Fuel Cell Anode Pressure Control During Shutdown Cooling
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Solution Overview
Problem
Fuel cell systems face challenges in maintaining anode pressure at atmospheric levels during shutdown, leading to potential oxygen inflow due to poor air cutoff valve airtightness and pressure changes caused by temperature and water condensation, which can reduce system lifetime.
Innovation Solution
A method and system that measure operating and outside temperatures, atmospheric pressure, and calculate a target anode pressure to adjust air supply and use a heater to exhaust oxygen, with an anode pressure regulator to maintain target pressure, ensuring the anode pressure matches atmospheric pressure during shutdown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the air cutoff valve is used to block air supply during shutdown, then oxygen inflow to the anode is prevented, but the valve airtightness degradation causes oxygen to leak into the anode due to pressure difference
Solution Approach 1:
The patent applies preliminary anti-action by actively pressurizing the anode with a nitrogen supply device before and during shutdown to create positive pressure that counteracts the pressure difference causing oxygen leakage. This preemptive pressure equalization prevents oxygen from leaking through the air cutoff valve even when airtightness degrades, directly resolving the contradiction between valve reliability and oxygen infiltration prevention.
Solution Approach 2:
The patent introduces nitrogen as an intermediary gas to maintain anode pressure. The nitrogen supply device acts as a mediator between the external environment and the anode, providing a inert gas that prevents oxygen from entering the anode while maintaining pressure balance, thus solving the oxygen leakage problem caused by air cutoff valve airtightness degradation.
2Object-affected harmful factors
If the COD heater is used to exhaust oxygen from the anode, then oxygen is removed, but the anode pressure decreases and becomes negative, increasing restart time
Solution Approach 1:
The patent merges the nitrogen supply function with the pressure maintenance function. The nitrogen supply device simultaneously performs oxygen displacement and pressure maintenance, eliminating the need for separate pressure recovery operations after heater operation. This combination prevents negative pressure formation and reduces restart time while still achieving oxygen exhaustion.
Solution Approach 2:
The patent changes the pressure parameter management by continuously maintaining positive anode pressure through nitrogen supply during and after heater operation. This parameter control prevents the pressure drop that would otherwise occur during oxygen exhaustion, avoiding negative pressure states and reducing the time required for system restart.
3Temperature
If the fuel cell stack temperature decreases during shutdown, then the system cools down, but the anode pressure decreases due to temperature and water condensation, making the anode vulnerable to oxygen inflow
Solution Approach 1:
The patent applies the counterweight principle by using nitrogen supply to counteract the pressure decrease caused by temperature reduction and water condensation. The continuous nitrogen injection provides a pressure counterbalance that offsets the natural pressure drop during cooling, maintaining positive anode pressure and preventing oxygen infiltration throughout the shutdown cooling process.
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
This approach prevents anode negative pressure and reduces oxygen inflow, thereby minimizing physical stress and extending fuel cell system durability and lifetime.
Implementation Method 1
connecting a resistor such as a cathode oxygen depletion (COD) heater to react oxygen of the anode with hydrogen
Implementation Method 2
A fuel cell system includes a fuel cell stack for generating electrical energy through electrochemical reaction of reaction gases (hydrogen that is a fuel gas and oxygen that is an oxidant gas)
Implementation Method 3
a decrease in the pressure caused by condensation of water in a vapor state after shutdown of the fuel cell
Data Source
AI summary
A fuel cell system of this disclosure includes a fuel cell stack; a water supply unit to selectively supply cooling water or heated water to a cooler of the fuel cell stack, and including a heater for heating the cooling water; an air cutoff valve to supply air to an anode of the fuel cell stack and drain a residue from the anode; an anode pressure regulator to drain the residue from the air cutoff valve and control a pressure of the anode; sensors to measure an operating temperature of the fuel cell stack, an outside air temperature, and an atmospheric pressure; and a controller to calculate a target pressure for the anode, control the air cut-off valve, control the anode pressure regulator, and stop an operation of the heater when a stack voltage of the fuel cell stack is lower than a predetermined reference voltage.