Energy-efficient recovery of tetrahydrofuran and ethyl acetate by triple-column extractive distillation:entrainer design and process optimization

An energy-efficient triple-column extractive distillation process is developed for recovering tetrahydrofuran and ethyl acetate from industrial effluent.The process development follows a rigorous hierarchical design procedure that involves entrainer design,thermodynamic analysis,process design and optimization,and heat integration.The computer-aided molecular design method is firstly used to find promising entrainer candidates and the best one is determined via rigorous thermodynamic analysis.Subsequently,the direct and indirect triple-column extractive distillation processes are proposed in the conceptual design step.These two extractive distillation processes are then optimized by employing an improved genetic algorithm.Finally,heat integration is performed to further reduce the process energy consumption.The results indicate that the indirect extractive distillation process with heat integration shows the highest performance in terms of the process economics.     

Retrofit of absorption heat pumps into manufacturing processes: Implementation guidelines

Integration of absorption heat pumps (AHP) in industrial processes has not yet been fully exploited due to the lack of clear implementation guidelines for this technology. In this work, a systematic methodology for the integration of AHPs in a process has been developed and is presented. Guidelines are formulated for the proper selection of heat sources and sinks that will maximise the benefit derived from heat pumping while respecting process constraints and operating requirements of the AHP. The principles of AHP operation and its efficient process integration are thus described. The methodology relies on data extracted from a Pinch Analysis of the plant. The advantages and outputs of the methodology are illustrated using an AHP implementation in a Kraft pulping process. Two realistic implementation options are presented along with their detailed design and preliminary economic evaluation.     

最小有效能损耗的多组分精馏流程优化设计

提出了以有效能损耗最小为目标、同时又考虑热集成的多组分复杂精馏塔序列优化设计新策略。该复杂精馏塔模型:1股进料、2股出料,每块理论板上均可有中间冷凝器或再沸器。复杂精馏过程的设计步骤是:①根据过程有效能最小确定优化塔序列;②对每个塔优化设计出含中间换热器的复杂塔;③考虑多效且允许热集成的复杂精馏流程,以塔压为决策变量,以精馏过程有效能损耗最小为目标,建立并优化设计出一个热集成的复杂精馏流程。一个3组分精馏过程的例子表明所提策略简单有效,可用来指导多组分精馏过程的优化设计。     

萃取精馏分离苯/环己烷共沸体系模拟与优化

以糠醛作为萃取剂分别使用常规萃取精馏、隔壁塔萃取精馏和差压热集成萃取精馏对苯和环己烷体系进行分离研究,使用流程模拟软件Aspen Plus V8.4进行模拟分析,对初步设计的三稳态流程,分别进行灵敏度分析,使用多目标遗传算法对过程进行整体优化以获得最优结构参数。结果表明,隔壁塔萃取精馏和差压热集成萃取精馏相对于常规萃取精馏所需再沸器热负荷可分别减小21.5%和15.7%。对三工艺流程进行经济性分析,发现与常规流程相比,隔壁塔萃取精馏的年总费用下降了6.0%,而差压热集成萃取精馏年总费用增加了50.8%,为萃取精馏分离苯/环己烷共沸体系工业化设计提供了理论依据和设计参考。     

Approximate design and cost evaluation of internally heat-integrated distillation columns (HIDiCs)

Commercial design programs do not provide a ready-to-use process simulation of tray-by-tray heat-integrated distillation columns, so the computation of the columns using the programs is difficult due to their convergence problem. An approximate procedure for the design of the internally heat-integrated distillation column (HIDiC) is proposed here, and its performance of the design and cost evaluation is demonstrated with two example processes. The approximate design procedure eliminates the artificial heat exchangers and in-tray streams required in the design with the commercial programs, and therefore no information of the exchangers and streams is necessary except the amount of the in-tray heat transfer rate. The economic evaluation indicates that a reduction of the total annual cost of 8.1% is possible with benzene-toluene process and that 59.3% is yielded with the propylene-propane process. The results also demonstrate that the HIDiC is especially efficient for the tight separation system.     

Economic value and environmental impact (EVEI) analysis of biorefinery systems

The selection of product portfolios, processing routes and the combination of technologies to obtain a sustainable biorefinery design according to economic and environmental criteria represents a challenge to process engineering. The aim of this research is to generate a robust methodology that assists process engineers to conceptually optimise the environmental and economic performances of biorefinery systems. A novel economic value and environmental impact (EVEI) analysis methodology is presented in this paper. The EVEI analysis is a tool that emerges from the combination of the value analysis method for the evaluation of economic potential with environmental footprinting for impact analysis. The methodology has been effectively demonstrated by providing insights into the performance of a bioethanol plant as a case study. The systematisation of the methodology allowed its implementation and integration into a computer-aided process engineering (CAPE) tool in the spreadsheet environment.     

Hybrid membrane and conventional processes comparison for isoamyl acetate production

Four process alternatives for the production of isoamyl acetate, by the liquid phase esterification of acetic acid with isoamyl alcohol, were evaluated by simulation in terms of product purity, energy integration and economics. The analysis involves a transition from conventional (two structures that use acetic acid or alcohol in excess) to hybrid membrane process (two distillation–pervaporation hybrid systems). Acetate recovery is identified as a crucial factor to minimize energy costs in all considered processes. For conventional processes, the amount of energy required for separation, at low acetate recovery levels, is considerably lower if acetic acid is used in excess. For the hybrid processes, there is an optimum value of acetate recovery that minimizes the total required heat duty and membrane area. Hybrid distillation–pervaporation process allows obtaining the specified product purity with lower energy requirements and more economical tradeoffs than the considered conventional processes. The economic optimum design maximizes energy savings and minimizes total annualized costs. After optimization and energy integration, the best process alternative includes, in a hybrid system, one packed bed reactor, two pervaporation units and a distillation column.     

Comparing three configurations of the externally heat-integrated double distillation columns (EHIDDiCs)

In terms of separation of a binary mixture of ethylene and ethane, three configurations of externally heat-integrated double distillation columns (EHIDDiCs), including a symmetrical EHIDDiC (S-EHIDDiC), an asymmetrical EHIDDiC (A-EHIDDiC), and a simplified asymmetrical EHIDDiC (SA-EHIDDiC), are compared with respect to aspects related to process design and controllability. It has been found that the A-EHIDDiC and SA-EHIDDiC are superior to the S-EHIDDiC in terms of thermodynamic efficiency as well as in terms of process dynamics and controllability. As for the comparison between the A-EHIDDiC and SA-EHIDDiC, the latter shows somewhat comparable behaviors with the former in terms of process design and controllability. These results demonstrate that the asymmetrical configuration should generally be favored over the symmetrical one for the development of the EHIDDiC. It is feasible to approximate external heat integration using three heat exchangers between the high- and low-pressure distillation columns involved.     

Process integration technology review: background and applications in the chemical process industry

Process integration is a holistic approach to process design and operation which emphasizes the unity of the process. Process integration design tools have been developed over the past two decades to achieve process improvement, productivity enhancement, conservation in mass and energy resources, and reductions in the operating and capital costs of chemical processes. The primary applications of these integrated tools have focused on resource conservation, pollution prevention and energy management. Specifically, the past two decades have seen the development and/or application of process integration design tools for heat exchange networks (HENs), wastewater reduction and water conservation networks, mass exchange networks (MENs), heat‐ and energy‐induced separation networks (HISENs and EISENs), waste interception networks (WINs) and heat‐ and energy‐induced waste minimization networks (HIWAMINs and EIWAMINs), to name a few. This paper provides an overview of some of these developments and outlines major driving forces and hurdles. The fundamental aspects of this approach along with their incorporation in an overall design methodology will be discussed. The paper also highlights several recent applications of process integration to industrial processes. Copyright © 2003 Society of Chemical Industry     

Towards Integrated Process and Control System Synthesis for Heat‐Integrated Plants

Most chemical processes are networks of different pieces of equipment, as reactors, distillation columns, compressors, heat exchangers, etc. Process integration is an area of chemical engineering that deals with the optimal design of these networks, from the point of view of energy efficiency, capital costs, emissions reduction, waster water minimization, and raw materials usage. Until recently, engineers developed conceptual process designs by experience and intuition, however, with the establishment of process integration methodologies, this activity can be performed systematically. One of the subjects that have received the most attention from researchers in this area is the steady state design of Heat Exchanger Networks (HENs). Several tools have been developed and are in use; however, the development of a tool for synthesis of HENs that takes into account network controllability is not available. Hence, the purpose of this paper is the development of a new methodology for design of heat‐integrated chemical processes, particularly HENs where controllability and energy recovery are both balanced during the design synthesis stage.     

Interpreting the dynamic effect of internal heat integration on reactive distillation columns

In this work,the impact of internal heat integration upon process dynamics and controllability by superposing reactive section onto stripping section,relocating feed locations,and redistributing catalyst within the reactive section is explored based on a hypothetical ideal reactive distillation system containing an exothermic reaction:A + B ←→ C + D.Steady state operation analysis and closed-loop controllability evaluation are carried out by comparing the process designs with and without the consideration of internal heat integration,For superposing reactive section onto stripping section,favorable effect is aroused due to its low sensitivities to the changes in operating condition,For ascending the lower feed stage,somewhat detrimental effect occurs because of the accompanied adverse internal heat integration and strong sensitivity to the changes in operating condition.For descending the upper feed stage,serious detrimental effect happens because of the introduced adverse internal heat integration and strong sensitivity to the changes in operating condition.For redistributing catalyst in the reactive section,fairly small negative influence is aroused by the sensitivity to the changes in operating condition.When reinforcing internal heat integration with a combinatorial use of these three strategies,the decent of the upper feed stage should be avoided in process development.Although the conclusions are derived based on the hypothetical ideal reactive distillation column studied,they are considered to be of general significance to the design and operation of other reactive distillation columns.     

Design of mixed energy‐integrated batch process networks by Pseudo‐direct approach

In this article, a novel framework for the design of mixed (combined direct and indirect) integration for batch process systems is presented. The framework is based on the concept of pseudo‐direct energy integration (PDEI) which reformulates indirect integration as direct integration using pseudo‐process streams. Two algorithms are presented to achieve energy integration for batch processes operating cyclically (in a campaign mode). The first algorithm targets maximization of energy recovery and overcomes the limitations of some of the existing contributions for design of mixed integrated systems. The second algorithm provides a network reduction methodology to generate a cadre of integrated designs while exploring the trade‐off between capital (number of heat exchangers and storage units) and operating costs (utility consumption). The proposed framework is illustrated using a benchmark example of two hot and two cold streams. © 2017 American Institute of Chemical Engineers AIChE J, 63: 55–67, 2018     

热泵热集成精馏流程的优化设计与综合

从综合的角度详细讨论了热泵精馏的原理,提炼出了用于综合的热泵精馏规则,并开发了综合所用的热泵精馏简捷经济评价方法,提出了一个两水平综合策略,给出了热泵精馏综合步骤。实例研究表明,本文开发的算法及提出的规则用于热泵热集成精馏流程的综合,能够得出最优的絷泵精馏流程。     

Exploration of a heat-integrated pressure-swing distillation process with a varied-diameter column for binary azeotrope separation

The pressure-swing distillation (PSD) processes with varied-diameter columns (VDCs) for separating methanol–chloroform and n-heptane–isobutanol are studied. Furthermore, two heat-integrated PSD processes, partial integration and full heat integration, are discussed with ordinary and VDCs. The results show that whether it is heat integrated or non-heat integrated, the processes using VDC have an advantage in the economy. Based on the minimum total annual cost (TAC), the dynamic controllability without and with full heat integration for an azeotrope system methanol/chloroform is explored. The dynamic controllability without and with partial heat integration for the azeotrope system n-heptane/isobutanol is discussed. The results indicated that compared with the dynamic responses without heat integration process, the heat-integrated PSD with a VDC did not increase the control difficulty while maintaining its economy. More azeotropic systems should be studied to investigate their economics and control effects, which will benefit PSD design and industrial application.     

Towards further internal heat integration in design of reactive distillation columns—Part IV: Application to a high-purity ethylene glycol reactive distillation column

In the first three papers of this series, it has been shown that strengthening internal heat integration within a reactive distillation column involving reactions with high thermal effect is really effective for the reduction of utility consumption and capital investment besides the improvement in process dynamics and operation. One important issue that remains unstudied so far is the influences of reaction selectivity upon the reinforcement of internal heat integration, since the reaction operation is often accompanied by side-reactions and the maintenance of a high selectivity is extremely necessary in process synthesis and design. A reactive distillation column synthesizing high-purity ethylene glycol through the hydration of ethylene oxide is chosen and studied in this work. Because of the unfavorable physicochemical properties of the reacting mixture separated (e.g., the fairly large volatility between the reactants and the existence of a consecutive side-reaction), the process represents a challenging problem for the reinforcement of internal heat integration. Intensive comparison is conducted between the process designs with and without the consideration of further internal heat integration between the reaction operation and the separation operation involved, and it has been found that seeking further internal heat integration still leads to a substantial reduction of energy requirement, in addition to a further abatement in capital investment. Moreover, a favorable effect is again observed upon the process dynamics and operability. These striking outcomes manifest evidently that seeking further internal heat integration should be considered in process synthesis and design irrespective of what a reaction selectivity has been assigned.     

Dynamic modeling and collocation‐based model reduction of cryogenic air separation units

High purity distillation columns and multi‐stream heat exchangers (MSHXs) are critical units in cryogenic air separation plants. This article focuses on modeling approaches for the primary section of a super‐staged argon plant. A full‐order stage‐wise model for distillation columns in air separation units (ASUs) that considers key process phenomena is presented, followed by a reduced‐order model using a collocation approach. The extent of model reduction that can be achieved without losing significant prediction accuracy is demonstrated. A novel moving boundary model is proposed to handle MSHXs with phase change. Simulation results demonstrate the capability of the proposed model for tracking the phase change occurrence along the length of the heat exchanger. Dynamic simulation studies of the integrated plant show that the thermal integration between the feed and product streams captured in the primary heat exchanger is critical to accurately capture the behavior of ASUs. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1602–1615, 2016     

间歇化工过程热集成研究进展

间歇化工过程热集成问题的研究能够促进过程系统的可持续发展并且提高产业经济性和技术竞争力,顺应了化工发展大环境。本文介绍了以系统综合优化为目标的间歇化工过程热集成研究的发展现状,整理了早期研究的三大通用图解模型,并讨论和比较了在建模求解过程中常见算法。总结了当前研究的重点在换热网络设计优化、热储罐系统和考虑调度的热集成三个方面,并评述了与之相关的进展、瓶颈和研究意义。指出了热集成问题已成为当前间歇化工过程的研究热点,其中热集成和生产调度的协同优化十分必要,能够从系统全局的角度上给出优化方案。但由于间歇化工过程中存在较多的不确定性和约束条件,增加了热集成的研究难度,因此对间歇化工过程优化设计提出了更高的要求。     

Towards further internal heat integration in design of reactive distillation columns—Part II. The process dynamics and operation

In the first paper of this series, it has been demonstrated that the capital investment and operating cost can frequently be reduced substantially through seeking further internal heat integration between the reaction operation and separation operation for a reactive distillation column involving reactions with highly thermal effect. In this paper, the dynamics and operation of the resultant reactive distillation system is to be examined, with special emphasis focused on the dynamic effect of the supplementary internal heat integration. It has been found that seeking further internal heat integration can sometimes improve process dynamics and lessen difficulties in process operation. This outcome stems from the refined relationship between the reaction operation and separation operation involved and is of great significance in tightening process design for a reactive distillation column containing reactions with highly thermal effect.It should, however, be pointed out that seeking further internal heat integration might also confine severely the flexibility of the resultant reactive distillation column due to the reduction of mass transfer driving forces. When encountering a sharp increase in the product specification that is more relevant to the supplementary internal heat integration, the process might show deteriorated dynamic performance and can even converge to an undesirable steady state where the economical advantages of the supplementary internal heat integration are lost totally. Therefore, some effective measures to increase the redundancy of the resultant process design have to be taken to deal with the side-effect during process development.     

A fundamental principle and systematic procedures for process intensification in reactive distillation columns

A fundamental principle is developed for process intensification through internal mass and energy integration in reactive distillation columns and three systematic procedures are devised for process synthesis and design. For reactive distillation columns involving reactions with highly thermal effect, process intensification can be achieved with an exclusive consideration of internal energy integration between the reaction operation and separation operation involved. However, in the case of a highly endothermic reaction with an extremely low reaction rate and/or small chemical equilibrium constant, internal mass integration has also to be considered between the reactive section and stripping section. For reactive distillation columns involving reactions with negligibly or no thermal effect, process intensification can be performed with an exclusive consideration of internal mass integration. For reactive distillation columns involving reactions with moderately thermal effect, process intensification must be conducted with a careful trade-off between internal mass and energy integration. Five hypothetical and two real reactive distillation systems are employed to evaluate the principle and procedures proposed. It is demonstrated that intensifying internal mass and energy integration is really effective for process intensification. Not only can the thermodynamic efficiency be improved substantially, but also the capital investment can be further reduced.