CA1144098A - Deaeration apparatus integral with a separation cell employed in a hot water process for extracting oil from oil sands - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A group (typically, three) of relatively small froth deserating cells are distributed directly around the periphery of each separation cell below the launders. Thus, deaerated froth, in effect, is obtained directly from the separation cell to obviate the need for and downstream equipment and realize improve-ments in process flexibility, operator convenience, installation cost, and plant floor space utilization, The hot froth provides an effective, closed-by head to the pumps which may therefore be smaller and are self primed. Winter restarts after system main-tenance are also facilitated.

Description

TC~E~NYAK
~14~ s-7g-025 DEAERATION APPARATUS INT~GRAL WITH A
SEPARATION CELL EMPLOY~D IN A HOT WATE~ PROCESS
FOR E~TRACTING OIL FROM OIL SANDS

BACKGROUND OF T~E INVENTION
-This invention relates to the separation of oil from bitumlnous sands such as Athabasca oil sands. More particu-larly,~ the invention relates to a modification to the hot water process for extracting bitumen from oil sands, by which modi-fication deaerated bitumen is produced in a deaeration zone directly adjacent the separation cell to obtain froth which is readily pumpabIe.

In the hot water process employed for recovering oil from oil sands (also known as tar and bituminous sands), such as presently practiced at the Suncor (formerly GCOS) and Syncrude plants in northern Alberta, the oil sands are mulled and jetted with steam together with a minor amount of hot water at temper-atures typically in the range 170F to 190F, and the resulting pulp is mixed with hot water and transferred -to a separation cell maintained at temperatures from 140F to 185F. In the separation cell, sand settles to the bottom as tailings, and oil rises to the top in the form of a froth. An aqueous middlings layer comprising clay, silt and some oil is formed between the sand and froth layers. This basic process may be combined with a scavenger step for further treatment of the middlings layer obtained from the primary separation step to recover additional amounts of oil therefrom.

In recovering bituminous froth utilizing the process disclosed in Canadian Patent No, 841,581 and the hot water sep-aration cell disclosed in Canadian Patent No. 882,667, the froth 3~4~
is recovered in overflow launders disposed on the upper edge of the extraction cel'l-. There~after, the froth flows by gravity into a collection vessel located near the separation cell be-low the level of the~froth collection launders. Often, one collection vessel serves four or more separation cells to pro-vide a central collection' means for recovered froth. Froth from secondary scavenger steps can also be` coll'ected in this same vessel. Thereafter1 the fro-th is heated and transferred to a centrifuge zone or to other means for effecting demineralization and dehydration. Normally, the froth is diluted with a liquid hydrocarbon before the demineralization and dehydration steps.
Methods for accomplishing water and mineral removal from the froth are disclosed in Canadian Patent No. 910,271 and Canadian Patent No~ 918,091.

The bituminous froth, as recovered from the hot water separation cell, resembles a liquid foam with poor flow charac-teristics. The froth'is difficult to pump and therefore must be treated to improve its liquid flow characteristics if it is to be handled by centrifugal pumps. The characteristics of the froth particularly detrimental to handling with centrifugal pumps ar'e: (i) high air content and (ii) high viscosity on the order of 7500 centipoise at 150F.

Canadian Patent No. 630,710 discloses that bituminous froth can be collected and transferred to a deaeration zone where it is heated with steam at subatmospheric pressures to remove'air bubbles from the froth. This end can be accomplished by adding the froth to a steam heated oil bath maintained at subatmospheric pressure. The froth is therein diluted with oil and a~itated to remove air bubbIes from the froth. Although this method'improves the'froth, transferring the froth to the treatment apparatus disclosed nevertheless renders the process cumbersome and expensive.

Canadian Patent Application Serial Number 338,510, filed October 26, 1979, and entitled "Bitumen Deaeration Process Carried Out in the Separation Cell", by Roy Wood, discloses means for obtaining deaerated froth directly f~om the separation cell by adding a defoaming agent (such as Dow Corning Silicone 200) to the oil sands feed ; on a conveyor belt as it flows into the conditioning drum or, alternatively, after the conditioning step in the feed to the separation cell or to the froth launder itself. This process achieves a readily pumpable froth directly from the separation cell, but is somewhat expensive to implement and operate. Additio~ally, and more importantly, the cumulative effects of long term use of defoaming agents in the hot water process may have adverse effects on the subsequent recovery of bitumen from the sludge layer of the tailings pond or ponds associated with the hot water process as well as the treatment of the sludge layer to meet certain ecological reguirements.
Thus, it will be appreciated by those skilled in the art that it would be highly desirable to provide means for deaerating bituminous froth which is simple and inexpensive and which does not bring about long term, possibly detrimental, side effects to the system.

OBJECTS OF THE IN~IENTION
It is therefore a broad object of this invention to provide an improved hot water process for extracting bitumen from oil sands.
It is a more particular object of this invention to provide imprsved means for deaerating bitumen froth obtained in a hot water process for extracting bitumen from oil sands such that the froth is readily pumpable and may be more easily subsequently processed into synthetic crude oil.

Still more specifically~ it is an object of this inven-tion to provide, in a hot water process for extracting bitumen from oil sands, a froth deaeration system including at least one deaerator box directly adjunct the periphery of each separation cell for receiving bitumen froth from the separation cell over-flow launders by gravity feed and pump means proximately situated below the deaeration box for transferring the deaerated froth downstream for further processing.
Thus, in accordance with the present teachings, an improve-ment is provided in a system for effecting a hot water process forextracting bitumen from oil sands wherein the process includes the steps of forming a mixture of oil sands and water, passing the mixture to a separation cell to form an upper bitumen froth layer, a middlings layer, and a sand tailings layer and recovering the bitumen froth layer by means of an overflow froth launder disposed circumferentially around the separation cell proximate the top thereof. The improvement which is provided comprises providing at least one deaerator box disposed adjacent the separa- -tion cell and generally below the launder and conduit means for conducting froth downwardly by gravity flow from the launder to the deaerator box whereby deaerated and more easily pumped froth is obtained from the deaerator box.
DESCRIPTION OF THE DRAWING
The subject matter of the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method,of operation, may best be understood by reference to the following description in conjunction with the accompanying drawing of which:
Figure 1 is a simplified schematic representation of a hot water process, employing the present invention, for extract-ing bitumen from oil sands;
Figure 2 is a top plan view of a practical installation for the present invention, which plan view omits, for clarity, certain steam lines and related structures shown in other Figures;
Figure 3 is an elevational view taken generally along and between the lines 3-3 of Figure 2, but showing additional structure;
Figure 4 is an elevational view, partially cutaway, taken generally along and between the lines 4-4 of Figure 2, but show-ing additional detail;
Figure 5 is a top plan view similar to Figure 1, but `-omitting, for clarity, certain structure included in Figure 1 and showing other structure not included in Figure l;
Figure 6 is a partially cutaway sectional view along the lines 6-6 of Figure 2; and Figure 7 is a partially cutaway fragmentary view taken along the lines 7-7 of Figure 2.

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DETA-ILED DESCRIPTION OF THE I:NVENTION
Referring now to Figure 1, mined oil sands are fed into the system through a line 10 and are carried by a conveyor 9 to a conditioning drum or muller 11. Water is fed to the muller by a line 12, and steam is introduced thereto through line 13. The total water so introduced in liquid and vapor form is a minor amount based on the weight of the oil sands processed. The con-ditioning drum lI is provided with suitable kneading or mixing means (not shown) to give the:`desired mulling action. Enough steam is introduced through line 13 to raise the temperature in the conditioning drum to within the range of 130-210F and preferably to above 170F. Mulling of the oil sands produces a pulp which then passes from the conditioning drum as indicated by line 14 to a screen indicated at 15. The purpose of the screen 15 is to remove from the oil sands pulp any debris, rocks, or oversize lumps as indicated generally at 16. The conditioned oil sands pass from the screen 15 to a pulp box 17 which serves ; as a zone for diluting the pulp with additional water before passage to a primary separation zone 15. Hot water ~rom a heater 27 is passed through a line 19 to pulp box 17, and additional steam is fed thereto through a line 20, if necessary, to main-tain the range of 130-210F and preferably above 170F. Also, a middlings stream, which is withdrawn from the primary separator 18, may be recycled through lines 21 and 19 to the pulp box.
; This recycle stream serves to provide sufficient liquid to flood the oil sands pulp from the pulp box and effect transfer of the pulp to the separator. Another function of the recycle stream is to cause dispersion of the pulped material as it is fed into the separation:zone 18.~ However, such recycling of middlings is not essential in all cases, partieularly when the clay content of the tar sands is high. In this event, a reIatively high rate `

of fresh water introduction through heater 27 can be employed to compensate for the high'clay content while the corresponding-ly high rate of transfer of middlings layer through line 26 as hereinafter described can be maintained. Under these circum-stances, recycling of the other stream of middlings through lines 21 and 19 to pulp box 17 is not required.

Modifications that may be made in -the process as a'bove described include sending a minor portion of the middlings re-cycle stream from line 21'through a suitable line (not shown) to muller lI to supply all or a part of the water therein other than that supplled through condensation of the steam which is consumed. Also, if desired, a stream of the middlings recycle can be introduced onto the'screen 15 to flush the pulp there-through and into pulp box 17.

Separation zone 18 may comprise a large cylindrical or rectangular -tank, or battery of tanks, which may, if desired, be provided with heating coils 22 for maintaining a temperature in the range of 130-2I0F, and preferabl'y above 170F. A launder 4 about the upper periphery of a separator collects froth as it floats to the top of the separator and flows over the upper lip thereof. A sand tailings removal line having a star valve 24 or any other suitable control discharge means is provided at the bottom of the separator 18. Separator 18 also has an intermedi-ate withdrawal line 26 through which astream of middlings layer is removed in addition to that recycled through line 21.

Because of the high air content in the froth which flows into the lauders 4, the froth is difficult to pump. Thus, accor-ding to the present invention, a deaerator box 1 affixed to the separator 18 receives froth from the launders by gravi-ty flow th.rough lines 2. Steam is injected into the deaerator through a line 3 to promote deaeration of the froth as more fully described 4C~

below. The deaerated froth then flows through a line 5 by gravity into a suction tank 6 from wh`i'ch'i-t is withdrawn through a line 7 by a pump 8. The deaerated froth'is conveyed downstream through a line 23 for further proces'sing.

The middlings layer obtained in separation zone 18 will contain most of the silt and clay which was pres'ent in the oil sands in the'ir natural state. In order to prevent the build up of clay in the'system, it is necessary to continually discard some of the middlings layer and supply en'ough water in the con-ditioning operations to c'ompensate for that so discarded. Therate at which the` middlings needs to be'removed from the system depends upon the content of clay and silt present in the oil sands feed, and this will vary from time to ~ime as the content '' of these fines varies~ If the clay and silt content is allowed to build up in the syst'em, both the density and the viscosity of the middlings layer will increase. Concurrently, with such in- -crease, an increase in the'proportions of both the oil and the sand retained by the middlings will occur. I~ the clay and silt content is allowed to build up too high in the system, effective separation will no longer occur, and the-process will become inoper~ative. Hence, it is important to regulate the withdrawal of middlings through line 26, and the addition of fresh water to the system to compensate for water thus removed, in a way that wi-ll keep the separation step operating properly. However, when this separation step is oeprating in an optimum manner, the middlings layer withdrawn through line 26 will contain a sub-stantial amount of oil which did not separate. Hence, the middlings layer withdrawn through line 26 is, for purpose of ' description, herein referred to as "oil-rich middlings."

The rate'of addition of fresh'water to the system and the rate'of removal of middlings layer -~rom separation zone 18 ~L~44~

through line 26 are regulated in accordance with either *he density or the viscosity of the` middlings layer or both. When densi-ty is used for the control, such addition and removal are carried out so that the middlings density is main-tained in the range of 1.03-1.50 gm/cc, more preferably 1.10-1.20 gm/cc. It is preferred, however, to utilize viscosity to effect the con-trol in which case the water addition and removal are carried out to maintain the middlings viscosity in the range of 0.5 to 10 centipoise, more preferably 0.6 to 3.0 centipoise. Periodic or continuous measurements of either viscosity or density for the middlings phase can be made, and the removal of middlings through line 26 and corresponding addition of fresh water to the system can be regulated in accordance with the measured values to maintain the value within the range desired. Whenever either density or viscosity tends to become higher than is de-sired; an increase is made in the rate of middlings removal and corresponding rate of fresh water addition; and if density or viscosity values tend to become too low, decreases in these removal rates are effected.

As previously men-tioned, the middlings layer withdrawn through line 26 will still contain a substantial amount of oil even though the separation step is operated under optimum con-ditions. The amount of oil remaining in the middlings layer appears to be more or less related to the percentage of clay and/or silt present in the oil sands being processed, varying directly with the amount of clay and/or silt present. For ex-ample, typical oil recovery values for the froth from oil sands in which 15% of the mineral matter is less than 44 microns and from sands in which 25-%0% is less than this slze are, respec-tively, 85% and 60%. ~or commercial operation, it is highly desirable -to obtain increased recoveries over such values, and -this is particularly true when the tar sands mined contain a relatively high proportion of clay and silt components. In a large sizé commercial operation~ an increase of oil recovery of even a few percentages values can amount to a large volume of additional oil per day.

To carry out such secondary recovery, the oil-rich middlings stream withdrawn from separator 18 through line 26 is sent to a scavenger zone 2g wherein an air flotation operation is conducted. The processing conducted in scavenger zone 29 provides a controlled zone of aeration in the flotation cell at a locus where agitation of the middlings is being effected so that air becomes dispersed in the middlings in the form of small bubbles. Figure 1 illustrates a flotation cell of the subaera-tion type wherein a motorized rotary agitator 30 is provided and air is fed thereto in controlled amount as by means of line 31. Alternatively, the air can be sucked in through the shaft of the rotor. The rotor effects dispersion of the air in the middlings. This air causes the formation of additional oil froth which passes from the scavenger zone 29 through line 32 and thence to line 23 for further processing in admi~ture with the froth derived from the primary separation in zone 18. An oil-lean middlings stream is removed from the bottom of scavenger zone 29 via line 33 and is discarded from the process. The oil-lean middlings contains a substantial proportion of the clay and silt components that were present in the original tar sands, and discarding thereof from the process prevents the build up of this fines material in the separation zone 18. The amount so discarded is such as to maintain the viscosity and density of the oil-rich middlings in zone 18 within the ranges as speci-fied hereinbefore.

The mixed froths from lines 23 and 32 will contain some water and an appreciable amount of the finer mineral matter that was present in the tar sands. Generally this material will be sent to a processing zone (not shown) wherein the water and mineral matter are removed. This can be achieved by diluting the froth with naphtha and -treating the mixture in an electro-static precipitator or in centrifuges to effect dehyclration and demineralization.
A practical installation employing the froth deaerating system of the present invention is shown in Figures 2-7. ~ach of an array of four separation cells 18a, 18b, 18c, 18d, carries, about its periphery, three deaeration boxes: lal, la2, la3;
lbl, lb2, lb3; lcl, lc2, lc3; and ldl, ld2, ld3; respectively-Downwardly inclines pipes 50 and 51 lead, respectively, from deaerator boxes lal and la2 to deaerator box la3 from which line 52 tees (with a corresponding line 55) into a line 56 through which deaerated bitumen is conveyed to a suction tank 57. Down-wardly inclined lines 53 and 54 lead, respectively, from deaer-ator boxes lbl and lb2 to deaerator box lb3 from which line 55 extends.
Similarly, downwardly inclined lines 58 and 59 from de-aerator boxes lcl and lc2 feed deaerated froth to deaerator box lc3, and downwardly inclined lines 61 and 62 feed deaerated froth from deaerator boxes ldl and ld2 to deaerator box ld3. ~he de-aera-ted froth from the deaerator boxes lc3 and ld3 flow, respec-tively, through pipes 60 and 63 to pipe 64 which feeds suction tank 65.
Deaerated froth is withdrawn from the suction tank 57 by parallel pumps 66 and 67 which feed ou-tput lin~ 68. Similarly, deaerated froth is withdrawn from suction tan~ 65 by parallel pumps 69 and 70 which feed output line 71. The output lines 68 ' and 71 merge into the primary output line 72 which is the counter-part of the line 23 shown in the simplified schematic represen-tation of ~igure 1.

As best shown in Figure 4, sparge steam for carrying out the deaerating process within the cleaerator boxes (deaerator box ldl in Figure ~) is introduced near the deaerator box bottom at inlet 73 which is coupled to a supply steam header (not shown in Figure 4) as will be described in more detail below. The sparge steam moves upwardly in the deaerator boxes and is col-lected in a steam vent header system as illustrated in Figure 5in which the various steam vent pipe branches 7~- feed steam vented from the deaerator boxes to a common steam vent output line 75.

The flow paths of the fluid within a typical deaeration box (ld ) may best be understood by reference to Figures 6 and 7.
Bituminous froth which has overflowed from the separation cell 18d into the launder 81 (illustrated in the simplified schematic of Figure 1 as launder ~) passes through conduit 82 to distribu-tion pipe 83 situated within the deaerator box ldl near the top.
The distribution pipe 83 has a series of openings 84 distributed along its length in order to spread the bitumen stream laterally and permit it to extend as a more or less uniform sheet across the full width of the deaerator box ldl. As the bitumen stream descends, it cascades from tier to tier of a shed deck 85. Steam from a header 86 is distributed across the width of the deaerator box ldl near the bottom by a perforated pipe 87. As the steam upwardly through the distribution box ldl it encounters the sheet of bitumen froth cascading downwardly over the individual elements of the shed deck and shears away the air from the bitu-men stream. Thus, the froth reaching the bottom of the deaerator ~; , , ` ~
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box ld is substantially purged of air and is withdrawn through line 61 as a pumpable liquid ready for downstream processing.

One presently preferred configuration for the shed deck 85 is illus-trated in Figure 6. The shed declc 85 comprises al-ternate downwardly slanted elements 88 and 89. The elements 89 extend from each side of the deaerator box interior wall and slope downwardly toward the center. The elements 89 are cen-trally disposed and have a roof-like configuration sloping down-wardly toward the inner walls of the deaerator box ldl from a central peak. Thus, it will be understood that the ~roth in-troduced into the top of the deaerator box ldl cascades back and forth between the alternate elements 88 and 89 to provide maxi-mum expose of the froth to the stripping action of the steam moving upwardly through the deaerator box.

While the principles of the invention have now been made clear in an illustrative embodiment, there will be immediately obvious to those skilled in -the art many modifications of struc-ture, arrangements, proportions, the elements, materials, and components, used in the practice of the invention which are par-ticularly adapted for specific environments and operating require-ments without departing from those principles. i -

Claims (9)

THE EMBODIMENTS OF THE PRESENT INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a system for effecting a hot water process for extracting bitumen from oil sands, which process includes the steps of:
a) forming a mixture of oil sands and water;
b) passing said mixture to a separation cell to form an upper bitumen froth layer, a middlings layer, and a sand tailings layer; and c) recovering said bitumen froth layer by means of an overflow froth launder disposed circumferentially around said separation cell proximate the top thereof;

the improvement comprising the provision of:
i) at least one deaerator box disposed ad-jacent said separation cell and generally below said launder; and ii) conduit means for conducting froth down-wardly by gravity flow from said launder to said de-aerator box whereby deaerated, and therefore more easily pumped, froth is obtained from said deaerator box.

2. The system of Claim 1 in which a plurality of gen-erally equally distributed deaerator boxes are disposed about the circumference of said separation cell.

3. The system of Claim 2 in which said deaerator boxes are affixed to and supported by said separation cell.

4. The system of Claim 1 in which each said deaerator box includes distribution means in its upper region for receiv-ing froth from said launders and distributing the froth laterally within said deaerator box such that the froth flows downwardly through said deaerator box as a sheet.

5. The system of Claim 4 in which the interior of said deaerator box includes a plurality of shed deck elements adap-ted to direct said froth sheet back and forth as it cascades downwardly.

6. The system of Claim 5 which includes injection means for introducing and laterally distributing stripper steam within-in said deaerator box in the lower region thereof and vent means in the upper region thereof for collecting and venting said stripper steam.

7. The system of Claims 4, 5, or 6 in which a plurality of generally equally distributed deaerator boxes are disposed about the circumference of said separation cell.

8. The system of Claims 4, 5, or 6 in which a plurality of said deaerator boxes are affixed to and supported by said separation cell.

9. The system of Claims 4, 5, or 6 in which a plural-ity of said deaerator boxes are affixed to and supported by said separation cell and are generally equally distributed about the circumference thereof.