纳米氧化钙碳酸化反应性能对甲烷蒸汽重整制氢的强化作用

发布时间：2018-05-06 19:19

本文选题：制氢 + 甲烷　；参考：《浙江大学》2017年博士论文

【摘要】：氢气是重要的石油化工原料,也是未来的清洁能源载体。以纳米氧化钙作为CO2反应吸附剂的反应吸附强化甲烷蒸汽重整(Reactive Sorption Enhanced Reforming,简称ReSER)制氢是一种高效的制氢技术,相比于传统的甲烷蒸汽重整制氢,ReSER制氢技术具有降低反应温度,提高甲烷转化率和氢气浓度,以及缩短流程等优势。在ReSER制氢反应体系中,纳米氧化钙与C02的反应特性是其对甲烷蒸汽重整制氢的强化作用的关键。因此,研究提高纳米氧化钙的CO2吸附性能,以及吸附性能与制氢反应强化作用之间关系,对ReSER制氢技术的工业化应用具有重要理论和实际意义。首先,本文以商用纳米氧化钙为例,就其碳酸化反应性能对甲烷蒸汽重整制氢的强化作用进行理论分析。结合固定床反应器中ReSER制氢的“三传一反”特点,首次以COMSOLMultiphysics软件作为计算平台,建立了本文的模拟计算方法,并对纳米氧化钙CO2吸附性能与强化作用之间的关系进行计算。结果表明:在ReSER制氢反应体系中,提高吸附剂的CO2吸附速率有利于提高对制氢反应的强化作用,但两者之间并非线性相关,且强化作用存在上限。纳米氧化钙的吸附容量对甲烷蒸汽重整的影响主要体现在强化作用时间的长短,吸附容量越大,强化作用时间越长。其次,本文首次提出采用碳球模板法制备不同球径的笼状纳米氧化钙,用于ReSER制氢的C02反应吸附脱除,并研究其吸附性能。结果表明:笼状纳米氧化钙的吸附速率和吸附容量都要高于平均粒径70纳米的商用纳米氧化钙。优选的笼状纳米氧化钙球径为1.62 μm,在碳酸化反应温度为600 ℃时能达到理论最大吸附容量0.786 gCO2/gCaO。为了提高笼状纳米氧化钙的循环吸附稳定性,本文采用锆添加制备了锆改性的笼状纳米氧化钙基吸附剂。研究表明:优选的样品Ca/Zr摩尔比为5,其在30次循环之后氧化钙转化率保持在76%,而未经锆改性的笼状纳米氧化钙在30次循环之后转化率只有20%。另外,与制备得到的Mg和Al改性的笼状纳米氧化钙循环稳定性对比,发现锆改性的笼状纳米氧化钙具有更好的循环稳定性,且锆改性和笼状结构在提高吸附剂循环稳定性中起显著协同作用。此外,本文根据笼状纳米钙基吸附剂的碳酸化反应特性,提出了适用于区分笼状纳米钙基吸附剂碳酸化反应快、慢段的新判据,并采用Boltzmann方程拟合了笼状吸附剂在快速反应段的动力学方程。结果表明:动力学方程平均相对误差为5.78%,具有较好的精度,得到反应活化能为26.661 kJ/mol,较商用纳米氧化钙低3.54 kJ/mol,且笼状纳米钙基吸附剂的最大吸附速率是商用纳米氧化钙的1.44 倍。最后,本文将锆改性笼状纳米钙基吸附剂用于强化甲烷蒸汽重整制氢反应,结合“三传一反”对反应进行模拟计算。经实验验证,模型计算得到的甲烷转化率误差为5.15%。实验证明:锆改性笼状纳米钙基吸附剂较商用纳米氧化钙有更高的制氢强化作用,尤其是在650℃,压力为5bar,水碳摩尔比等于3.5,空速为700 h-1的情况下,笼状纳米钙基吸附剂的强化因子是商用纳米氧化钙的2.02倍。对不同反应条件下的强化作用模拟计算发现,水碳摩尔比的提高有利于相同反应条件下甲烷转化率和产物氢气摩尔分率的提高。在水碳摩尔比为4,反应温度650 ℃,常压条件下甲烷转化率最高可达99.8%,氢气摩尔分率最高可达到99.9%。压力的增高并不利于甲烷转化率和氢气纯度的提高,要在高压反应条件下取得较好的反应效果可以提高反应温度或增加水碳摩尔比。不同水碳摩尔比条件下的强化因子响应面均呈凸形曲面,当水碳摩尔比为3,反应温度为611 ℃,压力为5bar时强化因子达到最大为67.2%。为了了解纳米氧化钙碳酸化反应性能对甲烷蒸汽重整以及变换反应的强化作用规律和影响过程,本文首次采用COMSOL Multiphysics软件对反应吸附强化作用的过程进行模拟计算,得到了床层轴向上各组分浓度和温度在反应过程中的变化情况。发现了强化作用峰面的存在与变化规律,认为其形成与移动取决于氧化钙碳酸化反应转化率的变化,且强化作用也主要集中于这个峰面内。通过对管内轴向温度随时间变化情况的分析,发现了入口段的低温区现象和高温峰的移动现象。
[Abstract]:Hydrogen is an important petrochemical raw material and a clean energy carrier in the future. The reaction adsorption enhanced methane steam reforming (Reactive Sorption Enhanced Reforming, abbreviated for short) using nano calcium oxide as a CO2 reaction adsorbent is a highly efficient hydrogen production technology. Compared to the traditional methane steam reforming and hydrogen production, ReSER hydrogen production technology is used. In the ReSER hydrogen production system, the reaction characteristics of nano calcium oxide and C02 are the key to the strengthening of methane steam reforming and hydrogen production in the ReSER hydrogen production system. Therefore, the adsorption properties of nano calcium oxide and the adsorption properties and hydrogen production are studied. The relationship between the strengthening effect and the industrial application of ReSER hydrogen production technology is of great theoretical and practical significance. First, in this paper, the commercial nano calcium oxide is used as an example to analyze the strengthening effect of the carbonation reaction on the steam reforming of methane, and the "three transmission and one inverse" characteristic of the ReSER hydrogen production in the fixed bed reactor. The simulation calculation method was established for the first time using COMSOLMultiphysics software as the calculation platform. The relationship between the adsorption properties of nano calcium oxide CO2 and the strengthening effect was calculated. The results showed that in the reaction system of ReSER hydrogen production, the enhancement of the adsorption rate of adsorbents was beneficial to the enhancement of the hydrogen production reaction, but both of them were enhanced. The influence of the adsorption capacity of nano calcium oxide on the steam reforming of methane is mainly reflected in the length of the strengthening time, the larger the adsorption capacity and the longer the strengthening time. Secondly, the carbon sphere template method is the first time to prepare the cage like nano calcium oxide with different ball sizes, which is used for ReSE. The adsorption and adsorption properties of R hydrogen are removed by C02 reaction, and the adsorption capacity is studied. The results show that the adsorption rate and adsorption capacity of caged nano calcium oxide are higher than that of commercial nano calcium oxide with the average particle size of 70 nanometers. The optimum cage like nano calcium oxide ball diameter is 1.62 mu m, and the maximum adsorption capacity can reach the theoretical maximum adsorption capacity of 0.7 when the carbonation reaction temperature is 600. 86 gCO2/gCaO. in order to improve the cyclic adsorption stability of caged nano calcium oxide, zirconium modified caged nano calcium oxide adsorbent was prepared by zirconium addition. The study showed that the optimized sample Ca/Zr molar ratio was 5, and the conversion of calcium oxide was kept at 76% after 30 cycles, while the non zirconium modified caged nano calcium oxide was 30 times without zirconium modification. After the cycle, the conversion rate is only 20%.. Compared with the stability of the caged nanocrystalline calcium oxide cyclic stability obtained by Mg and Al modification, it is found that the caged nano calcium oxide modified by zirconium has better cycling stability, and the zirconium modification and the cage like structure play a significant role in improving the stability of the adsorbent cycle. The characteristics of carbonation reaction of mica calcium based adsorbents are presented. A new criterion is proposed to distinguish the fast and slow stages of carbonation reaction of caged nano calcium based adsorbents. The kinetic equation of the cage like adsorbent in the rapid reaction section is fitted by Boltzmann equation. The results show that the average relative error of the kinetic equation is 5.78%, and the accuracy is better. The activation energy is 26.661 kJ/mol, 3.54 kJ/mol lower than commercial nano calcium oxide, and the maximum adsorption rate of caged nano calcium based adsorbents is 1.44 times as much as that of commercial nano calcium oxide. Finally, the zirconium modified cage like nano calcium adsorbent is used to strengthen the reaction of methane steam reforming and hydrogen production, combined with the "three trans" reaction to the reaction. It is proved by the experiment that the error of the methane conversion rate calculated by the model is 5.15%. experiment. It is proved that the zirconium modified cage like nano calcium adsorbent has a higher hydrogen production strengthening effect than the commercial nano calcium oxide, especially at 650 C, the pressure is 5bar, the water carbon mole ratio is equal to 3.5, the air velocity is 700 H-1, and the cage like nano calcium adsorbent is used. The enhancement factor is 2.02 times that of the commercial nanometer calcium oxide. The simulation calculation of the strengthening effect under different reaction conditions shows that the increase of the ratio of water carbon mole is beneficial to the increase of methane conversion and the molar fraction of hydrogen under the same reaction conditions. The ratio of the molar ratio of water to carbon is 4, the reaction temperature is 650, and the maximum methane conversion can reach 99. under the condition of atmospheric pressure. 8%, the increase of the maximum hydrogen molar fraction can reach the increase of 99.9%. pressure, which is not conducive to the increase of methane conversion and hydrogen purity. A better reaction effect under the condition of high pressure reaction can increase the reaction temperature or increase the ratio of water carbon mole. The response surface of the intensifying factor under the condition of different water carbon mole ratio is convex surface, when the water carbon friction is in the condition of water carbon mole ratio. The reaction temperature is 3, the reaction temperature is 611, the strengthening factor reaches the maximum when the pressure is 5bar is 67.2%., in order to understand the strengthening law and the influence process of the methane steam reforming and the transformation reaction of the nanometer calcium oxide acidification reaction, this paper uses the COMSOL Multiphysics software for the first time to simulate the process of the reaction adsorption strengthening. The variation of the concentration and temperature of each component in the axial direction of the bed was obtained. The existence and variation of the peak surface was found. It was found that its formation and movement depended on the change of the conversion rate of calcium oxide carbonation, and the intensifying effect was mainly concentrated in the peak surface. The phenomenon of low temperature zone and Gao Wenfeng's moving phenomenon were found in the analysis of the variation.

【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TQ116.2;TQ424

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