Nested-Channel Burner Assembly for Low-NOx Premix Combustion
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Solution Overview
Problem
Existing premix burners struggle to achieve low NOx emissions below 15 ppm with oxygen excesses of less than 3% and below 5 ppm with oxygen excesses of less than 7%, while maintaining compatibility with commercially available furnaces, and are prone to backfire.
Innovation Solution
A burner design featuring a combustion head with nested channels and a discharge channel that accelerates the premixed air-fuel mixture, combined with precise control of primary air and gas flow using flow controllers and nozzles, to stabilize the flame and optimize mixture ratios, reducing NOx emissions to less than 2.5 ppm with oxygen excesses of less than 8%.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If a long combustion head is used to achieve low NOx emissions, then NOx emissions are reduced, but the burner becomes less compatible with commercially available furnaces and harder to install
Solution Approach 1:
The combustion head is divided into multiple functional sections: a primary combustion section with inner and outer channels for controlled air-fuel mixing, and a secondary combustion section. This segmentation allows optimized combustion chemistry for low NOx emissions while maintaining a compact overall length that fits standard furnace configurations.
Solution Approach 2:
The combustion head employs nested channel structures where an inner channel is surrounded by an outer channel, creating concentric flow paths for primary air and fuel mixture. This nested arrangement maximizes mixing efficiency and combustion control within a compact footprint, improving both emission performance and installability.
2Productivity
If oxygen excess is reduced to below 12% to improve efficiency, then fuel efficiency increases, but NOx emissions increase above acceptable levels
Solution Approach 1:
Primary air is introduced through the inner channel before the fuel-air mixture reaches the combustion zone, pre-cooling the incoming mixture and controlling the timing of oxidation. This preliminary air introduction allows efficient combustion at low oxygen excess while suppressing thermal NOx formation by controlling peak temperatures and oxidation timing.
Solution Approach 2:
The burner controls the phasing and timing parameters of air-fuel mixing and combustion. By adjusting the relative timing of primary air injection and fuel injection, and controlling the mixture ratio parameters, the system achieves efficient combustion at low oxygen excess (improving productivity) while maintaining NOx emissions below acceptable levels through optimized combustion chemistry.
3Productivity
If primary air flow is increased to improve mixing, then combustion efficiency improves, but the risk of backfire increases
Solution Approach 1:
The nested channel structure acts as an intermediary flow control mechanism. The inner channel provides a controlled path for primary air to reach the combustion zone, while the outer channel manages the fuel-air mixture flow. This intermediary structure allows precise control of air-fuel mixing timing and rate, improving combustion efficiency while preventing excessive air flow that could cause backfire.
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 burner achieves low NOx emissions and improved compatibility with diverse combustion chambers, minimizing backfire risk and enhancing safety, while maintaining efficient operation.
Implementation Method 1
a burner (1) installable to a furnace for burning an air-fuel mixture and for generating a flame in the furnace
Implementation Method 2
burning a mixture of premixed fuel and air
Implementation Method 3
a flow controller (7) is provided in the flow space for primary air, at the distal end, for directing the flow of primary air in the flow space
Data Source
AI summary
A burner (1) installable to a furnace (9) for burning an air-fuel mixture and for generating a flame in the furnace (9), said burner (1) comprising a frame member (6) provided with an elongated combustion head (2) protruding from said frame member (6) and being adaptable inside the furnace (9), what in a view from the burner's (1) frame member (6) is a distal end (2a) of said combustion head (2) being adaptable to generate both a main flame (B) and a primary flame (E), said combustion head (2) comprising an outer, larger diameter channel (3) for a mixture (80) of combustion air and fuel, as well as a smaller diameter, inner channel (4), surrounded by said outer channel (3), for primary air (60) as well as for primary gas (70), wherebythe inner channel (4) extends from the burner's frame member (6) to the distal end (2a) and comprises an inner tube (4, 41) for primary gas (70) and an outer tube (4; 42) surrounding said inner tube (4; 41), wherein a flow space (4; 43) for primary air (60) is provided between the outer side of the jacket (41a) of said inner tube and the inner side of the jacket of the outer tube, and which combustion head's (2) outer channel (3) extends from the burner's frame member (6) to the combustion head's distal end (2a) and can be provided with a supply of premixed air-fuel mixture (80) from the burner's frame member (6), or from that section of the combustion head (2) which is associated with the frame member and located, in the flowing direction of the premixed air-fuel mixture (80), upstream of a combustion chamber (90), for generating the main flame B).In said burner the space delimited by the outer wall (31) of the outer channel (3) and the jacket of the outer tube (42) of the inner channel (4) is constructed as a discharge channel (10) extending from the frame member (6) to the distal end (2a) of the combustion head (2), whereby the discharge end (10a) of said discharge channel is veered away from the longitudinal center line (P) of the combustion head (2) so that the center line (10A) of said discharge end (10a), or an extension thereof, forms an inclined angle of incidence (t) with the combustion head's (2) longitudinal center line (P), said angle of incidence (t) being 90-140 degrees as said discharge end (10a) of the discharge channel (10) is viewed from the direction of the burner's (1) frame member (6),a flow controller (7) is provided in the flow space (4; 43) for primary air, at the distal end (2a) of the combustion head (2), for directing the flow of primary air (60) in the flow space (43) so that the primary air (60) flows from the flow controller (7) towards the mouth (43a) of the flow space (43), in the vicinity of the jacket (42a) of the outer tube (4; 42) of the inner channel (4),a plurality of nozzles (8) is provided in the inner tube (4; 41) of the inner channel (4), at the distal end (41a) of said inner tube (4) in the flowing direction of the primary gas (70), for directing the primary gas (70) into the flow space (4; 43), either upstream or downstream of the flow controller (7) in the flowing direction of the primary air (60).