Numerical Simulation On Extermal Flow Field Of Pulverized Coal Oxygen-rich Ignitor

The thermal coal used for pulverized-coal fired boiler in china are lowvolatile, high-ashed and low calorific at the present stage. The a lot of oilwill be assumed in the process of ignition of the power station in cold stateand low load state. The cost is very high. In recent years, the Oxygen-enriched combustion and Oxygen-enriched ignition as the new energy-savingcombustion technology play a great role in energy saving and environmentalprotection and attracts more and more attention.In this dissertation, pulverized-coal Oxygen-enriched igniter is appliedto the ignition of the conventional direct-flow burner. Structuraloptimization analysis of the external way and internal way of igniter isconducted by Fluent. The analysis indicates that if the igniter is under theburner, a recirculation region emerges when the distance between igniter andburner in external way is50mm,150mm,250mm,350mm respectively andhydrocyclone strength of over fire air is0.5. The mixture of air and coal isgood. When the distance is150mm and hydrocyclone strength is1.0, asteady recirculation region emerges. If the igniter is on the side wall, arecirculation region emerges when the distance is200mm,400mm,500mmrespectively and hydrocyclone strength of over fire air is0.5,1.0respectively.The mixture of air and coal is good. When the distance is200mm andhydrocyclone strength is1.5, a steady recirculation region emerges. a steadyrecirculation region emerges if the internal way is used and pulverized-coalcan go through the region. The mixture will become better. It is good forexchange of substance and energy and a steady ignition and combustion canbe achieved.Ignition in internal way is selected in this dissertation. And numericalsimulation is conducted by Fluent. The flow of cold air in the process ofignition, the position of local pulverized-coal Oxygen-enriched igniter, theamount of primary air are studied. The results show that the best position ofigniter in internal way is100mm, and the characteristic of flow is good for ignition and combustion. Under the condition of the same position anddifferent primary air velocity, the characteristic of recirculation regionaround nozzle and the distribution of Oxygen is gotten.Several critical factors of ignition and combustion of pulverized-coalOxygen-enriched igniter, such as concentration of coal, the amount ofprimary air, the temperature of primary air, are studied in EBU model. Theresults indicate that for the pulverized-coal Oxygen-enriched igniter, the bestconcentration range of coal is0.4~0.5kgC/kgA in the process of ignition. Thebest primary air velocity is about15m/s. A little increase of primary airtemperature is helpful for the ignition of pulverized-coal Oxygen-enrichedigniter.