METHOD AND SYSTEM FOR DEAERATING A BITUMEN FROTH

METHODE ET SYSTEME DE DESAERATION DE MOUSSE DE BITUME

English Abstract

A bitumen froth is deaerated by passing the froth through a screen to reduce the air content of the froth. The screen is preferably configured as a conveyor belt which is rotated slowly underneath a froth supply unit and the sieve opening is preferably selected such that necking of the froth that drips out of the sieve openings occurs and the surface area of the froth is increased whereby air escape from the froth is enhanced.

French Abstract

Une mousse de bitume est désaérée en faisant passer cette mousse à travers un tamis pour réduire la teneur en air de la mousse. Le tamis a de préférence une configuration de tapis roulant, tournant lentement en-dessous d'une unité d'alimentation en mousse et l'ouverture du tamis est de préférence choisie de sorte qu'il y ait étranglement de la mousse qui s'écoule des ouvertures du tamis et que la zone de surface de la mousse soit augmentée afin que l'air s'échappe mieux de la mousse.

Claims

CLAIMS:
1. A method for deaerating a bitumen froth, the method comprising passing the
froth
through a screen to reduce the air content of the froth.
2. The method of claim 1, wherein the sieve opening size of the screen is
selected such
that the surface area of the bitumen froth is expanded and air escapes from
the bitumen
froth.
3. The method of claim 1 or 2, wherein the sieve opening size of the screen is
at least 2
mm
4. The method of claim 3, wherein the sieve opening size is at least 6 mm.
5. The method of any one of claims 1-4, wherein the screen is continuously or
intermittently moved relative to a froth supply unit.
6. The method of claim 5, wherein the screen is formed by a permeable conveyor
belt,
which is continuously translated underneath the froth supply unit.
7. The method of claim 4 or 5, wherein the froth supply unit is arranged
downstream of a
primary bitumen enriched froth exhaust conduit of a gravity froth separation
vessel in
which a froth formed by injecting air into a slurry of oil sand and water is
separated
by gravity separation into a bitumen enriched primary froth stream and a water
and
sand enriched secondary froth stream.
8. The method of claim 7, wherein the oil sand is mined from an oil sand
deposit and
subsequently crushed and mixed with hot water and transported from the mining
site
to the froth separation vessel through a pipeline in which the slurry of hot
water and
oil sand is conditioned and air is injected into the slurry to create a froth
which is fed
into the gravity froth separation vessel.
9. A bitumen froth separation system, the system comprising a screen through
which in
use a bitumen froth is induced to flow and the air content of the froth is
reduced.
10. The system of claim 9, wherein the screen has a sieve opening size of at
least 2 mm.
11. The system of claim 10, wherein the screen has a sieve opening size of at
lest 2 mm.
12. The system of claim 10, wherein the screen is formed by a permeable
conveyor belt,
which is in use translated underneath a froth supply unit.
13. The system of claim 12, wherein the conveyor belt is provided with a
scraper and/or
spray cleaning unit for removing any bitumen froth from the screen during each
rotation cycle of the conveyor belt.

Description

CA 02425840 2003-04-17
METHOD AND SYSTEM FOR DEAERATING A BITUMEN FROTH
FIELD OF THE INVENTION
TS9298
The invention relates to a method and system for deaerating a bitumen froth.
It is known that bitumen froth produced from an oil sand deposit can be
difficult to pump
using centrifugal pumps due to its high viscosity and degree of aeration.
Various deaeration systems are disclosed in the prior art for the purpose of
making bitumen
froth more easily pumpable.
Canadian patent 1072474 discloses a system in which froth stxeams are fed by
gravity to
deaerator columns wherein the streams are heated and deaerated with steam to
produce a
pumpable micture of bitumen, water and solids.
Canadian patent 1071130 discloses the recovery of bitumen froth in overflow
launders
disposed on the upper edge of an extraction cell. The recovered froth flows
from the launders,
by gravity, into a lower collection vessel. Deaeration is accomplished by
adding steam
injection means to the launder so that the bitumen froth can be heated and
deaerated while
being transferred from the separation zone to the collection zone.
Canadian patent 1137906 discloses the use of chemical defoaming agents so that
a froth
deaerates in a separation call and becomes pumpable without further treatment.
API document No. 4270069 describes a tubular vertical deaeration tower wherein
a froth is
caused to cascade downward over a series of cones, flowing against the upward
flow of
steam. Such deaeration towers are commonly used in present day oiI sands
extraction plants.
The froth entering the deaeration tower typically contains about 20% by volume
of air and
may be at a temperature of about 40 degrees Celsius. The froth needs to be
deaerated such
that the air content is reduced by about 20% by volume of air before it can be
easily pumped
using conventional centrifugal pumps. The deaeration tower typically contains
a series of
cones, a distributor plate, internals and steam injection means and optionally
a froth recycle
loop to assist in process control. Typically the deaerated froth. stream from
the deaeration
tower will have a temperature of about 65 degrees Celsius, which needs to be
reduced to
about 48 degrees Celsius before the downstream solvent recovery of the bitumen
can be
attempted.
Accordingly, all of the above prior art systems to deaerate bitumen froth
involve the use of
costly equipment and the costly addition of either heat and/or chemicals.
Canadian patent application number 2,263,858 advocates overcoming these
disadvantages by
using mechanical deaeration whereby the froth is sheared with an impeller or a
recirculating
pump. This approach entails costly mechanical equipment that is difficult to
maintain in
operation.
An object of the present invention into reduce the cost of deaeration of
bitumen froths and to
provide a bitumen froth deaeration method and system which also protect
downstream
centrifugal pumps and/or other bitumen processing equipment from damage by
coarse solids.
SUMMARY OF THE INVENTION
'The bitumen froth deaeration method according to the invention comprises
passing the froth
through a screen to reduce the air content of the froth.
The sieve opening size is determined by the required throughput, froth
temperature and area
of the screen. Preferably, the sieve opening size of the screen is selected
such that the surface
area of the bitumen froth is expanded and air escapes from the bitumen froth
and is at least 2
mm, more particularly at least 6mm, across.

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The screen may be continuously or intermittently moved relative to a froth
supply unit, for
example by configuring the screen as a permeable conveyor belt, which is
continuously
translated underneath the froth supply unit.
Suitably, the froth supply unit is arranged downstream of a primary bitumen
enriched froth
exhaust conduit of a gravity froth separation vessel in which a froth formed
by injecting air
into a slurry of oil sand and water is separated by gravity separation into a
bitumen enriched
primary froth stream and a water and sand enriched secondary froth stream.
The oil sand may be mined from an oil sand deposit and subsequently crushed
and mixed with
hot water and transported from the mining site to the froth separation vessel
through a
pipeline in which the slurry of hot water and oil sand is conditioned and air
is injected into the
slurry to create a froth which is fed into the gravity froth separation
vessel.
The bitumen froth separation system according to the invention comprises a
screen through
which in use a bitumen froth is induced to flow and the air content of the
froth is reduced.
Preferably, the screen has a sieve opening size of at least six mm across and
the screen is
configured as a permeable conveyor belt which is in use slowly rotated and
thereby translated
underneath a froth supply unit. The conveyor belt may be provided with a
scraper and/or
spray cleaning unit for removing any bitumen froth from the screen during each
rotation
cycle.
These and other features, objects and advantages of the method and system
according to the
invention are detailed in the appended claims, abstract and detailed
description with reference
to the accompanying drawings.
DESCRIPTION OF PREFERRED EMBODIMENTS
The method and system according to the invention will be described in more
detail and by
way of example with reference to the accompanying drawings in which:
Fig.l shows a schematic overview of an oil sand processing plant, which
comprises a
deaeration screen according to the present invention;
Fig. 2 shows at a larger scale the deaeration screen of Fig.2; and
Fig.3 shows at a further enlarged scale a screen opening of the screen of Fig.
l and 2 in which
froth necking occurs.
Referring to Fig.l there is shown a schematic overview of an oil sand
processing plant in
which mined oil sand is fed from an oil sand truck 1 to a semi-mobile crusher
2 and then
transported by a conveyor belt 3 to a rotary breaker 4 in which the crushed
oil sand is mixed
with hot water 5 and oversized lumps are separated and supplied to a reject
disposal 6.
The remaining oil sand and water slurry is then pumped through a pipeline 7 in
which the oil
sand slurry is conditioned and aerated by an air injection unit 8.
The aearated slurry flows from the pipeline 7 into a primary froth separation
vessel 9 in which
a primary low density bitumen enriched froth is separated from a secondary
high density sand
and water enriched froth. The secondary high density sand and water enriched
froth is
removed from the separation vessel 9 via one or more lower exhaust conduits
and further
processed in a series of flotation cells 10 and a hydrocyclone 11 and pumped
into a tailings
settling pond 12 and a water treatment and/or recycling unit 13.
The primary bitumen enriched froth is discharged from the primary froth
separation vessel 9
via an upper exhaust conduit 14 and fed to a froth supply unit 15, which is
arranged above a
froth deaeration screen 16 according to the invention.
Fig.2 shows in greater detail that the screen 16 is configured as a conveyor
belt, which rotates
about a series of rollers 17 around a collector trough 18. The froth supply
unit 15 distributes

CA 02425840 2003-04-17
the froth across the substantially horizontal upper surface of the screen 16.
Fig.3 shows in
greater detail how froth necking occurs as the froth passes through the screen
16.
When field tested elongated streams of bitumen 20 were observed to be forming
under the
wire mesh of the rotating screen 16 according to the invention.
The elongated streams of bitumen 20 were either removed by scrapers 19 and/or
pulled away
by their own weight.
Testing of screens was conducted to verify that they would function to
deaerate oil sands froth
in addition to removing solids. Froth was aerated so that it contained over
60% air. A series
of tests Was conducted in which aerated froth, at temperatures of 25 °
Celsius and 40 ° Celsius,
was strained through screens having different mesh sizes. The amount of
resulting deaeration
is shown in the following table.
Results:
Air Reduction Air Reduction Air Reduction Air Reduction
over - -
with Time only an Inclined 6 mm Sieve 2.5 mm Sieve
Plate
2.3% 7.2% 20.2% 36.4%
2.9% 4.2% 8.7% _ _ 22.4%
_ _
3.4% 3.5% 12.4% 29.6%
Average: 2.9% 4.5% 13.8% 29.7%
As can be seen, the amount of deaeration when using the sieve having an
opening size of six
mm was on average a 13.8% reduction) and when using the screen having a sieve
opening
size of 2.5 mm was on average a 30% reduction).
As can be seen from these test results, a linear screen 16 can be used to not
only remove
debris from oil sands froth but to also replace costly conventional deaeration
means.
It is believed that the screen achieves deaeration by expanding the surface
area of the bitumen
to allow air to escape from the bitumen more easily. It is recognized that
steam can be added
to assist in deaeration, however it is not essential to do so. The objective
is to conduct the
deaeration using the screen in a manner which does not cause the raising of
the temperature of
the bitumen.
As illustrated in Fig. 1 the deaerated bitumen froth can be easily pumped from
the deaerated
froth collection trough 18 by a conventional centrifugal pump 21 into a
bitumen storage tank
22.