Note: Descriptions are shown in the official language in which they were submitted.
4979~
1 FI~Tn OF T~ INV~NTION
2 This invention relates to a process and apparatus for
3 improving the quality ~f bitumen froth produced by spontaneous
4 flotation in the course of extracting bitumen from oil sands
using the hot water process. More particularly it relates to
6 separating water and solids from bitumen froth, to thereby clean
7 and upgrade the froth.
8 ~CKGROUND OF T~ INV~NTION
9 Bitumen (a form of heavy oil) is commercially recovered
from oil sand in Alberta. This recovery is achieved by mining
11 the oil sand, extracting the bitumen from the oil sand in the
12 form of froth, cleaning the froth product to remove contained
13 water and solids, and upgrading the bitumen to produce a variety
14 of oil products. Extraction is achieved using a process referred
to in the industry as the hot water process. This process is
16 described in considerable detail in prior art patents and in the
17 technical literature. A short summary of the process is given
18 below.
19 To better understand the hot water process, it is
helpful to know about the nature of oil sand itself. Oil sand
21 comprises grains of sand which are individually sheathed or
22 wetted with a very thin layer of connate water. Small flecks of
23 bitumen are located in the interstices between the water-wet
24 grains. Minute clay particles (termed "fines") are dispersed in
the connate water phase.
26 In general, the hot water process involves slurrying
27 the as-mined oil sand in hot water with surfactant-forming
28 caustic and relying on a combination of heating, agitation, and
`J ~, ~
Z049793
1 surfactant actions to disperse the bitumen from the solids and
2 into the aqueous phase of the slurry. At this point, bitumen
3 flecks coalesce and some become attached to air bubbles, so that
4 the aerated bitumen floats as a froth. The froth is then
recovered.
6 The composition of the as-mined oil sand is variable.
7 The oil, water and solids contents of oil sand processed at
8 applicants' plant can typically vary as follows:
9 TABLE I
oil: 6 to 18% by wt.
11 water: 0 to 14% by wt.
12 fines (-44u)10 to 75% by wt.
13 total solids: 70 to 90% by wt.
14 This variability in composition leads to wide swings
in the processability of the feed when using the hot water
16 process. A "rich" oil sand, high in oil and low in fines, will
17 give a high yield of good quality extraction product; a "lean"
18 oil sand, low in oil and high in fines, will give a relatively
19 low yield of relatively poor quality product. By way of example,
Table II sets forth typical values for the composition of oil
21 sand feed, for rich and lean ores of sufficient quality to be
22 processed, and the recovery and composition of the primary froth
23 product which one would typically obtain.
2049793
1 ~ TABLE II
2 Lean Oil Sand: Percent Oil Recovered As:
3 Oil 6% Primary Froth 65%
4 Water 11% Froth Composition:
Fines 21% Oil 55%
6 Solids 83% Water 34%
7 Solids 11%
8 Rich Oil Sand: Percent Oil Recovered As:
9 Oil 12% Primary Froth 92%
Water 3% Froth Composition:
11 Fines 14% Oil 65%
12 Solids 85% Water 27%
13 Solids 8%
14 One of the disadvantages of producing a froth product
stream having such wide swings in its compositional make-up is
16 that the downstream equipment has to be sized to accommodate the
17 worst case. In addition, constantly adjusting the downstream
18 processing for optimization involves difficulty.
19 So any simple and effective means for reducing the
water and solids contents of the froth and smoothing out the
21 froth composition variations, would be desirable.
22 At this point it is useful to provide a short
23 description, in greater detail, of the hot water extraction
24 process, as practised at the plant of the present assignees, to
put the invention into context. The process involves:
26 - Mixing as-mined oil sand with hot water and a
27 small amount of NaOH in a rotating horizontal drum
28 for a period of several minutes to produce an
2049793
1 ~ aqueous slurry of thick consistency. Steam is
2 sparged into the slurry to develop an exit
3 temperature of about 180F. In this slurrying
4 step, the lumps of oil sand are ablated, the
bitumen flecks are heated and the NaOH reacts in
6 situ with bitumen moieties to form surfactants.
7 The bitumen flecks become liberated from the
8 solids and are dispersed into the aqueous phase.
9 In addition, air bubbles are entrained into the
slurry. Some of the bitumen flecks coalesce and
11 coat air bubbles;
12 - The slurry is then diluted with additional hot
13 water and is temporarily retained under quiescent
14 conditions in a large, cylindrical, conical-
bottomed, open-topped vessel referred to as a
16 primary separation vessel (hereafter "PSV"). In
17 the PSV, "spontaneous flotation" of the bitumen
18 occurs. More particularly, buoyant bitumen floats
19 to form an oily froth. This froth, (called
"primary froth"), overflows the upper lip of the
21 PSV and is conveyed away from the vessel in a
22 downwardly sloping, broad channel, referred to as
23 a launder. As the froth is forming in the PSV,
24 the coarse solids settle and are discharged from
the base of the vessel. This stream of coarse
26 solids, associated with some water and a small
27 amount of bitumen, is called "PSV tailings". Some
28 residual, insufficiently buoyant oil remains in
Z(~4979~
1 the watery main body of the PSV contents - this
2 fluid is referred to as "PSV middlings".
3 - The PSV middlings and PSV tailings are combined
4 and are fed into a vessel referred to as the
tailings oil recovery vessel (hereafter "TORV").
6 This is a cone settler, into which the PSV
7 middlings and tailings are fed and are caused to
8 move outwardly and laterally from a central feed
9 point. The feed is contacted from below by an
upwelling aerated stream of PSV middlings. A
11 second yield of bitumen froth forms and overflows
12 the vessel rim and is conveyed away in a launder.
13 In the vessel, the coarse solids settle, are
14 concentrated in the narrowing lower end of the
cone, and are discharged as tailings. (The TORV
16 process is described in greater detail in U.S.
17 Patent 4,545,892.) The process occurring in the
18 TORV is also characterized as spontaneous
19 flotation;
- As the last step in the extraction process, the
21 middlings from the TORV are fed to a bank of
22 induced flotation cells, in which the feed is
23 vigorously sub-aerated and agitated and from which
24 a third froth stream is recovered. This froth
(termed "secondary froth") is cleaned by settling
26 out some contained water and solids by temporarily
27 retaining the mixture in a settling tank.
2049793
1 The various froth streams are combined, deaerated,
2 diluted with naphtha, and then centrifuged, to remove contained
3 water and solids. Centrifuging involves passing the deaerated
4 and diluted froth through two stages of centrifugati~on, using
scroll and disc centrifuges.
6 As indicated, the various froth products (PSV, TORV and
7 secondary) contain water and solids as contaminants. It is the
8 concentration of these contaminants that can vary widely,
9 depending on the grade of the oil sand originally fed to the
process.
11 SUMM~Y OF TH~ INV~NTION
12 The present invention has been developed as a result
13 of making the following observations:
14 - That bitumen froth issuing from a flotation
vessel, such as the PSV or TORV, contains discrete
16 water particles ranging in size from microscopic
17 flecks to pea-size globules;
18 - That, when in a gently sloped channel or launder,
19 some of the water particles migrate downwardly
through the froth body and collect and coalesce
21 along the bottom wall of the channel in the form
22 of a discrete, water-rich layer, which
23 additionally contains some settled solids.
24 Having observed this action, applicants have devised
a system wherein:
26 - The water-rich bottom layer is at least partly
27 diverted through an aperture or outlet in the
28 channel bottom wall and is temporarily retained
204979~
1 ~ in an upstanding container positioned beneath the
2 channel;
3 - In addition, a weir is positioned immediately
4 downstream of the diversion aperture. The weir
extends transversely across the channel and
6 functions to keep a small head of the dirty water
7 with its surface above the aperture;
8 - Thus a column of fluid comprising upper and lower
9 layers, having distinctive compositions and a
discernible interface, is formed in the separator
11 consisting of the combination of the weir and
12 container. The upper layer is relatively clean
13 bitumen froth, containing some water and solids,
14 and the lower layer is mainly water containing
solids and traces/ of bitumen;
16 - The elevation of the interface is monitored; and
17 - A variable pump, controlling the rate of
18 withdrawal of fluid from the base of the
19 container, is operated in response to the location
of the interface so as to maintain the interface
21 at a substantially constant pre-determined level.
22 In a preferred feature, means are provided for
23 injecting make-up water into the lower end of the container
24 chamber. In the event that good quality oil sand is being
processed, the froth will contain solids but only a small
26 quantity of water. In this circumstance, it would only be
27 possible to drain water from the container at a slow rate,
28 otherwise the oil/water interface would be lowered to an
29 undesirable elevation. At such slow withdrawal rates, plugging
Z049793
1 ~ with solids becomes a problem. By adding water to the mainly
2 water layer in the container, as required, plugging can be
3 avoided by maintaining a desirable rate of water withdrawal.
4 As a result of implementing the foregoing system, it
has been found that the concentrations of water and solids in
6 bitumen froth can be reduced in a simple manner.
7 DFSC~TPTION OF TH~ DRAWINGS
8 Figure 1 is a side view, partly broken away, showing
9 an assembly incorporating the invention, said assembly having
been used on a pilot plant basis to test the system;
11 Figure 2 is a plot showing the bitumen content of
12 sixteen samples of each of PSV and knock-out froth;
13 Figure 3 is a plot using the same data as Figure 2, but
14 modified to account for predicted sampling error; and
Figure 4 is a comparative plot for sixteen samples,
16 showing the improvement achieved in froth quality by using the
17 invention.
18 D~SC~TPTION OF TH~ P~F~ D ~MRODIMFN~
19 Having noted that free water was associated with
bitumen froth flowing through the open-topped channel or launder
21 1 of a hot water process pilot plant spontaneous flotation vessel
22 or PSV 2, a downwardly extending c~ontainer 3 was attached to the
23 bottom wall 4 of the launder. The container 3 communicated with
24 the launder passageway 5 by m~ans of an aperture 6. A
transversely extending weir 7 was positioned across the
26 passageway 5, immediately downstream of the aperture 6. The weir
27 7 and container 3 together formed a separator. The container 3
2049793
1 was equipped with a drain line 8 and a variable discharge Moynol
2 pump 9. A water line 20, connected with a water source (not
3 shown), was provided to supply make-up water to the internal
4 chamber 21 of the container 3, when required. The froth/water
interface level 14 in the separator was monitored using an
6 interface level sensor 10. Specifically, an Endress and Hauser
7 FMC 480Z capacitance-type gauge was used. The pump 9 was
8 controlled using a Bailey Network 90 control assembly 11 in
9 response to the measurements taken by the sensor 10, to maintain
the interface level 14 substantially constant. The cleaned froth
11 16 overflowing the weir 7 was collected in a weigh tank 12.
12 Dirty water 15 collected in the chamber 21.
13 Froth samples were collected at the lip 13 of the PSV
14 2 and at the weigh tank 12. The bottom discharge stream of dirty
water from the container 3 was also sampled. Over 80 samples
16 were analyzed for oil, water and solids. Mass balance periods
17 of 20 minutes were conducted periodically. Mass flow rates of
18 the three streams were obtained during these periods.
19 Sixteen complete sets of data were accumulated. Figure
2 shows plots of quality (~ bitumen) of both the PSV froth and
21 the knock-out froth collected in the weigh tank 12.
22 The data showed that, while in most cases knock-out
23 froth was improved relative to PSV froth, there were several
24 samples where the quality had actually decreased. These
unfavourable results were felt to be due to the highly variable
26 quality of the froth, which changes composition from moment to
27 moment. In addition, mass balances conducted on the separator
28 did not exhibit mass closure.
29 ITrade-Mark
2049793
1 In an effort to rationalize the results to achieve mass
2 closure, the software program MATBAL2, available from CANMET,
3 was applied to the data. Measurement uncertainties were
4 assigned, based on applicants' years of experience operating the
pilot plant PSV. They were:
6 Froth:
7 bitumen - 3.5% uncertainty
8 solids -10% uncertainty
9 Flowrates:1% uncertainty.
The PSV froth and knock-out froth data, both modified
11 using MATBAL, are plotted in Figure 3. These rationalized
12 results indicated that knock-out froth quality is always equal
13 or superior to PSV froth quality, when the invention is
14 practised.
The scope of the invention is set forth in the claims
16 now following.
17 2Trade-Mark
11
