Abstract:
A fluid management system for use in water electrolysis systems for filtering the system water and recombining hydrogen and oxygen. The fluid management system includes a phase separation tank having a filter containing a catalyzed ion exchange resin. Hydrogen/water mixture and an oxygen/water mixture are introduced into the resin where hydrogen is recombined with oxygen to produce recovered water. Trace contaminant ions and particles are removed from the water by the ion exchange resin and the filter.

Description:
CROSS REFERENCE OF RELATED APPLICATION 
     This application is a continuation of U.S. patent Ser. No. 09/224,046 filed Dec. 31, 1998, now abandoned which is a continuation-in-part of U.S. patent application Ser. No. 09/087,476, filed May 29, 1998, now abandoned, which are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     This invention relates generally to water electrolysis systems. In particular, this invention relates to a fluid management system for a water electrolysis system which permits the conservation of water during steady state operation and the generation of high purity hydrogen and oxygen gases. 
     BACKGROUND OF THE INVENTION 
     Electrolysis systems are energy conversion systems for producing hydrogen and oxygen gases from water. Typical electrolysis systems include a number of individual cells arranged in a stack with fluid, typically water, forced through the cells at high pressures. 
     Hydrogen or oxygen gases produced through electrolytic methods often contain: appreciable quantities of atmospheric gases, such as nitrogen, carbon dioxide, and argon due to atmospheric air diffusing into the process water; trace quantities of oxygen and hydrogen, respectively, due to diffusion across the electrolyte membrane; and contaminants, such as iron, sulfur, nickel, chromium, and chlorides, due to leaching from the system components into the water recirculation stream. In systems where these contaminants are not removed, they typically contaminate the electrolyte membrane or catalysts, thereby decreasing the electrolysis cell operation efficiency, and contaminating the product gas stream. Gases produced from the electrolysis cell in this manner must be subsequently purified using expensive filters. 
     A fluid management system for a typical proton exchange membrane electrolysis system is shown schematically in FIG. 1. A water and hydrogen mixture  60  exits the hydrogen side of electrolysis cell stack  61  and enters high pressure hydrogen/water separator  62 . Product hydrogen  63  exits the separator and is directed to further processing (not shown). Hydrogen saturated water  64  passes from high pressure separator  62  to low pressure hydrogen water separator  65  which typically vents low pressure hydrogen gas  66  and collects water  67  in reservoir  68 A drains into reservoir  68 . Meanwhile, an oxygen/water mixture  69  exits the oxygen side of cell stack  61  and enters a cyclonic style phase separator  70  which vents oxygen gas  71  while collecting water  67  in reservoir  68 . Water in reservoir  68  is pumped by pump  72  through deionizer beds  73 ,  74  and filter vessel  75 . After deionizing and filtering, the water reenters the cell stack  61 . 
     What is needed is a fluid management system which provides for contaminant free recirculated water utilizing a minimum amount of equipment, and eliminates the expensive filtering steps of existing fluid management systems. 
     SUMMARY OF THE INVENTION 
     The above-described drawbacks and disadvantages of the prior art are alleviated by fluid management system, the separation tank and the method of the present invention. 
     The phase separation tank comprises: an inlet for introducing water containing dissolved oxygen to the tank, a catalyst bed capable of reacting hydrogen and oxygen to form water and of removing cations and anions from the water; a water permeable filter for containing said catalyst bed, and a second inlet for introducing hydrogen to the catalyst bed. 
     The present invention method for recovering water in an electrochemical system, comprises: introducing an oxygen and water stream to a catalyzed bed within a tank, introducing a hydrogen dissolved in water stream to an interior area of the catalyzed bed, reacting the hydrogen and oxygen to form water, removing any ionic impurities from the water in the tank; and directing the recycle water to an electrochemical cell. 
     The above discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring now to the drawings wherein like elements are numbered alike in the several FIGURES: 
     FIG. 1 is a schematic representation of a hydrogen generator system of the prior art; 
     FIG. 2 is a schematic representation of one embodiment of a hydrogen generation system incorporating the fluid management system of the present invention; 
     FIG. 3 is a cross sectional view of a phase separation tank of the present invention and a schematic representation of the fluid management system; and 
     FIG. 4 is a schematic representation of another embodiment of a hydrogen generation system incorporating the fluid management system of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 2, a fluid management system in accordance with the present invention is shown at  80 . Hydrogen and water mixture  60  exits the hydrogen side of electrolysis cell stack  61  and enters high pressure hydrogen/water separator  62 . Product hydrogen  63  exits the separator and goes on to further processing (not shown). Hydrogen saturated water  64  flows directly into catalyzed bed  81  of phase separation tank  82 . Meanwhile, an oxygen/water mixture  69  exits the oxygen side of cell stack  61  and enters the phase separation tank  82 . Oxygen gas  71  exits the system while oxygen saturated water from mixture  69  mixes with hydrogen saturated water mixture  64  in catalyzed bed  81 . 
     Referring to FIG. 3, the phase separation tank  82  comprises: an inlet  86  for accepting an oxygen/water mixture  69  from line  92 , an oxygen gas outlet  91 , a perforated dip tube  90  for receiving a hydrogen/water mixture  64  and introducing that mixture to catalyzed bed  81  through apertures  89 , a filter medium  84  for containing the catalyzed bed  81  and filtering particulates from the water, an optional support member  83  disposed about the filter medium  84  for providing structural integrity thereto, and a water outlet  95 . 
     The tank  82  should have a volume sufficient to process the hydrogen/water mixture and oxygen/water mixture from the electrolysis cell stack under normal operating conditions. For an electrolysis cell stack which produces about 300 scfh of hydrogen, under normal operating conditions, tank  82  will preferably have a volume sufficient to accommodate about 30 seconds of circulation flow, i.e., about 10 to about 20 liters of water, in order to enable sufficient low level detection response time, enabling good process control. 
     Once introduced to tank  82 , hydrogen and oxygen react in catalyst bed  81 . Catalyst  85 , distributed throughout catalyst bed  81 , deionizes water and provides reactive sites for recombination of hydrogen dissolved in mixture  64  with dissolved oxygen contained in mixture  67 , to form water. Therefore, the catalyzed bed  81  can contain any material, supported or unsupported, capable of recombining dissolved hydrogen and oxygen to form water and removing anions and cations from the water. Possible materials include ion exchange resins catalyzed with a conventional catalyst including, but not limited to, noble metal base catalysts, such as platinum, palladium, alloys thereof, and others. Preferably, the material is an ion exchange resin-platinum mixture having a high catalyst surface area (about 4 square meters per cubic meter, or greater). 
     The catalyst bed  81  is supported in a filter medium  84 , which may be supported by a support member  83 . The filter medium  84  can be any filtering source capable of sufficiently removing particulates in the water such that, when recirculated to the electrochemical cell stack, the water will not contaminate the electrochemical cells. Possible filter media include, but are not limited to, woven and non-woven fabrics, such as polypropylene non-woven material, or tetrafluoroethylene non-woven material, among others compatible with the tank environment and contents. The filter medium should be capable of removing particulates having a diameter of about 10 microns or greater, with a medium capable of removing particulates having a diameter of about 5 microns or greater, preferred. 
     The support member  83 , which provides structural integrity to the filter medium  84 , can be any water permeable medium having sufficient mechanical strength to support the filter medium and contain the catalyst  85 , while contributing minimal pressure drop to the system. Possible support members include, but are not limited to, perforated metal, ceramic, and/or plastic structures, such as screens and perforated plates, having an about 60% to about 90% open area, with openings of about 0.125 inches to about 0.25 preferred. It is additionally preferred to use a support member  83  which is porous on all sides due to reduce mass flow issues associated with filtering the water and directing the water to outlet  95 . 
     In order to prevent hydrogen gas from directly mixing with oxygen gas in tank  82  above the catalyst bed  81 , the hydrogen is preferably introduced to the tank beneath the catalyst surface. For example, tube  90 , which extends through tank  82 , into catalyst bed  81 , introduces the hydrogen/water mixture  64  to the catalyst bed  81 , subsurface. This tube  90  can be any means for introducing the hydrogen/water mixture to the catalyzed bed such that the hydrogen becomes substantially evenly distributed throughout the bed such as a perforated dip tube or similar structure, or a porous sheet with at least one internal channel for distributing the hydrogen/water mixture throughout the sheet, or another means. Note, it is feasible that small amounts of hydrogen gas could alternatively be introduced to the catalyst bed through the bottom of tank  82  such that the gas filters up through the catalyst bed  81  to react with the dissolved oxygen. 
     Another technique for inhibiting direct hydrogen gas and oxygen gas mixing is to maintain sufficient water within the tank  82 . Maintaining the water level additionally prevents catalyst dryout and replenishes water electrolyzed in the cell stack  61 . The desired water level is maintained using level sensor  93  which is any conventional device for monitoring liquid levels which is compatible with the tank environment. Possible sensors include, but are not limited to, electrical sensors and mechanical devices. For example, the level sensor  93  operably connects to a valve (not shown) to regulate the flow of make-up water  92  into tank  82 . The level sensor  93  monitors the combined oxygen/water mixture  69  and hydrogen/water mixture  64  level within tank  82  and enables the flow of sufficient make-up water  92  from an external source to maintain a sufficient water level to submerge the catalyzed bed and to replace water that has been electrolyzed. The make-up water  92  can be introduced to tank  82  in combination with the oxygen/water mixture  69 , the hydrogen/water mixture  64 , or directly. 
     During operation the oxygen/water mixture  69  is preferably introduced to tank  82  by directing the mixture against the wall  87  or an interior baffle (not shown) by any conventional means, including connecting line  92  to the tank  82  at an angle using a diverter  88 , or other means, or disposing a baffle within tank  82  within the oxygen/water mixture  69  flow stream. For example, oxygen/water mixture  69 , including make-up water, preferably enters tank  82  through inlet  86  at an angle sufficient to cause the mixture  69  to impinge against wall  87 . The impingement of mixture  69  against wall  87  or an extension baffle causes increased agitation of the mixture, resulting in the release of entrained gaseous oxygen  71  from the mixture. Released oxygen gas  71  exits tank  82  through outlet  91 . Water containing dissolved oxygen  67 , then enters catalyzed bed  81 , while hydrogen/water mixture  64  enters catalyzed bed  81  through apertures  89  in dip tube  90 . Within the catalyzed bed  81 , the dissolved hydrogen and oxygen recombine to form water, and any cationic and anionic impurities are removed by the ion exchange resin. The recovered, combined water exits the catalyzed bed  81  through filter medium  84  and support member  83 , and exits the tank  82  through outlet  95 . Recovered, combined water  94  is then routed from outlet  95  to pump  72  and reintroduced to electrolysis cell stack  61 . 
     It is preferred to operate the present system under a positive pressure. Referring to FIG. 4, the oxygen/water stream  98  exits the cell stack  61  and can be introduced to a phase separation tank  100 . The oxygen saturated stream  101  is drawn from the phase separation tank  100  by pump  102  which pressurizes the stream and pumps pressurized oxygen saturated stream  69 ′ to tank  82 . 
     The pressure employed within the catalyzed bed can be up to the tolerances of the cell stack, with a pressure of up to the operating pressure of the cell stack (up to or exceeding about 2,500 psi) preferred, and a pressure sufficient to enhance the reaction within the catalyzed bed up to the operating pressure more preferred. Typically, the positive pressure can be about 20 psi to about 3,500 psi, with about 25 psi to about 2,000 psi preferred for most electrochemical cell stacks. 
     A pressure of about 25 psi to about 450 psi especially preferred for an electrolysis cell stack having a 10 scfh hydrogen production rate. Similar 9 or higher pressures may be used for cell stacks having higher production rates such as up to or exceeding about 1,000 scfh, or even about 10,000 scfh or greater. It is believed that the pressure induced by the pump used to introduce the hydrogen containing water stream into the catalyzed bed may be sufficient to enhance the reaction within the catalyzed bed. 
     The electrolysis cell fluid management system of the present invention provides an improved method and apparatus over conventional systems in areas including hydrogen recovery from hydrogen/water mixture, oxygen/water separation, and polishing, deionizing and filtering circulation water. For example, in comparison to the prior art system of FIG. 1, the present system utilizes low pressure hydrogen  66  and replaces the low pressure hydrogen separator  65 , the reservoir  68 A, the cyclonic separator  70  deionizers  73 ,  74 , and filter vessel  75 , with tank  82 . In the present system the hydrogen recombines with dissolved oxygen in catalyzed bed  81  to form water which combines with water introduced with the dissolved oxygen and any make-up water, and the combined water is deionized and filtered to form recovered water  94  which exits tank  82  through outlet  95 . 
     While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustration and not limitation.