Fuel Cell Exhaust Gas Recirculation for Stable Catalytic Oxidation
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Solution Overview
Problem
Fuel cell exhaust gas has a low concentration of fuel components, requiring additional fuel input or limiting load changes to prevent misfire in flame combustion systems and necessitating periodic replacement of catalytic combustors, leading to increased costs.
Innovation Solution
A fuel cell power generation system where the exhaust fuel gas from the most downstream module is supplied to the oxygen-side electrode of any fuel cell module, allowing for catalytic combustion of unused fuel components without the need for a separate combustor, reducing system pressure loss and fuel supply power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a flame combustion type combustor is used to combust exhaust fuel gas, then combustion can be achieved, but additional fuel input is required or load change rate must be limited to prevent misfire
Solution Approach 1:
The patent replaces the flame combustion type combustor with a catalytic combustor that uses catalytic oxidation instead of flame combustion. This substitution eliminates the need for additional fuel input and allows the system to handle load changes without misfire, as the catalytic reaction occurs at lower temperatures and is not dependent on maintaining a stable flame kernel.
Solution Approach 2:
The patent changes the combustion mechanism from high-temperature flame combustion to lower-temperature catalytic oxidation. This parameter change in the combustion process allows for stable operation with low-concentration exhaust fuel gas without requiring additional fuel or limiting load change rates, thereby resolving the contradiction between combustion stability and operational flexibility.
2Ease of operation
If a catalytic combustor is used to combust exhaust fuel gas, then combustion can be achieved without additional fuel, but periodic replacement is required to maintain catalytic performance
Solution Approach 1:
The patent extracts the catalytic combustor from the exhaust fuel gas line and replaces it with a recirculation system that returns exhaust fuel gas to the fuel cell inlet. This eliminates the catalytic combustor entirely, removing the need for periodic replacement while still achieving complete combustion of unused fuel components through the fuel cell's electrochemical reaction.
Solution Approach 2:
Instead of discarding the exhaust fuel gas or using a consumable catalytic combustor, the patent recycles the exhaust fuel gas back to the fuel cell inlet where it is combusted electrochemically. This recovery approach eliminates the need for periodic catalyst replacement while maintaining complete fuel utilization.
3Reliability
If a combustor is added to treat exhaust fuel gas, then fuel components can be combusted, but system complexity and cost increase
Solution Approach 1:
The patent merges the exhaust treatment function with the existing fuel cell system by recirculating exhaust fuel gas to the fuel cell inlet. This eliminates the need for a separate combustor and integrates the combustion function into the fuel cell's electrochemical reaction process, thereby reducing system complexity while maintaining effective fuel component combustion.
Solution Approach 2:
The patent makes the fuel cell perform multiple functions: power generation from fresh fuel gas and combustion of exhaust fuel gas components. By utilizing the fuel cell's electrochemical reaction capability for both purposes, the system eliminates the need for dedicated exhaust treatment equipment, reducing overall system complexity and cost.
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 stabilizes combustion, reduces costs by eliminating the need for a combustor and additional fuel input, and enhances power generation efficiency by utilizing the heat generated from combustion to maintain optimal temperatures within the fuel cell module.
Implementation Method 1
the exhaust fuel is combusted in the catalyst combustor using oxygen in the exhaust air as an oxidizing agent
Implementation Method 2
the exhaust fuel is combusted in the catalyst combustor using oxygen in the exhaust air as an oxidizing agent
Implementation Method 3
the exhaust fuel gas is combusted by a combustor
Data Source
AI summary
A fuel cell power generation system is provided with at least one fuel cell module each of which includes a fuel cell having a fuel-side electrode, an electrolyte, and an oxygen-side electrode; at least one fuel supply line for supplying a fuel gas to the fuel-side electrode included in the at least one fuel cell module; at least one oxidizing gas supply line for supplying an oxidizing gas to the oxygen-side electrode included in the at least one fuel cell module; and a most downstream exhaust fuel gas line through which an exhaust fuel gas discharged from a most downstream module that is disposed most downstream in a flow of the fuel gas among the at least one fuel cell module flows.