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 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 the present invention aim to provide a solution to this problem. SUMMARY OF THE INVENTION

The method according to 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 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.

It is furthermore preferred that the recycled aromatic light gas oil is introduced to the reflux stream, so that the recycle stream and the reflux stream,

in combination, comprise at least 50 vol% of aromatic components and less than 50 vol% of paraffinic components .

The system according to 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 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. BRIEF DESCRIPTION OF THE DRAWING

FIG.l is a schematic flowscheme of a bitumen refining plant in which light gas oil is recycled from a 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.l, 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.l 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.