关键词: 隔离壁蒸馏塔, 蒸汽再压缩热泵, 轻组分绝对占优, 宽沸点物系, 综合与设计

Abstract:

The complicated topological structure of dividing-wall columns(DWC) with double columns and multiple separating sections allows many possibilities to use vapor recompressed heat pumps (VRHP), including single VRHP, multiple VRHPs, multi-stage VRHPs, and their various potential combinations, and this adds great complexities and tediousness to the synthesis and design of the vapor recompressed dividing-wall columns(DWC-VRHP).To address the issue, we derive the optimum topological configuration of the DWC-VRHP in the current work for the separations of light-component dominated and wide boiling-point ternary mixtures, based on which the structural searches involved in process synthesis and design can be avoided and the burden of process modeling and search computation can be reduced. The light-component dominance and wide boiling-points of the mixtures separated make the top condenser and the stripping section of the pre-fractionator the primary heat source and heat sink, respectively, and determine essentially the optimum topological configuration of the DWC-VRHP, i.e., a DWC plus a two-stage VRHP. The first-stage VRHP is employed to pre-heat the feed, not only taking the advantages of the small temperature elevation available but also favoring the intensification of mass transfer between the vapor and liquid phases through feed splitting. The second-stage VRHP is employed to heat the stripping section of the pre-fractionator(or the common stripping section), being capable of reducing the irreversibility to its fullest extent. With the separations of two ternary mixtures of benzene/toluene/o-xylene and n-pentane/n-hexane/n-heptane as examples, the derived optimum topological configuration of the DWC-VRHP is analyzed and validated through detailed comparison with the DWC and other potential configurations of the DWC-VRHP. The systematic comparison with DWC and other potential structures of DWC-VRHP shows the superiority of the proposed system structure in terms of steady-state performance.

Key words: dividing-wall column, vapor recompressed heat pump, light-component domination, wide boiling-point mixture, synthesis and design