Design And Control Structure Safety Analysis Of Extractive Dividing-wall Column And Different Pressure Thermally Coupled Reactive Distillation

Distillation is a high energy consumption process but widely used in industrial application.Energy consumption can be decreased significantly using energy-saving distillation technologies with more complex structures,but the highly-coupled process variables lead the system hard to control.A safety-based control structure design approach was proposed in this article,steady-state models and dynamic models for different pressure thermally coupled reactive distillation(DPTCRD)process and extractive dividing-wall column(EDWC)process were proposed,and the economy,controllability and safety were analyzed.The steady-statedynamic-safety scheme which is proposed in this paper can provided theory basis and novel approaches for the design and application of energy-saving distillation technologies.Aspen Plus is firstly applied to build up the steady-state models of conventional processes and energy-saving distillation process.Feasibility of the processes were researched and parameters were optimized with the aim of minimum total annual cost(TAC).Aspen Dynamics was used to design the control structure of the processes,and the dynamic responses under the disturbances were compared.Process route index(PRI)was used to analyze the hazard of the systems under different system failures,the main system failure with largest influence on the system hazard was identified and safety protect measures were applied.According to the research,in the DPTCRD process for isoamyl acetate synthesis,using a slightly excessive isoamyl alcohol feed can ensure occur of the liquid separation and the product specification.DPTCRD process can decease the operation cost by 39.65% and TAC by 1.25%-19.05% with the variation of payback period from 5 to 10 years.Control structure with product composition controller and feed composition controller achieves best control behaviors under the disturbances of ±10% feed flowrate and +10% water in Acetic Acid.Top vapor blocking is a major system failure which will increase the hazard of the process,and a relief valve installed at the top of the column can significantly decrease the hazard.In the EDWC process for the separation of cyclohexanol/cyclohexanone system,EDWC process can decease the operation cost by 11.16% and TAC by 0.80% with a payback period of 5 years.Control structure with C1 top product composition controller(CS2)and with feed/reboiler duty ratio controller(CS3)can both satisfy the product specification,but the CS3 structure shows advantages on safety analysis.Shut down of the cooling water have a large influence on the system hazard,and a relief valve installed at the top of the column can significantly decrease the hazard.