Method of species exchange and an apparatus therefore

Gas separation: apparatus – Solid sorbent apparatus – Plural solid sorbent beds

Reexamination Certificate

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Details

C096S130000, C096S150000, C096S154000

Reexamination Certificate

active

06780227

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a method, apparatus, and system for the management and control of flow streams. The present invention is a method, apparatus, and system for transferring a portion of a species of a first stream to a second stream, and more specifically to sealing systems and enhancement techniques that can improve the efficiencies of such a species transfer device.
2. Description of Related Art
Conventional heat transfer devices designed to remove both sensible and latent heat are commonly referred to as “enthalpy exchangers.” For example, rotary air-to-air heat exchangers have the ability to transfer heat, water vapor, or both between incoming and outgoing ventilation airstreams. Exchangers of the rotary wheel type typically incorporate a media of heat exchange material (capable of absorbing sensible heat) coated with a desiccant material (capable of adsorbing moisture, and, thus latent as well as sensible heat). The incoming airstream is directed through one sector of the slowly revolving wheel while an outgoing airstream is directed through another sector of the wheel. Passages formed in the heat exchange media permit passage of the streams through the wheel.
Use of these devices in ventilating, heating and/or air conditioning systems can reduce heating and cooling costs, while providing fresh outdoor air to lower internal air pollution levels. Heat and moisture are simultaneously absorbed from the warmer airstream at the one sector and removed from the wheel by the cooler, dryer airstream at the other sector. For stationary periodic flow regenerators, the airstream is alternately directed through the entire exchange device first in one direction and then in the opposite direction.
In a broader sense, a stream conditioning device like an enthalpy exchanger is a management device of species potential between streams flowing through the exchanger, wherein the species are, for example, latent and sensible heat. Species transfer devices that can be used particularly well in connection with a fuel cell engine are disclosed in U.S. Pat. No. 6,013,385 and U.S. application Ser. No. 09/447,764, both herein fully incorporated by reference. Such species transfer devices can be positioned in the path of at least one reactant stream of a fuel cell's inlet or outlet, which transfer devices condition that stream to improve the efficiency of the fuel cell.
In most fuel cell applications, relatively cool atmospheric air is used as the cathode reactant. The air must be heated and humidified before it is injected into the stack, or the membranes will dehydrate and the reaction will stop. In order to maintain proper operating conditions for the fuel cell, the temperatures and humidities of the anode and cathode circuits must be precisely controlled to avoid drying out the electrolyte or otherwise damaging the fuel cell, and thereby stopping the flow of electricity from the fuel cell. A sensible and latent heat transfer device such as an enthalpy wheel can be used for conditioning the pressurized oxidant. The enthalpy wheel operates by removing both sensible and latent heat from the fuel cell cathode exhaust stream to heat and humidify the cathode inlet stream.
The conventional enthalpy transfer device, such as a rotating heat exchanger for HVAC systems and the like, comprises a housing assembly incorporating a first and second inlet, and a first and second outlet, the housing assembly containing a rotatable heat wheel of exchange media with a desiccant. A heat-saturated first stream is routed through the first inlet and to an active section of the heat wheel, where sensible and latent heat are collected by the enthalpy wheel as the first stream passes therethrough via channels of the exchange media. Upon passing through the wheel, the first stream exits the assembly at the first outlet. As the enthalpy wheel rotates, this sensible and latent heat is released into the second stream, which second stream passes through the channels of the exchange media that were just traversed by the first stream. The rotation of the wheel causes each channel of the media to be exposed to the first stream, and then through a portion of heat wheel rotation, the second stream, alternately. The second stream thus accepts the heat of the first stream absorbed by the media and adsorbed by a desiccant of the heat wheel, and exits the housing via the first outlet. By controlling the rate of rotation of the enthalpy wheel and the rate of heat transfer, the relative humidity and wet bulb temperature of the streams can be controlled.
Through continued research and testing, it has been found that species transfer devices like those previously described can be improved upon in several respects. Namely, species transfer efficiencies can be optimized with certain modifications to the conventional transfer device. A first improvement is the provision of superior sealing systems limiting stream mixing during species transfer. The sealing system would prevent the higher-pressure stream from escaping into the lower-pressure stream. Preferably, the two streams do not mix at all in the housing. Yet another improvement includes the use of enhancement techniques to destabilize the thermal boundary level developed in the media, thus enhancing heat transfer. Further advantages are gained by varying the geometry of the media wheel, the types of media material used and the speed of rotation of the wheel, among many others. Another improvement includes formulating the heat wheel to resist changes in dimensions in response to changes in temperature. Thus it can be seen that a need yet exists for a lightweight and efficient means of species transfer that can be used in a number of different environments. It is to the provision of such a species transfer device meeting these and other needs that the present invention is primarily directed.
BRIEF SUMMARY OF THE INVENTION
Briefly described, in a preferred form, the present invention is a species transfer method, device, and system capable of managing species potential in a flow. In one aspect of the present invention, a stream conditioning system for a fuel cell gas management system is disclosed. The stream conditioning system manages species potential in fuel cell reactant streams. In another aspect, the species transfer device can comprise a media element, an optional sealing system and an optional enhancement system.
The media element is a rotatable exchange media element enclosed within a housing assembly. In one aspect of the invention, the media element preferably does not expand or contract significantly in response to changes in temperature. In another aspect of the present invention, the media element comprises an exchange medium, preferably a ceramic medium, more preferably a magnesium aluminum silicate having an average linear coefficient of thermal expansion (CTE) at 25 to 800° C. of less than about 20×10
−7
/° C., preferably less than about 10×10
−7
/° C., most preferably less than about 5×10
−7
/° C. In another aspect of the invention, the exchange medium has a CTE from about 1×10
−7
/° C. to about 20×10
−7
/° C., preferably about 2×10
−7
/° C. to about 10×10
−7
/° C., most preferred from about 3×10
−7
/° C. to about 8×10
−7
/° C. Having a CTE at 25 to 800° C. of less than about 20×10
−7
/° C. enables the exchange medium to preserve the integrity of seals separating different streams, or to avoid seals entirely, thereby preventing separate streams from intermixing or leaking. Exemplary transfer media include but are not limited to ceramics and ceramic composites including but not limited to magnesium aluminum silicates. Suitable transfer media include natural or synthetic cordierite, cordierite containing substances, modifed cordierites, or semi-cordierites. The media element can be a unitary cylinder of exchange media, or can comprise a plurality of cylindrically axial wedge

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