Oxy-combustion Windbox with Offset Inlets for NOx Reduction
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Solution Overview
Problem
Oxy-combustion systems in steam generators face challenges with high oxygen concentrations leading to increased costs, complexity, and parasitic power consumption due to significant flue gas recirculation, while also requiring expensive materials for ducts and components, and struggle with NOx emissions and corrosion issues in traditional oxy-fuel firing.
Innovation Solution
A tangentially fired oxy-combustion system with selectively enriched oxygen streams, utilizing a windbox with angularly offset inlets for fuel and oxidant injection, and oxygen-enriched gas recycle streams to moderate furnace temperatures and reduce NOx emissions, while maintaining heat transfer performance similar to air-fired combustion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If significant flue gas recirculation is used to moderate furnace temperatures in oxy-combustion systems, then furnace temperature control is improved, but system complexity, cost, and parasitic power consumption increase
Solution Approach 1:
The patent divides the single recirculation stream into multiple separate recirculation streams (first, second, and third streams) with different oxygen enrichment levels. Each stream serves a specific zone or function within the furnace, allowing temperature control in different regions independently while reducing the total recirculation rate needed, thereby lowering system complexity and power consumption.
Solution Approach 2:
Different regions of the furnace receive recirculation streams with locally optimized oxygen concentrations. The first stream with lower oxygen enrichment is directed to zones requiring temperature moderation, while streams with higher oxygen enrichment are directed to zones needing combustion support. This local optimization achieves temperature control without requiring high overall recirculation rates.
2Productivity
If high oxygen concentration is used in the oxidant stream, then combustion efficiency is improved, but material costs increase due to requirements for higher grade materials
Solution Approach 1:
The patent applies different oxygen concentrations to different locations and functions within the combustion system. High oxygen concentration streams are applied only where combustion efficiency is critical, while lower oxygen concentration streams are used in zones where temperature moderation is the primary concern. This localized approach maintains combustion efficiency while reducing the overall amount of high-grade oxygen-enriched material needed, thereby lowering material costs.
3Device complexity
If traditional air firing is used, then system simplicity is maintained, but harmful emissions including NOx are generated
Solution Approach 1:
The patent changes the chemical composition parameters of the oxidant stream by injecting pure oxygen or oxygen-enriched streams at multiple points. This parameter change transforms the combustion process from air-based (producing NOx) to oxygen-based (producing primarily CO2 and H2O), thereby eliminating NOx emissions while maintaining system operational simplicity through the use of standard combustion equipment.
4Productivity
If oxygen concentration in oxidant stream is increased above 21%, then combustion performance is improved, but duct and component material requirements become more expensive
Solution Approach 1:
The patent delivers high oxygen concentration streams only to specific locations where combustion performance is critical, such as primary combustion zones or areas requiring flame stabilization. Other regions receive lower oxygen concentration streams or standard air, allowing the use of conventional materials in those areas. This selective application maintains combustion performance while minimizing the extent of expensive material requirements.
Data Source
AI summary
A combustion system is provided for an oxy-combustion furnace. The combustion system includes at least one windbox mountable on the oxy-combustion furnace and having at least one main firing location. At least one primary inlet is positioned in the at least one main firing location for conveying fuel and the first oxidant into the oxy-combustion furnace. At least one secondary inlet is positioned in the at least one main firing location for conveying the second oxidant into the oxy-combustion furnace. The at least one secondary inlet is angularly offset from the at least one primary inlet.