Fuel Cell System Load-Following Control via Segmented Fuel Utilization
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Solution Overview
Problem
Existing fuel cell systems face instability in combustor performance during low-to-high load-following operations, where the power output of the fuel cell stack shifts from a lower level to a higher level, leading to potential misfires due to inadequate fuel utilization control.
Innovation Solution
A fuel cell system that divides the load-following operation into sub-periods, controlling the raw material feeder to adjust the flow rate and sub-period lengths, ensuring that the ratio of fuel utilization increase is milder with increasing power output, thereby maintaining stable combustion by reducing the likelihood of misfires.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the fuel supply to the combustor is increased to improve combustion stability during low-to-high load-following operations, then the combustor performance is improved, but the fuel utilization in the SOFC stack decreases leading to wasteful fuel consumption
Solution Approach 1:
The load-following operation period is divided into multiple sub-periods (n sub-periods where n≥2). The controller segments the fuel supply control into different phases, with each sub-period having different fuel utilization settings. During early sub-periods, fuel utilization is reduced to prevent combustor misfires, while during later sub-periods, fuel utilization is increased to improve overall system efficiency and reduce wasteful fuel consumption.
Solution Approach 2:
The fuel utilization in the SOFC stack is dynamically adjusted based on the current sub-period of the load-following operation. The controller changes the fuel utilization ratio over time, making it a dynamic parameter rather than a fixed value. This allows the system to optimize both combustor performance and fuel efficiency at different stages of the load transition.
2Reliability
If the fuel utilization in the SOFC stack is set lower in the low-load range to improve combustor combustion condition, then the combustor stability is improved, but the system efficiency decreases due to increased fuel waste
Solution Approach 1:
The operation is divided into sub-periods where different fuel utilization strategies are applied. In early sub-periods when the load is still relatively low, fuel utilization is set lower to ensure combustor stability. In later sub-periods as the load increases, fuel utilization is raised to improve system efficiency, thus segmenting the trade-off between stability and efficiency.
Solution Approach 2:
The controller preliminarily reduces fuel utilization at the beginning of the load-following operation to ensure stable combustor operation during the critical transition phase. This preliminary action prevents combustor misfires before the load fully transitions to the high range, after which normal fuel utilization can be restored.
3Reliability
If the fuel utilization decreases sharply with increasing load to maintain combustor stability, then the combustion reliability is improved, but the fuel efficiency deteriorates due to excessive fuel supply
Solution Approach 1:
The fuel utilization is dynamically controlled to decrease gradually rather than sharply as the load increases. The controller adjusts the fuel utilization ratio in steps across different sub-periods, creating a dynamic response that maintains combustion reliability while minimizing energy loss through excessive fuel supply.
Solution Approach 2:
The fuel utilization parameter is changed in a controlled manner across different sub-periods. Instead of a sharp decrease, the parameter changes gradually, allowing the system to maintain combustion reliability while improving fuel efficiency by avoiding excessive fuel supply that would occur with a sharp parameter change.
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
The system effectively manages fuel utilization during low-to-high load transitions, preventing misfires and ensuring efficient operation by maintaining a larger difference between normal and critical fuel utilization levels, thus performing better than prior art in low-to-high load-following operations.
Implementation Method 1
a reformer that produces the fuel gas by reforming a raw material
Implementation Method 2
a combustor that combusts anode off-gas discharged from an anode of the fuel cell stack
Implementation Method 3
a fuel cell stack that generates electricity using fuel gas and oxidant gas
Data Source
AI summary
A fuel cell system includes a fuel cell stack that generates electricity using fuel and oxidant gases, a reformer that produces the fuel gas by reforming a raw material, a raw material feeder that supplies the raw material to the reformer, a combustor that combusts anode off-gas discharged from the anode of the fuel cell stack, and a controller that controls the raw material feeder. The period of a load-following operation in which the power output of the fuel cell stack shifts from a lower level to a higher level, is divided into multiple sub-periods. For each sub-period, a ratio is determined from the increase amounts in the flow rate of the raw material during the sub-period and the length of the sub-period. The controller controls the raw material feeder to make a ratio on the higher output side smaller than another on the lower output side.