| Many low-NOx burners are introduced to China to meet the tighter NOx emission limit. But lots of them have problems in practical operation, such as serious slagging and poor load stable combusting capability, for coal used in coal-fired boiler in China are often low-grade and change day by day. In view of this, studies are conducted on a Low-NOx axial swirl burner (LNASB) produced by Mitsui Babcock Energy Limited Company and a improved Low-NOx axial swirl burner ( ILNASB ) . We used a three-component particle-dynamics anemometer to measure, in the near-burner region, the flow characteristics of two burners, in conjunction with a gas/particle two-phase test facility and the FLUENT6.3.26 software to simulate.The experiment data shows that an annular central recirculation zone (CRZ) is formed in the region of x/d =0.1-0.3 for two burners. The CRZ of LNASB exists between the primary and secondary air flow zone. The CRZ of ILNASB exists between the inner and outer secondary air flow zone. The CRZ of LNASB has the maximum size at x/d =0.1 cross-section, which region is 40mm≤r≤65mm and the maximum recirculating velocity can reach 4m/s.For the CRZ of LNASB has extended into burner nozzle and the particle volume flux is high in the CRZ, it can easily result in the burnout and slagging in the burner nozzle. What's more, the CRZ formed a high temperature, high oxygen and long retention time zone, it can easily result in a high NOx emission.The distance of the peak of particle volume flux and the CRZ boundary of ILNASB is 44mm at x/d =0.1 section, it can put off the particle entrained into CRZ, which benefit to prevent the burnout and slagging in the burner nozzle. What's more, most of coal burn in the center of the burner, which can inhibit NOx generating.Simulation results has good agreement with PDA experimental results. Though realizable k-εmodel has mechanism defect when simulate strong swirl flow, it can meet the requirement of engineering applications.
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