MPC Combustion Control for NOx and Ammonia Slip
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Solution Overview
Problem
Existing SCR systems face challenges in simultaneously controlling NOx and ammonia slip during transient conditions in combined cycle power plants, leading to NOx excursions and excessive ammonia waste due to overcompensation in control systems.
Innovation Solution
A combustion product control system utilizing model predictive control (MPC) processing to regulate NOx and ammonia slip by measuring NOx and ammonia concentrations, generating predetermined parameters based on transient conditions, and adjusting NH3 injection rates to maintain optimal NOx and ammonia slip levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional cascaded PID control is used to regulate NOx during steady-state operation, then NOx control is simple and effective, but during transients the system cannot simultaneously control both NOx and ammonia slip
Solution Approach 1:
The control system dynamically changes parameters based on operating conditions. During transients, the MPC controller adjusts NH3 injection rates based on predicted NOx and ammonia slip behavior, switching from steady-state PID control to transient-optimized control with varying injection parameters
Solution Approach 2:
The system transitions from static PID control to dynamic MPC control that adapts to changing conditions. The MPC controller continuously predicts future states and adjusts control actions in real-time during transients, making the control system dynamic rather than static
2Reliability
If NH3 injection flow rate is increased to mitigate NOx excursions during transients, then NOx control improves, but ammonia slip excursions increase causing waste
Solution Approach 1:
The MPC controller uses feedback from measured NOx and ammonia slip levels to continuously adjust NH3 injection rates. The controller predicts future emissions based on current conditions and adjusts injection to maintain both NOx and ammonia slip within limits, creating a closed-loop feedback system that prevents both types of excursions
Solution Approach 2:
The MPC controller performs preliminary calculations to predict future NOx and ammonia slip levels based on current operating conditions. By anticipating transient behavior before it fully develops, the controller can pre-adjust NH3 injection rates to prevent both NOx excursions and ammonia slip waste
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 system effectively regulates NOx and ammonia slip levels during transients, reducing unnecessary ammonia usage and associated costs while maintaining compliance with emission limits.
Implementation Method 1
Many known SCR systems include a bed of catalyst for removing at least some of the NOx from the exhaust gas stream
Implementation Method 2
a first sensing device configured to measure a concentration of oxides of nitrogen (NOx) in a fluid stream. The combustion product control system also includes a second sensing device configured to measure ammonia (NH3) slip in the fluid stream
Data Source
AI summary
A combustion product control system includes a first sensing device that measures a concentration of NOx in a fluid stream and a second sensing device that measures NH3 slip in the stream. The system also includes at least one combustion product control element. The system further includes at least one processor coupled to the sensing devices and the control element. The processor is programmed to generate predetermined parameters for NOx values in the stream at least partially as a function of transient stream conditions. The processor is also configured to use model predictive control (MPC) processing to generate predetermined values for a NH3 injection rate during stream transients. The predetermined values vary at least partially as a function of modeled stream characteristics. The processor is further configured to regulate the control element to facilitate simultaneous regulation of the NOx and NH3 slip in the stream within respective predetermined parameters.