Design and control of a middle-vessel batch distillation for separating DMC–EMC–DEC mixture

In this paper, the mixture of dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate was separated by middle-vessel batch distillation with feeding in middle-vessel and process control characteristics were researched. The steady state simulation results in Aspen Plus were exported to Aspen Dynamics. Then control effect of liquid level control with HighSelector, composition control(structure1, structure2) and temperature control(proportional action, proportional integration action) were proposed. Composition control structure 2 and temperature control with PI action were investigated to achieve a good control effect.

Shortcut Procedure for Inverted Batch Distillation Column (I) Multicomponent Ideal System

Inverted batch distillation column(stripper) is opposed to a conventional batch distillation column(rectifier). It has a storage vessel at the top and products leave the column at the bottom. The batch stripper is favourable to separate mixtures with a small amount of light components by removing the heavy components as bottom products. In this paper, we are presenting a shortcut procedure based on our earlier work for design and simulation of the inverted batch distillation column, which is equivalent to the Fenske-Underwood-Gilliland procedure for continuous distillation. Given a separation task, we propose to compute the minimum number of stages(Nbmin) and the minimum reboil ratio(Rbmin) required in a batch stripper,which are the stages and reboil ratio required in a hypothetical inverted batch distillation column operating in total reboil ratio or having an infinite number of stages,respectively. Then, it is shown that the performance of inverted batch columns with a finite number of stages and reboil ratios could be correlated in Gilliland coordinates with the minimum stages Nbmln and the minimum reboil ratio Rbmin.

Batch Extractive Distillation in a Column with a Middle Vessel

Batch extractive distillation was studied in a column with a middle vessel. The process was simulatedby a constant holdup model and solved by two point implicit method. Acetone and methanol mixture was separatedin such a setup using water as solvent. The simulation agrees well with experimental results. The experimental andsimulation results show that the solvent at the bottom and the product at the top of the column can be withdrawnsimultaneously for a long period of time. It needs more time for the solvent to reach high purity than that requiredfor the more volatile component to reach high purity, so that the time to withdraw solvent from the bottom isdelayed.

A Dynamic Modeling For Cyclic Total Reflux Batch Distillation

Cyclic total reflux(CTR) batch distillation is a promising mode of the process but lacking of appropriate modeling for the period of filling the reflux drum.A new dynamic modeling method for the simulation of CTR batch distillation is proposed in this work,in which the changes in column holdup and liquid flow rate during the filling of the drum,and the consequent change in valid number of theoretical plates are considered.The effect of drum holdup on operation time is investigated and the optimal drum holdup is obtained from the simulation.The dynamic modeling is compared to the conventional modeling without consideration of change in liquid flow rate. The experimental result shows that the present modeling is more reliable and more accurate,especially for the column with large liquid holdup.

Design and Operation of Batch Extractive Distillation with Two Reboilers

This paper proposes a modified operation mode of batch extractive distillation with two reboilers.The separation of ethanol and water using as ethylene glycol is well done to validate the feasibility of this mode.The pilot-plant experimental data under the identical operational conditions between the regular mode and the modified mode are in particular discussed.The studied results prove more practical advantages of the modified mode over the regular mode such as easier operation control,more flexibility and higher separation efficiency etc.So it supplies certain guidance for the industrial application of batch extractive distillation process.

A Quasi-steady-state Model for Numerical Simulation of Batch Extractive Distillation

Batch extractive distillation(BED)is a special method used in the distillation process by adding a solvent into the batch distillation column to alter the relative volatility of the components and improve the separation. A comprehensive design and simulation method is required due to the complexity of BED.In this study,a quasi-steady-state model for BED is proposed,the derivation and solution of the model are presented.This shortcut model can be used to simulate the composition and temperature of the reboiler,the top and other plates of the column in a batch extractive distillation operation.The calculated values are in good agreement with the experimental data.The results show that the quasi-steady-state model is a practical method because of some advantages such as high precision and fast calculation.

Separation of Benzene and Cyclohexane by Batch Extractive Distillation

Azeotropic liquid mixture cannot be separated by conventional distillation. But extractive distillation or combination of the two can be valid for them. An experiment to separate benzene and cyclohexane by batch extractive distillation was carried out with N,N-dimethylformide (DMF), dimethyl sulfoxide (DMSO) and their mixture as extractive solvent. The effect of the operation parameters such as solvent flow rate and reflux ratio on the separation was studied under the same operating conditions. The results show that the separation effect was improved with the increase of solvent flow rate and the reflux ratio; all the three extractive solvents can separate benzene and cyclohexane, with DMF being the most efficient one, the mixture the second, and DMSO the least. In the experiment the best operation conditions are with DMF as extractive solvent, the solvent flow rate being 12.33 mL/min, and the reflux ratio being 6. As a result, we can get cyclohexane from the top of tower with the average product content being 86.98%, and its recovering ratio being 83.10%.

Shortcut Algorithm for Simulation of Batch Extractive Distillation

The batch extractive distillation (BED) process has the advantages of both batch and extractive distillation. It is one of the most promising means for the separation of azeotropic and close-boiling point systems. However, so far this process has not been applied in industry due to its over-complexity. A new shortcut model was proposed to simulate the operation of the batch extractive distillation operations. This algorithm is based on the assumption that the batch extractive distillation column can be considered as a continuous extractive distillation column with changing feed at any time. Namely, the whole batch process is simulated as a succession of a finite number of steady states of short duration, in which holdup is considered as constant mole. For each period of time the batch extractive distillation process is solved through the algorithm for continuous extractive distillation. Finally, the practical implementation of the shortcut model is discussed and data from the laboratory and literature are presented. It is found that this model has better adaptability, more satisfactory accuracy and less calculative load than previous rigorous model. Hence the algorithm for simulating BED is verified.

Overhead Concentration Platform of Total Withdrawal Operation in Cyclic Total Reflux Batch Distillation

The total withdrawal operation is an inevitable section in cyclic total reflux batch distillation.In the operation,an interesting phenomenon "overhead concentration platform"(OCP) appears,which is defined as a period of time with high overhead concentrations when the operation is changed from total reflux to total withdrawal.The OCP phenomenon and its influential factors,such as the theoretical stage number,feed concentration,and feed composition,are examined by simulations and experiments.The experimental equipment is a column with random packings.It is shown that the number of theoretical stages influences the OCP more significantly than the other factors.

Composition Estimation of Reactive Batch Distillation by Using Adaptive Neuro-Fuzzy Inference System

Composition estimation plays very important role in plant operation and control.Extended Kalman filter(EKF) is one of the most common estimators,which has been used in composition estimation of reactive batch distillation,but its performance is heavily dependent on the thermodynamic modeling of vapor-liquid equilibrium,which is difficult to initialize and tune.In this paper an inferential state estimation scheme based on adaptive neuro-fuzzy inference system(ANFIS) ,which is a model base estimator,is employed for composition estimation by using temperature measurements in multicomponent reactive batch distillation.The state estimator is supported by data from a complete dynamic model that includes component and energy balance equations accompanied with thermodynamic relations and reaction kinetics.The mathematical model is verified by pilot plant data.The simulation results show that the ANFIS estimator provides reliable and accurate estimation for component concentrations in reactive batch distillation.The estimated states form a basis for improving the performance of reactive batch distillation either through decision making of an operator or through an automatic closed-loop control scheme.

OPERATION AND OPTIMIZATION OF BATCH DISTILLATION FOR A BINARY SYSTEM

Batch distillation,basically different from continuous distillation which is a steady stateprocess,appears to be an unsteady state process in its mathematical description.The theoreticalanalysis of its operation comprises a concomitant consideration of the stage-wise separation andthe equations of material balance as well as enthalpy balance.Based upon the batch distillationpractice of NMP-water system,this paper reveals the necessity and advantage of a computerizedtreatment for this purpose.Numerical results not only explain the experimental phenomena andprovide a design scheme,but also lead to the optimization of the operation condition.

A Short-Cut Design Technique to Batch Distillation Column

The effects of equipment parameters of batch distillation column on the yield proportion are discussed and analyzed, the relations between maximal yield proportion and the column equipment parameters are correlated, which not only can be used to appraise rationality of the design parameters of the columns being employed and which but also can be used to new batch distillation column design. Under the assistance of the separation difficulty defined in this paper, the minimum number of theoretical plates is determined by the limit loss proportion method given, and further the actual number of theoretical plates and the height for the batch distillation are calculated by using the redundancy coefficient found to complete the whole design of the batch distillation as shown in the computational sample. Research showed that the actual number of theoretical plates and the height of batch distillation column with the column diameter 0.6 m are 17 and 5.1 m in alcohol mixture separation system of the sample proposed. Moreover, the approach can be extended to the design of batch distillation column with a separation system of multi-component liquid mixture after those adjacent components are treated as numerous binary component systems.

A Novel Operation Policy for Dilute Component Separation-Quasi-batch Distillation

A new operation policy--quasi-batch distillation for recovering infinitesimal amounts species existing in a mixture is presented. In quasi-batch distillation operation, feed is introduced with a constant flow rate onto the feed stage of the column, and the flow rate of the distillate is the same as that of the feed, whereas the bottom product is withdrawn periodically. The behavior of quasi-batch distillation is simulated and analyzed through an example on heavy water separation. Comparing with continuous or batch distillation, the new operation policy is more reliable and efficient to achieve higher recovery of dilute component. This is especially suitable for separating small amount of precious species from large amount of raw material.

A Combination of Varying Column Pressure and Total Reflux-Total Efflux in Batch Distillation Operation

A novel operation of batch distillation-combination of varying colum pressure and total reflux-total efflux is studied experimentally. In the operation, the product is accumulated at the top of the column under total reflux and then drained off completely, and the column pressure is varying in the whole process. This process has been industrialized successfully with large profits. The conventional mode of batch distillation is improved by this method effectively: the separation eficiency and the yield of product are increased greatly, the operation time is shortened and the production cost is cut down. Moreover, the amount of condensation water is decreased and the over-high reboiler temperature is lowered.

Minimum Amount of Slop Cut in Batch Distillation

在分批蒸馏在全部的倒流操作和全部的流出操作之间轮流出现的脉搏控制操作技术与 slop 切割的最小的数量一起被学习。全部的倒流时间被动态模拟证实，并且全部的流出时间被统计方法采用。为己和环己烷和传统的经常的回流比操作策略的混合， slop 切割的数量是 1.8 - 2.1 次 slop 的最小的数量切了；而为脉搏控制操作策略，它是 1.2 - 1.4 次 slop 的最小的数量切了。那么与传统的经常的回流比操作相比， slop 的数量切了的 thepulse 控制操作罐头减少和操作预定，并且同时，提高分离效率和产量。

基于优化BP神经网络的非稳态精馏过程建模

间歇精馏已广泛应用于小批量、高附加值的精细化工和制药行业。然而在非稳态精馏过程中,一些重要的质量参数如产品组成等难以被直接测量,导致常规控制方法效果不佳。为解决这一问题,提出基于BP神经网络的非稳态精馏过程软测量模型,网络结构为3-12-1,再利用遗传算法、麻雀搜索算法等智能优化算法对网络进行优化,使用优化后的BP神经网络对非稳态精馏过程的产品质量进行预测。结果表明:经麻雀搜索算法优化后,BP神经网络的均方误差为4.32×10^(-5),与标准BP神经网络相比降低约59%,与遗传算法优化后的BP神经网络相比降低约26%。因此采用麻雀搜索算法优化后的BP神经网络建立非稳态精馏过程软测量模型,能够实现更高的预测精度。

双塔变压间歇精馏分离三元双共沸体系的工艺模拟与优化

提出多储罐双塔变压间歇精馏工艺用于分离丙酸甲酯-甲醇-水三元双共沸混合物,通过不同压力下的三元相图对工艺可行性进行了分析,基于每批次100 kmol的生产容量,提出了对应的控制结构以实现混合物的高效分离。以工艺的设备费用与操作费用为目标函数,采用多目标优化,确定了最优的高压塔操作压力。采用热集成技术进一步降低了工艺能耗,并计算了集成前后工艺的经济与环境性能。模拟结果表明,在相同的产品纯度和收率条件下,热集成后工艺的年度总费用与环境排放量分别降低了0.625%与4.688%。

乙烯焦油β-甲基萘的分离模拟

甲基萘是石油加工副产焦油、煤焦油洗油馏分、重质芳烃等大宗化工品中含量较高、用途广泛、价值较大的有机原料。文章研究以乙烯焦油230~250℃分馏点的甲基萘馏分为原料,采用间歇精馏过程制备β-甲基萘产品,采用Aspen BatchSep模块进行模拟计算,并优化操作条件,得到最佳塔顶压力14 kPa(A)和最佳回流比为20,此时模拟间歇精馏结果为:β-甲基萘产品纯度96.01%,收率60.61%,α-甲基萘产品纯度92.08%,收率17.52%,研究结果可为β-甲基萘的生产过程提供工艺参考。

基于改进MobileNetV2和主从网络的行人重识别方法

为增强行人重识别的适应性和通用性,提出了一种基于改进MobileNet-V2和主从网络的行人重识别方法。方法通过实例归一化(IN)和批归一化(BN)模块对MobileNet-V2进行改进,并将其作为骨干网络。此外,使用两个相同架构的骨干网络分别作为主网络和从网络,将主网络学习到的目标外观多样性特征传递给从网络,提高整体网络的语义捕捉能力,丢弃无用的背景和相机视角信息并将注意力集中在重要细节上,从而取得比主网络更好的行人重识别性能。实验结果表明,所提主从网络比主网络的平均识别mAP提升了3.83%,且整体性能显著优于其他先进方法。