Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02901863 2015-08-28
PROCESS AND APPARATUS FOR SPLITTING VAPOUR STREAMS
FIELD OF INVENTION
This invention relates to the process and apparatus for the treatment of
tailings streams that result
from oil sands mining operations, in particular the solvent vapours generated
during the treatment of tailings
stream from solvent based froth treatment.
BACKGROUND OF INVENTION
The Athabasca region of Alberta, Canada has world scale bitumen deposits, some
of which can be
produced efficiently through surface mining. The standard flow sheet for
removing the bitumen from the
sands in these "mined oil" facilities includes a water washing/flotation
process that results in a frothy
emulsion of the biturnen containing typically 30 wt% water and 10 wt% mineral
along with the bitumen and
some gas.
There are a variety of methods used for cleaning this product. High
temperature paraffinic froth
treatment is recently the preferred process because it produces a very clean,
partially upgraded (through
asphaltene rejection) bitumen product. At the tail end of this process the
water, mineral and asphaltene that
has been removed from the bitumen must be cleaned of solvent to minimize
impact to the environment and
to recover the solvent for re-use which is important to the economy of the
process. This is generally done
through progressive flashing/stripping operations performed on the tailings
stream.
Continuous flash vapourization is an established technology for the removal of
low boiling
substances from those with a higher boiling point. In the textbook "Mass
Transfer Operations" by Treybal
(McGraw-Hill 1980) the process is described on page 363 including a feed
heater, a pressure reduction valve
and a tangential/cyclonic entry into the drum.
Adding to this a loop to recirculate liquid back to the drum (allowing for
more shear and time for the
low boiling substance to evaporate) is taught in US patent 3,311,545 by
Rasmussen.
Canadian Patent 1,027,501 teaches flashing for the removal of solvent from
froth treatment tailings
using a sub-atmosphcrie flash and focusing on naphtha as the solvent. Canadian
Patents 2,272,035 and
2,272,045 teach flashing for the removal of solvent from froth treatment
tailings ¨ including paraffinic froth
treatment tailings ¨ both above and below atmospheric pressure and with steam
injet into the vapour or liquid
phase in the vessel. These patents also include an upstream pumpbox to feed
the recovery tower.
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Canadian Patent 2,750,845 teaches a two stage flashing of the tails stream
from a paraffinic froth
treatment plant including pressure moderation of the feed stream through a
valve or regulator, hot water
and/or steam addition.
Canadian patent 2,613,873 teaches the use of an inert gas to assist in the
mass transfer of solvent
from the tailings stream and identifies the value of a separation drum
substantially free of internals.
Canadian patents 2,733,312 and 2,733,342 teach similar recovery techniques for
the same stream.
There is further discussion of the internals and pressures in these patents.
US 8,741,107 B2 teaches the use of droplet size control (in this case through
nozzles) to improve the
efficiency of the recovery of the solvent.
The focus of the above mentioned prior art is the activity in the flash
vessel. The present invention is
directed to the management of pressure in the vessels through the overhead
system. Overhead systems using
large vacuum pumps and inlet feed valves are sources of significant capital
and maintenance costs and
unreliability of the extant processes. According to a preferred embodiment of
the present invention, there is
conversion of some of the heat put into the waste stream to support the
evaporation of the solvent into kinetic
and then potential energy (pressure) reducing the energy consumption arid
capital cost. The present invention
also allows, provided by the existence of the upstream pumpbox, the
perfortnance of part of the flash in a
vessel substantially free from internals. The system to which the present
invention is directed to is a
progressive flashing stripping operation for the removal of a volatile solvent
from a tails stream containing
water, mineral and other, non-volatile hydrocarbons.
SUMMARY OF THE INVENTION
The present invention is directed to a process in which the vapour resulting
from flashing and
stripping of paraffinic froth treatment tails is split between two vessels
positioned in series by allowing a
flash to occur in an empty pumpbox followed by an internalled stripping
column. According to a preferred
embodiment of the present invention, using this method of vapour production
also allows the use of the
primary vapour to create lower pressure in the secondary stripping vessel and
pressurize its overhead vapour
through gas ejection.
According to a first aspect of the present invention, there is provided a
process for the treatment of
paraffinic froth treatment tails comprising:
- providing a liquid tails stream;
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- introducing the liquid tails stream into a purnpbox, wherein the
pressure of the liquid tails stream
is sufficiently higher than the pressure inside the pumpbox, so that when the
liquid tails stream
enters the pumpbox, a flash converts a portion of the liquid tails stream to a
vapour, the
remaining liquid tails accumulating at a bottom portion of the pumpbox prior
to being removed
and injected into a tailings solvent recovery unit;
- removing a portion of the vapour through a vapour management
system located above the liquid
line inside the pumpbox;
- creating solvent vapours in the tailing solvent recovery unit; and
- removing a portion of the solvent vapours created in the tailing
solvent recovery unit through an
outlet on the tailing solvent recovery unit, said outlet being in fluid
connection with the pumpbox
overhead vapour.
Preferably, the process further comprises a step of heating the liquid tails
stream prior to introduction
into the pumpbox.
According to another preferred embodiment, the process further comprises a
step of heating the
underflow from the pumpbox prior to introduction into the tailings solvent
recovery unit.
According to another preferred embodiment, the process further comprises a
step of aspirating the
solvent vapours from the tailings recovery unit by using the vapour stream
from the pumpbox overhead.
Preferably, the vapour management system combines the vapour from the pumpbox
overhead and the vapour
from the tailings recovery unit overhead into a single vapour stream. More
preferably, the single vapour
stream undergoes condensation and liquid/vapour separation to obtain a stream
of recovered liquid solvent.
According to a first aspect of the present invention, there is provided an
apparatus for the treatment
of paraffinic froth treatment tails comprising:
- an inlet adapted with a liquid distributor to introduce liquid
tails into a pumpbox to flash a
portion of the liquid into a vapour;
- said pumpbox comprising a bottom portion comprising an outlet for
the underflow and a top
portion comprising an outlet for the overhead, said pumpbox underflow outlet
being in liquid
connection with a tailings solvent recovery unit,
- said tailings solvent recovery unit comprising a bottom section
comprising an outlet for the
underflow and a top section comprising an outlet for the overhead;
- a vapour management system located above the liquid line inside
the pumpbox, said vapour
tnanagetnent system comprising a first tubing fluidly connected to a top
portion of the pumpbox,
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a second tubing fluidly connected to the top section of the tailings solvent
recovery unit, a
venturi pump (ejector) connecting both the first and second tubing wherein, in
operation, the
flow of vapour travelling through the first tubing aspirates the vapour
travelling through the
second tubing.
According to a preferred embodiment, the apparatus further comprises a valve
located parallel to the
venturi pump and adapted to divert a portion of the flow of vapour travelling
through the first tubing around
the venturi pump.
According to a preferred embodiment, the apparatus further comprises a heating
element adapted to
heat the underflow from the pumpbox prior to introduction into the tailings
solvent recovery unit.
According to another preferred embodiment, the apparatus further comprises a
heating element
adapted to heat the liquid tails stream prior to introduction into the
putnpbox.
Preferably, the apparatus further comprises a recirculation of a portion of
the underflow from the
pumpbox back into the pumpbox.
According to a preferred embodiment, the apparatus further comprises a valve
located along the first
tubing in a position located upstream, of the venturi pump, said valve adapted
to control the flow and
superheat of vapour from the pumpbox into the venturi pump.
According to a first aspect of the present invention, there is provided a
method to recover solvent
from a tailings solvent recovery unit during the treatment of paraffinic froth
treatment tails comprising:
- providing a liquid tails stream;
- introducing the liquid tails stream into a purnpbox, wherein the
pressure of the liquid tails stream
is sufficiently higher than the pressure inside the pumpbox, so that when the
liquid tails stream
enters the pumphox, a flash converts a portion of the liquid tails stream to a
vapour, the
remaining liquid tails accumulating at a bottom portion of the pumpbox prior
to being removed
and introduced into a tailings solvent recovery unit;
- removing a portion of the vapour from the pumpbox through a vapour
management system
located above the liquid line inside the pumpbox;
- sending the under-flow from said pumpbox to said tailings solvent
recovery unit which comprises
a bottom section comprising an outlet for the underflow and a top section
comprising an outlet
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for the overhead, wherein said overhead of the tailing solvent recovery unit
is in fluid connection
with the vapour management system; and
- using a venturi pump driven by the flow of the pumpbox overhead
vapours to extract vapours
from the tailing solvent recovery unit overflow.
Preferably, the method further comprises adjusting the drive flow on the
venturi pump to control the
removal of the solvent vapours. Also preferably, the vapour management system
further comprises a valve in
parallel with the verituri pump to divert a portion of the pumpbox vapour flow
around the venturi pump.
According to a first aspect of the present invention, there is provided a
method to control of the
pressure in a tailing solvent recovery unit, said method comprising:
- providing a liquid tails stream;
- introducing the liquid tails stream into a pumpbox, wherein the
pressure of the liquid tails stream
is sufficiently higher than the pressure inside the pumpbox, so that when the
liquid tails stream
enters the pumpbox, a flash converts a portion of the liquid tails stream to a
vapour, the
remaining liquid tails accumulating at a bottom portion of the pumpbox prior
to being removed
and injected into a tailings solvent recovery unit;
- removing a portion of the vapour from the pumpbox through a vapour
management system
located above the liquid line inside the purnpbox;
- sending the underflow from said pumpbox to said tailings solvent recovery
unit which comprises
a bottom section comprising an outlet for the underflow and a top section
comprising an outlet
for the overhead, wherein said overhead of the tailing solvent recovery unit
is in fluid connection
with the vapour management system;
-
using a venturi pump driven by the flow of the pumpbox overflow vapours to
extract vapours
from the tailing solvent recovery unit overflow; and
- adjusting the flow through the venturi pump through the use of a
valve to divert a portion of the
pumpbox vapour flow around the venturi pump.
Preferably, the method further comprises adjusting the drive flow to the
venturi pump to control the
removal of the solvent vapours from the tailings solvent recovery unit.
According to a preferred embodiment,
a valve is positioned in parallel with the venturi pump. According to another
preferred embodiment, a valve
is positioned in series with the venturi pump. According to a preferred
embodiment, the apparatus has a valve
is positioned in parallel and a valve positioned in series with the venturi
pump. This last embodiment allows
for separate control of rate and superheat of the vapour driving the venturi
pump.
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The main pieces of process equipment are the pumpbox and the stripping column.
In this design both
pieces of equipment have a vapour release to an overhead treatment system. The
partial flash that occurs in
the pumpbox, does so at a pressure specified to both limit the flash to a
vapour velocity that can fully
segregate from the liquid droplets in the pumpbox headspace and to drive an
ejector that is used to suck
vapour from the stripping column and pressurize it into the downstream vapour
condensation and separation
processes.
According to a preferred embodiment of the present invention, there is no need
for an overhead
vacuum putnp, or compressor. or is there a need for modulating control valves
on the tails streams. This
embodiment also has no internals below the feed distributor in the pump box,
lt includes no agitator in the
first flashing stage (pumpbox). The elimination of the above mentioned
elements present significant
improvements in capital requirements and advantages in maintenance
requirements which are part of the
value proposition for the present invention.
According to another preferred embodiment of the present invention, one of the
advantages of this
process is that the most challenging part of the flash, from a reliability
perspective, is put into a very simple
vessel with very few internals and very simple controls. The importance of
this lies in the violence of the
initial flash since the pressure is dropped by roughly 6/7ths. The simplicity
of the pumpbox also allows for
better damage mitigation (such as internal hard surface) and simpler
maintenance (no internals to avoid or
remove). Another important reliability aspect of this preferred process is the
alternative to using control
valves on the tailings stream. A combination of fixed restrictions and
elevation of the feed distributor provide
the bulk of the pressure reduction and modulation is provided by the control
of the overhead system
backpressures and the stripping medium rate. This eliminates another cause of
required maintenance.
BRIEF DESCRIPTION OF THE FIGURES
The actual construction, operation, and apparent advantages of the present
invention will be better
understood by referring to the drawings which are not necessarily to scale and
in which:
Figure l is a schematic representation Of the prior art process.
Figure 2 is a schematic representation of the process according to an
embodiment of the present
invention.
Figure 3 is a schematic representation of the process according to another
embodiment of the present
invention.
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Figure 4 is a schematic representation of the process according to a third
embodiment of the present
invention.
Figure 5 is a schematic representation of the process according to a fourth
embodiment of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In the preferred embodiment, the unheated tails stream from the paraffinic
froth treatment separator
trains is introduced at pressure (I). This pressure is substantially reduced
by head loss in the incoming pipe
(2), and a restrictive spool upstream of the pumpbox (3).
In referring to Figure 2, upon entering the pumpbox (4), the tails stream (21)
is distributed with a
cyclonic distributor (5) and simultaneously a portion of the liquid flashes to
vapour. The remaining liquid
droplets disengage from the vapour and fall to the liquid pool below (6). The
liquid pool (6) creating a liquid
line above which the distributor must always remain. The rate of flashing is
controlled by the backpressure
from the pumpbox vapour management system (7), consisting of a combination of
full-stream control valve
(8), ejector nozzle (9) and ejector bypass control valve (1(>). The flow rate
of this stream (28) is managed to
control the amount of flash occurring in the pumpbox (4) to a level where the
vapour liquid disengagement is
approximately complete and the ejector (9) reduces the pressure of the vapour
on the passive side (11) to
approximately atmospheric, while discharging at some elevated pressure (12).
This stream is subsequently
treated to a combination of cooling/condensation and liquid vapour separation
to recover the flashed solvent
(13). The vapour management system is designed to accommodate the large
volumes of vapour and later
condensed liquid associated with accepting the flash vapour. Both vessels are
eventually connected to a
single vapour condensing and separation step designed for the entire load
(rather than two intermediately
sized systems, each having design and technical tolerances/margins. This has
for effect to provide significant
cost reductions.
A portion (17) of the uriderflow (24) can be recirculated back to the pumpbox
(4). The underflow
(24) from the pumpbox (4) is then charged into the tailings solvent recovery
unit (TSRU) (14) through inlet
(25).
The discharge of the pumpbox (4) is at a rate to stabilize the TSAI)
performance, to strip the
remaining solvent at the pressure set by the passive side of the ejector (11).
The tails stream (24) being
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charged to the TSRU (14) is heated (15) and stripping vapour (16) such as
Vapour Recovery Unit (VRU)-
produced-gas can be added to the column (14) as a stripping medium. The
overhead vapours (11) from the
TSRU (14) are pressurized in the ejector (9) and blended with the pumpbox
overhead vapours (12) prior to
cooling and condensation (13). The ejector (9) is adapted to allow the flow of
the overhead vapours (28)
from the pumpbox (4) to entrain the vapours (30) coming from the TSRU (14) and
thus act as a venturi
pump. This is desirable as it eliminates the need for conventional apparatus
such as an overhead vacuum
pump or compressor. In order to adjust the flow of the vapours being aspirated
from the TSRU (14), a valve
(10) located in parallel with the venturi pump (9) allows to adjust the flow
vapours coming from the
pumpbox (4) by diverting through valve (10) actuation, a portion of the vapour
flow (38) to bypass the
venturi pump (9). Control of the head pressure in the pumpbox is tuned and
adjusted to maintain a relatively
consistent vapour loading from the thermally neutral flash. The tailings (34)
are discharged from the TSRU
(14) through an outlet (32) located near the bottom of the column.
In the prior art process as seen in Figure 1, the tailings are introduced into
a steam stripping vessel
where the pressure is maintained at near atmospheric pressure
According to another preferred embodiment of the present invention, Figure 3,
the full streain
control valve (8) is positioned Mier the vapour flow bypass (38) but prior to
the venturi pump (9).
According to another preferred embodiment of the present invention, and a
variation of the
embodiment of Figure 3, is the process depicted by Figure 4, which process
does not provide for a heating
element prior to the tailings from the underflow (24) reaching the TSRU (14).
Rather than this, the entire
tailings stream is heated prior to introduction into the pump box generating a
coinbination of more flash
vapour and/or higher pressure flash vapour and leaving the tails at the
preferred temperature for introduction
into the TSRU.
According to another preferred embodiment of the present invention as depicted
in Figure 5., there is
provided a flow chart of the process according where the venturi pump (9) is
located within the TSKU (14).
According to another embodiment of the present invention, there is no
modulating pressure control
on the tails stream being charged to the pumpbox or the TSRU. There is no
valve on the slurry feed line to
either vessel. The vessel pressure is "set" by the overhead system, the flow
rate is "set" by the pump working
against a restriction and the flash occurs in such a way as these balance
(ideally the flash occurs in the
restriction). This eliminates a major reliability issue ¨ the valve ¨ which
can plug and wear. For the more
traditional naphthenie systems, the restriction was, in some cases, the pipe
rise going into the vessel, but that
is not sufficient for a typical paraffinic pressure drop.
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ACM-ding to another embodiment of the present invention, the tails stream (21)
is heated before
entering the pumpbox (4) instead of being heated after exiting the pumpbox.
This provides a tail stream
having a higher temperature, therefore upon entering the pumpbox more vapour
and/or higher pressure
vapour will be created upon flashing.
According to another embodiment of the present invention, the pumpbox vapour
system is pressure
controlled to allow the flashing of an amount of vapour consistent with proper
droplet disengagement within
the pumpbox head diameter. Preferably also, the feed distributors into the
pumpbox manage the liquid
droplet size to minimize foaming and to stabilize the flash behavior.
Preferably, the liquid flow is oriented
primarily downward. Also preferably, the feed system is placed in the vapour
head of the pumpbox (volume
already present to prevent liquid relief).
According to another embodiment of the present invention, the stripping vapour
in the TSRU vessel
is VRU-produced-gas.
The embodiments described herein are to be understood to be exemplary and
numerous modification
and variations of the present invention are possible in light of the above
teachings. It is therefore to be
understood that within the scope of the claims appended hereto, the invention
may be practiced otherwise =
than as specifically disclosed herein.
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