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浙江大学学报(工学版)
Journal of ZheJiang University (Engineering Science)  2019, Vol. 53 Issue (10): 1898-1906    DOI: 10.3785/j.issn.1008-973X.2019.10.007
Mechanical and Energy Engineering     
Numerical simulation of effects of flue gas recirculation on biomass combustion in grate boiler
Yan-ning LU1(),Hong-tao ZHANG1,Yan-wei XU2,Yan-qun ZHU1,*(),Kai-di WAN1,Zhe-ru SHAO2,Zhi-hua WANG1
1. State Key Laboratory of Clean Energy Utilization, Zhejiang University, Hangzhou 310027, China
2. Everbright Enviromental Technology Research Institute Limited Company, Nanjing 211000, China
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Abstract  

A method of mixing secondary air with reciprocating flue gas combustion was conducted on a 130 t/h biomass grate boiler in order to solve the problems of serious corrosion of water wall, excessive ash accumulation of screen superheater and high NOx emission in the operation of biomass boilers. The computational fluid dynamics (CFD) simulation approach was applied to simulate the combustion process in the furnace in order to provide theoretical guidance for the actual operation of the boiler. CFD simulation results indicate that flue gas injected with upper secondary air can improve the gas temperature distribution by facilitating the gas flow disturbance in the upper furnace, and mitigate the fouling and slagging issues of the platen superheater by lowering and uniforming the gas temperature; flue gas injected with lower secondary air helps to reduce the peak combustion temperature and inhibit the formation of thermal NOx. The combustion in the boiler was improved with a more uniform burning condition by optimizing secondary air distribution with the flue gas recirculation technology, and the NOx emission was reduced by 32.1% compared to the original condition before the optimization.

Key words： biomass grate boiler      computational fluid dynamics (CFD)      flue gas recirculation technology      secondary air      NOx     
Received: 22 June 2018      Published: 30 September 2019
CLC:  TK 16  
Corresponding Authors: Yan-qun ZHU     E-mail: 21627100@zju.edu.cn;yqzhu@zju.edu.cn
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Yan-ning LU
Hong-tao ZHANG
Yan-wei XU
Yan-qun ZHU
Kai-di WAN
Zhe-ru SHAO
Zhi-hua WANG
Cite this article:

Yan-ning LU,Hong-tao ZHANG,Yan-wei XU,Yan-qun ZHU,Kai-di WAN,Zhe-ru SHAO,Zhi-hua WANG. Numerical simulation of effects of flue gas recirculation on biomass combustion in grate boiler. Journal of ZheJiang University (Engineering Science), 2019, 53(10): 1898-1906.

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http://www.zjujournals.com/eng/10.3785/j.issn.1008-973X.2019.10.007     OR     http://www.zjujournals.com/eng/Y2019/V53/I10/1898


烟气再循环对生物质炉排炉燃烧影响的数值模拟

针对生物质锅炉实际运行过程中常出现水冷壁腐蚀严重、屏式过热器积灰多和NOx排放量高等问题，以一台某电厂额定蒸发量为130 t/h的生物质往复式水冷炉排炉为研究对象，提出二次风掺混再循环烟气燃烧的方法，采用计算流体力学（CFD）数值模拟技术对炉内燃烧过程进行热态模拟，旨在为锅炉的实际运行操作提供理论指导. 计算结果表明，采用烟气再循环可以增强炉膛上部气流扰动，改善炉内温度分布的均匀性，提高燃尽率，同时降低屏区火焰温度，减轻大屏积灰结渣风险；后墙下二次风掺混再循环烟气后，主燃区形成还原性气氛，温度下降，有效抑制热力型NOx的生成.后墙下二次风掺混30%再循环烟气的工况炉内气流均匀饱满，高温烟气分布从炉膛深度中心向前、后墙两侧稳定下降，NOx排放质量浓度相对于无再循环烟气时减少了32.1%.


关键词： 生物质炉排炉,  计算流体力学（CFD）,  烟气再循环技术,  二次风,  氮氧化物（NOx） 
元素分析wB/% 工业分析wB/%
注：1)表中数据为收到基.
C H O N S M V FC A
26.66 3.37 23.41 0.41 0.10 32.4 44.79 9.15 13.66
Tab.1 Ultimate analysis and proximate analysis of tested biomass
Fig.1 Geometry model of simulated biomass grate furnace
Fig.2 Schematic of NOx transformation model
Fig.3 Air distribution of calculation condition A1
工况编号 ${\alpha _{\rm{1}}}$/% ${\alpha _{{\rm{ign}}}}$/% ${\alpha _{{\rm{21}}}}$/% ${\alpha _{22}}$/% ${\alpha _{{\rm{23}}}}$/% ${\alpha _{{\rm{24}}}}$/%
A0 58.1 6.0 12.8 0 23.1 0
A1 58.1 6.0 12.8 0 23.1 0
B1 58.1 6.0 12.8 0 18 5.1
B2 58.1 6.0 12.8 0 14.6 8.5
B3 58.1 6.0 12.8 0 11.2 11.9
Tab.2 Air distribution of calculation conditions
工况编号 ${\beta _{{\rm{21}}}}$/% ${\beta _{22}}$/% ${\beta _{{\rm{23}}}}$/% ${\beta _{{\rm{24}}}}$/%
A0 0 0 0 0
A1 0 15.5 0 14.5
B1 0 15.5 4.4 10.1
B2 0 15.5 7.3 7.3
B3 0 15.5 10.1 4.4
Tab.3 Flue gas distribution of calculation conditions
Fig.4 Temperature distribution on center cross section of A0
Fig.5 Pathline distribution of A0
Fig.6 Temperature distribution on center cross section of A1
Fig.7 Pathline distribution of A1
Fig.8 Temperature distribution on center cross section under conditions with lower secondary air mixing recycling flue gas（B1，B2，B3）
工况编号 Tt /K Tf /K To /K ${\varphi _{\rm O_2}}$/% ${\varphi _{\rm CO}}$/10?6
A0 1277 1242 993 3.6% 2 220
A1 1283 1128 953 3.4% <1
B1 1291 1138 959 3.6% <1
B2 1266 1149 973 3.3% <1
B3 1286 1135 990 3.6% <1
Tab.4 Statistical values under conditions with different secondary air arrangements（A0，A1，B1，B2，B3）
Fig.9 Average temperature distribution along x direction on throat plane under conditions with different secondary air arrangements（A0，A1，B1，B2，B3）
Fig.10 Average temperature distribution along x direction on incinerator outlet plane under conditions with different secondary air arrangements（A0，A1，B1，B2，B3）
Fig.11 Pathline distribution under conditions with lower secondary air mixing recycling flue gas（B1，B2，B3）
工况编号 $\rho_{{\rm{NO}}_x} $/（mg·m?3）
A0 304.2
A1 246.3
B1 206.4
B2 247.8
B3 253.6
Tab.5 Simulation results of NOx under conditions with different secondary air arrangements（A0，A1，B1，B2，B3）
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