Note: Descriptions are shown in the official language in which they were submitted.
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INTEGRATING AN ATMOSPHERIC FRACTIONATOR WITH A DILUENT
RECOVERY UNIT AND A REBID HYDROCRACKER
TECHNICAL FIELD OF THE INVENTION
This invention relates to the optimization of a diluent recovery unit
with a resid hydrocracker by the use of an optimized atmospheric
fractionator in the conversion of a light sweet refinery to diluted bitumen.
BACKGROUND OF THE INVENTION
Extensive reserves in the form of "heavy crudes" exist in a number of
countries, including Western Canada, Venezuela, Russia, the United States,
and elsewhere. These deposits of heavy crudes often exist in areas that are
inaccessible by normal means. Generally, the term "heavy crude" refers to
a hydrocarbon material having an API gravity of less than 25.
"DilBits" are produced by blending heavy bitumen with a light diluent
(e.g. condensate, naphtha or natural gasoline) to reduce the viscosity for
pipeline specifications. The bitumen is often high in sulfur, high in nitrogen
and corrosive requiring significant metallurgy upgrades in refinery Crude,
Vacuum, and other downstream processing units.
A recent invention utilizes a diluent recovery unit (DRU) in front of a
Resid Hydrocracker. The DRU does not require significant metallurgy
upgrades because the corrosive organic acids are not a concern at its lower
operating temperatures (e.g. below 450 F). The bottoms product from the
DRU is whole bitumen which is high in sulfur, high in nitrogen and corrosive.
The whole bitumen material (including distillates and gas oils) is fed to a
Resid Hydrocracker where it is desulfurized, nitrogen is reduced and
corrosive elements are neutralized so that it can be processed in an existing
light sweet refinery.
It can cost billions of dollars to upgrade an existing light sweet
refinery to process heavy bitumen. There are concerns that the costs of
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converting refineries to process heavy bitumen will be hard to recoup. Long
term, the ability to use heavy bitumen is an issue that's expected to confront
the refining industry for an extended period of time.
A prior invention summarized the benefits of feeding the recovered
lowered boiling point hydrocarbonaceous feedstock from the Resid
Hydrocracker unit to existing fractionation towers (crude atmospheric and
vacuum) in an existing refinery. The diluent recovery unit (DRU) and Resid
Hydrocracker and further described in copending patent applications serial
no. 12/378,671 filed February 18, 2009, serial no. 12/378,610 filed on
February 18, 2009, the disclosures of which are herein incorporated by
reference.
SUMMARY OF THE INVENTION
This invention is an alternative that further optimizes the integration of
the Diluent Recovery with the Resid Hydrocracker for the conversion of a light
sweet refinery to a heavy Sour Refinery by including an integrated
atmospheric fractionation tower as part of the Resid Hydrocracker. The
benefits of this integration are: efficient use of capital, easier start-
up/shut-
down and reduced operating costs. This results in the optimization of a
diluent
recovery unit with a Resid Hydrocracker atmospheric fractionator in the
conversion of a light sweet refinery to diluted bitumen.
Rather than incur the cost of extensively retrofitting an existing light
sweet refinery, we have invented a unique way of conditioning the heavy sour
crude at the refinery location to make it acceptable for processing in the
existing light sweet refinery equipment. Our system does not significantly
modify an existing sweet refinery. Other objects and advantages of the
present invention will become apparent to those skilled in the art upon a
review of the following detailed description of the preferred embodiments and
the accompanying drawings.
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BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 shows a diluent recovery unit with a Resid Hydrocracker utilizing
the optimized atmospheric fractionator described in this application for the
conversion of a light sweet refinery to diluted bitumen.
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DETAILED DESCRIPTION OF THE INVENTION
Fig. 1 shows the configuration of this invention. This configuration
adds an integrated atmospheric fractionator to the Resid Hydrocracker in
place of fractionating all the Resid Hydrocracker light products in the
existing crude unit. The configuration that has been developed creates
several synergies between the DRU, Resid Hydrocracker and the
fractionation. This configuration is important because of the benefits it
provides. The benefits of this configuration include the following:
= The DRU rectifying section and overhead systems are
eliminated by sending the overhead material to the Resid Hydrocracker
atmospheric fractionator.
= The Resid Hydrocracker atmospheric fractionator pump
arounds and product streams are used to pre-heat the diluted bitumen
(DilBit) avoiding DRU exchanger investment.
= This configuration produces an atmospheric tower bottoms
product which can be processed in the existing refinery's vacuum unit.
Blending of the Resid Hydrocracker atmospheric tower bottoms (ATB) with
the conventional ATB can improve stability (reduce fouling).
= An atmospheric fractionator in the Resid Hydrocracker
eliminates any concerns with hydrocracker light gas production that might
overwhelm the existing crude unit.
= The Resid
Hydrocracker warm-up/cool-down
(startup/shutdown) are simplified because the heat integration can be
contained within the DRU and Resid Hydrocracker atmospheric fractionator
(i.e. the Crude Unit is not impacted during startup and shutdown).
The overhead material from the atmospheric fractionator heats the
diluted bitumens prior to feeding the blend to the DRU. The invention also
includes the step of blending Resid Hydrocracker ATB with conventional
ATB for stability.
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The disclosed atmospheric fractionator is shown in Fig. 1. The oil
entering the flash zone of an atmospheric fractionator is first heated to the
maximum temperature allowable for the crude being processed. An
atmospheric fractionator operates at a low pressure and as high a
5 temperature as practical in the flash zone to maximize the amount of oils
that will vaporize. This yields several distillate products and a bottoms
product, which is the residual liquid material that could not be vaporized
under the conditions of temperature and pressure existing in the
atmospheric tower. This bottoms liquid is then sent to a fractionating tower
(vacuum tower) that operates at sub-atmospheric pressure to yield distillates
described by the whole crude True Boiling Point (TBP) cut points of between
900 to 1150 F. The distillate in the atmospheric fractionator is material with
whole crude TBP of less than 700 to 800 F. The atmospheric fractionator
usually contains multiple sections consisting of alternating heat transfer and
fractionation zones. The heat transfer zones are used to remove heat from
the tower by withdrawing an internal liquid stream from the tower, cooling it
and returning it to the column. The cooling medium is usually the crude oil
feed being preheated before entering the crude furnace. The fractionation
zones are used to effect the separation between adjacent ASTM boiling
ranges commonly referred to as fractions. The following general classes of
distillate products or fractions are obtained from petroleum:
Liquefied Petroleum Gas (LPG), which includes ethane,
propane, butanes and isopentane.
Naphtha (Gasoline), which is characterized by Pentane
through 400 F ASTM end point.
iii. Light Distillate which has ASTM end points in the range of 525
to 575 F.
iv. Heavy Distillate which has ASTM end points in the range of
650 to 750 F.
v. Gas Oil which is essentially all distillate material heavier than
heavy distillate. Gas oil yielded from the atmospheric fractionator will have
an ASTM end point between 700 to 850 F.
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The design distillate products from an atmospheric fractionator are
determined by the owner and depend upon economic factors at the location
of the atmospheric fractionator.
The above detailed description of the present invention is given for
explanatory purposes. It will be apparent to those skilled in the art that
numerous changes and modifications can be made without departing from
the scope of the invention. Accordingly, the whole of the foregoing
description is to be construed in an illustrative and not a limitative sense,
the
scope of the invention being defined solely by the appended claims.
