Pre-mix burner assembly for low NOx emission furnace
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Solution Overview
Problem
Furnaces in HVAC systems face challenges in reducing NOx emissions due to factors like hydrocarbon fuel/air mixture ratio and residence time, leading to environmental pollution and regulatory compliance issues.
Innovation Solution
A pre-mix burner assembly with a thermally anisotropic protective covering and a gasket, along with an igniter, is used to control the hydrocarbon fuel/air mixture ratio and residence time, reducing NOx production by maintaining a consistent gas-air ratio and utilizing a fan to draw the mixture through a heat-exchange tube, which limits combustion residence time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If complete stoichiometric combustion is attempted, then heat energy production is maximized, but NOx emissions increase due to high combustion temperatures and extended residence time
Solution Approach 1:
The burner assembly dynamically adjusts the fuel-to-air ratio and combustion timing to optimize between heat production and NOx control. The pre-mix design allows real-time modulation of the combustion process characteristics
Solution Approach 2:
The system changes combustion parameters including reducing oxygen concentration in the burn zone, lowering peak combustion temperatures, and decreasing residence time of combustion gases to simultaneously maintain heat output while reducing NOx formation
2Productivity
If fuel/air mixture ratio is optimized for complete combustion, then combustion efficiency is improved, but NOx emissions increase due to higher combustion temperatures
Solution Approach 1:
The burner creates different local combustion zones with varying oxygen concentrations and temperature levels. The pre-mix section establishes a fuel-rich zone that transitions to a fuel-lean combustion zone, allowing efficient combustion while controlling peak temperatures
Solution Approach 2:
The system modifies the local combustion parameters by controlling the fuel-to-air ratio in the pre-mix section to be fuel-rich, which then combusts in a controlled manner to achieve high efficiency while limiting NOx formation through temperature and residence time control
3Reliability
If combustion residence time is extended, then complete combustion is achieved, but NOx emissions increase due to prolonged exposure to high temperatures
Solution Approach 1:
The burner design dynamically controls the residence time of combustion gases through the burner geometry and flow patterns, allowing complete combustion to occur rapidly while preventing prolonged exposure to high temperatures that would generate NOx
Solution Approach 2:
The combustion process is designed to complete rapidly in a short residence time, 'rushing through' the combustion event quickly to achieve complete combustion before temperatures can sustain NOx formation for extended periods
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 effectively reduces NOx production and emission by ensuring a lean hydrocarbon fuel/air mixture with short combustion residence times, enhancing combustion efficiency and compliance with environmental regulations.
Implementation Method 1
a thermally anisotropic protective covering located on the front side of the burner and surrounding a perimeter of the burner surface
Implementation Method 2
a thermal conductivity across a length and across a width of the thermally anisotropic protective covering is higher than a thermal conductivity across a thickness of the thermally anisotropic protective covering
Implementation Method 3
a gasket disposed between the burner and the housing
Implementation Method 4
an igniter positioned adjacent to the burner surface
Implementation Method 5
an igniter positioned adjacent to the burner surface
Implementation Method 6
utilizing a fan to draw the mixture through a heat-exchange tube
Data Source
AI summary
A burner assembly according to aspects of the disclosure includes a burner surface carried by a burner, the burner surface extending outward from a front side of the burner, a housing coupled to the burner on a side opposite the front side of the burner, a gasket disposed between the burner and the housing, a thermally anisotropic protective covering located on the front side of the burner and surrounding a perimeter of the burner surface, and an igniter positioned adjacent to the burner surface.