"Simultaneous Design" For The Complex Distillation Process:Process Intensification,Dynamic Control And Safety Analysis

Distillation,as the most widely used separation technology of liquid mixture,is also a recognized chemical operation unit with high energy consumption and low thermal efficiency.Therefore,more and more process intensification methods of distillation have been developed.However,the strong coupling and interaction of this complex and compositive process intensification may change the dynamic performance and cause the propagation of deviations in a potential and imperceptible way,and then,reduce the system controllability and safety.Great challenges will be presented to the effective control structure establishing and the conventional process safety analysis（such as HAZOP analysis）which depends on the knowledge and experience of experts.Obviously,an effective chemical process is built must be economically attractive,dynamically operable and safe,which requires the simultaneous consideration of steady-state economics,dynamic controllability and safety of the process during concept design phase.In addition,for the chemical industry,the treatment of chemical effluents is an important research topic for its green and sustainable development,and is a difficult problem restricting its development.Therefore,based on the simultaneous design thinking,the separation processes of two industrial relevant effluents that have rarely been studied（dichloromethane/methanol and cyclohexane/sec-butyl alcohol/water）were systematically investigated from the perspective of process improvement,plantwide control and safety analysis.The main research content and results are as follows:（1）To develop a distillation process that is energy-efficient,economically attractive,dynamically controllable and safe in the conceptual phase,a simultaneous design procedure was proposed,mainly including:problem definition,objective function definition,base case design,process intensification,rigorous simulation and optimization,economic and sustainability analysis,controllability study and simulation-assisted HAZOP analysis.The simultaneous design can effectively improve the feasibility of process conceptual design,which is of great significance to the initial conceptual design and the final industrial application.（2）The simultaneous design of the dichloromethane/methanol distillation process:first,the steady-state process intensification was conducted,and two extractive dividing-wall column（EDWC）processes were proposed and optimized,among which,the EDWC process with heat integration（EDWC-HI）has a better economic and environmental performance with energy cost saving of 50.0%and TAC reduction of27.7%and CO₂ emissions reduction of 35.6%;then,for the EDWC-HI process,four control structures are proposed and tested under the disturbances of±20%feed flowrate and±5%feed composition,among which,the new proposed control structure CS4integrating pressure-swing and pressure compensation shows the best dynamic performance,all product purities can meet the required specifications with small transient deviations and short settle time.Finally,four typical deviations（feed disturbances,over-temperature,over-pressure and flooding）were introduced into CS4,and the HAZOP analysis was combined with the quantified dynamic response to identify potential hazards more accurately,including its nature,scale and response time.Furthermore,specific safety recommendations were made accordingly.（3）The simultaneous design of the cyclohexane/sec-butyl alcohol/water distillation process:first,based on the existing basic process,four alternatives with significant advantages of energy-saving and economic were developed by applying the features of heterogeneous distillation,the heterogeneity of the system,and the technologies of dividing-wall column and innovative direct contact heat exchange.Among them,the HDHP process can save total energy consumption of 35.1%,and can reduce TAC 37.0%and CO₂ emissions 23.5%;for the HD-DDWC-FEHE process,significant reductions of 51.0%in total energy consumption,64.5%in TAC and 33.6%in CO₂ emissions can be achieved.Then,for the HDHP process with multiple recycles and complex heat pump,two effective and robust plantwide control strategy with conventional temperature control loop were developed and tested under large throughput and feed composition disturbances.Both control structures can effectively overcome the“snowball”phenomenon,and shows excellent robustness.Finally,based on the CS1,process safety analysis integrating dynamic simulation and HAZOP analysis was conducted,which can reveal the nature,scale and response time of hazards and help safety professional to identify the potential propagation of deviations.