A review of internally heat integrated distillation column

The energy consumption of distillation operation determines the amount of energy consumption throughout the chemical separation process. A heat integrated distillation column(HIDiC) could greatly reduce the irreversibility of the distillation process, so it gradually becomes a research hotspot. There are two major techniques for heat integration in HIDiC: internally and externally. This review paper describes the major research aspects of an internally heat integrated distillation column(IHIDiC), including the heat transfer models, various design structures(including the two-column HIDiC, Concentric HIDiC, Shell and tube HIDiC, Plate-fin HIDiC and the Super HIDiC, etc.), experimental research, simulation and optimization, process control research, as well as industrial plants and potential industrial applications. Among them, the heat transfer performance of various structures was analyzed of the various design structures based on experimental research, the effects of different factors(including relative volatility, reflux ratio, compression ratio, etc.) on HIDiC energy consumption or TAC is summarized in the simulation part. The calculation methods of the overall heat transfer coefficient and heat transfer models are summarized. The various optimization algorithms and optimization results of simplified HIDiC are summarized in the optimization part. The research status and the key technical issues in various aspects of HIDiC are summarized in this paper. In order to meet the requirements of industrial energy efficiency,the selection of multi-component separation distillation configurations needs to be considered more diversified,and internal complex coupling relationship of HIDiC needs to be further studied.     

Comparison of Energy Usage for the Vacuum Separation of Acetic Acid/Acetic Anhydride Using an Internally Heat Integrated Distillation Column (HIDiC)

Abstract

Energy savings for an internally heat-integrated distillation column (HIDiC) and a vapor recompression column for the vacuum separation of acetic acid/acetic anhydride was theoretically analyzed and compared to the simulation of a reference column configuration of the Eastman Chemical Company using ASPEN Plus. In these simulations, the design and operating variables were defined and optimized to minimize total energy used. The effects of design variables such as quantity and location of the heat integration stages, reflux ratio, and rectifying section absolute pressure on energy consumption and product purity revealed that one HIDiC configuration had 62% energy savings over the reference column. The distillation column using vapor recompression was evaluated as a benchmark for comparing the HIDiC configurations and the reference column. The VRC column simulation predicted both increased product purity and an energy savings of 91% over the reference unit.     

内部热耦合精馏塔构型研究

以丙烯-丙烷分离过程为例,研究了4种内部热耦合精馏塔的性能,并与常规精馏塔和热泵精馏塔进行了比较。结果发现,不同构型的内部热耦合精馏塔之间性能差异很大,其中提馏段与精馏段上端对齐,逐板进行热交换的构型性能最佳,其有效能耗比热泵精馏塔低25%—40%,节能效果显著。还探讨了内部热耦合精馏塔的压缩比与换热面积的关系,压缩比越小,换热面积越大,换热面积的逐板分布越不均匀。     

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.     

A novel multi-effect methanol distillation process

Crude methanol distillation is an energy-intensive separation process and contributes significantly to the cost of methanol production. Although a number of energy-efficient distillation systems have been proposed, there is potential for energy savings in methanol distillation. To further reduce the energy consumption of methanol distillation, a novel five-column multi-effect distillation process is proposed in this work, which is essentially an improved version of an existing four-column scheme. The four-column scheme is made up of a pre-run column, a higher-pressure column, an atmospheric column and a recovery column. The new five-column scheme adds a medium-pressure column after the original higher-pressure column. In this way, the load of the original higher-pressure and atmospheric columns can be decreased by about 30%. The five-column arrangement creates a multi-effect distillation configuration involving efficient heat integration between higher-pressure and medium-pressure columns, atmospheric and recovery columns, and recovery and pre-run columns. Steady-state process simulation results indicate that temperature differences at two sides of each heat exchanger are appropriate, allowing effective heat transfer. Economic analysis shows that the energy consumption of the five-column scheme can be reduced by 33.6% compared to the four-column scheme. Significant savings in operating costs can therefore be achieved, resulting in an economically viable process for methanol distillation.     

Parameter analysis and optimization of ideal heat integrated distillation columns

Parametric analysis is performed for ideal heat integrated distillation columns (HIDiC) and comparative studies are made with conventional distillation columns. Implications of process design and operation variables are clarified and heuristics are provided for the effective process design. A generalized process configuration is suggested, which is demonstrated to have both higher energy efficiency and higher flexibilities than its original configuration. Simulation studies are conducted and the obtained results confirm the conclusion.     

Heat‐integrated distillation columns: Vapor recompression or internal heat integration?

Internally, heat‐integrated distillation columns (HIDiC) and vapor recompression (VRC) constitute alternative design options to provide sustainable distillation processes. However, the design is often based on heuristic rules or the experience of the designer, as no systematic methodology driven by economics has been established so far. The increased complexity of heat‐integrated columns can hardly be dealt with using simulation studies but rather calls for a systematic design procedure. A new design methodology is presented here; it builds on a superstructure, mixed‐integer minimization of total annualized cost of operation and rigorous thermodynamic modeling. Optimal VRC and HIDiC designs are identified for the separation of binary, multicomponent, and nonideal mixtures and benchmarked against conventional distillation column designs. A small number of intermediate heat exchangers is optimal for these HIDiC configurations, eventually reducing to a single heat exchanger similar to VRC. Therefore, VRC designs are often more cost efficient due to simpler equipment. © 2012 American Institute of Chemical Engineers AIChE J, 2012     

A novel multistage vapor recompression reactive distillation system with intermediate reboilers

Most of the published studies have focused on the thermal integration of nonreactive distillation columns. The key limitation of reactive distillation (RD) technology is that the necessary conditions (such as pressure and temperature) for the reaction must match those of distillation. Owing to this constraint, the reaction conversion may be adversely affected at the elevated pressure in the reactive section of an internally heat integrated distillation column (HIDiC). This fact forces us to adopt an external heat integration approach for an industrial heterogeneously catalyzed ethyl tert‐butyl ether (ETBE) RD column. The direct vapor recompression column (VRC) is an external heat integration scheme that is successfully used as an energy efficient scheme for separating a close‐boiling mixture. Interestingly, there exists a large temperature difference between the two ends of the representative ETBE column, and it makes the external heat integration more challenging. Aiming to improve the thermal efficiency of the ETBE column under the VRC framework, various heat pump arrangements with intermediate reboiler(s) (IR(s)) are explored and analyzed with performing a comparative study in terms of energy consumption and economics. To improve further the thermal efficiency, in this contribution, a novel multistage vapor recompression RD column with IRs is introduced addressing a number of practical concerns. An algorithm for the proposed column is formulated showing the sequential steps involved in heat integration. It is inspected that the proposed multistage vapor recompression RD system appears overwhelmingly superior to the classical vapor recompression RD and its conventional stand alone column providing a significant savings in energy as well as cost. © 2012 American Institute of Chemical Engineers AIChE J, 59: 761–771, 2013     

Design and control of energy-efficient distillation columns

Distillation is the best option for the separation of hydrocarbon mixtures, unless the boiling points of the constituents are close together. Despite being widely utilized in field applications, the high energy demand of distillation calls for efficient columns in order to save energy. The efficient divided wall column (DWC), diabatic distillation column, and internally heat-integrated distillation column (HIDiC) are introduced here, and the design and control of the columns are briefly reviewed. The practical applications of the columns in the processes of natural gas production from raw gas drawn from underground and benzene separation from naphtha reformate are presented to show the energy-saving performance of the energy-efficient distillation columns. The side-rectifier DWC reduced the heating duty of the conventional system by 5.9%, and provided a compact construction, replacing the three-column conventional system with a single column suitable for offshore application. Moreover, the controllability of DWC was improved by utilizing the side-rectifier. The benzene removal process utilizing the extended DWC lowered the heating duty of the whole conventional process by 56.8%.     

内部能量集成精馏塔的模拟研究及其节能特性分析

针对苯-甲苯和丙烯-丙烷物系,模拟分析了压缩比、进料状态及换热量分布方式对理想内部能量集成精馏塔的操作特性、所需塔内换热面积及节能效果的影响。将模拟结果与传统精馏塔及热泵精馏塔进行比较,结果显示内部能量集成精馏塔的节能效果对于不同物系有较大差别。对苯-甲苯物系,热泵精馏塔的节能效果最好,节能百分率为40％。对丙烯-丙烷物系,理想内部能量集成精馏塔的节能优势明显,节能百分率在60％～80％。本文提出了内部能量集成精馏塔热温匹配的换热量分布方式。模拟结果表明,达到同样节能效果,采用热温匹配的换热量分布方式可以在压缩比较小时大幅度减小传热面积。采用热温匹配的换热量分布方式可以在压缩比较小时大幅度减小传热面积。     

Reversibility Analysis for Design Optimization of an Internally Heat‐Integrated Distillation Column

Internally heat‐integrated distillation columns (HIDiCs) need heat transfer between the two column sections. Intermediate condensing and reboiling of the rectifying and stripping sections favor the reversibility of the separation process and lead to the increase of heat loads for the two sections but the heat transfer to cover the heat load is costly and generates major difficulties in design. A higher number of stages can reduce the heat load but will also raise the investment cost. The influence of increasing stage numbers on operating cost and capital investment of the HIDiC was evaluated by two HIDiC design cases, and the stage numbers or equivalently the heat loads were optimized to achieve the balance between the two kinds of cost.     

Introducing vapor recompression mechanism in heat‐integrated distillation column: Impact of internal energy driven intermediate and bottom reboiler

A novel combination of internally heat‐integrated distillation column (HIDiC) and vapor recompression column (VRC) with intermediate reboiler (IR) is proposed. Supplying heat at the highest temperature point (i.e., column bottom) of the VRC scheme is not thermodynamically favorable and, therefore, we aim to install the IR for better distribution of heat along the column length, thereby reducing the compressor work. Introducing IR in the combined HIDiC‐VRC system formulates an open‐loop variable manipulation policy to evaluate the comparative impact of internal and external heat sources on bottom liquid reboiling. With internal energy driven bottom reboiler, we further investigate the hybrid HIDiC‐VRCIR column with proposing the two modes of compressor arrangement, namely parallel and series. Finally, a multicomponent distillation system is exampled to show the promising potential of the proposed HIDiC‐VRCIR configurations in improving the energetic and economic performance over the HIDiC‐alone and HIDiC‐VRC schemes with reference to a conventional standalone column. © 2014 American Institute of Chemical Engineers AIChE J, 61: 118–131, 2015     

Modeling and analysis of conventional and heat‐integrated distillation columns

A generic model that can cover diabatic and adiabatic distillation column configurations is presented, with the aim of providing a consistent basis for comparison of alternative distillation column technologies. Both a static and a dynamic formulation of the model, together with a model catalogue consisting of the conventional, the heat‐integrated and the mechanical vapor recompression distillation columns are presented. The solution procedure of the model is outlined and illustrated in three case studies. One case study being a benchmark study demonstrating the size of the model and the static properties of two different heat‐integrated distillation column (HIDiC) schemes and the mechanical vapor recompression column. The second case study exemplifies the difference between a HIDiC and a conventional distillation column in the composition profiles within a multicomponent separation, whereas the last case study demonstrates the difference in available dynamic models for the HIDiC and the proposed model. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4251–4263, 2015     

Optimal design of cryogenic distillation columns with side heat pumps for the propylene/propane separation

Propylene is one of the most important products in the petrochemical industry, which is used as raw material for a wide variety of products. The propylene/propane separation is a very energy-intensive process because their boiling points are quite similar. In addition, at atmospheric conditions, their boiling points are −47.6 °C and −42.1 °C, respectively. To separate this mixture conventional columns which operate at high pressure and cryogenic distillation columns which operate at low pressure have been used, however, this approaches are still energy-intensive. This work presents energy-efficient and intensified distillation columns which are adiabatic such as the vapor recompression column (VRC) or diabatic such as columns with heat-integrated stages. A design and optimization procedure, which minimizes the energy consumption in the propylene/propane separation is presented. Conceptual design, superstructure representation, rigorous simulations and mathematical programming techniques are effectively combined to assess all the candidate distillation structures, refrigeration cycles, and heat integration possibilities simultaneously. Results showed that VRC and diabatic distillation columns with heat-integrated stages can reduce the energy consumption between 58 and 75% when compared with conventional distillation at high pressure. Furthermore, the proposed synthesis procedure derived simplified optimal distillation structures with few heat-integrated stages and still attained important energy savings.     

无冷凝器及再沸器的热集成蒸馏塔技术进展

蒸馏塔内部热集成技术系指同一塔内通过精馏段和提馏段之间的热量集成。介绍了内部热集成蒸馏塔的结构、特点、节能原理以及发展概况。该项技术被认为是最具节能潜力的新型蒸馏技术之一,与传统蒸馏塔相比,内部热集成蒸馏塔节能可达到30%—60%。近年来,塔内部热集成技术研究呈现加速发展的势态,国外学者已成功地完成了中试,并开始工业化应用的研究。     

内部热耦合精馏塔节能特性研究

以苯-甲苯作为分离物系,对内部热耦合精馏塔进行模拟计算。模拟结果表明内部热耦合精馏塔的温度及液相流率分布等特性与传统精馏塔存在较大差异,分析讨论了压缩比对内部热耦合精馏塔特性的影响。文章对精馏装置节能改建具有重要指导意义。     

Higher energy saving with new heat integration arrangement in heat‐integrated distillation column

In conventional heat‐integrated distillation columns (HIDiCs), the internal heat exchange is executed between the pressurized rectifying section and the stripping section, which are located at the same elevation. In such a structure, the amount of heat exchanged between two sections depends on the temperature profile of both sections. The resulting enthalpy profile inside the column departs from that in reversible distillation, which is the ideal distillation operation in view of energy conservation. More energy saving may be achieved by providing appropriate arrangement of heat exchanges between sections. The interactive graphical design method to determine the appropriate heat exchange arrangement in a previous paper was developed for a binary system. The design method was extended and applied to a multicomponent system by adopting the idea of a quasi‐binary system. Also, a new HIDiC structure that can realize the outcomes of the proposed design method was developed. The economics of the proposed structure was precisely evaluated through a case study of a commercial scale column. It demonstrated that the proposed structure has attractive economics. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3479–3488, 2015     

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。     

内部热耦合空分塔的节能优化分析

内部热耦合精馏是迄今为止所提出的节能效果最好,而唯一没有商业化的节能技术。将内部热耦合技术用于空分塔,可以带来良好的节能效果。根据低温空气分离过程以及三组分精馏的特点,提出了一种新的内部热耦合空分精馏塔优化模型。在优化模型基础上,对热耦合塔进行了深入的节能优化与分析,并且与常规空分仿真结果进行了比较分析,压缩机能耗下降20.75%,产值增加17.46%,单位产值能耗下降32.53%。内部热耦合空分塔的提取率以及能耗均优于常规热耦合空分塔,节能效果显著。     

基于塔总组合曲线的内部热耦合精馏塔优化设计方法

基于塔总组合曲线（CGCC）,提出了一种简化内部热耦合精馏塔（HIDiC）结构的图形设计方法。在完成精馏段（或提馏段）单塔段中间换热器优化设置的基础上,结合精馏段与提馏段CGCC的集成图,以HIDiC的可减小过程总（火用）损为目标,确定HIDiC热耦合中间换热器的最优设计。以苯乙烯-乙苯HIDiC为例,计算结果表明,设置中间换热器后,HIDiC可减小过程总（火用）损最大值为1.951 MW,HIDiC的冷凝器、再沸器负荷分别下降63.6%和68.4%;热耦合中间换热器分别设置于精馏段第2、12、和38块塔板,提馏段第20、28和36块塔板,热负荷依次为0.841、1.496和2.053 MW。