Optimal retrofit of a side stream column to a dividing wall column for energy efficiency maximization

A side distillation column is widely used to separate multicomponent mixtures into three products. However, this kind of column consumes considerable amounts of energy due to thermodynamic restrictions and the nature of the distillation process. Retrofit of the side distillation column to a dividing wall column (DWC) can result in significant energy savings. This study evaluated a systematic method for optimal retrofit of a side stream column to a DWC. The minimum energy requirement for the separation of a multicomponent mixture was used for a feasibility study. Subsequently, design and optimization was performed using shortcut, rigorous and response surface methodology. One case study was illustrated to demonstrate the proposed methodology. The results showed that the optimal retrofit of a side distillation column to the DWC could not only save a significant amount of energy, but also increase the capacity. This study highlights the potential for retrofitting a side stream column to a DWC from a techno economic point of view.     

Real-time optimization for a laboratory-scale flotation column

In this paper, a supervisory layer with real-time optimization (RTO) has been implemented in an experimental laboratory-scale flotation column for copper concentration. A two-stage and modifier adaptation (MA) methodology for RTO has been compared under structural, experimental and dynamic uncertainty. In addition, a gradient-free alternative for MA, called nested modifier optimization, has been proposed and tested. The results show that the KKT updates of the MA approach allow the process optimum to be determined under uncertain scenarios, unlike the two-stage approach. From the perspective of gradient modifiers, the performance of the nested methodology is comparable to the dual approach because previous past values are used to update the modifiers without requiring the gradient estimation step. In addition, the interaction of RTO with the regulatory layer must be considered to propose an optimal implementation.     

Gas-holdup distribution and energy dissipation in an ejector-induced downflow bubble column: the case of non-Newtonian liquid

A precise knowledge of gas-holdup distribution and energy dissipation is essential for designing gas-liquid contactors. A semi-theoretical approach has been presented to obtain the axial distribution of gas holdup through the column for gas-non-Newtonian liquid two-phase flow system. The whole column is distinguished to have three zones based on gas holdup, viz. top, middle and bottom. The middle section where significant accumulation of bubbles takes place, contributes higher gas holdup towards the total compared to the other two sections. Energy dissipation in the column have been calculated from two-phase gas-liquid frictional losses. A comparative study shows that substantial gas holdup are observed in the present system with considerably lower energy losses. The experimental data of gas holdup have been correlated in terms of pressure drop by the modified Lockhart-Martinelli equation.     

转盘式萃取塔有效扩散系数的预测及其在设计中的应用

A rotating disc column (RDC) with inner diameter 68 mm and 28 compartments is used in this study. Parameters including Sauter mean diameter, hold-up and mass transfer coefficient are measured experimentally under different operating conditions. The correlations in literature for molecular diffusion and enhancement factor equation including eddy diffusion, circulation and oscillation of drops are evaluated. A new equation for the effective diffusion coefficient as a function of Reynolds number is proposed. The calculated values of mass transfer co-efficient and column height from the previous equations and present equation are compared with the experimental data. The results from the present equation are in very good agreement with the experimental results, which may be used in designing RDC columns.     

Conceptual design of single-feed hybrid reactive distillation columns

It is well known that reactive distillation offers benefits by integrating distillation and reaction within a single unit. While there are procedures available for the synthesis of non-reactive distillation processes and of reaction-separation systems, the design of reactive distillation columns is still a challenge. This work presents a new synthesis and design methodology for hybrid reactive distillation columns, featuring both reactive and non-reactive sections; reactive equilibrium is assumed. The approach is based on graphical techniques; therefore it is restricted to systems with two degrees of freedom according to Gibbs phase rule. The design method allows rapid and relatively simple screening of different reactive distillation column configurations. The results are useful for initialising more rigorous calculations. The methodology is illustrated for MTBE and ethyl formate production.     

Methodology for design and analysis of reactive distillation involving multielement systems

A new methodology for design and analysis of reactive distillation has been developed. In this work, the element-based approach, coupled with a driving force diagram, has been extended and applied to the design of a reactive distillation column involving multielement (multicomponent) systems. The transformation of ordinary systems to element-based ones and the aggregation of non-key elements allow the important design parameters, such as the number of stages, feed stage and minimum reflux ratio, to be determined by using simple diagrams similar to those regularly employed for non-reactive systems consisting of two components. Based on this methodology, an optimal design configuration is identified using the equivalent binary-element-driving force diagram. Two case studies of methyl acetate (MeOAc) synthesis and methyl-tert-butyl ether (MTBE) synthesis have been considered to demonstrate the successful applications of the methodology. Moreover, energy requirements for various column configurations corresponding to different feed locations are determined to verify whether the optimal design can be identified by following the proposed methodology.     

Measurement of Adsorption Properties at Different Scales: from Zero Length Column Experiments on Single Pellets to Breakthrough Curves

The ZLC technique is a powerful technique for the measurement of diffusion in nanoporous materials using mg quantities of a sample. Questions remain on whether the measured properties are representative of larger samples. A methodology has been developed to carry out single pellet experiments to determine average properties and variability of equilibrium and kinetic properties. To demonstrate the approach, n-pentane on HISIV3000 extrudates was used as the test system, which was shown to be macropore diffusion controlled. Results on nine pellets provided average values showing a perfect match to breakthrough column experiments with a sample two orders of magnitudes larger.     

流程模拟软件Aspen Plus在精馏塔设计中的应用

以Aspen Plus流程模拟软件对精馏塔进行了简捷设计和严格核算，对精馏塔设计的影响因素进行了分析，并对精馏塔的经济核算进行了初步说明。     

连续式双膜分离塔的数学模型

本文建立了适用于连续式双膜分离塔的数学模型。用实验数据验证了数学模型的可行性和合理性。将本模型与已发表的模型进行了比较,结果表明本模型具有形式简单、计算方便和适用范围更宽广等优点。     

Unified correlation for overall gas hold‐up in bubble column reactors for various gas–liquid systems using hybrid genetic algorithm‐support vector regression technique

The objective of this study is to collect the data on overall gas hold‐up (∈_G) for bubble column reactors handling various gas–liquid systems and further develop a unified data‐driven model for the estimation of the same. In this work, around 3300 experimental points for ∈_G have been collected from 85 open sources spanning the years 1963–2008. The data‐driven model for overall gas hold‐up has been established using hybrid Genetic Algorithm‐Support Vector Regression (GA‐SVR)‐based methodology. In the present study, GA has been used for nonlinear rescaling of the parameters. These exponentially scaled parameters are subsequently subjected for SVR training. The technique is an extension of conventional SVR technique, showing relatively enhanced results. The proposed hybrid model is based on various prominent design and operating parameters (15 in number) which includes superficial gas velocity, superficial liquid velocity, gas density, molecular weight of gas, sparger type, sparger hole diameter, number of sparger holes, liquid viscosity, liquid density, liquid surface tension, ionic strength of liquid, operating temperature, operating pressure, liquid height, and the column diameter. The estimations made by the SVR‐based unified model for ∈_G shows an excellent agreement with actual values with estimation accuracy of 98.5% and % AARE of 9.32%. For ease in applicability and ready reference of the practicing engineers, the hybrid GA‐SVR‐based model in the form of software and the entire database for ∈_G has been uploaded on the link http://www.esnips.com/web/UICT‐NCL .     

Synthesis of dividing-wall columns (DWC) for multicomponent distillations—A systematic approach

Dividing-wall columns (DWC) are intensified distillation systems for multicomponent separations. They have the potential to save significantly both energy and capital costs than conventional simple column configurations. In this paper, it is shown that the DWC columns can be systematically generated from the conventional simple column configurations. Because of the simple column sequences with sharp splits are the simple and widely studied conventional schemes for multicomponent distillation, the purpose of this work is to formulate a procedure for systematic synthesis of DWC columns for such simple conventional schemes. A four-step procedure is formulated which systematically generates all the possible DWC columns from the simple column sequences. First, the subspace of the original thermally coupled configurations corresponding to the simple column configurations is generated. Then, the subspace of the thermodynamically equivalent structures corresponding to the original thermally coupled configurations is produced. Finally, the subspace of the DWC columns corresponding to the thermodynamically equivalent structures is achieved. An example of quaternary distillation is used to illustrate the synthesis procedure which is applicable to a mixture with any number of components.     

A generic feasibility study of batch reactive distillation in hybrid configurations

A new graphical feasibility method is developed to investigate batch reactive distillation processes in middle vessel column. The suggested methodology can deal with fully reactive, nonreactive, and complex column configuration. A new formulation is suggested to describe the composition profiles in the reactive sections. Its application has made possible to develop a generic feasibility methodology containing the same model equations independently of the presence or absence of reaction. By combining the reactive and nonreactive models, not only the fully reactive and fully nonreactive but also hybrid configurations can be studied. Feasibility criteria related to the hybrid configurations are also presented. Application of the new methodology is demonstrated on the production of ethyl acetate in batch reactive distillation. Five configurations are found feasible; pure EtOAc is produced as distillate, and pure H₂O is produced at the bottom. In each case, continuous feeding of AcOH is necessary. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

CFD modeling of flow,macro-mixing and axial dispersion in a bubble column

The flow pattern in a bubble column depends upon the column diameter, height, sparger design, superficial gas velocity and the nature of gas–liquid system. In this paper, the effect of some of these parameters have been simulated using Computational Fluid Dynamics (CFD). The relationship of these parameters with the interphase force terms has been discussed. A complete energy balance has been established. Using this methodology, the flow patterns reported by Hills (1974), Menzel et al. (1990), Yao et al. (1991) and Yu and Kim (1991) have been simulated. Excellent agreement has been shown between the CFD predictions and the experimental observations. The above model has been extended to homogenization of an inert tracer. In order to confirm this model, mixing experiments were carried out in a 200 mm i.d. bubble column. A radioactive tracer technique was used for the measurement of mixing time. Tc-99m (^99m Tc), in the form of sodium pertechnate salt, was used as the liquid phase tracer. Good agreement has been shown between the predicted and the experimental values of mixing time. The model was further extended for the estimation of axial dispersion coefficient (D_L). Excellent agreement between the simulated and the experimental values of the axial dispersion coefficient confirms the predictive capability of the CFD simulations for the mixing process.     

Column fractionation of partially stereoregular poly(propylene oxide)

A column packed with glass beads has been used to fractionate partially stereoregular poly(propylene oxide) (PPO). PPO was first crystallized onto the glass beads from isooctane solution by stepwise lowering the column temperature. Each layer of PPO, which was deposited at different temperature ranges, was extracted by washing the beads with several columns full of isooctane. Thus several fractions differing in both stereoregularity and molecular weight were obtained by progressively increasing the extraction temperature and the solvent residence time in the column. It is concluded that in the procedure described above PPO can be fractionated on the basis of structural and steric regularity. The observed steady increase in the molecular weight of fractions with extraction temperature was interpreted as being due to the fact that the stereoregularity of chains increases with their molecular weight.     

Hydrodynamics and power consumption of a reciprocating plate gas–liquid column

An experimental program has been initiated to use a reciprocating plate column for aerobic fermentations. This paper reports the results of the initial phase consisting of the hydrodynamic studies and the evaluation of the power consumption as a function of the level of agitation and gas superficial velocity. The variation of the gas holdup is presented and compared to a correlation. It is shown that a simple correlation can predict adequately the gas holdup when water is used. The power consumption, necessary for scale-up and design considerations, was evaluated using the pressure variation at the base of the column, the pressure difference across the column and the force exerted on the central shaft to reciprocate the plate stack. Results for the power consumed by the fluid mixture obtained with the three methods are presented and analyzed. The three methods give approximately the same value of the power consumption.     

The Optimum Column Number for the Best Performance of Thermal Diffusion in the Frazier Scheme with the Total Sum of Column Height Fixed

The effect of column number N, as well as the column height h of thermal diffusion columns, on the degree of separation in the Frazier scheme with the total sum of the column height L (=Nh) fixed, has been investigated. The equations, which may be employed to predict the optimum column number N* for the maximum separation Δ _N,max, have been derived. Considerable performance in separation is obtainable if the column number, as well as the column height, in a Frazier scheme with the total sum of the column height fixed is properly assigned for a certain flow-rate operation.     

Development of Two‐point Dynamic Method for Evaluating Extraction Columns

The steady‐state method by measuring the concentration profile along the column height is an effective way, but it is a time and material consumption method for large extraction columns. In order to investigate the axial‐mixing and mass transfer performances in a large pulsed‐sieve‐plate extraction column with the diameter of 150mm, a two‐point dynamic method with mass transfer based on the diffusion model has been developed. The results proved that the two‐point dynamic method has the advantages of good accuracy, simple boundary equations and flexible sampling position over the traditional single‐point dynamic method. It is a reliable tool for studying the axial‐mixing and the mass transfer performances.     

多项式正交配置建立精馏塔简化动态模型

根据多项式正交配置原理,系统地给出了一种通用的精馏塔简化动态模型.其建模基本原理是将精馏塔的状态变量考虑成塔的轴向距离的连续可微函数,并用多项式近似描述,使得逐板机理模型大为简化,在简化动态模型中,综合考虑了物料及能量平衡、塔板水力学及再沸器动态特性,避免了汽液平衡的迭代计算,节省了计算时间.通过对脱乙烷精馏塔进行仿真,证明了该简化模型可以给出满意的计算精度.     

A simple model for a non-isothermal adsorption column

A simple analytic solution has been derived for the temperature response of a non-isothermal adsorption column in which a small concentration of an irreversibly adsorbed species is removed. The model is shown to provide a reasonable representation of the experimentally observed behaviour of an ethanol drying column using 3A molecular sieve as the moisture selective adsorbent.