Fuel Cell Heat Exchanger Network for Exhaust Heat Recovery

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Solution Overview

Problem

High temperature fuel cell systems, such as solid oxide fuel cells, face inefficiencies in heat transfer from anode and cathode exhaust streams to incoming fuel and air streams, leading to the need for additional heating sources and reduced system efficiency.

Innovation Solution

Implementing a fuel cell system with a cathode recuperator heat exchanger and an air preheater heat exchanger, where the air inlet stream is first heated by the anode exhaust stream and then by the cathode exhaust stream, optimizing heat transfer and eliminating the need for additional heating sources by utilizing the thermodynamic potential of exhaust gases.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If a single heat exchanger is used to heat the air inlet stream, then the device complexity is reduced, but the heat energy recapture efficiency is insufficient

Engineering Contradiction:

Improveheat energy recapture efficiencyVSAvoidheat exchanger network complexity

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The heat exchanger network is segmented into two distinct heat exchangers: a first heat exchanger that recovers heat from the anode exhaust stream to preheat the air inlet stream, and a second heat exchanger that recovers heat from the cathode exhaust stream to further heat the air inlet stream. This segmentation allows each heat exchanger to operate optimally within its temperature range, maximizing overall heat recovery efficiency without requiring excessive complexity in a single unit.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The first heat exchanger performs preliminary heating of the air inlet stream using the anode exhaust stream before the air enters the second heat exchanger. This preliminary action raises the air temperature to a level where the second heat exchanger can more efficiently transfer heat from the cathode exhaust stream, creating a cascaded heating effect that maximizes energy utilization.

Inventive Principle:

Principle #10Preliminary action

2Temperature

If additional heating sources are used to compensate for heat transfer inefficiencies, then the air inlet stream can reach required temperature, but the system efficiency decreases

Engineering Contradiction:

Improveair inlet stream temperatureVSAvoidsystem efficiency

Core Design Contradiction:

TemperatureVSLoss of energy

Solution Approach 1:

The system converts the previously wasted thermal energy in the anode and cathode exhaust streams into useful heating for the air inlet stream. By capturing heat that would otherwise be discarded and using it to preheat and heat the air, the system eliminates the need for additional fuel-based heating sources, thereby improving overall system efficiency while maintaining the required air inlet temperature.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The system recovers thermal energy from the anode and cathode exhaust streams that would otherwise be discarded to the environment. The first heat exchanger recovers heat from the anode exhaust, and the second heat exchanger recovers heat from the cathode exhaust, transforming waste heat into a valuable resource for heating the air inlet stream and improving system efficiency.

Inventive Principle:

Principle #34Discarding and recovering

3Loss of energy

If the cathode exhaust stream is cooled excessively in the heat exchanger, then heat transfer to air is maximized, but the system requires additional mass transfer devices

Engineering Contradiction:

Improveheat transfer efficiencyVSAvoidmass transfer devices requirement

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The system optimizes the outlet temperature parameter of the cathode exhaust stream from the second heat exchanger to be at least 200°C. This parameter change ensures that the exhaust stream retains sufficient thermal energy to avoid condensation and the need for additional mass transfer devices, while still achieving efficient heat transfer to the air inlet stream. The temperature parameter is carefully controlled to balance heat recovery efficiency with system simplicity.

Inventive Principle:

Principle #35Parameter changes

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 enhances the recapture of heat energy, increases system efficiency, and reduces the requirement for mass transfer devices or additional heat sources, while maintaining system stability and cost-effectiveness.

Implementation Method 1

a cathode recuperator heat exchanger adapted to heat an air inlet stream using heat from a fuel cell stack cathode exhaust stream

Methodology Applied

Scientific EffectHeat transfer: Heat Exchanger

Implementation Method 2

an air preheater heat exchanger which is adapted to heat the air inlet stream using heat from a fuel cell stack anode exhaust stream

Methodology Applied

Scientific EffectHeat transfer: Heat Exchanger

Data Source

PatentUS8691462B2High temperature fuel cell system with integrated heat exchanger network

Publication Date: 2014.04.08 BLOOM ENERGY CORP

AI summary

A fuel cell system (1) is provided and includes a fuel cell stack (3), a cathode recuperator heat exchanger (33) adapted to heat an air inlet stream using heat from a fuel cell stack cathode exhaust stream, and an air preheater heat exchanger (39) which is adapted to heat the air inlet stream using heat from a fuel cell stack anode exhaust stream.