Air Intake Coupling Noise Suppression for Low NOx Furnace
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Solution Overview
Problem
Furnaces in HVAC systems face challenges in reducing NOx emissions and operational noise due to incomplete combustion and resonance issues, respectively, which existing technologies have not adequately addressed.
Innovation Solution
The design incorporates an air intake coupling with noise suppression holes and a pre-mix burner system that controls the hydrocarbon fuel/air mixture ratio to minimize excess air combustion, coupled with a gas-air mixer elbow and heat-exchange tube configuration to reduce NOx production and operational noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional combustion is used in furnaces, then complete combustion is difficult to achieve, but increasing combustion residence time or adjusting fuel/air ratio to improve combustion completeness leads to increased NOx emissions
Solution Approach 1:
The combustion process is segmented into two distinct stages: first stage combustion in the burner box assembly with controlled air supply, and second stage combustion in the combustion chamber with additional atmospheric air. This segmentation allows incomplete combustion products from stage one to be further oxidized in stage two, achieving complete combustion without excessive residence time at high temperatures that would generate NOx
Solution Approach 2:
The two-stage combustion system maintains continuous combustion action throughout the furnace operation. The first stage continuously generates heat and partial combustion products, while the second stage continuously completes the combustion process. This continuous dual-stage operation ensures complete combustion efficiency while controlling peak temperatures and residence times to minimize NOx formation
2Object-generated harmful factors
If pre-mix burner system with controlled fuel/air mixture is used, then NOx emissions are reduced, but combustion residence time must be carefully controlled to maintain combustion efficiency
Solution Approach 1:
The combustion residence time is segmented into two phases: a first residence time in the burner box assembly for initial combustion of the pre-mixed fuel/air mixture, and a second residence time in the combustion chamber for completing combustion with additional air. This segmentation allows each stage to be optimized independently, maintaining efficient combustion while controlling overall residence time to prevent excessive NOx formation
Solution Approach 2:
Different local conditions are created in different zones of the combustion system. The burner box assembly provides a controlled environment for pre-mix combustion with specific temperature and residence time characteristics, while the combustion chamber provides a separate zone with different conditions for completing combustion. This local differentiation allows precise control of combustion residence time in each zone to optimize both efficiency and emissions
3Quantity of substance
If air intake coupling is used for furnace operation, then combustion air supply is provided, but resonance occurs during furnace operation causing operational noise
Solution Approach 1:
The harmful resonant frequencies are extracted and eliminated from the air intake coupling by drilling noise suppression holes through the coupling walls. These holes allow the resonant acoustic energy to escape rather than building up within the coupling, thereby reducing operational noise while maintaining the primary function of supplying combustion air to the furnace
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 configuration achieves low NOx emissions and significantly reduces operational noise by ensuring short combustion residence times and minimizing excess air combustion, thereby meeting environmental regulations and improving system efficiency.
Implementation Method 1
at least one noise suppression hole formed in the second tubular section
Implementation Method 2
the controlled combustion of a hydrocarbon fuel such as, for example, propane or natural gas, in the presence of atmospheric air
Implementation Method 3
A heat-exchange tube has a first end that is fluidly coupled to the burner box assembly
Data Source
AI summary
An air intake coupling has at least one noise suppression hole formed therein. A gas-air mixer elbow is fluidly coupled to the air intake coupling. A burner box assembly is fluidly coupled to the gas-air mixer elbow via a gas-air plenum box. A heat-exchange tube has a first end that is fluidly coupled to the burner box assembly. A fan is fluidly coupled to a second end of the heat-exchange tube via a cold-end header box.