Cascaded Fuel Cell System with Anode Gas Recirculation
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Solution Overview
Problem
High-temperature fuel cell systems face inefficiencies due to high water content in residual fuel gas reducing Nernst voltage and requiring excessive compressor power for air supply, leading to reduced power density and increased energy losses.
Innovation Solution
A cascaded fuel cell system with direct internal reforming and anode residual gas circulation, where the number of fuel cells and anode surfaces can be adjusted, and hydrocarbon compounds are supplied with reduced air volume flow, utilizing steam or partial oxidation reformers, and catalytic support for reforming, allowing for flexible operation and reduced thermal energy requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If air is supplied hyperstoichiometrically to dissipate heat, then heat dissipation is improved, but compressor power increases and total efficiency decreases
Solution Approach 1:
The anode residual gas circulation system allows the fuel cell system to utilize its own exhaust gas for cooling purposes. The residual gas from the anode is circulated back through a cooler and then re-introduced to the anode inlet, creating a self-sustaining cooling loop that eliminates the need for external hyperstoichiometric air supply for heat dissipation.
Solution Approach 2:
The system changes the temperature parameter of the anode inlet gas by introducing cooled residual gas instead of cold ambient air. This parameter change allows for effective heat dissipation while maintaining optimal operating conditions and avoiding the energy penalties associated with compressing large volumes of ambient air.
2Loss of energy
If air is cooled before entry to reduce volume flow, then compressor power is reduced, but electrolyte conductivity decreases and mechanical strains occur
Solution Approach 1:
Instead of cooling ambient air before entry, the system cools the anode residual gas that is already at operating temperature. This self-service approach allows cooling to occur without subjecting the electrolyte to thermal shock, as the gas being cooled has already equilibrated with the electrolyte temperature during its passage through the fuel cell stack.
3Quantity of substance
If water content in residual fuel gas is high, then Nernst voltage decreases and power density is reduced
Solution Approach 1:
The system implements a feedback mechanism where the composition and temperature of the anode residual gas are continuously monitored, and the cooling and recirculation parameters are adjusted accordingly. This feedback control optimizes the water content in the residual fuel gas to maintain high Nernst voltage and power density while effectively managing heat dissipation.
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 increases the total efficiency of the system by up to 5% by minimizing water content and compressor power, enabling more flexible operation and reducing the size of reformers and compressors, while maintaining power density and reducing inert components in residual fuel gas.
Implementation Method 1
a steam reformer (1) with which a fuel gas containing hydrogen can be provided from a hydrocarbon compound
Implementation Method 2
with which a reforming can be achieved by partial oxidation (POx) processes
Implementation Method 3
fuel cells which can be operated with at least one hydrocarbon compound... for the electrochemical reaction of the fuel cells
Implementation Method 4
The connection stub through which the hydrocarbon compound used is introduced into a stack should be provided with a cooler. Soot formation can be avoided by the cooling.
Implementation Method 5
At the sufficiently high temperatures, methane is broken down into hydrogen and carbon monoxide on the presence of water. A cooling of fuel cells at their anodes can be achieved by the endothermic reaction
Implementation Method 6
Further hydrogen becomes free on the conversion of carbon monoxide to carbon dioxide on the presence of water. This is, however, an exothermal reaction
Data Source
AI summary
The invention relates to a high-temperature fuel cell system which can be operated with at least one hydrocarbon compound, preferably with methane or a gas containing methane such as natural gas or biogas. It is the object of the invention to increase the efficiency of high-temperature fuel cell systems and to allow a more flexible operation. In the system in accordance with the invention, individual fuel cells are present which are connected electrically in series and form the stacks. The stacks are flowed through after one another by fuel gas which contains hydrogen and which flows into a first stack of the system from a reformer and a suitable hydrocarbon compound is supplied via further connection lines in the flow direction of the introduced fuel gas sequentially into further stacks to the respective stack for a direct internal reforming of a hydrocarbon compound at anodes of the fuel cells of the stack and air is supplied as an oxidation means at the cathode side to the individual fuel cells of the system.