Hydrodynamic Characteristics And SCR Inlet Flue Gas Temperature Adjustment Method Of 650ME Supercritical Boiler In Ultra-low Load

In recent years,the development of wind power and solar power in China has accelerated,while the development of thermal power has relatively slowed down.But new energy has the characteristics of randomness,intermittentness,and instability.Therefore,active thermal power units must enhance flexibility and in-depth peak shaving ability to maintain power grid stability,which has become the development trend of thermal power.For the operation flexibility technology of thermal power units,evaluation of flexibility,hydrodynamic characteristics under ultra-low load and the SCR inlet smoke temperature adjustment method should be focused on.The research firstly improved an IRRE index that was originally used to evaluate the power system’s ability to absorb wind power,so that it can be used to evaluate the flexibility of a single thermal power unit.Using the improved IRRE index calculation model,taking three units in a power plant as the object,the probability curves of insufficient flexibility of different units in different peak shaving directions,time scales and months are calculated and analyzed.The analysis results show that there is a peak shaving margin of about 100 MW for the unit.It is necessary to perform hydrodynamic safety check and analysis of the SCR inlet flue gas temperature adjustment method for the 30% BMCR with the lowest steady combustion load.Then,taking the water wall of 650 MW supercritical boiler as the object,based on the two-phase fluid pressure drop,the spiral water wall single tube enthalpy increase and the hydrodynamic characteristic calculation model,a hydrodynamic calculation program under ultra-low load was compiled.The flow rate and pressure drop of each pipe of the water wall from the lower header to the separator under 30% BMCR operating conditions are calculated to analyze the operating characteristics of the water wall,and the influence of inlet pressure,inlet temperature and heat flux density on hydrodynamic stability is analyzed.The results show that the water wall has good hydrodynamic safety under ultra-low load,and the problems of metal overtemperature,hydrodynamic multi-value and pulsation between pipes will not occur.The decrease of inlet pressure,the increase of inlet temperature and the decrease of heat flux density will reduce the hydrodynamic stability of the lower water wall.At last,with the 650 MW supercritical boiler as the object,a suitable boiler thermal calculation method was selected,and a detailed thermal calculation program of the boiler was compiled.Using the verified calculation program,the influence of different operating factors on the smoke temperature of the SCR inlet was calculated,and the load adaptability of the three wide-load denitrification transformation schemes including the economizer flue gas bypass,water side bypass,and graded economizer was analyzed.The results show that under ultra-low load,the operating factors have very limited effect on raising the SCR inlet flue gas temperature.The graded economizer is the optimal transformation solution.This scheme can meet the SCR inlet smoke temperature requirements of 30% to 100% load when the area of the first-level economizer is between 27% and 54%,and has little effect on boiler steam temperature and thermal economy.These research results can be used to evaluate and analyze the flexibility of the same type of units,provide a theoretical basis for the study of the hydrodynamic characteristics and the SCR inlet smoke temperature adjustment method under ultra-low load,and are of great significance for the flexibility modification of supercritical units.