Study On Flow Characteristics Of Reverse-Swirl Pulverized Coal Burner

The paper takes the reverse-swirl?RS?pulverized coal burner as research object.In order to reveal the flame stabilization mechanism of the reverse jet coupling the swirl flow and the influence of different working conditions and process parameters on the aerodynamic field of RS burner.A 1:2 single-phase flow characteristics test model and a 1:5 gas/particle two-phase flow characteristics test model were built respectively.Hot wire anemometer and coordinate frame tracer were used to study the influence of different reverse primary air?PRA?ratios,different inner/outer secondary air ratios and pre-combustion cone on the single-phase flow characteristics of RS burner.Based on the above research,PDA?Phase Doppler Anemometer?was used to study the influence of the DC secondary air on the flow characteristics of the reverse primary gas/particle and the different inner secondary air vane angles on the gas/particle two phase flow characteristics of the RS burner.Finally,the thermal verification was carried out on the 14 MW RS burner test bench.The conclusions were as follows:?1?According to experiments of the single-phase flow characteristics,for the cases of no pre-combustion cone,when the RPA ratio and inner/outer secondary air ratio reached 14.86%and 1:2 respectively,the area of the coupled recirculation zone?CRZ?,the relative reverse flow rate and swirling ability became suitable.Besides,the mixing between the inner secondary air?ISA?and outer secondary air?OSA?was relatively delayed and more violent.For the cases with the pre-combustion cone,with the increasing of the ratio of inner/outer secondary air from 2:5 to 1:1,the maximum diameter of CRZ increased from 0.67 D to 0.87 D?D refers to the inner diameter of outer secondary air duct?;the relative reverse flow rate increased from 0.83 to 1.29.The CRZ in the range of 0.3?X/D?0.8 would take action in term of flame stabilization which the velocity was low but the turbulence was strong?X refers to the axial direction of RS burner?.A high-speed and low turbulence air protective layer was formed near the wall of the pre-combustion cone.The area of CRZ,the relative reverse flow rate and the axial velocity were all smaller with the pre-combustion cone.?2?According to the experiments of the gas/particle two-phase flow characteristics,the gas velocity was significantly higher than the particle velocity for the section X/D=1.60.Under the effect of DC secondary air on the reverse primary gas/particle,the length of the CRZ was constant;the maximum diameter of the CRZ was smaller;the particle size distribution tended to be more uniform and the high concentration area outside the burner was far away from the outlet of the burner.With the increasing of inner secondary air vane angle,the particle concentration distribution near the jet boundary was closer to the outside of the burner.An obvious"low concentration,high concentration,low concentration"structure was formed in the case-45°.An inner lean and outer concentrated structure was formed in the case-50°and case-60°.?3?According to experiments of the thermal verification,O₂ concentration decreased along the axial direction.NO_x concentration increased first and then decreased along the axial direction,and there was a peak value near the cross section X/D=0.75,which further proved that the region had the effect of flame stabilization.With the increasing of inner/outer secondary air ratio,the concentration of O₂ near the pre-combustion cone was greater than 7%,which further proved that there was an air protective layer.The NO_x concentration near the pre-combustion cone of the RS burner was higher,which further proved that the concentration structure of the pulverized coal was inner lean and outer concentrated.