Fired Heater Mixing Nozzle for Low-NOx, Uniform Heat Transfer
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Solution Overview
Problem
Fired heaters and boilers produce harmful nitrogen oxides (NOx) and underutilize tube surface area due to high flame temperatures and localized heating, leading to tube oxidation and fouling, while existing technologies fail to address the root cause of locally high temperatures.
Innovation Solution
A fluid mixture nozzle assembly that injects a primary fuel mixture with vitiated atmospheric flue gas in a vitiated oxygen atmosphere, using a converging-diverging mixing channel to suppress flame formation and enhance mixing, reducing NOx production and increasing heat transfer efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If flames are used to generate heat in fired heaters, then heat transfer to process tubes is achieved, but nitrogen oxides (NOx) are produced due to high-temperature combustion
Solution Approach 1:
The patent changes the temperature parameter by introducing vitiated air (combustion products) to dilute the combustion mixture, reducing the flame temperature from typical high values to below 1500°F. This parameter change suppresses NOx formation while maintaining heat transfer to process tubes through controlled combustion in a diluted atmosphere
Solution Approach 2:
The patent creates an inert-like environment by introducing vitiated air containing CO2 and H2O into the combustion zone. These combustion products act as inert diluents that reduce oxygen concentration and flame temperature, suppressing NOx formation while allowing combustion to proceed and transfer heat to process tubes
2Power
If high-temperature flames are used for heating, then heat transfer efficiency increases, but tube oxidation and fouling occur
Solution Approach 1:
The patent reduces the temperature parameter by diluting the flame with vitiated air, maintaining temperatures below 1500°F. This temperature reduction prevents tube oxidation and fouling while sufficient heat transfer is maintained through the controlled combustion process and radiant heat transfer to process tubes
Solution Approach 2:
The patent introduces vitiated air as an intermediary substance between the fuel and oxygen. This intermediary dilutes the combustion mixture, reducing flame temperature and preventing direct high-temperature exposure of tubes, thereby preventing oxidation and fouling while maintaining heat transfer capability
3Speed
If flames concentrate heat in localized regions, then rapid heating is achieved, but tube surface area is underutilized
Solution Approach 1:
The patent changes the temperature distribution parameter by diluting the flame, transforming it from a concentrated high-temperature source to a more distributed lower-temperature source. This allows heat to be transferred across a broader tube surface area rather than concentrating on localized spots, improving overall surface area utilization while maintaining adequate heating rates
4Power
If fuel and air are mixed in conventional burners, then combustion occurs, but flame formation causes high local temperatures
Solution Approach 1:
The patent changes the composition parameter of the combustion mixture by introducing vitiated air containing CO2 and H2O. This dilution reduces the local temperature parameter during combustion while maintaining sufficient heat release through controlled burning in the diluted atmosphere, preventing excessive local temperatures
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 assembly effectively suppresses NOx formation and enhances heat transfer by maintaining uniform temperature, reducing tube oxidation and fouling, and maximizing tube surface area utilization.
Implementation Method 1
Fluid jets will entrain surrounding quiescent fluid because increased fluid velocity reduces the static pressure of the moving fluid
Implementation Method 2
Turbulent round jets expand and dissipate as the axial dimension away from the jet nozzle increases
Implementation Method 3
combustion occurs in a vitiated oxygen atmosphere, suppressing the maximum temperature rise resulting from the reactions
Implementation Method 4
The bulk of the heat is transferred through irradiation of the tubes
Implementation Method 5
The converging section has a contracting shape configured to entrain and mix the primary fluid mixture with the secondary fluid mixture
Data Source
AI summary
A method and assembly for supplying heat in the desired pattern while suppressing the production of nitrogen oxides and carbon dioxide. The assembly includes a fluid mixture nozzle assembly in fluid communication with an external conduit and a radiant section of a fired process heater. The fluid mixture nozzle assembly includes an open mixing channel having an upstream converging section, a midstream mixing section, and a downstream diverging section for entraining a fluid mixture with vitiated flue gas combustion products. The fluid mixture nozzle assembly is installed in the wall, floor, or ceiling of the fired heater.