Mechanism of CO2 Cracking by Gliding Arc
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摘要: 建立了一维滑动弧裂解CO2的反应机理模型. 利用对流冷却的特征频率计算横向气流对流引起的等离子体组分损失. 将等离子体密度和温度的数值模拟结果与文献中滑动电弧等离子体反应器的实验数据进行了对比，吻合较好. 模拟结果表明，滑动弧裂解CO2会产生大量O和O2等活性助燃粒子以及可燃的CO. 随着对流冷却特征频率的增加，放电过程中最大电子数密度和电子温度减小，CO2转化率下降. 在整个CO2裂解机制中e+CO2→e+CO+O的贡献最大，准稳态中贡献率为90.63%，瞬态中贡献率为98.43%. 反应CO+O+M→CO2+M对CO2生成的贡献率最大. 在实际应用中，为提高CO2转化率，可以通过增大放电电流，增大e+CO2→e+CO+O的反应速率，同时选择合适的气体流量，避免过大的速度引起CO2转化率下降.Abstract: In this paper, a one-dimensional gliding arc model and the detailed mechanism of CO2 cracking reaction were established. The characteristic frequency of convection cooling was used to calculate the plasma component loss caused by cross flow convection. The calculated plasma density and plasma temperature were compared with the experimental data of gliding arc plasma reactor in the literature. The calculation results show that a large number of active combustion supporting particles such as O and O2 and combustible CO gas will be produced during CO2 cracking by gliding arc. With the increase of the characteristic frequency of convection cooling, the maximum electron number density and electron temperature decrease, and the CO2 conversion rate decreases. The contribution rate of e+CO2→e+CO+O is the largest in the whole mechanism of CO2 cracking, which is 90.63% in quasi steady state and 98.43% in transient state. The contribution rate of CO+O+M→CO2+M to CO2 generation is the largest. In practical application, in order to improve the conversion rate of CO2, the discharge current and the reaction rate of e+CO2→e+CO+O should be appropriately increased. The gas flow rate should be appropriately selected to avoid the decline of CO2 conversion rate caused by excessive speed.
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Key words:
- CO2 cracking /
- gliding arc /
- non-equilibrium plasma /
- reaction mechanism
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图 3 不同特征冷却频率下电子数密度和电子温度随位置的演化
Figure 3. Evolution of electron number density and electron temperature with different cooling frequencies
图 4 CO2消耗反应速率随位置的演化
Figure 4. Evolution of CO2 consumption reaction rate with location
图 6 O2生成和消耗反应速率随位置的演化
Figure 6. Evolution of reaction rate of O2 generation and consumption with location
图 9 电子数密度和电子温度随时间的演化
Figure 9. Evolution of electron number density and electron temperature with time
图 10 不同特征冷却频率下的最大电子数密度和电子温度
Figure 10. Maximum electron number density and electron temperature at different cooling frequencies
图 13 O2生成和消耗反应速率随位置的演化
Figure 13. Evolution of reaction rate of O2 generation and consumption with location
图 14 不同特征冷却频率下CO2数密度随时间的演化
Figure 14. Evolution of CO2 number density with time at different cooling frequencies
表 1 模型中包含的粒子
Table 1. Particles contained in the model
neutral species and radicals charged particles CO2, CO, O, C, O2 CO2+, e 
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表 3 模型中中性粒子反应
Table 3. Neutral particle reactions
reaction reaction rate reference No. M+CO2→M+CO+O 4.39×10-7exp
(-65 000/Tg)[6] R11 O+CO2→O2+CO 7.77×10-12exp
(-16 600/Tg)[6] R12 CO+O+M→CO2+M 8.2×10-34exp
(-1 560/Tg)[27] R13 O2+CO→CO2+O 1.28×10-12exp
(-12 800/Tg)[6] R14 C+CO2→CO+CO 1.0×10-15 [28] R15 O2+C→CO+O 3.0×10-11 [27] R16 CO+M→C+O+M 1.52×10-4exp
(-12 800/Tg)[29] R17 C+O+M→CO+M 2.14×10-29exp
(-2 114/Tg)[26] R18 O+O+M→O2+M 1.27×10-32exp
(-170/Tg)[30] R19
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表 4 各反应对CO2裂解贡献率
Table 4. Contribution rate of each reaction to CO2 cracking
No. reaction relative contribution rate R7 e+CO2→e+CO+O 90.63% R11 M+CO2→M+CO+O < 0.01% R12 O+CO2→O2+CO 0.11% R15 C+CO2→CO+CO 9.26%
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表 5 各反应对CO2裂解贡献率
Table 5. Contribution rate of each reaction to CO2 cracking
No. reaction relative contribution rate R7 e+CO2→e+CO+O 98.43% R11 M+CO2→M+CO+O < 0.01% R12 O+CO2→O2+CO < 0.01% R15 C+CO2→CO+CO 1.57%
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