Azeotropic Dividing-wall Column Research Articles

Energy-saving design and optimization of pressure-swing-assisted ternary heterogenous azeotropic distillations

A huge amount of energy is always consumed to separate the ternary azeotropic mixtures by distillations. The heterogeneous azeotropic distillation and the pressure-swing distillation are two kinds of effective technologies to separate heterogeneous azeotropes without entrainer addition. To give better play to the synergistic energy-saving effect of these two processes, a novel pressure-swing assisted ternary heterogeneous azeotropic distillation process is proposed firstly. In this process, the ternary heterogeneous azeotrope is decanted into two liquid phases before refluxed into the azeotropic distillation column to avoid the aqueous phase remixing, and three columns’ pressures are modified to decrease the flowrates of the recycle streams. Then the dividing wall column and heat integration technologies are introduced to further reduce its energy consumption, and the pressure-swing assisted ternary heterogeneous azeotropic dividing wall column and its heat integration structure are achieved. Genetic Algorithm procedure is employed to optimize the proposed processes. The design results show that the proposed processes have higher energy efficiencies and lower CO2 emissions, compared with the published ternary heterogeneous azeotropic distillation process.

Investigation of energy-saving azeotropic dividing wall column to achieve cleaner production via heat exchanger network and heat pump technique

A thermally coupled azeotropic dividing wall column (ADWC) configuration is explored for the separation of industrial wastewater to recycle the organic solvent tert-butanol. Heat pump technology is used to the ADWC configuration to improve the released heat duty quality of the condenser achieving the energy-saving. A gas preheater before the compressor is installed in the heat pump assisted ADWC configuration in increasing the temperature of the inlet vapour stream of the compressor that achieves effectively reducing the power and compression ratio of the compressor. To fully utilize a large amount of superheat energy produced in heat pump system indicated by the temperature-enthalpy and Grand Composite Curve diagrams, a green and sustainable Heat Integrated ADWC (HI-ADWC) separation configuration is proposed by the combined use of heat exchange network and heat pump implementations. Three indexes involving total annual cost, CO2 emissions, and exergy loss are introduced to evaluate the economic, environmental and thermodynamic performances. The results illustrate that the TAC of the proposed green and sustainable HI-ADWC configuration is significantly reduced by 32.91% with a ten-year payback period compared to that of the existing configuration. CO2 emissions are reduced by 86.43% and exergy loss of the HI-ADWC configuration by 36.72%. The proposed method for the green and sustainable HI-ADWC configuration could be widely extended to other industrial processes reduce energy consumption and related CO2 emissions.

Dynamics and control of a heat pump assisted azeotropic dividing-wall column for biobutanol purification

An efficient downstream process has been developed for the acetone–butanol–ethanol (ABE), allowing about 60% energy savings as compared to a conventional separation sequence. This is achievable in an azeotropic dividing-wall column (A-DWC) coupled with a heat pump and applying heat integration. The energy use is reduced to only 2.7 MJ/kg butanol (or 7.5% of the energy content of butanol), but to take full advantage of the energy savings offered by this highly integrated process, the process must be also controllable. This work presents the dynamics and control of this novel A-DWC process used for biobutanol purification.A rigorous, pressure-driven dynamic simulation has been developed in Aspen Plus Dynamics. After adding the required PID controllers (e.g. flow, pressure, liquid level and temperature) to the base-case process, the system can handle small and short disturbances (e.g. 5% change of feed flow rate for 10 min.) but if the disturbance persists for a long time the process shuts down. To solve this problem, the controllability of the system is improved by adding an additional reboiler and condenser to control the temperature on the feed-side stripping section. Moreover, adding concentration controllers ensures that the products purity is kept constant when feed flowrate or composition disturbances occur.

Enhanced biobutanol separation by a heat pump assisted azeotropic dividing-wall column

Enhanced biobutanol separation by a heat pump assisted azeotropic dividing-wall column

Separation of azeotrope (2,2,3,3-tetrafluoro-1-propanol + water) via heterogeneous azeotropic distillation by energy-saving dividing-wall column: Process design and control strategies

To separate the azeotrope of 2,2,3,3-tetrafluoro-1-propanol (TFP) and water, the energy-saving heterogeneous azeotropic dividing-wall column (DWC) is proposed using chloroform as an azeotropic agent. Compared with the conventional design, the total condenser duty reduction of 44.57%, total reboiler duty reduction of 42.66% and TAC reduction of 37.79% by the DWC design are obtained. Based on the simulation results, the energy-saving in the DWC design is due to the thermal coupling of the conventional design and the separation of water by the decanter with the purity of 99.5mol%, rather not to the removal of remixing effect for the column sequence. The control strategy performance for the conventional and DWC designs are satisfactory, since TFP and water are separated with high purity, despite the disturbances of the flow rate of fresh feed, fresh feed composition and liquid split ratio.

Eco-efficient Downstream Processing of Biobutanol by Enhanced Process Intensification and Integration

The biobutanol stream obtained after the fermentation step in the acetone–butanol–ethanol process has a low concentration (less than 3 wt % butanol) that leads to high energy usage for conventional downstream separation. To overcome the high downstream processing costs, this study proposes a novel intensified separation process based on a heat pump (vapor recompression)-assisted azeotropic dividing-wall column (A-DWC). Pinch analysis and rigorous process simulations have been used for the process synthesis, design, and optimization of this novel sustainable process. Remarkably, the energy requirement for butanol separation using heat integration and vapor recompression assisted A-DWC is reduced by 58% from 6.3 to 2.7 MJ/kg butanol.

Design and Control of a Heat Pump-Assisted Azeotropic Dividing Wall Column for EDA/Water Separation

A novel heat pump-assisted azeotropic dividing wall column (HP-ADWC) has been proposed for the separation of a maximum-boiling ethylenediamine (EDA)/water system in this paper. Compared with conventional azeotropic distillation (CAD), HP-ADWC allows 42.93% energy savings and 24.36% total annual cost (TAC) savings if the payback period is assumed to be 8 years. To achieve the energy and economic benefits, this novel design must be controllable. However, it is challenging to control this complex and highly integrated HP-ADWC process since there are more interactive variables and fewer degrees of freedom than classic DWC process. In this paper, the dynamic controllability of HP-ADWC is studied by Aspen Dynamics and an effective control structure named CS4 is proposed, which works pretty well for the disturbances in both feed rate and feed composition.

Process Assessment of Heterogeneous Azeotropic Dividing-Wall Column for Ethanol Dehydration with Cyclohexane as an Entrainer: Design and Control

The heterogeneous azeotropic dividing-wall column (ADWC) features significant reduction of capital investment and energy consumption. Conventional azeotropic distillation sequences can be thermally coupled into two types of configurations of ADWCs, namely, the original ADWC with simple azeotropic–recovery section and the other with recovery section also serving as preconcentrator. The ADWC with a combined recovery–preconcentrator section has been investigated in both steady-state design and dynamic controllability. However, the original ADWC has only been proven to be more energy efficient than the conventional azeotropic–recovery column sequence, not compared with the conventional azeotropic–stripper column sequence. Furthermore, the dynamic performance of this ADWC are still unclear. Note that all the benefits of the ADWC are reasonable only under good dynamic controllability. Thus, in this work, we develop a comparative study of optimal design and dynamic performance of the ADWC with two conventional s...

Improving the Performance of Heat Pump-Assisted Azeotropic Dividing Wall Distillation

In this work, three vapor recompression heat pump (VRHP) models are designed for the azeotropic dividing-wall column (A-DWC) system to study the energy-saving effect. During the determination of these three models, how the top stream pipeline designs affect the energy consumption is discussed. As adding a preheater can cut down compressor pressure ratio and splitting top stream can decrease the feed flow of the compressor, all these methods can obviously help reduce compressor work for the process. Evaluation results show that the VRHP A-DWC systems have a better performance in energy consumption and environmental sustainability. Especially for Model 3, the savings of total operating cost (TOC) is 47.77% and that of the total annual cost (TAC) is 32.22%, compared with the conventional two-column azeotropic system. CO2 emissions in the process of model 3 can be reduced by 63.79%, and the thermodynamic efficiency increased to 22.64%.

Enhanced recovery of PGME and PGMEA from waste photoresistor thinners by heterogeneous azeotropic dividing-wall column

Propylene glycol monomethyl ether (PGME) and propylene glycol monomethyl ether acetate (PGMEA) are representative photoresistor thinners used extensively and generated as waste during the display and semiconductor material manufacturing processes. Although the waste thinner is normally retrieved by distillation, the azeotropes of these two thinner components with water limit the distillation performance. In this paper, an extensive design study of enhanced distillation processes was carried out to determine a favorable path for waste thinner recovery. Appropriate thermodynamic models for the design of a waste thinner recovery process were obtained through the regression and validation of experimental vapor-liquid-liquid equilibrium data. An optimal direct sequence using three conventional distillation columns with a decanter was introduced as a base design to overcome the distillation boundary by azeotropes. Several advanced distillation configurations were examined to further improve the energy efficiency of the conventional recovery process. A novel heterogeneous azeotropic dividing-wall column was developed based on process intensification and integration. The proposed enhanced recovery process reduced the energy requirement for waste thinner recovery significantly by 33.1%. The advanced distillation configuration can be an attractive option for improving the economic and environmental efficiency of the commercial waste thinner recovery and recycling processes.

Design and Control of Dividing-Wall Column for tert-Butanol Dehydration System via Heterogeneous Azeotropic Distillation

In this Article, a three-column model of azeotropic dividing-wall column (A-DWC) for heterogeneous azeotropic distillation (HAD) is investigated by demonstrating the design and control of tert-butanol (t-butanol) dehydration using cyclohexane as entrainer. Significant energy consumption savings of 23.80% and a minimal total annual cost (TAC) reduction of 19.93% between the optimum A-DWC design and the original two-column design can be obtained, respectively. Sensitivity analysis of whether the liquid split ratio (βL) can be a manipulated variable to maintain the product purities is conducted before the control structure for the A-DWC is established. Meanwhile, with two reboiler duties (QRs) still preserved in the A-DWC, the proposed control structure can solve disturbance issues and maintain the product purities very close to the set points with small deviation and short settling time.

Energy-Saving Dividing-Wall Column Design and Control for Heterogeneous Azeotropic Distillation Systems

In this paper, the energy-saving potential of a heterogeneous azeotropic dividing-wall column is investigated by demonstrating an example for the separation of pyridine and water using toluene as entrainer. The original two-column system includes a heterogeneous azeotropic column with top decanter and another column served as preconcentrator column for the fresh feed and also served as recovery column for aqueous outlet stream from decanter. It is demonstrated that this complex two-column system can be thermally coupled into a dividing-wall column with top decanter. By comparing the optimized design of this dividing-wall column with the original design, a significant reduction (29.48%) in steam cost can be obtained. Furthermore, because important control degree-of-freedoms (two reboiler duties) are still preserved in this dividing-wall column, control performance of this proposed design is found to be comparable to that of the original two-column system.