Mid-Zone Air Separation Cone for IRZ Expansion
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Solution Overview
Problem
Existing low-NOx fuel burners face challenges in safely and effectively increasing the size of the internal recirculation zone (IRZ) without damaging flow deflecting devices, causing increased NOx emissions, or raising pressure drop.
Innovation Solution
A large diameter mid-zone air separation cone with a short cylindrical leading edge is introduced, positioned farther from the burner centerline than conventional cones, splitting the secondary air flow into two streams and deflecting it radially outward, thus expanding the IRZ without adverse effects on burner operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the size of the internal recirculation zone (IRZ) is increased by extending flow deflecting devices or increasing their angle of attack, then the IRZ size is improved, but the devices are exposed to high flame temperatures causing damage
Solution Approach 1:
The patent introduces a mid-zone air separation cone positioned radially outward from the burner centerline, creating a new spatial dimension for IRZ expansion. This mid-zone cone works in conjunction with the conventional end-zone cone to divide the air zone into inner, mid, and outer zones, allowing IRZ enlargement without extending devices into the high-temperature flame path.
2Volume of moving object
If more swirl is imparted on the secondary air flow to increase IRZ size, then the IRZ size is improved, but fan power requirement increases due to higher pressure drop
Solution Approach 1:
The air separation cone is divided into multiple zones (inner, mid, outer) with the mid-zone cone positioned radially outward. This segmentation allows secondary air to be introduced at different radial locations, creating IRZ expansion through geometric configuration rather than relying solely on increased swirl intensity, thereby reducing fan power requirements.
3Volume of moving object
If the angle of attack on flow deflecting devices is increased to expand IRZ, then the IRZ size is improved, but air flow passages are restricted and pressure drop increases
Solution Approach 1:
The mid-zone air separation cone utilizes the radial dimension to expand IRZ size without increasing the angle of attack on existing devices. By positioning the cone at a mid-radial location and deflecting air outward, the system achieves IRZ expansion while maintaining open air flow passages and avoiding excessive pressure drop.
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 mid-zone air separation cone effectively enlarges the IRZ, stabilizes the flame, and reduces NOx emissions while maintaining burner performance and avoiding increased pressure drop, making it a cost-effective solution for various burner types.
Implementation Method 1
The mid-zone air separation cone splits the outer air zone secondary air flow into two equal or unequal streams depending on the position of the air separation cone with respect to the outer air zone, and deflects a portion of the secondary air flow radially outward
Implementation Method 2
Swirl can be imparted into the zones 914 and 916 via adjustable angle spin vanes 922 in the inner air zone 914 and both fixed spin vanes 920 and adjustable angle spin vanes 922 in the outer air zone 916
Implementation Method 3
The IRZ causes the NOx formed at the outer fringe of the flame to recirculate back along the fuel rich flame core, where hydrocarbon radicals react to reduce the NOx
Implementation Method 4
recycling heat and combustion products including NOx from fuel-lean regions into fuel-rich zones to sustain ignition, maintain flame stability, and convert NOx to N2
Data Source
AI summary
A large diameter mid-zone air separation cone is provided for decreasing NOx during burner operation by expanding the internal recirculation zone (IRZ) at the burner exit. The mid-zone air separation cone has a short cylindrical leading edge that fits in the outer air zone of a burner. The mid-zone air separation cone splits the outer air zone secondary air flow into two equal or unequal streams depending on the position of the air separation cone with respect to the outer air zone, and deflects a portion of the secondary air flow radially outward. Since the radial position of the air separation cone is farther from the burner centerline, the IRZ size is expanded and NOx emissions are minimized.