Dynamic Control Of Highly Heat-Integrated Energy-Efficient Extractive Distillation Processes

Distillation is one of the most important separation methods in the chemical industry,which is based on the differences of the relative volatility of different components.The steady-state design of the distillation process is an indispensable part of chemical engineering design.However,the impact of feed flowrate or composition disturbances cannot be considered in the steady-state design.Therefore,the study on the dynamic control performance is extremely important.This article firstly studies the dynamic control performance of azeotropic system with the relative volatility of feed components not reversed by the entrainer.The dynamic control performances of the energy-efficient two-column extractive distillation process and the conventional three-column extractive distillation process are compared by separating the mixture of isopropanol and water with dimethyl sulfoxide as the entrainer.The base controls are proposed for both processes.Especially,the singular value decomposition method is used to analyze the temperature files and to select the appropriate column trays to be controlled.The entrainer flowrate/feed flowrate forward ratio controller is used to develop the modified control for the two-column process.The reboiler duty/feed flowrate forward ratio controller is used to develop the modified control for the three-column process.The results indicate that the modified controls can hold the purity of the product within a reasonable range when the feed flow rate or composition disturbances are introduced.The modified controls of the two-column process and the three-column process are compared,and the results indicate that the former can better withstand the disturbance test.Therefore,the energy-efficient two-column extractive distillation process has advantages in controllability.Aiming at the azeotropic system in which the entrainer reverses the relative volatility between the components to be separated,the dynamic performances of the energy-efficient two-column extractive distillation process and the conventional three-column extractive process for the separation of ethanol and ethyl acetate mixture with furan as the entrainer are studied and compared.The results show that both the base control and the modified control of the energy-efficient two-column process have poor control stability when the feed flow or composition disturbances are introduced,because the products purities exhibit large transient deviations.The base control of the conventional three-column process is simple and stable,and the product purities can be controlled within the acceptable range when the feed flow or composition fluctuates.Although the two-column extractive distillation process is energy-efficient,the poor dynamic performance remains a problem.In the chemical production process,the energy duty and dynamic controllability should be comprehensively considered when separation process is selected for the azeotropic system with the relative volatility of feed components reversed by the entrainer.