Integrating An Atmospheric Fractionator With A Diluent Recovery Unit And A Resid Hydrocracker

Abstract

This is a unique way to optimize an existing refinery to process heavy bitumen. The upgrade utilizes a diluent recovery unit (DRU) in front of a Resid Hydrocracker. The recovered bitumen from the Resid Hydrocracker is fed to an integrated atmospheric fractionator to convert the light sweet refinery to diluted bitumen.

Description

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 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 application Ser. No. 12/378,671 filed Feb. 18, 2009, Ser. No. 12/378,610 filed on Feb. 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.

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.

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.

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 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:

• • i. Liquefied Petroleum Gas (LPG), which includes ethane, propane, butanes and isopentane.
  • ii. 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.

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.

Claims

1. A unique process for conditioning bitumen so that the bitumen can be processed in an existing light sweet refinery comprising the steps of:

providing a blend of a heavy whole bitumen and diluents to produce a diluted bitumen;

feeding the blend to a diluent recovery unit (DRU);

removing the diluents from the diluted bitumen, in the DRU without additional metallurgy upgrades, to produce a recovered whole bitumen;

feeding the recovered whole bitumen to a Resid Hydrocracker;

recovering a conditioned whole bitumen having reduced sulfur and nitrogen contents, having eliminated corrosive components, and having a boiling point which is lower than the boiling point of a heavy hydrocarbonaceous feedstock from the Resid Hydrocracker; and

feeding the recovered conditioned lowered boiling point whole bitumen from the Resid Hydrocracker to an integrated atmospheric fractionator.

2. The process according to claim 1 further comprising the steps of:

recovering an atmospheric tower bottoms (ATB) product from the atmospheric fractionator; and

feeding the ATB product to a vacuum unit.

3. The process according to claim 1 further comprising the step of:

feeding the diluents removed from the diluted bitumen at the DRU to the atmospheric fractionator for further processing to avoid a separate DRU overhead system.

4. The process according to claim 1 further comprising the steps of:

recovering an overhead material from the atmospheric fractionator and using the overhead material to preheat the diluted bitumens feeding the DRU.

5. The process according to claim 1 further comprising the step of blending Resid Hydrocracker ATB with conventional ATB for stability control.