Gas Turbine NOx Mass Flow Stabilization for Ammonia Slip Reduction
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Solution Overview
Problem
Gas turbine engines face challenges in controlling ammonia slip during load changes, as existing methods struggle to maintain a stable NOx production level, leading to fluctuations in ammonia demand and increased emissions during power level changes.
Innovation Solution
By maintaining a relatively constant mass flow of NOx throughout power level changes, rather than minimizing NOx production, the system stabilizes NOx output, allowing for a predictable ammonia flow and reduced slip through the selective catalytic reduction process, using a system controller to regulate fuel and ammonia injection based on NOx mass flow rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If ammonia flow is tightly regulated in response to detected ammonia and nitrogen oxide levels, then ammonia slip is minimized, but ammonia flow fluctuates substantially during load changes
Solution Approach 1:
The system performs preliminary action by proactively adjusting fuel flow to the pilot flame before significant load changes occur. The controller monitors exhaust gas properties and anticipates the need for ammonia flow adjustment, making preliminary modifications to fuel delivery to prevent excessive NOx production that would require large ammonia flow corrections, thereby stabilizing ammonia flow during load transitions
Solution Approach 2:
The system implements feedback control by continuously monitoring exhaust gas properties (NOx, O2, CO, HC) and using this information to adjust both fuel flow to the pilot flame and ammonia flow to the SCR system. This closed-loop feedback mechanism ensures that ammonia flow remains stable while maintaining effective NOx reduction, preventing the substantial fluctuations that occur with simple proportional control
2Object-generated harmful factors
If fuel delivery to pilot flame is minimized to reduce NOx production, then NOx emissions are reduced, but flame stability becomes difficult to maintain
Solution Approach 1:
The system applies parameter changes by dynamically adjusting the fuel-to-air ratio in the pilot flame based on real-time exhaust gas analysis. Rather than maintaining a fixed minimum fuel delivery, the controller modifies combustion parameters (excess air ratio, fuel flow rate) to optimize the balance between flame stability and NOx production, allowing flexible adaptation to different operating conditions and load levels
3Object-generated harmful factors
If NOx production is minimized at all power levels, then NOx emissions are reduced, but ammonia demand becomes unstable during load changes
Solution Approach 1:
The system implements dynamics by transitioning from static NOx minimization to dynamic NOx control. The controller continuously adjusts fuel delivery to the pilot flame based on real-time monitoring of exhaust gas properties and anticipated load changes. This dynamic approach allows the system to maintain stable ammonia demand across varying operating conditions while still achieving effective NOx reduction, preventing the instability that occurs with fixed minimization strategies
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 ensures compliance with air permit levels by maintaining a stable NOx mass flow, reducing ammonia slip and optimizing NOx control during load follow operations, even at higher NOx levels, thereby improving environmental compliance and operational stability.
Implementation Method 1
selective catalytic reduction (SCR) are known to reduce the amount of NOx in the exhaust gas stream to low levels prior to release to the environment
Implementation Method 2
ammonia is added on a stoichiometric basis relative to the amount of NOx in the exhaust gas introduced into the SCR system
Implementation Method 3
the majority of NOx is generated by the pilot flame, which burns at a high temperature
Implementation Method 4
NOx is generated from the combustion of any fuel in the presence of air
Data Source
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AI summary
Described herein are methods of operating a gas turbine engine (12) for reduced ammonia slip. An exemplary method (100) includes operating (102) the engine over a range of power output levels; controlling (104) a mass flow of NOx produced in exhaust (19) of the engine to be within 10% over the range of power output levels; and treating (106) the exhaust of the engine in a selective catalytic reduction process (22). In this way, the production of NOx and a corresponding flow of reducing agent (33) utilized in the SCR process remain relatively constant in terms of mass (molar) flow throughout the range of power output levels and ammonia slip is controlled.