Energy Saving Design And Dynamic Control Of Self-circulated Vapor Recompression Assisted Heat Pump Distillation Process

Vapor recompression is a typical energy saving distillation technology,while there are still some problems such as its limited application range and low energy saving efficiency.To expand its application range and improve its energy saving efficiency,the self-circulation vapor recompression processes are proposed in this paper,and their energy saving design and dynamic control are studied.The design idea of this kind of processes is to recycle the excess vapor generated in the vapor recompression system to improve the latent heat utilization efficiency.On this basis,the sensible heat utilization efficiency in the vapor recompression system is further improved by using the self-heat recuperation technology to preheat the raw material liquid and the overhead vapor.Four types of self-circulation vapor recompression processes are applied in the conventional single column and diving wall column to study their energysaving design methods and energy-saving efficiencies.The propylene/propane binary mixture is selected as the separation system,and four types of self-circulation vapor recompression single column processes are designed,and the structure and operation parameters such as total number of stages,feed stage and reflux ratio are optimized.The design results show that the total annual cost can be saved by 62.2% by the double preheated self-circulation vapor recompression single column process which has the highest energy saving efficiency compared with conventional distillation column.Then,four types of self-circulation vapor recompression dividing wall column processes are designed to separate the ternary n-butane/iso-pentane/n-pentane and benzene/toluene/ethylbenzene systems.The design results show that the double preheated self-circulation vapor recompression process which has the highest energy saving efficiency can reduce the total annual cost by 36.0% in n-butane/isopentane/npentane separation and by 36.5% in the benzene/toluene/ethylbenzene separation,compared with diving wall columnFinally,the dynamic control properties of the proposed processes which have the highest energy efficiency are studied.In the control process,the outlet temperature of the heat flow strand in the column bottom heat exchanger is controlled by controlling the reflux liquid flow rate.The purity of bottom product can be controlled by manipulating the compression duty,and the outlet temperature of the heat liquid from the reboiler can be controlled by manipulating the flowrate of the compressed vapor.The dynamic research results show that under this control scheme,the purities of the separation products can return to their original steady state values with slight oscillations and short settling times when feed disturbances are added in the double preheated self-circulation vapor recompression single column and dividing wall column processes.