Clean Coal Technology

2022, v.28;No.142(06) 150-158

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Numerical simulation of flow field and combustion characteristics of DRB-4Z swirl pulverized coal burner

HU Yaohui;PENG Zhimin;LI Yonghua;Department of Power Engineering,North China Electric Power University;Department of Energy and Power Engineering,Tsinghua University;

Abstract:

At present, hedge boilers are widely used in large capacity units, and the combustion effect of hedge boilers depends on the performance of burners. In order to analyze the flow and combustion characteristics of DRB-4 Z swirl pulverized coal burner, the flow field distribution of a single burner and the combustion process of a 1 000 MW ultra supercritical unit(using DRB-4 Z swirl pulverized coal burner)were simulated by Fluent software. The effects of primary air speed, internal and external secondary air speed and swirl intensity on primary air stiffness, location and range of reflux area were studied. The flow field simulation results of a single burner show that the primary air velocity of DRB-4 Z swirl pulverized coal burner is inversely proportional to the range of reflux area. When the primary air velocity is 16 m/s under rated load, the flow field distribution is better. The primary air velocity under low load should not be less than 12 m/s, so as to avoid the ignition point of pulverized coal being too close to the burner outlet, and the primary air velocity under high load should not exceed 20 m/s, so as to ensure that pulverized coal gets sufficient heat at the initial stage of combustion, the wind speed of internal and external secondary air is directly proportional to the range of reflux area, when the wind speed of internal secondary air is 28 m/s and the swirl intensity is 0.75,the flow field distribution is good. For combustible coal, the opening of internal secondary air blade can be set to 30°,and the swirl intensity is 0.52,so as to delay the mixing of primary air and internal secondary air and reduce the generation of NO_x. For difficult coal combustion, the opening of secondary air blade in the seed can be set to 50°,and the swirl intensity is 1.02 to ensure that enough high-temperature flue gas is entrained in the reflux area to make the stable combustion of pulverized coal. The simulation results of boiler combustion process show that the temperature in the middle and upper burner area of the furnace is the highest, and the maximum temperature can reach 1 900 K. The main combustion area is in a state of severe hypoxia. Although severe hypoxia in the main combustion area can reduce the generation of NO_x,a large number of reducing gases CO and H_2S are generated in the outlet area of the burner, which is easy to cause high-temperature corrosion of the water wall.

Key Words: swirl burner;swirl intensity;numerical simulation;flow field distribution;reflux zone;combustion characteristic

Abstract:

Keywords:

Foundation: 国家重点研发计划资助项目(2019YFB2006002);; 华能集团总部科技项目基础能源科技研究专项(一)资助项目(HNKJ20-H50)

Authors: HU Yaohui;PENG Zhimin;LI Yonghua;Department of Power Engineering,North China Electric Power University;Department of Energy and Power Engineering,Tsinghua University;

DOI: 10.13226/j.issn.1006-6772.21062399

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