Fuel Cell Anode Protection via Steam-Carbon Ratio Control
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Solution Overview
Problem
Fuel cell systems face challenges during shutdown operations due to anode oxidation and carbon deposition, leading to potential electrolyte cracking and decreased efficiency, requiring large amounts of reducing gas and frequent bottle changes, which is costly and inefficient.
Innovation Solution
A fuel cell system with an anode recirculation loop, voltage monitoring, and an anode protection controller that adjusts current and fuel flowrate to maintain a steam-to-carbon ratio, preventing anode oxidation and carbon deposition without additional gas supplies, using existing fuel supply devices for cost-effectiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If reducing gas is supplied to purge the anode chamber during shutdown to prevent re-oxidation, then the anode is protected from oxidation, but large amounts of reducing gas are consumed requiring frequent bottle changes
Solution Approach 1:
The system uses the fuel cell stack itself to generate protecting gas internally during shutdown. The voltage monitoring device detects when the stack voltage drops below a threshold, indicating shutdown conditions, and the controller automatically adjusts the fuel flow rate to maintain a reducing atmosphere in the anode chamber without external reducing gas supply.
Solution Approach 2:
The controller dynamically changes the fuel flow rate parameter based on the detected voltage condition. When voltage drops below the threshold during shutdown, the fuel flow rate is increased to ensure sufficient reducing gas is generated internally to prevent anode oxidation, thereby eliminating the need for external reducing gas bottles.
2Reliability
If fuel flowrate is increased to maintain reducing atmosphere during shutdown, then anode oxidation is prevented, but carbon deposition increases
Solution Approach 1:
The system implements a feedback control mechanism where the voltage monitoring device continuously monitors the fuel cell stack voltage and provides feedback to the controller. Based on this feedback, the controller adjusts the fuel flow rate to maintain optimal conditions that prevent both oxidation and carbon deposition by keeping the steam-to-carbon ratio above the predetermined threshold.
3Object-generated harmful factors
If steam is introduced to remove carbon deposition, then carbon is converted to CO and hydrogen, but this requires additional equipment and operational complexity
Solution Approach 1:
The system converts the potential harmful effect of carbon deposition into a beneficial process by utilizing the existing fuel composition (hydrocarbons) and controlling the steam-to-carbon ratio. The controlled steam presence converts carbon deposits into useful CO and hydrogen through gasification reactions, eliminating the need for separate carbon removal equipment or procedures.
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
Effectively protects the anode from oxidation and prevents carbon deposition during shutdown, reducing operational costs and maintaining system efficiency without the need for additional reducing gas, while ensuring safe operation by controlling steam and carbon ratios.
Implementation Method 1
the Ni in the anode may undergo a re-oxidation, where the Ni may react with the oxygen in the air diffused from the cathode layer or introduced into the anode chamber to form nickel oxide (NiO)
Implementation Method 2
there is a tendency for carbon formation and deposition on anode electrodes. The carbon could be formed by hydrocarbon cracking, Boudouard reaction or carbon monoxide (CO) reduction.
Implementation Method 3
Fuel cells are electro-chemical devices which can convert chemical energy from a fuel into electrical energy through an electro-chemical reaction of the fuel, such as hydrogen, with an oxidizer, such as oxygen contained in the atmospheric air.
Implementation Method 4
The voltage monitoring device is configured for monitoring a voltage of the fuel cell stack.
Data Source
AI summary
A fuel cell system is disclosed, which includes an anode recirculation loop including a fuel cell stack for generating power, a fuel supply device for providing a fuel to the anode recirculation loop, an air supply device for providing air to a cathode of the fuel cell stack, a voltage monitoring device for monitoring a voltage of the fuel cell stack, and an anode protection controller. The anode protection controller decreases a current drawn from the fuel cell stack by a predetermined amount whenever the voltage of the fuel cell stack drops below a predetermined voltage threshold and decreases a fuel flowrate provided to the anode recirculation loop based on the decreased current, so as to maintain a steam to carbon ratio in the anode recirculation loop above a predetermined steam to carbon ratio limit. A shutdown method for the fuel cell system are also disclosed.