Synthesis And Design Of Heat-integrated Middle Dividing Wall Columns

Dividing-wall columns(DWC)are capable of separating ternary mixtures in one unit with high thermodynamic efficiency;however,the separation process is still highly irreversible and has the potential for further enhancement.To solve this problem,we propose an effective process intensification method which applying internally heat-integrated technology in the DWC,i.e.,the DWC with middle dividing wall is divided into two parts(high pressure section and low pressure section),and the high pressure section serves to transfer heat to the low pressure section,thus reducing the irreversibility of the separation process.The presence of the dividing wall brings versatility to the application modes of internal heat-integrated technology in the DWC;more specially,one can transfer heat on one side of the dividing wall and the other on both sides of the dividing wall.Based on these,four topologies of heat-integrated dividing-wall column are presented in this paper: heat transfer on one side of the dividing wall,both sides of the dividing wall in the high pressure section release heat to the low pressure section(HIDWC-L),both sides of the dividing wall in the low pressure section absorb heat from one side of the high pressure section(HIDWC-U),and heat transfer on both sides of the dividing wall(HIDWC-A).In this paper,a kind of optimization procedure of the HIDWC based on heuristic searching method is developed with a design index of the minimum total annual cost(TAC),and the minimum value of TAC is determined through several iterations.In this paper,the separations of the two ternary systems(methanol,ethanol,isopropanol,and n-pentane,cyclopentane,and 2-methylpentane)are used for the synthesis and design of the HIDWC.The results show that despite the HIDWC require a certain increased capital equipment cost,it can significantly reduce the operating cost and can greatly reduce the reboiler heat load,which means it has significant energy-saving benefits.Meanwhile,in the cases of the separations of the two ternary mixtures,the optimum topological structures of the HIDWC should be HIDWC-U and HIDWC-L,respectively.