Low NOx Burner Internal Recirculation Flame Stability
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Solution Overview
Problem
Existing low NOx emitting burners require high amounts of flue gas recirculation, leading to increased energy costs and maintenance due to larger blower and conduit requirements, and are susceptible to overheating and flame instability.
Innovation Solution
A burner design that eliminates the need for a tubular enclosure, with a combustion air spinner and fuel spuds positioned within the combustion chamber, utilizing internal furnace gas recirculation to cool the flame and stabilize it, while reducing the radial footprint and avoiding high flow velocities that cause instability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If high amounts of flue gas recirculation are used to reduce NOx emissions, then NOx emissions are reduced, but the overall volume of gas increases requiring larger blower and conduits which increases energy costs and maintenance
Solution Approach 1:
The patent implements internal recirculation passages within the burner tube structure itself, nesting the recirculation system inside the burner assembly. This allows flue gas to be recirculated through internal passages (as shown in Figures 1-4 with passages 14, 16, 18) without requiring external blowers or large conduits, thereby reducing NOx emissions while avoiding increased blower energy consumption
Solution Approach 2:
The burner design uses the existing gas flow through the burner to drive the recirculation process internally. The recirculation passages are positioned to utilize the natural flow dynamics of the combustion gases, allowing the system to recirculate flue gas without requiring additional external energy input from blowers
2Object-generated harmful factors
If high amounts of flue gas recirculation are used to reduce NOx emissions, then NOx emissions are reduced, but larger conduits and blowers are required which increases installation and maintenance costs
Solution Approach 1:
The recirculation passages (14, 16, 18) are integrated within the burner tube structure, nesting the recirculation function inside the existing burner assembly. This eliminates the need for separate external conduits and blowers, reducing device complexity while maintaining effective flue gas recirculation for NOx reduction
Solution Approach 2:
The burner tube structure serves multiple functions: it acts as the combustion chamber, provides structural support, and incorporates internal recirculation passages. This multi-functionality eliminates the need for separate dedicated recirculation conduits, simplifying the overall system
3Object-generated harmful factors
If the burner uses a tubular enclosure with internal recirculation, then NOx emissions are reduced, but the tube is susceptible to overheating and damage when fuel burns inside the tube
Solution Approach 1:
The patent creates distinct zones within the burner structure: the internal recirculation passages (14, 16, 18) are positioned to provide cooling and dilution at specific locations, while the combustion occurs in the external region. This local differentiation ensures that the tube walls are protected from direct flame contact while maintaining effective recirculation for NOx reduction
Solution Approach 2:
The recirculated flue gas acts as an intermediary substance that absorbs excess heat and dilutes the combustion mixture. By introducing this intermediate cooling/diluting medium through the internal passages, the direct thermal load on the tube walls is reduced, preventing overheating and damage
4Object-generated harmful factors
If recirculated flue gas is used to lower flame temperatures, then NOx generation is reduced, but flame instability and blowout occur in excessive amounts
Solution Approach 1:
The patent carefully controls the parameters of recirculated flue gas, including its temperature (maintained in the range of 93°C to 204°C), flow rate, and mixing ratio with fresh combustion air. By optimizing these parameters, the system achieves sufficient flame temperature reduction for NOx control while maintaining flame stability through proper mixture composition
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 lower NOx emissions with improved flame stability and reduced operational costs by decelerating gas flows and reducing the need for larger blowers and conduits, while maintaining a compact and efficient burner structure.
Implementation Method 1
employ furnace gas recirculation inside the combustion chamber of the furnace to reduce NOx emissions
Implementation Method 2
Recirculated flue gas lowers flame temperatures and NOx generation
Implementation Method 3
decelerating gas flows and reducing the need for larger blowers and conduits
Implementation Method 4
mix the combustion air for the burner with flue gas going to the exhaust stack
Data Source
Figure 1
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Figure 3
AI summary
A low NOx burner for installation on a furnace wall. The burner has an elongated tube connected to a combustion air supply, the furnace side end of which mounts a combustion air spinner that is spaced a substantial distance from the furnace wall. A plurality of typically six elongated air ports extend through the wall from the windbox of the furnace into the combustion chamber and supply most of the required combustion air. Downstream ends of the air ports are spaced from the furnace wall as well as from the spinner, and they are configured to bias the discharged air flow towards the spinner. A plurality of first fuel gas spuds with fuel gas discharge orifices is arranged about the spinner and discharges fuel gas into the combustion chamber downstream of the spinner.