Heat-integrated Pressure-swing Distillation Research Articles

Exploring Exergy Performance in Tetrahydrofuran/Water and Acetone/Chloroform Separations

Distillation is significantly influenced by energy costs, prompting a need to explore effective strategies for reducing energy consumption. Among these, heat integration is a key approach, but evaluating its efficiency is paramount. Therefore, this study presents exergy as an energy quality indicator, analyzing irreversibility and efficiencies in tetrahydrofuran/water and acetone/chloroform distillations. Both systems have equimolar feed streams, yielding products with 99.99 mol% purity. The simulations are performed using Aspen Plus™, enabling evaluation at the column level, as a standalone process, or from a lean perspective that considers integration opportunities with other plants. The results show that, despite anticipated energy savings from heat integration, economic viability depends on pressure sensitivity. The results demonstrate that heat-integrated extractive distillation for acetone/chloroform raises utility energy consumption. Exergy calculations comparing standalone and total site integration reveal the variation in distillation efficiency with operation mode. Global exergy efficiency in both extractive and pressure-swing distillation depends on the fate of condenser duty. In heat-integrated extractive distillation, global exergy efficiency drops from 8.7% to 5.7% for tetrahydrofuran/water and 11.5% to 8.3% for acetone/chloroform. Similarly, heat-integrated pressure-swing distillation sees global exergy efficiency decrease from 34.2% to 23.7% for tetrahydrofuran/water and 9.5% to 3.6% for acetone/chloroform, underscoring the nuanced impact of heat integration, urging careful process design consideration.

Control of fully heat-integrated pressure-swing distillation with strict pressure manipulation: A case study of separating a maximum-boiling azeotrope with small pressure-induced shift

Pressure-swing distillation (PSD) is an alternative configuration used to separate pressure-sensitive azeotropes and avoid product contamination(s) in extractive or heterogeneous azeotropic distillation via the entrainer(s). Full heat integration between high- and low-pressure columns (HPC and LPC) can provide significant energy savings compared to the conventional case, while it also loses the control degree of freedom, trim condenser or reboiler heat load, via the integrated condenser/reboiler exchanger. Typically, the pressure of HPC is left uncontrolled, and additional pressure-compensated control strategies are implemented, which may create safety issues. To address this, the study proposes adding an auxiliary cooling-water-driven condenser to the fully heat-integrated PSD system, providing an extra manipulated variable to regulate the pressure of HPC. Compared to the conventional PSD system, the new modified process could achieve a 26.31% reduction in total annual cost. The research uses the maximum-boiling azeotropic mixture of acetone/chloroform as a case study which makes the distillation system characterized by high reflux ratios and a large recycle flow rate, leading to the unwelcome snowball effect. To achieve effective process control, robust control structures are proposed that rigorously regulate the pressure of the column by manipulating the heat removal in the trim condenser, attenuating or eliminating potential overpressure issues. Product purity and other evaluation indicators, such as product transient deviations, offsets, integral absolute error, and oscillation degrees, are also considered. Results show that the proposed control schemes can efficiently control the pressure of HPC, weaken the snowball effect, and maintain product purity. This study highlights the importance of pressure control for fully heat-integrated PSD systems, particularly for pressure-sensitive azeotropes with small pressure-induced shifts.

Improving control of Fully Heat-Integrated pressure Swing distillation through partially flooded Reboiler/Condenser

The binary mixture formed by acetonitrile (MeCN) and water (H2O) presents a minimum azeotrope highly sensitive to pressure variations, which can be separated through pressure-swing distillation (PSD), which is considered a very energy efficient process due to the possibilities of heat integration, in particular integration between the condenser and the reboiler of columns, known as Fully Heat-Integrated PSD (FHIPSD); in addition to being friendly from the environmental point of view. Despite promoting energy gains, integration reduces the freedom to control the process and, consequently, allows pressure fluctuation in the high-pressure column. This study evaluates the use of a partially flooded reboiler/condenser as a way to recover a degree of freedom of the process. The ability to maintain the purity specifications of products in two FHIPSD control configurations (conventional and with partially flooded reboiler/condenser) was evaluated for disturbances in the flow rate and feed composition. The use of a partially flooded reboiler/condenser allows controlling the heat exchange area by manipulating the level of liquid in the heat exchanger. The results showed that the partially flooded reboiler/condenser configuration promoted significant reductions in the steady state error values in the MeCN composition; and for positive flow disturbances, the steady state error value was reduced from 0.109 mol% to 0.004 mol%.

Energy-saving strategy for separation of methylcyclohexane/tert-butanol azeotrope

With the increase in industrialization, researchers are striving to pursue energy-saving and environment-friendly separation technologies. In this regard, effective separation of azeotropes is one of the focus areas in recent years. According to the characteristics of methylcyclohexane (MCH) and tert-butanol (TBA) azeotropes, a pressure-swing distillation (PSD) process is established in the current work. Combined with steam recompression and heat integration, two improved separation processes for reduced energy consumption are designed. The operating parameters had a significant effect on the efficiency and cost of the process. Therefore, the selection of parameters was discussed in detail. The proposed PSD processes were evaluated according to the assessment indices including total energy consumption (TEC), CO2 emissions and total annual cost (TAC). The results showed that the improved processes obviously decreased the energy consumption and improved the economy whether it is heat pump pressure swing distillation (HP-PSD) or heat integrated pressure swing distillation (HI-PSD). The HI-PSD process can achieve a TAC savings of 30.86%, TEC reduction of 37.59% and CO2 reduction of 36.34%. The HP-PSD process is found to be the most economical and environment-friendly process among the studied processes, and could achieve 34.92% TAC savings, 42.89% TEC reduction and 50.98% CO2 reduction.

Comparative optimal design and effective control of different pressure extractive distillation for separating acetone - Methanol

Acetone and methanol are critical industrial feedstocks as well as organic solvents. Previous studies on the separation of the minimum-boiling azeotrope acetone-methanol by pressure-swing extractive distillation have shown superiority in terms of energy and cost savings. However, the pressure-varying configuration inevitably requires high-grade heat steam. To surpass the limitation, a novel different pressure extractive distillation strategy is proposed in this paper. The conceptual design of the different pressure extractive distillation configuration is carried out from thermodynamic insights, and the feasible ranges of entrainer/feed flow rate ratio and reflux ratio are determined. The design parameters are optimized by an improved non-dominated sorting genetic algorithm. Compared with the conventional extractive distillation process, the total annual cost (TAC) and CO2 emissions of the proposed process are reduced by 22.17% and 48.14%, respectively. An alternative different pressure extractive distillation process with feed preheating is then obtained by changing feed thermal condition, which has a 24.08% reduction in TAC and a 48.33% reduction in CO2 emissions in comparison with the conventional extractive distillation process. Compared with the existing heat-integrated pressure-swing extractive distillation process, the new process has a 2.90% and 22.36% reduction in TAC and CO2 emissions, respectively. Subsequently, two control schemes are presented by calculating controllability indicators in the steady-state design stage. The results illustrate that the improved control scheme with multiple feedforward control loops performs the best robustness.

Economic and Environmental Evaluation of Heat-Integrated Pressure-Swing Distillation by Multiobjective Optimization

Economic and Environmental Evaluation of Heat-Integrated Pressure-Swing Distillation by Multiobjective Optimization

Design and control of a comprehensive Ethylenediamine (EDA) process with external/internal heat integration

Ethylenediamine (EDA), also known as Ethane-1,2-Diamine, is a valuable raw material, and the synthesis will produce several higher polyamines. This study proposes a systematic synthesis method for separating six products from the EDA plant as the fresh feed. For the separation of six components, there are forty-two possible sequences. There will be only seven promising sequences left with the constraint of azeotrope and heuristics in distillation. To minimize the total annual cost (TAC), the pressure-swing configuration and the purity of flow rate that how close to the azeotrope can be optimized. Furthermore, unlike ordinary optimization, this study provides a method that considers the heat-integrated pressure-swing distillation (PSD) system during the iterative procedure. It is proved that this method can indeed find the genuinely optimal sequence distinct from the traditional iterative result based on the objective function, the lowest TAC. Through the other energy-saving strategies, the optimal result will save TAC of 15.15% by the external and internal heat integration, known as dividing wall columns (DWC). Afterward, basic and improved control structures are explored based on the optimal results in steady-state design. With the proposed control strategies, the purities of all components can be kept within acceptable ranges when faced with the inevitable throughput and composition changes.

Energy-saving reactive pressure-swing distillation process for separation of methanol - dimethyl carbonate azeotrope via reacting with propylene oxide

Pressure-swing distillation (PSD) is a widely used in the chemical industry to separate azeotropes without the introduction of a any third component; however, the process involves high energy consumption and operating costs are required owing to the change in pressure. For the separation of methanol–dimethyl carbonate azeotropes, an intensified reactive pressure-swing distillation (R-PSD) process has been proposed, wherein a reactive distillation column is used, instead of a high-pressure column, and the propylene oxide (PO) is introduced into the system as a reactant to reacts with methonal. To compare the feasibility of the proposed R-PSD process with the conventional heat-integrated PSD process, three indicators—total energy requirements, total annual cost, and CO2 emissions—were used. The results show that the R-PSD process performs better than the conventional heat-integrated PSD process in terms of energy, economics and environmental owing to the partial consumption of methanol and the simultaneous co-production of high-value propylene glycol methyl ether (PGME). Moreover, at 50% methanol consumption, the total energy consumption, total annual cost, and the CO2 emissions were reduced by 46.0%, 34.3%, and 45.0%, respectively, compared with the conventional heat-integrated PSD process. This implies the improved R-PSD process has significant energy-saving potential.

An advanced optimization strategy for enhancing the performance of a hybrid pressure-swing distillation process in effective binary-azeotrope separation

The separation of binary azeotropes with low cost and energy consumption is important and challenging for the production of chemicals. A hybrid heat-integrated pressure-swing distillation process (HHIPSD) with heat pump was proposed for the separation of both maximum- and minimum-boiling azeotropes in this work. Compared to the conventional fully heat-integrated pressure-swing distillation process (FHIPSD), the HHIPSD process showed lower total annual cost and higher thermodynamic efficiency in the separation of seven minimum-boiling azeotropes of benzene-ethanol, methanol-acetone, methanol-ethyl acetate (EA), ethanol-EA, acetonitrile-ethanol, isobutanol (IBA)/isobutyl acetate (IBAc) and diisopropyl ether (DIPE)-isopropyl alcohol (IPA), and two maximum-boiling azeotropes of water-ethylenediamine (EDA) and acetone-chloroform. For the best performance of HHIPSD process, robustness and algorithm optimization were studied in this paper. Scenario analysis method was proven to greatly enhance the convergence of HHIPSD models. The improved genetic algorithm (GA) was modified by particle-swarm optimization and pattern search method and validated by 13 benchmark functions. Meanwhile, different constraint handling methods were studied to ensure the better performance of the improve GA method. With the improvement of model robustness and optimization algorithm, the HHIPSD process achieved 21.6 % and 4.2 % decrease of TAC for water-EDA and methanol-acetone separation, respectively, compared to FHIPSD process. The proposed HHIPSD process together with the optimization strategy suggests the pressure-swing distillation technology can be highly effective in azeotrope separation.

Study on energy saving of heat integrated distillation process for methyl acetate–methanol–tetrahydrofuran–water

ABSTRACT Based on the characteristics of binary azeotropic composition in the mixture of methyl acetate–methanol–tetrahydrofuran–water sensitive to pressure, pressure swing distillation (PSD) and double-solvent extraction distillation (DSED) were proposed to study the separation of the quaternary system. Numerical simulations were performed by ASPEN PLUS software (version 10.0) environment under the WILSON thermodynamic model. The economy of PSD and DSED process was performed, and the heat integration of two distillation processes was compared based on total annual cost (TAC). Research results of PSD indicated that compared with conventional PSD (CPSD), heat-integrated PSD (HIPSD) can save energy consumption and TAC by 33.87% and 30.70%, respectively, and moreover increase thermodynamic efficiency by 1.77%, so it had obvious energy-saving effect and economic advantage. Simulation results of DSED showed that water (H2O) and ethylene glycol (EG) were most suitable extractants for the system, and the suitable solvent ratios for H2O and EG were 0.28 and 0.38, respectively. Compared with conventional double-solvent ED (CDSED), heat-integrated double-solvent ED (HIDSED) can save energy consumption and TAC by 43.29% and 28.12%, respectively, and moreover increase thermodynamic efficiency by 3.25%, so it was superior to CDSED. The results indicated that the energy consumption and TAC of HIDSED are respectively 63.56% and 44.01% less than the HIPSD process, and the thermodynamic efficiency of the former is 3.9% larger than the latter, so the HIDSED process shows better economic and energy-saving effect.

Pressure control of fully heat-integrated pressure-swing distillation system using hot-vapor bypass

Fully heat-integrated pressure-swing distillation system is often more economically viable; however, the dynamic behavior of this system is subject to the effect of floating-pressure in the high-pressure column, making the control of this process a challenge. The most common way to control the pressure in distillation columns is by manipulating the coolant flow rate, but this strategy cannot be used in the heat-integrated pressure-swing distillation because of the coupling between reboiler and condenser. Therefore, this study evaluates the use of hot-vapor bypass to control the pressure of the high-pressure column of the pressure-swing distillation process applied to the separation of azeotropic acetonitrile–water system. Disturbances to the fresh feed flow rate and feed composition were performed. The scheme with dual pressure control presented the lowest average value of the IAE. Moreover, all configurations have shown satisfactory results in controlling the products’ composition with an offset of less than 0.013%.

Synthesis of heat‐integrated pressure‐swing azeotropic distillation using a graphical pinch analysis

AbstractA new graphical method for the fundamental design of pressure‐swing distillation (PSD) and valid heat integration of the designed process is demonstrated based on a pinch analysis. As the minimum pressure constraint, the pinch pressure is determined by this graphical method to secure the necessary temperature driving force and circumvent the distillation boundaries. For a feasibility evaluation of heat‐integrated PSD (HIPSD), the suggested approach requires visualization of the pinch temperature contours and the feasible composition region of an initial feed according to the pressure change and dynamic properties of ternary azeotropic systems. We thus carried out an in‐depth examination by conducting case studies to show the feasible integration into HIPSD. The new insight is that the HIPSD system can have different pinch pressures depending on the column sequence or the separation order of pure components. In addition, the analysis verifies that energy‐efficient HIPSD can be generated by considering pinch constraints.

CFD-aided design of internally heat-integrated pressure-swing distillation for ternary azeotropic separation constrained by pinch pressure

• Novel HIPSD for separating an azeotropic ternary mixture is proposed. • An extended pinch-based method to determine the pressure of HIPSD is introduced. • HIPSD alternatives are generated for the given initial feed composition. • Practical heat transfer rates in HIPSD are determined by the CFD method. • Significant energy savings in HIPSD are achieved for ternary azeotropic separation. This study addresses computational fluid dynamics (CFD) for designing internally heat-integrated pressure-swing distillation (HIPSD) with improved energy efficiency in azeotropic distillation. An extended concept of pinch pressure is applied to determine the operating pressure of the HIPSD in a double annular column configuration for the circumvention of a distillation boundary and adequate heat transfer. For the separation of a highly azeotropic ternary mixture of butyl acetate, butanol, and water, the combination of a single unit of HIPSD and a decanter is employed. This azeotropic mixture is separated in different design alternatives for the given initial feed compositions. In each sequence, the heat transfer rate inside the HIPSD was calculated by the CFD method, and the total utility consumption accordingly decreased by 9.72% and 15.44%. The reboiler and condenser duty in the HIPSD were reduced by up to 48.65%. The separation efficiency in the condenser of the high-pressure column was improved enough to reach a zero reflux by the internal heat integration.

Evaluation of membrane-assisted hybrid processes for the separation of a tetrahydrofuran-methanol-water mixture

The combination of pervaporation (PV) and distillation provide considerable potential for the separation of azeotropic multicomponent mixtures. However, only a proper techno-economic evaluation of these processes compared to a reference process enables a reliable evaluation of benefits. Within this work, the potential of a PV-assisted distillation process is evaluated for the mixture of tetrahydrofuran methanol and water compared to a heat-integrated pressure-swing distillation process. Since initial evaluations reveal a significant potential of the PV-assisted processes regarding the required energy demand, experimental investigations of three polymeric and two inorganic membranes were conducted. A detailed characterization of the most promising membranes PERVAP™ 4155–40 and Hybrid Silica HybSi® AR was performed, and the latter one provided the highest permeance and selectivity. Based on the derived flux models, an economical optimization was performed. Despite the energy-benefits of the PV-assisted processes, the reference process was still evaluated more favorable under the considered framework, mainly caused by high investment and cooling costs. The current study illustrates the benefits of a tight integration of model-based process design and experimental investigations. Despite possible energy savings and promising performance metrics of the membrane, an assessment of the techno-economic performance of these processes is of major importance to identify applications.

Energy-efficient and cost-effective alternative separation techniques for 2-methoxyethanol–toluene azeotropic mixture: Design and control studies

The separation of 2-Methoxyethanol–toluene azeotropic mixture has high practical significance in both industry and the laboratory because of their multipurpose solvating properties. However, both 2ME and toluene have adverse effects on human and animal health; therefore, researchers have become interested in their separation. A significant amount of 2-methoxyethanol–toluene forming a minimum-boiling azeotrope is discharged by the electrochemical industry. The presence of this azeotrope renders separation a challenging task. Separation techniques, namely pressure swing distillation (PSD) and azeotropic distillation (AD), have not yet been explored. In this study, these separation techniques are evaluated economically and dynamically using a well-known commercial simulator Aspen Plus®. This study includes the development of process schematics for these alternative separation processes and economic analysis involving total annual cost (TAC) calculations. It is concluded that the heat-integrated PSD technique leads to 21.35% savings in TAC compared to previously reported techniques. Furthermore, a decentralized plant-wide control structure for a suitable separation technique is also developed and tested for ±10% throughput manipulations in fresh feed flow rate and ±5% disturbances in feed composition. This study will significantly help the process engineers overcome the challenges of handling the electrochemical industry's hazardous effluent in environmentally and economically ways.

Energy-Efficient Design of a Novel Double Annular Separation Column Using Pinch Pressure

This study introduces a pinch-based method to design an internally heat-integrated pressure swing distillation (HIPSD) with a double annular column. In the configuration, the annular stripping sect...

Differential temperature control in heat-integrated pressure-swing distillation for separating azeotropes to deal with operating pressure fluctuations: Basic and explanatory data.

This data article contains basic and explanatory data of “Differential temperature control in heat-integrated pressure-swing distillation for separating azeotropes to deal with operating pressure fluctuations” [1], including thermodynamic models, vapor-liquid equilibrium diagrams, steady-state flowsheets, temperature profiles of columns, description and setpoint units of the abbreviation of inventory control loops, description of control loops of control flowsheet with DTC, control flowsheets of PCTC and DTC, temperature and composition tuning constants, faceplates and flowsheet equations, dynamic performances and integral absolute errors. It also contains other important information.

Differential temperature control in heat-integrated pressure-swing distillation for separating azeotropes to deal with operating pressure fluctuations

For heat-integrated pressure-swing distillation (PSD) in which the heat release of overhead vapor condensation of high-pressure column (HPC) is completely utilized to supply the reboiler duty of low-pressure column (LPC), the operating pressure (OP) of the HPC cannot be controlled. Pressure-compensated temperature control (PCTC) is widely used to hold the controlled temperature under OP fluctuations to achieve effective control. In this paper, differential temperature control (DTC) is applied to control the sensitive-stage temperature under OP fluctuations of the HPC in the control of a variety of heat-integrated PSD processes, including both conventional and entrainer-assisted PSD, both partially and fully heat-integrated PSD, both LPC->HPC and HPC->LPC sequence, and separating both minimum-boiling and maximum-boiling azeotropes. IAE of the product purities of all the processes are calculated. Systematic comparison between DTC and PCTC is implemented. The results show that effective control can be achieved when implementing DTC in these processes and the dynamic performances of DTC and PCTC are almost the same. Therefore, DTC can be applicable in the control of heat-integrated PSD for separating binary azeotropes, which is also a good inspiration for other heat-integrated distillation processes.

Economically and thermodynamically efficient heat pump-assisted side-stream pressure-swing distillation arrangement for separating a maximum-boiling azeotrope

The feasibility and effectiveness for the two types of heat pump-assisted side-stream pressure-swing distillation arrangements (vapor recompression and bottom flashing heat pump-assisted systems) are investigated with the separation of a maximum-boiling ethylenediamine and water azeotrope as the demonstrating example. To further improve the heat recovery within the process as much as possible and reduce the excessive utilization of cold and hot utilities, the efficient Heat Exchanger Network Synthesis (HENs) analysis tool is adopted. Total annual cost (TAC), carbon footprints and thermodynamic efficiency are as the evaluation indicators to assess and screen the eco-efficient arrangement in a series of pressure-swing distillation (PSD) processes. Compared to the partially heat-integrated PSD process, the economically optimum flowsheet is the intensified self-heat recuperative vapor recompression-assisted arrangement (VRC-SSPSD-PF-HEN) since it can achieve the reductions of 59.01% in energy consumption rates, 86.60% in CO2 emissions, 12.78% in TAC and enhancement of 143.38% in thermodynamic efficiency. And the amount of heat recovery within this process is 7028.0 kW with the requirement of cold utility 395 kW and without any hot utility consumptions (electrical power is required). Besides, the exergy destroyed in each component for the optimal intensified alternative is analyzed. Result shows that the major exergy losses mainly produce in columns, especially in high-pressure column.

Design and control of ethyl acetate/n-hexane azeotropic system separation via different heat-integrated pressure-swing distillation process

Design and control of ethyl acetate/n-hexane azeotropic system separation via different heat-integrated pressure-swing distillation process