GB2084179A - Recovery of bitumen from aqueous tailings - Google Patents

Abstract

Following the separation of bitumen from tar sands by the hot water process to produce an aqueous bitumen emulsion from which the bitumen froth is separated to leave aqueous tailings containing some incompletely separated bitumen, the incompletely separated bitumen is separated from the aqueous tailings by extraction with a solvent (e.g. naphtha) for the bitumen and can be recycled to the froth separation stage.

Description

SPECIFICATION Recovery of hydrocarbons from aqueous tailings Background of the Invention (1) Field of the Invention This invention relates to the recovery of hydrocarbons contained in aqueous tailings produced in the processing of tar sands and the like. More particularly, this invention relates to such recovery by contacting such tailings with a bitumen solvent serving as a diluent to yield a diluent-bitumen extract. This invention further relates to an integrated process for the enhanced recovery of bitumen involving the recycling of a bitumen soivent/diluent.

(2) Description of the Prior Art One of the processes employed in the production of hydrocarbons from tar sands is the hot water process of bitumen recovery. In this process, the bitumen is produced as a froth on top of the water. To facilitate water and solids separation, a diluent capable of dissolving the bitumen, usually a hydrocarbon liquid such as benzene, xylene, toluene, naphtha, kerosene, furnace distillates, Diesel fuels, or the like, is added to the bitumen containing froth to form a diluted aqueous bitumen. Such separation is then accomplished by centrifugation, utilizing, for example, low speed "Bird" scroll-type centrifuges (Bird Machine Company) followed by high speed "Westfalia" centrifuges (Westfalia Separator A.G.).

Among the patents describing processes of the above of similar type are Canadian Patent No.

918,091 to Evans and Camp and U.S. Patent No. 2,968,603 to Gordon R. Coulson, U.S.

Patent No. 3,900,389 to Robert A. Baillie, and U.S. Patent No. 4,035,282 to Frederick C.

Stuchberry and Alfred E. Backstrom. Most important of the tar sands to which such processes are applied are the Athabasca tar sands of northern Alberta, Canada.

Since the centrifuged diluted bitumen still contains a considerable quantity of water and particulate mineral solids, a process for producing a clean bitumen with minimum loss of hydrocarbons has been provided, as described in U.S. Patent No. 4,226,690 to Robert B.

Martin. This process makes use of a unidirectional current electrostatic field established between an energized electrode and an aqueous material surface serving as an electrical ground, the diluted bitumen to be cleaned up being introduced below the level of the aqueous material surface. A layer of dilute bitumen and a layer of aqueous material form in the treating vessel and these are separately drawn off.

In the separation of the oil and aqueous phases (the water phase still containing particulate solids) from the diluted bitumen as described above, either by centrifugation alone, electrostatic separation alone, or by some combination of the two, the aqueous phase obtained contains 2 to 9% oil. The oil is not only lost to the tailings pond but also poses a pollution problem. The bitumen-diluent ratio in the lost oil is in the same ratio as in the original blend.

The quantity of lost oil is considerable. For example, on the basis of 220,000 B/D (barrels per day) of diluted aqueous bitumen, the tailings could amount to 66,000 B/D, which can typically contain as much as 5,940 B/D of oil. This has a commercial value exceeding $ 11 5,000 per day at $16.00 per barrel of bitumen and $26.00 per barrel of diluent.

It is an object of this invention to recover the hydrocarbons, including bitumen and diluent contained in the above described aqueous tailings.

It is a further object of this invention to recycle recovered diluent and bitumen for use elsewhere in a bitumen recovery process.

Additional objects of the invention will become apparent from the following description.

Summary of the Invention The above and other objects of the invention are achieved by providing a process for the recovery of hydrocarbons from the predominantly aqueous phase separated as aqueous tailings from the organic phase of diluted bitumen emulsions having immiscible aqueous and organic phases. The process comprises contacting the aqueous tailings with a bitumen diluent, i.e., a solvent for bitumen, such as naphtha, and separately removing a hydrocarbon extract containing diluent and bitumen and de-oiled aqueous tailings from the system.The process may be carried out as an extraction process employing phase separation methods involving gravity separation, centrifugation, etc. and preferably by counter-current extraction: by subjecting the mixture of aqueous tailings and diluent, preferably with the addition of a demulsifying agent, to the action of an electrostatic field, whereby a layer of diluent-bitumen material and a layer of aqueous material form, and separately removing these materials; or by first carrying out an extraction process, then subjecting the diluent-bitumen extract to the action of the electrostatic field, recovering the diluent-bitumen material from the latter operation and removing aqueous material from both operations.

The electrostatic field may be an alternating current field or a unidirectional current, e.g., pulsed or continuous direct current, field.

The diluted bitumen emulsions which serve as the source of the aqueous tailings are ordinarily produced by prior art methods, as indicated above, involving extracting tar sands with hot water, whereby bitumen is obtained in a froth on top of the water, removing the froth and adding a diluent to it. Such diluent may be the diluent-bitumen extract separated from the deoiled aqueous tailings.

The diluted bitumen emulsion may be separated into the aqueous and organic phases by prior art methods, including centrifugation. Alternatively such separation may be by electrostatic methods, e.g., that disclosed and claimed in the above referred to Martin application, employing a unidirectional current electrostatic field established between an energized electrode and an aqueous material surface serving as an electrical ground, the emulsion being introduced below the aqueous material surface.

Bitumen product and diluent may be separately recovered from the diluted bitumen by fractionation. The recovered diluent fraction may be employed as at least part of the diluent used to contact the aqueous tailings. Naphtha from an external source may also be used as at least part of such diluent. Recovered diluent-bitumen hydrocarbon material may be similarly employed.

Brief Description of the Drawings Referring to the accompanying drawings, Figs. 1 through 6 are flowsheets, each illustrating a different variation of Applicant's process for recovering bitumen from aqueous tailings as incorporated in a cyclic process for recovering bitumen from froth.

Fig. 7 illustrates another variation of the process, as adapted to commercial scale operation.

Detailed Description of the Invention Referring to Figure 1 bitumen froth obtained by processes such as the hot water treatment of tar sands, is admixed with diluent recycled from a later stage of the process, the diluent having some bitumen contained therein. The resulting mixture, constituting a diluted bitumen emulsion having immiscible aqueous and organic liquid phases, the aqueous phase carrying undissolved minerals, is subjected to a two stage centrifugation as described above in connection with the prior art. The diluted bitumen recovered from the first centrifugation is passed to the second centrifugation.The diluted bitumen recovered from the latter step is passed to the diluent recovery operation, which is typically a conventional fractionation yielding a bitumen product stream and a diluent stream.An aqueous tailings stream is removed from each of the centrifugation steps. The two tailings streams are merged and the merged stream is passed to the aqueous tailings extraction step, wherein it is contacted with a diluent stream resulting from admixing fresh diluent with diluent coming from the diluent recovery operation.

In a typical process of this type, the oil content of the aqueous tailings is in the ratio of about 50 parts diluent to 50 parts bitumen. The diluent/bitumen ratio is increased by the addition of diluent to about 50 to 1, so that the oil phase specific gravity approaches that of the diluent.

The extraction may suitably be carried out as a conventional counter-current extraction operation. The extract phase, consisting of diluent having recovered bitumen dissolved therein, is utilized for admixing with the bitumen froth in the first step of the process, as described above. The separation of extract phase leaves a clean aqueous effluent that is relatively free from oil.

Figure 2 illustrates a process similar to that of Fig. 1 except that an electrostatic separation process is substituted for the two centrifugation stages.

Figure 3 illustrates a process similar to that of Fig. 1 except that the diluent-bitumen material recovered from the aqueous tailings extraction step is cleaned up by an electrostatic separation step before being recycled to the froth admixture step.

Figure 4 illustrates a process similar to that of Fig. 3 except that an electrostatic separation step is substituted for the two centrifugation stages.

Figure 5 illustrates a process similar to that of Fig. 1 except that an electrostatic separation process is substituted for the aqueous tailings extraction step.

Figure 6 illustrates a process similar to that of Fig. 5 except that an electrostatic separation process is substituted for the two centrifugation stages.

In the above described Figs. 1 through 6, the mixing of different process streams is shown only as a merging of the streams, but it is also contemplated that mixing operations be carried out by any conventional prior art procedure, such as the use of separate mixing vessels, mixing valves, etc.

Figure 7 illustrates a variation of the present process as adapted to commercial scale operation. A diluent-bitumen (i.e., diluent plus bitumen) recycle stram 1 is merged with a diluent stream 2 from a diluent recovery operation and the mixed stream 3 is then merged with a stream 4 of diluted aqueous tailings, such as those described in connection with Figs. 1 through 6. To the resulting stream 5 is added a demulsifier from storage vessel 6 and the thus treated stream 7 is mixed in mixer 8 and introduced into an electrostatic separator such as a Petreco single stage spherical electrostatic separator 9. A two electrode separator of this general type is shown in U.S. Patent No. 2,513,386 to Logan C. Waterman and Gordon B. Hanson, except that instead of the high velocity distributor of this patent, a low velocity distributor is employed.

An overhead stream 10 of bitumen-diluent (bitumen + diluent) is removed from treater 9 via pump 24 and flow ratio control valve 25, responsive to orifice run 26, and divided into a product stream 11 and recycle stream 1. Product stream 11 may be admixed with bitumen froth from the hot water extraction operation and the mixture further processed as shown in Figs. 1 through 6, or otherwise utilized. A side stream constituting an interface draw-off may be withdrawn from separator 9 via valve 12. Such side stream may be removed to a tailings sump for reprocessing and/or diverted to a tailings pond via streams 14 and 16 and pump 15, as indicated, or, alternatively (not indicated in the flowsheet) may be added to product stream 11 or added to the feed entering the diluent recovery unit shown in Figs. 1 through 6.A bottoms stream of aqueous tailings 16 is withdrawn via pump 17 which is regulated by interface level control 22, and valve 21 which is responsive to second interface level control 20, and removed to the tailings pond. An adjustable sample stream 19 may be withdrawn for control purposes via valve 18. An internal scraper system, designated 23, is provided to aid in solids removal from separator 9.

The electrostatic separation procedures of the present invention may be carried out in any conventional electrostatic separator, including standard Petreco low velocity separators such as the Petreco single stage spherical electrostatic separator 9 of Fig. 7. In horizontal cylindrical separators, an electrode structure similar to that shown in Patent No. 2,880,158 to Delber W.

Turner may suitably be employed. The electrostatic separator may employ either an alternating current field or a unidirectional current, e.g., pulsed or continuous direct current field. The latter is preferred as producing somewhat better results in the treatment of the aqueous tailingsbitumen diluent admixture. Separators such as disclosed in U.S. Patent No. 4,226,689 to Weldon D. Mayse and Frederick D. Watson, the disclosure of which is hereby incorporated by reference, may also be suitably employed. In such separators, an electric field is established between an energized electrode and an aqueous material surface serving as an electrical ground, the mixture of aqeuous tailings and diluent being introduced below the level of the aqueous material surface.

The preferred procedure for carrying out the electrostatic separation of the diluted bitumen froth is that disclosed in U.S. Patent No. 4,226,690, previously referred to, the disclosure-of which is hereby also incorporated by reference.

Examples 1 and 2 In a laboratory scale test of the prsent process, aqueous tailings from the centrifugation operations above described were admixed with additional diluent. About 100 ppm., based on total flow of a chemical demulsifier was added thereto and the resulting mixture was fed into a laboratory treater having a 3 inch diameter Teflon (polytetrafluoroethylene) lined upper treating column, a 7 inch diameter, approximately 1 foot long lower section, which serves as an accumulator,and a bottom draw-off (using a bomb assembly) for separating readily settleable solids, including large heavy solids that would otherwise plug the aqueous draw-off valve.The emulsion was fed into a body of aqueous material, the surface of which was maintained approximately 6 to 8 inches below a horizontal planar energized electrode, a second horizontal planar energized electrode being positioned about 6 inches above the first energized electrode.

An 8-10 kilovolt direct current electrostatic field was maintained between the lower electrode and the aqueous material surface, the higher voltage being used for the greater distance between the electrode and the aqueous material surface. Aqueous material and solids were withdrawn from the bottom portion of the accumulator at a rate calculated to maintain the level in the treater substantially constant. The treatment was carried out with the aqueous tailings heated to a temperature of about 180 F. The accumulator is merely a laboratory means to maintain level and flow and is not a necessary part of a commercial treating apparatus. The bottom draw-off (bomb-assembly) is also a laboratory convenience.

The results are summarized in the following table: Examples 1 2 Ratio-Diluent/Aqueous Tailing 2/1 2.1/1 Untreated Aqueous Tailings, Oil Content mg/l 7,1 30 7,1 30 Treated Aqueous Tailings, Oil Content mg/l 142 256 Percent Removal of oil 98.0 96.4 Overhead Oil, BSSW Vol. % 0.2 0.2 Bottom sediment and water These tests clearly indicate that the cleanup of aqueous tailings with additional diluent and treatment in an electrostatic field can removed substantially all (i.e. 98% or more) of the oil remaining in the aqueous tailing.

Example 3 A 48 hour test run was carried out on aqueous tailings from a bitumen separation process, using an electrostatic separator, as described in Examples 1 and 2. The following operating conditions were employed: Tailings Feed Rate, ml/min 250 Diluent Feed Rate, mi/min 256 Diluent Recycle Rate, mI/min 144 Total Diluent Rate, ml/min 400 Diluent to Feed Ratio 1.6 Operating Temperature, "F. 160 Operating Pressure, psig 60 Eastern Pump OR Mixer, volts 80 Aqueous Phase Residence Time, min. 40 Demulsifier Addition Rate (aqueous basis) ppm 160 Applied Voltage, kV 8 Current Consumption, ma < 0.1 * Diluent Recycle maintained by external mixing of Effluent Diluent with fresh feed in feed pot.

Samples drawn at intervals during the test were analyzed, with the results shown in the following summary: Feed Materials: High Low Average Feed Tailings Oil Content, wt.% 1.7 0.45 1.085 Feed Diluent (naphtha) BSSW, Vol. % 0.1 0.02 0.06 Solids, ppm 111 76 89.8 Gravity, "API 53.7 52.2 53.0 Effluent Materials:High Low Average Effluent Tailings Oil Content, Wt. % 0.29 0.07 0.1611 Mineral Content, Wt. % 2.11 0.57 1.39 Effluent Diluent Water Content, Wt. % 0.73 0.10 0.075 Mineral Content, Wt. % 0.01 0.20 0.27 Effluent Bottoms (Bomb Samples) Oil, Wt. % 0.29 Water, Wt. % 24.64 Mineral, Wt. % 75.07 Interface Sludge Oil, Wt. % 0.21 Water, Wt. % 24. 18 Mineral, Wt. % 75.61 Oil Recovered from Effluent Tailings Gravity, "API 53.5 In the above example, the treating process was not carried out at optimum efficiency due to variations in operating parameters, including the level of the aqueous material surface, which could not be adequately controlled in the laboratory equipment employed; problems with components such as mixers and pumps; and line and equipment plugging.In a commercial installation, a high level of efficiency may be expected.

The Teflon liner used in the laboratory treater used in the above runs is not necessary in large scale treaters. In small scale pilot and laboratory treaters it is not feasible to keep a sufficient distance between the energized electrode and the wall of the treating vessel to avoid undesired treatment at the electrode edges. In a large scale commercial treater, the use of such a lining would be very expensive. It is feasible to maintain sufficient space between the electrode and the vessel wall in such large scale treaters so that the treated diluted bitumen present in such space supplies the necessary insulation, even in the absence of the Teflon lining, to avoid treatment at the edges. Reference is made to the above noted Mayse and Watson application for a fuller discussion of this feature.

The fresh diluent employed in the above runs was a naphtha. However, the nature of the diluent is not critical, although hydrocarbon diluents are preferred and any of those mentioned in the Description of the Prior Art, above, may be employed.

The operating conditions described in Examples 1 and 2 and tabulated in Example 3, above, are not critical, but may be varied between wide limits. The preferred temperature range is about 80 F. to 180 F., although temperatures above and below this range may be successfully employed. However, lower temperatures may increase the quantity of aqueous and solids carryover in the separated diluent phase. The preferred pressure is about 80 psig., but higher and lower pressures may also be suitably employed, so long as the pressure is sufficient to maintain the separator content in the liquid phase and within the design pressure of the equipment.The preferred ratio range of diluent to tailings is about 1:1 to 2.1:1, but a far wider range of ratios may be employed, with only a lower limit of about 0.25:1. The ratio may be varied by varying either the amount of fresh diluent used or the amount recycled. Flow rates ranging between about 1/2 and 1 1/3 those shown in Example 3 are preferably employed with the laboratory treater of that example. Although flow rates outside this range may also be employed, such flow rates may entail an increase in solids carryover in the diluent. It is to be understood, however, that in commercial operations much higher flow rates, involving, for example, tens or hundreds of thousands of barrels per day, are contemplated. The aqueous residence time is dependent on the flow rate and the size of the treating equipment.It is not essential that the electrostatic field be maintained in the 8-10 kilovolt range as disclosed for Examples 1 and 2. Voltages as low as 2 kilovolts and as high as 20 kilovolts have been tried and found operable and even these limits are not critical. The preferred voltage is 8 kilovolts as shown in Example 3.

Any suitable demulsifier may be employed in the process. In the above example, as illustrative, a petroleum sulfonate was employed: Although the process is effective without the use of a demulsifier, optimum results are achieved with a demulsifier since its use effects greater sludge control and maximum contact and subsequent separation. Demulsifier addition rates up to about 320 ppm (aqueous basis) are preferably employed. However, rates substantially below 160 ppm result in higher solids carryover in the recovered diluent and the higher dosages may lead to both higher water and higher solids carryover.

The system described in Example 3 may also be operated without the application of electrical power to the electrodes, but this results in a tenfold increase in the aqueous and solids carryover in the effluent diluent phase.

The process has been described above in connection with aqueous tailings derived from the processing of diluted bitumen from the hot water treatment of tar sands. However, the process may be employed with aqueous tailings derived from a variety of separation procedures, including tailings from the primary hot water extraction step, and with various diluted bitumen feeds, including those derived from oil shale processing.

From the foregoing, it will be seen that there has been described a process well suited for enhancing the recovery of hydrocarbon from tar sands and the like. The foregoing description of the invention is to be taken as illustrative of the process and not limitative. Various changes may be made in the operation of the invention without departing from its spirit.

Claims (15)

1. A process for the recovery of hydrocarbons from the predominantly aqueous phase separated as aqueous tailings from the organic phase of a diluted bitumen emulsion having immiscible aqueous and organic phases, said process comprising contacting said aqueous tailings with a bitumen diluent and separately removing from the system a hydrocarbon phase containing diluent and bitumen and de-oiled aqueous tailings.

2. The process of claim 1 wherein said steps of contacting the aqueous tailings with a bitumen diluent and separately removing the diluent-bitumen hydrocarbon phase and the deoiled aqueous tailings are carried out in the form of a counter-current extraction process.

3. The process of claim 1 wherein said steps of contacting the aqueous tailings with a bitumen diluent and separately removing the diluent-bitumen hydrocarbon phase and the deoiled aqueous tailings are carried out by admixing said aqueous tailings with said bitumen diluent, subjecting the admixture to the action of an electrostatic field, whereby a layer of diluent-bitumen hydrocarbon material and a layer of aqueous material form, recovering said hydrocarbon material and removing said aqueous material.

4. The process of claim 3 wherein the bitumen diluent admixed with said aqueous tailings includes said recovered diluent-bitumen hydrocarbon material.

5. The process of claim 4 wherein said bitumen diluent includes diluent recovered from said organic phase of said diluted bitumen emulsion.

6. The process of claim 1 wherein said steps of contacting the aqueous tailings with a bitumen diluent and separately removing the diluent-bitumen extract and de-oiled aqueous tailings are carried out in the form of an extraction process and the diluent-bitumen extract is subsequently subjected to the action of an electrostatic field, whereby a layer of diluent-bitumen material and a layer of aqueous material form, and separately removing said materials.

7. The process of claim 1 wherein the method of separating said predominantly aqueous phase from said organic phase of said diluted bitumen emulsion comprises centrifugation.

8. The process of claim 1 wherein the method of separating said predominantly aqueous phase from said organic phase of said diluted bitumen emulsion comprises subjecting said emulsion to an electrostatic field.

9. The process of claim 1 wherein said diluted bitumen emulsion is produced by treating tar sands with hot water, whereby bitumen is obtained in a froth on top of the water, removing said froth and adding a bitumen diluent to it.

10. The process of claim 9, further comprising fractionating said organic phase separated from said diluted bitumen emulsion to recover a diluent fraction and a bitumen product fraction and employing said diluent fraction as at least part of the diluent used to contact said aqueous tailings.

11. The process of claim 9 wherein the diluent-bitumen extract separated from the de-oiled aqueous tailings is employed as the bitumen diluent added to said froth.

12. The process of claim 1 wherein at least part of the diluent used to contact said aqueous tailings is naphtha from an external source.

13. The process of claim 1 wherein at least part of the diluent used to contact said aqueous tailings is diluent recovered from said organic phase of said diluted bitumen emulsion.

14. The process of claim 1 wherein at least part of the diluent used to contact said aqueous tailings is said removed diluent-bitumen hydrocarbon phase.

15. A process for the enhanced recovery of bitumen from tar sands or the like comprising: (a) treating tar sands with hot water, whereby bitumen is obtained in a froth on top of the water; (b) removing said froth and adding a diluent to it to form a diluted bitumen emulsion; (c) separating said emulsion into separate predominantly organic and predominantly aqueous phases, and separately removing said phases, said predominantly organic phase constituting a diluent-bitumen extract and said predominantly aqueous phase constituting aqueous tailings, said aqueous tailings containing a small proportion of bitumen; (d) fractionating said organic phase and recovering a diluent fraction and a bitumen product fraction; (e) mixing said diluent fraction with fresh diluent from an external source to obtain a mixed diluent; ; (f) contacting said aqueous tailings with said mixed diluent and separately removing from the system a diluent-bitumen extract phase and de-oiled aqueous tailings; and (g) recycling said diluent-bitumen phase as the diluent to step (b).