Control And Dynamic Research Of Reactive Distillation Column With Double Reactive Sections:ideal Two-step Consecutive Reversible Reaction

As a technique of process intensification,reactive distillation is used extensively in the chemical industry.It is the intergration of chemical reactions and conventional distillation,which makes the system have lower energy consumption and equipment investment.It gives considerable economic benefit.However,when the chemical reaction is multi-step process,the separation results of the reactive distillation columns with single reactive section(RDC-SRS)is not good.RDC-SRS sometimes does not reach the product quality standard as required.Its effect even not as good as the result of traditional cascade chemical industrial process.For this kind of circumstance,the reactive distillation columns with double reactive sections(RDC-DRS)is used to separate the two-step consecutive reversible reaction.The configuration of the RDC-DRS is to arrange two reactive sections in one column,which is useful to strenthen the energy coupling and material coupling.Through an enhanced thermodynamic efficiency,the RDC-DRS has a better steady-state performance as compared with the RDC-SRS.Whether it is from the perspective of the effectiveness and reliablility of process or the actrual use,dynamics and control of this process-enhancement technology need to be studied.In this paper,the dynamic characteristics and control of the reactive distillation column with single reactive section and double reactive sections are studied in detail.In the control path,the RDC-DRS reinforces the coupling between the bottom product components and the reflux flow rate.On the other hand,the RDC-DRS alleviates the coupling between the overhead product components and the reboiler heat duty although it reduces the open loop gain between the overhead product component and the reflux flow rate.The net effect of the setting of double reactive sections on the control channel ultimately has a beneficial effect on the dynamic characteristics of the system.This result is also reflected in the calculated relative gain matrix.In the disturbance path,when there is a step change in the feed flow rate,the RDC-SRS is generally has a severe asymmetry in the open-loop responses of the bottom product concentration.The unfavorable open-loop dynamics can deteriorate the dynamic performance of the RDC-SRS.Through analyzing the operating variables and controlled variables of the RDC-SRS and RDC-DRS,the control structures of the two types of reactive distillation columns are built.In the case of using the same concentration control and control structures,the controllability of the RDC-DRS is better than the controllability of RDC-SRS.According to the closed-loop results,the RDC-DRS shows a stronger anti-disturbance capacity when subjected to feed flow rate disturbances and feed composition disturbance,and it also shows a better traceability.The results reveals that the arrangement of double reactive sections,as a process enhancement technology,can not only improve the steady-state performance of the system,but also improve the anti-disturbance ability and traceability of the system.The RDC-DRS is a valid plan of improving the dynamics and controllability.