U.S. patent application number 11/903137 was filed with the patent office on 2009-03-26 for lithium pellets coated with fluorinated oil.
This patent application is currently assigned to Hamilton Sundstrand Corporation. Invention is credited to Ronald Lee Bauman, Mark A. Brege, Joel M. Kelsey.
Application Number | 20090078182 11/903137 |
Document ID | / |
Family ID | 40470311 |
Filed Date | 2009-03-26 |
United States Patent
Application |
20090078182 |
Kind Code |
A1 |
Bauman; Ronald Lee ; et
al. |
March 26, 2009 |
Lithium pellets coated with fluorinated oil
Abstract
Lithium fuel pellets are coated with a fluorinated oil, rather
than a fluorinated polymer or telomer. The lithium pellets are
coated by placing the pellets inside the lithium reaction vessel
and then pouring a fluorinated oil into the reaction vessel. The
reaction vessel is rotated in order to evenly coat the lithium
pellets. The oil adheres to the lithium pellets and does not settle
to the low point of the boiler cavity.
Inventors: |
Bauman; Ronald Lee;
(Kenmore, WA) ; Brege; Mark A.; (Rockford, IL)
; Kelsey; Joel M.; (Belvidere, IL) |
Correspondence
Address: |
KINNEY & LANGE, P.A.
THE KINNEY & LANGE BUILDING, 312 SOUTH THIRD STREET
MINNEAPOLIS
MN
55415-1002
US
|
Assignee: |
Hamilton Sundstrand
Corporation
Rockford
IL
|
Family ID: |
40470311 |
Appl. No.: |
11/903137 |
Filed: |
September 20, 2007 |
Current U.S.
Class: |
114/20.2 ;
149/19.3; 149/20; 149/6; 44/530; 60/668 |
Current CPC
Class: |
F42B 19/18 20130101;
C06B 45/32 20130101; C06B 27/00 20130101 |
Class at
Publication: |
114/20.2 ;
149/19.3; 149/20; 149/6; 44/530; 60/668 |
International
Class: |
F42B 19/18 20060101
F42B019/18; C06B 45/32 20060101 C06B045/32 |
Claims
1. A alkali metal-based fuel comprising: a plurality of alkali
metal pellets; and a fluorinated oil that adheres to the alkali
metal pellets.
2. The alkali metal-based fuel of claim 1 wherein the alkali metal
is lithium.
3. The alkali metal-based fuel of claim 1 wherein the fluorinated
oil is a perfluoropolyether.
4. The alkali metal-based fuel of claim 1 wherein the fluorinated
oil forms a coating on the surface of the lithium pellets.
5. The alkali metal-based fuel of claim 1 wherein the plurality of
alkali metal pellets is a binary mixture of large and small alkali
metal pellets.
6. The alkali metal based fuel of claim 5 wherein the large pellets
have a diameter in excess of 8 times the diameter of the small
pellets.
7. The alkali metal-based fuel of claim 5 wherein the large pellets
have a volume in excess of 300 times the volume of the small
pellets.
8. A method of making a thermal power source comprising:
introducing a plurality of alkali metal pellets into a reaction
vessel; introducing a fluorinated oil into the reaction vessel;
sealing the reaction vessel; and agitating the reaction vessel to
coat the alkali metal pellets with the fluorinated oil.
9. The method of claim 8 wherein the alkali metal is lithium.
10. The method of claim 8 wherein the fluorinated oil is a
perfluoropolyether.
11. The method of claim 8 wherein the plurality of alkali metal
pellets is a binary mixture of large and small alkali metal
pellets.
12. The method of claim 11 wherein the large pellets have a
diameter in excess of 8 times the diameter of the small
pellets.
13. The method of claim 11 wherein the large pellets have a volume
in excess of 300 times the volume of the small pellets.
14. The method of claim 8 wherein the agitation is rotation.
15. A propulsion system comprising: a reaction vessel containing a
plurality of alkali metal pellets and a fluorinated oil adhering to
the plurality of alkali metal pellets, the reaction vessel heating
a fluid; and a turbine for converting energy from the fluid into
work to drive a propulsor.
16. The propulsion system of claim 15 wherein the alkali metal is
lithium.
17. The propulsion system of claim 15 wherein the fluorinated oil
is a perfluoropolyether.
18. The propulsion system of claim 15 wherein the fluorinated oil
forms a coating on the surface of the lithium pellets.
19. The propulsion system of claim 15 wherein the plurality of
alkali metal pellets is a binary mixture of large and small alkali
metal pellets.
20. The propulsion system of claim 21 wherein the large pellets
have a diameter in excess of 8 times the diameter of the small
pellets.
21. The propulsion system of claim 21 wherein the large pellets
have a volume in excess of 300 times the volume of the small
pellets.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to a power source in which an alkali
metal is oxidized to provide heat. More specifically, it relates to
lithium pellets that are coated with a fluorinated oil in a lithium
reaction vessel.
[0002] In certain situations, it is necessary to provide propulsion
in an environment where oxygen is not available. Underwater
vehicles, such as torpedoes, are one such situation. Torpedo
propulsion systems frequently use a vaporized fluid (such as water)
to drive a turbine, and the turbine then drives a suitable
propulsor. Typically, water is vaporized in a boiler that is heated
by an intensely exothermic chemical reaction, such as metallic
lithium oxidized with sulfur hexafluoride.
[0003] The lithium used in such a boiler may be either a solid
piece of lithium or lithium pellets coated with a fluorinated
polymer. However, both of these forms of lithium fuel have certain
drawbacks.
[0004] For example, using a solid block of lithium involves using
aluminum potassium perchlorate as a thermal starting device to heat
the boiler and the lithium inside it to operating temperature. The
aluminum potassium perchlorate generates high temperatures,
typically in the range of about 3000 to 4700.degree. C., and must
be formed into pellets that are closely packed together in order to
initiate the system. To achieve this, core holes are formed in the
lithium, and the core holes are filled with the aluminum potassium
perchlorate. A squib is also provided within the core hole, and the
core is then sealed with a lithium plug. Substantial pressures are
generated during ignition of the aluminum potassium perchlorate,
requiring the boiler structure to be very strong. Moreover, if the
aluminum potassium perchlorate, while undergoing oxidation,
contacts the boiler surfaces, it can burn through parts of the
boiler and damage the system.
[0005] To avoid these problems associated with using a solid
lithium core, encapsulated lithium pellets are more commonly used.
The lithium pellets are generally spherical in shape and have
diameters in the 1-25 millimeter range. The pellets are of varying
sizes to allow for close packing of the pellets. In addition, each
pellet is provided with a coating of a fluorine-substituted
hydrocarbon material, typically a polymer or telomer. Commercially
available materials suitable for such a coating include products
sold under the trademarks Teflon.RTM. and Vydax.RTM.. The coated
lithium pellets are placed inside a boiler and a starter squib is
fired, which melts the pellets adjacent to the starter squib. The
melted lithium pellets react with their coatings, generating
sufficient heat to propagate the reaction throughout the boiler.
Sulfur hexafluoride is supplied to the boiler in a controlled
fashion to maintain the reaction at a desired rate.
[0006] However, coating the lithium pellets with a fluorinated
hydrocarbon is a complex, multi-stage process. For example, a
typical process begins with placing the lithium pellets in a sealed
tumbler in which they can be agitated. The interior of the tumbler
is filled with an inert gas, such as argon. The coating material is
dispersed in a liquid, and the resulting slurry is sprayed on the
pellets inside the tumbler. The pellets are agitated during the
spraying in order to provide an even coating. After the desired
build-up of coating is achieved on the lithium pellets, the
spraying is stopped and a slight vacuum is formed in the interior
of the tumbler in order to evaporate the liquid applied to the
lithium pellets within the tumbler. After the liquid has
evaporated, the process is repeated several times until the desired
thickness of coating is achieved.
[0007] Alternatively, lithium pellets can also be coated inside of
the boiler. Lithium pellets are placed inside of the boiler, and a
fluorinated hydrocarbon dissolved or suspended in a solvent is
poured into the boiler. The solvent is evaporated under a vacuum
using heat. The process is repeated, if necessary, until a
sufficiently thick layer of fluorinated hydrocarbon coats the
lithium pellets.
[0008] Coating lithium pellets with a sufficiently thick layer of
fluorine-substituted polymer or telomer may require many layers to
be applied, so the process can take several days to complete. Thus,
there is an additional need for a simple, low-cost method of
applying a coating to lithium pellets. In addition, the
fluorine-substituted telomers commonly used to coat lithium pellets
are no longer available, having been removed from the market
because of environmental concerns. Thus, there is a need for a
commercially available, off-the-shelf material that can be used to
coat lithium pellets for use in a lithium reaction vessel. Both of
these needs should be satisfied without significantly diminishing
the advantages obtained by using coated lithium pellets in a
lithium reaction vessel.
BRIEF SUMMARY OF THE INVENTION
[0009] The present invention is a lithium fuel pellet that is
coated with a fluorinated oil, rather than a fluorinated polymer or
telomer, and a process for applying the coating to a lithium
pellet. An appropriate fluorinated oil is simply poured into the
boiler after it is loaded with a binary mixture of lithium pellets.
The oil adheres to the lithium pellets and does not settle to the
low point of the boiler cavity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a cross-sectional view of a portion of a lithium
boiler utilizing the invention.
[0011] FIG. 2 is a flow diagram illustrating the manner of coating
lithium pellets with a fluorinated oil for use in a lithium
boiler.
[0012] FIG. 3 is a block diagram of the propulsion system with a
lithium boiler utilizing the invention.
DETAILED DESCRIPTION
[0013] FIG. 1 shows an embodiment of the invention. A mixture of
lithium pellets including large lithium pellets 11 and small
lithium pellets 12 is placed into boiler 20 of a lithium reaction
vessel. Large lithium pellet 11 is roughly spherical in shape, with
a diameter of about 1.25 centimeters (cm). Small lithium pellet 12
is roughly spherical or cylindrical in shape, with a diameter of
about 1.5 millimeters (mm) and, for a cylindrical pellet, a length
of about 1.5 mm. Because of their smaller size, small lithium
pellets 12 react more readily than large lithium pellets 11, so
small lithium pellets 12 are used to initiate a reaction in boiler
20. Large lithium pellets 12, in turn, are used to maintain the
reaction for the desired period of time. Those skilled in the art
will recognize that the size and shape of lithium pellets used in
the mixture of pellets is a design choice, and the invention is not
limited to any particular size and shape of lithium pellets.
Similarly, while lithium is used as an example because it is the
metal most commonly used as fuel, other alkali metals, particularly
sodium and potassium, may also be used.
[0014] After large lithium pellets 11 and small lithium pellets 12
have been placed in boiler 20, fluorinated oil 30 is poured into
boiler 20. Fluorinated oil 30 is a liquid, and it fills the spaces
between and around large lithium pellets 11 and small lithium
pellets 12. Commercially available fluorinated oils that can be
used in connection with the invention include oil and grease
products sold under the trademark Krytox.RTM. by E.I. du Pont de
Nemours and Company, and particularly the Krytox.RTM. GPL 100-107
series. Krytox.RTM. is a perfluoropolyether (PFPE), also called
perfluoroalkylether (PFAE) or perfluoropolyalkylether (PFPAE).
Krytox.RTM. fluorinated oils are a series of low molecular weight,
fluorine end-capped, homopolymers of hexafluoropropylene epoxide.
The polymer chain is completely saturated and contains only the
elements carbon, oxygen and fluorine; hydrogen is not present. On a
weight basis, Krytox.RTM. contains 21.6% carbon, 9.4% oxygen and
69.0% fluorine.
[0015] After the fluorinated oil 30 is introduced into boiler 20,
boiler 20 is rotated or otherwise agitated in order to evenly coat
large lithium pellets 11 and small lithium pellets 12 with
fluorinated oil 30. Fluorinated oil 30 adheres to the surface of
large lithium pellets 11 and small lithium pellets 12, forming a
coating 32 on the lithium pellets. The period of agitation is
relatively short, typically only a few hours.
[0016] Lithium boiler 20 is now fueled and ready for use. A
reaction may be initiated in any conventional way, such as using a
squib and a detonation cord (not shown) to ignite small lithium
pellets 12. The detonation cord will raise the temperature of small
lithium pellets 12 above their melting point, and small lithium
pellets 12 will react with coating 32. This reaction is exothermic
and releases sufficient heat to melt large lithium pellets 11,
causing them to react with coating 32 and fluorinated oil 30. Thus,
the reaction spreads throughout boiler 20. An oxidizer, such as
sulfur hexafluoride, is then injected into boiler 20. The lithium
reacts with the sulfur hexafluoride in an intensely exothermic
manner, raising boiler 20 to its operating temperature of about
1100.degree. C. Boiler 20 then heats a working fluid, such as
water, above its boiling point, and the resulting steam is used to
turn a turbine.
[0017] FIG. 2 is a flow diagram illustrating the manner of coating
lithium pellets with fluorinated oil for use in a lithium reaction
vessel. The process 100 begins at Start box 110. Process 100 then
moves to box 120, where a binary mixture of lithium pellets is
introduced into the lithium reaction vessel of the boiler. As
discussed previously, the invention is not limited to any
particular size of lithium pellets. Different sizes and shapes of
lithium pellets are commonly mixed together when lithium pellets
are used as fuel. Optimally, the mixture of lithium pellets used at
box 120 is a binary mixture of pellets similar to large lithium
pellets 11 and small lithium pellets 12, which were discussed with
respect to FIG. 1.
[0018] Next, at box 130, fluorinated oil sufficient to coat the
lithium pellets is added to the binary mixture of lithium pellets
in the boiler. As discussed with respect to FIG. 1, commercially
available fluorinated oils that can be used in connection with the
invention include oil and grease products sold under the trademark
Krytox.RTM. by E.I. du Pont de Nemours and Company, and
particularly the Krytox.RTM. GPL 100-107 series.
[0019] At box 140, the boiler is agitated to uniformly coat the
mixture of lithium pellets with the fluorinated oil. Typically,
this agitation involves rotating the boiler containing the lithium
pellets and fluorinated oil. However, any sort of agitation
sufficient to coat the lithium pellets with fluorinated oil could
take place at this step.
[0020] The process ends at End box 150.
[0021] The present invention can be used in any application in
which lithium is used as fuel. The oxidation of lithium with sulfur
hexafluoride does not require oxygen, so it can occur in places
where oxygen is not available, such as underwater and outer space.
Most commonly, lithium reaction vessels are used as a heat source
for propulsion in underwater devices, particularly torpedoes, and
this invention can certainly be used in that application. Lithium
reaction vessels have also been considered for use as a heat source
for emergency power supplies for space vehicles, and the present
invention could also be used to fuel a lithium reaction vessel used
in that manner.
[0022] FIG. 3 is a block diagram showing one application of the
invention. Propulsion system 300 includes boiler 310, turbine 320
and propulsor 330. Boiler 310 corresponds to boiler 20 in FIG. 1
and is filled with a mixture of lithium pellets that are coated
with a fluorinated oil, as described in detail with respect to FIG.
1. Boiler 310 heats a working fluid, such as water, and the
resulting steam is used to turn turbine 320. Turbine 320 is
connected to propulsor 330, and propulsor 330 turns along with
turbine 320 to generate propulsion.
[0023] The present invention is a lithium pellet coated with a
fluorinated oil for use as fuel in a lithium reaction vessel and a
process for coating the pellets. The invention can use
readily-available commercial materials and takes a small fraction
of the amount of time needed to coat lithium pellets according to
the prior art.
[0024] Although the present invention has been described with
reference to preferred embodiments, workers skilled in the art will
recognize that changes may be made in form and detail without
departing from the spirit and scope of the invention.
* * * * *