Energy-saving Study For Close-boiling/Azeotropic Separation Via Heat Pump Technology

Distillation is the most widely used in chemical industry,while the major drawback is enormous energy consumption.With the rapid development of industrialization around the world,the energy and environment problems are becoming increasingly prominent.Hence,the energy-saving performance and the thermodynamic efficiency of distillation scheme attract more attention.Heat pump can effectively use the low-grade heat,with the help of a small amount of high-grade heat,which is a widely used technology to reduce energy consumption.In the paper,a systematic method is designed to decide the optimal vapor recompressed heat pump assisted distillation(VRC)scheme.Firstly,the performance of heat pump(COPs)is calculated to define weather the heat pump technology should be applied in distillation process.Secondly,the feature of working fluid is considered and determined weather the working fluid should be preheated before being compressed.Then comparing the heat contributed by compressed stream and the heat required of reboiler,and define the VRC scheme according the comparison.The heat pump assisted distillation process for the separations of close-boiling mixture(n-butane/isobutane and propylene/propane)are selected and compared to obtain the method for determining the optimal heat pump assisted distillation process.Then the proposed method for determining the optimal heat pump assisted distillation process was utilized in these azeotropic separations of ethyl acetate/n-hexane and the separation of tetrahydrofuran/ethanol/water.All heat pump technology assisted distillation processes show better performance in terms of total annual cost,energy-saving performance and thermodynamic efficiency when compared with the corresponding conventional process.When the heat provided by compressed stream is less than the heat required in reboiler,adding auxiliary bottom reboiler or preheater are favorable choices aspects of total annual cost,energy-saving performance and thermodynamic efficiency.When the heat provided by compressed stream is more than the heat required in reboiler,the heat pump assisted distillation process with the splitting overhead stream is the better scheme.Meanwhile,the heat pump assisted distillation with heat-integrated schemes show better performance than those without heat-integrated schemes.In industrial production,based on the proposed method for determining optimal heat pump assisted distillation process,the corresponding heat pump distillation process can be determined according to the characteristics of mixtures.