Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
This invention is concerned with an improve-
ment to a second stage centrifugal separator circuit for the
separation of hydrocarbons from degritted, diluted bitumen
froth. More particularly, the invention relates to the com-
bination of a plurality of disc-nozzle centrifugal separators
with a single capacitance vessel into which the excess heavy
phase outputs of the separators discharge. ~ydrocarbons,
which may be present in the heavy phase streams, are separated
in the vessel and a reservoir or pool of hydrocarDons-free
water is maintained to supply fluid to the separators if
required.
The invention has application as part of the
known hot water extraction process for recovering bitumen
from bituminous sands. In this process, the sands are mixed
with hot water, steam and a dispersant, such as sodium hydrox- ~ --
ide, in a rotating tumbler to heat and dilute the tar sand
; and initially disperse the contained bitumen. The thick slur-
ry which is produced is further diluted with hot flood water
and is then introduced into a primary separation vessel,
where the bitumen, contaminated with some solids and water,
forms primary froth, which is recovered. A middlings stream,
; containing bitumen, is withdrawn from the mid-section of the
primary separation vessel and is passed through a sub-aerated
secondary separation cell. Bitumen, contaminated with solids
and water, is recovered in the form of secondary froth from
the cell. This secondary froth is settled to remove some
contaminants and is then blended with the primary froth.
The combined froth is heated and deaerated and diluted with
naphtha to alter the specific gravity of the bitumen. This
stream is then introduced into a two stage centriiugal sep-
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`-- aration operation. In this operation, the diluted froth
`~ is first degritted by passing it through one or more scroll-
type centrifugal separators to remove coarse solids. The
product, comprising bitumen, fine solids and water, is then
conventionally treated in a circuit comprising one or more
disc-nozzle centrifugal separators to separate the water and
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solids from the bitumen and produce a relatively clean bitumen
product.
The present invention is concerned with the
excess heavy phase discharges from the disc-nozzle centri-
fugal separators. These separators are typically of thetype sold by DeLaval Company Limited under the model designa-
tion ~SX320T. The degritted, diluted bitumen-containing froth
feed stock to the separators typically comprises 75% by
weight hydrocarbons, 4% solids and 21% water. It is fed
centrally into the machine and passes through a distributor
into a disc stack zone, which is whirling in conjunction with
the separator bowl. Due to the action of centrifugal forces,
the heavier water and solids components move from a
cylindrical interface zone outwardly toward the bowl, where
they form a heavy phase pool, from whence they are dis-
charged through nozzles; the lighter hydrocarbons move in-
wardly from the interface zone through the disc stack to a
centripetal pump means involving a light phase paring disc.
This pump means forces the hydrocarbons out through a central
discharge line. A second centripetal pump means, also in-
volving a paring disc, is located at the base of the machine
and communicates with the heavy phase pool. If the separator
is fed froth which contains more water than is needed to r
satisfy the separator bowl nozzles, the excess heavy phase
fluid is pumped out of the separator through a bottom outlet
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by the second centripetal pump means. Under normal operating
conditions, this heavy phase discharge is water; under upset
conditions, however, the heavy phase discharge can comprise
as much as 75% by weight hydrocarbons, 4~ solids and 21
water. I~ tfie separator feed is low in water and the heavy
; phase pool is being depleted, water or heavy phase fluid
is introduced through the heavy phase paring disc into the
pool to maintain the interface zone within its normal operating
region. It will be appreciated, therefore, that the position
of the interface is affected by the fluid backpressure at the
; outlet of the second or heavy phase centripetal pump means.
It is conventional to connect an auxilliary
vessel, containing a reservoir of heavy phase fluid under
pressure, with the second centripetal pump means. This
vessel accepts excess heavy phase fluid from the separator
and supplies same to it when the heavy phase pool is being -~
depleted.
Heretofore, it has been the practice to provide
a separate auxilliary or capacitance vessel with each separator.
However, this is expensive; therefore it would be advantageous
to use a single capacitance vessel with a bank of separators.
However, certain problems arise when this is considered.
Firstly, the separators produce excess heavy phase streams
at varying rates - if the rate of discharge of one or more
of the separators is low, there is a danger of plugging the
capacitance vessel with deposited solids. Secondly, if the
hydrocarbons - heavy phase interface within an operating
separator is shifted too far toward the outside of the bowl,
as can occur when a slug of high hydrocarbons content feed
enters the separator, a large volume of hydrocarbons can sud-
denly escape into the capacitance vessel. These hydrocarbons
can then back up into another separator which is taking
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fluid from the vessel reservoir and the interface will be --
"lost" in that separator as well. That is, the second
, separator will begin producing hydrocarbons through its
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i bottom outlet. In this manner, by a process termed 'short-
circuiting', the entier bank of separators can swiftly be
rendered inoperative.
SU~RY OF THE INVENTION
In accordance with the present invention, the
heavy phase centripetal pump means of a plurality of disc-
nozzle centrifugal separators are connected by conduits witha reservoir or pool of heavy phase fluid retained in a single,
- closed capacitance vessel. The vessel comprises two com-
municating sections. The reservoir is contained in a reser-
voir chamber formed by the exterior walls of the first section
of the vessel and an interior weir extending across the open
end of the section. In operation, the excess heavy phase
fluid streams from the separators are transferred into the
reservoir through conduits having their ends submerged therein.
The transferred Eluid is retained in the reservoir long enough
20 to enable contained hydrocarbons to float to the surface. -
Surplus fluid, including the hydrocarbons, overflows the weir
; into the second section of the vessel. Here the overflowing
fluid may be separated (preferably by a weir system described
in detail below) into a hydrocarbon-rich fraction and a heavy
phase-rich fraction, or it may simply be discharged from the
vessel without undergoing separation. In the event of
separation, the two fractions are recovered separately from
the second section. Means for supplying make-up fluid to the
; reservoir are provided, to ensure sufficient fluid is available
in the event the separators are being starved for fluid, due
to the low heavy phase content of the feed, and a backflow
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; from the reservoir into tihe separators has to be established ``
to satisfy the needs of the separator ~owl nozzles. Means,
- such as a blanket of pressurized inert gas, are also provided -
to pressurize the fluid contents of the capacitance vessel
5 and thereby create the desired backpressure at the heavy phase -
outlets of the separators.
By having a single large capacitance vessel, it
has been possible, in a preferred embodiment of the invention,
to provide a plurality of blowdown outlets spaced along the
base of the reservoir chamber. These outlets can be opened
one by one to flush deposited solids out of the chamber and
prevent plugging, without causing a significant change in
pressure within the vessel which would deleteriously affect
the position of the hydrocarbons-heavy phase interfaces in the
separators.
The preferred form of the invention is charac- `~
terized by a number of desirable features. Firstly, due to
its relatively large size and the blowdown outlets, it is less
; likely to become plugged with solids when compared with the
: 20 prior art scheme of providing a separate capacitance vessel
for each separator. Secondly, by providing means for separ-
ating and removing hydrocarbons from the balance of the excess
heavy phase fluid in the reservoir, short-circuiting of the
bank of separators is reduced or eliminated. Finally, the
provision of a compressible gas blanket in the vessel, coupled
with the relatively large volume of the space occupied by the
gas in the single vessel, permits the system to cope with
surges of heavy phase in the feed stock without a significant
, pressure change.
Broadly stated, the invention is an improvement
in a second stage centrifugal separator circuit which separates
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heavy phase fluid fron~ degritted diluted bitumen froth. The
improvement comprises: a plurality of disc-nozzle centri-
fugal separators, each separator having a heavy phase centri-
petal pump means, including an outlet, for removing heavy
phase fluid from said separator and, in operation, a bitumen-
heavy phase fluid interface whose position can be shifted
; by a change in the fluid pressure at the pump means outlet; a
- capacitance vessel comprising a first section and a second
section which is an extension of the first section; a
first weir extending across the interior of the capacitance
vessel at the junction of the first and second sections, said
first weir and first section combining to form a reservoir
chamber for containing a reservoir of heavy phase fluid;
means, associated with the vessel, for supplying make-up fluid
to the reservoir when re~uired; conduit means connecting the
outlet of each centripetal pump means with the reservoir,
the end of each conduit means being submerged in the reservoir;
said first weir being positioned downstream of said conduit
means; means, associated with the capacitance vessel, for
pressurizing its contents, to thereby maintain fluid back-
pressure at the centripetal pump means outlets; and means,
associated with the second section, for removing fluid over-
flowing the first weir.
In another definition of the invention, it is
; 25 a method for treating a plurality of heavy phase fluid streams
produced by a plurality of disc-nozzle centrifugal separators,
each having bowl nozzles and being fed degritted diluted
bitumen froth comprising: transferring the streams into a
reservoir of heavy phase fluid contained in a vessel; retaining
transferred fluid in the reservoir to enable a portion of the
hydrocarbons contained in said fluid to reach the surface
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of the reservoir; separating floating hydrocarbons from the
reservoir and recovering it from tne vessel as a separate
; hydrocarbons-rich product; recovering the balance of the
transferred fluid from the vessel as a separate hydrocarbons-
poor product; and returning heavy phase fluid from the
reservoir to one or more of the separators when said separ-
ators require supplemental fluid to satisfy the bowl nozzles.
DESCRIPTION OF THE DRAWING
- Figure 1 is a diagrammatic illustration of the
preferred embodiment of the invention.
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DESCRIPTION OF THE PREFERRED EMBODIMENT ~ -
The separators 1 and capacitance vessel 2 form
the bulk of a second stage centrifugal separator circuit.
In the Figure, the balance of this circuit is not shown, as -
it forms no part of this invention.
As shown, the capacitance vessel is formed
in two sections, A and B. The downstream or second section B
being an extension of the upstream or first section A. The
; section A is an elongate tube 3 having a closing ~all 4 at
one end and a first weir 5 at the opposite end. The first
: weir 5 extends across the interior of the section A and com-
~ bines with the latter's walls to form a reservoir chamber 6
"
containing a reservoir 7 of heavy phase fluid. The section s
comprises a tubular segment 8 which opens into a vertical,
v 25 tubular segment 9 having a side wall 9a and closed ends 10, 11.
.
A bank of three disc-nozzle separators 1 are
;~ shown. Each separator is fed degritted diluted bitumen froth
through inlet conduits 12. A conduit 13 extends from the outlet
14 of each heavy phase centripetal pump means 15 and is sub-
merged in the reservoir 7.
In operation, heavy phase fluid, normally water,
is transferred from the separators 1 into the reservoir 7.
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On occasion, one or more of the separators will discharge
fluids, contaminated with varying amounts of hydrocarbons,
into a reservoir 7. These hydrocarbons tend to float to the
surface of the reservoir and are discharged over the first
weir 5 into section B . Thus the hydrocarbons are quickly
cleaned out of the reservoir and the threat of backing hydro-
carbons into properly operating separators is reduced.
A source (not shown) of make-up water supplies
fluid to the reservoir 7 through valve 16 and line 17. A suit-
10 able sensing device 1~ monitors the level of fluid in thereservoir chamber 6 and opens the valve 16 in the event that
the level is low. Under normal operating conditions, there
will be a steady flow over the weir 5 and the make-up valve 16
will be closed.
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Turning now to section B, it is shown to include
means for separating hydrocarbons from the stream overflowing
the first weir 5 and separately recovering same in the form
of a hydrocarbons-rich fraction. More particularly, a side
wall 19 and bottom wall 20 combine to form an open-topped
oil chamber 21. The side wall 19 is attached to the end 11
of section B segment 9 at 22. The upper lip 23 of side wall
19 forms a second weir whose operation is described below.
An outlet line 24 leads out of the bottom of the oil chamber
21 and is controlled by the valve 25 which, in turn, is control- ~-
led by a sensing device 26 responsive to the liquid level in
the oil chamber 21. ~ -
i An annular heavy phase chamber 30 is formed
between the side walls 19 and 9a. A double weir arrangement
controls admission of heavy phase fluid into chamber 30 and
provides a heavy phase fluid seal 31 to prevent hydrocarbons
entering therein. More particularly, a skirt 32 extends down-
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wardly to provide a submerged weir relative to the surface 33
of the fluid in the chamber 34 ~which chamber 34 is formed
by the first weir 5r tubular segment 8 and skirt 32). A
horizontal baffle 35 extends inwardly from side wall 9a in
spaced relation below the lowermost edge of skirt 32. A
weir 36 extends upwardly from baffle 35 between skirt 32
and side wall 19, however the upper edge of this weir 36 iS
spaced below the second weir 23.
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Heavy phase fluid is withdrawn from chamber 30
through line 37 and discharged to tailings. A valve 38 ~
operated by a sensing device 39 responsive to the fluid level
'- in chamber 30~ controls flow through the line 37.
~ During normal operations, the fluid level in
i; chamber 34 will be equal to that of the weir 36 and heavy
phase fluid will overflow steadily into chamber 30. In the
event of a surge of hydrocarbons over the first weir 5 ~ the
heavy phase surface in the chamber 34 Will be depressed (as
!
shown in the Figure) and the fluid surface in chamber 34
will rise until the hydrocarbons overflow the weir 23 and
discharge into chamber 21.
An inert gas blanket 40 is used to pres-
surize the fluid contents, to hold a fluid backpressure at
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the separator outlets 14. This gas is introduced into the
capacitance vessel through a line 41 and valve 42. The valve
is controlled by a pressure sensing device 43. A gas vent line
, 44~ controlled by a valve 45 and pressure sensing device 46
leads out of the vessel to bleed off excessive pressure.
A plurality of blowdown lines or outlets 50
lead out of the base of the tube 3. These outlets are con-
trolled by valves 51 and can be opened to wash out solids
collected on the bottom of the reservolr chamber 6.
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. The tube 3 is quite large, so that plugging
- by a build-up of solids is reduced. The cross sectional area
of tube 3 is several multiples of that of a pipe designed to
just accommodate the expected maximum flow from the separators. -
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