SOFC Anode Off-Gas Recirculation with Steam-Lubricated Bearings
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Solution Overview
Problem
Existing Solid Oxide Fuel Cell (SOFC) systems require an external source of deionized water and electrical-driven pumps, and they suffer from reduced anode and reformer lifetime due to oil lubrication in turbines, which complicates maintenance and efficiency.
Innovation Solution
An SOFC system that recirculates anode off-gas to produce steam internally, using a turbine-fan assembly driven by steam to propel a turbine and fan, eliminating the need for external water and electrical pumps, and utilizing steam-lubricated bearings to reduce maintenance and improve efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If oil-lubricated bearings are used in turbines, then the turbine can operate at high revolution speeds, but the oil is transferred to the recirculated off-gas and reaches the reformer and anode, reducing their lifetime
Solution Approach 1:
The harmful oil lubrication is extracted and removed from the turbine system. The patent uses steam-lubricated bearings instead of oil-lubricated bearings, eliminating the source of oil contamination that was being transferred to the recirculated off-gas and damaging the reformer and anode components.
Solution Approach 2:
Steam is introduced as an intermediary lubricant between the turbine bearing surfaces. Instead of using oil that contaminates the off-gas, steam serves as the lubricating medium, providing the necessary friction reduction while being compatible with the fuel cell system and not harmful to the reformer and anode.
2Duration of action of moving object
If external water sources and electrical-driven pumps are used, then the system can maintain continuous operation, but the system complexity and maintenance requirements increase
Solution Approach 1:
The system generates its own water supply through the electrochemical reactions in the fuel cell. Water is produced as a byproduct in the cathode and is automatically recirculated through the system, eliminating the need for external water sources and electrical-driven pumps. The system serves its own water needs internally.
Solution Approach 2:
The water production and recirculation functions are merged with the electrochemical energy generation process. The water produced during electricity generation is directly fed back into the reformer through the recirculation system, combining the power generation and water supply functions into a unified process.
3Speed
If ball bearings are used in turbines operating at high revolution speeds above 1000 turns per second, then the turbine can function, but the bearings require frequent maintenance and have short lifetime
Solution Approach 1:
The mechanical ball bearing system is replaced with a steam-lubricated bearing system. This substitution eliminates the need for mechanical contact and rolling elements that wear out at high speeds. The steam lubrication provides a non-contact or minimal-contact bearing mechanism that can sustain much higher revolution speeds without the wear and maintenance issues of traditional ball bearings.
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 system operates continuously without external water, increases electrical net efficiency, and extends the life of anode and reformer components by eliminating oil lubrication, while maintaining high revolution speeds and reducing maintenance needs.
Implementation Method 1
a turbine-fan assembly comprising a steam-driven rotatable turbine and a rotatable fan, coaxially connected to said turbine
Implementation Method 2
an evaporator assembly arranged for producing steam from water
Implementation Method 3
a condenser, arranged for condensing water contained in said anode off-gas
Implementation Method 4
the steam reforming reaction and the water gas shift reaction are described
Implementation Method 5
the hydrogen rich fuel stream is oxidized in a fuel cell
Implementation Method 6
A stream of anode exhaust and an oxidant stream comprising cathode exhaust and air are combusted in the burner
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
The present invention concerns an SOFC system comprising an anode off-gas recirculation arrangement in which anode off-gas is pumped by a fan or pump of a coaxial turbine-fan assembly, the system comprising a condenser for condensing water contained in said anode off -gas and an evaporator for producing steam from said condensed water, wherein said steam is used to drive the turbine. The method comprises further methods for operating the SOFC system and/or for producing electricity. In a preferred embodiment, the coaxial turbine- fan assembly comprises a stream lubricated bearing.