Research On Control Strategy Optimization Of SNCR Denitration System For 350MW CFB Unit

As China's requirements for pollutant emission standards for coal-fired power plants become more stringent,the process of using a SNCR denitration system to remove NOX by circulating fluidized bed units has also brought some problems while achieving the NOX concentration.For example,the denitration control system cannot quickly adjust the system to a stable state when the load changes,and in the event of interference,in order to control the NOx emission concentration to 50mg/Nm3,there is an excessive injection of urea solution leading to an increase in ammonia escape.In this paper,a Shanxi Power Generation Co.,Ltd.#2 350 MW circulating fluidized bed unit is used as a test unit to study the SNCR denitration system.After a detailed analysis of the factors affecting NOX generation and denitration efficiency,the urea solution flow from the SNCR denitration system to NOX is analyzed in detail.The study of the modeling of the emission concentration process and the optimization of the control strategy of the SNCR denitration system are carried out.1.This paper first analyzes the process flow of the SNCR denitration system of the test unit and the factors that affect NOX generation and SNCR denitration efficiency.It is determined that the SNCR denitration control system adjusts the flow rate of the urea solution by controlling the valve opening degree,and then controls the NOX emission concentration.By collecting on-site load operation data for three consecutive days,using the nuclear density estimation method to obtain the typical operating conditions of the test unit,and then performing a urea solution step input test on the SNCR denitration system under each typical operating condition of the test unit and recording the NOX emission concentration data.The model parameters from urea solution to NOX emission concentration were identified using particle swarm algorithm with adaptive weights to obtain the transfer function model of the denitration system.The output curve of the model was compared with the output curve of the field test to verify the built Model validity.2.Based on the model established for the SNCR denitration system,and by consulting the relevant literature and combining the actual operating characteristics of the field valve,a transfer function model was obtained from the valve opening to the urea solution flow rate process.Then,a cascade control strategy based on the combination of generalized predictive control and traditional PID is proposed to improve the existing single-loop PID control strategy of the test unit.By building an offline SNCR denitration control system,it is carried out with the conventional cascade PID control strategy The comparison shows that the control strategy has better model adaptability and anti-interference ability,which can effectively improve the dynamic performance and steady-state performance of the SNCR denitration control system.The data of this subject comes from the test unit,combining reality and theory,by establishing a circulating fluidized bed SNCR denitration system model,and optimizing the existing SNCR denitration control strategy,realizing fully automatic operation of the SNCR denitration system and energy saving and emission reduction Make a contribution.Secondly,the research ideas and results of this topic can also be used for reference in the optimization of SNCR denitration system automatic control strategies of similar units.