SOFC Stop Control for Oxidant Backflow and Reformed Gas Heat
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Solution Overview
Problem
In fuel cell systems, when the power generation stops, the reformed gas can exceed the upper heat-resistance temperature limit of the fuel cell stack, and miniaturization shortens the passage connecting the fuel cell stack and combustor, leading to rapid backflow of oxidant gas, potentially causing heat damage due to immediate additional fuel supply.
Innovation Solution
A fuel cell system with a solid oxide fuel cell, an oxidant gas supply device, a reforming unit, and a combustion unit, where a control unit manages the fuel supply to prevent oxidant gas backflow and controls the temperature of the reformed gas by gradually reducing fuel supply upon system stop, ensuring it does not exceed the heat-resistance limit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional fuel is supplied to prevent oxidant gas backflow, then the oxidant gas backflow is prevented, but the reformed gas temperature exceeds the upper heat-resistance temperature limit of the fuel cell stack
Solution Approach 1:
The control unit supplies fuel to the reforming unit before the additional fuel supply to lower the reformed gas temperature in advance. This preliminary action ensures that when additional fuel is supplied to prevent oxidant gas backflow, the reformed gas temperature does not exceed the upper heat-resistance temperature limit of the fuel cell stack.
Solution Approach 2:
The system applies a counter-action by supplying fuel to the reforming unit before the additional fuel supply, which creates a cooling effect that counteracts the temperature rise caused by the additional fuel supply and heat exchange with combustion gas.
2Volume of moving object
If the system is miniaturized, then the system size is reduced, but the passage connecting the fuel cell stack and combustor becomes shorter, causing faster oxidant gas backflow
Solution Approach 1:
The control unit supplies fuel to the reforming unit before the additional fuel supply to create a pressure and temperature condition that counteracts the rapid backflow of oxidant gas caused by the shortened passage in miniaturized systems.
Solution Approach 2:
By supplying fuel to the reforming unit in advance, the system prepares the reformed gas flow to prevent rapid oxidant gas backflow through the shortened passage, ensuring temperature control while maintaining compact dimensions.
3Productivity
If fuel supply is stopped immediately, then the power generation stop is rapid, but reformed gas remains in the reformer and undergoes excessive heat exchange, causing temperature to rise above safe limits
Solution Approach 1:
The control unit supplies fuel to the reforming unit before stopping additional fuel supply, ensuring that reformed gas is continuously produced and flow is maintained, which prevents excessive heat exchange and temperature rise during the power generation stop.
Solution Approach 2:
The system maintains continuous fuel supply to the reforming unit during the transition from power generation to stop, ensuring uninterrupted reformed gas flow that prevents excessive heat exchange and temperature rise, while still achieving rapid power generation stop.
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 heat damage to the fuel cell stack by maintaining the temperature within safe limits during system stop, allowing for controlled fuel supply and reducing the risk of heat-related damage.
Implementation Method 1
a reforming unit that supplies the reformed gas to the fuel cell, and wherein the reforming unit can reform the fuel into the reformed gas by exchanging heat with a combustion gas produced by the combustion unit
Implementation Method 2
a combustion unit that combusts discharged gases of the fuel cell
Data Source
AI summary
A fuel cell system includes a solid oxide fuel cell capable of generating power by receiving a supply of a reformed gas and an oxidant gas; an oxidant gas supply device that supplies the oxidant gas to the fuel cell; a reforming unit that supplies the reformed gas to the fuel cell; a fuel supply device that supplies a fuel which is a raw material for the reformed gas to the reforming unit; a combustion unit that combusts discharged gases of the fuel cell, wherein the reforming unit can reform the fuel into the reformed gas by exchanging heat with a combustion gas produced by the combustion unit; and a first control unit controls the fuel supply device to additionally supply the fuel to the fuel cell through the reforming unit in order to prevent the oxidant gas from flowing in from downstream of a fuel electrode of the fuel cell at the time of stopping the system. The fuel cell system further includes a second control unit that controls to supply the fuel to the reforming unit before the additional supply so that the temperature of the reformed gas flowing into the fuel cell does not exceed a predetermined temperature at the time of stopping the system.