Analysis Of The Uniformity Of External Loop In The 660MW Supercritical CFB Boiler Based On CPFD Method

Circulating Fluidized Bed(Circulating Fluidized Bed)boiler power plant can quickly and efficiently realize the consumption of coal gangue and coal slime,and improve the overall utilization value of coal,with good pollutant control and fuel adaptability.The circulating fluidized bed boiler is developing in the direction of larger capacity and higher parameters,which puts forward higher requirements for the uniformity of gas-solid flow inside the boiler and the uniformity of the solid flow rate of the circulating loop.The multiple cyclones of large CFB boilers are arranged in parallel,and the gas-solid two-phase distribution in the parallel circulation loop is often uneven,which is related to internal factors(boiler load,primary and secondary air ratio and separator outlet pressure)and external structure factor.This thesis takes a 660 MW supercritical circulating fluidized bed boiler put into production as the research object,establishes a proportional boiler model,and adopts Computational Particle Fluid Dynamics(CPFD)based on the Euler-Lagrangian gas-solid two-phase model.The effects of boiler load,cyclone outlet pressure,primary and secondary air distribution and non-uniform secondary air on the solid flow rate of each circuit were studied.The accuracy of the simulation is verified by the pressure data of the actual boiler furnace.The average relative deviation between the pressure simulation value and the boiler operation data is 9.6%,and the average relative deviation between the average solid flow rate of each circulation loop and the design material flow value is9.49%.A boiler model with no outlet flue structure was established,and the effects of load changes and primary and secondary air ratio changes on the uniformity of the parallel circulation loop were studied.The results show that the solid flow rate of the middle cyclone is higher than that of both sides when the load changes.Under the 100% load condition,the particle volume fraction in the bottom and top areas of the furnace is greater than 75% and 60% under the load condition;when the air distribution ratio is50:50,the solid flow rate uniformity of the cyclone is the best.In order to study the effect of different pressure at the outlet of the cyclone on the gas-solid flow,by changing the outlet pressure of the cyclone,it was found that when the average outlet pressure was low,the effect on the solid flow rate of the circulating loop was greater,and the effect became smaller when the average outlet pressure was high.A boiler model with no outlet flue structure was established,and the effects of load changes and primary and secondary air ratio changes on the uniformity of the parallel circulation loop were studied.The results show that the solid flow rate of the middle cyclone is higher than that of both sides when the load changes.Under the 100% load condition,the particle volume fraction in the bottom and top areas of the furnace is greater than 75% and 60% under the load condition;when the air distribution ratio is50:50,the solid flow rate uniformity of the cyclone is the best.In order to study the effect of different pressure at the outlet of the cyclone on the gas-solid flow,by changing the outlet pressure of the cyclone,it was found that when the average outlet pressure was low,the effect on the solid flow rate of the circulating loop was greater,and the effect became smaller when the average outlet pressure was high.