U.S. patent application number 12/368903 was filed with the patent office on 2010-08-12 for selective staging hydrocracking.
This patent application is currently assigned to Chevron U.S.A. Inc.. Invention is credited to Subhasis Bhattacharya.
Application Number | 20100200459 12/368903 |
Document ID | / |
Family ID | 42539517 |
Filed Date | 2010-08-12 |
United States Patent
Application |
20100200459 |
Kind Code |
A1 |
Bhattacharya; Subhasis |
August 12, 2010 |
SELECTIVE STAGING HYDROCRACKING
Abstract
This invention is directed to a high conversion hydrocracking
(HCR) unit to produce premium middle distillate fuel. Unconverted
oil which is low in sulfur is fed to a Fluid Catalytic Cracking
(FCC) unit. The process results in reduced hydrogen consumption and
optimum reactor capacity. Feed is hydrotreated and separated into
liquid and vapor streams. The vapor stream is passed to further
processing and light ends recovery. The liquid stream is passed to
a vacuum distillation column, where it is separated into at least
three streams, the first stream comprising low boiling products and
light ends, a second, higher boiling stream comprising the feed to
a second hydroprocessing zone and third stream comprising
unconverted oil. The second stream is passed to the second
hydroprocessing zone, producing effluents which boil in the
distillate range. The second hydroprocessing zone is generally a
fuels hydrocracking unit.
Inventors: |
Bhattacharya; Subhasis;
(Walnut Creek, CA) |
Correspondence
Address: |
CHEVRON CORPORATION
P.O. BOX 6006
SAN RAMON
CA
94583-0806
US
|
Assignee: |
Chevron U.S.A. Inc.
|
Family ID: |
42539517 |
Appl. No.: |
12/368903 |
Filed: |
February 10, 2009 |
Current U.S.
Class: |
208/59 |
Current CPC
Class: |
C10G 69/04 20130101;
C10G 2400/08 20130101; C10G 65/04 20130101; C10G 65/12 20130101;
C10G 2400/04 20130101; C10G 65/10 20130101 |
Class at
Publication: |
208/59 |
International
Class: |
C10G 65/00 20060101
C10G065/00 |
Claims
1. A method for hydroprocessing a hydrocarbon feedstock, which
provides maximum flexibility in terms of feed quality variations
and desired overall conversion to distillate products at minimum
investment cost, said method employing multiple hydroprocessing
zones within a single reaction loop, each zone having one or more
catalyst beds, comprising the following steps: (a) passing a
hydrocarbonaceous feedstock to a first hydroprocessing zone having
one or more beds containing hydroprocessing catalyst, the
hydroprocessing zone being maintained at hydroprocessing
conditions, wherein the feedstock is contacted with catalyst and
hydrogen; (b) passing the effluent of step (a) directly to a
separator, wherein the effluent is separated to produce a vapor
stream comprising hydrogen, hydrogen sulfide, ammonia, and
hydrocarbonaceous compounds boiling at a temperature below the
boiling range of a diesel stream, and a liquid stream comprising
hydrocarbonaceous compounds boiling at a temperature above the
range of a diesel stream; (c) passing the vapor stream of step (b)
to further processing and light ends recovery, and passing the
liquid stream of step (b) to a vacuum distillation column, where it
is separated into at least three streams, the first stream
comprising low boiling products and light ends, a second, higher
boiling stream comprising the feed to a second hydroprocessing zone
and third stream comprising unconverted oil; (d) passing the second
stream of step (c) to the second hydroprocessing zone, producing
effluents which boil in the distillate range.
2. The process of claim 1, wherein the second hydroprocessing zone
of step (d) is a fuels hydrocracker.
3. The process of claim 1, wherein production of specific products
may be optimized in the distillation column by recycle between
trays.
4. The process of claim 1, wherein at least a portion of the
stripped unconverted oil of step (c) is passed to a fluid catalytic
cracking unit as feed.
5. The process of claim 1, wherein the second hydroprocessing zone
contains at least one bed of hydroprocessing catalyst suitable for
aromatic saturation and ring opening.
6. The process of claim 1, wherein the second stream is contacted
under hydroprocessing conditions with the hydroprocessing catalyst,
in the presence of hydrogen to produce middle distillate
products.
7. The process of claim 1, wherein the hydroprocessing conditions
of step (a) comprise a reaction temperature of from 400.degree.
F.-950.degree. F. (204.degree. C.-510.degree. C.), a reaction
pressure in the range from 500 to 5000 psig (3.5-34.5 MPa), an LHSV
in the range from 0.1 to 15 hr-1 (v/v), and hydrogen consumption in
the range from 500 to 2500 scf per barrel of liquid hydrocarbon
feed (89.1-445 m.sup.3 H.sub.2/m.sup.3 feed).
8. The process of claim 7, wherein the hydroprocessing conditions
of step 1(a) comprise a temperature in the range from 650.degree.
F.-850.degree. F. (343.degree. C.-454.degree. C.), reaction
pressure in the range from 1500-3500 psig (10.4-24.2 MPa), LHSV in
the range from 0.25 to 2.5 hr-1, and hydrogen consumption in the
range from 500 to 2500 scf per barrel of liquid hydrocarbon feed
(89.1-445 m.sup.3 H.sub.2/m.sup.3 feed).
9. The process of claim 1, wherein the hydroprocessing conditions
of step 1(c) comprise a reaction temperature of from 400.degree.
F.-950.degree. F. (204.degree. C.-510.degree. C.), a reaction
pressure in the range from 500 to 5000 psig (3.5-34.5 MPa), an LHSV
in the range from 0.1 to 15 hr-1 (v/v), and hydrogen consumption in
the range from 500 to 2500 scf per barrel of liquid hydrocarbon
feed (89.1-445 m.sup.3 H.sub.2/m.sup.3 feed).
10. The process of claim 1, wherein the feed to step 1(a) comprises
hydrocarbons boiling in the range from 500.degree. F. to
1500.degree. F.
11. The process of claim 1, wherein the feed is selected from the
group consisting of vacuum gas oil, heavy atmospheric gas oil,
delayed coker gas oil, visbreaker gas oil, FCC light cycle oil, and
deasphalted oil.
12. The process of claim 1, wherein the hydroprocessing catalyst
comprises both a cracking component and a hydrogenation component,
wherein the cracking component may be amorphous or zeolitic.
13. The process of claim 12, wherein the hydrogenation component is
selected from the group consisting of Ni, Mo, W, Pt and Pd or
combinations thereof.
14. The process of claim 12, wherein the zeolitic component is
selected from the group consisting of Y, USY, REX, and REY
zeolites.
15. The process of claim 1, wherein the hydrotreating occurs in the
first reaction zone and hydrocracking occurs in the second reaction
zone.
Description
FIELD OF THE INVENTION
[0001] This invention is directed to a high conversion
hydrocracking (HCR) unit to produce premium middle distillate fuel.
Unconverted oil which is low in sulfur is fed to a Fluid Catalytic
Cracking (FCC) unit. The process results in reduced hydrogen
consumption and optimum reactor capacity.
BACKGROUND OF THE INVENTION
[0002] In the refining of crude oil, vacuum gas oil hydrotreaters
and hydrocrackers are employed to remove impurities such as sulfur,
nitrogen and metals from the feed. Typically, the middle distillate
boiling material (boiling in the range from 250.degree. F. through
735.degree. F.) from VGO hydrotreating or moderate severity
hydrocrackers does not meet the smoke point, the cetane number or
the aromatic specification required.
[0003] Removal of these impurities in subsequent hydroprocessing
stages (often known as upgrading), creates more valuable middle
distillate products. Hydroprocessing technology (which encompasses
hydrotreating, hydrocracking and hydrodewaxing processes) aims to
increase the value of the crude oil by fundamentally rearranging
molecules. The end products are also made more environmentally
friendly.
[0004] In most cases, this middle distillate is separately upgraded
by a middle distillate hydrotreater or, alternatively, the middle
distillate is blended into the general fuel oil pool or used as
home heating oil. Recently hydroprocessing schemes have been
developed which permit the middle distillate to be hydrotreated in
the same high pressure loop as the vacuum gas oil hydrotreating
reactor or the moderate severity hydrocracking reactor. The
investment cost saving and/or utilities saving are significant
since a separate middle distillate hydrotreater is not
required.
[0005] There are U.S. patents which are directed to multistage
hydroprocessing within a single high pressure hydrogen loop. In
U.S. Pat. No. 6,797,154, high conversion of heavy gas oils and the
production of high quality middle distillate products are possible
in a single high-pressure loop with reaction stages operating at
different pressure and conversion levels. The flexibility offered
is great and allows the refiner to avoid decrease in product
quality while at the same time minimizing capital cost. Feeds with
varying boiling ranges are introduced at different sections of the
process, thereby minimizing the consumption of hydrogen and
reducing capital investment.
[0006] U.S. Pat. No. 6,787,025 also discloses multi-stage
hydroprocessing for the production of middle distillates. A major
benefit of this invention is the potential for simultaneously
upgrading difficult cracked stocks such as Light Cycle Oil, Light
Coker Gas Oil and Visbroken Gas Oil or Straight-Run Atmospheric Gas
Oils utilizing the high-pressure environment required for
hydrocracking.
[0007] U.S. Pat. No. 7,238,277 provides very high to total
conversion of heavy oils to products in a single high-pressure
loop, using multiple reaction stages. The second stage or
subsequent stages may be a combination of co-current and
counter-current operation. The benefits of this invention include
conversion of feed to useful products at reduced operating
pressures using lower catalyst volumes. Lower hydrogen consumption
also results. A minimal amount of equipment is employed. Utility
consumption is also minimized.
[0008] U.S. Publication 20050103682 relates to a multi-stage
process for hydroprocessing gas oils. Preferably, each stage
possesses at least one hydrocracking zone. The second stage and any
subsequent stages possess an environment having a low heteroatom
content. Light products, such as naphtha, kerosene and diesel, may
be recycled from fractionation (along with light products from
other sources) to the second stage (or a subsequent stage) in order
to produce a larger yield of lighter products, such as gas and
naphtha. Pressure in the zone or zones subsequent to the initial
zone is from 500 to 1000 psig lower than the pressure in the
initial zone, in order to provide cost savings and minimize
overcracking.
[0009] A waxy vacuum column has traditionally been used downstream
of fractionator to segregate the feed to the isomerization dewaxing
unit from a slip stream from the vacuum column which is recycled to
second stage hydrocracker. Generally the first stage is run at
sufficiently high conversion to ensure that the unconverted oil is
suitable as second stage hydrocracking or isomerization dewaxing
feed.
SUMMARY OF THE INVENTION
[0010] Selective Staging Hydrocracking (SSH) is employed to process
high severity feed which contains high boiling straight run vacuum
gas oil (VGO). This VGO is obtained from difficult crude sources
which are blended with a high percentage of Heavy Coker Gas Oil
(high polycyclic aromatics, nitrogen content in the range of 5000
ppm and above). In this scheme, the first stage hydrocracker
operation and severity is optimized (lowered) to meet the FCC feed
quality requirements, which are much less stringent than the
requirements for the quality of the unconverted oil which feeds a
second stage hydrocracker or an isomerization dewaxing unit. In
addition, in the SSH scheme, 100% of second stage feed is the
middle cut, or heart cut side draw from the vacuum column.
[0011] This unique combination of selective conversions in the
first stage and second stage, using a vacuum column to process very
difficult feed containing a high percentage of heavy cracked stock
to produce premium grade jet and diesel fuel, is first of a kind
process application. Total reactor volume is about 30% lower
compared to previous schemes processing similar feed to achieve
similar performance targets.
[0012] This invention is directed to a high conversion
hydrocracking (HCR) unit to produce premium middle distillate fuel.
Unconverted oil which is low in sulfur is fed to a Fluid Catalytic
Cracking (FCC) unit. The process results in reduced hydrogen
consumption and optimum reactor capacity.
[0013] The patents disclosed above do not address the following
approaches to obtaining a high yield of premium quality jet and
diesel products: [0014] 1. Hydrotreating of fresh feed and
subsequent passing of unconverted oil to a vacuum column. A side
draw from the vacuum column is sent to a hydrocracking reactor
which processes clean feeds (feeds comprising few heteroatoms) and
the bottoms are sent to an FCC unit. The amount of bottoms sent to
FCC is dependent upon desired overall conversion. [0015] 2. A
process having flexibility to adjust the severity of the
hydrotreating reactor to handle relatively high end point feed as
well as feed variations from upstream adjustments, while
maintaining a steady feed from a vacuum column to the clean
hydrocracking reactor for full conversion to ultra high quality
distillate products. [0016] 3. Means of avoiding undesirable
over-saturation of the unconverted oil (UCO) from the hydrocracking
unit feeding the FCC unit, resulting in a significant reduction in
hydrogen consumption [0017] 4. Reduced reactor costs, due to the
fact that total reactor volume is about 30% lower compared to
previous schemes processing similar feed to achieve similar
performance targets.
[0018] A new, innovative hydrocracking process scheme has been
developed that provides maximum flexibility in terms of feed
quality variations and desired overall conversion to distillate
products at minimum investment cost. Fresh feed oil is first
processed in the ISOTREATING reactor containing hydrotreating and
some hydrocracking catalyst to achieve near complete demetallation,
hydrodenitrifrication, hydrodesulfurization and some aromatic
saturation to meet the FCC feed specifications.
[0019] The reactor effluents are send to recycle gas separation,
product fractionation and lights ends recovery sections. In this
new process scheme, the atmospheric fractionator bottom stream
containing heavier than diesel boiling material is sent to a vacuum
column, a first time application in fuels HDC, to separate the
second stage fed from the UCO. A heart-cut side draw is taken from
the vacuum column and sent to a clean Second-Stage ISOCRACKING
reactor for complete conversion to high quality distillate
products. The unconverted oil from Vacuum column bottom is an
excellent quality FCC feed.
[0020] The following are some of the unique advantages of this new
scheme with the new second stage feed vacuum column: [0021] 1.
Capability to adjust the first stage reactor severity to produce
on-specification FCC feed with varations in hydrocracker feedstocks
and flexibility to vary the second stage feed rate from the new
vacuum column to achieve desired overall conversion. [0022] 2.
Ability to maintain a sharp cut, steady feed flow to the clean
second stage reactor for full conversion to high quality
mid-distillate products. [0023] 3. Higher fraction of premium
quality distillate products from the clean second stage with lower
first stage conversion compared to the scheme without second stage
feed vacuum column. [0024] 4. Selective hydrogenation to minimize
overall hydrogen consumption. [0025] 5. Selective staging requires
lower reactor volume for similar catalyst system and performance
targets. With the second stage feed vacuum column, the first stage
reactor can be operated at much lower severity as compared to
existing industry practice to send fractionator bottoms to clean
second stage hydrocracking reactor. Also, the heart-cut side-draw
taken from the vacuum column constitutes a relatively easier to
process feed to the clean second stage reactor. Total reactor
weight for the combined first and second stage will be about 30%
lower in selective staging hydrocracking. [0026] 6. Flexibility to
draw high quality waxy lube base oil form the vacuum column
BRIEF DESCRIPTION OF THE FIGURE
[0027] The FIGURE illustrates the flow scheme of the current
invention.
DETAILED DESCRIPTION OF THE INVENTION
Feeds
[0028] A wide variety of hydrocarbon feeds may be used in the
instant invention. Typical feedstocks include any heavy or
synthetic oil fraction or process stream having a boiling point
above 392.degree. F. (200.degree. C.). Such feedstocks include
vacuum gas oils (VGO), heavy coker gas oil (HCGO), heavy
atmospheric gas oil (AGO), light coker gas oil (LCGO), visbreaker
gas oil (VBGO), demetallized oils (DMO), deasphalted oil (DAO),
Fischer-Tropsch streams, Light Cycle Oil, Light Cycle Gas Oil and
other FCC product streams.
Products
[0029] The process of this invention is especially useful in the
production of middle distillate fractions boiling in the range of
about 250-700.degree. F. (121-371.degree. C.). A middle distillate
fraction is defined as having an approximate boiling range from
about 250 to 700.degree. F. At least 75 vol %, preferably 85 vol %
of the components of the middle distillate have a normal boiling
point of greater than 250.degree. F. At least about 75 vol %,
preferably 85 vol % of the components of the middle distillate have
a normal boiling point of less than 700.degree. F. The term "middle
distillate" includes the diesel, jet fuel and kerosene boiling
range fractions. The kerosene or jet fuel boiling point range
refers to the range between 280 and 525.degree. F. (138-274.degree.
C). The term "diesel boiling range" refers to hydrocarbons boiling
in the range from 250 to 700.degree. F. (121-371.degree. C.).
[0030] Gasoline or naphtha may also be produced in the process of
this invention. Gasoline or naphtha normally boils in the range
below 400.degree. F. (204.degree. C.), or C.sub.5 to 400.degree. F.
Boiling ranges of various product fractions recovered in any
particular refinery will vary with such factors as the
characteristics of the crude oil source, local refinery markets and
product prices.
Conditions
[0031] "Hydroprocessing conditions" is a general term which refers
primarily in this application to hydrocracking or
hydrotreating.
[0032] Hydrotreating conditions include a reaction temperature
between 400.degree. F.-950.degree. F. (204.degree. C.-482.degree.
C.), preferably 600.degree. F.-850.degree. F. (315.degree.
C.-464.degree. C.); a pressure between 500 to 5000 psig (pounds per
square inch gauge) (3.5-34.6 MPa), preferably 1000 to 3000 psig
(7.0-20.8 MPa): a feed rate (LHSV) of 0.3 hr-1 to 20 hr-1 (v/v)
preferably from 0.5 to 4.0; and overall hydrogen consumption 300 to
2000 SCF per barrel of liquid hydrocarbon feed (63.4-356
m.sup.3/m.sup.3 feed).
[0033] Typical hydrocracking conditions include a reaction
temperature of from 400.degree. F.-950.degree. F. (204.degree.
C.-510.degree. C.), preferably 650.degree. F.-850.degree. F.
(315.degree. C.-454.degree. C.). Reaction pressure ranges from 500
to 5000 psig (3.5-4.5 MPa), preferably 1000-3000 psig (7.0-20.8
MPa). LHSV ranges from 0.1 to 15 hr-1 (v/v), preferably 0.5 to 5.0
hr-1. Hydrogen consumption ranges from 500 to 2500 SCF per barrel
of liquid hydrocarbon feed (89.1-445 m.sup.3H.sub.2/m.sup.3
feed).
Catalyst
[0034] A hydroprocessing zone may contain only one catalyst, or
several catalysts in combination.
[0035] The hydrocracking catalyst generally comprises a cracking
component, a hydrogenation component and a binder. Such catalysts
are well known in the 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 cracking activity often
employ REX, REY and USY zeolites. The binder is generally silica or
alumina. The hydrogenation component will be a Group VI, Group VII,
or Group VIII metal or oxides or sulfides thereof, preferably one
or more of molybdenum, tungsten, cobalt, or nickel, or the sulfides
or oxides thereof. If present in the catalyst, these hydrogenation
components generally make up from about 5% to about 40% by weight
of the catalyst. Alternatively, platinum group metals, especially
platinum and/or palladium, may be present as the hydrogenation
component, either alone or in combination with the base metal
hydrogenation components molybdenum, tungsten, cobalt, or nickel.
If present, the platinum group metals will generally make up from
about 0.1% to about 2% by weight of the catalyst.
[0036] Hydrotreating catalyst is typically a composite of a Group
VI metal or compound thereof, and a Group VIII metal or compound
thereof supported on a porous refractory base such as alumina.
Examples of hydrotreating catalysts are alumina supported
cobalt-molybdenum, nickel sulfide, nickel-tungsten, cobalt-tungsten
and nickel-molybdenum. Typically, such hydrotreating catalysts are
presulfided.
[0037] In some cases, high activity hydrotreating catalyst suitable
for high levels of hydrogenation, is employed. Such catalysts have
high surface areas (greater than 140 m.sup.2/gm) and high densities
(0.7-0.95 gm/cc). The high surface area increases reaction rates
due to generally increased dispersion of the active components.
Higher density catalysts allow one to load a larger amount of
active metals and promoter per reactor volume, a factor which is
commercially important. Since deposits of coke are thought to cause
the majority of the catalyst deactivation, the catalyst pore volume
should be maintained at a modest level (0.4-0.6). A high activity
catalyst is at times desired in order to reduce the required
operating temperatures. High temperatures lead to increased
coking.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0038] Please refer to the FIGURE:
[0039] In this process scheme, the feed which is hydrotreater
reactor effluent (Stream 7) is passed to furnace 15 and proceeds
through line 8 to the base of the stripping and rectification
section of the vacuum distillation column 20. Steam enters below
the bottom bed of the vacuum distillation column through stream 9.
The feed is separated in the distillation column into streams with
different boiling ranges. The lightest materials proceed to the
vacuum system through stream 11. Stream 12 is circulated by reflux
pump 65 through stream 13 to cooler 45 to a lighter level tray
through stream 14. Recirculation permits further processing of
streams for more complete separation and greater flexibility of
product specification.
[0040] Stream 16 is the middle, or "heart cut" side draw which is
transferred via pump 75 from the vacuum column, and as stream 17,
passes to storage drum 30.
[0041] The unconverted oil, stream 23, from the bottom of vacuum
column 20 is an excellent quality FCC feed. Stream 23 exits pump 85
as stream 24. Vacuum distillation is typically used to separate the
higher boiling material, such as the lubricating base oil
fractions, into different boiling range cuts. Fractionating the
lubricating base oil into different boiling range cuts enables the
lubricating base oil manufacturing plant to produce more than one
grade, or viscosity, of lubricating base oil. Stream 24 is heated,
via exchanger 35 and proceeds to the Fluid Catalytic Cracking Unit
as stream 26. Further saturation of the FCC feed is thus
avoided.
[0042] The heart cut stream exits storage drum 30 through stream 18
and is pumped, by means of pump 55, to stream 19. Stream 19 is
heated in exchanger 25 prior, and then exits the exchanger as
stream 21. Stream 21 is heated in furnace 5 prior to entering
hydrocracking reactor 10 for further aromatic saturation. Hydrogen
is depicted as entering between beds as streams 2 and 3.
Unconverted oil exits the reactor via stream 4. The unconverted oil
is cooled in exchanger 25 and exits as stream 6.
EXAMPLE
[0043] The following table highlights the advantages of the process
scheme of this invention over a conventional process scheme for a
45,000 BPOD (barrel per operating day) hydrocracking unit:
TABLE-US-00001 Conventional Process Scheme New Process Scheme
Process Scheme Two Stage Recycle Selective Staging Hydrocracking
Hydrocracking Fresh Feed Rate, BPSD 45,000 45,000 Overall
Conversion 70% to Diesel and 70% to Diesel and Lighter Products
Lighter Products Overall LGSV, 1/hr 0.54 0.70 Product Yield Base
Similar to Base case Jet and Diesel Quality Base Jet Smoke Point:
Base + 1 mm ULSD Cetane Index: Base + 2 Chemical H.sub.2
Consumption Base Base - 180 SCFB Reactor Weight Base Base - 450
Metric Ton Total Equipment Cost Base Base - 7.0 US$MM
[0044] Comparison of the two schemes indicates that, in the scheme
of the instant invention, there is greater space velocity, meaning
lower residence time in the reactors. The jet fuel shows an
improvement with higher smoke point and the diesel shows an
improved cetane number. Less hydrogen is consumed, smaller reactors
may be employed and total equipment cost is about $7 million
less.
* * * * *