Study On Emission Characteristics Of Pollutants In The Start-up Processof Circulating Fluidized Bed Boiler

Due to the advantages of high combustion efficiency,wide adaptability of coal,low concentration of pollutant gases NO_X and SO₂ and good peak shaving performance,the capacity and installed scale of CFB boilers have developed rapidly in recent years and become the main force of thermal power industry.Because of the dynamic balance of bed material,the instability of gas-solid two-phase and combustion caused by the time-varying bed temperature during the start-up of circulating fluidized bed boiler,the emission of pollutants in the start-up process is large and difficult to control effectively.Therefore,this paper studies the emission characteristics of pollutants during the start-up of CFB boilers through modeling and simulation,in order to provide technical support for the emission reduction of pollutants of CFB units in full operating conditions.Firstly,by analyzing the flow and combustion process of CFB boiler,the main mathematical models of flow,combustion,heat transfer,pollutant generation and dynamic equilibrium equations of energy,mass,oxygen concentration and carbon residue are established.Secondly,the adjustment characteristics of coal feed,primary air flow and secondary air flow in the process of ignition start-up,such as bed material preheating,coal feeding and evacuation of ignition gas gun,are analyzed and studied.Then,based on the modules of Sources,Sinks,Math Operations and Step in the simulation software of MATLAB/Simulink,the mathematical model is transformed into the simulation model,and the subsystem is built in the cell unit,then all subsystems are connected to form the overall simulation model.This paper takes Hepo 350MW supercritical circulating fluidized bed boiler as the research object to carry out simulation,The simulation results well reflect the dynamic characteristics of bed temperature during the start-up process of circulating fluidized bed boiler,which is consistent with the change trend of bed temperature during the start-up in actual operation,and show that the simulation model can describe the start-up process of the boiler more accurately.In addition,the effects of average coal particle size,Ca/S ratio,primary and secondary air ratio,upper and lower secondary air ratio,and air withdrawal gun temperature on bed temperature and pollutant generation were simulated and studied,and effective control strategies for pollutant generation during start-up were given.The study of pollutant emission characteristics during start-up of CFB boilers can provide a reference for pollutant control during start-up,so as to reduce pollutant emission during start-up.