Axial Zoning in Gas Turbine Combustion for Stable Part-Load Operation
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Solution Overview
Problem
Traditional premixed combustion chambers face limitations in regulating power at part load, leading to pulsations and high NOx emissions, with pilot stages causing additional issues, and existing solutions either require pilot stages or generate diffusion flames, which are inefficient and environmentally harmful.
Innovation Solution
A method involving a combustion chamber with first and second premixed fuel supply devices, where the first zones generate flames with higher temperatures than the second zones, allowing for safe operation at part load without pilot stages and minimizing NOx emissions by maintaining a richer mixture upstream to support lean mixtures downstream.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pilot stages or diffusion flames are used to stabilize combustion at part load, then combustion stability is improved, but NOx emissions increase
Solution Approach 1:
The combustion chamber is divided into multiple zones with different mixture ratios along the axial direction. Upstream zones operate with richer mixtures to provide stable combustion, while downstream zones use leaner mixtures to reduce NOx emissions. This spatial segmentation allows each zone to fulfill different functions simultaneously.
Solution Approach 2:
Different zones within the combustion chamber are assigned different local qualities in terms of mixture ratio. The upstream region has a richer mixture (higher fuel-to-air ratio) to ensure stable ignition and combustion, while the downstream region has a leaner mixture to minimize thermal NOx formation. This local differentiation resolves the contradiction between stability and emissions.
2Power
If all mixing devices are supplied with nominal fuel amount, then power output is maximized, but pulsations occur at part load
Solution Approach 1:
The fuel supply to mixing devices is made dynamically adjustable based on operating conditions. At part load, the upstream mixing devices maintain nominal or slightly enriched fuel supply for stability, while downstream devices reduce fuel supply. This dynamic adaptation allows the system to maintain stability across different power levels without continuous pulsations.
Solution Approach 2:
The upstream zones are designed to operate with richer mixtures in advance, creating a stable combustion environment before the leaner downstream zones. This preliminary stable combustion acts as a buffer that prevents pulsations from developing in the overall system, even when downstream zones operate with reduced fuel supply at part load.
3Reliability
If flame temperature is maintained above critical temperature Tp, then safe operation is ensured, but minimum power Pmin increases
Solution Approach 1:
The problem is shifted from a single-dimensional temperature control to a multi-dimensional spatial distribution of mixture ratios. Instead of uniformly maintaining high temperature throughout, the system uses axial zoning with richer upstream regions providing stability and leaner downstream regions reducing overall temperature and NOx. This dimensional transformation allows safe operation at lower minimum power.
Solution Approach 2:
The mixture ratio parameter is varied along the axial direction rather than being uniform. By changing the fuel-to-air ratio from rich in upstream zones to lean in downstream zones, the system achieves both stable combustion (through the rich zones) and reduced minimum power requirements (through the lean zones that lower overall flame temperature and NOx emissions).
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
Enables safe operation across a broad power range from very low to high load without pulsations or high NOx emissions, reducing waste and extending the operational window of gas turbines, while maintaining stable combustion and low emissions.
Implementation Method 1
a fuel and an oxidiser are fed, such that they mix forming a mixture that is burnt
Implementation Method 2
the hot gases coming from the first zones support the combustion in the second zones
Data Source
Figure 1~3
Figure 4~7
Figure 8~9
AI summary
The combustion chamber (10) of a gas turbine comprises first and second premixed fuel supply devices (11, 12) connected to a combustion device (13) having first zones (14) connected to the first premixed fuel supply devices (11) and second zones (15) connected to the second premixed fuel supply devices (12). The second fuel supply devices (12) are shifted along a combustion device longitudinal axis (16) with respect to the first fuel supply devices (11). The first zones (14) are axially upstream of the second premixed fuel supply devices (12).