Staged Recirculating Burner With Helical Fins for Low NOx
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Solution Overview
Problem
Existing combustion systems face challenges in reducing nitrogen oxides (NOx) emissions and achieving high efficiency and uniform temperature characteristics, particularly in high-temperature applications.
Innovation Solution
A staged recirculating burner system with a combustion tube having helical fins, a combustion nozzle, and a staging gas nozzle, combined with a heat exchanger, uses silicon carbide components to manage airflow and gas injection, creating a lean gas mixture to suppress NOx formation and enhance heat transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If flame temperature is increased to improve combustion efficiency, then combustion efficiency is improved, but nitrogen oxides (NOx) emissions increase
Solution Approach 1:
The combustion process is divided into multiple stages with separate air introduction zones. Primary combustion occurs in a fuel-rich zone with limited oxygen, followed by secondary combustion in a fuel-lean zone. This segmentation allows high combustion efficiency while maintaining lower peak temperatures that suppress NOx formation.
Solution Approach 2:
Different regions of the combustion chamber have different oxygen concentrations and temperature profiles. The burner creates a fuel-rich zone near the combustion surface with low oxygen availability, and a fuel-lean zone further away with higher oxygen. This local quality variation enables efficient combustion with reduced NOx emissions.
2Object-generated harmful factors
If air staging is used to reduce nitrogen oxides (NOx) emissions, then nitrogen oxides (NOx) emissions are reduced, but combustion efficiency decreases
Solution Approach 1:
Air is introduced in two distinct stages: primary air for initial combustion and secondary air for completing the combustion process. This segmentation ensures complete fuel combustion (high efficiency) while controlling peak temperatures (low NOx) by limiting oxygen availability during the high-temperature phase.
Solution Approach 2:
The burner geometry and air distribution are designed to create optimal fuel-rich conditions before secondary air is introduced. This preliminary action ensures that combustion occurs efficiently in the controlled low-oxygen environment, maximizing energy release before the lean combustion phase begins.
3Object-generated harmful factors
If recirculating flue gas is used to limit nitrogen oxides (NOx) emissions, then nitrogen oxides (NOx) emissions are limited, but combustion temperature decreases
Solution Approach 1:
The system creates localized high-temperature zones for efficient combustion while maintaining overall lower average temperatures through flue gas recirculation. The recirculated flue gas mixes with the combustion air, creating a fuel-rich zone with controlled temperature that suppresses NOx formation while allowing complete combustion.
Solution Approach 2:
Flue gas that would otherwise be wasted heat loss is recirculated back into the combustion process. This converts a harmful emission into a beneficial cooling agent that suppresses NOx formation while the heat contained in the recirculated gas is recovered to preheat combustion air, improving overall efficiency.
4Productivity
If high combustion temperature is used to achieve high efficiency, then combustion efficiency is improved, but thermal stresses increase
Solution Approach 1:
The combustion process is segmented into fuel-rich and fuel-lean zones, preventing extreme peak temperatures while maintaining high overall combustion efficiency. This reduces thermal stresses on burner components and radiant tubes, extending system life and reducing maintenance needs.
Solution Approach 2:
The system changes the combustion parameters by controlling oxygen availability and residence time in different zones. By maintaining fuel-rich conditions initially and then introducing secondary air, the system achieves high efficiency combustion with controlled temperature profiles that reduce thermal stress on components.
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 achieves low NOx emissions (less than 240 ppm) and CO emissions (less than 10 ppm), high efficiency, and uniform temperature distribution, with reduced thermal stresses and maintenance needs.
Implementation Method 1
a heat exchanger coupled to the combustion tube that heats the combustion gases provided to the combustion tube using the products of combustion from the combustion tube
Implementation Method 2
a ceramic wall as part of the combustion tube that separates the flow of the combustion gases and the flow of the products of combustion
Data Source
AI summary
Embodiments of the present invention include high-temperature staged recirculating burners and radiant tube burner assemblies that provide high efficiency, low NOx and CO emissions, and uniform temperature characteristics. One such staged recirculating burner includes a combustion tube having inside and outside helical fins forming opposing spiral pathways for combustion gases and products of combustion, a combustion nozzle coupled to the combustion tube, a gas tube running axially into the combustion tube, and a staging gas nozzle coupled to the gas tube, where the staging gas nozzle includes radial exit holes into the combustion tube and an axial gas staging tube extending into the combustion nozzle to stage combustion.