Note: Descriptions are shown in the official language in which they were submitted.
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I HYDROPROCESSING IN MULTIPLE BEDS WITH
2 INTERMEDIATE FLASH ZONES
3
4 This application is a continuation-in-part of co-pending application
10/001,737,
filed October 25, 2001 and claims priority therefrom.
6
7 FIELD OF THE INVENTION
8
9 The invention relates to hydrocracking, and more particularly to
hydrocracking
occurring in more than one stage.
11
12 BACKGROUND OF THE INVENTION
13
14 In the refining of crude oil, vacuum gas oil hydrotreaters and
hydrocrackers
are employed to remove impurities such as sulfur, nitrogen and metals from
16 the feed. Typically, the middle distillate boiling material (boiling in the
range
17 from 250 F - 735 F) from VGO hydrotreating or moderate severity
18 hydrocrackers does not meet the smoke point, the cetane number or the
19 aromatic specification required.
21 Removal of these impurities in subsequent hydroprocessing stages (often
22 known as upgrading), creates more valuable middle distillate products.
23 Hydroprocessing technology (which encompasses hydrotreating,
24 hydrocracking and hydrodewaxing processes) aims to increase the value of
the crude oil by fundamentally rearranging molecules. The end products are
26 also made more environmentally friendly.
27
28 In most cases, this middle distillate is separately upgraded by a middle
29 distillate hydrotreater or, alternatively, the middle distillate is blended
into the
general fuel oil pool or used as home heating oil. Recently hydroprocessing
31 schemes have been developed which permit the middle distillate to be
32 hydrotreated in the same high pressure loop as the vacuum gas oil
33 hydrotreating reactor or the moderate severity hydrocracking reactor. The
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1 investment cost saving and/or utilities saving are significant since a
separate
2 middle distillate hydrotreater is not required.
3
4 There are several U.S. patent publications which are directed to multistage
hydroprocessing within a single high pressure hydrogen loop. In U.S. Patent
6 Application 20030111386, high conversion of heavy gas oils and the
7 production of high quality middle distillate products is possible in a
single high-
8 pressure loop with reaction stages operating at different pressure and
9 conversion levels. The flexibility offered is great and allows the refiner
to
avoid decrease in product quality while at the same time minimizing capital
11 cost. Feeds with varying boiling ranges are introduced at different
sections of
12 the process, thereby minimizing the consumption of hydrogen and reducing
13 capital investment.
14
U.S. Patent Application 2003111387 also discloses multi-stage
16 hydroprocessing for the production of middle distillates. A major benefit
of
17 this invention is the potential for simultaneously upgrading difficult
cracked
18 stocks such as Light Cycle Oil, Light Coker Gas Oil and Visbroken Gas Oil
or
19 Straight-Run Atmospheric Gas Oils utilizing the high-pressure environment
required for mild hydrocracking.
21
22 SUMMARY OF THE INVENTION
23
24 This invention, as are those discussed in the Background, is directed to
processes for upgrading the fraction boiling in the middle distillate range
26 which is obtained from VGO hydrotreaters and moderate severity
27 hydrocrackers. This invention preferably involves a multiple stage process
28 employing a single hydrogen loop. It could, however, be used in any fixed
29 bed hydroprocessing scheme such as mild hydrocracking, conventional single
stage or two stage hydrocracking and hydrotreating applications.
31
32 In this invention, removing distillate products as they are formed helps to
33 improve the environment of the cracking reactions by more effective
utilization
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1 of the reactor space, hydrogen and catalyst. Improved selectivity for
2 distillates results, providing the yield of low per pass conversion, but
without
3 recycling large quantities of recycle oil.
4
The investment cost saving, as well as utilities savings, are significant
since
6 the hydrocracking reactor could be potentially taken out of a conventional
7 recycle gas loop. Less catalyst volume and less hydrogen are required in the
8 hydrocracking reactor as well. This invention may be employed in a reactor
9 having multiple catalyst beds, or in a scheme employing several small,
single
bed reactors in series. Improved catalyst kinetics and activity also result
from
11 this invention.
12
13 The hydroprocessing method of the instant invention, which has at least two
14 reaction stages, comprises the following steps:
16 (a) passing a hydrocarbon feed into a first reaction stage which is
17 maintained at hydroprocessing conditions, where it is contacted
18 with a catalyst in at least one fixed bed and at least a portion of
19 the feed is converted;
21 (b) passing the effluent of step (a) to a hot high pressure separation
22 zone;
23
24 (c) separating the stream of step (b) into an unconverted liquid
effluent and a stream comprising converted products having
26 boiling points below that of the feed, said products being
27 subsequently passed to fractionation;
28
29 (d) passing the unconverted liquid effluent from step (c) to a second
reaction stage, said stage comprising a plurality of reaction
31 zones, wherein each zone is maintained at hydrocracking
32 conditions and separation occurs between each zone;
33
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I (e) contacting the feed in the first reaction zone of step (d) with a
2 catalyst in a fixed bed, thereby converting at least a portion of
3 the feed;
4
(f) separating the effluent of step (e) into an unconverted liquid
6 effluent, and a hydrogen-rich converted stream;
7
8 (g) passing the unconverted liquid effluent from step (f) to a second
9 reaction zone of the second stage, the zone being maintained at
hydrocracking conditions;
11
12 (h) contacting the feed in the second reaction zone of step (g) with
13 a catalyst in a fixed bed, thereby converting at least a portion of
14 the feed;
16 (i) fractionating the effluent of step (h) to produce one or more
17 middle distillate product streams.
18
19 BRIEF DESCRIPTION OF THE FIGURE
21 The Figure illustrates a schematic flow diagram of the instant invention.
It is a
22 schematic of a two-stage hydrocracker. The second stage possesses at least
23 two reaction zones.
24
DETAILED DESCRIPTION OF THE INVENTION
26
27 Description Of The Preferred Embodiment
28
29 The Figure illustrates the preferred embodiment of the invention. The oil
feed
in line 1 is preheated, and pumped up to the first stage hydrotreating reactor
31 pressure by the first stage feed pump (not shown). Oil feed in line 1 is
32 combined with preheated recycle gas (line 2) to form line 3. Line 3 is
further
33 heated by process heat exchange (not shown). Line 3 is also heated in the
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1 first stage feed furnace 5.
2
3 The combined feed is sent to the first stage hydrotreating reactor 10. In
this
4 reactor, the feed is hydrotreated and partially hydrocracked. Hydrogen
recycle gas (line 4) is used to quench the reaction exothermic heat release.
6 The effluent from this reactor, line 6, is composed of H2S, NH3, light
gases,
7 naphtha, middle distillate and hydrotreated heavy gas oil.
8
9 This first stage reactor effluent 6 is then cooled by preheating feed and/or
steam generation (exchanger bank 25) and routed to a Hot High Pressure
11 Separator (HHPS) 30 situated between the first stage hydrotreating reactor
12 and the second stage hydrocracking reactor. In HHPS, most of the 700-
13 material is removed through line 8 and sent to hydrogen recovery and
product
14 fractionation. Material in line 8 is cooled (by steam generation or process
heat exchange) and sent to a Cold High Pressure Separator (not shown) on
16 its way to the recycle gas compressor.
17
18 HHPS is operated at a slightly lower pressure than the first stage
19 hydrotreating reactor. HHPS bottoms, line 7, mainly composed of
unconverted oil, is let-down under pressure (valve 35), combined with line 12,
21 mixed with fresh makeup hydrogen (line 13) and routed to the inlet of the
22 second stage hydrotreating or hydrocracking reactor 20. Line 12 is composed
23 of recycle oil from fractionation (line 9) and fresh aromatic feed oil
(line 11).
24
The liquid from the top bed (20a) of this hydrotreating or hydrocracking
26 reactor is taken out (line 16) and flashed in a side vessel 40. Distillate
27 products are removed overhead via line 17. The liquid from this side vessel
28 40 is removed via line 18 and is cooled in an indirect heat exchanger 45
29 heating a process stream and put back to the bed below (20b) after added
adequate fresh makeup hydrogen (line 23). This set is repeated for the
31 subsequent beds in the hydrocracking reactor, with the effluent of bed 20b
32 (line 19) being taken out and flashed in a side vessel 50. Distillate
products
33 are removed overhead via line 21. The liquid from this side vessel 50 is
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1 removed via line 22 and is cooled in an indirect heat exchanger 55 heating a
2 process stream and put back to the bed below (20c) under its own pressure
3 by gravity flow after added adequate fresh makeup hydrogen (line 26). The
4 final liquid product is removed via line 23.
6 The total fresh makeup hydrogen for the plant is routed through the second
7 stage hydrocracking reactor and the excess hydrogen arrives back in the
8 recycle gas loop at the recycle gas compressor suction to satisfy the needs
of
9 first stage reactor.
11 The concept of removing products as they are formed results in better
12 utilization of the given second stage hydrocracking reactor catalyst volume
by
13 incrementally increasing the true residence time available for the still
14 unconverted oil and by delivering shots of high purity hydrogen to where
specifically needed in the liquid phase. This further gives an incremental
16 kinetics boost and results in higher per pass conversion. This gives the
direct
17 benefit of less recycle liquid from fractionator bottoms to achieve desired
18 target conversion.
19
A customized hydrocracking catalyst system in an ascending/descending
21 temperature profile would be used in the second stage reactor using
relatively
22 mild hydrocracking catalyst at the top beds and progressively higher
activity
23 stable (zeolitic) hydrocracking catalysts in subsequent beds.
24
Converted material from the Cold High Pressure Separator, side vessels, and
26 reactor effluents from subsequent stages could be combined or kept separate
27 and sent to product distillation and recovery. Or the second stage effluent
28 could be post-treated by adding catalyst in the side vessels or in a
29 downstream, low pressure, cleaner environment post-treat step.
31 The product distillation (not shown) could be a combined unit operation for
the
32 first stage hydrotreating reactor and second stage hydrocracking reactor
33 products or could be a divided unit operation (within one shell) for
separate
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1 distillation of first stage hydrotreating reactor and second stage
hydrocracking
2 reactor products.
3
4 In either step, the HHPS bottoms liquid would be cooled only to around 650F
(or desired second stage hydrocracking reactor inlet temperature) and using a
6 hot high differential pressure pump directly sent to the second stage inlet
7 without the need for an intermediate cooling/heating train or storage or a
8 furnace. If required, any startup heating requirement of the second stage
9 hydrocracking reactor could be combined with the first stage hydrotreating
reactor feed furnace.
11
12 Feeds
13
14 A wide variety of hydrocarbon feeds may be used in the instant invention.
Typical feedstocks include any heavy or synthetic oil fraction or process
16 stream having a boiling point above 392F (200C). Feeds to this invention
17 generally include hydrocarbons boiling in the range form 500F to 1500F.
18 Such feedstocks include vacuum gas oils, demetallized oils, deasphalted
oil,
19 Fischer-Tropsch streams, FCC and coker distillate streams, heavy crude
fractions, etc. Other streams include heavy atmospheric gas oil, d-elayed
21 coker gas oils, visbreaker gas oils, aromatic extracts, heavy residue
thermal
22 or catalyst upgrader gas oils, and thermal or catalyst fluid cracker cycle
oils.
23 Typical feedstocks contain from 100-5000 ppm nitrogen and from 0.2-5 wt. %
24 sulfur.
26 The recycle oil (from the product distillation) can be introduced at the
second
27 stage hydrocracking inlet or at a suitable bed.
28
29 Products
31 The hydrocracking process of this invention is especially useful in the
32 production of middle distillate fractions boiling in the range of about 250
-
33 700F (121 - 371 C). A middle distillate fraction is defined as having a
boiling
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1 range from about 250 to 700F. The term "middle distillate" includes the
2 diesel, jet fuel and kerosene boiling range fractions. The kerosene or jet
fuel
3 boiling point range refers to the range between 280 and 525F (138-274C).
4 The term "diesel boiling range" refers to hydrocarbons boiling in the range
from 250 to 700F (121 - 371 C). Gasoline or naphtha normally boils in the
6 range below 400 (204C). Boiling ranges of various product fractions
7 recovered in any particular refinery will vary with such factors as the
8 characteristics of the crude oil source, local refinery markets and product
9 prices.
11 Conditions
12
13 [0032] Hydroprocessing conditions is a general term which refers primarily
in
14 this application to hydrocracking or hydrotreating, preferably
hydrocracking.
16 [0033] Hydrotreating conditions include a reaction temperature between 400F
17 - 900F (204)C - 482C), preferably 650F - 850F (343C - 454C); a pressure
18 between 500 to 5000 psig (pounds per square inch gauge) (3.5-34.6 MPa),
19 preferably 1000 to 3000 psig (7.0-20.8 MPa); a feed rate (LHSV) of 0.5 hr (-
1)
to 20 hr (-1) (v/v); and overall hydrogen consumption 300 to 2000 scf per
21 barrel of liquid hydrocarbon feed (53.4-356 m ( 3)/m (3 )feed).
22
23 [0034] Typical hydrocracking conditions include a reaction temperature of
24 from 400F - 950F (204C - 510C), preferably 650F - 850F (343C - 454C).
Reaction pressure ranges from 500 to 5000 psig (3.5-34.5 MPa), preferably
26 1500-3500 psig (10.4-24.2 MPa). LHSV ranges from 0.1 to 15 hr (-1)(v/v),
27 preferably 0.25-2.5 hr (-1). Hydrogen consumption ranges from 500 to 2500
28 scf per barrel of liquid hydrocarbon feed (89.1445m (3)H (2)/m (3)feed).
29
Cataiyst
31
32 A hydroprocessing zone may contain only one catalyst, or several catalysts
in
33 combination.
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1
2 The hydrocracking catalyst generally comprises a cracking component, a
3 hydrogenation component and a binder. Such catalysts are well known in the
4 art. The cracking component may include an amorphous silica/alumina phase
and/or a zeolite, such as a Y-type or USY zeolite. Catalysts having high
6 cracking activity often employ REX, REY and USY zeolites. The binder is
7 generally silica or alumina. The hydrogenation component will be a Group VI,
8 Group VII, or Group VIII metal or oxides or sulfides thereof, preferably one
or
9 more of molybdenum, tungsten, cobalt, or nickel, or the sulfides or oxides
thereof. If present in the catalyst, these hydrogenation components generally
11 make up from about 5% to about 40% by weight of the catalyst.
Alternatively,
12 noble metals(preferably used in lower beds), especially platinum and/or
13 palladium, may be present as the hydrogenation component, either alone or
in
14 combination with the base metal hydrogenation components molybdenum,
tungsten, cobalt, or nickel. If present, the platinum group metals will
generally
16 make up from about 0.1 % to about 2% by weight of the catalyst.
17
18 Hydrotreating catalyst is preferably used in the upper beds. Hydrotreating
19 catalysts will typically be a composite of a Group VI metal or compound
thereof, and a Group VIII metal or compound thereof supported on a porous
21 refractory base such as alumina. Examples of hydrotreating catalysts are
22 alumina supported cobalt-molybdenum, nickel sulfide, nickel-tungsten,
cobalt-
23 tungsten and nickel-molybdenum. Typically, such hydrotreating catalysts are
24 presulfided.
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