【作者】 段彦军；

【导师】 淮秀兰； 李勋锋；

【作者基本信息】 中国科学院研究生院（工程热物理研究所） ， 工程热物理， 2014， 博士

【摘要】 目前我国能源利用效率较低,与发达国家相比还有很大的进步空间,余热回收利用尤其是低温余热回收利用已成为提高能源利用效率、解决能源危机的重要手段。低温余热品位低难以直接利用,大部分被排放造成巨大的能源浪费。最好的利用低温余热的方式是将其温度提升,使之可以被直接利用。如果这一方法得以实现,不但可以大幅度提高能源利用效率,而且可以扩大能源利用的范围,如太阳能、地热能等低温自然能源,有效缓解能源危机。化学热泵因其高效率、无污染、低能耗、温度提升幅度高等优点而成为低温热品位提升的首选装置。异丙醇-丙酮-氢气化学热泵(IAH-CHP)则是众多化学热泵中应用潜力较大的一种。它利用一对可逆的化学反应,异丙醇低温(80℃)脱氢发生吸热反应生成丙酮和氢气；丙酮高温(200℃)加氢发生放热反应生成异丙醇,从而将低温热温度提升,使之可以在工业上直接应用。本文以锅炉低温烟气余热深度利用为研究背景,采用实验和数值模拟相结合的方法在分子尺度、多孔催化剂尺度、反应器尺度和系统尺度对IAH化学热泵丙酮高温加氢放热反应器传递及反应性能进行了多尺度研究。首先在分子尺度上对丙酮高温加氢放热反应进行了动力学实验研究。实验使用非晶态合金雷尼镍催化剂,通过改变空速、操作压力、氢气流量、反应温度等实验条件,对丙酮转化率、异丙醇选择性及反应产物进行了研究。实验确定了丙酮加氢的反应网络,分别对三种不同反应进行了机理研究,在实验数据和合理假设的基础上拟合出对应的Langmuir-Hinshelwood动力学方程,并分析了各操作条件对反应的具体影响。其次在多孔催化剂尺度上对化学反应与传热传质在多孔催化剂内的耦合和协同作用进行了数值研究,重点分析了催化剂颗粒内组分扩散对组分分布、温度分布、反应速率、丙酮转化率及异丙醇选择性的影响。模拟结果表明,催化剂微孔直径是扩散系数的决定因素,在催化剂颗粒边缘存在一个很薄的过渡区域,扩散系数及反应速率在此区域梯度十分明显；由于反应发生在催化剂颗粒内部,使得内部温度比外部流体温度稍高;丙酮转化率和异丙醇选择性都随催化剂颗粒直径的增加而增加,随微孔直径的增加而减小；异丙醇产量随催化剂颗粒直径增加而增加,随微孔直径增加先增加后减小。根据模拟结果,本文给出了催化剂颗粒直径和微孔直径的推荐值。然后在反应器尺度上对丙酮高温加氢放热反应器传递和反应性能使用Fluent多孔介质非热平衡模型进行了数值研究,分析了催化剂颗粒直径、催化剂导热系数、反应器直径和空速等参数对气固两相传热及丙酮加氢反应的影响。模拟结果表明在本研究中气固两相温差较小,不会对反应产生较大影响；催化剂导热系数和反应器直径对反应器温度场分布具有十分显著的影响,催化剂导热系数的增加能显著增强反应器传热能力,降低反应器温度及径向温差,反应器直径增加则会显著增加反应器温度；空速增加虽然会降低异丙醇选择性和丙酮转化率,但是也会增加异丙醇产量,因此有助于提高系统效率。在反应器性能数值研究的基础上对反应参数进行了优化,综合考虑能量品位、反应热、丙酮转化率与反应温度的关系,确定了最佳反应温度；结合数值模拟结果对比氢气丙酮摩尔比增加产生的丙酮转化率收益及压力损失,确定了最佳氢气丙酮摩尔比。为解决随机填充固定床反应器压力损失大和传热能力差的不足,本文提出一种结构化填充方法,并使用Fluent进行3D模拟,模拟结果表明此结构化填充方法不但可有效降低系统压力损失,而且传热能力更优秀。最后在系统尺度上提出了一种新型高效的多级放热反应器串联IAH化学热泵系统。与传统单级放热反应器IAH化学热泵相比,多级放热反应器串联IAH化学热泵的放热量得到了极大的提升,系统焓效率和火用效率也有较大幅度的增加；在放热量相同的情况下,多级放热反应器串联IAH化学热泵的物料流量,催化剂填装量,以及再沸器、增压器和加热器的热负荷都得到了极大幅度的降低,系统焓效率和火用效率都有一定的增加。由于多级串联放热反应器各级放热温度不同,可将各级反应器释放的热量分别用作不同途径,以减少能量混合带来的火用损失。更多还原

【Abstract】 The energy efficiency in China is much lower than developed countries and many other countries, so there is a lot to do to make the improvement. Waste heat recovery, especially the low-temperature waste heat recovery, is increasingly becoming an important way to enhance energy efficiency and to solve the energy crisis. The low quality of low-temperature waste heat makes it difficult to be used directly, so most is discharged into the air, and hence a large amount of energy is wasted. The best way to take advantage of low-temperature heat is to upgrade its temperature, so the upgraded heat can be used directly. If this measure is realized, not only the enery efficiency can be improved hugely, but also the energy utilization scope can be expand enormously, such as low-temperature natural energy, including solar energy and geothermal energy.Chemical heat pump (CHP) is the best choice to upgrade low-temperature heat for the reason of high efficiency, no pollution, low energy consumption, large extent of temperature promotion, and so on. Among many CHPs, Isopropanol-Acetone-Hydrogen (IAH) system is one of the most prospective CHPs. IAH-CHP takes advantage of a pair of reversible chemical reactions, the endothermic isopropanol dehydrogenation reacting at about80℃and the exothermic acetone hydrogenation reacting at about200℃, to upgrade the low quality heat and make it possible to be used directly in industry.This dissertation studies the high-temperature exothermic reaction of acetone hydrogenation in IAH-CHP on multi-scales of molecular scale, porous catalyst scale, reactor scale and system scale by adopting both experiment and numerical simulation on the background of deep utilization of low-temperature boiler exhaust gas.Firstly, on the molecular scale, the amorphous alloy Raney Ni is used as catalyst for the kinetic experiment of high-temperature acetone hydrogenation, through which the three reaction mechanisms and corresponding products are confirmed, and the Langmuir-Hinshelwood kinetic equation of every reaction are promoted based on the experiment data and reasonable assumptions. The influences of the experimental conditions including space velocity, operating pressure, reaction temperature,and hydrogen flow rate are conducted and analyzed.Secondly, on the porous catalyst scale, in order to study the synergistic effect of chemical reaction and heat and mass transfer in porous media, a microscale simulation on porous catalyst particles is carried out. The simulation focuses on the influence of species diffusion on species distribution, temperature field, reaction rate, acetone conversion and isopropanol selectivity. The simulation results show that the micropore diameter is the determinant of diffusion coefficient, and there is a very thin transient zone around the catalyst particle, and both the species diffusion coefficient and the reaction rate gradients in this zone are very sharp. The reactions are taking place inside the catalyst particles, so the temperature is a little higher than the external flow. When the catalyst particle diameter increases, the acetone conversion and the isopropanol selectivity and yield increase. When the micropore diameter increases, the the acetone conversion and isopropanol selectivity decrease, and the isopropanol yield increases firstly and then decreases. According to the simulation results, the recommended values of catalyst particle and micropore are suggested in this dissertation.Then on the reactor scale the transfer and reaction performance of reactor is simulated to study the influence of catalyst particle diameter, catalyst thermal conductivity, reactor diameter and space velocity on the gas-solid temperature difference and the reaction by using the non-heat-balance porous media model. According to the simulation results, the gas-solid temperature difference is too little to affect the reaction. A larger catalyst thermal conductivity can enhance the heat transfer capability of the reactor remarkably and reduce its temperature obviously, and a larger reactor diameter will increase the reactor temperature. A larger space velocity will decrease both the acetone conversion and isopropanol selectivity, but can increase the isopropanol yield, so a larger space velocity is beneficial to the system efficiency. Based on the simulation, the best reaction temperature and hydrogen-acetone mole ratio are optimized via theoretical design calculation by analyzing their influences on reaction energy quality, reaction heat amount, acetone conversion and pressure drop. In order to solve the problems of large pressure loss and low heat transfer capability in randomly packed bed reactor, this thesis proposes a structured packed bed reactor and makes3D simulation on the reactor, and the simulation results indicate that this structured packed method can reduce the pressure loss effectively and has a better heat transfer capability.At last on the system scale a new high efficient IAH-CHP with multi-in-series exothermic reactors is proposed and studied. Contrasting with traditional IAH-CHP with one single exothermic reactor, this new system gets huge promotion in reaction heat released, and the system performance and exergy efficiency are also improved. At the same amount of heat released, the new system has a sharp decrease in material flow rate and catalyst packing amount, as well as the heat load of reboiler, compressor and heater, so the system performance and exergy efficiency have a certain improvement. Another advantage of the IAH-CHP with multi-in-series exothermic reactors is the heat released from different reactors can be used in different ways to reduce exergy loss produced by energy mixing.更多还原