Modular Boiler Oxy-Combustion Flue Gas Recycle Reduction
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Solution Overview
Problem
The high flue gas recycle ratio in oxy-combustion systems reduces plant efficiency and increases costs, as it requires a large amount of recycled flue gas to control wall heat flux in boiler systems, leading to inefficiencies and higher operational expenses.
Innovation Solution
A modular boiler system with a staged, oxy-combustion process that significantly reduces the flue gas recycle ratio by separating intra-system flue gas into multiple streams, allowing for reduced oxygen concentration and increased efficiency, while also enabling deep turn-down capabilities and lower capital costs through off-site construction and flexible operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a high flue gas recycle ratio is used to control wall heat flux in oxy-combustion boilers, then wall heat flux is controlled within material constraints, but plant efficiency decreases and operational costs increase
Solution Approach 1:
The patent divides the single boiler system into multiple modular boiler units (first boiler, second boiler, third boiler) that can operate independently or in combination. This segmentation allows flexible distribution of thermal load and optimization of flue gas recycle ratios across different modules, improving overall plant efficiency while maintaining wall heat flux control in each unit.
Solution Approach 2:
The system enables dynamic operation where boilers can be started or shut down based on demand. The flue gas recycle ratio can be dynamically adjusted across different boiler configurations (single boiler mode, dual boiler mode, triple boiler mode) to optimize efficiency at different operating points while controlling wall heat flux within material constraints.
2Temperature
If a high flue gas recycle ratio is used to control wall heat flux, then combustion temperature is controlled, but the amount of recycled flue gas increases significantly
Solution Approach 1:
By dividing the system into multiple boiler modules, the patent distributes the flue gas recycle requirement across separate units. Each boiler can operate with optimized local flue gas recycle ratios, reducing the total quantity of recycled flue gas needed compared to a single large boiler operating at high recycle ratios to control combustion temperature.
Solution Approach 2:
The system changes operational parameters by allowing different flue gas recycle ratios in different boiler configurations. When multiple boilers operate in parallel, each can maintain lower individual recycle ratios while collectively providing the required temperature control, thereby reducing the total quantity of recycled flue gas.
3Loss of energy
If multiple boilers are used to reduce flue gas recycle ratio, then plant efficiency increases, but system complexity increases
Solution Approach 1:
The patent uses identical or similar modular boiler units that can be replicated. This standardization reduces design and operational complexity despite having multiple units, as each module follows the same design principles and can be operated independently or in combination, simplifying control and maintenance while improving plant efficiency.
Solution Approach 2:
Each boiler module is designed to be universal and multi-functional, capable of operating independently or in combination with other modules. This universality reduces system complexity by using standardized components that can serve multiple operational configurations, eliminating the need for complex custom-designed systems.
4Loss of energy
If flue gas recycle ratio is reduced from 70% to 30%, then plant efficiency increases by more than 3 percentage points, but wall heat flux control becomes more challenging
Solution Approach 1:
By segmenting the boiler system into multiple modular units, the patent enables better distribution and control of thermal loads. When operating with reduced flue gas recycle ratios (30%), each modular unit can be independently optimized to maintain appropriate wall heat flux levels, making temperature control more manageable compared to a single large boiler.
Solution Approach 2:
The system provides dynamic flexibility to adjust the number of operating boilers based on thermal demand. When operating at lower flue gas recycle ratios, the system can dynamically start or stop individual boiler modules to maintain optimal wall heat flux control, enabling efficient operation with improved plant efficiency.
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 modular boiler design increases plant efficiency by more than 3 percentage points when the flue gas recycle ratio is decreased from 70% to 30%, reducing capital costs and operational expenses, and allows for better flexibility in plant operations by adjusting thermal input or shutting down boilers.
Implementation Method 1
a flue gas separator to separate the intra-system flue gas into a first flue gas stream and a second flue gas stream
Implementation Method 2
combust fuel, e.g. pulverized coal, at atmospheric pressure in a stream of oxygen
Implementation Method 3
The first boiler is further configured to output intra-system flue gas
Data Source
AI summary
A modular boiler system for implementing fuel combustion is provided. The system includes a first boiler and a second boiler of a plurality of boilers, an oxygen input unit, a fuel input unit, a recycled flue gas input unit, and a flue gas separator. The first boiler receives oxygen from the oxygen input unit, fuel from the fuel input unit, and recycled flue gas from the recycled flue gas input unit. The first boiler outputs intra-system flue gas. The flue gas separator separates the intra-system flue gas into a first and second flue gas stream, transfers the first flue gas stream to the second boiler, and transfers the second flue gas stream to a gas cleaning system. The second boiler receives oxygen from the oxygen input unit, fuel from the fuel input unit, and the first flue gas stream from the flue gas separator.