Perforated Flame Holder for Low NOx Boiler Combustion
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Solution Overview
Problem
Conventional burners face challenges in achieving low NOx emissions and efficient combustion, often requiring complex systems and additional measures like selective catalytic reduction or flue gas recirculation to approach clean combustion standards.
Innovation Solution
The use of a perforated flame holder that supports combustion reactions within its perforations, allowing for lean fuel-to-oxidant mixtures and efficient heat transfer, which reduces NOx formation and maintains stable combustion without the need for additional systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If conventional burners are used, then combustion can be achieved, but NOx emissions are high and additional reduction systems are required
Solution Approach 1:
The flame holder is constructed with a porous structure that allows fuel and oxidant to percolate through numerous small pores, creating distributed combustion zones. This porous configuration enables lean combustion while preventing NOx formation by avoiding high-temperature concentrated reaction zones, thereby reducing NOx emissions without requiring additional reduction systems
Solution Approach 2:
The combustion process is segmented into multiple distributed reaction zones within the porous structure rather than a single concentrated flame. This segmentation allows the combustion to occur at lower temperatures across many small regions, preventing the high-temperature conditions necessary for NOx formation while maintaining efficient heat release
2Object-generated harmful factors
If lean fuel-to-oxidant mixtures are used, then NOx formation is reduced, but combustion stability becomes difficult to maintain
Solution Approach 1:
The porous flame holder structure provides extensive surface area and distributed flow paths that stabilize the lean fuel-to-oxidant mixture. The porous matrix maintains combustion stability by providing continuous contact between fuel and oxidant throughout the porous volume, preventing flameout even at lean ratios that would normally be unstable
Solution Approach 2:
The porous flame holder acts as an intermediary structure that mediates between the lean fuel-to-oxidant mixture and the combustion reaction. It provides a stable framework that sustains the combustion process at lean ratios by distributing the reactants uniformly and maintaining adequate residence time for stable burning
3Object-generated harmful factors
If additional reduction systems are added, then NOx emissions decrease, but device complexity and cost increase
Solution Approach 1:
The porous flame holder structure inherently provides NOx reduction through its physical design, eliminating the need for external reduction systems. The self-service mechanism of the porous structure naturally distributes fuel and oxidant to prevent high-temperature zones, achieving NOx reduction without requiring additional equipment like SCR or SNCR systems
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 achieves low NOx emissions (down to undetectable levels) and stable combustion, eliminating the need for extra reduction systems, with experimental results showing minimal NOx production and complete combustion even at lean fuel-to-oxidant ratios.
Implementation Method 1
a bluff body flame holder aligned to receive a fuel and combustion air mixture from an outlet end of the mixing tube. The bluff body flame holder may be configured to hold a combustion reaction for heating the combustion volume wall
Implementation Method 2
The combustion volume wall may be configured to heat a volume thermal load
Data Source
AI summary
According to an embodiment, a fired heater includes a fuel and combustion air source configured to output fuel and combustion air into a combustion volume, the combustion volume including a combustion volume wall defining a lateral extent separate from an exterior volume. According to an embodiment, the fired heater includes a boiler heater and the combustion volume wall comprises a combustion pipe defining a lateral extent of the combustion volume, the combustion pipe being disposed to separate the combustion volume from a water and steam volume. The fired heater includes a mixing tube aligned to receive the fuel and combustion air from the fuel and combustion air source. The mixing tube may be separated from the combustion volume wall by a separation volume. The fired heater includes a bluff body flame holder aligned to receive a fuel and combustion air mixture from an outlet end of the mixing tube. The bluff body flame holder may be configured to hold a combustion reaction for heating a combustion volume wall. The combustion volume wall may include a combustion pipe. The combustion pipe may be configured to heat the water in the water and steam volume.