1. Technical Field
[0001] This invention relates to upgrading and desulfurizing heavy hydrocarbon feeds containing
sulfur, metals, and asphaltenes, and more particularly, to a method of and apparatus
for upgrading and desulfurizing heavy crude oils or fractions thereof.
2. Background of the Invention
[0002] Many types of heavy crude oils contain high concentrations of sulfur compounds, organo-metallic
compounds, and heavy, non-distillable fractions called asphaltenes which are insoluble
in light paraffins such as n-pentane. Because most petroleum products used for fuel
must have a low sulfur content to comply with environmental restrictions, the presence
of sulfur compounds in the non-distillable fractions reduces their value to petroleum
refiners and increases their cost to users of such fractions as fuel or as raw material
for producing other products. In order to increase the saleability of these non-distillable
fractions, refiners must resort to various expedients for removing sulfur compounds.
[0003] A conventional approach to removing sulfur compounds in distillable fractions of
crude oil, or its derivatives, is catalytic hydrogenation in the presence of molecular
hydrogen at moderate pressure and temperature. While this approach is cost effective
in removing sulfur from distillable oils, problems arise when the feed includes metallic-containing
asphaltenes. Specifically, the presence of metallic-containing asphaltenes results
in catalyst deactivation by reason of the coking tendency of the asphaltenes, and
the accumulation of metals on the catalyst, especially nickel and vanadium compounds
commonly found in the asphaltenes.
[0004] Alternative approaches include coking, high-pressure, desulfurization, and fluidized
catalytic cracking of non- distillable oils, and production of asphalt for paving
and other uses. All of these processes, however, have disadvantages that are intensified
by the presence of high concentrations of metals, sulfur and asphaltenes. In the case
of coking non-distillable oils, the cost is high and a disposal market for the resulting
high sulfur coke must be found. Furthermore, the products produced from the asphaltene
portion of the feed to a coker are almost entirely low valued coke and cracked gases.
In the case of residual oil desulfurization, the cost of high-pressure equipment,
catalyst consumption, and long processing times make this alternative undesirably
expensive.
[0005] Metals contained in heavy oils contaminate and spoil the performance of catalysts
in fluidized catalytic cracking units. Asphaltenes present in such oils are converted
to high yields of coke and gas which burden an operator with high coke burning requirements.
While asphalt markets represent a viable way to dispose of asphaltenes because, normally,
no sulfur limits are imposed, such markets are limited in size and location, making
this alternative frequently unavailable to a refiner.
[0006] Another alternative available to a refiner or heavy crude user is to dispose of the
non-distillable heavy oil fractions as fuel for industrial power generation or as
bunker fuel for ships. Disposal of such fractions as fuel is not particularly profitable
to a refiner because more valuable distillate oils must be added in order to reduce
viscosity sufficiently to allow handling and shipping, and because the presence of
high sulfur and metals contaminants lessens the value to users. Refiners frequently
use a thermal conversion process, e.g., visbreaking, for reducing the heavy fuel oil
yield. This process converts a limited amount of the heavy oil to lower viscosity
light oil, but has the disadvantage of using some of the higher valued distillate
oils to reduce the viscosity of the heavy oil sufficiently to allow handling and shipping.
Moreover, the asphaltene content of the heavy oil restricts severely the degree of
visbreaking conversion possible due to the tendency of the asphaltenes to condense
into heavier materials, even coke, and cause instability in the resulting fuel oil.
[0007] Many proposals thus have been made for dealing with non-distillable fractions of
crude oil containing sulfur and metals. And while many are technically viable, they
appear to have achieved little or no commercialization due, in large measure, to the
high cost of the technology involved. Usually such cost takes the form of increased
catalyst contamination by the metals and/or the carbon deposition resulting from the
attempted conversion of the asphaltenes fractions.
[0008] An example of the processes proposed in order to cope with high metals and asphaltenes
is disclosed in U.S. Patent No. 4,500,416. In one embodiment, an asphaltene-containing
hydrocarbon feed is solvent deasphalted in a deasphalting zone to produce a deasphalted
oil (DAO) fraction, and an asphaltene fraction which is catalytically hydrotreated
in a hydrotreating zone to produce a reduced asphaltene stream that is fractionated
to produce light distillate fractions and a first heavy distillate fraction. Both
the first heavy distillate fraction and the DAO fraction are thermally cracked into
a product stream that is then fractionated into light fractions and a second heavy
distillate fraction which is routed to the hydrotreating zone.
[0009] In an alternative embodiment, an asphaltene-containing hydrocarbon feed is solvent
deasphalted in a deasphalting zone to produce a deasphalted oil (DAO) fraction, and
an asphaltene fraction which is catalytically hydrotreated in a hydrotreating zone
to produce a reduced asphaltene stream that is fractionated to produce light distillate
fractions and a first heavy distillate fraction. The first heavy distillate fraction
is routed to the deasphalting zone for deasphalting, and the DAO fraction is thermally
cracked into a product stream that is then fractionated into light fractions and a
second heavy distillate fraction which is routed to the hydrotreating zone.
[0010] In each embodiment in the '416 patent, asphaltenes are routed to a hydrotreating
zone wherein heavy metals present in the asphaltenes cause a number of problems. Primarily,
the presence of the heavy metals in the hydrotreater cause deactivation of the catalyst
which increases the cost of operation. In addition, such heavy metals also result
in having to employ higher pressures in the hydrotreater which complicates its design
and operation and hence its cost.
[0011] It is therefore an object of the present invention to provide a new and improved
method of and apparatus for upgrading and desulfurizing heavy hydrocarbon feeds containing
sulfur, metals, and asphaltenes, wherein the disadvantages as outlined are reduced
or substantially overcome.
SUMMARY OF THE INVENTION
[0012] In accordance with the present invention, a substantially asphaltene-free, and metal-free
distillate stream is produced from a heavy hydrocarbon feed stream by solvent deasphalting
the feed for producing a deasphalted oil fraction and an asphaltene fraction. The
deasphalted oil fraction is thermal cracked in the presence of a hydrogen diluent
for forming a thermally cracked stream which is fractionated in a fractionating zone
to produce a substantially asphaltene-free, and metal-free distillate fraction that
constitutes the distillate stream, and a non-distilled fraction that constitutes the
feed stream.
[0013] Preferably, hydrogen donor diluent is produced by catalytically hydrogenating at
least a portion of the substantially asphaltene-free, and metal-free distillate fraction
for forming a hydrotreated stream. Such stream is then fractionated for forming a
substantially asphaltene- free, and metal-free distillate, and the hydrogen donor
diluent. The preferred ratio of hydrogen donor diluent to deasphalted oil is about
0.25 to 4 parts of hydrogen donor diluent to 1 part of deasphalted oil.
[0014] In one embodiment of the invention, fractionation of the thermally cracked stream
includes fractionating a hydrocarbon feed containing sulfur, metals, and asphaltenes.
In another embodiment, a hydrocarbon feed containing sulfur, metals, and asphaltenes
is thermally cracked with the deasphalted oil fraction and the hydrogen diluent.
[0015] The presence of hydrogen donor diluent during thermal cracking of the deasphalted
oil serves to suppress or substantially eliminate the formation of asphaltenes in
the thermal cracker. Moreover, in the preferred form of the invention, the feed to
the catalytic hydrotreater is asphaltene-free and metal-free; and as a result only
moderate pressures are involved in the hydrotreater thereby reducing the cost of the
catalytic hydrotreating equipment. In addition, the improved feed to the catalytic
hydrotreater will result in much longer catalyst life, thus reducing operating costs.
[0016] The solvent deasphalting process of the present invention removes both asphaltenes
in the initial feed and asphaltenes formed as a by-product of the thermal cracking
process. The absence of asphaltenes in the DAO input to the thermal cracker permits
its operation under more severe conditions thereby maximizing the generation of distillate
products. As is known, the severity of a thermal cracking process is limited by the
level of asphaltenes present in the thermal cracker because too high a level will
result in precipitation of asphaltenes in the thermal cracker which fouls the cracker
heaters, or precipitation of asphaltenes from the thermal cracker liquid in subsequent
storage or transport. Since the presence of asphaltenes sets the limit on conversion
in a thermal cracker before excessive coking occurs, removal of asphaltenes from the
feed to the thermal cracker allows for higher severity operations and higher conversion
rates according to the present invention, and thus lower costs. Moreover, the donor
diluent present in the input to the thermal cracker suppresses asphaltene production
in the thermal cracker, providing an enhanced yield of light products.
[0017] An additional advantage of the present invention lies in using thermal, rather than
catalytic, conversion of deasphalted oil. This allows the deasphalting process to
be operated such that substantially only asphaltenes, and, therefore, very little
deasphalted oil fractions are rejected to the asphaltene phase by the solvent deasphalter
even though such operation results in deasphalted oil with a metals and Conradson
Carbon level which would be unacceptable if the deasphalted oil were used in a catalytic
cracker or catalytic hydrocracker. Since the conversion to distillable fractions occurs
thermally, the metals and coke forming fractions do not create a significant cost
penalty to the operation.
[0018] Substantially all of the metals in the feed are ultimately rejected into the asphaltene
phase through the recycle of non-distilled, unconverted heavy oil to the solvent deasphalting
unit. The inclusion of the hydrogen donor distillate with the deasphalted oil applied
to the thermal cracker will suppress or substantially eliminate the coke forming fractions
from condensing to form additional asphaltenes, thereby adding to the yield of valuable
products.
[0019] According to the present invention, the asphaltenes present in the hydrocarbon to
be upgraded are removed in the deasphalting step prior to the thermal cracking step.
In addition, by recycling to the solvent deasphalting step the non-distilled residual
fraction of the thermal cracker products, which fraction may contain asphaltenes created
as a by-product of the thermal cracking, any thermal cracker- produced asphaltenes
are removed and the deasphalted non-distilled residual fraction from the thermal cracker
can be returned to the thermal cracker for further cracking. Thus, according to the
present invention, the removal of asphaltenes from the initial and the recycled feedstocks
up-stream of the thermal cracker allows for a much-improved level of conversion of
non-distilled hydrocarbon into distillates as compared to the prior art.
[0020] According to the present invention the asphaltenes produced from the invention can
be used as fuel by another fuel user. For example, these asphaltenes can be used as
fuel in a fluidized bed combustor or high viscosity fuel oil boiler. Alternatively,
the asphaltenes can be used as feedstock to a gasifier, or they can be coked to produce
lighter liquid fuels and petroleum coke fuel. If gasified, the syngas produced from
the asphaltenes can be used as a source of hydrogen for the hydrotreater. If coked,
the distillate fuel produced from the asphaltenes optionally may be hydrotreated and
then combined with the distillate products that result from the cracking of the deasphalted
oil, and the coke can be sold in the solid fuel markets.
[0021] The distilled fractions from the process, which are asphaltene-free and metal-free
and have a reduced sulfur content, can be used without further treatment, as a replacement
for premium distillate fuels or refinery feedstocks.
[0022] Furthermore, the present invention also comprises apparatus for carrying out the
process of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] Embodiments of the present invention are described by way of example, and with reference
to the accompanying drawing wherein:
Fig. 1 is a block diagram of a first embodiment of the present invention for upgrading
a hydrocarbon feed containing sulfur, metals, and asphaltenes wherein the feed is
input to a distillation column; and
Fig. 2 is a block diagram of a second embodiment of the present invention for upgrading
a hydrocarbon feed containing sulfur, metals, and asphaltenes wherein the feed is
input to a thermal cracker.
DETAILED DESCRIPTION
[0024] Referring now to the drawings, reference numeral 10A designates a first embodiment
of apparatus according to the present invention for upgrading hydrocarbon feed 11
which typically contains sulfur, metals, and asphaltenes. Apparatus 10A comprises
heater 12 for heating feed 11 and producing heated feed 13 that is applied to distillation
column 14 which can be operated at' near-atmospheric pressure or, by the use of two
separate vessels, at an ultimate pressure that is subatmospheric. Fractionation takes
place within column 14 producing gas stream 15, one or more distillate streams shown
as combined stream 16 which is a substantially asphaltene-free, and metal-free, and
non-distilled fraction 18 containing sulfur, asphaltenes, and metals.
[0025] Gas stream 15 can be used as fuel for process heating. A portion of combined stream
16 may be withdrawn as output stream 37, and the balance of combined stream 16 is
converted by means 17 to produce hydrogen donor diluent 17A as described below; and
non-distilled, or reduced fraction 18 is applied to solvent deasphalting (SDA) unit
19 for processing the non-distilled fraction and producing deasphalted oil (DAO) stream
20 and asphaltene stream 21. SDA unit 19 is conventional in that it utilizes a recoverable
light hydrocarbon such as pentane, or hexane, or a combination thereof, for separating
fraction 18 into streams 20 and 21. The concentration of metals in DAO stream 20 produced
by SDA unit 19 is substantially lower than the concentration of metals in fraction
18 applied to SDA unit 19. In addition, the concentration of metals in asphaltene
stream 21 is substantially higher than concentration of metals in DAO stream 20. Node
22 serves as means to combine hydrogen donor diluent 17A with deasphalted oil stream
20 to form combined stream 23 which is thermally cracked in a cracking furnace or
cracking furnace combined with a soaking drum, shown as thermal cracker 24. Preferably,
deasphalted oil stream 20 is combined with the hydrogen donor stream 17A in the ratio
of 0.25 to 4 parts of hydrogen donor to 1 part of deasphalted oil. The heat applied
to thermal cracker 24 and the residence time of stream 23 therein serve to thermally
crack stream 23 into light hydrocarbon distillable parts. Any asphaltenes formed during
the thermal cracking of the non-distillable parts are a part of thermally cracked
stream 25.
[0026] Finally, input 26 to distillation column 14 serves as means for applying thermally
cracked stream 25 to the column. Within this column, the distillable parts in stream
25 are separated and recovered as a part of gas stream 15 and combined stream 16.
In the event that heavy hydrocarbon feed 11 does not contain a significant amount
of distillate, feed 11 can be directed to the solvent deasphalting unit 19 instead
of column 14 as shown in the drawing. Alternatively, when feed 11 contains sulfur,
metals, and asphaltenes, feed 11 may be directed to thermal cracker 24 in apparatus
10B shown in Fig. 2.
[0027] While Fig. 1 shows feeding-back thermally cracked stream 25 directly to column 14,
it is also possible to mix stream 25 with feed 11 thereby assisting the heating of
the feed in preparation for fractionating in column 14.
[0028] Preferably, at least a portion of the distillate produced by column 14, namely stream
16, is catalytically hydrotreated in hydrotreater 27 which also receives gaseous hydrogen
via line 28. The hydrotreated product in line 29 is then heated in heater 30 and fractionated
in distillation column 31 producing gas stream 32, light distillates 33, middle-range
distillates 34, and heavy distillates 35.
[0029] Gas stream 32 can be used, for example, as fuel for process heating; or, hydrogen
in the gas stream can be recovered for use in hydrotreater 27. Stream 29 will also
contain a significant amount of hydrogen sulfide from the desulfurization process
in the hydrotreater. This hydrogen sulfide can be easily removed from the gas fraction
using conventional technology for recovery of the sulfur.
[0030] A portion of the middle distillate fraction 34, which will have a boiling range of
approximately 500°F. to 900°F., is used as the hydrogen donor diluent for the thermal
cracking process and is recycled as stream 17A. The portion of the middle distillate
fraction 34 that is not used as the hydrogen donor is withdrawn from the system as
stream 36. Streams 32, 33, 35, 36, and 37 can be combined as an upgraded synthetic
crude oil for further processing in a refinery, or used as fuel for power generation
without further processing.
[0031] In one embodiment of the present invention the heater 12 functions as a thermal cracker
in order to crack the heavy hydrocarbons in the hydrocarbon feed.
[0032] According to a preferred embodiment of the present invention, thermal cracker 24
contains a catalyst. In that embodiment wherein the heater 12 functions as a thermal
cracker, it also can contain a catalyst. When a catalyst is present, thermal cracking
is practiced in the presence of this catalyst. The catalyst can reside in the thermal
cracker 24 and/or in the heater 12, but is preferably in the form of an oil dispersible
slurry carried by the relevant feed stream.
[0033] The catalyst preferably promotes cracking of the combined stream 23 or the contents
of the heater 12 when the heater 12 functions as a thermal cracker. In one embodiment
the catalyst suppresses the formation of asphaltenes. In the most preferred embodiment
it does both. The catalyst is preferably a metal selected from the group consisting
of a Groups IVB, VB, VIB, VIIB, and VIII of the Periodic Table of Elements, and mixtures
thereof. The most preferred catalyst is molybdenum. The catalyst can be employed in
its elemental form or in the form of a compound.
[0034] In another embodiment the thermal cracking, which occurs in thermal cracker 24, is
practiced in the presence of a hydrogen donor such as hydrogen gas or a hydrogen donor
diluent stream.
[0035] In an additional embodiment of the present invention hydrogen gas is supplied to
the thermal cracker 24 in order to improve performance. Furthermore hydrogen gas can
be added to the heater 12 in that embodiment wherein the heater 12 functions as a
thermal cracker.
[0036] It is believed that the advantages and improved results furnished by the method and
apparatus of the present in are apparent from the foregoing description of the invention.
Various changes and modifications may be made without departing from the spirit and
scope of the invention as described in the claims that follow.
1. A process for upgrading a hydrocarbon feed containing sulfur, metals, and asphaltenes,
said process comprising:
a) applying said feed to a distillation column for producing a substantially asphaltene-free,
and metal-free distillate fraction and a non-distilled fraction containing sulfur,
asphaltenes, and metals
b) converting at least some of said substantially asphaltene-free, and metal-free
distillate fraction to a hydrogen donor diluent;
c) processing said non-distilled fraction in a solvent deasphalting unit for producing
a deasphalted oil stream and an asphaltene stream;
d) combining said hydrogen donor diluent with said deasphalted oil stream to form
a combined stream;
e) thermal cracking said combined stream for forming a thermally cracked stream; and
f) applying said thermally cracked stream to said distillation column.
2. A process according to claim 1 wherein said hydrogen donor diluent is combined with
said deasphalted oil stream in the ratio of about 0.25 to 4 parts of hydrogen donor
diluent to 1 part of deasphalted oil.
3. A process according to claim 2 wherein converting at least some of said substantially
asphaltene-free, and metal-free distillate fraction to a hydrogen donor diluent includes:
a) catalytically hydrogenating at least a portion of said substantially asphaltene-free,
and metal-free distillate fraction for forming a hydrotreated stream;
b) fractionating said hydrotreated stream for forming substantially asphaltene-free,
and metal-free distillate, and said hydrogen donor diluent.
4. Apparatus for upgrading a hydrocarbon feed containing sulfur, metals, and asphaltenes,
said apparatus comprising:
a) a distillation column for receiving said feed and producing a substantially asphaltene-free,
and metal-free distillate fraction and a non-distilled fraction containing sulfur,
asphaltenes, and metals;
b) means for converting at least some of said substantially asphaltene-free, and metal-free
distillate fraction to a hydrogen donor diluent;
c) a solvent deasphalting unit for processing said non-distilled fraction and producing
a deasphalted oil stream and an asphaltene stream;
d) means for combining said hydrogen donor diluent with said deasphalted oil stream
to form a combined stream;
e) a thermal cracker for thermally cracking said combined stream and forming a thermally
cracked stream; and
f) means for applying said thermally cracked stream to said distillation column.
5. Apparatus according to claim 4 including:
a) a catalytic hydrotreater for treating at least a portion of said substantially
asphaltene-free, and metal- free distillate fraction and forming a hydrotreated stream;
b) a distillation column for fractionating said hydrotreated stream and forming substantially
asphaltene-free, and metal-free distillate, and said hydrogen donor diluent.
6. A process for producing a distillate stream from a heavy hydrocarbon feed stream comprising:
a) solvent deasphalting said feed for producing a deasphalted oil fraction and an
asphaltene fraction;
b) forming a hydrogen donor diluent;
c) heating and thermal cracking said deasphalted oil fraction in the presence of said
hydrogen diluent in a thermal cracking zone for forming a thermally cracked stream;
d) fractionating said thermally cracked stream in a fractionating zone to produce
a distilled fraction which constitutes said distillate stream, and a non-distilled
fraction which constitutes said feed stream.
7. A process according to claim 6 wherein said hydrogen donor diluent is combined with
said deasphalted oil fraction in the ratio of about 0.25 to 4 parts of hydrogen donor
diluent to 1 part of deasphalted oil.
8. A process according to claim 6 wherein said hydrogen donor diluent is produced by
hydrotreating a portion of said distillate stream.
9. A process according to claim 8 wherein the step of fractionating said thermally cracked
stream includes fractionating a hydrocarbon feed containing sulfur, metals, and asphaltenes.
10. A process according to claim 8 including thermal cracking a hydrocarbon feed containing
sulfur, metals, and asphaltenes in said thermal cracking zone.
11. A process according to claim 6 including burning at least a portion of said distillate
stream for producing power.
12. A process according to claim 6 including burning at least some of the asphaltene fraction
to provide at least some of the process heating requirements.
13. A process according to claim 6 wherein at least some of the hydrogen in said hydrogen
donor diluent is formed by gasifying at least a portion of said asphaltene fraction.
14. A process for upgrading a hydrocarbon feed stream containing sulfur, metals, and asphaltenes,
said process comprising:
a) cracking said hydrocarbon feed stream to form a cracked hydrocarbon teed stream;
b) applying said cracked hydrocarbon feed stream to a distillation column for producing
a substantially asphaltene-free, and metal-free distillate fraction and a non-distilled
fraction containing sulfur, asphaltenes, and metals;
c) converting at least some of said substantially asphaltene-free, and metal-free
distillate fraction to a hydrogen donor diluent;
d) processing said non-distilled fraction in a solvent deasphalting unit for producing
a deasphalted oil stream and an asphaltene stream;
e) combining said hydrogen donor diluent with said deasphalted oil stream to form
a combined stream;
f) thermal cracking said combined stream for forming a thermally cracked stream; and
g) applying said thermally cracked stream to said distillation column.
15. A process according to claim 1 wherein the thermal cracking of said combined stream
is practiced in the presence of a catalyst.
16. A process according to claim 15 wherein the catalyst promotes cracking of said combined
stream.
17. A process according to claim 15 wherein the catalyst suppresses the formation of asphaltenes.
18. A process according to claim 15 wherein the catalyst suppresses the formation of asphaltenes,
and wherein the catalyst promotes cracking of said combined stream.
19. A process according to claim 15 wherein the catalyst is a metal selected from the
group consisting of a Groups IVB, VB, VIB, VIIB, and VIII of the Periodic Table of
Elements, and mixtures thereof.
20. A process according to claim 15 wherein the catalyst is a molybdenum.
21. A process of claim 1 wherein the thermal cracking is practiced in the presence of
a hydrogen donor.
22. A process of claim 21 wherein the hydrogen donor is hydrogen gas.
23. A process of claim 21 wherein the hydrogen donor is a hydrogen donor diluent stream.
24. Apparatus for upgrading a hydrocarbon feed stream containing sulfur, metals, and asphaltenes,
said apparatus comprising:
a) a thermal cracker for cracking said hydrocarbon feed stream thereby producing a
cracked hydrocarbon feed stream;
b) a distillation column for receiving said cracked hydrocarbon feed stream and producing
a substantially asphaltene-free, and metal-free distillate fraction and a non-distilled
fraction containing sulfur, asphaltenes, and metals;
c) means for converting at least some of said substantially asphaltene-free, and metal-free
distillate fraction to a hydrogen donor diluent;
d) a solvent deasphalting unit for processing said non-distilled fraction and producing
a deasphalted oil stream and an asphaltene stream;
e) means for combining said hydrogen donor diluent with said deasphalted oil stream
to form a combined stream;
f) a thermal cracker for thermally cracking said combined stream and forming a thermally
cracked stream; and
g) means for applying said thermally cracked stream to said distillation column.
25. An apparatus according to claim 4 wherein the thermal cracker contains a catalyst.
26. An apparatus according to claim 24 wherein the catalyst promotes cracking of said
combined stream.
27. An apparatus according to claim 24 wherein the catalyst suppresses the formation of
asphaltenes.
28. An apparatus according to claim 24 wherein the catalyst both suppresses the formation
of asphaltenes, and promotes the cracking of said combined stream.
29. An apparatus according to claim 24 wherein the catalyst is a metal selected from the
group consisting of metals of Groups IVB, VB, VIB, VIIB, and VIII of the Periodic
Table of Elements, and mixtures thereof.
30. An apparatus according to claim 24 wherein the catalyst is molybdenum.
31. An apparatus according to claim 6 wherein the thermal cracker contains a catalyst.