Note: Descriptions are shown in the official language in which they were submitted.
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FLUID CONTAINMENT ~RTICLE FOR HOT HYDROCARBON
FLUID ~ND METHOD OF PREVENTING FUEL
THERMAL DECOMPOSITION DEPOSITS
Inventor: George A. Coffinberry
BACKGROUND OF THE INVENTION
The present invention relates generally ~o deposits
formed on surfaces in contact with hydrocarbon fluids, and
more particula:rly, to a method o~ preventing or reducing the
deposit of hydrocarbon fluid thermal decomposition products on
surfaces in contact therewith and to a fluid containment
article having a surface which inhibits the formation of gum,
coke, sulfur compounds and/or other impurities formed by
thermal decomposition of the fluid, without resorting to
modification of the fluid, without adoption of special
procedures and without installation of special equipment for
ehelr use.
Because high temperature is usually associated with
undesirable levels;of hydrocarbon fluid dep~sit for~ati~n, the
~15 technical subject herein is~customarily referred to as thermal
: instability, or in:the:case of fuels, as fuel instability.
The mechanisms for formation of deposits ~rom thermal
instability have been studied and documented. In the case of
fuels, it is generally accepted that there are two distinct
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mechanisms occurring at two levels of temperature. In the
first mechanism, referred to as the coking process, as
temperature increases from room temperature, there is
generally a consistent increase in the rate of formation of
coke deposits up to about 1200F where high levels of
hydrocarbon pyrolysis lead to coke formation and eventually
limit the usefulness of the fuel. A second lower temperature
mechanism generally peaks at about 700F and involves the
formation of gum deposits. This second mechanism is generally
better understood than the coking process. It involYes
oxidation reactions which lead to polymerization which
includes the formation of gums. Both coke and gum formation
and deposits can occur simultaneously in the mid-temperature
region.
Co)ce formation in hydrocarbons is discussed in U.S.
Patent No. 2,698,512, and heat stab:ility of jet fuel and the
consequences of thermal degradation of the fuel are discussed
in U.S. Patent No. 2,959,915, both patents being incorporated
herein by reference in their entire1:y. These patents suggest
specific formulations which place limitations on the fuel
chemistry and impurities associated with hydrocarbon fuels so
that the fuels will be usable at high temperatures without the
typical formation of gums and coke.
Gum and coke formation are discussed in U~S. Pat~nt
No. 3,173/247, which is incorporated by referance herein in
its entirety. It is indicated therein that t very high
flight speeds, heat must be transferred, particularly from the
engine, to some part of the flight vehicle or to its load, and
although the fuel which is stored on the vehicle, could serve
to receive this heat, in practice, such procedure is
unfeasible because jet ~uels are not stable to the high
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temperatures which are developed at multi-Mach speeds,
instead, they decompose to produce intolerable amounts of
insoluble gum or other deposits, for example coke. As with
the previously referenced patents, the solution to the problem
has been directed toward limitations on fuel ch~mistry and
impurities associated with the fuel.
Even with the most elaborate special treatment of
the fuel, coke ~ormation cannot be entirely eliminated even
when a pure hydrocarbon is used because if the temperature is
high enough and the time is long enough, coke formation will
occur. On the other hand, the chemistry of the hydrocarbon
fluid mixture and the chemistry of the containment vessel can
have a major influence on deposit mechanisms and deposit rates
at the temperatures where it is most desirable to use the
~luid. In the lower temperature region where gum formation
occurs, oxygen from air dissolved in the liquid is the major
adverse ingredient. Boiling amplifiles this adversity because
of the oxygen concentration effect of gas bubbles adjacent to
hot walls. If oxygen or air is absent, gum formati~n is not
likely to occur.
In much of the prior art, the problems associated
with gum and coke thermal deposits has predominatPly dealt
with bulk fluid chemistry and reactions which can take place
within the fluid. These investigations have involved a wide
range of hydrocarbon compositions and the presence of numerous
impurities such as sulfur compounds, nitrogen compounds,
oxygen and trace metals. It has been obserYed that deposits
attached to containment walls often contain very large
quantities of sulfur and nitro~en compounds or intermediates
thereof in addition to gums and cokes. Little attention has,
however, been given in the prior art to the role o~ the
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chemistry and reactions which directly take place between the
containment walls and the fluid.
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Even though wall reactions are not well understood,
it can be generally supposed thak fluid-wall deposit thickness
reactions might be reduced if the wall were coated with some
form of relatively inert material; for example, porcelain or
glass coatings are often used to generally prev~nt deposit on
such common items as stoves and water tanks. These coatings
are, however, not structurally suitable for the application
envisioned by the present invention. Other inert non-sticking
coatings include such polymers as Teflon, but these materials
are not suitable at the high temperatures under consideration.
In U.S. Patent No. 3,157,990, certain phosphate
additives are added to the monopropellant wherein the
phosphates decompose in the reaction chamber and form a
coating, probably a phosphate coating, on the internal
generator surfaces, and it is suggested that this coating
effectively inhibits carbon decomposition and scaling. In
U.S. Patent No. 3,236,046, which is incorporated by reference
herein in its entirety, the i~terior surfaces of stainless
steel gas generators are passivated ~with sulfurous materials
to overcome deposition of coke o~ the ~urfaces of the gas
generator, and passi~ation is defined as a pretreatment which
sub~tantially reduces initial cataly-tic coke ~o~mation. From
these pàt~nts, it is deduced that the coke inhibiting
mechanisms is in fact a passivation process in which the
phosphate or ~ulfur reacts with ~he wall in much the same way
as oxygen reacts with iron or copper to form oxides which
protect the wall from further reaction. Ordinarily red oxide
paint primer is a similarly well-known approach. The patents
are suggestive that some ~orm o~ r~action takes ~lace between
the fuel and the wall.
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In U.S. Patent No. 4,078,604, which is incorporated
by reference herein in its entirety, heat exchangers are
characterized by thin-walled corrosion resistant layers of
electro-deposited gold or similar corrosion-resistant metals
on the walls of the cooling channels within the inner wall,
and the cooling ohannels are covered with the
electro-deposited layer of gold in order to make the surfaces
corrosion resistant to such storable liquid fuels as red
fuming nitric acid. In this prior art case, the wall is
protected from corrosion by the propellent, but the intent is
not to prevent deposit formations. It is also known from
prior art that gold plating has been used to prevent surface
catalytic reactions with fuel in which case the objective is
not to interfere with gum formation for the purpose of
evaluatin~ fuel chemical stability.
Thermal instability and fuel instability, referred
to above, are becoming more significant with developing
technology, and it will become ~ven more significant as
processes and machinery will be required to operate at higher
temperatures as afforded by advances in materials technology
and as the chemical quality of hydrocarbons for fuels, oils,
lubricants, petrochemical processes (plastics and synthetics)
and the like, decreases. Furthermore, hydrocarbon fluids,
~5 fuels and oils deri~ed ~rom non-petroleum sources, such as
shale and coal, will have significantly more problems with
thermal instability because of their high content of olefins,
sulfur and other compounds. Accordingly, it i5 advantageous
to provide fluid containment articles and processes for
preventing the ~ormation of adverse decomposition products and
foulants in such applications where thermal instability,
including fuel ins~ability, is a problem as a result of
exposure to such fluids to high temperatures.
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In view of the foregoing, it can be seen that it
would be desirable to provide fuel containment articles for
containing hot hydrocarbon fluid in which decomposition
products formed by thermal decomposition of the hydrocarbon
fluid is avoided, eliminated or reducedO It would also be
desirable to provide a method of protecting metal surfaces
which contact hot hydrocarbon fluid, from the deposit of
decomposition products of the hydrocarbon fluid. It can also
be seen from the foregoing that it is desirable to provide
methods and articles for use with hydrocarbon fuels wherein
the hydrocarbon fuel can be used as a heat sink without the
undesirable deposit of insoluble gums, coke, sulfur compounds
or mixtures thereof on containment surfaces. It is also
desirable to provide methods and articles for containment of
vaporized fuel to reduce NOX emission and to provide methods
and articles for containment of low quality fuels derived from
coal, shale and low grade crude oil.
The disadvantages of the prior art processes and
techniques discussed above involve the need to alter the
hydrocarbon chemistry, maintain strict control of impurities
and/or provide additives and special processing such as
passivation treatments. All of these techniques constrain the
use of the fluid, increase cost and promote uncertainty as to
the ~uality level of the ~uel or treatment at a particular
time. The present invention overcomes all of these
limitation~ by providing a method and articles which eliminate
or reduce the surface reactions which lead to formation of
thermal instability deposits from hydrocarbon fluids and which
eliminate or reduce adherence o~ deposits on sur~aces using
ordinary low-cost fuels, oils and other hydrocarbons without :~
focusing special attention to impurities or quality.
Furthermore, there are a multitude of processes, systems and
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devices including petrochemical processes, machine tools,
automobile engines, aircraft gas turbine engines, and marine
and industrial engines in which surface deposits from
hydrocarbon fluids, fuels and oils are a major problem.
Deposits can foul heat exchangers, plug fuel injectors and
lubrication distribution jets, jam control valve and cause
problems with many other types of operating and control
devices associated with hydrocarbon fluids, fuels and oils.
It is a primary objective of this invention to overcome these
disadvantages.
SUMMARY OF THE INVENTION
These and other disadvantages are overcome in
lS accordance with the present invention by providing a coating,
hereinafter referred to as a liner, liner material, diffusion
barrier or diffusion barriex material on ~ fluid containment
metal surface, also referred to here:in as a substrate.
In accordance with the present invention, there is
provided a method and articles for preventing the deposit of
decomposition products and/or therma:L instability deposits
from hot hydrocarbon fluids on a metal substrate, and metal
surfaces are protected from the deposit of hydrocarbon fluid
decomposition products resulting from thermal decomposition of
hot hydrocarbon fluid in a fluid containment article or system
carrying hot hydrocarbon fluid. Thus, for example, as a
result of the present invention, heat generated by combustion
of fu~l in the operation of a combustor which utilizes
hydrocarbon fuel, or heat from other sources, can be
transferred by heat exchange principles to hydrocarbon fuel
without the undesirabl~ thermal decomposition of the fuel and
the subseguent deposit of thermal decomposition products on
the walls of the articles containing the fuel.
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In one aspect of the present invention, there is
provided a fluid containment article for containing hot
hydrocarbon fluid comprising a substrate having a surface
adapted for contact with the hydrocarbon fluid wherein the
surface comprises a liner selected from the group consisting
of a catalytically-active diffusion barrier material which
catalyzes thermal decomposition in the hydrocar~on fluid to
promote the formation of coke, the coke being subs-tantially
non-adherent to the liner, and a ca~alytically-inactive
diffusion barrier mat~rial which is inert to thermal
decomposition in th~ hydrocarbon fluid and inhibits the
formation of coke, the catalytically-active and catalytically-
inactive diffusion barrier materials inhibiting the *ormation
of gum, sulfur compounds or other decomposition impurities or
mixtures thereof formed by thermal decomposition of the
hydrocarbon ~luid, the liner material being a physical
diffusion barrier located between the substrate and
hydrocarbon fluido
In another aspect of the present invention, there
is provided a method of preventing the deposit of thermal
decomposition products in a hydrocarbon fluid on a metal
surface of a device adapted to contain the hydrocarbon fluid I ~:
comprising applying to the metal surface a layer o~ diffusion ~,
barrier material which is inert to chemical formation o~
thermal decomposition products in the fuel. In this
embodiment of the invention, the liner or liner material
itself is inert to chemical reaction with hydrocarbons and
hydrocarbon impurities, that is, it is inert to the chemical
3Q formation of such thermal dPcomposition products as gum, co~e, '! ~ '
sulfur compounds and other decomposition impurities in the ~:
fluid. As used herein, the liner in this instance is a
catalytically-inactive difusion barrier material.
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Dkt. No. 13-DV-10367
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In still another aspect of the present invention,
the deposit of thermal decomposition products in a hydrocarbon
fluid on a metal surface of a device adapted to contain the
hydrocarbon fluid is prevented by applying to the metal
surface a layer of diffusion barrier material which catalyzes
thermal decomposition in the hydrocarbon fluid to promote the
formation o~ coke, the diffusion barrier being a deterrent to
the formation of gum and sulfur compounds. Thus, in this
embodiment, the formation of coke, which is substantially
non-adheren~ or loosely-adherent to the diffusion barrier
material, is promoted while the formation of gum, sulfur
compounds and other decomposition impurities is inhibited. In
this embodiment of the invention the liner or liner material
itself is a catalyst which accelerates or promotes the
reaction of hydrocarbon and hydrocarbon impurity to beneficial
products (coke) which do not adhere or tend not to adhere to
the liner or liner material. The coke and any similar
non-polymer products can be tolerated in fuel because they do
not tend to adhere to surfaces, and they burn in the combustor
along with the fuel. As used herein, the liner in this
embodiment is a catalytically-active diffusion barrier
material.
The coating material or liner material is deposited
on a surface which is adapted for contact with a hydrocarbon
fluid, for example a distillate fuel, and depending on khe
particular material, it inhibits or prevents the formation of
gum, coke, sulfur compounds, or other decomposition impurities
or mixtures thereof formed by the thermal decomposition of the
hydrocarbon fluid, or it catalyzes the formation of coke while
inhibiting or preventing the formation o gum, sulfur
compounds and other decomposition impurities. The coating or
liner material is al~o a physical diffusion barrier to the hot
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hydrocarbon fluid, that is, it will ~ot permit the diffusion
of or pa~sing of the fluid through the material to the
substrate on which the coating material is deposited. Thus,
the liner material is a physical barrier located b~tween the
substrate and the hydrocarbon fluid.
From the foregoing, it is evident that the present
invention solves the problems related to the formation of gum,
coke, sulfur and other deposit-forming reactions which are
chemically associated with contact between hot hydrocarbon
fluid and the materials which the fluid contacts, for ex~mple
a wall. The present invention also solves the problems
associated with the attachment or adherence of deposits to
materials which the fluid contacts, by either physical or
chemical means. In certain embodiments, the present invention
also preferentially directs fluid-surface reactions toward
deposits which tend not to adhere to materials which the fluid
contacts.
Although there is no intention to be bound by any
particular theory or explanation of t:he mechanism(s) by which
the present invention inhibits the formation of gum, coke, ~-
sul~ur compounds and other deposit-forming species which are
~ormed by thermal decomposition of hydrocarbon fluid, it is
believed that chPmical reactlons ta~e place between specific
atoms and compounds which are part of the substrate chemistry
and react under the in~luence of temperature with hydrocarbons
and hydrocarbon impuritles such as nitrogen, oxygen and sulfur
and their compounds, to form metal nitrogen, metal oxygen and
metal sulfur compounds. These metal compounds form deposits
and/or precursors to deposits and provide an a tachment
mechanism between the substrate and other deposits. This
theory is supported by the argument that chemical-absorption
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provides a much stronger surface bond than would simple
physical absorption to the surface. In the specific case of -
gum deposits, it is theorized that metal atoms and metal
compounds in the substrate can react to form hydrocarbon
radicals which are then highly susceptible to further reaction
such as with oxygen, to lead ultimately to polymerization and
gums. Substrate reactions can also provide chemistry which is
known in the art to be precursors to gums, and after the
precursors attach to the substrate, they become the means for
which gums and cokes and other deposits can grow by means of
chemic~l or physical means, to consequential proportions.
In accordance with the present invention, a liner
material on the surface shields objectionable metal atoms and
metal compounds in the substrate or wall from reaction with
khe hydrocarbon fluid and its impurities. The same liner
material also physically prevents or :inhibits diffusion of
metal atoms and metal compounds into the hydrocarbon fluid.
The same liner material also prevents or inhibits diffusion of
the ~ydrocarbon fluid and any impurities that it contains, to
the substrate.
Two types of liner or liner materials may be used
in the processes and fluid containment materials of the
present invention. A first type of liner material is
catalytically-inactive diffusion barrier material. A
catalytically-inactive diffusion barrier material is one which
is inert to the formation of any decomposition products in hot
hydrocarbon fluid which contacts it. Thus, when such a
catalytically-inactive diffusion barrier material is used as
the liner on a hydrocarbon fluid containment article adapted
to contact hydrocarbon fluid, there is substantially no
thermal decomposition of the hydrocarbon fluid at elevated
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temperatures, for example, up to 900F, and there is no gum,
sulfur compound, coke or other decomposition impurity
formation in the heated fluid.
A second type of liner material is
catalytically-active diffusion barrier material. A
catalytically-active diffusion barrier material is one which
actively permits or promotes the formation in hot hydrocarbon
fluids of a compound or compounds which have no adverse effect
on the utilization of the fuel, on the flow and transport of
the fuel and/or on the components contacted by the fuel. More
specifically, a catalytically-active diffusion barrier
material is one which actively permits or promotes the
formation of coke in the hot hydrocarbon fluid, a coke which
remains substantially dispersed in the fluid as it flows and
is transported through containment articles and other
components and is ultimately burned, or otherwise utilized,
with the fluid. Coke which is so formed and remains
substantially dispersed in the fluid in which it is formed, is
defined herein as loosely-adhered or substantially
non-adherent coke because it tends not to stick to or adhere
to containment walls and elements either by physical or
chemical attraction. With the formation of coke in the
presence of the catalytically-active diffusion barrier
material is the simultaneous inhibition or repression of
formation of gumj sulfur compounds and/or other decomposition
impurities in the hydrocarbon fluid. In both types o~ liner
material, the diffusion barrier material is also a physical
barrier or obstacle located between:the substrat~ and the
hydrocarbon fluid and prevents physical contact of the fluid
and the substrate.
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As used herein, the phrase 'iother decomposition
impuritiesl' refers to any compounds which can form as a result
of the thermal instability of a hydrocarbon fluid, other than
gum, sulfur compounds and coke. The prior art and literature
disclose many such species and can include, for example,
metal-nitrogen compounds, metal-oxygen compounds, various
olefins and/or pol~mers formed therefrom, saturated and
unsaturated polymers, cyclic and aromatic hydrocarbon
compounds and the like. The other decomposition impurities
which can form in a hot hydrocarbon fuel are frequently
dependent on the initial fuel content including the starting
impurities therein.
BRIEF DESCRIPTION OF THE DRAUINGS
These and various other features and advantages of
the invention can be best understood from the following
description taken in conjunction with the accompanying
drawings in which:
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Figure 1 is a partial longitudinal view of a high
pressure turbine nozzle for a jet engine fueled by distillate
fuel and incorporating the heat exchanger wall construction of
the present invention~
Figure 2 is a sectional view taken along the line
of II - II of Figure 1 showing fual conkainment passages for
circulating distillate fuel.
Fi~ure 3 is a photograph of two (2) stainless steel
planchettes showing before and after exposures to hot jet-A
fuel.
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Dkt. No. 13-DV-10367
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Figure 4 is a scanning electxon beam micrograph
(magnified 2000X) of an uncoated area (prior to testing) of a
planchetke which has been sand blasted~
Figure 5 is a scanning electron beam micrograph
(magnified 5000X) of an uncoated area (after testing) of a
planchette.
Figure 6 is a scanning electron beam micrograph ~;
(magnified 2000X) of a coated area (prior to testing~ of a
planchette.
Figure 7 is a scanning electron beam micrograph
(magnified 2000X) of a coated area (after testing) of a
lS planchette.
DETAILED DESCRIPTION OF THE INVENTION
The terms hydrocarbon fluid, hydrocarbon fuel and
distillate fuel ~ay be used interchangeably herein.
The invention has applicab:ility to any hydrocarbon
fluid in which gum or other polymers, coke, sulfur compounds
or any other decomposition impurities form when the fluid is
exposed to heat. Although the invention i~ not directed to or
limited by any particular hydrocarbon fluid or hydrocarbon
fuel, typical ~uels for which the method and fluid containment
articles of the present invention are adapted, and typical
fu21s from which the substrates of fluid containment articles
are protected in accordance with the present invention, are
the hydrocarbon or distillate fuels generally discussed above
and include hydrocarbons and distillation products thereof
which are generally liquid at room temperature. The fluids
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may be pure hydrocarbon or mixtures of hydrocarbons,
distillation products, mixtures of such distillation products,
mixtures of hydrocarbons and distillation products, No. 1 or
No. 2 diesel fuels, jet engine fuels, such as Jet-A fuel, or
the foregoing fuels mixed with additives which are well-known
in the prior art. Hydrocarbon fuels refer to the liquid fuels
which are conventionally used in reaction motors, including,
but not limited to, industrial gas turbines, engines used in
jet propelled aircraft or any other gas turbine engine, all of
which are conventionally known in the art and, for example,
certain of the aviation and other gas turbine fuels discussed
in volume 3, third edition, ENCYCLOPEDIA OF CHEMICAL
TECHNOLOGY, pages 328 - 351 (1979). Various hydrocarbon fuels
which are particularly desirable or jet aircraft engines, are
also described at column 6, lines 30 - 74 of U.S. Patent No.
2,782,592 and at column 2, lines 28 to column 3, line 23 o~
U.S. Patent No. 2,959,315 both of which are incorporated by
reference herein in their entirety.
Although all of the foregoing hydrocarbon fluids
can be used in the present invention, and the advantages of
the present invention apply thereto, it is an unexpected
advantage of the present invention that pure, untreated,
low-cost hydrocarbon fluids can be used as fuel in jet engines
without ~pecial handling, without further treatment, without
costly quality control procedures, and without the need for
special processing either prior to or subsequent to loading
the fuel in the aircraft. Furthermore, these same advantages
apply to all other processes and systems which utilize
hydrocarbon fluids including, but not limited to, the
petrochemical and plastics industries, the synthetic fuels
industry, commercial and home heating industries and the like.
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The fluid containment article of the present ~ -
invention may be any component which is adapted to contain hot :
hydrocarbon fluid~ for example, liquid hydrocarbon jet engine
or diesel fuel heated at a temperature at which decomposition
products form in hydrocarbons, hydrocarbons circulating in
conduits, heat exchangers and the like o~ refineries, polymer
plants and power plants, furnaces and the like. Such articles
for containing hot hydrocarbon fluid are defined herein as
fluid containment articles. Examples of uch fluid
containment articles are discussed above and include any
device in which hot hydrocarbon fluid can be confined, stored,
transported or otherwise subjected to heat exchange without
ignition or combustion of the hot fluid. The present
invention is particularly adaptable to heat transfer surfaces
where heat is transferred from a combustor or other heat
source through a wall to liquid hydrocarbon fluid. Specific
examples of fluid containment articles for hot hydrocarbon
fluids in accordance with the present invention include fuel
storage tanks, conduits for transporting liquid fuel, coils
and other devices for heat exchange contact with fuel, fuel
injector surfaces and the like.
one such fluid containment article is shown in ~-
: Figure 1 which represents a heat exchanger for cooIing the
~: 25~ high pressure turbine no~le of a jet engine by transferring
the heat gen~rated therein to liquid hydrocarbon fuel confined
in and tra~sported through conduits or chambers adjacent the
nozzle wall.
.
In Figure 1, liquid hydrocarbon fuel enters the
high pressure turbine nozzle at condui~ 6 and passes through
heat exchanger 2 where h~at from combustion chamber 16, for
example, operating at a temperature such that the walls of the
nozzle which form chamber 1~ ha~e a temperature of about
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Dkt. No. 13-DV-10367
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1200F, is cooled by the liquid hydrocarbon fuel passing
through fuel passageway 2. Thus, ther~ is heat exchange
between the walls of chamber 16 and the liquid hydrocarbon
fuel passing through passageway 2. Liquid hydrocarbon fuel
also passes through passageway 4 where heat exchange also
occurs between the wall of the chamber 16 and the liquid
hydrocarbon fuel in passageway 4. Vaporized hydrocarbon gas
12 flows into chamber 16 through gas injection ports 10.
Referring to Figure 2 which shows in more dPtail
the fuel containment passageway of Figure 1, Figure 2 being
taken along the lines II - of Figure 1, liquid hydrocarbon
fuel passageway 2 contains walls 24 and 26 through which fuel
passageway 22 is ~ormed. Special barrier materials,
identified herein a5 fuel diffusion barrier material 20 is
coated on substrates 24 and 26 so that it forms a liner or
liner material in passageway 22. Thus, numeral 20 in Figure 2
represents the fuel diffusion barrier material or liner
material of the present invention.
Substrates 24 and 26 of Figure 2, which represent
the heat exchanger walls of chamber 16 in the high pressure
turbine no~zle of Figure 1, are generally constructed of any
conventional material as well known in the art. For example,
such substrates may ~e stainless steel, corrosion-resistant
alloys of nickel and chromium commercially available as
INCONEL~, a trademark of the International Nickel Company~
Inc., a high-strength, nickel-base, corrosion-resistant alloy
identified as H~STELLOY~, a trademark of Union Carbide
Corporation, and the like. It is these typical substrate
materials which appear to cause or promote the formation of
fuel thermal decomposition products, such as gum, various
polymers, coke, sulfur compounds, other decomposition
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impurities or mixtures thereof, in liquid hydrocarbon fluids
and fuels. It is the surface of substrates 26 and 24 which
are adapted for contact with the hydrocarbon fuel by the
formation of passageways, for example as shown by numeral 22
in Figure 2, therein. Liquid hydrocarbon fuel can be
transported through passageway 22 by any appropriate means
(not shown), and the hydrocarbon fuel as it passes through
passageway 22 contacts the substrate. However, in accordance
with the present invention, passageway 22 is actually formed
from liner material 20 which has been coated upon the surfaces
of substrates 24 and 26 which form passageway 22.
Accordingly, as the liquid hydrocaxbon passes thxough
passageway 22, it actually contacts liner material 20. For
best results, liner material 20 is continuous and completely
covers all surfaces of passageway 22 which are formed from
substrates 24 and 26 and which provide a heat exchanye
relationship because of its conta~t with the liquid
hydrocarbon fuel.
In accordance with the present invention, liner
material 20 which actually forms pas;ageway 22 by virtue of
the continuou~ coating of liner mate;rial 20 to the passageway
formed by substrates 24 and 26, is a diffusion barrier
material which is catalytically-inactive and inhibits or
prevents formation o~ fuel thermal decomposition products, for
example, amorphous tantalum oxide, or it is a diffusion
barrier material which is catalytically-active and catalyzes
the thermal decomposition in the fuel to promote the formation
of a loosely-adher~nt coke in the fluid, for example,
amorphous zirconium oxide. The liner is also a physical
diffusion barrier to the hydrocarbon fuel and prevents contact
between the fuel and the substrate. Thus, liner material 20
which coats substrates 24 and 26 and thereby ~orms passageway
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22, is an inert or catalytically-inactive diffusion barrier
material which prevents, reduces or inhibits the formation of
gum, cok~, sulfur compounds, and/or other decomposition
impurities and the like and thereby prevents, reduces or
inhibits the deposit of gum, coke, sulfur compounds and/or
other decomposition impurities on the surfaces of the
passageway, or a catalytically-active difusion barrier
material which catalyzes thermal decomposition in the fuel to
promote the formation of a loosely-adherent or substantially
non-adheren~ coke while simultaneously inhibiting the
formation of gum, sulfur compounds and/or o~her decomposition
impurities and the like and thereby prevents, reduces or
inhibits the deposit of gum, coke, sulfur compounds and/or
other decomposition impurities on the surfaces o~ the
passageway, the coke remaining suspended or dispersed in the
fuel wherein it is transported with the fuel to the combustor
for burning.
In accordance with the present invention, preferred
liner or diffusion barrier materials which may be applied to
the surfaces of the metal substrates in contact with the fuel
in fuel containment articles or in a fuel containment system,
and which causes catalytic formation of coke, for example coke
which loosely adheres to the liner material and remains
dispersed in the fuel, or which prevent or inhibit the
formation of all thermal decomposition products in the fuel,
include metal oxides, and more preferably, amorphous metal
oxides.
As explained above, the liner or liner material of
the present invention can b~ a metal oxide which is itself
inert to chemical reaction, that i~, catalytically-inactivs,
with the hydrocarbon and its impurities. In certain
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embodiments, the liner or lin~r material of the present
invention can be a metal oxide which is itself a catalyst
which accelerates hydrocarbon and impurities reaction to
products, such as c~ke which tends not to adhere to the liner.
The inert or catalytic liner can be deposi~ed on the substrate
by chemical vapor deposition. In the case of an inert
amorphous metal oxide, the liner can be amorphous tantalum
oxide (Ta2O5~. In the case of the catalytic amorphous metal
oxide, the liner can be amorphous zirconium oxide (ZrO2).
Although the thickness of the liner material, that
is, the metal oxide film is not critical, the metal oxide film
can be quite thin, on the order of about one-half micron in
order to prevent micro-cracking due to surface stresses which
could degrade the di~fusion-barrier nature of the liner. In
certain preferred embodiments, the metal oxide is amorphous so
as to be homogeneous and closely packed in order to prevent
diffusion and contact between the fluid and substrate.
Non-amorphous or crystalline metal oxides can also be
deposited on substrates in accordance with the present
invention as long as such deposits or coatings form a
continuous, closely packed coating to prevent diffusion and
contact between the ~luid and substrate.
~he metal oxides which may be coated on the surface
of the metal substrate to produce a diffusion barrier to
hydrocarbon fuel, and thereby prevent or inhibit ~uel thermal
decomposition products, such as gums and other polymers,
sulfur compounds and/or other decomposition impurities, and in
certain embodiments, coke, may be any of the known methods ~or
depositing metal oxide coatings on surfaces o~ metals. The
liner can be attached to the substrate, for example, by the
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Dkt. No. 13-DV-10367
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chemical vapor deposition (CVD) process, and more
specifically, by the chemical vapor infiltration (CVI)
process. The liner can also be attached by plasma CYD or by
the sol-gel precipitation process. The zirconium oxide,
tantalum oxide and other metal oxides whic~ form the liner of
the present invention may be deposited by any of the
conventional techniques, such as those disclosed in volume 15,
third edition of the Kirk-Othmer ENCYCLOPEDIA OF CHEMICAL
TECHNOLOGY, pages 252 - 269 entitled "~etallic Coatings
(Survey)". The plasma deposition of zirconia is discussed and
described in U.S. Patent No. 3,467,583 which is incorporated
by reference herein in its entirety.
Although, as explained above, the present invention
has utility in any fuel containment article or in any fuel
containment system in which fuel does not undergo combustion,
and it is particularly useful in forming a diffusion barrier
in fuel containment articles and fuel containment systems
wherein the fuel is used as a heat exchange medium to remove
heat from various systems in gas turbines, both industrial and
those used in aircraft and the like, it is particularly useful
in the heat exchanger surfaces in fuel systems of a gas
turbine, a scramjet engine, a ramjet engine, or a turbojet
engine or as a conduit for transporting heated hydrocarbon
fuel in a fuel system of any of the foregoing. Unlike the
prior art processes and fluid containment articles and
systems, the processes and fluid containment articles of the
present invention can use conventional low-cost fluids without
any disadvantage. The prior art processes and fluid
containment articles must use fuels containing additives,
special fuel processing procedures and/or special handling,
all oP which are costly, create additional problems and
generate or promote the generation of NOX. With the processes
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Dkt. No~ 13-DV-10367
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and articles of the present invention, there is a
substantially improved system in which NOX generation can be
minimized.
Application of the benefits to be derived from the
present invention are quite extensive. One application of
these benefits is to provide a heat exchanger surface which
can be used to gasi~y jet fuel without ~ouling of the heat
exchanger surface. The gaseous fuel can then ~e injected into
a gas turbine combustor in a uniform fashion rapidly mixing
with air so as to burn at a uni~orm temperature. Such uniform
temperature combustion would substantially reduce the
formation of nitrogen oxide pollutants. Another application
would also involve haating the jet fuel to a very high
lS temperature so as to obtain a high heat sink for cooling
various engin~ and aircraft parts ancl systems. Another
application would involve coating parts such as Xuel nozzles,
injectors, and flow distribution jets so as to avoid deposit
buildup which would plug the nozzles, injectors and jets.
Another application would involve coating of valves so as to
avoid sticking and seizing ~rom gums or cokes. These and
other applications and benefits of the present invention will
become obvious to those skilled in the art based on the
teachings o~ the present invention.
The following specific example describes the
methods and articles of this invention. It is intended for
illustrative purposes only and should not be construed as
limiting the present inYention.
A stainless steel planchette or coupon measuring
50mm long by 8mm wide by 2mm thick made from 304 stainless
steel was coated with a 0.4 micron thick layer o~ tantalum
oxide, Ta2O5, by a conventional chemical vapor deposition
process~
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Dkt. No. 13-DV-10367
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The test was conducted by flowing commercial grade
Jet-A kerosene aviation fuel over a planchette for 8 hours at
970F and 420 psia. A total of 0.74 pounds of hot (970F)
fuel was passed over the planchette during the 8-hour tPst.
No attempt was made to remove air from the fuel.
In Figure 3, planchette 30 was photographed prior
to exposure to coking conditions, that is, prior to the test
set forth above. On planchette 30, lower portions or section
34 was coated and remained coated with the tantalum oxid~, and
upper portion or section 32 was sand blasted to remove the
coating of tantalum oxide. Planchette 30 was exposed to the
test conditions specified above, and after exposure to the
flowing, hot Jet-A fuel, the planchette was removed and
photographed and is shown as planchette 40 in Figure 30
Comparison of planchettes 30 and 40 shows that a
deposit formed on uncoated (upper) portion 42 of planchette
40. Aft~r examination of coated reg:ion 44 and uncoated region
42 of planchette 40, the deposit on region 42 was removed by
burning in oxygen to form carbon dioxide and sulfur dioxide.
The total amount of deposit was dete:rmined to be O.2 mg which
corresponds to a deposit rate of 3.1 micrograms/hr/cm2 for the
8-hour test. ~ased on prior tests of uncoated samples, it is
judged that the deposit rate is highest during initial
exposure (up to 100 micrograms/hr/cm2 for ~ 0.5 hour duration
test), and that the weight ratio of car~on to sulfur
composition ~f the deposit is about 2 to 1.
Figure 4 shows uncoated (sand blasted) region 32 of
planchette 30 before the test. Figure 5 shows the deposit
formed on uncoated region 42 o~ planchette 40 after the test.
The rock-shaped crystalline deposit shown in Figure 5 was
found to contain up to 30 - 40~ sulfur. As the sulfur
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Dkt. No. 13-DV-10367
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conc~ntration in the Jet-A fuel is only about 200 ppm, this
represents a high concentration in the deposit. These same
crystals were determined by x-ray diffraction to be chromium
sulfide, indicating that the sulfur impurities in the fuel
reacted with chromium in the 304 stainless steel. No chromium
could be found in the Jet-A fuel feed, hence the chromium had
to come from the steel. The black appearance of the deposit
is characteristic of either carbon or chromium sulfide,
leading to the spPculation that chromium sulfide could easily
be misinterpreted as coke.
Figure 6 shows coated portion 34 of planchette 30
before the test. Figure 7 shows coatsd portion 44 (different
area) o~ planchette after the test. There is no evidence of
deposit on coated portion 44 even at 10,000 X magnification
(not shown) using a scanning electron beam microscope.
Clearly the Ta2O5 prevented contact between chromium in the
metal and sulfur in the fuel. No other type of deposit was
observed on the coating.
Tasts similar to those above were conducted at
700F and 100 psia for 10 hours using boiling J~t-A fuel. For
this test, air was bubbled into the l.iquid fuel to increase
oxygen concentration. The results wer~ identical to those
shown in Figure 3 insofar as depo~it~ formed on the uncoated
portion, and no deposit formed on the Ta205 coated portionO
The foregoing clearly establishes that the use of a
liner material of the present invention prevents diffusion
between the substrate and the hydrocarbon with subsequent
chemical reaction leading to surface deposit formations.
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Based on the foregoing results, it is further
evident to one skilled in the art that similar diffusion
barrier results can be obtained with other metal oxides on
other substrate materials using various coating deposition
processes.
While other modifications of the invention and
variations thereof which may be employed within the scope of
the invention, have not been described, the invention is
intended to include such modifications as may be embraced
wi~hin the following claims.
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