Note: Descriptions are shown in the official language in which they were submitted.
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TS 9500 CAN
Peb
METHOD AND SYSTEM FOR WASHING THE INTERNALS OF A VESSEL
FOR PROCESSING A HEAVY HYDROCARBON STREAM
BACKGROUND OF THE INVENTION
The invention relates to a method and system for
washing the internals of a vessel for processing a heavy
hydrocarbon stream.
Such a vessel may be a diluent recovery column and/or
other vessel for separating, heating, distilling and/or
fractionating a heavy hydrocarbon stream in a bitumen or
other heavy hydrocarbon refining plant.
It is known from International patent application
WO00/39251 to remove solids, particularly catalyst fines
from an asphaltene-containing hydrocarbon liquid by
contacting the liquid with a solvent which may comprise
an alkane, such as propane to pentanes, and the mixture
may be heated until the asphaltenes precipitate to a
separate phase and can be separated from the mixture. The
known method is not suitable to wash the internals of a
heavy hydrocarbon processing vessel in an efficient
manner.
Bitumen, that may be produced from a heavy oil or oil
sand deposit, either by surface mining or by steam
injection into the deposit, typically has such a high
viscosity that it is required to add a diluent to the
produced bitumen stream in order to reduce the viscosity
such that the bitumen is pumpable through a pipeline from
the production site to a processing facility.
The diluent may comprise paraffinic components such
as pentane and/or hexane, which are recovered in a
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diluent recovery column in a bitumen refining plant and subsequently recycled
to the
production site for reinjection into the bitumen transportation pipeline.
A problem with currently available diluent recovery columns and other
heavy hydrocarbon processing vessels is that the internals of these vessels
are
susceptible to fouling by asphaltene deposits and that these deposits cannot
be
adequately washed from these internals by means of currently available
cleansing
liquids. This is because the reflux stream, normally used to wash the
internals, is
highly paraffinic and therefore unable to effectively re-dissolve the
asphaltenes that
have precipitated on the internals.
The method and system according to some embodiments of the present
invention may provide a solution to this problem.
SUMMARY OF THE INVENTION
The method according to some embodiments of the invention for
washing the internals of a vessel for processing a heavy hydrocarbon stream
comprises introducing a cleansing stream comprising aromatic and/or naphthenic
components into the vessel such that the cleansing stream flows along at least
a
substantial part of the surface of the internals of the vessel and flushes
precipitated
asphaltene deposits from said internals.
The vessel may be a vessel for separating, heating, distilling and/or
fractionating a bitumen and/or other heavy hydrocarbon stream. In particular,
the
vessel may be a separating vessel formed by a diluent recovery column at the
upstream side of a bitumen refinery plant, in which column diluent, in
particular a
paraffinic diluent such as pentane and/or hexane, is separated from the
bitumen and
subsequently recycled to the production
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site for reinjection into the bitumen transportation
pipeline.
If the vessel is a diluent recovery column in a
bitumen refinery plant it is preferred to recycle an
aromatic light gas oil from a distillation column which
is located in the bitumen refinery plant downstream of
the diluent recovery column, such that the recycled
aromatic light gas oil flows along at least a substantial
part of the surface of the internals of the diluent
recovery column and flushes precipitated asphaltene
deposits from said internals.
The recycled aromatic light gas oil is typically
added to the reflux stream in the diluent recovery
column, on an intermittent basis.
In an embodiment the diluent recovery column is a
preflash column in which a pentane and/or hexane and/or
other diluent is separated from bitumen, which column is
located upstream of a bitumen heating furnace of the
bitumen refining plant and the recycled aromatic light
gas oil is recycled from an atmospheric distillation
column which is located downstream of the bitumen heating
furnace.
It is preferred that the internals of the preflash
column comprise a packing which at least partly made of
stainless steel in at least part of the region of the
interior of the preflash column where the diluted bitumen
stream enters the interior of the preflash column.
Preferably, the recycled aromatic light gas oil has
an average carbon number less than 18 and a boiling range
between 100 and 400 degrees Celsius at atmospheric
pressure and comprises at least 60 vol% of aromatic
components and less than 40vol% of paraffinic components.
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It is furthermore preferred that the recycled aromatic light gas oil is
introduced to the reflux stream, so that the recycle stream and the retlux
stream, in
combination, comprise at least 50 vol% of aromatic components and less
than 50 vol% of paraffinic components.
The system according to some embodiments of the invention for
washing the internals of a vessel for processing a heavy hydrocarbon stream
comprises means for introducing a cleansing stream comprising aromatic and/or
naphthenic components into the vessel such that the cleansing stream flows
along at
least a substantial part of the surface of the internals of the vessel and
flushes
precipitated asphaltene deposits from said internals.
If the vessel is a diluent recovery column in a bitumen refining plant
then the system may comprise a conduit for recycling an aromatic light gas oil
from a
distillation column which is located in a bitumen refining plant downstream of
the
diluent recovery column into the diluent recovery column such that in use the
recycled aromatic light gas oil flows along at least a substantial part of the
surface of
the internals and flushes precipitated asphaltene deposits from the internals.
These and other features and advantages of the method and system
according to some embodiments of the present invention are further detailed in
the
appended claims, abstract and detailed description of a preferred embodiment
in
which reference is made to the accompanying drawing.
According to one aspect of the present invention, there is provided a
system for washing the internals of a vessel for processing a heavy
hydrocarbon
stream, the system comprising means for introducing a cleansing stream
comprising
at least one of aromatic and naphthenic components into the vessel thereby
allowing
the cleansing stream to flow along at least a part of the surface of the
internals of the
vessel and flush precipitated asphaltene deposits from said internals wherein
the
vessel is a diluent recovery column in a bitumen refining plant, and the
system
comprises a conduit for recycling an aromatic light gas oil from a
distillation column
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which is located in the plant downstream of the diluent recovery column into
the
diluent recovery column, thereby allowing the recycled aromatic light gas oil
to flow
along at least a part of the surface of the internals and flush precipitated
asphaltene
deposits from the internals.
According to another aspect of the present invention, there is provided
a method for washing the internals of a vessel for processing a heavy
hydrocarbon
stream, the method comprising introducing a cleansing stream comprising at
least
one of aromatic and naphthenic components into the vessel, wherein the
cleansing
stream flows along at least a part of the surface of the internals of the
vessel and
flushes precipitated asphaltene deposits from said internals, wherein the
vessel is a
diluent recovery column in a bitumen refining plant as described herein and
the
cleansing stream comprises an aromatic light gas oil which is recycled from a
distillation column which is located in the plant downstream of the diluent
recovery
column.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a schematic flowscheme of a bitumen refining plant in which
light gas oil is recycled from a
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distillation column to a diluent recovery column in
accordance with the invention.
DESCRIPTION OF A PREFERRED EMBODIMENT
The invention will be described in more detail with
reference to FIG.1, which provides a flowscheme of a
bitumen refining plant in which light gas oil is recycled
from a distillation column into a diluent recovery
column.
In FIG.1 a refining unit is shown which comprises a
preflash diluent recovery column 1 and an atmospheric
distillation column 2 from which an aromatic light gas
oil (LGO) is recycled back into the diluent recovery
column 1 via a LGO recycling conduit 3. The aromatic LGO
is combined with the reflux stream 9 of the diluent
recovery unit 1.
The plant furthermore comprises a vacuum distillation
column 4, a diluent recovery unit 5 which is connected to
a diluent outlet conduit 6 at the upper end of the
preflash diluent recovery column 1 and various
pumps/condensors 7 and furnaces 8.
A diluted bitumen stream is pumped from an oil sand
production site (not shown) into the preflash diluent
recovery column 1 via a diluted bitumen transportation
pipeline 10
Several laboratory experiments have been carried out
to investigate the fouling of the preflash diluent
recovery column 1 which revealed that recirculation of
aromatic light oil LGO effectively flushes asphaltene
deposits from the internals of the preflash diluent
recovery column 1 and that it is beneficial that these
internals are made of smooth stainless steel packings.
