PEM FUEL CELL POWER SYSTEMS WITH EFFICIENT HYDROGEN GENERATION

Abstract

Methods and devices for generating power using PEM fuel cell power systems comprising a rotary bed reactor for hydrogen generation are disclosed. Hydrogen is generated by the hydrolysis of fuels such as lithium aluminum hydride and mixtures thereof Water required for hydrolysis may be captured from the fuel cell exhaust. Water is preferably fed to the reactor in the form of a mist generated by an atomizer. An exemplary 750 We-h, 400 We PEM fuel cell power system may be characterized by a specific energy of about 550 We-h/kg and a specific power of about 290 We/kg.

Claims

1. A method of producing power using a fuel cell power system, the method comprising: providing an open cathode PEM fuel cell stack comprising a plurality of fuel cells, each cell having an anode side and a cathode side that enables operation of the cathode side at substantially ambient pressure; feeding water from a water storage to a rotary bed reactor to generate hydrogen by the hydrolysis of a fuel in the reactor; routing hydrogen to the anode side of the fuel cell stack at a rate that is excess of that required by the fuel cell stack for producing power and a recirculation hydrogen stream; enriching recirculation hydrogen exiting the anode with water; and, routing the water-enriched recirculation hydrogen stream to the reactor.

2. The method of claim 1, wherein the feeding water step comprises feeding water from the water storage during start-up and stopping water feed during operation.

3. The method of claim 1 wherein the feeding water step comprises feeding water from the water storage at a first flow rate during start-up and reducing the water feed rate to a rate that is below the first flow rate during operation.

4. The method of claim 1 further comprising converting liquid water from the water storage to a mist comprising a plurality of water droplets using an atomizer and feeding the water mist to the reactor.

5. The method of claim 1 wherein the enriching step comprises increasing the water content of the recirculation hydrogen stream by water exchange with the wet cathode exhaust stream using a humidifier.

6. The method of claim 1 wherein the enriching step comprises: condensing water from the cathode air exhaust; converting the condensed water to a mist comprising a plurality of water droplets using an atomizer; and, entraining the water mist in the recirculation hydrogen stream.

7. The method of claim 1 wherein the enriching step comprises splitting the recirculation hydrogen stream into a first recirculation stream and a second recirculation stream using a 3-way valve and routing the first recirculation stream, to a humidifier and the second recirculation stream directly to the reactor bypassing a humidifier.

8. The method of claim 1 wherein the fuel comprises lithium aluminum hydride.

9. The method of claim 1 wherein the fuel comprises an admixture of lithium aluminum hydride and an additive comprising at least one of AlCl.sub.3, MgCl.sub.2, BeCl.sub.2, CuCl.sub.2, LiCl, NaCl, and KCl.

10. The method of claim 9 wherein the amount of additive in the admixture is <65 wt.-%.

11. The method of claim 4 wherein the atomizer is an ultrasonic water mist generator.

12. A method of producing power using a fuel cell power system, the method comprising: providing a closed cathode PEM fuel cell stack comprising a plurality of fuel cells, each cell having an anode side and a cathode side that enables operation of the cathode side at a pressure above ambient pressure; feeding water from a first water storage to a rotary bed reactor during start-up to generate hydrogen by the hydrolysis of a fuel in the reactor; stopping water feed from the first water storage during normal operation, using condensed water during normal operation; routing hydrogen to the anode side of the fuel cell stack at a hydrogen flow rate sufficient for producing power and a recirculation hydrogen stream; enriching the recirculation hydrogen stream exiting the anode with water; and, routing the water-enriched recirculation stream to the rotary bed reactor, wherein condensed water is removed from the cathode side of the fuel cell stack; wherein enriching further comprises converting water to a mist having a plurality of water droplets; and, wherein the atomizer is an ultrasonic water mist generator that is entrained by the recirculation hydrogen stream into the rotary bed reactor.

13. The method of claim 12 wherein the fuel comprises lithium aluminum hydride.

14. The method of claim 12 wherein the fuel comprises an admixture of lithium aluminum hydride and an additive comprising at least one of AlCl.sub.3, MgCl.sub.2, BeCl.sub.2, CuCl.sub.2, LiCl, NaCl, and KCl.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0055] The foregoing aspects and many of the attendant advantages of this disclosure will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:

[0056] FIG. 1 shows a schematic diagram of an exemplary implementation of an open cathode fuel cell power system with hydrogen recirculation that captures a substantial amount of water required for hydrogen generation.

[0057] FIG. 2 shows a schematic diagram of an exemplary embodiment of the aspect shown in FIG. 1 that does not use a humidifier.

[0058] FIG. 3 shows a schematic diagram of an exemplary aspect of a closed cathode fuel cell power system with hydrogen recirculation that captures a substantial amount of water required for hydrogen generation.

[0059] FIG. 4 shows a schematic diagram of another exemplary aspect of a fuel cell power system with hydrogen recirculation that captures a substantial amount of water required for hydrogen generation from the anode side of the fuel cell.

[0060] FIG. 5 shows a schematic diagram of an exemplary implementation of an open cathode fuel cell power system without hydrogen recirculation or water recovery.

[0061] FIG. 6 shows hydrogen yield as a function of time during hydrolysis of lithium aluminum hydride in a fixed bed reactor.

[0062] FIG. 7 shows hydrogen flow rate as a function of hydrogen yield during hydrolysis of lithium aluminum hydride in a fixed bed reactor.

[0063] FIG. 8(a) to FIG. 8(c) shows various views of an exemplary• rotary bed reactor for use in fuel cell power systems: FIG. 8(a) is cross section view; FIG. 8(b) is an exploded view—(outer tube not shown); and FIG. 8(c) is a perspective view with the outer tube cut open.

[0064] FIG. 9 shows hydrogen yield as a function of time during hydrolysis of lithium aluminum hydride in a both rotary bed and fixed bed reactors.

[0065] FIG. 10 shows hydrogen flow rate as a function of hydrogen yield during hydrolysis of lithium aluminum hydride in a both rotary bed and fixed bed reactors.

[0066] FIG. 11 shows various views of an exemplary 3-way valve for controlling the flow of hydrogen recirculating stream (FIG. 1) to the humidifier.

[0067] FIG. 12(a) shows a sectional perspective view of an exemplary rotary bed reactor; FIG. 12(b) shows the drive assembly that mates with the rotating parts of the reactor.

[0068] The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the disclosure. All reference numerals, designators and callouts in the figures and Appendices are hereby incorporated by this reference as if fully set forth herein. The failure to number an element in a figure is not intended to waive any rights. Unnumbered references may also be identified by alpha characters in the figures and appendices.

[0069] The following detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the fuel cell systems and methods may be practiced. These embodiments, which are also referred to herein as “examples” or ‘options,” are described in enough detail to enable those skilled in the art to practice the present invention. The embodiments may be combined, other embodiments may be utilized or structural or logical changes may be made without departing from the scope of the invention. The following detailed description is, therefore. not to be taken in a limiting sense and the scope of the invention is defined by the appended claims and their legal equivalents.

[0070] In this document, the terms “a” or “an” are used to include one or more than one, and the term “or” is used to refer to a nonexclusive “or” unless otherwise indicated. In addition, it is to be understood that the phraseology or terminology employed herein. and not otherwise defined, is for the purpose of description only and not of limitation.