Lean-Rich Burner with Pilot Combustor for Gas Turbine Stability
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Solution Overview
Problem
Gas turbine engines operating in lean partially premixed combustion mode face instability and emission challenges due to the need for reduced flame temperature to minimize NOx emissions, leading to fluctuations in flame speed and heat release, which result in unsteady combustion and thermo-acoustic instabilities.
Innovation Solution
A burner design that incorporates a pilot combustor to supply heat and free radicals to a main lean premixed swirl, utilizing a radial swirler and multi-quarl geometry to stabilize combustion, with internal fuel staging and a swirl number above 0.7 to ensure stable ignition and combustion across all engine load conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If more air is added to reduce flame temperature for NOx emission control, then NOx emissions are reduced, but combustion stability deteriorates due to leaner fuel-air mixture
Solution Approach 1:
The combustion system is divided into a main combustor operating in lean premixed mode for low NOx emissions and a pilot combustor operating independently to provide stabilization. The pilot combustor receives a portion of the fuel and air separately, allowing the main combustor to maintain very lean conditions (equivalence ratio below 0.5) while the pilot maintains a more robust combustion process to provide heat and radicals back to the main combustor through recirculation zones.
Solution Approach 2:
The pilot combustor acts as an intermediary that generates hot combustion products and free radicals which are then transported into the main lean premixed combustor through recirculation zones. This intermediary provides the necessary thermal and chemical energy to stabilize the otherwise unstable lean combustion process, enabling the main combustor to operate at equivalence ratios below 0.5 while maintaining stability.
2Object-generated harmful factors
If fuel-air mixture is made very lean to reduce flame temperature below dissociation point, then NOx emissions are significantly reduced, but flame extinction and re-ignition occur periodically
Solution Approach 1:
The pilot combustor performs preliminary combustion action to generate hot gases and free radicals before the main lean premixed combustion occurs. These pre-generated combustion products are continuously fed into the main combustor through recirculation zones, providing the necessary thermal and chemical environment to prevent flame extinction in the lean mixture region where equivalence ratio is below 0.5.
Solution Approach 2:
The system changes the operating parameters by introducing a dual combustor configuration where the pilot combustor operates at higher equivalence ratios to generate heat and radicals, while the main combustor operates at very lean conditions (Φ < 0.5). The recirculation zones enable transfer of thermal and chemical energy between these two regions with different parameter sets, stabilizing the lean combustion.
3Reliability
If swirl number is increased above 0.7 to stabilize flame front, then combustion stability improves, but device complexity increases due to radial swirler and multi-quarl geometry
Solution Approach 1:
The burner geometry is segmented into multiple functional components: radial swirler with specific blade angles to generate high swirl number (>0.7), multi-quarl structure with multiple passages for fuel-air mixing, and pilot combustor integration. This segmentation allows each component to be optimized independently for its specific function while collectively achieving stable combustion at high swirl conditions.
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 burner achieves stable and efficient combustion at all engine load conditions with reduced emissions by maintaining a stable flame front in the shear layer of the swirl-induced recirculation zone, minimizing NOx emissions and preventing flame extinction.
Implementation Method 1
a pilot combustor to supply heat and free radicals to a main lean premixed swirl
Implementation Method 2
utilizing a radial swirler and multi-quarl geometry to stabilize combustion, with internal fuel staging and a swirl number above 0.7
Implementation Method 3
fuel and air are provided to a burner chamber where they are mixed
Implementation Method 4
The heat and free radicals from the previously reacted fuel and air are required to initiate (pyrolyze fuel and initiate chain branching process) and sustain stable combustion
Implementation Method 5
Swirl stabilized combustion flows are commonly used in industrial gas turbine engines to stabilize combustion by, as indicated above, developing reverse flow (Swirl Induced Recirculation Zone) about the centreline, whereby the reverse flow returns heat and free radicals back to the incoming un-burnt fuel and air mixture
Implementation Method 6
flame temperature is reduced by an addition of more air than required for the combustion process itself. The excess air that is not reacted must be heated during combustion, and as a result flame temperature of the combustion process is reduced (below stoichiometric point) from approximately 2300K to 1800 K and below
Data Source
AI summary
The invention relates to a burner for a gas turbine comprising a burner housing (2). It is one object of the invention to provide a lean-rich partially premixed low emission burner for a gas turbine combustor that provides stable ignition and combustion process at all engine load conditions. According to the invention enclosed in that housing is a burner, at the upstream end of that burner (1) a pilot combustor (5) creating a flow of an unquenched concentration of radicals (32) and heat. Respectively provided is: a plurality of quarl sections (4a, 4b, 4c) surrounding the exit (6) of the pilot combustor (5), a main combustion room defined downstream said pilot combustor (5) and at least a first channel (10) defined as an annular space between an upstream quarl section (4a) and the closest downstream quarl section (4b) providing air (12) and fuel (14) to a main flame (7) in said combustion room.