Venturi Mixing Conduits for Low NOx Combustion
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Solution Overview
Problem
Conventional combustion devices fail to effectively mix recirculated cooled products of combustion with fuel and oxidant, leading to incomplete mixing and high NOx formation, especially in larger burners, due to limited penetration of recirculated gases into the central flame zone.
Innovation Solution
A two-stage mixing approach using multiple secondary mixing conduits with a venturi-type design to aspirate and mix oxidant, fuel, and recirculated combustion products uniformly, reducing peak flame temperatures and NOx formation by enhancing mixing and heat dissipation across the flame.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If recirculated cooled products of combustion are introduced into the root of the flame, then flame temperature uniformity is improved, but mixing effectiveness deteriorates in larger burners due to inability to penetrate into the central flame zone
Solution Approach 1:
The mixing system is divided into multiple separate mixing conduits (first conduit, second conduit, third conduit, etc.) arranged in parallel. Each conduit independently mixes recirculated gases with fresh fuel and oxidant, ensuring that cooled combustion products can effectively reach and mix with the central flame zone without being overwhelmed by a single large-scale mixing system.
Solution Approach 2:
The patent transitions from a single-point recirculation approach to a distributed multi-conduit arrangement that spans across the flame cross-section. This dimensional distribution allows recirculated gases to penetrate into the central flame zone by introducing them at multiple locations simultaneously, overcoming the limitation of single-point injection in larger burners.
2Object-generated harmful factors
If multiple secondary mixing conduits are used to improve mixing uniformity, then NOx formation is reduced, but device complexity increases
Solution Approach 1:
The combustion device incorporates multiple secondary mixing conduits (at least three: first, second, and third conduits) arranged in parallel, each performing the same mixing function. This segmentation allows recirculated gases to be distributed across multiple flow paths, ensuring uniform mixing and effective penetration into the flame zone, which reduces peak temperatures and NOx formation.
Solution Approach 2:
The patent changes the flow distribution parameters by using multiple conduits with controlled flow rates. Each conduit receives a portion of the recirculated gases and mixes it with fresh fuel and oxidant in specific ratios. This parameter control ensures that the mixed gases are uniformly distributed across the flame, reducing hot spots and NOx emissions.
3Length of stationary object
If recirculated gases are mixed with fuel and oxidant in a single conduit, then mixing length is reduced, but mixing uniformity deteriorates especially in the central flame zone
Solution Approach 1:
Instead of using a single long mixing conduit, the patent employs multiple shorter mixing conduits arranged in parallel. Each conduit independently mixes recirculated gases with fresh fuel and oxidant over a short length, ensuring uniform mixing within each conduit. The combined output from multiple conduits achieves overall uniformity across the entire flame zone without requiring excessive mixing length.
Solution Approach 2:
The patent distributes the mixing process across multiple spatial dimensions by arranging conduits in parallel rather than extending a single conduit through a long path. This multi-dimensional arrangement allows each conduit to maintain short mixing lengths while collectively achieving uniform gas distribution across the flame cross-section, particularly in the central zone.
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 solution achieves improved flame temperature uniformity, reduced peak oxygen concentrations, and lower NOx emissions by ensuring uniform distribution and mixing of gases across the flame, enhancing combustion efficiency and stability.
Implementation Method 1
The use of a venturi-type design for at least one of primary and secondary mixing conduits allows pressure drop recovery and minimizes overall pressure drop for effective mixing
Implementation Method 2
Motive energy in the first mixture is utilized to aspirate at least second portions of one or more fluids selected from the group of oxidant, fuel and recirculated products of combustion
Data Source
AI summary
Methods and combustion devices for reducing NOx formation upon combusting oxidant with fuel to form products of combustion are provided. Such methods and device may involve mixing at least first portions of at least two fluids selected from the group of oxidant, fuel and recirculated products of combustion in at least one first conduit to form a first mixture. The first mixture is subsequently supplied to a plurality of second conduits each in direct fluid communication with the first conduit. Motive energy is utilized to aspirate at least second portions of one or more fluids selected from the group of oxidant, fuel and recirculated products of combustion in at least one second conduit to form a combustible mixture that can be subsequently burned. In one embodiment, the motive energy may be provided or result from the first mixture.