Fuel Cell Heat Exchanger Reformer for Thermal Efficiency
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Solution Overview
Problem
Fuel cell systems face challenges in achieving high thermal efficiency and rapid startup, especially at low power output levels, due to limitations in reforming processes and heat management.
Innovation Solution
The system integrates partial external reforming and direct internal reforming, using a heat exchanger/reformer with an anode tailgas oxidizer to preheat and partially reform the anode feed, and adjusts the amount of direct internal reforming through fuel utilization control, allowing for efficient heat recycling and reduced parasitic losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If partial external reforming is used in the heat exchanger/reformer, then thermal efficiency is improved, but the system complexity increases
Solution Approach 1:
The patent combines the heat exchanger and reformer into a single integrated unit called the heat exchanger/reformer. This merging allows thermal energy recovery and fuel reforming to occur simultaneously in the same device, improving thermal efficiency while avoiding the need for separate complex systems for each function.
Solution Approach 2:
The heat exchanger/reformer performs multiple functions: it acts as a heat exchanger to preheat the anode feed using exhaust heat, and simultaneously serves as a reformer to partially convert hydrocarbon fuel into syngas. This multi-functionality reduces the number of components needed and simplifies the overall system architecture.
2Adaptability or versatility
If direct internal reforming is increased, then fuel flexibility is improved, but anode coking risk increases
Solution Approach 1:
The patent implements partial external reforming in the heat exchanger/reformer rather than complete reforming. This partial action converts only a portion of the hydrocarbon fuel into syngas externally, reducing the amount of reforming that must occur internally at the anode, thereby lowering coking risk while still providing fuel flexibility.
Solution Approach 2:
The reforming process is segmented into two stages: external reforming in the heat exchanger/reformer and internal reforming at the fuel cell anode. This segmentation allows the reforming to be distributed across different locations and conditions, with the external stage handling the bulk conversion and the internal stage completing the process, thus managing coking risk more effectively.
3Use of energy by moving object
If fuel utilization is increased to maximize internal reforming, then thermal efficiency is improved, but system stability at low power levels deteriorates
Solution Approach 1:
The patent implements dynamic control of the anode offgas recycle ratio based on operating conditions. At low power levels, the recycle ratio is increased to provide sufficient heat for reforming and maintain system stability. At high power levels, the recycle ratio is decreased to maximize thermal efficiency by directing more offgas to the anode for internal reforming. This dynamic adjustment allows the system to optimize performance across different operating ranges.
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 enables high thermal efficiency and stable operation at low power levels by maximizing internal reforming at high fuel utilization and minimizing it at low utilization, while reducing anode coking risks and parasitic losses, and allows for rapid startup and efficient heat management.
Implementation Method 1
The integrated heat exchanger/reformer transfers heat from the oxidized offgas from the anode tailgas oxidizer to the anode feed before the anode feed enters the anode side of the fuel cell stack
Implementation Method 2
an anode tailgas oxidizer (ATO) to provide a hot exhaust gas as the sole heat source for the heat exchanger/reformer
Implementation Method 3
an integrated heat exchanger/reformer operable to partially reform an anode feed prior to entry into the fuel cell stack
Implementation Method 4
that portion of the fuel not reformed within the heat exchanger/reformer is direct internally reformed at the fuel cell anodes
Data Source
AI summary
A fuel cell system includes a plurality of solid oxide fuel cells arranged in a fuel cell stack, an integrated heat exchanger/reformer operable to partially reform an anode feed prior to entry into the fuel cell stack, an anode tailgas oxidizer, and an offgas flow path extending away from an anode side of the fuel cell stack and having a first branch to selectively combine offgas from the anode side of the fuel cell stack with fuel from a fuel source to comprise the anode feed to the fuel cell stack and a second branch to supply offgas from the anode side of the fuel cell stack to the anode tailgas oxidizer. The integrated heat exchanger/reformer transfers heat from the oxidized offgas from the anode tailgas oxidizer to the anode feed before the anode feed enters the anode side of the fuel cell stack. The offgas from the anode tailgas oxidizer provides the sole heat source for the anode feed traveling through the integrated heat exchanger/reformer.