Research On Modelingn And Optimization Control Of SCR Denitration System In Thermal Fower Plant

Nitrogen oxides(NOx)from exhaust gases from thermal power plants are one of the major pollutants in the atmosphere,seriously damaging the environment.Ammonia denitrification scheme based on selective catalytic reduction(SCR)is an important means to control NOx emissions from thermal power plants.The ammonia denitration control has the following difficulties:(1)The NOx concentration control object of the SCR system has nonlinearity and large delay characteristics,and has high performance requirements for the controller.(2)Unreacted ammonia will corrode the downstream flue and the air preheater,so it is necessary to balance the ammonia slip while controlling the NOx concentration.Therefore,the establishment of an accurate SCR system model is of great significance to support the offline design and parameter debugging of the ammonia spray controller.Based on the above problems,this paper proposes a SCR system modeling method based on cascade structure,which mainly carries out the following research work:1.Based on the SCR system dynamics model and the technical data of the SCR system equipment and material manufacturers in thermal power plants,a cascade structure-based SCR system modeling method was designed to effectively solve the matching problem between the mechanism model and simulation step size.2.For the parameter identification problem in the established model,the SCR reaction process is complex,the number of parameters is large,the correlation between them is large,and it also has nonlinear and large delay characteristics,and the process of obtaining is difficult.In addition,as the reaction conditions change(changes in load,temperature,etc.),the parameters of the model will change accordingly,relying solely on equipment parameters to determine,obviously there will be large errors.Based on the operation data of a 600 MW unit in a power plant,this paper proposes a model parameter identification method based on particle swarm optimization to identify the parameters of the gas dynamics equation,such as gas adsorption and desorption,NO consumption rate,and NH3 oxidation rate.It can simultaneously take into account the two key objectives of SCR system outlet NOx concentration and ammonia slip.The optimization algorithm maintains the positive feedback mechanism of the particle swarm optimization algorithm,and the fast search capability can efficiently and accurately determine the optimal solution,avoiding the blindness and randomness of parameter identification.3.Based on the cascaded SCR mechanism simulation model,MPC and existing PID control are used to compare control effects and characteristics.The simulation model is built on the MATLAB/Simulink platform to control the outlet NOx concentration and ammonia leakage within the setpoint range.The realization of multi-objective control can provide the object of comprehensive optimization design research of ammonia-spraying system controller,especially suitable for developing practical control strategy considering amnonia escape control.4.The SCR mechanism modeling parameter optimization calculation platform based on Matlab GUI is designed.The software includes SCR reactor cascade number calculation module,SCR system simulation model,particle swarm algorithm mechanism parameter adjustment module,NOx concentration output curve drawing module model,Verification modules,etc.The model verification module provides support for the comprehensive optimization design of the ammonia spray system controller.