Fuel Cell Emergency Shutdown Thermal Stress Reduction

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Solution Overview

Problem

High-temperature fuel cell systems, such as those using solid oxide fuel cells, experience rapid temperature drops during emergency shutdowns due to natural disasters, leading to potential thermal stress and damage from rapid cooling.

Innovation Solution

Implementing a shutdown transition mode where the fuel gas flow rate is reduced and combusted after the on-off valve is closed, followed by a shutdown mode that gradually stops fuel gas supply, using a control unit to manage the flow rates of fuel gas, water, and oxygen-containing gas to prevent rapid temperature changes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If emergency shutdown is performed by closing the on-off valve to stop fuel gas supply, then the fuel cell system can respond quickly to natural disasters, but the fuel cell experiences rapid temperature drop and thermal stress damage

Engineering Contradiction:

Improveshutdown response speedVSAvoidfuel cell thermal stress resistance

Core Design Contradiction:

SpeedVSStrength

Solution Approach 1:

The emergency shutdown process is divided into multiple stages: normal operation mode, shutdown transition mode (with sub-stages), and shutdown mode. This segmentation allows the system to gradually reduce fuel gas flow rate and temperature rather than abrupt cessation, thereby reducing thermal stress on the fuel cell while maintaining responsive shutdown capability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Before complete shutdown, the system performs preliminary actions by reducing the fuel gas flow rate to a predetermined value and maintaining combustion in the combustion chamber. This preliminary phase prepares the system for safe shutdown by controlling temperature reduction rate and preventing sudden thermal contraction that would cause stress damage.

Inventive Principle:

Principle #10Preliminary action

2Reliability

If fuel gas supply is completely stopped during emergency shutdown, then the emergency shutdown function is achieved, but the fuel cell temperature rapidly decreases causing thermal stress

Engineering Contradiction:

Improveemergency shutdown functionVSAvoidfuel cell temperature stability

Core Design Contradiction:

ReliabilityVSTemperature

Solution Approach 1:

During the shutdown transition mode, the combustion of fuel gas in the combustion chamber is maintained continuously at a reduced flow rate. This continuous combustion action serves dual purposes: achieving the shutdown function by reducing fuel supply while simultaneously maintaining temperature stability to prevent thermal stress from rapid cooling.

Inventive Principle:

Principle #20Continuity of useful action

Solution Approach 2:

The system changes the fuel gas flow rate parameter from normal operation level to a predetermined reduced level during shutdown transition. This parameter change allows the system to maintain combustion for temperature stability while reducing fuel supply to achieve emergency shutdown, thereby balancing reliability and temperature control.

Inventive Principle:

Principle #35Parameter changes

3Strength

If the fuel gas flow rate is reduced during shutdown transition mode, then thermal stress is reduced, but the system complexity increases due to additional control modes

Engineering Contradiction:

Improvefuel cell thermal stress resistanceVSAvoidshutdown control system complexity

Core Design Contradiction:

StrengthVSDevice complexity

Solution Approach 1:

The control unit is designed to handle multiple functions: normal operation control, shutdown transition control, and shutdown control. By making the control unit multi-functional, the patent avoids adding separate dedicated devices for each mode, thereby reducing overall system complexity while still achieving the benefit of reduced thermal stress through controlled flow rate reduction.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 reduces thermal stress on the fuel cell during emergency shutdowns, preventing damage by gradually lowering the temperature and maintaining controlled conditions similar to power generation states.

Implementation Method 1

a fuel cell that generates electric power using fuel gas and oxygen-containing gas

Methodology Applied

Scientific EffectFuel cell electrochemical reaction: Fuel Cell

Implementation Method 2

combusts fuel gas remaining unused for generation of electric power

Methodology Applied

Scientific EffectCombustion: Combustion

Data Source

PatentUS9564646B2Fuel cell system and operating method thereof

Publication Date: 2017.02.07 KYOCERA CORP

AI summary

A fuel cell system includes a fuel cell that generates electric power using fuel gas and oxygen-containing gas and combusts fuel gas remaining unused for generation of electric power; a fuel gas supply line that supplies the fuel gas to the fuel cell; and an on-off valve disposed in the fuel gas supply line. A shutdown transition mode in which the fuel gas in the fuel gas supply line downstream from the on-off valve is supplied to the fuel cell at a flow rate smaller than that at a time of generation of electric power and is combusted therein after the on-off valve is closed, and a shutdown mode which is started after the shutdown transition mode are provided as an emergency shutdown mode in which the fuel cell undergoes emergency shutdown when the on-off valve of the fuel gas supply line is closed.