【作者】 许长春；

【导师】 李鑫钢；

【作者基本信息】 天津大学 ， 化学工程， 2010， 博士

【摘要】 随着国际上化工和医药市场竞争的日益激烈和环保意识的增强,对各种高效分离提纯技术的研究开发与应用得到了工业界的重视。熔融结晶是根据待分离物质之间凝固点的不同而实现物质分离与提纯的方法,与常规的精馏分离技术相比,它具有操作温度低、能耗低、产品纯度高和绿色环保等独特优点。国内外对以熔融结晶技术制备高纯度化工产品的研究日益活跃,本文以对甲酚结晶为研究对象,对垂直管内熔融结晶流动过程进行了全面深入研究。为考察降膜结晶器中气液两相的流动状况,采用激光多普勒测速仪和激光颗粒动态分析仪测试了结晶器中气泡的上升速度及液弹的长度分析。结果表明,在一定高度内,气泡在上升过程中呈先加速后匀速的变化趋势,随着表观气速的提高,气泡速度也不断提高,其轴向分布状态也随之更加不稳定;气液二相弹状流的液弹长度分布符合对数正态分布函数的规律;液弹长度对气速和液速变化不敏感。当气泡达到一定高度时,气弹速度对前方液弹长度的影响较小。通过分析弹状气泡在对甲酚熔体中形成的气-液两相流动特点,建立了降膜熔融体系的两相流流动数学模型,采用CFD技术对对甲酚熔融结晶过程气-液两相流流场及晶体生长过程进行了数值模拟。结果表明,脉冲式鼓泡有利于熔体与晶体壁面之间的层流层与液相主体之间的传质和传热,保持了边界层稳定的浓度和温度梯度,对对甲酚熔融结晶过程具有明显的优势。晶层厚度随时间的增长而增大,当达到一定时间后,晶层厚度随时间变化趋于平缓;随着Ste数增大,结晶过程的传热推动力越大,晶层厚度也变大;晶层厚度随着初始过热度的增加而急剧降低,随后趋于平缓。通过对降膜结晶工艺操作条件进行优化,得到对甲酚熔融结晶提纯过程中适宜的工艺操作参数为:①脉冲通气速率为90L/h;②对甲酚熔融结晶降温速率以0.6～0.8℃/min;③结晶操作时间40min;④结晶率控制在70%左右;⑤发汗升温速率0.2～0.3℃/min;⑥发汗操作时间40min。研究成果不仅对对甲酚熔融结晶提纯过程具有重要的理论意义和应用价值,同时对传质分离工程具有重要的实际意义。更多还原

【Abstract】 With the increasingly severe competition in chemical and pharmaceutical market and awareness of environmental protection,research, development and application of high efficiency separation and purification techniques have get attention of the industry. Melt crystallization is a technique used for separation and purification of mixtures of chemicals based on the different freezing point of mixtures. Compare with conventional distillation, melt crystallization process has advantages of low operation temperature, low energy consumption, high product purity and green environmental protection, etc. The researches of high purity chemical products prepared by melt crystallization become increasingly active. This using by P-cresol for object,the flow of melt crystallization of P-cresol in vertical tube was studied comprehensively in this paper.Bubble rise velocity and liquid slug length in crystallizer were measured by laser Doppler velocimeter and laser particle dynamic analyzer respectively to study on gas-liquid two phase flow in falling-film crystallizer. The results show: bubble rise velocity increased firstly and then kept invariant; with the increasing of superficial gas velocity, the rise velocity increased and axial distribution became unstable; liquid slug length in gas-liquid two phase slug flow accorded with logarithm normal distribution; gas and liquid velocities had little influence on liquid slug length. When bubble height is higher than a critical height, the effect of gas slug velocity on liquid slug length was slightly.Two phase flow model of falling-film melting system was built by analyzing the flow characteristic of gas slug in gas-liquid (p-cresol melt system) two phase flow. Gas-liquid two phase flow and crystal growth process of p-cresol melt crystallization process were simulated by CFD technique. The results show pulse-bubbling can intensify mass and heat transfer between melts-crystals wall laminar boundary layer and liquid bulk, and keep the stable of concentration and temperature gradient in the boundary layer, which were beneficial to p-cresol melt crystallization process. Crystal layer thickness increased with time and became flat finally. With the increasing of Ste number, driving force of heat transfer and the layer thickness largen. Crystal layer thickness decreased sharply and gradually stabilized when initial superheat degree increased.The optimal falling-film crystallization process conditions in p-cresol melt crystallization were as follows: (1) pulse gas flowrate is 90 L/h; (2) temperature drop rate is 0.6~0.8℃/min; (3) crystallization time is 40 min; (4) crystallization ratio is about 70 %; (5) the sweating heating rate is 0.2~0.3℃/min; (6) the sweating time is 40 min.The research results not only have important theoretical significance and practical value for studying on p-cresol melt crystallization purification process, and realistic significance to the development of mass transfer and separation engineering.更多还原