Note: Descriptions are shown in the official language in which they were submitted.
1 _~ FIELD OF THE INVENTION 2 0 2 9 7 9 5
2 This invention relates to simultaneously transporting and
3 conditioning oil sand in an aqueous slurry in a pipeline extending
4 between a mine and an extraction plant. More particularly, it relates
to a process comprising the steps of surface mining naturally water-wet
6 oil sand, mixing the as-mined oil sand, with heated water, air and
7 (optionally) process aid (e.g. NaOH) at the mine site to form an
8 aerated slurry, pumping the resultant slurry through the pipeline a
9 sufficient distance so that contained bitumen flecks separate from
sand, coalesce and are aerated, and feeding the slurry directly into
11 a gravity separation vessel to recover the major portion of the bitumen
12 as primary froth.
13 BACKGROUND OF THE INVENTION
14 The present invention is a modification of the conventional
commercial system used to extract bitumen from mineable oil sand. In
16 order to understand the manner in which the invention departs from
17 this conventional system and to appreciate the discoveries on which the
18 invention is based, it is first useful to describe the conventional
19 system.
As previously stated, the invention has to do with oil sand,
21 specifically the oils and of the Athabasca deposit which exists in
22 Northern Alberta. This oil sand comprises sand grains that are water-
23 wet or individually coated with a thin sheath of water. The bitumen
24 or oil is present as flecks located in the interstices between the wet
rains.
26 At applicantsl plant, the deposit is surface mined
27 by first removing overburden and then using a dragline to
28 excavate the oil sand and dump it to one side in the form of a windrow.
2029795
1 ~ A bucket wheel reclaimer transfers this windrowed oil sand on to
2 the feed end of a conveyor belt train, which carries it to an
3 extraction plant.
4 Applicant's operation involves mining about 300,000
tons of oil sand per day in this way. Four draglines are
6 employed, each feeding a separate reclaimer and conveyor belt
7 train.
8 Each such conveyor belt train comprises a plurality of
9 separate endless conveyors placed end to end in series. The
conveyors of one train typically can extend a length of 5
11 miles.
12 The conveyor system being utilized is characterized by
13 a number of disadvantages, including:
14 - That each conveyor consumes a large amount of
electric power. A 72 inch wide conveyor having
16 a length of 3 miles requires several 1200
17 horsepower motors for operation;
18 ~ That the conveyor train has to turn corners, which
19 is a difficult and expensive operation requiring
use of a multiplicity of short straight conveyors;
21 - That the tacky bitumen causes some oil sand to
22 adhere to and build up on the belt surface. This
23 creates a dead load which is difficult to prevent
24 and remove; and
- That the conveyors are subjected to heavy wear in
26 this service, due to impacts by rocks in the oil
27 sand and the erosive nature of the sand.
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1 ~ In summary, the conveyor systems used are a troublesome and
2 expensive means for transferring the oil sand from the mine to the
3 extraction plant.
4It will also be noted that a conveyor system transports the
whole oil sand to the plant, for the sole purpose of extracting the
6 bitumen, which constitutes only about 6-15% by weight of the oil sand
7 mass. Conveying all of the associated gangue material significantly
8 reduces the economic attractiveness of the operation.
9Once the oil sand arrives at assignees' bitumen extraction
plant, it is fed into one of four extraction circuits, each of which
11 begins with a tumbler. These tumblers are large, horizontal, rotating
12 drums. In the drum, the oil sand is mixed with hot water and a small
13 amount of process aid, normally sodium hydroxide. Steam is sparged into
14 the formed slurry as it proceeds down the length of the slightly
15inclined drum. In greater detail, each drum is 30.5 m long and 5.5 m
16in diameter. Each such drum is fed about 4500 tph of oil sand, 1100
17tph of hot water (95C) and 5 tph of aqueous 10% caustic solution.
18 Steam is injected into the slurry, as required, to ensure a final
19 slurry temperature of about 80C. The retention time in the drum is
about 3 minutes.
21The process in the tumbler seeks to attain several ends,
22 namely:
23 - heating the viscous bitumen, to reduce its viscosity
24 and render it more ~m~n~hle to separation from the
sand grains;
26 - dispersing the heated bitumen from the solids and into
27 the water;
5. 20297!~5
1 - ablating or disintegrating the normally present
2 lumps of oil sand, so that they will not be lost
3 with oversize rocks in a screening step which
4 immediately follows tumbling;
- entraining air bubbles in the slurry;
6 - coalescing some small bitumen flecks into larger
7 flecks to make them amenable to aeration and
8 subsequent separation; and
9 - aerating bitumen flecks by contacting them with air
bubbles, whereby the bitumen coats the air bubbles.
11 The expression, used in the industry to identify the sum
12 total of these various actions, is "conditioning" the slurry. A
13 definition is given below with respect to when conditioning is
14 "complete" for the purposes of this invention.
After being partly conditioned in the tumbler, the slurry
16 is screened, to reject oversize, and simultaneously diluted with
17 additional hot water to produce a slurry having about 50% solids by
18 mass (based on the initial oil sand feed).
19 The screened, diluted slurry is fed into a large,
thickener-like vessel referred to as a gravity separation vessel or
21 primary separation vessel (or "PSV"). The vessel is open-topped,
22 having a cylindrical upper section and a conical lower section
23 equipped with a bottom outlet. The diluted slurry is temporarily
24 retained in the PSV for about 15 minutes in a quiescent state. The
coarse solids sink (having a density of about 2.65), concentrate in
26 the cone, and exit through the bottom outlet as a fairly dense
27 tailings stream. The non-aerated bitumen flecks have a density of
28 about 1.0 and thus have little natural tendency to rise. However,
29 the bitumen has an affinity for air. Because of this property,
some of the non-aerated bitumen flecks form films around the air
31 bubbles present in the slurry and join with the aerated bitumen
32 created in the tumbler in rising to form bitumen froth at the
2029795
1 ~surface of the slurry. This froth overflows the upper lip of the
2 vessel into a launder and is recovered. The froth recovered in this
3 manner is referred to as "primary bitumen froth". The process
4 conducted in the PSV may be referred to as involving "spontaneous
flotation".
6 The watery suspension remaining in the central portion of
7 the PSV contains some residual bitumen. Much of this bitumen was not
8 sufficiently aerated so as to be recovered as primary froth from the
9 PSV. Therefore it is necessary to further process this fluid to
recover the remaining bitumen. This is done by means of vigorously
11 sub-aerating and agitating the fluid in one or more secondary recovery
12 vessels. For example, a dragstream of the middlings from the PSV may
13 be fed to a series of sub-aerated flotation cells. A yield of bitumen
14 froth, termed secondary froth, is recovered. Flotation in the PSV may
be referred to as "spontaneous flotation" while flotation in the
16 secondary recovery vessel may be referred to as ~forced air flotation~.
17 The combination of the PSV and the subsequent secondary
18 recovery means is referred to herein as the "separation circuit".
19 The primary bitumen froth is formed under quiescent
condition and hence has less entrainment of gangue material. Thus it
21 is considerably ''cleanerll than secondary froth, in that it contains
22 less water and solid contaminants. So it is desirable to maximize
23 production of the bitumen in the form of primary froth.
24 If conditioning has been properly accomplished, the
following desirable results are achieved:
26 - the total recovery of bitumen obtained, in the form of
27 the sum of primary and secondary froth, is high;
28 - the loss of bitumen with the tailings is low; and
29 - the bitumen is predominantly recovered in the form of
primary froth.
1- 202979~
1 At this point it is appropriate to make the point that
2 the nature of the oil sand being processed has a marked influence
3 on the results that are obtained. If the oil sand is of "good"
4 grade (i.e. high in bitumen content - e.g. 13.2% by weight - and
low in -325 mesh solids - e.g. 15% by weight) it will process well,
6 giving:
7 - a high total bitumen recovery (e.g. 95%); and
8 - low bitumen losses with the tailings (e.g. 3%).
9 If the oil sand is of "poor" grade (i.e. low in bitumen content
(e.g. 8%) and high in fines content (e.g. 30%)), it will process
11 relatively poorly, giving:
12 - a low total bitumen recovery (e.g. 85%); and
13 - high bitumen losses with the tailings (e.g. 12%).
14 In summary then, the conventional extraction circuit
comprises a tumbling step designed to condition the slurry.
16 Tumbling is followed by a sequence of spontaneous and forced air
17 flotation steps. If conditioning is properly conducted, the total
18 bitumen recovery and bitumen loss values for different grades of
19 feed will approximate those illustrative values just given.
Now, it has long been commonly known that particulate
21 solids may be slurried in water and conveyed by pumping them
22 through a pipeline, as an alternative to using conveyor belt
23 systems.
24 However, to the best of our knowledge the public prior
art is silent on whether oil sands can successfully be conveyed in
26 this fashion, as part of an integrated recovery process. More
27 particularly, the literature does not teach what would occur in
28 such an operation.
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The present invention arose from an experimental project
2 directed toward investigating pipeline conveying of oil sands in
3 aqueous slurry form.
4 The project was carried out because it was hoped that
5 pipelining a slurry of oil sand might prove to be an economically
6 viable substitute for the conveyor belt plus tumbler system previously
7 used to feed the separation circuit. There were questions that needed
8 to be answered to establish this viability. The answers to these
9 questions were not predictable. More particularly, it was questionable
10 whether:
11 - sufficient bitumen in the oils and slurry would become
12 properly aerated in a pipeline so as to yield:
13 - a high total bitumen recovery, and
14 - a high primary oil froth recovery; or
- the bitumen would become excessively emulsified in the
16 course of being pumped several miles through a pipeline, so
17 that the bitumen would become difficult to recovery from
18 the slurry.
19 SUMMARY OF THE INVENTION
This invention relates to simultaneously transporting and
21 conditioning oil sand in an aqueous slurry in a pipeline extending
22 between a mine and an extraction plant. More particularly, it relates
23 to a process comprising the steps of surface mining naturally water-wet
24 oil sand, mixing the as-mined oil sand, with heated water, air and
25 (optionally) process aid (e.g. NaOH) at the mine site to form an
26 aerated slurry, pumping the resultant slurry through the pipeline a
27 sufficient distance so that contained bitumen flecks separate from
28 sand, coalesce and are aerated, and feeding the slurry directly into
29 a gravity separation vessel to recover the major portion of the bitumen
30 as primary froth.
D
`-- 2029795
1 The present invention is based on having made certain
2 experimental discoveries, namely:
3 - That if a slurry, comprising oil sand, heated water and process4 aid, is formed so as to entrain air bubbles and is pumped through
a pipeline a distance in the order of about 2.5 km (which is
6 commonly less than the distance between the surface mine and
7 the extraction plant), complete conditioning of the slurry is
8 achieved. More particularly, a sufficient quantity of
9 the contained bitumen becomes aerated and is rendered
buoyant. As a result, the slurry may be introduced directly
,~
2029 795
1 into the PSV of a conventional separation circuit,2 in which PSV spontaneous bitumen flotation takes
3 place to yield total recovery, underflow loss, and4 froth quality values that are comparable to those
obtained by a conventional extraction train
6 involving a tumbler and separation circuit;
7 - That the slurry may be at a relatively low
8 temperature (e.g. in the order of 50C) and yet
9 conditioning may still be successfully completed
as aforesaid;
11 - That there is a "conditioning breakover point"
12 for a particular slurry during the course of
13 passage through a particular pipeline. More
14 particularly, with increasing retention time up
to the breakover point, there is:
16 - an increase in subsequent total bitumen
17 recovery from the separation circuit, and
18 - a diminishment in subsequent losses of
19 bitumen with the underflow tailings from the
separation circuit.
21 The breakover point indicates when conditioning
22 is "complete". Such complete conditioning of the
23 slurry is reflected in the total recovery and
24 tailings loss values resulting from subsequent
processing of the slurry in a conventlonal
26 separation circuit. More particularly, the total
27 recovery of bitumen will exceed 90% by weight and
28 the tailings loss of bitumen will be less than
29 10%, with respect to a feed of sufficient quality
202979s
to be acceptable for a conventional extraction
2 circuit;
3 - That if the slurry is pumped further through the
4 pipeline after conditioning is complete, significant
emulsification does not occur. Stated otherwise, the
6 total recovery and tailings loss values remain
7 generally constant, even though retention time in the
8 pipeline far exceeds that required for complete
9 conditioning; and
- That if the completely conditioned slurry is subjected
11 to separation of the coarse solids (as by settling)
12 part way along its passage through the pipeline, it is
13 found that the solids will readily separate in a
14 substantially clean condition. Stated otherwise, once
completely conditioned, passage of the slurry through
16 the pipeline may be interrupted and the coarse solids
17 may be separated and discarded without appreciable
18 bitumen loss. The remaining slurry may then be pumped
19 through the pipeline the remainder of the distance to
2 0 the extraction plant.
21 Having ascertained these unpredictable discoveries,
22 applicants conceived the following process:
23 As an optional preferred first step, oil sand oversize is
24 removed, by crushing or screening, prior to mixing, to reduce lumps to
25 a size less than about 1/3 of the internal diameter of the pipeline.
26 If the lumps are too large, plugging of the line can ensue.
27 The oil sand is heated at the mine site with heated water
28 (typically at 95C) and, preferably, alkaline process aid (usually
29 sodium hydroxide), in a manner whereby air bubbles are entrained, to
30 form an aerated slurry having a composition and temperature falling
31 within the following preferred ranges:
D
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comPonent % bY weiqht
2 oil sand 50 - 70
3 water 50 - 30
4 process aid 0.00 - 0.05
slurry temperature (C) 40 - 70
6 The slurry is then preferably screened, to remove residual
7 oversize, and pumped through a pipeline from the mine site toward an
8 extraction plant. The pipeline must be of sufficient length so that
9 substantially complete conditioning of the oil sand occurs.
Preferably, the slurry is moved through a first section of the
11 pipeline, in which substantially complete conditioning is accomplished,
12 and then separation of substantially all of the coarse solids (i.e.
13 greater than 200 mesh) is effected at this point. This may be
14 accomplished by gravity as in a settler or enhanced settling, such as
with cyclones. Depending on the density of the slurry, dilution with
16 water may be required for good separation. The remaining slurry is
17 then pumped through a second section of the pipeline to the extraction
18 plant. On reaching the extraction plant, the slurry is introduced
19 directly into a conventional separation circuit comprising spontaneous
and forced air flotation units. By ~directly~ is meant that the slurry
21 is not processed in a tumbler on its way to the gravity separator or
22 PSV. It is found that the total recovery of bitumen from the
23 separation circuit exceeds 90% of that contained in the oil sand feed
24 and the tailings losses are less than 10%.
Broadly stated, the invention is a process for
26 simultaneously transporting and conditioning naturally water-wet oil
27 sand containing bitumen, to enable recovery of bitumen in a gravity
28 separation vessel forming part of a bitumen extraction plant,
29 comprising: surface mining oil sand at a mine site; mixing the oil
sand, at the mine site, with heated water and entraining air in the
31 mixture during mixing, to form an aerated slurry; pumping the slurry
11
C'
2029795
1 ~through a pipeline from the mine site to the extraction plant, said
2 pipeline being of sufficient length so that separation of bitumen from
3 sand and subsequent aeration of bitumen both occur, to render the
4 aerated bitumen buoyant; and introducing the slurry from the pipeline
directly into the gravity separation vessel and processing it therein
6 by gravity separation under quiescent conditions to recover bitumen in
7 the form of froth.
8 DESCRIPTION OF THE DRAWINGS
9 Figure 1 is a schematic of the laboratory circuit used in
connection with development of the invention;
11 Figure 2 is a plot showing bitumen recovery variation with
12 distance pipelined, for a 13.2% bitumen-containing oil sand treated in
13 the laboratory circuit of Figure 1;
14 Figure 3 is a plot showing bitumen recovery variation with
distance pipelined, for a 9.2% bitumen-containing oil sand treated in
16 the laboratory circuit of Figure 1;
17 Figure 4 is a plot showing the variation in bitumen lost
18 with the tails with distance pipelined for a 9.2 bitumen-containing oil
19 sand treated in the laboratory circuit of Figure 1;
Figure 5 is a plot showing the variation in percent of
21 bitumen not ~mPn~hle to flotation with distance pipelined for a 9.2%
22 bitumen-containing oil sand treated in the laboratory circuit of Figure
23 1;
24 Figure 6 is a plot showing the variation in total bitumen
recovery with distance pipelined for a 9.2% bitumen-containing oil sand
26 treated in the laboratory circuit of Figure 1; and
12
1 Figure 7 is a schematic of an industrial scale system for
2 practising the process. 2 0 2 9 7 ~ 5
3 DESC,RIPTION OF THE PREFERRED EMBODIMENT
4 Experimental work was conducted that led to the process
discoveries previously referred to.
6 More particularly, a pilot pipeline loop 1, schematically
7 shown in Figure 1, was used. The loop 1 was 230 feet long and had
8 an internal diameter of 2 inches. The loop 1 was connected with a
9 pump box 2. Oil sand could be fed to the pump box 2 by a conveyor
3. A positive displacement pump 4 was connected to the bottom
11 outlet of the box 2. Slurry could be re-circulated back into the
12 pump box 2 from the initial section of the loop 1 via a pipe leg 5.
13 Valves 6,7 controlled the leg 5 and loop 1 (downstream of the leg
14 5) respectively. In operation, the pump box 2 would be filled with
an amount of water in excess over that required to fill loop 1.
16 Valve 6 would be opened and valve 7 closed. Oil sand would then be
17 fed into the pump box 2 and the mixture circulated through the box
18 2 tangentially to entrain air and form an aerated slurry. In some
19 runs, sodium hydroxide, in the form of a 10% solution, was added at
the pump box; in other runs, no sodium hydroxide was added. Re-
21 circulation was continued for 30 seconds, to form the slurry.
22 After such circulation, the valve 7 was opened and the valve 6
23 closed, so that the full loop 1 was now in use. Circulation
24 through the full loop would then be continued for the retention
time required to establish the pipeline distance to be travelled by
26 the slurry. In a typical run, 105 kg of oil sand
- 2029795
1 were added to 42 kg of hot water (having a temperature of 90C),
2 to yield a slurry having a temperature of 50C. Samples of the
3 slurry were periodically withdrawn through the valve 8 at the
4 outlet from the box 2. The pump speed was adjusted to provide
a slurry velocity of 8 feet/second.
6 It is to be noted that the slurry water content (30-
7 50%) was higher than that in the slurry processed in a
8 conventional tumbler (18-25%).
9 To compare the conditioning accomplished in the
pipeline with that of the conventional tumbler circuit, slurry
11 withdrawn from the loop 1 was tested in a laboratory scale
12 separation circuit. More particularly, withdrawn samples were
13 treated as follows:
14 - A slurry sample of 300 mL was collected in a lL
jar already containing 300 mL of water having a
16 temperature of 50C (so that the resultant mixture
17 now corresponded in water content with that of the
18 diluted slurry conventionally fed to a primary
19 separation vessel), and stirred;
- The diluted sample was settled for 1 minute under
21 quiescent conditions, to allow froth to rise by
22 spontaneous flotation and solids to settle;
23 _ The froth (which was the " primary" froth) was
24 skimmed off and analyzed for bitumen, water and
solids;
26 - The aqueous layer was decanted off and saved;
27 - The coarse solids were washed with 150 ml of 50C
28 water by capping the jar and rotating it gently
29 5 times. After settling for 1 minute, the aqueous
202979~
1 phase was decanted and saved. This washing
2 procedure was repeated twice more;
3 - The washed solids were analyzed for oil, water
4 and solids;
- The water decant fractions were combined. The
6 product was subjected to induced air flotation at
7 an impeller speed of 800 rpm and air rate of 50
8 mL/minute. The temperature of the charge was
9 maintained at 50C and air addition was continued
for 5 minutes. Secondary froth was produced and
11 collected. This secondary froth and the residual
12 tailings were analyzed for bitumen, water and
13 solids.
14 The analytical methods used to determine the oil, water
and solids contents were those set forth in "Syncrude Analytical
16 Methods for Oil Sand and Bitumen ProcessingU, published by The
17 Alberta Oil Sands Technology and Research Authority (1979).
18 The previously described laboratory scale process has
19 been used many times in the past by assignee's research group and
the results obtained have been shown to closely correspond with
21 those from the separation circuit in the commercial plant of the
22 assignee~ of this invention.
23 The various bitumen fractions were established using
24 the following relationships:
% primary recovery = bitumen i~ pri~ry fro~h x 100%
26 total bitumen i n feed
27 % total recovery = bitumen in primary and
28 seco~ry froths x 100%
29 total bitumen i n feed
202a7~
1% bitumen lost to coarse tailings =
2bitumen in coarse solids
3total solids in slurry x 100%
4bitumen in oil sand
5total solids in oil sand
6% bitumen not amenable to flotation =
7bitumen in secondary tailings
8total solids in slurry x 100%
9bitumen in oil sand
10total solids in oil sand
11Distance pipelined tkm) = elapsed time from start of run
12x pipeline velocity
13Two oil sands were used in the tests, as follows:
14Ore "A" - "good" grade - 13.2% bitumen
15.0% fines
16Ore "B" - "poor" grade - 9.2% bitumen
17 28.0% fines
18Having reference to Figure 2, it will be noted that,
19 at a distance pipelined of about 2.5 - 3 km, the following
results occurred for runs using a good grade oil sand:
21 Dec. 9 runs:
22Total bitumen recovery 97%
23Primary froth recovery 96%
24 Jan. 12 runs:
25Total bitumen recovery 95%
26Primary froth recovery 92%
27The recovery and losses reached fixed values and
28 remained virtually constant after the breakover point.
16
202979~
1 Having reference to Figure 3, at à distance pipelined
2 of about 3 km (i.e. the breakover point) the following results
3 occurred for a poor grade oil sand with the optimum amount of
4 sodium hydroxide (0.05 wt%):
Total bitumen recovery 93%
6 Primary froth recovery 72%
7 The same group of runs also show:
8 Bitumen lost with primary tailings 2%
9 Bitumen that remained with
secondary tailings 5%
11 Plots of oil losses to primary tailings, and oil remaining in
12 secondary tailings are given in Figures 4 and 5 respectively.
13 The following conclusions are apparent from the data,
14 namely:
- That pipelining an oil sand slurry beyond the
16 point where conditioning is complete does not
17 over-condition the slurry;
18 - That conditioning is complete within a short
19 distance travelled, said distance being
substantially less than the distance between the
21 mine and the plant (for most of the plant Life in
22 a typical case);
23 - That pipelining slurry will produce primary and
24 total bitumen recoveries as good as or better than
those from a conventional tumbler/flotation train;
- 202979~
1 - That, following completion of conditioning, the
2 coarse solids may be separated without prohibitive
3 bitumen losses;
4 - That a slurry conditioned in a pipeline can be
fed directly to a separation circuit and the
6 bitumen recoveries and losses will be found to be
7 comparable to those obtained with a slurry
8 conditioned in a tumbler; and
9 - That process aids are required for low grade oil
sand to achieve good recoveries.
11 A minor amount of light hydrocarbon added at the
12 slurry-formation stage serves to constantly clean the surface of
13 the bitumen where it interfaces with the water. By having a
14 clean surface, the bitumen globules more readily coalesce, which
leads to better separation. Attachment of bitumen to air is also
16 encouraged, which leads to improved subsequent flotation. The
17 hydrocarbon should be liquid at room temperature. It is best
18 added to the process as an emulsion in water. A concentration
19 of about 5% hydrocarbon is suitable. Cheap and readily available
hydrocarbons such as kerosene and naphtha may be used. Because
21 they are taken up in the bitumen, they are not lost but form part
22 of the upgraded synthetic crude product. The improvement
23 manifests itself as an improvement in primary recovery, and is
24 demonstrated in Figure 6.
Turning now to Figure 7, there is schematically shown
26 a recommended system for practising the invention.
27 More particularly, oil sand is surface mined and
28 deposited in a feed bin. The oil sand is then fed to a crusher
29 55 of the double roll type, to reduce the oversize to less than
18
2029795
1 24~. The crushed oil sand is fed by conveyor 56 to a mixer 57. This
2 mixer 57 is shown in Figure 7. It comprises an open-topped cylindrical
3 vessel 58 having a conical bottom 59 with a central outlet 60. The
4 vessel 58 thus has a circular cross-section. A pair of tangential
inlets 61, 62 extend into the base of the vessel chamber 58. Fresh hot
6 water, containing caustic, is fed into chamber 58 via the inlet 61.
7 Recycled hot slurry is fed in via inlet 62. The oil sand is mixed with
8 recycled slurry, water and caustic, which are circulating in the form
9 of a vortex in the chamber 58, and air bubbles are entrained in the
slurry. The hot water and caustic additions are controlled to yield
11 a slurry typically having the following values:
12 water content - 35%
13 NaOH content - 0.01%
14 temperature - 55C
The product slurry leaves the chamber 58 through the bottom outlet 60,
16 passes through a screen 63 that removes oversize and enters a pump box
17 64. The recycled slurry is withdrawn from pump box 64 and returned by
18 pump 65 and line 66 to the inlet 62. Slurry is pumped by pump 67 from
19 pump box 64 into pipeline 68. The slurry is conveyed through a first
section of pipeline 68, far enough to completely condition the slurry.
21 The extent of conditioning may be established using laboratory
22 equipment and procedures as previously described. At this point, the
23 slurry is diluted and introduced into a settler 69 and retained under
24 quiescent conditions, to allow the coarse solids to settle. The solids
are removed as tailings and discarded. In this manner, 60 to 70% of
26 the total mass of slurry is eliminated. The remaining slurry is pumped
27 through a second section 70 of pipeline to a conventional separation
28 circuit 71. Here the slurry is subjected to spontaneous flotation in
29 a primary separation vessel 72 and middlings from the vessel 72 are
subjected to forced air flotation in cells 73 to produce primary and
31 secondary froth respectively.
19
20297!~5
1 - AS has been previously pointed out, the step of removing
2 coarse solids from the slurry part way along its travel through the
3 pipeline is an optional step. Alternatively, one may elect to pump the
4 slurry, containing the coarse solids, directly from the pump box 64,
through the pipeline 68, to the separation vessel 72.
6 It will be noted that the slurry temperature (55C) is
7 considerably less than the conventional temperature (z80C). If a
8 tumbler were to be used with such a ~low temperature" slurry, it would
9 have to be very large, to provide a longer retention time. By the
combination of conditioning in a pipeline and feeding conditioned
11 slurry directly to the PSV, a low temperature process is now feasible,
12 without the need for a very large tumbler.
13 The scope of the invention is set forth in the claims now
14 following.
