Oxy-combustion Boiler Transition Control via Flue Gas Recycle
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Solution Overview
Problem
Implementing oxy-combustion on a commercial scale is hindered by challenges in adequately oxygenating the flue gas and developing a methodology for starting up and transitioning to oxy-combustion in utility coal boilers, particularly in controlling carbon dioxide emissions and minimizing nitrogen oxide emissions.
Innovation Solution
A boiler structure and methodology that allows for gradual transition between air and oxygen firing modes by controlling flue gas recycle flow, oxygen supply, and fresh air intake to maintain proper combustion conditions, with careful measurement and regulation of gas flow and oxygen levels to achieve full oxygen combustion mode, enabling efficient carbon dioxide processing and storage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If air is replaced with oxygen in combustion, then carbon dioxide concentration in flue gas increases, but system complexity increases due to need for oxygen supply and flue gas recycling systems
Solution Approach 1:
The combustion system is divided into separate oxygen supply and flue gas recycling subsystems, each independently controlled. This allows the complex oxy-combustion process to be managed through modular components rather than a monolithic system, making the high carbon dioxide concentration achievable while keeping system complexity manageable through structured segmentation.
Solution Approach 2:
The system dynamically adjusts oxygen concentration and flue gas recycling ratios as operational parameters to optimize carbon dioxide concentration in the flue gas. By continuously varying these parameters based on load conditions, the system achieves high CO2 concentration without requiring maximum complexity at all operating points.
2Quantity of substance
If flue gas recycling is increased to achieve oxy-combustion, then carbon dioxide concentration improves, but transition control difficulty increases
Solution Approach 1:
The transition control system incorporates feedback mechanisms that monitor oxygen levels, flue gas flow rates, and combustion parameters in real-time. This feedback allows the control system to automatically adjust flue gas recycling ratios and oxygen supply during transition phases, reducing the difficulty of detecting and measuring the optimal transition point while maintaining high carbon dioxide concentration.
Solution Approach 2:
The system employs dynamic control strategies that adapt flue gas recycling ratios and oxygen injection rates based on real-time combustion conditions. This dynamic approach smooths the transition between air-firing and oxy-combustion modes, making the transition control more manageable while achieving the desired carbon dioxide concentration in the flue gas.
3Productivity
If oxygen injection is increased to maintain combustion, then combustion efficiency improves, but energy consumption increases
Solution Approach 1:
The system optimizes oxygen injection rates and flue gas recycling ratios as variable parameters based on combustion load and efficiency requirements. By dynamically adjusting these parameters rather than maintaining constant high oxygen levels, the system achieves high combustion efficiency while minimizing the energy required for oxygen supply and gas recycling operations.
Solution Approach 2:
The system applies oxygen injection and flue gas recycling at partial levels sufficient to achieve the required combustion efficiency rather than using excessive oxygen throughout. This partial action approach maintains productivity while reducing the energy consumption associated with oxygen production and gas recycling systems.
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
Enables the production of a flue gas primarily composed of carbon dioxide and water, reducing nitrogen oxide emissions and eliminating the need for additional chemical scrubbing, while maintaining system pressure and equilibrium during transitions, facilitating carbon dioxide storage or industrial uses.
Implementation Method 1
combustion of fuel in a boiler furnace with an oxygenated gas instead of air to produce a flue gas having a high concentration of carbon dioxide
Implementation Method 2
recycle a portion of the flue gas from the stack back to the burner inlet where it mixes with fresh air and oxygen
Data Source
AI summary
A new and unique boiler and method of transition between air and Oxy-combustion in a coal fired combustion process wherein near pure oxygen may be introduced to the boiler furnace in several locations including directly into the flame through the burner and/or directly into the furnace as nearly pure oxygen, and/or into the recycle flue gas streams to the burners, including both primary and secondary streams.