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

摘要：

隔离壁蒸馏塔（DWC）的双塔多段拓扑结构导致蒸汽再压缩热泵（VRHP）的应用具有多种可能性，包括单VRHP、多VRHP、多级VRHP以及它们的相互组合等复杂结构，这显著加剧了蒸汽再压缩隔离壁蒸馏塔（DWC-VRHP）综合与设计的复杂性与烦琐性。为解决这一问题，针对轻组分绝对占优的三元宽沸点物系的分离问题推演了DWC-VRHP的最优拓扑结构，由此能够有效回避系统综合与设计过程中的结构搜索问题并显著降低模型化与搜索计算的工作强度。轻组分绝对占优与宽沸点物性导致了塔顶冷凝器与预分离蒸馏塔的提馏段是主要的热源与热阱，也决定了DWC-VRHP的最优拓扑结构，即一个二级VRHP与DWC的耦合系统。第一级VRHP用于进料预热，既充分利用温度提升跨度小的特点，又可以通过进料分流强化气液相间的物质传递。第二级VRHP用于加热预分离蒸馏塔的提馏段（或公共提馏段），能够最大限度地降低分离操作的非可逆性。采用苯/甲苯/邻二甲苯和正戊烷/正己烷/正庚烷两个物系的分离问题对所提出的DWC-VRHP的最优拓扑结构进行了分析与验证。通过与DWC以及DWC-VRHP其他潜在结构的系统性比较，显示了所提出系统结构在稳态性能方面的优越性。

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