Reheat Burner Vortex Mixing Zone Design
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Solution Overview
Problem
Traditional reheat burners face challenges with flashback, NOx, CO emissions, water consumption, and pressure drop when operating with hot gases at temperatures higher than design temperatures, disrupting the delicate equilibrium of hot gas speed, vortices, and turbulence.
Innovation Solution
A reheat burner design featuring a quadrangular channel with a lance for fuel injection, including a vortex generation zone and a mixing zone with a high speed area and a diffusion area, where the width and height increase towards the outlet, and a protrusion on the inner wall to manage flow detachment, reducing pressure drop and flashback risk while maintaining high mixing quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If hot gas speed through the burner channel is increased, then NOx emissions are reduced and flashback margin is increased, but CO emissions and pressure drop increase
Solution Approach 1:
The burner channel is divided into distinct functional zones: a vortex generation zone upstream of the injection plane with vortex generators to create turbulence, and a mixing zone downstream with diverging side walls forming a diffuser. This segmentation allows different regions to optimize for different functions - the vortex zone for mixing and the diffuser zone for maintaining velocity and pressure balance.
Solution Approach 2:
Different sections of the burner channel have different geometric properties tailored to their specific functions. The vortex generation zone has specific wall configurations to induce rotation, while the mixing zone has diverging walls at specific angles to control flow expansion. This local optimization of geometric quality allows simultaneous achievement of high velocity and good mixing.
2Object-affected harmful factors
If vortex strength and turbulence level are increased, then NOx and CO emissions are reduced through better mixing, but pressure drop increases reducing efficiency and achievable power
Solution Approach 1:
The burner design incorporates dynamic flow control through the interaction of vortex generators and diverging walls. The vortex generators create controlled turbulence that adapts to the flow conditions, while the diffuser geometry dynamically adjusts pressure and velocity profiles along the channel length, optimizing the balance between mixing intensity and pressure loss.
Solution Approach 2:
The burner channel geometry parameters are specifically optimized: the diverging side walls create a diffuser effect that changes pressure and velocity distributions, while vortex generator dimensions and positions are tuned to produce appropriate turbulence levels. These parameter optimizations allow achieving good mixing with minimal pressure penalty.
3Power
If the temperature of hot gases at the inlet and exit of the reheat burner is increased to increase gas turbine efficiency, then efficiency and performances are improved, but flashback, NOx, CO emissions, water consumption and pressure drop problems occur
Solution Approach 1:
The vortex generators are positioned upstream of the fuel injection plane to pre-condition the hot gas flow before fuel is introduced. This preliminary creation of turbulence and rotation ensures that when fuel is injected at high temperature, it is immediately and thoroughly mixed with the hot gases, preventing localized rich zones that could lead to flashback or excessive NOx formation.
Solution Approach 2:
The vortex generators and diffuser geometry act as intermediaries between the high-temperature fuel injection and the combustion chamber. They mediate the interaction by creating controlled turbulence and pressure distributions that promote complete combustion while preventing flashback, allowing high temperature operation without the associated problems.
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 design achieves low NOx emissions, reduced flashback risk, and efficient power generation by maintaining high hot gas speed through the burner while ensuring sufficient residence time for complete combustion, thereby minimizing CO emissions and pressure drop.
Implementation Method 1
vortex generators 7 are housed, projecting from each of the channel walls, to induce vortices and turbulence into the hot gases G
Implementation Method 2
The channel zone downstream of the injection plane 4 (in the hot gas direction G) is the mixing zone 9; typically this zone has plane, diverging side walls, to define a diffuser
Implementation Method 3
a fuel is injected into a compressed air stream to be combusted generating flue gases
Data Source
AI summary
A reheat burner (1) includes a channel (2) with a lance (3) protruding thereinto to inject a fuel over an injection plane (4) perpendicular to a channel longitudinal axis (15). The channel (2) and lance (3) define a vortex generation zone (6) upstream of the injection plane (4) and a mixing zone (9) downstream of the injection plane (4) in the hot gas (G) direction. The mixing zone (9) includes a high speed area (16) with a constant cross section, and a diffusion area (17) with a flared cross section downstream of the high speed area (16) in the hot gas (G) direction.