Abstract:
Integrated systems, including components for control of contaminants, sound, and humidity, are provided for a fuel cell system. The integrated system combines contamination control, sound control, and water management. The contamination control system provides filtration for the intake air that provides oxygen to the fuel cell cathode; materials removed can include sub-micrometer particulate matter, salts, oils, and chemicals. The sound control system reduces the level of noise emitted from the system by attenuating, resonating, or muffling the sound emitting from the air moving equipment, such as a compressor. The contamination control system can also provide security downstream of the compressor, by filtering the air to reduce the opportunity of lubricant from reaching the fuel cell. The water management system removes liquid water when excess is present. These systems are integrated in a variety of configurations to provide compact and thorough protection for the fuel cell.

Description:
[0001]     This application is a continuation of U.S. patent Ser. No. 10/241,117, filed Sep. 10, 2002, now U.S. Pat. No. ______, which claims priority to provisional application Ser. No. 60/322,106, filed on Sep. 11, 2001. The complete disclosures of these applications are incorporated by reference herein. 
     
    
     FIELD OF THE DISCLOSURE  
       [0002]     The present disclosure is related to integrated systems for use with fuel cells, the integrated system including components for control of contaminants, sound, humidity, and the like. In particular, the disclosure is directed to various systems that combine filter assemblies that remove contaminants from the intake air going into fuel cells with sound suppression, and to systems that modify the exhaust coming out from fuel cells.  
       BACKGROUND  
       [0003]     Fuel cell systems, although a probable, highly used power source for the future, have many issues associated with them. Fuel cell systems, which include the fuel cell (or fuel cell stack), a source of oxygen, a source of fuel, and the appropriate equipment needed to obtain sufficient, and preferably optimal, operation the fuel cell, include many parameters that are not completely understood. That is, it is not well understood what is the best configuration for fuel cell systems.  
         [0004]     The life, durability and performance of the fuel cells can be greatly affected by the quality of air used as the oxygen source for the cathode side of the fuel cell. Many types of contaminants present in atmospheric or ambient air can be detrimental to the operation of the fuel cell. The cathode catalyst and the electrolyte can be temporarily or permanently poisoned or damaged by any number of various contaminants, such as sub-micrometer particulate matter, sulfur compounds, VOCs, salts and NH x  etc. The concentration and type of these atmospheric contaminants vary with location, time of day and with season. Generally, the removal of these contaminants is beyond the capability of current air contamination control systems (e.g., particulate filters) used in power plants such as internal combustion engines and gas turbines. Therefore, to maximize the performance, life and durability of fuel cells, the fuel cell system should include at least some form of contaminant control.  
         [0005]     The catalytic reaction occurring within the fuel cell is a silent process, in that the hydrogen fuel, the reaction at the cathode, and the production of power, produce no sound audible by humans. However, although the fuel cell is silent, fuel cell systems generally utilize compressors/expanders, blowers or other air moving equipment to either move air through the fuel cell cathode at just above atmospheric pressure, or to pressurize the cathode air. In either case, the air moving equipment emits objectionable noise at significant sound pressure levels. Additionally, some types of compressors have been known to leak lubricant oil, which can damage a fuel cell.  
         [0006]     The humidity in the oxygen entering the fuel cell can also affect the performance of the fuel cell. Particulate contaminants in the air stream can cause vapor water to condense, as can compression of the air. To maximize the fuel cell performance, the water and/or moisture level throughout the fuel cell system should be controlled.  
         [0007]     As generally described above, proper performance of a fuel cell system has many issues associated therewith. In many instances, the numerous pieces of equipment present in the system form a tangled mess of housings, pipes, and fittings. Improvements are desired.  
       SUMMARY  
       [0008]     The present disclosure provides integrated systems for use with fuel cells, the integrated system including components for control of contaminants, sound, temperature, and humidity in the fuel cell system. In particular, the disclosure is directed to various assemblies that combine contamination control, sound control, and water management.  
         [0009]     The contamination control system provides filtration for the intake air that provides oxygen to the fuel cell cathode; materials removed can include sub-micrometer particulate matter, salts, oils, and chemicals. The sound control system provides broadband attenuation of the sound present in the fuel cell system. The sound control system, which can include a resonator, sonic choke, full choke, sound adsorbent material, etc., attenuates or otherwise reduces sound passing through the system by at least 3 dB at one meter, preferably by at least 6 dB. The contamination control system can also provide security downstream of the compressor, by filtering the air to reduce the opportunity of lubricant from reaching the fuel cell. The temperature control system controls the temperature of the system, by adding or removing heat, as desired. The water management system removes liquid water when excess is present. These systems are integrated in a variety of configurations to provide compact and thorough protection for the fuel cell.  
         [0010]     In one particular configuration, the various systems are arranged as an upstream integrated assembly, an attenuated heat exchanger assembly, a downstream integrated assembly, and an exhaust assembly.  
         [0011]     Also, the effects of cathode air contaminants on the performance of PEM fuel cells were compiled. Contaminants which affect fuel cell performance and reliability, along with technology in high efficiency filtration of particulate matter, oils, salts and chemicals, and acoustics were incorporated in the development of the various assemblies.  
         [0012]     In particular, the present disclosure is directed to a fuel cell system that has multiple integrated assemblies. The system comprises a fuel cell having an inlet for an air stream, and air moving equipment having an inlet and an outlet for the air stream, the outlet operably connected to the fuel cell inlet. A first integrated assembly is positioned in the air stream upstream from the air moving equipment, and a second integrated assembly is positioned in the air stream downstream from the air moving equipment, the first and second integrated assemblies including at least two systems of a contamination control system, a sound control system, a temperature control system, and a water management system. In one embodiment, the first integrated assembly includes a contamination control system and a sound control system. The contamination control system can include a particulate filter and a chemical filter. A third integrated assembly can also be present in the fuel cell system.  
         [0013]     The present disclosure is also directed to an integrated assembly for use with a fuel cell system, the system comprising sound-producing air moving equipment. The assembly comprises a housing having an air inlet and an air outlet, a sound control system constructed to reduce sound by at least 3 dB, and a temperature control system, each of the sound control system and the temperature control system being within the housing. The temperature control system can be a heat exchanger. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a schematic diagram of an integrated fuel cell system in according with the present disclosure.  
         [0015]      FIG. 2  is a partial, cross sectional, detailed view of various portions of the integrated fuel cell system of  FIG. 1 ; specifically,  FIG. 2  illustrates an upstream integrated assembly, a downstream integrated assembly, and an exhaust assembly.  
         [0016]      FIG. 3  is an isometric view of another portion of the integrated fuel cell system of  FIG. 1 ; specifically,  FIG. 3  illustrates an attenuated heat exchanger assembly.  
         [0017]      FIG. 4  is a cross-sectional view of a second embodiment of an attenuated heat exchanger assembly.  
         [0018]      FIG. 5  is a scanning electron microscopic photograph of contaminants collected on a particulate filter positioned downstream of an air compressor.  
         [0019]      FIG. 6  is a graphical representation of a spectrometer analysis of contaminant collected from the filter of  FIG. 5 .  
         [0020]      FIG. 7  is a graphical representation showing beneficial effects on fuel cell performance when a particulate filter is included in the air stream.  
         [0021]      FIG. 8  is a graphical representation of the effect of SO 2  on PEM fuel cell performance, under a first set of conditions.  
         [0022]      FIG. 9  is a graphical representation of the effect of SO 2  on PEM fuel cell performance, under a second set of conditions.  
         [0023]      FIG. 10  is a graphical representation of the effect of SO 2  on PEM fuel cell performance, under a third set of conditions. 
     
    
     DETAILED DESCRIPTION  
       [0024]     Referring to the figures, wherein like numerals represent like parts throughout the several views, there is schematically illustrated in  FIG. 1 , a fuel cell system  10 . Fuel cell system  10  includes a fuel cell  15 , a first compressor  50  and a second compressor  50 ′ upstream in the air flow to fuel cell  15 , and an expander  55  downstream of fuel cell  15  in the air flow.  
         [0025]     Although compressors  50 ,  50 ′ and expander  55  are shown, it is understood that any type of suitable air moving equipment, such as compressors, expanders, turbochargers, blowers or other air moving equipment can be used to move air to fuel cell  15 . As mentioned above, generally all air moving equipment emits some level of objectionable noise.  
         [0026]     Fuel cell system  10  includes an upstream integrated assembly  100 , an attenuated heat exchanger assembly  150 , a downstream integrated assembly  200 , and an exhaust assembly  300 . By use of the terms “upstream” and “downstream”, reference is to the air moving equipment upstream of fuel cell  15 , such as compressor  50 . By use of the term “integrated”, what is meant is having multiple systems, such as a contamination control system, sound control system, temperature control system, or water management system, in one assembly; preferably, the assembly is contained in a single housing, although in some embodiments, two or more housings are joined to form a single housing. As stated above, the air moving equipment can be a compressor, expander, turbocharger, blower, or any such item.  
         [0027]     Upstream integrated assembly  100 , illustrated schematically in  FIG. 1 , can include a particulate filter, a chemical removal filter, which is typically a carbon-based material, and a sound suppression element. Such upstream filter assemblies  100  are discussed, for example, in U.S. Pat. Nos. 6,780,534 and 6,783,881, the entire disclosures of which are incorporated herein by reference. Typically, each of the parts of upstream integrated assembly  100  (i.e., the particulate filter, chemical filter, and sound suppression) is housed within the same housing, but, in some embodiments, any one or more of these parts may be present in a separate housing or unit. Referring to  FIG. 2 , one preferred upstream integrated assembly  100  is illustrated in detail.  
         [0028]     In  FIG. 2 , upstream integrated assembly  100  comprises two portions arranged in series, a first portion in a housing  105   a  having a contamination control system and a sound control system, and a second portion in housing  105   b  having a sound control system. Assembly  100  has an inlet  102  and an outlet  104 . Inlet  102  feeds air, typically atmospheric or ambient air, into housing  105   a.  The air passes through a contaminant control or filtration system  110  that includes a particulate or physical contamination removal system and a chemical contamination removal system. In the embodiment illustrated, filtration system  110  has a chemical filter element  112 , which includes a first filter element  112   a  and a second filter element  112   b,  and a particulate filter element  114 .  
         [0029]     Chemical filter element  112  removes contaminants from the air by either adsorption or absorption. As used herein, the terms “adsorb”, “adsorption”, “adsorbent” and the like, are intended to also include the mechanisms of absorption and adsorption.  
         [0030]     The chemical contamination removal system typically includes a physisorbent or chemisorbent material, such as, for example, desiccants (i.e., materials that adsorb or absorb water or water vapor) or materials that adsorb or absorb volatile organic compounds and/or acid gases and/or basic gases. The terms “adsorbent material,” “adsorption material,” “adsorptive material,” “absorbent material,” absorption material,” absorptive material,” and any variations thereof, are intended to cover any material that removes chemical contaminants by adsorption or absorption. Suitable adsorbent materials include, for example, activated carbon, including carbon fibers, impregnated carbon, activated alumina, molecular sieves, ion-exchange resins, ion-exchange fibers, silica gel, and silica. Any of these materials can be combined with, coated with, or impregnated with materials such as, for example, potassium permanganate, calcium carbonate, potassium carbonate, sodium carbonate, calcium sulfate, citric acid, phosphoric acid, other acidic materials, or mixtures thereof. In some embodiments, the adsorbent material can be combined or impregnated with a second material.  
         [0031]     The adsorbent material typically includes particulates or granulated material and can be present in varied configurations, for example, as granules, beads, fibers, fine powders, nanostructures, nanotubes, aerogels, or can be present as a coating on a base material such as a ceramic bead, monolithic structures, paper media, or metallic surface. The adsorbent materials, especially particulate or granulated materials, can be provided as a bed of material. Alternately, the adsorbent material can be shaped into a monolithic or unitary form, such as, for example, a large tablet, granule, bead, or pleatable or honeycomb structure that optionally can be further shaped. In at least some instances, the shaped adsorbent material substantially retains its shape during the normal or expected lifetime of the filter assembly. The shaped adsorbent material can be formed from a free-flowing particulate material combined with a solid or liquid binder that is then shaped into a non-free-flowing article. The shaped adsorbent material can be formed by, for example, a molding, a compression molding, or an extrusion process. Shaped adsorbent articles are taught, for example, in U.S. Pat. No. 5,189,092 (Koslow), and U.S. Pat. No. 5,331,037 (Koslow), which are incorporated herein by reference.  
         [0032]     In the embodiment illustrated in  FIG. 2 , filter elements  112   a,    112   b  are hollow, cylindrical forms of extruded activated carbon.  
         [0033]     Particulate filter  114  removes physical or particulate contaminants, contaminants such as dust, dirt, smog, smoke, diesel particulate, pollen, insects, wood chips and sawdust, metal shavings, cosmic dust, and the like. Typically, the particulate removal portion contains a filter media, such as a fibrous mat or web, including cellulosic materials, to remove particles. The media used in filter element  114  can vary, depending on the particulate removal efficiency desired, the maximum level of acceptable pressure drop through filter  114 , and other such factors. The filter media can be treated in any number of ways to improve its efficiency in removing minute particulates; for example, electrostatically treated media can be used, as can cellulose or synthetic media or a combination thereof, having one or more layers of nanofiber, or other types of media known to those skilled in the art. For details regarding types of nanofiber that could be used, see for example, U.S. Pat. No. 4,650,506 (Barris et al.), which is incorporated herein by reference.  
         [0034]     In the preferred embodiment, particulate filter element  114  includes a cellulosic filter media that is wound about a central axis to form an obround shaped filter element. The filter element includes a sealing system for sealing filter  114  to housing  105   a,  a sealing system such as disclosed, for example, in U.S. Pat. No. 4,720,292. By the term “seal” or “sealing,” it is meant that sealing system  60 , under normal conditions, prevents unintended levels of air from passing through a region between the outer surface of filter element  114  and the interior sidewall of housing  105   a;  that is, the sealing system inhibits air flow from avoiding passage through filtering media of filter element  114 .  
         [0035]     In certain preferred arrangements, filter  114  is configured for straight-through flow. By “straight-through flow,” it is meant that filter  114  is configured so as to have a first flow face (corresponding to an inlet end) and an opposite, second flow face (corresponding to an outlet end). Straight-through flow is often desired because a straight-through flow filter can handle greater amounts of air passing therethrough compared to, for example, a pleated filter. It is intended that there is no distinction between “straight-though flow” and “in-line flow”. Air enters in one direction through the first flow face and exits in the same direction from second flow face.  
         [0036]     Additional and alternate details regarding chemical filter  112  and particulate filter  114  are described in U.S. Pat. Nos. 6,780,534 and 6,783,881.  
         [0037]     From this contaminant control system (i.e., filters  112 ,  114 ), the air progresses to a sound control system within upstream integrated assembly  100 . Specifically, the air progresses into housing  105   b  where a sound suppression configuration  130  is housed. Sound suppression configuration  130  includes a first resonator  132  and a second resonator  134 . Each of these resonators  132 ,  134  includes a plurality of perforations, their size and placement exactly engineered in order to resonate desired wavelengths of sound. Sound suppression configuration  130  also includes a sonic choke  135 .  
         [0038]     Sound suppression configuration  130  reduces or suppresses the level of noise or sound emanating from any of compressor  50 , compressor  50 ′, and expander  55 . Such noise reduction is preferably at least 3 dB at one meter, typically at least 6 dB, preferably at least 10 dB, and most preferably at least 25 dB. Sound suppression configuration  130  reduces the noise emanating from compressor  50  through upstream integrated assembly  100  and out to the surrounding environment, by attenuating the sound.  
         [0039]     Sound emanating from equipment such as compressor  50  will travel in any direction as permitted by fuel cell  15 , compressor  50 , and other assemblies such as upstream integrated assembly  100 , attenuated heat exchanger assembly  150 , downstream assembly  200  and exhaust assembly  300 . That is, sound travels upstream from compressor  50 , against the flow of the air, to upstream integrated assembly  100 ; and sound travels downstream to attenuated heat exchanger assembly  150 . Sound from compressor  50 ′ and expander  55  likewise travels upstream and downstream.  
         [0040]     Sound suppression configuration  130  can include any type of element that, together with other features of upstream integrated assembly  100  that may attenuate or otherwise reduce the sound by at least 3 dB, typically at least 6 dB, preferably by at least 10 dB, and more preferably by at least 25 dB. Examples of suitable sound suppression elements include mufflers, lined ducts, baffles, bends in the sound path, plenums, expansion chambers, resonators, sonic chokes, full chokes, sound adsorptive material, and various combinations thereof. As indicated above, the embodiment illustrated in  FIG. 2  has sound suppression configuration  130  having first resonator  132 , second resonator  134  and sonic choke  135 .  
         [0041]     Sound suppression configuration  130  is provided in housing  105   b.  It is preferred that the outer wall of housing  105   b  and any other structures have minimal surfaces that are planar or flat; rather, it is preferred that the surfaces are curved, to reduce the amount of vibration or drumming that often occurs with flat walls.  
         [0042]     Additional and alternate details regarding sound suppression configuration  130 , including resonators  132 ,  134 , sonic choke  135 , and other attenuating or resonating equipment are described in U.S. Pat. Nos. 6,780,534 and 6,783,881.  
         [0043]     The air, having passed through a contamination control system and a sound control system, exits upstream integrated assembly  100  via outlet  104  and progresses to compressor  50 . The air enters compressor  50  via inlet  52  and exits via outlet  54 . As mentioned above, compressor  50  can be any suitable air moving equipment.  
         [0044]     From compressor  50 , the air moves to attenuated heat exchanger assembly  150 . This assembly  150  can also be called an “intercooler assembly”, the assembly having a heat exchanger (or cooler) and being positioned between compressor  50  and compressor  50 ′. If no compressor  50 ′ was present, thus, assembly  150 , positioned downstream of compressor  50 , could be called an “aftercooler assembly”. One preferred embodiment for attenuated heat exchanger assembly  150  is illustrated in  FIG. 3 .  
         [0045]     Attenuated heat exchanger assembly  150  is so named due to its integration of a sound control system and a temperature control system retained in a housing  155 . Housing  155  has an inlet  152  and an outlet  154 ; assembly  150  receives air from outlet  54  of compressor  50  through inlet  152 . Inlet  152  connects to a sound suppression element  160 , which has a plurality of apertures designed to attenuate sound. Assembly  150  also includes a second sound suppression element  165 . Sound suppression elements  160 ,  165  attenuate or otherwise reduce the sound by at least 3 dB, typically at least 6 dB, preferably by at least 10 dB, and more preferably by at least 25 dB. Housing  155  also reduces the level of sound passing through assembly  150 ; housing  155  is a cylindrical shape, having a wall  156  extended between rounded first end  157  and rounded second end  158 . The surfaces of wall  156  and ends  157 ,  158  are curved, to reduce the amount of vibration or drumming.  
         [0046]     Positioned between sound suppression elements  160 ,  165  is a heat exchanger  170 . Heat exchanger  170  cools the air passing through assembly  150 , by removing heat via cooling water that is fed into heat exchanger  170  via cooling water inlet  172 ; heated water is removed via cooling water outlet  174 . The air entering assembly  150  via inlet  152  is at an elevated temperature, due to the compression by compressor  50 .  
         [0047]     A second embodiment for an attenuated heat exchanger assembly is illustrated in  FIG. 4  at  150 ′. Attenuated heat exchanger assembly  150 ′ includes a contamination control system.  
         [0048]     Similar to assembly  150  of  FIG. 3 , assembly  150 ′ has a housing  155 ′ having an inlet  152 ′ and an outlet  154 ′. Housing  155 ′ has a first end  157 ′ and an opposite second end  158 ′. First end  157 ′ includes a removable flange cover  159 , the use of which will be described below. Air from compressor  50  enters assembly  150 ′ via inlet  152 ′ and progresses to a filter element  180 . Filter element  180  is a particulate filter element, and preferably comprises PTFE material. Filter element  180  typically includes a perforated inner liner, used to provide stability and structure to the pleated media while permitting air flow therethrough. In some embodiments, it may be preferred to have the perforations designed to attenuate or resonate sound. As mentioned, first end  157 ′ includes flange  159 , which provides access to filter element  180 , for removal and replacement of filter element  180 , as desired.  
         [0049]     From filter element  180 , the now-filtered air passes to heat exchanger  170 ′ (which has cooling water inlet  172 ′ and outlet  174 ′) where the air is cooled. The cooled air progresses to resonator  165 ′ and then out via outlet  154 ′.  
         [0050]     Air from attenuated heat exchanger assembly  150 ,  150 ′ having passed through second compressor  50 ′, progresses to downstream integrated assembly  200 .  
         [0051]     Downstream integrated assembly  200 , schematically shown in  FIG. 1 , can have any of a contamination control system, a sound control system, and a water management system. Examples of downstream filter assemblies  200  are discussed, for example, in U.S. Pat. Nos. 6,780,534 and 6,783,881. Returning again to  FIG. 2 , one embodiment of a preferred downstream integrated assembly  200 , having a sound suppression element and a filter which manages water, is illustrated.  
         [0052]     Downstream integrated assembly  200  has an inlet  202 , an outlet  204 , and a housing  205 . Positioned within housing  205  is a filter  210 . Filter  210  has two filter elements  210   a  and  210   b.  In the shown embodiment, filter element  210   a,    210   b  are made from a material, such as expanded polytetrafluoroethylene (PTFE), which acts as both a particulate and chemical filter. The PTFE inhibits passage of salts and organic materials, such as oil, therethrough. Thus, the PTFE accomplishes both particulate and chemical filtration. PTFE also allows water vapor to pass through, yet coalesces and collects liquid water. This water is generally drained from assembly  200 .  
         [0053]     Assembly  200  also includes a sound suppression element  230  within housing  205 . Sound suppression element  230  attenuates or otherwise reduces the sound, by at least 3 dB, typically at least 6 dB, preferably by at least 10 dB, and more preferably by at least 25 dB. Housing  205 , and filter  210 , are preferably circular to increase the sound suppression of assembly  200 .  
         [0054]     The air flow through downstream filter assembly  200  can be monitored to determine if a potentially detrimental contamination may, or may have, occurred. At least three possible options for monitoring are available. An air mass flow sensor can be installed between filter  210  and fuel cell  15  to monitor the mass of air passing through filter  210 . As the mass decreases, the level of clogging of filter  210  can be estimated. As a second option, the pressure drop across filter  210  can be monitored. As a third option, a pressure relief valve can be installed upstream of filter  210 ; thus, if filter  210  becomes too clogged and does not allow sufficient air to flow therethrough, pressure will build up upstream of filter  210 , and the pressure relief valve will blow.  
         [0055]     Air enters downstream integrated assembly  200  via inlet  202 , is attenuated by sound suppression element  230  and then passes through filter  210 , either inside out or outside in. Filter  210  removes particulates that may have passed through, or been created by, compressor  50 ′. Air exits from downstream integrated assembly  200  via outlet  204  and progresses to fuel cell  15 .  
         [0056]     Fuel cell  15  utilizes oxygen from the inputted air and hydrogen to fuel a catalytic reaction and produce power. Water, either in the form of vapor or liquid, is produced as a by-product. The exhaust air from fuel cell  15  may have collected contamination, for example, from the catalyst on the anode or the electrolyte.  
         [0057]     The air entering fuel cell  15  is typically at an elevated pressure, in the system of  FIG. 1 , having passed through compressor  50  and compressor  50 ′. This increased pressure improves the efficiency of fuel cell  15 . Once through fuel cell  15 , the air can be return to atmospheric pressure, or at least reduced from its elevated pressure. In  FIG. 1 , the air stream passes through expander  55 . In one preferred embodiment, expander  55  is together with a compressor stage, compressor  50 ′ in  FIG. 3 , thus both compressor  50 ′ and expander  55  are incorporated into one turbocharger unit, as illustrated in  FIG. 3 .  
         [0058]     Fuel cell system  10  of  FIG. 1  further includes exhaust assembly  300 , positioned downstream of fuel cell  15 , to which the air progresses from expander  55 . Exhaust assembly  300  is positioned on the exhaust end of fuel cell  15 , so that the air passing through assembly  300  has a reduced level of oxygen. Also present in the exhaust air is water, both liquid water and water vapor.  
         [0059]     One preferred embodiment of exhaust assembly  300  is illustrated in  FIG. 2  having a contamination control system, a sound control system, and a water management system. Specifically, exhaust assembly  300  has a sound suppression element  330 , a chemical filter  320 , and a water removal element  340  all present within housing  305 . Water removal element  340  removes the liquid water, but allows the water vapor to pass out with the air stream.  
         [0060]     Housing  305  has an inlet  302  for receiving air from fuel cell  15 , and an outlet  304  for exiting air. Air enters exhaust assembly  300  via inlet  302  and progress to sound suppression element  330 . A chemical filter  320  is positioned downstream of element  330 . Liquid water is removed from the air stream by water removal element  340 ; an example of a preferred water removal element  340  for exhaust assembly  300  is a plurality of tubular structures, often referred to as “strata tubes”.  
         [0061]     The description given above provides a fuel cell system  10  having numerous integrated components provided for control of contaminants, sound, and humidity within system  10 . Various preferred embodiments of various assemblies have been described for use with the air stream for the cathode side of fuel cell  15 . It should be understood that any of the assemblies described above, and variations thereof, could be used on the fuel side (i.e., anode side) of the fuel cell, to protect the catalyst in the fuel cell or the catalyst in a fuel reformer.  
         [0062]     The following discussion is directed to discussing various contaminants that are believed to be detrimental to fuel cell operation.  
         [0000]     Ambient Air Contaminants  
         [0063]     Air contaminants vary with location in both composition and magnitude. Particulate matter, for example, varies nine orders of magnitude in concentration from calm days over the ocean to a windy day in the desert. In addition, the size distribution of the particulates varies depending on the source of the particulate matter. Table 1, below, describes in general terms how the contaminants vary with environmental conditions and location.  
         [0064]     Volatile Organic Compounds (VOCs) such as unburned hydrocarbon emissions from internal combustion engines vary greatly in concentration depending on location and the sources of emissions. Urban areas in cold climates experience days with significantly elevated levels of VOCs due to cold started internal combustion engines. Areas where two cycle internal combustion engines are operated have high concentrations of carbon monoxide and VOCs. A city can have relatively low average concentrations of VOCs, but have local areas where the concentrations are elevated. Sulfur compounds in the air are found wherever fuels containing sulfur are combusted, agricultural areas such as hog farms or industrial sources such as pulp mills.  
         [0065]     Ammonia is usually present in agricultural regions and close to sewage treatment plants. It has been found that 3-way catalytic converters in automobiles produce about 0.28 ounces of ammonia per 100 miles as a by-product when they reduce oxides of nitrogen in the exhaust stream. The ammonia produced has been found to accumulate in tunnels and other restricted areas.  
         [0066]     Salt concentration in the air is present particularly in coastal areas, in deserts, close to industrial discharges and on roadways in cold climates where salt is used for ice removal. Salts such as NaCl, KCl, ammonium sulfates, magnesium sulfate or other sulfates are carried in the air and deliquesce or change state depending on humidity conditions. The salts may be in either solid state as particulate matter, or in water solution. Dry salt particles range in size from 0.5 to 1.5 μm. Wetted salt particles range in size from 1 to 20 μm. The salt concentration in the air in coastal regions is greatly dependent on wind velocity, especially if the area is directly exposed to spray. The salt concentration in the air can be as high as  10  PPM at a wind velocity of 35 knots. If the area is moderately protected and not exposed to direct spray, the concentrations will be as displayed in Table 2 for altitudes up to 100 feet.  
         [0067]     Typical average concentrations of a few select pollutants in various cities are listed in Table 3. In extreme situations such as in battlefields, warfare gases and other pollutants can be present in the air in concentrations listed in Table 4.  
                                         TABLE 1                       Types of Contaminants vs. Geographic area                                GEOGRAPHIC   URBAN   RURAL/ARCTIC   OFF-SHORE AND   DESERT   TROPICAL       AREA   Major metropolitan   Forest, tundra and   MARITIME           areas with heavy   agriculture           industry and motor           vehicles       ENVIRONMENTAL   Rain, fog, smog,   Snow, freezing   Wet and dry salt,   Dry, sunny.   Heavy rainfall.       CONDITIONS   snow.   rain, frost   corrosive particles.   30° F. to 120° F.   40° F. to 120° F.           28° F. to 100° F.   −40° F. to 90° F.   0° F. to 90° F.   (0° C. to +50° C.)   (+5° C. to 50° C.)           (−1° C. to +40° C.)   (−40° C. C. to +31° C.)   (−18° C. to +31° C.)   Sandstorms,   Fibrous           Corrosive   Dry, noncorrosive   Blowing rain, salts,   whirlwinds, dry,   noncorrosive           chemicals, VOCs,   fibrous particles,   sea spray, fog, snow   corrosive   particles, molds           SO2, gummy soot   ammonia, SO2,   and ice.   particles, clays   and insects.           particles, NOx,   and blowing dust.       and salts.           NH3, and dried           salts.       PARTICLE     50-175   &lt;150   &lt;135   &gt;350,000   &lt;135       CONCENTRATION (μg/m 3 )       PARTICLE SIZE   0.01-30   0.01-75   0.01-10   0.01-500   0.01-10       RANGE (Micrometers)                  
 
         [0068]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                   
               
               
                 Mass concentration of salt vs. wind velocity in 
               
               
                 moderately protected coastal area 
               
               
                 Mass Concentration for salt particles 
               
             
          
           
               
                 Wind 
                   
                   
                   
                 Total 
               
               
                 Velocity 
                   
                 &lt;4 micrometer 
                 &lt;13 micrometer 
                 (ppm by 
               
               
                 (MPH) 
                 (Knots) 
                 (ppm by mass) 
                 (ppm by mass) 
                 mass) 
               
               
                   
               
             
          
           
               
                 10 
                 8.7 
                 0.004 
                 0.005 
                 0.006 
               
               
                 20 
                 17.4 
                 0.006 
                 0.009 
                 0.010 
               
               
                 30 
                 26.0 
                 0.008 
                 0.011 
                 0.012 
               
               
                 40 
                 34.7 
                 0.010 
                 0.012 
                 0.014 
               
               
                 50 
                 43.4 
                 0.012 
                 0.013 
                 0.018 
               
               
                   
               
             
          
         
       
     
         [0069]    
       
         
               
             
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                   
               
               
                 Average ambient air contaminants vs. location 
               
             
          
           
               
                   
                 SO2 
                 PM10 
                 Benzene 
               
               
                   
                 (ppb) 
                 (μg/m 3 ) 
                 (ppb) 
               
               
                   
                   
               
             
          
           
               
                   
                 Perth, Australia 
                 2.0 
                 21 
                   
               
               
                   
                 London, UK 
                 11.0 
                 29 
                 1.8 
               
               
                   
                 Rome, Italy 
                 1.0 
                 52 
                 3.7 
               
               
                   
                 Paris, France 
                 5.0 
               
               
                   
                 Berlin, Germany 
                 6.0 
                 31 
                 2.8 
               
               
                   
                 Shanghai, China 
                 20.0 
               
               
                   
                 Delhi, India 
                 9.0 
                 162 
               
               
                   
                 Taipei, Taiwan 
                 4.0 
                 44 
               
               
                   
                 Moscow, Russia 
                 41.0 
               
               
                   
                 Cairo, Egypt 
                 26.0 
               
               
                   
                 Stockholm, Sweden 
                 2.0 
                 25 
               
               
                   
                 New York, US 
                 9.0 
                 17 
                 3.0 
               
               
                   
                 Los Angeles, US 
                 2.0 
                 139 
                 1.0 
               
               
                   
                 Houston, US 
                 2.6 
                 29 
                 0.8 
               
               
                   
                 Minneapolis, US 
                 9.8 
                 25 
                 0.5 
               
               
                   
                 Vancouver, Canada 
                 2.0 
                 14 
                 0.7 
               
               
                   
                 Mexico City, Mexico 
                 28.0 
                 53 
               
               
                   
                 Sao Paulo, Brazil 
                 16.0 
                 54 
               
               
                   
                   
               
             
          
         
       
     
         [0070]    
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                   
               
               
                 Concentration of Contaminants in a Battlefield 
               
             
          
           
               
                   
                   
                 Concentration 
               
               
                   
                 Contaminant 
                 (PPM) 
               
               
                   
                   
               
             
          
           
               
                   
                 Carbon Monoxide 
                 20 
               
               
                   
                 Sulfur Dioxide 
                 0.5 
               
               
                   
                 Benzene 
                 50 
               
               
                   
                 Propane 
                 90 
               
               
                   
                 Nitrogen Dioxide 
                 0.4 
               
               
                   
                 Cyanogan Chloride (CNCL) 
                  780-1560 
               
               
                   
                 Hydrogen Cyanide (HCN) 
                 1780-3560 
               
               
                   
                 Sulfur Mustard 
                 15 
               
               
                   
                 Sarin 
                 170-340 
               
               
                   
                   
               
             
          
         
       
     
         [0071]     The various contamination control systems described above are preferably designed to reduce the amount of contaminants that would detrimentally affect fuel cell  15 .  
         [0000]     Contamination Emitted by Compressors  
         [0072]     In addition to the contaminants found in atmospheric air, contaminants, either particulate, chemical, or both, may be produced or emitted by the air moving or air handling equipment, such as compressors  50 ,  50 ′.  
         [0073]     There are at least two types of contaminants emitted by compressors that have been identified to be harmful to fuel cells, lubrication oil that is leaking past bearing seals, and wear particles from rotating components. One of the most common types of compressor used in fuel cell air handling systems is the twin screw Lysholm style compressor. One such compressor has been characterized, and was found to be emitting both particulate matter and small amounts of lubrication oil.  
         [0074]     The contaminants from the compressor were collected on two different types of filters downstream of the compressor, one membrane filter to trap particulate matter and one HEPA filter to collect lubrication oil. The compressor was fed clean-room quality HEPA filtered air to eliminate the possibility of collecting contaminant downstream of the compressor that did not originate from the compressor.  
         [0075]      FIG. 5  is a scanning electron microscope image of contaminant collected on a membrane filter. The symmetrical black shapes on the membrane are 3 μm etched holes, and the non-uniform shapes are the collected particulate matter. Even though the particles that were analyzed varied in size and shape, they all had the same elemental composition. The particles range in size from 1 to 10 μm in diameter, which is characteristic for particles of a hard material produced by high-speed abrasion.  
         [0076]     An elemental analysis was conducted using an Energy Dispersive Spectrometer (EDS), and the results from a typical particle are shown in  FIG. 6 . The oxygen and carbon peaks in  FIG. 6  indicate organic matter, likely originated from the compressor&#39;s lubricating oil. The trace amounts of copper and zinc also suggest lubricating oil, as typical oil-additives contain zinc and copper. The molybdenum and sulfur peaks most likely represents the MoS 2  coating used in the lobes in this compressor. All the particles that were analyzed had the same molybdenum to sulfur ratio, but the amount of organic material varied. None of the particles contained aluminum, which is the base material for the compressor housing and lobes. Table 5, below, provides the breakdown of the contaminant elemental analysis.  
                                                                           TABLE 5                           Elemental Analysis of Collected Contaminants                        K-                   Element   Wt %   At %   Ratio   Z   A   F                    C K (Carbon)   82.31   92.56   0.3289   1.0172   0.3928   1.0001       O K (Oxygen)   6.14   5.18   0.0069   1.003   0.115   1.0001       S K (Sulfur)   2.04   0.86   0.0193   0.9624   0.9838   1       CuK (Copper)   0.56   0.12   0.0049   0.8413   1.0293   1       ZnK (Zinc)   0.34   0.07   0.0029   0.8426   1.0278   1       MoK   8.62   1.21   0.0651   0.7489   1.0091   1       (molybdenum)               Total   100   100                  
 
 Effects of Air-Contamination on PEM Fuel Cells 
 
         [0077]     In general, the contamination issue for fuel cells is very different than that of traditional power systems such as internal combustion engines and gas turbines. Large particulate matter is filtered out of the combustion process. Sub-micron particulate matter and chemicals are not filtered from the combustion air in engines, as they are harmless. If the same level of filtration is applied to the cathode air in PEM fuel cells, contaminant ions and chemicals may permanently degrade the fuel cell.  
         [0078]     One study that was conducted on cathode air contamination by Sakamoto et al. clearly indicates the importance of keeping contaminants from entering the cathode. In  FIG. 7 , a comparison of cell voltage for single cells, with and without particulate filter, is plotted versus time. Sakamoto et al. found that only the cell that was operated without air filtration had an increase in Ca, K, Mg and Na ions at the end of the test.  
         [0079]      FIGS. 8, 9  and  10  demonstrate the effect of SO 2  in the air on the performance of PEM fuel cells. In each of the conducted tests, a hydrogen/air PEM fuel cell, having an anode of 0.17 mg platinum per cm 2 , and a cathode of 0.18 mg platinum per cm 2 , was used. The fuel cell was operated at a 50% excess of oxygen, at a temperature of 80° C., and with an air flow rate of  202  standard cm 3  per minute. The air fed to the cathode had either a level of 0 ppm SO 2  contamination or a level of 5 ppm SO 2  contamination.  
         [0080]     In the first test, the results of which are graphed in  FIG. 8 , the fuel cell was operated for two hours with clean air, after which the SO 2  contaminated air was started. The fuel cell output drastically dropped during the one hour of exposure to SO 2 , and did not recover after the contaminated air was replaced with clean air.  
         [0081]     In the second test, the results of which are graphed in  FIG. 9 , the fuel cell was started with SO 2  contaminated air for 3.4 hours. The performance began to drop after for 30 minutes and continued to drop the entire 3.4 hours. After the contaminated air was replaced with clean air, the output recovered only slightly, even after operating 87 hours on clean air.  
         [0082]     In the third test, the results of which are graphed in  FIG. 10 , a contamination of only 1 ppm SO 2  was present in the dirty air. The fuel cell performance dropped very slowly during the first 15 hours of exposure to SO 2  contamination, after which the performance drastically reduced. The exposure to SO 2  contamination was 44.5 hours. After 40 hours of exposure, the output stabilized, although about 60% less that the original output. After the contaminated air was replaced with clean air, the output improved slightly and stabilized.  
         [0083]     It is clear that SO 2  contamination has a dramatic effect on cell performance, and that the reduction in cell performance due to SO 2  contamination is largely irreversible. It is important to notice that the SO 2  concentration that was used to generate the data shown in  FIGS. 8 and 9  was 5 ppm, which is representative of being close to a source of SO 2  emissions. For reference, the threshold of odor is between 0.1 and 3 ppm. The time scale for the reduction in cell performance for unprotected fuel cells at typical atmospheric SO 2  levels will most likely be much longer than what is indicated in  FIGS. 8, 9 , and  10  unless the fuel cell is operating close to a SO 2  source.  
         [0084]     It is to be understood, however, that even though numerous characteristics and advantages of the present disclosure have been set forth in the foregoing description, together with details of the structure and function of the disclosure, such disclosure is illustrative only, and is not intended to be limiting to the scope of the invention in any manner, other than by the appended claims. The invention is not to be limited to the described embodiments, or to use with any particular type of fuel cell, or to the use of specific components, configurations or materials described herein. All alternative modifications and variations of the present invention which fall within the broad scope of the appended claims are covered.