Experimental And Numerical Research On Gas Vortex Structural Evolution And Interaction Mechanism Of Complex Gas-solid Multi-jets

The tangential firing pulverized coal boiler has been widely applied in the power plants in China because of its stable ignition,simple operation and high coal adaptability.With the continuous increase of single boiler power generation and the strict pollution emission control,the supercritical and ultra-supercritical boilers have become the main boilers nowadays.However,most previous research on tangentially-fired boilers were focused on the industrial-scale coal combustion,ignoring the studies on the meso-and micro-scale pulverized coal dispersion on such a corner-injected flow and the turbulent coal combustion.Hence,we employed the advanced experimental measurement and numerical methods to investigate the vortex coherent structure evolutions,gas-solid interaction mechanism and turbulent coal combustion in such a fundamental corner-injected flow.Firstly,we established a corner-injected measurement system,combining the flow visualization method and particle image velocimetry(PIV),to observe the vortex structure and particle dispersion qualitatively and measure the velocity and velocity gradient quantitatively.The influences of jet deflection,initial gas velocity and particle size on the turbulent corner-injected flow behaviors were been systematically studied.Limited to the measured parameters and measurement resolution,the coupled large eddy simulation(LES)and discrete phase model(DPM)has been applied to investigate the turbulent vortex structure evolution and the gas-solid interaction mechanism.The two-and four-way coupling method were employed to study the influences of particle collision,particle initial velocity and particle loading ratio on the dispersion of carried particles in corner-injected flow.An empirical equation for particle Stokes number was proposed to predict the particle motion in a complex gas-solid turbulent flow,and it was found that the particle motion was most affected by the particle size,then the particle concentration,and least the turbulent dissipation rate and the particle density.Base on the two-way coupling of LES and DPM numerical methods,the mixture fraction probability density function of premixed combustion model was implemented to simulate the coal combustion process.The influences of coal particle size and coal combustion atmosphere were systematically studied on the turbulent pulverized-coal combustion in such a corner-injected flow.The turbulent flame characteristics,coal burning features and the pollutant emissions were investigated carefully.Based on the low NOx combustion mechanism,the industrial test and numerical simulations were conducted to validate the novel staged air combustion system applied in the 660 MW ultrasupercritical tangential firing coal boiler built in Datang Nanjing Power Plant.The coal combustion efficiency and NOx emissions were systematically studied under the different air distribution of secondary air,over-fired air and additional air.Hence,the multiscale studies on such a tangential firing coal boiler was conducted in this dissertation,including complex turbulent flow behaviors,the coal particle dispersal,the turbulent coal combustion and the industrial boiler operation.