Ejector-Based Fuel Cell Shutdown Oxygen Removal
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Solution Overview
Problem
Existing fuel cell systems face inefficiencies in quickly and effectively removing oxygen from cathode chambers when switched off, leading to catalyst degradation and increased hydrogen consumption during the process of reacting residual oxygen with hydrogen.
Innovation Solution
A fuel cell system utilizing an ejector as a negative-pressure generation means, connected to the cathode supply path and compressor, to rapidly evacuate cathode operating gas, reducing the amount of hydrogen required for complete reaction with residual oxygen, and eliminating the need for additional energy sources or mechanical parts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hydrogen is supplied to react with residual oxygen in cathode chambers during shutdown, then oxygen removal is achieved, but hydrogen consumption increases and reaction speed is limited by diffusion
Solution Approach 1:
The ejector is activated before hydrogen supply to preemptively remove the majority of oxygen from cathode chambers. By creating negative pressure that draws oxygen out through the ejector, the system performs the bulk of oxygen removal before hydrogen introduction, thereby reducing the amount of hydrogen needed for subsequent reaction and minimizing hydrogen consumption while maintaining catalyst protection.
Solution Approach 2:
The invention employs a pneumatic ejector device that uses fluid dynamics to create negative pressure and extract oxygen from cathode chambers. The ejector utilizes a fluid stream (typically from the cathode supply) to generate a vacuum effect that actively removes oxygen, replacing the passive diffusion-based removal with an active pneumatic extraction process that is both faster and more efficient.
2Reliability
If hydrogen and oxygen are allowed to react in cathode chambers, then oxygen is removed, but the reaction proceeds slowly due to diffusion control
Solution Approach 1:
The ejector performs preliminary oxygen removal before hydrogen introduction, extracting the bulk of oxygen through pneumatic action. This preliminary step reduces oxygen concentration significantly, allowing the subsequent hydrogen-oxygen reaction to proceed more rapidly with less diffusion limitation, thereby increasing overall reaction speed while maintaining complete oxygen removal.
Solution Approach 2:
The pneumatic ejector creates forced convection currents and negative pressure that accelerate oxygen transport out of the cathode chambers. This active pneumatic removal replaces slow diffusion-controlled processes with rapid forced flow, dramatically increasing the speed of oxygen removal while ensuring complete elimination of oxygen before restart.
3Speed
If an ejector is used to generate negative pressure in cathode chambers, then oxygen removal speed increases, but device complexity increases
Solution Approach 1:
The ejector is designed to utilize the existing cathode supply fluid (compressed air or oxygen) as its driving medium. The ejector connects to the cathode supply line and uses the pressurized gas already present in the system to generate the vacuum effect, eliminating the need for separate power sources, motors, or complex control systems. This self-service approach increases oxygen removal speed while minimizing additional device complexity.
Solution Approach 2:
The invention employs a purely pneumatic ejector design that relies on fluid dynamics principles rather than mechanical moving parts. The ejector uses the momentum of a pressurized fluid stream to create a vacuum region that draws oxygen out of the cathode chambers. This pneumatic approach avoids complex mechanical components, reducing device complexity while achieving high-speed oxygen removal.
4Speed
If compressed air is used to drive the ejector, then negative pressure generation is effective, but additional energy consumption occurs
Solution Approach 1:
The cathode supply compressed air serves dual functions: it provides the operating gas for the fuel cell cathode and simultaneously drives the ejector to remove oxygen during shutdown. By making the compressed air supply multi-functional, the system achieves effective negative pressure generation without additional energy consumption, as the same compression process serves both purposes.
Solution Approach 2:
The ejector system is self-powered by utilizing the existing compressed cathode supply gas. No separate compressor, motor, or power source is required for ejector operation. The compressed air already present in the system for cathode operation automatically drives the ejector mechanism, eliminating additional energy consumption while maintaining effective negative pressure generation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system efficiently removes oxygen from cathode chambers with reduced hydrogen consumption, minimizing catalyst degradation and operational costs by using a passive, maintenance-free ejector to generate negative pressure, thereby facilitating quicker system shutdown and startup.
Implementation Method 1
an ejector (40), which is connected in a fluid-conducting manner on the pressure input side to a compressor (33) arranged in the cathode supply path (31) and on the suction side to the cathode chambers (12)
Data Source
AI summary
The disclosure relates to a fuel cell system comprising a fuel cell stack comprising anode chambers and cathode chambers, an anode supply comprising an anode supply path for supplying an anode operating gas to the anode chambers, and an anode exhaust path for discharging an anode exhaust gas from the anode chambers, and a cathode supply comprising a cathode supply path for supplying a cathode operating gas to the cathode chambers and a cathode exhaust path for discharging a cathode exhaust gas from the cathode chambers, and comprising a negative-pressure generation means for generating a negative pressure in the cathode chambers. It is provided that the negative-pressure generation means is designed as an ejector which is connected to a compressor arranged in the cathode supply path on the pressure input side, and to the cathode chambers of the fuel cell stack on the suction side, in a fluid-conducting manner.