Late Lean Injection Control for Gas Turbine NOx Reduction
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Solution Overview
Problem
Gas turbine engines face inefficiencies and high NOx emissions due to high combustion temperatures, which are challenging to mitigate with conventional premixed lean fuels, leading to significant thermal NOx formation.
Innovation Solution
A gas turbine engine design incorporating a combustor with a transition zone and multiple fuel injectors configured for late lean injection (LLI) fuel staging, allowing for controlled injection of fuels in various stages and configurations to manage combustion temperatures and reduce NOx formation, along with a control system to optimize fuel and air ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If conventional premixed lean fuels are used to control combustion temperature, then thermal NOx formation is reduced, but combustion efficiency and power output deteriorate due to insufficient temperature to achieve required combustion products
Solution Approach 1:
The combustion process is divided into two distinct zones: a premixed lean combustion zone that controls NOx formation, and a diffusion flame zone in the transition region that provides additional heat release. This segmentation allows each zone to perform its specialized function without interfering with the other's optimal operation.
Solution Approach 2:
Different fuel injection strategies are applied to different spatial regions: premixed lean fuel is injected in the combustor for low-temperature combustion, while additional fuel is injected directly into the transition zone where diffusion flames create localized high-temperature regions. This local quality approach allows temperature control in different locations to serve different purposes.
2Productivity
If high combustion temperatures are maintained to achieve required combustion products, then combustion efficiency is improved, but thermal NOx formation increases significantly
Solution Approach 1:
The combustion system separates the combustion process into a controlled premixed zone and a diffusion flame zone, allowing high temperatures to be confined to the diffusion region where they are necessary for complete combustion, while the premixed zone maintains lower temperatures to prevent NOx formation.
Solution Approach 2:
The transition zone, which naturally creates high temperatures that could lead to NOx formation, is instead utilized as a beneficial diffusion flame zone. By injecting additional fuel directly into this region, the high temperatures are harnessed to ensure complete combustion of the premixed fuel, converting a potential harm into a benefit.
3Object-generated harmful factors
If multiple fuel injectors are added for late lean injection fuel staging, then NOx emissions are reduced and combustion control is improved, but device complexity increases
Solution Approach 1:
The additional fuel injectors in the transition zone serve multiple functions: they create diffusion flames for enhanced heat release, control the temperature profile to prevent NOx formation, and provide fuel flexibility for different fuel types. This multi-functionality justifies the added complexity by delivering multiple benefits from a single system addition.
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 LLI system effectively reduces NOx emissions and improves operational efficiency by creating local zones of stable combustion, enabling the use of more reactive fuels and alternate gases, while maintaining high combustion temperatures below the thermal NOx formation threshold.
Implementation Method 1
a transition zone, including a second interior in which a second fuel supplied thereto by the fuel circuit and the products of the combustion of the first fuel are combustible
Implementation Method 2
oxidation of, e.g., molecular nitrogen, in gas turbine engines is dependent upon a high temperature in the combustor and the residence time for the reactants at the high temperature within the combustor, a level of thermal NOx formation is reduced by maintaining the combustor temperature below the level at which thermal NOx is formed
Data Source
AI summary
A gas turbine engine is provided and includes a combustor having a first interior in which a first fuel supplied thereto by a fuel circuit is combustible, a turbine, a transition zone, including a second interior in which a second fuel supplied thereto by the fuel circuit and the products of the combustion of the first fuel are combustible, a plurality of fuel injectors, which are structurally supported by the transition zone and coupled to the fuel circuit, and which are configured to supply the second fuel to the second interior in any one of a single axial stage, multiple axial stages, a single axial circumferential stage and multiple axial circumferential stages, and a control system coupled to the fuel circuit and configured to control relative amounts of the first and second fuels supplied by the fuel circuit to the first and second interiors.