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Integration of Fuel Cells and Electrically Driven Oxygen Separation Systems

IP.com Disclosure Number: IPCOM000019370D
Publication Date: 2003-Sep-12

Publishing Venue

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Abstract

Solid electrolyte membranes that have a high oxygen-ionic conductivity but negligible electronic conductivity form the basis of three important technologies: oxygen sensors, electrically driven oxygen generators, and solid oxide fuel cells. The first is commercial; the other two are emerging technologies. Electrically driven oxygen transfer membrane systems (to be abbreviated herein as SEOS, for Solid Electrolyte Oxygen Systems) have applications in medical oxygen generators and oxygen removal from process gas streams. Conventionally, DC power to SEOS is delivered from AC grids via AC-to-DC conversion. Fuel cells are established as a reliable power source for space and military applications, and are also the target of development efforts in light of their high efficiency (fuel to electric power) and low emissions (regulations). Fuel Cells generate DC power. By integrating the two technologies, the present invention seeks to avoid the power losses associated with AC/DC conversion. The invention will also promote the industrial use of oxygen in general, and SEOS in particular, in geographic areas that do not have traditional electric power grids, but have access to fuel (e.g., natural gas). Further, the invention can fulfill a need for compact/portable SEOS devices; alternatively, the invention will yield a device that can generate oxygen and or electric power. The Invention

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Integration of Fuel Cells and Electrically Driven Oxygen Separation Systems

Introduction

Solid electrolyte membranes that have a high oxygen-ionic conductivity but negligible electronic conductivity form the basis of three important technologies: oxygen sensors, electrically driven oxygen generators, and solid oxide fuel cells. The first is commercial; the other two are emerging technologies.
Electrically driven oxygen transfer membrane systems (to be abbreviated herein as SEOS, for Solid Electrolyte Oxygen Systems) have applications in medical oxygen generators and oxygen removal from process gas streams. Conventionally, DC power to SEOS is delivered from AC grids via AC-to-DC conversion.
Fuel cells are established as a reliable power source for space and military applications, and are also the target of development efforts in light of their high efficiency (fuel to electric power) and low emissions (regulations). Fuel Cells generate DC power.
By integrating the two technologies, the present invention seeks to avoid the power losses associated with AC/DC conversion. The invention will also promote the industrial use of oxygen in general, and SEOS in particular, in geographic areas that do not have traditional electric power grids, but have access to fuel (e.g., natural gas). Further, the invention can fulfill a need for compact/portable SEOS devices; alternatively, the invention will yield a device that can generate oxygen and or electric power.
The Invention

The present invention is a process or a device that encompasses the use of any type of fuel cell (i.e., phosphoric acid, polymer electrolyte membrane, alkaline, molten carbonate, solid oxide, etc.), singly or in various combinations, to power SEOS oxygen generators/removers, the fuel cell(s) and the SEOS integrated in the same device or housed in separate enclosures. By way of illustration, examples are given below for combining solid oxide fuel cells (SOFC) with SEOS.

In a conventional SOFC[1], the fuel cell is kept between 830-1030C, the fuel gas is fed at 800C, and the air enters at 400-600C.
SOFCs operating at a wider range of temperatures (450-950C) are goals of exploratory research[2].
SEOS, in principle, can operate in the same temperature range as the SOFC. In practice, SEOS (especially SEOS for oxygen removal as opposed to oxygen production) may be limited to a narrower temperature range (700-800C at present, for example) because of the materials considerations of gas-tight seals.
So, SOFC/SEOS configurations depend on the operating temperature(s). The configurations also depend on geometry (e.g., whether the devices are tubular or planar), stream-location (e.g., in the tubular SOFC, whether the fuel stream is inside or outside the tubes), flow arrangement (i.e., whether the flows are in series or parallel), and, electrical connections (series or parallel).
Methods of Housing Tubular SOFC and SEOS Systems
When the SOFC operates at a higher temperature (e.g., 950C versus 800C fo...