氢氧化镍沉淀动力学和搅拌槽中连续沉淀过程的数值模拟
文献类型：学位论文
| 作者 | 程景才 |
| 学位类别 | 博士 |
| 答辩日期 | 2009-08-14 |
| 授予单位 | 中国科学院过程工程研究所 |
| 授予地点 | 过程工程研究所 |
| 导师 | 毛在砂 |
| 关键词 | 粒数平衡方程 结晶动力学 二次过程 搅拌槽 数值模拟 多相流 |
| 其他题名 | Precipitation Kinetics of Nickel Hydroxide and Numerical Simulation of Continuous Precipitation Process in a Stirred Tank |
| 学位专业 | 化学工程 |
| 中文摘要 | 本文从粒数平衡方程出发，引入粒度分级思想，同时考虑成核、生长、团聚和破裂过程，结合体系质量平衡以及多分散体系浊度关系建立了描述氢氧化镍络合沉淀反应动力学模型。由实验测量和建立的结晶数学模型，通过复合形优化法得到了氢氧化镍沉淀动力学参数，模型计算与实验测量吻合较好。模型计算得到的不同温度下晶体生长速率、团聚速率、破裂速率以及粒度分布随反应时间的变化，较好地解释了氢氧化镍沉淀机理。 在硫酸钡连续沉淀模拟中，本文首先不考虑二次过程，分别采用SMM、两节点及三节点QMOM封闭PBE，三种方法的模拟结果非常接近，模拟值与实验结果在低浓度时接近，而浓度较高时则在定性和定量上均偏差非常大。 在考虑二次过程的模拟中，两节点和三节点QMOM模拟结果差别很小。嵌入团聚和破裂后，采用三个所选取的破裂速率其cv基本上都在实验结果范围内，cv值的预测改善较明显。对于不同的破裂速率，d32随浓度变化在定性上与实验数据均吻合很好，采用合适的破裂速率后，在定量上吻合也较好。本文还用QMOM模拟了采用与粒径相关的线性生长模型时的沉淀过程，与采用粒径无关的生长模型的模拟结果相比，采用粒径相关生长模型后由于在沉淀反应初始阶段成核作用在很大程度上被抑制，而晶体生长作用得到加强，因而得到的cv也较大些。 本文模拟了带挡板的标准Rushton搅拌槽内两种不同粒径固体颗粒的液固固三相体系的流体动力学特性和相含率分布。模拟结果表明，不管是对于r–z平面还是r–θ平面，两不同粒径固体颗粒的相含率分布存在明显差别，这种差别随搅拌转速增大而逐渐减小。同一转速下，两固体相在搅拌桨以下相含率分布差别明显大于搅拌桨以上。对于每种颗粒相，固体颗粒在搅拌槽底部存在明显堆积现象，提高转速能改善分散性。 |
| 英文摘要 | Based on population balance equation (PBE) and with the concept of particle classes, a mathematical model, which includes nucleation, crystal growth, aggregation, breakage, mass conservation and turbidity of the multi-dispersed system, is established to formulate the overall process of complexation-precipitation of nickel hydroxide. Kinetic parameters of nucleation, growth, aggregation and breakage are estimated through a complex optimization method based on experimental data and the established model, and a good agreement with experimental measurements is obtained. Growth rates, aggregation rates, breakage rates and particle size distribution (PSD) at different temperatures are also calculated from the optimized model parameters and the mechanism of nickel hydroxide precipitation is well explained. In the CFD simulation of continuous precipitation of barium sulfate in a stirred tank, the secondary processes are not taken into account first and the PBE is closed with SMM, 2-node and 3-node QMOM. The predicted results from the three closure methods are very close. Simulation predictions agree with experimental data at low concentrations but differ greatly from experimental data both qualitatively and quantitatively at relatively high concentrations. In the case of simulations incorporating secondary processes, difference between predictions of 2-node and 3-node QMOM is little. The predicted values of cv with three adopted breakage rates lie mostly in the range of experiment and the prediction of cv improves greatly when incorporating aggregation and breakage especially at relatively high concentrations. Variation of d32 with concentration qualitatively agrees well with experimental data for all applied breakage rates and good quantitative agreement can also be obtained with appropriate breakage rate. Mean crystal size d32 decreases with increasing breakage rates. In this work, CFD simulations of the precipitation process with a growth model which is dependent of crystal size are also performed using QMOM. Compared with results from the growth model, which is independent of crystal size, the values of cv are relatively higher due to the fact that the effect of nucleation is restricted and that of growth is strengthened at the beginning of reaction. In this work, the three-phase flow characteristics and holdup distributions of two solid materials with different sizes in a baffled stirred tank with a standard Rushton impeller is simulated. Simulation results show that there is much difference in holdup distributions of two solid phases both in the r–z and r–θ planes. This kind of difference lessens with increasing rotation speed. The difference is much more obvious in the region below the impeller than that in the region above the impeller at the same rotation speed. For each solid phase, the particles are prone to heap near the bottom of the tank, especially in the center and corner regions. The dispersion of solid particles is improved apparently when increasing agitation speed |
| 语种 | 中文 |
| 公开日期 | 2013-09-13 |
| 页码 | 163 |
| 源URL | [http://ir.ipe.ac.cn/handle/122111/1244]  |
| 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 | 程景才. 氢氧化镍沉淀动力学和搅拌槽中连续沉淀过程的数值模拟[D]. 过程工程研究所. 中国科学院过程工程研究所. 2009. |
入库方式： OAI收割
来源：过程工程研究所
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