Control Of Heat Pump Assisted Conventional And Azeotropic Dividing Wall Columns

Heat pump technology and the dividing wall column technology are typical distillation process energy-saving technology,the combination named heat pump assisted dividing wall column have greater advantages in the energy-saving and economy.However,due to the complicated structure and the strong coupling of internal variables,the control research of heat pump assisted dividing wall column has a certain degree of difficulty,which restricts its industrialization.The purpose of this paper is to study the controllability of heat pump assisted dividing wall column and heat pump assisted azeotropic dividing wall column,and explore the control law of the heat pump assisted azeotropic dividing wall column.A new configuration of heat pump assisted dividing wall column for the separation system of ethanol / n-propanol / n-butanol is estabilsed,saving 17.23 % of energy and saving 7.22% of TAC compared with the conventional dividing wall column.However,due to the strong mutual influence among the variables,it occurs that the components distribution disorder in the column during the control research.Therefore,more proportional control structures are used after analysis and testing.Finally,the improved four-point temperature control structure CS4 is proposed and proved effective.The key points of the control structure are: the ratio control of proportional control the main column liquid reflux and feedstock stream;the ratio control of column reboiler duty and the feed stream while the ratio controls the temperature of the 7th plate of the main column directly;the ratio control of the compressor outlet flow rate and the feed stream,while the proportional controller directly controls the temperature of the 29 th plate of the main column;at the same time,the heat transfer flow rate is proportional to the feed stream.A new configuration of heat pump assisted azeotropic dividing wall column is proposed for the ethylenediamine-water system which forms the highest azeotrope.Compared with the conventional dividing wall column proces,it can save energy by 42.93%,and save TAC by 24.36% when the payback period is 8 years.During the control study,based on the two point temperature control strucure,this article adds the third mutipulate variable in sequence.Finally,an improved three-point temperature control structure called CS4 is proposed which can effectively resist the disturbance of the feed flow and the feed composition: The flow rate of the organic phase controls the temperature of the 39 th plate of the main column;the compressor duty controls the temperature of the 23 rd plate of the main column;stripper reboiler duty controls the temperature of stripper column 2nd plate;? remains constant.Finally,aiming at the isopropanol-water system which forms the lowest azeotrope,a dynamic control structure of heat pump assisted azeotropic dividing wall column is established.After the test,it is found that the two point temperature contructure called CS3 with the reboiler duty of the two columns controlling corresponding sensitivity plate is the most ideal structure.In addition,based on CS3,this paper adds organic phase flow to control the temperature of the column sensitive plate,the result is still satisfactory,but not better than CS3.