WO2010118102A1

WO2010118102A1 - Gasdynamic laser supplied by catalytic decomposition for skid or vehicle mounting

Info

Publication number: WO2010118102A1
Application number: PCT/US2010/030196
Authority: WO
Inventors: Michael D. Lynch; Rolf E. Hamke
Original assignee: Aerojet-General Corporation
Priority date: 2009-04-09
Filing date: 2010-04-07
Publication date: 2010-10-14

Abstract

A gasdynamic laser utilizing carbon dioxide, carbon monoxide, or both, as the gain medium includes a catalytically operated hydrocarbon fuel decomposition unit to produce the carbon oxide(s). For vehicle mounting, the fuel can be a portion of the same fuel that is used to propel the vehicle. The decomposition unit, or combination of decomposition and combustion units, replaces the combustion chamber of conventional gasdynamic lasers and affords the laser a compact construction that is free of toxic gases.

Description

GASDYNAMIC LASER

SUPPLIED BY CATALYTIC DECOMPOSITION FOR SKID OR VEHICLE MOUNTING

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of United States Provisional Patent Application No. 61/168,077, filed April 9, 2009, the contents of which are incorporated herein by reference.

1. Field of the Invention

[0002] This invention resides in the field of gasdynamic lasers.

2. Description of the Prior Art [0003] A gasdynamic laser, also known by the terms "gas dynamic laser" and "gas-dynamic laser," operates by heating a mixture of hot gases serving as the laser gain medium, to "pump" the mixture to a high state of vibrational excitation, followed by rapidly expanding the excited gas mixture through a de Laval nozzle where the gases undergo a population inversion, and introducing the population inverted gas mixture into an optically resonant cavity where the photon emissions of the atoms interact with the atoms themselves to produce laser energy. As is well known, the population inversion is the condition where more atoms of a particular gas are in an excited state than are in their ground state, and arises from the fact that the atoms in the high vibrational excitation state relax more slowly than those in the low vibrational excitation state.

[0004] Prominent among the gases that are commonly used in gasdynamic lasers is carbon dioxide, which is typically obtained for use in the laser by the combustion of either gaseous or liquid fuels. Included among these fuels are simple combustible materials such as CO, H₂, CH₄, benzene, and hydrazine, but more complex materials such as gasoline, diesel, kerosene, or other petroleum fractions, and jet fuel have also been used. The use of automotive fuels and petroleum fractions in general has certain limitations, however. One such limitation is that the composition of the combustion products of these materials is difficult to control, and often includes toxic byproducts or soot. Another is that the use of combustion products requires the storage of combustible fuels that are specifically selected for and dedicated to the production of the gain medium and that may themselves include toxic substances. These limitations are of particular concern for lasers that are mounted on aircraft or other automotive vehicles. The need for a combustion chamber of sufficient capacity to produce the volume of gain medium that is needed is also a limitation, since such a chamber consumes critical space on the vehicle.

SUMMARY OF THE INVENTION

[0005] The present invention resides in a gasdynamic laser in which the gain medium is produced, at least in part, by catalytic decomposition rather than combustion. The source of gain medium in this invention is a continuous-flow, non-combusting system for generating carbon dioxide (CO₂), carbon monoxide (CO), or both, by catalytic decomposition of petroleum fractions. The CO₂ and/or CO produced by the decomposition system is typically used in conjunction with one or more other gases such as nitrogen or helium, and when the decomposition product is CO, the CO thus produced can either be used directly as the gain medium or combusted to CO₂ for use as the gain medium. While any of various petroleum fractions can be used as the source material for the decomposition, units for fractionation or refinement of a petroleum fraction are included in certain embodiments of the invention as part of the system for further control of the operation of the catalytic decomposition unit or of the gases passing through the system. When the laser is designed for mounting on an automotive vehicle, it is preferred that the petroleum fraction from which the oxide of carbon is to be generated be the same fuel as that used to propel the vehicle. Thus, when the laser is to be mounted on aircraft, the preferred petroleum fraction is aircraft fuel such as kerosene or jet fuel, which are also preferred for lasers mounted on water craft, and when the laser is to be mounted on a ground vehicle, the preferred petroleum fraction is automotive fuel such as gasoline or diesel. Other examples will be readily apparent to those skilled in the art.

[0006] Other embodiments, variations, and refinements, and additional units that can be included, will be apparent from the description that follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG. 1 is a diagram of a gasdynamic laser system in accordance with the present invention.

[0008] FIG. 2 is a diagram of an alternative gasdynamic laser system in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

[0009] Catalytic decomposition of the petroleum fraction in the practice of the present invention is performed in a reforming unit, which includes a reactor or a combination of reactors, at least one of which is a catalytic reactor for decomposition of hydrocarbons to CO, CO₂, or both, and to other decomposition products such as hydrogen gas. The design of such a reactor and the composition and form of the catalyst used in the reactor can vary widely and are known in the art. Examples of catalysts for this purpose are iron, cobalt, nickel, rhodium, palladium, osmium, indium, platinum, and ruthenium, and examples of inert supports for these metals are alumina and yttria-stabilized zirconia. Other examples will be readily apparent to those skilled in the art. Among the known technologies for reforming that can be used in this reactor are partial oxidation (POX), steam reforming (SR), and autothermal reforming (ATR). Descriptions of reforming units are found, for example, in Holladay et al. US 7,077,643 B2, July 18, 2006; Sammells US 6,793,711 Bl, September 21, 2004; and Ming et al. US 7,067,453, June 27, 2006. Many catalytic reformation reactors of these types will produce a mixture of carbon monoxide and hydrogen gas, known as synthesis gas. In certain embodiments of the invention, the reforming unit also includes a reactor that converts carbon monoxide to carbon dioxide, either by catalytic reformation or by combustion. Reactors of this type that involve catalytic reformation in many cases produce a mixture of carbon dioxide and hydrogen gas by steam reformation. Those that involve combustion are combustion chambers that utilize either oxygen or air.

[0010] The petroleum fraction in certain embodiments of this invention is pre-treated prior to entering the reformation unit to remove heavy hydrocarbon components, sulfur-bearing compounds, or both. The heavy hydrocarbons are generally hydrocarbons having boiling points above 200⁰C, and preferably above 300⁰C. The removal of heavy hydrocarbons and sulfur- bearing compounds can be achieved by fractional distillation in distillation units known in the art. Such units are described, for example, in Tonkovich et al. US 7,305,850 B2, December 11, 2007, and in Shaaban et al. US 2004/0006914 Al, January 15, 2004. Further sulfur removal can be achieved by a sulfur removal unit of conventional operation. Examples of sulfur-removal units that can be used are those operating by adsorption or hydrodesulfurization. Sulfur adsorbtion units are described, for example, in Feimer et al. US 7,074,324 B2, July 11, 2006, and Katikaneni et al. US 7,063,732 B2, June 20, 2006. Hydrodesulfurization units and processes are described, for example, in Bai et al. US 7,285,512 B2, October 23, 2007, Kaminsky et al. US 7,090,767, August 15, 2006, and Hatanaka et al. US 6,251,263, June 26, 2001.

[0011] With the use of reforming units that produce a gas mixture that contains both an oxide of carbon and hydrogen gas, the oxide (whether CO or CO₂) and hydrogen gas can be at least partially separated into separate streams by a gas separation unit. Such a unit, employing known technologies, can separate a carbon-oxide-rich fraction from a hydrogen-rich or carbon-oxide- lean fraction. By "carbon-oxide-rich" is meant rich in oxides of carbon relative to the gas mixture produced by the reforming unit, and likewise by "hydrogen-rich" and "carbon-oxide- lean" is meant rich and lean respectively relative to the gas mixture. The gas separation unit can likewise be one that utilizes conventional technologies, examples of which are membrane-based separation units, cyclonic separation units, and diffusive separation units. Examples of disclosures of membrane-based separation units are found in Roark et al. US 7,001,446 B2, February 21, 2006; Mundschau US 6,899,744 B2, May 24, 2005; and Bonchonsky et al. US 7,374,601 B2, May 20, 2008. An example of a disclosure of diffusive separation is found in

Pontius US 3,955,943, May 11, 1976. The hydrogen-rich gas stream from the gas separation unit can then be used as fuel for a combustion chamber for pumping the carbon-oxide-containing gain medium for the laser. This is one possible means of pumping, others are discussed below.

[0012] Prior to pumping, the concentration of the carbon oxide in the carbon-oxide-containing gas can be adjusted by addition of a diluent gas to achieve a concentration within the range that will produce a population inversion in the pumping and expansion stages. Effective concentrations are typically within the range of about 5% to about 10% by volume. Suitable diluent gases are well known to those skilled in the art of gas dynamic lasers, and one that is prominently used is nitrogen. In general, however, for vehicle-mounted systems, the diluent gas can be generated on the vehicle itself or as part of the skid on which the laser is mounted. Onboard inert gas generating systems are known in the art, and are available for example from Carleton Life Support Systems, Inc. (Davenport, Iowa, USA), Honeywell Aerospace Engineering (Morris Township, New Jersey, USA), and Air Products and Chemicals, Inc. (Lehigh Valley, Pennsylvania, USA).

[0013] The term "pumping" is used herein to denote the raising of the gain medium to a high state of vibrational excitation. In the present invention, as in gas dynamic lasers in general, pumping is achieved by heating, and any known means of heating a gas to the temperature that will produce the excitation state can be used. A convenient means in the systems of the present invention is by the use of sensible heat, i.e., the use of a heat transfer medium to heat the gain medium through a heat exchanger. Any heat transfer medium that supplies sufficient heat can be used, and since the present invention entails the generation of hydrogen gas in the reformation unit, the use of a combustion chamber for combustion of the hydrogen gas is particularly convenient. The construction and operating conditions of such a chamber are well known to those skilled in the art. The combustion can be supported by either oxygen or air, and when oxygen is used, the oxygen can be supplied by an on-board oxygen generating system. The heat exchanger can be of microchannel construction, with coating material on the inner surfaces of the microchannels. Examples of coating materials for microchannel heat exchangers are boron nitride (BN), silicon carbide (SiC), tantalum carbide (TaC), silicon nitride (Si₃N₄), tantalum suicide (TaSi₂), and titanium boride (TiB₂). The temperature to which the gain medium is heated may vary with the composition of the gain medium. In general, however, heating to a temperature of about 2500 K or above will be appropriate in most systems. [0014] Following the heating stage is an expansion nozzle, preferably a de Laval nozzle, to complete the population inversion. The specifications, configuration, and operation of the nozzle are conventional to gas dynamic lasers and can vary. In most applications, a nozzle that expands of the gases by a factor of about 100 or more while cooling them to a temperature of approximately 300 K or below will provide the best results. [0015] The population-inverted gas mixture then enters a resonant optical cavity of appropriate construction for extracting laser energy from the gases. Optical cavities designed for this purpose and their features are known in the art. A description of such a cavity and the mechanism by which laser action is achieved is presented by Wilson US 3,543,179, November 24, 1970. Variations developed subsequent to the Wilson disclosure are likewise known in the art. [0016] One example of a gasdynamic laser system in accordance with the present invention is represented by the diagram of FIG. 1. The system in this example is designed for use on an aircraft that is propelled by JP8 jet fuel or on a diesel-engine ground vehicle using JP8, in either case with a portion of the JP8 being used to generate the gain medium for the laser system. [0017] The JP8 feed 11 to the system is directed to a fractional distillation unit 12 in which the heavy fraction of the feed and 80-90% of the sulfur in the feed are removed in a side stream 13. The side stream can be recycled to the fuel system for the vehicle itself. Further sulfur removal from the remaining light fraction 14 is achieved by a sulfur removal unit 15, producing sulfur 16 that can either be disposed of or converted to a commercial use. A reforming unit 17 converts the sulfur-depleted light fraction 18 to CO₂ and H₂. In the process shown, the reforming unit is a dual-stage unit, the first stage 19 converting the light fraction 18 to CO and H₂ (synthesis gas), and the second stage 20 converting the CO to CO₂. As noted above, the second stage reforming unit can be replaced by a combustion chamber supplied by air or oxygen to oxidize the CO to CO₂. Following the reforming unit 17 is a gas separation unit 21 to separate a CO₂-rich fraction 22 from an H₂-rich fraction 23.

[0018] The CO₂ fraction 22 is combined with nitrogen gas from an on-board inert gas generation system (OBIGGS) 24. The resulting gas mixture is then heated in a heat exchanger 25 for thermal excitation. The excited gas mixture then undergoes expansion through a de Laval nozzle 26 to complete the population inversion, and the population-inverted gases are then processed by a conventional laser optics and stabilization platform 27. Gases leaving the platform are vented to exhaust 28.

[0019] The hydrogen-rich fraction 23 from the gas separation unit 21 is used for heating the process gases (i.e., the heat exchange medium) or the coating material in the heat exchanger 25, by combusting the hydrogen in a combustion chamber 31 with air or oxygen from an on-board oxygen generation system (OBOGS) 32. Any fuel can be used in place of, or in addition to, the hydrogen. The waste steam 33 from the combustion chamber 31 is recycled to the reforming unit 17.

[0020] A second example of a gasdynamic laser system in accordance with the present invention is represented by the diagram of FIG. 2. Like the system of FIG. 1, the system in this example is propelled by JP8 jet fuel or diesel. [0021] A microchannel fractional distillation unit 41 in the system of FIG. 2 separates the JP8 or diesel fuel feed 42 into a heavy fraction 43 and a light fraction 44, the heavy fraction containing high-boiling hydrocarbons and 80-90% of the sulfur originally present in the feed. The heavy fraction 43 can be recycled to the fuel system driving the vehicle on which the laser system is mounted, or can otherwise be put to commercial use, with further processing if needed. The light fraction 44 is passed through a hydrodesulfurization unit 45, reducing the sulfur level in the stream to about 1 ppm or less. A replaceable cartridge filter 46 can be placed in the vent line from the hydrodesulfurization unit 45 to collect molecular sulfur. A catalytic reforming unit 47 converts the remainder of the sulfur- free light fraction 48 to synthesis gas (a mixture of CO and H₂) 49. A portion 51 of the synthesis gas is fed directly to a gas separation unit 52 that separates the synthesis gas into an H₂-rich stream 53 and a CO-rich stream 54. The remainder 55 of the synthesis gas is fed to a second reforming unit, operating either by catalysis or combustion, that converts the carbon monoxide to carbon dioxide. The mixture of hydrogen and carbon dioxide 57 emerging from the second reforming unit is fed to a second gas separation unit 58 where the mixture is separated into an H₂-rich stream 59 and a CO-rich stream 60.

[0022] The CO-rich stream 54 and the CO₂-rich stream 60 are separately supplemented with nitrogen gas from an on-board inert gas generation system (OBIGGS) 61, while the two H₂-rich streams 53, 59 are combined and fed to a combustion chamber 62 together with air 63 and/or supplemental fuel 64 (JP8 or diesel), to generate heat for use in a dual heat exchanger 65 where the nitrogen-supplemented CO-rich stream 66 and the nitrogen-supplemented CO₂-rich stream 67 are separately heated. Each heated gas stream is then passed through a separate de Laval nozzle 68, 69 for supersonic expansion. The resulting population-inverted gas mixtures are then directed to a common optically resonant cavity 70 containing laser optics and a stabilization platform, to generate laser energy. Carbon monoxide and carbon dioxide are particularly compatible in a common optically resonant cavity since the primary wavelength of carbon dioxide, at 10.6 microns, is approximately twice the wavelength of 5.3 microns which is within the laser wavelength range of carbon monoxide. Gases leaving the cavity 70 are vented to exhaust 71.

[0023] Either of the gasdynamic laser systems shown in the two Figures can be mounted on a skid for transportability, with all components shown being on the skid. The systems can also be permanently mounted on, or incorporated into, a vehicle for on-vehicle generation and use of laser energy. For vehicles that are already equipped with oxygen-enriched air, this air can be used in the combustion chamber 62. Certain vehicles are likewise equipped with nitrogen- enriched air which can be used as a source of a nitrogen diluent for the carbon dioxide. In further variations, the system can contain an electrical circuit to produce a spark to ignite the combustion chamber 62, and the exhaust heat from the combustion chamber 62 can be used to preheat either the petroleum fraction 42, the air or oxygen used in the combustion chamber, or steam for steam reforming in the reforming unit 47. Other variations will be readily apparent to those skilled in the art.

[0024] In the claim or claims appended hereto, the term "a" or "an" is intended to mean "one or more." The term "comprise" and variations thereof such as "comprises" and "comprising," when preceding the recitation of a step or an element, are intended to mean that the addition of further steps or elements is optional and not excluded. All patents, patent applications, and other published reference materials cited in this specification are hereby incorporated herein by reference in their entirety. Any discrepancy between any reference material cited herein and an explicit teaching of this specification is intended to be resolved in favor of the teaching in this specification. This includes any discrepancy between an art-understood definition of a word or phrase and a definition explicitly provided in this specification of the same word or phrase.

Claims

WHAT IS CLAIMED IS:

1. Apparatus for producing laser energy from a petroleum fraction, said apparatus comprising: a reforming unit adapted to reform said petroleum fraction to a mixture of gases at least one of which is an oxide of carbon by catalytic decomposition; pumping means arranged to convert said mixture of gases to a vibrationally excited state; nozzle means for expanding said vibrationally excited gas mixture to form a population inversion therein; and an optical cavity comprising means for extracting laser energy from said population inversion-containing gas mixture.

2. The apparatus of claim 1, wherein said pumping means is a heat exchanger.

3. The apparatus of claim 1, wherein said nozzle means is a supersonic nozzle.

4. The apparatus of claim 1, wherein said oxide of carbon is carbon dioxide.

5. The apparatus of claim 1, wherein said oxide of carbon is carbon monoxide.

6. The apparatus of claim 1, wherein said mixture of gases produced by said reforming unit is configured to produce a first gas mixture comprising carbon monoxide and a second gas mixture comprising carbon dioxide, said apparatus comprises first and second pumping means to convert said first and second gas mixtures, respectively, to vibrationally excited states, and first and second nozzles for expanding said first and second vibrationally excited gas mixtures, respectively, to produce population inversions therein, and said optical cavity and means for extracting laser energy are configured to extract laser energy from both said population inversion-containing gas mixtures.

7. The apparatus of claim 1, wherein said reforming unit comprises a catalyst selected from the group consisting of iron, cobalt, nickel, rhodium, palladium, osmium, iridium, platinum, and ruthenium.

8. The apparatus of claim 1 , wherein said reforming unit comprises a first reforming reactor to produce carbon monoxide from said petroleum fraction and a second reforming reactor to convert said carbon monoxide to carbon dioxide.

9. The apparatus of claim 8, wherein said second reforming reactor is a combustion chamber.

10. The apparatus of claim 1, further comprising a gas separation unit arranged to separate said mixture of gases into a first gas stream rich in said oxide of carbon and a second gas stream lean in said oxide of carbon.

11. The apparatus of claim 1, further comprising a fractional distillation unit to remove sulfur-bearing compounds and heavy hydrocarbons from said petroleum fraction, thereby leaving a light fraction to enter said reforming unit.

12. The apparatus of claim 11, further comprising a member selected from the group consisting of a sulfur adsorption unit and a hydrodesulfurization unit, arranged to further remove sulfur from said light fraction.

13. The apparatus of claim 1, further comprising an on-board inert gas generation system arranged to add inert gas to said mixture of gases upstream of said pumping means.