Abstract:
A transportable solid oxide fuel cell and balance of plant in a portable enclosure. A fuel supply is provided in the enclosure. The fuel supply is refillable. Power conditioning of the electricity provided is also provided as part of the enclosure.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates to a solid oxide fuel cell device to provide portable electrical power. Among other applications, the device can be used for energy generation and distribution industries.  
         [0003]     2. Description of the Related Art  
         [0004]     Fuel cells generate electricity, quietly and cleanly. The Solid Oxide Fuel Cell (SOFC) is one of the most mature fuel cell technologies. It operates temperatures normally exceeding 650 C. The SOFC generates electricity by stripping electrons off oxygen. Oxygen from the air flows through the cathode. Negatively charged oxygen ions (Equation 1) migrate through the electrolyte membrane and react with hydrogen at the anode to form water. When hydrogen is used as a fuel Equation 2 exemplifies the anode reaction. Equation 3 shows the overall reaction. Carbon Monoxide may be used as a fuel the anode reaction is shown in Equation 4. Methane may also be used as a fuel, as shown in equation 5. A blend of the aforementioned fuels may also be used. Depending on the fuel water, carbon dioxide or both are the by-product of the generation of electricity. 
 
1/2 O 2 +2e − →O 2−  (cathode).   Equation 1 
 
H 2 +O 2− →H 2 O+2e −   Equation 2 
 
H 2+ 1/2 O 2 →H 2 O (anode).   Equation 3 
 
CO+O 2− →CO 2 +2e −   Equation 4 
 
CH 4 +4O 2− →2H 2 O+CO 2 +8e − (anode).    Equation 5 
 
         [0005]     SOFC&#39;s are known in the arts primarily for stationary use for use with very small portable electronic devices with small power needs.  
         [0006]     Disruptions in the electrical power grid or supply interfere with the safety and order of society. To minimize electrical disruptions portable combustion back-up power generators are available. Combustion-type power generators in the over 50 KW range using gasoline or diesel fuel are noisy operating 60 to 100 decibels and the exhaust emitted posses serious health risks. Since 1990, diesel exhaust has been listed as a known carcinogen under California&#39;s Proposition 65. In 1998, the California Air Resources Board (CARB) listed diesel particulate as a toxic air contaminant. Also, see Findings of the Scientific Review Panel (SRP): “The Report on Diesel Exhaust as adopted at the Panel&#39;s Apr. 22, 1998”. It would be desirable to have a portable power supply which could provide at lest 50 KW of electrical power with reduce noise and pollution.  
       SUMMARY OF THE INVENTION  
       [0007]     The transportable SOFC electrical power generator carries its own fuel supply.  
         [0008]     In one embodiment about 35 KG of hydrogen, which provides for extended operation. The hydrogen can be carried as a compressed gas stored in tanks at high pressure.  
         [0009]     The power SOFC generator can be placed in a transportable trailer or in a transportable enclosure.  
         [0010]     In another embodiment the transportable SOFC electrical power generator contains a hydrogen producing system, such as a reformer using hydrogen rich fuels, an electrolyzer, and/or electrolytic cell. The hydrogen producing system can be used to refill the tanks.  
         [0011]     In another embodiment the transportable SOFC electrical power generator carries compressed natural gas as the fuel supply.  
         [0012]     In another embodiment the transportable SOFC electrical power generator is supplied a reformate directly from a prereformer.  
         [0013]     A transportable generator self contained within an enclosure with its own fuel cell stack, balance of plant, fuel supply, and oxygen supply system is within the enclosure. A system controller and a power conditioning system may also be also provided as part of the enclosure whereby DC and/or AC can be provided for output. In some instances, the transportable SOFC generator may be disassociated from a transport trailer for local use.  
         [0014]     In some embodiments a hydrogen refilling system is also provided whereby gaseous hydrogen at a lower pressure can be fed into the transportable generator (through feed lines), and pressurized to a higher psi, and cooled, before storing the gaseous hydrogen in one or more hydrogen storage tanks.  
         [0015]     Other features and advantages of the present invention will be set forth, in part, in the descriptions which follow and the accompanying drawings, wherein the preferred embodiments of the present invention are described and shown, and in part, will become apparent to those skilled in the art upon examination of the following detailed description taken in conjunction with the accompanying drawings or may be learned by practice of the present invention. The advantages of the present invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appendent claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  is an overview of a transportable SOFC electrical generator.  
         [0017]      FIG. 2  is an overview of a transportable SOFC electrical generator.  
         [0018]      FIG. 3  is a schematic of a SOFC transportable generator.  
         [0019]      FIG. 4  is partial cut-away top view of component arrangement inside a transportable SOFC electrical generator.  
         [0020]      FIG. 5  is partial cut-away top view of component arrangement inside a transportable SOFC electrical generator. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     A transportable fuel cell generator within a trailer  10  is shown in  FIG. 1 . A substantially flat base  12 , with wheels  13 , which supports a lightweight shell  14  into which the fuel system, distribution system and electrical generation systems are placed. Vents  16  are provided in the lightweight shell  14 . An electrical panel  17 , accessible from the outside of the lightweight shell  14 , at which electricity can be distributed from the transportable fuel cell generator within a trailer  10  is provided. A fueling panel  18  is also provided. The fueling panel  18  provides access to the fuel cell fuel system within the lightweight shell  14 . A vehicle  19  can be used to tow the trailer  10 .  
         [0022]     A transportable fuel cell generator on a trailer  20  is shown in  FIG. 2 . In this embodiment a base  22 , with wheels  13 , which supports an enclosure module  24 . The enclosure module  24  has its own module-base  25 . Inside the enclosure module  24  are the fuel system, distribution system and electrical generation systems. The enclosure module  24  has vents  16 . The enclosure module  24  can be used while on the base  22 , or can be removed from the base  22  and set-up for local usage. An electrical panel  17 , accessible from the outside of the enclosure module  24  at which electricity can be distributed is provided. A fueling panel  18  is also provided. The fueling panel  18  provides access to the fuel cell fuel system within enclosure module  24 . Removal from the base can be facilitated by lifting the front edge  27  of the base  22  thereby lifting the base  22 . Attached to the module-base  25  may be wheels  28  or a sled (extended flat surface) as shown in  FIG. 5 .  
         [0023]      FIG. 3  is a schematic of a transportable SOFC generator. In this embodiment the fuel source is compressed hydrogen gas supplied from one or more internal hydrogen storage tanks  100 .  
         [0024]     Lightweight internal hydrogen storage tanks  100  should have a pressure rating of up to about 10,000 psi or more and a failure rating, or burst rating, of at least 2.25 times the pressure rating. One such hydrogen storage vessel is the Dynecell™ available from Dynetek Industries, Ltd. in Alberta, Canada. Another lightweight hydrogen storage vessel is the Tri-Shield™ available from Quantum Technologies, Inc. in Irvine, Calif.  
         [0025]     Before the fuel cell generator can generate electricity the internal hydrogen storage tanks  100  in the refueling station  10  must be filled. A hydrogen storage subsystem  30  is provided to refill or charge the hydrogen storage tanks  100 , a quick connect  32 , which can be any standard hydrogen connector, is used to connect an external hydrogen source to hydrogen storage subsystem  30 . The external hydrogen source can be a low-pressure source preferably at least about 2400 psi. However, lower pressure sources of at least about 600 psi can be used.  
         [0026]     Downstream from the quick connect  32  is a pressure release valve  34 . The pressure release valve  34  is a safety element to prevent hydrogen, at a pressure exceeding a pre-determined maximum, from entering the hydrogen storage subsystem  30 . If the pressure of hydrogen being introduced through the quick connect  32  exceeds a safe limit a restricted orifice  33  working in combination with a pressure relief valve  34  causes the excess hydrogen to be vented through a vent stack  36 . In general, the valves are used to affect the flow of hydrogen within the refueling station. A check valve  38 , between the vent stack  36  and pressure relief valve  34 , maintains a one-way flow of the flow of pressurized hydrogen being relived from the hydrogen storage subsystem  30 . The restrictive orifice  33  also prevents the hydrogen from entering the pressure rated feed line  40  at a rate which causes extreme rapid filling of the lightweight hydrogen storage tanks  100 . Prior to connecting the quick connect  32  nitrogen gas, or other inert gas can be introduced into the feed line  40  to purge any air from the feed line. Pressurized nitrogen dispensed from a nitrogen tank  1000  can be introduced through a nitrogen-filling valve  1002 .  
         [0027]     The feed line  40  should be constructed of stainless steel and typically has a safety margin of  4 . Safety margins for a pressurized hydrogen gas line are a measure of burst pressure to operating pressure.  
         [0028]     It is important to control the rate of fill of the hydrogen storage tanks  100  and in general the temperature of the gaseous hydrogen. Although a rapid fill is desired, physics dictates that as you increase the fill rate, all things being equal, an elevation in temperature will occur. With an elevation in temperature there is a corresponding decrease in the mass of hydrogen that can be stored at a predetermined input pressure. Accordingly, if the hydrogen entering the hydrogen storage tanks  100  is at an elevated temperature the density of the gaseous hydrogen will also be reduced. Cooling the gaseous hydrogen, by directing it through a cooling unit  300 , is used to reduce temperature elevations.  
         [0029]     The cooling unit  300  in this embodiment is a finned tube type heat exchanger, however, other heat exchangers, coolers, or radiators which can manage the temperature of the gaseous hydrogen may be used. Temperature is measured at various places on the feed line  40  by temperature sensors  42  which are monitored by a system controller  500  which is typically based on an 8-32 bit microprocessor.  
         [0030]     Connections between the feed line  40  sensors, valves, transducers, inlet or outlets, should be constructed to minimize any potential for leakage of hydrogen. Common construction techniques include welds, face seals, metal-to-metal seals and tapered threads. One or more hydrogen leak sensors  43  are also distributed and connected to the system controller  500 . The pressure of the gaseous hydrogen is measured by one or more pressure sensors  44  placed in the feed line  40 . No specific sensors is called out for but generally the sensor may be a transducer, or MEMS that incorporate polysilicon strain gauge sensing elements bonded to stainless steel diaphragms. The temperature and pressure of the hydrogen, entering the pressure rated feed line  40  can be checked as it passes into the first compressor subsystem  50 .  
         [0031]     The first compressor subsystem  50  contains an oil cooled first intensifier  52 . An intensifier switch  53 , connected to the system controller  500 , controls the start/stop function of the first intensifier  52 . An oil to air heat exchanger  54  for cooling hydraulic oil which is supplied to a first intensifier heat exchanger  56  to cool the first intensifier  52 . A hydraulic pump  58 , powered by a brushless motor  60 , supplies cooling oil from an oil reservoir  62  to the first intensifier heat exchanger  56 . A speed control  64  for the brushless motor  60  is provided. A brushless motor  60  is preferred to eliminate the risk of sparks. The system controller  500  receives data from the oil temperature sensor, the gaseous hydrogen temperature sensors  42 , the gaseous hydrogen pressure sensors  44 , and the hydrogen leak sensors  43 . The system controller  500  in turn is used to, among other things, affect the speed control  64 .  
         [0032]     The intensifier is a device, which unlike a simple compressor, can receive gas at varying pressures and provide an output stream at a near constant pressure. However, it may be suitable in some cases to use a compressor in place of an intensifier. The first intensifier  52  increases the pressure of the incoming gaseous hydrogen about four fold. Within the first compressor subsystem  50 , hydrogen gas from the feed line  40  enters the first intensifier  52  through an inlet valve  68 . The gaseous hydrogen exits the first intensifier through an outlet check valve  70 . At this point, the gaseous hydrogen is directed through a cooling unit  300  to manage any temperature increases in the gaseous hydrogen. The gaseous hydrogen passing through the cooling unit  300  may be directed to enter a second compressor subsystem  80  or into a by-pass feed line  90 .  
         [0033]     If entering the second compressor subsystem  80  the gaseous hydrogen passes through an inlet check valve  82  which directs it to the second intensifier  84 . The oil to air heat exchanger  54  for cooling the hydraulic oil which is supplied to a second intensifier heat exchanger  85  to cool the second intensifier  84 . An intensifier switch  86 , connects to the system controller  500 , and controls the start/stop function of the second intensifier  84 . The gaseous hydrogen exits the second intensifier  84  through an outlet check valve  87  and is directed down the inlet/outlet line  88  to a line control valve  92  which directs the gaseous hydrogen through a cooling unit  300  and into the inlet/outlet control valves  94  and  94 ′ for the lightweight composite hydrogen storage tanks  100  and  100 .  
         [0034]     The dual compressor sub-systems  50  &amp;  80  are not a limitation. If the storage pressure for the hydrogen gas can be achieved with a single compressor sub-system, the second compressor subsystem can be bypassed or eliminated. By closing the inlet check valve  82  to the second intensifier  84 , the gaseous hydrogen exiting the first intensifier  52  is directed through the by-pass feed line  90  and to a by-pass inlevoutlet control valve  96  which directs the flow of gaseous hydrogen to the lightweight composite hydrogen storage tanks  100  and  100 . Conversely, in those instances where storage pressure exceeding that which can be efficiently achieved with dual intensifiers is desired, additional intensifiers can be added.  
         [0035]     Alternatively, compressed natural gas “CNG” can be stored on the board in tanks and used to supply fuel to the SOFC stack  211 . In a compressed natural gas embodiment the high pressure hydrogen storage tanks  100  are replaced with tanks suitable to store compressed natural gas at pressures of up to about 3600 psi. Such tanks may be replaceable or refillable. Once filled such tanks are connected to the SOFC stack  211  when the line control valve  92  is open. The stream of natural gas flows through the inlevoutlet line  88  to a first regulator  240 . The first regulator  240  decreases the pressure of the natural gas. The reduced pressure stream of natural gas flows from the first regulator  240  through the fuel cell feed line  245  to a second regulator  250  with vent  255 . The second regulator  250  further reduces the pressure of the stream of gas. For the SOFC stack  211  a feed pressure to the anodes  213  of up to about 15 bar is a suitable. As previously described oxygen is supplied to the cathodes  215  by compressing atmospheric air. A device to reform natural gas into a gas stream primarily consisting of hydrogen, methane and carbon monoxide may be placed upstream of the fuel cell feed line.  
         [0036]     The heart of the electrical generation system  200  is the SOFC stack  211  and the associated balance of plant. The balance of plant in this embodiment includes an air supply system  221 . A heat exchanger  230  uses the waste heat from the exhaust  2000  to preheat the air supply and/or fuel supplies before entry into the anode  213  and/or cathode  215 . A stream of gaseous hydrogen is supplied from the storage tanks  100  when the line control valve  92  is open. The stream of hydrogen flows through the inlet/outlet line  88  to a first regulator  240 . The first regulator  240  decreases the pressure of the hydrogen gas. In this embodiment the regulators are diaphragm based. There are many types of pressure regulators known in the art and the use of a diaphragm-based regulator is not a limitation. The reduced pressure stream of hydrogen gas flows from the first regulator  240  through the fuel cell feed line  245  to a second regulator  250  with vent  255 . The second regulator  250  further reduces the pressure of the stream of hydrogen. For the SOFC a feed pressure to the anode  213  of up to about 15 bar is a suitable.  
         [0037]     The SOFC stack  211  operates when fuel, in this embodiment a stream of hydrogen flows into the anodes  213  of the SOFC stack  211 . Oxygen is supplied to the cathodes  215  of the SOFC stack  211  via the air supply system  221  which comprises an air compressor  222 , a compressor motor  224  an air inlet  226  and a heat exchanger  230 . The compressed atmospheric air is directed via the oxygen feed line  260  to the cathodes  215 .  
         [0038]     The system controller  500  controls the flow of hydrogen via the line control valve  92  and/or the air supply system  221  via the electric motor  224 . Varying the hydrogen supply or the oxygen supply is used to control the output of the SOFC stack  211 . A SOFC stack&#39;s electrical output can be controlled by altering input parameters such as gas pressure, gas flow rate and gas stream temperature. In general, the current density (A/cm2) of the electricity generated will vary with alteration in the input parameters while the voltage remains generally stable. If the voltage output increases past the SOFC stack&#39;s nominal rating, the current density will generally decrease.  
         [0039]     The electrical current is produced when negatively charged oxygen “0 2−  migrates through the electrolyte membrane  217 . The electrical generation system  200  produces a DC output  300 . A SOFC stack between about 20 and about 150 KW is preferred. For this embodiment, a 100 KW SOFC stack  211 , which can produce a current between about 100 and 800 volts, is provided. The DC output  300  passes into the power conditioning system  350  both a DC/DC converter  360  with controller  365  and a power inverter  370  with controller  375 . The DC/DC converter  360  can be used to step down the SOFC stack  211  voltage and power on board systems such as the air compressor motor  232 , other low voltage components, and recharge a back-up battery  380 . Although a 100 KW SOFC stack is indicated, the 100 KW size is not a limitation. The size of the stack in KWS and the stack configuration will affect the output in terms of voltage and amperage. The preferred stack for any usage will depend on the voltage and amperage requirements.  
         [0040]     The DC output  385  from the DC/DC converter  360  and the AC output  390  from the DC/AC inverter  370  is available for use at an output power panel  395 . Referring now to  FIGS. 1 and 2 , the output power panel  395  in  FIG. 3  is located at the electrical panel  17 .  
         [0041]     Fuel to the SOFC stack  211  may also be provided from a prereformer  400  with controller  410 . A hydrocarbon rich fuel is provided from a fuel tank  415 . The fuel passes through a valve  417  to the prereformer  400 . Reformation of hydrogen rich fuels is well known in the art and therefore a detailed description of the construction of a prereformer is not provided. The prereformer you need not deliver pure hydrogen. Hydrocarbons in the reformate stream can be used directly as fuel for the SOFC  211  stack. One benefit of a SOFC stack  211 , as opposed to a PEM stack, is that a pure hydrogen source of fuel is unnecessary and the partial reformation of a fuel stream containing unreformed hydrocarbons (carbon dioxide and/or carbon monoxide) is a sufficient fuel source for the SOFC stack  211 .  
         [0042]     One alternative hydrogen supply source is a reformer  420 . Reformers are well known in the art. Generally a reformer is a combustion device that uses a hydrocarbon fuel  415  to produce hydrogen. The hydrocarbon fuel can be stored on-board in a tank  415 . A control valve which can be operated by the system controller  500  feed a hydrocarbon rich fuel into the reformer  420 . The reformer  420  strips hydrogen from a hydrocarbon fuel. The hydrogen can then be introduced into the hydrogen storage subsystem  30 .  
         [0043]     Another alternative hydrogen supply source to feed hydrogen into the hydrogen storage subsystem  30  is an electrolyzer  430  which is comprised of a KOH electrolyzer module  432  and a cooling module  434 . One suitable KOH electrolyzer is an IMET electrolyzer manufactured by Vandenborre Hydrogen Systems. The cooling module  434  should be sufficient to reduce the temperature to at or below ambient for maximum volume in the hydrogen storage tanks  100 . The cooling module  434  may be a closed loop cooler, receive a water input, or use heat exchangers and or radiators.  
         [0044]     A polymer electrolyte membrane (PEM) electrolyzer  440  may be substituted for the IMET electrolyzer. A PEM electrolyzer splits hydrogen from a water source and generates a hydrogen gas stream. Both the electrolyzer and the polymer electrolyte membrane are known in the art and therefore a detailed description of their construction is not necessary.  
         [0045]     Both the electrolyzer module  430  and the PEM electrolyzer  440  require electricity to operate. The electricity may be from an electrical grid connection, or other electrical generator. In some instance the electricity to drive the electrolyzer module  430  or the PEM electrolyzer  440  can be obtained from renewable sources such as solar (photovoltaic) or wind-power.  
         [0046]     Shown in  FIGS. 4 and 5  are alternative component arrangements within a trailer  14  or an enclosure module  24  of the hydrogen storage subsystem  30 , electrical generation system  200  and the power conditioning system  350 . In  FIG. 5  the alternative hydrogen supply sources, reformer  400 , electrolyzer  430  and polymer electrolyte membrane (PEM) electrolyzers  440  are also shown.  
         [0047]     The transportable fuel cell generator may remain on the trailer as shown in  FIG. 4  or be removed ( FIG. 2 ) sleds  450  on the base of an enclosure module  24  are shown in  FIG. 5 .  
         [0048]     Since certain changes may be made in the above apparatus without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description, as shown in the accompanying drawing, shall be interpreted in an illustrative, and not a limiting sense.