蒸汽再压缩隔离壁蒸馏塔的非对称温度控制

Asymmetric temperature control of vapor recompressed dividing-wall distillation columns

蒸汽再压缩热泵(VRHP)可以提升隔离壁蒸馏塔(DWDC)的稳态性能,但也加剧了被控变量间的相互耦合,给蒸汽再压缩隔离壁蒸馏塔(VRHP-DWDC)的平稳操作带来困难。针对分离中间组分(甲苯)绝对占优的苯/甲苯/二甲苯三元物系的VRHP-DWDC,通过非方相对增益矩阵对操纵与被控变量进行配对,并依据闭环响应分析给出了一种新颖的单温度分散控制系统。由于采用塔顶/侧线热泵压缩机分别控制侧线段/公共提馏段的灵敏板温度,不但加快了侧线产品的响应速度,而且降低了塔底产品的峰值偏差。鉴于高度内部耦合以及失真的温度与组分对应关系导致二者存在较大的稳态偏差,采用双温差结构进一步强化系统设计,由此给出了一种非对称温度控制系统,降低了系统内在非线性因素的影响,因而能够减小侧线和塔底产品的稳态偏差。闭环仿真结果显示了该非对称温度控制系统的优越性。研究表明,VRHP的引入虽然加重了VRHP-DWDC的内部耦合,但也提供了压缩机功率这一潜在操作变量,其较好的控制通道特性与双温差结构的有效应用能在一定程度上改善VRHP-DWDC的闭环操作。

Although vapor recompression heat pumps(VRHP)can enhance the steady-state performance of a di-viding-wall distillation column(DWDC),they also exacerbate the coupling between the controlled variables,mak-ing the smooth operation of a vapor-recompressed dividing-wall distillation column(VRHP-DWDC)a challenging task.In this work,a novel single temperature decentralized control system based on a non-square relative gain ma-trix and in-depth analysis of closed-loop responses has been developed.The method has been evaluated using a VRHP-DWDC to separate an intermediate-component dominated benzene/tolulene/o-xylene ternary mixture.Since the top/side heat-pump compressors are used to control the sensitive stage temperatures of side/common stripping section,the transient responses of the side product can be accelerated.and the peak deviations of the bottom prod-uct can also be reduced.Since the high internal coupling and the distorted correspondence between temperature and composition are responsible for the large steady-state deviations in the side and bottom products,this work utilizes a double temperature difference structure to strengthen the control system further,thereby giving rise to an asymmetric temperature control system.Reducing the inherent non-linearities helps to reduce the steady-state deviations of side and bottom products.The closed-loop simulation results clearly demonstrate the superiority of the derived asymmet-ric temperature control system.This study highlights that although the introduction of the VRHP aggravates the in-ternal coupling of a VRHP-DWDC,it provides a variable which can potentially be manipulated,namely the com-pressor power.The better dynamic characteristics combined with the effective use of a double temperature difference structure can,to a certain extent,improve the closed-loop operation of a VRHP-DWDC.