Fuel Cell Stack Heat Exchanger for Fast Start-Up
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Solution Overview
Problem
Fuel cell devices face thermomechanical stresses during the heating-up phase due to significant temperature differences between fuel gas and oxidizing agent channels, leading to potential damage and prolonged start-up times, while existing solutions either increase start-up time or impose operational restrictions.
Innovation Solution
A heat exchanger is integrated into the fuel cell stack, allowing the hot fuel gas to transfer heat to the oxidizing agent before reaching the electrochemically active part, reducing temperature differences and enabling a shorter start-up time without increasing thermomechanical stresses, and optionally incorporating chemically active substances to reduce carburizing gases and sulfur content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the reformer output is increased to shorten heating-up time, then the start-up time is reduced, but the temperature difference between fuel gas and oxidizing agent channels increases, causing thermomechanical stresses that can damage the fuel cell stack
Solution Approach 1:
A heat exchanger is introduced as an intermediary component between the reformer and the fuel cell stack. This heat exchanger preheats the oxidizing agent using the hot fuel gas, thereby reducing the temperature difference between fuel and oxidant channels when they enter the stack, while still allowing high reformer output for fast start-up
Solution Approach 2:
The oxidizing agent is preheated in advance in the heat exchanger before entering the fuel cell stack. This preliminary heating action ensures that when high-temperature fuel gas enters the stack, the oxidizing agent is already at a comparable temperature, preventing thermal shock and thermomechanical stresses
2Object-affected harmful factors
If the reformer output is reduced to decrease thermomechanical loads, then the thermomechanical stresses are reduced, but the heating-up time exceeds 60 minutes, which is intolerable for users
Solution Approach 1:
The heat exchanger acts as a mediator that decouples the relationship between reformer output and temperature difference in the stack. This allows the reformer to operate at high output for fast start-up while the heat exchanger manages the temperature difference, preventing thermomechanical stresses
Solution Approach 2:
By preheating the oxidizing agent in advance through the heat exchanger, the system can tolerate high reformer output without causing excessive temperature differences in the stack, thus enabling fast start-up while maintaining structural integrity
3Object-affected harmful factors
If existing heat exchanger solutions are used, then thermomechanical loads are reduced, but additional components increase device complexity and space requirements
Solution Approach 1:
The heat exchanger is integrated with the fuel cell stack structure, merging two functions (heat exchange and electrochemical conversion) into a single compact unit. This eliminates the need for separate external heat exchanger components, reducing device complexity and space requirements while maintaining the temperature management function
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 heat exchanger reduces thermomechanical loads, shortens the heating-up phase, and enhances the homogeneity of the temperature field within the fuel cell stack, thereby improving its performance and longevity by minimizing carburization and reoxidation effects.
Implementation Method 1
the hot fuel gas is routed from the reformer into this heat exchanger. Here, the fuel gas can give off part of its heat to the oxidizing agent (cathode air) that is also fed into the heat exchanger
Implementation Method 2
a previously vaporized fuel, for example diesel fuel, is broken down into H2, CO, CO2, H2O and residual hydrocarbons, for example by partial oxidation of the higher hydrocarbons in the starting fuel
Implementation Method 3
The H2 and CO components can then be electrochemically converted into electricity in the fuel cell stack
Implementation Method 4
The combustible gas that is not converted during the electrochemical generation of electricity in the fuel cell stack is post-combusted after the fuel cell stack for safety and environmental reasons as well as for reasons of energy efficiency in the residual gas burner
Implementation Method 5
The resulting process heat is fed to the layer heat exchanger. This heats the oxidizing agent (cathode air) for the fuel cell stack with the process heat before the oxidizing agent is fed into the fuel cell stack
Data Source
AI summary
In order to provide a fuel cell device, comprising a fuel cell stack which comprises electrochemically active cathode-electrolyte-anode units, and a reformer for producing a combustion gas for the fuel cell stack from a primary fuel, wherein the combustion gas which is produced by the reformer and an oxidizing agent can be fed to the fuel cell stack, in which fuel cell device the thermomechanical loads in the heating phase are reduced and/or shortening of the heating phase is made possible, it is proposed that the fuel cell device comprises at least one heat exchanger through which the combustion gas and the oxidizing agent can flow upstream of the cathode-electrolyte-anode units of the fuel cell stack.