Abstract:
A system includes power modules received within a frame of a ventilation enclosure. Each of the power modules has a fuel cell stack. A ventilation shaft is arranged along a rear side of the ventilation enclosure and sealingly receives the power modules so that exhaust outlets of the power modules discharge into the ventilation shaft. Each of the power modules is removably attachable to the ventilation shaft through the front side of the ventilation enclosure. A fuel supply pipe in the ventilation shaft supplies fuel to fuel inlets of the power modules. An exhaust pump draws exhaust fluid out of the ventilation shaft.

Description:
FIELD 
     This invention relates to fuel cell power modules, and more particularly but not exclusively is related to fuel cell power modules located together in a common housing. 
     BACKGROUND 
     The following paragraphs are not an admission that anything discussed in them is prior art or part of the knowledge of persons skilled in the art. 
     Fuel cells provide a source of electrical power that can be used for a variety of different purposes. Fuel cells are commonly configured into stacks that generate useful voltages. Fuel cell stacks require a number of auxiliary components in order to function efficiently, e.g., conduits, valves, pumps, compressors and the like for delivering process gases; humidifiers for humidifying processed gases; control equipment. These additional components are commonly referred to as “balance of plant” or BOP. 
     To make a fuel cell stack readily useable for a variety of applications, fuel cell stacks are sometimes packaged with the associated balance of plants components to form a fuel cell power module. Such power modules can be integrated to the extent that they require no more than connections to necessary reactant supplies (e.g., hydrogen and air), and possibly a coolant (water, although sometimes air again is used as a coolant), and additionally electrical connections for the electricity generated by the fuel cell power module. 
     It has been proposed to use fuel cell power modules as backup power supplies. Such backup power supplies may be deployed at installations that require a high degree of integrity in their power supply and/or may be located in remote areas where a standard electricity power supply is not reliable. For example, remote transmitting towers for various functions often require backup power supplies. 
     In order to provide the necessary level of reliability, it is common to provide two or more power modules together. For example, sometimes three power modules are provided, with the intent that two would be sufficient to provide the necessary power and the third power module then acts as a further backup, in case one of the other two power modules fails. 
     INTRODUCTION 
     The following introduction is intended to introduce the reader to this specification but not to define any invention. One or more inventions may reside in a combination or sub-combination of the apparatus elements or method steps described below or in other parts of this document. The inventor does not waive or disclaim his rights to any invention or inventions disclosed in this specification merely by not describing such other invention or inventions in the claims. 
     The present invention is based on the realization that where fuel cell stacks or fuel cell power modules are provided together, it may be desirable to provide common elements for the plurality of fuel cell stacks or fuel cell power modules as the case may be. In particular, it may be desirable to provide common venting arrangements to deal with any possible hydrogen leaks. 
     In accordance with one aspect of the present invention, there is provided system, comprising: a ventilation enclosure having a front side, a rear side, and a frame generally between the front and rear sides; a plurality of power modules received in vertical arrangement within the frame, each of the power modules comprising an external casing, a fuel cell stack housed within the external casing, a fuel inlet for supplying fuel to the fuel cell stack and at least one exhaust outlet for discharging exhaust gases from the power module, the fuel inlet and the exhaust outlet being accessible through the external casing at a rear of the power module; a ventilation shaft arranged along the rear side of the ventilation enclosure and comprising a plurality of connection apertures, each of the connection apertures being adapted to sealingly receive the rear of a respective power module so that the exhaust outlet of the respective power module discharges into the ventilation shaft; a fuel supply pipe extending into the ventilation shaft, and arranged to supply fuel to the fuel inlets of the power modules; and an exhaust pump connected to the ventilation shaft and arranged to draw exhaust fluid out of the ventilation shaft, wherein each of the power modules is removably attachable to the ventilation shaft through the front side of the ventilation enclosure, and with the respective unoccupied connection aperture of the ventilation shaft being sealable to prevent air ingress into the ventilation shaft when the is not present. 
     In accordance with another aspect of the present invention, there is provided a power module, comprising: an external casing; a fuel cell stack housed in the external casing; a vent opening to provide air ingress into the external casing for supply of air to the fuel cell stack; a collar extending from the external casing for sealably connecting with a ventilation shaft; a fuel inlet for supplying fuel to the fuel cell stack, the fuel inlet being accessible through the collar so that fuel is supplied to the fuel cell stack throwgh the ventilation shaft; and at least one exhaust outlet for discharging exhaust gases from the power module, the exhaust outlet being directed through the collar so that the exhaust gases discharge into the ventilation shaft. 
     In accordance with another aspect of the present invention, there is provided a method, comprising: providing a plurality of power modules, each of the power modules comprising an external casing, a fuel cell stack housed within the external casing, a fuel inlet for supplying fuel to the fuel cell stack, and at least one exhaust outlet for discharging exhaust gases from the power module; mounting the power modules onto a frame; connecting the power modules to a ventilation shaft, so that, for each of the power modules, the fuel inlet is accessible through the ventilation shaft, and the exhaust outlet is directed into the ventilation shaft; supplying fuel through the ventilation shaft to the fuel inlets of the power modules; and discharging exhaust gases from the exhaust outlets of the power modules into the ventilation shaft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       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 in which: 
         FIG. 1  is a perspective view from the rear of a ventilation enclosure for fuel cell power modules showing a ventilation shaft partially open; 
         FIG. 2  is a perspective view from the rear of the ventilation enclosure of  FIG. 1  showing a closed ventilation shaft; 
         FIG. 3  is another perspective view from the rear of the ventilation enclosure, with the ventilation shaft; 
         FIG. 4  is a perspective view from rear of a single power module for mounting in the ventilation enclosure; 
         FIG. 5  is a schematic elevational view of components of the ventilation enclosure of  FIGS. 1 and 2 ; 
         FIG. 6  is a diagram of a fuel storage assembly; and 
         FIG. 7  is a diagram indicating connections within the ventilation enclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Various apparatuses or methods will be described below to provide an example of an embodiment of each claimed invention. No embodiment described below limits any claimed invention and any claimed invention may cover apparatuses or methods that are not described below. The claimed inventions are not limited to apparatuses or methods having all of the features of any one apparatus or method described below or to features common to multiple or all of the apparatuses described below. It is possible that an apparatus or method described below is not an embodiment of any claimed invention. The applicants, inventors and owners reserve all rights in any invention disclosed in an apparatus or method described below that is not claimed in this document and do not abandon, disclaim or dedicate to the public any such invention by its disclosure in this document. 
     Referring to  FIGS. 1 ,  2  and  3 , there is shown a ventilation enclosure  10  in a view from the rear. The ventilation enclosure  10  has sides  12 , a rear  14  and a front  16  (not fully shown in the drawings). It provides a frame generally indicated at  18  that provides racks  20 . Each rack comprises a pair of rack rails  22  into which a power module can be slid. 
     Power modules in the ventilation enclosure  10  can be intended to provide a backup power supply. For this purpose, connections need to be provided for process fluids for the power modules, for example, hydrogen gas, liquid coolant, as well as electrical power etc. In this embodiment, the power modules are based on fuel cell stacks that utilize air as the oxidant, so that no separate inlet need be provided for the air as a reactant gas, although other oxidants may be used. 
     An exemplary power module is shown at  40  in  FIG. 4 , and further variants of a power module configuration are detailed in application Ser. No. 11/876,425 filed Oct. 22, 2007, hereby incorporated herein by reference in its entirety. Here, it is noted that the power module  40  has a frame  42  with a central flange  44  to which is mounted a fuel cell stack  46 . Electronic control equipment  48  is mounted towards the front of the power module  40 , so as in use to be at the front of the ventilation enclosure  10  and readily accessible for maintenance. Back towards the rear of the power module  40 , there is generally indicated other balance of plant components  50 , e.g., valves, pumps, etc. 
     At the rear of the power module  40  there is a rear flange  52  of the frame  42 . On this rear flange  52 , as seen in  FIG. 4 , there are two connection sockets  54  (detailed further in Application No. 60/981,692 filed Oct. 22, 2007, hereby incorporated herein by reference in its entirety. These connection sockets  54  provide for connections to a coolant supply, e.g., deionized water. 
     In the rear flange  52 , there is an extension or circular collar  56 ; in this embodiment, it is located centrally, but this is not essential. Extension  56  is sealed with an annular seal  86  as described below. The extension  56  and seal  86  provides for a main vent from the power module  40 . Passing through the extension  56  is a hydrogen or fuel inlet  58 . 
     On the right hand side of the rear flange  52  (again as viewed in  FIG. 4 ), there are connections  60  for electrical power generated by the power module. 
     The frame  42  of each power module  40  includes side rails  62  that are dimensioned for a sliding fit with the rack rails  22  of the ventilation enclosure  10 . In use, the power modules  40  are slid into the ventilation enclosure  10  on the rails  22 , and the connection sockets  54  then make connections with conduits  70  for a coolant supply (e.g., water). The connectors  60  simultaneously make connection with electrical supply leads or bus bars. 
     Additionally, as shown in  FIG. 5 , individual connection lines  72  for a hydrogen supply are connected to the hydrogen fuel inlets  58 . 
     The ventilation enclosure  10  including the power modules  40  will usually, but not necessarily, be placed in an indoor and non-residential environment. For such a location, there is the need to make a system safe. In particular, it will usually be necessary to ensure that any hydrogen leaks do not give rise to potentially dangerous situations, e.g., formation of explosive or flammable mixtures of hydrogen and air. 
     The present invention is based on the concept of a boundary of dilution. All sources of potential hydrogen leakage are placed within the boundary of dilution, and this in turn is provided with a gas tight construction. Forced ventilation is then used to ventilate the boundary of dilution to safe hydrogen concentrations during all foreseeable events. 
     Additionally, ventilation is interlocked with hydrogen and control valves to ensure that there is no possibility of an ignition source igniting leaked hydrogen. This means that if there is no ventilation within the boundary of dilution, then hydrogen supply to the power modules is closed off and potential ignition sources are de-energized. All components that may be exposed to hydrogen within the dilution boundary are designed to eliminate ignition sources, e.g., by the use of brushless motors. The ventilation interlock is implemented by means of a pressure switch. If there is some interruption in the supply of ventilation or the boundary of dilution, then this area may be ventilated with five volume changes, to ensure venting and discharge of any hydrogen present, before electrical components within the boundary are re-energized. 
     Each fuel cell power module is designed to keep residual hydrogen contained inside the boundary of dilution. 
     Referring to  FIG. 5 , this shows greater detail of the ventilation enclosure. In  FIG. 5 , individual power modules are again indicated at  40 . Each power module  40  includes an external casing  64 , part of which can comprise, for example, the rear flange  52  and the side rails  62 . The external casing  64  is entirely closed and sealed, except at the rear where the extension  56  provides an opening to a ventilation shaft ( FIGS. 1 ,  3  and  5 ) and except for the provision of a vent opening  66 . The vent opening  66  may be provided at the front of each power module  40 , i.e., opposite the extension  56 , so as to establish a flow of air through the power module  40 , as detailed below, to flush out any leaking hydrogen. 
     The ventilation enclosure then includes a ventilation shaft  80 , that is a generally rectangular parallelepiped; it will be understood that the exact profile and shape of the ventilation shaft does not impact its function, and it could, for example, be cylindrical or elliptical in shape. As shown in  FIG. 1 , one, front side of the shaft  80  is arranged to provide connections to the individual power modules  60 . For this purpose, a front side  82  of the shaft  80  includes connection apertures  84  provided with annular seals  86 . As shown in  FIG. 5 , the extensions  56  of the individual power modules  40  then engage these seals  86  to form a sealing connection. 
     Where a power module  40  is not present, a plug  88  can be used to close off each unoccupied connection aperture  84 . 
     As shown in  FIG. 5 , a side panel  90  of the ventilation shaft  80  can be provided with an access opening  92 , that is normally closed and sealed in use. 
     A rear panel  94  of the ventilation shaft  80  (shown in  FIG. 2 ) can be removable (as shown in  FIG. 1 ), or connected by a hinge to the ventilation enclosure, to provide access to the connections to the individual power modules  40 , to enable these connections to be perfected. 
     Turning to details of the hydrogen supply, as indicated in  FIG. 5 , a main hydrogen supply pipe  100  may be connected to a supply of hydrogen provided externally of a boundary wall  102 , or otherwise located in a remote location for safety purposes. The hydrogen supply pipe  100  extends into the ventilation shaft  80  and is connected to a valve assembly  120  detailed below. The hydrogen supply pipe  100  may also connected to a hydrogen feed forward pipe  104 , that can be connected to other ventilation enclosures  10  with their respective power modules  40 , where it is required to have a number of power modules in operation or available for operation. 
     The valve assembly  120  has an outlet  122  connected to a distribution pipe  106 , that in turn is connected to the individual connection lines  72 . As shown in  FIG. 5 , two connection lines  72   a  are shown connected to respective power modules  40 , while a third connection line  72   b  is shown not connected with no power module present. 
     At the bottom of the ventilation shaft  80 , there is provided a water level sensor  96  connected to a valve or pump  98 , that in turn is connected to the bottom of the vertical shaft  80 . In response to a sensed level of condensate collecting at the bottom of the ventilation shaft  80 , the valve or pump  98  is actuated to discharge this from the shaft  80 . 
     A controller  130  is provided connected to the valve assembly  120  in known manner, the controller can also be connected to a variety of acoustic or visible warning devices generally indicated at  142 . 
     To vent the ventilation shaft  80 , there is provided an exhaust conduit  150  connected to an exhaust pump or fan  152  which in turn passes through the boundary wall  102  to an exterior vent  154 . A pressure switch  156  is connected to the ventilation shaft  80 , with both the pressure switch  156  and pump or fan  152  being connected to and controlled by the controller  130 . 
     Referring to  FIG. 5 , within each power module  40 , there can be provided a blower  110  for supply of air as the cathode reactant, connected to the fuel cell stack again indicated at  46 . There is also shown schematically in  FIG. 5  a fuel module  114  having a connection to the hydrogen fuel inlet  58  and an exhaust  116  for exhausted hydrogen. This fuel module  114 , in known manner, would provide functions such as humidification of fuel, recirculation of fuel, and would be connected to the fuel cell stack  46 . 
     An exhaust for spent cathode gas is also provided at  118 . The two exhaust outlets  116 ,  118  are directed through the extension  56  of the power module  40 , so as to discharge into the ventilation shaft  80 . A check valve may be arranged on the cathode exhaust to prevent any flow through the cell stack when the fuel cell is not in operation. 
     In normal use, the fuel cell stacks  46  may operate with a continuous through-flow of air as the cathode gas. For the fuel, this may be re-circulated, and may be purged on a periodic basis as required, with purging typically being carried out to prevent accumulation of contaminant gases and the like in the fuel cell stack  46 . 
     Turning to  FIG. 7 , there is shown details of the valve assembly  120 . The hydrogen supply  100  and the hydrogen feed forward line  104  are connected to valves  160  and  162 , that in turn are connected to the controller  140 . Downstream from these valves  160 ,  162 , a manual control valve  164 , as indicated in  FIG. 5 , may be arranged for operation from the exterior. A pressure indicator may be provided at  166  and a connection or filter provided at  168 . 
     A pressure measuring switch  156  is shown as part of the valve assembly  120  and is connected to the controller  140 . 
     Turning to  FIG. 6 , there is shown a fuel storage arrangement. One or more fuel storage containers or vessels  170  may be connected through a pressure reducing valve  172  to a manual control valve  174 , then to a connection point  176 . This connection point  176  may be connected to a pressure indicator or gauge  178  and also to a further manual valve  180  that enables venting to be provided. 
     From the connection point  176 , the line is connected through at least one further pressure reducing valve  182  and then to a solenoid valve  184  that provides connection to a further manual control valve  186 , and from there the fuel is connected to the hydrogen supply line  100 . A purge test valve is provided at  188 . 
     As indicated at  190 , additional and corresponding valving and other components can be provided to enable a hot swap option, i.e., to enable a new supply of hydrogen to be switched in and connected before a first supply vessel  170  is exhausted. 
     Referring to  FIG. 5 , the ventilation shaft  80  includes an additional vent opening  108  at the bottom thereof, that can also serve as an overflow for accumulated condensate. In use, the pump or blower  152  is operated so as to draw air from the interior of the ventilation shaft  80  and discharge it through the exterior vent  154 . Due to the presence of the vent opening  108  at the bottom of the shaft  80  and the individual vent openings  66  of each of the power modules  40 , ambient air will be drawn in through these openings, through the power modules  40  and up through the ventilation shaft  80 . Exhausted anode and cathode, i.e., hydrogen and air, from the power modules  40  is discharged through to the exhausts  116 ,  118  into the interior of the ventilation shaft  80 . With sufficient airflow, this is diluted below limits of combustion or flammability, and the diluted mixture is then vented out through the vent  154 . The pressure sensor  156  may be monitored by the controller  140  to ensure that a pressure within the ventilation shaft  80  is maintained below atmospheric pressure by a pre-set amount, this being indicative of adequate flow of air out of the ventilation shaft  80  to the exterior. 
     In use, various leakages can occur. Any “abnormal unlimited release” can occur where a component malfunction causes a leakage. During an abnormal unlimited release event ventilation should be adequate to dilute the hydrogen mixture to below 50% LEL (Lower Explosion Limit). For “a normal mode release” this being for somewhat slow leakages and diffusion that will always be present, the ventilation should dilute the mixture to below 25% LEL. 
     In normal usage, a fuel cell power module may have two anode purge levels. During normal mode operation the fuel cell may purge on a regular basis, for example, by way of 40 lpm pulse for three seconds repeated every two minutes, to give a two lpm discharge on average. 
     Additionally, when a fuel stack is performing badly, the fuel cell control system can enter a “hard recovery mode” to restore the fuel cell to proper operation. In this hard recovery mode, the purge solenoid valve may be kept open until the stack has recovered. This is considered an abnormal event and covered by the “abnormal and limited release”. 
     With reference to  FIG. 7 , there is shown details of some of the flow connections within each power module  40 . Thus, each power module  40  has a respective connection line  72  its respective hydrogen fuel inlet  58 . Internally within each power module  40 , there is a filter  190  that is connected to a solenoid valve  192 , that is in turn connected to a forward pressure regulating valve  194 . The cathode blower or fan  110  is shown connected by a line  196  to the actual fuel cell stack  46 . A connection  198  from the cathode gas supply line  196  to the valve  194  serves to control the pressure in the hydrogen line and depends upon the pressure of the cathode supply line. The hydrogen supply line can be biased to be either slightly above or below the pressure in the cathode line  196 . A pressure sensor may be provided at  200  and is connected to a respective control unit for each power module  40 . 
     Internally within each power module  40 , there is a filter  190  that is connected to a solenoid valve  192 , that is in turn connected to a forward pressure regulating valve  194 . The cathode blower or fan  110  is shown connected by a line  196  to the actual fuel cell stack  46 . A connection  198  from the cathode gas supply line  196  to the valve  194  serves to control the pressure in the hydrogen line and depends upon the pressure of the cathode supply line. The hydrogen supply line can be biased to be either slightly above or below the pressure in the cathode line  196 . A pressure sensor may be provided at  200  and is connected to a respective control unit for each power module  40 . 
     The stack  46  is provided with a recirculation line  202  that is connected through an anode or hydrogen recirculation pump to an anode inlet of the stack  406 . The exhaust lines  116 ,  118  for the cathode and anode, respectively, are shown for each power module and are discharged to a mixing point to within the ventilation shaft  80 . A control valve  206  is provided on the anode exhaust, so that the anode exhaust may be opened and anode purging take place in a controlled manner as desired. 
     As shown, the vent opening  66  in the power modules  40  permit ventilation air to be drawn into the power modules and then to flow through them towards the shaft  80 . The arrows then indicate that the air flows into the shaft  80  and is drawn upwards. 
     It will be understood that various modifications and variants are encompassed by the invention, in addition to the detailed embodiment described. For example, while each power module has been described as being largely self-contained, for reasons of economy, simplicity and even reliability, it may be preferable to provide some common balance of plant elements. For example, rather than providing a single blower in each power module, it may be preferable to provide a bank of blowers, for the cathode air supply, together and in parallel, so that if any one blower fails, the others will still be operational and capable of supplying air to all the active power modules. Other elements, e.g. a common filter for incoming air can be provided for the power modules. Aspects of the hydrant circuits in each power module and control systems may also be provided on a common basis and separate from any one power module. 
     Additionally, while the described embodiment envisages that each power module  40  would have its own casing that provides a completely sealed containment of the components of the power module, other variants are possible.