Systems and methods for external processing of flash zone gas oil from a delayed coking process

Abstract

Systems and methods for the external processing flash zone gas oil by recycling it through a vacuum residuum hydroprocessing unit before reentering the delayed coking process.

Description

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not applicable.

FIELD OF THE INVENTION

The present invention generally relates to systems and methods for the external processing of flash zone gas oil from a delayed coking process. More particularly, the present invention relates to the external processing of flash zone gas oil from a delayed coking process by recycling it through a vacuum residuum hydroprocessing unit before reentering the delayed coking process.

BACKGROUND OF THE INVENTION

The gas oil from the flash zone of a fractionator in a delayed coking process (hereinafter flash zone gas oil or “FZGO”) is a heavier product with a higher boiling point and lower quality than heavy coker gas oil. Thus, it has few uses as a refinery intermediate feedstock and would normally be used to produce heavy fuel oil, which is a low-value product. FZGO is normally recycled back as feed to the heater in a conventional delayed coking process system. This recycle, also known as a natural recycle, consumes unit capacity and thus, replaces the fresh coker feed, also known as crude vacuum residuum feed, with a vacuum residuum feed that includes recycled FZGO. Almost all delayed coking processes recycle the FZGO to extinction within the delayed coking process and thus, no external product with FZGO is produced. As a result, the conventional delayed coking process produces a lower yield of higher valued products such as, for example, gas, naphtha, light gas oil and heavy gas oil hereinafter referred to as lighter hydrocarbons. Additionally, the conventional delayed coking process produces a higher yield of low value petroleum coke.

In FIG. 1, a schematic diagram illustrates the recovery of FZGO in one embodiment of a standard delayed coking process system 100 that includes a heater 102, two coke drums 104, a fractionator 106 and a fractionator bottoms line 108. The fractionator bottoms line 108 includes vacuum residuum feed in the natural recycle that reenters the fractionator 106 with the crude vacuum residuum feed. The system 100 illustrates how a conventional delayed coking process system may be modified to remove FZGO as a separate product from the fractionator 106 for further processing or blending to produce fuel oil. Other separate products, such as gas, naphtha, light coker gas oil and heavy coker gas oil, are also removed from the fractionator 106. Although the system 100 will increase the unit capacity in the heater 102 for crude vacuum residuum feed by removing FZGO from the natural recycle, the FZGO can be difficult to process as a separate product because it contains a high asphaltene content and a high metals content. The removed FZGO thus, may adversely affect the operations and reliability of standard fixed bed catalyst hydrocracking/hydrotreating.

There are several types of hydroprocessing that can be used to upgrade crude vacuum residuum to lighter hydrocarbon products, which is referred to hereinafter as vacuum residuum hydroprocessing. Vacuum residuum hydroprocessing may include, for example, any process that converts crude vacuum residuum with hydrogen and a catalyst into lighter molecules. Vacuum residuum hydroprocessing thus, includes fixed bed catalyst hydrocracking/hydrotreating, ebullated bed hydrocracking, and dispersed catalyst hydrocracking that crack the crude vacuum residuum into hydrocarbons such as gas, naphtha, light gas oil and heavy gas oil.

In FIG. 2, a schematic diagram illustrates a vacuum residuum hydroprocessing unit 202 implemented with another embodiment of a standard delayed coking process system 200. The system 200 includes the same components as the standard delayed coking process system 100 in FIG. 1 except that the fractionator bottoms line 108 includes FZGO as part of the vacuum residuum feed in the natural recycle instead of removing FZGO as a separate product. The crude vacuum residuum enters the vacuum residuum hydroprocessing unit 202 for fixed bed catalyst hydrocracking/hydrotreating, ebullated bed hydrocracking or dispersed catalyst hydrocracking, which produces gas, naphtha, light gas oil, heavy gas oil and another source of vacuum residuum feed in feed line 204 that represents unconverted (uncracked) oil. The process illustrated in FIG. 2 suffers from the same disadvantages as the conventional delayed coking process.

SUMMARY OF THE INVENTION

The present invention therefore, meets the above needs and overcomes one or more deficiencies in the prior art by providing systems and methods for the external processing of flash zone gas oil from a delayed coking process, by recycling it through a vacuum residuum hydroprocessing unit before reentering the delayed coking process.

In one embodiment, the present invention includes a system for external processing of flash zone gas oil from a delayed coking process, which comprises: i) a vacuum residuum hydroprocessing unit for converting the flash zone gas oil by one of ebullated bed hydrocracking and dispersed catalyst hydrocracking; ii) a delayed coking process system for producing the flash zone gas oil; iii) a flash zone gas oil line in fluid communication between the vacuum residuum hydroprocessing unit and the delayed coking process system configured for carrying only the flash zone gas oil from the delayed coking process system to the vacuum residuum hydroprocessing unit; and iv) a feed line directly connecting the vacuum residuum hydroprocessing unit and a fractionator in the delayed coking process system.

In another embodiment, the present invention includes a method for external processing of flash zone gas oil from a delayed coking process, which comprises: i) producing flash zone gas oil from a delayed coking process system; ii) carrying only the flash zone gas oil from the delayed coking process system to a vacuum residuum hydroprocessing unit; and iii) converting the flash zone gas oil in the vacuum residuum hydroprocessing unit by one of ebullated bed hydrocracking and dispersed catalyst hydrocracking.

Additional aspects, advantages and embodiments of the invention will become apparent to those skilled in the art from the following description of the various embodiments and related drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described below with references to the accompanying drawings, in which like elements are referenced with like numerals, wherein:

FIG. 1 is a schematic diagram illustrating the recovery of flash zone gas oil in one embodiment of a standard delayed coking process system.

FIG. 2 is a schematic diagram illustrating a standard vacuum residuum hydroprocessing unit implemented within another embodiment of a standard delayed coking process system.

FIG. 3 is a schematic diagram illustrating another vacuum residuum hydroprocessing unit implemented within another embodiment of a delayed coking process system according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The subject matter of the present invention is described with specificity, however, the description itself is not intended to limit the scope of the invention. The subject matter thus, might also be embodied in other ways, to include different steps or combinations of steps similar to the ones described herein, in conjunction with other technologies. Moreover, although the term “step” may be used herein to describe different elements of methods employed, the term should not be interpreted as implying any particular order among or between various steps herein disclosed unless otherwise expressly limited by the description to a particular order. While the following description refers to external processing of delayed coker flash zone gas oil, the systems and methods of the present invention are not limited thereto and may include other applications in which the processing may be applied to achieve similar results.

Referring now to FIG. 3, a schematic diagram illustrates another vacuum residuum hydroprocessing unit 302 implemented within another embodiment of a delayed coking process system 300 according to the present invention. The system 300 includes the same components as the standard delayed coking process system 100 in FIG. 1 except that the FZGO is returned to the vacuum residuum hydroprocessing unit 302 through FZGO line 301 instead of removing it for further processing or blending to produce fuel oil. The crude vacuum residuum enters the vacuum residuum hydroprocessing unit 302 mixed with the FZGO for ebullated bed hydrocracking or dispersed catalyst hydrocracking, which produces gas, naphtha, light gas oil, heavy gas oil and another source of vacuum residuum feed for feed line 304 that includes unconverted (uncracked) FZGO. Because the conversion level within the vacuum residuum hydroprocessing unit 302 is relatively low (approx. 65%) the unconverted FZGO is recycled back to the system 300 until extinction. In this manner, the FZGO is recycled between the fractionator 106 and the vacuum residuum hydroprocessing unit 302, instead of sending it to a low-value disposition for further processing as illustrated in FIG. 1 or naturally recycling it as illustrated in FIG. 2, which yields more valuable light fuel products. In other words, removing the FZGO and returning it to the vacuum residuum hydroprocessor unit 302 for ebullated bed hydrocracking or dispersed catalyst hydrocracking converts much of the FZGO to higher quality lighter hydrocarbon products than if the FZGO remained in the natural recycle of the system 300. And, if the FZGO was processed in a vacuum residuum hydroprocessor designed for fixed bed catalyst hydrocracking/hydrotreating, the only product removed would be a low-value low-sulfur fuel oil.

Optionally, the Heavy Coker Gas Oil removed from the fractionator 106 may also be returned to the vacuum residuum hydroprocessing unit 302 through a heavy coker gas oil (“HCGO”) line 306. In this embodiment, the crude vacuum residuum enters the vacuum residuum hydroprocessing unit 302 mixed with the FZGO and the HCGO for producing the same products with a higher quality. In other words, the vacuum residuum hydroprocessing unit 302 is designed to handle FZGO much better than if it were designed for fixed bed catalyst hydrocracking/hydrotreating.

When FZGO is recycled within the natural recycle of a delayed coking process, approximately 50% of the FZG-O) is converted to coke while the rest is upgraded to more valuable lighter hydrocarbons. If the FZGO is removed from the delayed coking process and returned to the vacuum residuum hydroprocessing unit as illustrated in FIG. 3, then approximately 65% of the FZGO is converted to lighter hydrocarbons and the remaining unconverted FZGO is sent as feed to the delayed coking process where approximately 50% is converted to lighter hydrocarbons. Approximately 82% of the FIGO therefore, can be converted (upgraded), rather than 50% if it remains in the natural recycle of a delayed coking process.

Example

In this example, three cases are presented that represent the processes illustrated in FIGS. 1-3, respectively. Representative yields for the three cases are illustrated in FIGS. 1-3 and Table 1 (below), which are based upon a crude oil slate of 50% Arabian Light crude oil and 50% Arabian Heavy crude oil. The representative yields are also based on a 65% conversion of FZGO by weight in the vacuum residuum hydroprocessing unit (VR HP Unit). With Case 1 being the base, Case 2 represents an increase of 8.3% in the yield of lighter hydrocarbons. Case 3 represents an increase of 9.0% over Case 1 and 0.6% over Case 2. For a refinery with 50,000 barrels per day (BPD) of vacuum residuum, Case 2 shows an increase of 3,620 barrels per day of total liquid products over Case 1; however, 1,658 barrels per day of that production is FZGO, which can only be used for low-value residual fuel oil and not upgraded to transportation fuels. Case 3 shows an increase of 3,909 barrels per day over Case 1 and 289 barrels per day over Case 2.

	TABLE 1
	Units	Case 1	Case 2	Case 3
Vacuum Residuum	BPD	50000	50000	50000
Feed to VR HP Unit	BPD		50000	50655
Conversion	Wt. %		65.0%	65.0%
C4− Yield	Vol. %		1.1%	1.1%
C5-350F Yield	Vol. %		10.0%	10.0%
350F-650F yield	Vol. %		16.7%	16.7%
650F-950F	Vol. %		33.3%	33.3%
950F+ Yield	Vol. %		38.9%	38.9%
Unconverted Oil (FZGO)	BPD		19435	19689
Feed to Fractionator	BPD	50000	19435	19689
C4− Yield	Vol. %	18.9%	18.9000%	18.9%
C5-350F Yield	Vol. %	17.4%	17.3800%	17.4%
350F-650F yield	Vol. %	28.2%	28.1500%	28.2%
650F-950F Yield	Vol. %	19.3%	20.9820%	19.3%
FZGO Yield	Vol. %	3.3%	0.0000%	3.3%
Coke Yield	Wt. %	31.0%	33.3%	31.0%
VR HP 950-Products	BPD	0	30555	30954
Coker HCGO-Products	BPD	41877	16600	16490
Coker FZGO Product	BPD	1658	0	0
Total Liquid Products	BPD	43535	47155	47444
Percent Increase	%	Base	8.3%	9.0%
Increase over Case 2			Base	0.6%
Total C4− Products (Gas)	BPD	9450	4228	4283
C5-350F Product (Naptha)	BPD	8690	8378	8487
350F-650F Product (Light	BPD	14075	13806	13986
Coker Gas Oil and Light Gas Oil)
650F-950F Product (Heavy	BPD	9662	20743	20687
Coker Gas Oil and Heavy Gas
Oil)
FZGO Product (FZGO)	BPD	1658	0	0

As demonstrated by the foregoing example, the process illustrated in FIG. 3 improves the yield of total liquid products and significantly reduces the amount of HCGO products compared to the processes illustrated in FIGS. 1-2. In addition, the process illustrated in FIG. 3 also increases the yield of lighter hydrocarbons compared to the processes illustrated in FIGS. 1-2,

While the present invention has been described in connection with presently preferred embodiments, it will be understood by those skilled in the art that it is not intended to limit the invention to those embodiments. It is therefore, contemplated that various alternative embodiments and modifications may be made to the disclosed embodiments without departing from the spirit and scope of the invention defined by the appended claims and equivalents thereof.

Claims

1. A system for external processing of flash zone gas oil from a delayed coking process, which comprises: a vacuum residuum hydroprocessing unit for converting the flash zone gas oil by one of ebullated bed hydrocracking and dispersed catalyst hydrocracking;a delayed coking process system for producing the flash zone gas oil;a flash zone gas oil line in fluid communication between the vacuum residuum hydroprocessing unit and the delayed coking process system configured for carrying hydroprocessing unit; anda feed line directly connecting the vacuum residuum hydroprocessing unit and a fractionator in the delayed coking process system.

2. The system of claim 1, wherein at least 65% of the flash zone gas oil is converted by the vacuum residuum hydroprocessing unit to lighter hydrocarbons.

3. The system of claim 2, wherein the lighter hydrocarbons comprise at least one of gas, naphtha, light gas oil and heavy gas oil.

4. The system of claim 1, wherein the flash zone gas oil line carries only unfiltered flash zone gas oil directly from the delayed coking process system to the vacuum residuum hydroprocessing unit.

5. A method for external processing of flash zone gas oil from a delayed coking process, which comprises: producing flash zone gas oil from a delayed coking process system;carrying only the flash zone gas oil from the delayed coking process system to a vacuum residuum hydroprocessing unit; andconverting the flash zone gas oil in the vacuum residuum hydroprocessing unit by one of ebullated bed hydrocracking and dispersed catalyst hydrocracking.

6. The method of claim 5, further comprising carrying a vacuum residuum feed comprising unconverted flash zone gas oil from the vacuum residuum hydroprocessing unit to the delayed coking process system.

7. The method of claim 6, wherein at least 65% of the flash zone gas oil is converted by the vacuum residuum hydroprocessing unit to lighter hydrocarbons.

8. The method of claim 7, wherein the lighter hydrocarbons comprise at least one of gas, naphtha, light gas oil and heavy gas oil.