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  • 學位論文

反應性蒸餾系統的非線性動態行為研究

Understanding Nonlinear Dynamic Behavior of Reactive Distillation

指導教授 : 余政靖

摘要


反應蒸餾塔是在單元設備裡結合反應與分離程序,藉此可提高某些化學反應系統的經濟效益。由於反應蒸餾具有多功(Multifunctional)的本質,這使得反應或分離原本的非線性特性更加複雜。因此相較於單一功能單元的動態,反應蒸餾塔之動態與控制行為較不明顯。本研究目的主要探討反應蒸餾塔非線性的動態行為,由於分離程序與化學反應的交互作用下,導致產品組成與操作變數之穩態增益出現變號(Sign Reversal)行為。以程序控制觀點來看,表示有右半平面的零位(RHP Zeros)的產生,也就是具有非最小相位的行為(Non-Minimum Phase Behavior, NMP)。一般在反應蒸餾塔穩態設計的例子,操作點大多設計在最大效能的附近。如此一來,小幅的操作點改變,可能會產生右半平面的零位。因此,多功程序之單元的控制架構設計顯得格外重要。首先,由化學反應的化學計量數平衡與質量平衡來看,反應蒸餾塔使用部分控制是一個理想的選擇。接著,分析不同控制架構的程序特性-部分控制下的線性行為、動態特性以及非線性程度,找尋最適當的控制架構。藉由上述提出的系統化方法,我們針對乙酸甲酯反應蒸餾系統來描述其控制架構設計。結果顯示所提出來的部分控制架構設計方法是可以達成可接受的控制品質。更重要的,這是在使用相當簡單控制系統所獲得的結果。

並列摘要


Reactive distillation combines reaction and separation in a single unit, which provides substantial economic incentives for some chemical reaction systems. However, the multifunctional nature of the reactive distillation complicates already very nonlinear nature of either reaction or separation. Thus, the dynamics and control of reactive distillation are less obvious as compared to its single functional unit counterparts. The objective of this work is to explore the nonlinear dynamics of reactive distillation. The interaction between reaction and separation leads to possible “sign reversal” in the steady-state gains between the product compositions and typical manipulated inputs. In terms of process control, this implies the existence of right-half-plane (RHP) zeros, a non-minimum-phase (NMP) behavior. This is typically true as a near-optimal reactive distillation column design and, in many cases, the RHP zeros vary from zero to two in a small operating range. The situation worsens as the control structure grows larger, e.g., from 2x2 to 3x3 systems. Thus, the control structure design becomes important for this multifunctional unit. First, the stiochiometric of chemical reaction indicates that the “partial control” is an ideal candidate for reactive distillation control. Subsequently, the problem becomes the selection of controlled and manipulated variables. A systematic approach is proposed to select the most appropriate control structure. We analyze the process charaterictics of system - dynamic characteristic (NMP), nonlinearity measure, deviations of uncontrolled composition under setpoint and load changes. The methyl acetate example is used to illustrate the control structure design. The results clearly show that reasonable control performance can be achieved using partial control, provided with a careful control structure selection.

參考文獻


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