Study Of Gas-solid Two-phase Flow And Combustion Simulation On Impact Pre-combustion Chamber Pulverized Coal Burner

Pulverized coal burner,as a key equipment of boiler combustion,plays an important role in ignition as well as safe and stable operation of the boiler.The impact pre-combustion chamber pulverized coal burner is studied in this thesis,which aims at solving the problems of the low grade coal combustion,the narrow coal species adaptability,the unstable combustion in low load and the high pollutant generation in the current burners.By the simulation and experiment of gas-solid two-phase flow characteristics on the impact pre-combustion chamber pulverized coal burner,the characteristics of gas-solid two-phase flow of the burner are optimized from the flow field,concentration field and particle trajectory.Then the combustion characteristics of the optimized model are studied.Based on the cold modeling theory, the original model of impact pre-combustion chamber burner and gas-solid two-phase flow cold experiment system is established.The flow field and particle concentration field are researched on this system.It is concluded that there is open air in the burner when the tangential angle of the secondary air is 30° and the axial angle is 45°.Based on FLUENT platform, the impact pre-combustion chamber pulverized coal burner is modeled and divided into grid.By comparing different k-ε turbulence models,it is concluded that Realizable k-ε model can correctly describe the gas flow and particle concentration of the burner.Because of the large secondary air angle,the characteristics of gas-solid two-phase flow of burner is unreasonable.In order to optimize these characteristics,the flow field,concentration field and particle trajectory of the burner in different secondary air angle are studied.It is concluded that the secondary air tangential and axial angle can influence the characteristics of gas-solid two-phase flow.With the decrease of the tangential angle,the vortex intensity decreases and the air flow spreading angle decreases.On the other hand,the flow entrainment ability decreases,the flow jet length increases and the phenomenon of open air disappears.The influence of secondary air axial angle focus on rigidity of the swirl flow rather than vortex intensity and reflux area.With the decrease of axial angle,the flow penetration ability enhances and the flow jet length increases.The numerical simulation optimization results show that the flow field and particle trajectory are more reasonable when the secondary air tangential angle is 5° and the axial angle is 20°.At this time,the high temperature flue gas is entrained to the pre-combustion chamber,and the surrounding flue gas is entrained by external reflux zone to maintain the stable combustion. Pulverized coal particles move around the main swirl area.Based on FLUENT platform,the combustion characteristics on optimized model(the tangential angle is 5° and axial angle is 20°)were simulated.It is concluded that the combustion process of pulverized coal in impact pre-combustion chamber burner is divided into two stages.The first stage occurs in the pre-combustion chamber and the second stage occurs in the furnace.The temperature of pulverized coal and air flow reach 1200~1300K when they come into the furnace after the first combustion stage,which is important to stable combustion of low grade coal.For this model the flame in furnace is moderate, the length is about 1400 mm and the center temperature is about 1900 K.