Optimal Designs of Multiple Dividing Wall Columns

Since the optimal design of dividing wall columns (DWC) is a highly nonlinear and multivariable problem, an appropriate solving tool is required. In this paper a multi‐objective genetic algorithm with restrictions is considered to design columns with dividing walls. Also, a methodology is proposed for sizing the DWC. The proposed design methodology allows achieving appropriate designs for columns with two dividing walls. As expected, the physical structures that allow the use of one or two dividing walls are not so different from each other and, as a consequence, the difference in the total annual costs for both systems depends mainly on the energy requirements.     

Optimal Design and Economic Evaluation of Dividing‐Wall Columns

In an effort to reduce costs, a systematic optimization approach is proposed to address the energy consumption of dividing‐wall columns (DWCs). This iterative optimization procedure begins by minimizing the overall heat duty using an innovative objective function within a constrained design space. A sensitivity analysis is then carried out on the manipulated variables to obtain their optimal ranges. Optimal operating parameters are obtained through the evaluation of the total annualized cost (TAC). For the separation process of benzene/toluene/o‐xylene, the optimal DWC flow sheet exhibits a significant decrease in TAC when compared to conventional flow sheet optimum designs. The applied optimization method and sensitivity analysis have proven to produce results at the global optimum. This method is both practical and easily applied to other systems, even to systems with more than three components.     

Integrated process design and control of divided-wall distillation columns using molecular tracking

This work explores the dynamic and control behavior of dividing wall distillation columns from two different steady-state design approaches (molecular tracking and optimization method) for three different mixtures. The controllability of the six design cases was evaluated using singular value decomposition and the closed-loop performance was evaluated using integral absolute error in Aspen Dynamics. The results demonstrate that the side-draw location obtained by molecular tracking (MT) provides optimal controllability. As a result, there is a slight advantage in control properties while obtaining designs by reducing the time to find the optimal solution through the MT method.     

Design and optimization of heat integrated dividing wall columns for improved debutanizing and deisobutanizing fractionation of NGL

Dividing wall columns, capable of reducing the energy required for the separation of ternary mixtures, were explored for the energy-efficient integration of debutanization and deisobutanization. A new practical approach to the design and optimization of dividing wall columns was used to optimize dividing wall columns. A conventional dividing wall column and a multi-effect prefractionator arrangement were shown to reduce total annual cost considerably compared with conventional distillation sequence. Various configurations incorporating a heat pump in a bottom diving wall columns were also proposed to enhance energy efficiency further. The result showed that operating cost could be reduced most significantly through novel combinations of internal and external heat integration: bottom dividing wall columns employing either a top vapor recompression heat pump or a partial bottom flashing heat pump.     

Thermal coupling links to liquid‐only transfer streams: An enumeration method for new FTC dividing wall columns

Novel dividing wall columns (DWCs) can be obtained by converting thermal couplings to liquid‐only transfer streams. Here, we develop a simple four‐step method to generate a complete set of DWCs containing n ? 2 dividing walls, for a given n‐component fully thermally coupled (FTC) distillation. Among the novel DWCs, some easy‐to‐operate DWCs possess the property that the vapor flow in every section of the DWC can be controlled during operation by means that are external to the column. We develop a simple method to enumerate all such easy‐to‐operate DWCs. We expect that the easy‐to‐operate DWCs can be operated close‐to‐optimality; leading to a successful industrial implementation of the n‐component (n ≥ 3) FTC distillation in the form of a DWC. As an illustration, we show figures of all easy‐to‐operate DWCs with two dividing walls for the four‐component FTC distillation. © 2015 American Institute of Chemical Engineers AIChE J, 62: 1200–1211, 2016     

Feed distribution in distillation: Assessing benefits and limits with column profile maps and rigorous process simulation

This contribution describes the column profile map (CPM) methodology for designing distributed feed distillation columns. For non‐sharp product distributions, a case study shows that energy savings of approximately 35% can be obtained if the feed stage(s) are designed optimally. Feed distribution allows capital cost savings, expands operating leaves, and can obtain greater separation feasibility. However, this column only has benefits in ternary and higer‐order systems and when product distributions are non‐sharp. To validate these counter‐intuitive claims, a real Benzene, p‐Xylene, Toluene system is modeled using CPMs, and the resulting design parameters are transported to Aspen Plus^®. Using a sum of squared errors objective function to quantify savings, a cost saving trend very similar to the one predicted by the CPM method is obtained. This article therefore describes a complete design methodology for distributed feed systems and provides convincing evidence of benefits of such a system. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1668–1683, 2013     

A simplified calculation method for temperature evaluation of steel columns embedded in walls

Steel elements behave differently in fire case when isolated or embedded in building walls. The walls on one hand have a favorable effect protecting the elements from the excessive heating resulting from the fire and on the other hand they have a detrimental effect due to the thermal gradients originated in the elements cross‐section. The simplified calculation methods proposed in EN 1993‐1‐2 for fire design do not take into account the case of steel elements embedded in walls, stipulating only a formulation for the assessment of the resistance for uniform temperature distribution. This paper presents a proposal of a new simplified calculation method to evaluate the temperature of steel columns embedded in walls. The method is based on numerical simulations and fire resistance tests. Steel columns totally or partially embedded in walls, with the web perpendicular or parallel to the wall surface, were tested. In the study it was also observed that thicker walls or H steel columns with the web perpendicular to the wall surface provide greater thermal gradients in the cross‐sections. Copyright © 2010 John Wiley & Sons, Ltd.     

Eindimensionale Modellierung und Simulation von Blasensäulenreaktoren

Reactor models that feature a practical way to design bubble columns on the (semi‐)industrial scale have been published only rarely in the scientific literature. Creating a one‐dimensional model in the equation‐oriented simulation software ASPEN Custom Modeler^TM, a compromise between model precision and modeling can be reached. The model quantitatively describes the processes in a bubble column reactor with sufficient accuracy.     

Applying Model Predictive Control to Dividing Wall Columns

The technology of dividing wall columns can offer enormous energy savings compared to common distillation columns and configurations. The technology of model predictive control is also advantageous since such a controller minimizes the future deviation of the predicted controlled variable from the reference point. The practical application of model predictive controllers for dividing wall columns is still limited due to limited experience with high interactions among the process variables. The scope of this work is the development and analysis of a method for the design of model predictive controllers for dividing wall columns. An experimental investigation verifies the practicability of the applied approach. The methods generated are transferable to other applications. Thus, the industrial acceptance of model predictive controllers for dividing wall columns is enhanced.     

Extension of a Method for the Design of Divided Wall Columns

For most separations, a fully thermally coupled distillation column or divided wall columns are thermodynamically more efficient than conventional columns. This paper develops a method for the design of divided wall columns consisting of multi‐component mixtures (more than three components) with constant relative volatilities and a relatively sharp separation between the key components.     

Pervaporative Separation of Methanol–Methyl Acetate Mixtures with Commercial PVA Membranes

Pervaporation may successfully be implemented for the separation of azeotropic mixtures which generally requires energy intensive separation procedures. Separation of methanol from methyl acetate by pervaporation is a representative application. In this study the commercial polyvinyl alcohol (PVA)-based membranes PERVAP^TM 4155-30, PERVAP^TM 4155-70, and PERVAP^TM 4155-80 were used to recover methanol from binary methanol–methyl acetate mixtures. The separation performance was investigated for various operating parameters such as feed composition, feed temperature, and permeate pressure and discussed in terms of permeance and selectivity. An empirical model was developed to quantify the effect of membrane swelling on the permeate flux.     

Trickle‐bed scrubbing of flue gas SO2 using non‐aqueous solvents

Experiments were carried out on the performance of several ketone solvents for the scrubbing of dilute SO₂ from a gas stream and its conversion to sulfuric acid in a trickle‐bed reactor packed with activated carbon. Using a bench‐scale trickle bed packed with a structured packing based on Sulzer static mixers coated with Centaur^TM activated carbon and a Teflon binder, measurements of SO₂ removal, conversion to acid and catalyst productivity showed that all were considerably greater than levels achieved with water flushing. The combination of Teflon‐coated Centaur activated carbon with a non‐aqueous solvent as the flushing agent provided from 10 to 100 times higher catalyst productivity than those obtained with water alone and other activated carbons. Also, the productivities obtained by this combination were up to 40 times higher than the productivity of typical vanadium pentoxide catalyst operating at 350°C to 400°C.     

Investigation of the operability for four-product dividing wall column with two partition walls

For separating some specific four component mixtures into four products, the four-product dividing wall column (FPDWC) with two partition walls can provide the same utility consumption with the extended Petlyuk configuration, although with structure simplicity. However, the reluctance to implement this kind of four product dividing wall column industrially also consists in the two uncontrollable vapor splits associated with it. The vapor split ratios are set at the design stage and might not be the optimal value for changed feed composition, thus minimum energy consumption could not be ensured. In the present work, a sequential iterative optimization approach was initially employed to determine the parameters of cost-effective FPDWC. Then the effect of maintaining the vapor split ratios at their nominal value on the energy penalty was investigated for the FPDWC with two partition walls, in case of feed composition disturbance. The result shows that no more than + 2% above the optimal energy requirements could be ensured for 20% feed composition disturbances, which is encouraging for industrial implementation.     

Cyclic distillation technology – a mini‐review

Process intensification in distillation systems has received much attention during past decades, with the aim of increasing both energy and separation efficiency. Various techniques, such as internal heat‐integrated distillation, membrane distillation, rotating packed bed, dividing‐wall columns and reactive distillation were studied and reported in the literature. All these techniques employ the conventional continuous counter‐current contact of vapor and liquid phases. Cyclic distillation technology is based on an alternative operating mode using separate phase movement which leads to key practical advantages in both chemical and biochemical processes. This article provides a mini‐review of cyclic distillation technology. The topics covered include the working principle, design and control methods, main benefits and limitations as well as current industrial applications. Cyclic distillation can be rather easily implemented in existing columns by simply changing the internals and the operating mode, thus bringing new life to old distillation towers by significantly increasing the column throughput, reducing the energy requirements and offering better separation performance. © 2016 Society of Chemical Industry     

Thermal coupling links to liquid‐only transfer streams: A path for new dividing wall columns

We propose new dividing wall columns (DWCs) that are equivalent to the fully thermally coupled (FTC) configurations. While our method can draw such configurations for any given n‐component mixture (n ≥ 3), we discuss in detail the DWCs for ternary and quaternary feed mixtures. A special feature of all the new DWCs is that during operation, they allow independent control of the vapor flow rate in each partitioned zone of the DWC by means that are external to the column. Because of this feature, we believe that the new arrangements presented in this work will enable the FTC configuration to be successfully implemented and optimally operated as a DWC in an industrial setting for any number of components. Also, interesting column arrangements result when a new DWC drawn for an n‐component mixture is adapted for the distillation of a mixture containing more than n components. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2949–2961, 2014     

Large‐scale volatility models: theoretical properties of professionals’ practice

Abstract. This article examines the way in which GARCH models are estimated and used for forecasting by practitioners in particular using the highly popular Riskmetrics^TM approach. Although it permits sizable computational gains and provide a simple way to impose positive semi‐definitiveness of multivariate version of the model, we show that this approach delivers non‐consistent parameter’ estimates. The novel theoretical result is corroborated by a set of Monte Carlo exercises. A set of empirical applications suggest that this could cause, in general, unreliable forecasts of conditional volatilities and correlations.     

Influence of fiber slippage coefficient distributions on the geometry and performance of composite pressure vessels

In this article, the effects of several slippage coefficient distributions on the geometry, fiber trajectories, and the structural efficiency of non‐geodesic domes are evaluated for composite pressure vessels. Several functions, which ensure C¹ continuity of the winding trajectories, are respectively used to describe the slippage coefficient distributions along the fiber paths. With the aid of the fiber slippage law and the optimality condition of equal shell strains, the differential equations that govern the non‐geodesics–based dome shapes and related fiber trajectories are formulated. The meridian profiles and winding angle developments of the carbon–epoxy domes are obtained based on the given slippage coefficient distributions; their structural performances are then determined and compared with each other. The results conclude that the non‐geodesic dome designed using the maximum constant slippage coefficient exhibits better performance than those using other slippage coefficient distributions; this is mainly triggered by maximum utilization of the longitudinal strength of the laminate. It is also revealed that the structural efficiency of domed pressure vessels can be improved using non‐geodesics that provide higher degrees of freedom in the design of filament wound structures. POLYM. COMPOS., 315–321, 2016. © 2014 Society of Plastics Engineers     

Performance of Nanofiltration Membranes for Solvent Purification in the Oil Industry

The extraction stage of edible oil in the oil industry is commonly performed by using toxic solvents (e.g. hexane) and processes with high energy consumption (e.g. distillation, evaporation) to recover the solvent, which represents around 70–75 wt% in the oil–solvent mixture. In this paper, a membrane-based extraction method using nanofiltration (NF) membranes is presented. Commercial nanofiltration membranes made of different polymers (Desal-DK-polyamide NF from GE-osmonics^®, NF30 polyethersulfone NF from Nadir^®, STARMEM^TM122 polyimide from MET^® and SOLSEP NF030306 silicone base polymer SOLESP^®) were selected and tested to recover the solvent from soybean oil/solvent (10–20–30% w/w oil) mixtures at various separation pressures and constant temperature in a dead-end filtration set up. The selection of the solvent was made in order to compare solvents obtainable from renewable resources, such as ethanol, iso-propanol and acetone, with solvents traditionally used in the industry (i.e. cyclohexane and n-hexane). The structural stability of the membranes towards the different solvents used in this work was verified visually, by the variation of the membrane area and by means of permeate flux assessments. Desal-DK and NF30 showed poor filtration performance and even visible defects after exposure to acetone but a good performance was obtained for the nanofiltration membranes STARMEM^TM122 and SOLSEP NF030306 with ethanol, iso-propanol and acetone. For example, considering a mixture with 30% edible oil in acetone, STARMEM^TM122 shows a flux and oil rejection of 16.8 L m^?2 h and 70%, respectively. For the same conditions, SOLSEP NF030306 exhibited a flux of 4.8 L m^?2 h with 78% rejection, which shows the potential application of nanofiltration membranes in the oil industry.     

气相进料对隔板精馏塔优化设计的影响

隔板精馏塔（DWC）在节能和节省设备投资方面具有十分突出的优势,隔板精馏塔中隔板位置是重要的设计变量,影响分离效果及能耗,当进料中含有气相时这种影响更加显著。选用苯、甲苯和对二甲苯三元物系,研究了进料的气相分率对隔板位置的影响并确定最优隔板位置。采用严格模拟方法,以年度总费用（TAC）为评价指标,比较不同进料气相分率下隔板塔的经济性,其中气相进料较液相进料TAC最高可节省23.33%。并通过灵敏度分析展示了在进料中含有气相时确定最优隔板位置的重要性。