Push-Pull Furnace Blower Design to Reduce NOx Emissions Below 14 ng/J
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Solution Overview
Problem
Conventional furnaces face challenges in minimizing nitrogen oxides (NOx) production while maintaining reliable and efficient combustion for heating, as richer fuel/air mixtures increase NOx levels but are necessary for higher combustion temperatures and efficiency.
Innovation Solution
A 'push-pull' furnace design with a first blower that pushes a fuel/air mixture into a burner box and a second blower that pulls flue products through a heat exchanger, maintaining a lean fuel/air ratio to reduce NOx levels below 14 ng/J, while ensuring stable combustion and heating efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a richer fuel/air mixture is used to increase combustion temperature and efficiency, then heating efficiency is improved, but nitrogen oxides (NOx) production increases
Solution Approach 1:
The combustion process is segmented into two distinct phases: a premixing stage where fuel and air are combined in a controlled ratio, and a combustion stage where the mixture is burned. This segmentation allows the fuel/air mixture to be prepared with a lean ratio (reducing NOx) while still achieving efficient combustion through proper mixing and ignition control.
Solution Approach 2:
The patent changes the fuel/air ratio parameter to a lean mixture (excess air) to reduce combustion temperature and thereby minimize NOx formation. Additionally, the mixing time and combustion conditions are adjusted to ensure complete combustion despite the leaner mixture, maintaining heating efficiency while reducing harmful emissions.
2Object-generated harmful factors
If a leaner fuel/air ratio is used to reduce NOx levels, then nitrogen oxides (NOx) production decreases, but combustion stability and heating efficiency deteriorate
Solution Approach 1:
The fuel and air are premixed before combustion in a controlled environment (burner box) to ensure uniform distribution and proper mixing ratio. This preliminary mixing action guarantees that even with a lean fuel/air ratio, the combustion remains stable and reliable, as each portion of the mixture is properly prepared before ignition.
Solution Approach 2:
The system monitors combustion conditions and adjusts the fuel/air mixture ratio and flow rates to maintain stable combustion. Feedback control ensures that the lean mixture burns efficiently and reliably, preventing combustion instability while maintaining low NOx emissions through dynamic adjustment of operating parameters.
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 furnace effectively minimizes NOx production while maintaining reliable combustion and heating efficiency by precisely balancing the fuel/air ratio, achieving low NOx emissions and stable operation.
Implementation Method 1
The inlet nozzle is configured such that operation of the first blower is to pull air and fuel into the inlet nozzle via the air inlet and fuel inlet, respectively
Implementation Method 2
combustion assembly including at least one burner configured to combust the fuel/air mixture... producing flue products having less than 14 Nano-grams per Joule (ng/J) of nitrogen oxides (NOX)
Implementation Method 3
heat exchanger assembly fluidly coupled to the burner box through a vestibule... configured to receive flue products from the burner
Implementation Method 4
a second blower configured to pull the flue products through the heat exchanger assembly
Data Source
AI summary
Example furnaces and methods related thereto include a burner box including at least one burner configured to combust a fuel/air mixture. In addition, the furnace includes a first blower including an inlet nozzle having an air inlet and fuel inlet. The inlet nozzle is configured such that operation of the first blower is to pull air and fuel into the inlet nozzle to produce the fuel/air mixture at a fuel/air ratio that is configured to produce flue products having less than 14 Nano-grams per Joule of nitrogen oxides when combusted. Operation of the first blower is configured to push the fuel/air mixture into the burner box. Further, the furnace includes a heat exchanger assembly fluidly coupled to the burner box through a vestibule, and a second blower configured to pull the flue products through the heat exchanger assembly.