Sequential Combustor Hybrid Flame Control for Low NOx Hydrogen Operation
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Solution Overview
Problem
Current gas turbine systems face challenges in using highly reactive fuels like hydrogen due to increased NOx emissions and flashback risks, limiting their efficiency and flexibility, especially when operating with hydrogen-based fuels, as they require significant dilution or derating, which reduces performance and increases emissions.
Innovation Solution
The method involves operating sequential combustors with a combination of diffusion and premix flame modes in the first combustor, allowing for hybrid flames and optimizing fuel distribution to maintain low NOx production across the system, even when the first stage operates in diffusion mode, and controlling fuel feeding to both combustors to optimize the CF parameter based on emission requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If hydrogen-based fuel is used in the combustor, then the energy efficiency and flexibility of the gas turbine is improved, but the NOx emissions and flashback risk increase
Solution Approach 1:
The combustor is divided into multiple zones with different combustion modes. The first combustor uses premix combustion for low NOx emissions, while the second combustor uses diffusion combustion for complete hydrogen combustion. This segmentation allows the system to maintain high energy efficiency while controlling NOx emissions through zoned combustion strategies.
Solution Approach 2:
Different regions of the combustor are assigned different combustion characteristics. The premix zone provides low-temperature combustion for NOx reduction, while the diffusion zone provides high-temperature combustion for complete fuel utilization. This local differentiation resolves the contradiction between efficiency and emissions by optimizing each zone for its specific function.
2Reliability
If the first combustor operates in diffusion mode to ensure stable combustion, then the combustion stability is improved, but the NOx emissions increase
Solution Approach 1:
The combustor is segmented into a first combustor operating in premix mode for low NOx emissions and a second combustor operating in diffusion mode for complete combustion. This segmentation allows diffusion combustion to occur in a controlled zone where the resulting NOx can be managed, while the premix zone maintains overall emission levels low.
Solution Approach 2:
The patent converts the potential harm of diffusion combustion (high NOx) into a benefit by using it in the second combustor where it ensures complete hydrogen combustion. The high temperatures in the second combustor, which would normally produce NOx, are instead used to ensure complete fuel consumption, and the overall emission profile is managed through the coordinated operation of both combustors.
3Object-generated harmful factors
If diluents are added to reduce NOx emissions when using hydrogen fuel, then the emission level is reduced, but the gas turbine performance and efficiency decrease
Solution Approach 1:
The system uses itself to control emissions without external diluents. The first combustor's premix combustion inherently produces low NOx emissions, and the second combustor's diffusion combustion ensures complete fuel utilization. This self-regulating combustion system eliminates the need for performance-reducing diluents while maintaining low emissions and high efficiency.
4Productivity
If the fuel-air equivalence ratio is increased to improve combustion efficiency, then the energy release is improved, but the flashback risk and NOx emissions increase
Solution Approach 1:
The fuel combustion process is segmented into two stages with different equivalence ratios. The first combustor operates with a controlled equivalence ratio for stable premix combustion, while the second combustor operates with a higher equivalence ratio for complete diffusion combustion. This segmentation allows high efficiency combustion without flashback risk by separating the combustion stages.
Solution Approach 2:
The first combustor performs preliminary combustion of the hydrogen fuel in a controlled premix mode, reducing the fuel load and temperature before the second combustor. This preliminary action prevents flashback in the second combustor by ensuring that the remaining combustion occurs at safer conditions, while still achieving high overall efficiency.
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
This approach enables gas turbines to operate efficiently with pure hydrogen fuel without diluents, maintaining low NOx emissions and extending the lean blowout margin of the first stage, thus achieving high performance and flexibility without derating.
Implementation Method 1
an upstream first combustor (upstream combustor) configured for receiving the compressed air and mixing this air with fuel and combusting this mixture
Implementation Method 2
a downstream second combustor (or reheat combustor) configured for receiving the hot gas leaving the first combustor and adding fuel into this hot gas for performing a self/spontaneous ignition
Data Source
Figure 1~2
Figure 3~5
AI summary
A method for operating a sequential combustor (22) for a gas turbine; the method comprising the steps of: a) providing a sequential combustor (22) comprising: - a first combustor (31) provided with a plurality of first burners (12, 24) fed by compressed air and configured for injecting fuel in the compressed air in a diffusion mode and in a premix mode; - a second combustor (32) provided with a plurality of second burners (26, 33) fed by hot gas leaving the first combustor and configured for injecting fuel in the hot gas; b) feeding the first and second burners with a highly reactive fuel; c) switching off at least one of the first burners (12, 24); d) operating the remaining active first burners so as to generate hybrid flames as combination of diffusion mode and premix mode.