Professional Flow-sheet Simulator Research Articles

Investigating the processing capacity of batch distillation by applying a second, smaller column

Increasing the processing capacity is important, especially in the pharmaceutical industry, where a given amount of waste solvent must be processed in a specific time period, else the remaining amount of waste solvent must be incinerated, which results in organic solvent loss and considerable environmental impact. In this paper, the possibility of increasing the processing capacity of batch distillation by using a second, already available, smaller batch column in addition to the original one is studied. The size of the columns is not changed during the calculations performed. Two case studies are presented. In the first one (Mixture 1), acetone, in the second one (Mixture 2), acetic acid must be recovered in high purity from their aqueous mixtures by operating either the larger column only or both columns simultaneously. The smaller column serves for preliminary separation, and its main-cut (Mixture 1) or residue (Mixture 2) is further processed in the larger one. The goal of this work is to maximise the processing capacity of the two-column process with the same recovery as in the single-column process. Both processes are modelled with a professional flow-sheet simulator. For the single-column process, the only independent variable is the reflux ratio. For the two-column process, the independent variables are the reflux ratios of both columns and the amount of intermediate product (distillate or residue) of the first column transferred to the second one. The ranges of the independent variables are determined by sensitivity studies for different charge compositions (20–50-80 mass% acetone or acetic acid), and each case is optimised by a genetic algorithm coupled to the flow-sheet simulator. It is also shown in this work that the processing capacity maximum of the two-column process is not always at the equality of the processing times of the two columns.

Reduction of the energy demand of a second-generation bioethanol plant by heat integration and vapour recompression between different columns

The distillation separation technology of an existing second-generation bioethanol production plant is investigated by simulation with a professional flowsheet simulator. The plant contains three distillation columns in series with increasing pressure. Our aim is to compare different Heat Integration (HI) possibilities for the reduction of external heating and cooling energy demands. Besides ethanol and water, 13 further organic pollutant components are taken into account, which were usually neglected in the literature. Several levels of Heat Integration options are studied: first only streams are integrated (HI-A), then a reboiler and a condenser of two different columns are coupled (HI–B). After that streams and columns are heat integrated (HI–C), finally a vapour recompression heat pump is also applied (HI–C + VRC) in a new configuration. The external energy demand and total annual cost of the different configurations are compared. Considerable energy saving can be achieved by all configurations, but the application of a heat pump is not economical in this case. The influence of changing the pressure of the ethanol concentrating column on the different Heat Integration configurations is also investigated.

Optimisation of solvent recovery in two batch distillation columns of different size

The recovery of acetone from an aqueous industrial waste solvent mixture containing a small amount of dichloromethane is studied. This separation can be performed in a single, large enough batch distillation column. When the amount of the waste solvent mixture increases and exceeds the processing capacity of this column, either the excess of solvent must be incinerated, or the processing capacity must be increased. The incineration is very disadvantageous from both economic and environmental points of view. It is investigated whether capacity can be efficiently increased by applying an additional, much smaller column, which is already available in the plant. Dichloromethane is removed in fore-cuts from both columns. The charge of the larger column (Column2) consists of two main cuts obtained from two consecutive batches of Column1. High purity acetone is obtained in the main cut of Column2. The optimisation of both the single- and two-column processes is performed by a genetic algorithm coupled with a professional flow-sheet simulator. The objective function minimised is the specific energy demand of the production of acetone. The effects of the composition of the fresh feed on the optimal values of the parameters and of the objective function are studied: the specific energy demand changes favourably on the increase of water and the decrease of dichloromethane concentration. A response surface method is used to successfully predict the optimal operating parameters in the space of compositions studied. Each optimised case is evaluated from economic and environmental points of view, as well. For an average charge composition, also by considering recycling of the residues of both columns, the weekly profit is by 12% higher and the CO2 emission is by more than 20% lower compared to the single-column process. Moreover, the processing capacity is increased by about 30%. It is shown in our work that it is worth applying a second, possibly smaller batch distillation column available in the plant before a larger one in order to increase the processing capacity.

Modelling of Hybrid Method for VOC Removal from Process Wastewater: Distillation and Hydrophilic Pervaporation

The study is motivated by the industrial problem from pharmaceutical industry, which is ethanol and methanol removal from process wastewater. To complete this goal hybrid method is investigated and optimized. Two distillation columns are sufficient for separation of alcohol-water mixture. Suitable water can be purified as bottom product of first column. Ethanol and methanol purification is achieved with combination of second distillation column and pervaporation. The target of this research is to rigorously model and optimize the separation of water-ethanol-methanol ternary mixture in professional flowsheet simulator environment. The minimal sufficient membrane transfers area and number of minimal theoretical stages of the columns are determined. Cost estimation is also investigated according to Douglas methodology. Considering the simulation and economic results it can be determined that, the hybrid configuration is suitable for separation of ternary mixture in 99.5 weight percent purity.

Enhanced separation of maximum boiling azeotropic mixtures with extractive heterogeneous-azeotropic distillation

In the separation industry the extractive heterogeneous-azeotropic distillation (EHAD) is a new and powerful innovation, that is capable of making the separation of highly non-ideal mixtures feasible and economical. In the last years there has been much attention paid to the separation of the minimum boiling homogeneous azeotropes. Although maximum boiling azeotropes are fewer in numbers than the minimum boiling ones but their separation is more complicated but it could be solved with the EHAD, too. Since EHAD is not limited to the separation of minimum boiling azeotropes, the separation of the maximum boiling azeotropes is studied in this work. Our work is motivated by industrial problems because there are such maximum boiling azeotropes in the liquid wastes of the fine chemical industry. The separation of highly non-ideal Water–Acetone–Chloroform–Methanol and Water–Ethyl Acetate–Chloroform–Ethanol quaternary mixtures are investigated and optimized in professional flowsheet simulator environment. Total Annual Costs are also determined. The purity requirement is 99.5 m/m% for Chloroform and the bottom product should be as clear as possible in water so that less liquid organic waste has to be incinerated. It is also an important merit of the EHAD that the chemicals in the distillate can be usually reused supporting sustainability. Different solutions for the separations supplemented with heat integration are examined. On the basis of the computer simulations and the experimental verification it can be concluded, the first time on the literature, that the separation efficiency of EHAD is superior also for the separation of the maximum boiling azeotrope mixtures.

Influence of entrainer recycle for batch heteroazeotropic distillation

Dehydration of isopropanol applying batch heteroazeotropic distillation with toluene as entrainer (E) is investigated. The composition of the feed is near to that of the isopropanol (A)-water (B) azeotrope. The effects of recycling the entrainer and the off-cut are studied by dynamic simulation with a professional flow-sheet simulator. Three consecutive batches (one production cycle) is studied. Both operational modes (Mode I: decantation after distillation and Mode II: decantation during distillation) are simulated. For Mode II, calculations are performed both for Strategy A (distillate from the aqueous (E-lean) phase only) and Strategy B (partial withdrawal of the organic (Erich phase), as well). The E-rich phase, the final column hold-up and the off-cut (Mode II only) are recycled to the next batch. The influence of the following parameters are determined: quantity of entrainer, reflux ratios of the steps. The variations caused by the recycling in the 2nd and 3rd batches are also shown. The best results (lowest specific energy demand and highest recovery of A) are obtained by Mode II, Strategy A. Recycling increases the recovery, and drastically diminishes the entrainer consumption. However, it makes the production slower and decreases the quantity of fresh feed that can be processed.

Treatment of Pharmaceutical Process Wastewater with Hybrid Separation Method: Distillation and Hydrophilic Pervaporation

Abstract The work is motivated by an industrial problem, which is alcohol removal from pharmaceutical process wastewater. The aim of the study was to develop a complete hybrid operation is investigated. Ethanol dehydration, in combination with distillation and hydrophilic pervaporation, is used to investigate about the extent of separation of the ethanol-water mixture. The aim of this research is to rigorously model and optimize this hybrid operation in professional flowsheet simulator environment. The number of minimal theoretical plates of distillation column and minimal effective membrane transfer area are determined. Cost estimation is also examined according to Douglas methodology. Considering our results it can be concluded that, the distillation and hydrophilic pervaporation processes are suitable for separation ethanol and water in 99.5 weight percent purity

Improvement of Post-combustion Carbon Capture Process in Retrofit Case

Carbon dioxide emission, one of the core cause of global warming and other threats of nonreversible environmental effects, is in focus today. Among the several methods of CO2 emission mitigation, post-combustion carbon capture (PCC), based on absorberdesorber systems with amine absorbents, is one of the promising alternatives. The major anthropogenic CO2 point sources are power plants, natural gas extraction units, oil refineries, cement factories, biogas plants, etc. As these CO2 sources can be treated with a PCC absorber-desorber system, then these two units should cope with various conditions. To maintain a desired high removal efficiency, the capture unit must work in flexible conditions. The aim of this study is to evaluate the influence of the extent of the absorption of carbon dioxide on the overall performance of the acid gas removal process, considering that, generally, as the amount of removed CO2 increases, the separation becomes more challenging. In this work a verified computer based process model for the absorber-desorber system is used. Aspen Plus® professional flowsheet simulator is used for this purpose. Attention is paid on the proper operating parameters of a PCC absorber-desorber system for the case of increasing the CO2 capture efficiency up to 99%. As alternative solutions for these cases different scenarios are considered:•the increase of the capacity of a classic configuration of an absorber-desorber system;•the introduction of a second absorber column as extending the absorption column height;•the possible use of two absorbers and two desorbers working in series.This work deals with the detailed study on maximizing CO2 removal efficiency while maintaining the minimal energy consumption for the absorbent regeneration section.

Optimization of a batch extractive distillation process with recycling off-cuts

A multiple step solvent recovery distillation process is optimized where the components form several azeotropes, and the off-cuts are recycled. Both conventional and extractive batch distillation are studied. The recovery of methanol from an industrial waste solvent mixture (acetone–methanol–tetrahydrofuran–water–toluene) is rigorously simulated and optimized. The first fore-cut is incinerated; the second fore-cut, the after-cut and the hold-up are recycled to the next batch in order to decrease the loss of methanol. The optimization of both processes is performed by a genetic algorithm coupled with a professional flow-sheet simulator performing the dynamic simulation. The optimization of the batches is performed consecutively, with the objective function being the profit of the actual batch. The optimization variables are the reflux ratios of the steps (fore-cuts, main cut), duration of fore-cut withdrawals and for the batch extractive distillation the flow rate and duration of entrainer (water) feeding. The effects of the recycling of the off-cuts on the charge composition and on the optimal values of the parameters are studied, and the optimized batch distillation and batch extractive distillation processes are compared with each other and with the batch distillation process used in the plant. The extractive process gives a 67% higher profit than the optimized batch distillation, whose profit was in turn by 25% higher than without optimization. The environmental impact is also assessed by calculating the related CO2 emission and the waste water production. The specific CO2 emission (kg CO2/kg product) is by 20% lower for the extractive process than for the optimized and by 22% lower than for the non-optimized batch distillation.

Optimisation of a batch extractive distillation process with off-cut recycle

The recovery of methanol from an industrial waste solvent mixture (acetone (A) – methanol (B) – THF (C)–water (D) – toluene (E)) by a batch (BD) and batch extractive distillation (BED) process was simulated and optimised. For both processes a production cycle consists of six consecutive batches. The first fore- cut is incinerated; the second fore-cut, the after-cut and the hold-up are recycled to the next batch in order to decrease the loss of methanol. The optimization of both processes was performed by a genetic algorithm (GA) coupled with a professional flow-sheet simulator performing the dynamic simulation. The optimization of the batches was performed consecutively, with the objective function being the profit of the actual batch. The optimization variables were the reflux ratios of the steps (fore-cuts, main cut), duration of fore-cut withdrawals and for the BED the flow rate and duration of entrainer (water) feeding. The effects of the recycling of the off-cuts on the charge composition and on the optimal values of the parameters were studied, and the optimised BD and BED processes were compared.

Vapor Compression for Batch Distillation: Comparison of Different Working Fluids

Application of a heat pump system is a possibility for decreasing the high energy demand of distillation. The use of different working fluids for a vapor compression system for batch distillation is investigated. In this study working fluids are classified as “wet” and “dry” based on their behavior during the compression. The separation of a low relative volatility mixture (n-heptane–toluene) is investigated by rigorous simulation performed with a professional flow-sheet simulator. Standard reactor-reboiler is applied and simulated in a rigorous way (including the conditions of heat transfer). The basic criteria for the selection of the possible working fluids are determined. Based on these criteria n-hexane, n-pentane, ethanol, and isopropyl alcohol are studied as working fluids. The effectiveness of different working fluids is compared. The effect of the main operational parameters on the length of the payback period is examined. The minimal payback time is determined for the different working fluids. The best results are obtained for n-hexane.

Heat pump systems with mechanical compression for batch distillation

The operational and economic feasibility of different heat-pump systems with mechanical compression integrated to real batch distillation columns of different sizes is investigated. The systems studied are vapour recompression, vapour compression and vapour recompression with the application of an external heat exchanger. The issues of applying a mechanical compressor for a batch distillation column integrated with heat pump system are discussed. The separation of a low relative volatility mixture is investigated by rigorous simulation performed with a professional flow-sheet simulator. The systems studied are compared by payback times. For the vapour recompression system in the minimal payback time point the batch operation time was significantly longer than that of the conventional batch distillation. The payback time was considerably reduced by applying an external heat exchanger.

NEW COLUMN CONFIGURATIONS FOR PRESSURE SWING BATCH DISTILLATION II. RIGOROUS SIMULATION CALCULATIONS

The pressure swing distillation in different batch column configurations is investigated by rigorous simulation calculations. The calculations are made by a professional flow-sheet simulator for the separation of a minimum (ethanol-toluene) and a maximum boiling (water- ethylene-diamine) azeotropic mixture. Besides studying the well known configurations (rectifier, stripper) we also investigate two novel configurations such as double column batch rectifier and double column batch stripper. The alternate application of a batch rectifier and a batch stripper is also studied. The different column configurations are compared.