Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR CONVERTING HEAVY OIL RESIDUUM TO A
USEFUL FUEL
The present invention relates to a method for enabling
the use of heavy oil residuum to a useful product and more
particularly, the present invention relates to a method for
converting such residuum to a fuel which can be used for
power generation and steam production for heavy oil
recovery, and as a direct process heating source.
In view of escalating fuel prices and particularly
natural gas prices, there has been a resurgence in the need
to consider less costly fuel options.
One of the limitations in the fuel generation art is
that the art has not thoroughly considered the possibility
of using materials which are generally not considered as
fuels, but have the possibility of conversion to useful
fuel. One such material that is useful is residuum and in
particular, heavy oil residuum. Such materials present
numerous difficulties ir1 that the viscosity is quite high
to the point that the material almost comprises a solid and
thus handling and conversion to a form suitable for use as
a combustible fuel have presented difficulties. It is
known in the chemical engineering field that droplet size
range is important to produce a fuel which will burn in a
host of boiler types and not present problems in terms of
boiler selection, sufficient carbon burnout or violation of
existing flue gas opacity standards.
It has been proposed previously to convert other
materials to a fuel, however, such proposals have not
proved viable, since droplet. size could not be produced in
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a size distribution sufficient to be efficiently burned in
a wide variety of boilers or other combustion devices.
In United States Patent No. 5,551,956, issued to
Moriyama et al., September 3, 1996, there -is disclosed a
super heavy oil emulsion fuel arid method for generating
deteriorated oil and water super heavy oil emulsion fuel.
The fuel is indicated to have a relatively low viscosity
and adequate long-term stability and comprises in an
emulsified state 100 parts by weight of a super heavy oil,
25 to 80 parts by weight water and 0.02 to 5 parts by
weight of the non-ionic surfactant. This reference teaches
a useful fuel, however, there is no recognition of
formulating an emulsion which creates a particle size
sufficient for use as an energy source in a boiler for use
in power generation and steam recovery for heavy oil
recovery.
Ichinose et al., in United States Patent No.
6,036,473, issued March 14, 2000, teaches a heavy oil
emulsified fuel combustion apparatus. This reference is
primarily focused on the apparatus and does riot go into any
real detail with respect to a fuel or conversion process
for converting residuum to a useful combustible fuel.
United States Patent No. 6,001,886, issued to
Shirodkar, December 14,1999, teaches an asphalt emulsion
formation process. The process involves preheating the
asphalt residue for combination with emulsifier with
subsequent mixture to a homomixer. The temperature is
relatively low at 38 C iri order to prevent interference in
the emulsification. This is reflected in the Patentee's
comments concerning the importance of not exceeding 100 C
to prevent dehydration of the emulsion.
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Bando, in United States Patent No.6,183,629, issued
February 6, 2001, sets forth an emulsion formulating
apparatus for formulatirig liquid/solid emulsions. The
emulsions formed with the apparatus have a wide particle
distribution as opposed to a specific distribution required
for combustion. By the Bando device, it would appear that
the arrangement is specifically designed for fluid
(liquid/solid) emulsion transport instead of liquid/liquid
emulsion combustion.
It would be desirable if there were a method to
formulate a combustible fuel in a desirable size range for
the emulsified particles to be used iri any type of boiler
for use as an energy source. The present invention speaks
to the issues in the industr_y and presents a particle
having a droplet size necessary to achieve more efficient
burning.
One aspect of the present irivention is to provide a
method for converting heavy oil liquid residuum to a
combustible fuel, comprising the s~eps of:
providing a source of heavy oil liquid residuum having
a viscosity such that the residuum is substantially non
flowable;
reducing the viscosity of the residuum by preheating
in a temperature range sufficient to facilitate flow
without thermally degradirlg the residuum;
providing a mixing means;
providing a source of water;
mixing the water and reduced viscosity residuum in the
mixing means to form in the mixing means, an emulsion of
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predispersed residuum in an aqueous matrix in a size
distribution suitable for use as a combustible fuel; and
maintaining the emulsion under pressure to prevent
dehydration of the emulsion.
Advantageously, the present invention ensures a
relatively narrow size distribut_-on where the emulsified
particles fall within the size distribution of 0.5 microns
to 50 microns. In this size di_stribution, the choice for
boiler selection is fairly broad whereas particles in a
size distribution of greater than 50 microns present
complications in that boiler selection is restricted
generally to only fluid bed combustion technology. It also
becomes difficult to obtain sufficient carbon burnout with
a large size droplet and presents complications of flue gas
opacity.
It has been found that by providing a process for
generating a droplet within the size distribution indicated
above, there is a significant increase in the technology
options employable to the user, including the use of fluid
bed boilers, conventional radiant boilers and conventional
once through steam generators, commonly entployed in the
heavy oil recovery operations.
A further aspect of one embodiment of the invention is
to provide a method for converting heavy oil residuum to a
combustible fuel, comprising the steps of:
providing a source of heavy oil liquid residuum having
a viscosity such that the residuum is substantially non
flowable;
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progressively reducing the viscosity of the residuum
in at least two stages to facilitate flow of the residuum,
the stages comprising:
a first stage irlcluding treating the residuum with a
liquid diluent to form a reduced viscosity residuum;
a second stage iricludinq preheating the reduced
viscosity residuum;
providing a mixing means;
providing a source of water;
mixing the water and reduced viscosity residuum in the
mixing means to form in the mixing means, an emulsion of
predispersed residuum in ari aqueous matrix in a particle
size distribution of between 0.5 microns and 50 microns
suitable for use as a combustible fuel; and
maintaining the emulsi_on under pressure to prevent
dehydration of the emulsion.
It has been found that the contro-'~ of the viscosity of
the residuum is importarit so that the material can be mixed
in a mixer capable of formulatinq a micro-sized emulsion.
A suitable mixer that has been employed to effect the
present invention can consist of a variety of suitable
mixers manufactured by the Kenic;s Company among others.
The company produces a helical mixing arrangement which is
useful for particularly efficient mixing. Other suitable
devices, such as that manufacture by Chemicolloid
Laboratories Inc., capable of formulating the emulsion
include collation mills which may be ganged in series or
parallel, and other more generic devices such as backward
centrifugal and gear pumps positioned in series inter alia.
The type of mixer will be apparent to orie skilled in the
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art. The choice of the mixer will be selected to result in
entrainment of the heavy oil residuum within a liquid
(aqueous) matrix such that a particle distribution is
formed in the range of 0.5 microns to 50 microns.
According to a further aspect of one embodiment of the
present invention there is provided a process for
converting heavy oil residuum to a combustible fuel,
comprising the steps of:
providing a source of heavy oil;
pretreating the oil to remove at least a portion of
entrained water;
treating the oil to form fractions, at least one of
which is heavy oil residuum;
reducing the viscosity of the residuum by preheating
in a temperature range sufficient to facilitate flow
without thermally degrading the residuum;
providing a mixing means;
providing a source of water;
mixing the water arid reduced viscosity residuum in the
mixing means;
forming, in the mixing ineans, an emulsion of
predispersed residuum in an aqueous matrix in a size
distribution suitable for use as a combustible fuel; and
maintaining the emulsion under pressure to prevent
dehydration of the emulsion.
As a particular convenience, the fuel is kept in an
emulsified form by maintaining the pressure of the
emulsion. This allows direct use burn of the fuel in a
burner desirable by end users. Since no further processing
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is required; the fuel may be passed on directly to the
burner fuel supply and subsequently into the burner.
A further aspect of one embodiment of the present
invention is to provide a method for converting heavy oil
residuum to a combustible fuel, comprising the steps of:
providing a source of heavy oil;
pre-treating the oil to remove at least a portion of
entrained water;
treating the oil to form fractions, at least one of
which is heavy oil residuum;
progressively reducing the viscosity of the residuum
in at least two stages to facilitate flow of the residuum,
the stages comprising:
a first stage including treating the residuum with a
liquid diluent to form a reciuced viscosity residuum; and
a second stage including preheating the reduced
viscosity residuum in a temperature range of between 35 C
and 350 C;
providing a mixing means;
providing a source of water;
mixing the water and reduced viscosity residuum in the
mixing means to form in the mixing means, an emulsion of
predispersed residuum in an aqueous matrix in a size
distribution suitable for use as a combustible fuel; and
maintaining the emulsion under pressure to prevent
dehydration of the emulsion.
Considering the fact t::.hat the emulsions are somewhat
fragile, pressurization without further processing/handling
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is beneficial. In the fuel of this process, pumping is not
required. The fuel can be directly transported to the
burner.
A still further aspect of one embodiment of the
present invention is to provide a pressurized fuel for
direct use burn, comprising an emulsion of predispersed
residuum in an aqueous matrix in a size distribution
suitable for use as a combustible fuel under pressure
sufficient to prevent dehydration of the emulsion and in a
size distribution of between 0.5 and 5C) pm.
Having thus generally described the invention,
reference will now be made to the accompanying drawings
illustrating preferred embodiments and in which:
Figure 1 is a schematic illustration of a process for
converting heavy oil resi_duum into a fuel according to one
embodiment of the invention;
Figure 2 is a graphical representation of carbon
burnout as a function of droplet size;
Figure 3 is a schematic illustration of a process for
converting heavy oil residuum into a fuel according to one
embodiment of the invention using preheat for viscosity
reduction;
Figure 4 is graphical representation of fluid
viscosity as a function of reheat temperature requirements
for a variety of heavy fuels;
Figure 5 is a graphical representation showing final
emulsion fuel temperature and pressure for various preheat
residuum fuel and feed water temperatures;
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Figure 6 is a schematic illustration of a pressurized
process for converting heavy oil residuum into a fuel
according to one embodiment of the invention; and
Figure 7 is a schematic illustration of a process for
converting heavy oil residutim into a fuel according to one
embodiment of the invention using combined viscosity
reduction by preheat and diluent addition.
Similar numerals employed in the specification denote
similar elements.
Referring now to Figure 1, shown is one embodiment of
the present invention.
In Figure 1, reference numeral 10 globally denotes the
overall process. In the area bounded by the dash lines and
denoted numeral 12, there is schematically illustrated a
commercially practiced heavy oiL separation facility which
primarily results in the removal of water and solid
contaminants, from the oil recovered. A source of heavy
oil 14 undergoes dewatering in a known process denoted by
numeral 16 with the water and solids being removed from the
heavy oil, generally denoted by n_zmeral 18. Once this has
been done, the next step which is known in the art is shown
in the area bounded by the dash line indicated by numeral
20. This represents a common oil fractionating process
which resulted in distillation or solvent extraction of the
various fractions of oil by temperature or solubility
sensitivity. In these processes, a suitable diluent 22 can
be introduced into the circuit to reduce the viscosity of
the oil for transport and handling. The material is then
heated by a heater 24 and introduced into a fractionating
unit 26 where the fractions are separated based on their
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characteristic distillation temperatures or solubilities.
Diluent is recovered and recycled to the heavy oil
treatment stage denoted by riumeral 12. The light oils are
stored in storage vessel 28, while the heavy oils in vessel
30 and the vacuum gas oil. mixture are stored in vessel 32.
The light oil is in a concentration of about 10% by volume,
with the heavy oil approximating 25% by oil and the vacuum
gas oil mixture approximate:l_y 10% by volume. The material
is then pumped by pumps 34 and left as a product or
introduced to a pipeline 36 for further processing
(upgrading and refining). The fractionating unit is
depicted as a single unit operation, however, generally
such arrangements can iriclude multiple processing steps,
atmospheric and vacuum distillation units, and solvent
deasphalting units ( not shown ).
Turning to the area bounded by chain line and
indicated by numeral 38, shown is a schematic
representation of the process irl accordance with one
embodiment of the present invention. The material from the
heavy oil water recovery may be subjected tc> the heavy oil
treatment as indicated herein previously and subsequently
transported to the process denoted by numeral 38 by way of
a bypass line 40 which introduces pre-treated heavy oil
directly into the circuit for emulsification. The material
may be cooled by a medium 42 to a temperature for storage
and maintain suitable handl_i.ng viscosity or fed directly to
the emulsion preparation unit denoted by number 48. The
raw residuum, denoted by numeral 44, at this point is
essentially a non-flowable mass if allowed to cool to
ambient conditions. Suitable surfactant stored in vessel
46, is introduced to the material prior to being pumped
into an emulsification preparation unit, globally denoted
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by numeral 48. In the emulsification unit, water or steam
is added via line 50. In the emulsification unit, intimate
high sheer mixing is performed which may be done by the
mixers described herein previously. The desirable result
from the mixing is to provide a particle distribution in a
flat sized distribution range of 0.5 microns to 50 microns.
It is desirable also to have a water content in each
particle of between 25% by weight and 40'01~ by weight. The
quantity of water and surfactant to the raw residuum will
depend upon the final product considerations such as
stability of the emulsion over long periods of time or
short periods of time as well as other factors related to
the burning of the material. It has also been found that
in the process according to the present invention, the
residuum need not be in an liquid phase; desirable results
have been obtained where the irnm_iscible material has been
in a solid or liquid phase.
Product analysis of the final emulsion has
demonstrated that the material is capable of producing
4,000 to 10,000 Btu/lb as compared to the raw residuum
having between 12,000 and 14,000 Btu/ib or greater; (15,000
to 20,000 Btu/lb,) dependirig orl the degree of cut in the
fractionation unit and quality of feedstock. Accordingly,
approximately 70% retention of energy is achieved per unit
of aqueous fuel for a material that was previously not
considered viable for use as a f:uel.
One of the more attractive advantages of the process
is the fact that the process is reversible; the emulsion
can be de-emulsified readily to convert the material back
to its original form. This has positive ramifications for
further use or different uses entirely.
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In terms of suitable surfactants and other chemicals
which may be added to the raw residuum, the following are
representative of useful examples of such compounds
nonionic surfactants, anionic surfactants, cationic
surfactants inter alia.
Once the product has been emulsified, the final
product contains as indicated above, generally 70% by oil
weight and 30% by water weight. This material may be then
stored in a vessel 52 or pumped for further processing by
pump 54 to the processing stage broadly denoted by numeral
56 shown in dash line. In this process the emulsion may be
burned in a combustion device 58 such as a boiler/steam
generator or a cogeneration device with liberated steam
going to further use such as a power generation or process
heating, broadly denoted by numeral 60 or storage in a
reservoir 62.
Due to the high sulfur content of the material as
stated herein previously, the combustion products may be
passed into a flue gas desulfurization unit 64 prior to
being passed through stack 66 to the atmosphere. This
desulfurization can also be performed in the combustion
chamber, for boilers such as fluid bed type or external for
conventional and OTSG (once thru steam generator) type
boilers.
Figure 2 illustrates the effect of droplet size
relation to carbon burnout. The present invention, by
providing a droplet size in the range specified, maximizes
on the relationship for the emulsified fuel.
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Figure 3 illustrates the preheating of residuum 76 by
exchanger 75 to lower the viscosity to below 5000
centipoises and more particularly to below 500 centipoises
for greater ease in pumping, handling and mixing with an
aqueous emulsion. The preliminary stages are common with
Figure 1. This also has effect in the production of a
substantially narrow size distribution of between 0.5 and
50 microns.
For example, referring to Figure 4 from the viscosity
chart, the following preheat temperatures for the heavy
fuels are desirable as feed to the mixer to formulate the
micro-sized emulsion without diluent:
Heavy Fuel Description Fuel Preheat Requirements
#6 Light Fuel Oil 35 to 65 C
#6 Heavy Fuel Oil 65 to 100 C
Dry Bitumen Fuel 95 to 125 C
Soft Asphalt Residuum Fuel 100 to 135 C
Fractionated Residuum Fuel 135 to 180 C
Vacuum Residuum Fuel 200 to 250 C
Desaphalter Residuum Fuel 250 to 350 C
The viscosity of the emulsified fuel is typically less
than 100 Cp, ready for atomization in the burner.
Water temperature at 50 to the mixer 48 is controlled
as required to regulate the emulsion temperature exiting
the mixer to a suitable temperature for storage 52 and
burning, for example, 65 C to 95 C would be desirable for
atmospheric storage. Water preheating may be required for
lighter fuel oils such as #6 fuel oils.
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Further, the water temperature may also be regulated
to produce a pressurized fuel for feed directly to the
burners without the need for additional pumping indicated
by numeral 54. Figure 5 illustrates curves which show the
temperature and pressure operating parameters resulting
from the preheated residuum and feed water temperatures.
Figure 6 illustrates a further embodiment of the
present invention where the system is pressurized to
maintain the fuel emulsion. Common numerals used in the
Figure are representative of common description with
previous Figures. The residuum is pumped by pump 84 and
preheated by exchanger 75 into emulsification preparation
unit 48 where water 50 is added. The so-formed emulsion 85
may optionally cooled at 83 and stored in vessel 52 or
passed directly through to combustion device 58.
In view of the fact that the pressure is maintained
from the pump 84 to the combustion device 58, the emulsion
does not degrade or experience temperature increases which
would otherwise degrade the emulsion. The pressure is
maintained throughout the process from pump 84 to
combustion device 58 as denoted by numeral 100.
A pressurized emulsion fuel is produced and fed
immediately to the burner with pressurized fuel storage.
In this embodiment, emulsion fuel pumps 54 are eliminated,
which is very desirable as pumping of this fuel may have
adverse effects on fuel stability and other fuel
properties.
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EXAMPLES
Example 1 - Residuum Fuel from Atmospheric Distillation
Unit (ADU)
~ ADU Residuum Fuel Inlet Temperature = 180 C at 75
~ Recommended Feed Water Inlet Temperature = 20 C to
100 C at 50
~ Final Emulsion Fuel Temperature and Pressure Range =
115 C to 147 C at 85
The emulsion fuel, after mixing is maintained at a
pressure greater than 350 kPa(g) prior to atomization at
the burner 58. Optional heat exchanger is not required.
Example 2 - Residuum Fuel from Deasphalting Unit
~ Deasphalter Residuum Fuel Preheated = 300 C at 75
~ Recommended Feed Water Inlet Temperature = 25 C at 50
~ Final Emulsion Fuel Temperature and Pressure = 197 C
at 1400 kPa(g) at 85
In this example, the emulsion is fed directly from the
mixer to an optional heat exchanger 83 where the
temperature is reduced to the range of 115 C to 147 C prior
to atomization at the burner 58.
Referring to Figure 7, a further embodiment of this
invention is to combine the methods of adding diluent and
preheat to achieve the desired reduced viscosity for mixing
to enable production of aqueous based emulsion fuels.
Common numerical designations denote the common elements
from previous Figures. As an example, heavy vacuum
residuum 76, which can became un-pumpable at temperatures
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less than 150 C, can be premixed with a diluent at 77
immediately after the fractionation step to reduce the
viscosity to less than 5000 Cp, more specifically less than
1000 Cp and cooled to temperatures less than 95 C at 42 for
storage at 44. The aqueous fuel can be preheated to the
desired temperature on demand to facilitate viscosities
less than 500 Cp, more specifically less than 200 Cp at 75
for the formation of the required micro-sized emulsion.
This method is particularly desirous if the heavy residuum
requires long term or seasonal storage at 44 prior to
emulsion fuel preparation at 48. Further, this method
permits the use of a waste stream as diluent 77 for
disposition in the fuel. The addition of diluent 77
provides the specific minimum fuel properties required for
storage and handling at 44, from where the diluent residuum
fuel can then be preheated at 75 and mixed with water at 48
to form the fuel emulsion as required for immediate burning
at 58 without storage. Any form of diluent, compatible
with the burning properties of the emulsion fuel, can be
used to achieve the desired viscosity requirements. The
diluent may or may not contribute to the final heating
value of the emulsion fuel as the fuel rate can be adjusted
to maintain the desired heat content, however the diluent
must not affect the performance of the emulsion fuel.
Both the formation and mixing stages 48 and the
storage and handling stages 44 of the emulsion fuel may
occur at atmospheric conditions or pressurized conditions
as required by the properties of the original residuum
fuel, diluent, and the final emulsion fuel. It is
desirous, as known by those skilled in the art, that the
emulsion must be at a sufficient pressure greater than the
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vapour pressure of the emulsion fuel to maintain a liquid
fuel state until atomizing occurs at the burner 58.
The combustion products may be handled as discussed
with respect to Figure 2. Heavy oil residuum has been
discussed in detail here; however, it will be apparent that
any residuum may be processed by the process 38.
Variations will be appreciated by those skilled in the art.
Although embodiments of the invention have been
described above, it is not limited thereto and it will be
apparent to those skilled in the art that numerous
modifications form part of the present invention insofar as
they do not depart from the spirit, nature and scope of the
claimed and described invention.
