Anode Exhaust Diversion for Fuel Cell Hotbox Temperature Control
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Solution Overview
Problem
Conventional fuel cell systems require large and complex steam generators for humidification, leading to increased size, complexity, and cost, and generate unnecessary heat during steady-state operations, which can disrupt optimal temperature ranges and efficiency.
Innovation Solution
The system incorporates a water injector to vaporize water directly into the anode exhaust recycle stream, eliminating the need for a steam generator and reduces anode exhaust flow to the anode tail gas oxidizer during steady-state operations, diverting it to the exhaust oxidizer outside the hotbox for oxidation, thereby minimizing heat generation and optimizing temperature control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a steam generator is used for humidification, then humidification function is achieved, but system size and complexity increase
Solution Approach 1:
The patent extracts the humidification function from the traditional steam generator and relocates it to the anode exhaust recycle stream. Water is injected directly into the hot anode exhaust stream where it evaporates and humidifies the recycled exhaust, eliminating the need for a separate steam generator component.
Solution Approach 2:
The anode exhaust recycle stream serves as an intermediary medium that transfers heat from the hot exhaust gases to the injected water, causing evaporation. This intermediary approach allows humidification without direct thermal contact between the water source and the fuel cell stack.
2Reliability
If anode exhaust is provided to ATO during steady-state operations, then oxidation occurs, but unnecessary heat is generated disrupting optimal temperature ranges
Solution Approach 1:
The patent implements dynamic control of anode exhaust flow to the ATO based on operating conditions. During steady-state operations, the flow to ATO is reduced or diverted away, while during startup or transient conditions, flow is directed to ATO for oxidation. This dynamic adjustment prevents unnecessary heat generation during stable operation.
Solution Approach 2:
The system employs periodic or conditional activation of the ATO based on operational needs rather than continuous operation. The control system monitors stack temperature and operating mode, directing exhaust to ATO only when oxidation is needed (startup, low current draw), and diverting it during steady-state when it would cause temperature disruption.
3Ease of manufacture
If water is vaporized in a steam generator, then humidification is achieved, but response time is slow
Solution Approach 1:
The system pre-heats the injected water using the hot anode exhaust stream before it contacts the fuel cell stack. The water is introduced into the already-hot recycle stream, where it rapidly evaporates and mixes, providing immediate humidification without the thermal lag associated with traditional steam generators.
Solution Approach 2:
The patent uses a water injection system that introduces liquid water directly into the high-velocity anode exhaust stream. The kinetic energy and turbulence of the exhaust gas facilitate rapid atomization and evaporation of the injected water, achieving fast response times without mechanical steam generation equipment.
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 reduces system size and complexity, improves response times, and enhances efficiency by eliminating unnecessary heat generation, maintaining optimal fuel cell temperatures and reducing overall power consumption.
Implementation Method 1
The system incorporates a water injector to vaporize water directly into the anode exhaust recycle stream
Implementation Method 2
an anode tail gas oxidizer (ATO) configured to oxidize anode exhaust output from the stack
Implementation Method 3
Fuel cells, such as solid oxide fuel cells, are electrochemical devices which can convert energy stored in fuels to electrical energy
Data Source
AI summary
A method of operating a fuel cell system includes providing fuel and air to a stack of fuel cells located in a hotbox, operating the stack to generate an anode exhaust and a cathode exhaust, in a startup mode, providing a first amount of the anode exhaust and the cathode exhaust to an anode tail gas oxidizer (ATO) located in the hotbox to oxidize the anode exhaust and to generate heat which is provided to the stack, and in a steady-state mode, stopping providing the anode exhaust to the ATO or providing to the ATO a second amount of the anode exhaust which is smaller than the first amount, and providing the anode exhaust and the cathode exhaust outside the hotbox.