间歇蒸馏的优化操作

本文研究了间歇蒸馏操作的最佳经济收益问题.在二元物系的系统模型中考虑了塔板的持液及冷凝器的持液,并考虑了塔板效率.用多项式拟合相平衡关系.选择回流比作为控制函数,应用最优控制理论导出计算步骤,用数值方法叠代出使经济收益函数最大的回流比函数.将解出的最优操作方案与两种传统的操作方案进行了比较.为检验最优操作方案的可实施性,在一筛板塔上进行了实验,证明优于传统操作.     

带有过渡段循环的多元间歇精馏优化计算

采用最大馏出量、最小时间及最大负荷因子作为目标函数,以采出速率作为优化变量,间歇精馏过程采用分段恒回流比操作,利用改进的模拟退火算法进行了带有过渡段循环的三元体系间歇精馏过程的优化。分别获得了3种目标函数下的最优操作条件及最优值,并与文献结果进行了比较。采用改进的模拟退火算法得到的优化计算结果均优于文献值。不同的目标函数下得到的优化操作策略不同,且随着过渡段循环次数的增加精馏过程趋于稳定。     

二元提馏式间歇精馏的优化操作与最小汽化总量

理想操作条件下二元提馏式间歇精馏优化操作的汽化总量与最小汽化总量的计算是约束函数优化问题。本文采用罚函数法,将此约束函数优化转变为无约束函数优化,并采用固定双步长因子梯度法数值求解该函数的极值。计算表明:固定双步长因子梯度法具有良好的收敛性,同时,降低分段数较多时,数值截断误差积累对计算结果的影响。二元提馏式间歇精馏优化操作较恒残液组成操作的能耗低的原因如下:在理论板数相对较少(接近二元提馏式间歇精馏恒残液组成操作所需的最少理论板)时,优化操作通过控制再沸比提高了能耗效率;在理论板数相对较多时,优化操作通过控制再沸比,在保证过程的能耗效率较高的同时,可尽可能快地将物料移出系统,减少了精馏过程中塔顶贮槽内液体的混合熵产。通过对计算结果的归纳与外推,得到了理想操作条件下理论板数为无穷多时二元提馏式间歇精馏优化操作再沸比的变化方式以及最小汽化总量的计算公式。     

分批精馏最小过渡馏分量及过渡馏分脉冲控制法的研究

研究了分批精馏最小过渡馏分量 ,在此基础上针对分批精馏过渡馏分段的特点采用了全回流 全馏出交替进行的脉冲控制法。该法以动态模拟确定了全回流时间 ,统计法确定了全馏出时间。采用正己烷 环己烷物系进行对比实验结果表明 :与传统的恒回流比操作法相比 ,脉冲操作法可明显减少过渡馏分量、缩短操作时间和提高分离效率     

间歇蒸馏的新设计法

本文提出间歇塔的一种新的设计方法——序列稳态塔法。用此法可同时求出间歇蒸馏塔的理论板数、最佳操作回流比、塔釜组成和温度随时间的变化;导出釜液温度与最佳操作回流比的关系,实现由釜液温度前馈控制整个间歇蒸馏过程;以及求出整个间歇蒸馏过程所需的时间。计算速度快,其结果可满足工程设计的需要。     

Integrating product and process design with optimal control: A case study of solvent recycling

This paper proposes the simultaneous integration of environmentally benign solvent selection (product design), solvent recycling (process design) and optimal control for the separation of azeotropic systems using batch distillation. The previous work performed by Kim et al. (2004. Entrainer selection and solvent recycling in complex batch distillation. Chemical Engineering Communications 191(12), 1606-1633) combines the chemical synthesis and process synthesis under uncertainty. For batch distillation, optimal operation is also important due to the unsteady state nature of the process and high operating costs. Optimal control allows us to optimize the column operating policy by selecting a trajectory for the reflux ratio. However, there are time-dependent uncertainties in thermodynamic models of batch distillation due to the assumption of constant relative volatility. In this paper, the uncertainties in relative volatility were modeled using Ito processes and the stochastic optimal control problem was solved by combined maximum principle and non-linear programming (NLP) techniques. Then the previous work of optimal solvent selection and recycling was coupled with optimal control. As a real world example for this integrated approach, a waste stream containing acetonitrile-water was studied. The optimal design parameters obtained by Kim et al. (2004. Entrainer selection and solvent recycling in complex batch distillation. Chemical Engineering Communications 191(12), 1606-1633), for this separation were used and the optimal control policy is computed first without considering uncertainties by variable transformation technique. The deterministic optimal control policy improves the product yield by 4.0% as compared to the base case, verified using a rigorous simulator for batch distillation. When the stochastic optimal control policy was computed representing the relative volatility as an Ito process, a similar recovery rate was obtained from simulations, but the batch time was reduced significantly, producing the most profitable operation.     

用夹紧区原理确定多元恒回流比分批精馏最小回流比

夹紧区是精馏塔内出现的浓度几乎不变的区域,对于三元物系来说,根据夹紧区在塔内出现的位置可分为：上、中和下加紧区.在无穷板数和任一瞬时釜浓下选择不同的回流比可使分批精馏处于不同夹紧区下操作.文中讨论了三元恒回流比分批精馏过程中夹紧区的演变,在Rayleigh方程的基础上建立了应用夹紧区原理确定多元恒回流比分批精馏最小回流比的方法.该方法并不要求相对挥发度为常数,并且能准确计算顶浓,克服了通常所采用的Underwood公式法的缺陷,为多元分批精馏的简捷设计奠定了基础.     

间歇精馏过渡馏分脉冲馏出规律研究

建立了二元理想物系考虑全塔持液量的间歇精馏微分形式的数学模型,采用四阶定步长龙格－库塔法对间歇精馏过渡馏分的常规操作和脉冲式操作过程进行模拟计算。实验证明,模拟计算结果与实际符合较好。提出的Ｃ因子概念可用于考察间歇精馏操作效率和经济效益,通过过程模拟,计算了间歇精馏不同操作模式下Ｃ因子的值,并由此分析了不同操作模式的动态规律。     

萃取精馏分离甲醇-苯

采用萃取精馏的方法分离甲醇-苯的共沸物系。首先采用UNIFAC基团贡献理论并结合经验选取萃取剂,最终确定萃取剂为氯苯。对常压下甲醇 苯物系应用UNIFAC模型计算各组分的汽液相组成,并进行汽液平衡实验验证,计算结果与实验数据吻合较好。通过间歇萃取精馏实验进一步考察验证所选萃取剂的分离效果。结果表明,氯苯能够打破甲醇-苯的共沸,进而分离甲醇和苯。溶剂物质的量之比为1、回流比为3、填料塔理论板数为30、溶剂回收段理论塔板数为4时产品甲醇回收率达到98%,说明氯苯能够作为萃取剂分离甲醇-苯二元共沸物系。最后,对甲醇-苯物系的连续精馏过程应用Aspen Plus进行了模拟计算,并且考察了回流比、萃取剂进料流率等参数对产品纯度的影响规律,为进一步实验研究及工业应用提供理论和实践基础。     

多元间歇精馏拟夹紧区的变化规律

拟夹紧区是精馏塔内出现的浓度变化很小的区域,对于精馏塔的操作和设计具有重要意义。 本文通过恒摩尔持液模型进行模拟计算,讨论了理想多元物系间歇精馏过程中回流比和相对挥发度对拟夹紧区的影响及拟夹紧区的更替过程。在多元物系间歇精馏过程中,拟夹紧区的宽度随回流比和相对挥发度的大小而改变;拟夹紧区在塔内出现的位置是不断变化的,存在上拟夹紧区和中拟夹紧区的相互演化过程。     

Optimal operation of a batch packed distillation column

Optimal policies for a batch packed distillation unit are examined for the cases of variable reflux ratio and variable boilup rates. This work was to act as a follow-up to Converse's work⁽¹⁾ for a batch plate distillation column with variable reflux policy. For the cases studied, it would seem that the boilup rate optimal policy yields better performance for the still than the reflux ratio optimal policy. The results of the present analysis and those of other authors seem to indicate that more effort should in the future be devoted to new modes of operation rather than to various refinements of the model used in the present and past studies. The present exploratory work seems to support the need for further studies using a packed rectifying section with variable boilup policy along with a novel mode of operation such as that considered by Mayur et al,⁽⁶⁾.     

热敏物料的冷存料复合式分批精馏塔精馏过程

提出了冷存料的复合式分批精馏塔 ,建立了恒摩尔持液数学模型 ,模型计算结果与实验结果吻合良好 ,并对该设备分离热敏物料的可靠性进行了分析 ,结果表明 ,采用冷存料的复合式分批精馏塔分离热敏物料是合适的 .     

恒全回流塔顶累积间歇精馏过程的研究

提出了一种过程始终为全回流操作的间歇精馏新型操作方式,其特征在于沿塔身不同高度设置有多个中间累积罐,操作中整塔始终处于全回流状态,每隔一段时间将下一级储罐内的液体转移至上一级储罐,塔顶储罐内液体作为产品转移到产品储槽。建立了该流程的数学模型并采用Matlab软件进行模拟,当目标产品浓度相同时,新操作方式的可以节省操作时间,在最优化的中间累计罐密集程度下,可节省50%左右,与具体操作参数相关;最后采用乙酸-水二元物系对该操作方式进行了试验验证,且整塔运行稳定易于操作控制。     

分批蒸馏优化策略与微机控制的研究(Ⅰ)——分批蒸馏的优化策略

本文提出了塔顶累积全回流及变压强综合回流两个分批蒸馏的新操作策略及相应的优化操作法,通过数学模拟和θ收敛计算法求出了二元(乙醇—异丙醇)和多元(正庚烷—正辛烷—正壬烷—正癸烷)物系的数值解.计算结果表明,两种新操作法分别较传统的操作法缩短生产周期30%和50%以上.     

分批精馏过渡段放持液操作方式

The new mode of operation for slop cut withdrawal in batch distillation, i.e., draining Column liquid holdup at the end of slop cut period, was proposed. And the stopping criterion for the operation was investigated, Experiments were carded out with isopropanol-n-propanol binary system and isopropanol-n-propanol-n-butanol ternary system in a distillation column with a liquid collector installed between the reboiler and the column section, Experimental results in a Ф 45mm batch column show that the proposed policy can overcome the flywheel effect caused by column liquid holdup and thus cut down operation time and energy consumption 31%-61%.     

Reducing total annualized cost and CO2 emissions in batch distillation: Dynamics and control

In this contribution, the direct vapor recompression approach is introduced in a batch distillation operated at an unsteady state condition. This vapor recompressed batch distillation (VRBD) accompanies an isentropic compressor that runs at a fixed as well as variable speed. Aiming to ensure the optimal use of internal heat source, an open‐loop control policy is proposed for the VRBD that adjusts either the overhead vapor splitting or the external heat supply to the reboiler. Again, the variable speed VRBD additionally involves the manipulation of compression ratio. Developing two alternative configurations of VRBD column, the best heat integrated scheme is attempted to identify in the aspects of energy efficiency and total annualized cost for further advancement. A closed‐loop control algorithm for the best performing variable speed VRBD aiming to meet the end objective of relatively high‐purity product discharged at a constant composition is developed. The separation of a reactive system is considered to illustrate these results and demonstrate the effectiveness of the novel VRBD scheme. Performing simulation tests, it is investigated that the closed‐loop control operation substantially improves not only the distillate purity but also the total amount of product. Achieving significant improvement in thermodynamic efficiency and cost by the controlled heat integrated scheme over its conventional counterpart, finally the attractiveness of the VRBD column by investigating its potential to reduce the greenhouse gas (i.e., CO₂) emissions is shown. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2821–2832, 2013     

分批精馏中的持液作用

分批精馏中持液影响塔内的动态过程,因此许多学者一直致力于分批精馏过程中持液作用的研究,但由于研究缺乏系统性,持液的作用一直是学术上争论的热点.本文提出用全过程分离难度系数关联各参数对分离过程的影响,并建立了分批精馏的恒摩尔持液模型,用全过程的分离难度系数研究了分批精馏的持液作用,结果表明：塔顶持液对分离不利,但塔身持液在一定条件下增多可使所需回流比降低;塔内持液量与釜液量之比为一个因子,当q<0.7时,确定的分批精馏塔存在最佳投料量.采用甲苯-乙苯二元物系对最佳投料量进行了实验验证,实验结果与模拟结果吻合较好.     

Tracking the predefined optimal policies for multiple-fraction batch distillation by using adaptive control

Predefined optimal policies will be tracked with control systems to realize the optimum of multiple-fraction batch distillation. Adaptive control is proposed to carry out this task. Characteristics of batch distillation control are analyzed and a proper system is designed for controlling such processes. Besides tracking the optimal reflux ratio profile, the maximum vapor load will be maintained during the batch. In addition, a changing temperature profile of the condenser should be followed to reduce the operating energy with a possibly minimum subcooling. Recursive least square estimation (RLSE) with a variable forgetting factor is applied to the on-line identification of the plant to follow the changing dynamics of the process. Generalized predictive control (GPC) is used to track the predefined policies. The effectiveness of the control strategy is verified with a pilot batch column and the tracking performance is compared with that of PID controllers.     

催化精馏塔内甲酸甲酯水解制甲酸的研究

在催化精馏塔内以压制的强酸性阳离子交换树脂为催化剂填料对甲酸甲酯水解制甲酸进行了实验研究.在全回流操作条件下,通过改变操作参数获得了高于90%的水解转化率.考虑到反应过程中水的阻碍作用,根据实验结果提出了可用于催化精馏过程的动力学方程并建立了基于平衡级理论的反应与分离耦合的数学模型.通过设定进料水酯摩尔比、回流与进料比、反应段与分离段理论级数等参数获得了水解过程的仿真结果,并提出了较佳的工艺操作条件.研究表明:仿真结果与实测数据相吻合;通过改变操作条件可调整反应段内水与甲酸甲酯的浓度,提高水解速度;增加反应段的高度比增加分离段的高度更有利;产品甲醇和甲酸在催化精馏塔内能够完全分离,反应段两端反应速度高于中间段的反应速度.     

萃取精馏分离甲醇-甲苯共沸物的研究

利用UNIFAC基团贡献法对常用萃取剂进行了筛选,选取邻二甲苯作为该二元共沸物的萃取剂,并通过汽液平衡实验对其分离效果进行了验证;进行甲醇 甲苯分离的间歇萃取精馏实验考察所选萃取剂的效果。结果表明：邻二甲苯能够有效提高甲醇 甲苯的相对挥发度。间歇萃取精馏塔塔板数为30,溶剂比为1,恒回流比(R=3)操作下塔顶得到摩尔分数为99.688%的甲醇产品。