Double Dilution Burner for Low NOx Emissions
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Solution Overview
Problem
Existing radiant tube burners face challenges in achieving low nitrogen oxides (NOx) emissions while maintaining energy efficiency and flame stability, especially at varying temperature levels, due to limitations in dilution methods that can lead to flame instability and high NOx production at low temperatures.
Innovation Solution
A double dilution process is implemented, where combustion air is mixed with combustion products upstream of the burner, and the gaseous fuel is mixed with recirculated flame or partial combustion products at the burner nozzle, providing thermal energy and modifying the physical and chemical characteristics of the fuel for stable operation, even at low oxygen contents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If dilution of combustion air with flue gases is increased to reduce NOx emissions, then NOx emission level decreases, but flame stability and inflammability deteriorate
Solution Approach 1:
The patent divides the single dilution process into two sequential stages: first diluting combustion air with flue gases upstream of the burner, then further diluting the fuel-oxidant mixture within the burner body. This segmentation allows each stage to contribute partially to the total dilution, maintaining flame stability while achieving low NOx emissions.
Solution Approach 2:
The first dilution stage is performed preliminarily upstream of the burner, where flue gases are mixed with combustion air before reaching the combustion zone. This preliminary dilution reduces the oxygen concentration in advance, preparing the mixture for low-NOx combustion while maintaining sufficient flame stability through controlled mixing ratios.
2Object-generated harmful factors
If dilution of combustion air is increased to reduce NOx emissions, then NOx emission level decreases, but energy efficiency deteriorates
Solution Approach 1:
The patent modifies the composition and temperature parameters of the combustion mixture through two-stage dilution. By controlling the ratio of flue gases to combustion air and the extent of fuel mixing, the system achieves low NOx emissions while maintaining energy efficiency through optimized thermal conditions in the combustion zone.
3Object-generated harmful factors
If dilution of combustion air is increased to reduce NOx emissions, then NOx emission level decreases, but flame ignition capability deteriorates
Solution Approach 1:
The ignition process is supported by segmenting the dilution into two stages, where the first stage upstream of the burner maintains better ignition conditions with moderate dilution, while the second stage within the burner achieves additional dilution after ignition has been established, preventing flame extinction.
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 approach allows for significantly reduced NOx emissions, achieving levels as low as 100 mg/Nm3 @ 3% O2 across all operating temperatures without compromising flame stability, by modifying the thermochemical properties of the fuel and extending the inflammability limits of the air/fuel mixture.
Implementation Method 1
A large number of burners according to the prior art use dilution in order to reduce the level of NOx emitted, the combustion air or the flame being diluted by combustion products
Implementation Method 2
a second dilution is achieved by mixing the gaseous fuel with a recirculated portion of the flame or partial combustion products, this second dilution having an input of thermal energy at the meeting point of the gaseous fuel with the recirculated portion of the flame or the partial combustion products
Implementation Method 3
during the combustion of a gaseous fuel in a burner intended for an direct flame or controlled-atmosphere reheating furnace
Data Source
AI summary
A method for reducing nitrogen oxide NOx emissions during combustion of a gaseous fuel in a burner intended for a naked-flame or controlled-atmosphere reheating furnace, for reheating steel products or for continuous coating and/or annealing of metal strips, wherein a first dilution is carried out by mixing combustion air with combustion products upstream from or in the body of the burner, and a second dilution is carried out directly at the level at which the gaseous fuel reacts with the combustion air, mixing the fuel with a recirculated portion of the flame or products of partial combustion, the double dilution enabling the physical and chemical properties of the gas to be modified in order for the burner to operate with low oxygen rates and obtain a flame that produces a very low level of NOx production regardless of the temperature of the enclosure in which the combustion takes place.