Abstract:
Decontamination apparatus and methods involve catalytic decomposition of hydrogen peroxide to drive additional hydrogen peroxide to a contaminated location.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to decontamination. More particularly, the invention relates to decontamination against chemical and biological agents. 
     Well developed fields exist regarding the decontamination of areas contaminated with chemical and biological agents. Various techniques involve thermal decontamination. Some are typically useful for decontaminating thermally robust contaminated locations such as the exposed surfaces of a military vehicle. For example, U.S. Pat. No. 4,551,092 to Sayler discloses a jet engine decontamination system. In such a system, the jet exhaust is directed to the contaminated surfaces and heats them sufficiently to decompose chemical agents and kill biological agents. Various such systems are vehicle-mounted permitting the jet exhaust to be controllably swept over the surfaces to be contaminated. 
     More recently, concerns regarding laboratory and factory accidents, bio-terrorism, and the like encouraged development of principally chemical decontamination systems for decontaminating less robust (and often larger) locations. For example, the interior of an entire building or a portion thereof (e.g., a room) may need to be decontaminated. Exemplary chemical decontamination systems have typically involved use of chlorine (e.g., chlorine dioxide). However, use of chlorine dioxide raises certain safety considerations. Accordingly, use of hydrogen peroxide vapor for decontamination has been proposed. International Patent Publication WO 02/066082 of Steris, Inc. et al. discloses a flash vaporizer for providing antimicrobial hydrogen peroxide. Chemical systems may also be used in direct spray modes in lieu of the thermal systems. For example, it has been proposed to use a chemical system for the in situ decontamination of jet aircraft engines. 
     Separately, catalytic systems have been developed to decompose hydrogen peroxide into water and oxygen (e.g., to provide oxygen for use in rocket propulsion). For example, U.S. Pat. No. 6,532,741 to Watkins and U.S. Pat. No. 6,652,248 to Watkins et al. disclose such catalytic systems. 
     SUMMARY OF THE INVENTION 
     One aspect of the invention involves a decontamination method. At least a first flow of hydrogen peroxide is directed to a catalytic reactor. The first flow is passed through a catalyst so as to decompose at least a portion of the first flow into water and oxygen. A discharge flow of the water and oxygen and additional hydrogen peroxide is directed to a contaminated location so as to provide a decontamination. 
     Another aspect of the invention involves a decontamination apparatus. A vessel contains a supply of hydrogen peroxide. A catalytic reactor is coupled to the vessel to receive a first flow and at least partially decompose hydrogen peroxide from the first flow into decomposition products. An outlet is positioned to direct a discharge flow containing the decomposition products and undecomposed hydrogen peroxide to a contaminated location. 
     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a first decontamination system. 
         FIG. 2  is a schematic view of a second decontamination system. 
         FIG. 3  is a schematic view of a third decontamination system. 
         FIG. 4  is a schematic view of a fourth decontamination system. 
         FIG. 5  is a schematic view of a fifth decontamination system. 
         FIG. 6  is a longitudinal cross-sectional view of a catalyst bed assembly of a decontamination system. 
         FIG. 7  is a cross-sectional view of an outer housing of the catalyst bed assembly of  FIG. 6 . 
         FIG. 8  is a detailed cross-sectional view of a downstream end portion of the catalyst bed assembly of  FIG. 6 . 
         FIG. 9  is a longitudinal cross-sectional view of an alternate catalyst bed assembly. 
     
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     A catalytic decomposition system may decompose a first hydrogen peroxide flow or portion thereof and help drive an additional non-decomposing hydrogen peroxide flow or portion for decontamination.  FIG. 1  shows a first exemplary decontamination system  20  mounted on a vehicle  22  (e.g., a self-propelled or towed wheeled or tracked vehicle). The system  20  delivers an output/discharge flow or stream  24  (e.g., essentially a gaseous mixture) containing a quantity of hydrogen peroxide effective for decontamination use. The exemplary system  20  includes a vessel (e.g., a tank) containing a relatively high concentration of hydrogen peroxide (e.g., in excess of a 70% solution (weight percent unless noted), more advantageously in excess of a 90% solution, and most advantageously in excess of a 95% solution, such as an approximately 98% solution). The hydrogen peroxide is delivered through a conduit  30  to a catalytic reactor  32 . This flow from the tank may be a blow-down flow caused by a pressurant gas (e.g., nitrogen). An exemplary pressurant gas is stored in a separate vessel or tank  34  coupled to a headspace of the tank  26  via a conduit  36 . Valves (not shown) may control the flow through the conduits  30  and  36  and may be actuated by a control system (also not shown). The reactor  32  and/or an outlet therefrom may be capable of orientational and/or positional changes such as via an actuator system  40  (e.g., electromechanical, hydraulic, or pneumatic) to permit aiming of the stream  24  such as for sweeping a discharge pattern over a larger area to be contaminated. 
     The catalytic reaction in the reactor  32  converts just a portion of the hydrogen peroxide delivered to the reactor. For example, with a reactor input flow of 98% hydrogen peroxide, sufficient hydrogen peroxide may be decomposed into water vapor and oxygen that the discharge stream  24  will have a hydrogen peroxide content of approximately 35% (at a temperature of about 260° C. (500° F.) compared with about 950° C. (1750° F.) for full decomposition). The decomposition releases energy which heats and further expands the reaction products (in addition to the 50% molar expansion). The expansion may substantially drive the stream  24  including the entrained unreacted hydrogen peroxide. A broader range of the percentage of the hydrogen peroxide which may be decomposed may result in an output stream having 10–75% hydrogen peroxide. A narrower range is 15–35%. An exemplary stream may have at least 30%. An exemplary temperature of the stream  24  is 170–280° C. (800–1000° R). An exemplary flow rate may depend upon the particular application (e.g., 0.05–9 kg/s). With a system sized for decontaminating typical military vehicles, an exemplary flow rate may be in the range of 1–3 kg/s. An exemplary system for open area decontamination may have a rate of 2–5 kg/s per reactor. In various implementations, there may be a mass flow rate of 2–9 kg/s for a duration of at least 10 s. An exemplary reactor is self-heating due to the catalytic reaction and thus lacking external heating (e.g., electric) at least during post-start-up conditions. An external start-up preheater for the reactor is an option. 
     As noted above, the stream  24  may be directly against a surface to be decontaminated or may be directed for area decontamination (e.g., of a field, street, and the like). An alternate open air use is more of a point defense operation with the stream  24  directed against an incoming cloud of biological or chemical warfare agent or counterstream against an incoming stream of such agent (a contaminant stream). Agents may include nerve agents, blister agent, live bacteria, and bacterial spores. One particular example is anthrax. 
       FIG. 2  shows another application wherein such a system  50  is mounted in an aircraft  52  having a fuselage  54 . In an exemplary manned fixed-wing aircraft having a main wing  56  bearing engine nacelles  58 , the hydrogen peroxide and pressurant tanks  60  and  62  may be contained within the fuselage. A conduit network  64  extends from the hydrogen peroxide tank to a number of separate reactors  66  mounted along the wing (either externally or internally) and discharging streams  68 . The streams may be discharged in a generally downward direction for area decontamination (e.g., of open fields or other outdoor areas). An exemplary number of separate reactors is 2–8 with at least one on each of the port and starboard sides of the wing. Unmanned and rotary wing aircraft are alternate platforms as are less integrated systems (e.g., substantially externally mounted systems). 
       FIG. 3  shows a system  80  for decontaminating an enclosed area  82  (e.g., one or more rooms within a building  84 ). The system may be mounted on a self-propelled or towed wheeled or tracked vehicle  86  and may include pressurant and peroxide tanks  88  and  90  and a reactor  92  similarly connected as those of the system  20 . In the illustrated embodiment, rather than directly discharging an airborne stream, the reactor is coupled to a discharge conduit network  94  which may include several branches terminating in several nozzles  96  discharging respective streams  98 . These nozzles may be configured to distribute relatively diffuse (e.g., omnidirectional) gaseous streams  98 . The individual nozzles may be located in separate rooms, a common room, or may be coupled to a building HVAC system providing distribution of the hydrogen peroxide. In another variation, multiple reactors remote of the vehicle could replace the multiple nozzles in a plumbing arrangement similar to that of the system  50 . In yet another arrangement wherein the vehicle is sufficiently small (e.g., a hand-movable cart) the vehicle may be brought into the building or room to be decontaminated. Relatively small flow rates may be appropriate for decontamination of confined internal spaces. The confinement retains the hydrogen peroxide for a duration after the flow is shut-off thereby increasing effectiveness. For example, to decontaminate the interior of a vehicle such as an armored vehicle or an ambulance, a much smaller amount is required than to decontaminate the exterior. For such an internal vehicular decontamination, a flow rate of about 0.02–0.1 kg/s for a period of about 5–10 s could substantially fill the interior space. With the vehicle sealed, the hydrogen peroxide could largely persist for a period of 5–10 minutes or longer to provide the effective decontamination. 
       FIG. 4  shows the system  80  being used to decontaminate the engine(s) of an aircraft  100 . The conduit network  94  is positioned to discharge the hydrogen peroxide streams into one or more engine intakes (inlets)  102  forcing the hydrogen peroxide through the engine and ultimately out an engine exhaust nozzle  104 . This may be performed while the engine is not running (although its spools may be fixed or rotating (e.g., induced by the hydrogen peroxide flow)). In such a system, the nozzle(s) may be mounted to a temporary cover placed over the engine intake(s) or one or more ducts may engage the intake(s) to guide the discharge flow. 
       FIG. 5  shows a system  120  aboard a ship  122 . The system  120  may have one or more central hydrogen peroxide and pressurant tank groups feeding one or more central and/or remote reactors  124  (directly or via additional conduits) discharging streams  126  to decontaminate exposed surfaces of the ship. Other such variations on decontamination of a first ship or land vehicle by a second ship or land vehicle are possible. 
     Suitable reactors may be formed in a variety of ways. One example is the catalyst bed assembly of Watkins et al. noted above (the disclosure of which is incorporated by reference herein as if set forth at length). With such a system, the portion of the hydrogen peroxide flow to be decomposed may pass through the catalyst bed while a remaining portion passes around and cools the catalyst bed and/or a housing. Alternatively, or in combination, the catalyst bed may be relatively undersized (e.g., so as to not decompose substantially all the hydrogen peroxide passing through the catalyst bed). Exemplary catalysts include: silver (e.g., formed as a screen or screen plating); and silver-based alloys. However, any catalyst that is useful in decomposing the hydrogen peroxide could be used. 
       FIG. 6  shows details of a catalyst bed assembly  200  taken from Watkins et al. The catalyst bed assembly  200  includes a catalyst bed section  201  and a nozzle section  203 . The nozzle section  203  secures to the catalyst bed section  201  with suitable fasteners  205 . As an example, the catalyst bed section  201  has an inner diameter of approximately 10 cm when dimensioned for an exemplary use in a medium flow rate application such as building interior decontamination. 
     The nozzle section  203  resides at the downstream, or outlet, end of the catalyst bed  201 . The nozzle  203  receives the discharge from the catalyst bed section  201 . The nozzle accelerates the discharge from the catalyst bed section  201  to form the exhaust stream (e.g.,  24  et al.). Although shown as a convergent-divergent nozzle, other outlet structures are possible. 
     The nozzle section  203  can have threaded openings  229  for securing to any downstream component (e.g., the conduit assemblies  64  et al.). Also, the nozzle section  203  could be made from any suitable material, such as a high temperature, non-catalytic aerospace alloy. 
     The catalyst bed section  201  includes a catalyst can (cannister)  221  within an outer housing  207 . The outer housing  207  can be a cylindrical pipe having flanges  209  and  211  to secure the catalyst bed section  201  to other components (e.g., the associated vehicle, aiming actuators, or the like). However, other arrangements are possible. The outer housing  207  could be made from any suitable material, such as a high temperature, non-catalytic aerospace alloy. 
     The exemplary outer housing  207  secures to the nozzle section  203  using fasteners  205 . The flange  211  may include an annular groove  225  within which a C-shaped (in cross-section) annular metal seal  227  resides. The seal  227  keeps the hydrogen peroxide from escaping from the joint between the catalyst bed section  201  and the nozzle section  203 . Although described as a metallic C-shaped annular seal, any suitable seal or sealing arrangement could be used. 
     The exemplary outer housing  207  includes a threaded opening  213  in an upstream face  215 . The opening receives a correspondingly threaded coupling  217  to create an inlet. The coupling  217  secures to the supply conduit (e.g.,  30  et al., shown in phantom in  FIG. 6 ) supplying hydrogen peroxide to the catalyst bed assembly  200 . 
     The exemplary outer housing  207  includes an open interior  219 . The open interior  219  has a suitable size to receive the catalyst can  221 . The exemplary outer housing  207  has an annular shoulder  231  ( FIG. 7 ) in which a portion of the catalyst can  221  rests. The outer housing  207  also may have at least one threaded opening  233  for securing the catalyst can  221  on the shoulder  231  with a suitable fastener (not shown). 
     A first pressure baffle  223  resides within the open interior  219  of the outer housing  207 . The pressure baffle  223  is preferably made from a high temperature, non-catalytic aerospace alloy. The baffle  223  has an array of openings  239  therethrough. Exemplary openings  239  have a diameter of approximately 1–2 mm. However, other sizes, numbers and arrangements of the apertures could be used to achieve a suitable result. A ring  235  placed in an annular groove  237  on the inner surface of the outer housing  207  retains the pressure baffle  223  within the outer housing  207 . 
     The baffle  223  reduces the pressure of the liquid hydrogen peroxide in the direction of flow. In other words, the pressure of the hydrogen peroxide downstream of the baffle  223  is less than the pressure of the hydrogen peroxide upstream of the baffle. 
     As will be described in more detail below, in the exemplary embodiment, neither the outer housing  207  nor the nozzle section  203  require any cooling lines to manage the heat generated in the catalyst can  221  during decomposition of the hydrogen peroxide. Rather, a bypass flow of hydrogen peroxide (i.e., hydrogen peroxide that does not enter the catalyst bed) may cool the outer housing  207  and the nozzle section  203 . 
     The catalyst can  221  is preferably made from a suitable material, such as a high temperature, non-catalytic aerospace alloy. The exemplary catalyst can  221  has a cylindrical outer wall  241  ( FIG. 8 ) and downstream end flange  243 . The flange  243  includes a plurality of bypass apertures  245 . 
     The interior of the exemplary catalyst can  221  has an annular groove  247  ( FIG. 6 ) adjacent the upstream end. The groove  247  receives a metal ring  249 . The downstream end of the catalyst can  221  includes an annular internal shoulder  251 . The contents within the catalyst can  221  are retained between the metal ring  249  and the shoulder  251  and include: a second pressure baffle  253 ; a third pressure baffle  255 ; and catalyst material  257  forming a catalyst bed therebetween. The second pressure baffle  253  is located adjacent the ring  249 . The second pressure baffle  253  is also preferably made from a high temperature, non-catalytic aerospace alloy. The second pressure baffle  253  has an array of openings  259  therethrough. An exemplary baffle  253  has an outer diameter of approximately 7 cm and the openings  259  have a diameter of approximately 2.4 mm. However, other sizes, numbers and arrangements of the apertures  259  could be used to achieve a suitable result. 
     The ring  249  placed in the annular groove  247  retains the pressure baffle  253  in the catalyst can  221 . The baffle  253  serves to reduce the pressure of the liquid hydrogen peroxide in the direction of flow. In other words, the pressure of the hydrogen peroxide downstream of the baffle  253  is less than the pressure of the hydrogen peroxide upstream of the baffle. 
     The third pressure baffle  255  rests against the shoulder  251 . The third pressure baffle  255  is also preferably made from a high temperature, non-catalytic aerospace alloy. The third press baffle  255  has an array of openings  261  therethrough. Preferably, the baffle  255  has an outer diameter of approximately 7 cm and the openings  261  have a diameter of approximately 2 mm. However, other sizes, numbers and arrangements of the apertures  261  could be used to achieve a suitable result. 
     Once the nozzle section  203  is secured to the catalyst bed section  201  and the supply pipe of hydrogen peroxide is secured to the coupling  217 , the catalyst bed assembly  200  is ready to decompose the hydrogen peroxide. In an exemplary implementation, the supply of hydrogen peroxide enters the catalyst can  221  from the supply pipe with a diameter of approximately 8 cm at a flow rate of approximately 2–4 kg per second and a temperature of approximately 25° C. The catalyst material  257  decomposes the liquid hydrogen peroxide into water vapor, oxygen and heat. Other temperatures, flow rates and supply pipe sizes could be used to achieve a desired exhaust stream. Within the catalyst can  221 , a 98% hydrogen peroxide would decompose into water vapor and oxygen at approximately 6.9 MPa (100 psi) and 945° C. (2192° R). 
     In order to withstand such high temperatures without using complex and heavy cooling schemes, the catalyst bed assembly  200  is designed so that a portion of the supply of hydrogen peroxide bypasses the catalyst can  221 . An annular gap/passageway  263  ( FIG. 8 ) exists between the outer housing  207  and the catalyst can  221 . The bypass liquid hydrogen peroxide fills and flows downstream through the annular gap  263  and serves to cool the catalyst can  221 . The liquid hydrogen peroxide in the annular gap  263  also limits heat build-up in the outer housing  207 . The exemplary annular gap  263  terminates at the downstream flange  243  of the catalyst can  221 . However, the bypass hydrogen peroxide, upon reaching the flange  243 , passes through the apertures  245  in the flange  243 . The amount of bypass could be controlled by the size of the annular gaps  263 ,  265 , or by the number and the size of the apertures  245 . 
     Because the nozzle section  203  is likewise exposed to the heat created by the decomposition of the hydrogen peroxide in the catalyst can  221 , heat build-up in the nozzle section  203  should also be controlled. Similar to the annular gap  263 , a gap  265  ( FIG. 8 ) exists between the nozzle section  203  and the catalyst can  221  at the downstream end of the catalyst can  221 . Preferably, the liquid hydrogen peroxide provides film cooling along the interior surface of the nozzle section  203  while traveling through the nozzle section  203 . 
       FIG. 9  shows a catalyst bed assembly  300  wherein, relative to the assembly  200 , an intermediate mixing section  302  intervenes between the catalyst bed section  201  and the nozzle section  203  as disclosed in Watkins. The mixing section  302  includes concentric inner and outer housing sections  304  and  306 , respectively, defining an annular space/passageway  308  therebetween. The passageway  308  forms a continuation of the cooling passageway  263 . The exemplary mixing section facilitates the introduction of supplemental hydrogen peroxide flows  312 A and  312 B to mix with the flow  314  exiting the catalyst bed to dilute/cool that flow to form a diluted flow  316  which finally mixes with the cooling flow to form the discharge flow  318 . The exemplary flows  312 A and  312 B are expelled from apertures  320  in respective spray bars  322 A and  322 B. To feed the spray bars, the hydrogen peroxide feed conduit (e.g.,  30  et al.) is split into branches, with branches  324 A and  324 B feeding the respective spray bars and a branch  324 C feeding the catalyst bed. Flow through each of the branches may be controlled via an associated valve (not shown) actuated by the control system (not shown). Flow rates through the various branches may, in view of any start-up or cool-down considerations, control the total flow rate and the discharge composition and temperature. 
     The introduction of the flows  312 A and  312 B downstream of the catalyst bed (and distinguished from the cooling flow portion passing through the gap) adds further variables which may be used to achieve a desired output. For example, if substantially all the hydrogen peroxide passing through the catalyst bed is decomposed then it is likely that the decomposition products will cause partial decomposition of the hydrogen peroxide from the flows  312 A and  312 B as the latter cool the flow  314 . To achieve a desired hydrogen peroxide concentration in the discharge flow  318 , the supplemental/bypass flows  312 A and  312 B, in combination, would represent a greater mass flow than the hydrogen peroxide in the discharge stream  318 . For example, in one implementation, approximately 95% of the third branch  324 C hydrogen peroxide flow enters the catalyst can as a first flow for decomposition by the catalyst material. The remaining 5% of the hydrogen peroxide bypasses and may cool the catalyst bed assembly and mixing section. Substantially all the first flow may be decomposed. The combined mass flow rates through the branches  324 A and  324 B could be an exemplary 1–5 times of that through the branch  324 C, more narrowly 2–3 times. About half or more of the hydrogen peroxide flowing through the branches  324 A and  324 B could decompose upon encountering the catalyst output flow  314 . Overall bypass to through-catalyst flow rates could be similar. 
     In operation, the hydrogen peroxide and pressurant tanks may need to be frequently refilled (e.g., after each mission for an airborne system, or a given number of uses for other systems). The catalyst can may need replenishment or replacement less frequently, if at all. 
     One or more embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, various catalytic technologies may be adopted. Additionally, various system parameters may be tailored to particular applications. Accordingly, other embodiments are within the scope of the following claims.