甲烷蒸汽重整制氢反应路径研究

Study on Reaction Pathways of Steam Methane Reforming for Hydrogen Production

利用CFD建立了合理的重整管模型,在进口气体614℃、2 944 kPa,水碳比为2. 97的实验条件下进行甲烷蒸汽重整制氢的模拟计算,分析得到了由CH4生成H2的反应路径,研究了进口气体温度对反应路径的影响。研究结果表明:在甲烷蒸汽重整制氢反应中,CH4首先裂解为CH3,CH3合成C2H6,C2H6通过逐步的脱氢反应生成氢气;或者CH3转化为CH3OH,CH3OH发生一系列的脱氢反应生成氢气。从净反应速率来看,反应的重要中间产物CH3和CH3OH沿重整管轴线方向先生成后消耗,故其摩尔分数沿轴线方向先升高后降低。进口气体温度从600℃升高到1 000℃,氢气的产率从44. 91%提高至50. 21%。温度超过900℃时,基元反应R60和R112速率的显著减小使CH3脱氢及其转化为C2H6的过程受到阻碍,R100速率依旧增大使得更多的CH3转化为CH3OH;C2H6所参与的部分脱氢反应路径强度减小,更多的氢气通过CH4直接脱氢和CH3OH逐步脱氢生成。

A reasonable reforming tube model was established using CFD. The steam methane reforming process was numerically studied under experimental conditions of inlet gas of 614 ℃,2 944 k Pa and S/C = 2. 97( ratio of steam to carbon). The reaction pathways for H2 production were analyzed. The effects of temperature on the reaction pathways for H2 production were investigated. The results show that in the process of steam methane reforming,CH4 is first cracked into CH3. Then CH3 is synthesized into C2H6,and after that H2 is mainly generated from the successive dehydrogenation of C2H6;or CH3 is converted to CH3OH,and CH3OH is successively dehydrogenated to generate H2. From the perspective of the net reaction rate,the important intermediate species,CH3 and CH3OH,are generated first and then consumed along the axis of the tube,so their mole fractions increase first and then decrease along the tube. When the inlet gas temperature increases from 600 ℃ to 1 000 ℃,mole fraction of H2 at outlet increases from 44. 91% to50. 21%. When the temperature exceeds 900 ℃,the significant reduction in the elementary reaction rate of R60 and R112 retards the dehydrogenation of CH3 and its conversion to C2H6. The rate of R100 increases and more CH3 is converted to CH3OH. Pathways of C2H6 successive dehydrogenation are weakened,and more H2 is generated through direct dehydrogenation of CH4 and successive dehydrogenation of CH3OH.