Internal configurations for a multi-product dividing wall column

This paper addresses possibilities and peculiarities associated with establishing the most beneficial internal configuration of a complex dividing wall column (DWC), using as a base case the separation of a multicomponent aromatics mixture into four or five product streams. As expected, the V_min-diagram method proved to be an appropriate tool in such a study, as a means for identifying and assessing promising configurations and at the same time to provide the necessary inputs and reliable initial guesses for detailed simulation-based determination of energy and stage requirements. A new, energy efficient two-top product configuration is introduced that appears to be an interesting option for a four-product DWC.     

Designing four-product dividing wall columns for separation of a multicomponent aromatics mixture

Preliminary evaluations using a simple but reliable short-cut method indicated that a 15 component aromatics mixture can be separated very efficiently into four fractions according to the given product specifications employing either a single or a multiple partition wall dividing wall column (DWC). The obtained results have been used to initiate rigorous simulations, to determine the number of stages required in different sections, as well as to obtain internal flows of vapour and liquid necessary for dimensioning and adequate cost estimation for two design alternatives. Based on the comparison of total annualised costs it appears that a multi-partition wall configuration that maximizes energy efficiency is a more attractive option for implementation in aromatics processing plants than more practical single partition wall configuration.     

Investigation of the operability for four-product dividing wall column with two partition walls

For separating some specific four component mixtures into four products, the four-product dividing wall column (FPDWC) with two partition walls can provide the same utility consumption with the extended Petlyuk configuration, although with structure simplicity. However, the reluctance to implement this kind of four product dividing wall column industrially also consists in the two uncontrollable vapor splits associated with it. The vapor split ratios are set at the design stage and might not be the optimal value for changed feed composition, thus minimum energy consumption could not be ensured. In the present work, a sequential iterative optimization approach was initially employed to determine the parameters of cost-effective FPDWC. Then the effect of maintaining the vapor split ratios at their nominal value on the energy penalty was investigated for the FPDWC with two partition walls, in case of feed composition disturbance. The result shows that no more than + 2% above the optimal energy requirements could be ensured for 20% feed composition disturbances, which is encouraging for industrial implementation.     

Design and optimization of a dividing wall column for debottlenecking of the acetic acid purification process

The dividing wall column (DWC) has gained increasing application in a variety of chemical processes because of its potentiality in energy and capital cost savings in multicomponent separations. The main objective in this work is investigation of its use for removing the bottleneck phenomenon within the column when increasing the throughput of an existing distillation process, particularly, the acetic acid (AA) purification process. Optimal column sequence design, involving both conventional and DWC, is considered. The internal recycle flow distribution around the dividing wall was investigated as a primary optimizing variable. Several column arrangements were analyzed to show that the DWC requires less investment and energy costs than conventional distillation, the Petlyuk column, or the prefractionator arrangement.     

Decentralized temperature control of a pilot dividing wall column

The technology of dividing wall columns offers to save high amounts of operating and investment cost compared to conventional distillation columns and their configurations. The practical application is still limited due to a lack of experience and high interactions among the process variables.The present work deals with the development and test of a control system for a pilot dividing wall column. Within this, decentralized temperature control systems are designed by a systematic approach. Furthermore, these systems are evaluated concerning the process stability, the providing of defined product purities and the respective requirement of energy in case of disturbances. The focus is on simulative and experimental investigations in order to assure the practicability of the developments. The presented results show the effectiveness of the applied methods.     

Application of the dividing wall column to olefin separation in fluidization methanol to propylene (FMTP) process

Dividing wall column (DWC) is shown to be energy efficient compared to conventional column sequence for multi components separation, which is used for olefin separation in fluidization methanol to propylene process in the present work. Detailed design for pilot DWC was performed and five control structures, i.e. composition control (CC), temperature control (TC), composition-temperature control (CC-TC), temperature difference control (TDC), double temperature difference control (DTDC) were proposed to circumvent feed disturbance. Sensitivity analysis and singular value decomposition (SVD) were used as criterion to select the controlled temperature locations in TC, CC-TC, TDC and DTDC control loops. The steady simulation result demonstrates that 25.7％and 30.2％duty can be saved for condenser and reboiler by substituting conventional column sequence with DWC, respectively. As for control structure selection, TC and TDC perform better than other three control schemes with smal er maximum deviation and shorter settling time.     

Dividing wall column—A breakthrough towards sustainable distilling

Dividing wall column (DWC) is a single shell, fully thermally coupled distillation column capable of separating mixtures of three or more components into high purity products. Compared to conventional columns-in-series and/or in-parallel configurations a DWC requires much less energy, capital and space. This makes DWC to something that corresponds with the present day idea of sustainable process technology. Based on published papers and patent literature this paper aims to give a complete overview of the work done so far on the research and implementation of DWCs, from early ideas on thermal coupling of distillation columns to practical issues that needed to be solved for their successful implementation. Approaches to short-cut and rigorous simulation, optimization, and control are highlighted, with particular focus on column internals and dimensioning, which is only conceptually considered in academic publications. A survey of relevant patents is included providing information on equipment innovations and application areas of industrial interest. Finally authors look at what is needed on research and engineering side to enable maximization of potential gains by building DWCs for obtaining four or even more products containing two or more partition walls in parallel, which is something not yet attempted in industrial practice.     

Experimental study on pressure drops in a dividing wall distillation column

Previous studies in the fields of process design and process control [1] have shown the potential benefits that can be achieved through the implementation of thermally coupled distillation sequences, in particular, the dividing wall distillation column. The dividing wall distillation column meets important goals of process intensification, including energy savings, reduction in carbon dioxide emissions and miniaturization. In this paper, an experimental study on the hydrodynamic behavior of a dividing wall distillation column is presented. Several different values for gas and liquid velocities were tested in order to measure pressure drops and identify operational regions; the air/water system was used as the basis for the experimental setup. Results regarding pressure drops (fitted to the model of Stichlmair et al.) provide operational limits for the operation of the packed dividing wall distillation column. According to the results, the experimental dividing wall column can be operated at turbulent regime that is associated to proper mass transfer.     

反应精馏隔壁塔的模拟研究

以乙酸甲酯酯转换体系为例提出了一种反应精馏隔壁塔的设计和优化方法,应用该方法可将常规双塔反应精馏序列转化为反应精馏隔壁塔并保证各操作参数的最优值.首先通过在反应精馏塔与甲醇塔之间交换汽液相物流来实现反应精馏隔壁塔的简捷设计;然后利用Aspen Plus模拟软件,对常规反应精馏序列和反应精馏隔壁塔进行了模拟分析;最终以2...     

Dividing wall column for industrial multi purpose use

Dividing wall columns (DWC) for the distillation of multicomponent mixtures have received much attention in the past 15 years and have experienced a booming development. Since DWC demand higher efforts in equipment design and process control they are predominantly used in continuously operated dedicated production plants and spread only over a limited number of chemical companies. No open literature can be found where DWC are used in multi-purpose plants. The distillation equipment in those plants, typically batch wise operated, has to show a high degree of flexibility – an attribute that hardly seems to fit for dividing wall columns. Lonza set up the worldwide first multi-purpose DWC on the production site in Visp that fully meets the demands of a steadily changing production environment characterized by several different production campaigns, processes and products produced in the same plant throughout a year.This paper reports on the equipment design and the specific technical solutions that had to be implemented in order to satisfy the harsh specifications of multi-purpose production. Particular attention is put on the modelling and simulation of the column and the control scheme that has been applied. The paper contributes a new approach for setting up a flowsheet simulation that overcomes the frequently occurring problems in convergence and enhances robustness of the simulation.Since the launch of the column several different processes were successfully operated in this equipment. In each single case we directly transferred the process concept from simulation to the plant without piloting. The launch and operation of the column are explained in detail and finally the simulation results are compared to real operation data from the production.     

Optimal retrofit of a side stream column to a dividing wall column for energy efficiency maximization

A side distillation column is widely used to separate multicomponent mixtures into three products. However, this kind of column consumes considerable amounts of energy due to thermodynamic restrictions and the nature of the distillation process. Retrofit of the side distillation column to a dividing wall column (DWC) can result in significant energy savings. This study evaluated a systematic method for optimal retrofit of a side stream column to a DWC. The minimum energy requirement for the separation of a multicomponent mixture was used for a feasibility study. Subsequently, design and optimization was performed using shortcut, rigorous and response surface methodology. One case study was illustrated to demonstrate the proposed methodology. The results showed that the optimal retrofit of a side distillation column to the DWC could not only save a significant amount of energy, but also increase the capacity. This study highlights the potential for retrofitting a side stream column to a DWC from a techno economic point of view.     

Energy conserving effects of dividing wall column☆

The energy-conserving performance of dividing wal column (DWC) is discussed in this paper. The heat transfer through the dividing wall is considered and the results are compared with that of common heat insulation dividing wall column (HIDWC). Based on the thermodynamic analysis of heat transfer dividing wall column (HTDWC) and HIDWC, both computer simulation and experiments are employed to analyze the energy-conserving situation. Mixtures of n-hexane, n-heptane and n-octane are chosen as the example for separation. The results show that the energy consumption of HTDWC is 50.3%less than that of conventional distillation column, while it is 46.4% less than that of HIDWC. It indicates that DWC is efficient on separating three-component mixtures and HTDWC can save more energy than HIDWC. Thus it is necessary to consider the heat transfer while applying DWC to industry.     

气相进料对隔板精馏塔优化设计的影响

隔板精馏塔（DWC）在节能和节省设备投资方面具有十分突出的优势,隔板精馏塔中隔板位置是重要的设计变量,影响分离效果及能耗,当进料中含有气相时这种影响更加显著。选用苯、甲苯和对二甲苯三元物系,研究了进料的气相分率对隔板位置的影响并确定最优隔板位置。采用严格模拟方法,以年度总费用（TAC）为评价指标,比较不同进料气相分率下隔板塔的经济性,其中气相进料较液相进料TAC最高可节省23.33%。并通过灵敏度分析展示了在进料中含有气相时确定最优隔板位置的重要性。     

气相进料对隔板精馏塔优化设计的影响

隔板精馏塔（DWC）在节能和节省设备投资方面具有十分突出的优势,隔板精馏塔中隔板位置是重要的设计变量,影响分离效果及能耗,当进料中含有气相时这种影响更加显著。选用苯、甲苯和对二甲苯三元物系,研究了进料的气相分率对隔板位置的影响并确定最优隔板位置。采用严格模拟方法,以年度总费用（TAC）为评价指标,比较不同进料气相分率下隔板塔的经济性,其中气相进料较液相进料TAC最高可节省23.33%。并通过灵敏度分析展示了在进料中含有气相时确定最优隔板位置的重要性。     

隔壁精馏塔应用于空气分离的研究

以空气分离为例,考察了将隔壁精馏塔应用于空气分离的建模与基于年总成本的优化过程。首先对于空分上塔的氩浓度剖面进行了分析,提出了两种应用隔壁精馏塔的可能性,最终选择了带侧线精馏段的隔壁塔。然后考察了空分隔壁精馏塔上塔的各个结构参数与操作参数对其年总成本的影响,在保证产品质量的基础上得到优化的结构参数与操作参数。研究表明,与传统流程相比,将隔壁精馏塔应用于空气分离过程可使年总成本减少7.69%。     

A novel kind of multiple steady states characteristics in the dividing wall column

In this article, one kind of multiple steady states(MSS) phenomenon was investigated for a dividing wall column(DWC). The four-section model constructed in Aspen Plus was employed to simulate two DWC cases: mixture of n-hexane, n-heptane and n-octane; system of methanol, ethanol and n-propanol. It can be seen that there is a range of vapor split ratio in which multiple solutions of reflux ratio exist for fixed DWC configuration with the same feed and product streams. The width and the curve shapes of the MSS region, and the number of solutions change with the liquid split ratio. This MSS phenomenon was further explained using the component recovery around the prefractionator and the component recycling flow inside the DWC. This MSS phenomenon is helpful for DWC design by knowing the probable existence of multiple solutions in advance.     

四产品Kaibel隔壁精馏塔分离丙二醇混合物的模拟与节能分析

研究了包含甲醇、水、丙二醇和二丙二醇四组分混合物的分离问题,针对混合物的特征和分离要求,提出四产品Kaibel隔壁精馏塔的分离工艺,并利用Aspen Plus软件对Kaibel塔进行设计与节能分析。首先,设计了分离四组分混合物的三塔精馏流程（TCD）和热集成三塔精馏流程（HTCD）;其次,开展了四产品Kaibel塔分离四组分混合物的模拟研究,取得了满足分离要求的塔设计参数;最后,采用能量衡算和㶲损失分析相结合的方法,对Kaibel塔的用能特征进行了分析和比较。研究表明,与热集成三塔精馏流程相比,四产品Kaibel塔在操作费用方面不占优势,但在设备投资方面具有明显优势,可以实现在一个塔内四组分的分离,总㶲损失可降低9.41%。     

Composition control and temperature inferential control of dividing wall column based on model predictive control and PI strategies

The dividing wall column (DWC) is considered as a major breakthrough in distillation technology and has good prospect of industrialization. Model predictive control (MPC) is an advanced control strategy that has acquired extensive applications in various industries. In this study, MPC is applied to the process for separating ethanol, n-propanol, and n-butanol ternary mixture in a fully thermally coupled DWC. Both composition control and temperature inferential control are considered. The multiobjective genetic algorithm function “gamultiobj” in Matlab is used for the weight tuning of MPC. Comparisons are made between the control performances of MPC and PI strategies. Simulation results show that although both MPC and PI schemes can stabilize the DWC in case of feed disturbances, MPC generally behaves better than the PI strategy for both composition control and temperature inferential control, resulting in a more stable and superior performance with lower values of integral of squared error (ISE).     

隔壁式空分精馏塔应用性能研究

为了降低空气低温分离过程的设备投资和能耗,在分析空分体系的热力学性质及流程特点的基础上,提出了一种新型的隔壁式空分精馏塔流程。应用Aspen Plus模拟软件,对空气分离的传统流程和隔壁塔流程进行了模拟对比,考察了隔壁式空分精馏塔各结构参数与操作参数对其年总成本的影响,并分析比较了空分传统流程和隔壁式空分精馏塔流程的热力学效率。结果表明,隔壁式空分精馏塔的建模合理可行,通过年总成本优化得到了该隔壁塔的最优结构参数与操作参数,分别为:液氧流量为3 kmol/h,气相分配比(体积比)为0.05,精馏段理论板数为33,侧线精馏段理论板数为30,公共提馏段理论板数为22。与传统空分流程相比,隔壁式空分精馏塔流程的有效能损失降低并且在热力学效率方面高出4.7%。