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Experimental Study and Numerical Simulation on Aerodynamic Field of Tangential Bias Swirl Burner

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Tutor: LiZhengQi
School: Harbin Institute of Technology
Course: Thermal Power Engineering
Keywords: Swirl burner,Slagging,Aerodynamic field,Recirculation zone,Numerical simulation
CLC: TK223.23
Type: Master's thesis
Year:  2008
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Abstract:
The circumferential bias swirl bunner(CBSB) imported from babcock UK by Harbin Boiler Company was applied in the opposed wall firing boiler and caused slagging nearby the burner. Cold model experiments and numerical simulation combined with analyse of the working principle of the CBSB was performed to explore the reasons of this problem and to search for feasible scheme.Results of the aerodynamic experiments indicate that the central recirculation zone asymmetrically distributes. When the rate of the central air equal to design value, the recirculation zone started in the spout of CBSB, between the elongation line of the primary air and the secondary air spout and the pulverized coal fired easily in the premixing segment. Therefore, the primary air and the secondary air mix in advance ,which prompt the primary air with pulverized coal to rotate with the swiveling central air and secondary air and reach the water-wall after the premixing segment. That’s the reason of slaging in the water-wall around the nozzle of burner. The most expansion angle is 90°in the experiment. It is indicated that the expansion angle of the outer secondary air had little difference in the five Structures, which is about 60°in the smoke tracing experiment. The slagging is not caused by flash. The central recirculation zone became smaller while the nozzle of inner secondary air was moved towards furnace. The least central recirculation zone can be got while the nozzle of inner secondary air was just behind the flaring of outer secondary air. The high temperature flue gas entrained by the central recirculation zone reduces with the decrease of area of the central recirculation zone which helps to reduce slagging.Results of numerical simulation of the aerodynamic field indicate that the reason of central recirculation zone unsymmetrical distribution is that the primary air is injected to the internal barrel in a tangential direction through the nozzle, and it had a certain distance deviation from the central line of the burner. Along the circumferential direction the tangential velocity distributed unsymmetrically causing the whole aerodynamic unsymmetrical distribution.According to the figures of the axial velocity, radial velocity, tangential velocity at the nozzle of the CBSB, the conculsion can be drawn that the reason of slagging was also the primary air with pulverized coal driven to rotate with the swiveling central air and secondary air and the pulverized coal continuously diffusing widely near the water-wall. Tangential velocity had little difference. In the Structure 1, the axial velocity was the most fast attenuation, the radial velocity was the highest, it is the easiest slagging. While the nozzle of inner secondary air was moved towards furnace, the absolute value of radial velocity reduces, which is benefital to lessen slagging, but the movement of nozzle of inner secondary air can not eradicate slagging. It was also found that the jet was not flash in the simulation.This paper studys the results of slagging through the expriments and numerical simulation of the aerodynamic field ,and puts forward solution of slagging, which has important guiding significance and application value in engineering practice.
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