and the tailings stream may be subjected to diluent recovery in order to recover at least a portion of the diluent therefrom.
Where the bitumen product stream is the first overflow stream, the first overflow stream may therefore be subjected to diluent recovery. Where the bitumen product stream is the fourth overflow stream, the fourth overflow stream may therefore be subjected to diluent recovery.
Where the tailings stream is the third underflow stream, the third underflow stream may therefore be subjected to diluent recovery.

The process of the invention may be performed at any suitable temperature, pressure or combination of temperature and pressure. In preferred embodiments, the gravity separation stages are performed at or near ambient (atmospheric) pressure, thus eliminating the need for the gravity separation apparatus to be certified as pressure vessels.

Preferably the gravity separation stages are performed at a relatively elevated temperature, since separation may be enhanced at elevated temperatures due to reduced viscosity of the bitumen froth and increased coalescence of particles. In preferred embodiments at ambient (atmospheric) pressure, the gravity separation stages are preferably performed at an elevated temperature of between about 60 Celsius and about 120 Celsius or more preferably at an elevated temperature of about 80 Celsius.

All or portions of the process of the invention may alternatively be performed at a pressure exceeding ambient (atmospheric) pressure, thus facilitating higher elevated temperatures and further improved separation due to further reduced viscosity of the bitumen froth and further increased coalescence of particles.
SUMMARY OF DRAWINGS

Embodiments of the invention will now be described with reference to the accompanying drawings, in which:

Figure 1 is a process flow diagram of a first preferred embodiment of a process for treating a bitumen froth according to the invention, wherein the process includes three stages of gravity separation.

Figure 2 is a theoretical material balance prepared using preferred operating parameters for the process flow diagram of Figure 1, wherein the diluent is a naphtha type diluent.

Figure 3 is a process flow diagram of a second preferred embodiment of a process for treating a bitumen froth according to the invention, wherein the process includes four stages of gravity separation.

Figure 4 is a theoretical material balance prepared using preferred operating parameters for the process flow diagram of Figure 3, wherein the diluent is a paraffinic type diluent.
DETAILED DESCRIPTION

The present invention is a process for treating a bitumen froth using a diluent and gravity separation techniques. The bitumen froth to be treated may be obtained from any oil sand extraction process, and is comprised of bitumen, water and mineral material. The bitumen is comprised of maltenes and asphaltenes.

Referring to Figure 1, there is depicted a process flow diagram for a first preferred embodiment of the invention which includes three stages of gravity separation.
Referring to Figure 3, there is depicted a process flow diagram for a second preferred embodiment of the invention which includes four stages of gravity separation.

The first preferred embodiment and the second preferred embodiment may both be performed using any suitable diluent. The first preferred embodiment is, however, particularly suited to be performed using a naphtha type diluent, while the second preferred embodiment is particularly suited to be performed using a paraffinic type diluent.

As a result, the first preferred embodiment will be described in part with reference to a theoretical example using a naphtha type diluent and the second preferred embodiment will be described in part with reference to a theoretical example using a paraffinic type diluent.

Referring to Figure 1, a process flow diagram for the first preferred embodiment of the invention is provided.

A bitumen froth (1) is delivered to a first mixer to produce a first mixture (3) which comprises the bitumen froth (1) and a first added amount (2) of the diluent. The first mixture (3) is delivered to a first gravity separation apparatus (4) which comprises an inclined plate settling apparatus. The first mixture (3) is subjected to gravity separation in the first gravity separation apparatus (4) to produce a first overflow stream (6) and a first underflow stream (11).

In the first preferred embodiment as depicted in Figure 1, the first overflow stream (6) is a bitumen product stream. The bitumen product stream may be subjected to diluent recovery in a solvent recovery unit (SRU) or in another suitable process or apparatus (not shown) in order to recover all or a portion of the diluent from the bitumen product stream.
The recovered diluent may be recycled for reuse in the process of the invention. Depending upon the final composition of the bitumen product stream following diluent recovery therefrom, the bitumen product stream may be transported by pipeline or in some other manner to a bitumen upgrading process or facility (not shown).

The first underflow stream (11) is delivered to a second mixer to produce a second mixture (14) which comprises the first underflow stream (11) and a second added amount (13) of the diluent. The second mixture (14) is delivered to a second gravity separation apparatus (15) which comprises a gravity settling vessel. The second mixture (14) is subjected to gravity separation in the second gravity separation apparatus (15), preferably for an average residence time of at least about 30 minutes, to produce a second overflow stream (5) and a second underflow stream (16).

The second overflow stream (5) is recycled so that the first mixture (3) is further comprised of the second overflow stream (5). The second underflow stream (16) is delivered to a third mixer to produce a third mixture (18) which comprises the second underflow stream (16) and a third added amount (17) of the diluent. The third mixture (18) is delivered to a third gravity separation apparatus (19) which comprises a gravity settling vessel.
The third mixture (18) is subjected to gravity separation in the third gravity separation apparatus (19) , preferably for an average residence time of at least about 30 minutes, to produce a third overflow stream (20) and a third underflow stream (21).

The third overflow stream (20) is recycled so that the second mixture (14) is further comprised of the third overflow stream (20). The third underflow stream (21) is a tailings stream. The tailings stream may be subjected to diluent recovery in a tailings solvent recovery unit (TSRU) or in another suitable process or apparatus (not shown) in order to recover all or a portion of the diluent from the tailings stream. The recovered diluent may be recycled for reuse in the process of the invention. The tailings stream may be further processed in a thickener or in another suitable process or apparatus (not shown) before disposal or may be directly disposed of.

Referring to Figure 3, a process flow diagram for the second preferred embodiment of the invention is provided.

A bitumen froth (1) is delivered to a first mixer to produce a first mixture (3) which comprises the bitumen froth (1) and a first added amount (2) of the diluent. The first mixture (3) is delivered to a first gravity separation apparatus (4) which comprises an inclined plate settling apparatus. The first mixture (3) is subjected to gravity separation in the first gravity separation apparatus (4) to produce a first overflow stream (6) and a first underflow stream (11).

In the second preferred embodiment as depicted in Figure 3, the first overflow stream (6) is delivered to a fourth mixer to produce a fourth mixture (8) which comprises the first overflow stream (6) and a fourth added amount (7) of the diluent. The fourth mixture (8) is delivered to a fourth gravity separation apparatus (9) which comprises an inclined plate settling apparatus. The fourth mixture (8) is subjected to gravity separation in the fourth gravity separation apparatus (9) to produce a fourth overflow stream (10) and a fourth underflow stream (12).

In the second preferred embodiment, the fourth overflow stream (6) is a bitumen product stream. The bitumen product stream may be subjected to diluent recovery in a solvent recovery unit (SRU) or in another suitable process or apparatus (not shown) in order to remove all or a portion of the diluent from the bitumen product stream. The recovered diluent may be recycled for reuse in the process of the invention. Depending upon the final composition of the bitumen product stream following diluent recovery therefrom, the bitumen product stream may be transported by pipeline or in some other manner to a bitumen upgrading process or facility (not shown).

The first underflow stream (11) is delivered to a second mixer to produce a second mixture (14) which comprises the first underflow stream (11) and a second added amount (13) of the diluent. The fourth underflow stream (12) is also delivered to the second mixer so that the second mixture (14) is further comprised of the fourth underflow stream (12).
The second mixture (14) is delivered to a second gravity separation apparatus (15) which comprises a gravity settling vessel. The second mixture (14) is subjected to gravity separation in the second gravity separation apparatus (15), preferably for an average residence time of at least about 30 minutes, to produce a second overflow stream (5) and a second underflow stream (16).

The second overflow stream (5) is recycled so that the first mixture (3) is further comprised of the second overflow stream (5). The second underflow stream (16) is delivered to a third mixer to produce a third mixture (18) which comprises the second underflow stream (16) and a third added amount (17) of the diluent. The third mixture (18) is delivered to a third gravity separation apparatus (19) which comprises a gravity settling vessel.
The third mixture (18) is subjected to gravity separation in the third gravity separation apparatus (19), preferably for an average residence time of at least about 30 minutes, to produce a third overflow stream (20) and a third underflow stream (21).

The third overflow stream (20) is recycled so that the second mixture (14) is further comprised of the third overflow stream (20). The third underflow stream (21) is a tailings stream. The tailings stream may be subjected to diluent recovery in a tailings solvent recovery unit (TSRU) or in another suitable process or apparatus (not shown) in order to recover all or a portion of the diluent from the tailings stream. The recovered diluent may be recycled for reuse in the process of the invention. The tailings stream may be further processed in a thickener or in another suitable process or apparatus (not shown) before disposal or may be directly disposed of.

In the first preferred embodiment and the second preferred embodiment of the invention, the gravity settling vessels and the inclined plate settling apparatus are selected as the gravity separation apparatus because they both provide suitable settling performance without unnecessarily disrupting or interfering with the components of the bitumen froth and because they require significantly less energy input than enhanced gravity separation apparatus such as centrifuges and cyclones.

Alternate embodiments of the invention may include interchanging of the gravity settling vessels and the inclined plate settling apparatus and/or substitution of the gravity settling vessels and the inclined plate settling apparatus for other gravity separation apparatus.
Inclined plate settling apparatus may be preferred over gravity settling vessels where available space for the gravity separation apparatus is limited.

In all embodiments of the invention, the stages of gravity separation are preferably performed at a relatively elevated temperature of between about 60 Celsius and about 120 Celsius, or more preferably at a temperature of about 80 Celsius, in order to enhance the separation during the stages of gravity separation. Alternatively, one or more of the gravity separation stages may be performed at pressures exceeding ambient (atmospheric) pressure and at further elevated temperatures, in order to provide further enhanced separation.
In all embodiments of the invention, each of the added amounts of the diluent is controlled in order to provide a desired result at each of the stages of gravity separation. In the preferred embodiments, each of the added amounts of the diluent is controlled with the goal of achieving a desired diluent-to-bitumen ratio during each of the stages of gravity separation.
Having regard to the commingling of streams from the various gravity separation stages due to recycling etc., the desired diluent-to-bitumen ratio may be achieved by monitoring the actual diluent-to-bitumen ratios in the gravity separation apparatus and by providing suitable feedback control to control the added amounts of the diluent.

In the preferred embodiments of the invention, the actual diluent-to-bitumen ratios in the gravity separation apparatus may be monitored by constantly or periodically measuring the densities (absolute or relative) of the mixtures, which densities may be used to determine the relative proportions of diluent and bitumen in the mixtures, based upon known properties of the diluent and the bitumen froth.
In the preferred embodiments of the invention, the amounts of the added diluent for each of the stages of gravity separation are individually controlled so that each of the stages of gravity separation may be performed at a desired diluent-to-bitumen ratio for the particular stage, thus providing for increased opportunity to optimize the treatment of the bitumen froth.
In all embodiments of the invention, process aids may be used in one or more stages of gravity separation in order to assist the gravity separation. The need for process aids may be assessed, and the selection of appropriate process aids may be made using criteria known in the art of bitumen processing.
Figure 2 and Figure 4 are theoretical material balances which represent theoretical examples relating to the first preferred embodiment and the second preferred embodiment of the invention respectively. Figure 2 is an example based upon the use of a naphtha type diluent in conjunction with the process flow diagram of Figure 1.
Figure 4 is an example based upon the use of a paraffinic type diluent in conjunction with the process flow diagram of Figure 3.

Example 1 Example I is depicted in Figure 2. Referring to Figure 2, a theoretical material balance is provided for the first preferred embodiment of the invention, wherein preferred operating parameters using a typical naphtha type diluent have been applied to the process flow diagram of Figure 1. The theoretical material balance in Figure 2 has been prepared using typical operating characteristics for apparatus of the type depicted in Figure 1.

In Example 1, 330 tonnes per hour of bitumen froth are processed in three stages of gravity separation to provide a bitumen product stream of about 324.9 tonnes per hour as the first overflow stream (6).

The general goal in Example 1 is to maximize bitumen recovery from the bitumen froth while providing a first overflow stream (6) which is reasonably clean (i.e., which contains a reasonably low concentration of water and mineral material).

Pursuant to this general goal, the bitumen recovery in Example 1 is about 98.50 percent, and the bitumen product stream, comprising bitumen, diluent, water and mineral material, contains about 4.5 percent water and mineral material by total weight of the bitumen product stream. The bitumen product stream in Example 1 may be suitable for processing in a bitumen upgrading facility, but may not be suitable for pipeline transport to a bitumen upgrading facility, due to the relatively high amount of water and mineral material contained therein.
In Example 1, the naphtha type diluent functions essentially to assist in liberating the bitumen from the water and mineral material and to dilute the bitumen in order to enhance the ability to separate the diluent and bitumen from the water and mineral material. In Example 1, the cleaning effects resulting from asphaltene precipitation are not realized due to the use of the naphtha type diluent.

The effectiveness of gravity separation using a naphtha type diluent with respect to both bitumen recovery and rejection of water and mineral material is dependent upon the diluent-to-bitumen ratio. As a result, desired compositions of the overflow streams (6,5,20) and the underflow streams (11,16,21) produced by the three stages of gravity separation may be achieved by regulating the diluent-to-bitumen ratio of the mixtures (3,14,18).

In Example 1, the diluent-to-bitumen ratio of the first mixture (3) is regulated by controlling the first added amount (2) of the diluent, the diluent-to-bitumen ratio of the second mixture (14) is regulated by controlling the second added amount (13) of the diluent, and the diluent-to-bitumen ratio of the third mixture (18) is regulated by controlling the third added amount (17) of the diluent. The diluent-to-bitumen ratios are regulated so that each of the three stages of gravity separation will provide an overflow stream and an underflow stream having a desired composition which will assist in achieving the general goal of Example 1.

As a result, in Example 1, the diluent-to-bitumen ratios of the mixtures (3,14,18) are increased for each successive stage of gravity separation so that bitumen recovery is more aggressive in each successive stage of gravity separation, while the diluent-to-bitumen ratio of the first mixture (3) is regulated so that the first overflow stream (6) provides an acceptable balance between bitumen recovery and rejection of water and mineral material.

Example 2 Example 2 is depicted in Figure 4. Referring to Figure 4, a theoretical material balance is provided for the second preferred embodiment of the invention, wherein preferred operating parameters using a typical paraffinic type diluent have been applied to the process flow diagram of Figure 3. The theoretical material balance in Figure 4 has been prepared using typical operating characteristics for apparatus of the type depicted in Figure 3.

In Example 2, 330 tonnes per hour of bitumen froth are processed in four stages of gravity separation to provide a bitumen product stream of about 320 tonnes per hour as the fourth overflow stream (10).

The general goal in Example 2 is to minimize the amount of water and mineral material which is contained in the bitumen product stream while providing a reasonable level of bitumen recovery from the bitumen froth.

Pursuant to this goal, the bitumen recovery in Example 2 is about 97.00 percent, and the bitumen product stream, comprising bitumen, diluent, water and mineral material, contains about 0.11 percent water and mineral material by total weight of the bitumen product stream. The bitumen product stream in Example 2 is suitable for processing in a bitumen upgrading facility and is likely also suitable for pipeline transport to a bitumen upgrading facility. The very low concentration of water and mineral material in the bitumen product stream in Example 2 relative to Example 1 is achieved at the cost of a lower bitumen recovery in Example 2 relative to Example 1.

In Example 2, the very low concentration of water and mineral material in the bitumen product stream is achieved by selectively utilizing the phenomenon of asphaltene precipitation which occurs when bitumen is combined with paraffinic type diluent, due to the cleaning effects of asphaltene precipitation.

The phenomenon of asphaltene precipitation and the amount of asphaltene precipitation which is experienced using a paraffinic type diluent are dependent upon the diluent-to-bitumen ratio. As a result, desired amounts of asphaltene precipitation during the four stages of asphaltene precipitation may be achieved by regulating the diluent-to-bitumen ratios of the mixtures (3,8,14,18).
In Example 2, the diluent-to-bitumen ratio of the first mixture (3) is regulated by controlling the first added amount (2) of the diluent, the diluent-to-bitumen ratio of the second mixture (14) is regulated by controlling the second added amount (13) of the diluent, the diluent-to-bitumen ratio of the third mixture (18) is regulated by controlling the third added amount (17) of the diluent, and the diluent-to-bitumen ratio of the fourth mixture (8) is regulated by controlling the fourth added amount (7) of the diluent. The diluent-to-bitumen ratios are regulated so that each of the four stages of gravity separation will provide a desired amount of asphaltene precipitation.

In Example 2, the first gravity separation is intended to separate a large portion of the water and mineral material from the bitumen without causing any, or any significant precipitation of the first mixture dissolved asphaltenes. As a result, in Example 2, the first gravity separation is performed by regulating the diluent-to-bitumen ratio of the first mixture (3) so that it is less than the critical asphaltene precipitation diluent-to-bitumen ratio. In Example 2, the diluent-to-bitumen ratio of the first mixture is therefore about 0.80 and results in essentially no precipitation of the first mixture dissolved asphaltenes.

In Example 2, the fourth gravity separation is intended to produce a bitumen product stream as the fourth overflow stream (10) which has a relatively low concentration of water and mineral material contained therein. Preferably the bitumen product stream also has a relatively low concentration of undesirable constituents such as sulphur and heavy metals. As a result, in Example 2, the fourth gravity separation is performed by regulating the diluent-to-bitumen ratio of the fourth mixture (8) so that it is greater than the critical asphaltene precipitation diluent-to-bitumen ratio, but results only in a moderate amount of precipitation of the fourth mixture dissolved asphaltenes. In Example 2, the diluent-to-bitumen ratio of the fourth mixture (8) is therefore about 1.10, which results in precipitation of about 8.00 percent by weight of the fourth mixture dissolved asphaltenes.

In Example 2, the second gravity separation is intended to dilute further and selectively clean the second mixture (14) by providing a combined density of bitumen and diluent which is reasonably favourable for selective bitumen recovery and by causing further precipitation of the second mixture dissolved asphaltenes from the second mixture (14).
Increased precipitation of the second mixture dissolved asphaltenes relative to precipitation of the fourth mixture dissolved asphaltenes may be tolerated in the second gravity separation because the amount of bitumen contained in the second mixture (14) is significantly lower than the amount of bitumen contained in the fourth mixture (8). As a result, in Example 2, the second gravity separation is performed by regulating the diluent-to-bitumen ratio of the second mixture (14) so that it is higher than the diluent-to-bitumen ratio of the fourth mixture (8), and results in a higher amount of precipitation of the second mixture dissolved asphaltenes than was experienced by the fourth mixture dissolved asphaltenes. In Example 2, the diluent-to-bitumen ratio of the second mixture (14) is therefore about 2.17, which results in precipitation of about 16.10 percent by weight of the second mixture dissolved asphaltenes.

In Example 2, the third gravity separation is intended to dilute further and selectively clean the third mixture (18) by providing a combined density of bitumen and diluent which is favourable for bitumen recovery and by causing further precipitation of the third mixture dissolved asphaltenes from the third mixture (18). Increased precipitation of the third mixture dissolved asphaltenes relative to precipitation of the second mixture dissolved asphaltenes may be tolerated in the third gravity separation because the amount of bitumen contained in the third mixture (18) is significantly lower than the amount of bitumen contained in the second mixture (14). As a result, in Example 2, the third gravity separation is performed by regulating the diluent-to-bitumen ratio of the third mixture (18) so that it is higher than the diluent-to-bitumen ratio of the second mixture (14), and results in a higher amount of precipitation of the third mixture dissolved asphaltenes than was experienced by the second mixture dissolved asphaltenes. In Example 2, the diluent-to-bitumen ratio of the third mixture (18) is therefore about 5.07, which results in precipitation of about 33.30 percent by weight of the third mixture dissolved asphaltenes.

As indicated above, the first preferred embodiment of the process of the invention as depicted in Figure 1 is particularly suited to be performed using a naphtha type diluent, while the second preferred embodiment of the process of the invention as depicted in Figure 3 is particularly suited to be performed using a paraffinic type diluent.

The second preferred embodiment is particularly suited to be performed using a paraffinic type diluent because the second preferred embodiment provides for the first overflow stream (6) to be subjected to the fourth gravity separation under conditions which provide for a carefully controlled amount of asphaltene precipitation, thus providing the additional cleaning effects of asphaltene precipitation to the relatively clean first overflow stream (6).

Since naphtha type diluents do not typically provide the cleaning effects associated with paraffinic type diluents, the fourth gravity separation provided for in Figure 3 is not as advantageous where naphtha type diluents are used. Similarly, omitting the fourth gravity separation of Figure 3 where paraffinic type diluents are used does not provide the significant benefits of the further cleaning of the first overflow stream (6) using the phenomenon of asphaltene precipitation.

Despite these considerations, the treatment of bitumen froth in a plurality of stages of gravity separation with a diluent under conditions where the diluent-to-bitumen ratio is regulated for each stage provides significant advantages regardless of the type of diluent which is used, in terms of energy input to the process, efficient use of diluent, and properties of the resulting bitumen product stream.

In this document, the word "comprising" is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article "a" does not exclude the possibility that more than one of the elements is present, unless the context clearly requires that there be one and only one of the elements.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for treating a bitumen froth comprising bitumen, water and a mineral material, the process comprising:

(a) subjecting a first mixture comprising the bitumen froth and a first added amount of a diluent to first gravity separation in a first gravity separation apparatus, thereby producing a first overflow stream and a first underflow stream, wherein the first mixture has a first diluent-to-bitumen ratio and wherein the first diluent-to-bitumen ratio is between about 0.5 and about 1.1;

(b) subjecting a second mixture comprising the first underflow stream and a second added amount of the diluent to second gravity separation in a second gravity separation apparatus, thereby producing a second overflow stream and a second underflow stream, wherein the first underflow stream is comprised of bitumen, wherein the second mixture has a second diluent-to-bitumen ratio, and wherein the second diluent-to-bitumen ratio is between about 2 and about 4; and (c) subjecting a third mixture comprising the second underflow stream and a third added amount of the diluent to third gravity separation in a third gravity separation apparatus, thereby producing a third overflow stream and a third underflow stream, wherein the second underflow stream is comprised of bitumen, wherein the third mixture has a third diluent-to-bitumen ratio, and wherein the third diluent-to-bitumen ratio is between about 3 and about 8.

2. The process as claimed in claim 1 wherein the first gravity separation apparatus is comprised of an inclined plate settling apparatus.

3. The process as claimed in claim 2, further comprising adding an amount of a flocculant to the first mixture in order to enhance the first gravity separation.

4. The process as claimed in claim 2 wherein the second gravity separation apparatus is comprised of a gravity settling vessel.

5. The process as claimed in claim 4, further comprising adding an amount of a flocculant to the second mixture in order to enhance the second gravity separation.

6. The process as claimed in claim 4 wherein the second mixture has a second separation average residence time in the second gravity separation apparatus and wherein the second separation average residence time is at least about 30 minutes.

7. The process as claimed in claim 4 wherein the third gravity separation apparatus is comprised of a gravity settling vessel.

8. The process as claimed in claim 7, further comprising adding an amount of a flocculant to the third mixture in order to enhance the third gravity separation.

9. The process as claimed in claim 7 wherein the third mixture has a third separation average residence time in the third gravity separation apparatus and wherein the third separation average residence time is at least about 30 minutes.

10. The process as claimed in claim 1 wherein the first mixture is further comprised of the second overflow stream.

11. The process as claimed in claim 1 wherein the second mixture is further comprised of the third overflow stream.

12. The process as claimed in claim 10 wherein the second mixture is further comprised of the third overflow stream.

13. The process as claimed in claim 1, further comprising subjecting the third underflow stream to diluent recovery in order to recover at least a portion of the diluent from the third underflow stream.

14. A process for treating a bitumen froth comprising bitumen, water and a mineral material, the process comprising:

(a) subjecting a first mixture comprising the bitumen froth and a first added amount of a diluent to first gravity separation in a first gravity separation apparatus, wherein the diluent is a naphtha type diluent, thereby producing a first overflow stream and a first underflow stream, wherein the first mixture has a first diluent-to-bitumen ratio and wherein the first diluent-to-bitumen ratio is between about 0.5 and about 1.1;

(b) subjecting a second mixture comprising the first underflow stream and a second added amount of the diluent to second gravity separation in a second gravity separation apparatus, thereby producing a second overflow stream and a second underflow stream, wherein the first underflow stream is comprised of bitumen, wherein the second mixture has a second diluent-to-bitumen ratio, and wherein the second diluent-to-bitumen ratio is between about 2 and about 4; and (c) subjecting a third mixture comprising the second underflow stream and a third added amount of the diluent to third gravity separation in a third gravity separation apparatus, thereby producing a third overflow stream and a third underflow stream, wherein the second underflow stream is comprised of bitumen, wherein the third mixture has a third diluent-to-bitumen ratio, and wherein the third diluent-to-bitumen ratio is between about 3 and about 8.

15. The process as claimed in claim 14 wherein the first overflow stream is comprised of a first overflow amount of the bitumen, the diluent, the water and the mineral material and wherein the first diluent-to-bitumen ratio is selected so that the water and the mineral material in the first overflow stream together comprise less than about 7 percent by weight of the first overflow amount.

16. The process as claimed in claim 14 wherein the first underflow stream is comprised of a first underflow amount of the bitumen, the diluent, the water and the mineral material and wherein the first diluent-to-bitumen ration is selected so that the bitumen and the diluent in the first underflow stream together comprise less than about 20 percent by weight of the first underflow amount.

17. The process as claimed in claim 14 wherein the second overflow stream is comprised of a second overflow amount of the bitumen, the diluent, the water and the mineral material and wherein the second diluent-to-bitumen ratio is selected so that the water and the mineral material in the second overflow stream together comprise less than about 8 percent by weight of the second overflow amount.

18. The process as claimed in claim 14 wherein the second underflow stream is comprised of a second underflow amount of the bitumen, the diluent, the water and the mineral material and wherein the second diluent-to-bitumen ratio is selected so that the bitumen and the diluent in the second underflow stream together comprise less than about 18 percent by weight of the second underflow amount.

19. The process as claimed in claim 14 wherein the third overflow stream is comprised of a third overflow amount of the bitumen, the diluent, the water and the mineral material and wherein the third diluent-to-bitumen ratio is selected so that the water and the mineral material in the third overflow stream together comprise less than about 8 percent by weight of the third overflow amount.

20. The process as claimed in claim 14 wherein the third underflow stream is comprised of a third underflow amount of the bitumen, the diluent, the water and the mineral material and wherein the third diluent-to-bitumen ratio is selected so that the bitumen and the diluent in the third underflow stream together comprise less than about 15 percent by weight of the third underflow amount.

21. The process as claimed in claim 14 wherein the first gravity separation apparatus is comprised of an inclined plate settling apparatus.

22. The process as claimed in claim 21, further comprising adding an amount of a flocculant to the first mixture in order to enhance the first gravity separation.

23. The process as claimed in claim 21 wherein the second gravity separation apparatus is comprised of a gravity settling vessel.

24. The process as claimed in claim 23, further comprising adding an amount of a flocculant to the second mixture in order to enhance the second gravity separation.

25. The process as claimed in claim 23 wherein the second mixture has a second separation average residence time in the second gravity separation apparatus and wherein the second separation average residence time is at least about 30 minutes.

26. The process as claimed in claim 23 wherein the third gravity separation apparatus is comprised of a gravity settling vessel.

27. The process as claimed in claim 26, further comprising adding an amount of a flocculant to the third mixture in order to enhance the third gravity separation.

28. The process as claimed in claim 26 wherein the third mixture has a third separation average residence time in the third gravity separation apparatus and wherein the third separation average residence time is at least about 30 minutes.

29. The process as claimed in claim 14 wherein the first mixture is further comprised of the second overflow stream.

30. The process as claimed in claim 14 wherein the second mixture is further comprised of the third overflow stream.

31. The process as claimed in claim 29 wherein the second mixture is further comprised of the third overflow stream.

32. The process as claimed in claim 14, further comprising subjecting the third underflow stream to diluent recovery in order to recover at least a portion of the diluent from the third underflow stream.

33. The process as claimed in claim 32, further comprising subjecting the first overflow stream to diluent recovery in order to recover at least a portion of the diluent from the first overflow stream.

34. A process for treating a bitumen froth comprising bitumen, water and a mineral material, the process comprising:

(a) subjecting a first mixture comprising the bitumen froth and a first added amount of a diluent to first gravity separation in a first gravity separation apparatus, wherein the diluent is a paraffinic type diluent, thereby producing a first overflow stream and a first underflow stream, wherein the first mixture has a first diluent-to-bitumen ratio and wherein the first diluent-to-bitumen ratio is between about 0.5 and about 1.1;

(b) subjecting a second mixture comprising the first underflow stream and a second added amount of the diluent to second gravity separation in a second gravity separation apparatus, thereby producing a second overflow stream and a second underflow stream, wherein the first underflow stream is comprised of bitumen, wherein the second mixture has a second diluent-to-bitumen ratio, and wherein the second diluent-to-bitumen ratio is between about 2 and about 4; and (c) subjecting a third mixture comprising the second underflow stream and a third added amount of the diluent to third gravity separation in a third gravity separation apparatus, thereby producing a third overflow stream and a third underflow stream, wherein the second underflow stream is comprised of bitumen, wherein the third mixture has a third diluent-to-bitumen ratio, and wherein the third diluent-to-bitumen ratio is between about 3 and about 8.

35. The process as claimed in claim 34, further comprising subjecting a fourth mixture comprising the first overflow stream and a fourth added amount of the diluent to fourth gravity separation in a fourth gravity separation apparatus, thereby producing a fourth overflow stream and a fourth underflow stream.

36. The process as claimed in claim 35 wherein the first mixture is comprised of first mixture dissolved asphaltenes and wherein the first diluent-to-bitumen ratio is less than a critical asphaltene precipitation diluent-to-bitumen ratio, thereby minimizing precipitation of the first mixture dissolved asphaltenes when the first mixture is subjected to the first gravity separation.

37. The process as claimed in claim 36 wherein the first overflow stream is comprised of bitumen, wherein the fourth mixture has a fourth diluent-to-bitumen ratio, and wherein the fourth diluent-to-bitumen ratio is greater than the critical asphaltene precipitation diluent-to-bitumen ratio.

38. The process as claimed in claim 37 wherein the fourth mixture is comprised of fourth mixture dissolved asphaltenes and wherein the fourth diluent-to-bitumen ratio is selected so that a desired amount of the fourth mixture dissolved asphaltenes are precipitated when the fourth mixture is subjected to the fourth gravity separation.

39. The process as claimed in claim 37 wherein the fourth mixture is comprised of fourth mixture dissolved asphaltenes and wherein the fourth diluent-to-bitumen ratio is selected so that no greater than about 70 percent by weight of the fourth mixture dissolved asphaltenes are precipitated when the fourth mixture is subjected to the fourth gravity separation.

40. The process as claimed in claim 39 wherein the fourth diluent-to-bitumen ratio is selected so that at least about 5 percent by weight of the fourth mixture dissolved asphaltenes are precipitated when the fourth mixture is subjected to the fourth gravity separation.

41. The process as claimed in claim 37 wherein the fourth mixture is comprised of fourth mixture dissolved asphaltenes and wherein the fourth diluent-to-bitumen ratio is selected so that no greater than about 20 percent by weight of the fourth mixture dissolved asphaltenes are precipitated when the fourth mixture is subjected to the fourth gravity separation.

42 The process as claimed in claim 37 wherein the fourth diluent-to-bitumen ratio is less than about 1.5.

43. The process as claimed in claim 37 wherein the second diluent-to-bitumen ratio is greater than the fourth diluent-to-bitumen ratio.

44. The process as claimed in claim 37 wherein the second mixture is comprised of second mixture dissolved asphaltenes and wherein the second diluent-to-bitumen ratio is selected so that no greater than about 30 percent by weight of the second mixture dissolved asphaltenes are precipitated when the second mixture is subjected to the second gravity separation.

45. The process as claimed in claim 37 wherein the second diluent-to-bitumen ratio is less than about 2.5.

46. The process as claimed in claim 37 wherein the third diluent-to-bitumen ratio is greater than the second diluent-to-bitumen ratio.

47. The process as claimed in claim 37 wherein the third mixture is comprised of third mixture dissolved asphaltenes and wherein the third diluent-to-bitumen ratio is selected so that no greater than about 40 percent by weight of the third mixture dissolved asphaltenes are precipitated when the third mixture is subjected to the third gravity separation.

48. The process as claimed in claim 37 wherein the third diluent-to-bitumen ratio is less than about 6.

49. The process as claimed in claim 37 wherein the first gravity separation apparatus is comprised of an inclined plate settling apparatus.

50. The process as claimed in claim 49, further comprising adding an amount of a flocculant to the first mixture in order to enhance the first gravity separation.

51. The process as claimed in claim 49 wherein the fourth gravity separation apparatus is comprised of an inclined plate settling apparatus.

52. The process as claimed in claim 51, further comprising adding an amount of a flocculant to the fourth mixture in order to enhance the fourth gravity separation.

53. The process as claimed in claim 51 wherein the second gravity separation apparatus is comprised of a gravity settling vessel.

54. The process as claimed in claim 53, further comprising adding an amount of a flocculant to the second mixture in order to enhance the second gravity separation.

55. The process as claimed in claim 53 wherein the second mixture has a second separation average residence time in the second gravity separation apparatus and wherein the second separation average residence time is at least about 30 minutes.

56. The process as claimed in claim 53 wherein the third gravity separation apparatus is comprised of a gravity settling vessel.

57. The process as claimed in claim 56, further comprising adding an amount of a flocculant to the third mixture in order to enhance the third gravity separation.

58. The process as claimed in claim 56 wherein the third mixture has a third separation average residence time in the third gravity separation apparatus and wherein the third separation average residence time is at least about 30 minutes.

59. The process as claimed in claim 37 wherein the first mixture is further comprised of the second overflow stream.

60. The process as claimed in claim 37 wherein the second mixture is further comprised of the third overflow stream.

61. The process as claimed in claim 59 wherein the second mixture is further comprised of the third overflow stream.

62. The process as claimed in claim 37 wherein the second mixture is further comprised of the fourth underflow stream.

63. The process as claimed in claim 59 wherein the second mixture is further comprised of the fourth underflow stream.

64. The process as claimed in claim 60 wherein the second mixture is further comprised of the fourth underflow stream.

65. The process as claimed in claim 61 wherein the second mixture is further comprised of the fourth underflow stream.

66. The process as claimed in claim 37, further comprising subjecting the third underflow stream to diluent recovery in order to recover at least a portion of the diluent from the third underflow stream.

67. The process as claimed in claim 64, further comprising subjecting the fourth overflow stream to diluent recovery in order to recover at least a portion of the diluent from the fourth overflow stream.