题名 | 离子液体体系吸收CO2的数值模拟研究 |
作者 | 徐琰 |
学位类别 | 硕士 |
答辩日期 | 2011-05-24 |
授予单位 | 中国科学院研究生院 |
导师 | 张锁江 ; 张香平 |
关键词 | 离子液体 CO2 吸收 计算流体力学 群平衡模型 传质 |
其他题名 | Numerical Simulation of CO2 Absorption in Ionic Liquid System |
学位专业 | 化学工艺 |
中文摘要 | 近年来,CO2捕集受到了广泛的关注。溶剂吸收法是一种极具工业应用前景的CO2捕集方法。离子液体作为一种新型溶剂在CO2捕集领域有良好的应用潜力。反应器放大规律的研究是推动离子液体体系吸收CO2工艺产业化的核心课题之一。计算流体力学(CFD)可为反应器设计和优化提供科学依据。本文旨在建立考虑离子液体特殊物性和离子液体体系吸收CO2的传质及反应动力学的计算流体力学模型。论文的主要研究内容和创新性结论如下: (1)建立了鼓泡塔反应器中基于欧拉-欧拉方法的离子液体体系吸收CO2气液两相流流体体动力学模型,模型对动量方程中的曳力项进行改进,引入适用于离子液体的曳力系数模型,耦合了描述气泡聚并和破碎的群平衡模型(Population Balance Model,PBM),建立了基于渗透理论的异相反应模型,从而更真实的反映离子液体气液两相流的流动和传质过程。 (2)研究了传统曳力系数模型和新建立的离子液体曳力系数模型对流场模拟结果的影响。使用离子液体曳力系数模型模拟的离子液体-空气体系中气含率与实验值的误差为8.1%,而传统模型模拟的误差则为22.8%。该模型模拟得到的小型鼓泡塔中离子液体及离子液体与有机胺复合体系吸收CO2过程的气含率模拟值与实验值误差均在10%-20%之间。考察了气速变化对塔内流型的影响,气速较低时塔内为安静气泡流,当气速达到0.4-0.5 m∙s-1时塔内变为柱塞流,鼓泡塔内发生化学吸收的气含率低于物理吸收。采用PBM模型研究了鼓泡塔内气泡尺寸分布及其随表观气速的变化,不同表观气速下离子液体中气泡尺寸分布模拟值与实验值吻合。离子液体与CO2体系的模拟结果显示,随着气速的增大,塔内大气泡增多,气泡尺寸分布范围加宽。 (3)研究了表观气速对鼓泡塔内CO2物理吸收和化学吸收的相界面积密度及体积传质系数的影响,模拟结果表明两者均随着表观气速的增大先增大,后稍有减小。因此,在鼓泡塔操作条件选择时需要选择合适的表观气速。低气速下的相界面积密度和体积传质系数的模拟值与实验值吻合,可见,所用传质和反应模型对CO2吸收过程具有良好的预测能力。 |
英文摘要 | CO2 capture has been wildly investigated in recent years. Solvent absorption is a promising CO2 capture method in industry. Inoic liquids are a new kind of solvent, they has great potential in CO2 absorption. Reactor scale-up is the key aspect for the industrialization of a new technology. Computational fluid dyanmics (CFD) can support the scale-up of reactors. This research is aimed at establishing an effective CFD and mass transfer model for CO2 absorption using ionic liquids system in bubble columns, so that to supply theoretical direction for the design and optimization of reactors used in CO2 capture technology. The main contents and innovations of the present research are expressed as follow: (1) A CFD model based on Euler-Euler method for gas-liquid two phase fluid of CO2 absorption in ionic liquids was developed in this work. The present work introduced ionic liquid drag coefficient model into the momentum equation, and coupled the population balance model (PBM) to describe the coalesence and breakup of bubbles in bubble column, and established mass transfer and heterogeneous reaction model, thus the entire model could predict the flow and mass transfer in the reactor more exactly. (2) Both ionic liquid drag coefficient model and default drag model in FLUENT were used to simulate the two phase fluid in bubble column. The predicted general gas holdup with ionic liquid drag coefficient agree with the experimental data better than that of default model. Ionic liquid model overestimate the general gas holdup and the average error of simulation result is 8.1%. FLUETN default model underestimate general gas holdup and the average error of simulation result is 22.8%. When ionic liquid drag coefficient is used to simulate the CO2 absorption in ionic liquid and ionic liquid-amine composite solution, the error of simulated gas holdup are about 10%-20%. This work also investigates the influence of superficial gas velocity on flow regime. The fluid in the bubble column is bubble flow when the superficical gas velocity is small, and when the gas velocity is 0.4-0.5 m∙s-1, the fluid in the column is slug flow and gas holdup increase suddenly. Furthermore, the gas holdup of physical absorption is higher than that of chemical absorption at the same gas velocity. PBM is used to investigate bubble size distribution and relation between bubble size and gas velocity in the bubble column. The simulated air bubble size distribution in ionic liquid at different superficial gas velocities are agree well with that of experimental data. The simulation results of CO2 absorption in ionic liquid show that bubble size increased with the increase of gas velocity. (3) The influences of superficial gas velocity on specific interfacial area and volume mass transfer coefficient were investigated in this work. The simulation results show that the above two parameters increase with the increase of superficial gas velocity when the gas velocity is low, however, they decrease when the gas velocity is as higher as 0.4-0.5 m·s-1. The simulated interfacial area density and volume mass transfer coefficient of low superficial gas velocity agree well with those of experimental data. Thus, the mass transfer and heterogeneous reaction rate model can predict the CO2 absorption in ionic liquid system well. |
语种 | 中文 |
公开日期 | 2013-09-24 |
页码 | 99 |
内容类型 | 学位论文 |
源URL | [http://ir.ipe.ac.cn/handle/122111/1727] ![]() |
专题 | 过程工程研究所_研究所(批量导入) |
推荐引用方式 GB/T 7714 | 徐琰. 离子液体体系吸收CO2的数值模拟研究[D]. 中国科学院研究生院. 2011. |
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