Note: Descriptions are shown in the official language in which they were submitted.
CA 02594104 2007-06-05
METHOD OF UPGRADING A HEAVY OIL FEEDSTOCK
This application claims priority to U.S. provisional application Serial No.
60/812,099, filed June 9, 2006.
FIELD OF THE INVENTION
This invention relates to the upgrading of a heavy oil feedstock, for
example bitumen extracted from tar sands. This pretreatment process can be
tailored
for the specific hydrocarbon mixture used and the final upgraded oil
properties
desired. The process variables include electron dose, dose rate, temperature
during
electron treatment, pressure and selective additives to enhance the electron
effect.
BACKGROUND
Heavy oil and bitumen consist of large hydrocarbon molecules.
Upgrading processes add hydrogen atoms and/or remove carbon atoms, which
converts the bitumen into a product similar to conventional light crude oil.
The direct upgrading of heavy crude oils is difficult. Distillation typically
yields low levels of distillates. The remaining residual oils cannot be added
in
significant amounts to fluid catalytic crackers because of the extraordinarily
high
levels of metals and carbon residue, which result in a high level of hydrogen
generation and high coke on catalyst respectively. Therefore, coking, which is
one of
several thermal cracking processes, has traditionally been the process of
choice for
upgrading heavy oils. While coking does remove a significant amount of the
metals
and carbon residue, the quality of the produced liquids is poor. They are high
in sulfur,
olefins, diolefins and heavy aromatics and, as a result, require a substantial
amount of
additional hydrotreating.
One alternative to coking is visbreaking, which is another widely applied
thermal cracking process for the conversion of residual oils (J. F. LePage et
al.; Resid
CA 02594104 2007-06-05
2
and Heavy Oil Processing, Editions Technip, Paris, France, 1992). Thermal
visbreaking is characterized by high temperature and short residence time; so
that,
unlike coking, the cracking reactions are terminated before coke is made.
Visbreaking
alone does not significantly change the heteroatom content (S, N), metals or
asphaltene content of the feed. Its sole function is molecular weight (e.g.
boiling
range) reduction and, hence, lowering of viscosity.
An issue with thermal visbreaking is that visbreaking and other mild
thermal processes result in cleavage of the alkyl side chains from
asphaltenes,
resulting in the asphaltenes precipitating and subsequently forming deposits,
which, if
not controlled, foul processing equipment with coke. (R. C. Schucker and C. F.
Keweshan, The Reactivity of Cold Lake Asphaltenes, Prepr. Div. Fuel Chem.,
Amer.
Chem. Soc., 1980, 25(3), 155-165). Solvent extraction of the asphaltenes is
possible,
but results in high energy consumption for solvent removal and larger
equipment
sizes. Therefore, there remains a need in the art for improvements to heavy
feed
upgrading that will overcome the above shortcomings.
The process of radiation-thermal cracking (RTC) and its individual
fractions was investigated by Soviet scientists and these data are presented
in the
following documents:
Method for Oils and Oil Residua Refining, Patent of Republic of
Kazakstan N 4676 of 16 July 1996 (Priority of Kazakstan N 940434.1 of 14 April
1994).
Zaykin Y.A., Zaykina R.F., Nadirov N.K., Mirkin G. System for Complex
Natural and Industrial Chemical Compounds Reprocessing and Regeneration.
Priority
of Kazakstan 970592.1 of 26 July 97.
CA 02594104 2007-06-05
3
Chesnokov B.P., Nadirov N.K., Kiryshatov O.A., Kiryshatov A.I., Zaykin
Y.A., Zaykina R.F., Vaytsul A.N. Method for Chemical Reactions Initiations
During Oil
and Oil Products Processing and Device for Its Realization. Priority of Russia
N 97-
10-7263/25 (007710).
Mirkin G., Nadirov N.K., Zaikina R.F., Zaikin Y.A. System for processing
and refining chemical compositions. Priority of USA N 09/100, 453 of 06/19.
Other related references include:
Reference 1: G.M.Panchenko, A.V.Putilov, T.N.Zhuravlov et aI.
Investigations of the basic rule of the radiation thermal cracking of N-
hexadecane.
High Energy Chemistry, v. 15, #5, 1981, p. 426
In Reference 1, the process was demonstrated with n-hexane. The
gamma dose rate changed from 7.8 up to 16.7 Gy/s, the maximally absorbed dose
constituted 20 kGy. The autoclave pressure depended on temperature and
conditions
of the experiment and did not exceed 10 MPa. The experiments were conducted at
temperatures from 300 to 400 C. The experimental conclusions included the
possibility of using a high-temperature nuclear reactor to irradiate
production volumes
of heavy oil.
Reference 2: G.I.Zhuravlov, S.V.Voznesenskiy, I.V.Borisenko et al.
Radiation-thermal effect on the heavy oil residium, High Energy Chemistry, v.
25, #1,
1991, p. 27.
According to Reference 2 gas oil was subjected to radiation thermal
cracking at temperatures of 300 to 400 C in the dose range 50 to 200 kGy,
with a
gamma dose rate of 5.1 Gy/s. This study showed that the low dose rate RTC
process
increased the conversion of molecular weight compounds by 50 to 100% as
compared to the thermal process alone. Irradiation also contributed to the
process of
CA 02594104 2007-06-05
4
sulphur removal of the light oil products obtained. As in Reference 1, the
authors
described an industrial process of applying heat and radiation from a nuclear
reactor.
Reference 3: N.K.Nadirov, R,F,Zaykina, Yu.A.Zaykin. State and
perspectives of radiation treatment of heavy oil and natural bitumen. NIIETF
KazGY,
NPO "Kazneftebitum", Alma-Ata, Kazakhstan (1995).
Reference 3 presented the results of a study of RTC of a mixture of
heavy oil fractions with boiling point of greater than 400 C, using a 4 MeV
linear
accelerator. The dose rate was varied from 1 to 4 kGy/s, with an absorbed dose
of 1
to 40 kGy. Both static and flowing experiments were completed. Under these
irradiation conditions, the optimal temperature for the RTC process was 400 to
420 C.
The output of gasoline fractions with a boiling temperature of less than 200 C
was
50% higher than that for thermal cracking alone. The gasoline fraction
obtained had a
high octane range (76 to 80) and low sulfur content. The percentage of
aromatic and
naphthenes compounds also increased with the RTC process than with thermal
cracking alone.
Reference 4: Wu G., Katsumura Y., et al Effect of radiation on the
thermal cracking of n- hexadecane, Ind. And Eng. Chem. Res. - 1997, 36, N6,
p.1973
Reference 4 describes liquid and gas-phase RTC cracking of n-hexane
at 300 to 400 C, with gamma irradiation. The liquid phase was irradiated with
dose
rates ranging from 150 to 460 Gy/h and the gas phase was irradiated with dose
rates
ranging from 240 to 560 Gy/h. It was shown that irradiation abruptly increased
the
process rate, not affecting the set of final carboniferous cracking products.
A large
amount of molecular hydrogen was formed by radiation thermal cracking.
Reference 5: A.K.Pikaev. New elaboration of radiation technology in
Russia (review). High Energy Chemistry, v.33, #1, 1999, p.3
CA 02594104 2007-06-05
Reference 5 describes development work to commercialize RTC using
gamma irradiation in a closed static system. The volume of the test vessel was
120
cm3. The results obtained from this higher volume experiment corresponded to
literature data in the temperature range of 250 to 300 C. The volume of light
gas
5 fractions was increased by up to 5%, with a lowering of viscosity of the
remaining oil.
A large amount of hydrogen, saturated and unsaturated hydrocarbons, and
hydrogen
sulphide were also identified in the reaction vessel.
Reference 6: R.F. Zaykina, Yu. A. Zaykin, T.B. Mamonova, and N.K.
Nadirov, Radiation-thermal processing of high-viscous oil from Karazhanbas
field,
Rad. Phys. Chem, 60 (2001) 211-221.
Reference 6 examined the RTC process for high-viscous oil from
Karazhanbas, using electron beam (EB) treatment from a 2 MeV, 4 kW linear
accelerator. The unique feature of their experimental set-up was that the oils
were
heated from 200 C to 400 C by continuous EB treatment, and the volatiles were
removed from the oil during irradiation. The study confirmed that total dose
and dose
rate impact both the yield and the composition of the gas oil fractions with
boiling
temperatures up to 350 C. The mechanisms associated with the formation of
aromatic hydrocarbons were also discussed.
Reference 7: Yu. A. Zaykin and R.F. Zaykina, Simulation of radiation-
thermal cracking of oil products by reactive ozone-containing mixtures, Rad.
Phys.
Chem, 71 (2004) 475-478.
Reference 7 described the benefits of combining RTC and ozonolysis to
lower the temperature required to maximize the gas oil fractions with boiling
points
below 350 C. The RTC process required a preheating temperature of 420 C, while
bubbling ozone-containing air through the oil lowers the required treatment
CA 02594104 2007-06-05
6
temperature by 15 to 20 C. This combined process was shown to reduce the
concentration of high-molecular weight aromatic compounds as well.
Reference 8: R.F. Zaykina, Yu. A. Zaykin, Sh. G. Yagudin and I.M.
Fahruddinov, Specific approaches to radiation processing of high-sulfuric oil,
Rad.
Phys. Chem, 71 (2004) 467-470.
Reference 8, a follow-on to Reference 7, describes the beneficial effects
of the RTC/ozonolysis process for the desuphurization of light fractions of
gas oil and
considerably reduced the total amount of sulphur concentrated in high-
molecular
weight compounds.
A typical process for upgrading hydrocarbon feedstock is the thermal
cracking process. Illustratively, process fired heaters are used to provide
the requisite
heat for the reaction. The feedstock flows through a plurality of coils within
the fired
heater, the coils being arranged in a manner that maximizes the heat transfer
to the
hydrocarbon flowing through the coils. In conventional coil pyrolysis,
dilution steam is
used to inhibit coke formation in the cracking coil. A further benefit of high
steam
dilution is the inhibition of the coke deposition in the exchangers used to
rapidly
quench the cracking reaction. An illustration of the conventional process is
seen in
U.S. Pat. No. 3,487,121 (Hallee).
The use of steam in the hydrocarbon stream requires larger furnace
capacity and equipment than would be necessary for the hydrocarbon without
steam.
Further, when steam is used, energy and equipment must be provided to generate
and superheat the steam.
A variety of attempts have been made to pretreat heavy hydrocarbon
feedstock to render it suitable for thermal cracking. An option is the
vaporization of the
feedstock with large quantities of steam to create a very low system partial
pressure
CA 02594104 2007-06-05
7
(Gartside, U.S. Pat. No. 4,264,432). Others have proposed solvent extraction
pretreatment of the hydrocarbon to remove the asphaltene and coke precursors.
Another attempt is the thermal pretreatment of resids to yield a heavy
hydrocarbon,
then catalytically hydrotreating a portion of the heavy hydrocarbon feedstock
before
the steam cracking step (U.S. Pat. No. 4,065,379, Soonawala, et al.) and
similarly, the
pre-treatment of hydrocarbon feedstock by initial catalytic cracking to
produce a
naphtha or naphtha-like feed for ultimate thermal cracking (U.S. Pat. No.
3,862,898,
Boyd, et al.). These processes all improve the cracking of heavy hydrocarbon,
however, in most instances the process suffers from either the expense of
large
steam dilution equipment or the unsatisfactory increase of tar and coke
accumulation
in the process equipment.
Known attempts to upgrade a heavy oil feedstock have thus far yielded
unsatisfactory results.
SUMMARY
According to one aspect of the invention there is provided a method of
upgrading a heavy oii feedstock, the method comprising:
forming a continuous flow of the heavy oil feedstock;
heating the continuous flow to a prescribed temperature;
cracking the heavy oil feedstock in the continuous flow by directing
electrons or x-rays at the continuous flow.
The method may include recycling a separated portion comprising
volatized parts back into the continuous flow prior to electron and/or x-ray
cracking.
Constituents of the continuous flow subsequent to electron/x-ray
cracking can be varied by varying an amount of the separated portion recycled
back
into the continuous flow.
CA 02594104 2007-06-05
8
A separated portion, comprising parts of the continuous flow which are
volatized when heating the flow to said prescribed temperature, are preferably
recycled back into the flow.
Conditioning the continuous flow prior to electron/x-ray treatment, may
include adding to the flow a selected one or more of ozone, steam, a hydrogen
donor
gas, or recycling back into the flow a portion of the continuous flow which is
volatized
when preconditioning.
Electron/x-ray cracking is preferably done at or near atmospheric
pressure.
The continuous flow may be mixed during electron/x-ray cracking by
providing baffles in a path of the flow or by providing moving mixing blades
in a path
of the flow.
The electrons or x-rays are directed at the continuous flow from a
plurality of opposing directions.
As described herein a continuous flow process for the upgrading of a
heavy oil feedstock may comprise the steps of preheating the feedstock,
electron or x-
ray cracking said feedstock, using electron beams from an accelerator, at
conditions
that will produce a cracked product stream having a lower average molecular
weight
and boiling point than said feedstock without significant coke formation;
collecting
from said product stream light ends that volatilize, including any water that
might be in
the stream; and feeding both the volatized product stream and the heated
liquid
product stream to the heavy oil distillation process.
The feed may comprise a heavy oil stream having an API gravity of less
than 20 .
CA 02594104 2007-06-05
9
The electron accelerator may be either a pulsed or continuous beam
design, with a beam power ranging from 1 to 700 kW and a beam energy ranging
from 1 to 12 MeV.
The electron/x-ray treatment zone may be vented, with the volatized gas
stream being sent to the distillation process directly or circulated through
the
feedstock preheating tank prior to being sent to the distillation process.
Air may be circulated through the feedstock storage tank to incorporate
ozone into the feedstock. Ozone is produced during the electron treatment of
air.
The pretreatment system may introduce steam or a hydrogen donor
gas, or both, to the feedstock either prior to heating or just before electron
or x-ray
treatment.
The method may further include arranging a portion of the continuous
flow to comprise hydrocarbons having a boiling point lower than said
prescribed
temperature prior to electron or x-ray cracking by maintaining under pressure
in the
continuous flow at least a portion of hydrocarbons volatized during heating.
One embodiment of the invention will now be described in conjunction
with the accompanying drawings in which:
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic illustration of a preferred embodiment of the
method of upgrading a heavy oil feedstock according to the present invention.
DETAILED DESCRIPTION
The present invention relates to a process for upgrading petroleum
feedstocks, using a combination of electron cracking, with and without added
ozone,
steam or hydrogen, at conditions that will not produce significant amounts of
coke.
Suitable feedstocks for use in the present invention include heavy and reduced
CA 02594104 2007-06-05
petroleum crude oil; petroleum atmospheric distillation bottoms; petroleum
vacuum
distillation bottoms, or residuum; pitch; asphalt and tar sand bitumen. Such
feeds will
typically have a Conradson carbon content of at least 5 wt. %, generally from
about 5
to 50 wt. %. As to Conradson carbon residue, see ASTM Test D189-165.
5 Electron cracking, as employed herein, usually results in about 15 to 70
wt. % conversion of the heavy oil feed to lower boiling products (boiling
temperature
<350 C). This conversion rate is typically 50% to 100% higher than using the
current
thermal cracking process. The entire group of reactions takes place in the
"electron
treatment zone"; and the average residence time of the feed in the treatment
zone is a
10 function of the power of the machine being used and the design of the flow
chamber.
The residence time has to be sufficient to allow the feed stream to absorb 1
to 50 kJ
of electrons per kilogram of feedstock, depending on the composition of the
initial
feed.
Our process is typically carried out at or near atmospheric pressure;
however, some improvement in the quality and stability of the product can be
achieved by the introduction of a hydrogen donor gas and/or steam.
Referring now to the overall process shown in Figure 1, the feedstock is
first formed into a continuous flow through a first flow line #1 prior to
entering the inlet
of a pre-heater (20) in series with the first flow line and which preheats the
feedstock
to a prescribed temperature. The flow exits an outlet of the pre-heater (20)
at a
second flow line #2 to be directed into an inlet of an electron treatment zone
(22) in
series with the second flow line #2. Within this zone (22), the flow is
subjected to
electrons generated from an electron accelerator facility (24). After
treatment the flow
exits an outlet of the zone (22) through a third flow line #6 which directs
the flow to a
CA 02594104 2007-06-05
11
first inlet of a distillation unit (26) where the various fractions of
hydrocarbons in the
flow are separated and passed onto subsequent refining operations.
Turning now more particularly to the flow at the first flow line 1, prior to
entering the pre-heater (20), the feedstock may be preconditioned by the
addition of
steam and a hydrogen donor gas injected into either into flow line #1 prior to
entering
the pre-heater (20) or into flow line #2 between the pre-heater (20) and the
electron
treatment zone (22).
The pre-heater (20) in the illustrated embodiment is operated at low
pressure such that any parts of the flow which are volatized due to the
preheating can
be vented from an auxiliary outlet of the pre-heater (20) through a vent line
#3 to a
control valve (28) in series with the vent line #3. The control valve then
determines
whether the vented volatiles are fed directly to the distillation unit (26) at
an auxiliary
inlet of the distillation unit separate from flow line #6 or alternatively fed
through an
additional flow line #4 for injection back into the continuous flow at flow
line #2 just
prior to entering the electron treatment zone (22).
Similarly the electron treatment zone (22) may also be vented from an
auxiliary outlet at vent line #5 to remove any parts which are volatized
during the
electron treatment. A control valve #30 in series with the vent line #5
receives the
volatiles vented from the electron treatment zone and then subsequently
controls
whether these volatiles are either directed back into the continuous flow at
flow line #2
just prior to entering the electron treatment zone, or alternatively directed
to the
distillation unit (26) along with the volatiles vented from the pre-heater
through vent
line #3.
The electrons may be directed at the flow from multiple directions to
ensure that substantially the entirety of the flow is subjected to electron
beams.
CA 02594104 2007-06-05
12
When pre-treating or pre-conditioning the feedstock prior to entering the
pre-heater (20), a conditioning tank may be provided in series with the flow
line 1 of
the flow prior to entering the pre-heater. The pre-treatment or pre-
conditioning may
comprise the addition of one or more of ozone, steam or a hydrogen donor gas
as
noted above.
According to the method described herein, the heavy oil feedstock is
first formed as a continuous flow which is heated to a prescribed treatment
temperature prior to the electron treatment zone (22). Heating may occur at
the pre-
heater (20) or both at a pre-heater and pre-conditioning stage prior to the
treatment
zone (22). When heating, parts of the flow having a boiling point lower than
the
prescribed treatment temperature will be volatized, but according to the
present
invention these volatized parts may be arranged to be present in the
continuous flow
prior to the electron treatment zone. This is accomplished either by
maintaining the
volatiles under pressure in the flow or by returning the volatiles to the flow
just prior to
the electron treatment zone. These hydrocarbons of lower molecular weight
encourage a greater number of reactions and a greater degree of cracking of
heavier
oil molecules in the flow.
When it is desirable to vary the composition of molecules in the end
product at the distillation unit (26), the amount of volatiles from the pre-
heater or the
electron treatment zone which are returned back into the flow prior to further
electron
beam treatment can be varied in a controllable manner to, in turn, vary the
types of
reactions taking place in the treatment zone.
As described herein, the method according to the present invention
generally comprises the following steps:
CA 02594104 2007-06-05
13
1) A heavy oil feedstock is introduced to the process through Line #1.
The flow rate is a function of the accelerator power and the capacity of the
electron
treatment zone. For an electron dose of 10 kGy supplied to the feedstock,
throughput
is up to 1.70 barrels per hour for every kilowatt of installed electron power.
2) The feedstock may be conditioned with air containing ozone
produced by the electron/x-ray treatment of the cooling air stream. Ozone may
also
be added from other ozone-generating technologies. Any parts of the feedstock
which
are volatized during this preconditioning may be retained in the feedstock
flow or may
be vented off and returned to the feedstock flow just prior to subsequent
electron
treatment at Line #3.
3) The conditioned feedstock is pumped through Line #1 to the
continuous flow preheater, where the feedstock is raised in temperature, up to
a
maximum of 425 C. Steam and preheated hydrogen donor gas, such as methane,
may be injected into the feedstock either prior to the preheater or just prior
to
electron/x-ray treatment .to control specific reactions. The light fractions
released
during preheating are pumped through Line #3 to either the Distillation Unit
or
recirculated back to the feedstock via Line #4 to enhance the effects of the
cracking
process.
4) The feedstock exits the preheater through Line #2 and enters the
electron treatment Zone. As the temperature is maintained, the feedstock is
treated
with electrons or X-rays to a dose of up to 50 kGy. The treatment zone is
operated at
or near atmospheric pressure. The treatment zone is designed to insure that
the
feedstock depth during treatment is optimized for the electron or x-ray energy
used.
The flow rate, dictated by the required electron/x-ray dose, will be
sufficient to
minimize fouling within the apparatus. The process may include mixing the
feedstock
CA 02594104 2007-06-05
14
stream during electron treatment, either with baffles or blades in the flow
path. The
light fractions released during electron/x-ray treatment may be pumped through
Line
#5 to either the Distillation Unit or recirculated back to the feedstock
stream prior to
electron/x-ray treatment to further enhance the effects of the cracking
process.
5) The accelerator produces either a pulsed or a continuous electron
beam. The air stream from the electron/x-ray treatment zone with ozone
produced
during the electron/x-ray treatment, may be pumped to the inlet line for the
feedstock
(Line 7) to enhance the effects of the cracking process.
6) The accelerator facility may generate multiple beams, either with
multiple accelerators or the use of beam splitters to allow the feedstock to
be treated
from multiple sides in the electron treatment zone. Standard shielding designs
for
accelerator facilities may be used for this facility.
7) The cracked feedstock is now appropriately conditioned and fed
through Line #6 into the Distillation Unit. In the Distillation Unit, light
fractions are
volatilized and exit. The less volatile fraction of the feedstock stream exits
the
Distillation Unit and continues through the traditional heavy oil processing
stages.
Since various modifications can be made in the invention as herein
above described, and many apparently widely different embodiments of same made
within the spirit and scope of the claims without department from such spirit
and
scope, it is intended that all matter contained in the accompanying
specification shall
be interpreted as illustrative only and not in a limiting sense.
