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Combustion and NOx formation characteristics of a central fuel-rich direct current pulverized coal burner

2022 No. 04
535
245
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Authors:
SHEN Tao
SONG Minhang
XIA Liangwei
HUANG Ying
LU Pisi
Unit:
Harbin Boiler Co., Ltd.,;State Key Laboratory of Efficient and Clean Coal-fired Utility Boilers,Harbin Boiler Co.,Ltd.,;Institute of Process Engineering,Chinese Academy of Sciences
Abstract:

In order to improve the performance of direct-flow pulverized coal burner in promoting the coal ignition and stable combustion,and simultaneously reducing the NOx generation,Harbin Boiler Co.,Ltd. developed a central fuel-rich direct-current pulverized coal burner. In this burner,a combination of two stages of pulverized coal concentration,a blunt body and combustion stabilization teeth were used to enhance fuel rich/lean organization,stabilize combustion and reduce NOx generation. The overall combustion performance of this type of burner was obtained by using ANSYS fluent numerical calculation method,and the gas/solid flow,combustion and NOx generation characteristics of the burner were studied by adjusting the air distribution. The research results show that after the primary coal/air flow is concentrated in two stages,most of the coal particles (about 80%-90% of the total coal particles) can be concentrated in the middle fuel-rich flow channel,and the corresponding flow velocity is between 12 and 16 m/s. Therefore,a low-velocity and fuel-rich zone can be formed near the burner nozzle,which is beneficial to promote the timely ignition of the coal/air flow,and the ignition location is about 300 mm away from the burner nozzles. At the same time,the setting of the combustion stabilizing plate can form two symmetrical high-temperature recirculation zones at the burner outlet,and the corresponding recirculation zone length is around 160 mm. by decreasing the primary air flux and increasing the secondary air flux,the volatile reaction rate is reduced,the reaction time of CO and fixed carbon is prolonged,and the flame length area is simultaneously increased,which is not conducive to suppressing NOx generation. When the secondary air flux increases and the overfire air flux reduces,the entrainment effect of the high-velocity secondary air on the coal/air flow is enhanced,so as to continuously provide oxygen for the subsequent coal combustion and promote the further heat release. At the same time,due to the further weakening of the effect of air staged combustion,the reducing effect of the main combustion area is weakened,and the NOx emission concentration is maintained at a high level of 237.3 mg/m3 at 6% O2. According to the NOx generation characteristics of the burner under the reference working condition,under the benchmark conditions,due to the combined effect of the high-temperature recirculation zone and the low-velocity fuel-rich zone,an oxygen-lean and fuel-rich strong reducing atmosphere is formed near the burner nozzles,which obviously inhibits the NOx production,and a low NOx emission concentration of 162.34 mg/m3 at 6% O2 is achieved.

Keywords:
direct-current burner
pulverized-coal combustion
numerical simulation
ignition and burnout
NOx generation characteristics
Citation format:
沈涛(1986—),男,吉林丹东人,工程师,硕士。E-mail:shen1390498@126.com
通讯作者:宋民航(1986—),男,黑龙江绥化人,副研究员,博士。E-mail:songminhang@126.com
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