CA1251146A - Bitumen recovery system and process - Google Patents

Abstract

ABSTRACT
A system for recovering bitumen from waste tailings of a tar sands mining operation whereby bitumen contained in the tailings being sent to a tailings pond is skimmed off and recycled for further processing to useful hydrocarbon products.

Description

BITUMEN RECOVERY SYSTEM AND PROCESS

FIELD OF THE INVENTION
This invention relates to a system for recovering bitumen from waste tailings of a tar sands operation where tar sands are mined and bitumen hydrocarbons extracted therefrom. More particularly, the invention involves the placement of one or more skimming means in the waste tailings discharge conduit throu~h which such tailings are pumped, the skimming means being at a position near the waste discharge pond. The recovered bitumen is processed for recycle to the hydrocarbon recovery operation.

BACKGROUND OF THE INVENTION
Tar sands (which are also known as oil sands or bituminous sands) are sand deposits which are impregnated with dense, viscous, petroleum. Tar sands are found throughout the world, often in the same geographical areas as conventional petroleum. The largest deposit, and the only one of present commercial importance, is in the Athabasca region in the northeast of the province of Alberta, Canada.
This deposit is believed to contain perhaps 700 billion to one trillion barrels of bitumen. For comparison, 700 billion barrels is just about equal to the world-wide reserves of conventional oil, some 60% of which is found in the Middle East. While much of the Athabasca deposit is not economically recoverable on a commercial scale with current technology, nonetheless, a substantial portion is situated ~25~

at, or very near, the surface where it may fairly readily be mined and processed into synthetic crude oil, and this procedure is being carried out commercially. Athabasca sands is a three-component mixture of bitumen, mineral and water. Bitumen is the valuable component for the extraction of which tar sands are mined and processed. The bitumen content is variable, averaging 12 wt% of the deposit. Water typically runs 3 to 6 wt% oE the mixture, and generally increases as the bitumen content decreases. The mineral content is relatively constant, ranging from 84 to 86 w-t%.
While several basic extraction methods-to separate the bitumen from the sand have been known for many years, the "hot water" process is the only one of present commercial significance. The hot water process for achieving primary extraction of bitumen from tar sand consists of three major process steps (a fourth step, final ex-traction, is used to clean up the recovered bitumen from down-stream processing). In the first step, called conditioning, tar sand is mixed with water and heated with open steam to form a pulp of 70 to 85 wt% solids. Sodium hydroxide or other reagents are added as required to maintain pH in the range of 8.0-8.5. In the second step, called separation, the conditioned pulp is diluted further so that settling can take place. The bulk of the sand-size mineral rapidly settles and is withdrawn as sand tailings. Most of the bitumen rapidly floats up to the surface to Eorm a coherent mass known as froth which is recovered by skimming. A third stream, called the middlings drag stream, may be withdrawn from the settling vessel and is subjected to a third processing step, scavaging, to provide incre-mental recovery of suspended bitumen.

As previously indicated, conditioning tar sands for the re-covery oE bitumen consists of heating the tar sands/water feed mixture to a process temperature (180-200F.), physical mixing of the pulp to uniform composition and consistency, and the consumption (by chemical reaction) of the caustic or other reagents added. Under these conditions, bitumen is stripped from the individual sand grains and mixed into the pulp in the form of discrete droplets of a size on the same order as that of the sand grains.
The second process step, called separation, is actually the bitumen recovery step since separation occurs during the conditioning step. The conditioned tar sand pulp is first screened to remove rocks and unconditional lumps of tar sands and clay and the reject material, "screen oversize", is discarded. The screened pulp is then further diluted with water to promote two settling processes: Globules oE
bitumen, essentially mineral-free, float upwardly to form a coherent mass of froth on the surface of the separation cells; and, at the same time, mineral particles, particularly the sand-sized mineral, settle downwardly and are removed from the bottom of the separation cell as tailings. The medium through which these two settling processes take place is called the middlings. The middlings consist primarily of water with suspended fine material and bitumen particles.
The third step of the hot water process is scavenging. The feed fines content sets the process water requirement through the need to control middlings viscosity which is governed by the clay/water ratio. It is usually necessary to withdraw a drag stream of middlings to maintain the separation cell material balance, and this stream of middlings can be scavenged for recovery of incremental amounts of bitumen. Air flotation is an effective scavenging method for this middlings stream.
Final extraction or froth clean up is typically accomplished by centrifugation. Froth from primary extraction is diluted with naphtha, and the diluted froth is then subjected to a two-stage centrifugation. This proeess yields an essentially pure diluted bitumen oil product. Water and mineral removed from the froth during this step cons-titutes an additional tailings stream which must be disposed of.
In the terminology of extractive processing, tailings is the throw-away material generated in the course of extracting the valu-able material from an ore and may contain up to about 10% by weight of bitumen. In tar sands processing, tailings consists of the whole tar sand ore body plus net additions of process water less only the recovered bitumen product. Tar sand tailings can be subdivided into three categories; viz: (1) screen oversize, (2) sand tailings (the fraction that settles rapidly), and (3) tailings sludge (the fraction that settles slowly).
It is the tailings sludge fraction with which this invention is concerned and these tailings are pumped through pipes to a large tailings pond for discharge where the settling of the finely dispensed material may be aecelerated by the use of flocculants. However, it has been discovered, in accord with this invention, that a significant amount (about 25% by weight) of bitumen which is entrained in and carried away with the tailings sludge may be efficiently recovered before the sludge is discharged into the pond. This efficient recovery is unexpected because the required pumping pressure causes turbulent flow of the fluid in the pipe and thus would appear to preclude any opportunity to recover bitumen therefrom.

BRIEF STATEMENT OF THE INVENTION
The invention provides apparatus and a process for recovering bitumen dispersed in the waste tailings of a tar sands hot water processing plant whereby skimming means within a conduit conducting the waste tailings to a waste pond removes the bitumen and enables it to be processed for recycle to the bitumen processing operation.

DISCUSSION OF PRIOR ART
Skimming devices are, of course, known in the art. For example, U.S. 4,372,854 (Szereday) discloses a device for removing floating liquid impurities such as oil by a skimming type separator in a "practically flow-free zone". In contrast, the present invention makes a separation of bitumen from waste liquid during its flow through a conduit. Also of interest is U.S. 3,951,810 (Crisafulli) which discloses an adjustable weir on a floating barge for skimming oil from the surface of a large body of water. Such a system is not applicable to the problem solved by this invention.

BRIEF DESCRIPTION OF DRAWINGS
Fig. 1 is a schematic elevational view which illustrates the general arrangement of the apparatus that comprises the inven-tion.

Fig. 2 is a front elevational view of a portion of Fig. 1 showing in greater detail the construction and arrangement of com-ponents that comprise the skimming means and the temporary storage of recovered bitumen.
Fig. 3 is a plan view of the assembly shown in Fig. 2.
Fig. 4 is an enlarged fragmentary sectional elevational view, taken on line 4,4 of Fig. 3 showing additional details of a flexible outlet hose within the temporary storage container and the suspension and adjustment means.
Fig. 5 is an enlarged fragmentary elevational view, partially in section, taken on the line 5,5 of Fig. 3 showing details of the construction of the bitumen skimming device and the dynamic removal by skimming of the bitumen which comprises the upper portion of the tailings discharge fluid being transported through a condui-t.
Fig. 6 is a plan view of Fig. 5 with the valve removed.
Fig. 7 is an enlarged transverse sectional view taken on line 7,7 of Fig. 5 Fig. 8 is a side elevational view of a modified skimmer.
Fig. 9 is a plan view of the skimmer device shown in Fig. 8.
Fig. 10 is an enlarged fragmentary side elevational view partially in section showing additional details of the skimmer of Fig.
8 taken on the line 10,10, of Fig. 9.
Fig. 11 is an enlarged fragmentary of side elevational view partially in section showing additional details of the skimmer of Fig.
8 taken on the line 11,11 of Fig. 9.
Fig. 12 is a right hand end elevational view of the skimmer detail shown in Fig. 11, taken on the line 12,12 of Fig. 11.

_~_ Fig. 2 which appears beneath Fig. 4 on the second sheet of drawings is a front elevational view of a portion of Fig. 1 showing in greater detail the construction and arrangement of components that comprise the skimming means and the temporary storage of recovered bitumen.
Fig. 3 is a plan view of the assembly shown in Fig. 2.
Fig. 4 is an enlarged fragmentary sectional elevational view, taken on iine 4,4 of Fig. 3 showing additional details of a flexible outlet hose within the temporary storage container and the suspension and adjustment means.
Fig. 5 which appears beneath Fig. 6 on the first sheet of drawings is an enlarged fragmentary elevational view, partially in section, taken on the line 5,5 o Fig. 3 showing details of the construction of the bitumen skimming device and the dynamic removal by skimming of the bitumen which comprises the upper portion of the tailings discharge fluid being transported through a conduit.
Fig. 6 which appears beneath Fig. 1 is a plan view of Fig. 5 with the valve removed.
Fig. 7 which appears beneath Fig. 5 is an enlarged transverse sectional view taken on line 7,7 of Fig. 5.
Fig. 8 which appears beneath Fig. 9 on the third sheet of drawings is a side elevational view of a modified skimmer.
Fig. 9 is a plan view of the skimmer device shown in Fig. 8.
Fig. 10 is an enlarged ragmentary side elevational view partially in section showing additional details of the skimmer of Fig. 8 taken on the line 10,10 of Fig. 9.
Fig. 11 is an enlarged fragmentary of the side elevational view partially in section showislg additioilal details of the skimmer of Fig. 8 taken on the line 11,11 of Fig. 9.

~5~6 Fig. 12 is a right hand end elevational view of the skimmer detail shown in Fig. 11, taken or. the line 12,12 of Fig. 11.

Fig. 13 is a front elevational view of a modified settling and storage assembly for the skimmed off bitumen.
Fig. 14 is a plan view of the system shown in Fig. 13.
Fig. 15 which appears beneath Fig. 16 is an enlarged fragmentary sectional side elevational view of a modified skimming device taken on the line 15,15 of Fig. 1~.
Fig. 16 is a sectional plan view of the skimming device shown in Fig. 15 and taken on the line :L6,16 of Fig. 15.
Fig. 17 is a transverse sectional elevational view taken on the line 17,17 of Fig. 15 showing additional details of construction.
DETAILED DESCRIPTION OF THE _NVENTION
Referring now to Fig. 1, an overall front elevational view of the system of the invention is shown. Waste tailings comprised of water, minerals and bitumen is pumped from the tar sands conditioning operation through conduit 11 where it empties into tailings pond 13.
In a position before the tailings pond 13, a skimming apparatus is placed at point 15 and a take-off conduit 17 leads to a settling and storage tank 19. For optimum operation, the skimming apparatus should be no less than about 300 feet from the point of discharge to the tailings pond. A valve 21 in the takeoff conduit is useful to control the flow rate of the skimming operation. A valved spigot 23 posi-tioned approximately at the centerpoint of tank 19 enables the accumulated bitumen to be removed and conveyed to the truck 25 for recycle back to the bitumen processing plant. Instead of a truck, of course, the recovered bitumen may be transported by other means, e.g., by gravity means when the recovery system is located sufficiently high Turning now to Fig. 2, the separation storage tank 19 and its operation is shown in more detail. The bitumen skimmed ofE by the skimming device and forced through pipe 17 and 17a to tank 19 is, oE
course, an aqueous dispersion high in bitumen content, but also contains minerals. This dispersion is discharged from pipe 17a into tank 19 preferably at a point below the center of the tank as shown in Fig. 2 by numeral 39. As the tank 19 becomes filled the mineral content of the aqueous dispersion settles to the bottom (shown in cut-away section as 41) and the bitumen rises (shown in cut-away section 43). Mounted at a central position on the perimeter of the tank 19 is a take-off valve and spigot 23 to which is attached on the inside of the tank a vertically positioned dog-leg conduit 47. Connected to the top of the conduit 47 is a flexible hose 45 whose other end is fitted with a nozzle 49~ The nozzle end of the hose 45 is supported by a system of pulleys 51 and 53 and a winch 55 to permit raising and/or lowering the nozzle 49 of flexible hose 45. In operation, the nozzle 49 is positioned in the bitumen layer in the tank, valve 23 opened and the bitumen removed by gravity or by pumping it through flexible hose 45, through support 47, open valve 23 to a truck 25 (Fig. 1) or other means to transport it back to the bitumen recovery plant for process-ing. An alternative system to the pulley and winch system Eor hose 45 may be used, such as a floating support system (not shown). As shown in Fig. 2, tank 19 is surrounded with supporting framework 75 and may also be equipped with a standard cage ladder 57 and platEorm 59 (Fig. 3) to permit safe access to the winch at the top o:E the tank.

The tank is also equipped with a clean-out plug 61, a valve 27 and piping to enable the settled aqueous fluid to be sent to the pond 13 (see Fig. l).
Fig. 3 is a plan view oE the assembly shown in Fig. 2 and Fig.
4 is an enlarged fragmentary sectional elevational view, taken on line 4,4 of Fig. 3 to show details of the flexible hose and the pulley and winch system for its suspension and adjustment.
It will be understood that more than one skimming means may be placed in each conduit carrying the waste tailings, and, in fact, it is preferred to use three of the skimmer systems in each line in order to achieve optimum recovery of the bitumen.
Skimming of the bitumen in the tailings pipeline 11 by the skimming device is enhanced by injecting air into the tailings pipe prior to the skimmer and preferably at the discharge of the first stage tailings pumps. Air injection rates depend on the location of the skimmer along the tailings line; generally less air is required for skimmers located farthest from the final tailings pumphouse.
It will be understood that alternative skimming systems may also be employed and several such systems are illustrated in Figs. 8 to 17.
Figs. 8 to 11 describe a layered plate system for controlling the amount of bitumen-taken off. Figs. 8 and 11 are side elevational views of such a skimmer where 75a, 75b, 75c and 75d are discharge ports which are positioned to receive the bituminous tailings skimmed off by the series of laminar plates 77a, 77b, 77c and 77d fixed within conduit 79. Thus, the bitumen in the tailings flowing between the top ~.25~

of conduit 79 and plate 77a will be taken off through port 75a; the bitumen flowing between plate 77a and 77b will be taken off through port 77b; and similarly the bitumen between plates 77b and 77c and that between 77c and 77d will be taken off through ports 75c and 75d respectively. The laminated plates will generally be separated from each other by a distance of about one inch with a pipe twenty inches in diameter. It will be understood that valves (not shown) may be positioned above each of the ports in order to control the bitumen separation and the bitumen discharge from each port may be conducted into a common header or the ports can be individually engaged depending upon the bitumen content at the various levels.
Still another alternative skimming system is illustrated by Figs. 15, 16 and 17. As shown in Fig. 15, the skimmer plate 81 within conduit 83 is hinged at pivot point 85. Above the conduit 83 is a header box 87 into which the skimmed-off bitumen flows and thence through a take-off conduit 89 to the storage and settling tank 19 (Fig. 1). The hinged skimmer plate 81 is raised or lowered as desired by means of a mechanically operated screw device 91 supported by a frame 95, said screw gl being turned by wheel 93 connected to plate 81 through couplers 97a and g7b attached to screw 91 and plate 81 respectively. Thus, by raising or lowering the plate 81, the flow of bitumen into the header and to take-off conduit 89 can easily be controlled. Figs. 16 and 17 show further the details of this hinged skimmer plate arrangement.
Reference is now made to Fig. 13 showing a settling and storage system for the bi-tumen recovered by the skimming devices discussed ~L25~

above. This system enables additional water to be separated from the bitumen and gives a very hish yield of recovered bitumen. Fig. 13 illustrates two settling separator tanks 101 and 103 which may be operated alternately or together. As shown, bitumen froth skimmed off by skimmer 113 is conducted through feed pipe 107. Feed pipe 105 also conducts bitumen froth from a skimmer (not shown). The bitumen froth enters tanks 105 and 107 through pipes 109 and 111 resp~ctively. The feed to the tanks may be controlled by a gate valve 145 operated at the top of the tank to control the flow of bitumen froth from the skimmer. After the tank is filled as shown in-tank 103, i-t is allowed to stand and the bitumen froth 115 separates and rises to the upper portion of the tank and a water layer 117 settling to the bottom of the tank~ A collection box 119 within the tank is connected to an overflow pipe 121 which feeds the bitumen froth by gravity to a froth storage tank 123. After the storage tank is filled with bitumen it is removed through outlets 125 for further handling in the extraction plant. The bottom aqueous skimmer tailings layer 117 in tanks 101 and 103 are taken through discharge ]ines 127 and 129 and the discharge flow rate may be controlled by gate valves 131 and 133 so as to maintain the required froth level for continuous froth discharge from the collection box 119 to the storage tank 123 (Fig. 14). The aqueous tailings 117 thus flow into conduit 135 which is preferably below ground level and carries this aqueous waste together with the aqueous waste not skimmed off by skimmer 113 to a storage pond or to other holding or discharge facilities.

Tt will be noted from Fig. 13 that the entire system is mounted on skids 137 and is surrounded at the top by a platform 139 having protective rails 141. Access to the platform is by means of ladders 143.
Fig. 14 is a plan view of the system shown in Fig. 13 just described and shows the details from a different perspective.
The system has been used successfully to recover up to about 25% of bitumen previously lost to tailings. For example, when injecting 70 SCFM of air at the final tailings pumphouse the bitumen concentrates towards the top oE the pipe to a value oE about 1.8~ wt.
from an average value of 0.8~ wt. in the tailings pipe at a distance of 4360 ft. from the final tailings pumphouse. This concentrated tailings with 1.8% wt. bitumen content is skimmed from the top of the pipe at a rate of 900 US GPM and then fed to a separator tank where the bitumen is concentrated to 40.5% by weight and then overflows to a holding tank. The tailings from the separator tank contain 0.3% wt.
bitumen giving a separation efficiency of 84.0%. In this instance, the flow rate of bitumen recovered is 14.7 US GPM.
It is clear from the above description of the invention that a valuable contribution has been made to the art of processing tar sands in that the invention enables a significant amount of bitumen to be recovered which would otherwise go to waste. In addition, the invention alleviates a pollution problem since the bitumen in the tailings pond is a potential toxicity problem which is also mitigated by the invention.

Claims (10)

1. A skimming device to skim off bitumen from an upper portion of a tailings fluid flowing through a conduit and means to carry said skimmed-off bitumen to a separator or storage tank, com-prising an essentially horizontal conduit adapted to be positioned in the pipeline carrying tailings to a pond, a take-off conduit integral with said conduit and mounted at an angle of about 30° from the horizontal conduit, skimming means mounted within said conduit adapted to skim bitumen from the upper portion of said flowing tailings and divert said skimmed off bitumen through said take-off conduit to said separator or storage tank.

2. The device of Claim 1 where the skimming means is a plate.

3. The device of Claim 2 wherein the plate is hinged and may be raised or lowered within said conduit.

4. The device of Claim 1 wherein the skimming means is a series of laminar plates within said conduit.

5. A process for recovering bitumen contained in a tailings fluid which comprises skimming off bitumen from an upper portion of a tailings fluid flowing through a conduit and carrying said skimmed-off bitumen to a separator or storage tank, by skimming off said bitumen with an essentially horizontal conduit adapted to be positioned in the pipeline carrying said tailings to a pond and having skimming means mounted within said conduit adapted to skim bitumen from the upper portion of said flowing tailings and divert said skimmed off bitumen through a take-off conduit which leads to said separator or storage tank.

6. The process of Claim 5 where the skimming means is a plate.

7. The process of Claim 6 wherein the plate is hinged and may be raised or lowered within said conduit.

8. The process of Claim 5 wherein the skimming means is a series of laminar plates within said conduit.

9. The process of Claims 6 to 8 wherein air is injected prior to the skimming means to enhance bitumen recovery.

10. A skimming device to skim off bitumen from an upper por-tion of a tailings fluid flowing through a conduit in combination with a settling assembly and a storage assembly for the skimmed off bitumen wherein said skimming device comprises an essentially horizontal conduit adapted to be positioned in the pipeline carry-ing tailings to a pond, a take-off conduit integral with said conduit and mounted at an angle of about 30° from the horizontal conduit, skimming means mounted within said conduit adapted to skim bitumen from the upper portion of said flowing tailings and divert said skimmed off bitumen through said take-off conduit to said settling assembly which comprises a tank to contain the skimmed off bitumen, a bitumen collection box situated in the upper portion of said tank, an overflow pipe adapted to feed bitumen by gravity to said storage assembly for storage, and a discharge line at the bottom of said tank.