Technical Field

[0001] In a fuel cell power plant, a large number of porous, hydrophilic wafers having hollow centers and water holes are aligned with each other in a stack by o-ring seals in grooves, or by adhesive or bonding. The wafers include radial air channels, which receive air from a blower, and semi-peripheral water channels leading from inlet water holes to outlet water holes. The water in the porous wafers evaporates into the air, thus both cooling and humidifying the inlet air. The water flushes minute contaminants which are thereafter removed by a demineralizer. The tortuous route of the air muffles blower noise.

Background Art

[0002] It is typical in the fuel cell art to utilize enthalpy recovery devices which transfer enthalpy from the cathode exhaust air to the cathode inlet air, such as by means of membranes. However, such devices cannot provide the desired humidity without also raising the temperature of the inlet air. In some situations, such as in desert heat, reducing the temperature of the air provided to the cathodes is more important than energy conservation, and therefore typical enthalpy recovery devices cannot be used.

[0003] The process air provided to the cathodes of the fuel cell stack must be sufficiently humidified so as to avoid dry spots that result in reduced performance and reactant crossover, whereby the hydrogen and air can mix together and provide localized heating of the cell, thereby causing damage to the membrane electrode assembly. In many systems, humidification is provided externally of the fuel cell by means of

membranes, similar to the proton exchange membrane, but without catalysts thereon. In other systems, the inlet end of each fuel cell planform is devoid of catalyst so that the incoming air can absorb water from the fuel cell before reaching the catalycized portion of the fuel cell planform. However, this reduces the operative area of the fuel cell to an extent which can roughly equate to about 10% of the number of cells in a stack which is so designed. Improved output power can thus be achieved by eliminating the in-cell humidification zones.

[0004] Depending on the pressure and flow requirements of the blower, both the air blower inlet and outlet may generate significant amounts of noise. In many situations, noise is not a problem. But in some situations, such as in automotive applications, excessive noise may be intolerable. It is desirable to muffle the inlet and exit noise of the process air blower or pump.

[0005] Fuel cell stacks typically have filters to eliminate contaminants in the air provided to the cathodes. However, minute, particulate

contaminants still enter the air stream into the cathodes after

contemporary filtration. In particular, silicones that can reduce the hydrophilicity of the porous, hydrophilic reactant gas flow field plates (referred to also as water transport plates) are not blocked by a filter.

Thus, additional treatment is required.

Summary

[0006] The subject matter herein comprises a fuel cell stack inlet air processor which controls the temperature, including cooling, of the air that is provided to the cathodes of a fuel cell power plant. The inlet air processor also controls the relative humidity of the air provided to the cathodes. Because the processor also scrubs a portion of the air passing through it, the inlet air processor continuously removes at least a portion of airborne minute contaminants which are present in the air provided to it by a blower, even though that air is filtered; this is particularly true of silicones which reduce the hydrophilicity of porous, hydrophilic air flow field plates (also referred to as water transport plates). In addition, the inlet air processor muffles the air blower inlet noise and outlet noise which would otherwise be excessive in the surrounding environment.

[0007] The inlet air processor herein comprises a plurality of porous, hydrophilic wafers. The wafers include radial air grooves to pass air from the periphery of each wafer, over the wafer to a central, cylindrical space, which is the air outlet. Semi circumferential water grooves lead from a circulating water inlet to a water outlet. If the air grooves are on the front face of a porous, hydrophilic wafer and the water grooves are on an adjacent, liquid permeable wafer, the front surface of the water wafer is in intimate contact with the back surface of the air wafer. Or, the water grooves may be on the back surface of the same permeable wafer, having air grooves on its front surface. Water therefore transfuses through the air wafer and evaporates into the air as it passes through grooves to the air outlet, as controlled by the pressure and temperature of the water and air provided to the air inlet processor. In this manner, both the temperature and the relative humidity of the air entering the central, cylindrical opening (the air outlet) are controlled. In addition, the outlet water temperature is controlled by means of a selectively bypassed heat exchanger, and the water also passes through a demineralizer, thereby removing originally- airborne particulate contaminants, such as silicones. Because the route of passage of the air is somewhat of a labyrinth, the inlet air processor also muffles the noise of the inlet and outlet of the air blower.

[0008] This modality of humidifying fuel cell inlet air is more efficient than known methods, providing a saving of space.

[0009] Other variations will become more apparent in the light of the following detailed description of exemplary embodiments, as illustrated in the accompanying drawings.

Brief Description of the Drawings

[0010] Fig. 1 is a stylized, perspective view illustrating in general the manner in which an inlet air processor herein may relate to a pair of fuel cell stacks.

[0011] Fig. 2 is a simplified, stylized block diagram, partially in perspective, of a fuel cell power plant utilizing the inlet air processor of Fig. 1.

[0012] Fig. 3 is a sectioned, side elevation view of the inlet air processor of Fig. 1.

[0013] Fig. 4 is a front elevation view of an air disk for use in the processor of Fig. 3.

[0014] Fig. 5 is a rear elevation view of the air wafer of Fig. 4. [0015] Fig. 6 is a front elevation view of a water wafer for use in the processor of Fig. 3.

[0016] Fig 7 is a rear elevation view of the water wafer of Fig. 6.

[0017] Fig. 8 is an expanded, perspective view of the front surfaces of the water and air wafers of Figs. 4-7.

[0018] Fig. 9 is an expanded, perspective view of the rear surfaces of the water and air wafers of Figs. 4-7, with grooves 71 omitted for simplicity.

Mode(s) of Implementation

[0019] Referring to the fuel cell power plant 19 shown in Fig. 1 , a fuel cell inlet air processor 20 in accordance herewith is shown, in a stylized fashion, as it may serve two fuel cell stacks. A blower 22 which provides process air to the inlet air processor may, for instance, be mounted underneath the fuel cell stacks 27, 28 and the inlet air processor 20 may be mounted in front of the fuel cell stacks 27, 28. In the particular embodiment described herein, the processed air flows through conduits 30, 31 to the respective fuel cell stacks 27, 28.

[0020] In Fig. 2, a stylized perspective and block diagram illustrates the situation wherein the electrical output of the fuel cells, such as on lines 34 and 35, is connected to a contemporary converter 37. The converter 37 may provide three-phase electrical AC power on a group of electrical lines 38 which may connect to a load 40, such as a utility grid, a building, or a vehicle, all under responses to and commands from a controller 41. The lines 38 also provide power to a three-phase blower motor 43 which can operate the blower 22. The blower may also be configured to be started up with a low voltage motor 45, which is powered by a battery (not shown), such as at about 28 volts. Battery operation of the blower provides sufficient air for start up of the fuel cell power plant, which then generates enough power to run the blower with increasing loads. The blower may be a contemporary turbo pump of the type utilized in vehicle superchargers. Depending on the load and other factors, the blower motor 33, which operates the blower 22 during normal power generation by the fuel cells, may be operated with power of as much as 550 volts AC. In other circumstances, the voltage of the blower motor 43 may be selected so as to be compatible with other utilization of power generated by the fuel cell stacks 27, 28.

[0021] Referring to Fig. 3, an embodiment of the subject matter hereof comprises a plurality of pairs of stationary air wafers 52 and water wafers 53. Alt of the wafers 52, 53, in this embodiment, are porous and

hydrophilic disks. The front surface of the air wafer 52 is shown in Fig. 4 and the back surface of the air wafer 52 is shown in Fig. 5. The air wafer 52 has a plurality of radial channels 56, 57 shown in white in Fig. 4, which receive air in the outermost ring of channels 56, that is delivered from the air blower 52 to the wafers through an air inlet transition 58 (Fig. 3), and deliver the air through the innermost ring of channels 57 to a central, cylindrical opening 59, which is the air outlet. Once air reaches the opening 59, it passes through spaces 60 in tensioning brackets 61 to air outlet channels 58 at either end of the inlet air processor 20. The air outlet channels 58 are connected with the conduits 30, 31 to provide process air to the cathode flow fields within the fuel cell stacks 27, 28.

[0022] The front surface of the water wafer 53 is shown in Fig. 6 and the rear surface of the water wafer 53 is shown in Fig. 7. The front surfaces of the air wafers 52 are adjacent to the rear of the water wafers 53. The front surfaces of the water wafers 53 have a plurality of concentric, semi-circular channels 62, shown in white in Fig. 6, leading from a coolant inlet hole 63 to a coolant outlet hole 64. Coolant is provided to the inlet holes 63 from a coolant inlet port 67 (Fig. 3), and coolant passes from the outlet holes 64 to a coolant outlet port 68 (Fig. 3).

[0023] The water circulating around the passages 62 from the inlet hole 63 to the outlet hole 64 is in contact with concentric grooves 71 in the back surface of the air wafers 52. The water, having about 2 kPa (1.7 psi) pressure higher than the pressure of air in the channels 56 of the air wafer 52, evaporates into the air within the air wafer 52. As described

hereinafter, parameters are adjusted to reach a relative humidity in the air of about 60% as it reaches the central, cylindrical opening 59.

[0024] The air wafers 52 have water inlet holes 72 and water outlet holes 73 which are aligned with the holes 63, 64 in the water wafers 53. The alignment of the holes provides feed-through so that the coolant can flow all the way from the inlet port 67 to the inlet holes 63, 72 at the far left of Fig. 3. The coolant will flow through the outlet holes 64, 73, at the far left of Fig. 3 to the outlet port 68.

[0025] In this embodiment, the alignment of the wafers is maintained by o-ring seals within channels as illustrated in Figs. 8 and 9. The water inlet holes 63 in the water wafers 53 are sealed to the water inlet holes 72 in the air wafers 52 by o-ring seals 78 (Fig. 8 and Fig. 9) which fit into grooves 79 in the front surface of the air wafers 52 and into grooves 83 (Fig. 9) on the backside of the water wafers 53. Similarly, the water outlet holes 64, 73 are sealed by o-rings 85 that fit into channels 87 in the front surface of the air wafers, mating with channels 88 in the rear of the water wafers 53. To ensure that the water in the water wafers 53 is transferred only to the air in the air wafers 52, o-ring seals 91, 92 fit into grooves 94, 95 (Fig. 9) on the rear of the air wafers 52 and grooves 98, 99 (Fig. 8) on the front surface of the water wafer 53. Because the water inlet holes and water outlet holes are sealed only between the rear surface of each water wafer and the front surface of the corresponding air wafer to the left of that water wafer, the water will transfuse through the water wafer and move around freely in the thin layer of space between the outer and inner o-ring seals 9 , 92, and thereby flood the air grooves 56, 57 in the front surface of that air wafer 52.

[0026] At the completion of assembly, as illustrated in Fig. 3, the wafer pairs are held together with their water holes in alignment as just described, by means of a tie-rod 101 which is secured at either end by nuts and washers 102. The tie-rod 101 is anchored in holes in the tensioning brackets 61 which are a part of pressure plates 105, 106, within which the air outlet ports 64 are formed. The pressure plates 105, 106 have grooves that receive o-ring seals 109, 110 which contact the inner surface of end plates 112, 113.

[0027] The whole assemblage fits within a cylinder 116 which has an appropriate cutout to receive air from the air inlet transition 58. The structure of wafer pairs being held together by the tie-rod 101 is similarly aligned with the pressure plate 105 by means of an o-ring groove (not shown) in the pressure plate 05 which cradles an o-ring (not shown) that nestles into the grooves 83, 88 in the back of the first coolant plate 53 at the right end as seen in Fig. 3. The wafer pairs 52, 53 are disks which have a lesser diameter than the cylinder 116, providing an outer space 117 in the shape of a hollow cylinder (the air inlet to the wafers) which allows air to not only transfer toward the end-most pairs of wafers, but also to transfer circumferentially around the wafers. This assures that air enters most of the grooves 56 in most of the air wafers 52.

[0028] In operation, with the blower 22 being operated by the motor 43, air passes down through the transition 58, all around the wafers 52, 53 in the void 117, and into the slots 56, 57 of the air wafers 52. The air passes through the slots 57 to reach the central, cylindrical opening 59 (the air outlet). Because the air wafer 52 is porous and hydrophilic and the slots 62 of each water wafer 53 are in intimate contact with the back surface 71 of the air wafer 52 to its right, some of the water in the pores of the air wafer will evaporate into the air as it passes through the slots 56, 57 of the air wafer 52. The desired relative humidity of the air which enters the air inlet stream in the central cylindrical space 59 can be controlled depending on the pressure and pressure head of the blower 22, the temperature of the air and the temperature of the water, which is recycled through a conventional heat exchanger to remove heat therefrom (described hereinafter).

[0029] As an example, the compressor 22 providing air to the cathodes through the inlet air processor 20 at between about 20 kPag and 90 kPag (2.9 psi - 13.1 psig), the blower exit temperature, in a very warm

atmospheric environment, could exceed 100 C (212 F), and needs to be cooled prior to entering the cathodes. The water cools the incoming air, which is typically controlled to be between about 45 C (113 F) and 66 C (151 F).

[0030] In a water circulating means of Fig. 2, water is drawn from the outlet port 68 in a conduit 105 by a pump 106. Some or all of the water then passes through an air cooled heat exchanger 108, except to the extent that the heat exchanger is bypassed through a controller-operated valve 109. The water (or optionally, some portion of the water) then passes through a demineralizer 112, where it is filtered, and then enters the inlet port 67 via a conduit 114. The water pressure entering the inlet port can be controlled either by controlling the operation of the pump 106, or by means of a controlled, pressure reduction valve (not shown). The temperature of the water entering the inlet port 67 is controlled by the bypass valve 109 in response to the controller 41. Conventional water replenishment apparatus (not shown) makes up for water taken up into the inlet air. Recirculating water is passed through the demineralizer to remove any minute contaminants, especially previously-airborne silicones, a portion of which are taken up from the air in the non-evaporating portion of the water.

[0031] The water channels are adjacent to a thin layer of space between the back of an air wafer (which is to the left of a water wafer) and the front of that water wafer. The air wafer is made porous and hydrophilic to transfer water from this thin layer of space to the air in the air channels on the front surface of the air wafer. Similarly, the water wafer is made porous and hydrophilic so that water will pass right through it to reach the channels on the front surface of the air wafer to the right of that water wafer, by being in intimate contact with the front surface of that air wafer.

[0032] Instead of sealing the air and water passageways with o-rings and grooves as described hereinbefore, the wafers 52, 53 could be bonded together such as with adhesives, thermoplastic or other bonding methods. The bonding would occur on lands in the spaces where the embodiment of Figs. 4-7 have grooves for the o-rings, thereby not to inhibit the passage of fluids in the grooves as described hereinbefore.

[0033] In another embodiment, the air grooves 56, 57 shown on the face surface of the wafer 52 in Fig. 4 could be provided on one surface of a wafer, and the water grooves 62 shown in Fig. 6 could be provided on an opposite surface of that wafer.

[0034] Another embodiment may provide for the air channels 56, 57 and the water channels 62 to be on opposite surfaces of the same wafer, but not adhered to adjacent wafers. Instead, a fluid permeable or impermeable wafer or plate will be provided with grooves and o-rings on both of its surfaces so as to seal the air channel surface of one wafer as seen in Fig. 5 and the water channel surface of an adjacent wafer as seen in Fig. 7.

[0035] Thus, the modality herein may be achieved with wafers which are dedicated either to air or water or with singular wafers having air channels on one surface and water channels on the opposite surface. A method of forming the wafers into a unitary stack to provide a fuel cell inlet air processor 20 may be manifested in a variety of ways.

[0036] Although disclosed herein as disks, the air wafers 52 and the water wafers 53, and any gasketed plate, if required, need not be circular. In this application, the term "wafers" shall include "disks", but the wafers need not be circular, either on the periphery or on the perimeter of the central opening. Thus, the terms "disks" or "wafers" includes the circular wafers disclosed hereinbefore, and porous, hydrophilic wafers of other shapes that include sufficient space (see 117, Fig. 3) and channels for air leading from the periphery of the wafer to the perimeter of a central space, and sufficient channels for water leading from the water inlets to the water outlets, and fluid communication between the air and water channels.

[0037] Since changes and variations of the disclosed embodiments may be made without departing from the concept's intent, it is not intended to limit the disclosure other than as required by the appended claims.