Multi-Stack Fuel Cell Shutdown Using Exhaust Air Anode Inerting
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Solution Overview
Problem
Fuel cell degradation during start and stop phases due to hydrogen-air fronts and high voltages, exacerbated by air diffusion and moisture accumulation, is a challenge in multi-stack fuel cell systems, particularly in mobile applications where nitrogen inerting is impractical.
Innovation Solution
A two-phase shutdown process using exhaust air from one fuel cell stack to inert and dry the anode of another, involving depletion operation to reduce oxygen content and controlled valve management to introduce exhaust air into the anode circuit, followed by air drying to prevent moisture accumulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If exhaust air from one fuel cell stack is used to inert the anode of another fuel cell stack during shutdown, then the need for additional inert gas storage is eliminated, but moisture accumulation in the anode circuit may occur
Solution Approach 1:
The system uses its own exhaust air, which is already available from the fuel cell operation, to perform the inerting function. This eliminates the need for external nitrogen storage systems while utilizing a resource already present in the system.
Solution Approach 2:
The inerting process is performed in a first phase before a second drying phase. By preliminarily introducing exhaust air to displace oxygen, then subsequently drying the anode circuit, the system prevents moisture accumulation before it becomes problematic.
2Object-affected harmful factors
If shut-off valves are used to prevent air from entering the cathode during shutdown, then air diffusion is prevented, but pressure loss occurs and valve sealing effectiveness is limited
Solution Approach 1:
Instead of relying solely on shut-off valves to prevent air diffusion, the system creates an inert atmosphere in the anode circuit by introducing exhaust air. This actively displaces oxygen with inert gas, providing more reliable protection against harmful electrochemical reactions compared to passive valve sealing.
3Reliability
If nitrogen is used to render inert the anode before shutdown, then degradation is counteracted, but additional inert gas storage and maintenance are required
Solution Approach 1:
The fuel cell system uses its own exhaust air, already containing sufficient nitrogen from the air supply, to perform the inerting function. This eliminates the need for separate nitrogen storage bottles and refilling infrastructure, reducing system complexity while maintaining degradation protection.
Solution Approach 2:
Instead of discarding the exhaust air as waste, the system recovers and reuses it for the inerting function. The exhaust air, which would otherwise be vented, is redirected to the anode circuit of another stack to displace oxygen and prevent degradation.
4Reliability
If exhaust air is used to inert the anode, then inerting is achieved, but water accumulation may block gas supply during restart
Solution Approach 1:
The inerting process is performed in a first phase before a second drying phase. By preliminarily introducing exhaust air to displace oxygen, then subsequently drying the anode circuit with warm air or exhaust air, the system prevents water accumulation before restart.
Solution Approach 2:
The system changes the temperature parameter by using warm exhaust air or heated air for the drying phase. This temperature increase enhances water evaporation and prevents condensation, ensuring gas supply pathways remain clear during restart.
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
Reduces the risk of water accumulation and electrochemical damage, eliminates the need for additional inert gas storage, and ensures smooth shutdown without pressure loss, thereby extending fuel cell system lifespan.
Implementation Method 1
air diffuses into the cathode, the cell voltages increase and remain there for several hours
Implementation Method 2
the liquid water and/or condensate it contains can cause water to accumulate
Implementation Method 3
the liquid water and/or condensate it contains can cause water to accumulate
Implementation Method 4
Fuel cells are electrochemical energy converters. In particular, hydrogen (H2) and oxygen (O2) can be used as reaction gases. These are converted into electrical energy, water (H2O), and heat with the aid of a fuel cell.
Data Source
AI summary
The invention relates to a method for operating a fuel cell system (1) having multiple fuel cell stacks (100, 200), which each have a cathode (110, 210) and an anode (120, 220), air being supplied to the cathodes (110, 210) via at least one supply air path (111, 211), and exhaust air emitted from the fuel cell stacks (100, 200) being discharged via at least one exhaust air path (112, 212), and the anodes (120, 220) each being supplied with hydrogen via an anode circuit (121, 221). According to the invention, when the fuel cell system (1) is switched off, the exhaust air from a first fuel cell stack (100) is introduced into the anode circuit (221) of a further fuel cell stack (200). Using the introduced exhaust air, the anode (220) of the further fuel cell stack (200) is rendered inert in a first phase of the switch-off process and is dried in a second phase of the switch-off process.The invention also relates to a control device for a fuel cell system (1) for carrying out steps of a method according to the invention.