Heat Integrated Distillation Column Research Articles

Experimental Investigation on Heat Exchange and Separation Performance of an Annular Structured Internal Heat-integrated Distillation Column

In this paper heat exchange coefficient and separation efficiency of an annular structured internal heat-integrated distillation column (HIDiC) were experimentally measured. About 50% heat of the inner column could be transferred to the outer column. The overall heat exchange coefficient decreased with an increase in pressure ratio of the inner column and the outer column, but was little affected by the F-factor. The increase of the pressure ratio decreased obviously the separation efficiency of the outer column but had little effect on that of the inner column.

Feasibility study of heat-integrated distillation columns using rigorous optimization

In this work, rigorous optimization of HIDiC (Heat-Integrated Distillation Column) and VRC (Vapor Recompression Column) is implemented by GA (Genetic Algorithm) to find an alternative for CDiC (Conventional Distillation Column). The objective function is TAC (Total Annual Cost). Three different case studies are investigated, being composed of benzene-toluene, propane-propylene, and methanol-water. A novel strategy is proposed to consider all the heat integration possibilities resulting in more efficient search space than our previous attempt. It is observed that the heat exchangers arrangement of optimum HIDiCs are very similar to VRCs in ideal case studies. Although CDiC is the optimum configuration in the benzene-toluene separation, 6.6% reduction is achieved for the presented HIDiC compared to previous work. For propane-propylene splitter, VRC is the economical alternative with a 44.1% decrease in the TAC of CDiC. Moreover, VRC and HIDiC optimizations leads to 25.5% and 4.4% reductions in TAC compared to previous work, respectively. However, for the non-ideal methanol-water separation, which has a wide boiling point range, the TAC of optimum HIDiC is surprisingly lower than CDiC and optimum VRC by 3.4% and 31.2%, respectively.

Design and Optimization of Heat-Integrated Distillation Column Schemes through a New Robust Methodology Coupled with a Boltzmann-Based Estimation of Distribution Algorithm

The technology of the heat-integrated distillation column (HIDiC) has shown to be a potential energy-saving alternative for separating close-boiling mixtures. However, the economic aspects are a critical factor to extensive use of this distillation sequence in real applications. In this research, a novel stochastic optimization algorithm called Boltzmann univariate marginal distribution algorithm (BUMDA) with constraints handling has been implemented to optimize HIDiC sequences. Three binary mixtures were examined: butanol–isobutanol, n-heptane–cyclohexane, and benzene–toluene. The evaluation was performed by applying a new robust methodology using the interface Matlab–Excel–Aspen Plus. The model Radfrac was used in the simulations in Aspen Plus. The minimization of the total annual cost was established as the fitness function of the problem. Results showed the great robustness presented by the BUMDA algorithm for solving successfully this kind of complex optimization problem. Thus, the HIDiC design to separate the alcohol mixture showed energy savings of 84% and a cost that was lower (2%) than that of the conventional column. In addition, the hydrocarbon mixtures reached energy savings of 62.5% (n-heptane–cyclohexane) and 52.5% (benzene–toluene). Nevertheless, the total annual cost (TAC) of the HIDiC is larger than the TAC of the conventional column (32% and 35%, respectively).

内部熱交換式蒸留塔（HIDiC）の技術開発

内部熱交換式蒸留塔（HIDiC）の技術開発

内部熱交換式蒸留塔（HIDiC）の技術開発

内部熱交換式蒸留塔（HIDiC）の技術開発

A Modeling Framework for Conventional and Heat Integrated Distillation Columns

In this paper, a generic, modular model framework for describing fluid separation by distillation is presented. At present, the framework is able to describe a conventional distillation column and a heat-integrated distillation column, but due to a modular structure the database can be further extended by additional configurations. The framework provides the basis for fair comparison of both steady state and dynamic performance of the different column configurations for a given binary or multicomponent separation.

Internal and external HIDiCs (heat-integrated distillation columns) optimization by genetic algorithm

HIDiC (Heat-Integrated Distillation Column) is an effective energy-saving configuration especially for the separation of close boiling point mixtures. In this work, the stochastic methodology has been applied for optimization of both internal and external HIDiCs. The use of GA (Genetic Algorithm) to find the optimal HIDiC configuration is presented while the fitness function is set to be the TAC (Total Annual Cost). HIDiC simulation has been performed based on the modified MESH equations using a rigorous thermodynamic model. Introducing a novel integer variable (the Layout number) leading to a more effective solution for the examined case study. This variable can generate systematically more energy efficient candidates for both internal and external HIDiCs. Benzene-toluene separation has been investigated by the proposed optimization procedure. The multivariable problem can be successfully optimized by GA while a good initial estimation is not essential. Based on the final results, up to 6.60% and 9.75% TAC reduction have been accomplished in external and internal HIDiCs optimization using the proposed method compared to the reported solutions in a previous work for the examined case study. However, VRC (Vapor Recompression Column) optimization at the end of presented work results 7.89% TAC reduction rather than optimal HIDiC.

Design of heat integrated distillation column by using H-xy and T-xy diagrams

An interactive design methodology of HIDiC with finite internal heat exchange stages is proposed. When the number of heat integrated stages is limited, the number of possible combinations of heat integration increases. Thus, the optimal design problem usually becomes a complex mixed integer nonlinear programming problem. In this research, a novel design methodology using modified Ponchon–Savarit diagram is proposed. The first modification of the diagram is the introduction of the reversible distillation curve, which shows the enthalpy profile at reversible condition. By using this curve, the target enthalpy profile in the column can be determined and the plausible stages for heat exchange can be determined by taking the predetermined theoretical stages into account. The second modification is the integration of the T-xy diagram with H-xy diagram. By doing so, the temperature difference of side exchangers can easily be identified, and it becomes possible to determine the pairing of heat integration stages between the rectifying section and the stripping section in consideration of the heat transfer area of side exchangers. The conditions obtained by the diagram methodology can be directly used in rigorous process simulation. Case studies demonstrated that the results obtained from the proposed methodology have good agreement with the conditions obtained through numerical optimization. The designer can modify the design condition interactively by checking the obtained diagram. Thus, the proposed methodology is especially beneficial at the preliminary design stage of HIDiC.

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

AbstractInternally 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.

Comparison between Different Configurations of Internally and Externally Heat-Integrated Distillation by Numerical Simulation

The internally heat-integrated distillation column (HIDiC) is often compared with heat-pump-assisted distillation columns and claimed to be more energy efficient. Recently, the idea of simplifying the HIDiC by several external heat exchangers has come into favor and been thought to be a more practical configuration with greatly reduced capital costs. To investigate the energy and economic performances of heat-pump-assisted distillation along with the HIDiC and simplified HIDiC, comparisons based on numerical simulation were made in the present work. A propylene–propane splitter was chosen for the comparison. Compression ratios and total numbers of stages were optimized to achieve an optimal configuration in terms of total annualized costs for each scheme before comparison with others. For the HIDiC and its simplifications, the impacts of different heat distribution patterns were also considered. It was found that the results depend strongly on the basis selected for comparison, and some discussions and re...

Towards energy efficient distillation technologies – Making the right choice

In spite of claiming around half of the operational costs of chemical plants, distillation is still the most popular separation technology. Distillation has low thermodynamic efficiency, requiring the input of high quality energy in the reboiler – while rejecting a similar amount of heat at lower temperature, in the condenser. Several heat pump concepts have been proposed to upgrade that thermal energy and reduce the consumption of valuable utilities. Under certain conditions, the energy savings of heat pump assisted distillation is usually around 20–50%.This study proposes a novel selection scheme of energy efficient distillation technologies, with a special focus on heat pumps. The most promising technologies selected are vapor compression, mechanical or thermal vapor recompression, absorption, compression–resorption and thermo-acoustic heat pumps, multi-effect distillation, heat integrated distillation column, cyclic distillation, Kaibel and dividing-wall column. The scheme considers as the main selection criteria the type of separation tasks, product flow and specifications, operating pressure, difference in boiling points, reboiler duty and its temperature level. Moreover, this scheme is very practical, allowing major time and resources savings in the design of eco-efficient processes.

Mastering Heat Pumps Selection for Energy Efficient Distillation

A practical selection scheme of energy efficient distillation technologies is proposed, with a special focus on heat pumps. The most promising technologies selected are: vapour compression, mechanical or thermal vapour recompression, absorption, compression-resorption and thermo-acoustic heat pumps, heat integrated distillation column, cyclic distillation, Kaibel and dividing-wall column. The scheme considers the type of separation tasks, the product flow and purity specifications, the boiling point differences (?Tb), the reboiler duty (Qreb) and its temperature level (Treb) as the main technology selection criteria. The proposed scheme allows considerable savings in time and resources allocated for the selection of eco-efficient chemical processes.

Energy saving and thermodynamic efficiency of a double-effect distillation column using internal heat integration

The existing internally heat-integrated distillation column with the problem of utilizing a compressor is modified to propose a new heat-integrated distillation column without the compressor. Two identical columns of a conventional binary distillation are implemented to the heat integration. The energy used in the reboiler is recovered by the internal heat integration between the stripping section of one of the columns at lower pressure and the rectifying section of the other higher pressure column. The heat integration is similar to double-effect distillation, but internal heat integration requires less pressure elevation. The performance of energy saving and thermal efficiency improvement of the proposed system is evaluated with the two examples of the benzene-toluene and methanol-ethanol processes. The performance comparison indicates that the proposed system requires 17.4% less of reboiler duty for the benzene-toluene process and 15.8% less of heating duty for the methanol-ethanol process. The thermal efficiencies are 16.3% and 23.8% for the benzene-toluene and methanol-ethanol processes, respectively. Elimination of the compressor makes the column operation easy and the separate reboilers and condensers for the two columns in the proposed system provide flexible control, when the controllability of the proposed system is compared with that of the existing internally heat-integrated distillation column.

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

Improving the exergy efficiency of a cryogenic air separation unit as part of an integrated gasification combined cycle

The efficiency of a two-column cryogenic ASU (air separation unit) that is part of an IGCC (integrated gasification combined cycle) can be increased significantly by making better use of the heat of compression and by improving the heat integration of the distillation columns. The rational exergy efficiency of the ASU, which is defined as the desired increase in exergy content of the products divided by the amount of work that is added to the process, can be increased from 35% to over 70%. The exergy destruction per amount of feed is reduced with 1.6kJ/mol air, corresponding to a 0.74% increase in the net electric efficiency of the IGCC. The efficiencies are expected to increase even further because the full potential of using heat-integrated distillation columns is not yet achieved.

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

AbstractInternally, 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

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.

Simplified design and control of an ideal heat-integrated distillation column (ideal HIDiC)

Three kinds of process simplification are derived for an ideal heat-integrated distillation column (ideal HIDiC: S–0) using three heat exchangers between its rectifying and stripping sections. These include one with the heat exchangers located in the top, middle, and bottom of the ideal HIDiC, respectively (S–1), one with the vapor flows from the rectifying section and compressor as hot flows in the three heat exchangers (S–2), and one with the vapor flow from the rectifying section as sole hot flows in the three heat exchangers (S–3). The impact of process simplification is examined in terms of the separation of a binary mixture of ethylene and ethane. The S–1 appears inferior to the S–0 in thermodynamic efficiency, but with comparable dynamic behaviors. The S–2 and S–3 need lower capital investment and operating cost than the S–1, but with a sharp degradation in process dynamics and controllability. Although the augment of heat transfer areas leads to a reduction in operating cost, almost no favorable effect is identified on process operation. To derive a feasible design of the ideal HIDiC, one must therefore exercise a careful trade-off between design and operation via the locations of these heat exchangers. © 2012 Curtin University of Technology and John Wiley & Sons, Ltd.

Recent Advances in Internally Heat-Integrated Distillation Columns (HIDiC) for Sustainable Development

Recent Advances in Internally Heat-Integrated Distillation Columns (HIDiC) for Sustainable Development

Steady-state simulation of a reactive internally heat integrated distillation column (R-HIDiC) for synthesis of tertiary-amyl methyl ether (TAME)

Tertiary-amyl methyl ether (TAME) is a very important fuel additive, which has attracted the attention of many researchers. In this article, the synthesis of TAME by a reactive internally heat integrated distillation column (R-HIDiC) is investigated. A complex mathematical formulation is developed for simulating the proposed reactive heat integrated distillation column (R-HIDiC), based on material balance, equilibrium, summation of mole fractions and enthalpy balance (MESH) equations. The suggested model is used for simulating an R-HIDiC for industrial production of TAME. The performance of the proposed R-HIDiC is compared to the conventional reactive distillation column which is usually used in TAME production plants. The model verification has been performed using industrial data of the conventional TAME reactive distillation. The simulation results show that the total energy consumption of the proposed R-HIDiC is about 22% less than that of the conventional reactive distillation column.