Numerical on emissions mechanism of nitrogen oxides in gas-fired boilers blended with hydrogen

doi:10.16085/j.issn.1000-6613.2023-0016

Abstract

Abstract:

Combustion of adding hydrogen in industrial gas boilers can reduce the use of carbon-containing fuels, but it will cause an increase in NO _x emission. Therefore, this paper conducted a detailed study on the hydrogen mixed combustion characteristics of an existing industrial gas-fired HL75-2.5/260-Q boiler. The formation law and reduction path of NO and N₂O were explored to provide a fundamental guide for the subsequent development of low-nitrogen burners for hydrogen mixed combustion. Firstly, based on the detailed reaction mechanism of methane Gri-mesh 3.0, the combustion characteristics and pollutant formation characteristics of gas with a hydrogen content ratio of 0—90% were simulated. Secondly, the chemical reactor network model inside the boiler was established by Chemkin, and the generation path, sensitivity, and production rate characteristics of NO and N₂O under the optimal hydrogen mixing ratio were analyzed. The results showed that when the excess air coefficient was 1.2, the high-temperature area of the flame and the outlet temperature increased with the increase of the hydrogen doping ratio. The outlet NO concentration gradually increased from 85.59mg/m³ to 249.85mg/m³. The N₂O emission first decreased and then increased, and the N₂O emission was at least 0.16mg/m³ at the hydrogen mixed ratio of 0.2. NO mainly came from the elementary reactions R179 (N + O₂ NO + O) and R180 (N + O₂ NO + O)), and N₂O mainly came from the elementary reaction R185 [N₂ + O(+M) N₂O(+M)].

Key words: gas-fired boiler, hydrogen, nitrogen oxide, sensitivity analysis, rate of production analysis, numerical study

摘要：

工业燃气锅炉掺氢燃烧可减少含碳燃料的使用，但会引起NO _x 排放的增加。本文针对现有工业用HL75-2.5/260-Q型锅炉燃气掺氢燃烧特性展开详尽研究，探究NO和N₂O的生成规律及减少路径，为后续掺氢燃烧低氮燃烧器开发提供依据。首先，基于甲烷详细反应机理Gri-mesh 3.0，对0～90%掺氢比的燃气燃烧特性及污染物生成特性进行模拟研究。其次，利用Chemkin建立该锅炉内部的化学反应器网络模型，研究了最佳掺氢比下的NO和N₂O的生成路径、敏感性及生产速率特性。结果表明：在过量空气系数为1.2的情况下，随掺氢比增加炉膛内火焰高温区域增大，出口温度升高，出口NO由85.59mg/m³逐渐增多到249.85mg/m³；N₂O呈现先减少后增加趋势，在掺氢比为0.2时N₂O排放最少为0.16mg/m³；NO主要来源于基元反应R179 (N + O₂ NO + O)和R180 (N+O₂ NO + O)，N₂O主要来源于基元反应R185 [N₂ + O(+M) N₂O(+M)]。

关键词: 燃气锅炉, 氢, 氮氧化物, 敏感性分析, 生产速率分析, 数值模拟

CLC Number:

TK229

ZHAO Qiaonan, LIU Xuemin, LIU Feng, XU Hongtao, LIU Zhaohai, LIAO Xiaowei. Numerical on emissions mechanism of nitrogen oxides in gas-fired boilers blended with hydrogen[J]. Chemical Industry and Engineering Progress, 2023, 42(11): 5637-5647.

赵巧男, 刘雪敏, 刘峰, 徐洪涛, 刘兆海, 廖晓炜. 燃气锅炉掺氢燃烧氮氧化物排放机理数值模拟[J]. 化工进展, 2023, 42(11): 5637-5647.

Figures/Tables 16

References 23

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编号	氢气混合分数f(H₂)	燃气速度/kg·s^-1	空气速度/kg·s^-1
1	0	0.279	5.74
2	0.1	0.273	5.70
3	0.2	0.267	5.67
4	0.3	0.260	5.63
5	0.4	0.251	5.59
6	0.5	0.241	5.56
7	0.6	0.228	5.45
8	0.7	0.212	5.34
9	0.8	0.189	5.20
10	0.9	0.160	5.02

编号	氢气混合分数f(H₂)	燃气速度/kg·s^-1	空气速度/kg·s^-1
1	0	0.279	5.74
2	0.1	0.273	5.70
3	0.2	0.267	5.67
4	0.3	0.260	5.63
5	0.4	0.251	5.59
6	0.5	0.241	5.56
7	0.6	0.228	5.45
8	0.7	0.212	5.34
9	0.8	0.189	5.20
10	0.9	0.160	5.02

序号	基元反应	序号	基元反应
R33	H+O₂+MHO₂+M	R52	H+CH₃(+M)CH₄+(+M)
R34	H+2O₂HO₂+O₂	R84	OH+H₂H+H₂O
R36	H+O₂+N₂HO₂+N₂	R98	OH+CH₄CH₃+H₂O
R38	H+O₂O+OH	R119	HO₂+CH₃OH+CH₃O
R47	H+H₂O₂HO₂+H₂	R158	2CH₃(+M)C₂H₆(+M)

序号	基元反应	序号	基元反应
R33	H+O₂+MHO₂+M	R52	H+CH₃(+M)CH₄+(+M)
R34	H+2O₂HO₂+O₂	R84	OH+H₂H+H₂O
R36	H+O₂+N₂HO₂+N₂	R98	OH+CH₄CH₃+H₂O
R38	H+O₂O+OH	R119	HO₂+CH₃OH+CH₃O
R47	H+H₂O₂HO₂+H₂	R158	2CH₃(+M)C₂H₆(+M)

序号	基元反应	ROP	贡献率/%	方向
R178	N+NON₂+O	6.63×10^-3	0.37	生成
R179	N+O₂NO+O	1.13	63.11	生成
R180	N+OHNO+H	0.51	28.48	生成
R189	NO₂+HNO+OH	4.14×10^-3	0.23	生成
R190	NH+ONO+H	2.52×10^-2	1.41	生成
R208	NNH+ONH+NO	4.25×10^-2	2.37	生成
R214	HNO+HH₂+NO	6.50×10^-2	3.63	生成
R222	NCO+ONO+CO	6.98×10^-3	0.40	生成