A review on process intensification in internally heat-integrated distillation columns

Internally heat-integrated distillation column (HIDiC) is the most radical approach of a heat pump design, making efficient use of internal heat-integration: the rectifying section of a distillation column operating at a higher pressure becomes the heat source, while the stripping part of the column acts as a heat sink. Remarkably, a HIDIC can bring up to 70% energy savings compared to conventional distillation columns. This is highly appealing regarding the fact that distillation is one of the most energy intensive operations in the chemical process industry accounting for over 40% of the energy usage. This review paper describes the latest developments concerning this promising but difficult to implement process intensification technology, covering all the major aspects related to the working principle, thermodynamic analysis, potential energy savings, various design configurations and construction options (ranging from inter-coupled or concentric columns, shell and tube and plate–fin heat exchanger columns to SuperHIDiC), design optimization, process control and operation issues, as well as pilot-scale and potential industrial applications. Further advancement, i.e., development of HIDiC technology for multi-component mixture separations is an extremely challenging research topic, especially when HIDiC becomes associated with other technologies such as dividing-wall column (DWC) or reactive distillation (RD).     

Distillation technology – still young and full of breakthrough opportunities

Throughout history, distillation has been the most widespread separation method. However, despite its simplicity and flexibility, distillation still remains very energy inefficient. Novel distillation concepts based on process intensification, can deliver major benefits, not just in terms of significantly lower energy use, but also in reducing capital investment and improving eco‐efficiency. While very likely to remain the separation technology of choice for the next decades, there is no doubt that distillation technology needs to make radical changes in order to meet the demands of the energy‐conscious modern society. This article aims to show that in spite of its long age, distillation technology is still young and full of breakthrough opportunities. Moreover, it provides a broad overview of the recent developments in distillation based on process intensification principles, for example heat pump assisted distillation (e.g. vapor compression or compression–resorption), heat‐integrated distillation column, membrane distillation, HiGee distillation, cyclic distillation, thermally coupled distillation systems (Petlyuk), dividing‐wall column, and reactive distillation. These developments as well as the future perspectives of distillation are discussed in the context of changes towards a more energy efficient and sustainable chemical process industry. Several key examples are also included to illustrate the astonishing potential of these new distillation concepts to significantly reduce the capital and operating cost at industrial scale. © 2013 Society of Chemical Industry     

Optimal heat distribution in the internally heat-integrated distillation column (HIDiC)

The internally heat-integrated distillation column (HIDiC) is an interesting separation alternative to the conventional column or the vapor recompression distillation (VRC). In an HIDiC, the influence of heat distribution along the column section has a significant impact on the design and optimization in addition to the compressor pressure ratio. In this work, the optimization of heat distribution in the HIDiC is completely investigated through the application of flowsheet modeling and optimization solver in Aspen Plus. A commercial-scale propylene/propane splitter is used as a case study to illustrate the effect of heat distribution on energy or cost performance. A comparison of the optimum HIDiC structures obtained from different objective functions is discussed. Some optimum HIDiC structures could be evolved into Linde double columns with a side rectifier, which is a common application found in air separation process. This structure is potentially another interesting alternative to the conventional VRC.     

Design and control of an ideal heat-integrated distillation column (ideal HIDiC) system separating a close-boiling ternary mixture

Despite the fact that a stand-alone ideal heat-integrated distillation column (ideal HIDiC) can be thermodynamically efficient and operationally stable, the application of an ideal HIDiC system to separate a close-boiling multi-component mixture is still a challenging problem because of the possibility of strong interactions within/between the ideal HIDiCs involved. In this work, employment of two ideal HIDiCs to separate a close-boiling ternary mixture is studied in terms of static and dynamic performance. It is found that the ideal HIDiC system can be a competitive alternative with a substantial energy saving and comparable dynamic performance in comparison with its conventional counterpart. The direct sequence appears to be superior to the indirect sequence due to the relatively small vapor flow rates to the compressors. Controlling the bottom composition of the first ideal HIDiC with the pressure elevation from the stripping section to the rectifying section helps to suppress the disturbances from the feed to the second ideal HIDiC. Special caution should, however, be taken when the latent heat of the distillates is to be recovered within/between the ideal HIDiCs involved, because a positive feedback mechanism may be formed and give rise to additional difficulties in process operation.     

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.     

The structured heat integrated distillation column

This paper describes a unique, proof of the principle test facility and the results of a study carried out to provide experimental evidence needed to properly asses the techno-economic feasibility of heat integrated distillation column (HIDiC) utilizing structured internals to enhance both heat and mass transfer. The plate-packing configuration using structured packing exhibited a superior performance in comparison with the HIDIC based on the plate-fin heat exchanger. Experimental evidence shows that the mass transfer and heat transfer efficiency increase pronouncedly with increasing throughput, which however is accompanied by an increasing pressure drop per stage. Simulation of an industrial scale plate-packing unit revealed that an even better performance can be obtained by increasing the volumetric thermal load via further optimization of internals.     

Design of internally heat-integrated distillation column (HIDiC): Uniform heat transfer area versus uniform heat distribution

The internally heat-integrated distillation column (HIDiC) is a complex column configuration which is more energy efficient than the equivalent conventional column or the distillation column with direct vapor recompression scheme (VRC). Exploiting the heat integration between two diabatic sections operating at different pressures of the HIDiC can greatly enhance the energy performance of the system. On the other hand, the design and optimization of HIDiC is more difficult than those of the conventional distillation column or the column with VRC. The former involves many design parameters, and the most critical one is the pressure ratio between both diabatic sections. However, the heat distribution along the diabatic sections is also another significant factor not yet thoroughly investigated. In this work, two typical distribution schemes, i.e. uniform heat transfer area and uniform heat distribution, are studied by applying a novel approach to solve the simulation problem in Aspen Plus 2004.1. The comparison of both distributing schemes is discussed via two widely-used case studies, namely benzene-toluene separation and propylene-propane splitter.     

带有中间热集成的精馏塔序列及其性能

提出一种带有中间热集成的精馏塔序列(IHISDC)的流程,针对三组元混合物分离的简单塔直接序列,对该流程进行了分析。与传统热集成精馏序列(HISDC)相比,提出的IHISDC通过中间换热器将高压塔的精馏段与低压塔的提馏段进行局部热集成,使能量集成精馏塔之间的压力差更小,进而使能耗费用下降。同时发现,IHISDC中的高压塔再沸器热负荷和低压塔冷凝器热负荷增加,由于换热器数量的增加,IHISDC的投资费用较大。为了进一步降低IHISDC的年度总费用,需要对其设计参数进行优化。     

REDUCING STATIC DEVIATIONS OF PRODUCT QUALITIES IN THE TEMPERATURE CONTROL OF AN IDEAL HEAT-INTEGRATED DISTILLATION COLUMN

Two strategies are proposed in this work for the reduction of static deviations of product qualities in the dual-point temperature control of a simulated ideal heat-integrated distillation column. The key to achieve this purpose is to sense the changes in operating conditions and make appropriate adjustments simultaneously to the set-points of the top and bottom control loops. The first method is based on the inferential signals extracted from the composition of products and the second one from the temperatures of the top and bottom stages. Both strategies are intensively studied through the operation of the simulated ideal heat-integrated distillation column separating a binary equimolar mixture of benzene and toluene, and it is found that they could work effectively to decrease the static deviations in product qualities. The strategies are characterized by great simplicity in principle and a relatively small effort in process modeling, thereby allowing wide applications in the operation of various distillation columns with a dual-point temperature control scheme.     

Conceptual design of an internally heat integrated propylene-propane splitter

Huge quantities of energy are required in distillation columns used for polymer grade separations of close boiling mixtures. The purpose of this paper is to introduce an industrially viable, internally heat integrated (HIDiC) version of a state of the art propylene-propane splitter. The base case is one of the world's largest, heat-pump assisted, stand-alone columns of this type. The actual plant data formed the basis for the techno-economic evaluation, which indicated that the HIDiC could become an economically attractive option for new designs, provided the barriers related to increased design complexity could be overcome.