Abstract:
A system and reactor stack for generating hydrogen from a hydride solution in presence of a catalyst. The reactor stack includes a number of reactor plates and separator plates alternate with one another, to define reaction chambers alternating with coolant chambers. Each reactor plate has a first face defining a solution flow field and an opposing second face defining a coolant flow field. Each solution flow field comprises a common reaction chamber and a plurality of channels opening into the common reaction chamber. The catalyst is provided in the common reaction chamber. Each reaction chamber is configured to receive the hydride solution and to bring at least a portion of the hydride solution in contact with the catalyst. Each reaction chamber is in fluid communication with an adjacent reaction chamber and each coolant chamber is in fluid communication with an adjacent coolant chamber.

Description:
FIELD OF THE INVENTION 
     This invention relates to a hydrogen generation system and more particularly relates to a reactor for generating hydrogen from a chemical hydride. 
     BACKGROUND OF THE INVENTION 
     Hydrogen has been recognized as an environmentally friendly clean fuel of the future since it has various applications in power generation systems. For example, hydrogen can be used as a fuel for combustion engines, gas turbines, fuel cells, especially proton exchange membrane fuel cells, which use hydrogen and air to produce electricity, generating only water as a by-product. Fuel cells are being developed to replace traditional electricity generators because they produce clean, environmentally friendly energy. However, these fuel cells require external supply and storage devices for hydrogen. Extensive efforts have been made to develop a safe and efficient way to store hydrogen, especially in mobile applications. Conventional hydrogen storage technologies include liquid hydrogen, compressed gas cylinders, dehydrogenation of compounds, chemical adsorption into metal alloys and chemical storage as hydrides. However, each of these systems is either hazardous or bulky. 
     There are various prior art hydrogen generation systems that utilize chemical hydrides. One type of hydrogen generation system employs chemical hydrides in solid phase, e.g. granules. U.S. Pat. No. 5,372,617, comprises a closed vessel for mixing chemical hydride powder together with water. The water is introduced into the vessel through an inlet. The vessel contains a mechanical stirring device to ensure adequate contact between the powder and the water, and to prevent the powder from clumping. The hydrogen gas is removed through an outlet in the vessel, and is supplied directly to the fuel cell. These systems tend to be inefficient since the stirring mechanism consumes energy, and increases the overall weight and complexity of the system. Furthermore, the noise generated by the stirring is undesirable. In addition, the reaction rate tends to be low, making the hydrogen generation unpredictable and thus hard to control. The systems also tend to be large and cumbersome. 
     Another similar hydrogen generation system is disclosed in U.S. Pat. No. 5,702,491. The hydrogen generation system substantially comprises a thermally isolated container for containing chemical hydride, a preheater to heat the chemical hydride to a predetermined temperature before the chemical hydride is hydrolysed, a water pipe to supply water into the container to generate hydrogen. This system entails adiabatic arrangement and heating devices, hence results in lower energy efficiency and complicated structure. 
     U.S. Pat. No. 5,833,934 discloses a cartridge-type reactor comprising a storage compartment for storing chemical hydride particles, a water absorbent material for retaining water and a water distribution tube for introducing water into the mass of chemical hydride particles. Other cartridge arrangements can be found in, for example, U.S. Pat. Nos. 4,261,956, 5,514,353. Although the cartridge generator in U.S. Pat. No. 5,833,934 provides some improvement over prior art generator concepts, it still suffers, as all the above-mentioned generators, from poor thermal management of the reactor, and hence little if any control of reaction rate. The heating effects associated with the chemical hydride reaction, which is exothermic, can in turn positively or negatively affect the reaction rate and efficiency. Temperature plays an important role in chemical hydride reactions. It directly affects the reaction rate. Poor thermal management of the reactor may lead to undesirable reaction rate, deactivation of catalyst, production of unwanted by-product, and in extreme cases, clogging or damage to the reactor. 
     Another method of generating and storing hydrogen has been recently disclosed in WO 01/51410. This method uses a chemical hydride solution, such as NaBH 4 , as a hydrogen storage medium. Generally, chemical hydride reacts with water in the presence of a catalyst to generate hydrogen, as shown in the equation below:
 
NaBH 4 +2H 2 O→4H 2 +NaBO 2 +HEAT
 
     The chemical hydride acts as both the hydrogen carrier and the storage medium. Ruthenium, Cobalt, Platinum or any alloys thereof may be used to catalyze the above reaction. It is noted that hydrogen is liberated from both the borohydride (NaBH 4 ) solution and the water. The borohydride solution is relatively cheap, and is much easier and safer to handle and transport than liquid or pressurized hydrogen. As a result, there are a number of advantages associated with using borohydride as a method of storing hydrogen as a fuel for use in fuel cells. 
     WO 01/51410 discloses a system, where an aqueous chemical hydride solution contained in a vessel is brought into contact with a catalyst disposed in a containment system to generate hydrogen. However, there are still a number of problems associated with this liquid phased system. In particular, the reaction in the vessel is not regulated. The temperatures of the solution and catalyst are not uniform, resulting in unstable reaction rate and poor ability to respond in real time to the fuel (hydrogen) needs of the hydrogen consuming devices, such as fuel cells or the like. This ability is referred to as load following ability. Moreover, it is also difficult to control the amount of catalyst in contact with the chemical hydride solution, which makes it even more difficult to control the reaction. 
     Therefore, there remains a need for a chemical hydride reaction system and reactor which offer improved control of the reaction rate by providing improved thermal management of the hydride solution and more uniform contact between catalyst and chemical hydride solution. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a system and a reactor which provide improved scalability, reaction temperature control, and load following ability. 
     According to a first aspect of the present invention, a reactor vessel for generating hydrogen from a hydride solution in presence of a catalyst is provided. The reactor vessel comprises:
         a) at least one reaction chamber and at least one coolant chamber, each reaction chamber being configured to receive the hydride solution and to bring at least a portion of the hydride solution in contact with the catalyst, each coolant chamber being configured to receive a coolant flow;   b) at least one reactor plate having a first face and a second face in opposing relation with the first face, wherein the first face defines a portion of each reaction chamber and the second face defines a portion of each coolant chamber.
 
Preferably, the reactor vessel comprises a plurality of reactor plates and a plurality of separator plates alternating with one another, to define a plurality of reaction chambers alternating with a plurality of coolant chambers. Each reaction chamber is in fluid communication with an adjacent reaction chamber and each coolant chamber is in fluid communication with an adjacent coolant chamber.
       

     According to a second aspect of the invention, a reactor plate for a hydrogen generating reactor having a reaction chamber and a coolant chamber is provided. The reactor plate comprises:
         a) a first face defining at least a portion of the reaction chamber; and   b) an opposing second face defining at least a portion of the coolant chamber.
 
Preferably, the first face of the reactor defines a solution flow field therein and the second face defines a coolant flow field therein.
       

     According to a third aspect of the invention, a system for generating hydrogen from a hydride solution in presence of a catalyst is provided. The system comprises:
         a) a reactor vessel defining a reaction chamber and a coolant chamber, the reaction chamber being configured to bring at least a portion of the hydride solution in contact with the catalyst, the coolant chamber being located proximate to the reaction chamber for cooling of the hydride solution;   b) a solution supply means for delivering the hydride solution to the reaction chamber, the solution supply means being in fluid communication with the reaction chamber; and   c) a coolant supply means for delivering a coolant flow to the coolant chamber, the coolant supply means being in fluid communication with the coolant chamber;
 
wherein the coolant supply means is configured to control at least one of the flow rate and the temperature of the coolant flow through the coolant chamber, thereby improving control of the temperature of the hydride solution in the reaction chamber.
       

     According to a fourth aspect of the invention, a method of generating hydrogen is provided. The method comprises the steps of:
         a) contacting a catalyst with a hydride solution; and   b) providing a coolant flow proximate to the hydride solution for controlling the temperature thereof;   c) controlling at least one of the temperature and the flow rate of the coolant flow to improve temperature control of the hydride solution in contact with the catalyst.       

     The plate type chemical hydride hydrogen generation reactor according to the present invention is more compact than any existing reactors. Moreover, the plate reactor provides a better control of the reaction rate by controlling the amount of heat removed from the reactor. The reactor also provides the advantage of more uniform heat transfer and use of catalyst. The plate type reactor is especially useful for applications where constant or controlled amount of hydrogen is demanded by hydrogen consuming devices, such as fuel cells, engines and turbines. The plate type reactor is also simply to manufacture and assemble. It is also easy to be scaled up and hence has various applications. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, which show a preferred embodiment of the present invention and in which: 
         FIG. 1A  shows a cross-sectional view of a reactor vessel according to a preferred embodiment the present invention, taken along line A—A of  FIG. 1B ; 
         FIG. 1B  shows an exploded perspective view of the reactor vessel; 
         FIG. 2  shows an elevational view of a first face of the reactor plate according to the preferred embodiment of the present invention; 
         FIG. 3  shows an elevational view of the second face of the reactor plate; 
         FIG. 4  shows partial sectional view of the reactor plate taken along line A—A in  FIG. 2 ; 
         FIG. 5  shows a front elevational view of a separator plate according to the preferred embodiment of the present invention; 
         FIG. 6  shows an elevational view of an external face of a first end plate of the reactor vessel; 
         FIG. 7  shows an elevational view of an internal face of the first end plate of the reactor vessel; 
         FIG. 8  shows a front elevational view of a second end plate of the reactor vessel; and 
         FIG. 9  shows a schematic view of the hydrogen generation system according to the preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1A and 1B  show a chemical hydride reactor according to a preferred embodiment of the present invention, in which a first reactor vessel  110  and a second reactor vessel  120  are formed. However, it will be understood by those skilled in the art that the chemical hydride reactor may be constructed to include any number of reactor vessels, preferably disposed in parallel relation side by side or one on top of the other in a stack, as can best be seen in FIG.  1 B. Hereinafter, the chemical hydride reactor will be referred to as the “reactor stack”  100 . 
     Referring to  FIGS. 1A and 1B , the reactor stack  100  includes a first reactor plate  200  and a first catalyst layer  210  located between a first end plate  310  and a separator plate  300 . The above plates and the first catalyst layer  210  are preferably positioned substantially parallel to each other. Likewise, a second reactor plate  200   a  and a second catalyst layer  220  are positioned in a preferably identical configuration between the separator plate  300  and a second end plate  320 . The first end plate  310 , along with a rim  250  of the first reactor plate, and the separator plate  300  define the first reactor vessel  110 . The second end plate  320 , along with the rim  250  of the second reactor plate  200   a , and the separator plate define the second reactor vessel  120 . 
     Preferably, the first and second reactor plates  200 ,  200   a , and the first and second catalyst layers  210 ,  220  are identical. Consequently, only the first reactor plate  200  and the first catalyst layer  210  will be described in detail. 
     Referring to  FIGS. 1A and 4 , the first reactor vessel  110  includes a reaction chamber  119  and a coolant chamber  121 . The separator plate  300  abuts against the rim  250  that extends around the edge and protrudes from a first face  115  of the first reactor plate  200 . A first gasket groove  251  is formed along the rim  250  in the first face  115  of the first reactor plate  200 . A first gasket  400  (shown in  FIG. 2 ) located in the first gasket groove  251  provides a seal between the rim  250  of the first reactor plate  200  and the separator plate  300  to form a reaction chamber  119  within the first reactor vessel  110 . The first catalyst layer  210  is located in the reaction chamber  119 , preferably abutting the first face  115  of the first reactor plate  200 . 
     Referring again to  FIGS. 1A and 1B , a first end plate  310  abuts against the second face  117  of the first reactor plate  200 . A second gasket  401  (shown in  FIG. 3 ) located in the second gasket groove  252  (shown in  FIG. 4 ) of the rim  250  seals the second face  117  of the first reactor plate  200  against the first end plate  310  to form a coolant chamber  121  within the first reactor vessel  110 . The gaskets  400  and  401  may be made from any suitable resilient materials, such as rubber. 
     A second reaction chamber  124  and a second coolant chamber  126  are provided in the second reactor vessel  120  in a similar fashion, except that the rim  250  of a first face  116  of the second reactor plate  200   a  abuts against the second end plate  320  to form the second reaction chamber  124 , and a second face  118  of the second reactor plate  200   a  abuts against the separator plate  300  to form the second coolant chamber  126 . 
     In operation, pressure may be applied on the end plates  310 ,  320  to seal the reactor plates  200 ,  200   a , the separator plate  300 , and the end plates  310 ,  320  of the reactor stack  100 . Preferably, a number of tie rods (not shown) may also be provided. The tie rods are screwed into threaded bores  305  in a first end plate  310 , and pass through corresponding plain bores  325  in the second end plate  320 . Conventional fasteners, such as nuts, bolts, washers or the like may be used to clamp together the reactor plates  200 ,  200   a , separator plate  300  and catalyst layers  210 ,  220  and the entire reactor stack  100 . 
     Referring to  FIGS. 1B ,  6  and  7 , first and second coolant connection ports  312 ,  313 , and first and second solution connection ports  314 ,  315  are provided in the first end plate  310 . 
       FIG. 2  shows the first face  115  face at first reactor plate  200 , which forms a portion of the reaction chamber  119 . The first reactor plate  200  is preferably rectangular in shape and has two parts at each end thereof. At one end, a solution inlet  238  and a coolant outlet  240  are provided. At the opposite end, a solution outlet  237  and a coolant inlet  241  are provided. The rim  250  and gasket  400  surrounds the coolant inlet  241  and coolant outlet  240  to prevent the coolant from entering the reaction chamber  119 . A solution flow field  232  preferably having a number of open-faced parallel tortuous channels  235  is formed within the first face  115  of the first reactor plate  200 . The channels  235  extend between the solution inlet  236  and the solution outlet  237 . The solution inlet  236  and solution outlet  237  for chemical hydride solution communicate with the first and second solution connection ports  314 ,  315 , respectively. 
       FIG. 3  shows the second face  117  of the first reactor plate  200 , which forms a portion of the coolant chamber  121 . A coolant flow field  234  preferably composed of a number of substantially parallel tortuous open-faced channels  245  is formed in the second face  117 . The channels  245  extend between the coolant inlet  241  and coolant outlet  240 . The gasket  401  provides a seal around the solution inlet  236  and solution outlet  237  to prevent the hydride solution from entering the coolant chamber  121 . The coolant inlet  241  and coolant outlet  240  communicate with the first and second coolant connection ports  312 ,  313 , respectively. The preferred coolant is water, but may be any other conventional heat transfer fluid. 
     It will be understood by those skilled in the art the configuration of channels  235  on the first face  115  is only one possible configuration and the channels  235  may be configured in a number of different ways between the solution inlet  236  and solution outlet  237 . For example, the channels need not be parallel. Likewise, the coolant channels  245  may also be configured in different ways which may be identical or different from the solution channels  245 . For example (not shown), the second face  117  of the first reactor plate  200  may be smooth with only a recess extending between the coolant inlet  241  and outlet  240  for coolant flow. 
     Referring again to  FIG. 3 , the coolant flow field  245  according to the preferred embodiment of the present invention provides advantages by providing a longer flow path for the coolant and more even distribution of coolant, thereby providing a better cooling result. The longer flow path is achieved by locating solution inlet  236  and solution outlet  237  near two ends along a diagonal of the rectangular first reactor plate  200 . Similarly, the coolant inlet  241  and coolant outlet  240  are provided substantially near the two ends along other diagonal of the rectangular reactor plate  200 . 
     Referring now to  FIG. 1B , the first catalyst layer  210  may be a layer or layers of foam impregnated with a catalyst shaped to fit into the reaction chamber  119  of the first reactor vessel  110 , such that the first catalyst layer closes the open channels  235  of the flow field  232 . The catalyst may be any suitable compound for generating hydrogen from a chemical hydride solution. Preferably, the catalyst is one or more of Ruthenium, Cobalt, Platinum or any alloys thereof, and the hydride solution is NaBH 4  in water. 
     In accordance with an alternative embodiment of the invention (not shown), the catalyst layer may be replaced by catalyst material which is coated or deposited directly onto the flow field  232 . Accordingly, when chemical hydride solution enters the flow field from the inlet  236  and flows across the flow field, the solution comes into contact with the catalyst and generates hydrogen. In this embodiment, it would not be necessary to provide space between the separator plate  300  and the flow field  232 , hence the rim  250  does not need to be made protruding from the front face of the first reactor plate  200 . In addition, the catalyst can be in the form of pellets that is accommodated in the space between the separator plate  300  and the flow field  232 . These pellets can be placed on the plates during assembly of the reactor stack  100 . 
       FIG. 5  shows one face of the separator plate  300  which is identical to the opposing face (not shown). Preferably, the separator plate  300  is a flat rectangular plate with two ports provided near each end thereof. Specifically, a separator solution inlet  336  and a separator coolant outlet  340  are formed near one end of the separator plate  300  while a separator solution outlet  337  and a separator coolant inlet  341  are formed near the opposite end thereof. As shown most clearly in  FIG. 1B , the ports on the separator plate  300  communicate with ports on the first and second reactor plates  200  and  200   a  so that when the plates stack together, the inlets and outlets form four distribution conduits or ducts that extend throughout the reactor stack to distribute the solution and coolant from the first reactor plate  200  to second reactor plate  200   a . The ducts communicate with the respective ones of the ports  312 - 315 , as described above and shown in FIG.  1 B. 
     While only two reactor plates  200 ,  200   a  and one separator plate  300  are shown, it will be understood that a plurality of alternating reactor plates  200  and separator plates  300  could be provided, all sandwiched between the first and second end plates  310 ,  320 . 
     The reactor plates  200 ,  200   a  and separator plates  300  can be made from Titanium, stainless steel, graphite, or the like. 
       FIG. 8  shows a second end plate  320 . Preferably, the second end plate  320  does not include any connection ports for distributing fluids. The sealing between the end plates and the adjacent reactor plates is provided by the gasket  400  described above in the same manner as for the separator plate  300 . As shown in  FIGS. 6 ,  7  and  8 , the first and second end plates  310  and  320  are preferably provided with a plurality of notches  360  along its edges. These notches are used in assembly to facilitate alignment of the plates. 
     The operation of the hydrogen generation system according to the present invention will now be described with reference to  FIGS. 1B and 9 . The chemical hydride solution is delivered to the reactor stack  100  by a solution supply means. Preferably, the solution supply means is a conventional first pump  510  which draws the hydride solution from a solution storage tank  520  through a pipe  530 . The pipe  530  communicates with the first solution connection port  314 , which in turn communicates with the solution inlet  236  of the first reactor plate  200 . 
     Referring now to  FIGS. 1A and 1B , a portion of the chemical hydride solution enters the first reaction chamber  119  of the first reactor vessel  110  through the solution inlet  236 , and flows along the channels  235  in the flow field  232 , where the solution comes into contact with the first catalyst layer  210 . The chemical hydride solution generates hydrogen in the presence of the catalyst. The unreacted solution continues to flow along the flow field  232 , and ultimately exits the reactor plate  200  via the solution outlet  237 . The generated hydrogen is entrained in the solution and flushed out of the solution outlet  237  by the incoming solution. 
     As shown in  FIG. 1B , the remaining solution flows into separator solution inlet  336  of separator plate  300  and into the solution inlet  236  of second reactor plate  200   a , where it enters the second reaction chamber  124  and follows a path identical to that described above. 
     Referring to  FIG. 9 , the solution exits solution outlet  237  through second solution connection port  315  and is returned to the solution storage tank  520  via pipe  540 . The solution is then continuously recirculated through the reactor stack  100  in the manner described above. 
     Referring to  FIG. 9 , the coolant is delivered to the reactor stack  100  by a coolant supply means. Preferably, the solution supply means is a second pump  550  which draws the coolant from a coolant container  560  through a pipe  570 . The pipe  570  communicates with the first coolant connection port  312 , which in turn communicates with the coolant inlet  241  of the first reactor plate  200 . 
     Referring again to  FIGS. 1A and 1B , a portion of the coolant enters the coolant chamber  121  through the coolant inlet  241 , and flows along the channels  245  in the flow field  234 . The coolant comes into contact with the second face  117  of the first reactor plate  200  and to transfer the heat generated in the chemical hydride hydrogen generation reaction occurring on the first face  115  to the coolant. The coolant then exits the coolant chamber  121  via the coolant outlet  240 . 
     As shown in  FIG. 1B , the remaining coolant flows into separator coolant inlet  341  of separator plate  300  and into the coolant inlet  241  of second reactor plate  200   a , where it follows a path identical to that described above. 
     Referring to  FIG. 9 , the coolant exits coolant outlet  240  through second coolant connection port  313  and is returned to the coolant container  560  via pipe  580 . The coolant is then continuously recirculated through the reactor stack  100  in the manner described above. A temperature sensor  590  is placed within the reactor stack  100  to monitor the temperature of the solution. The sensor  590  is electrically connected to the second pump  550  through a conventional control device such that the pump  550  can alter the flow rate of the coolant to provide a desired solution temperature. 
     As is known in the art, the chemical hydride hydrogen generation reaction is exothermic and the reaction rate is sensitive to temperatures. Experiments have shown that approximately every 10° C. rise in temperature results in doubled reaction rate. In order to keep the reaction from running away, the heat has to be removed efficiently. On the other hand, the chemical hydride solution is usually circulated between the reactor stack  100  and a solution storage tank  520 , and hence, as the reaction proceeds, the concentration of chemical hydride in the solution decreases. This decrease will reduce the reaction. However, this can be effectively compensated by an increase in reaction temperature. Therefore, in order to achieve a constant reaction rate as may be required in some applications, such as supplying hydrogen to fuel cells, a better temperature control is desired. The reactor plate arrangement of the present invention provides a way of effectively controlling the temperature of reaction by adjusting the flow rate of coolant. 
     While the above description constitutes the preferred embodiments, it will be appreciated that the present invention is susceptible to modification and change without departing from the fair meaning of the proper scope of the accompanying claims. The spirit of the invention relates to using plate type reactor to achieve bettering thermal management of the chemical hydride hydrogen generation reaction. It should be appreciated that the shape of the reactor plates and/or reactor stacks of the present invention are not limited to those disclosed in the above description. For example, the coolant does not need to flow along counter-current direction with respect to chemical hydride flow although this arrangement provides the advantage of sufficiently heat exchange between the solution and the coolant. The reactor plates are not necessarily rectangular in shape. In addition, the chemical hydride solution used to generate hydrogen is not limited to borohydride water solution. Rather, the hydride can comprise one or a combination of: NaBH 4 , LiBH 4 , KBH 4 , RbH 4 , or the like. Additionally, the number and arrangement of the components in the system might be varied, but may still fall within the scope and spirit of the claims.