Fuel Cell Startup Shutdown Procedures Oxidation Prevention
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Solution Overview
Problem
Fuel cell assemblies face performance decay due to oxidation of carbonaceous catalyst supports during shutdown, affecting operational life, and existing techniques do not adequately address this issue for extending the useful life of fuel cell systems.
Innovation Solution
Implementing unique startup and shutdown procedures involving heating and purging with a hydrogen-nitrogen mixture, disabling auxiliary electrical loads, and controlled temperature reductions, along with periodic purging with hydrogen-nitrogen gas to minimize performance loss and prevent oxidation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional shutdown procedures are used, then the fuel cell assembly can be shut down quickly, but oxidation of the carbonaceous catalyst support occurs causing performance loss
Solution Approach 1:
The patent applies preliminary action by implementing a multi-stage shutdown procedure that prepares the fuel cell stack before final shutdown. The procedure includes initial shutdown at operating temperature with controlled reactant flows, followed by cooling to intermediate temperature, and finally to storage temperature. This staged approach prevents oxidation of the carbonaceous catalyst support by maintaining proper atmospheric conditions throughout the cooling process, thereby extending operational life while managing shutdown time systematically.
2Loss of time
If the fuel cell assembly is cooled rapidly during shutdown, then shutdown time is reduced, but performance decay increases due to oxidation
Solution Approach 1:
The patent applies segmentation by dividing the shutdown and cooling process into distinct stages: (1) initial shutdown at operating temperature with controlled reactant flows, (2) cooling to an intermediate temperature while maintaining protective atmosphere, and (3) final cooling to storage temperature. This segmented approach allows each stage to be optimized independently, preventing oxidation during cooling while managing overall shutdown time efficiently.
3Power
If auxiliary electrical loads are not disabled during heating, then power availability is maintained, but energy consumption and potential damage increase
Solution Approach 1:
The patent applies preliminary action by disabling auxiliary electrical loads before initiating the heating process during startup. This prevents excessive energy consumption and potential damage to the fuel cell stack that could occur if auxiliary loads operated during the vulnerable heating phase. Power availability is restored after the stack reaches operational temperature and is ready to generate power.
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 described procedures significantly extend the operational life of fuel cell assemblies by reducing performance decay and maintaining efficiency, thereby reducing the cost of electrical power generation.
Implementation Method 1
Fuel cells are well known. Typical arrangements include a fuel processing portion and a fuel cell stack or fuel cell portion. Fuel cell assemblies operate in a known manner to generate electrical power.
Implementation Method 2
heating at least the fuel cell portion and the fuel processing portion to bring the heated portions to a selected operational temperature
Implementation Method 3
cooling the fuel cell portion to a selected storage temperature
Implementation Method 4
oxidation of the carbonaeous catalyst support resulting from the combined effects of temperature and electrochemical potential causes performance loss
Data Source
AI summary
A fuel cell assembly (20) has an extended operational life, in part, because of unique startup and shutdown procedures used for operating the fuel cell assembly. In disclosed examples, a purge gas mixture of hydrogen and nitrogen includes less than 2% hydrogen for selectively purging portions of the assembly during a startup or shutdown procedure. In a disclosed example, the hydrogen-nitrogen mixture contains less than 0.1% hydrogen.