氧浓度对微通道内甲烷均相/非均相耦合反应特性的影响

doi:10.11949/0438-1157.20221301

摘要/Abstract

摘要：

基于详细的甲烷均相与非均相反应机理，对平板微通道内甲烷催化燃烧反应过程模拟，探究入口氧浓度变化对耦合反应特性的影响与调控机制。结果表明，氧浓度升高导致甲烷均相与非均相反应放热位置向入口侧移动，缩短均相着火距离，拓宽稳燃范围。固定入口甲烷浓度，氧浓度升高导致化学当量比降低，同时也改变了均相/非均相反应对反应物O₂的竞争机制；氧浓度与化学当量比共同作用改变了气相自由基的吸附与脱附行为。增加O₂浓度促进CH₄和H自由基的均相反应消耗同时抑制CH₄和H的非均相反应速率。随着O₂浓度的升高，O₂以及中间产物CO和H₂参与非均相反应速率先升高后降低。

关键词: 微尺度燃烧, 甲烷, 催化, 微通道, 氧气浓度, 反应动力学

Abstract:

Based on the detailed homogeneous and heterogeneous reaction mechanisms of methane, the catalytic combustion process of methane in a planar microchannel was simulated, and the effect of inlet oxygen concentration on the coupled reaction characteristics and its regulation mechanism were analyzed. The results show that the increase of oxygen concentration causes the exothermic position of the homogeneous and heterogeneous reactions of methane to move to the inlet side, shortening the homogeneous ignition distance and broadening the stable combustion range. At a fixed methane concentration at the inlet, increasing O₂ concentration lowers the equivalence ratio of mixture and changes the competition mechanism between homogeneous and heterogeneous reactions for reactant O₂; the combined effect of O₂ concentration and equivalence ratio changes the adsorption and desorption behavior of gas radicals. The increase of O₂ concentration promotes the homogeneous reaction consumption of CH₄ and H radicals and also inhibits the heterogeneous reaction rate of CH₄ and H on the catalytic surface. With the increase of O₂ concentration, the rates of O₂, and intermediate gas phase products CO and H₂ participating in the heterogeneous reaction first increase and then decrease.

Key words: microscale combustion, methane, catalysis, microchannels, oxygen concentration, reaction kinetics

中图分类号:

TK 16

杨霄, 丁锐, 李墨含, 宋正昶. 氧浓度对微通道内甲烷均相/非均相耦合反应特性的影响[J]. 化工学报, 2022, 73(12): 5427-5437.

Xiao YANG, Rui DING, Mohan LI, Zhengchang SONG. Effect of oxygen concentration on homogeneous/heterogeneous coupled reaction characteristics of methane in microchannel[J]. CIESC Journal, 2022, 73(12): 5427-5437.

图/表 13

图1 平板催化微燃烧器结构示意图

Fig.1 Schematic diagram of the planar catalytic microchannel structure

图2 Pt表面催化甲烷燃烧的均相/非均相耦合反应路径示意图

Fig.2 Schematic diagram of homogeneous/heterogeneous coupled reaction pathway for methane catalytic combustion over Pt

表1 入口工况

Table 1 Inlet flow conditions

工况	氧化剂		入口甲烷燃料体积分数/%	化学当量比
工况	O₂/%	N₂/%	入口甲烷燃料体积分数/%	化学当量比
1	19	81	9.5023	1.105
2	20	80	9.5023	1.050
3	21	79	9.5023	1.000
4	22	78	9.5023	0.955
5	23	77	9.5023	0.913

图3 归一化OH浓度分布

Fig.3 Normalized OH molar concentration distribution

图4 燃烧器中心线温度与OH浓度分布

Fig.4 Distribution of temperature and OH concentration along the centerline

图5 燃烧器催化表面非均相反应放热速率与中心线上均相反应放热速率分布

Fig.5 Distribution of heat release rate of heterogeneous reaction on the catalytic surface and homogeneous reaction along the centerline

图6 燃烧器内壁面温度与近内壁面（y=1.195 mm）气体温度分布

Fig.6 Distribution of inner wall temperature and gas temperature near inner wall （y=1.195 mm）

图7 火焰位置分布

Fig.7 Distribution of flame location

图8 燃烧器催化表面气相组分参与非均相反应速率分布

Fig.8 Profiles of reaction rate of radical depletion by heterogeneous reaction in the catalytic surface

图9 燃烧器中心线与近内壁面处关键组分浓度分布

Fig.9 Profiles of some radical concentration along the centerline and near catalytic surface

图10 燃烧器催化表面组分覆盖率

Fig.10 Profiles of surface coverage at the inner wall

图11 燃烧器催化表面气相组分平均反应速率

Fig.11 Average reaction rate of gas radical on the catalytic surface

图12 均相反应中关键基元反应放热对总放热的贡献比

Fig.12 Heat release contribution from some elementary reactions in homogeneous reaction

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