Effect of combustion-supporting air on NOx emission of ethylene cracking furnace

doi:10.11949/0438-1157.20190771

Abstract

Abstract:

Coupled simulation and optimization of complex physical and chemical processes in ethylene cracking furnace can meet the demand for design and operation of high efficiency, low pollution and low cost in ethylene plant. Therefore, it has great significance for improving the competitiveness of the ethylene industry. Aiming at the disadvantage of simple combustion mechanism that it is difficult to accurately predict the distribution of NO_x concentration produced by furnace combustion, are reduced GRI-Mesh 3.0 mechanism combined with eddy dissipation concept (EDC) model for cracking furnace was proposed. The combustion process of Sandia Flame D was simulated and the reliability of the coupled model was verified. Based on the established combustion model, the effect of combustion-supporting air on reducing NO emission of cracking furnace was studied. The results show that the best effect of reducing NO is when the air preheating temperature is 300—600 K and the excess air coefficient is 1.1 when the thermal efficiency of the cracking furnace is satisfied.

Key words: ethylene cracking furnace, simulation, optimization, reduced GRI-Mesh 3.0 mechanism, computational fluid dynamics, combustion-supporting air, NO_x emission

摘要：

乙烯裂解炉内复杂物理化学过程耦合模拟与优化能够满足乙烯装置对高效率、低污染和低成本的设计和操作要求，对提高乙烯工业的竞争力具有重要意义。针对简单燃烧机理难以准确预测炉膛燃烧生成NO_x浓度分布的弊端，提出了在裂解炉使用更准确的简化GRI-Mesh 3.0机理结合涡耗散概念(EDC)模型的方法，并对Sandia Flame D的燃烧过程进行计算流体力学(CFD)模拟，验证了此耦合模型的可靠性。在已建立的燃烧模型的基础上，研究了助燃空气对降低裂解炉NO排放的影响，结果表明：在满足裂解炉热效率的情况下，空气预热温度为300~600 K、过量空气系数为1.1时降低NO的效果最佳。

关键词: 乙烯裂解炉, 模拟, 优化, 简化GRI- Mesh 3.0机理, 计算流体力学, 助燃空气, NO_x排放

CLC Number:

TQ 021.1

Guihua HU, Zhencheng YE, Wenli DU. Effect of combustion-supporting air on NO_x emission of ethylene cracking furnace[J]. CIESC Journal, 2020, 71(2): 698-707.

胡贵华, 叶贞成, 杜文莉. 助燃空气对乙烯裂解炉NO_x排放的影响[J]. 化工学报, 2020, 71(2): 698-707.

Figures/Tables 16

References 32

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结构	直径/长×宽/mm	温度/K	速度/(m/s)	组分/(质量分数)
结构	直径/长×宽/mm	温度/K	速度/(m/s)	CH₄	O₂	N₂	CO₂	H₂O
主火焰	7.2	294	49.6	0.156	0.197	0.647	0	0
值班火焰	18.2	1880	11.4	0	0.054	0.742	0.11	0.094
空气伴流	300×300	291	0.9	0	0.23	0.77	0	0

结构	直径/长×宽/mm	温度/K	速度/(m/s)	组分/(质量分数)
结构	直径/长×宽/mm	温度/K	速度/(m/s)	CH₄	O₂	N₂	CO₂	H₂O
主火焰	7.2	294	49.6	0.156	0.197	0.647	0	0
值班火焰	18.2	1880	11.4	0	0.054	0.742	0.11	0.094
空气伴流	300×300	291	0.9	0	0.23	0.77	0	0

α	底部烧嘴燃料流量/(kg/s)	底部风门入口流量/(kg/s)	侧壁烧嘴总流量/(kg/s)
1.05	0.09375	1.70036	1.44857
1.07	0.09375	1.73274	1.47472
1.09	0.09375	1.76513	1.50087
1.10	0.09375	1.78132	1.51395
1.13	0.09375	1.82991	1.55317
1.16	0.09375	1.87849	1.59240
1.20	0.09375	1.94326	1.64470

α	底部烧嘴燃料流量/(kg/s)	底部风门入口流量/(kg/s)	侧壁烧嘴总流量/(kg/s)
1.05	0.09375	1.70036	1.44857
1.07	0.09375	1.73274	1.47472
1.09	0.09375	1.76513	1.50087
1.10	0.09375	1.78132	1.51395
1.13	0.09375	1.82991	1.55317
1.16	0.09375	1.87849	1.59240
1.20	0.09375	1.94326	1.64470

α	反应净生成热/(J/(cm³?s))	CH₄摩尔分数	温度/K	NO摩尔生成率/(mol/(cm³?s))
1.05	36.09	1.59×10^-5	2225.53	3.03×10^-7
1.07	36.05	1.60×10^-5	2218.58	2.89×10^-7
1.09	35.93	1.62×10^-5	2211.42	2.75×10^-7
1.1	35.88	1.63×10^-5	2207.03	2.68×10^-7
1.13	35.56	1.63×10^-5	2203.82	2.62×10^-7
1.16	35.34	1.65×10^-5	2197.88	2.51×10^-7
1.2	35.02	1.66×10^-5	2192.88	2.42×10^-7