DOCSLIB.ORG

Improving the Distillation Energy Network

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Improving the Distillation Energy Network Improving the distillation energy network Energy-efficient design applied to the refit of a distillation unit was achieved through optimisation between the distillation column and heat network system SOUN HO LEE GTC Technology KWANG GIL MIN GS Caltex Corporation nergy costs are the largest process conditions. The following location is a section of the distilla- percentage of a hydrocarbon are common strategies that can be tion column where the composition Eplant’s operating expenditures. applied to practical energy of column internal liquid traffic is This is especially true of the distil- improvement projects. similar to feed stream composition. lation process, which requires In this case, the composition gradi- substantial energy consumption. Feed temperature ent between feed stream and Concerns over recent high costs Feed temperature is a major factor distillation internal fluids is mini- and economic pressures continually influencing the overall heat balance mised. In actual operation of the emphasise the need for efficient of a distillation column system. distillation column, feed composi- distillation design and operation Increments in the feed enthalpy can tions are often changed from the without a loss of performance. help reduce the required energy original design conditions. In cases This article illustrates how input from the reboiler at the same of significant deviation, discrepancy energy-efficient design can be degree of separation. Installing a between column internal liquid applied in a distillation unit through feed preheater is a very common composition and feed stream optimisation between the distillation process option to minimise reboiler composition can increase, which column and heat network system. heat duty. If the feed preheater can results in a non-optimum feed loca- Through a case study, a successful be integrated with other valuable tion. Therefore, evaluating feed retrofit of an aromatics distillation process streams (as a heating location is an essential step for unit is discussed. Detailed retrofit medium), overall energy efficiency successful distillation unit energy activities, including complex heat of the distillation system can be improvement. network evaluation, process simula- improved further. However, tion modelling and energy-friendly, increasing the feed temperature Inter-condensers and inter-reboilers high-performance distillation equip- does not always improve the over- Adding inter-condensers and/or ment implementation, are described. all energy efficiency of a distillation inter-reboilers can help improve unit. Excessive feed temperature overall energy efficiency. Strategies for improving the increments can cause a significant Pumparound, one of the inter- distillation energy network amount of flash of heavy key and condenser concepts, has been As continuous distillation requires non-key components at the distilla- widely applied to numerous petro- simultaneous heat input and tion column feed zone. In this case, leum multi-product fractionators. removal (thus requiring significant a higher amount of reflux stream is On the other hand, implementing energy consumption), complex heat necessary to maintain required an intermediate reboiler can reduce integration becomes more common overhead distillate purities. This the main reboiler duty. As the for modern distillation units to augmented reflux ratio thus required temperature of an inter- improve unit energy efficiency. requires a higher boil-up ratio. mediate reboiler is lower than that Since a distillation column’s degree Overall energy efficiency is eventu- of the main reboiler, this strategy of separation and enthalpy balance ally aggravated.1 Therefore, careful may allow heat integration with influence each other, it is critical to review of the feed temperature and other valuable heat sources that are evaluate and optimise the distilla- phase is critical to minimise the not as costly or not fully utilised in tion column and heat exchanger overall energy consumption of the the plant. networks together in order to distillation unit. maximise plant economics. Column operating pressure There are numerous strategies to Feed location Relaxation of the column top oper- improve the energy efficiency of Improper feed location of a distilla- ating pressure decreases the distillation processes, with the tion column can also increase the distillation column’s temperature amount of improvement through reflux/boil-up ratio and energy profile and results in a lower each strategy varied according to consumption. An ideal feed reboiler duty. It has been observed www.eptq.com Revamps 2013 3 The function of the xylene column is to separate the feed mixture to xylene components and heavier C9+ components. This column has two different feed sources. The reformate splitter bottom stream and the toluene column bottom stream (which belongs to the aromatic extraction Reflux ratio unit) are introduced as the xylene column bottom feed stream. The Steep Moderate Flat sensitivity sensitivity zone sensitivity zone zone bottom feed stream is split equally and charged to two different feed trays. The reformate splitter’s Theoretical stage bottom stream is treated at the clay towers to eliminate traced olefin Figure 1 Typical column efficiency vs reflux ratio curve components before charging to the xylene column. Meanwhile, the that numerous commercial distilla- analysis. A typical curve is shown deheptaniser bottom stream (from tion columns have been operated in Figure 1. This curve visualises the xylene isomerisation unit) is with lower operating pressures column efficiency sensitivity and charged as the xylene column top than their original design values. energy-saving gain. The curve can feedstock. This stream is also split However, this strategy is not appli- be categorised by three district and introduced to three different cable to columns operated under an zones: steep, moderate and flat feed trays. atmospheric pressure range. sensitivity.2 The xylene column overhead Column overhead circuit pressure Column efficiency improvement vapour stream is split into three drop and condenser temperature is usually very feasible when the parallel streams. Two vapour approaches both heavily influence reflux ratio falls into the steep streams are utilised as the heat feasibility. In addition, column sensitivity zone and at ratios source of the extract column pressure reduction expands vapour considerably in excess of the mini- reboiler and the raffinate column traffic and pushes the limits of mum reflux ratio. In this scenario, reboiler, respectively. The existing distillation equipment. even the small addition of stages, condensed xylene column overhead or an increase in distillation equip- liquid streams are returned to the Column pressure drop ment efficiency, can enhance overall xylene column receiver. The other Reducing column pressure drop column separation with significant vapour stream is supplying heat to can lower reboiler duty at the same energy reductions. the xylene column overhead steam degree of separation. The amount Improvement gain is diluted in generator, which produces #250 of reboiler duty saving relies on the moderate sensitivity zone. steam. The condensed overhead operating pressure and enthalpy Further detailed feasibility study is liquid stream is also returned to the balance. This strategy is generally necessary through economic analy- xylene column receiver. The over- feasible when the distillation sis. The magnitude of energy head distillate of the xylene column column is operated under vacuum savings is negligible when reflux is sent to the paraxylene recovery pressure range. Meanwhile, pres- ratio variation follows flat motion unit. sure drop improvement does not in the remaining zone. In the xylene column reboiler often provide noticeable energy circuit, the xylene column bottom savings in high-pressure range Case study: unit description reboiler inlet stream is first trans- distillation service. The following is a revamp case ported to the other two distillation study of a xylene mixture separa- column reboilers as heating medi- Column efficiency improvement tion unit that demonstrates ums. After providing heat to these Column efficiency improvement well-thought-out, proven design reboilers, the xylene column bottom can reduce the reflux/boil-up ratio practices and a selection of the streams are combined and intro- at a given degree of separation. correct, high-efficiency distillation duced to the furnace-type xylene This strategy can be delivered by equipment to fulfill the improve- column reboiler. increasing the number of theoreti- ment in energy efficiency. Figure 2 In the paraxylene recovery unit, cal stages and/or enhancing the illustrates the xylene mixture sepa- the xylene components from the efficiency of distillation equipment. ration unit’s configurations under xylene column are separated The feasibility can be gauged by a discussion. This schematic reveals through the adsorption process. dedicated sensitivity analysis. that the original distillation units The pre-separated extract stream Constructing a column efficiency have implemented the full heat from the adsorption process is curve with a reflux ratio is one of integration network for energy- charged to the extract column in the core tools for sensitivity efficient operation. order to separate paraxylene from 4 Revamps 2013 www.eptq.com the desorbent. At the same time, the pre-separated raffinate stream Extract from the adsorption process is column charged to
Load more

Recommended publications
  • Distillation 6
    CHAPTER Energy Considerations in Distillation 6 Megan Jobson School of Chemical Engineering and Analytical Science, The University of Manchester, Manchester, UK CHAPTER OUTLINE 6.1 Introduction to energy efficiency ....................................................................... 226 6.1.1 Energy efficiency: technical issues................................................... 227 6.1.1.1 Heating.................................................................................... 227 6.1.1.2 Coolingdabove ambient temperatures...................................... 229 6.1.1.3 Coolingdbelow ambient temperatures ...................................... 230 6.1.1.4 Mechanical or electrical power.................................................. 232 6.1.1.5 Summarydtechnical aspects of energy efficiency ..................... 233 6.1.2 Energy efficiency: process economics............................................... 233 6.1.2.1 Heating.................................................................................... 233 6.1.2.2 Cooling..................................................................................... 235 6.1.2.3 Summarydprocess economics and energy efficiency ............... 237 6.1.3 Energy efficiency: sustainable industrial development........................ 237 6.2 Energy-efficient distillation ............................................................................... 237 6.2.1 Energy-efficient distillation: conceptual design of simple columns...... 238 6.2.1.1 Degrees of freedom in design ..................................................
    [Show full text]
  • Review of Extractive Distillation. Process Design, Operation
    Review of Extractive Distillation. Process design, operation optimization and control Vincent Gerbaud, Ivonne Rodríguez-Donis, Laszlo Hegely, Péter Láng, Ferenc Dénes, Xinqiang You To cite this version: Vincent Gerbaud, Ivonne Rodríguez-Donis, Laszlo Hegely, Péter Láng, Ferenc Dénes, et al.. Review of Extractive Distillation. Process design, operation optimization and control. Chemical Engineering Research and Design, Elsevier, 2019, 141, pp.229-271. 10.1016/j.cherd.2018.09.020. hal-02161920 HAL Id: hal-02161920 https://hal.archives-ouvertes.fr/hal-02161920 Submitted on 21 Jun 2019 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Open Archive Toulouse Archive Ouverte OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible This is an author’s version published in: http://oatao.univ-toulouse.fr/239894 Official URL: https://doi.org/10.1016/j.cherd.2018.09.020 To cite this version: Gerbaud, Vincent and Rodríguez-Donis, Ivonne and Hegely, Laszlo and Láng, Péter and Dénes, Ferenc and You, Xinqiang Review of Extractive Distillation. Process design, operation optimization and control. (2018) Chemical Engineering Research and Design, 141.
    [Show full text]
  • Distillation Theory
    Chapter 2 Distillation Theory by Ivar J. Halvorsen and Sigurd Skogestad Norwegian University of Science and Technology Department of Chemical Engineering 7491 Trondheim, Norway This is a revised version of an article published in the Encyclopedia of Separation Science by Aca- demic Press Ltd. (2000). The article gives some of the basics of distillation theory and its purpose is to provide basic understanding and some tools for simple hand calculations of distillation col- umns. The methods presented here can be used to obtain simple estimates and to check more rigorous computations. NTNU Dr. ing. Thesis 2001:43 Ivar J. Halvorsen 28 2.1 Introduction Distillation is a very old separation technology for separating liquid mixtures that can be traced back to the chemists in Alexandria in the first century A.D. Today distillation is the most important industrial separation technology. It is particu- larly well suited for high purity separations since any degree of separation can be obtained with a fixed energy consumption by increasing the number of equilib- rium stages. To describe the degree of separation between two components in a column or in a column section, we introduce the separation factor: ()⁄ xL xH S = ------------------------T (2.1) ()x ⁄ x L H B where x denotes mole fraction of a component, subscript L denotes light compo- nent, H heavy component, T denotes the top of the section, and B the bottom. It is relatively straightforward to derive models of distillation columns based on almost any degree of detail, and also to use such models to simulate the behaviour on a computer.
    [Show full text]
  • Distillation ­ Accessscience from Mcgraw­Hill Education
    6/19/2017 Distillation ­ AccessScience from McGraw­Hill Education (http://www.accessscience.com/) Distillation Article by: King, C. Judson University of California, Berkeley, California. Last updated: 2014 DOI: https://doi.org/10.1036/1097­8542.201100 (https://doi.org/10.1036/1097­8542.201100) Content Hide Simple distillations Fractional distillation Vapor­liquid equilibria Distillation pressure Molecular distillation Extractive and azeotropic distillation Enhancing energy efficiency Computational methods Stage efficiency Links to Primary Literature Additional Readings A method for separating homogeneous mixtures based upon equilibration of liquid and vapor phases. Substances that differ in volatility appear in different proportions in vapor and liquid phases at equilibrium with one another. Thus, vaporizing part of a volatile liquid produces vapor and liquid products that differ in composition. This outcome constitutes a separation among the components in the original liquid. Through appropriate configurations of repeated vapor­liquid contactings, the degree of separation among components differing in volatility can be increased manyfold. See also: Phase equilibrium (/content/phase­equilibrium/505500) Distillation is by far the most common method of separation in the petroleum, natural gas, and petrochemical industries. Its many applications in other industries include air fractionation, solvent recovery and recycling, separation of light isotopes such as hydrogen and deuterium, and production of alcoholic beverages, flavors, fatty acids, and food oils. Simple distillations The two most elementary forms of distillation are a continuous equilibrium distillation and a simple batch distillation (Fig. 1). http://www.accessscience.com/content/distillation/201100 1/10 6/19/2017 Distillation ­ AccessScience from McGraw­Hill Education Fig. 1 Simple distillations. (a) Continuous equilibrium distillation.
    [Show full text]
  • Computer Simulation Applied to Studying Continuous Spirit Distillation and Product Quality Control
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Elsevier - Publisher Connector Food Control 22 (2011) 1592e1603 Contents lists available at ScienceDirect Food Control journal homepage: www.elsevier.com/locate/foodcont Computer simulation applied to studying continuous spirit distillation and product quality control Fabio R.M. Batista, Antonio J.A. Meirelles* Laboratory EXTRAE, Department of Food Engineering, Faculty of Food Engineering, University of Campinas e UNICAMP, Campinas, Brazil article info abstract Article history: This work aims to study continuous spirit distillation by computational simulation, presenting some Received 7 June 2010 strategies of process control to regulate the volatile content. The commercial simulator Aspen (Plus and Received in revised form dynamics) was selected. A standard solution containing ethanol, water and 10 minor components rep- 2 March 2011 resented the wine to be distilled. A careful investigation of the vaporeliquid equilibrium was performed Accepted 8 March 2011 for the simulation of two different industrial plants. The simulation procedure was validated against experimental results collected from an industrial plant for bioethanol distillation. The simulations were Keywords: conducted with and without the presence of a degassing system, in order to evaluate the efficiency of Spirits fi Distillation this system in the control of the volatile content. To improve the ef ciency of the degassing system, fl Simulation a control loop based on a feedback controller was developed. The results showed that re ux ratio and Aspen Plus product flow rate have an important influence on the spirit composition. High reflux ratios and spirit Degassing flow rates allow for better control of spirit contamination.
    [Show full text]
  • Distillation Technology and Modelling Techniques
    ● DISTILLATION Distillation Technology and Modelling Techniques Commercial distillations Part 1: Concepts in Distillation Instead of the single-stage batch pot still described above, commercial In this review of distillation technology and modelling distillations are typically performed in a continuous manner, with multiple techniques, Konrad Miller and Katherine Shing offer a pot still equivalents (or ‘stages’) used broad survey of the science of distillation, including a to increase separation power. Consider conceptual framework of distillation; distillation column the set-up in Figure 1. Three pot stills are connected in a series of stages; components and, in part two, shortcut distillation design where the vapour from one stage rises methods such as the McCabe Thiele method and the and intermingles with the liquid in the stage above it, and liquid from a stage Fenske Underwood Gilliland algorithm. In part three, drains down to intermingle with the Konrad Miller will apply these principles to the production vapour in the stage below it. Since a series of connected pot processes of a modern brandy distillery. stills is an ineffi cient and needlessly complex design, distillation columns hat is distillation? Think back to water, so imagine your parents were are used industrially to achieve the Wyour childhood, when you fi rst boiling wine for a sauce. Water boils at same results. The internals of a distil- observed a pan of boiling water: you 100°C, but ethyl alcohol (the alcohol in lation column are comprised of a se- watched water vapour rise from the the wine) boils at 78.4°C. The liquid no ries of ‘plates’ or ‘trays’, each of which liquid surface at a temperature of ap- longer boiled at 100°C, but now some- allows for the thorough mixing of proximately 100°C (212°F).
    [Show full text]
  • Design of Batch Distillation Columns Using Short-Cut Method at Constant Reflux
    Hindawi Publishing Corporation Journal of Engineering Volume 2013, Article ID 685969, 14 pages http://dx.doi.org/10.1155/2013/685969 Research Article Design of Batch Distillation Columns Using Short-Cut Method at Constant Reflux Asteria Narvaez-Garcia,1 Jose del Carmen Zavala-Loria,2 Luis Enrique Vilchis-Bravo,1 and Jose Antonio Rocha-Uribe1 1 Universidad Autonoma de Yucatan, (UADY), Periferico Norte km 33.5, 97203 Merida, YUC, Mexico 2 Universidad Autonoma del Carmen, (UNACAR), Calle 56 No. 4, Colonia Benito Juarez, 24180 Ciudad del Carmen, CAM, Mexico Correspondence should be addressed to Jose Antonio Rocha-Uribe; [email protected] Received 17 December 2012; Revised 12 March 2013; Accepted 20 March 2013 Academic Editor: M. Angela Meireles Copyright © 2013 Asteria Narvaez-Garcia et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. A short-cut method for batch distillation columns working at constant reflux was applied to solve a problem of four components that needed to be separated and purified to a mole fraction of 0.97 or better. Distillation columns with 10, 20, 30, 40, and 50 theoretical stages were used; reflux ratio was varied between 2 and 20. Three quality indexes were used and compared: Luyben’s capacity factor, total annual cost, and annual profit. The best combinations of theoretical stages and reflux ratio were obtained for each method. It was found that the best combinations always required reflux ratios close to the minimum.
    [Show full text]
  • Optimization and Dynamics of Distillation Column Using Aspen Plus®
    Available online at www.sciencedirect.com ScienceDirect Procedia Engineering 148 ( 2016 ) 978 – 984 4th International Conference on Process Engineering and Advanced Materials Optimization and Dynamics of Distillation Column using Aspen Plus® Syed A. Taqvia , Lemma Dendena Tufaa,*, Shuhaimi Muhadizira aChemical Engineering Department, Universiti Teknologi Petronas, 32610 Bandar Seri Iskandar, Perak Darul Ridzuan, Malaysia Abstract Ever increasing global energy demand necessitates the need to enhance energy generation and efficient utilization. As energy prices continue to rise, energy conservation is the prime concern for every industry. Distillation is probably the most studied unit operation in terms of optimization and control. Since distillation columns are major energy-intensive units in chemical plants and given the recent increase in fuel cost, the plant engineers are obliged to find better operating strategies and control systems. One of the significant sections that can be worked upon is finding the optimum feed tray locations of distillation columns. The energy consumptions during distillation can have a strong impact on overall profitability. Hence, the optimization of a column is aimed towards greater production and an increase in quality. Since a column is multivariable system, disturbance in any parameter can affect the overall performance as well as production loss. This paper shows how an acetone manufacturing process can be conveniently simulated first to get temperature, pressure and composition profile followed by application of optimization techniques to enhance performance. It was performed by the means of using a simulator Aspen Plus®. Rebolier heat duty (MW) and minimum reflux ratio were successfully optimized by manipulating feed stage location and number of stages respectively.
    [Show full text]
  • Workshop 12: Instruction Sequence
    Materials for Participants – Module Instruction Sequence and Problem Statements by Core Course Workshop 12 “Simulators for Design Across the Curriculum” ASEE Summer School, Colorado, August 2002 Workshop Leaders: Daniel R. Lewin (DRL), Dept. of Chemical Engineering, Technion. Warren D. Seider (WDS), Dept. of Chemical Engineering, Penn. Workshop Objective: During the senior year design project, teams of students carry out an integrated process design, determining its technical, environmental, safety, and economic feasibility. Due to the problem scale, this inevitably involves the use of a process simulator to formulate and solve the material and energy balances, with phase and chemical equilibria and chemical kinetics, for cost estimation and economic evaluation. The availability of a reliable process model allows the design team to assess rapidly the economic potential for alternative designs, as well as to derive operating conditions using optimization methods that incorporate economics. To ensure that students are prepared to meet the challenges of the design project, they should be prepared for the competent and critical use of the process simulators. This is best achieved by a gradual exposure to aspects of their use through various exercises in the core courses. This workshop, which is intended for chemical engineering faculty, shows one way to achieve this objective. Contents: This document is an assembly of: (1) suggested instruction sequences, using the multimedia CD-ROM (Using Process Simulators in Chemical Engineering: A Multimedia Guide for the Core Curriculum), henceforth referred to as the multimedia, and (2) problem statements and solutions for class exercises and projects using process simulators to support many of the chemical engineering core courses.
    [Show full text]
  • Batch Processing
    4 Batch Distillation CONTENTS 4.1 Early Theoretical Analysis ........................................... 43 4.1.1 Simple Distillation ............................................. 45 4.1.2Copyrighted Operating Modes ............................................... 46 4.2 Hierarchy of Models .................................................. 53 4.2.1 Rigorous Model ................................................ 53 4.2.2 Low Holdup Semirigorous Model .............................. 53 4.3 Shortcut Model ........................................................ 55 4.4 Optimization and Optimal Control ................................... 58 4.5 Complex Systems ...................................................... 59 4.5.1 Azeotropic Distillation ......................................... 60 4.5.2 Reactive DistillationMaterial........................................... 61 4.6 Computer Aided Design Software ..................................... 62 4.7 Summary .............................................................. 63 Notations .............................................................. 63 - Batch distillation1 is the oldest separation processTaylor and the most widely used unit operation in pharmaceutical and specialty chemical industries. The most outstanding feature of batch distillation is its flexibility. This flexibility allows one to deal with uncertainties in feed stock or product specification. In the distillation process, it is assumed that the vapor& formed within a short pe- riod is in thermodynamic equilibrium with the liquid.
    [Show full text]
  • Batch Distillation Ki-Joo Kim Postdoctoral Researcher, Systems Analysis Branch, U.S
    DK3017_C005.fm Page 107 Wednesday, April 27, 2005 9:24 AM 5 Batch Distillation Ki-Joo Kim Postdoctoral Researcher, Systems Analysis Branch, U.S. Environmental Protection Agency, Cincinnati, OH ([email protected]) Urmila Diwekar Professor, BioEngineering, Chemical, and Industrial Engineering, University of Illinois, Chicago ([email protected]) CONTENTS 5.1 Introduction..............................................................................................108 5.2 Early Theoretical Analysis ......................................................................112 5.2.1 Simple Distillation.......................................................................112 5.2.2 Operating Modes .........................................................................114 5.2.2.1 McCabe–Thiele Graphical Method .............................114 5.2.2.2 Constant Reflux Mode .................................................115 5.2.2.3 Variable Reflux Mode..................................................117 5.2.2.4 Optimal Reflux Mode ..................................................118 5.3 Hierarchy of Models................................................................................120 5.3.1 Rigorous Model...........................................................................121 5.3.2 Low Holdup Semirigorous Model ..............................................124 5.3.3 Shortcut Model and Feasibility Considerations..........................125 5.3.4 Collocation-Based Models ..........................................................127 5.3.5 Model
    [Show full text]
  • Design Concept of Crude Oil Distillation Column Design
    2/16/2015 NPTEL :: Chemical Engineering ­ Petroleum Refinery Engineering Design concept of crude oil distillation column design. Distillation Column Design The design of a distillation can be divided in the following steps. Specify the degree of separation:­ Set product specification. Select the operating conditions:­ Operating pressure. Determine the stage and reflux requirement:­ The number of equilibrium stages. Select type of contacting device:­ Plates or packing. Size the column:­ Diameter, number of real stages. Design the column internals:­ Plates,Distributors,Packing Supports etc. Mechanical design:­ Vessel and Internal fittings. Arrangement of Towers Three types of arrangements ( How heat is removed) 1. Top Tray Reflux : Reflux is only at top tray only Reflux is cooled and sent into the Tower. Heat input: Through Tower bottom. Removal: at the top. Thus requires large tower diameter. Improper reflux and poor quality of fraction. Economic utilization of heat is not possible. 2. Pump back reflux. 3. Pump around Reflux. data:text/html;charset=utf­8,%3Ctable%20width%3D%2280%25%22%20border%3D%220%22%20align%3D%22center%22%20cellpadding%3D%220%22%… 1/24 2/16/2015 NPTEL :: Chemical Engineering ­ Petroleum Refinery Engineering Fig:2.25 Vacuum Distillation Unit Overview [7] Pump back Reflux: Reflux is provided at regular intervals. This helps every plate to act as a true fractionator.( because there is always good amount of liquid). Tower is uniformly loaded, hence uniform and lesser diameter tower will do. Heat from external refluc can be utilised as it is at progressively higher temperatures. However design of such tower is costly, but provides excellet service.
    [Show full text]