Dynamic Characteristics And Control Of Vapor Recompressed Dividing-wall Distillation Column

As the integrated product of two process intensification technologies,vapor recompression heat pump(VRHP)and dividing-wall distillation column(DWDC),vapor recompression heat pumps assisted dividing-wall distillation column(VRHPs-DWDC)has remarkable significant economic benefits and energy saving advantages.However,its high internal coupling poses challenges to the smooth operation and strict control of VRHPs-DWDC,which has hindered the application and development of VRHPs-DWDC.In order to solve the above issues,this paper analyses the dynamic characteristics of VRHPs-DWDC from both the control and disturbance channels,and designs effective closed-loop control systems.In the research of dynamic characteristics,due to the high coupling within the VRHPs-DWDC,both the control channels and disturbance channels exhibit strong asymmetric characteristics,which can lead to a reduction in the controllability of the system.Although the application of VRHP enlarges the time constants of the disturbance channels,making the VRHPs-DWDC more sensitive to disturbances,it also diminishes the gain of the control channel that leads to an intensification of the difficulty in closed-loop control.In the closed-loop control research,this paper proposes optimal single temperature decentralised control systems according to closed-loop response.The results illustrate that the single temperature decentralised control system can improve the dynamic response of the side and bottom products by employing compressor power of the top/side VRHP to control the sensitive stage temperatures of side/common stripping section,but cannot cope with the internal coupling of the VRHPs-DWDC and the distorted correspondence between sensitive stage temperature and product component,engendering large concentration residuals of the side and bottom products.The application of VRHP dwindles the concentration residuals of the side product partially,but generates surge steady-state deviations of the bottom product.In order to compensate for the shortcomings of single temperature decentralised control,this paper uses double temperature difference structure to strengthen the design of the temperature control loops of side section and common stripping section,thus proposes an asymmetric temperature control system based on double temperature difference reinforcement and tests its economic,effectiveness and generality.The research in this paper demonstrates that the application of VRHP intensifies the internal coupling of VRHPs-DWDC,but also speeds up the response of VRHPs-DWDC and provides a potential manipulated variable in the form of compressor power.The single temperature decentralised control system can improve the dynamic response of the VRHPs-DWDC by utilising the favourable channel characteristics of the compressor power.The employ of double temperature difference structure to optimise the temperature control loops in the side/common stripping sections of single temperature decentralised control systems can effectively reduce the steady-state deviations of product concentration of the VRHPs-DWDC and strengthen the closed-loop operation of the VRHPs-DWDC.