Simple Distillation Columns Research Articles

СПОСОБ РАСЧЕТА ПРОСТОЙ МНОГОКОМПОНЕНТНОЙ РЕКТИФИКАЦИИ СПОСОБОМ ФЕНСКЕ-АНДЕРВУДА-ДЖИЛЛИЛЭНДА

An approach to calculating a multicomponent simple distillation column according to the Fensky-Underwood-Gilliland method is considered

Critique on spreadsheet for relaxation methods

This critique discusses the Excel spreadsheet developed by Gómez-Siurana and Font-Escamilla for the application of relaxation methods to solve a simple multicomponent distillation column.

Process Intensification for the Recovery of Hydrogen Cyanide in the Andrussow Process

AbstractThe aim of this work was to determine a cost‐optimal design of the distillation unit of the Andrussow process. For this purpose, a feed with a mass flow rate of 121 t h−1 and a concentration of ca. 2 wt % hydrogen cyanide (HCN) was considered. An approach for a cost‐optimal process intensification was developed with the goal to achieve the desired product qualities, while minimizing the organonitrile accumulation in the column. For this purpose, the simple distillation column of the established cost‐optimal design of the base case was extended to a configuration with a side stripper with taking into consideration heat integration in the process. It was found that this new configuration allows a much smaller accumulation of organonitriles in the main column; reducing thereby the operation issues of the process while decreasing considerably the total annual cost of the distillation unit by 61 % as compared to that of the base case design.

Algorithm and software for the optimal technological design of a system of simple distillation columns

Objectives. The formalized problem of the optimal design of distillation column systems belongs to the class of mixed integer nonlinear program problems. Discrete search variables are the number of trays in the rectifying and stripping sections of columns, whereas the continuous ones are the operating modes of columns. This study aimed to develop an algorithm and a software package for the optimal technological design of a system of simple distillation columns based on the criterion of total reduced capital and energy costs using rigorous mathematical distillation models.Methods. The solution to this problem is based on the branch and bound method. A computer model of the distillation column system was developed in the environment of the Aspen Hysys software package. The Inside–Out module was used as the distillation model. The developed algorithm is implemented in the software environment of the Matlab mathematical package. To solve the conditional optimization problem, a sequential quadratic programming method-based model was used. The interaction between software add-ins in Matlab and Aspen Hysys is implemented using a Component Object Model interface.Results. Approaches to obtain the lower and upper bounds of the optimality criterion and the branching method for the implementation of the branch and bound method have been developed. In addition, an algorithm for the optimal design of a distillation column of a given topology based on the branch and bound method has been developed. Furthermore, using Matlab, a software package that implements the developed algorithm and is integrated with the universal modeling software AspenHysys has been created.Conclusions. An algorithm and a software package have been developed and implemented that allows automating the design process of distillation column systems and integration with advanced mathematical programming packages, respectively. The performance of the algorithm and software package has been evaluated using the optimal design of the debutanization column as an example.

A survey on fractionation: the optimal control of distilling in batch and semibatch configurations

Abstract Since the middle of the last century, discussion about the operation of discontinuous fractionation to meet multifarious goals, such as product purity and recovery rate, by monitoring process variables including reflux or/and heat duty, is been on. The engineering practice showed intolerable events to occur; hereof the operation must be supervised, which makes it difficult to be in agreement with the batch distillation objectives. Hence, to uphold the effectuation of new operating policies into the industrial “know-how” techniques, different optimal control strategies can be conceived. The objective of this work is to offer a literature survey on the investigations of optimal control functioning for selected simple distillation column configurations employed in batch/semibatch distillation of homogeneous/reactive mixtures, as well as the approaches used in this regard. Available optimal control schemes have been reviewed in detail, emphasizing its major assets.

A graphical method for the preliminary design of ternary simple distillation columns at finite reflux

The present study proposes a graphical method for the design of ternary distillation systems at finite reflux. Here key design parameters are determined, in particular feed stage location and the number of theoretical stages required for separation at finite reflux for ideal and nonideal systems in simple columns. The procedure provides designers with a visual tool to determine the design parameters simultaneously and no additional calculations are required unlike current approaches. The proposed graphical method correlated to the Fenske-Underwood-Gilliland (FUG) method for ideal systems. The parameters obtained from the proposed graphical allow for implementation in rigorous simulators as starting values to achieve a converged column with the first simulation and less computational difficulty.

Design and control of a novel side-stream extractive distillation column for separating methanol-toluene binary azeotrope with intermediate boiling entrainer

It is innovative and important to perform complex binary azeotrope separation via single distillation column. In the article, design and control of a novel and simple side-stream extractive distillation (SSED) column with extraction and solvent recovery function is investigated for the separation of methanol and toluene binary azeotrope with intermediate boiling triethylamine (Et3N) as solvent. The steady-state design parameters of the novel SSED column are optimized and obtained with the objective of minimal total annual cost (TAC) via conventional sequential iterative procedure. On the basis of steady-state design, four single-end temperature control structures (STCS), four dual-temperature control structures (DTCS) and four dual-composition control structures (DCCS) are developed and established successively to overcome the operation and control challenges caused by the novel scheme. To seek the robust control, the dynamic performance analysis on account of the above control structures is conducted for the SSED column, which is evaluated for feed flowrates and composition disturbances. The results show that the control performance of DCCS is significantly superior to that of STCS and DTCS while the integral squared error (ISE) and energy-consuming effect are equivalent, and can take shorter time to bring the product purities back to the original steady state in coping with specified feed disturbances.

Simulation and Parametric Study of the Innovative Process to Produce High Purity Isopropyl Acetate with Ethylene Oxide Hydration as an Auxiliary Reaction

Production of high purity isopropyl acetate by esterification is a difficult process since the equilibrium conversion is relatively low and there are azeotropes between isopropyl acetate with water and between isopropyl acetate with the reactants. In this research, an innovative process to produce high purity isopropyl acetate with auxiliary reaction of ethylene oxide hydration was proposed. The process consisted of a reactor and a simple distillation column. The auxiliary reaction abolished the water/isopropyl acetate azeotrope and shifted the esterification equilibrium to the right. Impacts of the reactor type, the feed temperature, the reflux ratio, and the bottoms rate were investigated by simulating the process in Aspen Plus software. The results revealed that the innovative IpAc production with auxiliary reaction of EO hydration gave very high esterification conversion (up to 99.8%) and very high purity of IpAc (up to 99.7%). These results were achieved when the reactor type was isothermal at feed temperature, the feed temperature was 77°C, the reflux ratio was 1, and the bottoms rate was 10 kmol/h.

From graphical to model‐based distillation column design: A McCabe‐Thiele‐inspired mathematical programming approach

AbstractWe propose a mixed‐integer nonlinear programming (MINLP) model for simple and complex distillation column design and optimization. The model is based upon the concepts and equations underpinning the McCabe‐Thiele method. Generalizing this method, we introduce material balances at various locations of the column and employ binary variables to determine the optimal number of trays and optimal feed locations. We model the vapor–liquid equilibrium using continuous piecewise linear approximating functions. The model is extended to account for multicomponent mixtures and non‐constant‐molar overflow. We also discuss how to estimate the minimum number of trays and the minimum reflux ratio.

Techno-economic modeling and optimization of catalytic reactive distillation for the esterification reactions in bio-oil upgradation

Equilibrium reactive distillation (RD) process simulation and economic evaluation were carried out for the esterification of complex mixtures of several fatty acids and water (representative of crude bio-oils) with n-butanol using Aspen PLUS process simulator and economic analyzer. Complete design and optimization were carried out using evolutionary techniques from simplest system to the most rigorous one with introduction of intermittent progressive complexity. Prior to distillation design, esterification reaction kinetics and binary/ternary interactions were analyzed using Aspen RGibbs reactor module and Property PLUS, respectively. Simple distillation column was designed and optimized to obtain the initial trial parameters to be used in RD simulation. UNIQUAC is used as base property method and reaction equilibria estimated by minimization of Gibbs free energy. Near atmospheric column pressure, reflux ratio of 0.95, distillate to feed ratio of 0.505 and total 18 stages were found to be optimum based on attainable reaction conversion, ester separation, heat duties, and capital and operating costs. The effects of n-butanol:acid feeding ratio and water percent in bio-oil and their relationship were also analyzed to predict n-butanol requirement. The results of this study, including the optimized parameters, could serve as design platforms for pyrolysis bio-oil upgradation to transportation fuels.

Flexibility analysis of a distillation column: Indexes comparison and economic assessment

The worldwide shared definition of “optimal design” refers to the cheapest and simplest design able to perform the required job; most of the time this definition is strictly related to given operating conditions, i.e. the input variables are seldom subjected to considerable variations. However, in process engineering, plenty of cases don’t fit this definition due to the uncertain nature of the feedstock needed to be processed. Therefore, if a system is likely to undergo several and substantial perturbations, an a priori flexibility assessment can be crucial for the good performance of the operation. In chemical engineering the leading separation process is distillation. Hence the first purpose of this paper is to define a procedure and compare the different flexibility indexes found in literature in order to perform a simple distillation column flexibility assessment. The second goal of this paper is to couple the flexibility and economic aspects related to the distillation column investment costs and again to compare the different indexes economic behaviours.

Optimization of Distillation Sequence Based on Integration of Reaction-Separation System

On the basis of the integration of reaction and distillation systems, a systematic method is proposed for optimizing the distillation sequence with components separated individually by simple distillation columns and analyzing the effect of reactor parameters. Matrixes are employed to illustrate splits and distillation sequences; the distribution law of elements in the matrixes and the universal logical algorithm are deduced for identifying the structure of distillation sequence. With the reaction kinetics and material balance incorporated, the procedure is developed for targeting the optimal distillation sequence with the minimum vapor rate. On the basis of this method, the optimal distillation sequence at different reaction conditions can be identified, as well as the optimal reactor parameters. The proposed method is used to analyze the reaction–separation system of a styrene unit, and the results are consistent with the energy consumptions obtained by the rigorous simulation of Aspen Plus.

A cost-effective retrofit of conventional distillation sequence to dividing-wall prefractionator configuration

A dividing-wall prefractionator configuration was investigated for a safe and economic retrofit of the conventional sequence using simple distillation columns. In the proposed retrofit configuration, the first column was modified to a dividing wall column as a prefractionator to supply prefractionated multi-feeds to the subsequent column. To investigate the effectiveness of the proposed configuration, nine near-ideal feed mixtures were considered for analysis. The proposed configuration was then compared with several other alternative configurations. The proposed dividing-wall prefractionator efficiently generates prefractionated multi-feed streams avoiding feed mismatch and remixing effect with low modification cost. Moreover, because the proposed retrofit configuration allows for flexible switching between the dividing-wall prefractionator and the conventional operating mode, a safe retrofit is also ensured by reducing the operational risks. Several industrial retrofit cases were studied to validate the proposed dividing-wall prefractionator configuration.

Alternative Petlyuk Distillation Configurations for the Separation of Four-Component Mixtures

The Petlyuk configuration represents an attractive alternative to the simple distillation column sequences because of its potential in energy saving. This point was extensively discussed for three-component mixtures. Moving to quaternary mixtures the complexity of the Petlyuk configuration represents the main barrier of its possible implementation in the industrial practice. In the present work, a set of new alternative distillation configurations to the four-component Petlyuk is presented. A hydrocarbon and an alcohol mixture are considered to prove their applicability. The total annual cost, together with the thermodynamic efficiency and the carbon dioxide emissions, are considered as comparison index between the Petlyuk and the alternative configurations. The results obtained proved that for the cases considered at least one of the alternative configurations showed a better or at least the same performance of the Petlyuk arrangement. For this reason, the new configurations are worth of consideration wh...

Synthesis of optimal systems of simple distillation columns with heat recovery

Synthesis of optimal systems of simple distillation columns with heat recovery

Optimal Synthesis of Ethylene Production Process

This work addresses the energetic and economic optimization for the synthesis of distillation-based ethylene production. We employ a model-based optimization approach to determine the optimal sequencing of processes for olefins separation that involves handling a multicomponent mixture. The optimization model is formulated based on a superstructure that embeds many possible and feasible structural alternatives for processing a number of hydrocarbon components constituting gaseous ethane or liquid naphtha. We adopt linear mass balance reactor models for conversion of materials into desirable products and simple sharp distillation column models based on split fractions for product recovery from a multicomponent feed stream. The formulation leads to a mixed-integer linear program (MILP) with discrete 0–1 variables on task selection and continuous variables on input flowrate to each task. To aid convergence to the optimal system synthesis with minimum total annualized cost, the model incorporates heuristic-based logical constraints that represent design and structural specifications on engineering knowledge, design experience, and rules of thumb. The model is implemented on case studies drawn from actual operating petrochemical plants in Malaysia with reasonable computational results.

Energy saving processes of biofuel production from fermentation broth

The energy used for distillation in bioethanol production reaches the 40 % of the total energy demand. The pervaporation is an important alternative process to distillation that can be applied as a hybrid process or even as a single process to produce high quality biofuel. It will be shown how the energy demand, MJ/kgEthanol energy, can be saved applying pervaporation process with different separation factors and operating modes. It is stated that relatively high separation factor is needed to lower the energy demand below a simple distillation column.

A techno‐economic comparison of various process options for the production of 1,1‐diethoxy butane

AbstractBACKGROUND: Acetals can be considered important bio‐based diesel additives. The production of most of these compounds, from an alcohol and an aldehyde, suffers from low conversion due to thermodynamic limitations. These limitations can be overcome through the removal of the by‐product water. Previous studies showed that the in situ dehydration options of reactive distillation and pervaporation membrane reactor integration offer little advantage or at least not at reasonable unit dimensions. The aim of the present work is the development of a membrane based process and comparison with other alternatives (based on experimental data).RESULTS: Three different membrane processes were developed. The one in which the reaction mixture is recycled over a first dehydration membrane module and subsequently through a simple distillation column, was found to give the highest overall conversion (100%) at low recycle rates and reasonable membrane area. This process was techno‐economically compared with other possible alternatives: (1) a process based on a conventional tubular reactor and several distillation columns; and (2) a process based on reactive distillation.CONCLUSIONS: Efficient water removal by membranes avoids possible azeotropes in downstream distillation units making them much simpler, reducing considerably the unit sizes and the energy demand (40% lower). Copyright © 2012 Society of Chemical Industry

Short-cut methods for the optimal design of simple and complex distillation columns

New short-cut methods providing optimal design parameters for distillation columns with simple and complex configurations including two-feed and one-feed-one-side-stream columns are presented. The methods assume constant relative volatilities and constant molar flow rates within each distillation section. The design equations are based on the Underwood equations for the calculation of minimum reflux (reboil) ratio, the analytical formulations of the distillation line, the Eigenfunction and the number of theoretical stages for each mass transfer section of the column. Furthermore, the geometrical properties of a given separation are considered. Optimization algorithms based on the minimization of the total number of theoretical stages of the column with taking into account the mass balance at each feed section have been elaborated. In comparison to the boundary value method the new short-cut methods require a minimum number of specifications; they do not need any graphical support, and provide a lower total number of theoretical stages particularly for complex configurations. The new short-cut methods have been extended to the design of columns separating azeotropic mixtures by approximating the latter by appropriate pseudo-ideal mixtures. Several separation examples for azeotropic mixtures, including different types of splits as well as columns with simple and complex configurations were tested and show a very good agreement with the simulation results obtained with Radfrac (Aspenplus).

Externally Heat-Integrated Double Distillation Column (EHIDDiC): Basic Concept and General Characteristics

In terms of the thermodynamic characteristics of simple distillation columns, a novel schematic of an externally heat-integrated double distillation column (EHIDDiC) is proposed and studied in this work. It consists of high-pressure and low-pressure distillation columns, with external heat integration between the whole rectifying section of the former and the whole stripping section of the latter. In comparison with conventional distillation systems (i.e., direct and indirect separation sequences), the EHIDDiC was found to require relatively small capital investment and low operating costs. It can even outperform conventional distillation systems with the condenser/reboiler type of heat integration under some favorable operating conditions. In terms of the separation of a ternary ideal mixture containing hypothetical components A, B, and C, the EHIDDiC was evaluated through intensive comparisons with its conventional counterparts. Sensitivity analysis was also conducted with respect to some relevant physical properties and design parameters, including the relative volatilities, feed composition, external heat-transfer area per stage, product specifications, and utility costs. It was confirmed that the EHIDDiC can be advantageous over conventional distillation systems with and without condenser/reboiler-type heat integration, and the results obtained reflect the salient characteristics of the EHIDDiC.