Synthetical Design Of Topologically Optimum Vapor Recompression Dividing-wall Distillation Columns

Compared with the conventional analogues,Dividing-Wall Distillation Columns(DWDC)could effectively reduce equipment investment,equipment space and energy consumption.The significant advantages of DWDC in process development not only accelerate its application in the chemical and petrochemical process industries,but also continue to expand its significant advantages through further process intensification.Vapor recompression heat pump(VRHP)assisted DWDC(VRHP-DWDC)is a promising process intensification technology with enormous development potential,which could significantly improve the thermodynamic efficiency of the system.Closely related to the given process design as well as its relevant operating conditions,the DWDC may involve plenty of combinations with the VRHP and consequently give rise to rather complicated,tedious,and time-consuming work in the development of the VRHP-DWDC.Two kinds of comprehensive methods for the development of VRHP-DWDC based on different principles are proposed in the paper to solve this problem.On the one hand,a synthetical strategy for the development of topologically optimum VRHP-DWDC is proposed for DWDC separating a heavy-component dominated and wide boiling-point ternary mixture in the research.In this system,a significant amount of excessive heat exists inevitably in stripping the heavy-component from the intermediate-component.The excessive heat should be not only withdrawn to benefit the associated separation operation,but also employed as a valuable heat source to pursue process intensification with the application of the VRHP technique.The topologically optimum VRHP-DWDC serves to compress overhead vapor stream of the light-component and the excessive heat resulted from the separation of the heavy-component from the intermediate-component and release latent heat to the pre-fractionator’s or the common stripping section.The processing of two heavy-component dominated and wide boiling-point ternary mixtures of benzene(BEN)/toluene(TOL)/o-xylene(OXY)and n-pentane(PEN)/n-hexane(HEX)/n-heptane(HEP)are selected for analogue simulation.The objective function of process synthesis and design is to minimize the total annual cost(TAC).The optimization problem is solved here with the commonly used grid search method.The economic costs of two VRHP-DWDCs involving only one VRHP circle and the optimum VRHP-DWDC involving two VRHP circles are taken to compare with the DWDC’s economic performance.The experimental results confirm that the two-stage VRHP-DWDC has the optimum economic benefits regardless of the different locations of dividing wall.The capability of determining in advance the optimum topological configuration of the VRHP-DWDC for separating a heavy-component dominated and wide boiling-point ternary can help to minimize the complexity in process development.On the other hand,an effective procedure for the developmet of VRHP-DWDCM which shloud be derived following the decreasing order of temperatures of the available heat sources is proposed for separating a generally equal-proportional and wide boiling-point ternary mixture in the dividing-wall distillation column with middle dividing wall(DWDCM)in the research.While the first step is to explore the economic feasibility of process intensification by the vapor stream of the intermediate product,the second step by the overhead vapor stream of the light-component.Two examples of BEN/TOL/OXY and PEN/HEX/HEP are employed to research the separation system with generally equal-proportional mixture.The results demonstrate that the development procedure is not only simple and efficient,but also can maximize the steady-state performance of VRHP-DWDC and reduce the complexity in the process development.Due to the detailed consideration of its thermodynamic characteristics,the proposed procedure is not essentially confined by the number of components in the mixtures but applicable to the development of the variously complicated VRHP-DWDC processing a quaternary mixture and the mixture with more than four components.Based on the in-depth analysis of the thermodynamic characteristics of DWDC in two different feeding conditions,two diverse methods for the development and synthesis of VRHP-DWDC are proposed in the research.Although the principles are totally different,the feasibility of the design methods are proved respectively by two examples,which proves that it could be a favorable choice for DWDC to apply VRHP to process intensification.