Abstract:
A system and method is described having a single reaction vessel ( 12 ) using superheated steam optionally augmented by oxygen for reducing nitrogen oxides present in a wide variety of organic compounds. Reduction takes place quickly when a steam/oxygen mixture is injected into a fluidized bed ( 22 ) of ceramic beads. Reducing additives are metered into the reaction vessel ( 12 ) and/or provide energy input to reduce nitrates to nitrogen. The speed of the fluidizing gas mixture agitates the beads that then help to break up solid wastes and to allow self-cleaning through abrasion thereby eliminating agglomerates, and the oxygen, when used, allows for some oxidation of waste by-products and provides an additional offset for thermal requirements of operation.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation-in-part application to U.S. patent application Ser. No. 10/111148 filed Apr. 19, 2002. 
     
    
     
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
         [0002]    Not applicable.  
         REFERENCE TO A SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISK APPENDIX  
         [0003]    Not Applicable.  
         BACKGROUND OF THE INVENTION  
         [0004]    The present invention relates generally to a single step process for removing NOx compounds from waste products, compounds and wastewaters. More specifically, the invention relates to a single step process utilizing a fluidized bed contactor to remove NOx compounds from explosive, hazardous and/or radioactive materials. The present invention further relates to the conversion of alkali metals into a stable mineral form  
           [0005]    Nitrogen oxides and alkali metals can be commonly found in many waste products and compounds. Nitrogen oxides (referred to herein as “NOx”) include such compounds as nitric acid, aluminum nitrate, sodium nitrate, ammonium nitrate, potassium nitrate and the like. Alkali metals include such compounds as sodium nitrate, potassium nitrate, sodium sulfates, and sodium chloride.  
           [0006]    Traditional approaches to removing NOx include dry contact reduction processes for solid and gaseous nitrate compounds and wet absorption processes for gaseous NOx. Dry contact reduction processes may be either catalytic or non-catalytic and may be either selective or non-selective. Selective reduction processes are characterized by the selective reduction of gaseous nitrogen oxides and their consequent removal in the presence of oxygen. A common selective reduction agent for gaseous NOx is ammonia. Ammonia, however, oxidizes to form unwanted nitrogen oxide at high temperatures. Moreover, excess ammonia is itself a pollutant. Other selective reduction methods employ catalysts such as iridium. The problem with catalyst reduction is that the presence of particulates, sulfurous acid gases and other poisons reduce catalyst effectiveness and life thereby increasing costs.  
           [0007]    Non-selective reduction processes generally involve the addition of a reducing agent to the gaseous NOx containing material, consuming all free oxygen through combustion and reducing the NOx to nitrogen by the remaining reducing agent. Catalysts are typically utilized in these processes. Reducing agents useful in these processes are both scarce and expensive.  
           [0008]    Wet absorption processes typically require large and expensive equipment such as absorption towers. An example of a wet absorption process is the absorption of nitrogen oxides by water or alkali solution. Another shortcoming of the wet absorption process is that these methods are not economically effective where the NOx concentration in the gaseous waste stream is above 5,000 ppm.  
           [0009]    In the nuclear industry, there is an annual production of significant amounts of wastes which are classified as radioactively contaminated salt cakes, ion exchange media, sludges and solvents. These radioactive wastes either contain nitrogen oxides or nitrogen oxides are produced as part of the treatment of these wastes. In particular, nuclear fuel reprocessing with nitric acid produces highly radioactive nitric acid and sodium nitrate waste by-products.  
           [0010]    For solid or slurry NOx wastes and compounds a variety of processes have been tried for NOx destruction. Rotary calciner and fluid bed processors have been utilized with typical results yielding less than 90% conversion of solid nitrates to gaseous NOx and nitrogen. The gaseous NOx generally exceeded 10,000 ppm which requires addition of extensive gaseous NOx removal methods as described above. In addition, severe agglomerations occur in processors as well as the presence of flammable or explosive mixtures of nitrates and reducing agents in the processors.  
           [0011]    Another problem associated with prior art waste processing methods involves sulfur-containing compounds. The presence of such sulfur compounds in a vitrification melter can cause a molten sulfur salt pool to accumulate on top of the molten inorganic residue (glass); this pool causes high corrosion rates for the melter equipment. The pool can also have a high electrical conductivity, which causes short-circuiting of the heating electrodes in the melter. Additionally, potentially explosive conditions can result if large quantities of water contact the molten sulfur salt pool.  
           [0012]    Further, the presence of heavy metals in the inorganic residues can render the final waste product hazardous, thereby requiring additional processing of the residue before disposal or higher disposal costs. Also, the inorganic residue can contain soluble components that may form aqueous solutions after processing; these solutions can result in contamination of the surroundings after disposal.  
           [0013]    A process which does not have the limitations and shortcomings of the above described prior art methods for nitrogen oxide removal from waste streams and compounds would be highly desirable.  
         SUMMARY OF THE INVENTION  
         [0014]    According to its major aspects and briefly recited, the present invention is a method and apparatus for converting nitrogen oxides directly to nitrogen using a steam-reformer vessel. Nitrogen oxide-containing compounds or wastes are fed into the vessel along with a fluidizing gas composed of steam and, optionally, oxygen. The vessel contains fluidizing media, such as ceramic media, carbonaceous materials, product solids, and/or catalysts. The fluidizing gases are injected at relatively high speeds, ranging up to 800 feet per second.  
           [0015]    Although the present invention mainly addresses the processing of nitrogen oxides, the waste feed may also contain other nitrogen containing materials, such as explosives, solid rocket propellants, and fertilizers, as well as organics. Further, the waste feed can have any pH value, any concentration of alkali metals, and any concentration of nitrogen oxides.  
           [0016]    In a first embodiment of the present invention, a single vessel containing fluidizing media is utilized. Carbonaceous materials are used in the reaction vessel are as the heat source to evaporate water in the waste feed and as the principal reducing agent, or reductant. The terms reducing agent and reductant are well-understood by those skilled in the art of removing nitrogen oxides from waste feeds to mean chemicals or materials that are useful in removing oxygen from a compound. Other reducing agents that may be employed include metals and metal oxides, and gaseous reductants, such as hydrogen, ammonia, methane, and carbon monoxide. Additionally, certain additives and/or co-reactants, such as kaolin clay and lime, may be used to both achieve higher melting point solid products and to form synthetic naturally occurring minerals.  
           [0017]    The single reaction vessel is divided into at least two, and, preferably, three zones with at least one zone operated under reducing conditions. The remaining zone or zones may be operated under either reducing or oxidizing conditions. The fluidizing media, which is in solids communication, is divided into these zones through the introduction of various reducing and oxidizing agents into select areas of the reaction vessel. The terms oxidizing agent and oxidizing are well-understood by those skilled in the art of removing nitrogen oxides from waste feeds to mean chemicals or materials that are useful in adding oxygen to a compound.  
           [0018]    In the case that the vessel includes three zones, various combinations of operating conditions may be used. In a first combination, the lowest most zone is operated under oxidizing conditions via the addition of superheated steam with oxygen that reacts with the carbon to form CO/CO 2  and generate heat to evaporate water content and heat nitrate compounds to reduction temperature. The middle zone is operated under strongly reducing conditions in which NO 3 , NO, N 2 O and NO 2  are reduced to N 2 . Steam reforming of carbonaceous materials in this zone forms CO, H 2  and CH 4  that serve as strong gaseous reducing agents. The upper zone is operated under oxidizing conditions via the addition of more oxygen that oxidizes the remaining C, CO, CH 4  and H 2  formed in the second or middle zone to form CO 2  and water. This process results in only trace NOx, CO and H 2  in off-gas from the single reaction vessel and requires little auxiliary energy to be added. In a second combination, the lowest zone is operated under oxidizing conditions and the middle and upper zones are operated under strongly reducing conditions. This process results in less NOx, more CO and H 2  output and also requires low auxiliary energy. Auxiliary energy can be provided by electrical heaters. In a third combination, all three zones are operated under strongly reducing conditions. This process results in less NOx, increased CO and H 2  and requires additional auxiliary energy. Finally, in a fourth combination, the lower and middle zones are operated under strongly reducing conditions and the upper portion is operated under oxidizing conditions. This process results in low NOx, no CO and H 2  output but requires auxiliary energy to be added.  
           [0019]    In a second embodiment of the present invention, a single vessel having two separate reaction beds containing fluidizing media is used. The single vessel is again divided into at least two, and, preferably, three zones with at least one zone operated under reducing conditions. The remaining zone or zones may be operated under either reducing or oxidizing conditions. Preferably, the reaction beds are vertically oriented so that the lower most bed includes the lower and, optionally, the middle zone, and the upper bed includes the upper zone. The zones are operated similarly to those of the first embodiment; however, the fluidizing media contained in the upper zone is no longer in solids communication with the lower zone. In the case that the vessel includes three zones, various combinations of operating conditions may be used as previously described.  
           [0020]    In a third embodiment of the present invention, plural reaction vessels, and preferably, two reaction vessels that are interconnected and that contain fluidizing media are used. The vessels are dividing into at least two, and, preferably, three zones with at least one zone operated under reducing conditions. The remaining zone or zones may be operated under either reducing or oxidizing conditions. Preferably, the reaction vessels are arranged side by side and are in fluid communication. The first reaction vessel includes a first zone and, optionally, a second zone, and the second reaction vessel includes a third zone. Similar to the second embodiment, at least two of the zones are separated. Again, in the case that the vessel includes three zones, various combinations of operating conditions as previously described may be employed.  
           [0021]    In addition to the organization and operation of the three zones, other features common to the above embodiments include product handling and off-gas handling. In particular, the process is such that the larger solid products are removed from the bottom of the reaction vessel. The undersized product that is potentially carried out of the reaction vessel through the gas stream can be recycled to the reaction vessel where it can be made to grow larger for more convenient disposal. Additionally, both catalysts and fluidizing media can further be recycled to the vessel. The off-gas produced in the process is also recycled through the use of a filter downstream of the reaction vessel.  
           [0022]    A feature of the present invention is the use of a reaction vessel containing fluidizing media. The structure of the reaction vessel is such that it is both explosion and corrosion resistant. Preferably, the reaction vessel has walls that are thick enough to withstand potential explosions. This aspect is particular useful considering the types of reactants that are involved in the process and the potential for flammable mixture. Further, the reaction vessel includes a metal insert that provides corrosion protection to the outer vessel wall.  
           [0023]    The fluidizing media can be any combination of carbonaceous materials, product solids, ceramic media, and catalysts. Depending on the types of nitrogen oxide containing material, the process can be optimized by using various combinations of fluidizing media.  
           [0024]    Another feature of the present invention is the use of either a reaction vessel having separate reaction beds, or plural interconnected reaction vessels. Preferably, the present invention includes a lower reaction bed and an upper reaction bed within the same reaction vessel. Alternatively, the present invention can include separate reaction vessels that are in fluid communication. The lower bed, or, in the case of multiple reaction vessel, the lower reaction vessel can contain high carbon content and be highly reducing for high NOx conversion and high energy generation, whereas the upper bed or upper reaction vessel can have no carbon content and be highly oxidizing. This arrangement will optimize the destruction (via oxidation) of reforming gases such as hydrogen and carbon monoxide, as well as volatile organics. Further, fine carbons can be oxidized in the upper bed.  
           [0025]    Yet another feature of the present invention is the use of co-reactants and/or additives, such as lime, kaolin clay, magnesia, aluminum compounds, phosphate compounds, and silica compounds, to form higher melting point solid products, as well as synthetic naturally occurring minerals that are water-insoluble. The formation of higher melting point compounds helps to prevent agglomeration in the reaction vessel. Further, the formation of water-insoluble minerals is advantageous because they are more easily disposed of and processed. Typically, water-soluble compounds that also contain radioactive isotopes will most likely require further stabilization prior to disposal to prevent water dissolution of the buried product into the ground water.  
           [0026]    Still another feature of the present invention is the use of a waste feed that can contain nitrogen oxide containing wastes with organics, as well as other nitrogen containing materials such as energetics, explosives, solid rocket propellants, and fertilizers. Further, the waste feed can have any pH value, any concentration of alkali metals, and any concentration of nitrogen oxides. Accordingly, the waste feed does not need to go through extensive pre-processing before being introduced into the reaction vessel.  
           [0027]    Another feature of the present invention is the use of catalysts such as cerium, platinum, and palladium compounds to catalyze the reduction of nitrogen oxides. These catalysts decrease the energy of activation required for the reduction of nitrogen oxides.  
           [0028]    Still another feature of the present invention is the use of carbonaceous reductants to regenerate metal catalysts in the reaction vessel. For example, carbonaceous reductants can be used to reduce Fe 2 O 3  and Fe 3 O 4  to FeO and/or Fe. The FeO can then serve as a very effective reducing agent to convert NOx to nitrogen gas.  
           [0029]    The use of certain reductants and co-reactants in the presence of sulfur and halogen gases is a further feature of the present invention. Co-reactants, such as lime, can bind S, Cl, and F, which may come from the waste feed, into solid product matrix. The high retention of normal acid gases allows scrubber solutions to be recycled to the reaction vessel thereby eliminating secondary scrubber solution wastes.  
           [0030]    Another feature of the present invention is the use of gaseous reductants, such as hydrogen, ammonia, methane, and carbon monoxide. The use of gaseous reductants can minimize carbon fines carryover with product. Further, the separation of product solid from the off-gas stream through the use of such means as downstream filters is also made easier if the product is carried by gas rather than a solids mixture or solution.  
           [0031]    Yet another feature of the present invention is the use chemical reductions in combination with the steam reforming reactions. For example, the use of FeO to reduce NOx is a form of chemical reduction. These reactions are exothermic and may reduce the need for auxiliary energy.  
           [0032]    Finally, the use of product and off-gas handling is a feature of the present invention. In particular, both product and off-gas is recycled through the use of various filters and separators. This feature improves the overall efficiency of the process and reduces the amounts of waste that is generated and must be further processed.  
           [0033]    Other features and advantages of the present invention will be apparent to those skilled in the art from a careful reading of the Detailed Description of the Preferred Embodiments presented below and accompanied by the drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0034]    [0034]FIG. 1 is a schematic illustration of a system for removing NOx from a waste stream or compound according to a preferred embodiment of the present invention;  
         [0035]    [0035]FIG. 2A is a front view of a reaction vessel having three zones that is used in a system for removing NOx from a waste stream or compound according to a preferred embodiment of the present invention;  
         [0036]    [0036]FIG. 2B is a front view of a reaction vessel having two zones that is used in a system for removing NOx from a waste stream or compound according to an alternative embodiment of the present invention;  
         [0037]    [0037]FIG. 3A is a front view of a reaction vessel having separate reaction beds that include two zones and that are used in a system for removing NOx from a waste stream or compound according to an alternative embodiment of the present invention;  
         [0038]    [0038]FIG. 3B is a front view of a reaction vessel having separate reaction beds that include three zones and that are used in a system for removing NOx from a waste stream or compound according to an alternative embodiment of the present invention; and  
         [0039]    [0039]FIG. 4A is a front view of interconnected reaction vessels including two zones that are used in a system for removing NOx from a waste stream or compound according to an alternative embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0040]    The present invention is an apparatus and process for removing NOx from nitrogen oxide-bearing compounds and waste product feeds. The present apparatus and processes will be described in particular with respect to radioactive waste; however, any nitrogen oxide-containing waste or product stream can be processed in accordance with the following process and with the components of the system. The wastes that can be processed according to the present invention include not only NOx containing waste streams resulting from the decomposition of ion exchange resins, but can also include nitric acid, nitrites, and NOx containing waste stream resulting from nuclear reprocessing, explosives and energetics, solid rocket propellants, fertilizer and gaseous off-gas streams and the like. The waste stream can further include nitrogen oxide-containing materials in the presence of organics. Organics can be volatized and destroyed in the reaction vessel by pyrolysis, steam reformation and oxidation reactions. Furthermore, the waste feed can have any pH value, any concentration of alkali metals, any concentration of alkali metals, and any concentration of nitrogen oxides. Accordingly, the waste feed does not need to be preprocessed before being introduced into the process.  
         [0041]    The process is based on a fluidizing bed reaction vessel using steam for fluidizing which may be operated under strongly reducing conditions or under strongly reducing conditions in combination with oxidizing conditions. Carbonaceous materials, such as sugars, charcoal, and activated carbon, that are present in the fluidizing reaction vessel are used as the heat source to evaporate water in the waste feed and as the principal reducing agent, or reductant. Other fluidizing gases or co-reactants may be utilized to further optimize the oxidizing or reducing conditions in the reactor. Typical other fluidizing gases include: hydrogen, oxygen (when oxidizing conditions are desired), methane, ammonia, etc. Further, the use of such co-reactants or additives as kaolin clay and lime results in higher melting point product, as well as the formation of water-insoluble minerals. Product handling and off-gas handling from the process includes the use of wet scrubbers and various filters and separators.  
         [0042]    Referring now to FIG. 1, there is shown a system according to a preferred embodiment of the present invention and generally indicated by reference number  10 . System  10  includes a single reaction vessel  12 . Waste feed, which may be comprised of liquid slurries and sludges  14  and/or solids  16 , are fed into the reaction vessel  12 . In the case of the liquid slurries and sludges  14 , a pneumatic pump, peristaltic pump or progressive cavity  18  may be employed for delivery of the pumpable fluids to the reacting vessel  12 . In the case of the solids  16 , a screw auger  20  may be employed to deliver the solid waste stream into the reaction vessel  12 .  
         [0043]    Reaction vessel  12  is preferably made explosion resistant through the use of heavy walls. Further, reaction vessel  12  includes an internal metallic insert  110  to provide corrosion protection the outer reaction vessel wall. Although other metals are contemplated, the insert  110  is preferably made of a metal alloy, and, most preferably of hastalloy.  
         [0044]    In reaction vessel  12 , fluidizing media  22  may include inert ceramic media, carbonaceous materials, catalysts, product solids, such as sodium compound product, in addition to the inert media. Various combinations of these materials may be used in the reaction vessel  12 . For example, fluidizing media  22  can include carbonaceous materials with product solids that have been formed during the process. The fluidizing media  22  may further include catalysts, such as cerium, platinum, and palladium compounds, in combination with product solids. These catalysts are useful in lowering the energy of activation required to reduce NOx to nitrogen. Fluidizing media  22  may also include any combination of carbonaceous material, product solids, ceramic media, and/or catalysts. Most preferably, fluidizing media  22  includes a combination of carbonaceous materials, catalysts, and product solids.  
         [0045]    The use of inert material is a feature of the present invention. Inert ceramic media such as silica, mullite, corundum, or alumin may serve as a heat sink. Preferably, amorphous alumina beads at least 200 and preferably up to 1000 microns in diameter are used, however beads up to 5,000 microns in diameter can be utilized. Such size beads do not easily elutriate out of the vessel and therefore minimize carryover. Another advantage of the amorphous alumina is that it will not form eutectic salt/glasses that can form harmful agglomerates that affect reactor efficiency as when common silica sand is utilized. The amorphous alumina is also exceptionally strong and hard and resists attrition due to reaction bed friction and impact.  
         [0046]    Another feature of the present invention is the use of carbonaceous materials that act as both a reducing agent and a heat generator. The addition of charcoal or carbonaceous solids to the bed in sizes ranging up to 0.5 inches in diameter is unique to the preferred embodiment. The large particles of carbon maintain a constant inventory of carbon that is not possible with typical fine sugars, organic powders or liquid chemicals previously used to facilitate nitrate reduction. The presence of larger carbon solids together with addition of soluble carbon in the form of formic acid, sugars, etc. provides superior nitrate reductions. The presence of carbon compounds in the bed will produce highly reducing CO and H 2  in the bed via steam reformation.  
         [0047]    In order to evaporate water present in the waste feeds and to serve as a heat source, charcoal, sugar and/or other carbonaceous materials are added to or included in reaction vessel  12 . Optionally, other reductants or catalysts such as iron or nickel oxalates, oxides, or nitrates may be used. Reaction vessel  12  materials can be modified to include these, or other metals, in order to further improve the denitration process. For example, the addition of 5 to 10% iron oxide to the reaction bed medium can improve NOx reduction by more than two-fold. These metal catalysts are further desirable for their ability to be regenerated in the reaction vessel  12 . For example, carbonaceous reductants can reduce Fe 2 O 3  and Fe 3 O 4  to FeO and/or Fe. The FeO then can serve as a very effective reducing agent to convert NOx to nitrogen gas. Further, the use of chemical reduction reactants is advantageous to the present invention because they are exothermic and can provide energy to the process.  
         [0048]    The denitration process is further optimized and improved through the addition of certain co-reactant or additive such as lime, to the reaction vessel  12 . As previously stated, the addition of co-reactants such as lime, kaolin clay, magnesia, aluminum compounds, phosphate compounds, and silica compounds, to form higher melting point solid products, as well as synthetic naturally occurring minerals that are water-insoluble. to both form higher melting is a feature of the present invention. The formation of higher melting point compound helps to prevent agglomeration in the reaction vessel. Another problem typically faced is that water-soluble compounds that also contain radioactive isotopes will most likely require further stabilizations such as grouting, solidification, or vitrification, prior to disposal to prevent water dissolution of the buried product into the ground water. Accordingly, the formation of water-insoluble minerals is both advantageous and desirable because they are more easily disposed of and processed. It is also desirable to select and produce a product that is non-hygroscopic. The term non-hygroscopic refers to compounds that do not form hydrates. Solids that form hydrates can swell over time and can rupture or damage the containers they are stored in.  
         [0049]    In an effort to address these problems, the following products listed with their main elemental constituents for simplicity are made in the present process through the addition of certain co-reactants: nosean (Na—Al—Si), nepheline (Na—Al—Si), fairchildite (K—Ca—CO 3 ), natrofairchildite (Na—Ca—CO 3 ), dawsonite (Na—Mg—CO 3 ), eitelite (Na—Mg—CO 3 ), shortite (Na—Ca—CO 3 ), parantisite (Na—Ti—Si), maricite (Na—Fe—PO 4 ), buchwaldite (Na—Ca—PO 4 ), bradleyite (Na—Mg—PO 4 —CO 3 ), combeite (Na—Ca—Si), olenite (Na—Al—BO 3 —Si), dravite (Na—Mg—AI—BO 3 —Si), as well as other compounds for which do not include common mineral names, such as Ca—Si, Na—PO 4 , Na—Al—PO 4 , Na—(Ca,Fe,Mg)—Si, and Na—Mg—PO 4 . Not only are these minerals desirable because they are water insoluble, but they can also help to further process such wastes as radioactive isotopes. For example, the product nephaline has the capability of forming a crystalline cage around bigger atoms, such as radionuclides.  
         [0050]    In order to produce these alkaline earth compounds, the following co-reactants can be utilized with each co-reactant being added in the proportions needed to generate the desired higher melting point compound, and/or water insoluble compound. The addition of lime (CaO) or other Ca compound such as calcium carbonate or calcium nitrate provides the conversion of alkaline earths to a Ca rich final product such as farchildite. The carbonate is provided by any CO2 that is present in the reaction vessel  12 . The addition of magnesia (MgO) would produce minerals rich in magnesia, such as eitelite. The addition of clays or alumina-silicates such as kaolin clay and bentonite can be used to produce nepheline, nosean, and other related sodium-alumina-silicates. The addition of aluminum compounds such as aluminum nitrate, aluminum hydroxide, aluminum tri-hydrate (Al(OH)3), or aluminum metal particles can be used to produce sodium aluminate. The addition of phosphate compounds to produce phosphate bonded ceramic media such as maricite, buchwaldite, bradleyite or other PO4 containing materials. The addition of silica compounds can be used to produce a sodium silicate product. The use of CO 2  to form a sodium carbonate produce is also utilized in the present invention. Typical wastes that are fed into reaction vessel  12  can include portions of Ca, Mg, B, P, and other potential co-reactants.  
         [0051]    The use of these co-reactants is further advantageous because of the behavior of sulfur and halogens, which may be present in the waste feed, in their presence. Co-reactants can bind S, Cl, and F into solid sodium or calcium product matrix, or other non-volatile stable products. The resultant off-gas contains &lt;5% of incoming S, Cl, and F. This high retention of normal acid gases allows scrubber solutions to be recycled to the reaction vessel  12  thereby eliminating secondary scrubber solution waste. For example, scrubber solution with S, Cl, and F based salts that are removed in the off-gas system scrubber can be recycled into the reaction vessel  12  as waste feed. A specific co-reactant that can be used is lime. The S and halogens can be directly bonded by the addition of lime (CaO) to form CaSO 4  (gypsum) as a stable product or the S can be “trapped” inside the crystalline structure of certain mineral forms such as nepheline thereby converting it to nosean.  
         [0052]    Another feature of the present invention includes the use of gaseous reductants. The benefit of the use of gaseous reductants, such as hydrogen, ammonia, methane, carbon monoxide, and other hydrocarbon gases, is the minimization of carbon fines carryover with product.  
         [0053]    Fluidizing medium (gases) is introduced into reaction vessel  12  via inlet  24 . Steam is preferred to combustion gases as the fluidizing medium because it is more reactive, and generates CO and H 2  that are highly reducing by steam reformation of carbonaceous materials. However, fluidizing medium can also include steam with oxygen, steam with reducing or fuel gases (including methane, carbon monoxide, and hydrogen), mixtures of steam, oxygen, reducing gases and/or fuel gases, steam with inert gas, inert gas with no oxygen, and steam with oxygen and with inert gas. Gaseous NOx compounds can be co-injected with the fluidizing gases through inlet  24 . Preferably, fluidizing gases can be recycled from the off-gas stream to save energy on the supply of fluidizing steam.  
         [0054]    The heat generated by the steam allows the reaction vessel to be operated at the temperature required for reduction of the nitrogen oxides. Preferably, the reaction temperature is within a range of approximately 200° C. to 900° C. This heat can also volatize sulfur-containing compounds, thereby separating them from the inorganic residues. As discussed above, the presence of such sulfur compounds can cause an equipment-damaging corrosive molten sulfur salt pool to accumulate on top of the molten inorganic residue. The electrically-conductive pool would also cause short-circuiting of the heating electrodes or potentially explosive conditions if contacted by large quantities of water. The present method, for example, converts sulfates such as Na 2 SO 4  by reduction into volatile SOx and/or H 2 S. By volatizing such sulfur-containing compounds, the present method avoids these problems that are traditionally associated with the reduction of nitrogen oxide-containing waste streams. The sulfur reduced residue can then be melted into glass without forming a sulfur salt pool on top of the melter glass pool.  
         [0055]    As previously discussed, the fluidizing medium can be an inert gas, but is preferably a reforming gas and may have oxygen present. Most preferably, the medium is superheated steam. The fluidizing velocity can range from about 1.0 feet per second or higher depending on the bed media, preferably 3 to 10 feet per second (FPS) depending upon the size of the bed media. Significantly, the injection of the waste feed at higher or lower velocity and/or higher or lower atomizing gas flow enables the control of product particle size in the reaction vessel  12 . Fluidizing gas distributors are designed to provide higher than normal gas/orifice velocities. Typical gas distributor velocities are 100 to 200 FPS, however, in the preferred embodiment gas velocities of &gt;400 FPS are desired.  
         [0056]    The high fluidizing gas jet speed has several advantages. High velocity fluidizing gas jets in a vertically oriented bed provides jet impingement on the media to help break down the softer, friable feed and to break-up agglomerates. Moreover, the media beads become self-cleaning due to abrasion in the high impact area around the fluidizing gas distributor.  
         [0057]    Reactor vessel  12  is preferably operated in elutriating mode. Sodium and other low melting eutectics are thereby present in only low concentration (&lt;2%) and are quickly carried out of the bed. The media beads are self-cleaning through abrasion. The low inventory of unconverted nitrates or sodium compounds greatly minimizes agglomeration potential.  
         [0058]    The nitrogen gas, steam, other fluidizing gas and fine particulates pass through scrubber/evaporator  40 . Any non-gaseous reformed residue or particulate collected in the scrubber/evaporator  40  is directed to residue separator  42  wherein the insoluble reformed residue are separated from the soluble salt solution. The reformed residue is directed to the stabilization processor  36  while the salt solution is directed to salt separator  44  then to a salt dryer  46  and finally to a salt package  48 . An optional filter (not shown) can be installed between the reactor gas outlet  28  and the scrubber/evaporator  40 . Solids collected by the optional filter can be directed to residue stabilization processor  36 . The cooled and scrubbed syn gas and water vapors then pass to condenser  50 . The resultant water is directed to the recycled water tank  52  while the syn gas moves to thermal converter  54 . Off-gases (OG) from the thermal converter  54  are then monitored for compliance with the applicable environmental requirements prior to release.  
         [0059]    As shown in FIGS. 2A and 2B, reaction vessel  12  of the preferred embodiment contains fluidizing media  22 , and is divided into at least two zones, including an upper zone  70  and a lower zone  72  (FIG. 2B). Preferably, reaction vessel  12  is divided into three zones (FIG. 2A), including upper zone  70 , a middle zone  74 , and lower zone  72 . Although there need be no structural division between these zones to designate their dimensions, fluidizing media  22  is divided into the zones through the introduction of various reducing and oxidizing agents into select areas of the reaction vessel  12  through plural inlets. In general, waste feed can be introduced at the top of lower zone  70  to provide particle size control, e.g., smaller particles can be made to grow larger as small particles are in higher proportion in the top of lower zone  70  than in the bottom of lower zone  70 . As shown, the zones are preferably vertically oriented. However, the use of other orientations, such as a horizontal orientation, is contemplated in the present invention.  
         [0060]    As discussed above, if the reactor vessel  12  includes three zones, it may be operated using one of four combinations. In combination 1, the lower zone  72  of reaction vessel  12  is operated under oxidizing conditions. To achieve this condition oxygen is mixed with the steam and introduced into the reactor vessel  12  via inlet  24  and may be optionally superheated. The pressure in the reactor vessel  12  is preferably about 13 to 15 psia. The reactor vessel  12  is preferably operated at 600 to 800 degrees centigrade. The fluidizing media  22  depth is preferably between about 3 to 8 feet, expanded. The middle portion  74  of fluidizing media  22  in reaction vessel  12  is operated under strongly reducing conditions, and the upper portion of the media bed is operated under oxidizing conditions by the addition of oxygen via inlet  25 . Temperature is maintained within reactor vessel  12  by heater  26  or by super heating fluidizing gases which provides auxiliary energy as needed, particularly during start-up. In combination 2, the lower zone  72  of the reaction vessel  12  may be operated under oxidizing conditions, and the middle and upper zones  74 ,  72 , respectively, are operated under strongly reducing conditions. In combination 3, all three zones are operated under strongly reducing conditions. Finally, in combination 4, only the upper zone  70  of the reaction vessel  12  is operated under oxidizing conditions, and the lower and middle zones  72 ,  74 , respectively are operated under strongly reducing conditions.  
         [0061]    Under the conditions of combination 1 set forth above, the process treatment results in final gaseous effluent very low in NOx with no CO and H 2  output. The system generally requires low auxiliary energy addition. This system does not require the removal of NOx in the off gas scrubber system as NOx levels exiting the reaction vessel  12  are routinely &lt;25 ppm. The addition of thermal converter  54  for CO and CH 4  oxidation is also not required.  
         [0062]    In combination 2, the lower zone  72  of the media bed in reaction vessel  12  may be operated under oxidizing conditions, as discussed above, the middle portion and the upper portions of the media bed are operated under strongly reducing conditions. Combination 2 results in lowered NOx exiting reaction vessel  12  as compared to combination 1 but has increased levels of CO and H 2  and other trace volatile organics in the reaction vessel  12  output. Additional auxiliary energy is generally needed in the reaction vessel  12  and thermal converter  54  is required.  
         [0063]    In combination 3, the reaction vessel  12  is operated only under strongly reducing conditions. Combination 3 results in lowered NOx, increased CO and H 2  and requires increased auxiliary energy and use of thermal converter  54 .  
         [0064]    In combination 4, only the upper zone  70  of the reactor vessel  12  media bed is operated under oxidizing conditions. Method 4 results in low NOx, no CO and H 2  output and increased auxiliary energy. The thermal converter  54  is not required in the practice of this method.  
         [0065]    Notably, gaseous NOx can also be processed by direct introduction to reaction vessel  12  with other waste feeds. For example, high NOx off-gas from a vitrification melter or thermal denitration process can be used as both the waste stream and the fluidizing gas; however, steam is co-injected to keep the total gas flow through the reaction bed at greater than 20% steam and to provide uniform fluidizing gas velocities.  
         [0066]    As shown in FIGS. 3A and 3B, an alternative embodiment of the present invention includes reaction vessel  12  having a lower reaction bed  92  and a separate upper bed  94 . Preferably, fluidizing media  22  of the reaction beds is separated by a gas distributor. Similar to the preferred embodiment, the reaction vessel  12  includes at least two, and, preferably three zones with at least one zone operated under reducing conditions. The remaning zone or zones may be operated under either reducing or oxidizing conditions. Preferably, reaction beds  92 ,  94 , are vertically oriented so that lower reaction bed  92  includes the lower zone  72  and, optionally, the middle zone  74 , and the upper reaction bed  94  includes the upper zone  70 . As with the preferred embodiment, the zones can be operated using the various combinations of oxidizing and reducing conditions as previously described.  
         [0067]    The use of the separate upper reaction bed  94  is a particular feature of the present invention. Lower reaction bed  92  can contain high carbon content and be highly reducing for high NOx conversion and high energy generation, whereas upper reaction bed  94  can have no carbon content and be highly oxidizing. This arrangement will optimize the destruction via oxidation of reforming gases such as hydrogen and carbon monoxide, as well as volatile organic from the waste feed in upper reaction bed  94 . Fine carbon can also be oxidized in upper reaction bed  94 .  
         [0068]    Alternatively, a second reaction vessel  100  that is connected to a first reaction vessel  12  can be utilized. As shown in FIGS. 4A and 4B, the two reaction vessels  12 ,  100 , are interconnected and in fluid communication. Similar to the previously described embodiments, this alternative embodiment includes at least two, and, preferably, three zones with at least one zone operated under reducing conditions. The remaining zones may be operated under either reducing or oxidizing conditions. Preferably, the reaction vessels are oriented side by side. However, a vertical orientation of the reaction vessels is also contemplated by the present invention. The first reaction vessel  12  preferably contains a first zone  72 , and, optionally, a second zone  74 , and the second reaction vessel  100  includes a third zone  70 .  
         [0069]    When the NOx has been reduced to nitrogen, the nitrogen, steam and other syn gases leave the reaction vessel  12  via port  28 . A filter  82  is provided downstream of reaction vessel  12  to remove fines elutriated from reaction vessel  12  off-gas. Preferably, filter  82  includes ceramic filter media. The fines are removed as the off-gas stream carrying the fines passes through filter  82 . However, downstream filter  82  need not be included if solids are separated from scrubber solution in a scrubber  40 . These separated solids may be introduced to the waste feed through an inlet  90 . Finally scrubber solution may also be recycled to the waste feed through inlet  90  for incorporation of the solids and salts into solid products. This alternative eliminates a secondary waste stream.  
         [0070]    Fine solid products are also largely retained in the reaction vessel  12  by means of a solids separation device built into reaction vessel  12 , such as a cyclone  80  (shown in FIG. 1), or a filter. Other small sized reformed residues, including entrained particulates also leave via port  28  and can thereafter be recycled to reaction vessel  12 . Heavier solids and debris leave via port  30  and are carried away by screw auger  32  to collector  34 . Auger  32  is preferably water cooled. From collector  34  the larger solids and debris may be directed to stabilization processor  36  or to final reformed residue waste collector  38 .  
         [0071]    Preferably, collector  34  includes a metal separator, pneumatic classifier, and/or a screen separator for the recycling of metal catalysts and reductants. In the case that reaction vessel  12  contains only product particles and no alumina beads, a simple magnetic separator could separate catalyst from product for recycling of the catalyst to the reaction vessel  12 .  
         [0072]    The screw auger  32  can be optionally fitted with water washing capability. Water can be introduced into the bottom of screw auger  32  through inlet  60 . Water dissolves any soluble sodium salt or other agglomerates that collect in the bottom of the reactor vessel  12 . Salt water solution is removed from the bottom of reactor vessel  12  through screened outlet port  62 . If desired, the salt water solution from outlet  62  can be collected in residue separator  42 .  
         [0073]    Testing has demonstrated the usefulness of metal additions to the bed to facilitate NOx reduction. Metal additives are not always required but are useful in maximizing NOx conversion to nitrogen gas. Typical metals that can be used include copper, cobalt, iron or nickel oxalate or nitrates that can be co-injected with the waste feed in concentrations of less than 0.5%.  
         [0074]    In the present method, heavy metals or inorganic cations can be converted into volatile fluoride or chloride compounds by the addition of appropriate fluorides and chlorides. As discussed above, the presence of heavy metals in the inorganic residues can render the final waste product hazardous, thereby requiring additional processing of the residue before disposal. For example, in a waste product that contains the relatively non-volatile CsO, chloride additives can convert the Cesium to very volatile CsCl 2 , thereby separating the heavy metal cation from the inorganic residue. By converting such hazardous metals or cations to the corresponding fluorides or chlorides and removing them from the inorganic residue by volatization, the present method avoids this problem that is traditionally associated with the reduction of nitrogen oxide-containing waste streams.  
         [0075]    Further, the present method can use additives to tailor the solubility of the resulting inorganic residue. As discussed above, soluble components in the residue may form aqueous solutions that can result in contamination of the surroundings after disposal. An example of such tailoring of the solubility of the residue in the present method is the addition of aluminum nitrate to sodium-containing waste; in the correct proportions, this additive produces sodium-aluminum oxides that are insoluble in water. By converting such soluble components into insoluble derivatives, the present method avoids this problem that is traditionally associated with the reduction of nitrogen oxide-containing waste streams.  
         [0076]    It will be apparent to those skilled in the art of removing NOx from waste feeds that many modifications and substitutions can be made to the preferred embodiments described above without departing from the spirit and scope of the present invention, which is defined by the appended claims.