Staged Liquid-Fuel Burner Layout for Ultra-Low NOx Emissions
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Solution Overview
Problem
Existing burners for liquid fuels and fuel gases produce high levels of NOx emissions, exceeding 200 ppm for liquid fuels with nitrogen compounds and 150 ppm for nitrogen-free fuels, while comparable gas burners achieve less than 30 ppm, necessitating a need for burners with reduced NOx emissions.
Innovation Solution
The burner design incorporates multiple injection points for combustion air and a NOx reducing medium, including a NOx reducing medium conduit surrounding the fuel injector, a passage through the burner tile, and optional staged fuel gas outlets, to create staged combustion zones that reduce NOx formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If liquid fuels are combusted in conventional burners, then high heat output is achieved, but NOx emissions exceed 200 ppm
Solution Approach 1:
The combustion process is divided into multiple staged zones (primary combustion zone, secondary combustion zone, and recombination zone) with distinct functions. The primary zone handles fuel atomization and initial combustion, the secondary zone completes oxidation, and the recombination zone merges products. This segmentation allows controlled temperature zones that reduce thermal NOx formation while maintaining overall heat output.
Solution Approach 2:
A recirculation system introduces flue gas as an intermediary substance into the combustion zones. The flue gas acts as a thermal mediator, absorbing excess heat and lowering peak temperatures in the combustion zones, thereby reducing thermal NOx formation while not significantly impacting the overall heat output of the burner.
2Object-generated harmful factors
If staged air and staged fuel burners are used, then thermal NOx formation is reduced, but flame temperature is lowered
Solution Approach 1:
Different zones are created with different stoichiometric ratios and temperature characteristics. The primary combustion zone operates with controlled excess air to limit thermal NOx, while the secondary combustion zone provides complete oxidation. The recombination zone restores adiabatic temperature conditions. This local differentiation allows NOx reduction without excessive temperature loss.
Solution Approach 2:
The system dynamically adjusts combustion parameters including air-to-fuel ratios, flame velocity, and temperature distribution across different zones. By optimizing these parameters in each zone, the system achieves low NOx emissions while maintaining sufficient flame temperature for effective heating.
3Object-generated harmful factors
If flue gas recirculation is introduced, then thermal NOx formation is reduced, but device complexity increases
Solution Approach 1:
The recirculation system is merged with the existing burner structure, combining the flue gas recirculation function with the primary and secondary combustion zones. The recirculation inlet is integrated into the burner assembly, allowing flue gas to be introduced directly into the combustion zones without requiring separate external systems, thereby reducing overall device complexity.
4Object-generated harmful factors
If multiple injection points for combustion air are used, then staged combustion zones are created, but device complexity increases
Solution Approach 1:
The combustion air injection system is designed with multi-functionality, where the same injection infrastructure supports both primary combustion air supply and secondary combustion air supply. The staged air injection system serves dual purposes: controlling primary zone stoichiometry and providing air for secondary zone oxidation, thereby reducing the need for separate complex injection systems for each function.
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
This design achieves NOx emissions of less than 10 ppmvd with modest amounts of NOx reducing medium, maintaining burner stability and continuous operation, and reduces the need for NOx credits.
Implementation Method 1
The introduction of a NOx reducing medium into the combustion zone lowers the flame temperature and reduces the formation of thermal NOx
Implementation Method 2
The flue gas, which is relatively cool, passes into and through the combustion zones thereby further cooling the combustion zone and reducing thermal NOx formation
Implementation Method 3
The water vapor in the flue gas also serves to mitigate NOx created via the prompt NOx mechanism by solvating and catalyzing hydrocarbon combustion
Implementation Method 4
The interior chamber is heated by a plurality of burners which receive a fuel which combusts to produce heat
Implementation Method 5
gaseous fuels and combustion air are thoroughly mixed and rapidly combusted
Data Source
AI summary
A liquid fuel or hybrid fuel burner and method of operating the burner are described. The combustion air and/or NOx reducing medium are introduced at more than one location in the burner. A portion of the combustion air and the NOx reducing medium can be injected into the primary combustion zone through the NOx reducing medium conduit which surrounds the fuel injector which injects atomized liquid fuel or fuel gas into the primary combustion zone. Another portion of the combustion air and the NOx reducing medium can be introduced into the primary combustion zone through a passage in the burner tile surrounding the NOx reducing medium conduit. A third portion of NOx reducing medium can be injected outside the burner tile. NOx reducing medium can be introduced into any combination of the three locations.