Patent Publication Number: US-2015064089-A1

Title: Fluidized bed reactors including conical gas distributors and related methods of fluorination

Description:
TECHNICAL FIELD 
     The present invention relates generally to fluidized bed processing and, more particularly, to embodiments of a fluidized bed fluorination system including a conical gas distributor that improves solids-gas mixing and eliminates dead zones within a reaction vessel, as well to fluorination methods carried-out utilizing such a fluidized bed fluorination system. 
     BACKGROUND 
     Fuel for nuclear power plants is commonly produced by uranium enrichment processes requiring uranium hexafluoride (UF6) as a feed/input. UF6 is, in turn, commonly produced by the fluorination of uranium hexafluoride (UF4). During one known fluorination process, solid UF4 is introduced into a fluidized bed reaction vessel (commonly referred to as a “fluorinator”) and reacted with fluorine gas at elevated temperatures to yield the desired product, gaseous UF6. The fluidized bed commonly contains an inert diluent material, such as calcium fluoride (CaF2; also commonly referred to as “fluorspar”), magnesium fluoride, or alumina, to improve the quality of fluidization and to moderate the reaction kinetics (e.g., to dissipate the considerable amounts of heat generated during the fluorination process). A gas distributor, which has traditionally assumed the form of a flat perforated or sintered plate (or grate) positioned near the bottom of the reaction vessel, is utilized to introduce the fluorine gas along with other fluidizing gases into the reaction vessel. The flat plate gas distributor provides high velocity gas flow into the reaction vessel to enhance fluidization of the bed material and to discourage back flow of the gaseous and solid materials through the distributor. The gaseous UF6 produced by the fluorination reaction is withdrawn from the reaction vessel through an upper manifold and then subjected to further downstream processing (e.g., filtering, purification, scrubbing, desubliming, condensation, and distillation). 
     During the above-described fluorination process, solids may aggregate within the reaction vessel and form relatively large, rock-like particles due to the highly reactive nature of fluorine, the heat released by the fluorination reaction, and impurities present within the bed material and UF4. Such aggregate masses tend to accumulate on the flat plate gas distributor and, specifically, within dead zones along the upper face of the gas distributor that remain relatively undisturbed by high velocity gas flow (note that the gas distributor dead zones generally cannot be eliminated by simply increasing the density of the gas flow openings through the gas distributor without negatively impacting the overall quality of fluidization). The solid aggregates may gradually grow so large as to cause critical operational issues within the reaction vessel, such as the obstruction of gas flow openings in the flat plate gas distributor and the development of hot spots within the reaction vessel. While some reaction vessels employ vertically-extending, sidewall-mounted drain pipes to remove solid aggregates from an area above the flat plate gas distributor, such drain pipes are typically limited in the amount of solid aggregates they are able to remove. Thus, even when the reaction vessel is equipped with such a sidewall-mounted drain pipe, solids may still aggregate on the flat plate gas distributor, particularly in sections far removed from the sidewall-mounted drain pipe, and eventually grow sufficiently large to force shutdown of the reaction vessel and cleaning of the gas distributor, which adds undesired expense and delay to the fluorination process. 
     It would thus be desirable to provide embodiments of fluidized bed fluorination reactor wherein the aggregation of solids within a reaction vessel is minimized. Ideally, embodiments of such a fluidized bed fluorination reactor would employ a unique fluorine gas distributor providing improved gas flow characteristics within the reaction vessel, such as improved solids-gas mixing within the reaction vessel to increase the mass and heat transfer between solids and gas phases during fluorination. It would further be desirable to provide embodiments of a fluidized bed reactor suitable for carrying-out such a fluorination process or other fluidized reaction wherein the accumulation of solids is minimized and wherein solids-gas mixing is improved. It would still further be desirable to provide embodiments of a fluorination process performed utilizing a fluidized bed fluorination reactor and providing the above-noted advantages. Other desirable features and characteristics of the present invention will become apparent from the subsequent Detailed Description and the appended Claims, taken in conjunction with the accompanying Drawings and the foregoing Background. 
     BRIEF SUMMARY 
     Embodiments of a fluidized bed fluorination reactor are provided. In one embodiment, the fluidized bed fluorination reactor includes a source of fluorine gas, a reaction vessel, a windbox fluidly coupled to the source of fluorine gas, and a conical gas distributor fluidly coupled between the reaction vessel and the windbox. The conical gas distributor has a plurality of gas flow openings directing fluorine gas flow from the windbox into the fluorination reaction vessel during the fluorination process. 
     Embodiments of a fluidized bed reactor are further provided. In one embodiment, the fluidized bed reactor includes a source of gaseous reactant, a reaction vessel, a windbox fluidly coupled to the source of gaseous reactant, and a conical gas distributor fluidly coupled between the reaction vessel and the windbox. The conical gas distributor has a plurality of gas flow openings directing gaseous reactant flow from the windbox and into the reaction vessel during the reaction. 
     Embodiments of a fluorination process are further provided, which are carried-out utilizing a fluidized bed fluorination reactor of the type that includes a reaction vessel and a conical gas distributor having a plurality of gas flow openings formed therein. In one embodiment, the fluorination process includes the steps of supplying uranium tetrafluoride to the reaction vessel, and directing fluorine gas into the reaction vessel through the conical gas distributor and along a plurality of gas flow paths that are non-parallel with the longitudinal axis of the reaction vessel to support a fluorination reaction yielding uranium hexafluoride. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       At least one example of the present invention will hereinafter be described in conjunction with the following figures, wherein like numerals denote like elements, and: 
         FIG. 1  is a simplified flow schematic of a fluidized bed fluorination reactor illustrated in accordance with an exemplary embodiment of the present invention; 
         FIG. 2  is a cross-sectional view of a windbox, a conical gas distributor, a solids drain pipe, and a fluorine inlet pipe suitable for inclusion within the exemplary fluidized bed fluorination reactor shown in  FIG. 1  and illustrated in accordance with an exemplary embodiment; and 
         FIG. 3  is a top-down plan view of the exemplary conical gas distributor shown in  FIG. 2  illustrating one manner in which the gas flow openings provided through the conical support wall of the gas distributor may be arranged. 
     
    
    
     DETAILED DESCRIPTION 
     The following Detailed Description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding Background or the following detailed description. 
     Although described below in conjunction with a particular type of fluidized bed reactor, namely, a fluorination reactor, embodiments of the fluidized bed reactor can be utilized to carry-out other types of fluidized bed reactions, such as fluidized bed hydro-fluorination and reduction reactions, oxidation reactions, or chlorination reactions. This notwithstanding, embodiments of the fluidized bed reactor described below are particularly well-suited for carrying-out fluorination reactions wherein aggregation of solids is especially problematic due, at least in part, to the highly reactive nature of fluorine and the tremendous amounts of heat generated by the fluorination reaction. Thus, in preferred embodiments, and by way of non-limiting example only, the fluidized bed reactor is implemented as a fluidized bed fluorination reactor suitable for carrying-out the fluorination of, for example, uranium tetrafluoride (UF4) to yield uranium hexafluoride (UF6). 
       FIG. 1  is a simplified flow schematic of a fluidized bed fluorination reactor  10  illustrated in accordance with an exemplary embodiment of the present invention. Fluidized bed fluorination reactor  10  includes a reaction vessel  12  and a windbox  14 , which is mounted to a lower section of reaction vessel  12 . Reaction vessel  12  includes a shell  16  defining a reaction chamber  18 , which is fluidly coupled to windbox  14  and, specifically, to a gas-receiving chamber provided within windbox  14  (shown in  FIG. 2  and described below). A solids inlet  20  is provided through the sidewall of reaction vessel  12  and, during operation of fluorination reactor  10 , receives solids from a solids conduit  22 . In particular, solids conduit  22  receives UF4 and a diluent from a UF4 source  24  and diluent source  26 , respectively, and conducts the UF4 and diluent into reaction chamber  18  of reaction vessel  12 . Although fluidized bed fluorination reactor  10  is by no means limited to usage with a particular type of diluent, the diluent preferably contains or consists entirely of calcium fluoride (CaF2), also commonly referred to as “fluorspar.” By way of non-limiting example, the UF4 may be produced pursuant to the dry fluoride volatility process developed and commercially implemented by the assignee of the Instant Application, Honeywell International, Inc., currently headquartered in Morristown, N.J. In one implementation, a uranium oxide mixture (commonly referred to as “yellowcake”) may be first be uniformly sized and subjected to reduction process during which the yellowcake is reacted with hydrogen at high temperatures to produce uranium dioxide (UO2). A fluidized-bed hydro-fluorination process may then be performed during which the UO2 is reacted with anhydrous hydrofluoric gaseous acid to produce UF4 or “green salt” for usage within the fluorination reaction described herein. 
     Windbox  14  includes a shell  28  defining an interior chamber, which is fluidly coupled to a source of fluorine gas  30  by way of a fluorine inlet pipe  32 . As utilized herein, the term “pipe” encompasses all types of flow conduits, as well as assemblies of flow conduits joined in fluid communication. The fluorine gas, which may be generically referred to as a “fluidizing gas” herein, flows through inlet pipe  32  into windbox  14 , through a conical gas distributor (hidden from view in  FIG. 1 ), and into reaction chamber  18  of reaction vessel  12 . Variable amounts of inert diluent gas may also be provided in conjunction with the fluorine gas. Within reaction chamber  18 , the fluorine gas reacts with the solid UF4 introduced into chamber  18  by way of solids conduit  22  to yield the desired product, gaseous UF6. The gaseous UF6 collects within an upper manifold  34  included within reaction vessel  12  and is ultimately withdrawn as a product stream through an upper conduit  36 . The product stream containing the UF6 may then be subjected to further downstream processing utilizing additional processing equipment, which is conventionally known within the uranium conversion industry and which is not illustrated in  FIG. 1  for clarity. For example, the products stream may be first passed through a series of filters to remove any unreacted UF4 and solid diluent therefrom and subsequently passed through a series of cold traps to chill the product stream and thereby desublimate the gaseous UF6 contained therein, thereby removing gaseous diluents. The UF6 may then be distilled or otherwise purified to complete the uranium conversion process. The diluent directed into reaction chamber  18  in conjunction with the UF4 improves the overall quality of fluidization and helps to dissipate the considerable amounts of heat released by the fluorination reaction. 
     A perforated flat plate gas distributor has traditionally been employed to conduct the fluorine gas from windbox  14  into reaction chamber  18  of reaction vessel  12 . The flat plate gas distributor, which typically assumes the form of a disk or grate-like structure, also supports the fluidized bed held within reaction vessel  12 . As noted above, such perforated flat plate gas distributors do not achieve optimal gas-solids mixing and are prone to the accumulation of solid aggregates thereon. The aggregation of solids is especially problematic in the context of fluorination reactions due, at least in part, to the highly reactive nature of fluorine, to the highly exothermic nature of the fluorination reaction, and to impurities unavoidably present within the UF4 and bed materials. To mitigate the above-described problems, and specifically to provide improved gas-solids mixing and a significant reduction in the accumulation of solids within the reaction vessel and over the gas distributor, fluidized bed fluorination reactor  10  is equipped with a unique conical gas distributor and, in preferred embodiments, further with a solids drain pipe fluidly coupled to a central opening provided in the conical gas distributor. An example of such a conical gas distributor and central solids drain pipe is described more fully below in conjunction with  FIGS. 2 and 3 . 
       FIG. 2  is a cross-sectional view of windbox  14  and fluorine inlet pipe  32  shown in  FIG. 1  and further illustrating a conical gas distributor  38  and a solids drain pipe  40  (also referred to as a “downcomer pipe”). Conical gas distributor  38  includes a conical support wall  44  through which a plurality of gas flow openings  46  is formed. The shape of conical support wall  44  and the shape, size, disposition, and dimensions of gas flow openings  46  are optimized to promote solids-gas mixing within reaction vessel  12  and the drainage of aggregate solids, as described more fully below in conjunction with  FIG. 3 . In addition to gas flow openings  46 , conical gas distributor  38  includes a solids opening  48  formed through a central portion  49  of conical support wall  44 . Solids drain pipe  40  extends through a portion of windbox  14  in a generally upward or vertical direction and into solids opening  48 . The upper end section of solids drain pipe  40  is thus fluidly coupled to solids opening  48 , as well as mechanically coupled (e.g., welded or threadably attached) to the inner circumferential surface of conical support wall  44  defining solids opening  48 . In the illustrated example, the lower end portion of solids drain pipe  40  extends through an opening  50  provided in the bottom of conical gas distributor  38 . In this case, conical gas distributor  38  may include a lower flange  52 , which is affixed to an upper flange  54  of a drainpipe mounting structure  56 ; an annular seal or gasket  58  may be disposed between flanges  52  and  54  to prevent leakage; and a port  60  may be fluidly coupled to solids drain pipe  40  to enable purging with an inert gas (e.g., nitrogen), as may be appropriate to clear drain pipe  40  of any solid debris that should become lodged therein. This example notwithstanding, solids drain pipe  40  may alternatively have a gently curved geometry and an intermediate section of solids drain pipe  40  may extend through a sidewall of windbox  14 ; in such an alternative embodiment, the solids are not discharged from the lowest vertical section of the windbox, which can be advantageous when vertical space is limited. Furthermore, while the lower end of solids drain pipe  40  connects directly to solids opening  48  in the illustrated example, this is by no means necessary; in alternative embodiments, solids drain pipe  40  may be connected to solids opening  48  by use of a male-female type coupling, or similar coupling to achieve the most desirable connection. 
     While conical gas distributor  38  can be mounted between reaction vessel  12  ( FIG. 1 ) and windbox  14  in a variety of different manners, it is generally preferred that the mounting means utilized provides sufficient structural strength and integrity to reliably support the weight of the fluidized bed within reaction vessel  12  ( FIG. 1 ) and to prevent leakage through thermal cycling of vessel  12 . In the illustrated example, specifically, conical gas distributor  38  further includes an annular mounting flange  62 , which extends radially outward from the outer circumferential surface of conical support wall  44 . As utilized herein, the term “annular mounting flange” encompasses a continuous annular structure or wall, as well as a plurality of radially-extending tabs. As indicated in  FIG. 2 , annular mounting flange  62  may be captured between an upper flange  64 , which extends radially outward from the upper end of windbox  14 , and a lower flange  66  (shown in  FIG. 1 ), which extends radially outward from the lower end of reaction vessel  12  ( FIG. 1 ); and a plurality of fastener openings  68  may be provided through flanges  62 ,  64 , and  66  to receive a plurality of bolts or other such fasteners (not shown) and thereby secure reaction vessel  12  ( FIG. 1 ), conical gas distributor  38 , and windbox  14  together, including such gasketing as needed to achieve a leak-tight configuration. 
     The dimensions of conical gas distributor  38 , the material or materials from which gas distributor  38  is formed, and the manner in which gas distributor  38  is fabricated will inevitably vary amongst different embodiments. However, by way of non-limiting example, it is noted that gas distributor  38  is preferably formed from a high temperature metal or alloy and fabricated to have a single piece or unitary construction. Gas flow openings  46  can be formed through conical support wall  44  of gas distributor  38  utilizing a suitable drilling process, such as mechanical drilling or laser drilling. If desired, the mouths or inlets of gas flow openings  46  (i.e., the bottom ends of openings  46  in the illustrated orientation) may be chamfered. While by no means limited to a particular range of thicknesses, conical support wall  44  and annular mounting flange  62  of gas distributor  38  are preferably fabricated to be sufficiently thick to support the fluidized bed held within reaction vessel  12  ( FIG. 1 ); e.g., in one implementation, conical support wall  44  and annular mounting flange  62  may have a substantially consistent thickness of approximately 0.5 inch. 
     With continued reference to the exemplary embodiment illustrated in  FIG. 2 , fluorine inlet pipe  32  extends through an outer annular sidewall of windbox  14  to fluidly couple the inner windbox chamber  70  to the source of fluorine gas (generically represented in  FIG. 1  by arrow  30 ). In a preferred embodiment, the outlet end  72  of fluorine inlet pipe  32  points in a generally downward direction to direct the flow of fluorine gas toward the lower portion of windbox  14  and away from conical gas distributor  38 . In this manner, the flow rate of fluorine gas flow through the gas flow openings  46  closer to the outlet of fluorine inlet pipe  32  can be brought into alignment with the gas flow through the openings  46  further from the discharge of pipe  32  to improve overall uniformity of gas flow through conical gas distributor  38 . As shown in  FIG. 2 , this may be accomplished by imparting outlet end  72  of fluorine inlet pipe  32  with a downwardly-tilting geometry. As further shown in  FIG. 2 , an auxiliary port  74  may be provided through the annular sidewall of windbox  14  to facilitate pressure measurements. 
     As noted above, the shape of conical support wall  44  and the shape, size, disposition, and dimensions of gas flow openings  46  are optimized to promote solids-gas mixing within reaction vessel  12  and drainage of aggregate solids through solids drain pipe  40 . With respect to conical support wall  44 , in particular, it will be readily appreciated that conical support wall  44  converges toward solids opening  48  and, thus, the inlet of solids drain pipe  40 . Conical support wall  44  preferably has a substantially smooth outer surface and a sufficient slant or declination to promote gravity flow of solids into solids openings  48  and, therefore, into solids drain pipe  40  for reliable and continual removal of the aggregate solids from reaction vessel  12  ( FIG. 1 ). In one exemplary embodiment, conical support wall  44  forms an angle with the longitudinal axis of reaction vessel  12  (represented in  FIG. 2  by dashed line  76 ) between approximately 30° and 75°, as taken in cross-section along a plane parallel to longitudinal axis  76 . In a more preferred embodiment, conical support wall  44  forms an angle with the longitudinal axis of reaction vessel  12  between approximately 45° and 65°. 
     Gas flow openings  46  are preferably configured to provide high velocity gas flow from windbox  14  into reaction vessel  12  ( FIG. 1 ). In contrast to conventional flat plate gas distributors of the type described above, gas flow openings  46  are non-parallel with the longitudinal axis  76  of reaction vessel  12  ( FIG. 1 ). Stated differently, the longitudinal axes of gas flow openings  46  each form a predetermined angle with the longitudinal axis  76  of reaction vessel  12  ( FIG. 1 ) of, for example, approximately 30°-75°. The longitudinal axes of gas flow openings  46  may or may not be orthogonal to the major faces of conical support wall  44 . As indicated in  FIG. 2  by arrows  78 , gas flow openings  46  may be configured to direct fluorine gas along flow paths that converge toward the longitudinal axis  76  of reaction vessel  12 . By directing high velocity gas flow along paths that are non-parallel with the longitudinal axis  76  of reaction vessel  12  ( FIG. 1 ), the length of the gas flow path and, thus, the residence time of the fluorine gas within reaction chamber  18  of reaction vessel  12  ( FIG. 1 ) is increased. This, in turn, results in an increased contact time of the solids and gasses, and therefore improved heat and mass transfer, during the fluorination process. 
     In a preferred embodiment, gas flow openings  46  cooperate to create vortices-like fluorine flow within a bottom portion of reaction vessel  12  immediately above conical gas distributor  38  to increase agitation of the fluidized bed and further improve solids-gas mixing. The creation of gas flow vortices within a bottom portion of reaction vessel  12  may be enhanced by imparting gas flow openings with a distribution or spatial arrangement that is non-symmetrical. The creation of gas flow vortices, along with a substantially widespread distribution of gas flow openings  46 , also helps reduce or eliminate the formation of dead zones across the upper surface of conical gas flow distributor  38 . Each gas flow opening  46  preferably has a substantially straight or non-tortuous geometry to optimize gas flow velocity. Although not shown in  FIG. 2 , gas flow openings  46  may be imparted with a nozzle-like geometry wherein the flow area converges toward the outlet ends of openings  46  to further improve gas flow velocity. The dimensions of gas flow openings  46  may be determined based, at least in part, on the desired operational parameters of fluidized bed fluorination reactor  10  ( FIG. 1 ) and the physical characteristics of the reactants and diluent (e.g., the weight of the fluorine gas as compared to the weight of the diluent). Gas flow openings  46  are further preferably arranged or distributed such that the gas flow rate through a central portion of conical gas distributor  38  exceeds the gas flow rate through an outer portion of distributor  38  so as to concentrate high velocity gas flow near the center of distributor  38  over which solids are more likely to aggregate. Due, at least in part, to the above-described characteristics of gas flow openings  46 , the high velocity flow of fluorine into reaction vessel  12  ( FIG. 1 ) provided by conical gas distributor  38  provides an enhanced solids-gas mixing, and therefore improved heat and mass transfer, during the fluorination process. 
       FIG. 3  is a top-down plan view of conical gas distributor  38  illustrating one manner in which gas flow openings  46  provided through conical support wall  44  may be arranged. In this particular example, gas flow openings  46  are arranged in a plurality of substantially concentric rings or circles. More specifically, and by way of non-limiting example only, a total of fifty four gas flow openings are shown in  FIG. 3  and arranged in the following pattern: (i) an innermost ring of six substantially equally-spaced openings, (ii) an inner-middle ring of twelve substantially equally-spaced openings, (iii) a middle ring of twelve substantially equally-spaced openings, (iv) an outer-middle ring of fourteen substantially equally-spaced openings, and (v) an outermost ring of substantially twenty substantially equally-spaced openings. Gas flow openings  46  are further non-symmetrically distributed in an angularly staggered pattern to promote the formation of gas flow vortices within the lower section of reaction vessel  12  ( FIG. 1 ). Creation of the gas flow vortices within reaction vessel  12  ( FIG. 1 ), as previously described, can generally be promoted by imparting gas flow openings  46  with such a non-symmetric or random spatial distribution; although openings  46  are typically formed to be perpendicular to conical support wall  44 , they may also impart additional mixing and vortices by being formed at a non-perpendicular angle with the support wall (into the page when visualized in two dimension), such that swirling action is imparted within the reaction vessel  12 . In the exemplary embodiment shown in  FIG. 3 , gas flow openings  46  are substantially identical in size and shape; i.e., each opening  46  has a substantially circular outlet. Exemplary conical gas distributor  38  also includes twenty four substantially equally-spaced fastener openings  68  formed through mounting flange  62  to facilitate mounting between upper flange  64  of windbox  14  ( FIGS. 1 and 2 ) and lower flange  66  of reaction vessel  12  ( FIG. 1 ) as previously described. 
     The foregoing has thus provided embodiments of a fluidized bed reactor, such as a fluidized bed fluorination reactor, employing a conical gas distributor, preferably in conjunction with a solids drain pipe fluidly coupled to a central opening in the conical gas distributor, to promote the continual removal of solid aggregates from within a reaction vessel and to thereby deter the accumulate of such solid aggregates to sizes that could otherwise interfere with operation of fluidized bed reactor and ultimately force reactor shutdown. Notably, the above-described conical gas distributor also improves overall fluidization quality, gas residence time, gas-solids mixing, and heat and mass transfer as compared to traditional perforated flat plate gas distributors. The foregoing has also provided embodiments of a fluorination process carried-out utilizing a fluidized bed fluorination reactor of the type that includes a reaction vessel and a conical gas distributor having a plurality of gas flow openings formed therein. In one embodiment, the fluorination process includes the steps of supplying uranium tetrafluoride to the reaction vessel and directing fluorine gas into the reaction vessel through the conical gas distributor and along a plurality of gas flow paths that are non-parallel with the longitudinal axis of the reaction vessel to support a fluorination reactor yielding uranium hexafluoride. 
     By way of non-limiting illustration, an exemplary implementation of the fluidized bed reactor has been described above wherein the reactor assumed the form of a fluorine reactor utilized to covert uranium tetrafluoride to uranium hexafluoride. Embodiments of the fluidized bed reactor are especially well-suited for usage as fluorine reactors, such as the fluidized bed fluorination reactors utilized to convert uranium tetrafluoride to uranium hexafluoride, as the fluorination reaction is especially prone to the aggregation of solids due to the highly reactive nature of fluorine, the large amounts of heat generated by the fluorination reaction, and impurities present in the uranium tetrafluoride and fluidized bed materials. This notwithstanding, embodiments of fluidized bed reactor are by no means limited to usage in conjunction with fluorination processes. In this regard, the foregoing description has provided embodiments of a fluidized bed reactor for use in conjunction with a fluidizing gas, which may or may not be a fluorination reactor utilized in conjunction with a fluorine gas. Thus, the foregoing has generally provided embodiments of a fluidized bed reactor that includes a source of gaseous reactant, a reaction vessel, and a windbox fluidly coupled to the source of gaseous reactant, and a conical gas distributor fluidly coupled between the reaction vessel and the windbox. The conical gas distributor having a plurality of gas flow openings directing gaseous reactant flow from the windbox and into the reaction vessel during the reaction. In certain embodiments, and depending upon the desired reactions, the gaseous reactant may be fluorine, chlorine, hydrogen fluoride, hydrogen, hydrogen chloride, oxygen, air, steam, and mixtures thereof. In certain cases, the gaseous reactant may be diluted by an inert gas, such as nitrogen, argon, or helium. 
     While multiple exemplary embodiments have been presented in the foregoing Detailed Description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing Detailed Description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set-forth in the appended Claims.