Abstract:
A method of purifying bleed air from an engine heats the bleed air only to an extent necessary for the bleed air to react under catalysis from a noble-metal-based reactor bed, converting the contaminants to filterable form. The contaminants are then removed with a post-treatment filter. A purifier functioning according to the present invention, which heats the bleed air to a temperature no greater than 450° F. which it attains without a combustor, thus releases less heat to adjoining components than a prior-art purifier, and outputs, purified air at a lower temperature than does a prior-art purifier, which typically needs to include a combustor. The purified air is sufficiently-cool as to be suitable for immediate release into interior compartments occupied by humans or the air conditioning system. Contaminants within the exhaust stream may be removed by a reactor bed either within the heat exchanger or separate from the heat exchanger, to produce a purified exhaust gas that may be released to the atmosphere with less environmental impact.

Description:
[0001]    This application is a continuation-in-part of Ser. No. 10/115,180, filed Apr. 1, 2002. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The present invention generally relates to purification of air and, more specifically, to the purification of bleed air from combustion engines and to the purification of the exhaust of an auxiliary power unit (APU).  
           [0003]    Modern large aircraft typically include, in addition to the main engines, APUs which are used primarily during taxiing, takeoff, or landing, or while the aircraft is standing at the gate. In operation, APUs may produce exhaust gas and bleed air. Exhaust gas is typically conducted to the outside, but bleed air may find its way to the aircraft&#39;s interior (which may include the passenger, crew, and cargo compartments). The bleed air may contain contaminants that originate from the APU itself or in the inlet air to the APU. Typically, these compounds are organic, and may include aviation lubricant, including its additives and breakdown products, for example aldehydes and esters; jet fuel; deicing fluid; engine exhaust; and hydraulic fluid. These compounds in the APU bleed air may reach the aircraft cabin and be objectionable as odors or smoke. This phenomenon is often termed “smell-in-cabin” or “smoke-in-cabin” (SIC).  
           [0004]    The exhaust gas from the APU may contain emissions that are harmful to the environment. The APU exhaust gas may contain contaminants such as nitrogen oxides, carbon monoxide and hydrocarbons.  
           [0005]    Methods of removing impurities from air are generally known in the prior art. For example, U.S. Pat. No. 5,294,410 to White teaches a system for removing impurities (primarily biological and chemical warfare impurities) from ambient air. White&#39;s system employs a gas turbine for compressing the gas and a combustor for combusting it, whereby operation is at a high temperature. The hot gas is first treated by a reactor bed of aluminum oxide to “crack” the larger target compounds, and then by a reactor bed of copper oxide to oxidize the cracked larger compounds and the remaining compounds. These kinds of reactor beds require that the gas be at a high temperature.  
           [0006]    Unfortunately, the past methods and devices have several drawbacks. One is that the required operating temperatures are high. This requires that a combustion source be present, as Well as heat exchangers to eventually cool the bleed air to a temperature that can be safely processed by the aircraft&#39;s air conditioning system or inserted into the aircraft&#39;s interior. Thus, the devices are large and heavy with too high a pressure drop and energy consumption. If the bleed air itself is heated by combustion, it will be contaminated with unburned fuel and by-products. In addition, heat transfer from such devices to adjoining components of the aircraft may be objectionable because of the safety impact.  
           [0007]    As can be seen, there is a need for a system for purifying air that operates at relatively low temperatures and that releases purified air of a relatively low temperature.  
         SUMMARY OF THE INVENTION  
         [0008]    One aspect of the present invention provides a method in which bleed air from an engine is heated, reacted in a catalytic reactor to produce reacted contaminant components, and optionally filtered to remove the reacted contaminant components, thus producing purified air for release.  
           [0009]    Another aspect of the present invention provides a method in which bleed air from an engine is heated to a temperature in the range of about 220-450° F., reacted in a catalytic reactor comprising a substrate coated with low-temperature catalyst to produce reacted contaminant components, and optionally filtered to remove the reacted contaminant components, thus producing purified air for release.  
           [0010]    Another aspect of the present invention provides a method in which bleed air from an engine is heated to a temperature in the range of about 220-450° F. by heat exchanging with exhaust gas of the engine; reacted in a catalytic reactor comprising a substrate coated with a low-temperature catalyst to produce reacted contaminant components including carbon dioxide reacted from carbon-containing contaminants, water reacted from hydrogen-containing contaminants, acid gas or an acid-gas precursor reacted from heteroatom-containing contaminants, such as hydrochloric acid reacted from chlorine contaminants, nitric oxide, nitrous oxide, nitrogen dioxide, and nitrogen reacted from nitrogen-containing contaminants; and filtered to remove the reacted contaminant components, thus producing purified air for release.  
           [0011]    Another aspect of the invention provides an apparatus for purifying bleed air from an engine which produces a bleed air stream and an exhaust gas stream, comprising a heat exchanger for exchanging heat from the exhaust stream to heat the bleed air to a temperature in the range of about 220-450° F.; a catalytic reactor comprising a substrate coated with a low-temperature catalyst to produce reacted contaminant components including carbon dioxide reacted from carbon contaminants, water reacted from hydrogen contaminants, acid gas or an acid-gas precursor reacted from heteroatom contaminants such as hydrochloric acid reacted from chlorine contaminants, and nitric oxide reacted from nitrogen contaminants; and a filter for removing the reacted contaminant components, thus producing purified air for release.  
           [0012]    Another aspect of the present invention provides a method of purifying bleed air from an engine which produces a bleed air stream and an exhaust gas stream having a temperature warmer than the bleed air stream, the method comprising the steps of: heating the bleed air to produce heated bleed air to a temperature between 220° F. and 450° F. by placing the bleed air and the exhaust gas in thermal contact but not in fluid contact by flowing each through a different chamber of a heat exchanger; reacting the heated bleed air in a bleed air catalytic reactor bed comprising a noble metal catalyst supported on a washcoat of metal oxide to produce reacted bleed air in which; carbon contaminants in the heated bleed air are reacted to CO 2 ; hydrogen contaminants in the heated bleed air are reacted to H 2 O; contaminating heteroatoms are reacted to one of an acid gas and an acid-gas precursor; chlorine contaminants in the heated bleed air are reacted to HCl, and nitrogen contaminants in the heated bleed air are reacted to at least one of dinitrogen, nitrous oxide, nitric oxide, and nitrogen dioxide; releasing the reacted bleed air; reacting the exhaust gas in an exhaust gas catalytic reactor bed to produce a purified exhaust gas; and releasing the purified exhaust gas.  
           [0013]    These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a flow diagram of the method of the present invention;  
         [0015]    [0015]FIG. 2 is a block diagram of one embodiment of an apparatus on which the method of the present invention may be practiced;  
         [0016]    [0016]FIG. 3 is a block diagram of another embodiment of an apparatus on which the method of the present invention may be practiced;  
         [0017]    [0017]FIG. 4 is a block diagram of yet another embodiment of an apparatus on which the method of the present invention may be practiced; and  
         [0018]    [0018]FIG. 5 is a block diagram depicting variant embodiment details of an apparatus on which the method of the present invention may be practiced.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]    The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.  
         [0020]    The present invention generally provides a system for purifying exhaust gases and bleed air from a combustion engine, the system operating at a relatively low temperature that enhances its suitability for placement proximate to other components, and that eliminates SIC events to enhance the usability by humans of the purified air. An embodiment of the system is for use in purifying the bleed air from auxiliary power units (APUs) employed aboard aircraft, but those skilled in the art will appreciate that the present invention may be useful with any engine producing a stream of bleed air and a hotter stream of exhaust. Aircraft APU systems must not excessively heat adjoining portions of the aircraft, lest those adjoining portions be impaired or damaged by excessive heat, and lest safety regulations be violated. Purified bleed air that may find its way into the aircraft&#39;s air conditioning system must not be so hot as to exceed the cooling capacity of the system or temperature limits of the construction material. Purified bleed air that may find its way into the aircraft&#39;s interior must not be so hot as to be uncomfortable or unsafe to passengers and crew. The benefit is that additional heat exchange is not required, saving weight, size, and pressure drop.  
         [0021]    The bleed air purification system may employ a catalyst employing a noble metal in order to be effective at a temperature lower than systems of the prior art, temperatures in the range of 220-450° F. As a result, the system of the present invention does not require a combustor for heating the bleed air, but is able to obtain sufficient heat for its operation by heat-exchanging with the exhaust gas flow from the same APU from which the bleed air emanates.  
         [0022]    Typically, noble metals including platinum, palladium, rhodium, silver, gold, iridium, may be supported on a high-surface area washcoat that has good adhesion to the substrate. The washcoat is typically a metal oxide such as alumina, titania, silica, zirconia, or other transition metal oxides or mixtures of these. The washcoat and catalyst have good adhesion such that there is no flaking, peeling, or loss of material in the operating environment of aircraft, including high vibrations. The adhesion may be ensured by proper formulation of the washcoat, as well as treatment of the substrate. The washcoat is applied as a slurry of the metal oxide, a binder, and solvent, as discussed in a related U.S. patent application, Ser. No. 101,140, filed Sep. 18, 1998, and which is incorporated herein by reference.  
         [0023]    The exhaust stream purification system may be formed either as a unit separate from the bleed air purification system or within the same structural component as the bleed air purification system. The exhaust stream purification system may employ any conventional catalyst known to be effective at removing engine exhaust stream pollutants. For example, catalysts known as a “three-way conversion” or “TWC” catalysts may be useful in the present invention. TWC catalysts are polyfunctional in that they have the capability of substantially simultaneously catalyzing the oxidation of hydrocarbons and carbon monoxide and the reduction of nitrogen oxides. Conventional TWC catalysts which exhibit good activity and long life may include one or more platinum group metals (e.g., platinum or palladium, rhodium, ruthenium and iridium). The catalyst may be supported on a high-surface area washcoat similar to that used in the bleed air purification system described above. The support may be carried on a suitable carrier or substrate such as a monolithic carrier comprising a refractory ceramic or metal honeycomb structure, or refractory particles such as spheres or short, extruded segments of a suitable refractory material.  
         [0024]    [0024]FIG. 1 depicts a high-level flow chart of the method of the present invention. Block  100  indicates that bleed air is retrieved from an APU into a heat exchanger. Following block  100  is block  102 , which specifies that bleed air is heated therein by thermal contact through the heat exchanger with exhaust air from the APU. One skilled in the art may specify the parameters of the heat exchanger so that the temperature of the bleed air is elevated to a temperature in a predetermined range, such as between 220° F. and 450° F.  
         [0025]    The bleed air from the APU may contain contaminants that originate within the APU itself or in the inlet air to the APU, including without limitation aviation lubricant (including its additives and breakdown products), jet fuel, deicing fluid, engine exhaust, and hydraulic fluid. Block  104 , which follows block  102 , indicates that the heated bleed air is passed through a reactor bed comprising a noble metal catalyst on a high-surface area washcoat with good adhesion to the substrate in order to induce reactions in which the carbon portion of contaminants reacts to carbon dioxide (CO 2 ), the hydrogen portion. reacts to water (H 2 O), and the various heteroatoms to an acid gas or acid-gas precursor: for example, chlorine to hydrochloric acid (HCl) and nitrogen to such compounds as dinitrogen, nitrous oxide, nitric oxide, and nitrogen dioxide.  
         [0026]    The exhaust gas may also contain contaminants from combustion, such as nitrogen oxides, carbon monoxide, and hydrocarbons. Block  110  indicates that the exhaust gas is catalytically treated to decompose the pollutants. The treated exhaust gas may then be released as purified exhaust gas, as indicated in block  112 . The dotted line connecting block  110  and block  104  indicates that the treatment of the exhaust gas and the bleed air may take place in a single reactor in separate chambers.  
         [0027]    After block  104 , block  106  specifies that the bleed air passes through an optional post-treatment filter (PTF), which adsorbs the acidic reaction products. The PTF may be similar to that shown in related U.S. patent application, Ser. No. 823,623, filed Mar. 31, 2001, and incorporated herein by reference. Acid-gases are permanently adsorbed onto the surface. In block  108  the bleed air, purified after block  106 , is released into the aircraft&#39;s air conditioning system before entering the aircraft interior. Some of the bleed air bypasses the air conditioning system and enters the aircraft interior directly. While the proportion of air entering the air conditioning system to the air entering the interior directly is determined by the desired temperature of the interior, both air streams are of sufficient purity and temperature as to be mixed safely. Because of the relatively low operating temperature of the present invention, less heat exchange is required before entering the air conditioning system of the aircraft. This results in reduced weight, volume, and pressure drop compared to the prior art. Also, it is not necessary to use all of the exhaust stream to heat the bleed air stream, which is safer and simpler than having to use all the exhaust stream. Those skilled in the art of heat transfer will appreciate that under these conditions the bleed air stream does not approach the temperature of the exhaust stream, while devices of the prior art operate at temperatures near that of the exhaust stream.  
         [0028]    [0028]FIG. 2 is a block diagram of an apparatus on which the method of the present invention may be performed. An APU  200  produces a stream of bleed air  202  and exhaust stream  204 , both of which enter a heat exchanger  210  in which they are in thermal contact but not in fluid contact. The temperature of exhaust stream  204  may be significantly higher than that of bleed air  202 , so that the temperature of bleed air  202  may be increased in heat exchanger  210 , and is referred to as heated bleed air  202   a  where it exits heat exchanger  210 . Heated bleed air  202   a  traverses reactor bed  220  where, as previously noted, contaminants contained in it may be catalytically induced to undergo oxidation reactions. The bleed air stream bearing reacted contaminant components is designated reacted bleed air  202   b  where it exits reactor bed  220 . Reacted bleed air  202   b  then traverses optional PTF  230 . PTF  230  adsorbs the acidic reacted contaminant components from reacted bleed air  202   b . The bleed air stream, designated purified bleed air  202   c , is released from PTF  230  and may safely be introduced into the air conditioning system of an aircraft and the interior. An exiting exhaust stream  204 a may be released directly to the atmosphere or optionally treated in a reactor bed  240  to remove pollutants prior to its release to the atmosphere.  
         [0029]    [0029]FIGS. 3 and 4 depict alternative apparatus in which the method of the present invention may be practiced, and in which the bleed air and exhaust stream reactor beds and optional PTF may be integral with heat exchanger  210 . FIG. 3 shows a section through heat exchanger  210  which comprises a central passage  212  traversing an outer chamber  214 . Bleed air  202  may be introduced into central passage  212 , while exhaust stream  204  traverses outer chamber  214 . Bleed air  202  and exhaust stream  204  are thus in thermal but not fluid contact through walls of central passage  212 , and bleed air  202  may be heated. Reactor bed  220  and PTF  230  may be positioned within central passage  212 . Bleed air  202  thus becomes heated into heated bleed air  202   a , such as at 220° F. to 450° F., catalytically reacted by reactor bed  220  into reacted bleed air  202   b , and optionally filtered by PTF  230  into purified bleed air  202   c  which may be released, and may be introduced into the air conditioning system or interior of an aircraft. Exhaust stream  204  may be catalytically reacted by reactor bed  240  within heat exchanger  210  to produce a purified exhaust gas stream  204   a . Reactor bed  240  may be positioned at any location within outer chamber  214  of heat exchanger  210 .  
         [0030]    [0030]FIG. 4 also shows a section through a heat exchanger  210  comprising a central passage  212  traversing an outer chamber  214 . In this embodiment, bleed air  202  may be conducted into outer-chamber  214  and exhaust stream  204  is conducted into central passage  212 . Reactor bed  220  and PTF  230  may be arranged so that gas passing through the outer chamber  214  passes through reactor bed  220  and PTF  230 . Thus, comparable to the operation described in connection with FIG. 3, bleed air  202  may be heated to become heated bleed air  202   a , may be reacted to become reacted bleed air  202   b , and may be filtered to become purified bleed air  202   c  for release. Exhaust stream  204  may be catalytically reacted by reactor bed  240  within heat exchanger  210  to produce a purified exhaust gas stream  204 a. Reactor bed  240  may be positioned at any location within inner chamber  212  of heat exchanger  210 .  
         [0031]    [0031]FIG. 5 shows another embodiment, in which the catalyst and washcoat  220  is deposited on the surfaces of heat exchanger  210  through which flow bleed air stream  202 . As the bleed air stream  202  is heated in heat exchanger  210  by heat exchanging with exhaust stream  204 , the contaminants are reacted as previously described to produce reacted bleed air  202   b . Reacted bleed air  202   b  may then optionally be filtered by PTF  230  to produce purified bleed air  202   c . Alternatively, PTF  230  may also be deposited on the surfaces of heat exchanger  210  through which flows bleed air stream  202 . Similiarly, as exhaust stream  204  passes through heat exchanger  210 , the contaminants therein are reacted as previously described to produce purified exhaust stream  204   a.    
         [0032]    As can be appreciated by those skilled in the art, the present invention provides an improved apparatus and method for purifying air that operates at relatively low temperatures and that releases purified air of a relatively low temperature.  
         [0033]    It should be understood, of course, that the foregoing relates to preferred embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.