Study On Quality Control Of Kaibel Dividing Wall Column

The function of Kaibel column is to achieve high purity separation of quaternary mixture in a single column.In this paper,five-component hydrocarbon system and four-component alcohol system are separated by Kaibel column.The separation requirements of each system are 98.5mol%,99.0mol% and 99.5mol%,respectively.Through thermodynamic analysis,the steady-state simulation of the two-column model(including prefractionator and main column)is established by using Aspen Plus software,and the separation process is optimized with the minimum Total Annual Cost(TAC)as the objective function.The dynamic control is studied by using Aspen Dynamics software at last.First,the hydrocarbon system separated by Kaibel column is taken as the research object,and the temperature control structure is proposed for the process with a separation requirement of 98.5mol%.The result shows that the control structure can handle ± 15% flow rate and composition disturbances.Then the control scheme with a separation requirement of 99.0mol% is analyzed to verify its handing ability.The disturbance results show that the overall control effect are good except for a few deviations in the purity of n-octane,but there are some problems such as longer stability time and larger fluctuation peak.The above problems can be effectively improved by adding the proportional control structure like L/F.Finally,the dynamic analysis of a process with 99.5mol% separation requirement is analyzed by the above-mentioned scheme.The disturbance result shows a large purity deviation between n-heptane and n-octane.The n-octane impurity at the top of the prefractionator is controlled by adding a component controller to control the liquid phase distribution ratio.At the same time,the cascade control structure of CC-TC is applied on the two sidelines to make the control effect good.The separation of alcohol system in Kaibel column is also simulated and studied.A temperature control structure is used for a process with the separation requirement of 98.5mol%.The disturbance result shows that the sub-control structure can handle ± 10% flow rate and composition disturbances,but the purity of n-propanol in the lower side line is slightly lower than the design requirement.Using the above control scheme to improve the separation requirements to 99.0mol%,the analytical control results show the purity of n-propanol and ethanol in two sidelines are slightly lower than the design requirements and all other components can meet the separation requirements.The above problems can be solved by controlling the flow rate to the bottom of the prefractionator and the flow rate of ethanol impurity in the main column streams to the prefractionator by adding CCP controller.Finally,the process with a separation requirement of 99.5mol% is optimized,and the problem that the purity of the ethanol and the n-propanol in the two sidelines are had a large deviation.In order to solve this problem,the control scheme is improved to control the n-propanol impurity at the top of the prefractionator by adding component and temperature cascade controllers and the L/F proportional controllers.By analyzing the control schemes with separation of hydrocarbon and alcohol systems in Kaibel column,the main control ideas of the two processes are similar,but control structures are also different due to the different properties of the systems.This paper provides more experiences on the control method of separating other component systems in Kaibel column.