考虑过程安全的半间歇搅拌釜加料速率优化

反应釜的半间歇操作广泛应用于精细化工和医药等行业中的强放热反应,在保证安全性的基础上缩短加料时间,降低操作周期是提高过程效率的主要途径。本工作建立了以边界图为约束条件的半间歇搅拌釜安全操作工艺条件的优化方法,比较了单段和分段恒速加料在优化条件下的反应效果。在反应开始阶段采用较大加料速率,可快速提高物料温度,启动反应。与单段恒速加料相比,采用分段恒速加料在确保安全的同时可有效地缩短反应时间,提高反应效率。     

搅拌槽中酯化反应热失控的CFD模拟

热失控是化工过程中常见的安全风险之一。在间歇釜式反应器中,桨叶的机械转动可以增强流体的循环流动、湍流强度、混合程度以及传热,进而有效防范热失控。防控效果与反应器结构和搅拌桨型密切相关。针对丙酸异丙酯酯化反应,采用计算流体力学模拟研究了桨型(Rushton桨、30o PBT桨及60o PBT桨)、转动方向和挡板对釜式反应器内温度演化的影响,从流动结构方面分析了原因。基于散度的失控判据比较了三种搅拌桨抑制热失控的能力,抑制能力为Rushton桨＞30° PBTD桨＞60° PBTD桨。本研究可为搅拌反应器热失控的优化设计提供一定的理论依据。     

氯乙烯悬浮聚合热进料工艺的实现

一般的PVC生产工艺,均采用冷水加料,再通过夹套和内冷挡板通入蒸气或热水升温,而后开始聚合反应,在目前我国DCS控制技术成熟的情况下,我们也可以采用热无离子水和冷的VCM同时加入釜内,当加料结束时釜内温度即为反应温度,采用这种热水加料工艺可以缩短单釜间歇反应周期,提高单釜生产效率.     

间歇釜式反应器控制策略与最优操作方案的研究

采用数学模拟方法 ,以不同控制策略综合研究了间歇釜式反应器中进行不同反应过程的最优反应操作时间和操作温度 ,可用于指导反应过程的开发及生产操作控制。     

硝酸氧化仲辛醇液液非均相反应过程热危险性分析

利用反应量热仪器RC1分析半间歇操作下的硝酸氧化仲辛醇的反应放热过程,通过不同的反应温度、搅拌速率、加料时间等反应条件的变化,研究氧化反应过程中放热速率情况和热转化速率的变化趋势,推导出反应失控条件下的绝热温升和所能到达的最大温度等参数。分析结果表明:在室温下该反应就可以进行,随着反应温度的升高,反应放热速率加大;搅拌速率对非均相反应的影响明显;随着加料时间的延长,放热速率减慢,但会延长反应时间;综合分析判定其反应热失控,危险属于中度危险。     

间歇反应器的热参数敏感性及其临界判据(Ⅱ)

根据间歇反应器出现热参数敏感性的理论依据和数学特征,证明了n级间歇反应器操作曲线与温度最大点曲线的拐点轨迹相切的点是反应系统的参数敏感点,从理论上给出了间歇反应器中进行n级反应时,反应系统安全操作所允许的温度上限,并运用小参数扰动法,给出了n级间歇反应系统的安全操作温度上限的简洁渐进表达式.利用临界操作曲线温度最大点和超临界操作曲线的拐点关系,推导出反应系统安全操作的临界判据通式,并将该临界判据与AE以及WMV经典判据进行了比较.比较发现,在反应热参数B值的某个范围内,两个经典判据比本文推导的判据保守,大于该值时,则本文推导的判据比经典判据保守,但当B趋向无穷大时,新判据与经典判据之间的差值趋于某一恒定值.     

DNTF氧化反应热失控的模拟计算

根据DNTF合成氧化反应实际情况,利用ChemCAD间歇动态反应器模块,建立了带控制条件的DNTF氧化反应动态模型。通过对热失控进行分析模拟,描述了反应温度失控后体系的变化历程,计算出反应放热速率、累积放热量和失控后体系达到的最高温度和压力。考察了DNTF合成中氧化剂的加料速度对反应放热性的影响;评估了热失控危险等级。根据模拟热失控得到反应热危险性的敏感性参数,可建立工艺参数和安全措施,从而预防DNTF氧化反应过程中的热失控事故。     

连续流氧化反应技术研究进展

氧化反应作为应急管理部门重点监管的危险化工工艺之一,具有强放热、反应剧烈等特点,存在反应易失控甚至引起燃烧或爆炸的风险.相对于传统的釜式反应器,连续流反应器在传质传热及自动化控制方面具有显著的优势.出于安全生产以及提高生产效率的考虑,将传统釜式氧化工艺改进为连续流工艺,可以提高其本质安全化水平和生产效率.本文综述了近年...     

非绝热式固定床反应器的参数敏感性及热失控临界参数

寻找安全有效的反应条件一直是绿色化工的重要研究内容之一。采用邻二甲苯氧化的反应动力学模型,分析了非绝热式固定床反应器的参数灵敏性和热失控行为,考察了非绝热式固定床反应器温度对冷却介质流量、进料温度和初始压力的敏感性。模拟计算结果表明,当反应进入敏感性区域后,反应器对冷却介质流量、进料温度和初始压力的改变极其敏感。采用系统散度判据（div>0）计算该反应的热失控临界操作参数,计算结果与文献中的判据进行了分析比较,得到类似的结果,但计算更简单。考虑冷却介质的影响,修正了div判据,得到更准确的热失控临界操作参数。研究结果表明,此判据能为反应器的设计及过程控制提供重要的参考依据。     

微通道反应器中二丁基二硫代氨基甲酸酯反应的研究

利用微通道反应器设计了连续合成二丁基二硫代氨基甲酸酯的新工艺及反应机理,考察了反应温度、停留时间、物料摩尔比对反应的影响,优化了工艺。结果表明,当n(二正丁胺)∶n(二硫化碳)∶n(碱液)∶n(二氯甲烷)=1∶1.1∶1.1∶0.55,反应温度为65℃,停留时间为50 s时,产品收率为91.5%,纯度为99.4%。与传统间歇釜式工艺相比,微通道反应器工艺的反应时间缩短明显,操作简便,产品收率高,纯度高。     

半间歇聚合反应分子量分布周期操作的迭代学习控制

通过对半间歇聚合反应的引发剂进料实施周期操作,研究了这类操作方式对聚合物分子量分布的影响。研究结果显示,周期操作能改善聚合反应过程,对分子量分布有明显的加宽作用。对性能指标进行改进,以引发剂周期进料的占空比为控制变量,采用基于粒子群优化的迭代学习算法,对分子量分布进行了优化控制。仿真分析表明,在实际对象和模型存在不匹配的情况下,运用迭代粒子群算法,控制输入随着批次学习的进行而逐渐趋于最优解,聚合反应的分子量分布则不断逼近希望的分子量分布。实验结果验证了以周期操作方式对半间歇聚合过程分子量分布进行迭代优化控制的可行性。     

Reactor design and operation for gas-phase ethylene polymerization using ziegler-natta catalysts

A well-instrumented, semi-batch reactor has been constructed for studying the gas-phase polymerization of ethylene using solid Ziegler—Natta type catalysts. This reactor can be operated over the entire range of temperatures and pressures used in the commercial production of linear low, and high density polyethylenes. Successful operation of the reactor depends on careful control of the reaction temperature which in turn is mainly dependent on the total rate of polymerization. If this rate is too large, then the reaction temperature increases uncontrollably (thermal runaway) until catalyst deactivation occurs when melting polymer encapsulates the catalyst particles. Operating conditions are described which resulted in precise and reproducible kinetic measurements for a δ-TiCl₃ δ 1/3AlCl₃ catalyst (Stauffer AA Type 2.1) with diethylaluminum chloride (DEAC) as the co-catalyst. This system displayed first-order kinetic behavior over the temperature range 20 to 90°C with an activation energy of 32.6 kJ/mol.     

微反应器内邻氨基苯甲酸甲酯的连续重氮化工艺

邻氨基苯甲酸甲酯（MA）的重氮盐是一种典型的重氮化合物,因其具有高化学选择性可高效合成结构复杂分子被广泛应用于现代有机合成领域。传统半间歇合成工艺中的固有缺陷以及MA重氮盐的潜在爆炸性,限制了其在工业规模上的应用。本文基于此提出了在“心形结构”的高通量微通道反应器内合成MA重氮盐的连续流工艺。在单因素实验的基础上,采用Box-Behnken design（BBD）中心组合原理构建响应面模型对工艺进行优化,研究了不同反应条件之间交互效应对反应的影响并与实验室规模的半间歇合成工艺进行了比较。结果表明,微反应器内连续重氮化合成工艺对降低因素交互效应、提高工艺可控性、抑制平行副反应有显著的效果。经优化后的最佳工艺条件为n(MA)∶n(亚硝酸钠)∶n(盐酸)=1∶1.15∶2.67,反应温度为34.62℃,停留时间为45.07s,在此条件下MA重氮盐收率可达92%,相比于半间歇合成工艺提高了10%。这种新的合成方式可有效解决传统半间歇工艺中重氮化合成体系对温度的高敏感性,避免了反应温度控制困难、高潜在热失控风险带来的安全隐患。     

Studies on parametric sensitivity and safe operation criteria of batch processes

Heat accumulation in batch reactors may eventually lead to a temperature runaway. Critical values of process parameters were used to investigate process safety. Parameter sensitivity is discussed for a wide range of operating conditions. Two criteria for safe operation are presented, based on critical values of process parameters.     

Modeling and Optimization of a Tunnel Crape Dryer

A mathematical model of a tunnel dryer for the dehydration of grapes is presented and applied to the determination of optimal operating conditions of the dryer. The dryer is of semi-batch structure, operating with trucks and trays. The cycle period is determined by meeting appropriate quality specifications for the final product. The nominal conditions were evaluated bv suitably minimizing. the total fuel demand, expressed as fuel consumption to production capacity, under some constraints regarding the production rate of the dryer and the maximum permissible air temperature. An nominal air humidity value was evaluated suggesting a minimum cycle period value for the production capacity and fuel demand. The nominal conditions required operation of the dryer on the maximum permissible air temperature. The optimum operation was evaluated by maximizing the total profit resulting from the operation of the dryer. The optimization variables were temperature and humidity of the drying air stream. A charteristic case study of industrial grape was included to illustrate the effectiveness of the proposed approach.     

Modeling and Optimization of a Tunnel Crape Dryer

ABSTRACT

A mathematical model of a tunnel dryer for the dehydration of grapes is presented and applied to the determination of optimal operating conditions of the dryer. The dryer is of semi-batch structure, operating with trucks and trays. The cycle period is determined by meeting appropriate quality specifications for the final product. The nominal conditions were evaluated bv suitably minimizing. the total fuel demand, expressed as fuel consumption to production capacity, under some constraints regarding the production rate of the dryer and the maximum permissible air temperature. An nominal air humidity value was evaluated suggesting a minimum cycle period value for the production capacity and fuel demand. The nominal conditions required operation of the dryer on the maximum permissible air temperature. The optimum operation was evaluated by maximizing the total profit resulting from the operation of the dryer. The optimization variables were temperature and humidity of the drying air stream. A charteristic case study of industrial grape was included to illustrate the effectiveness of the proposed approach.     

Selective Hydrogenation of Acetylene in an Ethylene Stream in an Adiabatic Reactor

In earlier studies the behavior of single catalyst pellets of Pd on alumina has been investigated for the reaction of acetylene in an ethylene stream with hydrogen. Particle runaway, temperature over‐ and undershoots and chemically induced temperature oscillations have been observed. After that, the steady state and dynamic behavior of an adiabatic packed bed reactor has been studied experimentally. Temperature profiles of both the gas and solid phase as well as local temperature differences between the two phases were measured. Also here the temperature in the reaction zone exhibited oscillatory behavior. On addition of CO, the oscillations disappeared and the selectivity improved. For a given set of operating conditions, there existed a relatively small range of CO contents with good selectivity and satisfactory conversion. This range depends strongly on the inlet temperature. The dynamic response of the reactor to changes in the CO content showed a considerable wrong‐way behavior. This high sensitivity to fluctuations in the CO content, found for our experimental reactor, indicates a probable cause for a thermal runaway in industrial practice. Recommendations for a stable reactor operation are given.     

化学放热系统热失控临界判据的研究进展

化工过程安全是绿色化工的主要研究内容之一。研究化学放热系统热失控临界判据,实质上就是确定反应系统安全操作区域,避免热失控行为的发生。本文对热失控临界判据进行了详细总结,对各判据的优缺点进行了分析比较,提出了临界判据有效性的判定方法。最后,对非线性科学在放热系统热失控领域的研究进行了展望。