Fuel Cell Recirculation Heat Exchanger Thermal Management
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Solution Overview
Problem
Fuel cell systems face high thermal loads on conveyor devices due to direct feeding of hot fuel cell exhaust gases, leading to increased demands on temperature resistance and potential overheating, along with high costs from separate conveyors.
Innovation Solution
The recirculation line is connected to both the anode waste gas line and the oxidizer line upstream of the delivery device, allowing the delivery device to handle both oxidant and anode waste gas, and a recirculation heat exchanger is integrated in both lines to preheat oxidant gas and cool anode waste gas, with a controllable bypass for efficient warm-up and condensation prevention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If hot fuel cell exhaust gases are fed directly to the oxidizer, then the oxidizer receives the recirculated gas, but the thermal load on the delivery device becomes excessively high
Solution Approach 1:
A recirculation heat exchanger is introduced as an intermediary component between the exhaust gas line and the oxidizer line. This heat exchanger transfers thermal energy from the hot recirculated exhaust gases to the incoming oxidizer, thereby cooling the exhaust gases before they reach the delivery device while simultaneously preheating the oxidizer. This resolves the contradiction by mediating the thermal interaction to protect the delivery device from excessive thermal load.
Solution Approach 2:
The high temperature of the exhaust gases, which initially represents a harmful thermal load on the delivery device, is converted into a beneficial resource by using it to preheat the incoming oxidizer through the heat exchanger. This transforms the harmful thermal energy into a useful function, reducing the energy required to heat the oxidizer while protecting the delivery device from overheating.
2Ease of operation
If a separate conveying device is arranged in the recirculation line to drive the anode waste gas, then the recirculation function is achieved, but the cost and device complexity increase
Solution Approach 1:
The delivery device of the oxidizer supply unit is designed to perform multiple functions: it not only supplies oxidizer to the reformer but also drives the recirculated anode waste gas to the reformer through the oxidizer line. By making the delivery device universal and capable of handling both oxidizer and recirculated exhaust gases, the patent eliminates the need for a separate conveying device in the recirculation line, thereby reducing device complexity and cost.
Solution Approach 2:
The functions of oxidizer supply and anode waste gas recirculation are merged into a single delivery device. The recirculation line is connected to the oxidizer line upstream of the delivery device, allowing both gas streams to be handled by the same conveying mechanism. This consolidation reduces the number of components and simplifies the overall system architecture.
3Loss of time
If the reformer is quickly brought to operating temperature during cold start, then the warm-up phase is shortened, but the risk of condensation in the recirculation line increases
Solution Approach 1:
A temperature sensor is installed in the recirculation line to monitor the temperature of the recirculated exhaust gases. This temperature information is fed back to the control unit, which adjusts the recirculation flow rate accordingly. When the temperature drops below a predetermined threshold indicating risk of condensation, the control unit reduces or stops the recirculation flow, preventing condensation while allowing rapid warm-up when temperatures are sufficient.
Solution Approach 2:
The recirculation flow rate is made dynamic and adjustable rather than fixed. The control unit can vary the recirculation flow rate based on operating conditions, particularly temperature. During cold start, the system can optimize warm-up by adjusting recirculation, and during normal operation, it can prevent condensation by reducing recirculation when temperatures are low, thus adapting the system behavior to current conditions.
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 configuration reduces the risk of conveyor device damage, enhances energetic efficiency by shortening the warm-up phase, and increases functional reliability by managing temperature and condensation effectively.
Implementation Method 1
a recirculation heat exchanger (32) is provided, which is integrated on the one hand in the recirculation line (28) and on the other hand in the oxidizer line (25)
Data Source
Figure 1
AI summary
The system (1) has a reformer (3) generating hydrogen gas containing reformate gases from hydrogen containing fuel e.g. diesel, and oxygen containing oxidizer. A fuel cell (2) e.g. solid oxide fuel cell, generates electric current by converting reformate gas serving as anode gas into oxygen gas containing cathode gas. An oxidizer supply device (24) supplies oxidizer for the reformer and has an oxidizer line (25) and a conveying device (26). A recirculation line (28) is attached to an exhaust line (12) discharging from the fuel cell and to upstream of the conveying device to the oxidizer line. An independent claim is also included for a method for operating a fuel cell system.