Abstract:
A gas/liquid separator comprises: a vessel having a fluid inlet, a liquid outlet, a vapor outlet and a vessel cross-sectional geometry, an initial baffle and a subsequent baffle disposed within the vessel, between the fluid inlet and the vapor outlet, and having a baffle geometry substantially similar to the vessel cross-sectional geometry, and a solid plate disposed between the initial baffle and the vapor outlet, wherein the vapor outlet is in gaseous communication with a side of the solid plate opposite the vapor outlet. The initial and subsequent baffles comprise a plurality of openings providing fluid communication from a fluid inlet side to a baffle vapor outlet side of the initial baffle and the subsequent baffle.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 60/370,059 filed Apr. 3, 2002, which is incorporated herein by reference in its entirety. 
     
    
     
       BACKGROUND OF INVENTION  
         [0002]    This disclosure relates to electrochemical cell systems, and, more particularly, to a phase separation unit having baffles that enhance the separation of liquid and vapor phases.  
           [0003]    Electrochemical cells are energy conversion devices, usually classified as either electrolysis cells or fuel cells. Proton exchange membrane electrolysis cells can function as hydrogen generators by electrolytically decomposing water to produce hydrogen and oxygen gases. Referring to FIG. 1, a section of an anode feed electrolysis cell of the prior art is shown generally at  10  and is hereinafter referred to as “cell  10 .” Reactant water  12  is fed into cell  10  at an oxygen electrode (anode)  14  to form oxygen gas  16 , electrons, and hydrogen ions (protons)  15 . The chemical reaction is facilitated by the positive terminal of a power source  18  connected to anode  14  and the negative terminal of power source  18  connected to a hydrogen electrode (cathode)  20 . Oxygen gas  16  and a first portion  22  of water are discharged from cell  10 , while protons  15  and second portion  24  of the water migrate across a proton exchange membrane  26  to cathode  20 . At cathode  20 , hydrogen gas  28  is formed and removed, generally through a gas delivery line. The removed hydrogen gas  28  is usable in a myriad of different applications. Second portion  24  of water, which is entrained with hydrogen gas, is also removed from cathode  20 .  
           [0004]    An electrolysis cell system may include a number of individual cells arranged in a stack with reactant water being directed through the cells via input and output conduits formed within the stack structure. The cells within the stack are sequentially arranged, and each one includes a membrane electrode assembly defined by a proton exchange membrane disposed between a cathode and an anode. The cathode, anode, or both may be gas diffusion electrodes that facilitate gas diffusion to the proton exchange membrane. Each membrane electrode assembly is in fluid communication with a flow field positioned adjacent to the membrane electrode assembly. The flow fields are defined by structures configured to facilitate fluid movement and membrane hydration within each individual cell.  
           [0005]    The portion of water entrained with the hydrogen gas is discharged from the cathode side of the cell and is fed to a phase separation unit to separate the hydrogen gas from the water, thereby increasing the hydrogen gas yield and the overall efficiency of the cell in general. Typical phase separation units facilitate the separation of water from hydrogen gas utilizing passive settling techniques in which the hydrogen diffuses through the liquid phase directly to a vapor phase. The vapor phase is then passed through a drying apparatus, which, depending on the water content of the hydrogen gas, oftentimes requires significant power inputs to attain the desired level of dryness of the product hydrogen gas.  
           [0006]    While existing phase separation units are suitable for their intended purposes, there still remains a need for improvements, particularly regarding the removal of water from the hydrogen gas exiting the phase separation unit. Therefore, a need exists for a phase separation unit that is capable of providing substantially completely dry product hydrogen gas in order to reduce the required power inputs to ancillary drying apparatuses.  
         SUMMARY OF INVENTION  
         [0007]    Disclosed herein are embodiments of a gas/liquid separator, a gas generating system, and a method of separating a gas phase from a liquid phase. In one embodiment, the gas/liquid separator comprises: a vessel having a fluid inlet, a liquid outlet, a vapor outlet and a vessel cross-sectional geometry, an initial baffle and a subsequent baffle disposed within the vessel, between the fluid inlet and the vapor outlet, and having a baffle geometry substantially similar to the vessel cross-sectional geometry, and a solid plate disposed between the initial baffle and the vapor outlet, wherein the vapor outlet is in gaseous communication with a side of the solid plate opposite the vapor outlet. The initial and subsequent baffles comprise a plurality of openings providing fluid communication from a fluid inlet side to a baffle vapor outlet side of the initial baffle and the subsequent baffle. In one embodiment, the gas generating system comprises an electrochemical cell, and the gas/liquid phase separator in fluid communication with said electrochemical cell.  
           [0008]    In one embodiment, the method of separating a gas phase from a liquid phase comprises: introducing a stream to a gas/liquid separator, passing an initial portion of the stream through an initial baffle, passing a subsequent portion of the stream through a subsequent baffle, wherein vapor and liquid are separated from the stream, and removing the vapor from the separator.  
           [0009]    The above discussed and other features will be appreciated and understood by those skilled in the art from the following detailed description and drawings. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0010]    Referring now to the drawings, which are meant to be exemplary and not limiting, and wherein like elements are numbered alike in the several FIGURES.  
         [0011]    [0011]FIG. 1 is a schematic representation of an anode feed electrolysis cell of the prior art.  
         [0012]    [0012]FIG. 2 is a schematic representation of a gas generating apparatus into which an electrolysis cell system may be incorporated.  
         [0013]    [0013]FIG. 3 is an exploded perspective view of a phase separator.  
         [0014]    [0014]FIG. 4 is an exploded perspective view of a phase separator incorporating a cooling apparatus therein to more efficiently effect the condensation of water from a vapor phase.  
     
    
     DETAILED DESCRIPTION  
       [0015]    Referring to FIG. 2, an exemplary embodiment of an electrolysis cell system is shown generally at  30  and is hereinafter referred to as “system  30 .” System  30  is suitable for generating hydrogen for use in gas chromatography, as a fuel, and for various other applications. It is to be understood that while the gas/liquid separator described below is described in relation to an electrolysis cell, it is generally applicable to both electrolysis and fuel cells, particularly regenerative fuel cells, as well as other systems. Furthermore, although the description and figures are directed to the production of hydrogen and oxygen gas by the electrolysis of water, the apparatus is applicable to the generation of other gases from other reactant materials.  
         [0016]    Exemplary system  30  includes a water-fed electrolysis cell capable of generating gas from reactant water and is in operable communication with a control system. Reactant water, preferably deionized, distilled water, is supplied from a water source  32 . The reactant water utilized by system  30  is stored in water source  32  and is fed by gravity or pumped through a pump  38  into an electrolysis cell stack  40 . The supply line, which is preferably clear plasticizer-free tubing, optionally includes an electrical conductivity sensor  34  disposed therewithin to monitor the electrical potential of the water, thereby determining its purity and ensuring its adequacy for use in system  30 .  
         [0017]    Cell stack  40  comprises a plurality of cells (e.g., similar to cell  10  described above with reference to FIG. 1) encapsulated within sealed structures (not shown). The reactant water is received by manifolds or other types of conduits (not shown) that are in fluid communication with the cell components. An electrical source  42  is disposed in electrical communication with each cell within cell stack  40  to provide a driving force for the dissociation of the water.  
         [0018]    Oxygen and water exit cell stack  40  via a common stream that recycles the oxygen and water to water source  32  where the oxygen is vented to the atmosphere. The hydrogen stream, which is entrained with water, exits cell stack  40  and is fed to a gas/liquid separator or phase separation tank, which is a hydrogen/water separation apparatus  44 , hereinafter referred to as “separator  44 ,” where the gas and liquid phases are separated. The exiting hydrogen gas (having a lower water content than the hydrogen stream to separator  44 ) is optionally further dried at a drying unit  46 , which may be, for example, a diffuser, a pressure swing absorber, desiccant, or the like.  
         [0019]    Water with trace amounts of hydrogen entrained therein is returned to water source  32  from separator  44  through a low-pressure hydrogen separator  48 . Low pressure hydrogen separator  48  allows hydrogen to escape from the water stream due to the reduced pressure, and also recycles water to water source  32  at a lower pressure than the water exiting separator  44 . Separator  44  also includes a release  50 , which may be a relief valve, to rapidly purge hydrogen to a hydrogen vent  52  when the pressure or pressure differential exceeds a pre-selected limit.  
         [0020]    Hydrogen from drying unit  46  is fed to a hydrogen storage facility  54 . Optional valves  56 ,  58 , disposed at various points on the system lines, are configured to release hydrogen to vent  52  under certain conditions, while an optional check valve  60  prevents the backflow of hydrogen to drying unit  46  and separator  44 .  
         [0021]    Additional equipment that can be employed in system  30  includes a ventilation system (e.g., a fan, a blower, and the like), control mechanisms (e.g., sensor(s), switch (es), transducer(s), and the like), compressor(s), pump(s), valves (e.g., check valve(s), purge valve(s), relief valve(s), and the like), and filter(s), as well as combinations comprising at least one of the foregoing pieces of equipment.  
         [0022]    Referring now to FIG. 3, one exemplary embodiment of separator  44  and its componentry is shown in greater detail. Separator  44  comprises various materials including metals, plastics, and combinations comprising at least one of the foregoing materials that preferably allow separator  44  to receive the gas/liquid stream at the pressure it exits the cell. Pressures can be up to and exceeding about 10,000 psi, with pressures of less than or equal to about 6,500 psi typical, pressures of less than or equal to about 2,500 psi more common, and pressures of about 1,000 psi to about 2,250 psi preferred. Metals that may be used to fabricate the various portions of separator  44  include, but are not limited to, ferrous materials (e.g., stainless steels and the like), titanium, nickel, and the like, as well as oxides, cermets, composites, alloys, and mixtures comprising at least one of the foregoing metals. Some possible plastics that may be used to fabricate the various portions of separator  44  include, but are not limited to, polycarbonates, polyethylenes, polypropylenes, and the like, as well as reaction products and mixtures comprising at least one of the foregoing plastics.  
         [0023]    Separator  44 , which is essentially a containment vessel, comprises a shell  68 , a flange  67 , and an end cap  65 . A fluid inlet  72  for receiving the wet hydrogen stream from the cell stack is disposed at flange  67 . Alternately, fluid inlet  72  may be disposed directly in shell  68  proximate the flange end of separator  44 . In either configuration, fluid inlet  72  receives the wet hydrogen stream via a connector  73  disposed at a union  75  that is in fluid communication with the cell stack. A check valve (not shown) may be disposed within the wet hydrogen stream to prevent the backflow of water from separator  44 . A liquid outlet  88  disposed either at flange  67  or proximate the flange end of separator  44  enables periodic drainage to allow the water collected in the vessel to be maintained at a selected level. Liquid outlet  88  is preferably disposed at the lowest point of separator  44  in order to effect the optimum drainage of separator  44 .  
         [0024]    End cap  65  can include an overflow port  86 , a vapor outlet  90 , and a pressure release port  92 . Overflow port  86  provides drainage of separator  44  in the event that shell  68  fills completely with water. Overflow port  86  is preferably dimensioned to accommodate a flow rate that is greater than the maximum flow rate of the wet hydrogen stream into shell  68  through fluid inlet  72 . By allowing shell  68  to be drained at a rate that exceeds the water input, the pressure of separator  44  is maintained at or below a desired limit. Vapor outlet  90  provides fluid communication between separator  44  and the drying apparatus and is preferably disposed at a distance from fluid inlet  72  to maximize the residence time of a wet hydrogen molecule within separator  44 . Pressure release port  92  provides fluid communication between separator  44  and release  50  for the rapid purge of hydrogen if the pressure exceeds a selected amount. The dimensions of separator  44 , particularly the diameter of shell  68 , affect the velocity of the wet hydrogen stream entering through fluid inlet  72 . In particular, the sudden expansion of the wet hydrogen stream as it enters separator  44  results in an abrupt increase in the flow area, thereby causing a decrease in the velocity of the hydrogen stream. The variation in velocity in turn affects the dispersion rate of hydrogen from the wet hydrogen stream.  
         [0025]    In one embodiment, a level sensor stem  70 , which houses a level sensing apparatus, is disposed within shell  68  of separator  44 , intermediate end cap  65  and flange  67 , and extends between end cap  65  and flange  67 . In alternate embodiments, level sensor stem  70  can be replaced with various other level sensing devices, such as ultrasonic or optical transmitters and receivers, as well as combinations comprising at least one of the foregoing devices.  
         [0026]    Also disposed within shell  68 , intermediate end cap  65  and flange  67 , are baffles  80 . Baffles  80  are disposed along the lower length of level sensor stem  70  to effectively facilitate the diffusion of hydrogen from the water. Baffles  80  can be retained on level sensor stem  70  by collars  82  or can be supported by or connected to shell  68 . The characteristic porosities of each baffle  80  may vary in relation to adjacently-positioned baffles, thereby imparting a porosity gradient over the length of shell  68 . In one exemplary configuration of separator  44 , baffles  80  proximate flange  67  are more porous than baffles  80  proximate end plate  84 . In other words, baffle  80  proximate flange  67  can have a larger mesh size than the subsequent baffle  80  proximate plate  84 . Additionally, any desired number of baffles  80  having the same or different mesh sizes can be employed. The desired number of baffles is typically a balance between a sufficient number to effectively separate the hydrogen from the water while minimizing the pressure drop across separator  44 . Possible types of baffles include screen(s), perforated plate(s), and the like, as well as combinations comprising at least one of the foregoing types.  
         [0027]    Baffle  80  has a cross-sectional geometry that substantially conforms to the separator shell  68  and comprises any material that is inert in the operating environment of separator  44 , and which has the desired structural integrity. Possible materials include plastics, ceramics, metals, as well as alloys, cermets, composites, and mixtures comprising at least one of the foregoing. Some possible metals includes ferrous materials such as stainless steel, titanium, zirconium, and the like, as well as mixtures and alloys comprising at least one of the foregoing metals. Depending upon this size of the separator  44 , and the desired degree of separation, one to several baffles  80  can be employed. For an electrochemical cell system, typically 1 to about 15 baffles are employed, with 1 to 5 baffles preferred.  
         [0028]    As stated above, the porosity (e.g., the void area in the baffle) of baffles  80  can be substantially uniform or varied (in the pore/mesh size and the amount of open volume) and the porosity of adjacent plates can be the same or different. The porosity can be about 25% to about 75%. Plates disposed proximate end plate  84  preferably have a porosity (i.e., an opening volume) of about 25% to about 50%, while plates proximate flange  67  preferably have a porosity of about 50% to about 75%.  
         [0029]    Shell  68  is preferably configured to include baffles  80  arranged such that upon diffusion of hydrogen gas to the vapor phase, the molecules of hydrogen gas encounter successively less porous baffles  80 . As the hydrogen gas molecules diffuse through baffles  80  of successively less porosities, the hydrogen gas molecules become increasingly drier. The removed water coalesces and is returned to the liquid phase proximate the end of the shell at which the fluid inlet is disposed.  
         [0030]    In order to more effectively remove water molecules from the hydrogen gas, a vapor cooling apparatus  100  can be disposed in separator  44 , preferably adjacent the vapor phase, as is shown in FIG. 4. Vapor cooling apparatus  100  can comprise any thermal exchange unit/technique compatible with the operating conditions of separator  44 . One exemplary embodiment of vapor cooling apparatus  100  comprises a coil disposed within shell  68  at an upper end of separator  44  (although anywhere in the shell is possible). The coil receives a coolant flow stream that removes heat from the vapor phase, causing the water to condense. Upon lowering the temperature of the vapor phase, water molecules attached to hydrogen molecules in the vapor phase are condensed out and returned to the liquid phase. Although the coil is shown as being disposed within shell  68 , it should be understood by those of skill in the art that other configurations may be employed. For example, the coil may alternatively or additionally be disposed on an outer surface of shell  68 . A cooling apparatus may further be disposed between the baffles and/or between a baffle and the plate. Typical coolants for the flow stream include, but are not limited to, liquids (e.g., water, ammonia, brines, alcohols, fluorocarbons, and halogenated hydrocarbons) and gases (e.g., air, nitrogen, hydrogen, and chloro-fluorinated methanes.) In alternate embodiments, the cooling apparatus can be a thermoelectrically cooled plate or tube.  
         [0031]    The porosity of the baffles enables separation of the hydrogen gas and water by reducing the surface tension and allowing release of the hydrogen from the liquid water. The hydrogen gas molecules that migrate through the baffles contain less water, and thereby allow a substantially drier gas to be delivered from the separator. By delivering a substantially drier gas, downstream-located drying apparatuses can be operated more economically and efficiently; thereby resulting in a cost savings that may be significant over the life of the electrochemical cell into which the apparatuses are incorporated.  
         [0032]    During operation of the electrochemical cell system into which separator  44  is incorporated, the wet hydrogen stream from the cell stack enters separator  44  through fluid inlet  72 . (See FIG. 3). As the water level engages the first side of baffle  80 , the stream is forced through the holes in the baffle, which enables hydrogen release from the wet hydrogen stream. The stream, which is now at least partially separated into a gas (e.g., hydrogen gas) and liquid (e.g., liquid water) phases, contacts a plate  84  that inhibits flow of the liquid water to the upper portion of the separator (e.g., past plate  84 ). For example, since the stream enters the separator under pressure, it is sprayed through the baffles and against the inlet side of the plate. Hydrogen gas that has been released from the stream passes through slot  94  toward vapor outlet  90 . Optionally, the gas is cooled to remove water vapor from the gas.  
         [0033]    While the disclosure has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the specification and drawings.