Hot Fuel Cell Heat Exchanger With Immersed Post-Combustion Cooling
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Solution Overview
Problem
Hot fuel cells generate high-temperature gases that are difficult to handle with standard boiler systems, as they require high-performance materials to manage the heat, which increases costs, especially in home applications.
Innovation Solution
A heat exchanger design that includes separate flow circuits for oxidizer and fuel gases, a pre-mixer chamber, and a combustion chamber immersed in a common cooling fluid, allowing for post-combustion and efficient heat recovery without the need for high-performance materials, using low-cost materials like stainless steel for components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-performance materials are used to withstand high-temperature gas flows, then the ability to handle high-temperature gases is improved, but the cost of the cogeneration system increases considerably
Solution Approach 1:
The patent applies preliminary action by cooling the high-temperature exhaust gases from the fuel cell before they enter the boiler system. A heat exchanger is positioned between the fuel cell and boiler to pre-cool the gases, reducing their temperature to a level that standard boiler materials can handle. This preliminary cooling action eliminates the need for expensive high-performance materials in the boiler while still enabling effective heat recovery from the originally high-temperature gases.
2Ease of manufacture
If standard boiler systems are used to process high-temperature gases, then the cost is reduced, but the control of gas injection and flow becomes very difficult
Solution Approach 1:
The system performs preliminary cooling of the high-temperature gases before they reach the standard boiler system. By reducing the gas temperature in advance through the heat exchanger, the subsequent handling, injection, and flow control in the standard boiler becomes manageable and reliable, eliminating the operational difficulties that would otherwise arise from direct exposure to extremely hot gases.
Solution Approach 2:
The heat exchanger acts as an intermediary between the high-temperature fuel cell exhaust and the standard boiler system. It mediates the temperature difference, allowing the standard boiler to process the gases without direct exposure to extreme temperatures, thus maintaining ease of operation while using cost-effective standard materials.
3Loss of energy
If high-temperature gases are processed directly in the boiler, then heat recovery is maximized, but the temperature of components in contact with gases remains very high requiring expensive materials
Solution Approach 1:
The heat recovery process is segmented into two distinct stages: first, a heat exchanger recovers heat from the high-temperature exhaust gases and uses it to preheat the cooling fluid; second, the now-cooled gases enter the standard boiler for further heat extraction. This segmentation allows heat recovery from the full temperature range while keeping component temperatures within manageable limits.
Solution Approach 2:
The heat exchanger performs preliminary heat recovery from the high-temperature gases before they enter the boiler. This preliminary action captures the highest temperature heat first, then the boiler recovers additional heat from the already-cooled gases, maximizing total heat recovery while protecting components from extreme temperatures.
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 effectively recovers both sensible heat and heating value from high-temperature gases, reduces the temperature of the gases and combustion chamber, limits components in direct contact with high-temperature gases, and reduces NOx emissions, enabling the use of low-cost materials and optimizing fuel/oxidizer mixing for stable combustion.
Implementation Method 1
immersing the various gas flow circuits (for oxidizer, fuel, and flue gases) and the combustion chamber in the same cooling fluid makes it possible to recover all of the heat energy, i.e. both the sensible heat and the heating value
Implementation Method 2
the first flow circuit for oxidizer gas, the second flow circuit for fuel gas, the combustion chamber, and the flow circuit for flue gas are immersed in a common cooling fluid
Implementation Method 3
a combustion chamber fed with the gaseous mixture from the pre-mixer chamber and with oxidizer gas from the first circuit
Data Source
AI summary
A heat exchanger for operating at an outlet of a hot fuel cell feeding the heat exchanger with oxidizer gas and with fuel gas, the heat exchanger including: a first flow circuit for oxidizer gas; a second flow circuit for fuel gas; a pre-mixer chamber fed both with oxidizer gas and with fuel gas from at least the second circuit; a combustion chamber fed with the gaseous mixture from the pre-mixer chamber and with oxidizer gas from the first circuit; and a flow circuit for flue gas, receiving the flue gas coming from the combustion chamber. The first flow circuit for oxidizer gas, the second flow circuit for fuel gas, the combustion chamber, and the flow circuit for flue gas are immersed in a common cooling fluid.