Existing system remodeling for a fully thermally coupled distillation column

The divided wall column (DWC) can achieve sharp separations of three or more components in a single shell, substituting conventional sequences of two or more binary<br /> distillation columns, with lower expenses. Despite these advantages, DWC models are not available in commercial chemical process simulators. To simulate DWC, users must employ instances of conventional column model and couple them in different configurations. In this paper, a DWC model was developed in EMSO (Environment for Modeling, Simulation and Optimization). DWC model was then used for simulating the separation of an equimolar mixture of three hydrocarbons. Results show that, depending on the number of trays, DWC presented energy savings compared to two ordinary distillation columns. Better separation was obtained when the number of divided trays was close to half the number of total trays. However, the liquid and vapor flow rates split into the divided section play a key role in the separation.

Energy, exergy, economic and environmental analysis of a novel steam-driven vapor recompression and organic Rankine cycle intensified dividing wall column

Energy savings is a major challenge in distillation operations. However, there is still one problem, which is how do we improve the energy efficiency of the existing distillation column systems without major modifications. Recently, a new energy efficient distillation columns methodology that will be able to improve energy efficiency of the existing separation systems without having major modifications has been developed. Therefore, the objective of this paper is to present a new improvement of the existing methodology by designing an optimal sequence of energy efficient distillation columns using a driving force method. Accordingly, the methodology is divided into four hierarchical sequential stages: i) existing sequence energy analysis, ii) optimal sequence determination, iii) optimal sequence energy analysis, and iv) energy comparison and economic analysis. The capability of this methodology is tested in designing an optimal synthesis of energy efficient distillation columns sequence of an aromatics separation unit. The existing aromatics separation unit consists of six compounds (Methylcyclopentane (MCP), Benzene, Methylcyclohexane (MCH), Toluene, m-Xylene and o-Xylene) with five direct sequence distillation columns being simulated using a simple and reliable short-cut method and rigorously tested within an Aspen HYSYS® simulation environment. The energy and economic analyses show that the optimal sequence determined by the driving force method has a better energy reduction with a total of 6.78% energy savings and a return of investment of 3.10 with a payback period of 4 months. It can be concluded that, the sequence determined by the driving force method is not only capable in reducing energy consumption, but also has a better economic cost for an aromatic separation unit

The energy demand and better utilization of by-products are areas with large potential improvements in the ethanol production process. The ethanol industry in Brazil has experienced successive increases in demand and production. This expansion of ethanol productivity will allow more profitable uses of products such as fusel oil, a mixture of various alcohols such as isobutanol, ethanol, propanol and, especially, isoamyl alcohol. Such alcohols have applications in various industries. However, current applications of fusel oil present low economic benefits for ethanol mills. Energy demand is another point that has great impact on increasing the sustainability and profitability of bioethanol production. The development of more efficient distillation technologies is very important because this unit operation is responsible for a considerable part of the utilities and investment costs in ethanol production. Moreover, this reduction in steam consumption can increase the quantity of bagasse available to be used for bioelectricity or cellulosic ethanol production. In these circumstances, the present study aims to investigate processes that increase the economic benefit and sustainability of ethanol production by reducing utilities and equipment distillation costs or by manufacturing of products with higher added value. With the premise of having relative ease application, the following processes are investigated: integrated process for isoamyl alcohol and ethanol production; use of high energy efficiency columns distillation for multi-component separations (divided wall column and multi-effect columns; energy demand optimization of the conventional distillation process of ethanol; distillation process of fusel oil to obtain ethanol, isoamyl alcohol and butanol. The integrated production of ethanol and isoamyl alcohol allows increasing the recovery of ethanol and producing isoamyl alcohol and its isomer active amyl alcohol with high purities from fusel oil. However, energy integration using a multi-effect distillation column for the integrated process was not an economically viable alternative due to the small temperature differentials obtained for energy transfer between columns. To make better use of other constituents of fusel oil, the investigation of an autonomous plant configuration for butanol, isoamyl alcohol and ethanol recovery from fusel oil was investigated, this process shows high recovery rates of these components by a process that does not use solvents and employs only conventional distillation columns and decanters. An additional contribution of this thesis is to demonstrate the influence of phlegm concentration on energy demand costs of industrial ethanol distillation. The optimal economic conditions allow savings in energy demand of about 15% in the current ethanol plants, only by controlling the composition of phlegm. The process of hydrated ethanol production using a Divided Wall Column (DWC) was developed and optimized. Compared with the conventional sequence of two distillation columns, the DWC proposal presented lower costs of utilities and equipment.

Space-constrained purification of dimethyl ether through process intensification using semicontinuous dividing wall columns

In chemical processes, beside main products, significant quantities of by-products are often produced due to thermodynamics. Therefore, separation techniques and methods play such an important role, in chemical technologies, as reactor systems. Rectification is one of the most frequently used fluid separation process, which usually involves significant energy consumption. The production of hot and cold energy causes notable environmental load (CO2 emission, dust pollution, etc.). Hence, from environmental point of view, research on energy saving in separation processes, for instance analysing divided wall columns (DWC), is exceedingly important. This article focuses on how to find more efficient structures with minimal energy consumption. The DWC system is a promising energy-saving alternative for separating multi-component mixtures (Chem Eng Process 38: 549–562, 1999; Chem Eng Process 49: 825–835, 2010). The innovation of this equipment is a wall which divides the inner space of the tower separating the feed and the side stream-product zones. The side stream and the feed stream are prevented from mixing by this wall. The DWC possesses greater efficiency than common column sequences. Conventional columns with side stream can be converted to DWC. In this article, several constructions of DWC are investigated with simulation experiments. The structure of the column is implemented in Aspen Plus in: 2006 Reference Guide, AspenTech Inc., Cambridge, 2006 simulator using the Radfrac unit of the software. The effects of the split ratio, the height and the vertical position of the wall, as the main parameters of DWC, are analysed.

Simulation study of alternatives for the efficient start-up of dividing-wall distillation column sequences

Design, optimization, and industrial-scale experimental study of a high-efficiency dividing wall column

Distillation Columns with Structured Packings in the Next Decade

This study focuses on the energy-efficient separation process of styrene monomer, avoiding the formation of an azeotrope by using a vacuum distillation, derived from the pyrolysis of waste polystyrene (PS). The direct-indirect sequence, which positions the separation column of ethylbenzene and styrene monomer as the last step, exhibited a 30% reduction in the total utility consumption and a 37% reduction in the total annual cost compared to that of the direct-direct sequence that separates lighter components sequentially. A dividing wall column (DWC) configuration derived from the direct-indirect sequence showed the most significant reduction of 40% in utility consumption. However, when the feed capacity was low, the increased capital cost of DWC resulted in a total annual cost similar to that of the direct-indirect sequence. As the capacity of the entire distillation system increased, the reduction in the total operating cost of the DWC was amplified, indicating the advantages of using the DWC in high product throughputs from both energy and economic perspectives. Therefore, implementing the DWC in large-scale PS recycling processes demonstrates superior performance compared to the conventional distillation process, resulting in a more streamlined process with substantial energy savings and CO2 emissions.

Design and operation of dividing-wall distillation columns. 1. Diminishing the black-hole problem through over-design

The reactive double dividing-wall distillation column (R-DDWDC) can simultaneously integrate and effectively coordinate reaction–separation coupling (RSC) and separation–separation coupling (SSC), thereby offering greater technical advantages and development potential than the conventional reactive distillation column and the reactive single dividing-wall distillation column. However, the application of two dividing walls and the introduction of external recycle flows inevitably lead to multiple candidate configurations of the R-DDWDC, and this significantly adds complexity and computational burden to its synthesis and design. To address the issue, we propose an effective methodology for developing the R-DDWDC, which involves a two-step strategy: the first step is to determine the configuration of external recycle flows by searching for the RSC from non-sharp separation to sharp separation of reaction mixtures, and the second step is to adjust the arrangement of the dividing walls to intensify the SSC. The former serves to provide the greatest flexibility for the inclusion of the SSC, and the latter helps to achieve full coordination with the RSC, thereby allowing the determination of the optimal design with low complexity and computational intensity. The methodology is fundamentally a conceptual design and structural optimization framework that can be implemented using either generic process simulation platforms or custom computational programs. Four representative examples, including the metathesis of 2-pentene; the acetalization of ethanol with butanal; the transesterification of propylene glycol monomethyl ether with methyl acetate; and the esterification of lactic acid with methanol, are selected to assess the derived procedure, and the obtained results confirm its simplicity and efficiency. Because the procedure proposed in this work is independent of the number of components contained in reaction mixtures and their relative volatility rankings, it can be regarded as a general methodology for developing other complicated reactive dividing-wall distillation columns.

Chapter 5 - Dividing-Wall Columns

Enhancing multi-component separation of aromatics with Kaibel columns and DWC

Heterogeneous azeotropic distillation is one of many method for breaking azeotrope. Azeotropic distillation is an energy intensive process, with high operating cost. Development of process intensification results in dividing wall column for combining two sequential distillation column into one column. Application of dividing wall column for azeotropic distillation is therefore a prospective process. Process control for azeotropic distillation with dividing wall column is studied to determine its controllability and feasibility for industrial applications. Systems studied in this paper includes isopropanol-water mixture with cyclohexane as entrainer. Product composition, as control objective, is controlled via tray temperature control, with reboiler duty and liquid split ratio as manipulated variables. Internal Model Control (IMC) and Ziegler-Nichols tuning method are also studied and compared. Simulation results with ASPEN Plus Dynamic shows that IMC and Ziegler-Nichols method are equally effective in achieving good process control. However, Ziegler-Nichols is concluded to be simpler for practical application, if compared to IMC.